阅读说明：本技术 一种三相负载不平衡条件下的逆变器前馈控制方法及系统 (Inverter feed-forward control method and system under three-phase load unbalance condition ) 是由 罗珊娜 彭开香 胡长斌 周京华 朴政国 景柳铭 于 2020-09-14 设计创作，主要内容包括：本发明公开一种三相负载不平衡条件下的逆变器前馈控制方法及系统,方法包括：根据dq坐标系下的电感电流和滤波电容电压确定dq坐标系下的电容电压的残差；根据dq坐标系下的电容电压的残差确定dq坐标系下的电压补偿量；根据dq坐标系下的电压补偿量确定dq坐标系下的电流补偿量；根据dq坐标系下的电压补偿量、电流补偿量、电感电流和滤波电容电压确定dq坐标系下的输出电压参考值；对dq坐标系下的输出电压参考值进行反坐标变换,生成PWM驱动信号,以使对逆变器中的开关管进行控制。本发明针对不平衡负载对逆变系统的扰动作用进行抵消,从而保证逆变器维持三相平衡的输出电压,不仅实现消除三相不平衡现象,还提高了控制精度和响应速度。(The invention discloses a feedforward control method and a feedforward control system for an inverter under a three-phase load unbalance condition, wherein the method comprises the following steps: determining a residual error of the capacitor voltage under the dq coordinate system according to the inductive current and the filter capacitor voltage under the dq coordinate system; determining a voltage compensation quantity in the dq coordinate system according to a residual error of the capacitor voltage in the dq coordinate system; determining a current compensation quantity in the dq coordinate system according to the voltage compensation quantity in the dq coordinate system; determining an output voltage reference value under the dq coordinate system according to the voltage compensation quantity, the current compensation quantity, the inductive current and the filter capacitor voltage under the dq coordinate system; and performing inverse coordinate transformation on the output voltage reference value in the dq coordinate system to generate a PWM (pulse-width modulation) driving signal so as to control a switching tube in the inverter. The invention counteracts the disturbance action of the unbalanced load on the inverter system, thereby ensuring that the inverter maintains three-phase balanced output voltage, not only realizing the elimination of the three-phase unbalance phenomenon, but also improving the control precision and the response speed.)

1. A feed-forward control method for an inverter under a three-phase load imbalance condition, the method comprising:

step S1: considering parasitic resistance in the dq coupling effect inductor, and constructing a mathematical model of the LC filter under a dq rotation coordinate system according to kirchhoff's theorem;

step S2: deriving an analytic expression of three-phase inductive current and filter capacitor voltage according to the mathematical model of the LC filter to obtain inductive current I under dq coordinate system_ldqAnd the filter capacitor voltage v_odq；

Step S3: according to the inductive current I in dq coordinate system_ldqAnd the filter capacitor voltage v_odqDetermining the residual r of the capacitor voltage in dq coordinate system_vodq；

Step S4: residual r according to the capacitor voltage in dq coordinate system_vodqDetermining a voltage compensation u in dq coordinate system_rvodq；

Step S5: according to the voltage compensation quantity u under the dq coordinate system_rvodqDetermining a current compensation u in dq coordinate system_rIldq；

Step S6: according to the voltage compensation quantity u under the dq coordinate system_rvodqCurrent compensation amount u_rIldqInductor current I_ldqAnd the filter capacitor voltage v_odqDetermining an output voltage reference value in dq coordinate system

Step S7: for output voltage reference value under dq coordinate systemPerforming inverse coordinate transformation to generate a PWM driving signal;

step S8: and controlling a switching tube in the inverter according to the PWM driving signal.

2. The feedforward control method of the inverter under the condition of the three-phase load imbalance according to claim 1, wherein a mathematical model of the LC filter under the dq rotation coordinate system is constructed according to kirchhoff's theorem in consideration of parasitic resistance in the dq coupling inductance, and the concrete formula is as follows:

wherein: omega denotes the angular frequency, R_fRepresenting the filter parasitic resistance, L_fRepresenting filter inductance, C_fRepresenting filter capacitance, v_odRepresenting the filter capacitor voltage, v, on the d-axis_oqRepresenting the filter capacitor voltage on the q-axis, I_ldRepresenting the inductor current on the d-axis, I_lqRepresenting the inductive current in the q-axis, v_idRepresenting the output voltage, v, of a three-phase inverter on the d-axis_iqRepresenting the output voltage of a three-phase inverter on the q-axis, I_odRepresenting the load current on the d-axis, I_oqRepresenting the load current on the q-axis.

3. Inverter feed-forward control method under three-phase load unbalance condition according to claim 2, characterized in that the inductor current I according to dq coordinate system_ldqAnd the filter capacitor voltage v_odqDetermining the residual r of the capacitor voltage in dq coordinate system_vodqThe method specifically comprises the following steps:

step S41: according to the inductive current I in dq coordinate system_ldqAnd the filter capacitor voltage v_odqAnd constructing a state space equivalent model of the LC filter, wherein the specific formula is as follows:

wherein: x is the number of_d,qRepresenting a state variable, x_d,q＝[I_ld I_lq v_od v_oq]^T，u_d,qRepresenting input variables, u_d,q＝[v_id v_iq]^T，d_d,qRepresenting disturbance input quantity, d_d,q＝[I_od I_oq]^T，y_d,qRepresenting an output variable, y_d,q＝[I_ld I_lq v_od v_oq]^TCoefficient matrix A, B₁、B₂、C、D₁、D₂Respectively as follows:

step S42: under a dq axis rotating coordinate system, establishing disturbance of an LC filter circuit, wherein the specific formula is as follows:

wherein: v. of_od、v_oq、v_o0Respectively the filter capacitor voltage on the d axis, the filter capacitor voltage on the q axis and the filter capacitor voltage on the zero sequence,respectively represent the voltage amplitudes of the filter capacitors on the d axis, the q axis and the zero sequence, alpha_P、α_N、α₀And the initial phase angles of the filter capacitor voltage on the d axis, the q axis and the zero sequence are respectively represented.

