DC link voltage control method for permanent magnet synchronous motor system without electrolytic capacitor

Abstract

The present invention discloses a DC link voltage control method for a non-electrolytic capacitor permanent magnet synchronous motor system. According to the maximum output capacity of a space vector modulation link and the output desired voltage vector, a minimum bus voltage based on the desired voltage vector angle is constructed in real time; when the rectifier output voltage is lower than the minimum bus voltage, the power switch device in the DC link is immediately turned on, so that the film capacitor is cut into the DC link, and the voltage of the film capacitor is used to compensate for the shortage of the rectifier output voltage, so as to ensure that the DC link voltage is always higher than the minimum bus voltage. The present invention effectively solves the contradiction between reducing the capacitance of the DC link film capacitor and the high-performance control of the drive system; in the case of applying the space vector modulation technology, the present invention can ensure the DC link voltage stability of the non-electrolytic capacitor permanent magnet synchronous motor system in high-performance operation, thereby realizing efficient and reliable control of the drive system.

Description

Technical Field

[0001] The present invention belongs to the technical field of permanent magnet synchronous motor system control, and in particular relates to a DC link voltage control method for a permanent magnet synchronous motor system without an electrolytic capacitor. Background Art

[0002] AC-DC-AC motor drive systems are widely used in industrial automation, HVAC (heating, ventilation and air conditioning) systems, and renewable energy. Traditionally, such drive systems require large-capacity electrolytic capacitors on the DC link side. However, large-capacity electrolytic capacitors are large and heavy, and their lifespan is significantly shortened under extreme temperature conditions, which in turn affects the reliability and service life of the drive system.

[0003] In order to deal with these problems, small-capacity film capacitors have gradually attracted attention as an alternative to large-capacity electrolytic capacitors. The use of film capacitors can not only significantly reduce the volume and weight of the system, but also improve the reliability of the system and extend its service life. In addition, due to the excellent working characteristics of film capacitors, this alternative usually does not require the addition of additional power factor correction circuits or inductor filters, thereby simplifying system design and reducing costs.

[0004] In brushless DC motor drive systems using small-capacity film capacitors, in order to further optimize space utilization and reduce costs, the focus of research has gradually shifted to reducing the capacitance of film capacitors. The literature [HKSamitha Ransara andU.K.Madawala, "A torque ripple compensation technique for a low-cost brushlessDC motor drive", IEEE Trans.Ind.Electron., vol.62, no.10, pp.6171-6182, Oct.2015] proposed a DC link topology structure using film capacitors in series with power switching devices (insulated gate bipolar transistors) to cope with the situation where the output voltage of the rectifier bridge is insufficient, such as Figure 1As shown, by turning on the insulated gate bipolar transistor (IGBT) of the DC link when needed, the film capacitor is cut into the DC link, thereby ensuring that the DC link voltage meets the requirements of motor operation; since the film capacitor only provides energy to the motor part of the time, a film capacitor with lower capacity can be used. In order to fully tap the output potential of the rectifier bridge, the literature [C.Xia, P.Li, X.Li and T.Shi, "Series IGBT chopping strategy to reduce DC-link capacitance for brushless DC motor drive system", IEEEJ.Emerg.Sel.Topics Power Electron., vol.5, no.3, pp.1192-1204, Sep.2017] proposed a PWM modulation strategy for connecting IGBT in series with the DC link, so that the film capacitor and the rectifier bridge alternately provide energy to the motor, thereby reducing the discharge time and energy demand of the film capacitor, and effectively reducing the capacitance demand of the film capacitor. In addition, the literature [X.Li et al., "A novel voltage-boosting modulation strategy to reduce DC-link capacitance for brushless DC motor drives", IEEE Trans.Power Electron., vol.37, no.12, pp.15397–15410, Dec.2022] proposes a DC link capacitor boost energy storage strategy, which optimizes the vector combination of the inverter by utilizing the redundant voltage output by the rectifier bridge to improve the energy storage capacity of the thin film capacitor, thereby further reducing the capacitance requirement of the thin film capacitor.

