Control method and device of power converter and power converter

Abstract

The application provides a control method and device of a power converter and the power converter, and relates to the technical field of converter control. The power converter comprises a plurality of power modules, and the midpoints of the direct current sides of the power modules are connected. The method comprises the following steps: acquiring the midpoint current data of the direct current side and the zero sequence current data of the alternating current side of each power module; the midpoint current data and the zero sequence current data are used to represent the balance state of the power module, and the length of the time window corresponding to the midpoint current data and the zero sequence current data is different; determining whether each power module is abnormal and the abnormal level of the abnormal power module according to the midpoint current data and the zero sequence current data of each power module; when there is an abnormal power module, generating the alarm information of the power module and / or reducing the power of the power module according to the preset control strategy corresponding to the abnormal level of the power module. The application can timely and accurately monitor the abnormality of the power module in the power converter.

Description

Technical Field

[0001] This application relates to the field of converter control technology, and in particular to a control method, device and power converter for a power converter. Background Technology

[0002] Power converters enable the directional conversion of electrical energy in different forms and are core equipment for power conversion and control. For example, in rail transit traction power supply systems, power converters can supply power to rail vehicles and other loads. These power converters are typically modular. A modular power converter usually includes multiple power modules. The potential at the connection point (i.e., the midpoint) of the two voltage-dividing capacitors on the DC side of each power module is the midpoint potential. Imbalance in this midpoint potential can affect the stability and reliability of the power converter.

[0003] Modular power converters include midpoint coupling and midpoint decoupling types. Midpoint coupling refers to the connection of the midpoints of the DC sides of each power module in a modular power converter. In related technologies, in midpoint-coupled modular power converters, it is typically necessary to obtain the voltages of the two voltage-dividing capacitors on the DC side of each power module to determine if the midpoint potential is balanced. Unbalanced power modules are then controlled to ensure the normal and stable operation of the power converter. However, because the midpoints of the power modules are connected, determining whether the midpoint potential is balanced usually requires calculations using the voltage information of the voltage-dividing capacitors in each power module. This results in a lag in the judgment and control of the power modules, affecting the timeliness of power module protection in the power converter. Summary of the Invention

[0004] This application provides a control method, device, and power converter for a power converter, which can accurately monitor abnormalities in the power modules of the power converter and protect the power converter in a timely manner.

[0005] In a first aspect, embodiments of this application provide a control method for a power converter, the power converter comprising multiple power modules, wherein the midpoint of the DC side of each power module is connected; the method includes: The midpoint current data on the DC side and the zero-sequence current data on the AC side of each power module are acquired; wherein the midpoint current data and the zero-sequence current data are used to characterize the balance state of the power module, and the time windows corresponding to the midpoint current data and the zero-sequence current data are of different lengths. Based on the midpoint current data and zero-sequence current data of each power module, determine whether each power module is abnormal, and the abnormality level of the abnormal power module. When an abnormal power module is present, an alarm message for the power module is generated and / or the power of the power module is reduced, based on the preset control strategy corresponding to the abnormality level of the power module.

[0006] In one possible implementation, the midpoint current data includes the peak-to-peak value of the midpoint current and the effective value of the midpoint current; The time window lengths corresponding to the peak-to-peak value of the midpoint current, the effective value of the midpoint current, and the zero-sequence current data are different.

[0007] In one possible implementation, a midpoint fuse is provided at the midpoint of the DC side of each power module; the method further includes: Obtain the effective value of the midpoint current at the current moment; The length of the time window corresponding to the effective value of the midpoint current is determined based on the current effective value of the midpoint current and the fusing parameters of the midpoint fuse.

[0008] In one possible implementation, the fusing parameters include rated current, maximum fusing duration, and the correspondence between current and fusing duration; Based on the current effective value of the midpoint current and the fusing parameters of the midpoint fuse, the length of the time window corresponding to the effective value of the midpoint current is determined, including: If the effective value of the midpoint current at the current moment is less than or equal to the rated current of the midpoint fuse, then the length of the time window corresponding to the effective value of the midpoint current is determined to be a preset duration; wherein, the preset duration is less than the maximum fusing duration of the midpoint fuse. If the effective value of the midpoint current at the current moment is greater than the rated current, then the fusing time of the midpoint fuse is determined based on the effective value of the midpoint current at the current moment and the correspondence between the current and the fusing time of the midpoint fuse. Based on the fuse duration, the length of the time window corresponding to the effective value of the midpoint current is determined; wherein, the length of the time window is less than the fuse duration.

[0009] In one possible implementation, acquiring the DC-side midpoint current data and the AC-side zero-sequence current data of each power module includes: For each power module, obtain the instantaneous value of the midpoint current on the DC side of the power module, and the phase current value of each phase on the AC side of the power module; Calculate the difference between the maximum and minimum values ​​of the instantaneous midpoint current within each first time window to obtain the peak-to-peak value of the midpoint current of the power module within each first time window; The effective value of the midpoint current of the power module in each second time window is calculated based on multiple instantaneous values ​​of the midpoint current within each second time window; the duration of the second time window is longer than the duration of the first time window.

[0010] The vector sum of the phase current values ​​of each phase within each third time window is calculated to obtain the zero-sequence current data of the power module within each third time window; the duration of the third time window is longer than the duration of the first time window.

[0011] In one possible implementation, the midpoint current data and the zero-sequence current data are provided with corresponding thresholds; wherein, the midpoint current data and the zero-sequence current data are current indicators for determining whether the power module is abnormal. Based on the midpoint current data and zero-sequence current data of each power module, determine whether each power module is abnormal, and the abnormality level of the abnormal power module, including: For each power module, determine whether the midpoint current data and zero-sequence current data of the power module meet at least one of the preset conditions; wherein, the preset conditions include the midpoint current data being greater than a corresponding threshold and the zero-sequence current data being greater than a corresponding threshold. If the midpoint current data and zero-sequence current data of the power module meet at least one of the preset conditions, then the power module is determined to be abnormal. When a power module is determined to be malfunctioning, the malfunction level is determined based on the current index exceeding the corresponding threshold.

[0012] In one possible implementation, the midpoint current data includes the peak-to-peak value of the midpoint current and the effective value of the midpoint current; The preset conditions include: The peak-to-peak value of the midpoint current data is greater than the corresponding threshold. The effective value of the midpoint current is greater than the corresponding threshold. And the zero-sequence current data is greater than the corresponding threshold.

[0013] In one possible implementation, determining the anomaly level of the power module based on a current index exceeding a corresponding threshold includes: The number of abnormal items in the abnormal current index is determined, and the current difference between each abnormal current index and the corresponding threshold is calculated based on each abnormal current index; wherein, the abnormal current index is a current index that is greater than the corresponding threshold. The abnormality level of the power module is determined based on the number of abnormal items and the current difference.

[0014] In one possible implementation, the anomaly level includes multiple levels; wherein each level corresponds to a set containing the range of differences in the current differences of various current indicators. The step of determining the anomaly level of the power module based on the number of anomalies and the current difference includes: If the number of abnormal items is 1, then the level corresponding to the difference range where the current difference is located is determined as the abnormal level of the power module. If the number of abnormal items is greater than 1, the level corresponding to the difference range of the current difference of each abnormal current index is determined to obtain multiple levels, and the highest level among the multiple levels is determined as the candidate level; if the candidate level is the highest level among all abnormal levels, the candidate level is determined as the abnormal level of the power module; otherwise, the level one level higher than the candidate level is determined as the abnormal level of the power module.

[0015] In one possible implementation, the method further includes: Obtain the real-time temperature, cumulative operating time, and load rate of the power module; The temperature coefficient of the power module is determined based on the real-time temperature and the preset reference temperature. The aging factor of the power module is determined based on the cumulative operating time. The load factor of the power module is determined based on the load rate and the rated load of the power module. Based on the temperature coefficient, the aging coefficient, the load coefficient, the preset midpoint current reference threshold and the zero-sequence current reference threshold, the corresponding thresholds for the midpoint current data and the corresponding thresholds for the zero-sequence current data of the power module are calculated.

[0016] In one possible implementation, the anomaly levels include a first level, a second level, a third level, and a fourth level; wherein the fourth level is higher than the third level, the third level is higher than the second level, and the second level is higher than the first level; The step of generating alarm information for the power module and / or controlling the power module to reduce its power according to a preset control strategy corresponding to the abnormal level of the power module includes: If the abnormality level of the power module is the first level, then an alarm message for the power module is generated. If the abnormality level of the power module is the second level, then control the output power of the power module to be reduced to the preset power value; If the abnormality level of the power module is the third level, then the drive signal of the power module is blocked to shut down the power module. If the abnormality level of the power module is the fourth level, then the drive signals of all power modules will be blocked to shut down all power modules.

[0017] Secondly, embodiments of this application provide a control device for a power converter, the power converter including multiple power modules, the midpoint of the DC side of each power module being connected; the device includes: The acquisition module is used to acquire the DC-side midpoint current data and AC-side zero-sequence current data of each power module; wherein the midpoint current data and the zero-sequence current data are used to characterize the balance state of the power module, and the time windows corresponding to the midpoint current data and the zero-sequence current data are of different lengths. The determination module is used to determine whether each power module is abnormal and the abnormality level of the abnormal power module based on the midpoint current data and the zero-sequence current data of each power module. The control module is used to generate alarm information for the power module and / or control the power module to reduce its power when an abnormal power module is present, based on a preset control strategy corresponding to the abnormality level of the power module.

[0018] Thirdly, embodiments of this application provide a power converter, including a controller and multiple power modules, wherein the controller is used to implement the method in the first aspect or any possible implementation of the first aspect.

[0019] Fourthly, embodiments of this application provide a computer-readable storage medium storing a computer program that, when executed by a processor, implements the methods described in the first aspect or any possible implementation thereof.

[0020] Fifthly, embodiments of this application provide a computer program product, including a computer program that, when executed by a processor, implements the method described in the first aspect or any possible implementation of the first aspect.

