Multi-objective hybrid modulation method, system and device for t-type three-level inverter

Abstract

The application belongs to the technical field of electronic power, and particularly relates to a multi-target hybrid modulation method, system and device of a T-type three-level inverter. The method firstly judges whether the inverter is operated at an extremely low modulation degree; if yes, the theoretical midpoint currents of DPWM1 and DPWM3 modes are calculated in parallel, and the extended midpoint currents corresponding to four hybrid modulation modes generated after the introduction of VSVPWM sequences in the two modes are calculated; then, according to the numerical relationship between the real-time calculated midpoint compensation current and the midpoint currents, the optimal hybrid modulation mode is dynamically selected or the basic DPWM mode is returned to; finally, three-phase double modulation waves are generated, and PWM signals for driving all power switches are output after carrier comparison. The application realizes multi-target optimization of the midpoint potential, switching loss and output waveform under extreme working conditions, and significantly improves the system stability and performance.

Description

Technical Field

[0001] This invention belongs to the field of electronic power technology, specifically relating to a multi-objective hybrid modulation method, system, and equipment for a T-type three-level inverter. Background Technology

[0002] In the field of electric vehicle drive applications, the T-type three-level inverter is becoming the preferred inverter topology for electric vehicle drives due to its outstanding advantages such as low output voltage harmonics and low switching stress. However, changing from a two-level to a three-level topology increases the number of switching transistors and significantly increases the complexity of the control algorithm, while also bringing many problems, especially under extremely low speed conditions. At extremely low speeds, the heat generated by the inner transistors in the T-type three-level inverter will be much higher than that of the outer transistors, and the severe uneven heating makes the inner transistors more prone to overheating and damage. Electric vehicles have small DC-side capacitors, and balancing the midpoint potential becomes even more difficult under extremely low voltage conditions. At low speeds, the stator current of a PMSM (Permanent Magnet Synchronous Motor) will exhibit severe distortion, which is a significant challenge for the stable operation of the motor under extremely low speed conditions. How to control the fluctuation of the midpoint potential to a minimum while balancing the heating of the inner and outer transistors and optimizing the stator current waveform quality under extremely low voltage conditions and small DC-side capacitors is an important problem with practical engineering value.

[0003] In traditional DPWM (Discontinuous Pulse Width Modulation) modulation, DPWM1 (clamping the phase with the highest voltage to the positive bus P) and DPWM3 (clamping the phase with the lowest voltage to the negative bus N) modulation algorithms can effectively reduce internal transistor losses, but they lead to insufficient midpoint potential balancing capability. VSVPWM (Virtual Space Vector Pulse Width Modulation) has excellent midpoint potential balancing capability and current harmonic performance, but it performs poorly in balancing internal and external transistor heat generation. Currently, the main method for balancing the midpoint potential and reducing switching losses is a hybrid modulation method based on DPWM1 and DPWM3. This method uses two modulation algorithms, DPWM1 and DPWM3, which have opposite effects on midpoint potential offset, and controls the midpoint potential offset within an acceptable range by employing hysteresis switching.

[0004] However, the above method has the following drawbacks:

[0005] First, relying solely on switching between the two modes has limited effect on balancing the midpoint potential, and its effect is poor in scenarios involving small capacitors and extremely low-speed motor drives.

[0006] Second, the output current THD is relatively high. Using only DPWM1 and DPWM3 modulation modes lacks a clamping mode during modulation, resulting in severe output current distortion. This distortion is particularly noticeable under extremely low voltage conditions. Summary of the Invention

[0007] The purpose of this invention is to provide a multi-objective hybrid modulation method, system, and device for T-type three-level inverters, in order to solve the problem that it is difficult to simultaneously achieve the following three aspects in T-type three-level inverters under extremely low voltage conditions (corresponding to extremely low speed operation of the driving load): unbalanced internal power switching losses, DC side midpoint potential fluctuations, and output current waveform quality.

[0008] The present invention achieves the above objectives through the following technical solutions:

[0009] In a first aspect, the present invention proposes a multi-objective hybrid modulation method for a T-type three-level inverter. When the fundamental modulation ratio of the three-phase sinusoidal modulation voltage is lower than a first threshold, the method includes:

[0010] Determine the maximum, intermediate, and minimum phases of the three-phase sinusoidal modulation voltage, determine the common-mode voltages corresponding to the DPWM1 mode where the maximum phase is clamped to the positive bus and the DPWM3 mode where the minimum phase is clamped to the negative bus, and generate two sets of three-phase modulation waves.

[0011] The duty cycle is determined based on the modulation wave, and the theoretical midpoint current of DPWM1 mode and DPWM3 mode is determined in combination with the phase current.

[0012] In DPWM1 mode, a zero level is introduced into the middle or minimum phase to obtain the first and second midpoint currents. In DPWM3 mode, a positive level is introduced into the maximum or middle phase to obtain the third and fourth midpoint currents.

[0013] Determine the midpoint compensation current based on the DC side parameters;

[0014] Based on the numerical relationship between the midpoint compensation current and each midpoint current, the corresponding hybrid modulation mode is selected.

[0015] A three-phase dual-modulation wave is generated based on the selected hybrid modulation mode;

[0016] The three-phase dual-modulation wave is compared with the in-phase dual carrier wave to generate switching signals that drive all power switches of the T-type three-level inverter.

[0017] Furthermore, the step of determining the common-mode voltages corresponding to DPWM1 mode and DPWM3 mode respectively, and generating two sets of three-phase modulation waves, includes:

[0018] Based on maximum phase modulation voltage and the minimum phase modulation voltage Determine the first common-mode voltage corresponding to the DPWM1 mode. and the second common-mode voltage corresponding to the DPWM3 mode. Including the following formulas:

[0019] ;

[0020] in, This is the DC bus voltage;

[0021] The first common-mode voltage Adding it to the three-phase sinusoidal modulation voltage, the first set of three-phase modulation waves in the DPWM1 mode is obtained. ; the second common-mode voltage Adding it to the three-phase sinusoidal modulation voltage, the second set of three-phase modulation waves in the DPWM3 mode is obtained. ; where x represents any one of the three phases.

[0022] Furthermore, the step of determining the duty cycle based on the modulation wave and determining the first midpoint current and the second midpoint current in conjunction with the phase current includes:

[0023] In DPWM1 mode, the first duty cycle is determined as follows:

[0024] ;

[0025] Calculate the theoretical midpoint current of DPWM1 mode As shown in the following formula:

[0026] ;

[0027] In DPWM3 mode, the second duty cycle is determined as follows:

[0028] ;

[0029] Calculate the theoretical midpoint current I in DPWM3 mode NP_N As shown in the following formula:

[0030] ;

[0031] in, .

