Power supply systems and power storage systems

Abstract

The uninterruptible power supply system (10) includes a converter (1), a first inverter (5), and a first control device (7). The first control device (7) controls the first inverter (5) to supply a first alternating current to the load (14) that includes a feedback component whose value corresponds to the deviation between the AC output voltage of the first inverter (5) and a reference AC voltage. The power storage system (20) includes a second inverter (8) and a second control device (9). The second inverter (8) is connected in parallel with the first inverter (5) to the load (14) and converts power bidirectionally between the second energy storage device (13) and the load (14). The second control device (9) controls the second inverter (8) to supply a second alternating current to the load (14) that includes a feedback component whose value corresponds to the deviation between the AC output voltage of the second inverter (8) and a reference AC voltage, and a feedforward component whose value corresponds to the load current detected by a current detector (CD6).

Description

Technical Field

[0001] The present disclosure relates to a power supply system and a power storage system.

Background Art

[0002] For example, International Publication No. 2020 / 026430 (Patent Document 1) discloses an uninterruptible power supply device including a converter, an inverter, and a bidirectional chopper. The converter converts alternating current power supplied from a power grid into direct current power and supplies it to a direct current line when the power grid is healthy. The bidirectional chopper supplies direct current power supplied from a power storage device to the direct current line when a power outage occurs in the power grid. The inverter converts the direct current power received from the direct current line into alternating current power and supplies it to a load.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In the above-described uninterruptible power supply device, the direct current voltage of the direct current line is maintained at a reference voltage by flowing an alternating current having a value corresponding to the deviation between the direct current voltage of the direct current line and the reference voltage from the power grid to the converter. In this method, in order to maintain the direct current voltage of the direct current line at the reference voltage even when the power consumption of the load fluctuates, the input power required from the power grid also fluctuates according to the fluctuation of the power consumption of the load.

[0005] In recent years, with the spread of AI (Artificial Intelligence) and IoT (Internet of Things) technologies, the demand for data centers supporting these technologies has been rapidly expanding. In data centers, the power consumption of the load may fluctuate periodically due to the synchronous operation of multiple servers, etc. If the above-mentioned uninterruptible power supply is applied to the power supply equipment of such a data center, the input power required for the power grid will also fluctuate periodically in accordance with the periodic fluctuations in the power consumption of the load. There are concerns that the increasing scale of data centers may lead to instability of the power grid.

[0006] This disclosure was made to solve the above-mentioned problems, and its purpose is to provide a power supply system and a power storage system that can stabilize the power grid against load fluctuations. [Means for solving the problem]

[0007] A power supply system according to one aspect of the present disclosure supplies power to a load. The power supply system comprises an uninterruptible power supply system connected between a power grid and a load, a power storage system connected in parallel with the uninterruptible power supply system to the load, and a current detector for detecting load current. The uninterruptible power supply system includes a converter, a first inverter, and a first control device. The converter converts alternating current power supplied from the power grid into direct current power and outputs it to a DC line. The first inverter converts direct current power supplied from the converter or a first energy storage device via a DC line into first alternating current power and supplies it to the load. The first control device controls the first inverter to supply a first alternating current to the load, which includes a feedback component whose value corresponds to the deviation between the AC output voltage of the first inverter and a reference AC voltage.

[0008] The power storage system includes a second inverter and a second control device. The second inverter is connected in parallel with the first inverter to the load and converts power bidirectionally between the second energy storage device and the load. The second control device controls the second inverter to supply a second AC current to the load, which includes a feedback component whose value corresponds to the deviation between the AC output voltage of the second inverter and a reference AC voltage, and a feedforward component whose value corresponds to the load current detected by a current detector. [Effects of the Invention]

[0009] According to this disclosure, it is possible to provide a power supply system and a power storage system that can stabilize the power grid in response to load fluctuations. [Brief explanation of the drawing]

[0010] [Figure 1] This is a circuit block diagram showing the configuration of a power supply system according to Embodiment 1. [Figure 2] This is a block diagram showing an example of the hardware configuration of a control device. [Figure 3] This is a block diagram showing the main components of the control device. [Figure 4] This block diagram shows the part of the control circuit related to the control of the inverter. [Figure 5] This is a block diagram showing the main components of the control device. [Figure 6] This block diagram shows the part of the control circuit related to the control of the inverter. [Figure 7] This is a circuit block diagram illustrating the operation of a power supply system when the load current is greater than the threshold current, assuming a healthy power grid. [Figure 8] This is a circuit block diagram illustrating the operation of a power supply system when the load current is below the threshold current, assuming a healthy power grid. [Figure 9] This figure shows an example of the temporal variation in the power consumption of a load and the AC input power supplied to the power system from the power grid. [Figure 10] This is a circuit block diagram showing the configuration of a power supply system according to Embodiment 2. [Modes for carrying out the invention]

[0011] Embodiments of this disclosure will be described in detail below with reference to the drawings. In the following, the same or corresponding parts in the drawings will be denoted by the same reference numerals, and their descriptions will not be repeated in principle.

