Power conversion equipment

Abstract

According to an embodiment of the present invention, a power conversion device includes an input unit connected to a DC link end and receiving an input of a voltage and a current at the DC link end, a power conversion unit converting the voltage at the DC link end, an output unit outputting the converted voltage, and a control unit comparing the voltage at the DC link end with a reference voltage, controlling the power conversion unit using a difference between the voltage at the DC link end and the reference voltage, and adjusting the reference voltage using a current at the DC link end resulting from operation of the power conversion unit.

Description

[Technical Field]

[0001] The present invention relates to a power conversion device, and more particularly to a power conversion device in which the voltage at the end of a DC link is stable. [Background technology]

[0002] Electric energy is widely used because it is easy to convert and transmit. To use electric energy efficiently, an energy storage system (ESS) is used. The energy storage system receives power and charges it into a battery. When power is needed, the energy storage system discharges the power stored in the battery to supply power. This allows the energy storage system to supply power continuously.

[0003] Specifically, when the power supply system includes an energy storage system, it operates as follows: When the load or the grid is overloaded, the energy storage system discharges the electrical energy stored in the battery, and when the load or the grid is lightly loaded, the energy storage system receives power from the power generation device or the grid and charges the battery.

[0004] In addition, when an energy storage system exists independently of a power supply system, the energy storage system receives idle power from an external power supply source and charges the battery. When the grid or load is overloaded, the energy storage system supplies power by discharging the power charged in the battery.

[0005] Such energy storage systems perform drop control to improve stability during battery charging or discharging. In particular, energy storage systems perform drop control based on the battery's state of charge (SOC). However, existing drop control methods have the disadvantage that the charge / discharge voltage and drop curve are fixed, and the operating point of the DC / DC converter changes only along the determined drop curve. Another problem is that the power output is fixed to zero in the idle section, creating a non-responsive section when the voltage drops or rises. Another problem is that discharging and idle operation are not possible when the link voltage is within the charging voltage section, and charging and idle operation are not possible when the link voltage is within the discharging voltage section, meaning that charging and discharging are not possible in the idle section. Summary of the Invention [Problem to be solved by the invention]

[0006] The technical problem to be solved by the present invention is to provide a power conversion device in which the voltage at the end of the DC link is stable. [Means for solving the problem]

[0007] In order to solve the above technical problems, a power conversion device according to an embodiment of the present invention includes an input unit connected to a DC link end and receiving a voltage and a current at the DC link end; a power conversion unit that converts the voltage at the DC link end; an output unit that outputs the converted voltage; and a control unit that compares the voltage at the DC link end with a reference voltage, controls the power conversion unit using a difference between the voltage at the DC link end and the reference voltage, and adjusts the reference voltage using a current at the DC link end due to an operation of the power conversion unit.

[0008] Furthermore, the control unit can repeat the adjustment of the reference voltage until the difference between the voltage at the DC link end and the reference voltage becomes zero or falls within a predetermined range.

[0009] Also, a device connected to the DC link end may operate under drop control in which power is controlled by the voltage at the DC link end, and the reference voltage may be an input of a drop control curve of the drop control.

[0010] The output unit may be connected to a battery, and the control unit may control the power conversion unit to charge or discharge the battery.

[0011] Furthermore, the control unit can calculate the amount of power to charge or discharge the battery by using the difference between the voltage at the DC link end and the reference voltage.

[0012] The control unit may also limit the operation of the power conversion unit within a predetermined power range.

[0013] Also, the initial reference voltage may be set to a voltage when the device connected to the DC link end is not being charged or discharged.

[0014] In addition, the control unit may adjust the reference voltage when the voltage or current at the DC link end changes due to a change in charging power or discharging power of a device connected to the DC link end.

