CN103219908A - Method for controlling balance of direct current side of cascaded grid-connected inverter based on zero sequence and negative sequence voltage injection - Google Patents

Abstract

The invention discloses a method for controlling the balance of a direct current side of a cascaded grid-connected inverter based on zero sequence and negative sequence voltage injection. The method is based on the combination of zero sequence voltage and negative sequence voltage injection; and the method comprises the following steps of (1) integrally controlling the direct current voltage by using a control method of positive sequence current decoupling, and correcting the unbalance of the system on the basis of positive sequence decoupling, and decomposing network voltage and the positive and negative sequence of the current by using a second harmonic filtering method; and (2) controlling the phase balance of the direct current side, respectively calculating the zero sequence voltage component and the negative sequence voltage component needing injecting, starting the zero sequence voltage injection method under a normal condition, and using the negative sequence voltage injection method when the power difference of each phase is large according to switching conditions. Furthermore, when the zero sequence voltage injection is used, the condition that the maximum output phase voltage does not exceed the maximum value provided by the inverter needs to be satisfied. Through the method, three phases can be comprehensively combined; the voltage of different phase sequences can be injected under different conditions, the output performance and interphase power adjustment ability of the device are both considered; and for the application of three-phase cascaded grid-connected inverter matched renewable energy sources large-scale synchronization and large-scale energy storage, the method has an important value.

Description

Cascade connection type combining inverter DC side balance control method based on zero sequence and negative sequence voltage injection

Technical field

The present invention relates to the high-voltage and high-power power electronic technology in the application on power system technical field, relate in particular to the alternate DC side balance control method of cascade connection type combining inverter.

Background technology

In recent years, development along with new forms of energy, H bridge cascade structure becomes the focus of research in fields such as parallel network reverse, energy storage, electric power electric transformers, regenerative resource is incorporated into the power networks on a large scale for cooperating for it, extensive energy storage and strengthen stability of power system and have great importance.

The combining inverter device of this type can insert high-voltage fence by transformer-free, be easy to modular implementation on the structure, and have than low switch loss and harmonic wave output, but each separate H bridge DC side exists parallel connection type loss and mixed type differential loss and pulse delay difference in its structure, there are factors such as Voltage unbalance in the electrical network that connects, and this has just caused the unbalanced problem of dc voltage.Use comparatively ripe cascade connection type STATCOM (STATCOM) occasion than engineering, the cascade connection type combining inverter is owing to exist the device that can equivalence becomes heavy load or current source in DC side, self may cause bigger uneven difference, this will cause very big influence to the output performance and the reliability of device.

Chinese invention patent CN1514525 asks for devices such as device, pulse-width modulator, pulse amplifier to carrying out the active power exchange between the Cascade H bridge by pressure measuring instrument, minimum capacity voltage, thereby realize the Balance Control of capacitance voltage, this method need increase extra device, has increased cost; Chinese invention patent CN102291030 passing ratio integration is asked voltage difference and is obtained amount of bias, again amount of bias is added to and has realized the balance of voltage of DC side on the basis of original modulating wave, need not to increase the additional hardware device, but this method is based on rest frame, calculate comparatively complexity, and the method for proportional integral needs certain delay; Chinese invention patent CN1913321 and U.S. patent of invention US6075350 also are based on the dc-voltage balance control method of control strategy, its essence is identical with Chinese invention patent CN102291030, all be that power or voltage deviation according to each H bridge obtains amount of bias, regulate control on the modulating wave that is added to again.Below all be interior mutually DC side balance control method, the Balance Control between the three-phase do not studied at cascaded inverter.

Summary of the invention

Problem at above-mentioned existence, the objective of the invention is to propose a kind of control method of the alternate DC side balance of injecting based on zero sequence and negative sequence voltage of cascade connection type combining inverter, this method is injected different phase sequence voltages according to unbalanced power supply degree and each phase load difference size, effectively assurance device stable operation, simultaneously need not increase additional hardware, the convenient realization.

