TWI836948B - Power conversion system - Google Patents

Abstract

A power conversion system (PCS) includes an alternating current (AC) power port, a first direct current (DC) power port, a second DC power port, a high voltage capacitor, a first DC converter, a second DC converter, a power inverter, and a microcontroller unit. The microcontroller unit adjusts a frequency of an AC power output by the power conversion system based on a voltage difference across the high voltage capacitor of the power conversion system to switch the frequency of the AC power between different frequencies.

Description

Power conversion system

The present invention relates to a power conversion system (Power conversion system; PCS), and in particular, to a power conversion system that can adjust the output AC frequency of a rechargeable battery according to its charged ratio.

A power conversion system (PCS) is a bidirectional power conversion inverter that can be used for on-grid and off-grid electrical energy storage applications. How to effectively operate a power conversion system has always been an important issue in this technical field.

The power conversion system of the present invention includes an AC power supply port, a first DC power supply port, a second DC power supply port, a high-voltage capacitor, a first DC converter, a second DC converter, a power inverter, and a microcontrol unit. The AC power port is coupled to the solar photovoltaic converter. The first DC power port is coupled to the rechargeable battery. The second DC power port is coupled to the solar panel. The first DC converter is coupled between the high voltage capacitor and the first DC power port. The second DC converter is coupled between the high voltage capacitor and the second DC power port. The power inverter is coupled between the high-voltage capacitor and the AC power port. The microcontrol unit is used to adjust the frequency of the AC power output by the power conversion system from the AC power port based on the voltage difference across the high-voltage capacitor. Among them, when the micro control unit detects that the mains power is off-grid and the voltage difference is greater than the When a critical value is reached, the microcontrol unit sets the frequency of the alternating current output from the alternating current power port to the cutoff frequency, so that the solar photovoltaic converter stops outputting electric energy. When the micro-control unit detects that the mains power is off-grid and the continuous time when the voltage difference is between the first critical value and the second critical value exceeds the preset time length, the micro-control unit will output the AC power from the AC power port. The frequency is set to the cutoff frequency. When the micro-control unit detects that the mains power is off-grid and the voltage difference is between the second critical value and the third critical value, the micro-control unit increases the frequency of the AC power output by the AC power port to the first preset value. The first critical value is greater than the second critical value, and the second critical value is greater than the third critical value.

10: Mains power

12: Mains power connection port

14:AC power port

16, 90: DC power port

20, 82: DC converter

22: Power inverter

30: Voltage ammeter

40:Micro control unit

50: Solar Photovoltaic Converter

60:Load

70: Rechargeable battery

80, 92: Solar panels

100:Power conversion system

C: high voltage capacitor

F: Frequency

F_min: minimum frequency

F_normal: normal frequency

F_Start: starting frequency

F_Stop: Stop frequency

F_Trip: Cutoff frequency

Ia: Current

P_Inv: power

Va: voltage

Vb: DC voltage

Vbus: voltage difference

SOC: state of charge signal

S200 to S212, S302 to S306, S401 to S409: steps

Figure 1 is a functional block diagram of a power conversion system and the coupled mains, load, rechargeable battery, solar photovoltaic converter and solar panel according to an embodiment of the present invention.

Figure 2 is a graph showing the relationship between the external output power ratio of the solar photovoltaic converter in Figure 1 and the frequency of the AC power output by the power conversion system.

Figures 3A and 3B are flow charts of the microcontroller unit in Figure 1 controlling the power conversion system.

Figure 4 is another flow chart of the microcontroller unit in Figure 1 controlling the power conversion system.

Figures 5A and 5B are another flow chart of the microcontroller in Figure 1 controlling the power conversion system.

FIG. 1 is a functional block diagram of a power conversion system (PCS) 100 of an embodiment of the present invention and the coupled mains 10, load 60, rechargeable battery 70, photovoltaic inverter (PV inverter) 50, solar panel 80 and solar panel 92. Solar panel 80 and solar panel 92 are used to convert sunlight into electrical energy. Solar photovoltaic inverter 50 is used to convert the direct current generated by solar panel 80 into alternating current, and feed the converted alternating current into load 60 and/or power conversion system 100.