[0012] [Embodiment 1] <Power System Configuration> Figure 1 is a circuit block diagram showing the configuration of a power supply system according to Embodiment 1. As shown in Figure 1, the power supply system 100 according to Embodiment 1 comprises an uninterruptible power supply system 10, a power storage system 20, and a current detector CD6. The uninterruptible power supply system 10 and the power storage system 20 are connected in parallel to each other to the load 14. In reality, the power supply system 100 receives three-phase AC power from the power grid 11 and supplies three-phase AC power to the load 14, but for the sake of simplicity in the drawing and explanation, only the circuit for one phase is shown in Figure 1.

[0013] (Configuration of the uninterruptible power supply system 10) The uninterruptible power supply system 10 is connected between the power grid 11 and the load 14. The uninterruptible power supply system 10 includes an input terminal T1, a DC terminal T2, and an output terminal T3. The input terminal T1 receives AC power at a predetermined frequency (e.g., commercial frequency) from the power grid 11.

[0014] The DC terminal T2 is connected to the battery 12. The battery 12 corresponds to one embodiment of the "first energy storage device" that stores DC power. A capacitor may be connected instead of the battery 12. The battery 12 is a secondary battery such as a lead-acid battery, nickel-metal hydride battery, or lithium-ion battery.

[0015] The output terminal T3 is connected to the load 14. The load 14 is driven by the AC power supplied from the power system 100. The load 14 includes, for example, electrical equipment (such as servers, storage, and air conditioning equipment) used in data sensors.

[0016] The uninterruptible power supply system 10 further includes a converter 1, a DC line 2, a capacitor 3, a bidirectional chopper 4, an inverter 5, switches S1 to S3, current detectors CD1 to CD3, an operation unit 6, and a control device 7.

[0017] The switch S1 is connected between the input terminal T1 and the AC node of the converter 1 and is controlled by the control device 7. When AC power is normally supplied from the power system 11 (when the power system 11 is healthy), the switch S1 is turned on, and AC power is supplied from the power system 11 to the converter 1 through the switch S1. When AC power is not normally supplied from the power system 11 (when the power system 11 is abnormal), the switch S1 is turned off, and the connection between the power system 11 and the converter 1 is interrupted.

[0018] The instantaneous value of the AC input voltage VI supplied from the power system 11 is detected by the control device 7. The control device 7 determines whether the power system 11 is healthy or abnormal based on the instantaneous value of the AC input voltage VI. The current detector CD1 detects the AC input current Ii flowing between the power system 11 and the converter 1 and gives a signal Iif indicating the detected value to the control device 7.

[0019] The converter 1 is controlled by the control device 7 and converts the AC power from the power system 11 into DC power and outputs it to the DC line 2 when the power system 11 is healthy. The converter 1 is a well-known one including a plurality of sets of semiconductor switching elements and diodes.

[0020] The capacitor 3 is connected to the DC line 2 and smoothes and stabilizes the DC voltage VD of the DC line 2. The instantaneous value of the DC voltage VD of the DC line 2 is detected by the control device 7.

[0021] When the power system 11 is functioning normally, the control device 7 controls the converter 1 so that the DC voltage VD of the DC line 2 becomes the reference DC voltage VDR. When the power system 11 malfunctions, the control device 7 stops the operation of the converter 1.

[0022] The DC line 2 is connected to the DC terminal T2 via the bidirectional chopper 4 and switch S2. Switch S2 is controlled by the control device 7. When the power supply system 100 is in use, switch S2 is turned on. When the battery 12 or the bidirectional chopper 4 is being maintained, switch S2 is turned off.

[0023] The instantaneous value of the terminal voltage (battery voltage) VB1 of the battery 12 is detected by the control device 7. The current detector CD2 detects the DC current (battery current) IB1 flowing between the battery 12 and the bidirectional chopper 4, and provides the control device 7 with a signal IB1f indicating the detected value.

[0024] The bidirectional chopper 4 is controlled by the control device 7 and exchanges DC power between the DC line 2 and the battery 12. The bidirectional chopper 4 is a well-known type that includes multiple sets of semiconductor switching elements and diodes, and a reactor.

[0025] When the power system 11 is functioning normally, the control device 7 basically controls the bidirectional chopper 4 so that the battery voltage VB1 becomes the reference DC voltage VB1R. When the power system 11 malfunctions, the control device 7 controls the bidirectional chopper 4 so that the DC voltage VD of the DC line 2 becomes the reference DC voltage VDR.

[0026] DC line 2 is connected to the DC node of inverter 5, and the AC node of inverter 5 is connected to output terminal T3 via switch S3. Switch S3 is controlled by control device 7. Switch S3 is turned on when using the uninterruptible power supply system 10. Switch S3 is turned off during maintenance of inverter 5.

[0027] The current detector CD3 detects the AC output current IO1 of the inverter 5 and provides the control device 7 with a signal IO1f indicating the detected value. The inverter 5 corresponds to one embodiment of the "first inverter," and the AC output current IO1 corresponds to one embodiment of the "first AC current." The instantaneous value of the AC output voltage VO1 applied to the load 14 from the uninterruptible power supply system 10 is detected by the control device 7.

[0028] The inverter 5 is controlled by the control device 7 and converts the DC power supplied from the converter 1 or bidirectional chopper 4 via the DC line 2 into AC power of a predetermined frequency (e.g., commercial frequency) and supplies it to the load 14. The inverter 5 is a well-known one that includes multiple sets of semiconductor switching elements and diodes.

