CN104917184A - Control system and control method for improving voltage quality of microgrid - Google Patents

Abstract

The invention discloses a control system for improving the voltage quality of a microgrid. The control system comprises a pair of current transformers VSC1 and VSC2 which are connected between a power distribution network and the microgrid in a back-to-back manner; a direct-current side capacitor C is connected between the current transformer VSC1 and the current transformer VSC2 in parallel; an electric reactor L1, a resistor R1 and a switch circuit breaker CB1 are further connected between the current transformer VSC1 and the power distribution network in sequence; a capacitor C1 is further connected between the resistor R1 and the switch circuit breaker CB1 and is then grounded; an electric reactor L2, a resistor R2 and a switch circuit breaker CB2 are further connected between the current transformer VSC2 and the microgrid in sequence; and a capacitor C2 is further connected between the resistor R2 and the switch circuit breaker CB2 and is then grounded. The invention also discloses a control method for improving the voltage quality of the microgrid. The control system and the control method solve the problem of frequency and voltage deviation caused by small capacity and little inertia of the microgrid during load change existing in the prior art.

Description

A kind of control system and control method improving micro-capacitance sensor quality of voltage

Technical field

The invention belongs to technical field of power systems, be specifically related to a kind of control system improving micro-capacitance sensor quality of voltage, the invention still further relates to the control method improving micro-capacitance sensor quality of voltage.

Background technology

Micro-capacitance sensor is that have isolated island and grid-connected two kinds of operational modes, wherein DG is usually via voltage source converter access electrical network by some distributed power sources (Distributed Generation, DG), energy storage device and the controllable system that forms of load on the spot.Usually DG application droop characteristic is exported to the power of expectation, to ensure power flow regulating and the voltage stabilization of electrical network.When micro-grid connection is run, in electrical network, the fluctuation of voltage magnitude and frequency can impact the DG in micro-capacitance sensor and load.And micro-capacitance sensor capacity is little, most of micro battery has intermittence and randomness, little by the grid-connected inertia of power electronic equipment, and therefore when load variations, the frequency of micro-capacitance sensor, voltage control strategy are the key issues of micro-capacitance sensor research.

Mainly contain for being carried out FMAM method by control inverter at present: by the primary frequency modulation (width) and frequency modulation frequency modulation (width) effect that utilize droop control to imitate conventional electric power system; Adopt and realize based on virtual synchronous generator thought the dual-use function that power controls and frequency modulation and voltage modulation controls.Because current method is all to simulate premised on actual generator, limit the function of inverter, and variable is more and there is coupled relation, makes the comparatively difficulty of adjusting of PI parameter, add the difficulty of device context debugging, extend debugging cycle.

Summary of the invention

The object of this invention is to provide a kind of control system improving micro-capacitance sensor quality of voltage, solve exist in prior art because micro-capacitance sensor capacity is little, inertia is little, the frequency brought when load variations, the problem of voltage deviation.

Another object of the present invention is to provide a kind of control method improving micro-capacitance sensor quality of voltage.

First technical scheme of the present invention is, a kind of control system improving micro-capacitance sensor quality of voltage, comprise current transformer VSC1 and VSC2 accessed back-to-back between power distribution network and micro-capacitance sensor for a pair, DC bus capacitor C is parallel with between current transformer VSC1 and VSC2, reactor L1 is also connected with in turn between current transformer VSC1 and power distribution network, resistance R1 and switch disconnector CB1, ground connection after electric capacity C1 is also connected between resistance R1 and switch disconnector CB1, reactor L2 is also connected with in turn between current transformer VSC2 and micro-capacitance sensor, resistance R2 and switch disconnector CB2, ground connection after electric capacity C2 is also connected between resistance R2 and switch disconnector CB2.

The feature of the present invention first technical scheme is also,

Micro-capacitance sensor by the distributed power source DG1 be connected in parallel on micro-capacitance sensor bus and distributed power source DG2 and on the spot load form.

Second technical scheme of the present invention is, a kind of control method improving the control system of micro-capacitance sensor quality of voltage is specifically implemented according to following steps:

Step 1, first current transformer VSC1 to be controlled:

Because back-to-back converter VSC1 is connected with current transformer VSC1 and current transformer VSC2 respectively with the DC bus capacitor C of current transformer VSC2, the therefore voltage u of DC bus capacitor C _dcthe active power being flowed into DC side by two side converter VSC1 and current transformer VSC2 determines jointly, and the voltage computing formula of DC bus capacitor C is specific as follows:

${\mathrm{Cu}}_{\mathrm{dc}}\frac{{\mathrm{du}}_{\mathrm{dc}}}{\mathrm{dt}}=P_1+P_2---\left(1\right)$

In formula (1), C is the capacitance of the DC bus capacitor between back-to-back converter VSC1 and current transformer VSC2, u _dcfor the voltage of DC bus capacitor, P ₁for the active power that current transformer VSC1 and power distribution network exchange, P ₂for the active power that current transformer VSC2 and micro-capacitance sensor exchange;

Step 2, maintenance current transformer VSC1 export as unit power factor, if the desired value i of the reactive current of current transformer VSC1 _q ^*=0, the formula (1) in integrating step 1, obtains the desired value i of the meritorious and idle component that VSC1 I/O electric current is fastened at two-phase rotational coordinates thus _p ^*and i _q ^*be respectively:

$\left\{\begin{array}{c}{i}_p^{*}=\frac{{\mathrm{Cu}}_{\mathrm{dc}}\frac{{\mathrm{du}}_{\mathrm{dc}}}{\mathrm{dt}}}{\left|e\right|}\\ i_q^{*}=0\end{array}\right.---\left(2\right)$

In formula (2), i _p ^*and i _q ^*be respectively the desired value of the meritorious and idle component that electric current is fastened at two-phase rotational coordinates, C is the capacitance of the DC bus capacitor between back-to-back converter VSC1 and VSC2, u _dcfor the voltage of DC bus capacitor, | e| is the amplitude of VSC1 input/output voltage vector;

Step 3, the i will obtained in step 2 _p ^*and i _q ^*transforming to three-phase static coordinate system by transformation matrix, obtaining the desired value of electric current in three-phase static coordinate system by analyzing transformation result:

$\left[\begin{array}{c}{i}_a^{*}\\ i_b^{*}\\ i_c^{*}\end{array}\right]=T_{\mathrm{abc}/\mathrm{pq}}\left[\begin{array}{c}{i}_p^{*}\\ i_q^{*}\end{array}\right]---\left(3\right)$

