JP6372642B2 - Reactive power control device, reactive power control method, and program - Google Patents

Description

  The present invention relates to a reactive power control device, a reactive power control method, and a program.

There are several known methods for performing reactive power compensation in an AC circuit using a power converter using a semiconductor. In particular, a method using a voltage type converter composed of a capacitor and a semiconductor switch is widely used.
A reactive power compensator called STATCOM (STATic synchronous COMPensator) is known as a technology that improves power factor by compensating for reactive power fluctuations consumed or generated by loads, or compensates for voltage fluctuations in distribution and transmission systems. (For example, Patent Document 1).
SSSC is a device that compensates reactance existing in series by connecting a voltage converter in series between an AC power source and a load or another AC power source, and controls power flow and increases power. (Static Synchronous Series Compensator) is known.
Further, MERS (Magnetic Energy Recovery Switch) is known as one in which a voltage type single-phase bridge is connected in series to an AC circuit to perform switching based on the power frequency and phase angle control based on the power voltage phase (Patent Literature). 2). MERS does not require control to make the DC side voltage of the voltage type converter constant. For this reason, it is known that reactive power can be generated in the same manner even when the capacitor capacity is reduced.
Since these can control reactive power at high speed and continuously compared to classic reactive power compensation by switching a fixed capacitor or a reactor in stages, they can cope with a rapid change in system voltage.

JP2007-280358 Japanese Patent No. 3735673

  However, in general, SSSC and STATCOM are controlled on the assumption that the DC side voltage is substantially constant, as in many voltage type conversion circuits. Therefore, it is necessary to sufficiently increase the capacity of the capacitor to be connected. In many cases this has the problem of increasing the size of the capacitor. By using an electrolytic capacitor, it is possible to reduce the size of a large-capacity capacitor, but the life of an electrolytic capacitor is very short compared to the life of a film capacitor or the like, and the reliability as a power device is insufficient. . There is also room for improvement in terms of reducing switching loss.

  The present invention has been made in view of the above-described problems, and an object thereof is to provide a reactive power control device, a reactive power supply method, and a program that can use a capacitor having a small capacity. Another object of the present invention is to provide a reactive power control device, a reactive power supply method, and a program with little switching loss.

In order to achieve the above object, a reactive power compensator according to a first aspect of the present invention includes:
A bridge circuit composed of first to fourth switches and at least one capacitor and connected to an AC power circuit;
A controller that controls on / off of the first to fourth switches at a frequency higher than the frequency of the AC power circuit, and controls reactive power supplied to the AC power circuit by controlling the switching timing;
With
Each of the first to fourth switches includes first and second terminals and a control terminal, and conducts current in both directions between the first and second terminals to which an ON signal is input to the control terminal. It is turned on, and the current from the first terminal to the second terminal is cut off and the current from the second terminal to the first terminal is turned on when an OFF signal is input to the control terminal It ’s off,
The bridge circuit is
The first terminal of the first switch and the first terminal of the third switch are connected, and the second terminal of the first switch and the first terminal of the second switch Are connected, the second terminal of the third switch and the first terminal of the fourth switch are connected, and the second terminal of the second switch and the fourth switch The second terminal of the first switch, and the capacitor is connected between the first terminal of the first switch and the second terminal of the second switch, Connected to an AC power circuit by the second terminal and the second terminal of the third switch;
The control unit controls the switching timing based on reactance of the capacitor.
It is characterized by that.

In order to achieve the above object, a reactive power compensation method according to a second aspect of the present invention includes:
The first and second terminals and a control terminal are provided, and an ON signal is input to the control terminal, and a current in both directions between the first and second terminals is turned on, and the control terminal is turned off. A first to a fourth state in which an electric current is cut off from the first terminal to the second terminal and a current from the second terminal to the first terminal is turned off. A switch, wherein the first terminal of the first switch and the first terminal of the third switch are connected, and the second terminal of the first switch and the second switch of the second switch A first terminal is connected, the second terminal of the third switch and the first terminal of the fourth switch are connected, and the second terminal of the second switch and the the fourth and the second terminal of the switch is connected, co the first scan the capacitor Connected between the first terminal of the switch and the second terminal of the second switch, and the second terminal of the first switch and the second terminal of the third switch. A reactive power control method for controlling reactive power supplied to the AC power circuit by controlling a bridge circuit connected to the AC power circuit by:
Switching on and off of the first to fourth switches at a frequency higher than the frequency of the AC power circuit, and controlling the switching timing based on reactance of the capacitor,
It is characterized by that.

In order to achieve the above object, a program according to the third aspect of the present invention provides:
The first and second terminals and a control terminal are provided, and an ON signal is input to the control terminal, and a current in both directions between the first and second terminals is turned on, and the control terminal is turned off. A first to a fourth state in which an electric current is cut off from the first terminal to the second terminal and a current from the second terminal to the first terminal is turned off. A switch, wherein the first terminal of the first switch and the first terminal of the third switch are connected, and the second terminal of the first switch and the second switch of the second switch A first terminal is connected, the second terminal of the third switch and the first terminal of the fourth switch are connected, and the second terminal of the second switch and the the fourth and the second terminal of the switch is connected, co the first scan the capacitor Connected between the first terminal of the switch and the second terminal of the second switch, and the second terminal of the first switch and the second terminal of the third switch. By controlling a reactive power supplied to the AC power circuit by controlling a bridge circuit connected to the AC power circuit.
Switching on and off the first to fourth switches at a frequency higher than the frequency of the AC power circuit, and controlling the switching timing based on the reactance of the capacitor;
It is characterized by that.

  According to the present invention, the present invention has been made in view of the above-described problems, and can provide a reactive power control device, a reactive power control method, and a program that can use a capacitor having a small capacity. In addition, it is possible to provide a reactive power control device, a reactive power control method, and a program with little switching loss.

It is a circuit diagram which shows the structure of the reactive power control apparatus which concerns on the 1st Embodiment of this invention. It is a block diagram which shows the control structure of the reactive power control apparatus shown in FIG. It is a wave form diagram for demonstrating the PWM control of the reactive power control apparatus shown in FIG. It is a wave form diagram for demonstrating the PWM control of the reactive power control apparatus shown in FIG. FIG. 2 is a waveform diagram showing currents and voltages of respective parts of the reactive power control device shown in FIG. 1. FIG. 2 is a waveform diagram showing currents and voltages of respective parts of the reactive power control device shown in FIG. 1. FIG. 2 is a waveform diagram showing currents and voltages of respective parts of the reactive power control device shown in FIG. 1. It is a circuit diagram which shows the structure of the reactive power control apparatus which concerns on the 2nd Embodiment of this invention. It is a circuit diagram which shows the detailed structure of the reactive power control apparatus shown in FIG. It is a block diagram which shows the control structure of the reactive power control apparatus shown in FIG. FIG. 10 is a waveform diagram showing currents and voltages of respective parts of the reactive power control device shown in FIG. 9. FIG. 10 is a waveform diagram showing currents and voltages of respective parts of the reactive power control device shown in FIG. 9. FIG. 10 is a waveform diagram showing currents and voltages of respective parts of the reactive power control device shown in FIG. 9. It is a figure which shows the circuit structure etc. of the modification of the power converter device of FIG.

