Power control of a wind park

Translation of description of equivalent WO 2007006565 A2

p0001Power control of wind farms

p0002The invention relates to a method for controlling a wind power installation having a generator driven by means of a rotor generator and a connected thereto inverter, and a controller, wherein the controller comprises a power control module controls the output through a connection line in a power transmission network performance, or a wind farm. The invention further relates to a powered by this method wind power plant or wind farm.

p0003To generate electrical energy using wind energy on a larger scale wind turbines are produced with ever higher performance. Often several established at a site wind turbines are combined to form a wind farm. However, it is so that it is the appropriate for the installation of wind turbines or wind farms high power high-wind sites are located in rural, sparsely populated areas. There, the power grid of the energy supply companies usually only a low transmission power. This often means that such restrictions for the operation are due to the limited transmission capacity of the power transmission network. The limitations of a power transmission network are determined by performance limitations of wires and an interposed components, such as transformers. The operating limits of the power transmission network enforce a limitation that prevents under favorable wind conditions, full power of the wind turbine or the wind farm could be exploited. This leads to economic disadvantages.

p0004The invention is based on the object, a

p0005Wind power plant or to create a wind farm and a method of operating that enable better utilization.

p0006The inventive solution lies in the features of the independent claims. Advantageous further developments are subject of the dependent claims. According to the invention, in a method for controlling a wind power installation having a generator driven by means of a rotor generator and a connected thereto inverter, and a controller, wherein the controller by means of a power control module controls the output through a connection line in a power transmission network capacity and means for measuring the power fed comprises, provided that one of Maximalström

p0007Link is determined, a residual in to the mains power to the maximum power current reserve is determined and a correction value is determined for readjusting the output power.

p0008The essence of the invention lies in the idea, always fully utilize the available capacity of the link for connection to the power grid, and if possible, regardless of the respective operating state. It is based on the realization that the operating limits of many used for the network connection to the power grid components, such as cables or transformers, by their respective thermal Limits are determined. To ensure operational safety, resulting in the individual components losses must even under unfavorable conditions do not exceed a critical value. When determining the critical value is to be noted that the voltage in a network is not a constant, but has a considerable variation range. Thus, the voltage in the high voltage grid can by +10% / according to the directives of the Association of network operator (Transmission Code 2003) - vary 13% of the rated voltage. To ensure operational safety, in any event, takes place traditionally an interpretation on the most critical point of the range. Based on the allowable feed-in power is calculated, where appropriate

p0009Consideration of additional reactive power delivery or -bezug. The invention has recognized that in this calculation, the components are not fully exploited. Based on the known formula for the resulting in a component having a complex resistor power dissipation P_v = I_8th x I_N / Real (Z_L) Results in the finding that the highest power dissipation occurs when in the power transmission network, the minimum allowable voltage occurs (according to the known relationship P = V x I). Then the largest current (maximum current) flows.

p0010The invention has recognized that with each other, higher voltage value actually produced in the component power dissipation is low due to the then lower current value. If the voltage is as accurate to the face value, the flow is no longer the maximum current, but a according to the equation P = U x I reduced power. Its amount is inversely proportional to the voltage. This results in a difference between the actual current flowing in the range of the rated point and the calculated maximum current. Thus, there is a current reserve. The invention utilizes this power reserve to increase the actually transmitted in the energy transmission system performance. The achievable gain depends on the actually available mains voltage in relation to the lowest permitted voltage. Behavior, as explained above, the allowable voltage variations +10 and -13% of the nominal voltage, resulting in an actual voltage in the power transmission network in the

p0011Of rated voltage a power reserve of 13%. Due to the inventive utilization of this current reserve the transmitted power may be increased by 13%, without it therefore leads to an overload of the components. If the actual voltage above the rated voltage at the upper permissible level, the power reserve is even 23%. This makes it possible according to the invention, even almost¹A transfer more power into the power grid, without the permitted losses exceeded. With such an increase in the potential

p0012Transmission power, the utilization of wind farms are significantly improved. Thus, the profitability of the operation increases.

p0013Expediently, a limiting device is provided which adjusts a phase angle between the output in the power transmission network current and network voltage when reaching the maximum current in response to a selection signal. The total amount of current is determined in this case, is in fact at the level of the maximum current, changing the angle between current and voltage. This can be achieved that can be specified with the selection signal whether primarily active power or primarily reactive power to be fed into the grid. The selection signal can thus be selected if a higher yield is to be given by higher active power feed or voltage support the grid by higher reactive power feed preference. Conveniently, the selection signal is generated by a voltage droop. It makes it possible to determine the necessary for the grid support reactive power demand. Based on it can be decided then whether the active substance or the

p0014Reactive power delivery priority must be given to. Alternatively or additionally, however, can also be provided to supply the selection signal from outside, in particular by the network operator. Thus, it is the network operator allows, in dependence on the state of the

p0015Power transmission network to decide whether more action is more or reactive power required and to be fed.

