TWI862067B - Power system and power control method - Google Patents

Abstract

A power system includes a power conversion circuit, a DC converter and an inverter. The power conversion circuit is coupled to a AC supply line and a DC supply line to convert voltage between the AC supply line and the DC supply line. The DC converter is coupled to the DC supply line and a charging device. The inverter is coupled to the AC supply line and the charging device. When the charging device provides a supply power to the inverter, the inverter is configured to convert the supply power into a recovered power and transmit the recovered power to the power conversion circuit.

Description

Power grid system and power grid control method

This disclosure relates to an electric energy management technology, in particular to an electric grid system and an electric grid control method.

After being generated and converted by power plants, electricity is supplied to commercial and household users through the mains grid. However, the mains grid may still experience unstable power supply due to unpredictable variables. For users with high electricity demand or extremely high power supply stability, in order to improve power stability, auxiliary microgrids can be established outside the mains grid to optimize or manage electricity.

The present disclosure relates to a power grid system, including a power conversion circuit, a DC converter and an inverter. The power conversion circuit is coupled to an AC bus and a DC bus to convert the voltage between the AC bus and the DC bus. The DC converter is coupled to the DC bus and a charging device. The inverter is coupled to the AC bus and the charging device. When the charging device provides supply power to the inverter, the inverter is used to convert the supply power into recovered power and transmit the recovered power to the power conversion circuit.

The present disclosure also relates to a power grid control method, comprising the following steps: stabilizing the DC voltage of the DC bus according to the AC voltage of the AC bus through a power conversion circuit, and transmitting the DC voltage to a DC converter, wherein the DC converter is used to provide the DC voltage to a charging device; connecting an inverter to the charging device to receive the supply power output by the charging device; and converting the supply power into recovered power through the inverter, and transmitting the recovered power to the power conversion circuit through the AC bus.

The disclosure also relates to a power grid system, including a power conversion circuit, a plurality of DC converters and a controller. The power conversion circuit is coupled to an AC bus and a DC bus to convert the voltage between the AC bus and the DC bus. The DC converter is coupled to the power conversion circuit through the DC bus. The controller is coupled to the power conversion circuit and the DC converter. When an AC voltage is established on the AC bus, the controller is used to control the power conversion circuit to stabilize the DC voltage of the DC bus according to the AC voltage, so as to output or receive power through the DC converter.

This disclosure uses a DC coupling architecture to establish a power grid, so that the power conversion circuit can control the power more stably. In addition, by forming a power recovery path through the inverter, the power grid system will be able to simulate and detect the operation status of the load in a low-consumption state.

100: Power grid system

110: Power conversion circuit

120A-120C: DC converter

130: Controller

D1-D3: Electrical equipment

GD: Mains electricity

LAC: AC bus

LDC: DC bus

V1: AC voltage

V2: DC voltage

200: Power grid system

210: Power conversion circuit

220A-220C: DC converter

230A-230B: Inverter

D1-D3: Electrical equipment

VA1: Supply electricity

VB1: supply power

VA2: Recycle electricity

VB2: Recycle electricity

W21-W25: switch

300: Power grid system

310: Power conversion circuit

320A-320C: DC converter

330: Controller

331: Power supply

340A-340B: Inverter

CS1-CS2: Charging device

SP: Renewable energy device

W31-W36: switch

UPS: Uninterruptible Power Supply

350: Energy storage equipment

351A-351B: Bidirectional converter

BT1-BT2:Battery

S401-S405: Steps

S501-S506: Steps

Figure 1 is a schematic diagram of a power grid system according to a partial embodiment of the present disclosure.

Figure 2 is a schematic diagram of a power grid system according to some embodiments of the present disclosure.

Figure 3 is a schematic diagram of a power grid system according to some embodiments of the present disclosure.

Figure 4 is a flow chart of a power grid control method according to some embodiments of the present disclosure.

Figure 5 is a flow chart of a power grid control method according to some embodiments of the present disclosure.

