Power conversion device, power supply system, and control method

Abstract

To provide a power conversion device, a power supply system, and a control method capable of responding promptly to instantaneous voltage drop of a system and recovery from the instantaneous voltage drop, and maintaining stable DC bus voltage while controlling cost increase and size increase.SOLUTION: A power conversion device has a first DC / DC converter having a first end and a second end connected to a DC power source, a capacitor connected in parallel to the first DC / DC converter via the second end, an inverter that converts the DC voltage between both terminals of the capacitor into an AC voltage, a control unit that controls the first DC / DC converter and the inverter, and a detection unit that detects the power supply status of a system. The control unit controls the output power of the first DC / DC converter even when the detection unit detects either the occurrence of an instantaneous voltage drop of the system or the recovery from the instantaneous voltage drop.SELECTED DRAWING: Figure 5

Description

Technical Field

[0001] The present disclosure relates to a power conversion device, a power supply system, and a control method.

Background Art

[0002] There is known a power storage system that is connected to a commercial power grid (hereinafter referred to as the grid), performs self-operation during a grid power outage, and supplies the power stored in a storage battery to a specific load via a power conversion device. There is also known a power storage system that is connected to a photovoltaic power generation system and stores the generated power (i.e., surplus power) exceeding the power supplied to the load in a storage battery. The power storage system connected to the photovoltaic power generation system can be interconnected with the grid, such as supplying the generated power to the grid according to the power generation state of the photovoltaic power generation system.

[0003] Distributed power sources connected to the grid as described above are subject to FRT (Fault Ride Through) requirements that require continuous operation even when a disturbance occurs in the grid. That is, if distributed power sources are simultaneously disconnected during a grid disturbance, it will have a significant impact on power quality. Therefore, in order to prevent problems such as simultaneous disconnection, distributed power sources are required to have continuous operation performance. The FRT requirements mean "requirements for the continuous operation performance of distributed power sources during grid disturbances necessary to ensure power quality" and are defined by the "Grid Interconnection Regulations (JEAC9701)".

[0004] FRT requirements include requirements related to voltage fluctuations and requirements related to frequency fluctuations. Regarding the requirements related to voltage fluctuations, it is required that operation continue during instantaneous voltage dips (hereinafter referred to as "sag"), when the voltage drops instantaneously (e.g., less than 1 second). However, it is permitted to stop the gate signals of semiconductor switching elements etc. that constitute the power converter for a few milliseconds (so-called gate pulse skipping). Also, during instantaneous power outages (hereinafter referred to as "power interruptions"), when the voltage becomes 0 for a short time (e.g., less than 1 minute), it is permitted to stop the gate signals of semiconductor switching elements etc. that constitute the power converter (so-called gate blocking). Furthermore, when recovering from a sag or power interruption, it is necessary to quickly return to the original output power. When recovering from a sag or power interruption, it is required that the output power return to 80% of the active power within 0.1 seconds or 0.2 seconds, respectively.

[0005] Patent Document 1 discloses a power converter that can reduce the degradation of output power quality when a power system recovers from a momentary voltage drop. This power converter includes a DC / DC converter that transforms DC power input from a distributed power source and a capacitor that holds the DC power supplied from the DC / DC converter, and the capacitor voltage is increased as the amount of voltage drop during a momentary voltage drop increases. Patent Document 2 discloses a power converter that can quickly recover to the original power level when recovering from a state where output power is reduced during a momentary voltage drop or power outage. This power converter includes a converter that boosts the input voltage from a DC power source and outputs it, and a capacitor that holds the power output from the converter, and the capacitor voltage is set to a voltage higher than the voltage immediately before the voltage drop occurs. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2015-195710 [Patent Document 2] Japanese Patent Publication No. 2015-223038 [Overview of the Initiative] [Problems that the invention aims to solve]

[0007] Figure 1 shows a conventional hybrid power supply system. Referring to Figure 1, the power converter 900 includes a PV (Photovoltaic) converter 904 connected to a PV panel 902, a battery converter 908 connected to a battery 906, and a capacitor 910 connected to the PV converter 904 and the battery converter 908. The power converter 900 further includes an inverter 912 connected to the capacitor 910. In Figure 1, two positive and negative wires are represented by a single solid line. For example, the two terminals of the PV converter 904 are connected one-to-one to both terminals of the capacitor 910, and the two terminals of the battery converter 908 are connected one-to-one to both terminals of the capacitor 910. That is, the PV converter 904 and the battery converter 908 are connected in parallel to the capacitor 910. The two wires to which both terminals of the capacitor 910 are connected are called the DC bus, and the voltage between the two wires is called the DC bus voltage.

[0008] The PV converter 904 boosts the DC voltage output from the PV panel 902 and outputs it to the capacitor 910. The energy storage converter 908 boosts the DC voltage output from the battery 906 and outputs it to the capacitor 910. The capacitor 910 holds the power supplied by the PV converter 904 and the energy storage converter 908. The energy storage converter 908 is also capable of bidirectional power conversion, converting the surplus power output from the PV converter 904 (i.e., surplus power) and charging the energy storage converter 908. The inverter 912 converts the DC voltage of the capacitor 910 into an AC voltage and outputs it to the relay 916. When the relay 916 is turned on (short-circuited), the power converter 900 supplies power to the load 930 via the distribution board 928. Furthermore, the inverter 912 is capable of bidirectional power conversion, monitors the current value with a current sensor 918, and enables grid connection with the power grid 926 via the main circuit breaker 922 and the energy meter 924.

