CN104393777A - Half-bridge MMC (Modular Multilevel Converter) sub-module voltage control method - Google Patents

Abstract

A half-bridge MMC (Modular Multilevel Converter) sub-module voltage control method comprises step A, presetting a half-bridge MMC direct current voltage given value the formula and a reactive power given value the formula; step B, measuring the direct current voltage udc and every phase alternating current voltage ua and current ia, obtaining a voltage amplitude value us and the phase position from the ua and performing the Park transformation on the ia and the phase position to obtain idg and iqg; step C, setting a weight coefficient aij, adding a formula value and the formula together and enabling the result to be minus the udc, enabling the result to be minus the idg through the output after the outer ring proportional integral link and adding the difference value and the us/n together after the inner ring proportional integral link to obtain udgi, wherein udci and udcj are the direct current capacitance voltages of an i<th> sub-module and a j<th> sub-module in n sub-modules respectively; step D, performing comparison on the difference of the measured reactive power and the formula and the iqg through the output after the outer ring proportional integral link and obtaining uqgi through the difference value after the inner ring proportional integral link; Step E, performing the Park inverse transformation on the udgi and the uqji to obtain the control quantity uagi of the i<th> sub-module and controlling a switch of the i<th> sub-module according to the control quantity.

Description

Half-bridge module multi-level converter submodule voltage control method

Technical field

The present invention relates to power electronic equipment field, particularly the control technology of each device for power switching in a kind of power electronic equipment.

Background technology

Along with developing rapidly of power electronic technology, the withstand voltage and power grade of single device for power switching is obtained for and significantly improves, and the application of various high-power switch device is also increasingly extensive.But in many high-power applications, two traditional level, three-level voltage source code converter topology cannot meet the requirement of more high voltage and power grade.Under the prerequisite that device for power switching does not have essence to break through, multi-level converter solves the preferably selection of high-power conversion beyond doubt.In order to improve its performance while lifting power electronic equipment capacity, people are studied the circuit topology of high-power multi-level converter and control technology.

Modular multilevel converter (Modular Multilevel Converter, MMC), owing to having public DC bus, MMC can realize running under inversion or rectification operating mode, and application is very wide.MMC submodule topological structure has multiple, and wherein modal is full bridge unit and half-bridge cells parallel connection direct capacitance structure.When group module topology structure is half-bridge cells parallel connection direct capacitance structure, it is 0 and positive level that each submodule exports.Half-bridge MMC is often made up of upper and lower 2 brachium pontis, and every brachium pontis is containing n submodule, and namely often by 2n sub-module composition, it is 2n-1 level that MMC exports phase voltage.The submodule of each brachium pontis can control independently, thus each brachium pontis can be equivalent to a controllable voltage source, by regulating the rate of change of each bridge arm voltage, just can obtain required sinusoidal voltage at output, waveform is better, submodule quantity is more, and output voltage waveforms is better, but cost also increases.

Because each brachium pontis submodule of phase every in half-bridge MMC is numerous, and each submodule switch motion may be inconsistent, cause submodule DC capacitor voltage unbalanced, half-bridge MMC output voltage waveforms amount of distortion is caused to increase like this, affect the quality of half-bridge MMC output voltage waveforms, the words that deviation is serious will damage submodule.

In addition, during electrical network generation unbalanced fault, more cause DC capacitor voltage to distort, affect the safety operation level of whole device.

Summary of the invention

Given this, the object of the invention is to the problem avoiding the half-bridge MMC output voltage waveforms amount of distortion caused when each submodule switch motion is inconsistent in half-bridge MMC to increase, improve the quality of half-bridge MMC output voltage waveforms.

In order to realize this object, the technical scheme that the present invention takes is as follows.

A kind of half-bridge module multi-level converter submodule voltage control method, comprises the following steps: A. predetermined DC voltage set-point with reactive power set-point b. direct voltage u is measured _dcwith every cross streams voltage u _awith alternating current i _a, from described u _amiddle acquisition voltage magnitude u _sand phase place; To i _acarry out Park Transformation with phase place and obtain i _dgand i _qg; C., weight coefficient a is set _ij, by Σ a _ij(u _dci-u _dcj) value with u is deducted after addition _dc, the output then after outer shroud proportional integral link deducts i _dg, its difference after inner ring proportional integral link with u _s/ n is added and obtains u _dgi, wherein u _dciand u _dcjto be respectively in n submodule the DC capacitor voltage of i-th and jth submodule; D. reactive power is measured, i is deducted with the output of difference after outer shroud proportional integral link of described reactive power _qg, its difference, through inner ring proportional integral link, obtains u _qgi; E. to u _dgiand u _qgicarry out the controlled quentity controlled variable u that Parker inverse transformation obtains the i-th submodule _agi, control two switches of described submodule.

