A power frequency off-grid power supply system

Abstract

The utility model discloses a kind of power frequency off-grid power supply systems, including inverter main power module, receive the direct current voltage of its input end direct current power supply, and it is inverted into the alternating voltage required by system;Power frequency transformer, receive the alternating voltage output by inverter main power module, output first grade alternating current and / or second grade alternating current by its own winding configuration;Output module, for receiving the first grade alternating current and / or second grade alternating current output by power frequency transformer, different voltage mode is selected by its own relay switching output;AC load, for receiving the output module output to AC load power supply;Chip control module, for sending control signal to inverter main power module to regulate inverter process and sending control signal to output module to regulate relay on-off.The system can realize flexible output of multiple voltages in a set of equipment, improve the adaptability of power frequency off-grid system, meet diversified power demand.

Description

Technical Field

[0001] This utility model relates to the field of power electronics and off-grid power supply, and in particular to a power frequency off-grid power supply system. Background Technology

[0002] Currently, off-grid power frequency systems typically employ a fixed output mode, achieving a single voltage AC output through a built-in inverter and power frequency transformer. Common solutions include two types: one is a system based on a single-phase power frequency transformer, capable of outputting only a single-phase 240V voltage, suitable for specific regional grid requirements; the other is a system using a split-phase power frequency transformer, capable of outputting only a split-phase 120V voltage, suitable for a different grid standard.

[0003] However, both of these solutions have limitations, failing to simultaneously accommodate load requirements with different voltage specifications. This restricts system applicability and increases equipment configuration costs for users in various application scenarios. Therefore, there is an urgent need for a power frequency off-grid system that can flexibly switch output modes and is compatible with multiple voltage specifications to address the problems of poor adaptability and resource waste in existing technologies. Utility Model Content

[0004] The purpose of this invention is to provide a power frequency off-grid power supply system to solve the problems of existing power frequency off-grid systems, such as limited functionality and inability to adapt to various voltage specifications. This invention provides a power frequency off-grid power supply system that enables flexible output of multiple voltages within a single device, thereby improving the adaptability of the power frequency off-grid system, reducing user costs, and meeting diverse power needs in different scenarios.

[0005] This utility model provides an off-grid power supply system for industrial frequency, including an inverter main power module, an industrial frequency transformer, an output module, a chip control module, and an AC load. The inverter main power module receives the DC voltage from its input DC power supply and inverts it into the AC voltage required by the system. The industrial frequency transformer has its input connected to the output of the inverter main power module to receive the AC voltage output by the inverter main power module and, through its winding configuration, outputs a first-level AC power and / or a second-level AC power, wherein the voltage of the first-level AC power is higher than that of the second-level AC power. The output module has its input connected to the output of the industrial frequency transformer to receive the first-level AC power and / or the second-level AC power output by the industrial frequency transformer and, through its own relay switching, selects different output voltage modes. The AC load has its input connected to the output of the output module to receive the voltage mode output by the output module and to supply power to the AC load.

[0006] Furthermore, the inverter main power module includes a DC power supply, a first capacitor, a first bridge arm, and a second bridge arm, with the first bridge arm and the second bridge arm connected in parallel with the DC power supply and the first capacitor, respectively.

[0007] Further, the first bridge arm includes a first switch and a second switch. The current output terminal of the first switch is connected to the current input terminal of the second switch to form a first terminal. The current input terminal of the first switch is connected to the positive terminal of the first capacitor and the positive terminal of the DC power supply. The current output terminal of the second switch is connected to the negative terminal of the first capacitor and the negative terminal of the DC power supply. The second bridge arm includes a third switch and a fourth switch. The current output terminal of the third switch is connected to the current input terminal of the fourth switch to form a second terminal. The current input terminal of the third switch is connected to the positive terminal of the first capacitor and the positive terminal of the DC power supply. The current output terminal of the fourth switch is connected to the negative terminal of the first capacitor and the negative terminal of the DC power supply.

[0008] Furthermore, the first switch, the second switch, the third switch, and the fourth switch are one or a combination of several of the following: MOSFET, transistor, or IGBT.