(First embodiment)
Hereinafter, a first embodiment of the present invention will be described with reference to the drawings. The reactive power control apparatus 100 according to the first embodiment of the present invention is an apparatus that generates an AC voltage having a phase advanced by 90 degrees with respect to the phase of an alternating current passing therethrough. Thereby, inductive reactance (for example, line reactance) connected in series is compensated.

(First Embodiment: Configuration)
As shown in FIG. 1, the reactive power control device 100 includes a bridge circuit 110, input / output terminals 111 and 112, a voltmeter 115, an ammeter 117, and a control unit 150. In the reactive power control apparatus 100, an AC power supply VS having an inductive reactance L is connected to an input / output terminal 111, and a load LD is connected to the input / output terminal 112 (the AC power supply VS and the load LD are connected). Connected in series in the AC power circuit). For example, the AC power supply VS is an output from a distant power plant, and the load LD is power consumption at a distant power consumer.

  The bridge circuit 110 includes connection points N1 to N4, first to fourth switches SWU to SWY, and a capacitor CM. In the bridge circuit 110, the first switch SWU and the second switch SWX are not turned on at the same time. Similarly, the third switch SWV and the fourth switch SWY do not turn on at the same time.

  An input / output terminal 111 is connected to the connection point N1. An input / output terminal 112 is connected to the connection point N2. As a result, the bridge circuit 110 is connected to the AC power source VS via the connection point N1, and is connected to the load LD via the connection point N2.

  The first switch SWU is composed of a switch part and a diode part connected in parallel (including a case where they are connected in parallel in an equivalent circuit). The first switch SWU includes, for example, a plurality of elements in which a diode element and a switching element (for example, an IGBT (Insulated Gate Bipolar Transistor)) are connected in parallel. The first switch SWU may be a reverse conducting semiconductor switch such as an N-channel silicon MOSFET (Metal-Oxide-Semiconductor Field-Effect Transistor). In this case, for example, the switch part is constituted by a part of a self-extinguishing element of an N channel type silicon MOSFET, and the diode part is constituted by a part of a parasitic diode of the N channel type silicon MOSFET.

  The switch SWU includes a gate (control terminal) GU. A control signal (gate signal), that is, either an on signal or an off signal is supplied from the control unit 150 to the gate GU.

  The switch SWU is turned on (conductive state) when an on signal is supplied to the gate GU. Therefore, the first switch SWU becomes conductive in both directions when the ON signal is supplied.

  In the switch SWU, when an off signal is supplied to the gate GU, the switch unit becomes non-conductive. Therefore, the switch SWU functions as a diode when an off signal is supplied.

  The second to fourth switches SWX to SWY have the same configuration as the first switch SWU. Similarly to the first switch SWU, each is turned on when turned on by an on signal, and functions as a diode when turned off by an off signal.

  The first switch SWU is arranged such that the cathode side (first terminal) of the diode part is connected to the connection point N3, and the anode side (second terminal) of the diode part is connected to the connection point N1. And the connection point N3.

  In the second switch SWX, the cathode side (first terminal) of the diode part is connected to the connection point N1, and the anode side (second terminal) of the diode part is connected to N4. It is connected between the connection point N1.

  In the third switch SWV, the cathode side (first terminal) of the diode part is connected to the node N3, and the anode side (second terminal) is connected to the node N2, and the node N2 and the node N3 are connected. Connected between and.

  The fourth switch SWY is arranged such that the cathode side (first terminal) of the diode portion is connected to the connection point N2, and the anode side (second terminal) is connected to the connection point N4. It is connected between the connection point N3.

  One end (positive electrode side) of the capacitor CM is connected to the connection point N3, and the other end (negative electrode side) is connected to the connection point N4. The capacitor CM has a capacity of 1/4 to 1/10 that of a general smoothing capacitor.

Voltmeter 115 measures the end of a voltage to the other end of the capacitor CM, and transmits the voltage value v _c to the controller 150.

  The ammeter 117 measures the current flowing from the input / output terminal 111 to the input / output terminal 112 of the bridge circuit 110 and transmits the current value i to the control unit 150.

  The control unit 150 includes a CPU (Central Processing Unit) 151, a RAM (Random Access Memory) 152, a ROM (Read Only Memory) 153, and an input / output unit 154. In the present embodiment, the storage unit of the control unit 150 is configured by the RAM 152 and the ROM 153, but this storage unit may be configured to include other storage devices. The storage unit may be outside the control unit 150. Furthermore, at least a part of the control unit 150 may be configured by a dedicated circuit (ASIC (Application Specific Integrated Circuit) or the like) that executes at least a part of the following processing performed by the CPU 151.

  The CPU 151 executes the following processing performed by the control unit 150 in accordance with a program stored in the ROM 153. The RAM 152 functions as a main memory for the CPU 151. The ROM 153 stores programs and various data used by the CPU 151 during the following processing. The CPU 151 performs the following process using data stored in the ROM 153 as appropriate. The input / output unit 154 includes various ports. Control signals, various data, etc. input / output to / from the control unit 150 are input / output to / from the CPU 151 via the input / output unit 154.

The control unit 150 performs control by reactance X ^* given from the human interface or the upper control system 155. The reactance X ^* is a command value that means an equivalent reactance (equivalent reactance) of the fundamental wave component of the bridge circuit 110.

  As shown in FIG. 2, the processing performed by the control unit 150 includes an input unit 159, a PLL unit 160, a comparison unit 162, calculation units 163 and 164, a PWM unit 165, a 1-pulse control unit 168, And an output unit 170.

In the following description, each symbol represents the following data. In each process, the control unit 150 reads / writes each data appropriately using the RAM 152 and the ROM 153. Note that the lowercase symbols represent data strings such as instantaneous voltage and instantaneous current whose values change continuously (for example, instantaneous value i of current). The capital letters represent data that is updated every cycle of the power supply (for example, the effective current value I). In addition, a command value commanded by a user or the like is marked with *.
i: Current flowing in the direction of the input / output terminals 111 to 112 of the bridge circuit 110 (actual measurement)
I: Effective current value of current value i (calculated from i)
v: A voltage value of 111 with respect to the input / output terminal 112 of the bridge circuit 110 (not used for control in the operation of the present embodiment).
V ^* : The effective voltage value of 111 with respect to the input / output terminal 112 of the bridge circuit 110 (calculated value)
θ: Phase of current i (calculated value, the time when the current becomes maximum is 0 degree)
v _c : voltage value of capacitor CM (actual measurement)
v _c ^*: the value of the voltage of the capacitor CM (calculated)
V _{c. peak} : The peak voltage value of the capacitor CM (set by the user, larger than the peak value of the voltage value v)
v _{ref +} : Reference voltage (the fundamental wave component waveform of the voltage generated in the bridge circuit 110, which is desired by the user)
X ^* : Command value of equivalent reactance of fundamental wave component of bridge circuit 110 _Xc : Reactance _Xc of capacitor CM of bridge circuit 110 (calculated value from capacitance of capacitor CM)
v _t0 : Triangular wave with amplitude of ± 1 and v _t : Triangular wave with voltage value v _c ^* as envelope.

