CN104953625A - Secondary voltage control based reactive power distribution method for distributed power supplies in micro-grid - Google Patents

Abstract

The invention discloses a secondary voltage control based reactive power distribution method for distributed power supplies in a micro-grid. The secondary voltage control based reactive power distribution method includes micro-grid secondary voltage control, distributed-power-supply active and reactive power control and local output voltage control. According to a micro-grid central controller, a secondary voltage control ring generates a micro-grid alternating busbar voltage compensation signal, the central controller sends the compensation signal to each distributed power supply in the micro-grid in a broadcast mode through low-bandwidth communication, and the compensation signal serves as public reference for reactive power of each distributed power supply. A local controller of each distributed power supply acquires a reference voltage according to an active and reactive power control equation by the aid of the compensation signal to further track the reference voltage, and an inverter is controlled through pulse width modulation of closed loop feedback output quantity. The secondary voltage control based reactive power distribution method has the advantage that on the condition of unmatched micro-grid feeder impedance, reactive power of the distributed power supplies can be reasonably distributed according to drooping coefficients on the basis of micro-grid busbar voltage recovery without addition of communication transmitted information.

Description

A kind of based on distributed power source reactive power distribution method in the micro-capacitance sensor of secondary voltage control

Technical field

The invention belongs to power supply unit control technology field, be specifically related to a kind of based on distributed power source reactive power distribution method in the micro-capacitance sensor of secondary voltage control.

Background technology

Along with the exhaustion day by day of traditional fossil energy, the exploitation of efficient, clean new and renewable sources of energy receive the common concern of society.Distributed power source can provide the interface with electrical network for different types of energy, obtains and applies more and more widely.Micro-capacitance sensor is coordinated and managed multiple distributed power source (DG), is the important channel of distributed energy efficiency utilization.

In the micro-capacitance sensor of island mode, distributed power source adopts the parallel running of droop control technology.Droop control technology frequency and voltage amplitude regulates meritorious, reactive power respectively, is conventional power distribution method.But traditional droop control has limitation to power division.Owing to being subject to the restrictions such as natural conditions, the distributed power source geographical position relative distribution in micro-capacitance sensor, feeder line distance, feed line impedance is comparatively large, and feed line impedance has perception and resistive composition usually simultaneously.Adopt the inverter of reactive power-voltage magnitude droop control when impedance mismatch, cannot realize distributing reactive power according to sagging coefficient.Virtual impedance method improves a kind of common method of distributed power source power division precision, can reduce the not matching degree of distributed power source output impedance, improves the assignment accuracy of reactive power.But the micro-grid system that virtual impedance technology directly applies to the larger feed line impedance of existence has certain contradiction.Consider the impact of feed line impedance in micro-capacitance sensor, the distribution realizing reactive power needs to arrange larger virtual impedance, can reduce the quality of voltage of micro-capacitance sensor; If arrange less virtual impedance, cannot make it in total impedance, account for leading role, the assignment accuracy of reactive power can be reduced.

In addition, power control droop characteristic and feeder line pressure drop cause micro-capacitance sensor ac bus voltage deviation rated value.The technology that current employing linear quadratic control recovers busbar voltage becomes to achieve some achievements.And when distributing the additional function as linear quadratic control using reactive power at present, need the reactive power information transmitting each distributed power source in communication network, add network communication loads, improve the complexity of communication.When distributed power source quantity is more in micro-capacitance sensor, easily produce network congestion.

Summary of the invention

For the above-mentioned technical problem existing for prior art, the invention provides a kind of based on distributed power source reactive power distribution method in the micro-capacitance sensor of secondary voltage control, in micro-capacitance sensor in the unmatched situation of feed line impedance, the reactive power that distributed power source (DG) exports can be realized distribute according to sagging coefficient, not need the reactive power information transmitting each distributed power source in communication system.Meanwhile, secondary voltage controls micro-capacitance sensor busbar voltage to return to rated value.