For achieving the above object, the technical solution used in the present invention is a kind of control method of the alternate DC side balance of injecting based on zero sequence and negative sequence voltage of cascade connection type combining inverter, is made of whole direct voltage control, the alternate Balance Control two parts of DC side.It is characterized in that, comprise the steps:

1) whole direct voltage control

1.1) gather each phase DC side total voltage value u _DcA, u _DcB, u _DcC, calculate the total mean value of all H bridge unit dc voltages

1.2) use the command voltage average

Deduct The gained difference is through the proportional integral pi regulator, obtains instructing the active current value

1.3) utilize the park conversion to form three-phase current i _{A, b, c}Positive sequence component

With three phase network voltage e _{A, b, c}Negative sequence component

1.4) positive sequence decoupling zero control, utilize

Obtain the modulation voltage under the rotating coordinate system

1.5)

Respectively with

Superpose, obtain each phase initial modulation voltage u through anti-park conversion again _a, u _b, u _c

2) the alternate Balance Control of DC side

2.1) usefulness step 1.1) in

Deduct u respectively _DcA, u _DcB, u _DcC, three differences of gained are passed through the proportional integral pi regulator respectively, obtain Δ P _A, Δ P _B, Δ P _C;

2.2) Δ P _A, Δ P _B, Δ P _CCarry out the park conversion and obtain Δ P _αWith Δ P _β;

2.3) in order to offset the electrical network negative sequence voltage, inverter need be exported identical negative sequence voltage, this negative sequence voltage in the active power that i produces mutually is

Use Δ P _α, Δ P _βDeduct respectively

The park transformation results, obtain Δ P ' _αWith Δ P ' _β;

2.4) utilize Δ P ' _αWith Δ P ' _βAnd inverter output positive sequence voltage, electric current and electrical network negative sequence voltage calculate the zero sequence voltage component V that needs injection _z, θ _zAnd negative sequence voltage component V _n, θ _n

2.5) use the residual voltage injection to need the phase voltage of satisfied maximum output to be no more than the peaked condition that inverter can provide, when can't having satisfied required power adjustments ability, the residual voltage injection method should automatically switch to the negative sequence voltage injection;

2.6) with zero sequence voltage component V _z, θ _zOr negative sequence voltage component V _n, θ _nBe superimposed to step 1.5) in u _a, u _b, u _c, obtain each final mutually modulation voltage

Utilize this modulation voltage can realize the alternate Balance Control of alternate DC side.

The present invention has following beneficial effect:

(1) can conveniently realize, need not to dispose the hardware power and the voltage balancing circuit of additional complexity, only need some transducer and digit chips etc. cheaply;

(2) take into account the output performance and the regulating power of device, not only dc voltage has been had stronger regulating power, and guaranteed the compensation performance that electrical network do not had bigger pollution and influence device;

(3) algorithm adopts the dq rotating coordinate system, realizes simple and convenient fast, and clear physics conception can the fine astatic control that must realize current on line side;

(4) this method has taken into full account the unbalanced factor from grid side, has increased the control to the electrical network negative sequence voltage, has higher engineering using value.

Description of drawings

The equivalent topologies structure of Fig. 1 cascade combining inverter;

The integral body control block diagram of Fig. 2 combining inverter;

The vectogram of Fig. 3 residual voltage injection method;

Each phase dc voltage test waveform during Fig. 4 load variations;

Behind Fig. 5 load changing, the electric current during the condition criterion;

Three-phase current test waveform when Fig. 6 negative sequence voltage injects.

Embodiment

The present invention is mainly used in the DC side Balance Control of cascade connection type combining inverter, the equivalent topologies structure of cascade connection type combining inverter as shown in Figure 1, each H bridge units in series by N unit forms, three-phase adopts star-like connection, and the control of three alternate dc-voltage balances need be regulated the active power of each phase under the constant situation of the total active power of three-phase.First-harmonic phase voltage and the electric current of choosing current transformer output define, suc as formula 1 with formula 2.

$\left\{\begin{array}{c}{u}_a=V_p\sin \left(\mathrm{\ωt}\right)+V_z\sin (\mathrm{\ωt}+{\mathrm{\θ}}_z)+\\ V_n\sin (\mathrm{\ωt}+{\mathrm{\θ}}_n)+V_n^s\sin (\mathrm{\ωt}+{\mathrm{\θ}}_n^s)\\ u_b=V_p\sin (\mathrm{\ωt}-\frac{2\mathrm{\π}}{3})+V_z\sin (\mathrm{\ωt}+{\mathrm{\θ}}_z)+\\ V_n\sin (\mathrm{\ωt}+{\mathrm{\θ}}_n+\frac{2\mathrm{\π}}{3})+V_n^s\sin (\mathrm{\ωt}+{\mathrm{\θ}}_n^s+\frac{2\mathrm{\π}}{3})\\ u_c=V_p\sin (\mathrm{\ωt}+\frac{2\mathrm{\π}}{3})+V_z\sin (\mathrm{\ωt}+{\mathrm{\θ}}_z)+\\ V_n\sin (\mathrm{\ωt}+{\mathrm{\θ}}_n-\frac{2\mathrm{\π}}{3})+V_n^s\sin (\mathrm{\ωt}+{\mathrm{\θ}}_n^s-\frac{2\mathrm{\π}}{3})\end{array}\right.---\left(1\right)$