Wherein, described weight coefficient a _ij=(u _dci-u _dcj)/Σ (u _dci-u _dcj).

Or, minimum for target with each submodule DC capacitor voltage capacity volume variance sum:

Σ _mina _ij(u _dci-u _dcj) ²，

Constraints is: $(u_{\mathrm{dci}}-u_{\mathrm{dcj}})\&le;{0.1u}_{\mathrm{dc}}^{*},$

u _a+u _b+u _c＝0，

Determine a that optimal value is corresponding _ijfor weight coefficient.

In addition, the parameter of described inner ring proportional integral link is: 1< proportionality coefficient <10,0.1< integral coefficient <1.

The parameter of described outer shroud proportional integral link is: 0.2< proportionality coefficient <1,0.01< integral coefficient <0.1.

On the other hand, when electrical network generation unbalanced fault, comprise further:

Carry out α β coordinate transform to the alternating voltage of every phase, obtain corresponding α β component, the FEEDBACK CONTROL of the control of passing ratio integral feedback and dual-integration, obtains the first group component; This component is multiplied with coefficient q simultaneously, obtains second component amount; Calculated the positive-negative sequence component of α β by this 2 group component, positive-negative sequence component is carried out to submodule and controls respectively;

Wherein q expression formula is as follows:

q＝Q ₀+Q _c2cos(2ωt)+Q _s2sin(2ωt)，

Q ₀for the fundamental reactive component of electrical network, Q _c2, Q _s2for idle quadratic component, ω is angular frequency.

By adopting half-bridge MMC submodule voltage control method of the present invention, each submodule switch motion can be made consistent, which thereby enhance the quality of half-bridge MMC output voltage waveforms.Meanwhile, the balance of half-bridge MMC submodule DC capacitor voltage, extends the useful life of submodule.Therefore, not only increase the performance of overall half-bridge MMC device, and improve the safety operation level of overall half-bridge MMC device.

On the other hand, by adopting half-bridge MMC submodule voltage control method of the present invention, when electrical network generation unbalanced fault, the distortion causing DC capacitor voltage can be avoided, and then improves the safety operation level of whole device.

Accompanying drawing explanation

Fig. 1 is the circuit diagram of embodiment of the present invention half-bridge MMC device.

Fig. 2 is the voltage-controlled schematic diagram of embodiment of the present invention half-bridge MMC submodule.

Fig. 3 is the voltage-controlled schematic diagram of another execution mode half-bridge of the present invention MMC submodule.

Fig. 4 is the output voltage waveform of the half-bridge MMC device of embodiment of the present invention.

Embodiment

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

The example embodiment that following discloses are detailed.But concrete structure disclosed herein and function detail are only the objects for describing example embodiment.

But should be appreciated that, the present invention is not limited to disclosed concrete example embodiment, but covers all modifications, equivalent and the alternative that fall within the scope of the disclosure.In the description to whole accompanying drawing, identical Reference numeral represents identical element.

Should be appreciated that, term "and/or" as used in this comprises one or morely relevant lists any of item and all combinations simultaneously.Should be appreciated that in addition, when parts or unit are called as " connection " or " coupling " to another parts or unit, it can be directly connected or coupled to miscellaneous part or unit, or also can there is intermediate member or unit.In addition, other words being used for describing relation between parts or unit should be understood according to identical mode (such as, " between " to " directly ", " adjacent " to " direct neighbor " etc.).

