CN103326551A - Method for hindering overshoot of turning-on currents of IGBT series connection type voltage source converter - Google Patents

Abstract

The invention relates to the fields of power systems and power electronics, in particular to a method for suppressing the overshoot of the turn-on current of an IGBT series voltage source converter. In this method, a wave trap unit is connected between the stray capacitance Cg and the half-bridge structure, and a second-order circuit is formed with the stray capacitance Cg; the method is used for the current caused by the stray capacitance Cg through the step response of the second-order circuit. The overshoot current is effectively suppressed, which provides a reliable guarantee for the operation of the IGBT series voltage source converter.

Description

A method for suppressing turn-on current overshoot of IGBT series voltage source converter

technical field

The invention relates to the fields of power systems and power electronics, in particular to a method for suppressing the overshoot of the turn-on current of an IGBT series voltage source converter.

Background technique

The voltage source converter can independently control the active power and reactive power to realize the rapid reversal of the power flow, and it has attracted more and more attention in the field of direct current transmission. In order to meet the requirements of high voltage and high power, some scholars have proposed the IGBT series voltage source converter, which can greatly simplify the main circuit structure, greatly reduce the control complexity, and greatly reduce the required components, thus making the device more compact , the floor area is greatly reduced. In the field of high-voltage and high-power power electronics in the future, IGBT series converters will be more widely used.

However, the primary equipment in the converter, such as commutation reactors and bushings, has a certain stray capacitance to the ground. The high-voltage and high-power IGBT series voltage source converter works in the switching state, and the dv/dt generated by it acts on On stray capacitance, current overshoot will occur when the device is turned on. As the voltage level increases, the current overshoot will become larger and larger, and eventually even exceed the withstand current of the IGBT, seriously affecting the normal operation of the converter. Therefore, we need to take corresponding measures to reduce the influence of stray capacitance. At present, there are no relevant research literature and products in China.

Contents of the invention

Aiming at the deficiencies of the prior art, the object of the present invention is to provide a method for suppressing the turn-on current overshoot of the IGBT series voltage source converter, which uses the principle of the step response of the second-order circuit to realize the current overshoot caused by the stray capacitance. It provides effective suppression and provides a reliable guarantee for the operation of the IGBT series voltage source converter.

The object of the present invention is to adopt following technical scheme to realize:

A method for suppressing the turn-on current overshoot of an IGBT series voltage source converter, the system used in the method is an IGBT series voltage source converter suppression system, which is used for a power system with a voltage level above ±10kV; including: a reactor - capacitive series branch, half-bridge structure, stray capacitance Cg, inductance L and voltage source u _s ;

The reactor-capacitor series branch is connected in parallel with the half-bridge structure; the stray capacitance Cg is connected in parallel with the voltage source u _s ; the inductance L is connected between the stray capacitance Cg and the voltage source u _s ;

The improvement is that a wave trap unit is connected between the stray capacitance Cg and the half-bridge structure, and forms a second-order circuit with the stray capacitance Cg;

The method suppresses the current overshoot current caused by the stray capacitance Cg through the step response of the second-order circuit.

Wherein, the wave trap unit is composed of a resistor R and an inductance _L1 connected in parallel; the wave trap unit includes two situations when it works:

(1) When the voltage across the stray capacitance Cg does not change, the overshoot current flows through the inductance L ₁ in the wave trap unit, and the inductance L ₁ is smaller than the commutation reactor;

(2) When the voltage across the stray capacitance Cg changes, it is a step signal acting on the second-order circuit, the current passing through the inductor _L1 does not change suddenly, and the overshoot current flows through the resistor R connected in parallel with the inductor _L1 , The resistor R absorbs the energy generated by the overshoot current, and suppresses the overshoot of the turn-on current of the IGBT1 valve module and the IGBT2 valve module.