In formula (3), i _p ^*and i _q ^*be respectively the desired value of the meritorious and idle component that electric current is fastened at two-phase rotational coordinates, i _a ^*, i _b ^*, i _c ^*be respectively a of electric current in three-phase static coordinate system, the expectation electric current of b, c phase;

A in step 4, the three-phase static coordinate system that obtains according to step 3, the expectation current i of b, c phase _a, ^*, i _b, ^*, i _c ^*, adopt hysteresis loop tracking PWM control mode, obtain the pwm signal of each device break-make in current transformer VSC1, control the actual I/O current i of current transformer VSC1 _a, i _b, i _c, make the actual I/O current i of current transformer VSC1 _a, i _b, i _cmeet the following conditions:

$i_a=i_a^{*},$

$i_b=i_b^{*},$

$i_c=i_c^{*};$

Step 5, after the control of step 4 couple current transformer VSC1 terminates, then current transformer VSC2 to be controlled:

If current transformer VSC2 ac phase voltage is u _c, u _cexpression formula be:

$u_c=\frac{1}{2}\mathrm{\λ}{U}_{\mathrm{dc}}\sin (\mathrm{\ωt}+\mathrm{\δ})---\left(7\right)$

In formula (7), U _dcfor current transformer VSC2 DC voltage, λ is modulation depth, and δ is the phase angle of current transformer VSC2 inverter output voltage relative to micro-capacitance sensor supply voltage, and ω is angular frequency;

Step 6, owing to there is active loss, current transformer VSC2 inverter output voltage u _cwith micro-capacitance sensor voltage not homophase, there is phase angle difference δ, current transformer VSC2 output current i and micro-capacitance sensor voltage u _salso there is phase angle difference, if be ahead of a phase angle δ, is expressed as by expression formula:

${\stackrel{\·}{U}}_s=\stackrel{\·}{I}(R+\mathrm{jX})+{\stackrel{\·}{U}}_c---\left(8\right)$

In formula (8), for the equivalent source of micro-capacitance sensor, for the equivalent source of current transformer VSC2, X represents the reactance of series reactor L2, and R represents the summation of current transformer VSC2 to the loss on the whole circuit of micro-capacitance sensor and resistance R2, for current transformer VSC2 output current,

With phase place be reference, then there is following relation:

${\stackrel{\·}{U}}_s=U_s+j0---\left(9\right)$

${\stackrel{\·}{U}}_c=U_c\cos \mathrm{\δ}+j{U}_c\sin \mathrm{\δ}---\left(10\right)$

In formula (9), for the equivalent source of micro-capacitance sensor, U _sfor the voltage magnitude of the equivalent source of micro-capacitance sensor,

In formula (10), for the equivalent source of current transformer VSC2, U _cfor the voltage magnitude of the equivalent source of VSC2, δ is the phase angle of current transformer VSC2 inverter output voltage relative to micro-capacitance sensor supply voltage,

Convolution (9) and formula (10), draw the output current of current transformer VSC2

$\stackrel{\·}{I}=\frac{{\stackrel{\·}{U}}_s-{\stackrel{\·}{U}}_c}{R+\mathrm{jX}}=\frac{U_s-U_c\cos \mathrm{\δ}-j{U}_c\sin \mathrm{\δ}}{R+\mathrm{jX}}---\left(11\right)$

In formula (11), for the equivalent source of VSC2, U _cfor the voltage magnitude of the equivalent source of VSC2, X represents the reactance of series reactor L2, and R represents the summation of current transformer VSC2 to the loss on the whole circuit of micro-capacitance sensor and resistance R2, U _sfor the voltage magnitude of the equivalent source of micro-capacitance sensor, U _cfor the voltage magnitude of the equivalent source of VSC2, δ is the phase angle of current transformer VSC2 inverter output voltage relative to micro-capacitance sensor supply voltage,

Due to X > > R, current transformer VSC2 output current be reduced to

$\stackrel{\·}{I}=-\frac{U_c\sin \mathrm{\δ}}{X}-j\frac{U_s-U_c\cos \mathrm{\δ}}{X}---\left(12\right)$

In formula (12), U _cfor the voltage magnitude of the equivalent source of VSC2, X represents the reactance of series reactor L2, U _sfor the voltage magnitude of the equivalent source of micro-capacitance sensor, U _cfor the voltage magnitude of the equivalent source of VSC2, δ is the phase angle of current transformer VSC2 inverter output voltage relative to micro-capacitance sensor supply voltage,

The complex power S that current transformer VSC2 and electrical network exchange is

$S={\stackrel{\·}{U}}_s{\stackrel{\·}{I}}^{*}=-\frac{U_s{U}_c\sin \mathrm{\δ}}{X}+j\frac{U_s(U_s-U_c\cos \mathrm{\δ})}{X}---\left(13\right)$

In formula (13), for the equivalent source of micro-capacitance sensor, X represents the reactance of series reactor L2, for the conjugation of current transformer VSC2 output current phasor, U _sfor the voltage magnitude of the equivalent source of micro-capacitance sensor, U _cfor the voltage magnitude of the equivalent source of current transformer VSC2, δ is the phase angle of current transformer VSC2 inverter output voltage relative to micro-capacitance sensor supply voltage,

To sum up obtain active-power P that current transformer VSC2 and micro-capacitance sensor exchange and reactive power Q is respectively:

$\left\{\begin{array}{c}P=-\frac{U_s{U}_c}{X}\sin \mathrm{\δ}\\ Q=-\frac{U_s(U_s-U_c\cos \mathrm{\δ})}{X}\end{array}\right.---\left(14\right)$

In formula (14), X represents the reactance of series reactor L2, U _sfor the voltage magnitude of the equivalent source of micro-capacitance sensor, U _cfor the voltage magnitude of the equivalent source of VSC2, δ is the phase angle of current transformer VSC2 inverter output voltage relative to micro-capacitance sensor supply voltage,

Convolution (14), formula (7), the active-power P exchange current transformer VSC2 and micro-capacitance sensor and reactive power Q are separately rewritten as follows:

$\left\{\begin{array}{c}P=-\frac{\frac{1}{2}\mathrm{\λ}{U}_s{U}_{\mathrm{dc}}}{X}\sin \mathrm{\δ}\\ Q=-\frac{U_s(U_s-\frac{1}{2}\mathrm{\λ}{U}_{\mathrm{dc}}\cos \mathrm{\δ})}{X}\end{array}\right.---\left(15\right)$

Known by formula (15): as long as make current transformer VSC2 inverter output voltage u _cwith micro-capacitance sensor voltage u _ssynchronous and can amplitude U be controlled _cwith phase place ω t+ δ, then can realize controlling between power distribution network and micro-capacitance sensor, to exchange meritorious P and reactive power Q, ensure the power supply quality of micro-capacitance sensor;

