CN103427700B - Imbalance compensating control method for three-phase four-switch power converter - Google Patents

Abstract

The invention discloses an imbalance compensating control method for a three-phase four-switch power converter. In order to achieve compensation for negative sequence and idle work, and regarding voltage outer ring control of the three-phase four-switch power converter, a secondary ripple remover is provided, a secondary ripple in a tracking error of direct current side voltage can be removed, and third harmonic output of a system is avoided. Regarding voltage-sharing control of capacitors on the direct current side, a primary ripple remover is disclosed, and the primary ripple in the voltage difference of the two capacitors can be removed, so that normal and stable operation of the device is achieved. Regarding current inner ring control of the three-phase four-switch power converter, an integrated control method of PR feedback control and feedforword control is disclosed, fast tracking of an output current is achieved, and dynamic control performance of the system is effectively improved.

Description

A kind of imbalance compensation control method of three-phase four switching power converter

Technical field

The present invention relates to negative phase-sequence, reactive power compensation and control method field thereof, particularly a kind of imbalance compensation control method of three-phase four switching power converter.

Background technology

Along with social industrial expansion, railway traffic, in the metallurgical and petroleum and petrochemical industry in mine, uncompensated load puts into operation, a large amount of idle and negative-sequence currents can be produced, serious harm is brought to the operation of the generating in electric power system, transmission of electricity and converting equipment, the loss of increase system, reduces transformer and exerts oneself, have a strong impact on the safety and economic operation of electric power system.Especially the locomotive load in high-speed railway, the single-phase haulage gear special due to it can produce a large amount of negative-sequence currents, has a strong impact on the safe and reliable operation of electric power system.Therefore, the power quality problems such as the idle and negative-sequence current that suppression uncompensated load of must adopting an effective measure produces.

For problems such as above-mentioned idle, negative phase-sequences, Chinese scholars has carried out certain research.Have scholar to propose to adopt and install passive filter (Passive Power Filter, PPF) and carry out the static compensation of reactive power, structure is simple, but it cannot dynamic adjustments, simultaneously easily and electrical network produce series parallel resonance.For this reason, scholar is had to also been proposed Static Var Compensator (Static Var Compensator, SVC), it is made up of jumbo fixed capacitor and thyristor controlled inductor, variable dynamic compensation can be realized by the Trigger Angle of dynamic adjustments thyristor, but it can produce a large amount of harmonic currents, affect the safe operation of electrical network.In recent years, the flexible convertor assembly of some full control types is as static reacance generator (StaticCompensator, and Dynamic Voltage Regulator (Dynamic Voltage Regulator STATCOM), etc. DVR) mounted industry spot carries out idle and dynamic compensation that is negative phase-sequence, and can export by harmonic carcellation, improve the quality of power supply of electric power system.Compensate occasion for low pressure and low power, three-phase compensation arrangement is generally with adopting common three-phase two-level inverter structure.But this kind of full casement 3-phase power converter adopts three switch arms, power device is more, and cost is high.For this reason, in order to reduce idle and cost that is negative sequence compensation device, on this basis, a kind of three-phase four of scholar's research switching power converter is had.This compensator remains the performance of three-phase inverter, does not increase the electric current and voltage grade of power device while reducing quantity of power switches.This device only adopts two switch arms and one group of series capacitance to form a three-phase inverter, compared with common three-phase inverter, structure is more simplified.

Summary of the invention

Technical problem to be solved by this invention is, not enough for prior art, a kind of imbalance compensation control method of three-phase four switching power converter is provided, calculate two duty cycle signals of three-phase four switching power converter, then by adopting corresponding PWM method driving switch pipe to obtain the offset current expected, improve the output current quality of three-phase four switching power converter, ensure that three-phase four switching power converter is stable, reliably run.

For solving the problems of the technologies described above, the technical solution adopted in the present invention is: a kind of imbalance compensation control method of three-phase four switching power converter, and three-phase four switching power converter comprises three-phase Four-switch converter; Three-phase Four-switch converter comprises two switch arms in parallel, and described switch arm comprises the switching tube of two series connection, and the DC side of three-phase Four-switch converter comprises the electric capacity of two series connection, and described DC side is in parallel with described switch arm; Each switch arm, the DC side of described three-phase Four-switch converter are respectively connected with three phase network by an output inductor, and the method is:

1) by three-phase Four-switch converter DC side reference voltage U _refwith the DC voltage u detected _dcsubtract each other, obtain three-phase Four-switch converter DC voltage tracking error △ u _dc;

2) by DC voltage tracking error △ u _dcsend into 2 ripple arresters, obtain the DC component △ E of three-phase Four-switch converter DC voltage tracking error, after the adjustment process of PI controller, then export the regulating command I of DC voltage tracking error _m;

3) by regulating command I _mbe multiplied by the voltage synchronous signal sy of three-phase Four-switch converter two switch arm respectively _aand sy _b, obtain the pressure regulation command signal i of three-phase four switching power converter two switch arm _da, i _db:

$\left\{\begin{array}{c}{i}_{\mathrm{da}}=I_M*s{y}_a\\ i_{\mathrm{db}}=I_M*s{y}_b\end{array}\right.;$

4) detect the voltage difference △ u of three-phase Four-switch converter DC side two electric capacity, then △ u is sent into base time ripple arrester, obtain the DC error △ e of three-phase Four-switch converter DC side two capacitance voltage difference;

