KR102369890B1 - Stand-alone and grid-connected compatible inverter system for supporting the restoration of grid power and operation method thereof - Google Patents

Abstract

Independent and grid-compatible inverter systems supporting power failure protection mode are provided. The inverter system includes a first current sensor sensing at least a portion of a grid current flowing from an AC grid power source to a first output node, and sensing an inductor current flowing from an inductor having one end connected to a second output node to the second output node. to at least one of a second current sensor, a voltage sensor sensing an output voltage between both ends of the second output node and the third output node, and a grid sensing current sensed by the first current sensor, the inductor current, and the output voltage. Based on the inverter system may include a processor that determines an operation mode to operate as any one of a standalone power supply, a grid-connected power supply, and an uninterruptible power supply (UPS).

Description

STAND-ALONE AND GRID-CONNECTED COMPATIBLE INVERTER SYSTEM FOR SUPPORTING THE RESTORATION OF GRID POWER AND OPERATION METHOD THEREOF

The following description relates to an independent and grid-connected compatible inverter system and an operating method thereof. More specifically, based on the grid sense current that is at least a portion of the grid current flowing from the AC grid power source, the inductor current and output voltage within the inverter system, etc., independent and It relates to a grid-connected compatible inverter system.

A standalone inverter refers to a power system that generates a single-phase AC voltage (220Vrms / 60Hz) as an output in an area where there is no utility grid. Specifically, in the case of a stand-alone inverter, various types of energy, such as gasoline combustion energy, wind energy, and solar energy, are converted into electrical energy and used as an input of the inverter system. A grid-connected inverter refers to a power system that is directly connected to a commercial AC grid and injects generated power into the grid. In the case of a grid-connected inverter, a single-phase AC current synchronized with the grid voltage is generated as an output.

If grid power is connected to the output of the existing stand-alone inverter, operation is impossible, and on the contrary, it is not possible to operate the output of the existing grid-connected inverter without grid power. It is necessary to study an inverter system that supports operation as either a standalone power supply, a grid-connected power supply, or a UPS to solve the above problems.

Republic of Korea Patent Registration No. 10-1704472 (2017.02.10.)

Standalone / grid compatible single-phase inverter. Goo-Young Jung, and Tae-Cheol Tae. Kyungsoo Kang. Roh Jung-wook (Proceedings of the Power Electronics Conference 2018. 07. 03. ~ 07. 06.)

According to one aspect, an independent and grid-connected inverter system supporting a power failure protection mode is provided. The inverter system includes a first current sensor sensing at least a portion of a grid current flowing from an AC grid power source to a first output node, and sensing an inductor current flowing from an inductor having one end connected to a second output node to the second output node. to at least one of a second current sensor, a voltage sensor sensing an output voltage between both ends of the second output node and the third output node, and a grid sensing current sensed by the first current sensor, the inductor current, and the output voltage. Based on the inverter system may include a processor that determines an operation mode to operate as any one of a standalone power supply, a grid-connected power supply, and an uninterruptible power supply (UPS).

According to an embodiment, when the magnitude of the grid sensing current sensed by the first current sensor is equal to or less than the first threshold, the processor may control the inverter system in an independent power mode operating as an AC voltage source.

According to another embodiment, when the magnitude of the grid sensing current sensed by the first current sensor exceeds a first threshold, the processor controls the inverter system in a grid-connected power mode operating as an AC current source. can

According to another embodiment, the inverter system may further include a communication unit configured to receive whether power consumption from a load exceeds a preset reference value from a current transformer connected to the grid power source.

According to another embodiment, when the inverter system operates in the grid-connected power mode, the communication unit receives a first control signal indicating a state in which the power consumption in the load exceeds a preset reference value from the current transformer Then, the processor may generate an inductor current flowing from the inductor to the second output node.

According to another embodiment, when the inverter system operates in the grid-connected power mode, when the communication unit receives a second control signal indicating a state in which power consumption in a load is less than or equal to a preset reference value from the current transformer, The processor may maintain the magnitude of an inductor current flowing from the inductor to the second output node.

