Control accuracy improvement method for constant torque control of ecm

Abstract

A control accuracy improvement method for constant torque control of an ECM. The method comprises the following steps: S1, by means of a dynamometer, measuring several sets of data within a constant torque control interval of a set torque T of an ECM, performing calculation to obtain a damping coefficient B of the ECM, and storing same; S2, the ECM performing constant torque control on the basis of a vector control mode, and converting into a given q-axis current value iq a torque T set by a user; S3, measuring a real-time rotational speed ω of the electric motor, and using the real-time rotational speed ω of the electric motor and the damping coefficient B to calculate a compensation current value iq_0; and S4, calculating a target q-axis current value iq_out=iq−iq_0, using the target q-axis current value iq_out to perform q-axis current loop PI control, and returning to step S3. The method can match a variety of air-conditioning load models, such that the number of electric motor part numbers is greatly reduced, thereby bringing considerable convenience to customers.

Description

A method for improving the control accuracy of constant torque control of ECM motors

[0001] Cross-reference to related applications

[0002] This application claims priority to Chinese Patent Application No. 202411176242.6, filed on August 26, 2024, entitled "A Method for Improving the Control Accuracy of Constant Torque Control of an ECM Motor", the entire contents of which are incorporated herein by reference. Technical Field

[0003] This application relates to a method for improving the control accuracy of constant torque control of an ECM motor. Background Technology

[0004] In recent years, with increasingly fierce competition in the electrical appliance industry, the technical requirements for products have been continuously raised, such as requiring energy-saving and environmentally friendly products, high controllability and intelligence, short development cycles, and low noise. As a core component, the motor has undoubtedly become a key component in solving the above-mentioned technical problems. Traditional household air conditioners generally use single-phase AC motors (PSCs). Single-phase AC motors are inefficient, energy-consuming, noisy, and have low controllability and intelligence. With the development of motor technology, DC motors are gradually replacing AC motors. DC motors have motor controllers, which realize the electronic commutation of current. Therefore, they are also referred to in the industry as ECM motors (electronically commutated motors), brushless DC motors (BLDC motors), or permanent magnet synchronous motors (PMSMs). They have the characteristics of energy saving and environmental protection, high reliability and controllability, low noise, and easy intelligent implementation, which can solve the shortcomings of single-phase AC motors. Therefore, the single-phase AC motors in existing air conditioners are gradually being replaced by brushless DC motors or ECM motors.

[0005] In typical ECM motor vector control, a common scheme for constant torque control involves taking an externally given torque, converting it into a target q-axis current value iq_out, and then using iq_out to achieve constant torque control. The specific implementation process is as follows: the given torque is converted into the target q-axis current value iq_out, and then the speed loop output is used to limit the target q-axis current value iq_out, thus achieving constant torque control, as shown in Figure 1.

[0006] Current methods for constant torque control of ECM motors have shortcomings: when an EM motor operates in the constant torque range, as the speed decreases, the output torque gradually increases due to the influence of the damping coefficient, making it impossible to achieve constant torque output. Summary of the Invention

[0007] The purpose of this application is to provide a method for improving the control accuracy of constant torque control of ECM motors, and to solve the technical problem in the existing ECM motor constant torque control process that, as the speed decreases, the output torque gradually increases due to the influence of the damping coefficient, deviating from the allowable error range of the output torque, and thus failing to achieve constant torque output.

[0008] The purpose of this application is achieved through the following technical solution.

[0009] A method for improving the control accuracy of constant torque control of an ECM motor, characterized by comprising the following steps:

[0010] S1: Obtain the damping coefficient B of the ECM motor;

[0011] S2: The ECM motor uses constant torque control based on vector control mode, converting the user-defined torque T into a current setpoint i for the q-axis. q ;

[0012] S3: Measure the real-time motor speed ω, and calculate the compensation current value i using the real-time motor speed ω and the damping coefficient B. q_0 ;

[0013] S4: Calculate the target current value i along the q-axis. q_out =i q -i q_0 Using the target current value i along the q-axis q_out Perform q-axis current loop PI control and return to step S3.