[0005] However, the control object in the above method is a brushless DC motor, which usually operates in a two-phase conduction mode, that is, only two phases of the winding are energized at the same time. The two-phase conduction mode itself will produce commutation torque fluctuations, resulting in significant torque fluctuations. In contrast, the inverter of the permanent magnet synchronous motor adopts a space vector modulation strategy, and its three-phase conduction mode can directly eliminate the commutation torque fluctuations, thereby achieving a smooth torque output. However, the DC link IGBT control strategy proposed in the above method is only applicable to brushless DC motors operating in a two-phase conduction mode; in this mode, the conduction area of ​​the DC link IGBT is limited by the reverse electromotive force and phase current of the brushless DC motor, while the permanent magnet synchronous motor usually operates in a three-phase conduction mode with a sinusoidal phase current. Therefore, the DC link IGBT control strategy proposed in the above method is not applicable to permanent magnet synchronous motors; for permanent magnet synchronous motor systems without electrolytic capacitors, there is currently no control scheme for the DC link series IGBT topology structure, resulting in the system performance failing to achieve the expected control effect, limiting the application of the system in high-performance scenarios. Summary of the invention

[0006] In view of the above, the present invention provides a DC link voltage control method for a permanent magnet synchronous motor system without an electrolytic capacitor, which can still ensure high performance operation of the permanent magnet synchronous motor while reducing the DC link capacitance.

[0007] A DC link voltage control method for a permanent magnet synchronous motor system without electrolytic capacitors, the permanent magnet synchronous motor system comprising a rectifier, a DC link and a three-phase inverter, wherein the rectifier adopts a single-phase diode rectifier bridge, the AC side of which is connected to an AC power supply, and the DC side is connected to the DC side of a three-phase inverter through a DC link; the DC link is connected across the DC bus, and is composed of a power switch device and a film capacitor connected in series; the three-phase inverter adopts space vector modulation, and the AC side of the inverter is connected to the permanent magnet synchronous motor;

[0008] The DC link voltage control method is to monitor and obtain the output voltage u of the rectifier in real time r According to the maximum output capacity of the space vector modulation link and the expected voltage vector of the current output, the minimum bus voltage U based on the expected voltage vector angle is calculated in real time. dc ; Real-time u r with U dc For comparison, when u r Lower than U dc When the voltage of the film capacitor is used to compensate for the insufficient output voltage of the rectifier, the DC link voltage is always higher than U dc , thereby realizing the DC link voltage control of the permanent magnet synchronous motor system.

[0009] Furthermore, the minimum bus voltage U based on the expected voltage vector angle is calculated in real time according to the following formula: dc :

[0010]

[0011] Where: V ref represents the expected voltage vector output by the current space vector modulation link, θ represents the expected voltage vector angle, It represents the remainder when θ is divided by π / 3.

[0012] Furthermore, the opening principle of the power switch device in the DC link is: when u r Lower than U dc When u r Higher than or equal to U dc When , the power switch device is turned off, the film capacitor cuts out of the DC link, and the rectifier provides energy for the motor; in the above two states, the DC link voltage expression is as follows:

[0013]

[0014] Where: u dc_link is the DC link voltage, u cap is the voltage of the film capacitor.

[0015] Furthermore, regardless of whether the power switch device in the DC link is turned on or not, the DC link voltage is always introduced into the space vector modulation link to suppress the interference of the DC link voltage fluctuation on the output of the three-phase inverter.

[0016] Furthermore, the minimum capacitance of the film capacitor is designed according to the rated parameters of the permanent magnet synchronous motor, and the specific relationship is as follows:

[0017]

[0018] Where: C is the minimum capacitance of the film capacitor, P mN is the rated power of the permanent magnet synchronous motor, T m is the maximum duration of the film capacitor being cut into the DC link, U m is the peak voltage of the AC power supply, U dcNm For U dc The maximum value of .

