CN105207219A - Multiple-resonance inhibition method for connecting multiple inverters into weak grid in parallel - Google Patents

Abstract

The invention discloses a multiple-resonance inhibition method for connecting multiple inverters into a weak grid in parallel. The method comprises the steps that capacitor voltage feedback quantities are introduced into current control ring forward channels of all the inverters and closed-loop links where the feedback quantities are located are set to be trap filter characteristics through control of active trap filters of capacitor voltage feedback of LCL filter circuits on the basis of the principle that in a parallel system of the multiple same-type current source inverters containing LCL filters, resonance peaks occur at the resonant frequencies of a transfer function of the parallel system, and therefore on the basis of active correction of the trap filters, the negative resonance peaks are achieved at the multiple resonant frequencies, and signals at the resonance points are shielded from the interiors of the inverters.

Description

The multiple resonance suppressing method of multi-inverter parallel access light current net

Technical field

The present invention relates to a kind of multiple resonance method suppressing to access weak network system multi-inverter.

Background technology

Along with the development of photovoltaic generation, extensive inverter is incorporated into the power networks with current source form access light current net becomes a kind of trend.Light current net for feature, causes the multi-inverter accessed to influence each other with its larger network impedance and less capacity of short circuit.The inverter with LCL form filter for same model accesses, its identical device parameter causes having regular resonance phenomena: and there are two resonance point frequency harmonics clearly in current on line side, this resonance point one immobilizes, and another moves to low frequency along with increasing of inverter parallel quantity.In order to the parallel resonance suppressing resonance frequency place to occur, existing extensively research, propose the resonance suppressing method such as passive damped method, active damping method, but passive damped method is owing to introducing physical component, brings unnecessary loss both at home and abroad; Active damping method is the effect realizing virtual impedance by the method controlled.But, research be yet there are no for the resonance suppressing method of two resonance point operating modes.

Summary of the invention

The object of the invention is the shortcoming overcoming prior art, propose a kind of multiple resonance suppressing method.The present invention is applied to the multi-inverter of current source form parallel connection access light current net, effectively can reduce the harmonic content that multiple resonant frequency point place is higher.

The present invention is based on the current source inverter parallel system of multiple same model containing LCL form filter, there is the principle of resonance spikes in the resonance frequency place of its transfer function, capacitance voltage feedback quantity is introduced in the current regulator forward path of each inverter, and the closed loop component characteristic at this feedback quantity place is adjusted into trapper characteristic, negative resonance spikes is realized at resonance frequency place, shield the signal of this resonance point from inverter internal, realize the active damping based on trapper; The trap frequency of this trapper is being worth in determined threshold range centered by resonance peak frequency.

The present invention can well suppress the problem at inverter outlet LCL circuit resonance peak, effectively improves the stability of inverter control system, suppresses the resonance of multiple different frequency point to occur, for the content then unrestraint effect of other effective frequency ranges.

The present invention is realized by the control system of the current source inverter containing LCL form filter.Described control system comprises phase locking unit, grid-connected current harmonic detecting unit and current transformation unit, capacitance voltage detection transform part, active correction link, current follow-up control link, instruction current calculating and converter unit and PWM instruction generation unit.

Described current source inverter control system grid-connected current harmonic detecting unit and current transformation unit gather grid-connected current, by grid-connected current i _a, i _b, i _cbecome α β 0 axle system component by coordinate transform, then according to the output phase angle theta of phase locking unit, grid-connected current is carried out to the coordinate transform of α β 0-dq, obtain the real-time current signal of dq axle system, and extract resonance frequency omega; Capacitance voltage detects the capacitance voltage U that transform part exports _{c_abc}in conjunction with the output phase angle theta of phase locking unit, by abc-α β 0-dq axle, system is transformed into U _cdqsignal; Active correction link receives the resonant frequency signal ω from grid-connected current harmonic detecting unit and current transformation unit ₁, ω ₂the capacitance voltage U of transform part is detected with capacitance voltage _cdqsignal, for different resonant frequency signal ω ₁, ω ₂after transfer function effect, export corresponding intermediate control signal U _{c_d1,}u _{c_q1}and U _{c_d2,}u _{c_q2}, described transfer function expression formula is as follows:

$L\left(S\right)=\frac{U_{c\_dq}}{U_{cdq}}=K_d\frac{T_{d}s+1}{{\mathrm{\αT}}_{d}s+1}$