[0009] Furthermore, the power frequency transformer includes an input winding and an output winding. The input winding is electrically connected to the output terminal of the inverter main power module and is used to receive the AC voltage output by the inverter main power module. The output winding outputs first-level AC power and / or second-level AC power through its different winding combinations.

[0010] Furthermore, the output winding includes three winding terminals. The first level of AC power is output through the combination of the first winding terminal and the third winding terminal, and the second level of AC power is output through the combination of the first winding terminal and the second winding terminal, and the combination of the second winding terminal and the third winding terminal, respectively.

[0011] Furthermore, the output module includes multiple relays, multiple filter capacitors, and output terminals. The multiple filter capacitors are electrically connected to the output terminals of the power frequency transformer, used to filter the first-level and / or second-level AC output from the power frequency transformer. The multiple relays are controlled by the chip control module to switch on and off, outputting the selected voltage mode to the AC load through the output terminals.

[0012] Furthermore, the multiple relays include a first relay, a second relay, and a third relay. The first terminal of the first relay, the first terminal of the second relay, and the first terminal of the third relay are respectively connected to the third winding terminal, the first winding terminal, and the second winding terminal. Multiple filter capacitors include a second capacitor, a third capacitor, and a fourth capacitor. The second capacitor is connected in parallel between the first winding terminal and the third winding terminal. The third capacitor is connected in parallel between the second terminal of the first relay and the second terminal of the third relay. The first-level AC power and / or second-level AC power output from the power frequency transformer is filtered by the multiple filter capacitors to form a sine wave. Through the switching of the multiple relays, the corresponding voltage mode is output from the output terminals.

[0013] Furthermore, it also includes a first current transformer and a second current transformer, which are used to detect the current flowing through the first relay and the second relay, respectively.

[0014] Furthermore, the first-level AC voltage is 240V, and the second-level AC voltage is 120V.

[0015] Compared with existing technologies, this invention can achieve flexible output of multiple voltages in one set of equipment, thereby improving the adaptability of the off-grid power frequency system, reducing user costs, and meeting diverse power needs in different scenarios. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of an off-grid power supply system according to an embodiment of the present invention; Figure 2 This is a circuit diagram of an off-grid power supply system for power frequency in one embodiment of the present invention; Figure 3 This is a circuit diagram of an off-grid power supply system for power frequency in 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 comprehensive 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 power frequency off-grid power supply system. Please refer to [link / reference]. Figure 1The system comprises an inverter main power module 1, a power frequency transformer 2, an output module 3, a chip control module 4, and an AC load 5. The inverter main power module 1 receives the DC voltage from its input DC power supply and inverts it into the AC voltage required by the system. The power frequency transformer 2 has its input connected to the output of the inverter main power module 1 to receive the AC voltage output from the inverter main power module 1. Through its winding configuration, it outputs a first-level AC voltage and / or a second-level AC voltage, wherein the first-level AC voltage is higher than the second-level AC voltage. The output module 3 has its input connected to the output of the power frequency transformer 2 to receive the first-level AC voltage and / or the second-level AC voltage output from the power frequency transformer 2. Through its own relay switching, it selects different output voltage modes. The AC load 5 has its input connected to the output of the output module 3 to receive the voltage output from the output module 3, thus powering the load.

[0020] In one embodiment, the off-grid power supply system further includes a chip control module 4, whose output terminal is connected to the control terminal of the inverter main power module 1 and the control terminal of the output module 3, respectively. It is used to send control signals to the inverter main power module 1 to regulate the inverter process, and at the same time send control signals to the output module 3 to regulate the on / off state of the relay.

