Power converter

Abstract

This application provides a power converter, including a controller and three power conversion modules. The controller controls the switching actions of the transistors in the three power conversion modules to achieve power conversion between DC and three-phase AC. The controller is configured to, when the absolute value of the difference between the effective voltage values ​​of two AC phases within a preset period exceeds a preset threshold, reduce the output current of the power conversion module corresponding to the AC phase with the lower effective voltage value within the preset period if the temperature exceeds its corresponding second temperature threshold. The second temperature threshold is less than a first temperature threshold. This allows for a safer control strategy to reduce the output current when three-phase asymmetry occurs in the power grid, ensuring device safety and enabling stable power generation by the power converter.

Description

Technical Field

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

[0002] Grid-connected power converters, such as grid-connected inverters, adjust their power conversion based on grid voltage, current, frequency, and power demand during normal grid operation to meet grid quality requirements. However, when grid faults occur, or when power failures occur in the lines between the power converter and the grid, continuing to adjust the converter's operation according to the original feedback regulation mode may lead to its own failure. For example, when three-phase asymmetry occurs in the grid (i.e., the three-phase AC voltage is unbalanced), continuing to adjust the power converter according to the original feedback regulation may cause a rapid increase in power device losses and temperatures, rendering traditional over-temperature protection mechanisms ineffective. Therefore, it is urgent to design a power converter capable of handling three-phase asymmetry to expand its application scenarios, enhance its stability, extend its lifespan, and increase its overall power generation throughout its lifecycle. Summary of the Invention

[0003] The power converter provided in this application can accurately identify three-phase asymmetrical operating conditions and effectively and safely respond to them.

[0004] In a first aspect, this application provides a power converter, including a controller and three power conversion modules; the controller is used to control the switching transistors in the three power conversion modules to perform switching operations using discontinuous pulse width modulation (DPWM) to achieve power conversion between DC and three-phase AC; when the absolute value of the difference between the effective voltage values ​​of two phases of the three-phase AC within a preset period does not exceed a preset threshold, if the temperature of the power conversion module corresponding to any phase of the three-phase AC exceeds its corresponding first temperature threshold, the output current of that phase is reduced; when the absolute value of the difference between the effective voltage values ​​of two phases of the AC within a preset period exceeds the preset threshold, if the temperature of the power conversion module corresponding to the phase with the lower effective voltage value in the preset period exceeds its corresponding second temperature threshold, the output current of that phase is reduced; wherein, the second temperature threshold is less than the first temperature threshold.

[0005] Under continuous sinusoidal pulse width modulation (SPWM), the switching transistors in the three power conversion modules of the power converter continuously switch on and off during operation. Under DPWM modulation, the switching transistors in the three power conversion modules of the power converter remain on or off for a period of time within an operating cycle. This state of remaining on or off for a period of time is called the clamping state, and this period of time is called the clamping time. Additionally, when the temperature of the three power conversion modules reaches a certain threshold, a derating strategy is triggered, such as reducing the output current, to prevent damage to the power conversion modules due to overheating. Under asymmetrical three-phase power grid conditions, the conduction time of some switches in the power conversion module becomes shorter, resulting in more switching actions and a greater accumulation of heat in a short period. Continuing to use the first temperature threshold as the trigger condition for the derating strategy may be insufficient to handle the large amount of heat buildup in a short time, failing to avoid the overheating risk of the switches in the power conversion module under asymmetrical three-phase power grid conditions. Therefore, it is necessary to change the temperature threshold for triggering the derating strategy when asymmetrical three-phase power grid conditions are identified to improve device safety. Under normal power grid conditions, the three-phase AC power is symmetrical, with identical waveforms, resulting in equal effective voltage values ​​across each phase. By comparing the absolute value of the difference between the effective voltage values ​​of any two phases of the three-phase AC power within a preset period with a preset threshold, the state of three-phase asymmetry in the power grid can be detected in a timely manner. By adopting a lower second temperature threshold, a safer control strategy to reduce the output current can be implemented when faults such as three-phase asymmetry occur in the power grid. The derating strategy can be triggered when the temperature of the power conversion module is lower, providing a safety margin and preventing the power conversion module from overheating due to rapid heat accumulation under three-phase asymmetry conditions. This ensures the safety of the device and allows the power converter to smoothly pass through the period of three-phase asymmetry in the power grid, thereby improving the overall power generation of the power converter throughout its entire life cycle.

[0006] It should be noted that the first and second temperature thresholds can be fixed values ​​set in advance, or values ​​that are adjusted in real time according to the operating conditions of the integrated power converter.

[0007] It should be noted that, similar to the above implementation, there is another possible implementation method in which, when a three-phase asymmetry scenario is detected, the temperature of the currently detected power conversion module is increased, for example, by superimposing a corresponding change, and then compared with a fixed temperature threshold (for example, the temperature threshold set under normal operating conditions). If the temperature threshold is exceeded, the current of that phase is reduced, which can also achieve the same effect as lowering the second temperature threshold.

[0008] In one implementation, the first temperature threshold is a fixed value, and the second temperature threshold is a variable value. That is, in this case, the second temperature threshold needs to be variable, adjusted to a lower value according to specific circumstances (the difference between the effective voltage values). The larger the absolute value of the difference between the effective voltage values ​​of the two-phase AC current within a preset period, the larger the difference between the first temperature threshold and the second temperature threshold.

