阅读说明：本技术 一种基于自适应虚拟阻尼控制的交直流混合微电网并联换流器环流抑制方法 (Circulating current suppression method for parallel converter of AC/DC hybrid micro-grid based on adaptive virtual damping control ) 是由 李朝阳 韩肖清 任春光 张佰富 王奕赫 赵多 于 2019-08-22 设计创作，主要内容包括：本发明涉及交直流混合微电网,具体是一种基于自适应虚拟阻尼控制的交直流混合微电网并联换流器环流抑制方法。交直流混合微电网由交流子网和直流子网组成,且两个子网由并联双向功率换流器连接。所提控制方法可实现交直流子网间的功率交互,彼此进行功率支撑。控制环节主要包括改进下垂控制与环流抑制控制两部分。改进下垂控制设计了无功控制环节的积分项,对电压进行无静差追踪,实现较好的电压控制效果,从而改善对零序环流的抑制效果。环流抑制环节采用dq0三轴控制取代传统的dq两轴控制,针对并联换流器由于器件参数差异、线路阻抗不平衡等引起的环流问题,给出基于自适应虚拟阻尼环流抑制方法,可有效抑制并联双向换流器间的环流产生。(The invention relates to an alternating current and direct current hybrid micro-grid, in particular to a circulating current restraining method of a parallel converter of the alternating current and direct current hybrid micro-grid based on self-adaptive virtual damping control. The alternating current-direct current hybrid micro-grid consists of an alternating current sub-grid and a direct current sub-grid, and the two sub-grids are connected by a parallel bidirectional power converter. The control method can realize power interaction between the AC and DC sub-networks and carry out power support mutually. The control link mainly comprises two parts of droop control improvement and circulation suppression control. The droop control is improved, an integral term of a reactive control link is designed, the voltage is tracked without static error, and a good voltage control effect is achieved, so that the inhibiting effect on zero-sequence circulation is improved. In the loop current suppression link, the dq0 three-axis control is adopted to replace the traditional dq two-axis control, and a self-adaptive virtual damping loop current suppression method is provided for solving the problem of loop current of the parallel bidirectional converters caused by device parameter difference, line impedance imbalance and the like, so that the loop current generation between the parallel bidirectional converters can be effectively suppressed.)

1. A circulating current restraining method of an AC-DC hybrid micro-grid parallel converter based on self-adaptive virtual damping control is characterized in that an AC side of each three-phase three-bridge arm converter is connected with an AC micro-grid through a filter inductor and a parasitic resistor, a DC side is connected with the DC micro-grid through a DC capacitor, the circulating current restraining method also comprises an AC voltage collecting module for collecting AC measured voltage and an AC current collecting module for collecting AC measured current, an output end of the AC voltage collecting module is connected with input ends of a power calculating module and an AC voltage coordinate conversion module, an output end of the AC current collecting module is connected with input ends of the power calculating module and the AC current coordinate conversion module, an output end of the power calculating module is connected with an input end of an improved droop control module, an output end of the improved droop control module is connected with input ends of the AC voltage coordinate conversion module, the AC current coordinate conversion module and a reference, the output ends of the alternating current voltage coordinate transformation module, the alternating current coordinate transformation module and the reference voltage coordinate transformation module are connected with the input end of the voltage and current double closed-loop control module, the output end of the voltage and current double closed-loop control module is connected with the input end of the reverse coordinate transformation module, the output ends of the alternating current coordinate transformation module and the reverse coordinate transformation module are connected with the input end of the self-adaptive virtual damping control zero-sequence circulating current suppression module, the output end of the self-adaptive virtual damping control zero-sequence circulating current suppression module is connected with the input end of the PWM driving module, and the output end of the PWM driving module is connected with the feedback end of the three-phase three-bridge-arm converter, and the:

the alternating voltage acquisition module acquires the alternating side voltage U_abcAnd input into a power calculation module and an AC voltage coordinate transformation module, and an AC current acquisition module acquires AC current I_abcAnd input to the power calculation module and the alternating current coordinate transformation module;

the power calculation module is provided with an input alternating-current side voltage U_abcAnd AC current I_abcOutputting active P and reactive Q of the system to an improved droop control module through power calculation;