[0029] When the power system 11 is functioning normally, the inverter 5 converts the DC power supplied from the converter 1 into AC power and supplies it to the load 14. When the power system 11 malfunctions, the inverter 5 converts the DC power supplied from the bidirectional chopper 4 into AC power and supplies it to the load 14. At this time, the control device 7 controls the inverter 5 so that the AC output voltage VO becomes the reference AC voltage VOR.

[0030] The control unit 6 includes multiple buttons, multiple switches, and a display. By operating the control unit 6, the user of the uninterruptible power supply system 10 can turn the power of the uninterruptible power supply system 10 on and off, and operate the uninterruptible power supply system 10 in automatic or manual mode. The control unit 6 outputs signals and information to the control device 7 indicating the actions taken by the user.

[0031] The control device 7 controls switches S1 to S3, converter 1, bidirectional chopper 4, and inverter 5 based on signals from the operation unit 6, AC input voltage VI, AC output voltage VO1, DC voltage VD, battery voltage VB1, AC input current Ii, battery current IB1, and AC output current IO1.

[0032] (Configuration of the power storage system 20) The power storage system 20 includes a DC terminal T4 and an AC terminal T5. The DC terminal T4 is connected to the battery 13. The battery 13 corresponds to one embodiment of a "second energy storage device" that stores DC power. A capacitor may be connected instead of the battery 13. The battery 13 is a secondary battery such as a lead-acid battery, nickel-metal hydride battery, or lithium-ion battery. The type and capacity of the secondary batteries of the battery 12 and the battery 13 may differ.

[0033] The AC terminal T5 is connected to node N1 between the output terminal T3 of the uninterruptible power supply system 10 and the load 14. The instantaneous value of the AC output voltage VO2 applied from the power storage system 20 to the load 14 is detected by the control device 9.

[0034] The power storage system 20 further includes switches S4 and S5, an inverter 8, and a control device 9. Switch S4 is connected between the DC terminal T4 and the DC node of the inverter 8 and is controlled by the control device 9. When the power storage system 20 is in use, switch S4 is turned on. Switch S4 is turned off during maintenance of the battery 13 or the inverter 8.

[0035] The instantaneous value of the terminal voltage (battery voltage) VB2 of the battery 13 is detected by the control device 9. The current detector CD4 detects the DC current (battery current) IB2 flowing between the battery 13 and the inverter 8, and provides the control device 9 with a signal IB2f indicating the detected value.

[0036] The AC node of inverter 8 is connected to AC terminal T5 via switch S5. That is, inverter 8 is connected in parallel with inverter 5 to load 14. Inverter 8 is a well-known type including multiple sets of semiconductor switching elements and diodes.

[0037] Switch S5 is controlled by the control device 9. Switch S5 is turned on when the power storage system 20 is in use. Switch S5 is turned off during maintenance of the inverter 8.

[0038] The current detector CD5 detects the AC output current IO2 of the inverter 8 and provides the control device 9 with a signal IO2f indicating the detected value. The inverter 8 corresponds to one embodiment of the "second inverter," and the AC output current IO2 corresponds to one embodiment of the "second AC current." The instantaneous value of the AC output voltage VO2 applied from the power storage system 20 to the load 14 is detected by the control device 9.

[0039] The inverter 8 is controlled by the control device 9 and converts the DC power supplied from the battery 13 into AC power of a predetermined frequency (e.g., commercial frequency) and supplies it to the load 14. At this time, the control device 9 controls the inverter 8 so that the AC output voltage VO2 becomes the reference AC voltage VOR. As will be described later, the inverter 8 operates in conjunction with the inverter 5 to supply AC power to the load 14. Therefore, the load current IL is equal to the sum of the AC output current IO1 of the inverter 5 and the AC output current IO2 of the inverter 8.

[0040] Furthermore, the inverter 8 converts the AC power supplied from node N1 via switch S5 into DC power and supplies it to the battery 13. At this time, the control device 9 controls the inverter 8 so that the battery voltage VB2 becomes the reference DC voltage VB2R. As will be described later, when the load current IL is less than or equal to the threshold current Ith, the inverter 8 supplies the battery 13 with the difference between the AC output current IO1 of the inverter 5 and the load current IL. The threshold current Ith is set based on the load current IL when the load 14 is under low load.

[0041] The current detector CD6 detects the load current IL flowing from the power supply system 100 to the load 14 and provides the control device 9 with a signal ILf indicating the detected value.

[0042] The control device 9 controls switches S4, S5 and inverter 8 based on the AC output voltage VO2, battery voltage VB2, battery current IB2, AC output current IO1, and load current IL, etc.

[0043] (Example hardware configuration of control devices 7 and 9) Figure 2 is a block diagram showing an example of the hardware configuration of control devices 7 and 9. Each of the control devices 7 and 9 can typically be configured by a microcomputer with a predetermined program pre-stored in it.

[0044] As shown in Figure 2, each of the control devices 7 and 9 is composed of a CPU (Central Processing Unit) 80, memory 82, and input / output (I / O) circuit 84. The CPU 80, memory 82, and I / O circuit 84 can exchange data with each other via a bus. A program is stored in a portion of the memory 82, and the CPU 80 can execute this program to realize various functions described later. The I / O circuit 84 exchanges signals and data between the control device and external devices.