The following will disclose multiple embodiments of the present invention with drawings. For the purpose of clarity, many practical details will be described together in the following description. However, it should be understood that these practical details should not be used to limit the present invention. In other words, in some embodiments of the present invention, these practical details are not necessary. In addition, in order to simplify the drawings, some commonly used structures and components will be shown in the drawings in a simple schematic manner.

In this article, when an element is referred to as "connected" or "coupled", it may refer to "electrically connected" or "electrically coupled". "Connected" or "coupled" may also be used to indicate the coordinated operation or interaction between two or more elements. In addition, although the terms "first", "second", etc. are used in this article to describe different elements, the terms are only used to distinguish elements or operations described with the same technical terms. Unless the context clearly indicates otherwise, the terms do not specifically refer to or imply an order or sequence, nor are they used to limit the present invention.

This disclosure relates to a power grid system and a power grid control method, which can be applied to establish a microgrid to provide power to multiple electrical devices or manage the power of electrical devices.

FIG. 1 is a schematic diagram of a power grid system 100 according to some embodiments of the present disclosure. The power grid system 100 includes a power conversion circuit 110, at least one DC converter 120A-120C and a controller 130. The power conversion circuit 110 is coupled to the AC bus LAC and the DC bus LDC, respectively, and is used to receive the mains voltage from the mains GD so that an AC voltage V1 is formed on the AC bus LAC. The power conversion circuit 110 can convert the AC voltage V1 to establish a DC voltage DC on the DC bus LDC.

In some embodiments, the power conversion circuit 110 may be an AC-DC converter for receiving an AC voltage V1 and outputting a specific DC voltage V2, so that it can be used to stabilize the DC bus LDC. Since people in this field can understand the circuit principle of the AC-DC converter, it will not be further described here.

The DC converters 120A-120C are coupled to the power conversion circuit 110 via the DC bus LDC, and are also used to connect to multiple electrical devices D1-D3 to provide power to the electrical devices D1-D3, or receive power from the electrical devices D1-D3. In some embodiments, the electrical devices D1-D3 may be charging poles, charging batteries, or solar panels of electric vehicles. The DC converters 120A-120C are used to convert the DC voltage V2 into a working voltage that meets the requirements of the electrical devices D1-D3.

The controller 130 is coupled to the power conversion circuit 110 and the DC converters 120A~120C to drive or shut down the power conversion circuit 110 and the DC converters 120A~120C. In some embodiments, when a stable AC voltage V1 is established/formed on the AC bus LAC, the controller 130 is used to control the power conversion circuit 110 to stabilize the DC voltage V2 of the DC bus LDC according to the AC voltage V1, and to make the DC converters 120A~120C output or receive electric energy. The method of establishing AC voltage on the AC bus LAC will be described in the following paragraphs.

The power grid system 100 shown in FIG. 1 is coupled to the AC bus LAC through the power conversion circuit 110, and the power conversion circuit 110 is connected to multiple DC converters 120A~120C through the DC bus LDC. In other words, the power grid system 100 is connected to the electrical equipment D1~D3 through the DC coupling structure formed by "power conversion circuit 110, DC bus, DC converters 120A~120C". Since the power transmission of the DC voltage V2 does not involve frequency, the power conversion circuit 110 only needs to control the DC voltage V2 on the DC bus LDC to stabilize the DC bus LDC, so it has higher controllability and stability.

FIG. 2 is a schematic diagram of a power grid system 200 according to some embodiments of the present disclosure. In FIG. 2, similar components related to the embodiment of FIG. 1 are represented by the same reference numerals for easy understanding, and the specific principles of similar components have been described in detail in the previous paragraph. If there is no need to introduce the components that have a coordinated operation relationship with the components of FIG. 2, they will not be described here.

The power grid system 200 includes a power conversion circuit 210, at least one DC converter 220A-220C and at least one inverter 230A-230B. The power conversion circuit 210 is coupled to the AC bus LAC and the DC bus LDC respectively, and is used to receive the mains voltage from the mains GD so that an AC voltage V1 is formed on the AC bus LAC. In some embodiments, the power conversion circuit 210 can be a bidirectional AC-DC converter for converting the voltage between the AC bus LAC and the DC bus LDC to transmit the AC voltage V1 or the DC voltage V2.

