Low common-mode PWM modulation method for variable frequency drive

Abstract

This invention discloses a low common-mode PWM modulation method for a variable frequency drive device. Based on a control system consisting of a basic carrier initialization setting stage, a switching frequency adaptive stage, a carrier phase shift calculation stage, a pulse optimization calculation stage, and a modulation stage, the method uses an impedance analyzer to test the common-mode impedance to ground of the variable frequency drive device, plots a two-dimensional impedance table, obtains the switching frequency corresponding to the maximum impedance within the switching frequency range under this operating condition, calculates the sector of the output voltage, determines the carrier number used by each bridge arm, compares the upper or lower bias of the register values, and achieves output common-mode control of the full-bridge converter through pulse width PWM modulation. This invention can balance the contradiction between common-mode voltage suppression and control performance, vibration and noise indicators.

Description

Technical Field

[0001] This invention belongs to the field of power electronics technology, and specifically relates to a low common-mode PWM modulation method for a frequency converter drive device. Background Technology

[0002] With the continuous improvement of manufacturing processes and design levels of third-generation semiconductor materials, new power devices such as high-power-density silicon carbide (SiC) and gallium nitride (GaN) have been widely used in fields with stringent requirements for efficiency and harmonic characteristics due to their outstanding advantages of low conduction loss and strong adaptability.

[0003] Parasitic distributed capacitance inevitably exists between the power module and the motor windings, frame, and core. As the switching frequency increases, these parasitic parameters exhibit lower impedance characteristics, directly causing a series of engineering problems such as increased leakage current and decreased system efficiency.

[0004] To mitigate the high-frequency impedance reduction problem caused by third-generation semiconductors, numerous researchers have proposed a series of low common-mode PWM modulation strategies, utilizing degrees of freedom such as instantaneous pulses, while maintaining a constant fundamental output. However, existing low common-mode PWM modulation methods have the following drawbacks.

[0005] 1. The research was conducted by reducing the amplitude of the common-mode interference source voltage, without considering the suppression of common-mode current from the coupling path.

[0006] 2. Using three phases as the smallest unit, carrier phase shifting is achieved through PWM modulation between the three phases, without considering the abnormal output pulse phenomenon caused by online carrier switching. Summary of the Invention

[0007] The purpose of this invention is to address the above problems by proposing a low common-mode PWM modulation method for a frequency converter drive device.

[0008] To achieve the above objectives, the technical solution adopted by this invention to solve its technical problem is: a low common-mode PWM modulation method for a frequency converter drive device, used in a full-bridge converter, based on a control system composed of a basic carrier initialization setting stage, a switching frequency adaptive stage, a carrier phase shift calculation stage, a pulse optimization calculation stage, and a modulation action stage, the steps of which are as follows: Step 1: In the basic carrier initialization setting stage, select the lower limit ƒ of the switching frequency based on the control performance and loss requirements of the frequency converter under rated operating conditions. min Within the switching frequency range, the common-mode impedance to ground of the frequency converter drive device is tested using an impedance analyzer to obtain the impedance value to ground at each switching frequency ƒ. z Then, a two-dimensional table of ground impedance was drawn. F (ƒ, z ); Step 2: In the switching frequency adaptive stage, based on the actual characteristics of the variable frequency drive device, the selectable switching frequency range for the current operating condition is obtained [ƒ]. min ,ƒ max [By consulting the table of ground impedance] F (ƒ, z This allows us to obtain the switching frequency ƒ corresponding to the maximum impedance within the switching frequency range under this operating condition. n ; Step 3: In the carrier phase shift calculation stage, the given value of the output voltage in the stationary two-phase coordinate system is first obtained based on control strategies such as vector control and direct torque control. u α and u β Then, based on the given value of the output voltage in the stationary two-phase coordinate system, calculate the sector of the output voltage. M Finally, the carrier numbering used by each bridge arm of the converter was determined. S n ; Step 4, in the pulse optimization calculation stage, based on the current switching frequency ƒ n and output voltage setpoint u α , u β And according to the current carrier number S n and the previous period carrier number S n-1 The upper or lower bias of the comparison register value is processed. Step 5: The modulation stage achieves common-mode control of the full-bridge converter output through pulse width modulation (PWM).

