Patent Application
20090261586
The invention relates to electrical power generation systems, and more particularly to electrical power generation systems with automatic regulation features.
Electrical power generation systems powered by variable speed prime movers that require highly regulated electrical output, such as electrical power generation systems used for aeronautical applications, generally use a wound field synchronous machine (WFSM) that serves as an electrical generator. This is because it is easy to adjust rotor current to regulate electrical output of a WFSM. In aeronautical applications, the prime mover is often a gas turbine engine that has a normal rotational velocity that exceeds 20,000 revolutions per minute (rpm). Due to the rotational velocity limitations of the WFSM, such electrical power generation systems generally require a reduction gearbox between the prime mover and the WFSM. This increases weight, cost and complexity of the electrical power generation systems.
Electrical power generation systems may alternatively employ an electrical machine of the permanent magnet type as an electrical generator. Such a permanent magnet (PM) machine is capable of much higher rotational velocity than a WFSM of similar output and therefore it is capable of direct coupling to the prime mover, thereby eliminating the reduction gearbox. This results in reduced weight, cost and complexity of an electrical power generation system. However, traditional PM machines have no convenient means to alter magnetic flux for regulating their output.
An electrical power generation system may alternatively use a regulated PM machine that has a control coil. Current level in the control coil regulates EMF that the PM machine develops by changing the magnetic flux linkage between its rotor and stator. A control coil current regulator system senses electrical output potential on a direct current (DC) bus for the electrical power generation system and adjusts the current level in the control coil to regulate the DC bus voltage.
Particularly in aeronautical applications, it is sometimes desirable to design an electrical power generation system that employs a prime mover driven generator with two stator windings, each dedicated to a separate power generation channel that supplies a common power system bus for purposes of system redundancy. It is possible to construct regulated PM machines that have two stator windings, each with their own respective control coils. Therefore, it is desirable to have a dual channel power generation system that operates with such machines.
The invention generally comprises a dual channel power generation system comprising: a prime mover; a permanent magnet (PM) dynamoelectric machine that has a PM rotor coupled to the prime mover, two multiphase alternating current (AC) stators that develop electromotive force (EMF) in response to rotation of the PM rotor due to the magnetic flux linkage between the PM rotor and the stators, two control coils that each change the magnetic flux linkage of a respective stator in response to the level of a control current that passes through the control coil; a multiphase AC rectifier for each stator that receives AC power from its respective stator to supply DC power on a respective rectifier bus; a current feedback loop for each rectifier bus; a voltage feedback loop for each rectifier bus; a load-sharing controller responsive to both current feedback loops to develop a voltage regulator reference signal for each rectifier bus that is representative of the value of voltage that its corresponding stator should produce to maintain equal values of current for both rectifier buses; and a voltage regulator for each rectifier bus responsive to its respective voltage feedback loop and voltage regulator reference signal to produce the control current for its respective control coil that changes the magnetic flux linkage of its respective stator to maintain the value of voltage that its corresponding stator should produce to maintain equal values of current for both rectifier buses.
As the prime mover 4 rotates the PM rotor 10, it induces multiphase electromagnetic force (EMF) in the stators 12a and 12b that each stator 12a, 12b couples to a respective multiphase AC stator bus 16a, 16b. Each stator 12a, 12b has a respective multiphase AC rectifier 18a, 18b that receives AC power from its respective stator bus 16a, 16b and converts it to DC power on a respective rectifier bus 20a, 20b. A main DC power bus 22 may receive the DC power from each rectifier bus 20a, 20b. At least one DC electrical load 24 receives the DC power from the main DC power bus 22.
A rectifier bus current sensor 26a, 26b for each rectifier bus 20a, 20b measures the level of electrical current for the DC power on the rectifier bus 20a, 20b and generates a rectifier bus current feedback signal that is representative of the measured level on a respective rectifier bus current feedback signal line 28a, 28b. A rectifier bus voltage sensor 30a, 30b for each rectifier bus 20a, 20b measures the level of voltage for the DC power on the rectifier bus 20a, 20b and generates a rectifier bus voltage feedback signal that is representative of the measured level on a respective rectifier bus voltage feedback signal line 32.
A load-sharing controller 34 receives the rectifier bus current feedback signal from each rectifier bus current sensor 26a, 20b on its respective rectifier bus current feedback signal line 28a, 28b that represents the level of current for its respective rectifier bus 20a, 20b. Based on the level of the current feedback signals, it generates a voltage reference signal for each rectifier bus 20a, 20b on a respective voltage reference signal line 36a, 36b that is representative of the value of voltage that its corresponding stator 12 should produce to maintain equal values of current for both rectifier buses 20.
