Power conversion system

Abstract

This power conversion system can respond to sharp power fluctuations in solar power generation equipment and simultaneously control power between solar power generation equipment, storage batteries, and the AC grid system while minimizing power generation suppression and power conversion losses in solar power generation equipment. [Solution] A power conversion system having one AC port and two DC ports, wherein a storage battery is connected to the first DC port, which is one of the DC ports, and a photovoltaic power generation device is connected to the second DC port, which is the other of the DC ports, and the output voltage of the photovoltaic power generation device is maximized by adjusting the voltage of the second DC port, and charging and discharging of the storage battery is controlled by adjusting the voltage of the first DC port according to the state of charge (SOC) of the storage battery, thereby controlling the AC power input and output at the AC port.

Description

Technical Field

[0001] The present invention relates to a power conversion system connected to a photovoltaic power generation apparatus.

Background Art

[0002] Disclosed in Patent Document 1 is a power conversion circuit that takes an input from a photovoltaic power generation apparatus and outputs power to a grid, wherein the power conversion circuit controls the output voltage of the photovoltaic power generation apparatus to maximize the power output from photovoltaic power generation. In this circuit, the variation amount of voltage control is increased as the output power difference is larger, and the variation amount of voltage control is decreased as the output power difference is smaller, thereby improving the tracking performance with respect to the generated power of the photovoltaic power generation apparatus.

Prior Art Literature

Patent Literature

[0003]

Patent Literature 1

Summary of the Invention

Problem to be Solved by the Invention

[0004] However, in the above-mentioned conventional technology, no storage battery is provided in the system, so when there is surplus grid power, the grid power cannot be effectively utilized, and control that suppresses the output of the photovoltaic power generation apparatus is required. Therefore, it is desired to implement a power conversion circuit that can maintain high power conversion efficiency and also maintain high utilization rate of the photovoltaic power generation apparatus.

Means for Solving the Problem

[0005] One aspect of the present invention is a power conversion system having one AC port and two DC ports, wherein a storage battery is connected to a first DC port, which is one of the DC ports, and a photovoltaic power generation device is connected to a second DC port, which is the other of the DC ports, and the power conversion system is characterized by controlling the output voltage of the photovoltaic power generation device to maximize the output voltage of the photovoltaic power generation device by adjusting the voltage of the second DC port, and controlling the charging and discharging of the storage battery by adjusting the voltage of the first DC port according to the state of charge (SOC) of the storage battery, thereby controlling the AC power that is input and output to the AC port.

[0006] In this case, it is preferable that the AC port is connected to at least one of the grid power system and a load.

[0007] Furthermore, it is preferable to control the voltage of the second DC port using the storage battery connected to the first DC port.

[0008] Furthermore, a first switching arm is formed by connecting a first switching element and a second switching element in series, a second switching arm is formed by connecting a third switching element and a fourth switching element in series, and a third switching arm is formed by connecting a fifth switching element and a sixth switching element in series, and these are connected in parallel, with the upper connection points of the first switching arm, the second switching arm and the third switching arm serving as the positive terminals of the second DC port, and the lower connection points of the first switching arm, the second switching arm and the third switching arm serving as the negative terminals of the second DC port, and a first transformer winding is connected between the connection point of the first switching element and the second switching element and the connection point of the third switching element and the fourth switching element It is preferable to provide a three-phase power conversion circuit in which a second transformer winding is connected between the connection point of the fifth switching element and the connection point of the sixth switching element, a third transformer winding is connected between the connection point of the fifth switching element and the sixth switching element and the connection point of the first switching element and the second switching element, one end of the first inductor is connected to a point in the middle of the conductor constituting the first transformer winding, one end of the second inductor is connected to a point in the middle of the conductor constituting the second transformer winding, one end of the third inductor is connected to a point in the middle of the conductor constituting the third transformer winding, the other ends of the first inductor, the second inductor and the third inductor are connected in common to form the positive terminal of the first DC port, and the connection points on the lower sides of the second switching arm and the third switching arm are the negative terminals of the first DC port. [Effects of the Invention]

[0009] According to the present invention, it is possible to provide a power conversion system that can respond to sharp power fluctuations in a photovoltaic power generation system and can simultaneously control power between a photovoltaic power generation system, a storage battery, and an AC grid system while minimizing power generation suppression and power conversion losses in the photovoltaic power generation system. [Brief explanation of the drawing]

[0010] [Figure 1] This figure shows the basic configuration of a power conversion system according to an embodiment of the present invention. [Figure 2] This figure shows an example of a power conversion circuit applicable to a power conversion system in an embodiment of the present invention. [Figure 3] This figure shows an example of a power conversion circuit applicable to a power conversion system in an embodiment of the present invention. [Figure 4] This figure shows the control block of a power conversion system according to an embodiment of the present invention. [Figure 5] This is a flowchart showing a control method for a power conversion system in an embodiment of the present invention. [Figure 6] This figure shows the results of a simulation of the control of a power conversion system in an embodiment of the present invention. [Figure 7] This figure shows the results of a simulation of the control of a power conversion system in an embodiment of the present invention. [Figure 8] This figure shows the results of a simulation of the control of a power conversion system in an embodiment of the present invention. [Figure 9] This figure shows the results of a simulation of the control of a power conversion system in an embodiment of the present invention. [Figure 10] This figure shows another example of a control block for a power conversion system in an embodiment of the present invention. [Figure 11] This flowchart shows another example of a control method for a power conversion system in an embodiment of the present invention. [Figure 12] This figure shows the results of a simulation of the control of a power conversion system in an embodiment of the present invention. [Figure 13] This figure shows the results of a simulation of the control of a power conversion system in an embodiment of the present invention. [Figure 14] This figure shows the results of a simulation of the control of a power conversion system in an embodiment of the present invention. [Figure 15]It is a diagram showing results of simulating control of the power conversion system according to an embodiment of the present invention. MODE FOR CARRYING OUT THE INVENTION

[0011] CONFIGURATION OF POWER CONVERSION SYSTEM As shown in FIG. 1, a power conversion system 100 according to an embodiment of the present invention includes a power conversion circuit 102 and a control device 104.

