A power supply soft start circuit of a high-frequency off-grid inverter

Abstract

The utility model discloses a kind of mains soft-starting circuit of high-frequency off-grid inverter, including PTC current-limiting protection unit, full-bridge rectifier unit, relay and bus capacitor;One end of PTC current-limiting protection unit is electrically connected to mains end, the other end of PTC current-limiting protection unit is electrically connected to full-bridge rectifier unit input end, relay is connected between full-bridge rectifier unit output end and bus capacitor in series;PTC current-limiting protection unit is configured to limit the instantaneous current of mains end;Full-bridge rectifier unit is configured to convert the alternating current of mains end into direct current;Relay is configured to make the direct current output by full-bridge rectifier unit flow into or be blocked into bus capacitor. Through this circuit, bus capacitor voltage can be quickly and reliably raised to target voltage to meet the requirements of normal operation, and this circuit has the advantages of high reliability, small impact current, simple structure, low cost, and can also achieve electrical isolation between mains and bus capacitor, improve safety performance.

Description

Technical Field

[0001] This utility model relates to the field of power electronics power supply technology, and in particular to a mains soft-start circuit for a high-frequency off-grid inverter. Background Technology

[0002] In areas with poor grid infrastructure or where there is no mains power coverage (such as some remote rural areas and remote construction sites), off-grid photovoltaic inverters become critical power supply devices. During the operation of an off-grid inverter, the bus capacitor is the core energy storage component. However, when mains power is connected to the inverter, if the bus capacitor is in an uncharged, empty state, directly switching the mains power into the bus capacitor circuit will generate a large instantaneous inrush current due to the initial zero voltage of the capacitor. This may damage the inverter and, in severe cases, cause fires or other safety accidents.

[0003] Existing solutions have significant drawbacks. First, some solutions directly convert AC mains power to DC to charge the bus capacitor via the inverter's power circuit and uncontrolled rectification. While this approach is simple and inexpensive, the inrush current depends heavily on the bus capacitor's size; a larger capacitor results in a stronger inrush current, compromising safety. Another solution uses a power frequency transformer to current-limit and regulate the AC mains power before charging the bus capacitor via a rectifier bridge. While this method achieves some current limiting and electrical isolation, the large size and numerous winding turns of power frequency transformers limit the inverter's overall power density and miniaturization, leading to higher costs and the inability to actively disconnect the AC mains power from the bus capacitor. Therefore, a soft-start solution for the bus capacitor is urgently needed to avoid these dangerous situations. Utility Model Content

[0004] The purpose of this invention is to provide a mains soft-start circuit for a high-frequency off-grid inverter to solve the problem in existing technologies where a large instantaneous inrush current is generated when the mains power is directly switched into the bus capacitor circuit when the mains power is connected to the inverter. This invention provides a mains soft-start circuit for a high-frequency off-grid inverter that achieves advantages such as high reliability, low inrush current, simple structure, and low cost. It also provides electrical isolation between the mains power and the bus capacitor, improving safety performance.

[0005] This utility model provides a mains soft-start circuit for a high-frequency off-grid inverter, including a PTC current limiting protection unit, a full-bridge rectifier unit, a relay, and a bus capacitor; One end of the PTC current limiting protection unit is electrically connected to the mains power terminal, and the other end of the PTC current limiting protection unit is electrically connected to the input terminal of the full-bridge rectifier unit. The relay is connected in series between the output terminal of the full-bridge rectifier unit and the bus capacitor. The PTC current limiting protection unit is configured to limit the instantaneous current at the mains terminal; the full-bridge rectifier unit is configured to convert the AC power at the mains terminal into DC power; the relay is configured to allow or block the DC power output by the full-bridge rectifier unit from flowing into or flowing into the bus capacitor.

[0006] Furthermore, the PTC current limiting protection unit includes a first PTC unit and a second PTC unit. The first PTC unit is connected in series in the live wire path of the mains terminal, and the second PTC unit is connected in series in the neutral wire path of the mains terminal. The first PTC unit and the second PTC unit are positive temperature coefficient thermistors.