According to another embodiment, while the inverter system is operating in the grid-connected power mode, when the magnitude of the grid detection current sensed by the first current sensor is less than or equal to a first threshold, the processor determines that the grid is out and control the inverter system in a UPS mode in which the inverter system operates as an AC voltage source.

According to another embodiment, when the inverter system operates in the UPS mode, the processor operates in a power failure protection mode and the magnitude of the inductor current flowing from the inductor to the second output node exceeds a second threshold. Alternatively, the relay switch included in the inverter system may be opened by detecting a power failure when the slope of the AC grid voltage exceeds the third threshold.

According to another embodiment, the relay switch is disposed between the first node and the third output node connecting the source node of the first MOSFET and the drain node of the second MOSFET of the full-bridge circuit included in the inverter system It can be characterized as being.

According to another embodiment, when the relay switch is opened, the processor operates in a standby mode and sets the inverter system to the independent power mode or It can be controlled in one of the grid-connected power modes.

According to another embodiment, when the power of the inverter system is turned on or the relay switch is opened, the processor returns to the standby mode according to the magnitude of the grid sensing current sensed by the first current sensor Whether to control the inverter system in one of the independent power mode or the grid-connected power mode may be determined again.

According to another aspect, there is provided a method of operating an independent and grid-connected compatible inverter system supporting a power failure protection mode. The method of operating the independent and grid-connected compatible inverter system includes: when the inverter system is turned on, a processor setting an operation mode of the inverter system to a standby mode; grid sensing current flowing from an AC grid power source to a first output node determining whether to control the inverter system in one of a standalone power mode or a grid-connected power mode according to the size of When the first threshold or less, the step of determining, by the processor, the grid failure, and when the grid failure occurs, the processor controlling the inverter system in a UPS mode in which the inverter system operates as an AC voltage source. there is.

According to an embodiment, in the method of operating the independent and grid-connected inverter system, when the inverter system operates in the UPS mode, the processor includes an inductor flowing from an inductor included in the inductor system to the second output node. A relay switch included in the inverter system by detecting a power failure when the magnitude of the current exceeds the second threshold or the slope of the output voltage at both ends of the second output node and the third output node exceeds the third threshold It may include operating in a power recovery protection mode to open.

According to another embodiment, the relay switch is to be disposed between the first node and the third output node connecting the source node of the first MOSFET and the drain node of the second MOSFET of the full-bridge circuit included in the inverter system. can

According to another embodiment, in the method of operating the independent and grid-connected compatible inverter system, when the power of the inverter system is turned on or the relay switch is opened, the processor controls the inverter according to the magnitude of the grid sensing current. and returning to the standby mode of re-judging whether to control the system in one of the independent power mode or the grid-connected power mode.

The accompanying drawings for use in the description of the embodiments of the present invention are only part of the embodiments of the present invention, and for those of ordinary skill in the art (hereinafter referred to as "those skilled in the art"), the invention Other drawings may be obtained based on these drawings without additional effort to
1 is a block diagram of an inverter system supporting a conventional off-line UPS function.
2 is a block diagram of an independent and grid-connected compatible inverter system according to an embodiment.
3 is a circuit diagram of an independent and grid-connected compatible inverter system according to an embodiment.
4 is a state diagram illustrating an operation mode of the inverter system of FIG. 3 .
5A, 5B and 5C are circuit diagrams illustrating a power recovery protection mode of an independent and grid-connected compatible inverter system according to an embodiment.
FIG. 6 shows a simulation graph of the inductor current I _L when power recovery protection is performed based on the inverter system of FIG. 5C .
7A is a circuit diagram of an inverter system that performs a power recovery protection mode according to a change in slope of the output voltage V ₀ in the independent and grid-connected compatible inverter system of FIG. 5C .
FIG. 7B shows a simulation graph of the output voltage V ₀ when power recovery protection is performed based on the inverter system of FIG. 7A .

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The following detailed description of the present invention refers to the accompanying drawings, which show by way of illustration a specific embodiment in which the present invention may be practiced, in order to clarify the objects, technical solutions and advantages of the present invention. These embodiments are described in detail to enable those skilled in the art to practice the present invention.

