Inverter, control method thereof, and power supply system
By detecting the temperature of the midpoint clamping diode and adjusting the conduction time of the switching transistor, the problem of overheating of the inverter's midpoint clamping diode was solved, achieving safe operation and cost optimization during low-voltage ride-through.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- HUAWEI DIGITAL POWER TECH CO LTD
- Filing Date
- 2022-08-10
- Publication Date
- 2026-07-10
AI Technical Summary
During low voltage ride-through, the inverter's midpoint clamping diode may overheat and damage the device. Existing technologies address this by using larger-sized devices or limiting output capacity, but this leads to increased costs or limited power generation capacity.
By detecting the temperature of the midpoint clamping diode, adjusting the conduction time of the switching transistor, and controlling the current flowing through the midpoint clamping diode, overheating is avoided. A dynamic adjustment strategy is adopted to reduce thermal stress and prevent damage under normal operating conditions.
While ensuring power generation capacity, reduce costs, avoid overheating of the midpoint clamping diode, ensure normal circuit operation, and reduce power loss.
Smart Images
Figure CN115411918B_ABST
Abstract
Description
Technical Field
[0001] This application relates to the field of electronic power technology, and in particular to an inverter and its control method, as well as a power supply system. Background Technology
[0002] During a low voltage ride-through (LVRT), power generation equipment must remain connected to the grid within a certain voltage range. Simultaneously, according to relevant standards, inverters and other power generation equipment must provide a certain amount of reactive power to support the grid during LVRT. In this situation, the increased output current may cause some components in the inverter (such as the midpoint clamping diode) to overheat, leading to damage. Current technical solutions generally use larger-sized components or limit output capacity; however, this increases costs and limits power generation capacity or prevents the provision of reactive power support in the event of a fault. Summary of the Invention
[0003] This application provides an inverter and its control method, as well as a power supply system. It ensures that the thermal stress borne by the two midpoint clamping diodes is within a safe range, preventing overheating and damage to the devices, thereby ensuring normal circuit operation.
[0004] In a first aspect, embodiments of this application provide an inverter, which includes a detection control unit, a first switch, a second switch, a third switch, a fourth switch, and two midpoint clamping diodes. The first, second, third, and fourth switches are connected in series. The two midpoint clamping diodes are connected in series to the series connection points of the first and second switches, and the series connection points of the third and fourth switches, respectively. When the first and fourth switches are off and the second and third switches are on, the two midpoint clamping diodes, the second switch, and the third switch form a current path. In this inverter, the detection control unit is coupled to the two midpoint clamping diodes to detect their temperature. Based on the temperature of the two midpoint clamping diodes, the on-time of the first switch and / or the fourth switch within one switching cycle is adjusted to control the current flowing through the two midpoint clamping diodes. This ensures that the thermal stress on the two midpoint clamping diodes remains within a safe range, preventing overheating and damage to the devices, and ensuring normal circuit operation. Furthermore, since there is no need to select larger components or limit output capacity, costs can be reduced, providing reactive power support while ensuring power generation capacity.
[0005] In another possible design, the detection control unit is also used to control the conduction duration of the first and / or fourth switching transistors within one switching cycle to a first duration when the temperature of the two midpoint clamping diodes exceeds a first preset threshold. The first duration is greater than a second preset threshold. The second preset threshold is the maximum value of the conduction duration of the first and / or fourth switching transistors within one switching cycle under normal operating conditions. Normal operating conditions refer to the operating state when the temperature of the two midpoint clamping diodes in the inverter does not exceed the first preset threshold. By increasing the conduction duration of the first and / or fourth switching transistors within one switching cycle, the first and fourth switching transistors are turned off, and the conduction duration of the second and third switching transistors is 0 within one switching cycle. This prevents current from passing through the two midpoint clamping diodes, thus reducing their temperature and ensuring that the thermal stress borne by the two midpoint clamping diodes remains within a safe range. This avoids overheating of the two midpoint clamping diodes, preventing device damage and ensuring normal circuit operation.
[0006] In another possible design, a detection control unit is used to control the conduction time of the first and fourth switching transistors within one switching cycle to a first duration when the temperature of the two midpoint clamping diodes exceeds a first preset threshold. This first duration is greater than a second preset threshold. The second preset threshold can be the maximum value of the conduction time of the first and / or fourth switching transistors within one switching cycle under normal operating conditions. Normal operating conditions refer to the operating state when the temperature of the two midpoint clamping diodes in the inverter does not exceed the first preset threshold. By increasing the conduction time of the first and / or fourth switching transistors within one switching cycle, the duration of the first and fourth switching transistors being off and the second and third switching transistors being on within one switching cycle is reduced, thereby reducing the current flowing through the two midpoint clamping diodes. This avoids excessively high temperatures due to prolonged current flow through the two midpoint clamping diodes, ensuring that the thermal stress borne by the two midpoint clamping diodes remains within a safe range.
[0007] In another possible design, the detection and control unit is also used to control the conduction duration of the first and / or fourth switching transistors to a second duration within one switching cycle when the temperatures of the two midpoint clamping diodes do not exceed a first preset threshold. This second duration falls within a preset threshold range, which is the time range during which the first and / or fourth switching transistors are in the conducting state within one switching cycle under normal inverter operation. Normal operation refers to the operating state when the temperatures of the two midpoint clamping diodes in the inverter do not exceed the first preset threshold. That is, when the temperatures of the two midpoint clamping diodes do not exceed the first preset threshold, the conduction duration of the first and / or fourth switching transistors is restored to the normal operating time range. This achieves dynamic adjustment of the current passing through the two midpoint clamping diodes based on their temperatures, ensuring that the thermal stress borne by the two midpoint clamping diodes remains within a safe range and guaranteeing the normal operation of the inverter.
