Soft switching control method, device and equipment of three-level converter and storage medium

Abstract

The application discloses a kind of soft switching control method, device, equipment and storage medium of three-level converter.Therein, the method comprises: obtaining the original reference signal corresponding to the multi-phase alternating side, the instantaneous voltage value corresponding to the multiple alternating phase lines of the multi-phase alternating side respectively, and the carrier signal of three-level converter;Determine the zero sequence voltage component based on the instantaneous voltage value corresponding to the multiple alternating phase lines respectively;Based on the zero sequence voltage component, the original reference signal is amplitude translated to obtain target reference signal;Based on target reference signal and carrier signal, generate target pulse width modulation signal;Based on target pulse width modulation signal, to three-level converter is carried out soft switching control.The present application solves the technical problem that the accuracy of soft switching control of three-level converter in related art is low.

Description

Technical Field

[0001] This invention relates to the field of electrical technology, and more specifically, to a soft-switching control method, apparatus, device, and storage medium for a three-level converter. Background Technology

[0002] Three-level converters are widely used in medium- and high-voltage, high-power applications due to their advantages such as low harmonics and low device voltage stress. Zero-voltage turn-on technology reduces losses by turning on the switching transistors when the drain-source voltage is clamped to zero, achieved through the reversal of the bridge arm current polarity. Currently, non-auxiliary circuit soft-switching technology has significant limitations. The triangular current mode causes the switching frequency to fluctuate drastically within the power frequency cycle, approaching infinity near the zero-crossing point, posing challenges to digital control and making it difficult to directly apply to three-phase coupled systems. Frequency conversion prediction methods are affected by three-phase coupling, resulting in limited prediction accuracy and a tendency to cause excessive soft switching of non-dominant phases, generating excessive current ripple and increasing conduction losses. The trapezoidal current mode, near the zero-crossing point of the reference signal, suffers from a small voltage amplitude and insufficient phase shift adjustment margin, making it difficult to generate sufficient circulating current to achieve polarity reversal, creating a soft-switching blind zone. This leads to hard-switching operation of devices, affecting overall efficiency and resulting in low accuracy in soft-switching control of three-level converters.

[0003] There is currently no effective solution to the above problems. Summary of the Invention

[0004] This invention provides a soft-switching control method, apparatus, device, and storage medium for a three-level converter, to at least solve the technical problem of low accuracy in soft-switching control of three-level converters in related technologies.

[0005] According to one aspect of the present invention, a soft-switching control method for a three-level converter is provided. The three-level converter includes multiple phase line converter modules. A first terminal of each phase line converter module is connected to a positive DC line, a second terminal of each phase line converter module is connected to a negative DC line, a third terminal of each phase line converter module is connected to a target midpoint, the target midpoint representing the midpoint of the potential difference between the positive and negative DC lines, and a fourth terminal of each phase line converter module is connected to an AC phase line corresponding to the multi-phase AC side. The method includes: acquiring an original reference signal corresponding to the multi-phase AC side, instantaneous voltage values ​​corresponding to the multiple AC phase lines of the multi-phase AC side, and a carrier signal of the three-level converter; determining a zero-sequence voltage component based on the instantaneous voltage values ​​corresponding to the multiple AC phase lines; performing amplitude shifting on the original reference signal based on the zero-sequence voltage component to obtain a target reference signal; generating a target pulse width modulation signal based on the target reference signal and the carrier signal; and performing soft-switching control on the three-level converter based on the target pulse width modulation signal.

[0006] In this embodiment of the invention, determining the zero-sequence voltage component based on the instantaneous voltage values ​​corresponding to multiple AC phase lines includes: sorting the instantaneous voltage values ​​corresponding to multiple AC phase lines to obtain a voltage sorting sequence; determining a first voltage value, a second voltage value, and a third voltage value in the voltage sorting sequence, wherein the first voltage value is greater than the second voltage value, and the second voltage value is greater than the third voltage value; and determining the zero-sequence voltage component based on the first voltage value, the second voltage value, and the third voltage value.

[0007] In this embodiment of the invention, the zero-sequence voltage component is either a positive zero-sequence voltage component or a negative zero-sequence voltage component. Determining the zero-sequence voltage component based on a first voltage value, a second voltage value, and a third voltage value includes: determining the absolute value corresponding to the first voltage value to obtain a first absolute value, and determining the absolute value corresponding to the third voltage value to obtain a second absolute value; generating a positive zero-sequence voltage component when the first absolute value is greater than the second absolute value and the second voltage value is less than a first preset threshold, or when the first absolute value is less than or equal to the second absolute value and the second voltage value is less than or equal to the second preset threshold, wherein the second preset threshold and the first preset threshold are opposites of each other; generating a negative zero-sequence voltage component when the first absolute value is less than or equal to the second absolute value and the second voltage value is greater than the second preset threshold, or when the first absolute value is greater than the second absolute value and the second voltage value is greater than or equal to the first preset threshold.

[0008] In this embodiment of the invention, the method further includes: generating a positive zero-sequence voltage component based on a first preset boundary value and a first voltage value; or, generating a negative zero-sequence voltage component based on a second preset boundary value and a third voltage value.

[0009] In this embodiment of the invention, generating a target pulse width modulation signal based on a target reference signal and a carrier signal includes: obtaining the phase shift angle corresponding to the three-level converter; determining the carrier start phase value based on the target reference signal and the phase shift angle; and generating the target pulse width modulation signal based on the carrier start phase value and the carrier signal.

[0010] In this embodiment of the invention, obtaining the phase shift angle corresponding to the three-level converter includes: obtaining the target potential difference between the positive DC line and the negative DC line, the output current corresponding to each of the multiple phase line converter modules, the reverse bias current of the three-level converter, the inductance of the coupling inductor of the three-level converter, and the target fixed-frequency switching period, wherein the target fixed-frequency switching period is the period of the carrier signal; determining the first product of the target potential difference and the target fixed-frequency switching period; and determining the phase shift angle based on the output current, reverse bias current, inductance, and the first product corresponding to each of the multiple phase line converter modules.

[0011] According to another aspect of the present invention, a soft-switching control device for a three-level converter is also provided. The three-level converter includes multiple phase line converter modules. A first end of a phase line converter module is connected to a positive DC line, a second end of a phase line converter module is connected to a negative DC line, a third end of a phase line converter module is connected to a target midpoint, the target midpoint representing the midpoint of the potential difference between the positive and negative DC lines, and a fourth end of a phase line converter module is connected to the corresponding AC phase line of the multi-phase AC side. The device includes: an acquisition module for acquiring an original reference signal corresponding to the multi-phase AC side, instantaneous voltage values ​​corresponding to the multiple AC phase lines of the multi-phase AC side, and a carrier signal of the three-level converter; a first determination module for determining a zero-sequence voltage component based on the instantaneous voltage values ​​corresponding to the multiple AC phase lines; a second determination module for amplitude shifting the original reference signal based on the zero-sequence voltage component to obtain a target reference signal; a generation module for generating a target pulse width modulation signal based on the target reference signal and the carrier signal; and a control module for performing soft-switching control on the three-level converter based on the target pulse width modulation signal.

[0012] In this embodiment of the invention, the first determining module is further configured to sort the instantaneous voltage values ​​corresponding to the multiple AC phase lines respectively to obtain a voltage sorting sequence; determine the first voltage value, the second voltage value and the third voltage value in the voltage sorting sequence, wherein the first voltage value is greater than the second voltage value and the second voltage value is greater than the third voltage value; and determine the zero-sequence voltage component based on the first voltage value, the second voltage value and the third voltage value.

[0013] In this embodiment of the invention, the zero-sequence voltage component is either a positive zero-sequence voltage component or a negative zero-sequence voltage component; the first determining module is further configured to determine the absolute value corresponding to the first voltage value to obtain the first absolute value, and determine the absolute value corresponding to the third voltage value to obtain the second absolute value; when the first absolute value is greater than the second absolute value and the second voltage value is less than the first preset threshold, or when the first absolute value is less than or equal to the second absolute value and the second voltage value is less than or equal to the second preset threshold, a positive zero-sequence voltage component is generated, wherein the second preset threshold and the first preset threshold are opposites of each other; when the first absolute value is less than or equal to the second absolute value and the second voltage value is greater than the second preset threshold, or when the first absolute value is greater than the second absolute value and the second voltage value is greater than or equal to the first preset threshold, a negative zero-sequence voltage component is generated.

[0014] In this embodiment of the invention, the first determining module is further configured to generate a positive zero-sequence voltage component based on a first preset boundary value and a first voltage value; or, to generate a negative zero-sequence voltage component based on a second preset boundary value and a third voltage value.

[0015] In this embodiment of the invention, the generation module is further configured to obtain the phase shift angle corresponding to the three-level converter; determine the carrier start phase value based on the target reference signal and the phase shift angle; and generate the target pulse width modulation signal based on the carrier start phase value and the carrier signal.

