Dual three-level inverter open winding motor single-bridge arm independent model prediction control method

Abstract

The invention relates to the technical field of motor driving and power electronic conversion devices, in particular to a double three-level inverter open winding motor single-bridge-arm independent model prediction control method. According to the method, a dual three-level open winding motor model predictive control method and a single-bridge-arm independent model predictive control idea are combined, a traditional priority model predictive control method is adopted, and all effective working states of six bridge arms need to be subjected to traversal vector optimization in a single sampling period; and by adopting the single-bridge-arm independent model prediction control method, the effective working state of each bridge arm only needs to be optimized in a single sampling period, the calculation amount is reduced from 729 times of calculation of the effective working state of each bridge arm to 27 times of calculation of the effective working state of each bridge arm, and the calculation amount is greatly reduced while a better control effect is ensured.

Description

Technical Field

[0001] The present invention relates to the technical field of motor drive and power electronic conversion device, and in particular to a motor control technology for reducing the amount of calculation of model predictive control of open-winding motors of dual three-level inverters. Background Art

[0002] The open-winding motor topology is powered by two separate inverters from both ends of the stator winding. It has many advantages, such as more switch combinations and multi-level output capabilities, relatively simple structure and high DC voltage utilization, and has been widely studied and applied.

[0003] According to the different DC bus power supply methods, open-winding asynchronous motor drive systems can be divided into two categories: common DC bus power supply type and independent DC bus power supply type. The common DC bus power supply type has a structure in which two three-phase inverters are connected to the same DC bus and are powered by a DC power supply. The existence of a zero-sequence loop will cause the motor stator winding to generate a large zero-sequence current under the action of the zero-sequence voltage. In the independent DC bus power supply type, the dual inverters are powered by two power supplies separately, which increases the system cost and complexity, but there will be no zero-sequence current loop, and no zero-sequence current will be generated.

[0004] The finite control set model predictive control (FCS-MPC) of motor drive selects the optimal vector through the cost function, and has the advantages of good dynamic performance, multi-objective control and low switching frequency. However, the application of traditional finite control set model predictive control to the open-winding motor of dual three-level inverter requires 729 traversal optimizations, which is a huge amount of calculation. Therefore, the field needs an improved model predictive control technology for open-winding motors, which can reduce the amount of calculation while achieving a better control effect. Summary of the invention

[0005] The purpose of the present invention is to solve the problem of excessive calculation amount in the current dual three-level inverter open-winding motor model predictive control, and to provide a dual three-level inverter open-winding motor single-bridge arm independent model predictive control method.

[0006] In order to achieve the above object, the technical solution adopted by the present invention is specifically as follows:

[0007] Step 1: The current i of the motor at time k ABC (k), speed ω r (k) and magnetic flux ψ(k), and convert each parameter into parameters in dq coordinate system;

[0008] Step 2: Set the flux linkage to a given value ψ * The difference between the actual observed flux ψ(k) and the given value of the d-axis stator current i is obtained after passing through the PI regulator. sd*; By giving the speed ω r * The actual measured speed ω r (k) Make a difference comparison and obtain the q-axis stator current given value i after passing through the PI regulator sq *;

[0009] Step 3: The result i obtained in step 2 sd *、i sq *After inverse Park and inverse Clark transformation, the current given value i in the three-phase stationary coordinate system is obtained ABC *;

[0010] Step 4: Establish a current prediction model according to the single-bridge-arm independent model predictive control method, and substitute the switch vector to be selected to obtain the current prediction value at time k+1;

[0011] Step 5: Substitute the current prediction value obtained in step 4 and the current given value obtained in step 3 into the value function for comparison, select the current prediction value when the value function is minimum, and output the corresponding switch vector;

[0012] Step 6: At time k+1, repeat steps 1 to 5, predict the optimal switching state corresponding to time k+2, and output it to the two three-level inverters, and repeat this process to achieve control of the open-winding motor.

[0013] Furthermore, in step 1, the voltage equation is established in the dq coordinate system as follows:

[0014]

[0015] In the formula, u sd 、u sq 、i sd 、i sq are the stator voltage and current in the dq coordinate system, u rd 、u rq 、i rd 、i rq are the rotor voltage and current in the dq coordinate system, R s is the stator resistance, L s is the stator inductance, L r is the rotor inductance, L m is the stator-rotor winding mutual inductance, ω l is the synchronous angular velocity, ω s is the synchronous angular velocity ω l The difference with the rotor angular velocity ω, p is the differential operator.