[0019] Furthermore, the maximum duration T m The calculation expression is as follows:

[0020]

[0021] Where:g is the voltage frequency of the AC power supply.

[0022] A computer device comprises a memory and a processor, wherein the memory stores a computer program, and the processor is used to execute the computer program to implement the DC link voltage control method of the electrolytic capacitor-free permanent magnet synchronous motor system.

[0023] A computer-readable storage medium stores a computer program, and when the computer program is executed by a processor, the DC link voltage control method of the above-mentioned electrolytic capacitor-free permanent magnet synchronous motor system is implemented.

[0024] Based on the above technical solution, the present invention has the following beneficial technical effects:

[0025] 1. The DC link voltage control method of the electrolytic capacitor-free permanent magnet synchronous motor system of the present invention can meet the application requirements of high torque control accuracy and high dynamic performance when a small-capacity film capacitor is used in the DC link.

[0026] 2. The present invention fully utilizes the rectifier output voltage, improves voltage utilization, and effectively reduces the capacity requirement of the DC link capacitor.

[0027] 3. The present invention is directed to a permanent magnet synchronous motor system without electrolytic capacitors, and under the premise of not affecting the system performance, the volume and weight of the drive system are significantly reduced, which is beneficial to the integration and low-cost development of the system.

[0028] In summary, the present invention provides a theoretical basis for the DC link voltage control of the electrolytic capacitor-free permanent magnet synchronous motor system, and effectively solves the contradiction between reducing the capacitance of the DC link film capacitor and the high-performance control of the drive system; when applying the space vector modulation technology, the present invention can ensure the DC link voltage stability of the electrolytic capacitor-free permanent magnet synchronous motor system in high-performance operation, thereby realizing efficient and reliable control of the drive system. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 It is a structural schematic diagram of the permanent magnet synchronous motor system without electrolytic capacitor in the present invention.

[0030] Figure 2 Schematic diagram of the voltage vector modulation boundary of the space vector modulation technology in the present invention.

[0031] Figure 3 Schematic diagram of the minimum bus voltage waveform based on the voltage vector angle in the present invention.

[0032] Figure 4 Schematic diagram of the waveforms of the rectifier output voltage and the DC link capacitor voltage in the present invention. DETAILED DESCRIPTION

[0033] In order to describe the present invention more specifically, the technical solution of the present invention is described in detail below in conjunction with the accompanying drawings and specific implementation methods.

[0034] The structure of the permanent magnet synchronous motor system without electrolytic capacitor in the present invention is as follows: Figure 1 As shown, the rectifier stage uses a single-phase diode rectifier bridge, the DC link is a topology structure of an IGBT and a film capacitor in series, and the three-phase inverter uses space vector modulation technology. r is the output voltage of the rectifier bridge, u cap is the film capacitor voltage, u dc_link is the DC link voltage.

[0035] For the permanent magnet synchronous motor system, the DC link voltage control method of the present invention is specifically implemented as follows: first, the controller calculates the expected voltage vector V according to the maximum output capacity of the space vector modulation technology and the output of the current space vector modulation link. ref , construct the minimum bus voltage U based on the expected voltage vector angle dc Under a fixed DC link voltage, the voltage vector boundary that can be output by space vector modulation technology is a hexagon, such as Figure 2 As shown, the voltage vector V on the hexagonal boundary m is the maximum voltage vector that can be output by the space vector modulation technology, which represents the maximum output capacity of the space vector modulation technology under a fixed DC link voltage. According to the sine theorem, its voltage vector amplitude |V m |With DC link voltage u dc_link And the voltage vector angle θ has the following relationship:

[0036]

[0037] Where: θ is the voltage vector V m The vector angle (which is the desired voltage vector V ref The angle between the two-phase stationary coordinate system and the α-axis is calculated using the expected voltage vector V ref The α-axis and β-axis components of are obtained using the inverse tangent function), and M(x,y) is a function that finds the remainder when x is divided by y.

