Power adjustment device for electric power systems, in particular for electric power systems with electric ovens.

0001The present invention relates to a power adjustment device for electric power systems, in particular for electric power systems with electric ovens.

0002As is known, in industrial systems comprising a plurality of electric users each whereof has its own connection times and durations, the power demands of the different users may give rise to periods of absorption equal to the maximum installed power, followed randomly by periods of low or even zero absorption, in particular when the connection and disconnection of the users are not correlated to one another.

0003This behaviour is disadvantageous, as it requires on one hand the availability of high power levels even when the power is not actually used, as occurs most of the time, and on the other hand it entails a penalization in terms of the costs related to the maximum available power.

0004The uncontrolled satisfaction of the power demands furthermore does not allow a rational management of the system.

0005GB-A-2 022 340 discloses a cooking oven having both a microwave generator and an electrical resistance heating element both operated from a common power source of limited power. The microwave generator requires less than the maximum current available from the source when operated at its full rated power level, while the resistance heating element draws the maximum available current when operated at its full rated power level. In order to optimize the cooking operation by minimizing the cooking time while avoiding demand which exceeds the maximum available power, the microwave generator and the resistance heating element are alternatively energised at their respective full rated power levels, while additionally the resistance heating element is energised from the power source at a reduced power level when the microwave generator is energised, in which the sum of the full rated power level of the microwave generator and the reduced power level of the resistance heating element is equal to the maximum available power of the power source.

0006EP-A-0 209 421 discloses a power adjustment apparatus for an electrical installation comprising a group of heating devices. The adjustment apparatus comprises means for powering the heating devices respectively at determined time intervals, and additionally, the apparatus can also be connected to means which measure the instantaneous total power consumption of the group of heating devices (considered to be non-priority users), regulated by the apparatus, and of other electrical devices not regulated by the apparatus, such as household appliances and lighting fixtures (considered to be priority users). Upon the detection by the measuring means that a threshold instantaneous total power consumption of all the users (including priority and non-priority users) has been reached, the apparatus is capable of shutting off power to one or more of the regulated heating devices, according to the sequence of turning on of the respective heating devices, thereby to assure that the priority users are powered.

0007The aim of the present invention is consequently to provide a power adjustment device for electric power systems, in particular for electric power systems with electric ovens, capable of solving the disadvantages of the known art, and in particular of optimizing the electric absorption of the system by reorganizing the power demands so as to eliminate, or at least reduce, the sequences of alternately maximum and zero absorption.

0008Within the scope of this aim, an object of the present invention is to provide a device capable of ensuring a constant absorption which is proximate to the average utilization value, without exceeding a preset threshold, therefore allowing the user to save on the fixed rate related to the available power.

0009Another object of the present invention is to provide a device which is capable of providing energy savings.

0010A further object of the present invention is to provide a device which is extremely flexible and adaptable to the system to be controlled and is easily modifiable to control any further users introduced into the system.

0011Not least object of the present invention is to provide a device which is capable of providing maximum reliability and safety, is easily applicable to existing systems and requires no particular knowledge and preparation for its use, as it entails the execution of very simple operations by its operator.

0012The above described aim, the objects mentioned and others which will become apparent hereinafter are achieved by a power adjustment device for electric power systems, in particular for electric power systems with electric ovens, as defined in the accompanying claims.

0013In particular, the power adjustment device according to the invention is based on the acknowledgement that the average power consumption of a system, e.g. an oven, in normal operating conditions is a fraction (e.g. 40%) of the maximum power, and that the operation of the system generally has very short power demand cycles. It is consequently possible to set a top power limit, close to the average used power level, and detect, store and redistribute the various random power demands, taking into account the preset power limit, so as to shift by only a few seconds the delivery of power without altering the thermal balance of the system but with considerable savings in the costs related to the available power.

0014Further characteristics and advantages of the invention will become apparent from the description of a preferred but not exclusive embodiment, illustrated only by way of non-limitative example in the accompanying drawings in the case of an electric bread-baking oven. In particular: <ul id="ul0001" list-style="none"><li>figure 1 is a general diagram of the oven equipped with the device according to the invention; and</li><li>figures 2, 2a and 3 are block diagrams of the power adjustment process obtainable with the adjustment device according to the invention.</li></ul>

0015Reference should initially be made to figure 1, illustrating the general diagram of the oven equipped with the adjustment device according to the invention.

