JP2008067512A - Power conversion system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To ensure stability in a control system by improving the transition response characteristics of cross current suppression control. <P>SOLUTION: A power conversion system is provided with inverter reactive power conversion sections 40a, 40b for calculating the reactive power of inverters 10a, 10b, based on the output current and voltage of the plurality of inverters 10a, 10b connected in parallel; load reactive power conversion sections 50a, 50b for calculating the reactive power of a load 20 based on the output voltage and load current of the inverters 10a, 10b; reactive power control sections 60a, 60b for calculating the difference to the reactive power of the inverters 10a, 10b by dividing the reactive power of the load 20 by the number of inverters; and voltage control sections 70a, 70b for controlling the voltage amplitude, based on the difference between the reactive power of the load 20 and that of the inverters 10a, 10b. The power conversion system also has current minor loop sections 80a, 80b for performing the three-phase biphase conversion of the output current of the inverters 10a, 10b, calculating a current amplitude component from the two-phase AC signal as the amount of DC, and subtracting it from the output of the reactive power control sections 60a, 60b. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a power conversion system including an inverter constituting a UPS (uninterruptible power supply) that protects a computer or server used in a large-scale system such as an online system of a financial institution from a power failure or a power failure.

  For example, in a power conversion system that constitutes a UPS (uninterruptible power supply) that protects computers and servers used in large-scale systems such as online systems of financial institutions from power outages and power failures, multiple inverters are connected in parallel. The three-phase alternating current output from the inverter is supplied to the load (see, for example, Patent Document 1).

  FIG. 4 illustrates a power conversion system in which two inverters 110a and 110b are connected in parallel. In this power conversion system, DC power supplies 100a and 100b such as a battery are connected to the input sides of the inverters 110a and 110b, and a load 130 is commonly connected to the output side of the inverters 110a and 110b, whereby the DC power supplies 100a and 100b are connected. Is converted into AC by inverters 110 a and 110 b, and the three-phase AC power is supplied to the load 120. In this power conversion system, since the three-phase AC power supplied to the load 120 is shared by the two inverters 110a and 110b, each of the inverters 110a and 110b has 1/3 of the three-phase AC power supplied to the load 120. Two are output at a time.

  Each of the inverters 110a and 110b is controlled by the control devices 130a and 130b having the circuit configuration shown in FIG. 5 so as to output a half of the three-phase AC power supplied to the load 120 by converting the DC voltage to AC. Is done. As shown in the figure, the control devices 130a and 130b include inverter reactive power converters 140a and 140b, load reactive power converters 150a and 150b, reactive power controllers 160a and 160b, and voltage controllers 170a and 170b. Yes.

  Inverter reactive power converters 140a and 140b calculate reactive power of inverters 110a and 110b based on the output current and output voltage of inverters 110a and 110b. On the other hand, load reactive power converters 150a and 150b calculate reactive power of load 120 based on the output voltages and load currents of inverters 110a and 110b.

  The reactive power control units 160a and 160b divide the reactive power of the load 120 output from the load reactive power conversion units 150a and 150b by the number of inverters, and the inverters 110a and 110b output from the inverter reactive power conversion units 140a and 140b. Calculate the difference from reactive power. The difference between the reactive power of the load 120 output from the reactive power control units 160a and 160b and the reactive power of the inverters 110a and 110b is output and added to the command values of the voltage control units 170a and 170b.

The voltage control units 170a and 170b operate the inverters 110a and 110b based on a command value obtained by taking the amplitude component of the output voltage of the inverters 110a and 110b and adding the outputs of the reactive power control units 160a and 160b.
Japanese Patent Laid-Open No. 8-140357

  By the way, in the power conversion system in which a plurality of inverters 110a and 110b are connected in parallel to supply power to the common load 120, when an amplitude difference or a phase difference occurs between the output voltages of the inverters 110a and 110b connected in parallel, the inverter 110a. , 110b generates a cross current in which current flows back and forth. When such a cross current occurs, the output voltages of the inverters 110a and 110b vary, and the efficiency and life of the inverters 110a and 110b are reduced. Moreover, overcurrent occurs due to the cross current, which adversely affects the device.