the improved droop control module respectively obtains a frequency value f and a voltage reference value U from the input active P and reactive Q through the active droop characteristic and the reactive droop characteristic_refThen, integral control is performed on the frequency value f to obtain the phase angle delta_iOutput to the voltage coordinate transformation module, the current coordinate transformation module and the reference voltage coordinate transformation module, and the reference voltage coordinate transformation module is composed of a voltage reference value U_refAnd phase angle delta_iObtaining three-phase voltage reference value U_abcrefOutputting a voltage reference value U under dq0 coordinate system through reference voltage coordinate transformation_dq0refTo a double closed loop control module;

the AC coordinate conversion module measures current I from input AC_abcOutputting the actual current value I under the shaft coordinate system of dq0 through coordinate transformation_dq0A double closed-loop control module and a self-adaptive virtual damping control module are provided;

the AC voltage coordinate transformation module measures the voltage U from the input AC_abcOutputting the actual voltage value U under the dq0 axial coordinate system through coordinate transformation_dq0To a double closed loop control module;

the double closed-loop control module firstly inputs a voltage reference value U_dq0refAnd the actual voltage value U_dq0Making difference, and then obtaining current reference value I through voltage control_dq0refThen reference the current to the value I_dq0refAnd the actual value of the current I_dq0And (4) performing difference calculation, and then obtaining a modulation voltage signal u under dq0 axial coordinate system through decoupling and current control links_dq0And obtaining a modulation voltage signal u under an abc axis coordinate system through conversion of an inverse coordinate transformation module_abcAnd inputting the data into a self-adaptive virtual damping control circulation current suppression module;

the self-adaptive virtual damping control circulation current suppression module firstly carries out zero sequence current actual value I₀Obtaining zero sequence voltage offset delta U through virtual damping capable of being dynamically adjusted in real time according to power oscillation caused by voltage fluctuation₀The virtual damping dynamic adjustment process comprises the following steps: z_v＝R_v+sX_v，R_v＝R₀-k_R(P_set-P)，X_v＝X₀-k_X(Q_set-Q), wherein R_vAnd X_vRespectively setting values of a virtual resistor and an inductive reactance in the system; r₀And X₀Respectively setting initial values of a virtual resistor and an inductive reactance; k is a radical of_RAnd k_XRespectively are the adjusting coefficients of the virtual resistor and the inductive reactance; pset and Q_setRespectively setting the power values of the active power and the reactive power of the self-adaptive virtual damping; p and Q are respectively the active value and the reactive value of the actual output of the converter, and the zero sequence voltage offset delta U is calculated₀Modulating voltage offset delta u under output abc axis coordinate system through inverse coordinate transformation_abcWill modulate the voltage signal u_abcOffset from the modulation voltage by an amount Deltau_abcDifferencing to obtain new modulation voltage signal u^* _abcIs output by the PWM module and input to a three-phase three-bridge arm converter bridgeAnd the IGBT control end realizes the circulation current suppression of the parallel bidirectional power converter.

Technical Field

The invention relates to the field of alternating current and direct current hybrid micro-grids, in particular to a circulating current restraining method of a parallel converter of an alternating current and direct current hybrid micro-grid based on self-adaptive virtual damping control.

Background

The bidirectional power converter is used as a connecting junction in an alternating current-direct current hybrid micro-grid, has the advantages of high efficiency, low harmonic, adjustable power factor, bidirectional power flow and the like, but due to the limitation of a switch device, a single module structure is difficult to meet the application occasion of low voltage and large current. Therefore, a multi-module parallel redundancy configuration with a common ac/dc bus is generally adopted to improve the capacity and operational reliability of the system. The common alternating current-direct current bus structure provides a circulation path for zero sequence circulation, and circulation among the parallel bidirectional power converter systems is inevitably generated due to parameter difference of system devices, unbalanced line impedance and the like. The zero sequence loop current causes distortion of output current, generates larger current stress, increases the switching loss of the system, reduces the stability of the system, and can cause the damage of a switching device in serious cases. Therefore, the method for restraining the parallel circulating current problem of the bidirectional power converter has very important significance.

