CN-121663955-B - Multi-target hybrid modulation method, system and equipment for T-shaped three-level inverter

CN121663955BCN 121663955 BCN121663955 BCN 121663955BCN-121663955-B

Abstract

The invention belongs to the technical field of electronic power, and particularly relates to a multi-target hybrid modulation method, a system and equipment of a T-shaped three-level inverter, wherein the method comprises the steps of firstly judging whether the inverter operates at an extremely low modulation degree; if so, calculating theoretical midpoint currents of DPWM1 and DPWM3 modes in parallel, and expanding midpoint currents corresponding to four mixed modulation modes generated after VSVPWM sequences are respectively introduced into the two modes, dynamically selecting an optimal mixed modulation mode or returning to a basic DPWM mode according to the numerical relation between the midpoint compensation currents calculated in real time and the midpoint currents, finally generating three-phase double-modulation waves, and outputting PWM signals for driving all power switches after carrier comparison. The invention realizes multi-objective optimization of midpoint potential, switching loss and output waveform under extreme working conditions, and remarkably improves the stability and performance of the system.

Inventors

WANG JINPING
YAN XIAOLEI
JIANG WEIDONG
An Lianshuo
LIU MENGHAO

Assignees

合肥工业大学

Dates

Publication Date: 20260508
Application Date: 20260206

Claims (8)

