JPH0199480A - Control device for pwm converter - Google Patents

Abstract

PURPOSE:To eliminate overcurrent, by setting up another smaller current detection level in addition to an overcurrent detection level, with which the switching elements of a PWM converter is turned off. CONSTITUTION:In a main circuit constitution a transformer 1 is connected to the AC side of a PWM converter 3 through an AC reactor 2, while a DC capacitor 4 and a load 5 are connected in parallel to the DC side. The PWM converter 3 is composed of switching elements 31-34 and rectifying devices 35-38. A control device serves a DC voltage control function and a phase control function. It is composed of a voltage regulator 7, a current regulator 16, a phase detector 10, a phase regulator 12, etc., and quipped with a coordinate converter 13 and a pulse width modulator 14. When the AC current gets above the overcurrent setting level, a gate-off command and a breaker starting command are outputted. The current detection setting level of a current limiter 19 is set up lower than the overcurrent setting level and the limiter 19 actuates first to set an FF 20.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a power converter control device, and particularly to a power converter control device suitable for use in railway vehicles.

[Conventional technology]

The conventional PWM converter control device for AC railway vehicles is
Proceedings of the 1986 National Conference of the Institute of Electrical Engineers of Japan [9] (1
9g 7) As described on pages 1099 to 1100, it consisted of a voltage regulator, current regulator, two-phase regulator, etc. The voltage regulator compares and calculates a target value of DC voltage and a feedback value, and outputs a target value of AC current. and,
A current regulator performs feedback control of the alternating current with respect to this target value. On the other hand, the phase adjuster controls the phase difference between the AC voltage and current, that is, the power factor angle. Usually the phase difference is 0 degrees (power factor 1)
I'm trying to make it happen.

Although it is not clear in this document, as one of the protection functions, when the alternating current reaches a predetermined overcurrent setting value, PWM
At the same time as turning off the switching elements that make up the converter, it also performs protective operations such as opening the circuit breaker on the power supply side.

[Problem that the invention seeks to solve]

In the above conventional technology, when the overcurrent detector is activated, not only does the operation of the PWM converter stop until the driver performs a reset operation, but also the operation of the PWM converter is stopped at startup due to DC bias in the transformer. In case of overcurrent, PWM
There was a problem that it became impossible to start the converter.

It is known that DC bias in the transformer of an AC railway vehicle is caused by an inrush current flowing when the power of one's own vehicle or another vehicle is turned on.

In the main circuit of the PWM converter shown in FIG. 3, the AC reactor 2 often utilizes the leakage impedance of the converter in order to reduce the size and weight of the device. When DC bias occurs, the transformer core saturates near the point where the power supply voltage changes polarity from positive to negative or from negative to positive. Therefore, the inductance of the AC reactor 2 is reduced to a value equivalent to that of an air-core reactor.

When the inductance of the AC reactor 2 becomes small, the rate of change of the AC current increases, which may increase the ripple and lead to overcurrent. FIG. 4 shows schematic waveforms of voltage and current at each part at this time.

An object of the present invention is to enable a PWM converter to continue operating without overcurrent even if a transformer causes DC bias.

[Means for solving problems]

The purpose of overloading is achieved by providing, in addition to the overcurrent detection level for alternating current, another current detection level smaller than the overcurrent detection level, and when this level is reached, the switching elements constituting the PWM converter are turned off. .

[Effect]

When the switching elements constituting the PWM converter are turned off, the PWM converter becomes equivalent to a simple full-wave rectifier bridge, and the energy stored in the AC reactor 2 charges the DC capacitor 4. At this time, if the DC voltage is higher than the secondary voltage of the transformer 1, the AC current is attenuated and no overcurrent occurs. Note that the direct current is P
When the WM converter is in operation, the voltage is increased to about twice the secondary voltage, and even at startup, the DC voltage is charged to the peak value of the secondary voltage through the rectifying element without waiting for the switching element to operate. Ru.

〔Example〕

An embodiment of the present invention is shown in FIG. 1. In the main circuit configuration, a transformer 1 is connected to the AC side of a PWM converter 3 via an AC reactor 2. As shown in FIG.

Further, on the DC side, a DC capacitor 4 and a load 5 are connected in parallel. A circuit breaker 17 is connected to the primary side of the transformer 1 . The PWM converter has switching elements 31 to 3
4 and rectifying elements 35 to 38.

The main functions of the control device are a DC voltage control function and a phase control function.

The voltage control function consists of an adder 6 for obtaining a deviation, a voltage regulator 7, an adder 15 and a current regulator 16 for controlling the alternating current.

The phase control function is based on the secondary set pressure es of the transformer 1 and the alternating current i.
s, a phase detector 10 for detecting their phase difference, an adder 11 for obtaining a phase deviation, and a phase adjuster 1
Consists of 2.

Others, coordinate converter 13. It consists of a pulse width modulator 14.

