JPS60156280A - Sinusoidal pwm control transistor inverter - Google Patents

Abstract

PURPOSE:To alleviate power loss by a main circuit transistor and its base drive circuit by interrupting the ON, OFF commands of the main circuit transistor when anti-parallel connection diodes are conducted. CONSTITUTION:A current command is converted by a transistor circuit 17 to a rectangular wave corresponding to positive and negative polarities provided with a small time lag at the rise. A current command and a current feedback signal are compared, and the output obtained by passing a current regulator is compared by a comparator 2 with a carrier triangular wave from an oscillator 7. The output of the comparator 2 is applied to an AND gate 18, and through a code converter 8 to an AND gate 18, and AND-calculated with the rectangular wave from the selector 17. The outputs of the gates 18, 19 are applied to base drive circuits 9, 10, and upper and lower transistors 3, 4 are turned ON or OFF.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a sinusoidal PWM controlled transistor inverter. When variable speed driving of an AC motor is performed, a transistor inverter with sinusoidal PWM control that makes the motor current a sinusoidal wave is often used.

Figure 1 shows a block diagram of the transistor inverter 1 and phase components. Compare the sine wave current command and the detected motor current, obtain the deviation, use it as a sine wave control voltage command, and compare it with the carrier triangular wave. In order to supply the electric current corresponding to the current command, the transistor is turned ON and 0FFIIJ, and the average value of the inverter output voltage is made into a sine wave. That is, the sine wave voltage amplified through the current HPti device (1) is compared with the carrier triangular wave in the comparator (2) to generate a pulse waveform with a width corresponding to the current command, and one of the transistors (3) is as the base input and its inverted signal as the base input of the other transistor (4), respectively. In addition, this upper and lower transistor (3)
, (4) are connected to these transistors (3),
In order to prevent both <4) from becoming conductive and becoming the power supply 'InIIB, the timing of the rise of 'ON from OFF is shifted to provide a slight time lag (waveform shaping circuit (
According to (5) and (6)), the timing at which one of the transistors becomes conductive is set so that the timing at which one of the transistors becomes conductive is always after the other transistor is switched to a non-conductive state.

In Figure 1, (7) is an oscillator that supplies a carrier triangular wave, (8) is a sign converter that forms an inverted pulse waveform, (
9), <10) are base drive circuits, (11), <1
2) is a diode connected in antiparallel to transistors (3) and (4), (13) is a current detector, (14) is one phase of motor load, and (15) and (16) are DC power supplies. be.

The time chart 17 in FIG. 2 shows the carrier triangular wave a and the sine wave control voltage waveform b1 of the current regulator (1) output from the comparator (
2) The pulse waveform c1 of the first transistor (3) base input signal and the second transistor (4) base input signal waveform C2, which is its inverted waveform, are respectively shown at output node j. The time chart in Figure 3 shows the waveform shaping circuit (5),
<6) shows the relationship between the input and output pulse waveforms; the rise of the pulse waveform on the output side has a slight time lag compared to the input pulse waveform, and as a result, both transistors (3)
, (4), a dead time always occurs when switching between conduction and non-conduction, and there is a period in which both are OFF.

In this way, in a sine wave PWM I controlled transistor inverter, in order to prevent the risk of power short circuit, it is essential to provide a dead time period in which both transistors are turned off when switching. As the motor current decreases and the average inverter output voltage decreases,
Its proportion increases, resulting in an expansion of the uncontrollable area. In other words, this type of inverter suffers from a decline in control performance in the micro current region of no load or light load.
This causes problems such as response delays.

By the way, if the motor current flows in a phase like the d waveform shown in the figure in response to the voltage command in FIG. Current flows through the diode (11) regardless of the current, and even in the positive region, an ON command is given to the transistor (4) in the dashed line section, but the actual motor current flows through the diode (12). It will flow. That is, in the continuous, flowing condition of the motor current, the main circuit transistor (3).

Diode (11) connected in antiparallel to (4).

Even during the period when (12) is conducting, -
〇When an N command is given, ← Su゛ conducts, consuming wasted power, and also supplies an ON command to transistors (3) and (4).
The switching operation (4) is driven when it is unnecessary, resulting in power loss.

In view of the above, in a state where current is continuously flowing, when the anti-parallel connected diodes are conductive, the main circuit transistor is
- It is intended to reduce the power loss of the transistor and its base drive circuit, and to significantly reduce the dead time for each period of the carrier triangular waveform for each reversal of the current phase. This will be explained in detail based on the embodiment shown in FIG.

