Power conversion device
By coordinating digital control units and switching transistors with an AC/DC converter, the problem of bus capacitor overvoltage explosion was solved, thus improving the safety and reliability of the circuit.
Patent Information
- Application Number
- CN202511777415.4
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-11-28
- Publication Date
- 2026-02-24
AI Technical Summary
In existing multilevel power conversion devices, the bus capacitor is prone to overvoltage explosion under fault conditions, leading to circuit damage and safety accidents.
The bus capacitor voltage is monitored by a digital control unit, which controls the switching transistors to turn on and off. Combined with the operating status of the AC/DC converter, overvoltage of the bus capacitor is avoided. Furthermore, the capacitor is prevented from exploding by discharging the load and rectifying the power supply.
It effectively prevents bus capacitor explosions, reduces circuit damage and safety accidents, and improves the reliability and safety of the equipment.
Smart Images
Figure CN121566944A_ABST
Abstract
Description
Technical Field
[0001] This application relates to the field of power supplies, and in particular to a power conversion device. Background Technology
[0002] Inverters are used to convert solar photovoltaic (PV) energy into electrical energy and have been widely used in recent years.
[0003] Inverters can be divided into single-level inverters and multi-level inverters. Photovoltaic inverters often use multi-level inverters. Please refer to [link / reference]. Figure 1 The diagram shown is of a typical photovoltaic inverter, which includes an inverter bridge 100. The DC terminal of the inverter bridge 100 is connected to the upper and lower half-bus capacitors. The half-bus capacitors need to have an intermediate level contact, i.e., the bus midpoint potential terminal N, as shown. Figure 1 The common node of the first DC bus capacitor C1 and the second DC bus capacitor C2 forms the bus midpoint potential terminal. The voltage difference between the bus midpoint potential terminal and the upper and lower half of the bus is half of the bus voltage.
[0004] It is evident that, for Figure 1 The multi-level power conversion device shown requires that the first DC bus capacitor C1 and the second DC bus capacitor C2 be selected to withstand the same voltage, referred to as the capacitor withstand voltage. Furthermore, the first DC bus capacitor C1 and the second DC bus capacitor C2 are selected such that the DC input voltage is approximately twice the withstand voltage of the first DC bus capacitor C1 and the second DC bus capacitor C2.
[0005] In actual operation, when the power conversion device malfunctions, such as a short circuit in the switching transistor of inverter bridge 100, the corresponding half-bus capacitor will also short-circuit. This causes the voltage across the other half-bus capacitor to change from the half-bus voltage to the total bus voltage (i.e., the DC input voltage), potentially leading to severe overvoltage and explosion of the half-bus capacitor. The first DC bus capacitor C1 and the second DC bus capacitor C2 are electrolytic capacitors. If these capacitors explode due to severe overvoltage, the ejected electrolyte may cause a high-voltage short circuit on the internal PCB of the power conversion device, resulting in severe circuit damage or even a fire, causing economic losses or even a safety hazard. Summary of the Invention
[0006] According to one embodiment, this application provides a power conversion device, including an inverter. The inverter includes: an inverter bridge, including a DC terminal, the DC terminal including a positive DC terminal, a negative DC terminal, and an intermediate level terminal; a first DC bus capacitor, a first end of the first DC bus capacitor connected to the positive DC terminal, and a second end of the first DC bus capacitor connected to the intermediate level terminal; a first load, connected in parallel with the first DC bus capacitor; a second DC bus capacitor, a first end of the second DC bus capacitor connected to the intermediate level terminal, and a second end of the second DC bus capacitor connected to the negative DC terminal; a second load, connected in parallel with the second DC bus capacitor; and a switching transistor connected to the positive DC bus input terminal of the inverter. The first terminal of the first DC bus capacitor is connected between or between the negative DC bus input terminal of the inverter and the second terminal of the second DC bus capacitor; the digital control unit controls the switching transistor according to the first capacitor voltage value of the first DC bus capacitor and the second capacitor voltage value of the second DC bus capacitor, and executes: S1: control the switching transistor to turn on; S2: determine whether the first capacitor voltage value or the second capacitor voltage value is greater than a first set value. If yes, execute step S3; if no, continue to execute step S2; S3: control the switching transistor to turn off; S4: determine whether the first capacitor voltage value and the second capacitor voltage value are less than a second set value. If yes, execute step S1; if no, continue to execute step S4.
