Converter device and control method for a converter device

Abstract

The application provides a current conversion device and a control method thereof. The current conversion device comprises a power device and a controller connected to the power device. The controller is configured to determine a maximum junction temperature of the power device in a current grid cycle during operation of the current conversion device, wherein the maximum junction temperature is a maximum value of the junction temperature of the power device in the current grid cycle; determine a derating state of the current conversion device according to a difference between the maximum junction temperature and a limited junction temperature of the power device, wherein the derating state is used to indicate whether the current conversion device is operated in a derating mode and / or used to indicate a relationship between an actual derating and an expected derating when the current conversion device is operated in the derating mode; and determine a limited current of the current conversion device in a next grid cycle according to the derating state of the current conversion device, wherein the limited current is a limit value of an output current of the current conversion device. The energy conversion effect of the current conversion device can be significantly improved on the basis of improving the safety of the power device of the current conversion device.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of power conversion equipment, and in particular to a power conversion equipment and a control method of the power conversion equipment. BACKGROUND

[0002] As an energy conversion equipment, the power conversion equipment generates heat in the working process. With the increase of temperature, the performance of the power device in the power conversion equipment gradually decreases. If the temperature continues to rise and exceeds the bearing limit of the device, a fire or other safety accidents may be caused. In order to cope with the influence of high temperature on the power device, the power conversion equipment usually reduces the output power or working current of the equipment to reduce the working temperature of the power device.

[0003] The power conversion equipment in the prior art usually adopts a passive derating control strategy. A fixed derating curve is fitted in advance according to the laboratory operating data of the research and development test, and the derating is passively performed according to the fixed derating curve in actual operation. However, the real operating condition is often more complex, and there is usually a certain difference between the laboratory operating condition and the real operating condition. Therefore, the passive derating control strategy often causes damage to the power device of the power conversion equipment or poor energy conversion effect of the power conversion equipment. SUMMARY

[0004] The present application provides a power conversion equipment, a control method of the power conversion equipment, a control device of the power conversion equipment, a computer readable storage medium and a computer program product, which can improve the energy conversion effect of the power conversion equipment on the basis of improving the safety and reliability of the power device of the power conversion equipment.

[0005] In a first aspect, a power conversion equipment is provided, comprising: a power device; a controller connected to the power device and configured to: determine a maximum junction temperature of the power device in a current grid period during operation of the power conversion equipment, wherein the maximum junction temperature is a maximum value of the junction temperature of the power device in the current grid period; determine a derating state of the power conversion equipment according to a difference between the maximum junction temperature and a limit junction temperature of the power device, wherein the derating state is used to indicate whether the power conversion equipment is derated or not and / or is used to indicate a relationship between an actual derating and an expected derating of the power conversion equipment when the power conversion equipment is derated; and determine a limit current of the power conversion equipment in a next grid period according to the derating state of the power conversion equipment, wherein the limit current is a limit value of an output current of the power conversion equipment.

[0006] In an embodiment, the de-rating state includes an under-de-rating state indicating that the power converter is not de-rated, an over-de-rating state indicating that the power converter is de-rated and the actual de-rating is greater than the expected de-rating, the controller determines the de-rating state of the power converter according to the difference between the maximum junction temperature and the limit junction temperature of the power device, and is configured to determine that the power converter is in the under-de-rating state or the over-de-rating state according to a current difference between the current limit and the current command received currently, in a case that the maximum junction temperature of the power device is less than the limit junction temperature of the power device; the controller determines the current limit of the power converter in the next grid period according to the de-rating state of the power converter, and is configured to determine that the current limit of the power converter in the next grid period is greater than or equal to the current limit in a case that the power converter is in the under-de-rating state or the over-de-rating state.

[0007] In an embodiment, the controller determines that the power converter is in the under-de-rating state or the over-de-rating state according to a current difference between the current limit and the current command received currently, and is configured to determine that the power converter is in the over-de-rating state in a case that the current difference is less than a current difference threshold, and / or determine that the power converter is in the under-de-rating state in a case that the current difference is greater than or equal to the current difference threshold; the controller determines that the current limit of the power converter in the next grid period is greater than or equal to the current limit in a case that the power converter is in the under-de-rating state or the over-de-rating state, and is configured to determine that the current limit of the power converter in the next grid period is greater than the current limit in a case that the power converter is in the over-de-rating state, and / or determine that the current limit of the power converter in the next grid period is equal to the current limit in a case that the power converter is in the under-de-rating state.

[0008] In an embodiment, the de-rating state includes an under-de-rating state indicating that the power converter is not de-rated, an over-de-rating state indicating that the power converter is de-rated and the actual de-rating is greater than the expected de-rating, the controller determines the de-rating state of the power converter according to the difference between the maximum junction temperature and the limit junction temperature of the power device, and is configured to determine that the power converter is in the under-de-rating state or the over-de-rating state according to a current difference between the current limit and the current command received currently, in a case that the maximum junction temperature of the power device is less than the limit junction temperature of the power device; the controller determines the current limit of the power converter in the next grid period according to the de-rating state of the power converter, and is configured to determine that the current limit of the power converter in the next grid period is greater than or equal to the current limit in a case that the power converter is in the under-de-rating state or the over-de-rating state.

[0009] In an embodiment, the controller is further configured to: acquire an actual operating parameter of the power device in the current grid period; determine, according to the actual operating parameter and historical operating parameters of the power device in the plurality of historical operating conditions, a first historical operating condition corresponding to the current operating condition, wherein a parameter difference between the historical operating parameter of the first historical operating condition and the actual operating parameter is smaller than a parameter difference between a historical operating parameter of a second historical operating condition and the actual operating parameter, the second historical operating condition being other than the first historical operating condition among the plurality of historical operating conditions; and determine, according to the stored maximum junction temperature of the power device in the first historical operating condition, the limit junction temperature of the power device in the current grid period.

[0010] In an embodiment, the controller determines, according to the actual operating parameter and the historical operating parameters of the power device in the plurality of historical operating conditions, the first historical operating condition corresponding to the current operating condition, and is configured to: in a case where parameter differences between the actual operating parameter and the historical operating parameters of the plurality of historical operating conditions are all greater than a parameter difference threshold, select two historical operating conditions from the plurality of historical operating conditions as two first historical operating conditions corresponding to the current operating condition; and the controller determines, according to the stored maximum junction temperature of the power device in the first historical operating condition, the limit junction temperature of the power device in the current grid period, and is configured to: interpolate and fit the limit junction temperature of the power device in the current grid period according to the stored maximum junction temperatures of the two first historical operating conditions.

[0011] In an embodiment, the controller determines, during operation of the power conversion device, the maximum junction temperature of the power device in the current grid period, and is configured to: acquire a thermal performance parameter of the power device, a loss data table and an actual operating parameter of the power device in the current grid period; determine, according to the actual operating parameter, the thermal performance parameter and the loss data table, a steady-state junction temperature and a pulse power of the power device in the current grid period; and determine, according to the steady-state junction temperature, the pulse power and a power factor of the power device in the current grid period, the maximum junction temperature of the power device in the current grid period.

[0012] In an embodiment, the thermal performance parameter comprises a steady-state thermal impedance of the power device, a transient thermal impedance data table, the actual operating parameter comprises a current of the power device in each switching period of the current grid cycle, a DC bus voltage, a heat sink temperature, a duty cycle and a power factor, the controller determines a steady-state junction temperature and a pulse power of the power device in the current grid cycle according to the actual operating parameter, the thermal performance parameter and the loss data table, and is configured to: fit an on-state loss of the power device in each switching period according to the current of the power device in each switching period, an assumed value of the steady-state junction temperature, the duty cycle and the loss data table; fit a switching loss of the power device in each switching period according to the current of the power device in each switching period, the DC bus voltage, the assumed value of the steady-state junction temperature and the loss data table; fit a total loss of the power device in the current grid cycle according to the switching loss and the on-state loss of the power device in each switching period; calculate an estimated value of the steady-state junction temperature by using a thermal balance equation according to the total loss, the heat sink temperature and the steady-state thermal impedance; in a case where a difference between the estimated value and the assumed value is greater than a junction temperature difference threshold, take the estimated value as the assumed value, continue to iteratively fit the estimated value of the steady-state junction temperature until the difference between the estimated value and the assumed value is less than or equal to the junction temperature difference threshold, and end the iteration; and determine the steady-state junction temperature of the power device in the current grid cycle according to the estimated value of the steady-state junction temperature fitted at the end of the iteration.

[0013] In an embodiment, the controller determines the steady-state junction temperature and the pulse power of the power device in the current grid cycle according to the actual operating parameter, the thermal performance parameter and the loss data table, and is further configured to: fit a final total loss of the power device in the current grid cycle according to the steady-state junction temperature of the power device in the current grid cycle; determine the pulse power of the power device in the current grid cycle according to the final total loss, a total duration of the current grid cycle and a loss duration within the current grid cycle; and determine a maximum junction temperature of the power device in the current grid cycle according to the steady-state junction temperature of the power device in the current grid cycle, the pulse power and the power factor, and is configured to: determine a transient thermal impedance corresponding to the pulse power according to the pulse power and the transient thermal impedance data table; and determine the maximum junction temperature of the power device in the current grid cycle according to the steady-state junction temperature, the transient thermal impedance, the pulse power and the power factor.

[0014] In a second aspect, a control method of a power conversion device is provided. The method comprises the following steps: determining a maximum junction temperature of a power device of the power conversion device in a current grid cycle during operation of the power conversion device, wherein the maximum junction temperature is a maximum value of junction temperatures of the power device in the current grid cycle; determining a derating state of the power conversion device according to a difference between the maximum junction temperature and a limit junction temperature of the power device, wherein the derating state is used to indicate whether the power conversion device is operated in a derated mode and / or is used to indicate a relationship between an actual derating and an expected derating when the power conversion device is operated in the derated mode; and determining a limit current of the power conversion device in a next grid cycle according to the derating state of the power conversion device, wherein the limit current is a limit value of an output current of the power conversion device.

[0015] In a third aspect, a control apparatus of a power conversion device is provided. The control apparatus comprises: a first determining module configured to determine a maximum junction temperature of a power device of the power conversion device in a current grid cycle during operation of the power conversion device, wherein the maximum junction temperature is a maximum value of junction temperatures of the power device in the current grid cycle; a second determining module configured to determine a derating state of the power conversion device according to a difference between the maximum junction temperature and a limit junction temperature of the power device, wherein the derating state is used to indicate whether the power conversion device is operated in a derated mode and / or is used to indicate a relationship between an actual derating and an expected derating when the power conversion device is operated in the derated mode; and a third determining module configured to determine a limit current of the power conversion device in a next grid cycle according to the derating state of the power conversion device, wherein the limit current is a limit value of an output current of the power conversion device.