In formula, U _cdqfor the dq axle system component of capacitance voltage, U _{c_dq}for the output voltage signal acted on through transfer function L (s).K _d, T _d, α is the proportionality coefficient of transfer function L (s), time coefficient and differential term coefficient, can according to relation between resonance frequency omega defined parameters: $\mathrm{\ω}=1/T_d\sqrt{\mathrm{\α}}.$

The instruction current i of current follow-up control link input _{dq_ref}with actual grid-connected current i _dqdo difference, export after PI controller and control current i _d1, i _q1; Instruction current calculates and converter unit receives the output control signal U coming from active correction link _{c_d12}, U _{c_q12}with the control current i of current follow-up control link _d1, i _q1signal, controls current i _d1, i _q1respectively with the output control signal U of active correction link _{c_d12}, U _{c_q12}do difference, the signal done after difference exports PWM instruction generation unit to through coordinate transform, and the pwm signal that PWM instruction generation unit exports drives described power switch pipe to produce the output current expected.The command signal outputting to PWM maker has the content that effect reduces resonant frequency signal.

Described active correction link exports control variables by capacitance voltage feedback quantity after transfer function L (s) conversion, with conventional current controller outlet side Signal averaging, the corresponding multiple resonance peak frequency of many group control signals can be obtained, realize the suppression of multiple resonance.

The present invention does not need additionally to install hardware device additional, has very strong feasibility, can replace passive damping, effectively reduces hardware cost and power consumption; Also the problem that additive method suppresses merely a frequency resonance or full rate section to suppress is solved.

Accompanying drawing explanation

Fig. 1 is circuit and the control method schematic diagram that multi-inverter parallel accesses weak network system;

Fig. 2 is inverter control system block diagram;

Fig. 3 multi-inverter parallel resonance inhibitory control system block diagram.

Embodiment

The present invention is further illustrated below in conjunction with the drawings and specific embodiments.

As shown in Figure 1, multiple current source inverter parallel systems containing LCL filter that the present invention applies comprise weak network system 10, multiple current source inverter 20 with control system 30.The multiple resonance suppressing method of the present invention is realized by the control system 30 of each inverter.

In the power switch pipe 203 of the switching signal input corresponding current source type inverter 20 that control system 30 exports, multiple current source inverter 20 is also attached to light current net system 10.

Described weak network system 10 can be equivalent to the physical model of ideal voltage source 101 and resistance sense circuit 102 series connection.

Described multiple current source inverters are made up of DC voltage source 201, Support Capacitor 202, power switch pipe 203, LCL output filter 204 and voltage measurement unit 205.The hardware configuration of described LCL output filter 204 can be that LC filter connects output transformer equivalence formation, also can be simple LCL output filter, also can be that the equivalence of LCL filter connection output transformer is formed.

Described DC voltage source 201 is connected with DC support electric capacity 202 parallel connection, be connected in parallel to the direct current input side of power switch pipe 203, the three-phase alternating current outlet side of power switch pipe 203 connects three-phase LCL output filter 204 respectively, the output of filter 204 is connected to the resistance sense line scan pickup coil side 102 of weak network system, filter capacity terminal voltage measuring unit 205 Detection capacitance voltage, and capacitance voltage signal being exported to controller 30 detects in transform part 303.

Described control system 30 comprises phase locking unit 301, grid-connected current harmonic detecting unit and current transformation unit 302, capacitance voltage detection transform part 303, active correction link 304, current follow-up control link 305, instruction current calculating and converter unit 306 and PWM instruction generation unit 307.

The conventional current ring control mode of combining inverter as shown in Figure 2, given control current i _l ^*with actual feedback currents i _ldo difference after, through inner ring current controller Gc (s) effect after controlled quentity controlled variable be directly inputted in PWM controller, output inverter outlet side voltage u after LCL circuit function, with i _lform feeds back to input.

The present invention adds active correction link on the basis of conventional current ring control method, and the multiple resonance completing grid-connected current suppresses.Wherein, weak network system 10 line voltage effective value is 380VAC, and electrical network equiva lent impedance 102 is Lg=0.01mH, and multiple current source type inverter 20 quantity in parallel is n, LC filter parameter is L ₁=0.25mH, C=369uF, the equivalent leakage inductance that 380V converted by transformer is L ₂=0.049mH.