[0007] Furthermore, it also includes: a first capacitor voltage detection circuit, connected to the first DC bus capacitor, used to detect the voltage on the first DC bus capacitor and output the first capacitor voltage value; and a second capacitor voltage detection circuit, connected to the second DC bus capacitor, used to detect the voltage on the second DC bus capacitor and output the second capacitor voltage value.
[0008] Furthermore, the first load is a resistive load, including at least one resistor, which is connected in series and / or in parallel; the second load is a resistive load, including at least one resistor, which is connected in series and / or in parallel.
[0009] Furthermore, the resistance of both the first load and the second load is 100kΩ, or the resistance is 100kΩ with a deviation of less than 20%.
[0010] Furthermore, it also includes: an AC / DC converter, wherein the AC terminal of the AC / DC converter is connected to the AC input terminal of the power conversion device, and the DC terminal of the AC / DC converter is connected to the first terminal of the first DC bus capacitor and the second terminal of the second DC bus capacitor.
[0011] Furthermore, during the turn-off period of the switch, the AC / DC converter is controlled to operate, rectifying the AC power received at the AC input terminal into DC power to supply power to the first DC bus capacitor and the second DC bus capacitor.
[0012] Furthermore, during the conduction of the switching transistor, the AC / DC converter is controlled to stop operating.
[0013] Furthermore, the AC / DC converter is a rectifier bridge.
[0014] Furthermore, the inverter bridge is a multi-level inverter bridge.
[0015] Furthermore, after step S3, the digital control unit also performs the following: S5: the timer starts counting and the counter increments by one; S6: it is determined whether the timer's counting time is greater than the set time. If yes, step S8 is executed; otherwise, step S7 is executed; S8: the timer is cleared and the counter is cleared, returning to step S4; S7: it is determined whether the counter's count is greater than the set count. If yes, step S9 is executed; otherwise, step S4 is returned; S9: Q1 is turned off, and the power conversion device is troubleshooted.
[0016] The features and technical advantages of this disclosure have been outlined quite extensively above to facilitate a better understanding of the detailed description that follows. Additional features and advantages of this disclosure, which form the subject matter of the claims, will be described below. Those skilled in the art will understand that the disclosed concepts and specific embodiments can be readily used as the basis for modifying or designing other structures or processes for achieving the same purpose as this disclosure. Those skilled in the art will also recognize that such equivalent structures do not depart from the spirit and scope of this disclosure as set forth in the appended claims. Attached Figure Description
[0017] To gain a more complete understanding of this disclosure and its advantages, the following description is given in conjunction with the accompanying drawings, wherein:
[0018] Figure 1 A schematic diagram of a typical photovoltaic inverter is shown;
[0019] Figure 2 A schematic diagram of a power conversion device according to an embodiment of this application is shown;
[0020] Figure 3 This invention provides a schematic diagram of the control process executed by a digital control unit according to an embodiment of the present application.
[0021] Figure 4 A schematic diagram of a power conversion device according to another embodiment of this application is shown;
[0022] Figure 5A schematic diagram of a power conversion device according to another embodiment of this application is shown;
[0023] Figure 6 A schematic diagram of the control process executed by the digital control unit according to another embodiment of this application is shown.
[0024] Unless otherwise stated, corresponding numbers and symbols in the various figures generally refer to corresponding parts. These figures are drawn to clearly illustrate relevant aspects of the various embodiments and are not necessarily drawn to scale. Detailed Implementation
[0025] The technical solutions of this application will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this application. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.
[0026] One embodiment of this application provides a power conversion device; please refer to [link to relevant documentation]. Figure 2 The diagram shown is a schematic representation of a power conversion device according to an embodiment of this application. Please refer to it in conjunction with... Figure 3 The diagram shown is a schematic of the control process executed by the digital control unit according to an embodiment of this application. The power conversion device proposed in this application includes an inverter 10, which includes:
[0027] The inverter bridge 100 includes a DC terminal, which includes a positive DC terminal d+, a negative DC terminal d-, and an intermediate level terminal N.
