Ac power generating system
First Claim
1. An AC power generating system including inverter means which are operable to convert an intermediate DC voltage into an AC power output, means for generating and maintaining the intermediate DC voltage at one level and voltage sensor means operable to monitor the intermediate DC voltage, characterised in that control means are provided for the inverter means, said control means being responsive to the voltage sensor means and being operable to control operation of the inverter means so the voltage and/or the frequency of the AC power output is/are reduced in response to a fall in the intermediate DC voltage to a certain level caused by the application of a step load to the AC power output, whereby to provide a transient off-loading effect which will give the generating means time to respond and thereby allow the intermediate DC voltage to be restored to said one level.
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Accused Products
Abstract
An electric power generating set which automatically varies its speed to match load variations at any time includes an engine driven generator G which provides a positive, Ga and a negative, Gb AC output voltage each of which is rectified by a respective rectifier Re3a, Re3b. Each rectifier Re3a,Re3b has one terminal connected to a common neutral line N. The DC output voltage of each rectifier Re3a, Re3b is boosted in a respective booster circuit which also has one terminal connected to the neutral line N. The combined output of the two booster circuits, Va+Vb is fed to an Inverter IN which converts it to the AC power output of the generating set. A DC load current between the booster circuits and the inverter IN is monitored and used to provide a speed demand feedback signal Srs to the speed control of the engine EN. The inverter IN is controlled so that the voltage and frequency of the AC power output of the generating set are reduced in response to a fall in the intermediate DC voltage Va+Vb that is fed to the inverter IN and which is monitored by a voltage sensor Vsab.
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Citations
50 Claims
- 1. An AC power generating system including inverter means which are operable to convert an intermediate DC voltage into an AC power output, means for generating and maintaining the intermediate DC voltage at one level and voltage sensor means operable to monitor the intermediate DC voltage, characterised in that control means are provided for the inverter means, said control means being responsive to the voltage sensor means and being operable to control operation of the inverter means so the voltage and/or the frequency of the AC power output is/are reduced in response to a fall in the intermediate DC voltage to a certain level caused by the application of a step load to the AC power output, whereby to provide a transient off-loading effect which will give the generating means time to respond and thereby allow the intermediate DC voltage to be restored to said one level.
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13. An AC power generating system including generator means operable to generate a variable voltage AC power supply, rectifier means having an output and being operable to rectify the variable voltage AC power supply, booster means having an input which is connected to the output of the rectifier means and which are operable to increase the voltage of the rectified output of said rectifier means to establish an intermediate DC voltage, a variable speed prime mover drivingly coupled with the generator means, and speed control means operable to control the speed of the motor, wherein current sensor means are provided, said current sensor means being operable to monitor a current caused by connection of a load across the intermediate DC voltage, the current sensor means being operable to emit a signal which is indicative of the monitored current, comparator means being provided for comparing an output signal from the current sensor means with a reference signal and for emitting a speed correction signal which is proportional to the amount by which the output signal from the current sensor means exceeds the reference signal, the output from the comparator means being supplied to the speed control means for the generator means to effect an increase in the speed of the variable speed prime mover, characterised in that said current sensor means are operable to monitor the DC load current on the side of said booster means remote from said rectifier means.
- 14. An AC power generating system including generator means operable to generate a variable voltage AC power supply, rectifier means having an output and operable to rectify the variable voltage AC power supply, booster means having an input which is connected to the output of the rectifier means and which is operable to increase the voltage of the rectified output of said rectifier means and thereby to provide an intermediate DC voltage, inverter means operable to convert the intermediate DC voltage into an AC power output for supplying to an external load, voltage sensor and control means operable to monitor the intermediate DC voltage and to provide a feedback control signal to the generator means whereby to vary the variable voltage AC power supply so as to counter a tendency of the intermediate DC voltage to vary, and electrical energy storage means connected across the intermediate DC voltage so as to be charged by the intermediate DC voltage, characterised in that bistable switching means and associated control means are provided, said bistable switching means normally being in one state in which they are operable to make the connection of the electrical energy storage means across the intermediate DC voltage to enable the electrical energy storage means to be charged and to interrupt a connection between the electrical energy storage means and a connection between the generator means and the input of the booster means, said bistable switching means being operable in its other state to isolate the electrical energy storage means from the intermediate DC voltage and to make said connection of the electrical energy storage means with the connection between the generator means and the input of the booster means, whereby to enable discharge of electrical energy from said electrical energy storage means into the connection between the generator means and the booster means, said control means associated with the bistable switching means being responsive to the monitored intermediate DC voltage and being operable in response to a fall in said intermediate DC voltage to a certain reference level to switch said bistable means from its normal said one state to said other state whereby to discharge electrical energy to augment the variable voltage AC power supply and thereby to counter the sensed fall in said intermediate DC voltage.