[0032] Furthermore, the method also includes:

[0033] In the DPWM1 mode where the maximum phase is clamped to the positive bus, a zero level is introduced into the modulation wave of the intermediate or minimum phase to form a modulation wave that gives the phase three level states, which are referred to as P-MID mode and P-MIN mode respectively.

[0034] In the DPWM3 mode where the minimum phase is clamped to the negative bus, a high level is introduced into the modulation wave of the middle or maximum phase of the DPWM3 mode to form a modulation wave that gives the phase three level states, which are referred to as N-MID mode and N-MAX mode respectively.

[0035] P-MID mode, P-MIN mode, N-MID mode and N-MAX mode are used as the hybrid modulation modes.

[0036] Furthermore, by introducing a zero level into the middle or minimum phase in DPWM1 mode, the corresponding duty cycles and the first and second midpoint currents are obtained as follows:

[0037] ;

[0038] First midpoint current As shown in the following formula:

[0039] ;

[0040] ;

[0041] Second midpoint current As shown in the following formula:

[0042] ;

[0043] In DPWM3 mode, a positive level is introduced into the maximum phase or the middle phase to obtain the third and fourth midpoint currents, as shown in the following formula:

[0044] ;

[0045] Third midpoint current As shown in the following formula:

[0046] ;

[0047] Fourth midpoint current As shown in the following formula:

[0048] .

[0049] Furthermore, the determination of the midpoint compensation current based on the DC side parameters includes the following formula:

[0050] ;

[0051] Where C is the DC-side capacitance value. This represents the voltage difference between the upper and lower DC sides. The switching cycle.

[0052] Furthermore, the step of selecting the corresponding hybrid modulation mode based on the numerical relationship between the midpoint compensation current and each midpoint current includes...

[0053] Combining the midpoint current output values ​​corresponding to the P-MID, P-MIN, N-MID, and N-MAX modes and the theoretical midpoint current output value of the DPWM1 mode. and the theoretical midpoint current output value of the DPWM3 mode. Determine the compensation midpoint current. The numerical range, and select the execution mode according to the following rules:

[0054] If satisfied If so, then the P-MID mode, which introduces a zero level in the intermediate phase based on the DPWM1 mode, is selected;

[0055] If satisfied Then, the P-MIN mode, which introduces a zero level in the minimum phase based on the DPWM1 mode, is selected;

[0056] If satisfied Then, the N-MID mode, which introduces a positive level in the middle phase based on the DPWM3 mode, is selected;

[0057] If satisfied Then, the N-MAX mode, which introduces a positive level on the maximum phase based on the DPWM3 mode, is selected;

[0058] If the midpoint compensation current If any of the above rules are not met, the system enters the uncontrollable midpoint potential region; within this uncontrollable region, the theoretical midpoint current output value of the DPWM1 mode is compared. Midpoint compensation current The absolute value of the first difference, and the theoretical midpoint current output value of DPWM3 mode. Midpoint compensation current The absolute value of the second difference; if the absolute value of the first difference is less than or equal to the absolute value of the second difference, then select DPWM1 mode as the current modulation mode; otherwise, select DPWM3 mode as the current modulation mode.

[0059] Furthermore, the generation of the tri-phase dual-modulation wave according to the selected hybrid modulation mode includes:

[0060] Based on the selected hybrid modulation mode and the midpoint compensation current Calculate the duty cycle adjustment amount corresponding to the required voltage level. And based on the duty cycle adjustment amount The original duty cycle corresponding to the hybrid modulation mode is used to determine the final three-phase dual-modulation wave.

[0061] Secondly, the present invention proposes a multi-objective hybrid modulation system for a T-type three-level inverter, applied to realize the multi-objective hybrid modulation method described above, the system comprising:

[0062] The modulation signal generation unit is used to determine the maximum phase, intermediate phase and minimum phase of the three-phase sinusoidal modulation voltage, determine the common mode voltage corresponding to DPWM1 mode and DPWM3 mode respectively, and generate two sets of three-phase modulation waves.

[0063] The midpoint current calculation unit is used to determine the duty cycle based on the modulation wave and to determine the theoretical midpoint current of DPWM1 mode and DPWM3 mode in combination with the phase current; in DPWM1 mode, a zero level is introduced into the middle phase or the minimum phase to obtain the first and second midpoint currents; in DPWM3 mode, a positive level is introduced into the maximum phase or the middle phase to obtain the third and fourth midpoint currents.

[0064] The midpoint compensation calculation unit is used to determine the midpoint compensation current based on the DC side parameters.

[0065] The mode selection decision unit is used to select the corresponding hybrid modulation mode based on the numerical relationship between the midpoint compensation current and each midpoint current.

[0066] A dual-modulation wave generation unit is used to generate a three-phase dual-modulation wave according to the selected hybrid modulation mode;

[0067] The PWM signal generation unit is used to compare the three-phase dual-modulation wave with the in-phase dual carrier wave to generate switching signals that drive all power switches of the T-type three-level inverter.

[0068] Thirdly, the present invention proposes a device, characterized in that it includes a memory and a processor, wherein the memory stores a computer program, and the processor executes the computer program to implement the multi-target hybrid modulation method as described above.

[0069] The beneficial effects of this invention are as follows:

[0070] 1. This invention employs a modulation method that switches between two modes, DPWM1 and DPWM3, which effectively reduces the conduction loss of the inner tube, effectively balances the heat generation of the inner and outer tubes, significantly improves the reliability of system operation, and effectively extends the system lifespan.

[0071] 2. In one switching cycle, the present invention has three output levels for one phase, and introduces a hybrid modulation strategy of VSV+DPWM, which effectively reduces the degree of output current distortion, improves the current harmonic characteristics during extremely low speed operation, and makes the motor run more smoothly.

[0072] 3. This invention compensates for the midpoint current in real time, based on the midpoint compensation current. By dynamically selecting the appropriate modulation mode, the midpoint potential fluctuation of the T-type three-level inverter can be effectively suppressed, avoiding the risk of voltage distortion and device damage caused by midpoint potential imbalance, and further improving the stability and control accuracy of the system under extremely low-speed conditions.

