JPH0446073B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a sine wave PWM controlled transistor inverter. When performing variable speed drive of an AC motor, use sine wave PWM that makes the motor current a sine wave.
Controlled transistor inverters are often used. Figure 1 shows a block diagram for one phase of a transistor inverter. Compare the sine wave current command and the detected motor current, obtain the deviation, use this as a sine wave control voltage command, and compare it with the carrier triangular wave. The transistor is controlled on/off to supply a motor current corresponding to the command, 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 regulator 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 is used as the base input of one transistor 3 and its inverted signal. are respectively used as base inputs of the other transistor 4. Note that the upper and lower transistors 3,
In order to prevent both transistors 3 and 4 from conducting and shorting the power supply, the base input of transistor 4 has a slight time lag by shifting the timing of the rise from off to on (by waveform shaping circuits 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 FIG. 1, 7 is an oscillator that supplies a carrier triangular wave; 8 is a code converter that forms an inverted pulse waveform; 9 and 10 are base drive circuits;
11 and 12 are diodes connected in antiparallel to the transistors 3 and 4, 13 is a current detector, 14 is one phase of the motor load, and 15 and 16 are DC power supplies. Second
The time chart in the figure shows the carrier triangular wave a, the sine wave control voltage waveform b of the current regulator 1 output, the pulse waveform C ₁ of the first transistor 3 base input signal of the comparator 2 output, and its inverted waveform. 2 and 4 represent the transistor 4 base input signal waveform C ₂ , respectively. The time chart in Figure 3 shows the relationship between the input and output pulse waveforms of the waveform shaping circuits 5 and 6. The rise of the pulse waveform on the output side has a slight time lag than the input pulse waveform, and as a result, A dead time always occurs when the transistors 3 and 4 are switched between conduction and non-conduction, and there is a period in which both transistors are turned off.

Thus, in sinusoidal PWM controlled transistor inverters, it is essential to provide a dead time period in which both transistors are turned off when switching, in order to prevent the risk of power supply short circuits. As the average value of the inverter output voltage decreases, its proportion increases.
It appears as an expansion of uncontrollable areas. That is, this type of inverter suffers from a decrease in control performance in the micro current region of no load or light load, and causes problems such as response delay.

By the way, in FIG. 2, if the motor current flows in a phase like the waveform d shown in the diagram in response to the voltage command b, then in the negative region, an ON command is given to the transistor 3 in the hatched area shown in the diagram. Regardless of the current, current flows through the diode 11, and even in the positive region, the current flows through the transistor 4 in the dashed line section.
An on command is given to the motor, but the actual motor current flows through the diode 12. In other words, when the motor current is flowing continuously,
Even during the period when the anti-parallel connected diodes 11 and 12 are conducting, an ON command is given to the main circuit transistors 3 and 4, which consumes wasteful base power, and the base input circuit supplies the ON command. also causes unnecessary power loss.

In view of the above, the present invention interrupts the on/off command of the main circuit transistor when the anti-parallel connected diode conducts in a state where current is continuously flowing, thereby reducing the power loss of the main circuit transistor and its base drive circuit. The purpose of this invention is to reduce the dead time for each cycle of the carrier triangular waveform and to significantly reduce the dead time for each cycle of the carrier triangular waveform for each reversal of the current phase. Explain.

In FIG. 3, 17, 18, and 19 are circuits according to the present invention, which compare the main circuit transistor selection circuit that discriminates the polarity of the current command I and selects a transistor with the carrier waveform of the inverter output voltage command. The obtained pulse waveform is newly inserted with the above-mentioned transistor selection command and an AND gate that performs an AND operation.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 I as a rectangular waveform with a slight rise delay and a time lag, compares this with the actual pulse waveform of the transistor on and off, and performs an AND operation. The present invention is characterized in that ON/OFF commands are given only to the transistors forming the current path, and OFF commands are given to the transistors in the other branch, thereby preventing conduction of the transistors in the same branch when the anti-parallel connected diodes are conductive.

4 is a time chart, the current command I is set by the transistor selection circuit 17,
It is converted into rectangular waves e ₁ and e ₂ corresponding to positive and negative polarities with a slight time lag in its rise, and on the other hand, the current command I and the current feedback signal If are compared and obtained via the current regulator 1. A pulse waveform C of a transistor on/off command is obtained as a result of comparing the voltage command b with the carrier triangular wave a. This pulse waveform C
and the inverted waveform and the square wave e ₁ corresponding to the previous current polarity,
The AND operation with e ₂ is performed, and the pulse waveforms f ₁ and f ₂ corresponding to the obtained current polarity are used as on/off commands for transistors 3 and 4 of each branch, and as a result, one of the upper and lower transistors 3 is turned on. While being turned on and off, the other branch transistor 4 remains off, and the load current flows between transistor 3 and diode 1.
2, and each combination of the transistor 4 and the diode 11 causes the current to flow depending on the positive or negative polarity.

The pulse waveforms e ₁ and e ₂ corresponding to the polarity of the current command are:
A time lag is provided at the rise of the signal to create a slight dead time, but this is of course equivalent to providing a dead time for every half period of the carrier triangular wave in the conventional example, and prevents a short circuit between the upper and lower transistors 3 and 4. This is to prevent both transistors from becoming conductive and shorting the power supply when the polarity of the current is reversed and switched from one of the upper and lower transistors to the other.

As described above, in the conventional sine wave PWM controlled transistor inverter, a dead time is required for every half period of the carrier triangular wave, which has various negative effects. , without applying the base input to that transistor, the pulse width of one of the upper and lower transistors is controlled to turn on and off, and the other transistor remains off, and the sine wave current command is used to switch the upper and lower transistors. At the time of phase inversion, a time lag is provided to avoid a power supply short circuit by confirming that one transistor is completely turned off and then turning on the other transistor, similar to the dead time for each half period of the carrier triangular wave. This type of sine wave PWM controlled transistor inverter focuses on the fact that the on/off state of the parallel transistors has no relation to the function while the diode is excited, and stops generating the base input during this period. In this case, various problems caused by dead time have been a concern, such as removing a constant voltage from the output voltage when the inverter output voltage and current are of the same polarity, and conversely adding it when the inverter output voltage and current are of the opposite polarity. This solves problems such as polarity modes having opposite effects and asymmetrical effects, and for similar reasons, if the power factor is close to 1, the output voltage always appears lower than the command value, resulting in a decrease in the maximum output voltage. It has the excellent feature of being able to

[Brief explanation of the drawing]

In the drawings, Fig. 1 is a one-phase block diagram of a conventional sine wave PWM control transistor inverter, Fig. 2 is a time chart for explaining its operation, Fig. 3 is a block diagram of an embodiment of the present invention, and Fig. 4. This is also a time chart explaining the operation. DESCRIPTION OF SYMBOLS 1... Current regulator, 2... Comparator, 3... Upper transistor, 4... Lower transistor, 7... Oscillator, 17...
Transistor selection circuit, 18...AND gate, 1
9...AND gate.

Claims (1)

[Claims] 1 In a sine wave PWM controlled transistor inverter that has a current control loop and adjusts the sine wave current to control speed and torque, it generates a rectangular wave according to the positive or negative polarity of the current command, and there is a time lag in the rise of the rectangular wave. a transistor selection circuit with an AND gate that performs an AND operation with the rectangular wave of the transistor selection circuit;
A sine wave PWM control transistor inverter characterized in that one of the upper and lower transistors is controlled on/off in response to the positive and negative polarities of the motor current, while the other transistor remains off.