  In the following description, it is assumed that the effective current flowing in the direction from the input / output terminals 111 to 112 of the bridge circuit 110 is constant (the current value I is constant) for easy understanding.

The input unit 159, the voltage value _{v c} and the current value i from the voltmeter 115 and an ammeter 117 is input. The control unit 150 appropriately updates the data in the RAM 152 based on the input data.
The input unit 159 receives various data from the external control system 155. The input unit 159 includes a user interface (not shown). The user instructs the control unit 150 of the equivalent reactance X ^* via the external control system 155 or this user interface. The control unit 150 updates the reactance X ^* of the RAM 152 based on the instructed equivalent reactance X ^* . Also, the input unit 159 calculates V ^* = X ^* × I and updates V ^* .
The input unit 159 can also allow the user to input other data via the user interface. The control unit 150 updates each data in the RAM 152 to each input data.
In addition, when there is a failure or data deficiency, the control unit 150 requests an appropriate measure from the user via the user interface of the input unit 159.

  The PLL unit 160 detects the phase θ, the frequency f, and the effective current value I of the current value i. The phase θ is set to 0 degree when the current value i becomes maximum. The detected frequency f and phase θ are stored in the RAM 152.

The comparison unit 162 compares the stored equivalent reactance X ^* with the reactance _Xc, and executes the calculation units 163, 164, or 168 depending on the magnitude.

When X ^* < _Xc , the calculation unit 163 is executed. Specifically, the calculation defined in Equation 1 below is executed. Using the reactance X _c of the capacitor CM, the voltage value v _c ^* (θ) of the capacitor CM in the next period when X ^* <X _c is obtained from Equation 1.

When X ^* > _Xc , the calculation unit 164 is executed. Specifically, the calculation defined in Equation 2 below is executed. According to Equation 2, the voltage value v _c ^* (θ) of the capacitor CM in the next cycle when X ^* > X _c is obtained using the reactance X _c of the capacitor CM.

When the current value v _c ^* (θ) is obtained by the calculation unit 163 or 164, the PWM control unit 165 is executed.

The PWM control unit 165 performs PWM control on the bridge circuit 110 using the voltage value v _c ^* (θ) of the capacitor CM obtained by Expression 1 or 2.
The PWM control unit 165 performs special PWM shown in FIGS. First, the PWM control unit 165 creates a triangular wave v _t whose amplitude changes with ± v _c ^* (θ) calculated by the calculation unit 163 or 164 as an envelope. Specifically, a triangular wave v _t0 having a magnitude of ± 1 having a desired switching frequency is multiplied by v _c ^* (θ).

Next, the PWM control unit 165 compares the reference voltage v _{ref +} with the triangular wave v _t and generates gate signals SGU and SGX. In the present embodiment, when the reference voltage v _{ref +} is larger than the triangular wave v _t , the PWM control unit 165 turns on the gate signal SGU and turns off the gate signal SGX. When the reference voltage is smaller than the triangular wave v _t , the PWM control unit 165 turns off the gate signal SGU and turns on the gate signal SGX.
Similarly, the PWM control unit 165 _compares the negative value v _ref− of the reference voltage v _{ref + with} the triangular wave v _t to generate gate signals SGV and SGY. When the triangular wave v _t is larger, the PWM control unit 165 turns off the gate signal SGV and turns on the gate signal SGY. When the triangular wave v _t is smaller, the PWM control unit 165 turns on the gate signal SGV and turns off the gate signal SGY.

Further, the PWM control unit 165 compares the actual voltage value v _c of the capacitor CM for the past one cycle of the power supply voltage cycle with the voltage value v _c ^* obtained by the calculation unit 163 so that the difference becomes zero. The feedback control is performed on the phase of the gate signal (specifically, the phase of v _{ref +} is controlled). For example, when the voltage value v _c ^* is larger, the phase is delayed, and when it is smaller, the phase is advanced.

When X ^* = _Xc , the 1-pulse controller 170 is executed. The control unit 150 performs switching control of the bridge circuit 110 at the frequency obtained by the PLL unit 160 (that is, the frequency of the AC power supply VS). Specifically, when 0 degree ≦ θ <180 degrees, the gate signals SGU and SGY are turned on, and the gate signals SGV and SGX are turned off. Further, when 180 ≦ θ <360, the gate signals SGU and SGY are turned off and the gate signals SGV and SGX are turned on. As described above, SGU and SGX are not simultaneously turned on, and SGV and SGY are not simultaneously turned on.

Also, the 1-pulse control unit 170 calculates the voltage value v _c ^* by calculating Equation 1 above. 1-Pulse control unit 170 compares the calculated voltage value v _c ^* with the actual voltage value v _c of capacitor CM for the past one cycle, and sets the gate signal from ON so that this difference becomes zero. Controls when to switch off.

  The output unit 170 outputs the gate signals determined by the calculation units 163 and 164 and the 1-pulse control unit 168 and supplies the gate signals to the gates GU to GY.

  The control unit 150 repeats the above processing as appropriate.

(First embodiment: specific control and operation)
With the configuration described above, the reactive power control apparatus 100 controls reactive power as described below.
In the following description, it is assumed that the equivalent reactance X ^* that is initially commanded is smaller than the reactance _{Xc of the} capacitor CM, and that the equivalent reactance X ^* gradually increases with the user's command.

  When the reactive power control apparatus 100 starts operation, the control unit 150 starts control of the bridge circuit 110 according to various data programs stored in the RAM 152 and the ROM 153.

Controller 150, an input unit 159, the voltage value _{v c} of the capacitor CM voltmeter 115, a current value i flowing through the bridge circuit 110 from the ammeter 117 is input the equivalent reactance ^{X *} from an external control system . Further, the control unit 150 specifies an effective voltage value V ^* of a voltage to be generated in the bridge circuit 110 from the input equivalent reactance X ^* at the input unit 159.

  In the calculation unit 160, the control unit 150 detects the phase θ, the frequency f, and the effective current value I of the current value i based on the current value i input by the input unit 159.

In the comparison unit 162, the control unit 150 compares the equivalent reactance X ^* input from the input unit 159 with the actual reactance _Xc of the capacitor CM.

(Operation when X ^* < _Xc )
Since the equivalent reactance X ^* is smaller than the reactance _{Xc in the} initial state, the control unit 150 executes the calculation of the calculation unit 163. That is, the control unit 150 calculates Formula 1 to obtain the voltage value v _c ^* (θ) of the capacitor CM from the voltage value V ^* calculated by the input unit 159.

In the PWM control unit 165, the control unit 150 creates a gate signal based on the voltage value v _c ^* (θ).

Specifically, the control unit 150 generates the triangular wave v _t by multiplying the triangular wave v _t0 by the voltage value v _c ^* (θ). The triangular wave v _t is a triangular wave whose envelope is ± v _c ^* (θ).
In the PWM control unit 165, the control unit 150 creates a gate signal by comparing the reference voltages v _{ref +} and v _ref− with the triangular wave V _t .

