Induction motor common-mode voltage suppression method based on dynamic switching of DPWM mode

Abstract

The application provides an induction motor common-mode voltage suppression method based on DPWM mode dynamic switching, relates to the technical field of power electronics and motor drive control, obtains an induction motor operation condition and a PWM drive boundary condition range, simultaneously obtains a current voltage space vector sector Sector and a modulation ratio m, calculates a common-mode voltage evaluation index according to the operation condition and the drive boundary condition, selects a target DPWM mode in a preset DPWM mode set according to the common-mode voltage evaluation index, the modulation ratio m and the sector Sector, determines corresponding clamping rules and zero vector allocation rules, and outputs a PWM drive signal; when the common-mode voltage evaluation index is out of limit, the modulation ratio crosses a preset segmentation boundary, or the sector changes to cause the target mode to change during the operation process, DPWM mode switching is performed; the current mode is maintained when the switching condition is not met; the common-mode voltage is stably reduced under multiple operation conditions, the common-mode interference to the ground is reduced, and the electromagnetic compatibility and operation reliability of an induction motor variable frequency drive system are improved.

Description

Technical Field

[0001] This invention relates to the field of power electronics and motor drive control technology, and in particular to a common-mode voltage suppression method for induction motors based on dynamic switching of DPWM mode. Background Technology

[0002] Induction motors, with their simple structure, high reliability, and low cost, are widely used in industrial drives, fans, pumps, compressors, and traction systems. With the popularization of variable frequency speed control technology, induction motors are mostly powered by PWM inverters to achieve speed regulation. At the same time, the high-speed switching of the inverter causes the motor terminal voltage to exhibit high-frequency pulse characteristics, leading to higher requirements for electromagnetic compatibility (EMC), with common-mode voltage and its resulting grounding interference being particularly prominent.

[0003] Under PWM inverter power supply conditions, the switching on and off of the switching devices causes a rapid transition in the potential of the three-phase terminals of the motor relative to the chassis, thus forming common-mode voltage (CMV). CMV can cause common-mode current to ground and electromagnetic interference, manifesting as increased leakage current to ground, interference with control and detection signals, and increased electrical stress on the insulation, thereby affecting the stable operation and reliability of the drive system. Since CMV is closely related to the inverter's switching state, zero-vector action mode, and modulation strategy, suppressing it from the control side is both direct and engineering-feasible.

[0004] In existing technologies, common-mode voltage or its switching characteristics are often reduced by changing the PWM modulation strategy. For example, discontinuous PWM (DPWM) is used to change the zero-vector action time, reduce switching state transitions, and lower the common-mode voltage level under certain operating conditions. However, DPWM modes typically have various clamping rules and implementation forms, and different modes have inconsistent effects on common-mode voltage, harmonics, and switching losses under different modulation ratios, sector positions, and operating conditions. If a fixed DPWM mode or fixed parameter settings are used, the suppression effect may fluctuate with changes in operating conditions, and may even have adverse effects under certain operating conditions, making it difficult to stably control the common-mode voltage across the entire operating range.

[0005] Therefore, a common-mode voltage suppression control method oriented towards changing operating conditions is needed. This method should be able to adaptively select and switch the DPWM mode based on operating conditions such as bus voltage, switching frequency, voltage rise time, modulation ratio, and sector information. Through reasonable clamping and zero-vector allocation rules, it should stably reduce common-mode voltage while ensuring basic operating performance, thereby improving the electromagnetic compatibility and operational reliability of the induction motor variable frequency drive system. Existing technologies mostly employ fixed DPWM modes or fixed zero-vector allocation parameters, making it difficult to simultaneously address common-mode voltage suppression effectiveness and switching stability under different modulation ratios, sectors, and operating conditions. Summary of the Invention

[0006] This invention proposes a common-mode voltage suppression method for induction motors based on dynamic switching of DPWM mode. It aims to solve the problem that in existing induction motor frequency conversion drive systems, the common-mode voltage suppression effect of fixed DPWM modulation strategy fluctuates greatly under different modulation ratios, sectors and operating conditions, and is difficult to be stably controlled across the entire operating range.