[0021] The beneficial effects of the embodiments in this application compared with the prior art are: This application embodiment acquires the DC-side midpoint current data and the AC-side zero-sequence current data of each power module in the power converter. Since the time windows corresponding to the midpoint current data and the zero-sequence current data are of different lengths (i.e., the periods for acquiring the midpoint current data and the zero-sequence current data are different), the current of each power module in the power converter can be accurately monitored at different time scales. This allows for a comprehensive assessment of the balance state of the power modules from different time scales, timely detection of current changes in the power modules, identification of whether a power module is abnormal, and determination of the abnormality level of the power module. Timely monitoring of imbalance in each power module enables early detection of abnormal states. When an abnormal power module is present, the power module can be controlled according to its abnormality level, generating alarm information and / or reducing the power of the power module. This timely and accurate protection of the power converter and its power modules reduces the risk of device damage. Attached Figure Description

[0022] To more clearly illustrate the technical solutions in the embodiments of this application, 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 this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0023] Figure 1 This is an application scenario diagram of the control method for the power converter provided in the embodiments of this application; Figure 2 This is a schematic diagram of the structure of a power converter provided in an embodiment of this application; Figure 3 This is a flowchart illustrating the implementation of the control method for the power converter provided in this application embodiment; Figure 4 This is a schematic diagram of another power converter provided in an embodiment of this application; Figure 5 This is a schematic diagram of the control device for the power converter provided in the embodiments of this application. Detailed Implementation

[0024] 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 this application. However, those skilled in the art will understand that this application may also be implemented in other embodiments without these specific details. In other instances, detailed descriptions of well-known systems, apparatuses, circuits, and methods have been omitted so as not to obscure the description of this application with unnecessary detail.

[0025] Currently, most rail transit power supply systems use unidirectional rectifiers to convert three-phase AC power into DC power to provide DC power to rail transit vehicles. To achieve bidirectional energy flow between the DC and AC sides of the rail transit power supply system and provide a stable DC contact voltage, a rechargeable bidirectional traction power supply device is introduced into this system. The rechargeable bidirectional traction power supply device connects to the AC power grid on the AC side and to the DC traction network on the DC side. When the rail transit vehicle is in traction mode, the power supply device operates in rectification mode, converting the AC power from the AC power grid into DC power to supply the DC traction network. When the rail transit vehicle is braking mode, the power supply device operates in inverter mode, converting the DC power from the DC traction network back into AC power and feeding it back to the AC power grid. The rechargeable bidirectional traction power supply device can be a modular power converter.

[0026] The inventors of this application have discovered that in midpoint-coupled modular power converters, determining whether the midpoint potential is balanced typically requires calculations using the voltages of the two voltage-dividing capacitors on the DC side of each power module to accurately obtain the potential at the connection point of the two capacitors in each power module, thus determining whether the midpoint potential is balanced. This process is time-consuming, resulting in a lag in the determination of midpoint potential balance and affecting the timeliness of power converter protection. Furthermore, the midpoint potential only reflects the result of balance and makes it difficult to monitor and obtain the causes and processes leading to midpoint voltage imbalance.

[0027] Furthermore, when a switching transistor in a power module fails or the power module's drive signal is blocked (drive ripple blocking), that power module loses active control over the midpoint, causing a sudden surge in the midpoint current. Due to midpoint coupling between power modules, this leads to increased circulating current in other power modules, affecting their normal operation. Moreover, due to the lag in determining whether the midpoint voltage is balanced, it is difficult to detect this current surge in a timely manner, potentially damaging the devices in the power modules.

[0028] When the sampling of one phase AC current or AC voltage of a power module fails, controlling that power module based on the erroneous sampling result will cause its output voltage to deviate from the output voltages of other power modules. This will lead to an increase in circulating current in other power modules, affecting their normal operation. If monitoring is based solely on the midpoint voltage, it will be difficult to detect this problem in a timely manner.

[0029] To improve the timeliness of power module monitoring, this application embodiment monitors the current of each power module in the power converter. Monitoring is performed at different time scales using midpoint current data from the DC side and zero-sequence current data from the AC side. This allows for timely detection of current changes in the power modules, identifying whether a power module is abnormal, and determining the abnormality level, thus enabling early detection of abnormal states. When an abnormal power module is present in the power converter, control is implemented for that module, generating alarm information and / or reducing its power output. This timely and accurate protection of each power module reduces the risk of device damage and ensures the safe and stable operation of the power converter.

[0030] To make the objectives, technical solutions, and advantages of this application clearer, the following description will be provided in conjunction with the accompanying drawings and specific embodiments.

[0031] Figure 1 This diagram illustrates an application scenario of the control method for a power converter provided in an embodiment of this application. For example... Figure 1 As shown, the power converter includes multiple power modules, with the DC side of each power module connected at the midpoint. The power modules can be inverter modules, rectifier modules, and bidirectional converter modules, etc., enabling unidirectional or bidirectional power conversion.

[0032] The power module includes a first bus capacitor C1, a second bus capacitor C2, and a power unit. The connection point of the two bus capacitors is the midpoint, used for connection to the midpoints of other power modules. The other end of the first bus capacitor C1 is connected to the positive bus BUS+ in the DC bus, and the other end of the second bus capacitor C2 is connected to the negative bus BUS- in the DC bus. The first bus capacitor C1 and the second bus capacitor C2 serve as DC bus capacitors, providing DC support for the power unit. When the power unit is an inverter unit, it converts DC to AC. When the power unit is a rectifier unit, it converts AC to DC. When the power unit is a bidirectional converter unit, it enables bidirectional conversion between DC and AC.

[0033] In addition, such as Figure 1 As shown, the AC side of each power module is connected to the AC bus. The AC bus can be connected to the AC power grid via transformer T1. For example, the A-phase, B-phase, and C-phase inputs of a three-phase AC power grid are converted into U-phase, V-phase, and W-phase inputs via transformer T1.

[0034] Figure 2 A schematic diagram of a power converter is shown, in which the power module can employ active neutral clamping. point The clamped (ANPC) type three-level converter enables bidirectional power conversion. Its power module includes multiple switching transistors: Sa1-Sa6, Sb1-Sb6, and Sc1-Sc6 form three sets of switches. These three sets of switches enable bidirectional conversion between DC and three-phase AC power. When the power module operates in rectification mode, it converts AC power from the mains to DC power to supply the DC side. When the power module operates in inverter mode, it converts DC power back to AC power to supply the AC mains.

[0035] For example, the aforementioned bidirectional power converter can be applied to the aforementioned rail transit power supply system. The AC side of this power converter is connected to the AC power grid, and the DC side is connected to the DC traction network. When the rail transit vehicle is in traction mode, the power module in the power converter operates in rectification mode, converting the AC power from the AC power grid into DC power to supply the DC traction network. When the rail transit vehicle is in braking mode, the power module in the power converter operates in inverter mode, converting the DC power from the DC traction network into AC power to feed back to the AC power grid.

[0036] See Figure 3 The flowchart illustrating the implementation of the control method for the power converter provided in this application embodiment is described in detail below: Step 301: Obtain the DC-side midpoint current data and AC-side zero-sequence current data for each power module; wherein, the midpoint current data and zero-sequence current data are used to characterize the balance state of the power module, and the time windows corresponding to the midpoint current data and zero-sequence current data are of different lengths.

[0037] In this embodiment, the midpoint current on the DC side refers to the current at the connection point (midpoint) of the two bus capacitors on the DC side of the power module. This midpoint current can reflect the charging and discharging status of the bus capacitors on the DC side and the fluctuation of the midpoint potential of the power module, thereby reflecting the balance on the DC side.

[0038] The zero-sequence current on the AC side refers to the vector sum of the three-phase AC currents on the AC side of the power module, which can reflect the balance of the three phases on the AC side.

[0039] Here, midpoint current data and zero-sequence current data are collected for each power module separately to obtain current data for each power module, enabling analysis of each module. The midpoint current of a power module is the current along the path between the DC-side midpoint of the power module and the DC-side midpoints of other power modules, and can be measured and calculated using a current sensor. The zero-sequence current is obtained by measuring the three-phase AC current on the AC side of the power module and calculating its vector sum.

[0040] Since the midpoint voltage only reflects the result of midpoint imbalance and is insufficient to monitor the causes and processes leading to it, this application addresses the multiple causes of midpoint imbalance. Specifically, a fault in a power module of the power converter can cause a sudden surge in midpoint current, affecting midpoint balance; the midpoint current can also chronically affect the lifespan of the midpoint fuse, leading to fuse failure and further impacting midpoint balance; and AC-side sampling failure can also increase midpoint current, affecting balance. Therefore, to accurately monitor the power converter and achieve comprehensive, multi-scale state perception and protection, current data from different perspectives—midpoint current data and zero-sequence current data—can be acquired to perceive the balance state of the DC and AC sides of the power converter. Furthermore, the different time windows corresponding to the midpoint current data and zero-sequence current data allow for the capture of different types of hazards in the power converter at different time scales.

[0041] Figure 4 A schematic diagram of another power converter is shown. The DC side of the power module is connected to the DC bus. The power module is connected to the positive bus BUS+ via contactor KM1 and disconnector S1, and to the negative bus BUS- via a third fuse F3 and disconnector S1. The AC side of the power module is connected to the AC bus and connected to the power grid via circuit breaker S2 and transformer T1.

[0042] On the DC side of each power module, one end of the first bus capacitor C1 is connected in series with inductor L1 and first fuse F1 to connect to the positive bus BUS+ in the DC bus. The other end of the first bus capacitor C1 is connected to one end of the second bus capacitor C2; this connection point is the midpoint of the DC side of the power module. The other end of the second bus capacitor C2 is connected to inductor L3 to connect to the negative bus BUS- in the DC bus. The midpoint of the DC side of each power module is connected to the second fuse F2 of other power modules and the midpoint of their DC sides via the second fuse F2.

[0043] Here, the fuse is designed to melt and break the connection on both sides when the current exceeds its limit. Figure 4 In the power converter shown, when a short circuit occurs on the positive half bus of a power module (such as a short circuit in the first bus capacitor C1), the positive bus BUS+ is directly connected to the midpoint of the power module, forming a low-impedance path. At this time, the potential of the midpoint is the same as the potential of the positive bus BUS+. At the instant of the short circuit, the current in the positive bus BUS+ of the power module rises rapidly. When this current exceeds the minimum melting current of the first fuse F1 at the power module, the first fuse F1 blows, cutting off the connection between the DC side of the power module and the DC bus. This decouples the positive DC terminal of the power module from other power modules, preventing any impact on the normal operation of other modules.