[0007] Furthermore, the full-bridge rectifier unit includes a full-bridge rectifier circuit.

[0008] Furthermore, the full-bridge rectifier unit also includes a second diode, which is a reverse-biased diode connected in series between the output terminal of the full-bridge rectifier circuit and the relay to prevent current from flowing back from right to left.

[0009] Furthermore, the full-bridge rectifier unit also includes a first capacitor, the two ends of which are connected across the output terminals of the full-bridge rectifier circuit.

[0010] Furthermore, it also includes a first diode, which is connected in series between the mains terminal and the input terminal of the full-bridge rectifier unit.

[0011] Furthermore, the relay is a double-pole single-throw relay, and the two sets of contacts of the double-pole single-throw relay are respectively connected in series between the DC positive terminal of the full-bridge rectifier unit and the positive terminal of the bus capacitor, and between the DC negative terminal of the full-bridge rectifier unit and the negative terminal of the bus capacitor.

[0012] Furthermore, the relay is a normally open relay or a normally closed relay.

[0013] Furthermore, it also includes a first resistor, the two ends of which are connected across the two ends of the first capacitor.

[0014] Furthermore, it also includes a relay drive circuit, the two output terminals of which are electrically connected to the two ends of the relay coil.

[0015] Compared with the prior art, this utility model has the advantages of high soft-start reliability, low inrush current, simple structure and low cost through a mains soft-start circuit for a high-frequency off-grid inverter. At the same time, by disconnecting the relay, electrical isolation between the mains power and the bus capacitor can be achieved, thereby improving safety performance. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the mains soft-start circuit of a high-frequency off-grid inverter according to one embodiment of the present invention; Figure 2 This is a schematic diagram of the mains soft-start circuit of a high-frequency off-grid inverter according to another embodiment of the present invention.

[0017] The following detailed description, in conjunction with the accompanying drawings, will further illustrate this utility model. Detailed Implementation

[0018] To facilitate understanding of this utility model, a more complete description will be given below with reference to the accompanying drawings. Several embodiments of this utility model are shown in the drawings. However, this utility model can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided so that the disclosure of this utility model will be more thorough and complete. Example

[0019] This embodiment provides a mains soft-start circuit for a high-frequency off-grid inverter. Please refer to [link to relevant documentation]. Figure 1 The system includes a PTC current limiting protection unit 1, a full-bridge rectifier unit DB1, a relay RY1, and a bus capacitor C1. One end of the PTC current limiting protection unit 1 is electrically connected to the mains power supply, and the other end is electrically connected to the input terminal of the full-bridge rectifier unit DB1. The relay RY1 is connected in series between the output terminal of the full-bridge rectifier unit DB1 and the bus capacitor C1. The PTC current limiting protection unit 1 is configured to limit the instantaneous current at the mains power supply. The full-bridge rectifier unit DB1 is configured to convert the AC power at the mains power supply to DC power. The relay RY1 is configured to allow or block the DC power output from the full-bridge rectifier unit DB1 from flowing into or flowing into the bus capacitor C1.

[0020] The mains power terminal is directly connected to the external AC power grid, and includes GRID-L (Grid Live) and GRID-N (Grid Neutral). GRID-L is the live wire terminal of the mains power, and GRID-N is the neutral wire terminal of the mains power.

[0021] When mains power is connected, the AC mains current flows into the PTC current limiting protection unit 1, limiting the current rise rate and preventing instantaneous large current surges. The current-limited AC power then enters the full-bridge rectifier unit DB1 and is converted into DC output. Relay RY1 is turned on, allowing the output DC power to flow into the bus capacitor C1 through relay RY1, charging the bus capacitor C1. When the voltage of the bus capacitor C1 reaches the target value, relay RY1 is turned off, achieving electrical isolation between the mains power terminal and the bus capacitor C1, thus completing the soft-start process.

