A modulation method for suppressing common-mode voltage high-frequency harmonics

Abstract

The application discloses a modulation method for suppressing common-mode voltage high-frequency harmonics. The method re-synthesizes a virtual voltage vector, adopts a virtual voltage vector to synthesize a reference vector, and adopts effective vectors with opposite phases to synthesize a zero vector, so that common-mode voltage waveforms between carrier periods are completely identical and positive and negative polarity acting time is equally divided. According to the characteristics of the common-mode voltage waveform, the modulation strategy can completely eliminate harmonics at even multiple carrier frequencies and sideband harmonics near each carrier frequency while reducing the common-mode voltage amplitude, and effectively reduces the adverse effects caused by the common-mode voltage amplitude and high-frequency harmonics. The modulation method greatly reduces the content of common-mode voltage high-frequency harmonics, reduces harmonic loss and the adverse effects of the common-mode voltage on a motor system, and has high research value and application value.

Description

Technical Field

[0001] This invention relates to a method for suppressing high-frequency harmonics in the common-mode voltage of a three-phase two-level inverter system. Background Technology

[0002] Three-phase voltage source inverter motor drive systems typically employ PWM technology. Voltage imbalance at the output terminals can lead to the generation of common-mode voltage. High-frequency, high-amplitude common-mode voltage acting on the common-mode circuit formed by stray capacitance to ground in the motor generates common-mode current, inducing common-mode electromagnetic interference. The resulting bearing current can damage the motor bearings, reducing their lifespan and decreasing the reliability of motor operation. The leakage current can also cause malfunctions in the system's grounding current relay protection devices, leading to serious consequences for the system.

[0003] Existing common-mode voltage suppression strategies for traditional inverters driving three-phase motors primarily avoid using zero vectors during the synthesis of the reference vector, effectively reducing the amplitude of the common-mode voltage. However, this approach is ineffective in suppressing the high-frequency components of the common-mode voltage, resulting in a still relatively large common-mode current amplitude. Current algorithms for suppressing high-frequency harmonics in common-mode voltage for three-phase two-level inverter systems mainly employ spread spectrum techniques to suppress high-frequency harmonic peak values. To further reduce the adverse effects of common-mode voltage on the system (especially the motor system), it is necessary to research common-mode voltage high-frequency harmonic suppression strategies that suppress both the amplitude and high-frequency harmonics. Summary of the Invention

[0004] The purpose of this invention is to provide a modulation method for suppressing high-frequency harmonics in common-mode voltage. This method involves resynthesizing a virtual voltage vector, using the virtual voltage vector to synthesize a reference vector, and synthesizing a zero vector using effective vectors with opposite phases. This ensures that the common-mode voltage waveform is identical between carrier cycles and that the positive and negative polarity durations are evenly distributed. Based on the characteristics of this common-mode voltage waveform, this modulation strategy can completely eliminate harmonics at even-numbered multiples of the carrier frequency and sideband harmonics near each carrier frequency while reducing the common-mode voltage amplitude, effectively reducing the adverse effects caused by the common-mode voltage amplitude and high-frequency harmonics.

[0005] The objective of this invention is achieved through the following technical solution:

[0006] A modulation method for suppressing high-frequency harmonics of common-mode voltage, wherein the method synthesizes a virtual voltage vector using an effective voltage vector and changes the order of the vectors according to the volt-second balance principle, the specific steps of which are as follows:

[0007] Step 1: Based on the six effective voltage vectors of the space vector modulation strategy V 1~ V 6. Combine two adjacent effective voltage vectors into a single virtual voltage vector to obtain the virtual voltage vector. V12 , V 23 , V 34 , V 45 , V 56 , V 61 Where: virtual voltage vector V 12 From the effective voltage vector V 1 and V 2. Synthesis; Virtual Voltage Vector V 23 From the effective voltage vector V 2 and V 3. Synthesis; Virtual Voltage Vector V 34 From the effective voltage vector V 3 and V 4. Synthesis; Virtual Voltage Vector V 45 From the effective voltage vector V 4 and V 5. Synthesis; Virtual Voltage Vector V 56 From the effective voltage vector V 5 and V 6. Synthesis; Virtual Voltage Vector V 61 From the effective voltage vector V 6 and V 1. Synthesis;