[0044] The aforementioned first fuse F1 is configured for each power module, allowing each power module to be decoupled from other modules. In this embodiment, a third fuse F3 is also installed on the bus line connecting each power module to the negative bus (BUS-). When the current in a power module increases, and the increased current fails to blow the first fuse F1, but the total current of all power modules is excessive, the third fuse F3 blows, cutting off the connection between the DC side of the power module and the DC bus, thus preventing any impact on the safe operation of the power converter.

[0045] The first fuse F1, which connects to each power module, can also be located at inductor L3. The end of the second bus capacitor C2 in the power module furthest from the midpoint is connected to the negative bus BUS- in the DC bus via inductor L3 and the first fuse F1. Correspondingly, the third fuse F3 can be located between contactor KM1 and each power module.

[0046] Because the power modules are connected at their midpoints, when a short circuit occurs on the positive half of the busbar of a power module (such as a short circuit in the first busbar capacitor C1), the midpoint potential of that power module will rise, and this midpoint potential will be greater than that of the midpoint potentials of the other power modules. This will generate a converging current between the midpoints of the power modules, flowing from the midpoint of the short-circuited power module to the midpoints of the other power modules. The fusing current of the second fuse F2 is set to be less than or equal to the aforementioned converging current. In this case, the second fuse F2 corresponding to the short-circuited power module will blow, thereby decoupling the midpoint of the short-circuited power module from the midpoints of the other power modules.

[0047] Additionally, on the AC side of each power module, the first terminal of the AC side of the power module is connected to the corresponding phase line in the AC bus via the fourth fuse F4, such as... Figure 4 The U-phase line in the circuit. The second terminal on the AC side of the power module is connected to the corresponding phase line in the AC bus via the fifth fuse F5, such as... Figure 4 The V-phase line in the circuit. The third terminal on the AC side of the power module is connected to the corresponding phase line in the AC bus via the sixth fuse F6, such as... Figure 4 The W phase line in the middle.

[0048] A filter module, comprising inductors and capacitors, is also provided on the AC side of the power module. The AC side of the power module is connected to the AC bus via the filter module for filtering. The filter module includes a first filter unit, a second filter unit, and a third filter unit. The first filter unit includes inductor L2a and capacitor C3a; the second filter unit includes inductor L2b and capacitor C3b; and the third filter unit includes inductor L2c and capacitor C3c. Correspondingly, the first terminal of the AC side of the power module is connected to the corresponding U-phase line of the AC bus via the first filter unit and the fourth fuse F4; the second terminal of the AC side of the power module is connected to the corresponding V-phase line of the AC bus via the second filter unit and the fifth fuse F5; and the third terminal of the AC side of the power module is connected to the corresponding W-phase line of the AC bus via the third filter unit and the sixth fuse F6.

[0049] Optionally, considering the drive ripple during switching transistor failure and overload protection in the power module, which can cause a momentary increase in the midpoint current, and the fact that other power modules operating under load when a power module failure exists, the midpoint fuse (e.g.) may be affected. Figure 4 The device lifespan of the second fuse (F2) in this embodiment. The midpoint current data in this embodiment includes the peak-to-peak value of the midpoint current and the effective value of the midpoint current. The time window lengths corresponding to the peak-to-peak value of the midpoint current, the effective value of the midpoint current, and the zero-sequence current data are different.

[0050] Here, the peak-to-peak value of the midpoint current is the difference between the maximum and minimum values ​​of the midpoint current within one cycle. This value reflects the instantaneous and drastic fluctuations in current and can be used to assess the instantaneous electrical or impact stress experienced by devices in the power module under conditions such as momentary ripple interruption and short-circuit damage. This is an interruption-level detection method capable of capturing transient problems in the power module. Furthermore, the magnitude of the instantaneous value of the midpoint current can also reflect the instantaneous impact stress experienced by the power module; that is, the instantaneous value of the midpoint current can also be used directly for judgment.

[0051] The effective value of the midpoint current is the value of the midpoint current over a relatively long time window, used to characterize the thermal stress borne by the power module. This effective value is directly related to the heat generation of the midpoint fuse and can be used to assess the heat accumulation effect under long-term operation, thereby detecting thermal stress. It operates at the second or tens of millisecond level, capable of capturing steady-state problems in the power module. When a group of power modules is powered on, if one power module fails while the others are running under load, the effective value of the midpoint current will persist for a long time, affecting the lifespan of the midpoint fuse. Monitoring only the midpoint potential cannot detect this chronic thermal stress, ultimately leading to the midpoint fuse blowing. However, by using the effective value of the midpoint current, the thermal stress borne by the power module can be accurately detected, allowing for timely control of the power module, reducing the risk of midpoint fuse blowing, and minimizing damage to the power module.

[0052] In some embodiments, a midpoint fuse is provided at the midpoint of the DC side of each power module, as detailed in the following reference. Figure 4 The method provided in this embodiment further includes: obtaining the effective value of the midpoint current at the current moment; and determining the length of the time window corresponding to the effective value of the midpoint current at the next moment based on the effective value of the midpoint current at the current moment and the fusing parameters of the midpoint fuse.

[0053] In this embodiment, the length of the time window for the effective value of the midpoint current can be set according to the fusing parameters of the midpoint fuse to ensure that the software control corresponding to the detection of the effective value of the midpoint current is before the midpoint fuse blows, that is, the length of the time window corresponding to the effective value of the midpoint current is less than the fusing time of the midpoint fuse.

[0054] Here, the effective value of the midpoint current can be calculated from the instantaneous value of the midpoint current within a time window. By sliding the time window, the number of moments corresponding to the effective value of the midpoint current can be changed. The multiple moments corresponding to the effective value of the midpoint current at the current moment can be moments within the length of the time window preceding the current moment. As the length of the time window changes, the number of moments corresponding to the effective value of the midpoint current also changes accordingly.

[0055] For example, if the instantaneous value of the midpoint current is collected every 20 μs, and the length of the time window corresponding to the current effective value of the midpoint current is 20 ms, then the current effective value of the midpoint current corresponds to 1000 time points. Based on the instantaneous values ​​of the midpoint current at these 1000 time points, the effective value of the midpoint current corresponding to these 1000 time points can be calculated. Then, using the calculated effective value of the midpoint current and the fusing parameters of the midpoint fuse, the fusing time of the midpoint fuse can be obtained. Thus, the length of the time window corresponding to the effective value of the midpoint current less than this fusing time can be obtained.

[0056] Optionally, the fusing parameters include rated current, maximum fusing time, and the relationship between current and fusing time. The rated current is the maximum current allowed to pass through the neutral point fuse during long-term operation. When the current flowing through the neutral point fuse is less than this rated current, the fuse will blow. The maximum fusing time is the maximum time it takes for the fuse wire to melt and disconnect the circuit. The relationship between current and fusing time corresponds to the time it takes for the fuse wire to melt and disconnect the circuit after the current flowing through the neutral point fuse exceeds the rated current, and is related to that current.

[0057] This embodiment determines the length of the time window corresponding to the effective value of the midpoint current at the current moment and the fusing parameters of the midpoint fuse, based on the current effective value of the midpoint current and the fusing parameters of the midpoint fuse. This can be achieved by: If the effective value of the midpoint current at the current moment is less than or equal to the rated current of the midpoint fuse, then the length of the time window corresponding to the effective value of the midpoint current at the next moment is determined as the preset duration; wherein, the preset duration is less than the maximum fusing duration of the midpoint fuse.

[0058] In this embodiment, when the effective value of the midpoint current is less than or equal to the rated current, it indicates that the current effective value of the midpoint current will not cause the midpoint fuse to blow. Therefore, a preset duration can be used as the length of the time window corresponding to the effective value of the midpoint current to effectively monitor the effective value of the midpoint current. The preset duration can generally be less than the maximum fusing time of the midpoint fuse, and can be specifically selected as described in the above embodiment, such as 1s, 2s, and 5s, or 20ms, 40ms, and 60ms.

[0059] If the effective value of the midpoint current at the current moment is greater than the rated current, then the fusing time of the midpoint fuse is determined based on the effective value of the midpoint current at the current moment and the correspondence between the current and the fusing time of the midpoint fuse. Based on the fusing time, the length of the time window corresponding to the effective value of the midpoint current at the next moment is determined. The length of this time window is less than the fusing time.

[0060] In this embodiment, when the effective value of the midpoint current is greater than the rated current, it indicates that the fuse of the midpoint fuse, which operates under this current for an extended period, will melt and break. Therefore, based on the aforementioned correspondence, the fusing duration corresponding to the effective value of the midpoint current at the current moment can be found. Then, using this fusing duration, the length of the time window corresponding to the effective value of the midpoint current at the next moment can be determined.

[0061] Here, the length of the time window corresponding to the effective value of the midpoint current at the next moment can be a preset proportion of the calculated fuse duration. For example, it can be 1 / 2, 1 / 3, 1 / 4, 1 / 8, and 1 / 10 of the fuse duration, ensuring that control can be completed through software before the midpoint fuse blows.

[0062] The relationship between the current and the fusing time of a midpoint fuse can be expressed as follows: ,in, This indicates the amount of heat required for the fusible element of the midpoint fuse to melt and break. This indicates the resistance of the midpoint fuse. and It is usually a fixed value; This indicates the current flowing through the midpoint fuse, i.e., the current at the midpoint. This indicates the fusing time of the midpoint fuse. Substituting the effective value of the midpoint current into this formula will give you the corresponding fusing time.

[0063] In addition, after determining the length of the time window corresponding to the effective value of the midpoint current at the next moment based on the fuse duration, if the length of the time window is greater than the preset duration, the length of the time window corresponding to the effective value of the midpoint current at the next moment can be updated to the preset duration to ensure that the corresponding time level monitoring is achieved.