The DC converters 220A-220C are coupled to the power conversion circuit 210 through the DC bus LDC and are connected to a plurality of electrical devices D1-D3. In some embodiments, the DC converters 220A-220C may be bidirectional DC conversion circuits, which are used to convert and output the working voltage that meets the requirements of the electrical devices D1-D3 according to the DC voltage V2 of the DC bus LDC, or receive the power provided by the electrical devices D1-D3 (such as solar panels, batteries) and convert it into a voltage that meets the power transmission specifications on the DC bus LDC.

The inverters 230A~230B are coupled to the AC bus LAC and are coupled to the electrical devices D1~D2 through power lines to form an energy recovery path. When the electrical devices D1~D2 output supply power to the inverters 230A~230B, the inverters 230A~230B include a DC-AC conversion circuit (such as a converter, a rectifier) to convert the supply power into recovered power, and transmit the recovered power back to the power conversion circuit 210 through the AC bus LAC to complete the energy recovery.

The power grid system 200 shown in FIG. 2 can be applied to power supply management or performance testing of electrical equipment D1~D3. For example, electrical equipment D1~D2 can be charging piles for electric vehicles. When testing the power supply performance of the power grid system 200 applied to the charging piles, in order to avoid energy waste, the power grid system 200 receives the supply power VA1 and VB1 output by the electrical equipment D1~D2 (charging piles) during simulated charging through the inverters 230A~230B. After receiving the supply power VA1 and VB1, the inverters 230A~230B convert them into recovered power VA2 and VB2, and transmit them back to the power conversion circuit 210 through the AC bus LAC.

During the simulation and energy recovery process, the power grid system 200 can control switches W21~W25 to connect the power conversion circuit 210 and inverters 230A~230B to the AC bus LAC or the mains GD. In other embodiments, switches W21~W25 can be set in the power conversion circuit 210 and inverters 230A~230B, or controlled by the power conversion circuit 210 and inverters 230A~230B respectively. The detailed control method of the switch will be described in the following paragraphs.

FIG. 3 is a schematic diagram of a power grid system 300 according to some embodiments of the present disclosure. In FIG. 3, similar elements related to the embodiment of FIG. 1 are represented by the same reference numerals for easy understanding, and the specific principles of similar elements have been described in detail in the previous paragraphs. If there is no need to introduce the elements that have a coordinated operation relationship with the elements in FIG. 3, they will not be described here.

The power grid system 300 includes a power conversion circuit 310, a DC converter 320A-320C, a controller 330 and an inverter 340A-340B. The power conversion circuit 310 is coupled to the AC bus LAC and the DC bus LDC respectively. In some embodiments, the power conversion circuit 310 may be a bidirectional AC-DC converter for converting the voltage between the AC bus LAC and the DC bus LDC to transmit AC voltage or DC voltage.

The DC converters 320A~320C are coupled to the power conversion circuit 310 through the DC bus LDC, and can be connected to multiple charging devices CS1, CS2 and renewable energy devices SP (such as solar panels). The DC converters 320A~320C are used to convert the voltage between the DC bus LDC and the charging devices CS1, CS2 and the renewable energy device SP to provide a voltage that meets the requirements of the charging devices CS1 and CS2, or convert the induced power generated by the renewable energy device SP into a transmission specification that meets the DC bus LDC.

The inverters 340A~340B are coupled to the AC bus LAC and are coupled to the charging devices CS1 and CS2 through power lines to form an energy recovery path. When the charging devices CS1 and CS2 output supply power to the inverters 340A~340B, the inverters 340A~340B are used to convert the supply power into recovery power and transmit the recovery power back to the power conversion circuit 310 to complete the energy recovery.

The controller 330 is coupled to the power conversion circuit 310, the DC converters 320A-320C and the inverters 340A-340B. The controller 330 is used to control the power conversion circuit 110 to stabilize the DC voltage V2 of the DC bus LDC according to the AC voltage V1, and to enable the DC converters 120A-120C to output or receive electrical energy.

