A control method, control system and drive system of an electric motor drive system

Abstract

The application discloses a control method, a control system and a driving system of a motor driving system, wherein the control method comprises the following steps: S1, after an inverter of the motor driving system receives a torque instruction, generating an inverter reference current given value; S2, obtaining a current change value caused by a DC side capacitor voltage change of each motor controller in the motor driving system, comparing the current change value with the reference current given value to obtain a comparison result; and S3, controlling the motor according to the comparison result. According to the application, the current change value caused by the DC side capacitor voltage change of each motor controller is fed forward to a current reference value link of the motor controller, the negative impedance of the motor controller load is changed into positive impedance through the feedforward control, and thus the problem of the negative impedance of the constant power characteristic of the motor controller load is solved; and the voltage equalization control link is used to solve the voltage equalization problem of the DC side of the series connection of each motor controller.

Description

Technical Field

[0001] This invention relates to the field of motor drive system technology, specifically to a control method, control system, and drive system for a motor drive system. Background Technology

[0002] As the DC voltage of motor drive systems increases, it becomes necessary to improve the voltage withstand capability of power devices in these systems. Selecting high-voltage power devices is a direct solution. However, high-voltage power devices are usually expensive and have significant losses. Therefore, using multiple low-voltage inverters connected in series on the DC side is a better solution that balances high voltage withstand requirements with low cost.

[0003] The DC-side series technology of inverters has precedents in the power supply and grid sectors. However, the AC-side output method and load type of inverters in these applications differ significantly from those in new energy motor drive systems. Therefore, the control methods for the motor drive systems require different approaches.

[0004] like Figure 1 As shown, the patent applicant previously designed a DC-side series application using a mature low-voltage inverter, enabling the application of low-voltage devices in high-voltage situations. This is suitable for matching DC power supplies composed of series-connected grouped power supplies, such as power battery packs connected in series, or power supplies composed of other power supply output sides connected in series. Figure 1 In (a), the load is a single motor, and each inverter corresponds to one motor; Figure 1 In (b) of the diagram, each inverter corresponds to one winding of the motor.

[0005] In an ideal situation, Figure 1 In a series connection, I1, I2, I3, ..., In are all equal, ensuring that the DC component of the operating current of the battery or electronic power supply is equal. However, in reality, due to inevitable deviations in the operating conditions of each motor load, I1, I2, I3, ..., In will not be equal. Furthermore, the DC input side of the motor controller is a constant power load for capacitors C1 (C2, C3). A constant power load has... Figure 2 The negative impedance characteristic shown is as follows, where Figure 2 In the diagram, Pconstant is the output power of each motor controller, Ucn is the voltage across the nth capacitor, and In is the DC current of the nth motor controller. That is, when the voltage Ucn increases (decreases), the input current will decrease (increase). This characteristic is detrimental to the stability of the capacitor voltage. Figure 3This is a small-signal circuit with multiple inverters connected in series. Let's explain this circuit. For example, if n motors have the same output power, and the voltage Uc1 on capacitor C1 drops slightly due to interference, I1 will rise slightly, and Uc1 will drop further. Simultaneously, since U = Uc1 + Uc2 + Uc3 + ... + Ucn, Uc2 + Uc3 + ... + Ucn will rise slightly, causing I2 or I3, ..., In to drop slightly. Uc2 + Uc3 + ... + Ucn will rise further, and Uc1 will drop further. This is a rapidly deteriorating positive feedback process; the voltage Uc2 + Uc3 + ... + Ucn will quickly increase, and the system will collapse. Other situations are similar. Therefore, if the output power of the n motors is inconsistent, the system will collapse immediately. Summary of the Invention

[0006] The technical problem to be solved by this invention is: in view of the technical problems existing in the prior art, this invention provides a control method, control system and drive system for a motor drive system that solves the constant power characteristics of the motor controller load.

[0007] To solve the above-mentioned technical problems, the technical solution proposed by this invention is as follows:

[0008] A control method for a motor drive system includes the following steps:

[0009] S1. After receiving the torque command, the inverter of the motor drive system generates the inverter reference current setpoint.

[0010] S2. Obtain the current change value caused by the change in DC side capacitor voltage of each motor controller in the motor drive system, and compare the current change value with the reference current setpoint to obtain the comparison result;

[0011] S3. Control the motor based on the comparison results.

