Power conversion device, control method, electronic device, and storage medium

Abstract

The application relates to the technical field of power distribution network flexible interconnection, and discloses a power conversion device, a control method, electronic equipment and a storage medium. The device comprises: a rectifier connected with a medium-voltage power distribution network on an alternating current side; an inverter connected with the rectifier on a direct current side through a direct current bus, connected with a low-voltage load area on an alternating current side, and electrically connected with a neutral point of a medium-voltage side and a low-voltage side; a common-mode suppression unit connected in series on the direct current bus and used for suppressing a common-mode current; and a controller configured to generate a modulation signal according to obtained power grid state parameters and load state parameters, perform spatial vector modulation, select a zero vector combination from multiple zero vector combinations to suppress a common-mode voltage, and generate a driving signal to control on-off of a switching device according to a modulation result. The application solves the problem that the common-mode voltage and the common-mode leakage current in the non-isolated current source type back-to-back topology are difficult to suppress by means of cooperation of the common-mode suppression unit and a zero vector screening strategy.

Description

Technical Field

[0001] This application relates to the field of flexible interconnection technology in power distribution networks, specifically to power conversion devices, control methods, electronic devices, and storage media. Background Technology

[0002] Flexible interconnection devices use power electronic converters to interconnect distribution networks of different voltage levels, enabling flexible power flow regulation and active voltage support between distribution stations. In non-isolated current source type back-to-back power converters, the rectifier and inverter are connected via a DC bus. The AC side of the rectifier is connected to the medium-voltage distribution network, and the AC side of the inverter is connected to the low-voltage load distribution area. The neutral point of the medium-voltage distribution network is electrically connected to the neutral point of the low-voltage load distribution area. Due to this electrical connection at the neutral point, the common-mode voltage generated by the high-frequency switching of the converter will form a common-mode circulating current path through the neutral point and grounding loop, thus generating a common-mode circulating current in the system. The presence of this common-mode circulating current not only increases system losses but may also cause electromagnetic interference, malfunctions of protection devices, and aging of equipment insulation.

[0003] However, traditional space vector modulation methods typically employ random selection or fixed allocation for zero vector selection, failing to actively utilize the redundancy characteristics of the zero vector to suppress common-mode voltage. This results in the common-mode voltage and common-mode leakage current being difficult to effectively suppress in non-isolated current source type back-to-back power converters. Summary of the Invention

[0004] This application provides a power conversion device, control method, electronic device, and storage medium to solve the problem that common-mode voltage and common-mode leakage current are difficult to effectively suppress in non-isolated current source type back-to-back power conversion devices.

[0005] In a first aspect, this application provides a power conversion device, comprising: a rectifier, the AC side of which is connected to a medium-voltage distribution network; an inverter, the DC side of which is connected to the DC side of the rectifier via a DC bus, the AC side of which is connected to a low-voltage load area, and the neutral point of the medium-voltage distribution network is electrically connected to the neutral point of the low-voltage load area; a common-mode suppression unit, connected in series with the DC bus, for suppressing common-mode current in the DC bus; and a controller, connected to the rectifier and the inverter, the controller being configured to: generate a modulation signal for controlling the rectifier and the inverter based on the obtained grid state parameters of the medium-voltage distribution network and the load state parameters of the low-voltage load area; perform space vector modulation on the modulation signal, and select a zero-vector combination from a variety of zero-vector combinations of the space vector modulation that makes the common-mode voltage of the power conversion device meet a preset condition, so as to suppress the common-mode voltage; and generate a drive signal based on the space vector modulation result to control the switching of switching devices in the rectifier and the inverter.

[0006] Beneficial Effects: This application, by connecting a common-mode suppression unit in series on the DC bus, can suppress the common-mode current in the DC bus at the hardware level. Simultaneously, the controller generates a modulation signal based on the acquired grid state parameters and load state parameters, and performs space vector modulation on the modulation signal. It then selects the zero-vector combination from various zero-vector combinations that ensures the device's common-mode voltage meets preset conditions, thereby actively reducing the common-mode voltage amplitude. This effectively solves the problem of difficulty in effectively suppressing common-mode voltage and common-mode leakage current caused by the common-mode loop formed by the neutral point electrical connection in non-isolated current source back-to-back power converters, achieving safe and reliable operation of the device without the need for a power frequency isolation transformer.

[0007] In one optional embodiment, the inverter includes: at least one inverter module, wherein a DC bias absorption unit is connected in series on the AC output side of the inverter module for blocking the DC voltage component generated by the inverter module.

[0008] Beneficial effects: By dividing the inverter into at least one inverter module, the inverter-side structure becomes modularly expandable, allowing for flexible configuration of the number of modules according to power level requirements. Connecting a DC bias absorption unit in series on the AC output side of the inverter module effectively blocks the DC voltage component generated by the series structure, preventing DC bias accumulation that could lead to AC output voltage distortion. This ensures output power quality and provides a reliable technical foundation for high buck ratio applications with multiple modules connected in series.

[0009] In one optional embodiment, the inverter includes: a plurality of inverter modules connected in series, wherein the DC bias absorption unit is connected in series on the AC output side of each inverter module; and a differential mode suppression unit is also connected in series on the DC bus to suppress the differential mode current in the DC bus.

[0010] Beneficial effects: The series connection of multiple inverter modules enables the inverter side to withstand higher DC bus voltages, adapting to the high step-down ratio conversion requirements between medium-voltage distribution networks and low-voltage load areas; each inverter module is independently equipped with a DC bias absorption unit, which can absorb the DC bias components generated by each module, preventing bias transmission and accumulation between modules. Simultaneously, the differential mode suppression unit connected in series on the DC bus effectively suppresses differential mode current ripple in the DC bus, improves the DC side current waveform quality, and reduces the adverse effects of differential mode ripple on device operational stability and component lifespan.

[0011] In one optional embodiment, the AC side of the rectifier is connected to a first filter module, which includes a first filter inductor and a first filter capacitor; the AC side of the inverter is connected to a second filter module, which includes a second filter capacitor and a second filter inductor. The second filter capacitor is connected between the AC output side of the inverter and the DC bias absorption unit, and the second filter inductor is connected between the DC bias absorption unit and the low-voltage load area.

[0012] Beneficial effects: The rectifier AC side is connected to a first filter module consisting of a first filter inductor and a first filter capacitor, while the inverter AC side is connected to a second filter module consisting of a second filter capacitor and a second filter inductor. The second filter capacitor is connected between the inverter AC output side and the DC bias absorption unit, and the second filter inductor is connected between the DC bias absorption unit and the low-voltage load area. This connection sequence places the DC bias absorption unit after the filter capacitor and before the filter inductor. The filter capacitor can first bypass and filter the high-frequency switching ripple of the inverter output, the DC bias absorption unit then blocks the DC component, and the filter inductor finally smooths the residual harmonics. The three work together to effectively filter out the switching frequency subharmonics and reduce the AC side current distortion rate, while ensuring that the normal operation of the DC bias absorption unit is not affected by the filter components.

[0013] In one optional implementation, the grid status parameters include the grid voltage and grid current of the medium-voltage distribution network, and the load status parameters include the load voltage of the low-voltage load area.

