Midpoint control method and control equipment of bidirectional converter, converter and power supply equipment

Abstract

The invention provides a midpoint control method and control equipment of a bidirectional converter, the converter and power supply equipment, and belongs to the technical field of power supplies. The method comprises the following steps: acquiring a positive bus voltage and a negative bus voltage of the converter and modulation wave fundamental waves of each phase; determining a clamping phase, a clamping level and a zero-sequence component according to the magnitude relationship between the positive bus voltage and the negative bus voltage and the modulation wave fundamental wave of each phase; obtaining the midpoint current of the converter after the zero-sequence component is injected; according to the magnitude relationship between the positive bus voltage and the negative bus voltage and the midpoint current, determining a quartic switching phase, and determining a modulation level of the quartic switching phase; the modulation level of the four switching phases comprises a P level and an N level in a single switching period; and performing midpoint control on the converter according to the clamping phase, the clamping level, the quartic switching phase and the modulation level of the quartic switching phase. According to the method, the full power factor, the midpoint balance of the whole modulation ratio range, relatively low switching loss and reasonable calculation complexity can be considered.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of power supply, in particular to a midpoint control method of bidirectional converter, control device, converter and power supply device. BACKGROUND

[0002] With the development of power electronics technology, three-level converters have been widely used in medium to high power applications, such as photovoltaic inverters, motor drives, uninterruptible power supplies and other systems, due to their low switching stress, small output voltage harmonics and high efficiency. However, three-level converters have an inherent technical problem - the fluctuation of the DC side midpoint potential. This fluctuation is mainly caused by the midpoint current flowing into or out of the midpoint of the DC bus capacitor during the operation of the converter, resulting in unbalanced charging and discharging of the two voltage dividing capacitors. If the midpoint potential imbalance is not effectively controlled, not only will the harmonic distortion rate of the output voltage increase, but also the switching devices will bear uneven voltage stress, and in severe cases, the power devices will be damaged, threatening the safety and reliability of the entire system.

[0003] In particular for bidirectional three-level converters, the energy can flow bidirectionally, and the direction and size of the midpoint current will change with the change of the power flow direction, which makes the control of the midpoint potential more complex. The traditional single control method is difficult to achieve fast and accurate balance control in the full power factor and the entire modulation ratio range. In addition, some existing high-performance methods are often computationally complex, requiring high real-time computing power of the processor, increasing the cost and difficulty of system implementation.

[0004] Therefore, there is an urgent need in the art for a midpoint control method suitable for bidirectional three-level converters, which can achieve fast and accurate control of the midpoint potential under various operating conditions, especially during bidirectional power flow, while taking into account lower switching losses and reasonable computational complexity. SUMMARY

[0005] The embodiments of the present application provide a midpoint control method of bidirectional converter, control device, converter and power supply device to solve the problem that the prior art cannot balance the midpoint in the full power factor and the entire modulation ratio range while taking into account lower switching losses and reasonable computational complexity.

[0006] In a first aspect, the embodiments of the present application provide a midpoint control method of bidirectional converter, comprising: obtaining the positive bus voltage, the negative bus voltage and the modulation wave fundamental wave of each phase of the converter; determining the clamping phase, the clamping level and the zero sequence component according to the size relationship of the positive bus voltage and the negative bus voltage and the modulation wave fundamental wave of each phase; obtaining the midpoint current of the converter after injecting the zero sequence component; The fourth switching phase is determined according to the size relationship between the positive bus voltage and the negative bus voltage and the midpoint current, and a modulation level of the fourth switching phase is determined; the modulation level of the fourth switching phase includes a P level and an N level in a single switching period; The midpoint of the converter is controlled according to the clamping phase, the clamping level, the fourth switching phase and the modulation level of the fourth switching phase.

[0007] In a possible implementation, the fourth switching phase is determined according to the size relationship between the positive bus voltage and the negative bus voltage and the midpoint current, and includes: If the positive bus voltage is greater than the negative bus voltage and the midpoint current is less than 0, the fourth switching phase is determined as a non-clamping phase with a current greater than 0; If the positive bus voltage is less than the negative bus voltage and the midpoint current is greater than 0, the fourth switching phase is determined as a non-clamping phase with a current less than 0.

[0008] In a possible implementation, the modulation level of the fourth switching phase is determined, and includes: A modulation wave of each non-clamping phase is determined according to a fundamental wave and a zero sequence component of the modulation wave of each non-clamping phase; A current of each non-clamping phase is obtained; The modulation level of the fourth switching phase is determined according to the modulation wave of each non-clamping phase and the current of each non-clamping phase, and includes a time of being at the P level, a time of being at the N level and a time of being at an O level in a single switching period; The modulation level of the fourth switching phase is determined according to the time of being at the P level, the time of being at the N level and the time of being at the O level in a single switching period.

[0009] In a possible implementation, each non-clamping phase includes the fourth switching phase and another non-clamping phase; The modulation level of the fourth switching phase is determined according to the modulation wave of each non-clamping phase and the current of each non-clamping phase, and includes a time of being at the P level, a time of being at the N level and a time of being at an O level in a single switching period, and includes: The time of being at the P level and the time of being at the N level in a single switching period are determined according to ; wherein, T is a time length of a single switching period, is a modulation wave of the fourth switching phase, is a current of the fourth switching phase, is a modulation wave of another non-clamping phase, is a current of another non-clamping phase; The time of being at the O level determining the modulation level of the fourth switching phase to be at the O level within a single switching cycle .

[0010] In a possible implementation, the clamping phase, the clamping level and the zero sequence component are determined according to the magnitude relationship between the positive bus voltage and the negative bus voltage and the modulation wave fundamental wave of each phase, and the method comprises the following steps: If the positive bus voltage is greater than the negative bus voltage, the phase with the maximum instantaneous value of the modulation wave fundamental wave of each phase is determined as the clamping phase, the clamping level is determined as P, and the value obtained by subtracting the maximum value in the instantaneous value of the modulation wave fundamental wave of each phase from 1 is determined as the zero sequence component; If the positive bus voltage is less than the negative bus voltage, the phase with the minimum instantaneous value of the modulation wave fundamental wave of each phase is determined as the clamping phase, the clamping level is determined as N, and the value obtained by subtracting the minimum value in the instantaneous value of the modulation wave fundamental wave of each phase from -1 is determined as the zero sequence component.