[0021] The inverter main power module 1 is the core component for DC-to-AC conversion. Its input is connected to a DC power source, such as a battery pack. Under the control of the chip control module 4, it can stably output a 28V AC voltage. The inverter main power module 1 achieves inversion through the switching logic of multiple internal power devices such as MOSFETs, controlled by the PWM signal of the chip control module 4. These MOSFETs can all be field-effect transistors, with a basic structure consisting of a source, drain, and gate. It is understood that the battery pack is just one example of a DC power source; other DC devices could also be used, and the output AC voltage could be of other voltage levels. This application does not limit this. The input of the power frequency transformer 2 is connected to the output of the inverter main power module 1. After receiving the AC voltage (e.g., 28V), it achieves voltage conversion through its internal winding structure. Its winding design includes a main winding and a center tap. Different winding configurations can boost the 28V to 240V (first-level AC) or 120V (second-level AC). The input terminal of output module 3 is connected to the winding output terminal of power frequency transformer 2. Output module 3 integrates multiple relays and filter capacitors. The on / off state of the relays is directly controlled by chip control module 4, and the filter capacitors are used to process the voltage output from the transformer into a pure sine wave. Chip control module 4 sends control signals according to the target voltage mode, switching the circuit path by closing or opening the relays, selecting the corresponding voltage from the transformer output and transmitting it to AC load 5. Chip control module 4 sends PWM (Pulse Width Modulation) signals to inverter main power module 1 to ensure a stable 28V AC voltage output, and sends relay control signals to output module 3 to precisely control the circuit on / off state. Simultaneously, it can be understood that chip control module 4 can also monitor the current and voltage status through sampling circuits to ensure system safety. AC load 5 is the power terminal, categorized by voltage level as 240V-compatible loads (such as high-power appliances) and / or 120V-compatible loads (such as small appliances), obtaining the corresponding voltage through the output terminal of output module 3. To illustrate the operating logic of the above system: When the off-grid power supply system is in single-phase 240V (first-level AC) mode, the main inverter power module 1 outputs 28V, which is controlled by the power frequency transformer 2 and the chip control module 4 to control the relay of the output module 3, thus outputting single-phase 240V (first-level AC). When the system is in single-phase 120V (second-level AC) mode, the main inverter power module 1 outputs 28V, which is controlled by the power frequency transformer 2 and the chip control module 4 to control the relay of the output module 3, thus outputting single-phase 120V (second-level AC). When the system is in split-phase mode, the main inverter power module outputs 28V, which is controlled by the power frequency transformer 2 and the chip control module 4 to control the relay of the output module 3, thus outputting split-phase 240V (first-level AC) and 120V (second-level AC).

[0022] The system of this invention can achieve flexible output of multiple voltages in one device, thereby improving the adaptability of the off-grid power frequency system, reducing user costs, and meeting the diverse power needs in different scenarios.

[0023] Further, please see Figure 2 The inverter main power module 1 includes a DC power supply BAT, a first capacitor C1, a first bridge arm, and a second bridge arm. The first and second bridge arms are connected in parallel with the DC power supply BAT and the first capacitor C1, respectively. The first bridge arm includes a first switch Q1 and a second switch Q2. The current output terminal of the first switch Q1 is connected to the current input terminal of the second switch Q2, forming a first terminal. The current input terminal of the first switch Q1 is connected to the positive terminal of the first capacitor C1 and the positive terminal of the DC power supply BAT. The current output terminal of the second switch Q2 is connected to the negative terminal of the first capacitor C1 and the negative terminal of the DC power supply BAT. The second bridge arm includes a third switch Q3 and a fourth switch Q4. The current output terminal of the third switch Q3 is connected to the current input terminal of the fourth switch Q4, forming a second terminal. The current input terminal of the third switch Q3 is connected to the positive terminal of the first capacitor C1 and the positive terminal of the DC power supply BAT. The current output terminal of the fourth switch Q4 is connected to the negative terminal of the first capacitor C1 and the negative terminal of the DC power supply BAT. The first and second terminals constitute the output terminals of the inverter main power module 1.