[0014] Beneficial effects: The grid voltage, grid current and load voltage can be obtained directly by conventional voltage and current sensors without the need for complex signal processing or state estimation, which helps to reduce the implementation difficulty and cost of the control system. At the same time, it provides accurate feedback for realizing closed-loop control of rectifier-side power factor and closed-loop control of inverter-side load voltage.

[0015] In one optional implementation, the controller is configured to: perform closed-loop adjustment of the rectifier's power factor angle and the DC bus current based on the grid voltage and the grid current to obtain the rectifier's modulation factor and current reference angle; perform closed-loop adjustment of the inverter's output voltage amplitude based on the load voltage to obtain the inverter's modulation factor, and determine the inverter's current reference angle based on the phase angle of the grid voltage; and generate the modulation signal based on the rectifier's modulation factor and current reference angle, and the inverter's modulation factor and current reference angle.

[0016] Beneficial Effects: By implementing dual closed-loop regulation of the rectifier's power factor angle and DC bus current based on grid voltage and current, the modulation factor and current reference angle of the rectifier are obtained. Simultaneously, the inverter's output voltage amplitude is adjusted in a closed loop based on the load voltage to obtain the inverter's modulation factor, and the inverter's current reference angle is determined based on the grid voltage phase angle. This control method enables coordinated operation between the rectifier-side constant DC current and the inverter-side constant load voltage, allowing the rectifier side to operate at unity power factor and the inverter side to maintain a stable output voltage amplitude. Together, they achieve flexible and precise power transfer between the medium-voltage distribution network and low-voltage load areas, improving the system's dynamic response speed and steady-state control accuracy.

[0017] In an optional implementation, the controller is further configured to: determine a reference value for the DC bus current based on the rated power of the power conversion device and the rated voltage of the low-voltage load area, and perform closed-loop regulation of the DC bus current based on the reference value of the DC bus current.

[0018] Beneficial effects: By calculating and determining the reference value of the DC bus current based on the rated power of the power conversion device and the rated voltage of the low-voltage load area, the operating point of the DC bus current can be matched with the rated parameters of the device and the voltage level of the load side. Closed-loop regulation based on this reference value ensures that the modulation factor of each inverter module on the inverter side operates within a reasonable range, avoiding overmodulation due to an excessively high modulation factor or insufficient DC bus current utilization due to an excessively low modulation factor, thereby optimizing the overall operating efficiency and output waveform quality of the device.

[0019] In one optional implementation, the controller is configured to: determine two first-type current space vectors for synthesizing a target current vector based on the sector where the rectifier's current reference vector is located, and calculate the first common-mode voltage component corresponding to each of the two first-type current space vectors; determine two second-type current space vectors for synthesizing a target current vector based on the sector where the inverter's current reference vector is located, and calculate the second common-mode voltage component corresponding to each of the two second-type current space vectors; determine a basic common-mode voltage component based on the first common-mode voltage component and the second common-mode voltage component; iterate through and calculate the device common-mode voltage prediction value corresponding to nine combinations of the three zero vectors corresponding to the rectifier and the three zero vectors corresponding to the inverter, and select the zero vector combination that minimizes the absolute value of the device common-mode voltage prediction value.

[0020] Beneficial Effects: By determining the current space vectors used to synthesize the target current vector based on the sectors where the current reference vectors of the rectifier and inverter reside, and calculating the common-mode voltage components corresponding to each current space vector, the basic common-mode voltage components are determined. Then, the predicted common-mode voltage values ​​of the device are calculated through nine combinations of the three zero vectors corresponding to the rectifier and the three zero vectors corresponding to the inverter, and the zero vector combination that minimizes the absolute value of the predicted value is selected. This method fully utilizes the redundancy of zero vectors in space vector modulation. By actively selecting the zero vector combination that minimizes the common-mode voltage through traversal screening, it replaces the randomness of zero vector selection in existing technologies. This significantly reduces the overall common-mode voltage amplitude of the device, effectively suppressing common-mode circulating current. Furthermore, this suppression effect does not depend on adding additional hardware filtering devices, demonstrating good engineering practicality and economy.

[0021] In an alternative implementation, the controller is further configured to: extract the third harmonic component from the first common-mode voltage component and the second common-mode voltage component before determining the fundamental common-mode voltage component, and determine the fundamental common-mode voltage component based on the third harmonic component.

[0022] Beneficial effects: Since the third harmonic is the main component of the common-mode voltage generated by space vector modulation, the controller extracts the third harmonic component from the first and second common-mode voltage components before determining the basic common-mode voltage component, and determines the basic common-mode voltage component based on the third harmonic component. This processing method enables the zero-vector screening strategy to specifically suppress the main harmonic components in the common-mode voltage, improving the targeting and effectiveness of common-mode voltage suppression, avoiding the increased computational complexity caused by wideband processing, and ensuring both suppression effect and the real-time performance and feasibility of the algorithm.

[0023] Secondly, this application provides a control method for a power conversion device, comprising: acquiring grid state parameters of a medium-voltage distribution network and load state parameters of a low-voltage load area; generating a modulation signal for controlling a rectifier and an inverter based on the grid state parameters and the load state parameters; performing space vector modulation on the modulation signal, and selecting a zero vector combination from a variety of zero vector combinations of the space vector modulation that makes the common-mode voltage of the power conversion device meet a preset condition, so as to suppress the common-mode voltage; and generating a drive signal based on the space vector modulation result to control the switching on and off of the switching devices in the rectifier and the inverter.

[0024] In one optional implementation, generating a modulation signal for controlling the rectifier and inverter based on the grid state parameters and the load state parameters includes: performing closed-loop adjustment of the rectifier's power factor angle and DC bus current based on the grid voltage and grid current of the medium-voltage distribution network to obtain the rectifier's modulation factor and current reference angle; performing closed-loop adjustment of the inverter's output voltage amplitude based on the load voltage of the low-voltage load area to obtain the inverter's modulation factor, and determining the inverter's current reference angle based on the phase angle of the grid voltage; and generating the modulation signal based on the rectifier's modulation factor and current reference angle, and the inverter's modulation factor and current reference angle.

[0025] In one optional implementation, the step of selecting zero vector combinations that make the common-mode voltage meet the preset conditions includes: based on the common-mode voltage components generated by the large current space vectors corresponding to the rectifier and the inverter, traversing and calculating the device common-mode voltage prediction value corresponding to the combination of the zero vector corresponding to the rectifier and the zero vector corresponding to the inverter, and selecting zero vector combinations that make the device common-mode voltage prediction value meet the preset conditions.

[0026] Thirdly, this application provides an electronic device, including: a memory and a processor, which are communicatively connected to each other. The memory stores computer instructions, and the processor executes the computer instructions to perform the control method of the power conversion device of the first aspect or any corresponding embodiment described above.

