Control methods for the synchronization and phase shift of the pulse width modulation (PWM) strategy of power converters
First Claim
1. A method of controlling a plurality of power converters interfacing to an ac supply network, each power converter including a network bridge operating in accordance with a pulse width modulation (PWM) strategy and an individual controller, the method comprising:
- operating, the PWM strategy of the network bridge of each power converter, at a nominal switching frequency as determined by the controller based on an internal time of the controller;
generating, by a stand-alone timing controller in communication with each individual controller of the network bridges, a common time signal;
receiving the common time signal at the individual controller, and measuring and time-stamping the common time signal, via the individual controller based upon the internal time of the individual controller;
adjusting, by the individual controller, the switching period of each of the network bridges in response to the variations of the common time signal as measured;
varying, by the individual controller, a switching frequency of the PWM strategy responsive to a time-varying frequency of the supply network; and
obtaining only integer harmonics of the time-varying frequency upon varying the switching frequency of the PWM strategy, and setting the time period of the common time signal to be equal to the reciprocal of the switching frequency.
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Abstract
A method of controlling a plurality of power converters 1a, 1b and 1c can be used to interface to a supply network, ac busbar etc. Each power converter includes a network bridge 14 operating in accordance with a pulse width modulation (PWM) strategy having the same switching period and which causes at least one unwanted harmonic in the supply network voltage. The method includes the step of providing the switching period of the PWM strategy of each network bridge with a different time offset relative to a time datum such that the at least one unwanted harmonic in the supply network voltage is at least partially cancelled. Two alternative ways of providing the time offset are described.
69 Citations
18 Claims
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1. A method of controlling a plurality of power converters interfacing to an ac supply network, each power converter including a network bridge operating in accordance with a pulse width modulation (PWM) strategy and an individual controller, the method comprising:
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operating, the PWM strategy of the network bridge of each power converter, at a nominal switching frequency as determined by the controller based on an internal time of the controller; generating, by a stand-alone timing controller in communication with each individual controller of the network bridges, a common time signal; receiving the common time signal at the individual controller, and measuring and time-stamping the common time signal, via the individual controller based upon the internal time of the individual controller; adjusting, by the individual controller, the switching period of each of the network bridges in response to the variations of the common time signal as measured; varying, by the individual controller, a switching frequency of the PWM strategy responsive to a time-varying frequency of the supply network; and obtaining only integer harmonics of the time-varying frequency upon varying the switching frequency of the PWM strategy, and setting the time period of the common time signal to be equal to the reciprocal of the switching frequency. - View Dependent Claims (2, 3, 4, 5, 6, 7)
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8. A system comprising:
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a plurality of power converters interfacing an electrical machine to an ac supply network, each power converter including a network bridge operating in accordance with a pulse width modulation (PWM) strategy and an individual controller configured to control the PWM strategy of the network bridge, wherein the PWM strategy of the network bridge of each power converter operates at a nominal switching frequency as determined by the controller based on an internal time of the controller; and a stand-alone timing controller for generating the common time signal and transmitting the common time signal to each controller of the power converters, each controller measuring and time-stamping the common time signal based upon the internal time of the individual controller; and wherein the individual controllers of the power converters are arranged to adjust the switching period of each network bridge in response to variations of the common time signal as measured, and each individual controller is adapted to vary a switching frequency of the PWM strategy responsive to a time-varying frequency of the supply network to obtain only integer harmonics of the time-varying frequency, and to set the time period of the common time signal to be equal to the reciprocal of the switching frequency. - View Dependent Claims (9, 10, 11, 12, 13, 14, 15, 16, 17, 18)
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Specification