p0016Depending on the respective abgeforderten active or reactive power, the respective other parameters, ie reactive or active power, are determined by a predetermined characteristic. For this, a characteristic module can be provided which is for example integrated into the voltage droop. It is adapted to determine a function of a size, for example, the active power, the other size, for example, the reactive power from the input characteristic. The characteristic is to be freely selected. It is preferable that this is an ellipse function, which is conveniently normalized to the maximum power which is as follows: 1 = P²: a² + Q²: b², By choosing the coefficients a, b may favor the active and reactive power feed to be achieved.

p0017Conveniently, an additional stream is intended to compensate for pipeline capacity and additionally fed. This current can be determined independently of the mains voltage and the current limit or the actual active current injection. This is preferably done be x calculated jwc about Formula iq = U / Z = U. This current is used to compensate the capacitive loads, wind power plant side of the link and thus remains without influence up the current limit toward the network. The compensation of this capacitive load is particularly in the interconnection of several wind turbines at a wind farm of importance.

p0018Appropriately, a limit signal is applied to the wind turbine to limit the discharge level of its current. It can for example be in the range of 0 to 100% of the permissible current. This action is taken at the source of electrical power, in particular with respect to the active current. Appropriately, in determining the limit signal of the complex impedance of the line is included for wind turbine with.

p0019The invention further relates to a method for controlling a wind farm having a wind farm master and at least one wind turbine having the features of claims 1 to 8. FIG.

p0020Appropriately, different correction values ​​are determined for the individual wind turbines. While the correction value may also apply to all Wind turbines of a park are given the same, but usually it is better to specify the respective proportions of active and reactive power between the different wind turbines differently. This loss can be reduced and a higher utilization can be achieved.

p0021Furthermore, it is expedient to determine individual limit signals for the wind turbines and to apply. Even so can be done to optimize the overall parking capacity by higher limits are specified in more powerful wind turbines than in low-power installations of the wind park. Here refer powerful and inefficient, not only on the structural design of the individual wind turbines, but also include location-dependent parameters, such as the best available location for wind etc.

p0022The invention further relates to a

p0023Wind power plant and a wind farm for carrying out the above method.

p0024The invention will be explained with reference to the drawing, in the advantageous

p0025Exemplary embodiments are shown. Show it:

p0026Figure 1 is a schematic view of a wind power plant according to a first embodiment of the 'invention.

p0027Fig. 2 is a diagram of the power of the wind turbine shown in Figure 1 fed via the voltage output.

p0028FIG. 3 is a detailed schematic view for determining a correction value according to the first

p0029Embodiment; and

p0030Figure 4 is a schematic detail view of a characteristic module.

p0031Fig. 5 is a schematic view of a wind farm according to a second embodiment of the invention.

p0032In the wind turbine shown in FIG. 1 is a basic structure of a conventional variable-speed wind turbine. The wind turbine 1 comprises a tower 11 with a thereon nacelle 12. At one end face is a rotor 13 rotatably mounted and a drive shaft (not shown) connected to a generator 14th The generator 14 is preferably a double-fed asynchronous, but also other types such as synchronous, asynchronous or permanent-magnet machines are used. The generator 14 is electrically connected to a further inverter 15 and to a line 3rd The inverter 15 can be designed and connected as full or as partial converters. To control a controller 2 is provided .an the wind power plant. 1 She is showing deposed by the wind turbine 1 shown, in fact it is provided spatially usually at the wind power plant 1 itself, often even in the nacelle 12 arranged. The controller 2 is designed to operate the wind power plant 1 according to adjustable default. The specifications can be defined internally or supplied externally via a connector 29th This is often referred to as a data connection via a modem designed so that access is possible via a telephone or data network or a wireless data transmission. The controller 2 is provided with measuring devices, of which an example a voltage measuring device 22 and a Stromesseinrichtung 23 shown in the line. 3 They are used to determine the output from the wind turbine 1 in the line 3 performance and the corresponding control of the wind turbine 1. Other measuring devices can be provided, but are not shown for clarity.

