EP1708070A1

EP1708070A1 - Solar power generating device

Info

Publication number: EP1708070A1
Application number: EP06005204A
Authority: EP
Inventors: Masaki Madenokoji; Tomohide Funagoshi; Yasuhiro Makino
Original assignee: Sanyo Electric Co Ltd
Current assignee: Sanyo Electric Co Ltd
Priority date: 2005-03-30
Filing date: 2006-03-14
Publication date: 2006-10-04
Anticipated expiration: 2026-03-14
Also published as: CN100517159C; TW200643678A; ES2306310T3; TWI400594B; JP2006278858A; JP4794189B2; CN1841254A; KR20060106646A; DE602006001067D1; ATE394727T1; EP1708070B1; KR100993652B1

Abstract

A solar power generating device including a first solar battery (1, 2, 3) for generating DC power, a second solar battery (4, 5) for generating DC power having a voltage lower than the voltage of the first solar battery, a boosting circuit (16A, 16B) for boosting the voltage of the DC power generated by the second solar battery, and an inverter circuit (8) for converting the DC power to AC power and carrying out MPPT (maximum power point tracking) control, a voltage sensor (23) for detecting the voltage of the DC power generated by the first solar battery, a timer (25) for counting a continuing time for which a state where the detection voltage of the voltage sensor is not more than a predetermined voltage is continued from the time when the first and second solar batteries start power generation, and a controller (24) for starting the operation of the boosting circuit when the count time of the timer is equal to a predetermined time.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a solar power generating device for supplying power generated by a solar battery, and more particularly to a solar power generating device for boosting DC power generated by a solar battery, converting the thus-boosted solar power to AC power and supplying the AC power thus achieved.

2. Description of the Related Art

As this type of solar power generation device has been known a solar power generating device in which DC power generated by a solar battery is boosted by a boosting circuit, the DC power thus boosted is converted to AC power by an inverter circuit, and the AC power thus converted is controlled to be regenerated to a commercial power source system by a controller (for example, see JP-A-2003-9398 ).
The solar battery used in the solar power generating device as described above has such a characteristic that the output power of the solar battery increases gradually when the output voltage of the solar battery ranges from Vmax (release voltage) to the maximum power point Pm, and the output power decreases gradually from the maximum power point Pm when the output voltage exceeds the maximum power point Pm and then decreases. Therefore, as the control for taking out the maximum power from the solar battery is known Maximum Power Point Tracking control (hereinafter referred to as "MPPT control") in which the operating point of the solar battery is varied so as to track the maximum power point Pm at all times by an inverter circuit (for example, see JP-A-11-282553 ).
However, according to a solar power generating device disclosed in JP-A-11-282553 , a standard battery in which a predetermined number of solar battery panels are connected to one another in series and rated DC power, that is, standard DC power can be generated is connected to an inverter circuit, and also a fractional solar battery in which solar battery panels whose number is smaller than the predetermined number are connected to one another in series, the DC power generated by these solar battery panels is smaller than the standard DC power and the voltage of the DC power concerned is smaller than the voltage of the standard DC power is connected to the inverter circuit through a boosting circuit. In this solar power generating device, when the sunlight is weak in the morning or evening or under a bad weather, for example, the inverter circuit falls into an intermittent operation state due to lack of the amount of generated electricity, and thus when the boosting circuit starts it operation before the inverter circuit falls into a continuous operation state, the MPPT control of the inverter circuit is adversely affected.
Accordingly, it is required to start the operation of the boosting circuit at the stage that it has been checked that the inverter circuit operates continuously. In this case, the continuous operation of the inverter circuit can be checked by making communications with a control microcomputer of the inverter circuit. Alternatively, the continuous operation of the inverter circuit can be checked by providing voltage and current sensors to the input portion from the standard battery circuit and measuring the power on the basis of the outputs of the voltage and current sensors.
However, in the former case, it is possible to connect to only an inverter circuit adapted to communications, and it is impossible to connect to an inverter circuit which is not adapted to communications. In the latter case, the number of parts is increased, and the cost rises up.