Throughout this description and claims, the word 'comprise' and variations thereof are not intended to exclude other technical features, additions, components or steps. In addition, 'one' or 'an' is used to mean more than one, and 'another' is limited to at least a second or more.

In addition, terms such as 'first' and 'second' of the present invention are for distinguishing one component from other components, and unless it is understood to indicate an order, the scope of rights is limited by these terms. is not For example, a first component may be referred to as a second component, and similarly, the second component may also be referred to as a first component.

When a component is referred to as being “connected” to another component, it may be directly connected to the other component, but it should be understood that another component may intervene. On the other hand, when it is mentioned that a certain element is "directly connected" to another element, it should be understood that the other element does not exist in the middle. Meanwhile, other expressions describing the relationship between elements, that is, “between” and “immediately between” or “neighboring to” and “directly adjacent to”, etc., should be interpreted similarly.

In each step, identification symbols (eg, a, b, c, etc.) are used for convenience of explanation, and identification codes do not describe the order of each step unless it necessarily results in logic, and each The steps may occur out of the order specified. That is, each step may occur in the same order as specified, may be performed substantially simultaneously, or may be performed in the reverse order.

Other objects, advantages and characteristics of the present invention will become apparent to a person skilled in the art, in part from this description, and in part from practice of the present invention. The following illustrations and drawings are provided by way of illustration and are not intended to limit the invention. Accordingly, the details disclosed herein with respect to a specific structure or function should not be construed in a limiting sense, but merely provide a representative guideline for those skilled in the art to variously practice the present invention with substantially any suitable detailed structures. It should be interpreted as basic data.

Moreover, the invention encompasses all possible combinations of the embodiments indicated herein. It should be understood that various embodiments of the present invention are different but need not be mutually exclusive. For example, specific shapes, structures, and characteristics described herein may be implemented in other embodiments without departing from the spirit and scope of the invention in relation to one embodiment. In addition, it should be understood that the position or arrangement of individual components in each disclosed embodiment may be changed without departing from the spirit and scope of the present invention. Accordingly, the following detailed description is not intended to be taken in a limiting sense, and the scope of the present invention, if properly described, is limited only by the appended claims, along with all scope equivalents to those claimed. Like reference numerals in the drawings refer to the same or similar functions throughout the various aspects.

In this specification, unless indicated otherwise or clearly contradicted by context, items referred to in the singular encompass the plural unless the context requires otherwise. In addition, in describing the present invention, if it is determined that a detailed description of a related known configuration or function may obscure the gist of the present invention, the detailed description thereof will be omitted.

Hereinafter, in order to enable those skilled in the art to easily practice the present invention, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

1 is a circuit diagram of an inverter system supporting a conventional off-line UPS function. Referring to FIG. 1 , an inverter system 100 including a battery 110 , an AC/DC converter 120 , a DC/AC converter 130 , and a relay switch 140 is shown. The conventional inverter system 100 requires the operation of the AC grid breaker 170 , the transfer switch 180 , and the relay switch 140 in the process of being connected to the AC grid power source 150 and the load 160 . Specifically, if a power outage occurs while the AC grid power source 150 is connected, the relay switch 140 is changed to a turned-on state, and the transfer switch 180 is newly connected to the inverter system 100 so that the inverter system 100 ) can operate as an uninterruptible power supply.

However, the conventional inverter system 100 has a problem in that a reaction speed is slow due to a delay generated while the plurality of switches 140 , 170 , and 180 operate. In general, it takes about 500ms to 1 second to change the operation, but there is a limit that most loads are designed to respond only to an instantaneous power failure of 50ms or less. Therefore, the conventional hybrid inverter system 100 has a disadvantage in that it is difficult to substantially perform a function as an uninterruptible power supply device. In addition, when all three switches 140 , 170 , and 180 are in an on state due to an error in the switching operation, there is a problem in that it is impossible to determine the presence or absence of a grid voltage. In addition, the conventional AC mode fastening of the inverter system 100 is complicated and there is a limitation in that a separate electrical work is required.

