Battery power supply system

Abstract: A battery power supply system permits inexpensive introduction of a transfer break system to a solar cell generation system and quick release of reverse charge phenomenon. The battery power supply system comprises a solar cell array 1, a DC-AC inverter 2, a brake device 3 for a commercial power system, and wireless communication means 4 as control means for controlling the conduction and break of the break device based on the information derived through wireless communication.

Description: BACKGROUND OF THE INVENTION Field of the Invention The present invention relates to a power supply system, and more particularly to an inexpensive battery power supply system which may quickly release a reverse charge phenomenon. Related Background Art Interest to the global environment has recently been very much enhanced and a great expectation has been paid to a solar cell which is representative of battery power supplies which are inexhaustible and clean energy sources. Today, the cost of a solar cell is less than 1000 Yen/W and it is 1/10 when compared with that of a few years ago. The electricity generated by the solar cell is more expensive than the existing commercial electric power as of 1994 but it is said that the cost of the solar sell will go down to 200 Yen/W in 2000, when the electricity can be generated by the solar cell with a comparable cost to that of the commercial power supply. Since the solar cell is operative only during sun shine, some backup means for the night and rainy day is required when it is to be used in a home. To this end, a system for using the power supply and the solar cell output in linkage through an inverter has been proposed and it has been put into practice. One example of such linkage system is shown in Fig. 9. A DC power generated by a solar cell is converted to an AC power by a DC-AC inverter 2 and it is supplied to a load 5. In the absence of sun shine, the commercial power is supplied to the load 5 through a break device 3, which disconnects the solar generation system from the system line in response to a short circuiting accident in the system or an accident of the commercial system. In most cases, it stops the DC-AC inverter 2. However, in many cases, the power generated by the solar cell is in excess in daytime. The flow of the excess power to the power system is called a "reverse current". By the reverse current, the electricity generated by the solar cell can be used without waste. Such a reverse current type solar cell generation system would be an ideal manner of use of the solar cell. However, a problem of "reverse charge phenomenon" which is inherent to the reverse current system has not yet been solved. The "reverse charge phenomenon" may occur when the quantity of power generated by the solar cell generation system and the power consumption of a load connected thereto are substantially equal. In such a case, even if the electricity of the commercial power supply system is stopped or it stops by some cause, the solar cell generation system cannot detect the stop of the commercial power system and the solar cell generation system continues its independent operation. As a result, lines which are not to be active are charged and a risk occurs in a maintenance operation of the lines. Further, when the commercial power system is reclosed, the commercial power system and the solar cell generation system are not in synchronism and an excess current is generated and the reclosure may fail. When many solar cell generation systems are used in future, the "reverse charge phenomenon" may occur over a wide area. In order to prevent the "reverse charge phenomenon", various methodshave been proposed as shown in Table 1 and tests of those methods have been conducted but no definite solution therefor has been found yet. Method Content Remarks 1. Countermeasure on solar cell generation system (1) Methodic countermeasure a. Adoption of current controlled inverter · Use constant current source and no function to maintain voltage. · Can localize condition of occurence of reverse charge operation. (2) Passive countermeasure a. Phase monitor system · Detect transitional variation of line voltage phase. · Not operable in a complete balanced condition. Very effective for other cases. · Detect abrupt change in phase difference between inverter output voltage and current. b. Harmonics monitor system · Monitor harmonic voltage generated by line load. · Effect is influenced by line load status and is unstable. · Combine with current controlled inverter to primarily detect third harmonic component generated by pole transformer. · Not influenced by load status and is stable, but inverter output voltage should be sine wave. (3) Active countermeasure a. Frequency variation system · Diverse inverter output frequency when system power supply losses. · System for modulating phase of feedback waveform of system voltage and system for biasing frequency of oscillation circuit. Both are normally synchronized with frequency of line. b. Output voltage or current variation system · Continuously and finely vary inverter output voltage or current. · Sine wave variation system and variation system by quasi-random pattern. Effect may be lowered when a number of solar cell generation systems are parallelly operated. c. Output power variation system · System for initially (1) Active power variation · Continuously and finely vary inverter output active power. imparting large AC amplitude variation and system for imparting small (2) Reactive power variation · Continuously and finely vary inverter output reactive power. variation and forming positive feedback loop in reverse charge operation mode to amplify amplitude to detect resulting increase of voltage or frequency variation. In both systems, effect may be lowered when a number of solar cell generation systems are parallelly operated. 