JPH04261366A - Controller of multiple inverter - Google Patents

Abstract

PURPOSE:To get a multiple inverter device which can prevent the biased magnetization of each individual insulating transformer by adding a feedback control system. CONSTITUTION:This comprises a voltage detector 11, which detects the output voltages of inverters 3a, 3b, and 3c at multistage, an integrator 12, which integrates the detected output voltages within a certain time being set by an integration time setting circuit, and a dead zone circuit 15 for providing this integral value with a certain dead zone.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a control device for multiple inverters, and more particularly to control of the output voltage on the alternating current side of the inverters.

0002

[Prior Art] Generally, when removing harmonic components of the output voltage of an inverter or when the voltage required by the load is large, inverter outputs that are out of phase with each other are added together via an isolation transformer. The next harmonic is removed,
At the same time, it can output high voltage. Conventionally, as a control performed to prevent biased magnetization of the isolation transformer, there is a circuit configuration of a multiplex inverter control device as shown in FIG. In FIG. 5, 1 is a constant voltage source, 2 is a smoothing capacitor for smoothing the output voltage of this constant voltage source, and 3 is a constant voltage source.
is an inverter group whose input voltage is the output of a constant voltage source, and is composed of multistage inverters from the first stage to the nth stage of each inverter 3a, 3b, and 3c. 4
is a group of current detectors for detecting the output current of the inverters from the first stage to the nth stage, and each current detector 4a
, 4b and 4c, each of which detects the output current of the inverter at each stage. 5 is a group of isolation transformers for insulating the inverters from the first stage to the nth stage and the load 7, and each isolation transformer 5a, 5b,
5c, each inverter is composed of an isolation transformer for each stage. 6 is a current detector for detecting a load current flowing through the secondary side of the isolation transformer, and 7 is a load for the inverter group.

Reference numeral 8 denotes a voltage sharing control circuit that generates voltage command values for the inverters at each stage, and voltage sharing control circuits 8a and 8b that generate voltage command values for each stage of the inverters.
, 8c. Reference numeral 9 denotes a pulse width modulation circuit that generates a pulse by comparing the voltage command value of each stage of the inverter with a phase-shifted triangular wave output from the triangular wave generator 10, and generates a gate pulse for the inverter of each stage. It is composed of pulse width modulation circuits 9a, 9b, and 9c. Further, as an example of application of this control for preventing biased magnetization of an insulating transformer to other devices, there is a circuit configuration shown in Japanese Utility Model Publication No. 1-171543.

Next, the operation will be explained. The voltage command value V* generated from the difference between the load current and the current command value is used by the voltage sharing control circuit 8 to create voltage command values V1 to Vn for each stage. Here, since it is common that the inverter voltage command value of each stage is equally divided into voltages, it is set as a voltage sharing signal divided by the number of inverters in each stage. The difference between the output current of each stage of the inverter detected by the current detector 4 and the load current flowing to the load 7 detected by the current detector 6 via the isolation transformer 5 is added to the voltage sharing signal of each stage of the inverter. Subtract.

[0005] Here, the difference between the output current of the inverter and the load current is determined by the transformation ratio of the isolation transformer: primary: secondary = 1:1.
In other cases, the value multiplied by the transformation ratio is used. This difference between the inverter output current and the load current is the part that detects the biased magnetization of the isolation transformer. Normally, this difference is 0, but as the magnetization becomes biased, the primary current of the isolation transformer increases. The difference becomes larger. Finally, by comparing the voltage command value of each stage of the inverter and the difference between the above-mentioned inverter output current and load current with the triangular wave with a phase shift generated by the triangular wave generator 10, the pulse width modulation circuit 9 Pulse width modulation is performed by , and applied as a gate pulse to the switching elements 3 of the inverters at each stage. This generates AC power as an inverter.