[0015] In order to solve the above technical problems, a solar power generation system according to one embodiment of the present invention includes a DC link end, a solar power generation module connected to the DC link end, an inverter connected between the DC link end and a grid, and one or more DC-DC converters connected between the DC link end and a battery, wherein devices connected to the DC link end operate under drop control in which power is controlled by a reference voltage, and the DC-DC converter compares a voltage at the DC link end with a reference voltage when power of any of the devices connected to the DC link end changes, charges or discharges the battery using a difference between the voltage at the DC link end and the reference voltage, and adjusts the reference voltage using a current at the DC link end due to charging or discharging of the battery.

[0016] Furthermore, the DC-DC converter can repeat the adjustment of the reference voltage until the difference between the voltage at the DC link end and the reference voltage becomes zero or falls within a predetermined range. [Effects of the Invention]

[0017] According to an embodiment of the present invention, it is possible to perform drop control with stable voltage at the DC link end. In addition, since the link end voltage is tracked along the drop curve using power consumed (supplied) by an inverter or the like, parallel operation with other power conversion devices is possible. By controlling the voltage operating point that tracks the link voltage through voltage control, the link end voltage is stabilized compared to when only a current controller is present. [Brief explanation of the drawings]

[0018] [Figure 1] 1 is a block diagram of a power conversion device according to an embodiment of the present invention; [Figure 2] 1 is a block diagram of a solar power generation system according to an embodiment of the present invention. [Figure 3] 2 is a diagram showing the connection relationship of each component of the solar power generation system according to the embodiment of the present invention; FIG. [Figure 4] 1 is a diagram illustrating a power conversion device according to an embodiment of the present invention; [Figure 5] 1 is a diagram illustrating a power conversion device according to an embodiment of the present invention; [Figure 6] 1 is a diagram illustrating a power conversion device according to an embodiment of the present invention; [Figure 7] 1 is a diagram illustrating a power conversion device according to an embodiment of the present invention; [Figure 8] 1 is a diagram illustrating a power conversion device according to an embodiment of the present invention; [Figure 9] 1 is a diagram illustrating a power conversion device according to an embodiment of the present invention; [Figure 10] 1 is a diagram illustrating a power conversion device according to an embodiment of the present invention; [Figure 11] 1 is a diagram illustrating a power conversion device according to an embodiment of the present invention; DETAILED DESCRIPTION OF THE INVENTION

[0019] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

[0020] However, the technical concept of the present invention is not limited to the described embodiments, but can be implemented in various different forms, and one or more of the components of the embodiments can be selectively combined or substituted for each other within the scope of the technical concept of the present invention.

[0021] Furthermore, unless otherwise clearly defined and described, terms (including technical and scientific terms) used in the embodiments of the present invention may be interpreted in the sense that they are commonly understood by a person of ordinary skill in the art to which the present invention belongs, and commonly used terms, such as dictionary-defined terms, may be interpreted in the context of the relevant art.

[0022] Furthermore, the terms used in the examples of the present invention are intended to explain the examples and are not intended to limit the present invention.

[0023] In this specification, unless otherwise specified, the singular form can also include the plural form, and when it is stated as "A and (and) at least one (or more) of B and C," it can include one or more of all combinations of A, B, and C.

[0024] Furthermore, when describing components of the embodiments of the present invention, terms such as first, second, A, B, (A), (B), etc. are used to distinguish the components from other components, and the terms do not limit the essence, order, or sequence of the components.

[0025] Furthermore, when a component is described as being "coupled," "coupled," or "connected" to another component, it includes not only cases where the component is directly "coupled," "coupled," or "connected" to the other component, but also cases where the component is "coupled," "coupled," or "connected" by another component between the component and the other component.

[0026] Furthermore, when described as being formed or disposed "above" or "below" each component, "above" or "below" includes not only cases where two components are in direct contact with each other, but also cases where one or more other components are formed or disposed between the two components. Furthermore, when expressed as "above" or "below," it can include not only the upward direction but also the downward direction based on one component.