[0014] The damping coefficient B of the ECM motor in step S1 above is obtained as follows: several sets of data are measured by a dynamometer within the constant torque control range of the set torque T of the ECM motor. Each set of data includes the rotational speed and the corresponding motor output torque. The damping coefficient B of the ECM motor is then calculated and stored.

[0015] In step S1 above, two sets of data are measured by a dynamometer within the constant torque control range. The first set of data is the speed ω_min and motor output torque T_max corresponding to the end of the constant torque range. The second set of data is the speed ω_max and motor output torque T_min corresponding to the beginning of the constant torque range. The damping coefficient B of the ECM motor is obtained as follows: B=(T_max-T_min) / (ω_max-ω_min).

[0016] The compensation current value i in step S3 above q_0 This is how it's calculated: i q_0 =B*(ω_max-ω) / φ f

[0017] Where ω_max is the rotational speed corresponding to the starting point of the constant torque interval, ω is the real-time rotational speed of the motor, and φ f These are the flux linkage parameters of the permanent magnet in the motor.

[0018] In step S1 above, m sets of data are measured using a dynamometer within the constant torque control range. Starting from the speed ω_max corresponding to the beginning of the constant torque range, the motor output torque is obtained every 50 rpm decrease in speed, and the points are plotted on a graph to draw a curve, thus obtaining the calculation equation for the damping coefficient B of the ECM motor. This establishes a second- or third-order equation relating the damping coefficient B to the speed, where m is an integer.

[0019] The aforementioned ECM motor has 5 set torque levels T. For each set torque level T, a dynamometer is used to measure several sets of data within the constant torque control range of the corresponding set torque level T of the ECM motor. Each set of data includes the speed and the corresponding motor output torque, and the damping coefficient B of the corresponding set torque level T is calculated and stored in the microprocessor of the ECM motor.

[0020] Compared with the prior art, this application has the following advantages:

[0021] Effect 1: By measuring several sets of data within the constant torque control range of the ECM motor's set torque T using a dynamometer, each set of data includes the motor speed and corresponding output torque, and the damping coefficient B of the ECM motor is calculated; the compensation current value i is calculated using the motor's real-time speed ω and damping coefficient B. q_0 It also corrects the given target current value on the q-axis to improve the linearity of constant torque control, that is, to improve the control accuracy of constant torque control of the ECM motor.

[0022] Effect 2: Any constant torque can be calibrated by introducing a damping coefficient B, which has strong versatility. Attached Figure Description

[0023] Figure 1 is a block diagram of the existing ECM motor constant torque control principle;

[0024] Figure 2 is a perspective view of the ECM motor of this application;

[0025] Figure 3 is a perspective view of the motor controller of the ECM motor of this application;

[0026] Figure 4 is a structural cross-sectional view of the ECM motor of this application;

[0027] Figure 5 is a block diagram of the implementation circuit of the motor controller of the ECM motor of this application;

[0028] Figure 6 is a block diagram of the ECM motor constant torque control principle of this application;

[0029] Figure 7 is a schematic diagram of the rotational speed and motor output torque corresponding to the starting point of the constant torque region captured by this application;

[0030] Figure 8 is a schematic diagram of the rotational speed and motor output torque corresponding to the end point of the constant torque region captured by this application;

[0031] Figure 9 is a schematic diagram of the improved control accuracy of the constant torque control of the ECM motor using the method described in this application.

[0032] Figure 10 is a comparison diagram of constant torque control lines with and without the control method of this application. Detailed Implementation

[0033] The present application will now be described in further detail with reference to specific embodiments and accompanying drawings.

[0034] Example 1: As shown in Figures 2, 3, and 4, the ECM motor in this example consists of a motor unit 1 and a motor controller 2. The motor unit 1 includes a stator assembly 12, a rotor assembly 13, and a housing assembly 11, including a stator core and coil windings wound on the stator core. The stator assembly 13 is mounted on the housing assembly 11, and the rotor assembly 13 is fitted inside the stator assembly 12. The motor controller 2 includes a control box 22 and a control circuit board 21 installed inside the control box 22. Several electrolytic capacitors are installed on the control circuit board 21 as DC bus capacitors 23.

