Power conversion system and method

Abstract

The present invention relates to a power conversion device and method. To this end, one embodiment of the present invention allows at least one power converter to identify whether the grid is currently in a power outage or unstable state through the voltage or frequency of the grid and notify at least one adjacent power converter. Accordingly, when a plurality of power converters within a microgrid change from a grid-connected mode to a seamless disconnection mode during non-communication parallel operation, it may be possible to change the mode of a power converter that is unable to perform such a mode change.

Description

Technology Field

[0001] The present invention relates to a power conversion device and method. Background Technology

[0002] Generally, an Energy Storage System (ESS) can provide a peak power sharing function that charges power when load power usage is low and discharges the stored power when load power usage is high. Such an energy storage system can be installed and operated for the purpose of reducing ripple power generated by renewable energy generation.

[0003] Furthermore, energy storage systems are also required to function as distributed power sources, independently supplying power to loads in the event of a grid failure (power outage) at the request of consumers. Moreover, this independent operation capability is being applied not only as a substitute for emergency generators but also as a solution for configuring microgrids in isolated areas.

[0004] However, it is inefficient, and in some cases impossible, for current energy storage system manufacturers to develop customized products for every customer requirement. Therefore, energy storage system companies are responding to the market demanding diverse capacity conditions by adding parallel operation capabilities to single products.

[0005] These parallel operation methods can be broadly divided into communication-based parallel control and non-communication-based parallel control. A representative example of communication-based parallel control is Master-Slave control. In this method, the master energy storage system (or master board) calculates the power requirements of the grid and load, and receives power commands via communication for the remaining slave energy storage systems to handle.

[0006] While this method has the advantage of receiving power commands to be handled by each energy storage system relatively quickly and accurately, the operation of the energy storage system relies heavily on communication, so system operation may be disrupted if communication-related problems occur.

[0007] In contrast, non-communication parallel control often utilizes droop control, which distributes active and reactive power through the voltage amplitude and frequency of power lines. Since communication lines are not connected, this method is suitable for distributing loads between inverters that make up a large-scale microgrid. However, this method has the disadvantage that it is highly dependent on the voltage of the power lines, resulting in slower voltage recovery times in transient states compared to master-slave, and voltage and frequency fluctuations depending on the load amount.

[0008] As such, in the case of non-communication parallel operation in a microgrid, the detection of a power outage is performed through the output voltage amplitude and frequency of each energy storage system. When a power outage occurs due to the opening of a grid circuit breaker, an islanding state occurs in which the load voltage instantaneously drops and rises depending on the difference between the load of the microgrid and the commanded power of the energy storage system. However, seamless disconnection technology transitions from the grid-connected power control operation mode to the independent voltage control operation mode when such an islanding state is detected. At this time, each energy storage system may exhibit relatively sensitive power outage detection characteristics compared to other energy storage systems due to manufacturing process errors. The biggest reason for this problem is the error in the turn ratio of the transformers configured between the energy storage system and the microgrid; this is because even transformers designed with the same turn ratio exhibit a manufacturing error of 3 to 5%.

[0009] If there is a difference in the power outage detection voltage due to such process errors, when a power outage occurs, the energy storage system that is sensitive to power outage detection will first detect the independent operation state. In this case, the load voltage amplitude may rise due to the energy storage system that first switched its operation mode to independent operation mode, and the remaining energy storage systems may not be able to detect the power outage state.

[0010] Therefore, the need for synchronization regarding power outages among multiple energy storage systems within a microgrid arises. The problem to be solved

[0011] Conventionally, there was a problem in that synchronization regarding power outages could not be achieved between multiple energy storage systems within a microgrid.

[0012] Accordingly, the present invention provides synchronization of power outages between a plurality of energy storage systems within a microgrid.

[0013] In addition, the present invention provides a power conversion device and method for converting the frequency of a grid voltage to another frequency so that at least one energy storage system that detects a power outage can enable at least one energy storage system adjacent to itself to detect the power outage.

[0014] In addition, the present invention provides a power conversion device and method for applying a voltage having a controlled frequency through a power line so that at least one energy storage system that has detected a power outage can enable at least one energy storage system adjacent to itself to detect the power outage.

[0015] In addition, the present invention provides a power conversion device and method in which at least one energy storage system that detects a power outage applies a voltage having a controlled frequency through a power line and then operates in an independent operation mode.

[0016] In addition, the present invention provides a power conversion device and method in which at least one energy storage system can operate independently based on the frequency through the power line.

[0017] The objects of the present invention are not limited to those mentioned above, and other unmentioned objects and advantages of the present invention may be understood from the following description and will be more clearly understood by the embodiments of the present invention. Furthermore, it will be readily apparent that the objects and advantages of the present invention can be realized by the means and combinations thereof set forth in the claims. means of solving the problem

[0018] To achieve this objective, the present invention can synchronize the power supply mode according to the power outage or unstable state among a plurality of power conversion devices within a microgrid by at least one power conversion device identifying whether the system is currently in a power outage or unstable state through the voltage or frequency of the system and notifying at least one adjacent power conversion device.

[0019] In addition, the power conversion device of the present invention may include a processor that identifies at least one of the voltage and frequency of a system and can adjust a first frequency for the voltage of the system to a second frequency.

[0020] In addition, the present invention may include a processor that generates a voltage having a frequency that enables at least one other power converter adjacent to the power converter to identify that the system has become unstable or has a power outage.

[0021] In addition, the present invention may include a processor that calculates the time during which the power converter operates at the frequency, and if the calculated time exceeds a predetermined threshold time, operates the power converter independently based on a rated frequency corresponding to at least one load connected to the power converter.

[0022] In addition, the present invention may include a processor that connects a power control unit and a current control unit, and connects a grid phase detection unit and a three-phase command voltage generation unit, when the grid is identified as restored while the power conversion device is operating independently based on a rated frequency.

[0023] In addition, the method of the power conversion device according to the present invention may include the process of identifying whether the power system has become unstable or has a power outage through at least one of the amplitude and frequency of the power system voltage, and operating the power conversion device by adjusting the first frequency of the identified power system voltage to a second frequency different from the first frequency.

[0024] In addition, the method of the power conversion device according to the present invention may further include the process of generating a three-phase command voltage having the second frequency so that at least one other power conversion device adjacent to the power conversion device identifies that the system has become unstable or in a blackout state. Effects of the invention

[0025] The present invention can supply stable power to at least one load within a microgrid by synchronizing the power outage or unstable state between a plurality of power conversion devices within the microgrid.

[0026] In addition, the present invention enables a mode change for power conversion devices that are unable to perform such a mode change when multiple power conversion devices within a microgrid switch from a grid-connected mode to a seamless mode during non-communication parallel operation.