Step S43: determining residual r of capacitor voltage under dq coordinate system according to state space equivalent model of LC filter by using disturbance of LC filter circuit as input_vodqThe concrete formula is as follows:

wherein, I_odRepresenting the load current on the d-axis, I_oqRepresenting the load current on the q-axis, r_IlqRepresenting the residual of the inductor current on the q-axis, r_IldRepresenting the residual of the inductor current on the d-axis, r_vodRepresenting the residual of the capacitor voltage on the d-axis, r_voqResidual error representing the capacitance voltage on the q-axis, e_vodRepresenting the filter capacitor voltage error on the d-axis, e_voqRepresenting the filter capacitor voltage error on the q-axis, e_IldRepresenting the inductor current error on the d-axis, e_IlqRepresenting the inductor current error on the q-axis, L represents the gain matrix obtained by pole placement,representing the filter capacitor voltage reference on the d-axis,representing the filter capacitor voltage reference on the q-axis,representing the inductor current reference on the d-axis,representing the reference value of the inductor current on the q-axis, I_ldRepresenting the inductor current on the d-axis, I_lqRepresenting the inductor current on the q-axis.

4. A feed forward control system for an inverter under three phase load imbalance conditions, the system comprising:

the first abc-dq coordinate converter is used for carrying out dq coordinate conversion on the three-phase inductive current acquired according to the mathematical model of the LC filter to acquire the inductive current in a dq coordinate system;

the second abc-dq coordinate converter is used for carrying out dq coordinate conversion on the three-phase filter capacitor voltage obtained according to the mathematical model of the LC filter to obtain the filter capacitor voltage under a dq coordinate system;

a disturbance observer for observing the inductive current I in dq coordinate system_ldqAnd the filter capacitor voltage v_odqDetermining the residual r of the capacitor voltage in dq coordinate system_vodq；

A parameter matrix for residual r of the capacitor voltage according to dq coordinate system_vodqDetermining a voltage compensation u in dq coordinate system_rvodq；

An inductance model for compensating the amount u according to the voltage in dq coordinate system_rvodqDetermining a current compensation u in dq coordinate system_rIldq；

A voltage controller with feedforward compensation control for compensating the voltage u according to the voltage in dq coordinate system_rvodqCurrent compensation amount u_rIldqInductor current I_ldqAnd the filter capacitor voltage v_odqDetermining an output voltage reference value in dq coordinate system

A PWM drive signal generation unit for generating an output voltage reference value in dq coordinate systemAnd performing inverse coordinate transformation to generate a PWM driving signal so as to control a switching tube in the inverter according to the PWM driving signal.

5. The feed-forward control system for the inverter under the three-phase load imbalance condition according to claim 4, wherein the PWM driving signal generator specifically comprises:

a dq-abc coordinate converter for converting the output voltage reference value in dq coordinate systemCarrying out inverse coordinate transformation;

a PWM drive signal generator for generating a PWM drive signal according to the output voltage reference value after the inverse coordinate transformationA PWM drive signal is generated.

6. The feed-forward control system for an inverter under three-phase load imbalance condition of claim 5, wherein the inductance model comprises:

a first comparator for compensating the voltage u on the d-axis_rvodAnd a first compensation parameter u'_dAnd comparing to obtain a first compensation error, wherein the specific formula is as follows: u ═ u_rvod+u′_d(ii) a Wherein Δ u' represents a first compensation error;

a first integral controller for determining a current compensation amount u on the d-axis according to the first compensation error Δ u_rIldThe concrete formula is as follows:

wherein R is_fRepresenting the filter parasitic resistance, L_fRepresenting a filter inductance;

a first proportional controller for compensating the current compensation amount u on the q-axis_rIlqAmplifying to obtain a first compensation parameter u'_dThe concrete formula is as follows:

u′_d＝L_fωu_rIlq(ii) a Wherein ω represents an angular frequency;

a second comparator for compensating the voltage on the q-axis by an amount u_rvoqAnd a second compensation parameter u'_qAnd comparing to obtain a second compensation error, wherein the specific formula is as follows: u ″, Δ u ═ u_rvoq+u′_q(ii) a Wherein Δ u "represents a second compensation error;

a second integral controller for determining a current compensation amount u on the q-axis according to the second compensation error Δ u ″_rIlqThe concrete formula is as follows:

a second proportional controller for compensating the current on the d-axis by an amount u_rIldAmplifying to obtain a second compensation parameter u'_qThe concrete formula is as follows:

u′_q＝Lfωu_rIld。

7. the feed-forward control system for the inverter under the three-phase load imbalance condition according to claim 4, wherein the voltage controller with the feed-forward compensation control specifically comprises:

a third comparator, a fourth comparator, a fifth comparator, a sixth comparator, a seventh comparator, an eighth comparator, a ninth comparator, a tenth comparator, a first PI controller, a second PI controller, a third PI controller, a fourth PI controller, a third ratio controller, a fourth ratio controller, a fifth ratio controller and a sixth ratio controller, wherein the third comparator is respectively connected with the dq-abc coordinate converter, the parameter matrix, the third ratio controller and the first PI controller, the fourth comparator is respectively connected with the dq-abc coordinate converter, the fourth ratio controller, the parameter matrix, the fourth ratio controller and the second PI controller, and the fifth comparator is respectively connected with the first abc-dq coordinate converter, the fourth ratio controller and the first PI controller, the sixth comparator is connected to the first abc-dq coordinate converter, the third ratio controller, and the second PI controller, respectively, the seventh comparator is connected to the inductance model, the fifth ratio controller, the fifth comparator, and the third PI controller, respectively, the eighth comparator is connected to the inductance model, the sixth ratio controller, the sixth comparator, and the fourth PI controller, respectively, the ninth comparator is connected to the second abc-dq coordinate converter, the sixth ratio controller, and the third PI controller, respectively, and the tenth comparator is connected to the second abc-dq coordinate converter, the fifth ratio controller, and the fourth PI controller, respectively.

8. The feed-forward control system for an inverter under a three-phase load imbalance condition of claim 7, wherein the coefficients of the third and fourth proportional controllers are both ω C_f(ii) a The fifth and sixth proportional controllers are both ω L_fWhere ω denotes the angular frequency, L_fRepresenting filter inductance, C_fRepresenting the filter capacitance.

