JP2005318755A - Inverter control system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To raise a voltage of an inverter and increase an output of the inverter by effectively utilizing a power supply voltage. <P>SOLUTION: A PWM signal generation part 100 is constituted such that a pulse of a prescribed pulse width is output from a pulse generation device on the basis of the comparison of magnitudes of a carrier wave TRI generated at a carrier wave generation part and a voltage command signal Vref generated at a voltage command generation part. The carrier wave generation part of the PWM signal generation part is associated with the voltage command signal Vref or an output value of the inverter, and a carrier wave frequency is made variable. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an inverter device used for driving a load device such as a motor, and a PWM type inverter control system applied to inverter control of a reactive power compensation or load leveling device in an electric power system.

  A conventional example of a PWM inverter will be described with reference to FIG. As shown in FIG. 1, the PWM inverter includes an inverter main circuit 1 connected between a DC power supply 70 and a load 80, and a triangular wave comparison PWM control system connected to the inverter main circuit 1.

  The inverter main circuit 1 includes switching elements 1A and 1B such as IGBTs. Further, the triangular wave comparison PWM control system has a pulse generator 2 that generates a pulse for turning on and off the switching elements 1A and 1B. This pulse generator 2 is connected to a carrier wave generator 5 that generates a carrier wave TRI that is a triangular wave, and a voltage command generator 6 that generates a voltage command Vref for controlling the width of a pulse generated by the pulse generator 2. Yes.

  FIG. 2 shows the operation of the pulse generator 2, and the on / off state of the switching elements 1A and 1B is determined based on the magnitude relationship between the voltage command Vref and the carrier wave signal TRI. In FIG. 2, the pulse for turning on 1A is generated when the magnitude relation between the voltage command Vref and the carrier signal TRI is Vref> TRI, and the pulse for turning on 1B is generated when the voltage command Vref <TRI (see, for example, Patent Document 1). .

JP 2001-231265 A

  By the way, in the conventional PWM signal generation method, the maximum level of the voltage command Vref is set to be less than the maximum level of the carrier wave signal TRI, and the duty ratio of the PWM signal is approximately 90% or less and does not reach 100%. Controlled by range. Therefore, when the load is driven by the PWM inverter, there is a problem that the voltage of the DC power source 70 cannot be used effectively.

  The present invention takes the following means in order to solve the above-described problems.

  That is, the inverter control system of the present invention performs PWM control on a controlled object by the inverter output by turning on and off the switching element of the inverter main circuit based on the PWM signal generated in the PWM signal generation unit, The signal generator is configured to output a pulse having a predetermined pulse width from the pulse generator based on the magnitude comparison between the carrier wave signal generated by the carrier wave generator and the voltage command signal generated by the voltage command generator, The carrier wave generation unit is characterized in that the carrier wave frequency is varied in association with the voltage command signal or the inverter output value.

  The carrier wave generator preferably performs variable control that lowers the carrier frequency when the voltage command signal or the inverter output value increases, and increases the carrier frequency when the voltage command signal or the inverter output value decreases.

  In particular, the carrier wave generation unit slows the carrier frequency at the timing when the voltage command signal or the inverter output value becomes maximum, and makes the carrier frequency the fastest at the timing when the voltage command signal or the inverter output value becomes minimum, It is preferable that the carrier frequency is continuously variable according to a change in the voltage command signal or the inverter output value.

  As a component of the reactive power compensator, when the power supply to the power system to be controlled is controlled through the inverter output voltage, the carrier wave generation unit is a timing at which the inverter output voltage increases at least when the instantaneous voltage drops Thus, the frequency of the carrier signal may be decreased and variable control may be performed to increase the frequency of the carrier signal at the timing when the inverter output voltage is lowered.

When driving the load to be controlled through the inverter output voltage, the carrier wave generator lowers the frequency of the carrier signal at the timing when the inverter output voltage becomes high, and the frequency of the carrier signal at the timing when the inverter output voltage becomes low What is necessary is just to comprise so that the variable control which raises may be performed.

  When the load to be controlled is driven according to the inverter output current, the carrier wave generation unit lowers the frequency of the carrier signal at a timing when the inverter output current increases and the carrier signal at a timing when the inverter output current decreases. What is necessary is just to comprise so that the variable control of raising the frequency may be performed.