Wherein, the reactor-capacitor series branch is composed of reactor ESL ₁ , capacitor C ₁ , reactor ESL ₂ and capacitor C ₂ in series; the reactor-capacitor series branch is grounded;

The half-bridge structure is composed of an IGBT1 valve module and an IGBT2 valve module in series; the IGBT1 valve module and the IGBT2 valve module are both composed of an IGBT and a diode antiparallel to it.

Wherein, the stray capacitance Cg and the voltage source u _s are both grounded.

Compared with prior art, the beneficial effect that the present invention reaches is:

1. In the case of high voltage (high voltage is above ±10kV) and high frequency (above 1000Hz), the influence of stray capacitance on the overshoot of IGBT turn-on current is effectively suppressed, providing a reliable operation for high voltage IGBT series voltage source converter a certain guarantee.

2. The realization of the method only needs a parallel connection of a resistor and an inductor, and the structure is simple, the price is low, and it is easy to realize.

3. This method has a limiting effect on the overshoot current generated by stray capacitance, and will not affect the normal operation of the circuit.

Description of drawings

Fig. 1 is the implementation structure diagram of the current overshoot limiting method of the high-voltage IGBT series voltage source converter provided by the present invention

Fig. 2 is a change waveform diagram of the IGBT valve opening current overshoot before and after installing the wave trap provided by the present invention.

Detailed ways

The specific implementation manners of the present invention will be further described in detail below in conjunction with the accompanying drawings.

The implementation structure diagram of the high-voltage IGBT series voltage source converter current overshoot limiting method provided by the present invention is shown in Figure 1, which is an IGBT series voltage source converter suppression system for power systems with voltage levels above ±10kV ; Including: reactor-capacitor series branch, half-bridge structure, stray capacitance Cg, inductance L and voltage source u _s ;

The reactor-capacitor series branch is connected in parallel with the half-bridge structure; the stray capacitance Cg is connected in parallel with the voltage source u _s ; the inductance L is connected between the stray capacitance Cg and the voltage source u _s ;

A wave trap unit is connected between the stray capacitance Cg and the half-bridge structure, and forms a second-order circuit with the stray capacitance Cg. Cg is the total stray capacitance to ground of the commutation reactors ESL ₁ and ESL ₂ and the valve side wall bushing. The wave trap unit is composed of resistor R and inductor _L1 connected in parallel. The reactor-capacitor series branch is composed of reactor ESL ₁ , capacitor C ₁ , reactor ESL ₂ and capacitor C ₂ in series; the reactor-capacitor series branch is grounded; the half-bridge structure is composed of IGBT1 valve module and IGBT2 valve module in series ; Both the IGBT1 valve module and the IGBT2 valve module are composed of IGBTs and diodes connected in antiparallel with them. Both the stray capacitance Cg and the voltage source u _s are grounded.

Let the current direction shown in Figure 1 be the positive direction of the current Ic. When the voltage across the stray capacitance Cg changes from negative to positive, the current passing through the stray capacitance Cg is as shown in the figure, and its magnitude is C*du/dt. For the high-voltage IGBT series voltage source converter, since the DC side voltage is high and its operating frequency is high, the current will be very large. If no limiting measures are taken, this current will completely act on the IGBT valve group of the upper bridge arm. When the DC side voltage increases to a certain level, the current will exceed the tolerance of the IGBT valve, seriously affecting the normal operation of the converter.

Similarly, when the voltage at both ends of the stray capacitance Cg changes from positive to negative, a large current completely acts on the IGBT2 valve module of the lower bridge arm, which can also have a serious impact on the normal operation of the converter.

This current will have a serious impact on both the upper and lower bridge arms. At the same time, in order to reduce the cost, when the damper Damper in Figure 1 is installed, it forms a second-order circuit with the stray capacitance Cg. When the wave trap unit works, it is divided into the following situations:

(1) When the voltage across the stray capacitance Cg does not change, the current basically passes through the inductance L ₁ in it, and the inductance L ₁ is much smaller than the commutation reactor, which basically has no effect on the normal operation of the circuit.