  As means for suppressing this cross current, reactive power is calculated from the output voltage and output current of the inverters 110a and 110b, and a value obtained by dividing the reactive power of the load 120 by the number of inverters 110a and 110b connected in parallel is used as a command value. The reactive power output from each inverter 110a, 110b is matched by causing the reactive power output from each inverter 110a, 110b to follow the value.

  This reactive power is controlled by adjusting the amplitude of the output voltage of the inverters 110a and 110b, and the reactive power output from each of the inverters 110a and 110b is the same, so that the amplitude of the output voltage of the inverters 110a and 110b is also the same. Thus, since the amplitude difference between the inverters 110a and 110b is eliminated, the cross current is suppressed.

  However, in the parallel operation control of the plurality of inverters 110a and 110b, when the control based on the reactive power is performed on the basis of the instantaneous value, ripples are superimposed on the reactive power due to the influence of voltage and current imbalance and harmonics. It ’s difficult. In order to alleviate this, practical filtering by a low-pass filter is necessary. As a result, the average value of reactive power is controlled and the response to a steep cross current caused by disturbances is slow and sufficient cross current suppression effect. It becomes difficult to obtain.

  Further, by increasing the gain of the cross current suppression control based on the average value of the reactive power, it is possible to improve the transient response and the control accuracy with respect to the command value. However, simply increasing the gain of the feedback control causes the stability of the entire control system to be impaired due to interference with the voltage control unit.

  Therefore, the present invention has been proposed in view of the above-described problems, and the purpose of the present invention is to obtain a high-speed response to a steep cross current caused by a disturbance or the like. It is to provide a power conversion system that can improve only the control system and ensure the stability of the control system.

  As a technical means for achieving the above-mentioned object, the present invention is commonly used for the output of each inverter by connecting a plurality of inverters in parallel and controlling the voltage of each inverter with a control device attached to each inverter. The present invention is applied to a power conversion system that supplies power to a connected load.

  The control device according to the present invention includes an inverter reactive power converter that calculates the reactive power of the inverter based on the output current and output voltage of the inverter, and a load reactive power that calculates the reactive power of the load based on the output voltage and load current of the inverter. The power converter, the reactive power controller that calculates the difference between the reactive power of the inverter by dividing the reactive power of the load by the number of inverters, and the voltage amplitude based on the difference between the reactive power of the load and the reactive power of the inverter A voltage control unit that generates an inverter command value by controlling, three-phase to two-phase conversion of the output current of the inverter, calculates a current amplitude component from the two-phase AC signal as a DC amount, and outputs the reactive power control unit A current minor loop section to be subtracted from is provided between the output of the inverter and the output of the reactive power control section.

  In the present invention, the output current of the inverter is three-phase to two-phase converted, the current amplitude component is calculated as a DC amount from the two-phase AC signal, and the current minor loop portion subtracted from the output of the reactive power control unit is defined as the inverter output. By providing it between the output of the reactive power control unit and subtracting the current amplitude component from the output of the reactive power control unit, only the transient response characteristics of the cross current suppression control can be obtained without degrading the stability of the control system. It is possible to improve the speed of response to a steep cross current.

  The current minor loop unit in the above-described configuration can be configured as a circuit mainly composed of a current amplitude conversion unit that extracts the amplitude component of the output current of the inverter and a filter that extracts the change in the current amplitude component. is there. In the current minor loop section having this circuit configuration, the change in the current amplitude component is subtracted from the output of the reactive power control section.

  The current minor loop unit in the above-described configuration includes a current amplitude conversion unit that extracts an amplitude component of the output current of the inverter, a current invalid component conversion unit that extracts an invalid component of the current amplitude component, and an amplitude of the invalid component. It is possible to configure a circuit with a filter for extracting a change as a main part. In the current minor loop portion having this circuit configuration, the amplitude change amount of the reactive component of the current amplitude component is subtracted from the output of the reactive power control portion.

