A bus capacitor DC soft start system

Abstract

A DC soft-start system for bus capacitors, relating to the field of power electronics technology, enables soft-start charging of bus capacitors. The system includes a drive-on subsystem, a drive-off subsystem, and a bus capacitor soft-start circuit. The drive-on subsystem includes a drive-on energy supply unit, a drive-on unit, and a drive undervoltage lockout unit. The bus capacitor soft-start circuit is used to charge the bus capacitor. The bus capacitor soft-start circuit includes a power switch and a bus capacitor. The power switch is used to control the charging of the bus capacitor. The drive-off subsystem is used to drive the power switch to turn off. The drive-on energy supply unit provides drive voltage and current to the drive terminal of the power switch. The drive-on unit transmits the drive voltage to the drive undervoltage lockout unit. The drive undervoltage lockout unit disconnects the power switch when the drive voltage is insufficient.

Description

Technical Field

[0001] This application relates to the field of power electronics technology, and in particular to a bus capacitor DC soft-start system. Background Technology

[0002] When a photovoltaic energy storage inverter is not connected to the grid and is only connected to the battery, to start the inverter, the bus capacitor voltage must first be charged to near the battery voltage before closing the contactor or circuit breaker connecting the battery and the bus capacitor. Otherwise, a huge current surge will occur, damaging electronic components and endangering the safety of equipment operation. Summary of the Invention

[0003] This application provides a DC soft-start system for bus capacitors, which can realize the charging soft start of bus capacitors.

[0004] To achieve the above objectives, the embodiments of this application provide the following technical solutions:

[0005] In a first aspect, a DC soft-start system for a bus capacitor is provided, comprising a drive-on subsystem, a drive-off subsystem, and a bus capacitor soft-start circuit; the drive-on subsystem includes a drive-on energy supply unit, a drive-on unit, and a drive undervoltage lockout unit; the bus capacitor soft-start circuit is used to charge the bus capacitor; the bus capacitor soft-start circuit includes a power switch and a bus capacitor, the power switch being used to control the charging of the bus capacitor; the drive-off subsystem is used to drive the power switch to turn off; the drive-on energy supply unit is used to provide drive voltage and current to the drive terminal of the power switch; the drive-on unit is used to transmit the drive voltage to the drive undervoltage lockout unit; the drive undervoltage lockout unit is used to disconnect the power switch when the drive voltage of the power switch is insufficient.

[0006] In some embodiments, the drive undervoltage lockout unit includes: a first transistor, a fourth resistor, a fifth resistor, a second Zener diode, a sixth resistor, and a third capacitor; the first terminal of the first transistor is connected to the drive turn-on unit; the third terminal of the first transistor is sequentially connected to the fifth resistor and the cathode of the second Zener diode; the fourth resistor is connected in parallel with the first terminal and the third terminal of the first transistor; the second terminal of the first transistor is connected to the drive terminal of the power switch, one end of the sixth resistor, and one end of the third capacitor; the other end of the sixth resistor is connected to the other end of the third capacitor, the first terminal of the power switch, and the anode of the second Zener diode.

[0007] In some embodiments, the drive undervoltage lockout unit includes: a first transistor, a second Zener diode, a comparator, a fourth resistor, a fifth resistor, a sixth resistor, an eleventh resistor, a twelfth resistor, and a third capacitor; the first terminal of the first transistor is connected to the drive turn-on unit; the first terminal of the first transistor is also connected to the first power supply terminal of the comparator, the first terminal of the fifth resistor, and the first terminal of the eleventh resistor; the second terminal of the fifth resistor is connected to the positive input terminal of the comparator and the cathode of the second Zener diode; the second terminal of the eleventh resistor is connected to the first terminal of the twelfth resistor and the negative input terminal of the comparator; the third terminal of the first transistor is connected to the output terminal of the comparator; the fourth resistor is connected in parallel with the first and third terminals of the first transistor; the second terminal of the first transistor is connected to the drive terminal of the power switch, one end of the sixth resistor, and one end of the third capacitor; the other end of the sixth resistor is connected to the other end of the third capacitor, the first terminal of the power switch, the anode of the second Zener diode, the second terminal of the twelfth resistor, and the second power supply terminal of the comparator.

[0008] In some embodiments, the drive undervoltage lockout unit includes: a first transistor, a comparator, a fifth resistor, an eleventh resistor, a fourth resistor, a sixth resistor, and a third capacitor; the first terminal of the first transistor is connected to the drive turn-on unit, the positive power supply terminal of the comparator, and the first terminal of the fifth resistor; the second terminal of the fifth resistor is connected to the negative input terminal of the comparator and the first terminal of the eleventh resistor; the third terminal of the first transistor is connected to the output terminal of the comparator; the fourth resistor is connected in parallel with the first and third terminals of the first transistor; the second terminal of the first transistor is connected to the drive terminal of the power switch, one end of the sixth resistor, and one end of the third capacitor; the other end of the sixth resistor is connected to the other end of the third capacitor, the first terminal of the power switch, the second end of the eleventh resistor, and the negative power supply terminal of the comparator.

[0009] In some embodiments, the drive-on power supply unit includes: a first resistor, a second resistor, a first capacitor, and a first Zener diode; the drive-on unit includes a switch; the first resistor, the second resistor, and the first capacitor are connected in sequence; the first Zener diode is connected in parallel with the first capacitor; the first resistor is connected to the soft-start circuit of the bus capacitor; the connection point between the second resistor and the first capacitor is connected to the first terminal of the switch; and the first capacitor is connected to the first terminal of the power switch transistor.