[0016] The magnetic flux equation in dq coordinates is:

[0017]

[0018] In the formula, ψ sd , sq is the stator flux in the dq coordinate system, ψ rd , rq is the rotor flux in the dq coordinate system.

[0019] Furthermore, in step 3, the voltage equation in the three-phase stationary coordinate system is:

[0020]

[0021] Where R, L, and M are the resistance, inductance, and mutual inductance of the three-phase winding of the motor in the three-phase stationary coordinate system.

[0022] Furthermore, in the step 4, the voltage equation in the three-phase stationary coordinate system is discretized using the forward Euler method, and the mathematical model of the current prediction value at time k+1 is obtained as follows:

[0023]

[0024] In the formula, i A (k), i B (k), i C (k) represents the actual measured three-phase current value, i A (k+1), i B (k+1), i C (k+1) represents the predicted current value at the next moment, T S Represents a control cycle.

[0025] Furthermore, in step 5, a cost function is established:

[0026]

[0027] Where j = [A, B, C]

[0028] In each control cycle, only 9 switching vectors need to be selected for each phase, and a total of 27 calculations need to be performed.

[0029] Compared with the prior art, the technical solution of the present invention has the following beneficial effects:

[0030] Compared with the existing technology, this method combines the dual three-level open-winding motor model predictive control method with the single bridge arm independent model predictive control idea, and transforms the need to traverse vector optimization for all effective working states of the six bridge arms in a single sampling cycle into only optimizing the effective working state of each bridge arm separately in a single sampling cycle. The amount of calculation is reduced from 729 calculations of the effective working state of each bridge arm to 27 calculations of the effective working state of each bridge arm, which ensures better control effect while greatly reducing the amount of calculation. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] The accompanying drawings are used to provide further understanding of the present invention and constitute a part of the specification. They are used to explain the present invention together with the embodiments of the present invention and do not constitute a limitation of the present invention.

[0032] Figure 1 The present invention is a flowchart of the method.

[0033] Figure 2 A control block diagram of the method of the present invention.

[0034] Figure 3 is the motor speed in the example of the present invention.

[0035] Figure 4 This is a three-phase current effect diagram of the motor in an example of the present invention.

[0036] Figure 5 This is a comparison chart between the given load torque and the actual load torque. DETAILED DESCRIPTION

[0037] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments.

[0038] The present invention provides a dual three-level inverter open-winding motor single bridge arm independent model predictive control method, referring to Figure 1-2 , the method comprises the following steps:

[0039] Step 1: The current i of the motor at time k ABC (k), speed ω r (k) and magnetic flux ψ(k), and convert each parameter into parameters in dq coordinate system;

[0040] Step 2: Set the flux linkage to a given value ψ * The difference between the actual observed flux ψ(k) and the given value of the d-axis stator current i is obtained after passing through the PI regulator. sd *; By giving the speed ω r * The actual measured speed ω r (k) Make a difference comparison and obtain the q-axis stator current given value i after passing through the PI regulator sq *;

[0041] Step 3: The result i obtained in step 2 sd *、i sq *After inverse Park and inverse Clark transformation, the current given value i in the three-phase stationary coordinate system is obtained ABC *;

[0042] Step 4: Establish a current prediction model according to the single-bridge-arm independent model predictive control method, and substitute the switch vector to be selected to obtain the current prediction value at time k+1;

[0043] Step 5: Substitute the current prediction value obtained in step 4 and the current given value obtained in step 3 into the value function for comparison, select the current prediction value when the value function is minimum, and output the corresponding switch vector;

[0044] Step 6: At time k+1, repeat steps 1 to 5, predict the optimal switching state corresponding to time k+2, and output it to the two three-level inverters, and repeat this process to achieve control of the open-winding motor.

[0045] In the step 1, the voltage equation is established in the dq coordinate system:

[0046]

[0047] In the formula, u sd 、u sq 、i sd 、i sq are the stator voltage and current in the dq coordinate system, u rd 、u rq 、i rd 、i rq are the rotor voltage and current in the dq coordinate system, R s is the stator resistance, L s is the stator inductance, L r is the rotor inductance, L m is the stator-rotor winding mutual inductance, ω l is the synchronous angular velocity, ω s is the synchronous angular velocity ω l The difference with the rotor angular velocity ω, p is the differential operator.

[0048] The magnetic flux equation in dq coordinates is:

[0049]

[0050] In the formula, ψ sd , sq is the stator flux in the dq coordinate system, ψ rd , rq is the rotor flux in the dq coordinate system.