[0006]

[Problems to be Solved by the Invention] As described above, the conventional control device shown in the cross-sectional view uses the load current detected by the current detector 6 to detect biased magnetism of the isolation transformer 5. However, since the offset of the operational amplifier included in the voltage sharing control circuit 8 and the pulse width control of the pulse width control circuit 9 are asynchronous, the triangular wave that is compared with the voltage command value can be prevented. It is not possible to compensate for the DC component caused by the phase shift of the inverter, and there is a possibility that the output voltage of each stage of the inverter varies in positive and negative, and that the isolation transformer 5 becomes biased.

The present invention was made to solve the above-mentioned problems, and by adding a feedback control system, it is possible to obtain a multiplex inverter device that can prevent biased magnetization of each individual isolation transformer. The purpose is

[Means to solve the problem]

The multiplex inverter control device according to the present invention includes a voltage detector 11 that detects the output voltage of the inverters 3a, 3b, and 3c at each stage, and a voltage detector 11 that detects the output voltage of the inverters 3a, 3b, and 3c in each stage, and a voltage detector 11 that detects the output voltage of the inverters 3a, 3b, and 3c in each stage, and a voltage detector 11 that detects the output voltage of the inverters 3a, 3b, and 3c in each stage, and a voltage detector 11 that detects the output voltage of the inverters 3a, 3b, and 3c in each stage, and a voltage detector 11 that detects the output voltage of the inverters 3a, 3b, and 3c in each stage. It consists of an integrator 12 that integrates within a certain period of time and a dead band circuit 15 that provides a certain dead band for this integrated value.

[0009]

[Operation] The multiple inverter control device of the present invention detects the output voltage of the inverters 3a, 3b, and 3c in each stage, integrates the output voltage by an integrator for a certain predetermined time, and calculates the integrated value for each stage. By comparing and mutually correcting the deviation, offsets of operational amplifiers included in the control system and DC components caused by asynchronous pulse width modulation are eliminated, and an isolation transformer corresponding to each stage of inverters 3a, 3b, and 3c is created. To prevent biased magnetization of 5a, 5b, and 5c.

0010

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. In FIG. 1, 11 is a voltage detector group that detects the output voltage of the inverter group 3, and the inverter 3a of each stage
, 3b, 3c, voltage detectors 11a, 1, respectively.
There are 1b and 11c. 12 is an integrator group that integrates the output voltages of the inverters 3a, 3b, 3c of each stage detected by the voltage detectors 11a, 11b, 11c;
Integrators 12a, 12b, 12c correspond to
A common one is a time constant setter 13 that determines the time constant of the integrator 12 for a certain period of time. There is a coefficient multiplier group 14 that multiplies a certain coefficient by subtracting the values integrated by the integrator 12 from each other. There is. A dead band setter group 15 sets a dead band for a certain period of time in the output value of this coefficient unit, and dead band setters 15a, 15b, 15c correspond to inverters 3a, 3b, 3c in each stage, respectively.
It is made up of.

The operation will be explained below with reference to FIGS. 1 to 3. Figure 1
When voltage sharing control is performed by the voltage sharing control circuits 8a, 8b, and 8c in each stage of the multiplex inverter, a phase shift between the signal wave and the triangular wave due to the offset of the operational amplifier, etc. in the control system and asynchronous pulse width modulation occurs. Assume that the DC component generated by is in the state shown in FIG. 2, for example. Here, the output current of the inverter is a sine wave, and the load is a reactance.
Assume that the fundamental wave of the next-side voltage is as shown in Figure 2A. In this case, the secondary voltage of the isolation transformer does not include a DC component, but the voltage shared by the first stage of the inverter in Figure 2B is -ε
It is assumed that there is a DC component of +ε in the voltage shared by the second stage of the inverter in FIG. 2C. In this case, isolation transformers 5a corresponding to the first stage and second stage of the inverter
, 5b do not become biased immediately because this direct current component is small, but the output current of the inverter becomes biased toward the positive 000 as shown in the period from point A to point B in FIG. On the contrary, the output current of the second stage of the inverter tends toward the negative side. On the other hand, the secondary current of the isolation transformer exhibits a substantially symmetrical waveform between points A and B in FIG. 3C. In the conventional method, this is calculated as the deviation between the inverter second stage output current detected by the current detector 4b in FIG. 1 and the secondary current of the isolation transformer 5 detected by the current detector 6, that is, the If you try to suppress it by the difference of
This phenomenon was originally caused by the offset of the control system and the direct current generated due to asynchronous pulse width modulation, so sufficient correction could not be made and the isolation transformer became biased after point B in Figure 3 (ro). Correction is performed only after the excitation current begins to flow rapidly.

