Automatic adaption of the control range of a pressure control loop in multiple pump arrangements

0001The invention relates to a pump arrangement for pressure control with at least two parallel-connected centrifugal pumps for the variable-volume delivery of liquids in piping systems, wherein a sensor for detecting the delivery pressure of the pump assembly is arranged on the pressure side and a microprocessor system in response to the signal of the pressure-side sensor by influencing the speed of at least one centrifugal pump controls the delivery pressure of the pump assembly.

0002If in a pipeline system the flow or demand conditions on the pressure side of the centrifugal pumps, which is caused by a change in consumer behavior, as may be the case for example by water extraction in a pipe network or opening thermostatic valves in a heating system, then such fluctuations in demand exercise a Influence on the behavior of the pressure control loop. For a balanced control behavior, exact adjustment of the control range limits is necessary in the event of strong fluctuations in demand. A manual setting during commissioning or during operation is in most cases not possible for the operating staff due to different qualifications.

0003From DE-A-27 56 916 an arrangement of parallel operated centrifugal pumps is known, with a demand-dependent regulation of a flow rate. Such pump assemblies of centrifugal pumps can be found in a variety of piping systems in which a certain discharge pressure is to be maintained. The previously known solution provides for this purpose a single variable-speed centrifugal pump, which is responsible for fluctuating decrease in a flow rate, referred to here as demand fluctuation, in conjunction with a linear PID controller and a frequency converter as a control pump for maintaining a discharge pressure. When changing the delivery demand, which is outside the performance range of this control pump, additional pumps are switched on under negative pressure and switched off at overpressure. These run at a constant speed and deliver at the same pressure conditions a constant flow rate.

0004Next are through the prospectus <img file="EP0905596A2_D0001.tif" />Hydrovar ", List 5810 d - 2, the company Vogel Pumpen GmbH, Stockerau, Austria Pump assemblies are known in which each pump is equipped with its own frequency converter and its own pressure sensor.Using an internal communication system based on an electronic RS-485 interface are up to The type of switching of the pumps is not disclosed.

0005In such pump arrangements, the switching point is critical, at which another pump is switched on or an excess pump is switched off. Such a process requires a high amount of control effort if adverse pressure surges are to be prevented during the switch-on or switch-off. The before the time of switching an auxiliary pump in operation pumps, hereinafter referred to as control pumps are also switched at the time of switching an auxiliary pump in the operating range. This must be taken into account on the part of the controller setting by the Stellbereichsgrenzen adapted to the new situation. Ia exact knowledge of the plant conditions necessary. This requires a high manual effort and involves the risk of inaccuracies or incorrect entries on the part of the operator having a different qualification.

0006Very important for the energy consumption of the system or the hydraulic system is the choice of the lower limit for the control or output range of the controller. The lower setting range limit, which is identical to the minimum speed n_{min '} with which the respective variable-speed variable-displacement pump is operated exerts a decisive influence on the control behavior. Becomes n_min If chosen too high, this would have the disadvantageous effect that a physically necessary adjustment range determined by the characteristic of the variable-speed variable-displacement pump is not sufficiently utilized. A resulting in the system overpressure could lead to early deactivation of a control pump. Such deactivation could cause the pressure in the system to drop below a threshold. The sensor monitoring the system pressure on the pressure side of the pump assembly would then cause the control system to provide a signal to reactivate a previously stopped pump. Such short-term switching operations are unnecessary, lead to increased mechanical wear on the pump units and generate unnecessary pressure fluctuations in the system.

0007Unfavorable control behavior also results if the minimum speed of the respective variable speed control pump representing the lower control range limit is selected too low. Too low a choice of n_min makes itself especially at a very low flow q_is disturbing noticeable. This operating point is also under the term small quantity requirement<maths id="math0001" num=""><math display="inline"><mrow><msub><mrow><mtext>q</mtext></mrow><mrow><mtext>is</mtext></mrow></msub><msub><mrow><mtext> = q</mtext></mrow><mrow><mtext>min</mtext></mrow></msub><mtext> ≈ 0</mtext></mrow></math><img file="EP0905596A2_D0002.tif" /></maths> known and will be used in the following. In such a case, the control intervention of the pressure regulator, ie the rotational speed n of the respective variable-speed variable-displacement pump, would have no effect on the delivery pressure p used as the control variable_is stay. The control pump would thus press the circulating fluid in the system against a nearly or completely closed fitting, which would have the consequence that the electrical energy used for the operation of the control pump is unnecessarily consumed by the heating of the fluid in the pipeline. This could also result in that the drives of all active pumps are unnecessarily heated, which would lead in the best case, in the presence and response of a thermal motor protection, to a fault condition by switching off the respective engine.

0008An upper setting range limit n_Max is set by the manufacturer and corresponds to the maximum speed of the respective variable speed control pump. It is dependent on the frequency of the power grid and the design of the electric pump drive and has no significant influence on the control behavior.

0009In addition to the demand fluctuations described, the pressure on the suction side of the centrifugal pumps, hereinafter referred to as pre-pressure p_{in front} designated, exert an influence on the control behavior. The metrologically accurate detection of a fluctuating form p_{in front} on the suction side or a differential pressure Δp between the suction and the pressure side of the pump assembly with an additional sensor is often not performed for cost reasons.

0010In the case of very large fluctuations in the admission pressure, the control system may be involved in switching cycles of the control pumps, as have already been described using the example of the excessively high minimum speed when neither an additional admission pressure sensor nor a differential pressure sensor is used. However, a plant manufacturer or a later user of a pump system expects a pressure control loop even with a wide range of variation of the form p_{in front} a consistently good control behavior.