  The control unit 150 transmits a gate signal from the output unit 170 to the gates GU, GV, GX, and GY. The switches SWU, SWV, SWX, and SWY switch on / off according to the received gate signal.

As a result, as shown in FIG. 5, a voltage in which the fundamental component is shifted by 90 degrees from the phase of the current (current value i) flowing through the bridge circuit 110 is generated in the bridge circuit (voltage value v). That is, reactive power is generated here. In addition, since the actual equivalent reactance X of the bridge circuit 110 is smaller than the actual reactance of the capacitor CM, the voltage (voltage value v _c ) of the capacitor CM has dropped to 0 voltage. In FIG. 5, in order to make the waveform easier to see, the frequency of the reference voltage v _{ref +} is reduced and displayed.
Further, by using a triangular wave v _t having an envelope of the capacitor voltage value v _c ^* ,
A voltage (voltage value v) with less harmonics (harmonics having a frequency component lower than the switching frequency) can be generated.

(Operation when X ^* = _Xc )
When the user changes the value of the equivalent reactance X via the input unit 159, the value of the equivalent reactance X ^{* in} the RAM 152 is updated. As the reactance X ^* changes, the control unit 150 updates the values of various data such as the voltage value v _c ^* . When the update is completed, the control unit 150 transmits a gate signal based on the updated data from the output unit 170 to the gates GU, GV, GX, and GY. The switches SWU, SWV, SWX and SWY receive the gate signal and switch the switch on and off.
Furthermore, the user changes the equivalent reactance ^{X *} value, the equivalent reactance ^{X *} is the same value as the reactance _{X c} of a capacitor CM, the control unit 150 determines ^X * = _{X c} in the comparison section 162, 1 -Run the pulse controller 168;

The controller 150 uses the 1-pulse controller 168 to turn on the gate signals SGU and SGY and turn off the gate signals SGV and SGX at the peak of the current flowing in the direction from the input / output terminals 111 to 112. Then, the control unit 150 causes the 1-pulse control unit 168 to turn off the gate signals SGU and SGY and turn on the gate signals SGV and SGX at the peak of the current flowing in the direction from the input / output terminal 112 to 111.
The created gate signal is supplied from the output unit 170 to each gate. The switches SWU, SWV, SWX and SWY receive the gate signal and switch the switch on and off.

As a result, as shown in FIG. 6, a voltage in which the fundamental component is shifted by 90 degrees from the phase of the current (current value i) flowing through the bridge circuit 110 is generated in the bridge circuit (voltage value v). Further, since the actual equivalent reactance X of the bridge circuit 110 is the same as the actual reactance of the capacitor CM, the voltage (voltage value v _c ) of the capacitor CM becomes equal to the absolute value of the voltage of the bridge circuit 110. In this case, since it means the same as the case where the capacitor CM is directly connected, there are few harmonics. Further, since switching is performed only once in one cycle of the power supply frequency, loss is not great.

(Operation when X ^* > _Xc )
When the user further increases the value of the equivalent reactance X ^* to be larger than the reactance _Xc , the control unit 150 determines X ^* > _Xc in the comparison unit 162 and executes the calculation of the calculation unit 154. That is, the control unit 150 updates the voltage value v _c ^* (θ) of the capacitor CM by calculating Formula 2.

When the voltage value v _c ^* (θ) is updated, the control unit 150 causes the PWM control unit 165 to create a gate signal based on the voltage value v _c ^* (θ).
The controller 150 multiplies the triangular wave v _t0 by the voltage value v _c ^* (θ) to generate a triangular wave v _t . In the present embodiment, the control unit 150 becomes a triangular wave v _t whose envelope is ± v _c (θ).

Next, in the PWM control unit 165, the control unit 150 creates a gate signal by comparing the reference voltage value v _{ref +} with the triangular wave v _t .

  When the gate signal is generated, the control unit 150 transmits the gate signal from the output unit 170 to the gates GU, GV, GX, and GY. The switches SWU, SWV, SWX, and SWY receive the gate signal from the control unit 150 and switch the switch on and off.

As a result, as shown in FIG. 7, a voltage in which the fundamental component is shifted by 90 degrees from the phase of the current (current value i) flowing through the bridge circuit 110 is generated in the bridge circuit (voltage value v). That is, reactive power is generated here. In addition, since the actual equivalent reactance X of the bridge circuit 110 becomes larger than the actual reactance of the capacitor CM, the voltage (voltage value v _c ) of the capacitor CM does not drop to 0 voltage. In FIG. 7, in order to make the waveform easier to see, the frequency of the reference voltage value v _{ref + and the} like is reduced and displayed.
Further, by using a triangular wave v _t having an envelope of the capacitor voltage value v _c ^* ,
Harmonic small voltages (triangular wave v _t lower frequency components than the switching frequency of) (voltage value v) can be generated.

As described above, the reactive power control apparatus 100 can control any X ^* . Therefore, it is possible to arbitrarily compensate for an inductive reactance having an arbitrary magnitude between the power supply VS and the load LD. That is, the reactive power control apparatus 100 can control arbitrary reactive power.

(First embodiment: summary)
As described above, any reactive power can be supplied to the AC power circuit by the reactive power control apparatus 100 according to the present embodiment. The reactive power control apparatus 100 can control reactive power by controlling the equivalent reactance X of the bridge circuit 110.

In particular, since the equivalent reactance X of the bridge circuit 110 at the output frequency of the AC power supply VS is smaller than the reactance of the capacitor CM, it is necessary to use a capacitor having a very small capacity compared to a capacitor used in a general SSSC or the like. it can.
Further, by generating a triangular wave v _t from the voltage value v _c ^* of the capacitor CM obtained based on the reactance X _c of the capacitor CM, it is possible to appropriately control reactive power even for a large pulsation of the capacitor voltage. .
Further, it is possible to control with less harmonics by switching the control depending on whether the voltage of the capacitor CM drops to 0 voltage or not (when X < _Xc and X = _Xc or X> _Xc ). . In particular, since the voltage of the capacitor CM in the future can be obtained by Formulas 1 and 2, more stable control than actual measurement is possible.
When the equivalent reactance X ^* of the bridge circuit 110 and the reactance _Xc of the capacitor CM of the bridge circuit 110 are the same, switching can be performed at the same frequency as the power supply frequency, so that the switching loss can be kept low.
In the case of PWM control, the phase of the voltage of the capacitor CM and the phase of the current flowing through the bridge circuit 110 are shifted by 90 degrees, so that the switching loss becomes lower. The switching loss is halved in comparison with a general voltage source converter in which the capacitor voltage is constant.

(First embodiment: application and modification)
The first embodiment of the present invention has been described above, but the embodiment of the present invention is not limited to the above.
For example, in the above description, 1-pulse control has been described as when X ^* = _Xc , but of course, it is not limited to this one point, and 1-pulse control may be performed in accordance with the operation method of the reactive power control apparatus 100. It is preferable to appropriately set the range. For example, the range may be X ^* = _Xc ± 5%. It is preferable to set appropriately depending on the amount of harmonics allowed. In this case, it is preferable to adjust the on-time or control the phase of each gate signal. In addition, a period in which current flows without passing through the capacitor CM may be provided. For example, in the vicinity of θ = 0 degrees and θ = 180 degrees, the first switch SWU and the third switch SWV are turned on, the second switches SWX and SWY are turned off, or the first switch SWU and A period is provided in which the third switch SWV is turned off and the second switches SWX and SWY are turned on. Further, the above-described 1-pulse control may be performed when X ^* < _Xc or X ^* > _Xc , and the above-described PWM control may be performed otherwise.