[0011] In a possible implementation, the midpoint current of the converter after the zero sequence component is injected is obtained, and the method comprises the following steps: The currents of each non-clamping phase are obtained; The modulation wave of each non-clamping phase is determined according to the modulation wave fundamental wave of each non-clamping phase and the zero sequence component; The midpoint current of the converter after the zero sequence component is injected is determined according to the current of each non-clamping phase and the modulation wave of each non-clamping phase.

[0012] In a possible implementation, the method further comprises the following steps: If the positive bus voltage is greater than the negative bus voltage and the midpoint current is greater than 0, or if the positive bus voltage is less than the negative bus voltage and the midpoint current is less than 0, the midpoint control of the converter is performed according to a preset method.

[0013] In a second aspect, an embodiment of the present application provides a midpoint control device of a bidirectional converter, comprising: An obtaining module is configured to obtain the positive bus voltage, the negative bus voltage and the modulation wave fundamental wave of each phase of the converter; A clamping phase determining module is configured to determine the clamping phase, the clamping level and the zero sequence component according to the magnitude relationship between the positive bus voltage and the negative bus voltage and the modulation wave fundamental wave of each phase; A midpoint current determining module is configured to obtain the midpoint current of the converter after the zero sequence component is injected; A fourth switching phase determining module is configured to determine the fourth switching phase according to the magnitude relationship between the positive bus voltage and the negative bus voltage and the midpoint current, and determine the modulation level of the fourth switching phase; the modulation level of the fourth switching phase comprises the P level and the N level within a single switching cycle; A midpoint control module is configured to control the converter according to the clamping phase, the clamping level, the fourth-switching phase and the modulation level of the fourth-switching phase.

[0014] In a third aspect, an embodiment of the present application provides a control device, including a processor and a memory, the memory being configured to store a computer program, and the processor being configured to invoke and run the computer program stored in the memory to execute the midpoint control method of the bidirectional converter as described in the first aspect or any possible implementation manner of the first aspect.

[0015] In a fourth aspect, an embodiment of the present application provides a bidirectional converter, including three-phase corresponding conversion units and the control device as described in the third aspect; the conversion units are controlled by the control device.

[0016] In a fifth aspect, an embodiment of the present application provides a power supply device, including the bidirectional converter as described in the fourth aspect.

[0017] In a sixth aspect, an embodiment of the present application provides a computer readable storage medium, the computer readable storage medium stores a computer program, and the computer program is executed by a processor to implement the midpoint control method of the bidirectional converter as described in the first aspect or any possible implementation manner of the first aspect.

[0018] The midpoint control method of the bidirectional converter, the control device, the converter and the power supply device provided by the embodiments of the present application can determine the clamping phase, the clamping level and the zero sequence component according to the size relationship between the positive bus voltage and the negative bus voltage and the modulation wave fundamental wave of each phase, and can determine the fourth-switching phase and the modulation level of the fourth-switching phase according to the size relationship between the positive bus voltage and the negative bus voltage and the midpoint current of the converter after injecting the zero sequence component, and the modulation level of the fourth-switching phase includes the P level and the N level in a single switching period, so that the midpoint control of the converter can be performed according to the clamping phase, the clamping level, the fourth-switching phase and the modulation level of the fourth-switching phase, the midpoint balance control in the full range (full power factor and full modulation ratio) can be realized, the switching times are the same as those of the conventional midpoint control method, the switching loss is not increased, the high efficiency can be maintained, the calculation process is relatively reasonable and not too complex, and therefore, the midpoint balance in the full power factor and the whole modulation ratio range, the lower switching loss and the reasonable calculation complexity can be considered. BRIEF DESCRIPTION OF DRAWINGS

[0019] To more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0020] Figure 1 This is a schematic diagram of the structure of a bidirectional converter provided in an embodiment of the present invention; Figure 2 This is a flowchart illustrating the implementation of a midpoint control method for a bidirectional converter according to an embodiment of the present invention. Figure 3 This is a schematic diagram of the modulation level of a certain phase under two control strategies provided in an embodiment of the present invention; Figure 4 This is a schematic diagram of a midpoint control device for a bidirectional converter provided in an embodiment of the present invention; Figure 5 This is a schematic diagram of a control device provided in an embodiment of the present invention. Detailed Implementation

[0021] In the following description, specific details such as particular system architectures and techniques are set forth for illustrative purposes and not for limitation, in order to provide a thorough understanding of the embodiments of the invention. However, those skilled in the art will understand that the invention can be implemented in other embodiments without these specific details. In other instances, detailed descriptions of well-known systems, apparatuses, circuits, and methods are omitted so as not to obscure the description of the invention with unnecessary detail.

[0022] To make the objectives, technical solutions, and advantages of the present invention clearer, specific embodiments will be described below in conjunction with the accompanying drawings.

[0023] See Figure 1 The diagram illustrates a structural schematic of a bidirectional converter according to an embodiment of the present invention. The bidirectional converter may include three corresponding conversion units for each phase and a control device; each phase's conversion unit is controlled by the control device. The control device is used to execute the midpoint control method for the bidirectional converter in subsequent embodiments.

[0024] See Figure 1 The bidirectional converter may also include a positive DC bus BUS+, a negative DC bus BUS-, a midpoint O1 on the DC side, a positive bus capacitor Cp located between the positive DC bus BUS+ and the midpoint O1, and a negative bus capacitor Cn located between the negative DC bus BUS- and the midpoint O1.

[0025] A bidirectional converter can operate in inverter mode, which converts DC power on the DC side to AC power on the AC side, or it can operate in rectification mode, which converts AC power on the AC side to DC power on the DC side.

