Discharge circuit for flying capacitor boost and control method thereof

Abstract

The application relates to a discharging circuit for flying capacitor BOOST and a control method thereof. A plurality of groups of flying capacitor BOOST circuits are connected with photovoltaic cells. The circuit is connected after an input inductor and a current sensor in each group of flying capacitor BOOST circuits and before IGBT bridge arms MOS1 and MOS2 in the flying capacitor BOOST circuit. The circuit comprises a detection unit, a driver ON3, a switch tube T1 connected with the IGBT bridge arms MOS1 and MOS2, and a discharging resistor R1 connected in series with the switch tube T1. The detection unit detects a voltage difference between the IGBT bridge arms MOS1, triggers the switch tube T1 to be turned on, and turns on the discharging circuit. The detection unit detects an input current value of the flying capacitor BOOST circuit, controls the switch tube T1 to be turned off, and turns off the discharging circuit. The circuit does not work when the photovoltaic panel is normally connected and runs. When the panel is not connected and a PV capacitor generates a voltage, the circuit clamps the voltage to a safe voltage. The flying capacitor BOOST topology photovoltaic inverter use safety is improved. The circuit can be applied to a charger, an off-grid inverter and other similar flying capacitor BOOST topology circuits.

Description

TECHNICAL FIELD

[0001] The application relates to a photovoltaic power generation related device, in particular to a discharging circuit for flying capacitor BOOST and a control method thereof. BACKGROUND

[0002] The new energy photovoltaic industry accounts for an increasing proportion in the world year by year, and the photovoltaic power generation scale is continuously expanding and is in an overall upward state. New technologies are continuously applied in the photovoltaic inverter field, and the flying capacitor BOOST topology is adopted in the photovoltaic inverter, which has the advantages of saving device cost, reducing IGBT withstand voltage, reducing inductance volume, and being relatively convenient for system installation compared with the symmetric BOOST topology. Figure 1 As shown in the existing flying BOOST circuit, the MPPT (maximum power point tracking) function is realized by controlling the charging and discharging of C2 connected in parallel to the positive and negative electrodes of the photovoltaic panel through the switching tubes MOS1 and MOS2.

[0003] As shown in the existing flying BOOST circuit, the MPPT (maximum power point tracking) function is realized by controlling the charging and discharging of C2 connected in parallel to the positive and negative electrodes of the photovoltaic panel through the switching tubes MOS1 and MOS2. Figure 2 The existing flying BOOST circuit and the photovoltaic cell connection schematic diagram, the existing flying capacitor BOOST circuit topology in the actual photovoltaic panel access, if one of the MPPTs does not access the photovoltaic panel, the other MPPTs will generate a voltage on the PV input capacitor C1 through the BUS, and the generated voltage is the voltage of the BUS capacitor C3, the flying capacitor C2 and the input capacitor C1 (as shown by the arrow in Figure 2 The current path of the voltage generated by the C1 capacitor), if the voltage cannot be eliminated, it will cause trouble to the operation and maintenance and background monitoring personnel, and it will be mistakenly thought that this MPPT has accessed the photovoltaic panel. The voltage is directly connected to the PV terminal, which will also cause hidden dangers to the safety of the on-site personnel. If a load resistor is connected in parallel to the input capacitor to eliminate the voltage, a very large power load resistor is necessarily required to clamp the voltage within a safe voltage, and if a large power load resistor is used in the normally accessed photovoltaic string, additional energy loss will be generated, the internal ring temperature of the machine will be increased, and the overall power generation efficiency will be reduced. SUMMARY

[0004] In view of the safety hidden trouble problem existing in the connection of the flying BOOST circuit and the photovoltaic cell, a discharging circuit for flying capacitor BOOST and a control method thereof are provided, which does not work when the photovoltaic panel is normally accessed, and clamps the voltage to a safe voltage when the PV capacitor generates a voltage without accessing the photovoltaic panel.