The creation of the gate signal in PWM is not limited to the above example. It is important to create a switching pattern from the voltage value v _c ^* (θ) obtained based on the actual reactance X _c of the capacitor CM, and other generally known controls can be applied.

In the above embodiment, the PWM control by the triangular wave comparison method is performed, but the control is not limited to this. For example, a fixed pulse pattern may be used.
If X ^* < _Xc , the duty of the gate signal in one cycle of the power supply frequency is substantially constant. Therefore, in the case of X * ^<X _c, may be set a duty for the equivalent reactance X ^* in advance, corresponding to the equivalent reactance X ^*, it may be set the duty of the cycle.

  Moreover, although the said embodiment demonstrated that there was no active power consumed with the reactive power control apparatus 100, you may supplement the consumed active power. For example, power may be supplied from an external power source.

  In the above description, the current is constant. However, the voltage may be constant.

  The reactive power control apparatus 100 controls and supplies reactive power by connecting the bridge circuit 110 in series with an AC power circuit. On the other hand, it is possible to supply reactive power by connecting the bridge circuit 110 in parallel with an AC power circuit. That is, it can be applied to STATCOM.

(Second Embodiment)
Hereinafter, a second embodiment of the present invention in which the reactive power control apparatus 100 is applied to STATCOM will be described with reference to the drawings.

(Second Embodiment: Configuration)
As shown in FIG. 8, reactive power control apparatus 200 according to the embodiment of the present invention includes three units 201 that are delta-connected to three-phase AC power circuit 280.

  The three-phase AC power circuit 280 includes an R phase, an S phase, and a T phase. In the present embodiment, the three-phase AC power circuit 280 is a transmission line supplied with an AC voltage from a 200 V, 50 Hz three-phase AC power source.

The three units 201 have the same configuration. These are composed of a series circuit of a reactive power control device 200 and a reactor 205. The voltage generated in the reactive power control device 200 when the _{V conv,} the difference between the line voltage and _{V conv} is applied to the reactor 205. As a result, a current flows through the reactor 205 and reactive power is generated. Since each reactive power control device 200 controls the voltage applied to the reactor 205 by controlling the voltage V _conv , the reactive power can be controlled.

  In the following, for ease of understanding, the single-phase unit 201 connected between the R phase and the S phase will be described as a representative.

  As shown in FIG. 9, the unit 201 includes a series circuit of a reactor 205 and a reactive power control device 200.

One end of the reactor 205 is connected to the R phase.
The reactive power control device 200 includes a bridge circuit 110, a voltmeter 246 and 247, and a control unit 250.

  The bridge circuit 110 is the same as the bridge circuit 110 of the first embodiment described above.

  In the bridge circuit 110, the input / output terminal 111 is connected to the other end of the reactor 205, and the input / output terminal 112 is connected to the S phase.

Voltmeter 246, the voltage value _{v c} of the capacitor CM of the bridge circuit 110 measures and sends the value to the control unit 250.
Voltmeter 247 measures the line voltage value _{v s} between the R-phase and S-phase, and transmits to the control unit 250.

The control unit 250 includes a CPU, a memory, and a RAM. The control unit 250 switches control according to the magnitude of the equivalent reactance X of the bridge circuit 110.
Specifically, the below-described control is performed by realizing each functional unit shown in FIG.
In the following description, each symbol represents the following data. In each process, the control unit 250 reads / writes each data as appropriate using the internal RAM and ROM.
The lowercase symbols are data strings whose values change continuously (for example, instantaneous value i of current). The capital letter is data updated every cycle of the power supply (for example, the effective value I of the current). The command value is marked with *.
i: Current value flowing in the direction of the input / output terminals 111 to 112 of the bridge circuit 110 (not used for control in the operation of the present embodiment)
I ^* : Effective current value (command value) flowing in the direction of the input / output terminals 111 to 112 of the bridge circuit 110
I _max : Expected maximum value of current flowing in the direction of the input / output terminals 111 to 112 of the bridge circuit 110 (value set by the user)
v _conv : voltage of 111 with respect to the input / output terminal 112 of the bridge circuit 110 (not used for control in the operation of the present embodiment)
V ^* _conv : Effective voltage 111 for the input / output terminal 112 of the bridge circuit 110 (calculation)
v _c : Capacitor voltage (actual measured value)
v _c ^* : Capacitor voltage (calculated value and command value obtained from I ^* and V _conv )
V _c ^* _peak:. Peak voltage of the capacitor CM (command value)
v _s : line voltage (actual measured value)
V _s : Effective value of line voltage (calculated value obtained from v _s )
theta: voltage v _s of the phase (. The calculated value positively switched zeros from negative obtained from v _s to 0 °.)
v _{ref +} : Reference voltage (voltage having a desired waveform between the input / output terminals 111 and 112)
X ^* : equivalent reactance of the bridge circuit 110 (the control unit 150 switches the control of the single-phase voltage bridge circuit 110 depending on the magnitude of this value)
X _c : reactance of the capacitor CM of the bridge circuit 110 (stored in the control unit 250 as an initial value)
X _L : Reactance of reactor 205 (stored in control unit 250 as an initial value)

  As shown in FIG. 10, the control unit 250 includes an input unit 251, a PLL unit 252, a calculation unit 253, 255, 256, 257, 258 and 259 and 260, and an output unit 270.

The input unit 251 includes a user interface (not shown). The user inputs the current value I _max via this user interface. The current value I _max is the maximum value of the current that should flow through the bridge circuit 110 in order to supply the desired reactive power.
Further, the input unit 251, the voltage value _{V c} of the capacitor CM voltmeter 246, the line voltage value _{v s} voltmeter 247 is inputted. The input data is stored in the above-mentioned RAM and used for various operations described later.
Further, the user can browse and update various data via the input unit 251.

PLL unit 252 detects the frequency f and phase of the line voltage value _{v s.} The detected frequency f and phase θ are stored in the RAM. Also, PLL unit 252 calculates the effective voltage value _{V s} of the line voltage value _{v s.} The calculated effective voltage value V _s is stored in RAM.

Calculator 253 calculates the current value ^{I *} corresponding to the line voltage value _{v s.} Specifically, the current value I ^* is greater as the voltage value v _s small, the larger the voltage value v _s decreases. When the current value I ^* is calculated, I ^* is updated that is stored in RAM. When a current corresponding to the current value I ^* actually flows, the reactive power compensator 200 supplies desired reactive power to the three-phase AC power circuit 280.
The calculation unit 253 can also make the current value I ^* constant. For example, when the purpose is to make the power factor of the target portion constant, it is desirable to set the current value I ^* suitable for it.
In the following, the calculation unit 253 will be described as to calculate the current value I ^* corresponding to the line voltage value v _s.