  Furthermore, the control device according to the present invention calculates an inverter reactive power converter that calculates the reactive power of the inverter based on the output current and output voltage of the inverter, and calculates the reactive power of the load based on the output voltage and load current of the inverter. Voltage based on the difference between the reactive power of the load, the reactive power control unit that calculates the difference between the reactive power of the inverter by dividing the reactive power of the load by the number of inverters, and the reactive power of the load A voltage control unit that controls the amplitude and generates an inverter command value, and calculates a change amount of the reactive power based on the reactive power of the inverter, and a reactive power minor loop unit that subtracts from the output of the reactive power control unit It is provided between the output of the inverter reactive power conversion unit and the output of the reactive power control unit.

  In the present invention, the reactive power minor loop unit that calculates the change in reactive power based on the reactive power of the inverter and subtracts it from the output of the reactive power control unit is output to the output of the inverter reactive power conversion unit and the output of the reactive power control unit. By subtracting the amount of change in reactive power from the output of the reactive power control unit, only the transient response characteristics of the cross current suppression control are improved without sacrificing the stability of the control system. It is possible to speed up the response to a cross current.

  According to the present invention, the output current of the inverter is three-phase to two-phase converted, the current amplitude component is calculated from the two-phase AC signal as a DC amount, and the current minor loop portion subtracted from the output of the reactive power control unit is Transient response characteristics of cross current suppression control without degrading the stability of the control system by subtracting the current amplitude component from the output of the reactive power control unit by providing it between the output and the output of the reactive power control unit It is possible to improve the speed of response to a steep cross current.

  In addition, the reactive power change is calculated based on the reactive power of the inverter, and the reactive power minor loop part to be subtracted from the output of the reactive power control part is connected to the output of the inverter reactive power conversion part and the output of the reactive power control part. By interposing it, subtracting the amount of change in reactive power from the output of the reactive power control unit improves only the transient response characteristics of the cross current suppression control without impairing the stability of the control system, and steep cross current The response speed can be increased.

  As described above, for the steep cross current, the current minor loop section or the reactive power minor loop section can suppress the cross current at high speed, and for low speed and steady cross current, the reactive power conversion is performed. The cross current can be suppressed by the feedback control of the control section, so that both the stability of the control system and the transient response characteristics of the cross current suppression control can be improved. Can be provided.

  FIG. 1 illustrates an embodiment in which two inverters 10a and 10b are connected in parallel in a power conversion system according to the present invention. In this embodiment, the case where two inverters 10a and 10b are connected in parallel is illustrated, but the present invention is not limited to this, and is also applicable to the case where three or more inverters are connected in parallel. Is possible. Moreover, although the following embodiment demonstrates the case where it applies to a three-phase alternating current, it is applicable also to a single phase alternating current.

  In the power conversion system of this embodiment, a DC power source (not shown) such as a battery is connected to the input sides of the inverters 10a and 10b, and the load 20 is commonly connected to the output sides of the inverters 10a and 10b. The DC voltage from the DC power source is AC converted by the inverters 10a and 10b, and the load 20 is supplied with the three-phase AC power. In this power conversion system, since the three-phase AC power fed to the load 20 is shared by the two inverters 10a and 10b, each of the inverters 10a and 10b has 1/3 of the three-phase AC power fed to the load 20. Output 2 each.

  Each of the inverters 10a and 10b is provided with control devices 30a and 30b that perform control so as to output a half of the three-phase AC power supplied to the load 20 by converting the DC voltage to AC. The control devices 30a and 30b include inverter reactive power conversion units 40a and 40b, load reactive power conversion units 50a and 50b, reactive power control units 60a and 60b, voltage control units 70a and 70b, and current minor loop units 80a and 80b. Has been.

  Inverter reactive power converters 40a and 40b include reactive power converters 42a and 42b connected to instrument current transformers CTa and CTb and instrument transformers VTa and VTb provided on the output side of inverters 10a and 10b, The low-pass filters 44a and 44b are connected to the outputs of the reactive power converters 42a and 42b, and the reactive powers of the inverters 10a and 10b are calculated based on the output currents and output voltages of the inverters 10a and 10b.