[0010] In some embodiments, the drive undervoltage lockout unit includes: an integrated chip, a fifth resistor, an eleventh resistor, a twelfth resistor, a first transistor, a fourth resistor, a sixth resistor, and a third capacitor. The integrated chip has an input hysteresis voltage setting function and includes a first comparator and a second comparator internally. The first terminal of the first transistor is connected to the drive turn-on unit, the positive power supply terminal of the integrated chip, and the first terminal of the fifth resistor. The second terminal of the fifth resistor is connected to the negative input terminal of the first comparator inside the integrated chip and the first terminal of the eleventh resistor. The second terminal of the eleventh resistor is connected to the first terminal of the twelfth resistor and the positive input terminal of the second comparator inside the integrated chip. The third terminal of the first transistor is connected to the output terminal of the integrated chip. The fourth resistor is connected in parallel with the first and third terminals of the first transistor. The second terminal of the first transistor is connected to the drive terminal of the power switch, one end of the sixth resistor, and one end of the third capacitor. The other end of the sixth resistor is connected to the other end of the third capacitor, the first terminal of the power switch, the second end of the twelfth resistor, and the power supply ground terminal of the integrated chip.

[0011] In some embodiments, the drive shutdown subsystem includes a drive latch-up unit; the drive latch-up unit includes: a fourth Zener diode, a third transistor, and a tenth resistor; the anode of the fourth Zener diode is connected to the first terminal of the third transistor; the second terminal of the third transistor is connected to one end of the tenth resistor, and the other end of the tenth resistor is connected to the drive terminal of the power switch; the third terminal of the third transistor is connected to the first terminal of the power switch, and the cathode of the fourth Zener diode is connected to the drain of the power switch.

[0012] In some implementations, the resistance of the sixth resistor is greater than 100 times the resistance of the tenth resistor.

[0013] In some embodiments, the drive shutdown subsystem further includes a drive unlocking unit; the drive unlocking unit includes a third diode; the connection between the cathode of the fourth Zener diode and the drain of the power switch includes: the cathode of the third diode is connected to the drain of the power switch, and the anode of the third diode is connected to the cathode of the fourth Zener diode.

[0014] In some embodiments, the first transistor is a PNP transistor, with the first electrode being the emitter, the second electrode being the collector, and the third electrode being the base; or, the first transistor is a PMOS field-effect transistor, with the first electrode being the source, the second electrode being the drain, and the third electrode being the gate.

[0015] The above system not only ensures the normal soft start of the bus capacitor, but also improves reliability by adding the undervoltage lockout unit.

[0016] In a second aspect, a photovoltaic energy storage inverter is provided, including a controller and the bus capacitor DC soft-start system described in the first aspect, wherein the controller is electrically connected to the bus capacitor soft-start system.

[0017] In some implementations, the controller is a microcontroller.

[0018] In some implementations, the controller is a digital signal processor.

[0019] In some implementations, the controller is a field-programmable gate array (FPGA). Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the DC soft starter system structure provided in the embodiments of this application;

[0021] Figure 2 This is a schematic diagram of a bus capacitor DC soft start system provided in another embodiment of this application;

[0022] Figure 3 This is a schematic diagram of a bus capacitor DC soft start system provided in another embodiment of this application;

[0023] Figure 4 This is a schematic diagram of a bus capacitor DC soft start system provided in another embodiment of this application;

[0024] Figure 5 This is a schematic diagram of a bus capacitor DC soft start system provided in another embodiment of this application. Detailed Implementation

[0025] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0026] It should be noted that although a logical order is shown in the flowchart, in some cases, the steps shown or described may be performed in a different order than that shown in the flowchart. The terms "first," "second," etc., in the specification, claims, and the aforementioned drawings are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence.

[0027] When a photovoltaic energy storage inverter is not connected to the grid and is only connected to the battery, to start the inverter, the bus capacitor voltage must first be charged to near the battery voltage before closing the contactor or circuit breaker connecting the battery and the bus capacitor. Otherwise, a huge current surge will occur, damaging electronic components and endangering the safety of equipment operation.

[0028] To address this issue, related technology 1 proposes using a switch and a current-limiting resistor to achieve pre-charge soft starting of the bus capacitor. However, this technology does not specify the implementation method of the switch, which can generally only be understood as a mechanical switch, such as a relay, circuit breaker, or contactor. For high-voltage energy storage inverters above several hundred volts, DC contactors are usually required, but DC contactors are costly, bulky, and have high drive losses.

[0029] Related technology 2 proposes a method of pre-charging the capacitor using a transformer, but this method is relatively complex to implement.

[0030] Based on this, this application provides a DC cold start system for a bus capacitor, which uses a power switching transistor connected in series with a current-limiting and power-limiting resistor to form the main charging current path from the battery to the bus capacitor. This system ensures that the high-voltage battery provides a soft-start pre-charge function to the bus capacitor, while also reducing circuit size and cost, and offering high reliability. The power switching transistor refers to a transistor or field-effect transistor that can withstand large currents, has low leakage current, and exhibits good saturation conduction and cutoff characteristics under certain conditions. Its function is emphasized as an electronic switch, operating in both on and off states to control the circuit's on / off state.