A multi-target hybrid modulation method for a t-type three-level inverter, characterized in that when a fundamental modulation ratio of three-phase sinusoidal modulation voltage is lower than a first threshold value, the method comprises: Determining a maximum phase, an intermediate phase and a minimum phase of three-phase sinusoidal modulation voltage, respectively determining a common mode voltage corresponding to a DPWM1 mode of clamping the maximum phase to a positive bus and a DPWM3 mode of clamping the minimum phase to a negative bus, and generating two groups of three-phase modulation waves; Determining a duty ratio according to the modulation wave, and determining theoretical midpoint currents of the DPWM1 mode and the DPWM3 mode by combining phase currents; introducing zero level into the middle phase or the minimum phase in the DPWM1 mode to obtain a first midpoint current and a second midpoint current, and introducing positive level into the maximum phase or the middle phase in the DPWM3 mode to obtain a third midpoint current and a fourth midpoint current; determining a midpoint compensation current according to the direct-current side parameters; selecting a corresponding mixed modulation mode based on the numerical relation between the midpoint compensation current and each midpoint current; generating a three-phase double-modulation wave according to the selected mixed modulation mode; comparing the three-phase double-modulation wave with the in-phase double-carrier wave to generate switching signals for driving all power switches of the T-shaped three-level inverter; In the DPWM1 mode of clamping the maximum phase to the positive bus, zero level is introduced into the modulated wave of the intermediate phase or the minimum phase to form the modulated wave which enables the phase to have three level states, namely a P-MID mode and a P-MIN mode; in a DPWM3 mode of clamping the minimum phase to a negative bus, introducing a high level into a modulation wave of an intermediate phase or a maximum phase of the DPWM3 mode to form modulation waves of the phase with three level states, namely an N-MID mode and an N-MAX mode; Taking the P-MID mode, the P-MIN mode, the N-MID mode and the N-MAX mode as the mixed modulation modes; The selecting the corresponding mixed modulation mode based on the numerical relation between the midpoint compensation current and each midpoint current comprises combining the midpoint current output values corresponding to the P-MID mode, the P-MIN mode, the N-MID mode and the N-MAX mode respectively And the theoretical midpoint current output value I NP_P of the DPWM1 mode and the theoretical midpoint current output value I NP_N of the DPWM3 mode, judging the numerical interval of the midpoint compensation current I CMP , and selecting an execution mode according to the following rules: if it meets Selecting a P-MID mode of introducing zero level into the intermediate phase based on the DPWM1 mode; if it meets Selecting a P-MIN mode of introducing zero level into the minimum phase based on the DPWM1 mode; if it meets Selecting an N-MID mode of introducing a positive level into the intermediate phase on the basis of the DPWM3 mode; if it meets Selecting an N-MAX mode for introducing a positive level into the maximum phase based on the DPWM3 mode; If the midpoint compensating current I CMP does not meet any condition of the rule, entering a midpoint potential uncontrollable area, comparing a first difference absolute value of the midpoint compensating current I CMP of a theoretical midpoint current output value I NP_P of the DPWM1 mode and a second difference absolute value of a theoretical midpoint current output value I NP_N of the DPWM3 mode and the midpoint compensating current I CMP in the uncontrollable area, if the first difference absolute value is smaller than or equal to the second difference absolute value, selecting the DPWM1 mode as a current modulation mode, otherwise, selecting the DPWM3 mode as the current modulation mode.
2. The method of claim 1, wherein determining the common-mode voltages corresponding to the DPWM1 mode and the DPWM3 mode, respectively, and generating two sets of three-phase modulation waves comprises determining a first common-mode voltage u zvsP corresponding to the DPWM1 mode and a second common-mode voltage u zvsN corresponding to the DPWM3 mode based on a maximum phase modulation voltage u max and the minimum phase modulation voltage u min , and comprising: ; Wherein, the Is the voltage of a direct current bus; Setting the first common-mode voltage Adding the three-phase sinusoidal modulation voltage to obtain a first group of three-phase modulation waves in the DPWM1 mode And the second common-mode voltage is set Adding the three-phase sinusoidal modulation voltage to obtain a second group of three-phase modulation waves in the DPWM3 mode Wherein, the method comprises the steps of, Representing any one of the three phases.
3. The method of multi-target hybrid modulation of a T-type three-level inverter of claim 2, wherein determining the duty cycle from the modulated wave and determining the first midpoint current and the second midpoint current in combination with the phase current comprises determining a first set of duty cycles in DPWM1 mode as follows: ; The theoretical midpoint current I NP_P for DPWM1 mode is calculated as follows: ; Wherein, the Is the 1 level duty ratio of the three phases in the DPWM1 mode; Three-phase load currents respectively; In DPWM3 mode, a second set of duty cycles is determined as follows: ; Calculating theoretical midpoint current of DPWM3 mode The following formula: ; Wherein, the 。
4. The multi-target hybrid modulation method of a T-type three-level inverter of claim 1, wherein zero level is introduced into the intermediate phase or the minimum phase in the DPWM1 mode, respectively, to obtain the corresponding duty cycle, first and second midpoint currents as follows: ; In the middle of Three-phase 1 level duty ratios after zero level is introduced into the minimum phase of the DPWM1 mode respectively, Modulating the wave for the minimum phase at that time; First midpoint current The formula is as follows: ; In the middle of The duty ratios of the three phases 1 level after the zero level is introduced into the intermediate phase of the DPWM1 mode are respectively, Modulated wave for the intermediate phase at this time, second midpoint current The formula is as follows: ; Introducing positive level into the maximum phase or the intermediate phase in the DPWM3 mode to obtain third and fourth midpoint currents, the following formula: ; In the middle of Three-phase 1-level duty ratios after zero level is introduced into the intermediate phase of the DPWM3 mode respectively, Modulated wave for the intermediate phase at this time, a third midpoint current The formula is as follows: ; In the middle of Three-phase 1-level duty ratios after zero level is introduced into the maximum phase of the DPWM3 mode respectively, Modulated wave for the intermediate phase at this time, fourth midpoint current The formula is as follows: 。
5. The multi-target hybrid modulation method of a T-type three-level inverter according to claim 4, wherein the determining the midpoint compensation current according to the direct current side parameter comprises the following formula: ; Wherein, C is the capacitance value of the direct current side, For the difference between the upper and lower dc side voltages, Is a switching period.
6. The multi-target hybrid modulation method of a T-type three-level inverter according to claim 5, wherein the generating a three-phase dual modulation wave according to the selected hybrid modulation mode comprises: Compensating current according to the selected hybrid modulation mode and the midpoint Calculating the duty cycle adjustment amount corresponding to the level to be introduced And determining a final three-phase double-modulation wave based on the duty ratio adjustment quantity delta d and the original duty ratio corresponding to the mixed modulation mode.
A multi-target hybrid modulation system for 7.T-type three-level inverter, for implementing a multi-target hybrid modulation method according to any one of claims 1 to 6, said system comprising: the modulation signal generation unit is used for determining the maximum phase, the middle phase and the minimum phase of the three-phase sinusoidal modulation voltage, respectively determining common-mode voltages corresponding to the DPWM1 mode and the DPWM3 mode, and generating two groups of three-phase modulation waves; the neutral point current calculation unit is used for determining the duty ratio according to the modulation wave and determining theoretical neutral point currents of the DPWM1 mode and the DPWM3 mode by combining the phase currents, introducing zero level into an intermediate phase or a minimum phase in the DPWM1 mode to obtain first and second neutral point currents, and introducing positive level into a maximum phase or an intermediate phase in the DPWM3 mode to obtain third and fourth neutral point currents; The midpoint compensation calculation unit is used for determining midpoint compensation current according to the direct-current side parameters; The mode selection decision unit is used for selecting a corresponding mixed modulation mode based on the numerical relation between the midpoint compensation current and each midpoint current; A dual modulation wave generation unit for generating a three-phase dual modulation wave according to the selected mixed modulation mode; And the PWM signal generating unit is used for comparing the three-phase double-modulation wave with the double-carrier wave with the same phase to generate switching signals for driving all power switches of the T-type three-level inverter.
8. An apparatus comprising a memory storing a computer program and a processor that when executing the computer program implements the multi-target hybrid modulation method of any one of claims 1-6.