[0012] The power conversion circuit 102 includes one alternating-current port and two direct-current ports. A grid power system 110 and / or a load 118 is connected to the alternating-current port of the power conversion circuit 102. The grid power system refers to a power supply network comprehensively including all of power generation, power transmission, voltage transformation and power distribution. A storage battery 112 is connected to a first direct-current port, which is one of the two direct-current ports. A photovoltaic power generation device 114 and a generator 116 are connected in parallel to a second direct-current port, which is the other of the two direct-current ports.

[0013] In the following description, the second direct-current port may be referred to as a DC grid, the voltage of the second direct-current port may be referred to as a DC grid voltage, and the current thereof may be referred to as a DC grid current. Further, the alternating-current port may be referred to as an AC grid, the voltage of the alternating-current port may be referred to as an AC voltage, and the current thereof may be referred to as an AC current.

[0014] The control device 104 is connected to the power conversion circuit 102, and controls power conversion in the power conversion circuit 102 by controlling switching elements included in the power conversion circuit 102. In the power conversion system 100, by controlling the power conversion circuit 102 with the single control device 104, power distribution control can be performed at high speed. Therefore, the power conversion system can cope with steep power fluctuations (several tens of microseconds) in the photovoltaic power generation device 114, and can perform power distribution with the storage battery 112 and the grid power system 110 while controlling the power of the photovoltaic power generation device 114 to the maximum.

[0015] The solar power generation device 114 has the characteristic that the amount of power that can be extracted varies depending on the voltage. Therefore, in order to extract the maximum amount of power generated by the solar power generation device 114, it is necessary to control the voltage of the solar power generation device 114. When the control device 104 controls the voltage of the solar power generation device 114, it monitors the power supplied from the solar power generation device 114 and determines the voltage value so that the power is maximized. At the same time, the distribution destination of the power supplied from the solar power generation device 114 is determined by the power of the grid power system 110 and the load 118, and the SOC (state of charge) of the storage battery 112. If the SOC of the storage battery 112 is within the operating range (below the upper limit of the SOC and above the lower limit of the SOC), the power from the solar power generation device 114 is supplied to the load 118, and if the power from the solar power generation device 114 is greater than the power required by the load 118, the storage battery 112 is charged. Furthermore, if the power of the solar power generation system 114 decreases, and the State of Charge (SOC) of the storage battery 112 at that time is above the lower limit, power is supplied from the storage battery 112 to the load 118. If the power of the solar power generation system 114 decreases and the SOC of the storage battery 112 at that time falls below the lower limit, power is supplied to the load 118 from the generator 116 or the grid power system 110.

[0016] The power conversion circuit 102 can be configured, for example, as shown in Figure 2. The power conversion circuit 102 can be configured to include power converters (capacitor-split type power converters) 200a to 200c, transformer couplers 202a to 202c, a three-phase power converter 204, and inverter circuits 206a to 206c (see Figure 13 of Japanese Patent Application Publication No. 2023-44947).

[0017] The power converter 200a includes a circuit in which a U-phase switching arm, formed by connecting switching elements S1 and S2 in series, and a V-phase switching arm, formed by connecting switching elements S3 and S4 in series, are connected in parallel. It also includes a capacitor arm, formed by connecting an upper capacitor and a lower capacitor in series. The capacitor arm is connected in parallel with the U-phase switching arm and the V-phase switching arm. The upper positive terminal and lower negative terminal of the U-phase switching arm, the V-phase switching arm, and the capacitor arm are each connected to the inverter circuit 206a.

[0018] The secondary winding of the transformer coupler 202a is connected between the connection point of switching elements S1 and S2 and the connection point of switching elements S3 and S4. The secondary winding, together with the primary winding connected to the three-phase power converter 204, constitutes a transformer. A reactor La is connected between a tap located midway through the conductors constituting the secondary winding and the connection point between the upper and lower capacitors on the capacitor arm. The tap may also be a center tap located midway through the conductors constituting the secondary winding.

[0019] Power converters 200b and 200c have the same configuration as power converter 200a. Inverter circuits 206a to 206c, connected to power converters 200a to 200c respectively, convert the output of power converters 200a to 200c into three-phase AC, which is then output from AC ports ACu, ACv, and ACw, respectively.

[0020] The three-phase power converter 204 includes a circuit in which switching arm A, which has switching elements Sap and San connected in series, switching arm B, which has switching elements Sbp and Sbn connected in series, and switching arm C, which has switching elements SCP and Scin connected in series, are connected in parallel. Capacitors are connected in parallel to switching arm A, switching arm B, and switching arm C, and the positive and negative terminals of the capacitors are the positive terminal DC2A and negative terminal DC2B of the second DC port, respectively.

[0021] The primary winding of transformer coupler 202a is connected between the connection point between switching element Sap and switching element San, and between the connection point between switching element Sbp and switching element Sbn. Similarly, the primary winding of transformer coupler 202b is connected between the connection point between switching element Sbp and switching element Sbn, and between the connection point between switching element Scp and switching element Scin. In addition, the primary winding of transformer coupler 202c is connected between the connection point between switching element Scp and switching element Scin, and between the connection point between switching element Sap and switching element San.