As shown in Figure 1, half-bridge MMC of the present invention, by 3 phase compositions, often comprises upper and lower 2 brachium pontis mutually, and each brachium pontis is made up of n submodule and a controller, and each submodule is made up of 2 half-bridges that control switching device and anti-paralleled diode are formed entirely; The DC bus positive pole of described submodule is connected with the positive pole of corresponding submodule DC capacitor, the DC bus negative pole of described submodule is connected with the negative pole of corresponding submodule DC capacitor, the output two two-phase series winding of described submodule, the overlying one end of the superiors' submodule of the upper brachium pontis of MMC is connected with MMC DC bus, below the orlop submodule of the upper brachium pontis of MMC, one end is connected with filter inductance, and this cross streams output of the other end and MMC of filter inductance is connected; The signal controlling end that the control end of described submodule is corresponding with controller is connected, and the ac voltage signal input that the ac output end of described MMC is corresponding with described controller is connected.

Therefore, half-bridge MMC submodule voltage control method of the present invention comprises the following steps:

A. predetermined DC voltage set-point with reactive power set-point described set-point is determined according to system requirements;

B. direct voltage u is measured _dcwith every cross streams voltage u _aand current i _a, from described u _amiddle acquisition voltage magnitude u _sand phase place; To i _acarry out Park Transformation with phase place and obtain i _dgand i _qg;

C., weight coefficient a is set _ij, described weight coefficient 0<a _ij<1, by Σ a _ij(u _dci-u _dcj) value with u is deducted after addition _dc, the output then after outer shroud proportional integral link deducts i _dg, its difference after inner ring proportional integral link with u _s/ n is added and obtains u _dgi, wherein u _dciand u _dcjto be respectively in n submodule the DC capacitor voltage of i-th and jth submodule;

D. reactive power is measured, i is deducted with the output of difference after outer shroud proportional integral link of described reactive power _qg, its difference, through inner ring proportional integral link, obtains u _qgi;

E. to u _dgiand u _qgicarry out the controlled quentity controlled variable u that Parker inverse transformation obtains the i-th submodule _agi, and control the switch of this submodule according to this.Specifically, each submodule is by 2 switch T _i1, T _i2composition, T _i1with T _i2switch controlling signal interlocks, T _i1conducting and Ti2 locking time, submodule export positive level, otherwise, export zero level; Therefore, 1 sub-module controls amount u _agi2 switches can be controlled.

By carrying out dynamic sensing to each submodule DC capacitor voltage difference, effectively inhibit the dynamic differential of submodule DC capacitor voltage.Therefore make each submodule switch motion consistent, which thereby enhance the quality of half-bridge MMC output voltage waveforms.

As one embodiment of the present of invention, determine that weight coefficient is a _ij=(u _dci-u _dcj)/Σ (u _dci-u _dcj), the difference of each submodule can be specialized like this, therefore further increase the quality of output voltage waveforms.

As an alternative embodiment of the invention, determine that the method for weight coefficient is:

Minimum for target with each submodule DC capacitor voltage capacity volume variance sum:

Σ _mina _ij(u _dci-u _dcj) ²，

Constraints is: $(u_{\mathrm{dci}}-u_{\mathrm{dcj}})\&le;{0.1u}_{\mathrm{dc}}^{*},$

u _a+u _b+u _c＝0，

Determine a that optimal value is corresponding _ijfor weight coefficient.

Determine that the method for optimal value can be conventional various optimization methods, those skilled in that art generally can know target determine after optimal way.

In this execution mode, take submodule DC capacitor voltage capacity volume variance sum minimum and be target, switching device can be made to operate in optimum state.

As an embodiment of the invention, the parameter of described inner ring proportional integral link is: 1< proportionality coefficient <10,0.1< integral coefficient <1; And the parameter of described outer shroud proportional integral link is: 0.2< proportionality coefficient <1,0.01< integral coefficient <0.1.

In addition, in order to when electrical network generation unbalanced fault, avoid the distortion causing DC capacitor voltage, and then improve the safety operation level of whole device, in another embodiment of the present invention, when electrical network generation unbalanced fault, comprise further:

Carry out α β coordinate transform to the alternating voltage of every phase, obtain corresponding α β component, the FEEDBACK CONTROL of the control of passing ratio integral feedback and dual-integration, obtains the first group component; This component is multiplied with coefficient q simultaneously, obtains second component amount; Calculated the positive-negative sequence component of α β by this 2 group component, positive-negative sequence component is carried out to submodule and controls respectively;

Wherein q expression formula is as follows:

q＝Q ₀+Q _c2cos(2ωt)+Q _s2sin(2ωt)