  The load reactive power converters 50a and 50b are reactive power converters 52a connected to instrument transformers VTa and VTb provided on the output side of the inverters 10a and 10b and an instrument current transformer CT provided on the load side. , 52b and low-pass filters 54a, 54b connected to the outputs of the reactive power converters 52a, 52b, and calculates the reactive power of the load 20 based on the output voltages and load currents of the inverters 10a, 10b.

  The reactive power control units 60a and 60b include dividers 62a and 62b connected to the low-pass filters 54a and 54b of the load reactive power conversion units 50a and 50b, and outputs of the dividers 62a and 62b via subtractors 64a and 64b. The reactive power of the load 20 output from the load reactive power converters 50a and 50b is divided by the number of inverters 10a and 10b, and the inverter reactive power converter 40a is connected. , 40b and the reactive power of the inverters 10a, 10b output from the inverter 40b. The difference between the reactive power of the load 20 output from the reactive power control units 60a and 60b and the reactive power of the inverters 10a and 10b is output and added to the command values of the voltage control units 70a and 70b. The subtractors 64a and 64b are connected to the low-pass filters 44a and 44b of the inverter reactive power converters 40a and 40b.

  The voltage control units 70a and 70b are voltage amplitude control units 72a and 72b connected to the outputs of the average value control units 66a and 66b of the reactive power control units 60a and 60b through the subtracters 68a and 71a, 68b and 71b, respectively. And active power control units 76a and 76b connected to the multipliers 74a and 74b connected to the outputs of the voltage amplitude control units 72a and 72b, and an instrument transformer provided on the output side of the inverters 10a and 10b The voltage amplitude converters 78a and 78b connected to the VTa and VTb, and the inverter based on the command value obtained by taking the amplitude component of the output voltage of the inverters 10a and 10b and adding the outputs of the reactive power control units 60a and 60b. 10a and 10b are operated. The multipliers 74a and 74b are connected to the inverters 10a and 10b. The voltage amplitude converters 78a and 78b are input-connected to the subtracters 71a and 71b. In the above-described active power control units 76a and 76b, the active power supplied to the load 20 is divided by the number of inverters 10a and 10b as in the reactive power control, and the phase of the inverter output voltage is shared by the inverters 10a and 10b. To control.

  The current minor loop units 80a and 80b include current amplitude conversion units 82a and 82b connected to instrument current transformers CTa and CTb provided on the output side of the inverters 10a and 10b, and current amplitude conversion units 82a and 82b. It comprises filters 84a and 84b connected to the outputs and amplifiers 86a and 86b connected to the outputs of the filters 84a and 84b. The current amplitude components are calculated based on the output currents of the inverters 10a and 10b. The outputs of the amplifying units 86a and 86b are connected to the subtracters 68a and 68b connected to the outputs of the average value control units 66a and 66b of the reactive power control units 60a and 60b.

  By the way, in the power conversion system in which a plurality of inverters 10a and 10b are connected in parallel to supply power to the common load 20, when an amplitude difference or a phase difference occurs between the output voltages of the inverters 10a and 10b connected in parallel, the inverter 10a , 10b, a cross current in which current flows back and forth is generated. When such a cross current is generated, the output voltages of the inverters 10a and 10b vary and the efficiency and life of the inverters 10a and 10b are reduced. Moreover, overcurrent occurs due to the cross current, which adversely affects the device.

  As means for suppressing this cross current, in the power conversion system in the above-described embodiment, the reactive power is calculated from the output voltage and output current of the inverters 10a and 10b, and the reactive power of the load 20 is calculated by the number of inverters 10a and 10b connected in parallel. By making the divided value a command value and causing the reactive power output from each inverter 10a, 10b to follow the command value, the reactive power output from each inverter 10a, 10b is matched. This reactive power is controlled by adjusting the amplitudes of the output voltages of the inverters 10a and 10b, and the reactive powers output from the inverters 10a and 10b are the same, so that the amplitudes of the output voltages of the inverters 10a and 10b are the same. Thus, the amplitude difference between the inverters 10a and 10b is eliminated. In this way, for the low speed and steady cross current, the cross current can be suppressed by feedback control of the inverter reactive power converters 40a and 40b and the load reactive power converters 50a and 50b.

