CN103427700A - 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 switch power current transformers

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 switch power current transformers.

Background technology

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

For problems such as above-mentioned idle, negative phase-sequences, Chinese scholars has been carried out certain research.There is the scholar to propose to adopt the static compensation that passive filter (Passive Power Filter, PPF) carries out reactive power is installed, simple in structure, but it can't dynamic adjustments, easy and electrical network generation series parallel resonance simultaneously.For this reason, there is the scholar to propose again Static Var Compensator (Static Var Compensator, SVC), it is comprised of jumbo fixed capacitor and thyristor control inductor, can realize variable dynamic compensation 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 (Static Compensator, STATCOM) and Dynamic Voltage Regulator (Dynamic Voltage Regulator, DVR) etc. be mounted industry spot and carry out idle and dynamic compensation negative phase-sequence, and can export by harmonic carcellation, improve the quality of power supply of electric power system.For low pressure and low power compensation occasion, the three-phase compensation arrangement is generally with adopting common three-phase two-level inverter structure.Yet this kind of full casement 3-phase power converter adopts three switch arms, and power device is more, and cost is high.For this reason, in order to reduce the idle and cost negative sequence compensation device, on this basis, scholar's research has been arranged a kind of three-phase four switch power current transformers.This compensator has retained the performance of three-phase inverter, does not increase the electric current and voltage grade of power device when reducing quantity of power switches.This device only adopts two switch arms and one group of series capacitance to form a three-phase inverter, with common three-phase inverter, compares, and on structure, more simplifies.

Summary of the invention

Technical problem to be solved by this invention is, for the prior art deficiency, a kind of imbalance compensation control method of three-phase four switch power current transformers is provided, calculate two duty cycle signals of three-phase four switch power current transformers, then by adopting corresponding PWM modulator approach driving switch pipe to obtain the offset current of expectation, improve the output current quality of three-phase four switch power current transformers, ensure that three-phase four switch power current transformers are stable, operation reliably.

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 switch power current transformers, and three-phase four switch power current transformers comprise three-phase four switch inversion device; Three-phase four switch inversion device comprises the switch arm of two parallel connections, and described switch arm comprises the switching tube of two series connection, and the DC side of three-phase four switch inversion device comprises the electric capacity of two series connection, and described DC side is in parallel with described switch arm; Each switch arm of described three-phase four switch inversion device, DC side respectively are connected with three phase network by an output inductor, and the method is:

1) by three-phase four switch inversion device DC side reference voltage U _refWith the DC voltage u detected _DcSubtract each other, obtain three-phase four switch inversion device DC voltage tracking error △ u _Dc

2) by DC voltage tracking error △ u _DcSend into the ripple arrester 2 times, obtain the DC component △ E of three-phase four switch inversion device DC voltage tracking error, then the regulating command I of output DC voltage tracking error after the adjusting of PI controller is processed _M

3) by regulating command I _MBe multiplied by respectively the voltage synchronizing signal sy of three-phase four switch inversion device two switch arms _aAnd sy _b, obtain the pressure regulation command signal i of three-phase four switch power current transformer two switch arms _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 inversion device DC side two electric capacity, then △ u is sent into to base time ripple arrester, obtain the poor DC error △ e of three-phase four switch inversion device DC side two capacitance voltages;

5) by two capacitance voltages, poor DC error △ e sends into the PI controller, obtains all pressures modulation instructions △ I of two electric capacity of three-phase four switch inversion device DC side _n

6) according to pressure regulation command signal i _Da, i _Db, all press modulation instructions △ I _nAnd idle and negative phase-sequence is with reference to compensating signal

With

Obtain current inner loop always with reference to instruction current signal i _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 current inner loop always with reference to instruction current signal i _ArAnd i _BrDeduct respectively the output current signal i of three-phase four switch inversion device two switch arms that detect _CaAnd i _Cb, obtain current error signal e _aAnd e _b

8) by current error signal e _aAnd e _bSend into respectively current inner loop PR controller, obtain the dynamic adjustments signal △ d of three-phase four switch inversion device _aWith △ d _b

9), according to the feedfoward control link, try to achieve the expectation duty cycle signals d of three-phase four switch inversion device two switch arms while stablizing _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 the output inductor value,

With

The expectation fundamental voltage of output inductor during for three-phase four switch inversion device stable state;

10) according to the dynamic adjustments signal △ d of three-phase four switch inversion device _aWith △ d _b, and the expectation duty cycle signals d of three-phase four switch inversion device two switch arms while stablizing _A1And d _B1, calculate total duty cycle signals d of two switch arms of three-phase four switch inversion device _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 inversion device two switch arms _aAnd d _b, by the PWM link, the switching tube that obtains three-phase four switch inversion device drives signal, the voltage and current signal of driving switch pipe output expectation.