[0016] In this embodiment of the invention, the generation module is further configured to obtain the target potential difference between the positive and negative DC lines, the output currents corresponding to the multiple phase line converter modules, the reverse bias current of the three-level converter, the inductance of the coupling inductor of the three-level converter, and the target fixed-frequency switching period, wherein the target fixed-frequency switching period is the period of the carrier signal; determine the first product of the target potential difference and the target fixed-frequency switching period; and determine the phase shift angle based on the output currents, reverse bias currents, inductances, and the first product corresponding to the multiple phase line converter modules.

[0017] According to another aspect of the present invention, an electronic device is also provided, comprising: a memory storing an executable program; and a processor for running the program, wherein the program executes the methods of various embodiments of the present invention during runtime.

[0018] According to another aspect of the present invention, a computer-readable storage medium is also provided, the computer-readable storage medium including a stored executable program, wherein, when the executable program is executed, it controls the device where the computer-readable storage medium is located to perform the methods of various embodiments of the present invention.

[0019] According to another aspect of the present invention, a computer program product is also provided, including a computer program that, when executed by a processor, implements the methods of various embodiments of the present invention.

[0020] According to another aspect of the present invention, a computer program product is also provided, including a non-volatile computer-readable storage medium storing a computer program that, when executed by a processor, implements the methods of various embodiments of the present invention.

[0021] According to another aspect of the present invention, a computer program is also provided, which, when executed by a processor, implements the methods of the various embodiments of the present invention.

[0022] In this embodiment of the invention, the method is applied to a three-level converter, which includes multiple phase line converter modules. The first end of each phase line converter module is connected to the positive DC line, the second end is connected to the negative DC line, the third end is connected to a target midpoint (representing the midpoint of the potential difference between the positive and negative DC lines), and the fourth end is connected to the corresponding AC phase line on the multi-phase AC side. The method includes: acquiring the original reference signal corresponding to the multi-phase AC side, the instantaneous voltage values ​​corresponding to the multiple AC phase lines on the multi-phase AC side, and the carrier signal of the three-level converter; determining the zero-sequence voltage component based on the instantaneous voltage values ​​corresponding to the multiple AC phase lines; performing amplitude shifting on the original reference signal based on the zero-sequence voltage component to obtain a target reference signal; generating a target pulse width modulation signal based on the target reference signal and the carrier signal; and performing soft-switching control on the three-level converter based on the target pulse width modulation signal. This application accurately calculates the required zero-sequence voltage component using the instantaneous voltage values ​​corresponding to the multiple AC phase lines. The zero-sequence voltage component is injected into the original reference signal to shift its amplitude, generating the target reference signal. By injecting an appropriate zero-sequence voltage component, the target reference signal is shifted upwards or downwards as a whole, avoiding the near-zero blind zone of the reference signal. This ensures sufficient adjustment range for the carrier phase shift angle even at the minimum voltage value of the power frequency cycle. A pulse width modulation signal is generated based on the target reference signal and the carrier signal to control the switching timing of the two parallel bridge arms, generating the required trapezoidal circulating current. This solves the problem of phase shift angle calculation deviation caused by reference signal amplitude fluctuations, ensuring accurate driving of bridge arm current polarity reversal throughout the entire power frequency cycle, including under harsh conditions such as voltage zero crossings. This achieves high-accuracy full-range zero-voltage turn-on, thereby solving the technical problem of low accuracy in soft-switching control of three-level converters in related technologies. Attached Figure Description

[0023] The accompanying drawings, which are included to provide a further understanding of the invention and form part of this application, illustrate exemplary embodiments of the invention and, together with their description, serve to explain the invention and do not constitute an undue limitation thereof. In the drawings:

[0024] Figure 1 This is a flowchart of a soft-switching control method for a three-level converter according to an embodiment of the present invention;

[0025] Figure 2 This is a schematic diagram of a soft-switching control process for an optional three-level converter according to an embodiment of the present invention;

[0026] Figure 3 This is a schematic diagram of the soft-switching control process of another optional three-level converter according to an embodiment of the present invention;

[0027] Figure 4This is a schematic diagram of the soft-switching control process of another optional three-level converter according to an embodiment of the present invention;

[0028] Figure 5 This is a schematic diagram of an optional target reference signal and phase shift angle waveform according to an embodiment of the present invention;

[0029] Figure 6 This is a schematic diagram of a soft-switching control device for a three-level converter according to an embodiment of the present invention. Detailed Implementation

[0030] To enable those skilled in the art to better understand the present invention, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of the present invention.

[0031] It should be noted that the terms "first," "second," etc., in the specification, claims, and accompanying drawings of this invention are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that the embodiments of the invention described herein can be implemented in orders other than those illustrated or described herein. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover a non-exclusive inclusion; for example, a process, method, system, product, or apparatus that comprises a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to such processes, methods, products, or apparatus.

[0032] According to one aspect of the present invention, a soft-switching control method for a three-level converter is provided. The three-level converter includes multiple phase line converter modules. The first end of the phase line converter module is connected to the positive DC line, the second end of the phase line converter module is connected to the negative DC line, the third end of the phase line converter module is connected to a target midpoint, the target midpoint being used to represent the midpoint of the potential difference between the positive DC line and the negative DC line, and the fourth end of the phase line converter module is connected to the corresponding AC phase line of the multi-phase AC side.

[0033] The aforementioned three-level converter refers to a power electronic conversion device with three output levels, specifically two parallel three-phase three-level T-type neutral point clamping converters. This three-level converter consists of a DC side and an AC side. The DC side includes a positive DC line and a negative DC line, with a voltage-dividing capacitor forming the neutral point. The AC side is connected to a three-phase load or the power grid. Each phase arm of the three-level converter can output three voltage levels: positive bus voltage, neutral point potential, and negative bus voltage, thereby reducing the harmonic content of the output voltage and the voltage stress on the components.

[0034] The aforementioned multiple phase-line converter modules refer to the specific power circuit units that constitute each phase arm of a three-level converter. For a three-phase system, there are three phase-line converter modules, corresponding to phases A, B, and C respectively. Each phase-line converter module can contain two parallel arms, and each arm consists of multiple sets of complementary switches. The first terminal of each phase-line converter module is connected to the positive DC line, the second terminal is connected to the negative DC line, the third terminal is connected to the target midpoint, and the fourth terminal serves as the output terminal connected to the corresponding AC phase line on the multi-phase AC side, responsible for converting DC power into AC power and performing soft-switching operations.

[0035] The target midpoint mentioned above can refer to the midpoint of the potential difference between the positive and negative DC lines, which can be derived from the neutral point of the two series-connected voltage-dividing capacitors on the DC bus. In the circuit topology, it serves as the zero-level reference point for the three-level output. The third terminal of the phase-line converter module is connected to the target midpoint, enabling the three-level converter to achieve three-level output through clamping diodes or by directly conducting the midpoint path when outputting positive and negative levels, thereby reducing the voltage change rate and electromagnetic interference.

[0036] The aforementioned multiphase AC side can refer to a three-phase AC power grid or a three-phase load system connected to the output of the three-level converter. The multiphase AC side includes three AC phase lines: A, B, and C. The three-level converter is coupled to the multiphase AC side through a low-frequency filter inductor on the AC side. The voltage and current states of the multiphase AC side serve as feedback for the control algorithm and are also the port for generating the fundamental power output.

[0037] It should be noted that the steps shown in the flowchart in the accompanying drawings can be executed in a computer system such as a set of computer-executable instructions, and although a logical order is shown in the flowchart, in some cases the steps shown or described may be executed in a different order than that shown here.

[0038] Figure 1 This is a flowchart of a soft-switching control method for a three-level converter according to an embodiment of the present invention, such as... Figure 1 As shown, the method includes the following steps:

[0039] Step S102: Obtain the original reference signal corresponding to the multiphase AC side, the instantaneous voltage values ​​corresponding to the multiple AC phase lines of the multiphase AC side, and the carrier signal of the three-level converter.

[0040] The aforementioned original reference signal can refer to the fundamental modulated wave signal generated by the controller based on the target output voltage or current command, without zero-sequence component injection correction. It can be a sinusoidal signal, representing the waveform and phase of the desired three-phase AC voltage or current output. The amplitude and phase of the original reference signal determine the fundamental component of the converter output. Because the amplitude of the original reference signal is relatively small near the zero-crossing point, it is difficult to obtain sufficient phase shift margin for modulation to achieve full-range zero-voltage turn-on, requiring further processing.

[0041] The instantaneous voltage values ​​corresponding to the aforementioned multiple AC phase lines can refer to the actual voltage sample values ​​of each phase line on the multi-phase AC side, i.e., phase A, phase B, and phase C, relative to a reference ground, such as the neutral point or the midpoint of the DC bus, at any given time. These instantaneous voltage values ​​are used to monitor the state of the AC side in real time and serve as input data for calculating the zero-sequence voltage component. By sorting and comparing the three-phase instantaneous voltage values, the relative magnitudes of the three-phase voltages at the current moment can be determined, thereby guiding the zero-sequence component injection strategy.

[0042] The aforementioned carrier signal can refer to a high-frequency triangular wave or sawtooth wave signal used for pulse width modulation. Each phase converter module has two parallel arms with their own independent carrier signal. By adjusting the phase difference, or phase shift angle, between the carrier signals of the two parallel arms, a voltage difference can be generated between the two arms, thereby driving the circulating current within the phase. The frequency of the carrier signal is the switching frequency, which can be a fixed switching frequency with a constant carrier signal period.