When inverter parallel quantity is 2, grid-connected current resonance times is 25.9 times, 22.5 times, and resonance frequency is respectively 8133rad/s and 7079rad/s; When quantity in parallel is 4, grid-connected current resonance times is 25.9 times, 20.5 times, and resonance frequency is respectively 8133rad/s and 6426rad/s; When quantity in parallel is 8, grid-connected current resonance times is 25.9 times, 18 times, and resonance frequency is respectively 8133rad/s and 5643rad/s.

Carry out execution mode for four current source inverter parallel connections and the inventive method be described:

Described phase locking unit 301 carries out phase-locked control, exports phase angle theta.

Grid-connected current harmonic detecting unit and current transformation unit 302 gather grid-connected current, and extract resonance frequency, by grid-connected current i _a, i _b, i _cα β 0 axle system component i is become by coordinate transform _α, i _β, i ₀:

$\left[\begin{array}{c}{i}_{\mathrm{\α}}\\ i_{\mathrm{\β}}\\ i_0\end{array}\right]=\sqrt{3}\left[\begin{array}{ccc}1& -0.5& -0.5\\ 0& \sqrt{3}/2& -\sqrt{3}/2\end{array}\right]\left[\begin{array}{c}{i}_a\\ i_b\\ i_c\end{array}\right]$

Then according to the output phase angle theta of phase locking unit 301, grid-connected current is carried out to the coordinate transform of α β 0-dq, obtain the real-time current signal i of dq axle system _d, i _q:

$\left[\begin{array}{c}{i}_d\\ i_q\end{array}\right]=\left[\begin{array}{cc}cos\mathrm{\θ}& sin\mathrm{\θ}\\ -sin\mathrm{\θ}& cos\mathrm{\θ}\end{array}\right]\left[\begin{array}{c}{i}_{\mathrm{\α}}\\ i_{\mathrm{\β}}\end{array}\right]$

Capacitance voltage detects the capacitance voltage U of transform part 303 _{c_abc}be transformed to U in accordance with the following steps _cdqsignal.

$\left[\begin{array}{c}{U}_{c\mathrm{\α}}\\ U_{c\mathrm{\β}}\\ U_{c0}\end{array}\right]=\sqrt{3}\left[\begin{array}{ccc}1& -0.5& -0.5\\ 0& \sqrt{3}/2& -\sqrt{3}/2\end{array}\right]\left[\begin{array}{c}{U}_a\\ U_b\\ U_c\end{array}\right]$

$\left[\begin{array}{c}{U}_{cd}\\ U_{cq}\end{array}\right]=\left[\begin{array}{cc}cos\mathrm{\θ}& sin\mathrm{\θ}\\ -sin\mathrm{\θ}& cos\mathrm{\θ}\end{array}\right]\left[\begin{array}{c}{U}_{c\mathrm{\α}}\\ U_{c\mathrm{\β}}\end{array}\right]$

Active correction link 304 is lead-lag links, receives the capacitance voltage U detecting transform part 303 from the resonant frequency signal of grid-connected current harmonic detecting unit and current transformation unit 302 and capacitance voltage _cdqsignal, its transfer function expression formula is

$L\left(S\right)=\frac{U_{c\_dq}}{U_{cdq}}=K_d\frac{T_{d}s+1}{{\mathrm{\αT}}_{d}s+1}$

In formula, U _cdqfor the dq axle system component of capacitance voltage, U _{c_dq}for the output voltage signal acted on through transfer function L (s).The parameter K of L (s) _d, T _d, α detects according to grid-connected current harmonic detecting unit 301 resonance frequency omega obtained and sets, relation is as follows:

$\mathrm{\ω}=\frac{1}{T_d\sqrt{\mathrm{\α}}}$

For two resonant frequency point ω ₁ω ₂suppression, right select one group of parameter alpha ₁=0.0001, T _d1=0.0123, K _d1=2; Right selection parameter α ₂=0.0001, T _d2=0.01556, K _d2=2.

Described active correction link 304 exports intermediate control signal U _{c_d12}and U _{c_q12}.

The control signal exported by PWM controller 307 is added on inverter switching device pipe 203, the capacitance voltage U that switching tube outlet side voltage u and voltage detection unit 205 record _cbetween pass be:

$E\left(s\right)=\frac{U_c}{u}=\frac{1}{L_{1}C}\×\frac{L_1{L}_{2}C}{L_1{L}_2{\mathrm{Cs}}^2+(L_1+L_2)}$

Wherein, LC filter parameter is L ₁=0.25mH, C=369uF, the equivalent leakage inductance that 380V converted by transformer is L ₂=0.049mH.

