Electrical computers and digital processing systems: support – Computer power control – Power sequencing
Reexamination Certificate
2000-12-13
2004-11-02
Lee, Thomas (Department: 2115)
Electrical computers and digital processing systems: support
Computer power control
Power sequencing
C361S111000, C323S237000, C323S239000, C324S521000
Reexamination Certificate
active
06813720
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a device for supplying electrical power to a load, for example one or more lamps, by means of a power modulation system with controlled switch(es) that can operate in either of two operating modes referred to hereinafter as a “reverse phase control” mode and a “forward phase control” mode.
The invention also relates to a device for supplying power to a load adapted to implement the method.
2. Description of the Prior Art
When electrical power is supplied by means of a switched mode power modulation system, the operating mode of the power modulation system must be matched to the type of load, which is either inductive or capacitive. This problem is encountered more and more frequently, including in the lighting field where low-voltage halogen lamps are increasingly used. The voltage-reducing transformer that feeds the lamp can be a conventional transformer with windings, i.e. a transformer formed by coupling two self-inductances, or a so-called “electronic” transformer, whose behavior is capacitive. To control one or more low-voltage halogen lamps provided with a voltage-reducing transformer by adding a power modulation system between the alternating current supply and the “transformer(s)” providing the low-voltage conversion, it is necessary to adapt the operation of the power modulation system to suit the type of load, in particular to its inductive or capacitive behavior.
To be more precise, a capacitive or resistive load must be supplied with power by a power modulation system that can operate in the “reverse phase control” mode. In this case the semiconductor switches, which can be turned on and off, are turned on to allow the current to flow into the load at the beginning of a half-cycle of the AC voltage and are opened before the end of the half-cycle, after a time-delay depending on the required level of illumination.
In contrast, an inductive load must be supplied with power by a power modulation system operating in the “forward phase control” mode, in which the controlled switches of the power modulation system are not turned on at the beginning of each half-wave of the mains voltage but at a given time within its duration and until the end of the half-wave.
A purely resistive load can be supplied with power by a power modulation system operating in either mode.
The facility to change from one operating mode to another requires the designer of the power modulation system to include bipolar transistors, field-effect power transistors or insulated-gate bipolar transistors (ICBT); this list is not limiting, on the other hand, thyristors and/or triacs cannot operate in the “reverse phase control” mode.
Various solutions to the above problem have already been proposed.
EP 0 618 667 describes a system for supplying power to a load including controlled switches that can operate with a selected synchronization mode in either of two operating modes, namely a “reverse phase control” mode and a “forward phase control” mode.
To choose the correct operating mode, which depends on the nature of the load, which the user does not always know, there is provision for analyzing the load beforehand to find out if the power modulation system must be configured to operate in the “reverse phase control” mode if the load is capacitive or resistive or must be configured in the “forward phase control” mode if it is inductive. According to the teaching of the above document, during a test program independent of the normal power supply conditions for the load a control pulse is applied to the load and the nature of the load (inductive or capacitive) is deduced from its reaction to the pulse. The power supply system is then set to the required operating mode by a particular switch synchronization configuration. Only then is the load actually connected to the power modulation system to be supplied normally with power in the chosen operating mode.
WO-A-92/15052 describes a device in which the load is first supplied with power normally by setting the power modulation system to the “reverse phase control” mode a priori. If overvoltages appear at the terminals of the load, the operating mode is switched. However, with a system of this kind overvoltage detection applies regardless of the operating conditions. High voltage spikes can damage the circuits before the operating mode can be changed. The invention solves this problem.
SUMMARY OF THE INVENTION
The invention provides a method of supplying power to a load via a power modulation system including at least one controlled switch adapted to operate in either of two operating modes, namely a “reverse phase control”, mode and a “forward phase control” mode, wherein the power modulation system is switched on in the “reverse phase control” mode, the load is supplied with power via the power modulation system, which is commanded to operate under predetermined low-load operating conditions, and then, when the low-load operating conditions are established, overvoltages are detected during a given period and the power modulation system is caused to change to the forward phase control mode if an excessive number of overvoltages is detected during the given period.
Overvoltages are preferably detected at the terminals of the controlled switch(es). They could equally well be detected at the terminals of the load.
According to an advantageous feature of the invention, the decision whether to change the operating mode allows for the number of overvoltages that have occurred during the aforementioned predetermined time interval. If the number of overvoltages during that time interval is greater than a given number, the power modulation system switches automatically to the “forward phase control” mode. The operating mode is changed by modifying the synchronization of the controlled switches of the power modulation system. This is known in the art. To be more precise when the power modulation system is operating in the “reverse phase control” mode the controlled switches are synchronized to the zero-crossing of the mains voltage. When the power modulation system is operating in the “forward phase control” mode the controlled switches are synchronized to the zero-crossing of the current flowing in the load. Both control modes are compatible with purely resistive loads. The power modulation system could simply remain in the reverse phase control mode.
In one embodiment, the “forward phase control” operating mode is selected if the number of overvoltages is at least equal to a given percentage of the number of halt-periods of the mains voltage during the predetermined time interval. That percentage can be fixed at around 50%, for example.
According to another advantageous feature of the invention, each time the power modulation system is commanded to achieve the predetermined low-load operating conditions, the conduction time of the switches is progressively increased until the power modulation system is operating under the predetermined low-load operating conditions. For example, this progressive starting phase (which precedes the analysis phase during which operation stabilizes under the low-load operating conditions) can last about 500 milliseconds. During the progressive starting phase the conduction time of the controlled switches during a half-period of the AC voltage varies progressively from a very small value up to 2 milliseconds. When the conduction time has stabilized at 2 milliseconds per half-cycle in the “reverse phase control” mode, the power modulation system is deemed to have stabilized under the predetermined low-load operating conditions. Detection of overvoltages at the terminals of the load then begins, and continues for a period of the order of 200 milliseconds, for example. If an excessive number of overvoltages is detected during that period, a microprocessor generates an instruction Lo change operating mode and the power modulation system changes to the “forward phase control” mode.
On the other hand, at the end of the period for detecting overvoltages under the afo
Chung Chi Whan
Lee Thomas
LeGrand
LandOfFree
Method of and device for supplying electrical power to a... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method of and device for supplying electrical power to a..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method of and device for supplying electrical power to a... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3297957