JP2745728B2 - Inverter control method - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an inverter control method capable of performing high-precision pulse width modulation control by removing a DC voltage component included in an AC output voltage of an inverter. It is.

(Prior art) Pulse width modulation (PWM) is one of the inverter control methods
There is a control method, and a system shown in FIG. 3 is known as an example of the control circuit. That is, in FIG.
The output of the DC power supply 11 is input to an inverter 12, which converts DC power into AC power, and supplies the AC power from an output terminal A to a load (not shown) via an AC filter 13. You. Here, the AC filter 13 includes an AC reactor 14 connected in series to an output terminal of the inverter 12 and a capacitor 15 connected in parallel.

Then, in order to actually perform the PWM control, first, the voltage between both terminals of the capacitor 15 is measured, and the AC output voltage of the inverter 12 is measured by the transformer 16 as an insulation detecting means.
Take out through. Then, the detection value is input to one input terminal of the adder 17. Further, a reference wave generating means 18 is connected to the other input terminal of the adder 17. The reference wave generating means 18 includes a reference signal generating circuit 19, a setting device 20, and a multiplier 21, and the multiplier 21 uses the multiplied value of the output signals of the reference signal generating circuit 19 and the setting device 20 as a reference. The signal is output to the adder 17 as a wave signal.

Then, the adder 17 outputs a deviation between the reference wave signal and the detected value of the AC output voltage to the adjuster 22, and the adjuster 22 outputs a pulse width control signal such that the input becomes zero to a minimum. . The output of the controller 22 is compared with the output of a modulation signal generator (a sawtooth wave generator 23 in FIG. 3) by a comparator 24, and the comparator 24 outputs a pulse signal as a result of the comparison to a control terminal of the inverter 12. input. This pulse signal turns on / off each switching element included in the inverter 12, and an output voltage waveform substantially equal to the reference wave signal is output from the inverter 12.

(Problem to be Solved by the Invention) The conventional control method described above has the following problems. That is, the DC component included in the reference wave signal output from the reference wave generation means 18 and the saw-tooth wave signal output from the saw-tooth wave generator 23, and the switching time of the switching element used in the inverter 12 vary. For the inverter
The output voltage of 12 contains a DC component. Further, even when a load such as a half-wave rectifier circuit that flows a positive / negative asymmetric current is connected as the load of the inverter 12,
A DC component is included in the output voltage of the inverter 12.

When such a DC component increases, the AC reactor 14 provided for shaping the output voltage waveform of the inverter 12 becomes magnetically saturated, or when a transformer or the like is connected to the output terminal A of the inverter 12. In this case, the transformer may be magnetically saturated. As a result, there has been a problem that it becomes impossible for the inverter 12 to normally supply AC power to the load. In addition, the transformer and the like connected to the output terminal A of the inverter 12 have a disadvantage that a special structure having a low magnetic flux density is required.

The present invention has been proposed to solve the above problems, and removes a minute DC voltage component included in an AC waveform of an output voltage of an inverter, thereby stably and accurately removing a PW signal.
An object of the present invention is to provide an inverter control method capable of performing M control and enabling use of a general-purpose transformer or the like.

(Means for Solving the Problems) In order to achieve the above object, a first invention detects insulation of an AC output voltage of an inverter via an AC filter by first insulation detection means, and detects the detected value and a reference wave. The deviation from the reference wave signal from the generating means is input to a first controller, and the output of the controller and the modulation signal from the modulation signal generator are compared by a comparator. In a control method of an inverter of a pulse width modulation control method for turning on / off a switching element of an inverter, a first capacitor constituting the AC filter is connected to a series circuit of a reactor and a second capacitor for detecting a DC voltage. Are connected in parallel, and the terminal tube voltage of the second capacitor is measured via the second insulation detecting means to directly measure the AC output voltage. A flow component is detected, a detected DC voltage component is input to a second controller, and an output of the controller and a detection value of the first insulation detecting means are subtracted from the reference wave signal. Is input to the first controller to turn on / off the switching element so that the DC voltage component becomes zero. According to a second aspect of the present invention, an AC output voltage of a three-phase bridge inverter is input to a phase voltage conversion DC component operation circuit via a filter circuit and insulation detection means, and an output for each phase of the operation circuit is output to each controller. Then, the deviation between each controller output and the reference wave signal of each phase from the reference wave generation means is compared with the modulation signal from the modulation signal generator by each comparator, and based on the comparison result by these comparators In a method of controlling an inverter of a pulse width modulation control method for turning on / off a switching element of the three-phase bridge inverter, the phase voltage conversion DC component operation circuit outputs an output of the three-phase bridge inverter from an output voltage of the insulation detecting means. The DC voltage components of each phase are calculated respectively, and the DC voltage components of each phase are input to the controller to reduce the DC voltage component to zero. The so that it performs on / off of the switching element.

