Electricity: power supply or regulation systems – Input level responsive – Phase controlled switching using electronic tube or a three...
Patent
1999-04-07
2000-08-15
Berhane, Adolf Deneke
Electricity: power supply or regulation systems
Input level responsive
Phase controlled switching using electronic tube or a three...
318805, 318814, G05F 502, H02P 7622
Patent
active
061041777
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to a three-phase power controller for controlling a load which is connected to a three-phase mains system, having a microcontroller, having voltage detection devices which produce voltage zero signals which are associated with the voltage zeroes in the individual mains-system phases, from which signals the microcontroller derives trigger signals for driving phase-related semiconductor valves. The present invention furthermore relates to a method for phase-gating control of a three-phase power controller.
A three-phase power controller is described in European Patent No. 0 435 038 B1. In this case, the time at which the semiconductor valves are triggered in order to carry out phase-gating control is derived from the time difference between the voltage zero of one phase of the three-phase mains system and the switching-off of the semiconductor valve associated with this phase.
British Patent Application No. 2 084 359 describes an apparatus for controlling a three-phase asynchronous motor. To this end, controllable semiconductor valves, in particular a triac or back-to-back connected thyristors are assigned to each supply phase in the motor and allow power to be supplied to the motor in a controlled manner via phase-gating control. The time of the current zero is used as the time reference for determining the triggering times for the semiconductor valves in the conventional apparatus, this time being determined by measuring the voltage drop across the semiconductor valve. This voltage is supplied to a comparator whose output states correspond to the switching states of the semiconductor valve. The current zero then corresponds to one flank of the output signal of the comparator, from which a monoflop is used to produce a sampling pulse for a ramp voltage which is synchronized to the supply voltage zero. The sampled value of the ramp voltage is subtracted from a reference voltage, which is entered externally via a potentiometer, and is passed to the inverting input of a differential amplifier. Its output voltage is supplied together with the ramp voltage in a further comparator, which uses a downstream trigger pulse generator to produce a primary trigger signal when the ramp voltage exceeds the output voltage of the differential amplifier.
These conventional devices use the current zeroes or a combination of voltage and current zeroes in the individual phases to derive the trigger time for the semiconductor valves in three-phase power controllers. When determining the current zero, the voltage across the semiconductor valve is generally evaluated, and an ON or OFF signal is derived. In this case, the use of the voltage across the semiconductor valve may be regarded as being problematic, since this voltage is the difference between the mains-system voltages and the induced motor voltage. In the event of any voltage drops in the mains-system voltage, this difference can, for example tend to zero, which then results in the current zero not being detected.
The present invention is based on an object of providing a three-phase power controller of the type mentioned above which is particularly simple, that is to say it can be constructed using cost-effective components. Another object is to specify a method for phase-gating control of a three-phase power controller of the type mentioned above, which allows a hardware design with low costs.
The first object is achieved in that the voltage zero signals are square-wave signals whose flanks are used for interrupt control of an executive program in the microcontroller, the interrupt routines which are associated with the interrupt control in the executive program controlling the switch-on times of the trigger signals exclusively on the basis of the voltage zeroes as information about the three-phase mains system.
A particularly simple development of the present invention consists in that only two voltage detection devices are provided which produce, as voltage zero signals of two mains-system phases, square-wave signa
REFERENCES:
patent: 5187419 (1993-02-01), De Lange
patent: 5206572 (1993-04-01), Farag et al.
Fritsch Andreas
Seitz Johann
Berhane Adolf Deneke
Siemens Aktiengesellschaft
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