In some embodiments, the controller 330 is also coupled to the charging devices CS1 and CS2 to receive charging detection data from the inverters 340A~340B or the charging devices CS1 and CS2. The charging detection data includes the voltage change or current change of the inverters 340A~340B or the charging devices CS1 and CS2 during the detection period. The controller 330 will be able to determine whether the power management of the power grid system 300 meets the standard or evaluate whether the charging performance of the charging devices CS1 and CS2 meets expectations by analyzing the charging detection data. For example, when the charging devices CS1 and CS2 operate at full load, the controller 330 can detect whether the power regulation mechanism in the power grid system 300 is normal or detect whether the voltage protection mechanism operates normally.

In some embodiments, the power grid system 300 further includes an uninterruptible power supply UPS and an energy storage device 350. The uninterruptible power supply UPS is coupled to the AC bus LAC and the controller 330. The energy storage device 350 is coupled to the DC bus LDC, the controller 330 and the uninterruptible power supply UPS, and includes a plurality of bidirectional converters 351A~351B (e.g., bidirectional DC conversion circuits) and a plurality of batteries BT1~BT2.

As mentioned above, the uninterruptible power supply UPS has an internal battery that can be charged when the power grid system 300 is operating normally. When the power grid system 300 lacks a stable power supply input, the controller 330 can be driven according to the uninterruptible power supply UPS. Then, the driven controller 330 will start the energy storage device 350 to establish a DC voltage on the DC bus LDC according to the power in the energy storage device 350, and then drive the power conversion circuit 310 accordingly.

In addition, when the power conversion circuit 310 is driven according to the DC voltage of the DC bus LDC, the power conversion circuit 310 will establish an AC voltage on the AC bus LAC. Then, the power conversion circuit 310 provides power to the DC converters 320A~320C. The timing of driving the controller 330 with the uninterruptible power device UPS will be explained in the following paragraphs.

The power grid system 300 disclosed herein can have different control methods according to different usage scenarios. The following will use Figures 4 and 5 to respectively explain the control methods of the power grid system 300 when it is running in "On-Grid" and "Off-Grid".

FIG. 4 shows a flow chart of the steps of a power grid control method according to a partial embodiment of the present disclosure, which is applied to a "grid-connected" scenario. That is, the power grid system 300 can establish a stable AC voltage through the city power GD.

In step S401, switches W31 and W32 corresponding to the mains GD and the power conversion circuit 310 in the power grid system 300 will be turned on (e.g., controlled by the controller 330) so that the power conversion circuit 310 receives the mains voltage through the AC bus LAC. When the mains GD is stable, the mains voltage will form a stable AC voltage on the AC bus LAC. At this time, other switches W33~W36 remain in the off state.

In step S402, the power conversion circuit 310 establishes a DC voltage in the DC bus LDC according to the AC voltage/AC voltage. The power conversion circuit 310 can output a fixed voltage as a DC voltage according to the AC voltage to achieve the function of stabilizing the DC bus LDC.

In step S403, a DC voltage is established on the DC bus LDC, and after both the AC voltage and the DC voltage are stable, the controller 330 will start the DC converters 320A~320C. The DC converters 320A~320C will receive the DC voltage to output electrical energy to the charging devices CS1 and CS2.

In some embodiments, the controller 330 is also used to transmit charging power data to the charging devices CS1 and CS2. The "charging power data" is used to limit the charging power of each or all charging devices CS1 and CS2. For example, the charging power data includes the upper limit of the output power of the charging devices CS1 and CS2 (such as: the upper limit of each individual power, or the upper limit of the total power), or the operating voltage/current range of the charging devices CS1 and CS2. Different charging programs can be installed in the charging devices CS1 and CS2 to selectively use fast charging or normal power supply mode. Since people in this field can understand the charging method of the charging device, it will not be elaborated here.