p0033The output of the wind power plant 1 in line 3. Electric power is transmitted via a link 4 in a power transmission system. 9 The link 4 is used for connection of the wind turbine 1 to the power transmission network 9. Depending on the location of the wind turbine 1 with respect to the energy transmission system 9, the link 4 have a sometimes considerable extent. Distances of several kilometers are not uncommon here. For offshore installations, the distances can be up to 100 km, here often parallel links are provided for safety. The link consists of a 4 shown

p0034Medium-voltage line 41, a transformer 42 and a high voltage line 43 and a node 49 to the power transmission network 9. In the illustrated Embodiment is in the power transmission network 9 to a high-voltage grid. If the port is provided at a medium or low voltage grid, the transformer 42 may be omitted.

p0035^■The controller 2 of the wind turbine 1, a power control module 25. It is designed to operate the wind power plant according to internal specifications and / or externally by the operator of the power transmission network 9 applied via terminal 29 specifications. These acts, the power control module 25 to the inverter 15 a, possibly also on the rotor 13. In order to measure the output from the wind turbine 1 in the line 3 power measurement devices are used 22, 23, with them, the entire electrical power output, the

p0036Active power component and the reactive power are determined. Thus, specific requirements regarding the dispensed active power and reactive power can be met.

p0037The transmission path 4 is for a specific rated power P_N designed. This rating may be determined by the deliverable maximum at the connection point 49 in the power transmission network performance, but you can also go through the dimensioning of the individual components of the link 4, as lines or transformers, to be determined. With this rating ensures that in compliance with the standard conditions for the voltage in the energy transmission system 9 congestion will not occur. The invention makes use now that the

p0038Power limitation of these components is generally determined from the thermal load by power dissipation. To ensure safe operation, should the not exceed power dissipation even under unfavorable conditions a certain critical limit. It should be noted that the voltage is not constant in network 9th As seen from Fig. 2, there is a tolerance range around the nominal voltage. at

p0039High voltage networks it is for example in accordance with the relevant guidelines of the Association of system operators VDN (Transmission Code 2003) +10 and -13% of the rated voltage. In this area the voltage network must operate safely, together with its associated components. Accordingly, the link 4 is designed. This means that the link 4, the rated power P_N also can transfer must, if the voltage at the lower end of the voltage range is, therefore, for example, 13% below the nominal voltage. The case to be transmitted maximum power is obtained from the relationship P = V x I to I_N = P_N / (U_N X 0.87). This maximum current is 13% greater than the nominal current in accordance with a calculation I_N = P_N / U_N results. This means that the link is designed for a 13% higher power than the nominal power at P_N and rated voltage U_N mathematically results rated current I_N,

p0040Operates at the transmission path 4 now with the proviso that to comply with the permissible power loss of the maximum current I_M is not exceeded, it is apparent from the lower limit value for the mains voltage rising higher voltage power gain. It is shown in Fig. 2 as a hatched region. Is the voltage in the energy transmission system 9 actually on the nominal value, so this results in a profit over the rated power P_N of 13% and in the case where the actual voltage in the energy transmission system 9 reaches the upper tolerance value, a gain of 23%. The invention utilizes the fact that here, despite exceeding the rated power by almost¹A by the current I_M certain power dissipation within the permissible range is such that no overloading of the transmission line 4 is present. The invention enables thus without making changes to a significantly better utilization of a given transmission path 4. The wind energy installation 1 in this mode in compliance with the maximum current I_M to operate, an additional power device 6 is provided.

p0041The additional power device 6 is shown in detail in its schematic structure in Fig. 3. It comprises a difference element 63 and a multiplier 65 as

p0042Main components. At an input 61 of the differential element

p004363 is an input value for the maximum current I_M connected. This input value can be entered via a manual unit, are made from a memory area of ​​the controller 2 or externally available, and can be varied over time. To another input 62 of the actually flowing through the line 3 into the link 4 current is applied. The differential element 63 determines from a current reserve .DELTA.l and submit them via a connecting line

p004464 and the multiplier to 65th At another terminal of the multiplier 65, the voltage U is applied to the connecting line 3 via a terminal 66th

p0045From this a correction value .DELTA.P is calculated for the deliverable power and output at an output 67th This

p0046Output terminal 67 is connected to the power controller 25 of the controller. 2 Thus, by the Wind turbine power output to be increased accordingly.