Step 7, at the end of to the control of current transformer VSC1 and current transformer VSC2 respectively, finally micro-capacitance sensor to be controlled:

Employing droop control method controls the distributed power source DG in described micro-capacitance sensor, and the pass obtained between micro-capacitance sensor medium frequency increment Delta f and active power increment Delta P is:

$\frac{\mathrm{\Δf}}{\mathrm{\ΔP}}=\frac{f_1-f_0}{P_1-P_0}=k_{\mathrm{Pf}}---\left(5\right)$

In formula, P ₀for the active power of micro-capacitance sensor when specified running status, f ₀for the frequency of micro-capacitance sensor when specified running status, Δ P is the added value that load increase causes micro-capacitance sensor active power of output, f ₁for cause when load increase micro-capacitance sensor active power of output increase Δ P time micro-capacitance sensor change after frequency values, Δ f is the changing value that load increase causes micro-capacitance sensor frequency, p ₁for the value after the micro-capacitance sensor active power change when load increase causes the changes delta f of micro-capacitance sensor frequency, k _pffor the sagging coefficient of active power-frequency (P-f) droop control,

In like manner the pass that can obtain between voltage increment Δ U and reactive power increment Delta Q is:

$\frac{\mathrm{\ΔU}}{\mathrm{\ΔQ}}=\frac{U_1-U_0}{Q_1-Q_0}=k_{\mathrm{QU}}---\left(6\right)$

In formula, Q ₀for the reactive power of micro-capacitance sensor when specified running status, U ₀for the voltage magnitude of micro-capacitance sensor when specified running status, Δ Q is the added value that load increase causes micro-capacitance sensor output reactive power, U ₁when increasing Δ Q for causing micro-capacitance sensor output reactive power when load increase, the voltage magnitude after micro-capacitance sensor change, Δ U is the changing value that load increase causes micro-capacitance sensor voltage magnitude, Q ₁value during for causing micro-capacitance sensor voltage magnitude changes delta U when load increase after the change of micro-capacitance sensor reactive power, k _qUfor the sagging coefficient of reactive power-voltage (Q-U) droop control;

Step 8, after step 7 pair micro-capacitance sensor controls, and then control and then realize the non differential regulation of micro-capacitance sensor electric voltage frequency by step 5 couple current transformer VSC2.

The feature of the present invention second technical scheme is also,

Transformation matrix T in step 3 _abc/pqexpression formula be specially:

$T_{\mathrm{abc}/\mathrm{pq}}=\sqrt{\frac{2}{3}}\left[\begin{array}{cc}\sin \mathrm{\ωt}& -\cos \mathrm{\ωt}\\ \sin (\mathrm{\ωt}-\frac{2}{3}\mathrm{\π})& -\cos (\mathrm{\ωt}-\frac{2}{3}\mathrm{\π})\\ \sin (\mathrm{\ωt}+\frac{2}{3}\mathrm{\π})& -\cos (\mathrm{\ωt}+\frac{2}{3}\mathrm{\π})\end{array}\right]---\left(4\right)$

In formula (4), ω is angular frequency.

The invention has the beneficial effects as follows, a kind of control system improving micro-capacitance sensor quality of voltage, by a pair current transformer VSC1 and VSC2 is accessed between power distribution network and micro-capacitance sensor back-to-back, it is made to export as unit power factor for power distribution network, whole system structure is simple, and improve the control method of micro-capacitance sensor quality of voltage, achieve two-way flow and the good power supply quality of micro-capacitance sensor of power between power distribution network and micro-capacitance sensor.

Accompanying drawing explanation

Fig. 1 is a kind of system construction drawing improving the control system of micro-capacitance sensor quality of voltage of the present invention;

Fig. 2 is the control block diagram that the present invention improves current transformer VSC1 in the control method of micro-capacitance sensor quality of voltage;

Fig. 3 is the control block diagram that the present invention improves current transformer VSC2 in the control method of micro-capacitance sensor quality of voltage;

Fig. 4 is the droop control schematic diagram that the present invention improves the control method of micro-capacitance sensor quality of voltage;

Fig. 5 is the voltage and current oscillogram that the present invention improves current transformer VSC1 and power distribution network tie point in the control method of micro-capacitance sensor quality of voltage;

Fig. 6 is A phase voltage and the A phase current waveform figure that the present invention improves current transformer VSC1 and power distribution network tie point in the control method of micro-capacitance sensor quality of voltage;

Fig. 7 is the voltage oscillogram that the present invention improves the DC bus capacitor C in the control method of micro-capacitance sensor quality of voltage between current transformer VSC1 and current transformer VSC2;

Fig. 8 is that the present invention improves the active power of DG output and the electric voltage frequency oscillogram of micro-capacitance sensor PCC point in the control method of micro-capacitance sensor quality of voltage;

Fig. 9 is that the present invention improves the reactive power of DG output and the voltage magnitude oscillogram of micro-capacitance sensor PCC point in the control method of micro-capacitance sensor quality of voltage;

Figure 10 is the A phase voltage waveform figure that the present invention improves microgrid PCC point in the control method of micro-capacitance sensor quality of voltage.

In figure, 1. power distribution network, 2. micro-capacitance sensor.

Embodiment

Below in conjunction with the drawings and specific embodiments, the present invention is described in detail.

A kind of control system improving micro-capacitance sensor quality of voltage of the present invention, structure as shown in Figure 1, comprise current transformer VSC1 and VSC2 accessed back-to-back between power distribution network 1 and micro-capacitance sensor 2 for a pair, DC bus capacitor C is parallel with between current transformer VSC1 and VSC2, reactor L1 is also connected with in turn between current transformer VSC1 and power distribution network 1, resistance R1 and switch disconnector CB1, ground connection after electric capacity C1 is also connected between resistance R1 and switch disconnector CB1, reactor L2 is also connected with in turn between current transformer VSC2 and micro-capacitance sensor 2, resistance R2 and switch disconnector CB2, by coordinating control two switch disconnector CB1 and CB2, micro-capacitance sensor is made to be in grid-connected or island state, ground connection after electric capacity C2 is also connected between resistance R2 and switch disconnector CB2, micro-capacitance sensor 2 by the distributed power source DG1 be connected in parallel on micro-capacitance sensor bus and distributed power source DG2 and on the spot load form.

