Control precision improvement method for constant torque control of ECM motor

Abstract

The invention discloses a control precision improvement method for constant torque control of an ECM motor, and the method comprises the following steps: S1, measuring a plurality of groups of data in a constant torque control interval of a set torque T of the ECM motor through a dynamometer, calculating a damping coefficient B of the ECM motor, and storing the damping coefficient B; s2, performing constant torque control on the ECM motor based on a vector control mode, and converting into a current given value iq of a q axis according to a torque T set by a user; s3, measuring the real-time rotating speed omega of the motor, and calculating a compensation current value iq0 by using the real-time rotating speed omega of the motor and the damping coefficient B; s4, calculating a target current value iqout = iq-iq0 of the q-axis, performing q-axis current loop PI control by using the target current value iqout of the q-axis, and returning to the step S3; the motor can be matched with various air conditioner load models, the number of motor parts is greatly reduced, and great convenience is brought to customers.

Description

Technical field:

[0001] The invention relates to a method for improving control accuracy of constant torque control of an ECM motor. Background technology:

[0002] In recent years, with the increasingly fierce competition in the field of electrical appliances, the technical requirements for products have been continuously improved, such as requiring products to be energy-saving and environmentally friendly, with high controllability and intelligence, short development cycle, and low noise. As a core component, the motor has undoubtedly become a key component to solve the above technical problems. The motor in traditional household air conditioners generally adopts single-phase AC motor PSC. Single-phase AC motors have low efficiency, relatively high energy consumption, high noise, and low controllability and intelligence. With the development of motor technology, DC motors have gradually replaced AC motors. DC motors are equipped with motor controllers, which use motor controllers to achieve the purpose of electronic commutation of current. Therefore, some people in the industry also call them ECM motors (electronically commutated motors) or brushless DC motors (BLDC MOTOR) and permanent magnet synchronous motors (PMSM). They have the characteristics of energy saving and environmental protection, high reliability and controllability, low noise, and easy to realize intelligence. They can solve the shortcomings of single-phase AC motors. Therefore, the single-phase AC motors in existing air conditioners are gradually replaced by brushless DC motors or ECM motors.

[0003] Usually, the ECM motor is vector controlled. The common solution for constant torque control is to convert the given torque into the q-axis target current value iq_out according to the external given torque, and use the q-axis target current value iq_out to achieve constant torque control. The specific implementation process is: convert the given torque into the q-axis target current value iq_out, and then limit the q-axis target current value iq_out through the output of the speed loop to achieve constant torque control. See the attached Figure 1 shown.

[0004] The current method of constant torque control of ECM motors still has shortcomings: when the EM motor is used to work in the constant torque range, as the speed decreases, due to the influence of the damping coefficient, the output torque gradually increases, and constant torque output cannot be achieved. Summary of the invention:

[0005] The purpose of the present invention is to provide a method for improving the control accuracy of the constant torque control of an ECM motor, so as to solve the technical problem that in the constant torque control process of the ECM motor in the prior art, as the speed decreases, due to the influence of the damping coefficient, the output torque gradually increases, deviates from the allowable error range of the output torque, and cannot achieve constant torque output.

[0006] The purpose of the present invention is achieved through the following technical solutions.

[0007] A method for improving the control accuracy of constant torque control of an ECM motor, characterized in that it comprises the following steps:

[0008] S1: Obtain the damping coefficient B of the ECM motor;

[0009] S2: The ECM motor performs constant torque control based on the vector control mode, and converts the torque T set by the user into the current given value iq of the q axis;

[0010] S3: Measure the real-time speed ω of the motor, and calculate the compensation current value iq_0 using the real-time speed ω of the motor and the damping coefficient B;

[0011] S4: Calculate the target current value iq_out of the q-axis = iq-iq_0, use the target current value iq_out of the q-axis to perform PI control of the q-axis current loop, and return to step S3.

[0012] The damping coefficient B of the ECM motor described in step S1 is obtained as follows: a plurality of sets of data are measured by a dynamometer within the constant torque control interval of the set torque T of the ECM motor, each set of data including the rotational speed and the corresponding motor output torque, and the damping coefficient B of the ECM motor is calculated and stored.

[0013] In the above step S1, two sets of data are measured by the dynamometer in the constant torque control range. The first set of data is the speed ω_min and the motor output torque T_max corresponding to the end point of the constant torque range, and the second set of data is the speed ω_max and the motor output torque T_min corresponding to the starting point of the constant torque range, and the damping coefficient B of the ECM motor is obtained:

[0014] B=(T_max-T_min) / (ω_max-ω_min).

[0015] The compensation current value iq_0 in the above step S3 is calculated as follows:

[0016] iq_0=B*(ω_max-ω) / φf

[0017] Where ω_max is the speed corresponding to the starting point of the constant torque interval, ω is the real-time speed of the motor, and φf is the flux parameter of the motor permanent magnet.