[0043] In one optional embodiment, initialization and data acquisition can be performed to obtain the global state information required for executing the control algorithm. The controller can generate or acquire a raw reference signal, which is generated based on the desired output voltage or current command and represents an ideal sinusoidal waveform reference. Instantaneous voltage values ​​of each phase line on the multi-phase AC side can be sampled in real time using voltage sensors. These instantaneous voltage values ​​reflect the real-time electrical state of the power grid or load and are used for subsequent dynamic calculation of the zero-sequence component. A carrier signal, which is a high-frequency triangular wave or sawtooth wave with a fixed period, can also be acquired for pulse width modulation comparison. The raw reference signal, the instantaneous voltage values ​​corresponding to the multiple AC phase lines on the multi-phase AC side, and the carrier signal constitute the input basis of the control system. The raw reference signal determines the output fundamental characteristics, the instantaneous voltage values ​​are used to evaluate system boundary conditions, and the carrier signal provides a time reference. Together, they provide data support for the subsequent generation of the target reference signal and the calculation of the phase shift angle, ensuring that the control strategy can respond to changes in system state in real time.

[0044] The above settings achieve closed-loop feedback and dynamic adaptability of the control strategy. By acquiring instantaneous voltage values ​​in real time, the relative distribution of the three-phase voltages can be accurately determined, thereby accurately calculating the zero-sequence voltage component and preventing the reference signal from exceeding the modulation limit. Acquiring the original reference signal and carrier signal facilitates phase-shift control at a fixed switching frequency, retaining the simplicity of carrier modulation, and fulfilling soft-switching requirements through dynamic adjustment of the phase shift angle. This data acquisition method requires no complex additional hardware; relying on standard sensors and control algorithms, it can accurately adjust the bridge arm circulating current throughout the entire power frequency cycle, providing a data foundation for eliminating soft-switching blind spots and achieving full-range zero-voltage turn-on, thus improving the system's control accuracy and operational stability.

[0045] Step S104: Determine the zero-sequence voltage component based on the instantaneous voltage values ​​corresponding to the multiple AC phase lines.

[0046] The aforementioned zero-sequence voltage component refers to the components in a three-phase system that have the same amplitude and phase among the three-phase voltages. Since the line voltage of a three-phase system is only affected by the phase-to-phase voltage difference, injecting a zero-sequence component does not change the output line voltage, but it will change the level distribution of the reference signals for each phase. In this application, the zero-sequence voltage component is dynamically calculated based on the instantaneous three-phase voltage values ​​and is used to shift the original reference signal upwards or downwards as a whole, thereby avoiding the region near the zero-crossing point of the reference signal where the phase shift angle is limited, and expanding the implementation range of soft switching.

[0047] In one optional embodiment, the symmetry of the three-phase voltages can be utilized to adjust the level of the reference signal by dynamically injecting a zero-sequence component, thereby creating favorable conditions for soft switching. Specifically, the acquired instantaneous three-phase voltage values ​​can be sorted by magnitude to identify the maximum, median, and minimum values ​​at the current moment. Then, based on the numerical distribution characteristics of these three-phase voltages and a preset threshold, the phase region of the current power frequency cycle is determined, such as near a zero-crossing point or peak value. Based on the determination result, a suitable zero-sequence voltage component is calculated, which has a specific amplitude and polarity, such as positive or negative. Finally, this zero-sequence voltage component is superimposed on the original reference signal to achieve an overall shift of the reference signal. This process, based on real-time voltage feedback, requires no external additional signals, ensuring the real-time nature and accuracy of the zero-sequence component injection.

[0048] With the above settings, in eliminating the soft-switching dead zone, the relevant modulation method has a small reference signal amplitude near the voltage zero-crossing point, which limits the available carrier phase shift angle range and makes it difficult to generate sufficient circulating current to achieve zero-voltage turn-on. This application, by dynamically determining and injecting the zero-sequence voltage component based on the instantaneous voltage value, can raise or lower the reference signal, which was originally close to zero level, moving it away from the zero-level region. This not only expands the adjustment margin of the phase shift angle but also ensures that a larger phase shift angle that meets the zero-voltage turn-on condition can be calculated throughout the entire power frequency cycle, regardless of the voltage phase. This method utilizes the characteristic that the zero-sequence component of a three-phase system does not change the line voltage, improving the soft-switching capability of the converter under light load or near the zero-crossing point without increasing hardware costs, achieving efficient operation across the entire range.

[0049] Step S106: The original reference signal is amplitude shifted based on the zero-sequence voltage component to obtain the target reference signal.

[0050] The aforementioned target reference signal can refer to the modified modulated wave signal obtained by superimposing the zero-sequence voltage component onto the original reference signal. By shifting the amplitude of the original reference signal, the values ​​of the target reference signal near the zero-crossing point and peak value are adjusted, allowing for the calculation of a larger phase shift margin required to satisfy the zero-voltage turn-on condition under the same phase shift angle constraint. The target reference signal can serve as the basis for generating the target pulse width modulation signal. The waveform of the target reference signal exhibits discontinuous or abrupt characteristics near the zero-crossing point, reflecting the characteristics of multi-segment discontinuous modulation.

[0051] In one optional embodiment, the calculated zero-sequence voltage component can be directly superimposed on the original reference signal to achieve waveform shifting. After obtaining the zero-sequence voltage component, the controller uses this zero-sequence voltage component as a constant offset and adds it to the original reference signal of each phase in real time. For example, the zero-sequence voltage component can be added to the original reference signal to obtain the target reference signal. This addition operation can be completed in the digital control system through arithmetic instructions without the need for complex waveform reconstruction. The direction of shifting depends on the polarity of the zero-sequence component: if a positive zero-sequence component is injected, the reference signal shifts upward as a whole, causing the voltage value near the zero crossing point to move away from zero level; if a negative zero-sequence component is injected, the reference signal shifts downward as a whole. Through this dynamic amplitude shifting, the level distribution of the original reference signal is readjusted, thereby changing the relative position of the original reference signal in the carrier comparison process and providing a corrected reference waveform for the subsequent generation of the pulse width modulation signal.

[0052] The above settings effectively eliminate the soft-switching blind zone and expand the phase shift adjustment margin. Under pure sinusoidal modulation, the reference signal amplitude is small near the zero-crossing point, causing the required phase shift angle calculated based on the soft-switching conditions to exceed the upper limit of the carrier's allowable boundary, resulting in zero-voltage turn-on failure. By shifting the amplitude, even if the reference signal is near the zero-crossing point, the absolute value of the reference signal is raised to a sufficiently large level, allowing for a larger phase shift angle under the same carrier amplitude constraint. This zero-sequence component-based shifting strategy utilizes the theoretical degree of freedom that the zero-sequence component in a three-phase system does not change the line voltage, cleverly reconstructing the level distribution of the modulated wave without adding additional hardware circuitry. It solves the problem that related methods cannot achieve zero-voltage turn-on at the zero-crossing point and enables the converter to achieve zero-voltage turn-on throughout the entire power frequency cycle at a fixed switching frequency, improving system efficiency.

[0053] Step S108: Generate a target pulse width modulation signal based on the target reference signal and the carrier signal.

[0054] The aforementioned target pulse width modulation signal can refer to the switching transistor drive signal generated by comparing a target reference signal with a carrier signal. Specifically, the target reference signal can be compared with the carrier signal corresponding to each phase parallel bridge arm. When the reference signal is higher than the carrier signal, the corresponding switching transistor is turned on; when the reference signal is lower than the carrier signal, the corresponding switching transistor is turned off. The generated target pulse width modulation signal can control the on / off state of each power switching transistor in the phase line converter module, thereby realizing soft-switching control of the three-level converter, ensuring that the switching transistors are turned on under zero-voltage conditions, and reducing switching losses.

[0055] In one optional embodiment, a target reference signal and a carrier signal are compared to generate a target pulse width modulation signal for controlling the operation of the switching transistors. Specifically, the target reference signal, shifted by a zero-sequence component, and the fixed-frequency carrier signals corresponding to the two parallel bridge arms can be obtained. Due to the introduction of phase-shift control, the carriers of the two parallel bridge arms have a specific phase difference. The generation process involves comparing the target reference signal of each bridge arm with its corresponding carrier signal in real time. When the instantaneous value of the target reference signal is greater than the carrier signal, a high level is output; when the instantaneous value of the target reference signal is greater than the carrier signal, a low level is output. This comparison process is completed in the digital controller through table lookup or real-time calculation, generating two target pulse width modulation signals with a specific phase difference. These two signals drive the switching devices of the two parallel bridge arms under the same phase. By adjusting the phase shift angle of the carrier, the output voltages of the two bridge arms are time-shifted, thereby generating the required circulating current between the parallel branches.

