PWM Drive Control Phase Difference Setting
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Solution Overview
Problem
Conventional drive control devices for DC motors using PWM signals face challenges in reducing ripple currents and associated electromagnetic noise, especially when multiple motors with different rotational speeds and load torques are controlled, as simple phase shifting methods may not effectively minimize total ripple current values.
Innovation Solution
A drive control device that sets phase differences among PWM signals based on effective current, voltage, or electric power of each load, using equations to distribute the timing of signal rise and fall evenly, thereby reducing total ripple currents and electromagnetic noise, and allowing for adjustable phase settings according to motor conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If phase difference is set by dividing PWM cycle by number of loads, then device complexity is reduced, but ripple current reduction effectiveness deteriorates
Solution Approach 1:
The patent changes the parameter basis for phase difference calculation from a simple uniform division (t_pwm/N) to a parameter-based calculation using effective current, voltage, or power of each load. This allows the phase difference to adapt to actual load conditions, improving ripple current reduction effectiveness while maintaining computational simplicity.
2Object-generated harmful factors
If smoothing capacitor capacity is increased, then ripple current influence is reduced, but cost increases
Solution Approach 1:
The patent converts the harmful ripple current effect into a beneficial control parameter by using phase difference adjustment based on load parameters. Instead of passively suppressing ripple currents with large capacitors, the system actively manages them through intelligent PWM phase control, reducing the need for large smoothing capacitors and lowering costs.
3Device complexity
If PWM signals with same phase are used, then device complexity is minimized, but electromagnetic noise increases
Solution Approach 1:
The patent applies different phase differences to different PWM signals based on their respective load parameters (effective current, voltage, or power). This local differentiation in phase configuration optimizes ripple current reduction for each specific load condition while maintaining overall system simplicity, thereby reducing electromagnetic noise without significantly increasing control complexity.
Data Source
AI summary
A PWM signal generator section for generating a plurality of PWM signals with different phases to be respectively fed to a plurality of loads, and a phase difference setting section for setting phase differences among the PWM signals are provided. The phase difference setting section sets phase differences Δt_shift(n,n+1) calculated based on an effective current Ia(n) flowing to each of the loads, where the number of the loads is N, according to the equations below:Ia_all=∑n=1NIa(n)t_shift(n,n+1)=t_pwn×Ia(n)/Ia_allwhere n=1 to N (where N is an integer of two or more, and n+1=1 when n+1>N), and t_pwm is a cycle of the PWM signals.