[0027] Modifications of the present embodiments may include some components of each embodiment and some components of other embodiments. That is, a modification may include one embodiment of various embodiments, but omit some components and include some components of the corresponding other embodiment. Or vice versa. Features, structures, effects, etc. described in the embodiments are included in at least one embodiment and are not necessarily limited to one embodiment. Furthermore, features, structures, effects, etc. exemplified in each embodiment may be combined or modified in other embodiments by a person skilled in the art to which the embodiments belong. Therefore, content related to such combinations and modifications should be interpreted as being included within the scope of the embodiments.

[0028] Fig. 1 is a block diagram of a power conversion device according to an embodiment of the present invention, Fig. 2 is a block diagram of a solar power generation system according to an embodiment of the present invention, Fig. 3 is a diagram showing the connection relationship of each component of the solar power generation system according to an embodiment of the present invention, and Figs. 4 to 11 are diagrams for explaining a power conversion device according to an embodiment of the present invention.

[0029] The power conversion device 100 according to an embodiment of the present invention may include an input unit 110, a power conversion unit 120, an output unit 130, and a control unit 140.

[0030] 2, the power conversion device 100 according to the embodiment of the present invention is connected to a DC link end 210, and can be connected in parallel with a photovoltaic power generation module 230, an inverter 240, other power conversion devices 100, a load 250, etc. The input unit 110 is connected to the DC link end 210 and receives the voltage and current of the DC link end 210 as input.

[0031] The input unit 110 is connected to the DC link end 210 to receive the voltage of the DC link end 210 or to receive a signal for sensing the voltage or current of the DC link end 210. The voltage of the DC link end may be the voltage of a DC link capacitor connected to the DC link end. The input unit 110 may include a sensing unit (not shown) for sensing the voltage or current of the DC link end 210.

[0032] The power conversion unit 120 converts the voltage at the DC link end input to the input unit 110 .

[0033] The power conversion unit 120 is a device that converts input power and outputs it, and may be a converter. It may be a boost converter that increases voltage, a buck converter that decreases voltage, or a buck-boost converter that increases or decreases voltage. It may also be a DC-DC converter that converts direct current to direct current. It may include various devices that convert power, voltage, and current.

[0034] The output unit 130 outputs the converted voltage to the power conversion unit 120 .

[0035] The output unit 130 may be connected to the battery 220, and the power conversion unit 120 may charge or discharge the battery 220. The power conversion unit 120 may convert power from the DC link end 210 to charge the battery 220, or may convert power stored in the battery 220 and output it to the DC link end 210. When converting power from the battery 220 and outputting it to the DC link end 210, the output unit 130 may operate as an input unit to which a battery voltage is applied, and the input unit 110 may operate as an output unit. The power conversion unit 120 may include a battery DC-DC converter and a battery monitoring system (BMS).

[0036] The control unit 140 controls the operation of the power conversion unit 120 according to the voltage of a DC link end of a DC link end (LINK) 220 connected to the power conversion unit 120. The control unit 140 compares the voltage of the DC link end with a reference voltage and controls the power conversion unit 120 using the difference between the voltage of the DC link end and the reference voltage. When the power conversion unit 120 operates, the reference voltage can be adjusted using the current of the DC link end.

[0037] The control unit 140 can perform drop control of the power conversion unit 120 according to the voltage at the DC link end, thereby controlling the power charged or discharged from the battery 220. The control unit 140 performs drop control by controlling the power conversion operation of the power conversion unit 120. Drop control is a control that prevents excessive output and maintains a constant output. This control method utilizes the characteristics that the frequency of the output voltage drops when the active power output by the converter increases, and the characteristics that the magnitude of the output voltage drops when the reactive power output increases, and is called load sharing control. The control unit 140 can control the operation of the power conversion unit 120 according to the magnitude of the voltage at the DC link end, thereby controlling the battery 220 to charge or discharge.

[0038] The control unit 140 may divide the range according to the magnitude of the voltage (V_LINK) at the DC link end as shown in Fig. 4 and perform drop control in each range. The horizontal axis of Fig. 2 represents the voltage (V_LINK) at the DC link end, and the vertical axis represents the output power (OUTPUT POWER). The output power may be the charging power or discharging power of the battery 220, and if it is greater than 0, it represents the charging power being charged, and if it is less than 0, it represents the discharging power being discharged.