The power conversion system 100 includes a mains connection port 12, an AC power port 14, a DC power port 16, a high voltage capacitor C, a DC converter 20, a power inverter 22, a voltage ammeter 30, a DC converter 82, a DC power port 90, and Microcontroller unit (MCU) 40. The power conversion system 100 can be connected to the mains 10 through the mains connection port 12 and receive power from the mains 10 . The DC power port 16 is coupled to the rechargeable battery 70 , and the power conversion system 100 can charge the rechargeable battery 70 or receive power from the rechargeable battery 70 through the DC power port 16 . The voltage and ammeter 30 is coupled to the AC power port 14 for detecting the voltage Va and current Ia output by the power conversion system 100 from the AC power port 14 . Wherein, voltage Va and current Ia are alternating current voltage and alternating current current respectively. The micro control unit 40 is used to control the operation of the power conversion system and receive the state of charge signal SOC from the rechargeable battery 70 . The micro control unit 40 can obtain the current charging ratio of the rechargeable battery 70 based on the state of charge signal SOC, and obtain the external output power P_Inv of the power conversion system 100 based on the voltage Va and current Ia detected by the voltage and ammeter 30 . When the external output power P_Inv is positive, it means that the power conversion system 100 outputs electric energy to the outside through the AC power port 14 ; and when the external output power P_Inv is negative, it means that the power conversion system 100 receives electric energy from the outside through the AC power port 14 . The DC converter 20 is coupled between the high-voltage capacitor C and the DC power port 16 for converting the DC voltage Vb output by the rechargeable battery 70 into the voltage difference Vbus across the high-voltage capacitor C. The DC converter 82 is coupled between the high-voltage capacitor C and the DC power port 90 for converting the DC voltage output by the solar panel 92 into the voltage difference Vbus across the high-voltage capacitor C. Therefore, the size of the voltage difference Vbus is determined by the DC voltage Vb and the DC voltage output by the solar panel 92 . The power inverter 22 is coupled between the high-voltage capacitor C and the AC power port 14 for converting the voltage difference Vbus into a voltage Va in the form of AC power, and the frequency of the AC voltage Va is F.

Please refer to FIG. 2, which is a relationship diagram between the external output power ratio of the solar photovoltaic converter 50 of FIG. 1 and the frequency F of the AC power output by the power conversion system 100. The horizontal axis of FIG. 2 represents the frequency F of the AC power output from the AC power supply port 14 of the power conversion system 100, and the vertical axis of FIG. 2 represents the external output power ratio of the solar photovoltaic converter 50. The vertical axis marked 100 in FIG. 2 represents that the solar photovoltaic converter 50 outputs at the maximum value (i.e., 100%), and the vertical axis marked 0 represents that the solar photovoltaic converter 50 stops outputting. In addition, when the frequency F is between F_Start and F_Stop, the external output power ratio and the frequency F present a linear inverse relationship, that is, the greater the external output power ratio at this time, the lower the frequency F of the AC power will be. Among them, F_min<F_normal<F_Start<F_Stop, and F_min represents the minimum value of the frequency F of the AC power output by the power conversion system 100, F_normal is the frequency of the normal operation of the power conversion system 100, the external output power ratio corresponding to F_Start is equal to 100%, and the external output power ratio corresponding to F_Stop is equal to 0%. Among them, F_min can be simply referred to as "minimum frequency", F_normal can be simply referred to as "normal frequency", F_Start can be simply referred to as "starting frequency", and F_Stop can be simply referred to as "stop frequency". The starting frequency F_Start is, for example, 60 Hz, and the stopping frequency F_Stop is, for example, 60.5 Hz. In addition, there is a cutoff frequency F_trip, which is used to force the solar photovoltaic inverter 50 to stop outputting power, so that the power conversion system 100 enters overfrequency protection (F_Trip is, for example, 60.6 Hz. Once the frequency F of the alternating current reaches F_Trip or above, the solar photovoltaic inverter 50 will stop outputting power, so the frequency F_trip can be called the "cutoff frequency").

The DC converter 82 can detect the voltage difference Vbus between the two ends of the high voltage capacitor C, and transmit the data of the voltage difference Vbus to the micro control unit 40, so that the micro control unit 40 adjusts the frequency F according to the voltage difference Vbus to control the output power of the solar photovoltaic converter 50. More specifically, when the micro control unit 40 detects that the mains power is off-grid (for example, the connection between the mains power connection port 12 and the mains power 10 is cut off or the mains power 10 is powered off), the micro control unit 40 can adjust the frequency F according to the voltage difference Vbus, thereby adjusting the output power of the solar photovoltaic converter 50. For example, the normal value of the voltage difference Vbus is 400 to 430 volts. When the voltage difference Vbus exceeds 450 volts, it means that the energy accumulated by the high-voltage capacitor C is too much. Therefore, the micro-control unit 40 will first turn off the solar panel 92 and then turn off the solar photovoltaic converter 50. In addition, if the voltage difference Vbus is less than 450 volts but greater than 430 volts, the frequency F is increased to make the solar photovoltaic converter 50 reduce the power output.