Based on a distributed power source reactive power distribution method in the micro-capacitance sensor that secondary voltage controls, comprise the steps:

(1) micro-capacitance sensor master controller gathers micro-capacitance sensor busbar voltage, and calculates the effective value V of busbar voltage _com;

(2) the secondary voltage control ring in micro-capacitance sensor master controller is according to the effective value V of described busbar voltage _comwith the specified effective value V of busbar voltage _com ^*, passing ratio-integration (PI) controller calculates generatrix voltage compensation signal E _cmp, and by voltage compensation signal E _cmpeach distributed power source is given by communication network transmission with broadcast mode;

(3) each distributed power source gathers local output voltage and output current, calculates instantaneous active power p and reactive power q, and by firstorder filter, filtering obtains average active power P and reactive power Q;

(4) each distributed power source is according to described average active power P and reactive power Q, and the voltage compensation signal E obtained by communication network _cmp, pass through the amplitude E of proposed improvement droop control algorithm determination reference voltage _iand angular frequency _i;

(5) each distributed power source is according to the amplitude E of described reference voltage _iand angular frequency _icarry out closed loop feedback to control to obtain modulation signal, finally obtain three groups of pwm signals to control the three-phase inverter of distributed power source according to described modulation signal by SPWM (sinusoidal pulse width modulation) technical construction.

In described step (1), calculate the line voltage effective value V of ac bus according to following formula _com:

$r_{com}=\sqrt{\frac{v_{com\_ab}^2-+v_{com\_bc}^2-+v_{com\_ca}^2}{3}}$

Wherein: v _{com_ab}, v _{com_bc}and v _{com_ca}be respectively bus ab line voltage, bc line voltage and the ca line magnitude of voltage in current sample period.

In described step (2), calculate generatrix voltage compensation signal E according to following formula _cmp:

$E_{cmp}=k_{pV}(V_{com}^{*}-V_{com})+k_{iV}\∫(V_{com}^{*}-V_{com})dt$

Wherein: k _pVand k _iVbe respectively scale parameter and the integral parameter of PI controller; V _com ^*for the specified effective value of busbar voltage.

In described step (3), according to instantaneous active power p and the reactive power q of following formula Computation distribution formula power supply, and average active power P and reactive power Q:

$\left\{\begin{array}{c}p=v_a{i}_a+v_b{i}_b+v_c{i}_c\\ q=\frac{1}{\sqrt{3}}\[(v_b-v_c)i_a+(v_c-v_a)i_b+(v_a-v_b)i_c\]\end{array}\right.$

$\left\{\begin{array}{c}P=\frac{{\mathrm{\ω}}_c}{s+{\mathrm{\ω}}_c}p\\ Q=\frac{{\mathrm{\ω}}_c}{s+{\mathrm{\ω}}_c}q\end{array}\right.$

Wherein: v _a, v _band v _cbe respectively the three-phase output voltage of three-phase inverter in distributed power source in current sample period; i _a, i _band i _cbe respectively the output line electric current of three-phase inverter in distributed power source in current sample period; ω _cfor the corner frequency of low-pass first order filter.

In described step (4), improve droop control algorithm based on following formula:

$\left\{\begin{array}{c}{\mathrm{\ω}}_i={\mathrm{\ω}}_0-m_{pi}{P}_i\\ E_i=E_0-n_{qi}{Q}_i+k_E\∫(E_{cmp}-n_{qi}{Q}_i)dt\end{array}\right.$

Wherein: m _piand n _qibe respectively i-th (i=1,2 ..., the n) active power of platform distributed power source and the sagging coefficient of reactive power, ω ₀and E ₀for distributed power source rated output voltage angular frequency and amplitude, ω _iand E _ibe angular frequency and the amplitude of the reference voltage of inverter in i-th distributed power source; E _cmpfor generatrix voltage compensation signal; T is the time; k _efor integral coefficient.