[0022] One end of reactor LLa is connected to the tap of the primary winding of transformer coupler 202a. Similarly, one end of reactor LLb is connected to the tap of the primary winding of transformer coupler 202b, and one end of reactor LLC is connected to the tap of the primary winding of transformer coupler 202c. The other ends of reactors LLa, LLb, and LLC are commonly connected to the positive terminal DC1A of the first DC port. The parallel connection points on the lower side of switching arms A to C are connected to the negative terminal DC1B of the first DC port and the negative terminal DC2B of the second DC port. A capacitor is connected between the positive terminal DC1A and the negative terminal DC1B of the first DC port.

[0023] In such a power conversion circuit 102, the control device 104 controls the switching elements in each switching arm of the power converters (capacitor-split type power converters) 200a to 200c, the three-phase power converter 204, and the inverter circuits 206a to 206c, thereby enabling mutual power conversion between the first DC port of positive terminal DC1A and negative terminal DC1B, the second DC port of positive terminal DC2A and negative terminal DC2B, and the three-phase AC ports of U-pole terminal ACu, V-pole terminal ACv, and W-pole terminal ACw.

[0024] The power conversion circuit 102 can also be configured as shown in Figure 3, for example. The power conversion circuit 102 can include a power converter (capacitor-splitting type power converter) 210, a transformer coupler 212, a three-phase power converter 214, and an inverter circuit 216 (see Figure 12 of Japanese Patent Application Publication No. 2024-20918).

[0025] The power converter 210 includes a circuit in which a U-phase switching arm, formed by connecting switching elements S1 and S2 in series, a V-phase switching arm, formed by connecting switching elements S3 and S4 in series, and a W-phase switching arm, formed by connecting switching elements S5 and S6 in series, are connected in parallel. It also includes a capacitor arm, formed by connecting an upper capacitor and a lower capacitor in series. The capacitor arm is connected in parallel with the U-phase switching arm, the V-phase switching arm, and the W-phase switching arm. The upper positive terminal and lower negative terminal of the U-phase switching arm, the V-phase switching arm, the W-phase switching arm, and the capacitor arm are connected to the inverter circuit 216.

[0026] The UV phase primary winding of the transformer coupler 212 is connected between the connection point between switching element S1 and switching element S2, and between the connection point between switching element S3 and switching element S4. Similarly, the VW phase primary winding of the transformer coupler 212 is connected between the connection point between switching element S3 and switching element S4, and between the connection point between switching element S5 and switching element S6. In addition, the WU phase primary winding of the transformer coupler 212 is connected between the connection point between switching element S5 and switching element S6, and between the connection point between switching element S1 and switching element S2.

[0027] Furthermore, one end of reactor La is connected to a tap located midway through the conductor constituting the UV phase primary winding. Similarly, one end of reactor Lb is connected to a tap located midway through the conductor constituting the VW phase primary winding, and one end of reactor Lc is connected to a tap located midway through the conductor constituting the WU phase primary winding. The other ends of reactors La, Lb, and Lc are commonly connected to the connection point between the upper and lower capacitors on the capacitor arm.

[0028] The inverter circuit 216 connected to the power converter 210 converts the output of the power converter 210 into three-phase AC, which is then output from the AC ports ACu, ACv, and ACw, respectively.

[0029] The three-phase power converter 214 includes a circuit in which switching arm A, which has switching elements Sap and San connected in series, switching arm B, which has switching elements Sbp and Sbn connected in series, and switching arm C, which has switching elements SCP and Scin connected in series, are connected in parallel. Capacitors are connected in parallel to switching arm A, switching arm B, and switching arm C, and the positive and negative terminals of the capacitors are the positive terminal DC2A and negative terminal DC2B of the second DC port, respectively.

[0030] The UV phase secondary winding of the transformer coupler 212 is connected between the connection point between switching element Sap and switching element San, and between the connection point between switching element Sbp and switching element Sbn. Similarly, the VW phase secondary winding of the transformer coupler 212 is connected between the connection point between switching element Sbp and switching element Sbn, and between the connection point between switching element Scp and switching element Scin. In addition, the WU phase secondary winding of the transformer coupler 212 is connected between the connection point between switching element Scp and switching element Scin, and between the connection point between switching element Sap and switching element San.

[0031] One end of reactor LLa is connected to the tap of the UV phase secondary winding of transformer coupler 212. Similarly, one end of reactor LLb is connected to the tap of the VW phase secondary winding of transformer coupler 212, and one end of reactor LLC is connected to the tap of the WU phase secondary winding of transformer coupler 212. The other ends of reactors LLa, LLb, and LLC are commonly connected to the positive terminal DC1A of the first DC port. The parallel connection points on the lower side of switching arms A to C are connected to the negative terminal DC1B of the first DC port and the negative terminal DC2B of the second DC port. A capacitor is connected between the positive terminal DC1A and the negative terminal DC1B of the first DC port.

[0032] In such a power conversion circuit 102, the control device 104 controls the switching elements in the switching arms of the power converter (capacitor-split type power converter) 210, the three-phase power converter 214, and the inverter circuit 216, thereby enabling mutual power conversion between the first DC port (positive terminal DC1A and negative terminal DC1B), the second DC port (positive terminal DC2A and negative terminal DC2B), and the three-phase AC ports (U-pole terminal ACu, V-pole terminal ACv, and W-pole terminal ACw).

[0033] [Control of power conversion systems] Figure 4 shows a control block diagram of the power conversion system 100. Figure 5 shows a control flowchart of the power conversion system 100. The sequence in the control block diagram corresponds to the sequence in the control flowchart.