[0024] The DC power supply BAT provides the raw DC power to the entire module, typically using a battery pack or other DC power supply equipment. Its output DC voltage is the input for the inverter conversion. The first capacitor C1 serves as an energy storage and filtering element, with its two ends connected in parallel with the positive and negative terminals of the DC power supply BAT, respectively. The first and second bridge arms are the core power units that realize the inverter function. Both have symmetrical structures and are connected in parallel with the DC power supply BAT and the first capacitor C1. When the first switch Q1, the second switch Q2, the third switch Q3, and the fourth switch Q4 are all MOSFETs, they can be referred to as the first MOSFET Q1, the second MOSFET Q2, the third MOSFET Q3, and the fourth MOSFET Q4. In this case, the first bridge arm is composed of the first MOSFET Q1 and the second MOSFET Q2 connected in series, and they are electrically connected through their drain and source (i.e., the source of the first MOSFET Q1 is connected to the drain of the second MOSFET Q2). In this configuration, the drain of the first MOSFET Q1 is connected to the positive terminal of the first capacitor C1 and the positive terminal of the DC power supply BAT. The source of the second MOSFET Q2 is connected to the negative terminal of the first capacitor C1 and the negative terminal of the DC power supply BAT. The second bridge arm has the same structure as the first bridge arm, consisting of a third MOSFET Q3 and a fourth MOSFET Q4 connected in series (the source of the third MOSFET Q3 is connected to the drain of the fourth MOSFET Q4). The drain of the third MOSFET Q3 is also connected to the positive terminal of the first capacitor C1 and the positive terminal of the DC power supply BAT, while the source of the fourth MOSFET Q4 is connected to the negative terminal of the first capacitor C1 and the negative terminal of the DC power supply BAT. The four MOSFETs act as switching elements, and their on / off states are controlled by PWM signals sent by the chip control module 4. This control method is conventional and existing technology, and will not be elaborated here.

[0025] Understandably, besides MOSFETs, the first switch Q1, the second switch Q2, the third switch Q3, and the fourth switch Q4 can also be IGBTs, transistors, or combinations of two or more types. For example, in one embodiment, the first switch Q1 and the third switch Q3 are MOSFETs, and the second switch Q2 and the fourth switch Q4 are IGBTs; or, in another embodiment, the first switch Q1 and the third switch Q3 are IGBTs, and the second switch Q2 and the fourth switch Q4 are MOSFETs; or, in another embodiment, the first switch Q1 and the second switch Q2 are MOSFETs, and the third switch Q3 and the fourth switch Q4 are IGBTs; or, in another embodiment, the first switch Q1 and the second switch Q2 are IGBTs, and the third switch Q3 and the fourth switch Q4 are MOSFETs, and so on.

[0026] In actual operation, the first and second bridge arms work through complementary conduction logic to ultimately convert the DC voltage to a set AC voltage (e.g., 28V). The first capacitor C1 charges and discharges to supplement the current, ensuring voltage continuity and reducing waveform distortion. This scheme has the advantages of high conversion efficiency, stable output, simple and reliable control, and flexible adaptability.

[0027] Further, please see Figure 2 The power frequency transformer 2 includes an input winding and an output winding. The input winding (primary winding) is electrically connected to the output terminal of the inverter main power module 1 and is used to receive the AC voltage output by the inverter main power module 1. The output winding (secondary winding) outputs first-level AC power and / or second-level AC power through different winding combinations. The output winding includes three winding terminals. The first-level AC power is output through the combination of the first winding terminal 11 and the third winding terminal 33, and the second-level AC power is output through the combination of the first winding terminal 11 and the second winding terminal 22, and the combination of the second winding terminal 22 and the third winding terminal 33, respectively.

[0028] The power frequency transformer 2 is a key component for voltage level conversion. Its core structure consists of an input winding (primary winding) and an output winding (secondary winding), which transmits and boosts voltage through electromagnetic induction. The two terminals (S and F) of the input winding are electrically connected to the output terminals (second and first terminals) of the inverter main power module 1, respectively. Specifically, when the first switch Q1, second switch Q2, third switch Q3, and fourth switch Q4 are all MOSFETs, the S terminal is electrically connected to the source of the third MOSFET Q3 and the drain of the fourth MOSFET Q4, and the F terminal is electrically connected to the source of the first MOSFET Q1 and the drain of the second MOSFET Q2. This allows for stable reception of AC voltage (e.g., 28V). This voltage generates an alternating magnetic field through the current in the winding, providing the energy basis for subsequent voltage conversion. The output winding is unique in that different winding combinations can be formed through a preset winding turn design. For example, the input 28V AC voltage can be boosted to the first level AC voltage (e.g., 240V) through the first winding terminal 11 and the third winding terminal 33. The second level AC voltage (e.g., 120V) can be output through the first winding terminal 11 and the second winding terminal 22, and the second winding terminal 22 and the third winding terminal 33, respectively.