5) the DC error △ e of two capacitance voltage differences is sent into PI controller, obtain all pressures modulation instructions △ I of three-phase Four-switch converter DC side two electric capacity _n;

6) according to pressure regulation command signal i _da, i _db, all press modulation instructions △ I _nand idle and negative phase-sequence reference compensating signal with obtain the total with reference to instruction current signal i of current inner loop _ar, i _br:

$\left\{\begin{array}{c}{i}_{\mathrm{ar}}=i_{\mathrm{Ca}}^r+i_{\mathrm{da}}+\mathrm{\Δ}{I}_n\\ i_{\mathrm{br}}=i_{\mathrm{Cb}}^r+i_{\mathrm{db}}+\mathrm{\Δ}{I}_n\end{array}\right.;$

7) by total reference instruction current signal i of current inner loop _arand i _brdeduct the output current signal i of three-phase Four-switch converter two switch arm detected respectively _caand i _cb, obtain current error signal e _aand e _b;

8) by current error signal e _aand e _bsend into current inner loop PR controller respectively, obtain the dynamic adjustments signal △ d of three-phase Four-switch converter _awith △ d _b;

9) according to feedfoward control link, the expectation duty cycle signals d of two switch arms when three-phase Four-switch converter is stablized is tried to achieve _a1and d _b1be respectively:

$\left\{\begin{array}{c}{d}_{a1}=\frac{v_{\mathrm{Sac}}}{u_{\mathrm{dc}}}-\frac{2L}{u_{\mathrm{dc}}}\frac{{\mathrm{di}}_{\mathrm{Ca}}^r}{\mathrm{dt}}-\frac{L}{u_{\mathrm{dc}}}\frac{{\mathrm{di}}_{\mathrm{Cb}}^r}{\mathrm{dt}}+\frac{1}{2}=\frac{v_{\mathrm{Sac}}-2u_{\mathrm{La}}^r-u_{\mathrm{Lb}}^r}{u_{\mathrm{dc}}}+\frac{1}{2}\\ d_{b1}=\frac{v_{\mathrm{Sbc}}}{u_{\mathrm{dc}}}-\frac{L}{u_{\mathrm{dc}}}\frac{{\mathrm{di}}_{\mathrm{Ca}}^r}{\mathrm{dt}}-\frac{2L}{u_{\mathrm{dc}}}\frac{{\mathrm{di}}_{\mathrm{Cb}}^r}{\mathrm{dt}}+\frac{1}{2}=\frac{v_{\mathrm{Sbc}}-u_{\mathrm{La}}^r-2u_{\mathrm{Lb}}^r}{u_{\mathrm{dc}}}+\frac{1}{2}\end{array}\right.;$

Wherein, v _sacand v _sbcfor the line voltage of three phase network, L is output inductor value, with for the expectation fundamental voltage of output inductor during three-phase Four-switch converter stable state;

10) according to the dynamic adjustments signal △ d of three-phase Four-switch converter _awith △ d _b, and the expectation duty cycle signals d of two switch arms when three-phase Four-switch converter is stablized _a1and d _b1, calculate total duty cycle signals d of two switch arms of three-phase Four-switch converter _aand d _b:

$\left\{\begin{array}{c}{d}_a=\mathrm{\Δ}{d}_a+d_{a1}\\ d_b=\mathrm{\Δ}{d}_b+d_{b1}\end{array}\right.;$

11) according to total duty cycle signals d of three-phase Four-switch converter two switch arm _aand d _b, by PWM link, obtain the switching tube drive singal of three-phase Four-switch converter, driving switch pipe exports the voltage and current signal expected.

Described step 2) in, the computing formula of the DC component △ E of three-phase Four-switch converter DC voltage tracking error is:

$\mathrm{\ΔE}=\mathrm{\Δ}{u}_{\mathrm{dc}}-\frac{I^{-}[-1.5U+3\mathrm{\ωL}{I}_q]\sin (2\mathrm{\ωt}+{\mathrm{\θ}}^{-})}{2\mathrm{\ωC}{U}_d},$

Wherein, U and ω is respectively amplitude and the angular frequency of three phase network phase voltage, I _qthe reactive current amplitude of desired output, I ^-and θ ^-be respectively negative-sequence current amplitude and the phase angle of desired output, C is the equivalence value of three-phase Four-switch converter DC side two electric capacity, and L is output inductor value, U _dfor the DC component of three-phase Four-switch converter DC voltage.

In described step 4), the computing formula of the DC error △ e of three-phase Four-switch converter DC side two capacitance voltage difference is:

$\mathrm{\Δe}=\mathrm{\Δu}+\frac{1}{\mathrm{\ω}{C}_m}[I_q\cos (\mathrm{\ωt}+7\mathrm{\π}/3)+I^{-}\cos (\mathrm{\ωt}-2\mathrm{\π}/3+{\mathrm{\θ}}^{-})],$

Wherein, C _mfor the capacitance of the single electric capacity of three-phase Four-switch converter DC side, and C=C _m/ 2.

Compared with prior art, the beneficial effect that the present invention has is: the present invention is directed to DC voltage outer shroud and control, according to the principle of power-balance, propose a kind of removing method of secondary voltage ripple, avoid the 3 subharmonic instructions outputs that secondary voltage ripple causes, improve the output current quality of system; For the Pressure and Control of DC bus capacitor, according to circuit theory, propose the removing method of a kind of base time voltage ripple, eliminate the base time ripple voltage in two capacitance voltage differences, to avoid introducing in current inner loop control, ensure stable, the reliability service of system; Current inner loop for three-phase four switching power converter controls, propose the integrated control method of a kind of PR FEEDBACK CONTROL+feedfoward control, effective combination of closed loop feedback tracking performance and fast feedforward response performance can be realized, the dynamical output performance of converter system is greatly improved.