[0022] Through the above technical measures, the advantages of high reliability and low inrush current are achieved. At the same time, electrical isolation between the mains power and the bus capacitor is realized, improving safety performance and ensuring the normal operation of the inverter.

[0023] Please see Figure 1 The PTC current limiting protection unit 1 includes a first PTC unit PTC1 and a second PTC unit PTC2. The first PTC unit PTC1 is connected in series in the live wire path of the mains power supply, and the second PTC unit PTC2 is connected in series in the neutral wire path of the mains power supply. Both the first PTC unit PTC1 and the second PTC unit PTC2 are positive temperature coefficient thermistors.

[0024] In this design, one end of the first PTC unit, PTC1, is connected in series to the live wire of the mains power supply, and the other end is electrically connected to the positive input terminal 1' of the full-bridge rectifier unit DB1. One end of the second PTC unit, PTC2, is connected in series to the neutral wire of the mains power supply, and the other end is electrically connected to the negative input terminal 2' of the full-bridge rectifier unit DB1. Both the first PTC unit, PTC1, and the second PTC unit, PTC2, use their own characteristics to limit the instantaneous current at the mains power supply.

[0025] By employing the first PTC unit PTC1 and the second PTC unit PTC2, large-volume components such as power frequency transformers are not required. Soft starting of the bus capacitor can be achieved simply by combining these components with a relay, resulting in advantages such as high reliability, low inrush current, simple structure, and low cost.

[0026] Please see Figure 1 In one embodiment, the full-bridge rectifier unit DB1 includes a full-bridge rectifier circuit DB1'.

[0027] In another embodiment, the full-bridge rectifier unit DB1 further includes a first capacitor C2, the two ends (positive and negative) of the first capacitor C2 are connected across the output ends (DC positive 4', DC negative 3') of the full-bridge rectifier circuit. The first capacitor C2 is a filter capacitor used to filter out high-frequency ripple.

[0028] In another embodiment, the full-bridge rectifier unit DB1 further includes a second diode D1, which is disposed (connected in series) between the output terminal of the full-bridge rectifier circuit DB1' and the relay RY1. The second diode D1 is a reverse protection diode, used to prevent current from flowing back from right to left (e.g., from the relay to the full-bridge rectifier circuit) when the voltage of the bus capacitor C1 is higher than the mains voltage. In one embodiment, the anode of the second diode D1 is electrically connected to the DC positive terminal 4' of the full-bridge rectifier circuit DB1', and the cathode of the second diode D1 is electrically connected to one end of the relay RY1 (the first end 21 in the first group of contacts). Of course, the connection method of the second diode D1 can also be other methods, for example, the cathode of the second diode D1 is electrically connected to the DC negative terminal 3' of the full-bridge rectifier circuit DB1', and the anode of the second diode D1 is electrically connected to one end of the relay RY1 (the first end 51 in the second group of contacts).

[0029] The full-bridge rectifier circuit DB1' receives AC mains power after passing through the PTC current-limiting protection unit 1, converts the AC power to DC power, and has two key electrical terminals: DC positive terminal 4' and DC negative terminal 3', for outputting the converted DC power. The second diode D1 prevents reverse voltage from being generated in subsequent circuits (e.g., relay RY1, bus capacitor C1) during abnormal operation, thus avoiding damage to DB1'. The first capacitor C2 serves a filtering function, removing ripple from the DC power output of the full-bridge rectifier circuit DB1', making the output DC power more stable; the first capacitor C2 does not perform energy storage.

[0030] Understandably, the full-bridge rectifier circuit is existing technology, and will not be described in detail here.

[0031] By employing a full-bridge rectifier circuit DB1', a second diode D1, and a first capacitor C2, the three components work together to achieve the functions of rectification, filtering, and protection, ensuring the safe charging of the bus capacitor C1.