[0009] The larger the absolute value of the difference between the effective voltage values ​​of the two-phase AC current within a preset period, the more severe the three-phase asymmetry of the power grid, and the more severe the temperature rise of the power conversion module. In this case, a lower second temperature threshold value can better prevent the power conversion module from overheating, ensuring device safety and allowing the power converter to smoothly navigate the three-phase asymmetry period, thus improving the overall power generation throughout the power converter's lifespan. Furthermore, when three-phase asymmetry is not occurring, the power converter's operating conditions are relatively stable. A preset fixed value determined based on empirical data can be used to ensure the safety of the power conversion module. Compared to real-time adjustments, this saves computing power.

[0010] In one implementation, both the first and second temperature thresholds are fixed values. In this case, the first and second temperature thresholds are pre-set thresholds, and the temperature thresholds correspond one-to-one with the two operating conditions of the three-phase power grid (symmetrical or asymmetrical). Therefore, the temperature can be directly adjusted to the corresponding threshold under the corresponding operating condition.

[0011] In one implementation, the two-phase AC current is the AC current with the largest effective voltage value and the AC current with the smallest effective voltage value within the preset period.

[0012] Since three-phase asymmetry in the power grid is first manifested by the difference in the effective voltage values ​​between the phase AC with the largest and smallest effective voltage values, directly comparing the effective voltage values ​​between the two phases avoids invalid comparisons between intermediate values ​​and maximum or minimum values, allowing for a faster determination of whether three-phase asymmetry has occurred in the power grid and saving computational resources.

[0013] In one implementation, the preset period is any positive integer multiple of the shortest time period covering half a cycle of each phase of the three-phase AC power.

[0014] Under normal power grid operating conditions, the three-phase alternating current (AC) is symmetrical, with identical waveforms and equal effective voltage values ​​across all phases. Furthermore, the positive and negative half-cycles of each phase are symmetrically distributed. Therefore, the effective voltage values ​​during the positive or negative half-cycles of any two phases are also equal. However, when the three-phase AC is asymmetrical, significant differences in the effective voltage values ​​during the positive or negative half-cycles can occur between any two phases. Therefore, by directly comparing the effective voltage values ​​during the positive or negative half-cycles of each phase—for example, using the nearest half-cycle of each phase—comparison can be completed in the shortest possible time, enabling faster identification of three-phase asymmetry in the power grid and saving computational resources. Similarly, a complete fundamental frequency period can be defined as an integer multiple of the positive or negative half-cycle, such as twice the positive or negative half-cycle. The effective voltage value of the entire fundamental frequency period can also be used to determine whether three-phase asymmetry has occurred.

[0015] In one implementation, the controller is further configured to, when the absolute value of the difference between the effective voltage values ​​of two phases of the three-phase AC power supply within a preset period exceeds a preset threshold, reduce the output current of the phase corresponding to the power conversion module of the phase with the lower effective voltage value within the preset period if the temperature exceeds a corresponding second temperature threshold. Specifically, the controller is configured to, after the negative sequence voltage component of the three-phase AC power supply is greater than a preset component threshold, reduce the output current of the phase corresponding to the power conversion module of the phase with the lower effective voltage value within the preset period if the absolute value of the difference between the effective voltage values ​​of two phases of the three-phase AC power supply within a preset period exceeds a preset threshold.

[0016] When an asymmetrical operating condition occurs, the negative sequence voltage component often increases. By taking the negative sequence voltage component as a premise that it exceeds a certain threshold, relevant judgments and controls are only performed after it is confirmed that an asymmetrical operating condition may occur. This can prevent the controller from performing unnecessary detections and save computing power.

[0017] Secondly, this application provides another power converter, including a controller and three power conversion modules; the controller is used to: control the switching transistors in the three power conversion modules to perform switching actions using discontinuous pulse width modulation (DPWM) to achieve power conversion between DC and three-phase AC; when the absolute value of the difference in the duration of the clamping state held by the switching transistors in the power conversion modules corresponding to two phases of the three-phase AC does not exceed a preset time threshold, if the temperature of any power conversion module corresponding to any phase of the three-phase AC exceeds its corresponding first temperature threshold, then the output current of that phase is reduced; when the absolute value of the difference in the duration of the clamping state held by the switching transistors in the power conversion modules corresponding to two phases of the three-phase AC exceeds a preset time threshold, if the temperature of the power conversion module whose switching transistors hold the clamping state for a shorter duration within the preset period exceeds its corresponding second temperature threshold, then the output current of that phase is reduced; wherein, the second temperature threshold is less than the first temperature threshold.

[0018] In DPWM modulation, the power conversion module is in a clamped state for a period during both the positive and negative half-cycles. This means the switching transistors in the power conversion module remain either on or off. During this time, the transistors do not perform switching actions, resulting in no switching losses, and the power conversion module does not accumulate heat. Furthermore, in DPWM modulation, the larger the effective voltage value of the three-phase AC power within a half-cycle, the longer the clamping time of the power conversion module within that half-cycle, and the lower the switching losses. Therefore, by determining the effective voltage value of the three-phase AC power through the clamping time of the power conversion module and adjusting the derating strategy accordingly, it is possible to more quickly determine whether three-phase asymmetry has occurred in the power grid and save computing power.

[0019] In one implementation, the first temperature threshold is a fixed value, the second temperature threshold is a variable value, and the greater the absolute value of the difference in the duration of the holding clamp state of the switching transistors in the power conversion modules corresponding to the two phases of AC power within a preset period, the greater the difference between the first temperature threshold and the second temperature threshold.

[0020] In one implementation, the power conversion modules corresponding to the two phases of AC power are the power conversion module whose switch holds the clamp state for the longest time within the preset period and the power conversion module whose switch holds the clamp state for the shortest time.

