CN104218808A - Output voltage positive and negative polarity inversion method based on modular multilevel converter - Google Patents

Abstract

The invention provides an output voltage positive and negative polarity inversion method based on a modular multilevel converter. The method includes 1, constructing a modular multilevel converter module; 2, inverting the output voltage positive and negative polarities by adjusting the bridge voltage of the modular multilevel converter module; modulating the upper bridge voltage uu and lower bridge voltage ul of each phase, according to a bridge voltage wave image, into sine wave voltage symmetrical about a horizontal line U = UN/2 vertically, and allowing that the LCC terminal output voltage ULCC = UN; modulating the upper bridge voltage uiu and lower bridge voltage uil of each phase into sine wave voltage symmetrical about a horizontal line U = -UN/2 vertically, and allowing that the LCC terminal output voltage ULCC = -UN. Compared with the prior art, the method has the advantages that the operation requirements of LCC-HVDC and VSC-HVDC interface converters are met, and LCC-HVDC and VSC-HVDC interconnection implementation is benefited.

Description

Based on the output voltage positive-negative polarity inverting method of Modular multilevel converter

Technical field

The present invention relates to a kind of output voltage positive-negative polarity inverting method, be specifically related to a kind of output voltage positive-negative polarity inverting method based on Modular multilevel converter.

Background technology

By point-to-point HVDC (High Voltage Direct Current) transmission line being expanded to multiterminal and setting up direct current transportation electrical network in direct current transportation, it is the key technology realizing extensive wide area direct current transmission and distribution; Identical with conventional AC transmission line, direct current network is also adopt DC-DC converter to realize the interconnected of different high-voltage dc transmission electric network.

High voltage direct current transmission mainly comprises LCC-HVDC and VSC-HVDC; LCC-HVDC employing thyristor device Phase-controlled Converters LCC polarity of voltage when trend is reversed reverses, the sense of current is constant, when voltage converter trend in VSC-HVDC is reversed, polarity of voltage is constant, electric current is reverse, VSC-HVDC and LCC-HVDC can not directly be connected, thus have impact on the construction that high-voltage dc transmission electrical network falls.

Therefore need to provide a kind of interface DC-DC converter that simultaneously can meet LCC-HVDC and VSC-HVDC trend reversion demand; Namely, during the reversion of VSC-HVDC trend, the polarity of voltage of interface DC-DC converter VSC port is constant; During the reversion of VSC-HVDC trend, the voltage positive-negative polarity of interface DC-DC converter LCC port reverses.

Summary of the invention

In order to meet the needs of prior art, the invention provides a kind of output voltage positive-negative polarity inverting method based on Modular multilevel converter, described method comprises:

Step 1: build Modular multilevel converter model;

Step 2: by adjusting described Modular multilevel converter model bridge arm voltage, realizes the reversion of output voltage positive-negative polarity.

Preferably, described Modular multilevel converter model comprises the VSC side converter and LCC side converter that are connected by isolating transformer; Described VSC side converter is connected with the voltage source converter of high-voltage dc transmission electrical network by VSC port; Described LCC side converter is connected with the line commutation converter of high-voltage dc transmission electrical network by LCC port;

Preferably, adjust described bridge arm voltage in described step 2 to comprise:

The upper bridge arm voltage u of every phase in step 2-1: Real-time Collection LCC side converter _iuwith lower bridge arm voltage u _il, and obtain bridge arm voltage oscillogram;

Step 2-2: according to the upper bridge arm voltage u of described bridge arm voltage oscillogram by described every phase _iuwith lower bridge arm voltage u _ilbe modulated to respectively about horizontal linear U=U _n/ 2 laterally zygomorphic sine voltages, then the output voltage U of LCC port _lCC=U _n;

Step 2-3: according to the upper bridge arm voltage u of described bridge arm voltage oscillogram by described every phase _iuwith lower bridge arm voltage u _ilbe modulated to respectively about horizontal linear U=-U _n/ 2 laterally zygomorphic sine voltages, then the output voltage U of LCC port _lCC=-U _n;

Preferably, the output voltage U of described LCC port _lCC=u _iu+ u _il; The AC phase voltage of described LCC side converter $u_i=\frac{u_{\mathrm{il}}-u_{\mathrm{iu}}}{2};$

Preferably, the input number upper bridge arm voltage of every phase and lower bridge arm voltage being modulated to every phase brachium pontis Neutron module during symmetrical sine voltage is described u _ifor bridge arm voltage value, described u _Δfor the magnitude of voltage of submodule each in brachium pontis;

Preferably, the direct voltage positive-negative polarity conversion of described LCC port comprises limit inversion mode and step-down inversion mode;

Described limit inversion mode is directly control LCC port DC voltage polarity reversion;

Described step-down inversion mode is progressively be reduced to zero mode being progressively oppositely elevated to negative rated value again by control LCC port direct voltage to realize the reversion of LCC port DC voltage polarity.

