CN103944171B - The circular current control method of a kind of corner connection chain type SVG - Google Patents

Abstract

The circular current control method of a kind of corner connection chain type SVG, described circular current control method is by the feedforward controller adopting susceptance equilibrium principle, combine with the feedback controller of employing current on line side closed loop, make chain type SVG device under line voltage asymmetrical, idle and negative sequence compensation can be carried out to three-phase imbalance load.Described current on line side closed-loop control is by detecting idle and negative sequence component remaining in the grid side electric current after compensating, and respectively proportional plus integral control is carried out to it under synchronous rotating frame, residual components is decayed to zero gradually, thus the impact that auto-compensation unbalanced source voltage causes idle and negative sequence compensation effect.Feedfoward control and FEEDBACK CONTROL combine by described circular current control method, make SVG device keeping, fast while dynamic response, realizing good stable state compensation effect, and can resist the impact that unbalanced source voltage causes.

Description

The circular current control method of a kind of corner connection chain type SVG

Technical field

The invention belongs to electronic power convertor technical field, be specifically related to the circular current control method of corner connection chain type SVG device.

Background technology

Chain type SVG is divided into corner connection and star to connect two kinds of basic topologies, research shows, star chain link formula SVG does not possess negative sequence compensation ability, even if adopt special control method, also can only carry out very limited negative sequence compensation, thus star chain link formula SVG is only applied to reactive power compensation field usually; Corner connection chain type SVG then can carry out idle, negative phase-sequence and harmonic compensation simultaneously, but corner connection chain type SVG is when carrying out negative sequence compensation, can face special circulation control problem.

Due in topology, when corner connection chain type SVG carries out negative sequence compensation or runs under asymmetrical voltage condition, there will be meritorious flowing between three-phase, cause alternate DC capacitor voltage disequilibrium.In the triangle of angle connecting structure, the zero-sequence current simultaneously flowing through three-phase can be there is, namely circulation.Circulation does not affect the output current of angle joint, but can affect the flow of power between three-phase.The degree of freedom that circulation formation one is extra, for alternate power balances the condition of providing again, this is the basic reason that corner connection chain type SVG can realize negative sequence compensation and asymmetric operation.

Circular current control method conventional at present comprises zero-sequence current injection method and susceptance equilibrium principle two kinds.Zero-sequence current injection method is amplitude and the phase place of using the zero-sequence current (circulation namely in triangle) needed for method Derivation of resolving, and be added in the desired value of each phase output current of SVG device by this zero-sequence current, thus realize alternate power-balance.Susceptance equilibrium principle is then the method utilizing circuit analysis, directly asks for each compensation susceptance required mutually of SVG device, thus obtains the reactive current desired value of each phase.Susceptance equilibrium principle does not directly ask for size and the amplitude of circulation, but automatically contains the Circulation Components for active power between equilibrium phase in its three-phase target current.

In actual industrial power distribution network, the situation of load is very complicated.The large scale industry loads such as arc furnace are in running, and three-phase current is random acute variation independently, produce a large amount of negative-sequence current; Meanwhile, due to load big ups and downs, reactive power impact is formed to electrical network, causes three-phase power grid voltage seriously uneven.Idle and negative sequence compensation to be carried out to industrial loads such as arc furnace, not only require that compensation arrangement can compensate the negative-sequence current of load, also require that compensation arrangement can tackle certain unbalanced source voltage condition, resist the adverse effect that negative sequence voltage causes compensation effect.But, above-mentioned two kinds of conventional circular current control methods are all the conclusions drawn under the condition of grid voltage three-phase symmetrical, and when line voltage is asymmetric, its general principle is no longer set up, compensation effect is greatly affected, and cannot meet the application demand of the medium-and-large-sized industrial load of power distribution network.