[0008] In another possible design, the detection control unit is also used to start detecting the temperature of the two midpoint clamping diodes when the voltage at the inverter grid connection point is detected to be less than a third preset threshold, or the current at the inverter grid connection point is detected to be greater than a fourth preset threshold. When the voltage at the inverter grid connection point is detected to be no less than the third preset threshold and the current at the inverter grid connection point is no greater than the fourth preset threshold, the detection of the temperature of the two midpoint clamping diodes can be stopped. That is, the circuit will not be detected unless a low-voltage ride-through occurs, ensuring circuit operating efficiency and reducing power loss.
[0009] In another possible design, the inverter is a three-level neutral-point clamped inverter.
[0010] Secondly, embodiments of this application provide a control method for an inverter. This method is applicable to the detection and control unit in an inverter. The inverter further includes a first switch, a second switch, a third switch, a fourth switch, and two midpoint clamping diodes. The first, second, third, and fourth switches are connected in series. The two midpoint clamping diodes are connected in series to the series connection points of the first and second switches, and the series connection points of the third and fourth switches, respectively. When the first and fourth switches are turned off, the two midpoint clamping diodes, the second switch, and the third switch form a current path. In this method, the temperature of the two midpoint clamping diodes is detected; based on the temperature of the two midpoint clamping diodes, the conduction duration of the first switch and / or the fourth switch within one switching cycle is adjusted to control the current flowing through the two midpoint clamping diodes. This ensures that the thermal stress borne by the two midpoint clamping diodes is within a safe range, preventing overheating and device damage, and ensuring normal circuit operation. Furthermore, since there is no need to select larger components or limit output capacity, costs can be reduced, and reactive power support can be provided while ensuring power generation capacity.
[0011] In one possible design, when the temperature of the two midpoint clamping diodes exceeds a first preset threshold, the conduction duration of the first and / or fourth switching transistors is controlled to a first duration. This first duration is greater than a second preset threshold. The second preset threshold is the maximum conduction duration of the first and / or fourth switching transistors within one switching cycle under normal operating conditions. Normal operating conditions refer to the operating state when the temperature of the two midpoint clamping diodes in the inverter does not exceed the first preset threshold. By increasing the conduction duration of the first and / or fourth switching transistors within one switching cycle, the first and fourth switching transistors are turned off, and the conduction duration of the second and third switching transistors is zero within one switching cycle. This prevents current from passing through the two midpoint clamping diodes, thus reducing their temperature and ensuring that the thermal stress borne by the two midpoint clamping diodes remains within a safe range. This prevents overheating of the two midpoint clamping diodes from causing device damage and ensures normal circuit operation.
[0012] In another possible design, when the temperature of the two midpoint clamping diodes exceeds a first preset threshold, the conduction time of the first and fourth switching transistors within one switching cycle is controlled to a first duration, where the first duration is greater than a second preset threshold. The second preset threshold is the maximum value of the conduction time of the first and / or fourth switching transistors within one switching cycle under normal operating conditions. Normal operating conditions refer to the operating state when the temperature of the two midpoint clamping diodes in the inverter does not exceed the first preset threshold. By increasing the conduction time of the first and / or fourth switching transistors within one switching cycle, the duration of the first and fourth switching transistors being off and the second and third switching transistors being on within one switching cycle is reduced, thereby reducing the current flowing through the two midpoint clamping diodes. This avoids excessively high temperatures due to prolonged current flow through the two midpoint clamping diodes, ensuring that the thermal stress borne by the two midpoint clamping diodes remains within a safe range.
[0013] In another possible design, when the temperature of the two midpoint clamping diodes does not exceed a first preset threshold, the conduction duration of the first and / or fourth switching transistors within one switching cycle is controlled to a second duration. This second duration falls within a preset threshold range, which is the time range during which the first and / or fourth switching transistors are in the conducting state within one switching cycle under normal operating conditions. Normal operating conditions refer to the operating state when the temperature of the two midpoint clamping diodes in the inverter does not exceed the first preset threshold. That is, when the temperature of the two midpoint clamping diodes does not exceed the first preset threshold, the conduction duration of the first and / or fourth switching transistors is restored to the time range under normal operating conditions. This achieves dynamic adjustment of the current passing through the two midpoint clamping diodes based on their temperature, ensuring that the thermal stress borne by the two midpoint clamping diodes is within a safe range and guaranteeing the normal operation of the inverter.
[0014] In another possible design, during a low-voltage ride-through, the inverter grid-connected point voltage is lower than a third preset threshold, or the inverter grid-connected point current is higher than a fourth preset threshold. The temperature of the two midpoint clamping diodes may only exceed the safe range during a low-voltage ride-through. Temperature monitoring of the two midpoint clamping diodes begins when the inverter grid-connected point voltage is detected to be lower than the third preset threshold, or the inverter grid-connected point current is detected to be higher than the fourth preset threshold. Temperature monitoring of the two midpoint clamping diodes can be stopped when the inverter grid-connected point voltage is not lower than the third preset threshold and the inverter grid-connected point current is not higher than the fourth preset threshold. That is, the circuit is not monitored when a low-voltage ride-through does not occur, ensuring circuit operating efficiency and reducing power loss.