[0029] Understandably, the turns ratio of the primary and secondary windings of a power frequency transformer can be set according to the actual needs and the ratio of the primary and secondary voltages. For example, when the AC voltage between the S and F terminals of the primary winding is Vp, and the first-level AC current between the first winding terminal 11 and the third winding terminal 33 of the secondary winding is Vs1; the second-level AC current of the secondary winding, namely the AC current between the first winding terminal 11 and the second winding terminal 22 is Vs21, and the AC current between the second winding terminal 22 and the third winding terminal 33 is Vs22, let the number of turns of the coil between the S and F terminals of the primary winding be Np, and the number of turns of the coil between the first winding terminal 11 and the third winding terminal 33 of the secondary winding be Np. The number of turns is Ns1, the number of turns of the coil between the first winding end 11 and the second winding end 22 on the secondary side is Ns21, and the number of turns of the coil between the second winding end 22 and the third winding end 33 on the secondary side is Ns22. Then Np:Ns1:Ns21:Ns22=Vp:Vs1:Vs21:Vs22. When Vp, Vs1, Vs21, and Vs22 are 28V, 240V, 120V, and 120V respectively, Np:Ns1:Ns21:Ns22=7:60:30:30.

[0030] With this winding combination design, the power frequency transformer 2 does not require additional structural adjustments. It can output first-level or second-level AC power simply by connecting different winding terminals, and can also output both levels of AC power simultaneously, providing hardware support for the system to flexibly switch voltage modes.

[0031] It should be noted that the connection relationship in this utility model refers to the electrical connection relationship.

[0032] Further, please see Figure 2 Output module 3 includes multiple relays, multiple filter capacitors, and output terminal CN1. The multiple filter capacitors are electrically connected to the output terminals of the power frequency transformer, used to filter the first-level AC and / or second-level AC output from the power frequency transformer. The multiple relays are controlled by chip control module 4 to switch on and off, outputting the selected voltage mode to the AC load 5 through output terminal CN1. Specifically, the multiple relays include a first relay, a second relay, and a third relay. The first terminals of the first, second, and third relays are respectively connected to the third winding terminal, the first winding terminal, and the second winding terminal. The multiple filter capacitors include a second capacitor, a third capacitor, and a fourth capacitor. The second capacitor is connected in parallel between the first winding terminal and the third winding terminal. The third capacitor is connected in parallel between the second terminals of the first and third relays. The fourth capacitor is connected in parallel between the second terminals of the third and second relays. The first-level AC and / or second-level AC output from the power frequency transformer is filtered by the multiple filter capacitors to form a sine wave, which is then switched on and off by the multiple relays, and the corresponding voltage mode is output through output terminal CN1.

[0033] The system includes multiple relays, including a first relay RY1, a second relay RY2, and a third relay RY3. Their wiring logic corresponds to the output winding terminals of the power frequency transformer 2 as follows: the first terminal of the first relay RY1 is connected to the third winding terminal 33; the first terminal of the second relay RY2 is connected to the first winding terminal 11; and the first terminal of the third relay RY3 is connected to the second winding terminal 22. This connection method allows direct acquisition of the output voltage from different winding combinations of the transformer. Multiple filter capacitors, including a second capacitor C2, a third capacitor C3, and a fourth capacitor C4, are all AC filter capacitors. Their function is to filter out high-frequency noise in the transformer's output voltage, making the voltage waveform closer to a pure sine wave. The second capacitor C2 is connected in parallel between the first winding terminal 11 and the third winding terminal 33, corresponding to filtering noise from the first-level AC voltage (e.g., 240V). The third capacitor C3 is connected in parallel between the second terminal of the first relay RY1 and the second terminal of the third relay RY3, used to filter noise from the second-level AC voltage output (e.g., 120V). The fourth capacitor C4 is connected in parallel to the second terminal of the third relay RY3 and the second terminal of the second relay RY2 to filter out noise from another second-level AC power output (such as 120V). The use of filter capacitors can effectively improve the quality of voltage waveforms and prevent noise from interfering with the load. The on / off control of the relay is directly driven by chip module 4, which has a fast response speed and clear switching logic, and can accurately match the requirements of different voltage modes. Understandably, in one embodiment, the first and fourth MOSFETs can be turned on while the second and third MOSFETs are turned off, or the second and third MOSFETs can be turned on while the first and fourth MOSFETs are turned off, through the chip control module, to obtain AC power (e.g., 28V) at the primary winding of the power frequency transformer (i.e., the S and F terminals).