[0008] Step 2: Based on the virtual voltage vector obtained in Step 1 V 12 , V 23 , V 34 , V 45 , V 56 , V 61 Redefining the six sectors: Virtual Vector V 12 and V 23 The area between these two points is the first sector, a virtual vector. V 23 and V 34 The area between these two sectors is the second sector, and the virtual vector is... V 34 and V 45 The area between these two sectors is the third sector, and the virtual vector is... V45 and V 56 The area between these two sectors is the fourth sector, and the virtual vector is... V 56 and V 61 The area between these two sectors is the fifth sector, a virtual vector. V 61 and V 12 The area between these two sectors is the sixth sector.

[0009] Step 3: Use the two virtual voltage vectors synthesized in Step 1 as the reference vector for synthesizing new effective voltage vectors. Use effective voltage vectors with opposite phases to synthesize a zero vector. At the same time, avoid the upper or lower bridge arm of the three phases of the inverter being turned on at the same time to suppress the common-mode voltage amplitude.

[0010] Step 4: The six effective voltage vectors correspond to the two polarities of the common-mode voltage. According to the volt-second balance principle, the order of the selected effective voltage vectors is changed so that the common-mode voltage polarity changes only twice within each carrier cycle, and the duration of the positive common-mode voltage is the same as that of the negative common-mode voltage, both being half the carrier cycle. Simultaneously, the common-mode voltage waveform is identical between each carrier cycle within a fundamental cycle. Specifically, when the reference voltage vector is located within each of the six sectors, the selection of the effective voltage vectors and their specific order of action are as follows:

[0011] Vector selection within the first sector: V 1 and V 4. Synthesize a zero voltage vector. V 12 and V 23 The synthesized reference voltage vector is applied in the following order: V 1→ V 3→ V 4→ V 2→ V 4→ V 3→ V 1.

[0012] Vector selection within the second sector: V 2 and V 5. Synthesize a zero voltage vector. V 23 and V 34 The synthesized reference voltage vector is applied in the following order: V 3→ V 5→ V 4→ V 2→ V 4→ V 5→ V 3.

[0013] Vector selection within the third sector: V 3 and V 6. Synthesize a zero voltage vector. V 34 and V 45 The synthesized reference voltage vector is applied in the following order: V 3→ V 5→ V 6→ V 4→ V 6→ V 5→ V 3.

[0014] Vector selection within the fourth sector: V 1 and V 4. Synthesize a zero voltage vector. V 45 and V 56 The synthesized reference voltage vector is applied in the following order: V 5→ V 1→ V 6→ V 4→ V 6→ V 1→ V 5.

[0015] Vector selection within the fifth sector: V 2 and V 5. Synthesize a zero voltage vector. V 56 and V 61 The synthesized reference voltage vector is applied in the following order: V 5→ V 1→ V 2→ V 6→ V 2→ V 1→ V 5.

[0016] Vector selection within sector 6: V 3 and V 6. Synthesize a zero voltage vector. V 61 and V 12 The synthesized reference voltage vector is applied in the following order: V 1→ V 3→ V 2→ V 6→ V 2→ V 3→ V 1.

[0017] Compared with the prior art, the present invention has the following advantages:

[0018] 1. This invention utilizes virtual voltage vectors, synthesizes zero voltage vectors from effective voltage vectors, and changes the order of effective voltage vectors within a carrier period to suppress common-mode voltage amplitude and eliminate harmonics at even multiples of the carrier frequency and sideband harmonics near integer multiples of each carrier frequency.