[0031] Reference Figure 1 Compared to traditional solutions, this application embodiment adds a drive undervoltage lockout unit ( Figures 1 to 5 (As shown in dashed box 3 in any one of the embodiments). During the driving of power switch Q2, if the voltage of the first capacitor C1 drops or is low, the second Zener diode Z2 is turned off, and the first transistor Q1 is turned off. Due to the small size of the third capacitor C3, the gate voltage of power switch Q2 also drops rapidly, and power switch Q2 is quickly turned off. Without the drive latch-up unit included in dashed box 3, the system does not monitor the voltage of the first capacitor C1. When the voltage of the first capacitor C1 is low and switch S1 is still in the on state, power switch Q2 will enter an incomplete conduction state. When the charging current of power switch Q2 to bus capacitor C4 is large, it will cause large losses or even damage to power switch Q2. The embodiment of this application adds undervoltage latch-up, which can effectively avoid the incomplete conduction of power switch Q2 and greatly reduce the risk of power switch Q2 being damaged due to insufficient voltage of the first capacitor C1.

[0032] Reference Figure 1The bus capacitor DC cold start system includes: a drive turn-on subsystem, a drive turn-off subsystem, and a bus capacitor soft start circuit.

[0033] The bus capacitor soft-start circuit is used to charge the bus capacitors. For example... Figure 1 As shown in the dashed box 1, the bus capacitor soft-start circuit includes: a power interface, a bus capacitor C4, a first diode D1, a power switch Q2, a second diode D2, and a bus resistor R7. The power interface includes a positive power interface (not shown) and a negative power interface (not shown). The positive power interface, the first diode D1, the power switch Q2, the second diode D2, the bus resistor R7, the bus capacitor C4, and the negative power interface are connected sequentially. The bus resistor R7 refers to the resistor in the bus capacitor soft-start circuit.

[0034] For example, the power switch Q2 can be implemented as an insulated gate bipolar transistor (IGBT), a metal-oxide-semiconductor field-effect transistor (MOSFET), a transistor, a silicon carbide MOS, or a GANFET.

[0035] For example, if the power switch Q2 is a MOSFET, then the cathode of the first diode D1 is connected to the drain of the power switch Q2. As another example, if the power switch Q2 is an IGBT or a transistor, then the cathode of the first diode D1 is connected to the collector of the power switch Q2. The positive and negative power supply interfaces can be connected to an external power supply. For example, refer to... Figure 1 The external power source is indicated by Bat. C4 can be charged via the power connector.

[0036] The drive-on subsystem is used to drive the power switching transistors to turn on. The drive-on subsystem includes a drive-on energy supply unit, a drive-on unit, and a drive-undervoltage lockout unit.

[0037] The drive-on energy supply unit is used to provide drive voltage and current to the drive electrode of the power switching transistor. For example... Figure 1 As shown in the dashed box 2, the drive-on energy supply unit consists of a series resistor and a drive energy storage capacitor connected in series, and the drive energy storage capacitor is connected in parallel with a voltage limiting functional component.

[0038] Specifically, the first resistor R1, the second resistor R2, and the first capacitor C1 are connected in sequence. The first Zener diode Z1 is connected in parallel with the first capacitor C1. The first resistor R1 is connected to the cathode of the first diode D1. The connection point of the second resistor R2 and the first capacitor C1 is connected to one end of the switch S1. When the power supply connected to the bus capacitor soft-start circuit is turned on, the first capacitor C1 is charged through the first resistor R1 and the second resistor R2, and the first Zener diode Z1 limits the charging voltage of the first capacitor C1. Current flows to the switch S1 through the first resistor R1 and the second resistor R2.

[0039] For example, switch S1 is a mechanical switch such as a relay or a push button. Even more exemplarily, switch S1 is an electronic switch such as a controlled optocoupler or a photo-metal-oxide-semiconductor solid-state relay (PhotoMOS).

[0040] In some embodiments, the first resistor R1 and the second resistor R2 are implemented using a single resistor. For example, the first resistor R1 and the second resistor R2 are implemented as the same resistor.

[0041] In other embodiments, the first resistor R1 and the second resistor R2 are implemented using multiple resistors. For example, the first resistor R1 is composed of two resistors, and the second resistor R2 is composed of two resistors.

[0042] The drive turn-on unit is used to transmit the drive voltage to the drive undervoltage lockout unit. For example... Figure 1 As shown in the dashed box 4, the drive activation unit consists of a switch S1, a third resistor R3, and a second capacitor C2. The other end of switch S1 is connected sequentially to the third resistor R3 and the second capacitor C2. When switch S1 is closed, the current flows to the third resistor R3. The third resistor R3 performs current limiting. The second capacitor C2 performs filtering. The drive activation unit can receive drive activation commands or signals through the switch, and after the switch is closed, the drive voltage is transmitted to the drive undervoltage lockout unit.

[0043] In some embodiments, the drive-on unit may not include the second capacitor C2 used for filtering.

[0044] The undervoltage lockout unit is used to promptly disconnect the power switch when the drive voltage is insufficient. In other words, the undervoltage lockout unit disconnects the power switch when the actual drive voltage received by the power switch is less than the required drive voltage. Figure 1As shown in the dashed box 3, the drive undervoltage lockout unit consists of a drive voltage amplitude discrimination function component and a drive energy output component. The drive undervoltage lockout unit can monitor the level of the drive voltage amplitude supplied to the power switch in real time and disconnect the power switch in time when the drive voltage is insufficient.