- 16. An AC power generating system including variable voltage AC power supply generator means, rectifier means having an output and operable to rectify the variable voltage AC power supply to establish an intermediate DC voltage, inverter means which are operable to convert the intermediate DC voltage into an AC power output, voltage sensor means operable to monitor the intermediate DC voltage and control means responsive to an output from the voltage sensor means and operable to maintain the intermediate DC voltage at one level, characterized in that the generator means is operable to generate two variable voltage AC power supplies, the rectifier means comprise two full-wave rectifiers, each full-wave rectifier being operable to rectify a respective one of the two variable voltage AC power supplies and each being connected on one side to a neutral terminal and having an output voltage terminal on its other side, the output voltage terminal of one of the full-wave rectifiers being positive and the output voltage terminal of the other full-wave rectifier being negative such that the two variable voltage AC power supplies are severally rectified to produce a positive and a negative potential respectively which together comprise the intermediate DC voltage, the voltage sensor means comprising two voltage sensors severally responsive to a respective one of the positive and negative output potentials of the two fullwave rectifiers and the control means comprising two controllers severally operable to maintain each of those positive and negative potentials at a certain level whereby to maintain the intermediate DC voltage at said one level.
- 23. A method of converting a DC voltage having a positive and negative level of electrical potential into an AC power output in which the positive and negative levels of electrical potential are connected to an AC power output terminal alternately, characterized in that each connection of one of the positive and negative levels of electrical potential to the output terminal is separated in time from a connection of the other of the positive and negative levels of the electrical potential to the output terminal by an intermediate period of zero voltage.
- 25. A DC to AC converter including a first source of electrical energy operable to be charged with a positive DC potential, a second source of electrical energy operable to be charged with a negative DC potential, first bistable switching means operable in one state to connect the first electrical energy source to an AC power output terminal through an inductor means of an output filter means and to break that connection in its other state, and second bistable switching means operable in one state to connect the second electrical energy source to the AC power output terminal through said inductor means and to break that connection in its other state, characterized by third bistable switching means operable in one state to connect said inductor means to neutral and to break that connection in its other state, and control means operable to control operation of said first, said second and said third bistable switching means so that said first and said second bistable switching means are switched to their said one state alternately and are in their said other state when the other of said first and second bistable switching means are in their said one state and said third bistable switching means is switched to its said one state whilst said first and second bistable switching means are both switched to their said other state between each alternate switching of said first and second bistable switching means to their said one state so that the positive and negative levels of electrical potential with which said first and second electrical energy sources are charged when said converter is operated are connected to the AC power output terminal alternately and each connection of the one of the positive and negative levels of electrical potential to the output terminal is separated in time from a connection of the other of the positive and negative levels of electrical potential to the output terminal by an intervening period of zero voltage.
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30. A method of operating an AC power generating system of the kind which includes an engine driven generator which provides a variable voltage electrical output, rectifier means operable to rectify the variable voltage electrical output, booster means operable to boost the voltage of the variable voltage electrical output and thereby to provide an intermediate DC voltage, inverter means which are operable to convert the intermediate DC voltage into an AC power output, characterized by means operable to maintain the intermediate DC voltage at one level up to a predetermined speed of the engine driven generator which is less than the maximum speed thereof, wherein the means operable to maintain the intermediate DC voltage at said one level is disenabled when the speed of the engine driven generator rises to at least said predetermined speed and the speed of the engine driven generator and the intermediate DC voltage are allowed to rise so that, when the engine driven generator is running at maximum speed, the AC power output is allowed to increase until a balance is achieved.
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31. A method of operating an AC power generating system including the steps of:
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(i) operating a variable speed prime mover driven generator to generate a variable voltage AC power supply;
(ii) rectifying the variable voltage AC power supply to establish an intermediate DC voltage;
(iii) monitoring the intermediate DC voltage and responding to transient variations therein whereby to maintain it at a substantially constant level; and
(iv) operating an inverter to convert the intermediate DC voltage into an AC power output;
characterised by the further step of(v) monitoring DC current flow to the inverter;
wherein the monitored DC voltage and DC current are compared with a number of references whereby, whenever one of the monitored DC voltage and DC current deviates from an acceptable normal level at least transiently, an appropriate control correction is applied automatically, the nature of the applied control correction depending on the severity of the deviation from the acceptable level.