[0021] Thirdly, this application provides another power converter, including a controller and three power conversion modules; the controller is used to control the switching transistors in the three power conversion modules to perform switching operations using DPWM modulation to realize power conversion between DC and three-phase AC; the controller is further used to reduce the output current of the phase when the absolute value of the difference between the effective voltage value and the reference value of one phase of the three-phase AC within a preset period does not exceed a preset threshold, and the temperature of the power conversion module corresponding to the phase of the AC exceeds its corresponding first temperature threshold; the controller is further used to reduce the output current of the phase when the absolute value of the difference between the effective voltage value and the reference value of one phase of the AC within a preset period exceeds a preset threshold, and the temperature of the power conversion module corresponding to the phase of the AC exceeds its corresponding second temperature threshold; wherein the second temperature threshold is less than the first temperature threshold.

[0022] Under normal grid operating conditions, the three-phase AC power is symmetrical, and the effective voltage value of the three-phase AC power remains basically unchanged. Therefore, by setting a reference value in advance, the absolute value of the difference between the effective voltage value of any phase AC power within a preset period and the reference value can be compared with a preset threshold. This allows for timely detection of three-phase asymmetry in the grid. A lower second temperature threshold is then used as the condition to trigger a derating output strategy that reduces the output current. This enables a safer control strategy to reduce the output current when three-phase asymmetry occurs in the grid, preventing the power conversion module from overheating, ensuring device safety, and allowing the power converter to smoothly navigate the period of three-phase asymmetry in the grid, thereby improving the overall power generation of the power converter throughout its entire life cycle.

[0023] In one implementation, the first temperature threshold is a fixed value, the second temperature threshold is a variable value, and the greater the absolute value of the difference between the effective voltage value of one phase of the alternating current within a preset period and the reference value, the greater the difference between the first temperature threshold and the second temperature threshold.

[0024] The larger the absolute value of the difference between the effective value of the voltage of a phase of a three-phase AC power supply and the reference value, the more severe the three-phase asymmetry of the power grid, and the more severe the temperature rise of the power conversion module will be. At this time, the value of the second temperature threshold is lower, which can better prevent the power conversion module from overheating in advance, ensure the safety of the device, enable the power converter to smoothly pass through the three-phase asymmetry period of the power grid, and improve the overall power generation of the power converter throughout its entire life cycle.

[0025] In one implementation, both the first temperature threshold and the second temperature threshold are fixed values.

[0026] In one implementation, the reference value is the average value of the effective voltage of the three-phase alternating current.

[0027] In some cases, the grid voltage will change evenly and will not cause three-phase asymmetry in the grid. However, it will cause the effective value of the three-phase AC voltage output by the power converter to change. Therefore, using the average value of the three-phase AC voltage as a reference value can effectively reduce misjudgment of three-phase asymmetry conditions.

[0028] Fourthly, this application provides another power converter, wherein the controller is used to: control the switching transistors in the three power conversion modules to perform switching operations using discontinuous pulse width modulation (DPWM) to achieve power conversion between DC and three-phase AC; when the absolute value of the difference between the duration of the clamping state of the switching transistor in the power conversion module corresponding to any phase of the three-phase AC and the time reference value within the preset period does not exceed a preset time threshold, if the temperature of the power conversion module corresponding to any phase of the three-phase AC exceeds its corresponding first temperature threshold, then the output current of that phase is reduced; when the absolute value of the difference between the duration of the clamping state of the switching transistor in the power conversion module corresponding to any phase of the three-phase AC and the time reference value within the preset period exceeds a preset time threshold, if the temperature of the power conversion module corresponding to any phase of the three-phase AC exceeds its corresponding second temperature threshold, then the output current of that phase is reduced; wherein the second temperature threshold is less than the first temperature threshold.

[0029] In one implementation, the first temperature threshold is a fixed value, the second temperature threshold is a variable value, and the greater the absolute value of the difference between the duration of the clamping state of the switching transistor in the power conversion module corresponding to any phase of the three-phase AC power and the time reference value within the preset period, the greater the difference between the first temperature threshold and the second temperature threshold.

[0030] It should be understood that the implementation and beneficial effects of the above four aspects of this application can be referenced from each other. Attached Figure Description

[0031] Figure 1 This is a schematic diagram of an application scenario for a power converter provided in this application;

[0032] Figure 2 This application provides a schematic diagram of a three-phase unbalanced power grid voltage operation.

[0033] Figure 3 This application provides a schematic diagram of a three-phase modulation wave under asymmetrical grid voltage conditions.

[0034] Figure 4This application provides a schematic diagram of a three-phase unbalanced power grid voltage operation.

[0035] Figure 5 This is a schematic diagram of a power converter control flow provided in this application;

[0036] Figure 6 This is a schematic diagram of a power converter control flow provided in this application;

[0037] Figure 7 This is a schematic diagram of a power converter control flow provided in this application;

[0038] Figure 8 This is a schematic diagram of a power converter control process provided in this application. Detailed Implementation

[0039] To make the above-mentioned objectives, features and advantages of this application more apparent and understandable, the application will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0040] The term "an embodiment" or "embodiment" as used herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of this application. The phrase "in one embodiment" appearing in different places throughout this specification does not necessarily refer to the same embodiment, nor is it a single or selective embodiment that excludes other embodiments. Unless otherwise specified, the terms "connected," "linked," and "connected" used herein to indicate electrical connection mean direct or indirect electrical connection.

[0041] In the following description, the terms "first," "second," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined with "first," "second," etc., may explicitly or implicitly include one or more of that feature. In the description of this application, unless otherwise stated, "a plurality of" means two or more.

[0042] With the increase in the grid-connected capacity of new energy sources, there are more and more power conversion devices such as inverters in the power system, and a large number of new energy power plants are transmitting electricity to the large power grid through long-distance transmission lines. Due to the differences in three-phase impedance of transmission equipment and lines or the existence of three-phase unbalanced loads, there is a three-phase voltage imbalance in the grid at distant locations. When the three-phase grid voltage is unbalanced, the safety of electrical equipment needs to be considered.