2 is a circuit diagram of an independent and grid-connected compatible inverter system according to an embodiment. Referring to FIG. 2 , an independent and grid-connected compatible inverter system 200 according to an embodiment includes a battery 210 , a DC/DC converter 220 , a DC/AC converter 230 and a relay switch 240 . may include In the independent and grid-connected compatible inverter system 200 according to this embodiment, the relay switch 240 and the AC grid breaker 270 are connected to one end of the load 260 . In the independent and grid-connected compatible inverter system 200 , the operation of the independent power mode or the grid-connected power mode may be determined based on whether the inverter system 200 is connected to the AC grid power source 250 . In addition, in a situation in which the AC grid power source 250 is dropped and the grid breaker 270 is not opened in the grid-connected power mode, the independent and grid-connected inverter system 200 can be determined to operate in the UPS mode. . Independent and grid-connected compatible inverter system 200 according to this embodiment does not use a transfer switch compared to the existing inverter system, and only a simple connection with the AC grid power source 250 provides an independent power mode, grid-connected power mode And it is possible to implement a compatible inverter system operating in the UPS mode.

3 is a circuit diagram of an independent and grid-connected compatible inverter system according to an embodiment. Referring to FIG. 3 , the independent and grid-connected compatible inverter system 300 includes a first current sensor 310 , a second current sensor 320 , a voltage sensor 330 , a processor 340 , and a relay switch 350 . and a communication unit 370 . The first current sensor 310 may detect at least a portion of the grid current I _GRID flowing to the first output node 361 by the AC grid power V _GRID as the grid sensing current I _{GRID_DETECTED} . Exemplarily, between the first output node 361 and the second output node 362 , a current transformer CT ₁ (CT: Current Transformer) is disposed so that the first current sensor 310 detects the grid sensing current I _{GRID_DETECTED} . do.

The second current sensor 320 may sense the inductor current I _L flowing from the inductor to the second output node 362 . Specifically, the inductor may be disposed between the source terminal and the second output node 362 of the third MOSFET M ₃ in the full-bridge circuit included in the independent and grid-connected inverter system 300 .

The voltage sensor 330 may sense the output voltage V _O of both ends of the second output node 362 and the third output node 363 . The processor 340 determines that the inverter system 300 is configured as one of a standalone power source, a grid-connected power supply and an uninterruptible power supply (UPS) based on at least one of the grid sensing current I _{GRID_DETECTED} , the inductor current I _L and the output voltage V _O . It is possible to determine an operation mode to operate.

Additionally, a second current transformer CT ₂ for measuring power consumption consumed by the load may be connected to the AC grid power source V _GRID . Specifically, the second current transformer CT ₂ may determine whether power consumption in the load exceeds a preset reference value. Specifically, the second current transformer CT ₂ is a first control signal indicating a state in which power consumption in the load exceeds a preset reference value (eg, 1.5 kW) or a second control signal indicating a state in which power consumption is less than or equal to a preset reference value may be generated, and one of the generated control signals may be transmitted to the communication unit 370 connected to the processor 340 .

The communication unit 370 receives a signal for controlling the inverter system 300 in one of the ESS mode or the grid standby mode in the grid-connected power mode from the second current transformer CT ₂ . The communication unit 370 may generate a first voltage signal (eg, high voltage) or a second voltage signal (eg, low voltage) according to the first control signal or the second control signal and transmit it to the processor 340 . Specifically, the communication unit 370 may be communicatively connected to the second current transformer CT ₂ based on a short-range wireless communication method such as Bluetooth or a wireless LAN (WLAN) communication method such as Wi-Fi.

The relay switch 350 is between the first node and the third output node 363 connecting the source node of the first MOSFET M ₁ and the drain node of the second MOSFET M ₂ of the full bridge circuit included in the inverter system 300 . can be placed in The relay switch 350 may be opened to protect the load in a power recovery situation in which the AC grid power V _GRID is restored while the inverter system 300 operates in the UPS mode. A detailed operation of the relay switch 350 will be described in detail with FIG. 4 to be added below.