Summary of the invention

The object of the invention is in order under solving line voltage asymmetrical, adopt the SVG device of traditional circular current control method cannot realize the problem of effectively idle and negative sequence compensation.The present invention proposes the circular current control method of a kind of corner connection chain type SVG, and described circular current control method by the feedforward controller adopting susceptance equilibrium principle, and adopts the feedback controller of current on line side closed loop to combine.Current on line side closed-loop control and susceptance equilibrium principle combine by described circular current control method, make chain type SVG device under line voltage asymmetrical, can carry out idle and negative sequence compensation to three-phase imbalance load.

The application is concrete by the following technical solutions.

A circulation control system of corner connection chain type SVG, is characterized in that: described circulation control system comprises the feedforward controller adopting susceptance equilibrium principle, and adopts the feedback controller of current on line side closed loop, and the input signal of feedback controller is net side three-phase current i _sa, i _sb, i _sc, output signal as correction component i _ea, i _eb, i _ec; The input signal of feedforward controller is load three-phase current i _ra, i _rb, i _rcwith correction component i _ea, i _eb, i _ecsum, outputs signal the desired value into corner connection chain type SVG three-phase output current.

The circular current control method of a kind of corner connection chain type SVG disclosed in the present application, is characterized in that, said method comprising the steps of:

(1) by the three-phase current i of grid side _sa, i _sb, i _scbe input to described feedback controller, and utilize phase-locked loop to obtain the phase angle θ of three-phase voltage positive sequence component, namely realize voltage oriented;

(2) with anglec of rotation ω t+ θ corresponding to power frequency to three phase network current i _sa, i _sb, i _sccarry out coordinate transform, obtain d axle and the q axle component of forward-order current, wherein the corresponding idle component of q axle;

(3) by the positive sequence q axle component i after conversion _qpbe input to pi controller, obtain outputing signal I ' _qp; Positive sequence d axle component I ' _dpbe set to zero, and with anglec of rotation ω t+ θ to I ' _dpand I ' _qpcarry out dq-abc inverse transformation;

(4) with-ω t for the anglec of rotation is to three phase network current i _sa, i _sb, i _sccarry out abc-dq rotating coordinate transformation, obtain d axle and the q axle component of negative phase-sequence;

(5) by negative phase-sequence d, the q axle component i after conversion _dn, i _qnbe input to pi controller respectively, obtain outputing signal I ' _dn, I ' _qn, and with the anglec of rotation-ω t to I ' _dnand I ' _qncarry out dq-abc inverse transformation;

(6) by the results added of inverse transformation in above-mentioned steps (3) and step (5), correction component i is obtained _ea, i _eb, i _ec;

(7) by correction component i _ea, i _eb, i _ecwith threephase load current i _ra, i _rb, i _rcbe added, as the input signal i ' of feedforward controller _ra, i ' _rb, i ' _rc;

(8) the compensation admittance desired value B between three phase network AB, BC, CA phase is calculated respectively ^* _ab, B ^* _bc, B ^* _ca;

(9) according to the compensation admittance desired value of described AB, BC and CA phase, and the line voltage of three phase network AB, BC and CA, the instantaneous value i of target current of corner connection SVG device AB, BC and CA phase is calculated ^* _ab, i ^* _bc, i ^* _ac.

Current on line side closed loop controller of the present invention is by detecting idle and negative sequence component remaining in the grid side electric current after compensating, under synchronous rotating frame, respectively proportional plus integral control is carried out to it, residual components is decayed to zero gradually, thus the impact that auto-compensation unbalanced source voltage causes idle and negative sequence compensation effect, the stable state compensation effect of realizing ideal; Meanwhile, described feedforward controller adopts susceptance equilibrium principle, utilizes the instantaneous value of load current to carry out feedfoward control, ensures that SVG device has fast dynamic response ability when load variations.Therefore, circular current control method of the present invention can make corner connection SVG device keep, fast while dynamic responding speed, realizing good stable state compensation effect, and can resist the impact that unbalanced source voltage causes.

Accompanying drawing explanation

Fig. 1 is the circulation control system the general frame of chain type SVG device proposed by the invention;

Fig. 2 is corner connection chain type SVG circular current control method schematic flow sheet disclosed by the invention;

Fig. 3 is corner connection chain type SVG device circulation control system block diagram disclosed by the invention.