[0043] The technical solutions provided in this application can be applied to different application scenarios, especially to photovoltaic power generation or energy storage power supply scenarios such as industrial and commercial distributed power stations and large ground power stations.

[0044] like Figure 1The diagram shown illustrates an application scenario of the photovoltaic system provided in this application embodiment. The photovoltaic system provided in this application embodiment includes a photovoltaic string 200, which can be one or more strings. A photovoltaic string is formed by connecting one or more photovoltaic panels in series or parallel. The photovoltaic string 200 is used to convert received solar energy into direct current (DC) electricity under illumination and transmit it to the inverter 100. The inverter 100 is used to convert the DC electricity input from the photovoltaic string 200 into alternating current (AC) electricity and output it to the load. It should be understood that the load can be the power grid, electrical equipment, energy storage devices, etc. The inverter 100 provided in this application embodiment can be connected to electrical equipment, energy storage devices, etc., individually, or connected to the power grid, simultaneously, or connected to the power grid, electrical equipment, and energy storage devices, etc. Figure 1 In the illustrated application scenario of inverter 100, the output terminal of inverter 100 is directly connected to the load and connected to the transformer through AC bus AC Bus1. After being stepped up by the transformer, it is connected to AC bus AC Bus2 and then connected to the main power grid.

[0045] In one embodiment, such as Figure 1 As shown, the inverter circuit 120 in inverter 100 is directly connected to the photovoltaic string 200 via a DC bus, which is a single-stage inverter architecture. The controller 110 in inverter 100 controls the inverter circuit 120 to convert the DC power provided by the photovoltaic string 200 into AC power for output to the back end. In practical applications, inverter 100 can also adopt a two-stage inverter architecture, and the technical solution of this application embodiment does not limit this. In addition, inverter 100 can also be replaced with an energy storage converter, and photovoltaic string 200 can be replaced with an energy storage device to form an energy storage power supply system.

[0046] Photovoltaic power plants typically transmit their electricity to the grid via long-distance transmission. However, this can lead to three-phase voltage asymmetry at the inverter's grid connection port, such as... Figure 2 As shown, the voltage amplitudes of the three phases are not equal. When the three-phase voltages are unbalanced, because the inverter follows the grid voltage for feedback regulation and grid-connected control, the inverter's three-phase modulation wave also exhibits three-phase asymmetry, as shown in the example. Figure 2 The figure shows the modulation waveform of the DPWM modulation method. The clamping time of the three-phase modulation waveform is not equal.

[0047] It should be understood that in DPWM modulation, the three power conversion modules in the inverter will be in a clamped state for a period of time during both the positive and negative half-cycles, which corresponds to... Figure 2The modulation wave shown represents a time interval of ±1, which is the clamping time. During this period, the switching transistors in the power conversion module remain either on or off; they do not perform any switching action and are in a clamped state, thus incurring no switching losses. The power conversion module does not continue to accumulate heat during this time. Under asymmetrical grid voltage conditions, the clamping time of a particular power conversion module may be significantly compressed, leading to a sharp increase in heat accumulation compared to normal operating conditions. If the existing derating protection strategy for the power conversion module is designed based on the heat loss of the three-phase bridge arm switching transistors under symmetrical three-phase voltage conditions, it cannot effectively protect the switching transistors. It should be noted that derating refers to reducing the output current of the power converter under specific operating conditions to reduce the power loss of the power conversion module and prevent damage due to overheating.

[0048] Continue to refer to Figure 1 In one embodiment, the inverter circuit 120 in the inverter 100 includes three power conversion modules (not shown in the figure). The controller 110 controls the switching transistors in the three power conversion modules to perform switching operations using DPWM modulation to achieve power conversion between DC and three-phase AC. That is, the inverter circuit 120 is a three-phase inverter circuit, and the three power conversion modules correspond to three-phase inverter bridge arms. Each phase inverter bridge arm can convert DC into AC through power conversion, and the three-phase output currents ultimately form three-phase AC with a phase difference of 120° and equal amplitude. To prevent the power conversion modules from being damaged due to excessive temperature, a first temperature threshold is preset. When the temperature of any of the three power conversion modules exceeds its corresponding first temperature threshold, the controller 110 reduces the output current of that phase. Furthermore, the controller 110 is also configured to reduce the output current of the phase when the absolute value of the difference between the effective voltage values ​​of two phases of the three-phase AC power in the power grid exceeds a preset threshold, and if the temperature of the power conversion module corresponding to the phase with the lower effective voltage value in the preset period exceeds its corresponding second temperature threshold. The first temperature threshold is greater than the second temperature threshold. For example, refer to the accompanying drawings. Figure 2 and Figure 3 Under the condition of three-phase voltage asymmetry in the power grid, the voltage amplitude of one phase decreases, that is, as... Figure 2 As shown, the voltage amplitude of phase C voltage Usc decreases, and the effective value of phase C voltage decreases during the positive or negative half-cycle. Correspondingly, the clamping time of the phase C modulation wave, that is, as shown... Figure 3The time during which the magnitude of the C-phase modulation wave is equal to 1 or -1 is shortened. In the corresponding power conversion module, the time the switching transistor remains on or off is shortened, increasing switching losses and accelerating heat accumulation. Therefore, by comparing the absolute value of the difference between the effective values ​​of the two-phase voltages within a certain preset period with a preset threshold, it is possible to effectively determine whether a three-phase voltage imbalance has occurred in the power grid. In this case, a lower second temperature threshold is needed to derating the power conversion module in advance and promptly to prevent overheating, thus allowing the power conversion module to safely weather the period of three-phase voltage imbalance in the power grid. In one embodiment, the larger the absolute value of the difference between the effective values ​​of the two-phase AC voltages within the preset period, the larger the difference between the first and second temperature thresholds.