[0018] In the above step S1, m groups of data are measured by the dynamometer in the constant torque control range, starting from the speed ω_max corresponding to the starting point of the constant torque range, the motor output torque is obtained every time the speed decreases by 50rpm, and the points are plotted on the graph to draw a curve, and the calculation equation of the damping coefficient B of the ECM motor is obtained, that is, a second-order or third-order equation of the relationship between the damping coefficient B and the speed is established, where m is an integer. .

[0019] The above-mentioned ECM motor has 5 gears of set torque T. Each gear of set torque T needs to be measured by a dynamometer within the constant torque control range of the set torque T of the corresponding gear 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 gear set torque T is calculated and stored in the microprocessor of the ECM motor.

[0020] Compared with the prior art, the present invention has the following effects:

[0021] Effect 1: Several groups of data are measured by the dynamometer within the constant torque control range of the set torque T of the ECM motor, each group of data includes the speed and the corresponding motor output torque, and the damping coefficient B of the ECM motor is calculated; the compensation current value iq_0 is calculated using the real-time speed ω of the motor and the damping coefficient B, and the given target current value of the q-axis is corrected to improve the linearity of the constant torque control, that is, to improve the control accuracy of the constant torque control of the ECM motor.

[0022] Effect 2: Any constant torque setting can be calibrated by introducing the damping coefficient B, which has a strong universality. Description of the drawings:

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

[0024] Figure 2 is a three-dimensional diagram of the ECM motor of the present invention;

[0025] Figure 3 is a three-dimensional diagram of a motor controller of an ECM motor of the present invention;

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

[0027] Figure 5 is a block diagram of an implementation circuit of a motor controller for an ECM motor of the present invention;

[0028] Figure 6 It is a block diagram of the constant torque control principle of the ECM motor of the present invention;

[0029] Figure 7 It is a schematic diagram of the rotation speed and motor output torque corresponding to the starting point of the constant torque zone captured by the present invention;

[0030] Figure 8 It is a schematic diagram of the rotation speed and motor output torque corresponding to the end point of the constant torque zone captured by the present invention;

[0031] Fig. 9 is a schematic diagram of a method for improving control accuracy of a constant torque control of an ECM motor according to the present invention;

[0032] Fig.10 It is a comparison diagram of the constant torque control line without adopting the control method of the present invention and adopting the control method of the present invention. Specific implementation method:

[0033] The present invention is further described in detail below through specific embodiments in conjunction with the accompanying drawings.

[0034] Embodiment 1: Figure 2 , Figure 3 , Figure 4 As shown, the ECM motor of this embodiment is composed 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 a coil winding wound on the stator core. The stator assembly 13 is installed on the housing assembly 11, and the rotor assembly 13 is sleeved on the inner side of the stator assembly 12. The motor controller 2 includes a control box 22 and a control circuit board 21 installed in the control box 22. Several electrolytic capacitors are installed on the control circuit board 21 as DC bus capacitors 23.

[0035] See Figure 5 As shown, the permanent magnet synchronous motor includes a motor monomer B7 and a motor controller. The motor monomer B7 includes a stator assembly and a permanent magnet rotor assembly. The stator assembly includes a stator core and a coil winding 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) charges the DC bus film capacitor B5 through the AC filter circuit B2, the rectifier circuit B3 and the DC filter circuit B4 in sequence. The DC bus film capacitor B5 provides high-voltage DC power to the inverter circuit B6; the phase line current detection circuit detects the phase current flowing through the coil winding and sends it to the microprocessor MCU. The microprocessor MCU controls the operation of the inverter circuit. The inverter circuit controls the power on and off of each phase coil winding of the stator assembly. The permanent magnet synchronous motor adopts FOC magnetic field oriented control mode; the method of FOC magnetic field oriented control can be found in textbooks or on the Internet and will not be described in detail here. Figure 5 As shown, it is assumed that the ECM motor is a three-phase brushless DC permanent magnet synchronous motor, and the inverter circuit B6 is composed of electronic switch tubes Q1, Q2, Q3, Q4, Q5, and Q6. The control ends of the electronic switch tubes Q1, Q2, Q3, Q4, Q5, and Q6 are respectively controlled by six PWM signals (P1, P2, P3, P4, P5, and P6) output by the microprocessor.

[0036] In the constant torque mode control of the permanent magnet synchronous motor under vector control, the constant torque control is generally achieved by limiting the iq current of the q axis. However, due to the existence of the motor damping coefficient, the output torque will have deviation in the constant torque control mode. The specific analysis process is as follows.

[0037] The torque equation of permanent magnet synchronous motor is known:

[0038]

[0039] Where Te is the electromagnetic torque output by the motor, np is the number of motor pole pairs, iq is the motor q-axis current, and φf is the permanent magnet flux parameter of the motor.