[0045] The undervoltage lockout drive unit includes a first transistor Q1, a fourth resistor R4, a fifth resistor R5, a second Zener diode Z2, a sixth resistor R6, and a third capacitor C3. The first terminal of the first transistor Q1 is connected to the drive turn-on unit. The third terminal of the first transistor Q1 is sequentially connected to the fifth resistor R5 and the cathode of the second Zener diode Z2. The fourth resistor R4 is connected in parallel with both the first and third terminals of the first transistor Q1. The second terminal of the first transistor Q1 is connected to the drive terminal (or gate terminal) of the power switch Q2, one end of the sixth resistor R6, and one end of the third capacitor C3. The other end of the sixth resistor R6 is connected to the other end of the third capacitor C3, the first terminal of the power switch Q2, the first capacitor C1, the first Zener diode Z1, the second capacitor C2, and the anode of the second Zener diode Z2, serving as a common reference point for the drive voltage of the power switch Q2.

[0046] In some embodiments, the positions of the second Zener diode Z2 and the fifth resistor R5 can be interchanged. That is, the third terminal of the first transistor Q1 is connected in sequence to the second Zener diode Z2 and the fifth resistor R5.

[0047] In some embodiments, the first terminal of the first transistor Q1 is connected to the connection point of the third resistor R3 and the second capacitor C2 in the drive turn-on unit.

[0048] The sixth resistor R6 and the third capacitor C3 provide filtering functionality. The fifth resistor R5 limits the current in the path containing the first transistor Q1 and the second Zener diode Z2. The second Zener diode Z2 is used to determine the threshold of the drive voltage. When the voltage at the input terminal (first electrode) of the first transistor Q1 increases, causing the voltage of the second Zener diode Z2 to reach the turn-on voltage and trigger conduction, the first transistor Q1 also turns on. After the first transistor Q1 turns on, the power switch Q2 receives the drive voltage. When this drive voltage is higher than the turn-on threshold voltage of the power switch Q2, the power switch Q2 begins to conduct and charges the bus capacitor C4.

[0049] In some embodiments, the regulated voltage of the second Zener diode Z2 can be adjusted. For example, this can be achieved by connecting multiple Zener diodes in series. Another example is by making the fifth resistor R5 an adjustable resistor. The method for adjusting the regulated voltage of the second Zener diode can be found in related technologies and will not be elaborated further here.

[0050] The gate voltage applied to the power switch Q2 can be adjusted by regulating the voltage of the second Zener diode Z2. When the voltage at the first terminal of the first transistor Q1 decreases, the voltage of the second Zener diode Z2 also decreases. When the voltage at the first terminal of the first transistor Q1 falls below the conduction threshold of the second Zener diode Z2 (an example of the second threshold), both the second Zener diode Z2 and the first transistor Q1 are turned off. The voltage of the third capacitor C3 is discharged by the sixth resistor R6, causing the gate drive voltage of the power switch Q2 to drop rapidly below its turn-on threshold voltage, and the power switch Q2 is turned off. Therefore, the gate drive voltage of the power switch Q2 is controlled by two stages: switch S1 and the first transistor Q1. S1 is externally controlled, while the first transistor Q1, in conjunction with the fourth resistor R4, the fifth resistor R5, and the second Zener diode Z2, achieves automatic undervoltage lockout. When the terminal voltage of the first capacitor C1 is lower than the threshold set by the second Zener diode Z2, the switch S1 cannot apply the drive voltage to the gate of the power switch Q2, ensuring that the power switch Q2 will not operate in an undersaturated state with a low drive voltage, thus reducing the risk of damage to the power switch Q2 due to high losses.

[0051] In some embodiments, the positions of the fifth resistor R5 and the second Zener diode Z2 can be interchanged. For example, the third terminal of the first transistor Q1 is connected in sequence with the Zener diode Z2 and the fifth resistor R5.

[0052] In some embodiments, the drive undervoltage lockout unit may not include a fifth resistor R5, which has a current-limiting function.

[0053] In some embodiments, the drive undervoltage lockout unit may not include the sixth resistor R6 and the third capacitor C3, which have filtering functions.

[0054] In some embodiments, the first transistor Q1 is a PNP transistor, with the first electrode of the first transistor Q1 being the emitter, the second electrode being the collector, and the third electrode being the base.

[0055] In other embodiments, the first transistor Q1 is a PMOS field-effect transistor, with the first electrode of the first transistor Q1 being the source, the second electrode being the drain, and the third electrode being the gate.

[0056] The drive shutdown subsystem is used to drive the power switch transistor to turn off. The drive shutdown subsystem includes a drive latching unit and a drive unlocking unit. In some embodiments, the drive shutdown subsystem further includes a drive shutdown energy supply unit.

[0057] The drive-off energy supply unit provides drive voltage and current to the drive-lock unit. See also Figure 1The dashed box 5 shown illustrates the drive-off power supply unit, which includes an eighth resistor R8, a ninth resistor R9, and a fifth capacitor C5. One end of the eighth resistor R8 is connected to the cathode of the first diode D1, and the other end of the eighth resistor R8 is connected to one end of the ninth resistor R9. The other end of the ninth resistor R9 is connected to one end of the fifth capacitor C5, and the other end of the fifth capacitor C5 is connected to the common reference point of the drive voltage of the aforementioned power switch Q2. When the power supply Bat connected to the bus capacitor soft-start circuit is turned on, current flows through the eighth resistor R8 and the ninth resistor R9 to the fifth capacitor C5. The fifth capacitor C5 is charged through the eighth resistor R8 and the ninth resistor R9.

[0058] Similar to the first resistor R1 and the second resistor R2 mentioned above, the eighth resistor R8 and the ninth resistor R9 can be implemented using a single resistor or multiple resistors.

[0059] In some embodiments, the drive to shut down the power supply unit further includes a third Zener diode Z3. The third Zener diode Z3 is connected in parallel with the fifth capacitor. The third Zener diode Z3 limits the charging voltage of the fifth capacitor C5.

