CN104426160A - Positive and negative sequence decoupling control method for low-voltage ride-through compatible with grid-connected photovoltaic inverter - Google Patents

Abstract

A positive and negative sequence decoupling control method for low-voltage ride-through compatible with a grid-connected photovoltaic inverter comprises the following steps: (1) a detected grid voltage is decomposed into a positive sequence component and a negative sequence component by a positive and negative sequence decoupling method, the output current of the inverter is also decomposed into a positive sequence component and a negative sequence component, and the components are controlled; and (2) the positive sequence component of the output current of the inverter is made to track the positive sequence component of the grid voltage, and the negative sequence component of the output current of the inverter is controlled to be zero so as to enable the inverter to correctly calculate the phase of the grid voltage in real time according to the drop of the grid voltage to realize phase control of the output current. The true phase of the grid voltage during low-voltage ride-through is detected by the positive and negative sequence decoupling method. Moreover, the positive sequence component and the negative sequence component of the current are controlled, and the power factor output by the inverter during low-voltage ride-through is precisely controlled. The same active current as normal operation can be output at low voltage, the output power remains unchanged, and the stability of the grid is maintained to the maximum.

Description

The positive-negative sequence decoupling control method of the compatible low voltage crossing of photovoltaic combining inverter

Technical field

The invention belongs to field of solar thermal power generation, be specifically related to a kind of inverter output current control method.

Background technology

Along with national generation of electricity by new energy implementation, the exploitation prospect of this clean energy resource of solar power generation is wide.That has set up at present has grid-connected photovoltaic system and large-sized photovoltaic power station.Solar panel generates electricity through solar radiation, exports as direct current, and cannot be connected to the grid operation, therefore needs inverter that DC conversion is become industrial-frequency alternating current.According to national standard, photovoltaic combining inverter needs to possess low voltage ride-through capability.Low voltage crossing comprises three kinds of situations: 1, three-phase equilibrium is fallen; 2, single-phasely to fall; 3, two-phase is fallen.National standard requires that inverter can bear the low-voltage process that duration is 3 seconds, can normal power generation at this process inverter.

Conventional method is when low voltage crossing, and often adopt the method for open current loop to run, the deficiency of this method is: 1, output current wave has distortion, 2, low voltage crossing time uncontrollable active power and reactive power.

Summary of the invention

The technical problem to be solved in the present invention is: low voltage ride through of photovoltaic inverter problem, provides the positive-negative sequence decoupling control method of the compatible low voltage crossing of a kind of photovoltaic combining inverter.

For achieving the above object, the present invention is by the following technical solutions:

A positive-negative sequence decoupling control method for the compatible low voltage crossing of photovoltaic combining inverter, it comprises the steps:

1., adopt positive-negative sequence decoupling method that the line voltage detected is decomposed into positive sequence component and negative sequence component, inverter output current is also divided into positive sequence component and negative sequence component, it is controlled respectively;

2. the positive sequence component of inverter output current, is made to follow the tracks of the positive sequence component of line voltage, the negative sequence component of inverter output current is controlled to be zero, thus make inverter correctly calculate electric network voltage phase according to the situation of falling of line voltage in real time, realize output current phase control.

Step 1. in, line voltage to be decomposed and the step that controls is:

I), to line voltage gather in real time, adopt positive-negative sequence decoupling method that the line voltage detected is decomposed into positive sequence component e _pwith negative sequence component e _n, line voltage is expressed as:

Wherein, e _afor A phase voltage, e _bfor B phase voltage, e _cfor C phase voltage, for the phase place of positive sequence component, for the phase place of negative sequence component;

Ii), by above-mentioned line voltage by AD sampling enter processor, first by 3/2 conversion by its by three-phase abc coordinate system transformation to two-phase rotation alpha β coordinate system; Voltage after conversion in α β reference axis is expressed as, wherein, and e _αfor α shaft voltage, e _βfor β shaft voltage,

Iii), to after the voltage phase shift in α β reference axis 90 degree, (2) formula becomes:

Wherein, e _α' be the α shaft voltage after phase shift 90 degree, e _β' be the β shaft voltage after phase shift 90 degree;

Iv), simultaneous (2), (3) two prescription journeys, calculate the positive-negative sequence component of voltage in α β reference axis:

$\left[\begin{array}{c}{e}_{\mathrm{\αP}}\\ e_{\mathrm{\βP}}\\ e_{\mathrm{\αN}}\\ e_{\mathrm{\βN}}\end{array}\right]=\left[\begin{array}{cccc}1& 0& 0& -1\\ 0& 1& 1& 0\\ 1& 0& 0& 1\\ 0& 1& -1& 0\end{array}\right]\left[\begin{array}{c}{e}_{\mathrm{\α}}\\ e_{\mathrm{\β}}\\ {e_{\mathrm{\α}}}^{\′}\\ {e_{\mathrm{\β}}}^{\′}\end{array}\right]---\left(4\right)$

V), by the positive-negative sequence component of voltage in α β reference axis transform to abc coordinate system, namely obtain positive-negative sequence component and the phase place of voltage.

