CN105119322A - Control method for improving grid-connected voltage source inverter system stability - Google Patents

Abstract

The invention discloses a control method for improving grid-connected voltage source inverter system stability. The method comprises the steps of (1) generating a grid-connected converter modulating wave initial order; (2) calculating a power grid side current control circuit gain T, obtaining corresponding cut-off frequency omega 1 and cut-off frequency omega 2 when an amplitude-versus-frequency curve of the T passes through 0dB twice before a resonant frequency omega r of an LCL filter, and obtaining an s-domain transfer function of a lag compensation link according to the cut-off frequency omega 1 and the cut-off frequency omega 2; (3) performing discretization on the s-domain transfer function of the lag compensation link, and bringing the grid-connected converter modulating wave initial order obtained in the step (1) into an express form, in a digital controller, of the s-domain transfer function of the lag compensation link obtained through the discretization, so as to obtain a final modulating wave order value of the converter; (4) obtaining a modulating signal according to the final modulating wave order value of the converter obtained in the step (3), and controlling various switching elements of the converter according to the modulating signal; the control method provided by the invention can effectively improve the system stability.

Description

A kind of control method improving the grid-connected voltage source inverter stability of a system

Technical field

The invention belongs to automation field, relate to a kind of control method improving the grid-connected voltage source inverter stability of a system.

Background technology

In recent years, along with the fast development of China's economy, the problem such as energy shortage and environmental pollution is day by day serious.In order to solve the problem, obtain large-scale exploitation with the regenerative resource that wind power generation, photovoltaic generation are representative, thus the grid-connected voltage source inverter accessed by new forms of energy required for electrical network be obtained a wide range of applications.Voltage source inverter mostly adopts again full-control type power electronic switching device to coordinate PWM strategy to carry out work, and therefore in order to improve and the quality of power supply of site, reduce switch time ripple, the filter between current transformer and electrical network is just essential.Compared with traditional L filter, LCL filter can provide more outstanding switch time Ripple Suppression ability, simultaneously its volume and capacity all less, ensureing and to provide cost savings and floor space while the quality of power supply of site, thus obtaining the favor of engineer applied.But the resonance characteristic of LCL filter makes the design of stable converter system become more difficult with complexity.In addition, under weak grid condition, net side impedance is comparatively large, even if be stable based on the grid-connected voltage source inverter system unit operation of LCL filter, when its access electrical network, whole system also very easily produces unstable phenomenon.

In recent years, more based on the control method research of the grid-connected voltage source inverter stability of a system of LCL filter for improvement.Wherein a class solution is by suppressing the resonance peak of LCL filter to reach the object improving the stability of a system.The resonance peak of LCL filter is suppressed mainly to be realized by the method adding extra damping.Compared with traditional passive damping method adding passive device, the method for active damping forms double-loop control by the state variable of feedback filter to realize, and it can not produce extra energy loss.But the method for active damping needs extra transducer to carry out detected state variable, the structure of its double-loop control is also comparatively complicated simultaneously.Further research finds, when the resonance frequency of LCL filter is greater than the system sampling frequency of 1/6 times, even if do not add any damping, the stable grid-connected voltage source inverter system based on LCL filter also can be obtained by the internal damping effect of converter system PWM time delay process.This design makes current transformer without any need for extra damping or transducer, only needs the current on line side FEEDBACK CONTROL of self can obtain stable system.But, in order to the cost obtained required for enough stability margins is exactly the bandwidth of sacrificing current on line side controller.In addition, under weak grid condition, even if be stable based on the grid-connected voltage source inverter system of LCL filter, when its access electrical network, whole system also very easily produces unstable phenomenon.

Summary of the invention

The object of the invention is to the shortcoming overcoming above-mentioned prior art, provide a kind of control method improving the grid-connected voltage source inverter stability of a system, the method effectively can improve the stability of grid-connected voltage source inverter system.