[0012] Preferably, in step S2, the current change value is compared with zero to obtain a comparison result, and then the comparison result is adjusted by PI to obtain an adjustment result, and then the adjustment result is compared with the reference current setpoint.

[0013] Preferably, in step S2, the current change value ΔI n for:

[0014]

[0015] Where ΔI n ΔU Cn For I n U Cn The change value within a single control cycle, U Cn P is the capacitor voltage. constant for:

[0016]

[0017] Where u dn i dn u qn i qn These represent the d-axis voltage, d-axis current, q-axis voltage, and q-axis current in the nth motor controller.

[0018] Preferably, between step S1 and step S2, a voltage equalization control stage is further included to achieve voltage equalization control on the DC side of the series inverter.

[0019] Preferably, the specific process of the voltage equalization control stage is as follows: calculate the average value U / n of the n inverter input voltages, and then convert the actual capacitor voltage U... C1 U C2 U C3 ...U Cn Subtract the average value U / n, and use the difference for PI adjustment to obtain the adjustment result. Then, subtract the inverter reference current setpoint obtained in step S1 from this adjustment result to obtain a new inverter reference current setpoint.

[0020] Preferably, in step S3, the comparison results are redistributed to obtain the allocation results, and then conventional current loop control is performed based on the allocation results.

[0021] Preferably, the specific process of step S1 is as follows: after receiving the torque command, the motor parameters are calibrated according to the maximum torque per unit current requirement, and the control parameters of the nth motor are obtained. Find its root mean square value As the reference current setpoint for the inverter.

[0022] Preferably, the control parameters of the nth motor are obtained by using a lookup table method or a curve fitting method.

[0023] The present invention also discloses a control system for a motor drive system, including a memory and a processor, wherein the memory stores a computer program, and the computer program executes the steps of the method described above when run by the processor.

[0024] The present invention further discloses a motor drive system, including a motor drive device and a control system as described above, wherein the motor drive device includes a battery module, multiple inverters and multiple motor loads, the multiple inverters are connected in series, and the input terminals of the multiple inverters are connected to the battery module, and the output terminals of each inverter are connected to the motor loads in a one-to-one correspondence.

[0025] Compared with the prior art, the advantages of the present invention are as follows:

[0026] This invention solves the problem of negative impedance in the constant power characteristic of the motor controller load by feeding forward the current change value caused by the change of DC side capacitor voltage of each motor controller to the current reference value of the motor controller. Through this feedforward control, the negative resistance of the motor controller load is changed to positive impedance.

[0027] This invention solves the problem of voltage equalization on the DC side of various motor controllers connected in series by calculating the average value of the input voltage of n inverters, subtracting the average value from the actual capacitor voltage, and applying the difference to PI regulation to obtain the PI regulation result. Then, the reference current setpoint of each inverter is subtracted from this PI regulation result, and the corresponding difference is used as the reference current setpoint of the actual inverter. Attached Figure Description

[0028] Figure 1 This is a schematic diagram of the drive system of the present invention in an embodiment; wherein (a) the motor load is multiple motors; and (b) the motor load is multiple windings of a motor.

[0029] Figure 2 This is a diagram showing the negative impedance characteristics of the constant power load of the present invention.

[0030] Figure 3 This is a small-signal circuit diagram of multiple inverters connected in series according to the present invention.

[0031] Figure 4 This is a circuit diagram of the voltage equalization control stage and the negative impedance suppression stage of the present invention.

[0032] Figure 5 This is a control block diagram of the overall control system of the present invention in a specific application. Detailed Implementation

[0033] The present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0034] First, the motor drive system to which the control method of the present invention is applicable will be described below: For example... Figure 1 As shown, mature low-voltage inverters are used for DC-side series applications, enabling the application of low-voltage devices in high-voltage situations. This is suitable for matching DC power supplies composed of series-connected grouped power supplies, such as series-connected power battery packs or series-connected power supply outputs. The number of low-voltage inverters to be connected in series is calculated based on the withstand voltage rating of the low-voltage inverters and the high voltage value of the actual application. For example, for a peak DC voltage of 1500V, two low-voltage electric drive systems with a peak voltage of 750V can be connected in series. It is required that the power rating of each low-voltage inverter and its connected load be consistent. Figure 1 R1, R2, and R3 are voltage equalizing resistors, and their resistance values ​​must be the same.