2. Countermeasure on line (1) Passive countermeasure a. Line zero-voltage check device · Check line zero-voltage after sub-station breaker has been opened. · Need to parallelly use transfer break. (2) Active countermeasure a. Reactive power injection system (Capacitor throw-in system) · Check line zero-voltage after substation breaker has been opened. If voltage is present, balance of reactive power is destroyed by connecting capacitor. · Very effective as post protection. Note) There is shown an equilibrium range which can be detected by a conventional frequency and voltage monitor function at the time of equilibrium between power generation amount and load amount. On the other hand, in a special high potential power transmission line, a "transfer break system" is used to avoid the reverse charge status. Such a system is known e.g. from the publication "Demonstration Test at Rokko Advanced Energy Experiment Center", published by A. Kitamura et al. in the "Technical Digest of the International PVSEC-5", Kyoto, Japan, 1990, pages 1013 to 1016. In the "transfer break", a break device is actuated by a break signal from a host substation to stop the system. However, in order to apply it to a low potential solar cell generation system, it is necessary to install a communication line to each of the solar cell generation systems, and it is not feasible because of a huge amount of costs. A telephone line may be used as the communication line for the transfer break. In this case, the cost to install the communication line for each system may be significantly reduced. However, as described above, when a number of solar cell generation systems are widely used, the reverse charge phenomenon may possibly occur over a wide area. In such a case, all or most of the solar cell generation systems in the area of the reverse charge phenomenon must be broken. In order to simultaneously break several tens to several thousands solar cell generation systems, a telephone line system which assigns the number to each of the users is not appropriate. To break one hundred systems, for example, telephone calls must be made at least one hundred times. Assuming that one user can be accessed in five seconds, it takes 500 seconds or more than eight minutes. Document EP-A-0 415 228 discloses a power supply system according to the preamble of claim 1. That is, this power supply system comprises a battery power supply and a DC-AC-inverter for converting a DC output of the battery power supply to an AC output to be fed to a load. There are further provided a power supply which supplies an AC power to the load and a break device connected between the further power supply and the load. In addition, a break device control means controls the conduction or break of the break device which can disconnect the battery power supply from the system line. Further, an energy consumption control system is known from US-A-4 360 881 which enables the reduction of energy consumption. If one of a plurality of radio receivers each positioned at a particular location receives a control signal, it disconnects selected appliances. It is an object of the present invention to provide a power supply system in which a reverse charge phenomenon can be prevented. According to the invention this object is accomplished by a power supply system as defined in claim 1. The present invention will be described hereinbelow by way of example and with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 shows a configuration of a battery power supply system of the present invention. Fig. 2 shows a configuration of wireless communication means used in the battery power supply system of the present invention. Fig. 3 shows an embodiment of the wireless communication means used in the battery power supply system of the present invention. Figs. 4A-4E show timing charts of operations of the embodiment. Fig. 5 shows another embodiment of the wireless communication means used in the battery power supply system of the present invention. Fig. 6 shows a system for recovering a power after a predetermined time interval by using time information, used in the battery power supply system of the present invention. Fig. 7 shows a system for recording break operation by using time information and sender identification information, used in the battery power supply system of the present invention. Fig. 8 shows a system combined with the system of the present invention. Fig. 9 shows a configuration of a prior art battery power supply system. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention is now described in detail with reference to the drawings. An embodiment of the battery power supply system of the present invention is shown in Fig. 1. A solar cell array 1 having a plurality of solar cell modules converts sun shine to a DC power. As the solar cell module, a photo-electromotive device such as single crystal silicon, poly-crystalline silicon, amorphous silicon or a combination thereof may be used. A DC-AC inverter 2 converts the DC power from the solar cell array to an AC power and supplies it to a load 5. The DC-AC inverter 2 may be a self-excited type or a separately excited type, and among others, a PWM self-excited inverter which uses IGBT, power MOSFET and power transistor as switching devices is preferable. The inverter includes gate control means for the switching devices to start and stop the inverter. A break device 3 having control means therein mechanically separates a commercial power system