[0045] Alternatively, unlike the example in Figure 2, at least a portion of each of the control devices 7 and 9 can be configured using circuits such as FPGAs (Field Programmable Gate Arrays) or ASICs (Application Specific Integrated Circuits). Furthermore, at least a portion of each of the control devices 7 and 9 can also be configured using analog circuits.

[0046] (Functional configuration of control device 7) Figure 3 is a block diagram showing the main components of the control device 7. As shown in Figure 3, the control device 7 is composed of voltage detectors 21-24, an anomaly detector 25, and a control circuit 26.

[0047] The voltage detector 21 detects the instantaneous value of the AC input voltage VI supplied from the power system 11 and outputs a signal VIf indicating the detected value to the control circuit 26.

[0048] The voltage detector 22 detects the instantaneous value of the AC output voltage VO1 applied to the load 14 and outputs a signal VO1f indicating the detected value to the control circuit 26.

[0049] The voltage detector 23 detects the instantaneous value of the DC voltage VD on the DC line 2 and outputs a signal VDf indicating the detected value to the control circuit 26.

[0050] The voltage detector 24 detects the instantaneous value of the terminal voltage VB1 of the battery 12 and outputs a signal VB1f indicating the detected value to the control circuit 26.

[0051] The anomaly detector 25 detects whether an anomaly has occurred in the power system 11 based on the output signal VIf from the voltage detector 21, and outputs an anomaly detection signal DET to the control circuit 26 indicating the detection result. If the power system 11 is healthy, the anomaly detection signal DET is set to the deactivation level "H". If an anomaly has occurred in the power system 11, the anomaly detection signal DET is set to the activation level "L".

[0052] For example, if the AC input voltage VI is within the normal range, the anomaly detector 25 determines that the power system 11 is healthy and sets the anomaly detection signal DET to the "H" level. Conversely, if the AC input voltage VI is outside the normal range, the anomaly detector 25 determines that an anomaly has occurred in the power system 11 and sets the anomaly detection signal DET to the "L" level.

[0053] The control circuit 26 controls the entire uninterruptible power supply system 10 based on the output signals VIf, VO1f, VDf, VB1f from voltage detectors 21 to 24, the output signals Iif, IB1f, IO1f from current detectors CD1 to CD3, the anomaly detection signal DET, and signals from the operation unit 6.

[0054] Specifically, when the power system 11 is healthy (DET=H), the control circuit 26 controls the converter 1 so that the DC voltage VD of the DC line 2 becomes the reference DC voltage VDR, and controls the bidirectional chopper 4 so that the battery voltage VB1 becomes the reference DC voltage VB1R. The control circuit 26 also controls the inverter 5 so that the AC output voltage VO1 becomes the reference AC voltage VOR.

[0055] If the power system 11 is abnormal (DET=L), the control circuit 26 turns off switch S1, stops the operation of converter 1, and controls the bidirectional chopper 4 so that the DC voltage VD of DC line 2 becomes the reference DC voltage VDR. The control circuit 26 also controls the inverter 5 so that the AC output voltage VO1 becomes the reference AC voltage VOR.

[0056] Figure 4 is a block diagram showing the portion of the control circuit 26 related to the control of the inverter 5. As shown in Figure 4, the control circuit 26 consists of subtractors 30 and 34, a voltage control unit 32, a current control unit 36, and a PWM (Pulse Width Modulation) circuit 38.

[0057] The subtractor 30 calculates the difference ΔVO1 = VOR - VO1 between the reference AC voltage VOR and the AC output voltage VO1 indicated by the output signal VO1f of the voltage detector 22.

[0058] The voltage control unit 32 generates a current command value IO1* to control the output current IO1 of the inverter 5 so that the deviation ΔVO1 is eliminated. The voltage control unit 32 generates the current command value IO1* by, for example, performing a proportional or proportional-integral operation on the deviation ΔVO1. The current command value IO1* corresponds to a feedback component of the value corresponding to the deviation ΔVO1.

[0059] The subtractor 34 calculates the difference ΔIO1 = IO1* - IO1 between the current command value IO1* from the voltage control unit 32 and the AC output current IO1 indicated by the output signal IO1f from the current detector CD3.

[0060] The current control unit 36 ​​generates a voltage command value VO1* such that the deviation ΔIO1 is eliminated. The current control unit 36 ​​generates the voltage command value VO1* by, for example, performing a proportional or proportional-integral operation on the deviation ΔIO1.

[0061] The PWM circuit 38 generates a PWM signal according to the voltage command value VO1* and controls the inverter 5 with that PWM signal.

[0062] (Functional configuration of control device 9) Figure 5 is a block diagram showing the main components of the control device 9. As shown in Figure 5, the control device 9 is configured to include voltage detectors 41 and 42 and a control circuit 43.

[0063] The voltage detector 41 detects the instantaneous value of the terminal voltage VB2 of the battery 13 and outputs a signal VB2f indicating the detected value to the control circuit 43.

[0064] The voltage detector 42 detects the instantaneous value of the AC output voltage VO2 applied to the load 14 and outputs a signal VO2f indicating the detected value to the control circuit 43.