[0019] 2. The modulation method of the present invention can effectively eliminate even-numbered carrier frequency harmonics and sideband harmonics near each carrier frequency while suppressing the common-mode voltage amplitude. It significantly reduces the high-frequency harmonic content of the common-mode voltage, reduces harmonic losses and the adverse effects of the common-mode voltage on the motor system, and has high research and application value. Attached Figure Description

[0020] Figure 1 This is a schematic diagram illustrating the sector definition and reference vector synthesis of the modulation strategy of the present invention;

[0021] Figure 2 The modulation strategy proposed in this invention is shown in the PWM waveform and theoretical common-mode voltage waveform in each newly defined sector.

[0022] Figure 3 The common-mode voltage waveform within the carrier period using the modulation strategy of this invention;

[0023] Figure 4 The high-frequency harmonic spectrum of the motor common-mode voltage after adopting the effective zero-state PWM1 (AZSPWM1) modulation strategy;

[0024] Figure 5 The high-frequency harmonic spectrum of the common-mode voltage of the motor using the modulation strategy of this invention. Detailed Implementation

[0025] The technical solution of the present invention will be further described below with reference to the accompanying drawings, but it is not limited thereto. Any modifications or equivalent substitutions to the technical solution of the present invention that do not depart from the spirit and scope of the technical solution of the present invention should be covered within the protection scope of the present invention.

[0026] like Figure 1 As shown, the six dashed arrows represent a virtual voltage vector synthesized from six effective voltage vectors. V 12 From the effective voltage vector V 1 and V 2. Synthesis; Virtual Voltage Vector V 23 From the effective voltage vector V 2 and V 3. Synthesis; Virtual Voltage Vector V34 From the effective voltage vector V 3 and V 4. Synthesis; Virtual Voltage Vector V 45 From the effective voltage vector V 4 and V 5. Synthesis; Virtual Voltage Vector V 56 From the effective voltage vector V 5 and V 6. Synthesis; Virtual Voltage Vector V 61 From the effective voltage vector V 6 and V 1. Composition. The regular hexagon shown by the dashed lines is composed of 6 virtual voltage vectors. The sector is redefined based on the regular hexagon formed by the dashed lines, where the virtual voltage vectors... V 12 and V 23 The area between these points is the first sector; virtual voltage vector. V 23 and V 34 The area between these two points is the second sector; virtual voltage vector. V 34 and V 45 The area between these two points represents the third sector; virtual voltage vector. V 45 and V 56 The area between these two points is the fourth sector; virtual voltage vector. V 56 and V 61 The area between these two points represents the fifth sector; virtual voltage vector. V 61 and V 12 The area between these two points is the sixth sector.

[0027] Taking the reference voltage vector in the sixth sector as an example, the virtual voltage vector selection during its synthesis process... V 12 and V 61 Zero voltage vector selection of effective voltage vector V 3 and V 6. Synthesis. The calculation of the virtual voltage vector and the effective voltage vector's duration for synthesizing the zero voltage vector is similar to the AZSPWM1 modulation strategy. Among the selected effective voltage vectors, the one used for synthesizing the zero voltage vector... V 3. V 6 vectors, composition V 12 of V1. V 2 vectors, composition V 61 of V 6. V The duration of action of each vector is equal. According to the formula for calculating common-mode voltage, V 1. V A 3-vector will generate a negative common-mode voltage. V 2. V Six vectors will generate a positive common-mode voltage. Therefore, the duration of the positive common-mode voltage within a carrier cycle is equal to the duration of the negative common-mode voltage, both being half the carrier cycle. According to the volt-second balance principle, changing the vector order without changing the duration of the vectors does not affect the final result. In the first half of the carrier cycle, the effective vectors generating the negative common-mode voltage are grouped together, and the effective vectors generating the positive common-mode voltage are grouped together. The second half of the carrier cycle is symmetrical to the first half. By minimizing the number of switching operations, the effective voltage vector order within a carrier cycle is set to... V 1→ V 3→ V 2→ V 6→ V 2→ V 3→ V 1. The common-mode voltage waveform changes as follows within a carrier cycle: first, it is negative for one-quarter of the carrier cycle; then, it is positive for one-half of the carrier cycle; and finally, it is negative again for one-quarter of the carrier cycle. The common-mode voltage waveform is exactly the same within each carrier cycle of this sector.