(2) When the voltage across the stray capacitance Cg changes, it is equivalent to a step signal acting on the second-order circuit. Since the current passing through the inductor will not change abruptly, most of the current will pass through the capacitor connected in parallel with the inductor. Resistance, the resistance will consume this part of energy, thereby reducing its impact on the overshoot of the IGBT valve module's turn-on current, thereby preventing the current overshoot from exceeding the tolerance of the IGBT valve module due to the high DC side voltage, and the device Burn out, seriously affect the normal work of the converter. At the same time, due to the clamping effect of the anti-parallel diode, the voltage at both ends of the wave stopper will not affect the turn-off voltage stress of the IGBT valve module. Therefore, this measure can provide an effective guarantee for the reliable operation of the IGBT. Before and after installing the wave trap unit, the overshoot change of the turn-on current of the IGBT valve is shown in Figure 2.

Example

The circuit current simulation results when the resistance R in the wave trap unit is 3kΩ and the inductance _L1 is 6mH are shown in the table below:

Table 1 Current comparison simulation results of various circuit forms

circuit type IGBT turn-on current maximum Current glitch deviation value in valve side line No stray capacitance 254.9A 0A With stray capacitance, no trap 303.0A 61.4A If there is stray capacitance, add a wave trap 256.1A 4.0A

The present invention provides a novel limiting method for suppressing the turn-on current overshoot of the IGBT series voltage source converter, which effectively suppresses the current overshoot caused by stray capacitance by using the principle of the step response of the second-order circuit. It provides a reliable guarantee for the operation of the IGBT series voltage source converter.

Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to the above embodiments, those of ordinary skill in the art should understand that: the present invention can still be Any modification or equivalent replacement that does not depart from the spirit and scope of the present invention shall be covered by the scope of the claims of the present invention.

Claims (4)

1. an IGBT series-type voltage source converter is opened current over pulse inhibition method, and the system that described method is used is that IGBT series-type voltage source converter suppresses system, is used for ± electric power system of 10kV above; Comprise: reactor-capacitances in series branch road, half-bridge structure, stray capacitance Cg, inductance L and voltage source u _s

Described reactor-capacitances in series branch road is in parallel with half-bridge structure; Described stray capacitance Cg and voltage source u _sIn parallel; Described inductance L is connected to stray capacitance Cg and voltage source u _sBetween;

It is characterized in that, access trap unit forms second-order circuit with described stray capacitance Cg between described stray capacitance Cg and half-bridge structure;

Described method is by the step response of described second-order circuit, and the current over pulse electric current that stray capacitance Cg is caused suppresses.

2. the current over pulse inhibition method of opening as claimed in claim 1 is characterized in that, described trap unit is by resistance R and inductance L ₁Compose in parallel; Comprise two kinds of situations during described trap cell operation:

(1) when stray capacitance Cg both end voltage does not change, the overshoot current inductance L in the trap unit of flowing through ₁, described inductance L ₁Less than commutating reactor, i.e. inductance L ₁In 5% of commutating reactor inductance value, can the normal operation of circuit not exerted an influence;

(2) when stray capacitance Cg both end voltage changes, be step signal effect and second-order circuit, pass through inductance L ₁Electric current do not undergo mutation, overshoot current is flowed through and inductance L ₁Resistance R in parallel, resistance R absorbs the energy that overshoot current produces, and suppresses the current over pulse of opening to IGBT1 valve module and IGBT2 valve module.

3. the current over pulse inhibition method of opening as claimed in claim 1 is characterized in that, described reactor-capacitances in series is propped up route reactor ESL ₁, capacitor C ₁, reactor ESL ₂And capacitor C ₂Be composed in series successively; Reactor-capacitances in series grounding;

Described half-bridge structure is composed in series by IGBT1 valve module and IGBT2 valve module; Described IGBT1 valve module and IGBT2 valve module form by IGBT and diode antiparallel with it.

4. the current over pulse inhibition method of opening as claimed in claim 1 is characterized in that, described stray capacitance Cg and voltage source u _sEqual ground connection.

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