阅读说明：本技术 一种提高矩阵变换器系统低电压穿越能力的控制方法 (Control method for improving low voltage ride through capability of matrix converter system ) 是由 阎彦 段永辉 史婷娜 曹彦飞 于 2019-10-28 设计创作，主要内容包括：本发明公开了一种提高矩阵变换器系统低电压穿越能力的控制方法,包括：1)通过对电网三相电压实时采样并计算来检测电网电压是否发生跌落,当发生跌落后,在负载为电机负载的工况下,计算电机负载下系统可运行的最高转速值,若电机转速大于最高转速值,系统切换到穿越控制模式；2)穿越期间将箝位电容作为能量转换机构,通过维持箝位电容电压恒定的方式实现穿越；3)当通过步骤1)切换到穿越控制时,系统由正常工作模式转换到穿越模式；将电压环PI控制器的输出作为电机q轴电流控制器的输入参考值。本发明控制方法可以实现电网电压跌落后系统不停机运行的低电压穿越能力,同时抑制系统过流现象,电网电压恢复后系统能够快速恢复运行。(The invention discloses a control method for improving low voltage ride through capability of a matrix converter system, which comprises the following steps: 1) detecting whether the voltage of the power grid drops or not by sampling and calculating the three-phase voltage of the power grid in real time, calculating the highest rotating speed value of the system which can be operated under the motor load under the working condition that the load is the motor load after the voltage of the power grid drops, and switching the system to a ride-through control mode if the rotating speed of the motor is greater than the highest rotating speed value; 2) in the ride-through period, the clamping capacitor is used as an energy conversion mechanism, and the ride-through is realized in a mode of maintaining the voltage of the clamping capacitor constant; 3) when the system is switched to the crossing control through the step 1), the system is switched from a normal working mode to a crossing mode; and taking the output of the voltage loop PI controller as an input reference value of the motor q-axis current controller. The control method can realize the low voltage ride through capability of the system which does not stop running after the voltage of the power grid drops, simultaneously inhibit the over-current phenomenon of the system, and the system can quickly recover running after the voltage of the power grid recovers.)

1. A control method for improving the low voltage ride through capability of a matrix converter system is characterized by comprising the following steps:

step one, detecting whether the voltage of a power grid drops, and judging whether to switch to ride-through control: detecting whether the voltage of the power grid drops or not by sampling and calculating the three-phase voltage of the power grid in real time, calculating the highest rotating speed value of the system which can stably operate under the motor load after the voltage of the power grid drops under the working condition that the load is the motor load after the voltage of the power grid drops, and switching the system to a ride-through control mode if the rotating speed of the motor is greater than the highest rotating speed value, otherwise, continuing to operate the system according to the control mode before failure;

step two, designing a low-voltage ride-through operation auxiliary circuit: in the ride-through period, the clamping capacitor is used as an energy conversion mechanism, and the ride-through is realized in a mode of maintaining the voltage of the clamping capacitor constant;

step three, designing a low voltage ride through controller: the low voltage ride through controller is structured that when the low voltage ride through controller is switched to ride through control through the step one, the system is switched from a normal working mode to a ride through mode; and realizing ride-through in a mode of maintaining the voltage of the clamping capacitor to be constant, and taking the output of the voltage loop PI controller as an input reference value of a motor q-axis current controller.

2. The control method for improving the low voltage ride through capability of the matrix converter system according to claim 1, wherein in the step one, when the grid voltage drops, the drop depth h is calculated as follows:

in the formula of U_RMSFor sampled effective values of the grid voltage, U_{RMS_N}The effective value is the effective value of the power grid in the normal state;

calculating the maximum rotating speed n of the motor which can stably operate under different falling depths and different loads after the voltage of the power grid falls_maxExpression (c):

wherein R is_sIs a motor stator resistor; l is_sIs a motor stator inductance; psi_fThe amplitude of the permanent magnet flux linkage of the motor is obtained; n is the motor rotation speed; p is the number of pole pairs of the motor; t is_LLoading the motor; u shape_mInputting a phase voltage amplitude for the matrix converter;

The motor operates at n r/min in steady state before the grid fault, and the load is T_LUnder the working condition of N.m, calculating T after the voltage of the power grid falls_LMaximum rotation speed value n of system under load_maxIf n is>n_maxAnd switching the system to a crossing control mode, otherwise, continuing to operate according to the control mode before the fault.

3. The method as claimed in claim 1, wherein in step two, energy flows between the motor and the clamp capacitor in two directions during the ride-through, a switching device is connected in anti-parallel to two ends of the diode in the topology clamp circuit of the matrix converter system, and the switching device is always in a conducting state during the ride-through.