[0049] It is understandable that the larger the absolute value of the difference between the effective voltage values ​​of the two-phase AC current within a preset period, the more severe the three-phase asymmetry of the power grid. The modulation wave corresponding to the term with the smaller effective voltage value remains at 1 or -1 for a shorter period. Consequently, the switching time of the power conversion module becomes shorter, leading to a more severe temperature rise in the power conversion module. Therefore, a functional relationship can be established between the absolute value of the difference between the effective voltage values ​​of the two-phase AC current within the preset period and the difference between the first and second temperature thresholds. The larger the absolute value of the first difference, the larger the second difference; that is, given a fixed first temperature threshold, a smaller second temperature threshold is preferable. By using a lower second temperature threshold, it is possible to better prevent the power conversion module from overheating, ensuring device safety and allowing the power converter to smoothly navigate the three-phase asymmetry period of the power grid, thereby improving the overall power generation throughout the power converter's lifespan. For example, the absolute value of the difference between the effective voltage values ​​of phases A and B in a three-phase alternating current within a preset period is taken as the independent variable X, and the difference between a first temperature threshold and a second temperature threshold is taken as the dependent variable Y, where Y = aX + b, and a and b are empirical coefficients with positive values. When X increases, Y also increases, meaning the second temperature threshold becomes smaller relative to the first temperature threshold. It should be understood that those skilled in the art can design and adjust the empirical coefficients a and b according to specific application conditions. a and b can be fixed coefficients or variable coefficients related to the independent variable. This application embodiment does not impose specific limitations in this regard.

[0050] The aforementioned embodiments can also be implemented in the following way: the controller 110 internally presets a variable temperature threshold. When three-phase balance is achieved, this temperature threshold is higher. For example, if a first temperature threshold is selected, derating will be triggered when the temperature of the power conversion module exceeds the first temperature threshold. When three-phase asymmetry occurs, this temperature threshold is lower. For example, if a second temperature threshold is selected, derating will be triggered when the temperature of the power conversion module exceeds the second temperature threshold. That is, when three-phase asymmetry occurs, the controller 110 will lower the temperature threshold, and the greater the absolute value of the difference between the effective voltage values ​​of the two-phase AC currents within a preset period, the greater the reduction in temperature threshold. The controller 110 internally presets a constant temperature threshold. When three-phase balance is achieved, the controller 110 directly uses the temperature of the power conversion module detected by the temperature sensor. If this temperature exceeds the temperature threshold, derating is triggered. When three-phase asymmetry occurs, the controller 110 uses the temperature of the power conversion module detected by the temperature sensor plus a value as the temperature of the power conversion module. If the added value exceeds the temperature threshold, derating is triggered. Furthermore, the larger the absolute value of the difference between the effective voltage values ​​of two phases of AC power within a preset period, the larger the added value. It should be noted that the first temperature threshold can be a variable threshold determined in real time based on the operating conditions of the power converter, or it can be a fixed value.

[0051] In one embodiment, the first temperature threshold is a fixed value, and the second temperature threshold is a variable value. When the three-phase AC power is in a balanced state, the inverter 100 operates relatively stably, and using a fixed value as the first temperature threshold can save computing power. It should be understood that each power conversion module can share a single first temperature threshold, or each module can set its own first temperature threshold.

[0052] In one embodiment, the first and second temperature thresholds are two pre-set thresholds. The temperature thresholds correspond one-to-one with the two operating conditions of the three-phase power grid, which are either symmetrical or asymmetrical. Therefore, the temperature can be directly adjusted to the corresponding threshold under the corresponding operating condition.

[0053] It should be noted that the two-phase AC power can be any two phases of AC power from phases A, B, and C. The balance of the three-phase AC power can be determined by the difference between the maximum and minimum effective values ​​of the AC power from phases A, B, and C, or by using the maximum value and the intermediate value, or by using the intermediate value and the minimum value. This application does not limit this.

[0054] In one embodiment, the aforementioned two-phase AC power is the AC power with the largest effective voltage value and the AC power with the smallest effective voltage value within a preset period.

[0055] It is understandable that when using the absolute value of the difference between the effective voltage values ​​of two phases of AC within a preset period as the comparison object with a preset threshold to determine whether three-phase asymmetry has occurred, directly comparing the effective voltage values ​​between the phase with the largest effective voltage value and the phase with the smallest effective voltage value can effectively reduce the number of comparisons, enabling a faster determination of whether three-phase asymmetry has occurred in the power grid and saving computing power. In one embodiment, the aforementioned preset period is any positive integer multiple of the shortest time period covering half a cycle of each phase of the three-phase AC.