Accompanying drawing explanation

Fig. 1 is the system construction drawing of three-phase four switching power converter;

The oscillogram of DC capacitor voltage when Fig. 2 is stable operation;

Fig. 3 is the imbalance compensation control block diagram of one embodiment of the invention three-phase four switching power converter.

Embodiment

As shown in Figure 1, three-phase four switching power converter comprises three-phase Four-switch converter, and the A phase switch arm of three-phase Four-switch converter comprises the switch transistor T of series connection _a1and T _a2; The B phase switch arm of three-phase Four-switch converter comprises the switch transistor T of series connection _b1and T _b2; The C phase arm of three-phase Four-switch converter comprises the electric capacity C of series connection ₁and C ₂.The AC of three-phase Four-switch converter is connected with three phase network by three outputting inductances.Compared with common three-phase inverter, save two device for power switching, but there is identical compensation ability.Therefore, this collocation structure is more simplified.

In Fig. 1, v _sa, v _sb, v _scbe three-phase alternating-current supply voltage respectively, output inductor is L, and DC bus capacitor is C ₁and C ₂, the interchange end electric current of inverter is i _ca, i _cb, i _cc.The C phase of three-phase alternating current system is directly connected to the mid point of two DC capacitors.The voltage that power switch pipe bears is the half of DC bus-bar voltage.In each brachium pontis, only have a switching tube to be in closed condition at any time, therefore each brachium pontis only has two kinds of effective on off states, and 2 kinds of output voltages can be produced in alternating voltage side.2 kinds of switching functions are as follows to deserved each brachium pontis output state:

If we suppose that the capacitance voltage of DC bus is equal, then exchange terminal voltage as follows:

$\left\{\begin{array}{c}{v}_{\mathrm{ac}}=v_{\mathrm{ao}}-v_{\mathrm{co}}=g_a*\frac{u_{\mathrm{dc}}}{2}\\ v_{\mathrm{bc}}=v_{\mathrm{bo}}-v_{\mathrm{co}}=g_b*\frac{u_{\mathrm{dc}}}{2}\end{array}\right.---\left(2\right)$

As can be seen here, the brachium pontis of three-phase Four-switch converter exports and has ambipolar feature.Control due to two switch arms is independently, the output voltage of the respective switch arm that can not influence each other, therefore this inverter has 4 kinds of state of a controls outputs.According to circuit diagram, there is following voltage-current relationship:

$\left\{\begin{array}{c}L\frac{{\mathrm{di}}_{\mathrm{Ca}}}{\mathrm{dt}}=v_{\mathrm{Sa}}-v_{\mathrm{ao}}+L\frac{{\mathrm{di}}_{\mathrm{Cc}}}{\mathrm{dt}}-v_{\mathrm{Sc}}\\ L\frac{{\mathrm{di}}_{\mathrm{Cb}}}{\mathrm{dt}}=v_{\mathrm{Sb}}-v_{\mathrm{bo}}+L\frac{{\mathrm{di}}_{\mathrm{Cc}}}{\mathrm{dt}}-v_{\mathrm{Sc}}\end{array}\right.---\left(3\right)$

Wherein, v _aoand v _bofor the output voltage of two switch arms of three-phase Four-switch converter.

DC voltage waveform during three-phase four switching power converter stable operation as shown in Figure 2.In figure, Vc1 and Vc2 represents the voltage of DC side two electric capacity respectively.As seen from the figure, when carrying out idle and negative sequence compensation, there are base time and 2 ripple voltages in its two capacitance voltage.

The secondary ripple wave voltage of A, DC voltage calculates

Suppose that three-phase power grid voltage is balanced, symmetrical, and be:

$\left\{\begin{array}{c}{v}_{\mathrm{Sa}}=U\sin \left(\mathrm{\ωt}\right)\\ v_{\mathrm{Sb}}=U\sin (\mathrm{\ωt}-2\mathrm{\π}/3)\\ v_{\mathrm{Sc}}=U\sin (\mathrm{\ωt}+2\mathrm{\π}/3)\end{array}\right.---\left(4\right)$

By detecting the electric current (i of three-phase imbalance load _la, i _lb, i _lc), utilize ip-iq algorithm can calculate positive sequence real component (i in threephase load electric current _lpa, i _lpb, i _lpc).During full remuneration, the expectation of three-phase four switching power converter is idle and negative sequence compensation current signal is:

$\left\{\begin{array}{c}{i}_{\mathrm{Ca}}^r=i_{\mathrm{La}}-i_{\mathrm{Lpa}}=I_q\sin (\mathrm{\ωt}+\mathrm{\π}/2)+I^{-}\sin (\mathrm{\ωt}+{\mathrm{\θ}}^{-})\\ i_{\mathrm{Cb}}^r=i_{\mathrm{Lb}}-i_{\mathrm{Lpb}}=I_q\sin (\mathrm{\ωt}-\mathrm{\π}/6)+I^{-}\sin (\mathrm{\ωt}+2\mathrm{\π}/3+{\mathrm{\θ}}^{-})\\ i_{\mathrm{Cc}}^r=i_{\mathrm{Lc}}-i_{\mathrm{Lpc}}=I_q\sin (\mathrm{\ωt}+7\mathrm{\π}/3)+I^{-}\sin (\mathrm{\ωt}-2\mathrm{\π}/3+{\mathrm{\θ}}^{-})\end{array}\right.----\left(5\right)$