[0060] The drive-lock unit is used to accelerate the shutdown of the power switch in the bus capacitor soft-start circuit. See also Figure 1 The dashed box 6 shown indicates that the drive lockout unit includes a series drive resistor and a drive lockout functional component.

[0061] The anode of the fourth Zener diode Z4 is connected to the first terminal of the third transistor Q3. The second terminal of the third transistor Q3 is connected to one end of the tenth resistor R10, and the other end of the tenth resistor R10 is connected to the gate of the power switch Q2. The third terminal of the third transistor Q3 is connected to the first terminal of the power switch Q2, that is, the third terminal of the third transistor Q3 is connected to the common reference point of the drive voltage of the power switch Q2. The cathode of the fourth Zener diode Z4 is connected to the drive-off power supply unit.

[0062] The power switch Q2 can be slowly turned off by gradually discharging the energy of the third capacitor C3 through the sixth resistor R6. With the addition of the drive-lock unit (dashed box 6), when the third transistor Q3 is turned on, it's equivalent to adding a discharge circuit with the tenth resistor R10 to the third capacitor C3. The resistance of R10 is 50-1000 times smaller than that of R6 (for example, R10 is 10 kilohms, and R6 is 1000 kilohms). Therefore, by setting up the drive-lock unit, the discharge of the third capacitor C3 can be accelerated, thus accelerating the turn-off of the power switch Q2.

[0063] In some embodiments, the third transistor Q3 is a bipolar transistor, with the first electrode being the emitter, the second electrode being the collector, and the third electrode being the base.

[0064] The drive unlocking unit is used to accelerate the discharge of energy from the fifth capacitor C5 in the drive energy supply unit when the power switch Q2 is turned on, thereby speeding up the conduction process of the power switch Q2. See also... Figure 1 The dashed box 7 shown indicates that the drive unlocking unit includes a fast discharge component.

[0065] For example, the fast discharge component is implemented using a third diode D3. The positive terminal of the third diode D3 is connected to the drive-off power supply unit through the connection point of the ninth resistor R9 and the fifth capacitor C5. The negative terminal of the third diode D3 is connected to the drive-off power supply unit through a connection with the eighth resistor.

[0066] In some embodiments, the resistance of the sixth resistor R6 is much greater than the resistance of the tenth resistor R10. For example, the resistance of the sixth resistor R6 is greater than 100 times the resistance of the tenth resistor R10. For instance, the resistance of the sixth resistor R6 is 1000 kΩ, and the resistance of the tenth resistor R10 is 10 kΩ. Or, for another example, the resistance of the sixth resistor R6 is 500 kΩ, and the resistance of the tenth resistor R10 is 5 kΩ. When the voltage across the fourth Zener diode Z4 exceeds its forward voltage, the fourth Zener diode Z4 turns on, and the third transistor Q3 turns on. When the third transistor Q3 turns on, the tenth resistor R10 is connected in parallel between the gate and emitter of the power switch Q2. That is, the gate of the power switch Q2 is connected to the emitter by the tenth resistor R10, which is connected in parallel with the sixth resistor R6 and the third capacitor C3. This causes the resistance across the third capacitor C3 to decrease rapidly, allowing the voltage across the third capacitor C3 to discharge quickly, and thus the drive voltage of the power switch Q2 to discharge. This ensures that the power switch Q2 is reliably turned off, or in other words, that the power switch Q2 is locked out.

[0067] In some embodiments, the resistance of the tenth resistor R10 is much greater than the resistance of the third resistor R3. For example, the resistance of the tenth resistor R10 is greater than five times the resistance of the third resistor R3. For instance, the resistance of the third resistor R3 is 100 ohms, and the resistance of the tenth resistor R10 is 5 kiloohms. Or, for another example, the resistance of the third resistor R3 is 1 kiloohm, and the resistance of the tenth resistor R10 is 5 kiloohms.

[0068] When power switch Q2 needs to be turned on, the gate voltage of power switch Q2 is quickly established because the current flowing out of the first transistor Q1 is much greater than the discharge current of the tenth resistor R10. At this time, the collector voltage of power switch Q2 drops rapidly, and simultaneously pulled low by the third diode D3, the third transistor Q3 can be quickly turned off. The third diode D3 achieves fast unlocking.

[0069] The working principle of the embodiments of this application will be explained below by describing two states after the external power supply Bat is turned on: switch S1 is open and switch S1 is on.

[0070] When switch S1 is in the open state, the current is divided into two main paths:

[0071] Path 1: Current flows from the positive terminal of the external power supply Bat, through the first diode D1, the eighth resistor R8, the ninth resistor R9, the fifth capacitor C5, the second diode D2, the bus resistor R7, and the bus capacitor C4, returning to the negative terminal of the external power supply Bat. The main purpose of this path is to charge the fifth capacitor C5 in the drive-off power supply unit. In some embodiments, the value of the fifth capacitor C5 is 100nF, C1 = 1000uF, C2 = 1-10uF, and C3 = 0.1-1uF. Due to the small capacitance of the fifth capacitor C5, it will charge quickly and trigger the fourth Zener diode Z4 and the third transistor Q3 to conduct. This reliably turns off the power switch Q2 through the tenth resistor R10.

