PWM Inductive Load Control via Counter-Based Duty Cycle Alignment
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Solution Overview
Problem
The control of inductive loads by pulse width modulation faces challenges due to slow current and voltage variations (slew rate) causing discrepancies in the effective duty cycle, which are difficult to compensate for, especially in high-frequency applications where precision is critical and closed-loop systems require fast adaptation.
Innovation Solution
A device and method that utilize counters to determine and adjust the durations of logic states in control signals based on a periodic set point control signal, ensuring the effective duty cycle matches the set point duty cycle by slaving the second duration to the first duration, and using an up-down counter to account for edges of a clock signal, thereby compensating for slew rate effects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If pulse width modulation is used to control inductive loads, then the load can be controlled effectively, but slow current and voltage variations cause the effective duty cycle to differ from the set point duty cycle
Solution Approach 1:
The patent employs feedback by measuring the actual effective duty cycle through counters that track the duration of control signals, comparing it with the set point duty cycle, and adjusting the control signals accordingly to eliminate the discrepancy caused by slew rate effects
Solution Approach 2:
The patent replaces software-based compensation methods with a hardware-based counter system that directly measures and adjusts duty cycle timing, providing more precise and reliable control without the computational delays and complexity of software tables
2Manufacturing precision
If software compensation is used to correct duty cycle errors, then some accuracy can be restored, but the implementation is tedious and does not resolve the problem in all situations
Solution Approach 1:
The patent replaces complex software compensation algorithms with a straightforward hardware counter system that automatically measures control signal durations and adjusts timing, eliminating the need for tedious software table implementations while providing universal applicability across different operating conditions
3Adaptability or versatility
If closed loop control is used, then the system can adapt to provide desired behavior, but the adaptation speed may be insufficient for high-frequency applications
Solution Approach 1:
The patent replaces software-based closed loop adaptation with a hardware counter system that operates at clock frequency speeds, enabling the control system to adapt instantly to duty cycle discrepancies and achieve the desired effective behavior in the load with much faster response times suitable for high-frequency applications
Data Source
AI summary
Method and device for controlling an inductive load by pulse width modulation, on the basis of a periodic set point control signal having a given set point duty cycle. The set point control signal is, in each period of the set point control signal, in a first logic state determined from the high and low logic states for at least a first duration, and is in the other logic state during the rest of the period. Control signals are generated for activating the inductive load, on the basis of the set point control signal. With the aid of a first counter, the first duration (t0) is determined on the basis of the set point control signal. Via a second counter, a second duration (t0−td2) is determined, for which a logic signal corresponding to an effective control signal observed in the load is in the first determined logic state.