[0056] Under normal power grid operating conditions, the three-phase AC power is symmetrical, with identical waveforms and equal effective voltage values ​​between each phase. Furthermore, the positive and negative half-cycles of each phase are symmetrically distributed. Therefore, the effective voltage values ​​between any two phases during either the positive or negative half-cycle are also equal. By directly comparing the effective voltage values ​​during the positive or negative half-cycles of each phase, it is possible to more quickly determine if three-phase asymmetry has occurred in the power grid, saving computational effort. For example, refer to... Figure 4 The phases of phases A, B, and C are 120° apart, and there is a misalignment between them. The three closest half-cycles of the three-phase voltages are selected as the comparison objects. That is, the nearest half-cycle of each phase AC is used as the comparison objects. For example, the effective voltage value of the nearest positive half-cycle 1 / 2Ta of phase A, the effective voltage value of the negative half-cycle 1 / 2Tb of phase B, and the effective voltage value of the negative half-cycle 1 / 2Tc of phase C are used as the comparison objects. The effective values ​​of each half-cycle of the three-phase voltage can be obtained in the shortest time to determine whether three-phase asymmetry has occurred in the power grid. It is timely, efficient, and saves computing power. After that, the data of the effective values ​​of each phase half-cycle are refreshed in sequence. The latest data can be used to judge the difference between the absolute value of the difference between any two phases of the effective value of the three-phase voltage and the preset threshold, thereby determining whether three-phase asymmetry has occurred in the power grid. Similarly, a complete fundamental frequency period can be defined as an integer multiple of the positive or negative half-cycle, such as twice the positive or negative half-cycle. The effective voltage value of this entire fundamental frequency period can also be used to determine whether three-phase asymmetry has occurred. For example, three times the positive half-cycle is 1.5 times the fundamental frequency period, and the effective voltage value within this 1.5 times fundamental frequency period can also be used to determine whether three-phase asymmetry has occurred.

[0057] Continue to refer to Figure 3The modulation wave emitted by the controller 110 to the inverter circuit 120 under DPWM modulation mode is such that the magnitude of the modulation wave signal is equal to 1 or -1 for a period of time within each half cycle, which keeps the switching transistors in the three power conversion modules of the inverter 120 in a clamped state. It can be seen that the shorter the time when the magnitude of the modulation wave signal is equal to 1 or -1, the smaller the area enclosed by the modulation signal curve and the 0 axis, that is, the smaller the effective voltage value.

[0058] In one embodiment, the method described in the foregoing embodiments for determining whether the absolute value of the difference between the effective voltage values ​​of two phases of three-phase AC power within a preset period exceeds a preset threshold can be implemented as follows: when the absolute value of the difference between the duration of the holding clamping state of the switching transistors in the power conversion modules corresponding to two phases of three-phase AC power within a preset period exceeds a preset time threshold, it is considered that the absolute value of the difference between the effective voltage values ​​of two phases of three-phase AC power within a preset period exceeds the preset threshold.

[0059] It should be understood that, in the specific implementation of the control of the three power conversion modules, the controller 110 can determine whether three-phase asymmetry has occurred based on the relevant data involved in the aforementioned embodiments, through methods such as linear fitting calculation, table lookup interpolation calculation, and positive correlation function relationship, and then perform corresponding control on the three power conversion modules.

[0060] In one embodiment, the controller 110 only begins to determine whether three-phase asymmetry has occurred and then performs corresponding control after the negative sequence voltage component of the three-phase AC power exceeds a preset component threshold. When asymmetrical operating conditions occur, the negative sequence voltage component often increases. By using the premise that the negative sequence voltage component exceeds a certain threshold, and ensuring that asymmetrical operating conditions are likely before performing relevant judgments and control, unnecessary detection by the controller can be prevented, saving computing power.

[0061] In addition to comparing the effective voltage values ​​of two phases of the three-phase AC power to determine whether the power grid is three-phase unbalanced, one can also select the effective voltage value of one phase of the AC power and compare it with a reference value to determine whether the power grid is three-phase unbalanced.

[0062] In one embodiment, the controller 110 is used to control the switching action of the switching transistors in the three power conversion modules using DPWM modulation to achieve power conversion between DC and three-phase AC. The controller 110 is also used to reduce the output current of any one of the three power conversion modules if the temperature of any one of the power conversion modules exceeds its corresponding first temperature threshold, when the absolute value of the difference between the effective voltage value and the reference value of one phase of the three-phase AC within a preset period does not exceed a preset threshold. The controller 110 is further used to reduce the output current of any one of the three power conversion modules if the absolute value of the difference between the effective voltage value and the reference value of one phase of the three-phase AC within a preset period exceeds a preset threshold, and the temperature of the power conversion module corresponding to that phase exceeds its corresponding second temperature threshold. This embodiment uses a different three-phase asymmetry judgment method than the previous embodiments, and also adopts a derating strategy with a lower second temperature threshold. This can also prevent the power conversion module temperature from becoming too high, ensuring device safety and allowing the power converter to smoothly pass through the three-phase asymmetry period of the power grid, thereby improving the overall power generation of the power converter throughout its entire life cycle.

[0063] In one embodiment, the larger the absolute value of the difference between the effective voltage value of one phase of AC power and the reference value within a preset period, the larger the difference between the first temperature threshold and the second temperature threshold. Similar to the principle of the aforementioned embodiments, the larger the absolute value of the difference between the effective voltage value of a phase of three-phase AC power and the reference value, the more severe the three-phase asymmetry in the power grid, and the more severe the temperature rise of the power conversion module. In this case, by increasing the rate of decrease in the temperature threshold, it is possible to better prevent the power conversion module from overheating in advance, ensuring the safety of the devices and enabling the power converter to smoothly navigate the period of three-phase asymmetry in the power grid, thereby increasing the overall power generation of the power converter throughout its entire lifecycle.

[0064] Similarly, the first temperature threshold can be a fixed value or a variable value.

[0065] In one embodiment, the aforementioned reference value is the average of the effective voltage values ​​of the three-phase AC power. In some cases, the grid voltage may experience uniform changes that do not lead to three-phase asymmetry in the grid, but they can cause changes in the effective voltage values ​​of the three-phase AC power output by the power converter. Therefore, using the average of the effective voltage values ​​of the three-phase AC power as a reference value can effectively reduce misjudgments of three-phase asymmetry conditions.

