GB2224403A - No-break power supply - Google Patents

Abstract

A load L is normally supplied from a main source P via a rectifier Rec 1, overcurrent breaker NFB2 and inverter IV. Failure of the main source P is sensed by an undervoltage relay RY1 causing start-up of an engine-generator E-G providing an emergency supply via a rectifier Rec2, diode D1 and overcurrent breaker NFB1. A battery B is charged via a current limiter LC from whichever of the main source P and generator E-G is in operation. If during normal supply from source P, a malfunction in overcurrent breaker NFB2 or rectifier Rec1 occurs, the inverter IV is energised from the battery B. An undervoltage relay RY2 starts the generator E-G if the battery voltage falls below a predetermined level. <IMAGE>

Description

"A NO-BREAK POWER SUPPLY SYSTEM" The present invention relates to a no-break power supply system for supplying power to a load in the event of an interruption of normal service power and, more particularly, to an apparatus for protecting a battery provided in a power supply system when components provided therein break down.

A conventional no-break power supply system is shown in Figure 1. The system comprises an enginegenerator E-G for supplying power to a load L such as a computer or the like in the event of long term service interruption, an undervoltage power supply source P, an engine operating means or block PC arranged to receive the output of a relay RY for automatically starting and driving the engine E, a switch S having contacts a and b for selecting the commercial power supply or the engine generator, an overcurrent circuit breaker NFB, a rectifier Rec which also serves as a floating charge device, a battery B connected to the rectifier Rec, and an inverter IV connected to the rectifier Rec and the battery B and having an automatic voltage adjusting facility.

In the system thus constructed, when the components thereof are operating correctly, the system functions normally without any trouble. When the system fails to operate due to malfunction or failure of the rectifier Rec or trip of the breaker NFB, the battery B discharges continuously until the voltage reaches the final discharge voltage, whereupon the system is automatically stopped and operated by an automatic stop circuit (not shown). Under this condition, it takes a long time for the battery B to become restored to the charged condition, while the pole substance separation occurs often so that life time of the battery is decreased. Under this condition, moreover, the sedimentation amount of the pole substance is increased so that sulfation is induced resulting in exchange of the battery and thus a large expense.

Generally, a floating charge device for a battery must be operated in such a manner that it does not affect the battery itself, thereby increasing the life time thereof and utilising the battery with stable conditions. To this end, constant voltage charging or constant current charging is usually utilised.

In operation, when a service interruption occurs, the supply from the commercial power source is immediately changed to the supply from the battery.

In this case, when the battery itself has poor capacity, overcharging current flows in the battery which serves as a load for the generator, so that the generator becomes overloaded.

If the capacity of the generator is increased it becomes expensive and more overcurrent flows in the battery so that the above described pole substance separation arises therein, resulting in a decrease of the battery life-time.

The present invention seeks to eliminate or reduce the above described disadvantages of the conventional no-break power supply system by providing a nobreak power supply system capable of continuously supplying power to the load without stopping the system even in the case of failure or malfunction of the system, thereby increasing reliability, and which further is capable of supplying suitable charging current to the battery without requiring an increased generator capacity.

According to the invention, there is provided a no-break power supply system comprising a first rectifier means for connection to a main or commercial supply source, an inverter whose input is connected to the output of the first rectifier through an over current breaker, said inverter being operable to apply to a load a supply of constant voltage and constant frequency, an emergency generator means connected for supplying power to the input of said inverter, said emergency generator means being operable to generate a supply voltage for a long duration in the event of service interruption or failure of components, an emergency battery means connected for supplying current to the input of said inverter for a short duration in the event of service interruption or failure of components, an under-voltage relay means connected between the emergency generator means and the emergency battery means for monitoring the voltage of the battery means and for starting the emergency generator means when the battery voltage falls below a set level, and a floating charge means connected for charging said emergency battery means, the input of said floating charge means being connected for receiving power either from said main power source or from said emergency generator means, whichever is in operation.

In order that the invention may be better understood, an embodiment thereof will now be described by way of example only and with reference to the accompanying drawings in which: Figure 1 is a block diagram showing a conventional no-break power supply system; and Figure 2 is a block diagram showing one embodiment of a no-break power supply system according to the present invention.

Referring to Figure 2, there is shown one embodiment of a no-break power supply system according to the present invention. In Figure 2, circuit elements or components corresponding to those in Figure 1 bear the same reference numerals, and its constructional explanation is omitted.