[0009] Furthermore, in step S2, if there are multiple switching frequencies ƒ n For the same impedance value, the maximum switching frequency ƒ is selected in low vibration and noise mode. max In other modes, select the minimum switching frequency ƒ min .

[0010] Furthermore, in step 3, for multiphase motors, the aforementioned steps are repeated according to a specific rule (the three phases are in opposite phases).

[0011] Furthermore, in step 4, the current switching frequency ƒ is first determined... n and output voltage setpoint u α , u β Calculate the values ​​of each phase comparison register, and then base them on the current carrier number. S n and the previous period carrier numberS n-1 Determine whether S n-1 =0, S n =1, then the comparison register values ​​are all shifted up until the original maximum value is reached. T pr End; otherwise, further judgment is needed. S n-1 =1, S n =0, otherwise end; if yes, the comparison register values ​​are all shifted down until the original maximum value reaches 0 and ends.

[0012] Furthermore, the full-bridge converter employs silicon carbide and / or gallium nitride power semiconductor devices.

[0013] This invention patent has the following characteristics: This invention utilizes phase shifting of the interference source carrier to suppress common-mode interference voltage sources, and maximizes common-mode impedance through self-optimization of the switching frequency, thereby achieving online adjustment of low common-mode PWM.

[0014] This invention can balance the contradictions between common-mode voltage suppression, control performance, and vibration and noise performance, further expands control ideas, and is easy to implement.

[0015] This invention can be applied to high-quality frequency conversion drive devices designed with third-generation high-frequency power semiconductor devices such as silicon carbide and gallium nitride, to meet the stringent electromagnetic compatibility requirements of scenarios such as emergency UPS power supplies and electric propulsion. Attached Figure Description

[0016] Figure 1 This is a block diagram of the system composition of the present invention.

[0017] The labels for each figure are as follows: 1—basic carrier initialization setting stage, 2—switching frequency adaptive stage, 3—carrier phase shift calculation stage, 4—pulse optimization calculation stage, 5—modulation stage. Detailed Implementation

[0018] The present invention will now be described in further detail with reference to the accompanying drawings.

[0019] Reference Figure 1 As shown, the present invention discloses a low common-mode PWM modulation method for a frequency converter drive device, used in a full-bridge converter, i.e., a power module with a full-bridge topology, wherein the power module adopts silicon carbide and / or gallium nitride power semiconductor devices; and a control system based on the sequential connection of a basic carrier initialization setting stage 1, a switching frequency adaptive stage 2, a carrier phase shift calculation stage 3, a pulse optimization calculation stage 4, and a modulation action stage 5, the steps of which are as follows.

[0020] Step 1, in the basic carrier initialization setting stage 1, select the lower limit ƒ of the switching frequency based on the control performance, loss, and other requirements of the frequency converter under rated operating conditions. min Within the switching frequency range, the common-mode impedance to ground of the frequency converter drive device is tested using an impedance analyzer to obtain the impedance value to ground at each switching frequency ƒ. z Then, a two-dimensional table of ground impedance was drawn. F (ƒ, z ).

[0021] Step 2, in the switching frequency adaptive stage 2, first combine the actual characteristics of the variable frequency drive device to obtain the switching frequency range that can be selected under the current operating conditions [ƒ]. min ,ƒ max Then, by consulting the table of impedance to ground... F (ƒ, z This allows us to obtain the switching frequency ƒ corresponding to the maximum impedance within the switching frequency range under this operating condition. n .

[0022] If there are multiple switching frequencies ƒ n For the same impedance value, the maximum switching frequency ƒ is selected in low vibration and noise mode. max In other modes, select the minimum switching frequency ƒ min .

[0023] Step 3, in the carrier phase shift calculation stage 3, firstly, based on control strategies such as vector control and direct torque control, obtain the given value of the output voltage in the stationary two-phase coordinate system. u α and u β Then, based on the given value of the output voltage in the stationary two-phase coordinate system, calculate the sector of the output voltage. M Finally, based on the sector of the output voltage M Determine the carrier number used by each bridge arm of the converter. S n .