In described step (5), carry out closed loop feedback control according to reference voltage based on following formula:

$\left[\begin{array}{c}{d}_{id}\\ d_{iq}\end{array}\right]=G_{PI}\left[\begin{array}{c}{E}_i-v_{id}\\ 0-v_{iq}\end{array}\right]$

θ＝∫ω _idt

Wherein: v _idand v _iqfor the output voltage values of three-phase inverter under dq coordinate system in i-th distributed power source in current sample period; ω _iand E _ifor angular frequency and the amplitude of reference voltage; G _pIfor the transfer function of PI controller; θ _ifor the angle of abc coordinate system and dq coordinate system transformation matrix; d _idand d _iqfor the modulation signal under dq coordinate system.

The equal separate connection of each distributed power source of parallel running in micro-capacitance sensor is integrated with to the control module of above-mentioned steps (3)-(5) control method; Last closed loop feedback controlling unit act as the reference voltage followed the tracks of power droop control and provide, various feedback control structure can be used to realize, as voltage monocycle, outer voltage current inner loop dicyclo etc.In addition, closed loop feedback controlling unit can realize under multiple coordinate system, as natural system of coordinates, rest frame, rotating coordinate system.

Compared with prior art, in the unmatched situation of the inventive method feed line impedance in micro-capacitance sensor, in communication system, do not transmit the reactive power information of each distributed power source, the reactive power achieving distributed power source is distributed according to sagging coefficient, and communication system is simplified.Meanwhile, control based on secondary voltage, the busbar voltage of micro-capacitance sensor can return to rated value, improves power supply quality.

Accompanying drawing explanation

Fig. 1 is the general structure of micro-capacitance sensor.

Fig. 2 is the equivalent model schematic diagram of distributed power source parallel connection.

Fig. 3 is the control block diagram of the distributed power source reactive power apportion design based on secondary voltage control.

Fig. 4 (a) is for distributed power source is meritorious, reactive power oscillogram.

Fig. 4 (b) is the oscillogram of micro-capacitance sensor ac bus voltage effective value.

Fig. 5 is secondary voltage control procedure oscillogram.

Fig. 6 is the stable state oscillogram of two distributed power source output currents and micro-capacitance sensor ac bus voltage.

Embodiment

In order to more specifically describe the present invention, below in conjunction with the drawings and the specific embodiments, technical scheme of the present invention is described in detail.

Fig. 1 is the general structure of micro-capacitance sensor, and composed in parallel by n distributed power source (DG), each DG comprises the DC side energy, inverter circuit, local controller, and is connected to the public exchange bus of micro-capacitance sensor by feeder line, for load provides energy.Feed line impedance includes isolating transformer leakage inductance and transmission line impedance.Micro-capacitance sensor master controller (MGCC) adopts distance sensor to measure the running status with monitoring micro-capacitance sensor, and signal is sent to the local controller of DG by the communication of low bandwidth.When static switch between micro-capacitance sensor and major network disconnects, micro-capacitance sensor is operated in island mode.

Fig. 2 is n distributed power source parallel equivalent model, can calculate i-th (i=1,2 ..., n) the active power p of individual distributed power source output _iwith reactive power q _ibe respectively

Wherein: total impedance Z _i=Z _oi+ Z _li, Z _oifor inverter equivalent output impedance in distributed power source, Z _lifor feed line impedance value, total impedance can be expressed as Z _i=R _i+ jX _i.

The distributed power source reactive power apportion design control block diagram based on secondary voltage control that present embodiment proposes as described in Figure 3.The master controller of micro-capacitance sensor measures micro-capacitance sensor public exchange busbar voltage by distance sensor, calculates the line voltage effective value V of ac bus _com:

$V_{com}=\sqrt{\frac{v_{com\_ab}^2-+v_{com\_bc}^2-+v_{com\_ca}^2}{3}}---\left(3\right)$

In formula: v _{com_ab}, v _{com_bc}and v _{com_ca}be respectively the bus line magnitude of voltage in current sample period.