[0009] In the normal state of the grid, the DC bus voltage is adjusted to balance power supply and demand with respect to the power generated by the PV panel 902, the power charged and discharged by the energy storage converter 908, and the reverse and forward converted powers by the inverter 912 (hereinafter referred to as DC bus voltage control). The reverse conversion of the inverter 912 means output to the capacitor 910 side, and the forward conversion means output to the relay 916 side. At this time, the PV converter 904 performs MPPT (Maximum Power Point Tracking) control to maximize the output power. The energy storage converter 908 performs load-following control, that is, optimal battery operation according to the power generated and consumed. Therefore, DC bus voltage control is performed by the inverter 912. That is, the magnitude of the reverse and forward converted powers is adjusted so that the DC bus voltage (i.e., the voltage across the capacitor 910) remains constant. The inverter 912, PV converter 904, and energy storage converter 908 operate as shown in Figures 2, 3, and 4, respectively. In the following, unless a clear distinction is made between momentary dips and momentary power outages, the term "momentary dip" will be used for convenience to encompass both.

[0010] Referring to Figure 2, in step 940, the inverter 912 detects the power grid voltage and determines whether a voltage sag has occurred in the grid. If no voltage sag has occurred, in step 942, the inverter 912 performs DC bus voltage control as a steady-state operation. If a voltage sag occurs, in step 944, the inverter 912 reduces the output or performs a gate block. Then, in step 946, the inverter 912 determines whether to terminate or not. If it terminates, in step 948, the inverter 912 stops. If it does not terminate, the control returns to step 940. Therefore, once the voltage recovers from the voltage sag, step 942 is executed.

[0011] Referring to Figure 3, in step 960, the PV converter 904 detects the DC bus voltage and determines whether the DC bus voltage is higher than a predetermined value. If it is higher, in step 962, the PV converter 904 suppresses power generation. If it is not higher, in step 964, the PV converter 904 performs MPPT control as a steady-state operation. Then, in step 966, the PV converter 904 determines whether to terminate or not. If it terminates, in step 968, the PV converter 904 stops. If it does not terminate, the control returns to step 960.

[0012] Referring to Figure 4, in step 980, the energy storage converter 908 detects the DC bus voltage and determines whether the DC bus voltage is higher than a predetermined upper limit. If it is higher, in step 982, the energy storage converter 908 suppresses the discharge of the battery 906. If it is not higher, in step 984, the energy storage converter 908 determines whether the DC bus voltage is lower than a predetermined lower limit. If it is lower, in step 986, the energy storage converter 908 suppresses the charging of the battery 906. If it is not lower, in step 988, the energy storage converter 908 performs steady-state control. That is, it discharges the battery 906 according to the power consumption of the load 930 and charges the battery 906 with surplus power from the PV converter. Then, in step 990, the energy storage converter 908 determines whether to terminate or not, and if it terminates, in step 992, the energy storage converter 908 stops. If it does not terminate, the control returns to step 980.

[0013] As described above, during a momentary sag or power outage, the inverter 912 continues to operate by reducing the output current or by executing a gate block in order to meet the requirements of the FRT. As a result, the inverter 912 is unable to perform DC bus voltage control. While the inverter 912 is unable to perform DC bus control, it is conceivable that the PV converter 904 or the energy storage converter 908 could perform DC bus control. However, as described above, since the control is divided into the smallest units of power conversion and the inverter 912, PV converter 904, and energy storage converter 908 operate independently, there is a problem with responsiveness in this case. That is, since the PV converter 904 and the energy storage converter 908 each operate by monitoring the DC bus voltage, they are unaware that the inverter 912 has stopped performing DC bus voltage control. Therefore, they cannot respond quickly to the occurrence of a momentary sag or power outage. If the PV panel 902 is generating power or the PV converter 904 is discharging, the DC bus voltage cannot be controlled to an appropriate value. The PV converter 904 and the energy storage converter 908 are unaware that the grid has recovered from a momentary dip or power outage and that the inverter 912 has resumed DC bus voltage control. Therefore, they are unable to quickly restore output in accordance with FRT requirements.

[0014] Patent documents 1 and 2 solve the above-mentioned problems by setting the DC bus voltage higher than usual. For example, in Patent Document 2, the DC bus voltage is set approximately 50V higher than the steady state. However, setting the DC bus voltage higher requires the use of capacitors and surrounding circuit components with high voltage ratings. This leads to problems such as increased costs and an increase in the size of the device.

[0015] Therefore, the present disclosure aims to provide a power converter, power supply system, and control method that can respond quickly to power grid dips and recovery from dips, and maintain a stable DC bus voltage, while suppressing increases in cost and size. [Means for solving the problem]

[0016] A power conversion device according to one aspect of the present disclosure includes a first DC / DC converter having a first end connected to a DC power source and a second end, a capacitor connected in parallel to the first DC / DC converter via the second end, an inverter that converts the DC voltage between both terminals of the capacitor into an AC voltage, a control unit that controls the first DC / DC converter and the inverter, and a detection unit that detects the power supply status of the grid, wherein the control unit controls the output power of the first DC / DC converter when the detection unit detects either the occurrence of a momentary power dip or recovery from a momentary power dip in the grid.