0011DE-U-296 10 050 relates to a control device for optimum adjustment of the operating values ​​of electronic, stepless speed controls in heating systems and water supply systems. For this purpose, it is proposed that a transducer in a system detects the respective head of a feed pump and transmitted to an electronic continuously variable speed controller. A microcomputer is to automatically determine the operating parameters required for the normal operation of the feed pump in the hydraulic system from these measured values ​​waiving an input by the operator. Furthermore, the innovation should determine the automatic determination and adjustment of the required for the normal operation of the feed pump in the hydraulic system head, minimum speed and minimum and maximum head. Unfortunately, the innovation lacks the necessary revelation, so that a person skilled in the art can also understand this teaching. Due to the lack of information, this solution is not executable.

0012The invention is therefore based on the problem to develop a way to easily adjust a pressure regulator, which ensures a simple operation a wear-minimal control behavior in a large operating range and requires neither an explicit determination of the flow rate nor the respective pre- or differential pressure value by consuming sensors.

0013The solution to this problem is provided by the features of claim 1. With this solution, the microprocessor system fits the lower set point limit n_min automatically. This makes it possible to achieve good behavior with regard to a minimum quantity shutdown and a low switching frequency of the control pumps.

0014The operator or manufacturer of a pump system only specifies the following three parameters. Although these are also system-specific, they change in contrast to the minimum speed n_min under normal operating conditions not:<ul id="ul0001" list-style="bullet"><li>A setpoint specification for the delivery pressure p_should of the control loop.</li><li>The lower limit n_u the permissible value range for the adaptation of n_min, It is generally of the order of 30% of the maximum speed n_Max, The microprocessor system prevents an illegal value of n_min below n_u is set. An upper limit for n_min On the other hand, it is not explicitly given, since it is automatically determined by the method as a function of p_should is determined.</li><li>Lower value of the fluctuation range of the admission pressure value p_{before, min}, This value is known in a system design and also serves the suction-side design of the pump, for example, to ensure their Kavitationsfreiheit. If the fluid to be delivered on the suction side comparatively pressure-less available, p_{before, min} = 0. This is often the case when the fluid is removed from a reservoir which is at the same geodetic level as the site of the pump assembly.</li></ul>

0015Furthermore, in the microprocessor system, the value of the zero flow pressure p_Max stored for each variable-speed pump used. This value gives as a pump-specific constant the delivery pressure of a centrifugal pump at delivery q = 0 on.

0016A manufacturer or user can use the pump assembly in a variety of piping systems. The lower setting range limit n_min thus receives for the particular application only a very rough basic setting by the specification of n_u, The exact adaptation of n_min to the existing conditions then takes place automatically with the features of claim. 1 The specification of the mentioned parameters resp. the input of the necessary data in the microprocessor system can be done for example in the simplest way using a combination of keyboard and display, which allows communication with the microprocessor. It would also be possible to store corresponding values ​​in the microprocessor system by means of switching elements or via a bus system.

0017During operation, the automatic adjustment of the lower control range limit n then takes place_min at discrete times t₀ when connecting or disconnecting feed pumps. The microprocessor system divides the minimum value from the preset target pressure p_should (Reference variable) and measured actual value of the delivery pressure p_is (Controlled variable) by the zero feed pressure p_Max (fixed parameter) of the variable-speed centrifugal pump to be activated or deactivated in the next switching operation. The quotient thus formed is then etched and finally multiplied by a normalization factor k.

0018This approach leads to erratic changes of n_min and is described by formula (1):<maths id="math0002" num="(1)"><math display="block"><mrow><msub><mrow><mtext>n</mtext></mrow><mrow><mtext>min</mtext></mrow></msub><msub><mrow><mtext>(t</mtext></mrow><mrow><mtext>0</mtext></mrow></msub><mtext>) = k * </mtext><msqrt><mfrac><mrow><msub><mrow><mtext>MINIMUM {p</mtext></mrow><mrow><mtext>should</mtext></mrow></msub><msub><mrow><mtext>(t</mtext></mrow><mrow><mtext>0</mtext></mrow></msub><msub><mrow><mtext>) P</mtext></mrow><mrow><mtext>is</mtext></mrow></msub><msub><mrow><mtext>(t</mtext></mrow><mrow><mtext>0</mtext></mrow></msub><mtext>)}</mtext></mrow><mrow><msub><mrow><mtext>p</mtext></mrow><mrow><mtext>Max</mtext></mrow></msub></mrow></mfrac></msqrt></mrow></math><img file="EP0905596A2_D0003.tif" /></maths>

0019Background of the root operation is the quadratic relationship between speed and delivery pressure of a centrifugal pump. The minimum formation prevents the determination of too high a value for n_min at overpressure (p_is > p_should) before deactivation of a control pump. The normalization factor k is usually constant and fits the calculated and calculated with the root operation<img file="EP0905596A2_D0004.tif" />1 "normalized value for n_min to the control or output range of the controller. This in turn depends on the parameterization of a connected, the pump speed changing frequency.

0020The root operation described in DE-A-27 56 916 serves completely different purposes. A linearization of the output value to be carried out with centrifugal pumps provides root formation due to the quadratic pump characteristic. The resulting control signal is squared to compensate for a pressure drop occurring in the pipeline network and superimposed on a pressure setpoint in a summation circuit, on the other hand it is used in a Autteilungsstufe to influence the switching state of all control pumps. In contrast, in the invention, an adaptation of the lower control range limit n_minbut not an influence on the actuating signal itself.

0021The approach according to formula (1) applies to the majority of water supply systems, where at constant delivery pressure p_is is regulated on the pressure side of the pump assembly. In such systems, the pre-pressure encountered on the suction side of the pump assembly is often relatively low, since the fluid to be pumped is relatively depressurized available or removed from a reservoir which is located at the same geodetic height as the site of the pump assembly. The form must therefore not be taken into account for such applications in formula (1).