[0005] The technical solution of this invention is as follows: a discharge circuit for a flying capacitor booster, wherein multiple flying capacitor boosters are connected to a DC power supply, and the circuit is connected after the input inductor and current sensor in each flying capacitor booster and before the first and second high-frequency switching transistors of the upper and lower IGBT bridge arm circuits in the flying capacitor booster, including a detection unit, a driver ON3, a switching transistor T1 connected to both ends of the first and second high-frequency switching transistors of the upper and lower IGBT bridge arm circuits, and a current-limiting clamping element connected in series with it. The detection unit detects the voltage difference across the first high-frequency switching transistor of the upper IGBT bridge arm, triggers the driver ON3 to turn on the switching transistor T1, and the discharge circuit is turned on; the detection unit detects the input current value of the flying capacitor booster, controls the switching transistor T1 to turn off, and the discharge circuit is turned off.

[0006] Preferably, the detection unit includes a comparator COMP1. The input terminals of the comparator COMP1 are connected to the two terminals of the first high-frequency switch in the photovoltaic inverter. The positive input terminal of the comparator COMP1 is connected to the series connection point of the first and second high-frequency switches in the upper and lower IGBT bridge arm circuits. The output of the comparator COMP1 is connected to the control terminal of the switch T1 through the driver ON3.

[0007] Preferably, the detection unit includes a switch T2, a flying capacitor BOOST current sensor current signal is sent to a driver ON1, the output of driver ON1 is connected to the control terminal of switch T2, and the two ends of switch T2 are connected in parallel to the control terminal of switch T1 and ground.

[0008] Preferably, the current sensor is a Hall sensor, and the output of the Hall sensor is connected to the driver ON1 and the flying capacitor BOOST control unit DSP.

[0009] Preferably, the flying capacitor BOOST control unit DSP is connected to the control terminal of the switching transistor T2 via driver ON2.

[0010] Preferably, the first high-frequency switching transistor and the second high-frequency switching transistor are IGBTs or MOSFETs, and the switching transistors T1 and T2 are any one of IGBTs, MOSFETs, and relay switches.

[0011] Preferably, the discharge resistor R1 connected in series with the switching transistor T1 is a power resistor, which clamps the flying capacitor BOOST circuit under static conditions.

[0012] Preferably, the switching transistor T1 is a MOSFET, and T2 is any one of IGBT, MOSFET, and relay switch.

[0013] Preferably, the drivers ON1, ON2, and ON3 are either optocouplers or pulse transformers.

[0014] A control method for a discharge circuit of a flying capacitor BOOST is provided. In the PV discharge circuit, comparator COMP1 outputs a high level to driver ON3 to control switch T1 to turn on. After turning on, switch T1, discharge resistor R1, and input inductor L1 are connected in series and in parallel with input capacitor C1 to form a discharge circuit for input capacitor C1, clamping the input PV voltage of the flying capacitor BOOST. After switch T1 is turned on, if the Hall sensor of the flying capacitor BOOST detects a positive current passing through it and it is greater than a set value, switch T2 is turned on by driver ON1. At the same time, a signal is sent to the DSP for current sampling. After switch T2 is turned on, switch T1 is turned off, and the discharge circuit is cut off.

[0015] Furthermore, after the switch T1 is turned on, the DSP outputs a control signal to the driver ON2 based on the current value detected by the Hall sensor of the flying capacitor BOOST. The driver ON2 turns on the switch T2 and turns off the switch T1 at the same time, thus cutting off the discharge circuit.

[0016] The beneficial effects of this invention are as follows: the discharge circuit and control method for the fly-through capacitor boost topology improve the safety of photovoltaic inverters using this invention. It can be applied to chargers, off-grid inverters, and other similar fly-through boost topology circuits. Attached Figure Description

[0017] Figure 1 For the existing Flying BOOST circuit diagram;

[0018] Figure 2 This is a schematic diagram showing the connection between multiple existing flying BOOST circuits and photovoltaic cells.

[0019] Figure 3 This is a schematic diagram of the PV discharge circuit connection location and discharge loop for the BOOST of the flying capacitor in this invention.

[0020] Figure 4 This is a PV discharge circuit diagram for the BOOST of a flying capacitor according to the present invention. Detailed Implementation

[0021] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments. These embodiments are based on the technical solution of the present invention and provide detailed implementation methods and specific operating procedures. However, the scope of protection of the present invention is not limited to the following embodiments.

