A pulse width modulation method for PWM rectifier

Abstract

The present invention discloses a PWM rectifier pulse width modulation method, comprising: collecting the three-phase output voltage of the three-phase alternating current, the effective value of which is E AC ; The PWM signal controls the insulated gate bipolar transistor IGBT, initially based on the SVPWM modulation method, while monitoring the DC voltage V at the three-phase AC output end. dc ; Collect the DC voltage V at the output end of the three-phase AC power dc , and judge the DC voltage V at the output end of the three-phase AC power dc With the effective value E AC When the DC voltage V at the output of the three-phase AC power is dc More than 2 times E AC The present invention uses the SPWM modulation method when starting the PWM rectifier. When the rectifier reaches a steady state, it switches to the SPWM method. This solves the current suppression problem at the moment of starting the PWM rectifier and the EWI problem in the steady state. It has the advantages of suppressing the starting current and suppressing the third harmonic when reaching a steady state.

Description

Technical Field

[0001] The present invention relates to the technical field of power electronics, and more particularly to a pulse width modulation method for a PWM rectifier. Background Art

[0002] With the development of power electronics technology, the performance of power semiconductor switching devices has continuously improved. They have evolved from the widely used half-controlled power semiconductor switches of the early days, such as ordinary thyristors (SCRs), to today's fully controlled power switches with diverse performance and types, including bipolar transistors (BITs), gate turn-off (GTO) thyristors, insulated-gate bipolar transistors (IGBTs), integrated gate-commutated thyristors (ICCTs), power field-effect transistors (IGBTFETs), and field-controlled thyristors (MCTs). The development of intelligent power modules (IPMs) in the 1990s has pioneered a new direction for the development of power semiconductor switching devices. Advances in power semiconductor switching device technology have spurred the rapid development of power electronic converters, resulting in the emergence of various converters based on pulse-width modulation (PWM) control, such as frequency converters, inverters, high-frequency switching power supplies, and various specialized converters. These converters have found widespread application across various sectors of the national economy. However, a large portion of these current converters currently require a rectifier stage to generate DC voltage. Since conventional rectifiers widely utilize diode-uncontrolled rectifier circuits or thyristor-controlled rectifier circuits, they inject significant amounts of harmonics and reactive power into the power grid, causing serious grid "pollution." The most fundamental measure to address this grid "pollution" is to ensure that the grid-side current in the converter is sinusoidal and operates at unity power factor. Therefore, rectifiers, as a major source of grid "pollution," have initially attracted academic attention, leading to extensive research. The key approach is to incorporate PWM technology into rectifier control, making the grid-side current sinusoidal and enabling operation at unity power factor.

[0003] Rectifiers are one of the earliest AC / DC converters used. Their development has progressed from uncontrolled rectifiers (diode rectification), phase-controlled rectifiers (thyristor rectification), to PWM rectifiers (gate-turned-off power switches). A PWM rectifier is essentially an AC device operating in four phases with controllable AC and DC sides.

[0004] Sinusoidal pulse width modulation (SPWM) is a relatively mature and widely used PWM method. When narrow pulses of equal impulse but different shapes are applied to a link with inertia, the effect is essentially the same. The SPWM method is based on this principle. It uses a PWM waveform, equivalent to a sine wave, whose pulse width varies according to a sinusoidal pattern to control the switching of switching devices in the inverter circuit. This waveform ensures that the area of ​​the output pulse voltage is equal to the area of ​​the desired sine wave within the corresponding interval. By varying the frequency and amplitude of the modulation waveform, the frequency and amplitude of the inverter circuit's output voltage can be adjusted. Sinusoidal pulse width modulation (SVPWM) uses the ideal stator flux circle of a three-phase symmetrical motor powered by a three-phase symmetrical sinusoidal voltage as a reference standard. By appropriately switching the three-phase inverter's switching modes, the PWM waveform is generated, and the resulting actual flux vector is used to track the exact flux circle. The traditional SPWM method starts from the perspective of power supply to generate a sinusoidal power supply with adjustable frequency and voltage, while the SVPWM method considers the inverter system and asynchronous motor as a whole. The model is relatively simple and is also convenient for real-time control by the microprocessor.