Please refer to FIG. 3A and FIG. 3B, which are flowcharts of the micro-control unit 40 in FIG. 1 controlling the power conversion system 100. When the micro-control unit 40 detects that the mains power is off-grid (for example, the connection between the mains power connection port 12 and the mains power 10 is cut off or the mains power 10 is powered off) or when reconnecting to the grid for feeding, the micro-control unit 40 will execute the process of FIG. 3A and FIG. 3B, which includes the following steps: Step S200: The micro-control unit 40 determines whether the power conversion system 100 is reconnected to the grid? Among them, when the conversion system 100 is reconnected to the mains power 10 or the solar photovoltaic inverter 50 starts to supply power, it means that the power conversion system 100 is reconnected to the grid. When the micro-control unit 40 determines that the power conversion system 100 is reconnected to the network, step S201 is executed; otherwise, step S204 is executed; Step S201: The micro-control unit 40 determines whether the current charging ratio of the charging battery 70 is less than a preset ratio S1 according to the state of charge signal SOC? The preset ratio S1 may be between 10% and 80%. If the micro-control unit 40 determines that the current charging ratio of the rechargeable battery 70 is not less than the preset ratio S1, step S202 is executed; otherwise, step S203 is executed. Step S202: The micro-control unit 40 resets the accumulated time T of its timer to zero (T=0), and sets the frequency F of the AC power output from the AC power port 14 of the power conversion system 100 to the cut-off frequency F. The stop frequency F_trip is used to stop the solar photovoltaic converter 50 from outputting power, and the power conversion system 100 enters over-frequency protection; return to step S201; step S203: the micro-control unit 40 reduces the frequency F from the stop frequency F_Stop by a preset value Min_Step (i.e.: F=F_Stop-Min_Step) to enable the solar photovoltaic converter 50 to resume outputting power, and return to step S200. The preset value Min_Step can be equal to ((F_Stop-F_Start)/8); step S204: the micro-control unit 40 determines whether the voltage difference Vbus at both ends of the high-voltage capacitor C is greater than the critical value V2? Among them, the critical value V2 can be, for example, 445 volts to 455 volts; if the micro-control unit 40 determines that the voltage difference Vbus is greater than the critical value V2, step S205 is executed; otherwise, step S210 is executed; step S205: the timer in the micro-control unit 40 adds 1 to its accumulated time; step S206: the micro-control unit 40 determines whether the voltage difference Vbus across the high-voltage capacitor C is greater than the critical value V3? The critical value V3 may be between 465 volts and 475 volts. If the micro-control unit 40 determines that the voltage difference Vbus is greater than the critical value V3, step S207 is executed. Otherwise, step S208 is executed. Step S207: The micro-control unit 40 increases the frequency F to (F_Trip+Max_step) so that the solar photovoltaic inverter 50 coupled to the AC power port 14 stops outputting power and enters over-frequency protection. Max_step is, for example, 0.3 Hz or equal to ((F_Stop-F_Start)/2). Specifically, once the frequency F of the alternating current reaches or exceeds F_Trip, the solar photovoltaic inverter 50 will stop outputting electrical energy. Therefore, when the frequency F of the alternating current is equal to (F_Trip+Max_step), it can be more ensured that the solar photovoltaic inverter 50 will stop outputting electrical energy. Return to step S200. Step S208: The micro-control unit 40 determines whether the time T currently accumulated by its timer is greater than the preset time length Th. The preset time length Th may be, for example, 5 seconds. When the micro-control unit 40 determines that the time T currently accumulated by its timer is greater than the preset time length Th, it executes step S209; otherwise, it returns to step S204; Step S209: The micro-control unit 40 increases the frequency F to (F_Trip+Max_step) so that the AC power port 14 coupled to the micro-control unit 40 increases the frequency F to (F_Trip+Max_step). The solar photovoltaic converter 50 stops outputting power and enters over-frequency protection. After the micro-control unit 40 completes step S209, it returns to step S200. Step S210: the micro-control unit 40 resets the current accumulated time T of its timer to zero (T=0). Step S211: the micro-control unit 40 determines whether the voltage difference Vbus across the high-voltage capacitor C is greater than the critical value V1. Among them, the critical value V1 can be 425 volts to 435 volts; if the micro-control unit 40 determines that the voltage difference Vbus is greater than the critical value V1, then execute step S212; otherwise, return to step S204; and step S212: the micro-control unit 40 increases the frequency F by Max_step, that is, F=(F+Max_step), so that the solar photovoltaic converter 50 reduces the power output; return to step S204.

