Zero Current Switching Shunt Regulator for AC Alternator
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Solution Overview
Problem
Existing AC alternator control circuits using pulse width modulated shunt regulators experience switch noise and power loss due to the internal body diode shunting the negative portion of the current cycle, leading to inefficiencies.
Innovation Solution
A control circuit with individual current sensing and zero crossing detection for each MOSFET, allowing precise switching at zero crossing points to minimize power dissipation and noise, with a gate driver that selectively opens and closes MOSFETs based on current flow and output voltage levels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If pulse width modulation control is used to shunt the alternator at random times, then the output voltage can be regulated, but switch noise and power loss occur due to the MOSFET internal body diode shunting the negative portion of the cycle
Solution Approach 1:
The control circuit detects the zero crossing point of the current waveform in advance and triggers the MOSFET switching action at this precise moment. By performing the switching action preliminarily at the zero crossing point rather than at random times, the current through the MOSFET is minimized, thereby reducing power loss and eliminating the need for the internal body diode to shunt the negative portion of the cycle.
2Power
If pulse width modulation control is used to shunt the alternator at random times, then the output voltage can be regulated, but switch noise is generated
Solution Approach 1:
The control circuit detects the zero crossing point of the current waveform in advance and triggers the MOSFET switching action at this precise moment. By performing the switching action preliminarily at the zero crossing point rather than at random times, the current through the MOSFET is minimized, thereby reducing power loss and eliminating the need for the internal body diode to shunt the negative portion of the cycle.
3Ease of operation
If the MOSFET internal body diode shunts the negative portion of the cycle, then current can be directed, but power dissipation increases
Solution Approach 1:
The control circuit detects the zero crossing point of the current waveform in advance and triggers the MOSFET switching action at this precise moment. By performing the switching action preliminarily at the zero crossing point rather than at random times, the current through the MOSFET is minimized, thereby reducing power loss and eliminating the need for the internal body diode to shunt the negative portion of the cycle.
Data Source
Figure 1
Figure 2~3
AI summary
A control circuit (30) for use with an AC alternator (22) has a plurality of outlet lines (26A,26B,26C) leading from the alternator, each receiving a phase of current generated by the alternator (22). Tap lines (30A,30B,30C) are associated with each of the power lines and are associated with a switch (32A,32B,32C). The switches drain power to a drain (36) when in a first state, and allow the power to pass downstream to a system load (28) when in a second state. A switch control (40,42) changes the switches (32A,32B,32C) between the first and second state. A detector (38) detects when the current signal is approaching a zero crossing between a cycle positive portion and a negative portion. The switch control (40,42) takes in the information with regard to the approaching zero crossing, and change the switches (32A,32B,32C) between the first and second states based upon the detected zero crossing point. An alternator (22) is also disclosed.