[0027] In addition, the present invention allows a power converter to identify whether the power system has become unstable or has a power outage through at least one of the voltage amplitude and frequency of the power system, control the voltage so that the load voltage is equal to the command voltage, and adjust the first frequency of the power system voltage to a second frequency different from the first frequency, thereby enabling the power converter to recognize the power outage or unstable state.

[0028] In addition, the present invention enables the other power converter to recognize the power outage or unstable state more quickly by generating and applying a three-phase command voltage having the second frequency through a power line so that the power converter can identify that at least one other power converter adjacent to itself has become unstable or has a power outage.

[0029] In addition, the present invention can accurately determine whether the power system is in a power outage or safe by identifying the system as being in a power outage or unstable state when the power conversion device determines that the amplitude of the voltage of the system has a value other than a predetermined ratio of the amplitude of the reference rated voltage.

[0030] In addition, the present invention can accurately determine whether the power system is experiencing a power outage by identifying that the system is experiencing a power outage or instability when the frequency of the system deviates from a predetermined range.

[0031] In addition, the present invention calculates the time during which the power converter operates at the second frequency, and if the calculated time exceeds a predetermined threshold time, the power converter is operated independently based on the rated frequency corresponding to at least one load connected to the power converter, thereby enabling faster power to be provided to the load in the event of a power outage or unstable condition.

[0032] In addition, the present invention allows power to be supplied more quickly from the grid by connecting the power control unit and the current control unit and connecting the grid phase detection unit and the three-phase command voltage generation unit when the grid is identified as restored while the power conversion device is operating independently based on the rated frequency.

[0033] In addition to the effects described above, the specific effects of the present invention are described together with the specific details for implementing the invention below. Brief explanation of the drawing

[0034] FIG. 1 is an exemplary diagram showing a system for synchronizing power outage detection between power conversion devices according to an embodiment of the present invention. FIG. 2 is an exemplary diagram showing a power conversion device according to one embodiment of the present invention. FIG. 3 is an example diagram for determining whether the system is in a stable state through the amplitude and frequency of the system voltage according to one embodiment of the present invention. FIG. 4 is an example diagram showing that at least one power converter recognizes a power outage and performs independent operation while a plurality of power converters are connected to a microgrid according to one embodiment of the present invention. FIG. 5 is an example diagram illustrating how a power converter according to one embodiment of the present invention synchronizes power outage detection with another power converter. FIG. 6 is a flowchart illustrating the process of a power converter according to an embodiment of the present invention detecting a power outage and performing independent operation. FIG. 7 is a flowchart illustrating the process of a power converter according to another embodiment of the present invention detecting a power outage and performing independent operation. Specific details for implementing the invention

[0035] The aforementioned objectives, features, and advantages are described in detail below with reference to the attached drawings, thereby enabling those skilled in the art to easily implement the technical concept of the present invention. In describing the present invention, detailed descriptions of known technologies related to the present invention are omitted if it is determined that such descriptions would unnecessarily obscure the essence of the invention. Hereinafter, preferred embodiments according to the present invention will be described in detail with reference to the attached drawings. In the drawings, the same reference numerals are used to indicate the same or similar components.

[0036] Although terms such as "first," "second," etc., are used to describe various components, it goes without saying that these components are not limited by these terms. These terms are used merely to distinguish one component from another, and unless specifically stated otherwise, the first component may also be the second component.

[0037] In the following, the statement that any configuration is placed on the "upper (or lower)" of a component or on the "upper (or lower)" of a component may mean not only that any configuration is placed in contact with the upper (or lower) surface of said component, but also that another configuration may be interposed between said component and any configuration placed on (or below) said component.

[0038] In addition, where it is stated that one component is "connected," "combined," or "connected" to another component, it should be understood that while the components may be directly connected or connected to each other, another component may be "interposed" between each component, or each component may be "connected," "combined," or "connected" through another component.

[0039] Throughout the specification, unless specifically stated otherwise, each component may be singular or plural.

[0040] Singular expressions used in this specification include plural expressions unless the context clearly indicates otherwise. In this application, terms such as "composed of" or "comprising" should not be interpreted as necessarily including all of the various components or steps described in the specification, and should be interpreted as meaning that some of the components or steps may be omitted or additional components or steps may be included.

[0041] Throughout the specification, "A and / or B" means A, B, or A and B unless specifically stated otherwise, and "C to D" means C or more and D or less, unless specifically stated otherwise.

[0042] Hereinafter, a power conversion device and method according to some embodiments of the present invention will be described.

[0043] FIG. 1 is an exemplary diagram showing a system for synchronizing power outage detection between power conversion devices according to an embodiment of the present invention.

[0044] Referring to FIG. 1, a system (100) for synchronizing power outage detection between power conversion devices according to an embodiment of the present invention may include a power supply system (140), at least one load (150, 160, 170) receiving power supplied from the power supply system (140), at least one power conditioning system (110, 120, 130) supplying power to the at least one load (150, 160, 170) when the power supply by the power supply system (140) is cut off, and at least one transformer (111, 121, 131) converting power supplied from each power conditioning system.

[0045] The configuration of the system (100) for synchronizing power outage detection between power conversion devices shown in FIG. 1 is according to one embodiment, and the components of the system (100) for synchronizing power outage detection between power conversion devices are not limited to the embodiment shown in FIG. 1, and some components may be added, changed, or deleted as needed.

[0046] According to one embodiment, a system (100) for synchronizing power outage detection between the power conversion devices may include a power line (180) through which power and power control signals are transmitted between each load (150, 160, 170) and each power conversion device (110, 120, 130). The power line (180) may be connected to each load (150, 160, 170) and each power conversion device (110, 120, 130).

[0047] According to one embodiment, a power conversion device may be included in an Energy Storage System (ESS). For example, the Energy Storage System may include a power conversion device, an Energy Management System (EMS), a plurality of batteries, and a Battery Management System (BMS). The plurality of batteries may be configured in parallel.

[0048] According to one embodiment, the energy storage system (ESS) is an energy storage device that stores electricity produced at a power plant and transmits the stored electricity when there is a shortage of electricity required by the load. The energy storage system can improve power utilization efficiency by storing idle electricity and supplying electricity during peak demand hours.

[0049] For example, it plays a role in enhancing the usability of next-generation energy by storing renewable energy, such as solar and wind power, which are difficult to generate during desired times, in advance and using them when needed. Such an energy storage system is not a single device but can be composed of a battery, a power converter, an energy management system, a battery management system, and multiple batteries.

[0050] According to one embodiment, the energy management system (EMS) can perform the role of controlling the overall system while monitoring and controlling the operation of the energy storage system (ESS). The energy management system can analyze the energy storage system in real time and monitor and control it through a communication network.

[0051] For example, an energy management system may simply control charging or discharging, or it may formulate an optimal operation plan by algorithmizing consumption patterns or weather information to predict power demand and generation.

[0052] According to one embodiment, a battery in an energy storage system (ESS) is a device for storing power. A cell of the battery may be composed of a positive electrode, a negative electrode, an electrolyte, and a separator.

