CN103311935B

CN103311935B - Comprehensive compensation instruction current obtaining method of angle-shaped chain-type SVG (static var generator) of power distribution network

Info

Publication number: CN103311935B
Application number: CN201310249997.XA
Authority: CN
Inventors: 罗安; 何志兴; 熊桥坡; 马伏军; 黎小聪; 刘月华
Original assignee: Hunan University
Current assignee: Hunan University
Priority date: 2013-06-21
Filing date: 2013-06-21
Publication date: 2015-04-15
Anticipated expiration: 2033-06-21
Also published as: CN103311935A

Abstract

The invention discloses an comprehensive compensation instruction current obtaining method of an angle-shaped chain-type SVG of a power distribution network. The method comprises the following steps of detecting load currents of ila, ilb and ilc; obtaining load current fundamental active components through ip-iq conversion based on an instantaneous reactive power theory and LPF (lowpass filtering); subtracting the load current fundamental active components from the load current and negating the calculation result to obtain line current compensation instruction signal load currents ia*, ib*, ic* which contain fundamental reactive components, fundamental negative sequence components and reactive components; performing matrix transformation and LPF on the line current compensation instruction signal load currents to obtain a fundamental negative sequence active component and a fundamental negative sequence negative component; and multiplying the fundamental negative sequence active component and the fundamental negative sequence negative component with cos (omega t) and sin (omega t) respectively to obtain a zero sequence loop current instruction i0*, and combining the line current compensation instruction with the zero sequence loop current instruction to obtain an angle-shaped chain-type SVG phase current instruction iab*, ibc* and ica*. The comprehensive compensation instruction current obtaining method of the angle-shaped chain-type SVG of the power distribution networkload current instantaneous value takes load current instantaneous value to achieve simple calculation and can be effectively combined with an existing single-phase chain-type SVG control strategy to achieve an angle-shaped chain-type SVG comprehensive compensation function.

Description

Power distribution network angular chain type SVG comprehensive compensation instruction current acquisition method

Technical Field

The invention relates to a power distribution network angular chain type SVG comprehensive compensation instruction current acquisition method.

Background

Nonlinear loads exist in a power distribution network, a large amount of reactive, negative sequence and harmonic currents are generated, electric energy loss of a power system is caused, and safe operation of the system is threatened. In order to eliminate the influence of nonlinear loads on a power grid, many scholars research the control of the power quality of medium and high voltage distribution networks. The compensation current can be classified into: reactive current compensation of the power grid, fundamental negative sequence current compensation and harmonic current compensation. The common power quality control device for the power distribution network only performs reactive compensation or harmonic control on the power grid, and has a complex structure and a large volume. The SVG that adopts angular form chain structure does not need the transformer can directly be applied to in, high voltage distribution network, and angular form chain SVG is three-phase triangle-shaped connection structure, and angular form chain SVG each looks cascade by a plurality of H bridges and constitute, and the H bridge includes single-phase bridge converter and the parallelly connected direct current side electric capacity with single-phase bridge converter, and the H bridge includes single-phase bridge converter and direct current side electric capacity. The angular chained SVG is connected between a three-phase power grid and a three-phase load in parallel. At present, students apply chain type SVG to medium and high voltage power distribution networks for reactive power compensation or harmonic wave treatment, and the angular chain type SVG is rarely considered for carrying out comprehensive compensation function on reactive power, negative sequence and harmonic wave and researching control command signals of the reactive power, negative sequence and harmonic wave.

Theoretically, a detection method based on Steinmetz principle and an ip-iq harmonic detection method based on instantaneous power theory can be combined for obtaining phase current instruction signals required by reactive, negative sequence and harmonic current comprehensive compensation, but the algorithm is complex and the engineering is difficult to realize, and the method for obtaining the angular chained SVG comprehensive compensation instruction current of the power distribution network has important significance on medium and high voltage power quality control.

Disclosure of Invention

The invention aims to solve the technical problem that aiming at the defects of the prior art, the invention provides the method for acquiring the angular chained SVG comprehensive compensation command current of the power distribution network, solves the problem of electric energy quality caused by reactive power, negative sequence and harmonic in a medium-voltage and high-voltage power distribution network, simply and quickly calculates the reactive power, negative sequence and harmonic comprehensive compensation command signal in the power distribution network, and effectively combines the method with the existing single-phase chained SVG control strategy to realize the angular chained SVG comprehensive compensation function.