As one component of the load leveling device, when leveling the load of the power system to be controlled through the inverter output current, the carrier wave generator generates the inverter output current at least during peak cut operation or charge operation. The frequency of the carrier signal may be decreased at the timing when the frequency becomes higher, and the variable control may be performed to increase the frequency of the carrier signal at the timing when the inverter output current becomes lower.

  As one component of the load leveling device, when smoothing the load of the electric power system to be controlled through the inverter output voltage, the carrier wave generator generates the inverter output voltage at least during peak cut operation or charge operation. The frequency of the carrier signal may be decreased at a timing when the frequency becomes higher and the frequency of the carrier signal may be increased at the timing when the inverter output voltage becomes lower.

As a component of the instantaneous voltage drop compensator, when compensating for the voltage drop of the power system to be controlled through the inverter output voltage, the carrier wave generator generates at least a voltage for compensating for the instantaneous voltage drop. In addition, it may be configured to perform variable control in which the frequency of the carrier signal is decreased at the timing when the inverter output voltage is increased and the frequency of the carrier signal is increased at the timing when the inverter output voltage is decreased.

  In the above, in order to be able to freely set the pulse width and the like on the user side, it is desirable that the voltage command generator generates a voltage command signal based on the applied input signal.

  A triangular wave signal is suitable as the carrier signal.

  Next, a means for solving the problem will be specifically described. The inverter control system employed by the system of the present invention, for example, variably controls the frequency of the carrier signal in accordance with the output voltage of the inverter and effectively uses the power supply voltage, thereby increasing the inverter voltage and output. Is.

  FIG. 3 is a block diagram showing the operation of the PWM signal generation unit 100.

  The input signal Vref is a signal that controls the inverter output voltage. The input signal X is a control signal for variably controlling the carrier frequency and takes a value of | X | ≦ 1. The input signal fh is the carrier frequency at the timing when the input signal X becomes 0, and fl is the carrier frequency at the timing when the input signal X becomes 1. The input signal Reset is a signal for initializing the outputs of the calculation units 2, 5, and 6 whose output signal values have history characteristics with respect to time at the start of the PWM signal generation unit to S3, 0, and −1, respectively. The other relationship between the input signals and output signals of the calculation units 1 to 7 is as shown in FIG. The calculation units 1 to 6 correspond to the carrier wave generation unit of the present invention corresponding to the carrier wave generation unit 6 of FIG. 1, and the calculation unit 7 corresponds to the pulse generation device of the present invention corresponding to the pulse generation device 2 of FIG. The CPU 10 described below corresponds to the voltage command generator of the present invention corresponding to the voltage command generator 6 of FIG.

  Next, the operation of the PWM signal generation unit 100 will be described.

  The input signal Reset is set to 0 value in advance. The CPU 10 and the arithmetic unit 1 are always operating, and values corresponding to the input signals fh, fl, and X are output as the signal S3. Here, when the value of the input signal Reset is changed to 1 for initialization of the PWM signal generation unit 100, the outputs of the calculation units 2, 5, and 6 are fa = S3 and t = 0, respectively, as described above. , TRI = −1.

  The calculation unit 2 holds the output signal fa in S3 until the time when the input signal S2 changes to a positive value. The computing unit 5 outputs the elapsed time from the time when Reset has changed from 0 to 1 to the signal t. The arithmetic unit 3 outputs the value 1 as the signal S1 until t reaches 1 / 2fa, and the output signal TRI of the arithmetic unit 6 increases in proportion to the time change, and at time t = 1 / 2fa, TRI = 1 Next, during 1 / 2fa ≦ t <1 / fa, the calculation unit 3 outputs the value −1 as the signal S1. The output signal TRI of the arithmetic unit 6 decreases in proportion to the time change, and becomes TRI = -1 at the time of t = 1 / fa. With the above operation, the output signal TRI of the calculation unit 6 generates a triangular wave with the frequency fa, and the calculation unit 7 compares the input signal Vref and TRI to generate a PWM signal.

  At the time when t = 1 / fa, the output signal S1 of the calculation unit 3 changes from a negative value to a positive value, so that S2 becomes a positive value via the calculation unit 4. The output signal fa of the calculation unit 2 is changed to the output S3 of the calculation unit 1 at that time. Further, the output signal t of the arithmetic unit 5 is initialized to 0.

  Thereafter, the frequency of the carrier wave signal is variably controlled according to the input signal X by the same operation.