An voltage regulator 38a, 38b for each rectifier bus 20a, 20b receives the current feedback signal from its respective rectifier bus current sensor 26a, 26b on its respective rectifier bus current feedback signal line 28a, 28b and the rectifier bus voltage feedback signal from its respective rectifier bus voltage sensor 30a, 30b on its respective rectifier bus voltage feedback signal line 32a, 32b. It also receives the voltage reference signal for its respective rectifier bus 20a, 20b on its respective voltage reference signal line 36a, 36b. Each voltage regulator 38a, 38b uses DC power from its respective rectifier bus 20a, 20b to produce control current on a respective control current bus 40a, 40b that drives the control coil 14a, 14b associated with the stator 12a, 12b that supplies the rectifier bus 20a, 20b. Each voltage regulator 38a, 38b also has a control current sensor 42a, 42b that measures the level of control current for its associated control current bus 40a, 40b and generates a control current feedback signal on a respective control current feedback signal line 44a, 44b that is representative of the measured level.
Each voltage regulator 38a, 38b receives the current feedback signal for its associated control current sensor 42a, 42b on its respective control current feedback signal line 44a, 44b. In response to the received current feedback, voltage feedback, voltage reference, and control current feedback signals, each voltage regulator 38a, 38b modifies the level of control current for its associated control current bus 40a, 40b to a value that lets its respective control coil 14a, 14b regulate the voltage of its associated stator 12a, 12b to bring the voltage of its respective rectifier bus 20a, 20b to the value of the voltage reference signal on the voltage reference signal line 36a, 36 associated with the rectifier bus 20a, 20b. In this way, each rectifier bus 20a, 20b provides equal amounts of DC power to the main DC bus 22.
Current feedback signal comparators 54a and 54b receive respective rectifier bus current feedback signals on associated rectifier bus current feedback signal lines 28a and 28b as well as the average current signal on the average current line 52 and compare their difference to produce current difference signals on respective current difference signal lines 56a and 56b. Inverters 58a and 58b receive respective current difference signals on associated current difference signal lines 56a and 56b to produce inverted current difference signals on respective inverted current difference signal lines 60a and 60b.
For purposes of system stability, lag functions 62a and 62b receive respective inverted current difference signals on their associated inverted current difference signal lines 60a and 60b to produce voltage difference bias signals on respective voltage bias signal lines 64a and 64b. The lag functions typically will be of the form K/TS+1, wherein K is a gain constant and Ts is a lag period. Alternatively, proportional-plus-integral (PI) functions may substitute for the lag functions 62a and 62b.
voltage signal summers 66a and 66b receive respective voltage difference bias signals on associated voltage bias signal lines 64a and 64b as well as a voltage reference signal on a voltage reference signal line 68 and combine them to produce respective voltage regulator reference signals on their associated voltage regulator reference signal lines 36a and 36b. The voltage regulator reference signals on the voltage regulator reference signal lines 36a and 36b control their associated voltage regulators 38a and 38b as hereinbefore described in connection with
A PI regulator 74 receives the voltage difference signal on the voltage difference signal line 72 to produce a control current reference signal on a control current reference signal line 76. A control current comparator 78 receives the control current reference signal on the control current reference signal line 76 and the control current feedback signal on its associated control current feedback signal line 44a, 44b and compares their difference to produce a control current difference signal on a control current difference signal line 80.
A variable gain PI regulator 82 receives the control current difference signal on the control current difference signal line 80 and its variable gain input receives the rectifier bus current feedback signal on its associated rectifier bus current feedback signal line 28a, 28b to produce a control current regulating signal on a control current regulating signal line 84. A pulse width modulator (PWM) circuit 86 receives the control current regulating signal on the control current regulating signal line 84 and generates corresponding PWM control signals on a PWM control signal bus 88. A gate drive circuit 90 receives the PWM control signals on the PWM control signal bus 88 and generates corresponding gate drive signals on a gate drive signal bus 92. An H-bridge circuit 94 receives the gate drive signals on the gate drive signal bus 90 as well as DC power on its associated rectifier bus 20a, 20b to produce the control current on its respective control current bus 40a, 40b that drives the control coil 14a, 14b associated with the stator 12a, 12b that supplies the rectifier bus 20a, 20b.
Referring back to
The described embodiments of the invention are only some illustrative implementations of the invention wherein changes and substitutions of the various parts and arrangement thereof are within the scope of the invention as set forth in the attached claims.