0016In its general structure, the oven is constituted by a plurality of cooking chambers, of which only one is illustrated in the figures and is indicated by the reference numeral 1. Each cooking chamber has two distinct heating sectors, respectively in the lower part of the chamber (corresponding to the cooking level) and in its upper part, each comprising a battery or bank of resistors, respectively 2 and 3.

0017Each battery is controlled by a respective remote control switch 4, 5 which is in turn controlled by a timer 6, 7 (with closed switch C₁ = unregulated operation) or by a control and management unit 10 (with open switch C₁ = adjusted operation according to the invention). Said timer which has the function of generating operating impulses, is connected to the control and management unit 10 which ensures the distribution of power to all the users in the different chambers according to the request and to the available power, as will become apparent hereinafter. Points C₁ (which are open during normal operation, controlled by unit 10) and C₂ (which are closed during normal operation) are switching points allowing the connection and disconnection of the various elements, depending on the system being operating with or without the control unit as already mentioned. The points C₁ and C₂ can be made, differently from what has been described and without thereby requiring switches, for example, by means of manually connectable and disconnectable bridges or deviators. Each pair of timers 6 and 7 (connected to a memory 11 resp. 12 which is internal to the control unit 10 and may be implemented e.g. by an up and down counter), is controlled by a temperature controller 13 arranged in an intermediate region of the chamber and provided with a thermometer to control the temperature in the chamber. The temperature controller 13, which is a single one for both batteries of resistors, generates a continuous signal which is fed to the timers 6, 7 which transform it into intermittent activations which are variable according to the position of a knob 9 provided on said timers according to the requirements of the user. In particular the knob allows to adjust the connection time of the resistors, therefore the average power of that specific battery of resistors which is required by the user for his own requirements, from a minimum of 20% up to stable connection, corresponding to 100%, so as to obtain in any case minimum active and disconnection times of the remote control switches not lower than 7-10 seconds.

0018Each chamber has a steam generator 15 controlled by its own remote control switch 16 which is in turn controlled by a thermostat 17 which is also connected to the control unit 10. In this case, however, the adjustment of the steam generator is completely assigned to its respective temperature controller (or thermostat), and the connection to the control unit merely has the function of notifying said control unit of the switch-on and switch-off times of the generator, since its operation, being prioritized, determines the cutoff of any power exceeding the preset load according to the operating cycle preset for that instant as will be explained hereinafter.

0019The control unit 10 is also connected, (arrows 18) to the other chambers of the oven to exchange the information required for their operation, as illustrated in the figure for chamber 1 and as will become apparent hereinafter. The control unit 10 typically comprises a microprocessor (e.g. NEC 78C10) with data and program memories (including memories 11, 12), a display controlled by an own microprocessor and a keyboard for operator dialogue, as well as a watchdog circuit to check the correct operation of the device, in a per se known manner which is therefore not illustrated. The unit 10 finally has further inputs, schematically indicated at 19 in the figure and connected to setup pushbuttons and to a key to allow programming of some parameters. In particular, according to the present embodiment, the following parameters may be set: nominal power of the resistors and of the steam generator for each individual chamber; top power limit (power not to be exceeded during the operation of the adjustment device; top power limit may be modified by an external signal which indicate the absorption of power of all other devices not directly connected to the embodiment but included in the electrical sistem to be controlled); extra power (top power limit replacing the preceding one, which can be set by the operator in particular instances); cycle time (cycle time of each battery - two for each chamber -); alarm delay time (time after which the control unit warns the user that the set top power limit is insufficient for the correct operation of all the chambers); priority (allows to select two types of operation, with and without priority; in the first case the connection of the chambers is performed according to the order of demands, in the second the demands of the chambers having higher priorities are privileged); and priority order. The adjustment device according to the illustrated embodiment furthermore allows to select two different types of startup, i.e. slow startup, in which the batteries are switched on according to the demand, and quick startup, in which the adjustment device switches on all the batteries it is able to in compliance with the power limit, distributing the available power equally among the switched-on chambers. The alarm indicating insufficient power is disabled during startup and until the preset temperature is reached in all the chambers.