[0065] The control circuit 43 controls the entire power storage system 20 based on the output signals VB2f, VO2f from the voltage detectors 41 and 42, and the output signals IB2f, IO2f, ILf from the current detectors CD4 to CD6.

[0066] Specifically, if the load current IL is greater than the threshold current Ith, the control circuit 43 controls the inverter 8 so that the AC output voltage VO2 becomes the reference AC voltage VOR. The threshold current Ith is set based on the load current IL when the load 14 is under low load. In this case, AC output current IO1 is supplied to the load 14 from the inverter 5, and AC output current IO2 is supplied to the load 14 from the inverter 8. Therefore, the load current IL is equal to the sum of AC output current IO1 and AC output current IO2.

[0067] If the load current IL is less than or equal to the threshold current Ith, the control circuit 43 controls the inverter 8 so that the battery voltage VB2 becomes the reference DC voltage VB2R. In this case, the difference between the AC output current IO1 of the inverter 5 and the load current IL is supplied to the inverter 8. This current is converted to DC current by the inverter 8 and supplied to the battery 13.

[0068] Figure 6 is a block diagram showing the portion of the control circuit 43 related to the control of the inverter 8. As shown in Figure 6, the control circuit 43 consists of subtractors 50, 58, 64, 68, voltage control units 52, 66, adder 56, current control units 60, 70, PWM circuits 62, 72, and selector 74.

[0069] The subtractor 50 calculates the difference ΔVO2 = VOR - VO2 between the reference AC voltage VOR and the AC output voltage VO2 indicated by the output signal VO2f of the voltage detector 42.

[0070] The voltage control unit 52 determines a feedback component Ifb to control the output current IO2 of the inverter 8 so that the deviation ΔVO2 is eliminated. The voltage control unit 52 determines a feedback component Ifb with a value corresponding to the deviation ΔVO2, for example, by performing a proportional or proportional-integral operation on the deviation ΔVO2.

[0071] The load current FF unit 54 generates a feedforward component Iff of the current command value IO2* based on the load current IL indicated by the output signal ILf of the current detector CD6. For example, the load current FF unit 54 generates the feedforward component Iff by multiplying the load current IL by a predetermined gain.

[0072] The adder 56 adds the feedback component Ifb from the voltage control unit 52 and the feedforward component Iff from the load current FF unit 54 to generate the current command value IO2*=Ifb+Iff.

[0073] The subtractor 58 calculates the difference ΔIO2 = IO2* - IO2 between the current command value IO2* and the AC output current IO2 indicated by the output signal IO2f of the current detector CD5.

[0074] The current control unit 60 generates a voltage command value VO2A* such that the deviation ΔIO2 is eliminated. The current control unit 60 generates the voltage command value VO2A* by, for example, performing a proportional or proportional-integral operation on the deviation ΔIO2. The PWM circuit 62 generates a PWM signal according to the voltage command value VO2A*.

[0075] The subtractor 64 calculates the difference ΔVB2 = VB2R - VB2 between the reference DC voltage VB2R and the battery voltage VB2 indicated by the output signal VB2f of the voltage detector 41.

[0076] The voltage control unit 66 generates a current command value IO2* to control the output current IO2 of the inverter 8 so that the deviation ΔVB2 is eliminated. The voltage control unit 66 generates the current command value IO2* by, for example, performing a proportional or proportional-integral operation on the deviation ΔVB2.

[0077] The subtractor 68 calculates the difference ΔIO2 = IO2* - IO2 between the current command value IO2* from the voltage control unit 66 and the AC output current IO2 indicated by the output signal IO2f from the current detector CD5.

[0078] The current control unit 70 generates a voltage command value VO2B* such that the deviation ΔIO2 is eliminated. The current control unit 70 generates the voltage command value VO2B* by, for example, performing a proportional or proportional-integral operation on the deviation ΔIO2. The PWM circuit 72 generates a PWM signal according to the voltage command value VO2B*.

[0079] The selector 74 connects either of the PWM circuits 62 or 72 to the inverter 8 based on the load current IL indicated by the output signal ILf of the current detector CD6.

[0080] Specifically, the selector 74 compares the magnitude of the load current IL and the threshold current Ith. If IL > Ith, the selector 74 connects the PWM circuit 62 and the inverter 8. The PWM circuit 62 controls the inverter 8 with a PWM signal generated according to the voltage command value VO2A*. That is, if IL > Ith, the control circuit 43 controls the inverter 8 so that the AC output voltage VO2 becomes the reference AC voltage VOR.

[0081] If IL ≤ Ith, the selector 74 connects the PWM circuit 72 and the inverter 8. The PWM circuit 72 controls the inverter 8 with a PWM signal generated according to the voltage command value VO2B*. That is, if IL ≤ Ith, the control circuit 43 controls the inverter 8 so that the battery voltage VB2 becomes the reference DC voltage VB2R.

[0082] Here, we will explain the operation of the inverter 8 by the control circuit 43 shown in Figure 6. When the load current IL is greater than the threshold current Ith, the selector 74 connects the PWM circuit 62 and the inverter 8. The voltage control unit 52 generates a feedback component Ifb with a value corresponding to the deviation ΔVO2=VOR-VO2 between the reference AC voltage VOR and the AC output voltage VO2. The load current FF unit 54 generates a feedforward component Iff with a value corresponding to the load current IL. The feedback component Ifb and the feedforward component Iff are added together to generate the current command value IO2*. The current control unit 60 generates a voltage command value VO2A* with a value corresponding to the deviation ΔIO2=IO2*-IO2 between the current command value IO2* and the AC output current IO2 of the inverter 8. The PWM circuit 62 controls the output voltage VO2 of the inverter 8 according to the voltage command value VO2A*.

