Electricity: motive power systems – Synchronous motor systems – Hysteresis or reluctance motor systems
Patent
1998-02-23
2000-03-14
Masih, Karen
Electricity: motive power systems
Synchronous motor systems
Hysteresis or reluctance motor systems
318254, 318138, 318439, 318561, H02P 146
Patent
active
060377402
DESCRIPTION:
BRIEF SUMMARY
This invention relates to a switched reluctance electric machine system including an electric machine, a rechargeable DC energy store, principal voltage terminals and a controller.
In such a system the electric machine may be designed primarily to act as a motor or a generator. Where it is a motor, it is advantageous to drive the motor from a rechargeable energy store, so that the motor does not always need to be connected to an AC supply for operation, as this restricts the portability of the appliance powered by the motor. In such motor systems the energy store (normally a battery) is usually recharged from an AC supply using a charger including a transformer operating from the AC supply to step down the voltage, and means for rectifying and smoothing the supply before charging the energy store. Such a charger, although simple, is bulky and heavy, as the transformer is a relatively large electromagnetic device. Recent chargers based on switched mode power supply technology use power electronic switching circuits to provide a controllable DC output to the energy store from the AC input. These chargers are smaller than those using transformers, but are more expensive. Thus, incorporating a charger into an electric machine system increases the size or the cost of the system and the appliance in which the system is incorporated. However, including a charger may have the advantage that if the energy store is fully discharged, the motor can still be operated if the charger is connected, as this can provide an equivalent DC voltage.
GB 1 604 066 shows a system in which a charger is formed by utilising existing components. Here the power converter circuit, which controls current flow from the battery to pairs of closely-coupled motor windings to operate the motor, is also used to control current flow from a rectified AC supply to pairs of closely-coupled motor windings, which operate as an isolating transformer, isolating the battery from the rectified AC supply when on charge. For charging, the power converter circuit operates to build up current in a main winding of a pair, the current then being transferred to an auxiliary winding of the pair and from there to the battery. Electromechanical contactors must be operated after charging to enable the battery to drive the motor, again using the main windings. The system therefore incorporates a charger by using existing components. However, it does not allow the motor to be operated from the rectified AC supply, and it requires operation of the electromechanical contactors after charging for motor operation. Furthermore, it is only suitable for applications where the voltage of the rectified AC supply and the battery are similar.
U.S. Pat. No. 5,412,268 shows a system in which an electric motor operates a vehicle from a battery, current flow through the motor stator windings being controlled by diodes and switches. The system is also able to operate in a brake generator mode, to charge the battery, and to charge the battery from an AC supply. The charger is formed by using the stator windings, which are re-configured into a transformer. The rotor winding is also disconnected. For charging, current flows in the opposite direction through the windings, again controlled by the diodes and switches. Electromechanical contactors are operated to perform the re-configuration, through several contacts. Although the charger utilises existing components, the motor cannot be operated from the AC supply, and the system must be manually switched between charging and motoring modes.
According to the present invention, a switched reluctance electric machine system has a switched reluctance machine including a rotor, a stator and windings including at least two closely-coupled coils, a rechargeable DC energy store, principal voltage terminals, a power converter for controlling current flow in the machine windings during operation of the machine, the power converter having a first circuit containing a first of the closely-coupled coils and the principal voltage terminals and a seco
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Barnes Mike
Pollock Charles
Masih Karen
The University of Warwick
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