[0034] For details, please refer to the following three working modes. Figure 2 .

[0035] The first mode is as follows: When the voltage mode is the mode of outputting only single-phase first-level AC power: the first relay RY1 and the second relay RY2 are closed, and the third relay RY3 is open; using the electromagnetic induction principle of the transformer winding, the power frequency transformer outputs first-level AC power (e.g., 240V) through the first winding terminal 11 and the third winding terminal 33; the second capacitor C2 in the output module 3 filters the output first-level AC power and transmits it to the first AC load R3 (such as a high-power appliance), thereby realizing the power supply to the corresponding load.

[0036] The second mode is as follows: When the voltage mode is the mode of outputting only single-phase second-level AC power: the first relay RY1, the second relay RY2 and the third relay RY3 are closed; using the electromagnetic induction principle of the transformer winding, the power frequency transformer outputs second-level AC power (e.g., 120V) through the first winding 11 and the second winding 22, the second winding 22 and the third winding 33 respectively; the third capacitor C3 and the fourth capacitor C4 in the output module 3 filter the two output second-level AC power and transmit them to the second AC load (R1, R2, such as lighting equipment, small power appliances), thereby realizing the power supply to the corresponding load.

[0037] The third mode is as follows: When the off-grid power supply system is in split-phase mode, the first relay RY1, the second relay RY2, and the third relay RY3 are all closed. Utilizing the electromagnetic induction characteristics of the transformer windings, a first-level AC current (e.g., 240V) is generated between the first winding end 11 and the third winding end 33. Simultaneously, second-level AC currents (e.g., 120V) are generated between the first winding end 11 and the second winding end 22, and between the second winding end 22 and the third winding end 33, respectively. The output first-level AC current (e.g., 240V), one second-level AC current (e.g., 120V), and another second-level AC current (e.g., 120V) are each filtered by the second capacitor C2, the third capacitor C3, and the fourth capacitor C4 in the output module 3, respectively. Then, the filtered first-level AC current is transmitted to the first AC load R3, and the two second-level AC currents are transmitted to the second AC loads (R1 and R2), respectively.

[0038] This design uses relays to direct the voltage output from a specific winding of the transformer to the corresponding load, ensuring voltage adaptability and improving power supply quality through capacitor filtering. This fully demonstrates the flexibility and reliability of the system in a single voltage output mode.

[0039] Further, refer to Figure 2 The output terminal CN1 in output module 3 has three clearly defined ports: the first live wire port HOT1, the neutral wire port N, and the second live wire port HOT2. The first live wire port HOT1 is electrically connected to the second terminal of the first relay RY1, the neutral wire port N is electrically connected to the second terminal of the third relay RY3, and the second live wire port HOT2 is electrically connected to the second terminal of the second relay RY2. These three ports work together to accurately output the processed voltage signal after the chip control module 4 controls the relays in output module 3 to perform corresponding actions, providing a stable power connection to the AC load 5.

[0040] Further, refer to Figure 2The first live wire port HOT1 is electrically connected to the first end of load R1 and the first end of the first AC load R3. The second end of load R1 and the first end of load R2 are electrically connected to the neutral wire port N. The second live wire port HOT2 is electrically connected to the second end of load R2 and the second end of the first AC load R3.

[0041] Further, refer to Figure 3 The off-grid power supply system also includes a first current transformer CT1 and a second current transformer CT2. The first current transformer CT1 is used to detect the current flowing through the first relay RY1, and the second current transformer CT2 is used to detect the current flowing through the second relay RY2.

[0042] The embodiments described above are merely illustrative of several implementations of this utility model, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of this utility model patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this utility model, and these all fall within the protection scope of this utility model. Therefore, the protection scope of this utility model patent should be determined by the appended claims.