In step S404, the switches W33-W35 corresponding to the AC bus LAC and the inverters 340A-340B in the power grid system 300 will be turned on (e.g., controlled by the controller 330), and the inverters 340A-340B will be connected to the charging devices CS1 and CS2 to form an energy recovery path. At this time, the charging devices CS1 and CS2 will provide supply power to the corresponding inverters 340A-340B. The inverters 340A-340B convert the supply power into recovered power, and transmit the recovered power to the power conversion circuit 310 through the AC bus LAC to achieve energy recovery.

In step S405, after the energy recovery path is formed, the controller 330 can receive charging detection data from the inverters 340A~340B or the charging devices CS1 and CS2 to determine whether the power supply performance of the charging devices CS1 and CS2 meets expectations. In other embodiments, the controller 330 can also detect whether the voltage on the AC bus LAC or the DC bus LDC is stable at any time to confirm whether the operation status of the power grid system 300 is normal.

FIG. 5 shows a flow chart of the steps of a power grid control method according to a partial embodiment of the present disclosure, which is applied in an "off-grid" scenario. That is, the power grid system 300 establishes a stable AC voltage by itself.

In step S501, the switch W31 corresponding to the AC bus LAC and the mains GD in the power grid system 300 is in the off state, and the power grid system 300 will automatically establish a stable DC/AC voltage. The "off-grid" scenario is applied to the situation where the mains GD is interrupted or unstable. In one embodiment, "on-grid" and "off-grid" are two different independent application methods, but the disclosure is not limited to this. The power grid system 300 can also switch between the "on-grid" and "off-grid" modes according to the preset conditions.

In some embodiments, the switch W31 can be actively turned off by the controller 330 to set the off-grid mode. In other embodiments, when the mains GD provides the mains voltage to the AC bus LAC as the AC voltage, the controller 330 can detect the mains voltage/AC voltage on the AC bus LAC in real time or periodically. When the mains voltage/AC voltage is unstable (such as: the variation exceeds the preset value, or the AC voltage is lower than the preset value), or when the AC bus LAC/DC bus LDC is unstable due to the unstable mains power supply, the controller 330 will turn off the switch W31 between the AC bus LAC and the mains GD to switch the power grid system 300 from the on-grid mode to the off-grid mode.

In step S502, the AC bus LAC has not yet formed a stable AC voltage, so the switches W32~W36 remain in the off state. The uninterruptible power device UPS will be triggered when no AC voltage is received, and drive the controller 330 (such as: the power supply 331 that supplies power to the controller 330). After the uninterruptible power device UPS is driven, the controller 330 will start the energy storage device 350 to use the power of the energy storage device 350 to establish a DC voltage on the DC bus LDC. Then, the power conversion circuit 310 can be driven by the DC voltage of the controller 330 and the DC bus LDC.

In step S503, after the power conversion circuit 310 is activated, the switch W32 corresponding to the AC bus LAC and the power conversion circuit 310 in the power grid system 300 will be turned on, and the power conversion circuit 310 will establish and stabilize the AC voltage of the AC bus LAC according to the DC voltage on the DC bus LDC.

In step S504, after the AC voltage of the AC bus LAC is established, the switch W36 corresponding to the AC bus LAC and the uninterruptible power supply UPS in the power grid system 300 will be turned on. In addition, after the AC voltage and the DC voltage are both stable, the controller 330 will start the DC converters 320A~320C. The DC converters 320A~320C will receive the DC voltage to output power to the charging devices CS1 and CS2. At this time, the switches W33~W35 are still kept in the off state.

As mentioned above, the controller 330 can also transmit charging power data to the charging devices CS1 and CS2 to limit the charging power of the charging devices CS1 and CS2.

In step S505, the switches W33~W35 corresponding to the AC bus LAC and the inverters 340A~340B in the power grid system 300 will be turned on (e.g., controlled by the controller 330), and the inverters 340A~340B will be connected to the charging devices CS1 and CS2 to form an energy recovery path. At this time, the charging devices CS1 and CS2 will provide supply power to the corresponding inverters 340A~340B. The inverters 340A~340B convert the supply power into recovered power, and transmit the recovered power to the power conversion circuit 310 through the AC bus LAC to achieve energy recovery.