  The PWM inverter needs to turn on and off the switching device with a pulse width of a very short time interval. However, this pulse width cannot be made infinitely small, and it is necessary to ensure a sufficient pulse width in consideration of the operation speed of the switching device and the delay of the control circuit. In PWM control, the pulse width becomes the narrowest at the timing when the output voltage of the inverter takes a peak value. To ensure a sufficient pulse width, the upper limit of the duty ratio, that is, the upper limit of the output voltage of the inverter is limited. Occurs.

For example, in the inverter of FIG. 1, a restriction of Formula 1 occurs between the voltage Vdc of the DC power supply 70, the frequency f of the carrier wave TRI, the voltage command Vref, and the minimum pulse width Tp.

  On the other hand, if the inverter control method according to the present invention is used to make the waveform of X coincide with │Vref│ and the arithmetic processing is performed in the CPU 10 so that X becomes 1 when Vref takes a peak value, the output of the inverter When the voltage is near the peak value, the value is about fl, and when the output voltage is about 0, the value is about fh. Further, when the relationship between fl and fh is set such that fl <fh, PWM control is performed at a slow carrier frequency at a timing when the output voltage is near the peak value, and at a fast carrier frequency at a timing at which the output voltage is near the zero value. It will be. As a result, in the PWM inverter using this control method, the inverter is operated with a PWM signal having a wider pulse width as compared with the conventional method even when the output voltage is near the peak value. Therefore, even in an inverter using the same main circuit, it is possible to output a larger voltage by using this control method, and as a result, high output of the inverter can be realized.

  Further, the input signal X does not necessarily need to match Vref. For example, if processing is performed in the CPU 10 so that the waveform of X coincides with the inverter output current and X becomes 1 when the inverter output current takes a peak value, the carrier frequency is slow at the timing when the output current is large. As a result, switching loss can be reduced, and high efficiency of the inverter can be realized.

Embodiment 1 FIG.
Hereinafter, Embodiment 1 of the present invention will be described in detail with reference to FIG. FIG. 4 is a circuit diagram of an example in which the reactive power compensator 200 using the PWM control method is applied to the power system 300. The reactive power compensator 200 compensates for the reactive power component of the load 26 with respect to the power system 300 during normal times, and when the voltage of the power system 300 fluctuates due to an instantaneous voltage drop or the like, the voltage of the bus 22 is rated. It operates to maintain voltage, i.e. to maintain normal power supply to the load 26.

  The reactive power compensator 200 is linked to the bus 22 via a 10% grid reactor 21, and the back impedance 23 when the power system is viewed from the bus 22 is assumed to be 10%. The voltage Vdc of the DC power supply 24 used in the reactive power compensator 200 is 1.375 pu with respect to the peak value of the system voltage. The switching devices 51 and 52 used in the inverter unit are devices having a slow switching speed such as HVIGBT, and the minimum pulse width Tp is 50 μs.

  For the control of the inverter unit, the PWM signal generation unit 100 shown in FIG. 3 is used. Input signals fl and fh to the PWM signal generator 100 are set to 1.25 kHz and 2 kHz, respectively.

  Next, the effect when the technique invented this time is applied to the reactive power compensator 200 will be described. Assume that the input signal X is always set to 0, and the reactive power compensator 200 supplies reactive power to the power system 300 by PWM control with a constant carrier frequency of 2 kHz (= fh).

  From fh, Vdc, Tp, and Equation 1, the upper limit of Vref and the inverter output voltage is 1.1 pu, and the reactive power that can be supplied is 0.5 pu. Further, if a failure occurs in the power system 300 and an instantaneous voltage drop of about 1 second occurs, the output voltage upper limit of the reactive power compensator remains 1.1 pu, and the voltage of the bus 22 is maintained at the rated voltage. The lower limit of the voltage of the power system 300 that can be used is up to 0.9 pu.

  However, if the X waveform is made to coincide with | Vref | while the instantaneous voltage drop occurs, and the CPU 10 performs arithmetic processing so that X becomes 1 when Vref takes a peak value, Vdc, fl , Tp and Equation 1, the upper limit of Vref and the inverter output voltage can be up to 1.2 pu, and the upper limit of the output voltage of the reactive power compensator 200 can be up to 1.2 pu. This corresponds to the fact that the voltage of the bus 22 can be maintained at the rated voltage even when the voltage of the power system 300 is reduced to 0.8 pu, which is 2.0 times that in the case where the conventional control method is used. The instantaneous voltage drop of the voltage drop width can also be compensated.