4 is a state diagram illustrating an operation mode of the inverter system of FIG. 3 . When the inverter system 300 is turned off, it maintains the off mode 410 . In this case, when the inverter system 300 is newly turned on, the inverter system 300 enters the standby mode 420 . In the standby mode 420, the processor 340 operates the inverter system 300 as an AC voltage source when the magnitude of the grid sensing current I _{GRID_DETECTED} detected by the first current sensor 310 is less than or equal to the first threshold. 430) can be controlled. The grid sensing current I _{GRID_DETECTED} may represent at least a portion of the grid current I _GRID flowing from the AC grid power V _GRID toward the first current sensor 310 . In the embodiment of FIG. 4 , the first threshold is set to “0 A”, but this is only an exemplary description for helping understanding, and should not be construed as limiting or limiting the scope of rights. For example, setting the first threshold to various values such as 10 mA according to a circuit diagram to which the inverter system 300 is connected will also be included in the scope of the present embodiment.

As another embodiment, when the magnitude of the grid detection current I _{GRID_DETECTED} sensed by the first current sensor 310 exceeds the first threshold, the processor 340 operates the inverter system 300 as an AC current source. One can control the grid-connected power mode 441. Specifically, in the grid-connected power mode, the first grid-connected power mode 441 indicating the grid standby state and the second grid-connected power mode in which the inverter system 300 operates in the ESS (energy storage system) mode ( 442) may exist. Illustratively, but not limitedly, in the first grid-connected power mode 441 , the inductor current I _L generated by the inverter system 300 may be 0 A. That is, in the corresponding mode, the inverter system 300 operates as an AC current source, but may not emit current.

A second current transformer CT ₂ for measuring power consumption consumed by the load may be connected to the AC grid power source V _GRID . In addition, the processor 340 may be connected to the communication unit 370 that receives the measured power from the second current transformer CT ₂ . The communication unit 370 may receive one of the first control signal or the second control signal from the second current transformer CT ₂ to control the inverter system 300 in one of the grid-connected power modes 441 and 442 . , when the inverter system 300 operates in the first grid-connected power mode 441, the communication unit 370 indicates a state in which power consumption in the load from the second current transformer CT ₂ exceeds a preset reference value A first control signal may be received. In this case, the processor 340 increases the inductor current I _L flowing from the inductor to the second output node 362 so that the inverter system 300 operates as an ESS (energy storage system) in a second grid-connected power mode ( 442 , the inverter system 300 may be controlled.

However, when the communication unit 370 receives the second control signal from the second current transformer CT ₂ indicating a state in which power consumption in the load is less than or equal to a preset reference value, the processor 340 controls the grid for maintaining the size of the inductor current _IL . It is possible to maintain the first grid-connected power supply mode 442 indicating the standby state. Illustratively, but not limitedly, in this mode, the processor 340 may maintain the inductor current I _L as 0 A.

In addition, while the inverter system 300 is operating in one of the two grid-connected power modes 441 and 442 , the magnitude of the grid detection current I _{GRID_DETECTED} sensed by the first current sensor 310 is less than or equal to the first threshold. If so, the processor 340 may determine the grid failure of the AC grid power source. In this case, the processor 340 may control the inverter system 300 in the UPS mode 450 in which the inverter system 300 operates as an AC voltage source.

As another embodiment, when the inverter system 300 operates in the UPS mode 450 , the processor 340 may operate in the power recovery protection mode. The processor 340 may detect a power failure when the magnitude of the inductor current I _L sensed by the second current sensor 320 exceeds the second threshold or the slope of the AC grid voltage V _GRID exceeds the third threshold. . In this case, the processor 340 may protect the load in a power failure situation by opening the relay switch 350 included in the inverter system 300 .

When the relay switch 350 is opened as described above, the processor 340 operates in the standby mode 420 , and the inverter system 300 according to the magnitude of the grid detection current I _{GRID_DETECTED} detected from the first current sensor 310 . can be controlled in one of the independent power mode 430 or the grid-connected power mode 441 and 442 . The standby mode 420 represents a mode in which the inverter system 300 enters when the inverter system 300 is newly turned on or a forced end signal is transmitted to the inverter system 300 such as opening of the relay switch 350 . In the standby mode 420, the processor 340 determines whether to control the inverter system 300 in either the stand-alone power mode 430 or the grid-tied power mode 441 based on the magnitude of the grid sensing current I _{GRID_DETECTED} . can be re-evaluated.