[0027] Fourthly, this application provides a computer-readable storage medium storing computer instructions for causing a computer to execute the control method of the power conversion device according to the first aspect or any corresponding embodiment. Attached Figure Description

[0028] To more clearly illustrate the technical solutions in the specific embodiments of this application or the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this application. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0029] Figure 1 This is a schematic diagram of the electrical connection structure of a power conversion device according to an embodiment of this application; Figure 2 This is a schematic diagram of the modulus inductance parameter tuning according to an embodiment of this application; Figure 3 This is a schematic diagram of DC blocking capacitor parameter setting according to an embodiment of this application; Figure 4 This is a control block diagram of a high buck ratio non-isolated current source power converter according to an embodiment of this application; Figure 5 This is a spatial vector diagram of the current source according to an embodiment of this application; Figure 6 This is a schematic diagram illustrating the implementation process of the current space vector modulation method with common-mode suppression according to an embodiment of this application; Figure 7 This is a waveform diagram of the inverter-side DC blocking capacitor voltage, output voltage, inductor voltage, and load voltage of the device according to an embodiment of this application; Figure 8 This is a simulation diagram of the device current and current THD of the embodiments of this application; Figure 9 This is a schematic flowchart of a control method for a power conversion device according to an embodiment of this application; Figure 10 This is a schematic diagram of the hardware structure of an electronic device according to an embodiment of this application. Detailed Implementation

[0030] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0031] It is understood that before using the technical solutions disclosed in the various embodiments of this application, users should be informed of the types, scope of use, and usage scenarios of the personal information involved in this application in an appropriate manner in accordance with relevant laws and regulations, and user authorization should be obtained.

[0032] The terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this application, "multiple" means two or more, unless otherwise explicitly specified.

[0033] The large-scale integration of high-penetration distributed energy resources and stochastic loads such as electric vehicles poses challenges to distribution networks, including bidirectional power flow, harmonic distortion, and insufficient power supply reliability. Flexible interconnection devices, through power electronic converters, achieve power flow regulation and voltage support between different distribution stations, becoming an effective means to solve these problems. In medium-voltage, high-power scenarios, current-source topologies exhibit significant technical competitiveness due to their strong short-circuit withstand capability and good modular scalability. Furthermore, non-isolated structures can further eliminate the need for power frequency isolation transformers, reducing system cost and size. However, in non-isolated current-source back-to-back topologies, because the neutral points of the medium-voltage and low-voltage sides are electrically connected, the common-mode voltage generated by converter switching modulation forms a common-mode circulating current through the grounding loop. This leads to increased system losses, electromagnetic interference, and equipment insulation aging, becoming a key bottleneck restricting reliable operation.

[0034] To address this issue, this application provides a power conversion device to solve the problem of effectively suppressing common-mode voltage and common-mode leakage current in non-isolated current source type back-to-back power conversion devices.

[0035] Reference Figure 1 As shown, this application provides a power conversion device. The power conversion device includes a rectifier, an inverter, a common-mode rejection unit, and a controller. The AC side of the rectifier is used to connect to a medium-voltage distribution network. The DC side of the inverter is connected to the DC side of the rectifier via a DC bus, and the AC side of the inverter is used to connect to a low-voltage load area. The neutral point of the medium-voltage distribution network is electrically connected to the neutral point of the low-voltage load area. The common-mode rejection unit is connected in series on the DC bus to suppress common-mode current in the DC bus. The controller is connected to the rectifier and the inverter.

[0036] In this embodiment, the controller is configured to perform the following functions: generate modulation signals for controlling the rectifier and inverter based on the acquired grid state parameters of the medium-voltage distribution network and the load state parameters of the low-voltage load area; perform space vector modulation on the modulation signals, and select from various zero vector combinations of space vector modulation a zero vector combination that makes the common-mode voltage of the power conversion device meet a preset condition to suppress the common-mode voltage; and generate drive signals based on the space vector modulation results to control the switching devices in the rectifier and inverter.

[0037] The aforementioned power conversion device, configured as a back-to-back topology using rectifiers and inverters, is used in applications where the neutral point of a medium-voltage distribution network is electrically connected to the neutral point of a low-voltage load area. By connecting a common-mode suppression unit in series with the DC bus, it can suppress common-mode current in the DC bus at the hardware level. Simultaneously, the controller generates a modulation signal based on acquired grid and load state parameters and performs space vector modulation on the signal. It then selects the zero-vector combination from various zero-vector combinations that satisfies the preset conditions for the device's common-mode voltage, thereby actively reducing the common-mode voltage amplitude. Through the synergistic effect of the common-mode suppression unit and the zero-vector selection strategy, the problem of effectively suppressing common-mode voltage and leakage current caused by the common-mode loop formed by the electrical connection of the neutral point in non-isolated current source type back-to-back power conversion devices is effectively solved, achieving safe and reliable operation of the device without the need for a power frequency isolation transformer.

[0038] Specifically, in some embodiments, the rectifier is a three-phase current source rectifier consisting of six fully controlled switching modules Sr1 to Sr6. Each fully controlled switching module includes a diode and a fully controlled switching device, with the cathode of the diode connected to the collector of the fully controlled switching device. The rectifier is used to convert the AC power input from the medium-voltage distribution network into DC power and output DC current to the DC bus. The use of a current source rectifier topology gives the device inherent short-circuit withstand capability, effectively suppressing current spikes in the event of a DC-side fault, achieving reliable protection without the need for additional protection circuitry.

[0039] As a variation, the rectifier can also employ other current-source topologies. For example, in applications with higher voltage or higher power levels, the rectifier can consist of multiple current-source rectifier modules connected in parallel or series to form a multi-level rectifier, adapting to different voltage and power requirements. Conversely, in applications with lower power levels or single-phase power supply, the rectifier can also employ a single-phase current-source rectifier topology to reduce system complexity and manufacturing costs.

[0040] Specifically, in some implementations, the inverter is a three-phase current source inverter composed of multiple fully controlled switching modules, used to convert DC power on the DC bus into AC power and supply it to low-voltage load areas. The DC side of the inverter and the DC side of the rectifier are connected via the DC bus, thus forming a back-to-back power conversion structure. This back-to-back topology allows for decoupling of the control between the rectifier and inverter sides. The rectifier side focuses on DC current regulation and power factor control, while the inverter side focuses on load voltage regulation. Power is naturally transferred between the two sides through the balancing of the DC bus current, resulting in a clear control structure and rapid dynamic response. The back-to-back power conversion circuit controls the magnitude and direction of power flow between the two load areas by controlling the magnitude and direction of the DC current and the converter output current.

[0041] It should be noted that the common-mode suppression unit is connected in series with the DC bus to suppress common-mode current in the DC bus. Since the neutral point on the medium-voltage side is directly connected to the neutral point on the low-voltage side, the common-mode voltage generated by the converter switching action will form a common-mode circulating current through the grounding loop. The common-mode suppression unit can provide a high-impedance path for the common-mode current, thereby effectively limiting the amplitude of the common-mode circulating current, forming a hardware-software coordinated suppression mechanism with the zero-vector optimization strategy executed by the controller.