For achieving the above object, the control method of the grid-connected voltage source inverter stability of a system of improvement of the present invention comprises the following steps:

1) grid-connected converter modulating wave initial order v is generated _{ca0_ref}, v _{cb0_ref}and v _{cc0_ref};

2) calculate grid side current controlled circuit gain T, obtain the resonance frequency omega in LCL filter _rcut-off frequency ω corresponding when the amplitude-versus-frequency curve of grid side current controlled circuit gain T passes twice through 0dB before ₁and ω ₂, wherein, ω ₁< ω ₂, then according to described cut-off frequency ω ₁and ω ₂obtain the s territory transfer function G of lag compensation link _l(s);

3) by step 2) the s territory transfer function G of lag compensation link that obtains _ls () discretization, obtains the s territory transfer function G of lag compensation link _l(s) representation in digitial controller, then by step 1) the grid-connected converter modulating wave initial order v that obtains _{ca0_ref}, v _{cb0_ref}and v _{cc0_ref}be brought into the s territory transfer function G of lag compensation link _lin (s) representation in digitial controller, obtain the modulating wave command value v that current transformer is final _{ca_ref}, v _{cb_ref}and v _{cc_ref};

4) by step 3) the final modulating wave command value v of the current transformer that obtains _{ca_ref}, v _{cb_ref}and v _{cc_ref}carry out SPWM modulation, obtain modulation signal, finally control each switching device of current transformer according to described modulation signal.

Step 1) concrete operations be:

1.1) the voltage on line side v of three phase network system is detected _sa, v _sband v _sc, then according to the voltage on line side v of three phase network system _sa, v _sband v _scthe angular frequency of current electric grid is obtained by phase-locked loop pll ₀with phase theta;

1.2) according to step 1.1) angular frequency of current electric grid that obtains ₀three-phase current on line side instruction i is obtained with phase theta _{sa_ref}, i _{sb_ref}and i _{sc_ref};

1.3) the current on line side i of three phase network system is detected _sa, i _sband i _sc, then by the current on line side i of three phase network system _sa, i _sband i _scwith step 1.2) three-phase current on line side instruction i _{sa_ref}, i _{sb_ref}and i _{sc_ref}carry out making difference operation, PR adjuster obtains grid-connected converter modulating wave initial order v according to the result making difference operation _{ca0_ref}, v _{cb0_ref}and v _{cc0_ref}.

Step 1.2) middle three-phase current on line side instruction i _{sa_ref}, i _{sb_ref}and i _{sc_ref}expression formula be:

$\left\{\begin{array}{c}{i}_{sa\_ref}=I_{sa}\sin \mathrm{\&theta;}\\ i_{sb\_ref}=I_{sb}sin(\mathrm{\&theta;}-\frac{2}{3}\mathrm{\&pi;})\\ i_{sc\_ref}=I_{sc}\sin (\mathrm{\&theta;}+\frac{2}{3}\mathrm{\&pi;})\end{array}\right.$

Wherein, I _sa, I _sband I _scbe respectively the amplitude of three-phase current on line side instruction.

Step 2) in the expression formula of grid side current controlled circuit gain T be: T=G _c(s) G _d(s) Y _mwherein, Y _mfor the AC output voltage of current transformer is to the small-signal transfer function of current on line side, G _cs s territory transfer function that () is PR controller, G _ds () is the s territory transfer function of current transformer PWM link time delay.

The AC output voltage of described current transformer is to the small-signal transfer function Y of current on line side _mexpression-form be:

$Y_m=\frac{Z_c}{Z_c{Z}_1+Z_c{Z}_2+Z_1{Z}_2}$

$Z_c=\frac{1}{{\mathrm{sC}}_f}+r_c$

Z ₁＝sL ₁+r ₁

Z ₂＝sL ₂+r ₂

Wherein, Z _c, Z ₁and Z ₂be respectively the impedance of LCL filter filter capacitor, current transformer side inductive impedance and net side inductive impedance, C _f, L ₁, L ₂be respectively LCL filter capacitance, current transformer side inductance value and net side inductance value, r _c, r ₁and r ₂be respectively the dead resistance of LCL filter filter capacitor, the dead resistance of current transformer side inductance and the dead resistance of net side inductance.

The s territory transfer function G of PR controller _cs the expression formula of () is: wherein, k _pand k _rbe respectively proportionality coefficient and the resonance coefficient of PR controller.

The s territory transfer function G of current transformer PWM link time delay _ds the expression formula of () is:

$G_d\left(s\right)=e^{-1.5T_{s}s}$

Wherein, T _sfor the sampling period of system.