[0073] 4. The multi-objective cooperative hybrid modulation strategy proposed in this invention comprehensively considers multiple key indicators such as switching loss, current distortion rate, and midpoint potential balance. Through refined mode switching logic and duty cycle calculation method, it achieves cooperative optimization of multiple objectives, enabling the T-type three-level permanent magnet synchronous motor drive system to simultaneously achieve high efficiency, low harmonics, and high reliability when operating at extremely low speeds, thus possessing strong engineering application value. Attached Figure Description

[0074] Figure 1 This is a schematic flowchart of the multi-target hybrid modulation method in this invention;

[0075] Figure 2 This is a topology diagram of a T-type inverter driving a PMSM in this invention;

[0076] Figure 3 This is another flowchart illustrating the multi-target hybrid modulation method of the present invention;

[0077] Figure 4 This is a schematic diagram of the dual-modulation wave dual-carrier comparison in this invention;

[0078] Figure 5 This is a schematic diagram of the switching sequence of the P-MIN mode in this invention;

[0079] Figure 6 This is a schematic diagram of the switching sequence of the P-MID mode in this invention;

[0080] Figure 7 This is a schematic diagram of the switching sequence in the N-MAX mode of this invention;

[0081] Figure 8 This is a schematic diagram of the switching sequence of the N-MID mode in this invention;

[0082] Figure 9 This is a schematic diagram of the controllable region of the midpoint potential in the P-MIN mode of this invention;

[0083] Figure 10 This is a schematic diagram of the controllable region of the midpoint potential in the P-MID mode of the present invention;

[0084] Figure 11 This is a schematic diagram of the controllable region of the midpoint potential in the N-MAX mode of this invention;

[0085] Figure 12 This is a schematic diagram of the controllable region of the midpoint potential in the N-MID mode of the present invention;

[0086] Figure 13 This is a schematic diagram of the controllable region of the midpoint potential under the hybrid modulation mode in this invention;

[0087] Figure 14 This is a system block diagram of the multi-target hybrid modulation system in this invention. Detailed Implementation

[0088] The present application will now be described in further detail with reference to the accompanying drawings. It should be noted that the following specific embodiments are only used to further illustrate the present application and should not be construed as limiting the scope of protection of the present application. Those skilled in the art can make some non-essential improvements and adjustments to the present application based on the above application content.

[0089] The well-known technical terms used in this disclosure are explained as follows:

[0090] DPWM stands for Discontinuous Pulse Width Modulation. It is a modulation technique that injects a specific zero-sequence component (common-mode voltage) into a three-phase sinusoidal modulation wave, causing the voltage of one phase of the three phases to be clamped to the positive or negative DC bus during a single switching cycle. This keeps the power switch of that phase arm in a constant state (no switching action) for a period of time. Its main purpose is to reduce the switching losses of the system.

[0091] DPWM1 and DPWM3 are two specific implementation modes of DPWM. DPWM1 mode specifically refers to the modulation method that clamps the phase with the largest amplitude (maximum phase) of the current three-phase voltage to the positive DC bus. DPWM3 mode specifically refers to the modulation method that clamps the phase with the smallest amplitude (minimum phase) to the negative DC bus.

[0092] VSVPWM stands for Virtual Space Vector Pulse Width Modulation, a modulation strategy specifically designed for three-level or multi-level inverter topologies. It constructs a synthesized vector sequence within a single switching cycle that contributes zero or controllable net to the midpoint potential by synthesizing specific basic voltage vector pairs. Therefore, it inherently possesses excellent midpoint potential balancing capabilities while generating high-quality voltage waveforms and reducing output current harmonics.

[0093] Inner and outer switches: In a T-type three-level inverter topology, the outer switch specifically refers to the upper switching transistor in each phase arm that is directly connected between the DC positive bus and the output terminal (e.g., ...). Figure 2 S in A1 ), and the lower switching transistor (such as) directly connected between the DC negative bus and the output terminal. Figure 2 S in A4The inner tube (also known as the midpoint clamping tube) specifically refers to two switching tubes connected in series between the upper and lower outer tubes, with their midpoint connected to the DC side neutral point (e.g., ...). Figure 2 S in A2 and S A3 During the switching process, the current stress and loss characteristics of the inner and outer tubes are different.

[0094] This disclosure proposes a multi-objective hybrid modulation method. By setting the activation time and sequence of VSVPWM and DPWM, and utilizing the complementary advantages of the two modulation strategies, it simultaneously achieves multiple control objectives under extremely low-voltage conditions (corresponding to extremely low-speed load operation), such as high-precision balance of the DC side midpoint potential, loss balancing and heat generation improvement of the internal and external power switches of the inverter, and low harmonic distortion (THD) of the output current. Ultimately, this ensures the overall stability and high-performance operation of the drive system under extreme conditions.

[0095] Please combine Figure 2 This illustrates a typical topology for driving a PMSM using a T-type three-level inverter, as applied in this disclosure. The T-type three-level inverter is connected between a DC power supply and a three-phase permanent magnet synchronous motor. Its DC side consists of a positive bus (P), a negative bus (N), and its midpoint (O). Typically, two capacitors C1 and C2 connected in series support and filter the bus voltage. The midpoint O is the connection point of the two capacitors.

[0096] The inverter body consists of three phase arms: A, B, and C. Each phase arm is composed of four fully controlled power switching transistors. Taking phase A as an example, the four switching transistors are S... A1 S A2 S A3 S A4 Among them, S A1 The connection between the positive busbar (P) and the output terminal A is called the upper external tube; S A4 The section connected between the negative busbar (N) and the output terminal A is called the lower outer tube; S A2 and S A3 After being connected in series between the upper and lower outer tubes, with their midpoint connected to the DC side midpoint (O), these two tubes are collectively referred to as the inner tubes or midpoint clamping tubes. Phase B and Phase C have the same structure, each containing a switching transistor S. B1 -S B4 With S C1 -S C4 Therefore, all 12 power switches in the inverter need to be coordinated and controlled. The three-phase output terminals A, B, and C are connected to the three-phase stator windings of the permanent magnet synchronous generator, forming a closed loop.

[0097] The multi-objective hybrid modulation method described in this disclosure aims to generate and output precise PWM switching signals to the control electrodes (gates) of these 12 switching transistors, thereby controlling the sequence and timing of their on and off states. This results in the inverter outputting a three-phase voltage with three-level characteristics, low harmonic content, balanced midpoint potential, and optimized switching losses, driving the PMSM to operate smoothly and efficiently, especially under harsh conditions at extremely low speeds.

[0098] Please combine Figure 1 and Figure 3 One embodiment of this disclosure proposes a multi-objective hybrid modulation method for a T-type three-level inverter. This method aims to address the technical challenges faced by T-type three-level inverters under extremely low-voltage operating conditions (typically corresponding to extremely low-speed operation of loads such as permanent magnet synchronous motors), including unbalanced internal and external power switching losses, DC-side midpoint potential fluctuations, and difficulties in coordinating and optimizing output current harmonic distortion. By rationally arranging the working mechanisms of VSVPWM (Virtual Space Vector Pulse Width Modulation) and DPWM (Discontinuous Pulse Width Modulation), a multi-objective collaborative hybrid modulation strategy is constructed.

