DC Voltage Conversion Circuit With Hybrid PWM and Phase Shift Control
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Solution Overview
Problem
Existing DC voltage conversion circuits face challenges in stabilizing output voltage when input voltage fluctuates, particularly in applications like electric vehicles where voltage changes during charging and discharging, leading to instability and inefficiency.
Innovation Solution
A DC voltage conversion circuit employing a controller that switches between asymmetric PWM control and phase shift control to adjust duty ratios and step-down ratios, ensuring stable output voltage by matching step-down ratios and utilizing a full-bridge circuit with series and parallel connections of switching elements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If phase shift control is used to increase duty ratio when input voltage decreases, then output voltage stability is improved, but the conduction ratio is limited to below 50% due to dead-time requirements, making it difficult to stabilize output voltage when input voltage decreases significantly
Solution Approach 1:
The patent applies dynamics by switching between two different control methods (phase shift control and asymmetric PWM control) depending on the operating conditions. When the duty ratio is below a predetermined threshold, phase shift control is used; when it exceeds the threshold, asymmetric PWM control is used. This dynamic switching allows the system to adapt to different input voltage conditions and maintain output voltage stability across a wider duty ratio range.
Solution Approach 2:
The patent changes the control parameter from phase shift amount to pulse width asymmetry. In asymmetric PWM control, the pulse widths of switching elements connected in series are made asymmetric (different from each other), allowing the duty ratio to exceed 50% while preventing shoot-through currents. This parameter change enables broader duty ratio adjustment range for maintaining output voltage stability.
2Adaptability or versatility
If asymmetric PWM control is used with duty ratio above predetermined ratio, then duty ratio adjustment range is improved, but control complexity increases due to switching between different control methods
Solution Approach 1:
The patent uses feedback by monitoring the duty ratio and comparing it with a predetermined threshold value. Based on this feedback, the controller automatically switches between phase shift control and asymmetric PWM control. This feedback mechanism simplifies the overall control logic by providing clear switching criteria, reducing the complexity of managing multiple control methods.
Solution Approach 2:
The patent segments the control range into two distinct regions: one for phase shift control (duty ratio below threshold) and another for asymmetric PWM control (duty ratio at or above threshold). This segmentation allows each control method to operate in its optimal range, simplifying the control strategy for each segment while achieving broad overall adaptability.
3Reliability
If dead-time period is provided between ON periods of switching elements to prevent shoot-through current, then reliability is improved, but conduction ratio is inevitably lower than 50%, reducing productivity
Solution Approach 1:
The patent applies asymmetry by making the pulse widths of switching elements connected in series asymmetric (different from each other) in asymmetric PWM control. This asymmetry allows one switching element to have a longer ON time while the other has a shorter ON time, enabling the overall duty ratio to exceed 50% while still maintaining adequate dead-time between their ON periods to prevent shoot-through currents. This resolves the contradiction between reliability and productivity.
Data Source
AI summary
A DC voltage conversion circuit includes: a switching circuit having a plurality of switching elements; and a controller that controls operations of the plurality of switching elements. The DC voltage conversion circuit can suppress variations in an output voltage even when an input voltage fluctuates. The controller can execute asymmetric PWM control and phase shift control, performs the phase shift control when a duty ratio is lower than a predetermined ratio, and performs the asymmetric PWM control when the duty ratio is higher than or equal to the predetermined ratio. When switching between the phase shift control and the asymmetric PWM control is performed with the step-down ratios being made to match each other, a control range of the duty ratio can be increased.