[0056] The above settings achieve zero-voltage turn-on at a fixed switching frequency. By generating a target pulse width modulation signal based on the target reference signal and the carrier signal, the amplitude and waveform of the circulating current within the phase can be accurately controlled without changing the switching frequency. The carrier misalignment causes a voltage difference in the bridge arms, which in turn drives the circulating current through the coupling inductor, causing the bridge arm current to reverse polarity before the switch is turned on, thus satisfying the zero-voltage turn-on condition. This method avoids the frequency fluctuation problem of the triangular current mode and simplifies filter design. Since the target reference signal has been modified with zero-sequence components, sufficient phase shift angle can be guaranteed even near the voltage zero-crossing point, thereby eliminating the soft-switching dead zone. This modulation method has clear logic, is easy to implement digitally, and improves the overall efficiency and power density of the converter.

[0057] Step S110: Based on the target pulse width modulation signal, perform soft switching control on the three-level converter.

[0058] In one optional embodiment, the generated target pulse width modulation (PWM) signal can be applied to the power switching device drive circuit of a three-level converter. Specifically, the controller connects the two target PWM signals generated for each phase to the gate drive circuits of the corresponding power switches in the two parallel bridge arms of that phase. The target PWM signals serve as timing control commands, accurately controlling the turn-on and turn-off times of the switches. Since the target PWM signals are generated by comparing a carrier wave with a phase-shifted angle with a target reference signal, they contain duty cycle information and the time misalignment relationship between the two parallel bridge arms. When the signal drives the switch to operate, the output voltages of the two parallel bridge arms differ in time. This voltage difference acts on the coupling inductance between the parallel branches, establishing the required intra-phase circulating current. Through this direct signal drive, the switch is ensured to switch when the voltage crosses zero or the reverse current is sufficient, thus completing the soft-switching control.

[0059] The above settings achieve efficient and stable full-range zero-voltage turn-on. By directly applying the target pulse width modulation signal generated by the improved modulation strategy, zero-voltage conditions can be established before the switch is turned on without additional hardware auxiliary circuitry, reducing switching losses. Since the modulation strategy is based on a fixed switching frequency, the impact of frequency fluctuations on filter performance is avoided, improving system electromagnetic compatibility. Modulation based on the target reference signal ensures sufficient phase shift angle to maintain circulating current polarity reversal throughout the entire power frequency cycle, including voltage zero-crossing points and peak regions, eliminating soft-switching dead zones. This control method simplifies the system structure, reduces costs, and improves the converter's operating efficiency and reliability over a wide load range.

[0060] In this embodiment of the invention, the method is applied to a three-level converter, which includes multiple phase line converter modules. The first end of each phase line converter module is connected to the positive DC line, the second end is connected to the negative DC line, the third end is connected to a target midpoint (representing the midpoint of the potential difference between the positive and negative DC lines), and the fourth end is connected to the corresponding AC phase line on the multi-phase AC side. The method includes: acquiring the original reference signal corresponding to the multi-phase AC side, the instantaneous voltage values ​​corresponding to the multiple AC phase lines on the multi-phase AC side, and the carrier signal of the three-level converter; determining the zero-sequence voltage component based on the instantaneous voltage values ​​corresponding to the multiple AC phase lines; performing amplitude shifting on the original reference signal based on the zero-sequence voltage component to obtain a target reference signal; generating a target pulse width modulation signal based on the target reference signal and the carrier signal; and performing soft-switching control on the three-level converter based on the target pulse width modulation signal. This application accurately calculates the required zero-sequence voltage component using the instantaneous voltage values ​​corresponding to the multiple AC phase lines. The zero-sequence voltage component is injected into the original reference signal to shift its amplitude, generating the target reference signal. By injecting an appropriate zero-sequence voltage component, the target reference signal is shifted upwards or downwards as a whole, avoiding the near-zero blind zone of the reference signal. This ensures sufficient adjustment range for the carrier phase shift angle even at the minimum voltage value of the power frequency cycle. A pulse width modulation signal is generated based on the target reference signal and the carrier signal to control the switching timing of the two parallel bridge arms, generating the required trapezoidal circulating current. This solves the problem of phase shift angle calculation deviation caused by reference signal amplitude fluctuations, ensuring accurate driving of bridge arm current polarity reversal throughout the entire power frequency cycle, including under harsh conditions such as voltage zero crossings. This achieves high-accuracy full-range zero-voltage turn-on, thereby solving the technical problem of low accuracy in soft-switching control of three-level converters in related technologies.

[0061] In this embodiment of the invention, determining the zero-sequence voltage component based on the instantaneous voltage values ​​corresponding to multiple AC phase lines includes: sorting the instantaneous voltage values ​​corresponding to multiple AC phase lines to obtain a voltage sorting sequence; determining a first voltage value, a second voltage value, and a third voltage value in the voltage sorting sequence, wherein the first voltage value is greater than the second voltage value, and the second voltage value is greater than the third voltage value; and determining the zero-sequence voltage component based on the first voltage value, the second voltage value, and the third voltage value.

[0062] The aforementioned voltage sorting sequence refers to the sequential set formed by arranging the instantaneous voltage values ​​of the three-phase AC side at a specific sampling moment from largest to smallest or smallest to largest. The three-phase instantaneous voltage values ​​can be arranged in descending or ascending order, depending on the definition of the zero-sequence component injection strategy. Logically, the magnitude relationship must be clearly defined to obtain an ordered sequence. This voltage sorting sequence is used to identify the relative magnitude relationship of the three-phase voltages within the current power frequency cycle, serving as the basis for subsequently determining the polarity and amplitude of the zero-sequence voltage component injection, reflecting the voltage distribution state of the three-phase system at different times.

[0063] The aforementioned first voltage value can refer to the instantaneous value of the phase voltage with the larger value in the voltage sorting sequence, reflecting the upper limit of the three-phase voltage envelope at the current moment. When determining the zero-sequence voltage component, the first voltage value is used to define the limiting boundary of the modulation wave, preventing the reference signal from exceeding the carrier comparison range after the zero-sequence component is injected, thereby ensuring the effectiveness of the pulse width modulation signal generation.

[0064] The aforementioned second voltage value can refer to the instantaneous phase voltage value in the voltage sorting sequence that falls between the first and third voltage values, i.e., the intermediate value among the three-phase voltages, reflecting the phase voltage state at the intermediate potential in the three-phase system. In the logic for determining the zero-sequence voltage component, the second voltage value is used to determine the current operating region, such as near the zero-crossing point or near the peak value, and serves as one of the reference benchmarks for calculating the amplitude of the zero-sequence voltage component.

[0065] The aforementioned third voltage value can refer to the instantaneous value of the phase voltage with the smaller value in the voltage sorting sequence. When determining the zero-sequence voltage component, the third voltage value and the first voltage value together define the overall distribution range of the three-phase voltage. By comparing the absolute values ​​of the first and third voltage values ​​and combining them with the state of the second voltage value, the algorithm can dynamically select a better zero-sequence component injection strategy to maximize the phase shift margin, eliminate the soft-switching blind zone, and ensure zero-voltage turn-on throughout the entire power frequency cycle.

[0066] In one optional embodiment, the relative magnitudes of the three-phase voltages can be identified. Specifically, the controller reads the instantaneous voltage samples from the A, B, and C phase AC sides. These voltage values ​​are then compared and sorted, arranging the three-phase voltages in descending order to form a voltage sorting sequence. In this sequence, the highest voltage value is defined as the first voltage value, the middle voltage value as the second voltage value, and the lowest voltage value as the third voltage value. This sorting clarifies the current distribution of the three-phase voltages. This sorting process serves as the basis for determining the zero-sequence component injection strategy. The injection direction and magnitude of the zero-sequence component depend on the polarity and amplitude distribution of the three-phase voltages. By identifying the first, second, and third voltage values, a clear basis is provided for subsequent judgments on whether to inject positive or negative zero-sequence components, ensuring that the reference signal shift does not exceed the modulation limit.

[0067] The above settings achieve automation and versatility in zero-sequence component injection. By sorting the three-phase voltages in real time, it can dynamically adapt to three-phase imbalances caused by grid voltage fluctuations or load changes, without requiring a fixed phase sequence or phase angle. This voltage amplitude-based sorting method can accurately capture the envelope boundaries of the three-phase voltages, thereby calculating a better zero-sequence offset. It simplifies the logical complexity of the control algorithm, avoids complex trigonometric function calculations, and ensures that the reference signal can be effectively shifted to a safe range within any power frequency cycle. This dynamic adjustment mechanism enables the converter to maintain stable soft-switching performance under various operating conditions, effectively expanding the phase shift margin near the voltage zero-crossing point, eliminating the soft-switching blind zone, and improving system efficiency.

[0068] In this embodiment of the invention, the zero-sequence voltage component is either a positive zero-sequence voltage component or a negative zero-sequence voltage component. Determining the zero-sequence voltage component based on a first voltage value, a second voltage value, and a third voltage value includes: determining the absolute value corresponding to the first voltage value to obtain a first absolute value, and determining the absolute value corresponding to the third voltage value to obtain a second absolute value; generating a positive zero-sequence voltage component when the first absolute value is greater than the second absolute value and the second voltage value is less than a first preset threshold, or when the first absolute value is less than or equal to the second absolute value and the second voltage value is less than or equal to the second preset threshold, wherein the second preset threshold and the first preset threshold are opposites of each other; generating a negative zero-sequence voltage component when the first absolute value is less than or equal to the second absolute value and the second voltage value is greater than the second preset threshold, or when the first absolute value is greater than the second absolute value and the second voltage value is greater than or equal to the first preset threshold.