[0005] PWM rectifiers using the traditional SPWM method experience current spikes during startup. The SVPWM method can suppress this current spike during startup. However, because the traditional SVPWM method uses vector synthesis calculations, it injects third-order harmonics during steady-state, causing saturation of EMI inductors. Based on this, the present invention designs a parameter-adjustable pulse width modulation method that uses the SVPWM method during startup and switches to the SPWM method when the rectifier reaches steady-state. This method simultaneously solves the current suppression issues during startup and the EWI problem during steady-state, offering the advantages of suppressing both startup current and third-order harmonics during steady-state. Summary of the Invention

[0006] In view of this, the present invention provides a pulse width modulation method for a PWM rectifier.

[0007] In order to achieve the above object, the present invention adopts the following technical solutions:

[0008] A PWM rectifier pulse width modulation method, comprising:

[0009] Collect the three-phase output voltage of three-phase AC power, and its effective value is E AC ;

[0010] The PWM signal controls the insulated gate bipolar transistor IGBT, initially based on the SVPWM modulation method, while monitoring the DC voltage V at the three-phase AC output terminal. dc ;

[0011] Collect the DC voltage V at the output end of the three-phase AC powerdc , and judge the DC voltage V at the output end of the three-phase AC power dc With the effective value E AC When the DC voltage V at the output of the three-phase AC power is dc More than 2 times E AC When , SPWM modulation is adopted.

[0012] Preferably, based on the SVPWM modulation method, when the DC voltage V dc More than 2 times E AC When SPWM modulation is used, the specific implementation method is:

[0013]

[0014]

[0015]

[0016] inject=-K×(max(u 0a ,u 0b ,u 0c )+min(u 0a ,u 0b ,u 0c ))

[0017] Among them, K is an adjustable parameter, and inject is an adjustable additional component added to the modulation wave. At the moment of startup, K = 0.5, which is equivalent to SVPWM. dc More than 2 times E AC When K decays to 0, it is equivalent to SPWM, u 0a 、u 0b 、u 0c Indicates the SPWM modulation voltage of each phase output of three-phase AC, Represents the modulation signal of the two IGBTs connected to each phase of the corresponding three-phase current.

[0018] It can be seen from the above technical solution that, compared with the prior art, the present invention discloses a PWM rectifier pulse width modulation method, which enables the PWM rectifier to adopt the SVPWM method at startup and switch to the SPWM method when the rectifier reaches a steady state. At the same time, it solves the current suppression problem at the moment of startup of the PWM rectifier and the EWI problem in steady state, and has the advantages of suppressing the startup current and suppressing the third harmonic when reaching a steady state. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are merely embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying any creative work.

[0020] Figure 1 The accompanying drawing is a schematic diagram of a PWM rectifier circuit provided by the present invention.

[0021] Figure 2 The accompanying drawing is a schematic diagram of the SPWM waveform provided by the present invention.

[0022] Figure 3 The accompanying drawing is a flow chart of the pulse width modulation method of the PWM rectifier provided by the present invention. DETAILED DESCRIPTION

[0023] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0024] The schematic diagram of the PWM rectifier circuit is as follows Figure 1 As shown, Ea, Eb, and Ec are the three-phase output voltages of the three-phase AC power, and their effective values ​​are all set to E AC , all are 220V. R is the resistor, S is the switch, L is the inductor, V1, V2, V3 are the base frequency voltage, that is, the voltage value at this location, Ua+, Ua-, Ub+, Ub-, Uc+, Uc- are the PWM control signals of the six IGBTs respectively, V dc To output DC voltage, the specific connection relationship is: Ea, Eb, and Ec are connected to resistor R and inductor L in three ways respectively, and switch S is connected in parallel with resistor R. Each way is connected to two IGBTs respectively, and finally the three ways are combined to output, and the DC voltage V is output from the output end. dc .