  In this embodiment, the reactive power supplied by the reactive power compensator 200 at the time of instantaneous voltage drop compensation is 2.0 pu and exceeds the device rating. However, if the inverter is designed in advance assuming a short overload operation, Good.

  As described above, by using the control method according to the present invention for the reactive power compensator 200, it is possible to improve performance by increasing the output voltage of the inverter unit.

Embodiment 2. FIG.
Next, the effect when applied to a load driving device will be described in detail with reference to FIG. FIG. 5 is a circuit diagram of an example in which the load 600 is driven by the PWM control type inverter device 500.

  It is assumed that the inverter device 500 drives the load 600 via the transformer 21. The voltage Vdc of the DC power supply 24 used for the inverter device 500 is 1.25 pu. The switching devices 51 and 52 used in the inverter unit are devices having a slow switching speed such as GTO, and the minimum pulse width Tp needs to be 100 μs.

  In the inverter device 500 described in the present embodiment, the PWM signal generation unit 100 shown in FIG. 3 is used to control the inverter unit. The input signals fl and fh to the PWM signal generator 100 are set to 0.5 kHz and 1 kHz, respectively.

  Assume that the input signal X is always 0, and the inverter device 500 drives the load 600 by PWM control with a constant carrier frequency of 1 kHz (= fh).

  From fh, Vdc, Tp and Equation 1, the upper limit of Vref and the inverter output voltage is 1 pu. When the inverter output current is 1 pu, the power supplied to the load is 1 pu.

  However, if the calculation processing is performed in the CPU 10 so that the waveform of X coincides with | Vref | and X becomes 1 when Vref takes the peak value, Vref and Vref The upper limit of the inverter output voltage is 1.125 pu. At this time, the maximum inverter output voltage is 1.125 pu, and there is no change in the restrictions on the inverter output current.

In order to utilize the increase in the maximum voltage that can be output from the inverter, the winding tap on the inverter device 500 side of the transformer 21 is adjusted to 1.125 pu to operate the entire system. Since the output current of the inverter device 500 is 1 / 1.125 pu, the copper loss generated in the section from the inverter device 500 to the winding on the inverter device 500 side of the transformer 21 is proportional to the square of the inverter output current. Therefore, 1 / 1.125 ² pu (≈0.79 pu), and a reduction in copper loss exceeding 20% can be realized.

  Further, since the energization loss caused by the ON voltage of the switching devices 51 and 52 of the inverter device 500 is substantially proportional to the inverter output current, it becomes 1 / 1.125 pu (≈0.89 pu), and the energization of the inverter exceeding 10%. Loss can be reduced.

  As described above, by using the control method according to the present invention for the inverter device 500, it is possible to achieve higher efficiency of the system by reducing loss as well as higher voltage and higher output of the inverter unit.

Embodiment 3 FIG.
Next, Embodiment 3 of the present invention will be described in detail with reference to FIG. The circuit configuration, fl, and fh are the same as those in the second embodiment.

If the input signal X is always set to 0 and the inverter device drives the load 600 by PWM control with a constant carrier frequency of 1 kHz (= fh), the switching loss L1 generated from the switching devices 51 and 52 is approximately 2 It can be expressed as Here, Vdc is a voltage value of the DC power supply 24, In is a peak value of the rated load current, tsw is a switching time of the switching devices 51 and 52, and C is a constant depending on characteristics of the switching devices 51 and 52.

However, if the calculation process is performed in the CPU 10 so that the waveform of the input signal X coincides with the inverter output current and X becomes 1 when the inverter output current takes a peak value, it is generated from the switching devices 51 and 52. The switching loss L2 can be generally expressed as Equation 3. If the previous fl and fh are substituted here, L2 / L1 becomes 61%, and it can be seen that the switching loss can be reduced by about 40%.

  As described above, by using the control method according to the present invention for the inverter device 500, the switching loss generated in the inverter unit can be greatly reduced, and the system can be highly efficient.

Embodiment 4 FIG.
Next, a fourth embodiment of the present invention will be described in detail with reference to FIG. FIG. 6 is a circuit diagram of an example in which the load leveling apparatus 700 using the PWM control method is applied to the power system 800. The load leveling device 700 has two operation functions: a connected operation for inputting / outputting active power to / from the power system 300 and a self-supporting operation for opening the circuit breaker 25 and supplying power to the load 26.