For recovering ac bus voltage, in the master controller of micro-capacitance sensor, secondary voltage controls passing ratio-integration (PI) controller generatrix voltage compensation signal E _cmp:

$E_{cmp}=k_{pV}(V_{com}^{*}-V_{com})+k_{iV}\∫(V_{com}^{*}-V_{com})dt---\left(4\right)$

In formula: k _pVand k _iVbe respectively scale parameter and the integral parameter of PI controller.V _com ^*for the specified effective value of busbar voltage.

Micro-capacitance sensor master controller by the communication network of low bandwidth, by voltage compensation signal E _cmpeach distributed power source is given with broadcast transmission.In the local controller of each distributed power source, utilize voltage compensation signal E _cmprealize power dividing function.

Rated output in the local controller of distributed power source.With reference to instantaneous power computational methods in the instantaneous power theory (instantaneous power theory) of H.Akagi, obtain following formula:

The power control equations that the local controller of distributed power source adopts is

$\left\{\begin{array}{c}p=v_a{i}_a+v_b{i}_b+v_c{i}_c\\ q=\frac{1}{\sqrt{3}}\[(v_b-v_c)i_a+(v_c-v_a)i_b+(v_a-v_b)i_c\]\end{array}\right.---\left(5\right)$

In formula, v _a, v _band v _cbe respectively the three-phase output voltage of three-phase inverter in distributed power source in current sample period, i _a, i _band i _cbe respectively the output line electric current of three-phase inverter in distributed power source in current sample period.V _a, v _band v _ccommon reference point in measurement elects the mid point of wye connection filter capacitor as.P is the instantaneous active power exported, and q is the instantaneous reactive power exported.

In formula (5), institute's calculating formula is that the instantaneous power being applicable to three-phase inverter calculates, and adopts low-pass filtering to obtain average power to instantaneous power:

$\{\begin{array}{c}P=\frac{{\mathrm{\ω}}_c}{s+{\mathrm{\ω}}_c}p\\ Q=\frac{{\mathrm{\ω}}_c}{s+{\mathrm{\ω}}_c}q\end{array}---\left(6\right)$

In above formula: ω _cfor the corner frequency of low-pass first order filter.P is average active power and Q is average reactive power.

The power control equations that the local controller of distributed power source adopts is

ω _i＝ω ₀-m _iP _i(7)

E _i＝E ₀-n _qiQ _i+k _E∫(E _cmp-n _qiQ _i)dt (8)

Wherein: m _piand n _qibe respectively the active power of i-th distributed power source and the sagging coefficient of reactive power, ω ₀and E ₀for distributed power source rated output voltage angular frequency and amplitude, ω _iand E _ibe angular frequency and the amplitude of the reference voltage of inverter in i-th distributed power source.E _cmpfor the generatrix voltage compensation signal from micro-capacitance sensor master controller.T is the time.K _efor the integral coefficient of regulating system dynamic property.

The integration item of formula (8) makes reactive power with sagging coefficient for inverse ratio reasonable distribution.After system reaches stable state, integration item be input as 0, so have n during stable state _qiq _i=E _cmp.Generatrix voltage compensation signal E _cmpsend with the forms of broadcasting, every platform distributed power source receives identical E _cmp.Therefore n is had _q1q ₁=n _q2q ₂=...=n _qnq _n.To formula (4), in like manner during stable state integration item be input as 0, have V _com=V _com ^*, secondary voltage controls micro-capacitance sensor busbar voltage to return to rated value.

As described in Figure 3, the amplitude E of the reference voltage obtained through power control equations _cmpiand angular frequency _icontrol for closed loop feedback, obtain the modulation signal controlling inverter output voltage in distributed power source, through the switching device of SPWM driver drives inverter.In present embodiment, output voltage controller carries out closed loop feedback control based on following formula:

$\left[\begin{array}{c}{d}_{id}\\ d_{iq}\end{array}\right]=G_{PI}\left[\begin{array}{c}{E}_i-v_{id}\\ 0-v_{iq}\end{array}\right]---\left(9\right)$

θ＝∫ω _idt (10)

Wherein: d _idand d _iqfor the modulation signal under dq coordinate system, θ _ifor the angle of abc coordinate system and dq coordinate system transformation matrix.V _idand v _iqfor the output voltage values of three-phase inverter under dq coordinate system in i-th distributed power source in current sample period; ω _iand E _ifor angular frequency and the amplitude of reference voltage; G _pIfor the transfer function of PI controller.