(Operation) In the first aspect, the DC component included in the output voltage of the inverter is relatively accurately detected by the second capacitor and the second insulation detecting means as an average value of the output voltage. The second controller performs a proportional operation, an integral operation or a proportional integral operation on the detected value. This allows
The stability of the control loop for removing the DC component of the output voltage is ensured.

On the other hand, a component of the AC output voltage from which the DC component has been removed is detected via the first insulation detecting means as a voltage between terminals of the first capacitor for the AC filter. The sum of the detection signal and the output signal of the second controller is subtracted from the reference wave signal (the output of the reference wave generator), and the result of the subtraction is input to the first controller. The output of the controller is compared with the modulation signal by a comparator, and the result of the comparison controls the inverter.

As a result, in addition to high-speed waveform control of the AC output voltage of the inverter, PWM control in which minute DC voltage components included in the AC voltage waveform are removed can be performed stably and with high accuracy.

In the second invention, the DC voltage component included in the output voltage of the three-phase bridge inverter is insulated from the average value of the output voltage for each line voltage, and this detection signal is converted into each phase voltage component. A DC component control signal for each phase is generated by a controller that performs a proportional operation, an integral operation, or a proportional-integral operation for each phase based on these phase voltage operation values. These DC component control signals are added to the reference wave signal from the reference wave generator whose amplitude is appropriately adjusted for each phase, and the addition result is compared with a triangular wave or sawtooth wave as a modulation signal. A pulse width modulation signal is obtained and used as an on / off signal for the switching element of the three-phase bridge inverter, thereby acting to remove a DC component included in the AC output voltage of the three-phase bridge inverter.

(Embodiment) Hereinafter, an embodiment of a method for controlling an inverter according to the first invention will be described with reference to FIG. In FIG. 1, the same components as those shown in FIG. 3 are denoted by the same reference numerals.

First, FIG. 1 is a configuration diagram of a control circuit for implementing the present invention. As shown in FIG. 1, an output side of a DC power supply 11 is connected to a DC input side of an inverter 12, and an output side thereof is connected to an AC reactor 14. Is connected to the output terminal A via An AC load (not shown) is connected to the output terminal A. A first capacitor 15 is connected to the output terminal A of the AC reactor 14, and the AC reactor 14 and the first capacitor 15 constitute an AC filter 13.

Further, both terminals of the first capacitor 15 are connected to both terminals of a primary side of a transformer 16 as a first insulation detecting means, and a first side of an adder 17 of a secondary side of the transformer 16 is connected to the first side. Is connected to the negative input terminal. The first capacitor 15
And the transformer 16, the component (AC component) of the output voltage of the inverter 12 from which the DC component has been removed is input to the first negative input terminal of the adder 17.

A multiplier 21 is connected to a positive input terminal of the adder 17, and a setter 20 and a reference signal generating circuit 19 for generating a sine wave are connected to two input terminals of the multiplier 21. . By adjusting the setting unit 20, the amplitude of the sine wave generated by the reference signal generation circuit 19 can be adjusted. Note that the multiplier 21, the reference signal generating circuit 19, and the setting device 20 constitute a reference wave generating means 18.

Further, in the present embodiment, a filter circuit 1 composed of a series circuit of a reactor 2 and a second capacitor 3 for detecting a DC component is provided on the output terminal A side of the AC reactor 14, that is, both ends of the first capacitor 15. Is connected. An input terminal of an insulation detector 4 as a second insulation detection means is connected to both ends of the second capacitor 3.
Its output terminal is connected to the input terminal of the second regulator 5. The output terminal of the controller 5 is connected to the second negative input terminal of the adder 17.

The second controller 5 is capable of performing a proportional operation, an integral operation, or a proportional integral operation in order to obtain the stability of the control loop.

The output terminal of the adder 17 is connected to the input terminal of the first controller 22, and the output terminal of the first controller 22 is connected to one input terminal of the comparator 24. Also,
The other input terminal of the comparator 24 is connected to an output terminal of a sawtooth wave generator 23 as a modulation signal generator. Here, the sawtooth wave generator 23 may generate a triangular wave. The output terminal of the comparator 24 is connected to the control terminal of the inverter 12.

Next, the operation of each unit when the present invention is implemented by the control circuit will be described.

First, the AC filter 13 provided on the output side of the inverter 12
Among the voltages generated in the first capacitor 15, the AC voltage waveform from which the DC component is removed is insulated and detected by the transformer 16.