p0047Fig. 4 is a characteristic module 7 is shown. It serves to identify a subject to the limits nor transferable reactive power based on a predetermined value for the active power to be transmitted. In characteristic module 7 an elliptical curve is to be implemented. It follows the relationship 1 = P²: a² + Q²: b²Which is based in the presentation of the maximum transmittable power. By specifying an active power component P, or of a phase angle φ allows the characteristic module 7 to determine the respective maximum value pair for active power P and reactive power Q with reference to the implemented elliptic curve. The characteristic module 7 may be provided in the controller 2 of the wind turbine or in the case of a wind farm with several wind turbines expediently in the Park Master. 5

p0048First, 5 reference is made to the schematic representation of a wind farm constructed in accordance with the invention in Fig.. There are four wind turbines 1 are shown as an example, which are connected via two branches 3 'of the line. 3 With respect to the construction and operation of the individual wind turbines, reference is made to the above representations. Differences are explained below.

p0049In addition to the wind turbines 1, the wind farm on a Park Master. 5 This provides a higher-level management for all wind turbines of the wind farm 1 ready and monitors the connection of wind farms to the power grid 9. specifications from the outside, as for example, those of the operator of

p0050Power transmission network 9, are applied via a terminal 59 at the Park Master 5 and not transmitted directly to the individual wind energy installations. 1 The Park Master 5 determined by the operating conditions and the specifications desired quantities for the operation of the individual wind turbines 1. It shall be sent via a communication link 32 to the control device 2 of each wind turbine. 1 For this, the power control module 55 is provided in the Park Master. 5 Further, the additional power device 6 is disposed in the Park Master. 5 It corresponds in its structure substantially to the embodiment shown in the single wind turbine 1 according to the embodiment in FIG. 1. Accordingly, at the Park Master are 5 input terminals for entering the

p0051Maximum current I_M and measuring devices 52, 53 are provided for current and voltage. Accordingly, the output terminal 67 of the auxiliary power unit 6 is connected via the control lines 32 to the control means 2 of the individual wind turbines. 1

p0052Further optional features are explained with reference to the second embodiment. In the Park Master 5 a limiting device 68 is additionally provided. It is adapted that, when an increase in the

p0053Line 3, the current flowing to the value of the maximum current I_M in response to a selection signal input 59 of a phase angle between the current I and the mains voltage U_N is set. This phase angle is determined according to the selection signal such that either primarily active power (phase angle as small as possible) or primarily reactive power (amount of phase angle in the range of 90 °) is fed into the power grid. 9 This can be adjusted by the selection signal at the input 59, if the supply of active power or supply of reactive power to be given priority. The selection signal may be applied by the operator or the operator of the power transmission network 9 from the outside. but it can also be provided that it is determined based on a voltage-phase angle characteristic. Given a characteristic module (not shown) is provided in the park controller 5, determines a reactive power requirement from the voltage and accordingly adjusts the selection signal.

p0054Next 69 may be provided in the farm controller 5 a superimposed voltage regulator. At its input, the measuring device 52 is connected to the voltage. It serves to stress risers at the point 41 I due to ohmic or inductive losses due to the higher current_M to detect and counteract accordingly. This can be done by engaging in the auxiliary power module 6 and reducing the output power, or preferably by specifying a larger

p0055Reactive power to the controllers 2 of the individual wind turbines. 1

p0056In the farm controller 5 may be further 57 provided a compensation current module. It is designed to compensate by selective assignment of the reactive power at the individual wind energy installations the effect of line capacitances of the lines 3 and 3 '. This compensation is aimed at the interior of the wind farms, ie wind power plant side of the link 4. The module determines the required compensation for reactive power, either controlled by measuring by means of the measuring devices 52, 53 or controlled according to the relationship iq = U / Z = U xjx wC (where Z is the complex resistance of the lines 3, 3 ', and C is the frequency, and w is the angular frequency of 2 x π xf stands). This ensures that even a far remote wind farm of the link 4 wind turbines 1, despite the results from the performance capacity risk of power surges can feed (up to surge at the respective wind turbine) the greatest possible active power in the energy transmission system. 9

p0057Preferably a single setting device 60 is arranged at the Park Master 5 further. It works with the additional service device 6 together in such a way that for the individual wind energy installations 1 custom preset values ​​are received for them to be delivered maximum current. This could serve certain wind turbines to the increased provision of effective power, while others are used for increased provision of reactive power. Thus, an adaptation to the characteristics of the individual wind turbines take place, for example, can positioned at particularly favorable locations for wind turbines increased

p0058Provision of active power are used, while the remaining increasingly provide reactive power. This allows the utilization of the wind farms and thus the economy further.