[0038] For the desired voltage vector V output by the space vector modulation link ref According to the maximum output capability of the space vector modulation technology, the minimum bus voltage U based on the expected voltage vector angle constructed by the controller dc As shown below:

[0039]

[0040] When the desired voltage vector V ref When the trajectory is circular, the minimum bus voltage U based on the expected voltage vector angledc The waveform that changes with the voltage vector angle θ is as follows Figure 3 shown.

[0041] The expected voltage vector V output by the space vector modulation link ref It will fluctuate with the change of the operating conditions of the permanent magnet synchronous motor, resulting in the minimum bus voltage U based on the expected voltage vector angle. dc In order to ensure the stability of the system, it is necessary to obtain and dynamically adjust the minimum bus voltage U based on the expected voltage vector angle in real time according to the actual working conditions of the permanent magnet synchronous motor. dc .

[0042] In each rectification cycle, the controller converts the current rectifier output voltage u r The minimum DC bus voltage U based on the expected voltage vector angle dc The switching state of the series IGBT is controlled by comparison. The switching principle of the DC link series IGBT is as follows: when the rectifier bridge output voltage u r Lower than the minimum bus voltage U based on the desired voltage vector angle dc When the DC link is connected in series with the IGBT, the capacitor is cut into the DC link to ensure the high voltage of the DC link, thereby ensuring the stability of the permanent magnet synchronous motor operation; when the rectifier bridge output voltage u r Higher than or equal to the minimum bus voltage U based on the desired voltage vector angle dc When the DC link IGBT is turned off, the capacitor is cut out of the DC link, and the rectifier bridge directly provides energy to the permanent magnet synchronous motor. In this process, the system can r Minimum DC bus voltage U with expected voltage vector angle dc The relationship between the capacitor and the capacitor is automatically adjusted to ensure that the DC link voltage is always maintained at a high level. Based on the above working principle, the change of the DC link voltage is as follows:

[0043]

[0044] Where: u dc_link is the DC link voltage; u cap is the DC link capacitor voltage; u r is the output voltage of the rectifier bridge.

[0045] Taking the zero-crossing moment of the power supply voltage as the time reference, the output voltage u of the rectifier bridge r for:

[0046] u r =U m |sinω g t

[0047] Where:g is the angular frequency of the AC power supply, U m is the voltage peak value.

[0048] As the DC link IGBT is turned on and off, the DC link voltage will change accordingly, such as Figure 4 As shown in Figure 2, by controlling the DC link IGBT, the system can dynamically adjust the DC link voltage to ensure that it is always higher than the minimum bus voltage U based on the desired voltage vector angle. dc In addition, due to U dc It is not a constant value, which means that in different rectification cycles, the switching-in and switching-out moments of the capacitor will vary depending on U dc changes with fluctuations; Figure 4 Points A and C, and points B and D in the figure respectively illustrate the specific changes in the switching on and off of the capacitor in different rectification cycles. This real-time adjustment can effectively adapt to various operating conditions of the permanent magnet synchronous motor, thereby ensuring that the DC link voltage always meets the following constraints:

[0049] u dc_link ≥U dc

[0050] According to the rated parameters of the permanent magnet synchronous motor, the minimum capacitance required for the DC link capacitor is calculated: When the permanent magnet synchronous motor works at rated conditions, the minimum bus voltage U based on the expected voltage vector angle is dc The rated value U dcN , at this time, the film capacitor cuts into the DC link for the longest time; when the permanent magnet synchronous motor is in rated working condition, its voltage equation is:

[0051]

[0052] Where: u dN 、u qN is the stator voltage on the dq axis under rated conditions, i dN 、i qN is the stator current on the dq axis under rated conditions, R s is the stator resistance, L d , L q is the stator inductance on the dq axis, ω eN is the electrical angular velocity of the motor rotor under rated conditions.