  The load leveling device 700 performs a peak cut operation that outputs active power during the daytime when the load 26 becomes a heavy load, and contributes to a reduction in the capacity of the power facility on the power system 800 side from the bus 22. At night when the load 26 is light, a charging operation for charging the DC power supply 24 is performed to prepare for peak cut operation during the daytime of the next day. Further, when a power failure or instantaneous voltage drop occurs in the power system 800 throughout the day, the circuit breaker 25 is opened, and power supply to the load 26 is continued in a self-sustaining operation.

  The load leveling device 700 is connected to the bus 22 via a 10% connected reactor 21. The voltage of the DC power supply 24 used in the load leveling device 700 is 1.25 pu with respect to the peak value of the system voltage. Further, the DC power source 24 is a secondary battery having a capacity that can cope with the peak cut operation / charge operation described above.

  For the control of the inverter unit, the PWM signal generation unit 100 shown in FIG. 3 is used. Input signals fl and fh to the PWM signal generator 100 are set to 1 kHz and 2 kHz, respectively.

  Next, the effect when the technique invented this time is applied to the load leveling apparatus 700 will be described. At the time of peak cut operation or charge operation, the input signal X is always set to 0, and the inverter device uses the switching loss L3 when PWM control is performed with a constant carrier frequency of 2 kHz (= fh), and the method according to the present invention. When comparing the switching loss L4 when the calculation processing is performed in the CPU 10 so that the waveform of the input signal X matches the inverter output current, and X becomes 1 when the inverter output current takes a peak value, As in the third embodiment, L4 / L3 is 61%, and the switching loss can be reduced by about 40%.

Next, when the method invented this time is used, the harmonic current flowing out to the power system 800 is evaluated. When PWM control is performed at a constant frequency fh, the positive peak-negative peak value Δi1 of the harmonic current among the inverter output currents is the largest at the timing when the inverter output voltage takes a value of approximately zero. Is generally obtained from Equation 4. The left side of the first equation is the difference between the system voltage and the inverter output voltage (instantaneous value). The denominator value 0.5 of the right side of the second equation is that the duty ratio of the PWM signal is 50% when the inverter output voltage is 0. by. Here, L is the sum of the inductance values of the interconnection reactor 21 and the rear impedance 23.

On the other hand, in the PWM control using the method invented this time, at the timing when the inverter output voltage becomes the peak value and the carrier frequency becomes the slowest, the positive peak-negative peak value Δi2 of the harmonic current of the inverter output current is approximately several. It is represented by 5. The left side of the first equation is the difference between the system voltage and the inverter output voltage (instantaneous value), and the denominator value 0.1 of the right side of the second equation is Vd = 1.25 pu to output a voltage of 1 pu from the inverter. This is because the duty ratio is 90%.

From Equations 4 and 5, Δi2 / Δi1 is as shown in Equation 6.

  Thus, even at the timing when the carrier frequency becomes the slowest, the positive peak-negative peak value Δi2 of the harmonic current in the inverter output current is about the maximum value (= Δi1) when PWM control is performed at a constant frequency. It can be seen that the peak value of the harmonic current that falls within 70%, that is, flows out to the power system does not increase.

  In general, the harmonic current flowing into the system from the interconnection inverter is proportional to the PWM carrier frequency, and the harmonics of the carrier frequency and the switching loss are in a trade-off relationship. In addition, both suppression of harmonic current and high efficiency of the inverter can be achieved.

  As described above, by using the control method according to the present invention for the load leveling apparatus 700, a high-efficiency and high-quality load leveling apparatus can be realized.

Embodiment 5 FIG.
Hereinafter, Embodiment 5 of the present invention will be described in detail with reference to FIG. FIG. 7 is a circuit diagram of an example in which the voltage sag compensator 400 using the PWM control method is applied to the power system 450. The voltage sag compensator 400 normally closes the circuit breaker 25 and does not affect the power system 450 and the load 26 at all. On the other hand, when an instantaneous voltage drop occurs in the power system 450, after detecting this and opening the circuit breaker 25, a voltage for compensating for the voltage drop of the power system 450 is output from the inverter, and the load It operates to maintain the supply voltage to 26 normally. The relationship between the above system voltage, compensation voltage, and load voltage is as shown in FIG.

