Electric power conversion systems – Current conversion – Using semiconductor-type converter
Patent
1997-01-23
1999-06-29
Nguyen, Matthew
Electric power conversion systems
Current conversion
Using semiconductor-type converter
H02M 75387
Patent
active
059177225
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND TO THE INVENTION
The present invention relates to a commutator circuit for coupling power to a load, and in particular to a circuit suitable for use in a digital power amplifier. The present invention is not however limited in this respect, and the circuit may find use in a variety of different fields.
A commutator used, for example, in a digital power amplifier may be required to switch at high frequencies and relatively high power levels. This combination tends to result in the production of high levels of electromagnetic interference (EMI). In consequence, much effort has to be directed to limiting the EMI generated by any device incorporating such a commutator circuit so as to meet the increasingly stringent statutory limitations on EMI. Conventionally, it has been necessary, for example, to provide extensive shielding around the circuits and to tailor the physical layout of the circuits to minimise the EMI from the device as a whole.
SUMMARY OF THE INVENTION
According to a first aspect of the present invention a commutator circuit including a commutator bridge having switches in each arm of the bridge and arranged to have a load coupled to a mid-point of the bridge is characterised by a switched resonant arm also coupled to the mid-point of the bridge and arranged to provide controlled resonant commutation of the load.
In the context of the present specification, the term "bridge" encompasses both full and half-bridge topologies. The term "coupling" as used in the present specification encompasses connection via a current buffer and transformer-coupling as well as direct electrical connection.
The present invention adopts a radically different approach to the problem of EMI. Instead of using a commutator circuit which generates high levels of EMI, and then relying upon appropriate shielding, the present invention uses a modified commutator configuration with resonant control of the voltage switching. This allows precise control over the shape of the leading and trailing edges of the switched waveform and so allows the EMI to be eliminated or reduced at source. The topology enables well defined commutation rates for high current or high energy carrying loads and the consequent delivery of high resolution pulse energy shapes to the load. As well as being of value in limiting EMI, circuits embodying the present invention are also particularly advantageous where it is necessary to drive a complex load, such as inductive, capacitive or inductive plus capacitive combinations. Such loads occur, for example, in motor windings, magnetic windings, transformers, inductors and the like. In circuits embodying the invention, the timing of the commutator switches and the resonant arm switch can be controlled independently of the time-constant characteristic of the resonant components, for example by a PWM signal derived from an audio waveform.
The circuits of the present invention may be particularly advantageous in motor servo drives in which precision power delivery to the motor is required. The circuit when driving a complex load such as a motor can use simple PWM as a method of control and stability. This is by contrast with conventional circuit topologies using resonant elements. The use of the topologies of the present invention with PWM control can result in faster response times.
The commutation rates (rate of change of voltage) experienced in the power leads connecting a drive circuit to a complex impedance load are determined by the component values in the drive circuit. This provides a predictable method of controlling commutation rates so as to keep them to a minimum thereby limiting EM radiation. As a consequence of this reduction in the radiation from the leads connecting the drive circuit to the load the distance between the load and the drive circuit can be increased whilst still avoiding interference problems.
Preferably the resonant arm is connected to a potential having a value of substantially V/2, where V is the drive potential across the bridge.
The potential at V/2 may possibly,
REFERENCES:
patent: 4639849 (1987-01-01), Noworolski et al.
patent: 4833584 (1989-05-01), Divan
patent: 4855888 (1989-08-01), Henze et al.
patent: 5047913 (1991-09-01), De Doncker et al.
patent: 5563775 (1996-10-01), Kammiller
patent: 5594635 (1997-01-01), Gegner
"A Novel Low-loss Switching Method for Converters Using Turn-off Power Switches (IGBTs, GTOs etc.)", by L.L. Erhartt et al., Fifth European Conference On Power Electronics And Applications, Sep. 13, 1993, pp. 46-51.
"A Three-Phase Soft-Switched High Power Density DC/DC Converter for High Power Applications, " by R.W. De Doncker et al., IEEE Industry Applications Society Annual Meeting, Pittsburgh, Oct. 2, 1988, No. Part 1, pp. 796-805.
B&W Loudspeakers Ltd.
Nguyen Matthew
University of Brighton
LandOfFree
Controlled commutator circuit does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Controlled commutator circuit, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Controlled commutator circuit will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-1381532