9. The feed-forward control system for the inverter under the three-phase load imbalance condition of claim 4, wherein the mathematical model of the LC filter is specifically represented by the formula:

wherein: omega denotes the angular frequency, R_fRepresenting the filter parasitic resistance, L_fRepresenting filter inductance, C_fRepresenting filter capacitance, v_odRepresenting the filter capacitor voltage, v, on the d-axis_oqRepresenting the filter capacitor voltage on the q-axis, I_ldRepresenting the inductor current on the d-axis, I_lqRepresenting the inductive current in the q-axis, v_idRepresenting the output voltage, v, of a three-phase inverter on the d-axis_iqRepresenting the output voltage of a three-phase inverter on the q-axis, I_odRepresenting the load current on the d-axis, I_oqRepresenting the load current on the q-axis.

10. A feed-forward control system for an inverter under a three-phase load imbalance condition as claimed in claim 9, wherein the disturbance observer specifically comprises:

a state space equivalent model construction module for constructing the inductance current I according to the dq coordinate system_ldqAnd the filter capacitor voltage v_odqAnd constructing a state space equivalent model of the LC filter, wherein the specific formula is as follows:

wherein: x is the number of_d,qRepresenting a state variable, x_d,q＝[I_ld I_lq v_od v_oq]^T，u_d,qRepresenting input variables, u_d,q＝[v_id v_iq]^T，d_d,qRepresenting disturbance input quantity, d_d,q＝[I_od I_oq]^T，y_d,qRepresenting an output variable, y_d,q＝[I_ld I_lq v_od v_oq]^TCoefficient matrix A, B₁、B₂、C、D₁、D₂Respectively as follows:

the disturbance construction module is used for establishing disturbance of the LC filter circuit under a dq axis rotating coordinate system, and the specific formula is as follows:

wherein: v. of_od、v_oq、v_o0Respectively the filter capacitor voltage on the d axis, the filter capacitor voltage on the q axis and the filter capacitor voltage on the zero sequence,respectively represent the voltage amplitudes of the filter capacitors on the d axis, the q axis and the zero sequence, alpha_P、α_N、α₀And the initial phase angles of the filter capacitor voltage on the d axis, the q axis and the zero sequence are respectively represented.

A residual constructing module for determining the residual r of the capacitor voltage under the dq coordinate system according to the state space equivalent model of the LC filter by taking the disturbance of the LC filter circuit as input_vodqThe concrete formula is as follows:

wherein, I_odRepresenting the load current on the d-axis, I_oqRepresenting the load current on the q-axis, r_IlqRepresenting the residual of the inductor current on the q-axis, r_IldRepresenting the residual of the inductor current on the d-axis, r_vodRepresenting the residual of the capacitor voltage on the d-axis, r_voqResidual error representing the capacitance voltage on the q-axis, e_vodRepresenting the filter capacitor voltage error on the d-axis, e_voqRepresenting the filter capacitor voltage error on the q-axis, e_IldRepresenting the inductor current error on the d-axis, e_IlqRepresenting the inductor current error on the q-axis, L represents the gain matrix obtained by pole placement,representing the filter capacitor voltage reference on the d-axis,representing the filter capacitor voltage reference on the q-axis,representing the inductor current reference on the d-axis,representing the reference value of the inductor current on the q-axis, I_ldRepresenting the inductor current on the d-axis,I_lqrepresenting the inductor current on the q-axis.

Technical Field

The invention relates to the technical field, in particular to a feed-forward control method and a feed-forward control system for an inverter under a three-phase load unbalance condition.

Background

In the field of inverter control of a microgrid, the unbalanced phenomenon of the output voltage of the microgrid inverter is very common due to the existence of a large amount of single-phase loads and the occurrence of short-circuit or open circuit asymmetric faults. The existence of three-phase imbalance in a low-voltage power system can affect the use of single-phase electric equipment such as lighting equipment, household appliances and the like, and can cause that the equipment cannot normally run due to insufficient voltage of the electric equipment or damage is caused due to overhigh voltage; the capacity utilization rate of the generator and the transformer is easily reduced due to the unbalanced voltage; voltage imbalances may cause additional harmonic currents to be generated by the converter equipment; the unbalanced voltage can also reduce the insulation life of the motor and increase the line loss rate. The three-phase unbalance index is one of the important indexes of the power quality. A series of hazards can be caused by the excessive unbalance of the three phases, and are definitely specified in the national standard 'three-phase voltage unbalance of electric energy quality': when the power grid normally operates, the voltage unbalance degree cannot exceed 2%, and the short-term voltage unbalance degree cannot exceed 4%. The reduction of the unbalance degree of the three-phase voltage is important for ensuring the stable operation of the micro-grid.

Under the influence of the unbalanced voltage, a higher negative-sequence component (i.e., the q-axis upper component) appears in the grid. The CN105490291A respectively calculates the power of each single-phase system through an inverter droop control method and sums the power to obtain the total demand of the active power and the reactive power of the unbalanced load of the whole three-phase inverter, thereby realizing the effect of resisting the three-phase unbalanced load. CN107508298A proposes a hierarchical optimization control method for unbalanced voltages of a micro-grid, which introduces a multi-agent structure to realize system coordination optimization control, wherein the first compensation of asymmetric voltages is realized by local negative sequence voltage droop control, and the second compensation is realized by second coordination optimization control. CN107493024A controls the negative sequence current by detecting the negative sequence current component and adopting the internal model principle of PR resonance controller, thus realizing the elimination of the voltage unbalance of the three-phase PWM rectifier. But the scheme has low control precision and slow response speed.

Disclosure of Invention

Based on this, the present invention provides a feedforward control method and system for an inverter under a three-phase load imbalance condition to eliminate the phenomenon of unbalanced output voltage of the inverter caused by the three-phase load imbalance.