5A, 5B and 5C are circuit diagrams illustrating a power recovery protection mode of an independent and grid-connected compatible inverter system according to an embodiment. Referring to FIG. 5A, a circuit diagram of an inverter system operating in a UPS mode is shown. In the circuit diagram of FIG. 5A , the stage before C _{DC_LINK} in the circuit diagram of FIG. 3 is shown as a DC LINK battery for convenience of explanation. In addition, in FIG. 5A, the full bridge circuit of FIG. 3 is represented by a block D(t). Also, blocks supporting the power recovery protection mode, such as the current sensors 310 and 320 , the voltage sensor 330 , and the processor 340 included in FIG. 3 , are omitted from FIG. 5A , but functions are assumed to operate normally.

Referring to FIG. 5A , a circuit diagram in which the AC grid power V _GRID is off-grid and the inverter system operates in the UPS mode is shown. The inverter system is connected to the load R _load by the relay switch 510 and provides power to the load R _load as an AC voltage source. Since the home circuit breaker 520 is opened in an overcurrent or short circuit situation, it is not blocked in a power outage situation. Accordingly, there is a need for the processor in the inverter system to operate in a power failure protection mode to protect the load.

5B is a circuit diagram of the inverter system in a situation in which the power recovery protection mode is not operated. If the AC grid power V _GRID is restored while the inverter system is operating in UPS mode, the AC voltage generated by the inverter system and the voltage transmitted from the AC grid power are transmitted as the output voltage V _O of the load R _load . collision will occur. Therefore, if the above problems are not quickly dealt with in the inverter system, there is a possibility that an inverter system failure, load failure, as well as an accident such as a fire may occur. Accordingly, the inverter system according to the present embodiment provides a new power recovery protection mode.

FIG. 5C is a circuit diagram in which the voltage transmitted from the D(t) block becomes 0 V as the relay switch 510 is opened in a power recovery situation. The processor of the inverter system of the present embodiment may perform the power recovery protection mode based on the magnitude of the inductor current I _L or the slope of the AC grid voltage V _GRID . Exemplarily, the AC grid voltage according to time may be expressed as in Equation 1 below.

For example, the amplitude A of the AC grid voltage V _GRID in Korea may represent 220 V. In addition, the output value D(t) of the full bridge circuit may be expressed as in Equation 2 below.

Illustratively, k may be set to 0.8 to create a duty within the inverter system. It is assumed that the time at which the power recovery occurs when the AC grid voltage V _GRID is restored is t ₀ , and the time at which the power recovery protection mode is executed is Δt. In this case, the average voltage input to the load during the time the relay switch is opened as the power recovery protection mode when power recovery occurs may be expressed as Equation 3 below.

In this case, the current I _L flowing along the inductor may be calculated as in Equation 4 below based on the relationship between voltage and current of the inductor.

In the above case, I _L (t ₀ ) is calculated as in Equation 5 below, where B represents the root mean square (rms) of the inverter voltage.

As a result, I _L in a power recovery situation in which the AC grid voltage V _GRID is restored may be summarized as in Equation 6 below.

As shown in Equation 6, the inductor current I _L may be affected by various variables such as the inductor current I _L (t ₀ ) at the time of restoration and the phase angle θ of the AC grid voltage V _GRID . The processor of the inductor system may perform the restoration mode by setting a second threshold value of a predetermined value to perform the restoration protection mode, and comparing the magnitude of the inductor current I _L with the second threshold value.

