Modulation method for suppressing common-mode voltage of five-level three-phase H-bridge inverter

Abstract

The invention relates to the technical field of motor alternating-current control systems, and discloses a modulation method for suppressing common-mode voltage of a five-level three-phase H-bridge inverter, which comprises the following steps of: generating four triangular carriers of which the phase difference is 90 degrees; adding 1 to the amplitude value of the modulation wave in the negative half cycle, and enabling all the modulation waves in the modulation range to be located in the positive half cycle; judging the size of the modulation ratio, and comparing the modulation wave with the triangular carrier according to the size of the modulation ratio to generate a PWM control signal; and the PWM control signal is further converted into a driving signal of a corresponding full-control power device, and the driving signal is input into each corresponding switching tube. According to the modulation method for suppressing the common-mode voltage of the five-level three-phase H-bridge inverter, the amplitude of the common-mode voltage output by the five-level three-phase H-bridge inverter is effectively suppressed, and the harm of the common-mode voltage to an alternating-current speed regulation system is reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of motor AC control systems, and in particular to a modulation method for suppressing a common mode voltage of a five-level three-phase H-bridge inverter. Background Art

[0002] With the continuous progress of power electronic device technology, information and control technology, the fields involved and applied by power electronic inverters are becoming more and more extensive, becoming an important direction for the development of the industry. The AC variable frequency speed regulation system composed of inverters and AC motors has the advantages of wide speed regulation range, high speed regulation accuracy, improved dynamic performance of AC motor systems, and improved motor efficiency, and has been widely used in industry, military and other fields.

[0003] At present, high-performance inverters generally use pulse width modulation (PWM) technology to improve the quality of the inverter output waveform. However, PWM modulation also causes the sum of the inverter output voltage to ground to be not always equal to zero, generating an alternating common-mode voltage in the stator winding of the motor. The common-mode voltage will induce casing leakage current on the junction capacitance between the stator, rotor and casing of the motor, forming common-mode electromagnetic interference, which may cause the ground protection current relay to malfunction and affect the normal operation of the equipment.

[0004] On the other hand, a large common-mode leakage current will damage the insulation performance of the motor, accelerate the aging of the motor bearings, and reduce the life of the motor. According to statistics, motor bearing failures account for about 40% of the total motor failures, and 25% of the bearing damage failures are caused by the PWM power supply of the inverter.

[0005] Limited by the voltage level of existing power devices, traditional two-level inverters cannot be directly applied to applications with DC voltage levels above 4kV. In the field of medium and high voltage inverters, multi-level topologies have been widely studied and paid attention to. The five-level active neutral point clamp topology is a novel multi-level topology with the advantages of high output quality, high power density, and relatively simple control. It is very suitable for medium voltage applications with a voltage level of 10kV.

[0006] However, for the five-level three-phase H-bridge inverter driving the three-phase open-winding motor, the system insulation pressure is high due to the high DC voltage level, and the common-mode voltage problem is more serious. In order to improve the safety of the transmission system and reduce the impact of common-mode voltage, the output common mode is usually reduced by improving the PWM modulation strategy. The existing modulation strategies mainly include the sinusoidal pulse width modulation strategy based on carrier amplitude shift and the modulation strategy based on space vector, but the output common-mode voltage amplitude of these two methods is large, and there is no effective solution yet. Summary of the invention

[0007] The purpose of the present invention is to address the deficiencies of the above-mentioned technology and provide a modulation method for suppressing the common-mode voltage of a five-level three-phase H-bridge inverter, thereby effectively suppressing the amplitude of the common-mode voltage output by the five-level three-phase H-bridge inverter and reducing the harm of the common-mode voltage to the AC speed regulation system.

[0008] To achieve the above object, the modulation method for suppressing the common mode voltage of a five-level three-phase H-bridge inverter designed by the present invention comprises the following steps:

[0009] A) Generate four triangular carrier waves with a phase difference of 90°;

[0010] B) Increase the amplitude of the modulation wave in the negative half cycle by +1, so that all the modulation waves in the modulation range are in the positive half cycle;

[0011] C) Determine the size of the modulation ratio, and compare the modulated wave triangular carrier according to the size of the modulation ratio to generate a PWM control signal;

[0012] D) converting the PWM control signal obtained in step C) into a driving signal corresponding to the fully controlled power device and inputting it into each corresponding switch tube.

[0013] Preferably, in step A), the four triangular carriers are c r1 、c r2 、c r3 、c r4 The phases are 0°, 90°, 180° and 270° respectively.

