Abstract: A short circuit within the dynamic voltage restorer (1) is immediately detected by a short circuit detection units (9) which permanently monitors currents and voltages in the voltage source converter (3) and energy storage capacitor bank (2). Upon detection a fast discharge of the capacitor bank (2) including firing of all available semiconductors of the voltage source converter (3) and distributing the resulting current stress as evenly as possible within the voltage source converter (3) is initiated. Instead of letting costly fuses interrupt the high short circuit currents, these currents are detected and evenly distributed within the converter.

Abstract: A power controller for controlling an engine-driven generator includes a high voltage DC bus interconnecting various power modules. In electrical communication with the DC bus are: a bi-directional DC-DC converter constructed to transfer electrical power from the DC bus to a battery to charge the battery, and from the battery to the DC bus; a rectifier constructed to rectify electrical power from the generator and to supply the rectified power to the DC bus; an inverter constructed to convert DC bus electrical power to AC electrical power and to supply the AC power to an output connector; and an AC-DC constructed to convert AC electrical power, supplied via an input connector, to DC bus electrical power. The controller may be employed in a power supply on a mobile vehicle or boat, for example. The power modules of the controller cooperate in various combinations to provide a wide variety of power transfer functions.

Abstract: A method of predicting by non-invasive testing the available energy of a battery at any state of charge by acquiring data of the parameters of internal resistance (IR), open circuit voltage (OCV) and temperature (T), the points of voltage and current of the slope on a positive current ramp of Vup and Iup at the transition from charge to overcharge and on a negative current ramp of Vdn and Idn at the transition from overcharge to charge for a plurality of batteries. Next an algorithm in the form of a linear equation is developed using this data. The available energy of a battery under test is predicted by acquiring from it the numerical data values of these parameters and applying them to the algorithm.

Abstract: A notebook computer in which power is generated by either alternating current power supply or external force. The notebook computer has a computer mainframe, a display, a battery, a first A/D transforming device coupled to the computer mainframe for transforming the alternating current power supply to a first direct current voltage, a power generator having an external force transmission device for generating an induced voltage by external force, and a constant voltage regulator to generate a regulated voltage by regulating the first direct current voltage and the induced voltage. In the notebook computer, external force transmission device further provides a rotatable shaft and a crank disposed on the shaft for applying external force. Further, the power generator can be a DC generator or an AC generator with a second A/D transforming device.

Abstract: A circuit arrangement for supplying electrical energy to a power supply has a fuel cell and an accumulator arrangement. Electrical energy is delivered by the accumulator arrangement during the starting procedure, and is fed into the power supply by the accumulator arrangement via at least one DC/DC converter during starting of the circuit arrangement.

Abstract: A direction and a magnitude of a current flowing between an external alternating current power source (20) and a load (30) are detected by a current transformer (11). A voltage generated to a secondary winding (11B) of the current transformer as a result of detection is superimposed upon a voltage of the alternating current power source (20), and is supplied to the synchronous power source (S). The synchronous power source (S) generates a voltage having an instantaneous value which is the same as that of the voltage supplied thereto, and applies the generated voltage to the load (30) in parallel. Since the voltage applied by the synchronous power source (S) has a value for lowering the current detected by the current transformer (11), there is substantially no current flowing between the alternating current power source (20) and the load (30).

Abstract: A power system stabilization system is provided between power generation equipment significantly fluctuating in output and a power system required to maintain a predetermined voltage. In the power system stabilization system, a voltage detection device and a current detection device detect voltage and current, respectively, of the power system and voltage and current thus detected are used to calculate a level of active power required and that of reactive power required which are referred to to provide charging and discharging from a rechargeable battery to the power system via an A-D converter.

Abstract: A plurality of voltage compensation circuits P1-P3, N1-N3 converts DC voltages accumulated in a capacitor 11 having respectively different charging voltages (which is 2K times of the minimum voltage (K=0, 1, 2, . . . )) into AC voltages. The plurality of voltage compensation circuits are connected to the electric power system in series. When the voltage dip occurs in an electric power system, a desired combination is selected from the plurality of voltage compensation circuits P1-P3, N1-N3. The total sum of the output voltage compensates the voltage dipped. At the normal time, the high speed mechanical short circuit switch by-passes the voltage compensation circuits to reduce apparatus loss.