0022In the claims 2 and 3 described embodiments of the invention see in those cases where due to other feed conditions a pre-pressure on the suction side of the pump assembly is pending, a consideration of this form in the determination of n_min in front. Exceeds the suction-side form p_{in front} the limit of about 20% of the zero flow pressure p_Max the control pump used, increased switching frequencies can occur in the control pumps. The value for the minimum speed n determined via the equation (1)_min would then be a few percentage points too high. The pump to be activated would then run at an excessively high minimum speed n_min on, however, the subsequent adjusting delivery pressure would also be too high, which in turn would lead to an immediate shutdown of this then seemingly supraordinary control pump. Then the discharge pressure would drop so far that the last stopped feed pump started again, which would then possibly happen again with too high a minimum speed.

0023In such higher, but of the nature forth constant admission pressure ratios, these switching operations according to an embodiment of the invention by taking into account the fixed parameter p_{before, min} in equation (2) are suppressed.<maths id="math0003" num="(2)"><math display="block"><mrow><msub><mrow><mtext>n</mtext></mrow><mrow><mtext>min</mtext></mrow></msub><msub><mrow><mtext>(t</mtext></mrow><mrow><mtext>0</mtext></mrow></msub><mtext>) = k * </mtext><msqrt><mfrac><mrow><msub><mrow><mtext>MINIMUM {p</mtext></mrow><mrow><mtext>should</mtext></mrow></msub><msub><mrow><mtext>(t</mtext></mrow><mrow><mtext>0</mtext></mrow></msub><msub><mrow><mtext>) P</mtext></mrow><mrow><mtext>is</mtext></mrow></msub><msub><mrow><mtext>(t</mtext></mrow><mrow><mtext>0</mtext></mrow></msub><msub><mrow><mtext>)} - p</mtext></mrow><mrow><mtext>before, min</mtext></mrow></msub></mrow><mrow><msub><mrow><mtext>p</mtext></mrow><mrow><mtext>Max</mtext></mrow></msub></mrow></mfrac></msqrt></mrow></math><img file="EP0905596A2_D0005.tif" /></maths>

0024This value of p_{before, min} can, as already described in the setting of the operating parameters, be entered into the system in a simple and conventional manner.

0025In those cases where the inlet pressure on the suction side is subject to considerable fluctuations, according to further embodiments of the invention by using a sensor for the detection of the suction-side form p_{in front} at time t₀ the adaptation according to equation (3) the switching cycles already described are avoided.<maths id="math0004" num="(3)"><math display="block"><mrow><msub><mrow><mtext>n</mtext></mrow><mrow><mtext>min</mtext></mrow></msub><msub><mrow><mtext>(t</mtext></mrow><mrow><mtext>0</mtext></mrow></msub><mtext>) = k * </mtext><msqrt><mfrac><mrow><msub><mrow><mtext>MINIMUM {p</mtext></mrow><mrow><mtext>should</mtext></mrow></msub><msub><mrow><mtext>(t</mtext></mrow><mrow><mtext>0</mtext></mrow></msub><msub><mrow><mtext>) P</mtext></mrow><mrow><mtext>is</mtext></mrow></msub><msub><mrow><mtext>(t</mtext></mrow><mrow><mtext>0</mtext></mrow></msub><msub><mrow><mtext>)} - p</mtext></mrow><mrow><mtext>in front</mtext></mrow></msub><msub><mrow><mtext>(t</mtext></mrow><mrow><mtext>0</mtext></mrow></msub><mtext>)</mtext></mrow><mrow><msub><mrow><mtext>p</mtext></mrow><mrow><mtext>Max</mtext></mrow></msub></mrow></mfrac></msqrt></mrow></math><img file="EP0905596A2_D0006.tif" /></maths>

0026If the measured form p_{in front} the required target pressure p_should exceed, occurs a corresponding error message to prevent damage to the Pumpenanordung or the subsequent piping system.

0027According to another embodiment of the invention, a differential pressure measurement is possible instead of the pre-pressure measurement. When using a sensor for the differential pressure Δp between the suction and the pressure side of the pump assembly results in the minimum speed according to formula (4).<maths id="math0005" num="(4)"><math display="block"><mrow><msub><mrow><mtext>n</mtext></mrow><mrow><mtext>min</mtext></mrow></msub><msub><mrow><mtext>(t</mtext></mrow><mrow><mtext>0</mtext></mrow></msub><mtext>) = k * </mtext><msqrt><mfrac><mrow><msub><mrow><mtext>MINIMUM {(p</mtext></mrow><mrow><mtext>should</mtext></mrow></msub><msub><mrow><mtext>(t</mtext></mrow><mrow><mtext>0</mtext></mrow></msub><msub><mrow><mtext>) - p</mtext></mrow><mrow><mtext>is</mtext></mrow></msub><msub><mrow><mtext>(t</mtext></mrow><mrow><mtext>0</mtext></mrow></msub><msub><mrow><mtext>) + Dp (t</mtext></mrow><mrow><mtext>0</mtext></mrow></msub><msub><mrow><mtext>)), Dp (t</mtext></mrow><mrow><mtext>0</mtext></mrow></msub><mtext>)}</mtext></mrow><mrow><msub><mrow><mtext>p</mtext></mrow><mrow><mtext>Max</mtext></mrow></msub></mrow></mfrac></msqrt></mrow></math><img file="EP0905596A2_D0007.tif" /></maths>

0028By measuring suction and delivery pressure or differential and delivery pressure and their explicit consideration in the formulas (3) and (4) switching cycles are suppressed as a result of Vordruckschwankungen.

0029Is only the pressure-side signal of the delivery pressure p_is the pump arrangement available and a metrological detection of the pre- or differential pressure is not possible, then, in the case of particularly strong admission pressure fluctuations on the suction side of the pump assembly in formula (2), the lower physically meaningful fixed value <maths id="math0006" num=""><math display="inline"><mrow><msub><mrow><mtext>p</mtext></mrow><mrow><mtext>in front</mtext></mrow></msub><msub><mrow><mtext> = p</mtext></mrow><mrow><mtext>before, min</mtext></mrow></msub></mrow></math><img file="EP0905596A2_D0008.tif" /></maths> used. However, if the admission pressure fluctuations reach an order of magnitude which can not be compensated with this method, then with further embodiments of the invention the effects of this fluctuating form can also be suppressed.

