AC-to-DC Converter Voltage Balancing via DC-to-DC Current Control
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Solution Overview
Problem
AC-to-DC converters with power factor correction (PFC) circuits face issues such as noisy DC signals, low power factor, and high harmonic distortion, which are exacerbated by multilevel outputs leading to additional harmonic distortion.
Innovation Solution
An AC-to-DC converter system with a PFC circuit, including positive, center, and negative DC voltage terminals, uses a controller to determine voltage differences between these terminals and adjusts current draws through a DC-to-DC converter to balance loads and reduce voltage differences, employing a PID controller for precise control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If a PFC circuit provides a multilevel output (both positive DC and negative DC voltage), then the power factor is improved, but additional harmonic distortion is introduced
Solution Approach 1:
The system dynamically changes operating parameters by adjusting current draw from positive and negative DC voltage terminals based on real-time voltage difference measurements. The controller modifies the duty cycle of the DC-to-DC converter to balance voltage levels across capacitors, thereby reducing harmonic distortion while maintaining improved power factor.
Solution Approach 2:
The system implements a feedback mechanism where the controller continuously monitors the voltage difference between positive and negative DC voltage terminals relative to center terminal, and adjusts the current draw accordingly. This closed-loop control reduces voltage imbalance and associated harmonic distortion while preserving power factor correction benefits.
2Power
If a PFC circuit is used to improve power factor, then current draw becomes in phase with voltage, but the DC signal becomes noisy
Solution Approach 1:
The controller uses feedback from voltage difference measurements to dynamically adjust the current draw from positive and negative terminals. This active balancing reduces voltage ripple and noise on the DC output by preventing capacitor voltage imbalance, while maintaining the in-phase current draw characteristic for power factor improvement.
3Device complexity
If voltage difference between positive and negative DC terminals is not controlled, then the system is simpler, but load balancing and voltage stability deteriorate
Solution Approach 1:
The system employs feedback control where the controller measures voltage differences and adjusts DC-to-DC converter duty cycle accordingly. This maintains voltage balance across capacitors, ensuring stable operation and proper current sharing between positive and negative terminals without requiring complex additional hardware.
Data Source
AI summary
Technologies for controlling AC-to-DC converters are disclosed. In one illustrative embodiment, a controller of an AC-to-DC converter measures two voltage levels of a split voltage bus of a power factor correction (PFC) circuit. The controller controls current drawn from the positive and negative terminals of the PFC circuit by a DC-to-DC converter. By controlling the current drawn from the two terminals, the controller can control the voltages on the terminals to be equal (but opposite).