SUMMARY OF THE INVENTION

Therefore, the present invention has an object to provide a solar power generating device that can keep general versatility, avoid rise-up of the cost and prevent MPPT control of an inverter circuit from being adversely affected when a boosting circuit starts its operation.
In order to attain the above object, according to a first aspect of the present invention, a solar power generating device including a first solar battery (1, 2, 3) for generating DC power having a prescribed voltage, a second solar battery (4,5)for generating DC power having a voltage lower than the voltage of the first solar battery (1, 2, 3), a boosting circuit (16A, 16B) for boosting the voltage of the DC power generated by the second solar battery (4, 5), and an inverter circuit (8) that converts the DC power boosted by the boosting circuit (16A, 16B) and the DC power generated by the first solar battery to AC power and also carries out MPPT (maximum power point tracking) control, is characterized by comprising: a voltage sensor (23) for detecting the voltage of the DC power generated by the first solar battery; a timer (25) for counting a continuing time for which a state where the detection voltage of the voltage sensor (23) is not more than a predetermined voltage is continued from the time when the first and second solar batteries start power generation; and a controller (24) for starting the operation of the boosting circuit when the count time of the timer is equal to a predetermined time.
In the solar power generating device, the predetermined voltage is set to a value achieved by subtracting a predetermined voltage from a preset maximum output voltage of the first solar battery.
In the solar power generating device, when the controller (24) judges that the voltage of the DC power (Vs) generated by the first solar battery (1, 2, 3) is higher than the preset maximum output voltage (Vmax), the controller sets the voltage of the DC power to the preset maximum output voltage, and stops the operation of the boosting circuit (16A, 16B).
According to the present invention, it is unnecessary to make the inverter circuit adaptable to the communications, the general versatility can be kept and the rise-up of the cost can be avoided. Furthermore, when the boosting circuit starts to operate, it can be prevented from adversely affecting the MPPT control of the inverter circuit.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 is a diagram showing the overall system of a solar power generating device;
Fig. 2 is a circuit diagram of a connecting device containing a boosting circuit; and
Fig. 3 is a flowchart showing the control when the boosting circuit starts to operate.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