[0017] A power supply system relating to another aspect of this disclosure includes a power source including a battery or solar panels, and the power conversion device described above, wherein the first DC / DC converter converts power between the power source and a capacitor.

[0018] A power supply system relating to yet another aspect of this disclosure includes a battery, a photovoltaic panel, and the above-mentioned power converter, wherein a first DC / DC converter converts power between the battery and a capacitor, and a second DC / DC converter converts the output power of the photovoltaic panel and supplies it to the capacitor.

[0019] A control method relating to yet another aspect of the present disclosure is a control method for a power conversion device including a first DC / DC converter connected to a DC power supply, a capacitor connected in parallel to the DC / DC converter, and an inverter that converts a DC voltage between the terminals of the capacitor into an AC voltage, the method comprising a detection step for detecting the power supply status of a grid, and a control step for controlling the output power of the DC / DC converter in the event that the detection step detects either the occurrence of a power sag or a recovery from a power sag in the grid. [Effects of the Invention]

[0020] According to this disclosure, it is possible to provide a power converter, power supply system, and control method that can respond quickly to power grid dips and recovery from dips, and maintain a stable DC bus voltage, while suppressing increases in cost and size. [Brief explanation of the drawing]

[0021] [Figure 1] FIG. 1 is a block diagram showing the configuration of a hybrid system including a conventional power conversion device. [Figure 2] FIG. 2 is a flowchart showing the processing performed by the inverter shown in FIG. 1. [Figure 3] FIG. 3 is a flowchart showing the processing performed by the PV converter shown in FIG. 1. [Figure 4] FIG. 4 is a flowchart showing the processing performed by the power storage converter shown in FIG. 1. [Figure 5] FIG. 5 is a block diagram showing the configuration of a hybrid system including a power conversion device according to an embodiment of the present disclosure. [Figure 6] FIG. 6 is a flowchart showing the processing performed by the control unit shown in FIG. 5. [Figure 7] FIG. 7 is a block diagram showing the state changes of the inverter, the power storage converter, and the PV converter accompanying the occurrence of a momentary voltage dip or power outage and the subsequent recovery. [Figure 8] FIG. 8 is a block diagram showing the configuration of a hybrid system including a plurality of PV panels. [Figure 9] FIG. 9 is a block diagram showing the configuration of a power storage system. [Figure 10] FIG. 10 is a block diagram showing the configuration of a solar power generation system.

MODE FOR CARRYING OUT THE INVENTION

[0022] [Description of Embodiments of the Present Disclosure] The contents of the embodiments of the present disclosure will be listed and described. At least a part of the embodiments described below may be arbitrarily combined. As described above, unless clearly distinguishing between a momentary voltage dip and a power outage, for convenience, the term "momentary voltage dip" is used as a term including both.

[0023] (1) A power converter according to the first aspect of the present disclosure includes a first DC / DC converter having a first end connected to a DC power source and a second end, a capacitor connected in parallel to the first DC / DC converter via the second end, an inverter that converts the DC voltage between both terminals of the capacitor into an AC voltage, a control unit that controls the first DC / DC converter and the inverter, and a detection unit that detects the power supply status of the grid, wherein the control unit controls the output power of the first DC / DC converter when the detection unit detects either the occurrence of a voltage sag or recovery from a voltage sag in the grid. As a result, the power converter can respond quickly to the occurrence of a voltage sag and recovery from a voltage sag. Furthermore, since it is not necessary to set the voltage of the capacitor high, it is not necessary to use components with high voltage resistance. Therefore, cost increases and size increases can be suppressed. "Voltage sag" here is not limited to "instantaneous voltage drop", but includes at least one of "instantaneous voltage drop" and "instantaneous power outage".

[0024] (2) In (1) above, the control unit can control the output power of the second terminal of the first DC / DC converter so that the DC voltage of the capacitor remains constant when the detection unit detects the occurrence or recovery of a momentary voltage sag. As a result, the power converter can maintain a stable capacitor voltage (i.e., DC bus voltage) during momentary voltage sags and when recovering from momentary voltage sags.

[0025] (3) In (2) above, the control unit may, in a steady state where no momentary sag is detected by the detection unit, operate either the inverter or the 1 DC / DC converter as the operating unit so that the DC voltage of the capacitor remains constant, and then, upon detection of the occurrence of a momentary sag by the detection unit, switch the operating unit between the inverter and the 1 DC / DC converter. This allows the power converter to respond more quickly to the occurrence of a momentary sag.

[0026] (4) In (3) above, when the control unit is in a state where the first DC / DC converter is the primary operator after the detection unit has detected a momentary power dip, the control unit may switch to the inverter as the primary operator after the detection unit has detected a recovery. This allows the power converter to respond more quickly to a recovery from a momentary power dip.

[0027] (5) In (3) above, the power conversion device may further include a second DC / DC converter having a third end and a fourth end connected to a solar power generation panel, the DC power source may be a storage battery, the second DC / DC converter may be connected in parallel to a capacitor via the fourth end, and the control unit may, in a steady state, operate the inverter as the main unit, and upon detection of a momentary voltage drop by the detection unit, operate either the first DC / DC converter or the second DC / DC converter as the main unit depending on whether the storage battery is rechargeable or not. This makes it possible to realize a power supply system that can respond quickly to the occurrence of a momentary voltage drop and recovery from a momentary voltage drop.