Wherein, I _qrepresent the amplitude compensating positive sequence reactive current; I ^-and θ ^-represent the amplitude and phase angle that compensate negative-sequence current.Three-phase inverter net side input power is:

$P_S=v_{\mathrm{Sa}}{i}_{\mathrm{Ca}}+v_{\mathrm{Sb}}{i}_{\mathrm{Cb}}+v_{\mathrm{Sc}}{i}_{\mathrm{Cc}}=-\frac{3}{2}{\mathrm{UI}}^{-}\cos (2\mathrm{\ωt}+{\mathrm{\θ}}^{-})---\left(6\right)$

As can be seen here, the interaction of positive sequence voltage and negative-sequence current makes input power contain two frequency multiplication compositions, thus causes DC voltage to produce two double-frequency fluctuation.In fact, under the uneven condition of output current, the instantaneous power on filter inductance is also non-vanishing, and the power fluctuation on inductance will affect the fluctuation of DC voltage.The expectation fundamental voltage that can calculate output inductor during stable state is:

$\left\{\begin{array}{c}{u}_{\mathrm{La}}^r=L\frac{{\mathrm{di}}_{\mathrm{Ca}}^r}{\mathrm{dt}}=\mathrm{\ωL}[I_q\sin (\mathrm{\ωt}+\mathrm{\π})+I^{-}\sin (\mathrm{\ωt}+{\mathrm{\π}/2+\mathrm{\θ}}^{-})]\\ u_{\mathrm{Lb}}^r=L\frac{{\mathrm{di}}_{\mathrm{Cb}}^r}{\mathrm{dt}}{=\mathrm{\ωL}[I}_q\sin (\mathrm{\ωt}+\mathrm{\π}/3)+I^{-}\sin (\mathrm{\ωt}+7\mathrm{\π}/3+{\mathrm{\θ}}^{-})]\\ u_{\mathrm{Lc}}^r=L\frac{{\mathrm{di}}_{\mathrm{Cc}}^r}{\mathrm{dt}}={\mathrm{\ωL}[I}_q\sin (\mathrm{\ωt}-\mathrm{\π}/3)+I^{-}\sin (\mathrm{\ωt}-\mathrm{\π}/6+{\mathrm{\θ}}^{-})]\end{array}\right.----\left(7\right)$

Therefore the instantaneous power that can calculate on three pole reactor is:

$P_L=L\frac{{\mathrm{di}}_{\mathrm{Ca}}}{\mathrm{dt}}{i}_{\mathrm{Ca}}+L\frac{{\mathrm{di}}_{\mathrm{Cb}}}{\mathrm{dt}}{i}_{\mathrm{Cb}}+L\frac{{\mathrm{di}}_{\mathrm{Cc}}}{\mathrm{dt}}{i}_{\mathrm{Cc}}=3\mathrm{\ωL}{I}_q{I}^{-}\sin (2\mathrm{\ωt}+\mathrm{\π}/2+{\mathrm{\θ}}^{-})---\left(8\right)$

From formula above, when three-phase inverter compensates unbalanced load, due to the impact of negative-sequence current, in the instantaneous power of inverter ac, there is secondary wave kinetic power.If ignore the loss of inductance and power device, according to the principle of both sides power-balance, then also can there is secondary ripple wave power in DC side, is secondary ripple wave voltage.Suppose that DC voltage is u _dc=U _d+ δ sin (2 ω t+ φ), U _dfor DC component, δ sin (2 ω t+ φ) is voltage ripple component.The instantaneous power of DC bus capacitor is then had to be:

$P_d=u_{\mathrm{dc}}*C\frac{{\mathrm{du}}_{\mathrm{dc}}}{\mathrm{dt}}=C[U_d+\mathrm{\δ}\sin (2\mathrm{\ωt}+\mathrm{\φ})]*2\mathrm{\ω\δ}\cos (2\mathrm{\ωt}+\mathrm{\φ})$

$=2\mathrm{\ω\δC}{U}_d\cos (2\mathrm{\ωt}+\mathrm{\φ})+\mathrm{\ω}{\mathrm{\δ}}^{2}C\sin (4\mathrm{\ωt}+2\mathrm{\φ})---\left(9\right)$

Wherein, C is the equivalence value of DC bus capacitor, is C _m/ 2, C _mfor C ₁or C ₂capacitance.According to the principle of alternating current-direct current side power-balance, ignore its four ripple components, then have:

$2\mathrm{\ωC}{U}_d\mathrm{\δ}\cos (2\mathrm{\ωt}+\mathrm{\φ})=-\frac{3}{2}{\mathrm{UI}}^{-}\cos (2\mathrm{\ωt}+{\mathrm{\θ}}^{-})+3\mathrm{\ωL}{I}_q{I}^{-}\sin (2\mathrm{\ωt}+\mathrm{\π}/2+{\mathrm{\θ}}^{-})---\left(10\right)$

The secondary ripple wave component of DC voltage is then had to be:

$\mathrm{\δ}\sin (2\mathrm{\ωt}+\mathrm{\φ})=\frac{I^{-}[-1.5U+3\mathrm{\ω}L{I}_q]\sin (2\mathrm{\ωt}+{\mathrm{\θ}}^{-})}{2\mathrm{\ωC}{U}_d}---\left(11\right)$

As can be seen here, due to the impact of negative-sequence current, can cause there is secondary ripple wave voltage in DC capacitor voltage, ripple voltage frequency is 2 times of rated frequency, the size of ripple voltage is directly proportional to the amplitude of negative-sequence current, is inversely proportional to DC bus capacitor and magnitude of voltage.