[0053] According to one embodiment, the battery management system (BMS) is a device that controls the battery to ensure safe use while optimizing the battery's performance. The battery management system may be installed at each stage of the battery (cell / module / rack / system). Furthermore, the battery management system monitors the battery's status information and transmits the result to the EMS, thereby improving the overall stability of the ESS system.

[0054] According to one embodiment, the power conversion device (PCS) converts electrical characteristics, such as frequency and voltage, to store power in a battery or to transmit power from the stored battery to a load after receiving power from an energy storage system. The power conversion device can adjust the power characteristics that differ when storing power (DC) and when using power (AC).

[0055] For example, the power converter converts alternating current (AC) into direct current (DC) when storing power in a battery, and converts DC into alternating current when transmitting the stored power. In this way, in addition to the power conversion function, the power converter undertakes core functions of the energy storage system, such as monitoring the operating status and quality control of the energy storage system, grid protection in the event of a power outage, and standalone operation.

[0056] FIG. 2 is an exemplary diagram showing a power conversion device according to one embodiment of the present invention.

[0057] Referring to FIG. 2, a power conversion device (110) according to one embodiment of the present invention may include a power control unit (211), a voltage control unit (212), a first switch (213), a current control unit (214), a three-phase command voltage generation unit (215), a grid power outage determination unit (216), a grid phase detection unit (217), a processor (218), and a second switch (219).

[0058] The configuration of the power conversion device (110) shown in FIG. 2 is according to one embodiment, and the components of the power conversion device (110) are not limited to the embodiment shown in FIG. 2, and some components may be added, changed, or deleted as needed.

[0059] According to one embodiment, the power control unit (211) may receive command power from an energy management system (EMS). The command power is power required for the power converter (110) to operate, and the power converter (110) may operate based on the command power (e.g., 100 kW).

[0060] According to one embodiment, the power control unit (211) can obtain the power (e.g., actual power) that the power converter (110) is actually operating through a current sensor (not shown) or a voltage sensor (not shown) disposed inside the power converter (110) while the power converter (110) is in operation.

[0061] According to one embodiment, the power control unit (211) can perform power control so that the actual power becomes the commanded power and output the controlled power. The power control unit (211) can be controlled by a processor (218) through a grid phase detection unit (217) so that the commanded power and the actual power become the same. The power control unit (211) can transmit the outputted power to a first switch (213).

[0062] According to one embodiment, the voltage control unit (212) may receive a command voltage from an energy management system (EMS). The command voltage is a voltage required for the power converter (110) to operate, and the power converter (110) may operate based on the command voltage (e.g., 220V). The voltage control unit (212) may receive a command voltage (e.g., 220V) having a predetermined frequency (e.g., 60Hz) from the energy management system (EMS).

[0063] According to one embodiment, the voltage control unit (212) can obtain an actual load voltage measured from a load line while the power converter (110) is in operation. The load voltage may include the voltage consumed by a load connected to a power line (180). The voltage control unit (212) can identify an actual load voltage by at least one load connected to the power converter (110). The voltage control unit (212) can perform voltage control so that the actual load voltage becomes the command voltage (e.g., 220V). The voltage control unit (212) can transmit the controlled voltage to the first switch (213).

[0064] According to one embodiment, the output of the power control unit (211) and the output of the voltage control unit (212) can be switched to the current control unit (214) by a first switch (213). The first switch (213) can be placed at the output terminal of the power control unit (211) and the output terminal of the voltage control unit (212). Then, when the grid is determined to be in a corrected (or unstable) state by the grid power outage determination unit (216), the first switch (213) can receive a power outage detection signal from the grid power outage determination unit (216) indicating that a power outage has occurred. Then, the first switch (213) can perform a switching operation to connect the voltage control unit (212) and the current control unit (214) under the control of the processor (218).

[0065] According to one embodiment, either of the power control unit (211) and the voltage control unit (212) may be connected to the current control unit (214) based on the switching of the first switch (213) and may transmit an output value (e.g., power or voltage) to the current control unit (214).

[0066] According to one embodiment, the current control unit (214) can receive power switched by the first switch (213) (e.g., power from the power control unit (211) or power from the voltage control unit (212). The voltage control unit (212) and the current control unit (214) can control the output voltage output from the power conversion module so that a voltage having a constant frequency and magnitude can be supplied to the load (150, 160, 170) with the command voltage as input.

[0067] According to one embodiment, the voltage control unit (212) and the current control unit (214) can generate a gating reference voltage that causes the output voltage to follow the command power by comparing the command power to be supplied to the load (150, 160, 170) with the output voltage output and fed back from the power conversion module. Then, the voltage control unit (212) and the current control unit (214) can modulate the gating reference voltage into a Pulse Width Modulation (PWM) signal and supply it to the inverter of the power conversion module. The power conversion module can convert the DC power supplied from the battery management system into AC power and supply it to the load.

[0068] According to one embodiment, the system power outage determination unit (216) can identify whether the system is currently in a power outage state or not by analyzing at least one of the amplitude and frequency of the system voltage (or actual load voltage). The system power outage determination unit (216) recognizes the amplitude of the system voltage, and if it is determined that the recognized amplitude of the system voltage has a value other than a predetermined ratio (e.g., 88% to 110%) of the amplitude of the reference rated voltage, the system can be identified as being in a power outage. The system power outage determination unit (216) can transmit a signal indicating that the system is in a power outage to a processor (218). According to one embodiment, when voltage is applied from the system, the system voltage may be equal to the actual load voltage.

[0069] According to one embodiment, a power outage in the system can be identified based on at least one of the amplitude and frequency of the system voltage (or actual load voltage). Alternatively, if a voltage (or frequency) lower than the rated voltage (or frequency) is detected, the voltage control unit (212) can perform voltage control so that the actual voltage becomes the commanded voltage.

[0070] For example, if the above standard rated voltage is 100V and the above system voltage is detected to be within 88V to 110V, the above system power outage determination unit (216) can determine that the system is in a stable state (e.g., a state where no power outage has occurred).

[0071] For example, if the above standard rated voltage is 100V and the above system voltage is less than 88V or exceeds 110V, the above system power outage determination unit (216) can determine that the system is in an unstable state (e.g., a state where a power outage has occurred).

[0072] According to one embodiment, the system phase detection unit (PLL) (217) can adjust the frequency of the output signal to correspond to the input signal. The system phase detection unit (217) can control the output signal using the phase difference between the input signal and the signal fed back from the output signal. The system phase detection unit (217) can detect the phase difference between the input signal input to the system phase detection unit (217) and the signal output from the system phase detection unit (217), and determine the detected phase difference as an error.