In the present invention, the isolation transformer (
4b), the inverter output voltage of each stage detected by the voltage detectors 11a, 11b, 11c corresponding to each stage of the voltage detector 11 in FIG. Corresponding integrators 12a, 12b
, 12c. In other words, for example, as a command to be given to the second stage of the inverter, the integrator 1 corresponding to each of the other inverter stages 3a, 3c is subtracted from the value of the inverter output voltage integrated by the integrator 12b.
The value of the output voltage of each stage of the inverter integrated by 2a and 12c is subtracted. Further, the time constant for integration at this time can be set by a time constant setting device 13. This integral value is expressed as
The coefficient is multiplied by the coefficient multiplier 14b corresponding to the second stage 3b of the inverter No. 4. After that, the value multiplied by the coefficient is applied to the dead band circuit 1 corresponding to the second stage inverter 3b of the dead band circuit 15.
5b provides a dead zone and subtracts it from the output of the voltage sharing control circuit 8b corresponding to the second stage inverter 3b of the voltage sharing control circuit 8. This process is similarly performed for each stage of inverters 3a and 3c. As a result, the DC component of the inverter output voltage can be corrected during the period from point A to point B in FIG. 3B, and biased magnetization of the isolation transformer 5 can be prevented.

Example 2. In the above embodiment, the integrated values of the output voltages of the inverters at each stage are subtracted from each other, but the integration may be performed after the output voltages are subtracted from each other.

Example 3. Further, in the above embodiment, the voltage sharing control circuit 8 performs voltage sharing control such that voltage sharing is equal, but the voltage sharing may not be equal.

Example 4. Furthermore, in the above embodiment, all isolation transformers 5 are installed corresponding to each stage of the inverter 3, but if the load 7 also requests power from a synchronous motor or DC component, at least one inverter 3 Therefore, there is a method in which the isolation transformer 5 is not installed. An example in this case is shown in FIG. Inverter 3-1
Inverters 3a, 3b corresponding to the nth to first stages from the stage
3c, isolation transformers 5a, 5b, 5c, respectively.
is installed and there is no isolation transformer for the n-th stage inverter 3d, voltage detectors 11a,
The DC component of the inverter output voltage, which is obtained by integrating the inverter output voltage detected by the inverter output voltages 11b and 11c by the integrators 12a, 12b, and 12c, is passed through the dead band circuits 15a, 15b,
15c from the voltage command value corresponding to each stage of the inverter 3, and all subtracted DC components are added and added to the voltage command value corresponding to the n-th stage inverter 3d that does not go through the isolation transformer 5. In this case, the same effect as in the above embodiment is exhibited.

Example 5. In the embodiment shown in FIG. 1, control is performed using the inverter output voltage detected by the voltage detector 11 in order to prevent biased magnetization of the isolation transformer 5. However, if you want to improve accuracy, you can use the isolation transformer 5. 5, a search coil for internal magnetic flux detection is installed, a voltage signal proportional to the magnetizing force is taken out, and similar control can be performed using this voltage signal 12.