[0016] In a fourth aspect, a computer-readable storage medium is provided. The computer-readable storage medium stores a computer program. When the computer program is executed by a control apparatus of a power conversion device, the control apparatus of the power conversion device performs the control method of the power conversion device in the second aspect.

[0017] In a fifth aspect, a computer program product is provided. The computer program product comprises a computer program. When the computer program is executed by a power conversion device, the power conversion device performs the control method of the power conversion device in the second aspect.

[0018] The first aspect of the embodiment of the present application provides the current conversion device. The current conversion device determines the maximum junction temperature of the power device in the current grid period in time during the operation of the current conversion device, and accurately determines the derating state of the current conversion device according to the difference between the maximum junction temperature and the limited junction temperature of the power device. Since the derating state can indicate whether the current conversion device is derated or not and / or indicate the relationship between the actual derating and the expected derating when the current conversion device is derated, the limited current of the current conversion device in the next grid period can be quickly and accurately determined according to the derating state of the current conversion device. The active derating control mode of dynamically adjusting the limited current of the current conversion device can make the current conversion device stably operate under different load conditions or grid fluctuations, improve the response speed and stability of the power system. In addition, the scheme first determines the derating state of the current conversion device in the current grid period, and then dynamically adjusts the limited current of the current conversion device in the next grid period according to the derating state, which realizes more refined derating control of the current converter, reduces unnecessary energy waste, and improves energy utilization efficiency. Moreover, in the case that the derating state of the current conversion device can indicate the relationship between the actual derating and the expected derating when the current conversion device is derated, the actual derating of the current conversion device in the next grid period can be closer to the expected derating, so that the derating control can be more accurate, and the energy conversion effect of the current conversion device can be improved on the basis of improving the safety and reliability of the power device of the current conversion device. That is, the grid-connected power generation effect can be more optimal, the economic benefit can be improved, and the economy and reliability of the product can be better balanced.

[0019] It can be understood that the beneficial effects of the second aspect to the fifth aspect can be referred to the related description in the first aspect, which will not be repeated here. BRIEF DESCRIPTION OF DRAWINGS

[0020] Figure 1 A flowchart of a control method of a current conversion device is shown;

[0021] Figure 2 A schematic diagram of a curve of the junction temperature of a power device of a current converter changing with time is shown;

[0022] Figure 3 A schematic diagram of a curve of the voltage of a power device of a current converter changing with time is shown;

[0023] Figure 4a And Figure 4b Flowcharts of different parts of a control method of a current conversion device are shown respectively;

[0024] Figure 5Fig. 1 shows a structural schematic diagram of a control device of a power conversion device according to an embodiment of the present application;

[0025] Figure 6 Fig. 1 shows a structural schematic diagram of a control device of a power conversion device according to an embodiment of the present application;

[0026] Figure 7 Fig. 1 shows a structural schematic diagram of a control device of a power conversion device according to an embodiment of the present application; DETAILED DESCRIPTION

[0027] The technical solutions in the embodiments of the present application will be described below with reference to the drawings in the embodiments of the present application. In the description of the embodiments of the present application, unless otherwise specified, " / " represents the meaning of or, for example, A / B can represent A or B; in this document, "and / or" is only a description of the association relationship of the associated objects, which means that there can be three relationships, for example, A and / or B, which can represent the three cases of A alone, A and B together, and B alone. In addition, in the description of the embodiments of the present application, "multiple" means two or more than two.

[0028] Hereinafter, the terms "first", "second", "third" are only for the purpose of description, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of indicated technical features. Therefore, the features defined with "first", "second", "third" can explicitly or implicitly include one or more of the features.

[0029] For the purpose of illustration and not for limitation, specific details such as specific system structures, technologies, etc. are presented in order to thoroughly understand the embodiments of the present application. However, it should be clear to those skilled in the art that the present application can also be implemented in other embodiments without these specific details. In other cases, detailed descriptions of well-known systems, devices, circuits and methods are omitted to avoid unnecessary details that hinder the description of the present application.

[0030] As mentioned above, the existing converter device usually adopts a passive derating control strategy. Taking the converter device as a converter, the traditional passive derating control method usually fits a fixed derating curve according to the laboratory operating data of the research and development test. In actual operation, according to the temperature collection point on the radiator inside the converter and the operating parameters that the converter can collect under the actual operating condition, passive derating is performed according to the derating curve. However, the real operating condition is relatively complex, and there are various complex conditions such as high and low wear, and the installation mode of the terminal customer also has differences, such as whether the converter is blocked by the air duct, the different installation angles of the converter, the sealing of the installation environment and other problems, which will cause differences between the actual operating condition of the converter and the laboratory condition when the derating strategy is formulated. The method of passive derating according to the derating curve often leads to inaccurate triggering of the actual converter operation. In some cases, passive derating may cause the converter device to excessively reduce the output power, thereby affecting the energy conversion performance and efficiency of the converter device, causing less power generation and poor economic benefits. In other cases, passive derating may also cause the converter to be insufficiently derated, causing overheating or overloading of the power device, which seriously reduces the reliability and safety of the product. That is, the passive derating control strategy in the prior art may cause damage to the power device of the converter device or poor energy conversion effect of the converter device, and it is more difficult to balance the economy and reliability of the product.

[0031] In order to at least partially solve the above technical problems, the embodiments of the present application provide a converter device, a control method of a converter device, a control device of a converter device, a computer readable storage medium and a computer program product, which can significantly improve the energy conversion effect of the converter device on the basis of improving the safety and reliability of the power device of the converter device, that is, the optimal grid-connected power generation effect can be realized under the condition of ensuring the reliability of the junction temperature of the power device, the economic benefit is improved, and the economy and reliability of the product are better balanced.

[0032] Firstly, the embodiments of the present application provide a control method of a converter device. The control method can be applied to various converter devices, including but not limited to various converters (such as phase-controlled converters, pulse width modulation converters, etc.), rectifier devices, inverter devices, alternating current conversion devices, direct current conversion devices and other auxiliary devices and components. For simplicity, the control method of the converter device provided by the embodiments of the present application will be described below taking the converter device as a converter. Specifically, each step of the control method of the converter device of the embodiments of the present application can be executed by the controller of the converter (for example, a household energy storage converter controller).

[0033] As shown in Figure 1 The control method of the converter device provided by the embodiments of the present application includes the following steps:

[0034] Step S110: During the operation of the converter equipment, determine the maximum junction temperature of the power devices in the current grid cycle. The maximum junction temperature is the highest value of the junction temperature of the power devices in the current grid cycle.

[0035] In this embodiment, the grid cycle of the converter can be the total duration during which the current or voltage starts from a certain initial state, passes through a positive maximum value, a zero value, a reverse maximum value, and then returns to the initial state. (See reference...) Figure 2 One grid cycle of the converter can be t in the diagram. grid The time indicated. It's understandable that the grid cycle for converters can differ in different regions. For example, one grid cycle for a converter could be 20ms.

[0036] In this embodiment, the power devices in the converter equipment can be power semiconductor devices capable of converting and controlling electrical power. The power semiconductor devices can be packaged as a single device in a single package (discrete device), or they can be integrated with other semiconductor devices. For example, the power devices in the converter equipment may include, but are not limited to: diodes, insulated-gate bipolar transistors (IGBTs), thyristors, metal-oxide-semiconductor field-effect transistors (MOSFETs), etc.

[0037] In this embodiment, the converter's controller can operate according to the commanded current or commanded power from the upper-layer software. Specifically, the upper-layer software is responsible for generating control commands and sending them to the converter's controller via a communication interface. The controller can adjust its output current and output voltage parameters according to the received control commands to meet the system's requirements. In other words, the commanded current can be the current command value required for the converter's operation, and the commanded power can be the power command value required for the converter's operation. In the example where the converter's controller operates according to the commanded power, the controller can calculate the commanded current based on the commanded power, and then determine the converter's output current based on the commanded current.

[0038] As we understand it, a converter is a device that converts electrical energy using its internal power devices. These power devices generate losses during switching, which are converted into heat, causing the junction temperature of the devices to rise. Typically, as the output current of the converter increases, the conduction and switching losses of the power devices also increase, leading to a rise in the junction temperature of the power devices. In some cases, the rise in junction temperature may exceed the limiting junction temperature of the power devices (e.g., the rated operating temperature), affecting the reliability and lifespan of the power devices.

[0039] In the embodiments of the present application, considering the influence of the output current of the converter on the junction temperature of the power device, the junction temperature data of the power device can be monitored during the operation of the converter. Then, in the subsequent steps, the output current of the converter can be determined in combination with the monitored junction temperature data and the command current, so that the junction temperature data of the power device is kept within the corresponding safe junction temperature range, and the difference between the output current and the command current of the converter is reduced, so that the converter generates power with the maximum capacity.

[0040] Specifically, in the embodiments of the present application, during the operation of the converter, the controller can determine the maximum junction temperature of each power device of the converter in the current grid cycle in real time. It should be understood that the maximum junction temperature of the power device in the current grid cycle is the maximum value of the junction temperature of the power device in the current grid cycle. Taking the grid cycle of 20 ms as an example, the maximum value of the junction temperature of each power device in the converter in every 20 ms can be determined. Referring to Figure 2 Taking the IGBT in the converter as an example, the junction temperature of the IGBT in every 20 ms is in a fluctuating state. The maximum junction temperature T j.max may be the temperature corresponding to the peak of the junction temperature waveform. It should be noted that although the waveform curve shown in the figure does not change much in different grid cycles, in actual working conditions, the junction temperature-time curve of the power device in different grid cycles may be different due to the influence of many factors. Therefore, the maximum junction temperature of each power device in different grid cycles determined by the controller of the converter may be different.

[0041] In the embodiments of the present application, the controller of the converter device can determine the maximum junction temperature of each power device in the current grid cycle by using various suitable junction temperature fitting methods. Specifically, the converter device can include sensors for collecting the actual operating parameters of each power device (e.g., the current of each switching cycle of the power device in the current grid cycle, the DC bus voltage, the radiator temperature, etc.). For example, the storage module (e.g., memory, register, etc.) of the converter device can store the thermal performance parameters, loss data table, and other junction temperature reference data of each power device of the converter device. For example, during the operation of the converter, the controller can control the sensors to collect the actual operating parameters of each power device in each grid cycle in real time, and can accurately determine the maximum junction temperature of each power device in the current grid cycle by combining the actual operating parameters of each power device collected by the sensors and the junction temperature reference data of each power device. For example, but not limited to, the steady-state junction temperature and the pulse power of the power device in the current grid cycle can be iteratively fitted by discretizing the loss data of the power device in each switching cycle of the current grid cycle. Then, the maximum junction temperature of the power device in the current grid cycle can be accurately fitted according to the steady-state junction temperature and the pulse power. Specific examples of this scheme will be described later. For the sake of brevity, they will not be described here.