On the other hand, the inductance of the reactor 2 and the capacitance of the second capacitor 3 are adjusted to appropriate values, and a voltage having the same value as the DC voltage of the voltage generated in the first capacitor 15 is applied to the DC voltage of the filter circuit 1. Capacitor for detection 3
Occur at both ends. Then, after the DC voltage component is insulated and detected by the insulation detector 4, the DC voltage component is input to the adder 17 via the second controller 5. Here, the DC voltage component is detected, for example, as an average value of the output voltage of the inverter 12.

That is, the adder 17 detects the DC voltage component from the AC output voltage of the inverter 12 from which the DC voltage component has been removed. Each value will be entered. Then, the difference between the sine wave signal containing no DC component output from the multiplier 21 and the above + is calculated by the adder 17, and the calculation result is input to the first controller 22. Next, the comparator 24 compares the output of the controller 22 with the output of the sawtooth wave generator 23 to generate a desired pulse pattern, and controls the inverter 12.

With the above operation, the AC voltage component from which the DC component has been removed is controlled so that the difference between the AC voltage component and the sine wave signal output from the multiplier 21 in the reference wave generating means 18 becomes zero, and the inverter is controlled. The DC voltage component in the 12 output voltage waveforms is
It is controlled to be zero or a minimum.

Next, an embodiment of the second invention will be described with reference to FIG. The present invention is for removing a DC voltage component included in an AC output voltage when a PWM-controlled three-phase bridge inverter is used as the inverter.

In the control circuit shown in FIG. 2, the DC power supply 11 is connected to the DC input side of the three-phase bridge inverter 12A, and the R, S, and T phases on the output side thereof are connected to the AC reactor 14 and the first connection Δ-connected. An AC filter 13A including a capacitor 15 is connected. In addition, between each output line of the inverter 12A,
Reactor 2 and second capacitor 3 for detecting DC component
Is connected to input terminals of insulation detectors 4a, 4b, and 4c as insulation detection means at both ends of each capacitor 3, and the output terminal of each of the terminals detects the DC component of each line voltage. One input terminal of each of the adders 31a, 31b, 31c in the phase voltage conversion DC component calculation circuit 30 for converting the DC component of the phase voltage is connected to the input side of the inverting amplifiers 32a, 32b, 32c, respectively. .

In the phase voltage conversion DC component calculation circuit 30, for example, the R-phase DC voltage components are (R-phase DC voltage detection value-S-phase DC voltage detection value) and (T-phase DC voltage detection value-R phase Is calculated by adding the value obtained by inverting the DC voltage of the inverting amplifier 32c by the inverting amplifier 32c by the adder 31a, and the calculation result is input to the adjuster 22a. The outputs of the adders 31b and 31c become the inputs of the adjusters 22b and 22c in substantially the same combination, though the target phases are different for the other two phases.

On the other hand, the output terminals of the reference signal generation circuits 19a, 19b, and 19c that output a sine wave or a similar waveform for each of the R, S, and T phase voltages and the output terminal of the setting unit 20 are connected to the multipliers 21a, 21b, and 21c. These are connected to the input terminals, respectively, and these multipliers 21a, 21b, 21c
Are connected to one input terminals of adders 25a, 25b, 25c provided on the output side of the controllers 22a, 22b, 22c, respectively. Here, the reference signal generating circuits 19a, 19b, 19c, the setting device 20, and the multipliers 21a, 21b, 21c constitute a reference wave generating means 18A.

Then, the adders 25a, 25b, and 25c add the outputs of the adjusters 22a, 22b, and 22c and the outputs of the multipliers 21a, 21b, and 21c with the polarity shown in each phase. ,twenty four
The signals are input to one of the input terminals b and 24c, respectively.
Further, a sawtooth wave is input to the other input terminals of the comparators 24a, 24b, 24c from a sawtooth wave generation circuit 23 as a modulation signal generator. Note that a triangular wave may be used as the modulation signal instead of the sawtooth wave. Thus, the outputs of the comparators 24a, 24b, 24c become firing pulses for the respective switching elements of the three-phase bridge inverter 12A.