In order to achieve the above object, the present invention provides a feed-forward control method for an inverter under a three-phase load imbalance condition, the method comprising:

step S1: considering parasitic resistance in the dq coupling effect inductor, and constructing a mathematical model of the LC filter under a dq rotation coordinate system according to kirchhoff's theorem;

step S2: deriving an analytic expression of three-phase inductive current and filter capacitor voltage according to the mathematical model of the LC filter to obtain inductive current I under dq coordinate system_ldqAnd the filter capacitor voltage v_odq；

Step S3: according to the inductive current I in dq coordinate system_ldqAnd the filter capacitor voltage v_odqDetermining the residual r of the capacitor voltage in dq coordinate system_vodq；

Step S4: residual r according to the capacitor voltage in dq coordinate system_vodqDetermining a voltage compensation u in dq coordinate system_rvodq；

Step S5: according to the voltage compensation quantity u under the dq coordinate system_rvodqDetermining a current compensation u in dq coordinate system_rIldq；

Step S6: according to the voltage compensation quantity u under the dq coordinate system_rvodqCurrent compensation amount u_rIldqInductor current I_ldqAnd the filter capacitor voltage v_odqDetermining dq seatingOutput voltage reference under the standard

Step S7: for output voltage reference value under dq coordinate systemPerforming inverse coordinate transformation to generate a PWM driving signal;

step S8: and controlling a switching tube in the inverter according to the PWM driving signal.

Optionally, a mathematical model of the LC filter in the dq rotation coordinate system is constructed according to kirchhoff's theorem in consideration of parasitic resistance in the dq coupling inductance, and the specific formula is as follows:

wherein: omega denotes the angular frequency, R_fRepresenting the filter parasitic resistance, L_fRepresenting filter inductance, C_fRepresenting filter capacitance, v_odRepresenting the filter capacitor voltage, v, on the d-axis_oqRepresenting the filter capacitor voltage on the q-axis, I_ldRepresenting the inductor current on the d-axis, I_lqRepresenting the inductive current in the q-axis, v_idRepresenting the output voltage, v, of a three-phase inverter on the d-axis_iqRepresenting the output voltage of a three-phase inverter on the q-axis, I_odRepresenting the load current on the d-axis, I_oqRepresenting the load current on the q-axis.

Optionally, the inductor current I according to the dq coordinate system_ldqAnd the filter capacitor voltage v_odqDetermining the residual r of the capacitor voltage in dq coordinate system_vodqThe method specifically comprises the following steps:

step S41: according to the inductive current I in dq coordinate system_ldqAnd the filter capacitor voltage v_odqAnd constructing a state space equivalent model of the LC filter, wherein the specific formula is as follows:

wherein: x is the number of_d,qRepresenting a state variable, x_d,q＝[I_ld I_lq v_od v_oq]^T，u_d,qRepresenting input variables, u_d,q＝[v_idv_iq]^T，d_d,qRepresenting disturbance input quantity, d_d,q＝[I_od I_oq]^T，y_d,qRepresenting an output variable, y_d,q＝[I_ld I_lq v_od v_oq]^TCoefficient matrix A, B₁、B₂、C、D₁、D₂Respectively as follows:

step S42: under a dq axis rotating coordinate system, establishing disturbance of an LC filter circuit, wherein the specific formula is as follows:

wherein: v. of_od、v_oq、v_o0Respectively the filter capacitor voltage on the d axis, the filter capacitor voltage on the q axis and the filter capacitor voltage on the zero sequence,respectively represent the voltage amplitudes of the filter capacitors on the d axis, the q axis and the zero sequence, alpha_P、α_N、α₀And the initial phase angles of the filter capacitor voltage on the d axis, the q axis and the zero sequence are respectively represented.

Step S43: with disturbance of LC filter circuit as input, according to the shape of LC filterDetermining residual r of capacitor voltage under dq coordinate system by state space equivalent model_vodqThe concrete formula is as follows:

wherein, I_odRepresenting the load current on the d-axis, I_oqRepresenting the load current on the q-axis, r_IlqRepresenting the residual of the inductor current on the q-axis, r_IldRepresenting the residual of the inductor current on the d-axis, r_vodRepresenting the residual of the capacitor voltage on the d-axis, r_voqResidual error representing the capacitance voltage on the q-axis, e_vodRepresenting the filter capacitor voltage error on the d-axis, e_voqRepresenting the filter capacitor voltage error on the q-axis, e_IldRepresenting the inductor current error on the d-axis, e_IlqRepresenting the inductor current error on the q-axis, L represents the gain matrix obtained by pole placement,representing the filter capacitor voltage reference on the d-axis,representing the filter capacitor voltage reference on the q-axis,representing the inductor current reference on the d-axis,representing the reference value of the inductor current on the q-axis, I_ldRepresenting the inductor current on the d-axis, I_lqRepresenting the inductor current on the q-axis.

The invention also provides a feed-forward control system of an inverter under the condition of three-phase load unbalance, which comprises the following components:

the first abc-dq coordinate converter is used for carrying out dq coordinate conversion on the three-phase inductive current acquired according to the mathematical model of the LC filter to acquire the inductive current in a dq coordinate system;

the second abc-dq coordinate converter is used for carrying out dq coordinate conversion on the three-phase filter capacitor voltage obtained according to the mathematical model of the LC filter to obtain the filter capacitor voltage under a dq coordinate system;

a disturbance observer for observing the inductive current I in dq coordinate system_ldqAnd the filter capacitor voltage v_odqDetermining the residual r of the capacitor voltage in dq coordinate system_vodq；

A parameter matrix for residual r of the capacitor voltage according to dq coordinate system_vodqDetermining a voltage compensation u in dq coordinate system_rvodq；

An inductance model for compensating the amount u according to the voltage in dq coordinate system_rvodqDetermining a current compensation u in dq coordinate system_rIldq；

A voltage controller with feedforward compensation control for compensating the voltage u according to the voltage in dq coordinate system_rvodqCurrent compensation amount u_rIldqInductor current I_ldqAnd the filter capacitor voltage v_odqDetermining an output voltage reference value in dq coordinate system

A PWM drive signal generation unit for generating an output voltage reference value in dq coordinate systemAnd performing inverse coordinate transformation to generate a PWM driving signal so as to control a switching tube in the inverter according to the PWM driving signal.