Abstract: A line driver supplied with a power supply voltage from a power supply uses whole or part of the power supply voltage to generate the output voltage if the input voltage is within a predefined range; loads at least one capacitor with at least one capacitor voltage; and uses whole or part of the at least one capacitor voltage in addition to whole or part of the power supply voltage to generate the output voltage if the input voltage is outside the predefined range.

Abstract: In an energy supply circuit for a motor vehicle on-board electrical system with two voltage supply branches at different voltage levels, the first voltage supply branch can be fed by way of an electric direct voltage converter by the second voltage supply branch and the second voltage supply branch can be fed by a generator. A multi-level controller W3 with three voltage levels is provided whose first in/output is connected with the second voltage supply branch, whose second in/output is connected with the first voltage supply branch and whose third in/output is connected with the energy accumulator B1 assigned to the first voltage supply branch.

Abstract: A power conditioner interfaces a load to a fuel cell 10 that produces a low voltage that varies with the load. A dc-to-ac inverter 16 operates with a low voltage input provided by a dc bus 14. When a positive step load change occurs, a low voltage battery 22 provides power equal to the step change until the fuel cell 10 is able to provide enough power to support the entire load. The power from the battery 22 is supplied to the varying dc bus 14 through a boost converter 12. When very large positive load step changes occur, the battery can feed power to the dc bus through diode D1, rather than through the boost converter. Diode D1 does not need to be used, but its use allows the boost converter to be sized for common load changes rather than for the maximum possible load change (such as might be seen during a faulted output). A buck converter converts the variable voltage on the dc bus 14 to the appropriate float charging voltage of the battery.

Abstract: An uninterruptable power supply system for producing an AC voltage from at least one of a DC power source or an AC power source includes an input terminal configured to receive an AC voltage from an AC power source, and an inverter operative to produce an AC voltage at an output thereof from a DC power source. A ferroresonant transformer circuit includes a transformer having an input winding, a output winding, and a third winding that forms part of a resonant circuit that produces saturation in the output winding when an AC voltage on the input winding exceeds a predetermined amplitude. A transformer input control circuit is coupled to the input terminal and to the inverter output and is operative to couple at least one of the input terminal and the inverter output to the input winding.

Abstract: An energy management system for a motor vehicle has a first voltage supply terminal having a first nominal voltage and a second voltage supply terminal having a second nominal voltage. At least one of the first and second voltage supply terminals has a battery. A universal bi-directional DC-DC converter is coupled to exchange energy between the first and second voltage supply terminals. A third voltage supply terminal is provided for exchanging energy between the DC-DC converter and an external vehicle electrical system or battery charger. The energy exchanged between the first or second voltage supply terminals and the third voltage supply terminal is independent of the voltage and polarity of the external vehicle electrical system or battery charger.

Abstract: To reduce a power loss and elongate the service life of a battery in a power supply circuit for a widely variable power-consuming load. In a device with a dry battery and a rechargeable battery, the rechargeable battery supplies the power while its output voltage is higher than a 3.4V-voltage increased voltage by a voltage increasing circuit. When the output voltage of the rechargeable battery decreases lower than 3.4V, the voltage increasing circuit operates and the dry battery works as a power supply. The power voltage increased by the voltage increasing circuit through a choke coil is fed to respective voltage decreasing circuits. The current is also fed to recharge the rechargeable battery when the output voltage of the choke coil is higher than the output voltage of the rechargeable battery. When the load is increased by the operation of a pickup, the power stored in the rechargeable battery together with the power from the dry battery after increased to 3.

Abstract: Disclosed is an integrated uninterruptable power supply (UPS) for a computer powered by a commercial power supply. The uninterruptable power supply is operative to feed power from a normal power supply to a first load to be operated at a first DC voltage and a second DC voltage that is lower than the first DC voltage. If a characteristic of the normal power supply is deviated from a defined value, the UPS of the present invention will continue feeding power from a battery power supply to the first load. The uninterruptable power supply includes a power supply unit, having an output connected to the first load, for converting a voltage of the normal power supply to the first DC voltage and for outputting the same. The UPS also includes a first voltage converter having an input connected to the battery and an output connected to the first load, for converting an output voltage of the battery to the second DC voltage and for outputting the same.

