JPH044759A - Inverter control circuit - Google Patents

Abstract

PURPOSE:To reduce at least one of the DC component and low-frequency component of an inverter output voltage by adding at least one of DC shifted excitation correction signal and low-frequency shifted excitation correction signal to a pulse width command. CONSTITUTION:In a DC regulation circuit 51, a DC shifted excitation correction value is outputted by a setting device 51A. This output is added to a pulse width command value by an adder 53. In a power-frequency voltage regulation circuit 52, a low-frequency shifted excitation correction value is outputted by a setting device 52A. The pulse width command value or polarity signal from a sine-wave generator is inputted to a zero-cross comparator 52E, of which the output is inputted to the ON/OFF control terminal of a switch 52C via logic inverting circuit 52F and directly to the ON/OFF control terminal of a switch 52D. When the output of the switches 52C, 52D is inputted to an adder 52H, a low-frequency shifted excitation correction signal is obtained and is added to the pulse width command value by the adder 53 like a DC shifted excitation correction signal.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an inverter control circuit that prevents biased excitation of a transformer connected to an output end of an inverter.

[Conventional technology]

FIG. 5 is a configuration diagram showing a conventional example of an inverter control circuit.

In the figure, 1 is the inverter main circuit, 2 is the transformer, and 3 is the inverter main circuit.
is a load, and 4 is a control circuit. As shown in the figure, the inverter main circuit 1 is constructed by connecting semiconductor switches (hereinafter simply referred to as switches) Tl and T2 in series between the positive and negative sides of a DC power source E, and similarly connecting switches T3 and T4 in series. . Each switch is composed of one or more semiconductor elements, and has the function of controlling conduction and cutoff of forward current through a control terminal, and conduction of reverse current independently of the control terminal. . If the connection point between switches T1 and T2 and the connection point between T3 and T4 are inverter output terminals a and b, respectively, the input terminals of transformer 2 are connected to terminals a and b, and the load is connected to the output terminal of transformer 2. Connect 3.

The control circuit 4 includes a rectifier 41. Filter 42. Voltage setting device 4
3. PI regulator 44. Sine wave generator 45° multiplier 46.
Adder/subtractor 47. It is composed of a comparator 48, a carrier generator 49, etc., and outputs a low frequency AC signal (also referred to as a pulse width command).

That is, the rectifier 41 rectifies the inverter output voltage,
Filter 42 smooths it. The PI regulator 44 performs adjustment calculations to make the DC output from the filter 42 match the command voltage set in the voltage setter 43. The multiplier 46 multiplies the output of the PI regulator 44 and the output from the sine wave generator 45, and outputs a sine wave signal (pulse width command) with a magnitude proportional to the command voltage set in the voltage setting device 43. do. The output is given to the adder/subtractor 47, where the detected output voltage of the inverter is also led, and waveform shaping is performed thereby. Therefore, the adder/subtractor 47 can be omitted if there is no particular need. Adder/subtractor 47
The output of the carrier generating circuit 4 is sent to the comparator 48
It is compared with the carrier C from 9, and depending on the magnitude relationship, the switches T1 to T4 are controlled to be turned on or off via a drive circuit (not shown).

That is, in the configuration shown in FIG. 5, the switches T1 and T4
is on and switches T2 and T3 are off, there is a positive voltage pulse (hereinafter simply referred to as positive pulse), and when switches T2 and T3 are on and switches T1 and T4 are off, there is a negative voltage pulse (hereinafter simply referred to as positive pulse). (simply referred to as a negative pulse) is output, and switches TI and T3 are turned on and switch T2
and T4 are off, or when switches T2 and T4 are on and switches T1 and T3 are off, the output voltage is zero volts. In other words, the width of the inverter output voltage pulse is proportional to the absolute value of the pulse width command, and the carrier generating circuit 49
(hereinafter also referred to as carrier polarity signal)
When the polarity of the U/D signal matches the polarity of the pulse width command, the output voltage pulse becomes positive, and when the polarity of the U/D signal and the polarity of the pulse width command do not match, the output voltage pulse becomes negative. Switches T1 to T4 are turned on.

Off is controlled.

FIG. 6 is a waveform diagram for explaining the operation of FIG. 5, in which (a) is the U/D signal, (b) is the pulse width command, (c) is the inverter output voltage, (d) and ( e) shows each waveform of the transformer magnetic flux.

[Problem to be solved by the invention]

As is clear from the above explanation, in the inverter as shown in Fig. 5, the frequency of the voltage input to the load 3 is determined by the U/D signal, and its effective value is controlled by the pulse width command. .