[0034] The control device 104 is composed of a voltage detection unit 300, a current detection unit 302, an SOC receiving unit 304, a power calculation unit 306, a PV maximum power tracking unit 308, a DC side voltage / current command generation unit 310, and a load voltage command generation unit 312.

[0035] The voltage detection unit 300 detects the DC grid voltage of the power conversion circuit 102, the battery voltage 112, and the AC voltage, and outputs them to the power calculation unit 306, the PV maximum power tracking unit 308, and the load voltage command generation unit 312. The current detection unit 302 detects the current of the photovoltaic power generation device 114, the battery current 112, and the AC current, and outputs them to the power calculation unit 306 and the load voltage command generation unit 312. The SOC receiving unit 304 calculates the SOC of the battery 112 and outputs it to the DC-side voltage / current command generation unit 310. The power calculation unit 306 receives the outputs of the voltage detection unit 300 and the current detection unit 302, calculates the required power of the battery 112, the photovoltaic power generation device 114, and the load 118, and outputs them to the PV maximum power tracking unit 308 and the DC-side voltage / current command generation unit 310.

[0036] The PV maximum power tracking unit 308 performs the processing shown in sequence 2 below. The DC side voltage / current command generation unit 310 performs the processing shown in sequence 1 and sequence 3 below. The load voltage command generation unit 312 performs the processing shown in sequence 4 below.

[0037] Sequence 1: Determine whether the State of Charge (SOC) of the battery 112 is normal (step S10). If it is normal, proceed to step S24 of Sequence 2. If the SOC of the battery 112 is not normal, determine whether the SOC of the battery 112 is higher than a predetermined upper limit (step S12). If the SOC is higher than the upper limit, proceed to step S16. If the SOC is below the upper limit, proceed to step S14. If the SOC of the battery 112 is higher than the upper limit, determine whether the output power of the solar power generation device 114 is greater than the power required by the load 118 (step S16). If it is greater, control is performed to increase the DC grid voltage, i.e., the voltage of the solar power generation device 114, to suppress the output of the solar power generation device 114. After that, proceed to step S34 of Sequence 3. If the output power of the solar power generation device 114 is less than the power required by the load 118, proceed to step S24 of Sequence 2.

[0038] If the State of Charge (SOC) of the battery 112 is below the upper limit, it is determined whether the SOC of the battery 112 is below a predetermined lower limit (step S14). If the SOC is below the lower limit, the process proceeds to step S18. If the SOC of the battery 112 is below the lower limit, it is determined whether the power demanded by the load 118 is greater than the output power of the solar power generation device 114 (step S18). If it is greater, control is performed to prevent discharge from the battery 112. At this time, power is supplied from the generator 116 to the load 118. After that, the process proceeds to step S44 of sequence 4. If the power demanded by the load 118 is less than the output power of the solar power generation device 114, the process proceeds to step S24 of sequence 2.

[0039] Sequence 2: The current value of the output power of the solar power generation device 114 is compared with the previous value (a value calculated from the previous measurement) (step S24). If the output power of the solar power generation device 114 has increased, the process proceeds to step S28; otherwise, the process proceeds to step S26. If the output power of the solar power generation device 114 has increased, the current value of the voltage of the solar power generation device 114, i.e., the DC grid voltage, is compared with the previous value (a previous measurement) (step S28). If the DC grid voltage has increased, control is performed to increase the DC grid voltage command value (step S30). On the other hand, if the output power of the solar power generation device 114 has increased but the DC grid voltage has not increased, control is performed to decrease the DC grid voltage command value (step S32). After that, the process proceeds to step S34 of Sequence 3.

[0040] If the output power of the solar power generation device 114 has not increased, the current value of the voltage of the solar power generation device 114, i.e., the DC grid voltage, is compared with the previous value (previous measurement) (step S26). If the DC grid voltage has increased, control is performed to decrease the DC grid voltage command value (step S32). On the other hand, if the output power of the solar power generation device 114 has not increased and the DC grid voltage has not increased, control is performed to increase the DC grid voltage command value (step S30). After that, the process proceeds to step S34 of sequence 3.

[0041] In other words, in sequence 2, if both the power of the solar power generation device 114 and the DC grid voltage are increasing, or if both the power of the solar power generation device 114 and the DC grid voltage are not increasing, control is performed to increase the DC grid voltage command value. Conversely, if the power of the solar power generation device 114 is increasing and the DC grid voltage is not increasing, or if the power of the solar power generation device 114 is not increasing and the DC grid voltage is increasing, control is performed to decrease the DC grid voltage command value.

[0042] In this way, by controlling the DC grid voltage, the system tracks the maximum power of the solar power generation device 114. If the power of the solar power generation device 114 is greater than the power required by the load 118, the battery 112 is charged. If the power of the solar power generation device 114 is less than the power required by the load 118, the battery 112 is discharged.

[0043] Sequence 3: If a voltage range is set for the DC grid voltage, it is determined whether the DC grid voltage is within the normal range (step S34). If it is within the normal range, the process proceeds to step S44 of Sequence 4. If the DC grid voltage is not within the normal range, it is determined whether the DC grid voltage is higher than a predetermined upper limit (step S36). If it is higher than the upper limit, the DC grid voltage command value is controlled so that the DC grid voltage becomes the upper limit (step S40). Also, if the DC grid voltage is below the upper limit, it is determined whether the DC grid voltage is below a predetermined lower limit (step S38). If it is below the lower limit, the DC grid voltage command value is controlled so that the DC grid voltage becomes the lower limit (step S42).

[0044] Sequence 4: Control the load voltage command value of load 118 connected to the AC port by inputting an arbitrary voltage.

[0045] By repeating the above control, power control is performed in the power conversion system 100.