[0072] Path 2: Current flows from the positive terminal of the external power supply Bat, through the first diode D1, the first resistor R1, the second resistor R2, the first capacitor C1, the second diode D2, the bus resistor R7, and the bus capacitor C4, returning to the negative terminal of the external power supply Bat. The main purpose of this path is to charge the first capacitor C1 in the drive turn-on energy supply unit, storing sufficient drive energy for the subsequent drive power switch Q2. In some embodiments, the first capacitor C1 is a capacitor in the thousands of uF range. For example, the value of the first capacitor C1 is 2000 uF, the value of the second capacitor C2 is 10 uF, the value of the third capacitor C3 is 20 uF, and the value of the fifth capacitor C5 is 100 nF. The first capacitor C1 is 100-1000 times larger than the second capacitor C2, the third capacitor C3, and the fifth capacitor C5. Due to the large capacitance of the first capacitor C1, the voltage at the terminal of the first capacitor C1 rises slowly. After rising to the conduction voltage of the first Zener diode Z1, the voltage at the terminal of the first capacitor C1 no longer rises and remains constant.

[0073] In some embodiments, the forward voltage of the first Zener diode Z1 is higher than a first threshold and lower than the highest threshold withstand voltage of the power switch Q2. For example, the first threshold is 80% of the highest threshold withstand voltage of the power switch Q2. For instance, if the threshold voltage VGSmax of the power switch Q2 is 20V, then the Zener voltage of Z1 can be 18V. This ensures the gate voltage of the power switch Q2 is safe and reliable. In some embodiments, the forward voltage of the second Zener diode Z2 is lower than that of the first Zener diode Z1 and higher than the lowest turn-on threshold voltage of the power switch Q2.

[0074] When switch S1 is in the ON state:

[0075] In some embodiments, when the voltage of the first capacitor C1 approaches the voltage that triggers the first Zener diode Z1 to turn on, that is, when the first capacitor C1 is nearly fully charged, the switch S1 turns on.

[0076] In some embodiments, the controller determines the time required for the first capacitor C1 to charge to the regulated voltage value of the first Zener diode Z1, i.e., the time it takes for the first capacitor C1 to fully charge. When the first capacitor C1 is nearly fully charged or fully charged, switch S1 is turned on. This ensures that the voltage of the first capacitor C1 is sufficiently high, providing ample energy, thereby enabling the bus capacitor C4 to complete its soft start-up in a single charge cycle.

[0077] In some embodiments, the switch S1 can be controlled by a controller to turn on and off.

[0078] After switch S1 is turned on, the first transistor Q1 turns on, simultaneously triggering the power switch Q2 to turn on. The soft-start circuit Bat of bus capacitor C4, the first diode D1, the power switch Q2, the second diode D2, the bus resistor R7, and the bus capacitor C4 are connected, and the external power supply Bat charges the bus capacitor C4. When switch S1 is on, current first flows through the third resistor R3, the first transistor Q1, the fifth resistor R5, and the second Zener diode Z2. Afterward, the first transistor Q1 conducts normally. The drive current then flows through the third resistor R3 and the first transistor Q1, causing the gate voltage of the power switch Q2 to rise rapidly, and Q2 quickly turns on. The collector voltage of the power switch Q2 drops rapidly, and the third diode D3 quickly turns off the third transistor Q3. The fourth resistor R4 plays a role in reliably turning off the first transistor Q1 when it turns off. During the conduction of the power switch Q2, the first capacitor C1 has no energy supply, and its voltage drops slowly. When the voltage across the first capacitor C1 drops to the point where the second Zener diode Z2 is turned off, the first transistor Q1 is turned off. Because the third capacitor C3 has a small capacitance, the gate voltage of the power switch Q2 also drops rapidly, turning Q2 off.

[0079] Without the undervoltage lockout unit included in dashed box 3, since the voltage of the first capacitor C1 is not monitored, if S1 is still conducting when the voltage of C1 is low, the power switch Q2 will enter an undersaturated conduction state. When the charging current flowing through the power switch Q2 to the bus capacitor C4 is large, it will cause significant losses in the power switch Q2 and may even damage Q2. Therefore, the undervoltage lockout unit in dashed box 3 plays an important protective role for the power switch Q2.

[0080] In some embodiments, the drive undervoltage lockout unit can be implemented as follows: Figure 2The dashed box 3 in the diagram. The drive undervoltage lockout unit includes a drive voltage discrimination circuit, a fourth resistor R4, a first transistor Q1, a sixth resistor R6, and a third capacitor C3. The drive voltage discrimination circuit uses a comparator U1. The drive voltage discrimination circuit includes an eleventh resistor R11, a twelfth resistor R12, a fifth resistor R5, a second Zener diode Z2, and a comparator U1. The first terminal of the first transistor Q1 is connected to the drive turn-on unit. The first terminal of the first transistor Q1 is also connected to the first power supply terminal of the comparator U1, the first terminal of the fifth resistor R5, and the first terminal of the eleventh resistor R11. The second terminal of the fifth resistor is connected to the positive input terminal of the comparator U1 and the cathode of the second Zener diode Z2. The second terminal of the eleventh resistor R11 is connected to the first terminal of the twelfth resistor and the negative input terminal of the comparator U1. The third terminal of the first transistor Q1 is connected to the output terminal of the comparator U1. The fourth resistor R4 is connected in parallel with the first and third terminals of the first transistor Q1. The second terminal of the first transistor Q1 is connected to the driving terminal (also called the gate) of the power switch Q2, one end of the sixth resistor R6, and one end of the third capacitor C3. The other end of the sixth resistor R6 is connected to the other end of the third capacitor C3, the first terminal of the power switch Q2, the first capacitor C1, the first Zener diode Z1, the second capacitor C2, the anode of the second Zener diode Z2, the second terminal of the twelfth resistor R12, and the second power supply terminal of the comparator U1. The second Zener diode Z2 is used to generate the comparison reference voltage.