0030For this purpose, the microprocessor system is equipped with or connected to an instance for evaluating the time interval .DELTA.T between the respectively last activation and deactivation processes of one or more control pumps and a mathematical operation arithmetic unit. This calculation block can be realized on the basis of fuzzy logic.

0031If an unexpectedly high pre-pressure triggers higher switching cycles of the control pumps, a further embodiment of the invention provides that the adaptation method formulated in claim 2 is extended according to formulas (5) and (6). The previously set formula (2) for the minimum speed n_min(t₀) is about another size <i>tolerance</i> Δn (t) is lowered until the switching behavior of the control pumps has calmed down.<maths id="math0007" num="(5)"><math display="block"><mrow><msub><mrow><mtext>n</mtext></mrow><mrow><mtext>min</mtext></mrow></msub><msub><mrow><mtext>(t) = n</mtext></mrow><mrow><mtext>min</mtext></mrow></msub><msub><mrow><mtext>(t</mtext></mrow><mrow><mtext>0</mtext></mrow></msub><mtext>) - Δn (t)</mtext></mrow></math><img file="EP0905596A2_D0009.tif" /></maths>

0032In the same way, the value of n_min(t) slowly increase again with a negative tolerance value as soon as the switching behavior of the control pumps has calmed over a longer period of time. Thus, a safe shutdown of the last running control pump is guaranteed even with a shortage demand.

0033In contrast to the previously described methods corresponding to formulas (1) to (4), this lowering or raising does not take place abruptly but in a continuous manner.

0034The thus modified lower speed limit n_min(t) can thus fluctuations of the form to values ​​above p_{before, min} tolerate. Values ​​of the admission pressure below this design limit permanently lead to serious problems (eg damage due to dry running of the pumps in the event of pipe breakage on the intake side) and are not the subject of this invention.

0035The value of the tolerance Δn (t) is determined by means of a recursive summation. For this purpose, the mean time duration .DELTA.T between two switching operations in the control pumps and the already set in the previous calculation cycle tolerance .DELTA.n (tT₀) with the help of the function ν (·). The time value T₀ corresponds to the sampling time constant of the microprocessor system.<maths id="math0008" num="(6)"><math display="block"><mrow><msub><mrow><mtext>Δn (t) = Δn (t - T</mtext></mrow><mrow><mtext>0</mtext></mrow></msub><msub><mrow><mtext>) + ν (ΔT (t), Δn (t - T</mtext></mrow><mrow><mtext>0</mtext></mrow></msub><mtext>))</mtext></mrow></math><img file="EP0905596A2_D0010.tif" /></maths>

0036The new tolerance value Δn (t) determined in this way, in turn, enters into the next calculation cycle in formula (5).

0037The result of a calculation of the function ν (·) is referred to below as tolerance change ν. If the functional ν (·) is implemented on the basis of fuzzy logic with the aid of a calculation block, the manufacturer can store his expert knowledge in almost ideal form. This expert knowledge is transferred to a fuzzy calculation block in the form of a rule base and the associated reference sets. The rule base contains the structural links between the inputs and outputs, the reference sets are called fuzzy sets and subdivide the value ranges of the inputs and outputs of the fuzzy computational block into subsets with blurred and flowing transitions.

0038Within the rule base of the fuzzy module, nine individual rules are defined, which can be grouped into four rule groups:<ul id="ul0002" list-style="none"><li><b>1. Increase the tolerance</b> (or lowering n_min):<dl id="dl0001" compact="compact"><dt>(1a) <b>If</b> ΔT = <i>short</i></dt><dd><b>And</b> Δn = <i>zero</i><b>Or</b></dd><dt>(1b) <b>If</b> ΔT = <i>short</i></dt><dd><b>And</b> Δn = <i>low</i><b>Or</b></dd><dt>(1c) <b>If</b> ΔT = <i>very short</i></dt><dd><b>And</b> Δn = <i>low</i><b>Then</b> ν = <i>positive</i></dd></dl></li><li><b>Second Great increase in tolerance:</b><dl id="dl0002" compact="compact"><dt>(2a) <b>If</b> ΔT = <i>very short</i></dt><dd><b>And</b> Δn = <i>zero</i><b>Then</b> ν = <i>very positive</i></dd></dl> The control groups (1) and (2) describe the reaction of the fuzzy module to a high switching frequency of the control pumps, which is identical to a short switching distance, whereby it is still distinguished whether n_min already strongly lowered (Δn <i>high</i>) or still at a high level (Δn <i>Zero or low</i>) is located. To a corresponding extent, n_min fast (ν <i>positive</i>) or very fast (ν <i>very positive</i>) lowered. In the same way, the control groups (3) and (4) work to increase n_min after a reassurance of the switching behavior of the control pumps or to maintain the currently achieved value of n_min,</li><li><b>Third Lowering the tolerance</b> (or increasing n_min):<dl id="dl0003" compact="compact"><dt>(3a) <b>If</b> ΔT = <i>long</i></dt><dd><b>And</b> Δn = <i>low</i><b>Or</b></dd><dt>(3b) <b>If</b> ΔT = <i>long</i></dt><dd><b>And</b> Δn = <i>high</i><b>Then</b> ν = <i>negative</i></dd></dl></li><li><b>4th Adhering to the tolerance</b> (n_min remains unchanged):<dl id="dl0004" compact="compact"><dt>(4a) <b>If</b> ΔT = <i>long</i></dt><dd><b>And</b> Δn = <i>zero</i><b>Or</b></dd><dt>(4b) <b>If</b> ΔT = <i>short</i></dt><dd><b>And</b> Δn = <i>high</i><b>Or</b></dd><dt>(4c) <b>If</b> ΔT = <i>very short</i></dt><dd><b>And</b> Δn = <i>high</i><b>Then</b> ν <i>= Stop</i></dd></dl></li></ul>

0039The linguistic terms for the quantities ν (<i>very positive, positive, negative stop</i>), ΔT (<i>long, short, very short</i>) and Δn (<i>Zero low, high</i>) are described numerically by fuzzy sets, so-called fuzzy sets. These are specified by means of supporting or characteristic values ​​in triangular or trapezoidal course. This approach corresponds to the usual procedure in fuzzy theory.