[0066] In one embodiment, the method of determining whether the three-phase AC power is balanced by the difference between the effective voltage value of one phase of the three-phase AC power and the reference value within a preset period can be implemented as follows: if the difference between the duration of the clamping state of the switching transistor in the power conversion module corresponding to any phase of the three-phase AC power and the time reference value within a preset period is greater than a preset threshold, then it is considered that three-phase asymmetry has occurred.

[0067] In one embodiment, the aforementioned preset period can also be an integer multiple of the half-cycle of one phase of alternating current.

[0068] It should be understood that, in the specific implementation of the control of the three power conversion modules, the controller 110 can determine whether three-phase asymmetry has occurred based on the relevant data involved in the aforementioned embodiments, through methods such as linear fitting calculation, table lookup interpolation calculation, and positive correlation function relationship, and then perform corresponding control on the three power conversion modules.

[0069] In one embodiment, the controller 110 only begins to determine whether three-phase asymmetry has occurred and then performs corresponding control when the negative sequence voltage component of the three-phase alternating current is greater than a preset component threshold.

[0070] The two main control strategies in the aforementioned embodiments are described below in the form of flowcharts.

[0071] refer to Figure 5 Controller 110 executes:

[0072] S101: Whether the absolute value of the difference between the effective voltage values ​​of two phases of the three-phase AC power within a preset period exceeds a preset threshold.

[0073] If yes, execute S102: The temperature of the power conversion module corresponding to the phase with the lower effective voltage value in the preset period of the two-phase AC power exceeds its corresponding second temperature threshold; if no, execute S103: Whether the temperature of the power conversion module corresponding to any phase of the three-phase AC power exceeds its corresponding first temperature threshold.

[0074] If S102 is executed and the result is yes, or if S103 is executed and the result is yes, then S104 is executed: reduce the output current of that phase.

[0075] In another embodiment, reference Figure 6 Controller 110 executes:

[0076] S201: Whether the absolute value of the difference between the effective voltage value and the reference value of one phase of the three-phase AC power within a preset period exceeds a preset threshold.

[0077] If yes, execute S202: whether the temperature of the power conversion module corresponding to one phase of AC power exceeds its corresponding second temperature threshold; if no, execute S203: whether the temperature of the power conversion module corresponding to one phase of AC power exceeds its corresponding first temperature threshold.

[0078] If S202 is executed and the judgment is yes, or if S203 is executed and the judgment is yes, then S204 is executed: reduce the output current of that phase.

[0079] In another embodiment, reference Figure 7 Controller 110 executes:

[0080] S301: Whether the absolute value of the difference between the duration of the clamping state of the switching transistor in the power conversion module corresponding to any phase of the three-phase AC power and the time reference value exceeds the preset time threshold.

[0081] If yes, execute S302: whether the temperature of the power conversion module whose switching transistors in the power conversion modules corresponding to two phases of AC power maintain the clamping state for a shorter period of time within the preset cycle exceeds its corresponding second temperature threshold; if no, execute S303: whether the temperature of the power conversion module corresponding to any phase of AC power in the three-phase AC power exceeds its corresponding first temperature threshold.

[0082] If S302 is executed and the judgment is yes, or if S303 is executed and the judgment is yes, then S304 is executed: reduce the output current of this phase.

[0083] In another embodiment, reference Figure 8 Controller 110 executes:

[0084] S401: Whether the absolute value of the difference between the duration of the clamping state of the switching transistor in the power conversion module corresponding to any phase of the three-phase AC power and the time reference value exceeds the preset time threshold.

[0085] If yes, execute S402: whether the temperature of the power conversion module corresponding to any phase of the AC power exceeds its corresponding second temperature threshold; if no, execute S403: whether the temperature of the power conversion module corresponding to any phase of the three-phase AC power exceeds its corresponding first temperature threshold.

[0086] If S402 is executed and the result is yes, or if S403 is executed and the result is yes, then S404 is executed: reduce the output current of that phase.

[0087] In the aforementioned embodiments, before executing S101, S201, S301, or S401, the controller 110 may first determine whether the negative sequence component of the three-phase AC power is greater than a preset component threshold. Only when the negative sequence component exceeds the negative sequence component threshold will it start executing S101, S201, S301, or S401.

[0088] The specific execution and effects of the above-described control process embodiments can be found in the previous embodiments concerning inverter 100, and will not be repeated here.

[0089] The preferred embodiments disclosed above are merely illustrative of this application. These preferred embodiments do not exhaustively describe all details, nor do they limit the application to the specific implementations described. Clearly, many modifications and variations can be made based on the embodiments of this application. These embodiments are selected and specifically described in this application to better explain the principles and practical applications of this application, thereby enabling those skilled in the art to better understand and utilize this application. This application is limited only by the claims and their full scope and equivalents.

Claims

1. A power converter, characterized in that, Includes a controller and three power conversion modules; The controller is used for: Discontinuous pulse width modulation (DPWM) is used to control the switching action of the switching transistors in the three power conversion modules to achieve power conversion between DC and three-phase AC. When the absolute value of the difference between the effective voltage values ​​of two phases of the three-phase AC power within a preset period does not exceed a preset threshold, if the temperature of the power conversion module corresponding to any phase of the three-phase AC power exceeds its corresponding first temperature threshold, the output current of that phase is reduced. When the absolute value of the difference between the effective voltage values ​​of two phases of the three-phase AC power within a preset period exceeds a preset threshold, if the temperature of the power conversion module corresponding to the phase with the lower effective voltage value within the preset period exceeds its corresponding second temperature threshold, the output current of that phase is reduced. Wherein, the second temperature threshold is less than the first temperature threshold.