[0015] Thirdly, this application provides a power supply system including a photovoltaic array module and an inverter connected to the photovoltaic array as described in the first aspect and any possible embodiment of the first aspect. The photovoltaic array is used to send the converted electrical energy to the inverter for inversion processing. In this inverter, the temperature of two midpoint clamping diodes is detected by a detection control unit; based on the temperature of the two midpoint clamping diodes, the conduction duration of the first switching transistor and / or the fourth switching transistor within one switching cycle is adjusted to control the current flowing through the two midpoint clamping diodes. This ensures that the thermal stress borne by the two midpoint clamping diodes is within a safe range, preventing overheating of the two midpoint clamping diodes and damage to the devices, and ensuring normal circuit operation. Since there is no need to select larger-sized devices or limit output capacity, costs can be reduced, and reactive power support can be provided while ensuring power generation capacity. Attached Figure Description
[0016] To more clearly illustrate the technical solutions in the embodiments of this application or the background art, the accompanying drawings used in the embodiments of this application or the background art will be described below.
[0017] Figure 1 This is a schematic diagram of an application scenario of the inverter provided in this application;
[0018] Figure 2 This is a schematic diagram of another application scenario of the inverter provided in this application;
[0019] Figure 3 This is a structural schematic diagram of the inverter provided in this application;
[0020] Figure 4 This is a schematic diagram of the detection control unit provided in this application;
[0021] Figure 5 This is a schematic diagram of a pulse width modulation signal in a three-level operating mode provided in an embodiment of this application;
[0022] Figure 6 This is a schematic diagram showing the current flow when the inverter is operating at the "+1" level;
[0023] Figure 7 This is a schematic diagram showing the current flow when the inverter is operating at the "-1" level;
[0024] Figure 8 This is a schematic diagram showing the current flow when the inverter is operating at the "0" level;
[0025] Figure 9 This is a schematic diagram of a pulse width modulation signal in a two-level operating mode provided in an embodiment of this application;
[0026] Figure 10 This is a schematic diagram of another pulse width modulation signal in a three-level operating mode provided in an embodiment of this application;
[0027] Figure 11 This is a structural schematic diagram of the power supply system provided in this application;
[0028] Figure 12 This is a flowchart illustrating a control method for an inverter provided in this application. Detailed Implementation
[0029] The embodiments of this application are described below with reference to the accompanying drawings.
[0030] The inverter provided in this application is applicable to various fields, including new energy smart microgrids, power transmission and distribution, new energy fields (such as photovoltaic grid-connected fields or wind power grid-connected fields), photovoltaic-storage power generation (such as powering household appliances (such as refrigerators and air conditioners) or the power grid), wind-storage power generation, and high-power converter fields (such as converting DC power to high-power high-voltage AC power). The specific application can be determined according to the actual application scenario, and no restrictions are imposed here. The power supply system provided in this application is adaptable to different application scenarios, such as photovoltaic-storage power supply scenarios, wind-storage power supply scenarios, pure energy storage power supply scenarios, or other application scenarios. The following explanation will use the energy storage power supply application scenario as an example, and will not be elaborated further.
[0031] Figure 1 This is a schematic diagram of an application scenario for the inverter provided in this application. In a pure energy storage power supply application scenario, such as... Figure 1 As shown, the power supply system includes a battery pack and an inverter, where the inverter can be a direct current (DC) / alternating current (AC) converter. During the power supply process, the inverter converts the DC power output from the battery pack into AC power for use by AC loads such as communication base stations or household appliances in the AC power grid.
[0032] Figure 2 This is a schematic diagram illustrating another application scenario of the inverter provided in this application. In a photovoltaic system application scenario, the inverter can be a photovoltaic inverter. The output terminal of the photovoltaic array can be connected to the input terminal of the photovoltaic inverter, and the output terminal of the photovoltaic inverter is connected to the AC power grid. The photovoltaic inverter can convert the DC power input from the photovoltaic array into AC power and send it to the AC power grid. Figure 2 In the photovoltaic system shown, the photovoltaic array can be a photovoltaic module group, and a photovoltaic module group can be composed of one or more photovoltaic modules connected in series and parallel. A photovoltaic module string can be composed of one or more photovoltaic modules connected in series. Here, the photovoltaic module can be a solar panel, a photovoltaic panel, or an energy storage battery. In other words, in... Figure 2 In the photovoltaic system shown, a photovoltaic string can be a series of one or more solar panels, photovoltaic panels, or energy storage batteries connected in series. The output current of multiple photovoltaic strings can provide DC input voltage to the photovoltaic inverter. After voltage-power conversion by the photovoltaic inverter, the voltage is used by electrical equipment such as batteries in the AC grid, communication base stations, or household appliances.
[0033] exist Figure 1 and Figure 2 In the application scenario shown, during a low-voltage ride-through, power generation equipment such as inverters need to provide a certain amount of reactive power to support the grid. In this situation, the increased current at the inverter's grid connection point may cause some components in the inverter (such as the midpoint clamping diode) to overheat, resulting in damage. Therefore, during low-voltage ride-through, by monitoring the temperature of the midpoint clamping diode, the modulation method is changed to reduce the current flowing through the midpoint clamping diode. This ensures reactive power support while preventing overheating and electrical damage to the components.
[0034] The following will combine Figures 3 to 10 The inverter, power supply system, and their working principle provided in this application are illustrated with examples. In the embodiments of this application, "and / or" indicates one of them, but it can also indicate all of them. For example, the first switch T1 and / or the fourth switch T4 can represent either the first switch T1 or the second switch T2, or it can represent both the first switch T1 and the second switch T2.