The s territory transfer function G of lag compensation link _ls the expression formula of () is:

$G_l\left(s\right)=\frac{1+{\mathrm{\&tau;}}_{1}s}{1+{\mathrm{\&tau;}}_{2}s}$

Wherein, τ ₁determine compensation tache dead-center position, τ ₂determine compensation tache pole location, ${\mathrm{\&omega;}}_2<\frac{1}{{\mathrm{\&tau;}}_2}<{\mathrm{\&omega;}}_r.$

Step 3) concrete operations be:

By step 2) the s territory transfer function G of lag compensation link that obtains _ls () discretization, obtains the s territory transfer function G of lag compensation link _ls () representation in digitial controller is:

$y\left(k\right)=\frac{T_s+2{\mathrm{\&tau;}}_1}{T_s+2{\mathrm{\&tau;}}_2}x\left(k\right)+\frac{T_s-2{\mathrm{\&tau;}}_1}{T_s+2{\mathrm{\&tau;}}_2}x(k-1)-\frac{T_s-2{\mathrm{\&tau;}}_2}{T_s+2{\mathrm{\&tau;}}_2}y(k-1)$

Wherein, x (k) is for lag compensation link is in the input in a kth sampling period, and y (k) is for lag compensation link is in the output in a kth sampling period; X (k-1) is for lag compensation link is in the input in-1 sampling period of kth; Y (k-1) is for lag compensation link is in the output in-1 sampling period of kth;

By step 1) the current transformer modulating wave initial order v that obtains _{ca0_ref}, v _{cb0_ref}and v _{cc0_ref}input x (k) as lag compensation link is brought in above formula, obtains y ₁(k), y ₂(k) and y ₃k (), then by y ₁(k), y ₂(k) and y ₃k () is successively as the modulating wave command value v that current transformer is final _{ca_ref}, v _{cb_ref}and v _{cc_re}f.

The present invention has following beneficial effect:

The control method of the grid-connected voltage source inverter stability of a system of improvement of the present invention in operation, obtains the resonance frequency omega in LCL filter _rcut-off frequency ω corresponding when the amplitude-versus-frequency curve of grid side current controlled circuit gain T passes twice through 0dB before ₁and ω ₂, then according to described cut-off frequency ω ₁and ω ₂obtain the s territory transfer function G of lag compensation link _ls (), thus introduce lag compensation link in the original current on line side of current transformer controls, reaches the object improving whole system stability, and then according to the s territory transfer function G of lag compensation link _ls () obtains the final modulating wave command value of current transformer, finally control each switching device of current transformer according to the modulating wave instruction that current transformer is final, thus make the work of whole system normal table.

Accompanying drawing explanation

Fig. 1 is the circuit theory diagrams of grid-connected voltage source inverter system;

Fig. 2 is traditional single phase current on line side control block diagram;

Fig. 3 is the control block diagram of current transformer current on line side in the present invention;

Fig. 4 is with or without lag compensation link three-phase current on line side simulation waveform figure in the present invention.

Embodiment

Below in conjunction with accompanying drawing, the present invention is described in further detail:

With reference to figure 1 and Fig. 3, improve the control method of the grid-connected voltage source inverter stability of a system, it is characterized in that, comprise the following steps:

1) grid-connected converter modulating wave initial order v is generated _{ca0_ref}, v _{cb0_ref}and v _{cc0_ref}, wherein, step 1) concrete operations be:

1.1) the voltage on line side v of three phase network system is detected _sa, v _sband v _sc, then according to the voltage on line side v of three phase network system _sa, v _sband v _scthe angular frequency of current electric grid is obtained by phase-locked loop pll ₀with phase theta;

1.2) according to step 1.1) angular frequency of current electric grid that obtains ₀three-phase current on line side instruction i is obtained with phase theta _{sa_ref}, i _{sb_ref}and i _{sc_ref}, wherein,

$\left\{\begin{array}{c}{i}_{sa\_ref}=I_{sa}\sin \mathrm{\&theta;}\\ i_{sb\_ref}=I_{sb}sin(\mathrm{\&theta;}-\frac{2}{3}\mathrm{\&pi;})\\ i_{sc\_ref}=I_{sc}\sin (\mathrm{\&theta;}+\frac{2}{3}\mathrm{\&pi;})\end{array}\right.$

Wherein, I _sa, I _sband I _scbe respectively the amplitude of three-phase current on line side instruction;

1.3) the current on line side i of three phase network system is detected _sa, i _sband i _sc, then by the current on line side i of three phase network system _sa, i _sband i _scwith step 1.2) three-phase current on line side instruction i _{sa_ref}, i _{sb_ref}and i _{sc_ref}carry out making difference operation, PR adjuster obtains grid-connected converter modulating wave initial order v according to the result making difference operation _{ca0_ref}, v _{cb0_ref}and v _{cc0_ref}.

