AC/DC Battery Charger Input Power Controller
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Solution Overview
Problem
Conventional AC/DC converters for Electric Vehicles suffer from inefficient power factor correction, high conduction losses, and poor transient response due to the need for low bandwidth voltage control loops to manage second harmonic ripple, leading to suboptimal performance and stability issues.
Innovation Solution
A control system that directly regulates the input power of the AC/DC converter based on the battery charging profile, using nonlinear controllers and flatness theory to optimize the PFC converter's performance across a wide range of operations, allowing the DC-link voltage to adjust dynamically with load conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If the voltage control loop bandwidth is reduced to remove second harmonic ripple, then the power factor is improved, but the transient response becomes sluggish
Solution Approach 1:
The control system is segmented into two independent loops: a fast current control loop that handles transient responses and a slow voltage control loop that removes second harmonic ripple. The current loop operates at high bandwidth to provide fast response, while the voltage loop operates at low bandwidth to eliminate ripple, allowing both functions to coexist without interference.
Solution Approach 2:
The patent introduces an intermediary component - the current control loop - that mediates between the fast transient response requirement and the slow ripple removal requirement. The current loop acts as a buffer that can respond quickly to load changes while the voltage loop independently removes ripple, solving the contradiction through hierarchical control structure.
2Device complexity
If the DC-bus voltage is fixed to simplify control, then the converter operation is simplified, but the downstream converter operates with suboptimal duty ratio
Solution Approach 1:
The patent transitions from a static fixed DC-bus voltage to a dynamic variable DC-bus voltage that adapts to load conditions. The DC-bus voltage is dynamically adjusted based on the charging profile and power stage requirements, enabling the downstream converter to operate with optimal duty ratio across different load conditions while maintaining simple control architecture.
3Loss of energy
If the converter operates with small duty ratios at light loads, then the fixed DC-bus voltage is maintained, but reactive current increases leading to higher conduction losses
Solution Approach 1:
The patent changes the operating parameters of the converter by allowing the DC-bus voltage to vary with load conditions. At light loads, the DC-bus voltage is adjusted to enable larger duty ratios, which reduces reactive current circulation and minimizes conduction losses. This parameter adaptation allows the system to maintain ease of operation while reducing energy losses.
Data Source
AI summary
A control approach of adjusting the input power of a power factor correction (PFC) stage so that the output voltage (DC-link) of the input AC/DC stage to an intermediate DC voltage (DC-Bus voltage) is adjusted based on the amount of power required to charge a high energy battery is disclosed. The present invention controls the input power of the PFC instead of the DC-bus voltage as is common in conventional methods. Therefore, a very fast response compared to the conventional sluggish voltage loop can be achieved. Also, having different DC-bus voltages for different output load conditions allows the DC/DC converter to work with an optimal duty cycle for a whole range of load variations.