[0026] The bidirectional converter can be any bidirectional converter that includes the midpoint of the DC side, such as a bidirectional three-level converter, a bidirectional five-level converter, or other multi-level bidirectional converters, etc. This application does not impose specific restrictions on the topology of the bidirectional converter; any bidirectional topology that meets the above requirements is acceptable. Figure 1 This application only provides one example of a bidirectional converter topology and is not intended to limit the scope of this application. The midpoint control method for bidirectional converters provided in this application is applicable to both rectifier and inverter modes.

[0027] The following is based on Figure 1 , combined Figure 2 The midpoint control method of the bidirectional converter provided in the embodiments of this application will be described.

[0028] See Figure 2 The diagram illustrates the implementation flowchart of the midpoint control method for a bidirectional converter provided in this embodiment of the invention. The execution subject of the midpoint control method for the bidirectional converter is a control device.

[0029] See Figure 2 The midpoint control method of this bidirectional converter is described in detail below: In S201, the positive bus voltage, negative bus voltage, and fundamental modulation wave of each phase of the converter are obtained.

[0030] The converter in this embodiment is the aforementioned bidirectional converter. The positive bus voltage of the converter is the voltage across the aforementioned positive bus capacitor, and the negative bus voltage of the converter is the voltage across the aforementioned negative bus capacitor.

[0031] The fundamental modulation waves of each phase of the converter include the fundamental modulation waves of phase A, phase B, and phase C. Each phase's fundamental modulation wave can be a sine wave, which can be understood as a sine wave signal with the same frequency as the desired output sine wave voltage.

[0032] In S202, the clamping phase, clamping level, and zero-sequence component are determined based on the relationship between the positive and negative bus voltages and the fundamental frequency of each phase's modulation wave.

[0033] In this context, the clamping phase is the phase whose modulation level remains at the same level throughout a switching cycle. In other words, the modulation level of the clamping phase remains at the same level throughout a switching cycle without switching. The clamping level is the level that the clamping phase needs to maintain within a switching cycle. That is, the clamping phase remains at the clamping level throughout a switching cycle without switching.

[0034] Zero-sequence component is used to control the midpoint current on the DC side of the converter in order to achieve midpoint balance on the DC side of the converter. It requires zero-sequence component to be injected into the fundamental frequency of the modulation wave in each phase.

[0035] The embodiments of this application can determine the clamping phase, clamping level, and zero-sequence component by comparing the magnitudes of the positive bus voltage and the negative bus voltage, based on the relationship between the two and the fundamental frequency of the modulation wave of each phase.

[0036] This application does not impose specific restrictions on the specific means of determining the clamping phase, clamping level, and zero-sequence component based on the magnitude relationship between the positive and negative bus voltages and the fundamental frequency of each phase modulation wave; any feasible solution is acceptable.

[0037] In S203, the midpoint current of the converter after the zero-sequence component is injected is obtained.

[0038] The midpoint current of the converter after injecting the zero-sequence component can be understood as the current at the midpoint of the DC-side of the converter after injecting the zero-sequence component, such as... Figure 1 In i np As shown.

[0039] The embodiments of this application do not impose specific restrictions on the means of obtaining the midpoint current of the converter after the injection of the zero-sequence component. For example, it can be obtained by calculation through relevant parameters or by any other feasible means, etc.

[0040] In S204, the four switching phases are determined based on the relationship between the positive bus voltage and the negative bus voltage and the midpoint current, and the modulation level of the four switching phases is also determined. The modulation level of the four switching phases includes P level and N level within a single switching cycle.

[0041] In this context, a four-way switching phase is a phase in which the modulation level switches four times within one switching cycle. The modulation level of a four-way switching phase switches four times within one switching cycle, and the level within one switching cycle includes both P and N levels. That is, when the modulation level of a four-way switching phase switches within one switching cycle, it switches to P level at least once and to N level at least once.

[0042] The four switching phases and the aforementioned clamping phases are two different phases among the three phases of the converter.

[0043] The modulation level of the four-phase switching is the modulation level of the four-phase switching, which includes at least one switching cycle.

[0044] The embodiments of this application can determine the modulation levels of the four switching phases by comparing the magnitudes of the positive bus voltage and the negative bus voltage, based on the relationship between the two and the aforementioned midpoint current.

[0045] This application does not impose specific limitations on the specific means of determining the four switching phases and their modulation levels based on the relationship between the positive and negative bus voltages and the midpoint current. Any feasible solution is acceptable.

[0046] In S205, the converter is controlled at the midpoint based on the clamping phase, clamping level, fourth switching phase, and modulation level of the fourth switching phase.

[0047] In addition to the clamping phase and the four-phase switching phase mentioned above, the converter has one remaining phase. The modulation level of this remaining phase can be determined according to the modulation method in relevant technologies, that is, it can be determined according to a preset method. This preset method can be a conventional method for controlling the bidirectional converter to balance the midpoint voltage, such as SVPWM (Space Vector Pulse Width Modulation), SPWM (Sine Pulse Width Modulation), or DPWM (Discontinuous Pulse Width Modulation), etc. It can also be a method of switching between two or more modulation methods according to actual needs, or other applicable methods, without specific limitations here.

[0048] Based on the aforementioned clamping phase and its clamping level, the four switching phases and their modulation levels, and the remaining phase and its modulation level, the converter can be controlled to achieve the balance of the DC side midpoint of the converter.

[0049] Based on the magnitude relationship between the positive and negative bus voltages and the fundamental frequency of each phase modulation wave, this application embodiment can determine the clamping phase, clamping level, and zero-sequence component. Furthermore, based on the magnitude relationship between the positive and negative bus voltages and the midpoint current of the converter after injecting the zero-sequence component, it can determine the four-phase switching and their modulation levels. The modulation levels of the four-phase switching include both P and N levels within a single switching cycle. Therefore, based on the clamping phase, clamping level, four-phase switching, and their modulation levels, midpoint control of the converter can be achieved, enabling midpoint balance control across the entire range (full power factor and full modulation ratio). Meanwhile, the number of switching operations is the same as that of conventional midpoint control methods (the clamping phase maintains the clamping level, with zero switching operations; the four-phase switching operates four times in one switching cycle, effectively transferring the two switching operations of the clamping phase to the four-phase switching, without increasing the total number of switches). Compared to related technologies that use a nine-segment control method to control the converter when midpoint balance cannot be achieved, this method saves switching operations and improves efficiency. It does not increase switching losses, maintains high efficiency, and has a relatively reasonable calculation process that is not overly complex, reducing the real-time computing power requirements of the processor and lowering system cost and implementation difficulty. Therefore, this method can balance midpoint balance across the entire power factor and modulation ratio range with low switching losses and reasonable computational complexity.