[0039] Other devices can be connected to the DC link terminal 210, and each device can be operated independently by performing drop control using the voltage of the DC link terminal.

[0040] The control unit 140 does not operate the power conversion unit 120 when the voltage of the DC link end is within a first range (IDEAL AREA). Here, the first range may be a state in which the DC link voltage is stable. Another power conversion unit may be connected to the DC link end 210, and the first range of the voltage of the DC link end may be a range in which the difference between the power input to the DC link end 210 and the power output from the DC link end 210 is within a first value. For example, the first range may be a state in which the power input to the DC link end 210 is output from the DC link end 210 to another power conversion unit, leaving no surplus power. Alternatively, the first range may be a state in which there is no power input to the DC link end 210 or no power output from the DC link end 210.

[0041] Here, the other device may include a power conversion unit, one side of which may be connected to the DC link end 210, and the other side of which may be connected to at least one of a solar power generation unit, a load unit, a grid, and a charging unit.

[0042] The solar power generation module 230 may include a solar panel (PV panel) and an optimizer (PV optimizer). The optimizer may perform maximum power point estimation (MPPT) to maximize the power output from the solar panel. The solar panel may include multiple cell strings. Solar cells that generate solar power may be expressed as cell strings, in which multiple cells are connected in series. A cell string may include at least one cell, and when multiple cells are included, the multiple cells may be connected in series. A cell string may be a solar cell string including solar cells. A solar cell string may form a solar panel. A solar panel may also be a photovoltaic (PV) panel or photovoltaic panel. Solar cells generate electricity through photovoltaic (PV) effects. The photovoltaic effect occurs when light above a certain frequency comes into contact with a specific metal material, emitting electrons. This forms a PN junction between a P-type semiconductor and an N-type semiconductor, and the electrons generated by the photoelectric effect are used to generate a current, thereby generating power. Solar cells are made of silicon and can be formed in wafer form. Solar cells are placed in areas that receive plenty of sunlight, such as outdoors, on the exterior walls of buildings, or on rooftops, and use sunlight to generate electricity. In this case, solar cells can be formed as BIPV (Building Integrated Photovoltaics), which are integrated with buildings.

[0043] Because the amount of power generated by a single solar cell is insufficient for use by loads or power grids, connecting multiple solar cells in series to form a solar cell string can generate the appropriate amount of power for use. A solar cell string can be the basic unit for generating power. A photovoltaic panel can be formed by combining multiple cell strings, which are basic units, into a panel. Solar cells have different voltage-current characteristics depending on factors such as the amount of sunlight and temperature, and their maximum power points (MPPs) also fluctuate. (Generated power = voltage x current) An optimizer optimizes the output power of a cell string so that solar cells can operate at their maximum power points (MPPs), the operating points at which the solar cells generate the maximum power under each condition. The optimizer can include module-level power electronics (MLPE). This is called maximum power point tracking (MPPT), and using MPPT can increase the efficiency of solar power generation. In solar power generation, due to the characteristics of the relationship between current and voltage and the relationship between voltage and power, maximum power can be the power when the maximum voltage is approximately 80% of the maximum voltage, not the maximum voltage. Because this maximum power point continues to change depending on the magnitude of the voltage and current generated by the solar panel, it is necessary to continue searching for a point where the maximum power point can be generated. In other words, to track maximum power that is not the maximum voltage, the magnitude of the voltage and current can be varied to achieve maximum power. In other words, the voltage can be decreased to increase the current in the direction of increasing power, or the voltage can be increased to decrease the current.