Optionally, the PWM driving signal generator specifically includes:

a dq-abc coordinate converter for converting the output voltage reference value in dq coordinate systemCarrying out inverse coordinate transformation;

a PWM drive signal generator for generating a PWM drive signal according to the output voltage reference value after the inverse coordinate transformationA PWM drive signal is generated.

Optionally, the inductance model comprises:

a first comparator for compensating the voltage u on the d-axis_rvodAnd a first compensation parameter u'_dAnd comparing to obtain a first compensation error, wherein the specific formula is as follows: u ═ u_rvod+u′_d(ii) a Wherein Δ u' represents a first compensation error;

a first integral controller for determining a current compensation amount u on the d-axis according to the first compensation error Δ u_rIldThe concrete formula is as follows:

wherein R is_fRepresenting the filter parasitic resistance, L_fRepresenting a filter inductance;

a first proportional controller for compensating the current compensation amount u on the q-axis_rIlqAmplifying to obtain a first compensation parameter u'_dThe concrete formula is as follows:

u′_d＝L_fωu_rIlq(ii) a Wherein ω represents an angular frequency;

a second comparator for compensating the voltage on the q-axis by an amount u_rvoqAnd a second compensation parameter u'_qAnd comparing to obtain a second compensation error, wherein the specific formula is as follows: u ″, Δ u ═ u_rvoq+u′_q(ii) a Wherein Δ u "represents a second compensation error;

a second integral controller for determining a current compensation amount u on the q-axis according to the second compensation error Δ u ″_rIlqThe concrete formula is as follows:

a second proportional controller for compensating the current on the d-axis by an amount u_rIldAmplifying to obtain a second compensation parameter u'_qThe concrete formula is as follows:

u′_q＝Lfωu_rIld。

optionally, the voltage controller with feedforward compensation control specifically includes:

a third comparator, a fourth comparator, a fifth comparator, a sixth comparator, a seventh comparator, an eighth comparator, a ninth comparator, a tenth comparator, a first PI controller, a second PI controller, a third PI controller, a fourth PI controller, a third ratio controller, a fourth ratio controller, a fifth ratio controller and a sixth ratio controller, wherein the third comparator is respectively connected with the dq-abc coordinate converter, the parameter matrix, the third ratio controller and the first PI controller, the fourth comparator is respectively connected with the dq-abc coordinate converter, the fourth ratio controller, the parameter matrix, the fourth ratio controller and the second PI controller, and the fifth comparator is respectively connected with the first abc-dq coordinate converter, the fourth ratio controller and the first PI controller, the sixth comparator is connected to the first abc-dq coordinate converter, the third ratio controller, and the second PI controller, respectively, the seventh comparator is connected to the inductance model, the fifth ratio controller, the fifth comparator, and the third PI controller, respectively, the eighth comparator is connected to the inductance model, the sixth ratio controller, the sixth comparator, and the fourth PI controller, respectively, the ninth comparator is connected to the second abc-dq coordinate converter, the sixth ratio controller, and the third PI controller, respectively, and the tenth comparator is connected to the second abc-dq coordinate converter, the fifth ratio controller, and the fourth PI controller, respectively.

Optionally, the coefficients of the third and fourth proportional controllers are both ω C_f(ii) a The fifth proportional controller andthe sixth proportional controllers are all omega L_fWhere ω denotes the angular frequency, L_fRepresenting filter inductance, C_fRepresenting the filter capacitance.

Optionally, the mathematical model of the LC filter has a specific formula:

wherein: omega denotes the angular frequency, R_fRepresenting the filter parasitic resistance, L_fRepresenting filter inductance, C_fRepresenting filter capacitance, v_odRepresenting the filter capacitor voltage, v, on the d-axis_oqRepresenting the filter capacitor voltage on the q-axis, I_ldRepresenting the inductor current on the d-axis, I_lqRepresenting the inductive current in the q-axis, v_idRepresenting the output voltage, v, of a three-phase inverter on the d-axis_iqRepresenting the output voltage of a three-phase inverter on the q-axis, I_odRepresenting the load current on the d-axis, I_oqRepresenting the load current on the q-axis.

Optionally, the disturbance observer specifically includes:

a state space equivalent model construction module for constructing the inductance current I according to the dq coordinate system_ldqAnd the filter capacitor voltage v_odqAnd constructing a state space equivalent model of the LC filter, wherein the specific formula is as follows:

wherein: x is the number of_d,qRepresenting a state variable, x_d,q＝[I_ld I_lq v_od v_oq]^T，u_d,qRepresenting input variables, u_d,q＝[v_idv_iq]^T，d_d,qRepresenting disturbance input quantity, d_d,q＝[I_od I_oq]^T，y_d,qRepresenting an output variable, y_d,q＝[I_ld I_lq v_od v_oq]^TIs a system ofNumber matrix A, B₁、B₂、C、D₁、D₂Respectively as follows:

the disturbance construction module is used for establishing disturbance of the LC filter circuit under a dq axis rotating coordinate system, and the specific formula is as follows:

wherein: v. of_od、v_oq、v_o0Respectively the filter capacitor voltage on the d axis, the filter capacitor voltage on the q axis and the filter capacitor voltage on the zero sequence,respectively represent the voltage amplitudes of the filter capacitors on the d axis, the q axis and the zero sequence, alpha_P、α_N、α₀And the initial phase angles of the filter capacitor voltage on the d axis, the q axis and the zero sequence are respectively represented.

A residual constructing module for determining the residual r of the capacitor voltage under the dq coordinate system according to the state space equivalent model of the LC filter by taking the disturbance of the LC filter circuit as input_vodqThe concrete formula is as follows:

wherein, I_odRepresenting the load current on the d-axis，I_oqRepresenting the load current on the q-axis, r_IlqRepresenting the residual of the inductor current on the q-axis, r_IldRepresenting the residual of the inductor current on the d-axis, r_vodRepresenting the residual of the capacitor voltage on the d-axis, r_voqResidual error representing the capacitance voltage on the q-axis, e_vodRepresenting the filter capacitor voltage error on the d-axis, e_voqRepresenting the filter capacitor voltage error on the q-axis, e_IldRepresenting the inductor current error on the d-axis, e_IlqRepresenting the inductor current error on the q-axis, L represents the gain matrix obtained by pole placement,representing the filter capacitor voltage reference on the d-axis,representing the filter capacitor voltage reference on the q-axis,representing the inductor current reference on the d-axis,representing the reference value of the inductor current on the q-axis, I_ldRepresenting the inductor current on the d-axis, I_lqRepresenting the inductor current on the q-axis.