[0046] Figure 6 shows the simulation results when the State of Charge (SOC) of the battery 112 is within the normal operating range. In Figure 6, control was started at time t=0.15sec. In the simulation, the amount of solar radiation was set high to make the power of the photovoltaic power generation device 114 greater than the power required by the load 118 of the grid power system 110 during the period up to time t=0.4sec. After time t=0.4sec, the amount of solar radiation was set low to make the power of the photovoltaic power generation device 114 less than the power required by the load 118. In the simulation, the power required by the load 118 (load power) was kept constant.

[0047] After control begins, the voltage of the solar power generation device 114 (DC grid voltage) is controlled to approach the voltage of the solar power generation device 114 at the time of maximum solar power generation calculated from the amount of solar radiation. Also, as shown in the enlarged view of Figure 7, the power of the solar power generation device 114 is controlled to approach the maximum solar power generation calculated from the amount of solar radiation, similar to the voltage of the solar power generation device 114 (DC grid voltage). During this time, because the power of the solar power generation device 114 is greater than the power required by the load 118, the surplus power of the solar power generation device 114 is charged into the battery 112.

[0048] From time t=0.4sec onward, the voltage of the solar power generation device 114 is controlled to maximize solar power generation according to the amount of solar radiation. During this time, since the power of the solar power generation device 114 is less than the power required by the load 118, the deficit is discharged from the storage battery 112.

[0049] As described above, the output power of the solar power generation device 114 is controlled to be maximized by adjusting the voltage of the solar power generation device 114 according to the amount of solar radiation. During this time, the charging and discharging of the storage battery 112 is performed appropriately according to the State of Charge (SOC) value of the storage battery 112, the power of the solar power generation device 114, and the power demanded by the load 118.

[0050] Figure 8 shows the simulation results when the State of Charge (SOC) of the battery 112 is higher than a predetermined upper limit. In Figure 8, control was started at time t=0.15sec. During the period up to time t=0.4sec, the amount of solar radiation was set high in order to make the power of the photovoltaic power generation device 114 greater than the power required by the load 118. After time t=0.4sec, the amount of solar radiation was set low in order to make the power of the photovoltaic power generation device 114 less than the power required by the load 118. In the simulation, the power required by the load 118 (load power) was kept constant.

[0051] After control begins, the voltage of the solar power generation device 114 (DC grid voltage) is controlled to approach the voltage of the solar power generation device 114 at the maximum solar power generation time calculated from the amount of solar radiation. The power of the solar power generation device 114 is also controlled to approach the maximum solar power generation time calculated from the amount of solar radiation. During this time, the power of the solar power generation device 114 is greater than the power required by the load 118, but the State of Charge (SOC) of the storage battery 112 has reached its upper limit, and the storage battery 112 cannot be charged. Therefore, control is performed to suppress the solar power generation device 114 so that there is no surplus power.

[0052] From time t=0.4sec onward, the voltage of the solar power generation device 114 is controlled to maximize solar power generation according to the amount of solar radiation. During this time, since the power of the solar power generation device 114 is less than the power required by the load 118, the deficit is discharged from the storage battery 112.

[0053] As described above, the output power of the solar power generation device 114 is controlled to be maximized by adjusting the voltage of the solar power generation device 114 according to the amount of solar radiation. In addition, if the State of Charge (SOC) of the storage battery 112 reaches its upper limit during this time, the solar power generation device 114 is suppressed so that its output power does not exceed the power demanded by the load 118, according to the power demanded by the load 118.

[0054] Figure 9 shows the simulation results when the State of Charge (SOC) of the battery 112 is below a predetermined lower limit. In Figure 9, control was started at time t=0.15sec. During the period up to time t=0.4sec, the amount of solar radiation was set high in order to make the power of the photovoltaic power generation device 114 greater than the power required by the load 118. After time t=0.4sec, the amount of solar radiation was set low in order to make the power of the photovoltaic power generation device 114 less than the power required by the load 118. In the simulation, the power required by the load 118 (load power) was kept constant.

[0055] After control begins, the voltage (DC grid voltage) of the solar power generation device 114 is controlled to approach the voltage of the solar power generation device 114 at the maximum solar power generation time calculated from the amount of solar radiation. The power of the solar power generation device 114 is also controlled to approach the maximum solar power generation time calculated from the amount of solar radiation. During this time, because the power of the solar power generation device 114 is greater than the power required by the load 118, the surplus power is used to charge the storage battery 112.

[0056] From time t=0.4sec onward, the voltage of the solar power generation device 114 is controlled to maximize solar power generation according to the amount of solar radiation. During this time, since the power of the solar power generation device 114 is less than the power required by the load 118, if there is sufficient capacity in the state of charge (SOC) of the storage battery 112, it will discharge from the battery. However, since the SOC of the storage battery 112 is below the lower limit, it cannot discharge, and the power shortage is supplied from the generator 116.

[0057] As described above, the output power of the solar power generation device 114 is controlled to be maximized by adjusting the voltage of the solar power generation device 114. During this time, if the State of Charge (SOC) of the storage battery 112 is below the lower limit, the storage battery 112 is charged or power is supplied from the generator 116 according to the power of the solar power generation device 114 and the power required by the load 118.

[0058] [Another example of power conversion system control] Figure 10 shows another example of a control block diagram for the power conversion system 100. Figure 11 shows a flowchart of another example of a control method for the power conversion system 100. The sequences in the control block diagrams correspond to the sequences in the control flowcharts.

[0059] The control device 104 is comprised of a voltage detection unit 320, a current detection unit 322, an SOC receiving unit 324, a power calculation unit 326, a PV maximum power tracking unit 328, a DC-side voltage command generation unit 330, and an AC-side power command generation unit 332.

