Multiplexed PFC and DC-DC Converter for EMC and Inductor Heat
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Solution Overview
Problem
Existing uninterruptible power supplies (UPS) with multiplexed AC-DC power factor control (PFC) and DC-DC circuits face issues of electromagnetic compatibility (EMC) problems and inductor overheating due to high-frequency potential jumping and low inductor utilization, especially when connected to a single battery.
Innovation Solution
A power factor correction and DC-DC multiplexing converter design using a single inductor, mechanical switches, semiconductor switches, and rectifier bridge arms to manage connections to mains and battery, ensuring stable potential differences and efficient energy transfer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If clamping diodes are added to prevent high-frequency potential jumping in battery mode, then electromagnetic compatibility (EMC) is improved, but one inductor is shorted causing inductor overheating
Solution Approach 1:
The patent introduces a third capacitor C3 coupled to the common node of diodes D7 and D8 as an intermediary element. This capacitor acts as a mediator that stabilizes the voltage at the common node, preventing high-frequency potential jumping without requiring clamping diodes that would short the inductor. The third capacitor provides a low-impedance path for high-frequency currents, thereby improving EMC while maintaining inductor functionality and preventing overheating.
2Reliability
If AC-DC PFC circuit and DC-DC circuit are separately designed, then circuit functionality is ensured, but system size and costs increase
Solution Approach 1:
The patent merges the AC-DC PFC circuit and the DC-DC battery discharge circuit into a single multiplexed circuit topology. The same inductor L1, capacitors, and switching elements are used for both PFC operation during mains supply and DC-DC conversion during battery discharge. This consolidation maintains full circuit functionality while significantly reducing the number of power components, decreasing system size, and lowering costs compared to separate designs.
Solution Approach 2:
The circuit elements, particularly the inductor L1 and the switching network, are designed to perform multiple functions: during mains supply mode, they execute PFC to correct power factor and regulate input current; during battery discharge mode, the same elements execute DC-DC conversion to discharge the battery and regulate output voltage. This multi-functionality ensures full operational capability while reducing component quantity and system footprint.
3Area of stationary object
If single inductor is used for multiplexing PFC and DC-DC, then system size is reduced, but inductor utilization becomes low causing overheating
Solution Approach 1:
The patent employs periodic switching control where the semiconductor switches Q1-Q4 are alternately activated in different modes. During mains supply mode, the switches operate in PFC mode with specific duty cycles; during battery discharge mode, the same switches operate in DC-DC mode with different duty cycles. This periodic alternation between operational modes ensures that the single inductor is actively utilized in both modes without being shorted, distributing the energy processing load and preventing overheating while maintaining compact size.
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 design improves EMC performance, prevents inductor overheating, and optimizes inductor utilization, reducing system size and costs by effectively multiplexing battery discharge and mains supply circuits.
Implementation Method 1
an inductor L1, one end of which is connected to the mains supply through the first mechanical switch RY1, and connected to a positive electrode of the battery B21 through the second mechanical switch RY2
Implementation Method 2
a first rectifier bridge arm 213, connected between the first node N1 and the second node N2, where the first rectifier bridge arm 213 has a first intermediate node N3, and the first intermediate node N3 is connected to the other end of the inductor L1
Data Source
Figure 1~2
Figure 3~4
Figure 5~6a
AI summary
The present invention provides a power factor correction and DC-DC multiplexing converter. One end of an inductor is selectively connected to a mains supply or a positive electrode of a battery. A first rectifier bridge arm with a first intermediate node and a second rectifier bridge arm with a second intermediate node are separately connected between a first node and a second node, the first intermediate node is connected to the other end of the inductor, and the second intermediate node is connected to a neutral point. A first semiconductor switch controls conduction between the first node and the second node. A second semiconductor switch controls conduction between the second node and a negative direct current bus. A third semiconductor switch controls conduction between the neutral point and a negative electrode of the battery. The positive and negative direct current buses are configured to provide a direct current output.