The present invention improves the control method of the control system of micro-capacitance sensor quality of voltage, specifically implements according to following steps:

Step 1, first current transformer VSC1 to be controlled:

Because back-to-back converter VSC1 is connected with current transformer VSC1 and current transformer VSC2 respectively with the DC bus capacitor C of current transformer VSC2, the therefore voltage u of DC bus capacitor C _dcthe active power being flowed into DC side by two side converter VSC1 and current transformer VSC2 determines jointly, and the voltage computing formula of DC bus capacitor C is specific as follows:

${\mathrm{Cu}}_{\mathrm{dc}}\frac{{\mathrm{du}}_{\mathrm{dc}}}{\mathrm{dt}}=P_1+P_2---\left(1\right)$

In formula (1), C is the capacitance of the DC bus capacitor between back-to-back converter VSC1 and current transformer VSC2, u _dcfor the voltage of DC bus capacitor, P ₁for the active power that current transformer VSC1 and power distribution network 1 exchange, P ₂for the active power that current transformer VSC2 and micro-capacitance sensor 2 exchange, P ₂numerical value determined by the effective power flow on micro-capacitance sensor and electric voltage frequency, P ₂change can cause u _dcchange, can by the active-power P regulating current transformer VSC1 and power distribution network 1 exchange ₁carry out control u _dcfor constant, therefore by control u _dcthe desired value that VSC1 inputs or outputs active current can be obtained.

Step 2, in order to keep current transformer VSC1 to export as unit power factor, i.e. current transformer VSC1 only active power of output, so establish the desired value i of the reactive current of current transformer VSC1 _q ^*=0, the formula (1) in integrating step 1, obtains the desired value i of the meritorious and idle component that VSC1 I/O electric current is fastened at two-phase rotational coordinates thus _p ^*and i _q ^*be respectively:

$\left\{\begin{array}{c}{i}_p^{*}=\frac{{\mathrm{Cu}}_{\mathrm{dc}}\frac{{\mathrm{du}}_{\mathrm{dc}}}{\mathrm{dt}}}{\left|e\right|}\\ i_q^{*}=0\end{array}\right.---\left(2\right)$

In formula (2), i _p ^*and i _q ^*be respectively the desired value of the meritorious and idle component that electric current is fastened at two-phase rotational coordinates, C is the capacitance of the DC bus capacitor between back-to-back converter VSC1 and VSC2, u _dcfor the voltage of DC bus capacitor, | e| is the amplitude of VSC1 input/output voltage vector;

Step 3, the i will obtained in step 2 _p ^*and i _q ^*transforming to three-phase static coordinate system by transformation matrix, obtaining the desired value of electric current in three-phase static coordinate system by analyzing transformation result:

$\left[\begin{array}{c}{i}_a^{*}\\ i_b^{*}\\ i_c^{*}\end{array}\right]=T_{\mathrm{abc}/\mathrm{pq}}\left[\begin{array}{c}{i}_p^{*}\\ i_q^{*}\end{array}\right]---\left(3\right)$

In formula (3), i _p ^*and i _q ^*be respectively the desired value of the meritorious and idle component that electric current is fastened at two-phase rotational coordinates, i _a ^* _,, i _b ^* _,, i _c ^*be respectively a of electric current in three-phase static coordinate system, the expectation electric current of b, c phase,

Change matrix T _abc/pqexpression formula be specially:

$T_{\mathrm{abc}/\mathrm{pq}}=\sqrt{\frac{2}{3}}\left[\begin{array}{cc}\sin \mathrm{\ωt}& -\cos \mathrm{\ωt}\\ \sin (\mathrm{\ωt}-\frac{2}{3}\mathrm{\π})& -\cos (\mathrm{\ωt}-\frac{2}{3}\mathrm{\π})\\ \sin (\mathrm{\ωt}+\frac{2}{3}\mathrm{\π})& -\cos (\mathrm{\ωt}+\frac{2}{3}\mathrm{\π})\end{array}\right]---\left(4\right)$

In formula (4), ω is angular frequency;

A in step 4, the three-phase static coordinate system that obtains according to step 3, the expectation current i of b, c phase _a, ^*, i _b, ^*, i _c ^*, adopt hysteresis loop tracking PWM control mode, obtain the pwm signal of each device break-make in current transformer VSC1, control the actual I/O current i of current transformer VSC1 _a, i _b, i _c, make the actual I/O current i of current transformer VSC1 _a, i _b, i _cmeet the following conditions:

$i_a=i_a^{*},$

$i_b=i_b^{*},$

$i_c=i_c^{*},$

Namely the actual I/O current tracking controlling current transformer VSC1 expects electric current; Comprehensive above two control objectives, the control strategy of VSC1 is as shown in Figure 2;

Step 5, after the control of step 4 couple current transformer VSC1 terminates, again current transformer VSC2 is controlled, adopt the meritorious and reactive power that PI regulable control current transformer VSC2 exports, frequency modulation frequency modulation (width) effect of simulation conventional electric power system, makes current transformer VSC2 and micro-capacitance sensor 2 tie point voltage u _camplitude equal with desired value with frequency, and in control procedure, make active current two-way flow between micro-capacitance sensor 2 and power distribution network 1:

If current transformer VSC2 ac phase voltage is u _c, u _cexpression formula be:

$u_c=\frac{1}{2}\mathrm{\λ}{U}_{\mathrm{dc}}\sin (\mathrm{\ωt}+\mathrm{\δ})---\left(7\right)$

In formula (7), U _dcfor current transformer VSC2 DC voltage, λ is modulation depth, and δ is the phase angle of current transformer VSC2 inverter output voltage relative to micro-capacitance sensor supply voltage, and ω is angular frequency,

Step 6, owing to there is active loss, current transformer VSC2 inverter output voltage u _cwith micro-capacitance sensor voltage not homophase, there is phase angle difference δ, current transformer VSC2 output current i and micro-capacitance sensor voltage u _salso there is phase angle difference, if be ahead of a phase angle δ, is expressed as by expression formula:

${\stackrel{\·}{U}}_s=\stackrel{\·}{I}(R+\mathrm{jX})+{\stackrel{\·}{U}}_c---\left(8\right)$

In formula (8), for the equivalent source of micro-capacitance sensor, for the equivalent source of current transformer VSC2, X represents the reactance of series reactor L2, and R represents the summation of current transformer VSC2 to the loss on the whole circuit of micro-capacitance sensor and resistance R2, for current transformer VSC2 output current,

With phase place be reference, then there is following relation:

${\stackrel{\·}{U}}_s=U_s+j0---\left(9\right)$

${\stackrel{\·}{U}}_c=U_c\cos \mathrm{\δ}+j{U}_c\sin \mathrm{\δ}---\left(10\right)$