[0060] The voltage detection unit 320 detects the DC grid voltage of the power conversion circuit 102, the battery voltage 112, and the AC voltage, and outputs them to the power calculation unit 326 and the PV maximum power tracking unit 328. The current detection unit 322 detects the current of the photovoltaic power generation device 114, the battery current 112, the AC current, and the load current, and outputs them to the power calculation unit 326. The SOC receiving unit 324 calculates the SOC of the battery 112 and outputs it to the AC side power command generation unit 332. The power calculation unit 326 receives the outputs of the voltage detection unit 320 and the current detection unit 322, calculates the power of the battery 112, the photovoltaic power generation device 114, the grid power system 110, and the power required by the load 118, and outputs them to the PV maximum power tracking unit 328 and the AC side power command generation unit 332.

[0061] The PV maximum power tracking unit 328 performs the processing shown in sequence 1 below. The DC side voltage command generation unit 330 performs the processing shown in sequence 2 below. The AC side power command generation unit 332 performs the processing shown in sequence 3 below.

[0062] Sequence 1: The current value of the output power of the solar power generation device 114 is compared with the previous value (step S50). If the output power of the solar power generation device 114 has increased, the process proceeds to step S54; otherwise, the process proceeds to step S52. If the output power of the solar power generation device 114 has increased, the current value of the voltage of the solar power generation device 114, i.e., the DC grid voltage, is compared with the previous value (step S54). If the DC grid voltage has increased, control is performed to increase the DC grid voltage command value (step S56). On the other hand, if the output power of the solar power generation device 114 has increased but the DC grid voltage has not increased, control is performed to decrease the DC grid voltage command value (step S58). After that, the process proceeds to step S60 of Sequence 2.

[0063] If the output power of the solar power generation device 114 has not increased, the current value of the voltage of the solar power generation device 114, i.e., the DC grid voltage, is compared with the previous value (step S52). If the DC grid voltage has increased, control is performed to decrease the DC grid voltage command value (step S58). On the other hand, if the output power of the solar power generation device 114 has not increased and the DC grid voltage has not increased, control is performed to increase the DC grid voltage command value (step S56). After that, the process proceeds to step S60 of sequence 2.

[0064] In other words, in sequence 1, if both the power of the solar power generation device 114 and the DC grid voltage are increasing, or if both the power of the solar power generation device 114 and the DC grid voltage are not increasing, control is performed to increase the DC grid voltage command value. Conversely, if the power of the solar power generation device 114 is increasing and the DC grid voltage is not increasing, or if the power of the solar power generation device 114 is not increasing and the DC grid voltage is increasing, control is performed to decrease the DC grid voltage command value.

[0065] In this way, by controlling the DC grid voltage, the system tracks the maximum power of the solar power generation device 114. If the power of the solar power generation device 114 is greater than the power required by the load 118, the battery 112 is charged. If the power of the solar power generation device 114 is less than the power required by the load 118, the battery 112 is discharged.

[0066] Sequence 2: If a voltage range is set for the DC grid voltage, it is determined whether the DC grid voltage is within the normal range (step S60). If it is within the normal range, the process proceeds to step S70 of Sequence 3. If the DC grid voltage is not within the normal range, it is determined whether the DC grid voltage is higher than a predetermined upper limit (step S62). If it is higher than the upper limit, the DC grid voltage command value is controlled so that the DC grid voltage becomes the upper limit (step S66). Also, if the DC grid voltage is below the upper limit, it is determined whether the DC grid voltage is below a predetermined lower limit (step S64). If it is below the lower limit, the DC grid voltage command value is controlled so that the DC grid voltage becomes the lower limit (step S68).

[0067] Sequence 3: Determine whether the State of Charge (SOC) of the battery 112 is normal (step S70). If it is normal, control the AC power to match the power requirements of the load 118 (step S76). In this case, power is supplied from the battery 112 to the load 118 according to the power requirements of the load 118, or the battery 112 is charged by the surplus power of the solar power generation device 114.

[0068] If the State of Charge (SOC) of the battery 112 is not normal, it is determined whether the SOC of the battery 112 is higher than a predetermined upper limit (step S72). If the SOC is higher than the upper limit, the process proceeds to step S78; if the SOC is below the upper limit, the process proceeds to step S74. If the SOC of the battery 112 is higher than the upper limit, it is determined whether the power demanded by the load 118 is greater than the output power of the solar power generation device 114 (step S78). If it is greater, the AC power is controlled to match the power demanded by the load 118 (step S82). In this case, power is supplied from the battery 112 to the load 118 according to the power demanded by the load 118. If the power demanded by the load 118 is not greater than the output power of the solar power generation device 114, the AC power is controlled by the power generated by the solar power generation device 114 (step S84). In this case, the surplus power of the solar power generation device 114 is regenerated to the grid power system 110.

[0069] If the State of Charge (SOC) of the battery 112 is below the upper limit, it is determined whether the SOC of the battery 112 is below a predetermined lower limit (step S74). If the SOC of the battery 112 is below the lower limit, it is determined whether the power required by the load 118 is greater than the output power of the solar power generation device 114 (step S78). If it is greater, the AC power is controlled by the power generated by the solar power generation device 114 (step S84). In this case, the output power of the solar power generation device 114 is less than the power required by the load 118, and the SOC of the battery 112 is also below the lower limit, so the battery 112 cannot discharge. Therefore, the grid power system 110 supplies the remaining power to the load 118. If the power required by the load 118 is not greater than the output power of the solar power generation device 114, the AC power is controlled to match the power required by the load 118 (step S82). In this case, control is performed to charge the battery 112 using the surplus power of the solar power generation device 114.