[0028] Similarly, when the reference voltage vector is located in the sixth sector, the selection of the effective voltage vector and its specific order of action when the reference voltage vector is located in each of the six sectors are as follows:

[0029] Selection of effective voltage vector within the first sector: V 1 and V 4. Synthesize a zero voltage vector. V 12 and V 23 The synthesized reference voltage vector operates in the following order: V 1→ V 3→ V 4→ V 2→ V 4→ V 3→ V 1.

[0030] Selection of effective voltage vector within the second sector: V 2 and V 5. Synthesize a zero voltage vector. V23 and V 34 The synthesized reference voltage vector operates in the following order: V 3→ V 5→ V 4→ V 2→ V 4→ V 5→ V 3.

[0031] Selection of effective voltage vector within the third sector: V 3 and V 6. Synthesize a zero voltage vector. V 34 and V 45 The synthesized reference voltage vector operates in the following order: V 3→ V 5→ V 6→ V 4→ V 6→ V 5→ V 3.

[0032] Effective voltage vector selection in the fourth sector: V 1 and V 4. Synthesize a zero voltage vector. V 45 and V 56 The synthesized reference voltage vector operates in the following order: V 5→ V 1→ V 6→ V 4→ V 6→ V 1→ V 5.

[0033] Effective voltage vector selection within sector 5: V 2 and V 5. Synthesize a zero voltage vector. V 56 and V 61 The synthesized reference voltage vector operates in the following order: V 5→ V 1→ V 2→ V 6→ V 2→ V 1→ V 5.

[0034] Effective voltage vector selection in sector 6: V 3 and V 6. Synthesize a zero voltage vector. V61 and V 12 The synthesized reference voltage vector operates in the following order: V 1→ V 3→ V 2→ V 6→ V 2→ V 3→ V 1.

[0035] Theoretically, the PWM waveform and common-mode voltage waveform within each sector are as follows: Figure 2 As shown. By Figure 2 It can be seen that the amplitude of the common-mode voltage is suppressed, and the waveform of the common-mode voltage is exactly the same in each carrier cycle of a fundamental period and is even-symmetric about the midpoint of the carrier cycle. Fourier analysis shows that it can completely eliminate harmonics at even multiples of the carrier frequency and does not contain sideband harmonic components.

[0036] When the carrier frequency is set to 10 kHz, the common-mode voltage waveform generated by the motor using the modulation strategy of this invention is as follows: Figure 3 As shown. By Figure 3 It can be seen that the duration of both the positive and negative common-mode voltages is 50 μs within each carrier cycle, proving that this strategy can be implemented. The high-frequency spectrum of the motor common-mode voltage using the AZSPWM1 modulation strategy is as follows: Figure 4 As shown, the high-frequency spectrum of the motor common-mode voltage using the modulation strategy of this invention is as follows: Figure 5 As shown in the figure, the harmonics at even-number multiples of the carrier frequency and the sideband harmonics near integer multiples of the carrier frequency are eliminated. The modulation strategy of the present invention can effectively eliminate harmonics at even-number multiples of the carrier frequency and the sideband harmonics near integer multiples of the carrier frequency while suppressing the common-mode voltage amplitude, and can further reduce the damage caused by common-mode voltage to the motor system.