Abstract: A multiple voltage alternator system for directing power in a vehicle between an alternator, a single battery and loads connected thereto which require power at a higher DC voltage and a lower DC voltage. In one embodiment, first and second bi-directional converters operate synchronously and are coupled together through a transformer having first and second windings. The alternator supplies power directly at one voltage and indirectly through the bi-directional converters at the other voltage when the vehicle engine is running. The battery operates at the opposite voltage from the alternator, preferably at the lower voltage, and directly supplies power at one voltage and indirectly at the other voltage when the alternator is not providing power. In an alternative embodiment the bi-directional converters are coupled through an autotransformer.

Abstract: A hub for a local area network according to one embodiment of the present invention includes a plurality of communication ports connected to each of nodes in the network, through which a signal is transmitted among the nodes, a signal processing circuit having at least the functions of repeating the signal among the nodes and reshaping a waveform thereof, and a power supply circuit for supplying a dc current for driving the signal processing circuit.

Abstract: Power is supplied to a load from either a first power source or a second power source. A transfer switch determines which of the power sources provides the power to the load. A switch control detects a loss in the power provided by a first power source and signals the transfer switch to switch to a second power source. A small energy storage device provides power to the load, during the switch from the first power source to the second power source.

Abstract: A starting/generating system for a small aircraft having engines which can be battery started includes a permanent magnet generator (PMG) which can directly supply frequency-insensitive loads and a power converter for developing regulated DC power from the output of the PMG.

Abstract: Circuitry for extending the sustain time of a DC converter power supply in the event of interruption of AC power.

Abstract: A method for controlling an inverter to improve the ability of the inverter to support power factor corrected (PFC) loads under transient conditions is provided. Changes in the load being provided power by an inverter may cause the RMS output voltage level of the inverter to drop. A PFC load may respond to such drops in the applied voltage level by increasing its current demand. This may cause the inverter current limit to be reached, forcing the inverter to be turned off, and causing the load to be dropped. This problem is avoided by responding to such load changes by immediately increasing the RMS output voltage level of the inverter to a level sufficient to minimize the voltage drop and prevent excessive current demands from the PFC load. The output voltage level of the inverter is then gradually reduced from the high voltage level to prevent the occurrence of oscillations due to interactions between the PFC load and the inverter controller.

Abstract: A battery temperature compensation circuit for a DC/DC converter which is used to charge an auxiliary battery for an electric vehicle and including, among other things, a voltage sensitive resistance, such as a thermistor, coupled to a clamped voltage divider network which generates a resistance vs. temperature characteristic so as to control the DC/DC converter and provide an output voltage for charging the auxiliary battery which matches the voltage vs. temperature profile of the battery.

Abstract: In an electric car drive system having a car drive motor powered by a mounted direct current power supply, a control system including a signal generating means is provided to generate signals which control motor speed. The direct current power supply is composed of a power battery having secondary cells connected to the motor and an energy battery formed by fuel cells connected in parallel to said power battery via an energy battery control switch. The electric car drive system is composed of a charge control means which charges the power battery using the energy battery if the charge of the power battery is below the specified value when said key switch is turned off, and suspends charging if the charge is equal to or greater than the specified value.

Abstract: A device that may be inserted into a power cord or power distribution system prior to a computer, monitor or like devices for correcting the inherently bad power quality of such devices and for eliminating the losses and damage to and within the power distribution system. The device can also provide a unique low cost method of supplying uninterruptable power to said electronic equipment. This uninterruptable power supply (UPS) is continuously active and limits may be set to limit the peak demand drawn from said power distribution system to an amount slightly above the average power consumed by the electronic equipment to which it is connected. The demand may also be controlled in response to directions of an energy management system. The concepts disclosed may also be incorporated directly into the power supply of any electronic device to achieve high power quality and peak demand control.

Abstract: Disclosed is a battery charger that can be connected in series to a power feed line, which lies between an external power source and an electric/electronic device, and that monitors the power consumption state of the electric/electronic device and begins and halts the charging of a battery in consonance with the power consumption state.Since a battery charger according to the present invention can be inserted in series into a power feed line that lies between an AC/DC adaptor and an electric/electronic device, the wiring arrangement is not complicated and a spare battery can be automatically charged. Since the charging is performed only during a period in which power consumption by the electric/electronic device is relatively low, the charging operation does not affect the system operation. As the battery charger does not require AC to DC conversion circuit, it is compact and light and is suitable for use along with a portable device.