The active power of each phase constitutes by three parts, and following form is write in unification:

$P_i=\stackrel{\‾}{P}+\mathrm{\Δ}{P}_{\mathrm{ji}}+\mathrm{\Δ}{P}_{\mathrm{in}}^s,(i=A,B,C;j=n,z)---\left(3\right)$

Total control block diagram of cascade connection type combining inverter as shown in Figure 2, among Fig. 2, the Δ P in the alternate Balance Control module of DC side _αWith Δ P _βBe calculated as follows:

$\left[\begin{array}{c}\mathrm{\Δ}{P}_{\mathrm{\α}}\\ \mathrm{\Δ}{P}_{\mathrm{\β}}\end{array}\right]=\frac{\sqrt{2}}{2}\left[\begin{array}{c}\sqrt{3}\mathrm{\Δ}{P}_A\\ \mathrm{\Δ}{P}_B-\mathrm{\Δ}{P}_C\end{array}\right]---\left(4\right)$

For the power that counteracting electrical network negative sequence voltage is produced is revised, will

Carry out abc/ α β conversion, thereby obtain:

With Δ P _ZA, Δ P _ZBAnd Δ P _ZCThrough abc/ α β conversion, convolution (4) and (5) thus obtain the amplitude V of zero sequence injecting voltage _zAnd phase angle theta _zComputational methods:

$V_z=\frac{2}{3I_p}\sqrt{6(\mathrm{\Δ}{P}_{\mathrm{\α}}^{\′2}+\mathrm{\Δ}{P}_{\mathrm{\β}}^{\′2})}---\left(6\right)$

With Δ P _NA, Δ P _NBAnd Δ P _NCThrough identical abc/ α β conversion, can try to achieve the amplitude V of negative phase-sequence injecting voltage _nAnd phase angle theta _nAs follows:

$V_n=\frac{2}{3}\sqrt{\frac{6(\mathrm{\&Delta;}{P}_{\mathrm{\&alpha;}}^{\&prime;2}+\mathrm{\&Delta;}{P}_{\mathrm{\&beta;}}^{\&prime;2})}{{\mathrm{<figure-callout\; id="2"\; label="M"\; filenames="130326132903.png"\; state="\{\{state\}\}">M</figure-callout>}}^2+N^2}}---\left(8\right)$

${\mathrm{\&theta;}}_n\left\{\begin{array}{cc}{\tan }^{-1}\left(\frac{\mathrm{N\&Delta;}{P}_{\mathrm{\&alpha;}}^{\&prime;}+\mathrm{M\&Delta;}{P}_{\mathrm{\&beta;}}^{\&prime;}}{\mathrm{M\&Delta;}{P}_{\mathrm{\&alpha;}}^{\&prime;}-\mathrm{N\&Delta;}{P}_{\mathrm{\&beta;}}^{\&prime;}}\right)& \mathrm{M\&Delta;}{P}_{\mathrm{\&alpha;}}^{\&prime;}\&NotEqual;\mathrm{N\&Delta;}{P}_{\mathrm{\&beta;}}^{\&prime;}\\ \frac{\mathrm{\&pi;}}{2}\mathrm{sign}(\mathrm{N\&Delta;}{P}_{\mathrm{\&alpha;}}^{\&prime;}+\mathrm{M\&Delta;}{P}_{\mathrm{\&beta;}}^{\&prime;})& \mathrm{M\&Delta;}{P}_{\mathrm{\&alpha;}}^{\&prime;}=\mathrm{N\&Delta;}{P}_{\mathrm{\&beta;}}^{\&prime;}\end{array}\right.---\left(9\right)$

As shown in Figure 3, the inverter output voltage after residual voltage injects is

The as can be seen from the figure maximal phase voltage of inverter output Be residual voltage