[0035] As shown in Figure 5, the permanent magnet synchronous motor consists of a motor unit B7 and a motor controller. The motor unit B7 includes a stator assembly and a permanent magnet rotor assembly. The stator assembly includes a stator core and coil windings wound on the stator core. The motor controller includes an AC filter circuit B2, a rectifier circuit B3, a DC filter circuit B4, a DC bus film capacitor B5, an inverter circuit B6, a microprocessor MCU, and a phase current detection circuit. The three-phase power supply B1 (which is an AC power supply) sequentially passes through the AC filter circuit B2, the rectifier circuit B3, and the DC filter circuit B4 to charge the DC bus film capacitor B5. The DC bus film capacitor B5 provides high-voltage DC power to the inverter circuit B6. The phase current detection circuit detects the phase current flowing through the coil windings and sends it to the microprocessor MCU. The microprocessor MCU controls the operation of the inverter circuit, which in turn controls the on / off state of each phase coil winding of the stator assembly. The permanent magnet synchronous motor adopts the FOC field-oriented control method. The methods of FOC field-oriented control can be found in textbooks or online and will not be described in detail here. As shown in Figure 5, assuming the ECM motor is a 3-phase brushless DC permanent magnet synchronous motor, the inverter circuit B6 consists of electronic switches Q1, Q2, Q3, Q4, Q5, and Q6. The control terminals of electronic switches Q1, Q2, Q3, Q4, Q5, and Q6 are controlled by 6 PWM signals (P1, P2, P3, P4, P5, and P6) output by the microprocessor.

[0036] In the constant torque mode control of a permanent magnet synchronous motor using vector control, the i-axis of the q-axis is typically limited. q Constant torque control is achieved using current. However, due to the motor's damping coefficient, there will be a deviation in the output torque under constant torque control mode. The specific analysis process is as follows.

[0037] The torque equation for a permanent magnet synchronous motor is known as follows:

[0038] In the formula, Te is the electromagnetic torque output by the motor, np is the number of pole pairs of the motor, and i q φ is the q-axis current of the motor. f These are the flux linkage parameters of the permanent magnet in the motor.

[0039] From the torque equation, it can be seen that controlling constant i q This allows for constant torque control, and the block diagram for constant torque control is shown in Figure 6.

[0040] Given the mechanical motion equations of a permanent magnet synchronous motor:

[0041] In the formula, J is the moment of inertia of the motor, t is time, ω is the mechanical angular frequency of the motor, Te is the electromagnetic torque output by the motor, TL is the load torque, and B is the damping coefficient.

[0042] Assuming the load torque TL remains constant, and the motor controller controls i q This allows for constant torque control of the motor output. However, in constant torque control at different speeds, due to the damping coefficient B, the output torque of the motor increases accordingly as the motor speed decreases, making constant torque control impossible to achieve.

[0043] To achieve a constant output electromagnetic torque, this application proposes a method for identifying the ECM motor damping coefficient B using a dynamometer, and then supplementing this coefficient into the q-axis current i. q Given the parameters, the linearity of constant torque control is improved (i.e., the control accuracy is improved).

[0044] The first step is to calculate the motor damping coefficient B using a dynamometer. Taking the constant torque range dynamometer data of a certain ECM motor as an example, the ECM motor is run at a set constant torque T, and the speed and motor output torque corresponding to the beginning of the constant torque range are captured. As shown in Figure 7, 1050 rpm corresponds to 0.585 Nm. The speed and motor output torque corresponding to the end of the constant torque range are then captured. As shown in Figure 8, 285 rpm corresponds to 0.639 Nm.

