JP5726555B2 - Solar power system - Google Patents

Description

  The present invention relates to a photovoltaic power generation system including a plurality of storage battery charge / discharge sets in parallel.

  In recent years, the development of a photovoltaic power generation system that has little impact on the environment has been actively promoted from the viewpoint of protecting the global environment.

  In this solar power generation system, DC power generated by a solar cell is converted into AC power at a commercial frequency by a power conditioner that is a power conversion device including a DC / DC converter and an inverter, and is connected to a commercial power system. In addition, the surplus power is reversely flowed to the commercial power system while being supplied to the load (see, for example, Patent Document 1).

  In contrast to such a grid-connected photovoltaic power generation system, there is a photovoltaic power generation system that does not perform grid interconnection.

  In this type of solar power generation system, surplus power out of the generated power of the solar cell at daytime cannot be reversely flowed for selling power, so the surplus power is charged to the storage battery, It is assumed that the surplus power accumulated in the storage battery is discharged to the load side and used at night when the generated power is insufficient.

JP 2001-161032 A

  However, in the above solar power generation system, the power generated by the solar cell and the power consumed by the load constantly fluctuate. Therefore, the power generation amount of the solar cell and the power consumed by the load are detected and controlled by the current sensor and voltage sensor It is necessary to control charging / discharging of the storage battery by the controller, and such control has problems such as complicating the configuration of the entire photovoltaic power generation system and greatly increasing the equipment cost.

  In order to solve this problem, the present inventor has diligently studied, and in a photovoltaic power generation system that stores the generated power of the solar cell in the storage battery without being connected to the grid, the bidirectional DC is provided so that the system configuration can be configured at low cost. A storage battery charge / discharge set including a DC / DC converter and a storage battery was considered.

  And when using this charging / discharging set multiple units | sets and charging / discharging each storage battery in each set, charging / discharging of the storage battery in one set is performed preferentially over that of another set, for example. In such a case, the life of each storage battery is likely to vary, for example, the life of the storage battery in the set is shorter than that of the storage batteries in other sets.

  For example, using a storage battery voltage detection sensor and a host computer in the power conditioner to control the storage battery life variation of each set causes an increase in complexity and cost of the power system. There is a problem.

  Therefore, a main problem to be solved by the present invention is that a plurality of charge / discharge sets including a bidirectional DC / DC converter and a storage battery are stored in a solar power generation system that stores the generated power of the solar battery in the storage battery without being connected to the grid. When the storage batteries are provided in parallel and are charged and discharged in each set, there is no problem such as complication of the power system and the life of the storage batteries in each set does not vary.

  Note that other problems to be solved by the present invention are clear from the description to be described later.

  A photovoltaic power generation system according to the present invention includes a solar cell and a power conditioner that converts direct current power of the solar cell into alternating current power and outputs the alternating current power to a load, and is bidirectional to a DC bus line in the power conditioner. A plurality of sets of series connection circuits of DC / DC converters and storage batteries are connected in parallel, and a control unit is provided to operate each set by switching at regular intervals. Each bidirectional DC / DC converter in each set The DC line voltage in the DC bus line is DC / DC converted to charge each corresponding storage battery, the charging voltage of each storage battery is DC / DC converted and discharged to the DC bus line, Further, the control unit is characterized in that each of the sets is switched and operated at regular intervals.

  In the present invention, the bidirectional DC / DC converters are alternately switched at fixed time intervals by the control unit to charge and discharge the storage batteries, so that the lifetimes of the storage batteries are equalized and variations in the lifetimes are suppressed.

  In this case, in the present invention, the control unit may have a simple and inexpensive configuration in which each of the sets is switched and operated at regular intervals, and the operation of each set is performed by a complicated and expensive computer or the like above them. There is no need to control.

  In a preferred aspect, any one of the sets is a master set, the other is a slave set, and the storage battery in the master set is discharged to increase the line voltage to the first command voltage, and the storage battery When the line voltage decreases from the first command voltage to a second command voltage that is lower than the first command voltage due to a decrease in discharge, the storage battery in the slave set is discharged to increase the line voltage to the first command voltage. To control.

  In another preferred aspect, the storage battery in the master set is charged to lower the line voltage to the third command voltage, and the line voltage is higher than the third command voltage by a certain voltage as the charge of the storage battery decreases. When the voltage rises to the fourth command voltage, the line voltage is controlled to fall to the third command voltage by charging the storage battery in the slave set.

  According to the present invention, it is possible to equalize the life of the storage batteries in each set without complicating the system configuration and increasing costs.