and the solar cell generation system. Wireless communication means 4 is connected to the break device 3 and the control means in the DC-AC inverter 2. An embodiment of the wireless communication means 4 is shown in Fig. 2. In Fig. 2, numeral 41 denotes an antenna which may be a bar antenna, a Yagi antenna, a parabola antenna or a rod antenna depending on a frequency and electric field intensity of an electromagnetic wave used. Numeral 42 denotes a tuning circuit for receiving a target frequency. Numeral 43 denotes a demodulation circuit which extracts a signal from the received electromagnetic wave. The frequency for the communication may be any frequency from a long wave to an UHF but a large antenna is principally needed for a frequency shorter than a relatively long short wave. In order to receive a frequency band of shorter than the short wave by a small antenna, it is necessary to transmit as strong electromagnetic wave as that of a broadcast station. When a frequency around a TV broadcast band is used, a TV antenna already installed in a home may be used and there is no need to additionally install the antenna. The signal used for the communication may be a coded signal which uses the on/off of the electromagnetic wave or a coded signal which uses frequency deviation. Alternatively, a signal in an audio frequency band may be used. The break signal preferably includes at least an ID signal for specifying a region and operation command information. The ID information (code number) may be assigned to a region having several hundreds or more users. By assigning one ID information to many users, more solar cell generation systems may be broken by one signal transmission. For example, one ID number code may be assigned throughout Japan and the break signal may be transmitted by using a BS system so that the solar cell generation systems throughout Japan can be simultaneously broken. In actual, the assignment region may be determined while taking the power transmission system into account. Time information or sender identification information may be further added to attain fine operation. For example, as shown in Fig. 6, when the time information is to be utilized, "recovery time" information may be transmitted so that the solar cell generation system can be restarted at any desired time by a timer circuit 56 after the recovery of the power failure. By transmitting "start time" and "stop time", it is possible to activate the system for only a desired time period of the sender. As shown in Fig. 7, by utilizing the sender identification information and the time information, the time of break and the person who broke can be recorded in a memory 58 by a time signal detector 59 and a sender detector 57. Accordingly, it is possible to determine whether a controller (electric power service company) who controls many regions has broken because of the reverse charge or an operator has broken for a work on site, and can grasp the risk condition of the reverse charge in the region. However, if the amount of information is too much, it may cause the reduction of the transmission rate and the transmission reliability. Accordingly, the amount of information to be transmitted should be carefully determined. The wireless communication means need not have transmission means but the object of the present invention can be achieved only by the reception means. (Embodiment 1) The solar cell array 1 comprises 20 amorphous silicon solar cell modules (rated voltage 12 volts, rated power 22 watts) to form 240 V - 440 W solar cell array. The inverter 2 is a self-excited transistor inverter (rated output 50 W, 100 V). The break device 3 is a combination of a sequencer and a transducer which breaks the commercial power system when an AC excess current or excess voltage occurs, as shown in Fig. 1. The wireless communication means 4 is constructed as shown in Fig. 3. The antenna 44 is a middle wave broadcast bar antenna having a receiving frequency of 1630 KHz. The received signal is detected by a diode 45, converted to a pulse signal by a transistor 46, and it is supplied to a pulse counter 47. An output of the pulse counter 47 is compared with an ID number stored in an ID ROM 48 by a code comparator 49. When the output coincides with the ID number, the code comparator 49 produces a control output. The control output is supplied to the inverter 2 and the control unit in the break device 3. Since only the break operation is carried out in the present embodiment, the ID information and the operation command information are shared. The ID number is 5. Thus, when five pulses are inputted, the count "5" in the pulse counter 47 and the value from the ID ROM 48 (the ID number which is equal to 5) coincide so that the code comparator 49 produces the control output to break the power. The load 5 comprises four 100 watts bulbs. The procedures of operation are shown below. (1) First, the solar cell generation system is started while the commercial power system is in an ON state. (2) Then, the commercial power system is turned OFF and the solar cell generation system is operated singly. (3) A break pulse is generated by the transmitter to break the solar cell generation system. Operation charts are shown in Figs. 4A - 4E. The control output is ON when five pulses have been applied and the inverter and the break device are actuated to stop the solar cell generation system. (Embodiment 2) The solar cell array 1, the inverter 2 and the break device 3 are of the same configuration as those of Fig. 1, and the wireless communication means 4 is constructed as shown in Fig. 5. In the present embodiment, a code is transmitted in an audio frequency band by using a