[0045] Based on the different output torques corresponding to different speeds of the dynamometer within the constant torque range, the formula for calculating the damping coefficient B can be obtained:

[0046] The damping coefficient of this example motor can then be calculated using the formula:

[0047] The second step involves compensation using the damping coefficient B during the torque setting process, as detailed below:

[0048] A method for improving the control accuracy of constant torque control of an ECM motor, characterized by comprising the following steps:

[0049] S1: Obtain the damping coefficient B of the ECM motor;

[0050] S2: The ECM motor uses constant torque control based on vector control mode, converting the user-defined torque T into a current setpoint i for the q-axis. q ;

[0051] S3: Measure the real-time motor speed ω, and calculate the compensation current value i using the real-time motor speed ω and the damping coefficient B. q_0 ;

[0052] S4: Calculate the target current value i along the q-axis. q_out =i q -i q_0 Using the target current value i along the q-axis q_outPerform q-axis current loop PI control and return to step S3.

[0053] The damping coefficient B of the ECM motor in step S1 above is obtained as follows: several sets of data are measured by a dynamometer within the constant torque control range of the set torque T of the ECM motor. Each set of data includes the rotational speed and the corresponding motor output torque. The damping coefficient B of the ECM motor is then calculated and stored.

[0054] In step S1 above, two sets of data are measured by a dynamometer within the constant torque control range. The first set of data is the speed ω_min and motor output torque T_max corresponding to the end of the constant torque range. The second set of data is the speed ω_max and motor output torque T_min corresponding to the beginning of the constant torque range. The damping coefficient B of the ECM motor is obtained as follows: B=(T_max-T_min) / (ω_max-ω_min).

[0055] This method only requires the first set of data to be the rotational speed ω_min and the motor output torque T_max corresponding to the end of the constant torque interval, and the second set of data to be the rotational speed ω_max and the motor output torque T_min corresponding to the beginning of the constant torque interval, to obtain the damping coefficient B of the ECM motor. It uses a first-order linear equation, which reduces the workload and the computational load on the motor's microprocessor, making it simple and convenient.

[0056] Figure 9 is a constant torque control curve of the constant torque control of an ECM motor according to the method for improving the control accuracy of constant torque control in this application, within the constant torque control range of the set torque T; Figure 10 is a comparison diagram of constant torque control lines without the control method of this application and with the control method of this application. As can be seen from the figure, this application corrects the given target current value of the q-axis to improve the linearity of constant torque control, that is, to improve the control accuracy of constant torque control of the ECM motor.

[0057] The compensation current value i in step S3 above q_0 This is how it's calculated: i q_0 =B*(ω_max-ω) / φ f

[0058] Where ω_max is the rotational speed corresponding to the starting point of the constant torque interval, ω is the real-time rotational speed of the motor, and φ f These are the flux linkage parameters of the permanent magnet in the motor.

[0059] In step S1 above, m sets of data can also be measured using a dynamometer within the constant torque control range. Starting from the speed ω_max corresponding to the beginning of the constant torque range, the motor output torque is obtained every 50 rpm decrease in speed, and the points are plotted on a graph to draw a curve, thus obtaining the calculation equation for the damping coefficient B of the ECM motor. The relationship between the damping coefficient B and the speed can be described using a second-order or third-order equation, making the calculation of the damping coefficient B more accurate.

[0060] In addition, a typical ECM motor has five set torque levels T (T1, T2, T3, T4, and T5). For each set torque level T, a dynamometer is used to measure several sets of data within the constant torque control range of the corresponding set torque level T on the ECM motor. Each set of data includes the motor speed and the corresponding output torque. The damping coefficient B for the corresponding set torque level T is then calculated and stored in the ECM motor's microprocessor. See Table 1 for details.

[0061] 1. Custom terms or abbreviations

[0062] In the text, regular text represents English abbreviations, and italics represents variable variables in the software.

[0063] SVPWM: Space Vector Pulse Width Modulation, is a method that superimposes a high-frequency carrier frequency onto the input signal and then outputs a high-frequency pulse signal to control the inverter's power transistors.

[0064] d-axis: The axis in the same direction as the motor's N pole.

[0065] q-axis: Axis with a 90-degree electrical angle leading the N-pole of the motor.

[0066] PI: Proportional-Integral Control

[0067] Clark transformation: Transforms the parameters of the three-phase ABC coordinate system to obtain the α-axis and β-axis.

