A robust position-free control method for a three-phase permanent magnet synchronous motor

Abstract

This invention discloses a robust positionless control method for a three-phase permanent magnet synchronous motor, belonging to the technical field of power generation, substation, or distribution. This method combines high-dynamic rotor position identification technology with a high-dynamic speed controller. High-dynamic positionless identification is achieved through a novel real-time back-EMF calculation algorithm and a phase-locked loop. The high-dynamic speed controller, connected in parallel with a speed controller and a q-axis current controller, rapidly compensates for torque, achieving rapid speed stabilization under dynamic loads. This reduces rotor position estimation errors, improves the load-carrying performance of the positionless control system, and effectively enhances the load-carrying performance and robustness of the positionless control system at low speeds.

Description

Technical Field

[0001] This invention discloses a robust positionless control method for a three-phase permanent magnet synchronous motor (PMSM), belonging to the technical field of power generation, transformation, or distribution. Background Technology

[0002] Field-Oriented Control (FOC) has become a standard technology in the field of variable frequency speed control. However, the use of rotor position sensors limits the application range of three-phase electric drive systems. Therefore, sensorless rotor position control technology has emerged, also known as positionless control technology. Currently, positionless control technology has been successfully applied in the home appliance industry, where the characteristics are high motor operating speed and good load predictability. Besides home appliances, due to the installation difficulties of mechanical position sensors, positionless control technology also has an urgent need in applications such as ship electric propulsion, wind power generation, and aircraft engine start-up / generation. However, due to the poor dynamic performance of current positionless control systems, this technology faces significant challenges in these applications.

[0003] Based on the operating speed range, positionless control technology can be divided into mid-to-high speed domain positionless control and low-speed domain positionless control. Typically, the mid-to-high speed domain corresponds to 1 / 4 to 2 times the rated speed, while the low-speed domain can be represented by electrical frequency within a few hertz. A smooth transition between the mid-to-high speed and low-speed domains is achieved through a flexible switching algorithm. Numerous positionless control methods are suitable for the mid-to-high speed domain, among which motor model-based positionless control algorithms dominate. Depending on the observation object, these can be divided into back-electromagnetic observation and flux linkage observation methods. The observers used include sliding mode variable structure observers, active disturbance rejection observers, model reference adaptive system observers, extended Kalman filters, etc., and most employ closed-loop structures. Since all these observers are established based on the fundamental frequency model of the motor, they do not offer substantial breakthroughs in improving the dynamic performance of positionless control systems. Furthermore, a prerequisite for the operation of these closed-loop observers is stable estimated speed; however, under dynamic loads, the estimated speed fluctuates significantly with load changes, causing nonlinearity in the positionless control system. This can lead to local oscillations or, in severe cases, positionless control failure. It is evident that three-phase permanent magnet synchronous motors exhibit poor dynamic response in positionless control mode. Specifically, under dual closed-loop speed and current control, the output speed characteristics are relatively soft, resulting in severe speed drops and frequent positionless control failures when a sudden load is applied at low speeds. Therefore, existing positionless control systems for three-phase permanent magnet synchronous motors suffer from poor dynamic performance and difficulty in extending their application to lower speed ranges.

[0004] The poor dynamic performance and difficulty in extending to lower speed ranges of positionless control systems stem from two aspects: (1) slow rotor position recognition speed, and (2) slow response of the speed regulation system. The former is mostly caused by closed-loop observers and the use of filters, while the latter is caused by the adoption of a speed-current dual closed-loop structure.

[0005] To address this, the present invention proposes a robust positionless control method for a three-phase permanent magnet synchronous motor, and provides a solution that combines high dynamic rotor position identification technology with a high dynamic speed regulator to overcome the above-mentioned defects. Summary of the Invention

[0006] The purpose of this invention is to address the technical problems of current sensorless control technology, such as soft speed characteristics at low speeds, weak load-carrying capacity, and poor stability. This invention proposes a robust sensorless control method for three-phase permanent magnet synchronous motors. By combining a real-time back EMF calculation algorithm, phase-locked loop technology, and a parallel speed-current regulator, robust sensorless control of the three-phase permanent magnet synchronous motor is achieved, thereby improving the performance of sensorless control systems in handling dynamic loads.

[0007] To achieve the above-mentioned objectives, the present invention employs the following technical solution:

[0008] This invention employs a real-time back electromotive force calculation algorithm for sensorless low-speed control of PMSM, which can be specifically expressed as follows:

[0009]

[0010] The back electromotive force calculation algorithm used in traditional positionless control algorithms can be expressed as:

[0011]

[0012] In equations (1) and (2), e α and e β These represent the extended back electromotive forces along the α and β axes of the two-phase stationary coordinate system of the motor, respectively; u α and u β These are the motor input voltages on the α and β axes of the two-phase stationary coordinate system of the motor, respectively; i α and i β These are the stator winding currents of the motor on the α-axis and β-axis of the two-phase stationary coordinate system of the motor, respectively; R s The resistance of the motor stator winding; For differential operators; L d and L q These are the stator inductances on the d-axis and q-axis of the synchronous rotating coordinate system, respectively.

[0013] Comparing equations (1) and (2), it is easy to see that the real-time back EMF algorithm used in this invention avoids the differential terms required in traditional algorithms, thus eliminating the need for filters. Combined with the orthogonal phase-locked loop technology shown below, the bandwidth of the rotor position / speed identification algorithm is improved. Therefore, the rotor position / speed identification algorithm used in this invention has an inherent advantage over traditional algorithms in resisting load changes.

[0014] Furthermore, the back electromotive force e will be extended. α and e β The rotor position is tracked by inserting a phase-locked loop:

[0015]

[0016] In equation (3), The rotor position angle is extracted by the phase-locked loop, Δθ is the rotor position angle error input to the phase-locked loop, and the extended back electromotive force e is... α and e β Includes the actual rotor position angle θ e Information:

[0017]

[0018] In equation (4), ω e ψ is the actual electric angular velocity. f It is a permanent magnet flux linkage.

[0019] The phase detector in a phase-locked loop can be approximated by equation (5):

[0020]

[0021] In equation (5), k = ω e ψ f Δθ, as the input to the phase-locked loop, is locked near 0 by the closed-loop feedback of the PI regulator, thereby enabling the extraction of the rotor position angle from the observed back electromotive force.

[0022] A real-time back EMF calculation algorithm combined with phase-locked loop (PLL) technology is used to achieve positionless control of the PMSM (Power Management System). However, to improve the load-carrying capacity and speed stability at low speeds, a parallel-type speed-current regulator is required. Its specific description is as follows:

[0023] with i d =0 control strategy as an example (but not limited to i) d =0 control), estimated speed output by phase-locked loop With reference speed ω ref The difference is calculated and used as the input to the speed regulator; the output of the speed regulator is no longer used as i. q Instead of feeding the reference value into the current loop, the reference voltage u is used directly.q1 The form is transformed by coordinate transformation and comparison circuit to generate a three-phase drive signal, thus changing from the traditional dual-loop speed and current control to a single-loop speed control. At low speeds, the estimated angle without position control is more susceptible to external disturbances, leading to larger estimation errors. Furthermore, the dual-loop system has slow torque compensation, causing a severe drop in motor speed or even stalling under sudden heavy loads. However, with single-loop speed control, i is rapidly increased when the position estimation error is not too large. q This compensates for the torque, thus minimizing motor speed fluctuations during sudden load increases or decreases, further improving the stability of the positionless control system at low speeds.

[0024] While a single-loop speed control can achieve rapid compensation for motor torque, it may lead to increased current i. q To address the issue of torque exceeding the rated value while simultaneously preventing overcurrent, this invention improves upon the single-loop speed control, and can be described as follows:

[0025] Take the sampled current i q With rated current i qmax The difference is calculated and used as the input to the current loop. After passing through the current regulator, the output reference voltage u is determined. q2 The output u of the speed loop q1 and the current loop output u q2 For comparison, take u q ={u q1 ,u q2} min And used as the reference voltage u for the motor. q When a sudden load is applied to the motor, and the load is within the motor's carrying capacity, the current loop outputs u. q2 Limiting saturation, the speed loop rapidly compensates for motor torque; when the load exceeds the motor's carrying capacity, i... q Greater than the rated current i qmax Current loop output u q2 Desaturation, speed loop output u q1 When the speed limit saturates, the motor speed decreases, and the current loop clamps the motor output current to near the rated current to prevent overcurrent. Since only one of the speed loop and current loop is active at any given time, it is essentially a single-loop control; therefore, the above method is called a parallel speed-current regulator.

[0026] Furthermore, a system for implementing a robust position-free control method for a three-phase permanent magnet synchronous motor includes:

[0027] Current and voltage samplers are used to collect the components of the motor stator current and stator voltage in a stationary coordinate system in real time.

[0028] The real-time back EMF calculation module observes the motor's back EMF based on the components of the motor stator current and stator voltage in the stationary coordinate system and the speed estimated by the phase-locked loop.

[0029] A phase-locked loop (PLL) estimates the rotational speed based on the error between the observed rotor position angle and the rotor position angle measured by observing the motor's back electromotive force; and,

[0030] The parallel-type speed and current regulator adjusts the speed to obtain the q-axis component of the motor stator voltage when the motor load is not overloaded, based on the error between the estimated speed and the rated speed. When the motor load is overloaded, it adjusts the current to obtain the q-axis component of the motor stator voltage based on the error between the q-axis component of the motor stator current and the rated motor stator current. Based on the control strategy of the d-axis component of the motor stator voltage, it obtains the d-axis component of the motor stator voltage and sends the d-axis component and q-axis component of the motor stator voltage into the current loop for closed-loop control.

[0031] Furthermore, in a system implementing a robust position-free control method for a three-phase permanent magnet synchronous motor, a parallel speed-current regulator includes:

[0032] The first subtractor has one input terminal connected to the rated speed and the other input terminal connected to the estimated speed value. It outputs the error between the estimated speed value and the rated speed.

[0033] The speed regulator, whose input is connected to the output of the first subtractor, performs PI regulation on the error between the estimated speed and the rated speed, and outputs the q-axis component of the first motor stator voltage.

[0034] The second subtractor has one input terminal connected to the rated stator current of the motor, and the other input terminal connected to the q-axis component of the stator current of the motor. It outputs the error between the q-axis component of the stator current of the motor and the rated stator current of the motor.

[0035] A current regulator, whose input is connected to the output of the second subtractor, performs PI regulation on the error between the q-axis component of the motor stator current and the rated motor stator current, and outputs the q-axis component of the second motor stator voltage; and,

[0036] The minimum value acquisition module has one input terminal connected to the output terminal of the speed regulator and the other input terminal connected to the output terminal of the current regulator. It selects the minimum value between the q-axis component of the first motor stator voltage and the q-axis component of the second motor stator voltage as the output of the q-axis component of the motor stator voltage.

[0037] The present invention, by adopting the above technical solution, has the following beneficial effects:

[0038] (1) This invention combines a real-time back EMF calculation algorithm with phase-locked loop technology to achieve rotor position / speed estimation, avoiding the influence of signal-to-noise ratio on the current differential term in the traditional extended back EMF observation algorithm. It can achieve deadbeat observation of back EMF without iteration. Compared with the commonly used sliding mode observer method and model reference adaptive method, it is less affected by noise interference at low speeds and avoids the distortion of differential term caused by load fluctuations, thus improving the dynamic performance of the positionless control system.

[0039] (2) The parallel speed current regulator proposed in this invention replaces the commonly used dual closed-loop PI speed control system. It can quickly compensate torque and stabilize speed through single closed-loop speed control, and avoid overcurrent under motor overload conditions. The control structure is simple and easy to implement in software algorithm.

[0040] (3) The robust positionless control method proposed in this invention combines rotor position identification technology with a high dynamic speed controller. The rotor position is accurately predicted by rotor position identification technology, and the magnetic flux is directly intervened by a parallel speed current regulator to resist load disturbances. This can greatly increase the PMSM's ability to resist load disturbances at low speeds without position control. The maximum torque output at the same speed is comparable to that of a control scheme with a position sensor, improving the low-speed load-carrying performance and robustness of the positionless control system. It has important application value for positionless control system engineering that requires heavy-load operation.

[0041] (4) The robust positionless control method proposed in this invention does not require any changes to the structure of the motor body, and is applicable to various types of motors such as induction motors and brushless DC motors to increase the ability to resist load torque disturbances at low speeds without position control. It has universality for robust positionless control systems. Attached Figure Description

[0042] Figure 1 This is a system block diagram of a three-phase PMSM without position control mentioned in this invention.

[0043] Figure 2 This is a schematic diagram illustrating the analysis of the invention's ability to resist load disturbances under dynamic conditions without position control.

[0044] Figure 3 This is a schematic diagram of the working state of a parallel-type speed current regulator.

[0045] Figure 4 This is a waveform diagram from an experiment on a traditional dual-closed-loop positionless control system subjected to a sudden load disturbance.

[0046] Figure 5 This is a waveform diagram from an experiment on a parallel-type speed-current regulator's non-position control system subjected to a sudden load disturbance. Detailed Implementation

[0047] To make the implementation method and technical advantages of the present invention clearer and easier to understand, the technical solution of the present invention will be described in detail below with reference to the accompanying drawings.

[0048] The system block diagram of the three-phase PMSM without position control mentioned in this invention is as follows: Figure 1 As shown. This control system mainly consists of a parallel speed-current regulator, coordinate transformation, comparison and drive circuit, real-time back EMF algorithm, and phase-locked loop. When the motor load is not excessive, a reference speed ω is given. ref The input is fed into a parallel-type speed and current regulator. At this time, the speed regulator ASR is in an active state, and the current regulator ACR is in a saturated state. The outputs of the two regulators are then compared with the output of the reference voltage u. q =u q1 Simultaneously, the d-axis current loop outputs the d-axis reference voltage u. d u d and u q Position angle extracted based on phase-locked loop technology The u in the α-β coordinate system is obtained through the inverse Park transform. α and u β u α and u β The variable u in the three-phase stator coordinate system is obtained by using Clarke inverse transform (or space voltage vector modulation technique). A u B u C After comparison with the drive circuit, a drive signal is generated to control the inverter switching transistors to turn on / off, thereby generating the three-phase current to control the motor's motion. The motor stator current is sampled using a current sensor, and i is calculated through coordinate transformation. α i β i d and i q Among them, i d i q The feedback current is fed into the current regulator to achieve closed-loop current control, and i α i β u α and u β Together, they are used as input to the real-time back electromotive force calculation algorithm, and the following calculations are performed:

[0049]

[0050] In equation (6), The rotational speed calculated for the phase-locked loop. The calculated back electromotive force e. α e βThe signal is fed into the phase-locked loop (PLL). The PLL uses equation (5) to calculate the error between the estimated position angle and the actual position angle. This error is then proportional-integrated to output the estimated rotational speed. Estimated speed The estimated position angle is obtained through integration.

[0051] Figure 2 This paper describes the principle behind the relatively small torque compensation in traditional dual-loop control systems without position control. For PMSMs with position sensors, achieving low-speed, high-torque output is easy because the position parameters provided to the controller by the position sensor are accurate at all times. Therefore, the compensated current can quickly increase the torque, making the motor's mechanical characteristics stiffer. However, in dynamic situations (such as sudden load increases, acceleration / deceleration, etc.), the position estimation of positionless control systems may not be accurate. Figure 2 As shown, T e1 T is the torque used to compensate for accurate positioning. e2 The torque compensated for positional deviations is such that when the estimation error Δθ is large, even if the current loop regulator compensates for the same current, the actual compensated torque will be smaller (T). e1 <T e2 If the torque compensation is too small, the speed will drop further, and the extended back-electric calculation will also be distorted due to the rapid drop in speed, which will further increase the position estimation error.

[0052] Because the angle error Δθ estimated by the position control system under dynamic conditions is difficult to calculate and compensate, the estimated position angle... It may sometimes lead and sometimes lag behind the true position angle θ. e Therefore, this invention does not follow the angle compensation approach, but instead improves the control loop by proposing a parallel speed-current regulator.

[0053] Figure 3 This is a schematic diagram illustrating the operating state of a parallel-type speed-current regulator. Unlike traditional dual-closed-loop control systems that use the output of the speed loop as the input of the current loop, the parallel-type speed-current regulator uses the outputs of both the speed loop and the current loop as the reference voltage for the motor. However, only one of the speed loop and the current loop is in an effective operating state, while the other is in a saturated state. (Combined with...) Figure 1 The speed ring uses the reference speed ω ref Compared with estimated speed The difference is used as input, and the current loop uses the rated current i qmax With feedback current i q The difference is used as input. When the load on the motor is small, the corresponding i... q It is also relatively small, at this time (i qmax -i q If )>0, after positive proportional and integral operations, the output u is... q2It is saturated and limited. To maintain a constant speed, only the output u of the speed loop needs to be used. q1 This can be used as a reference voltage, at which point u q1 q2 The speed loop is in an effective working state. When the load on the motor is overloaded, the corresponding i... q It will also be higher than the rated current i qmax At this time (i qmax -i q When the voltage is less than 0, the current loop begins to desaturate, while the speed loop requires a higher voltage to maintain a constant speed. Therefore, the reference value u output by the speed loop decreases. q2 When it reaches the saturation limit value, u q1 >u q2 The current loop is in an effective working state, limiting the current to i. qmax Nearby, avoid overcurrent. When the current loop is in effective operation, this positionless control system can be regarded as a single closed-loop system. A slight drop in speed can trigger rapid current (or torque) compensation, so that the speed and position estimation error can be amplified before the motor returns to steady state, avoiding a larger drop in speed caused by the amplification of the position estimation deviation, thus achieving strong robustness of the positionless control system.

[0054] In summary: when the motor load is less than the maximum load switching point (motor current is less than the rated current), the speed loop is effective and the current loop is saturated. At this time, the current magnitude is not limited, but the main goal is to quickly compensate for the load torque, quickly stabilize the speed, and avoid a significant drop in speed. When the motor load is greater than the maximum load switching point (motor current is greater than the rated current), the current loop is effective and the speed loop is saturated. At this time, the goal is no longer to run at a given speed under load, but to avoid overcurrent. Under this state, a decrease in motor speed is inevitable.

[0055] To verify the practical effectiveness of this invention, an experimental platform was built based on an STM32 digital controller. The experimental motor was a three-phase, four-pole PMSM. Figure 4 The waveform diagram shows a sudden load disturbance test on a traditional dual-closed-loop positionless control system. The reference speed for the positionless control system is set to 100 rpm, indicating that the motor is operating in the low-speed range. A sudden load disturbance is applied to the motor at approximately 1.5 seconds. The diagram shows a rapid drop in the estimated motor speed, distortion of the estimated position angle, and a significant increase in the angle estimation error, indicating that the mechanical characteristics of the motor in this positionless control system are very soft.

[0056] Figure 5 ​The waveforms shown are from an experiment involving a sudden load disturbance in a positionless control system under the action of the parallel speed-current regulator proposed in this invention. The reference speed is also 100 rpm. A sudden load disturbance is applied to the motor at approximately 1.8 s. It can be seen that the estimated motor speed only decreases slightly before quickly recovering, indicating a slight speed overshoot. The estimated position angle remains almost constant after the sudden load disturbance, maintaining the same frequency as in steady-state conditions. The angle estimation error is consistently limited to -0.05 to 0.05 rad. This demonstrates that the method proposed in this invention can significantly improve the mechanical characteristics of the positionless control system at low speeds and exhibits strong robustness to load disturbances.

[0057] The above embodiments are merely illustrative of the technical concept of the present invention and should not be construed as limiting the scope of protection of the present invention. Any modifications made to the technical solutions based on the technical concept proposed in this invention shall fall within the scope of protection of this invention.

Claims

1. A robust position-free control method for a three-phase permanent magnet synchronous motor, characterized in that, The components of the motor stator current and stator voltage in the stationary coordinate system are collected in real time. The back electromotive force of the motor is observed. The rotational speed is estimated based on the error between the observed rotor position angle and the rotor position angle measured by observing the back electromotive force of the motor. When the motor load is not overloaded, the speed is adjusted based on the error between the estimated speed and the rated speed. The q-axis component of the motor stator voltage is obtained. The d-axis component of the motor stator voltage is obtained according to the control strategy of the d-axis component of the motor stator voltage. After coordinate transformation and comparison with the drive circuit, the d-axis component and q-axis component of the motor stator voltage are used to obtain the drive signal for the inverter switching transistor to be turned on / off, and the dual closed-loop control of speed and current is changed to single-loop control of speed. When the motor is overloaded, the error between the q-axis component of the motor stator current and the rated motor stator current is adjusted to obtain the q-axis component of the motor stator voltage. The d-axis component of the motor stator voltage is obtained according to the control strategy of the d-axis component of the motor stator voltage. The d-axis component and q-axis component of the motor stator voltage are sent into the current loop for closed-loop control.

2. The robust positionless control method for a three-phase permanent magnet synchronous motor according to claim 1, characterized in that, The mathematical model for the observed motor back electromotive force is as follows: ,in, , These are the two-phase stationary coordinate systems of the motor. shaft and Extended back electromotive force on the axis, , These are the two-phase stationary coordinate systems of the motor. shaft and The stator winding current of the motor on the shaft, , These are the two-phase stationary coordinate systems of the motor. shaft and The voltage at the motor input terminal on the shaft, This is the resistance of the motor stator winding. According to The actual electric angular velocity obtained, To determine the rotor position angle by observing the back electromotive force of the motor, It is a quadrature axis inductor. , It is a permanent magnet flux linkage.

3. The robust positionless control method for a three-phase permanent magnet synchronous motor according to claim 2, characterized in that, The rotational speed is estimated by using phase-locked loop (PLL) technology based on the error between the observed rotor position angle and the rotor position angle measured by observing the motor back electromotive force.

4. The robust positionless control method for a three-phase permanent magnet synchronous motor according to claim 3, characterized in that, The error between the observed rotor position angle and the rotor position angle measured by observing the back electromotive force of the motor is: ,in, The error between the observed rotor position angle and the rotor position angle measured by observing the motor's back electromotive force is denoted as . , The observed rotor position angle.

5. A system for implementing the robust position-free control method for a three-phase permanent magnet synchronous motor as described in claim 1, characterized in that, include: Current and voltage samplers are used to collect the components of the motor stator current and stator voltage in a stationary coordinate system in real time. The real-time back EMF calculation module observes the motor's back EMF based on the components of the motor stator current and stator voltage in the stationary coordinate system and the speed estimated by the phase-locked loop. A phase-locked loop (PLL) estimates the rotational speed based on the error between the observed rotor position angle and the rotor position angle measured by observing the motor's back electromotive force; and, The parallel-type speed-current regulator adjusts the speed based on the error between the estimated speed and the rated speed when the motor load is not overloaded, obtaining the q-axis component of the motor stator voltage. Based on a control strategy for the d-axis component of the motor stator voltage, it obtains the d-axis component of the motor stator voltage. After coordinate transformation and comparison with the drive circuit, the d-axis and q-axis components of the motor stator voltage are used to obtain the drive signal for the inverter switching transistors to turn on / off, changing the dual-loop speed-current control to a single-loop speed control. When the motor load is overloaded, it adjusts the current based on the error between the q-axis component of the motor stator current and the rated motor stator current, obtaining the q-axis component of the motor stator voltage. Based on a control strategy for the d-axis component of the motor stator voltage, it obtains the d-axis component of the motor stator voltage, and sends the d-axis and q-axis components of the motor stator voltage into the current loop for closed-loop control.

6. The system for implementing a robust position-free control method for a three-phase permanent magnet synchronous motor according to claim 5, characterized in that, The parallel-type speed current regulator includes: The first subtractor has one input terminal connected to the rated speed and the other input terminal connected to the estimated speed value. It outputs the error between the estimated speed value and the rated speed. The speed regulator, whose input is connected to the output of the first subtractor, performs PI regulation on the error between the estimated speed and the rated speed, and outputs the q-axis component of the first motor stator voltage. The second subtractor has one input terminal connected to the rated stator current of the motor, and the other input terminal connected to the q-axis component of the stator current of the motor. It outputs the error between the q-axis component of the stator current of the motor and the rated stator current of the motor. A current regulator, whose input is connected to the output of the second subtractor, performs PI regulation on the error between the q-axis component of the motor stator current and the rated motor stator current, and outputs the q-axis component of the second motor stator voltage; and, The minimum value acquisition module has one input terminal connected to the output terminal of the speed regulator and the other input terminal connected to the output terminal of the current regulator. It selects the minimum value between the q-axis component of the first motor stator voltage and the q-axis component of the second motor stator voltage as the output of the q-axis component of the motor stator voltage.

Images