[0070] By repeating the above control, power control is performed in the power conversion system 100.

[0071] Figure 12 shows the simulation results when the State of Charge (SOC) of the battery 112 is within the normal operating range. In Figure 12, control was started at time t=0.15sec. In the simulation, the amount of solar radiation was set high to make the power of the photovoltaic power generation device 114 greater than the power required by the load 118 of the grid power system 110 during the period up to time t=0.4sec. After time t=0.4sec, the amount of solar radiation was set low to make the power of the photovoltaic power generation device 114 less than the power required by the load 118 of the grid power system 110. In the simulation, the power required by the load 118 (load power) was kept constant.

[0072] After control begins, the voltage of the photovoltaic power generation device 114 (DC grid voltage) is controlled to approach the voltage of the photovoltaic power generation device 114 at the time of maximum solar power generation calculated from the amount of solar radiation. Also, as shown in the enlarged view of Figure 13, the power of the photovoltaic power generation device 114 is controlled to approach the maximum solar power generation calculated from the amount of solar radiation, similar to the voltage of the photovoltaic power generation device 114 (DC grid voltage). During this time, because the power of the photovoltaic power generation device 114 is greater than the power required by the load 118 of the grid power system 110, the surplus power of the photovoltaic power generation device 114 is charged into the storage battery 112.

[0073] From time t=0.4sec onward, the voltage of the solar power generation device 114 is controlled to maximize solar power generation according to the amount of solar radiation. During this time, because the power of the solar power generation device 114 is less than the power required by the load 118 of the grid power system 110, the deficit is discharged from the storage battery 112.

[0074] As described above, the output power of the solar power generation device 114 is controlled to be maximized by adjusting the voltage of the solar power generation device 114 according to the amount of solar radiation. During this time, the charging and discharging of the storage battery 112 is performed appropriately according to the State of Charge (SOC) value of the storage battery 112, the power of the solar power generation device 114, and the power demands of the load 118 of the grid power system 110.

[0075] Figure 14 shows the simulation results when the State of Charge (SOC) of the battery 112 is higher than a predetermined upper limit. In Figure 14, control was started at time t=0.15sec. During the period up to time t=0.4sec, the amount of solar radiation was set high in order to make the power of the photovoltaic power generation device 114 greater than the power required by the load 118 of the grid power system 110. After time t=0.4sec, the amount of solar radiation was set low in order to make the power of the photovoltaic power generation device 114 less than the power required by the load 118 of the grid power system 110. In the simulation, the power required by the load 118 (load power) was kept constant.

[0076] After control begins, the voltage of the solar power generation device 114 (DC grid voltage) is controlled to approach the voltage of the solar power generation device 114 at the time of maximum solar power generation calculated from the amount of solar radiation. The power of the solar power generation device 114 is also controlled to approach the maximum solar power generation calculated from the amount of solar radiation. During this time, although the power of the solar power generation device 114 is greater than the power required by the load 118 of the grid power system 110, the State of Charge (SOC) of the battery 112 has reached its upper limit, and the battery 112 cannot be charged. Therefore, control is performed so that the surplus power is regenerated back into the grid power system 110 (controlling the grid power to become negative).

[0077] From time t=0.4sec onward, the voltage of the solar power generation device 114 is controlled to maximize solar power generation according to the amount of solar radiation. During this time, since the power of the solar power generation device 114 is less than the power required by the load 118 of the grid power system 110, the deficit is discharged from the storage battery 112.

[0078] As described above, the output power of the solar power generation device 114 is controlled to be maximized by adjusting the voltage of the solar power generation device 114 according to the amount of solar radiation. In addition, when the State of Charge (SOC) of the storage battery 112 reaches its upper limit, and the output power of the solar power generation device 114 exceeds the power required by the load 118, the surplus power is regenerated to the grid power system 110. Also, when the power required by the load 118 exceeds the output power of the solar power generation device 114, the storage battery 112 supplies the insufficient power to the load 118.

[0079] Figure 15 shows the simulation results when the State of Charge (SOC) of the battery 112 is below a predetermined lower limit. In Figure 15, control was started at time t=0.15sec. During the period up to time t=0.4sec, the amount of solar radiation was set high in order to make the power of the photovoltaic power generation device 114 greater than the power required by the load 118 of the grid power system 110. After time t=0.4sec, the amount of solar radiation was set low in order to make the power of the photovoltaic power generation device 114 less than the power required by the load 118 of the grid power system 110. In the simulation, the power required by the load 118 (load power) was kept constant.

[0080] After control begins, the voltage of the solar power generation device 114 (DC grid voltage) is controlled to approach the voltage of the solar power generation device 114 at the maximum solar power generation time calculated from the amount of solar radiation. In addition, the power of the solar power generation device 114 is also controlled to approach the maximum solar power generation time calculated from the amount of solar radiation. During this time, since the power of the solar power generation device 114 is greater than the power required by the load 118 of the grid power system 110, the surplus power is used to charge the storage battery 112.

[0081] From time t=0.4sec onward, the voltage of the solar power generation device 114 is controlled to maximize solar power generation according to the amount of solar radiation. During this time, since the power of the solar power generation device 114 is less than the power required by the load 118 of the grid power system 110, if there is sufficient capacity in the state of charge (SOC) of the storage battery 112, it will discharge from the storage battery. However, since the SOC of the storage battery 112 is below the lower limit, it cannot discharge, and the system is controlled to supply the power deficit from the grid power system 110.

