CN102761127B - Reactive current compensation method for three-phase grid-connected inverter in situation of unbalanced drop of grid - Google Patents

Abstract

The invention discloses a reactive current compensation method for a three-phase grid-connected inverter in a situation of unbalanced drop of a grid. The method is characterized in that as for a grid-connected power generation system based on which a DC side power supply is connected with the grip through the three-phase grid-connected inverter, in the situation of unbalanced drop of the grid voltage, through adding the reactive power compensation of the three-phase grid-connected inverter for the reactive current output by grid drop phase and through changing the corresponding active current, the reactive current is offset to an extent that the current sum of the three phases is zero. Due to the adoption of the method, the reactive power independent compensation in the situation of unbalanced drop of the grid is realized, and the reactive power over-compensation for un-dropped phase in the situation of the unbalanced drop is avoided.

Description

The reactive-current compensation method of three-phase grid-connected inverter in the time that unbalanced power supply falls

Technical field

The present invention relates to the reactive-current compensation method of a kind of three-phase grid-connected inverter in the time that unbalanced power supply falls.Belong to power electronics applied technical field, relate generally to unbalanced power supply and fall the combining inverter Technique of Compensating Capacitance for Reactive under condition.

Background technology

In recent years, along with the quantity of grid-connected system access electrical network increases, grid-connected system capacity is also increasing, various countries' grid company is also more and more higher for the requirement of grid-connected system low voltage crossing (can keep grid-connected when electrical network falls in short-term), reactive power compensation is the important component part of low voltage crossing control, instant effectively reactive power compensation can strengthen the ability of grid-connected system low voltage crossing to a certain extent, therefore many grid company are had higher requirement to the reactive power compensation generating electricity by way of merging two or more grid systems in electricity generation system low voltage crossing process, when the imbalance providing as the German energy and Shui Ye association is fallen, the related request of reactive power compensation is: when line voltage occurs that imbalance is fallen, grid-connected system can maintain certain grid-connected operating time, provide reactive power support to electrical network.Require line voltage to fall and carry out mutually reactive power compensation, and voltage does not fall Xiang Bufa or send out idle less (voltage must not exceed rated voltage 110%), the state of unbalanced power supply was not considered in the reactive power compensation of traditional three-phase grid-connected inverter system in the time that electrical network falls, and was easy to cause in the case line voltage not fall the idle overcompensation of phase place.

Summary of the invention

The present invention is for avoiding the existing weak point of above-mentioned prior art, the reactive-current compensation method of a kind of three-phase grid-connected inverter in the time that unbalanced power supply falls is provided, fall the grid-connected inverting system reactive power independent compensation under condition to realize unbalanced power supply, avoid imbalance to fall not falling in situation the reactive power overcompensation of phase place.

The present invention is that technical solution problem adopts following technical scheme:

The feature of the reactive-current compensation method of three-phase grid-connected inverter of the present invention in the time that unbalanced power supply falls is: for the grid-connected system that DC side power supply is connected to the grid by three-phase grid-connected inverter, in the time that line voltage generation imbalance is fallen, carry out reactive power compensation by increasing the reactive current that three-phase grid-connected inverter falls mutually output at electrical network, the active current that simultaneously changes corresponding phase is offset reactive current to three-phase current and is zero.

The feature of the reactive-current compensation method of three-phase grid-connected inverter of the present invention in the time that unbalanced power supply falls is also: described compensation method is carried out as follows:

Step 1: in three-phase grid-connected inverter electricity generation system, every phase current corresponding real component and idle component after decoupling zero differs 90 degree, supposes to occur as electrical network A that mutually voltage falls, and determines reactive power compensation electric current by formula (1):

$\left\{\begin{array}{c}{I}_{a\_Q}=(1-E_{a\_m}/E_{\mathrm{base}})\·K\sin \mathrm{\θ};\\ I_{b\_Q}=0;\\ I_{c\_Q}=0;\end{array}\right.---\left(1\right)$

In formula (1), I _{a_Q}, I _{b_Q}and I _{c_Q}be respectively A phase, B phase and C phase reactive power compensation electric current; K is A phase current penalty coefficient, E _basefor A phase electrical network falls front voltage magnitude, E _{a_m}for A phase electrical network falls rear voltage magnitude, θ is A phase line voltage angle;

Step 2: by the B phase that obtained by formula (2) and the corresponding real component electric current I of C phase _{b_P}and I _{c_P}offset A phase reactive power compensation electric current:

In formula (1) and formula (2): I _{a_Q}+ I _{b_P}+ I _{c_P}=0

The feature of the reactive-current compensation method of three-phase grid-connected inverter of the present invention in the time that unbalanced power supply falls is also: described compensation method is carried out as follows:

Step 1, in the time that electrical network generation two-phase imbalance is fallen, suppose to occur with B that mutually voltage falls when electrical network A phase, and it is consistent to fall amplitude, and the reactive power compensation electric current that through type (3) obtains A phase, B phase and C phase is respectively I _{a_Q}, I _{b_Q}and I _{c_Q};

Step 2: the B being obtained by through type (4) and formula (5) respectively, C two-phase and A, the active current I of C two-phase _{b_P}, I _{c_P}' and I _{a_P}, I _{c_P}" offset A, B two-phase reactive power compensation electric current, described I _{c_P}' and I _{c_P}" be respectively the C phase active current of corresponding A phase reactive power compensation electric current and the C phase active current of corresponding B phase reactive power compensation electric current;

Obtaining three-phase real component electric current by formula (6) is again:

I _{c_P}＝I _{c_P}′+I _{c_P}″ (6)。

Compared with the prior art, beneficial effect of the present invention is embodied in:

Grid-connected system of the present invention is three-phase grid contravariant generating system, in the time that line voltage generation imbalance is fallen, realize unbalanced power supply by the reactive power compensation electric current of control three-phase three-wire system combining inverter and fall the grid-connected inverting system reactive power independent compensation under condition.By the control to grid-connected current, the reactive power that electrical network falls phase has obtained effective independent compensation.Avoid electrical network not fall the reactive power overcompensation of not falling mutually phase place.The grid-connected system falling under condition for imbalance provides effective reactive power compensation algorithm.By increase corresponding phase active power output offset the zero-sequence current that brings of reactive power compensation electric current, make three-phase inverter output current sum is zero during line voltage falls, the adverse effect of having avoided zero-sequence current to bring power system transformer,

Brief description of the drawings

Fig. 1 is three-phase grid contravariant generating system structural representation of the present invention;

Fig. 2 is that the single-phase imbalance of the present invention is fallen Non Power Compensation Process schematic diagram;

Fig. 3 is that two-phase imbalance of the present invention is fallen Non Power Compensation Process schematic diagram.

Embodiment

As shown in Figure 1, three-phase grid contravariant generating system structure is made up of three-phase grid-connected inverter 102 and electrical network 104, and three-phase grid-connected inverter 102 effects are generating that the energy of DC side 101 is connected with electrical network 104 by inversion control; Electrical network part generally includes line impedance L and transformer 103, because transformer 103 is generally star delta connection, zero-sequence current cannot pass through, and the zero-sequence current that inverter sends can affect equipment stable operation, in transformer, can produce leakage field and make iron core excitation, zero-sequence current need to be eliminated.For three-phase grid-connected inverter, the reactive-current compensation method in the time that unbalanced power supply falls is in the present invention: for three-phase grid contravariant generating system, in the time that line voltage generation imbalance is fallen, the reactive current of falling output mutually at electrical network by increase three-phase grid-connected inverter is carried out reactive power compensation, the amplitude that the amplitude of reactive power compensation is fallen to electrical network is directly proportional, and the active current that simultaneously changes corresponding phase is offset reactive current to three-phase current be zero.

Embodiment 1:

Suppose to occur as electrical network A that mutually voltage falls, compensation method is carried out as follows:

Step 1: in three-phase grid-connected inverter electricity generation system as shown in Figure 2, A, B, C is respectively the meritorious reference axis of three-phase, A ', B ', C ' is respectively the idle reference axis of three-phase, and the meritorious reference axis that each is corresponding and idle reference axis differ 90 °, the reactive power compensation rule while falling according to unbalanced source voltage, when electrical network A occurs that voltage falls mutually, determine reactive power compensation electric current by formula (1):

$\left\{\begin{array}{c}{I}_{a\_Q}=(1-E_{a\_m}/E_{\mathrm{base}})\·K\sin \mathrm{\θ};\\ I_{b\_Q}=0;\\ I_{c\_Q}=0;\end{array}\right.---\left(1\right)$

In formula (1), I _{a_Q}, I _{b_Q}and I _{c_Q}be respectively A phase, B phase and C phase reactive power compensation electric current; K is A phase current penalty coefficient (this penalty coefficient is by the concrete electrical network of administration of power networks department basis), E _basefor A phase electrical network falls front voltage magnitude, E _{a_m}for A phase electrical network falls rear voltage magnitude, θ is A phase line voltage angle; (1-E in formula _{a_m}/ E _base) fall the computing formula of amplitude for line voltage.

As shown in Figure 2, there is reactive power compensation electric current I in the mutually idle reference axis of A after compensation _{a_Q}, B, C two-phase reactive power compensation electric current is 0.

Step 2: as shown in Figure 2, the reactive power producing mutually in order to offset A, can on the active power axle of bearing merit power shaft and C phase of B phase, apply two equal-sized active currents, the corresponding real component electric current I of the B phase being obtained by formula (2) and C phase _{b_P}and I _{c_P}offset A phase reactive power compensation electric current:

As shown in Figure 2, owing to differing 90 ° between every meritorious reference axis mutually and idle reference axis, and often between three-phase differ 120 °, therefore I _{b_P}vector angle is °-90 °, θ-120, I _{c_P}vector angle is θ+120 °+90 °.

