FET Shunt Regulator Logic OR Gate Control
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Solution Overview
Problem
FET shunt regulators used with permanent magnet alternators experience inefficiency and reduced lifespan due to power dissipation caused by the body-drain diode voltage drop when current returns through it, rather than the lower-loss source-drain connection.
Innovation Solution
Incorporating a logical OR gate connected to each FET shunt's control input, which activates the FET shunt when the phase voltage is negative or a PWM control signal is received, allowing current to return through the lower-loss source-drain connection instead of the body-drain diode, and using a PWM controller to manage the FET shunts' on/off states to maintain efficient DC output.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If the FET shunt is turned off to reduce power loss, then power dissipation decreases, but the return current must flow through the body-drain diode causing voltage drop and efficiency loss
Solution Approach 1:
The control system predicts when return current will occur and proactively turns on the FET shunt in advance, ensuring the low-resistance source-drain path is available before the current needs to return, thereby preventing the high-voltage-drop body-drain diode path from being used
Solution Approach 2:
The control system monitors the state of the FET shunt and the AC current waveform, using this feedback to determine the optimal timing for turning the FET on and off, ensuring it remains on during return current periods to maintain efficiency while minimizing unnecessary conduction losses
2Reliability
If the FET shunt remains on continuously to provide a low-loss return path, then efficiency increases, but power dissipation and heat generation increase during non-shunting periods
Solution Approach 1:
The FET shunt is switched on and off periodically based on the AC current waveform and shunting requirements, remaining on only during periods when return current is expected or shunting is needed, rather than remaining continuously on, thereby reducing unnecessary power dissipation while maintaining efficiency during critical periods
Solution Approach 2:
The FET shunt transitions from a static on/off state to a dynamic state where it can be rapidly switched between conduction and non-conduction modes based on real-time operational requirements, allowing the system to optimize between efficiency and power loss by adapting the FET's state to the instantaneous needs of the circuit
3Loss of energy
If the FET shunt is turned off to minimize conduction losses, then power dissipation decreases, but the lifespan of the FET is reduced due to high voltage stress across the body-drain diode
Solution Approach 1:
The FET shunt is turned on in advance before return current occurs, establishing the low-stress source-drain conduction path beforehand, thereby preventing the high-voltage-stress body-drain diode from conducting and extending the FET's operational lifespan by reducing cumulative electrical stress
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This configuration significantly increases the efficiency of the shunt regulator and extends the lifespan of the FETs by minimizing power dissipation and ensuring a consistent DC output, even when the FET shunts are turned off.
Implementation Method 1
An FET shunt uses FET's to create a short circuit from a phase voltage line connected to the source node of the FET to a neutral line connected to the drain node of the FET. The short circuit is created when the FET is turned on via a control signal thereby connecting the source and drain nodes in a virtually unimpeded manner.
Implementation Method 2
In a typical design in the art the current will return across a body-drain connection in the FET. The connection is referred to as a body-drain diode. The body-drain diode connection acts in a similar manner as a diode and typically has a voltage drop of around 1.4V across it. This voltage drop causes power dissipation within the FET
Implementation Method 3
Each of the FET shunts has a logical OR gate connected to its control input that is capable of turning on the FET shunt when a control signal from the controller indicates that the FET shunt should be on or when the phase voltage connected to the FET shunt is negative.
Implementation Method 4
Each logical OR gate accepts inputs from the controller and from a comparator
Data Source
AI summary
A current controlled shunt regulator uses logical OR gates and comparators corresponding to each field effect transistor (FET) shunt to redirect power to a neutral line whenever a controller indicates that power should be redirected, or whenever a phase voltage connected to the FET shunt is negative. The logical OR gate accepts inputs from the comparator and from the controller and outputs a control signal based on these inputs. When power is not being redirected by the FET shunts, AC power from a permanent magnet alternator is allowed to flow unimpeded to a DC rectifier which converts the power to a different format.