Described step 2), in, the computing formula of the DC component △ E of three-phase four switch inversion device 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 are 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, the equivalence value that C is three-phase four switch inversion device DC side two electric capacity, L is the output inductor value, U _dDC component for three-phase four switch inversion device DC voltage.

In described step 4), the computing formula of the DC error △ e that three-phase four switch inversion device DC side two capacitance voltages are poor 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 appearance value of the single electric capacity of three-phase four switch inversion device 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 the DC voltage outer shroud and control, principle according to power-balance, a kind of removing method of secondary voltage ripple has been proposed, the 3 subharmonic instructions of having avoided the secondary voltage ripple to cause are exported, and have improved the output current quality of system; For the Pressure and Control of DC bus capacitor, according to circuit theory, the removing method of a kind of base time voltage ripple has been proposed, eliminated the base time ripple voltage during two capacitance voltages are poor, to avoid introducing during current inner loop controls, ensured stable, the reliability service of system; Current inner loop for three-phase four switch power current transformers is controlled, a kind of integrated control method of PR FEEDBACK CONTROL+feedfoward control has been proposed, can realize closed loop feedback tracking performance and effective combination of feedforward response performance fast, the dynamic output performance of converter system is greatly improved.

The accompanying drawing explanation

The system construction drawing that Fig. 1 is three-phase four switch power current transformers;

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

The imbalance compensation control block diagram that Fig. 3 is one embodiment of the invention three-phase four switch power current transformers.

Embodiment

As shown in Figure 1, three-phase four switch power current transformers comprise three-phase four switch inversion device, and the A phase switch arm of three-phase four switch inversion device comprises the switch transistor T of series connection _A1And T _A2The B phase switch arm of three-phase four switch inversion device comprises the switch transistor T of series connection _B1And T _B2The C phase arm of three-phase four switch inversion device comprises the capacitor C of series connection ₁And C ₂.The AC of three-phase four switch inversion device is connected with three phase network by three outputting inductances.Compare with common three-phase inverter, saved 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 respectively three-phase alternating-current supply voltage, 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 of three-phase alternating current system is directly connected to the mid point of two DC capacitors mutually.The voltage that power switch pipe bears is half of DC bus-bar voltage.In each brachium pontis, only have at any time a switching tube in closed condition, therefore each brachium pontis only has two kinds of effective on off states, and can produce 2 kinds of output voltages in the 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 equates, exchanges 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 output of the brachium pontis of three-phase four switch inversion device has ambipolar characteristics.Because the control of two switch arms is independently, the output voltage of switch arm separately that can not influence each other, therefore this inverter has 4 kinds of state of a controls outputs.According to circuit diagram, following voltage-current relationship is arranged:

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

Wherein, v _AoAnd v _BoOutput voltage for two switch arms of three-phase four switch inversion device.

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

The secondary ripple voltage of A, DC voltage calculates

Suppose that three phase network 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 the ip-iq algorithm can calculate the positive sequence real component (i in the threephase load electric current _Lpa, i _Lpb, i _Lpc).During full remuneration, the expectation of three-phase four switch power current transformers is idle and the 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 _qThe amplitude that means compensation positive sequence reactive current; I ^-And θ ^-The amplitude and the phase angle that mean the compensation 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, thereby causes DC voltage to produce two frequency multiplication fluctuations.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.In the time of can calculating stable state, the expectation fundamental voltage of output inductor 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 top formula, when three-phase inverter compensation unbalanced load, due to the impact of negative-sequence current, in the instantaneous power that inverter exchanges, there is the secondary wave kinetic power.If ignore the loss of inductance and power device, according to the principle of both sides power-balance, also can there be secondary ripple power in DC side, is the secondary ripple 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 the voltage ripple component.Have the instantaneous power of DC bus capacitor 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, the equivalence value that C is DC bus capacitor, be 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, have:

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

Have the secondary ripple component of DC voltage 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 in DC capacitor voltage existing the secondary ripple voltage, the ripple voltage frequency is rated frequency 2 times, the size of ripple voltage is directly proportional to the amplitude of negative-sequence current, with DC bus capacitor and magnitude of voltage, is inversely proportional to.