[0069] The aforementioned first absolute value can refer to the absolute value corresponding to the first voltage value in the voltage sorting sequence. In the calculation logic of the zero-sequence voltage component, the first absolute value is mainly used to compare with the absolute value of the third voltage value, thereby determining whether the overall distribution of the three-phase voltage is biased towards the positive bus side or the negative bus side, providing a basis for selecting the injection direction of the zero-sequence component.

[0070] The aforementioned second absolute value can refer to the absolute value corresponding to the third voltage value with the smaller value in the voltage sorting sequence. By comparing the magnitudes of the first and second absolute values, the degree of asymmetry of the three-phase voltage envelope can be quantified, thereby determining whether to shift the reference signal upward or downward, so as to maximize the use of the available space within the modulation period and expand the adjustment range of the phase shift angle.

[0071] The aforementioned first preset threshold can refer to a set positive voltage threshold, corresponding to half of the DC bus voltage or a critical value related to a relatively large positive offset allowed by the reference signal. In the logic for determining whether to generate a positive zero-sequence voltage component, if the first absolute value is greater than the second absolute value, and the second voltage value is less than the first preset threshold, it indicates that the intermediate phase voltage is at a low level. In this case, injecting a positive zero-sequence component can raise the overall reference signal, moving the reference signal near the zero-crossing point away from the zero-level region, thereby obtaining a larger phase shift margin. This first preset threshold is one of the boundary conditions for determining whether the current operating point is at a point where positive zero-sequence injection is required.

[0072] The aforementioned second preset threshold can refer to a set negative voltage threshold, and the second preset threshold is the opposite of the first preset threshold. In the logic for determining whether to generate a negative zero-sequence voltage component, the second preset threshold is used to define the boundary for downward shift of the reference signal. When the first absolute value is less than or equal to the second absolute value, if the second voltage value is greater than the second preset threshold, it indicates that the intermediate phase voltage is at a high level and the three phases are generally biased towards the negative side. In this case, injecting a negative zero-sequence component can pull down the reference signal as a whole, which also aims to avoid the range where the reference signal is close to zero level, ensuring that there is a sufficient phase shift angle to achieve zero-voltage turn-on throughout the entire power frequency cycle.

[0073] The aforementioned positive zero-sequence voltage component refers to a zero-sequence voltage component with positive polarity, which shifts the original three-phase reference signal upwards as a whole based on the original waveform. In this application, a positive zero-sequence voltage component is generated when specific conditions are met, such as a first absolute value being greater than a second absolute value and a second voltage value being less than a first preset threshold. By injecting the positive zero-sequence voltage component, the reference signal, which was originally small near the zero-crossing point, can be raised to a higher level. Thus, during carrier phase-shift modulation, a larger phase shift angle can be calculated without exceeding the carrier comparison range, effectively eliminating the soft-switching dead zone near the zero-crossing point and achieving zero-voltage turn-on.

[0074] The aforementioned negative zero-sequence voltage component refers to a zero-sequence voltage component with negative polarity, which shifts the original three-phase reference signal downwards as a whole from its original waveform. A negative zero-sequence voltage component is generated when specific conditions are met, such as a first absolute value being less than or equal to a second absolute value and a second voltage value being greater than a second preset threshold. By injecting the negative zero-sequence voltage component, the reference signal can be pulled down, also to ensure that the reference signal avoids the zero-level region near the zero-crossing point. By adjusting the absolute distribution of the three-phase voltages, the usable margin of the phase shift angle is maximized, thereby ensuring that sufficient intra-phase circulating current can be generated near the zero-crossing point and peak value of the three-phase current, achieving full-range zero-voltage turn-on soft-switching control.

[0075] In one optional embodiment, the decision process for dynamically selecting the polarity of the zero-sequence component involves comparing the absolute value of the voltage amplitude with a polarity threshold. Specifically, the controller first calculates the absolute values ​​of the sorted first and third voltage values, obtaining the first and second absolute values ​​respectively. Then, it proceeds to the following judgment logic: if the first absolute value is greater than the second absolute value, it indicates that the positive phase voltage amplitude is larger. If the second voltage value is less than the first preset threshold, it is determined that an upward shift is needed to generate a positive zero-sequence component. If the first absolute value is less than or equal to the second absolute value, it indicates that the negative phase voltage amplitude is dominant. If the second voltage value is less than or equal to the second preset threshold, a positive zero-sequence component is also generated to raise the voltage level. If the first absolute value is less than or equal to the second absolute value, and the second voltage value is greater than the second preset threshold, or vice versa, i.e., the positive phase amplitude is dominant and the intermediate voltage is high, or the negative phase amplitude is dominant and the intermediate voltage is low, a negative zero-sequence component is generated to lower the voltage level. This combination of absolute value magnitude and intermediate voltage level ensures that the reference signal always shifts away from the zero level boundary, avoiding over-modulation.

[0076] Through the above settings, adaptive improvement of the reference signal level is achieved, eliminating the soft-switching dead zone. By distinguishing between the dominant positive and negative amplitude ranges and comparing the intermediate voltage positions, this logic can intelligently determine whether a positive or negative zero-sequence component should be injected in the current power frequency cycle. Near the voltage zero-crossing point, regardless of which phase voltage amplitude is larger, this strategy ensures that the reference signal is pushed away from the zero-level region, thereby maximizing the usable range of the carrier phase shift angle. This dynamic polarity selection mechanism enables the converter to obtain sufficient phase shift margin to generate the required circulating current throughout the entire power frequency cycle, including at voltage minimum points, achieving full-range zero-voltage turn-on, improving system efficiency and simplifying control logic.

[0077] In this embodiment of the invention, the method further includes: generating a positive zero-sequence voltage component based on a first preset boundary value and a first voltage value; or, generating a negative zero-sequence voltage component based on a second preset boundary value and a third voltage value.

[0078] The aforementioned first preset boundary value refers to the maximum positive level limit that the reference signal is allowed to reach during pulse width modulation (PWM) of a three-level converter. This first preset boundary value corresponds to half of the DC bus voltage, which is 1 in a normalized coordinate system, depending on the normalization method. It represents the upper limit of the amplitude that the modulated wave can reach in the positive direction without clipping or distortion. When generating the positive zero-sequence voltage component, the algorithm determines the upward shift of the original reference signal by associating the first voltage value with the first preset boundary value. This ensures that the target reference signal after injecting the zero-sequence component does not exceed the positive level boundary, maximizing the utilization of the phase shift margin.

[0079] The aforementioned second preset boundary value refers to the negative level limit that the reference signal is allowed to reach during the pulse width modulation process of a three-level converter. The second preset boundary value corresponds to the lower limit of the negative half-cycle of the DC bus voltage, which is -1 in a normalized coordinate system. It represents the lower limit of the amplitude that the modulated wave can reach in the negative direction without clipping or distortion. When generating the negative zero-sequence voltage component, the algorithm determines the downward shift of the original reference signal by associating the third voltage value with the second preset boundary value. This ensures that the target reference signal after injecting the zero-sequence component is not lower than the negative level boundary, and also aims to expand the phase shift angle range of the soft-switching operation through limit shifting.

[0080] In one alternative embodiment, an auxiliary or specific mode for generating zero-sequence components can be directly generated based on voltage boundary conditions. Specifically, the system introduces a first preset boundary value and a second preset boundary value. When a positive zero-sequence voltage component needs to be generated, the controller performs an operation on the first preset boundary value and the currently sorted first voltage value, for example, calculating the difference between the first preset boundary value and the first voltage value, as the injection amount of the zero-sequence component. This calculation method ensures that after zero-sequence injection, the higher phase voltage can reach the modulation boundary, thereby achieving a larger positive offset. When a negative zero-sequence voltage component needs to be generated, the second preset boundary value is operated on with a third voltage value to calculate the required negative offset. This process uses the difference between the voltage extreme value and the boundary value to determine the zero-sequence component; the logic is simple and clear, avoiding complex conditional judgment branches, and is suitable for scenarios requiring fast response or specific boundary control.

[0081] The above settings maximize the use of the modulation space to expand the soft-switching margin. By directly pushing the reference signal to the upper and lower boundaries of the modulation waveform, this step ensures the maximization of the zero-sequence component injection. Near the voltage zero-crossing point, this extreme boundary control strategy generates the maximum reference signal shift amplitude, thereby expanding the adjustable range of the carrier phase shift angle. This enhances the ability to eliminate soft-switching dead zones and ensures sufficient circulating current to achieve zero-voltage turn-on even under extreme conditions. Direct calculation based on boundary values ​​simplifies the execution path of the control algorithm, improves the real-time performance and stability of digital control, and enables the system to maintain efficient soft-switching performance over a wide load range.