0040For this purpose, the manufacturer or user of the pump assembly predetermined a total of five other characteristics as constant reaction variables. These five characteristics comprise two thresholds ΔT₁ and ΔT₂, upon reaching an increase or decrease in the minimum speed n_min according to formula (5) and three characteristic values ​​ν₁ to ν₃, the degree of increase or decrease of the minimum speed n_min mark. These parameters determine the reaction rate for the continuous reduction of the minimum speed according to formula (5).

0041While the characteristic values ​​for the corresponding fuzzy sets of the first input variable .DELTA.T or the output variable .nu. Are given by specifying the characteristic values ​​.DELTA.T₁ and ΔT₂ or ν₁, ν₂ and ν₃ are defined as constant reaction quantities by the manufacturer or user, the subject matter of the invention automatically calculates the characteristic values ​​Δn₁ and Δn₂ the fuzzy sets for the second input variable Δn of the fuzzy block.

0042The basic values ​​Δn₁ and Δn₂ The fuzzy sets for the input variable Δn are directly dependent on the lower or upper limit of the permissible value range for the lowering or raising of n_min, The lower setting range limit n_min takes at the lower allowable limit n specified by the manufacturer or user_u their minimum value, a further decrease of n_min is not possible. The support value Δn₂ results as the maximum permissible tolerance value by conversion from formula (5):<maths id="math0009" num="(7)"><math display="block"><mrow><msub><mrow><mtext>.DELTA.n</mtext></mrow><mrow><mtext>2</mtext></mrow></msub><msub><mrow><mtext> = n</mtext></mrow><mrow><mtext>min</mtext></mrow></msub><msub><mrow><mtext>(t</mtext></mrow><mrow><mtext>0</mtext></mrow></msub><msub><mrow><mtext>) - n</mtext></mrow><mrow><mtext>u</mtext></mrow></msub></mrow></math><img file="EP0905596A2_D0011.tif" /></maths>

0043The remaining support value Δn₁ corresponds to the geometric mean of the permissible tolerance range <maths id="math0010" num=""><math display="inline"><mrow><msub><mrow><mtext>Δn = [0, Δn</mtext></mrow><mrow><mtext>2</mtext></mrow></msub><mtext>]</mtext></mrow></math><img file="EP0905596A2_D0012.tif" /></maths>, It follows from formula 8 to:<maths id="math0011" num="(8)"><math display="block"><mrow><msub><mrow><mtext>.DELTA.n</mtext></mrow><mrow><mtext>1</mtext></mrow></msub><mtext> = </mtext><mfrac><mrow><msub><mrow><mtext>.DELTA.n</mtext></mrow><mrow><mtext>2</mtext></mrow></msub></mrow><mrow><mtext>2</mtext></mrow></mfrac></mrow></math><img file="EP0905596A2_D0013.tif" /></maths>

0044By constantly changing during operation different degrees of individual statements within the rule base shown above is obtained by means of known in fuzzy theory sum-prod-method finally by averaging the individual results of all nine individual rules (1 a - 4 c) a value for the tolerance change ν or for the tolerance Δn (t) according to formula (6), which then uses formula (5) to adapt the lower control range limit n_min leads.

0045The operating case according to single rule (4c) is critical. Here is the by n_u given tolerance range already exhausted, further lowering of n_min is not possible. Nevertheless, the control pumps are switched with great frequency. In such a case, the design of the controller provides an error message and, for example, reacts with the deactivation of all control pumps.

0046An embodiment of the invention is illustrated in the drawings and will be described in more detail below. It show the<ul id="ul0003" list-style="bullet"><li>Fig. 1 is a system diagram of a typical pump assembly with associated control system without separate detection of the pre- or differential pressure between suction and pressure side, the</li><li>2a-2c an overview of the permissible value ranges of the manipulated variable n and the lower control range limit n_min, the</li><li>Fig. 3-7 block diagrams and time histories of n_min in different procedures, the</li><li>Fig. 8a - 8c the fuzzy sets used in the fuzzy computational block and the</li><li>Fig. 9 -12 diagrams in which the control behavior of the pump assembly is shown.</li></ul>

0047The in Fig. 1 Pump assembly shown consists of three parallel working centrifugal pumps 11 and 21, which is a fluid, for. B. Water, in a pipeline system from a common inflow 8 via a common outlet 9 to one or more - not consumers - promote. The inflow 8 is located on the suction side of the pump assembly and the drain 9 on the pressure side. At least one of the centrifugal pumps used is designed to be variable in speed with the aid of a frequency converter 12. The configuration shown consists of a variable-speed centrifugal pump 11, an associated frequency converter 12 and two other via contactors 22 on the power network 23 switchable centrifugal pumps 21st Instead of the switchable pumps 21, other variable speed pumps 11 with associated frequency inverters 12 can be used. All activated at a given time during operation pumps are hereinafter referred to as control pumps.

0048To prevent backflow, the centrifugal pumps are equipped with check valves 6. It was dispensed with the representation of manual shut-off valves, which are often still provided at the connecting piece of the pump to prevent the service outlet, when removing a centrifugal pump, after a complete closing the discharge of the pumped medium.

