CN102856927B - DC voltage balance control method for single-phase H-bridge cascaded devices - Google Patents

Abstract

The invention discloses a DC voltage balance control method for single-phase H-bridge cascaded devices. The method is based on a mathematic model of a device in a d-q rotary coordinate system and comprises the following steps: 1, voltage mean-value control is used for realizing the mean-value of DC voltage to track a given value to regulate the total active power of the system; 2, forward-feed decoupling current control can realize the independent control of the active power and the reactive power, and the current loop cannot be influenced by the voltage of the power grid; and 3, voltage balance control avoids voltage unbalance caused by the active power difference between H bridges through compositing the numerical value of control components on Axis d. Compared with the control strategy in an a-b-c static coordination system, the DC voltage balance control method for single-phase H-bridge cascaded devices realizes the no static error control on grid side current, and the voltage balance section is simple in the structure, clear in concept and easy in implementation, and has high engineering application value.

Description

The DC voltage balance control method of single-phase H bridge cascade connection type device

Technical field

The invention belongs to the applied technical field of high-voltage and high-power power electronic technology in electric power system, relate to the dc-voltage balance control method of single-phase H bridge cascade connection type device.

Background technology

Along with the development of intelligent grid, increasing high-voltage and high-power power electronic application of installation is in electric power system, promote the development of flexible AC transmission technology, and the multilevel converter being wherein core with H bridge (convertor circuit be made up of four turn-off devices and capacitor, as the unit of in Fig. 1) cascaded topology be present stage the power electronic device of low withstand voltage level be applied to high-power field and provide strong support.

Dc-voltage balance be single-phase H bridge cascade connection type device can safety, reliability service prerequisite.Otherwise the DC bus overvoltage caused because of Voltage unbalance will cause the catastrophe failures such as capacitor damages, IGBT burns, gently then device will be shut down, heavy then cause power grid security and stability and have a strong impact on.

Direct voltage imbalance mainly causes due to the active power difference between each H bridge, is common in active loss, and because the device parameters such as IGBT, capacitor of each H-bridge unit can not be completely the same, therefore its parallel equivalent loss is incomplete same.Changing based on this kind of active loss caused because of fine difference accumulation is cause the unbalanced main cause of single-phase H bridge cascade connection type device direct voltage.

Chinese invention patent CN1514525 is by realizing dc-voltage balance at DC side additional firmware device, but this method cost is higher; Chinese invention patent CN1933274, CN101599708 and U.S. patent Nos US6075350 are proposed the balance of voltage method based on control strategy, but they are all the control methods based on rest frame, realize comparatively complicated.

Control method based on d-q rotating coordinate system is widely used in PWM rectifier, but rarely found its for single phase system, especially single-phase H bridge cascade connection type system, and adopt this rotating coordinate system can the fine astatic control that must realize current on line side, simultaneously, voltage balancing control based on this coordinate system realizes easy, clear physics conception, has higher engineer applied and is worth.

Summary of the invention

Goal of the invention: for above-mentioned Problems existing, the object of the invention is to propose a kind of voltage balancing control method based on H bridge cascade connection type device single-phase under d-q rotating coordinate system, the method does not need extra hardware circuit, and control structure is simple simultaneously, is convenient to realize.

Technical scheme: for achieving the above object, the technical solution used in the present invention is the balance of voltage method of a kind of single-phase H bridge cascade connection type device under d-q coordinate system, comprises the steps: 1) average voltage control;

2) Feedforward Decoupling Current Control; 3) voltage balancing control.

1) average voltage controls

1.1). gather each H bridge DC side voltage, calculate their mean value, and average value processing is done to the mean value obtained, to obtain a constant value

1.2). will and instruction average voltage after comparing, through proportional integral (PI) adjuster, obtain instruction active current value i _d ^*;

2) Feedforward Decoupling Current Control, for providing d-q axle control voltage

2.1). the virtual three-phase component of structure voltage on line side, electric current, and component of voltage u under utilizing park conversion formation two-phase d-q rotating coordinate system _d, u _q, current component i _d, i _q;

2.2). by i _dand i _qand instruction value i respectively _d ^*and i _q ^*relatively, through proportional integral (PI) adjuster, obtain d axle and q axle PI regulated value u _pIdand u _pIq;

2.3). by u _ddeduct u _pId, add i _qbe multiplied by mains frequency ω and be multiplied by the long-pending of grid-connected inductance L, obtain d shaft voltage controlling value component common

2.4). by u _qdeduct u _pIq, then deduct i _dbe multiplied by mains frequency ω and be multiplied by the long-pending of grid-connected inductance L, obtain q shaft voltage controlling value component common

3) voltage balancing control, for carrying out value revision to existing d-q axle control voltage

3.1) each H bridge direct voltage is made comparisons with average voltage respectively, and through proportional integral (PI) adjuster, obtain the d shaft voltage controlling value balance component of each H bridge

3.2), after the d shaft voltage controlling value component common of each H bridge and balance component being carried out numerical value addition, its d axle virtual voltage controlling value is obtained

Beneficial effect:

(1) specific implementation is simple and convenient, without the need to configuring the power-balance circuit of additional complexity, only needs the signal transducer and digit chip etc. of some low costs;

(2) single-phase H bridge cascade connection type device is made can to realize current on line side astatic control;

(3) balance of voltage link only needs pi regulator, and structure is simple, is convenient to realize.