  On the other hand, in the parallel operation control of the plurality of inverters 10a and 10b, when the reactive power control is performed on the instantaneous value basis, ripples are superimposed on the reactive power due to the influence of voltage and current imbalance and harmonics. It ’s difficult. In order to alleviate this, it is practically necessary to perform filtering by the low-pass filters 44a and 44b of the inverter reactive power converters 40a and 40b and the low-pass filters 54a and 54b of the load reactive power converters 50a and 50b. It becomes control over the average value of electric power, and it becomes difficult to obtain a sufficient cross current suppression effect with a slow response to a steep cross current caused by disturbance or the like.

  Therefore, for this steep cross current, the current minor loop portions 80a and 80b are effective as means for suppressing the cross current. In the current minor loop sections 80a and 80b, only the transient response characteristic of the cross current suppression control is improved without degrading the stability of the control system by subtracting the current amplitude component from the output of the reactive power control sections 60a and 60b. Therefore, it is possible to speed up the response to a steep cross current.

  As described above, for the steep cross current, the current minor loop sections 80a and 80b can suppress the cross current at high speed, and for the low speed and steady cross current, the inverter reactive power conversion section 40a. , 40b and the load reactive power converters 50a, 50b, the cross current can be suppressed, so that the stability of the control system can be improved and the transient response characteristics of the cross current suppression control can be improved.

  In the above embodiment, the case where the current minor loop sections 80a and 80b are configured by the current amplitude conversion sections 82a and 82b, the filters 84a and 84b, and the amplification sections 86a and 86b has been described, but the present invention is limited to this. It is also possible to configure the circuit as in the other embodiment shown in FIG. In FIG. 2, the same circuit configuration as that of FIG.

  Current minor loop portions 80a and 80b of this embodiment include current amplitude converters 82a and 82b connected to instrument current transformers CTa and CTb provided on the output side of inverters 10a and 10b, and current amplitude converters thereof. 82a, 82b connected to the output of the current invalid component conversion units 88a, 88b, filters 84a, 84b connected to the outputs of the current invalid component conversion units 88a, 88b, and the outputs of the filters 84a, 84b. The amplifiers 86a and 86b are configured to calculate the current amplitude component based on the output currents of the inverters 10a and 10b, and further calculate the ineffective component of the current amplitude component. As a result, it is possible to improve only the transient response characteristics of the cross current suppression control without impairing the stability of the control system, and to speed up the response to the steep cross current.

  The current minor loop portions 80a and 80b of the embodiment shown in FIG. 1 include an effective component of current, whereas the current minor loop portions 80a and 80b of the embodiment of FIG. Exclude and calculate the current amplitude based only on the ineffective component. From this, in the current minor loop portions 80a and 80b of the embodiment of FIG. 2, the cross current can be suppressed with higher accuracy than the current minor loop portions 80a and 80b of the embodiment of FIG.

  Further, in the power conversion system in the embodiment of FIGS. 1 and 2, the current minor loop units 80a and 80b are adopted as means for suppressing the cross current. However, as in the embodiment shown in FIG. 3, the reactive power minor loop unit. It is also possible to adopt a circuit configuration provided with 90a and 90b. In FIG. 3, the same circuit configurations as those in FIGS. 1 and 2 are denoted by the same reference numerals, and redundant description is omitted.

  The reactive power minor loop units 90a and 90b in the power conversion system of the embodiment shown in FIG. 3 include filters 92a and 92b connected to the outputs of the reactive power conversion units 42a and 42b of the inverter reactive power conversion units 40a and 40b, The amplifiers 94a and 94b are connected to the outputs of the filters 92a and 92b. The outputs of the amplifiers 94a and 94b are provided on the output side of the average value controllers 66a and 66b of the reactive power controllers 60a and 60b. Are connected to the subtracters 68a and 68b.

