JPH0442913B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a variable frequency power supply, and more particularly to a current source inverter provided with a circuit for detecting commutation failure of an inverter.

[Technical background of the invention and its problems]

Voltage source inverters and current source inverters are often used as control devices using variable frequency power sources, and the present invention is applied to variable frequency power sources using current source inverters.

FIG. 1 is a block diagram of a conventional example of AC motor control configured using a current source inverter. In the figure, 1 is a commercial power supply, 2 is a rectifier that converts the commercial power supply into DC, 3 is a DC reactor that smoothes the DC, 4 is an inverter circuit that converts DC to AC, and 5 is driven by the output of the inverter circuit 4. It is an induction motor. 6 to 17 constitute a control circuit that controls the rectifier 2 and the inverter circuit 4, 6 is an input limit, 7 is an oscillator that converts the V/F signal obtained through the input limit into a frequency, and 8
is a ring counter, 9 is a pulse amplification circuit,
This output controls the inverter circuit 4, and 10 is a voltage detector that detects the output voltage of the inverter circuit. 11 is a comparator that compares the V/F signal from the input limiter 6 and the output signal from the voltage detector 10. ,
12 is a voltage control circuit that receives the output of the comparator 11 and outputs it as a current reference signal; 13 and 14 are current transformers and current detectors for detecting the current of the input power source 1; and 15 is a voltage control circuit from the current detector 14. a comparator 1 that compares the current detection signal of the input power supply 11 output and the current reference signal output from the voltage control circuit 12;
6 is a current limiting circuit, and 17 is a phase control circuit that controls the control angle of the rectifier 2 based on the output from the current limiting circuit.

Next, a circuit diagram of the inverter circuit 4 is shown in FIG. In the figure, thyristors 18 to 23 are fired by pulses from the pulse amplification circuit 9;
4 to 29 are commutating capacitors, and 30 to 35 are diodes.

Now, if the thyristor 18 is firing, the thyristor 18 is energized for 120 degrees, and the thyristor 22,
23 are energized for 60 degrees each, thyristor 18 diode 30, motor 5, diode 3
A current of 120° flows through the paths of thyristors 4 and 35 and thyristors 22 and 23. Next, when commutating from thyristor 18 to thyristor 19, commutation capacitor 2
4 is the (+) polarity of the cathode side of the thyristor 18;
The cathode side of the thyristor 19 was charged with (-) polarity, but by applying the ignition pulse of the thyristor 19, a reverse voltage is applied to the thyristor 18, turning it off, and the cathode side of the thyristor 19 becomes (+) polarity. Charge and discharge in the direction. Similarly, commutation is performed from thyristor 19 to thyristor 20 and from thyristor 20 to thyristor 18 one after another.

As mentioned above, in normal operation, the inverter side output current of a current source inverter, in terms of phase current, flows to the (+) side for 120 degrees, rests for 60 degrees, and then flows for 120 degrees to the (-) side. However, if the charging voltage of the commutation capacitor is insufficient, the reverse voltage applied to the thyristor is insufficient, making it impossible to turn off the thyristor and causing commutation failure. At this time, in voltage control, the current determined by the current reference flows through the rectifier 2, DC reactor 3, inverter circuit 4, and rectifier 2, stops flowing to the motor, and current flows through the DC reactor 3 as a load, and furthermore, the inverse conversion output voltage By decreasing, the current reference increases and the current reference reaches its maximum value,
Performs the same operation as in an overload state during operation. Conventionally, this has been used to protect against commutation failure as overload, making it impossible to detect commutation failure or overload status.

[Purpose of the invention]

The present invention provides a current source inverter that can detect commutation failure in an inverter circuit of a variable frequency power source, distinguishing it from an overload state, by controlling the speed of a motor driven by the variable frequency power source. With the goal.

[Summary of the invention]

If the motor is speed-controlled and operated under no-load conditions, the current reference will not increase because the speed will not decrease even if a commutation failure occurs. In this case, even if one thyristor causes a commutation failure, the current will be blocked by the commutating capacitor voltage in the other phase and the motor induced voltage, so no phenomenon such as a DC short circuit in the inverter circuit will occur, and the motor Although current flows to the current, it becomes an abnormal current with disordered phase current.

The present invention was made by focusing on the disturbance of the phase current that occurs when commutation fails in the output of the inverter circuit of this speed-controlled variable frequency power supply. That is, the present invention includes a converter section that obtains a direct current from an alternating current power source, a reactor that smoothes the direct current, an inverter section that converts the smoothed direct current into alternating current, and a control that controls the converter section and the inverter section. a current detecting means for detecting positive and negative energization sections of a phase current from the output current of the inverter section; This current source inverter is equipped with commutation failure detection means that detects commutation failure by comparing the energization command sections of the gate pulse signals of the relevant phases, thereby making it possible to distinguish between an overload state and a commutation failure state.