[0042] For example, if one grid cycle is 20 ms, in this step, the controller of the converter can calculate the maximum junction temperature T j.max of the power device every 20 ms, thereby achieving dynamic monitoring of the junction temperature of the power device of the converter. Moreover, the maximum junction temperature of the power device in one grid cycle also accurately reflects the change of the junction temperature of the power device in a short time (i.e., the junction temperature fluctuates between the highest temperature corresponding to the peak and the lowest temperature corresponding to the trough). Thus, it is convenient to adjust the output current in time according to the change of the junction temperature.

[0043] In the prior art, some schemes determine the output current of the converter by monitoring the steady-state junction temperature of the power device of the converter and according to the steady-state junction temperature. However, the steady-state junction temperature can only reflect the temperature of the power device in a stable working state, and cannot reflect the temperature of the power device in a non-stable scenario (such as a scenario in which the output current of the converter changes rapidly). Therefore, the steady-state junction temperature of the power device of the converter cannot accurately reflect the junction temperature of the power device, and the scheme of determining the output current of the converter according to the steady-state junction temperature has poor accuracy. Some other schemes determine the output current of the converter by monitoring the instantaneous junction temperature of the power device of the converter and according to the instantaneous junction temperature. Although the instantaneous junction temperature can reflect the dynamic change of the temperature of the power device, it is very difficult to monitor the instantaneous junction temperature of the power device in actual working conditions, especially in scenarios in which the temperature changes rapidly. The determination of the instantaneous junction temperature usually has a large delay, and the calculation method is very complex and has a very large calculation amount, resulting in poor availability of the actually monitored instantaneous junction temperature. Therefore, the scheme of determining the output current of the converter according to the instantaneous junction temperature of the power device has poor feasibility and accuracy. In the embodiments of the present application, the controller determines the maximum junction temperature of the power device of the converter in each power grid cycle in real time. On the one hand, the maximum junction temperature of the power device in each power grid cycle can accurately reflect the change of the junction temperature of the power device in a short time; on the other hand, compared with the instantaneous junction temperature, it is easier and more accurate to monitor the maximum junction temperature of the power device in each power grid cycle. Therefore, after the controller accurately monitors the maximum junction temperature of the power device of the converter in each power grid cycle, it can provide a more reliable decision basis for subsequent determination of the derating state of the converter and dynamic adjustment of the limit current of the converter.

[0044] In step S120, the derating state of the converter device is determined according to the difference between the maximum junction temperature and the limit junction temperature of the power device. The derating state is used to indicate whether the converter device is running at a derated state and / or to indicate the relationship between the actual derating and the expected derating when the converter device is running at a derated state.

[0045] In the embodiments of the present application, considering the influence of the output current of the converter on the junction temperature of the power device, not only the junction temperature data of the power device is monitored, but also the output current of the converter is limited during the operation of the converter, so that the junction temperature of the power device is kept within the corresponding safe junction temperature range. For example, the controller can set the limit value of the output current of the converter, and limit the output current of the converter according to the limit value. That is, in the embodiments of the present application, the controller can determine the output current of the converter according to the instruction current, the junction temperature data of the power device and the limit value of the output current of the converter during the operation of the converter. In the embodiments of the present application, the limit value of the output current of the converter is referred to as the limit current of the converter. Specifically, the controller can set the initial value of the limit current of the converter in advance according to the design parameters, thermal management capability, external operating conditions and the like of the converter. For example, the initial value of the limit current can be set as the rated current of the converter. For example, at the initial moment, the controller of the converter can limit the output current of the converter according to the initial value of the limit current, and during the operation, the limit current of the converter can be dynamically updated according to the real-time monitored junction temperature data of each power device, and then the output current of the converter can be limited according to the updated limit current. It can be understood that the purpose of dynamically updating the limit current in the embodiments of the present application is to reduce the difference between the output current of the converter and the instruction current on the basis of keeping the junction temperature data of the power device within the corresponding safe junction temperature range, so that the converter generates power with the maximum capacity.

[0046] In the embodiments of the present application, the limit junction temperature of the power device can be a limit value of the junction temperature of the power device at present. Various suitable methods can be used to determine the limit junction temperature of the power device. In one example, the limit junction temperature of the power device can be pre-set and stored according to the rated junction temperature or the limit working junction temperature of the power device. The limit junction temperature of the power device can be less than or equal to the limit working junction temperature of the power device. For example, the limit working junction temperature of a certain power device is equal to 175℃, and the limit junction temperature of the power device can be set to 148℃ according to a 0.85 times derating. In another example, the historical running parameters and the maximum junction temperature of the power device under a plurality of historical working conditions can be pre-stored in a storage module of the converter. Then, according to the actual running parameters of the power device in the current grid cycle and the historical running parameters of the power device under a plurality of historical working conditions, a first historical working condition corresponding to the current working condition can be determined. That is, the historical working condition that is the same as or close to the current working condition is selected from the past historical working conditions as the first historical working condition. And the limit junction temperature of the power device in the current grid cycle can be determined according to the maximum junction temperature of the power device under the first historical working condition. That is, the limit junction temperature of the power device in the current grid cycle can be determined according to the maximum junction temperature of the historical working condition that is close to or the same as the actual running working condition of the power device. Specific examples of this scheme will be explained later, and for the sake of brevity, will not be described here.

[0047] In the embodiments of the present application, the derating state of the converter device is used to indicate whether the converter device is running in a derated mode and / or to indicate the relationship between the actual derating and the expected derating when the converter device is running in a derated mode. In one example, the derating state of the converter device is used to indicate whether the converter device is running in a derated mode. For example, the derating state of the converter device includes a non-derated state used to indicate that the converter device has not yet run in a derated mode and a derated state used to indicate that the converter device is running in a derated mode. In another example, the derating state of the converter device is used to indicate the relationship between the actual derating and the expected derating when the converter device is running in a derated mode. For example, the derating state of the converter device includes an over-derated state used to indicate that the converter device is running in a derated mode and the actual derating is greater than the expected derating, and an under-derated state used to indicate that the converter device is running in a derated mode and the actual derating is less than the expected derating. Alternatively, in some special examples, the derating state of the converter device can also include an ideal derated state used to indicate that the converter device is running in a derated mode and the actual derating is equal to the expected derating. That is, the derated state of the converter device can be subdivided into different states according to the relationship between the actual derating and the expected derating when the converter device is running in a derated mode.

[0048] In the embodiments of the present application, a plurality of suitable methods can be used to determine the derating state of the power conversion device according to the difference between the maximum junction temperature of the power device in the current grid cycle and the limit junction temperature of the power device. Alternatively, the derating state of the power conversion device can be determined only according to the difference between the maximum junction temperature in the current grid cycle and the limit junction temperature of the power device. Alternatively, the derating state of the power conversion device can be determined according to the difference between the maximum junction temperature in the current grid cycle and the limit junction temperature of the power device in combination with other derating reference parameters. For example, the other derating reference parameters can include the command current received by the power conversion device, the command power, the current output current of the power conversion device, the current limit current, and the like. For example, the power conversion device can be determined to be in the under-derating state when the maximum junction temperature of the power device in the current grid cycle is greater than or equal to the limit junction temperature of the power device. For another example, the power conversion device can be determined to be in the non-derating state, the over-derating state, or the ideal derating state in combination with other derating reference parameters when the maximum junction temperature of the power device in the current grid cycle is less than the limit junction temperature of the power device. In one example, the power conversion device can be determined to be in the non-derating state or the over-derating state according to the difference between the command current currently received by the power conversion device and the current output current. For example, the output current is usually close to the command current when the power conversion device is not derated in order to improve the power generation efficiency. When the power conversion device is over-derated, the output current of the power conversion device is limited, resulting in an increase in the difference between the output current and the command current. That is, the power conversion device can be determined to be in the non-derating state when the absolute value of the difference between the output current and the command current of the power conversion device is small, and the power conversion device can be determined to be in the over-derating state when the absolute value of the difference between the output current and the command current of the power conversion device is large. In another example, the power conversion device can be determined to be in the non-derating state or the over-derating state according to the difference between the command current currently received by the power conversion device and the current limit current. For example, the limit current is usually greater than or equal to the command current when the power conversion device is not derated. When the power conversion device is over-derated, the limit current is less than the command current.

[0049] In step S130, the limit current of the power conversion device in the next grid cycle is determined according to the derating state of the power conversion device, wherein the limit current is a limit value of the output current of the power conversion device.

[0050] In the embodiments of the present application, the limit current of the power conversion device in the next grid cycle is dynamically adjusted according to the derating state of the power conversion device at the end of the current grid cycle, so that the junction temperature of the power device in the next grid cycle is less than the limit junction temperature of the power device, and the difference between the output current of the power conversion device and the command current received in the next grid cycle is reduced.

[0051] In the embodiments of the present application, different derating states of the power conversion device can correspond to different limited current adjustment strategies. For example, the non-derating state of the power conversion device can correspond to a maintaining strategy of maintaining the limited current unchanged, i.e., the limited current of the power conversion device in the next grid cycle can be determined to be equal to the current limited current. For example, the under-derating state of the power conversion device can correspond to a decreasing strategy of decreasing the limited current, i.e., the limited current of the power conversion device in the next grid cycle can be determined to be less than the current limited current. For example, the over-derating state of the power conversion device can correspond to a releasing strategy of increasing the limited current, i.e., the limited current of the power conversion device in the next grid cycle can be determined to be greater than the current limited current. Specific examples of these schemes will be described below. For the sake of brevity, they will not be described here.