In order to solve the technical problems, the technical scheme adopted by the invention is as follows: the utility model provides a distribution network angular form chain SVG comprehensive compensation instruction electric current acquisition method, is including the angular form chain SVG that is used for idle work, negative sequence and harmonic comprehensive compensation, angular form chain SVG is three-phase triangle-shaped connection structure, angular form chain SVG each is cascaded by a plurality of H bridges and is constituteed mutually, between angular form chain SVG parallel access three-phase electric wire netting and the load, this method is:

1) detecting three-phase load current i_la、i_lb、i_lc；

2) The three-phase load current is subjected to ip-iq current transformation and low-pass filtering based on the instantaneous reactive power theory to obtain a load current fundamental wave active component;

3) subtracting the load current base from the three-phase load currentObtaining the SVG line current instruction signal containing the fundamental wave reactive component, the fundamental wave negative sequence component and the harmonic component by taking the wave active component and negating

4) Will three-phase load current i_la、i_lb、i_lcTransformed matrix C_abc/dq ^-Obtaining the active component of the fundamental negative sequence by low-pass filteringAnd fundamental negative sequence reactive component

5) According to the negative sequence active component of the fundamental waveAnd fundamental negative sequence reactive componentReference instruction for calculating zero sequence circulating current instantaneous value

Omega is the angular frequency of the three-phase power grid voltage;

6) utilizing SVG line current command signalsReference instruction of zero-sequence circulating current instantaneous valueSynthesizing angular chained SVG phase current control instructions

[\begin{matrix} {i_{ab}}^{*} \\ {i_{bc}}^{*} \\ {i_{ca}}^{*} \end{matrix}] = \frac{1}{3} [\begin{matrix} i_{a}^{*} - i_{b}^{*} \\ i_{b}^{*} - i_{c}^{*} \\ i_{c}^{*} - i_{a}^{*} \end{matrix}] + [\begin{matrix} {i_{0}}^{*} \\ {i_{0}}^{*} \\ {i_{0}}^{*} \end{matrix}] .

In step 4), the active component of the fundamental negative sequenceAnd a reactive componentThe calculation formula is as follows:

compared with the prior art, the invention has the beneficial effects that: the power distribution network angular chained SVG comprehensive compensation command current acquisition method provided by the invention can provide command basis for a medium and high voltage power distribution network power quality control device, the superposed zero sequence circulating current can maintain the stability of the capacitance voltage at the direct current side of each phase link, the command current calculation is simple, the engineering realization is easy, and the power quality control of the medium and high voltage power distribution network can be realized by combining with the existing single-phase chained SVG control strategy.

Drawings

FIG. 1 is a schematic diagram of an angular chained SVG for reactive, negative sequence and harmonic comprehensive compensation;

FIG. 2 is a diagram of negative sequence compensation and zero sequence circulating phasor according to an embodiment of the present invention;

FIG. 3 is a schematic diagram of phase current command signal acquisition according to an embodiment of the present invention;

FIG. 4 is a block diagram of an angular chained SVG control for current integration compensation according to an embodiment of the present invention; FIG. 4(a) control block diagram of an AB chain link main module in an angular chained SVG; FIG. 4(b) is a control block diagram of an AB chain link slave module in an angular chained SVG;

FIG. 5 is a diagram of an angular chained SVG comprehensive compensation simulation effect according to an embodiment of the present invention; FIG. 5(a) is a load current waveform; FIG. 5(b) is a zero sequence circulating current command signal waveform; FIG. 5(c) is a waveform of the integrated compensated phase current command signal; FIG. 5(d) is an angular chained SVG output phase current waveform; fig. 5(e) shows a net-side current waveform.