이고, f는 60 Hz, θ는 180 degree, L가 24 mH, R은 32.267Ω으로 파라미터를 설정하고 시뮬레이션이 진행된 경우를 나타낸다. 예시적으로, 제2 임계치가 20 mA로 설정되어서 프로세서는 복전 보호 모드를 수행한다. 이 경우에, 복전이 발생된 t₀ 시점으로부터 릴레이 스위치가 개방된 시점(t₀ + Δt)까지는 1 ms가 소요됨으로써 인덕터 시스템과 부하의 고장을 방지할 수 있다.FIG. 6 shows a simulation graph of the inductor current I _L when power recovery protection is performed based on the inverter system of FIG. 5C . 6 is V _GRID in the circuit diagram of FIG. 5c

, f is 60 Hz, θ is 180 degree, L is 24 mH, R is 32.267Ω, and the parameters are set and the simulation is performed. Exemplarily, the second threshold is set to 20 mA so that the processor performs a power recovery protection mode. In this case, 1 ms is taken from the time t ₀ when power recovery occurs to the time when the relay switch is opened (t ₀ + Δt), thereby preventing failure of the inductor system and the load.

7A is a circuit diagram of an inverter system that performs a power recovery protection mode according to a change in slope of the output voltage V ₀ in the independent and grid-connected compatible inverter system of FIG. 5C . Referring to FIG. 7A , an inverter system for detecting a change in slope of an AC grid voltage V _GRID based on an op-amp is illustrated. The inverter system may detect a change in the slope of the AC grid voltage V _GRID in order to prevent a failure of the inverter system and the load when the AC grid voltage V _GRID is restored. For example, the processor in the inverter system may open the relay switch 710 when a change in the slope of the AC grid voltage V _GRID equal to or greater than the third threshold is detected. Specifically, the processor periodically receives the magnitude of the output voltage V ₀ from the voltage sensor. The processor may quantize the sensed analog data (= the magnitude of the output voltage V ₀ ) to a predetermined level and store the level of the output voltage V ₀ . The processor repeatedly receives the magnitude of the output voltage V ₀ from the voltage sensor according to a preset period. The processor may detect a change in slope of the AC grid voltage V _GRID according to a previous output voltage level, a current output voltage level, and a measurement period.

FIG. 7B shows a simulation graph of the output voltage V ₀ when power recovery protection is performed based on the inverter system of FIG. 7A . FIG. 7B illustrates a case where the measurement period of the output voltage V ₀ is set to 800 ns in FIG. 7A . Under normal operation, the slope of the output voltage V ₀ will be within the amplitude range. However, in the case of the power recovery mode, the processor may detect a power recovery situation because voltage fluctuations greater than or equal to the third threshold are accompanied.

Although not shown in the drawings, a method of operating an independent and grid-connected compatible inverter system supporting a power failure protection mode according to another embodiment is provided. Specifically, the operating method of the independent and grid-connected compatible inverter system includes the steps of, when the inverter system is turned on, the processor setting the operation mode of the inverter system to the standby mode, and the grid current flowing from the AC grid power source to the first output node determining whether to control the inverter system in one of a standalone power mode or a grid-tied power mode according to a magnitude of a grid-sensing current I _{GRID_DETECTED} representing at least a portion of the inverter system, wherein the inverter system operates in a grid-tied power mode During the process, when the magnitude of the grid detection current I _{GRID_DETECTED} becomes less than or equal to a first threshold, the processor determines the grid failure, and when the grid failure occurs, the processor operates the inverter system as an AC voltage source. UPS mode and controlling the inverter system.

In the method of operating the independent and grid-connected compatible inverter system, when the inverter system operates in the UPS mode, the processor determines that the magnitude of the inductor current flowing from the inductor included in the inductor system to the second output node is the second In a power recovery protection mode that opens a relay switch included in the inverter system by detecting a power failure when the threshold value is exceeded or the slope of the output voltage between both the second output node and the third output node exceeds the third threshold value It may further include a step of operating.

Specifically, the relay switch may be disposed between the first node and the third output node connecting the source node of the first MOSFET and the drain node of the second MOSFET of the full bridge circuit included in the inverter system.

In the method of operating the independent and grid-connected compatible inverter system, when the power of the inverter system is turned on or the relay switch is opened, the processor sets the inverter system according to the magnitude of the grid sensing current I _{GRID_DETECTED} to the independent power mode Alternatively, the method may further include returning to the standby mode of re-determining whether to control in one of the grid-connected power modes.