[0042] In some implementations, the common-mode suppression unit is specifically implemented as a common-mode inductor. L cm The common-mode inductor is connected in series with the DC bus. Based on the principle of a common-mode reactor, since the common-mode current flows in the same direction through the coils, the magnetic flux generated by the two inductor coils reinforces each other, thus presenting a high impedance to the common-mode current and reducing it. Conversely, when the differential-mode current flows, the magnetic flux generated by the two coils cancels each other out, presenting a lower impedance, and therefore having little impact on normal differential-mode power transmission. Regarding parameter selection, increasing the inductance value increases the impedance to the common-mode current, theoretically which should more effectively suppress leakage current. However, considering the parasitic capacitance of actual inductor components and the potential saturation of the core material at high frequencies, continuously increasing the inductance of the common-mode inductor does not necessarily lead to a linear decrease in the common-mode current; instead, it may exhibit marginal effects. (Refer to...) Figure 2 As shown, when the common-mode inductance increases, the common-mode leakage current gradually decreases, but the decreasing trend gradually becomes smoother when the common-mode inductance is greater than 400mH. Considering the design cost and size of the common-mode inductor, the design value of the common-mode inductor in this embodiment is selected as 400mH.

[0043] As a variation, the common-mode suppression unit can also employ other magnetic components or circuit structures that present high impedance to common-mode current and low impedance to differential-mode current. For example, in applications requiring further improvement in common-mode suppression, a combination of multiple common-mode inductors connected in series or parallel can be used; or, in applications with strict limitations on size and weight, an active common-mode suppression circuit can be used, which achieves common-mode suppression by detecting the common-mode current and injecting a reverse compensation current.

[0044] The controller connects to the rectifier and inverter, and performs functions such as generating modulation signals, space vector modulation, zero-vector combination filtering, and generating drive signals. In some implementations, the controller can be implemented by a device with computing capabilities, such as a digital signal processor, field-programmable gate array, or microcontroller, which internally stores computer program instructions for performing the aforementioned control functions. The controller acquires grid state parameters and load state parameters through sampling circuits, processes them internally, and outputs drive signals to the switching devices of the rectifier and inverter, thereby achieving closed-loop control.

[0045] In some implementations, the inverter includes at least one inverter module, with a DC bias absorption unit connected in series on the AC output side of the inverter module. This DC bias absorption unit is used to block the DC voltage component generated by the inverter module. By dividing the inverter into at least one inverter module, the inverter-side structure has modular expansion capabilities, facilitating flexible configuration of the number of modules according to power level requirements. Connecting the DC bias absorption unit in series on the AC output side of the inverter module effectively blocks the DC voltage component generated by the series structure of the inverter module, preventing DC bias accumulation that could lead to AC output voltage distortion, thereby ensuring output power quality and providing a reliable technical basis for high buck ratio applications with multiple modules connected in series.

[0046] Specifically, in some implementations, the DC bias absorption unit may include a DC blocking capacitor. The DC blocking capacitor is primarily used to block the DC component while allowing AC signals to pass. The DC blocking capacitor is connected in series between the AC output terminal of the inverter module and the subsequent filter circuit, utilizing the capacitor's DC blocking and AC passing characteristics to allow AC components to pass while blocking DC components. (See reference...) Figure 3 As the DC blocking capacitor capacity increases, the DC withstand voltage level decreases accordingly. Based on the simulation parameters of this embodiment and the number of inverter modules on the inverter side, it can be analyzed that the DC blocking capacitors on the AC sides of the two inverters closest to the positive and negative DC buses bear the largest DC voltage. Therefore, based on the trend relationship between withstand voltage level and capacity, 1000μF is selected as the design parameter value for the DC blocking capacitor. In practical applications, capacitors of the same series with higher withstand voltage usually have lower capacitance. The DC blocking capacitor type is generally an aluminum electrolytic capacitor, a ceramic capacitor, or a film capacitor; the specific type can be selected based on cost and performance requirements.

[0047] As a variation, the DC bias absorption unit can employ multiple capacitors connected in parallel, in addition to a single DC blocking capacitor, to increase the current-carrying capacity or reduce the equivalent series resistance, thereby reducing power loss on the capacitor. Alternatively, a DC blocking filter circuit composed of capacitors and resistors can be used, utilizing the resistors to dampen the charging and discharging process of the capacitors, further improving the DC blocking performance.

[0048] In some implementations, the inverter may include multiple inverter modules connected in series, each with a DC bias absorption unit connected in series on its AC output side. Additionally, a differential mode suppression unit may be connected in series on the DC bus to suppress differential mode current in the DC bus. The series connection of multiple inverter modules allows the inverter side to withstand a higher DC bus voltage, thus meeting the high step-down ratio conversion requirements between medium-voltage distribution networks and low-voltage load areas. Each inverter module is independently configured with a DC bias absorption unit, which can absorb the DC bias component generated by each module separately, preventing the transmission and accumulation of DC bias between modules. Simultaneously, the differential mode suppression unit connected in series on the DC bus effectively suppresses differential mode current ripple in the DC bus, improves the waveform quality of the DC side current, and reduces the adverse effects of differential mode ripple on device operational stability and power device lifespan.

[0049] Specifically, in some implementations, the inverter includes inverter modules #1 to #2 inverter modules. n ,in n This represents the number of series current source converter modules on the inverter side. Each inverter module includes a fully controlled switching module S. i11 To S i61 To S i1n To S i6n Each fully controlled switching module consists of a diode and a fully controlled switching device connected together, with the cathode of the diode connected to the collector of the fully controlled switching device. Multiple inverter modules connected in series mean that the DC negative terminal of one inverter module is sequentially connected to the DC positive terminal of the next inverter module, forming a series link. The first end of this series link is connected to the positive terminal of the DC bus, and the last end is connected to the negative terminal of the DC bus. Each inverter module's AC output side is connected to its own DC blocking capacitor, and then connected in parallel to the same AC bus. After subsequent filtering, it is connected to the low-voltage load area. Because each inverter module is at a different potential in the DC link, there is a stepped DC potential difference between its AC output side and ground. Therefore, each module must be independently equipped with a DC blocking capacitor to block this DC component and ensure normal AC output.

[0050] In some implementations, the differential mode suppression unit can be specifically implemented as a differential mode inductor. L dm It is connected in series to the DC bus. The differential mode inductor presents high impedance to the differential mode current ripple present in the DC bus, which can effectively smooth the DC current waveform, reduce the DC current ripple amplitude, thereby reducing the current stress on the switching devices of the rectifier and inverter, and improving the operating efficiency of the system.

[0051] As a variation, the differential mode suppression unit can also employ a differential mode filter network composed of inductors and capacitors to achieve better filtering performance. Alternatively, in applications where DC bus current ripple requirements are not high or the DC bus itself already has a sufficiently large inductance, the differential mode suppression unit can be omitted to reduce the cost and size of the device.

[0052] In some implementations, a first filter module is connected to the AC side of the rectifier. This first filter module includes a first filter inductor and a first filter capacitor. A second filter module is connected to the AC side of the inverter. This second filter module includes a second filter capacitor and a second filter inductor. The second filter capacitor is connected between the AC output side of the inverter and the DC bias absorption unit, and the second filter inductor is connected between the DC bias absorption unit and the low-voltage load area. This connection sequence places the DC bias absorption unit after the second filter capacitor and before the second filter inductor. The second filter capacitor first bypasses and filters the high-frequency switching ripple at the inverter output, the DC bias absorption unit then blocks the DC component, and the second filter inductor finally smooths the residual harmonics. These three components work together to effectively filter out subharmonics of the switching frequency and reduce the AC side current distortion rate, while ensuring that the normal operation of the DC bias absorption unit is not affected by the filter components.