[0032] Please see Figure 1 The mains soft-start circuit of the high-frequency off-grid inverter also includes a first diode D2. The cathode of the first diode D2 is electrically connected to the other end of the first PTC unit PTC1, and the anode of the first diode D2 is electrically connected to the positive input terminal 1' of the full-bridge rectifier unit DB1 (i.e., the positive input terminal 1' of the full-bridge rectifier circuit DB1'). Due to the forward conduction and reverse cutoff characteristics of the diode, this setting allows soft-start to be performed only during the negative half-cycle of the mains voltage, thereby effectively reducing current surges.

[0033] Understandably, in order to achieve soft-start only during the negative half-cycle of the mains voltage, the connection relationship of the first diode D2 is not limited to the above: For example, in one embodiment, the first diode D2 can be connected in series between the second PTC unit PTC2 and the negative input terminal 2' of the full-bridge rectifier unit DB1 (i.e., the negative input terminal 2' of the full-bridge rectifier circuit DB1'). Specifically, the anode of the first diode D2 is electrically connected to the other end of the second PTC unit PTC2, and the cathode of the first diode D2 is electrically connected to the negative input terminal 2' of the full-bridge rectifier unit DB1 (i.e., the negative input terminal 2' of the full-bridge rectifier circuit DB1'). Or, in one embodiment, the first diode D2 can be connected in series between the mains live wire GRID-L and the first PTC unit PTC1. Specifically, the anode of the first diode D2 is electrically connected to one end of the first PTC unit PTC1, and the cathode of the first diode D2 is electrically connected to the mains live wire GRID-L. Alternatively, in one embodiment, the first diode D2 is connected in series between the mains neutral terminal GRID-N and the second PTC unit PTC2. Specifically, the anode of the first diode D2 is electrically connected to the mains neutral terminal GRID-N, and the cathode of the first diode D2 is electrically connected to one end of the second PTC unit PTC2.

[0034] The foregoing Figure 1 In other alternative embodiments, the connection of the first diode D2 is configured such that the mains power is turned on only during the negative half-cycle and turned off during the positive half-cycle. At this time, during the negative half-cycle of the mains power, the mains current is processed by the PTC current limiting protection unit 1 and the full-bridge rectifier unit DB1 to charge the bus capacitor C1, thereby performing a soft start. Since the soft start is performed only during half a cycle (negative half-cycle) of the mains power, the current surge can be effectively reduced.

[0035] Please see Figure 2 , and Figure 1 Compared to the previous embodiment, the anode of the first diode D2 is electrically connected to the other end of the first PTC unit PTC1, and the cathode of the first diode D2 is electrically connected to the positive input terminal 1' of the full-bridge rectifier unit DB1 (i.e., the positive input terminal 1' of the full-bridge rectifier circuit DB1'). Due to the forward conduction and reverse cutoff characteristics of the diode, this configuration allows soft-start to occur only during the positive half-cycle of the mains voltage, thereby effectively reducing current surges.

[0036] Understandably, in order to achieve soft-start only during the positive half-cycle of the mains voltage, the connection of the first diode D2 is not limited to the above: For example, in one embodiment, the first diode D2 can be connected in series between the second PTC unit PTC2 and the negative input terminal 2' of the full-bridge rectifier unit DB1 (i.e., the negative input terminal 2' of the full-bridge rectifier circuit DB1'). Specifically, the cathode of the first diode D2 is electrically connected to the other end of the second PTC unit PTC2, and the anode of the first diode D2 is electrically connected to the negative input terminal 2' of the full-bridge rectifier unit DB1 (i.e., the negative input terminal 2' of the full-bridge rectifier circuit DB1'). Or, in one embodiment, the first diode D2 can be connected in series between the mains live wire GRID-L and the first PTC unit PTC1. Specifically, the cathode of the first diode D2 is electrically connected to one end of the first PTC unit PTC1, and the anode of the first diode D2 is electrically connected to the mains live wire GRID-L. Alternatively, in one embodiment, the first diode D2 is connected in series between the mains neutral terminal GRID-N and the second PTC unit PTC2. Specifically, the cathode of the first diode D2 is electrically connected to the mains neutral terminal GRID-N, and the anode of the first diode D2 is electrically connected to one end of the second PTC unit PTC2.

