Generator Excitation Control Reducing Phase Delay
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Solution Overview
Problem
Traditional digital regulators for polyphase rotating electrical machines, such as alternators, suffer from a high response time to load variations, leading to phase delays and limited regulation bandwidth, which can cause 'hunting' and vibrations, especially as modern vehicles require faster adjustments to onboard power supply.
Innovation Solution
The method involves determining the duty cycle of the excitation current twice per cycle, using a microcontroller to calculate switching times based on sampled DC voltage values at the start and middle of the cycle, allowing for increased regulation loop frequency without modifying the switching frequency of the excitation current, thereby reducing phase delay and enhancing regulation bandwidth.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of time
If the regulation loop frequency is increased to reduce phase delay, then the response time to load variations is improved, but the switching frequency of the excitation current must be increased which leads to increased power dissipation and temperature rise in the switching transistor
Solution Approach 1:
The patent segments the determination of duty cycle into two separate calculations per excitation cycle: one for establishing the excitation current (at the start of the cycle) and one for cutting it (at the middle of the cycle). This segmentation allows the regulation loop to operate at twice the frequency of the excitation current switching, effectively doubling the response speed without increasing the switching frequency and associated power losses.
Solution Approach 2:
The patent performs preliminary calculation of the duty cycle values at specific predetermined moments within the excitation cycle (at the start and middle points). By pre-calculating these values based on sampled voltage measurements taken at these moments, the system reduces the phase delay inherent in digital control systems without requiring faster switching transistors, thus avoiding increased power dissipation.
2Productivity
If the excitation frequency is increased to improve regulation bandwidth, then the response to load variations is improved, but the maximum junction temperature of the switching component is exceeded
Solution Approach 1:
The patent divides the control of excitation current into two separate PWM signals: one controlling the establishment phase and another controlling the cutting phase. Each PWM signal operates at half the frequency of the other, allowing the regulation bandwidth to be effectively doubled while keeping the actual switching frequency (and associated temperature rise) at acceptable levels.
Solution Approach 2:
The patent changes the timing parameters within the excitation cycle by sampling the DC voltage at two different moments (start and middle of the cycle) and calculating corresponding duty cycle values. This parameter change approach allows the system to achieve faster effective regulation response without increasing the fundamental switching frequency that determines power dissipation and temperature.
3Device complexity
If a traditional digital regulator with single duty cycle determination per cycle is used, then the device complexity is low, but the phase delay causes hunting and vibrations in the power supply
Solution Approach 1:
The patent segments the single duty cycle control into two independent duty cycle determinations per excitation cycle. The first duty cycle value controls the establishment of excitation current while the second controls its cutting. This segmentation reduces the effective phase delay by half, preventing hunting and vibrations in the power supply while maintaining relatively simple microcontroller-based implementation.
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 approach significantly reduces phase delay and increases regulation bandwidth, enabling faster servo control and improved performance without increasing switching losses or temperature constraints, thus addressing the limitations of traditional digital regulators.
Implementation Method 1
controlling the duty cycle of a periodic excitation current by means of a microcontroller, or the like, as a function of sampled values of this DC voltage
Implementation Method 2
a DC voltage is slaved to a predetermined setpoint, said voltage being produced by rectifying an AC voltage generated by the machine
Data Source
AI summary
The regulating method is employed in a polyphase rotating electrical machine operating as a generator and having an excitation coil (10). The method is of the type in which a DC voltage (B+) is slaved to a predetermined setpoint, the voltage being produced by rectifying an AC voltage generated by the machine by controlling the duty cycle of a periodic excitation current (+EXC,−EXC) by means of a microcontroller (11), or the like, as a function of sampled values of the DC voltage (B+). The duty cycle is determined by the microcontroller (11) twice during an excitation current cycle (+EXC, −EXC).