[0007] This invention provides a common-mode voltage suppression method for induction motors based on dynamic switching of DPWM mode, the method comprising the following steps: Step 1: Obtain the operating conditions and drive boundary conditions of the induction motor. The operating conditions include speed command and torque command, and the drive boundary conditions include the DC bus voltage V. dc Switching frequency f sw And the voltage rise time dV / dt range, while obtaining the current voltage space vector sector and modulation ratio m; Step 2: Calculate the common-mode voltage evaluation index based on the operating conditions and drive boundary conditions; Step 3: In the preset DPWM mode set, select the target DPWM mode according to the common mode voltage evaluation index, modulation ratio m and sector, and determine the clamp vector selection rule and zero vector allocation rule corresponding to the target DPWM mode. Step 4: Generate a PWM switching sequence based on the target DPWM mode and output the inverter gate drive signal to suppress common-mode voltage; Step 5: During operation, continuously determine whether the switching triggering conditions are met. The switching triggering conditions include at least: the common mode voltage evaluation index exceeds a preset threshold, the modulation ratio m crosses a preset segment boundary, or the sector changes and the target DPWM mode determined according to the preset mode selection rule in Step 3 is different from the current DPWM mode. Step 6: When the switching trigger condition is met, update the target DPWM mode and return to step 4 under the constraints of minimum hold time and hysteresis condition; when the switching trigger condition is not met, maintain the current DPWM mode and continue to output the gate drive signal so that the common mode voltage evaluation index does not exceed the preset threshold.

[0008] Furthermore, the common-mode voltage evaluation index mentioned in step 2 is the peak common-mode voltage V of the motor's three-phase terminal voltage relative to the ground terminal of the motor housing. cm,pk , Common-mode voltage root mean square value V cm,rms The evaluation function R for common-mode voltage risk; The common-mode voltage is defined as:

[0009] Among them, V a V b V c These are the three-phase terminal voltages relative to the ground voltage of the chassis grounding terminal; The common-mode voltage peak V cm,pk , Common-mode voltage root mean square value V cm,rms The calculation formula is:

[0010] in, Let be the instantaneous value of the common-mode voltage, and t be the time variable. To obtain the maximum value, T is the evaluation time length, which can be one or more electrical cycles; The evaluation function R is composed of the driving boundary conditions and the operating conditions, and satisfies:

[0011] The evaluation function R and the preset threshold R are used to evaluate the evaluation function R. th The comparison result serves as one of the criteria for selecting the target DPWM mode in step 3 and triggering mode switching in step 6.

[0012] Furthermore, the DPWM mode set preset in step 3 includes at least two discontinuous PWM modes with different clamping rules. The different clamping rules include: a phase clamping rule that clamps any one of the three phases, a sector clamping rule that selects the zero vector according to the voltage space vector sector, and a zero vector allocation rule that allocates the zero vector's action time.

[0013] Furthermore, the selection of the target DPWM mode in step 3 is related to the voltage space vector sector, and the clamping phase or clamping vector is determined according to the voltage space vector sector, so that the number of common mode voltage transitions or the transition amplitude are reduced when switching between adjacent sectors.

[0014] Furthermore, in step 3, the DPWM mode set is segmented and selected according to the modulation ratio m. Specifically, the modulation ratio m is divided into at least two intervals [0,m1] and [m1,1] or further divided into multiple intervals, and different DPWM modes are selected as target DPWM modes in different intervals to reduce the common-mode voltage evaluation index.

