DC Voltage Conversion Circuit With Asymmetric PWM and Phase Shift Control
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Solution Overview
Problem
Existing direct-current voltage conversion circuits in EVs face challenges in stabilizing output voltage when input voltage fluctuates, particularly during charging and discharging, leading to instability and potential shoot-through currents due to limited duty ratio control in phase shift control methods.
Innovation Solution
A direct-current voltage conversion circuit employing asymmetric PWM control and phase shift control, allowing discontinuous duty ratio changes to maintain a step-down ratio within a predetermined range, thereby extending the control range and preventing shoot-through currents by switching between the two controls based on input voltage conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If phase shift control is used to maintain output voltage stability when input voltage decreases, then the duty ratio must be increased, but the conduction ratio is limited to about 45% due to dead-time requirements, making it practically difficult to stabilize the output voltage when input voltage decreases significantly
Solution Approach 1:
The patent applies asymmetric PWM control where the duty ratios of the two switching elements are set differently (first duty ratio for one switching element, second duty ratio for the other switching element). This asymmetry allows the circuit to achieve higher effective duty ratios and extend the control range beyond the 45% limitation of conventional symmetric phase shift control, enabling stable output voltage even when input voltage decreases significantly.
Solution Approach 2:
The control method dynamically switches between phase shift control and asymmetric PWM control based on the required duty ratio. When the required duty ratio exceeds the 45% threshold, the system transitions to asymmetric PWM control, adapting the control strategy to maintain output voltage stability across a wider range of input voltage conditions.
2Reliability
If the conduction ratio of switching elements is increased to maintain output voltage when input voltage fluctuates, then the duty ratio must exceed 45%, but this increases the risk of shoot-through currents breaking the switching elements
Solution Approach 1:
Asymmetric PWM control allows different duty ratios for different switching elements, enabling the circuit to achieve the required effective duty ratio without requiring any single switching element to exceed the safe 45% conduction ratio threshold, thereby maintaining output voltage stability while preventing shoot-through currents.
Solution Approach 2:
The patent introduces a control switching portion that acts as an intermediary, selecting between phase shift control and asymmetric PWM control based on operating conditions. This intermediary control mechanism ensures that the circuit operates within safe duty ratio limits while maintaining output voltage stability across varying input conditions.
3Adaptability or versatility
If asymmetric PWM control is implemented to extend the duty ratio control range, then the control complexity increases with the need to switch between phase shift control and asymmetric PWM control
Solution Approach 1:
The control switching portion uses feedback from the required duty ratio to automatically select the appropriate control mode. When the required duty ratio exceeds the 45% threshold, the system automatically switches to asymmetric PWM control, providing an intelligent, self-regulating control system that manages complexity through conditional logic rather than manual intervention.
Solution Approach 2:
The control system is designed to perform multiple functions: it can operate in phase shift control mode for normal conditions and switch to asymmetric PWM control mode when extended duty ratio range is required. This multi-functionality allows a single control system to handle a wide range of operating conditions without requiring separate dedicated control circuits.
Data Source
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AI summary
In a direct-current voltage conversion circuit 10 according to the present invention which comprises a switching circuit SW1 having a plurality of switching elements and a controller 60 that controls operations of the plurality of switching elements and which can suppress variations in an output voltage even when an input voltage fluctuates, the controller 60 can execute asymmetric PWM control and phase shift control, performs the phase shift control when a duty ratio D is lower than a predetermined ratio, and performs the asymmetric PWM (Pulse Width Modulation) control when the duty ratio D 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 R being made to match each other, a control range of the duty ratio D can be increased.