Embodiment

Below in conjunction with specification drawings and specific embodiments, technical scheme of the present invention is described in further detail.

In the overall control block diagram shown in Fig. 1, be the sub-block diagram of feedback controller in the square frame of the lower left corner, upper right corner square frame is the sub-block diagram of feedforward controller.Wherein the input signal of feedback controller is net side three-phase current i _sa, i _sb, i _sc, output signal as correction component i _ea, i _eb, i _ec; The input signal of feedforward controller is load three-phase current i _ra, i _rb, i _rcwith correction component i _ea, i _eb, i _ecsum, outputs signal the desired value i* into corner connection chain type SVG three-phase output current _ab, i* _bc, i* _ac.When line voltage is asymmetric, offset the impact of negative sequence voltage by this correction component, eliminate the deviation of compensation result; And when line voltage is symmetrical, correction component becomes very little, and control system is similar to and returns to the balanced compensated process of susceptance.In fact, because correction component introduces closed loop feedback, when line voltage is symmetrical, the departure of open loop structure also effectively can be eliminated.

Figure 2 shows that circular current control method flow chart disclosed by the invention, specifically comprise the following steps:

(1) by the three-phase current i of grid side _sa, i _sb, i _scbe input to described feedback controller, and utilize phase-locked loop (PhaseLockLoop, PLL) to obtain the phase angle θ of three-phase voltage positive sequence component, namely realize voltage oriented;

(2) according to voltage oriented to three phase network current i _sa, i _sb, i _sccarry out abc-dq rotating coordinate transformation, the anglec of rotation is ω t+ θ (ω is power frequency angular frequency), obtains d axle and the q axle component of positive sequence;

$\left[\begin{array}{c}{i}_{\mathrm{dp}}\\ i_{\mathrm{qp}}\end{array}\right]=\sqrt{\frac{2}{2}}\left[\begin{array}{ccc}\cos (\mathrm{\ωt}-\mathrm{\θ})& \cos (\mathrm{\ωt}+\mathrm{\θ}-\frac{2\mathrm{\π}}{3})& \cos (\mathrm{\ωt}+\mathrm{\θ}+\frac{2\mathrm{\π}}{3})\\ -\sin (\mathrm{\ωt}+\mathrm{\θ})& -\sin (\mathrm{\ω}+\mathrm{\θ}-\frac{2\mathrm{\π}}{3})& -\sin (\mathrm{\ωt}+\mathrm{\θ}+\frac{2\mathrm{\π}}{3})\end{array}\right]\left[\begin{array}{c}{i}_{\mathrm{sa}}\\ i_{\mathrm{sb}}\\ i_{\mathrm{sc}}\end{array}\right]$

(3) by the positive sequence q axle component i after conversion _qpbe input to pi controller, obtain outputing signal I ' _qp; Positive sequence d axle component I ' _dpbe set to zero, and with anglec of rotation ω t+ θ to I ' _dpand I ' _qpcarry out dq-abc inverse transformation;

$\left[\begin{array}{c}{i}_{\mathrm{ap}}^{\′}\\ i_{\mathrm{bp}}^{\′}\\ i_{\mathrm{cp}}^{\′}\end{array}\right]=\sqrt{\frac{2}{3}}\left[\begin{array}{cc}\cos (\mathrm{\ωt}+\mathrm{\θ})& -\sin (\mathrm{\ωt}+\mathrm{\θ})\\ \cos (\mathrm{\ωt}+\mathrm{\θ}-\frac{2\mathrm{\π}}{3})& -\sin (\mathrm{\ωt}+\mathrm{\θ}-\frac{2\mathrm{\π}}{3})\\ \cos (\mathrm{\ωt}+\mathrm{\θ}+\frac{2\mathrm{\π}}{3})& -\sin (\mathrm{\ωt}+\mathrm{\θ}+\frac{2\mathrm{\π}}{3})\end{array}\right]\left[\begin{array}{c}{I}_{\mathrm{dp}}^{\′}\\ I_{\mathrm{qp}}^{\′}\end{array}\right]$