FIG. 1 is a schematic configuration diagram of a photovoltaic power generation system according to an embodiment of the present invention. FIG. 2 is a circuit configuration diagram of the bidirectional DC / DC converter in the charge / discharge set of FIG. FIG. 3 is a diagram used for explaining the charging operation to the storage battery using the bidirectional DC / DC converter in the charge / discharge set of FIG. 1. FIG. 4 is a diagram used for explaining the discharge operation from the storage battery using the bidirectional DC / DC converter in the charge / discharge set of FIG. 1. FIG. 5 is a diagram illustrating an on / off relationship of each switching element with respect to a charging path and a discharging path of the bidirectional DC / DC converter in the charge / discharge set. FIG. 6 is a diagram used for explaining the charging / discharging operation of the storage battery in response to changes in line voltage, with time on the horizontal axis and line voltage on the vertical axis. FIG. 7 is a diagram for explaining the parallel operation of two charge / discharge sets. FIG. 8 is a diagram showing an operation timing chart in the description of the parallel operation of FIG. FIG. 9 is a diagram used for explaining the operation when the horizontal axis represents time, the vertical axis represents line voltage, and the storage batteries in the charge / discharge sets on the master side and the slave side are in the charge mode. FIG. 10 is a diagram used for explaining the operation when the horizontal axis indicates time, the vertical axis indicates line voltage, and the storage batteries in the charge / discharge sets on the master side and the slave side are in the discharge mode.

  Hereinafter, a solar power generation system according to an embodiment of the present invention will be described in detail with reference to the accompanying drawings.

  FIG. 1 shows a schematic configuration of the photovoltaic power generation system of the embodiment. With reference to FIG. 1, the photovoltaic power generation system of the embodiment is an electric power system including a solar cell 1, a power conditioner 3, a load 5, and storage battery charge / discharge sets 7 and 9.

  The power conditioner 3 converts the DC power of the solar cell 1 into AC power and outputs it to the load 5 and includes a DC / DC converter 3a and a DC / AC inverter 3b.

  The DC / DC converter 3a and the DC / AC inverter 3b are connected by a DC bus line 3c.

  The DC / DC converter 3a boosts the direct current output of the solar cell 1 and outputs it as a line voltage to the DC bus line 3c. The DC / AC inverter 3b converts the output of the DC / DC converter 3a into AC power and supplies it to various AC loads 5.

  Each of the storage battery charge / discharge sets 7 and 9 controls the bidirectional DC / DC converters 7a and 9a and the storage batteries 7b and 9b connected in series and the bidirectional DC / DC converters 7a and 9a, respectively. And a controller 7c, 9c for controlling the charging / discharging operation.

  Hereinafter, the storage battery charge / discharge set is simply referred to as a set for the sake of simplicity. Each set 7, 9 is connected in parallel to the DC bus line 3 c of the power conditioner 3.

  The bidirectional DC / DC converters 7a and 9a in the sets 7 and 9 respectively perform DC / DC conversion of the DC line voltage supplied to the DC bus line 3c to the step-down side under the control of the control units 7c and 9c. Thus, while charging the respective storage batteries 7b and 9b, the charging voltage of the storage batteries 7b and 9b can be DC / DC converted to the boost side and supplied to the DC bus line 3c of the power conditioner 3. .

  The control units 7c and 9c in each set 7 and 9 have a built-in CPU and the like, and are connected to each other via a communication line 8 to communicate according to a required control program.

  With reference to FIG. 2, the structure of the set 7 of the sets 7 and 9 will be described. Since the set 9 has the same configuration as the set 7, its description is omitted.

  In the set 7, the bidirectional DC / DC converter 7a includes a first switching element Q1, a second switching element Q1, and the like that are connected in series between the DC bus line 3c and a negative pole that is one pole of the storage battery 7b. Q2, first and second diodes D1 and D2 connected in antiparallel to the first and second switching elements Q1 and Q2, respectively, a common connection portion of both switching elements Q1 and Q2, and the other pole of the storage battery 7b A step-up / step-down coil CL1 connected in series with the positive electrode, a capacitor C1 parallel to the storage battery 7b, and a capacitor C2 connected in parallel to the first and second switching elements Q1, Q2 are included.

  The bidirectional DC / DC converter 7a further includes a voltage sensor S1 for detecting a line voltage in the DC bus line 3c, a voltage sensor S2 for detecting a charging voltage of the storage battery 7b, a current flowing through the step-up / down coil CL1, and its direction. Current sensor S3 to detect.

