JPH0767291B2 - Power converter - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a rectifier, a converter section in which an arm made of a semiconductor switching element connected in antiparallel with the rectifier and capable of self-extinguishing is bridge-connected, and a converter section. The power converter includes a smoothing capacitor for smoothing the output of the control circuit and a control circuit for generating and applying a drive signal to the semiconductor switching element of the converter section.

[Conventional technology]

FIG. 3 is a circuit diagram of a conventional example of this kind of power converter, which includes a circuit breaker 1, a control transformer 2, and transistors TR ₁ , TR ₂ , TR ₃ , TR ₄ , TR ₅ , TR ₆ with flywheel diodes. A converter unit 3 composed of a DC voltage circuit, an inverter unit 4 composed of a transistor with a flywheel diode, a base signal 5 to the converter unit 3 and a base signal 6 to the inverter unit 4. It includes a control circuit 8 for outputting the AC voltage, an AC reactor ACL, and an AC motor 7.

The transistors TR _{1 to} TR ₆ with flywheel diodes of the converter unit 3 form bidirectional switches by applying the base signals as shown in FIG. 5 to the transistors TR _{1 to} TR ₆ . That is, in the state where the base signal is cut off, the flywheel diode section becomes a three-phase full-wave rectifier circuit, but the base signal shown in FIG. , Given to the transistor paired with its flywheel diode.

_One of the transistors TR _{1 to} TR ₆ is connected to the power supply side, and the other is connected to the DC side (either the positive side or the negative side of the capacitor C). Current flows from the higher potential to the lower potential on the DC side, and energy is propagated. Fig. 6 shows the transistor TR
_One example will be given. In FIG. 6, when V _R > V _P , the current flows as shown by the solid line (→), and when V _P > V _R , the dotted line ().
The current flows like. Further, this situation will be described in the case where the electric motor 7 is driven by receiving the power supply.

First, in the electric mode in which the electric motor 7 is driven while receiving energy from the power source, the electric potential of the capacitor C decreases due to the driving of the electric motor 7, and the state of “electric potential on the power source side> potential on the direct current side” occurs. The diode becomes conductive, and energy is supplied from the power supply side to the DC side.

On the contrary, when the electric motor 7 is stopped, the rotational energy of the electric motor 7 is supplied to the capacitor C via the inverter unit 4, so that the voltage of the capacitor C rises and "potential on the power source side <potential on the DC side". Transition to the state of. At this time, the flywheel diode is reverse-biased, so that the flywheel diode is cut off, the transistor to which the base signal is applied becomes conductive, and energy flows to the power supply side. That is, the electric motor 7
This is the power regeneration operation in which the rotational energy of is regenerated to the power source side.

The base signals of the transistors TR _{1 to} TR ₆ are the voltage signals of the power source and the control circuit 8 via the transformer 2 as described later.
It is generated on the basis of the zero crossing point of the signal whose waveform is shaped by the filter and is synchronized with the power supply phase.

The operation when the AC power supply is disconnected is as follows.

When the power supply side is viewed from the converter section 3, the control transformer 2 becomes the main load and is represented as shown in FIG.

When the AC power supply is disconnected with the base signal of the transistor being applied (for example, when the circuit breaker 1 in FIG. 3 is turned off), at this time, as shown in FIG. ) And the voltage of the capacitor C between the main circuit PN
Since V _C remains for a certain period of time (T is the time during which stable control is possible), the state of "potential on the power supply side <potential on the DC side" is established,
The voltage V _C of the capacitor C is supplied to the control transformer 2 by the transistor (the cut waveform at this time is similar to the base signal). This situation is shown in FIG. 8 as the phase voltage of each phase shown in FIG.

Also, as shown in FIG. 10, the base signal of the transistor
e ₃ is generated with reference to the zero crossing point of the signal e ₂ obtained by filtering the power supply voltage waveform e ₁ .