The base of B, DC voltage time ripple voltage calculates

While 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 shown in Fig. 1 has:

$i_{\mathrm{Cc}}=i_1-{\mathrm{<figure-callout\; id="2"\; label="i"\; filenames="HDA0000375954000000011.png"\; state="\{\{state\}\}">i</figure-callout>}}_2=C_m\frac{d(u_{c1}-u_{c2})}{\mathrm{dt}}---\left(12\right)$

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, according to the front formula, have:

$\mathrm{\&Delta;u}=\frac{1}{C_m}\&Integral;[I_q\sin (\mathrm{\&omega;t}+7\mathrm{\&pi;}/3)+I^{-}\sin (\mathrm{\&omega;t}-2\mathrm{\&pi;}/3+{\mathrm{\&theta;}}^{-})]\mathrm{dt}$

$=\frac{-1}{\mathrm{\&omega;}{C}_m}[I_q\cos (\mathrm{\&omega;t}+7\mathrm{\&pi;}/3)+I^{-}\cos (\mathrm{\&omega;t}-2\mathrm{\&pi;}/3+{\mathrm{\&theta;}}^{-})]+\mathrm{\&Delta;e}---\left(13\right)$

Wherein △ e is DC quantity, has meaned the DC error component of two capacitance voltages.From, due to the particularity of three-phase four switch inversion device 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 _CcDirect relation is arranged, and its amplitude is directly proportional to the amplitude of mid point input current, with the DC bus capacitor value, is inversely proportional to.In conjunction with above analysis, when three-phase four switch inversion device, during at compensating reactive power and negative-sequence current, following some conclusion is arranged:

1, when three-phase four switch inversion device compensation negative-sequence current, because there is the secondary pulsating power in it in the three-phase alternating current side, can produce the secondary ripple voltage of a correspondence on DC voltage, the size of ripple is directly proportional to the amplitude of negative-sequence current.

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

3, due to the structure particularity of this kind of three-phase four switch inversion device, when carrying out idle and negative sequence compensation, can produce a large amount of base time and secondary ripple 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 increase system cost, 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.

While utilizing three-phase four switch inversion device to compensate idle and negative-sequence current, after stable operation, DC side two capacitance voltage values can be expressed as:

The imbalance compensation control method of three-phase four switch power current transformers as shown in Figure 3.

In order to realize the compensation of System Reactive Power and harmonic current, the present invention a kind of imbalance compensation control method of three-phase four switch power current transformers, it is by outer voltage, Pressure and Control and current inner loop three parts form.For the DC voltage outer shroud, adopt a kind of PI regulating and controlling, can maintain the loss of stablizing and make up power switch of DC voltage, and maintain system safety and move reliably.Equal pressure balanced control problem for two electric capacity of DC side, adopted a kind of pressure equalizing control method to realize the balance of DC voltage.Then the idle of outer shroud output signal and expectation and the stack of negative current instructions signal are obtained to total current inner loop reference signal.Current inner loop is calculated the duty cycle signals of two switch arms of three-phase four switch inversion device by the integrated control method that adopts a kind of closed loop feedback+feedforward, effectively in conjunction with the advantage of feedfoward control and FEEDBACK CONTROL, improve the performance of dynamic tracking of system.Concrete control method is as follows:

For the control of DC voltage, according to derivation and the analysis of front, known DC voltage exists 2 the ripple component δ sin (2wt+ φ) that caused by the negative phase-sequence output current.If this ripple voltage is introduced in closed-loop control system and can be made to have harmonic current in three-phase four switch inversion device output current.Being calculated as follows of harmonic wave command signal: the tracking error △ u of outer voltage _DcAfter controller is regulated, be multiplied by the voltage synchronizing signal, obtain the command signal of current inner loop.Suppose that outer voltage is that P controls, its gain is K, and because there is ripple voltage in outer voltage, 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 the DC voltage outer shroud for this reason, proposed the compensation method of 2 ripple voltages, eliminate ripple and disturb, realize the normal control of DC voltage.