[0064] In some embodiments, acquiring the DC-side midpoint current data and AC-side zero-sequence current data of each power module may involve: for each power module, acquiring the instantaneous value of the DC-side midpoint current of the power module and the phase current value of each phase on the AC side of the power module; calculating the difference between the maximum and minimum values ​​among multiple instantaneous midpoint current values ​​within each first time window to obtain the peak-to-peak value of the midpoint current of the power module within each first time window; calculating the effective value of the midpoint current of the power module within each second time window based on multiple instantaneous midpoint current values ​​within each second time window; wherein the duration of the second time window is greater than the duration of the first time window; calculating the vector sum of the phase current values ​​of each phase within each third time window to obtain the zero-sequence current data of the power module within each third time window; wherein the duration of the third time window is greater than the duration of the first time window.

[0065] In this embodiment, the first time window can be the switching period of the switching transistor in the power module, or an integer multiple of the switching period, such as 50μs, 55μs, 58μs, or 60μs. By obtaining multiple instantaneous values ​​of the midpoint current within a first time window, the change in the midpoint current within the first time window can be obtained. Then, by calculating the difference between the maximum and minimum values ​​within the first time window, the peak-to-peak value of the midpoint current in the first time window can be obtained.

[0066] The second time window can also be the switching cycle of the power module, or its duration can be longer than the switching cycle, such as 10ms, 15ms, 20ms, or 25ms. By calculating the effective value of the midpoint current within a longer time window, the thermal stress of the midpoint current can be accurately reflected. The duration of the second time window is usually longer than that of the first time window. The selection of the second time window duration is related to the performance of the power module and the fuse (see the description in the above embodiments for details), and the second time window duration can also be set to the second level, such as 1s, 2s, or 3s.

[0067] Here, the calculation of both the peak-to-peak value and the effective value of the midpoint current are based on multiple instantaneous midpoint current values ​​on the DC side of the power module. These instantaneous midpoint current values ​​can be obtained by sampling using a current sensor connected to the DC side of the power module.

[0068] Within the third time window, the phase current values ​​of each phase on the AC side of the power module can be collected, including the first, second, and third phase current values. By calculating the vector sum of these three phase current values, the corresponding zero-sequence current data can be obtained, accurately reflecting whether the neutral point on the AC side is balanced. In a balanced three-phase system, the value of this zero-sequence current data is typically 0. If the calculated zero-sequence current data value is greater than 0, it indicates that there is an imbalance in the three-phase system.

[0069] For example, if a power module has a problem such as a failed AC current or AC voltage sampling, adjusting the AC output of that power module based on the incorrectly sampled current or voltage will cause a deviation in the phase current or phase voltage of the failed phase, resulting in an imbalance among the three phases on the AC side. Furthermore, controlling based on the incorrectly sampled current or voltage will also increase the midpoint current on the DC side of the power module, leading to an increase in circulating current between the various power modules.

[0070] Therefore, zero-sequence current data can be used to quickly detect problems such as single-phase AC current or AC voltage sampling failure, and to detect the balance of the three-phase system. The duration of the third time window can be 100μs, 150μs, 200μs, or 250μs, etc. Within this third time window, the instantaneous value of the phase current of each phase on the AC side of the power module can be acquired. By calculating the vector sum of the three-phase phase currents, the instantaneous value of the zero-sequence current is obtained. Filtering this instantaneous value yields the zero-sequence current data within the third time window, which can be used to monitor the balance of the AC side of the power module. Alternatively, the duration of the third time window can also be on the order of hundreds of milliseconds, such as 100ms, 150ms, 200ms, or 250ms. By analyzing the instantaneous value of the zero-sequence current within the third time window, three-phase balance problems in the power module can be detected, achieving a detection level of hundreds of microseconds or hundreds of milliseconds. Furthermore, after filtering the instantaneous value of the zero-sequence current within the third time window, the average value of the zero-sequence current can be calculated, and this average value can be used to determine anomalies in the power module.

[0071] Here, the length of the third time window is usually shorter than the length of the second time window, and the length of the third time window is usually longer than the length of the first time window. That is, after determining the lengths of the first and second time windows, the length of the third time window can be selected based on the lengths of the first and second time windows to achieve monitoring of the power converter at different time scales.

[0072] For each power module, the peak-to-peak value of the midpoint current, the effective value of the midpoint current, and the zero-sequence current data on the DC side are acquired. This allows for the evaluation of the power module's balance from both DC and AC side perspectives. Furthermore, the power module can be comprehensively evaluated from three aspects—transient, steady-state, and overall—and at three different time levels to analyze the instantaneous impact stress and thermal stress borne by the power module, as well as the balance of the three-phase system. It is important to note that the first, second, and third time windows mentioned above have different durations and time levels to achieve multi-timescale monitoring of the power module.

[0073] Step 302: Based on the midpoint current data and zero-sequence current data of each power module, determine whether each power module is abnormal, and the abnormality level of the abnormal power module.

[0074] In this embodiment, the state of the power module can be evaluated by acquiring the midpoint current data and zero-sequence current data, and the presence of any abnormalities in the power module can be accurately determined.

[0075] The midpoint current data can be used to assess the instantaneous electrical stress experienced by the devices in the power module and the cumulative thermal effects during operation. The zero-sequence current data can be used to assess the balance of the three phases on the AC side. This allows for a comprehensive evaluation of whether the power module is malfunctioning from multiple perspectives.

[0076] Furthermore, when the power module malfunctions, the level of malfunction can be further determined by using midpoint current data and zero-sequence current data, clarifying the degree of malfunction and enabling targeted control of the power module to avoid over-control or under-control.

[0077] Step 303: When an abnormal power module is present, generate alarm information for the power module and / or control the power module to reduce its power according to the preset control strategy corresponding to the abnormality level of the power module.

[0078] In this embodiment, when an abnormal power module is present, different controls are applied based on the abnormality level of the power module, enabling targeted and flexible control. By reducing the power of the abnormal power module, the current of the abnormal power module can be reduced, preventing the module from developing from a slight imbalance to a module failure. Furthermore, by controlling according to the preset control strategy corresponding to the abnormality level, the control method of blocking or disconnecting the power module at the mere presence of an abnormality can be avoided, maintaining the operation of the power module within a reasonable range and adapting to the needs of the scenario.

[0079] This application embodiment acquires the DC-side midpoint current data and the AC-side zero-sequence current data of each power module in the power converter. Since the time windows corresponding to the midpoint current data and the zero-sequence current data are of different lengths (i.e., the periods for acquiring the midpoint current data and the zero-sequence current data are different), the current of each power module in the power converter can be accurately monitored at different time scales. A comprehensive judgment of the balance state of the power modules can be made from transient, steady-state, and overall perspectives and at different time scales. This allows for timely detection of current changes in the power modules, identification of whether a power module is abnormal, and determination of the abnormality level of the power module. Timely monitoring of imbalance in each power module enables early detection of abnormal states. When an abnormal power module is present, the power module can be controlled according to its abnormality level, generating alarm information and / or reducing the power of the power module. This can protect the power converter and its power modules in a timely and accurate manner, reducing the risk of device damage.

[0080] In some embodiments, the midpoint current data and zero-sequence current data are provided with corresponding thresholds; wherein, the midpoint current data and zero-sequence current data are current indicators for determining whether the power module is abnormal. The thresholds can indicate the normal range of the corresponding current data, specifically the upper limit of the normal range. By using the corresponding threshold for the midpoint current data, the midpoint current data can be judged to determine whether it deviates from the normal range, leading to a risk of power module failure. Similarly, by using the corresponding threshold for the zero-sequence current, the zero-sequence current data can be judged to determine whether it deviates from the normal range, leading to a risk of system imbalance.

[0081] This embodiment determines whether each power module is abnormal and the abnormality level of the abnormal power module based on the midpoint current data and zero-sequence current data of each power module. This can be achieved by: for each power module, determining whether the midpoint current data and zero-sequence current data of the power module meet at least one of the preset conditions; wherein the preset conditions include the midpoint current data being greater than a corresponding threshold and the zero-sequence current data being greater than a corresponding threshold; if the midpoint current data and zero-sequence current data of the power module meet at least one of the preset conditions, then the power module is determined to be abnormal; when the power module is determined to be abnormal, the abnormality level of the power module is determined based on the current index exceeding the corresponding threshold.

[0082] In this embodiment, the midpoint current data and zero-sequence current data are judged separately to evaluate the current of the power module from different aspects. When either current data exceeds the corresponding threshold, it indicates that the power module has deviated from the normal or safe state. Therefore, when the midpoint current data and zero-sequence current data of the power module meet at least one of the preset conditions, the power module can be considered to be abnormal.

[0083] Anomaly level is a quantitative classification of the severity of current data deviating from the normal range, enabling targeted control. When an anomaly is determined in a power module, the current index exceeding a corresponding threshold can be used to clarify the situation, thus accurately identifying the anomaly level of the power module. This allows for appropriate subsequent control measures, avoiding the crude approach of shutting down the module at the first sign of a fault, and improving the availability and online rate of the power module.

[0084] When the zero-sequence current data is the instantaneous value of the zero-sequence current, it can be directly compared with the corresponding threshold to determine whether the zero-sequence current data is greater than the corresponding threshold. When the zero-sequence current data is detected at the level of hundreds of milliseconds, the effective value or average value of the zero-sequence current can be calculated based on each instantaneous value of the zero-sequence current within the third cycle. The effective value of the zero-sequence current can then be compared with the corresponding threshold, or the average value of the zero-sequence current can be compared with the corresponding threshold.

[0085] Here, the midpoint current data includes the peak-to-peak value and the effective value of the midpoint current. Preset conditions include: the peak-to-peak value of the midpoint current is greater than the corresponding threshold; the effective value of the midpoint current is greater than the corresponding threshold; and the zero-sequence current is greater than the corresponding threshold.

[0086] Correspondingly, threshold values ​​are set for both the peak-to-peak value and the RMS value of the midpoint current. A peak-to-peak value threshold is set for the peak-to-peak value of the midpoint current, and an RMS value threshold is set for the RMS value. Similarly, a zero-sequence current threshold is set for the zero-sequence current data. The peak-to-peak value of the midpoint current can be compared with its corresponding peak-to-peak value threshold, the RMS value of the midpoint current can be compared with its corresponding RMS value threshold, and the zero-sequence current data can be compared with its corresponding zero-sequence current threshold for a comprehensive evaluation from three aspects: instantaneous impact stress, thermal stress, and system balance. If the peak-to-peak value, RMS value, and zero-sequence current data of the power module meet at least one of the preset conditions, the power module is determined to be abnormal.