[0028] The first DC bus capacitor C1 has its first end connected to the positive DC terminal d+, and its second end connected to the intermediate level terminal N.
[0029] The first load 210 is connected in parallel with the first DC bus capacitor C1;
[0030] The second DC bus capacitor C2 has its first end connected to the intermediate level terminal N, and its second end connected to the negative DC terminal d-.
[0031] The second load 220 is connected in parallel with the second DC bus capacitor C2;
[0032] The switching transistor Q1 is connected between the positive DC bus input terminal of the inverter 10 and the first terminal of the first DC bus capacitor C1, or between the negative DC bus input terminal of the inverter and the second terminal of the second DC bus capacitor C2.
[0033] The digital control unit 400, based on the first capacitor voltage value of the first DC bus capacitor C1 and the second capacitor voltage value of the second DC bus capacitor C2, controls the switching transistor Q1 to execute:
[0034] S1: Control the switching transistor Q1 to conduct;
[0035] S2: Determine whether the voltage value of the first capacitor or the voltage value of the second capacitor is greater than the first set value. If yes, proceed to step S3; otherwise, continue to proceed to step S2.
[0036] S3: Control the switching transistor Q1 to turn off;
[0037] S4: Determine whether the voltage values of the first capacitor and the second capacitor are less than the second set value. If yes, execute step S1; otherwise, continue to execute step S4.
[0038] like Figure 2 As shown, the switching transistor Q1 is connected between the positive DC bus input terminal (i.e., the positive input terminal of the DC input terminal VDCin) of the inverter 10 and the first terminal of the first DC bus capacitor C1. Please refer to... Figure 4 The schematic diagram of a power conversion device according to another embodiment of this application shows that the switching transistor Q1 is connected between the negative DC bus input terminal (i.e., the negative input terminal of the DC input terminal) of the inverter 10 and the second terminal of the second DC bus capacitor C2. Thus, when the switching transistor Q1 is turned on, the high-voltage DC power supplied through the DC input terminal VDCin, such as between 800V and 1000V, supplies power to the DC bus formed by the first DC bus capacitor C1 and the second DC bus capacitor C2 connected in series. This power is then inverted by the inverter bridge 100 into AC power at the AC output terminal VACout to supply power to the AC load. When the switching transistor Q1 is turned off, the high-voltage DC power supplied through the DC input terminal VDCin is disconnected from the DC bus and cannot supply power to it. Therefore, this application, by adding the switching transistor Q1 and controlling its on and off states, achieves the control of whether the high-voltage DC power supplies power to the DC bus or not.
[0039] Specifically, in one embodiment, the inverter is a photovoltaic inverter, that is, the DC input terminal VDCin of the power conversion device receives solar energy, such as when a solar panel is connected. Its voltage is usually between 800V and 1000V. The first DC bus capacitor C1 and the second DC bus capacitor C2 are connected in series to withstand the high voltage DC input voltage. Therefore, the rated voltage of the first DC bus capacitor C1 and the second DC bus capacitor C2 is usually selected to be slightly higher than half of the high voltage DC input voltage, such as between 450V and 550V.
[0040] Furthermore, when the power conversion device is powered on, or in the default state, the control switch Q1 is in the conducting state, and the high voltage DC power supplies the DC bus. The digital control unit 400 determines whether the first DC bus capacitor C1 and the second DC bus capacitor C2 are over-voltaged and whether there is a risk of explosion based on the received first capacitor voltage value and second capacitor voltage value.
[0041] In practice, if inverter 10 is fault-free and operating normally, the first DC bus capacitor C1 and the second DC bus capacitor C2 will not experience overvoltage. Therefore, the switching transistor Q1 will remain on, and inverter 10 will convert high-voltage DC to AC to power AC loads. However, if inverter 10 malfunctions, such as a short circuit in the switching transistor of inverter bridge 100, the corresponding half-bus capacitor (either the first DC bus capacitor C1 or the second DC bus capacitor C2) will also short-circuit. This will cause the voltage across the other half-bus capacitor to change from the half-bus voltage (i.e., half of the high-voltage DC) to the total bus voltage (i.e., high-voltage DC), potentially leading to severe overvoltage and explosion of that half-bus capacitor. Since the first DC bus capacitor C1 and the second DC bus capacitor C2 are electrolytic capacitors, an explosion of these capacitors can cause electrolyte leakage, potentially resulting in a high-voltage short circuit on the internal PCB of the power conversion device. This can lead to severe circuit damage or even a fire, causing economic losses or safety hazards.
