JP3002934B2 - Solar cell power system control circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a control circuit for controlling charging and discharging of a storage battery in a power supply system using a solar cell.

[0002]

2. Description of the Related Art A typical conventional solar cell power supply system comprises a solar cell 1, a storage battery 2 and a charge / discharge control circuit 3, as shown in FIG. Charge / discharge control circuit 3
Is connected between the solar cell 1 and the storage battery 2 and the load 4, and is connected between the backflow prevention diode 5, the switch 6 inserted on the anode side thereof, and the cathode and the load 4 It comprises a switch 7 and a control unit 8 that detects the charging voltage V _batt of the storage battery 2 and controls ON / OFF of the switches (relay contacts) 6 and 7.

When the detected charging voltage V _batt is within a predetermined range, the control unit 8 turns on both switches 6 and 7 to charge the storage battery 2 with the current generated by the solar cell 1 and load the storage battery 2. 4 is supplied. Detected charging voltage V
_{When batt} reaches the overcharge protection voltage which is the upper limit of the predetermined range, the control unit 8 turns off the switch 6 to disconnect the solar cell 1 from the storage battery 2 and protect the storage battery 2 from overcharge.
Power is continuously supplied to the load 4 from the storage battery 2. When the detected charging voltage V _batt reaches the overdischarge protection voltage, which is the lower limit of the predetermined range, as a result of discharging the storage battery 2 beyond a certain level, the control unit 8 turns off the switch 7 and turns off the storage battery 2.
Is disconnected from the load 4 to protect the storage battery 2 from overdischarge. The storage battery 2 is continuously charged from the solar cell 1.

In the conventional solar cell power supply system control circuit, the maximum power of the solar cell 1 is stored in the storage battery 2.
Is not considered, and the solar cell 1 is directly connected to the storage battery 2, so that the charging voltage V _batt of the storage battery 2 becomes the operating point of the solar cell 1 as it is, and the solar cell 1 The maximum power of the storage battery 2 cannot be charged.

There has also been proposed a configuration in which a storage battery is charged with the maximum power of a solar cell (Japanese Patent Laid-Open No. 62-15 / 1987).
No. 4122). This involves inserting a DC / DC converter between a solar cell, a storage battery, and a load, connecting a maximum power point tracking control unit to the solar cell, and using a DC / DC converter based on the output voltage and output current of the solar cell. By adjusting the output voltage of the storage battery, the storage battery is charged with the maximum power of the solar battery. Also in the case of this conventional example, a full charge detection control unit is provided, and when the charge voltage of the storage battery reaches the overcharge protection voltage, the switch is turned off by O.
The FF is used to separate the solar cell from the storage battery to prevent overcharge of the storage battery.

[0006]

In both the conventional example of FIG. 7 and the conventional example of the above-mentioned publication, the switch is turned off at the stage where the overcharge protection voltage is detected, and the solar battery is removed from the storage battery. It is only for disconnecting, regardless of the change in the difference between the charge voltage of the storage battery and the overcharge protection voltage, the battery is charged with the same charging current until the overcharge protection voltage is reached, and when the overcharge protection voltage is reached It suddenly shuts off charging. Therefore, the charging control is very rough, and depending on the charging voltage according to the amount of received light, the storage battery may be overcharged before the switch is turned off.

The present invention has been made in view of such circumstances, and has as its object to enable a storage battery to be charged with the maximum power of a solar cell and to increase the accuracy of a protection function against overcharge. I do.

[0008]

A solar cell power supply system control circuit according to the present invention controls a solar cell power supply system for charging an output of a solar cell to a storage battery via a power control circuit and supplying power from the storage battery to a load. A circuit,
The power control circuit includes a DC /
ON / OFF of DC converter and the switching element
A control unit that controls the duty ratio of the switching element so as to track the maximum output point of the solar cell based on the operating voltage of the solar cell and the operating voltage of the storage battery. When the operating voltage of the solar cell approaches the full charge voltage value, the duty ratio is fixed at a constant value, and the operating point of the solar cell is shifted from the maximum output point to the open voltage side so that the storage battery operating voltage does not exceed the full charge voltage value. It is characterized by that.