[0044] The inverter 240 can supply power to or receive power from the grid 241. The inverter 240 is connected to the DC link end 210 and can receive DC power from the DC link end 210, convert the received DC power into AC power, and supply the power to a load or the grid 241. The inverter 240 can supply AC power to a load that requires AC power and transmit excess power to the grid, i.e., a system. Alternatively, the inverter 240 can receive AC power from the grid 241, convert the AC power into DC power, and output the DC power to the DC link end 210. Here, the inverter 240 can include a DC-AC inverter.

[0045] The power generated by the photovoltaic power generation module unit 230 is transmitted to the DC link terminal 210 and can be provided to the grid 241 through the inverter 240 .

[0046] The power generated by the solar power generation module 230 can be transmitted to the DC link end 210 and can charge the battery 220 through the power conversion unit 120. Alternatively, the power received from the grid 241 can be transmitted to the DC link end 210 through the inverter 240 and can charge the battery 220 through the power conversion unit 120. Furthermore, the power stored in the battery 220 can be transmitted to the DC link end 210 through the power conversion unit 120 and can be provided to a load or the grid 241 through the inverter 240.

[0047] The load may be directly connected to the DC link end 210. Here, the load 250 may be a load that uses DC power. In addition, various devices such as a charging module such as a vehicle quick charger, a switching mode power supply (SMPS), etc. may be connected to the DC link end.

[0048] As described above, in a configuration in which multiple devices are connected in parallel, the control unit 140 can control the power conversion unit 120 using the voltage at the DC link end, rather than information about other power conversion units or correspondingly connected devices.

[0049] In the first section (IDESL AREA) of FIG. 4, the power output from the solar power generation module 230 and transmitted to the DC link end 210 is provided to the grid 241 through the inverter 240, and the voltage of the DC link end is stable. At this time, the control unit 140 can prevent the power conversion unit 120 from operating.

[0050] The control unit 140 can operate the power conversion unit 120 to discharge the battery 220 in a second section (discharging area) where the voltage at the DC link end is lower than the first section, and can operate the power conversion unit 120 to charge the battery 220 in a third section (charging area) where the voltage at the DC link end is higher than the first section.

[0051] The power conversion units of the photovoltaic power generation module 230, the inverter 240, and the load 250 may also be drop-controlled according to the voltage at the DC link end 210. That is, even if a large number of devices are connected to the DC link, the power conversion units of each device can be independently operated through drop-control according to the voltage at the DC link end. When a large number of devices are connected to the DC link and control is performed based on communication, the charging and discharging of the energy storage unit may be determined according to the power generation and output amounts of the associated PV module, inverter module, and charger module, and the time required to receive the corresponding data through communication may increase in proportion to the number of devices connected in parallel. That is, as the number of connected devices increases, the control period becomes longer and the control may become more complex.

[0052] By utilizing the fact that changes in the power of each device cause changes in the voltage at the DC link end, independent operation is possible without sending or receiving information through drop control using the DC link voltage.

[0053] When the condition that the amount of power obtained by subtracting the DC-AC inverter output and charger DC-DC output from the amount of power generated by the PV module and the amount of battery DC-DC charging and discharging is equal is met, the voltage at the DC link end will not fluctuate. In other words, if the amount of power generated and the amount of consumption are the same, the voltage at the DC link end will remain constant. In this case, a low voltage at the DC link end means that consumption is greater than power generation, and a high voltage at the DC link end means that power generation is greater than power consumption. Drop control detects changes in the power of each component through changes in the voltage at the DC link end and takes necessary measures (determines the operation of each component). This drop control enables power control regardless of the number of parallel-connected products, and drop control based on the voltage at the DC link end is simple and enables quick load response even in isolated operation.

[0054] During drop control, the output power of each device is changed in a step form depending on the voltage at the link end, which can cause voltage ripple.In the case of various inverters that use small caps, if the current command is changed in a step form depending on the feedback voltage difference from the reference voltage, ringing at the link end or voltage divergence can occur, making stable operation difficult.