[0073] In addition, the system phase detection unit (217) can change the output frequency by adjusting the input voltage (e.g., system voltage) to reduce the error. The system phase detection unit (217) can adjust the frequency of the output relative to the input so that the phase lock state is maintained when the feedback phase difference between the input and the output is synchronized. The system phase detection unit (217) can extract the system voltage and adjust the phase of the extracted voltage.

[0074] According to one embodiment, when the system is determined to be in power outage by the system power outage determination unit (216), the processor (218) adjusts the first frequency (e.g., 60Hz) of the system voltage to a second frequency (e.g., 55Hz) and transmits it to the second switch (219).

[0075] According to one embodiment, the output of the power control unit (211) and the output of the voltage control unit (212) can be switched to the current control unit (214) by a first switch (213). The first switch (213) can be placed at the output terminal of the power control unit (211) and the output terminal of the voltage control unit (212).

[0076] And, when the system power outage determination unit (216) determines that the system is in a corrected (or unstable) state, the first switch (213) can receive a power outage detection signal from the system power outage determination unit (216) indicating that a power outage has occurred. And, the first switch (213) can perform a switching operation under the control of the processor (218) so that the voltage control unit (212) and the current control unit (214) are connected.

[0077] According to one embodiment, information regarding the frequency controlled by the system phase detection unit (217) and information regarding the frequency controlled by the processor (218) (e.g., 55 Hz) can be switched to the three-phase command voltage generation unit (215) by the second switch (219). The second switch (219) may be placed at the output terminal of the system phase detection unit (217) and the output terminal of the processor (218).

[0078] And, when the system power outage determination unit (216) determines that the system is in a corrected (or unstable) state, the second switch (219) can receive a power outage detection signal from the system power outage determination unit (216) indicating that a power outage has occurred. And, the second switch (219) can perform a switching operation under the control of the processor (218) so that the processor (218) and the three-phase command voltage generation unit (215) are connected.

[0079] According to one embodiment, the three-phase command voltage generation unit (215) can generate a three-phase command voltage based on information about a frequency controlled by the system phase detection unit (217) and information about a frequency controlled by the processor (218) (e.g., 55 Hz). The three-phase command voltage has a frequency of 55 Hz. Alternatively, the three-phase command voltage may have a frequency different from the frequency of the command voltage (e.g., 60 Hz).

[0080] According to one embodiment, the three-phase command voltage generation unit (215) can generate a voltage having a frequency different from the frequency of the command voltage (e.g., 60Hz) (e.g., 50Hz, 55Hz, 65Hz, or 70Hz) based on information about the frequency controlled by the system phase detection unit (217) and information about the frequency controlled by the processor (218) (e.g., 55Hz).

[0081] According to one embodiment, the three-phase command voltage generating unit (215) can control the operation of the power conversion device (110) based on the frequency-controlled three-phase voltage.

[0082] According to one embodiment, the processor (218) can identify whether the system has a power outage through at least one of the amplitude and frequency of the system voltage identified by the system power outage determination unit (216). The processor (218) can determine that the system has a power outage if it determines that the amplitude of the system voltage has a value that falls within a range other than a predetermined ratio (e.g., 88% to 110%) of the amplitude of the reference rated voltage.

[0083] According to one embodiment, the processor (218) may determine that the system has a power outage if the frequency of the system voltage (e.g., 60Hz) deviates from a predetermined range (e.g., 59.3Hz to 60.5Hz). The predetermined ratio for the voltage (e.g., 88% to 110%) and the predetermined range for the frequency (e.g., 59.3Hz to 60.5Hz) may be variably adjusted by taking into account the performance of the power conversion device (100), the performance of the system (100) that synchronizes power outage detection between the power conversion devices, and the influence of the load on the power system.

[0084] According to one embodiment, the voltage control unit (212) may obtain a command voltage (e.g., 220V) having a predetermined frequency (e.g., 60Hz) from an energy management system (EMS). The voltage control unit (212) may obtain an actual load voltage measured at a load line while the power conversion device (110) is in operation. The load voltage may include the voltage consumed by a load connected to a power line (180).

[0085] According to one embodiment, when the processor (218) identifies that the system has been deactivated, it can control (or adjust) the voltage through the voltage control unit (212) so that the load voltage input to the voltage control unit (212) is equal to the command voltage (e.g., command voltage received from the EMS). The processor (218) can control the voltage control unit (212) to perform voltage control so that the actual load voltage becomes the command voltage (e.g., 220V). The command voltage is the voltage required for the power converter (110) to operate, and the processor (218) can operate the power converter (110) based on the command voltage (e.g., 220V).

[0086] According to one embodiment, the processor (218) can operate the power conversion device by adjusting the first frequency of the system voltage to a second frequency different from the first frequency. The processor (218) can determine whether the system has been deactivated or not by controlling the system power outage determination unit (216).

[0087] According to one embodiment, the processor (218) may determine that the system has a power outage if it determines that the amplitude of the system voltage has a value other than a predetermined ratio of the amplitude of the reference rated voltage. Additionally, the processor (218) may determine that the system has a power outage if the frequency of the system voltage deviates from a predetermined range.

[0088] According to one embodiment, if the system is not identified as being out of order, the processor (218) can control the first switch (213) to connect the power control unit (211) and the current control unit (214). Additionally, if the system is not identified as being out of order, the processor (218) can control the second switch (219) to connect the system phase detection unit (217) and the three-phase command voltage generation unit (215).

[0089] According to one embodiment, if it is determined through the system power outage determination unit (216) that the system is in power outage, the processor (218) can adjust the first frequency (e.g., 60Hz) of the system voltage to a second frequency (e.g., 55Hz). The processor (218) can transmit the voltage adjusted to the second frequency (e.g., 55Hz) to the three-phase command voltage generation unit (215) through the second switch (219).

[0090] According to one embodiment, the processor (218) can control the three-phase command voltage generation unit (215) to generate a three-phase command voltage having the second frequency (e.g., 55 Hz) and apply the generated three-phase command voltage to the power line (180). When a power outage (or unstable state) of the grid is detected by the power converter (e.g., the first power converter (110)), the processor (218) can apply the three-phase command voltage having the second frequency to the power line (180) so that an adjacent other power converter (e.g., at least one of the second power converter (120) and the third power converter (120)) recognizes the power outage of the grid.

[0091] According to one embodiment, the processor (218) can apply a three-phase command voltage having the second frequency to the power line (180) and then control a power converter (e.g., a first power converter (110)) to operate the power converter (e.g., a first power converter (110)) independently. For example, the processor (218) can operate the power converter (e.g., a first power converter (110)) independently for a predetermined time. For example, the processor (218) can operate the power converter (e.g., a first power converter (110)) independently until the power system is restored (e.g., the power outage in the system is resolved, or the system is switched to a stable state).

[0092] FIG. 3 is an example diagram for determining whether the system is in a stable state through the amplitude and frequency of the system voltage according to one embodiment of the present invention.