[0050] In some embodiments, in S202, determining the clamping phase, clamping level, and zero-sequence component based on the magnitude relationship between the positive bus voltage and the negative bus voltage and the fundamental frequency of the modulation wave of each phase includes: If the positive bus voltage is greater than the negative bus voltage, the phase with the largest instantaneous value of the fundamental modulator of each phase is taken as the clamping phase, the clamping level is determined as P, and the value obtained by subtracting the maximum instantaneous value of the fundamental modulator of each phase from 1 is taken as the zero-sequence component. If the positive bus voltage is less than the negative bus voltage, the phase with the smallest instantaneous value of the fundamental modulator of each phase is taken as the clamping phase, the clamping level is determined to be N, and the value obtained by subtracting the minimum instantaneous value of the fundamental modulator of each phase from -1 is taken as the zero-sequence component.

[0051] In this embodiment, when the positive bus voltage is greater than the negative bus voltage or vice versa, it indicates that the converter's midpoint is unbalanced, requiring midpoint balancing control using the method provided in this embodiment. When the positive bus voltage is equal to the negative bus voltage, it indicates that the converter's midpoint is balanced. In this case, conventional methods can be used to control the converter, such as the aforementioned preset method, etc.

[0052] Specifically, if the positive bus voltage is greater than the negative bus voltage, the maximum instantaneous value of the fundamental frequency modulation wave of each phase is determined, and the phase corresponding to this maximum value is taken as the clamping phase. Simultaneously, the clamping level can be determined to be P level. Furthermore, to ensure the clamping phase can be clamped to P level, the zero-sequence component can be determined to be 1-m. max m max It represents the maximum instantaneous value of the fundamental wave of the modulation wave in each phase.

[0053] If the positive bus voltage is less than the negative bus voltage, then the minimum instantaneous value of the fundamental frequency modulation wave of each phase is determined, and the phase corresponding to this minimum value is taken as the clamping phase. Simultaneously, the clamping level can be determined to be the N level. Furthermore, to ensure the clamping phase can be clamped to the N level, the zero-sequence component can be determined to be -1-m. min m min It is the minimum instantaneous value among the fundamental values ​​of the modulation wave of each phase.

[0054] This application strongly correlates the direction of bus voltage imbalance with the instantaneous extreme value phase (the phase with the largest or smallest instantaneous value) of the fundamental wave of the modulation wave. When the positive bus voltage is greater than the negative bus voltage, it means that the positive bus capacitor stores more charge, requiring the consumption of positive bus charge to achieve midpoint balance. At this time, the phase with the largest instantaneous value of the fundamental wave of the modulation wave is taken as the clamping phase, and the clamping level is determined to be P. This is because the phase with the largest instantaneous value of the fundamental wave of the modulation wave has the highest instantaneous voltage demand. Clamping it to P is equivalent to extending the time that phase is connected to the positive DC bus, that is, extending the time for extracting charge from the positive bus capacitor, which can reduce the positive bus voltage and restore the midpoint voltage balance. At the same time, the zero-sequence component is determined as 1 minus the maximum value among the instantaneous values ​​of the fundamental wave of the modulation wave of each phase. After injecting the zero-sequence component into the fundamental wave of the three phases, the modulation wave of the clamping phase is exactly 1, thus achieving clamping to P.

[0055] When the positive bus voltage is less than the negative bus voltage, the situation is reversed. The phase with the smallest instantaneous value of the fundamental modulation wave of each phase is selected as the clamping phase and clamped to N, which can also restore the neutral point voltage balance. At the same time, the zero-sequence component is determined as -1 minus the minimum instantaneous value of the fundamental modulation wave of each phase. After injecting the zero-sequence component into the fundamental modulation waves of the three phases, the modulation wave of the clamping phase is exactly -1, thus achieving clamping to N.

[0056] The embodiments of this application determine the clamping phase and clamping level by using the real-time status of the bus voltage and the fundamental frequency of the modulation wave. This allows for alternating clamping of each phase, reducing the overall average switching frequency and switching losses of the system, thereby improving the efficiency of the converter.

[0057] In some embodiments, obtaining the midpoint current of the converter after injecting the zero-sequence component in S203 includes: Obtain the current in each non-clamped phase; Based on the fundamental frequency and zero-sequence component of the modulation wave of each non-clamping phase, determine the modulation wave of each non-clamping phase. The midpoint current of the converter after injecting the zero-sequence component is determined based on the current of each non-clamped phase and the modulation wave of each non-clamped phase.

[0058] Among them, each of the above-mentioned non-clamping phases includes the other two phases besides the clamping phases mentioned above. For example, if the clamping phase is phase A, then the non-clamping phases are phases B and C, and so on.

[0059] By adding the fundamental modulation wave of each non-clamped phase to the aforementioned zero-sequence component, the modulation wave corresponding to each non-clamped phase can be obtained. It should be noted that during the converter control process, the fundamental modulation waves of all three phases need to be added to the aforementioned zero-sequence component to obtain the modulation wave corresponding to each phase. However, in this embodiment, only the modulation waves of two non-clamped phases are needed when calculating the midpoint current of the converter after injecting the zero-sequence component. Therefore, this embodiment only describes determining the modulation wave of each non-clamped phase based on the fundamental modulation wave and the zero-sequence component of each non-clamped phase.