[0087] Furthermore, the peak-to-peak value of the midpoint current, the effective value of the midpoint current, and the zero-sequence current data can be detected and judged simultaneously or separately. For example, the peak-to-peak value of the midpoint current is obtained in each first cycle, and the effective value of the midpoint current is obtained in each second cycle, where the duration of the second cycle is an integer multiple of the duration of the first cycle (e.g., 5 times). If the peak-to-peak value of the midpoint current of the power module is obtained in the first cycle, it can be directly compared with its corresponding peak-to-peak value threshold to determine if the power module is abnormal. Similarly, if the peak-to-peak value of the midpoint current of the power module is obtained in the second to fourth cycles, it can be compared with its corresponding threshold to determine if the power module is abnormal. If the peak-to-peak value of the midpoint current of the power module is obtained in the fifth cycle, and the duration of the first to fifth cycles is the same as the duration of the second cycle, the effective value of the midpoint current of the power module can be obtained. Then, the peak-to-peak value and the effective value of the midpoint current can be used separately to determine if the power module is abnormal. In addition, the second cycle can also be a sliding window. For example, in the sixth first cycle, the duration of the second to sixth first cycles is the same as the duration of the second cycle. The instantaneous value of the midpoint current during the second to sixth first cycles can be used to calculate the effective value of the midpoint current during this period to determine whether the power module is abnormal.

[0088] Optionally, in this embodiment, the abnormality level of the power module can be determined based on the current index that is greater than the corresponding threshold. This can be achieved by: determining the number of abnormal items of the abnormal current index, and calculating the current difference between each abnormal current index and the corresponding threshold; wherein, the abnormal current index is the current index that is greater than the corresponding threshold; and determining the abnormality level of the power module based on the number of abnormal items and the current difference.

[0089] The number of abnormal items refers to the number of current indicators that exceed the corresponding threshold. For example, if the zero-sequence current data is greater than its corresponding zero-sequence current threshold, and the peak-to-peak value and effective value of the midpoint current are not greater than their corresponding thresholds, then the number of abnormal items is 1; if the zero-sequence current data is greater than its corresponding zero-sequence current threshold, the peak-to-peak value of the midpoint current is greater than its corresponding peak-to-peak value threshold, and the effective value of the midpoint current is not greater than its corresponding effective value threshold, then the number of abnormal items is 2; if the zero-sequence current data is greater than its corresponding zero-sequence current threshold, the peak-to-peak value of the midpoint current is greater than its corresponding peak-to-peak value threshold, and the effective value of the midpoint current is greater than its corresponding effective value threshold, then the number of abnormal items is 3.

[0090] The current difference indicates the extent to which an abnormal current indicator exceeds its corresponding threshold. A larger current difference indicates a greater deviation from the threshold, a greater degree of deviation from the normal range, and a more severe abnormality or fault. The current difference can be either an algebraic difference or a proportional difference, whichever is required. If the current difference is an algebraic difference, it can be obtained by subtracting the corresponding threshold from the value of the abnormal current indicator. If the current difference is a proportional difference, it can be obtained by subtracting the corresponding threshold from the value of the abnormal current indicator and then dividing the result by the corresponding threshold. For example, if the effective value of the midpoint current is greater than its corresponding effective value threshold, using an algebraic difference, the current difference for this abnormal current indicator is: effective value of midpoint current - effective value threshold. Using a proportional difference, the current difference for this abnormal current indicator is: effective value of midpoint current - effective value threshold) / effective value threshold.

[0091] In this embodiment, when determining the anomaly level of the power module, not only are the current differences of the abnormal current indicators in the power module considered to determine the degree of a single anomaly or fault, but also the number of abnormal items in the abnormal current indicators are considered to accurately identify situations where multiple anomalies or faults are combined, avoiding insufficient control of the power module and improving the accuracy of power module control.

[0092] Optionally, the anomaly level includes multiple levels; each level corresponds to a set containing the range of current difference values ​​for various current indicators.

[0093] For a given level, this level can correspond to the range of current differences between the peak-to-peak value of the midpoint current and its corresponding peak-to-peak value threshold, the range of current differences between the effective value of the midpoint current and its corresponding effective value threshold, and the range of current differences between the zero-sequence current data and its corresponding zero-sequence current threshold. Additionally, the difference range can also be an algebraic range or a proportional range, corresponding to the current difference. If the current difference is an algebraic difference, then the difference range is also an algebraic range. If the current difference is a proportional difference, then the difference range is also a proportional range, such as (20%, 30%).

[0094] For the same current index, the difference ranges corresponding to different levels do not overlap. That is, the current difference of the current index will only correspond to one difference range and belong to one level. It will not belong to two levels at the same time.

[0095] For example, the exception levels include Level 1, Level 2, Level 3, and Level 4.

[0096] The set corresponding to the first level may include: the difference range of peak-to-peak values ​​of midpoint current [a1, a2], the difference range of effective values ​​of midpoint current [b1, b2], and the difference range of zero-sequence current data [c1, c2].

[0097] The set corresponding to the second level may include: the difference range of peak-to-peak values ​​of midpoint current [a2, a3], the difference range of effective values ​​of midpoint current [b2, b3], and the difference range of zero-sequence current data [c2, c3].

[0098] The set corresponding to the third level may include: the difference range of peak-to-peak values ​​of midpoint current (a3, a4), the difference range of effective values ​​of midpoint current (b3, b4), and the difference range of zero-sequence current data (c3, c4).

[0099] The set corresponding to the fourth level may include: the difference range of peak-to-peak values ​​of midpoint current (a4, +∞), the difference range of effective values ​​of midpoint current (b4, +∞), and the difference range of zero-sequence current data (c4, +∞).

[0100] When the current difference is calculated using an algebraic difference, a1, b1, and c1 can all be 0A. When the current difference is calculated using a proportional difference, a1, b1, and c1 can all be 0%.

[0101] In this embodiment, the abnormality level of the power module is determined based on the number of abnormal items and the current difference. For example, if the number of abnormal items is 1, the level corresponding to the difference range of the current difference is determined as the abnormality level of the power module.

[0102] In this embodiment, when the number of abnormal items is 1, it means that only one current indicator of the power module deviates from the normal range, that is, only one current indicator is abnormal. Therefore, based directly on the current difference of this abnormal current indicator (abnormal current indicator), the range of differences where this current difference falls within all levels can be determined to obtain the abnormality level of the power module. For example, if the current difference of the abnormal current indicator is within the range of the current difference corresponding to the second level, then the abnormality level of the power module can be determined to be the second level.

[0103] This embodiment determines the abnormality level of the power module based on the number of abnormal items and the current difference. Alternatively, if the number of abnormal items is greater than 1, the level corresponding to the difference range of the current difference of each abnormal current index is determined, resulting in multiple levels. The highest level among these multiple levels is then determined as the candidate level. If the candidate level is the highest level among all abnormal levels, then the candidate level is determined as the abnormality level of the power module. Otherwise, the level one level higher than the candidate level is determined as the abnormality level of the power module.

[0104] In this embodiment, when the number of abnormal items is greater than 1, that is, when the number of abnormal items is 2 or 3, it indicates that multiple current indicators of the power module deviate from the normal range, and there are multiple abnormal current indicators. Then, for each abnormal current indicator, its corresponding level can be determined, resulting in multiple levels. These multiple levels may be the same or different. Taking a number of abnormal items of 3 as an example, the level corresponding to the current difference between the peak-to-peak value of the midpoint current and its corresponding threshold is the second level; the level corresponding to the current difference between the effective value of the midpoint current and its corresponding threshold is the first level; and the level corresponding to the current difference between the zero-sequence current data and its corresponding threshold is the second level. That is, the multiple levels obtained are the second level, the first level, and the second level.

[0105] Here, a higher level indicates a greater deviation from the abnormal current index. For accurate control of the power module, the highest level among multiple levels can be determined as the candidate level. Taking multiple levels as the second level, the first level, and the second level as an example, the highest level, i.e., the second level, is selected as the candidate level.

[0106] If the candidate level is the highest among all abnormal levels, it indicates that the deviation of the abnormal current index has reached the most severe level. Control can then be implemented according to the preset control strategy corresponding to the highest level. Therefore, the direct candidate level, which is also the highest among all abnormal levels, is determined as the abnormal level of the power module. For example, if the highest level among all abnormal levels is the third level, and the candidate level is the third level, which is the highest among all abnormal levels, then the abnormal level of the power module is determined to be the third level.

[0107] If the candidate level is not the highest among all anomaly levels, considering the existence of multiple abnormal current indicators and their multifaceted impact on the power module, to avoid underestimating complex anomalies and leading to insufficient control of the power module, resulting in the spread of anomalies or faults, the level can be increased. The level one level higher than the candidate level can be designated as the anomaly level for the power module, thereby improving the safety and reliability of the protection for the power module and power converter. For example, if the highest anomaly level is the third level and the candidate level is the second level, but the second level is not the highest among all anomaly levels, then the third level, which is one level higher than the candidate level (second level), can be designated as the anomaly level for the power module.

[0108] In addition, the anomaly level includes multiple levels; each level corresponds to a set, which contains the level threshold range of various current indicators.

[0109] The abnormality level of the power module can be determined based on current indicators exceeding a corresponding threshold. Alternatively, it can be achieved by determining the number of abnormal current indicators; where the abnormal current indicator is a current indicator exceeding a corresponding threshold. If the number of abnormal indicators is 1, the level corresponding to the threshold range of the abnormal current indicator is determined as the abnormality level of the power module. If the number of abnormal indicators is greater than 1, the level corresponding to the threshold range of each abnormal current indicator is determined, resulting in multiple levels. The highest level among these multiple levels is determined as a candidate level. If the candidate level is the highest among all abnormal levels, it is determined as the abnormality level of the power module; otherwise, the level one level higher than the candidate level is determined as the abnormality level of the power module.