[0015] Furthermore, the zero-vector allocation rule in step 3 includes a zero-vector allocation ratio ρ, where 0 ≤ ρ ≤ 1, used to characterize the ratio of the two zero vectors' operating time within a switching cycle; the zero-vector allocation ratio ρ is updated based on the sector, modulation ratio m, and common-mode voltage evaluation index to reduce the common-mode voltage peak value V. cm,pkand root mean square value V cm,rms .

[0016] Furthermore, the switching triggering condition described in step 5 includes at least one of the following: (1) The common-mode voltage peak V cm,pk Greater than the target peak value V pk,tar , or the root mean square value of the common-mode voltage V cm,rms Greater than the target root mean square value V rms,tar ; (2) The modulation ratio m crosses the preset segment boundary; (3) The sector changes and the target DPWM mode determined according to the preset mode selection rule in step 3 is different from the current DPWM mode; (4) The evaluation function R exceeds the preset threshold R th .

[0017] Furthermore, in step 6, a minimum holding time T is set. hold After completing a DPWM mode switch, during the minimum hold time T hold Switching to DPWM mode again within a certain time period is prohibited to suppress jitter caused by frequent mode switching; The hysteresis condition is defined by setting a hysteresis band Δ, and the common-mode voltage evaluation index satisfies V. cm,pk >V pk,tar +Δ or V cm,rms >V rms,tar Switching is triggered when +Δ is applied, and the common-mode voltage evaluation index meets V. cm,pk <V pk,tar -Δ or V cm,rms <V rms,tar -Δ releases the switching condition, thereby reducing DPWM mode switching jitter and improving operational stability.

[0018] Compared with the prior art, the present invention has the following advantages: 1. This invention introduces an adaptive selection and switching mechanism for DPWM mode, so that common-mode voltage control no longer depends on a fixed modulation strategy. It can dynamically adjust the clamping and zero vector rules according to changes in operating conditions, thereby improving the stability of common-mode voltage suppression effect across the entire operating range.

[0019] 2. This invention uses the peak value and / or root mean square value of common mode voltage as evaluation indicators, and incorporates key operating variables such as sector and modulation ratio into the mode selection criteria, so that DPWM mode switching has clear triggering conditions and decision logic, which can achieve continuous suppression of common mode voltage and reduce common mode interference to ground.

[0020] 3. This invention introduces stability constraints such as minimum hold time and hysteresis during mode switching, reducing jitter and discontinuity caused by frequent modulation mode switching, ensuring the engineering feasibility and operational stability of the control process, and improving the reliability of the drive system.

[0021] Based on the implementation methods provided in the above aspects, this application can be further combined to provide more implementation methods. Attached Figure Description

[0022] The above and other objects, features, and advantages of exemplary embodiments of the present invention will become readily apparent upon reading the following detailed description with reference to the accompanying drawings. In the drawings, several embodiments of the invention are illustrated by way of example and not limitation, with the same or corresponding reference numerals denoteing the same or corresponding parts, wherein: Figure 1 A flowchart of a common-mode voltage suppression method for induction motors based on dynamic switching of DPWM mode provided by the present invention; Figure 2 This is a schematic diagram of the DPWM mode library and mode switching logic provided by the present invention; Figure 3 The three-phase voltage waveform diagram is shown when the DPWM clamping rule is adaptively switched according to the present invention. Detailed Implementation

[0023] The exemplary embodiments disclosed in this application will now be described in more detail with reference to the accompanying drawings. While exemplary embodiments of this application are shown in the drawings, it should be understood that this application can be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided to enable a more thorough understanding of this application and to fully convey the scope of this application to those skilled in the art. Unless otherwise specified, the technical means used in the embodiments are conventional means well known to those skilled in the art.