[0014] Preferably, in step C), if the modulation ratio is greater than 0.5 and the modulation wave is in the positive half cycle, the left half arm of the H bridge and the right half arm of the H bridge both use the triangular carrier wave c r1 and the triangular carrier c r3 Compared with the modulated wave;

[0015] If the modulation ratio is greater than or equal to 0.5 and the modulation wave is in the negative half cycle, both the left half arm of the H bridge and the right half arm of the H bridge use the triangular carrier c r2 and the triangular carrier c r4 Compared with the modulated wave;

[0016] If the modulation ratio is less than 0.5, the left half of the H bridge uses a triangular carrier c r1 and the triangular carrier c r3 Compared with the modulation wave, the whole process of the right half bridge arm of the H bridge adopts a triangular carrier wave c r2 and the triangular carrier c r4 Compare with the modulated wave.

[0017] Preferably, if the modulation ratio is greater than or equal to 0.5, and the modulation wave is in the positive half cycle, the low-frequency outer tube T1 is always on, and the modulation wave and the triangular carrier c r1Compare and generate PWM control signal to control high frequency inner tube T5, the modulation wave and the triangular carrier c r3 The comparison generates a PWM control signal for controlling the high-frequency inner tube T7.

[0018] Preferably, if the modulation ratio is greater than or equal to 0.5, and the modulation wave is in the negative half cycle, the low-frequency outer tube T1 is constantly turned off, and the modulation wave and the triangular carrier c r2 Compare and generate PWM control signal to control high frequency inner tube T7, the modulation wave and the triangular carrier c r4 The time comparison generates a PWM control signal for controlling the high-frequency inner tube T5.

[0019] Preferably, the PWM signals of the remaining switch tubes of the bridge arm are matched according to the obtained PWM signals of the low-frequency outer tube T1, the high-frequency inner tube T5 and the high-frequency inner tube T7.

[0020] Preferably, the switching signal of the low-frequency outer tube T3 is consistent with that of the low-frequency outer tube T1, the switching signals of the low-frequency outer tubes T2 and T4 are complementary to those of the low-frequency outer tube T1, the switching signal of the high-frequency inner tube T6 is complementary to that of the high-frequency inner tube T5, and the switching signal of the high-frequency inner tube T8 is complementary to that of the high-frequency inner tube T7.

[0021] Compared with the prior art, the present invention has the following advantages:

[0022] 1. Effectively suppress the amplitude of the common-mode voltage output by the five-level three-phase H-bridge inverter, and reduce the harm of the common-mode voltage to the AC speed regulation system;

[0023] 2. The inverter output common mode voltage is reduced by pure software through PWM strategy optimization, without adding any hardware;

[0024] 3. While reducing the common mode voltage, the harmonic performance of the bridge arm output voltage can be basically kept unchanged without affecting the output quality. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 A schematic flow chart of a modulation method for suppressing a common-mode voltage of a five-level three-phase H-bridge inverter according to the present invention;

[0026] Figure 2 A topological structure diagram of a five-level active clamped three-phase H-bridge inverter targeted by the present invention;

[0027] Figure 3 It is a schematic diagram of the modulation mode when the modulation ratio is greater than 0.5;

[0028] Figure 4 Schematic diagram of the modulation mode of the left half bridge arm when the modulation ratio is less than 0.5;

[0029] Figure 5 It is a schematic diagram of the modulation mode of the right half bridge arm when the modulation ratio is less than 0.5;

[0030] Figure 6 The waveform comparison diagram of the bridge arm output voltage and the system common mode voltage of the conventional carrier amplitude shift modulation method and the modulation method of the present invention when the modulation ratio is greater than 0.5;

[0031] Figure 7 The figure is a waveform comparison diagram of the bridge arm output voltage and the system common mode voltage of the traditional carrier amplitude shift modulation method and the modulation method of the present invention when the modulation ratio is less than 0.5. DETAILED DESCRIPTION

[0032] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and specific examples. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention. In addition, the technical features involved in each embodiment of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0033] like Figure 1 and Figure 2 As shown, a modulation method for suppressing the common mode voltage of a five-level three-phase H-bridge inverter includes the following steps:

[0034] A) Generate four triangular carriers with a phase difference of 90°. The four triangular carriers are c r1 、c r2 、c r3 、c r4 , the phases are 0°, 90°, 180° and 270°, respectively, and the amplitudes are 0 to 1. In this embodiment, the triangular carrier wave c r1 and the triangular carrier c r3 Set as carrier combination 1, triangular carrier c r2 and the triangular carrier c r4 Set to carrier combination 2;