[0110] Here, each level can have its own threshold range set for various current indicators. Each current indicator is directly compared to its corresponding threshold range to determine the power module's anomaly level. The threshold ranges for all levels of each current indicator are continuous and do not overlap. For example, the anomaly levels include Level 1, Level 2, Level 3, and Level 4, ranging from mild to severe. Using the minimum shutdown threshold TH that triggers the power module's shutdown as a benchmark, the thresholds for each level are set as a percentage of this shutdown threshold. The peak-to-peak shutdown threshold for the midpoint current is THa, the RMS shutdown threshold for the midpoint current is THb, and the zero-sequence current shutdown threshold for zero-sequence current data is THc. The threshold ranges for each level can then be as follows.

[0111] In the first level, the level threshold range corresponding to the peak-to-peak value of the midpoint current can be (70%THa, 90%THa), the level threshold range corresponding to the effective value of the midpoint current can be (70%THb, 90%THb), and the level threshold range corresponding to the zero-sequence current data can be (70%THc, 90%THc).

[0112] In the second level, the level threshold range corresponding to the peak-to-peak value of the midpoint current can be (90%THa, 100%THa), the level threshold range corresponding to the effective value of the midpoint current can be (90%THb, 100%THb), and the level threshold range corresponding to the zero-sequence current data can be (90%THc, 100%THc).

[0113] In the third level, the level threshold range corresponding to the peak-to-peak value of the midpoint current can be (100%THa, 120%THa), the level threshold range corresponding to the effective value of the midpoint current can be (100%THb, 120%THb), and the level threshold range corresponding to the zero-sequence current data can be (100%THc, 120%THc).

[0114] In the fourth level, the level threshold range corresponding to the peak-to-peak value of the midpoint current can be greater than 120%THa, the level threshold range corresponding to the effective value of the midpoint current can be greater than 120%THb, and the level threshold range corresponding to the zero-sequence current data can be greater than 120%THc.

[0115] In some embodiments, the anomaly level is divided into four levels according to the severity of the power module anomaly and fault, from mild to severe: Level 1, Level 2, Level 3, and Level 4. That is, the anomaly level includes Level 1, Level 2, Level 3, and Level 4; wherein, Level 4 is higher than Level 3, Level 3 is higher than Level 2, and Level 2 is higher than Level 1.

[0116] This embodiment generates alarm information for the power module and / or controls the power module to reduce its power according to a preset control strategy corresponding to the abnormality level of the power module. Specifically: if the abnormality level of the power module is level one, then an alarm information for the power module is generated; if the abnormality level of the power module is level two, then the output power of the power module is reduced to a preset power value; if the abnormality level of the power module is level three, then the drive signal of the power module is blocked to shut down the power module; if the abnormality level of the power module is level four, then the drive signals of all power modules are blocked to shut down all power modules.

[0117] In this embodiment, different control strategies are adopted for different anomaly levels. The lower the anomaly level, the milder the corresponding anomaly or fault, and the more moderate the control strategy adopted to ensure continuous system operation. As the severity of the anomaly or fault increases, the output power of the power modules can be limited in different ways to accurately isolate the abnormal power modules, avoid expanding the fault range, and thus balance the operational continuity of the power converter with equipment safety.

[0118] The first level represents the mildest anomaly, where the abnormal current index deviates only slightly from the normal range and does not pose a substantial risk of failure. Examples include minor anomalies such as momentary load disturbances in the power converter system or imbalances in module startup. In this case, the operation of the power module can be maintained without altering its behavior; instead, alarm messages, such as indicator lights, logs, or alarm flags on the host computer, can be used to alert relevant personnel and provide a basis for preventative maintenance, preventing small problems from accumulating into major failures.

[0119] The second level represents a more severe anomaly, such as sampling failure or continuous overload, but not yet reaching a dangerous level for the equipment. In this case, software can be used to control the power module, actively limiting the output power of the malfunctioning module to ensure uninterrupted operation. This can be achieved by issuing power or current commands to the power module, controlling its power output to decrease to a given value, or clamping the current to the commanded value, thus limiting the output power of the malfunctioning module and preventing the anomaly from escalating. Specifically, this can be achieved by changing the drive signal of the malfunctioning power module or adjusting the on / off state of the switching transistors within the module (e.g.,...). Figure 2 The switching transistors Sa1~Sa6, ​​Sb1~Sb6, and Sc1~Sc6 of the medium power module allow the output power of the power module to be flexibly reduced to the set safe power, thereby reducing the stress on the power module and suppressing the development of abnormal situations.

[0120] The preset power value is less than or equal to the rated power of the power module, or the preset power value is less than or equal to the current power value of the power module, so as to reduce the output power of the power module.

[0121] The third level represents a further escalation of the anomaly, such as sampling failures or severe overloads in the power modules, rendering them unable to operate safely at their current capacity. In this case, the malfunctioning power module can be shut down to protect the normal operation of other power modules, reducing the risk of damage to the entire power converter system while sacrificing some performance. This can be achieved by software-based blocking of the drive signal (drive blocking), shutting down the switching transistors in the power module, and disconnecting the malfunctioning power module, allowing it to exit the system while other power modules continue operating normally, thus minimizing the impact on the power converter.

[0122] Level 4 represents the most severe level of abnormality, indicating a fatal fault, such as a bus short circuit or AC short circuit in a power module. In this case, it is necessary to immediately block the drive signals of all power modules, completely shutting down the entire power converter to prevent the fault from spreading. Specifically, when a power module's abnormality level reaches Level 4, a hardware blocking signal can be triggered, blocking the drive signal of that power module. Simultaneously, a shutdown flag is sent to other power modules, causing them to block their drive signals, thereby shutting down all power modules.

[0123] In some embodiments, the control method for the power converter provided in this embodiment may further include: acquiring the real-time temperature, cumulative operating time, and load rate of the power module; determining the temperature coefficient of the power module based on the real-time temperature and a preset reference temperature; determining the aging coefficient of the power module based on the cumulative operating time; determining the load coefficient of the power module based on the load rate and the rated load of the power module; and finally, calculating the corresponding thresholds for the midpoint current data and the corresponding thresholds for the zero-sequence current data of the power module based on the temperature coefficient, aging coefficient, load coefficient, preset midpoint current reference threshold, and zero-sequence current reference threshold.

[0124] The threshold values ​​for the midpoint current data and the zero-sequence current data in the above embodiments are affected by factors such as the real-time temperature, cumulative operating time, and load rate of the power module. Therefore, the threshold values ​​corresponding to the midpoint current data and the zero-sequence current data of the power module can be dynamically adjusted according to the real-time temperature, cumulative operating time, and load rate of the power module to improve the accuracy and adaptability of anomaly judgment and protection control.

[0125] The real-time temperature of a power module can be the real-time temperature of its core components, such as the midpoint fuse or the temperature of adjacent components, which can be obtained through a temperature sensor. Temperature affects the current withstand capability of components in the power module. As the temperature rises, the overload capacity of components decreases. Consequently, the allowable current threshold of components at high temperatures needs to be reduced to avoid overheating damage. In other words, the real-time temperature of the power module is negatively correlated with the threshold value.

[0126] Here, a temperature coefficient can be used to correlate the real-time temperature with a threshold. For example, the temperature coefficient can be calculated using the real-time temperature of the power module and the temperature decay coefficient; a specific expression could be... ,in, Indicates the temperature coefficient. Indicates the temperature decay coefficient. This indicates the real-time temperature of the power module. This indicates the reference temperature of the power module. The temperature decay coefficient can be obtained through prior experimental measurements or by consulting the power module's technical datasheet, which contains the product's technical parameters, characteristics, and functions. The reference temperature of the power module is the optimal operating temperature, such as 25°C.

[0127] The cumulative operating time can be considered as the total operating time of the power module from commissioning to the current moment, which can be obtained through the counting time in the controller. The cumulative operating time reflects the aging degree of the power module; the longer the cumulative operating time, the higher the aging degree, the lower the expected reliability of the equipment, and correspondingly, the lower the current threshold. In other words, the cumulative operating time of the power module is negatively correlated with the threshold.

[0128] Here, the relationship between the aging factor and the cumulative operating time can be established using the aging factor. For example, the aging factor decreases as the cumulative operating time increases, thus establishing a correlation between the aging factor and the cumulative operating time. Alternatively, the aging factor corresponding to the cumulative operating time can be obtained by consulting the power module's technical datasheet.

[0129] The load factor is the ratio of the power module's output power to its rated power, specifically calculated from the AC power of the power module. The load factor reflects the current operating load of the power module. When the rated load is exceeded, the higher the load factor, the greater the peak-to-peak value, RMS value, and zero-sequence current will be. In this case, the detection threshold should be increased. That is, the cumulative operating time of the power module is positively correlated with the threshold.

[0130] Here, the relationship between the load factor and the load rate can be established using the load factor. For example, the load factor increases as the load rate increases, thus revealing the correspondence between the load factor and the load rate.

[0131] The midpoint current reference threshold is a reference threshold for the midpoint current data set under rated load conditions at the optimal operating temperature of the new power module. It can include the corresponding reference thresholds for the peak-to-peak value and the effective value of the midpoint current. The zero-sequence current reference threshold is also a reference threshold for the midpoint current data set under rated load conditions at the optimal operating temperature of the new power module. For example, the reference threshold for the peak-to-peak value of the midpoint current can be 1100A, 1150A, 1200A, or 1250A, etc.; the reference threshold for the effective value of the midpoint current can be 90A, 95A, 100A, or 105A, etc.; and the reference threshold for the zero-sequence current data can be 90A, 95A, 100A, or 105A, etc.

[0132] The reference threshold for the effective value of the midpoint current can be set based on the fusing threshold of the midpoint fuse. This reference threshold is usually lower than the fusing threshold of the midpoint fuse, so that the power module can be controlled via software before the midpoint fuse blows. The aforementioned fusing threshold can be determined by the correspondence between the current of the midpoint fuse and the fusing duration. The fusing duration is the length of the time window for the effective value of the midpoint current. Through this correspondence, the current corresponding to the fusing of the midpoint fuse, i.e., the fusing threshold of the midpoint fuse, can be clearly defined. For example, the reference threshold for the effective value of the midpoint current can be 1 / 2, 1 / 3, 1 / 6, or 1 / 10 of the fusing threshold of the midpoint fuse, etc.