The base time ripple voltage of B, DC voltage calculates

When supposing stable state, order: i _cc=I _qsin (ω t+7 π/3)+I ^-sin (ω t-2 π/3+ θ ^-).Circuit diagram according to Fig. 1, then have:

$i_{\mathrm{Cc}}=i_1-i_2=C_m\frac{d(u_{c1}-u_{c2})}{\mathrm{dt}}---\left(12\right)$

Wherein, C _mfor DC bus capacitor value, u _c1, u _c2be respectively the magnitude of voltage of two DC side two electric capacity, i ₁, i ₂be respectively and flow through DC bus capacitor C ₁and C ₂current value.Make △ u=u _c1-u _c2, then have according to preceding formula:

$\mathrm{\Δu}=\frac{1}{C_m}\∫[I_q\sin (\mathrm{\ωt}+7\mathrm{\π}/3)+I^{-}\sin (\mathrm{\ωt}-2\mathrm{\π}/3+{\mathrm{\θ}}^{-})]\mathrm{dt}$

$=\frac{-1}{\mathrm{\ω}{C}_m}[I_q\cos (\mathrm{\ωt}+7\mathrm{\π}/3)+I^{-}\cos (\mathrm{\ωt}-2\mathrm{\π}/3+{\mathrm{\θ}}^{-})]+\mathrm{\Δe}---\left(13\right)$

Wherein △ e is DC quantity, illustrates the DC error component of two capacitance voltages.From upper, due to the particularity of three-phase Four-switch converter structure, mid point input current i _ccmiddle fundamental current can produce a corresponding first-harmonic alternating current component on DC capacitor voltage, mid point input current size i when this alternating current component and stable state _cchave direct relation, its amplitude is directly proportional to the amplitude of mid point input current, is inversely proportional to DC bus capacitor value.Analyze in conjunction with above, when three-phase Four-switch converter is at compensating reactive power and negative-sequence current, have some conclusion following:

1, when three-phase Four-switch converter compensates negative-sequence current, because it exists secondary pulsating power in three-phase alternating current side, meeting produces a corresponding secondary ripple wave voltage on DC voltage, and the size of ripple is directly proportional to the amplitude of negative-sequence current.

2, when compensating reactive power and negative-sequence current, due to the effect of C phase output current, can inject fundamental current to DC bus capacitor mid point, therefore can produce the secondary ripple voltage of a corresponding base on DC voltage, the size of ripple is relevant with size that is negative-sequence current to idle.

3, due to the structural particularity of this kind of three-phase Four-switch converter, when carrying out idle and negative sequence compensation, can produce a large amount of base time and secondary ripple wave voltage to direct voltage, the capacity of compensation is larger, and ripple voltage is larger; Increase DC bus capacitor and can reduce all voltage ripples, but can system cost be increased, worsen the response time of DC voltage control, reduce the service behaviour of system, therefore this kind of structure is not suitable for carrying out high-power compensation application.

When utilizing three-phase Four-switch converter to compensate idle and negative-sequence current, after stable operation, DC side two capacitance voltage value can be expressed as:

The imbalance compensation control method of three-phase four switching power converter as shown in Figure 3.

In order to realize the compensation of System Reactive Power and harmonic current, a kind of imbalance compensation control method of three-phase four switching power converter of the present invention, it is by outer voltage, Pressure and Control and current inner loop three part composition.For DC voltage outer shroud, adopt a kind of PI regulating and controlling, stablizing and making up the loss of power switch of DC voltage can be maintained, and maintain system safety and run reliably.For the equal pressure balanced control problem of DC side two electric capacity, have employed a kind of pressure equalizing control method to realize the balance of DC voltage.Then outer shroud output signal is obtained total current inner loop reference signal with the idle of expectation with negative current instructions Signal averaging.The duty cycle signals of current inner loop by adopting a kind of integrated control method of closed loop feedback+feedforward to calculate two switch arms of three-phase Four-switch converter, effectively in conjunction with the advantage of feedfoward control and FEEDBACK CONTROL, improves the performance of dynamic tracking of system.Concrete control method is as follows:

For the control of DC voltage, according to derivation above and analysis, known DC voltage also exists 2 the ripple component δ sin (2wt+ φ) caused by negative phase-sequence output current.If this ripple voltage is introduced in closed-loop control system and can make to there is harmonic current in three-phase Four-switch converter output current.Being calculated as follows of harmonic wave command signal: the tracking error △ u of outer voltage _dcafter controller regulates, be multiplied by voltage synchronous signal, namely obtain the command signal of current inner loop.Suppose that outer voltage is that P controls, its gain is K, and because outer voltage exists ripple voltage, then the harmonic wave instruction current produced by ripple voltage is:

K*△u _dc*sinωt=Kδsin(2ωt+φ)*sinωt=Kδ[cos((2ω-ω)t+φ)-cos((2ω+ω)t+φ)]/2(15)

As can be seen here, ripple voltage can produce two kinds of current command signals that frequency is 2 ω ± ω, and its amplitude is K δ/2.The present invention is directed to DC voltage outer shroud for this reason, propose the compensation method of 2 ripple voltages, eliminate ripple interference, realize the normal control of DC voltage.