[0060] See Figure 1 It also shows the A-phase current on the AC side. i a Phase B current on the AC side i b C-phase current on the AC side i c The current in each of the above non-clamped phases is the current in two of those phases.

[0061] After obtaining the current and modulation waveform of the two unclamped phases, the midpoint current of the converter after injecting the zero-sequence component can be calculated based on these currents and modulation waveforms. Specifically, this can be done using the formula... Calculate the midpoint current of the converter after injecting the zero-sequence component. Wherein, The modulation wave is a four-phase switching waveform. The current for the four switching phases, For another non-clamped phase modulated wave, For the current of another non-clamped phase.

[0062] As can be seen from the foregoing, since one of the two non-clamping phases will serve as a fourth-stage switching phase, the remaining non-clamping phase can be referred to as the other non-clamping phase. Therefore, each of the aforementioned non-clamping phases can include the aforementioned fourth-stage switching phase and the other non-clamping phase.

[0063] This embodiment determines the converter's midpoint current after injecting the zero-sequence component based on the current and modulation wave of each non-clamped phase, rather than directly measuring the current midpoint current. This is because the measured midpoint current reflects the result of the current switching state, while the injection of the zero-sequence component in this embodiment will change the future switching state. Therefore, using the current measured midpoint current value as the result of future control actions will result in lag and mismatch. This embodiment determines the modulation wave of each non-clamped phase based on the fundamental modulation wave and the zero-sequence component of each non-clamped phase. In effect, it pre-determines the final modulation wave of each phase after injecting the zero-sequence component. Based on the final modulation wave of each phase, the midpoint current after injecting the zero-sequence component can be obtained, making the subsequent selection of the four switching phases based on this midpoint current more accurate. This reduces control delay at the source and improves the dynamic performance and stability of midpoint balance control.

[0064] In some embodiments, in S204, determining the four switching phases based on the magnitude relationship between the positive bus voltage and the negative bus voltage and the midpoint current includes: If the positive bus voltage is greater than the negative bus voltage and the midpoint current is less than 0, then the four switching phases are determined to be non-clamping phases with current greater than 0. If the positive bus voltage is less than the negative bus voltage and the midpoint current is greater than 0, then the four switching phases are determined to be non-clamped phases with current less than 0.

[0065] In this embodiment, when the positive bus voltage is greater than the negative bus voltage, it indicates a midpoint imbalance. If the midpoint current is greater than 0, it means that the midpoint current flows out of the midpoint, which is equivalent to the positive bus capacitor discharging and the negative bus capacitor charging. That is, the positive bus voltage decreases and the negative bus voltage increases, thus achieving midpoint balance. In this case, no additional midpoint control is needed; simply controlling the converter according to the preset method is sufficient to achieve midpoint balance. However, if the midpoint current is less than 0, it means that the midpoint current flows into the midpoint, which will further exacerbate the midpoint imbalance. If the preset method is still used to control the converter, midpoint balance cannot be achieved. In this case, the method described in the previous embodiment needs to be used to determine a four-phase switching device and control it accordingly to achieve midpoint balance.

[0066] When the positive bus voltage is greater than the negative bus voltage and the midpoint current is less than 0, based on the phase relationship between the current and voltage of each phase, it can be determined that only one of the two non-clamped phases has a current greater than 0. The non-clamped phase with a current greater than 0 is then taken as the fourth switching phase.

[0067] When the positive bus voltage is less than the negative bus voltage, it also indicates a midpoint imbalance. If the midpoint current is less than 0, it means current is flowing into the midpoint, which is equivalent to charging the positive bus capacitor and discharging the negative bus capacitor. This results in a rise in the positive bus voltage and a decrease in the negative bus voltage, achieving midpoint balance. In this case, no additional midpoint control is needed; simply controlling the converter according to the preset method will achieve midpoint balance. However, if the midpoint current is greater than 0, it means current is flowing out of the midpoint, further exacerbating the midpoint imbalance. If the preset method is still used to control the converter, midpoint balance cannot be achieved. In this case, the method described in the previous embodiment needs to be used to determine a four-phase switching device and control it accordingly to achieve midpoint balance.

[0068] When the positive bus voltage is less than the negative bus voltage and the midpoint current is greater than 0, based on the phase relationship between the current and voltage of each phase, it can be determined that only one of the two non-clamped phases has a current less than 0. The non-clamped phase with a current less than 0 is then taken as the fourth switching phase.

[0069] In some embodiments, the above method may further include: If the positive bus voltage is greater than the negative bus voltage and the midpoint current is greater than 0, or if the positive bus voltage is less than the negative bus voltage and the midpoint current is less than 0, then the converter is controlled at the midpoint according to the preset method.

[0070] As mentioned earlier, when the positive bus voltage is greater than the negative bus voltage and the midpoint current is greater than 0, or when the positive bus voltage is less than the negative bus voltage and the midpoint current is less than 0, a preset method can be used to achieve midpoint balance. Therefore, the converter can be controlled at the midpoint according to the preset method, which can save switching losses and improve efficiency. The preset method can be referred to the relevant description in the foregoing embodiments, and will not be repeated here.

[0071] In some embodiments, determining the modulation level of the four switching phases in S204 includes: Based on the fundamental frequency and zero-sequence component of the modulation wave of each non-clamping phase, determine the modulation wave of each non-clamping phase. Obtain the current in each non-clamped phase; Based on the modulation wave of each non-clamping phase and the current of each non-clamping phase, determine the time during which the modulation level of the four switching phases is at the P level, the time during which it is at the N level, and the time during which it is at the O level within a single switching cycle. The modulation level of the four switching phases is determined by the time the modulation level of the four switching phases is at the P level, the time it is at the N level, and the time it is at the O level within a single switching cycle.

[0072] In some embodiments, each non-clamping phase includes a four-switch phase and another non-clamping phase; The above determination, based on the modulation wave and current of each non-clamping phase, of the durations of the modulation level of the four switching phases at the P level, N level, and O level within a single switching cycle includes: according to Determine the time during which the modulation level of the four switching phases is at level P within a single switching cycle. and the time at N level ;in, The duration of a single switching cycle. The modulation wave is a four-phase switching waveform. The current for the four switching phases, For another non-clamped phase modulated wave, For the current in another non-clamped phase; according to Determine the time during which the modulation level of the four switching phases is at zero level within a single switching cycle. .