P ₀, Q ₀for being respectively fundamental active, the idle component of electrical network, Q _c2, Q _s2for idle quadratic component.Specifically be expressed as:

$Q_{c2}=\frac{{2P}_0}{(v_d^{+2}+v_q^{+2}-v_d^{-2}-v_q^{-2})}(v_q^{-}{v}_d^{+}-v_d^{-}{v}_q^{+})$

$Q_{s2}=\frac{-2P_0}{(v_d^{+2}+v_q^{+2}-v_d^{-2}-v_q^{-2})}(v_d^{+}{v}_d^{-}+v_q^{+}{v}_q^{-})$

Wherein with be respectively the positive-negative sequence component of d, q axle component of voltage.

By adopting half-bridge MMC submodule voltage control method of the present invention, each submodule switch motion can be made consistent, which thereby enhance the quality of half-bridge MMC output voltage waveforms.As shown in Figure 4, as can be seen from Figure 4, voltage waveform is mild, it is little to distort, the quality of power supply is high for the voltage waveform that half-bridge MMC device of the present invention exports.

It should be noted that; above-mentioned execution mode is only the present invention's preferably embodiment; can not limiting the scope of the invention be understood as, not depart under concept thereof of the present invention, all protection scope of the present invention is belonged to modification to any minor variations that the present invention does.

Claims (6)

1. a half-bridge module multi-level converter submodule voltage control method, comprises the following steps:

A. predetermined DC voltage set-point with reactive power set-point

B. direct voltage u is measured _dcwith every cross streams voltage u _awith alternating current i _a, from described u _amiddle acquisition voltage magnitude u _sand phase place; To i _acarry out Park Transformation with phase place and obtain i _dgand i _qg;

C., weight coefficient a is set _ij, by Σ a _ij(u _dci-u _dcj) value with u is deducted after addition _dc, the output then after outer shroud proportional integral link deducts i _dg, its difference after inner ring proportional integral link with u _s/ n is added and obtains u _dgi, wherein u _dciand u _dcjto be respectively in n submodule the DC capacitor voltage of i-th and jth submodule;

D. reactive power is measured, i is deducted with the output of difference after outer shroud proportional integral link of described reactive power _qg, its difference, through inner ring proportional integral link, obtains u _qgi;

E. to u _dgiand u _qgicarry out the controlled quentity controlled variable u that Parker inverse transformation obtains the i-th submodule _agi, control two switches of described submodule.

2. the half-bridge module multi-level converter submodule voltage control method described in claim 1, is characterized in that, described weight coefficient a _ij=(u _dci-u _dcj)/Σ (u _dci-u _dcj).

3. the half-bridge module multi-level converter submodule voltage control method described in claim 1, is characterized in that, minimum for target with each submodule DC capacitor voltage capacity volume variance sum:

Σ _mina _ij(u _dci-u _dcj) ²，

Constraints is: $(u_{\mathrm{dci}}-u_{\mathrm{dcj}})\&le;{0.1u}_{\mathrm{dc}}^{*},$

u _a+u _b+u _c＝0，

Determine a that optimal value is corresponding _ijfor weight coefficient.

4. the half-bridge module multi-level converter submodule voltage control method described in claim 1, it is characterized in that, the parameter of described inner ring proportional integral link is: 1< proportionality coefficient <10,0.1< integral coefficient <1.

5. the half-bridge module multi-level converter submodule voltage control method described in claim 1, it is characterized in that, the parameter of described outer shroud proportional integral link is: 0.2< proportionality coefficient <1,0.01< integral coefficient <0.1.

6. the half-bridge module multi-level converter submodule voltage control method described in claim 1, is characterized in that, when electrical network generation unbalanced fault, comprises further:

Carry out α β coordinate transform to the alternating voltage of every phase, obtain corresponding α β component, the FEEDBACK CONTROL of the control of passing ratio integral feedback and dual-integration, obtains the first group component; This component is multiplied with coefficient q simultaneously, obtains second component amount; Calculated the positive-negative sequence component of α β by this 2 group component, positive-negative sequence component is carried out to submodule and controls respectively;

Wherein q expression formula is as follows:

q＝Q ₀+Q _c2cos(2ωt)+Q _s2sin(2ωt)，

Q ₀for the fundamental reactive component of electrical network, Q _c2, Q _s2for idle quadratic component, ω is angular frequency.