[0053] Specifically, in some implementations, the rectifier-side filter inductor in the first filter module L r One end is connected to the three-phase output terminal of the medium-voltage distribution network, and the other end is connected to the rectifier-side filter capacitor. C r After connecting, connect it to the rectifier output terminal, and then connect the rectifier-side filter capacitor. C r The ends are connected to a single point, forming a star connection. In the second filter module, the inverter-side filter capacitor... C i Connect to the output of each inverter module, and then to the DC blocking capacitor. C di Connected, DC blocking capacitor C di The other end is connected to the inverter-side filter inductor. L i Connections. All inverter-side filter inductors. L i The end of the circuit is connected to the input terminal of the low-voltage load area.

[0054] As a variation of the implementation, the first and second filtering modules can also employ other filter topologies. For example, in applications requiring higher suppression of high-frequency harmonics, an LCL-type filter can be used, suppressing resonance by connecting a damping resistor in series with the filter capacitor branch; alternatively, an LC series resonant filter can be used to perform notch filtering for specific harmonics.

[0055] In some implementations, grid state parameters include the grid voltage and grid current of the medium-voltage distribution network, and load state parameters include the load voltage of the low-voltage load area. Specifying the grid state parameters as grid voltage and grid current, and the load state parameters as load voltage, makes the controller's input signals clearly measurable and operable. These electrical quantities can be directly acquired using current and voltage sensors. Specifically, current sensors are installed and measure the grid output current and DC current at both ends, and voltage sensors are installed and measure the grid voltage at both ends. This eliminates the need for complex signal processing or state estimation, reducing the implementation difficulty and hardware cost of the control system, while providing accurate feedback for achieving closed-loop control of the rectifier-side power factor and closed-loop control of the inverter-side load voltage.

[0056] Reference Figure 4 In some implementations of the control block diagram shown, the controller can generate a modulation signal by: performing closed-loop adjustment of the rectifier's power factor angle and DC bus current based on the grid voltage and grid current to obtain the rectifier's modulation factor and current reference angle; performing closed-loop adjustment of the inverter's output voltage amplitude based on the load voltage to obtain the inverter's modulation factor, and determining the inverter's current reference angle based on the grid voltage's phase angle; and generating a modulation signal based on the rectifier's modulation factor and current reference angle, as well as the inverter's modulation factor and current reference angle.

[0057] This control method achieves coordinated operation between the rectifier-side constant DC current and the inverter-side constant load voltage. Specifically, in the rectifier controller, the power factor angle can be calculated based on the voltage and current of the medium-voltage distribution network. φ , calculate φ Compared with reference value φ ref In comparison, the modulation delay angle can be obtained through a power factor controller. α r Therefore, the rectifier current reference angle can be calculated. θ r Its expression is:

[0058] in, G φ (s) is a power factor controller.k p_φ and k i_φ These are the proportional coefficient and integral coefficient of the power factor, respectively. θ g The voltage of the medium-voltage distribution network on the rectifier side v r(abc) The real-time grid voltage phase angle is calculated using a phase-locked loop.

[0059] Meanwhile, the device controls the DC bus current through the rectifier controller. i dc . i dc After passing through a low-pass filter, it is compared with a given reference current. i dc_ref In comparison, the resulting error is processed by the DC current controller and divided by... i dc It is then used as the modulation factor of the rectifier. m ar Its expression is:

[0060] in, G I ( s It is a DC current controller. k p_I and k i_I These are the proportional and integral coefficients of the DC current controller. i dc_LPF It is the DC current after low-pass filtering. ω c This is the cutoff frequency of the low-pass filter.

[0061] Regarding the selection of the DC current reference value, since the inverter side is directly connected to the transformer load and other losses of the power flow transfer device are ignored, the effective value of the steady-state output current of the dual-sided converter can be calculated based on power conservation and the system modulation ratio. The definition of the modulation ratio of the dual-sided converter is:

[0062] in, I sr and I si These are the effective values ​​of the output phase current of the power conversion device for the medium-voltage distribution network and the low-voltage load area, respectively.

[0063] Since the inverter side is typically connected in parallel to the low-voltage distribution network, and given a fixed power supply, the total AC current is large due to the low voltage level, requiring more inverter modules to shunt the current. This allows us to determine the minimum DC current.i dc_min :

[0064] However, when the device's DC voltage is i dc_min At this time, the modulation factor of each inverter module is 1. However, under normal operating conditions, the modulation factor of the inverter module should not be too high. This is to ensure that the modulation factor of each converter module on the inverter side is 1. m ai Operating at around 0.8, it can be controlled by the device's rated power. S 0 and low voltage load area rated voltage RMS value V gi First, calculate the effective value of the output current on the inverter side of the device, and then use the modulation ratio definition formula to calculate the DC current reference value. i dc_ref Its specific expression is:

[0065] In the inverter controller, the voltage of the load area is measured by a sensor. v load（abc） The magnitude of its load voltage can be calculated. E load Its expression is:

[0066] In the formula, v load_a , v load_b and v load_c These are the instantaneous values ​​of the three-phase voltage in the load area.

[0067] Based on reference load voltage amplitude E ref The inverter uses a load voltage controller to control the voltage amplitude of the load area. After standardization, the modulation factor of the inverter can be calculated. m ai Its expression is:

[0068] in, G L ( s It is a load voltage controller. k p_L and k i_L These are the proportional and integral coefficients of the load voltage controller. E refThis is the load voltage amplitude reference. The inverter reference current angle is also shown at this time. θ i The voltage directly from the medium voltage distribution network v r（abc） It is obtained via a phase-locked loop. Finally, the rectifier modulation factor is... m ar 1. Rectifier current reference angle θ r Inverter modulation factor m ai and inverter current reference angle θ i A modulation method with common-mode suppression is introduced to generate the switching signal of the power module of the device through space vector modulation.

[0069] The aforementioned control parameters together constitute the modulation signal, enabling the rectifier side to operate at unity power factor and the inverter side to output a stable voltage amplitude. Together, they achieve flexible and precise power transfer between the medium-voltage distribution network and the low-voltage load area, improving the system's dynamic response speed and steady-state control accuracy.

[0070] As a variation of the implementation, the control objective on the rectifier side can be adjusted according to actual needs. For example, in situations where reactive power support to the power grid is required, constant AC current control or constant reactive power control can be used on the rectifier side. The inverter side can also employ alternative solutions such as constant AC current control or droop control based on load characteristics.

[0071] Reference Figure 5 and Figure 6 In some implementations, the controller can select zero-vector combinations that make the common-mode voltage of the power conversion device meet preset conditions in the following manner.

[0072] Space vector modulation (SVM) is the most common modulation method for current source converters. Its basic principle is to synthesize a reference vector sequentially according to the sampling period. Within each sampling period, the reference current vector is obtained by synthesizing a triangle of current vectors, with each current vector having a suitable duration. Assuming the reference vector falls within a certain sector at a certain moment, the reference current vector can be synthesized from the two nearest large vectors and a zero vector through different durations. When the sampling period is sufficiently small, the current reference vector in each switching cycle fits the sinusoidal current better. The duration of each vector can be calculated using the ampere-second balance principle, synthesized from the two nearest large vectors and a zero vector.