According to the specific embodiment provided by the invention, the invention discloses the following technical effects:

the invention discloses a feedforward control method and a feedforward control system for an inverter under a three-phase load unbalance condition, wherein the method comprises the following steps: determining a residual error of the capacitor voltage under the dq coordinate system according to the inductive current and the filter capacitor voltage under the dq coordinate system; determining a voltage compensation quantity in the dq coordinate system according to a residual error of the capacitor voltage in the dq coordinate system; determining a current compensation quantity in the dq coordinate system according to the voltage compensation quantity in the dq coordinate system; determining an output voltage reference value under the dq coordinate system according to the voltage compensation quantity, the current compensation quantity, the inductive current and the filter capacitor voltage under the dq coordinate system; and performing inverse coordinate transformation on the output voltage reference value in the dq coordinate system to generate a PWM (pulse-width modulation) driving signal so as to control a switching tube in the inverter. The invention counteracts the disturbance action of the unbalanced load on the inverter system, and effectively compensates the load due to the unbalanced load, thereby ensuring that the inverter can still maintain three-phase balanced output voltage under various unbalanced loads, not only realizing the elimination of the three-phase unbalanced phenomenon, but also improving the control precision and the response speed.

Drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings needed to be used in the embodiments will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and it is obvious for those skilled in the art to obtain other drawings without inventive exercise.

FIG. 1 is a schematic diagram of a prior art three-phase DC-AC inverter system with an LC filter;

FIG. 2 is a block diagram of the overall structure of the feedforward control method of the inverter under the condition of unbalanced three-phase load according to the present invention;

FIG. 3 is a block diagram of the present invention with feed forward current compensation voltage control;

FIG. 4 is a diagram of the compensation effect of the d-axis component of the inverter output voltage obtained by MATLAB/SIMULINK software simulation according to the method of the present invention;

FIG. 5 is a diagram of the compensation effect of the q-axis component of the inverter output voltage obtained by MATLAB/SIMULINK software simulation according to the method of the present invention;

FIG. 6 shows the unbalance before compensation in the MATLAB/SIMULINK software simulation according to the method of the present invention;

FIG. 7 shows the unbalance after compensation in MATLAB/SIMULINK software simulation according to the method of the present invention.

Detailed Description

The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

The invention aims to provide a feedforward control method and a feedforward control system for an inverter under a three-phase load unbalance condition, so as to eliminate the phenomenon of unbalanced output voltage of the inverter caused by the three-phase load unbalance.

In order to make the aforementioned objects, features and advantages of the present invention comprehensible, embodiments accompanied with figures are described in further detail below.

The invention provides a feed-forward control method of an inverter under a three-phase load unbalance condition, which comprises the following steps:

step S1: considering parasitic resistance in the dq coupling effect inductor, and constructing a mathematical model of the LC filter under a dq rotation coordinate system according to kirchhoff's theorem.

Step S2: and deducing analytic expressions of three-phase inductive current and filter capacitor voltage according to the mathematical model of the LC filter to obtain the inductive current and the filter capacitor voltage under the dq coordinate system.

Step S3: according to the inductive current I in dq coordinate system_ldqAnd the filter capacitor voltage v_odqDetermining the residual r of the capacitor voltage in dq coordinate system_vodq。

Step S4: residual r according to the capacitor voltage in dq coordinate system_vodqDetermining a voltage compensation u in dq coordinate system_rvodq。

Step S5: according to the voltage compensation quantity u under the dq coordinate system_rvodqDetermining a current compensation u in dq coordinate system_rIldq。

Step S6: according to the voltage compensation quantity u under the dq coordinate system_rvodqCurrent compensation amount u_rIldqInductor current I_ldqAnd the filter capacitor voltage v_odqDetermining an output voltage reference value in dq coordinate system

Step S7: for output voltage reference value under dq coordinate systemAnd performing inverse coordinate transformation to generate a PWM driving signal.

Step S8: and controlling a switching tube in the inverter according to the PWM driving signal.

The individual steps are discussed in detail below:

as an optional implementation manner, in the invention, a mathematical model of the LC filter in the dq rotation coordinate system is constructed according to kirchhoff's theorem in consideration of parasitic resistance in the dq coupling inductance, and a specific formula is as follows:

wherein: omega denotes the angular frequency, R_fRepresenting the filter parasitic resistance, L_fRepresenting filter inductance, C_fRepresenting filter capacitance, v_odRepresenting the filter capacitor voltage, v, on the d-axis_oqRepresenting the filter capacitor voltage on the q-axis, I_ldRepresenting the inductor current on the d-axis, I_lqRepresenting the inductive current in the q-axis, v_idRepresenting the output voltage, v, of a three-phase inverter on the d-axis_iqRepresenting the output voltage of a three-phase inverter on the q-axis, I_odRepresenting the load current on the d-axis, I_oqRepresenting the inductor current on the q-axis.

As an alternative embodiment, the invention provides that the inductor current I is based on the dq coordinate system_ldqAnd the filter capacitor voltage v_odqDetermining the residual r of the capacitor voltage in dq coordinate system_vodqThe method specifically comprises the following steps:

step S41: according to the inductive current I in dq coordinate system_ldqAnd the filter capacitor voltage v_odqAnd constructing a state space equivalent model of the LC filter, wherein the specific formula is as follows:

wherein: x is the number of_d,qRepresenting a state variable, x_d,q＝[I_ld I_lq v_od v_oq]^T，u_d,qRepresenting input variables, u_d,q＝[v_idv_iq]^T，d_d,qRepresenting disturbance input quantity, d_d,q＝[I_od I_oq]^T，y_d,qRepresenting an output variable, y_d,q＝[I_ld I_lq v_od v_oq]^TCoefficient matrix A, B₁、B₂、C、D₁、D₂Respectively as follows:

step S42: under a dq axis rotating coordinate system, establishing disturbance of an LC filter circuit, wherein the specific formula is as follows:

wherein: v. of_od、v_oq、v_o0Respectively the filter capacitor voltage on the d axis, the filter capacitor voltage on the q axis and the filter capacitor voltage on the zero sequence,respectively represent the voltage amplitudes of the filter capacitors on the d axis, the q axis and the zero sequence, alpha_P、α_N、α₀And the initial phase angles of the filter capacitor voltage on the d axis, the q axis and the zero sequence are respectively represented.