[0133] The aforementioned midpoint current reference threshold and zero-sequence current reference threshold can be obtained experimentally on the new power module at the optimal temperature, or from the power module's technical datasheet. To conveniently and accurately obtain the reference thresholds, the threshold for triggering the third level of the power module can be obtained; that is, the turn-off threshold required to control the power module's drive shielding to turn it off. Then, the threshold for triggering the first level, and the thresholds for triggering other levels (second or fourth level), can be calculated using this turn-off threshold. The turn-off threshold refers to the midpoint current data or zero-sequence current data corresponding to the minimum value of the difference range for the third level. The threshold for triggering the first level refers to the midpoint current data or zero-sequence current data corresponding to the minimum value of the difference range for the first level; that is, the threshold for judging whether the midpoint current data or zero-sequence current data is abnormal. For example, the current data corresponding to the minimum value of the difference range for the third level is the 100% turn-off threshold, the threshold for triggering the first level is the 70% turn-off threshold, the threshold for triggering the second level is the 90% turn-off threshold, and the threshold for triggering the fourth level is the 120% turn-off threshold.

[0134] Optionally, based on the temperature coefficient, aging coefficient, load coefficient, preset midpoint current reference threshold, and zero-sequence current reference threshold, the corresponding thresholds for the midpoint current data and zero-sequence current data of the power module are calculated. This can be achieved by: calculating the product of the temperature coefficient, aging coefficient, load coefficient, and midpoint current reference threshold to obtain the corresponding threshold for the midpoint current data of the power module; and calculating the product of the temperature coefficient, aging coefficient, load coefficient, and zero-sequence current reference threshold to obtain the corresponding threshold for the zero-sequence current data of the power module.

[0135] That is, the threshold corresponding to the midpoint current data = temperature coefficient × aging coefficient × load coefficient × midpoint current reference threshold, and the threshold corresponding to the zero-sequence current data = temperature coefficient × aging coefficient × load coefficient × zero-sequence current reference threshold.

[0136] By correcting the reference threshold using temperature coefficient, aging coefficient, and load coefficient, the threshold values ​​for midpoint current peak-to-peak value, midpoint current RMS value, and zero-sequence current data are not fixed but dynamically adjusted according to operating conditions such as operating temperature, aging time, and load. This ensures that the final threshold values ​​better match the real-time status of the power module, thereby accurately judging the power module and improving the accuracy and adaptability of power converter protection.

[0137] Furthermore, when dynamically adjusting thresholds based on real-time temperature, cumulative operating time, and load rate, the real-time temperature, cumulative operating time, and load rate can be acquired within each fourth cycle to recalculate the corresponding thresholds for the midpoint current and zero-sequence current of the power module. The duration of the fourth cycle can be longer than that of the second cycle, and also longer than that of the third cycle. Considering potential load fluctuations in the power module, when the load rate change exceeds a preset change, real-time temperature, cumulative operating time, and load rate can be acquired in real-time to recalculate the corresponding thresholds for the midpoint current and zero-sequence current of the power module. The preset change can be set based on the impact of the load rate on the power module's thresholds; for example, the preset change could be 10%, 15%, or 20%.

[0138] This application embodiment acquires the DC-side midpoint current data and the AC-side zero-sequence current data of each power module in the power converter. Since the time windows corresponding to the midpoint current data and the zero-sequence current data are of different lengths (i.e., the periods for acquiring the midpoint current data and the zero-sequence current data are different), the current of each power module in the power converter can be accurately monitored at different time scales. This allows for a comprehensive assessment of the balance state of the power modules from different time scales, timely detection of current changes in the power modules, identification of whether a power module is abnormal, and determination of the abnormality level of the power module. Timely monitoring of imbalance in each power module enables early detection of abnormal states. When an abnormal power module is present, the power module can be controlled according to its abnormality level, generating alarm information and / or reducing the power of the power module. This timely and accurate protection of the power converter and its power modules reduces the risk of device damage. Specifically, by using midpoint current peak-to-peak value, midpoint current RMS value, and zero-sequence current data, the power module is comprehensively monitored from three aspects—transient, steady-state, and overall—and at three different time levels. This accurately analyzes the instantaneous impact stress and thermal stress borne by the power module, as well as the system's balance, thereby determining whether the power module exhibits any abnormalities. By using current indicators exceeding corresponding thresholds and the number of abnormal items, the extent to which abnormal current indicators exceed the thresholds and the number of abnormal current indicator items can be considered, accurately identifying multiple abnormalities or combined faults, avoiding insufficient control of the power module, and improving the accuracy of power module control. In addition, the thresholds of current indicators are dynamically adjusted based on the power module's real-time temperature, cumulative operating time, and load rate, improving the accuracy and adaptability of anomaly detection and protection control.

[0139] 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 this application.

[0140] The following are device embodiments of this application. For details not described in detail, please refer to the corresponding method embodiments described above.

[0141] Figure 5 A schematic diagram of the control device for a power converter provided in an embodiment of this application is shown. For ease of explanation, only the parts related to the embodiment of this application are shown, and are described in detail below: A power converter consists of multiple power modules, with the DC side of each module connected at its midpoint. For example... Figure 5 As shown, the control device 50 of the power converter includes: The acquisition module 51 is used to acquire the DC side midpoint current data and AC side zero-sequence current data of each power module; wherein, the midpoint current data and zero-sequence current data are used to characterize the balance state of the power module, and the time window lengths corresponding to the midpoint current data and zero-sequence current data are different. The determination module 52 is used to determine whether each power module is abnormal and the abnormality level of the abnormal power module based on the midpoint current data and zero-sequence current data of each power module. The control module 53 is used to generate alarm information for the power module and / or control the power module to reduce its power when an abnormal power module is present, based on a preset control strategy corresponding to the abnormality level of the power module.

[0142] In one possible implementation, the midpoint current data includes the peak-to-peak value of the midpoint current and the effective value of the midpoint current; The time window lengths corresponding to the peak-to-peak value of the midpoint current, the effective value of the midpoint current, and the zero-sequence current data are different.

[0143] In one possible implementation, a midpoint fuse is provided at the midpoint of the DC side of each power module; the acquisition module 51 is also used for: Obtain the effective value of the midpoint current at the current moment; Based on the current effective value of the midpoint current and the fusing parameters of the midpoint fuse, determine the length of the time window corresponding to the next effective value of the midpoint current.

[0144] In one possible implementation, the fusing parameters include the rated current, the maximum fusing duration, and the correspondence between the current and the fusing duration; Module 51 is specifically used for: If the effective value of the midpoint current at the current moment is less than or equal to the rated current of the midpoint fuse, then the length of the time window corresponding to the effective value of the midpoint current at the next moment is determined as the preset duration; wherein, the preset duration is less than the maximum fusing duration of the midpoint fuse. If the effective value of the midpoint current at the current moment is greater than the rated current, then the fusing time of the midpoint fuse is determined based on the effective value of the midpoint current at the current moment and the correspondence between the current of the midpoint fuse and the fusing time. Based on the fuse duration, determine the length of the time window corresponding to the effective value of the midpoint current at the next moment from the current moment; wherein the length of this time window is less than the fuse duration.

[0145] In one possible implementation, module 51 is specifically used for: For each power module, obtain the instantaneous value of the midpoint current on the DC side of the power module, and the phase current value of each phase on the AC side of the power module; Calculate the difference between the maximum and minimum values ​​of the instantaneous midpoint current within each first time window to obtain the peak-to-peak value of the midpoint current of the power module within each first time window; The effective value of the midpoint current of the power module in each second cycle is calculated based on multiple instantaneous values ​​of the midpoint current within each second time window; the duration of the second time window is longer than that of the first time window.

[0146] The vector sum of the phase current values ​​of each phase within each third time window is calculated to obtain the zero-sequence current data of the power module within each third time window; the duration of the third time window is longer than that of the first time window.

[0147] In one possible implementation, the midpoint current data and the zero-sequence current data are provided with corresponding thresholds; wherein, the midpoint current data and the zero-sequence current data are current indicators for determining whether the power module is abnormal. Module 52 is specifically used for: For each power module, determine whether the midpoint current data and zero-sequence current data of the power module meet at least one of the preset conditions; wherein, the preset conditions include the midpoint current data being greater than the corresponding threshold and the zero-sequence current data being greater than the corresponding threshold. If the midpoint current data and zero-sequence current data of the power module meet at least one of the preset conditions, the power module is determined to be abnormal. When a power module is determined to be malfunctioning, the malfunction level is determined based on the current index exceeding the corresponding threshold.

[0148] In one possible implementation, the midpoint current data includes the peak-to-peak value of the midpoint current and the effective value of the midpoint current; The preset conditions include: The peak-to-peak value of the midpoint current data is greater than the corresponding threshold. The effective value of the midpoint current is greater than the corresponding threshold. And the zero-sequence current data is greater than the corresponding threshold.

[0149] In one possible implementation, the determining module 52 is specifically used for: Determine the number of abnormal items in the abnormal current index, and calculate the current difference between each abnormal current index and the corresponding threshold based on each abnormal current index; where abnormal current index is the current index that is greater than the corresponding threshold. The anomaly level of the power module is determined based on the number of abnormal items and the current difference.

[0150] In one possible implementation, the anomaly level includes multiple levels; where each level corresponds to a set containing the range of differences in the current differences of various current indicators. Module 52 is specifically used for: If the number of abnormal items is 1, then the level corresponding to the difference range where the current difference is located is determined as the abnormal level of the power module. If the number of abnormal items is greater than 1, the level corresponding to the difference range of the current difference of each abnormal current index is determined, resulting in multiple levels. The highest level among these multiple levels is then determined as the candidate level. If the candidate level is the highest level among all abnormal levels, then the candidate level is determined as the abnormal level of the power module. Otherwise, the level one level higher than the candidate level is determined as the abnormal level of the power module.

[0151] In one possible implementation, the determining module 52 is further used for: Obtain the real-time temperature, cumulative operating time, and load rate of the power module; The temperature coefficient of the power module is determined based on the real-time temperature and the preset reference temperature. The aging factor of the power module is determined based on the cumulative operating time. Determine the load factor of the power module based on the load rate and the rated load of the power module; Based on the temperature coefficient, aging coefficient, load coefficient, preset midpoint current reference threshold and zero-sequence current reference threshold, the corresponding thresholds for the midpoint current data and the corresponding thresholds for the zero-sequence current data of the power module are calculated.