Compared with immediate prior art, excellent effect of the present invention is:

1, in technical solution of the present invention, the continuous adjustment of LCC port voltage and acute reversion can be realized by modulation bridge arm voltage control LCC port output voltage polarity;

2, in technical solution of the present invention, adopt limit inversion mode, response speed, can reverse by power direction fast, the emergency DC power support that LLC is got access to grid can be realized;

3, in technical solution of the present invention, adopt step-down inversion mode, the rush of current of device and circuit in circuit can be reduced by level and smooth regulation voltage continuously, ensure system reliability service;

4, a kind of output voltage positive-negative polarity inverting method based on Modular multilevel converter provided by the invention, in polarity of voltage Umklapp process, the former secondary voltage of isolating transformer and VSC port voltage unaffected; Meet the operation demand of LCC-HVDC and VSC-HVDC docking port converter simultaneously, contribute to LCC-HVDC and VSC-HVDC and realize interconnected.

Accompanying drawing explanation

Below in conjunction with accompanying drawing, the present invention is further described.

Fig. 1 is: the interface DC-DC converter circuit structure chart of LCC-HVDC and VSC-HVDC in the embodiment of the present invention;

Fig. 2 is: the equivalent circuit diagram of the side interface of LCC shown in Fig. 1 DC-DC converter;

Fig. 3 is: the A phase voltage waveform figure of the side interface of LCC shown in Fig. 1 DC-DC converter;

Fig. 4 is: the DC voltage waveform of limit inversion mode downconverter LCC port when polarity of voltage reverses in the embodiment of the present invention;

Fig. 5 is: the DC voltage waveform of step-down inversion mode downconverter LCC port when polarity of voltage reverses in the embodiment of the present invention.

Embodiment

Be described below in detail embodiments of the invention, the example of described embodiment is shown in the drawings, and wherein same or similar label represents same or similar element or has element that is identical or similar functions from start to finish.Be exemplary below by the embodiment be described with reference to the drawings, be intended to for explaining the present invention, and can not limitation of the present invention be interpreted as.

A kind of output voltage positive-negative polarity inverting method based on Modular multilevel converter provided by the invention, carries out bridge arm voltage modulation by building Modular multilevel converter model, thus realizes the output voltage positive-negative polarity reversion of converter; This modular multi-level converter model as shown in Figure 1, comprises the VSC side converter and LCC side converter that are connected by isolating transformer; VSC side converter is connected with the voltage source converter of high-voltage dc transmission electrical network by VSC port; LCC side converter is connected with the line commutation converter of high-voltage dc transmission electrical network by LCC port;

In the present embodiment, the rated voltage of VSC port is the rated voltage of 800V, LCC port is 900V, and converter capacity is 30kW; VSC side converter and LCC side converter all adopt five level topological structures, and the voltage of each submodule is 225V; The rated power of isolating transformer is 5kW.

Fig. 2 shows the equivalent circuit diagram of Modular multilevel converter, U _lCCfor the direct voltage of LCC port, u _aufor bridge arm voltage in the A phase of LCC side converter, u _alfor the lower bridge arm voltage of A phase; O is voltage reference points; Then:

The direct voltage U of LCC port _lCC=u _iu+ u _il(1);

A cross streams voltage $u_a=\frac{u_{\mathrm{al}}-u_{\mathrm{au}}}{2}---\left(2\right);$

Modulate A phase bridge arm voltage, voltage waveform as shown in Figure 3;

1.: upper bridge arm voltage and lower bridge arm voltage are modulated to respectively about horizontal linear U=U _n/ 2 laterally zygomorphic sine voltages, through type (1) obtains the output voltage U of LCC port _lCC=U _n, it is ideal sinusoidal voltage signal that through type (2) obtains A cross streams voltage;

2.: upper bridge arm voltage and lower bridge arm voltage are modulated to respectively about horizontal linear U=-U _n/ 2 laterally zygomorphic sine voltages, through type (1) obtains the output voltage U of LCC port _lCC=-U _n, through type (2) obtains A cross streams voltage and is similarly ideal sinusoidal voltage signal;

3.: the input number upper bridge arm voltage of every phase and lower bridge arm voltage being modulated to every phase brachium pontis Neutron module during symmetrical sine voltage is described u _ifor bridge arm voltage value, described u _Δfor the magnitude of voltage of submodule each in brachium pontis, y=[x] is bracket function;

By control A phase bridge arm voltage above-mentioned operating state 1. and 2. between change, the direct voltage positive-negative polarity conversion of LCC port can be realized, thus coordinate the polarity of voltage reversion caused during the reversion of LCC-HVDC network trend.