[0082] In this embodiment of the invention, generating a target pulse width modulation signal based on a target reference signal and a carrier signal includes: obtaining the phase shift angle corresponding to the three-level converter; determining the carrier start phase value based on the target reference signal and the phase shift angle; and generating the target pulse width modulation signal based on the carrier start phase value and the carrier signal.

[0083] The phase shift angle mentioned above refers to the phase difference of the carrier signal between the two parallel arms of a three-level converter. The phase shift angle is used to adjust the time misalignment between the output voltages of the two parallel arms, thereby generating a voltage difference between the two arms and driving the circulating current within the phase. By dynamically adjusting the magnitude of the phase shift angle, the amplitude of the circulating current can be controlled, causing the arm current to reverse polarity before the switching transistor turns on, thus achieving zero-voltage turn-on. The phase shift angle can be dynamically calculated based on parameters such as real-time phase current, DC bus voltage, and reverse bias current to ensure soft-switching performance and minimize conduction losses.

[0084] The aforementioned carrier initial phase value refers to the initial phase offset of the carrier signals of the two parallel bridge arms used to generate the pulse width modulation signal at the beginning of a new switching cycle. This carrier initial phase value is determined by the target reference signal and the phase shift angle. Specifically, the carrier initial phase value reflects the phase relationship of the carrier signal relative to the starting point of the target reference signal. By calculating the carrier initial phase value based on the target reference signal and the phase shift angle, it can be ensured that the carrier signals of the two parallel bridge arms maintain the correct phase shift angle in each switching cycle, thereby accurately generating a pulse width modulation signal with the required in-phase circulating current and achieving accurate soft-switching control of the converter.

[0085] In one alternative embodiment, a dynamic phase shift angle can be applied to carrier modulation to generate a drive signal. Specifically, the controller acquires a phase shift angle calculated based on the current operating conditions, reflecting the magnitude of the in-phase circulating current required to achieve zero-voltage turn-on. Then, based on the target reference signal and the phase shift angle, the carrier start phase values ​​of the two parallel bridge arms are determined. Specifically, the carrier start phase of one bridge arm is directly determined by the target reference signal, while the carrier start phase of the other bridge arm is determined by superimposing or subtracting the normalized phase shift angle from the target reference signal, thus forming two carrier waveforms with a phase difference. Finally, the controller compares these two carrier signals with different start phases with their corresponding target reference signals, generating two pulse-width modulated signals with time misalignment. This misalignment causes a time difference in the output voltages of the two parallel bridge arms, thereby creating a circulating current between the parallel branches.

[0086] The above settings enable accurate control of the circulating current at a fixed switching frequency. By dynamically adjusting the carrier start phase based on the phase shift angle, the duration of the phase-to-phase voltage difference can be flexibly adjusted without changing the switching frequency, thereby accurately controlling the amplitude of the circulating current. This control method allows the converter to meet the reverse current conditions required for zero-voltage turn-on throughout the entire power frequency cycle, including near the voltage zero-crossing point, by adjusting the phase shift angle. It avoids the filter design challenges caused by frequency fluctuations, and, combined with zero-sequence component injection, effectively eliminates the soft-switching dead zone, achieving efficient soft-switching operation across the entire range, and improving the system's power density and control stability.

[0087] In this embodiment of the invention, obtaining the phase shift angle corresponding to the three-level converter includes: obtaining the target potential difference between the positive DC line and the negative DC line, the output current corresponding to each of the multiple phase line converter modules, the reverse bias current of the three-level converter, the inductance of the coupling inductor of the three-level converter, and the target fixed-frequency switching period, wherein the target fixed-frequency switching period is the period of the carrier signal; determining the first product of the target potential difference and the target fixed-frequency switching period; and determining the phase shift angle based on the output current, reverse bias current, inductance, and the first product corresponding to each of the multiple phase line converter modules.

[0088] The aforementioned target potential difference can refer to the voltage difference between the positive DC line and the negative DC line in a three-level converter, or it can be the DC bus voltage.

[0089] The output currents corresponding to the aforementioned multiple phase-to-phase converter modules refer to the output current flowing from each phase of the three-level converter to the AC side. These output currents reflect the load demand and the magnitude and direction of the current within the current power frequency cycle. When determining the phase shift angle, the magnitude and polarity of the output current affect the reverse current amplitude required to achieve zero-voltage switching. By acquiring these output currents and combining them with other parameters, the phase shift angle is dynamically adjusted to ensure that sufficient and correctly polarized circulating current is generated in each switching cycle to meet the soft-switching conditions.

[0090] The aforementioned reverse bias current refers to the reverse current amplitude required to ensure that the junction capacitance of the power switching device can be fully discharged before turn-on, thereby achieving zero-voltage turn-on at the instant the switching transistor turns on. This reverse bias current is determined by the output capacitance parameters of the switching device and can be a preset or a fixed value or range value obtained from a table. In phase shift angle calculation, the reverse bias current can serve as a lower limit standard for determining the required circulating current amplitude. Only when the bridge arm current flips due to the circulating current and exceeds this reverse bias current can the device safely achieve zero-voltage turn-on and avoid hard switching losses.

[0091] The aforementioned coupling inductor refers to a high-frequency inductor connected between two parallel arms of the same phase in a three-level converter. The inductance of the coupling inductor is much smaller than that of the low-frequency filter inductor on the AC side, and its main function is to conduct high-frequency circulating current between the two parallel arms. By adjusting the phase shift angle between the carrier waves of the two parallel arms, a high-frequency voltage difference is generated across the coupling inductor, thereby driving the circulating current within the phase. The presence of the coupling inductor allows the current in the two parallel arms to fluctuate independently, providing a hardware foundation for soft switching based on phase shift control. This enables zero-voltage turn-on to be achieved through control strategies without adding auxiliary circuitry.

[0092] The inductance mentioned above refers to the inductance value of the coupled inductor, which is a physical quantity that measures the ability of the coupled inductor to impede changes in current. In the analytical calculation of the phase shift angle, the inductance, the target potential difference, the switching period, and the required reverse bias current jointly determine the carrier phase shift angle required to generate a circulating current of a specific amplitude. The larger the inductance, the longer the voltage difference needs to act to generate the same amplitude circulating current, or in other words, the smaller the amplitude of the circulating current generated at the same phase shift angle.

[0093] The aforementioned target fixed-frequency switching period can refer to the fixed period of the carrier signal of the three-level converter, i.e., the time interval between the switching actions of the switching transistors. This application can employ fixed switching frequency control, and the target fixed-frequency switching period can be a constant value, unaffected by load or grid voltage fluctuations. In phase shift angle calculation, the product of this target fixed-frequency switching period and the target potential difference constitutes a reference quantity used to determine the slope and duration of the circulating current change within a switching period. A fixed switching period simplifies filter design and digital controller implementation, avoiding stability problems caused by drastic frequency fluctuations in frequency conversion control strategies.

[0094] In one alternative embodiment, an optimal phase shift angle can be calculated using physical parameters. Specifically, the controller acquires the DC bus voltage (i.e., the potential difference between the positive and negative terminals), the output current of each phase, the preset reverse bias current, the inductance value of the coupling inductor, and a fixed switching cycle. Next, the DC bus voltage is multiplied by the switching cycle to obtain a first product. Subsequently, the controller uses the sum of the output current and the reverse bias current as the target amplitude of the desired circulating current. Combining the inductance value and the first product, it substitutes these values ​​into an analytical formula derived from the inductor voltage equation to calculate the required phase shift angle. This analytical formula essentially establishes a relationship between the voltage integral across the inductor and the current change, thereby determining the carrier phase difference required to generate a specific circulating current amplitude. The calculated result is the phase shift angle required to achieve zero-voltage turn-on at the current moment, ensuring that the circulating current precisely meets the zero-voltage turn-on condition to minimize conduction losses.

[0095] The above settings enable soft-switching control with low conduction losses. By analytically calculating the phase shift angle based on real-time current and inductance parameters, the amplitude of the circulating current within the phase can be accurately controlled, ensuring that the reverse current boundary required for zero-voltage turn-on is met and avoiding additional conduction losses caused by excessive circulating current. This direct calculation method based on the physical model allows the phase shift angle to be dynamically adjusted according to the load current, guaranteeing zero-voltage turn-on across the entire range and maximizing the converter's operating efficiency.

[0096] Figure 2 This is a schematic diagram of the soft-switching control process of an optional three-level converter according to an embodiment of the present invention, as shown below. Figure 2As shown, firstly, the original reference signal corresponding to the multi-phase AC side, the instantaneous voltage values ​​corresponding to multiple AC phase lines on the multi-phase AC side, and the carrier signal of the three-level converter are acquired. Next, the instantaneous voltage values ​​corresponding to the multiple AC phase lines are sorted to obtain a voltage sorting sequence; the first voltage value, second voltage value, and third voltage value in the voltage sorting sequence are determined; the absolute value corresponding to the first voltage value is determined to obtain the first absolute value, and the absolute value corresponding to the third voltage value is determined to obtain the second absolute value; when the first absolute value is greater than the second absolute value and the second voltage value is less than a first preset threshold, or when the first absolute value is less than or equal to the second absolute value and the second voltage value is less than or equal to the second preset threshold, a positive zero-sequence voltage component is generated; when the first absolute value is less than or equal to the second absolute value and the second voltage value is greater than the second preset threshold, or when the first absolute value is greater than the second absolute value and the second voltage value is greater than or equal to the first preset threshold, a negative zero-sequence voltage component is generated. Next, the original reference signal is amplitude-shifted based on the zero-sequence voltage component to obtain the target reference signal. Finally, a target pulse width modulation signal is generated based on the target reference signal and the carrier signal. Finally, based on the target pulse width modulation signal, soft-switching control is performed on the three-level converter.