[0009]

[Function] The DC / DC is controlled so as to track the maximum output point of the solar cell.
Since the duty ratio of the switching element of the DC converter is determined, the storage battery can be charged with the maximum power of the solar cell, and when the storage battery approaches a fully charged state, the operating point of the solar cell is shifted from the maximum output point to a lower side. Since the control is performed so that the operating voltage of the storage battery does not exceed the full charge voltage value, the accuracy of the protection function against overcharge of the storage battery can be improved.

[0010]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram showing an embodiment of a solar cell power supply system control circuit according to the present invention.

FIG. 1 is a block diagram showing an electrical configuration of a solar cell power supply system. In FIG. 1, 11 is a solar cell, 12 is a power control circuit, 13 is a storage battery, and 14 is a load. The output of the solar cell 11 supplies power to the load 14 while charging the storage battery 13 via the power control circuit 12. The load 14 includes a DC-driven device 15 that is directly operated with DC power from the storage battery 13, an inverter 16 that converts DC into AC, and an inverter 1.
6 is constituted by at least one of the AC drive type devices 17 operated by the AC power from the AC power supply 6.

When the operating voltage V _batt of the storage battery 13 is smaller than a preset full charge voltage value Va, the power control circuit 12 performs control so that the operating voltage of the solar cell 11 becomes the maximum output. Have been. When charging of the storage battery 13 progresses and the operating voltage V _batt of the storage battery 13 approaches the full charge voltage value Va, the power control circuit 12 sets the operating voltage of the solar cell 11 to a lower side (open voltage side) than the maximum output point. The storage battery 13 is brought into a fully charged state while _{reducing the} charging power so that the operating voltage V _batt of the storage battery 13 does not exceed the full charge voltage value Va.

FIG. 2 shows current-voltage characteristics of the solar cell 11 and the storage battery 13, and the vertical axis represents current (unit:
A) is plotted, and the voltage (unit: V) is plotted on the horizontal axis. In the figure, the solid line indicates the current-voltage characteristic of the solar cell 11, the one-dot chain line and the two-dot chain line indicate the charging current-voltage characteristic of the storage battery 13, and the two-dot chain line indicates that the storage battery 13 is in a state close to a fully charged state The characteristics of The dotted line shows the equal power characteristic curve. A _{1 to} a ₄ represent operating points of the solar cell 11, and b _{1 to} b ₃ and c _{1 to} c ₄ represent operating points of the storage battery 13. In particular, the operating points a _{1 to} a ₃
At the point where the output power of the solar cell 11 is maximized on each current-voltage characteristic curve of the solar cell 11 when the received solar radiation intensities E _{1 to} E ₃ (E ₁ > E ₂ > E ₃ ) are parameters. is there.

The operation of controlling the charging of the storage battery 13 from the solar cell 11 by the power control circuit 12 will be described. When the charging current-voltage characteristic of the storage battery 13 is represented by a dashed line, the power control circuit 12 sets the operating point b at which the operating points a ₁ , a ₂ , and a ₃ of the solar cell 11 intersect with the equal power characteristic curves. _{At 1} , b ₂ and b ₃ , the solar battery 11 charges the storage battery 13. Which of the operating points b ₁ , b ₂ and b ₃ is the received solar radiation intensity E ₁ , E ₁ of the solar cell 11
According to the _2, E _3.

When the storage battery 13 is close to a fully charged state and the charging current-voltage characteristic of the storage battery 13 is represented by a two-dot chain line, the power control circuit 12 operates at the operating points a ₁ , At the operating points c ₁ , c ₂ , and c ₃ that intersect with the equal power characteristic curves of a ₂ and a ₃ ,
To it will be charged, will be exceeding the full charge voltage value Va of the operating point c ₁ in the storage battery 13 in the light receiving solar radiation intensity E _1, there is a possibility that the storage battery 13 is overcharged.

In order to prevent the charging voltage for the storage battery 13 from exceeding the full charging voltage value Va, the power control circuit 12 sets the operating point a ₁ of the solar cell 11 to a lower power (open voltage side). shifted to the point a _4, a storage battery 13
Than it is controlled so as to charge the c ₄ that the charge voltage does not exceed the full charge voltage value Va to. Either a point a ₄ to which power levels are calculated back to determined from the operating point c _4.