[0028] (6) In (5) above, the control unit, upon receiving detection of a momentary power dip by the detection unit, may operate the first DC / DC converter if the battery is rechargeable, or the second DC / DC converter if the battery is not rechargeable. This makes it possible to realize a power supply system that can reliably respond to momentary power dips.

[0029] (7) The power supply system relating to the second aspect of the present disclosure includes a DC power supply and one of the power converters described in (1) to (4) above, wherein the first DC / DC converter converts power between the DC power supply and a capacitor. This allows the power supply system to respond quickly to the occurrence of voltage dips and recovery from them. Furthermore, since it is not necessary to set the capacitor voltage high, it is not necessary to use components with high voltage resistance. Therefore, cost increases and size increases can be suppressed.

[0030] (8) The power supply system relating to the third aspect of the present disclosure includes a battery, a photovoltaic panel, and the power converter described in (5) or (6) above, wherein the first DC / DC converter converts power between the battery and the capacitor, and the second DC / DC converter converts the output power of the photovoltaic panel and supplies it to the capacitor. This allows the power supply system to respond quickly to the occurrence of voltage dips and recovery from them. Furthermore, since it is not necessary to set the capacitor voltage high, it is not necessary to use components with high voltage resistance. Therefore, cost increases and size increases can be suppressed.

[0031] (9) A control method relating to the fourth aspect of the present disclosure is a control method for a power conversion device including a DC / DC converter connected to a DC power supply, a capacitor connected in parallel to the DC / DC converter, and an inverter that converts the DC voltage between the terminals of the capacitor into an AC voltage, comprising a detection step for detecting the power supply status of the grid, and a control step for controlling the output power of the DC / DC converter in the event that the detection step detects either the occurrence of a voltage sag or recovery from a voltage sag in the grid. This enables a rapid response to the occurrence of a voltage sag and recovery from a voltage sag. Furthermore, since it is not necessary to set the voltage of the capacitor high, it is not necessary to use components with high voltage resistance. Therefore, cost increases and size increases can be suppressed.

[0032] [Details of the embodiments of this disclosure] In the following embodiments, identical parts are assigned the same reference numeral. Their names and functions are also identical. Therefore, detailed descriptions of them will not be repeated.

[0033] (System Configuration) Referring to Figure 5, the power converter 100 according to the embodiment of this disclosure includes a PV converter 104 connected to a PV panel 102, a battery converter 108 connected to a battery 106, and a capacitor 110 connected to the PV converter 104 and the battery converter 108. The power converter 100 further includes an inverter 112 connected to the capacitor 110, and a control unit 114 that controls the PV converter 104, the battery converter 108, and the inverter 112. The power converter 100, the PV panel 102, the battery 106, and the relay 116 constitute a hybrid power supply system. In Figure 5, two positive and negative wires are represented by a single solid line. For example, the two terminals of the PV converter 104 are connected one-to-one to both terminals of the capacitor 110, and the two terminals of the battery converter 108 are connected one-to-one to both terminals of the capacitor 110. That is, the PV converter 104 and the battery converter 108 are connected in parallel to the capacitor 110.

[0034] The PV panel 102 consists of multiple solar cells connected in series, arranged on a plane and sealed using reinforced glass or the like. The PV panel 102 functions as a DC power source. The PV converter 104, under the control of the control unit 114, boosts the DC voltage output from the PV panel 102 and outputs it to the capacitor 110. The storage battery 106 is a rechargeable storage battery such as a lithium-ion secondary battery. The storage battery 106 functions as a DC power source. The energy storage converter 108, under the control of the control unit 114, boosts the DC voltage output from the storage battery 106 and outputs it to the capacitor 110. The capacitor 110 holds the power supplied by the PV converter 104 and the energy storage converter 108. The energy storage converter 108 is also capable of bidirectional power conversion, converting surplus power output from the PV converter 104 and charging the storage battery 106. The inverter 112, under the control of the control unit 114, converts the DC voltage of the capacitor 110 into an AC voltage and outputs it to the relay 116. When the relay 116 is turned on (short-circuited), the power converter 100 supplies power to the load 130 via the distribution board 128. The inverter 112 is also capable of bidirectional power conversion, and the current value is monitored by the current sensor 118, enabling grid connection with the power system 126 via the main breaker 122 and the energy meter 124.

[0035] The PV converter 104 and the energy storage converter 108 are DC / DC converters, and are implemented, for example, by a bridge circuit using semiconductor switching elements (FETs (Field Effect Transistors) etc.). The inverter 112 is a DC / AC converter, and is implemented, for example, by a bridge circuit using semiconductor switching elements.

[0036] The control unit 114 controls the power conversion functions of each component, namely the input and output voltages and currents, by outputting control signals (e.g., gate signals) for the switching elements (e.g., FETs) that constitute each of the PV converter 104, the energy storage converter 108, and the inverter 112. The control unit 114 includes, for example, a CPU (Central Processing Unit) and memory. The functions of the control unit 114 are realized by the CPU executing a program stored in memory. The power conversion device 100 has sensors (not shown) that measure the voltage and current of each part, and the control unit 114 controls the PV converter 104, the energy storage converter 108, and the inverter 112 based on the current and voltage detected by the sensors.

[0037] The voltage sensor 120 detects the voltage and outputs the detected voltage to the control unit 114. By monitoring the system voltage via the voltage sensor 120, the control unit 114 can directly detect when a voltage dip occurs in the system and when it recovers from a dip. When the voltage sensor 120 detects the occurrence of a voltage dip or recovery from a dip, the control unit 114 controls the PV converter 104, the energy storage converter 108, and the inverter 112 accordingly to maintain a constant DC bus voltage, i.e., the voltage between both terminals of the capacitor 110.