[0024] like Figure 1The diagram shows the overall flowchart of a common-mode voltage suppression method for induction motors based on dynamic switching of DPWM modes provided by this invention. This method, with operation control as its core, first acquires the operating conditions and drive boundary conditions of the induction motor (such as bus voltage, switching frequency, modulation ratio, and sector), and calculates common-mode voltage evaluation indicators (such as common-mode voltage peak / root mean square value or risk indicators). Then, based on the evaluation results, it selects a target DPWM mode from a preset DPWM mode set and outputs a PWM drive signal. During operation, the switching trigger conditions are determined in real time: if the common-mode voltage evaluation indicator does not exceed the threshold and the operating condition does not cross the preset range, the current DPWM mode continues to output drive; if the trigger conditions are met (such as evaluation indicator exceeding limits, sector changes, or operating condition changes), DPWM mode switching is executed and relevant parameters are updated to maintain the common-mode voltage indicator within the target range, thereby achieving adaptive suppression of common-mode voltage and improving operational stability. The specific implementation steps are as follows: Step 1: Obtain operating conditions and drive boundary conditions; Operating conditions include speed and torque commands, and drive boundary conditions include DC bus voltage V. dc Switching frequency f sw The controller obtains the voltage rise time dV / dt range, and simultaneously acquires the current voltage space vector sector and modulation ratio m. The controller determines the voltage space vector sector based on the phase angle of the reference voltage vector in the α-β coordinate system, and calculates the modulation ratio m based on the reference voltage vector amplitude and the reference voltage corresponding to the current DC bus voltage. The sector and m can also be directly read by the existing PWM modulation module as input parameters for subsequent evaluation and mode selection.

[0025] This step provides real-time data for DPWM mode selection and switching by acquiring the operating and boundary quantities available from the driver. Specifically, the speed and torque commands are obtained from the motor drive controller or the host controller; the DC bus voltage Vdc is acquired by a DC bus voltage sensor; the switching frequency fsw is obtained from the carrier frequency setting of the PWM controller; and the voltage rise time dV / dt can be calculated by high-speed sampling of the inverter output or motor terminal voltage, or its range can be determined based on the switching characteristics of the power devices and offline calibration results.

[0026] Step 2: Calculate the common-mode voltage evaluation index; The common-mode voltage evaluation index is calculated based on the operating conditions and drive boundary conditions. The common-mode voltage evaluation index is the peak common-mode voltage V. cm,pk , Common-mode voltage root mean square value V cm,rms And an evaluation function R used to characterize the common-mode voltage risk. Wherein, the peak common-mode voltage V... cm,pkThe root mean square value of the common-mode voltage (Vm) is used to characterize the maximum instantaneous electrical stress of the common-mode voltage during switching. cm,rms The evaluation function R is used to characterize the overall impact level of common-mode voltage over a certain evaluation period. It comprehensively reflects the influence of DC bus voltage, switching frequency, voltage rise time, and changes in operating conditions on common-mode voltage risk. By simultaneously using the above three types of indicators, the transient peak value, sustained impact level, and condition-related risks of common-mode voltage can be taken into account, avoiding the mode selection bias caused by using only a single common-mode voltage indicator, and improving the accuracy of DPWM mode selection and switching under different operating conditions.

[0027] The three evaluation indicators participate in the DPWM mode selection from three dimensions: transient amplitude, degree of sustained effect, and operating condition risk, respectively, so that the modulation mode switching is transformed from a single threshold judgment to a multi-indicator adaptive decision based on the actual common-mode voltage suppression requirements.

[0028] Common-mode voltage is defined as:

[0029] Where V a V b V c These are the three-phase terminal voltages relative to the ground voltage of the chassis grounding terminal; Simultaneously define common-mode voltage evaluation metrics:

[0030] in, Let be the instantaneous value of the common-mode voltage, and t be the time variable. To obtain the maximum value, T is the evaluation time length.

[0031] The evaluation function R is composed of the driving boundary conditions and the operating conditions, and satisfies:

[0032] The evaluation function R and the preset threshold R are used to evaluate the evaluation function R. th The comparison result serves as one of the criteria for selecting the target DPWM mode in step 3 and triggering mode switching in step 6.