[0073] Based on the fundamental and zero-sequence components of the modulation wave of each non-clamped phase, the modulation wave of each non-clamped phase is determined, and the current of each non-clamped phase is obtained. Please refer to the relevant descriptions in the foregoing embodiments, which will not be repeated here.

[0074] See Figure 3 Taking a bidirectional three-level converter as an example, the left side shows the modulation level of a certain phase determined by a conventional preset method, and the right side shows the modulation level after the phase is determined as a four-switch phase using the method of the embodiment of this application. Figure 3 As shown, the modulation level on the left is switched twice within one switching cycle, while the modulation level on the right is switched four times within one switching cycle.

[0075] For example, assuming the modulation level of a certain phase is a switch between 0 and N levels, when it is determined to be a four-switch phase, a P level needs to be added to form a switch between P, 0, and N levels, and four switches are performed within one switching cycle. Similarly, assuming the modulation level of a certain phase is a switch between 0 and P levels, when it is determined to be a four-switch phase, an N level needs to be added to form a switch between N, 0, and P levels, and four switches are performed within one switching cycle.

[0076] The durations of the modulation level of the four switching phases at the P, N, and O levels within a single switching cycle are determined using the aforementioned set of formulas. The first formula ensures the correct output voltage of the four switching phases, constraining them to meet their basic output voltage requirement: their output cannot deviate from the modulation wave requirements. This is fundamental to guaranteeing the sine wave required for normal converter output. The second formula forces the midpoint current to instantaneously become zero, ensuring that the midpoint current generated by the four switching phases exactly cancels out the midpoint current generated by the other non-clamped phase, resulting in a total average midpoint current of zero over one switching cycle. Based on this set of formulas, the durations of the modulation level of the four switching phases at the P, N, and O levels within a single switching cycle can be determined.

[0077] After determining the time for the modulation level of the four-phase switching to be at the P level, the time for it to be at the N level, and the time for it to be at the O level within a single switching cycle, and knowing that the modulation level of the four-phase switching needs to be switched four times within one switching cycle, mature technologies in related fields can be used to determine the modulation level of the four-phase switching, which will not be elaborated further.

[0078] This application embodiment determines the duration of the modulation level of the four switching phases at the P level, N level, and O level within a single switching cycle based on the modulation wave and current of each non-clamped phase. By controlling the duration of the four switching phases at different levels, a precise midpoint current is generated to offset the net current caused by all other phases (mainly the other non-clamped phase) that leads to midpoint imbalance. This enables quantitative management and instantaneous compensation of midpoint charge flow. It no longer involves a rough increase in the P or N level, but rather the calculation of the required P or N level time to inject or extract a precise amount of charge, thereby achieving extremely high-precision midpoint voltage control and suppressing voltage fluctuations within a very small range.

[0079] Furthermore, this application embodiment explicitly specifies the need to determine the time for the zero level, indicating that the final switching sequence is continuous, such as a standard switching sequence like PON or NOP, rather than directly switching from P to N or from N to P. Directly switching between P and N would cause output waveform distortion and generate a large number of low-order harmonics. By retaining and calculating the zero level time, this application embodiment can maintain excellent output harmonic performance to the maximum extent while completing the midpoint balancing task, ensuring that the total harmonic distortion rate of the current waveform does not significantly increase due to the balancing operation.

[0080] It should be understood that the sequence number of each step in the above embodiments does not imply the order of execution. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of the present invention.

[0081] Figure 4 A schematic diagram of the midpoint control device for a bidirectional converter provided in an embodiment of the present invention is shown. For ease of explanation, only the parts related to the embodiment of the present invention are shown, and are described in detail below: like Figure 4 As shown, the midpoint control device 30 of the bidirectional converter includes: an acquisition module 31, a clamping phase determination module 32, a midpoint current determination module 33, a four-stage switching phase determination module 34, and a midpoint control module 35.

[0082] The acquisition module 31 is used to acquire the positive bus voltage, negative bus voltage, and fundamental modulation wave of each phase of the converter; The clamping phase determination module 32 is used to determine the clamping phase, clamping level and zero-sequence component based on the magnitude relationship between the positive bus voltage and the negative bus voltage and the fundamental frequency of the modulation wave of each phase. Midpoint current determination module 33 is used to obtain the midpoint current of the converter after injecting zero-sequence components; The four-phase switching determination module 34 is used to determine the four-phase switching based on the relationship between the positive bus voltage and the negative bus voltage and the midpoint current, and to determine the modulation level of the four-phase switching; the modulation level of the four-phase switching includes P level and N level in a single switching cycle. The midpoint control module 35 is used to perform midpoint control on the converter based on the clamping phase, clamping level, fourth switching phase, and modulation level of the fourth switching phase.

[0083] In one possible implementation, the four-phase switching determination module 34 determines the four-phase switching based on the relationship between the positive bus voltage and the negative bus voltage, as well as the midpoint current, including: If the positive bus voltage is greater than the negative bus voltage and the midpoint current is less than 0, then the four switching phases are determined to be non-clamping phases with current greater than 0. If the positive bus voltage is less than the negative bus voltage and the midpoint current is greater than 0, then the four switching phases are determined to be non-clamped phases with current less than 0.

[0084] In one possible implementation, the modulation level of the four-phase switching is determined in the four-phase switching determination module 34, including: Based on the fundamental frequency and zero-sequence component of the modulation wave of each non-clamping phase, determine the modulation wave of each non-clamping phase. Obtain the current in each non-clamped phase; Based on the modulation wave of each non-clamping phase and the current of each non-clamping phase, determine the time during which the modulation level of the four switching phases is at the P level, the time during which it is at the N level, and the time during which it is at the O level within a single switching cycle. The modulation level of the four switching phases is determined by the time the modulation level of the four switching phases is at the P level, the time it is at the N level, and the time it is at the O level within a single switching cycle.