[0042] As described above, during the conduction of the switching transistor Q1, the digital control unit 400 of this application determines whether the voltage values of the first capacitor C1 and the second capacitor C2 are greater than a first set value, thereby determining whether there is a risk of overvoltage and explosion of the first DC bus capacitor C1 and the second DC bus capacitor C2. If so, the switching transistor Q1 is turned off, the high voltage DC power is disconnected from the DC bus, and power is no longer supplied to it, thus avoiding the voltage across the first DC bus capacitor C1 and the second DC bus capacitor C2 from continuing to increase and causing overvoltage and explosion. Furthermore, during the off-state of switch Q1, the overvoltage first DC bus capacitor C1 or second DC bus capacitor C2 discharges through the load connected in parallel with it, which can effectively prevent the bus capacitor from exploding. During the discharge process, the digital control unit 400 determines whether the voltage values of the first capacitor and the second capacitor are less than a second set value, that is, whether the voltage values of the first capacitor and the second capacitor have been discharged to a safe range. If so, switch Q1 can be controlled to return to the conducting state, so that the high voltage DC power is restored to power the DC bus. If not, switch Q1 can be controlled to remain in the off state to continue discharging the first DC bus capacitor C1 or the second DC bus capacitor C2.
[0043] Thus, the power conversion device provided in this application can effectively prevent bus capacitor explosion accidents in inverters, reduce damage to inverters caused by capacitor explosions, reduce economic losses and safety accidents caused by such explosions, significantly reduce the inverter damage rate, improve inverter safety, and better protect the personal and property safety of users.
[0044] In practical applications, both the first load 210 and the second load 220 are resistive loads, which can be a single resistor or multiple resistors connected in series and / or in parallel. This application does not limit this.
[0045] Continue reading Figure 2 and Figure 4 During the period when the DC bus is powered, the first load 210 also discharges the first DC bus capacitor C1, and the second load 220 also discharges the second DC bus capacitor C2. To reduce power loss, in one embodiment of this application, the resistance values of both the first load 210 and the second load 220 are selected to be 100kΩ. In practical applications, this can have a certain deviation, such as within 20%. Therefore, during the period when the DC bus is powered, the power loss of the first load 210 discharging the first DC bus capacitor C1 and the second load 220 discharging the second DC bus capacitor C2 is very small, for example, less than 1W, and can be ignored.
[0046] Please refer to the following: Figure 2 and Figure 4 The power conversion device further includes:
[0047] The first capacitor voltage detection circuit 310 is connected to the first DC bus capacitor C1 and is used to detect the voltage on the first DC bus capacitor C1 and output the first capacitor voltage value.
[0048] The second capacitor voltage detection circuit 320 is connected to the second DC bus capacitor C2 and is used to detect the voltage on the second DC bus capacitor C2 and output the second capacitor voltage value.
[0049] Please see Figure 5 The schematic diagram of another embodiment of the power conversion device shown in this application further includes an AC / DC converter 21. The power conversion device also includes an AC input terminal VACin. The AC terminal of the AC / DC converter 21 is connected to the AC input terminal VACin to receive AC input power. The DC terminal of the AC / DC converter 21 is connected to the first terminal of the first DC bus capacitor C1 and the second terminal of the second DC bus capacitor C2 to supply power to the DC bus.
[0050] For details, please refer to Figure 5When the switching transistor Q1 is turned off due to overvoltage of either the first DC bus capacitor C1 or the second DC bus capacitor C2, the AC / DC converter 21 can be controlled to operate, rectifying the AC input power into DC power to supply the first DC bus capacitor C1 and the second DC bus capacitor C2. In practical applications, the AC / DC converter 21 can be implemented as a rectifier bridge. Then, the AC / DC converter 21 can rectify the 220V AC input power into 380V DC power to supply the first DC bus capacitor C1 and the second DC bus capacitor C2, and then invert it through the inverter bridge 100 to achieve uninterrupted power supply to the AC load, improving the reliability of the power conversion device.