[0052] As described above, the passive derating control strategy in the prior art can cause damage to the power device of the power conversion device or poor energy conversion effect of the power conversion device, and it is more difficult to balance the economy and reliability of the product. According to the control method of the power conversion device in the embodiments of the present application, the maximum junction temperature of the power device in the current grid cycle is determined in time during the operation of the power conversion device, and the derating state of the power conversion device is accurately determined according to the difference between the maximum junction temperature and the limited junction temperature of the power device. Since the derating state can indicate whether the power conversion device is running in a derated state and / or indicate the relationship between the actual derating and the expected derating of the power conversion device when running in a derated state, the limited current of the power conversion device in the next grid cycle can be quickly and accurately determined according to the derating state of the power conversion device. This active derating control mode of dynamically adjusting the limited current of the power conversion device can enable the power conversion device to stably operate under different load conditions or grid fluctuations, improve the response speed and stability of the power system. In addition, this scheme first determines the derating state of the power conversion device in the current grid cycle, and then dynamically adjusts the limited current of the power conversion device in the next grid cycle according to the derating state, which realizes more refined derating control of the power conversion device, reduces unnecessary energy waste, and improves energy utilization efficiency. Moreover, in the case where the derating state of the power conversion device can indicate the relationship between the actual derating and the expected derating of the power conversion device when running in a derated state, the actual derating of the power conversion device when running in a derated state in the next grid cycle can be closer to the expected derating, so that the derating control can be more accurate, and the energy conversion effect of the power conversion device can be improved on the basis of improving the safety and reliability of the power device. That is, in the case of improving the reliability of the junction temperature of the power device, a more optimal grid-connected power generation effect can be achieved, the economic benefit can be improved, and the economy and reliability of the product can be better balanced.

[0053] In an embodiment, the derating state includes a non-derating state indicating that the power conversion device has not yet run in a derated state, and an over-derating state indicating that the power conversion device runs in a derated state and the actual derating is greater than the expected derating.

[0054] Step S120 determines the derating state of the power conversion device according to the difference between the maximum junction temperature and the limit junction temperature of the power device, including: step S121, in the case that the maximum junction temperature of the power device in the current grid cycle is less than the limit junction temperature of the power device, determining that the power conversion device is in a non-derating state or an over-derating state according to the current difference between the current limit current and the current received instruction current.

[0055] It can be understood that, if the maximum junction temperature of the power device in the current grid cycle is less than the limit junction temperature of the power device, it can be explained that the junction temperature of the power device in the current grid cycle is always less than the limit junction temperature of the power device. This situation can correspond to multiple scenarios: first, it can be that the power conversion device has not yet entered the derating operation state (for example, the power demand in the grid is small, and the received instruction current of the power conversion device is small); second, it can be that the power conversion device has entered the derating operation state, but the derating amplitude is too large, and the actual derating exceeds the expected derating, which is intuitively manifested as that the output current of the power conversion device cannot meet the actual power demand; third, in some special cases, it can be that the power conversion device has entered the derating operation state, but the derating amplitude exactly meets the expectation, that is, the actual derating of the power conversion device is equal to the expected derating. In the embodiments of the present application, the special scenario in which the actual derating of the power conversion device is equal to the expected derating is not considered, and the first and second scenarios are mainly analyzed, wherein the first scenario is the scenario in which the power conversion device is in a non-derating state, and the second scenario is the scenario in which the power conversion device is in an over-derating state.

[0056] In the embodiments of the present application, in order to accurately distinguish whether the power conversion device is in a non-derating state or an over-derating state, in the case that the maximum junction temperature of the power device of the power conversion device in the current grid cycle is less than the limit junction temperature of the power device, it is further determined that the current difference between the current limit current and the current received instruction current of the power conversion device.

[0057] It can be understood that the current received instruction current of the power conversion device represents the actual power generation demand, and therefore, the current difference between the current limit current and the current received instruction current of the power conversion device can accurately reflect whether the power conversion device is in a derating operation state. Therefore, in the embodiments of the present application, according to the current difference between the current limit current and the instruction current of the power conversion device, it can be accurately distinguished whether the power conversion device is in a non-derating state or an over-derating state.

[0058] Step S130 determines the limit current of the power conversion device in the next grid cycle according to the derating state of the power conversion device, including: step S131, in the case that the power conversion device is in a non-derating state or an over-derating state, determining that the limit current of the power conversion device in the next grid cycle is greater than or equal to the current limit current.

[0059] For example, the current limit of the power conversion device can be the current limit of the power conversion device at the current time (i.e., at the end of each power grid cycle) or the average current limit of the power conversion device in the current power grid cycle. Alternatively, the current limit of the power conversion device in each power grid cycle can be the same. Alternatively, the current limit of the power conversion device in each power grid cycle can vary regularly.

[0060] In one example, in a case where it is determined that the power conversion device is in the under-rating state, it can be determined that the current limit of the power conversion device in the next power grid cycle is equal to the current limit. In a case where it is determined that the power conversion device is in the over-rating state, it can be determined that the current limit of the power conversion device in the next power grid cycle is greater than the current limit. In some specific examples, in a case where it is determined that the power conversion device is in the under-rating state or the over-rating state, it can be determined that the current limit of the power conversion device in the next power grid cycle is greater than the current limit, but the adjustment range of the current limit corresponding to the two rating states can be different. For example, in a case where it is determined that the power conversion device is in the under-rating state, it can be determined that the current limit of the power conversion device in the next power grid cycle is equal to m1 times the current limit, and in a case where it is determined that the power conversion device is in the over-rating state, it can be determined that the current limit of the power conversion device in the next power grid cycle is equal to m2 times the current limit, where 1 < m1 < m2.

[0061] In the above scheme, by comparing the difference between the current limit of the power conversion device and the received instruction current, it can be quickly and accurately determined whether the power conversion device is in the under-rating state or the over-rating state. Furthermore, in a case where it is determined that the power conversion device is in the under-rating or over-rating state, it can be determined that the current limit in the next power grid cycle can remain at the current level or be appropriately increased. Thus, the stability and efficiency of power supply can be improved. Therefore, by accurately measuring and analyzing the current difference between the current limit of the power conversion device and the instruction current, accurate determination of the rating state of the power conversion device is achieved, and the current limit in the next power grid cycle is dynamically adjusted accordingly, improving the flexibility, efficiency and stability of power supply.

[0062] In one embodiment, step S121 determines whether the power conversion device is in the under-rating state or the over-rating state according to the current difference between the current limit and the current received instruction current, including: step S121a, in a case where the current difference is less than the current difference threshold, determining that the power conversion device is in the over-rating state; and step S131, in a case where the power conversion device is in the under-rating state or the over-rating state, determining that the current limit of the power conversion device in the next power grid cycle is greater than or equal to the current limit, including: step S131a, in a case where the power conversion device is in the over-rating state, determining that the current limit of the power conversion device in the next power grid cycle is greater than the current limit.

[0063] In the embodiments of the present application, the current difference threshold value can be set according to actual needs. For example, the current difference threshold value is equal to 0. The current difference between the current limit and the current received instruction current can be a current difference value obtained by subtracting the instruction current from the limit current. That is, it can be determined that the power conversion device is in the over-de-rated state when the power converter is in a current limit that is less than the current instruction current. And it can be determined that the limit current of the power conversion device in the next power grid cycle is greater than the current limit current when it is determined that the power conversion device is in the over-de-rated state. Exemplarily, the limit current of the power conversion device in the next power grid cycle can be equal to m times the current limit current, and m can fall within the interval (1, 1.5].

[0064] It can be understood that in the over-de-rated state, the power converter fails to fully exert its output capability, resulting in insufficient power supply. By increasing the limit current in the next power grid cycle when it is determined that the power conversion device is in the over-de-rated state, the output capability of the power converter can be more effectively utilized to meet more power demand, thereby improving the supply efficiency of the entire power system.

[0065] In an embodiment, step S121 determines whether the power conversion device is in the de-rated state or the over-de-rated state according to the current difference between the current limit and the current received instruction current, including: step S121b, determining that the power conversion device is in the de-rated state when the current difference is greater than or equal to the current difference threshold value; and step S131, determining that the limit current of the power conversion device in the next power grid cycle is greater than or equal to the current limit current when the power conversion device is in the de-rated state or the over-de-rated state, including: step S131b, determining that the limit current of the power conversion device in the next power grid cycle is equal to the current limit current when the power conversion device is in the de-rated state.

[0066] Similarly, taking the current difference threshold value equal to 0 as an example, it can be determined that the power conversion device is in the de-rated state when the power converter is in a current limit that is greater than or equal to the current instruction current. And it can be determined that the limit current of the power conversion device in the next power grid cycle is equal to the current limit current when it is determined that the power conversion device is in the de-rated state.

[0067] It can be understood that in the de-rated state, the power converter itself can output power according to the requirements of the instruction current, and by keeping the limit current unchanged, the current power demand can continue to be met. Potential risks and uncertainties caused by adjustment can also be reduced, and stable operation of the system can be maintained. Moreover, keeping the current limit current unchanged can reduce unnecessary energy waste and equipment wear and tear.

[0068] In an embodiment, the derated state includes an under-derated state indicating that the current device is derated but the actual derating is less than the expected derating. The step S120 of determining the derated state of the current device according to the difference between the maximum junction temperature and the limit junction temperature of the power device includes: a step S122 of determining that the current device is in the under-derated state when the maximum junction temperature of the power device is greater than or equal to the limit junction temperature of the power device; and a step S130 of determining the limit current of the current device in the next grid cycle according to the derated state of the current device, including: a step S132 of determining that the limit current of the current device in the next grid cycle is less than the current limit current when the current device is in the under-derated state.

[0069] For example, when the maximum junction temperature of the diode in the current transformer is greater than or equal to the limit junction temperature of the diode in a certain grid cycle, it is determined that the current transformer is in the under-derated state, and it can be determined that the limit current of the current transformer in the next grid cycle is less than the current limit current. For example, it can be determined that the limit current of the current transformer in the next grid cycle is equal to k times the current limit current, 0 < k < 1. Specifically, 0.5 < k < 1.

[0070] In the above scheme, when the maximum junction temperature of the power device of the current device is greater than or equal to the limit junction temperature thereof, it is determined that the current transformer is in the under-derated state. And when the current transformer is in the under-derated state, the limit current of the current transformer in the next grid cycle is reduced, which can reduce the risk of damage to the power device due to overheating, not only helps to prolong the service life of the device and reduce maintenance and replacement costs. It can also improve the reliability of the power device, which helps to reduce energy waste and equipment loss.

[0071] In an embodiment, the control method of the current device of the embodiment of the present application further includes the following steps:

[0072] Step S101, obtaining the actual operating parameters of the power device in the current grid cycle;

[0073] Step S102, determining a first historical working condition corresponding to the current working condition according to the actual operating parameters and the historical operating parameters of the power device in a plurality of historical working conditions, wherein the parameter difference between the historical operating parameters of the first historical working condition and the actual operating parameters is less than the parameter difference between the historical operating parameters of a second historical working condition and the actual operating parameters, and the second historical working condition is other historical working condition in the plurality of historical working conditions except the first historical working condition;

[0074] Step S103, determining the limit junction temperature of the power device in the current grid cycle according to the stored maximum junction temperature of the power device in the first historical working condition.

