Patent CA-2635442-A1 (CA)
Title: Engine start system with regulated permanent magnet machine
Inventor: ROZMAN GREGORY I
IPC: H02P27/00
Filed: 2008-06-19
Abstract: An electromechanical power transfer system that transfers power between a direct current (DC) electrical power system and a prime mover, comprises: a permanent magnet machine (PMM) comprising a permanent magnet (PM) rotor that rotates a drive shaft of the prime mover, a stator with a multiphase alternating current (AC) winding coupled to the AC bus for developing a rotating magnetic field with a magnetic flux path that causes rotation of the PM rotor and a control coil with a winding that has a configuration to generate a magnetic field with flux that varies the reactance of the stator winding upon the application of current through the control coil; a plurality of AC current sensors for sensing the current in each phase of the multi-phase AC bus and generating respective AC bus current signals that represent the current level of each phase; an average current detector that receives the AC bus current signals and generates a respective current load feedback signal; a back electromotive force (emf) detector coupled to the AC bus that detects back emf generated by the stator in response to the application of AC power to the stator and generates a back emf signal representative of the detected level of back emf;  a rotor position/speed estimator that receives the back emf signal and generates an estimated rotor position signal that is representative of the position of the rotor, an estimated rotor speed signal that is representative of the speed of the rotor and a closed loop enable signal that indicates a speed for the electrical starting system to switch from an open loop mode of operation to a closed loop mode of operation;  a control coil current sensor for generating a control coil current signal in a control coil current feedback loop that is representative of the level of electrical current in the control coil; a first speed switch that switches between an open loop position reference signal that represents a desired position of the rotor in an open loop mode and the estimated rotor position signal that represents the position of the rotor in a closed loop mode to provide a position reference signal; a second speed switch that switches between an open loop current reference signal that represents a desired control coil current level in the open loop mode and a closed loop current reference signal that represents a desired control coil current level in the closed loop mode to provide a control coil current reference signal; an inverter/rectifier system for converting DC power from the DC power system to multiphase alternating current (AC) power on an AC bus; a control coil current regulator system for regulating current through the control coil; wherein the inverter/rectifier system responds to the position reference signal, the current load feedback signal and a current load reference signal to regulate acceleration of the PMM; wherein the control coil current regulator system responds to the control coil current reference signal and the control coil current feedback signal to regulate current in the PMM; and wherein the power transfer system starts in the open loop mode, the rotor position/speed estimator generates the closed loop enable signal that indicates a speed for the electrical starting system to switch from the open loop mode of operation to the closed loop mode of operation at a predetermined rotor speed, and the first and second speed switches respond to the closed loop enable mode to switch from their open loop mode to their closed loop mode.