Abstract: An electrical power management system for supplying power to a computer peripheral having a relatively high intermittent power demand, such as a packet-switched data radio. A first self-contained rechargeable power supply, outputting power appropriate for the electrical appliance, stores electrical energy and supplies power to the appliance. A second self-contained rechargeable power supply stores electrical energy and supplies electrical power to intermittently recharge the first power supply. The first and the second power supplies can be such self-contained units as single or multicell batteries or capacitors. Preferably, the first power supply is a battery or a capacitor and the second power source is an internal power supply of a portable personal computer.

Abstract: A power supply for regulating energy delivered to a power consuming apparatus operating at low current levels includes a power source comprising at least one battery for generating an output voltage greater than a desired operating level. The power supply further includes a voltage regulator circuit comprising a light emitting diode (LED). The light emitting diode, which is preferably configured as a gallium arsenide diode, operates at a substantially constant voltage within a current range of between 10 to 25 micro amps. As a result, reliable and economical voltage regulating circuits can be constructed with substantially improved performance, as compared to circuits utilizing zener diodes as the active voltage regulating component, at the very low current levels required for such applications as line powered telecommunication devices.

Abstract: In a backup power system capable of deriving power from alternate AC primary and DC backup power sources to provide continuous AC power to an AC load and including an inverter/switch module having DC and AC inputs and an AC output, a maintenance bypass switch for, and method of decoupling the AC primary and DC backup power sources from the backup power module to allow maintenance to be performed thereon.

Abstract: A modular fail-safe uninterruptible lighting system in which lights are identified singly and/or in clusters to form separately controllable entities. Each entity is provided with a modular receiver that is individually controllable to any of six selected states; and one or more modular switched logic controllers is provided to produce signals individually representing the six states. These signals are conducted from the switched logic controllers to the receivers at relatively low control voltages so as to cause the entities to function according to selected states when an outage occurs on the normal lighting system power source.

Abstract: A power generation technique to generate power for use in, for instance, a communication device having a transmitter and a receiver, where communication occurs over atmosphere, or airways (e.g., wireless). The present invention provides a battery-based system that generates power at a high current and high voltage while accommodating the required duty cycles using batteries with sizes that are not prohibitive given the size constraints associated with portable devices in general.

Abstract: A booster type DC-DC conversion circuit and a voltage reduction type DC-DC conversion circuit are connected in series with a battery. When battery voltage is high, the booster type DC-DC conversion circuit does not operate, and the voltage reduction type DC-DC conversion circuit outputs a constant voltage lower than the battery voltage. When the battery voltage drops, the booster type DC-DC conversion circuit operates, and converts the battery voltage to a constant voltage higher than the operation voltage of the voltage reduction type DC-DC conversion circuit. The voltage reduction type DC-DC conversion circuit outputs a constant voltage. The power supply apparatus can continuously output a constant voltage from when the battery voltage is high until it becomes low, and can efficiently utilize the battery capacity.

Abstract: A method for determining gross engine horsepower of an internal combustion engine coupled in driving relationship to an alternating current electric alternator, the alternator supplying electric power to variable loads, comprises measuring the field current and average per phase armature current supplied by the alternator; computing the magnitude of electric power supplied by the alternator from the measured values of field current and armature phase current; determining the engine efficiency at the computed magnitude of electric power; and converting the computed electric power to engine horsepower at the determined efficiency.

Abstract: Disclosed is a battery disconnection detecting apparatus which can accurately detect whether or not the interruption of electric power supply from a battery to a storage device is continuously caused by the disconnection of an electric power line, or the like. The voltage of a battery is continuously supplied to a backup RAM through a second electric power line. An EEP-ROM is provided which can hold the stored data even when electric power supply is interrupted. When a power switch is turned ON, and an ECU is operative, a CPU detects the interruption of the electric power supply through the second electric power line based on the state of a standby bit. After detecting the interruption of the electric power supply, the CPU makes the count of the counter in the EEP-ROM count up. When the count reaches or exceeds the preset number n, i.e.

Abstract: The system comprises a central module supplying a distribution network, for example formed by a bus, with permanent DC power. Terminal modules, located near the loads, convert the DC power distributed by the distribution network into DC or AC electrical power adapted to the requirements of each load. A communication bus enables data communication between the various modules.