[0093] Referring to FIG. 3, a power converter (110) (e.g., processor 218) can identify whether the power grid has been depleted through at least one of the amplitude and frequency of the voltage of the grid identified by a grid depletion determination unit (216) within the power converter (110).

[0094] According to one embodiment, when the voltage of the system measured by the system power outage determination unit (216) is within a predetermined ratio (e.g., a range of 88% to 110% (88V to 110V)) based on a reference voltage (e.g., 100V), the power conversion device (110) (e.g., processor (218)) can determine that the system is in a stable state (e.g., not in a power outage state) (310).

[0095] According to one embodiment, if the frequency of the voltage of the system measured by the system power outage determination unit (216) (e.g., 60Hz) is within a predetermined range (e.g., 59.3Hz to 60.5Hz), the power conversion device (110) (e.g., processor (218)) can determine that the system is in a stable state (e.g., not in a power outage state) (310).

[0096] According to one embodiment, if the voltage of the system measured by the system power outage determination unit (216) is less than a predetermined ratio based on a reference voltage (e.g., 100V) (e.g., less than 88% (e.g., 88V) or more than 110% (e.g., 110V)), the power conversion device (110) (e.g., processor (218)) may determine that a power outage has occurred in the system or that the system is in an unstable state (320).

[0097] According to one embodiment, if the frequency of the voltage of the system measured by the system power outage determination unit (216) (e.g., 60Hz) is outside a predetermined range (e.g., less than 59.3Hz or greater than 60.5Hz), the power conversion device (110) (e.g., processor (218)) may determine that the system is in an unstable state (e.g., not in a power outage state) (320).

[0098] FIG. 4 is an example diagram showing that at least one power converter recognizes a power outage and performs independent operation while a plurality of power converters are connected to a microgrid according to one embodiment of the present invention.

[0099] FIGS. 2 and 3 describe a first power converter (110) recognizing a power outage (or unstable state) in the grid and recognizing the power outage in the grid to at least one of the second power converter (120) and the third power converter (130). However, it is obvious that the present invention can recognize a power outage or unstable state in the grid to at least two power converters (e.g., the first power converter (110) and the second power converter (120)) and then recognize the power outage in the grid to another power converter (e.g., the third power converter (130)).

[0100] Referring to FIG. 4, the first power converter (110) and the second power converter (120) can identify a power outage (or unstable state) of the system simultaneously (or with a negligible time difference). For example, if a power outage (or unstable state) occurs in the system (414), the first power converter (110) and the second power converter (120) can identify the power outage of the system (414) simultaneously (or with a negligible time difference).

[0101] According to one embodiment, when a power outage (or unstable state) occurs in the system (414), power is not supplied to the load (415). In this way, when a power outage occurs in the system (414), at least one of the first power converter (110) and the second power converter (120) is operated at a low frequency (e.g., 55Hz), thereby inducing at least one adjacent power converter (e.g., third power converter (130)) to recognize that the system (414) has a power outage (or unstable state).

[0102] According to one embodiment, at least one of the first power converter (110) and the second power converter (120) can be operated in an independent operation mode by converting the first frequency of the grid voltage to the second frequency during a predetermined time in which the low frequency (e.g., 55 Hz) can be recognized.

[0103] And, when at least one power converter (e.g., third power converter (130)) detects the low frequency (e.g., 55Hz), at least one of the first power converter (110) and the second power converter (120) may be operated in an independent operation mode based on the rated frequency (e.g., 60Hz). Additionally, the at least one power converter (e.g., third power converter (130)) may be operated in an independent operation mode at the rated frequency (e.g., 60Hz) based on the detection of the power outage.

[0104] FIG. 5 is an example diagram illustrating how a power converter according to one embodiment of the present invention synchronizes power outage detection with another power converter.

[0105] Referring to FIG. 5, when a power outage occurs in the system, the system voltage (e.g., actual load voltage) (510) may be reduced to a first voltage (520) at which the first power converter (110) can detect that the system has a power outage. The first power converter (110) can detect that the system has a power outage when the system voltage is less than the first voltage (520). When the system is detected to have a power outage, the first power converter (110) converts the first frequency (e.g., 60Hz) (580) of the system voltage (510) to a second frequency (e.g., 55Hz) (590) and can apply the frequency-converted system voltage (510) to the power line (180). The above frequency-converted grid voltage is output as a three-phase command voltage by the three-phase command voltage generation unit (215), and the phases (540, 550, 560) of the three-phase command voltage are 120 o It has a phase difference.

[0106] According to one embodiment, when the system voltage is less than the second voltage (530), at least one of the second power converter (120) and the third power converter (130) can detect that the system has a power outage. When the system voltage is less than the second voltage (530), after the first power converter (110) detects that the system has a power outage, at least one of the second power converter (120) and the third power converter (130) can detect the power outage.

[0107] Alternatively, if the system voltage is less than the second voltage (530), at least one of the second power converter (120) and the third power converter (130) may recognize the power outage before the first power converter (110) recognizes that the system has a power outage to at least one of the second power converter (120) and the third power converter (130).

[0108] According to one embodiment, if a power outage occurs in the system at a first time (571), the first power converter (110) can detect that the system has a power outage at a second time (572). Then, if the system voltage becomes lower than the first voltage (520) at a third time (573), the first power converter (110) can switch the first frequency (580) of the system voltage to a second frequency (590). At this time, at least one of the second power converter (120) and the third power converter (130) can detect a first power second frequency (e.g., 55Hz) that is lower than the frequency at which the first to third power converters (110, 120, 130) can detect a power outage at a fourth time (574). And, at least one of the second power converter (120) and the third power converter (130) can be switched to independent operation at the fifth time (575).

[0109] According to one embodiment, the first power converter (110) may operate in a connected state to the grid until a third time (573), and then operate in an independent operation mode from the third time (573) onwards. The second power converter (120) and the third power converter (130) may operate in a connected state to the grid until a fifth time (575), and then operate in an independent operation mode from the fifth time (575) onwards.

[0110] FIG. 6 is a flowchart illustrating the process of a power converter according to an embodiment of the present invention detecting a power outage and performing independent operation.

[0111] Hereinafter, with reference to FIG. 6, the process of a power conversion device according to one embodiment of the present invention detecting a power outage and performing independent operation is described in detail as follows.

[0112] According to one embodiment, a power conversion device (110) (e.g., a grid power outage determination unit (216)) can identify at least one of a grid voltage and a frequency (S610). The power conversion device (110) (e.g., a grid power outage determination unit (216)) can identify whether the grid is currently in a power outage state or not by analyzing at least one of the amplitude and frequency of the grid voltage (or actual load voltage).

[0113] The power conversion device (110) (e.g., grid power outage determination unit (216)) recognizes the amplitude of the grid voltage, and if it is determined that the recognized grid voltage amplitude has a value other than a predetermined ratio (e.g., 88% to 110%) of the amplitude of the reference rated voltage, the grid can be identified as having a power outage. The grid power outage determination unit (216) can transmit a signal indicating that the grid has a power outage to a processor (218).