In such a circuit configuration, a DC voltage component generated in the first capacitor 15 of the AC filter 13A is generated at both ends of the second capacitor 3 of the filter circuit 1A, and the insulation detector
The signal is detected as a DC voltage component between the lines by 4a, 4b, and 4c. Then, the DC voltage components between these lines are converted by the phase voltage conversion DC component calculation circuit 30 into R, S, and T phase components and converted into phase voltages. These phase voltage operation values are adjusted by the controllers 22a and 22 that perform proportional operation, integral operation, or proportional integral operation.
b, 22c become a DC component control signal for each phase, and thereafter, are added to the reference wave signal from the reference wave generation means 18A in the adders 25a, 25b, 25c and are compared with the modulation signal by the comparators 24a, 24b, 24c. Accordingly, an on / off signal for the switching element of the three-phase bridge inverter 12A is generated.

Here, since the regulators 22a, 22b, and 22c perform an adjusting operation such that the DC voltage components of the respective phases are zero or minimal, the DC components included in the AC output voltage of the three-phase bridge inverter 12A become zero. Control is performed.

(Effects of the Invention) As described above, according to the first invention, not only the component obtained by removing the DC component contained in the output voltage of the inverter, but also
Since the DC voltage component is also detected and added to one of the control elements, in addition to the high-speed waveform control of the AC voltage waveform, PWM control that removes the minute DC component contained in the AC voltage waveform can be performed. .

Since the detection of the AC voltage component of the output voltage of the inverter can be performed at a high speed with an inexpensive transformer, the instantaneous control of the output voltage waveform can be performed while maintaining high stability. Since the component detection is performed in a cycle longer than the cycle of the AC output voltage waveform, an inexpensive DC insulation detector or the like can be used as the second insulation detecting means, and the control of the minute DC component is performed by the AC output voltage. There are effects such as high-accuracy control without impairing high-speed control of the voltage waveform.

Further, according to the second aspect, the DC component in the three-phase AC voltage generated by the three-phase bridge inverter can be made substantially zero, so that when the transformer is connected to the output terminal of the inverter, This eliminates the risk of magnetic saturation of the transformer, and allows the use of a general-purpose transformer to reduce costs.

[Brief description of the drawings]

FIG. 1 is a block diagram of a PWM inverter system for explaining an embodiment of the first invention, FIG. 2 is a block diagram of a PWM inverter system for explaining an embodiment of the second invention, and FIG. FIG. 11 is a block diagram of a PWM inverter system for explaining a conventional technique. 1,1A ... Filter circuit, 2 ... Reactor 3,15 ... Capacitor 4,4a, 4b, 4c ... Insulation detector 5,22,22a, 22b, 22c ... Controller 11 ... DC power supply, 12 , 12A ... Inverter 13, 13A ... AC filter, 14 ... AC reactor 16 ... Transformer 17, 25a, 25b, 25c, 31a, 31b, 31c ... Adder 18, 18A ... Reference wave generating means 19 , 19a, 19b, 19c …… Reference signal generating circuit 20 …… Setter, 21,21a, 21b, 21c …… Multiplier 23… Sawtooth wave generator 24,24a, 24b, 24c… Comparator 30… Phase voltage conversion DC component calculation circuit 32a, 32b, 32c …… Inverting amplifier

Claims (2)

(57) [Claims] An AC output voltage of an inverter is insulated and detected by a first insulation detecting means via an AC filter, and a deviation between the detected value and a reference wave signal from a reference wave generating means is determined by a first insulation detection means.
Pulse width modulation control for comparing the output of the controller with the modulation signal from the modulation signal generator by a comparator, and turning on / off the switching element of the inverter based on the comparison result by the comparator. A method of controlling an inverter, comprising: connecting a filter circuit comprising a series circuit of a reactor and a second capacitor for detecting a DC voltage in parallel to a first capacitor constituting the AC filter; Is measured via a second insulation detecting means to detect the DC component of the AC output voltage, and the detected DC voltage component is input to a second regulator, and the output of the regulator and the The detection value of the first insulation detecting means is subtracted from the reference wave signal, and the result of the subtraction is input to the first controller to reduce the DC voltage component to zero. Controlling the switching element so as to turn on / off the switching element. 2. An AC output voltage of a three-phase bridge inverter is input to a phase voltage conversion DC component operation circuit via a filter circuit and insulation detection means, and an output for each phase of the operation circuit is input to each controller. Then, the deviation between the output of each controller and the reference wave signal of each phase from the reference wave generation means is compared with the modulation signal from the modulation signal generator by each comparator, and based on the comparison result by these comparators, the three-phase In a control method of an inverter of a pulse width modulation control method for turning on / off a switching element of a bridge inverter, the phase voltage conversion DC component calculation circuit calculates an output phase of each of the three-phase bridge inverters based on an output voltage of the insulation detection means. Are calculated, and the DC voltage components of each of these phases are input to the controller, and the DC voltage components become zero. A method for controlling an inverter, comprising: turning on / off the switching element.