[0053] When the permanent magnet synchronous motor runs stably, i d with i q Basically remain unchanged, so the voltage on the d-axis inductance and q-axis inductance can be ignored. Further, the voltage vector V output by the space vector modulation technology when the permanent magnet synchronous motor is running stably under rated conditions can be obtained. refN =u dN +ju qN, the minimum bus voltage U based on the expected voltage vector angle constructed by the controller dcN As shown below:

[0054]

[0055] Where: θ0 is the expected voltage vector angle at the moment when the power supply voltage crosses zero; U dcN It is not a constant value, which results in that the cut-out time of the capacitor is not fixed in different rectification cycles. The maximum value U dcNm ; Assume that when the rectifier bridge output voltage u r Lower than U dcNm When the capacitor is cut into the DC link, the output voltage of the combined rectifier bridge is u r The maximum duration T of the capacitor being cut into the DC link can be obtained by using the equation m for:

[0056]

[0057] Where: Under rated conditions, when the function When the value is π / 3, U dc Reach the maximum value U dcNm .

[0058] When running smoothly under rated conditions, the permanent magnet synchronous motor can be regarded as a constant power load. Ignoring the switching and conduction losses of the inverter, the inverter input power P invN With motor power P mN Equal, that is:

[0059]

[0060] Where: u dN 、u qN 、i dN 、i qN They are respectively the d-axis voltage, q-axis voltage, d-axis current, and q-axis current in the dq axes under rated conditions.

[0061] When the film capacitor is cut into the DC link, the energy consumed by the permanent magnet synchronous motor is provided by the DC link capacitor, and the capacitor voltage at the time of capacitor cut-in is U m , the highest point of the capacitor voltage when the capacitor is cut out is U dcNm According to the law of conservation of energy, we can get:

[0062]

[0063] The left side of the equation is the maximum energy required by the permanent magnet synchronous motor, and the right side of the equation is the minimum energy output by the capacitor. The capacitance value can be estimated as follows:

[0064]

[0065] The capacitance of the DC link film capacitor in the present invention only needs to be greater than the above formula.

[0066] Example

[0067] The method of the present invention can be applied to a non-electrolytic capacitor permanent magnet synchronous motor drive system, and the system structure is as follows: Figure 1 As shown, the rectifier is a diode rectifier bridge, the DC link is composed of an IGBT and a film capacitor in series, and the three-phase inverter adopts space vector modulation technology. The parameters of the permanent magnet synchronous motor and the AC power supply in this embodiment are shown in Table 1:

[0068] Table 1

[0069]

[0070] For surface-mounted permanent magnet synchronous motor loads, the three-phase inverter adopts a space vector modulation strategy, using i d =0 control mode. In order to drive the permanent magnet synchronous motor, the desired voltage vector output by the space vector modulation link is V ref , the controller constructs the minimum bus voltage based on the expected voltage vector angle in real time according to the maximum output capacity of the space vector modulation technology:

[0071]

[0072] The expected voltage vector V output by the space vector modulation link ref It will fluctuate with the change of the operating conditions of the permanent magnet synchronous motor, resulting in the minimum bus voltage U based on the expected voltage vector angle. dc In order to ensure the stability of the system, it is necessary to obtain and dynamically adjust the minimum bus voltage U based on the expected voltage vector angle in real time according to the actual working conditions of the permanent magnet synchronous motor. dc When the permanent magnet synchronous motor is in a stable operating condition, the minimum bus voltage U based on the expected voltage vector angle is dc The waveform that changes with the voltage vector angle θ is as follows Figure 3 shown.