The calculation unit 255 calculates the effective voltage value V ^* _conv of the bridge circuit 110 suitable for compensating for the desired reactive power. Specifically, the calculation defined in Equation 3 below is executed. The voltage value V _conv ^* is obtained from Equation 3.

The calculation unit 256 calculates the voltage value v _c ^* that the capacitor CM should have from the calculated optimum voltage value V ^* _conv and the calculated current value I ^* that should flow. Specifically, X ^* = V ^* _conv / I ^* is calculated, and when X ^* ≦ _Xc , the following formula 4, and when X ^* > _Xc , the calculations defined in formulas 5 and 6 are executed. To do. The voltage value v _c ^* that the capacitor CM should have is calculated by Equations 4 to 6.

In other words, when X ^* ≦ _Xc , the voltage value v _c ^* that the capacitor CM should have when the current value I ^* flows is obtained by Equation 4.

That is, in the case of X ^* > _Xc , the peak voltage value of the capacitor CM necessary for the current value to be I _{max at the} maximum is calculated by Formula 5, and the capacitor when the current value I ^* flows by Formula 6 The voltage value v _c ^* that the CM should have is calculated.

The calculation unit 257 calculates active power to be supplemented to the capacitor CM.
Specifically, the calculation unit 257 compares the calculated voltage of the capacitor voltage (voltage value v _c ^* ) with the actually measured voltage of the capacitor CM (voltage value v _c ), and effectively calculates the difference to be zero. The voltage value V _act is feedback controlled. For example, feedback control is performed by comparing moving averages during one period of the three-phase AC power circuit 280.

The calculation unit 258 obtains an ideal waveform of the voltage of the input / output terminal 111 with respect to the input / output terminal 112. Specifically, the calculation defined in Equation 7 below is executed. The reference voltage v _{ref +} is obtained from Equation 7.

  According to Equation 7, a reference voltage considering both reactive power to be generated (corresponding to the first term on the right side) and active power to be supplemented (corresponding to the second term on the right side) is obtained.

The calculation unit 259 calculates a triangular wave v _t having an envelope with the voltage value v _c ^* of the capacitor CM when the current value I ^* flows. Specifically, the triangular wave v _t0 is multiplied by the voltage value v _c ^* .

The calculation unit 260 compares the calculated reference voltage value v _{ref +} with the calculated triangular wave v _t .
When the reference voltage value v _{ref +} is larger than the triangular wave v _t , the calculation unit 260 turns on the gate signal SGU and turns off the gate signal SGX. When the reference voltage value v _{ref +} is smaller than the triangular wave v _t , the calculation unit 260 turns off the gate signal SGU and turns on the gate signal SGX.
Similarly, the calculation unit 260 compares the negative value −V _ref− of the reference voltage value v _{ref + with} the triangular wave v _t to generate gate signals SGV and SGY. When the triangular wave v _t is larger, the calculation unit 260 turns off the gate signal SGV and turns on the gate signal SGY. When the triangular wave v _t is smaller, the calculation unit 260 turns on the gate signal SGV and turns off the gate signal SGY.

  The output unit 270 transmits the gate signal obtained by the calculation unit 260 to the gates GU, GV, GX, and GY.

(Second Embodiment: Specific Control and Operation)
With the configuration described above, the reactive power control apparatus 201 controls reactive power as follows.
The initial state will be described on the assumption that the current value I ^* is small and X ^* (= V ^* _conv / I ^* ) is larger than _Xc because there is little reactive power to be generated.

  When the reactive power control apparatus 201 starts operation, the control unit 250 executes the above-described units in accordance with various data programs stored in the RAM and ROM, and starts control of the bridge circuit 110.

Controller 250, the voltage value _{v c} of the capacitor CM voltmeter 246 in the input unit 251, the line voltage value _{v s} voltmeter 247 is inputted.

Control unit 250 based on the input data, the PLL unit 252, detects the phase theta, frequency f and the effective voltage value _{V s} of the line voltage value _{v s.}

Controller 250, the calculation unit 253 calculates the current value ^{I *} corresponding to the line voltage value _{v s.}

In the calculation unit 255, the control unit 250 calculates the voltage value V ^* _conv using Equation 3.

(Operation when X ^* > _Xc )
In the initial state, the control unit 250 calculates the voltage value v _c ^* that the capacitor CM should have, using Equations 5 and 6, since X ^* > X _c in the initial state.

In the calculation unit 257, the control unit 250 compares the calculated capacitor voltage value v _c ^* with the actually measured capacitor voltage value v _c to calculate the effective power V _act to be supplemented to the capacitor.

In the control unit 250, the reference voltage value v _{ref +} is obtained by Equation 7 in the calculation unit 258.

In the calculation unit 259, the control unit 250 multiplies the triangular wave v _t0 by v _c ^* to calculate a triangular wave v _t having the voltage value v _c ^* in the envelope.

Controller 250, the calculation unit 260, _v and _{ref +} calculated, compares the triangular wave _{v t} with capacitor voltage value _{v c,} which is calculated in the envelope.
When the reference voltage value v _{ref +} is larger than the triangular wave v _t , the control unit 250 turns on the gate signal SGU and turns off the gate signal SGX. When the reference voltage value v _{ref +} is smaller than the triangular wave v _t , the calculation unit 260 turns off the gate signal SGU and turns on the gate signal SGX.
Similarly, in the calculation unit 260, the control unit 250 compares the negative value v _ref− of the reference voltage value v _{ref + with} the triangular wave v _t to generate gate signals SGV and SGY. When the triangular wave v _t is larger, the calculation unit 260 turns on the gate signal SGV and turns off the gate signal SGY. When the triangular wave v _t is smaller, the calculation unit 260 turns off the gate signal SGV and turns on the gate signal SGY.

  The control unit 250 transmits the gate signal obtained by the calculation unit 260 from the output unit 270 to the gates GU, GV, GX, and GY.

The switches SWU to SWY are turned on / off by a gate signal received at the gate. As a result, each voltage and current is generated as shown in FIG.
As the switches SWU to SWY are turned on and off, the voltage of the capacitor CM (voltage value v _s ) is generated as the voltage of the bridge circuit 110 (voltage value v _conv ). In addition, since the equivalent reactance X of the bridge circuit 110 becomes larger than the reactance of the capacitor CM, the voltage (voltage value v _c ) of the capacitor CM does not drop to zero voltage. In addition, a voltage represented by a voltage value v _conv1 in the figure is generated as a voltage of the bridge circuit 110 as a fundamental wave component, and the voltage (voltage value v _conv ) of the bridge circuit 110 is a harmonic (triangular wave v _t switching). There are few harmonics below the frequency.
The line voltage (voltage value v _s ) and the voltage of the bridge circuit 110 (voltage v _conv ) are applied to the reactor 205. As a result, a current (current value i) flows through the reactor 205 and the bridge circuit 110. Since the voltage of the bridge circuit 110 has few harmonics, the current (current value i) has a waveform close to a sine wave.
That is, the reactive power control apparatus 200 can generate reactive power by flowing a current having a waveform close to a sine wave through the reactor 205.