4. The control method for improving the low voltage ride through capability of the matrix converter system according to claim 1, wherein in step three, the design method of the low voltage ride through controller comprises:

during the crossing period, the motor works in a generator state, the directions defined by all physical quantities of the motor still adopt a motor convention, and a unified mathematical model of the motor and the matrix converter inversion stage is established:

in the formula, v_d、v_qD and q axis components of the stator voltage; i.e. i_d、i_qD and q axis components of the stator current; c_claIs a clamping capacitor; v. of_claIs the clamp capacitor voltage; r_LA bleeder resistor for the clamp capacitor;

the parameters of the voltage loop PI controller are designed and defined by adopting the active damping concept

In the formula i_q1As output of a voltage loop PI controller, B_aIs a damping coefficient;

control of i during ride through_dWhen is equal to 0, i is_qSubstituting the expression into the established unified mathematical model of the motor and the matrix converter inverter stage, and configuring the pole to the expected closed-loop bandwidth β to obtain the voltage

and combining the transfer function of the controlled object with the voltage ring PI controller, and then obtaining the parameters of the voltage ring PI controller through parameter setting, thereby completing the design of the low-voltage ride-through controller.

Technical Field

The invention relates to the technical field of power converter control of a driving motor, in particular to a control method of low voltage ride through capability of a matrix converter system.

Background

The motor system usually adopts a power grid as an input power supply, and is influenced by factors such as line short circuit, ground fault, overload and the like, so that the power quality problems such as voltage drop, short-time interruption, voltage change and the like can occur in the power grid. Among various power quality problems, voltage sag is a type of fault which occurs most frequently, and the continuous operation capability of a motor system is seriously influenced. Once the motor system is shut down, the production process can be interrupted in some important industrial occasions, and severe economic loss is brought. In contrast, the motor system is required to have a Low Voltage Ride-through (LVRT) capability of operating without shutdown for 0.06-0.6 s under the condition that the Voltage of the power grid drops by 10% -30% of a rated value.

The Matrix Converter-Permanent magnet synchronous Motor system (MC-PMSM) is a Motor system with high power density, capability of feeding regenerated energy of a Motor into a power grid, sine input current waveform and flexible and adjustable power factor. The development of the technical level of the motor has important significance for breakthrough of key technology of a high-integration-level integrated motor system. However, the output side of the system is extremely susceptible to the input side due to the fact that no large-capacity energy storage element exists in the power topology structure. When the grid voltage drops and the system does not have the LVRT capability, the system needs to be shut down to operate. In view of the above, experts and scholars at home and abroad propose various solutions. These schemes can be divided into three categories:

1) and an energy storage device is added in the topological structure to realize ride-through, such as a super capacitor, a battery or a flywheel. Under normal conditions, the energy storage device is charged by the power grid, and the energy storage device supplies power to the system after the power grid fails to maintain normal operation of the system;

2) the system topology structure is modified to realize the crossing, for example, three switching devices and a direct current energy storage capacitor are added in the traditional MC topology, a virtual voltage type inverter is formed by combining three switches in the MC, and the crossing is realized by a method of maintaining the constant voltage of the capacitor and the constant magnetic flux of the motor;

3) the LVRT control is applied and an auxiliary circuit is designed to realize the ride-through based on the load inertia principle, and the method can be divided into two types, wherein firstly, energy is stored by using an input filter capacitor, three IGBTs are added in a topological structure, a power grid is isolated from a system by the IGBTs after the power grid fails, the power grid does not transmit energy to the system any more, and the zero power control is adopted to realize the ride-through; secondly, the energy storage of the clamping capacitor is utilized to realize the ride through, and the ride through method is divided into 3 modes: the method adopts a mode of applying clamping capacitor voltage or effective power grid voltage by flux linkage hysteresis loop control, a mode of switching in three modes of clamping loop follow current, zero vector follow current and non-zero vector follow current in one control period, and a mode of switching in two circuit loops by current hysteresis loop control.

The existing method for increasing the energy storage device and modifying the topology weakens the advantages of compact system volume and high power density to a certain extent, the method for realizing ride-through by utilizing the rotating inertial mechanical energy of the motor emphasizes the design of a ride-through strategy, the hysteresis control effect is poor, and the control quantity has large fluctuation during ride-through.

Disclosure of Invention

Aiming at the prior art, the invention aims to solve the technical problems that when the system does not have low voltage ride through capability after the voltage of the power grid drops, the system needs to be stopped to operate so as to cause the interruption of operation, and meanwhile, the system correction, positioning and other programs can cause time delay after the power grid is recovered, which can bring serious economic loss in some important occasions.