The details of the power control circuit 12 that controls charging in the above-described solar cell power supply system will be described below.
FIG. 3 shows a specific example of the circuit configuration of the power control circuit 12.

The power control circuit 12 includes a DC / DC converter 20, a backflow prevention diode 29, a switch 30, and a control unit 3.
It consists of 1. The DC / DC converter 20 is configured as follows. That is, a series circuit of a choke coil 21 and a smoothing capacitor 22 is connected between output terminals of the solar cell 11, and a series circuit of a primary winding of a high-frequency transformer 23 and a switching element 24 is connected in parallel between both ends of the smoothing capacitor 22. Have been. The switching element 24 is composed of an N-channel type power MOS-FET.
A rectifier diode 25 and a flywheel diode 26 are connected to the secondary winding of the high-frequency transformer 23 in a state of common cathode connection, and a series circuit of a choke coil 27 and a smoothing capacitor 28 is provided between the cathode and the anode of the flywheel diode 26. Connected, choke coil 2
A storage battery 13 is connected to a connection point between the capacitor 7 and the smoothing capacitor 28 via a backflow prevention diode 29, and a load 14 is connected via a switch (relay contact) 30. The control unit 31 detects the operating voltage V _PV of the solar cell 11 and the operating voltage V _batt of the storage battery 13, and _turns on the switching element 24 including the duty ratio based on the two operating voltages V _PV and V _batt. / OFF control. The choke coil 21 and the smoothing capacitor 22 prevent the output current of the solar cell 11 from becoming intermittent, and suppress a sudden change in the operating point of the solar cell 11. The backflow prevention diode 29 prevents backflow from the storage battery 13 to the smoothing capacitor 28 side.

When the switching element 24 of the DC / DC converter 20 is switched by the control unit 31, power can be supplied to the storage battery 13. That is, when the switching element 24 is turned on, the output voltage of the solar cell 11 is applied to the primary winding of the high-frequency transformer 23,
A voltage is induced in the secondary winding. The induced voltage biases the rectifier diode 25 in the forward direction, and the rectifier diode 2
5, a current flows through the path of the choke coil 27 and the smoothing capacitor 28, and charges the smoothing capacitor 28. And
The storage battery 13 is charged by the voltage across the smoothing capacitor 28 and power is supplied to the load 14.

Next, when the switching element 24 is inverted to the OFF state, transmission of power from the primary side of the high-frequency transformer 23 is stopped, and back electromotive force is generated in the choke coil 27, and the choke coil 27, the smoothing capacitor 28, A current flows through the flywheel diode 26.

In the power control circuit 12, the average current I _IN flowing on the primary side of the high frequency transformer 23 can be expressed by the following equation (1).

I _IN = V _PV · T _ON ² / {2 · (N ₂ / N ₁ ) ² · L · T _S } (1) where, in the equation (1), V _PV : solar cell 11 Operating voltage T _ON : ON time of switching element 24 N ₁ : number of primary windings of high-frequency transformer 23 N ₂ : number of secondary windings of high-frequency transformer 23 L: inductance of choke coil 27 T _S : switching element 24 The switching period. From the equation (1), the input resistance R _IN of the power control circuit 12 is as shown in the following equation (2).

[0023] _{R IN = V PV / I IN} = 2 · (N 2 / N 1) 2 · L · T S / T ON 2 ‥‥‥‥‥‥‥‥ (2) duty ratio of the input resistor R _IN When expressed using D = T _ON / T _S , R _IN = 2 · (N ₂ / N ₁ ) ² · L · / (T _S / D ² ) ‥‥‥‥‥‥ (3)