[0073] Specifically, firstly, based on the modulation factors of the rectifier side and the inverter side of the device. m ar , m ai and phase angle θr , θ i Spatial vector modulation is then applied to each module. The sector containing the current vector reference is then determined. Based on the vector triangle, the current vector references for each converter module on both the rectifier and inverter sides of the device can be calculated. I→ r_ref and I→ i_ref amplitude I r_ref , I i_ref :

[0074] Current vector reference I→ r_ref and I→ i_ref The phase angles follow respectively θ r and θ i Therefore, based on θ r and θ i Size, determine I→ r_ref and I→ i_ref The sector in which the current vector resides. Based on the ampere-second balance principle, the product of the current vector reference and the sampling period is equal to the algebraic sum of the products of the large and zero current vectors of the two sectors in which the current vector resides and their respective durations. Assuming the switching periods on both sides of the device are equal and synchronized, the duration of each vector of the converter on both sides of the device can be calculated, and its expression is:

[0075] in, T r1 , T r2 and T r0 These represent the duration of the synthesized vector of the rectifier in the device. T i1 , T i2 and T i0 These represent the combined action time of each converter on the inverter side of the device. T s The sampling period.

[0076] The common-mode current of the device mainly flows back through the differential-mode inductor of the DC bus, the common-mode inductor, and the AC filter circuits on both sides, before returning to the neutral points of the power grids on both sides. Based on this common-mode circuit and the voltage of the medium-voltage distribution network, the common-mode voltage of the rectifier section of the device can be calculated. v cm_r Its expression is:

[0077] in, v po1 and v no1 These are the positive and negative DC bus terminals of the rectifier section of the device, respectively, leading to the neutral point of the medium-voltage distribution network. o 1 voltage, G r1 ~ G r6 The switching function of the rectifier-side converter of the device is expressed as follows:

[0078] Since the switching transistor drive signals used in the series current source inverter modules are obtained through the same control and modulation strategy, the sum of the voltage at the midpoint of the filter capacitor of the lower arm of the inverter module and the voltage at the midpoint of the filter capacitor of the upper arm of the inverter module connected to its DC negative terminal is equal to the DC voltage of a single inverter module in the device at any given time. Because of the DC blocking capacitors in each module, this DC voltage does not affect the common-mode current. Therefore, calculating the common-mode voltage on the inverter side of the device can be equivalent to calculating the common-mode voltage of the first converter module on the inverter side. Similar to the rectifier side, the common-mode voltage of the inverter side of the device can be obtained. v cm_i The expression is:

[0079] in, v p1o2 and v n1o2 These are the positive and negative DC bus terminals of the inverter section of the device, respectively, leading to the neutral point of low-voltage load area #2. o 2 voltage, G i1 ~ G i6 The switching function for the first converter module on the inverter side of the device is expressed as follows:

[0080] By substituting the switching states corresponding to the large and zero vectors of the current space of the converters on both sides of the device into the common-mode voltage expression of the rectifier and inverter sides of the device, the common-mode voltage values ​​corresponding to the large and zero vectors of the current space of the rectifier and inverter sides of the device can be calculated.

[0081] When sampling period T s When the current is sufficiently small, all AC quantities are considered to be fixed values ​​within the sampling period. Therefore, the common-mode voltage generated by the dual-sided converter is obtained by superimposing the common-mode voltage values ​​corresponding to each synthesized current vector over their respective synthesis times. The large vector has no redundancy, while the zero vector has redundancy. Therefore, the average common-mode voltage generated by the large vector in the device is fixed, while the average common-mode voltage generated by the zero vector varies with the choice of the zero vector. Based on the volt-second balance principle and the calculated common-mode voltage value corresponding to the large vector in the current space, the average common-mode voltage generated by the large vector can be calculated in each sampling period. v cm_active Its expression is:

[0082] in, v cm_r1 , v cm_r2 The common-mode voltage value corresponding to the large vector of the rectifier-side converter reference sector, calculated according to the above steps, is used. v cm_i1 , v cm_i2 The common-mode voltage value corresponding to the large vector of the current vector reference sector of each converter module on the inverter side of the device is used.

[0083] Since the common-mode voltage is dominated by the third harmonic when using space vector modulation, therefore... v cm_active Its third harmonic component was extracted using a bandpass filter. v cm_active_3rd Its expression is:

[0084] in, ω 0 is the fundamental angular frequency. ω c This represents the filter bandwidth.

[0085] Since three different zero vectors are available for modulation on both the rectifier and inverter sides of the device, the average common-mode voltage generated by the zero vector in the dual-sided converter is... v cm_0 There are nine possibilities, and their expression is:

[0086] in, v cm_r0 ( i The rectifier side of the device is controlled by a zero vector. I→ 0i The corresponding common-mode voltage value, v cm_i0 ( j The inverter side of the device is controlled by a zero vector. I→ 0j The corresponding common-mode voltage value. Based on the obtained common-mode voltage expression generated by the large vector and zero vector of the dual-sided converter, the common-mode voltage value of the device can be calculated. By traversing nine zero-vector combination schemes, the optimal combination that minimizes the common-mode voltage value of the device is selected, thereby maximizing the suppression of the common-mode circulating current of the device. Its expression is:

[0087] in, v cm_min This is the minimum common-mode voltage of the device.

[0088] The above steps are used to calculate the large and zero vectors of the current space selected by the dual-sided converters of the device and their duration of action, thereby obtaining the drive signals of each converter in the device.

[0089] This method fully utilizes the redundancy of zero vectors in space vector modulation. By actively selecting the combination of zero vectors that minimizes the common-mode voltage through traversal filtering, it replaces the randomness of zero vector selection in existing technologies. This method can significantly reduce the overall common-mode voltage amplitude of the device, thereby effectively suppressing common-mode circulating current. Moreover, this suppression effect does not depend on adding additional hardware filtering devices, demonstrating good engineering practicality and economy.

[0090] As a variation of the implementation, the controller may not traverse all nine combinations, but instead perform rapid filtering based on the polarity of the common-mode voltage or the optimal result of the previous control cycle. This reduces computational load and is suitable for applications with high real-time requirements. Alternatively, weighting coefficients can be introduced into the filtering criteria to optimize the common-mode voltage suppression effect against other performance indicators.

[0091] Reference Figure 7 The simulation waveforms shown are used to conduct simulation experiments and analysis on the power conversion device of this embodiment. Figure 7 The waveforms of the DC blocking capacitor voltage, output voltage, inductor voltage, and load voltage on the inverter side of the device are displayed. V out1 The voltage at the output point of each inverter module relative to the load neutral point. V d1 and VCd1 These are the DC component of the inverter's output voltage and the output voltage, respectively. V Li1 and V Load These are the filter inductor voltage and the load voltage, respectively. It can be seen that the AC component of the output voltage of each module is basically the same, while the DC component differs by one-third of the DC voltage. The DC bias output from the series current source inverter can be completely absorbed by the DC blocking capacitor, resulting in a relatively low harmonic distortion rate of the load voltage after filtering.