Therefore first by DC side reference voltage U _refwith the DC voltage u detected _dcsubtract each other, obtain DC voltage tracking error △ u _dc, then deduct 2 ripple components calculated by formula (11), the DC component △ E of the tracking error of DC voltage can be obtained, after the adjustment process of PI controller, then export the regulating command I of DC voltage _m;

Then then by I _mbe multiplied by the voltage synchronous signal sy of A, B two-phase respectively _aand sy _b, the pressure regulation command signal of power converter two-phase switch arm can be obtained:

$\left\{\begin{array}{c}{i}_{\mathrm{da}}=I_M*s{y}_a\\ i_{\mathrm{db}}=I_M*s{y}_b\end{array}\right.---\left(16\right)$

There are two series capacitances for DC voltage, this two electric capacity is easily subject to external disturbance and controls the impact of output bias and make capacitance voltage occur error, thus make Voltage unbalance, the control of inverter output current will be affected, therefore will employing even pressure controller be needed to realize the stable of DC voltage and balance.According to derivation above with analyze known, due to the impact of the first-harmonic input current of DC side two electric capacity mid point, a corresponding base time ripple voltage will be produced on DC side two capacitance voltage.If this base time ripple signal is directly carried out Pressure and Control, then the first-harmonic command signal that in current inner loop command signal, superposition one is additional can be given, thus the normal table affecting three-phase Four-switch converter runs.Therefore the Pressure and Control process that this patent adopts is as follows:

First by detecting the voltage difference △ u=u of DC side two electric capacity _c1-u _c2, then △ u is subtracted the base time ripple voltage signal and calculated by formula (13), the DC error △ e of DC side two capacitance voltage difference can be obtained.

Then, after the DC error △ e of two capacitance voltage differences being passed through the process of PI controller, all pressures modulation instructions △ I of DC side two electric capacity can be obtained _n.

Then according to the output of the outer ring controller of DC voltage, the output of even pressure controller and idle and negative phase-sequence reference compensating signal, can obtain the reference instruction current signal that current inner loop is total:

$\left\{\begin{array}{c}{i}_{\mathrm{ar}}=i_{\mathrm{Ca}}^r+i_{\mathrm{da}}+\mathrm{\Δ}{I}_n\\ i_{\mathrm{br}}=i_{\mathrm{Cb}}^r+i_{\mathrm{db}}+\mathrm{\Δ}{I}_n\end{array}\right.---\left(17\right)$

Because idle and negative sequence current signal are AC signal, adopt traditional PI controller, it has limited follow-up control, there is error during stable state; There is scholar to propose ratio resonance (ProportionalResonant, the PR) controller of electric current, to the electric current of specific time, there is unlimited open-loop gain, the no error following to AC signal can be realized like this.The s territory expression formula of PR controller is:

G(s)=K _m+2K _is/(s ²+ω ²)(18)

Wherein K _mrepresent proportionality coefficient, K _irepresent integral coefficient.Simultaneously according to track with zero error principle, the value of proportionality coefficient is K _m=L*T _s/ u _dc, T _sfor control cycle, u _dcfor DC voltage, L is output inductor value.By total reference command signal i of current inner loop _arand i _brsubtract and to detect three-phase Four-switch converter output current signal i _caand i _cb, current error signal e can be obtained _aand e _b.

By current error signal e _aand e _brespectively by the process of current inner loop PR controller, the dynamic adjustments signal △ d of three-phase Four-switch converter can be obtained _awith △ d _b.The closed-loop control of such passing ratio resonant controller, this adjustment is that a kind of closed loop feedback controls, and can realize regulating the dynamic tracking of fundamental current.

According to formula (3) and bipolar modulation principle, can in the hope of the output average voltage v of two of a three-phase Four-switch converter switch arm _aoand v _bofor:

$\left[\begin{array}{c}{v}_{\mathrm{ao}}\\ v_{\mathrm{bo}}\end{array}\right]=\left[\begin{array}{c}{v}_{\mathrm{Sa}}-v_{\mathrm{Sc}}-L\frac{d}{\mathrm{dt}}({2i}_{\mathrm{Ca}}+i_{\mathrm{Cb}})\\ v_{\mathrm{Sb}}-v_{\mathrm{Sc}}-L\frac{d}{\mathrm{dt}}(i_{\mathrm{Ca}}+2i_{\mathrm{Cb}})\end{array}\right]=\left[\begin{array}{c}(2d_a-1)\frac{u_{\mathrm{dc}}}{2}\\ (2d_b-1)\frac{u_{\mathrm{dc}}}{2}\end{array}\right]---\left(19\right)$

Wherein, d _aand d _bbe respectively the duty cycle signals of two switch arms of three-phase Four-switch converter, and meet d _aand d _b∈ [0,1].Then duty cycle signals can be expressed as:

$\left\{\begin{array}{c}{d}_a=\frac{1}{u_{\mathrm{dc}}}{v}_{\mathrm{Sac}}-\frac{2L}{u_{\mathrm{dc}}}\frac{{\mathrm{di}}_{\mathrm{Ca}}}{\mathrm{dt}}-\frac{L}{u_{\mathrm{dc}}}\frac{{\mathrm{di}}_{\mathrm{Cb}}}{\mathrm{dt}}+\frac{1}{2}\\ d_b=\frac{1}{u_{\mathrm{dc}}}{v}_{\mathrm{Sbc}}-\frac{L}{u_{\mathrm{dc}}}\frac{{\mathrm{di}}_{\mathrm{Ca}}}{\mathrm{dt}}-\frac{2L}{u_{\mathrm{dc}}}\frac{{\mathrm{di}}_{\mathrm{Cb}}}{\mathrm{dt}}+\frac{1}{2}\end{array}\right.---\left(20\right)$