With its positive sequence voltage Angle θ _zMinimum phase.Be no more than the maximum V that inverter can provide and use residual voltage to inject the phase voltage that needs to satisfy maximum output _MaxCondition, that is:

$\sqrt{V_{\mathrm{<figure-callout\; id="2"\; label="z"\; filenames="130326132903.png"\; state="\{\{state\}\}">z</figure-callout>}}^2+{\mathrm{<figure-callout\; id="2"\; label="V\; p"\; filenames="130326132903.png"\; state="\{\{state\}\}">V</figure-callout>}}_p^{}+2V_p{V}_z\cos ({\mathrm{\&theta;}}_z-\frac{2\mathrm{\&pi;}}{3}\mathrm{sign}\left({\mathrm{\&theta;}}_z\right[\left|\frac{3{\mathrm{\&theta;}}_z}{\mathrm{\&pi;}}\right|\left]\right))}\&le;V_{\max }---\left(10\right)$

In addition, during unbalanced power supply, combining inverter need be exported the negative sequence voltage that offsets, and this also can exert an influence to the scope of injecting voltage.On the condition basis of formula (10), increase restriction to the electrical network negative sequence voltage, the negative sequence voltage amplitude must not surpass when injecting residual voltage

That is:

$\sqrt{{\left(e_d^n\right)}^2+{\left(e_q^n\right)}^2}\&le;e_{\max }^n---\left(11\right)$

Fig. 4 is for carrying out the dc voltage waveform of load changing when stablizing, after DC side fluctuateed, the adjusting dc voltage through after a while tended towards stability again.

Electric current during Fig. 5 the back takes place and be in condition criterion for load changing, still be in residual voltage and inject state this moment, and three-phase current still keeps symmetry as can be seen, but distorts.

Fig. 6 is through the stable three-phase current test waveform behind the load changing, and residual voltage injected and can not satisfy the power adjustments requirement this moment, so automatically switch to the negative sequence voltage injection method.

The above only is a preferred implementation of the present invention; be noted that for those skilled in the art; under the prerequisite that does not break away from the principle of the invention, can also make some improvements and modifications, these improvements and modifications also should be considered as protection scope of the present invention.

Claims (1)

1. cascade connection type combining inverter DC side balance control method that injects based on zero sequence and negative sequence voltage, this method comprises the steps:

1) whole direct voltage control

1.1) gather each phase DC side total voltage value u _DcA, u _DcB, u _DcC, calculate the total mean value of all H bridge unit dc voltages

1.2) use the command voltage average

Deduct

The gained difference is through the proportional integral pi regulator, obtains instructing the active current value

1.3) utilize the park conversion to form three-phase current i _{A, b, c}Positive sequence component

With three phase network voltage e _{A, b, c}Negative sequence component

1.4) positive sequence decoupling zero control, utilize

Obtain the modulation voltage under the rotating coordinate system

1.5) Respectively with

Superpose, obtain each phase initial modulation voltage u through anti-park conversion again _a, u _b, u _c

2) the alternate Balance Control of DC side

2.1) usefulness step 1.1) in

Deduct u respectively _DcA, u _DcB, u _DcC, three differences of gained are passed through the proportional integral pi regulator respectively, obtain Δ P _A, Δ P _B, Δ P _C;

22) Δ P _A, Δ P _B, Δ P _CCarry out the park conversion and obtain Δ P _αWith Δ P _β;

2.3) in order to offset the electrical network negative sequence voltage, inverter need be exported identical negative sequence voltage, this negative sequence voltage in the active power that i produces mutually is

Use Δ P _α, Δ P _βDeduct respectively

The park transformation results, obtain.P ' _αWith Δ P ' _β;

Z4) utilize Δ P ' _αWith Δ P ' _βAnd inverter output positive sequence voltage, electric current and electrical network negative sequence voltage calculate the zero sequence voltage component V that needs injection _z, θ _zAnd negative sequence voltage component V _n, θ _n

2.5) use the residual voltage injection to need the phase voltage of satisfied maximum output to be no more than the peaked condition that inverter can provide, when can't having satisfied required power adjustments ability, the residual voltage injection method should automatically switch to the negative sequence voltage injection;

2.6) with zero sequence voltage component V _z, θ _zOr negative sequence voltage component V _n, θ _nBe superimposed to step 1.5) in u _a, u _b, u _c, obtain each final mutually modulation voltage

Utilize this modulation voltage can realize the alternate Balance Control of alternate DC side.

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