DC/DC Converter Feedforward Control for Output Ripple Suppression
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Solution Overview
Problem
Current resonant type DC/DC converters face issues with overcontrol, leading to uncontrolled output current ripples, especially in electric vehicle charging systems, which affect battery health and require larger, more costly filter circuits.
Innovation Solution
A DC/DC converter with a control unit that includes an input voltage ripple extraction unit, an output ripple extraction unit, and a second control unit that generates a gain based on the polarity of input voltage ripples to suppress overcontrol, using feedforward control to stabilize output ripples.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of stationary object
If the cutoff frequency of the filter circuit is increased to reduce its size and cost, then the filter circuit becomes smaller and cheaper, but low frequency components of ripple noise flow out from the filter circuit
Solution Approach 1:
The control unit performs preliminary action by extracting the input voltage ripple in advance and generating a compensation signal through feedforward control before the ripple propagates to the output. This proactive approach allows the system to counteract the ripple effects without requiring an oversized filter circuit, thus resolving the contradiction between filter size and ripple suppression effectiveness
2Object-generated harmful factors
If the cutoff frequency of the filter circuit is lowered to reduce low frequency ripple noise, then the ripple noise is reduced, but the choke coil and electrolytic capacitor size increase, leading to larger filter circuit
Solution Approach 1:
The control unit implements feedback control by continuously monitoring the input voltage ripple and dynamically adjusting the compensation signal. This feedback mechanism enables the system to maintain effective ripple suppression with a smaller filter circuit, as the control system actively compensates for ripple variations rather than relying solely on passive filter components
3Object-generated harmful factors
If feedforward control gain is increased to reduce output current ripple, then the output current ripple is reduced, but overcontrol occurs and cannot be detected or suppressed
Solution Approach 1:
The control unit employs feedback control to monitor the actual output current ripple and compare it with the target value. When overcontrol occurs, the feedback mechanism detects the deviation and adjusts the feedforward control gain accordingly, preventing excessive correction and ensuring stable operation. This closed-loop approach resolves the reliability issue associated with high-gain feedforward control
Data Source
AI summary
A DC/DC converter 20 includes a power unit 21 and a control unit 22, in which the control unit 22 includes a first control unit 23 that generates a first control command value CC for bringing an output of the power unit 21 close to a target value, an input voltage ripple extraction unit 24 that extracts an input voltage ripple VR, an output current ripple extraction unit 25 that extracts an output current ripple IR, a second control unit 26 that calculates an output ripple with polarity FIR by multiplying the output current ripple IR by a sign F related to polarity of the input voltage ripple VR, and generates a second control command value FG by multiplying the input voltage ripple VR by a gain G for bringing the output ripple with polarity FIR close to a ripple target value, and a switching control unit 27 that controls a switching element of the power unit 21 on the basis of the first control command value CC and the second control command value FG.