[0099] Specifically, when the fundamental modulation ratio (i.e., modulation index m) of the three-phase sinusoidal modulation voltage is lower than the first threshold, the system is determined to have entered the extremely low modulation index operating condition. The relationship between modulation index and rotational speed is as follows:

[0100] ;

[0101] in, Adjust the system to achieve the goal. This refers to the motor speed, measured in rpm. Let be the pole logarithm of PMSM. For PMSM Shaft inductor, for PMSM in coordinate system shaft current, The flux linkage is a permanent magnet. The duty cycle corresponding to a rotational speed of 50 rpm is considered the first threshold.

[0102] And perform the following steps:

[0103] S1: Determine the maximum phase, intermediate phase, and minimum phase of the three-phase sinusoidal modulation voltage, determine the common-mode voltage corresponding to the DPWM1 mode where the maximum phase is clamped to the positive bus and the DPWM3 mode where the minimum phase is clamped to the negative bus, and generate two sets of three-phase modulation waves.

[0104] Specifically, the three-phase sinusoidal modulation voltages are compared first. The instantaneous values ​​are used to determine the maximum phase modulation voltage with the largest amplitude. The intermediate phase modulation voltage with moderate amplitude And the minimum phase modulation voltage with the smallest amplitude Subsequently, based on the working principle of the T-type three-level inverter, the first common-mode voltage injected to achieve the maximum phase clamping in DPWM1 mode was calculated. And the second common-mode voltage required to inject for achieving minimum phase clamping in DPWM3 mode. The first common-mode voltage Adding this to the original three-phase modulation voltage yields the first set of three-phase modulation waves in DPWM1 mode. Similarly, the second common-mode voltage Adding this to the original three-phase modulation voltage yields the second set of three-phase modulation waves in DPWM3 mode. , where x represents any one of the three phases A, B, and C.

[0105] Step S1 includes the following sub-steps:

[0106] (1-1) Comparison The amplitude is determined to identify the maximum, intermediate, and minimum phases. This step is performed according to the following formula:

[0107] ;

[0108] in In order to adjust the system, , This represents the amplitude of the three-phase modulated wave. The expression is:

[0109] , This is the DC bus voltage.

[0110] (1-2) The division of the maximum phase, intermediate phase, and minimum phase is specifically carried out according to the rules in Table 1:

[0111] Table 1

[0112] ;

[0113] (1-3) Based on the maximum phase modulation voltage and the minimum phase modulation voltage Determine the first common-mode voltage corresponding to the DPWM1 mode. and the second common-mode voltage corresponding to the DPWM3 mode. Including the following formulas:

[0114] ;

[0115] (1-4) The first common-mode voltage Adding it to the three-phase sinusoidal modulation voltage, the first set of three-phase modulation waves in the DPWM1 mode is obtained. ; the second common-mode voltage Adding it to the three-phase sinusoidal modulation voltage, the second set of three-phase modulation waves in the DPWM3 mode is obtained. ;in, It represents any one of the three phases. ; as shown in the following formula:

[0116] ;

[0117] S2: Determine the duty cycle based on the modulation wave, and determine the theoretical midpoint current of DPWM1 mode and DPWM3 mode in combination with the phase current.

[0118] In this step, based on the first set of three-phase modulation waves obtained in step S1 Second group of three-phase modulated waves Using the carrier comparison principle (e.g., regular sampling method), the duty cycle of each phase output positive level, zero level, and negative level in DPWM1 mode is calculated respectively. ; and the corresponding duty cycle in DPWM3 mode. Simultaneously, the phase current corresponding to the current three-phase voltage is obtained. Then, based on the product of duty cycle and phase current, the theoretical contribution of DPWM1 mode to the DC-side midpoint current without introducing any additional sequence is calculated, i.e., the first theoretical midpoint current. ; and the second theoretical midpoint current corresponding to DPWM3 mode. .

[0119] In a preferred embodiment, determining the duty cycle based on the modulation wave and determining the first midpoint current and the second midpoint current in conjunction with the phase current includes:

[0120] In DPWM1 mode (maximum phase clamp to positive bus), the first duty cycle is determined as follows:

[0121] ;

[0122] Calculate the theoretical midpoint current of DPWM1 mode As shown in the following formula:

[0123] ;

[0124] In DPWM3 mode (minimum phase clamped to negative bus), the second duty cycle is determined as follows:

[0125] ;

[0126] Calculate the theoretical midpoint current of DPWM3 mode As shown in the following formula:

[0127] ;

[0128] in, .

[0129] S3: Construct a hybrid modulation model.

[0130] To enhance midpoint potential control and improve output waveform, this step introduces a VSVPWM sequence into the basic DPWM mode, constructing four hybrid modulation modes. Specifically:

[0131] In the DPWM1 mode with the maximum phase clamped to the positive bus, a zero-level sequence is actively introduced into the modulation wave of the intermediate phase based on the volt-second balance principle. This allows the phase to have three states within one switching cycle: positive level (2 level), zero level (1 level), and negative level (0 level). This constructed mode is denoted as P-MID mode. Falling and The P-MID modulation mode is used between them.

[0132] In DPWM1 mode where the maximum phase is clamped to the positive bus, a 0 level is introduced into the minimum phase, giving the minimum phase three levels: 2, 1, and 0. This modulation mode is denoted as P-MIN. Falling and The P-MIN modulation mode is used between them.

[0133] When the minimum phase is clamped to the negative bus, a 2-level signal is introduced into the intermediate phase, giving the intermediate phase three levels: 2, 1, and 0. This modulation mode is denoted as N-MID. Falling and The modulation mode of N-MID is used between them.

[0134] When the minimum phase is clamped to the negative bus, a 2-level signal is introduced into the maximum phase, giving the maximum phase three levels: 2, 1, and 0. This modulation mode is denoted as N-MAX. If... Falling and The modulation mode is N-MAX.

[0135] Thus, P-MID mode, P-MIN mode, N-MID mode, and N-MAX mode together constitute the set of hybrid modulation modes that can be selectively executed in this embodiment.

[0136] S4: Calculate the extended midpoint current corresponding to each hybrid modulation mode.