[0033] Step 3: Select the target DPWM mode and determine the rule parameters; The target DPWM mode is selected from the preset DPWM mode set based on the common-mode voltage evaluation index, voltage space vector sector, and modulation ratio m.

[0034] Specifically, the operating range is first divided into low modulation ratio region, medium modulation ratio region and high modulation ratio region according to the modulation ratio m, and the available clamping phase or zero vector corresponding to each DPWM mode is determined according to the current sector. Then, candidate DPWM modes are determined according to the DPWM mode selection mapping table obtained in advance through simulation or experiment. The mapping table records the common mode voltage peak value, root mean square value and evaluation function R corresponding to each DPWM mode under different modulation ratio ranges and different sectors. The controller selects the mode that meets the common mode voltage target value and evaluation function threshold requirements from the candidate DPWM modes as the target DPWM mode.

[0035] The DPWM mode set preset in step 3 includes at least two discontinuous PWM modes with different clamping rules. The different clamping rules include: a phase clamping rule that clamps any one of the three phases, a sector clamping rule that selects the zero vector according to the voltage space vector sector, and a zero vector allocation rule that allocates the zero vector's action time.

[0036] In step 3, the DPWM mode set is segmented and selected according to the modulation ratio m. Specifically, the modulation ratio m is divided into at least two intervals [0,m1] and [m1,1] or further divided into multiple intervals, and different DPWM modes are selected as target DPWM modes in different intervals to reduce the common mode voltage evaluation index.

[0037] The zero-vector allocation rule in step 3 includes a zero-vector allocation ratio ρ, where 0 ≤ ρ ≤ 1, which characterizes the ratio of the two zero vectors' operating time within a switching cycle. The zero-vector allocation ratio ρ is updated based on the sector, modulation ratio m, and common-mode voltage evaluation index to reduce the common-mode voltage peak value V. cm,pk and root mean square value V cm,rms .

[0038] The selection of the target DPWM mode in step 3 is related to the voltage space vector sector, and the clamping phase or clamping vector is determined according to the voltage space vector sector, so as to reduce the number of common mode voltage transitions or the transition amplitude when switching between adjacent sectors.

[0039] Common-mode voltage evaluation metrics are used to further screen or refine candidate DPWM modes initially determined based on modulation ratio m and Sector. When V cm,pk V cm,rmsIf neither the evaluation function R nor the evaluation function R exceeds the corresponding target value or preset threshold, the current candidate DPWM mode is maintained; if at least one of the indicators exceeds the corresponding target value or preset threshold, the DPWM mode with the lower common-mode voltage evaluation indicator is reselected from the candidate DPWM modes corresponding to the current modulation ratio range and Sector, and the corresponding clamping rules and zero vector allocation ratio ρ are updated.

[0040] Step 4: Generate a PWM switching sequence and output the gate drive signal; A PWM switching sequence is generated based on the target DPWM mode, and an inverter gate drive signal is output, so that the inverter switches the switching state according to the clamping rule and the zero vector allocation rule, thereby constraining and suppressing the common-mode voltage jump process.

[0041] Step 5: Switch the trigger condition judgment; During operation, it continuously determines whether the switching triggering conditions are met. The switching triggering conditions include at least: the common-mode voltage evaluation index exceeds a preset threshold, the operating condition crosses a preset range, or the sector changes and the target DPWM mode determined according to the preset mode selection rule is different from the current DPWM mode. When any of the above triggering conditions occur, it indicates that the current DPWM mode may not be able to continue to meet the common-mode voltage suppression requirements under this operating condition, and a switching update process is required.

[0042] The switching triggering condition mentioned in step 5 includes at least one of the following: (1) The common-mode voltage peak V cm,pk Greater than the target peak value V cm,tar , or the root mean square value of the common-mode voltage V cm,rms Greater than the target root mean square value V cm,tar ; (2) The modulation ratio m crosses the preset segment boundary; (3) The sector changes and the target DPWM mode determined according to the preset mode selection rule in step 3 is different from the current DPWM mode; (4) The evaluation function R exceeds the preset threshold R th .