In the implementation case, micro-capacitance sensor is made up of two identical distributed power source parallel connections, and design distributed power source is according to the pro rate power of 1:1.In every platform distributed power source, inverter adopts three-phase half-bridge topology, and filter inductance is 6mH, and filter capacitor is 2 μ F, and DC bus-bar voltage is 400V.Often be in series 0.5 Ω resistance in the feeder line of the 2nd distributed power source.Master controller, by CAN and Distributed Power Communication, also can adopt other fieldbus.Every phase load by 16.7 Ω resistance and 9mH inductance in series, connect into star-like.

The controling parameters that the implementation case adopts is respectively: in formula (4), V _com ^*=190V, k _pV=2, k _iV=1s ^-1; In formula (6), ω _c=2 π × 10rad/s; In formula (7)-Shi (8), E ₀=190V, ω ₀=2 π × 50rad/s, m _pi=0.0002rad/ (s ^.w), n _qi=0.002V/var, k _e=2s ^-1; The proportionality coefficient that in formula (10), PI regulates is set as 0.01126, and integral coefficient is set as 35.39s ^-1.

Fig. 4 (a) is that distributed power source is meritorious, reactive power experimental waveform figure.In figure, P ₁, P ₂represent the active power of two distributed power sources respectively, Q ₁, Q ₂represent the reactive power of two distributed power sources respectively.Fig. 4 (b) is the experimental waveform figure of micro-capacitance sensor ac bus voltage effective value.Can find out, originally under the control of traditional droop method, the reactive power of two distributed power sources has larger distribution error, busbar voltage offrating.After enable secondary voltage controls, the reactive power of two distributed power sources is tending towards identical gradually, and busbar voltage returns to rated value gradually.

Fig. 5 is the oscillogram of secondary voltage control procedure.V in figure _combusbar voltage, i ₁, i ₂represent the output current of two distributed power sources respectively.Originally, under the control of traditional droop method, the output current discrepancy delta i of two distributed power sources is larger.After the secondary voltage control strategy proposed making the subject of knowledge and the object of knowledge, two distributed power source output current differences obtain and reduce more significantly, and busbar voltage amplitude also slightly improves.Compensation process is comparatively level and smooth, and source current and busbar voltage all do not occur overshoot.

Fig. 6 is stable state oscillogram.Under can finding out present embodiment, two distributed power source output currents are almost identical, and two distributed power source output currents and micro-capacitance sensor ac bus voltage sinusoidal degree higher.

Therefore, use the present invention can realize the function of distributed power source reactive power by sagging coefficient reasonable distribution on the basis realizing the recovery of micro-capacitance sensor busbar voltage simultaneously, do not need the information increasing communication transfer.The present invention is applicable to the isolated island micro-capacitance sensor controlled based on secondary voltage.

Claims (6)

1., based on a distributed power source reactive power distribution method in the micro-capacitance sensor of secondary voltage control, comprise the steps:

(1) micro-capacitance sensor master controller gathers micro-capacitance sensor busbar voltage, and calculates the effective value V of busbar voltage _com;

(2) the secondary voltage control ring in micro-capacitance sensor master controller is according to the effective value V of described busbar voltage _comwith the specified effective value V of busbar voltage _com ^*, calculate generatrix voltage compensation signal E by PI controller _cmp, and by voltage compensation signal E _cmpeach distributed power source is given by communication network transmission with broadcast mode;

(3) each distributed power source gathers local output voltage and output current, calculates instantaneous active power p and reactive power q, and by firstorder filter, filtering obtains average active power P and reactive power Q;

(4) each distributed power source is according to described average active power P and reactive power Q, and the voltage compensation signal E obtained by communication network _cmp, pass through the amplitude E of proposed improvement droop control algorithm determination reference voltage _iand angular frequency _i;

(5) each distributed power source is according to the amplitude E of described reference voltage _iand angular frequency _icarry out closed loop feedback to control to obtain modulation signal, finally obtain three groups of pwm signals to control the three-phase inverter of distributed power source according to described modulation signal by SPWM technical construction.