In FIG. 3, (17), (1B), and (19) are circuits according to the present invention, including a main circuit transistor selection circuit for determining the polarity of the current command (■) and selecting a transistor;
A new AND gate has been inserted to perform an AND operation on the pulse waveform obtained by comparing the carrier waveform of the inverter output voltage command with the transistor selection command.The rest of the configuration is the same as the conventional example and is indicated by the same reference numerals. .

That is, the present invention detects the polarity of the sine wave current command l as a rectangular waveform with a slight rise delay and a time lag, and turns on the transistor.

Compare and AND operation with the actual OFF pulse 1 waveform, and turn ON only the transistor that becomes the current path.

It is characterized in that an OFF command is given to the transistors in the other branch, and conduction of the same branch transistors is prevented when the anti-parallel connected diodes are conductive.

To explain using the time chart in Figure 4, the current command ■
The transistor selection circuit (17) generates a rectangular wave e1. corresponding to positive and negative polarity with a slight time lag in its rise. e2, and on the other hand, the current command I and the current feedback signal If are compared, and the voltage command obtained through the current regulator (1) is compared.

Transistor ON which is the comparison result with carrier triangular wave 8
, 'Obtain the pulse waveform C@ of the OFF command. A rectangular wave e1.corresponding to the pulse waveform C and the inverted waveform and the previous current polarity. e
2, and the pulse waveform fllf2 corresponding to the obtained current polarity is applied to the transistor of each branch <3),
(4) ON.

As a result, while one of the upper and lower transistors (3) is turned ON and OFF, the other branch transistor (4) remains OFF, and the negative current flows between the transistor (3) and the diode (12). , and transistor (
4) and a diode <11), the current flows depending on the positive and negative polarities.

The pulse waveform al182 corresponding to the polarity of the current command is designed to have a time lag at its rise, which causes a slight dead time, but of course this is due to the fact that a dead time is provided for every half cycle of the carrier triangular wave in the conventional example. , and are equal to each other, and are intended to prevent short circuits between the upper and lower transistors (3) and (4). When the polarity of the current is reversed and switches from one of the upper and lower transistors to the other, both transistors become conductive, resulting in a short circuit of the power supply. This is to prevent this from happening.

As described above, in the conventional sine wave PWM controlled transistor inverter, a dead time was required for every half cycle of the carrier triangular wave, which caused various negative effects. During this time, do not apply the base input to that transistor,
Turn on and off one of the upper and lower transistors
When the phase of the sine wave current command is reversed to switch the upper and lower transistors, the dead time of one half of the carrier triangular wave '1 is the same as the dead time of the half-open can of carrier triangular wave '1. The transistor is completely turned off! The feature is that a time lag is provided to avoid the voltage Sfl condition in which the other transistor is turned on after the diode is excited, and the parallel transistor is turned on while the diode is excited.

OFF stops the generation of anything related to any function (focusing on this, the base input during this period), and in this type of sine wave PWM control transistor input,
Various problems caused by dead time (X For similar reasons, if the power factor is close to 1, the output voltage will always appear lower than the command value, causing a decrease in the maximum output voltage. It has the excellent feature of being able to solve problems such as IL.

[Brief explanation of drawings]

In the drawings, Fig. 1 shows the conventional sine wave P W M @till
2 is a block diagram for one phase of the transistor inverter, FIG. 2 is a time chart illustrating its operation, FIG. 3 is a block diagram of an embodiment of the present invention, and FIG. 4 is a time chart illustrating the same operation. (1) Current regulator (2) Comparator (3) Upper transistor (4) Lower transistor (7) Oscillator (17) Transistor selection circuit ( 18)...AND gate (19)...AND gate applicant Shinko Electric Co., Ltd. agent Patent attorney Haruya Saifuji

Claims (1)

[Claims] 1. In a sine wave PWM controlled transistor inverter that has a current #A double loop and adjusts the sine wave current to perform fast lean/1-lux control, it generates a rectangular wave according to the positive and negative polarities of the current command, and A transistor selection circuit with a time lag at the rise of the rectangular wave compares the voltage command of the current regulator and the carrier triangular wave of the oscillator, and turns on the upper and lower transistors.
, a comparator that outputs a pulse waveform for OFF control, and an AND gate that ANDs the pulse waveform of the comparator and its inverted waveform with the rectangular wave of the transistor selection circuit,
Depending on the positive or negative polarity of the motor current, one of the upper and lower transistors is turned ON, 0FFII is controlled, and the other transistor is turned OFF.
characterized by being left as is