  The capacitor 24 is used as the DC power source and energy source of the voltage sag compensator 400, and the initial charging voltage Vdc (0) is 1.375 pu with respect to the peak value of the system voltage. It is assumed that the switching devices 51 and 52 used in the inverter unit are devices having a low switching speed such as HVIGBT, and the minimum pulse width Tp needs to be 50 μs.

  For the control of the inverter unit, the PWM signal generation unit 100 shown in FIG. 3 is used. Input signals fl and fh to the PWM signal generator 100 are set to 1.25 kHz and 2 kHz, respectively.

  Note that the voltage sag compensator 400 has some charging means for the capacitor 24, but these are very general and have nothing to do with the essence of the present invention, so illustration and details are omitted. To do.

  Next, the effect when the technique invented this time is applied to the voltage sag compensator 400 will be described. Although the inductance of the filter circuit 27 is preferably as small as possible from the viewpoint of the cost of the voltage sag compensator 400, at the time of instantaneous voltage compensation at the timing when the transient voltage fluctuation on the power system side is large as just after the start of the instantaneous voltage drop compensation. In order to make the supply voltage to the load 26 accurate, it is desirable to increase the carrier frequency.

  Assuming that the input signal X is always 0, the voltage sag compensator 400 compensates the instantaneous voltage drop when the voltage of the power system 450 is completely reduced to 0 by PWM control with a constant carrier frequency of 2 kHz (= fh). And

In the compensation for the instantaneous voltage drop, the charging voltage Vdc of the capacitor 24 decreases with the relationship of approximately several 7 with time. Here, C1 is the capacitance of the capacitor 24, P is the active power consumed by the load 26, and time T is the duration of the instantaneous voltage drop.

  From fh, Vdc, Tp and Equation 1, the lower limit of Vdc (T) that satisfies Vref ≧ 1 is 1.25 pu. Therefore, by substituting this in Equation 7, the capacitance C1 necessary for the voltage sag compensator 400 is obtained.

  However, if the control method according to the present invention is used, once the input signal X is always set to 0 and compensated with the carrier frequency fh (= 2 kHz), and the Vdc drops to 1.25 pu, the waveform of X matches | Vref |. It is also possible to perform arithmetic processing in the CPU 10 so that X becomes 1 when Vref takes a peak value. At this time, from Vdc, fl, Tp and Equation 1, the lower limit of Vdc (T) satisfying Vref ≧ 1 is 1 / 0.875 (≈1.143) pu. Therefore, in the voltage sag compensator 400 using the present invention, the necessary capacitance C2 is obtained by substituting this in Equation 7.

From the above, C2 / C1 is obtained from Equation 8. That is, by using the present invention, the capacitance of the capacitor 24 that the voltage sag compensator 400 needs can be reduced by about 40%.

  If this method is used, instantaneous voltage drop compensation can be performed at a high carrier frequency at a timing when the transient voltage fluctuation on the power system side immediately after the start of instantaneous voltage drop compensation is large, so that the accuracy of the supply voltage to the load 26 is also good. Can be maintained.

  Generally, in a voltage sag compensator using a capacitor as an energy source, the capacitance of the capacitor occupies a large weight in the cost and size of the device.

  On the other hand, by using the control method according to the present invention for the sag compensator 400, the capacitance of the capacitor to the load 26 can be reduced, and the cost and size of the device can be reduced.

  Here, the series type voltage sag compensator shown in FIG. 7 is taken as an example. However, in the circuit configuration of FIG. In the parallel type voltage sag compensator that compensates the voltage sag for the load 26 by the output from the power source, since the voltage drop of the DC power supply 24 dominates the voltage sag compensation time, the maximum voltage using the present invention The same effect can be realized by the increase.

  The present invention has been described with reference to the first to fifth embodiments. However, the present invention is not limited to these embodiments, and various modifications can be made. For example, the inverter is not limited to a single-phase half bridge, and a 3-phase inverter or three single-phase full-bridge inverters can be Y-connected and applied to a 3-phase AC system or a load. It is also possible to realize a system control device having both functions of the reactive power compensation device according to the first embodiment and the load leveling device according to the third embodiment.