[0038] (Operation of the control unit) Referring to Figure 6, the operation of the control unit 114 will be explained. In step 300, the control unit 114 determines from the voltage input from the voltage sensor 120 whether or not a momentary voltage drop has occurred in the system 126. If it is determined that a momentary voltage drop has occurred, the control proceeds to step 308. Otherwise, the control proceeds to step 302.

[0039] In step 302, the control unit 114 causes the inverter 112 to perform DC bus voltage control. After that, the control proceeds to step 304. The PV converter 104 and the energy storage converter 108 are made to perform steady-state operation.

[0040] In step 304, the control unit 114 determines whether to terminate. Termination is performed, for example, by turning off the power supply (not shown) that supplies power to operate the various parts of the power converter 100. If it is determined to terminate, the control proceeds to step 306. Otherwise, the control returns to step 300.

[0041] In step 306, the control unit 114 stops the power converter 100. Specifically, it stops outputting control signals to the PV converter 104, the energy storage converter 108, and the inverter 112.

[0042] If the result of the determination in step 300 is YES (i.e., a momentary dip has occurred), in step 308, the control unit 114 determines whether the storage battery 106 is rechargeable (including cases where it can be charged and discharged). If it is determined to be rechargeable, the control proceeds to step 310. Otherwise, the control proceeds to step 312.

[0043] In step 310, the control unit 114 causes the energy storage converter 108 to perform DC bus voltage control. The control unit 114 causes the PV converter 104 to perform steady-state operation and causes the inverter 112 to reduce the voltage or perform gate blocking to satisfy the FRT requirements. After that, the control proceeds to step 304.

[0044] In step 312, the control unit 114 causes the PV converter 104 to perform DC bus voltage control. The control unit 114 causes the energy storage converter 108 to perform steady-state operation and causes the inverter 112 to reduce the voltage or perform gate blocking to satisfy the FRT requirements. After that, the control proceeds to step 304.

[0045] Figure 7 shows how the operating modes (i.e., operating states) of the PV converter 104, the energy storage converter 108, and the inverter 112 change as a result of the process shown in Figure 6. In Figure 7, the horizontal axis is the time axis, and the upper, middle, and lower sections show the operating modes of the inverter 112, the energy storage converter 108, and the PV converter 104, respectively.

[0046] At time t0, the power converter 100 starts operation. At this point, no momentary voltage dip occurs. That is, step 302 shown in Figure 6 is repeatedly executed. Specifically, the control unit 114 causes the inverter 112 to perform DC bus voltage control. That is, the control unit 114 outputs a control signal to operate the inverter 112 so that the DC bus voltage remains constant. The control unit 114 causes the energy storage converter 108 to perform load following control as a steady-state operation. That is, the control unit 114 determines a command value (i.e., charge / discharge current value) using the output current value detected by the current sensor 118, and performs feedback control so that the current of the energy storage converter 108 reaches the command value. The control unit 114 also causes the PV converter 104 to perform MPPT control as a steady-state operation. That is, the control unit 114 determines a command value (i.e., voltage or current) so that the power generated by the PV panel 102 is maximized, and performs feedback control so that the current of the PV converter 104 reaches the command value.

[0047] Subsequently, assume that a momentary voltage dip occurred at time t1 (i.e., the determination result in step 300 shown in Figure 6 is YES). The control unit 114 can quickly detect the momentary voltage dip in the grid using the voltage sensor 120. At this time, assume that the battery 106 is in a rechargeable state (i.e., the determination result in step 308 is YES). The control unit 114 causes the energy storage converter 108 to perform DC bus voltage control. That is, the control unit 114 outputs a control signal to operate the energy storage converter 108 so that the DC bus voltage remains constant. The control unit 114 causes the PV converter 104 to maintain MPPT control as steady-state operation. The control unit 114 causes the inverter 112 to reduce the voltage or execute a gate block.

[0048] Subsequently, at time t2 (for example, t2-t1 ≤ 1 second), the momentary voltage dip is resolved (i.e., the determination result of step 300 shown in Figure 6 is NO). The control unit 114 can quickly detect that the power system has recovered from the momentary voltage dip using the voltage sensor 120. As a result, the system returns to a state where step 302 shown in Figure 6 is repeatedly executed, similar to the period from time t0 to time t1.

[0049] Subsequently, assume that a momentary voltage dip occurred at time t3 (i.e., the result of step 300 shown in Figure 6 is YES). At this time, assume that the battery 106 is in a state where it cannot be charged (i.e., the result of step 308 is NO). The control unit 114 causes the PV converter 104 to perform DC bus voltage control. That is, the control unit 114 outputs a control signal to operate the PV converter 104 so that the DC bus voltage remains constant. The control unit 114 causes the inverter 112 to reduce the voltage or execute a gate block. The control unit 114 causes the energy storage converter 108 to maintain load-following control as the steady-state operation.

[0050] Subsequently, let's assume that the momentary slack has been resolved at time t4 (for example, t4-t3 ≤ 1 second) (i.e., the result of the determination in step 300 shown in Figure 6 is NO). As a result, the state returns to one where step 302 shown in Figure 6 is repeatedly executed, similar to the period from time t2 to time t3.