Wherein, v _sacand v _sbcfor the line voltage of three phase network.Three-phase Four-switch converter desired output electric current according to formula (5), can calculate the stable state fundamental voltage of inverter ac side inductance as shown in formula (7).Simultaneously according to formula (20), formula (7) is substituted into, then can in the hope of three-phase Four-switch converter stable time two switch arms expectation duty cycle signals d _a1and d _b1for:

$\left\{\begin{array}{c}{d}_{a1}=\frac{v_{\mathrm{Sac}}}{u_{\mathrm{dc}}}-\frac{2L}{u_{\mathrm{dc}}}\frac{{\mathrm{di}}_{\mathrm{Ca}}^r}{\mathrm{dt}}-\frac{L}{u_{\mathrm{dc}}}\frac{{\mathrm{di}}_{\mathrm{Cb}}^r}{\mathrm{dt}}+\frac{1}{2}=\frac{v_{\mathrm{Sac}}-2u_{\mathrm{La}}^r-u_{\mathrm{Lb}}^r}{u_{\mathrm{dc}}}+\frac{1}{2}\\ d_{b1}=\frac{v_{\mathrm{Sbc}}}{u_{\mathrm{dc}}}-\frac{L}{u_{\mathrm{dc}}}\frac{{\mathrm{di}}_{\mathrm{Ca}}^r}{\mathrm{dt}}-\frac{2L}{u_{\mathrm{dc}}}\frac{{\mathrm{di}}_{\mathrm{Cb}}^r}{\mathrm{dt}}+\frac{1}{2}=\frac{v_{\mathrm{Sbc}}-u_{\mathrm{La}}^r-2u_{\mathrm{Lb}}^r}{u_{\mathrm{dc}}}+\frac{1}{2}\end{array}\right.---\left(21\right)$

It can thus be appreciated that, formula (21) is derived according to the switch control rule principle of three-phase Four-switch converter and comes, and is the expectation duty cycle signals that can calculate two switch arms of three-phase Four-switch converter according to three-phase Four-switch converter desired output electric current.Therefore this duty cycle signals d _a1and d _b1can to feedover command signal as one, be used for realizing the quick response of three-phase Four-switch converter to instruction current signal.

According to the dynamic adjustments signal △ d that current inner loop PR controller exports _awith △ d _b, and the feedforward command signal d that feedfoward control exports _a1and d _b1, the duty cycle signals that two switch arms of three-phase Four-switch converter are total can be calculated:

$\left\{\begin{array}{c}{d}_a=\mathrm{\Δ}{d}_a+d_{a1}\\ d_b=\mathrm{\Δ}{d}_b+d_{b1}\end{array}\right.---\left(22\right)$

The duty cycle signals d total according to two switch arms of three-phase Four-switch converter _aand d _b, utilize PWM device, can obtain the switching drive signal of three-phase four switch inversion, then driving power switching tube exports the voltage and current signal expected.

Such current inner loop controls the integrated control method that have employed PR FEEDBACK CONTROL+feedfoward control, achieves effective combination of closed loop feedback performance and fast feedforward performance, substantially increases the control performance of three-phase Four-switch converter.When three-phase Four-switch converter carries out the idle compensation with negative-sequence current, there is base time and secondary ripple wave voltage in DC voltage, control for DC voltage outer shroud for this reason, invent a kind of removing method of secondary ripple wave voltage, simultaneously for the Pressure and Control of DC bus capacitor, invented the removing method of a kind of base time ripple voltage, the normal table achieving three-phase Four-switch converter like this controls, and has ensured that it runs reliably and with long-term.

Claims (3)

1. an imbalance compensation control method for three-phase four switching power converter, three-phase four switching power converter comprises three-phase Four-switch converter; Three-phase Four-switch converter comprises two switch arms in parallel, and each switch arm comprises the switching tube of two series connection, and the DC side of three-phase Four-switch converter comprises the electric capacity of two series connection, and described DC side is in parallel with described switch arm; Each switch arm, the DC side of described three-phase Four-switch converter are respectively connected with three phase network by an output inductor, and it is characterized in that, the method is:

1) by three-phase Four-switch converter DC side reference voltage U _refwith the DC voltage u detected _dcsubtract each other, obtain three-phase Four-switch converter DC voltage tracking error Δ u _dc;

2) by DC voltage tracking error Δ u _dcsend into 2 ripple arresters, obtain the DC component Δ E of three-phase Four-switch converter DC voltage tracking error, after the adjustment process of PI controller, then export the regulating command I of DC voltage tracking error _m;

3) by regulating command I _mbe multiplied by the voltage synchronous signal sy of three-phase Four-switch converter two switch arm respectively _aand sy _b, obtain the pressure regulation command signal i of three-phase four switching power converter two switch arm _da, i _db:

$\left\{\begin{array}{c}{i}_{\mathrm{da}}=I_M*{\mathrm{sy}}_a\\ i_{\mathrm{db}}=I_M*{\mathrm{sy}}_b\end{array}\right.;$