[0022] like Figure 3The diagram shows the connection location and discharge loop of the discharge circuit used for the flying capacitor BOOST. The circuit is installed after the BOOST inductor and current sensor, and before MOS1 and MOS2 of the IGBT bridge arms in the flying BOOST circuit. The positive and negative voltages here are connected to the PV input terminals. In a static state, clamping this voltage is equivalent to clamping the PV input port voltage.

[0023] like Figure 4 The circuit diagram shown is for PV discharge circuitry used for flying capacitor BOOST. The circuit includes two switching transistors, comparator COMP1, a driver, and a discharge resistor R1. The input terminals of comparator COMP1 are connected to the two ends of MOS1, the upper arm of the IGBT in the photovoltaic inverter. The positive input terminal of comparator COMP1 is connected to the series connection point of IGBT arms MOS1 and MOS2. The output of comparator COMP1 is connected to the control terminal of switching transistor T1 (the gate G of the MOS transistor or the base B of the transistor) and one end of the conduction terminal of switching transistor T2 (the drain D of the MOS transistor or the collector C of the transistor) through driver ON3. The discharge resistor R1 connected in series with switching transistor T1 is connected to the two ends of the IGBT arms (MOS1 and MOS2 connected in series). The current Hall sensor Isen terminal of the photovoltaic inverter is connected to the control terminal of switching transistor T2 (the gate G of the MOS transistor or the base B of the transistor) through driver ON1. The DSP control output terminal is connected to the control terminal of switching transistor T2 (the gate G of the MOS transistor or the base B of the transistor) through driver ON2. The other end of the conduction terminal of switching transistor T2 is grounded. The switching transistors T1 and T2 can be designed as MOSFETs, transistors, or relay switches as required.

[0024] In the circuit described, the switching transistor T1, which controls the opening of the discharge circuit, is a MOSFET. By comparing the current-sink voltage (S) of the existing upper IGBT in the flying crossover circuit with the current-sink voltage (D), MOSFET T1 is driven to conduct, discharging through resistor R1 to capacitor C1. The output signal of the Hall effect sensor in the main circuit is sampled to control the turn-off of MOSFET T1. The inverter's own DSP samples the output signal of the Hall effect sensor in the main circuit and controls MOSFET T1 to turn off. A discharge resistor R1, which is a power resistor, is connected in series with MOSFET T1. It is used for current limiting protection and clamping voltage control of the MOSFET in the IGBT. Here, T1 is the preferred MOSFET.

[0025] After T1 is turned on, if the Hall sensor detects a positive current flowing through it and that is greater than the set value, then the driver (ON1) turns on transistor T2. After T2 is turned on, T1 is turned off, and the discharge circuit is cut off. At this time, it can be assumed that this MPPT is connected to a solar panel and its voltage is lower than that of the BUS or other MPPTs.

[0026] Figure 4The circuit shown is a simplified diagram intended to illustrate the basic principles and application methods. The device contains transistors T1 and R1 forming the main discharge circuit. Comparator COMP1, connected to MOS1 via the flying transistor, primarily detects the voltage difference between the current and current channels (DS) of MOS1. If node 2 of MOS1 is greater than 1, comparator COMP1 outputs a high level to driver ON3 to control T1 to turn on. After turning on, T1, R1, and L1 are connected in series and in parallel with the input capacitor C1. The resistance value of R1 can be selected according to actual conditions. The conduction of T1 forms a circuit with C1 to clamp the PV voltage. After T1 turns on, if the Hall effect sensor detects a positive current flowing through it and it exceeds a set value, driver ON1 turns on transistor T2. Simultaneously, a signal is sent to the DSP for current sampling. After T2 turns on, T1 turns off, and the discharge circuit is cut off. At this point, it can be assumed that this MPPT is connected to a solar panel and its voltage is lower than that of the BUS or other MPPTs. The inverter's own DSP can also issue commands according to user settings to control the shutdown of this discharge unit module via driver ON2. Using the principles described above, when the PV input is left floating, the port voltage can be clamped to 0V or below a safe voltage. It automatically shuts off when a solar panel is normally connected, or can be intentionally disabled to save power. Drivers ON1, ON2, and ON3 can be any type of isolation driver, such as an optocoupler or a pulse transformer.