In formula (9), for the equivalent source of micro-capacitance sensor 2, U _sfor the voltage magnitude of the equivalent source of micro-capacitance sensor 2,

In formula (10), for the equivalent source of current transformer VSC2, U _cfor the voltage magnitude of the equivalent source of VSC2, δ is the phase angle of current transformer VSC2 inverter output voltage relative to micro-capacitance sensor supply voltage,

Convolution (9) and formula (10), draw the output current of current transformer VSC2

$\stackrel{\·}{I}=\frac{{\stackrel{\·}{U}}_s-{\stackrel{\·}{U}}_c}{R+\mathrm{jX}}=\frac{U_s-U_c\cos \mathrm{\δ}-j{U}_c\sin \mathrm{\δ}}{R+\mathrm{jX}}---\left(11\right)$

In formula (11), for the equivalent source of VSC2, U _cfor the voltage magnitude of the equivalent source of VSC2, X represents the reactance of series reactor L2, and R represents the summation of current transformer VSC2 to the loss on the whole circuit of micro-capacitance sensor 2 and resistance R2, U _sfor the voltage magnitude of the equivalent source of micro-capacitance sensor 2, U _cfor the voltage magnitude of the equivalent source of VSC2, δ is the phase angle of current transformer VSC2 inverter output voltage relative to micro-capacitance sensor supply voltage,

Due to X > > R, current transformer VSC2 output current be reduced to

$\stackrel{\·}{I}=-\frac{U_c\sin \mathrm{\δ}}{X}-j\frac{U_s-U_c\cos \mathrm{\δ}}{X}---\left(12\right)$

In formula (12), U _cfor the voltage magnitude of the equivalent source of VSC2, X represents the reactance of series reactor L2, U _sfor the voltage magnitude of the equivalent source of micro-capacitance sensor (2), U _cfor the voltage magnitude of the equivalent source of VSC2, δ is the phase angle of current transformer VSC2 inverter output voltage relative to micro-capacitance sensor supply voltage,

The complex power S that current transformer VSC2 and electrical network exchange is

$S={\stackrel{\·}{U}}_s{\stackrel{\·}{I}}^{*}=-\frac{U_s{U}_c\sin \mathrm{\δ}}{X}+j\frac{U_s(U_s-U_c\cos \mathrm{\δ})}{X}---\left(13\right)$

In formula (13), for the equivalent source of micro-capacitance sensor 2, X represents the reactance of series reactor L2, for the conjugation of current transformer VSC2 output current phasor, U _sfor the voltage magnitude of the equivalent source of micro-capacitance sensor 2, U _cfor the voltage magnitude of the equivalent source of current transformer VSC2, δ is the phase angle of current transformer VSC2 inverter output voltage relative to micro-capacitance sensor supply voltage,

To sum up obtain active-power P that current transformer VSC2 and micro-capacitance sensor exchange and reactive power Q is respectively:

$\left\{\begin{array}{c}P=-\frac{U_s{U}_c}{X}\sin \mathrm{\δ}\\ Q=-\frac{U_s(U_s-U_c\cos \mathrm{\δ})}{X}\end{array}\right.---\left(14\right)$

In formula (14), X represents the reactance of series reactor L2, U _sfor the voltage magnitude of the equivalent source of micro-capacitance sensor (2), U _cfor the voltage magnitude of the equivalent source of VSC2, δ is the phase angle of current transformer VSC2 inverter output voltage relative to micro-capacitance sensor supply voltage,

Convolution (14), formula (7), the active-power P exchange current transformer VSC2 and micro-capacitance sensor and reactive power Q are separately rewritten as follows:

$\left\{\begin{array}{c}P=-\frac{\frac{1}{2}\mathrm{\λ}{U}_s{U}_{\mathrm{dc}}}{X}\sin \mathrm{\δ}\\ Q=-\frac{U_s(U_s-\frac{1}{2}\mathrm{\λ}{U}_{\mathrm{dc}}\cos \mathrm{\δ})}{X}\end{array}\right.---\left(15\right)$

Formula (15) reflects P, Q and circuit parameter (X, U _s) and controlled variable (λ, δ, U _dc) between inner link, can be obtained by formula (15) and control conclusion as follows:

A) u _cbe ahead of u _s, namely during δ >0, P<0, represents that micro-capacitance sensor 2 absorbs energy from power distribution network 1,

B) u _clag behind u _s, namely during δ <0, P>0, represents that micro-capacitance sensor 2 is to power distribution network 1 feedback energy,

C) U _c<U _stime, Q<0, current transformer VSC2 sends capacitive reactive power,

D) U _c>U _stime, it is idle that Q>0, current transformer VSC2 send perception,

Thus, draw and finally control conclusion: as long as make current transformer VSC2 inverter output voltage u _cwith micro-capacitance sensor voltage u _ssynchronous and can amplitude U be controlled _cwith phase place ω t+ δ, then can realize controlling between power distribution network 1 and micro-capacitance sensor 2, to exchange meritorious P and reactive power Q, ensure the power supply quality of micro-capacitance sensor, according to above derivation, the control strategy of VSC2 can be obtained as shown in Figure 3,

When load changes, frequency and the amplitude at the PCC point place of micro-capacitance sensor change, by comparing actual frequency and reference frequency, virtual voltage amplitude and the reference voltage amplitude of micro-capacitance sensor, deviation that is meritorious and reactive power is obtained after frequency departure and amplitude deviation are multiplied by sagging coefficient, then after PI regulates, fuzzy respectively according to its degree of correlation is parameter δ and λ, then synthesized reference voltage, and the method finally adopting indirect current to follow the tracks of obtains pwm signal;

Step 7, at the end of to the control of current transformer VSC1 and current transformer VSC2 respectively, finally micro-capacitance sensor to be controlled:

Adopt the distributed power source DG in droop control method control micro-capacitance sensor 2, as shown in Figure 4, operate in rated point A at initial time micro-some net 2, when load increase causes micro-capacitance sensor 2 active power of output to increase Δ P, the frequency of micro-capacitance sensor 2 is by f ₀be reduced to f ₁, being similar to the primary frequency modulation of electric power system, is droop control, and the pass that can obtain between micro-capacitance sensor 2 medium frequency increment Delta f and active power increment Delta P is:

$\frac{\mathrm{\&Delta;f}}{\mathrm{\&Delta;P}}=\frac{f_1-f_0}{P_1-P_0}=k_{\mathrm{Pf}}---\left(5\right)$