[0082] As described above, the output power of the solar power generation device 114 is controlled to be maximized by adjusting the voltage of the solar power generation device 114. In addition, if the State of Charge (SOC) of the storage battery 112 is below the lower limit, the storage battery 112 is charged or power is supplied from the grid power system 110 according to the power demands of the solar power generation device 114 and the load 118 of the grid power system 110.

[0083] [Overview of the prefecture] [Configuration 1] A power conversion system having one AC port and two DC ports, A storage battery is connected to the first DC port, which is one of the aforementioned DC ports. A solar power generation device is connected to the second DC port, which is the other DC port mentioned above. A power conversion system characterized by controlling the output voltage of the photovoltaic power generation device to maximize the output voltage by adjusting the voltage of the second DC port, controlling the charging and discharging of the battery by adjusting the voltage of the first DC port according to the state of charge (SOC) of the battery, and controlling the AC power input and output at the AC port. [Configuration 2] The power conversion system described in Configuration 1, A power conversion system characterized in that at least one of a grid power system and a load is connected to the AC port. [Configuration 3] A power conversion system according to configuration 1 or 2, A power conversion system characterized by controlling the voltage of the second DC port using the storage battery connected to the first DC port. [Structure 4] A power conversion system as described in any one of items 1 to 3, A first switching arm, comprising a first switching element and a second switching element connected in series, a second switching arm, comprising a third switching element and a fourth switching element connected in series, and a third switching arm, comprising a fifth switching element and a sixth switching element connected in series, are connected in parallel. The upper connection points of the first switching arm, the second switching arm, and the third switching arm are designated as the positive terminals of the second DC port, and the lower connection points of the first switching arm, the second switching arm, and the third switching arm are designated as the negative terminals of the second DC port. A first transformer winding is connected between the connection point of the first switching element and the second switching element and the connection point of the third switching element and the fourth switching element; a second transformer winding is connected between the connection point of the third switching element and the fourth switching element and the connection point of the fifth switching element and the sixth switching element; and a third transformer winding is connected between the connection point of the fifth switching element and the sixth switching element and the connection point of the first switching element and the second switching element. One end of the first inductor is connected to a point in the middle of the conductor constituting the first transformer winding, one end of the second inductor is connected to a point in the middle of the conductor constituting the second transformer winding, and one end of the third inductor is connected to a point in the middle of the conductor constituting the third transformer winding. A power conversion system characterized by comprising a three-phase power conversion circuit, wherein the other ends of the first inductor, the second inductor, and the third inductor are connected in common to form the positive terminal of the first DC port, and the connection points on the lower sides of the second switching arm and the third switching arm are formed to form the negative terminal of the first DC port. [Explanation of Symbols]

[0084] 100 Power conversion system, 102 Power conversion circuit, 104 Control device, 110 Grid power system, 112 Storage battery, 114 Solar power generation device, 116 Generator, 118 Load, 200a~200c Power converter (capacitor split type power converter), 202a~202c Transformer coupler, 204 3-phase power converter, 206a~206c Inverter circuit, 210 Power converter (capacitor split type power converter), 212 Transformer coupler, 214 3-phase power converter, 216 Inverter circuit, 300 Voltage detection unit, 302 Current detection unit, 304 SOC receiver, 306 Power calculation unit, 308 PV maximum power tracking unit, 310 DC side voltage / current command generation unit, 312 Load voltage command generation unit, 320 Voltage detection unit, 322 Current detection unit, 324 SOC receiver, 326 Power calculation unit, 328 PV maximum power tracking unit, 330 DC side voltage command generation unit, 332 AC side power command generation unit.

Claims

1. A power conversion system having one AC port and two DC ports, A storage battery is connected to the first DC port, which is one of the aforementioned DC ports. A solar power generation device is connected to the second DC port, which is the other DC port of the aforementioned DC port. A power conversion system characterized by controlling the output voltage of the solar power generation device to maximize the output voltage by adjusting the voltage of the second DC port, controlling the charging and discharging of the battery by adjusting the voltage of the first DC port according to the state of charge (SOC) of the battery, and controlling the AC power input and output at the AC port.

2. A power conversion system according to claim 1, A power conversion system characterized in that at least one of a grid power system and a load is connected to the aforementioned AC port.

3. A power conversion system according to claim 1 or 2, A power conversion system characterized by controlling the voltage of the second DC port using the storage battery connected to the first DC port.

4. A power conversion system according to claim 1, A first switching arm, comprising a first switching element and a second switching element connected in series, a second switching arm, comprising a third switching element and a fourth switching element connected in series, and a third switching arm, comprising a fifth switching element and a sixth switching element connected in series, are connected in parallel. The upper connection points of the first switching arm, the second switching arm, and the third switching arm are set as the positive terminals of the second DC port, and the lower connection points of the first switching arm, the second switching arm, and the third switching arm are set as the negative terminals of the second DC port. A first transformer winding is connected between the connection point of the first switching element and the second switching element and the connection point of the third switching element and the fourth switching element; a second transformer winding is connected between the connection point of the third switching element and the fourth switching element and the connection point of the fifth switching element and the sixth switching element; and a third transformer winding is connected between the connection point of the fifth switching element and the sixth switching element and the connection point of the first switching element and the second switching element. One end of the first inductor is connected to a point in the middle of the conductor constituting the first transformer winding, one end of the second inductor is connected to a point in the middle of the conductor constituting the second transformer winding, and one end of the third inductor is connected to a point in the middle of the conductor constituting the third transformer winding. A power conversion system characterized by comprising a three-phase power conversion circuit, wherein the other ends of the first inductor, the second inductor, and the third inductor are connected in common to form the positive terminal of the first DC port, and the connection points on the lower sides of the second switching arm and the third switching arm are formed to form the negative terminal of the first DC port.

Images