Thyristor PFC Circuit with Segmented Resonant Control
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Solution Overview
Problem
High-power power factor correction (PFC) circuits using thyristors face inefficiencies due to non-instantaneous current cancellation, leading to oversized resonant circuit currents and increased losses at low input currents, and existing solutions are not scalable.
Innovation Solution
A PFC circuit with multiple parallel elementary circuits, each with a resonant circuit, where the control circuits sequentially activate circuits to manage current distribution and use a variable inductance depending on input current, and a saturable inductance produced by transformers to optimize performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a single resonant circuit is used with thyristors for current cancellation, then the circuit can achieve power factor correction, but the resonant circuit current becomes oversized and losses increase when input current is low
Solution Approach 1:
The single resonant circuit is divided into multiple parallel elementary circuits (first, second, third circuits), each with its own thyristor and resonant components. Each elementary circuit is optimized for specific current ranges, allowing the system to select appropriate circuits based on input current levels, thereby preventing oversized resonant currents and reducing losses at low input currents.
Solution Approach 2:
The system dynamically selects and activates specific elementary circuits based on the input current level. Control circuits sequentially activate circuits in increasing order of current delivery capability, and maintain already-conducting circuits in conductive state. This dynamic adaptation ensures optimal performance across varying input currents and minimizes energy losses.
2Power
If MOS transistors are used as controlled switches, then the circuit works well in low power converters, but it cannot be generalized to high power domain
Solution Approach 1:
The patent changes the switch type from MOS transistors to thyristors, which can handle high power applications. Thyristors are equipped with resonant circuits that enable reliable current cancellation and controlled opening, maintaining reliability in the high power domain where MOS transistors fail.
3Power
If thyristors are used as power controlled switches, then high power handling is achieved, but the opening is not instantaneous and requires recovery time
Solution Approach 1:
The resonant circuit is designed to prepare the current cancellation before the thyristor needs to open. By using multiple parallel elementary circuits with optimized L/C ratios, the system pre-establishes current paths that enable faster effective opening, reducing the impact of thyristor recovery time on overall circuit performance.
4Reliability
If a resonant circuit is used for current cancellation, then thyristor opening time is managed, but the circuit complexity increases
Solution Approach 1:
Instead of using a single complex resonant circuit, the patent segments the system into multiple simpler elementary circuits connected in parallel. Each elementary circuit has its own thyristor and resonant components, allowing independent optimization and control, which reduces overall complexity while maintaining reliability.
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
This configuration optimizes current distribution and reduces losses by allowing each circuit to operate optimally, maintaining efficiency across varying input currents and minimizing high-frequency losses.
Implementation Method 1
said current cancellation means comprise a resonant circuit comprising a second series inductance connected between said first series inductance and the series diode, and a second capacitor connected to the terminal common to said second series inductance and to the series diode
Implementation Method 2
said variable inductance can be produced using two transformers whose primary windings are in series and the secondary windings are in opposition
Implementation Method 3
using as a second inductance a variable inductance depending on the input current and of high value when this current is low
Data Source
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Figure 5~6
AI summary
The invention relates to a power factor correction circuit, comprising a boost converter having a switch controlled by a control circuit (12), a first output capacitor (C1), and a first series input inductor (L1), a diode (D) being connected in series with said first inductor between the controlled switch and the output capacitor. Said controlled switch is formed of a thyristor (10) and an antiparallel diode (11), and means (Lr, Cr) are provided to ensure that the current in the thyristor is turned off for a sufficient time after the latter is opened.