  Naturally, the reactive power compensator 200, the inverter device 500, the load leveling device 700, and the voltage sag compensator 400 measure the voltage and current necessary for the protection and control of the device and the necessary circuits and operations. Although it has a function, since these are very general and have nothing to do with the essence of the present invention, illustration and detailed description are omitted.

  Furthermore, when the carrier frequency is variably controlled according to the inverter output value, it can be selected in various ways depending on the purpose and application whether it conforms to the inverter output voltage or the inverter output current.

The block diagram which shows the structure of a general inverter control system. The figure which shows operation | movement of the pulse generator in the same system. The block diagram which shows the structure of the PWM signal generation part which concerns on this invention. 1 is a block diagram showing Embodiment 1 of the present invention. The block diagram which shows Embodiment 2, 3 of this invention. The block diagram which shows Embodiment 4 of this invention. The block diagram which shows Embodiment 5 of this invention. Action explanatory drawing corresponding to FIG.

Explanation of symbols

100: PWM signal generator Vref ... Voltage command signal TRI ... Carrier wave signal

Claims (11)

By turning on and off the switching element of the inverter main circuit based on the PWM signal generated in the PWM signal generation unit, the control target is PWM controlled by the inverter output,
The PWM signal generation unit is configured to output a pulse having a predetermined pulse width from the pulse generator based on a magnitude comparison between a carrier wave signal generated by the carrier wave generation unit and a voltage command signal generated by the voltage command generation unit, The inverter control system characterized in that the carrier wave generation unit varies the carrier wave frequency in association with the voltage command signal or the inverter output value. The carrier wave generation unit performs variable control that lowers the carrier wave frequency when the voltage command signal or the inverter output value increases and increases the carrier frequency when the voltage command signal or the inverter output value decreases. The inverter control system according to claim 1. The carrier generation unit slows the carrier frequency at the timing when the voltage command signal or the inverter output value becomes maximum, and makes the carrier frequency the fastest at the timing when the voltage command signal or inverter output value becomes the minimum. 3. The inverter control system according to claim 2, wherein the inverter control system is continuously variable according to a change in the voltage command signal or the inverter output value. As a component of the reactive power compensator, the power supply to the power system to be controlled is controlled through the inverter output voltage,
The carrier generation unit performs variable control to lower the frequency of the carrier signal at a timing when the inverter output voltage becomes high and to increase the frequency of the carrier signal at a timing when the inverter output voltage becomes low, at least when the instantaneous voltage drops. The inverter control system according to claim 2 or 3. A load to be controlled is driven through an inverter output voltage,
4. The carrier wave generation unit performs variable control to lower a carrier signal frequency at a timing when the inverter output voltage becomes higher and to raise a carrier signal frequency at a timing when the inverter output voltage becomes lower. The inverter control system described. The load to be controlled is driven according to the inverter output current,
The carrier generation unit performs variable control such that the frequency of the carrier signal is decreased at a timing when the inverter output current is increased and the frequency of the carrier signal is increased at a timing when the inverter output current is decreased. 3. The inverter control system according to 3. As a component of the load leveling device, the load of the power system to be controlled is leveled through the inverter output current,
The carrier wave generation unit performs variable control that lowers the frequency of the carrier signal at a timing when the inverter output current becomes high and increases the frequency of the carrier signal at a time when the inverter output current becomes low at least during peak cut operation or charge operation. The inverter control system according to claim 2, wherein the inverter control system is performed. As one component of the load leveling device, the load of the power system that is the control target is smoothed through the inverter output voltage,
The carrier wave generator is configured to perform variable control such that at least during peak cut operation or charge operation, the frequency of the carrier signal is decreased at a timing when the inverter output voltage is increased and the frequency of the carrier signal is increased at a timing when the inverter output voltage is decreased. The inverter control system according to claim 2 or 3, wherein: As a component of the instantaneous voltage drop compensator, the voltage drop of the power system to be controlled is compensated through the inverter output voltage,
The carrier wave generation unit lowers the frequency of the carrier signal at a timing when the inverter output voltage becomes high and outputs the voltage for compensating for the instantaneous voltage drop, and the frequency of the carrier signal at a timing when the inverter output voltage becomes low 4. The inverter control system according to claim 2, wherein variable control is performed to increase the value. The inverter control system according to any one of claims 1 to 9, wherein the voltage command generator generates a voltage command signal based on a given input signal. The inverter control system according to claim 1, wherein the carrier wave signal is a triangular wave signal.