Abstract: A fail safe power supply system specially adapted for supplying power to devices such as lights. A battery is provided to supply power to the devices, and during normal operation, charge on the battery is maintained within selected levels by a charging control system that is connected to a source of commercial power. During a commercial power outage, the battery continues to supply normal power to the devices for a prolonged period of time, usually until commercial power is restored, thus obviating the necessity for a separate backup power source.

Abstract: In a MOS integrated circuit is provided a first differential amplifying circuit for receiving complementary sets of input data at the gates of its two p-channel MOS transistors and for transmitting complementary sets of internal data. There is also provided a second differential amplifying circuit for receiving the complementary sets of internal data at the gates of its two n-channel MOS transistors and for transmitting complementary sets of output data. This realizes high-speed data transmission in which data transmission speed is independent of the generation of a clock signal. By preventing the flow of current from a power supply terminal to a ground terminal, a differential transmission circuit which consumes reduced current can be obtained.

Abstract: A power converter provides an AC output selectively using power from either a battery source or an alternator. The power converter includes a static converter (100) that is connected to receive DC from a battery (30), converting the DC to a relatively high frequency AC using a pulse width modulator (200). The high frequency AC is transformed to a higher voltage AC that is rectified and is used to charge a capacitor bank (104). The DC on the capacitor bank is converted to 120 (or 240) volts AC at 50/60 Hz by an inverter comprising an inverter (106) to provide power for an AC load. As the requirement for power by the AC load increases above a predefined level, a dynamic converter (24a) is energized to supply power to charge the capacitor bank in place of the static converter. The dynamic converter draws its power from a three-phase alternator (12) that includes three-phase AC output terminals connected to three-phase primary windings (140) of a transformer having a plurality of secondary windings.

Abstract: An ac electric drive system includes a bidirectional power semiconductor interface between a battery, or an auxiliary energy storage device, and a power inverter for boosting an input dc voltage and for decoupling the dc link voltage from the input dc voltage such that the dc link voltage is substantially independent of the input dc voltage and the parameters of the battery or energy storage device. The input dc voltage is controlled to maximize efficiency along predetermined torque envelopes.

Abstract: A standby power supply system is provided for supplying normal AC power to a critical load from an AC power source during normal operating conditions, and for supplying emergency AC power to the load during failure of the AC power source. During normal operation, the standby power supply system actively neutralizes undesirable harmonic components in the input current drawn by the load. The standby power supply system includes a power conversion device having a DC side coupled to a back-up power source and an AC side in parallel with the load and the AC source. A harmonic distortion sensor senses a harmonic distortion current component of a load current drawn by the load during normal operating conditions. A controller is responsive to the harmonic distortion sensor for causing the power conversion device to produce a harmonics neutralizing current to substantially neutralize the harmonic distortion current component produced by the load.

Abstract: A standby power supply system is provided for supplying normal AC power to a critical load from an AC power source during normal operating conditions, and for supplying emergency AC power to the load during failure of the AC power source. During normal operation, the standby power supply system actively neutralizes undesirable harmonic components in the input current drawn by the load. The standby power supply system includes a power conversion device having a DC side coupled to a back-up power source and an AC side in parallel with the load and the AC source. A harmonic distortion sensor senses a harmonic distortion current component of a load current drawn by the load during normal operating conditions. A controller is responsive to the harmonic distortion sensor for causing the power conversion device to produce a harmonics neutralizing current to substantially neutralize the harmonic distortion current component produced by the load.

Abstract: A power conservation circuit for a battery-powered voltage inverter is capable of conserving battery power. In a first embodiment, the circuit includes a switch, connected between the input terminals and the output terminals, for switching the circuit between an ON state wherein AC voltage is connected to the output terminals, and an OFF state wherein the inverter is disconnected from the battery. A first sensor senses in the ON state the absence of a load connected to the output terminals and switches the circuit from the ON state to the OFF state. A second sensor senses in the OFF state the presence of a load connected to the output terminals and switches the circuit from the OFF state to the ON state. The switch includes a relay having a pole terminal connected to the output terminals, a first contact terminal connected to the AC output of the inverter, and a second contact terminal connected to battery voltage.