When the AC power supply is disconnected, a waveform as illustrated as V _{RS in} FIG. 9 is applied as the signal e _{1 in} FIG. 10 and is filtered to generate a base signal as shown in FIG. 10 e ₃ . Are generated without being supplied with AC power.

That is, even if the AC power supply is disconnected, if the base signal is not interrupted at this time, the converter unit 3 disconnects the DC voltage V _C of the capacitor C and outputs the output as shown in FIG. Supply to the circuit 8. Further, a base signal is generated by this signal, the DC voltage V _C of the capacitor C is cut off again, and so on, and the operation of the converter unit 3 continues.

[Problems to be Solved by the Invention]

This operation corresponds to a self-excited inverter operation that does not rely on an AC power source. That is, the drive signal (base signal) of its own is generated by the signal output by the converter itself, and the operation of cutting off the DC voltage V _C of the capacitor again by this drive signal is continued (self-excited oscillation).

Loss of power supply voltage usually monitors the level of power supply voltage,
When a voltage goes below a certain level, it is detected as an undervoltage and the base signal is cut off.However, in the state of self-excited transmission like this, in order to go below a certain level, must drop to a DC voltage V _C itself its constant level of capacitor C, relative to the amount of energy stored in the capacitor C, the energy consumed by the control circuit 8 is usually very undervoltage smaller detection It takes time to be done.

As described above, the base signal of the transistor is generated on the basis of the zero cross point of the signal whose waveform is shaped by filtering the AC power supply voltage. When the AC power supply is normal, e _{1 in} Fig. 10
Is the AC power supply voltage, but when AC power is lost, e _{1 in} Fig. 10
Is a signal like V _RS in FIG. This signal is 60 °
Since there is a gap of 2α for each (electrical angle), even if it is filtered, it cannot be held at a constant frequency that is properly synchronized with the power supply frequency, and the frequency of regenerative power and the frequency of the base signal generated from this are not maintained. By comparison, the frequency of the base signal becomes slightly higher, and therefore the frequency of regenerative power in the next cycle also becomes slightly higher. By repeating this process, the frequency of regenerative power gradually increases.

The fact that the frequency of the regenerated AC power is higher than the power supply frequency of the AC power supply means that a phase shift with the AC power supply occurs, and when the circuit breaker 1 is turned on again in this state, the transistor TR The ON section of _{1 to} TR ₆ is not synchronized with the AC power supply side, resulting in a short circuit between phases of the AC power supply.

An object of the present invention is to provide a power converter that stops the self-excited inverter operation when the power is turned off and prevents the interphase short circuit when the power is turned on again to ensure the stability.

[Means for Solving the Problems]

The power converter of the present invention, in order to solve the above problems,
When the power is off, the converter section cuts off the DC voltage of the smoothing capacitor, outputs a signal to the control circuit, and cuts off the DC voltage of the smoothing capacitor again by the drive signal generated by the control circuit according to the signal. Means for detecting that the oscillation frequency of the self-excited inverter operation, which is a continuous operation, becomes higher than the power supply frequency, and to the converter section when this means detects that the oscillation frequency becomes higher than the power supply frequency. And a power regeneration control circuit including means for cutting off the drive signal.

〔Example〕

Next, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram of an embodiment of a power regeneration control circuit of a power converter according to the present invention.

The filter 11 waveform-shapes and outputs one phase of the control power source input via the step-down transformer. The ramp wave generator 12 receives the output e _{1 of the} filter 11, rises with the zero cross point as a reference, and generates a ramp wave e ₂ that is reset at the next zero cross point. The comparator 13 compares the output e ₂ of the ramp wave generator 12 with a predetermined reference voltage (slightly smaller than the peak value of the output e ₂ ) and outputs a pulse e ₃ of the difference between the ramp wave e ₂ and the reference voltage. .
The monostable multivibrator 14 outputs a pulse e _{3 of a} fixed time from the leading edge of the differential pulse e ₃ . The integrator 15 is composed of a capacitor, a resistor, and a diode, and is an integrator that receives the output e ₄ of the monostable multivibrator 14 and a negative level DC voltage (zener voltage -V _Z ) as input, and the pulse width of these outputs e ₄ And the negative level are set so that the output e _S is clamped to the negative level when the entire device (power converter) is operating normally. Relay drive circuit 16
Outputs a high-level base block signal when the output e _S of the integrator 15 exceeds the zero level, and drives a relay (not shown) (contact opens) to interrupt the base drive signal.