[0055] The control unit 140 of the power conversion device 100 according to an embodiment of the present invention compares the voltage at the DC link end with a reference voltage, controls the power conversion unit 120 using the difference between the voltage at the DC link end and the reference voltage, adjusts the reference voltage using the current at the DC link end due to the operation of the power conversion unit 120, and other devices connected to the DC link end 210 operate according to the adjusted reference voltage, thereby preventing voltage ripple at the DC link end 210.

[0056] A battery 220 can be connected to the output unit 130, and the control unit 140 can charge or discharge the battery 220 by controlling the power conversion unit 120. Here, the control unit 140 can calculate the amount of power to charge or discharge the battery using the difference between the voltage at the DC link end and the reference voltage. If the calculated amount of power is also reflected, there is a possibility that the operating range may be exceeded due to sudden operation. To prevent this risk of malfunction, the control unit 140 can limit the operation of the power conversion unit 120 to within a predetermined power range. For example, the power conversion unit 120 can be limited to a range of 0.3 to 0.95 within the entire operating range.

[0057] The control unit 140 may adjust the reference voltage when the voltage or current at the DC link end changes due to a change in charging power or discharging power of a device connected to the DC link end.

[0058] When the voltage of the DC link end 210 deviates from an ideal range, i.e., the first range in FIG. 4 , and a change in power occurs, the control unit 140 does not immediately use the voltage of the DC link end 210 to operate, but instead compares the voltage of the DC link end 210 with a reference voltage. The initial reference voltage may be set to a voltage in a state in which a device connected to the DC link end is not being charged or discharged. For example, in FIG. 4, the initial reference voltage may be set to 420 V. By comparing the voltage of the DC link end 210 with the reference voltage and using the difference between the two values, the control unit 140 can calculate the power to charge or discharge the battery 220 through the power conversion unit 120. In this way, the power conversion unit 120 can receive power from the DC link end 210 during a charging operation and supply power to the DC link end 210 during a discharging operation. As a result, a change in the DC link end current may occur, and the reference voltage used to control the power conversion unit 120 can be adjusted using the DC link end current.

[0059] The control unit 140 may repeatedly adjust the reference voltage until the difference between the voltage at the DC link end and the reference voltage becomes zero or falls within a predetermined range. The power supplied to or consumed from the DC link end 210 due to the operation of the power conversion unit 120 charges or discharges the battery 220, which may cause the voltage at the DC link end to fluctuate. During this process, the control of the power conversion unit 120 and the adjustment of the reference voltage may be repeated until the reference voltage adjusted to reflect the current at the link end becomes equal to the voltage at the link end. Voltages that change due to surges quickly return to their original state, so the adjustment of the reference voltage can be completed quickly. Alternatively, if power is continuously input or output to or from the DC link end 210, the adjustment of the reference voltage may be repeated until the voltage at the DC link end becomes equal to the reference voltage. When the voltage at the DC link end becomes equal to the reference voltage, stable operation is achieved. Even if the difference between the voltage at the DC link end and the reference voltage is not zero, the reference voltage adjustment process can be repeated until it falls within a predetermined range, for example, within an error range.

[0060] By repeating the process of adjusting the reference voltage, it is possible to prevent ripples from occurring due to sudden changes in power at the DC link end, and to ensure stable operation according to the voltage caused by changes in power at the DC link end.

[0061] The process of adjusting the reference voltage according to the change in the power input or output to the DC link terminal 210 can be performed through the processes of FIGS.

[0062] The control unit 140 can operate through the process of Fig. 5. First, V_REF1 is an initial reference voltage, and when the voltage at the DC link end changes due to a change in power at the DC link end 210, the control unit 140 compares the reference voltage V_REF2 with the DC link end voltage V_FDK to calculate the difference V_ERR. Because the reference voltage has not yet been adjusted, V_REF1 and V_REF2 have the same value.

[0063] Then, a reference current I_REF is calculated using the difference V_ERR between the DC link end voltage and the reference voltage. Here, I_CMD can be I_REF. A power to control the power converter 120 is calculated based on this, and a PWM signal to control the power converter 120 can be generated based on this. At this time, the power variation can be limited to 0.3 to 0.95 through a filter. When the power converter 120 operates using the generated PWM signal and a DC link current flows, the inverter current I_IPI_FBK (I_INV) is used to reflect the reference voltage V_REF1, and the reference voltage is adjusted to V_REF2.