[0075] Exemplarily, the historical operating parameters of the power device of the converter under a plurality of historical working conditions and the maximum junction temperature of the power device under each historical working condition can be stored in advance in a storage module of the converter. The operating parameters of the power device can include voltage, current, etc. The historical operating parameters of the power device of the converter under a plurality of historical working conditions can be obtained through a large number of tests, or can be continuously stored and updated during actual operation. For example, the number of historical working conditions is n, n≥3. For example, the voltage V1, the current I1, and the maximum junction temperature T1 of the diode of the converter under the historical working condition H1 can be stored, the voltage V2, the current I2, and the maximum junction temperature T2 of the diode of the converter under the historical working condition H2 can be stored, and so on. The voltage Vn, the current In, and the maximum junction temperature Tn of the diode of the converter under the historical working condition Hn can be stored. During actual operation of the converter, the voltage V0 and the current I0 of the diode of the converter in the current grid cycle can be monitored. The voltage V0 and the current I0 can be compared with the voltage and the current under the n historical working conditions stored in the storage module. Specifically, the voltage difference and the current difference between the voltage V0 and the current I0 and the voltage and the current under each historical working condition can be calculated, and the absolute value of the voltage difference and the absolute value of the current difference can be obtained. For example, for the case that the absolute value of the voltage difference determined by comparing with a historical working condition is less than a voltage threshold (for example, 0.1V) and the absolute value of the current difference is less than a current threshold (for example, 0.1A), the historical working condition can be determined as the first historical working condition corresponding to the current working condition. The maximum junction temperature of the diode under the first historical working condition stored can be used to determine the limit junction temperature of the diode in the current grid cycle. For example, the maximum junction temperature can be directly used as the limit junction temperature of the diode in the current grid cycle.

[0076] In this scheme, the actual operating parameters of the power device of the converter under the current working condition are obtained in real time, and the historical operating parameters under the historical working conditions are compared to find the historical working condition close to the current working condition. The limit junction temperature of the power device in the current grid cycle is accurately determined according to the maximum junction temperature of the power device under the close historical working condition. The determined limit junction temperature is more accurate and meets the requirements of the actual working condition, which can improve the accuracy of the de-rating state determination of the converter, and thus the stability and safety of the power system can be improved.

[0077] In an embodiment, step S102 determines the first historical working condition corresponding to the current working condition according to the actual operating parameter and the historical operating parameters of the power device in the plurality of historical working conditions, including: step S102.1, in the case that the parameter difference between the actual operating parameter and the historical operating parameters of the plurality of historical working conditions is greater than the parameter difference threshold, screening two historical working conditions from the plurality of historical working conditions as two first historical working conditions corresponding to the current working condition; and step S103 determines the limiting junction temperature of the power device in the current grid cycle according to the stored maximum junction temperature of the power device in the first historical working condition, including: step S103.1, interpolating and fitting the limiting junction temperature of the power device in the current grid cycle according to the maximum junction temperatures of the two first historical working conditions.

[0078] In the above example of comparing the voltage V0 and the current I0 with the voltage and the current in the n historical working conditions stored in the storage module, if the current working condition does not satisfy the condition that the absolute value of the voltage difference is less than the voltage threshold and the absolute value of the current difference is less than the current threshold with each historical working condition. Two historical working conditions can be determined from the n historical working conditions, in which the actual operating parameter in the current working condition is closest to the historical working condition, as the first historical working condition corresponding to the current working condition. For example, the voltage V0 of the diode in the current grid cycle is greater than the voltage V1 in the historical working condition H1 and less than the voltage V2 in the historical working condition H2, the current I0 is greater than the current I1 in the historical working condition H1 and less than the current I2 in the historical working condition H2, and V0 is closest to V1 and V2, and I0 is closest to I1 and I2. In this example, the historical working condition H1 and the historical working condition H2 can be selected as the two first historical working conditions corresponding to the current working condition. And the limiting junction temperature of the diode in the current grid cycle can be determined by using the linear interpolation method according to the maximum junction temperature T1 in the historical working condition H1 and the maximum junction temperature T2 in the historical working condition H2.

[0079] In the above scheme, even in the case that the current working condition of the converter device is different from the historical working condition, the limiting junction temperature closer to the actual working condition can be obtained by interpolating and fitting the two closest historical working conditions selected. And with the change of the actual operating parameter of the converter, the scheme can dynamically adjust the selected historical working condition and obtain a new limiting junction temperature by interpolation fitting, so that the power device can obtain reasonable junction temperature limiting data in different working conditions. Therefore, the accuracy and dynamic adaptability of the derating control of the converter are further improved.

[0080] In one embodiment, the step S110 determines the maximum junction temperature of the power device in the current grid cycle during the operation of the power conversion device, including the following steps: a step S111, obtaining the thermal performance parameters of the power device, the loss data table and the actual operation parameters of the power device in the current grid cycle; a step S112, determining the steady-state junction temperature and the pulse power of the power device in the current grid cycle according to the actual operation parameters, the thermal performance parameters and the loss data table; and a step S113, determining the maximum junction temperature of the power device in the current grid cycle according to the steady-state junction temperature, the pulse power and the power factor of the power device in the current grid cycle.

[0081] Exemplarily, the thermal performance parameters of the power device can include the steady-state thermal impedance and the transient thermal impedance data table of the power device. The actual operation parameters of the power device can include the current, the DC bus voltage, the radiator temperature, the duty cycle and the power factor of the power device in each switching cycle in the current grid cycle. The actual operation parameters of the power device can be obtained by real-time collection through the sensors of the power converter. The thermal performance parameters and the loss data table of the power device can be pre-stored in the storage module of the power converter. In the embodiments of the present application, a plurality of suitable methods can be used to determine the steady-state junction temperature and the pulse power of the power device in the current grid cycle according to the actual operation parameters, the thermal performance parameters and the loss data table. Exemplarily, the steady-state junction temperature of the power device in the current grid cycle can be fitted by using the iterative method or the approximation method. Then, the pulse power of the power device in the current grid cycle can be determined according to the steady-state junction temperature. Subsequently, the maximum junction temperature of the power device in the current grid cycle can be determined according to the steady-state junction temperature, the pulse power and the power factor of the power device in the current grid cycle.

[0082] The above method for determining the maximum junction temperature of the power device in the current grid cycle not only considers the thermal performance parameters and the loss data of the power device, but also combines the actual operation parameters of the power device in the current grid cycle. This comprehensive consideration can more accurately reflect the thermal state of the power device in the actual operation, improve the accuracy of the maximum junction temperature, and thus further improve the accuracy of the derating control of the power converter.

[0083] In one embodiment, the thermal performance parameters include the steady-state thermal impedance and the transient thermal impedance data table of the power device, and the actual operation parameters include the current, the DC bus voltage, the radiator temperature, the duty cycle and the power factor of the power device in each switching cycle in the current grid cycle. In the embodiments of the present application, the loss data table can include the conduction loss data table and the switching loss data table.

[0084] The step S112 determines the steady-state junction temperature and the pulse power of the power device in the current grid cycle according to the actual operation parameters, the thermal performance parameters and the loss data table, including the following steps S112.1 to S112.6.

[0085] Step S112.1, according to the current of the power device in each switching cycle, the assumed value of the steady-state junction temperature, the duty cycle and the loss data table, fitting the conduction loss of the power device in each switching cycle.

[0086] In the embodiments of the present application, the switching cycle represents the time duration of each switching operation of the power device, that is, the time required for a complete switching process (from turn-on to turn-off, or from turn-off to turn-on) of the power device. Since the switching frequency of the power device is much higher than the grid frequency, in one grid cycle, the switching device of the electronic device may experience multiple turn-ons and turn-offs. For example, if the switching frequency is 20 kHz (switching cycle 50 us), in a 50 Hz grid cycle (20 ms), the switching device will turn on and off 400 times. And the duty cycle represents the ratio of the time when the signal is in a certain state (such as high level) to the whole switching cycle time. In combination Figure 3 , the switching cycle of the power device can be represented by t c , and the duty cycle of the power device can be represented by Duty.

[0087] In the embodiments of the present application, in the case where the steady-state junction temperature is unknown, a suitable assumed value (for example, the temperature of the heat sink of the power device) can be set for the steady-state junction temperature, and an iterative method can be used to solve the steady-state junction temperature. The conduction loss data of the power device can be obtained by actual test or obtained from the specification. Exemplarily, the conduction loss data of the power device can be stored in the storage module by table lookup, and the conduction loss of the IGBT and the diode in the current converter can be calculated in each switching cycle of the current grid cycle. Taking the IGBT as an example, the conduction loss E con of each switching cycle can be solved by using the following formula (1):

[0088] E con = I c × V CE × t c × Duty = I c × f(I c , T j.av ) × t c × Duty... (1)

[0089] Wherein, I c represents the current of the power device (IGBT) in each switching cycle of the current grid cycle, T j.av represents the steady-state junction temperature (which can be specifically an assumed value of the steady-state junction temperature), V CE represents the voltage between the C pole (collector) and the E pole (emitter) of the power device (IGBT), t cThis indicates the switching period, and "Duty" represents the duty cycle. Specifically, after the power device (IGBT) is turned on, conduction occurs between the collector (C) and emitter (E), which can be measured by the voltage V between the collector and emitter as specified in the datasheet. CE Curve lookup yields V for each switching cycle. CE The value of .

[0090] Step S112.2: Based on the assumed values ​​of current, DC bus voltage, steady-state junction temperature, and loss data of the power device in each switching cycle, fit the switching loss of the power device in each switching cycle.

[0091] It is understood that the switching losses of power devices stored in the specifications are all under ideal conditions. In this embodiment, the switching loss data table of the power devices can be obtained in advance based on actual double-pulse data testing and stored in the converter's storage module. The switching loss of the power devices in each switching cycle can be calculated by looking up the table. For example, the turn-on loss E of the power devices in each switching cycle can be solved using the following formula (2). on The turn-off loss E of the power device in each switching cycle is solved using the following formula (3). off :

[0092] E on =f on (I c V bus ,T j.av ...(2)

[0093] E off =f off (I c V bus ,T j.av (3)

[0094] Among them, I c This represents the current (V) of a power device (IGBT) during each switching cycle of the current power grid cycle. bus T represents the DC bus voltage for each switching cycle. j.av This represents the steady-state junction temperature (specifically, it can be an assumed value for the steady-state junction temperature).

[0095] Step S112.3: Based on the switching loss and conduction loss of the power device in each switching cycle, fit the total loss of the power device in the current power grid cycle.