As mentioned above, although the technical idea of the present invention has been described in detail with reference to preferred embodiments, the technical idea of the present invention is not limited to the above embodiments, and the technical idea of the present invention is not limited to the above embodiments. Various transformations and modifications are possible by a person having ordinary knowledge in the technical field within the scope of the idea.

Claims (8)

In the inverter system supporting the power failure protection mode,
a first current sensor sensing at least a portion of a grid current flowing from the AC grid power source to the first output node;
a second current sensor for sensing an inductor current flowing from an inductor having one end connected to a second output node to the second output node;
a voltage sensor sensing an output voltage at both ends of the second output node and the third output node; and
a processor that determines an operating mode of the inverter system based on at least one of a grid sense current sensed by the first current sensor, the inductor current, and an output voltage
including,
While the inverter system is operating in the grid-connected power mode, if the magnitude of the grid sensing current sensed by the first current sensor is less than or equal to a first threshold, the processor determines that the inverter system is out of the grid, and the inverter system uses the AC voltage source Controls the inverter system in a UPS mode that operates as
When the inverter system operates in the UPS mode, the processor operates in a power failure protection mode and the magnitude of the inductor current flowing from the inductor to the second output node exceeds a second threshold or the slope of the AC grid voltage is Opening the relay switch included in the inverter system by detecting a power failure when exceeding the third threshold,
The first output node represents a node connecting one end of a load connected to the AC grid power source and the inverter system,
The second output node represents one end of the inductor connected to the full bridge circuit included in the inverter system,
The third output node represents a node connecting one end of the relay switch and one end of the voltage sensor.
According to claim 1,
When the inverter system operates in the UPS mode, the processor operates in a power failure protection mode and the magnitude of the inductor current flowing from the inductor to the second output node exceeds a second threshold or the slope of the AC grid voltage is An inverter system that opens a relay switch included in the inverter system by detecting a power failure when a third threshold is exceeded.
3. The method of claim 2,
The relay switch is
Inverter system, characterized in that it is disposed between the first node and the third output node connecting the source node of the first MOSFET and the drain node of the second MOSFET of the full bridge circuit included in the inverter system.
4. The method of claim 3,
When the relay switch is opened, the processor operates in a standby mode and controls the inverter system according to the magnitude of the grid sensing current sensed from the first current sensor.
5. The method of claim 4,
When the power of the inverter system is turned on or the relay switch is opened, the processor returns to the standby mode to reset the operation mode of the inverter system according to the magnitude of the grid sensing current sensed from the first current sensor. Inverter system to judge.
In the operating method of the inverter system supporting the power recovery protection mode,
setting, by a processor, an operation mode of the inverter system to a standby mode when the inverter system is turned on;
determining an operation mode of the inverter system according to a magnitude of a grid sensing current flowing from an AC grid power source to a first output node;
determining, by the processor, out of the grid when the magnitude of the grid sensing current becomes less than or equal to a first threshold while the inverter system is operating in the grid-connected power mode;
controlling, by the processor, the inverter system in a UPS mode in which the inverter system operates as an AC voltage source when the grid failure occurs; and
When the inverter system operates in the UPS mode, the processor determines that the magnitude of the inductor current flowing from the inductor included in the inverter system to the second output node exceeds a second threshold or the second output node and the third output Operating in a power recovery protection mode to open a relay switch included in the inverter system by detecting a power failure when the slope of the output voltage at both ends of the node exceeds a third threshold
including,
The first output node represents a node connecting one end of a load connected to the AC grid power source and the inverter system,
The second output node represents one end of the inductor connected to the full bridge circuit included in the inverter system,
The third output node represents a node connecting one end of the relay switch and one end of the second output node and a voltage sensor sensing an output voltage of both ends of the third output node.
7. The method of claim 6,
The relay switch is
Operating method of an inverter system, characterized in that it is disposed between the first node and the third output node connecting the source node of the first MOSFET and the drain node of the second MOSFET of the full bridge circuit included in the inverter system.
8. The method of claim 7,
When the power of the inverter system is turned on or the relay switch is opened, returning to the standby mode in which the processor determines the operation mode of the inverter system again according to the magnitude of the grid sensing current
Operating method of the inverter system further comprising a.

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