Detailed Description

As shown in figure 1, the angular chained SVG is connected to a three-phase three-wire system power distribution network and is used for compensating reactive, negative sequence and harmonic currents caused by nonlinear loads. The angle chain type SVG is three-phase triangle-shaped connection structure, and each looks of angle chain type SVG is cascaded by a plurality of H bridges and is constituteed, and the H bridge includes single-phase bridge type converter and the parallelly connected direct current side electric capacity with single-phase bridge type converter, and the H bridge includes single-phase bridge type converter and direct current side electric capacity. Load current i_la、i_lb、i_lcThe system comprises active power, reactive power, a negative sequence and harmonic current, wherein the reactive power, the negative sequence and the harmonic current are injected into a power grid to cause power loss of the power grid and threaten the stable operation of the system. Angular chained SVG line current i_a、i_b、i_cThe amplitude of the current is the same as that of reactive, negative sequence and harmonic current in the load current, and the direction of the current is opposite to that of the reactive, negative sequence and harmonic current in the load current. The angular chained SVG line current and the load current are superposed to eliminate reactive power, negative sequence and harmonic current in the network side current, and the power quality of the power grid is ensured. Zero sequence circulating current i₀The current flows in the angle, so that the phase current phasor is perpendicular to the line voltage, and the voltage on the direct current side of each phase link is maintained to be stable.

Fig. 2 is a negative sequence compensation and zero sequence circulating phasor diagram.

The phase current command signals for supplementing reactive, negative sequence and harmonics are decomposed as follows:

wherein,is the amplitude of the fundamental positive sequence reactive component, I^-Is a negative sequence of fundamental wavesMagnitude of component, θ^-Is the initial phase angle, i, of the negative sequence component of the fundamental wave_ah、i_bh、i_bhAre harmonic components.

The three-phase symmetrical grid voltage is:

[\begin{matrix} U_{ab} \\ U_{bc} \\ U_{ca} \end{matrix}] = [\begin{matrix} \frac{\sqrt{3}}{2} U_{s} + j \frac{U_{s}}{2} \\ - {jU}_{s} \\ - \frac{\sqrt{3}}{2} U_{s} + j \frac{U_{s}}{2} \end{matrix}] - - - (2)

wherein, U_sIs the amplitude of the line voltage.

Negative sequence component I in phase current command signal_ab ^-、I_bc ^-、I_ca ^-Are respectively as

The negative sequence components in the zero sequence circulation and phase current instruction signals are superposed to obtain phasor I_ab、I_bc、I_ca：

Wherein, zero sequence circulating component I₀Comprises the following steps:

I₀=X+jY (5)

wherein X is the real axis component of the zero sequence current, and Y is the imaginary axis component of the zero sequence current.

The phase current phasor is perpendicular to the line voltage so as to maintain the stable solving of the capacitance voltage at the direct current side of each phase link to obtain a zero-sequence circulating current phasor expression

Fig. 3 is a schematic diagram of phase current command signal acquisition.

Load current i_la、i_lb、i_lcTransformed matrix C_abc/dq ^-Obtaining the active component of the fundamental negative sequence by low-pass filteringAnd a reactive component。

Wherein the expression of the transformation matrix is:

negative sequence current amplitude I in AND-line current command signal^-And initial phase angle theta^-The relationship of (a) to (b) is as follows:

obtaining zero sequence circulation instantaneous value i₀ ^*Comprises the following steps:

the phase information ω t is obtained by phase-locking the phase-A voltage by the phase-locked loop.

Detecting three-phase load current i_la、i_lb、i_lcObtaining a fundamental wave active component of the load current through an ip-iq algorithm and low-pass filtering, subtracting the fundamental wave active component from the load current to obtain a fundamental wave reactive component, a fundamental wave negative sequence component and a harmonic component in the load current, and obtaining a compensator line current instruction by negatingLoad current i_la、i_lb、i_lcTransformed matrix C_abc/dq ^-Obtaining the active component of the fundamental negative sequence by low-pass filteringAnd a reactive componentFundamental negative sequence active componentMultiplication by cos (ω t), fundamental reactive componentMultiplication by sin (ω t), summation and division byAnd obtaining a zero sequence circulating current instantaneous value instruction.

Compensator line current commandRespectively multiplying by 1/3, and respectively adding a zero-sequence circulating current instantaneous value instruction to obtain a phase current instruction vertical to the line voltage

The above current instruction calculation algorithm may be implemented in a DSP.