[0064] Through the process of adjusting and repeating the reference voltage, the value at each point in time may be adjusted or changed as shown in FIG. 6, and in this case, changes between each configuration may be made as shown in FIGS. 7 to 11.

[0065] First, at time K-1 when the power supplied to the DC link terminal 210 is stable at 0 kW, the DC link terminal voltage V_LINK and the reference voltage V_REF may be 420V, which is the initial reference voltage.

[0066] At this time, if 3.5 kW is supplied from the inverter 240 to the DC link terminal 210 at time K, the DC link terminal voltage increases from 420 V to 435 V, and a DC link terminal current of 12 A is applied, as shown in Figure 7. Also, V_ERR, which is the difference between the DC link terminal voltage and the reference voltage, becomes 15 V. The power converter 120 is not yet operating.

[0067] Then, the reference voltage is adjusted using the difference between the DC link end voltage and the reference voltage. At time point K+1, the control unit 140 controls the power converter 120 to charge the battery 220 at 4 kW, and the power converter 120 applies 12 A to the power converter 100. As a result, the DC link end voltage drops to 430 V and the reference voltage rises to 422 V, so that the difference between the DC link end voltage and the reference voltage, V_ERR, becomes 8 V.

[0068] After that, because there is still a difference between the DC link end voltage and the reference voltage, the reference voltage is adjusted repeatedly. At time K+2, the decrease in the DC link voltage is reflected, the current input to the DC link end becomes 8.1A, the current applied to the power conversion device changes from 12A to 9A, the DC link end voltage returns to 433V, the reference voltage rises to 430V, and V_ERR, the difference between the DC link end voltage and the reference voltage, decreases to 5V.

[0069] Since there is still a difference between the DC link end voltage and the reference voltage, the reference voltage is adjusted repeatedly. At time K+3, the DC link voltage drops, and the current input to the DC link end becomes 8.1A. The current applied to the power converter changes from 9A to 8.1A, causing the DC link end voltage to become 430V, which is the same as the reference voltage of 430V. As a result, V_ERR, the difference between the DC link end voltage and the reference voltage, becomes 0V.

[0070] At time K+3, the DC link end voltage and the reference voltage become equal, and the final reference voltage becomes 430V, thereby operating the power conversion device 100. If a change occurs in the power input to the DC link end 210, the above process is repeated to track the voltage of the DC link end 210. During this process, the increased DC link end voltage drops to a stable voltage, and the reference voltage is also adjusted to become equal to the voltage of the DC link end.

[0071] This enables stable drop control of the voltage at the DC link end.In addition, since the link end voltage is tracked according to a drop curve in response to the power consumed (supplied) by inverters, etc., parallel operation with other power conversion devices is possible.

[0072] The devices connected to the DC link terminal 210 operate under drop control, in which power is controlled by the voltage of the DC link terminal, and the reference voltage is an input to a drop control curve of the drop control. The reference voltage can be the same for each device or can be applied individually. The devices connected to the DC link terminal 210 can be drop-controlled using the reference voltage adjusted by the control unit 140, or can be drop-controlled using the voltage of the DC link terminal 210 as the reference voltage.

[0073] A solar power generation system according to an embodiment of the present invention includes a DC link end 210, a solar power generation module 230 connected to the DC link end 210, an inverter 240 connected between the DC link end 210 and a grid 241, and one or more DC-DC converters 101, 102 connected between the DC link end 210 and a battery 220. The devices connected to the DC link end 210 operate under drop control, in which power is controlled by a reference voltage. When the power of any of the devices connected to the DC link end 210 changes, the DC-DC converters 101, 102 compare the voltage at the DC link end with a reference voltage, charge or discharge the battery using the difference between the voltage at the DC link end and the reference voltage, and adjust the reference voltage using the current at the DC link end resulting from the charging or discharging of the battery. The DC-DC converters 101, 102 can repeatedly adjust the reference voltage until the difference between the voltage at the DC link end and the reference voltage becomes zero or falls within a predetermined range.