[0092] Reference Figure 8 The simulation results of the device current and total harmonic current distortion (THD) show that, using the topology and modulation method with common-mode suppression of this application, the peak common-mode current is only 0.5A and the effective value is only 0.24A, which has a very small impact on the converter output current. The converter output current waveform quality is good, and the common-mode inductor effectively suppresses the third component of the common-mode leakage current. The total harmonic distortion of the AC side current of the rectifier and inverter are 3.17% and 2.56%, respectively. A third-order ripple is observed in the DC current, with a ripple magnitude of 1.2A. In summary, the power conversion device and its common-mode suppression strategy provided in this application demonstrate excellent performance in all aspects, including common-mode leakage current suppression, DC current ripple control, and output current power quality.

[0093] According to an embodiment of this application, a control method embodiment for a power conversion device is provided. 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. Furthermore, 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.

[0094] This embodiment provides a control method for a power conversion device, which can be used in any of the power conversion devices described above. (Refer to...) Figure 9 The flowchart shown includes the following control methods: Step S201: Obtain the grid status parameters of the medium-voltage distribution network and the load status parameters of the low-voltage load area.

[0095] Step S202: Generate modulation signals for controlling the rectifier and inverter based on grid state parameters and load state parameters.

[0096] Step S203: Perform space vector modulation on the modulation signal, and select from the various zero vector combinations of space vector modulation the zero vector combination that makes the common mode voltage of the power conversion device meet the preset conditions, so as to suppress the common mode voltage.

[0097] Step S204: Generate a drive signal based on the space vector modulation result to control the switching devices in the rectifier and inverter.

[0098] The aforementioned control method implements control of the power conversion device through a clearly defined step-by-step process. First, parameters such as the grid voltage and current of the medium-voltage distribution network, as well as the load voltage of the low-voltage load area, are acquired through a sampling circuit, providing a real-time data basis for control decisions. Then, the controller executes a closed-loop control algorithm based on these parameters to generate the modulation factor and current reference angle required by the rectifier and inverter, forming the modulation signal. Next, space vector modulation is performed on the modulation signal. When the zero vector is determined, the predicted common-mode voltage value corresponding to each zero-vector combination is calculated iteratively, and the combination that satisfies the preset conditions is selected. Finally, a drive signal is generated based on the selected vector and its duration to control the on / off state of each switching device. This method can effectively suppress common-mode voltage and common-mode circulating current in non-isolated topologies without relying on a power frequency isolation transformer, improving the operational safety and power quality of the device.

[0099] It should be noted that the order in which the above methods and steps are written does not imply a strict execution order. The specific execution order of each step should be determined by its function and internal logic. Unless explicitly specified, there may be other intermediate steps between steps, or some steps may be executed in parallel.

[0100] In some implementations, in step S202 above, the grid state parameters include the grid voltage and grid current of the medium-voltage distribution network, and the load state parameters include the load voltage of the low-voltage load area. The step of generating the modulation signal may include: Step a1: Perform closed-loop adjustment of the rectifier's power factor angle and DC bus current based on the grid voltage and grid current to obtain the rectifier's modulation factor and current reference angle. Step a2: Perform closed-loop adjustment of the inverter's output voltage amplitude based on the load voltage to obtain the inverter's modulation factor, and determine the inverter's current reference angle based on the phase angle of the grid voltage. Step a3: Generate a modulation signal based on the modulation factor and current reference angle of the rectifier and the modulation factor and current reference angle of the inverter.

[0101] In some implementations, step S203 above, the step of selecting zero-vector combinations that satisfy preset conditions for the common-mode voltage, may include: Step b1: Based on the common-mode voltage components generated by the large current space vectors corresponding to the rectifier and inverter, the predicted common-mode voltage of the device is calculated by iterating through the zero vectors corresponding to the rectifier and the inverter, and the zero vector combinations that make the predicted common-mode voltage of the device meet the preset conditions are selected.

[0102] The aforementioned control method, through the separation and coordination of control objectives on the rectifier and inverter sides, enables the rectifier side to operate at unity power factor and stabilize the DC bus current, while the inverter side can precisely regulate the load voltage. Power transfer is achieved naturally through the balance of DC bus currents on both sides, making it suitable for power flow transfer and voltage support in flexible interconnection scenarios of medium- and low-voltage distribution networks. Simultaneously, zero-vector screening optimizes both converter sides as a whole, fully considering the superposition effect of common-mode voltages on the rectifier and inverter sides, achieving globally optimal common-mode voltage suppression.

[0103] Figure 10 This is a schematic diagram of the structure of an electronic device provided in an embodiment of this application.

[0104] The following is a detailed reference. Figure 10 The diagram illustrates a structural schematic suitable for implementing the electronic device described in the embodiments of this application. The electronic device may include a processor (e.g., a central processing unit, graphics processor, etc.) 901, which can perform various appropriate actions and processes according to a program stored in read-only memory (ROM) 902 or a program loaded from memory 908 into random access memory (RAM) 903. The RAM 903 also stores various programs and data required for the operation of the electronic device. The processor 901, ROM 902, and RAM 903 are interconnected via a bus 904. An input / output (I / O) interface 905 is also connected to the bus 904.

[0105] Typically, the following devices can be connected to I / O interface 905: input devices 906 including, for example, touchscreens, touchpads, keyboards, mice, cameras, microphones, accelerometers, gyroscopes, etc.; output devices 907 including, for example, liquid crystal displays (LCDs), speakers, vibrators, etc.; memory devices 908 including, for example, magnetic tapes, hard disks, etc.; and communication devices 909. Communication device 909 allows electronic devices to communicate wirelessly or wiredly with other devices to exchange data. Although Figure 10 Electronic devices with various devices are shown, but it should be understood that it is not required to implement or have all of the devices shown, and more or fewer devices may be implemented or have instead.

[0106] Specifically, according to embodiments of this application, the processes described above with reference to the flowcharts can be implemented as computer software programs. For example, embodiments of this application include a computer program product comprising a computer program carried on a non-transitory computer-readable medium, the computer program containing program code for performing the methods shown in the flowcharts. In such embodiments, the computer program can be downloaded and installed from a network via a communication device 909, or installed from a memory 908, or installed from a ROM 902. When the computer program is executed by the processor 901, it performs the functions defined in the control method of the power conversion apparatus of embodiments of this application.

[0107] Figure 10 The electronic device shown is merely an example and should not impose any limitation on the functionality and scope of use of the embodiments of this application.

[0108] This application also provides a computer-readable storage medium. The methods described in this application can be implemented in hardware or firmware, or implemented as recordable on a storage medium, or implemented as computer code downloaded over a network and originally stored on a remote storage medium or a non-transitory machine-readable storage medium and then stored on a local storage medium. Thus, the methods described herein can be processed by software stored on a storage medium using a general-purpose computer, a dedicated processor, or programmable or dedicated hardware. The storage medium can be a magnetic disk, optical disk, read-only memory, random access memory, flash memory, hard disk, or solid-state drive, etc.; further, the storage medium can also include combinations of the above types of memory. It is understood that computers, processors, microprocessor controllers, or programmable hardware include storage components capable of storing or receiving software or computer code. When the software or computer code is accessed and executed by the computer, processor, or hardware, the control method of the power conversion device shown in the above embodiments is implemented.

