CN102856927A - 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

Development along with intelligent grid, increasing high-voltage and high-power power electronic application of installation is in electric power system, promoting the development of flexible AC transmission technology, and wherein with H bridge (convertor circuit that is comprised of four turn-off devices and capacitor is such as a unit among Fig. 1) cascaded topology for the multilevel converter of core for present stage low withstand voltage level power electronic device be applied to the high-power field strong support be provided.

Dc-voltage balance be single-phase H bridge cascade connection type device can safety, the prerequisite of reliability service.Otherwise, the catastrophe failure such as the dc bus overvoltage that causes because of Voltage unbalance will cause capacitor to damage, IGBT burns, gently then device is shut down, and is heavy then electricity net safety stable caused have a strong impact on.

The direct voltage imbalance mainly is because the active power difference between each H bridge causes, is common in active loss, and because the device parameters such as the IGBT of each H bridge unit, capacitor can not be in full accord, so its equivalent loss in parallel is incomplete same.The active loss variation that causes because fine difference accumulates based on this class is to cause the unbalanced main cause of single-phase H bridge cascade connection type device direct voltage.

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

Control method based on the d-q rotating coordinate system has been widely used in the PWM rectifier, but rarely found its is used 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, balance of voltage control realization based on this coordinate system is easy, and clear physics conception has higher engineering using value.

Summary of the invention

Goal of the invention: for the problem of above-mentioned existence, the object of the invention is to propose a kind of balance of voltage control method based on single-phase H bridge cascade connection type device under the 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 the d-q coordinate system, comprises the steps: 1) average voltage control;

2) Feedforward Decoupling Current Control; 3) balance of voltage control.

1) average voltage control

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

1.2). will The and instruction average voltage

After comparing, through proportional integral (PI) adjuster, obtain instruction active current value i _d ^*

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

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

2.2). with i _dAnd i _qDifference and instruction value i _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). with u _dDeduct u _PId, add i _qMultiply by mains frequency ω and multiply by the long-pending of the inductance L that is incorporated into the power networks, obtain d shaft voltage controlling value component common

2.4). with u _qDeduct u _PIq, deduct again i _dMultiply by mains frequency ω and multiply by the long-pending of the inductance L that is incorporated into the power networks, obtain q shaft voltage controlling value component common

3) balance of voltage control is used for existing d-q axle control voltage is carried out the numerical value correction

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

Beneficial effect:

(1) specific implementation is simple and convenient, need not to dispose the power-balance circuit of additional complexity, only needs some cheaply signal transducer and digit chips etc.;

(2) so that single-phase H bridge cascade connection type device can be realized the current on line side astatic control;

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

(4) the method is well arranged, and clear physics conception has higher engineering using value.

Description of drawings

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

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

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

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

Dc voltage oscillogram when Fig. 5 adopts the present invention to put forward control algolithm.

Embodiment

Described average voltage control comprises the steps:

(1) gathers each H bridge DC side voltage, calculate their mean value, and the mean value that obtains is made average value processing, to obtain a constant value;

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

Described Feedforward Decoupling Current Control comprises the steps:

(1) constructs the virtual three-phase component of voltage on line side, electric current by virtual trichotomy, and utilize the park conversion to form two-phase rotation d axle and q axle component;

(2) with d axle and q axle component respectively the 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 multiply by mains frequency and multiply by the long-pending of the inductance that is incorporated into the power networks, obtain d shaft voltage controlling value component common;

(4) voltage on line side q axle component is deducted q axle PI regulated value, deduct again current on line side d axle component and multiply by mains frequency and multiply by the long-pending of the inductance that is incorporated into the power networks, obtain q shaft voltage controlling value component common;

Described balance of voltage 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) the d shaft voltage controlling value component common of each H bridge and balance component are carried out the numerical value addition after, obtain its d axle virtual voltage controlling value.

Example:

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

In order to set up the Mathematical Modeling of single-phase chain type STATCOM under the d-q rotating coordinate system, at first adopt virtual trichotomy structure three-phase voltage on line side and three-phase current on line side, suc 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 the formula (2), k={a, b, c}, i=1,2 ... n.

Consider the three-phase system full symmetric of structure, then satisfy on the basis of formula (1) at voltage on line side and electric current that other parameters of three-phase circuit are all strict symmetrical, have

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

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 the d-q coordinate system, systematic steady state operation clock-face diagram as shown in Figure 2.

According to instantaneous power theory as can be known, each H bridge active power and reactive power of flowing through can be expressed as respectively

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

Can be pushed away by formula (7)

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

By formula (8) as can be known, if need to satisfy each H bridge DC side balance of voltage, i.e. u _Dc1=u _Dc2=...=u _Dcn, then at r _iWhen 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 and be comprised of two parts, the former is component common, and the latter is the balance component, is used for remedying each H bridge r _iBetween relative error.

Therefore, control strategy is controlled three parts and is formed by Feedforward Decoupling Current Control, average voltage control, the balance of voltage, and they all adopt pi regulator to realize, concrete control strategy as shown in Figure 3, average voltage control is used for stable DC side average voltage, and obtains d axle instruction current; The controlled voltage component common of Feedforward Decoupling Current Control; Balance of voltage control calculates control balance of voltage component, obtains modulating wave by the park inverse transformation at last, and adopts corresponding modulation strategy to act on power tube.

Fig. 4 is the voltage oscillogram when not adopting balance control, because the switching pulse existence is delayed time, each H bridge loss is different, therefore, direct voltage can't balance.

The oscillogram of Fig. 5 for adopting control strategy of the present invention to obtain, each DC side can be good at realizing balance, has avoided the capacitor damage.

Claims (1)

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

1) average voltage control

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

1.2). will The and instruction average voltage

After comparing, through proportional integral (PI) adjuster, obtain instruction active current value i _d ^*

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

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

2.2). with i _dAnd i _qDifference and instruction value i _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). with u _dDeduct u _PId, add i _qMultiply by mains frequency ω and multiply by the long-pending of the inductance L that is incorporated into the power networks, obtain d shaft voltage controlling value component common

2.4). with u _qDeduct u _PIq, deduct again i _dMultiply by mains frequency ω and multiply by the long-pending of the inductance L that is incorporated into the power networks, obtain q shaft voltage controlling value component common

3) balance of voltage control is used for existing d-q axle control voltage is carried out the numerical value correction

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

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