Variable ZVS Angle Control for Wireless Power Transfer Efficiency
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Solution Overview
Problem
Current wireless power charging (WPC) systems for electric vehicles (EVs) face challenges in maintaining stable charging voltage and current, minimizing switching losses, achieving maximum transfer efficiency, and reducing the number of converters, while also requiring a multi-objective control method to adapt to varying operating conditions.
Innovation Solution
A joint control method with variable zero-voltage-switching (ZVS) angles (JC-VZA) is introduced, which adjusts phase-shift duty cycles and power angles of the primary inverter and secondary active rectifier using closed loops and a perturb-and-observe method to identify the optimal operating point for maximum efficiency, minimizing power losses and maintaining stability under ZVS conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If ZVS control is implemented to reduce switching losses, then switching losses are minimized, but the control complexity increases due to the need for multiple closed loops
Solution Approach 1:
The control system is segmented into three independent closed loops: primary ZVS angle control loop, secondary ZVS angle control loop, and charging voltage/current control loop. Each loop independently controls specific parameters to achieve ZVS for both primary and secondary switches while maintaining charging stability, thereby reducing switching losses without overwhelming complexity
Solution Approach 2:
The control method dynamically adjusts the phase-shift duty cycle and power angle in real-time based on operating conditions. The primary and secondary ZVS angles are dynamically optimized through separate closed loops that respond to changing load conditions, enabling the system to maintain minimum switching losses across varying operating points
2Device complexity
If the number of converters is reduced to lower system cost and complexity, then system cost and complexity are reduced, but achieving stable charging voltage and current becomes more difficult
Solution Approach 1:
The secondary active rectifier is designed to perform multiple functions: it provides charging voltage/current regulation through phase-shift duty cycle control, achieves ZVS through power angle control, and maintains system stability. This multi-functional design eliminates the need for separate voltage regulation and ZVS control circuits, reducing converter count while maintaining stability
Solution Approach 2:
The control system implements feedback mechanisms where the charging voltage and current are continuously monitored and used to adjust the phase-shift duty cycle of the secondary active rectifier. This feedback ensures stable charging output while the same device also maintains ZVS conditions through coordinated power angle control
3Device complexity
If fixed ZVS angles are used to simplify control, then control is simplified, but transfer efficiency cannot be optimized under varying operating conditions
Solution Approach 1:
The control method transitions from fixed ZVS angles to dynamic ZVS angle adjustment. The primary ZVS angle is dynamically optimized through a dedicated closed loop that adjusts the primary phase-shift duty cycle, while the secondary ZVS angle is independently optimized through another closed loop adjusting the power angle. This dynamic adaptation ensures maximum transfer efficiency across all operating conditions
Solution Approach 2:
The system changes the ZVS angle parameters in real-time based on operating conditions. The primary ZVS angle and secondary ZVS angle are independently adjusted as control variables to optimize efficiency at different power levels and load conditions, rather than using fixed angle values
4Loss of energy
If multiple closed loops are implemented for joint control of ZVS angles, then transfer efficiency is optimized, but the system requires more control variables and increased complexity
Solution Approach 1:
The control problem is segmented into independent ZVS angle optimization for primary and secondary sides. Each side has its own closed loop with dedicated control variables: primary phase-shift duty cycle for primary ZVS angle, and power angle for secondary ZVS angle. This segmentation allows parallel optimization without requiring complex multi-variable coordination
Solution Approach 2:
The system dynamically determines the operating point by coordinating adjustments across multiple closed loops. The primary and secondary ZVS angles are dynamically optimized based on real-time operating conditions, with each loop independently adjusting its control variable to achieve overall system efficiency optimization
Data Source
AI summary
A joint control method with variable ZVS angles for dynamic efficiency optimization in a WPC system for EVs under ZVS conditions, including: adjusting a phase-shift duty cycle of a secondary active rectifier to control a charging voltage and a charging current of EV's batteries through a charging voltage closed loop and a charging current closed loop, respectively; adjusting a power angle of the secondary active rectifier to control a ZVS angle of the secondary active rectifier through a secondary ZVS angle closed loop; adjusting a phase-shift duty cycle of a primary inverter to control a ZVS angle of the primary inverter through the primary ZVS angle closed loop; determining the current operating case of the WPC system and adjusting the ZVS angles of the primary inverter and the secondary active rectifier to automatically identify an optimal operating point with a maximum charging efficiency through the P&O method.