[0081] In some embodiments, Figure 2 The second Zener diode Z2 in the chip is replaced with a reference chip.

[0082] In some embodiments, the drive undervoltage lockout unit can be implemented as follows: Figure 3 The dashed box 3 in the diagram shows the driving voltage discrimination circuit for the undervoltage lockout unit, which uses an integrated chip U1 with a built-in reference. The first terminal of the first transistor Q1 is connected to the junction of the third resistor R3 and the second capacitor C2. The first terminal of the first transistor Q1 is also connected to the first power supply terminal (or positive power supply terminal) of comparator U1 and the first terminal of the fifth resistor R5. The second terminal of the fifth resistor R5 is connected to the negative input terminal of comparator U1 and the first terminal of the eleventh resistor R11. The third terminal of the first transistor Q1 is connected to the output terminal of comparator U1. The fourth resistor R4 is connected in parallel with the first and third terminals of the first transistor Q1. The second terminal of the first transistor Q1 is connected to the driving terminal of the power switch Q2, one end of the sixth resistor R6, and one end of the third capacitor C3. The other end of the sixth resistor R6 is connected to the other end of the third capacitor C3, the first terminal of the power switch Q2, the first capacitor C1, the first Zener diode Z1, the second capacitor C2, the second end of the eleventh resistor R11, and the second power supply terminal (or the negative power supply terminal of the comparator U1).

[0083] In some embodiments, the drive undervoltage lockout unit can be implemented as follows: Figure 4 The dashed box 3 in the diagram. The drive voltage discrimination circuit for the undervoltage lockout unit uses an integrated chip U1 with an internal reference, and the integrated chip U1 also has an input hysteresis voltage setting function. Specifically, the first terminal of the first transistor Q1 is connected to the junction of the third resistor R3 and the second capacitor C2. The first terminal of the first transistor Q1 is also connected to the first power supply terminal (positive terminal) of the integrated chip U1 and the first terminal of the fifth resistor R5. The second terminal of the fifth resistor R5 is connected to the negative input terminal of the first comparator inside the integrated chip U1 and the first terminal of the eleventh resistor R11. The second terminal of the eleventh resistor R11 is connected to the first terminal of the twelfth resistor and the positive input terminal of the second comparator inside the integrated chip U1. The third terminal of the first transistor Q1 is connected to the output terminal of the integrated chip U1. The fourth resistor R4 is connected in parallel with the first and third terminals of the first transistor Q1. The second terminal of the first transistor Q1 is connected to the drive terminal of the power switch Q2, one end of the sixth resistor R6, and one end of the third capacitor C3. The other end of the sixth resistor R6 is connected to the other end of the third capacitor C3, the first terminal of the power switch Q2, the first capacitor C1, the first Zener diode Z1, the second capacitor C2, the second end of the twelfth resistor R12, and the second power supply terminal (or power ground terminal) of the integrated chip U1.

[0084] In some embodiments, refer to Figure 5 The first transistor Q1 and the third transistor Q3 can be field-effect transistors (FETs). Specifically, Q1 is a P-channel FET, and Q3 is an N-channel FET.

[0085] It should be noted that the multiple embodiments in this application can be combined with each other to form a new embodiment. The execution order between the steps of each process in the method embodiment is merely exemplary and does not constitute a limitation on the execution order between the steps; other execution orders are also possible.

[0086] Furthermore, the terms "comprising" and "having," and any variations thereof, used in the description of this application are intended to cover non-exclusive inclusion. For example, a process, method, system, product, or apparatus that includes a series of steps or units is not limited to the steps or units listed, but may optionally include other steps or units not listed, or may optionally include other steps or units inherent to such process, method, product, or apparatus.

[0087] It should be noted that in the embodiments of this application, the words "exemplary" or "for example" are used to indicate examples, illustrations, or explanations. Any embodiment or design scheme described as "exemplary" or "for example" in the embodiments of this application should not be construed as being more preferred or advantageous than other embodiments or design schemes. Specifically, the use of the words "exemplary" or "for example" is intended to present the relevant concepts in a specific manner.

Claims

1. A bus capacitor DC soft start system, comprising a drive-on subsystem, a drive-off subsystem and a bus capacitor soft start loop; characterized in that, the drive-on subsystem comprises a drive-on energy supply unit, a drive-on unit and a drive-under-voltage lockout unit; the bus capacitor soft start loop comprises a power switch tube and a bus capacitor, the power switch tube being used to control the charging of the bus capacitor; the drive-off subsystem comprises a drive-off energy supply unit and a drive lockout unit, and is used to drive the power switch tube to be off; the drive-on energy supply unit has a first end connected to a first pole of the power switch tube, a second end connected to a second pole of the power switch tube, and a third end connected to the drive-on unit, and is used to provide a drive voltage and a current for a third pole, i.e., a drive pole, of the power switch tube; the drive-on unit is composed of a switch, a resistor and a capacitor, the switch receiving a drive-on instruction or signal, and the drive voltage provided by the drive-on energy supply unit being transmitted to the drive-under-voltage lockout unit after the switch is closed; the drive-under-voltage lockout unit comprises a first transistor, the power switch tube obtaining the drive voltage transmitted by the drive-on unit when the first transistor is turned on, the power switch tube starting to be turned on and charging the bus capacitor when the drive voltage is higher than an on threshold voltage of the power switch tube, and the drive-under-voltage lockout unit being further used to turn off the power switch tube when the drive voltage of the power switch tube is insufficient; wherein the drive lockout unit comprises a fourth zener diode, a third transistor and a tenth resistor; an anode of the fourth zener diode is connected to a first pole of the third transistor, a second pole of the third transistor is connected to one end of the tenth resistor, the other end of the tenth resistor is connected to the third pole of the power switch tube, a third pole of the third transistor is connected to the first pole of the power switch tube, and a cathode of the fourth zener diode is connected to the second pole of the power switch tube through the drive-off energy supply unit.