0049Depicted in gray is a microprocessor system 4, which continuously determines the fluid pressure prevailing on the pressure side of the centrifugal pumps 11, 21 with the aid of a sensor 5. The possible use of a sensor 55 for measuring a pre-pressure on the suction side 8 or the use of a sensor 555 for detecting a differential pressure between suction side 8 and pressure side 9 is shown in this illustration by dashed lines. Such finds use for a Pumpenanordung, as described in claims 4 and 6. For fluidic minimization of occurring pressure surges during switching operations, a pressure equalization tank 3 may be mounted on the part of the piping system.

0050In the microprocessor system 4, a coordination entity 49 controls the interaction of all subfunctions 40 to 48 and 400. For the clarity of the illustration in FIG. 1 ensure only the signal paths between these sub-functions 40 to 48 or 400 shown as arrows. The technical connections between the coordination instance 49 and the remaining sub-functions 40 to 48 and 400, however, are not explicitly shown. For communication with a user or another computer system is an interface 7, which may be in the form of a keyboard, a display or in the form of a bus or modem connection. All required parameters, in particular p_should, n_u, p_{before, min} and the fuzzy constants ν₁ to ν₃ and ΔT₁ to ΔT₂, entered into the microprocessor system 4.

0051A sample and hold circuit 40 detects at fixed intervals with a sampling time constant T specified by the user or manufacturer₀ the value p_is of the connected pressure sensor 5. A controller module 42, which may also be designed as a linear PID controller, calculated from the supplied by a differential image 41 control error (p_should - p_is) the control value n for the connected frequency converter 12. Of course, depending on the system, other types of controllers can be used. The coordination instance 49 ensures that this control value n neither the lower limit n determined by an identification instance 45_min is still below the maximum allowable, fixed upper pump speed n_Max exceeds.

0052The identification instance 45 calculates the lower control range limit n_min when activating or deactivating a control pump 11, 21. The computational process is also monitored by the coordination instance 49. In the case of fluctuating but not measured form p_{in front}, the calculated value for n_min be reduced by using a switching distance evaluation 46 with subsequent calculation block 400 so far that the problems resulting from the Vordruckschwankungen no effect on the required constancy of the controlled variable p_is demonstrate. The computing block 400 may be implemented based on fuzzy logic.

0053For this purpose, the switching interval evaluator 46 determines the average time duration ΔT between two switching operations in the control pumps 11, 21. In conjunction with the tolerance value Δn (tT₀) calculates the computing block 400 using the tolerance change ν according to formula (6) from a new value for Δn (t), which in turn is then passed to the identification instance 45. There, in the next calculation step, with the aid of the difference formation according to formula (5), a new adaptation of the lower control range limit n takes place_min(T).

0054A switching block 44 assumes at negative pressure (p_is <p_should) activating further pumps 21 or when overpressure occurs (p_is > p_should) the deactivation of redundant control pumps 11, 21, if the calculated by the controller 42 control value n already at their respective upper (n_Max) or lower (n_min) Limit is located. In order to reduce the pressure surges when switching fixed-speed pumps 21, an opposing control of all variable-speed control pumps 11 in the form of an up or down ramp using a ramp generator 43 instead of the pressure-dependent control of the pump speed n done. For this purpose, a switch 48 is used, in which case the instance 49 takes over the coordination of all processes.

0055The control device in the form of the microprocessor system 4 contains even more functions, wherein z. B. an error detection 47 for detecting, monitoring, processing and display of irregularities or deviations within the pump assembly is used.

0056FIGS. 2a and 2b show, in the manner of a diagram, the ranges of values ​​of the control system for the pressure p as a controlled variable and FIG. 2c shows the pump speed n as a manipulated variable in a simplified form as signals which are constant in time.

00572a and 2b are shown against a horizontal time axis on a vertical axis:<ul id="ul0004" list-style="bullet" compact="compact"><li>as a dashed line, the values ​​for the setpoint pressure p_should as a reference,</li><li>as narrow dotted line the measured discharge pressure p_is as a controlled variable and</li><li>as a wide dotted line the form p_{in front} as a disturbance.</li></ul>

0058In Fig. 2a, the case is shown in which the pending on the suction side of the pump assembly form p_{in front} tends to zero. By contrast, the form p_{in front} in Fig. 2b in the order of 30% of the required target pressure p_should for the pressure side of the pump assembly. However, the most important variable for adjusting the adjustment range is the pressure difference Δp between the upstream pressure p_{in front} on the suction side and the delivery pressure p_is on the pressure side of the pump assembly. If this pressure difference is high (FIG. 2a), then the lower control range limit n_min tend to be set higher than at low pressure difference (Figure 2b).

0059In Fig. 2c, the allowable ranges of values ​​for the manipulated variable n and their lower limit n_min shown as gray bars. The first bar C (far left) shows the permissible setting range for the lower setting range limit n_min, This lies between the user-defined lower limit n_u and that of the system by means of equation (1) for <maths id="math0012" num=""><math display="inline"><mrow><msub><mrow><mtext>p</mtext></mrow><mrow><mtext>is</mtext></mrow></msub><msub><mrow><mtext> = p</mtext></mrow><mrow><mtext>should</mtext></mrow></msub></mrow></math><img file="EP0905596A2_D0014.tif" /></maths> determined maximum value max (n_min). This maximum value occurs as soon as the controlled variable p_is their setpoint p_should has reached or exceeded. The lower setting range limit n_min is set to the high value n according to formula (1)_A set when the form according to Fig. 2a disappears. This results in an adjustment range, which is represented by the third bar A (center right). In the same way, the lower limit value n becomes n_min according to the formulas (2), (3) or (4) to the lower value n_B set when the form of Fig. 2b assumes a significant value. This results in an adjustment range, which is represented by the second bar B (center left). The fourth bar D (far right) shows the minimal occurring setting range for the pressure regulator, which results after having neglected form p_{in front} = 0 the controlled variable p_is their setpoint p_should has reached or exceeded.