[0040] From the torque equation, we can know that constant torque control can be achieved by controlling constant iq. The constant torque control block diagram is shown in the attached figure. Figure 6 :

[0041] The mechanical motion equation of permanent magnet synchronous motor is known:

[0042]

[0043] Where J is the motor's moment of inertia, t is time, ω is the motor's mechanical angular frequency, Te is the motor's output electromagnetic torque, TL is the load torque, and B is the damping coefficient.

[0044] Assuming that the load torque TL remains unchanged and the motor controller controls iq, the motor output torque can be controlled to remain unchanged. However, when the constant torque is controlled at different speeds, due to the existence of the damping coefficient B, as the motor speed decreases, the torque output by the motor increases accordingly to balance the motion equation, and constant torque control cannot be achieved.

[0045] In order to achieve constant electromagnetic torque output, the present invention proposes a method for obtaining the damping coefficient B of the ECM motor using a dynamometer, and adding the coefficient to the iq given of the q-axis current to achieve constant torque control linearity improvement (i.e., improve control accuracy).

[0046] The first step is to calculate the motor damping coefficient B through dynamometer test. Take the dynamometer data of a certain ECM motor in constant torque range as an example. Make the ECM motor run in the constant torque running state of the set torque T, and capture the speed and motor output torque corresponding to the starting point of the constant torque area. Figure 7 As shown in the figure, 1050rpm corresponds to 0.585Nm. The speed and motor output torque corresponding to the end point of the constant torque zone are captured. Figure 8 As shown, 285 rpm corresponds to 0.639 Nm.

[0047] According to the different output torques corresponding to different speeds of the dynamometer in the constant torque range, the calculation formula of the damping coefficient B can be obtained:

[0048]

[0049] The damping coefficient of the motor in this example can be calculated according to the formula:

[0050]

[0051] The second step is to compensate by the damping coefficient B in the torque given link, as follows:

[0052] A method for improving the control accuracy of constant torque control of an ECM motor, characterized in that it comprises the following steps:

[0053] S1: Obtain the damping coefficient B of the ECM motor;

[0054] S2: The ECM motor performs constant torque control based on the vector control mode, and converts the torque T set by the user into the current given value iq of the q axis;

[0055] S3: Measure the real-time speed ω of the motor, and calculate the compensation current value iq_0 using the real-time speed ω of the motor and the damping coefficient B;

[0056] S4: Calculate the target current value iq_out of the q-axis = iq-iq_0, use the target current value iq_out of the q-axis to perform PI control of the q-axis current loop, and return to step S3.

[0057] The damping coefficient B of the ECM motor described in step S1 is obtained as follows: a plurality of sets of data are measured by a dynamometer within the constant torque control interval of the set torque T of the ECM motor, each set of data including the rotational speed and the corresponding motor output torque, and the damping coefficient B of the ECM motor is calculated and stored.

[0058] In the above step S1, two sets of data are measured by the dynamometer in the constant torque control range. The first set of data is the speed ω_min and the motor output torque T_max corresponding to the end point of the constant torque range, and the second set of data is the speed ω_max and the motor output torque T_min corresponding to the starting point of the constant torque range, and the damping coefficient B of the ECM motor is obtained:

[0059] B=(T_max-T_min) / (ω_max-ω_min).

[0060] This method only requires that the first set of data is the speed ω_min and the motor output torque T_max corresponding to the end point of the constant torque interval, and the second set of data is the speed ω_max and the motor output torque T_min corresponding to the starting point of the constant torque interval, to obtain the damping coefficient B of the ECM motor; using a first-order linear equation, the workload is small, the motor's microprocessor has less calculation, and it is simple and convenient.

[0061] Fig. 9 A constant torque control curve diagram of a method for improving control accuracy of constant torque control of an ECM motor of the present invention in a constant torque control interval of a set torque T; Fig.10 It is a comparison diagram of the constant torque control line without adopting the control method of the present invention and adopting the control method of the present invention. It can be seen from the figure that the present invention corrects the given q-axis target current value to improve the constant torque control linearity, that is, improves the control accuracy of the constant torque control of the ECM motor.

[0062] The compensation current value iq_0 in the above step S3 is calculated as follows:

[0063] iq_0=B*(ω_max-ω) / φf

[0064] Where ω_max is the speed corresponding to the starting point of the constant torque interval, ω is the real-time speed of the motor, and φf is the flux parameter of the motor permanent magnet.

[0065] In the above step S1, m groups of data can also be measured by a dynamometer in the constant torque control range, starting from the speed ω_max corresponding to the starting point of the constant torque range, the motor output torque is obtained every time the speed decreases by 50rpm, and the points are plotted on the graph to draw a curve to obtain the calculation equation of the damping coefficient B of the ECM motor. The relationship between the damping coefficient B and the speed can be described by a second-order equation or a third-order equation, so that the damping coefficient B can be calculated more accurately.