[0096] For example, the total loss P of the power device in the current grid cycle total The discretization solution can be obtained using the following formula (4):

[0097]

[0098] Among them, tgrid Indicates the power grid cycle.

[0099] Step S112.4: Based on the total loss, radiator temperature and steady-state thermal impedance, the estimated value of steady-state junction temperature is calculated using the thermal balance equation.

[0100] For example, the estimated steady-state junction temperature T of the power device can be calculated using the following formula (5). j.av :

[0101] T j.av =T heat sin k +R th.jh ×P total …(5)

[0102] Among them, T heat sin k R represents the heatsink temperature of the power device during the current power grid cycle. th.jh This represents the steady-state thermal impedance of the stored power device.

[0103] Step S112.5: If the difference between the estimated value and the assumed value is greater than the junction temperature difference threshold, the estimated value is used as the assumed value, and the iteration continues to fit the estimated value of the steady-state junction temperature until the difference between the estimated value and the assumed value is less than or equal to the junction temperature difference threshold, and the iteration ends.

[0104] Step S112.6: Determine the steady-state junction temperature of the power device in the current power grid cycle based on the estimated steady-state junction temperature fitted at the end of the iteration.

[0105] In this embodiment, the junction temperature difference threshold can be set according to actual needs. For example, the junction temperature difference threshold is 1°C. Through iterative fitting, the steady-state junction temperature of the power device in the current power grid cycle can be determined quickly and accurately.

[0106] The above-mentioned method for calculating steady-state junction temperature is more accurate and requires less computation. Therefore, it can accurately determine the steady-state junction temperature of each power device in real time at the end of each power grid cycle, further improving the accuracy and real-time performance of converter derating control.

[0107] In one embodiment, step S112 determines the steady-state junction temperature and pulse power of the power device in the current power grid cycle based on actual operating parameters, thermal performance parameters and loss data table, and further includes the following steps S112.7 and S112.8.

[0108] Step S112.7, fitting the final total loss of the power device in the current grid cycle according to the steady-state junction temperature of the power device in the current grid cycle. Exemplarily, the final total loss of the power device in the current grid cycle can be the total loss fitted at the end of the iteration, or the steady-state junction temperature can be substituted into the above formulas (1) to (4) to obtain the final total loss of the power device in the current grid cycle.

[0109] Step S112.8, determining the pulse power of the power device in the current grid cycle according to the final total loss, the total duration of the current grid cycle, and the loss duration in the current grid cycle.

[0110] Reference Figure 2 , the pulse power P total of the power device in the current grid cycle can be determined according to the final total loss L loss , the total duration T grid of the current grid cycle, and the loss duration t grid in the current grid cycle. pulse loss = P total * t grid , thus, the pulse power P total of the power device in the current grid cycle can be solved by the following formula (6):

[0111]

[0112] Step S113, determining the maximum junction temperature of the power device in the current grid cycle according to the steady-state junction temperature, the pulse power, and the power factor of the power device in the current grid cycle, including the following step S113.1 and step S113.2.

[0113] Step S113.1, determining the transient thermal impedance corresponding to the pulse power according to the pulse power and the transient thermal impedance data table.

[0114] Exemplarily, the pulse width can be obtained according to the pulse power, and the transient thermal impedance corresponding to the pulse power can be found from the transient thermal impedance data table according to the pulse width.

[0115] Step S113.2, determining the maximum junction temperature of the power device in the current grid cycle according to the steady-state junction temperature, the transient thermal impedance, the pulse power, and the power factor.

[0116] ​It can be understood that the maximum junction temperature of the power device is fluctuant and greater than the steady-state junction temperature of the power device. Considering the circulating current of the power device, the loss of the power device is mainly related to the power factor in one grid cycle, and therefore, the maximum junction temperature T of the power device in the current grid cycle can be solved by using the following formula (7) j.max :

[0117] T j.max = T j.av + R th.jh_duty × P pulse × cosφ…(7)

[0118] wherein R th.jh_duty represents the steady-state thermal impedance of the power device, and cosφ represents the power factor, for example, 1 / 2.

[0119] The above method of discretely solving the maximum junction temperature of the power device in each grid cycle has higher precision and smaller calculation amount, and therefore, the precision and real-time performance of the de-rating control of the converter are further improved.

[0120] The control method of the converter device of another embodiment of the present application will be described below in combination with Figure 4a and Figure 4b .

[0121] As shown in Figure 4a , the converter device (converter) can realize adaptive dynamic de-rating control by performing the following steps.

[0122] S401, the converter operates according to the current instruction current and the current limit current;

[0123] S402, the maximum junction temperature of each power device in the converter in the current grid cycle is calculated in real time according to the calculation method of the discretized maximum junction temperature.

[0124] S403, it is determined whether the current real-time calculated maximum junction temperature exceeds the junction temperature required for de-rating (limit junction temperature). If yes, go to S404; if no, go to S405;

[0125] S404, it is determined that the converter is in an under-de-rating state (at this time, the junction temperature is in a risk state), and the limit current of the next grid cycle is determined to be equal to k times of the current limit current, wherein k<1; go to S401 to enter the next grid cycle;

[0126] S405, it is determined whether the current limit current is less than the instruction current. If yes, it is determined that the converter is in an over-de-rating state, and the de-rating needs to be released, and the maximum capacity that can be output by the converter is used for power generation, and go to S406; if no, it is determined that the converter is in a non-de-rating state, and go to S407;

[0127] S406, determining that the converter is in the de-rated state, determining that the limit current of the next grid cycle is equal to m times of the current limit current, where m>1; turning to S401 to enter the next grid cycle;

[0128] S407, determining that the converter is in the non-de-rated state, continuing to determine the output current according to the current limit current, and stably running; turning to S401 to enter the next grid cycle.

[0129] As shown in the figure, the calculation method of the discretized maximum junction temperature in S402 includes the following steps: Figure 4b

[0130] S402.1, obtaining the thermal performance parameters, the loss data table of the power device, and the current, the DC bus voltage, the heat sink temperature, the duty cycle and the power factor of the power device in the current grid cycle;

[0131] Specifically, the loss data and the transient thermal resistance data of the device can be updated into the memory in advance according to the data in the specification book of the power device or the data measured by experiment;

[0132] S402.2, fitting the conduction loss of the power device in each switching cycle according to the current, the assumed value of the steady-state junction temperature, the duty cycle and the loss data table of the power device in each switching cycle;

[0133] S402.3, fitting the switching loss of the power device in each switching cycle according to the current, the DC bus voltage, the assumed value of the steady-state junction temperature and the loss data table of the power device in each switching cycle;

[0134] That is, in each control cycle, the conduction loss and the switching loss of the power device in the current control cycle are calculated in real time according to the voltage and current information sampled and fed back in a table lookup manner;

[0135] S402.4, fitting the total loss of the power device in the current grid cycle according to the switching loss and the conduction loss of the power device in each switching cycle;

[0136] That is, in each control cycle, the loss data in the power frequency cycle is discretely and cumulatively calculated according to the current power factor, and the corresponding total loss is calculated;

[0137] S402.5, using the heat balance equation to calculate the estimated value of the steady-state junction temperature according to the total loss, the heat sink temperature and the steady-state thermal resistance;

[0138] S402.6, judging whether the difference between the fitted estimated value and the assumed value is greater than the junction temperature difference threshold value; if yes, turning to S402.7; if no, turning to S402.8;

[0139] ​S402.7, take the estimated value as the hypothesis value, and go to S402.2 to continue iteratively fitting the estimated value of steady-state junction temperature;

[0140] S402.8, the iteration ends, and the estimated value of the fitted steady-state junction temperature is used as the steady-state junction temperature of the power device in the current power grid cycle;

[0141] S402.9, Fit the final total loss of the power device in the current power grid cycle based on the steady-state junction temperature of the power device in the current power grid cycle;

[0142] Specifically, the total loss fitted at the end of the iteration can be used as the final total loss, or the total loss of the power device in the current grid cycle can be refitted according to the methods in S402.2 to S402.4 as the final total loss;

[0143] S402.10, determine the pulse power of the power device in the current power grid cycle based on the final total loss, the total duration of the current power grid cycle, and the duration of loss within the current power grid cycle;

[0144] S402.11, Based on the pulse power and transient thermal impedance data table, determine the transient thermal impedance corresponding to the pulse power;

[0145] S402.12 determines the maximum junction temperature of a power device in the current power grid cycle based on steady-state junction temperature, transient thermal impedance, pulse power, and power factor.

[0146] It should be understood that the above examples are provided to help those skilled in the art understand the embodiments of this application, and are not intended to limit the embodiments of this application to the specific values ​​or scenarios illustrated. Those skilled in the art can obviously make various equivalent modifications or changes based on the above examples, and such modifications or changes also fall within the scope of the embodiments of this application.

[0147] The above text combined Figures 1 to 4b The control method of the converter device according to the embodiments of this application is described in detail below. Figure 5 This application describes the device embodiments in detail. It should be understood that the control device of the converter equipment in the embodiments of this application can execute the control methods of various converter equipment described in the foregoing embodiments of this application. That is, the specific working processes of the various products below can be referred to the corresponding processes in the foregoing method embodiments.

[0148] Figure 5 A schematic diagram of the control device for a converter in some embodiments of this application is shown. For example... Figure 5 As shown, the control device 500 of the converter equipment in this embodiment includes:

[0149] The first determining module 510 is configured to determine a maximum junction temperature of the power device of the power conversion device in a current power grid cycle during operation of the power conversion device, where the maximum junction temperature is a maximum value of the junction temperature of the power device in the current power grid cycle.

[0150] The second determining module 520 is configured to determine a derating state of the power conversion device according to a difference between the maximum junction temperature and a limit junction temperature of the power device, where the derating state is used to indicate whether the power conversion device is derated or not and / or is used to indicate a relationship between an actual derating and an expected derating when the power conversion device is derated.

[0151] The third determining module 530 is configured to determine a limit current of the power conversion device in a next power grid cycle according to the derating state of the power conversion device, where the limit current is a limit value of an output current of the power conversion device.

[0152] The various unit modules of the control device 500 of the power conversion device described above can respectively perform the corresponding steps in the method embodiments described above, and thus the unit modules will not be described in detail here, and the details can be referred to the description of the corresponding steps above.

[0153] It should be noted that the control device 500 of the power conversion device described above is in the form of a functional unit. The term "unit" herein can be implemented in the form of software and / or hardware, and is not specifically limited.

[0154] For example, the "unit" can be a software program, a hardware circuit or a combination of both, which implements the above functions. The hardware circuit can include an application specific integrated circuit (ASIC), an electronic circuit, a processor (such as a shared processor, a dedicated processor or a group processor, etc.) and a memory for executing one or more software or firmware programs, and other suitable components for supporting the described functions.