In order to solve the above technical problem, the present invention provides a control method for improving low voltage ride through capability of a matrix converter system, comprising the following steps:

step one, detecting whether the voltage of a power grid drops, and judging whether to switch to ride-through control: detecting whether the voltage of the power grid drops or not by sampling and calculating the three-phase voltage of the power grid in real time, calculating the highest rotating speed value of the system which can stably operate under the motor load after the voltage of the power grid drops under the working condition that the load is the motor load after the voltage of the power grid drops, and switching the system to a ride-through control mode if the rotating speed of the motor is greater than the highest rotating speed value, otherwise, continuing to operate the system according to the control mode before failure;

step two, designing a low-voltage ride-through operation auxiliary circuit: in the ride-through period, the clamping capacitor is used as an energy conversion mechanism, and the ride-through is realized in a mode of maintaining the voltage of the clamping capacitor constant;

step three, designing a low voltage ride through controller: the low voltage ride through controller is structured that when the low voltage ride through controller is switched to ride through control through the step one, the system is switched from a normal working mode to a ride through mode; and realizing ride-through in a mode of maintaining the voltage of the clamping capacitor to be constant, and taking the output of the voltage loop PI controller as an input reference value of a motor q-axis current controller.

Further, the control method for improving the low voltage ride through capability of the matrix converter system of the invention comprises the following steps:

in the first step, after the voltage of the power grid drops, the dropping depth h is calculated:

in the formula of U_RMSFor sampled effective values of the grid voltage, U_{RMS_N}The effective value is the effective value of the power grid in the normal state;

calculating the maximum rotating speed n of the motor which can stably operate under different falling depths and different loads after the voltage of the power grid falls_maxExpression (c):

wherein R is_sIs a motor stator resistor; l is_sIs a motor stator inductance; psi_fThe amplitude of the permanent magnet flux linkage of the motor is obtained; n is the motor rotation speed; p is the number of pole pairs of the motor; t is_LLoading the motor; u shape_mInputting a phase voltage amplitude for the matrix converter;

by using i_dIn the 0-vector control mode, the amplitude of the stator current is T_L/1.5pψ_f；

The motor is arranged before the power grid faultThe steady state operation is carried out at the rotating speed of n r/min and the load of T_LUnder the working condition of N.m, calculating T after the voltage of the power grid falls_LMaximum rotation speed value n of system under load_maxIf n is>n_maxAnd switching the system to a crossing control mode, otherwise, continuing to operate according to the control mode before the fault.

And step two, performing bidirectional energy circulation between the motor and the clamping capacitor during the ride-through period, and connecting a switching device in anti-parallel at two ends of a diode in the topological structure clamping circuit of the matrix converter system, wherein the switching device is always in a conducting state during the ride-through period.

In step three, the design method of the low voltage ride through controller includes:

during the crossing period, the motor works in a generator state, the directions defined by all physical quantities of the motor still adopt a motor convention, and a unified mathematical model of the motor and the matrix converter inversion stage is established:

in the formula, v_d、v_qD and q axis components of the stator voltage; i.e. i_d、i_qD and q axis components of the stator current; c_claIs a clamping capacitor; v. of_claIs the clamp capacitor voltage; r_LA bleeder resistor for the clamp capacitor;

the method adopts the concept of 'active damping' to design and define the parameters of the voltage loop PI controller

In the formula i_q1As output of a voltage loop PI controller, B_aIs a damping coefficient;

control of i during ride through_dWhen is equal to 0, i is_qSubstituting the expression into the established unified mathematical model of the motor and the matrix converter inverter stage, and configuring the pole to the expected closed-loop bandwidth β to obtain the voltage

Controlled object transfer function with respect to q-axis current:

and combining the transfer function of the controlled object with the voltage ring PI controller, and then obtaining the parameters of the voltage ring PI controller through parameter setting, thereby completing the design of the low-voltage ride-through controller.

The control method for improving the low voltage ride through capability of the matrix converter system can be applied to the fields of matrix converters, motor control and the like. Compared with the prior art, the invention has the beneficial effects that:

(1) and the occurrence of the system overcurrent phenomenon during the voltage drop of the power grid is restrained.

(2) During the ride-through period, the system continuously operates, the motor works in a constant power state, the generator operates to charge the clamping capacitor and maintain the voltage of the clamping capacitor constant, and the rotating speed of the motor is basically reduced at a constant acceleration and is not reduced to zero.

(3) When the voltage of the power grid drops, the system does not need to be stopped to operate, and after the voltage of the power grid is recovered, the system can be started quickly from a non-zero rotating speed and non-zero magnetic flux state.