[0114] According to one embodiment, the power conversion device (110) (e.g., processor (218)) can identify whether the grid is in a power outage (or unstable state) based on at least one of the identified grid voltage and frequency (S612).

[0115] According to one embodiment, when the reference rated voltage of the power converter (110) is 100V and the system voltage is detected to be within 88V to 110V, the power converter (110) (e.g., system power outage determination unit (216)) can determine that the system is in a stable state (e.g., a state where no power outage has occurred).

[0116] According to one embodiment, when the reference rated voltage is 100V, if the system voltage is less than 88V or exceeds 110V, the power conversion device (110) (e.g., system power outage determination unit (216)) can determine that the system is in an unstable state (e.g., a state where a power outage has occurred).

[0117] According to one embodiment, the reference rated voltage can be variably adjusted according to the performance and condition of the power conversion device (110).

[0118] According to one embodiment, if the frequency of the voltage of the system measured by the system power outage determination unit (216) (e.g., 60Hz) is within a predetermined range (e.g., 59.3Hz to 60.5Hz), the power conversion device (110) (e.g., system power outage determination unit (216)) can determine that the system is in a stable state (e.g., not in a power outage state).

[0119] According to one embodiment, if the frequency of the voltage of the system measured by the system power outage determination unit (216) (e.g., 60Hz) is outside a predetermined range (e.g., less than 59.3Hz or greater than 60.5Hz), the power conversion device (110) (e.g., system power outage determination unit (216)) may determine that the system is in an unstable state (e.g., not in a power outage state).

[0120] According to one embodiment, the power conversion device (110) (e.g., processor (218)) may measure at least one of the identified system voltage and frequency once and determine the state of the system (e.g., power outage or non-power outage) by comparing at least one of the measured voltage and frequency with a corresponding threshold value (or range). Alternatively, the power conversion device (110) (e.g., processor (218)) may measure at least one of the identified system voltage and frequency multiple times, or measure multiple times over a predetermined period of time and calculate an average value.

[0121] And, the power conversion device (110) (e.g., processor (218)) can determine the state of the system (e.g., power outage / non-power outage, or unstable / stable) by comparing at least one average value among the voltage and frequency measured multiple times with each corresponding threshold value (or threshold range).

[0122] Alternatively, the power conversion device (110) (e.g., processor (218)) may determine that the system is in a power outage or unstable state as shown in [Table 1] below if the value measured once maintains a threshold value (or threshold range) for a predetermined time.

[0123] System voltage (e.g., 100V) Frequency (e.g., 65Hz) Time (sec) 80%~90% of grid voltage 80%~90% relative to frequency 10S 70%~80% of grid voltage 60%~80% relative to frequency 0.5S 0% to 70% relative to system voltage 0%~70% relative to frequency 20mS

[0124] As shown in [Table 1] above, if the measured system voltage is maintained within 80% to 90% of the reference voltage (e.g., 100V) for 10 seconds, the system may be determined to be in a state of power outage or instability. Also, if the measured system voltage is maintained within 70% to 70% of the reference voltage (e.g., 100V) for 0.5 seconds, the system may be determined to be in a state of power outage or instability. Furthermore, if the measured system voltage is maintained within 0% to 70% of the reference voltage (e.g., 100V) for 20 seconds, the system may be determined to be in a state of power outage or instability. The predetermined time may be shorter as the ratio of the system voltage to the reference voltage decreases.

[0125] In addition, if the frequency of the measured system voltage is maintained within 80% to 90% of the reference frequency (e.g., 60Hz) for 10 seconds, the system may be determined to be in a state of power outage or instability. Also, if the frequency of the measured system voltage is maintained within 70% to 70% of the reference frequency (e.g., 60Hz) for 0.5 seconds, the system may be determined to be in a state of power outage or instability.

[0126] In addition, if the frequency of the measured system voltage is maintained within 0% to 70% of the reference frequency (e.g., 60Hz) for 20 m seconds, the system may be determined to be in a state of power outage or instability. The ratio and the time may be variably adjusted.

[0127] According to one embodiment, if it is identified that the grid is not in a state of power outage, the power converter (110) (e.g., processor (218)) can control grid connection (S614). The power converter (110) (e.g., processor (218)) can identify that the grid is in a stable state if at least one of the grid voltage (e.g., 100V) and frequency (e.g., 60Hz) measured by the grid power outage determination unit (216) is included within a threshold range of each voltage and frequency (e.g., within approximately 88V to approximately 110V for voltage, or within approximately 59.3Hz to 60.5Hz for frequency). And, if it is identified that the grid is in a stable state, the power converter (110) (e.g., processor (218)) can perform control operations for grid connection based on the power supplied from the grid.

[0128] According to one embodiment, the power converter (110) (e.g., processor (218)) can synchronize the detection of a power outage (S616). The power converter (110) (e.g., processor (218)) can identify that the power system is in an unstable state (e.g., power outage) if at least one of the system voltage (e.g., 100V) and frequency (e.g., 60Hz) measured by the system power outage determination unit (216) is not included within a threshold range of each voltage and frequency (e.g., within approximately 88V to approximately 110V for voltage, or within approximately 59.3Hz to 60.5Hz for frequency).

[0129] According to one embodiment, the power converter (110) (e.g., processor (218)) may perform a power outage detection synchronization process with another power converter (120, 130) adjacent to the power converter (110). The power outage detection synchronization process may include the process of applying a low frequency (e.g., 65 Hz) voltage to a power line (180) so that the power converter (110) (e.g., processor (218)) can enable the other power converter (120, 130) to detect a power outage.

[0130] According to one embodiment, the power converter (110) (e.g., processor (218)) can identify whether a certain time has elapsed (S618). After performing power outage detection synchronization, the power converter (110) (e.g., processor (218)) can identify whether a certain time (e.g., 3 seconds) has elapsed, allowing at least one of the adjacent other power converters (120, 130) to recognize the power outage or unstable state of the system. The certain time (e.g., 3 seconds) can be variably adjusted based on the distance between the power converters or the situation of the system (100) synchronizing power outage detection between the power converters.

[0131] According to one embodiment, a system (100) for synchronizing power outage detection between the power conversion devices may be connected via a signal line (not shown) capable of transmitting and receiving signals between each power conversion device. For example, each power conversion device may transmit and receive a signal indicating a power outage or an unstable state of the system via the signal line (not shown).

[0132] For example, at least one of the other power conversion devices (120, 130) may determine that the system is in a corrected or unstable state when a voltage having a frequency varied by the power conversion device (110) is recognized. And, at least one of the other power conversion devices (120, 130) may transmit a response signal indicating such recognition to the power conversion device (110) through the signal line (not shown) when the system is recognized as being in a corrected or unstable state.