[0137] For the four hybrid modulation modes constructed in step S3, calculate the midpoint current corresponding to each mode after introducing the VSVPWM sequence. That is, in DPWM1 mode, a zero level is introduced into the middle or minimum phase to obtain the first and second midpoint currents, and in DPWM3 mode, a positive level is introduced into the maximum or middle phase to obtain the third and fourth midpoint currents.

[0138] In a preferred embodiment, a zero level is introduced into the middle phase or the minimum phase in DPWM1 mode, respectively, to obtain the corresponding duty cycles and the first and second midpoint currents as follows:

[0139] P-MID mode:

[0140] ;

[0141] In the formula These represent the duty cycles of the three-phase 1-level circuits in DPWM1 mode after introducing a zero-level signal in the minimum phase. This is the minimum phase modulation wave at this time;

[0142] First midpoint current As shown in the following formula:

[0143] ;

[0144] P-MIN mode:

[0145] ;

[0146] Second midpoint current As shown in the following formula:

[0147] ;

[0148] In DPWM3 mode, a positive level is introduced into the maximum phase or the middle phase to obtain the third and fourth midpoint currents, as shown in the following formula:

[0149] N-MID mode:

[0150] ;

[0151] In the formula These represent the duty cycles of the three-phase 1-level circuits after introducing a zero-level signal in the intermediate phase in DPWM3 mode. This is the intermediate phase modulation wave at this time;

[0152] Third midpoint current As shown in the following formula:

[0153] ;

[0154] N-MAX mode:

[0155] ;

[0156] In the formula These represent the duty cycles of the three-phase 1-level circuits in DPWM3 mode after introducing a zero-level signal on the maximum phase. This is the intermediate phase modulation wave at this time;

[0157] Fourth midpoint current As shown in the following formula:

[0158] .

[0159] S5: Determine the midpoint compensation current based on the DC side parameters.

[0160] This step involves detecting the capacitance C of the upper and lower filter capacitors on the DC side and the voltage difference between the upper and lower capacitors. And in conjunction with the system's switching cycle The required midpoint compensation current is calculated according to the preset relationship. The current It is a key decision variable that reflects the degree of midpoint potential imbalance in real time and drives the switching of modulation modes.

[0161] In a preferred embodiment, determining the midpoint compensation current based on DC-side parameters includes the following formula:

[0162] ;

[0163] Where C is the DC-side capacitance value. This represents the voltage difference between the upper and lower DC sides. The switching cycle.

[0164] S6: Based on the numerical relationship between the midpoint compensation current and each midpoint current, select the corresponding hybrid modulation mode.

[0165] In a preferred embodiment, the step of selecting a corresponding hybrid modulation mode based on the numerical relationship between the midpoint compensation current and each midpoint current includes...

[0166] Combining the midpoint current output values ​​corresponding to the P-MID, P-MIN, N-MID, and N-MAX modes and the theoretical midpoint current output value of the DPWM1 mode. and the theoretical midpoint current output value of the DPWM3 mode. Determine the compensation midpoint current. The numerical range, and select the execution mode according to the following rules:

[0167] If satisfied If so, then the P-MID mode, which introduces a zero level in the intermediate phase based on the DPWM1 mode, is selected;

[0168] If satisfied Then, the P-MIN mode, which introduces a zero level in the minimum phase based on the DPWM1 mode, is selected;

[0169] If satisfied Then, the N-MID mode, which introduces a positive level in the middle phase based on the DPWM3 mode, is selected;

[0170] If satisfied Then, the N-MAX mode, which introduces a positive level on the maximum phase based on the DPWM3 mode, is selected.

[0171] In P-MID modulation mode, the duty cycles of intermediate phase 2, 1, and 0 levels are respectively , The value of the midpoint current introduced at this time should be the same as... Equal to each other, the duty cycles of the three levels can be obtained according to the duty cycle relationship and the midpoint current relationship, and the three-phase dual-modulation wave in P-MID mode can be further calculated. and :

[0172] ;

[0173] Based on DPWM1, the intermediate phase introduces a duty cycle of... The 0-level sequence is called the P-MID mode. Its switching sequence is as follows: Figure 6 As shown, the introduced duty cycle Δd is specifically calculated according to the following formula:

[0174] ;

[0175] Mode These represent the intermediate phase load current, minimum phase load current, minimum phase 1 level duty cycle, and intermediate phase 1 level duty cycle, respectively. C is the DC-side capacitor value. This is a proportionality coefficient, which is obtained through trial and error based on actual application conditions. This represents the voltage difference between the upper and lower DC sides. The switching cycle.

[0176] like Figure 4 As shown, based on the carrier comparison rules, the expression for the three-phase dual-modulation wave in P-MID mode is calculated as follows:

[0177] ;

[0178] The other three modes Similar to the calculation method for three-phase dual-modulation waves, the switching sequence is as follows: Figures 5-8 As shown.

[0179] In P-MIN modulation mode, the duty cycles of intermediate phase 2, 1, and 0 levels are respectively , The value of the midpoint current introduced at this time should be the same as... Equal to each other, the duty cycles of the three levels can be obtained according to the duty cycle relationship and the midpoint current relationship. Further calculations yield the three-phase dual-modulation wave in P-MIN mode. and .

[0180] The formula for calculating the duty cycle in P-MIN mode is:

[0181] ;

[0182] Expression for a three-phase dual-modulation wave in P-MIN mode:

[0183] ;

[0184] In N-MID modulation mode, the duty cycles of intermediate phase 2, 1, and 0 levels are respectively , The value of the midpoint current introduced at this time should be the same as... Equal to each other, the duty cycles of the three levels can be obtained according to the duty cycle relationship and the midpoint current relationship, and the three-phase dual-modulation wave in N-MID mode can be further calculated. and .

[0185] The formula for calculating the duty cycle in N-MID mode is:

[0186] ;

[0187] Expression for a three-phase dual-modulation wave in N-MID mode:

[0188] ;

[0189] In N-MAX modulation mode, the duty cycles of intermediate phase 2, 1, and 0 levels are respectively , The value of the midpoint current introduced at this time should be the same as... Equal to each other, the duty cycles of the three levels can be obtained according to the duty cycle relationship and the midpoint current relationship. Further calculations yield the three-phase dual-modulation wave in N-MAX mode. and .

[0190] The formula for calculating the duty cycle in N-MAX mode is:

[0191] ;

[0192] Expression for a three-phase dual-modulation wave in N-MAX mode:

[0193] ;

[0194] If the midpoint compensation current If none of the above rules are met, that is:

[0195] ;

[0196] Then it enters the region where the midpoint potential is uncontrollable; within the region where it is uncontrollable, compare the theoretical midpoint current output value of DPWM1 mode. Midpoint compensation current The absolute value of the first difference, and the theoretical midpoint current output value of DPWM3 mode. Midpoint compensation current The absolute value of the second difference; if the absolute value of the first difference is less than or equal to the absolute value of the second difference, then select DPWM1 mode as the current modulation mode; otherwise, select DPWM3 mode as the current modulation mode.

