Electricity: power supply or regulation systems – Output level responsive – Phase controlled switching using electronic tube or a three...
Reexamination Certificate
1999-12-28
2001-01-09
Nguyen, Matthew (Department: 2838)
Electricity: power supply or regulation systems
Output level responsive
Phase controlled switching using electronic tube or a three...
C323S235000
Reexamination Certificate
active
06172489
ABSTRACT:
BACKGROUND
This invention relates to the reduction of AC voltage to a load. In particular, the system or method reduces AC utility power provided to a load.
AC utility voltage reduction is conventionally performed using large and heavy step-down AC transformers. Step-down AC transformers operate with about 96% efficiency.
Where miniaturization is desired, a variety of switchmode power supplies and conditioners have been developed, offering much smaller size and weight than conventional power transformers. However, switchmode power controllers operate at efficiencies of around 80-90 percent, much less than the standard transformer. Switch mode power controllers also operate at high frequencies (e.g. 50 kHz and higher) which generates copious amounts of electromagnetic interference (EMI). EMI is reduced by filtering and other techniques.
The use of switchmode power conditioners has been accelerated by government encouragement of the use of power factor controllers (PFCs). PFCs help maintain a high power factor, improving the utility's operating efficiency by reducing losses in power delivery. However, the utility's increase in operating efficiency through the use of switchmode PFCs is offset by the 10-20 percent efficiency loss penalty created by the PFCs.
U.S. Pat. Nos. 5,583,423 and 5,754,036 disclose energy saving power control systems and methods. The closed loop systems disclosed in these patents use the power measured at the load to control circuit functions, providing for efficient power reduction and power factor adjustment.
SUMMARY
The present invention is defined by the following claims, and nothing in this section should be taken as a limitation on those claims. By way of introduction, the preferred embodiment described below includes an AC power regulation system and method providing highly efficient reduction of utility voltage with minimal EMI. The systems and methods may also be used to improve overall facility power factor.
The AC power provided to a load, such as a group of lighting ballasts connected on a single circuit, is regulated by a controllable switch coupled in parallel with a capacitor between the AC source and the load. The switch is controlled to turn-on after a load current zero-crossing and turn-off prior to the next zero-crossing. The turn-off time is selected in an open loop configuration independently of a measured load voltage or power characteristic. In order to provide proper operation of gas discharge lighting, the switch is initially turned off just in advance of the AC source current zero-crossing. To reduce the voltage and related power and provide more power savings, the turn-off time is gradually moved to a time more prior to the zero-crossing.
In one aspect, an AC voltage reduction system for controlling load power to a load has an input for coupling to an AC voltage source and an output for coupling to the load. The voltage reduction system includes a controllable switch coupled in series between the input and the output. A capacitor is coupled in parallel with the controllable switch. Circuitry for turning-on and turning-off the controllable switch to a conducting state and a non-conducting state, respectively, is also provided. Switch control circuitry for generating control signals to control turn-on and turn-off times is operable to select the turn-off time independent of a measured load voltage or power characteristic. Circuitry for ensuring that the turn-off time initially occurs just in advance of a line current zero-crossing point is also provided.
In a second aspect, a method of AC voltage reduction for controlling power to a load in an electrical system is provided. A controllable switch is operated during a first mode of operation such that substantially full voltage is supplied to the load. A voltage reduction mode is initiated. The power supplied to the load is gradually reduced during the voltage reduction mode from a substantially full power to a target value over a period of time. The controllable switch is initially turned-off just in advance of a load current zero-crossing in the voltage reduction mode. The switch is caused to be off prior to the next successive load current zero-crossing and on each following successive load current zero-crossing. The turn-off time of the switch is controlled independent of a measured voltage or power characteristic of the load waveform.
In a third aspect, an AC voltage reduction system for controlling voltage to a load comprises an input for coupling to an AC voltage source and an output for coupling to the load. At least two types of load devices characterized by different impedances are connected with the output. A controllable switch and parallel capacitor are coupled in series between the input and the output. Circuitry and control circuitry for turning-on and turning-off the switch is also provided.
In a fourth aspect, the capacitor provided in parallel with the controllable switch has a capacitance that is proportional to the line current and operable to pass line current during a substantial portion of a half cycle of the line current. Circuitry for turning-on and turning-off the switch and controlling operation of the switch operates independent of a measured voltage or power characteristic of the load current.
Further aspects and advantages of the invention are disclosed below in conjunction with the preferred embodiments.
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Brinks Hofer Gilson & Lione
Nguyen Matthew
Summerfield Craig A.
Ultrawatt.com Inc.
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