The deviation between the target value Ed· of the DC voltage and the feedback value Ed is provided from the adder 6 to the voltage regulator 7. The voltage regulator 7 calculates this deviation and outputs the target value IsI of the alternating current.

The voltage regulator 7 controls the DC voltage by adjusting the power obtained from the AC side.

As for the current regulator, an adder 15 and a current regulator 16 control the alternating current. Current regulator 16 outputs an imaginary component Im[Ecl of converter input voltage ea.

The phase adjuster 12 receives the deviation between the phase target value φ and the feedback value φ detected by the phase detector 10 from the adder 11, calculates this deviation, and calculates the real component Re[ of the converter input voltage ec.
Output Ecl.

The converter input voltage ea given in DC coordinates from the current regulator 16 and the phase regulator 12 is transferred to the coordinate converter 13.
The signal is converted into polar coordinates and further modulated by the pulse width modulator 14 to operate the converter 3.

The alternating current is passed through an overcurrent detector 18 in all directions, and when a current exceeding a set overcurrent level is detected, a gate off signal is output to the pulse width modulator 14 and a breaker open command is output to the circuit breaker 17.

The alternating current is also passed through the current limiter 19. The current detection setting level of the current limiter 19 is set lower than that of the overcurrent detector 18. Therefore, if the current is becoming excessive, the current limiter 19 operates first. When the gate-off signal is output from the current limiter 19, the flip-flop 20 holds the gate-off signal. however,
In order to continue operation of the PWM converter, the command to open the circuit breaker 17 is not output. The output of flip-flop 2o is
It is reset by a timing signal from pulse width modulator 14. This timing signal is output every cycle of pulse width control, and from the next cycle of pulse width control gated off by the current limiter 19, P W M ,
:! The converter can resume operation.

Note that if the current continues to increase despite outputting the gate-off signal due to a short-circuit failure of a switching element, etc., the conventional overcurrent detector 18 detects the circuit breaker 17.
is open, so safety is not compromised.

FIG. 2 shows operating waveforms when the transformer 1 experiences direct current bias. ep is the primary voltage of main transformer 1, ip is the primary current, is
is the secondary current, and ec is the PWM converter input voltage.

Further, R is a reset signal of the flip-flop 20, Go
ff is the output of the flip-flop 20.

Now, assume that the iron core becomes saturated when the primary voltage ep changes from a negative half cycle to a positive half cycle due to direct current biased magnetism. At this time, in order to obtain a magnetic flux density corresponding to the primary voltage ep,
A large excitation current flows through the primary voltage ip. When the iron core is saturated, the leakage inductance of transformer 1 becomes smaller, and 2
When the rate of change of the next current is increases 6 and reaches the set value 11 of the current limiter 19, a gate-off signal Goff is output, turning off the switching elements 31 to 34. As a result, the current flowing through the AC reactor 2 passes through the rectifying elements 35 and 38 and flows in a direction to charge the DC capacitor 4. Therefore, the current attenuates rapidly and does not lead to overcurrent.

Gate-off signal Go held in flip-flop 20
ff is reset by a timing signal from pulse width modulator 14. Since this reset signal is output in synchronization with the cycle of pulse width control, normal operation can be resumed from the next pulse.

FIG. 5 shows waveforms at various parts when the primary voltage ep of the transformer 1 suddenly increases. Since the voltage across the AC reactor rises rapidly, the rate of change of the AC current is increases, and control can be achieved without causing an overcurrent as in the case of DC bias magnetization of the transformer.

【Effect of the invention〕

According to the present invention, even if the rate of change in current increases due to DC bias in the transformer or a sudden increase in the transformer's primary voltage, the PWM converter continues to operate without overcurrent. be able to.

[Brief explanation of the drawing]

Fig. 1 is a diagram showing a PWM converter for a railway vehicle and its control device, which is an embodiment of the present invention, and Fig. 2 is a diagram of waveforms at various parts when a transformer causes DC bias (to which the present invention is applied). , Figure 3 is a configuration diagram of the conventional system, Figure 4 is a diagram of waveforms at various parts (conventional system) when the transformer causes DC bias, and Figure 5 is a diagram of each part when the transformer's primary voltage suddenly increases. It is a waveform (present invention) diagram of . 14... Pulse width modulator, 18... Overcurrent detector,
19...Current limiter, 20...Flip-flop. Figure 2;

Claims (1)

[Claims] 1. Pulse width modulation power converter (PWM converter) capable of converting AC power to DC power and vice versa
In addition to the overcurrent detection level, a control device that has an overcurrent detection and protection function for alternating current has another current detection level that is smaller than the overcurrent detection level, and when the alternating current reaches that value. A control device for a PWM converter, characterized in that it turns off a switching element constituting the PWM converter. 2. A control device for a PWM converter according to item 1, wherein the state in which the switching element is turned off is maintained only during a period in which the switching element is turned off.