2. The system of claim 1, wherein, the drive-under-voltage lockout unit comprises a first transistor, a fourth resistor, a fifth resistor, a second zener diode, a sixth resistor and a third capacitor; a first pole of the first transistor is connected to the drive-on unit, a third pole of the first transistor is connected to the fifth resistor and a cathode of the second zener diode in sequence, the fourth resistor is connected to the first pole and the third pole of the first transistor in parallel, a second pole of the first transistor is connected to the drive pole of the power switch tube, one end of the sixth resistor and one end of the third capacitor, the other end of the sixth resistor is connected to the other end of the third capacitor, the first pole of the power switch tube and an anode of the second zener diode.

3. The system of claim 1, wherein, the drive-under-voltage lockout unit comprises a first transistor, a second zener diode, a comparator, a fourth resistor, a fifth resistor, a sixth resistor, an eleventh resistor, a twelfth resistor and a third capacitor. The first electrode of the first transistor is connected with the driving opening unit; the first electrode of the first transistor is also connected with the first power supply end of the comparator, the first end of the fifth resistor and the first end of the eleventh resistor; the second end of the fifth resistor is connected with the positive input end of the comparator and the cathode of the second voltage stabilizing diode; the second end of the eleventh resistor is connected with the first end of the twelfth resistor and the negative input end of the comparator; the third electrode of the first transistor is connected with the output end of the comparator; the fourth resistor is connected in parallel with the first electrode and the third electrode of the first transistor; the second electrode of the first transistor is connected with the driving electrode of the power switch tube, one end of the sixth resistor and one end of the third capacitor; the other end of the sixth resistor is connected with the other end of the third capacitor, the first electrode of the power switch tube, the anode of the second voltage stabilizing diode, the second end of the twelfth resistor and the second power supply end of the comparator.

4. The system of claim 1, wherein, The driving under-voltage locking unit comprises a first transistor, a comparator, a fifth resistor, an eleventh resistor, a fourth resistor, a sixth resistor and a third capacitor. The first electrode of the first transistor is connected with the driving opening unit, the positive power supply end of the comparator and the first end of the fifth resistor; the second end of the fifth resistor is connected with the negative input end of the comparator and the first end of the eleventh resistor; the third electrode of the first transistor is connected with the output end of the comparator; the fourth resistor is connected in parallel with the first electrode and the third electrode of the first transistor; the second electrode of the first transistor is connected with the driving electrode of the power switch tube, one end of the sixth resistor and one end of the third capacitor; the other end of the sixth resistor is connected with the other end of the third capacitor, the first electrode of the power switch tube, the second end of the eleventh resistor and the negative power supply end of the comparator.

5. The system according to any of claims 1-4, characterized in that, The driving opening energy supply unit comprises a first resistor, a second resistor, a first capacitor and a first voltage stabilizing diode; the first resistor, the second resistor and the first capacitor are connected in sequence, the first voltage stabilizing diode is connected in parallel with the first capacitor, the first resistor is connected with the bus capacitor soft start loop, the connecting point between the second resistor and the first capacitor is connected with the first end of the switch, and the other end of the first capacitor is connected with the first electrode of the power switch tube.

6. The system according to any one of claims 1 to 4, characterized in that The driving under-voltage locking unit comprises an integrated chip, a fifth resistor, an eleventh resistor, a twelfth resistor, a first transistor, a fourth resistor, a sixth resistor, a third capacitor, wherein the integrated chip has an input hysteresis voltage setting function, and the integrated chip internally comprises a first comparator and a second comparator; The first electrode of the first transistor is connected with the driving opening unit, the positive electrode of the power supply of the integrated chip, and the first end of the fifth resistor; the second end of the fifth resistor is connected with the negative input end of the first comparator inside the integrated chip and the first end of the eleventh resistor; the second end of the eleventh resistor is connected with the first end of the twelfth resistor and the positive input end of the second comparator inside the integrated chip; the third electrode of the first transistor is connected with the output end of the integrated chip; the fourth resistor is connected in parallel with the first and third electrodes of the first transistor; the second electrode of the first transistor is connected with the driving electrode of the power switch tube, one end of the sixth resistor, and one end of the third capacitor; the other end of the sixth resistor is connected with the other end of the third capacitor, the first electrode of the power switch tube, the second end of the twelfth resistor, and the power supply ground end of the integrated chip.

7. The system according to any one of claims 1 to 4, characterized in that, The driving closing subsystem further comprises a driving unlocking unit; the driving unlocking unit comprises a third diode; The negative electrode of the third diode is connected with the second electrode of the power switch tube, and the positive electrode of the third diode is connected with the cathode of the fourth voltage stabilizing diode.

8. The system of any one of claims 1 to 4, wherein, The first transistor is a PNP transistor, the first electrode of the first transistor is an emitter, the second electrode is a collector, and the third electrode is a base; or, The first transistor is a PMOS field effect transistor, the first electrode of the first transistor is a source, the second electrode is a drain, and the third electrode is a gate.

9. A photovoltaic energy storage inverter, characterized by, The bus capacitor DC soft start system comprises a controller and the bus capacitor DC soft start system according to any one of claims 1-8, and the controller is electrically connected with the bus capacitor DC soft start system.

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