Therefore at 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 that calculated by formula (11), can obtain the DC component △ E of the tracking error of DC voltage, then the regulating command I of output DC voltage after the adjusting of PI controller is processed _M

Then by I _MBe multiplied by respectively the voltage synchronizing signal sy of A, B two-phase _aAnd sy _b, can obtain the pressure regulation command signal of power converter two-phase switch arm:

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

There are two series capacitances for DC voltage, this two electric capacity easily is subject to the impact of external disturbance and control output bias and makes capacitance voltage error occur, thereby make Voltage unbalance, will affect the control of inverter output current, therefore will need to adopt an even pressure controller to realize the stable and balance of DC voltage.According to top derivation with analyze knownly, due to the impact of the first-harmonic input current of DC side two electric capacity mid points, will on DC side two capacitance voltages, produce a corresponding base time ripple voltage.If this base time ripple signal is directly carried out to Pressure and Control, can give an additional first-harmonic command signal of stack on the current inner loop command signal, thereby affect the normal stable operation of three-phase four switch inversion device.Therefore the Pressure and Control process that this patent adopts is as follows:

At first by detecting the voltage difference △ u=u of DC side two electric capacity _C1-u _C2, then △ u is subtracted and the base time ripple voltage signal calculated by formula (13), can obtain the poor DC error △ e of DC side two capacitance voltages.

Then, after poor DC error △ e passes through the processing of PI controller by two capacitance voltages, can obtain all pressures modulation instructions △ I of two electric capacity of DC side _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, with reference to compensating signal, can obtain the total reference instruction current signal of current inner loop:

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

Because idle and negative-sequence current signal are AC signal, adopt traditional PI controller, it has limited follow-up control, has error during stable state; The ratio resonance of electric current (Proportional Resonant, the PR) controller that had the scholar to propose, have unlimited open-loop gain to the electric current of specific time, can realize like this indifference of AC signal is followed the tracks of.The s territory expression formula of PR controller is:

G(s)=K _m+2K _is/(s ²+ω ²)(18)

K wherein _mMean proportionality coefficient, K _iMean integral coefficient.According to the dead beat control principle, the value of proportionality coefficient is K simultaneously _m=L*T _S/ u _Dc, T _SFor control cycle, u _DcFor DC voltage, L is the output inductor value.By current inner loop always with reference to command signal i _ArAnd i _BrSubtract and to detect three-phase four switch inversion device output current signal i _CaAnd i _Cb, can obtain current error signal e _aAnd e _b.

By current error signal e _aAnd e _bBy the processing of current inner loop PR controller, can obtain the dynamic adjustments signal △ d of three-phase four switch inversion device respectively _aWith △ d _b.The closed-loop control of passing ratio resonant controller like this, this adjusting is that a kind of closed loop feedback is controlled, and can realize the dynamic tracking of fundamental current is regulated.

According to formula (3) and bipolarity modulation principle, can be in the hope of the output average voltage v of two switch arms of three-phase four switch inversion device _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 inversion device, and meet d _aAnd d _b∈ [0,1].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 _SbcLine voltage for three phase network.Three-phase four switch inversion device desired output electric current according to shown in formula (5), can calculate the stable state fundamental voltage of inverter Inductor as shown in formula (7).Simultaneously according to formula (20), by formula (7) substitution, can in the hope of three-phase four switch inversion device stable the time two switch arms expectation duty cycle signals d _A1And d _B1For:

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

Hence one can see that, and formula (21) is to derive according to the switch control principle of three-phase four switch inversion device, is the expectation duty cycle signals that can calculate two switch arms of three-phase four switch inversion device according to three-phase four switch inversion device desired output electric current.So this duty cycle signals d _A1And d _B1Can, as a kind of feedforward command signal, be used for realizing the quick response of three-phase four switch inversion device to the instruction current signal.

Dynamic adjustments signal △ d according to the output of current inner loop PR controller _aWith △ d _b, and the feedforward command signal d of feedfoward control output _A1And d _B1, can calculate the total duty cycle signals of two switch arms of three-phase four switch inversion device:

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

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

Current inner loop is controlled the integrated control method that has adopted PR FEEDBACK CONTROL+feedfoward control like this, has realized closed loop feedback performance and effective combination of feed forward performance fast, has greatly improved the control performance of three-phase four switch inversion device.When three-phase four switch inversion device carries out the compensation of idle and negative-sequence current, DC voltage exists base time and secondary ripple voltage, for the DC voltage outer shroud, control for this reason, invented a kind of removing method of secondary ripple voltage, while is for the Pressure and Control of DC bus capacitor, invented the removing method of a kind of base time ripple voltage, realized so normal stable control of three-phase four switch inversion device, ensured that it moves reliably and with long-term.