In addition, after the DC converters 320A~320C are activated, the DC converter 320C can also receive charging energy from the renewable energy device SP and provide the charging energy to the DC bus LDC.

In step S506, after the energy recovery path is formed, the controller 330 can receive charging detection data from the inverters 340A~340B or the charging devices CS1 and CS2 to determine whether the power supply performance of the charging devices CS1 and CS2 meets expectations. In other embodiments, the controller 330 can also detect whether the voltage on the AC bus LAC or the DC bus LDC is stable at any time to confirm whether the operation status of the power grid system 300 is normal.

As mentioned above, the power grid system 300 can be connected to the charging devices CS1 and CS2 through the inverters 340A~340B to form an energy recovery path on the DC side, and then transmit the recovered energy back to the AC side. Accordingly, the electric energy can be recycled in the power grid system 300. The power grid system 300 only needs to draw a small amount of electricity from the mains GD to simulate the actual operating state to verify the correctness of the power grid operation.

In addition, during the simulation process, the controller 330 of the power grid system 300 can also plan the charging schedule, using the inverters 340A~340B to simulate different charging requirements (such as controlling the charging amount of the charging pile for the electric vehicle) to test the plan that is most conducive to the power grid dispatch.

In some embodiments, the power grid system 300 can be applied as a microgrid with a power of one million watts (MW). Under normal circumstances, the power grid system 300 can operate in a grid-connected mode; if an abnormality occurs in the mains GD, the power grid system 300 will be able to cut off the connection with the mains GD and switch to an off-grid mode to maintain power supply to the load.

The various elements, method steps or technical features in the aforementioned embodiments can be combined with each other and are not limited to the order of text description or diagram presentation in this disclosure.

Although the contents of this disclosure have been disclosed in the form of implementation as above, they are not intended to limit the contents of this disclosure. Anyone familiar with this art can make various changes and modifications within the spirit and scope of the contents of this disclosure. Therefore, the protection scope of this disclosure shall be subject to the scope of the patent application attached hereto.

300: Power grid system

310: Power conversion circuit

320A-320C: DC converter

330: Controller

331: Power supply

340A-340B: Inverter

350: Energy storage equipment

351A-351B: Bidirectional converter

CS1-CS2: Charging device

BT1-BT2:Battery

W31-W36: switch

SP: Renewable energy device

UPS: Uninterruptible Power Supply

GD: Mains electricity

LAC: AC bus

LDC: DC bus

Claims (20)