The operating point of the solar cell 11 is determined by the input resistance R _IN of the power control circuit 12 represented by the equation (2).
Since the input resistance R _IN is adjusted by the duty ratio D of the switching element 24 according to the equation (3), the operating point of the solar cell 11 can be controlled by adjusting the duty ratio D of the switching element 24. That is, the operating voltage V _PV of the solar cell 11 can be changed by adjusting the duty ratio D, and the output of the power control circuit 12 can be adjusted. Thereby, the maximum output point of the solar cell 11 can be tracked according to the equal power characteristic curve shown in FIG. According to the equation (3), as the duty ratio D increases, the input resistance R _IN also increases, and the current-voltage characteristics of the storage battery 13 approach from the one-dot chain line to the two-dot chain line.
Until the operating voltage V _batt of the storage battery 13 exceeds the full charge voltage value Va, the storage battery 13 follows the equal power characteristic curve indicated by the dotted line.
Operating point moves. FIG. 4 shows the switching element 2
4 shows the relationship between the duty ratio D of 4 and the output power of the power control circuit 12.

The charging voltage of the storage battery 13 is a full charging voltage value Va.
, The tracking of the maximum output point of the solar cell 11 is released, and the operating voltage V _batt of the storage battery 13 is set to be constant at the full charge voltage value Va as set in the following equation (4).

Va = V _batt = (N ₂ / N ₁ ) · D · V _PV ‥‥‥‥‥‥‥‥‥‥‥ (4) By transforming the equation (4), the duty ratio D is obtained. D = Va · N ₁ / (V _PV · N ₂ ) ‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥ (5) That is, the duty ratio D of the switching element 24 is not gradually increased, and the solar cell 11
Is fixed at a value uniquely determined by the operating voltage V _PV of Instead of the equal power characteristic curve whose operating point has been moved until then, an equal power characteristic curve in a direction in which the current value at the intersection with the straight line passing V = Va gradually decreases is used.
For example it is the shifts to be closer gradually to equal power characteristic curve from equal power characteristic curve operating point a ₁ is riding riding operating point a _4. Thus, when the operating voltage V _batt of the storage battery 13 reaches the full charge voltage value Va, the storage battery 1
3, the charging current is gradually reduced. Therefore, the storage battery 13 is not overcharged, and the accuracy of the protection function against overcharge can be improved.

The control section 31 is composed of, for example, a circuit as shown in FIG. 32 is an oscillation circuit, 33 is a toggle flip-flop circuit, 34 is a sawtooth wave generation circuit, 35 is a microcomputer, 36 is a D / A converter, 37 is a set value of a duty ratio D, 38 is a comparison circuit, and 39 is an AND gate. , 40 are switching element drive circuits. The microcomputer 35 has a built-in A / D converter, and has an operating voltage V _PV of the solar cell 11 and an operating voltage V _{batt of the} storage battery 13.
, The output power of the solar cell 11 is obtained according to the equation (3) or (5) based on the equal power characteristic curve of FIG. 2, and the duty ratio D (digital value) is determined according to FIG. Is converted into a duty ratio D of an analog value by the D / A converter 36, and is input to the non-inverting input terminal (+) of the comparison circuit 38. The sawtooth wave signal from the sawtooth wave generation circuit 34 is input to the inverting input terminal (-) of the comparison circuit 38, and the comparison circuit 38 outputs a rectangular wave signal having a duty ratio D to the AND gate 39 to drive the switching element. The switching of the switching element 24 is controlled at a duty ratio D via a circuit 40.

The control unit 31 also turns off the switch 30 when the operating voltage V _batt of the storage battery 13 reaches a preset end-of-discharge voltage Vb as a result of the storage battery 13 being discharged beyond a certain level. The discharge from the load to the load 14 is stopped. Then, when the storage battery 13 is charged by the solar cell 11 and reaches a preset power supply start voltage Vc to the load 14, the switch 30 is turned on to turn on the storage battery 1
The power supply from 3 to the load 14 is restarted. Note that Vb <
Vc <Va.