Step S43: determining residual error of capacitor voltage under dq coordinate system according to state space equivalent model of LC filter by using disturbance of LC filter circuit as inputr_vodqThe concrete formula is as follows:

wherein, I_odRepresenting the load current on the d-axis, I_oqRepresenting the load current on the q-axis, r_IlqRepresenting the residual of the inductor current on the q-axis, r_IldRepresenting the residual of the inductor current on the d-axis, r_vodRepresenting the residual of the capacitor voltage on the d-axis, r_voqResidual error representing the capacitance voltage on the q-axis, e_vodRepresenting the filter capacitor voltage error on the d-axis, e_voqRepresenting the filter capacitor voltage error on the q-axis, e_IldRepresenting the inductor current error on the d-axis, e_IlqRepresenting the inductor current error on the q-axis, L represents the gain matrix obtained by pole placement,representing the filter capacitor voltage reference on the d-axis,representing the filter capacitor voltage reference on the q-axis,representing the inductor current reference on the d-axis,representing the reference value of the inductor current on the q-axis, I_ldRepresenting the inductor current on the d-axis, I_lqRepresenting the inductor current on the q-axis.

As shown in fig. 2, the present invention further provides a feed-forward control system for an inverter under a three-phase load imbalance condition, the system comprising:

and the first abc-dq coordinate converter is used for carrying out dq coordinate conversion on the three-phase inductive current acquired according to the mathematical model of the LC filter to acquire the inductive current in a dq coordinate system.

And the second abc-dq coordinate converter is used for carrying out dq coordinate conversion on the three-phase filter capacitor voltage acquired according to the mathematical model of the LC filter to acquire the filter capacitor voltage under a dq coordinate system.

A disturbance observer for observing the inductive current I in dq coordinate system_ldqAnd the filter capacitor voltage v_odqDetermining the residual r of the capacitor voltage in dq coordinate system_vodq。

A parameter matrix for residual r of the capacitor voltage according to dq coordinate system_vodqDetermining a voltage compensation u in dq coordinate system_rvodq。

An inductance model for compensating the amount u according to the voltage in dq coordinate system_rvodqDetermining a current compensation u in dq coordinate system_rIldq。

A voltage controller with feedforward compensation control for compensating the voltage u according to the voltage in dq coordinate system_rvodqCurrent compensation amount u_rIldqInductor current I_ldqAnd the filter capacitor voltage v_odqDetermining an output voltage reference value in dq coordinate system

A PWM drive signal generation unit for generating an output voltage reference value in dq coordinate systemAnd performing inverse coordinate transformation to generate a PWM driving signal so as to control a switching tube in the inverter according to the PWM driving signal.

As an embodiment, the PWM driving signal generator of the present invention specifically includes:

a dq-abc coordinate converter for converting the output voltage reference value in dq coordinate systemAnd performing inverse coordinate transformation.

A PWM drive signal generator for generating a PWM drive signal according to the output voltage reference value after the inverse coordinate transformationA PWM drive signal is generated.

As an embodiment, the inductance model of the present invention includes:

a first comparator for compensating the voltage u on the d-axis_rvodAnd a first compensation parameter u'_dAnd comparing to obtain a first compensation error, wherein the specific formula is as follows: u ═ u_rvod+u′_d(ii) a Where Δ u' represents the first compensation error.

A first integral controller for determining a current compensation amount u on the d-axis according to the first compensation error Δ u_rIldThe concrete formula is as follows:

wherein R is_fRepresenting the filter parasitic resistance, L_fRepresenting the filter inductance.

A first proportional controller for compensating the current compensation amount u on the q-axis_rIlqAmplifying to obtain a first compensation parameter u'_dThe concrete formula is as follows:

u′_d＝L_fωu_rIlq(ii) a Where ω represents the angular frequency.

A second comparator for compensating the voltage on the q-axis by an amount u_rvoqAnd a second compensation parameter u'_qAnd comparing to obtain a second compensation error, wherein the specific formula is as follows: u ″, Δ u ═ u_rvoq+u′_q(ii) a Where Δ u "represents the second compensation error.

A second integral controller for determining a current compensation amount u on the q-axis according to the second compensation error Δ u ″_rIlqThe concrete formula is as follows:

a second proportional controller for compensating the current on the d-axis by an amount u_rIldAmplifying to obtain a second compensation parameter u'_qThe concrete formula is as follows:

u′_q＝Lfωu_rIld。

as shown in fig. 3, the voltage controller with feedforward compensation control according to the present invention specifically includes:

a third comparator, a fourth comparator, a fifth comparator, a sixth comparator, a seventh comparator, an eighth comparator, a ninth comparator, a tenth comparator, a first PI controller, a second PI controller, a third PI controller, a fourth PI controller, a third ratio controller, a fourth ratio controller, a fifth ratio controller and a sixth ratio controller, wherein the third comparator is respectively connected with the dq-abc coordinate converter, the parameter matrix, the third ratio controller and the first PI controller, the fourth comparator is respectively connected with the dq-abc coordinate converter, the fourth ratio controller, the parameter matrix, the fourth ratio controller and the second PI controller, and the fifth comparator is respectively connected with the first abc-dq coordinate converter, the fourth ratio controller and the first PI controller, the sixth comparator is connected to the first abc-dq coordinate converter, the third ratio controller, and the second PI controller, respectively, the seventh comparator is connected to the inductance model, the fifth ratio controller, the fifth comparator, and the third PI controller, respectively, the eighth comparator is connected to the inductance model, the sixth ratio controller, the sixth comparator, and the fourth PI controller, respectively, the ninth comparator is connected to the second abc-dq coordinate converter, the sixth ratio controller, and the third PI controller, respectively, and the tenth comparator is connected to the second abc-dq coordinate converter, the fifth ratio controller, and the fourth PI controller, respectively.