[0097] Figure 3 This is a schematic diagram of the soft-switching control process of another optional three-level converter according to an embodiment of the present invention, as shown below. Figure 3 As shown, firstly, the original reference signal corresponding to the multi-phase AC side, the instantaneous voltage values ​​corresponding to multiple AC phase lines on the multi-phase AC side, and the carrier signal of the three-level converter are acquired. Next, the instantaneous voltage values ​​corresponding to the multiple AC phase lines are sorted to obtain a voltage sorting sequence; the first voltage value, second voltage value, and third voltage value in the voltage sorting sequence are determined; the absolute value corresponding to the first voltage value is determined to obtain the first absolute value, and the absolute value corresponding to the third voltage value is determined to obtain the second absolute value; when the first absolute value is greater than the second absolute value and the second voltage value is less than a first preset threshold, or when the first absolute value is less than or equal to the second absolute value and the second voltage value is less than or equal to the second preset threshold, a positive zero-sequence voltage component is generated based on the first preset boundary value and the first voltage value; when the first absolute value is less than or equal to the second absolute value and the second voltage value is greater than the second preset threshold, or when the first absolute value is greater than the second absolute value and the second voltage value is greater than or equal to the first preset threshold, a negative zero-sequence voltage component is generated based on the second preset boundary value and the third voltage value. Next, the original reference signal is amplitude-shifted based on the zero-sequence voltage component to obtain the target reference signal. Then, a target pulse width modulation (PWM) signal is generated based on the target reference signal and the carrier signal. Finally, soft-switching control is performed on the three-level converter based on the target PWM signal.

[0098] Figure 4This is a schematic diagram of the soft-switching control process of another optional three-level converter according to an embodiment of the present invention, as shown below. Figure 4 As shown, firstly, the original reference signal corresponding to the multi-phase AC side, the instantaneous voltage values ​​corresponding to multiple AC phase lines on the multi-phase AC side, and the carrier signal of the three-level converter are acquired. Next, based on the instantaneous voltage values ​​corresponding to the multiple AC phase lines, the zero-sequence voltage component is determined. Then, the phase shift angle corresponding to the three-level converter is acquired; based on the target reference signal and the phase shift angle, the carrier start phase value is determined; based on the carrier start phase value and the carrier signal, a target pulse width modulation signal is generated. Next, based on the target reference signal and the carrier signal, the target pulse width modulation signal is generated. Finally, based on the target pulse width modulation signal, soft-switching control is performed on the three-level converter.

[0099] Figure 5 This is a schematic diagram of an optional target reference signal and phase shift angle waveform according to an embodiment of the present invention, such as... Figure 5 As shown, the horizontal axis of this waveform diagram represents time, in seconds (s), and the vertical axis represents the normalized voltage amplitude. The grid intervals in the diagram represent the clamping intervals. The diagonal lines indicated by the up and down arrows represent the upward and downward shift intervals, respectively. The waveforms shown, from top to bottom, represent the target reference signals corresponding to A. v refa The phase shift angle corresponding to A α a B corresponds to the target reference signal v refb The phase shift angle corresponding to B α b C corresponds to the target reference signal v refc The phase shift angle corresponding to C α c The reference signals for each target shown in the diagram are obtained by shifting the amplitude of the original reference signal vertically.

[0100] According to another aspect of the present invention, a soft-switching control device for a three-level converter is also provided. The three-level converter includes multiple phase-line converter modules. The first end of each phase-line converter module is connected to the positive DC line, the second end of each phase-line converter module is connected to the negative DC line, the third end of each phase-line converter module is connected to a target midpoint, which represents the midpoint of the potential difference between the positive and negative DC lines, and the fourth end of each phase-line converter module is connected to the corresponding AC phase line on the multi-phase AC side. This device can execute the soft-switching control method of the three-level converter described in the above embodiments. The specific implementation method and preferred application scenarios are the same as those in the above embodiments and will not be repeated here.

[0101] Figure 6This is a schematic diagram of a soft-switching control device for a three-level converter according to an embodiment of this application, as shown below. Figure 6 As shown, the device includes the following: an acquisition module 602, a first determination module 604, a second determination module 606, a generation module 608, and a control module 610.

[0102] The three-level converter includes: an acquisition module 602 for acquiring the original reference signal corresponding to the multi-phase AC side, the instantaneous voltage values ​​corresponding to the multiple AC phase lines of the multi-phase AC side, and the carrier signal of the three-level converter; a first determination module 604 for determining the zero-sequence voltage component based on the instantaneous voltage values ​​corresponding to the multiple AC phase lines; a second determination module 606 for amplitude shifting the original reference signal based on the zero-sequence voltage component to obtain the target reference signal; a generation module 608 for generating a target pulse width modulation signal based on the target reference signal and the carrier signal; and a control module 610 for performing soft-switching control on the three-level converter based on the target pulse width modulation signal.

[0103] In this embodiment of the invention, the first determining module is further configured to sort the instantaneous voltage values ​​corresponding to the multiple AC phase lines respectively to obtain a voltage sorting sequence; determine the first voltage value, the second voltage value and the third voltage value in the voltage sorting sequence, wherein the first voltage value is greater than the second voltage value and the second voltage value is greater than the third voltage value; and determine the zero-sequence voltage component based on the first voltage value, the second voltage value and the third voltage value.

[0104] In this embodiment of the invention, the zero-sequence voltage component is either a positive zero-sequence voltage component or a negative zero-sequence voltage component; the first determining module is further configured to determine the absolute value corresponding to the first voltage value to obtain the first absolute value, and determine the absolute value corresponding to the third voltage value to obtain the second absolute value; when the first absolute value is greater than the second absolute value and the second voltage value is less than the first preset threshold, or when the first absolute value is less than or equal to the second absolute value and the second voltage value is less than or equal to the second preset threshold, a positive zero-sequence voltage component is generated, wherein the second preset threshold and the first preset threshold are opposites of each other; when the first absolute value is less than or equal to the second absolute value and the second voltage value is greater than the second preset threshold, or when the first absolute value is greater than the second absolute value and the second voltage value is greater than or equal to the first preset threshold, a negative zero-sequence voltage component is generated.

[0105] In this embodiment of the invention, the first determining module is further configured to generate a positive zero-sequence voltage component based on a first preset boundary value and a first voltage value; or, to generate a negative zero-sequence voltage component based on a second preset boundary value and a third voltage value.

[0106] In this embodiment of the invention, the generation module is further configured to obtain the phase shift angle corresponding to the three-level converter; determine the carrier start phase value based on the target reference signal and the phase shift angle; and generate the target pulse width modulation signal based on the carrier start phase value and the carrier signal.

[0107] In this embodiment of the invention, the generation module is further configured to obtain the target potential difference between the positive and negative DC lines, the output currents corresponding to the multiple phase line converter modules, the reverse bias current of the three-level converter, the inductance of the coupling inductor of the three-level converter, and the target fixed-frequency switching period, wherein the target fixed-frequency switching period is the period of the carrier signal; determine the first product of the target potential difference and the target fixed-frequency switching period; and determine the phase shift angle based on the output currents, reverse bias currents, inductances, and the first product corresponding to the multiple phase line converter modules.

[0108] According to another aspect of the present invention, an electronic device is also provided, comprising: a memory storing an executable program; and a processor for running the program, wherein the program executes the methods of various embodiments of the present invention during runtime.

[0109] According to another aspect of the present invention, a computer-readable storage medium is also provided, the computer-readable storage medium including a stored executable program, wherein, when the executable program is executed, it controls the device where the computer-readable storage medium is located to perform the methods of various embodiments of the present invention.

[0110] According to another aspect of the present invention, a computer program product is also provided, including a computer program that, when executed by a processor, implements the methods of various embodiments of the present invention.

[0111] According to another aspect of the present invention, a computer program product is also provided, including a non-volatile computer-readable storage medium storing a computer program that, when executed by a processor, implements the methods of various embodiments of the present invention.

[0112] According to another aspect of the present invention, a computer program is also provided, which, when executed by a processor, implements the methods of the various embodiments of the present invention.

[0113] Embodiments of this application also provide an electronic device, including: a memory storing an executable program; and a processor for running the program, wherein the program executes the methods in various embodiments of the present invention during runtime.