[0068] Park transformation: Transforms the coordinate system parameters of the α-axis and β-axis to obtain the d-axis and q-axis.

[0069] U d The target voltage in the d-axis direction output by the PI regulation of the d-axis current loop.

[0070] U q The target voltage in the q-axis direction output by the PI regulation of the q-axis current loop.

[0071] U A Phase A winding voltage

[0072] U B Phase B winding voltage

[0073] U C C-phase winding voltage

[0074] i d d-axis current feedback value

[0075] i q : q-axis current feedback value

[0076] B: Motor damping coefficient

[0077] Motor permanent magnet flux linkage parameters

[0078] ω: Mechanical angular frequency of the motor

[0079] T e The electromagnetic torque output by the motor

[0080] n p Number of pole pairs of the motor

[0081] J: Moment of inertia of the motor

[0082] T e : The electromagnetic torque output by the motor

[0083] T L : for load torque

[0084] The above embodiments are preferred embodiments of this application, but the embodiments of this application are not limited thereto. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of this application are equivalent substitutions and are included within the protection scope of this application.

Claims

1. A method for improving the control accuracy of constant torque control of an ECM motor, characterized in that: It includes the following steps: S1: Obtain the damping coefficient B of the ECM motor; S2: The ECM motor uses constant torque control based on vector control mode, converting the user-defined torque T into a current setpoint i for the q-axis. q ; S3: Measure the real-time motor speed ω, and calculate the compensation current value i using the real-time motor speed ω and the damping coefficient B. q_0 ; S4: Calculate the target current value i along the q-axis. q_out =i q -i q_0 Using the target current value i along the q-axis q_out Perform q-axis current loop PI control and return to step S3.

2. The method for improving the control accuracy of constant torque control of an ECM motor according to claim 1, characterized in that: The damping coefficient B of the ECM motor in step S1 is obtained as follows: several sets of data are measured by a dynamometer within the constant torque control range of the set torque T of the ECM motor. Each set of data includes the rotational speed and the corresponding motor output torque. The damping coefficient B of the ECM motor is then calculated and stored.

3. The method for improving the control accuracy of constant torque control of an ECM motor according to claim 2, characterized in that: In step S1, two sets of data are measured using a dynamometer within the constant torque control range. The first set of data is the rotational speed ω_min and the motor output torque T_max corresponding to the end of the constant torque range. The second set of data is the rotational speed ω_max and the motor output torque T_min corresponding to the beginning of the constant torque range. The damping coefficient B of the ECM motor is obtained as follows: B = (T_max - T_min) / (ω_max - ω_min).

4. The method for improving the control accuracy of constant torque control of an ECM motor according to claim 3, characterized in that: The compensation current value i in step S3 q_0 This is how it's calculated: i q_0 =B*(ω_max-ω) / φ f Where ω_max is the rotational speed corresponding to the starting point of the constant torque interval, ω is the real-time rotational speed of the motor, and φ f These are the flux linkage parameters of the permanent magnet in the motor.

5. The method for improving the control accuracy of constant torque control of an ECM motor according to claim 1, characterized in that: In step S1, m sets of data are measured within the constant torque control range using a dynamometer. Starting from the speed ω_max corresponding to the beginning of the constant torque range, the motor output torque is obtained every 50 rpm decrease in speed, and the points are plotted on the graph to draw a curve, thereby obtaining the calculation equation for the damping coefficient B of the ECM motor, that is, establishing a second-order or third-order equation for the relationship between the damping coefficient B and the speed, where m is an integer.

6. The method for improving the control accuracy of constant torque control of an ECM motor according to any one of claims 1-4, characterized in that: The ECM motor has 5 set torque levels T. For each set torque level T, a dynamometer is used to measure several sets of data within the constant torque control range of the corresponding set torque level T of the ECM motor. Each set of data includes the speed and the corresponding motor output torque. The damping coefficient B of the corresponding set torque level T is calculated and stored in the microprocessor of the ECM motor.

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