[0035] B) the amplitude of the modulation wave in the negative half cycle is increased by 1, so that all the modulation waves in the modulation range are in the positive half cycle. Specifically, the amplitude of the negative half cycle of the modulation waves ma1 to mc2 of the three-phase H bridge is increased by 1, so that the amplitude of the six-phase modulation wave is between 0 and 1 in the full modulation range;

[0036] C) Determine the size of the modulation ratio, and compare the modulation wave triangle carrier according to the size of the modulation ratio to generate a PWM control signal, specifically:

[0037] If the modulation ratio is greater than 0.5 and the modulation wave is in the positive half cycle, both the left half arm of the H bridge and the right half arm of the H bridge use the triangular carrier c r1 and the triangular carrier c r3 Compared with the modulated wave;

[0038] If the modulation ratio is greater than or equal to 0.5 and the modulation wave is in the negative half cycle, both the left half arm of the H bridge and the right half arm of the H bridge use the triangular carrier c r2 and the triangular carrier c r4 Compared with the modulated wave;

[0039] If the modulation ratio is less than 0.5, the left half of the H bridge uses a triangular carrier c r1 and the triangular carrier c r3 Compared with the modulation wave, the whole process of the right half bridge arm of the H bridge adopts a triangular carrier wave c r2 and the triangular carrier c r4 Compared with the modulated wave;

[0040] In this embodiment, Figure 3 As shown in the figure, if the modulation ratio is greater than or equal to 0.5 and the modulation wave is in the positive half cycle, the low-frequency external tube T1 is always on, and the modulation wave and the triangular carrier c r1 Compare and generate PWM control signal to control high frequency inner tube T5, the modulation wave and the triangular carrier c r3 Comparison generates a PWM control signal for controlling the high-frequency inner tube T7;

[0041] If the modulation ratio is greater than or equal to 0.5, and the modulation wave is in the negative half cycle, since the modulation wave amplitude is increased by 1 in step B), it is still between 0 and 1, and the low-frequency external tube T1 is constantly turned off, and the modulation wave and the triangular carrier c r2 Compare and generate PWM control signal to control high frequency inner tube T7, the modulation wave and the triangular carrier c r4 The time comparison generates a PWM control signal for controlling the high-frequency inner tube T5;

[0042] If the modulation ratio is less than 0.5, such as Figure 4 As shown, the left half arm of the H bridge uses triangular carrier cr1 and triangular carrier cr3 to compare with the modulation wave to generate PWM control signal, as shown in Figure 5 As shown, the whole process of the right half bridge arm of the H bridge uses the triangular carrier cr2 and the triangular carrier cr4 to compare with the modulation wave to generate the PWM control signal;

[0043] D) converting the PWM control signal obtained in step C) into a driving signal corresponding to the fully controlled power device and inputting it into each corresponding switch tube, wherein the PWM signals of the remaining switch tubes of the bridge arm are matched according to the obtained PWM signals of the low-frequency outer tube T1, the high-frequency inner tube T5 and the high-frequency inner tube T7, specifically, the switch signal of the low-frequency outer tube T3 is consistent with the low-frequency outer tube T1, the switch signals of the low-frequency outer tube T2 and the low-frequency outer tube T4 are complementary to the low-frequency outer tube T1, the switch signal of the high-frequency inner tube T6 is complementary to the high-frequency inner tube T5, and the switch signal of the high-frequency inner tube T8 is complementary to the high-frequency inner tube T7.

[0044] The modulation method for suppressing the common mode voltage of a five-level three-phase H-bridge inverter of the present invention staggers the voltage edges output by different bridge arms by phase shifting and screening the carrier, thereby achieving the purpose of suppressing the common mode voltage amplitude. Figure 6 It is a comparison of the bridge arm output voltage and system common mode voltage of the conventional method and the modulation method proposed by the present invention when the modulation ratio is greater than 0.5. Figure 7 The comparison of the bridge arm output voltage and system common mode voltage of the conventional method and the modulation method proposed in the present invention when the modulation ratio is less than 0.5 shows that the bridge arm output voltage of the present invention maintains a good output quality, and the maximum common mode voltage of the five-level three-phase H-bridge inverter corresponding to the present invention is 16.7V (V dc / 12), when the modulation ratio is less than 0.5, it is 8.35V (V dc / 24), the maximum common-mode voltage of the traditional carrier amplitude shift modulation method within the full modulation range is 25V (V dc / 8), when the modulation ratio is greater than or equal to 0.5 and less than 0.5 respectively, the common mode voltage amplitude of the method proposed in the present invention is reduced by 33.2% and 66.4% respectively.