When the solar photovoltaic converter 50 detects that the voltage or frequency exceeds the normal operating range, it will start protection (for example: overvoltage, undervoltage, overfrequency, underfrequency, islanding, etc.), and then no longer output power to the grid. At this time, the micro control unit 40 will determine whether the solar photovoltaic converter 50 is tripped, and adjust the power conversion system 10 according to the state. 0 AC output frequency to determine whether the solar photovoltaic inverter 50 can be reconnected to the grid for power feeding. If the solar photovoltaic inverter 50 detects that the voltage and frequency of the mains end meet the normal working range, it will be determined that the conditions for reconnecting to the grid for power feeding are met. After counting a specific number of seconds (for example, 300 seconds as specified by the grid-connection regulations), the solar photovoltaic inverter 50 will feed back the grid for output.

In another embodiment of the present invention, in addition to executing the processes of FIGS. 3A and 3B based on the voltage difference Vbus, the micro control unit 40 also executes the fourth step based on the current charged ratio of the rechargeable battery 70 . Diagram of process. The process in Figure 4 includes the following steps: Step S200: This step is the same as step S200 in Figure 3A, that is, the micro control unit 40 will determine whether the power conversion system 100 is reconnected to the network? When the micro control unit 40 determines that the power conversion system 100 is reconnected, step S201 in FIG. 3A is executed; otherwise, step S302 is executed; step S302: the micro control unit 40 determines the current state of the rechargeable battery 70 according to the state of charge signal SOC. Is the charged ratio greater than a preset ratio S2? The preset ratio S2 is, for example, between 20% and 90%. When the microcontrol unit 40 determines that the currently charged ratio of the rechargeable battery 70 is greater than the preset ratio S2, step S304 is executed; otherwise, step S200 is returned; Step S304: The micro control unit 40 determines whether the external output power P_Inv is less than the preset power P1? The preset power P1 is, for example, 500 watts, and can be adjusted according to different control requirements. Dangwei When the control unit 40 determines that the external output power P_Inv is less than the preset power P1, step S306 is executed; otherwise, it returns to step S200; and step S306: the micro control unit 40 converts the AC power output by the power conversion system 100 from the AC power port 14 to The frequency F is increased, so that the solar photovoltaic converter 50 coupled to the AC power port 14 stops outputting electric energy and enters over-frequency protection. For example: the micro control unit 40 increases the frequency F of the alternating current to (F_Trip+Max_step). Among them, F_Trip is, for example, 60.6 Hertz (Hz), and Max_step is, for example, 0.3 Hz. Furthermore, once the frequency F of the alternating current reaches above F_Trip, the solar photovoltaic converter 50 will stop outputting electric energy, and the frequency F_trip can be called the cut-off frequency. Therefore, when the frequency F of the alternating current is equal to (F_Trip+Max_step), it is more ensured that the solar photovoltaic converter 50 will stop outputting electric energy; after the micro control unit 40 completes step S306, it returns to step S200.