[0133] According to one embodiment, the power converter (110) (e.g., processor (218)) can perform independent operation (S620). The power converter (110) (e.g., processor (218)) can operate in an independent operation mode after operating for a certain period of time (e.g., 3 seconds) by adjusting the first frequency (e.g., 60Hz) of the grid voltage to a second frequency (e.g., 55Hz).

[0134] According to one embodiment, the other power converter (120, 130) that detects the voltage of the low frequency (e.g., 65Hz) can be operated in an independent operation mode, just like the power converter (110).

[0135] According to one embodiment, after the power converter (110) (e.g., processor (218)) performs a power outage detection synchronization process, if a certain time (e.g., 3 seconds) is exceeded during which at least one of the adjacent other power converters (120, 130) can recognize a power outage or unstable state of the system, the power converter (110) (e.g., processor (218)) can perform independent operation at 60 Hz.

[0136] The above independent operation may include supplying power charged in the battery of the power converter (110) to a load connected to the power converter (110). The power converter (110) (e.g., processor (218)) may perform an independent operation until the power outage or unstable state of the grid is resolved.

[0137] FIG. 7 is a flowchart illustrating the process of a power converter according to another embodiment of the present invention detecting a power outage and performing independent operation.

[0138] Hereinafter, with reference to FIG. 7, the process of a power converter according to another embodiment of the present invention detecting a power outage and performing independent operation is described in detail as follows.

[0139] According to one embodiment, the power conversion device (110) (e.g., grid power outage determination unit (216)) can identify at least one of grid voltage and frequency (S710). The power conversion device (110) (e.g., grid power outage determination unit (216)) can identify whether the grid is currently in a power outage state or not by analyzing at least one of the amplitude and frequency of the grid voltage (or actual load voltage). The process (S710) may include the operation or process performed in the process (S610) of FIG. 6.

[0140] According to one embodiment, the power conversion device (110) (e.g., grid power outage determination unit (216)) can compare the magnitude of the grid voltage with a reference rated voltage (e.g., 100V) and determine that the grid is in an unstable state (e.g., a state where a power outage has occurred) if the grid voltage is not included within a certain range (e.g., the grid voltage is less than 88V or exceeds 110V).

[0141] Additionally, the system power outage determination unit (216) may determine that the system is in an unstable state (e.g., not a power outage state) if the frequency of the voltage of the system (e.g., 60Hz) is outside a predetermined range (e.g., less than 59.3Hz or greater than 60.5Hz). The process (S712) may include the operation or process performed in the process (S612) of FIG. 6.

[0142] According to one embodiment, the power converter (110) (e.g., processor (218)) may apply load power forward compensation (S714). If the power converter (110) (e.g., processor (218)) identifies in the operation (S712) that the grid is in a blackout or unstable state, the power converter (110) may determine that it must supply power to at least one load. The power converter (110) (e.g., processor (218)) may control the operation of the components of the power converter (110) to supply power stored in the battery to the at least one load.

[0143] According to one embodiment, the power converter (110) (e.g., processor (218)) may execute a power outage detection synchronization mode (S716). The power converter (110) (e.g., processor (218)) may perform a power outage detection synchronization process with at least one other power converter (120, 130) adjacent to the power converter (110). The power outage detection synchronization process may include the process of applying a low frequency (e.g., 65Hz) voltage to a power line (180) so that the power converter (110) (e.g., processor (218)) can enable the at least one other power converter (120, 130) to detect a power outage.

[0144] Additionally, the above power outage detection synchronization process may include a process in which at least one other power conversion device (120, 130) detects a power outage or unstable state of the system through the power conversion device (110) and then transmits a response to the detection to the power conversion device (110).

[0145] According to one embodiment, the power converter (110) (e.g., processor (218)) can identify whether the power outage state is a misjudgment (S718). The power converter (110) (e.g., processor (218)) can periodically check for a power outage or unstable state of the system. The power converter (110) (e.g., processor (218)) can periodically check for a power outage or unstable state of the system to identify whether there was an error in detecting the power outage or unstable state of the system. If the power converter (110) (e.g., processor (218)) identifies that an error has occurred in the power outage detection, it can prepare a control operation associated with the system.

[0146] According to one embodiment, the power converter (110) (e.g., processor (218)) can identify whether the time for executing the power outage detection synchronization mode exceeds a predetermined time (S720). If the power converter (110) (e.g., processor (218)) identifies in the operation (S718) that there is no error in detecting a power outage or unstable state of the system, it can identify whether the time for executing the power outage detection synchronization mode exceeds a predetermined time.

[0147] According to one embodiment, the power converter (110) (e.g., processor (218)) can operate a timer while simultaneously executing the power outage detection synchronization mode. Then, the power converter (110) (e.g., processor (218)) can measure the time during which the power outage detection synchronization mode is executed and compare the measured time with a predetermined time (e.g., 3 seconds).

[0148] According to one embodiment, the predetermined time (e.g., 3 seconds) may be the time required for the power converter (110) to operate in a power outage detection synchronization mode, or the time required for at least one adjacent power converter (120, 130) to detect a power outage and operate in an independent operation mode. The predetermined time (e.g., 3 seconds) may be variably adjusted based on the distance between the power converters, or the situation of the system (100) synchronizing power outage detection between the power converters.

[0149] According to one embodiment, the power converter (110) (e.g., processor (218)) can perform independent operation (S722). If the power converter (110) (e.g., processor (218)) identifies that the time for executing the power outage detection synchronization mode has exceeded the predetermined time, the power converter (110) can be operated in an independent operation mode.

[0150] According to one embodiment, the power converter (110) (e.g., processor (218)) can identify whether the power grid has been restored (S724). The power converter (110) (e.g., processor (218)) can periodically check whether the power grid has been restored while operating the power converter (110) in an independent operation mode. The power converter (110) (e.g., processor (218)) can identify whether the power grid has been restored by detecting the voltage or frequency of the power grid.

[0151] According to one embodiment, the power converter (110) (e.g., processor (218)) can perform operation synchronized with the grid (S726). The power converter (110) (e.g., processor (218)) can perform operation synchronized with the grid when it is identified that the grid has been restored. Alternatively, the power converter (110) (e.g., processor (218)) can continuously perform independent operation of the process (S722) when it is identified that the grid has not been restored.

[0152] According to one embodiment, the power converter (110) (e.g., processor (218)) can identify whether synchronization with the grid is complete (S728). When the grid is restored, the power converter (110) (e.g., processor (218)) can initiate a series of processes (i.e., grid synchronization operation) to receive power required by at least one load through the grid.