0020During normal operation the adjustment device according to the invention controls the connection and disconnection of the individual batteries according to the reading of the inputs and in compliance with the value of the programmed parameters as listed above. In this step the display indicates the correct operational status of the system, the values of the nominal power absorbed by the oven and the top power limit. If during this step the top power limit is such as not to allow the unit to feed all the switched-on batteries within the alarm delay time, the display indicates this condition so that the operator can provide the appropriate remedy or remedies.

0021The operation of the illustrated embodiment of the adjustment device according to the invention is now described with reference to figures 2, 2a and 3.

0022Reference should thus be made first to figure 2. Initially, when the device is activated or when a specifically provided startup push button is pressed, the microprocessor initialization procedure is started to preset the inputs and the outputs and to program the display (block POWER ON). At the end of this step the program enters a step in which it waits for keyboard commands to program the power and to enable or disable priority operation, and also checks if the key which allows the user to access the programming step is inserted. In detail, after initialization, the device checks if the priority change push-button has been pressed and if this is true the device asks whether the priority operation is to be enabled or disabled and then performs the requested change. If the priority button has not been activated, the device checks if the top power limit change button has been pressed. If it has, then it asks whether normal power or extra power is to be enabled and it acquires the supplied data from keyboard. If the power button has not been activated, it checks if the startup button has been activated and, if it has, it reruns the initialization procedure; if even the startup button has not been activated, then it checks if the key has been turned and if it has it enters the programming step, in which the operator can modify the presettable parameters. Then all the preset parameters are displayed, confirmation of the data is requested and said data are then stored. Then the sequence returns to its initial point.

0023During the execution of the sequence shown in fig. 2, an interrupt is generated for carrying out power adjustment according to the present invention, as schematically shown in fig. 2a. In particular, in the instant embodiment, the interrupt, which is not enabled only during the programming step, is automatically generated by the processor every 10 ms synchronously with respect to the microprocessor clock but fully independently from the operations performed with the buttons.

0024The actual adjustment program, symbolized in fig. 2a by block ADJUSTMENT and illustrated in the block diagram of figure 3, therefore runs every 10 ms and may be executed at any point of diagram of fig. 2, except as said, during the programming step.

0025Reference should now be made to the diagram of figure 3, which illustrates, as mentioned, the adjustment program. At the beginning of the adjustment program the device verify the condition of slow-startup or quick-startup operation. If the operator presets quick startup, the unit 10 increments the all battery memories (hereinafter also simply termed memories) regardless of the position of the knob on the timer. In the case of slow startup the program individually scans the various inputs to check if they have submitted a request for power, and when it verifies a request it enables the memory of said battery so that it begins to increment up to the value required by the timer. At the end of this scanning of all the inputs the program starts a further scanning of all the memories to activate the related batteries according to the adjustment program.

0026In detail, for each memory the program asks if priority operation has been enabled. If it has not, it asks if the number stored in the memory is greater than the alarm time; if it is, it activates an acoustic or lightning and a display alarm and then asks if the memory is greater than the preset cycle time. If it is not, the program advances to check the reached temperature as described hereafter; if it has, the program checks if the already engaged power plus the power of the battery which is being checked at that instant exceeds the preset top power limit. If the power limit is exceeded, then the program again checks the reached battery temperatures; if the power limit is not exceeded, a second memory (hereafter named counter) of the checked battery is set equal to the cycle time supplied by the respective timer. Similarly, if priority operation is preset (the YES output of the block "PRIORITY OPERATION") the device checks if the memory has exceeded the cycle time. If it has not, the program goes to the successive memory; if it has, it checks if switching on of the battery causes the total top power limit to be exceeded. If it does, the program checks if the battery to be switched on has a higher priority than at least one of the batteries which is already on, and in this case the battery with lowest priority is switched off and the total power is checked again. If the battery to be switched on has a lower priority than the batteries already connected, the program checks the next memory. If instead after checking the power the limit is not exceeded, the memory currently being checked is set to the time supplied by the related timer, as in unprioritized operation. After this operation, regardless of the type of operation (prioritized or unprioritized) the control unit checks if the temperature controller of the chamber has sent a signal indicating that the required temperature has been reached. If it has not, the remote control switch of the battery is enabled to turn on and the decrement of the controlled counter is enabled. Then the counter is checked, and if it has reached zero then turning on of the remote control switch is no longer enabled and the remote control switch is thus turned off. Then the program checks the next memory. When the chamber related to the battery memory being checked has reached the temperature set by means of the temperature controller, and therefore the latter has sent the related signal indicating that the required temperature has been reached (the output of the block TEMPERATURE REACHED is YES), the program memorizes the reception of said signal, resets the memory of the two batteries corresponding to the chamber, resets the slow-startup operation (since by now an advanced adjustment stage has been reached) and checks if all the chambers have already reached the required temperature. If they have not, the program checks the next memory, otherwise priority operation (which is used only during the startup step to reach the preset temperatures but it is not used during normal temperature-maintaining operation) is reset and control is then returned to the push-button control loop (diagram of figure 2).