[0083] By controlling it in this way, the inverter 8 can supply an AC output current IO2 to the load 14 that includes a feedback component Ifb and a feedforward component Iff whose value corresponds to the load current IL. By introducing this feedforward component Iff, the inverter 8 can be controlled at high speed in response to fluctuations in the load current IL.

[0084] In contrast to inverter 8, inverter 5 in the uninterruptible power supply system 10 supplies the load 14 with an AC output current IO1 that includes a feedback component corresponding to the deviation ΔVO1 = VOR - VO1 between the reference AC voltage VOR and the AC output voltage VO1, as shown in Figure 4. By increasing the response speed of inverter 8 to fluctuations in the load current IL, it becomes possible to control the feedback component in inverter 5 at a low speed.

[0085] By controlling the inverter 5 at a low speed in this manner, fluctuations in the DC voltage VD of the DC line 2 are suppressed when the load current IL changes suddenly. As a result, fluctuations in the AC input current Ii that flows from the power system 11 to the converter 1 in order to maintain the DC voltage VD at the reference DC voltage VDR are also suppressed. Consequently, fluctuations in the power required from the uninterruptible power supply system 10 to the power system 11 in response to fluctuations in the load current IL are suppressed, making it possible to stabilize the power system 11.

[0086] Figure 7 is a circuit block diagram illustrating the operation of the power supply system 100 when the load current IL is greater than the threshold current Ith, assuming the power system 11 is healthy. In Figure 7, for the sake of simplicity of the drawing and explanation, terminals T1 to T5, current detectors CD1 to CD6, the operating unit 6, and control devices 7 and 9 are omitted from the illustration. In Figure 7, arrows indicate the power supply path.

[0087] As shown in Figure 7, when the power grid 11 is healthy, in the uninterruptible power supply system 10, switch S1 is turned on, the AC power supplied from the power grid 11 is converted to DC power by converter 1, and this DC power is stored in battery 12 by bidirectional chopper 4 and also supplied to inverter 5.

[0088] The inverter 5 converts the DC power from the converter 1 into AC power and supplies it to the load 14. At this time, the inverter 5 supplies the load 14 with an AC output current IO1 that includes a feedback component whose value corresponds to the deviation ΔVO1 between the reference AC voltage VOR and the AC output voltage VO1.

[0089] In the power storage system 20, the inverter 8 converts DC power from the battery 13 into AC power and supplies it to the load 14. At this time, the inverter 8 supplies the load 14 with an AC output current IO2 which includes a feedback component whose value corresponds to the deviation ΔVO2 between the reference AC voltage VOR and the AC output voltage VO2, and a feedforward component whose value corresponds to the load current IL.

[0090] Here, we assume that the power that each of the converter 1, bidirectional chopper 4, and inverter 5 in the uninterruptible power supply system 10 can supply is 100%, and that the power consumption of the load 14 fluctuates up to 150%. Figure 7 shows the case where the power consumption of the load 14 increases to 150%. In this case, 100% of the power is supplied from the power grid 11 to the inverter 5 via the converter 1, and 100% of the power is supplied from the inverter 5 to the load 14. However, we assume that the battery 12 is already fully charged and that the current flowing to the battery 12 is sufficiently small.

[0091] Furthermore, 50% of the excess power is supplied from the battery 13 to the inverter 8, and 50% of the power is supplied from the inverter 8 to the load 14. Since the inverter 8 is controlled at high speed in response to load fluctuations, fluctuations in the input power required for the power system 11 are suppressed. Therefore, it is possible to stabilize the power system 11 while responding to load fluctuations.

[0092] Returning to Figure 6, when the load current IL is less than or equal to the threshold current Ith, the selector 74 couples the PWM circuit 72 and the inverter 8.

[0093] The voltage control unit 66 generates a current command value IO2* whose value corresponds to the deviation ΔVB2 = VB2R - VB2 between the reference DC voltage VB2R and the battery voltage VB2. The current control unit 70 generates a voltage command value VO2B* whose value corresponds to the deviation ΔIO2 = IO2* - IO2 between the current command value IO2* and the AC output current IO2 of the inverter 8. The PWM circuit 72 controls the output voltage VO2 of the inverter 8 according to the voltage command value VO2B*.

[0094] Figure 8 is a circuit block diagram illustrating the operation of the power supply system 100 when the load current IL is less than or equal to the threshold current Ith, assuming the power system 11 is healthy, and is shown in comparison to Figure 7.

[0095] In this case as well, similar to Figure 7, in the uninterruptible power supply system 10, when switch S1 is turned on, AC power supplied from the power grid 11 is converted to DC power by converter 1, and this DC power is stored in battery 12 by bidirectional chopper 4, and is also converted to AC power by inverter 5 and supplied to load 14.