[0051] In step 3, the voltage equation in the three-phase stationary coordinate system is:

[0052]

[0053] Where R, L, and M are the resistance, inductance, and mutual inductance of the three-phase winding of the motor in the three-phase stationary coordinate system.

[0054] In the step 4, the voltage equation in the three-phase stationary coordinate system is discretized using the forward Euler method, and the mathematical model of the current prediction value at time k+1 is obtained as follows:

[0055]

[0056] In the formula, i A (k), i B (k), i C (k) represents the actual measured three-phase current value, i A (k+1), i B (k+1), i C (k+1) represents the predicted current value at the next moment, T S Represents a control cycle.

[0057] In step 5, a cost function is established:

[0058]

[0059] Where j = [A, B, C]

[0060] In each control cycle, only 9 switching vectors need to be selected for each phase, and a total of 27 calculations need to be performed.

[0061] like Figure 3-5 As shown, under the method proposed in the present invention, the open-winding motor can run smoothly. This shows that the control strategy proposed in the present invention is effective, and can still achieve the smooth operation of the open-winding motor while greatly reducing the amount of model prediction calculation.

Claims

1. A single-bridge-arm independent model predictive control method for open-winding motors with dual three-level inverters, characterized in that: The method specifically comprises the following steps: Step 1: The current i of the motor at time k ABC (k), speed ω r (k) and magnetic flux ψ(k), and convert each parameter into parameters in dq coordinate system; Step 2: Set the flux linkage to a given value ψ * The difference between the actual observed flux ψ(k) and the given value of the d-axis stator current i is obtained after passing through the PI regulator. sd *; By giving the speed ω r * The actual measured speed ω r (k) Make a difference comparison and obtain the q-axis stator current given value i after passing through the PI regulator sq *; Step 3: The result i obtained in step 2 sd *、i sq *After inverse Park and inverse Clark transformation, the current given value i in the three-phase stationary coordinate system is obtained ABC *; Step 4: Establish a current prediction model according to the single-bridge-arm independent model predictive control method, and substitute the switch vector to be selected to obtain the current prediction value at time k+1; Step 5: Substitute the current prediction value obtained in step 4 and the current given value obtained in step 3 into the value function for comparison, select the current prediction value when the value function is minimum, and output the corresponding switch vector; Step 6: At time k+1, repeat steps 1 to 5, predict the optimal switching state corresponding to time k+2, and output it to the two three-level inverters. Repeat this process to achieve control of the open-winding motor.

2. A single-bridge-arm independent model predictive control method for a dual three-level inverter open-winding motor according to claim 1, characterized in that: In the step 1, the voltage equation is established in the dq coordinate system: In the formula, u sd 、u sq 、i sd 、i sq are the stator voltage and current in the dq coordinate system, u rd 、u rq 、i rd 、i rq are the rotor voltage and current in the dq coordinate system, R s is the stator resistance, L s is the stator inductance, L r is the rotor inductance, L m is the stator-rotor winding mutual inductance, ω l is the synchronous angular velocity, ω s is the synchronous angular velocity ω l The difference with the rotor angular velocity ω, p is the differential operator. The magnetic flux equation in dq coordinates is: In the formula, ψ sd , sq is the stator flux in the dq coordinate system, ψ rd , rq is the rotor flux in the dq coordinate system.

3. A single-bridge-arm independent model predictive control method for an open-winding motor of a dual three-level inverter according to claim 1, characterized in that: In step 3, the voltage equation in the three-phase stationary coordinate system is: Where R, L, and M are the resistance, inductance, and mutual inductance of the three-phase winding of the motor in the three-phase stationary coordinate system.

4. A single-bridge-arm independent model predictive control method for an open-winding motor of a dual three-level inverter according to claim 1, characterized in that: In the fourth step, the voltage equation in the three-phase stationary coordinate system is discretized using the forward Euler method, and the mathematical model of the current prediction value at time k+1 is obtained as follows: In the formula, i A (k), i B (k), i C (k) represents the actual measured three-phase current value, i A (k+1), i B (k+1), i C (k+1) represents the predicted current value at the next moment, T S Represents a control cycle.

5. A single-bridge-arm independent model predictive control method for an open-winding motor of a dual three-level inverter according to claim 1, characterized in that: In step 5, a cost function is established: Where j = [A, B, C] In each control cycle, only 9 switching vectors need to be selected for each phase, and a total of 27 calculations need to be performed.

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