[0037] The foregoing Figure 2 In other alternative embodiments, the connection of the first diode D2 is configured such that the mains power is only turned on during the positive half-cycle and turned off during the positive half-cycle. At this time, during the positive half-cycle of the mains power, the mains current is processed by the PTC current limiting protection unit 1 and the full-bridge rectifier unit DB1 to charge the bus capacitor C1, thereby performing a soft start. Since the soft start is only performed during half a cycle (positive half-cycle) of the mains power, the current surge can be effectively reduced.

[0038] Understandably, in order to ensure that the mains power flows from left to right only in half a cycle, the first diode D2 can be connected in series between the mains power terminal and the input terminal of the full-bridge rectifier unit DB1.

[0039] Understandably, when the first diode D2 is not used, both the positive and negative half-cycles (full cycle) of the mains power can directly enter the full-bridge rectifier unit DB1 through the PTC current limiting protection unit 1. The positive and negative half-cycle currents do not need to be filtered by the diode, resulting in a shorter soft-start time.

[0040] By employing the first diode D2, the conduction half-cycle of the mains power can be selected (only the positive half-cycle or the negative half-cycle is conducted), effectively reducing the inrush current when the bus capacitor C1 is charging. At the same time, a balance can be achieved between soft-start time and inrush current intensity, adapting to the dual considerations of safety and start-up speed in different scenarios.

[0041] Please see Figure 1Relay RY1 is electrically connected between the output terminal of the full-bridge rectifier unit DB1 and the bus capacitor C1. In one embodiment, the relay is a double-pole single-throw relay RY1, and the two sets of contacts of the double-pole single-throw relay RY1 are respectively connected in series between the DC positive terminal 4' of the full-bridge rectifier unit DB1 (i.e., the DC positive terminal 4' of the full-bridge rectifier circuit DB1') and the positive terminal of the bus capacitor C1, and between the DC negative terminal 3' of the full-bridge rectifier unit DB1 (i.e., the DC negative terminal 3' of the full-bridge rectifier circuit DB1') and the negative terminal of the bus capacitor C1.

[0042] Specifically, the first terminal 21 of the first set of contacts of the double-pole single-throw relay RY1 (or via the second diode D1) is electrically connected to the DC positive terminal 4' of the full-bridge rectifier unit DB1 (i.e., the DC positive terminal 4' of the full-bridge rectifier circuit DB1'), and the second terminal 31 of the first set of contacts of the double-pole single-throw relay RY1 is electrically connected to the positive terminal of the bus capacitor C1. The first terminal 51 of the second set of contacts of the double-pole single-throw relay RY1 is electrically connected to the DC negative terminal 3' of the full-bridge rectifier unit DB1 (i.e., the DC negative terminal 3' of the full-bridge rectifier circuit DB1'), and the second terminal 41 of the second set of contacts of the double-pole single-throw relay RY1 is electrically connected to the negative terminal of the bus capacitor C1.

[0043] The double-pole single-throw relay RY1 is a key control and isolation device in the soft-start circuit. The double-pole structure ensures circuit safety. When the double-pole single-throw relay RY1 operates, both sets of contacts can simultaneously connect or disconnect, thus avoiding the risk of one circuit remaining energized while only one circuit is disconnected, as is common in single-pole structures. This prevents potential hazards caused by continuous power supply to the bus capacitor C1 on one side. Furthermore, once the voltage of the bus capacitor C1 reaches the specified level, the contacts disconnect, achieving strict electrical isolation. In summary, by using the double-pole single-throw relay RY1, the risk of unipolar energization can be effectively avoided, improving circuit safety.

[0044] Understandably, relay RY1 can be a normally closed relay or a normally open relay.

[0045] When relay RY1 is a normally closed relay, its contacts are closed before soft start. During the power-on soft start phase, the mains power directly begins to charge the bus capacitor C1. Specifically, the mains power flows to the bus capacitor C1 (BUS terminal) after passing through the PTC current limiting protection unit 1, the full-bridge rectifier unit DB1, and relay RY1, thus achieving initial charging of the BUS terminal.