0060FIGS. 3 to 7 are block diagrams and time histories of n_min shown at different boundary conditions, with Figs. 3 and 4, the internal processes of the identification instance 45 of FIG. 1 show. FIG. 6 additionally shows the internal sequences of the instances of the switching distance evaluation 46 and of the calculation block 400.

0061FIG. 3 shows a block diagram of a setting range adaptation, as would occur according to claims 1 or 2. The conversion takes place in the arithmetic block 453. A sample-and-hold element 451 hereby guarantees a hold-on of the time t₀ the last switching operation of a control pump determined value of n_min, The switching process recognizes the time differentiator 452. The only in formula (2) incoming fixed value p_{before, min} is shown in Fig. 3 as a dashed arrow.

00624 shows a block diagram of a setting range adjustment, as would be done according to claims 4 or 6. In contrast to the representation of FIG. 3, here also the form p detected by means of a sensor is shown_{in front} or differential pressure Δp between suction and pressure side in the adjustment of the adjustment range.

0063FIG. 5 shows a time characteristic of the value for the lower setting range limit n resulting according to claims 1, 2, 4 or 6_minbased on the structures shown in Figs. 3 or 4. When there is a change in the number N of active control pumps, a time t occurs₀₁ a sudden increase in the value of n_minwhereas at a later time t₀₂ a sudden decrease of n_min he follows.

0064FIG. 6 shows a block diagram for a setting range adjustment. Here, in addition to the jump-shaped change of the lower control range limit n_min according to FIG. 3 or 4 and FIG. 5 at the times t₀₁ or t₀₂ a continuous decrease or increase of n_min taking into account formulas (5) and (6). This is done by means of a computing block 400, which can be realized on the basis of fuzzy logic. It consists of a memory element 401 and a block 402 for calculating the tolerance change ν (t). Block 402 uses the information about the time interval ΔT between two switching processes in the control pumps, which is supplied by the Schaltabstandsauswerter 46.

0065FIG. 7 shows the time characteristic of the value for the lower setting range limit n belonging to FIG. 6_min(T). On the basis of the curve it is clear that by the continuous reduction or increase of n_min one beyond the mere snapshot of the plant state at time t₀₁ or t₀₂ the jump-shaped change beyond adjustment of the control range is possible.

0066FIGS. 8a to 8c show in diagrammatic form the fuzzy sets used by a fuzzy computation block 400 in different line shapes, if such according to FIG. 1 or FIG. 6 applies.

0067Fig. 8a shows the three fuzzy sets <i>very short and long</i> for the first input variable <i>Operating distance</i> ΔT of the calculation block 402 in FIG. 6, which is defined by the two parameters ΔT given by the manufacturer or user of the system₁ and ΔT₂ be determined. The triangular or trapezoidal shape of these fuzzy sets is fixed by the manufacturer in this case.

0068Fig. 8b shows the three fuzzy sets <i>Zero, low and high</i> for the second input variable, tolerance Δn of the calculation block 402 in FIG. 6, which is determined by the two parameters Δn determined by the system with the aid of the formulas (7) and (8)₁ and Δn₂ be determined. Also for this variable, the course of the three fuzzy sets is fixed by the manufacturer.

0069Finally, Fig. 8c shows the four fuzzy sets <i>negative stop, positive and very positive</i> for the output variable <i>tolerance change</i> ν of the calculation block 402 in Fig. 6. While the fuzzy set <i>stop</i> fixed by the manufacturer to ν = 0, the three remaining fuzzy sets are from the manufacturer or user of the system by specifying the parameters ν₁ to ν₃ variable. Also for the output variable<i>tolerance change</i> ν is the form of all fuzzy sets as so-called singletons fixed.

0070FIGS. 9 to 12 show diagrams of the temporal signal curves, in which the control behavior of a test run pump arrangement is shown. For this purpose, the constructed on a test stand pump assembly consisted of a variable speed and other rigidly operated on the power grid centrifugal pumps. Shown are always the measured time courses of a control cycle of 60 seconds duration.

0071In FIGS. 9 and 10, the starting process of the pump arrangement is in the temporal section of the first 5 seconds. Here, the variable-speed pump 11 is ramped up in the form of a linear ramp in their speed, wherein the delivery pressure p_is according to the characteristics of the pump used and builds up from 0 m head. This ramp starts at the currently set value of the lower setting range limit n_minin Fig. 9 at about 80% of the maximum speed n_Max lies. It ends when the maximum speed n is reached_Max or when the setpoint value p is exceeded_should for the delivery pressure p_is, The setpoint is at 60 m head and is reached only after switching on a second pump 21. For this purpose, the timing of four different signals are shown. These are:<ul id="ul0005" list-style="bullet" compact="compact"><li>the controlled variable of the delivery pressure p_is (in meters of delivery),</li><li>the manipulated variable n of the variable pump speed (as a percentage of the upper limit n_Max)</li><li>the lower setting range limit n_min (as a percentage of the upper limit n_Max) and</li><li>the number N of active additional variable-speed control pumps 21.</li></ul>

0072The temporal signal curves for a run-up process and a subsequent control behavior is at a pressure p_{in front}= 0 shown. When recording the temporal waveforms of the flow rate requirement or the opening of the pressure-side outlet 9 was constant.

0073In FIG. 9, in the lowest signal curve N (t), an increased switching frequency of the variable speed control pumps 21 can be ascertained. The diagram indicates the number of active variable-speed control pumps 21 with N = 1 or N = 2. There is a constant switching on and off of the second speed-rigid control pump. The cause of the undesired switching behavior is a manually set too high value for n_minwhich is about 80%. This leads to undesirable pressure peaks and pressure drops in the waveform of the controlled variable p_is, In a corresponding manner, the pressure regulator 42 reacts with the manipulated variable n of the variable pump speed.