(4) with-ω t for the anglec of rotation is to three phase network current i _sa, i _sb, i _sccarry out abc-dq rotating coordinate transformation, obtain d axle and the q axle component of negative phase-sequence;

$\left[\begin{array}{c}{i}_{\mathrm{dn}}\\ i_{\mathrm{qn}}\end{array}\right]=\sqrt{\frac{2}{3}}\left[\begin{array}{ccc}\cos (-\mathrm{\ωt})& \cos (-\mathrm{\ωt}-\frac{2\mathrm{\π}}{3})& \cos (-\mathrm{\ωt}+\frac{2\mathrm{\π}}{3})\\ -\sin (-\mathrm{\ωt})& -\sin (-\mathrm{\ωt}-\frac{2\mathrm{\π}}{3})& -\sin (-\mathrm{\ωt}+\frac{2\mathrm{\π}}{3})\end{array}\right]\left[\begin{array}{c}{i}_{\mathrm{sa}}\\ i_{\mathrm{sb}}\\ i_{\mathrm{sc}}\end{array}\right]$

(5) by negative phase-sequence d, the q axle component i after conversion _dn, i _qnbe input to pi controller respectively, obtain outputing signal I ' _dn, I ' _qn, and with the anglec of rotation-ω t to I ' _dnand I ' _qncarry out dq-abc inverse transformation;

$\left[\begin{array}{c}{i}_{\mathrm{an}}^{\′}\\ i_{\mathrm{bn}}^{\′}\\ i_{\mathrm{cn}}^{\′}\end{array}\right]=\sqrt{\frac{2}{3}}\left[\begin{array}{cc}\cos (-\mathrm{\ωt})& -\sin (-\mathrm{\ωt})\\ \cos (-\mathrm{\ωt}-\frac{2\mathrm{\π}}{3})& -\sin (-\mathrm{\ωt}-\frac{2\mathrm{\π}}{3})\\ \cos (-\mathrm{\ωt}+\frac{2\mathrm{\π}}{3})& -\sin (-\mathrm{\ωt}+\frac{2\mathrm{\π}}{3})\end{array}\right]\left[\begin{array}{c}{I}_{\mathrm{dn}}^{\′}\\ I_{\mathrm{qn}}^{\′}\end{array}\right]$

(6) by the results added of inverse transformation in above-mentioned steps (3) and step (5), correction component i is obtained _ea, i _eb, i _ec;

(7) by correction component i _ea, i _eb, i _ecwith threephase load current i _ra, i _rb, i _rcbe added, as the input signal i ' of feedforward controller _ra, i ' _rb, i ' _rc.

(8) according to following integral expression, the compensation admittance B between AB, BC, CA is calculated respectively ^* _ab, B ^* _bc, B ^* _ca;

A) by the A phase i ' of described feedforward controller input signal _rawith the line voltage u between electrical network B, C phase _bc, in a power frequency period, carry out integration and average, obtaining Section 1 integral mean;

B) by the B phase i ' of described feedforward controller input signal _rbwith the line voltage u between electrical network C, A phase _ca, in a power frequency period, carry out integration and average, obtaining Section 2 integral mean;

C) by the C phase i ' of described feedforward controller input signal _rcwith the line voltage u between electrical network A, B phase _ab, in a power frequency period, carry out integration and average, obtaining Section 3 integral mean.

D) described Section 1 integral mean to be added with Section 2 integral mean, poorer with third phase integral mean, then by difference divided by phase voltage square, then divided by the radical sign three of three times, obtain the compensation admittance desired value B of AB phase ^* _ab;

E) described Section 2 integral mean to be added with Section 3 integral mean, poorer with first-phase integral mean, then by difference divided by phase voltage square, then divided by the radical sign three of three times, obtain the compensation admittance desired value B of BC phase ^* _bc;

F) described Section 3 integral mean to be added with Section 1 integral mean, poorer with second-phase integral mean, then by difference divided by phase voltage square, then divided by the radical sign three of three times, obtain the compensation admittance desired value B of CA phase ^* _ca.