2) calculate grid side current controlled circuit gain T, obtain the resonance frequency omega in LCL filter _rcut-off frequency ω corresponding when the amplitude-versus-frequency curve of grid side current controlled circuit gain T passes twice through 0dB before ₁and ω ₂, wherein, ω ₁< ω ₂, then according to described cut-off frequency ω ₁and ω ₂obtain the s territory transfer function G of lag compensation link _l(s); Step 2) in the expression formula of grid side current controlled circuit gain T be:

T＝G _c(s)·G _d(s)·Y _m

Wherein, Y _mfor the AC output voltage of current transformer is to the small-signal transfer function of current on line side, G _cs s territory transfer function that () is PR controller, G _ds () is the s territory transfer function of current transformer PWM link time delay;

The AC output voltage of described current transformer is to the small-signal transfer function Y of current on line side _mexpression-form be:

$Y_m=\frac{Z_c}{Z_c{Z}_1+Z_c{Z}_2+Z_1{Z}_2}$

$Z_c=\frac{1}{{\mathrm{sC}}_f}+r_c$

Z ₁＝sL ₁+r ₁

Z ₂＝sL ₂+r ₂

Wherein, Z _c, Z ₁and Z ₂be respectively the impedance of LCL filter filter capacitor, current transformer side inductive impedance and net side inductive impedance, C _f, L ₁, L ₂be respectively LCL filter capacitance, current transformer side inductance value and net side inductance value, r _c, r ₁and r ₂be respectively the dead resistance of LCL filter filter capacitor, the dead resistance of current transformer side inductance and the dead resistance of net side inductance.

The s territory transfer function G of PR controller _cs the expression formula of () is: wherein, k _pand k _rbe respectively proportionality coefficient and the resonance coefficient of PR controller.

The s territory transfer function G of current transformer PWM link time delay _ds the expression formula of () is:

$G_d\left(s\right)=e^{-1.5T_{s}s}$

Wherein, T _sfor the sampling period of system.

The s territory transfer function G of lag compensation link _ls the expression formula of () is:

$G_l\left(s\right)=\frac{1+{\mathrm{\&tau;}}_{1}s}{1+{\mathrm{\&tau;}}_{2}s}$

Wherein, τ ₁determine compensation tache dead-center position, τ ₂determine compensation tache pole location, ${\mathrm{\&omega;}}_2<\frac{1}{{\mathrm{\&tau;}}_2}<{\mathrm{\&omega;}}_r;$

3) by step 2) the s territory transfer function G of lag compensation link that obtains _ls () discretization, obtains the s territory transfer function G of lag compensation link _l(s) representation in digitial controller, then by step 1) the grid-connected converter modulating wave initial order v that obtains _{ca0_ref}, v _{cb0_ref}and v _{cc0_ref}be brought into the s territory transfer function G of lag compensation link _lin (s) representation in digitial controller, obtain the modulating wave command value v that current transformer is final _{ca_ref}, v _{cb_ref}and v _{cc_ref};

4) by step 3) the final modulating wave command value v of the current transformer that obtains _{ca_ref}, v _{cb_ref}and v _{cc_ref}carry out SPWM modulation, obtain modulation signal, finally control each switching device of current transformer according to described modulation signal.