2. distributed power source reactive power distribution method according to claim 1, is characterized in that: in described step (1), calculates the line voltage effective value V of ac bus according to following formula _com:

$V_{com}=\sqrt{\frac{v_{com\_ab}^2+v_{com\_bc}^2+v_{com\_ca}^2}{3}}$

Wherein: v _{com_ab}, v _{com_bc}and v _{com_ca}be respectively bus ab line voltage, bc line voltage and the ca line magnitude of voltage in current sample period.

3. distributed power source reactive power distribution method according to claim 1, is characterized in that: in described step (2), calculates generatrix voltage compensation signal E according to following formula _cmp:

$E_{cmp}=k_{pV}(V_{com}^{*}-V_{com})+k_{iv}\∫(V_{com}^{*}-V_{com})dt$

Wherein: k _pVand k _iVbe respectively scale parameter and the integral parameter of PI controller; V _com ^*for the specified effective value of busbar voltage.

4. distributed power source reactive power distribution method according to claim 1, it is characterized in that: in described step (3), according to instantaneous active power p and the reactive power q of following formula Computation distribution formula power supply, and average active power P and reactive power Q:

$\left\{\begin{array}{c}p=v_a{i}_a+v_b{i}_b+v_c{i}_c\\ q=\frac{1}{\sqrt{3}}\[(v_b-v_c)i_a+(v_c-v_a)i_b+(v_a-v_b)i_c\]\end{array}\right.$

$\left\{\begin{array}{c}P=\frac{{\mathrm{\ω}}_c}{s+{\mathrm{\ω}}_c}p\\ Q=\frac{{\mathrm{\ω}}_c}{s+{\mathrm{\ω}}_c}q\end{array}\right.$

Wherein: v _a, v _band v _cbe respectively the three-phase output voltage of three-phase inverter in distributed power source in current sample period; i _a, i _band i _cbe respectively the output line electric current of three-phase inverter in distributed power source in current sample period; ω _cfor the corner frequency of low-pass first order filter.

5. distributed power source reactive power distribution method according to claim 1, is characterized in that: in described step (4), improves droop control algorithm based on following formula:

$\left\{\begin{array}{c}{\mathrm{\ω}}_i={\mathrm{\ω}}_0-m_{pi}P\\ E_i=E_0-n_{qi}{Q}_i+k_E\∫(E_{cmp}-n_{qi}{Q}_i)dt\end{array}\right.$

Wherein: m _piand n _qibe respectively i-th (i=1,2 ..., the n) active power of platform distributed power source and the sagging coefficient of reactive power, ω ₀and E ₀for distributed power source rated output voltage angular frequency and amplitude, ω _iand E _ibe angular frequency and the amplitude of the reference voltage of inverter in i-th distributed power source; E _cmpfor generatrix voltage compensation signal; T is the time; k _efor integral coefficient.

6. distributed power source reactive power distribution method according to claim 1, is characterized in that: in described step (5), carry out closed loop feedback control according to reference voltage based on following formula:

$\left[\begin{array}{c}{d}_{id}\\ d_{iq}\end{array}\right]=G_{PI}\left[\begin{array}{c}{E}_i-v_{id}\\ 0-v_{iq}\end{array}\right]$

θ＝∫ω _idt

Wherein: v _idand v _iqfor the output voltage values of three-phase inverter under dq coordinate system in i-th distributed power source in current sample period; ω _iand E _ifor angular frequency and the amplitude of reference voltage; G _pIfor the transfer function of PI controller; θ _ifor the angle of abc coordinate system and dq coordinate system transformation matrix; d _idand d _iqfor the modulation signal under dq coordinate system.