  The control unit 7c controls on / off of the first and second switching elements Q1, Q2 by the sensor signals from these sensors S1-S3 to control charging / discharging of the storage battery 7b, while the other party set via the communication line 8 The charge / discharge data of the storage battery 9b is acquired, and the charge / discharge of the storage battery 7b is further controlled.

  In the bidirectional DC / DC converter 7a having the above configuration, when charging the storage battery 7b, the control unit 7c controls the DC bus line 3c → the first switching element Q1 → the step-up / step-down coil as shown in FIG. The line voltage is stepped down in the first charging path L1 of CL1 → the storage battery 7b to charge the storage battery 7b.

  Further, the energy stored in the step-up / step-down coil CL1 is controlled by the control unit 7c, as shown in FIG. 3, in the step-up / step-down coil CL1 → the storage battery 7b (including the capacitor C1) → the second charging path L2 of the second diode D2. Charge.

  When discharging from the storage battery 7b, energy is stored in the step-up / step-down coil CL1 through the first discharge path L3 of the storage battery 7b → the step-up / step-down coil CL1 → the second switching element Q2 as shown in FIG. 4 under the control of the control unit 7c. To do. Further, as shown in FIG. 4, the storage battery voltage is boosted and discharged through the second discharge path L4 of the storage battery 7b → the step-up / step-down coil CL1 → the first diode D1 under the control of the control unit 7c.

  On / off of the first and second switching elements Q1 and Q2 with respect to the first and second charging paths L1 and L2 and the first and second discharging paths L3 and L4 as shown in FIG. The first switching element Q1 is on (circle), the second switching element Q2 is off (x), and the first and second switching elements Q1, Q2 are both off in the second charging path L2. In the first discharge path L1, the first switching element Q1 is off and the second switching element Q2 is on, and in the second charging path L2, both the first and second switching elements Q1 and Q2 are off.

  Next, the charge / discharge control operation for the storage battery 7b by the bidirectional DC / DC converter 7a of the embodiment will be described with reference to FIG.

  The controller 7c in the charge / discharge set 7 that performs this control can control the charge / discharge operation for the storage battery 7b by controlling the bidirectional DC / DC converter 7a by a control program stored in a memory (not shown). It has become.

  FIG. 6 is a diagram in which time is plotted on the horizontal axis and line voltage is plotted on the vertical axis, and is used to explain the charge / discharge operation of the storage battery 7b in response to changes in the line voltage.

  First, when the generated power of the solar cell 1 is, for example, 3 kW and the load 5 consumes, for example, 1 kW, 2 kW of power is surplus.

  In this case, the line voltage at the power conditioner 3 is higher than a predetermined voltage 380V (this predetermined voltage is a command voltage value set by PWM control in the power conditioner 3) as shown by a solid line LV in FIG. If it is a voltage, the data of the line voltage is given to the control part 7c from the voltage sensor S3.

  Since the line voltage V1 is equal to or higher than a predetermined voltage of 380 V, the controller 7c turns on the first switching element Q1 and turns off the second switching element Q2 to form the first charging path L1 as shown in FIG. Control is performed to charge the storage battery 7b with the line voltage via the first charging path L1.

  Next, as shown in FIG. 3, the control unit 7c turns off both the first and second switching elements Q1 and Q2 to form the second charging path L2, and the step-up / down coil via the second charging path L2. The stored energy is released from CL1, and the storage battery 7b is charged with this stored energy.

  When the storage battery 7b is charged in this way, the line voltage decreases as shown in FIG.

  In this case, the controller 7c charges / discharges the storage battery 7b within a voltage range of a constant voltage, for example, ± 5V, centered on the 385V, which is a predetermined voltage, and the line voltage is ± 5V including the 385V. The range is to be controlled.

  The lower limit value of this voltage range is 380V, and the upper limit value is 390V. The values of the upper limit and the lower limit are examples, and are not limited thereto.

  Thus, charging of the storage battery 7b is continued until the line voltage drops to 380 V, which is the lower limit value of the constant voltage range. When the line voltage reaches the lower limit value of 380 V, the charging operation is stopped and the first discharging path L3 and the second discharging path L4 are formed as shown in FIG. 4 to start the discharging operation.

  Thus, the discharge of the storage battery 7b is continued until the line voltage rises to the upper limit value 390V of the constant voltage range by the discharge, and when the line voltage reaches the upper limit value 390V, the discharging operation is stopped and the charging operation is started.