[0109] A portion of this application can be applied as a computer program product, such as computer program instructions, which, when executed by a computer, can invoke or provide the methods and / or technical solutions according to this application through the operation of the computer. Those skilled in the art will understand that the forms in which computer program instructions exist in a computer-readable medium include, but are not limited to, source files, executable files, installation package files, etc. Correspondingly, the ways in which computer program instructions are executed by a computer include, but are not limited to: the computer directly executing the instructions, or the computer compiling the instructions and then executing the corresponding compiled program, or the computer reading and executing the instructions, or the computer reading and installing the instructions and then executing the corresponding installed program. Here, the computer-readable medium can be any available computer-readable storage medium or communication medium accessible to a computer.

[0110] Although embodiments of this application have been described in conjunction with the accompanying drawings, those skilled in the art can make various modifications and variations without departing from the spirit and scope of this application, and all such modifications and variations fall within the scope defined by the appended claims.

Claims

1. A power conversion device, characterized in that, include: A rectifier, wherein the AC side of the rectifier is connected to a medium-voltage power distribution network; The inverter has its DC side connected to the DC side of the rectifier via a DC bus, and its AC side connected to the low-voltage load area. The neutral point of the medium-voltage distribution network is electrically connected to the neutral point of the low-voltage load area. A common-mode suppression unit is connected in series with the DC bus to suppress the common-mode current in the DC bus; A controller, connected to the rectifier and the inverter, is configured to: Based on the obtained grid state parameters of the medium-voltage distribution network and the load state parameters of the low-voltage load area, a modulation signal for controlling the rectifier and the inverter is generated; The modulation signal is subjected to space vector modulation, and from the various zero vector combinations of the space vector modulation, a zero vector combination that makes the common-mode voltage of the power conversion device meet the preset conditions is selected to suppress the common-mode voltage. A drive signal is generated based on the space vector modulation result to control the switching devices in the rectifier and the inverter.

2. The power conversion device according to claim 1, characterized in that, The inverter includes: At least one inverter module, wherein a DC bias absorption unit is connected in series on the AC output side of the inverter module to block the DC voltage component generated by the inverter module.

3. The power conversion device according to claim 2, characterized in that, The inverter includes: The inverter modules are connected in series, and the DC bias absorption unit is connected in series on the AC output side of each inverter module. A differential mode suppression unit is also connected in series on the DC bus to suppress the differential mode current in the DC bus.

4. The power conversion device according to claim 2, characterized in that, The AC side of the rectifier is connected to a first filter module, which includes a first filter inductor and a first filter capacitor. The inverter's AC side is connected to a second filter module, which includes a second filter capacitor and a second filter inductor. The second filter capacitor is connected between the inverter's AC output side and the DC bias absorption unit, and the second filter inductor is connected between the DC bias absorption unit and the low-voltage load area.

5. The power conversion device according to claim 1, characterized in that, The grid status parameters include the grid voltage and grid current of the medium-voltage distribution network, and the load status parameters include the load voltage of the low-voltage load area.

6. The power conversion device according to claim 5, characterized in that, The controller is configured to: Based on the grid voltage and the grid current, the power factor angle of the rectifier and the DC bus current are adjusted in a closed loop to obtain the modulation factor and current reference angle of the rectifier. Based on the load voltage, the output voltage amplitude of the inverter is adjusted in a closed loop to obtain the modulation factor of the inverter, and the current reference angle of the inverter is determined based on the phase angle of the grid voltage. The modulation signal is generated based on the modulation factor and current reference angle of the rectifier, and the modulation factor and current reference angle of the inverter.

7. The power conversion device according to claim 6, characterized in that, The controller is also configured to: determine a reference value for the DC bus current based on the rated power of the power conversion device and the rated voltage of the low-voltage load area, and perform closed-loop regulation of the DC bus current based on the reference value of the DC bus current.

8. The power conversion device according to claim 1, characterized in that, The controller is configured to: Based on the sector where the current reference vector of the rectifier is located, two first-type current space vectors for synthesizing the target current vector are determined, and the first common-mode voltage component corresponding to each of the two first-type current space vectors is calculated. Based on the sector where the inverter's current reference vector is located, determine two second-type current space vectors for synthesizing the target current vector, and calculate the second common-mode voltage component corresponding to each of the two second-type current space vectors; The fundamental common-mode voltage component is determined based on the first common-mode voltage component and the second common-mode voltage component; After iterating through and calculating the three zero vectors corresponding to the rectifier and the three zero vectors corresponding to the inverter, nine combinations are made to obtain the predicted common-mode voltage value of the corresponding device, and the zero vector combination that minimizes the absolute value of the predicted common-mode voltage value of the device is selected.

9. The power conversion device according to claim 8, characterized in that, The controller is also configured to: Before determining the basic common-mode voltage component, the third harmonic component is extracted from the first common-mode voltage component and the second common-mode voltage component, and the basic common-mode voltage component is determined based on the third harmonic component.

10. A control method for a power conversion device, characterized in that, include: Obtain the grid status parameters of the medium-voltage distribution network and the load status parameters of the low-voltage load area; Based on the grid state parameters and the load state parameters, a modulation signal for controlling the rectifier and inverter is generated. The modulation signal is subjected to space vector modulation, and from the various zero vector combinations of the space vector modulation, a zero vector combination that makes the common-mode voltage of the power conversion device meet the preset conditions is selected to suppress the common-mode voltage. A drive signal is generated based on the space vector modulation result to control the switching devices in the rectifier and the inverter.

11. The control method according to claim 10, characterized in that, The step of generating modulation signals for controlling the rectifier and inverter based on the grid state parameters and the load state parameters includes: The power factor angle and DC bus current of the rectifier are adjusted in a closed loop based on the grid voltage and grid current of the medium-voltage distribution network to obtain the modulation factor and current reference angle of the rectifier. The inverter's output voltage amplitude is closed-loop regulated based on the load voltage of the low-voltage load area to obtain the inverter's modulation factor, and the inverter's current reference angle is determined based on the phase angle of the grid voltage. The modulation signal is generated based on the modulation factor and current reference angle of the rectifier and the modulation factor and current reference angle of the inverter.

12. The control method according to claim 11, characterized in that, The process of selecting zero-vector combinations that satisfy the preset conditions for the common-mode voltage includes: Based on the common-mode voltage components generated by the large current space vectors corresponding to the rectifier and the inverter, the predicted common-mode voltage of the device is calculated by iterating through the zero vectors corresponding to the rectifier and the inverter, and the zero vector combinations that make the predicted common-mode voltage of the device satisfy the preset conditions are selected.

13. An electronic device, characterized in that, include: A memory and a processor are communicatively connected, the memory storing computer instructions, and the processor executing the computer instructions to perform the control method of the power conversion device according to any one of claims 10 to 12.

14. A computer-readable storage medium, characterized in that, The computer-readable storage medium stores computer instructions for causing a computer to execute the control method of the power conversion device according to any one of claims 10 to 12.

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