[0035] Figure 3 This is a structural schematic diagram of the inverter provided in this application. Figure 3 As shown, the inverter includes at least one bridge arm 10 and a detection and control unit 20. Bridge arm 10 may include a first switch T1, a second switch T2, a third switch T3, a fourth switch T4, a midpoint clamping diode D5, and a midpoint clamping diode D6. The first switch T1, second switch T2, third switch T3, and fourth switch T4 are connected in series. The midpoint clamping diodes D5 and D6 are connected in series and then connected to the series connection points of the first switch T1 and second switch T2, and the series connection points of the third switch T3 and fourth switch T4, respectively. Bridge arm 10 may also include freewheeling diodes D1, D2, D3, and D4. Specifically, freewheeling diode D1 is connected in series with the first switch T1, freewheeling diode D2 is connected in series with the second switch T2, freewheeling diode D3 is connected in series with the third switch T3, and freewheeling diode D4 is connected in series with the fourth switch T4.
[0036] Figure 4 This is a schematic diagram of the detection control unit 20 provided in this application. Figure 4As shown, the detection control unit 20 may include a temperature detection unit 21 and a controller 22. The temperature detection unit 21 may include a thermistor or a temperature sensor. The temperature detection unit 21 is coupled to midpoint clamping diodes D5 and D6 to detect the temperatures of the midpoint clamping diodes D5 and D6. The controller 22 may be connected to the temperature detection unit 21 and the first switch T1, the second switch T2, the third switch T3, and the fourth switch T4, respectively. Optionally, the controller 22 may be wirelessly connected to the temperature detection unit 21, the first switch T1, the second switch T2, the third switch T3, and the fourth switch T4, respectively. The specific connection can be determined according to the actual application scenario and is not limited here. The controller 22 is used to acquire the temperatures of the midpoint clamping diodes D5 and D6 detected by the temperature detection unit 21, and then control the turn-off or turn-on of the first switch T1, the second switch T2, the third switch T3 or the fourth switch T4 according to the temperatures of the midpoint clamping diodes D5 and D6.
[0037] The first switch T1, the second switch T2, the third switch T3, and the fourth switch T4 mentioned above can be MOSFETs, IGBTs, controllable power switching devices, or diodes made of silicon semiconductor material (Si), or silicon carbide (SiC), or gallium nitride (GaN), or diamond, or zinc oxide (ZnO), or other materials.
[0038] In this embodiment, the inverter is a three-level neutral point clamped (NPC) inverter. Under normal circumstances, the three-level neutral point clamped inverter operates in a three-level operating mode. Figure 5 This is a schematic diagram of a pulse width modulation (PWM) signal in a three-level operating mode provided in an embodiment of this application. The detection and control unit 20 controls the on / off state of the first switch T1, the second switch T2, the third switch T3, and the fourth switch T4 via the PWM signal. During the first half-cycle, the PWM signal level states include "+1" and "0", and during the second half-cycle, the PWM signal level states include "0" and "-1". The duration of the "+1", "0", and "-1" levels can be different or the same. For ease of description, the current direction is defined as follows: when current flows out of the inverter's output terminal, the current direction is positive; when current flows into the inverter's output terminal, the current direction is negative.
[0039] Figure 6This is a schematic diagram showing the current flow when the inverter is operating at the "+1" level. For example... Figure 6 As shown, when the level of the pulse width modulation signal is "+1", the first switch T1 and the second switch T2 are turned on, while the third switch T3 and the fourth switch T4 are turned off. If the current direction is positive, current path 1 is: DC positive terminal DC+, first switch T1, second switch T2, power supply / load. If the current direction is negative, current path 2 is: power supply / load, freewheeling diode D2, freewheeling diode D1, DC positive terminal DC+.
[0040] Figure 7 This is a schematic diagram showing the current flow when the inverter is operating at the "-1" level. For example... Figure 7 As shown, when the level of the pulse width modulation signal is "-1", the third switch T3 and the fourth switch T4 are turned on, while the first switch T1 and the second switch T2 are turned off. If the current direction is negative, the current path 3 is: power supply / load, third switch T3, fourth switch T4, DC negative terminal DC-. If the current direction is positive, the current path 4 is: DC negative terminal DC-, freewheeling diode D4, freewheeling diode D3, power supply / load.
[0041] Figure 8 This is a schematic diagram showing the current flow when the inverter is operating at a "0" level. For example... Figure 8 As shown, when the level state in the pulse width modulation signal is "0", the second switch T2 and the third switch T3 are turned on, while the first switch T1 and the fourth switch T4 are turned off. If the current direction is positive, the current path 5 is: neutral potential point N, midpoint clamping diode D5, second switch T2, power supply / load. If the current direction is negative, the current path 6 is: power supply / load, third switch T3, midpoint clamping diode D6, neutral potential point N.
[0042] from Figures 6 to 8It can be seen that when the first switch T1 and the second switch T2 are on, and the third switch T3 and the fourth switch T4 are off, or when the third switch T3 and the fourth switch T4 are on, and the first switch T1 and the second switch T2 are off, the current does not pass through the midpoint clamping diodes D5 and D6. When the second switch T2 and the third switch T3 are on, and the first switch T1 and the fourth switch T4 are off, the midpoint clamping diode D5 and the second switch T2 form a current path. The current flows in from the input terminal of the inverter, passes through the midpoint clamping diode D5 and the second switch T2, and flows out from the output terminal of the inverter. Alternatively, when the second switch T2 and the third switch T3 are turned on, and the first switch T1 and the fourth switch T4 are turned off, the third switch T3 and the midpoint clamping diode D6 form a current path. The current flows in from the output terminal of the inverter, passes through the third switch T3 and the midpoint clamping diode D6, and flows out from the input terminal of the inverter.