(4) the method is well arranged, clear physics conception, has higher engineer applied and is worth.

Accompanying drawing explanation

The topology diagram of Fig. 1 single-phase H bridge cascade connection type device;

The stable state commonality vector service chart of Fig. 2 device under d-q rotating coordinate system;

Fig. 3 is based on the theory diagram of the voltage balancing control method of d-q rotating coordinate system;

DC voltage oscillogram when Fig. 4 does not adopt balance to control;

Fig. 5 adopt the present invention DC voltage oscillogram when putting forward control algolithm.

Embodiment

Described average voltage controls to comprise the steps:

(1) gather each H bridge DC side voltage, calculate their mean value, and average value processing is done to the mean value obtained, to obtain a constant value;

(2), after the constant value and instruction average voltage obtained being compared, carry out proportional plus integral control, obtain d axle command current value.

Described Feedforward Decoupling Current Control comprises the steps:

(1) constructed the virtual three-phase component of voltage on line side, electric current by virtual three-phase method, and utilize park to convert formation two-phase rotation d axle and q axle component;

(2) by d axle and q axle component respectively and instruction value relatively after, carry out proportional plus integral control, obtain d axle and q axle PI regulated value;

(3) voltage on line side d axle component is deducted d axle PI regulated value, add current on line side q axle component and be multiplied by mains frequency and be multiplied by the long-pending of grid-connected inductance, obtain d shaft voltage controlling value component common;

(4) voltage on line side q axle component is deducted q axle PI regulated value, then deduct current on line side d axle component and be multiplied by mains frequency and be multiplied by the long-pending of grid-connected inductance, obtain q shaft voltage controlling value component common;

Described voltage balancing control comprises the steps:

(1) each H bridge direct voltage is made comparisons with average voltage respectively, and carry out proportional plus integral control, obtain the d shaft voltage controlling value balance component of each H bridge;

(2), after the d shaft voltage controlling value component common of each H bridge and balance component being carried out numerical value addition, its d axle virtual voltage controlling value is obtained.

Example:

As shown in Figure 1, wherein, L is net side filter inductance to the topological structure of the individual unit cascaded single-phase chain type STATCOM of n, C ₁, C ₂... C _nbe respectively each H bridge DC side Support Capacitor, R is net side inductance L internal resistance and chain H bridge equivalent series loss resistance sum, r ₁, r ₂... r _nbe respectively the parallel loss resistance of each H-bridge unit.

In order to set up the Mathematical Modeling of single-phase chain type STATCOM under d-q rotating coordinate system, first adopt virtual three-phase method structure three-phase voltage on line side and three-phase current on line side, such as formula (1).

$\left\{\begin{array}{c}{x}_a=x_s\\ x_b=e^{-\mathrm{Ts}/3}{x}_s\\ x_c=-(1+e^{-\mathrm{Ts}/3})x_s\end{array}\right.,x\∈\{u,i\}---\left(1\right)$

Definition H bridge AC voltage switch function is

In formula (2), k={a, b, c}, i=1,2 ... n.

Consider the three-phase system full symmetric of structure, then meet on the basis of formula (1) at voltage on line side and electric current, the equal Striking symmetry of other parameters of three-phase circuit, has

$\left\{\begin{array}{c}{X}_a=X_b=X_c\\ X\∈\{C_i,u_{\mathrm{dci}},r_i,L,R\},i=\mathrm{1,2}...n\end{array}\right.---\left(3\right)$

Therefore, in three-phase static coordinate system a-b-c, the switch function model of single-phase chain type STATCOM is

$\left\{\begin{array}{c}L\frac{{\mathrm{di}}_k}{\mathrm{dt}}+{\mathrm{Ri}}_k=u_k-\underset{i=1}{\overset{n}{\mathrm{\Σ}}}{u}_{\mathrm{dci}}{s}_{\mathrm{ki}}\\ C_i\frac{{\mathrm{du}}_{\mathrm{dci}}}{\mathrm{dt}}=i_k{s}_{\mathrm{ki}}-\frac{u_{\mathrm{dci}}}{r_i}\\ \underset{k=a,b,c}{\mathrm{\Σ}}{u}_k=\underset{k=a,b,c}{\mathrm{\Σ}}{i}_k=0\end{array}\right.---\left(4\right)$

Can derive the Mathematical Modeling of single-phase chain type STATCOM in two-phase synchronous rotating frame d-q according to formula (4) and park transformation equation is