Abstract: A power supply for a computer system manager, wherein the power supply has its own secondary power source operable when primary input power to the system manager no longer meets preset threshold values. The power supply monitors the primary input power as well as the secondary power source. Further, the power supply includes a regulating circuit which maintains the power emitted by the secondary power source to within a very narrowly defined voltage range. The power supply regulates the secondary power source while the secondary power source is being used by the computer system manager and while the primary input power is being used by the computer system manager. The power supply switches among power modes to conserve secondary power while the secondary power source provides power. The power supply includes a charger for the secondary power source.

Abstract: An auxiliary power supply system includes an internal combustion engine driving an alternator the output of which is rectified and supplied to DC bus lines across which a storage battery is connected. The DC bus lines may supply a consuming device such as an uninterruptible power supply or telecommunications system. The voltage across the bus lines is sensed and when the voltage drops below a selected value, indicating that the consuming devices is drawing power from the battery beyond a desired limit, the engine is turned on for a period of time to warm it up, during which the power from the generator is not supplied to the DC bus lines. Thereafter, the generator supplies power to the DC bus lines to supply the consuming device and partially recharge the battery until the consuming device is no longer drawing power, after which the engine is shut off.

Abstract: A 3-phase converter apparatus, in which a 3-phase A.C. power supply and a 3-phase converter operate in parallel on a common load BUS so as to share the load power, has an output voltage command generating device for generating an instantaneous command of the output voltage from the converter, and instantaneous voltage control device for controlling the converter so as to reduce the deviation of the instantaneous value of the output voltage of the converter from the instantaneous command generated by the output voltage command generating device. The converter includes at least one semiconductor switch for effecting a plurality of switching cycles in a half cycle of the A.C. power, so that the control of the phase of the output voltage of the converter with respect to the A.C. power supply is started at any moment.

Abstract: A standby power supply system is provided for supplying normal AC power to a critical load from an AC power source during normal operating conditions, and for supplying emergency AC power to the load during failure of the AC power source. During normal operation, the standby power supply system actively neutralizes undesirable harmonic components in the input current drawn by the load. The standby power supply system includes a power conversion device having a DC side coupled to a back-up power source and an AC side in parallel with the load and the AC source. A harmonic distortion sensor senses a harmonic distortion current component of a load current drawn by the load during normal operating conditions. A controller is responsive to the harmonic distortion sensor for causing the power conversion device to produce a harmonics neutralizing current to substantially neutralize the harmonic distortion current component produced by the load.

Abstract: An electronic switching power supply (10) is adapted to provide uninterrupted power during transient glitches in a voltage input received from a primary power source. The power supply (10) comprises a transformer (12) having two primary windings (WP1, WP2). Current flow through the first primary (WP1) is enabled during normal operation while current flow through the second primary (WP2) is disabled. When a transient glitch in the voltage input is sensed, current flow from a storage capacitor (126) through the second primary (WP2) is enabled.

Abstract: A single transformer converter which may switchably disconnect all of its converter outputs, or alternatively just some of the converter outputs. In some electronic systems this would allow the turning-off of some units, such as printers, while leaving on other units, such as a CPU or a twenty-four hour clock. Further, an uninterruptible output is provided by the converter to maintain applications and operating systems software stored a CMOS RAM even in the event of a power outage.

Abstract: A back-up battery system for a switching equipment load in a telephone central office wherein the back-up battery system includes one or more rechargeable batteries having cells floated at a given float voltage and of a number such that when the batteries are switched in circuit across the load, the voltage of the batteries exceeds a minimum load voltage for a preselected period, and further being of a number such that the float voltage of the batteries exceeds a maximum load voltage.

Abstract: An electric automobile driving apparatus installed in an electric automobile for driving the same. The driving force of the electric automobile is generated by a main battery as the rotating force of a motor. The motor is an AC motor and driven by an AC current output from the main battery and converted into a DC voltage by an inverter. Electric appliances installed in the automobile are driven by a DC voltage having a different value which is output from an auxiliary battery. The auxiliary battery is charged with the DC voltage obtained by rectifying the output from a secondary coil which is disposed in close proximity to a primary coil of the motor.

Abstract: A power supply is energized by an external power source and a battery, and supplies electric power to a load. The power supply includes a battery voltage detector and a current detector for detecting a discharge current from the battery. The remaining capacity of the battery is detected in accordance with a change in the battery voltage when the external power source is free of power failure. The battery voltage change is defined as the difference between an initial voltage of the battery and an active voltage of the battery obtained when the battery is discharged by the detected discharge current for a predetermined period of time.