[0043] In summary, when both the first switch T1 and the fourth switch T4 are off, the current can flow through the current path between the neutral point N and the power supply / load, meaning the current can flow through the midpoint clamping diodes D5 and D6. When either the first switch T1 or the fourth switch T4 is on, the current flows through either the DC positive terminal (DC+) or the DC negative terminal (DC-) between the power supply / load, but not through the current path between the neutral point N and the power supply / load, meaning the current does not flow through the midpoint clamping diodes D5 and D6.
[0044] During low-voltage ride-through, the current at the inverter grid connection point is high. If this state persists for a long time, the midpoint clamping diodes D5 and D6 will generate high temperatures, potentially causing them to experience thermal stress exceeding safe limits. Therefore, in this embodiment, the temperature of the midpoint clamping diodes D5 and D6 is detected by the detection control unit 20. Based on the temperature of the midpoint clamping diodes D5 and D6, the conduction duration of the first switch T1 and / or the fourth switch T4 within one switching cycle is adjusted to control the current flowing through the midpoint clamping diodes D5 and D6. This ensures that the thermal stress experienced by the midpoint clamping diodes D5 and / or D6 remains within safe limits, preventing overheating and device damage, and ensuring normal circuit operation. The specific implementation is as follows.
[0045] The switching cycle can be a fixed duration. Within one switching cycle, the pulse width modulation signal can include three level states: "+1", "0", and "-1". That is, within one switching cycle, the following three situations can occur: First switch T1 and second switch T2 are on, and third switch T3 and fourth switch T4 are off. Alternatively, third switch T3 and fourth switch T4 are on, and first switch T1 and second switch T2 are off. Alternatively, second switch T2 and third switch T3 are on, and first switch T1 and fourth switch T4 are off. The duration of the "+1", "0", and "-1" level states within one switching cycle can be different or the same. The on-time can be the duration for which first switch T1 and / or fourth switch T4 are in the on-state within one switching cycle.
[0046] In one possible implementation, the detection control unit 20 is configured to control the conduction duration of the first switch T1 and / or the fourth switch T4 within one switching cycle to a first duration when the temperature of the midpoint clamping diode D5 and / or the midpoint clamping diode D6 exceeds a first preset threshold. The first duration is greater than a second preset threshold. The second preset threshold can be the maximum value of the conduction duration of the first switch T1 and / or the fourth switch T4 within one switching cycle under normal operating conditions. Normal operating conditions refer to the operating state when the temperature of the midpoint clamping diode D5 and / or the midpoint clamping diode D6 in the inverter does not exceed the first preset threshold. By increasing the conduction duration of the first switch T1 and / or the fourth switch T4 within one switching cycle, the current flows entirely through current path 1, current path 2, current path 3, or current path 4, but not through current path 5 or current path 6, thus ensuring that the current does not pass through the midpoint clamping diode D5 and / or the midpoint clamping diode D6.
[0047] For example, Figure 9 This is a schematic diagram of a pulse width modulation (PWM) signal in a two-level operating mode provided in an embodiment of this application. When the midpoint clamping diode D5 and / or the midpoint clamping diode D6 exceeds a first preset threshold, the duration of the "+1" or "-1" level state in the PWM signal is increased within one switching cycle, so that the duration of the "0" level state in the PWM signal is 0. Figure 9As shown, within switching cycle 1, the pulse width modulation signal level only includes "+1" and "-1" levels, and within switching cycle 2, the pulse width modulation signal level also only includes "+1" and "-1" levels. The duration of the "0" level is 0 in both switching cycles 1 and 2. That is, within one switching cycle, only the first switch T1 and the second switch T2 will be on, and the third switch T3 and the fourth switch T4 will be off, and / or the third switch T3 and the fourth switch T4 will be on, and the first switch T1 and the second switch T2 will be off; the second switch T2 and the third switch T3 will not be on, and the first switch T1 and the fourth switch T4 will not be off. Thus, the current does not pass through the midpoint clamping diode D5 and / or the midpoint clamping diode D6.
[0048] By modulating the three-level operating mode to a two-level operating mode, the first switch T1 and the fourth switch T4 are turned off, and the conduction duration of the second switch T2 and the third switch T3 is 0 within one switching cycle. This prevents current from passing through the midpoint clamping diodes D5 and / or D6, thus reducing their temperature and ensuring that the thermal stress borne by the midpoint clamping diodes D5 and / or D6 remains within a safe range. This prevents overheating of the midpoint clamping diodes D5 and / or D6, which could damage the devices and ensures the normal operation of the circuit.
[0049] In one possible implementation, the detection control unit 20 is configured to control the conduction duration of the first switch T1 and / or the fourth switch T4 within one switching cycle to a first duration when the temperature of the midpoint clamping diode D5 and / or the midpoint clamping diode D6 exceeds a first preset threshold. The first duration is greater than a second preset threshold. The second preset threshold can be the maximum value of the conduction duration of the first switch T1 and / or the fourth switch T4 within one switching cycle under normal operating conditions of the inverter. Normal operating conditions refer to the operating state when the temperature of the midpoint clamping diode D5 and / or the midpoint clamping diode D6 in the inverter does not exceed the first preset threshold. By increasing the conduction duration of the first switch T1 and / or the fourth switch T4 within one switching cycle, the current passes through current path 1, current path 2, current path 3, or current path 4 for as long as possible, and through current path 5 or current path 6 for as short a time as possible, thereby reducing the current passing through the midpoint clamping diode D5 and / or the midpoint clamping diode D6.