Description

Multi-target hybrid modulation method, system and equipment for T-shaped three-level inverter Technical Field The invention belongs to the technical field of electronic power, and particularly relates to a multi-target hybrid modulation method, system and equipment of a T-shaped three-level inverter. Background In the field of electric automobile driving application, a T-shaped three-level inverter is becoming a preferred inverter topology for electric automobile driving by virtue of the prominent advantages of low output voltage harmonic, small switching stress and the like. However, the two-level topology is changed into the three-level topology, the number of switching tubes is increased, the complexity of a control algorithm is remarkably improved, and meanwhile, various problems are brought, and particularly the problems are more prominent and troublesome under the condition of extremely low rotating speed. When the rotating speed is extremely low, the T-shaped three-level inner tube heats far higher than the outer tube, and the inner tube is easier to overheat and damage due to serious unbalanced heating. The dc side capacitance of the electric vehicle is small, and it becomes more difficult to balance the neutral point potential in addition to an extremely low modulation degree. At low rotational speeds, serious distortion will occur in the PMSM (permanent magnet synchronous motor ) stator current, which is also a great challenge for stable operation of the motor at very low rotational speeds. How to control the fluctuation of the midpoint potential in the minimum range under the conditions of extremely low modulation degree and small direct current side capacitance, and balance the heating of the inner tube and the outer tube and optimize the stator current waveform quality is an important problem with practical engineering value. In the conventional modulation algorithm of DPWM (discontinuous pulse width modulation ), the modulation algorithm of DPWM1 (clamping the voltage maximum phase to positive bus P) and DPWM3 (clamping the voltage minimum phase to negative bus N) can effectively reduce the inner tube loss, but can result in insufficient neutral-point potential balancing capability. VSVPWM (virtual space vector pulse width modulation ) has excellent neutral potential balancing capability and current harmonic performance, but does not perform well in balancing heating of inner and outer tubes. The main method for balancing the midpoint potential and reducing the switching loss at present is a mixed modulation method based on DPWM1 and DPWM3, wherein the method uses two modulation algorithms of DPWM1 and DPWM3 which act on midpoint potential offset in opposite directions, and the midpoint potential offset is controlled within an acceptable range by adopting a hysteresis switching mode. However, the above method has the following disadvantages: 1. only two modes are used for switching, so that the effect on neutral point potential balance is limited, and the effect is poor in a motor driving scene with small capacitance and extremely low rotating speed. 2. The THD of the output current is larger, and only two modulation modes, namely DPWM1 and DPWM3, are used, so that one clamping mode is absent in modulation, and the output current is severely distorted. This distortion effect is more pronounced, especially at very low modulation levels. Disclosure of Invention The invention aims to provide a multi-target hybrid modulation method, a system and equipment of a T-shaped three-level inverter, so as to solve the problem that the internal power switch loss is unbalanced, and the three types of neutral point potential fluctuation at the direct current side and output current waveform quality are difficult to simultaneously consider under the working condition of extremely low modulation degree (corresponding to extremely low-speed operation of a driving load) of the T-shaped three-level inverter. The invention realizes the above purpose through the following technical scheme: in a first aspect, the present invention provides a multi-target hybrid modulation method of a T-type three-level inverter, where when a fundamental modulation ratio of a three-phase sinusoidal modulation voltage is lower than a first threshold value, the method includes: Determining a maximum phase, an intermediate phase and a minimum phase of three-phase sinusoidal modulation voltage, respectively determining a common mode voltage corresponding to a DPWM1 mode of clamping the maximum phase to a positive bus and a DPWM3 mode of clamping the minimum phase to a negative bus, and generating two groups of three-phase modulation waves; Determining a duty ratio according to the modulation wave, and determining theoretical midpoint currents of the DPWM1 mode and the DPWM3 mode by combining phase currents; introducing zero level into the middle phase or the minimum phase in the DPWM1 mode to obtain a first midpoint current and a second m