[0035] like Figure 4 and Figure 5 As shown, the control method of the motor drive system according to an embodiment of the present invention includes the following steps:

[0036] S1. After receiving the torque command, the inverter of the motor drive system generates the inverter reference current setpoint.

[0037] S2. Obtain the current change value caused by the change in DC side capacitor voltage of each motor controller in the motor drive system, and compare the current change value with the reference current setpoint to obtain the comparison result;

[0038] S3. Control the motor based on the comparison results.

[0039] In one specific embodiment, in step S2, the current change value caused by the change in the DC-side capacitor voltage of each motor controller is fed forward to the current reference value stage of the motor controller. This feedforward control changes the negative resistance of the motor controller load to a positive impedance, thereby solving the negative impedance problem of the constant power characteristic of the motor controller load. Specifically, in step S2, the current change value is compared with zero to obtain a comparison result. Then, the comparison result is PI-adjusted to obtain an adjustment result, which is then compared with the reference current setpoint. The current change value ΔI... n for:

[0040]

[0041] Where ΔI n ΔU Cn For I n U Cn The change value within a single control cycle, U Cn Let I be the capacitor voltage, where I is the capacitor voltage. n I is the steady-state value of the DC-side current of the motor controller with output power Pconstant. n =P constant / U c1 , where P constant for:

[0042]

[0043] Where u dn i dn u qn i qn These represent the d-axis voltage, d-axis current, q-axis voltage, and q-axis current in the nth motor controller.

[0044] From equation (1), it can be seen that the current ΔI n With capacitor voltage U Cn The change in value is in the opposite direction, which is detrimental to the stability of the capacitor voltage. Therefore... Figure 4The negative impedance suppression control algorithm in the text aims to reduce the negative impedance ΔI that affects capacitor voltage stability through a PI control algorithm. n By suppressing the current to near 0, the implementation of this control loop stabilizes the inverter's DC current at I. n =P constant / U c1 At this point, the inverter load is equivalent to a constant current source load, instead of the constant power load before the addition of the negative impedance suppression stage.

[0045] In one specific embodiment, to solve the voltage equalization problem on the DC side of the series-connected motor controllers, the average value U / n of the input voltages of n inverters is calculated, and the actual capacitor voltage U is then calculated. C1 U C2 U C3 ...U Cn Subtracting the average value U / n, the difference is PI-adjusted, and then the adjusted value is subtracted from the reference current setpoint of each inverter. The difference is used as the actual reference current setpoint of the inverter. Specifically, when a capacitor voltage U... Cn When the value is too large (too small), the difference between it and the average value U / n is positive (negative), the PI regulator output increases (decreases), and the original inverter reference current setpoint I... s * n The output value of the PI regulator needs to be subtracted, therefore the actual reference current setpoint of the inverter needs to be determined. Decrease (increase), then the next control cycle U Cn This will reduce (increase) the DC side voltage equalization control of the series inverter.

[0046] This invention also discloses a control system for a motor drive system, including a memory and a processor. The memory stores a computer program, which, when run by the processor, executes the steps of the method described above. The control system of this invention corresponds to the control method described above and also possesses the advantages described above.

[0047] like Figure 1 As shown in the figure, the present invention also discloses a motor drive system, including a motor drive device and the control system described above. The motor drive device includes a battery module, multiple inverters and multiple motor loads. The multiple inverters are connected in series, and the input terminals of the multiple inverters are connected to the battery module. The output terminals of each inverter are connected to the motor loads one by one.

[0048] The aforementioned motor drive system uses a low-voltage inverter and its drive motor to achieve high-voltage applications. Compared with products that directly use high-voltage power devices and high-voltage withstand voltage designs, it has the advantages of low cost, short development cycle, and high reliability. At the same time, it achieves product standardization for both high and low voltage working environments, without adding extra equipment or inspection tools to the production line.

[0049] The following is in conjunction with the appendix Figure 5 The specific control method of the motor drive system of the present invention will be further described below:

[0050] Figure 5 in,i dn i qn Let ω be the d-axis and q-axis currents of the motor. n L dn L qn and φ Mn These are the motor speed, d-axis inductance, q-axis inductance, and rotor flux, respectively.