[0051] As a result, the control unit 114 can quickly detect the occurrence of a momentary power dip and recovery from the dip, and when it detects the occurrence of a momentary power dip, it sends the FRT requirements to the inverter 112. FullBy executing an action to add power, the PV converter 104 or the energy storage converter 108 can be quickly instructed to perform DC bus voltage control depending on whether the battery 106 is rechargeable or not. Furthermore, when recovery from a momentary dip is detected, the inverter 112 can be quickly instructed to perform DC bus voltage control, and the PV converter 104 and the energy storage converter 108 can be instructed to perform steady-state operation. In conventional technology, the DC bus voltage had to rise or fall to some extent, but the DC bus voltage can always be maintained at an appropriate value. Therefore, the power converter 100 can quickly respond to the occurrence of momentary dips and recovery from them without setting the capacitor voltage high. Since there is no need to set the capacitor voltage high, there is no need to use components with high voltage resistance. Therefore, cost increases and size increases can be suppressed.

[0052] Upon detection of a momentary voltage dip or recovery by the voltage sensor 120, the control unit 114 controls the output power from the energy storage converter 108 to the capacitor 110 so that the DC voltage of the capacitor 110 remains constant. As a result, the power converter 100 can stably maintain the voltage between both terminals of the capacitor 110 (i.e., the DC bus voltage) during momentary voltage dips and recovery from dips.

[0053] In a steady state where no voltage sag is detected by the voltage sensor 120, the control unit 114 operates either the inverter 112 or the energy storage converter 108 as the operating unit to maintain a constant voltage between the terminals of the capacitor 110 (i.e., the DC bus voltage). Upon detection of a voltage sag by the voltage sensor 120, the control unit 114 switches the operating unit between the inverter 112 and the energy storage converter 108. This allows the power converter to respond more quickly to the occurrence of a voltage sag.

[0054] Upon detecting a momentary voltage dip by the voltage sensor 120, the control unit 114, if the battery 106 is rechargeable, instructs the energy storage converter 108 to perform DC bus voltage control; if the battery 106 is not rechargeable, instructs the PV converter 104 to perform DC bus voltage control. This ensures that the power converter 100 can reliably respond to momentary voltage dips.

[0055] The CPU constituting the control unit 114 is not limited to a single-core CPU. It may be a CPU with multiple cores, such as a dual-core CPU. Furthermore, the control unit 114 may be composed of multiple CPUs. The multiple CPUs share the tasks of detecting momentary voltage dips and recovery based on the voltage input from the voltage sensor 120, and controlling the PV converter 104, the energy storage converter 108, and the inverter 112, respectively. Therefore, in order to enable a quick response during momentary voltage dips and recovery from dips, it is preferable that the communication speed between the multiple CPUs be very fast. By "very fast," I mean a speed that is delayed by, for example, one or two cycles relative to the control cycle of the power conversion device (for example, the cycle of frequencies within the range of approximately 10 kHz to approximately 100 kHz).

[0056] (First variation) The above describes an example of a system including one set of PV panels and PV converters. However, the disclosure is not limited thereto. The system may include multiple sets of PV panels and PV converters. Referring to Figure 8, the power converter 200 according to the first modification includes a plurality of PV panels 102, ... and a plurality of PV converters 104, ... and PV converter 204 connected one-to-one to a plurality of PV panels 102, ... and PV panel 202, and a storage converter 108 connected to a battery 106. The power converter 200 further includes a capacitor 110 connected to the PV converters 104, ... and PV converter 204, and the storage converter 108, an inverter 112 connected to the capacitor 110, and a control unit 206 that controls the PV converters 104, ... and PV converter 204, the storage converter 108, and the inverter 112. The power converter 200, PV panels 102, ... and PV panel 202, battery 106, and relay 116 constitute a hybrid power supply system. The power converter 200 is the same as the power converter 100 shown in Figure 5, but with multiple sets of PV panels 102, ..., and PV panels 202, as well as PV converters 104, ..., and PV converters 204, and the control unit 114 replaced by the control unit 206. The other configurations of the power converter 200 are the same as those of the power converter 100.

[0057] The control unit 206 controls the PV converters 104, ..., and the PV converter 204, the energy storage converter 108, and the inverter 112, respectively, in the same way as the control unit 114. The control unit 206 detects the occurrence of a voltage sag and recovery from a voltage sag in the grid using the voltage sensor 120, similar to the control unit 114 shown in Figure 5. The operation of the control unit 206 during a voltage sag and recovery is the same as the operation of the control unit 114 (see the flowchart shown in Figure 6). However, if a voltage sag occurs and the battery 106 cannot be charged (the result of the determination in step 308 in Figure 6 is NO), the control unit 206 causes the PV panels 102, ..., and the entire PV panel 202 to perform DC bus voltage control. That is, the control unit 206 controls the DC bus voltage so that it remains constant based on the total output power from the PV panels 102, ..., and the PV panel 202. How each of the PV panels 102, ..., and the PV panel 202 is controlled at will. For example, the power required to keep the DC bus voltage constant can be apportioned according to the power generation state (i.e., the power generated at that time) of each PV panel 102, ..., and PV panel 202, thereby determining the output power of each PV panel 102, ..., and PV panel 202. Alternatively, the output power of each PV panel 102, ..., and PV panel 202 may be varied uniformly.