[0073] In each rectification cycle, the controller converts the current rectifier output voltage u r The minimum DC bus voltage U based on the expected voltage vector angle dc The switching state of the series IGBT is controlled by comparison. The switching principle of the DC link series IGBT is as follows: when the rectifier bridge output voltage u r Lower than the minimum bus voltage U based on the desired voltage vector angle dc When the DC link is connected in series with the IGBT, the capacitor is cut into the DC link to ensure the high voltage of the DC link, thereby ensuring the stability of the permanent magnet synchronous motor. rGreater than or equal to the minimum bus voltage U based on the desired voltage vector angle dc When , the DC link IGBT is turned off, the capacitor is cut out of the DC link, and the rectifier bridge directly provides energy to the permanent magnet synchronous motor. Based on the above working principle, the change of DC link voltage is as follows:

[0074]

[0075] Where: u dc_link is the DC link voltage; u cap is the DC link capacitor voltage; u r is the output voltage of the rectifier bridge. Taking the zero-crossing moment of the power supply voltage as the time reference, let the angular frequency of the AC power supply be ω g , the peak voltage of the AC power supply is U m , rectifier bridge output voltage u r for:

[0076] u r =U m |sinω g t|

[0077] As the DC link IGBT is turned on and off, the DC link voltage will change accordingly, such as Figure 4 By controlling the DC link IGBT, the system can dynamically adjust the DC link voltage to ensure that it is always higher than the minimum bus voltage U based on the desired voltage vector angle. dc In addition, due to U dc It is not a constant value, which means that in different rectification cycles, the switching-in and switching-out moments of the capacitor will vary depending on U dc changes with fluctuations; Figure 4 Points A and C, and points B and D in the figure respectively illustrate the specific changes in the switching on and off of the capacitor in different rectification cycles. This real-time adjustment can effectively adapt to various operating conditions during motor operation, thereby ensuring that the DC link voltage always meets the following constraints under different operating conditions:

[0078] u dc_link ≥U dc

[0079] In this embodiment, the minimum capacitance of the DC link film capacitor is designed according to the permanent magnet synchronous motor parameters in Table 1. d =0 control, the voltage equation under rated working condition is:

[0080]

[0081] Where: u dN 、u qN is the stator voltage on the dq axis under rated conditions, idN 、i qN is the stator current on the dq axis under rated conditions, R s is the stator resistance, L d , L q is the stator inductance on the dq axis, ω eN is the electrical angular velocity of the motor rotor under rated conditions. When the permanent magnet synchronous motor is running stably, it can be seen from Table 1 that i dN =0,i qN =1.84A, and i d with i q The voltage vector V required for the permanent magnet synchronous motor to operate stably under rated conditions is: refN =u dN +ju qN , which can be obtained by calculating the relevant parameters in Table 1. The minimum bus voltage based on the desired voltage vector angle constructed by the controller is as follows:

[0082]

[0083] Where: θ0 is the expected voltage vector angle at the moment when the power supply voltage crosses zero; U dcN It is not a constant value, which results in that the capacitor cut-out time is not fixed in different rectification cycles. Take the maximum value of the minimum bus voltage based on the expected voltage vector angle U dcNm , assuming that when the rectifier bridge output voltage u r Lower than U dcNm When the capacitor is cut into the DC link, the output voltage of the combined rectifier bridge is u r The maximum duration of the capacitor cutting into the DC link is obtained by using the equation:

[0084]

[0085] When running smoothly under rated conditions, the permanent magnet synchronous motor can be regarded as a constant power load. Ignoring the switching and conduction losses of the inverter, the inverter input power P invN With motor power P mN Equal, that is:

[0086]

[0087] Where: u dN 、u qN 、i dN 、i qN They are respectively the d-axis voltage, q-axis voltage, d-axis current, and q-axis current in the dq axis under rated working conditions. From the above formula and according to Table 1, the rated power P of the permanent magnet synchronous motor can be obtained. mN .

[0088] When the capacitor is cut into the DC link, the energy required by the permanent magnet synchronous motor is provided by the DC link capacitor. The capacitor voltage at the time of capacitor cut-in is U m , the highest point of the capacitor voltage when the capacitor is cut out is U dcNm According to the law of conservation of energy, we can get:

[0089]

[0090] The left side of the equation is the maximum energy required by the permanent magnet synchronous motor, and the right side of the equation is the minimum energy output by the capacitor. The capacitance value can be estimated as follows:

[0091]

[0092] Finally, the capacitance value calculated based on the data in Table 1 is about 35uF.