0027In practice the control unit 10, by means of the described program, cyclically checks all the batteries to verify the ignition demand and activate the increment of the related memories in the case of slow startup. After a time equal to the cycle time has elapsed, the control unit checks if the remaining available power is sufficient to operate the battery, possibly by disconnecting one or more batteries according to their priority or operating time, and then the battery ignition procedure is activated. When the chamber has reached the required temperature, the two related batteries are switched off. The continuous scanning of all the battery memories every 10 ms ensures that the batteries are checked with a sufficient frequency and with a good redistribution of the available power, without exceeding the preset power limits. However, the various memories have a programmable alarm threshold which checks the still-loaded storage and ignition time, and if it exceeds a given value because, e.g. the related battery can never be turned on it issues an alarm signal which is displayed so that the operator can intervene e.g. by turning off some not essential users or by setting a higher power limit value (extra power) or in another manner.

0028As can be seen from the above description, the invention fully achieves the intended objects. In fact the power adjustment device according to the invention allows to optimize the electric power absorption of the various users, distributing the available power according to the demand and priority or to the battery connection time. In particular, by turning off and on the individual batteries according to the indicated criteria a substantially constant absorption is achieved which is close to the power consumption average, and the preset threshold is not exceeded. This is achieved by simply delaying for a few seconds the delivery of power, without altering the thermal balance of the system. However, by virtue of the invention it is possible to save on the fixed rate related to the available power. Furthermore, regarding the actual power absorption, though there should be no savings, except for a reduction in the losses on the line, it has been observed that there is an induced saving due to the greater attention requested from the operator when e.g. the power limit is exceeded, besides the fact that when the chambers reach the preset temperature the operating times still stored in the related battery memories are unloaded and no longer recovered.

0029The device according to the invention is furthermore very easy to use, since it only requires the operator to enter the variable parameters (this entry being also executable only once permanently if there are no reasons to modify it) and it furthermore requires no complicated operations for its installation. The device can furthermore be easily modified if further controlled users are to be inserted or if some are to be excluded, as it is sufficient to change the number of batteries set in the program and perform the required connections for the inputs and outputs and to also replace the program so that it better suits the operating requirements of other machines. Finally, the adjustment device is reliable and requires no particular maintenance.

0030The invention thus conceived is susceptible to numerous modifications and variations, all of which are within the scope of the inventive concept.

0031It is possible to expand the field of control of the power regulation devices to cover all of the electrical plant in the laboratory, having an oven or an apparatus or a series of apparatuses to be regulated installed therein, by inserting a signal which informs the device of the power absorted by the apparatus in that moment while operating. In this way, the maximum programmed power will be that which is available at the meter and the device will assign to the oven the power that is left available by the other apparatuses during operation.

0032The device is not only advantageously for the utilizer, but also affords a major advantage for the power distribution agency by virtue of the fact that razionalization of the apparatuses permits the requirements of more utilizers with currently used power, thereby avoiding the need to construct new power stations.

0033Where technical features mentioned in any claim are followed by reference signs, those reference signs have been included for the sole purpose of increasing the intelligibility of the claims and accordingly, such reference signs do not have any limiting effect on the scope of each element identified by way of example by such reference signs.