A power grid system includes: a power conversion circuit coupled to an AC bus and a DC bus to convert the voltage between the AC bus and the DC bus; at least one DC converter coupled to the DC bus and at least one charging device; and at least one inverter coupled between the AC bus and the at least one charging device to form an energy recovery path, wherein when the at least one charging device provides a supply power to the at least one inverter, the at least one inverter is used to convert the supply power into a recovery power, and transmit the recovery power to the power conversion circuit through the energy recovery path. The power grid system as described in claim 1 further includes: a controller coupled to the power conversion circuit, the at least one inverter and the at least one charging device, and used to receive charging detection data from the at least one inverter or the at least one charging device. The power grid system as described in claim 2, wherein the charging detection data includes the voltage change or current change of the at least one inverter or the at least one charging device during a detection period. A power grid system as described in claim 2, wherein the controller is used to turn on a switch on the AC bus, so that the power conversion circuit receives a mains voltage through the AC bus, and establishes a DC voltage on the DC bus according to the mains voltage. The power grid system as described in claim 2 further comprises: an uninterruptible power supply device coupled to the AC bus and the controller, wherein the controller is used to be driven according to the uninterruptible power supply device; and an energy storage device coupled to the DC bus and the controller, wherein the controller is used to establish a DC voltage on the DC bus according to the energy storage device to drive the power conversion circuit; wherein after the DC voltage is established on the DC bus, the power conversion circuit is used to establish an AC voltage on the AC bus according to the DC voltage. The power grid system as described in claim 5, wherein the controller is also used to determine whether a mains voltage on the AC bus is stable. When the mains voltage is unstable, the controller is used to close a switch between the AC bus and the mains. The power grid system as described in claim 1, wherein the power grid system includes a plurality of DC converters, one of which is coupled to a renewable energy device to receive charging power from the renewable energy device. The power grid system as described in claim 1, wherein the power grid system further comprises: A controller coupled to a plurality of the DC converters and a plurality of the inverters, and the controller is used to transmit a charging power data to a plurality of the charging devices, and the charging power data is used to limit a charging power of the charging devices. A power grid control method includes: stabilizing a DC voltage of a DC bus according to an AC voltage of an AC bus through a power conversion circuit, and transmitting the DC voltage to at least one DC converter, wherein the at least one DC converter is used to provide the DC voltage to at least one charging device; connecting at least one inverter between the at least one charging device and the AC bus to form an energy recovery path; receiving a supply power output by the at least one charging device; and converting the supply power into a recovery power through the at least one inverter, and transmitting the recovery power to the power conversion circuit through the AC bus. The power grid control method as described in claim 9 further comprises: receiving charging detection data from the at least one inverter or the at least one charging device through a controller, wherein the charging detection data comprises a voltage change or a current change of the at least one inverter or the at least one charging device during a detection period. The power grid control method as described in claim 10 further includes: turning on a switch on the AC bus to allow the power conversion circuit to receive a mains voltage through the AC bus; and establishing the DC voltage on the DC bus according to the mains voltage. The power grid control method as described in claim 10 further includes: driving the controller through an uninterruptible power device; using the controller to use the electric energy in an energy storage device to establish the DC voltage on the DC bus to drive the power conversion circuit; and using the power conversion circuit to establish the AC voltage on the AC bus according to the DC voltage. The power grid control method as described in claim 11 further includes: determining whether a mains voltage on the AC bus is stable through the controller; and when the mains voltage is unstable, closing a switch between the AC bus and a mains. The power grid control method as described in claim 9 further comprises: transmitting a charging power data to the at least one charging device through a controller, wherein the charging power data is used to limit a charging power of the at least one charging device. The grid control method as described in claim 9, wherein the method of connecting the at least one inverter to the at least one charging device to receive the supply power output by the at least one charging device comprises: After the AC voltage of the AC bus and the DC voltage of the DC bus are stabilized by the power conversion circuit, a switch on the AC bus is turned on to electrically connect the at least one inverter to the at least one charging device and the AC bus. A power grid system includes: a power conversion circuit coupled to an AC bus and a DC bus for converting the voltage between the AC bus and the DC bus; a plurality of DC converters coupled to the power conversion circuit through the DC bus; and a controller coupled to the power conversion circuit and the DC converters, wherein the controller is used to control the power conversion circuit to control the size of the DC voltage of the DC bus according to the AC voltage when an AC voltage is established on the AC bus, so as to stabilize the DC bus, and output or receive power through the DC converters. The power grid system as described in claim 16, wherein the DC converters are coupled to at least one charging device, and the power grid system further comprises: an inverter coupled to the AC bus and the charging device, wherein when the charging device provides a supply power to the inverter, the inverter is used to convert the supply power into a recovery power and transmit the recovery power to the power conversion circuit. The power grid system as described in claim 17, wherein the controller is also used to receive a charging detection data from the inverter or the charging device, and the charging detection data includes the voltage change or current change of the inverter or the charging device during a detection period. A power grid system as described in claim 16, wherein the controller is used to turn on a switch on the AC bus, so that the power conversion circuit receives a mains voltage through the AC bus, and establishes the DC voltage on the DC bus according to the mains voltage. The power grid system as described in claim 16 further comprises: an uninterruptible power device coupled to the AC bus and the controller, wherein the controller is used to be driven according to the uninterruptible power device; and an energy storage device coupled to the DC bus and the controller, wherein the controller is used to establish the DC voltage on the DC bus according to the energy storage device to drive the power conversion circuit; wherein after establishing the DC voltage on the DC bus, the power conversion circuit is used to establish the AC voltage on the AC bus according to the DC voltage.

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