[0093] In summary, it can be seen that this embodiment can ensure that the DC link voltage meets the constraint conditions while ensuring that the DC link capacitance is reduced, thereby achieving efficient and reliable control of the drive system.

[0094] The above description of the embodiments is to facilitate the understanding and application of the present invention by those skilled in the art. It is obvious that those skilled in the art can easily make various modifications to the above embodiments and apply the general principles described herein to other embodiments without creative work. Therefore, the present invention is not limited to the above embodiments. Improvements and modifications made by those skilled in the art to the present invention based on the disclosure of the present invention should be within the protection scope of the present invention.

Claims

1. A DC link voltage control method for a permanent magnet synchronous motor system without electrolytic capacitors, wherein the permanent magnet synchronous motor system comprises a rectifier, a DC link and a three-phase inverter, wherein the rectifier adopts a single-phase diode rectifier bridge, the AC side of which is connected to an AC power supply, and the DC side is connected to the DC side of the three-phase inverter through a DC link; the DC link is connected across the DC bus, and is composed of a power switch device and a film capacitor in series, the three-phase inverter adopts space vector modulation, and the AC side of the inverter is connected to the permanent magnet synchronous motor; The DC link voltage control method is characterized in that: real-time monitoring is performed to obtain the output voltage u of the rectifier r According to the maximum output capacity of the space vector modulation link and the expected voltage vector of the current output, the minimum bus voltage U based on the expected voltage vector angle is calculated in real time. dc ; Real-time u r with U dc For comparison, when u r Lower than U dc When the voltage of the film capacitor is used to compensate for the insufficient output voltage of the rectifier, the DC link voltage is always higher than U dc , thereby realizing the DC link voltage control of the permanent magnet synchronous motor system.

2. The DC link voltage control method according to claim 1, characterized in that: The minimum bus voltage U based on the expected voltage vector angle is calculated in real time according to the following formula: dc : Where: V ref represents the expected voltage vector output by the current space vector modulation link, θ represents the expected voltage vector angle, It represents the remainder when θ is divided by π / 3.

3. The DC link voltage control method according to claim 1, characterized in that: The opening principle of the power switch device in the DC link is: when u r Lower than U dc When u r Higher than or equal to U dc When the power switch device is turned off, the film capacitor is cut out of the DC link, and the rectifier provides energy for the motor; in the above two states, the DC link voltage expression is as follows: Where: u dc_link is the DC link voltage, u cap is the voltage of the film capacitor.

4. The DC link voltage control method according to claim 1, characterized in that: Regardless of whether the power switch device in the DC link is turned on or not, the DC link voltage is always introduced into the space vector modulation link to suppress the interference caused by the DC link voltage fluctuation on the output of the three-phase inverter.

5. The DC link voltage control method according to claim 1, characterized in that: The minimum capacitance of the film capacitor is designed according to the rated parameters of the permanent magnet synchronous motor, and the specific relationship is as follows: Where: C is the minimum capacitance of the film capacitor, P mN is the rated power of the permanent magnet synchronous motor, T m is the maximum duration of the film capacitor being cut into the DC link, U m is the peak voltage of the AC power supply, U dcNm For U dc The maximum value of .

6. The DC link voltage control method according to claim 5, characterized in that: The maximum duration T m The calculation expression is as follows: Where: g is the voltage frequency of the AC power supply.

7. A computer device comprising a memory and a processor, characterized in that: The memory stores a computer program, and the processor is used to execute the computer program to implement the DC link voltage control method of the electrolytic capacitor-free permanent magnet synchronous motor system according to any one of claims 1 to 6.

8. A computer-readable storage medium storing a computer program, characterized in that: When the computer program is executed by the processor, the DC link voltage control method of the electrolytic capacitor-free permanent magnet synchronous motor system according to any one of claims 1 to 6 is implemented.

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