In the present embodiment, the direct voltage positive-negative polarity conversion of current transformer LCC port comprises limit inversion mode and step-down inversion mode;

The DC voltage waveform of limit inversion mode downconverter LCC port as shown in Figure 4;

Reversed by instruction control LCC port DC voltage polarity; As shown in the figure when 0.2s, the reversion of converter ACTIVE CONTROL LCC port direct voltage makes LCC-HVDC trend reverse; Be specially when 0.2s, voltage given is revised as negative value, by the u shown in Fig. 3 simultaneously when modulating _auand u _albe displaced downwardly to u ' _auwith u ' _allCC port direct voltage is reversed.

The DC voltage waveform of step-down inversion mode downconverter LCC port as shown in Figure 5;

Progressively be reduced to zero mode being progressively oppositely elevated to negative rated value again by control LCC port direct voltage and realize the reversion of LCC port DC voltage polarity, can smooth voltage sudden change time rush of current to circuit;

As shown in the figure when 0.2s, converter ACTIVE CONTROL LCC port direct voltage is progressively reduced to zero and is progressively oppositely elevated to negative rated value again; Be specially and voltage given is reduced to negative value according to staircase waveform, by the u shown in Fig. 3 simultaneously when modulating _auand u _alu ' is displaced downwardly to according to staircase waveform mode _auwith u ' _althe step-down of LCC port direct voltage is reversed.

Finally should be noted that: described embodiment is only some embodiments of the present application, instead of whole embodiments.Based on the embodiment in the application, those of ordinary skill in the art are not making the every other embodiment obtained under creative work prerequisite, all belong to the scope of the application's protection.

Claims (6)

1., based on an output voltage positive-negative polarity inverting method for Modular multilevel converter, it is characterized in that, described method comprises:

Step 1: build Modular multilevel converter model;

Step 2: by adjusting described Modular multilevel converter model bridge arm voltage, realizes the reversion of output voltage positive-negative polarity.

2. a kind of output voltage positive-negative polarity inverting method based on Modular multilevel converter as claimed in claim 1, is characterized in that, described Modular multilevel converter model comprises the VSC side converter and LCC side converter that are connected by isolating transformer; Described VSC side converter is connected with the voltage source converter of high-voltage dc transmission electrical network by VSC port; Described LCC side converter is connected with the line commutation converter of high-voltage dc transmission electrical network by LCC port.

3. a kind of output voltage positive-negative polarity inverting method based on Modular multilevel converter as claimed in claim 1, is characterized in that, adjust described bridge arm voltage and comprise in described step 2:

The upper bridge arm voltage u of every phase in step 2-1: Real-time Collection LCC side converter _iuwith lower bridge arm voltage u _il, and obtain bridge arm voltage oscillogram;

Step 2-2: according to the upper bridge arm voltage u of described bridge arm voltage oscillogram by described every phase _iuwith lower bridge arm voltage u _ilbe modulated to respectively about horizontal linear U=U _n/ 2 laterally zygomorphic sine voltages, then the output voltage U of LCC port _lCC=U _n;

Step 2-3: according to the upper bridge arm voltage u of described bridge arm voltage oscillogram by described every phase _iuwith lower bridge arm voltage u _ilbe modulated to respectively about horizontal linear U=-U _n/ 2 laterally zygomorphic sine voltages, then the output voltage U of LCC port _lCC=-U _n.

4. a kind of output voltage positive-negative polarity inverting method based on Modular multilevel converter as claimed in claim 2, is characterized in that, the output voltage U of described LCC port _lCC=u _iu+ u _il; The AC phase voltage of described LCC side converter $u_i=\frac{u_{\mathrm{il}}-u_{\mathrm{iu}}}{2}.$

5. a kind of output voltage positive-negative polarity inverting method based on Modular multilevel converter as claimed in claim 3, it is characterized in that, the input number upper bridge arm voltage of every phase and lower bridge arm voltage being modulated to every phase brachium pontis Neutron module during symmetrical sine voltage is described u _ifor bridge arm voltage value, described u _Δfor the magnitude of voltage of submodule each in brachium pontis.

6. a kind of output voltage positive-negative polarity inverting method based on Modular multilevel converter as claimed in claim 3, is characterized in that, the direct voltage positive-negative polarity conversion of described LCC port comprises limit inversion mode and step-down inversion mode;

Described limit inversion mode is directly control LCC port DC voltage polarity reversion;

Described step-down inversion mode is progressively be reduced to zero mode being progressively oppositely elevated to negative rated value again by control LCC port direct voltage to realize the reversion of LCC port DC voltage polarity.