As an embodiment, the coefficients of the third and fourth proportional controllers are ω C_f(ii) a The fifth and sixth proportional controllers are both ω L_fWhere ω denotes the angular frequency, L_fRepresenting filter inductance, C_fRepresenting the filter capacitance.

As an implementation mode, the mathematical model of the LC filter of the present invention has a specific formula:

wherein: omega denotes the angular frequency, R_fRepresenting the filter parasitic resistance, L_fRepresenting filter inductance, C_fRepresenting filter capacitance, v_odRepresenting the filter capacitor voltage, v, on the d-axis_oqRepresenting the filter capacitor voltage on the q-axis, I_ldRepresenting the inductor current on the d-axis, I_lqRepresenting the inductive current in the q-axis, v_idRepresenting the output voltage, v, of a three-phase inverter on the d-axis_iqRepresenting the output voltage of a three-phase inverter on the q-axis, I_odRepresenting the load current on the d-axis, I_oqRepresenting the load current on the q-axis.

As an implementation manner, the disturbance observer of the present invention specifically includes:

a state space equivalent model construction module for constructing the inductance current I according to the dq coordinate system_ldqAnd the filter capacitor voltage v_odqAnd constructing a state space equivalent model of the LC filter, wherein the specific formula is as follows:

wherein: x is the number of_d,qRepresenting a state variable, x_d,q＝[I_ld I_lq v_od v_oq]^T，u_d,qRepresenting input variables, u_d,q＝[v_idv_iq]^T，d_d,qRepresenting disturbance input quantity, d_d,q＝[I_od I_oq]^T，y_d,qRepresenting an output variable, y_d,q＝[I_ld I_lq v_od v_oq]^TCoefficient matrix A, B₁、B₂、C、D₁、D₂Respectively as follows:

the disturbance construction module is used for establishing disturbance of the LC filter circuit under a dq axis rotating coordinate system, and the specific formula is as follows:

wherein: v. of_od、v_oq、v_o0Respectively the filter capacitor voltage on the d axis, the filter capacitor voltage on the q axis and the filter capacitor voltage on the zero sequence,respectively represent the voltage amplitudes of the filter capacitors on the d axis, the q axis and the zero sequence, alpha_P、α_N、α₀And the initial phase angles of the filter capacitor voltage on the d axis, the q axis and the zero sequence are respectively represented.

A residual constructing module for determining the residual r of the capacitor voltage under the dq coordinate system according to the state space equivalent model of the LC filter by taking the disturbance of the LC filter circuit as input_vodqThe concrete formula is as follows:

wherein, I_odRepresenting the load current on the d-axis, I_oqRepresenting the load current on the q-axis, r_IlqRepresenting the residual of the inductor current on the q-axis, r_IldRepresenting the residual of the inductor current on the d-axis, r_vodRepresenting the residual of the capacitor voltage on the d-axis, r_voqResidual error representing the capacitance voltage on the q-axis, e_vodRepresenting the filter capacitor voltage error on the d-axis, e_voqRepresenting the filter capacitor voltage error on the q-axis, e_IldRepresenting the inductor current error on the d-axis, e_IlqRepresenting the inductor current error on the q-axis, L represents the gain matrix obtained by pole placement,representing the filter capacitor voltage reference on the d-axis,representing the filter capacitor voltage reference on the q-axis,representing the inductor current reference on the d-axis,representing the reference value of the inductor current on the q-axis, I_ldRepresenting the inductor current on the d-axis, I_lqRepresenting the inductor current on the q-axis.

According to the method, the thought that the effect of disturbance on the LC filter circuit of the control object and the effect of the compensation signal on the LC filter circuit of the control object are mutually offset is adopted, the compensation signal output by any unbalanced load disturbance on the three-phase inverter is theoretically calculated and offset, the sinusoidal disturbance caused by the three-phase imbalance of the load on the dq axis can be eliminated, the method is easy to realize, the stability of the output of the inverter is improved, and the problem of three-phase imbalance in the microgrid can be well solved.

The invention establishes a disturbance observer by taking disturbance as input and residual error as output, obtains corresponding specific residual error values aiming at different disturbances, and controls the specific residual error values through a feedforward controller. According to the characteristics of the traditional double-closed-loop control of the inverter, after the compensation quantity of the voltage control signal is calculated, the compensation quantity of the current control signal is calculated through an inductance model, the output of the voltage and current double-closed loop is compensated respectively, a new thought is provided for the research of the control strategy of the inverter under the condition of three-phase unbalanced load, the three-phase unbalanced phenomenon can be eliminated, and the control precision and the response speed are improved.

The method is adopted to carry out simulation by MATLAB/SIMULINK software simulation, and the detailed description is shown in fig. 4 and fig. 5 which are d-axis and q-axis voltage simulation waveforms output by the inverter respectively. It can be seen that without the feedforward control method, after the load imbalance of 0.25s occurs, the d-axis voltage and the q-axis voltage generate 2 times of power frequency fluctuation. And when the feedforward control method is used, the 2-time power frequency fluctuation can be eliminated.

Fig. 6 and 7 respectively show the unbalance degree of the three-phase voltage output by the inverter with or without the action of the feed-forward control method. As can be seen from fig. 6, without the feedforward control method, after the load imbalance of 0.25s occurs, the imbalance of the three-phase voltage output by the inverter is 3.9%. While in fig. 7 the feed forward control method acts, the three phase imbalance drops to 0.3% after a 0.25s load imbalance has occurred.

The embodiments in the present description are described in a progressive manner, each embodiment focuses on differences from other embodiments, and the same and similar parts among the embodiments are referred to each other.

The principles and embodiments of the present invention have been described herein using specific examples, which are provided only to help understand the method and the core concept of the present invention; meanwhile, for a person skilled in the art, according to the idea of the present invention, the specific embodiments and the application range may be changed. In view of the above, the present disclosure should not be construed as limiting the invention.