[0096] In the power storage system 20, the inverter 8 is supplied with a current equal to the difference between the AC output current IO1 of the inverter 5 and the load current IL. The inverter 8 converts this current into a DC current and supplies it to the battery 13. Figure 8 shows the case where the power consumption of the load 14 is 50%. In this case, 100% of the power is supplied from the power grid 11 to the inverter 5 via the converter 1, and 50% of the power is supplied from the inverter 5 to the load 14. However, it is assumed that the battery 12 is already fully charged and that the current flowing to the battery 12 is sufficiently small.

[0097] Furthermore, 50% of the surplus power is stored in the battery 13 via the inverter 8. In this way, when the load current IL is less than or equal to the threshold current Ith, the surplus power can be used to charge the battery 13.

[0098] <Effects and Effects> Next, the operation and effects of the power supply system 100 according to Embodiment 1 will be described.

[0099] FIG. 9 is a diagram showing an example of the time variation of the power consumption of the load 14 and the AC input power supplied from the power grid 11 to the uninterruptible power supply system 10. In FIG. 9, the power consumption of the load 14 is shown as a load factor (%). A load factor of 100% corresponds to the rated load of the power supply system 100. The power that each of the converter 1, the bidirectional chopper 4, and the inverter 5 in the uninterruptible power supply system 10 can supply is set to 100%.

[0100] In the example of FIG. 9, the power consumption of the load 14 periodically varies within a range of A% or more and C% or less. However, A% < 100% < C%. The variation period of the power consumption has a length of about several tens of milliseconds to several seconds. In one variation period, there is a period during which the power consumption exceeds 100%. During this period, the power supply system 100 temporarily becomes overloaded.

[0101] In Embodiment 1, when the load current IL is greater than the threshold current Ith, as shown in FIG. 7, power is supplied from the power grid 11 to the converter 1, and power is supplied from the inverter 5 to the load 14. Also, power is supplied from the battery 13 to the inverter 8, and power is supplied from the inverter 8 to the load 14.

[0102] At this time, the control device 9 controls the inverter 8 at high speed in response to the variation in the power consumption of the load 14. On the other hand, the control device 7 controls the inverter 5 at low speed. Therefore, as shown in FIG. 9, as the power consumption of the load 14 varies, the ratio of the output power of the inverter 8 in the power consumption of the load 14 increases. In contrast, the ratio of the output power of the inverter 5 in the power consumption of the load 14 decreases. As a result, during the period when the power consumption of the load 14 exceeds 100%, the AC input power from the power grid 11 is suppressed to 100%.

[0103] Furthermore, in Embodiment 1, when the load current IL is less than or equal to the threshold current Ith, power is supplied from the power system 11 to the converter 1, and power is supplied from the inverter 5 to the load 14, as shown in Figure 8. In addition, any surplus power supplied from the inverter 5 to the load 14 is stored in the battery 13 via the inverter 8.

[0104] In this way, during periods when the power consumption of load 14 is low, the battery 13 is charged using a portion of the output power of inverter 5, so that the AC input power from power grid 11 during that period is kept at B%, which is higher than the minimum power consumption A% of load 14.

[0105] In other words, in response to the periodic fluctuations in the power consumption of the load 14, the AC input power from the power system 11 fluctuates periodically within the range of B% to 100%. The range of fluctuation in the AC input power from the power system 11 is smaller than the range of fluctuation in the power consumption of the load 14. Therefore, according to Embodiment 1, it is possible to stabilize the power system 11 while responding to the fluctuations in the power consumption of the load 14.

[0106] [Embodiment 2] Figure 10 is a circuit block diagram showing the configuration of the power supply system according to Embodiment 2. As shown in Figure 10, the power supply system 110 according to Embodiment 2 differs from the power supply system 100 shown in Figure 1 in that the DC terminal T4 of the power storage system 20 is connected to an electric double layer capacitor (EDLC) 15 instead of a battery 13. The configuration and operation of the power supply system 110 according to Embodiment 2 are the same as those of the power supply system 100 according to Embodiment 1, so a description is omitted.

[0107] In Embodiment 2, the DC terminal T2 of the uninterruptible power supply system 10 is connected to the battery 12, and the DC terminal T4 of the power storage system 20 is connected to the EDLC 15. The battery 12 corresponds to one embodiment of the "first energy storage device," and the EDLC 15 corresponds to one embodiment of the "second energy storage device."

[0108] The energy stored in the first energy storage device is used to supply power to the load 14 in the event of a malfunction in the power system 11. In the event of a malfunction in the power system 11, a large amount of energy is required to stably compensate for the operation of the load 14 over a predetermined blackout compensation period. The blackout compensation period is the time during which power can be continuously supplied from the power system 110 to the load 14 during a blackout. For this reason, it is preferable to use an energy storage device with a high energy density (amount of energy that can be stored per unit weight or volume) as the first energy storage device. Battery 12 is suitable as the first energy storage device.

[0109] On the other hand, as shown in Figure 7, the energy stored in the second energy storage device is used to compensate for fluctuations in the power consumption of the load 14. For this reason, it is preferable to use an energy storage device with a high power density (the amount of power that can be instantaneously extracted per unit weight or volume) for the second energy storage device.