Active correction link 304 equivalent transfer function is:

$D\left(s\right)=\frac{1}{1+L\left(s\right)\×E\left(s\right)}$

As shown in Figure 3, L ₁(s), L ₂s () is the transfer function in active correction link 304, the capacitance voltage U that E (s) records for switching tube outlet side voltage u and voltage detection unit 205 _cbetween relation.

The instruction current i of current follow-up control link 305 _{dq_ref}do difference with actual grid-connected current and export after PI controller and control current i _d1, i _q1.

Instruction current calculates and converter unit 306 receives the U coming from active correction link 304 _{c_d12}, U _{c_q12}with the control current i of current follow-up control link 305 _d1, i _q1signal, do difference after signal through coordinate transform export to PWM instruction generation unit 307, PWM instruction generation unit 307 export PWM switching drive signal control described power switch pipe 202 produce expect output current.

Its control effects is, the command signal outputting to PWM instruction generation unit 307 has the content that effect reduces resonant frequency signal.

Claims (3)

1. the multiple resonance suppressing method of a multi-inverter parallel access light current net, it is characterized in that, described multiple resonance suppressing method is based on the current source inverter parallel system of multiple same model containing LCL form filter, there is the principle of resonance spikes in the resonance frequency place of its transfer function, LCL capacitance voltage feedback quantity is introduced in the current regulator forward path of each inverter, and the closed loop link at this feedback quantity place is adjusted into trapper characteristic, realize the active damping based on trapper; The trap frequency of this trapper is being worth in determined threshold range centered by resonance peak frequency.

2. the multiple resonance suppressing method of multi-inverter parallel access light current net as claimed in claim 1, it is characterized in that, described multiple resonance suppressing method realizes negative resonance spikes at described resonance frequency place, and shield the signal of this resonance point from inverter internal, concrete steps are as follows:

The grid-connected current harmonic detecting unit of current source inverter control system (30) and current transformation unit (302) gather grid-connected current, by grid-connected current i _a, i _b, i _cbecome α β 0 axle system component by coordinate transform, then according to the output phase angle theta of phase locking unit (301), grid-connected current is carried out to the coordinate transform of α β 0-dq, obtain the real-time current signal of dq axle system, and extract resonance frequency omega; Capacitance voltage detects the capacitance voltage U that transform part (303) exports _{c_abc}in conjunction with the output phase angle theta of phase locking unit (301), by abc-α β 0-dq axle, system is transformed into U _cdqsignal; Active correction link (304) receives the resonant frequency signal ω from grid-connected current harmonic detecting unit and current transformation unit (302) ₁, ω ₂the capacitance voltage U of transform part (303) is detected with capacitance voltage _cdqsignal, for different resonant frequency signal ω ₁, ω ₂after transfer function effect, export corresponding intermediate control signal U _{c_d1}, U _{c_q1}and U _{c_d2}, U _{c_q2}, described transfer function expression formula is as follows:

$L\left(s\right)=\frac{U_{c\_dq}}{U_{cdq}}=K_d\frac{T_{d}s+1}{{\mathrm{\αT}}_{d}s+1}$

In formula, U _cdqfor the dq axle system component of capacitance voltage, U _{c_dq}for the output voltage signal acted on through transfer function L (s), K _d, T _d, α is respectively the proportionality coefficient of transfer function L (s), time coefficient and differential term coefficient, parametric relationship defines according to resonance frequency omega:

The instruction current i that current follow-up control link (305) inputs _{dq_ref}with actual grid-connected current i _dqdo difference, export after PI controller and control current i _d1, i _q1; Instruction current calculates and converter unit (306) receives the output control signal U coming from active correction link (304) _{c_d12}, U _{c_q12}with the control current i of current follow-up control link (305) _d1, i _q1signal, controls current i _d1, i _q1respectively with the output control signal U of active correction link (304) _{c_d12}, U _{c_q12}do difference, the signal done after difference exports PWM instruction generation unit (307) to through coordinate transform, and the pwm signal that PWM instruction generation unit (307) exports drives described power switch pipe to produce the output current expected.

3. the multiple resonance suppressing method of multi-inverter parallel access light current net as claimed in claim 2, it is characterized in that, described active correction link exports control variables by capacitance voltage feedback quantity through lead-lag conversion, with conventional current controller outlet side Signal averaging, the corresponding multiple resonance peak frequency of many group control signals can be obtained, realize the suppression of multiple resonance.