2. The power converter according to claim 1, characterized in that, The first temperature threshold is a fixed value, the second temperature threshold is a variable value, and the greater the absolute value of the difference between the effective voltage values ​​of the two phases of alternating current within a preset period, the greater the difference between the first temperature threshold and the second temperature threshold.

3. The power converter according to claim 1, characterized in that, Both the first temperature threshold and the second temperature threshold are fixed values.

4. The power converter according to any one of claims 1-3, characterized in that, The two phases of alternating current are the phase with the largest effective voltage value and the phase with the smallest effective voltage value within the preset period.

5. The power converter according to any one of claims 1-4, characterized in that, The preset period is any positive integer multiple of the shortest time period covering half a cycle of each phase of the three-phase AC power.

6. The power converter according to any one of claims 1-5, characterized in that, When the absolute value of the difference between the effective voltage values ​​of two phases of the three-phase AC power supply within a preset period exceeds a preset threshold, if the temperature of the power conversion module corresponding to the phase with the lower effective voltage value within the preset period exceeds its corresponding second temperature threshold, the output current of that phase is reduced, specifically: When the negative sequence voltage component of the three-phase AC power exceeds a preset component threshold, if the absolute value of the difference between the effective voltage values ​​of two phases of the three-phase AC power within a preset period exceeds a preset threshold, and the temperature of the power conversion module corresponding to the phase with the lower effective voltage value within the preset period exceeds its corresponding second temperature threshold, the output current of that phase is reduced.

7. A power converter, characterized in that, Includes a controller and three power conversion modules; The controller is used for: Discontinuous pulse width modulation (DPWM) is used to control the switching action of the switching transistors in the three power conversion modules to achieve power conversion between DC and three-phase AC. When the absolute value of the difference in the duration of the clamping state of the switching transistors in the power conversion modules corresponding to two of the three-phase AC power does not exceed a preset time threshold, if the temperature of the power conversion module corresponding to any one of the three-phase AC power exceeds its corresponding first temperature threshold, the output current of that phase is reduced. When the absolute value of the difference between the durations of the switching transistors in the power conversion modules corresponding to two phases of the three-phase AC power supply in the clamping state within a preset period exceeds a preset time threshold, if the temperature of the power conversion module whose switching transistors in the power conversion modules corresponding to the two phases of the AC power supply have a shorter duration of clamping state within the preset period exceeds its corresponding second temperature threshold, then the output current of that phase is reduced. Wherein, the second temperature threshold is less than the first temperature threshold.

8. The power converter according to claim 7, characterized in that, The first temperature threshold is a fixed value, the second temperature threshold is a variable value, and the greater the absolute value of the difference in the duration of the holding clamp state of the switching transistors in the power conversion modules corresponding to the two phases of AC power within a preset period, the greater the difference between the first temperature threshold and the second temperature threshold.

9. The power converter according to claim 7 or 8, characterized in that, The power conversion modules corresponding to the two-phase AC power are the power conversion modules with the longest duration of the switch holding the clamp state and the power conversion modules with the shortest duration of the switch holding the clamp state within the preset period.

10. A power converter, characterized in that, Includes a controller and three power conversion modules; The controller is used for: The switching action of the switching transistors in the three power conversion modules is controlled by DPWM modulation to realize the power conversion between DC and three-phase AC. When the absolute value of the difference between the effective voltage value and the reference value of one phase of the three-phase AC power within a preset period does not exceed a preset threshold, if the temperature of the power conversion module corresponding to the one phase of AC power exceeds its corresponding first temperature threshold, the output current of that phase is reduced. When the absolute value of the difference between the effective voltage value and the reference value of one phase of the three-phase AC power within a preset period exceeds a preset threshold, if the temperature of the power conversion module corresponding to the one phase of AC power exceeds its corresponding second temperature threshold, the output current of that phase is reduced. Wherein, the second temperature threshold is less than the first temperature threshold.

11. The power converter according to claim 10, characterized in that, The first temperature threshold is a fixed value, the second temperature threshold is a variable value, and the greater the absolute value of the difference between the effective voltage value of one phase of the alternating current within a preset period and the reference value, the greater the difference between the first temperature threshold and the second temperature threshold.

12. The power converter according to claim 10, characterized in that, Both the first temperature threshold and the second temperature threshold are fixed values.

13. The power converter according to any one of claims 10-12, characterized in that, The reference value is the average value of the effective voltage of the three-phase AC power.

14. A power converter, characterized in that, Includes a controller and three power conversion modules; The controller is used for: Discontinuous pulse width modulation (DPWM) is used to control the switching action of the switching transistors in the three power conversion modules to achieve power conversion between DC and three-phase AC. When the absolute value of the difference between the duration of the clamping state of the switching transistor in the power conversion module corresponding to any phase of the three-phase AC power and the time reference value within the preset period does not exceed the preset time threshold, if the temperature of the power conversion module corresponding to any phase of the three-phase AC power exceeds its corresponding first temperature threshold, the output current of that phase is reduced. When the absolute value of the difference between the duration of the clamping state of the switching transistor in the power conversion module corresponding to any phase of the three-phase AC power and the time reference value exceeds the preset time threshold, if the temperature of the power conversion module corresponding to any phase of AC power exceeds its corresponding second temperature threshold, the output current of that phase is reduced. Wherein, the second temperature threshold is less than the first temperature threshold.

15. The power converter according to claim 14, characterized in that, The first temperature threshold is a fixed value, the second temperature threshold is a variable value, and the greater the absolute value of the difference between the duration of the clamping state of the switching transistor in the power conversion module corresponding to any phase of the three-phase AC power and the time reference value within the preset period, the greater the difference between the first temperature threshold and the second temperature threshold.

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