Electrical transmission or interconnection systems – Plural supply circuits or sources – Substitute or emergency source
Patent
1995-09-28
1997-11-11
Shoop, Jr., William M.
Electrical transmission or interconnection systems
Plural supply circuits or sources
Substitute or emergency source
307 66, 323212, 363 15, H02J 906
Patent
active
056867689
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention concerns an emergency power system of the type defined in the introductory portion of claim 1.
2. Description of the Prior Art
Emergency power systems of this type are connected between an electric device and an AC voltage supply. Many electric devices are now in use where mains outage will be destructive to the function of the device. The devices are in particular such as have a built-in execution of programs, such as computers, since these are sensitive to mains outage that may course erasure of data or faulty execution of the programs. The emergency power systems ensure a stable voltage supply during mains outage for a duration of up to several hours.
It is known e.g. from U.S. Pat. No. 4,366,390 to use a battery which is charged in normal operation and is discharged in emergency operation, and which provides continuous voltage supply to the connected electric device or devices until the mains voltage has been re-established. The battery is connected to the mains connection through a power converter, which serves as a charging rectifier (charger) in normal operation and serves as an inverter (AC/DC voltage converter) in emergency operation. The power converter moreover stabilizes the voltage on the output of the emergency power system, thereby eliminating fluctuations on the mains. The emergency power system according to this principle is connected with a large choke coil on the input side, which absorbs the differences between the fluctuating input and the stabilizing output without losses. Although voltage stabilization takes place without losses, the choke coil gives rise to a power factor which varies with the load and the mains voltage because the choke coil is reactive.
The structure disclosed in said U.S. patent may be called a parallel power converter, since a passive series element in the form of the choke coil cooperates with an active parallel element in the form of the regulating inverter.
SUMMARY OF THE INVENTION
FIGS. 1 and 2 show two well-known structures of UPS systems which both supply a consumer or a load Z with a stabilized voltage. Both systems are connected to an AC voltage generator 10, which may e.g. by a mains connection.
The system shown in FIG. 1 operates as a series power converter, said system comprising a charging rectifier 11 which will normally by thyristor-controlled to generate strong harmonics which will be returned to the mains, unless suitable filtration takes place at the mains connection. The charging rectifier 11 converts an AC voltage, supplied to the input, to an essentially constant output voltage, thereby ensuring that a battery 12 is fully charged. This DV voltage is conducted to an inverter 13 which converts the DC voltage to an AC voltage which is conducted to the load Z. The structure involves two individually regulated converters which operate in series. Accordingly, each of the converters is to convert the full output power, resulting in a low efficiency.
FIG. 2 shows another known UPS system which is described in detail in the U.S. Pat. No. 4,366,390, and which connects an AC voltage source 10 a load Z. The emergency power system has a power converter 14 which operates as a charging rectifier in normal operation, thereby charging the battery 12, and which operates as an inverter in emergency operation, thereby converting the battery voltage to an AC voltage which is supplied to the consumer Z. The emergency power system has a choke coil 15 which absorbs the differences between the stabilized output voltage, supplied to the load Z, and the fluctuating mains voltage received from the voltage source 10. The choke absorbs this difference without losses, but gives rise to a connection power factor which is a function of the angle between the emitted voltage and current. This power factor should be as close to it as possible owing to the voltage source, which requires that current and voltage are in phase. However, with a large reactive component such as a choke coil 15, this is not possib
REFERENCES:
patent: 4195233 (1980-03-01), Udvardi-Lakos
patent: 4277692 (1981-07-01), Small
patent: 4366390 (1982-12-01), Rathmann
patent: 4488057 (1984-12-01), Clarke
patent: 4719550 (1988-01-01), Powell et al.
patent: 4782241 (1988-11-01), Baker et al.
patent: 4860185 (1989-08-01), Brewer et al.
patent: 5502634 (1996-03-01), Lavrisa
Nielsen Henning Roar
Rathmann S.o slashed.ren Henrik Nielsen
Thomsen Ove Lyck
Paladini Albert W.
Shoop Jr. William M.
Silicon Power Electronics A/S
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