4) detect the voltage difference delta u of three-phase Four-switch converter DC side two electric capacity, then Δ u is sent into base time ripple arrester, obtain the DC error Δ e of three-phase Four-switch converter DC side two capacitance voltage difference;

5) the DC error Δ e of two capacitance voltage differences is sent into PI controller, obtain all pressures modulation instructions Δ I of three-phase Four-switch converter DC side two electric capacity _n;

6) according to pressure regulation command signal i _da, i _db, all press modulation instructions Δ I _nand idle and negative phase-sequence reference compensating signal with obtain the total with reference to instruction current signal i of current inner loop _ar, i _br:

$\left\{\begin{array}{c}{i}_{\mathrm{ar}}=i_{\mathrm{Ca}}^r+i_{\mathrm{da}}+\mathrm{\Δ}{I}_n\\ i_{\mathrm{br}}=i_{\mathrm{Cb}}^r+i_{\mathrm{db}}+\mathrm{\Δ}{I}_n\end{array}\right.;$

7) by total reference instruction current signal i of current inner loop _arand i _brdeduct the output current signal i of three-phase Four-switch converter two switch arm detected respectively _caand i _cb, obtain current error signal e _aand e _b;

8) by current error signal e _aand e _bsend into current inner loop PR controller respectively, obtain the dynamic adjustments signal delta d of three-phase Four-switch converter _awith Δ d _b;

9) according to feedfoward control link, the expectation duty cycle signals d of two switch arms when three-phase Four-switch converter is stablized is tried to achieve _a1and d _b1be respectively:

$\left\{\begin{array}{c}{d}_{a1}=\frac{v_{\mathrm{Sac}}}{u_{\mathrm{dc}}}-\frac{2L}{u_{\mathrm{dc}}}\frac{{\mathrm{di}}_{\mathrm{Ca}}^r}{\mathrm{dt}}-\frac{L}{u_{\mathrm{dc}}}\frac{{\mathrm{di}}_{\mathrm{Cb}}^r}{\mathrm{dt}}+\frac{1}{2}=\frac{v_{\mathrm{Sac}}-2u_{\mathrm{La}}^r-u_{\mathrm{Lb}}^r}{u_{\mathrm{dc}}}+\frac{1}{2}\\ d_{b1}=\frac{v_{\mathrm{Sbc}}}{u_{\mathrm{dc}}}-\frac{L}{u_{\mathrm{dc}}}\frac{{\mathrm{di}}_{\mathrm{Ca}}^r}{\mathrm{dt}}-\frac{2L}{u_{\mathrm{dc}}}\frac{{\mathrm{di}}_{\mathrm{Cb}}^r}{\mathrm{dt}}+\frac{1}{2}=\frac{v_{\mathrm{Sbc}}-u_{\mathrm{La}}^r-2u_{\mathrm{Lb}}^r}{u_{\mathrm{dc}}}+\frac{1}{2}\end{array}\right.;$

Wherein, v _sacand v _sbcfor the line voltage of three phase network, L is output inductor value, with for the expectation fundamental voltage of output inductor during three-phase Four-switch converter stable state;

10) according to the dynamic adjustments signal delta d of three-phase Four-switch converter _awith Δ d _b, and the expectation duty cycle signals d of two switch arms when three-phase Four-switch converter is stablized _a1and d _b1, calculate total duty cycle signals d of two switch arms of three-phase Four-switch converter _aand d _b:

$\left\{\begin{array}{c}{d}_a=\mathrm{\Δ}{d}_a+d_{a1}\\ d_b=\mathrm{\Δ}{d}_b+d_{b1}\end{array}\right.;$

11) according to total duty cycle signals d of three-phase Four-switch converter two switch arm _aand d _b, by PWM link, obtain the switching tube drive singal of three-phase Four-switch converter, driving switch pipe exports the voltage and current signal expected.

2. the imbalance compensation control method of three-phase four switching power converter according to claim 1, is characterized in that, described step 2) in, the computing formula of the DC component Δ E of three-phase Four-switch converter DC voltage tracking error is:

$\mathrm{\ΔE}=\mathrm{\Δ}{u}_{\mathrm{dc}}-\frac{I^{-}[-1.5U+3\mathrm{\ωL}{I}_q]\sin (2\mathrm{\ωt}+{\mathrm{\θ}}^{-})}{2\mathrm{\ω}{\mathrm{CU}}_d},$

Wherein, U and ω is respectively amplitude and the angular frequency of three phase network phase voltage, I _qthe reactive current amplitude of desired output, I ^-and θ ^-be respectively negative-sequence current amplitude and the phase angle of desired output, C is the equivalence value of three-phase Four-switch converter DC side two electric capacity, U _dfor the DC component of three-phase Four-switch converter DC voltage.

3. the imbalance compensation control method of three-phase four switching power converter according to claim 2, is characterized in that, described step 4) in, the computing formula of the DC error Δ e of three-phase Four-switch converter DC side two capacitance voltage difference is:

$\mathrm{\Δe}=\mathrm{\Δu}+\frac{1}{\mathrm{\ω}{C}_m}[I_q\cos (\mathrm{\ωt}+7\mathrm{\π}/3)+I^{-}\cos (\mathrm{\ωt}-2\mathrm{\π}/3+{\mathrm{\θ}}^{-})],$

Wherein, C _mfor the capacitance of the single electric capacity of three-phase Four-switch converter DC side, and C=C _m/ 2.