[0155] Therefore, the units of each example described in the embodiments of the present application can be implemented in electronic hardware or a combination of computer software and electronic hardware. Whether the functions are implemented in hardware or software depends on the specific application and design constraints of the technical solution. A person skilled in the art can use different methods to implement the described functions for each specific application, but such implementation should not be considered beyond the scope of the embodiments of the present application.

[0156] The embodiments of the present application also provide a power conversion device. As shown in Figure 6 The power conversion device 600 provided by the embodiments of the present application includes at least one power device 610 Figure 6a power device 610, and a controller 620 connected to the power device 610 and configured to: determine a maximum junction temperature of the power device 610 in a current grid period during operation of the power conversion device 600, wherein the maximum junction temperature is a maximum value of junction temperatures of the power device 610 in the current grid period; determine a derating state of the power conversion device 600 according to a difference between the maximum junction temperature and a limit junction temperature of the power device 610, wherein the derating state is used to indicate whether the power conversion device 600 is derated or not and / or to indicate a relationship between an actual derating and an expected derating of the power conversion device 600 when the power conversion device 600 is derated; and determine a limit current of the power conversion device 600 in a next grid period according to the derating state of the power device 610, wherein the limit current is a limit value of an output current of the power conversion device 600.

[0157] In an embodiment, the derating state comprises an underrated state indicating that the power conversion device 600 is not derated, and an overderated state indicating that the power conversion device 600 is derated and an actual derating is greater than an expected derating, the controller 620 is configured to determine the derating state of the power conversion device 600 according to the difference between the maximum junction temperature and the limit junction temperature of the power device 610, and determine the limit current of the power conversion device 600 in the next grid period according to the derating state of the power device 610, wherein the controller 620 is configured to determine that the power conversion device 600 is in the underrated state or the overderated state according to a current difference between a current limit current and a current received command current in a case that the maximum junction temperature of the power device 610 is less than or equal to the limit junction temperature of the power device 610, and determine that the limit current of the power conversion device 600 in the next grid period is greater than or equal to the current limit current in a case that the power conversion device 600 is in the underrated state or the overderated state.

[0158] In an embodiment, the controller 620 is configured to determine that the power conversion device 600 is in the underrated state or the overderated state according to the current difference between the current limit current and the current received command current, and determine that the limit current of the power conversion device 600 in the next grid period is greater than or equal to the current limit current in a case that the power conversion device 600 is in the underrated state or the overderated state, wherein the controller 620 is configured to determine that the limit current of the power conversion device 600 in the next grid period is greater than the current limit current in a case that the power conversion device 600 is in the overderated state, and / or determine that the limit current of the power conversion device 600 in the next grid period is equal to the current limit current in a case that the power conversion device 600 is in the underrated state.

[0159] In an embodiment, the de-rating state includes an under-de-rating state indicating that the current converter 600 is de-rated but the actual de-rating is less than the expected de-rating, the controller 620 determines the de-rating state of the current converter 600 according to the difference between the maximum junction temperature and the limit junction temperature of the power device 610, and is configured to determine that the current converter 600 is in the under-de-rating state if the maximum junction temperature of the power device 610 is greater than the limit junction temperature of the power device 610; the controller 620 determines the limit current of the current converter 600 in the next grid cycle according to the de-rating state of the power device 610, and is configured to determine that the limit current of the current converter 600 in the next grid cycle is less than the current limit current if the current converter 600 is in the under-de-rating state.

[0160] In an embodiment, the controller 620 is further configured to obtain an actual operating parameter of the power device 610 in the current grid cycle; determine a first historical operating condition corresponding to the current operating condition according to the actual operating parameter and historical operating parameters of the power device 610 in a plurality of historical operating conditions, wherein a parameter difference between the historical operating parameter of the first historical operating condition and the actual operating parameter is less than a parameter difference between a historical operating parameter of a second historical operating condition and the actual operating parameter, the second historical operating condition being other than the first historical operating condition among the plurality of historical operating conditions; and determine the limit junction temperature of the power device 610 in the current grid cycle according to the stored maximum junction temperature of the power device 610 in the first historical operating condition.

[0161] In an embodiment, the controller 620 determines the first historical operating condition corresponding to the current operating condition according to the actual operating parameter and the historical operating parameters of the power device 610 in the plurality of historical operating conditions, and is configured to select two historical operating conditions from the plurality of historical operating conditions as two first historical operating conditions corresponding to the current operating condition if the parameter differences between the actual operating parameter and the historical operating parameters of the plurality of historical operating conditions are all greater than a parameter difference threshold; and the controller 620 determines the limit junction temperature of the power device 610 in the current grid cycle according to the stored maximum junction temperature of the power device 610 in the first historical operating condition, and is configured to interpolate and fit the limit junction temperature of the power device 610 in the current grid cycle according to the stored maximum junction temperatures of the two first historical operating conditions.

[0162] In one embodiment, the controller 620 is configured to determine the maximum junction temperature of the power device 610 in the current grid period during the operation of the power conversion device 600, and is configured to: obtain the thermal performance parameters of the power device 610, the loss data table, and the actual operation parameters of the power device 610 in the current grid period; determine the steady-state junction temperature and the pulse power of the power device 610 in the current grid period according to the actual operation parameters, the thermal performance parameters, and the loss data table; and determine the maximum junction temperature of the power device 610 in the current grid period according to the steady-state junction temperature, the pulse power, and the power factor of the power device 610 in the current grid period.

[0163] In one embodiment, the thermal performance parameters include the steady-state thermal impedance and the transient thermal impedance data table of the power device 610, the actual operation parameters include the current, the DC bus voltage, the heat sink temperature, the duty cycle, and the power factor of the power device 610 in each switching period in the current grid period, and the controller 620 is configured to determine the steady-state junction temperature and the pulse power of the power device 610 in the current grid period according to the actual operation parameters, the thermal performance parameters, and the loss data table, and is configured to: fit the conduction loss of the power device 610 in each switching period according to the current, the assumed value of the steady-state junction temperature, the duty cycle, and the loss data table of the power device 610 in each switching period; fit the switching loss of the power device 610 in each switching period according to the current, the DC bus voltage, the assumed value of the steady-state junction temperature, and the loss data table of the power device 610 in each switching period; fit the total loss of the power device 610 in the current grid period according to the switching loss and the conduction loss of the power device 610 in each switching period and the power factor; calculate the estimated value of the steady-state junction temperature by using a thermal balance equation according to the total loss, the heat sink temperature, and the steady-state thermal impedance; in the case where the difference between the estimated value and the assumed value is greater than the junction temperature difference threshold, take the estimated value as the assumed value, continue to iteratively fit the estimated value of the steady-state junction temperature until the difference between the estimated value and the assumed value is less than or equal to the junction temperature difference threshold, and end the iteration; and determine the steady-state junction temperature of the power device 610 in the current grid period according to the estimated value of the steady-state junction temperature fitted at the end of the iteration.

[0164] In one embodiment, the controller 620 determines the steady-state junction temperature and pulse power of the power device 610 in the current grid cycle based on actual operating parameters, thermal performance parameters, and a loss data table. It is further configured to: fit the final total loss of the power device 610 in the current grid cycle based on the steady-state junction temperature of the power device 610 in the current grid cycle; and determine the pulse power of the power device 610 in the current grid cycle based on the final total loss, the total duration of the current grid cycle, and the duration of losses within the current grid cycle. The controller 620 determines the maximum junction temperature of the power device 610 in the current grid cycle based on the steady-state junction temperature, pulse power, and power factor. It is configured to: determine the transient thermal impedance corresponding to the pulse power based on a pulse power and transient thermal impedance data table; and determine the maximum junction temperature of the power device 610 in the current grid cycle based on the steady-state junction temperature, transient thermal impedance, pulse power, and power factor.

[0165] Figure 6 This is merely an example of a converter device and does not constitute a limitation on converter devices. Converter devices may include more or fewer components than shown in the figure, or combine certain components, or use different components.

[0166] like Figure 7 As shown, the controller 620 may include at least one processor 621. Figure 7 (Only one processor is shown in the diagram). The converter device 600 may also include a memory 630 and a computer program 640 stored in the memory 630 and executable on at least one processor 621. When the processor 621 executes the computer program 640, it implements the steps of the control method of the converter device described above.

[0167] The processor 621 may be a Central Processing Unit (CPU), or it may be other general-purpose processors, digital signal processors (DSPs), application-specific integrated circuits (ASICs), field-programmable gate arrays (FPGAs), or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, etc. A general-purpose processor may be a microprocessor or any conventional processor.

[0168] The memory 630 can be an internal storage unit of the power conversion device 600, such as a hard disk or a memory of the power conversion device 600 in some embodiments. The memory 630 can also be an external storage device of the power conversion device 600, such as a plug-in hard disk, a smart media card (SMC), a secure digital (SD) card, a flash card, and the like in other embodiments. Further, the memory 630 can include both an internal storage unit and an external storage device of the power conversion device 600. The memory 630 can be used to store thermal performance parameters of power devices, loss data tables, and the like for calling by the processor, and to store operating systems, application programs, boot loaders, data, and other programs, such as program codes of computer programs, and the like. The memory 630 can also be used to temporarily store data that has been output or is to be output.

[0169] The application further provides a computer program product, which, when executed by the processor 621, implements the control method of the power conversion device of any method embodiment of the application.

[0170] The computer program product can be stored in the memory, for example, a program, which is finally converted into an executable object file capable of being executed by the processor 621 through a processing process such as preprocessing, compiling, assembling, and linking.

[0171] The application further provides a computer readable storage medium, which stores a computer program, which, when executed by a computer, implements the control method of the power conversion device of any method embodiment of the application. The computer program can be a high-level language program or an executable object program.

[0172] The computer readable storage medium is, for example, a memory. The memory can be a volatile memory or a non-volatile memory, or the memory can include both volatile and non-volatile memory. Among them, the non-volatile memory can be a read-only memory (ROM), a programmable read-only memory (PROM), an erasable programmable read-only memory (EPROM), an electrically EPROM (EEPROM), or a flash memory. The volatile memory can be a random access memory (RAM) used as an external cache. By way of example, but not limitation, many forms of RAM are available, such as static RAM (SRAM), dynamic RAM (DRAM), synchronous DRAM (SDRAM), double data rate SDRAM (DDR SDRAM), enhanced SDRAM (ESDRAM), synchlink DRAM (SLDRAM), and direct Rambus RAM (DRRAM).