Claims

1. A power frequency off-grid power supply system, characterized in that, It includes the inverter main power module, power frequency transformer, output module, chip control module and AC load; The inverter main power module is used to receive the DC voltage from its input DC power supply and invert it into the AC voltage required by the system. The power frequency transformer has its input terminal connected to the output terminal of the inverter main power module to receive the AC voltage output by the inverter main power module, and outputs first-level AC power and / or second-level AC power through the configuration of its own windings, wherein the voltage of the first-level AC power is higher than that of the second-level AC power. The output module has its input terminal connected to the output terminal of the power frequency transformer, and is used to receive the first-level AC power and / or the second-level AC power output by the power frequency transformer, and to select different output voltage modes by switching through its own relay. The AC load has its input terminal connected to the output terminal of the output module, and is used to receive the voltage mode output by the output module and to supply power to the AC load.

2. The off-grid power supply system according to claim 1, characterized in that, The inverter main power module includes a DC power supply, a first capacitor, a first bridge arm, and a second bridge arm, wherein the first bridge arm and the second bridge arm are connected in parallel with the DC power supply and the first capacitor, respectively.

3. The off-grid power supply system according to claim 2, characterized in that, The first bridge arm includes a first switch and a second switch. The current output terminal of the first switch is connected to the current input terminal of the second switch to form a first terminal. The current input terminal of the first switch is connected to the positive terminal of the first capacitor and the positive terminal of the DC power supply. The current output terminal of the second switch is connected to the negative terminal of the first capacitor and the negative terminal of the DC power supply. The second bridge arm includes a third switch and a fourth switch. The current output terminal of the third switch is connected to the current input terminal of the fourth switch to form a second terminal. The current input terminal of the third switch is connected to the positive terminal of the first capacitor and the positive terminal of the DC power supply. The current output terminal of the fourth switch is connected to the negative terminal of the first capacitor and the negative terminal of the DC power supply.

4. The off-grid power supply system according to claim 3, characterized in that, The first switch, the second switch, the third switch, and the fourth switch are one or a combination of several of the following: MOSFET, transistor, or IGBT.

5. The off-grid power supply system according to claim 1, characterized in that, The power frequency transformer includes an input winding and an output winding; the input winding is electrically connected to the output terminal of the inverter main power module and is used to receive the AC voltage output by the inverter main power module; the output winding outputs the first-level AC power and / or the second-level AC power through its different winding combinations.

6. The off-grid power supply system according to claim 5, characterized in that, The output winding includes three winding terminals. The first level of AC power is output through the combination of the first winding terminal and the third winding terminal, and the second level of AC power is output through the combination of the first winding terminal and the second winding terminal, and the combination of the second winding terminal and the third winding terminal, respectively.

7. The off-grid power supply system according to claim 6, characterized in that, The output module includes multiple relays, multiple filter capacitors, and output terminals; the multiple filter capacitors are electrically connected to the output terminals of the power frequency transformer, and are used to filter the first-level AC power and / or the second-level AC power output by the power frequency transformer; the multiple relays are controlled to switch on and off by the chip control module, and output the selected voltage mode to the AC load through the output terminals.

8. The off-grid power supply system according to claim 7, characterized in that, The plurality of relays includes a first relay, a second relay, and a third relay; the first terminal of the first relay, the first terminal of the second relay, and the first terminal of the third relay are respectively connected to the third winding terminal, the first winding terminal, and the second winding terminal; the plurality of filter capacitors includes a second capacitor, a third capacitor, and a fourth capacitor; the second capacitor is connected in parallel to the first winding terminal and the third winding terminal; the third capacitor is connected in parallel to the second terminal of the first relay and the second terminal of the third relay; the fourth capacitor is connected in parallel to the second terminal of the third relay and the second terminal of the second relay.

9. The off-grid power supply system according to claim 8, characterized in that, It also includes a first current transformer and a second current transformer, which are used to detect the current flowing through the first relay and the second relay, respectively.

10. The off-grid power supply system according to claim 1, characterized in that, The first level of AC power is 240V, and the second level of AC power is 120V.

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