Drawings

FIG. 1 is a flow chart of a control method of the present invention;

FIG. 2 is a control block diagram of the control method of the present invention;

FIG. 3 is an IMC-SPMSM system torque-speed operating range;

FIG. 4 is a functional block diagram of a ride-through control decision;

FIG. 5 is a block diagram of a ride-through phase voltage closed loop control architecture;

FIG. 6 is a system crossing waveform of the motor under the working condition of 300r/min and 0 N.m when the power grid falls to 10% of depth;

FIG. 7 is a system crossing waveform of a motor under the working conditions of 300r/min and 15 N.m, wherein the power grid falling depth is 10%;

FIG. 8 is a system crossing waveform of the motor under the working condition of 0 N.m at 300r/min, with the power grid dropping depth of 20%;

FIG. 9 is a system crossing waveform of the motor under the working conditions of 300r/min and 15 N.m, wherein the grid falling depth is 20%.

Detailed Description

The invention will be further described with reference to the following figures and specific examples, which are not intended to limit the invention in any way.

The invention discloses a control method capable of improving low voltage ride through capability of a matrix converter system, which comprises the following steps as shown in figure 1:

step one, detecting whether the voltage of a power grid drops, and judging whether to switch to ride-through control:

whether the grid voltage drops or not is detected by sampling and calculating the three-phase voltage of the power grid in real time, and when the grid voltage drops, the drop depth h is calculated:

in the formula of U_RMSFor sampled effective values of the grid voltage, U_{RMS_N}The effective value is the effective value of the power grid in the normal state;

calculating the maximum rotating speed n of the motor which can stably operate under different falling depths and different loads after the voltage of the power grid falls_maxExpression (c):

wherein R is_sIs a motor stator resistor; l is_sIs a motor stator inductance; psi_fThe amplitude of the permanent magnet flux linkage of the motor is obtained; n is the motor rotation speed; p is the number of pole pairs of the motor; t is_LLoading the motor; u shape_mInputting a phase voltage amplitude for the matrix converter;

by using i_dIn the 0-vector control mode, the amplitude of the stator current is T_L/1.5pψ_f。

Assuming that the motor operates at a steady state at a rotating speed of n (r/min) and a load of T before a power grid fault_LUnder the working condition of (N.m), calculating T after the voltage of the power grid drops_LMaximum rotation speed value n of system under load_maxIf n is>n_maxIf not, the system continues to operate according to the control mode before the fault;

step two, designing a crossing auxiliary circuit:

in the ride-through period, the clamping capacitor is used as an energy conversion mechanism, and the ride-through is realized in a mode of maintaining the voltage of the clamping capacitor constant; in the clamping circuit of the topological structure of the original system, a diode only has one-way conductivity, in order to realize the two-way flow of energy between a motor and a clamping capacitor, two ends of the diode are connected with a switch device in an anti-parallel mode, and the switch device is always in a conducting state when passing through the device;

step three, designing a traversing controller:

when the first step is switched to the crossing control, the system is switched from the normal working mode to the crossing mode; and realizing ride-through in a mode of maintaining the voltage of the clamping capacitor to be constant, and taking the output of the voltage loop PI controller as an input reference value of a motor q-axis current controller.

During the crossing period, the motor works in a generator state, the directions defined by all physical quantities of the motor still adopt a motor convention, and a unified mathematical model of the motor and the matrix converter inversion stage is established:

in the formula, v_d、v_qD and q axis components of the stator voltage; i.e. i_d、i_qD and q axis components of the stator current; c_claIs a clamping capacitor; v. of_claIs the clamp capacitor voltage; r_LA bleeder resistor for the clamp capacitor;

the method adopts the concept of 'active damping' to design and define the parameters of the voltage loop PI controller

In the formula i_q1As output of a voltage loop PI controller, B_aIs a damping coefficient;

control of i during ride through_dWhen is equal to 0, i is_qSubstituting the expression into the established unified mathematical model of the motor and the matrix converter inverter stage, and configuring the pole to the expected closed-loop bandwidth β to obtain the voltage

Controlled object transfer function with respect to q-axis current:

and combining the transfer function of the controlled object with the voltage ring PI controller, and then obtaining the parameters of the voltage ring PI controller through parameter setting, thereby completing the design of the low-voltage ride-through controller. The parameter setting methods are many, engineering design methods are also available in engineering, and all the methods belong to common knowledge of persons in the industry (Yuanli, Shenjiaqing, Xiaofei, et al. design of a nonsingular terminal sliding mode observer for an inserted permanent magnet low-speed synchronous motor [ J ]. physical report, 2013,62(3):030501.), and are not described herein again.