CN105140906A - Modular multilever converter (MMC) module topological structure applicable for flexible direct current transmission - Google Patents

Abstract

The invention provides a module topology which is applied to a modular multilever converter (MMC) type flexible direct current transmission system and has improved power density. The module topology comprises four insulated gate bipolar translators (IGBTs) VT1, VT2, VT3 and VT4, wherein the four IGBTs are respectively and reversely connected in parallel with diodes VD1, VD2, VD3 and VD4; a direct-current capacitor C is input or removed by controlling the switch-on or switch-off of the two IGBTs VT1 and VT2 in a first H half-bridge structure so as to generate a required alternating-current voltage; and an extra LC circuit is controlled by the two IGBTs VT3 and VT4 in a second H half-bridge structure to absorb a fundamental frequency on the direct-current capacitor and the frequency fluctuation of a second harmonic frequency, so that the frequency fluctuation is reduced, the capacitance and the volume of the direct-current capacitor are reduced. The capacitance of the direct-current capacitor can be reduced through the introduction of an auxiliary circuit, thus, the module volume is reduced, and the power density is improved.

Description

A kind of MMC module topology structure being applied to flexible DC power transmission

[technical field]

The present invention relates to flexible power transmission and distribution technical field, be specifically related to a kind of MMC module topology structure being applied to flexible DC power transmission.

[background technology]

Compared with traditional electrical Source Con-verters, modularization multi-level converter (ModularMultileverConverter, MMC) there is favorable expandability, harmonic wave is little, switching frequency is low, the advantages such as requirement is few are unanimously triggered to device, be particularly useful for direct current transportation application scenario.

For single-phase brachium pontis, direct current, fundamental current and fundamental voltage produce the power fluctuation of a fundamental frequency and two frequencys multiplication, the DC capacitor that this power fluctuation is embodied in module can cause the voltage of DC capacitor to have fundamental frequency and a small amount of two double-frequency fluctuation, therefore need larger capacitance to tackle the fluctuation of this fundamental frequency voltages when choosing electric capacity, cause capacitor's capacity larger, therefore volume is comparatively large, cost is higher.Therefore, a kind of novel topological structure is needed badly to solve the problems of the technologies described above.

[summary of the invention]

The object of the present invention is to provide a kind of MMC module topology structure being applied to flexible DC power transmission, reduced the capacitance of DC capacitor by the introducing of auxiliary circuit, thus reduce module volume, improve power density.

For achieving the above object, the present invention adopts following technical scheme:

A kind of MMC module topology structure being applied to flexible DC power transmission, comprise 4 IGBTVT1, VT2, VT3 and VT4,4 IGBT respectively inverse parallel have diode VD1, VD2, VD3 and VD4, wherein IGBTVT1, VT2 form a H half-bridge structure, IGBTVT3, VT4 form the 2nd H half-bridge structure, and the 2nd H half-bridge structure parallel connection direct electric capacity C, LC loop is connected between the emitter of two IGBTVT3, VT4 in the 2nd H half-bridge; Drop into and excise DC capacitor C by controlling turning on and off of two IGBTVT1, VT2 in a H half-bridge structure, thus the alternating voltage required for producing; The power fluctuation that additional LC loop absorbs fundamental frequency on DC capacitor and two frequencys multiplication is controlled by two IGBTVT3, VT4 in the 2nd H half-bridge structure.

Further, the collector electrode of described IGBTVT1 is connected with the negative pole of diode VD1, the emitter of IGBTVT1 is connected with the positive pole of IGBTVD1, the emitter of IGBTVT1 is connected with the collector electrode of IGBTVT2, the positive pole of diode VD2 is connected with the emitter of IGBTVT2, and the negative pole of diode VD2 is connected with the collector electrode of IGBTVT2 formation the one H half-bridge structure; The collector electrode of described IGBTVT3 is connected with the negative pole of diode VD3, the emitter of IGBTVT3 is connected with the positive pole of diode VD3, the emitter of IGBTVT3 is connected with the collector electrode of IGBTVT4, the collector electrode of IGBTVT4 is connected with the negative pole of diode VD4, and the emitter of IGBTVT4 is connected with the positive pole of diode VD4 formation the 2nd H half-bridge structure; LC loop is connected between the emitter of IGBTVT3 and the emitter of IGBTVT4, and DC capacitor C is connected between the collector electrode of IGBTVT3 and the emitter of IGBTVT4, and the grid of IGBTVT1, VT2, VT3, VT4 connects drive singal.

Further, described LC loop is made up of inductance L a and electric capacity Ca.

The new topological structure that the present invention proposes comprises 4 IGBT and IGBT anti-paralleled diodes, wherein IGBTVT1, VT2 form a H half-bridge structure, IGBTVT3, VT4 form the 2nd H half-bridge structure, and the 2nd H half-bridge structure parallel connection direct electric capacity C, LC loop is connected between the emitter of two IGBTVT3, VT4 in the 2nd H half-bridge; Drop into by turning on and off of control VT1 and VT2 and excise electric capacity, thus the alternating voltage required for producing, VT3 and VT4 is used for controlling additional LC loop to absorb the power fluctuation of fundamental frequency on DC capacitor and two frequencys multiplication, thus reduction power fluctuation, reduce capacitance and the volume of DC capacitor, reduced the capacitance of DC capacitor by the introducing of auxiliary circuit, thus reduce module volume, improve power density.