[0051] After receiving the torque command, the inverter calibrates the motor parameters according to the maximum torque per unit current (MTPA) requirement. This is typically done using a lookup table method or curve fitting to obtain the control parameters for the nth motor. Find its root mean square value As the initial inverter reference current setpoint

[0052] Then The adjustment results of the added voltage equalization control stage are used to obtain the reference current setpoint for the intermediate inverter. The adjustment result of the voltage equalization control stage is the actual capacitor voltage U. C1 U C2 U C3 ...U Cn The result after subtracting the difference between the average value U / n of the input voltages of n inverters and applying PI regulation;

[0053] intermediate inverter reference current setpoint Based on the adjustment results of adding a negative impedance suppression stage, the final inverter reference current setpoint is obtained. The adjustment result of the negative impedance suppression circuit is obtained by comparing the current change value with zero, and then adjusting the comparison result with PI.

[0054] Then, the final inverter reference current is given. The allocation will be redistributed according to the following principles: After that, targeting The motor control strategy using the traditional current loop will not be elaborated upon here.

[0055] As shown in this disclosure and the claims, unless the context clearly indicates otherwise, the words "a," "an," "an," and / or "the" are not specifically singular and may include plural forms. The terms "first," "second," and similar terms used in this disclosure do not indicate any order, quantity, or importance, but are merely used to distinguish different components. Similarly, the terms "comprising" or "including" mean that the element or object preceding the word covers the element or object listed after the word and its equivalents, without excluding other elements or objects. The terms "connected" or "linked" are not limited to physical or mechanical connections but may include electrical connections, whether direct or indirect.

[0056] The above are merely preferred embodiments of the present invention. The scope of protection of the present invention is not limited to the above embodiments. All technical solutions falling within the scope of the present invention's concept are within the scope of protection of the present invention. It should be noted that for those skilled in the art, any improvements and modifications made without departing from the principles of the present invention should be considered within the scope of protection of the present invention.

Claims

1. A control method for a motor drive system, characterized in that, Including the following steps: S1. After receiving the torque command, the inverter of the motor drive system generates the inverter reference current setpoint. S2. Obtain the current change value caused by the change in DC side capacitor voltage of each motor controller in the motor drive system, and compare the current change value with the reference current setpoint to obtain the comparison result; S3. Control the motor based on the comparison results; In step S2, the current change value is compared with zero to obtain the comparison result. Then, the comparison result is adjusted by PI to obtain the adjustment result. Finally, the adjustment result is superimposed on the reference current setpoint. In step S2, the change in current value for: in , for , The change value within a single control cycle, The voltage across the capacitor. The steady-state value of the DC-side current of the motor controller with output power Pconstant; for: in , , , These represent the d-axis voltage, d-axis current, q-axis voltage, and q-axis current in the nth motor controller.

2. The control method for the motor drive system according to claim 1, characterized in that, Between step S1 and step S2, there is also a voltage equalization control stage, which is used to realize the voltage equalization control of the DC side of the series inverter.

3. The control method for the motor drive system according to claim 2, characterized in that, The specific process of the pressure equalization control step is as follows: Calculate the average value U / n of the n inverter input voltages, and then convert the actual capacitor voltage... Subtract the average value U / n, and use the difference for PI adjustment to obtain the adjustment result. Then, subtract the inverter reference current setpoint obtained in step S1 from this adjustment result to obtain a new inverter reference current setpoint.

4. The control method for the motor drive system according to claim 1, 2, or 3, characterized in that, In step S3, the comparison results are redistributed to obtain the allocation results, and then traditional current loop control is performed based on the allocation results.

5. The control method for the motor drive system according to claim 1, 2, or 3, characterized in that, The specific process of step S1 is as follows: After receiving the torque command, the motor parameters are calibrated according to the maximum torque per unit current requirement, and the control parameters of the nth motor are obtained. , Find its root mean square value. This serves as the reference current setpoint for the inverter.

6. The control method for the motor drive system according to claim 5, characterized in that, The control parameters of the nth motor can be obtained by using a lookup table method or a curve fitting method.

7. A control system for a motor drive system, comprising a memory and a processor, wherein the memory stores a computer program, characterized in that, The computer program, when run by a processor, performs the steps of the method as described in any one of claims 1 to 6.

8. A motor drive system, characterized in that, The system includes a motor drive device and a control system as described in claim 7, wherein the motor drive device includes a battery module, multiple inverters and multiple motor loads, the multiple inverters are connected in series, and the input terminals of the multiple inverters are connected to the battery module, and the output terminals of each inverter are connected to the motor loads in a one-to-one correspondence.

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