  The reactive power minor loop units 90a and 90b extract the reactive power change based on the reactive power of the inverters 10a and 10b, and subtract the reactive power change from the outputs of the reactive power control units 60a and 60b. Thus, it is possible to improve only the transient response characteristic of the cross current suppression control without impairing the stability of the control system, and to speed up the response to the steep cross current. In the reactive power minor loop units 90a and 90b, since signals are extracted from the front side of the low-pass filters 44a and 44b of the inverter reactive power conversion units 40a and 40b, the response speed is increased for a steep cross current. Is possible.

  The present invention is not limited to the above-described embodiments, and can of course be implemented in various forms without departing from the scope of the present invention. The scope of the present invention is not limited to patents. It includes the equivalent meanings recited in the claims, and the equivalent meanings recited in the claims, and all modifications within the scope.

It is a block diagram which shows the circuit structure of the power conversion system which provided the electric current minor loop part in embodiment of this invention. It is a block diagram which shows the circuit structure of the power conversion system which provided the electric current minor loop part different from FIG. 1 in other embodiment of this invention. It is a block diagram which shows the circuit structure of the power conversion system which provided the reactive power minor loop part in other embodiment of this invention. It is a block diagram which shows the structure of the power conversion system which connected two inverters in parallel. It is a block diagram which shows the prior art example of a power conversion system.

Explanation of symbols

10a, 10b Inverter 20 Load 30a, 30b Control device 40a, 40b Inverter reactive power conversion unit 50a, 50b Load reactive power conversion unit 60a, 60b Reactive power control unit 70a, 70b Voltage control unit 80a, 80b Current minor loop unit 82a, 82b Current amplitude converter 84a, 84b Filter 88a, 88b Current reactive component converter 90a, 90b Reactive power minor loop

Claims (4)

A power conversion system in which a plurality of inverters are connected in parallel and each inverter is voltage-controlled by a control device attached to each inverter, thereby supplying power to a load commonly connected to the output of each inverter,
The control device includes an inverter reactive power converter that calculates an inverter reactive power based on an output current and an output voltage of the inverter, and a load reactive power conversion that calculates a reactive power of a load based on the output voltage and load current of the inverter. And the reactive power control unit that calculates the difference between the reactive power of the inverter by dividing the reactive power of the load by the number of inverters, and controls the voltage amplitude based on the difference between the reactive power of the load and the reactive power of the inverter. A voltage control unit that generates an inverter command value, three-phase to two-phase conversion of the output current of the inverter, a current amplitude component is calculated as a DC amount from the two-phase AC signal, and the output of the reactive power control unit A power conversion system characterized in that a current minor loop section for subtracting from the inverter is provided between the output of the inverter and the output of the reactive power control section.   2. The power conversion system according to claim 1, wherein the current minor loop unit includes a current amplitude conversion unit that extracts an amplitude component of an output current of an inverter and a filter that extracts a change amount of the current amplitude component. .   The current minor loop unit extracts a current amplitude conversion unit that extracts an amplitude component of an output current of an inverter, a current invalid component conversion unit that extracts an invalid component of the current amplitude component, and an amplitude change amount of the invalid component The power conversion system according to claim 1, wherein a main part is constituted by a filter. A power conversion system in which a plurality of inverters are connected in parallel and each inverter is voltage-controlled by a control device attached to each inverter, thereby supplying power to a load commonly connected to the output of each inverter,
The control device includes an inverter reactive power converter that calculates an inverter reactive power based on an output current and an output voltage of the inverter, and a load reactive power conversion that calculates a reactive power of a load based on the output voltage and load current of the inverter. And the reactive power control unit that calculates the difference between the reactive power of the inverter by dividing the reactive power of the load by the number of inverters, and controls the voltage amplitude based on the difference between the reactive power of the load and the reactive power of the inverter. And a voltage control unit that generates an inverter command value, calculates a change amount of the reactive power based on the reactive power of the inverter, and subtracts a reactive power minor loop unit that subtracts from the output of the reactive power control unit from the inverter A power conversion system provided between an output of a reactive power conversion unit and an output of a reactive power control unit.

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