[0017]

As described above, according to the present invention, since the DC component of the inverter output voltage of each stage is fed back to the inverter voltage command value of each stage, biased magnetization of the isolation transformer can be prevented. It has the effect of preventing

[Brief explanation of the drawing]

FIG. 1 is a connection diagram showing a multiple inverter control device according to an embodiment of the present invention.

FIG. 2 is a waveform diagram showing an example of inverter shared voltages.

FIG. 3 is a waveform diagram showing an example of the states of the shared voltage of a certain inverter, the inverter output current, and the secondary current of an isolation transformer.

FIG. 4 is a connection diagram showing a multiplex inverter control device showing another embodiment of the present invention.

FIG. 5 is a connection diagram showing a conventional multiplex inverter control device.

[Explanation of symbols]

1 Constant voltage source 2 Smoothing capacitor 3 Inverter 4 Current detector 5 Isolation transformer 6 Load current detector 7 Load 8 Voltage sharing control circuit 9 Pulse width modulation circuit 10　Triangle wave generator 11 Voltage detector 12 Integrator 13 Time constant setter 14 Coefficient unit 15 Dead band circuit

Claims (4)

[Claims] 1. The output voltage of at least one or more second inverters is added to the output voltage of a first inverter whose output side is connected to an isolation transformer, and the output voltage of the first and second inverters is added via the isolation transformer. A multiple inverter control device for supplying AC power obtained by combining output voltages of the second inverters to a load, comprising: a voltage detector for detecting the output voltages of the first and second inverters; An integrator connected to the output of the voltage detector, a time constant setter that sets the time constant of this integrator, and an integrator corresponding to the other inverter from the output of the integrator corresponding to one inverter. It includes a coefficient unit connected after subtracting the output, and a dead band setter connected to the output of the coefficient unit, and the bias of the isolation transformer is determined by subtracting the output of the dead band setter from the voltage command value of the inverter. A multiplex inverter control device characterized by preventing magnetism. 2. Adding the output voltage of at least one or more second inverters to the output voltage of the first inverter to which no isolation transformer is connected on the output side via the isolation transformer, and a multiplex inverter control device for supplying AC power obtained by combining respective output voltages of the second inverter to a load, comprising: a voltage detector for detecting the output voltage of the second inverter; It is equipped with an integrator connected to the output of the detector, a time constant setter for setting the time constant of this integrator, and a dead band setting device connected to the output of the integrator. Said first
A control device for a multiplex inverter, characterized in that biased magnetization of the isolation transformer is prevented by adding the voltage to the voltage command value of the second inverter and subtracting it from the voltage command value of the second inverter. 3. Adding the output voltage of at least one or more second inverters to the output voltage of the first inverter whose output side is connected to the isolation transformer, and adding the output voltage of at least one or more second inverters via the isolation transformer, and a control device for a multiplex inverter for supplying AC power obtained by combining respective output voltages of the second inverters to a load, the insulator connected to the output sides of the first and second inverters. A search coil installed in the transformer, an integrator connected to the output of this search coil, a time constant setting device that sets the time constant of this integrator, and a After subtracting the output of the integrator corresponding to the inverter, the system includes a connected coefficient unit and a dead band setting device connected to the output of the coefficient unit, and subtracts the output of the dead band setting unit from the voltage command value of the inverter. 1. A control device for a multiplex inverter, characterized in that biased magnetization of the isolation transformer is thereby prevented. 4. Adding the output voltage of at least one or more second inverters to the output voltage of the first inverter to which no isolation transformer is connected to the output side via the isolation transformer, In a multiplex inverter control device for supplying alternating current power obtained by combining the respective output voltages of the second inverter to a load, a search coil provided in the isolation transformer and a search coil connected to the output of the search coil are provided. a dead band setter connected to a time constant for setting a time constant of the integrator and an output of the integrator, and adds the output of the dead band setter to the voltage command value of the first inverter. A multiple inverter control device characterized in that, on the other hand, biased magnetization of the isolation transformer is prevented by subtracting it from the voltage command value of the second inverter.