[0045] The modulation method for suppressing the common-mode voltage of a five-level three-phase H-bridge inverter of the present invention effectively suppresses the amplitude of the common-mode voltage output by the five-level three-phase H-bridge inverter, and reduces the harm of the common-mode voltage to an AC speed regulation system; the common-mode voltage output by the inverter is reduced in a pure software manner through PWM strategy optimization, without adding any hardware; while reducing the common-mode voltage, the harmonic performance of the bridge arm output voltage can be basically kept unchanged, without affecting the output quality.

[0046] It should be easy for those skilled in the art to understand that the above is only a preferred application example of the present invention and is not intended to limit the present invention. In addition to the above-mentioned example of the five-level active clamped three-phase H-bridge topology, the present invention can also be applied to a variety of different five-level structures, including three-phase half-bridge, five-phase half-bridge, five-phase H-bridge, etc. In addition to the above examples, there can also be other implementation methods, and all technical solutions formed by equivalent replacement or equivalent transformation fall within the scope of protection required by this patent.

Claims

1. A modulation method for suppressing the common mode voltage of a five-level three-phase H-bridge inverter, characterized in that: The steps include: A) Generate four triangular carrier waves with a phase difference of 90°; B) Increase the amplitude of the modulation wave in the negative half cycle by +1, so that all the modulation waves in the modulation range are in the positive half cycle; C) Determine the size of the modulation ratio, and compare the modulated wave triangular carrier according to the size of the modulation ratio to generate a PWM control signal; D) converting the PWM control signal obtained in step C) into a driving signal corresponding to the fully controlled power device and inputting it into each corresponding switch tube.

2. The modulation method for suppressing the common mode voltage of a five-level three-phase H-bridge inverter according to claim 1, characterized in that: In step A), the four triangular carriers are c r1 、c r2 、c r3 、c r4 The phases are 0°, 90°, 180° and 270° respectively.

3. The modulation method for suppressing the common mode voltage of a five-level three-phase H-bridge inverter according to claim 2, characterized in that: In the step C), if the modulation ratio is greater than 0.5 and the modulation wave is in the positive half cycle, the left half arm of the H bridge and the right half arm of the H bridge both use the triangular carrier wave c r1 and the triangular carrier c r3 Compared with the modulated wave; If the modulation ratio is greater than or equal to 0.5 and the modulation wave is in the negative half cycle, both the left half arm of the H bridge and the right half arm of the H bridge use the triangular carrier c r2 and the triangular carrier c r4 Compared with the modulated wave; If the modulation ratio is less than 0.5, the left half of the H bridge uses a triangular carrier c r1 and the triangular carrier c r3 Compared with the modulation wave, the whole process of the right half bridge arm of the H bridge adopts a triangular carrier wave c r2 and the triangular carrier c r4 Compare with the modulated wave.

4. The modulation method for suppressing the common mode voltage of a five-level three-phase H-bridge inverter according to claim 3, characterized in that: If the modulation ratio is greater than or equal to 0.5, and the modulation wave is in the positive half cycle, the low-frequency external tube T1 is always on, and the modulation wave and the triangular carrier c r1 Compare and generate PWM control signal to control high frequency inner tube T5, the modulation wave and the triangular carrier c r3 The comparison generates a PWM control signal for controlling the high-frequency inner tube T7.

5. The modulation method for suppressing the common mode voltage of a five-level three-phase H-bridge inverter according to claim 4, characterized in that: If the modulation ratio is greater than or equal to 0.5, and the modulation wave is in the negative half cycle, the low-frequency external tube T1 is always off, and the modulation wave and the triangular carrier c r2 Compare and generate PWM control signal to control high frequency inner tube T7, the modulation wave and the triangular carrier c r4 The time comparison generates a PWM control signal for controlling the high-frequency inner tube T5.

6. The modulation method for suppressing the common mode voltage of a five-level three-phase H-bridge inverter according to claim 5, characterized in that: According to the obtained PWM signals of the low-frequency outer tube T1, the high-frequency inner tube T5 and the high-frequency inner tube T7, the PWM signals of the remaining switch tubes of the bridge arm are matched.

7. The modulation method for suppressing the common mode voltage of a five-level three-phase H-bridge inverter according to claim 6, characterized in that: The switching signal of the low-frequency outer tube T3 is consistent with that of the low-frequency outer tube T1, the switching signals of the low-frequency outer tube T2 and the low-frequency outer tube T4 are complementary to the low-frequency outer tube T1, the switching signal of the high-frequency inner tube T6 is complementary to that of the high-frequency inner tube T5, and the switching signal of the high-frequency inner tube T8 is complementary to that of the high-frequency inner tube T7.

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