[accompanying drawing explanation]

The topological diagram that Fig. 1 carries for the present invention;

Fig. 2 is the application schematic diagram of new topology in MMC type flexible direct current power transmission system;

The schematic diagram of the control strategy 1 of Fig. 3 auxiliary circuit;

Fig. 4 is the voltage waveform view of auxiliary capacitor;

Fig. 5 is the schematic diagram of the control strategy 2 of auxiliary circuit;

Fig. 6 is the schematic diagram that after adopting new topology, voltage fluctuation of capacitor reduces;

[embodiment]

Below in conjunction with the accompanying drawing in the present invention, carry out clear, complete description to the technical scheme in the present invention, obviously, described embodiment is a part of embodiment of the present invention, instead of whole embodiments.Based on the embodiment in the present invention, the every other embodiment that those of ordinary skill in the art obtain under the prerequisite not making creative work, all belongs to the scope of protection of the invention.

Below in conjunction with Fig. 1,2,3,4, principle of the present invention is described in detail.

See Fig. 1, new topography module of carrying comprises: 4 IGBT (InsulatedGateBipolarTransistor guides insulated gate bipolar transistor): VT1, VT2, VT3, VT4,2 electric capacity: C and Ca, and 4 anti-paralleled diode: VD1, VD2, VD3, VD4, wherein VT1 and VT2 and anti-paralleled diode VD1 and VD2 that comprise is main switching device, the input of primary responsibility module capacitance and excision thus voltage needed for producing, be called main switching device below.VT3 and VT4 and anti-paralleled diode VD3 and VD4 comprised is auxiliary switch device, and primary responsibility absorbs the power of fundamental frequency and two frequencys multiplication, is called auxiliary switch device below.

Concrete connected mode is: the collector electrode of VT1 is connected with the negative pole of diode VD1, and the emitter of VT1 is connected with the positive pole of VD1.The emitter of VT1 is connected with the collector electrode of VT2, and the positive pole of VD2 is connected with the emitter of VT2, and the negative pole of VD2 is connected with the collector electrode of VT2.The collector electrode of VT3 is connected with the negative pole of VD3, and the emitter of VT3 is connected with the positive pole of VD3.The emitter of VT3 is connected with the collector electrode of VT4, and the collector electrode of VT4 is connected with the negative pole of VD4, and the emitter of VT4 is connected with the positive pole of VD4.LC loop is connected between the emitter of VT3 and the emitter of VT4.Described LC loop is made up of inductance L a and electric capacity Ca.DC capacitor C is connected between the collector electrode of VT3 and the emitter of VT4.The grid of VT1, VT2, VT3, VT4 connects drive singal.

In 4 full-controlled switch devices, wherein 2 form half-bridge structures, are main switching device, control this main switching device turn on and off control DC bus capacitor and whether access major loop, to meet the control objectives of flexible direct current power transmission system; 2, as auxiliary switch device, turn on and off the power that control LC loop absorbs fundamental frequency and two frequencys multiplication, to reduce the voltage fluctuation on DC capacitor by it.Thus reduce the capacitance of DC capacitor, reach the object improving power density.The control objectives of auxiliary circuit absorbs fundamental frequency on DC capacitor and the fluctuation of two double frequency power, can different control methods be taked, such as, be the voltage close loop of control objectives with DC capacitor voltage, with the auxiliary capacitor voltage opened loop control that is control objectives and the power closed-loop control etc. that is control objectives with fundamental frequency and two double frequency power.

Fig. 2 is the carried application of new topography module in MMC type flexible direct current power transmission system.For the single ended system of flexible DC power transmission, Ag, Bg, Cg incoming transport three-phase system.Flexible direct current power transmission system is often mutually containing two brachium pontis, upper brachium pontis and lower brachium pontis.Each brachium pontis contains n series connection MMC module.During normal work, main switching device controls the input of main capacitor and excision by turning on and off of upper and lower switching tube, realizes control objectives.When VT1 closes, DC capacitor is connected into circuit, VT2 disconnect time, DC capacitor by short circuit, no longer place in circuit.During normal work, direct current and alternating current is flow through in the brachium pontis of above system, for single-phase brachium pontis, direct current, fundamental current and fundamental voltage produce the power fluctuation of a fundamental frequency and two frequencys multiplication, and the DC capacitor that this power fluctuation is embodied in module can cause the voltage of DC capacitor to have fundamental frequency and a small amount of two double-frequency fluctuation.Shown in formula specific as follows, Ppa represents the instantaneous power of brachium pontis in A phase, and Pna represents the instantaneous power of brachium pontis under A phase, can find out, comprise constant, base band power and two double frequency power below in two power.Consider that the impact of circulation can make in capacitance voltage containing fundamental frequency and two a small amount of double frequency voltage simultaneously.