FIG. 6 shows the control unit 3 in the power control circuit 12.
3 is a flowchart illustrating the operation of FIG. Step S
In step S1, the duty ratio D is set to zero. In step S2, it is determined whether the operating voltage V _batt of the storage battery 13 has reached the full charge voltage value Va. If not, the process proceeds to step S7 via step S3. After the duty ratio D is incremented by ΔD for one step, the process returns to step S2. If the determination in step S2 is negative, the process proceeds to step S3 to determine whether the operating voltage V _batt is higher than the power supply start voltage Vc. If larger, step S
In step 5, the switch 30 is turned on to start power supply from the storage battery 13 to the load 14. If not, the process proceeds to step S4 to determine whether the operating voltage V _batt has reached the discharge end voltage Vb. When the discharge end voltage Vb is reached, the process proceeds to step S6, where the switch 30 is turned off, and the power supply from the storage battery 13 to the load 14 is stopped.

When the operating voltage V _{batt of the} storage battery 13 is Vb <V
_{When batt} <Vc, the switch 30 has not been turned on yet, and the charging of the storage battery 13 from the solar cell 11 is advanced while the duty ratio D is rapidly increased by repeatedly executing step S7. Eventually, the operating voltage V _{batt of the} storage battery 13
Reaches the power supply start voltage Vc, the process proceeds from step S3 to step S5, where the switch 30 is turned on, and the power supply from the storage battery 13 to the load 14 is started. Subsequently, the duty ratio D is increased to charge the storage battery 13 and supply power to the load 14. Until the operating voltage V _batt of the storage battery 13 reaches the full charge voltage value Va, the increase of the duty ratio D is continued.
Can be charged at the maximum output point. After the operating voltage V _batt of the storage battery 13 reaches the full charge voltage value Va, if the duty ratio D is increased, it may exceed the full charge voltage value Va and become overcharged. Then, the process proceeds to step S8 to fix the duty ratio D constant.

[0031]

As described above, according to the present invention, the storage battery can always be charged with the maximum power of the solar cell until the operation voltage of the storage battery reaches the full charge voltage value. When the value approaches the full charge voltage value, the operating point of the solar cell is shifted from the maximum output point to a lower side to narrow the charging current, so that the accuracy of the protection function against overcharging of the storage battery can be improved.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an electrical configuration of a solar cell power supply system according to one embodiment of the present invention.

FIG. 2 shows current of a solar cell and a storage battery in an example.
It is a voltage characteristic figure.

FIG. 3 is a specific circuit configuration diagram of a power control circuit in the embodiment.

FIG. 4 is a characteristic diagram illustrating a relationship between a duty ratio of a switching element and an output power of a power control circuit in the example.

FIG. 5 is a specific circuit configuration diagram of a control unit in the embodiment.

FIG. 6 is a flowchart for explaining the operation of the embodiment.

FIG. 7 is a block circuit diagram schematically showing a solar cell power supply system according to a conventional example.

[Explanation of symbols]

 11 solar cell 12 power control circuit 13 storage battery 14 load 20 DC / DC converter 23 high-frequency transformer 24 switching element (power MOS-FET) 27 choke coil 28 Smoothing capacitor 29 Backflow prevention diode 30 Switch (relay contact) 31 Control unit

──────────────────────────────────────────────────続 き Continuation of front page (72) Inventor Hiroshi Nakata 22-22 Nagaikecho, Abeno-ku, Osaka-shi, Osaka Inside Sharp Corporation (56) References JP-A-62-154121 (JP, A) JP-A-3-3 18911 (JP, A) JP-A-63-133214 (JP, A) JP-A-1-224817 (JP, A) Japanese Utility Model Laid-Open No. 62-165,731 (JP, U) (58) Fields investigated (Int. ⁷ , DB name) G05F 1/67

Claims (1)

(57) [Claims] 1. A solar battery power supply system control circuit for charging an output of a solar battery to a storage battery via a power control circuit and supplying power from the storage battery to a load, wherein the power control circuit includes a switching element. It comprises a DC / DC converter and a control unit for controlling ON / OFF of the switching element. The control unit tracks the maximum output point of the solar cell based on the operating voltage of the solar cell and the operating voltage of the storage battery. The duty ratio of the switching element is determined, and when the operating voltage of the storage battery approaches the full charge voltage value, the duty ratio is fixed at a constant value so that the storage battery operating voltage does not exceed the full charge voltage value. A solar cell power supply system control circuit, wherein an operating point is shifted from a maximum output point to an open voltage side.