$B_{\mathrm{ab}}^{*}=\frac{1}{3\sqrt{3}{U}^2}[\frac{1}{T}{\∫}_0^T{u}_{\mathrm{bc}}{i}_{\mathrm{ra}}^{\′}\mathrm{dt}+\frac{1}{T}{\∫}_0^T{u}_{\mathrm{ca}}{i}_{\mathrm{rb}}^{\′}\mathrm{dt}-\frac{1}{T}{\∫}_0^T{u}_{\mathrm{ab}}{i}_{\mathrm{rc}}^{\′}\mathrm{dt}]$

$B_{\mathrm{bc}}^{*}=\frac{1}{3\sqrt{3}{U}^2}[\frac{1}{T}{\∫}_0^T{u}_{\mathrm{ca}}{i}_{\mathrm{rb}}^{\′}\mathrm{dt}+\frac{1}{T}{\∫}_0^T{u}_{\mathrm{ab}}{i}_{\mathrm{rc}}^{\′}\mathrm{dt}-\frac{1}{T}{\∫}_0^T{u}_{\mathrm{bc}}{i}_{\mathrm{ra}}^{\′}\mathrm{dt}]$

$B_{\mathrm{ca}}^{*}=\frac{1}{3\sqrt{3}{U}^2}[\frac{1}{T}{\∫}_0^T{u}_{\mathrm{ab}}{i}_{\mathrm{rc}}^{\′}\mathrm{dt}+\frac{1}{T}{\∫}_0^T{u}_{\mathrm{bc}}{i}_{\mathrm{ra}}^{\′}\mathrm{dt}-\frac{1}{T}{\∫}_0^T{u}_{\mathrm{ca}}{i}_{\mathrm{rb}}^{\′}\mathrm{dt}]$

(9) according to the susceptance desired value of described AB, BC and CA phase, and the line voltage of three phase network AB, BC and CA, the instantaneous value i of target current of corner connection SVG device AB, BC and CA phase is calculated ^* _ab, i ^* _bc, i ^* _ac.

$i_{\mathrm{ab}}^{*}=-{\mathrm{ju}}_{\mathrm{ab}}{B}_{\mathrm{ab}}^{*}$

$i_{\mathrm{bc}}^{*}=-{\mathrm{ju}}_{\mathrm{bc}}{B}_{\mathrm{bc}}^{*}$

$i_{\mathrm{ca}}^{*}=-{\mathrm{ju}}_{\mathrm{ca}}{B}_{\mathrm{ca}}^{*}$

In the circular current control method system block diagram shown in Fig. 3, the target compensation electric current of SVG is made up of two parts: Part I is from load current (i by classical susceptance equilibrium principle _ra, i _rb, i _rc) the compensate component that directly calculates of real-time sampling value; Part II is the output (i by pi regulator FEEDBACK CONTROL under dq coordinate system _ea, i _eb, i _ec) correcting value that calculates through susceptance equilibrium principle.Wherein Part I is the fundamental component of target compensation electric current, and the ratio shared by correcting value is less.Therefore, the advantage of the fast response time that this control method can keep this opened loop control of susceptance equilibrium principle to have, can eliminate again the impact that the external disturbance divided rings such as unbalance voltage control to cause simultaneously, realize good stable state compensation effect.

Present invention applicant has done detailed description and description in conjunction with Figure of description to embodiments of the invention; but those skilled in the art should understand that; above embodiment is only the preferred embodiments of the invention; detailed explanation is just in order to help reader to understand spirit of the present invention better; and be not limiting the scope of the invention; on the contrary, any any improvement of doing based on invention of the present invention spirit or modify all should drop within protection scope of the present invention.