[0085] In one possible implementation, each non-clamping phase includes a four-switch phase and another non-clamping phase; In the four-phase switching determination module 34, based on the modulation wave of each non-clamping phase and the current of each non-clamping phase, the time during which the modulation level of the four-phase switching is at the P level, the time during which it is at the N level, and the time during which it is at the O level within a single switching cycle are determined, including: according to Determine the time during which the modulation level of the four switching phases is at level P within a single switching cycle. and the time at N level ;in, The duration of a single switching cycle. The modulation wave is a four-phase switching waveform. The current for the four switching phases, For another non-clamped phase modulated wave, For the current in another non-clamped phase; according to Determine the time during which the modulation level of the four switching phases is at zero level within a single switching cycle. .

[0086] In one possible implementation, the clamp phase determination module 32 is specifically used for: If the positive bus voltage is greater than the negative bus voltage, the phase with the largest instantaneous value of the fundamental modulator of each phase is taken as the clamping phase, the clamping level is determined as P, and the value obtained by subtracting the maximum instantaneous value of the fundamental modulator of each phase from 1 is taken as the zero-sequence component. If the positive bus voltage is less than the negative bus voltage, the phase with the smallest instantaneous value of the fundamental modulator of each phase is taken as the clamping phase, the clamping level is determined to be N, and the value obtained by subtracting the minimum instantaneous value of the fundamental modulator of each phase from -1 is taken as the zero-sequence component.

[0087] In one possible implementation, the midpoint current determination module 33 is specifically used for: Obtain the current in each non-clamped phase; Based on the fundamental frequency and zero-sequence component of the modulation wave of each non-clamping phase, determine the modulation wave of each non-clamping phase. The midpoint current of the converter after injecting the zero-sequence component is determined based on the current of each non-clamped phase and the modulation wave of each non-clamped phase.

[0088] In one possible implementation, the midpoint control module 35 is also used for: If the positive bus voltage is greater than the negative bus voltage and the midpoint current is greater than 0, or if the positive bus voltage is less than the negative bus voltage and the midpoint current is less than 0, then the converter is controlled at the midpoint according to the preset method.

[0089] Figure 5 This is a schematic diagram of the control device provided in an embodiment of the present invention. Figure 5 As shown, the control device 4 in this embodiment includes a processor 40 and a memory 41. The memory 41 stores a computer program 42, and the processor 40 calls and runs the computer program 42 stored in the memory 41 to execute the steps in the midpoint control method embodiments of the various bidirectional converters described above. Alternatively, the processor 40 calls and runs the computer program 42 stored in the memory 41 to implement the functions of each module / unit in the various device embodiments described above.

[0090] For example, the computer program 42 may be divided into one or more modules / units, which are stored in the memory 41 and executed by the processor 40 to complete the present invention. The one or more modules / units may be a series of computer program instruction segments capable of performing a specific function, which describe the execution process of the computer program 42 in the control device 4.

[0091] The control device 4 may include, but is not limited to, a processor 40 and a memory 41. Those skilled in the art will understand that... Figure 5 This is merely an example of control device 4 and does not constitute a limitation on control device 4. It may include more or fewer components than shown, or combine certain components, or different components. For example, the control device may also include input / output devices, network access devices, buses, etc.

[0092] The processor 40 can be a Central Processing Unit (CPU), or other general-purpose processors, digital signal processors (DSPs), application-specific integrated circuits (ASICs), field-programmable gate arrays (FPGAs), or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, etc. The general-purpose processor can be a microprocessor or any conventional processor.

[0093] The memory 41 can be an internal storage unit of the control device 4, such as a hard disk or memory of the control device 4. The memory 41 can also be an external storage device of the control device 4, such as a plug-in hard disk, smart media card (SMC), secure digital (SD) card, flash card, etc., equipped on the control device 4. Furthermore, the memory 41 can include both internal storage units and external storage devices of the control device 4. The memory 41 is used to store the computer program and other programs and data required by the control device. The memory 41 can also be used to temporarily store data that has been output or will be output.

[0094] Corresponding to the control device described above, this embodiment of the invention also provides a bidirectional converter, including three conversion units corresponding to each of the three phases and the control device described above; the conversion units are controlled by the control device.

[0095] Corresponding to the bidirectional converter described above, this application embodiment also provides a power supply device, including the bidirectional converter as described above.

[0096] The relevant descriptions of the bidirectional converter and power supply equipment can be found in the descriptions in the foregoing embodiments, and will not be repeated here.

[0097] This application also provides a computer-readable storage medium storing a computer program that, when executed by a processor, implements the steps of any of the bidirectional converter midpoint control methods described above.

[0098] This application also provides a computer program product, including a computer program that, when executed by a processor, implements any of the above-described bidirectional converter midpoint control methods.

[0099] Those skilled in the art will clearly understand that, for the sake of convenience and brevity, the above-described division of functional units and modules is merely an example. In practical applications, the above functions can be assigned to different functional units and modules as needed, that is, the internal structure of the device can be divided into different functional units or modules to complete all or part of the functions described above. The functional units and modules in the embodiments 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. Furthermore, the specific names of the functional units and modules are only for easy differentiation and are not intended to limit the scope of protection of this application. The specific working process of the units and modules in the above system can be referred to the corresponding process in the foregoing method embodiments, and will not be repeated here.

[0100] In the above embodiments, the descriptions of each embodiment have different focuses. For parts that are not described in detail or recorded in a certain embodiment, please refer to the relevant descriptions of other embodiments.

[0101] Those skilled in the art will recognize that the units and algorithm steps of the various examples described in conjunction with the embodiments disclosed herein can be implemented in electronic hardware, or a combination of computer software and electronic hardware. Whether these functions are implemented in hardware or software depends on the specific application and design constraints of the technical solution. Those skilled in the art can use different methods to implement the described functions for each specific application, but such implementations should not be considered beyond the scope of this invention.