In formula, P ₀for the active power of micro-capacitance sensor 2 when specified running status, f ₀for the frequency of micro-capacitance sensor 2 when specified running status, Δ P is the added value that load increase causes micro-capacitance sensor 2 active power of output, f ₁for cause when load increase micro-capacitance sensor 2 active power of output increase Δ P time micro-capacitance sensor 2 change after frequency values, Δ f is the changing value that load increase causes micro-capacitance sensor 2 frequency, P ₁value during for causing the changes delta f of micro-capacitance sensor 2 frequency when load increase after the change of micro-capacitance sensor active power, k _pffor the sagging coefficient of active power-frequency (P-f) droop control,

In like manner the pass that can obtain between voltage increment Δ U and reactive power increment Delta Q is:

$\frac{\mathrm{\&Delta;U}}{\mathrm{\&Delta;Q}}=\frac{U_1-U_0}{Q_1-Q_0}=k_{\mathrm{QU}}---\left(6\right)$

In formula, Q ₀for the reactive power of micro-capacitance sensor 2 when specified running status, U ₀for the voltage magnitude of micro-capacitance sensor 2 when specified running status, Δ Q is the added value that load increase causes micro-capacitance sensor 2 output reactive power, U ₁when increasing Δ Q for causing micro-capacitance sensor 2 output reactive power when load increase, the voltage magnitude after micro-capacitance sensor 2 changes, Δ U is the changing value that load increase causes micro-capacitance sensor 2 voltage magnitude, Q ₁value during for causing micro-capacitance sensor 2 voltage magnitude changes delta U when load increase after the change of micro-capacitance sensor reactive power, k _qUfor the sagging coefficient of reactive power-voltage (Q-U) droop control;

Step 8, after described step 7 pair micro-capacitance sensor 2 controls, and then control and then realize the non differential regulation of micro-capacitance sensor 2 electric voltage frequency by described step 5 couple current transformer VSC2.

In order to verify when load variations, adopt back-to-back converter to solve the effect of micro-capacitance sensor frequency, voltage deviation problem, MATLAB/Simulink emulate:

Build the system diagram of micro-capacitance sensor access power distribution network according to Fig. 1, back-to-back converter VSC1 and current transformer VSC2 adopts derived control strategy respectively, and DG adopts droop control strategy, the voltage e of current transformer VSC1 and power distribution network 1 tie point _abcwith output current i _abcas shown in Figure 5, sine degree is fine, and harmonic wave is less, A phase voltage e for waveform _awith A phase current i _abetween phase relation as shown in Figure 6, be unit power factor, DC voltage u _dcas shown in Figure 7, when 1s, VSC1's waveform puts into operation, u _dcbe stabilized in 800V, these three groups of simulation results illustrate that current transformer VSC1 adopts the control strategy designed by this paper, change active current with power distribution network top-cross in the course of the work and the harmonic wave injected electrical network is very small, DC voltage is stabilized in constant in control procedure simultaneously.

Emulation arranges as follows: during t=0 ~ 0.2s, DG is with rated load operation, nominal load active load P _nbe set to P _n=1kW, nominal reactive load Q _nbe set to Q _n=0; The t=0.2s moment, load of uprushing, it is P=2.8kW that load of uprushing is set to active load, and reactive load is Q=1.1kVar; During t=0.3s, drop into VSC2 and start frequency adjustment, starting amplitude during t=0.4s and regulate.

The change waveform of the electric voltage frequency f of the PCC point of the active-power P that DG exports and micro-capacitance sensor 2 as shown in Figure 8, the reactive power Q of DG output and the voltage magnitude U of PCC point of micro-capacitance sensor 2 _schange waveform as shown in Figure 9, as t=0.2 ~ 0.3s, can be followed the tracks of load exactly from Fig. 8 and Fig. 9, DG and gain merit and the change of reactive power, and simulate the primary frequency modulation of conventional electric power system and the effect of an amplitude modulation by droop control; As t=0.3s, VSC2 is connected to the PCC point of micro-capacitance sensor 2, and starts FREQUENCY CONTROL, and electrical network injects active power by back-to-back converter to microgrid, and after 0.1s, frequency retrieval is desired value 50Hz; During t=0.4s, VSC2 adds voltage magnitude and controls, and after 0.15s, voltage magnitude reverts to desired value 311V, the A phase voltage u of the PCC point of micro-capacitance sensor 2 _saas shown in Figure 10, can find out that voltage sinusoidal degree is better, meet demand for control.

The present invention is applicable to adopt back-to-back converter access power distribution network to improve the situation of micro-capacitance sensor quality of voltage, based on the control to back-to-back converter, achieves the non differential regulation of micro-capacitance sensor electric voltage frequency, amplitude.By controlling the DC capacitor voltage be coupled between the active power of grid side current transformer I/O, the electric voltage frequency of micro-capacitance sensor side converter access point and amplitude and two current transformers, realize to and fro flow of power and the good power supply quality of micro-capacitance sensor between power distribution network and micro-capacitance sensor.Electric voltage frequency and amplitude control to be the key that micro-capacitance sensor stability controls, and its essence is balance and the reallocation of power.When the active power that all DG of micro-capacitance sensor provide is less than the active power of all load absorption in microgrid, can cause the electric voltage frequency deviation of micro-capacitance sensor current transformer access point, now VSC1 is absorbed active power from power distribution network and is provided to micro-capacitance sensor by VSC2; With should the power that exports of micro-capacitance sensor DG be greater than the power of load needs time, micro-capacitance sensor, makes to remain power-balance in micro-capacitance sensor to power distribution network active power of output by VSC2 and VSC1, the raising micro-capacitance sensor quality of voltage of powering.When causing micro-capacitance sensor voltage magnitude deviation due to reactive power in micro-capacitance sensor, perception or capacitive reactive power can be provided to carry out regulation voltage amplitude to micro-capacitance sensor by VSC2.

Claims (4)

1. one kind is improved the control system of micro-capacitance sensor quality of voltage, it is characterized in that, comprise current transformer VSC1 and VSC2 accessed back-to-back for a pair between power distribution network (1) and micro-capacitance sensor (2), DC bus capacitor C is parallel with between current transformer VSC1 and VSC2, reactor L1 is also connected with in turn between described current transformer VSC1 and power distribution network (1), resistance R1 and switch disconnector CB1, ground connection after electric capacity C1 is also connected between described resistance R1 and switch disconnector CB1, reactor L2 is also connected with in turn between described current transformer VSC2 and micro-capacitance sensor (2), resistance R2 and switch disconnector CB2, ground connection after electric capacity C2 is also connected between described resistance R2 and switch disconnector CB2.