Claims

1. A modulation method for suppressing high-frequency harmonics of common-mode voltage, characterized in that... The method includes the following steps: Step 1: Based on the six effective voltage vectors of the space vector modulation strategy V 1~ V 6. Combine two adjacent effective voltage vectors into a single virtual voltage vector to obtain the virtual voltage vector. V 12 , V 23 , V 34 , V 45 , V 56 , V 61 Where: virtual voltage vector V 12 From the effective voltage vector V 1 and V 2. Synthesis; Virtual Voltage Vector V 23 From the effective voltage vector V 2 and V 3. Synthesis; Virtual Voltage Vector V 34 From the effective voltage vector V 3 and V 4. Synthesis; Virtual Voltage Vector V 45 From the effective voltage vector V 4 and V 5. Synthesis; Virtual Voltage Vector V 56 From the effective voltage vector V 5 and V 6. Synthesis; Virtual Voltage Vector V 61 From the effective voltage vector V 6 and V 1. Synthesis; Step 2: Based on the virtual voltage vector obtained in Step 1 V 12 , V 23 , V 34 , V 45 , V 56 , V 61 Redefining the six sectors: virtual vector V 12 and V 23 The area between these two points is the first sector, a virtual vector. V 23 and V 34 The area between these two sectors is the second sector, and the virtual vector is... V 34 and V 45 The area between these two sectors is the third sector, and the virtual vector is... V 45 and V 56 The area between these two sectors is the fourth sector, and the virtual vector is... V 56 and V 61 The area between these two sectors is the fifth sector, a virtual vector. V 61 and V 12 The area between these two sectors is the sixth sector. Step 3: Use the two virtual voltage vectors synthesized in Step 1 as new effective voltage vectors to synthesize a reference voltage vector. Use effective voltage vectors with opposite phases to synthesize a zero vector. At the same time, avoid the upper or lower bridge arm of the three phases of the inverter from being turned on at the same time to suppress the common-mode voltage amplitude. Step 4: The six effective voltage vectors correspond to the two polarities of the common-mode voltage. According to the volt-second balance principle, the order of the selected effective voltage vectors is changed so that the polarity of the common-mode voltage changes only twice in each carrier cycle and the duration of the positive common-mode voltage is the same as that of the negative common-mode voltage, which is half of the carrier cycle. At the same time, the common-mode voltage waveform is exactly the same between each carrier cycle in a fundamental cycle. When the reference voltage vector is located in each of the six sectors, the selection and order of action of the effective voltage vector are as follows: Selection of effective voltage vector within the first sector: V 1 and V 4. Synthesize a zero voltage vector. V 12 and V 23 The synthesized reference voltage vector operates in the following order: V 1→ V 3→ V 4→ V 2→ V 4→ V 3→ V 1; Selection of effective voltage vector within the second sector: V 2 and V 5. Synthesize a zero voltage vector. V 23 and V 34 The synthesized reference voltage vector operates in the following order: V 3→ V 5→ V 4→ V 2→ V 4→ V 5→ V 3; Selection of effective voltage vector within the third sector: V 3 and V 6. Synthesize a zero voltage vector. V 34 and V 45 The synthesized reference voltage vector operates in the following order: V 3→ V 5→ V 6→ V 4→ V 6→ V 5→ V 3; Effective voltage vector selection in the fourth sector: V 1 and V 4. Synthesize a zero voltage vector. V 45 and V 56 The synthesized reference voltage vector operates in the following order: V 5→ V 1→ V 6→ V 4→ V 6→ V 1→ V 5; Effective voltage vector selection within sector 5: V 2 and V 5. Synthesize a zero voltage vector. V 56 and V 61 The synthesized reference voltage vector operates in the following order: V 5→ V 1→ V 2→ V 6→ V 2→ V 1→ V 5; Effective voltage vector selection in sector 6: V 3 and V 6. Synthesize a zero voltage vector. V 61 and V 12 The synthesized reference voltage vector operates in the following order: V 1→ V 3→ V 2→ V 6→ V 2→ V 3→ V 1.

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