[0050] For example, Figure 10This is a schematic diagram of another pulse width modulation signal in a three-level operating mode provided in an embodiment of this application. When the temperature of the midpoint clamping diode D5 and / or the midpoint clamping diode D6 exceeds a first preset threshold, the duration of the "+1" or "-1" level state in the pulse width modulation signal within one switching cycle is increased, thereby reducing the duration of the "0" level state, so that the duration of the "0" level state within one switching cycle is less than the preset duration. Figure 10 As shown, within switching cycle 1, the pulse width modulation signal includes three level states: "+1", "0", and "-1", with the duration of the "0" level state being T1. Within switching cycle 2, the pulse width modulation signal includes three level states: "+1", "0", and "-1", with the duration of the "0" level state being T2. T1 and T2 are controlled within a very short time range, ensuring that the duration of the second switch T2 and the third switch T3 being turned on, and the duration of the first switch T1 and the fourth switch T4 being turned off, are less than a preset duration. This reduces the current flowing through the midpoint clamping diode D5 and / or the midpoint clamping diode D6.
[0051] By increasing the duration of the "+1" or "-1" level state of the pulse width modulation signal within a switching cycle and decreasing the duration of the "0" level state within a switching cycle, the duration of the first switch T1 and the fourth switch T4 being off and the second switch T2 and the third switch T3 being on within a switching cycle is reduced. This decreases the current flowing through the midpoint clamping diodes D5 and / or D6. This prevents excessively high temperatures caused by prolonged current flow through the midpoint clamping diodes D5 and / or D6, ensuring that the thermal stress borne by the midpoint clamping diodes D5 and / or D6 remains within safe limits, thus guaranteeing normal circuit operation.
[0052] In one possible implementation, the detection control unit 20 is configured to control the conduction duration of the first switch T1 and / or the fourth switch T4 within one switching cycle to a second duration when the temperatures of the two midpoint clamping diodes do not exceed a first preset threshold. This second duration falls within a preset threshold range, which is the time range during which the first switch T1 and / or the fourth switch T4 are in the conducting state within one switching cycle when the inverter is in normal operating condition. Normal operating condition refers to the operating state when the temperatures of the midpoint clamping diodes D5 and / or D6 in the inverter do not exceed the first preset threshold.
[0053] When the temperature of the midpoint clamping diode D5 and / or the midpoint clamping diode D6 does not exceed the first preset threshold, the duration of the "+1", "-1", and "0" level states of the pulse width modulation signal can be restored to the normal operating time range, thus restoring the conduction time of the first switch T1 and / or the fourth switch T4 to the normal operating time range. This achieves dynamic adjustment of the current passing through the midpoint clamping diodes D5 and / or D6 based on their temperature, ensuring that the thermal stress borne by the two midpoint clamping diodes is within a safe range and guaranteeing the normal operation of the inverter.
[0054] In one possible implementation, the detection control unit 20 can detect the temperature of the midpoint clamping diode D5 and / or the midpoint clamping diode D6 in real time; based on the real-time detected temperature of the midpoint clamping diode D5 and / or the midpoint clamping diode D6, the on-time duration of the first switch T1 and / or the fourth switch T4 within one switching cycle is adjusted to control the current flowing through the midpoint clamping diode D5 and / or the midpoint clamping diode D6. That is, regardless of the circumstances, by real-time detection of the temperature of the midpoint clamping diode D5 and / or the midpoint clamping diode D6, the thermal stress borne by the midpoint clamping diode D5 and / or the midpoint clamping diode D6 is ensured to be within a safe range.
[0055] In one possible implementation, during a low-voltage ride-through, the voltage at the inverter grid connection point is less than a third preset threshold, or the current at the inverter grid connection point is greater than a fourth preset threshold. The temperature of the midpoint clamping diode D5 and / or the midpoint clamping diode D6 may exceed the safe range only during a low-voltage ride-through. The detection control unit 20 is configured to begin detecting the temperature of the midpoint clamping diode D5 and / or the midpoint clamping diode D6 when the voltage at the inverter grid connection point is detected to be less than the third preset threshold, or the current at the inverter grid connection point is detected to be greater than the fourth preset threshold. When the voltage at the inverter grid connection point is not less than the third preset threshold and the current at the inverter grid connection point is not greater than the fourth preset threshold, the detection of the temperature of the midpoint clamping diode D5 and / or the midpoint clamping diode D6 can be stopped. No circuit detection is performed when a low-voltage ride-through does not occur, ensuring circuit operating efficiency.
[0056] Please see Figure 11 , Figure 11 This is a structural schematic diagram of the power supply system provided in this application. For example... Figure 11 As shown, the power supply system 2 includes a power supply module 20 and an inverter 21 (as described above). Figures 3 to 10The inverter 21 shown can be connected to an AC load or an AC power grid at its output. In pure energy storage power supply applications, the power supply module 20 can be composed of multiple battery packs connected in series and parallel. A battery pack can be composed of one or more battery cells (the voltage of the battery cells is usually between 2.5V and 4.2V) connected in series and parallel to form the smallest energy storage and management unit. Optionally, the power supply module can also be a power generation component, which may include, but is not limited to, solar power generation components, wind power generation components, hydrogen power generation components, and diesel generator power generation components. In a photovoltaic-storage hybrid power supply scenario, the aforementioned power supply module 20 is a photovoltaic array, which can be composed of multiple photovoltaic strings connected in series and parallel. Each photovoltaic string can include multiple photovoltaic modules (also referred to as solar panels or photovoltaic panels). The inverter 21 converts the DC power output from the power supply module 20 into AC power for use by the AC grid and / or AC loads. In the inverter 21, the detection and control unit can detect the temperature of the midpoint clamping diodes D5 and D6 in each bridge arm of the inverter; based on the temperature of the midpoint clamping diodes D5 and D6, it adjusts the conduction duration of the first switch T1 and / or the fourth switch T4 within one switching cycle to control the current flowing through the midpoint clamping diodes D5 and D6. This prevents damage to the devices due to overheating of the midpoint clamping diodes D5 and / or D6, thereby ensuring the normal operation of the circuit.