A preferred embodiment according to the present invention will be described hereunder with reference to the accompanying drawings.
Fig. 1 is a systematic diagram showing the overall system of a solar power generating device. In Fig. 1, reference numerals 1 to 3 represent standard solar batteries (firsts solar batteries) . Each solar standard solar battery has a predetermined number, for example, five solar battery panels connected to one another in series, and can generate rated DC power, that is, standard DC power. Reference numerals 4 and 5 represent fractional solar batteries (second solar batteries). Each fractional solar battery has solar battery panels whose number is smaller than the predetermined number, for example, three solar battery panels connected to one another in series. The DC power generated by each fractional solar battery is smaller than the standard DC power and the voltage of the DC power concerned is smaller than the voltage of the standard DC power.
Reference numeral 6 represents a connection device containing a boosting circuit (DC/DC converter) described later which is accommodated in a housing 6A. Reference numeral 7 represents a power conditioner having an inverter circuit 8 connected to the connection device 6, and the power conditioner 7 is connected to a commercial power system. The power conditioner 7 carries out MPPT control (Maximum Power Point Tracking control) of varying the operating point of the solar battery so that the operating point of the solar battery tracks the maximum power point at all times in order to take out the maximum power from the solar battery.
The connection device 6 will be described hereunder in detail with reference to Fig. 2.
Reference numerals 10A, 10B and 10C represent standard input circuits connected to the standard solar batteries 1, 2 and 3 through terminals 11A, 11B and 11C respectively, and the number of the standard input circuits is equal to the number of the solar batteries to be connected. Reference numerals 12A, 12B and 12C represent backflow preventing diodes connected to the output sides of the standard input circuits 10A, 10B and 10C respectively.
Reference numerals 16A and 16B represent boosting circuits (DC/DC converter), and the boosting circuits 16A and 16B are connected to the fractional solar batteries 4 and 5 through terminals 17A and 17B and first and second voltage sensors 18A and 18B. Reference numeral 22 represents a third voltage sensor for detecting the output voltages of the boosting circuits 16A and 16B, and reference numeral 23 represents a fourth voltage sensor for detecting the output voltages of the standard input circuits 10A, 10B and 10C (hereinafter referred to as "standard input voltages"). Here, control power for the boosting circuits 16A and 16B is achieved from the fractional solar batteries 4 and 5, and thus it does not serve as a load on the solar batteries 1, 2 and 3.
Reference numeral 24 represents a controller such as a microcomputer or the like. The controller 24 is equipped with CPU (central processing unit), RAM (random access memory), ROM (read only memory), which are not shown in the figures, and a timer 25. The controller 24 is further equipped with an input voltage detector 26 and an output voltage detector 27. Furthermore, the controller 24 outputs a control signal to the boosting circuits 16A and 16B through a PWM (pulse width modulation) control circuit (pulse width modulation control circuit) 28. The connection device 6 is connected to the power conditioner 7 through an output side terminal 30.
The operation of the solar power generating device, particularly, the operation of the solar power generating device when it starts to operate will be described with reference to the flowchart of Fig. 3.
First, the controller 24 sets the maximum value Vmax of the standard input voltage to zero (reset to zero) (S1), and read in the present standard input voltage Vs detected by the fourth voltage sensor 23 (S2). Subsequently, the controller 24 judges whether the boosting circuits 16A and 16B are stopped (S3) . If they are stopped, the controller 24 reads in the standard input voltage maximum value Vmax which is stored in RAM in advance, and compares the present standard input voltage Vs with the standard input voltage maximum value Vmax (S4).
If the present standard input voltage Vs is not more than the standard input voltage maximum value Vmax, the controller 24 judges whether the present standard input voltage Vs is lower than the value achieved by subtracting a preset boosting circuit start judgment voltage Vn stored in RAM from the standard input voltage maximum value Vmax (S5) . If the present standard input voltage V is lower than the value concerned (hereinafter referred to as "lower state"), the timer 25 starts the time counting. When the lower state concerned is continued for a time longer than a start judging time Tn of the inverter circuit 8 pre-stored in RAM (on the basis of the start judging time Tn, it can be judged that the inverter circuit 8 operates, particularly the inverter circuit 8 operates continuously) and the timer 25 counts the start judging time Tn and then times out (S6), the controller 24 judges that the inverter circuit 8 of the power conditioner 7 operates. Therefore, the controller 24 outputs a starting signal to the boosting circuits 16A, 16B and starts the operation of each of the boosting circuits 16A and 16B (S7).
As described above, on the basis of the standard input voltage Vs, the standard input voltage maximum value Vmax and the boosting circuit start judging voltage Vn, it is judged through the time counting of the timer 25 that the inverter circuit 8 operates continuously, and then each of the boosting circuits 16A and 16B is controlled to start its operation. Therefore, the inverter circuit 8 provided to the power conditioner 7 is not required to be designed so as to be adaptable to communications. Therefore, the general versatility can be kept, and it is unnecessary to newly provide a current sensor, etc. at the standard input circuit 10A, 10B, 10C side. Accordingly, the rise-up of the cost can be avoided, and when the operation of the boosting circuits 16A, 16B is started, it can be avoided from adversely affecting the MPPT control of the inverter circuit 8.
Furthermore, when the standard input voltage maximum value Vmax is read in and compared with the present standard input voltage Vs, the present standard input voltage Vs is kept to the standard input voltage maximum value Vmax (S8) if the controller 24 judges that the present standard input voltage Vs is larger than the standard input voltage maximum value Vmax. In this case, the time counting of the timer 25 is set to zero (reset to zero) (S9) and the operation of the boosting circuit 16A, 16B is stopped (S10) as in the case where the present standard input voltage Vs is not more than the standard input voltage maximum value Vmax, and as a result of the judgment as to whether the present standard input voltage Vs is lower than the value achieved by subtracting the preset boosting circuit start judging voltage Vn stored in RAM from the standard input voltage maximum value Vmax, the present standard input voltage Vs is not lower than the value concerned. In this case, the resetting of the timer 25 is not necessarily required to stop the boosting circuits 16A, 16B, and the timer 25 may be reset with some time lag after the boosting circuits 16A, 16B are stopped to check the judgment as to whether the lower state of Vs is continued for a time longer than Tn. However, it is preferable that the timer 25 is reset at the same time when the operation of the boosting circuits 16A, 16B is stopped.
Furthermore, it is preferable that the stop state of the boosting circuits 16A, 16B is kept from the start time of the time counting until the time-out of the timer when the present standard input voltage Vs is not more than the standard input voltage maximum value Vmax and it is judged whether the present standard input voltage Vs is lower than the value achieved by subtracting the preset boosting circuit start judging voltage Vn stored in RAM from the standard input voltage maximum value Vmax.
After each of the boosting circuits 16A and 16B starts its operation, on the basis of the output voltages of the fractional solar batteries 4 and 5 detected by the first and second voltage sensors 18A and 18B and the output voltages of the boosting circuits 16A and 16B detected by the third voltage sensor 22, the input voltage detector 26 and the voltage detector 27 of the controller 24 are operated, and the controller 24 controls the boosting circuits 16A and 16B through the PWM control circuit 28 so that the output voltage of the boosting circuits 16A, 16B is kept to be equal to the output voltage of the standard input circuits 10A, 10B and 10C, so that power having a predetermined voltage can be supplied from the solar power generating device.
The present invention is not limited to the above embodiment, and various alternatives, corrections and modifications may be made on the basis of the foregoing description with out departing from the subject matter of the present invention.
For example, in the above-described embodiment, the number of the first solar batteries, the number of the second solar batteries, the number of the boosting circuits, and the numbers of the other parts are not limited to those of the above-described embodiment, and they may be properly set to any arbitrary numbers as occasion demands.

