A built-in permanent magnet synchronous motor MTPV flux-weakening control method based on virtual square wave signal injection

Abstract

The application discloses a built-in permanent magnet synchronous motor MTPV flux-weakening control method based on virtual square wave signal injection. Firstly, the establishment of the flux-weakening control of the permanent magnet synchronous motor on the basis of vector control is analyzed, and the flux-weakening control is divided into three regions. Secondly, the precision and existing problems of the traditional virtual signal injection MTPV control strategy are analyzed, and an improved virtual square wave signal injection MTPV control strategy is designed to improve the traditional method. Finally, an improved virtual square wave signal MTPV overall flux-weakening control scheme suitable for the built-in permanent magnet synchronous motor is designed. The application effectively reduces the calculation complexity of the control algorithm, reduces the influence of the parameter change of the high-speed motor on the MTPV control, improves the system control precision, and enables the motor to have good running performance in the full-speed domain.

Description

Technical Field

[0001] This invention relates to the field of motor drive control technology, and more specifically to a deep field weakening control method for a permanent magnet synchronous motor. Background Technology

[0002] Permanent magnet synchronous motors (PMSMs) offer advantages such as high power density, high efficiency, and fast dynamic response, leading to their widespread application in industrial drives, electric vehicles, and aerospace. However, as motor speed increases, the stator back electromotive force gradually increases, limiting the inverter's output voltage to the DC bus voltage. This results in decreased current regulation capability, reduced motor output torque, and consequently, restricted high-speed operating range. Therefore, at speeds above the base speed, field weakening control methods are typically employed to reduce the air gap flux linkage by adjusting the direct-axis current, thereby achieving wide-range operation.

[0003] Existing field weakening control methods for built-in permanent magnet synchronous motors typically include maximum torque-to-current ratio control below the base speed, lead angle field weakening control above the base speed, and maximum torque-to-voltage ratio control in the deep field weakening region. For maximum torque-to-voltage ratio control, existing methods often employ lookup table methods or parameter model-based control methods. The former relies on offline experimental data and has poor versatility; the latter usually involves numerous filtering and parameter calculation steps, is significantly affected by changes in motor parameters, and the switching between the ordinary and deep field weakening regions is complex. Therefore, it is necessary to propose a deep field weakening control method for built-in permanent magnet synchronous motors that is structurally simple, has good parameter adaptability, and is easy to implement. Summary of the Invention

[0004] The purpose of this invention is to provide a field weakening control method for a built-in permanent magnet synchronous motor (MTPV) based on virtual square wave signal injection, so as to improve the problems of high parameter sensitivity, many filtering links, and complex control interval switching in the existing maximum torque-voltage ratio control.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] In a first aspect, the present invention provides a field weakening control method for an embedded permanent magnet synchronous motor (MTPV) based on virtual square wave signal injection, the method comprising the following steps:

[0007] S1: Establish a control model for the built-in permanent magnet synchronous motor under field weakening operation, and determine the current and voltage limiting conditions.

[0008] S2: Construct a traditional virtual signal injection maximum torque-voltage ratio control model to obtain the flux linkage vector angle extraction method.

[0009] S3: Inject a virtual square wave signal into the dq axis current and extract the maximum torque-voltage ratio flux linkage vector angle based on the change in electromagnetic torque.

[0010] S4: Construct an overall field weakening control scheme based on the extracted flux linkage vector angle to achieve coordinated operation between maximum torque current ratio control, lead angle field weakening control and maximum torque voltage ratio control.

[0011] In step S1, based on the voltage equation of the permanent magnet synchronous motor in the two-phase stationary coordinate system, the voltage equation in the two-phase rotating coordinate system is obtained through coordinate transformation:

[0012]

[0013] Neglecting stator resistance and current differential terms, the steady-state voltage equation of the IPMSM can be expressed as:

[0014]

[0015] During field weakening operation, the motor's operating state is simultaneously constrained by the motor's own parameters and the inverter's output capability. These constraints include current limits and voltage limits, which can be expressed as follows:

[0016]

[0017] In the formula, The stator current composite vector. This is the voltage composite vector.

[0018] When operating below the base speed, a maximum torque-to-current ratio control strategy is adopted to balance torque output and copper loss levels. Based on the Lagrange extreme value theorem and combined with motor parameters, the trajectory equation for the maximum torque-to-current ratio can be obtained:

[0019]

[0020] When the stator current composite vector runs along the maximum torque-to-current ratio trajectory to the current limiting circle, the motor cannot continue to increase speed along this trajectory. If the speed increases further, the amplitude of the d-axis current and q-axis current is adjusted by increasing the current vector angle, which is the lead angle. At this time, the motor enters the constant power field weakening region.

[0021] The equations for the dq-axis currents are as follows:

[0022]

[0023] Lead angle field weakening control can make the stator current synthesized vector Running along the current-limited circular arc allows the motor speed to continue increasing. During the field weakening process, two current regulators respectively... and To control, and then regulate and . and The limit value is ,when and Increase or decrease to or At this time, the current regulator saturates and loses its regulating capability. If and If both current regulators are saturated, then both current regulators will completely fail, and the voltage limiter will be ineffective.

[0024] Ellipse If it increases while contracting inward, there exists a saturation runaway line. When When the motor is constrained by voltage and current and reaches the operating point corresponding to the saturation runaway line, it can no longer weaken the magnet.

[0025] The voltage limiting ellipse is:

[0026]

[0027] For a built-in permanent magnet synchronous motor, the slope of the saturation runaway line in the dq-axis current plane can be obtained as follows:

[0028]

[0029] When the characteristic current point is located within the current limiting circle, the motor exhibits a deep field weakening region. In this case, to obtain a larger torque under voltage-limited conditions, the stator current synthesis vector needs to follow the maximum torque-voltage ratio trajectory. Based on the Lagrange extremum theorem and combined with motor parameters, the equation for the maximum torque-voltage ratio trajectory can be obtained:

[0030]

[0031] Currently, besides using lookup tables, the main MTPV control method employs negative q-axis current compensation to limit the direct-axis current. This results in a limited control range and a relatively complex control method. At low speeds, the motor can operate at any point on the MTPA curve. When the voltage curve crosses the MTPA region, a field weakening (FW) strategy must be applied to keep the stator voltage within its limits. Depending on the torque level, operation occurs within the speed range where the torque value can be maintained. This region is known as Constant Torque Control (CTC). All possible strategies in the FW region are based on voltage limits: Current and Voltage Limiting Control (CVLC), CTC, and MTPV.

[0032] Permanent magnet synchronous motors (PMSMs) can be classified into surface-mounted permanent magnet synchronous motors (SPMSMs) and internally mounted permanent magnet synchronous motors (IPMSMs) based on their rotor mounting position. This difference is reflected in the motor parameters by whether the d-axis and q-axis inductances are the same. If the d-axis and q-axis inductances are the same, it is an SPMSM; if they are different, it is an IPMSM. In field weakening control, the stator current composite vector... Their operating modes differ in the d- and q-axis planes. SPMSM, due to... Its MTPA and MTPV trajectories are linear, while IPMSM is due to Its MTPA and MTPV trajectories are curves.

[0033] Furthermore, in S2, to avoid the influence of motor parameter changes on the formula method, a VSI-MTPV control strategy is proposed, which is less affected by motor parameter changes and can thus track the operating point more accurately.

[0034] The magnetic flux linkage of the motor is as follows:

[0035]

[0036] Define the flux linkage vector angle for:

[0037]

[0038] Therefore, the dq-axis current can be obtained as:

[0039]

[0040] Therefore, electromagnetic torque can be expressed as:

[0041]

[0042] For a given flux linkage amplitude, there exists an optimal flux linkage angle that maximizes the electromagnetic torque. :

[0043]

[0044] When tracking the MTPV operating point It equals zero. Because the flux linkage angle is always less than zero. ,so The relationship with the magnetic flux angle is as follows:

[0045]

[0046] therefore, This can be used as a characteristic signal to detect whether the MTPV operating point has been tracked. When the motor is running stably, assuming the dq-axis current does not change with time, then we have...

[0047]

[0048] According to the above formula, we can obtain... and The expression is as follows:

[0049]

[0050] The expression for electromagnetic torque is thus obtained as follows:

[0051]

[0052] Traditional virtual signal injection methods are directed towards the flux linkage vector angle. Inject a high-frequency, small-amplitude sine wave signal into the middle. A is the amplitude of the injected signal, typically ranging from 0.02 to 0.05. The frequency of the injected signal, The expression after injecting the virtual signal is as follows:

[0053]

[0054] In the formula, and represent the dq-axis currents after virtual signal injection, respectively. The electromagnetic torque after virtual signal injection is as follows:

[0055]

[0056] In the formula, This represents the electromagnetic torque after the virtual signal is injected, avoiding the influence of the q-axis inductance and the motor's permanent magnet flux linkage on the operating point, although it still includes the motor's stator windings. and d-axis inductance Two quantities that change due to the motor's operating state, but in the above formula, The value is very small, so it is affected by the quadrature axis inductance. The effect is minimal. The electromagnetic torque is... Taylor expansion yields:

[0057]

[0058] Ignoring the second and higher partial derivatives in the Taylor expansion, we obtain the following equation:

[0059]

[0060] First By using a bandpass filter to remove the DC and high-frequency terms, the signal obtained from the bandpass filter is: The signal and After multiplying, we get:

[0061]

[0062] After passing through a low-pass filter, frequencies in the formula can be filtered out. The term is used to obtain the constant term. By using an integrator to set it to 0, the MTPV flux linkage angle can be obtained. .

[0063] Based on the above analysis, in terms of control accuracy, extraction During the process, the second-order and higher-order partial derivatives in the Taylor expansion are ignored. These ignored higher-order terms still contain dq-axis inductance and flux linkage parameters, thus reducing the adaptability of the VSI-MTPV control strategy to changes in motor parameters. Furthermore, ignoring higher-order terms will lead to… The value is incorrect, which in turn leads to an error in the flux linkage angle. Errors are generated during the tracking process, reducing the accuracy of system control.

[0064] Furthermore, in S3, to improve the performance of the VSI-MTPV control strategy in terms of control accuracy and speed, an improved Virtual Square Wave Signal Injection MTPV (IVSWSI-MTPV) control strategy was designed. The designed control strategy differs from the traditional VSI-MTPV control strategy in its handling of the torque equation. Specifically, the IVSWSI-MTPV control strategy treats the electromagnetic torque... Viewed as about the independent variable and The binary function. Therefore, the VSI-MTPV control strategy... Perform the following equivalent transformation:

[0065]

[0066] From the above formula, we can see that It can be equivalent to The designed control strategy uses an integrator to obtain the flux linkage vector angle. .

[0067] After injecting the virtual signal, to ensure that the control strategy can extract the required information from the torque equation in each control cycle, the virtual square wave signal is defined as follows:

[0068]

[0069] In the formula, A is the amplitude of the injected virtual square wave signal. When the value of A is between 0.02 and 0.05, the impact on the performance of the control system is basically the same. The injected virtual square wave signal, where n is a positive integer. The step size is [value]. The current after directly injecting a virtual square wave signal into the dq-axis current can be expressed as:

[0070]

[0071] This allows us to obtain the electromagnetic torque after the injection of the virtual square wave signal, and to determine its... The Taylor expansion of the bivariate function at point is shown below:

[0072]

[0073] In the formula, electromagnetic torque It's about the dq axis current. and It is a linear function, therefore, electromagnetic torque Regarding the dq axis current and When calculating the second-order partial derivative, its value is 0. Therefore, the second-order and higher-order partial derivative terms do not need to be ignored in the Taylor expansion, which can improve control accuracy. The above equation is processed as follows:

[0074]

[0075] As shown in the above formula, no filter is needed; the result can be obtained simply through regular addition and subtraction operations. Then, by integrating it with an integrator until it equals 0, the flux linkage vector angle is obtained. .

[0076] Furthermore, in S4, an overall field weakening control strategy is designed to realize the control of the built-in permanent magnet synchronous motor MTPA, ordinary field weakening, and MTPV. Below the base speed, the speed loop PI receives the current reference command. The current reference vector angle is then obtained through the MTPA control module. At this point, the voltage has not reached the limit value, and the voltage closed-loop feedback output lead angle is 0. In the stator composite vector... When the motor moves along the MTPA curve to the current limiting circle, it can no longer accelerate along the MTPA curve. At this time, voltage closed-loop feedback control can be used to make the motor run under the current limiting circle and voltage limiting circle at the same time, so that the motor can continue to accelerate.

[0077] In the current composite vector When the motor travels downwards along the current limiting circle to the intersection with the MTPV curve, to avoid motor field weakening and runaway, the current vector... It needs to operate along the MTPV curve. The MTPV control module tracks the MTPV flux vector angle using the designed IVSWSI-MTPV control strategy. After obtaining the quadrature-axis current command from the lead angle field weakening control, it passes through the flux vector angle... The corresponding direct-axis current reference value is obtained. Since the direct-axis current is negative, it is compared with the initial direct-axis command current output by the lead angle field weakening module, and the maximum value is taken. The trajectory range is limited to the MTPV curve. This method avoids the calculation and selection of inflection points in ordinary and deep magnetic weakening regions, and the portion exceeding the area enclosed by the current limit circle and the MTPV curve is automatically included on the MTPV curve.

[0078] The above method can be used to construct a control strategy for MTPV based on virtual square wave signal injection.

[0079] The beneficial effects of this invention are:

[0080] 1. The improved virtual square wave signal injection MTPV control strategy proposed in this invention reduces the problem of excessive changes in motor parameters in formula-based MTPV. Compared with traditional high-frequency signal injection MTPV, it improves the system control accuracy, reduces the use of filters, and can achieve MTPV curve tracking with only simple mathematical calculations.

[0081] 2. The built-in permanent magnet synchronous motor field weakening control scheme proposed in this invention avoids the calculation and selection of the switching point between the ordinary field weakening zone and the deep field weakening zone, simplifies the control scheme, and improves the control efficiency of the system. Attached Figure Description

[0082] Figure 1 This is a block diagram of the overall magnetic weakening control of IPMSM according to an embodiment of the present invention.

[0083] Figure 2 This is a block diagram of the IVSWI-MTPV control according to an embodiment of the present invention.

[0084] Figure 3 This is a schematic diagram of the IPMSM voltage limiting circle according to an embodiment of the present invention.

[0085] Figure 4 This is a schematic diagram of the three operating modes of IPMSM according to an embodiment of the present invention.

[0086] Figure 5 This is a graph showing the magnetic weakening characteristics of the PMSM according to an embodiment of the present invention.

[0087] Figure 6 This is a graph showing the relationship between electromagnetic torque and flux rotation under constant flux amplitude according to an embodiment of the present invention.

[0088] Figure 7This is a VSI-MTPV control block diagram according to an embodiment of the present invention.

[0089] Figure 8 This is a simulation result diagram of a novel field-weakening system motor with constant load torque according to an embodiment of the present invention.

[0090] Figure 9 This is a simulation result diagram of the motor of the novel variable load torque field weakening system according to an embodiment of the present invention. Detailed Implementation Plan

[0091] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0092] Example 1

[0093] Figure 1 This is a block diagram of the overall field weakening control of IPMSM based on virtual square wave signal injection into MTPV according to an embodiment of the present invention. Figure 2 This is a control block diagram of MTPV based on virtual square wave signal injection according to an embodiment of the present invention. The method includes the following steps:

[0094] S1: Establish a mathematical model for field weakening operation of the built-in permanent magnet synchronous motor and determine the current and voltage limiting conditions.

[0095] S2: Construct a traditional virtual signal injection maximum torque-voltage ratio control model to obtain the extraction method of flux linkage vector angle.

[0096] S3: Inject a virtual square wave signal into the dq axis current, and extract the maximum torque-voltage ratio flux linkage vector angle based on the change in electromagnetic torque.

[0097] S4: Construct an overall field weakening control scheme based on the extracted flux linkage vector angle to achieve coordinated operation between maximum torque current ratio control, lead angle field weakening control and maximum torque voltage ratio control.

[0098] I. Mathematical Model of Permanent Magnet Synchronous Motor under Field Weakening Control

[0099] Based on the voltage equation of the permanent magnet synchronous motor in the two-phase stationary coordinate system, the voltage equation of the motor in the two-phase rotating coordinate system is obtained through the coordinate transformation matrix as follows:

[0100]

[0101] Ignoring stator resistance and differential terms, the steady-state voltage equation of the IPMSM can be expressed as:

[0102]

[0103] The operation of a PMSM is limited by the characteristics of the motor itself and the output capacity of the inverter. This limitation includes both current and voltage, with the maximum current limit set to [value missing]. Voltage amplitude limit set to These two limiting parameters can be represented by the following equation:

[0104]

[0105] In the formula, The stator current composite vector. This is the voltage composite vector.

[0106] When the motor is below its base speed, in order to ensure minimum copper loss and achieve optimal efficiency, a maximum torque-to-current ratio (MTPA) control strategy is adopted. Based on the Lagrange extreme value theorem and introducing the motor parameter formula, the MTPA curve equation below the base speed is obtained:

[0107]

[0108] In the stator current composite vector When the speed reaches the current limiting circle along the MTPA curve, it cannot continue to increase along the MTPA curve. If the speed continues to increase at this point, the current vector can be controlled. Angle increases, thereby adjusting , The amplitude of this angle is called the lead angle. At this time, the motor is operating in the constant power field weakening region.

[0109] The equations for the dq-axis currents are as follows:

[0110]

[0111] Lead angle field weakening control can make the stator current synthesized vector Running along the current-limited circular arc allows the motor speed to continue increasing. During the field weakening process, two current regulators respectively... and To control, and then regulate and . and The limit value is ,when and Increase or decrease to or At this time, the current regulator saturates and loses its regulating capability. If and If both current regulators are saturated, then both current regulators will completely fail, and the voltage limiting ellipse will follow. If it increases while contracting inward, there exists a saturation runaway line, such as... Figure 3 As shown. When When the motor is constrained by voltage and current and reaches the operating point corresponding to the saturation runaway line, it can no longer weaken the magnet.

[0112] The voltage limiting ellipse is:

[0113]

[0114] Due to the built-in permanent magnet synchronous motor It is easy to obtain the saturation runaway line on the dq-axis current plane. slope for:

[0115]

[0116] exist Figure 3 In the middle, the saturated runaway line intersects the current limiting circle at point R. Before reaching point R, the trajectory operation needs to be switched. There is an MTPV trajectory that intersects the current-limiting circle at point P. When switching to the MTPV trajectory at point P, the current regulator can be prevented from failing, and the motor can achieve its maximum load capacity under the inverter voltage limit.

[0117] If the characteristic current point If the stator current is located within the current-limiting circle, a deep weak magnetic field exists, and the stator current composite vector... The motor can continue to accelerate by running along the new trajectory. If the motor has a deep magnetic field weakness region, limiting the amplitude along the maximum torque-voltage ratio (MTPV) trajectory can obtain the maximum torque. Based on Lagrange's extremum theorem and introducing the motor parameter formula, the MTPV curve equation is obtained:

[0118]

[0119] Currently, besides the lookup table method, the main MTPV control method uses negative q-axis current compensation to limit the direct-axis current. This results in a limited control range and a relatively complex control method. At low speeds, the motor can operate at any point on the MTPA curve. When the voltage curve crosses the MTPA region, a field weakening (FW) strategy must be applied to keep the stator voltage within its limits. Depending on the torque level, it operates within the speed range where the torque value can be maintained. This region is called constant torque control (CTC). All possible strategies in the FW region are based on voltage limits: current and voltage limiting control (CVLC), CTC, and MTPV. Specifically, it can be divided into three operating modes, such as... Figure 4 As shown.

[0120] Permanent magnet synchronous motors (PMSMs) can be classified into surface-mounted permanent magnet synchronous motors (SPMSMs) and internally mounted permanent magnet synchronous motors (IPMSMs) based on their rotor mounting position. This difference is reflected in the motor parameters by whether the d-axis and q-axis inductances are the same. If the d-axis and q-axis inductances are the same, it is an SPMSM; if they are different, it is an IPMSM. In field weakening control, the stator current composite vector... Their operating modes differ in the d- and q-axis planes. SPMSM, due to... Its MTPA and MTPV trajectories are linear, while IPMSM is due to Its MTPA and MTPV trajectories are curves, such as Figure 5 As shown.

[0121] The control methods in the MTPA control region and the ordinary magnetic weakening control region are relatively simple. In the deep magnetic weakening domain, a better control method is to... It runs on the MTPV trajectory, but the current MTPV control is quite complex.

[0122] II. Control Strategy for Built-in Permanent Magnet Synchronous Motor (MTPV) with Traditional Virtual Signal Injection

[0123] The magnetic flux linkage of the motor is as follows:

[0124]

[0125] Define the flux linkage vector angle for:

[0126]

[0127] Therefore, the dq-axis current can be obtained as:

[0128]

[0129] Therefore, electromagnetic torque can be expressed as:

[0130]

[0131] For a given flux linkage amplitude, there exists an optimal flux linkage angle that maximizes the electromagnetic torque. :

[0132]

[0133] Figure 4 This shows the relationship between electromagnetic torque and flux linkage angle under constant flux linkage amplitude. For example... Figure 4 As shown, when tracking the MTPV operating point, It equals zero. Because the flux linkage angle is always less than zero. ,so The relationship with the magnetic flux angle is as follows:

[0134]

[0135] therefore, This can be used as a characteristic signal to detect whether the MTPV operating point has been tracked. When the motor is running stably, assuming the dq-axis current does not change with time, then we have...

[0136]

[0137] According to the above formula, we can obtain... and The expression is as follows:

[0138]

[0139] The expression for electromagnetic torque is thus obtained as follows:

[0140]

[0141] Traditional virtual signal injection methods are directed towards the flux linkage vector angle. Inject a high-frequency, small-amplitude sine wave signal into the middle. A is the amplitude of the injected signal, typically ranging from 0.02 to 0.05. The frequency of the injected signal, The expression after injecting the virtual signal is as follows:

[0142]

[0143] In the formula, and represent the dq-axis currents after virtual signal injection, respectively. The electromagnetic torque after virtual signal injection is as follows:

[0144]

[0145] In the formula, This represents the electromagnetic torque after the virtual signal is injected, avoiding the influence of the q-axis inductance and the motor's permanent magnet flux linkage on the operating point, although it still includes the motor's stator windings. and d-axis inductance Two quantities that change due to the motor's operating state, but in the above formula, The value is very small, so it is affected by the quadrature axis inductance. The effect is minimal. The electromagnetic torque is... Taylor expansion yields:

[0146]

[0147] Ignoring the second and higher partial derivatives in the Taylor expansion, we obtain the following equation:

[0148]

[0149] Figure 7 The control block diagram of VSI-MTPV is shown, where BPF and LPF represent the bandpass and low-pass filters, respectively. First, [the following text is incomplete and likely refers to a separate section:] By using a bandpass filter to remove the DC and high-frequency terms, the signal obtained from the bandpass filter is: The signal and After multiplying, we get:

[0150]

[0151] After passing through a low-pass filter, frequencies in the formula can be filtered out. The term is used to obtain the constant term. By using an integrator to set it to 0, the MTPV flux linkage angle can be obtained. .

[0152] Based on the above analysis, in terms of control accuracy, extraction During the process, the second-order and higher-order partial derivatives in the Taylor expansion are ignored. These ignored higher-order terms still contain dq-axis inductance and flux linkage parameters, thus reducing the adaptability of the VSI-MTPV control strategy to changes in motor parameters. Furthermore, ignoring higher-order terms will lead to… The value is incorrect, which in turn leads to an error in the flux linkage angle. Errors are generated during the tracking process, reducing the accuracy of system control.

[0153] III. Improved MTPV Control Strategy for Virtual Square Wave Signal Injection

[0154] To improve the performance of the VSI-MTPV control strategy in terms of control accuracy and speed, an improved MTPV control strategy with virtual square wave signal injection is designed. The designed control strategy differs from the conventional VSI-MTPV control strategy in its treatment of the torque equation. Specifically, the IVSWSI-MTPV control strategy treats the electromagnetic torque... Viewed as about the independent variable and The binary function. Therefore, the VSI-MTPV control strategy... Perform the following equivalent transformation:

[0155]

[0156] From the above formula, we can see that It can be equivalent to The designed control strategy uses an integrator to obtain the flux linkage vector angle. .

[0157] After injecting the virtual signal, to ensure that the control strategy can extract the required information from the torque equation in each control cycle, the virtual square wave signal is defined as follows:

[0158]

[0159] In the formula, A is the amplitude of the injected virtual square wave signal. When the value of A is between 0.02 and 0.05, the impact on the performance of the control system is basically the same. The injected virtual square wave signal, where n is a positive integer. The step size is [value]. The current after directly injecting a virtual square wave signal into the dq-axis current can be expressed as:

[0160]

[0161] This allows us to obtain the electromagnetic torque after the injection of the virtual square wave signal, and to determine its... The Taylor expansion of the bivariate function at point is shown below:

[0162]

[0163] In the formula, electromagnetic torque It's about the dq axis current. and It is a linear function, therefore, electromagnetic torque Regarding the dq axis current and When calculating the second-order partial derivative, its value is 0. Therefore, the second-order and higher-order partial derivative terms do not need to be ignored in the Taylor expansion, which can improve control accuracy. The above equation is processed as follows:

[0164]

[0165] As shown in the above formula, no filter is needed; the result can be obtained simply through regular addition and subtraction operations. Then, by integrating it with an integrator until it equals 0, the flux linkage vector angle is obtained. The specific process is as follows: Figure 2 As shown.

[0166] IV. Overall Field Weakening Control Scheme Based on Improved Virtual Square Wave Signal Injection into MTPV Control

[0167] To achieve control of the built-in permanent magnet synchronous motor MTPA, ordinary field weakening, and MTPV, an overall field weakening control strategy block diagram is designed as follows: Figure 1 As shown. Figure 1 In the middle, when the speed is below the base speed, the speed loop PI receives the current reference command. The current reference vector angle is then obtained through the MTPA control module. At this point, the voltage has not reached the limit value, and the voltage closed-loop feedback output lead angle is 0. In the stator composite vector... When the motor moves along the MTPA curve to the current limiting circle, it can no longer accelerate along the MTPA curve. At this time, voltage closed-loop feedback control can be used to make the motor run under the current limiting circle and voltage limiting circle at the same time, so that the motor can continue to accelerate.

[0168] In the current composite vector When the motor travels downwards along the current limiting circle to the intersection with the MTPV curve, to avoid motor field weakening and runaway, the current vector... It needs to operate along the MTPV curve. The MTPV control module tracks the MTPV flux vector angle using the designed IVSWSI-MTPV control strategy. After obtaining the quadrature-axis current command from the lead angle field weakening control, it passes through the flux vector angle... The corresponding direct-axis current reference value is obtained. Since the direct-axis current is negative, it is compared with the initial direct-axis command current output by the lead angle field weakening module, and the maximum value is taken. The trajectory range is limited to the MTPV curve. This method avoids the calculation and selection of inflection points in ordinary and deep magnetic weakening regions, and the portion exceeding the area enclosed by the current limit circle and the MTPV curve is automatically included on the MTPV curve.

[0169] To verify the effectiveness of this invention, simulations were performed in MATLAB / Simulink. Taking the IPMSM as an example, the motor was controlled to start with a ramp function, achieving a final speed of 12000 r / min. The rated speed of the motor was 4000 r / min, and the torque was set to 6 N·m. The simulation results are as follows: Figure 8 As shown, below the rated speed, the motor uses MTPA control, followed by lead angle field weakening control. No additional control is required at the switching point. After passing through the MAX comparator module, the stator current is synthesized into a vector. Automatically switches to the MTPV trajectory. When switching to the MTPV trajectory, the IVSWSI-MTPV control module output automatically converges to the flux linkage angle. The overall magnetic field weakening trajectory transition was smooth, and no current saturation or runaway occurred during the entire process.

[0170] Figure 9 The simulation results show that after 5 seconds, the load torque increases by 2 N·m every 1.5 seconds. During this time, the d-axis current gradually increases negatively, the q-axis current gradually increases positively, and the output flux angle of the IVSWSI-MTPV module, which automatically converges, gradually increases. Simulation experiments demonstrate that the algorithm proposed in this invention can achieve precise control of MTPV, simplify the control process, and improve the system control accuracy.

[0171] This invention has good portability in deep weak magnetic fields. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this invention should be included within the protection scope of this invention.

Claims

1. A method for maximum torque-voltage ratio field weakening control of a built-in permanent magnet synchronous motor based on virtual square wave signal injection, characterized in that, Includes the following steps: S1: Under the vector control framework, a current reference command is generated based on the speed setpoint, speed feedback and motor operating status; the current reference vector angle is determined by the maximum torque-current ratio control below the base speed; after entering the field weakening region, the initial d-axis current command under the lead angle field weakening control is obtained through the voltage closed loop. S2: When the motor enters the deep field weakening zone, a virtual square wave signal is injected into the d-axis current and q-axis current, and the maximum torque-voltage ratio operating point tracking characteristic is constructed based on the change in electromagnetic torque after injection. S3: Based on the flux linkage vector angle obtained by integrating the tracking feature quantity and the q-axis current command, calculate the d-axis current command corresponding to the maximum torque-voltage ratio trajectory, and compare it with the initial d-axis current command to obtain the maximum value, thus obtaining the final d-axis current command. S4: Perform current closed-loop control based on the final d-axis current command and q-axis current command, and drive the inverter output to enable the motor to switch between the maximum torque current ratio control zone, the normal field weakening zone, and the maximum torque voltage ratio control zone.

2. The method for maximum torque-to-voltage ratio field weakening control of a built-in permanent magnet synchronous motor based on virtual square wave signal injection according to claim 1, characterized in that, In step S1, the current reference vector angle is determined by maximum torque-to-current ratio control below the base speed, specifically as follows: The current reference command is output from the speed loop, and the current reference vector angle is obtained through the maximum torque current ratio control module. When the voltage does not reach the limit value, the lead angle output by the voltage closed loop is 0. When the stator current composite vector runs to the current limit circle, the lead angle is adjusted by the voltage closed loop so that the stator current composite vector continues to accelerate under the combined constraints of current limit and voltage limit.

3. The method for maximum torque-voltage ratio field weakening control of a built-in permanent magnet synchronous motor based on virtual square wave signal injection according to claim 1, characterized in that, In step S2, the virtual square wave signal is a square wave signal that alternates between positive and negative signs in adjacent control cycles, and the amplitude of the virtual square wave signal is 0.02~0.

05. The virtual square wave signal is directly injected into the d-axis current and q-axis current to obtain the d-axis current, q-axis current and corresponding electromagnetic torque in the positive injection state and the negative injection state.

4. The method for maximum torque-voltage ratio field weakening control of a built-in permanent magnet synchronous motor based on virtual square wave signal injection according to claim 1, characterized in that, In step S2, the tracking feature quantity is obtained by calculating the difference between the electromagnetic torque in the positive injection state and the negative injection state, and the discrimination quantity corresponding to the maximum torque-voltage ratio operating point is extracted by addition and subtraction operation. Then, the discrimination quantity is adjusted by an integrator to make the discrimination quantity approach zero so as to obtain the flux linkage vector angle. No bandpass filter or low-pass filter is used in the extraction process of the discrimination quantity.

5. The method for maximum torque-voltage ratio field weakening control of a built-in permanent magnet synchronous motor based on virtual square wave signal injection according to claim 1, characterized in that, In steps S3 and S4, based on the flux linkage vector angle and the q-axis current command output by the lead angle field weakening control obtained in step S2, the d-axis current reference value corresponding to the maximum torque-voltage ratio trajectory is calculated. Since the d-axis current reference value is negative, it is compared with the maximum value of the initial d-axis current command output by the lead angle field weakening control. The comparison result is used as the d-axis current command of the inner current loop so that the stator current synthesis vector is limited to the maximum torque-voltage ratio trajectory.

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