[0058] Therefore, the power converter 200, like the power converter 100, can quickly detect the occurrence of a momentary power dip and recovery from a momentary power dip, and when it detects the occurrence of a momentary power dip, it can send an FRT (Frequency Relay Time) to the inverter 112. FullBy executing a control to enable charging, the power converter 108 or PV panels 102, ..., and PV panels 202 can be quickly instructed to perform DC bus voltage control depending on whether the battery 106 is rechargeable or not. Furthermore, when recovery from a momentary voltage dip is detected, the inverter 112 can be quickly instructed to perform DC bus voltage control, and the power converter 108, PV panels 102, ..., and PV panels 202 can be instructed to perform steady-state operation. Therefore, the power converter 200 can quickly respond to the occurrence of momentary voltage dips and recovery from them without setting the capacitor voltage high. Since there is no need to set the capacitor voltage high, there is no need to use components with high voltage resistance. As a result, cost increases and size increases can be suppressed.

[0059] (Second variation) The above description concerns a hybrid system including PV panels and a battery, but is not limited thereto. A battery storage system without PV panels may also be described. Referring to Figure 9, the power converter 220 according to the second modified example includes a battery 106 connected to a battery 108 and a capacitor 110 connected to the battery 108. The power converter 220 further includes an inverter 112 connected to the capacitor 110 and a control unit 222 that controls the battery 108 and the inverter 112. The battery 106, the power converter 220 and the relay 116 constitute a battery storage system. The power converter 220 is the same as the power converter 100 shown in Figure 5, but with the PV panels 102 and PV converter 104 removed and the control unit 114 replaced by the control unit 222. The other configurations of the power converter 220 are the same as those of the power converter 100.

[0060] The control unit 222 controls the energy storage converter 108 and the inverter 112, respectively, in the same way as the control unit 114 shown in Figure 5. Similar to the control unit 114, the control unit 222 detects the occurrence of a voltage dip and recovery from a dip in the grid using the voltage sensor 120. The operation of the control unit 222 during a voltage dip and recovery is the same as the flowchart shown in Figure 6, excluding steps 308 and 312. That is, if a voltage dip occurs (i.e., the result of step 300 is YES), the control unit 222 causes the energy storage converter 108 to perform DC bus voltage control without determining whether the battery 106 is rechargeable (see step 310).

[0061] Therefore, the power converter 220, like the power converter 100, can quickly detect the occurrence of a power sag and recovery from a power sag, and when it detects the occurrence of a power sag, it can send an FRT (Frequency Relay Time) signal to the inverter 112. Full By executing a control to add power, the power storage converter 108 can be quickly made to perform DC bus voltage control. Furthermore, when recovery from a momentary dip is detected, the inverter 112 can be quickly made to perform DC bus voltage control, and the power storage converter 108 can be made to perform steady-state operation. Therefore, the power converter 220 can quickly respond to the occurrence of momentary dips and recovery from them without setting the capacitor voltage high. Since there is no need to set the capacitor voltage high, there is no need to use components with high voltage resistance. As a result, cost increases and size increases can be suppressed.

[0062] As described above, when the power storage converter 108 is performing DC bus voltage control in response to a momentary voltage dip detected by the voltage sensor 120, the control unit 222, upon detecting a recovery by the voltage sensor 120, causes the inverter 112 to perform DC bus voltage control. This allows the power converter 220 to respond more quickly to a recovery from a momentary voltage dip.

[0063] (Third variation) The above description concerns a system including a battery, but is not limited to this. A solar power generation system without a battery may also be described. Referring to Figure 10, the power converter 240 according to the third modified example includes a PV converter 104 connected to a PV panel 102 and a capacitor 110 connected to the PV converter 104. The power converter 240 further includes an inverter 112 connected to the capacitor 110 and a control unit 242 that controls the PV converter 104 and the inverter 112. The PV panel 102, the power converter 240 and the relay 116 constitute a solar power generation system. The power converter 240 is the same as the power converter 100 shown in Figure 5, except that the battery 106 and the energy storage converter 108 are excluded and the control unit 114 is replaced by the control unit 242. The other components of the power converter 240 are the same as those of the power converter 100.

[0064] The control unit 242 controls the PV converter 104 and the inverter 112, respectively, in the same way as the control unit 114 shown in Figure 5. Similar to the control unit 114, the control unit 242 detects the occurrence of a voltage dip and recovery from a dip in the power grid using the voltage sensor 120. The operation of the control unit 242 during a voltage dip and recovery is the same as the flowchart shown in Figure 6, but with steps 308 and 310 removed. That is, if a voltage dip occurs (i.e., the result of step 300 is YES), the control unit 242 causes the PV converter 104 to perform DC bus voltage control (see step 312).

[0065] Therefore, the power converter 240, like the power converter 100, can quickly detect the occurrence of a momentary power dip and recovery from a momentary power dip, and when it detects the occurrence of a momentary power dip, it can send the FRT requirements to the inverter 112. FullBy executing a control to achieve this, the PV converter 104 can be quickly instructed to perform DC bus voltage control. Furthermore, when recovery from a momentary dip is detected, the inverter 112 can be quickly instructed to perform DC bus voltage control, allowing the PV converter 104 to perform steady-state operation. Therefore, the power converter 240 can quickly respond to the occurrence of momentary dips and recovery from them without setting the capacitor voltage high. Since there is no need to set the capacitor voltage high, there is no need to use components with high voltage resistance. As a result, cost increases and size increases can be suppressed.