[0197] Furthermore, to more clearly illustrate the midpoint compensation current in step S6... The physical meaning of mode selection Figures 9-13 This illustrates the region where the midpoint potential can be balanced in the hybrid modulation mode proposed in this disclosure. The vertical axis in the figure... This represents the normalized (per-unit) current to be compensated. For each hybrid modulation mode (P-MID, P-MIN, N-MID, N-MAX), the controllable current range capable of stabilizing the midpoint potential has clearly defined upper and lower boundaries. The upper boundary of the controllable region is determined by the following formula:

[0198] ;

[0199] in This refers to the absolute value of the minimum compensation current that can be balanced under this modulation mode.

[0200] The lower boundary of the controllable region is calculated according to the following formula:

[0201] ;

[0202] in This refers to the absolute value of the maximum compensation current that can be balanced under this modulation mode.

[0203] S7: Generate a three-phase dual-modulation wave based on the selected hybrid modulation mode.

[0204] Based on the selected hybrid modulation mode and the midpoint compensation current Calculate the duty cycle adjustment amount corresponding to the required voltage level. And based on the duty cycle adjustment amount The original duty cycle corresponding to the hybrid modulation mode is used to determine the final three-phase dual-modulation wave.

[0205] S8: Compare the three-phase dual-modulation wave with the in-phase dual carrier wave to generate switching signals that drive all power switches of the T-type three-level inverter.

[0206] Optional, combined Figure 4 Based on the modulation wave expressions of the four modes and compared with the in-phase carrier waves, the drive signals for the 12 switching transistors can be obtained. Figure 4 middle This represents a dual-modulation wave in any phase of a three-phase system. This indicates a dual-carrier configuration with an amplitude of [value missing]. ; This is the carrier period, also known as the switching period.

[0207] In a switching cycle Within this range, the modulation voltage can be considered a constant value, according to... Figure 2 The topology diagram of the T-type inverter is used for switching signal allocation, and the specific comparison logic is as follows:

[0208] when and At that time, the inverter bridge arm outputs a 2-level signal. The sequential switch signals are 1100, where 1 represents the corresponding switch being turned on and 0 represents the corresponding switch being turned off.

[0209] when and When the inverter bridge arm outputs a 1 level, press... The sequential switch signals are 0110.

[0210] when and When the inverter bridge arm outputs a 1 level, press... The sequential switch signals are 0110.

[0211] when and At that time, the inverter bridge arm outputs a 0 level, and press... The sequential switch signals are 0011.

[0212] The corresponding switching signal is obtained by modulation according to the above rules, and then sent to the gate of the corresponding switching device through the driving circuit to realize the control of the entire system.

[0213] Understandably, when applied to scenarios involving extremely low-speed operation of loads such as permanent magnet synchronous motors, this disclosure aims to reduce the heating of the transverse tube at extremely low speeds. It selects two modulation modes, DPWM1 and DPWM3, for switching. To enhance the midpoint potential balance and reduce current distortion, a 0-level is introduced into the middle or minimum phase of the DPWM1 mode, resulting in three level states (VSVPWM sequence) within one carrier cycle. After adding the VSVPWM sequence to the original logic, four modulation modes are obtained: a hybrid VSVPWM and DPWM modulation. Each modulation mode is based on the DC-side current to be compensated. Whether it is within the controllable range of this modulation mode is the entry criterion. If the voltage is not within the controllable region of the midpoint potential of any modulation mode, it is considered to have entered the uncontrollable region, and a mode that can provide the same voltage is selected. The modulation mode of the closest midpoint current is obtained. After obtaining the modulation mode, the switching signals of the 12 switching transistors are obtained by comparing the dual-carrier dual-modulation waves, thereby realizing the control of the T-type three-level inverter.

[0214] Combination Figure 14 Another embodiment of this disclosure proposes a multi-objective hybrid modulation system for a T-type three-level inverter, which is applied to implement the multi-objective hybrid modulation method as described in the above embodiments. The system includes a modulation signal generation unit 10, a midpoint current calculation unit 20, a midpoint compensation calculation unit 30, a mode selection decision unit 40, a dual modulation wave generation unit 50, and a PWM signal generation unit 60.

[0215] The modulation signal generation unit 10 is used to determine the maximum phase, intermediate phase and minimum phase of the three-phase sinusoidal modulation voltage, determine the common mode voltage corresponding to DPWM1 mode and DPWM3 mode respectively, and generate two sets of three-phase modulation waves.

[0216] Specifically, the unit receives a three-phase voltage command and determines the maximum, intermediate, and minimum phases of the voltage by comparison. Based on the maximum and minimum phase voltages, it calculates a first common-mode voltage for clamping the maximum phase to the positive bus and a second common-mode voltage for clamping the minimum phase to the negative bus. Subsequently, these two common-mode voltages are added to the original three-phase voltages to generate a first set of three-phase modulation waves corresponding to DPWM1 mode and a second set of three-phase modulation waves corresponding to DPWM3 mode.

[0217] The midpoint current calculation unit 20 is used to determine the duty cycle based on the modulation wave and, in conjunction with the phase current, determine the theoretical midpoint current for DPWM1 mode and DPWM3 mode. In DPWM1 mode, a zero level is introduced into the middle phase or the minimum phase to obtain the first and second midpoint currents. The first midpoint current is calculated by introducing a zero level into the middle phase in DPWM1 mode and taking the extreme case where the duty cycle of the middle phase 1 level is 0 (at which point the introduced zero level duty cycle is the largest). In this case, the first midpoint current is calculated. In DPWM3 mode, a positive level is introduced into the maximum phase or the middle phase to obtain the third and fourth midpoint currents. The calculation methods for the third and fourth midpoint currents are similar to those for the first and second midpoint currents.

[0218] Specifically, this unit receives the two sets of modulation waves and the three-phase currents. First, it calculates the duty cycle of each phase output level in DPWM1 and DPWM3 modes based on the two sets of modulation waves. Then, combining the corresponding phase currents and duty cycles, it calculates the theoretical midpoint current in DPWM1 mode and the theoretical midpoint current in DPWM3 mode.