[0051] As described above, when the first DC bus capacitor C1 and the second DC bus capacitor C2 are powered by the 380V DC power rectified by the AC / DC converter 21, the voltage supplied to the first DC bus capacitor C1 and the second DC bus capacitor C2 is less than the voltage that the first DC bus capacitor C1 or the second DC bus capacitor C2 can withstand under overvoltage conditions. Therefore, the overvoltage first DC bus capacitor C1 or the second DC bus capacitor C2 can still continue to discharge to a safe value. Furthermore, since half of the 380V DC power rectified by the AC / DC converter 21 is lower than the rated voltage that the first DC bus capacitor C1 and the second DC bus capacitor C2 can withstand, the first DC bus capacitor C1 and the second DC bus capacitor C2 will not suffer overvoltage and will not be at risk of explosion.
[0052] More specifically, when the switch Q1 is turned on, the AC / DC converter 21 is stopped, and the high-voltage DC power supplied by the DC input terminal VDCin of the power conversion device powers the first DC bus capacitor C1 and the second DC bus capacitor C2.
[0053] In one embodiment, the inverter bridge 100 is a multi-level inverter bridge 100, such as a three-level inverter bridge. This application does not limit its specific circuit, and any applicable inverter bridge is applicable to this application.
[0054] In one embodiment, the switch Q1 can be any suitable switch, such as an IGBT (Insulated Gate Bipolar Transistor), a MOSFET (Metal-Oxide-Semiconductor Field-Effect Transistor), or other transistors. From an efficiency perspective, the switch Q1 is preferably a SiC (silicon carbide) MOSFET. In practical applications, a suitable switch can be selected based on the bus voltage, bus current, and temperature rise.
[0055] For further details, please refer to Figure 6The diagram shown below illustrates the control process executed by the digital control unit 400 according to another embodiment of this application. After step S3, the digital control unit 400 further executes:
[0056] S5: Timer starts counting, counter increments by one;
[0057] S6: Determine whether the timer's timing duration is greater than the set time. If yes, proceed to step S8; otherwise, proceed to step S7.
[0058] S8: Timer reset, counter reset, return to step S4;
[0059] S7: Determine whether the counter count is greater than the set count. If yes, proceed to step S9; otherwise, return to step S4.
[0060] S9: Switch Q1 is turned off, and troubleshooting is performed on the power conversion device.
[0061] In actual operation, inverter 10 may experience non-self-repairable faults. To avoid frequent faults in inverter 10 within a short period (such as a set time), and to prevent frequent switching between on and off of switching transistor Q1, as well as frequent switching between operating and non-operating states of inverter 10, a timer can be started when switching transistor Q1 is first turned off, and continuously incremented. During the timer's operation, the counter increments by one each time switching transistor Q1 is turned off. If the counter reaches the set count within the set time, it indicates that inverter 10 has frequently failed within the set time, suggesting a possible non-self-repairable fault. In this case, switching transistor Q1 should be turned off, and the power conversion device should be troubleshooted. If the timer reaches the set time before the counter reaches the set count, it indicates that inverter 10 has not frequently failed within the set time. In this case, the timer and counter are reset to zero, and the timing and counting restart. This further improves the reliability of the power conversion device.
[0062] In practical applications, the first setting value, the second setting value, the setting time, and the number of settings can be set according to the actual product, and this application does not limit them.
[0063] In practical applications, the digital control unit 400 can be implemented as a digital controller such as a DSP or MCU. For the aforementioned power conversion device, the digital control unit 400 can also be used to control the switching transistors in the inverter bridge 100 to achieve the inverter function, and can also be used to control the switching transistors in the AC / DC converter 21 to achieve the rectification function.
[0064] Although embodiments of the present disclosure and their advantages have been described in detail, it should be understood that various changes, substitutions and alterations may be made herein without departing from the spirit and scope of the present disclosure as defined by the appended claims.