[0046] When relay RY1 is a normally open relay, its contacts are open before soft start. During the power-on soft start phase, after relay RY1 (contacts) closes, the mains power begins to charge the bus capacitor C1. Specifically, the mains power flows to the bus capacitor C1 (BUS terminal) after passing through the PTC current limiting protection unit 1, the full-bridge rectifier unit DB1, and relay RY1, thus achieving initial charging of the BUS terminal.

[0047] In the circuit, Bus+ (positive bus of BUS terminal) and Bus- (negative bus of BUS terminal) are two high-voltage or high-current main lines that carry the power of the main circuit. The bus capacitor C1 is directly connected between Bus+ and Bus-.

[0048] As described above, relay RY1 is a normally closed relay, enabling rapid soft-start charging. Relay RY2 is a normally open relay, providing safer and more reliable soft-start.

[0049] In one embodiment, a main control chip is also included, which is configured to disconnect relay RY1 when the voltage of bus capacitor C1 is detected to reach a threshold, and so on.

[0050] The main control chip monitors the voltage across the bus capacitor C1 in real time. When the detected voltage rises to a preset threshold (the target voltage for normal inverter operation), it outputs a control signal to the drive circuit of relay RY1, driving the two sets of contacts to open synchronously and stop the soft start process.

[0051] By disconnecting the relay after the voltage of bus capacitor C1 reaches the standard, electrical isolation between the mains power terminal and bus capacitor C1 can be quickly achieved, ensuring the safe operation of the inverter system.

[0052] Please see Figure 1 The mains soft-start circuit of the high-frequency off-grid inverter also includes a first resistor. In one embodiment, the first end of the first resistor is electrically connected to the cathode of the second diode, and the second end of the first resistor is electrically connected to the DC negative terminal of the full-bridge rectifier unit DB1. In other embodiments, the two ends of the first resistor are connected across the two ends of the first capacitor C2.

[0053] The first resistor can be a single resistor or, depending on the actual circuit requirements, multiple resistors can be connected in series (e.g., four resistors R1, R2, R3, and R4 connected in series). The first resistor has a relatively large resistance value, such as 4 megohms to 10 megohms, or other values. The first resistor is used to eliminate the floating voltage on the first capacitor C2 after the soft start is completed, reducing its voltage to a safe range.

[0054] The design of a high-resistance first resistor enables safe discharge, which can slowly release the residual floating voltage of the first capacitor C2 after soft start, thereby improving the safety of circuit operation.

[0055] Please see Figure 1 The relay RY1 also includes an electromagnetic coil (referred to as the coil), and the on / off state of the electromagnetic coil is configured to control the working state of the relay RY1.

[0056] In one embodiment, the mains soft-start circuit of the high-frequency off-grid inverter further includes a relay drive circuit, which controls the operating state (on / off) of relay RY1. In one embodiment, the relay RY1 drive circuit includes a power supply positive voltage terminal +VCC and a ground terminal GND that provide the operating voltage (e.g., 3-15V, etc.), a filter capacitor C3 for power supply filtering, a freewheeling diode D3, an input control signal terminal RY-AC-DRV, a current-limiting resistor R5, a pull-down resistor R6, and a switching transistor Q1. The two output terminals of the relay RY1 drive circuit are electrically connected to the two ends of the relay RY1 coil. In one embodiment, filter capacitor C3 is connected in series between the positive voltage terminal +VCC and the ground terminal GND. The cathode of freewheeling diode D3 is connected to the positive voltage terminal +VCC and the first terminal 11 of the coil of relay RY1, and the anode of freewheeling diode D3 is connected to the second terminal 61 of the coil of relay RY1 and the current input terminal of switching transistor Q1. Current-limiting resistor R5 is connected in series between the input control signal terminal RY-AC-DRV and the driving terminal of switching transistor Q1. Pull-down resistor R6 is connected in series between the driving terminal of switching transistor Q1 and the ground terminal GND. The current output terminal of switching transistor Q1 is electrically connected to the ground terminal GND. When the control system (main control chip) sends a conduction signal, the input control signal terminal RY-AC-DRV causes switching transistor Q1 to close, and current flows through the coil of relay RY1. The coil is energized and generates a magnetic field, which drives the internal contacts of the relay to switch, realizing the connection or disconnection of the relay. When the control system (main control chip) sends a disconnect signal, the input control signal terminal RY-AC-DRV causes the switching transistor Q1 to disconnect, the current in the coil of relay RY1 is interrupted, the magnetic field disappears, and the relay returns to its initial state.