[0219] Furthermore, this unit simulates, based on the DPWM1 mode, introducing zero-level sequences into the middle and minimum phases respectively (corresponding to the construction of P-MID and P-MIN modes), and calculating the corresponding first and second extended midpoint currents based on the adjusted duty cycle and phase current. Similarly, based on the DPWM3 mode, it simulates, based on the maximum and middle phases respectively, introducing positive-level sequences into the maximum and middle phases respectively (corresponding to the construction of N-MAX and N-MID modes), and calculating the corresponding third and fourth extended midpoint currents.

[0220] The midpoint compensation calculation unit 30 is used to determine the midpoint compensation current based on the DC side parameters. This unit detects the voltage difference between the upper and lower support capacitors on the DC side in real time, and calculates the midpoint compensation current required to balance the midpoint potential by combining the capacitor value and the system switching cycle. This current value directly reflects the degree of imbalance of the current midpoint potential and the intensity of the required correction.

[0221] The mode selection decision unit 40 is used to select the corresponding hybrid modulation mode based on the numerical relationship between the midpoint compensation current and each midpoint current.

[0222] Specifically, this unit receives the midpoint compensation current from unit 30, and two theoretical midpoint currents and four extended midpoint currents from unit 20. An interval judgment logic is used: the real-time midpoint compensation current value is compared sequentially with the four numerical intervals corresponding to the first to fourth midpoint currents and the theoretical midpoint currents. Based on the interval position of the midpoint compensation current, the corresponding hybrid modulation mode is selected, thus making the extended midpoint current equal to the compensation current. Depending on which interval the midpoint compensation current falls into, the corresponding P-MID, P-MIN, N-MID, or N-MAX hybrid modulation mode is selected as the output. If the midpoint compensation current does not fall into any preset interval, it is determined to have entered the uncontrollable midpoint potential region; at this time, by comparing the closeness of the midpoint compensation current to the theoretical midpoint currents of the two basic DPWM modes, the closest DPWM1 or DPWM3 mode is selected as the output.

[0223] The dual-modulation wave generation unit 50 is used to generate a three-phase dual-modulation wave according to the selected hybrid modulation mode; this unit receives the mode selection signal, the midpoint compensation current, and related raw data. Based on the selected specific modulation mode and the adjustment intensity required to accurately match the midpoint compensation current, the duty cycle adjustment amount of the VSVPWM sequence to be introduced is calculated. Based on this adjustment amount, the original duty cycle distribution corresponding to the selected mode is corrected, and finally, a three-phase dual-modulation wave for comparison with the carrier wave is reconstructed and generated.

[0224] The PWM signal generation unit 60 is used to compare the three-phase dual-modulation wave with the in-phase dual carrier wave to generate switching signals that drive all power switches of the T-type three-level inverter.

[0225] Specifically, this unit receives the generated three-phase dual-modulation wave. By comparing the dual-modulation wave of each phase with a pair of in-phase and out-of-phase positive load waves in real time, a defined logic level is generated based on the comparison result. According to a preset mapping rule, these logic levels are combined and converted into 12 PWM drive signals that directly control the on / off state of the four power switches (upper outer switch, lower outer switch, and two inner switches) of each phase. These signals, after being amplified by subsequent drive circuitry, are applied to the gates of each power device in the inverter, achieving precise control of the output voltage.

[0226] It should be noted that each module in the above-described multi-target hybrid modulation system corresponds to a step in implementing the multi-target hybrid modulation method in the above embodiments. The instances and application scenarios implemented by multiple modules and their corresponding steps are the same, but are not limited to the content disclosed in the above embodiments.

[0227] Another embodiment of this disclosure provides an apparatus including a memory and a processor, the memory storing a computer program, the processor executing the computer program to implement the multi-target hybrid modulation method as described in the above embodiments.

[0228] It is worth noting that the device specifically refers to a controller or control unit that generates and outputs PWM control signals. In a preferred scenario, the permanent magnet synchronous motor serves as the driven load, which is the application scenario and beneficiary of this disclosure; however, it is not itself a component of the device claimed in this embodiment. The claims protect the control device for implementing the multi-objective hybrid modulation method.

[0229] Those skilled in the art will recognize that the units and algorithm steps of the various examples described in conjunction with the embodiments disclosed herein can be implemented in electronic hardware, or a combination of computer software and electronic hardware. Whether these functions are implemented in hardware or software depends on the specific application and design constraints of the technical solution. Those skilled in the art can use different methods to implement the described functions for each specific application, but such implementation should not be considered beyond the scope of this application.

[0230] In addition, the functional modules in the various embodiments of this application can be integrated into one processing unit, or each unit can exist physically separately, or two or more units can be integrated into one unit.

[0231] The above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of this application.

Claims

1. A multi-objective hybrid modulation method for a T-type three-level inverter, characterized in that, When the fundamental modulation ratio of the three-phase sinusoidal modulation voltage is lower than a first threshold, the method includes: Determine the maximum, intermediate, and minimum phases of the three-phase sinusoidal modulation voltage, determine the common-mode voltages corresponding to the DPWM1 mode where the maximum phase is clamped to the positive bus and the DPWM3 mode where the minimum phase is clamped to the negative bus, and generate two sets of three-phase modulation waves. The duty cycle is determined based on the modulation wave, and the theoretical midpoint current of DPWM1 mode and DPWM3 mode is determined in combination with the phase current. In DPWM1 mode, a zero level is introduced into the middle or minimum phase to obtain the first and second midpoint currents. In DPWM3 mode, a positive level is introduced into the maximum or middle phase to obtain the third and fourth midpoint currents. Determine the midpoint compensation current based on the DC side parameters; Based on the numerical relationship between the midpoint compensation current and each midpoint current, the corresponding hybrid modulation mode is selected. A three-phase dual-modulation wave is generated based on the selected hybrid modulation mode; The three-phase dual-modulation wave is compared with the in-phase dual carrier wave to generate switching signals that drive all power switches of the T-type three-level inverter. In the DPWM1 mode where the maximum phase is clamped to the positive bus, a zero level is introduced into the modulation wave of the intermediate or minimum phase to form a modulation wave that gives the phase three level states, which are referred to as P-MID mode and P-MIN mode respectively. In the DPWM3 mode where the minimum phase is clamped to the negative bus, a high level is introduced into the modulation wave of the middle or maximum phase of the DPWM3 mode to form a modulation wave that gives the phase three level states, which are referred to as N-MID mode and N-MAX mode respectively. P-MID mode, P-MIN mode, N-MID mode, and N-MAX mode are used as the hybrid modulation modes; The step of selecting the corresponding hybrid modulation mode based on the numerical relationship between the midpoint compensation current and each midpoint current includes: combining the midpoint current output values ​​corresponding to the P-MID mode, P-MIN mode, N-MID mode, and N-MAX mode. and the theoretical midpoint current output value of the DPWM1 mode. I NP_P and the theoretical midpoint current output value of the DPWM3 mode. I NP_N Determine the midpoint compensation current. I CMP The numerical range, and select the execution mode according to the following rules: If satisfied If so, then the P-MID mode, which introduces a zero level in the intermediate phase based on the DPWM1 mode, is selected; If satisfied Then, the P-MIN mode, which introduces a zero level in the minimum phase based on the DPWM1 mode, is selected; If satisfied Then, the N-MID mode, which introduces a positive level in the middle phase based on the DPWM3 mode, is selected; If satisfied Then, the N-MAX mode, which introduces a positive level on the maximum phase based on the DPWM3 mode, is selected; If the midpoint compensation current I CMP If any of the above rules are not met, the system enters the uncontrollable midpoint potential region; within this uncontrollable region, the theoretical midpoint current output value of the DPWM1 mode is compared. I NP_P Midpoint compensation current I CMP The absolute value of the first difference, and the theoretical midpoint current output value of DPWM3 mode. I NP_N With midpoint compensation current I CMP The absolute value of the second difference; if the absolute value of the first difference is less than or equal to the absolute value of the second difference, then select DPWM1 mode as the current modulation mode; otherwise, select DPWM3 mode as the current modulation mode.