[0153] According to one embodiment, the power converter (110) (e.g., processor (218)) can prepare control connected to the grid (S730). When synchronization with the grid is completed, the power converter (110) (e.g., processor (218)) can prepare control operation connected to the grid. When synchronization with the grid is completed, the power converter (110) (e.g., processor (218)) can control the operation of each component of the power converter (110) to receive power from the grid. When synchronization with the grid is not completed, the power converter (110) (e.g., processor (218)) can continuously execute independent operation of the process (S722).

[0154] According to one embodiment, if the power converter (110) (e.g., processor (218)) identifies that an error has occurred in the power outage detection during the process (S718), it may prepare a control operation connected to the grid. If the power converter (110) (e.g., processor (218)) identifies that an error has occurred in the power outage detection, it may cancel the execution of the power outage detection synchronization mode of the process (S716). Subsequently, the power converter (110) (e.g., processor (218)) may control the operation of each component of the power converter (110) so that the power converter (110) operates in connection with the grid.

[0155] According to one embodiment, the power converter (110) (e.g., processor (218)) can receive instructions for charging and / or discharging (S732). The power converter (110) (e.g., processor (218)) can receive instructions for charging and / or discharging from an energy management system (EMS). The energy management system (EMS) can transmit instructions for charging and / or discharging to the power converter (110) to monitor and control the operation of the power converter (110). The energy management system can analyze the power converter (110) in real time and monitor and control it through a communication network.

[0156] According to one embodiment, the power conversion device (110) (e.g., processor (218)) may be operated to be connected to the grid (S734). The power conversion device (110) (e.g., processor (218)) may receive a command for charging or a command for discharging, and may perform an operation connected to the grid based on the received command.

[0157] The voltage magnitude and frequency magnitude described above are merely examples, and power outages or unstable conditions between power conversion devices can be synchronized through various magnitudes. Furthermore, the voltage magnitude and frequency magnitude described herein can be adjusted to voltages or frequencies having different magnitudes.

[0158] Each step in each of the flowcharts described above may be operated independently of the illustrated order or may be performed simultaneously. Additionally, at least one component of the present invention and at least one operation performed by said at least one component may be implemented in hardware and / or software.

[0159] Although the present invention has been described above with reference to the illustrated drawings, the present invention is not limited by the embodiments and drawings disclosed in this specification, and it is obvious that various modifications can be made by a person skilled in the art within the scope of the technical concept of the present invention. Furthermore, even if the effects of the configuration of the present invention were not explicitly described while explaining the embodiments of the present invention above, it is natural to acknowledge that the effects predictable by said configuration should also be recognized. Explanation of the symbols

[0160] 110: 1st PCS 111: 1st Transformer 120: 2nd PCS 121: 2nd Transformer 140: System 180: Microgrid 211: Power control unit 212: Voltage control unit 213: First switch 214: Current control unit 215: 3-phase command voltage generation unit 216: System power outage determination unit 217: System phase detection unit 218: Processor 219: Second switch

Claims

Claim 1 A power conversion device comprising: a grid power outage determination unit; a voltage control unit; a three-phase command voltage generation unit; and a processor electrically connected to the grid power outage determination unit, the voltage control unit, and the three-phase command voltage generation unit, wherein the processor identifies that the grid is in a power outage or unstable state when the frequency of the grid voltage identified by the grid power outage determination unit deviates from a predetermined range, and when the grid is identified as being in a power outage or unstable state, controls the voltage through the voltage control unit so that the load voltage input to the voltage control unit is equal to the command voltage, and operates the power conversion device by adjusting the first frequency of the identified grid voltage to a second frequency different from the first frequency, and generates a three-phase command voltage having the second frequency through the three-phase command voltage generation unit so that at least one other power conversion device adjacent to the power conversion device identifies that the grid is in a power outage or unstable state. Claim 2 delete Claim 3 A power converter according to claim 1, further comprising: a first switch; a current control unit; and a power control unit receiving command power from a power management system, wherein the processor controls the first switch to connect the power control unit and the current control unit when the system is not identified as being in a blackout or unstable state, and is configured to control the power of the power converter such that the command power and the power actually operated by the power converter are the same. Claim 4 A power conversion device according to claim 3, further comprising: a second switch; and a grid phase detection unit that extracts the grid voltage and controls the phase of the output voltage to correspond to the phase of the extracted grid voltage, wherein the processor is configured to control the second switch to connect the grid phase detection unit and the three-phase command voltage generation unit when the grid is not identified as being in a power outage or unstable state. Claim 5 A power converter according to claim 1, wherein the processor is configured to identify the system as being in a power outage or unstable state if, through the system power outage determination unit, it is determined that the amplitude of the system voltage has a value other than a predetermined ratio of the amplitude of the reference rated voltage. Claim 6 delete Claim 7 A power converter according to claim 1, wherein the processor calculates the time during which the power converter operates at the second frequency, and when the calculated time exceeds a predetermined threshold time, the power converter is configured to operate the power converter independently based on a rated frequency corresponding to at least one load connected to the power converter. Claim 8 In claim 4, the power converter is configured such that, when the power converter is operating independently based on a rated frequency, if the power grid is identified as restored through the grid power failure determination unit, the processor controls the first switch to connect the power control unit and the current control unit, and controls the second switch to connect the grid phase detection unit and the three-phase command voltage generation unit. Claim 9 In claim 1, the power converter and at least one other power converter adjacent to the power converter are connected via a power line, and the processor is a power converter that generates a three-phase command voltage through a three-phase command voltage generator and applies a three-phase command voltage having the second frequency via the power line. Claim 10 A method for a power conversion device comprising: a process of identifying that the system is in a state of power outage or instability when the frequency of the system voltage deviates from a predetermined range; a process of controlling the voltage so that the load voltage input to the voltage control unit is equal to the command voltage when the system is identified as being in a state of power outage or instability; a process of operating the power conversion device by adjusting the first frequency of the identified system voltage to a second frequency different from the first frequency; and a process of generating a three-phase command voltage having the second frequency so that at least one other power conversion device adjacent to the power conversion device identifies that the system is in a state of power outage or instability. Claim 11 delete Claim 12 In claim 10, the process of identifying whether the system is in a state of power outage includes the process of determining that the system is in a state of power outage or instability if it is determined that the amplitude of the system voltage has a value other than a predetermined ratio of the amplitude of the reference rated voltage. Claim 13 delete Claim 14 A method according to claim 10, further comprising: a process of calculating the time of operation at the second frequency; and a process of independently operating the power converter based on a rated frequency corresponding to at least one load connected to the power converter when the calculated time exceeds a predetermined threshold time. Claim 15 A method according to claim 10, further comprising: a process of identifying whether the power system is restored while the power converter is operating independently; a process of controlling a first switch to connect a power control unit and a current control unit when the power system is restored; and a process of controlling a second switch to connect a power system phase detection unit and a three-phase command voltage generation unit. Claim 16 A method according to claim 10, further comprising the process of applying a three-phase command voltage having the second frequency through a power line connected to at least one other power converter adjacent to the power converter.

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