It should be noted that, step 3) concrete operations be:

By step 2) the s territory transfer function G of lag compensation link that obtains _ls () discretization, obtains the s territory transfer function G of lag compensation link _ls () representation in digitial controller is:

$y\left(k\right)=\frac{T_s+2{\mathrm{\&tau;}}_1}{T_s+2{\mathrm{\&tau;}}_2}x\left(k\right)+\frac{T_s-2{\mathrm{\&tau;}}_1}{T_s+2{\mathrm{\&tau;}}_2}x(k-1)-\frac{T_s-2{\mathrm{\&tau;}}_2}{T_s+2{\mathrm{\&tau;}}_2}y(k-1)$

Wherein, x (k) is for lag compensation link is in the input in a kth sampling period, and y (k) is for lag compensation link is in the output in a kth sampling period; X (k-1) is for lag compensation link is in the input in-1 sampling period of kth; Y (k-1) is for lag compensation link is in the output in-1 sampling period of kth;

By step 1) the current transformer modulating wave initial order v that obtains _{ca0_ref}, v _{cb0_ref}and v _{cc0_ref}input x (k) as lag compensation link is brought in above formula, obtains y ₁(k), y ₂(k) and y ₃k (), then by y ₁(k), y ₂(k) and y ₃k () is successively as the modulating wave command value v that current transformer is final _{ca_ref}, v _{cb_ref}and v _{cc_re}f.

With reference to figure 4, as can be seen from simulation waveform, make lag compensation link invalid before 0.2s, whole system plays pendulum; After 0.2s, make control method of the present invention effective, can find out that whole system enters stable state from labile state, thus demonstrate correctness and the reliability of the method.

Claims (9)

1. improve a control method for the grid-connected voltage source inverter stability of a system, it is characterized in that, comprise the following steps:

1) grid-connected converter modulating wave initial order v is generated _{ca0_ref}, v _{cb0_ref}and v _{cc0_ref};

2) calculate grid side current controlled circuit gain T, obtain the resonance frequency omega in LCL filter _rcut-off frequency ω corresponding when the amplitude-versus-frequency curve of grid side current controlled circuit gain T passes twice through 0dB before ₁and ω ₂, wherein, ω ₁< ω ₂, then according to described cut-off frequency ω ₁and ω ₂obtain the s territory transfer function G of lag compensation link _l(s);

3) by step 2) the s territory transfer function G of lag compensation link that obtains _ls () discretization, obtains the s territory transfer function G of lag compensation link _l(s) representation in digitial controller, then by step 1) the grid-connected converter modulating wave initial order v that obtains _{ca0_ref}, v _{cb0_ref}and v _{cc0_ref}be brought into the s territory transfer function G of lag compensation link _lin (s) representation in digitial controller, obtain the modulating wave command value v that current transformer is final _{ca_ref}, v _{cb_ref}and v _{cc_ref};

4) by step 3) the final modulating wave command value v of the current transformer that obtains _{ca_ref}, v _{cb_ref}and v _{cc_ref}carry out SPWM modulation, obtain modulation signal, finally control each switching device of current transformer according to described modulation signal.

2. the control method of the grid-connected voltage source inverter stability of a system of improvement according to claim 1, is characterized in that, step 1) concrete operations be:

1.1) the voltage on line side v of three phase network system is detected _sa, v _sband v _sc, then according to the voltage on line side v of three phase network system _sa, v _sband v _scthe angular frequency of current electric grid is obtained by phase-locked loop pll ₀with phase theta;

1.2) according to step 1.1) angular frequency of current electric grid that obtains ₀three-phase current on line side instruction i is obtained with phase theta _{sa_ref}, i _{sb_ref}and i _{sc_ref};

1.3) the current on line side i of three phase network system is detected _sa, i _sband i _sc, then by the current on line side i of three phase network system _sa, i _sband i _scwith step 1.2) three-phase current on line side instruction i _{sa_ref}, i _{sb_ref}and i _{sc_ref}carry out making difference operation, PR adjuster obtains grid-connected converter modulating wave initial order v according to the result making difference operation _{ca0_ref}, v _{cb0_ref}and v _{cc0_ref}.

3. the control method of the grid-connected voltage source inverter stability of a system of improvement according to claim 2, is characterized in that, step 1.2) middle three-phase current on line side instruction i _{sa_ref}, i _{sb_ref}and i _{sc_ref}expression formula be:

$\left\{\begin{array}{c}{i}_{sa\_ref}=I_{sa}\sin \mathrm{\&theta;}\\ i_{sb\_ref}=I_{sb}\sin (\mathrm{\&theta;}-\frac{2}{3}\mathrm{\&pi;})\\ i_{sc\_ref}=I_{sc}\sin (\mathrm{\&theta;}+\frac{2}{3}\mathrm{\&pi;})\end{array}\right.$

Wherein, I _sa, I _sband I _scbe respectively the amplitude of three-phase current on line side instruction.

