Parallel Power Converter Current Sharing via PWM Duty Cycle
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Solution Overview
Problem
Existing power converters face challenges in achieving high efficiency, high power density, and good Line Regulation and Load Regulation due to complex circuit designs required for adjusting duty cycles with varying input voltages, and often require multiple converters in parallel, which complicates current equalization.
Innovation Solution
A power conversion system with multiple power converters connected in parallel, each equipped with a switching circuit, output sense circuit, and PWM controller that adjusts the duty cycle based on local and average current signals, input voltage, and output voltage to equalize output currents and maintain stable output voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the duty cycle of the switching circuit is adjusted within a wide range to maintain fixed output voltages, then good Line Regulation and Load Regulation are achieved, but the circuit design becomes complicated and efficiency decreases
Solution Approach 1:
The patent changes the control parameter from wide-range duty cycle adjustment to narrow-range duty cycle adjustment combined with output voltage feedback. By monitoring the actual output voltage and adjusting the duty cycle within a limited range to compensate for deviations, the system achieves good regulation without requiring complex wide-range control circuits.
2Reliability
If the duty cycle is adjusted within a wide range to maintain fixed output voltages, then good Line Regulation is achieved, but the power conversion efficiency decreases
Solution Approach 1:
The patent changes the control strategy from wide-range duty cycle modulation to narrow-range duty cycle modulation with output voltage feedback. By keeping the duty cycle within a limited range and using feedback to maintain regulation, switching losses are reduced and efficiency is improved while still achieving good Line Regulation.
3Power
If multiple power converters are connected in parallel to meet power requirements, then the total power output is sufficient, but current equalization becomes complicated
Solution Approach 1:
The patent implements a current equalization feedback mechanism where each power converter monitors its own output current and the total load current. The PWM controller adjusts the duty cycle of each converter based on the difference between its current and the average current, automatically achieving current equalization without complex external control circuits.
4Device complexity
If a fixed duty cycle is used for the switching circuit, then the circuit design is simple and power density is high, but the output voltage changes with input voltage resulting in poor Line Regulation
Solution Approach 1:
The patent introduces output voltage feedback to the PWM controller. The controller monitors the actual output voltage and adjusts the duty cycle within a limited range to compensate for input voltage variations. This feedback mechanism maintains good Line Regulation while keeping the circuit design simple and the duty cycle adjustment range limited.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The system achieves good load regulation, high efficiency, and high power density by dynamically adjusting duty cycles within a narrow range, ensuring current equalization and stable output voltage across multiple converters.
Implementation Method 1
an output sense circuit (150) configured to detect the local output current and to generate a local output current sense signal
Data Source
AI summary
A power conversion system includes at least two power converters and a current sharing bus, each power converter including a switching circuit, a power conversion circuit configured to receive an input voltage via the switching circuit and to provide a local output current, an output sense circuit configured to detect the local output current and to generate a local output current sense signal, a current sharing terminal coupled to the local output current sense signal via a resistor and coupled to the current sharing bus; and a PWM controller configured to adjust a duty cycle of the switching circuit based at least in part on the local output current sense signal provided by the output sense circuit and an average current signal on the current sharing bus.