[0152] In one possible implementation, the exception levels include a first level, a second level, a third level, and a fourth level; wherein the fourth level is higher than the third level, the third level is higher than the second level, and the second level is higher than the first level. Control module 53 is specifically used for: If the power module's anomaly level is Level 1, then an alarm message for the power module will be generated. If the abnormality level of the power module is level two, then control the output power of the power module to be reduced to the preset power value; If the abnormality level of the power module is level three, then the drive signal of the power module is blocked to shut down the power module. If the abnormality level of the power module is level four, then the drive signals of all power modules will be blocked to shut down all power modules.

[0153] For the sake of simplicity and clarity, only the above-described functional modules / units are used as examples. In practical applications, the functions described above can be assigned to different functional modules / units as needed. These modules / units can be implemented in hardware, software, or a combination of both.

[0154] This application also provides a power converter. For details not described in detail, please refer to the corresponding method embodiments described above.

[0155] In some embodiments, the power converter includes a controller and multiple power modules. The controller is used to implement the methods in the various method embodiments described above.

[0156] This application also provides a computer-readable storage medium storing a computer program. When the computer program is executed by a processor, it implements the methods described in the above-described method embodiments.

[0157] This application also provides a computer program product, including a computer program. When the computer program is executed by a processor, it implements the methods in the above-described method embodiments.

[0158] Computer programs include computer program code, which can be in the form of source code, object code, executable files, or certain intermediate forms. Computer-readable media can include: any entity or device capable of carrying computer program code, recording media, USB flash drives, portable hard drives, magnetic disks, optical disks, computer memory, read-only memory (ROM), random access memory (RAM), electrical carrier signals, telecommunication signals, and software distribution media, etc.

[0159] In the above embodiments, the descriptions of each embodiment have their own emphasis. Parts not detailed or described in a particular embodiment can be referred to in the relevant descriptions of other embodiments. Unless otherwise specified or in conflict with logic, the terminology and / or descriptions between different embodiments are consistent and can be referenced interchangeably. Technical features in different embodiments can be combined to form new embodiments based on their inherent logical relationships.

[0160] The above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of this application, and should all be included within the protection scope of this application.

Claims

1. A control method for a power converter, characterized in that, The power converter includes multiple power modules, and the midpoint of the DC side of each power module is connected; the method includes: The process involves acquiring the DC-side midpoint current data and the AC-side zero-sequence current data for each power module. The midpoint current data and the zero-sequence current data characterize the balance state of the power module, and the time windows corresponding to the midpoint current data and the zero-sequence current data have different lengths. The midpoint current data includes the peak-to-peak value and the effective value of the midpoint current. The time windows corresponding to the peak-to-peak value, the effective value, and the zero-sequence current data have different lengths. Based on the midpoint current data and zero-sequence current data of each power module, determine whether each power module is abnormal, and the abnormality level of the abnormal power module. When an abnormal power module is present, an alarm message for the power module is generated and / or the power of the power module is reduced, according to the preset control strategy corresponding to the abnormality level of the power module. The acquisition of the DC-side midpoint current data and AC-side zero-sequence current data of each power module includes: For each power module, obtain the instantaneous value of the midpoint current on the DC side of the power module, and the phase current value of each phase on the AC side of the power module; Calculate the difference between the maximum and minimum values ​​of the instantaneous midpoint current within each first time window to obtain the peak-to-peak value of the midpoint current of the power module within each first time window; The effective value of the midpoint current of the power module in each second time window is calculated based on multiple instantaneous midpoint current values ​​within each second time window; the duration of the second time window is longer than the duration of the first time window. The vector sum of the phase current values ​​of each phase within each third time window is calculated to obtain the zero-sequence current data of the power module within each third time window; the duration of the third time window is longer than the duration of the first time window.

2. The control method for a power converter according to claim 1, characterized in that, A midpoint fuse is installed at the midpoint of the DC side of each power module; the method further includes: Obtain the effective value of the midpoint current at the current moment; Based on the current effective value of the midpoint current and the fusing parameters of the midpoint fuse, determine the length of the time window corresponding to the next effective value of the midpoint current.

3. The control method for a power converter according to claim 2, characterized in that, The fusing parameters include rated current, maximum fusing duration, and the correspondence between current and fusing duration; Based on the current effective value of the midpoint current and the fusing parameters of the midpoint fuse, determine the length of the time window corresponding to the next effective value of the midpoint current, including: If the effective value of the midpoint current at the current moment is less than or equal to the rated current of the midpoint fuse, then the length of the time window corresponding to the effective value of the midpoint current at the next moment is determined to be a preset duration; wherein, the preset duration is less than the maximum fusing duration of the midpoint fuse. If the effective value of the midpoint current at the current moment is greater than the rated current, then the fusing time of the midpoint fuse is determined based on the effective value of the midpoint current at the current moment and the correspondence between the current and the fusing time of the midpoint fuse. Based on the fuse duration, determine the length of the time window corresponding to the effective value of the midpoint current at the next moment from the current moment; wherein the length of the time window is less than the fuse duration.

4. The control method for a power converter according to any one of claims 1 to 3, characterized in that, The midpoint current data and the zero-sequence current data are provided with corresponding thresholds; wherein, the midpoint current data and the zero-sequence current data are current indicators for determining whether the power module is abnormal. Based on the midpoint current data and zero-sequence current data of each power module, determine whether each power module is abnormal, and the abnormality level of the abnormal power module, including: For each power module, determine whether the midpoint current data and zero-sequence current data of the power module meet at least one of the preset conditions; wherein, the preset conditions include the midpoint current data being greater than a corresponding threshold and the zero-sequence current data being greater than a corresponding threshold. If the midpoint current data and zero-sequence current data of the power module meet at least one of the preset conditions, then the power module is determined to be abnormal. When a power module is determined to be malfunctioning, the malfunction level is determined based on the current index exceeding the corresponding threshold.

5. The control method for a power converter according to claim 4, characterized in that, The step of determining the abnormality level of the power module based on a current index exceeding a corresponding threshold includes: The number of abnormal items in the abnormal current index is determined, and the current difference between each abnormal current index and the corresponding threshold is calculated based on each abnormal current index; wherein, the abnormal current index is a current index that is greater than the corresponding threshold. The abnormality level of the power module is determined based on the number of abnormal items and the current difference.

6. The control method for a power converter according to claim 5, characterized in that, The anomaly levels include multiple levels; each level corresponds to a set, which contains the range of differences in the current differences of various current indicators. The step of determining the anomaly level of the power module based on the number of anomalies and the current difference includes: If the number of abnormal items is 1, then the level corresponding to the difference range where the current difference is located is determined as the abnormal level of the power module. If the number of abnormal items is greater than 1, the level corresponding to the difference range of the current difference of each abnormal current index is determined to obtain multiple levels, and the highest level among the multiple levels is determined as the candidate level; if the candidate level is the highest level among all abnormal levels, the candidate level is determined as the abnormal level of the power module; otherwise, the level one level higher than the candidate level is determined as the abnormal level of the power module.

7. The control method for a power converter according to claim 4, characterized in that, The method further includes: Obtain the real-time temperature, cumulative operating time, and load rate of the power module; The temperature coefficient of the power module is determined based on the real-time temperature and the preset reference temperature. The aging factor of the power module is determined based on the cumulative operating time. The load factor of the power module is determined based on the load rate and the rated load of the power module. Based on the temperature coefficient, the aging coefficient, the load coefficient, the preset midpoint current reference threshold and the zero-sequence current reference threshold, the corresponding thresholds for the midpoint current data and the corresponding thresholds for the zero-sequence current data of the power module are calculated.

8. The control method for a power converter according to any one of claims 1 to 3, characterized in that, The anomaly levels include a first level, a second level, a third level, and a fourth level; wherein the fourth level is higher than the third level, the third level is higher than the second level, and the second level is higher than the first level. The step of generating alarm information for the power module and / or controlling the power module to reduce its power according to a preset control strategy corresponding to the abnormal level of the power module includes: If the abnormality level of the power module is the first level, then an alarm message for the power module is generated. If the abnormality level of the power module is the second level, then control the output power of the power module to be reduced to the preset power value; If the abnormality level of the power module is the third level, then the drive signal of the power module is blocked to shut down the power module. If the abnormality level of the power module is the fourth level, then the drive signals of all power modules will be blocked to shut down all power modules.

9. A control device for a power converter, characterized in that, The power converter includes multiple power modules, and the midpoint of the DC side of each power module is connected; the device includes: An acquisition module is used to acquire the DC-side midpoint current data and AC-side zero-sequence current data of each power module; wherein, the midpoint current data and the zero-sequence current data are used to characterize the balance state of the power module, and the time window lengths corresponding to the midpoint current data and the zero-sequence current data are different; the midpoint current data includes the peak-to-peak value of the midpoint current and the effective value of the midpoint current; the time window lengths corresponding to the peak-to-peak value of the midpoint current, the effective value of the midpoint current, and the zero-sequence current data are different; The determination module is used to determine whether each power module is abnormal and the abnormality level of the abnormal power module based on the midpoint current data and the zero-sequence current data of each power module. The control module is used to generate alarm information for the power module and / or control the power module to reduce its power when an abnormal power module is present, based on a preset control strategy corresponding to the abnormality level of the power module. The acquisition module is specifically used for: For each power module, obtain the instantaneous value of the midpoint current on the DC side of the power module, and the phase current value of each phase on the AC side of the power module; Calculate the difference between the maximum and minimum values ​​of the instantaneous midpoint current within each first time window to obtain the peak-to-peak value of the midpoint current of the power module within each first time window; The effective value of the midpoint current of the power module in each second time window is calculated based on multiple instantaneous midpoint current values ​​within each second time window; the duration of the second time window is longer than the duration of the first time window. The vector sum of the phase current values ​​of each phase within each third time window is calculated to obtain the zero-sequence current data of the power module within each third time window; the duration of the third time window is longer than the duration of the first time window.

10. A power converter, characterized in that, It includes a controller and multiple power modules, the controller being used to implement the method as described in any one of claims 1 to 8.

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