Control arrangement for a multilevel convertor
First Claim
1. Control arrangement for a multilevel convertor connected to an AC system for regulating an AC voltage of the system, the convertor having a plurality of energy storage elements and a plurality of switching means, said energy storage elements and switching means being configured to enable an AC multilevel signal of N levels per cycle to be provided at output terminals of the convertor, the control arrangement comprising an AC reference signal generating means for generating an AC reference signal from the AC system voltage, a DC threshold level generating means for generating a plurality of DC threshold levels, and a comparator means connected to said reference signal generating means and to said threshold level generating means for comparing said threshold levels with said reference signal, said comparator means in use providing a plurality of drive signals for driving control inputs of said switching means such as to provide said convertor multilevel AC signal.
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Accused Products
Abstract
A control arrangement for a multilevel convertor employs an AC reference signal which is locked to the AC system frequency and is compared with a number of DC threshold levels. Intersections of the reference signal and threshold levels triggers the firing and turning-off of GTOs within the convertor to produce the desired multilevel voltage output. Normal changes in system voltage, for example, are compensated by variation of the phase relationship of the reference signal with respect to the system voltage, and/or of the voltage values of the threshold levels. Sudden and drastic changes, especially reductions, in system voltage level are sensed and used to alter the amplitude of the reference signal so as to reduce the difference between the convertor multilevel voltage and the system voltage, thereby reducing the stress on the GTOs during faults.
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Citations
25 Claims
- 1. Control arrangement for a multilevel convertor connected to an AC system for regulating an AC voltage of the system, the convertor having a plurality of energy storage elements and a plurality of switching means, said energy storage elements and switching means being configured to enable an AC multilevel signal of N levels per cycle to be provided at output terminals of the convertor, the control arrangement comprising an AC reference signal generating means for generating an AC reference signal from the AC system voltage, a DC threshold level generating means for generating a plurality of DC threshold levels, and a comparator means connected to said reference signal generating means and to said threshold level generating means for comparing said threshold levels with said reference signal, said comparator means in use providing a plurality of drive signals for driving control inputs of said switching means such as to provide said convertor multilevel AC signal.
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6. Control arrangement for a multilevel convertor connected to an AC system for regulating an AC voltage of the system, the convertor having a plurality of energy storage elements and a plurality of switching means, said energy storage elements and switching means being configured to enable an AC multilevel signal of N levels per cycle to be provided at output terminals of the convertor, the control arrangement comprising:
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a) an AC reference signal generating means for generating an AC reference signal from the AC system voltage, b) a DC threshold level generating means for generating a plurality of DC threshold levels, c) a comparator means connected to said reference signal generating means and to said threshold level generating means for comparing said threshold levels with said reference signal, said comparator means providing, in use, a plurality of drive signals for driving control inputs of said switching means such as to provide said convertor multilevel AC signal, d) means for varying a phase of the AC reference signal with respect to a phase of the AC system voltage, said phase varying means including an error signal forming means having a first input for receiving a signal proportional to an AC system parameter to be controlled by the convertor, and a second input for receiving a DC reference signal, and a phase-shift generator fed from an output of the error signal forming means, said phase-shift generator having an output providing, in use, the AC reference signal, e) said reference signal generating means including a phase-locked loop fed from the AC system and locked, in use, to a frequency thereof, and f) said phase-shift generator including two multipliers fed, on the one hand, from respective quadrature outputs of said phase-locked loop and, on the other hand, from respective outputs of a sine generator and a cosine generator, said sine and cosine generators being fed from the output of said error signal forming means, said multipliers having respective outputs which are connected to respective inputs of a summing means, said summing means having an output providing, in use, a reference signal which is phase-shifted in proportion to a value of said error signal. - View Dependent Claims (13, 22)
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7. Control arrangement for a multilevel convertor connected to an AC system for regulating an AC voltage of the system, the convertor having a plurality of energy storage elements and a plurality of switching means, said energy storage elements and switching means being configured to enable an AC multilevel signal of N levels per cycle to be provided at output terminals of the convertor, the control arrangement comprising:
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a) an AC reference signal generating means for generating an AC reference signal from the AC system voltage, b) a DC threshold level generating means for generating a plurality of DC threshold levels, c) a comparator means connected to said reference signal generating means and to said threshold level generating means for comparing said threshold levels with said reference signal, said comparator means providing, in use, a plurality of drive signals for driving control inputs of said switching means such as to provide said convertor multilevel AC signal, d) means for varying a phase of the AC reference signal with respect to a phase of the AC system voltage, said phase varying means including an error signal forming means having a first input for receiving a signal proportional to an AC system parameter to be controlled by the convertor, and a second input for receiving a DC reference signal, and a phase-shift generator fed from an output of the error signal forming means, said phase-shift generator having an output providing, in use, the AC reference signal, e) said reference signal generating means including a filter arrangement fed from the AC system, f) said phase-shift generator including a variable phase-shift circuit fed from an output of the filter arrangement, said variable phase-shift circuit having a control input fed from the output of the error signal forming means, said variable phase-shift circuit providing, in use, a reference signal which is phase-shifted in proportion to a value of said error signal, and g) a signal regulating means for maintaining, during normal operating conditions, the AC reference signal at a one per-unit level. - View Dependent Claims (8, 9, 14, 15, 16, 24)
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- 20. A multilevel convertor connected to an AC system for regulating an AC voltage of the system, the convertor having a plurality of energy storage elements and a plurality of switching means, said energy storage elements and switching means being configured to enable an AC multilevel signal of N levels per cycle to be provided at output terminals of the convertor, the convertor being connected to a control arrangement comprising an AC reference signal generating means for generating an AC reference signal from the AC system voltage, a DC threshold level generating means for generating a plurality of DC threshold levels, and a comparator means connected to said reference signal generating means and to said threshold level generating means for comparing said threshold levels with said reference signal, said comparator means in use providing a plurality of drive signals for driving control inputs of said switching means such as to provide said convertor multilevel AC signal.
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23. Control arrangement for a multilevel convertor connected to an AC system for regulating an AC voltage of the system, the convertor having a plurality of energy storage elements and a plurality of switching means, said energy storage elements and switching means being configured to enable an AC multilevel signal of N levels per cycle to be provided at output terminals of the convertor, the control arrangement comprising:
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a) an AC reference signal generating means for generating an AC reference signal from the AC system voltage; b) a DC threshold level generating means for generating a plurality of DC threshold levels, c) a comparator means connected to said reference signal generating means and to said threshold level generating means for comparing said threshold levels with said reference signal, said comparator means providing, in use, a plurality of drive signals for driving control inputs of said switching means such as to provide said convertor multilevel AC signal, d) means for varying a phase of the AC reference signal with respect to a phase of the AC system voltage, said phase varying means including an error signal forming means having a first input for receiving a signal proportional to an AC system parameter to be controlled by the convertor, and a second input for receiving a DC reference signal, and a phase-shift generator fed from an output of the error signal forming means, said phase-shift generator having an output providing, in use, the AC reference signal, e) said reference signal generating means including a filter arrangement fed from the AC system, f) said phase-shift generator including a variable phase-shift circuit fed from an output of the filter arrangement, said variable phase-shift circuit having a control input fed from the output of the error signal forming means, said variable phase-shift circuit providing, in use, a reference signal which is phase-shifted in proportion to a value of said error signal, and g) said filter arrangement including quadrature outputs, and said variable phase-shift circuit including two multipliers fed, on the one hand, from respective said quadrature outputs of said filter arrangement and, on the other hand, from respective outputs of a sine generator and a cosine generator, said sine and cosine generators being fed from the output of said error signal forming means, said multipliers having respective outputs which are fed to respective inputs of a summing means, said summing means having an output providing, in use, a reference signal which is phase-shifted in proportion to a value of said error signal.
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Specification