[0057] like Figure 12 As shown, Figure 12 This is a flowchart illustrating a control method for an inverter provided in this application. This method is applicable to inverters (…). Figures 3-10 The inverter also includes a detection and control unit, a first switch, a second switch, a third switch, a fourth switch, and two midpoint clamping diodes. The first, second, third, and fourth switches are connected in series. The two midpoint clamping diodes are connected in series to the series connection points of the first and second switches, and the series connection points of the third and fourth switches, respectively. When the first and fourth switches are off, and the second and third switches are on, the two midpoint clamping diodes, the second switch, and the third switch form a current path. This method includes at least the following steps:
[0058] S1201 detects the temperature of two midpoint clamping diodes.
[0059] In one possible implementation, the temperature of the two midpoint clamping diodes can be monitored in real time by a detection control unit. That is, the temperature of the two midpoint clamping diodes can be monitored under any circumstances.
[0060] In one possible implementation, during a low-voltage ride-through, the voltage at the inverter grid connection point is less than a third preset threshold, or the current at the inverter grid connection point is greater than a fourth preset threshold. The temperature of the two midpoint clamping diodes may only exceed the safe range during a low-voltage ride-through. Temperature monitoring of the two midpoint clamping diodes begins when the voltage at the inverter grid connection point is detected to be less than the third preset threshold, or the current at the inverter grid connection point is detected to be greater than the fourth preset threshold. Temperature monitoring of the two midpoint clamping diodes can be stopped when the voltage at the inverter grid connection point is not less than the third preset threshold and the current at the inverter grid connection point is not greater than the fourth preset threshold. That is, the circuit is not monitored when a low-voltage ride-through does not occur, ensuring the circuit's operating efficiency.
[0061] S1202 adjusts the conduction duration of the first and / or fourth switching transistors within one switching cycle based on the temperature of the two midpoint clamping diodes, thereby controlling the current flowing through the two midpoint clamping diodes.
[0062] The switching cycle can be a fixed duration. Within one switching cycle, the pulse width modulation signal can include three voltage levels: "+1", "0", and "-1". That is, within one switching cycle, three situations can occur: the first and second switches are on, and the third and fourth switches are off; or the third and fourth switches are on, and the first and second switches are off; or the second and third switches are on, and the first and fourth switches are off. The duration of the "+1", "0", and "-1" voltage levels within one switching cycle can be different or the same. The on-time can be the duration for which the first and / or fourth switches are on within one switching cycle.
[0063] In one possible implementation, when the temperature of the two midpoint clamping diodes exceeds a first preset threshold, the conduction duration of the first and / or fourth switching transistors within one switching cycle is controlled to a first duration, which is greater than a second preset threshold. The second preset threshold can be the maximum value of the conduction duration of the first and / or fourth switching transistors within one switching cycle under normal operating conditions. Normal operating conditions refer to the operating state when the temperature of the two midpoint clamping diodes in the inverter does not exceed the first preset threshold. By increasing the conduction duration of the first and / or fourth switching transistors, controlling the first and fourth switching transistors to be off, and maintaining the conduction state of the second and third switching transistors for 0 duration within one switching cycle, current does not pass through the two midpoint clamping diodes, thus reducing the temperature of the two midpoint clamping diodes and ensuring that the thermal stress borne by the two midpoint clamping diodes is within a safe range.
[0064] In one possible implementation, when the temperature of the two midpoint clamping diodes exceeds a first preset threshold, the conduction time of the first and / or fourth switching transistors within one switching cycle is controlled to a first duration, which is greater than a second preset threshold. The second preset threshold can be the maximum conduction time of the first and / or fourth switching transistors within one switching cycle under normal inverter operation. By increasing the conduction time of the first and / or fourth switching transistors, the duration of their off-state and conduction states within one switching cycle is reduced, thereby reducing the current flowing through the two midpoint clamping diodes. This avoids excessively high temperatures due to prolonged current flow through the two midpoint clamping diodes, ensuring that the thermal stress borne by the two midpoint clamping diodes remains within a safe range.
[0065] In one possible implementation, when the temperature of the two midpoint clamping diodes does not exceed a first preset threshold, the conduction duration of the first and / or fourth switching transistors within one switching cycle is controlled to be a second duration. This second duration falls within a preset threshold range, which is the time range during which the first and / or fourth switching transistors are in the conducting state within one switching cycle under normal inverter operation. Normal operation refers to the operating state when the temperature of the two midpoint clamping diodes in the inverter does not exceed the first preset threshold. That is, when the temperature of the two midpoint clamping diodes does not exceed the first preset threshold, the conduction duration of the first and / or fourth switching transistors is restored to the time range under normal operating conditions. This achieves dynamic adjustment of the current passing through the two midpoint clamping diodes based on their temperature, ensuring that the thermal stress borne by the two midpoint clamping diodes is within a safe range and guaranteeing the normal operation of the inverter.
[0066] In specific implementation, further details regarding the operations performed by the detection and control unit in the inverter control method provided in this application can be found in [reference needed]. Figures 2 to 10 The implementation method of the control unit in the inverter and its working principle shown will not be elaborated here.