For the problem of parallel circulation of bidirectional power converters in an alternating current-direct current hybrid micro-grid, the existing circulation suppression method which is researched more is to adjust the zero-sequence voltage difference between parallel modules by taking self zero-sequence current as feedback quantity under the condition of not increasing communication lines, so that the purpose of suppressing zero-sequence circulation is achieved, and meanwhile, the independent adjustment of each parallel module is guaranteed. The virtual damping values introduced in the methods are all constant, if the virtual damping values are introduced improperly, unbalance of three-phase impedance of the system is aggravated, unbalance of the system is increased, efficiency of the system is reduced, zero-sequence circulating current of the system is increased, no good suppression effect is provided for zero-sequence circulating current mutation caused by power fluctuation in the system, and impact on the system is large. Meanwhile, the virtual damping introduced in the methods only presents the inductive property, is not matched with the inductive resistance of the line impedance, the load impedance and the like, and has poor inhibiting effect on the zero-sequence circulating current. Therefore, a zero-sequence circulating current suppression method which comprehensively considers the factors and is more optimized is needed.

Disclosure of Invention

The invention provides a circulating current restraining method of a parallel converter of an alternating current-direct current hybrid microgrid based on self-adaptive virtual damping control, which aims to solve the circulating current problem caused by device parameter difference, line impedance imbalance and the like of a common alternating current-direct current bus parallel bidirectional power converter in the alternating current-direct current hybrid microgrid and overcome the defects of the prior art.

The method is realized by adopting the following technical scheme:

according to the method for restraining the circulating current of the parallel converter of the alternating current-direct current hybrid micro-grid based on the self-adaptive virtual damping control, the alternating current side of each three-phase three-bridge arm converter is connected into the alternating current micro-grid through a filter inductor and a parasitic resistor, and the direct current side of each three-phase three-bridge arm converter is connected into the direct current micro-grid through a direct current capacitor. The device also comprises an alternating current voltage acquisition module for acquiring alternating current measurement voltage and an alternating current acquisition module for acquiring alternating current measurement current. The output end of the alternating current voltage acquisition module is connected with the input ends of the power calculation module and the alternating current coordinate transformation module, the output end of the alternating current acquisition module is connected with the input ends of the power calculation module and the alternating current coordinate transformation module, the output end of the power calculation module is connected with the input end of the improved droop control module, the output end of the improved droop control module is connected with the input ends of the alternating current coordinate transformation module, the alternating current coordinate transformation module and the reference voltage coordinate transformation module, the output ends of the alternating current voltage coordinate transformation module, the alternating current coordinate transformation module and the reference voltage coordinate transformation module are connected with the input end of the voltage current double closed-loop control module, the output end of the voltage current double closed-loop control module is connected with the input end of the inverse coordinate transformation module, and the output ends of the alternating current coordinate transformation module and the inverse coordinate transformation module are connected with the input end of the, the output end of the self-adaptive virtual damping control zero-sequence circulating current suppression module is connected with the input end of the PWM driving module, and the output end of the PWM driving module is connected with the feedback end of the three-phase three-bridge-arm converter.

The method specifically comprises the following steps:

the alternating voltage acquisition module acquires the alternating side voltage U_abcAnd input into a power calculation module and an AC voltage coordinate transformation module, and an AC current acquisition module acquires AC current I_abcAnd input to the power calculation module and the alternating current coordinate transformation module.

The power calculation module is provided with an input alternating-current side voltage U_abcAnd AC current I_abcAnd outputting the active P and the reactive Q of the system to the improved droop control module through power calculation.

The improved droop control module respectively obtains a frequency value f and a voltage reference value U from the input active P and reactive Q through the active droop characteristic and the reactive droop characteristic_refAnd an integral link is added in the reactive droop design. Then, integral control is carried out on the frequency value f to obtain the phase angle delta_iOutput to the voltage coordinate transformation module, the current coordinate transformation module and the reference voltage coordinate transformation module, and the reference voltage coordinate transformation module is composed of a voltage reference value U_refAnd phase angle delta_iObtaining three-phase voltage reference value U_abcrefOutputting a voltage reference value U under dq0 coordinate system through reference voltage coordinate transformation_dq0refTo the double closed loop control module.