[0027] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A discharge circuit for flying capacitor boosters, wherein multiple flying capacitor boosters are connected to a DC power supply, characterized in that, The discharge circuit is connected after the input inductor and current sensor in each group of flying capacitor BOOST, and before the first and second high-frequency switches in the upper and lower bridge arm circuits of the flying capacitor BOOST. The discharge circuit includes a detection unit, a driver ON3, a series switch T1 connected to the two ends of the upper and lower bridge arm circuits connected in series with the first and second high-frequency switches, and a current limiting clamping element R1. The detection unit detects the voltage difference across the first high-frequency switch of the upper bridge arm, triggers the driver ON3 to turn on the switch T1, and the discharge circuit is turned on; the detection unit detects the input current value of the flying capacitor BOOST, controls the switch T1 to turn off, and the discharge circuit is turned off. The detection unit includes a comparator COMP1. The input terminals of comparator COMP1 are connected to the two terminals of the first high-frequency switch. The positive input terminal of comparator COMP1 is connected to the series connection point of the first and second high-frequency switches in the upper and lower bridge arm circuits. The output of comparator COMP1 is connected to the control terminal of switch T1 through driver ON3. By comparing the drain (D) and source (S) voltages of the first high-frequency switch, if the source (S) voltage is greater than the drain (D) voltage, switch T1 is driven to turn on. The input capacitor C1 connected in parallel across the DC power supply is discharged through the current-limiting clamping element R1. The output signal of the Hall effect sensor in the sampling main circuit is used to control the turn-off of switch T1. The DC power supply can be any one of a photovoltaic cell, an energy storage battery, or a DC charging and discharging circuit. The detection unit includes a switch T2, a flying capacitor BOOST current sensor current signal is sent to a driver ON1, the output of driver ON1 is connected to the control terminal of switch T2, and the two ends of switch T2 are connected in parallel to the control terminal of switch T1 and the ground terminal.

2. The discharge circuit for a flying capacitor boost as described in claim 1, characterized in that, The current sensor is a Hall sensor, and the output of the Hall sensor is connected to the driver ON1 and the flying capacitor BOOST control unit DSP.

3. The discharge circuit for a flying capacitor boost as described in claim 2, characterized in that, The flying capacitor BOOST control unit DSP is connected to the control terminal of the switching transistor T2 via driver ON2.

4. The discharge circuit for a flying capacitor boost as described in claim 1, characterized in that, The first high-frequency switching transistor and the second high-frequency switching transistor are IGBTs or MOSFETs, and the switching transistors T1 and T2 are any one of IGBTs, MOSFETs, and relay switches.

5. The discharge circuit for a flying capacitor boost as described in claim 4, characterized in that, The current-limiting clamping element R1, which is connected in series with the switching transistor T1, is a power resistor that clamps the flying capacitor BOOST circuit under static conditions.

6. The discharge circuit for a flying capacitor boost according to claim 3, characterized in that, The drivers ON1, ON2, and ON3 are either optocouplers or pulse transformers.

7. A control method for the discharge circuit of the flying capacitor BOOST as described in claim 1, characterized in that, In the discharge circuit, the comparator COMP1 outputs a high level to the driver ON3 to control the switch T1 to turn on. After turning on, the switch T1, the current-limiting clamping element R1, and the input inductor are connected in series and in parallel with the input capacitor C1 to form a discharge circuit for the input capacitor C1, clamping the input PV voltage of the flying capacitor BOOST. After the switch T1 is turned on, if the Hall sensor of the flying capacitor BOOST detects a positive current passing through it and it is greater than the set value, the driver ON1 turns on the switch T2. At the same time, the signal is sent to the DSP for current sampling. After the switch T2 is turned on, the switch T1 is turned off, and the discharge circuit is cut off.

8. The control method for the discharge circuit of the flying capacitor BOOST according to claim 7, characterized in that, After the switch T1 is turned on, the DSP outputs a control signal to the driver ON2 based on the current value detected by the Hall sensor of the flying capacitor BOOST. The driver ON2 turns on the switch T2 and turns off the switch T1 at the same time, thus cutting off the discharge circuit.

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