4. the control method of the grid-connected voltage source inverter stability of a system of improvement according to claim 2, is characterized in that, step 2) in the expression formula of grid side current controlled circuit gain T be:

T＝G _c(s)·G _d(s)·Y _m

Wherein, Y _mfor the AC output voltage of current transformer is to the small-signal transfer function of current on line side, G _cs s territory transfer function that () is PR controller, G _ds () is the s territory transfer function of current transformer PWM link time delay.

5. the control method of the grid-connected voltage source inverter stability of a system of improvement according to claim 4, is characterized in that, the AC output voltage of described current transformer is to the small-signal transfer function Y of current on line side _mexpression-form be:

$Y_m=\frac{Z_c}{Z_c{Z}_1+Z_c{Z}_2+Z_1{Z}_2}$

$Z_c=\frac{1}{{\mathrm{sC}}_f}+r_c$

Z ₁＝sL ₁+r ₁

Z ₂＝sL ₂+r ₂

Wherein, Z _c, Z ₁and Z ₂be respectively the impedance of LCL filter filter capacitor, current transformer side inductive impedance and net side inductive impedance, C _f, L ₁, L ₂be respectively LCL filter capacitance, current transformer side inductance value and net side inductance value, r _c, r ₁and r ₂be respectively the dead resistance of LCL filter filter capacitor, the dead resistance of current transformer side inductance and the dead resistance of net side inductance.

6. the control method of the grid-connected voltage source inverter stability of a system of improvement according to claim 4, is characterized in that, the s territory transfer function G of PR controller _cs the expression formula of () is:

$G_c\left(s\right)=k_p+\frac{k_r\&CenterDot;s}{s^2+{{\mathrm{\&omega;}}_0}^2}$

Wherein, k _pand k _rbe respectively proportionality coefficient and the resonance coefficient of PR controller.

7. the control method of the grid-connected voltage source inverter stability of a system of improvement according to claim 4, is characterized in that, the s territory transfer function G of current transformer PWM link time delay _ds the expression formula of () is:

$G_d\left(s\right)=e^{-1.5T_{s}s}$

Wherein, T _sfor the sampling period of system.

8. the control method of the grid-connected voltage source inverter stability of a system of improvement according to claim 1, is characterized in that, the s territory transfer function G of lag compensation link _ls the expression formula of () is:

$G_l\left(s\right)=\frac{1+{\mathrm{\&tau;}}_{1}s}{1+{\mathrm{\&tau;}}_{2}s}$

Wherein, τ ₁determine compensation tache dead-center position, τ ₂determine compensation tache pole location, ${\mathrm{\&omega;}}_2<\frac{1}{{\mathrm{\&tau;}}_2}<{\mathrm{\&omega;}}_r.$

9. the control method of the grid-connected voltage source inverter stability of a system of improvement according to claim 8, is characterized in that, step 3) concrete operations be:

By step 2) the s territory transfer function G of lag compensation link that obtains _ls () discretization, obtains the s territory transfer function G of lag compensation link _ls () representation in digitial controller is:

$y\left(k\right)=\frac{T_s+2{\mathrm{\&tau;}}_1}{T_s+2{\mathrm{\&tau;}}_2}x\left(k\right)+\frac{T_s-2{\mathrm{\&tau;}}_1}{T_s+2{\mathrm{\&tau;}}_2}x(k-1)-\frac{T_s-2{\mathrm{\&tau;}}_2}{T_s+2{\mathrm{\&tau;}}_2}y(k-1)$

Wherein, x (k) is for lag compensation link is in the input in a kth sampling period, and y (k) is for lag compensation link is in the output in a kth sampling period; X (k-1) is for lag compensation link is in the input in-1 sampling period of kth; Y (k-1) is for lag compensation link is in the output in-1 sampling period of kth;

By step 1) the current transformer modulating wave initial order v that obtains _{ca0_ref}, v _{cb0_ref}and v _{cc0_ref}input x (k) as lag compensation link is brought in above formula, obtains y ₁(k), y ₂(k) and y ₃k (), then by y ₁(k), y ₂(k) and y ₃k () is successively as the modulating wave command value v that current transformer is final _{ca_ref}, v _{cb_ref}and v _{cc_ref}.