$\left\{\begin{array}{c}L\frac{{\mathrm{di}}_d}{\mathrm{dt}}-{\mathrm{\ωLi}}_q+{\mathrm{Ri}}_d=u_d-\underset{i=1}{\overset{n}{\mathrm{\Σ}}}{u}_{\mathrm{dci}}{s}_{\mathrm{di}}\\ L\frac{{\mathrm{di}}_q}{\mathrm{dt}}+\mathrm{\ω}{\mathrm{Li}}_d+{\mathrm{Ri}}_q=u_q-\underset{i=1}{\overset{n}{\mathrm{\Σ}}}{u}_{\mathrm{dci}}{s}_{\mathrm{qi}}\\ C_i\frac{{\mathrm{du}}_{\mathrm{dci}}}{\mathrm{dt}}=\frac{1}{2}(i_d{s}_{\mathrm{di}}+i_q{s}_{\mathrm{qi}})-\frac{u_{\mathrm{dci}}}{r_i}\end{array}\right.---\left(6\right)$

Dc-voltage balance is the prerequisite of chain type STATCOM reliability service, and under d-q coordinate system, systematic steady state runs clock-face diagram as shown in Figure 2.

According to instantaneous power theory, the active power that each H bridge flows through and reactive power can be expressed as

$\left\{\begin{array}{c}{p}_i=\frac{1}{2}{i}_d{u}_{\mathrm{Hdi}}=\frac{u_{\mathrm{dci}}^2}{r_i}\\ q_i=\frac{1}{2}{i}_q{u}_{\mathrm{Hqi}}=u_{\mathrm{dci}}{C}_i\frac{{\mathrm{du}}_{\mathrm{dci}}}{\mathrm{dt}}\end{array}\right.---\left(7\right)$

Be can be derived from by formula (7)

$\left\{\begin{array}{c}\frac{1}{2}{i}_d{s}_{\mathrm{di}}{r}_i{=u}_{\mathrm{dci}}\\ \frac{1}{2}{i}_q{s}_{\mathrm{qi}}=C_i\frac{{\mathrm{du}}_{\mathrm{dci}}}{\mathrm{dt}}\end{array}\right.---\left(8\right)$

From formula (8), if desired meet each H bridge DC side balance of voltage, i.e. u _dc1=u _dc2=...=u _dcn, then at r _itime incomplete same, each H bridge control switch function s _dialso incomplete same.

Order

$u_{\mathrm{Hdi}}={\stackrel{\‾}{u}}_{\mathrm{Hd}}+{\tilde{u}}_{\mathrm{Hdi}}---\left(9\right)$

Then control voltage is made up of two parts, and the former is component common, and the latter is balance component, is used for making up each H bridge r _ibetween relative error.

Therefore, control strategy is controlled by Feedforward Decoupling Current Control, average voltage, voltage balancing control three part forms, and they all adopt pi regulator to realize, and concrete control strategy as shown in Figure 3, average voltage controls to be used for stable DC side average voltage, and obtains d axle instruction current; Feedforward Decoupling Current Control obtains control voltage component common; Voltage balancing control calculates control voltage balance component, obtains modulating wave, and adopt corresponding modulation strategy to act on power tube finally by park inverse transformation.

Fig. 4 be do not adopt balance control time voltage oscillogram, due to switching pulse there is time delay, each H bridge loss is different, therefore, direct voltage cannot balance.

Fig. 5 is the oscillogram adopting control strategy of the present invention to obtain, and each DC side can be good at realizing balance, avoids capacitor and damages.

Claims (1)

1. a DC voltage balance control method for single-phase H bridge cascade connection type device, it is characterized in that, the method comprises the steps:

1) average voltage controls

1.1). gather each H bridge DC side voltage, calculate their mean value, and average value processing is done to the mean value obtained, to obtain a constant value

1.2). will and instruction average voltage after comparing, through proportional integral (PI) adjuster, obtain instruction active current value i _d ^*;

2) Feedforward Decoupling Current Control, for providing d-q axle control voltage

2.1). the virtual three-phase component of structure voltage on line side, electric current, and component of voltage u under utilizing park conversion formation two-phase d-q rotating coordinate system _d, u _q, current component i _d, i _q;

2.2). by i _dand i _qand instruction value i respectively _d ^*and i _q ^*relatively, through proportional integral (PI) adjuster, obtain d axle and q axle PI regulated value u _pIdand u _pIq;

2.3). by u _ddeduct u _pId, add i _qbe multiplied by mains frequency ω and be multiplied by the long-pending of grid-connected inductance L, obtain d shaft voltage controlling value component common

2.4). by u _qdeduct u _pIq, then deduct i _dbe multiplied by mains frequency ω and be multiplied by the long-pending of grid-connected inductance L, obtain q shaft voltage controlling value component common

3) voltage balancing control, for carrying out value revision to existing d-q axle control voltage

3.1) each H bridge direct voltage is made comparisons with average voltage respectively, and through proportional integral (PI) adjuster, obtain the d shaft voltage controlling value balance component of each H bridge

3.2), after the d shaft voltage controlling value component common of each H bridge and balance component being carried out numerical value addition, its d axle virtual voltage controlling value is obtained