[0066] As described above, when the PV converter 104 is performing DC bus voltage control in response to a momentary voltage dip detected by the voltage sensor 120, the control unit 242, upon detecting a recovery by the voltage sensor 120, causes the inverter 112 to perform DC bus voltage control. This allows the power converter 240 to respond more quickly to a recovery from a momentary voltage dip.

[0067] The above describes a power supply system that includes at least PV panels or a battery as a DC power source, but is not limited to this. The power supply system may include a DC power source other than either PV panels or a battery.

[0068] The present disclosure has been described above by describing embodiments, but the embodiments described above are illustrative and the present disclosure is not limited to the embodiments described above. The scope of the present disclosure is as indicated by the claims, with reference to the detailed description of the invention, and includes all modifications within the meaning and scope equivalent to the wording contained herein. [Explanation of Symbols]

[0069] 100, 200, 220, 240, 900 Power Converters 102, 202, 902 PV panels Converters for 104, 204, and 904 PV 106, 906 storage batteries 108, 908 Energy Storage Converters 110, 910 Capacitors 112, 912 Inverter 114, 206, 222, 242 Control Unit 116, 916 relays 118, 918 Current Sensor 120 Voltage Sensor 122, 922 chief 124, 924 Electric energy meter 126, 926 lines 128, 928 distribution boards 130, 930 load 300, 302, 304, 306, 308, 310, 312, 940, 942, 944, 946, 948, 960, 962, 964, 966, 968, 980, 982, 984, 986, 988, 990, 992 steps t0, t1, t2, t3, t4 time

Claims

1. A first DC / DC converter having a first end connected to a DC power supply and a second end, A capacitor connected in parallel to the first DC / DC converter via the second end, An inverter that converts the DC voltage between both terminals of the aforementioned capacitor into an AC voltage, A control unit that controls the first DC / DC converter and the inverter, It includes a detection unit that detects the power supply status of the grid, The control unit controls the inverter and the first DC / DC converter so that the DC voltage of the capacitor is maintained at a predetermined value regardless of whether the detection unit detects the occurrence of a momentary voltage drop or the recovery from the momentary voltage drop in the system. The control unit, In a steady state where the detection unit has not detected the momentary voltage drop, the inverter is operated primarily to maintain the DC voltage of the capacitor at the predetermined value. A power conversion device that, upon detection of the occurrence of the momentary voltage drop by the detection unit, switches the operating unit from the inverter to the first DC / DC converter.

2. The power conversion device according to claim 1, wherein the control unit, in the state in which the first DC / DC converter is the operating unit after the detection unit has detected the momentary voltage drop, makes the inverter the operating unit after the detection unit has detected the return to normal operation.

3. A first DC / DC converter having a first end connected to a DC power supply and a second end, A capacitor connected in parallel to the first DC / DC converter via the second end, An inverter that converts the DC voltage between both terminals of the aforementioned capacitor into an AC voltage, A control unit that controls the first DC / DC converter and the inverter, A detection unit for detecting the power supply status of the grid, It includes a second DC / DC converter having a third end and a fourth end connected to a solar power generation panel, The DC power source is a storage battery, The second DC / DC converter is connected in parallel to the capacitor via the fourth terminal, The control unit controls the inverter, the first DC / DC converter, and the second DC / DC converter so that the DC voltage of the capacitor is maintained at a predetermined value regardless of whether the detection unit detects the occurrence of a momentary voltage drop or recovery from the momentary voltage drop in the system. The control unit, In a steady state where the detection unit has not detected the momentary voltage drop, the inverter is configured to primarily operate to maintain the DC voltage of the capacitor at the predetermined value. A power conversion device that, upon detection of the occurrence of the momentary voltage drop by the detection unit, operates either the first DC / DC converter or the second DC / DC converter as the main operating device, depending on whether the storage battery is rechargeable or not.

4. Upon receiving the detection of the occurrence of the momentary dip by the detection unit, the control unit... If the storage battery is rechargeable, the first DC / DC converter will be the operating unit. The power conversion device according to claim 3, wherein if the storage battery is unable to be charged, the second DC / DC converter is the main operating component.

5. DC power supply and Includes a power converter according to any one of claims 1 to 4, The first DC / DC converter is a power supply system that converts power between the DC power supply and the capacitor.

6. Storage batteries and Solar power generation panels and Includes the power conversion device described in claim 3 or claim 4, The first DC / DC converter converts power between the battery and the capacitor, The second DC / DC converter is a power supply system that converts the output power of the solar power generation panel and supplies it to the capacitor.

7. A control method for a power conversion device including a DC / DC converter connected to a DC power supply, a capacitor connected in parallel to the DC / DC converter, and an inverter that converts the DC voltage between the terminals of the capacitor into an AC voltage, A detection step for detecting the power supply status of the grid, The detection step includes a control step that controls the inverter and the DC / DC converter so that the DC voltage of the capacitor is maintained at a predetermined value regardless of whether a momentary voltage drop or recovery from the momentary voltage drop is detected in the system, The control step described above is: In a steady state where the momentary dip has not been detected by the detection step, the inverter is operated as the main unit for maintaining the DC voltage of the capacitor at the predetermined value. A control method comprising the step of switching the operating entity from the inverter to the DC / DC converter in response to the detection of the occurrence of the momentary voltage drop by the detection step.

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