[Embodiments of the invention]

The invention will be described with reference to one embodiment shown in FIG. In the figure, 50 is an output current detector for detecting the output current of the inverter circuit, 51 and 52 are rectifiers, 53 is a NOT circuit, 54 and 55 are variable resistors for setting the peak value of the gate pulse, 56,
57 is a comparator, 58 and 59 are amplifiers, 60 is OR
The circuit 61 is a T/D circuit that causes a detection delay corresponding to the commutation overlap time.

In the circuit shown in Fig. 3, one phase of the output of the inverter circuit is taken out and designated as _I0 , and when _I6 is flowing 120° to the (+) side, the pulse width multiplier 22 is 120°. The pulse between these two times is output, and the thyristor of the inverter circuit 4 is turned on for 120 degrees. The same thing is done with a gate pulse and a thyristor that are 180° out of phase on the (-) side. Therefore, one phase of the output current flowing through the motor 5 is taken out, and (+)
The current on the side is passed through the rectifier 51 to the comparator 5.
6 is input. On the other hand, the gate pulse with a 120° waveform output from the pulse amplification circuit 9 is sent to the NOT circuit 5.
3 (U), the peak value of the gate pulse is adjusted to the excitation current value by the variable resistor 54, and is input to the comparator 56 as a detected value of the current amount. The comparator compares the (+) side current of I ₀ as the (+) reference and the inverted gate pulse U as the (-) reference.
When the side current becomes less than the excitation current value, the amplifier 5
Output to 8. The output of the amplifier 58 is an OR circuit 60
The signal is input to the TD circuit 61 via the TD circuit 61. TD circuit 6
1, in order to prevent malfunctions due to rises and falls of current due to commutation in the inverter circuit 4, a detection delay corresponding to the commutation time is generated and output as a commutation failure detection signal.

Regarding the (-) side current of _I0 , the comparator 57 uses the (-) side current as the (-) reference, and uses the output from the pulse amplifier circuit 9 as the (+) reference without inverting it.
When the (-) side current exceeds the excitation current, it is amplified by the amplifier 59, inputted to the OR circuit 60, and its output is sent as a commutation failure detection signal via the TD circuit. Output.

By providing a circuit like the one described above, it is possible to detect an output current for one phase and compare it with the gate pulse to distinguish between an overload condition and a commutation failure, which can be done quickly and reliably. commutation failure can be detected.

Furthermore, as another embodiment, it is also possible to detect the output current of the inverter circuit in three phases 1, attach the above-mentioned circuits to each phase, and use the three circuits in combination. In the detection of one phase, if the current flows longer than the gate pulse width, it will not be detected within the first 120°, but it will be detected within 360° in order to detect when the width of the current after the next commutation becomes shorter. It is possible. On the other hand, when this three-phase detection is performed, even if the output current for one phase flows for a longer time than the gate pulse width due to commutation failure, no current flows in other phases at the same timing as the gate pulse. From this, three-phase detection allows detection within 120 degrees in electrical angle.

As yet another example, in the above-mentioned example, the gate pulse signal was converted into an analog quantity and the levels were compared; however, by converting the current component into a digital quantity,
The same effect can be obtained by comparing gate pulse and logic.

〔Effect of the invention〕

According to the configuration of the present invention, commutation failure can be detected separately from an overload state.

[Brief explanation of drawings]

FIG. 1 is a block diagram of AC motor control in a conventional example, FIG. 2 is a circuit diagram of the inverter circuit in FIG. 1, and FIG. 3 is a failure detection circuit diagram of the present invention. 1... Power source, 2... Rectifier, 3... DC reactance, 4... Inverter circuit, 5... AC motor, 6...
input limit, 7... oscillator, 8... ring counter, 9
...Pulse amplifier circuit, 10...Voltage detector, 11...Comparator, 12...Voltage control circuit, 13...Current transformer, 14
... Current detector, 15... Comparator, 16... Current control circuit, 17... Phase control circuit, 50... Output current detector, 53... NOT circuit, 54, 55... Variable resistor,
56, 57... Comparator, 58, 59... Amplifier, 60
...OR circuit, 61...TD circuit.

Claims (1)

[Claims] 1. Equipped with a converter section that obtains direct current from an alternating current power source, a reactor that smoothes the direct current, an inverter section that converts the smoothed direct current to alternating current, and a control section that controls the converter section and the inverter section. In the device, current detection means detects positive and negative energization sections of the phase current from the output current of the inverter section, and a gate of the corresponding phase that is output from the energization section and the control section to control the inverter section. A current source inverter characterized in that a commutation failure detection means is provided for detecting a commutation failure by comparing energization command sections of pulse signals, thereby making it possible to distinguish between an overload state and a commutation failure state.