The AC coordinate conversion module measures current I from input AC_abcOutputting the actual current value I under the shaft coordinate system of dq0 through coordinate transformation_dq0To a double closed-loop control module and an adaptive virtual damping control module.

The AC voltage coordinate transformation module measures the voltage U from the input AC_abcOutputting the actual voltage value U under the dq0 axial coordinate system through coordinate transformation_dq0To the dual closed loop control module.

The double closed-loop control module firstly inputs a voltage reference value U_dq0refAnd the actual voltage value U_dq0Making difference, and then obtaining current reference value I through voltage control_dq0refThen reference the current to the value I_dq0refAnd the actual value of the current I_dq0And (4) performing difference calculation, and then obtaining a modulation voltage signal u under dq0 axial coordinate system through decoupling and current control links_dq0And obtaining a modulation voltage signal u under an abc axis coordinate system through conversion of an inverse coordinate transformation module_abcAnd input to the self-adaptive virtual damping control circulation current suppression module.

The self-adaptive virtual damping control circulation current suppression module firstly carries out zero sequence current actual value I₀Obtaining zero sequence voltage offset delta U through virtual damping capable of being dynamically adjusted in real time according to power oscillation caused by voltage fluctuation₀. The virtual damping dynamic adjustment process comprises the following steps:

Z_v＝R_v+sX_v (1)

R_v＝R₀-k_R(P_set-P) (2)

X_v＝X₀-k_X(Q_set-Q) (3)

wherein R is_vAnd X_vRespectively setting values of a virtual resistor and an inductive reactance in the system; r₀And X₀Respectively setting initial values of a virtual resistor and an inductive reactance; k is a radical of_RAnd k_XRespectively are the adjusting coefficients of the virtual resistor and the inductive reactance; pset and Q_setRespectively setting the power values of the active power and the reactive power of the self-adaptive virtual damping; p and Q are respectively the active value and the passive value of the actual output of the converter. Then the zero sequence voltage offset delta U is calculated₀Modulating voltage offset delta u under output abc axis coordinate system through inverse coordinate transformation_abc. Will modulate the voltage signal u_abcOffset from the modulation voltage by an amount Deltau_abcDifferencing to obtain new modulation voltage signal u^* _abcAnd the current is output by the PWM module and input to the control end of the three-phase three-bridge arm converter bridge IGBT to realize the circulation suppression of the parallel bidirectional power converter.

The control link of the invention mainly comprises two parts of droop control improvement and circulation suppression control. The droop control is improved, an integral term of a reactive control link is designed, the voltage is tracked without static error, and a good voltage control effect is achieved, so that the inhibiting effect on zero-sequence circulation is improved. In the loop current suppression link, the dq0 three-axis control is adopted to replace the traditional dq two-axis control, and a self-adaptive virtual damping loop current suppression method is provided for solving the problem of loop current of the parallel bidirectional converters caused by device parameter difference, line impedance imbalance and the like, so that the loop current generation between the parallel bidirectional converters can be effectively suppressed.

Drawings

Fig. 1 is a converter parallel main circuit topology according to the present invention.

Fig. 2 is a control block diagram of a parallel converter circulating current suppression system according to the present invention.

Detailed Description

A control principle block diagram of the method is shown in figure 2, an alternating current side of each three-phase three-bridge-arm converter is connected to an alternating current microgrid through a filter inductor and a parasitic resistor, and a direct current side of each three-phase three-bridge-arm converter is connected to a direct current microgrid through a direct current capacitor. The device also comprises an alternating current voltage acquisition module for acquiring alternating current measurement voltage and an alternating current acquisition module for acquiring alternating current measurement current. The output end of the alternating current voltage acquisition module is connected with the input ends of the power calculation module and the alternating current coordinate transformation module, the output end of the alternating current acquisition module is connected with the input ends of the power calculation module and the alternating current coordinate transformation module, the output end of the power calculation module is connected with the input end of the improved droop control module, the output end of the improved droop control module is connected with the input ends of the alternating current coordinate transformation module, the alternating current coordinate transformation module and the reference voltage coordinate transformation module, the output ends of the alternating current voltage coordinate transformation module, the alternating current coordinate transformation module and the reference voltage coordinate transformation module are connected with the input end of the voltage current double closed-loop control module, the output end of the voltage current double closed-loop control module is connected with the input end of the inverse coordinate transformation module, and the output ends of the alternating current coordinate transformation module and the inverse coordinate transformation module are connected with the input end of the, the output end of the self-adaptive virtual damping control zero-sequence circulating current suppression module is connected with the input end of the PWM driving module, and the output end of the PWM driving module is connected with the feedback end of the three-phase three-bridge-arm converter.