[0065] Furthermore, the scope of this application is not intended to be limited to the specific embodiments of the processes, machines, manufactures, compositions of matter, apparatuses, methods, and steps described in the specification. As will be readily understood by those skilled in the art from the disclosure of this publication, processes, machines, manufactures, compositions of matter, means, methods, or steps that perform substantially the same function, currently exist or will be developed or implemented thereafter, will yield substantially the same results as the corresponding embodiments described herein that are available according to this disclosure. Therefore, the appended claims are intended to include such processes, machines, manufactures, compositions of matter, apparatuses, methods, or steps within their scope.
Claims
1. A power conversion device, characterized in that, Includes an inverter, the inverter comprising: An inverter bridge includes a DC terminal, which includes a positive DC terminal, a negative DC terminal, and an intermediate level terminal. A first DC bus capacitor, the first end of which is connected to the positive DC terminal, and the second end of which is connected to the intermediate level terminal. The first load is connected in parallel with the first DC bus capacitor; The second DC bus capacitor has its first end connected to the intermediate level terminal and its second end connected to the negative DC terminal. The second load is connected in parallel with the second DC bus capacitor; The switching transistor is connected between the positive DC bus input terminal of the inverter and the first terminal of the first DC bus capacitor, or between the negative DC bus input terminal of the inverter and the second terminal of the second DC bus capacitor. The digital control unit, based on the first capacitor voltage value of the first DC bus capacitor and the second capacitor voltage value of the second DC bus capacitor, controls the switching transistor to execute: S1: Control the switching transistor to turn on; S2: Determine whether the voltage value of the first capacitor or the voltage value of the second capacitor is greater than the first set value. If yes, proceed to step S3; otherwise, continue to proceed to step S2. S3: Control the switching transistor to turn off; S4: Determine whether the voltage values of the first capacitor and the second capacitor are less than the second set value. If yes, execute step S1; otherwise, continue to execute step S4.
2. The power conversion device according to claim 1, characterized in that, Also includes: The first capacitor voltage detection circuit is connected to the first DC bus capacitor and is used to detect the voltage on the first DC bus capacitor and output the first capacitor voltage value. The second capacitor voltage detection circuit is connected to the second DC bus capacitor and is used to detect the voltage on the second DC bus capacitor and output the second capacitor voltage value.
3. The power conversion device according to claim 2, characterized in that, The first load is a resistive load, including at least one resistor, wherein the at least one resistor is connected in series and / or in parallel; The second load is a resistive load, including at least one resistor, which is connected in series and / or in parallel.
4. The power conversion device according to claim 3, characterized in that, The resistance of both the first load and the second load is 100kΩ, or the resistance is 100kΩ with a deviation of less than 20%.
5. The power conversion device according to claim 1, characterized in that, Also includes: An AC / DC converter, wherein the AC terminal of the AC / DC converter is connected to the AC input terminal of the power conversion device, and the DC terminal of the AC / DC converter is connected to the first terminal of the first DC bus capacitor and the second terminal of the second DC bus capacitor.
6. The power conversion device according to claim 5, characterized in that, During the period when the switch is off, the AC / DC converter is controlled to operate, and the AC power received at the AC input terminal is rectified into DC power to supply power to the first DC bus capacitor and the second DC bus capacitor.
7. The power conversion device according to claim 6, characterized in that, During the conduction of the switching transistor, the AC / DC converter is controlled to stop operating.
8. The power conversion device according to claim 5, characterized in that, The AC / DC converter is a rectifier bridge.
9. The power conversion device according to claim 1, characterized in that, The inverter bridge is a multi-level inverter bridge.
10. The power conversion device according to claim 1 or 5, characterized in that, The digital control unit further performs the following after step S3: S5: Timer starts counting, counter increments by one; S6: Determine whether the timer's timing duration is greater than the set time. If yes, proceed to step S8; otherwise, proceed to step S7. S8: Timer reset, counter reset, return to step S4; S7: Determine whether the counter count is greater than the set count. If yes, proceed to step S9; otherwise, return to step S4. S9: Q1 is turned off, and the power conversion device is troubleshooted.