[0067] In this embodiment, the temperature of the two midpoint clamping diodes is detected by a detection control unit. Based on the temperature of the two midpoint clamping diodes, the conduction duration of the first and / or fourth switching transistors within one switching cycle is adjusted to control the current flowing through the two midpoint clamping diodes. This ensures that the thermal stress borne by the two midpoint clamping diodes is within a safe range, preventing overheating and device damage, and ensuring normal circuit operation. Furthermore, since there is no need to select larger-sized components or limit output capacity, costs can be reduced, providing reactive power support while ensuring power generation capacity.
[0068] The above are merely specific embodiments of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.
Claims
1. An inverter, characterized in that, The inverter includes a detection control unit, a first switch, a second switch, a third switch, a fourth switch, and two midpoint clamping diodes. The first switch, the second switch, the third switch, and the fourth switch are connected in series. The two midpoint clamping diodes are connected in series to the series connection point of the first switch and the second switch, and the series connection point of the third switch and the fourth switch, respectively. When the first switch and the fourth switch are turned off, the two midpoint clamping diodes, the second switch, and the third switch form a current path. The detection control unit is coupled to the two midpoint clamping diodes and is used to start detecting the temperature of the two midpoint clamping diodes when the voltage of the inverter grid connection point is less than a third preset threshold or the current of the inverter grid connection point is greater than a fourth preset threshold. Based on the temperature of the two midpoint clamping diodes, the conduction duration of the first switching transistor and / or the fourth switching transistor within one switching cycle is adjusted to control the current flowing through the two midpoint clamping diodes.
2. The inverter according to claim 1, characterized in that, The detection control unit is further configured to increase the conduction duration of the first switch and / or the fourth switch in a switching cycle when the temperature of the two midpoint clamping diodes exceeds a first preset threshold, so as to reduce the current flowing through the two midpoint clamping diodes.
3. The inverter according to claim 2, characterized in that, The detection and control unit is further configured to control the conduction duration of the first switch and / or the fourth switch in one switching cycle to a first duration when the temperature of the two midpoint clamping diodes exceeds the first preset threshold. The first duration is greater than a second preset threshold, and the second preset threshold is the maximum value of the conduction duration of the first switch and / or the fourth switch in one switching cycle when the inverter is in normal operating condition.
4. The inverter according to any one of claims 1-3, characterized in that, The detection and control unit is further configured to control the conduction duration of the first switch and / or the fourth switch in one switching cycle to a second duration when the temperature of the two midpoint clamping diodes does not exceed a first preset threshold. The second duration is located within a preset threshold range, which is the time range during which the first switch and / or the fourth switch are in the conducting state in one switching cycle when the inverter is in normal operating condition.
5. The inverter according to any one of claims 1-3, characterized in that, The inverter is a three-level neutral point clamped inverter.
6. A control method for an inverter, characterized in that, The method is applicable to the detection and control unit in an inverter. The inverter further includes a first switch, a second switch, a third switch, a fourth switch, and two midpoint clamping diodes. The first switch, the second switch, the third switch, and the fourth switch are connected in series. The two midpoint clamping diodes are connected in series to the series connection points of the first switch and the second switch, and the third switch and the fourth switch, respectively. When the first switch and the fourth switch are turned off, the two midpoint clamping diodes, the second switch, and the third switch form a current path. The method includes: When the voltage at the inverter grid connection point is detected to be less than the third preset threshold, or the current at the inverter grid connection point is greater than the fourth preset threshold, the temperature of the two midpoint clamping diodes is detected. Based on the temperature of the two midpoint clamping diodes, the conduction duration of the first switching transistor and / or the fourth switching transistor within one switching cycle is adjusted to control the current flowing through the two midpoint clamping diodes.
7. The method according to claim 6, characterized in that, The step of adjusting the conduction duration of the first switching transistor and / or the fourth switching transistor within a switching cycle based on the temperature of the two midpoint clamping diodes, in order to control the current flowing through the two midpoint clamping diodes, includes: When the temperature of the two midpoint clamping diodes exceeds a first preset threshold, the conduction time of the first switch and / or the fourth switch in one switching cycle is increased to reduce the current flowing through the two midpoint clamping diodes.
8. The method according to claim 7, characterized in that, The step of increasing the conduction time of the first switch and / or the fourth switch within one switching cycle when the temperature of the two midpoint clamping diodes exceeds a first preset threshold includes: When the temperature of the two midpoint clamping diodes exceeds the first preset threshold, the conduction time of the first switch and / or the fourth switch in one switching cycle is controlled to be a first duration, which is greater than a second preset threshold. The second preset threshold is the maximum value of the conduction time of the first switch and / or the fourth switch in one switching cycle when the inverter is in normal working condition.
9. The method according to any one of claims 6-8, characterized in that, The step of adjusting the conduction duration of the first switching transistor and / or the fourth switching transistor within a switching cycle based on the temperature of the two midpoint clamping diodes, in order to control the current flowing through the two midpoint clamping diodes, includes: When the temperature of the two midpoint clamping diodes does not exceed the first preset threshold, the conduction time of the first switch and / or the fourth switch in one switching cycle is controlled to be the second duration. The second duration is within the preset threshold range, which is the time range during which the first switch and / or the fourth switch are in the conducting state in one switching cycle when the inverter is in normal working condition.
10. The method according to any one of claims 6-8, characterized in that, The inverter is a three-level neutral point clamped inverter.
11. A power supply system, characterized in that, The power supply system includes a photovoltaic array and an inverter as described in any one of claims 1-5 connected to the photovoltaic array, wherein the photovoltaic array is used to send the converted electrical energy to the inverter for inversion processing.