In principle, the voltage-time product of the positive pulse is equal to that of the negative pulse, so the inverter output voltage does not include frequency components lower than the output frequency, but in reality, errors in the control circuit 4 and switch T1 ~Due to variations in the characteristics of T4, the positive and negative voltage time products often become uneven, and DC components and low frequency components occur in the inverter output voltage. As a result, biased excitation as shown in Figure 6(e) occurs, and if this is severe, magnetic saturation occurs, which not only causes the transformer to no longer output the normal voltage, but also causes the inverter output current to become excessive. A problem arises. Note that FIG. 6(d) shows the transformer magnetic flux under normal conditions.

Therefore, an object of the present invention is to prevent DC components and/or low frequency components contained in the inverter output voltage.

[Means to solve the problem]

An inverter that connects multiple self-extinguishing switching elements in series between positive and negative DC power supplies, and converts the DC input voltage into an AC output voltage pulse train whose polarity becomes alternately positive or negative by turning on and off each element. , a transformer connected to its output terminal, and a control circuit that controls on/off of the switching element, the width of the AC output voltage pulse being proportional to the absolute value of the pulse width command inside the control circuit. In an inverter control circuit that inverts the polarity of the AC output voltage pulse by a carrier polarity signal having a sufficiently high frequency with respect to the frequency of the pulse width command inside the control circuit, a DC bias excitation correction circuit that adds a DC bias excitation correction signal of the same phase to the pulse width command; and a DC bias excitation correction signal that has the same frequency and the same phase as the carrier polarity signal, either directly or after polarity reversal, to the pulse width command. At least one of a low frequency biased excitation correction circuit is provided that selects and executes an operation of adding to the command depending on the polarity of the pulse width command.

[Effect]

By adding at least one of a DC biased excitation correction signal and a low frequency biased excitation compensation signal to the pulse width command, at least one of the DC component and the low frequency component of the inverter output voltage is reduced.

〔Example〕

FIG. 1 shows an embodiment of the invention, and FIG. FIG. 3 shows an example of its operating waveforms.

As is clear from FIG. 1, this embodiment is different from the conventional example shown in FIG. 5 in that a DC component adjustment circuit 51, a commercial frequency component (low frequency component) adjustment circuit 52, and an adder 53 are provided. It is.

That is, if the magnetic flux of the transformer 2 includes a positive DC component as shown in FIG. 2(a), the U/D signal shown in FIG. A negative DC correction signal as shown in (d) is added to the pulse width command value shown in (c) of the figure. As a result, when the pulse width command value is of positive polarity, the absolute value of the pulse width command value decreases when the positive pulse is output, so the width of the positive pulse decreases. Furthermore, when the pulse width command value has negative polarity, the absolute value of the pulse width command value increases when a negative pulse is output, so the width of the negative pulse increases. As a result of the above, the negative time product of the inverter output voltage increases relatively over the entire cycle of the pulse width command value, so that the positive DC bias excitation component decreases.

On the other hand, if the magnetic flux of the transformer 2 contains a low frequency biased excitation component as shown in Figure 3(a), the positive half period of the pulse width command value is Adds a low frequency correction signal of opposite polarity to the U/D signal, and adds a low frequency correction signal of the same polarity to the U/D signal to the pulse width command value in the negative half cycle of the pulse width command value. do. As a result, when the pulse width command value is of positive polarity, the absolute value of the pulse width command value decreases when the positive pulse is output, so the width of the positive pulse decreases. Furthermore, when the pulse width command value has negative polarity, the absolute value of the pulse width command value decreases when a negative pulse is output, so the width of the negative pulse decreases. As a result, the negative voltage-time product relatively increases during the positive half-cycle of the pulse width command value, and the positive voltage-time product relatively increases during the negative half-cycle, so the low-frequency biased excitation component decreases.

FIG. 4 shows a specific example of the DC component adjustment circuit 51 and the commercial frequency component adjustment circuit 52.

In the same figure, 51A, 52A are setting devices, 51B, 52
B to 52D are analog switches, 52E is a comparator, 52F is a logic inversion circuit, 52G is an inversion amplifier, 52H
, 53 is an adder.

That is, in the DC component adjustment circuit 51, the setter 51A outputs a DC bias excitation correction value. The setting device 51A is adjusted manually while observing the biased magnetic state with an oscilloscope or the like so that the DC biased excitation component is minimized. By inputting this DC bias excitation correction value into the analog switch 51B and turning it on and off using the U/D signal, the
d) is obtained, and this signal is sent to the adder 53.
Add it to the pulse width command value at . The corrected pulse width command is shown in FIG. 2(e), and each waveform of the inverter output voltage is shown in FIG. 2(f).

On the other hand, in the commercial frequency adjustment circuit 52, the setting device 52A
This outputs a low frequency biased excitation correction value.