2. a kind of control system improving micro-capacitance sensor quality of voltage according to claim 1, is characterized in that, described micro-capacitance sensor (2) by the distributed power source DG1 be connected in parallel on micro-capacitance sensor bus and distributed power source DG2 and on the spot load form.

3. improve a control method for micro-capacitance sensor quality of voltage, it is characterized in that, specifically implement according to following steps:

Step 1, first current transformer VSC1 to be controlled:

Because back-to-back converter VSC1 is connected with current transformer VSC1 and current transformer VSC2 respectively with the DC bus capacitor C of current transformer VSC2, the therefore voltage u of DC bus capacitor C _dcthe active power being flowed into DC side by two side converter VSC1 and current transformer VSC2 determines jointly, and the voltage computing formula of DC bus capacitor C is specific as follows:

${\mathrm{Cu}}_{\mathrm{dc}}\frac{{\mathrm{du}}_{\mathrm{dc}}}{\mathrm{dt}}=P_1+P_2---\left(1\right)$

In formula (1), C is the capacitance of the DC bus capacitor between back-to-back converter VSC1 and current transformer VSC2, u _dcfor the voltage of DC bus capacitor, P ₁for the active power that current transformer VSC1 and power distribution network (1) exchange, P ₂for the active power that current transformer VSC2 and micro-capacitance sensor (2) exchange;

Step 2, maintenance current transformer VSC1 export as unit power factor, if the desired value i of the reactive current of current transformer VSC1 _q ^*=0, in conjunction with the formula (1) in described step 1, obtain the desired value i of the meritorious and idle component that VSC1 I/O electric current is fastened at two-phase rotational coordinates thus _p ^*and i _q ^*be respectively:

$\left\{\begin{array}{c}{i}_p^{*}=\frac{{\mathrm{Cu}}_{\mathrm{dc}}\frac{{\mathrm{du}}_{\mathrm{dc}}}{\mathrm{dt}}}{\left|e\right|}\\ i_q^{*}=0\end{array}\right.---\left(2\right)$

In formula (2), i _p ^*and i _q ^*be respectively the desired value of the meritorious and idle component that electric current is fastened at two-phase rotational coordinates, C is the capacitance of the DC bus capacitor between back-to-back converter VSC1 and VSC2, u _dcfor the voltage of DC bus capacitor, | e| is the amplitude of VSC1 input/output voltage vector;

Step 3, the i will obtained in described step 2 _p ^*and i _q ^*transforming to three-phase static coordinate system by transformation matrix, obtaining the desired value of electric current in three-phase static coordinate system by analyzing transformation result:

$\left[\begin{array}{c}{i}_a^{*}\\ i_b^{*}\\ i_c^{*}\end{array}\right]=T_{\mathrm{abc}/\mathrm{pq}}\left[\begin{array}{c}{i}_p^{*}\\ i_q^{*}\end{array}\right]---\left(3\right)$

In formula (3), i _p ^*and i _q ^*be respectively the desired value of the meritorious and idle component that electric current is fastened at two-phase rotational coordinates, i _a ^* _,, i _b ^* _,, i _c ^*be respectively a of electric current in three-phase static coordinate system, the expectation electric current of b, c phase;

A in step 4, the three-phase static coordinate system that obtains according to described step 3, the expectation current i of b, c phase _a, ^*, i _b, ^*, i _c ^*, adopt hysteresis loop tracking PWM control mode, obtain the pwm signal of each device break-make in current transformer VSC1, control the actual I/O current i of current transformer VSC1 _a, i _b, i _c, make the actual I/O current i of current transformer VSC1 _a, i _b, i _cmeet the following conditions:

$i_a=i_a^{*},$

$i_b=i_b^{*},$

$i_c=i_c^{*};$

Step 5, after the control of described step 4 couple current transformer VSC1 terminates, then current transformer VSC2 to be controlled:

If current transformer VSC2 ac phase voltage is u _c, u _cexpression formula be:

$u_c=\frac{1}{2}\mathrm{\&lambda;}{U}_{\mathrm{dc}}\sin (\mathrm{\&omega;t}+\mathrm{\&delta;})---\left(7\right)$

In formula (7), U _dcfor current transformer VSC2 DC voltage, λ is modulation depth, and δ is the phase angle of current transformer VSC2 inverter output voltage relative to micro-capacitance sensor supply voltage, and ω is angular frequency;

Step 6, owing to there is active loss, current transformer VSC2 inverter output voltage u _cwith micro-capacitance sensor voltage not homophase, there is phase angle difference δ, current transformer VSC2 output current i and micro-capacitance sensor voltage u _salso there is phase angle difference, if be ahead of a phase angle δ, is expressed as by expression formula:

${\stackrel{\&CenterDot;}{U}}_s=\stackrel{\&CenterDot;}{I}(R+\mathrm{jX})+{\stackrel{\&CenterDot;}{U}}_c---\left(8\right)$

In formula (8), for the equivalent source of micro-capacitance sensor, for the equivalent source of current transformer VSC2, X represents the reactance of series reactor L2, and R represents the summation of current transformer VSC2 to the loss on the whole circuit of micro-capacitance sensor and resistance R2, for current transformer VSC2 output current,

With phase place be reference, then there is following relation:

${\stackrel{\&CenterDot;}{U}}_s=U_s+j0---\left(9\right)$

${\stackrel{\&CenterDot;}{U}}_c=U_c\cos \mathrm{\&delta;}+j{U}_c\sin \mathrm{\&delta;}---\left(10\right)$

In formula (9), for the equivalent source of micro-capacitance sensor (2), U _sfor the voltage magnitude of the equivalent source of micro-capacitance sensor (2),

In formula (10), for the equivalent source of current transformer VSC2, U _cfor the voltage magnitude of the equivalent source of VSC2, δ is the phase angle of current transformer VSC2 inverter output voltage relative to micro-capacitance sensor supply voltage,

Convolution (9) and formula (10), draw the output current of current transformer VSC2

$\stackrel{\&CenterDot;}{I}=\frac{{\stackrel{\&CenterDot;}{U}}_s-{\stackrel{\&CenterDot;}{U}}_c}{R+\mathrm{jX}}=\frac{U_s-U_c\cos \mathrm{\&delta;}-j{U}_c\sin \mathrm{\&delta;}}{R+\mathrm{jX}}---\left(11\right)$

In formula (11), for the equivalent source of VSC2, U _cfor the voltage magnitude of the equivalent source of VSC2, X represents the reactance of series reactor L2, and R represents the summation of current transformer VSC2 to the loss on micro-capacitance sensor (2) whole circuit and resistance R2, U _sfor the voltage magnitude of the equivalent source of micro-capacitance sensor (2), U _cfor the voltage magnitude of the equivalent source of VSC2, δ is the phase angle of current transformer VSC2 inverter output voltage relative to micro-capacitance sensor supply voltage,