0074In the waveform of Figure 10 was the setting of n_min automatically from the microprocessor system 4 according to claim 1. The lower Stellbereichsgrenze n_min always corresponds to the system requirements and thus the variable-speed pump is always operated in the optimum setting range. A switching back and forth of the second speed-rigid control pump does not take place. In contrast to the signal curve of the controlled variable p_is According to FIG. 9, no undesired pressure peaks and burglaries are shown in the signal curve of FIG. 10.

0075FIGS. 11 and 12 show the temporal signal curves for the control behavior of the pump arrangement when high pre-pressure values ​​and high pre-pressure fluctuations are present. The form p_{in front} follows a temporal profile, which provides that p_{in front} initially in the time range of 0 to 10 seconds in the order of magnitude of the setpoint value p specified here_should The pressure of 60 m head, then in the time range between 10 and 15 seconds to near 0 m head high sinks, again significantly increases in the period of 30 to 35 seconds to about 50 m head, to last in the time range between 45 and 50 seconds again to drop to near 0 m head. During the entire measuring time, the delivery volume requirement or the opening of the discharge side discharge was constant.

0076The Fig. 11 shows the effect of severe Vordruckschwankungen on a pump assembly, take place with no remedial action. Activation of the variable-speed variable-displacement pump 11, which is set by the control system as the only operating mode, takes place when the pre-pressure value falls below 50 m delivery height at time t = 11 seconds. It becomes clear from the course of the measurement that extremely large undesired switching operations occur in the conventional control method used here. As soon as the form p_{in front} at the time of about t = 35 seconds half the predetermined target pressure value p_should reached by about 30 m head, it comes to the constant switching on and off the variable-speed variable-displacement pump 11. The violent reactions of the controlled variable p_is make themselves extremely unpleasant in a connected piping system by noise and pressure surges noticeable. This switching behavior of the control pump calms down only after the later drop in the admission pressure value p_{in front} below about 30 m head, which takes place at about time t = 47 seconds. The regulated delivery pressure p_is then moves again close to its set point p_should of about 60 m head.

0077In Fig. 12, the control behavior of the invention is shown. The control system responds to the sudden drop in the form at time t = 11 seconds with the activation of a variable speed control pump as in Fig. 11. The computing block 400, which was constructed in this measurement based on fuzzy logic, caused by the Fuzzy algorithm the continuous lowering of the lower limit value n_minuntil it reaches the value of n at time t = 30 seconds_u = 30% has reached. This reduction was triggered by the switch-on of the variable speed control pump 11. To the main effect, the continuous lowering of n_minIn order to be able to show in a time diagram a short measurement duration, the fuzzy algorithm in the test setup used was given by specifying very high values ​​for the threshold values ​​ΔT₁ and ΔT₂ parameterized so that he reacted immediately and not, as usual in practical systems, only after several shifts in the space of a few minutes.

0078This low value for n_min prevents the constant switching on and off according to FIG. 11. Since there is no increased switching frequency of control pumps, the lower control range limit n_min from the time t = 52 seconds slowly raised again to ensure a safe shutdown of all control pumps even in the case of a minimum quantity requirement. During the period from t = 10 to t = 60 seconds, the manipulated variable n runs counter to the form p_{in front}to the delivery pressure p_is in the range of its associated setpoint p_should to keep.

List of abbreviations used

0079<dl id="dl0005" compact="compact"><dt>k</dt><dd>= Normalization factor</dd><dt>n</dt><dd>= Speed ​​of the control pump (control value of the pressure regulator)</dd><dt>n_min</dt><dd>= Minimum speed of the control pump (lower control range limit)</dd><dt>n_Max</dt><dd>= Maximum speed of the control pump (upper control range limit)</dd><dt>n_u</dt><dd>= lower limit for a variable setting of n_min</dd><dt>.DELTA.n</dt><dd>= Tolerance value for lowering or raising the lower setting range limit n_min</dd><dt>ν</dt><dd>= Tolerance change to adjust Δn</dd><dt><b>N</b></dt><dd>= Number of active control pumps</dd><dt>p_is</dt><dd>= Delivery pressure (controlled variable: measurement on the pressure side of the pump arrangement)</dd><dt>p_should</dt><dd>= Setpoint for the delivery pressure (reference variable)</dd><dt>p_{in front}</dt><dd>= Admission pressure (disturbance variable: pressure on the suction side of the pump arrangement)</dd><dt>p_{before, min}</dt><dd>= Minimum value of the pre-pressure (static size, which is only taken into account in the system design)</dd><dt>Ap</dt><dd>= Differential pressure between suction and discharge side of the pump arrangement</dd><dt>p_Max</dt><dd>= Zero delivery pressure (maximum delivery pressure of a centrifugal pump at delivery q = 0)</dd><dt>q_is</dt><dd>= Flow or flow rate per unit time (disturbance variable)</dd><dt>q_min</dt><dd>= Shortage requirement (very low flow: <maths id="math0013" num=""><math display="inline"><mrow><msub><mrow><mtext>q</mtext></mrow><mrow><mtext>is</mtext></mrow></msub><msub><mrow><mtext> = q</mtext></mrow><mrow><mtext>min</mtext></mrow></msub><mtext> ≈ 0</mtext></mrow></math><img file="EP0905596A2_D0015.tif" /></maths>)</dd><dt>t_O</dt><dd>= Time of measurement</dd><dt>T_O</dt><dd>= Sampling time constant of the microcomputer system</dd><dt>.DELTA.T</dt><dd>= Time interval between two switching processes of control pumps</dd><dt>.DELTA.T₁ and ΔT₂</dt><dd>= Characteristic values ​​for the first input variable of the fuzzy block</dd><dt>.DELTA.n₁ and Δn₂</dt><dd>= Characteristic values ​​for the second input variable of the fuzzy block</dd><dt>ν₁ to ν₃</dt><dd>= Characteristic values ​​for the output variable of the fuzzy block</dd></dl>