[0025] The whole rectification process can be divided into three steps: The first step is pre-charging, that is, when the power is turned on, the switch S is in the off state, and the current is limited by the resistor. If there is no resistor, the charging current will be very large, causing the components to be burned. Through the first step, V dc The second step is to close the switch S, and the resistor is short-circuited. After the circuit stabilizes, the output DC voltage is equal to the input AC voltage. times, that is The third step is to use PWM signal to control IGBT. 0a+ 、u 0b+ 、u 0c+ 、u 0a- 、u 0b- 、u 0c- As a control signal, such as Figure 1 As shown, the six IGBTs are controlled to be on and off respectively, thereby achieving the modulation of the output voltage. The PWM modulation signal is the key point of the design of this method. If the traditional SPWM modulation is used, the amplitude of the base frequency voltage V1, V2, and V3 formed at this time is smaller than E AC Therefore, there is a current spike problem. Although the SVPWM method can suppress the current spike at startup, the traditional SVPWM method uses a vector synthesis calculation method, which will inject a third harmonic in steady state, causing saturation of the EMI inductor.

[0026] Based on this, the present invention designs a parameter-adjustable PWM rectifier pulse width modulation method. This method uses the SVPWM method at startup and switches to the SPWM method when the rectifier reaches steady state. This method simultaneously solves the current suppression problem at the instant of startup and the EWI problem at steady state, achieving the advantages of suppressing the startup current and the third harmonic when steady state is reached. The specific method is as follows:

[0027] Traditional SPWM uses a sine wave (u r ) and triangle wave (u c ) is compared to generate an SPWM waveform (u0) whose pulse width changes according to the sinusoidal law and is equivalent to a sine wave, such as Figure 2 shown.

[0028] For three-phase AC, the SPWM modulation wave output by each phase corresponds to u 0a 、u 0b 、u 0c , each phase difference is 120°, and the corresponding PWM signal output to Ua+, Ub+, Uc+, Ua-, Ub-, and Uc- is u 0a+ 、u 0b+ 、u 0c+ 、u 0a- 、u 0b- 、u 0c- , and the relationship is as follows:

[0029] u 0a+ =-u 0a- =u 0a ,

[0030] u 0b+ =-u 0b- =u 0b ,

[0031] u 0c+ =-u 0c- =u 0c

[0032] This method adds an adjustable additional component to the traditional SPWM modulation wave, set as inject, then the improved SPWM modulation wave is The corresponding PWM signals output to Ua+, Ub+, Uc+, Ua-, Ub-, and Uc- are The relationship is as follows:

[0033]

[0034]

[0035]

[0036] inject=-K×(max(u 0a ,u 0b ,u 0c )+min(u 0a ,u 0b ,u 0c ))

[0037] Among them, K is an adjustable parameter. At the moment of startup, K = 0.5. This method is equivalent to SVPWM. DC More than 2 times E AC When K decays to 0, it is equivalent to SPWM. This realizes the switch from SVPWM to SPWM, and solves the current suppression problem at the moment of PWM startup and the EWI problem in steady state.

[0038] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments. Reference can be made to the common and similar parts between the various embodiments. For the devices disclosed in the embodiments, since they correspond to the methods disclosed in the embodiments, the description is relatively simple, and the relevant parts can be referred to the method description.

[0039] The above description of the disclosed embodiments is intended to enable one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be readily apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention is not limited to the embodiments shown herein but is intended to conform to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A PWM rectifier pulse width modulation method, characterized in that: include: Collect the three-phase output voltage of three-phase AC power, and the effective value of each phase is E AC ; The PWM signal controls the insulated gate bipolar transistor IGBT, initially based on the SVPWM modulation method, while monitoring the DC voltage V at the three-phase AC output terminal. dc ; Collect the DC voltage V at the three-phase AC output terminal dc , and judge the DC voltage V at the output end of the three-phase AC power dc With the effective value E AC When the DC voltage V at the output of the three-phase AC power is dc More than 2 times E AC When SPWM modulation is used; At startup, based on the SVPWM modulation method, when the DC voltage V dc More than 2 times E AC When SPWM modulation is used, the specific implementation method is: inject=-K×(max(u 0a ,in 0b ,in 0c )+min(in 0a ,in 0b ,in 0c )) Among them, K is an adjustable parameter, and inject is an adjustable additional component added to the modulation wave. At the moment of startup, K = 0.5, which is equivalent to SVPWM. dc More than 2 times E AC When K decays to 0, it is equivalent to SPWM, u 0a 、u 0b 、u 0c Indicates the SPWM modulation voltage of each phase output of three-phase AC, Represents the modulation signal of the two IGBTs connected to each phase of the corresponding three-phase current.

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