Generator Excitation Control Circuit for Load Dump Transient Mitigation
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Solution Overview
Problem
Conventional generator assemblies face instability in vehicle electrical system voltage due to sudden load variations, leading to excessive voltage transients and the need for overdimensioning of protective components, which increases cost, size, and weight.
Innovation Solution
A control circuit with a two-quadrant chopping circuit using N-channel MOSFET transistors and freewheeling diodes to rapidly control excitation coil current, allowing for quick degaussing of the excitation coil and reducing transient voltages by applying a negative field voltage, thereby minimizing peak transient voltages and reducing the number of protective components required.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional field regulator with single quadrant chopping circuit is used, then the generator can maintain stable operation under normal conditions, but during load dumps the excitation coil current decays slowly causing excessive voltage transients and requiring overdimensioning of protective components
Solution Approach 1:
The patent applies dynamic switching between two operating modes of the MOSFET transistor: linear operation mode for normal regulation and switch operation mode for rapid current reduction. This dynamic adaptation allows the field regulator to optimize performance for different operating conditions, achieving both stable normal operation and fast response during load dumps.
Solution Approach 2:
The patent changes the operating parameters of the MOSFET transistor between linear region and saturation region (switch mode). By detecting load dump conditions and switching the transistor operating mode, the system rapidly reduces excitation coil current decay time constant, thereby reducing voltage transients without compromising normal operation stability.
2Reliability
If protective components are overdimensioned to accommodate extreme voltage variations during load dumps, then the system can handle voltage spikes, but the cost, size, and weight of the generator assembly increase
Solution Approach 1:
The patent converts the potentially harmful effect of slow excitation coil current decay during load dumps into a beneficial fast decay response. By using the MOSFET transistor in switch operation mode with near-zero on-resistance, the system rapidly dissipates the magnetic energy stored in the excitation coil, transforming the harmful voltage transient into a controlled, rapid current reduction that protects the system without requiring heavy protective components.
3Ease of operation
If the MOSFET transistor is operated in linear mode only, then the excitation coil current can be regulated smoothly, but the current decay time constant remains large during load dumps
Solution Approach 1:
The patent dynamically switches the MOSFET transistor between linear operation mode and switch operation mode based on operating conditions. During normal operation, the linear mode provides smooth current regulation. During load dumps, the switch mode with near-zero on-resistance enables rapid current decay, reducing the time constant significantly.
4Reliability
If a freewheeling diode is used for the excitation coil, then the current can continue to flow when the MOSFET is off, but this extends the duration of voltage transients during load dumps
Solution Approach 1:
The patent extracts or removes the freewheeling diode from the circuit topology. Instead of allowing current to continue flowing through a diode with forward voltage drop, the system uses the MOSFET transistor in switch operation mode to provide a low-impedance path for current decay, thereby reducing the duration of voltage transients while maintaining current continuity.
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
The solution effectively reduces transient excess voltages and breakthrough voltages, minimizing the need for overdimensioned components, resulting in a more cost-effective and lightweight generator assembly.
Implementation Method 1
a control circuit (310) for an excitation coil (12) of a generator (15) to rapidly control a current (if) through the excitation coil (12)
Implementation Method 2
The corresponding control process within a conventional generator controller can be characterized as follows: If the rectified generator output voltage UBN is lower than the reference voltage UBN—ref, the duty cycle of the driving circuit 24 for field regulator 11 of the excitation coil 12 is increased
Implementation Method 3
a current if through a excitation coil 12 (also referred to as field current) and the corresponding excitation coil voltage uf (also referred to as field voltage)
Data Source
AI summary
A generator control circuit is disclosed. One embodiment provides a first active switching circuit configured to connect a first terminal of an excitation coil either to a first or to a second terminal of a voltage source, a second active switching circuit configured to connect a second terminal of the excitation coil either to the first or to the second terminal of the voltage source, and a generator controller to set the duty cycle of the active switching circuit to rapidly control the current through the excitation coil to an excitation coil current setpoint.