modem for a telephone line. The modulation of the electromagnetic wave is done by a frequency modulation at frequency of 140 MHz. In this frequency band, the antenna 50 may be an inexpensive TV broadcast Yagi antenna. The signal received by the antenna 50 is applied to an FM demodulator 51 which demodulates ID signal comprising a code of the audio frequency band. It is then converted to digital data by an audio frequency-digital converter 52, and to parallel data by a serial-parallel converter 53, and it is compared with ID information from the ID ROM 55 by a code comparator 54, which generates a control output when both are coincident. The ID signal is "TEST2" and the operation command signal is shared by the ID information. The operation was checked in the same procedures as those of the embodiment 1. The ID information "WRONG" was then sent in the same procedures but the system was not broken and it operated as designed. (Embodiment 3) The communication frequency is 420 MHz and three solar cell generation systems of the same configuration as that used in the embodiment 2 are parallelly connected to form a solar cell generation system shown in Fig. 8. The antenna is a UHF TV antenna. ID information "A" is assigned to two (solar cell generation systems 1 and 2) of the three solar cell generation systems and ID information "B" is assigned to the remaining one (solar cell generation system 3). The load is adjusted to singly operate the solar cell generation system, and the ID code "A" was transmitted. The two systems 1 and 2 having the coincident ID code stopped the operation, and immediately thereafter, the system 3 having the ID code "B" assigned thereto stopped the operation. This is because an excess voltage occurs in the last system 3 and the break operation is caused by the excess voltage. In this manner, when a portion of the system does not operate, it affects to all of the reverse charge system so that other solar cell generation systems are blocked. Thus, the system is highly safe. In the above embodiments, the solar cell generation system comprises the solar cell array 1, the DC-AC inverter 2, the commercial power system break device 3 and the wireless communication means 4, and the break device 3 is controlled its conduction and break by the wireless communication means 4. It offers the following effects: (1) Since all of the solar cell generation systems in the specified region can be simultaneously broken by one transmission of the break signal, the reverse charge phenomenon occurred over a wide region can be quickly released. (2) Since the transfer break system is used, the solar cell generation system can be broken without failure. (3) Where complex operation command information such as that including time information and sender identification information is used, fine control may be made to the solar cell generation system. (4) Since the power supply service company can centrally control the solar cell generation systems, the solar cell generation systems can be safely installed in the operation sequence of the automatic reclosure. (5) Even if a system which is not sensitive to the break signal is included, it is eventually broken when most systems are broken. Accordingly, the system is safe. (6) Where the frequency of the wireless communication is set to the frequency band of the TV broadcast, there is no need to separately install an antenna and the present solar cell generation system can be easily and inexpensively installed. The value of industrial utilization of the present invention having such excellent effects is very high.

Claims: A power supply system comprising: a battery power supply (1) connected in a system line; a DC-AC inverter (2) for converting a DC output of said battery power supply (1) to an AC output so as to supply the converted AC output to a load (5); a further power supply for supplying an AC power to the load (5) connected in the system line; a break device (3), electrically connected between said further power supply and said load (5), for electrically disconnecting the battery power supply (1) from the system line; and break device control means (3) for controlling the conduction/break of said break device (3); characterized by further comprising wireless communication means (4); said break device control means (3) controlling the conduction/break of said break device (3) in accordance with information derived from said wireless communication means (4). A power supply system according to Claim 1, characterized in that the frequency of said wireless communication means (4) is around a middle wave broadcast band. A power supply system according to Claim 1, characterized in that the frequency of said wireless communication means (4) is around a TV broadcast band. A power supply system according to Claim 1, characterized in that said break device control means (3) includes time information control means for controlling said break device (3) on the basis of time information. A power supply system according to Claim 1, characterized in that said break device control means (3) includes identification information control means for controlling said break device (3) on the basis of time information. A power supply system according to Claim 1, characterized in that said battery power supply (1) comprises solar cell battery power supplying means. A power supply system according to Claim 1, characterized by further comprising means for turning off said DC-AC inverter (2).

Inventors: TAKEHARA NOBUYOSHI, TAKEHARA, NOBUYOSHI, TAKEHARA, NOBUYOSHI, C/O CANON KABUSHIKI KAISHA
Applicants: CANON KK, CANON KABUSHIKI KAISHA
Application year: 1993
Main classification: H02J9
IPC codes: H02J13, H02J5