In another embodiment of the present invention, in addition to executing the processes of FIGS. 3A and 3B based on the voltage difference Vbus, the micro control unit 40 also executes the 5A process based on the current charged ratio of the rechargeable battery 70 . Figure and the flow of Figure 5B. The processes in Figures 5A and 5B include the following steps: Step S200: This step is the same as step S200 in Figure 3A, that is, the micro control unit 40 will determine whether the power conversion system 100 is reconnected to the network? When the micro control unit 40 determines that the power conversion system 100 is reconnected, step S201 in FIG. 3A is executed; otherwise, step S401 is executed; step S401: the micro control unit 40 determines the current state of the rechargeable battery 70 according to the state of charge signal SOC. Is the charged ratio greater than the preset ratio S2? The preset ratio S2 can be between 20% and 90%. When the micro control unit 40 determines that the currently charged ratio of the rechargeable battery 70 is greater than the preset ratio S2, step S402 is executed; otherwise, step S403 is executed; S402: The micro control unit 40 increases the frequency F of the AC power output by the power conversion system 100 from the AC power port 14 to (F_Trip+Max_Step), so that the solar photovoltaic converter 50 coupled to the AC power port 14 stops outputting electric energy. , and enter overfrequency protection. Among them, F_Trip is 62 for example Hertz (Hz), and Max_step is, for example, 0.3 Hz. Furthermore, once the frequency F of the alternating current reaches above F_Trip, the solar photovoltaic converter 50 will stop outputting electric energy, and the frequency F_Trip can be called the "cutoff frequency". Therefore, when the frequency F of the alternating current is equal to (F_Trip+Max_step), it is more ensured that the solar photovoltaic converter 50 will stop outputting electric energy; in addition, Max_Step can be equal to ((F_Stop-F_Start)/2), and F_Trip is greater than F_Stop; After the micro control unit 40 completes step S402, it returns to step S200; step S403: The micro control unit 40 determines whether the current charged ratio of the rechargeable battery 70 is greater than the preset ratio S3 according to the state of charge signal SOC. The preset ratio S3 is smaller than the preset ratio S2 and can range from 15% to 85%. When the micro control unit 40 determines that the currently charged ratio of the rechargeable battery 70 is greater than the preset ratio S3, step S404 is executed; otherwise, step S407 is executed; step S404: the micro control unit 40 determines the negative value of the external output power P_Inv (i.e. :-P_Inv) is greater than the preset power P2? When the negative value of the external output power P_Inv is positive, it means that the power conversion system 100 receives power from the outside, and the preset power P2 is, for example, 1000 watts, but is not limited thereto. When the micro control unit 40 does not determine that the negative value of the external output power P_Inv is greater than the preset power P2, step S405 is executed; and when the micro control unit 40 determines that the negative value of the external output power P_Inv is greater than the preset power P2, step S405 is executed. Step S409; Step S405: The micro control unit 40 determines whether the external output power P_Inv is less than the preset power P1? The preset power P1 is smaller than the preset power P2, and the preset power P1 is, for example, 500 watts, but is not limited to this. When it is determined that the external output power P_Inv is less than the preset power P1, step S406 is executed; otherwise, step S401 is returned; step S406: the micro control unit 40 increases the frequency F by a preset value Min_Step (ie: F=F+ Min_Step), and return to step S401; wherein, the default value Min_Step can be equal to ((F_Stop-F_Start)/8), and the frequency F is adjusted up to F_Stop in this step, that is, the frequency F in this step is The maximum value F_Max is F_Stop. The function of step S406 is: when the current charged proportion of the rechargeable battery 70 is greater than the preset proportion S3 and the external output power P_Inv is less than the preset power P1, by increasing the frequency F, to reduce the output power of the solar photovoltaic converter 50; Step S407: The micro control unit 40 determines whether the current charged proportion of the rechargeable battery 70 is less than the preset proportion S1 according to the state of charge signal SOC? The preset ratio S1 is smaller than the preset ratios S2 and S3, and can be between 10% and 80%. When the micro control unit 40 determines that the currently charged ratio of the rechargeable battery 70 is smaller than the preset ratio S1, step S408 is executed. ; Otherwise, return to step S401; Step S408: The micro control unit 40 decreases the frequency F by a preset value Min_Step (ie: F=F-Min_Step), and returns to step S401; wherein, the frequency F is in this step The lowest value is adjusted to F_Start, that is, the minimum value of frequency F in this step, F_Min, is F_Start. The function of step S408 is to: when the current charged ratio of the rechargeable battery 70 is less than the preset ratio S1, increase the output power of the solar photovoltaic converter 50 by lowering the frequency F; and step S409: micro control unit 40 Increase the frequency F by a preset value Mid_Step (ie: F=F+Mid_Step), and return to step S401; where the preset value Mid_Step can be equal to ((F_Stop-F_Start)/4), and the frequency F is at this step The highest value is adjusted to F_Stop, that is, the maximum value of frequency F in this step, F_Max, is F_Stop. The function of step S409 is to: when the current charged ratio of the rechargeable battery 70 is greater than the preset ratio S3, and the power received by the power conversion system 100 from the outside is greater than the preset power P2, the frequency F is increased to reduce the solar power variation. The output power of the current converter 50.

When the micro-control unit 40 of the present invention detects that the mains power is off-grid, it will cause the power conversion system 100 to output the alternating current frequency F, thereby inducing the solar photovoltaic converter 50 to generate electricity and feed the grid without entering the islanding (Islanding) protection. It can supply the load 60 and the power conversion system 100. The micro control unit 40 can dynamically adjust the power conversion system 100 according to the voltage difference Vbus across the high-voltage capacitor C, the current charged ratio of the rechargeable battery 70, and the positive and negative magnitude of the external output power P_Inv. Therefore, the overall power flow of the power conversion system 100 can be efficiently controlled.