[0110] The EDLC 15 has a lower energy density than the battery 12, but a higher power density. Furthermore, it exhibits less degradation due to repeated high-current charging and discharging compared to the battery 12. When the power consumption of the load 14 changes rapidly, the inverter 8 needs to be controlled quickly in response to fluctuations in the load current IL, requiring instantaneous high-current discharge from the second energy storage device. Even when the power consumption of the load 14 fluctuates periodically, minimal degradation due to repeated charging and discharging is required. Therefore, the EDLC 15 is suitable as the second energy storage device.

[0111] Furthermore, the first energy storage device is not particularly limited as long as it has a higher energy density than the second energy storage device. Similarly, the second energy storage device is not particularly limited as long as it has a higher power density than the first energy storage device.

[0112] By having such a configuration, the same effects and advantages as in Embodiment 1 can be obtained in Embodiment 2 as well.

[0113] <Other configuration examples> In the embodiments 1 and 2 described above, a configuration was described in which the second energy storage device, the battery 13 or EDLC 15, is attached externally to the power storage system 20. However, the battery 13 or EDLC 15 may also be built into the power storage system 20.

[0114] Furthermore, the power storage system 20 according to this embodiment may be retrofitted to an existing uninterruptible power supply system. By connecting the power storage system 20 in parallel with the existing uninterruptible power supply system to the load, it becomes possible to stabilize the power grid that supplies power to the uninterruptible power supply system.

[0115] The embodiments disclosed herein should be considered in all respects to be illustrative and not restrictive. The scope of this disclosure is indicated by the claims and not by the foregoing description, and all modifications within the meaning and scope of the claims are intended to be included. [Explanation of symbols]

[0116] 1 Converter, 2 DC line, 3 Capacitor, 4 Bidirectional chopper, 5,8 Inverter, 6 Control unit, 10 Uninterruptible power supply system, 11 Power system, 12,13 Battery, 14 Load, 15 EDLC, 20 Power storage system, 21~24,41,42 Voltage detector, 25 Anomaly detector, 26,43 Control circuit, 30,34,50,58,64,68 Subtractor, 32,52,66 Voltage control unit, 36,60,70 Current control unit, 38,62,72 PWM circuit, 54 Load current FF unit, 56 Adder, 74 Selector, 80 CPU, 82 Memory, 84 I / O circuit, 100,110 Power supply system, CD1~CD6 Current detector, S1~S5 Switch, T1 Input terminal, T2,T4 DC terminal, T3 Output terminal, T5 AC terminal.

Claims

1. A power supply system that supplies power to a load, An uninterruptible power supply system connected between the power grid and the load, A power storage system connected in parallel with the uninterruptible power supply system to the aforementioned load, The system includes a current detector that detects the load current flowing through the load, The aforementioned uninterruptible power supply system is A converter that converts AC power supplied from the aforementioned power system into DC power and outputs it to a DC line, A first inverter that converts DC power supplied from the converter or the first energy storage device via the DC line into first AC power and supplies it to the load, The system includes a first control device that controls the first inverter to supply a first AC current to the load, which includes a feedback component whose value corresponds to the deviation between the AC output voltage of the first inverter and a reference AC voltage. The aforementioned power storage system is A second inverter is connected between the node between the first inverter and the load and the second energy storage device, and converts power bidirectionally between the node and the second energy storage device. A power supply system including a second control device that controls the second inverter to supply a second AC current to the load, the second AC current comprising a feedback component whose value corresponds to the deviation between the AC output voltage of the second inverter and the reference AC voltage, and a feedforward component whose value corresponds to the load current detected by the current detector.

2. The power supply system according to claim 1, wherein if the load current is greater than the threshold current, the second inverter supplies the load with a current equal to the difference between the load current and the first AC current by discharge from the second energy storage device.

3. The power supply system according to claim 2, wherein if the load current is less than the threshold current, the second inverter supplies the second energy storage device with a current equal to the difference between the first AC current and the load current.

4. The power supply system according to any one of claims 1 to 3, wherein, when the power consumption of the load fluctuates periodically, the range of fluctuation of the AC input power supplied from the power system to the uninterruptible power supply system is smaller than the range of fluctuation of the power consumption of the load.

5. The power supply system according to any one of claims 1 to 3, wherein the second energy storage device has a higher power density than the first energy storage device.

6. The first energy storage device is a secondary battery, The power supply system according to claim 5, wherein the second energy storage device is an electric double-layer capacitor.

7. A power storage system connected in parallel with an uninterruptible power supply system to a load, A current detector for detecting the load current flowing through the aforementioned load, An inverter is connected between the node and the energy storage device between the uninterruptible power supply system and the load, and converts power bidirectionally between the node and the energy storage device. A power storage system comprising a control device that controls the inverter to supply an AC current to the load, which includes a feedback component whose value corresponds to the deviation between the AC output voltage of the inverter and a reference AC voltage, and a feedforward component whose value corresponds to the load current detected by the current detector.

8. The power storage system according to claim 7, wherein if the load current is greater than the threshold current, the inverter supplies to the load a current equal to the difference between the load current and the AC output current of the uninterruptible power supply system by discharge from the energy storage device.

9. The power storage system according to claim 8, wherein, when the load current is smaller than the threshold current, the inverter supplies to the energy storage device a current equal to the difference between the AC output current of the uninterruptible power supply system and the load current.

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