Due to A phase reactive power compensation electric current and B, the active current of C two-phase closes and is:

I _{a_Q}+I _{b_P}+I _{c_P}=0

In formula (1) and formula (2), real component electric current can be offset sent reactive power compensation electric current.

Embodiment 2:

Suppose to occur with B that mutually voltage falls when electrical network A phase, and it is consistent to fall amplitude, in full accord in the mode of compensation and embodiment 1, difference is, separately A phase is carried out to the calculating of reactive power compensation electric current and real component electric current mutually with B respectively, finally will calculate vector superposed on gained same phase, carry out as follows:

Step 1, in the time that electrical network generation two-phase imbalance is fallen, suppose to occur with B that mutually voltage falls when electrical network A phase, and it is consistent to fall amplitude, and the reactive power compensation electric current that through type (3) obtains A phase, B phase is respectively I _{a_Q}, I _{b_Q}, as shown in Figure 3:

Step 2: as shown in Figure 3, the B being obtained by through type (4) and formula (5) respectively, C two-phase and A, the active current I of C two-phase _{b_P}, I _{c_P}' and I _{a_P}, I _{c_P}" offset A, B two-phase reactive power compensation electric current, I _{c_P}' and I _{c_P}" be respectively the C phase active current of corresponding A phase reactive power compensation electric current and the C phase active current of corresponding B phase reactive power compensation electric current:

The amplitude of meritorious compensate component is equally all:

$\frac{\sqrt{3}}{2}(1-\frac{E_{a\_m}}{E_{\mathrm{base}}})\·K$

Obtaining three-phase real component electric current by formula (6) is again:

I _{c_P}＝I _{c_P}′+I _{c_P}″ (6)

The reactive power compensation electric current being calculated by above formula and real component electric current can meet the effect of cancelling out each other equally, therefore:

I _{a_Q}+I _{b_Q}+I _{a_P}+I _{b_P}+I _{c_P}=0

Because combining inverter output grid-connected current is now the unsymmetrical current that comprises negative sequence component, inverter direct-flow side there will be larger ripple.But while falling due to electrical network, DC side voltage of converter do not had the requirement of ripple.Can not consider.

Claims (2)

1. the reactive-current compensation method of three-phase grid-connected inverter in the time that unbalanced power supply falls, it is characterized in that: for the grid-connected system that DC side power supply is connected to the grid by three-phase grid-connected inverter, in the time that line voltage generation imbalance is fallen, carry out reactive power compensation by increasing the reactive current that three-phase grid-connected inverter falls mutually output at electrical network, the active current that simultaneously changes corresponding phase is offset reactive current to three-phase current and is zero;

Described compensation method is carried out as follows:

Step 1: in three-phase grid-connected inverter electricity generation system, every phase current corresponding real component and idle component after decoupling zero differs 90 degree, supposes to occur as electrical network A that mutually voltage falls, and determines reactive power compensation electric current by formula (1):

In formula (1), I _{a_Q}, I _{b_Q}and I _{c_Q}be respectively A phase, B phase and C phase reactive power compensation electric current; K is A phase current penalty coefficient, E _basefor A phase electrical network falls front voltage magnitude, E _{a_m}for A phase electrical network falls rear voltage magnitude, θ is A phase line voltage angle;

Step 2: by the B phase that obtained by formula (2) and the corresponding real component electric current I of C phase _{b_P}and I _{c_P}offset A phase reactive power compensation electric current:

In formula (1) and formula (2): I _{a_Q}+ I _{b_P}+ I _{c_P}=0.

2. the reactive-current compensation method of three-phase grid-connected inverter according to claim 1 in the time that unbalanced power supply falls, is characterized in that described compensation method carries out as follows:

Step 1, in the time that electrical network generation two-phase imbalance is fallen, suppose to occur with B that mutually voltage falls when electrical network A phase, and it is consistent to fall amplitude, and the reactive power compensation electric current that through type (3) obtains A phase, B phase and C phase is respectively I _{a_Q}, I _{b_Q}and I _{c_Q};

Step 2: B, C two-phase and the A being obtained by through type (4) and formula (5) respectively, the active current I of C two-phase _{b_P}, I _{c_P}' and I _{a_P}, I _{c_P}" offset A, B two-phase reactive power compensation electric current, described I _{c_P}' and I _{c_P}" be respectively the C phase active current of corresponding A phase reactive power compensation electric current and the C phase active current of corresponding B phase reactive power compensation electric current;

Obtaining three-phase real component electric current by formula (6) is again:

I _{c_P}=I _{c_P}′+I _{c_P}″ (6)。