2. The multi-objective hybrid modulation method for a T-type three-level inverter according to claim 1, characterized in that, The process of determining the common-mode voltages corresponding to DPWM1 and DPWM3 modes and generating two sets of three-phase modulation waves includes: based on the maximum phase modulation voltage. u max and the minimum phase modulation voltage u min Determine the first common-mode voltage corresponding to the DPWM1 mode. u zvsP and the second common-mode voltage corresponding to the DPWM3 mode. u zvsN Including the following formulas: ; in, This is the DC bus voltage; The first common-mode voltage Adding it to the three-phase sinusoidal modulation voltage, the first set of three-phase modulation waves in the DPWM1 mode is obtained. ; the second common-mode voltage Adding it to the three-phase sinusoidal modulation voltage, the second set of three-phase modulation waves in the DPWM3 mode is obtained. ;in, It represents any one of the three phases.

3. The multi-objective hybrid modulation method for a T-type three-level inverter according to claim 2, characterized in that, The step of determining the duty cycle based on the modulation wave and determining the first midpoint current and the second midpoint current in conjunction with the phase current includes: in DPWM1 mode, determining the first set of duty cycles as follows: ; Calculate the theoretical midpoint current of DPWM1 mode I NP_P As shown in the following formula: ; in, This refers to the duty cycle of the three-phase 1-level circuit in DPWM1 mode. These are the three-phase load currents; In DPWM3 mode, the second duty cycle is determined as follows: ; Calculate the theoretical midpoint current of DPWM3 mode As shown in the following formula: ; in, .

4. The multi-objective hybrid modulation method for a T-type three-level inverter according to claim 1, characterized in that, By introducing a zero level into the middle or minimum phase in DPWM1 mode, the corresponding duty cycles and the first and second midpoint currents are obtained as follows: ; In the formula These represent the duty cycles of the three-phase 1-level circuits in DPWM1 mode after introducing a zero-level signal in the minimum phase. This is the minimum phase modulation wave at this time; First midpoint current As shown in the following formula: ; In the formula These represent the duty cycles of the three-phase 1-level circuits after introducing a zero-level signal in the middle phase of the DPWM1 mode. This is the intermediate phase modulation wave at this time; the second midpoint current. As shown in the following formula: ; In DPWM3 mode, a positive level is introduced into the maximum phase or the middle phase to obtain the third and fourth midpoint currents, as shown in the following formula: ; In the formula These represent the duty cycles of the three-phase 1-level circuits after introducing a zero-level signal in the intermediate phase in DPWM3 mode. This is the intermediate phase modulation wave at this time; the third midpoint current. As shown in the following formula: ; In the formula These represent the duty cycles of the three-phase 1-level circuits in DPWM3 mode after introducing a zero-level signal on the maximum phase. This is the intermediate phase modulation wave at this time; the fourth midpoint current. As shown in the following formula: 。 5. The multi-objective hybrid modulation method for a T-type three-level inverter according to claim 4, characterized in that, The determination of the midpoint compensation current based on DC side parameters includes the following formula: ; in, C This is the DC-side capacitance value. This represents the voltage difference between the upper and lower DC sides. The switching cycle.

6. The multi-objective hybrid modulation method for a T-type three-level inverter according to claim 5, characterized in that, The generation of a tri-phase dual-modulation wave according to the selected hybrid modulation mode includes: Based on the selected hybrid modulation mode and the midpoint compensation current Calculate the duty cycle adjustment amount corresponding to the required voltage level. And based on the duty cycle adjustment amount Δ d The original duty cycle corresponding to the hybrid modulation mode is used to determine the final three-phase dual-modulation wave.

7. A multi-objective hybrid modulation system for a T-type three-level inverter, used to implement the multi-objective hybrid modulation method as described in any one of claims 1-6, characterized in that, The system includes: The modulation signal generation unit is used to determine the maximum phase, intermediate phase and minimum phase of the three-phase sinusoidal modulation voltage, determine the common mode voltage corresponding to DPWM1 mode and DPWM3 mode respectively, and generate two sets of three-phase modulation waves. The midpoint current calculation unit is used to determine the duty cycle based on the modulation wave and to determine the theoretical midpoint current of DPWM1 mode and DPWM3 mode in combination with the phase current; in DPWM1 mode, a zero level is introduced into the middle phase or the minimum phase to obtain the first and second midpoint currents; in DPWM3 mode, a positive level is introduced into the maximum phase or the middle phase to obtain the third and fourth midpoint currents. The midpoint compensation calculation unit is used to determine the midpoint compensation current based on the DC side parameters. The mode selection decision unit is used to select the corresponding hybrid modulation mode based on the numerical relationship between the midpoint compensation current and each midpoint current. A dual-modulation wave generation unit is used to generate a three-phase dual-modulation wave according to the selected hybrid modulation mode; The PWM signal generation unit is used to compare the three-phase dual-modulation wave with the in-phase dual carrier wave to generate switching signals that drive all power switches of the T-type three-level inverter.

8. A device, characterized in that, It includes a memory and a processor, the memory storing a computer program, and the processor executing the computer program to implement the multi-target hybrid modulation method according to any one of claims 1-6.

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