In this embodiment, the system comprises a series combination of a second rectifier Rec 2, a diode D' and an overcurrent breaker NFB1 which is connected between the engine-generator E-G of an emergency generator means and the inverter IV. The system also comprises a floating charge means which includes a second diode D connected between the inverter IV and the battery B and a current limiter LC with a DC voltage meter V connected in parallel with the second diode D and for preventing overcurrent to the battery B. The floating charge means also comprises the first rectifier Rec 1 which serves as a rectifier for the inverter IV. The engine-generator E-G comprises an engine and a three phase AC generator having four poles which is driven by the engine. The generator is driven at a speed of two times the rated speed.The engine is operated by an instruction signal from the engine operating means PC which is triggered by the undervoltage relays RY1 and RY2. The relay RY1 is connected between the main power supply source P and the engine operating means PC. The relay RY2 monitors the voltage of the battery B to supply an instruction signal to the engine operating means PC when the voltage of the battery B becomes lower than a predetermined value and the rectifier Rec 1 fails.

In operation, under normal power transmission, the undervoltage relay RYl does not operate and does not supply the instruction signal to the engine operating means PC so that the engine-generator does not operate and thus the inverter IV receives the DC current from the main power supply source P through the rectifier Rec 1. This DC current is also supplied to the emergency battery B through the current limiter LC thereby charging the battery B in the floating condition.

Under such a condition, when a service interruption occurs the undervoltage relay RYl detects this condition and supplies an instruction signal to the engine operating means PC so that the engine-generator E-G begins to operate. The output of the generator E G is converted into DC power by the rectifier Rec 2 and supplies current to the inverter IV through the first diode D' and the overcurrent breaker NFB1. At the same time, this DC power is supplied to the battery B through the current limiter LC thereby charging the battery B in the floating condition. This charging condition is maintained during service interruption so that the load L such as a computer is held at normal operating condition.

As soon as the main power supply source P is restored to the normal power transmission state the undervoltage relay RYl detects this condition and stops to supply the instruction signal to the engine operating means PC so that the load L receives the power under the normal power transmission.

In the above described apparatus, use is made of a generator capable of operating at a speed two times the rated speed, thereby obtaining an output voltage with a frequency two times the generated frequency so that the output of the rectifier Rec 2 includes only a very small ripple resulting in a DC power with high quality and high efficiency. At the same time, the second diode D, inserted between the inverter IV and the battery B with reverse polarity, ensures that charging currents from the rectifiers Rec 1 and Rec 2 cannot be directly supplied to the battery B but instead are supplied to the battery B through the current limiter LC which limits the charging current to a suitable amount, and thus the generator does not suffer abnormal overload condition. The battery B, furthermore, is connected to the engine operating means PC through the undervoltage relay RY2 so that under normal power transmission, even if the rectifier Rec 1 fails, suitable supply and charging by the engine generator E-G can be performed.

Claims (4)

1. A no-break power supply system comprising a first rectifier means for connection to a main or commercial supply source, an inverter whose input is connected to the output of the first rectifier through an overcurrent breaker, said inverter being operable to apply to a load a supply of constant voltage and constant frequency, an emergency generator means connected for supplying power to the input of said inverter, said emergency generator means being operable to generate a supply voltage for a long duration in the evens of service interruption or failure O;; components, an emergency battery means connected for supplying current to the input of said inverter for a short duration in the event of service interruption or failure of components, an under-voltage relay means connected between the emergency generator means and the emergency battery means for monitoring the voltage of the battery means and for starting the emergency generator means when the battery voltage falls below a set level, and a floating charge means connected for charging said emergency battery means, the input of said floating charge means being connected for receiving power either from said main power source or from said emergency generator means, whichever is in operation.

2. A no-break power supply system as claimed in Claim 1, wherein the emergency generator means comprises an engine-generator driven at a speed two times the rated speed, an engine operating means connected to the engine for driving the enginegenerator, an undervoltage relay for connection between the main supply source and the engine operating means for monitoring the voltage of the main supply source and for triggering the engine operating means when the voltage of the main supply source falls below a set level, a second rectifier means connected to the output of the generator, and a series combination of a first diode and a further overcurrent breaker which is connected between the second rectifier means and the input of the inverter.

3. A no-break power supply system as claimed in claim 1, wherein the floating charge means comprises a second diode connected between the input of the inverter and the emergency battery means, and a current limiter connected between the first rectifier means and the emergency battery means in such a manner that it is connected in parallel with the second diode.

4. A no-break power supply system substantially as hereinbefore described with reference to Figure 2 of the accompanying drawings.