[0043] Step 6: Adaptive switching and hold; When the switching trigger condition is met, the target DPWM mode is updated and the process returns to step 4, subject to the constraints of minimum hold time and hysteresis condition. If the switching trigger condition is not met, the current DPWM mode is maintained, and the gate drive signal continues to be output to reduce the common-mode voltage. The minimum hold time limits the shortest time between two adjacent DPWM mode switches, preventing continuous mode switching within a short period. The hysteresis condition establishes a stable range between the mode trigger threshold and the release threshold, preventing repeated mode switching when the common-mode voltage evaluation index fluctuates near the threshold. By combining these two conditions, mode switching jitter, additional switching actions, and abrupt changes in the switching sequence can be reduced, improving control stability and inverter operational reliability.

[0044] In step 6, set the minimum holding time T. hold After completing a DPWM mode switch, during the minimum hold time T hold Switching to DPWM mode again within a certain time period is prohibited to suppress jitter caused by frequent mode switching; the hysteresis condition is to set a hysteresis band Δ, when the common-mode voltage evaluation index meets V cm,pk >V cm,tar +Δ or V cm,rms >V cm,tar Switching is triggered when +Δ is applied, and the common-mode voltage evaluation index meets V. cm,pk <V cm,tar -Δ or V cm,rms <V cm,tar -Δ releases the switching condition, thereby reducing DPWM mode switching jitter and improving operational stability.

[0045] like Figure 2 As shown, a DPWM mode library and adaptive switching logic for common-mode voltage suppression of induction motors were constructed: First, a DPWM mode library containing various clamping rules (such as DPWM_A, DPWM_B, and DPWM_C, where DPWM_A is the first-phase clamping mode, DPWM_B is the second-phase clamping mode, and DPWM_C is a mode based on sector selection of the zero vector; different modes correspond to different clamping phases, zero vector action sequences, and zero vector allocation ratios) was pre-set. During operation, input parameters were acquired, including the modulation ratio m, voltage space vector sector, and common-mode voltage evaluation index (V0). cm(and risk index R). Then, based on the "DPWM mode selection mapping table," the corresponding target DPWM mode is selected according to the segmented intervals of m (i.e., m < m1, m1 ≤ m < m2, m ≥ m2) and different sectors, thereby outputting the PWM drive signal. When m < m1, the DPWM mode corresponding to the low modulation ratio region is selected first; when m1 ≤ m < m2, the DPWM mode corresponding to the medium modulation ratio region is selected first; when m ≥ m2, the DPWM mode corresponding to the high modulation ratio region is selected first. Within each modulation ratio interval, the final target DPWM mode is further determined by combining the sector and common-mode voltage evaluation index. Based on this, a "switching and updating" mechanism is set: the zero vector allocation ratio ρ is updated using a lookup table or a piecewise function; different ρ values ​​are preset for different sectors and different modulation ratio intervals; when the common-mode voltage evaluation index increases, the preferred zero vector action ratio corresponding to the target DPWM mode is appropriately increased to reduce V. cm,pk and V cm,rms Simultaneously, hysteresis Δ and minimum hold time T are introduced. hold As a constraint, to avoid jitter caused by frequent mode switching, and to ensure that the common-mode voltage suppression effect is stably achieved under different operating conditions.

[0046] Example

[0047] To verify the effectiveness of the DPWM mode dynamic switching method of this invention, an experimental platform for induction motor frequency conversion drive was built. The experimental system included a DC power supply, a three-phase two-level inverter, an induction motor, a common-mode voltage acquisition device, and a digital controller. During the experiment, the DC bus voltage, switching frequency, motor load, and grounding conditions were kept constant. By changing the modulation ratio and the sector where the reference voltage vector was located, the controller was made to meet the DPWM mode switching conditions. The three-phase output voltage and the peak common-mode voltage V were recorded before and after the mode switching. cm,pk and root mean square value V cm,rms And compare the results with those in the fixed DPWM mode.