(Operation when X ^* = _Xc )
For example, it is assumed that the line voltage value v _s decreases (in a general AC power circuit, and the like reactive power is decreased, it is known that the voltage drops). Then, the control unit 250 increases the current value I ^* in the calculation unit 253. The above operation is repeated while updating each data until X ^* > _Xc .
When I ^* further increases and X ^* = _Xc , the control unit 250 calculates the voltage value v _c ^* to be possessed by the capacitor CM by Equation 4 in the calculation unit 256. Note that when X ^* = _Xc , the calculation is X ^* = _Xc = V _conv / I ^* . Then, Formula 4 used by the control unit 250 in the calculation unit 256 is equivalent to the following formula.

Equation 8 means that when X ^* = _Xc , the capacitor voltage (voltage value v _c ^* ) is equal to the absolute value of the voltage between the input / output terminals 111-112.

In the calculation unit 257, the control unit 250 compares the calculated capacitor voltage value v _c ^* with the actually measured capacitor voltage value v _c to calculate the effective power V _act to be supplemented to the capacitor.

In the calculation unit 258, the control unit 250 obtains the reference voltage value v _{ref +} using Equation 7.

Controller 250, the calculation unit 259 is multiplied by the size _v ^{c *} triangular wave _{v t0} frequency 2500Hz at _1, the _v ^{c *} to calculate a triangular wave _{v t} with the envelope.

Controller 250, the calculation unit 260, _v and _{ref +} calculated, compares the triangular wave _{v t} with capacitor voltage value _{v c,} which is calculated in the envelope.
When the reference voltage value v _{ref +} is smaller than the triangular wave v _t , the controller 250 turns on the gate signal SGU and turns off the gate signal SGX. When the reference voltage value v _{ref +} is greater than the triangular wave v _t , the calculation unit 260 turns on the gate signal U and turns off the gate signal X.
Similarly, in the calculation unit 260, the control unit 250 compares the negative value V _ref− of the reference voltage value v _{ref + with} the triangular wave v _t to generate gate signals SGV and SGY. When the triangular wave v _t is smaller, the calculation unit 260 turns on the gate signal SGV and turns off the gate signal SGY. When the triangular wave v _t is larger, the calculation unit 260 turns on the gate signal SGV and turns off the gate signal SGY.

By the way, as shown in Equation 8, when X = _Xc , the capacitor voltage (voltage value v _c ^* ) is equal to the absolute value of the voltage between the input / output terminals 111-112. Therefore, the triangular wave v _t has ± v _c ^* as an envelope, and the absolute value of v _{ref +} is equal to v _c ^* . That is, the envelope of the triangular wave v _t and the reference voltage value v _{ref +} have substantially the same waveform. Therefore, the gate signal generated by the calculation unit 260 comparing the triangular wave v _t and the reference voltage value v _{ref +} once remains on for half a cycle of the power cycle once turned on, and once turned off, It will continue to turn off for half the period.

  When the calculation unit 260 creates the gate signal, the control unit 250 transmits the output signal from the output unit 270 to the gates GU, GV, GX, and GY.

The switches SWU to SWY are turned on / off by a gate signal received at the gate. As a result, each voltage / current is generated as shown in FIG.
Since X = _Xc , the voltage of the capacitor CM (voltage value v _c ) drops to 0 voltage every cycle. As the switches SWU to SWY are turned on / off, the polarity of the voltage of the capacitor CM (voltage value vs) is switched every time it falls to 0 voltage, and the voltage is generated in the bridge circuit 110 (voltage value v _conv ). Voltage of the bridge circuit 110 (voltage value v _conv) harmonic has a sinusoidal waveform (triangular wave v harmonics below the switching frequency of _t) is small.
The line voltage (voltage value v _s ) and the voltage of the bridge circuit 110 (voltage v _conv ) are applied to the reactor 205. As a result, a current (current value i) flows through the reactor 205 and the bridge circuit 110. Since the voltage (voltage v _conv ) of the bridge circuit 110 has few harmonics, the current (current value i) has a waveform close to a sine wave.
That is, the reactive power control apparatus 200 can generate reactive power by flowing a current having a waveform close to a sine wave through the reactor 205.

(Operation when X < _Xc )
^{I *} increases with decrease in the line voltage value _{v s} In addition, at the X> _{X c,} the control unit 250, the calculating unit 256, subsequently by Equation 4, the ^* voltage value _v ^c should have a capacitor CM calculate.

In the calculation unit 257, the control unit 250 compares the calculated capacitor voltage value v _c ^* with the actually measured capacitor voltage value v _c to calculate the effective power V _act to be supplemented to the capacitor.

In the calculation unit 258, the control unit 250 obtains the reference voltage value v _{ref +} using Equation 7.

Controller 250, the calculation unit 259 is multiplied by the size _v ^{c *} triangular wave _{v t0} frequency 2500Hz at _1, the _v ^{c *} to calculate a triangular wave _{v t} with the envelope.

Controller 250, the calculation unit 260, _v and _{ref +} calculated, compares the triangular wave _{v t} with capacitor voltage value _{v c,} which is calculated in the envelope.
When the reference voltage value v _{ref +} is smaller than the triangular wave v _t , the controller 250 turns on the gate signal SGU and turns off the gate signal SGX. When the reference voltage value v _{ref +} is greater than the triangular wave v _t , the calculation unit 260 turns on the gate signal U and turns off the gate signal X.
Similarly, in the calculation unit 260, the control unit 250 compares the negative value V _ref− of the reference voltage value v _{ref + with} the triangular wave v _t to generate gate signals SGV and SGY. When the triangular wave v _t is smaller, the calculation unit 260 turns on the gate signal SGV and turns off the gate signal SGY. When the triangular wave v _t is larger, the calculation unit 260 turns on the gate signal SGV and turns off the gate signal SGY.

  The control unit 250 transmits the gate signal obtained by the calculation unit 260 from the output unit 270 to the gates GU, GV, GX, and GY.

The switches SWU to SWY are turned on / off by a gate signal received at the gate. As a result, each voltage and current is generated as shown in FIG.
Since X < _Xc , the voltage of the capacitor CM (voltage value v _c ) drops to 0 voltage every cycle. As the switches SWU to SWY are turned on / off, the voltage of the capacitor CM (voltage value v _s ) is generated in the bridge circuit 110 (voltage value v _conv ). The voltage (v _conv ) of the bridge circuit 110 has a fundamental wave component represented by a voltage value v _conv1 . The voltage (v _conv ) of the bridge circuit 110 has few harmonics (harmonics below the switching frequency of the triangular wave v _t ).
The difference between the line voltage (voltage value v _s ) and the voltage of the bridge circuit 110 (voltage v _conv ) is applied to the reactor 205. As a result, a current (current value i) flows through the reactor 205 and the bridge circuit 110. Since the voltage of the bridge circuit 110 has few harmonics, the current (current value i) has a waveform close to a sine wave.
That is, the reactive power control apparatus 200 can generate reactive power by flowing a current having a waveform close to a sine wave through the reactor 205.

  As described above, any reactive power can be generated by the reactive power control apparatus 200 according to the second embodiment of the present invention. As a result, voltage fluctuations in the AC power circuit can be suppressed. In other words, the reactive power control device 100 described above can be applied as STATCOM.