Due to X > > R, current transformer VSC2 output current be reduced to

$\stackrel{\&CenterDot;}{I}=-\frac{U_c\sin \mathrm{\&delta;}}{X}-j\frac{U_s-U_c\cos \mathrm{\&delta;}}{X}---\left(12\right)$

In formula (12), U _cfor the voltage magnitude of the equivalent source of VSC2, X represents the reactance of series reactor L2, U _sfor the voltage magnitude of the equivalent source of micro-capacitance sensor (2), U _cfor the voltage magnitude of the equivalent source of VSC2, δ is the phase angle of current transformer VSC2 inverter output voltage relative to micro-capacitance sensor supply voltage,

The complex power S that current transformer VSC2 and electrical network exchange is

$S={\stackrel{\&CenterDot;}{U}}_s\stackrel{\&CenterDot;}{I^{*}}=-\frac{U_s{U}_c\sin \mathrm{\&delta;}}{X}+j\frac{U_s(U_s-U_c\cos \mathrm{\&delta;})}{X}---\left(13\right)$

In formula (13), for the equivalent source of micro-capacitance sensor (2), X represents the reactance of series reactor L2, for the conjugation of current transformer VSC2 output current phasor, U _sfor the voltage magnitude of the equivalent source of micro-capacitance sensor (2), U _cfor the voltage magnitude of the equivalent source of current transformer VSC2, δ is the phase angle of current transformer VSC2 inverter output voltage relative to micro-capacitance sensor supply voltage,

To sum up obtain active-power P that current transformer VSC2 and micro-capacitance sensor exchange and reactive power Q is respectively:

$\left\{\begin{array}{c}P=-\frac{U_s{U}_c}{X}\sin \mathrm{\&delta;}\\ Q=-\frac{U_s(U_s-U_c\cos \mathrm{\&delta;})}{X}\end{array}\right.---\left(14\right)$

In formula (14), X represents the reactance of series reactor L2, U _sfor the voltage magnitude of the equivalent source of micro-capacitance sensor (2), U _cfor the voltage magnitude of the equivalent source of VSC2, δ is the phase angle of current transformer VSC2 inverter output voltage relative to micro-capacitance sensor supply voltage,

Convolution (14), formula (7), the active-power P exchange current transformer VSC2 and micro-capacitance sensor and reactive power Q are separately rewritten as follows:

$\left\{\begin{array}{c}P=-\frac{\frac{1}{2}\mathrm{\&lambda;}{U}_s{U}_{\mathrm{dc}}}{X}\sin \mathrm{\&delta;}\\ Q=-\frac{U_s(U_s-\frac{1}{2}\mathrm{\&lambda;}{U}_{\mathrm{dc}}\cos \mathrm{\&delta;})}{X}\end{array}\right.---\left(15\right)$

Known by formula (15): as long as make current transformer VSC2 inverter output voltage u _cwith micro-capacitance sensor voltage u _ssynchronous and can amplitude U be controlled _cwith phase place ω t+ δ, then can realize controlling between power distribution network (1) and micro-capacitance sensor (2), to exchange meritorious P and reactive power Q, ensure the power supply quality of micro-capacitance sensor;

Step 7, at the end of to the control of current transformer VSC1 and current transformer VSC2 respectively, finally micro-capacitance sensor to be controlled:

Employing droop control method controls the distributed power source DG in described micro-capacitance sensor (2), and the pass obtained between micro-capacitance sensor (2) medium frequency increment Delta f and active power increment Delta P is:

$\frac{\mathrm{\&Delta;f}}{\mathrm{\&Delta;P}}=\frac{f_1-f_0}{P_1-P_0}=k_{\mathrm{Pf}}---\left(5\right)$

In formula, P ₀for the active power of micro-capacitance sensor (2) when specified running status, f ₀for the frequency of micro-capacitance sensor (2) when specified running status, Δ P is the added value that load increase causes micro-capacitance sensor (2) active power of output, f ₁for cause when load increase micro-capacitance sensor (2) active power of output increase Δ P time micro-capacitance sensor (2) change after frequency values, Δ f is the changing value that load increase causes micro-capacitance sensor (2) frequency, p ₁value during for causing the changes delta f of micro-capacitance sensor (2) frequency when load increase after the change of micro-capacitance sensor active power, k _pffor the sagging coefficient of active power-frequency (P-f) droop control,

In like manner the pass that can obtain between voltage increment Δ U and reactive power increment Delta Q is:

$\frac{\mathrm{\&Delta;U}}{\mathrm{\&Delta;Q}}=\frac{U_1-U_0}{Q_1-Q_0}=k_{\mathrm{QU}}---\left(6\right)$

In formula, Q ₀for the reactive power of micro-capacitance sensor (2) when specified running status, U ₀for the voltage magnitude of micro-capacitance sensor (2) when specified running status, Δ Q is the added value that load increase causes micro-capacitance sensor (2) output reactive power, U ₁when increasing Δ Q for causing micro-capacitance sensor (2) output reactive power when load increase, the voltage magnitude after micro-capacitance sensor (2) change, Δ U is the changing value that load increase causes micro-capacitance sensor (2) voltage magnitude, Q ₁value during for causing micro-capacitance sensor (2) voltage magnitude changes delta U when load increase after the change of micro-capacitance sensor reactive power, k _qUfor the sagging coefficient of reactive power-voltage (Q-U) droop control;

Step 8, after described step 7 pair micro-capacitance sensor (2) controls, and then control and then realize the non differential regulation of micro-capacitance sensor (2) electric voltage frequency by described step 5 couple current transformer VSC2.

4. a kind of control method improving micro-capacitance sensor quality of voltage according to claim 3, is characterized in that, change matrix T in described step 3 _abc/pqexpression formula be specially:

$T_{\mathrm{abc}/\mathrm{pq}}=\sqrt{\frac{2}{3}}\left[\begin{array}{cc}\sin \mathrm{\&omega;t}& -\cos \mathrm{\&omega;t}\\ \sin (\mathrm{\&omega;t}-\frac{2}{3}\mathrm{\&pi;})& -\cos (\mathrm{\&omega;t}-\frac{2}{3}\mathrm{\&pi;})\\ \sin (\mathrm{\&omega;t}+\frac{2}{3}\mathrm{\&pi;})& -\cos (\mathrm{\&omega;t}+\frac{2}{3}\mathrm{\&pi;})\end{array}\right]---\left(4\right)$

In formula (4), ω is angular frequency.