Next, the operation of this embodiment will be described with reference to the waveform chart of FIG.

The solid line in the normal operation, the comparator 13 every half cycle of the power supply voltage e ₁
Since the pulse e ₃ is output from the output, the output e _S of the integrator 15 is clamped to the negative level, and the relay drive circuit 16 does not output the base block signal.

Next, when the power supply is turned off, the frequency of the power supply voltage e ₁ becomes higher as shown by the broken line, so that the peak value of the ramp wave e ₂ becomes smaller than the reference voltage and the pulse e ₃ is not output, and the integrator 15
The output e ₅ of the signal continues to rise from the time t ₀ as shown by the broken line, and the base signal e ₆ is output from the time t ₁ when it exceeds the zero level. Therefore, the base signal of the transistor of the converter section is cut off, the self-excited inverter operation is immediately stopped, and the interphase short circuit of the power supply is prevented.

〔The invention's effect〕

As described above, according to the present invention, a means for detecting that the oscillation frequency of the self-excited inverter operation when the power is off is higher than the power supply frequency, and this means that the oscillation frequency is higher than the power supply frequency. Since the electric power regeneration control circuit including the means for cutting off the drive signal to the converter when it is detected is provided, there is an effect that the inter-phase short circuit of the AC power supply when the power is turned on is prevented.

[Brief description of drawings]

FIG. 1 is a block diagram of an embodiment of a power regeneration control circuit according to the present invention, FIG. 2 is a waveform diagram of the output of each circuit showing the operation of FIG. 1, and FIG. 3 is a circuit of a conventional example of a power converter. 4 and FIG. 4 are diagrams showing voltage changes of the capacitor C and the control power source when the circuit breaker 1 is switched from “closed” to “open” in FIG. 3,
Figure 5 is a diagram showing the on / off timing of the power supply voltage and the transistor TR ₁ to Tr ₆ of FIG. 3, FIG. 6 is a transistor
FIG. 7 is a diagram for explaining the operation of TR ₁ , FIG. 7 is a diagram showing the power source side from the converter unit 3 when the AC power source is disconnected, and FIG. 8 is a phase voltage of each phase at the point of FIG. FIG. 9 and FIG. 9 are voltage waveform diagrams, and FIG. 10 is a circuit diagram of a circuit for generating the base signal e ₃ from the power supply voltage e ₁ and a waveform diagram of each signal e ₁ , e ₂ , e ₃ . 11 …… Filter 12 …… Ramp wave generator 13 …… Comparator 14 …… Monostable multivibrator 15 …… Integrator 16 …… Relay drive circuit

Claims (1)

[Claims] 1. A rectifier, a converter section in which an arm made of a semiconductor switching element connected in antiparallel with the rectifier and capable of self-extinguishing is bridge-connected, a smoothing capacitor for smoothing the output of the converter section, and an AC power supply voltage. In a power converter configured by a control circuit that inputs a signal to generate a drive signal for a semiconductor switching element of the converter unit and applies the drive signal to the converter, the converter unit disconnects the DC voltage of the smoothing capacitor when the power is off. In addition, by outputting a signal to the control circuit, the drive signal generated by the control circuit by the signal, the oscillation frequency of the self-excited inverter operation is a continuous operation to disconnect the DC voltage of the smoothing capacitor again from the power supply frequency. And the means to detect that the oscillation frequency is higher than the power supply frequency. A power converter comprising a power regeneration control circuit including means for cutting off the drive signal to the converter unit when it is detected that the voltage has risen.