The setting device 52A is adjusted in the same way as the setting device 51A. The correction value from the setting device 52A is input to the analog switch 52B, and its output is input to the analog switch 52C via an inverting amplifier 52G with a gain of 1, and directly to the analog switch 52D. On the other hand, the pulse width command value or the polarity signal (sine wave polarity signal) from the sine wave generator 45 is input to the zero cross comparator 52E, and its output is sent to the on/off control terminal of the switch 52C via the logic inversion circuit 52F. , and is directly input to the on/off control terminal of the switch 52D. The switch 52C inverts the polarity of the correction signal and outputs it when the pulse width command value is negative, and the switch 52D directly outputs the correction signal when the pulse width command value has positive polarity. These switches 52C,
The output of 52D is input to an adder 52H to obtain a low frequency biased excitation correction signal as shown in FIG. The corrected pulse width command is shown in FIG. 3(e), and each waveform of the inverter output voltage is shown in FIG. 3(f).

In the above description, both the DC component adjustment circuit 51 and the commercial frequency component adjustment circuit 52 are provided, but it goes without saying that only one of them can be provided.

〔Effect of the invention〕

According to the present invention, since the inverter output voltage time product is equalized between positive and negative, there is an advantage that there is no risk of malfunction or destruction of the device due to magnetic saturation of the transformer.

[Brief explanation of drawings]

Fig. 1 is an overall configuration diagram showing an embodiment of the present invention, Figs. 2 and 3 are waveform diagrams for explaining the operation of Fig. 1, and Fig. 4 shows a commercial frequency component adjustment circuit and a DC component. FIG. 5 is a circuit diagram showing a specific example of an adjustment circuit, FIG. 5 is an overall configuration diagram showing a conventional example of an inverter control circuit, and FIG. 6 is a waveform diagram for explaining its operation. Symbol explanation 1... Inverter main circuit, 2... Transformer, 3...
Load, 4... Control circuit, 41... Rectifier, 42...
・Filter, 43.51A, 52A...Setting device, 44
...PI controller, 45...Sine wave generator, 46...
- Multiplier, 47... Adder/subtractor, 48.52E... Comparator, 49... Carrier generator, 52H, 53
...Adder, 51...DC component adjustment circuit, 52...
Commercial frequency adjustment circuit, 51B 52B-5 2D...Analog switch, F...Logic inversion circuit, 2G...Inversion amplifier.

Claims (1)

[Claims] 1) A plurality of self-extinguishing switching elements are connected in series between positive and negative DC power sources, and the polarity of the DC input voltage becomes alternately positive or negative by turning on and off each element. It consists of an inverter that converts into an AC output voltage pulse train, a transformer connected to the output end of the inverter, and a control circuit that controls turning on and off of the switching element. An inverter control circuit that changes the polarity of the AC output voltage pulse in proportion to the absolute value of the pulse width command and inverts the polarity of the AC output voltage pulse by a carrier polarity signal having a sufficiently high frequency with respect to the frequency of the pulse width command inside the control circuit, a DC bias excitation correction circuit that adds a DC bias excitation correction signal having the same frequency and the same phase as the carrier polarity signal to the pulse width command; and a DC bias excitation correction signal having the same frequency and the same phase as the carrier polarity signal directly or An inverter control circuit comprising: a low frequency biased excitation correction circuit that selects and executes an operation of adding to the pulse width command after polarity reversal according to the polarity of the pulse width command. 2) Multiple self-extinguishing switching elements are connected in series between the positive and negative DC power supplies, and the on/off operation of each element converts the DC input voltage into an AC output voltage pulse train whose polarity is alternately positive or negative. an inverter connected to the output terminal of the inverter, a transformer connected to the output end of the inverter, and a control circuit that controls on/off of the switching element. and inverts the polarity of the AC output voltage pulse by a carrier polarity signal having a sufficiently high frequency with respect to the frequency of the pulse width command inside the control circuit, An inverter control circuit comprising a DC bias excitation correction circuit that adds a DC bias excitation correction signal having the same frequency and the same phase to the pulse width command. 3) Multiple self-extinguishing switching elements are connected in series between the positive and negative DC power supplies, and the on/off operation of each element converts the DC input voltage into an AC output voltage pulse train whose polarity is alternately positive or negative. an inverter connected to the output terminal of the inverter, a transformer connected to the output end of the inverter, and a control circuit that controls on/off of the switching element. and inverts the polarity of the AC output voltage pulse by a carrier polarity signal having a sufficiently high frequency with respect to the frequency of the pulse width command inside the control circuit, A low frequency bias excitation correction circuit is provided which selects and executes an operation of adding a DC bias excitation correction signal having the same frequency and the same phase to the pulse width command directly or after reversing the polarity, depending on the polarity of the pulse width command. An inverter control circuit characterized by: