Electrolytic capacitor-free permanent magnet synchronous motor copper loss optimization control method and device based on MTPA method

Abstract

The invention discloses an MTPA method-based copper loss optimization control method and device for a permanent magnet synchronous motor without an electrolytic capacitor, and belongs to the field of permanent magnet synchronous motors. The method comprises the steps that q-axis reference current is made to fluctuate in a frequency doubling mode along with bus voltage, and it is ensured that a system obtains a high power factor; the method comprises the following steps: calculating MTPA critical voltage and weak magnetic control critical voltage by combining operation constraint conditions of a permanent magnet synchronous motor without an electrolytic capacitor, dividing each bus voltage fluctuation period into three working areas, namely a weak magnetic control area, a buffer area and an MTPA control area, and giving d-axis reference current in one bus voltage fluctuation period in sections; a feed-forward power compensation mechanism is introduced, the grid-side current quality is improved, and a PWM signal used for controlling the duty ratio of an inverter is generated. The effective improvement of the grid-side current performance is realized, and the MTPA control method can be utilized to reduce the copper loss to the greatest extent.

Description

Technical Field

[0001] This invention belongs to the field of permanent magnet synchronous motors, and more specifically, relates to a method and device for optimizing copper loss control of electrolytic capacitor-free permanent magnet synchronous motors based on the MTPA method. Background Technology

[0002] Chapter 1. Built-in permanent magnet synchronous motors (PMSMs) are widely used in various fields due to their high power density, low energy consumption, and low operating noise. Electrolytic capacitors of hundreds or thousands of microfarads are used in traditional PMSM drive systems to stabilize the DC link circuit and provide a stable bus voltage for the drive system. However, electrolytic capacitors are bulky and have a short lifespan, significantly reducing the reliability of the inverter circuit. Simultaneously, to improve the grid-side power factor and reduce grid-side current harmonics, the drive system must add a power factor correction (PFC) circuit, which leads to further power losses and increases product size and weight.

[0003] To address the aforementioned issues, researchers invented a capacitor-free motor drive system. This topology uses a few microfarad thin-film capacitor instead of a large-capacity electrolytic capacitor as the bus capacitor, significantly reducing the size of the motor drive system. Furthermore, the drive system eliminates the need for a PFC circuit, greatly improving its efficiency and reliability. In addition, the significantly reduced capacitance after capacitor replacement causes the bus voltage to fluctuate with the grid voltage. Simultaneously, the coupling between the grid input side and the inverter output side is strengthened, and the performance of the grid-side current can be effectively improved by controlling the inverter output power.

[0004] However, due to drastic fluctuations in bus voltage, the motor primarily operates in field-weakening mode, resulting in a generally large negative d-axis current. Consequently, its stator current amplitude is high, leading to excessive copper losses and low motor efficiency. To address the issue of excessive copper losses in electrolytic capacitor-less motor drive systems, the current main approach is to combine MTPA (Medium-to-Magnetic Field Amplifier) ​​with a traditional DC current feed. The paper "Copper Loss Minimization Control at Zero Output Voltage for ElectrolyticCapacitor-Less Inverter" studies the initial current response in the zero output voltage region of the motor and proposes combining a field-weakening control algorithm with MTPA to calculate the d-axis current feed, thereby enabling efficient motor operation.

[0005] However, the above method relies on DC bus current control to reduce grid-side current harmonics, increasing the control difficulty and making it harder to implement. It also introduces new constraints, making it impossible to maximize the use of the MTPA method to reduce copper losses. Summary of the Invention

[0006] To address the shortcomings of related technologies, the present invention aims to provide a method and apparatus for optimizing copper loss control of electrolytic capacitor-free permanent magnet synchronous motors based on the MTPA method. This aims to solve the problems of existing methods relying on DC bus current control, which presents significant control difficulties and cannot maximize the utilization of MTPA to reduce copper losses.

[0007] To achieve the above objectives, in a first aspect, the present invention provides a method for optimizing copper loss control of a capacitor-free permanent magnet synchronous motor based on the MTPA method, comprising: S1. In the current cycle, perform PI adjustment on the difference between the motor's given speed and its actual speed to obtain the q-axis current reference value. A reference value is given for the q-axis current. Harmonic injection is performed to obtain a q-axis reference current that fluctuates at a frequency of twice the bus voltage. ; S2. Under the MTPA control method, the d-axis current is: ; set the q-axis reference current With d-axis current Substituting the voltage limiting equation of the capacitorless permanent magnet synchronous motor, the MTPA control critical voltage is obtained. ; Make the bus voltage greater than time The average value is denoted as the d-axis reference current of the MTPA control region. ; S3. According to the voltage limiting equation, take the peak value of the bus voltage. One-third as the critical voltage for weak magnetic control Substituting the voltage limiting equation, the d-axis reference current in the field weakening control region is calculated. ; S4. Control the critical voltage according to MTPA. and the critical voltage for weak magnetic control The bus voltage fluctuation cycle is divided into three working regions: the field weakening control region, the buffer region, and the MTPA control region; according to the calculation formula... Calculate over one bus voltage fluctuation period Inside and Corresponding time nodes and ;according to , , and The segmentation is given within one bus voltage fluctuation cycle. Inner d-axis reference current The expression is:

[0008] in, , ; S5, Set the d-axis reference current q-axis reference current The difference between the current and the feedback current is calculated, and the difference is adjusted using a PI controller to obtain the d-axis voltage. and q-axis voltage , respectively with the d-axis feedforward decoupling voltage and q-axis feedforward decoupling voltage Add them together to obtain the d-axis reference voltage. and q-axis reference voltage Then, through Clark and Park inverse transformations, it is converted into a three-phase voltage. The three-phase voltage The SVPWM modulation generates a PWM signal to control the inverter's duty cycle, thus executing control for the current cycle.

[0009] Optional, q-axis reference current Represented as:

[0010] in, Provide a reference value for the q-axis current. For grid voltage The phase angle.

[0011] Optionally, under the MTPA control method, the d-axis current formula is:

[0012] in, For permanent magnet flux linkage in motors, , These are the d-axis and q-axis inductances, respectively. This is the q-axis current.

[0013] Optionally, the voltage limiting equation for the electrolytic capacitor-free permanent magnet synchronous motor is:

[0014] in, The stator current is the maximum current value that the thyristor can withstand. The maximum stator voltage amplitude that the inverter can provide; , For grid voltage amplitude, For grid voltage The phase angle.

[0015] Optionally, the d-axis reference current of the MTPA control region The expression is: .

[0016] Optionally, the d-axis reference current of the field weakening control region The expression is:

[0017] in, The electric angular velocity of the motor rotor. The critical voltage for weak magnetic field control. , These are the d-axis and q-axis inductances, respectively. For grid voltage phase angle, For permanent magnet flux linkage in motors.

[0018] Optionally, the d-axis feedforward decoupling voltage The expression is obtained by decoupling from the d-axis voltage equation: ; The q-axis feedforward decoupling voltage The expression is obtained by decoupling from the q-axis voltage equation: .

[0019] Optionally, the voltage is converted into a three-phase voltage by Clark and Park inverse transformation. The three-phase voltage The PWM signal used to control the inverter duty cycle is generated through SVPWM modulation, including: Calculate the input power on the ideal network side With actual inverter output power The difference is the feedforward compensation power. ;in, , ; Based on feedforward compensation power Calculate the corresponding , The compensation voltage of the shaft is compared with the voltage generated by the inverse transformation of the park. , Add them together to get , Shaft reference voltage , ; right , Shaft reference voltage , SVPWM modulation is performed to obtain the PWM signals of each transistor in the inverter.

[0020] Secondly, the present invention also provides a copper loss optimization control device for an electrolytic capacitor-free permanent magnet synchronous motor based on the MTPA method, comprising: The speed control module is used to perform PI regulation on the difference between the motor's given speed and its actual speed in the current cycle to obtain the reference value for the q-axis current. A reference value is given for the q-axis current. Harmonic injection is performed to obtain a q-axis reference current that fluctuates at a frequency of twice the bus voltage. ; The Q-axis reference current generation module is used to provide a reference value for the q-axis current. Harmonic injection is performed to obtain a q-axis reference current that fluctuates at a frequency of twice the bus voltage. ; The MTPA control region calculation module is used to calculate the d-axis current under the MTPA control method. ; set the q-axis reference current With d-axis current Substituting the voltage limiting equation of the capacitorless permanent magnet synchronous motor, the MTPA control critical voltage is obtained. ; Make the bus voltage greater than time The average value is denoted as the d-axis reference current of the MTPA control region. ; The field weakening control zone calculation module is used to obtain the peak bus voltage based on the voltage limiting equation. One-third as the critical voltage for weak magnetic control Substituting the voltage limiting equation, the d-axis reference current in the field weakening control region is calculated. ; The D-axis reference current generation module is used to control the critical voltage according to MTPA. and the critical voltage for weak magnetic control The bus voltage fluctuation cycle is divided into three working regions: the field weakening control region, the buffer region, and the MTPA control region; according to the calculation formula... Calculate over one bus voltage fluctuation period Inside and Corresponding time nodes and ;according to , , and The segmentation is given within one bus voltage fluctuation cycle. Inner d-axis reference current The expression is:

[0021] in, , ; The dq-axis voltage generation module is used to generate the d-axis reference current. q-axis reference current The difference between the current and the feedback current is calculated, and the difference is adjusted using a PI controller to obtain the d-axis voltage. and q-axis voltage , respectively with the d-axis feedforward decoupling voltage and q-axis feedforward decoupling voltage Add them together to obtain the d-axis reference voltage. and q-axis reference voltage ; Voltage conversion module, used to convert d-axis reference voltage and q-axis reference voltage The voltage is converted into three-phase voltage via Clark and Park inverse transformation. ; SVPWM modulation module is used to convert three-phase voltage The PWM signal is generated by SVPWM modulation to control the duty cycle of the inverter and execute the control of the current cycle.

[0022] Thirdly, the present invention also provides a capacitor-free permanent magnet synchronous motor system, characterized in that it includes: a capacitor-free permanent magnet synchronous motor, and the capacitor-free permanent magnet synchronous motor copper loss optimization control device based on the MTPA method described in the second aspect.

[0023] Compared with the prior art, the above-described technical solutions conceived in this invention can achieve the following beneficial effects: 1. This invention provides a copper loss optimization control method for capacitor-free permanent magnet synchronous motors based on the MTPA method. It combines MTPA control with the operating constraints of capacitor-free permanent magnet synchronous motors, deriving a copper loss optimization control strategy suitable for capacitor-free permanent magnet synchronous motors without relying on DC bus current control. A bus voltage fluctuation cycle is divided into three segments: a field weakening control region, a buffer zone, and an MTPA control region. Based on the time variable t, a d-axis reference current is given for each segment, effectively optimizing motor copper losses and improving motor efficiency. Furthermore, it effectively improves motor efficiency and maintains a high power factor without requiring additional hardware.

[0024] 2. The present invention provides a copper loss optimization control method for capacitorless permanent magnet synchronous motors based on the MTPA method. On the basis of the copper loss optimization control strategy of capacitorless permanent magnet synchronous motors, feedforward power correction is further introduced. Based on the error value between the actual inverter power and the ideal grid-side input power, the voltage reference value is compensated to further improve the quality of the grid-side current and improve the input power factor of the motor. Attached Figure Description

[0025] Figure 1 A block diagram of a copper loss optimization control method for an electrolytic capacitor-free permanent magnet synchronous motor drive system based on the MTPA method provided in an embodiment of the present invention; Figure 2 This is a diagram showing the operating constraints of a permanent magnet synchronous motor without electrolytic capacitors. Figure 3 This is a schematic diagram of the d-axis reference current in the copper loss optimization control method for an electrolytic capacitor-free permanent magnet synchronous motor drive system based on the MTPA method. Figure 4(a) shows the experimental results of the traditional method, including grid-side voltage, d-axis current, q-axis current, motor speed and copper loss value; Figure 4(b) shows the experimental results of the copper loss optimization control method for the electrolytic capacitor-free permanent magnet synchronous motor drive system based on the MTPA method provided in the embodiment of the present invention, including grid-side voltage, d-axis current, q-axis current, motor speed and copper loss value; Figure 5 A comparison diagram of grid-side current harmonics between the conventional method and the copper loss optimization control method for an electrolytic capacitor-free permanent magnet synchronous motor drive system based on the MTPA method provided in the embodiments of the present invention; Figure 6 This is a comparison of power factor and efficiency between the traditional method and the electrolytic capacitor-free permanent magnet synchronous motor copper loss optimization control method based on MTPA. Detailed Implementation

[0026] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0027] The following description, in conjunction with a preferred embodiment, illustrates the content involved in the above embodiments.

[0028] Example 1 This invention provides a method for optimizing copper loss control of a capacitor-free permanent magnet synchronous motor based on the MTPA method, comprising: S1. In the current cycle, perform PI adjustment on the difference between the motor's given speed and its actual speed to obtain the q-axis current reference value. A reference value is given for the q-axis current. Harmonic injection is performed to obtain a q-axis reference current that fluctuates at a frequency of twice the bus voltage. ; S2. Under the MTPA control method, the d-axis current is: ; set the q-axis reference current With d-axis current Substituting the voltage limiting equation of the capacitorless permanent magnet synchronous motor, the MTPA control critical voltage is obtained. ; Make the bus voltage greater than time The average value is denoted as the d-axis reference current of the MTPA control region. ; S3. According to the voltage limiting equation, take the peak value of the bus voltage. One-third as the critical voltage for weak magnetic control Substituting the voltage limiting equation, the d-axis reference current in the field weakening control region is calculated. ; S4. Control the critical voltage according to MTPA. and the critical voltage for weak magnetic control The bus voltage fluctuation cycle is divided into three working regions: the field weakening control region, the buffer region, and the MTPA control region; according to the calculation formula... Calculate over one bus voltage fluctuation period Inside and Corresponding time nodes and ;according to , , and The segmentation is given within one bus voltage fluctuation cycle. Inner d-axis reference current The expression is:

[0029] in, , ; S5, Set the d-axis reference current q-axis reference current The difference between the current and the feedback current is calculated, and the difference is adjusted using a PI controller to obtain the d-axis voltage. and q-axis voltage , respectively with the d-axis feedforward decoupling voltage and q-axis feedforward decoupling voltage Add them together to obtain the d-axis reference voltage. and q-axis reference voltage Then, through Clark and Park inverse transformations, it is converted into a three-phase voltage. The three-phase voltage The SVPWM modulation generates a PWM signal to control the inverter's duty cycle, thus executing control for the current cycle.

[0030] This solution addresses the problem of increased stator current amplitude and excessive copper losses caused by severe fluctuations in bus voltage in traditional capacitor-less permanent magnet synchronous motor systems, which lead to deep field weakening. An innovative segmented control strategy is proposed. The core of this invention lies in: firstly, based on the principle that the ideal grid-side input power equals the inverter output power, the q-axis reference current fluctuates at twice the frequency with the bus voltage, ensuring a high power factor for the system; secondly, considering the operating constraints of the capacitor-less permanent magnet synchronous motor, the MTPA critical voltage is calculated, dividing each bus voltage fluctuation cycle into three operating regions: a field weakening control region, a buffer region, and an MTPA control region; based on this, different d-axis current reference strategies are adopted in different regions according to the real-time sampled bus voltage value, achieving seamless switching from deep field weakening to MTPA control. Furthermore, this method introduces a feedforward power compensation mechanism to further improve grid-side current quality by compensating for the difference between the ideal grid-side input power and the actual inverter output power.

[0031] In this embodiment, the grid voltage can be obtained through a current sensor, a voltage sensor, and a position sensor. Grid current Motor speed Three-phase current And rotor position information.

[0032] In step S1, under ideal conditions, the grid-side power factor is 1, and the ideal grid-side input power is... It can be represented as:

[0033] in, For grid voltage amplitude, For grid current amplitude, Represented as grid voltage phase angle, This can be obtained through a phase-locked loop (PLL), and can be used with respect to time. With the power grid frequency Functional representation:

[0034] Inverter power It can be represented as:

[0035] in, The electric angular velocity of the motor rotor. , These are the d-axis and q-axis inductances, respectively. For permanent magnet flux linkage in motors.

[0036] If the power of the bus thin-film capacitor is ignored, the ideal grid-side input power and inverter power can be considered approximately equal, i.e. At this time, the q-axis reference current in S1 It can be represented as:

[0037] in, Provide a reference value for the q-axis current.

[0038] Therefore, in order to obtain an ideal grid-side power factor, the q-axis reference current should be set as described above.

[0039] Optionally, under the MTPA control method, the d-axis current formula is:

[0040] in, For permanent magnet flux linkage in motors, , These are the d-axis and q-axis inductances, respectively. This is the q-axis current.

[0041] Optionally, the voltage limiting equation for the electrolytic capacitor-free permanent magnet synchronous motor is:

[0042] in, The stator current is the maximum current value that the thyristor can withstand. This is the maximum stator voltage amplitude that the inverter can provide.

[0043] In a capacitor-free permanent magnet synchronous motor drive system, the bus voltage is approximately equal to the absolute value of the grid-side input voltage, exhibiting a second-harmonic fluctuation, and SVPWM modulation is used. It can be represented as:

[0044] Therefore, the operating constraints of a capacitorless permanent magnet synchronous motor drive system can be obtained through... Figure 2 Indicates. For example... Figure 2 As shown, when the bus voltage fluctuates to a low point, the MTPA control of the electrolytic capacitor-free permanent magnet synchronous motor drive system provides... It cannot always meet the operational constraints of a permanent magnet synchronous motor drive system without electrolytic capacitors.

[0045] To maximize the utilization of MTPA control and apply it to the control of an electrolytic capacitor-free permanent magnet synchronous motor drive system, in step S2 of this embodiment, the following steps are performed: and Substituting the voltage limiting equations of a capacitorless permanent magnet synchronous motor into the equations, the voltage limiting equations are transformed as follows:

[0046]

[0047]

[0048] For ease of calculation, let... , The inequality can be transformed into:

[0049] by Using the independent variable, the solution to the equation can be calculated. Multiplying this solution by the peak value of the grid-side input voltage allows us to calculate the theoretical lower limit of the critical voltage in the MTPA control region, which is the MTPA control critical voltage. That is, when the bus voltage is less than At that time, the d-axis current given by MTPA will not be able to meet the operating constraints of the electrolytic capacitor-free permanent magnet synchronous motor drive system.

[0050] To ensure the effectiveness of MTPA control, and considering the limited performance of the current controller, for bus voltages greater than [a certain value], [further measures will be taken]. time Take the average value, and denote it as The calculation formula is as follows:

[0051] in, This represents one bus voltage fluctuation cycle.

[0052] In step S3 of this embodiment, according to the operating constraints of the electrolytic capacitor-free permanent magnet synchronous motor drive system, deep field weakening must be performed when the bus voltage is low to reduce the back electromotive force when the bus voltage is at its lowest point, thus ensuring the normal operation of the motor.

[0053] One-third of the peak bus voltage is taken as the critical voltage for field weakening control. Substituting the voltage limiting equation, the maximum value that its d-axis current can reach is denoted as... The calculation formula is shown below.

[0054]

[0055] To optimize motor copper losses, and combining the MTPA control method with the operational constraints of the electrolytic capacitor-free permanent magnet synchronous motor drive system, step S4 of this embodiment relies on the results obtained in steps S2 and S3 of the previous embodiment. , , and According to the calculation formula:

[0056] Calculate over one bus voltage fluctuation period Inside and Corresponding time nodes and The critical voltage is controlled according to MTPA. and the critical voltage for weak magnetic control The bus voltage fluctuation cycle is divided into three working regions: the weak magnetic control region, the buffer region, and the MTPA control region.

[0057] Using one bus voltage fluctuation cycle as a standard, the d-axis reference current is adjusted according to time. The change segments are given, as shown in the specific diagram. Figure 3 As shown, the calculation formula is as follows:

[0058] in, , for Figure 3 The slope of the d-axis ramp current in the buffer zone is given, and its calculation depends on the calculations obtained in steps S2, S3, and S4 of the example. , , and The specific formula is as follows:

[0059] After calculating the given d-axis and q-axis reference currents using the above method, the MTPA method can be used to the maximum extent to reduce motor copper losses and improve motor efficiency while ensuring a high power factor for the motor.

[0060] In step S5 of this embodiment, the difference between the d-axis reference current, the q-axis reference current, and the feedback current is calculated and input to the current controller. The current controller then performs PI regulation on the difference and outputs the d-axis voltage. q-axis voltage Then decoupled from the d-axis feedforward voltage q-axis feedforward decoupling voltage Add them together to obtain the d-axis reference voltage. q-axis reference voltage Among them, the d-axis feedforward decoupling voltage q-axis feedforward decoupling voltage It is obtained by decoupling the d-axis voltage and q-axis voltage equations, and the specific calculation formula is as follows:

[0061] in, Feedback current for the motor's d-axis This is the q-axis feedback current of the motor.

[0062] In order to further improve the grid-side current quality and increase the motor power factor, this embodiment introduces feedforward power compensation, which uses the difference between the ideal grid-side input power and the actual inverter output power to compensate the control signal.

[0063] Specifically, in step S5 of the embodiment, the d-axis reference voltage... q-axis reference voltage Then, after passing through Clark and Park, it is converted into a three-phase voltage. Then, SVPWM modulation is used to generate a PWM signal for controlling the inverter's duty cycle, including: Calculate the input power on the ideal network side With actual inverter output power The difference is the feedforward compensation power. The actual inverter output power The calculation formula is: ; in, This is the actual d-axis output voltage. This is the actual q-axis output voltage, therefore... Represented as: ; Received according to Calculate the corresponding , The compensation voltage of the shaft is compared with the voltage generated by the inverse transformation of the park. , Add them together to get Shaft reference voltage , Shaft reference voltage This enables power compensation.

[0064] Then regarding its actual Shaft reference voltage , Shaft reference voltage SVPWM modulation is performed to obtain the PWM signals of each transistor in the inverter.

[0065] Figure 4 shows a comparison of the copper loss optimization method for electrolytic capacitor-free permanent magnet synchronous motors based on the MTPA method provided in this example with the experiment using the original field-weakening DC input. It can be seen that the motor still operates normally before and after the method, and the motor copper loss is significantly reduced. This demonstrates that this method can optimize motor copper loss and improve motor efficiency.

[0066] Figure 5 The chart compares the copper loss optimization method for electrolytic capacitor-free permanent magnet synchronous motors based on the MTPA method provided in this example with the Fourier analysis of the grid-side current under the original field-weakening DC reference, and the IEC-61000-3-2 harmonic current limit standard. It can be seen that after using this method, the grid-side current harmonics meet the IEC-61000-3-2 harmonic current limit standard, and the power factor still reaches above 0.98. This demonstrates that this example guarantees a high power factor and effectively improves the grid-side current quality.

[0067] Figure 6 The changes in motor efficiency and power factor under varying torque loads are illustrated. It can be seen that the improvement in motor efficiency is significant under different torque load conditions, with an increase of at least three percent, demonstrating the wide applicability of this embodiment.

[0068] This invention, through studying the MTPA control method and the constraints of an electrolytic capacitor-free permanent magnet synchronous motor drive system, divides a bus voltage fluctuation cycle into three segments: a field weakening control region, a buffer region, and an MTPA control region. Based on the time variable t, a segmented d-axis reference current is provided, effectively optimizing motor copper losses and improving motor efficiency without the need for additional control measures. Furthermore, based on this, feedforward power correction further improves the grid-side current quality and power factor. This solves the problems of existing methods relying on DC bus current control, which suffers from high control difficulty, and the inability to maximize the use of the MTPA method to reduce copper losses. It achieves effective improvement in grid-side current performance, maximizing the use of the MTPA method to reduce copper losses.

[0069] Example 2 This invention provides a capacitor-free permanent magnet synchronous motor copper loss optimization control device based on the MTPA method, comprising: The speed control module is used to perform PI regulation on the difference between the motor's given speed and its actual speed in the current cycle to obtain the reference value for the q-axis current. A reference value is given for the q-axis current. Harmonic injection is performed to obtain a q-axis reference current that fluctuates at a frequency of twice the bus voltage. ; The Q-axis reference current generation module is used to provide a reference value for the q-axis current. Harmonic injection is performed to obtain a q-axis reference current that fluctuates at a frequency of twice the bus voltage. ; The MTPA control region calculation module is used to calculate the d-axis current under the MTPA control method. ; set the q-axis reference current With d-axis current Substituting the voltage limiting equation of the capacitorless permanent magnet synchronous motor, the MTPA control critical voltage is obtained. ; Make the bus voltage greater than time The average value is denoted as the d-axis reference current of the MTPA control region. ; The field weakening control zone calculation module is used to obtain the peak bus voltage based on the voltage limiting equation. One-third as the critical voltage for weak magnetic control Substituting the voltage limiting equation, the d-axis reference current in the field weakening control region is calculated. ; The D-axis reference current generation module is used to control the critical voltage according to MTPA. and the critical voltage for weak magnetic control The bus voltage fluctuation cycle is divided into three working regions: the field weakening control region, the buffer region, and the MTPA control region; according to the calculation formula... Calculate over one bus voltage fluctuation period Inside and Corresponding time nodes and ;according to , , and The segmentation is given within one bus voltage fluctuation cycle. Inner d-axis reference current The expression is:

[0070] in, , ; The dq-axis voltage generation module is used to generate the d-axis reference current. q-axis reference current The difference between the current and the feedback current is calculated, and the difference is adjusted using a PI controller to obtain the d-axis voltage. and q-axis voltage , respectively with the d-axis feedforward decoupling voltage and q-axis feedforward decoupling voltage Add them together to obtain the d-axis reference voltage. and q-axis reference voltage ; Voltage conversion module, used to convert d-axis reference voltage and q-axis reference voltage The voltage is converted into three-phase voltage via Clark and Park inverse transformation. ; SVPWM modulation module is used to convert three-phase voltage The PWM signal is generated by SVPWM modulation to control the duty cycle of the inverter and execute the control of the current cycle.

[0071] In this embodiment, the specific implementation of each module can be referred to the description in Embodiment 1 above, and has the same beneficial effects, so it will not be repeated here.

[0072] Example 3 This invention provides a capacitor-free permanent magnet synchronous motor system, characterized in that it includes: a capacitor-free permanent magnet synchronous motor, and a capacitor-free permanent magnet synchronous motor copper loss optimization control device based on the MTPA method as described in Embodiment 2.

[0073] The connection relationship between the capacitor-free permanent magnet synchronous motor and the capacitor-free permanent magnet synchronous motor copper loss optimization control device based on the MTPA method can be found in [reference needed]. Figure 1 .

[0074] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for optimizing copper loss control of a capacitor-free permanent magnet synchronous motor based on the MTPA method, characterized in that, include: S1. In the current cycle, perform PI adjustment on the difference between the motor's given speed and its actual speed to obtain the q-axis current reference value. A reference value is given for the q-axis current. Harmonic injection is performed to obtain a q-axis reference current that fluctuates at a frequency of twice the bus voltage. ; S2. Under the MTPA control method, the d-axis current is: ; q-axis reference current With d-axis current Substituting the voltage limiting equation of the capacitorless permanent magnet synchronous motor, the MTPA control critical voltage is obtained. ; Make the bus voltage greater than time The average value is denoted as the d-axis reference current of the MTPA control region. ; S3. According to the voltage limiting equation, take the peak value of the bus voltage. One-third as the critical voltage for weak magnetic control Substituting the voltage limiting equation, the d-axis reference current in the field weakening control region is calculated. ; S4. Control the critical voltage according to MTPA. and the critical voltage for weak magnetic control The bus voltage fluctuation cycle is divided into three working regions: the field weakening control region, the buffer region, and the MTPA control region; according to the calculation formula... Calculate over one bus voltage fluctuation period Inside and Corresponding time nodes and ;according to , , and The segmentation is given within one bus voltage fluctuation cycle. Inner d-axis reference current The expression is: in, , ; S5, Set the d-axis reference current q-axis reference current The difference between the current and the feedback current is calculated, and the difference is adjusted using a PI controller to obtain the d-axis voltage. and q-axis voltage , respectively with the d-axis feedforward decoupling voltage and q-axis feedforward decoupling voltage Add them together to obtain the d-axis reference voltage. and q-axis reference voltage Then, through Clark and Park inverse transformations, it is converted into a three-phase voltage. The three-phase voltage The SVPWM modulation generates a PWM signal to control the inverter's duty cycle, thus executing control for the current cycle.

2. The method as described in claim 1, characterized in that, q-axis reference current Represented as: in, Provide a reference value for the q-axis current. For grid voltage The phase angle.

3. The method as described in claim 1, characterized in that, Under the MTPA control method, the d-axis current formula is: in, For permanent magnet flux linkage in motors, , These are the d-axis and q-axis inductances, respectively. This is the q-axis current.

4. The method as described in claim 3, characterized in that, The voltage limiting equation for the electrolytic capacitor-free permanent magnet synchronous motor is as follows: in, The stator current is the maximum current value that the thyristor can withstand. The maximum stator voltage amplitude that the inverter can provide; , For grid voltage amplitude, For grid voltage The phase angle.

5. The method as described in claim 4, characterized in that, The d-axis reference current of the MTPA control region The expression is: 。 6. The method as described in claim 5, characterized in that, The d-axis reference current of the field weakening control region The expression is: in, The electric angular velocity of the motor rotor. The critical voltage for weak magnetic field control. , These are the d-axis and q-axis inductances, respectively. For grid voltage phase angle, For permanent magnet flux linkage in motors.

7. The method as described in claim 6, characterized in that, The d-axis feedforward decoupling voltage The expression is obtained by decoupling from the d-axis voltage equation: ; The q-axis feedforward decoupling voltage The expression is obtained by decoupling from the q-axis voltage equation: .

8. The method as described in claim 7, characterized in that, The voltage is converted into a three-phase voltage by Clark and Park. The three-phase voltage The PWM signal used to control the inverter duty cycle is generated through SVPWM modulation, including: Calculate the input power on the ideal network side With actual inverter output power The difference is the feedforward compensation power. ;in, , ; Based on feedforward compensation power Calculate the corresponding , The compensation voltage of the shaft is compared with the voltage generated by the inverse transformation of the park. , Add them together to get , Shaft reference voltage , ; right , Shaft reference voltage , SVPWM modulation is performed to obtain the PWM signals of each transistor in the inverter.

9. A copper loss optimization control device for electrolytic capacitor-free permanent magnet synchronous motors based on the MTPA method, characterized in that, include: The speed control module is used to perform PI regulation on the difference between the motor's given speed and its actual speed in the current cycle to obtain the reference value for the q-axis current. A reference value is given for the q-axis current. Harmonic injection is performed to obtain a q-axis reference current that fluctuates at a frequency of twice the bus voltage. ; The Q-axis reference current generation module is used to provide a reference value for the q-axis current. Harmonic injection is performed to obtain a q-axis reference current that fluctuates at a frequency of twice the bus voltage. ; The MTPA control region calculation module is used to calculate the d-axis current under the MTPA control method. ; q-axis reference current With d-axis current Substituting the voltage limiting equation of the capacitorless permanent magnet synchronous motor, the MTPA control critical voltage is obtained. ; Make the bus voltage greater than time The average value is denoted as the d-axis reference current of the MTPA control region. ; The field weakening control zone calculation module is used to obtain the peak bus voltage based on the voltage limiting equation. One-third as the critical voltage for weak magnetic control Substituting the voltage limiting equation, the d-axis reference current in the field weakening control region is calculated. ; The D-axis reference current generation module is used to control the critical voltage according to the MTPA. and the critical voltage for weak magnetic control The bus voltage fluctuation cycle is divided into three working regions: the field weakening control region, the buffer region, and the MTPA control region; according to the calculation formula... Calculate over one bus voltage fluctuation period Inside and Corresponding time nodes and ;according to , , and The segmentation is given within one bus voltage fluctuation cycle. Inner d-axis reference current The expression is: in, , ; The dq-axis voltage generation module is used to generate the d-axis reference current. q-axis reference current The difference between the current and the feedback current is calculated, and the difference is adjusted using a PI controller to obtain the d-axis voltage. and q-axis voltage , respectively with the d-axis feedforward decoupling voltage and q-axis feedforward decoupling voltage Add them together to obtain the d-axis reference voltage. and q-axis reference voltage ; Voltage conversion module, used to convert d-axis reference voltage and q-axis reference voltage The voltage is converted into three-phase voltage via Clark and Park inverse transformation. ; SVPWM modulation module is used to convert three-phase voltage The PWM signal is generated by SVPWM modulation to control the duty cycle of the inverter and execute the control of the current cycle.

10. A permanent magnet synchronous motor system without electrolytic capacitors, characterized in that, include: A capacitor-free permanent magnet synchronous motor, and the copper loss optimization control device for a capacitor-free permanent magnet synchronous motor based on the MTPA method as described in claim 9.

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