Claims (3)

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

1) by three-phase four switch inversion device DC side reference voltage U _refWith the DC voltage u detected _DcSubtract each other, obtain three-phase four switch inversion device DC voltage tracking error △ u _Dc

2) by DC voltage tracking error △ u _DcSend into the ripple arrester 2 times, obtain the DC component △ E of three-phase four switch inversion device DC voltage tracking error, then the regulating command I of output DC voltage tracking error after the adjusting of PI controller is processed _M

3) by regulating command I _MBe multiplied by respectively the voltage synchronizing signal sy of three-phase four switch inversion device two switch arms _aAnd sy _b, obtain the pressure regulation command signal i of three-phase four switch power current transformer two switch arms _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 inversion device DC side two electric capacity, then △ u is sent into to base time ripple arrester, obtain the poor DC error △ e of three-phase four switch inversion device DC side two capacitance voltages;

5) by two capacitance voltages, poor DC error △ e sends into the PI controller, obtains all pressures modulation instructions △ I of two electric capacity of three-phase four switch inversion device DC side _n

6) according to pressure regulation command signal i _Da, i _Db, all press modulation instructions △ I _nAnd idle and negative phase-sequence is with reference to compensating signal

With

Obtain current inner loop always with reference to instruction current signal i _Ar, i _Br:

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

7) by current inner loop always with reference to instruction current signal i _ArAnd i _BrDeduct respectively the output current signal i of three-phase four switch inversion device two switch arms that detect _CaAnd i _Cb, obtain current error signal e _aAnd e _b

8) by current error signal e _aAnd e _bSend into respectively current inner loop PR controller, obtain the dynamic adjustments signal △ d of three-phase four switch inversion device _aWith △ d _b

9), according to the feedfoward control link, try to achieve the expectation duty cycle signals d of three-phase four switch inversion device two switch arms while stablizing _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 the output inductor value,

With The expectation fundamental voltage of output inductor during for three-phase four switch inversion device stable state;

10) according to the dynamic adjustments signal △ d of three-phase four switch inversion device _aWith △ d _b, and the expectation duty cycle signals d of three-phase four switch inversion device two switch arms while stablizing _A1And d _B1, calculate total duty cycle signals d of two switch arms of three-phase four switch inversion device _aAnd d _b:

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

11) according to total duty cycle signals d of three-phase four switch inversion device two switch arms _aAnd d _b, by the PWM link, the switching tube that obtains three-phase four switch inversion device drives signal, the voltage and current signal of driving switch pipe output expectation.

2. the imbalance compensation control method of three-phase four switch power current transformers according to claim 1, is characterized in that described step 2) in, the computing formula of the DC component △ E of three-phase four switch inversion device DC voltage tracking error is:

$\mathrm{\&Delta;E}=\mathrm{\&Delta;}{u}_{\mathrm{dc}}-\frac{I^{-}[-1.5U+3\mathrm{\&omega;L}{I}_q]\sin (2\mathrm{\&omega;t}+{\mathrm{\&theta;}}^{-})}{2\mathrm{\&omega;C}{U}_d},$

Wherein, U and ω are 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, the equivalence value that C is three-phase four switch inversion device DC side two electric capacity, U _dDC component for three-phase four switch inversion device DC voltage.

3. the imbalance compensation control method of three-phase four switch power current transformers according to claim 2, is characterized in that, in described step 4), the computing formula of the DC error △ e that three-phase four switch inversion device DC side two capacitance voltages are poor is:

$\mathrm{\&Delta;e}=\mathrm{\&Delta;u}+\frac{1}{\mathrm{\&omega;}{C}_m}[I_q\cos (\mathrm{\&omega;t}+7\mathrm{\&pi;}/3)+I^{-}\cos (\mathrm{\&omega;t}-2\mathrm{\&pi;}/3+{\mathrm{\&theta;}}^{-})],$

Wherein, C _mFor the appearance value of the single electric capacity of three-phase four switch inversion device DC side, and C=C _m/ 2.

Images