(Second Embodiment: Summary)
As described above, in this embodiment, the reactive power supplied to the AC power circuit can be controlled using a capacitor having a small capacity. Further, even when the equivalent reactance of the bridge circuit is smaller than the reactance of the capacitor, appropriate reactive power can be supplied with less harmonics by using a control different from the case where the equivalent reactance is large.

(Explanation of modification etc.)
It should be noted that the present invention can be variously modified and modified. Further, the above-described embodiments and modifications are for explaining examples of the present invention and do not limit the scope of the present invention. Although the modification of the said embodiment is illustrated below, each modification can be combined suitably.

(Modification 1)
The reactive power control apparatus 100 has been described as an example in which control is performed using a current value flowing through the bridge circuit 110. However, you may control using the line voltage of the vicinity where the reactive power control apparatus 100 is connected. In that case, a line voltage may be detected by the voltmeter 116 instead of detecting the current by the ammeter 117 as in the reactive power control apparatus 300 shown in FIG. In this case, the phase and frequency may be detected from the detected line voltage, and the current flowing through the bridge circuit 110 may be used as a command value.

(Modification 2)
Although the reactive power control devices 100 and 200 have been described as devices that supply reactive power, they may not only supply reactive power but also consume reactive power in the same way as general STATCOM.

(Modification 3)
In the above embodiment, the program for executing the above processing is stored in a predetermined computer-readable storage medium (in the above, RAM 152 and ROM 153 constituting the storage unit) from the beginning. However, a program for executing the above processing is stored in a portable computer-readable storage medium such as a flexible disk, a CD-R (Compact Disc Recordable), or a CD-ROM (Compact Disk Read Only Memory) and distributed. Also good. The program for executing the processing may be supplied to the computer via the Internet or the like so that the computer becomes the reactive power control apparatus 100. The program for executing the above process may be a program for executing the above process in cooperation with an OS (Operating System) or the like.

(Modification 4)
The calculation process used in the above description is an example, and various applications are possible as long as the object of the present invention is achieved. For example, the gate signal for the command value may be calculated externally in advance. If the reactive power controller 200 measures the line voltage v _s, presetting gate signals with respect to the size of the measured line voltage v _s. Further, the effective voltage of the bridge circuit 110 can be feedback-controlled so that an appropriate pattern is selected from preset gate signal patterns.

In the above description, the timing for switching on / off the switches SWU to SWY is controlled based directly on the reactance _{Xc of the} capacitor CM. However, it may be controlled substantially based on the reactance _Xc, and another value correlated with the reactance _Xc , for example, admittance or capacitance may be used.
Other values are not limited to the above description, and the present invention can be implemented by implementing the present invention by using other correlated values.

In the above description, the reactive power control apparatus 100 uses the 1-pulse control unit 168 with X = _Xc , but this is not essential. Even in the case of X = _Xc, the calculation unit 163 may be used. In reactive power control apparatus 200, calculation unit 256 does not have to be used when X = _Xc . Instead, the same control as that of the 1-pulse control unit 168 may be used.
In any of the embodiments, mutual control can be used.

100, 200, 300 Reactive power control device VS AC power supply LD Load L Reactance 110 Bridge circuit SWU, SWV, SWX, SWY Switch CM Capacitor 111, 112 Input / output terminal 115 116 Voltmeter 117 Ammeter 150, 250 Control unit 201 Unit 205 Reactor 246, 247 Voltmeter 280 Three-phase AC power circuit LD Load 150 Control unit

Claims (5)

A bridge circuit composed of first to fourth switches and at least one capacitor and connected to an AC power circuit;
A controller that controls on / off of the first to fourth switches at a frequency higher than the frequency of the AC power circuit, and controls reactive power supplied to the AC power circuit by controlling the switching timing;
With
Each of the first to fourth switches includes first and second terminals and a control terminal, and conducts current in both directions between the first and second terminals to which an ON signal is input to the control terminal. It is turned on, and the current from the first terminal to the second terminal is cut off and the current from the second terminal to the first terminal is turned on when an OFF signal is input to the control terminal It ’s off,
The bridge circuit is
The first terminal of the first switch and the first terminal of the third switch are connected, and the second terminal of the first switch and the first terminal of the second switch Are connected, the second terminal of the third switch and the first terminal of the fourth switch are connected, and the second terminal of the second switch and the fourth switch The second terminal of the first switch, and the capacitor is connected between the first terminal of the first switch and the second terminal of the second switch, Connected to the AC power circuit by the second terminal and the second terminal of the third switch;
The control unit controls the switching timing based on reactance of the capacitor.
The reactive power control apparatus characterized by the above-mentioned. The controller is
Identifying the capacitor voltage based on the reactance of the capacitor, and controlling the switching timing based on the identified capacitor voltage;
The reactive power control apparatus according to claim 1. A voltage detection unit for detecting the voltage of the capacitor and transmitting the detected capacitor voltage to the control unit;
The control unit controls the switching timing based on the identified capacitor voltage and the detected capacitor voltage.
The reactive power control apparatus according to claim 2. The first and second terminals and a control terminal are provided, and an ON signal is input to the control terminal, and a current in both directions between the first and second terminals is turned on, and the control terminal is turned off. A first to a fourth state in which an electric current is cut off from the first terminal to the second terminal and a current from the second terminal to the first terminal is turned off. A switch, wherein the first terminal of the first switch and the first terminal of the third switch are connected, and the second terminal of the first switch and the second switch of the second switch A first terminal is connected, the second terminal of the third switch and the first terminal of the fourth switch are connected, and the second terminal of the second switch and the the fourth and the second terminal of the switch is connected, co the first scan the capacitor Connected between the first terminal of the switch and the second terminal of the second switch, and the second terminal of the first switch and the second terminal of the third switch. A reactive power control method for controlling reactive power supplied to the AC power circuit by controlling a bridge circuit connected to the AC power circuit by:
Switching on and off of the first to fourth switches at a frequency higher than the frequency of the AC power circuit, and controlling the switching timing based on reactance of the capacitor,
And a reactive power control method. The first and second terminals and a control terminal are provided, and an ON signal is input to the control terminal, and a current in both directions between the first and second terminals is turned on, and the control terminal is turned off. A first to a fourth state in which an electric current is cut off from the first terminal to the second terminal and a current from the second terminal to the first terminal is turned off. A switch, wherein the first terminal of the first switch and the first terminal of the third switch are connected, and the second terminal of the first switch and the second switch of the second switch A first terminal is connected, the second terminal of the third switch and the first terminal of the fourth switch are connected, and the second terminal of the second switch and the the fourth and the second terminal of the switch is connected, co the first scan the capacitor Connected between the first terminal of the switch and the second terminal of the second switch, and the second terminal of the first switch and the second terminal of the third switch. By controlling a reactive power supplied to the AC power circuit by controlling a bridge circuit connected to the AC power circuit.
Switching on and off the first to fourth switches at a frequency higher than the frequency of the AC power circuit, and controlling the switching timing based on the reactance of the capacitor;
A program characterized by that.

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