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Sensorless power angle control for a vehicle alternator
| Details |
Inventors: Crecelius, David R.;
Assignee: Delco Remy America, Inc. (Anderson, IN)
Primary Examiner: Nappi; Robert E.
Assistant Examiner: Leykin; Rita
Attorney, Agent or Firm: Ice Miller Donadio & Ryan, Taylor; Jay G., Fowler, II; Russell E.
An alternator having a sensorless power angle control includes a three phase stator winding and three stator winding outputs connected to a controlled full wave rectifier bridge with a dc output. The controlled full wave rectifier bridge includes upper MOSFET switches and lower MOSFET switches with body diodes. Operation of the alternator results in a three phase back EMF generated in the stator windings and phase voltages across each of the stator windings. The output of the alternator is increased by introducing a phase shift between the back EMF and the phase voltages, resulting in an optimized power angle. In order to provide a reference for the phase of the back EMF, a zero crossing detector is provided which monitors the zero voltage crossings across the body diodes of the lower MOSFET switches. The negative to positive zero voltage crossings across the body diodes of the lower MOSFET devices correspond to the negative to positive zero crossings of the three phase back EMF. With an indication of the zero crossings of the back EMF, the MOSFET switches of the controlled full wave rectifier bridge may be controlled to introduce a desired phase delay in each of the phase voltages. A phase delay between the back EMF and each of the phase voltages results in an optimized power angle and increased alternator output. |
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DETAILED DESCRIPTION An alternator of present invention comprises a field winding, stator windings, a controlled full wave rectifier bridge (i.
e.
, an "active" bridge), and a dc output.
The controlled bridge includes six separate MOSFET switching devices, each including a body diode.
The switching devices include a set of upper devices and a set of lower devices.
When in an active state, the switching devices of the controlled bridge are sequentially turned on and off by a microcontroller and a 3 phase gate driver in a six-step control fashion, as is known in the art.
A zero crossing detector is positioned to accept voltage inputs from the body diodes of the lower devices.
The zero crossing detector provides a signal to the microcontroller indicative of the zero voltage crossings for the body diodes of the lower switching devices.
In operation, the field winding begins to rotate upon starting of a vehicle engine.
Rotation of the field winding produces a back EMF in each of the stator windings.
Following resistive and inductance losses in each of the stator windings, a phase voltage is output from each of the stator windings.
The phase voltages are full wave rectified by the controlled bridge to produce a dc output to the vehicle electrical load.
If the dc output is not sufficient to produce the required output power, the microcontroller adjusts the field current to a maximum value by controlling a transistor regulator.
If the required power is still not achieved after increasing the field current to a maximum value, the microcontroller instructs the three phase gate driver to adjust the power angle.
To increase the power angle, the microcontroller must have a reference of the phase of the back EMF.
This reference is provided to the microcontroller by the zero crossing detector.
The zero crossing detector senses the voltages across the lower diodes in the diode bridge.
The microcontroller uses these zero crossings as representations of the zero crossings of the back EMF.
With a representation of the zero crossings of the back EMF, the micro-controller has a reference for the period and the exact phase of the back EMF, and a phase shift can be introduced between the phase voltage and the back EMF based upon this reference
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Electrical and Wave 