[0024] For multiphase motors, repeat the above steps according to a specific rule (reversed phases among the three phases).

[0025] Step 4, in the pulse optimization calculation stage 4, based on the current switching frequency ƒ n and output voltage setpoint u α , u β And according to the current carrier number S n and the previous period carrier number S n-1 The upper or lower bias of the comparison register value is processed. In this step, the current switching frequency ƒ is first determined. n and output voltage setpoint u α , u β Calculate the values ​​of each phase comparison register, and then base them on the current carrier number. S n and the previous period carrier number S n-1 Judgment: Whether S n-1 =0, S n =1, then the comparison register values ​​are all shifted up until the original maximum value is reached. T pr End. Otherwise, further judgment is needed. S n-1 =1, S n =0, otherwise end; if yes, the comparison register values ​​are all shifted down until the original maximum value reaches 0 and ends.

[0026] Step 5: Implement common-mode control of the full-bridge converter output through pulse width modulation (PWM).

[0027] The above embodiments are merely illustrative of the principles and effects of the present invention, as well as some of the application examples. For those skilled in the art, various modifications and improvements can be made without departing from the inventive concept of the present invention, and these all fall within the protection scope of the present invention.

Claims

1. A low common-mode PWM modulation method for a frequency converter drive device, characterized in that: For a full-bridge converter, a control system consisting of a basic carrier initialization setting stage (1), a switching frequency adaptive stage (2), a carrier phase shift calculation stage (3), a pulse optimization calculation stage (4), and a modulation stage (5) is used. The steps are as follows: Step 1: Select the lower limit ƒ of the switching frequency based on the control performance and loss requirements of the variable frequency drive under rated operating conditions. min An impedance analyzer was used to test the common-mode impedance to ground of the frequency converter drive unit to obtain the impedance value to ground for each switching frequency ƒ. z Then, a two-dimensional table of ground impedance was drawn. F (ƒ, z ); Step 2: Based on the actual characteristics of the variable frequency drive device, obtain the range of switching frequencies that can be selected under the current operating conditions [ƒ]. min ,ƒ max The switching frequency ƒ corresponding to the maximum impedance within the switching frequency range under this operating condition can be obtained by consulting the impedance-to-ground table. n ; Step 3: First, obtain the output voltage setpoint in the stationary two-phase coordinate system based on vector control or direct torque control. u α and u β Then calculate the sector of the output voltage. M Finally, the carrier numbering used by each bridge arm of the converter was determined. S n ; Step 4, based on the current switching frequency ƒ n and output voltage setpoint u α , u β And according to the current carrier number S n and the previous period carrier number S n-1 The upper or lower bias of the comparison register value is processed. Step 5: Implement common-mode control of the full-bridge converter output through pulse width modulation (PWM).

2. The low common-mode PWM modulation method for a frequency converter drive device according to claim 1, characterized in that, In step S2, if there are multiple switching frequencies ƒ n For the same impedance value, the switching frequency ƒ is selected in low vibration and noise mode. max In other modes, select the switching frequency ƒ min .

3. The low common-mode PWM modulation method for a frequency converter drive device according to claim 2, characterized in that, In step 3, for multiphase motors, the process is repeated according to the rule of reverse phases between the three phases.

4. The low common-mode PWM modulation method for a frequency converter drive device according to claim 3, characterized in that, In step 4, first, based on the current switching frequency ƒ n and output voltage setpoint u α , u β Calculate the values ​​of each phase comparison register, and then base them on the current carrier number. S n and the previous period carrier number S n-1 Determine whether S n-1 =0, S n =1, then the comparison register values ​​are all shifted up until the original maximum value is reached. T pr End; otherwise, further judgment is needed. S n-1 =1, S n =0, otherwise end; if yes, the comparison register values ​​are all shifted down until the original maximum value reaches 0 and ends.

5. A low common-mode PWM modulation method for a frequency converter drive device according to claim 1, 2, 3, or 4, characterized in that, The full-bridge converter uses silicon carbide and / or gallium nitride power semiconductor devices.

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