[0066] In addition, a general ECM motor has 5 gear setting torque T (respectively T1, T2, T3, T4 and T5), and each gear setting torque T needs to be measured by a dynamometer in the constant torque control range of the setting torque T of the corresponding gear 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 gear setting torque T is calculated and stored in the microprocessor of the ECM motor. See Table 1:

[0067]

[0068]

[0069] 1. Custom terms or abbreviations

[0070] The English in the text represents English abbreviations, and italics represent variable variables in the software.

[0071] SVPWM: Space Vector Pulse Width Modulation, is a method of superimposing a high-frequency carrier frequency on the input signal and then outputting a high-frequency pulse signal to control the inverter power tube

[0072] D-axis: The axis in the same direction as the N pole of the motor

[0073] q-axis: The axis that leads the N-pole of the motor by 90 degrees

[0074] PI: Proportional Integral Control

[0075] Clark transformation: transform the three-phase ABC coordinate system parameters to obtain the α-axis and β-axis

[0076] Park transformation: transform the α-axis and β-axis coordinate system parameters to obtain the d-axis and q-axis

[0077] U d : Target voltage in the d-axis direction of the d-axis current loop PI regulation output

[0078] U q : q-axis current loop PI regulation output q-axis direction target voltage

[0079] U A : A phase winding voltage

[0080] U B : B phase winding voltage

[0081] U C : C phase winding voltage

[0082] i d : d-axis current feedback value

[0083] i q : q-axis current feedback value

[0084] B: Motor damping coefficient

[0085] Motor permanent magnet flux parameters

[0086] ω: Motor mechanical angular frequency

[0087] T e : Electromagnetic torque output by the motor

[0088] n p : Number of motor pole pairs

[0089] J: Motor moment of inertia

[0090] T e : The electromagnetic torque output by the motor

[0091] T L : is the load torque

[0092] The above embodiments are preferred implementation modes of the present invention, but the implementation modes of the present invention are not limited thereto. Any other changes, modifications, substitutions, combinations, and simplifications made without departing from the spirit and principle of the present invention are all equivalent replacement methods and are included in the protection scope of the present invention.

Claims

1. A method for improving the control accuracy of constant torque control of an ECM motor, characterized by: It includes the following steps: S1: Obtain the damping coefficient B of the ECM motor; S2: The ECM motor performs constant torque control based on the vector control mode, and converts the torque T set by the user into the current given value iq of the q axis; S3: Measure the real-time speed ω of the motor, and calculate the compensation current value iq_0 using the real-time speed ω of the motor and the damping coefficient B; S4: Calculate the target current value iq_out of the q-axis = iq-iq_0, use the target current value iq_out of the q-axis to perform PI control of the q-axis current loop, and return to step S3.

2. The method for improving 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: a plurality of sets of data are measured by a dynamometer within a constant torque control interval of a set torque T of the ECM motor, each set of data including a rotational speed and a corresponding motor output torque, and the damping coefficient B of the ECM motor is calculated and stored.

3. The method for improving 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 by the dynamometer in the constant torque control interval. The first set of data is the speed ω_min and the motor output torque T_max corresponding to the end point of the constant torque interval, and the second set of data is the speed ω_max and the motor output torque T_min corresponding to the starting point of the constant torque interval, and the damping coefficient B of the ECM motor is obtained: B=(T_max-T_min) / (ω_max-ω_min).

4. The method for improving control accuracy of constant torque control of an ECM motor according to claim 3, characterized in that: The compensation current value iq_0 in step S3 is calculated as follows: iq_0=B*(ω_max-ω) / φf Where ω_max is the speed corresponding to the starting point of the constant torque interval, ω is the real-time speed of the motor, and φf is the flux parameter of the motor permanent magnet.

5. The method for improving control accuracy of constant torque control of an ECM motor according to claim 1, characterized in that: In step S1, m groups of data are measured in the constant torque control interval by the dynamometer. Starting from the speed ω_max corresponding to the starting point of the constant torque interval, the motor output torque is obtained every time the speed decreases by 50 rpm, and the points are plotted on the graph to draw a curve to obtain the calculation equation of the damping coefficient B of the ECM motor, that is, a second-order or third-order equation of the relationship between the damping coefficient B and the speed is established, where m is an integer.

6. A method for improving control accuracy of constant torque control of an ECM motor according to claim 1, 2, 3 or 4, characterized in that: There are 5 gears of set torque T in the ECM motor. For each gear of set torque T, a dynamometer is required to measure several groups of data within the constant torque control range of the set torque T of the corresponding gear of the ECM motor. Each group of data includes the speed and the corresponding motor output torque, and the damping coefficient B of the corresponding gear set torque T is calculated and stored in the microprocessor of the ECM motor.

Images