  While the line voltage is controlled in a voltage range of ± 5 V of a constant voltage centering on a predetermined voltage of 385 V by the charge / discharge operation for the storage battery 7 b, the storage battery 7 b is a surplus power out of the generated power of the solar cell 1 at daytime etc. When the generated power of the solar cell 1 is reduced due to insufficient sunshine at night, rainy weather, cloudy weather, shade, etc., the stored voltage of the storage battery 7b is discharged to the DC bus line 3c, and the discharged power is supplied to the load 5 side. It can be used in.

  The 385V is set as a command voltage value by a control unit (not shown) in the power conditioner 3 and is controlled by PWM control in the power conditioner 3 from the DC / DC converter 3a as indicated by A1 and A2 in FIG. The output line voltage is controlled around 385V.

  Then, the line voltage falls from the voltage value before the area A1 where the line voltage is 390V or higher and is PWM controlled to the vicinity area 385V. However, the line voltage is lowered from 385V to 380V due to the solar cell 1 output drop or the like Until it reaches, the storage battery 7b is charged.

  When the voltage decreases to 380V, the storage battery 7b is switched from charging to discharging and discharge control is performed. When the line voltage increases and reaches the command voltage 385V, PWM control is performed in the region 385 near 385V.

  Then, the discharge of the storage battery 7b is continued until the line voltage rises from 385V and reaches 390V. When the line voltage reaches 390V, the storage battery 7b is reversely controlled from discharge to charge.

  Next, the case where the sets 7 and 9 perform charge / discharge operations in parallel will be described with reference to FIGS.

  FIG. 7 is a diagram for explaining the parallel operation of the sets 7 and 9, and FIG. 8 is a diagram showing an operation timing chart in the explanation of the parallel operation of FIG.

  With reference to these drawings, when the respective storage batteries 7b and 9b in the sets 7 and 9 are not uniformly charged and discharged, there is a high possibility that their lifetimes will not be uniform.

  On the other hand, since the sets 7 and 8 are connected to the same DC bus line 3c, the storage batteries 7b and 9b in either one of the sets 7 or 9 are repeatedly charged and discharged with priority over the other. There is a possibility that.

  In such a case, the storage batteries 7b and 9b in each of the sets 7 and 9 can be equally charged / discharged by the host computer or the like, but in that case, the wiring and configuration with the host computer or the incorporation of programs in those computers, etc. As a result, the price becomes complicated and expensive, and the simplicity and low cost are impaired.

  Therefore, in the present embodiment, as shown in FIG. 7, the control units 7c and 9c of the respective sets 7 and 9 communicate via the communication line 8, and as shown in FIG. The storage batteries 7b and 9b are switched between charging and discharging every period T.

  In this case, the set 7 is charged / discharged between the time t0 and the time t2, the set 9 is charged / discharged between the time t1 and the time t4, and the set 7 is charged / discharged between the time t3 and the time t6. The charging / discharging of the other sets 7 and 9 is started slightly before the end time.

  As described above, in the embodiment, the storage batteries 7b and 9b in each of the sets 7 and 9 are switched and charged / discharged at regular intervals T. Therefore, the life of the storage batteries 7b and 9b in each of the sets 7 and 8 is as follows. It is equalized and the variation in the lifetime is suppressed.

  Next, with reference to FIG. 9, a case will be described in which one of the sets 7 and 9 is set as a master side set and the other is set as a slave side set to control charging / discharging in each.

  The master side and slave side sets communicate with each other via the communication line 8 on the premise that the master side and slave side sets are alternately switched.

  Between the master side and the slave side, when the master side is discharged and power is insufficient, data that the power is insufficient, data that the master side is charged and power is surplus, and other necessary data are communicated.

  Further, the line voltage and the voltage at the storage batteries 7b and 9b are detected by the respective sensors, and the data can also be communicated.

  In the following description, for convenience of description, set 7 is a master side set and set 9 is a slave side set.

  In FIG. 9, the horizontal axis represents time, and the vertical axis represents line voltage. A period Ta in FIG. 10 is a period indicating a discharge operation to the DC bus line 3c in the storage battery 7b in the master-side set 7, and a period Tb is a discharge to the DC bus line 3c in the storage battery 9b in the slave-side set 9. This is a period showing the operation.

  At time t0 within the period Ta, the storage battery 7b in the set 7 starts discharging and raises the line voltage of the DC bus line 3c to the first command voltage, for example, 385V.

  The set 7 controls the discharge so as to maintain the first command voltage on the master side. Then, when the storage battery 7b cannot maintain the first command voltage due to the discharge with the passage of time, the line voltage starts to decrease from time t1.