Claims

A solar power generating device including a first solar battery (1,2,3) for generating DC power having a prescribed voltage, a second solar battery (4,5)for generating DC power having a voltage lower than the voltage of the first solar battery (1,2,3), a boosting circuit (16A,16B)for boosting the voltage of the DC power generated by the second solar battery (4,5), and an inverter circuit (8) that converts the DC power boosted by the boosting circuit (16A,16B) and the DC power generated by the first solar battery to AC power and also carries out MPPT (maximum power point tracking) control, characterized by comprising:
a voltage sensor (23) for detecting the voltage of the DC power generated by the first solar battery;

a timer (25) for counting a continuing time for which a state where the detection voltage of the voltage sensor (23) is not more than a predetermined voltage is continued from the time when the first and second solar batteries start power generation; and

a controller (24) for starting the operation of the boosting circuit when the count time of the timer is equal to a predetermined time.
The solar power generating device according to claim 1, wherein the predetermined voltage is set to a value achieved by subtracting a predetermined voltage from a preset maximum output voltage of the first solar battery.
The solar power generating device according to claim 3, wherein when the controller (24) judges that the voltage of the DC power (Vs) generated by the first solar battery (1, 2, 3) is higher than the preset maximum output voltage (Vmax), the controller sets the voltage of the DC power to the preset maximum output voltage, and stops the operation of the boosting circuit (16A, 16B).
The solar power generating device according to claim 3, wherein when the controller (24)judges that the voltage of the DC power (Vs) generated by the first solar battery (1, 2, 3) is higher than the preset maximum output voltage (Vmax), the timer (25) resets the counting time to zero.