Claims (2)

1. the circular current control method based on the corner connection chain type SVG of circulation control system, described circulation control system comprises the feedforward controller adopting susceptance equilibrium principle, with the feedback controller adopting current on line side closed loop, the input signal of feedback controller is net side three-phase current i _sa, i _sb, i _sc, output signal as correction component i _ea, i _eb, i _ec; The input signal of feedforward controller is load three-phase current i _ra, i _rb, i _rcwith correction component i _ea, i _eb, i _ecsum, outputs signal the desired value into corner connection chain type SVG three-phase output current; It is characterized in that, described circular current control method comprises the following steps:

(1) by the three-phase current i of grid side _sa, i _sb, i _scbe input to described feedback controller, and utilize phase-locked loop to obtain the phase angle θ of three-phase voltage positive sequence component, namely realize voltage oriented;

(2) with anglec of rotation ω t+ θ corresponding to power frequency to three phase network current i _sa, i _sb, i _sccarry out coordinate transform, obtain d axle and the q axle component of forward-order current, wherein the corresponding idle component of q axle;

(3) by the positive sequence q axle component i after conversion _qpbe input to pi controller, obtain outputing signal I ' _qp; Positive sequence d axle component I ' _dpbe set to zero, and with anglec of rotation ω t+ θ to I ' _dpand I ' _qpcarry out dq-abc inverse transformation;

(4) with-ω t for the anglec of rotation is to three phase network current i _sa, i _sb, i _sccarry out abc-dq rotating coordinate transformation, obtain d axle and the q axle component of negative phase-sequence;

(5) by negative phase-sequence d, the q axle component i after conversion _dn, i _qnbe input to pi controller respectively, obtain outputing signal I ' _dn, I ' _qn, and with the anglec of rotation-ω t to I ' _dnand I ' _qncarry out dq-abc inverse transformation;

(6) by the results added of inverse transformation in above-mentioned steps (3) and step (5), correction component i is obtained _ea, i _eb, i _ec;

(7) by correction component i _ea, i _eb, i _ecwith threephase load current i _ra, i _rb, i _rcbe added, as the input signal i ' of feedforward controller _ra, i ' _rb, i ' _rc;

(8) the compensation admittance desired value B between three phase network AB, BC, CA phase is calculated respectively ^* _ab, B ^* _bc, B ^* _ca;

(9) according to the compensation admittance desired value of described AB, BC and CA phase, and the line voltage of three phase network AB, BC and CA, the instantaneous value i of target current of corner connection SVG device AB, BC and CA phase is calculated ^* _ab, i ^* _bc, i ^* _ac.

2. the circular current control method of the corner connection chain type SVG of circulation control system according to claim 1, is characterized in that: described step (8) comprising:

A) by the A phase i ' of described feedforward controller input signal _rawith the line voltage u between electrical network B, C phase _bc, in a power frequency period, carry out integration and average, obtaining Section 1 integral mean;

B) by the B phase i ' of described feedforward controller input signal _rbwith the line voltage u between electrical network C, A phase _ca, in a power frequency period, carry out integration and average, obtaining Section 2 integral mean;

C) by the C phase i ' of described feedforward controller input signal _rcwith the line voltage u between electrical network A, B phase _ab, in a power frequency period, carry out integration and average, obtaining Section 3 integral mean;

D) described Section 1 integral mean to be added with Section 2 integral mean, poorer with Section 3 integral mean, then by difference divided by phase voltage square, then divided by the radical sign three of three times, obtain the compensation admittance desired value B of AB phase ^* _ab;

E) described Section 2 integral mean to be added with Section 3 integral mean, poorer with Section 1 integral mean, then by difference divided by phase voltage square, then divided by the radical sign three of three times, obtain the compensation admittance desired value B of BC phase ^* _bc;

F) described Section 3 integral mean to be added with Section 1 integral mean, poorer with Section 2 integral mean, then by difference divided by phase voltage square, then divided by the radical sign three of three times, obtain the compensation admittance desired value B of CA phase ^* _ca.