FIG. 4 is a diagram of angular chained SVG master-slave control for current synthesis compensation. Taking the AB link as an example, fig. 4(a) is a control block diagram of the AB link master module, and fig. 4(b) is a control block diagram of the AB link slave module. One of H bridges in the chain link is selected as a master module, and the other H bridges are selected as slave modules. The main module control strategy is voltage and current double closed loop control to maintain the stability of capacitor voltage and simultaneously realize the rapid tracking of current. The voltage outer ring of the main module adopts PI control, the output of the PI control is taken as an active component, and the active component is multiplied by AB, BC and CA chain link phase information sin (ω t + π/6), sin (ω t- π/2) and sin (ω t +5 π/6) to be the active current reference command of the chain linkActive current reference command and current reference command for comprehensive compensationThe total current reference instruction is obtained by superpositionComparing the current reference command with the instantaneous value of each link current, and comparing the error with the voltage feedforward quantity of the three-phase power grid through a proportion link KSuperposing to obtain a reference waveform of a modulated wave of a main moduleWherein K can be taken as L/T_sWherein L is an inductance value of the connecting reactor, T_sFor the DSP control period, N is the number of H bridges contained in one chain link.

The control mode of the slave module is as follows: voltage closed loop PI control, obtaining the voltage phasor needed for maintaining the voltage balance of the DC side after the deviation of the slave module instruction voltage and the actual voltage is subjected to PIOutput voltage reference instruction phasor of main moduleMinusObtaining a slave module modulated wave reference waveformWherein i represents the ith module, and the value of i is 2-N.

Master and slave module modulated wave reference waveformsAndand obtaining signals for controlling the on-off of each switching tube through normalization processing and carrier phase shift modulation.

The above control strategy can be implemented in DSP + FPGA.

Fig. 5 is a five-level angular chained SVG simulation waveform. The load includes two groups: a first set of loads: single-phase resistive load connected between AB phases, L₁=2mH，R₁=4 Ω; a second group of loads: three-phase uncontrollable rectifier circuit with resistance-inductance load, L_d=5mH，R_d=20 Ω. Fig. 5(a) shows a load current waveform. The instruction signal obtained by the zero-sequence circulating current calculation method provided by the invention is shown in fig. 5(b), and the obtained comprehensive compensation phase current instruction signalAs shown in fig. 5 (c). Using the above master slaveThe actual output waveform of the compensator obtained by the control strategy is shown in fig. 5(d), the compensated power grid side current is three-phase symmetrical and close to sine, and because the load current of the rectifier circuit changes suddenly during phase change and is influenced by the response speed of the SVG, the compensation current can be tracked only after a period of time delay, so that the network side current generates burrs during phase change, as shown in fig. 5 (e). Simulation results show that the angular chained SVG comprehensive compensation function can be realized by combining the extracted phase current instruction signal acquisition method with the existing single-phase SVG control strategy.

The above simulation is implemented in PSIM 9.0.

Claims

1. A method for acquiring angular chained SVG comprehensive compensation instruction current of a power distribution network is characterized by comprising the following steps:

1) detecting three-phase load current i_la、i_lb、i_lc；

3) subtracting the load current fundamental wave active component from the three-phase load current and taking the inverse to obtain a negative sequence containing a fundamental wave reactive component and a fundamental wave negative sequenceSVG line current instruction signal of component and harmonic component

4) Will three-phase load current i_la、i_lb、i_lcTransformed matrix C_abc/dp ^-Obtaining the active component of the fundamental negative sequence by low-pass filteringAnd fundamental negative sequence reactive componentTransformation matrix C_abc/dq ^-The expression of (a) is:

fundamental negative sequence active componentAnd fundamental negative sequence reactive componentThe calculation formula is as follows:

5) according to the negative sequence active component of the fundamental waveAnd negative fundamental waveSequence reactive componentReference instruction for calculating zero sequence circulating current instantaneous value

Omega is the angular frequency of the three-phase power grid voltage;

[\begin{matrix} {i_{ab}}^{*} \\ {i_{bc}}^{*} \\ {i_{ca}}^{*} \end{matrix}] = \frac{1}{3} [\begin{matrix} i_{a}^{*} - i_{b}^{*} \\ i_{b}^{*} - i_{c}^{*} \\ i_{c}^{*} - i_{a}^{*} \end{matrix}] + [\begin{matrix} {i_{0}}^{*} \\ {i_{0}}^{*} \\ {i_{0}}^{*} \end{matrix}] .