[0048] like Figure 3 As shown, the changes in the three-phase modulated output voltage waveform during the adaptive switching of the DPWM mode of this invention are illustrated. Before switching, the system uses clamping rule output PWM modulation, and the three-phase waveform exhibits corresponding clamping characteristics. When triggering conditions such as exceeding the common-mode voltage evaluation index or operating condition crossing zones are detected, the controller switches the DPWM mode to clamping rule B at the switching moment, causing the clamping phase and switching sequence of the three-phase voltage waveform to change accordingly. This switching process intuitively demonstrates the control mechanism of this invention that dynamically selects and updates the DPWM mode according to operating conditions, providing modulation waveform-level support for subsequent common-mode voltage suppression.

[0049] Under the same DC bus voltage, switching frequency, speed, and load conditions, the peak common-mode voltage V in the fixed DPWM mode is... cm,pk The common-mode voltage is 168V, and the root mean square value is V. cm,rms The voltage is 96V. After adopting the common-mode voltage suppression method based on dynamic switching of DPWM mode according to this invention, the controller adaptively selects the target DPWM mode based on the current modulation ratio, sector, and common-mode voltage evaluation index. The peak common-mode voltage V... cm,pk The voltage is reduced to 112V, a decrease of approximately 33.3% compared to the fixed DPWM mode. cm,rms The voltage was reduced to 69V, a decrease of approximately 28.1%. Simultaneously, the three-phase output voltage remained continuous during changes in operating conditions and mode switching, without any significant abnormal pulses. The results indicate that, compared to a fixed DPWM mode, this invention can dynamically select a DPWM mode with superior common-mode voltage suppression based on operating conditions, thereby reducing the peak and root-mean-square (RMS) values ​​of the common-mode voltage and improving the stability and adaptability of the common-mode voltage suppression effect under different operating conditions.

[0050] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A common-mode voltage suppression method for induction motors based on dynamic switching of DPWM mode, characterized in that, The method includes the following steps: Step 1: Obtain the operating conditions and drive boundary conditions of the induction motor. The operating conditions include speed command and torque command, and the drive boundary conditions include the DC bus voltage V. dc Switching frequency f sw And the voltage rise time dV / dt range, while obtaining the current voltage space vector sector and modulation ratio m; Step 2: Calculate the common-mode voltage evaluation index based on the operating conditions and drive boundary conditions; Step 3: In the preset DPWM mode set, select the target DPWM mode according to the common mode voltage evaluation index, modulation ratio m and sector, and determine the clamp vector selection rule and zero vector allocation rule corresponding to the target DPWM mode. Step 4: Generate a PWM switching sequence based on the target DPWM mode and output the inverter gate drive signal to suppress common-mode voltage; Step 5: During operation, continuously determine whether the switching triggering conditions are met. The switching triggering conditions include at least: the common mode voltage evaluation index exceeds a preset threshold, the modulation ratio m crosses a preset segment boundary, or the sector changes and the target DPWM mode determined according to the preset mode selection rule in Step 3 is different from the current DPWM mode. Step 6: When the switching trigger condition is met, update the target DPWM mode and return to step 4 under the constraints of minimum hold time and hysteresis condition; when the switching trigger condition is not met, maintain the current DPWM mode and continue to output the gate drive signal so that the common mode voltage evaluation index does not exceed the preset threshold.