The above are only preferred embodiments of the present invention, and all equivalent changes and modifications made in accordance with the patentable scope of the present invention shall fall within the scope of the present invention.

F_min: minimum frequency

F_normal: normal frequency

F_Start: starting frequency

F_Stop: Stop frequency

F_Trip: cutoff frequency

Claims (10)

A power conversion system (PCS), including: an AC power supply port, coupled to a solar photovoltaic converter; a first DC power supply port, coupled to a rechargeable battery; a second DC power supply port, coupled to a solar panel; a high-voltage capacitor; a first DC converter coupled between the high-voltage capacitor and the first DC power port; a second DC converter coupled between the high-voltage capacitor and the first DC power port between the second DC power port; a power inverter (DC/AC inverter) coupled between the high-voltage capacitor and the AC power port; and a microcontroller unit (MCU) for controlling the The voltage difference across the high-voltage capacitor adjusts the frequency of an alternating current output by the power conversion system from the alternating current power port; when the micro control unit detects that the mains power is off-grid, and the voltage difference is greater than At the first critical value, the micro-control unit sets the frequency of the alternating current output from the alternating current power port to a cut-off frequency, so that the solar photovoltaic converter stops outputting electric energy; wherein when the micro-control unit detects When the mains power is off-grid and the voltage difference between the first critical value and a second critical value exceeds a preset time length, the micro control unit will output the AC power from the AC power port. The frequency is set as the cut-off frequency; wherein when the micro-control unit detects that the mains power is off-grid and the voltage difference is between the second critical value and a third critical value, the micro-control unit switches the AC power port to The frequency of the output alternating current is increased by a first preset value; and the first critical value is greater than the second critical value, and the second critical value is greater than the third critical value. A power conversion system as described in claim 1, wherein the first critical value is 465 volts to 475 volts, the second critical value is 445 volts to 455 volts, and the third critical value is 425 volts to 435 volts. A power conversion system as described in claim 1, wherein when the microcontroller detects that a mains disconnection occurs, and the current charging ratio of the rechargeable battery is greater than a first preset ratio, and an external output power of the power conversion system is less than a first preset power, the microcontroller increases the frequency of the alternating current to stop the solar photovoltaic inverter from outputting electrical energy. The power conversion system as described in claim 3, wherein when the micro-control unit detects that the mains power is off-grid, it determines that the currently charged proportion of the rechargeable battery is greater than the first preset proportion and the external output power is less than the When the first preset power and the voltage difference is less than the first threshold, the power conversion system provides electric energy from the rechargeable battery to a load. A power conversion system as described in claim 1, wherein when the microcontroller detects that a mains disconnection occurs and determines that the current charging ratio of the rechargeable battery is greater than a first preset ratio and an external output power of the power conversion system is less than a first preset power, and the voltage difference is less than the first critical value, the power conversion system provides power from the rechargeable battery to a load. The power conversion system of claim 1, wherein when the micro-control unit detects that the mains power is off-grid and determines that the current charged ratio of the rechargeable battery is greater than a first preset ratio, the micro-control unit will The frequency of the alternating current is adjusted to a first frequency so that the solar photovoltaic converter stops outputting electric energy. A power conversion system as described in claim 6, wherein when the microcontroller detects that a mains disconnection occurs and determines that the current charging ratio of the rechargeable battery is less than the first preset ratio and greater than a second preset ratio, and the negative value of an external output power of the power conversion system is greater than a first preset power, the microcontroller increases the frequency of the AC power output by the AC power port by a first preset value. The power conversion system as described in claim 7, wherein when the micro-control unit detects that the mains power is off-grid and determines that the current charged ratio of the rechargeable battery is less than a third preset ratio, the AC power port The frequency of the output alternating current is reduced by a second preset value. A power conversion system as described in claim 8, wherein when the microcontroller detects that a mains disconnection occurs and determines that the current charging ratio of the rechargeable battery is less than the first preset ratio and greater than the second preset ratio, the negative value of the external output power is not greater than the first preset power, and the external output power is less than a second preset power, the microcontroller increases the frequency of the AC power output by the AC power port by a third preset value. A power conversion system as described in claim 9, wherein the second preset value is equal to the third preset value.

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