The control method comprises the following steps:

the alternating voltage acquisition module acquires the alternating side voltage U_abcAnd input into a power calculation module,An AC voltage coordinate transformation module, an AC current collection module for collecting AC measuring current I_abcAnd input to the power calculation module and the alternating current coordinate transformation module.

The power calculation module is provided with an input alternating-current side voltage U_abcAnd AC current I_abcAnd outputting the active P and the reactive Q of the system to the improved droop control module through power calculation.

The improved droop control module respectively obtains a frequency value f and a voltage reference value U from the input active P and reactive Q through the active droop characteristic and the reactive droop characteristic_refAnd an integral link is added in the reactive droop design. Then, integral control is carried out on the frequency value f to obtain the phase angle delta_iOutput to the voltage coordinate transformation module, the current coordinate transformation module and the reference voltage coordinate transformation module, and the reference voltage coordinate transformation module is composed of a voltage reference value U_refAnd phase angle delta_iObtaining three-phase voltage reference value U_abcrefOutputting a voltage reference value U under dq0 coordinate system through reference voltage coordinate transformation_dq0refTo the double closed loop control module.

The AC coordinate conversion module measures current I from input AC_abcOutputting the actual current value I under the shaft coordinate system of dq0 through coordinate transformation_dq0To a double closed-loop control module and an adaptive virtual damping control module.

The AC voltage coordinate transformation module measures the voltage U from the input AC_abcOutputting the actual voltage value U under the dq0 axial coordinate system through coordinate transformation_dq0To the dual closed loop control module.

The double closed-loop control module firstly inputs a voltage reference value U_dq0refAnd the actual voltage value U_dq0Making difference, and then obtaining current reference value I through voltage control_dq0refThen reference the current to the value I_dq0refAnd the actual value of the current I_dq0And (4) performing difference calculation, and then obtaining a modulation voltage signal u under dq0 axial coordinate system through decoupling and current control links_dq0And obtaining a modulation voltage signal u under an abc axis coordinate system through conversion of an inverse coordinate transformation module_abcAnd input to the self-adaptive virtual damping control circulation current suppression module.

Adaptive virtualThe quasi-damping control circulation current suppression module firstly carries out zero sequence current actual value I₀Obtaining zero sequence voltage offset delta U through virtual damping capable of being dynamically adjusted in real time according to power oscillation caused by voltage fluctuation₀. The virtual damping dynamic adjustment process comprises the following steps:

Z_v＝R_v+sX_v (1)

R_v＝R₀-k_R(P_set-P) (2)

X_v＝X₀-k_X(Q_set-Q) (3)

wherein R is_vAnd X_vRespectively setting values of a virtual resistor and an inductive reactance in the system; r₀And X₀Respectively setting initial values of a virtual resistor and an inductive reactance; k is a radical of_RAnd k_XRespectively are the adjusting coefficients of the virtual resistor and the inductive reactance; pset and Q_setRespectively setting the power values of the active power and the reactive power of the self-adaptive virtual damping; p and Q are respectively the active value and the passive value of the actual output of the converter.

Then the zero sequence voltage offset delta U is calculated₀Modulating voltage offset delta u under output abc axis coordinate system through inverse coordinate transformation_abc. Will modulate the voltage signal u_abcOffset from the modulation voltage by an amount Deltau_abcDifferencing to obtain new modulation voltage signal u^* _abcAnd the current is output by the PWM module and input to the control end of the three-phase three-bridge arm converter bridge IGBT to realize the circulation suppression of the parallel bidirectional power converter.