[0074] A detailed description of each component of the solar power generation system according to the embodiment of the present invention corresponds to the detailed description of the power conversion device shown in FIGS. 1 to 11, and therefore, duplicated descriptions will be omitted below.

[0075] When multiple DC-DC converters are connected, they can share and bear the change in power supplied to the DC link terminal, and the magnitude of the power change that can be tolerated increases, allowing for faster stabilization.

[0076] Meanwhile, the embodiments of the present invention can be realized as computer-readable codes on a computer-readable recording medium, which includes all kinds of recording devices that store data readable by a computer system.

[0077] Examples of computer-readable recording media include ROM, RAM, CD-ROM, magnetic tape, floppy disk, optical data storage device, etc. Computer-readable recording media can also be distributed among network-connected computer systems, so that computer-readable code can be stored and executed in a distributed manner. Functional programs, codes, and code segments for implementing the present invention can be easily construed by programmers skilled in the art to which the present invention pertains.

[0078] Those skilled in the art will understand that the present invention can be embodied in various modified forms without departing from the essential characteristics thereof. Therefore, the disclosed method should be considered from an illustrative rather than a restrictive perspective. The scope of the present invention is defined by the claims, not the foregoing description, and all differences within the scope of the claims should be construed as being within the scope of the present invention.

Claims

1. an input unit connected to a DC link end and receiving an input of a voltage and a current of the DC link end; a power conversion unit that converts the voltage at the DC link end; an output unit that outputs the converted voltage; and a control unit that compares a voltage at the DC link end with a reference voltage, controls a power conversion unit using a difference between the voltage at the DC link end and the reference voltage, and adjusts the reference voltage using a current at the DC link end due to an operation of the power conversion unit.

2. The control unit The power conversion device according to claim 1 , wherein the adjustment of the reference voltage is repeated until a difference between the voltage at the DC link end and the reference voltage falls within zero or a predetermined range.

3. The device connected to the DC link terminal operates under drop control in which power is controlled by the voltage of the DC link terminal; 2. The power conversion device of claim 1, wherein the reference voltage is an input of a drop control curve of the drop control.

4. The output unit is connected to a battery, The power conversion device of claim 1 , wherein the control unit controls the power conversion unit to charge or discharge the battery.

5. The control unit The power conversion device according to claim 4 , wherein the amount of power to charge or discharge the battery is calculated using a difference between the voltage at the DC link end and the reference voltage.

6. The control unit The power conversion device of claim 1 , wherein the power conversion unit is configured to limit operation within a predetermined power range.

7. The power conversion device of claim 1 , wherein the initial reference voltage is set to a voltage when a device connected to the DC link end is not being charged or discharged.

8. The control unit The power conversion device of claim 1 , wherein the reference voltage is adjusted when a voltage or a current at the DC link end changes according to a change in charging power or discharging power of a device connected to the DC link end.

9. DC link end, a photovoltaic power generation module connected to the DC link end; an inverter connected between the DC link end and a grid; and one or more DC-DC converters connected between the DC link terminal and a battery; The device connected to the DC link end operates in drop control mode, in which power is controlled by a reference voltage; The DC-DC converter comprises: When the power of any of the devices connected to the DC link end changes, the voltage at the DC link end is compared with a reference voltage, and the battery is charged or discharged using a difference between the voltage at the DC link end and the reference voltage, and the reference voltage is adjusted using a current at the DC link end due to charging or discharging of the battery.

10. The DC-DC converter comprises: The photovoltaic power generation system according to claim 9 , wherein the adjustment of the reference voltage is repeated until a difference between the voltage at the DC link end and the reference voltage becomes zero or falls within a predetermined range.

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