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32. A method of operating an AC power generating system including the steps of:
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(i) operating a variable speed prime mover driven generator to generate a variable voltage AC power supply;
(ii) rectifying the variable voltage AC power supply to establish an intermediate DC voltage;
(iii) controlling the intermediate DC voltage to maintain it at a substantially constant level;
(iv) operating an inverter to convert the intermediate DC voltage into an AC power output;
(v) monitoring the intermediate DC voltage; and
(vi) controlling operation of the prime mover driven generator by feedback control so as to increase its speed when the monitored intermediate DC voltage falls to the level of the first reference voltage whereby to restore the intermediate DC voltage to said substantially constant level;
characterised by the further steps of (vii) comparing the intermediate DC voltage with a first reference voltage which is lower than the substantially constant level; and
wherein (viii) the intermediate DC voltage is also compared with a second reference voltage which is lower than said first reference voltage, and (ix) operation of the inverter is controlled so as to reduce the voltage and/or frequency of the AC power output when the monitored intermediate DC voltage falls to the level of the second reference voltage whereby to provide a transient off-loading effect which assists restoration of the intermediate DC voltage to said substantially constant level. - View Dependent Claims (33, 34, 35, 36)
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- 37. An electrical power generating system including generator means operable to generate a variable voltage generator output, a variable speed prime mover drivingly coupled with the generator means, speed control means operable to control the speed of the prime mover, converter means operable to establish a DC link by converting the variable voltage generator output into a DC voltage and to derive an electrical power output from that DC voltage for supply to an external load, sensing means operable to monitor the DC link when the load is connected across the DC voltage and to provide a feedback to the speed control means whereby to effect variation of the variable voltage electrical output thereby to counter a tendency of the DC voltage to vary so as to maintain the DC voltage at one level characterised in that control means are provided for said converter means, said control means being responsive to the sensing means and being operable to control operation of said converter means so that the voltage of the electrical power output is reduced in response to a fall in the DC voltage to a certain level caused by the application of a step load to the electrical power output whereby to provide a transient off-loading effect which will give the generator means time to respond and thereby allow the DC voltage to be restored to said one level.
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44. An electrical power generating system including generator means operable to generate a variable voltage AC power supply, rectifier means having an output and being operable to rectify the variable voltage AC power supply, booster means having an input which is connected to the output of the rectifier means and which are operable to increase the voltage of the rectified output of said rectifier means to establish an intermediate DC voltage, a variable speed prime mover drivingly coupled with the generator means, and speed control means operable to control the speed of the motor, wherein current sensor means are provided said current sensor means being operable to monitor a current caused by connection of a load across the intermediate DC voltage, the current sensor means being operable to emit a signal which is indicative of the monitored current, comparator means being provided for comparing an output signal from the current sensor means with a reference signal and for emitting a speed correction signal which is proportional to the amount by which the output signal from the current sensor means exceeds the reference signal, the output from the comparator means being supplied to the speed control means for the generator means to effect an increase in the speed of the variable speed prime mover, characterised in that said current sensor means are operable to monitor the DC load current on the side of said booster means remote from said rectifier means.
- 45. An electrical power generating system including generator means operable to generate a variable voltage power supply, booster means having an input which is connected to the output of the generator means and which is operable to increase the voltage of the output of said generator means and thereby to provide a DC voltage, voltage sensor and control means operable to monitor the DC voltage and to provide a feedback control signal to the generator means whereby to vary the variable voltage power supply so as to counter a tendency of the DC voltage to vary, and electrical energy storage means connected across the DC voltage so as to be charged by the DC voltage, characterised in that bistable switching means and associated control means are provided, said bistable switching means normally being in one state in which they are operable to make the connection of the electrical energy storage means across the DC voltage to enable the electrical energy storage means to be charged and to interrupt a connection between the electrical energy storage means and a connection between the generator means and the input of the booster means, said bistable switching means being operable in its other state to isolate the electrical energy storage means from the DC voltage and to make said connection of the electrical energy storage means with the connection between the generator means and the input of the booster means, whereby to enable discharge of electrical energy from said electrical energy storage means into the connection between the generator means and the booster means, said control means associated with the bistable switching means being responsive to the monitored DC voltage and being operable in response to a fall in said DC voltage to a certain reference level to switch said bistable means from its normal said one state to said other state whereby to discharge electrical energy to augment the variable voltage power supply and thereby to counter the sensed fall in said DC voltage.
- 47. An electrical power generating system including variable voltage power supply generator means, converter means operable to establish a DC link by converting the variable voltage power supply to a DC voltage, voltage sensor means operable to monitor the DC voltage and control means responsive to an output from the voltage sensor means and operable to maintain the DC voltage at one level, characterized in that the generator means is operable to generate two variable voltage power supplies each connected on one side to a common terminal and having an output voltage terminal on its other side, the output voltage terminal of one of the power supplies being positive and the output voltage terminal of the other power supply being negative such that the two variable voltage power supplies together comprise the DC voltage, the voltage sensor means comprising two voltage sensors severally responsive to a respective one of the power supplies and the control means comprising two controllers severally operable to maintain the voltage of each of those power supplies at a certain level whereby to maintain the DC voltage at said one level.
Specification