[0057] By setting up the relay RY1 drive circuit as described above, the weak current signal can control the strong current, thus achieving safe isolation.

[0058] Understandably, the switching transistor Q1 can be a transistor, IGBT, MOSFET, etc.

[0059] The embodiments described above are merely illustrative of the present invention, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the present invention. 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 modifications and improvements all fall within the protection scope of the present invention. Therefore, the protection scope of this patent should be determined by the appended claims.

Claims

1. A mains soft-start circuit for a high-frequency off-grid inverter, characterized in that, Includes PTC current limiting protection unit, full-bridge rectifier unit, relays and bus capacitors; One end of the PTC current limiting protection unit is electrically connected to the mains power terminal, and the other end of the PTC current limiting protection unit is electrically connected to the input terminal of the full-bridge rectifier unit. The relay is connected in series between the output terminal of the full-bridge rectifier unit and the bus capacitor. The PTC current limiting protection unit is configured to limit the instantaneous current at the mains terminal; the full-bridge rectifier unit is configured to convert the AC power at the mains terminal into DC power; the relay is configured to allow or block the DC power output by the full-bridge rectifier unit from flowing into or flowing into the bus capacitor.

2. The mains soft-start circuit for a high-frequency off-grid inverter according to claim 1, characterized in that, The PTC current limiting protection unit includes a first PTC unit and a second PTC unit. The first PTC unit is connected in series in the live wire path of the mains power supply, and the second PTC unit is connected in series in the neutral wire path of the mains power supply. The first PTC unit and the second PTC unit are positive temperature coefficient thermistors.

3. The mains soft-start circuit for a high-frequency off-grid inverter according to claim 1, characterized in that, The full-bridge rectifier unit includes a full-bridge rectifier circuit.

4. The mains soft-start circuit for a high-frequency off-grid inverter according to claim 3, characterized in that, The full-bridge rectifier unit also includes a second diode, which is a reverse protection diode connected in series between the output terminal of the full-bridge rectifier circuit and the relay to prevent current from flowing back from right to left.

5. The mains soft-start circuit for a high-frequency off-grid inverter according to claim 3 or 4, characterized in that, The full-bridge rectifier unit also includes a first capacitor, the two ends of which are connected across the output terminals of the full-bridge rectifier circuit.

6. The mains soft-start circuit for a high-frequency off-grid inverter according to claim 1, characterized in that, It also includes a first diode, which is connected in series between the mains terminal and the input terminal of the full-bridge rectifier unit.

7. The mains soft-start circuit for a high-frequency off-grid inverter according to claim 1, characterized in that, The relay is a double-pole single-throw relay, and the two sets of contacts of the double-pole single-throw relay are respectively connected in series between the DC positive terminal of the full-bridge rectifier unit and the positive terminal of the bus capacitor, and between the DC negative terminal of the full-bridge rectifier unit and the negative terminal of the bus capacitor.

8. The mains soft-start circuit for a high-frequency off-grid inverter according to claim 1, characterized in that, The relay is either a normally open relay or a normally closed relay.

9. The mains soft-start circuit for a high-frequency off-grid inverter according to claim 5, characterized in that, It also includes a first resistor, the two ends of which are connected across the two ends of the first capacitor.

10. The mains soft-start circuit for a high-frequency off-grid inverter according to claim 1, characterized in that, It also includes a relay drive circuit, the two output terminals of which are electrically connected to the two ends of the relay coil.

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