[0114] The aforementioned memory can refer to devices inside a computer used to store data and programs, including RAM, hard disks, etc. RAM can be used to temporarily store running programs and data, while hard disks can be used to store programs and data long-term. Memory enables the computer to read and write data and execute programs. The aforementioned processor is responsible for executing instructions in computer programs and performing data processing. It can also be responsible for controlling and executing various operations, including arithmetic operations, logical operations, and data transmission.

[0115] Embodiments of this application also provide a computer-readable storage medium including a stored executable program, wherein, when the executable program is running, it controls the device where the computer-readable storage medium is located to perform the methods of various embodiments of the present invention.

[0116] The aforementioned computer storage media can refer to the media used in computer memory to store certain discontinuous physical quantities. Computer storage media mainly include semiconductors, magnetic cores, magnetic drums, magnetic tapes, laser discs, etc. Computer-readable storage media include stored programs, which can be a set of instructions that a computer can recognize and execute, running on an electronic computer to meet certain information needs.

[0117] Embodiments of this application also provide a computer program product, including a computer program that, when executed by a processor, implements the methods of various embodiments of the present invention.

[0118] The aforementioned computer program products can refer to software programs that have been written, tested, and released, and can run on computers or other devices. Computer program products can include application programs, operating systems, utility software, etc., used to achieve specific functions or solve specific problems.

[0119] Embodiments of this application also provide a computer program product, including a non-volatile computer-readable storage medium for storing a computer program that, when executed by a processor, implements the methods in various embodiments of the present invention.

[0120] The aforementioned non-volatile computer-readable storage medium can refer to a medium for storing data. Non-volatile computer-readable storage media can retain data without loss when power is off and can be used to store long-term data, such as operating systems, applications, and user files. Non-volatile storage media can include hard disk drives, solid-state drives, optical disks, and flash memory storage devices, etc.

[0121] Embodiments of this application also provide a computer program that, when executed by a processor, implements the methods described in the various embodiments of the present invention.

[0122] The aforementioned computer program can refer to a set of instructions used to tell the computer to perform specific tasks or operations. Computer programs can be written by programmers using specific programming languages ​​and can include algorithms, data structures, logic, and control flow. Computer programs can be used for a variety of purposes, including application software, operating systems, etc.

[0123] In the above embodiments of the present invention, the descriptions of each embodiment have different focuses. For parts not described in detail in a certain embodiment, please refer to the relevant descriptions of other embodiments.

[0124] In the several embodiments provided in this application, it should be understood that the disclosed technical content can be implemented in other ways. The device embodiments described above are illustrative; for example, the division of units can be a logical functional division, and in actual implementation, there may be other division methods. For example, multiple units or components may be combined or integrated into another system, or some features may be ignored or not executed. Furthermore, the displayed or discussed mutual coupling, direct coupling, or communication connection can be through some interfaces; the indirect coupling or communication connection between units or modules can be electrical or other forms.

[0125] The units described as separate components may or may not be physically separate. The components shown as units may or may not be physical units; that is, they may be located in one place or distributed across multiple units. Some or all of the units can be selected to achieve the purpose of this embodiment according to actual needs.

[0126] Furthermore, the functional units in the various embodiments of the present invention 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. The integrated unit can be implemented in hardware or as a software functional unit.

[0127] If the integrated unit is implemented as a software functional unit and sold or used as an independent product, it can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of the present invention, in essence, or the part that contributes to the prior art, or all or part of the technical solution, can be embodied in the form of a software product. This computer software product is stored in a storage medium and includes several instructions to cause a computer device (which may be a personal computer, server, or network device, etc.) to execute all or part of the steps of the methods described in the various embodiments of the present invention. The aforementioned storage medium includes various media capable of storing program code, such as USB flash drives, read-only memory (ROM), random access memory (RAM), portable hard drives, magnetic disks, or optical disks.

[0128] The above description represents the preferred embodiments of the present invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A soft-switching control method for a three-level converter, characterized in that, The three-level converter includes multiple phase line converter modules. The first terminal of each phase line converter module is connected to the positive DC line, the second terminal is connected to the negative DC line, the third terminal is connected to a target midpoint (representing the midpoint of the potential difference between the positive and negative DC lines), and the fourth terminal is connected to the corresponding AC phase line on the multi-phase AC side. The method includes: The original reference signal corresponding to the multiphase AC side, the instantaneous voltage values ​​corresponding to the multiple AC phase lines of the multiphase AC side, and the carrier signal of the three-level converter are obtained. The zero-sequence voltage component is determined based on the instantaneous voltage values ​​corresponding to the multiple AC phase lines. The target reference signal is obtained by amplitude shifting the original reference signal based on the zero-sequence voltage component. Based on the target reference signal and the carrier signal, a target pulse width modulation signal is generated; Based on the target pulse width modulation signal, the three-level converter is subjected to soft-switching control.

2. The soft-switching control method for a three-level converter according to claim 1, characterized in that, Based on the instantaneous voltage values ​​corresponding to the multiple AC phase lines, the zero-sequence voltage component is determined, including: The instantaneous voltage values ​​corresponding to the plurality of AC phase lines are sorted to obtain a voltage sorting sequence; Determine a first voltage value, a second voltage value, and a third voltage value in the voltage sorting sequence, wherein the first voltage value is greater than the second voltage value, and the second voltage value is greater than the third voltage value; The zero-sequence voltage component is determined based on the first voltage value, the second voltage value, and the third voltage value.

3. The soft-switching control method for a three-level converter according to claim 2, characterized in that, The zero-sequence voltage component is either a positive zero-sequence voltage component or a negative zero-sequence voltage component; Determining the zero-sequence voltage component based on the first voltage value, the second voltage value, and the third voltage value includes: Determine the absolute value corresponding to the first voltage value to obtain the first absolute value, and determine the absolute value corresponding to the third voltage value to obtain the second absolute value; The positive zero-sequence voltage component is generated when the first absolute value is greater than the second absolute value and the second voltage value is less than the first preset threshold, or when the first absolute value is less than or equal to the second absolute value and the second voltage value is less than or equal to the second preset threshold, wherein the second preset threshold and the first preset threshold are opposites of each other. The negative zero-sequence voltage component is generated when the first absolute value is less than or equal to the second absolute value and the second voltage value is greater than the second preset threshold, or when the first absolute value is greater than the second absolute value and the second voltage value is greater than or equal to the first preset threshold.

4. The soft-switching control method for a three-level converter according to claim 3, characterized in that, The method further includes: The positive zero-sequence voltage component is generated based on the first preset boundary value and the first voltage value; or, The negative zero-sequence voltage component is generated based on the second preset boundary value and the third voltage value.

5. The soft-switching control method for a three-level converter according to any one of claims 1 to 4, characterized in that, Based on the target reference signal and the carrier signal, a target pulse width modulation signal is generated, including: Obtain the phase shift angle corresponding to the three-level converter; Based on the target reference signal and the phase shift angle, the carrier start phase value is determined; The target pulse width modulation signal is generated based on the carrier start phase value and the carrier signal.

6. The soft-switching control method for a three-level converter according to claim 5, characterized in that, Obtaining the phase shift angle corresponding to the three-level converter includes: The target potential difference between the positive DC line and the negative DC line is obtained, the output current corresponding to the plurality of phase line converter modules, the reverse bias current of the three-level converter, the inductance of the coupling inductor of the three-level converter, and the target fixed-frequency switching period, wherein the target fixed-frequency switching period is the period of the carrier signal; Determine the first product of the target potential difference and the target fixed-frequency switching period; The phase shift angle is determined based on the output current corresponding to the plurality of phase line converter modules, the reverse bias current, the inductance, and the first product.

7. A soft-switching control device for a three-level converter, characterized in that, The three-level converter includes multiple phase line converter modules. The first terminal of each phase line converter module is connected to the positive DC line, the second terminal is connected to the negative DC line, the third terminal is connected to a target midpoint (representing the midpoint of the potential difference between the positive and negative DC lines), and the fourth terminal is connected to the corresponding AC phase line on the multi-phase AC side. The device includes: The acquisition module is used to acquire the original reference signal corresponding to the multiphase AC side, the instantaneous voltage values ​​corresponding to the multiple AC phase lines of the multiphase AC side, and the carrier signal of the three-level converter. The first determining module is used to determine the zero-sequence voltage component based on the instantaneous voltage values ​​corresponding to the plurality of AC phase lines respectively; The second determining module is used to perform amplitude shifting on the original reference signal based on the zero-sequence voltage component to obtain the target reference signal; A generation module is used to generate a target pulse width modulation signal based on the target reference signal and the carrier signal; The control module is used to perform soft-switching control on the three-level converter based on the target pulse width modulation signal.

8. An electronic device, characterized in that, include: Memory, which stores executable programs; A processor for running the program, wherein the program, when running, executes the soft-switching control method for a three-level converter according to any one of claims 1 to 6.

9. A computer-readable storage medium, characterized in that, The computer-readable storage medium includes a stored executable program, wherein, when the executable program is executed, it controls the device on which the storage medium is located to perform the soft-switching control method for a three-level converter according to any one of claims 1 to 6.

10. A computer program product, characterized in that, The system includes a computer program that, when executed by a processor, implements the soft-switching control method for a three-level converter according to any one of claims 1 to 6.

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