[0102] In the embodiments provided by this invention, it should be understood that the disclosed apparatus / control devices and methods can be implemented in other ways. For example, the apparatus / control device embodiments described above are merely illustrative. For instance, the division of modules or units is only 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 coupling or direct coupling or communication connection shown or discussed may be through some interfaces; the indirect coupling or communication connection between apparatuses or units may be electrical, mechanical, or other forms.

[0103] 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 network units. Some or all of the units can be selected to achieve the purpose of this embodiment according to actual needs.

[0104] 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.

[0105] If the integrated module / 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, all or part of the processes in the above embodiments of the present invention can also be implemented by a computer program instructing related hardware. The computer program can be stored in a computer-readable storage medium, and when executed by a processor, it can implement the steps of the midpoint control method embodiments of the various bidirectional converters described above. The computer program includes computer program code, which can be in the form of source code, object code, executable files, or certain intermediate forms. The computer-readable medium can include: any entity or device capable of carrying the computer program code, a recording medium, a USB flash drive, a portable hard drive, a magnetic disk, an optical disk, a computer memory, a read-only memory (ROM), a random access memory (RAM), an electrical carrier signal, a telecommunication signal, and a software distribution medium, etc.

[0106] The above-described embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention, and should all be included within the protection scope of the present invention.

Claims

1. A midpoint control method for a bidirectional converter, characterized in that, include: Obtain the positive bus voltage, negative bus voltage, and fundamental modulation wave of each phase of the converter; Based on the magnitude relationship between the positive bus voltage and the negative bus voltage, as well as the fundamental frequency of the modulation wave of each phase, determine the clamping phase, clamping level, and zero-sequence component. Obtain the midpoint current of the converter after injecting the zero-sequence component; Based on the relationship between the positive bus voltage and the negative bus voltage, and the midpoint current, the four switching phases are determined, and the modulation level of the four switching phases is determined. The modulation levels of the four switching phases include P level and N level within a single switching cycle; The converter is controlled at the midpoint based on the clamping phase, the clamping level, the four-phase switching phase, and the modulation level of the four-phase switching phase.

2. The midpoint control method for a bidirectional converter according to claim 1, characterized in that, The step of determining the four switching phases based on the relationship between the positive bus voltage and the negative bus voltage, and the midpoint current, includes: If the positive bus voltage is greater than the negative bus voltage and the midpoint current is less than 0, then the fourth switching phase is determined to be a non-clamping phase with a current greater than 0. If the positive bus voltage is less than the negative bus voltage and the midpoint current is greater than 0, then the fourth switching phase is determined to be a non-clamping phase with a current less than 0.

3. The midpoint control method for a bidirectional converter according to claim 1, characterized in that, Determining the modulation level of the four switching phases includes: Based on the fundamental modulator of each non-clamped phase and the zero-sequence component, the modulator of each non-clamped phase is determined. Obtain the current in each non-clamped phase; Based on the modulation wave of each non-clamping phase and the current of each non-clamping phase, determine the time during which the modulation level of the four switching phases is at the P level, the time during which it is at the N level, and the time during which it is at the O level within a single switching cycle. The modulation level of the four switching phases is determined based on the time the modulation level of the four switching phases is at the P level, the time it is at the N level, and the time it is at the O level within a single switching cycle.

4. The midpoint control method for a bidirectional converter according to claim 3, characterized in that, Each non-clamping phase includes the four switching phases and another non-clamping phase; The step of determining the time during which the modulation level of the four switching phases is at the P level, the N level, and the O level within a single switching cycle, based on the modulation wave and current of each non-clamping phase, includes: according to Determine the time during which the modulation level of the four switching phases is at level P within a single switching cycle. and the time at N level ;in, The duration of a single switching cycle. The modulation wave of the four switching phases, The current of the four switching phases is... For the other non-clamped phase modulation wave, For the current of the other non-clamped phase; according to Determine the time during which the modulation level of the four switching phases is at 0 level within a single switching cycle. .

5. The midpoint control method for a bidirectional converter according to any one of claims 1 to 4, characterized in that, The step of determining the clamping phase, clamping level, and zero-sequence component based on the magnitude relationship between the positive bus voltage and the negative bus voltage and the fundamental frequency of each phase modulation wave includes: If the positive bus voltage is greater than the negative bus voltage, the phase with the largest instantaneous value of the fundamental modulator of each phase is taken as the clamping phase, the clamping level is determined as P, and the value obtained by subtracting the maximum instantaneous value of the fundamental modulator of each phase from 1 is taken as the zero-sequence component. If the positive bus voltage is less than the negative bus voltage, the phase with the smallest instantaneous value of the fundamental modulator of each phase is taken as the clamping phase, the clamping level is determined to be N, and the value obtained by subtracting the minimum instantaneous value of the fundamental modulator of each phase from -1 is taken as the zero-sequence component.

6. The midpoint control method for a bidirectional converter according to any one of claims 1 to 4, characterized in that, The step of obtaining the midpoint current of the converter after injecting the zero-sequence component includes: Obtain the current in each non-clamped phase; Based on the fundamental modulator of each non-clamped phase and the zero-sequence component, the modulator of each non-clamped phase is determined. The midpoint current of the converter after injecting the zero-sequence component is determined based on the current of each non-clamped phase and the modulation wave of each non-clamped phase.

7. The midpoint control method for a bidirectional converter according to any one of claims 1 to 4, characterized in that, Also includes: If the positive bus voltage is greater than the negative bus voltage and the midpoint current is greater than 0, or if the positive bus voltage is less than the negative bus voltage and the midpoint current is less than 0, then the converter is subjected to midpoint control according to a preset method.

8. A control device, characterized in that, It includes a memory and a processor, the memory being used to store a computer program, and the processor being used to call and run the computer program stored in the memory to perform the midpoint control method of the bidirectional converter as described in any one of claims 1 to 7.

9. A bidirectional converter, characterized in that, It includes three corresponding conversion units for each phase and a control device as described in claim 8; the conversion units are controlled by the control device.

10. A power supply device, characterized in that, Includes the bidirectional converter as described in claim 9.

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