2. The common-mode voltage suppression method for induction motors based on dynamic switching of DPWM mode according to claim 1, characterized in that, The common-mode voltage evaluation index mentioned in step 2 is the peak common-mode voltage V of the motor's three-phase terminal voltage relative to the ground terminal of the motor casing. cm,pk , Common-mode voltage root mean square value V cm,rms The evaluation function R for common-mode voltage risk; The common-mode voltage is defined as: Among them, V a V b V c These are the voltages of phases A, B, and C relative to the grounding terminal of the chassis, respectively. The common-mode voltage peak V cm,pk , Common-mode voltage root mean square value V cm,rms The calculation formula is: in, Let be the instantaneous value of the common-mode voltage, and t be the time variable. To obtain the maximum value, T is the evaluation time length, which can be one or more electrical cycles; The evaluation function R is composed of the driving boundary conditions and the operating conditions, and satisfies: The evaluation function R and the preset threshold R are used to evaluate the evaluation function R. th The comparison result serves as one of the criteria for selecting the target DPWM mode in step 3 and triggering mode switching in step 6.

3. The common-mode voltage suppression method for induction motors based on dynamic switching of DPWM mode according to claim 1, characterized in that, The DPWM mode set preset in step 3 includes at least two discontinuous PWM modes with different clamping rules. The different clamping rules include: a phase clamping rule that clamps any one of the three phases, a sector clamping rule that selects the zero vector according to the voltage space vector sector, and a zero vector allocation rule that allocates the zero vector's action time.

4. The common-mode voltage suppression method for induction motors based on dynamic switching of DPWM mode according to claim 1, characterized in that, The selection of the target DPWM mode in step 3 is related to the voltage space vector sector, and the clamping phase or clamping vector is determined according to the voltage space vector sector, so as to reduce the number of common mode voltage transitions or the transition amplitude when switching between adjacent sectors.

5. The common-mode voltage suppression method for induction motors based on dynamic switching of DPWM mode according to claim 1, characterized in that, In step 3, the DPWM mode set is segmented and selected according to the modulation ratio m. Specifically, the modulation ratio m is divided into at least two intervals [0,m1] and [m1,1] or further divided into multiple intervals, and different DPWM modes are selected as target DPWM modes in different intervals to reduce the common mode voltage evaluation index.

6. The common-mode voltage suppression method for induction motors based on dynamic switching of DPWM mode according to claim 1, characterized in that, The zero vector allocation rule in step 3 includes a zero vector allocation ratio ρ, where 0 ≤ ρ ≤ 1, which is used to characterize the ratio of the action time of the two zero vectors within a switching cycle; The zero-vector allocation ratio ρ is updated based on the sector, modulation ratio m, and common-mode voltage evaluation index to reduce the common-mode voltage peak value V. cm,pk and root mean square value V cm,rms .

7. The common-mode voltage suppression method for induction motors based on dynamic switching of DPWM mode according to claim 1, characterized in that, The switching triggering condition mentioned in step 5 includes at least one of the following: (1) The common-mode voltage peak V cm,pk Greater than the target peak value V pk,tar , or the root mean square value of the common-mode voltage V cm,rms Greater than the target root mean square value V rms,tar ; (2) The modulation ratio m crosses the preset segment boundary; (3) The sector changes and the target DPWM mode determined according to the preset mode selection rule in step 3 is different from the current DPWM mode; (4) The evaluation function R exceeds the preset threshold R th .

8. The common-mode voltage suppression method for induction motors based on dynamic switching of DPWM mode according to claim 1, characterized in that, In step 6, set the minimum holding time T. hold After completing a DPWM mode switch, during the minimum hold time T hold Switching to DPWM mode again within a certain time period is prohibited to suppress jitter caused by frequent mode switching; The hysteresis condition is defined by setting a hysteresis band Δ, and the common-mode voltage evaluation index satisfies V. cm,pk >V pk,tar +Δ or V cm,rms >V rms,tar Switching is triggered when +Δ is applied, and the common-mode voltage evaluation index meets V. cm,pk <V pk,tar -Δ or V cm,rms <V rms,tar -Δ releases the switching condition, thereby reducing DPWM mode switching jitter and improving operational stability.

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