Step I i described) in, the force feed that the α β reference axis obtained powered on enters low pass filter and carries out filtering.

Adopt the present invention of technique scheme, propose a kind of according to employing positive-negative sequence decoupling computation electric network voltage phase, control the control method of output current.When detecting low voltage crossing by the method for positive-negative sequence decoupling zero, the true phase of line voltage, controls positive sequence and the negative sequence component of electric current, the power factor that accurate control inverter exports when low voltage crossing simultaneously.Can export the active current the same with when normally running when low-voltage, power output remains unchanged, and at utmost keeps the stability of electrical network, can also send required reactive current according to dispatching of power netwoks instruction.This method not only can be used for low voltage crossing, adjusts the situation that also can be used for high voltage crossing a little.Specifically, advantage is as follows:

1, the present invention achieve when inverter normally runs by the method for positive-negative sequence decoupling zero and low voltage crossing time algorithm unification; Without the need to carrying out algorithm changeover.It can stable operation under various low voltage condition, and can the continuous service long period, super GB required time far away.

2, the present invention not only can be applied to novel inverter, can also carry out software upgrading to existing inverter, and the present invention can utilize the original transducer of inverter to realize its function in addition, and not needing increases ancillary equipment, only needs change control program.

3, under normal operating conditions can negative sequence component in real-Time Compensation electrical network, effectively can optimize the waveform of output current, reduce the even-order harmonic in electric current.

4, adopting said method coordinate the energy-conservation ability enough making inverter possess to a certain degree high voltage crossing of the voltage control loop of inverter.

Accompanying drawing explanation

Fig. 1 is flow chart of the present invention.

Fig. 2 is the schematic diagram of positive-negative sequence decoupling method.

Embodiment

The said parallel networking type photovoltaic electricity generation system of the present invention comprises: photovoltaic module, three-phase photovoltaic grid-connected inverting device and electrical network.Three-phase grid type photovoltaic generating system is the principal mode of large-sized photovoltaic electricity generation system, complex structure, and power is large, and technical requirement is high, and efficiency is high.It generally adopts three phase full bridge type inverter.Photovoltaic module forms by solar cell is monomer series-connected usually.

The said low voltage crossing of the present invention, refers to: when Voltage Drop fault appears in electrical network, and electricity generation system possesses in the short time lasting normally to the ability of mains supply.The Voltage Drop fault that national standard is mentioned, comprises three-phase equilibrium and falls, and single-phase falling falls three kinds of situations with two-phase.

As shown in Figure 1, the positive-negative sequence decoupling control method of the compatible low voltage crossing of a kind of photovoltaic combining inverter, it comprises the steps:

1., adopt positive-negative sequence decoupling method that the line voltage detected is decomposed into positive sequence component and negative sequence component, inverter output current is also divided into positive sequence component and negative sequence component, it is controlled respectively; Above-mentioned said positive-negative sequence decoupling method: the normal wiring of electrical network is A phase B phase and C phase, now rotates according to clockwise direction for positive sequence voltage vector.If wiring changes A phase C phase and B phase into, now rotate according to clockwise direction for negative sequence voltage vector.Line voltage has positive sequence component and negative sequence component simultaneously.The method be separated by these two kinds of components is exactly positive-negative sequence decoupling method.

2. the positive sequence component of inverter output current, is made to follow the tracks of the positive sequence component of line voltage, the negative sequence component of inverter output current is controlled to be zero, thus make inverter correctly calculate electric network voltage phase according to the situation of falling of line voltage in real time, realize output current phase control.

Step 1. in, line voltage to be decomposed and the step that controls is:

I), to line voltage gather in real time, adopt positive-negative sequence decoupling method that the line voltage detected is decomposed into positive sequence component e _pwith negative sequence component e _n, line voltage is expressed as:

Wherein, e _afor A phase voltage, e _bfor B phase voltage, e _cfor C phase voltage, for the phase place of positive sequence component, for the phase place of negative sequence component;

Ii), by above-mentioned line voltage enter processor by AD sampling, first by 3/2 conversion by its by three-phase abc coordinate system transformation to two-phase rotation alpha β coordinate system, and the force feed that the α β reference axis obtained powered on enters low pass filter carries out filtering; Voltage after conversion in α β reference axis is expressed as, wherein, and e _αfor α shaft voltage, e _βfor β shaft voltage,

Iii), to after the voltage phase shift in α β reference axis 90 degree, (2) formula becomes:

Wherein, e _α' be the α shaft voltage after phase shift 90 degree, e _β' be the β shaft voltage after phase shift 90 degree;

Iv), simultaneous (2), (3) two prescription journeys, calculate the positive-negative sequence component of voltage in α β reference axis:

$\left[\begin{array}{c}{e}_{\mathrm{\αP}}\\ e_{\mathrm{\βP}}\\ e_{\mathrm{\αN}}\\ e_{\mathrm{\βN}}\end{array}\right]=\left[\begin{array}{cccc}1& 0& 0& -1\\ 0& 1& 1& 0\\ 1& 0& 0& 1\\ 0& 1& -1& 0\end{array}\right]\left[\begin{array}{c}{e}_{\mathrm{\α}}\\ e_{\mathrm{\β}}\\ {e_{\mathrm{\α}}}^{\′}\\ {e_{\mathrm{\β}}}^{\′}\end{array}\right]---\left(4\right)$

V), by the positive-negative sequence component of voltage in α β reference axis transform to abc coordinate system, namely obtain positive-negative sequence component and the phase place of voltage.

Adopting uses the same method can calculate the positive-negative sequence component of electric current, and inverter phase-locked loop follows the tracks of the positive sequence component of line voltage, controls respectively output current positive-negative sequence component, and control positive sequence component identical with current-order, negative sequence component is zero.

When low voltage crossing, imbalance of three-phase voltage can introduce larger negative sequence component.If adopt conventional method to follow the tracks of line voltage, output current has larger low-order harmonic and frequency change.Output current can be made like this to produce serious distortion, produced under-frequency, the faults such as overcurrent, and even can not realize low voltage crossing.The method of application positive-negative sequence decoupling zero can when low voltage crossing the positive sequence component of a floating voltage, export good current waveform.

Claims (3)

1. a positive-negative sequence decoupling control method for the compatible low voltage crossing of photovoltaic combining inverter, it is characterized in that, it comprises the steps:

1., adopt positive-negative sequence decoupling method that the line voltage detected is decomposed into positive sequence component and negative sequence component, inverter output current is also divided into positive sequence component and negative sequence component, it is controlled respectively;

2. the positive sequence component of inverter output current, is made to follow the tracks of the positive sequence component of line voltage, the negative sequence component of inverter output current is controlled to be zero, thus make inverter correctly calculate electric network voltage phase according to the situation of falling of line voltage in real time, realize output current phase control.

2. the positive-negative sequence decoupling control method of the compatible low voltage crossing of photovoltaic combining inverter according to claim 1, is characterized in that: step 1. in, line voltage to be decomposed and the step that controls is:

I), to line voltage gather in real time, adopt positive-negative sequence decoupling method that the line voltage detected is decomposed into positive sequence component e _pwith negative sequence component e _n, line voltage is expressed as:

Wherein, e _afor A phase voltage, e _bfor B phase voltage, e _cfor C phase voltage, for the phase place of positive sequence component, for the phase place of negative sequence component;

Ii), by above-mentioned line voltage by AD sampling enter processor, first by 3/2 conversion by its by three-phase abc coordinate system transformation to two-phase rotation alpha β coordinate system; Voltage after conversion in α β reference axis is expressed as, wherein, and e _αfor α shaft voltage, e _βfor β shaft voltage,

Iii), to after the voltage phase shift in α β reference axis 90 degree, (2) formula becomes:

Wherein, e _α' be the α shaft voltage after phase shift 90 degree, e _β' be the β shaft voltage after phase shift 90 degree;

Iv), simultaneous (2), (3) two prescription journeys, calculate the positive-negative sequence component of voltage in α β reference axis:

$\left[\begin{array}{c}{e}_{\mathrm{\αP}}\\ e_{\mathrm{\βP}}\\ e_{\mathrm{\αN}}\\ e_{\mathrm{\βN}}\end{array}\right]=\left[\begin{array}{cccc}1& 0& 0& -1\\ 0& 1& 1& 0\\ 1& 0& 0& 1\\ 0& 1& -1& 0\end{array}\right]\left[\begin{array}{c}{e}_{\mathrm{\α}}\\ e_{\mathrm{\β}}\\ {e_{\mathrm{\α}}}^{\′}\\ {e_{\mathrm{\β}}}^{\′}\end{array}\right]---\left(4\right)$

V), by the positive-negative sequence component of voltage in α β reference axis transform to abc coordinate system, namely obtain positive-negative sequence component and the phase place of voltage.

3. the positive-negative sequence decoupling control method of the compatible low voltage crossing of photovoltaic combining inverter according to claim 2, is characterized in that: the step I i described) in, the force feed that the α β reference axis obtained powered on enters low pass filter and carries out filtering.