$P_{pa}\left(t\right)=\frac{U_{dc}{I}_{dc}}{6}\[1-mk+(m-k){\mathrm{sinw}}_{0}t+mkcos\left(2w_{0}t\right)\]$

$P_{na}\left(t\right)=\frac{U_{dc}{I}_{dc}}{6}\[1-mk+(k-m){\mathrm{sinw}}_{0}t+mkcos\left(2w_{0}t\right)\]$

The discharge and recharge of the electric capacity in IGBTVT3 and VT4 control LC loop absorbs the power fluctuation of fundamental frequency and two frequencys multiplication, thus reduces the fluctuation of capacitance voltage.

The control mode of auxiliary circuit can have a variety of, and Fig. 3 gives a kind of method of simple closed-loop control, by detecting the voltage of DC capacitor, after and instruction value compares, controlled by PI, final comparison with triangular carrier produces PWM ripple, is given to the grid of VT3 and VT4.Possible method comprises but not only contains, and adopts the method for power detection to obtain fundamental frequency and two double frequency power, by this fundamental frequency and two double frequency power as command value, controls the power on auxiliary capacitor.Simultaneously also can by the voltage needing the power meter absorbed to calculate auxiliary capacitor, adopt the control mode of auxiliary capacitor voltage open loop, as shown in Figure 4 and Figure 5, Fig. 4 is the voltage waveform of auxiliary capacitor, and Fig. 5 is control block diagram.According to the voltage waveform shown in Fig. 4, the energy that auxiliary capacitor absorbs is for shown in following formula, and as can be seen from formula, auxiliary capacitor can compensate the power fluctuation of fundamental frequency and the power fluctuation of two frequencys multiplication.Optimum auxiliary capacitor value and the voltage value of auxiliary capacitor can be determined by the base band power in contrast brachium pontis horse-power formula and two double frequency power simultaneously.

$p_{c\_aux}=U_0{C}_{aux}{U}_1\cos wt+\frac{1}{2}{U_1}^2{C}_{aux}sin2wt$

Fig. 6 is for after employing auxiliary circuit, and the change of the fluctuation of voltage on DC capacitor contrasts.As can be seen from the figure, absorbed the power fluctuation of fundamental frequency and two frequencys multiplication by auxiliary circuit control LC loop, the voltage fluctuation on DC capacitor significantly decreases.The minimizing of voltage fluctuation can reduce the requirement to capacitance.The minimizing of capacitance all has greatly improved for the minimizing of cost and electric capacity volume.

Be understandable that, the illustrative embodiments that above execution mode is only used to principle of the present invention is described and adopts, but the present invention is not limited thereto.For those skilled in the art, without departing from the spirit and substance in the present invention, can make various modification and improvement, these modification and improvement are also considered as protection scope of the present invention.

Claims (3)

1. one kind is applied to the MMC module topology structure of flexible DC power transmission, it is characterized in that: comprise 4 IGBTVT1, VT2, VT3 and VT4,4 IGBT respectively inverse parallel have diode VD1, VD2, VD3 and VD4, wherein IGBTVT1, VT2 form a H half-bridge structure, IGBTVT3, VT4 form the 2nd H half-bridge structure, and the 2nd H half-bridge structure parallel connection direct electric capacity C, LC loop is connected between the emitter of two IGBTVT3, VT4 in the 2nd H half-bridge; Drop into and excise DC capacitor C by controlling turning on and off of two IGBTVT1, VT2 in a H half-bridge structure, thus the alternating voltage required for producing; The power fluctuation that additional LC loop absorbs fundamental frequency on DC capacitor and two frequencys multiplication is controlled by two IGBTVT3, VT4 in the 2nd H half-bridge structure.

2. the MMC module topology structure being applied to flexible DC power transmission according to claim 1, it is characterized in that: the collector electrode of described IGBTVT1 is connected with the negative pole of diode VD1, the emitter of IGBTVT1 is connected with the positive pole of IGBTVD1, the emitter of IGBTVT1 is connected with the collector electrode of IGBTVT2, the positive pole of diode VD2 is connected with the emitter of IGBTVT2, and the negative pole of diode VD2 is connected with the collector electrode of IGBTVT2 formation the one H half-bridge structure;

The collector electrode of described IGBTVT3 is connected with the negative pole of diode VD3, the emitter of IGBTVT3 is connected with the positive pole of diode VD3, the emitter of IGBTVT3 is connected with the collector electrode of IGBTVT4, the collector electrode of IGBTVT4 is connected with the negative pole of diode VD4, and the emitter of IGBTVT4 is connected with the positive pole of diode VD4 formation the 2nd H half-bridge structure;

LC loop is connected between the emitter of IGBTVT3 and the emitter of IGBTVT4, and DC capacitor C is connected between the collector electrode of IGBTVT3 and the emitter of IGBTVT4, and the grid of IGBTVT1, VT2, VT3, VT4 connects drive singal.

3. the MMC module topology structure being applied to flexible DC power transmission according to claim 1 and 2, is characterized in that: described LC loop is made up of inductance L a and electric capacity Ca.