[0173] In this application, "at least one" means one or more, and "multiple" means two or more. "At least one of the following" or the like means any combination of these items, including a single item or a combination of multiple items. For example, at least one of a, b, or c can mean a, b, c, a-b, a-c, b-c, or a-b-c, where a, b, and c can be single or multiple.

[0174] It should be understood that in various embodiments of the present application, the size of the sequence number of the above-mentioned processes does not mean the order of execution, and the execution order of the processes should be determined according to its function and inherent logic, and should not constitute any limitation on the implementation process of the embodiments of the present application.

[0175] Those skilled in the art can clearly understand that the units and algorithm steps of each example described in combination with the embodiments disclosed herein can be realized by electronic hardware or a combination of computer software and electronic hardware. Whether the functions are performed in hardware or software depends on the specific application and design constraints of the technical solution. Those skilled in the art can use different methods to implement the described functions for each specific application, but such implementation should not be considered beyond the scope of the present application.

[0176] Those skilled in the art can clearly understand that, for the convenience and brevity of the description, the specific working processes of the above-described system, device and unit can refer to the corresponding processes in the foregoing method embodiments, which will not be repeated here.

[0177] In several embodiments provided in the present application, it should be understood that the disclosed devices and methods can be implemented in other ways. For example, the device embodiments described above are only schematic; for example, the division of units is only a logical function division, and actual implementation can have another division manner; for example, a plurality of units or components can be combined or integrated into another system, or some features can be omitted or not executed. In addition, the coupling or direct coupling or communication connection between the displayed or discussed units can be indirect coupling or communication connection through some interface, device or unit, which can be electrical, mechanical or other forms.

[0178] The units described as separate components can or can not be physically separated, and the components shown as units can or can not be physical units, i.e. they can be located in one place or distributed on a plurality of network units. Part or all of the units can be selected according to actual needs to achieve the purpose of the embodiment.

[0179] In addition, the functional units in each embodiment of the present application can be integrated in one processing unit, or each unit can be physically present separately, or two or more units can be integrated in one unit.

[0180] The above is only a specific implementation of the present application, but the protection scope of the present application is not limited thereto, and any person skilled in the art can easily think of changes or replacements within the technical scope disclosed in the present application, which should be covered within the protection scope of the present application. Therefore, the protection scope of the present application should be subject to the protection scope of the claims.

Claims

1. A power conversion device, characterized by, The method comprises: determining a maximum junction temperature of the power device in a current grid cycle during operation of the power conversion device, wherein the maximum junction temperature is a maximum value of junction temperatures of the power device in the current grid cycle; determining a derating state of the power conversion device according to a difference between the maximum junction temperature and a limit junction temperature of the power device, wherein the derating state is used to indicate whether the power conversion device is derated and / or to indicate a relationship between an actual derating and an expected derating of the power conversion device when the power conversion device is derated; determining a limit current of the power conversion device in a next grid cycle according to the derating state of the power conversion device, wherein the limit current is a limit value of an output current of the power conversion device; wherein the derating state comprises a non-derated state indicating that the power conversion device is not derated, an over-derated state indicating that the power conversion device is derated and an actual derating is greater than an expected derating, and the controller, when determining the derating state of the power conversion device according to a difference between the maximum junction temperature and a limit junction temperature of the power device, is configured to: determine that the power conversion device is in the non-derated state or the over-derated state according to a current difference between a current limit current and a current received command current, when the maximum junction temperature of the power device is less than the limit junction temperature of the power device; determine the limit current of the power conversion device in the next grid cycle to be greater than or equal to the current limit current, when the power conversion device is in the non-derated state or the over-derated state. The controller, when determining the derating state of the power conversion device according to a difference between the maximum junction temperature and a limit junction temperature of the power device, is configured to: determine that the power conversion device is in the over-derated state, when the current difference is less than a current difference threshold; and / or determine that the power conversion device is in the non-derated state, when the current difference is greater than or equal to the current difference threshold.

2. The current conversion device according to claim 1, characterized in that The controller, when determining the limit current of the power conversion device in the next grid cycle according to the derating state of the power conversion device, is configured to: determine the limit current of the power conversion device in the next grid cycle to be greater than the current limit current, when the power conversion device is in the over-derated state; and / or determine the limit current of the power conversion device in the next grid cycle to be equal to the current limit current, when the power conversion device is in the non-derated state. The derating state comprises an under-derated state indicating that the power conversion device is derated and an actual derating is less than an expected derating, and the controller, when determining the derating state of the power conversion device according to a difference between the maximum junction temperature and a limit junction temperature of the power device, is configured to: determine that the power conversion device is in the under-derated state, when the maximum junction temperature of the power device is greater than or equal to the limit junction temperature of the power device. ​ ​ 3. The current conversion device of claim 1, wherein, ​ ​ The controller is configured to determine the limiting current of the power conversion device in the next grid cycle according to the derating state of the power conversion device. In a case where the power conversion device is in an underderating state, the controller is configured to determine that the limiting current of the power conversion device in the next grid cycle is less than the current limiting current.

4. The current transforming device according to any of claims 1-3, characterized in that, The controller is further configured to: obtain actual operating parameters of the power device in the current grid cycle; determine a first historical working condition corresponding to the current working condition according to the actual operating parameters and historical operating parameters of the power device in a plurality of historical working conditions, wherein a parameter difference between the historical operating parameters of the first historical working condition and the actual operating parameters is less than a parameter difference between historical operating parameters of a second historical working condition and the actual operating parameters, the second historical working condition being a historical working condition other than the first historical working condition among the plurality of historical working conditions; determine the limiting junction temperature of the power device in the current grid cycle according to the maximum junction temperature of the power device in the first historical working condition which has been stored.

5. The current conversion device according to claim 4, characterized in that The controller is configured to determine a first historical working condition corresponding to the current working condition according to the actual operating parameters and historical operating parameters of the power device in a plurality of historical working conditions, wherein: in a case where parameter differences between the actual operating parameters and the historical operating parameters in the plurality of historical working conditions are all greater than a parameter difference threshold, two historical working conditions are selected from the plurality of historical working conditions as two first historical working conditions corresponding to the current working condition; the controller is configured to determine the limiting junction temperature of the power device in the current grid cycle according to the maximum junction temperatures of the two first historical working conditions which have been stored. The controller is configured to determine the maximum junction temperature of the power device in the current grid cycle during operation of the power conversion device, wherein:

6. The power conversion device according to any one of claims 1 to 3, characterized by obtaining a thermal performance parameter of the power device, a loss data table and actual operating parameters of the power device in the current grid cycle; determining a steady-state junction temperature and a pulse power of the power device in the current grid cycle according to the actual operating parameters, the thermal performance parameter and the loss data table; determining the maximum junction temperature of the power device in the current grid cycle according to the steady-state junction temperature, the pulse power and a power factor of the power device in the current grid cycle. The thermal performance parameter includes a steady-state thermal impedance, a transient thermal impedance data table of the power device, the actual operating parameters include a current, a DC bus voltage, a heat sink temperature, a duty cycle and a power factor of the power device in each switching cycle in the current grid cycle, and the controller is configured to determine the steady-state junction temperature and the pulse power of the power device in the current grid cycle according to the actual operating parameters, the thermal performance parameter and the loss data table, wherein:

7. The current conversion device according to claim 6, characterized in that the on-state loss of the power device in each switching cycle is fitted according to the current, an assumed value of the steady-state junction temperature, the duty cycle and the loss data table of the power device in each switching cycle. ​ fitting, according to the current, the DC bus voltage, the assumed value of the steady-state junction temperature and the loss data table of the power device in each switching cycle, a switching loss of the power device in each switching cycle; fitting, according to the switching loss and the conduction loss of the power device in each switching cycle, a total loss of the power device in the current grid cycle; calculating, according to the total loss, the temperature of the heat sink and the steady-state thermal impedance, an estimated value of the steady-state junction temperature by using a thermal balance equation; in a case where a difference between the estimated value and the assumed value is greater than a junction temperature difference threshold, taking the estimated value as the assumed value and continuing to iteratively fit the estimated value of the steady-state junction temperature until the difference between the estimated value and the assumed value is less than or equal to the junction temperature difference threshold, and ending the iteration; determining, according to the estimated value of the steady-state junction temperature fitted at the end of the iteration, the steady-state junction temperature of the power device in the current grid cycle.

8. The current conversion device according to claim 7, characterized in that The controller, according to the actual operating parameters, the thermal performance parameters and the loss data table, determines the steady-state junction temperature and the pulse power of the power device in the current grid cycle, and is further configured to: fit, according to the steady-state junction temperature of the power device in the current grid cycle, a final total loss of the power device in the current grid cycle; determine, according to the final total loss, a total duration of the current grid cycle and a loss duration within the current grid cycle, the pulse power of the power device in the current grid cycle; The controller, according to the steady-state junction temperature of the power device in the current grid cycle, the pulse power and the power factor, determines the maximum junction temperature of the power device in the current grid cycle, and is configured to: determine, according to the pulse power and the transient thermal impedance data table, a transient thermal impedance corresponding to the pulse power; determine, according to the steady-state junction temperature, the transient thermal impedance, the pulse power and the power factor, the maximum junction temperature of the power device in the current grid cycle.

9. A control method of a power conversion device, characterized by, comprises: determining, during operation of the power conversion device, a maximum junction temperature of a power device of the power conversion device within a current grid cycle, wherein the maximum junction temperature is a maximum value of junction temperatures of the power device within the current grid cycle; determining, according to a difference between the maximum junction temperature and a limit junction temperature of the power device, a derating state of the power conversion device, wherein the derating state is used to indicate whether the power conversion device is derated and / or to indicate a relationship between an actual derating and an expected derating of the power conversion device when the power conversion device is derated; determining, according to the derating state of the power conversion device, a limit current of the power conversion device in a next grid cycle, wherein the limit current is a limit value of an output current of the power conversion device; wherein the derating state comprises an underated state indicating that the power conversion device has not been derated, and an overderated state indicating that the power conversion device is derated and an actual derating is greater than an expected derating, and the determining, according to the difference between the maximum junction temperature and the limit junction temperature of the power device, the derating state of the power conversion device comprises: In a case that the maximum junction temperature of the power device is less than the limit junction temperature of the power device, determining that the current transformer device is in a non-de-rating state or an over-de-rating state according to a current difference between a current limit and a current instruction currently received; The determining the limit current of the current transformer device in the next grid cycle according to the de-rating state of the current transformer device comprises: In a case that the current transformer device is in the non-de-rating state or the over-de-rating state, determining that the limit current of the current transformer device in the next grid cycle is greater than or equal to the current limit.

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