  When the line voltage drops from the first command voltage to 382 V, which is a second command voltage that is lower by 3 V than the first command voltage, at time t2, the storage battery 9b in the slave-side set 9 starts discharging at that time t2.

  This discharge raises the line voltage. Then, the line voltage rises to the first command voltage at time t3. When the line voltage reaches the first command voltage, the set 9 controls the discharge so that the first command voltage can be maintained. For such control, the sets 7 and 9 on the master side and the slave side communicate with each other by the internal control units 7c and 9c, monitor the voltage status of the storage batteries 7b and 9b, and operate as a master or a slave. .

  Next, the charge / discharge operation in the sets 7 and 9 will be described with reference to FIG. In FIG. 10, the horizontal axis represents time, and the vertical axis represents line voltage. Also in this case, for convenience of explanation, the set 7 is a master side set and the set 9 is a slave side set.

  A period Ta in FIG. 10 is a period indicating a charging operation of the storage battery 7b in the set 7 on the master side, and a period Tb is a period indicating a charging operation of the storage battery 9b in the set 9 on the slave side.

  When the storage battery 7b in the set 7 starts to be charged at time t0 within the period Ta, the line voltage of the DC bus line 3c decreases. When the line voltage drops to a third command voltage, for example, 385 V, due to this charging, the set 7 controls the charging so as to maintain the third command voltage.

  If the line voltage cannot be maintained at the third command voltage even if the storage battery 7b in the master side set 7 continues to be charged, the line voltage starts to rise from time t1 accordingly.

  Then, when the line voltage rises from the third command voltage to 388 V, which is a fourth command voltage that is 3V higher than the third command voltage at time t2, the slave-side set 9 starts charging the storage battery 9b at time t2. The line voltage decreases with the start of charging of the storage battery 9b.

  The problem of controlling the line voltage to a voltage range of ± 5V including the 385V by charging / discharging the storage battery 7b with a constant voltage, for example, a voltage range of ± 5V, centered on the 385V where the line voltage is a predetermined voltage is a problem. The master set is involved.

  From the above, by the above control, the master side and the slave side sets 7 and 9 communicate with each other inside the control units 7c and 9c, monitor the voltage status of the storage batteries 7b and 9b, and operate as a master or a slave. To do.

  As described above, in the solar power generation system of the present embodiment, the sets 7, 9 including the bidirectional DC / DC converter and the storage battery are connected in parallel to the DC bus line 3c, and the sets 7, 9 are fixed. Since the storage batteries 7b and 9b are charged and discharged by switching over time, the life of each of the storage batteries 7b and 9b is equalized and variation in the life is suppressed.

  In this case, since the sets 7 and 9 are switched and operated at regular intervals, it is not necessary to control the operations of the sets by a complicated and expensive computer or the like above them.

DESCRIPTION OF SYMBOLS 1 Solar cell 3 Power conditioner 3a DC / DC converter 3b DC / AC inverter 5 Load 7 Storage battery charging / discharging set 7a Bidirectional DC / DC converter 7b Storage battery 7c Control part 9 Storage battery charging / discharging set 9a Bidirectional DC / DC converter 9b Storage battery 9c Control unit

Claims (2)

A solar battery and a power conditioner that converts the direct current power of the solar battery into alternating current power and outputs the converted power to a load, and a bidirectional DC / DC converter and a storage battery are connected in series to a DC bus line in the power conditioner. A plurality of sets connected in parallel are connected in parallel, and a control unit is provided for switching each set to operate at regular time intervals. Each bidirectional DC / DC converter in each set has a direct current on the DC bus line. The line voltage is DC / DC converted to charge each corresponding storage battery, the charging voltage of each storage battery is DC / DC converted to discharge to the DC bus line, and the control unit The storage battery in each set is switched at regular intervals to charge and discharge ,
Any one of the sets is a set on the master side, the other is a set on the slave side, and the storage battery in the set on the master side is discharged to raise the line voltage to the first command voltage, When the line voltage decreases from the first command voltage to a second command voltage that is lower than the first command voltage due to a decrease in discharge of the storage battery in the master side set, the storage battery in the slave side set is discharged to discharge the line. A photovoltaic power generation system, characterized in that a voltage is controlled to increase to the first command voltage . The storage battery in the master side set is charged to lower the line voltage to a third command voltage, and the line voltage becomes constant from the third command voltage as the charge of the storage battery in the master side set decreases. 2. The system according to claim 1 , wherein, when the voltage increases to a fourth command voltage that is higher, the line voltage is controlled to decrease to the third command voltage by charging a storage battery in the set on the slave side.

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