Multilevel Converter Control Without Zero-Current Detection
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Solution Overview
Problem
Conventional multi-level AC/DC and DC/DC conversion circuits face inefficiencies due to inaccurate turn-off timing of synchronous rectification switches, which can lead to increased losses or malfunction, and the addition of zero-current or zero-crossing detection circuits complicates the design and introduces current direction variations and cost issues.
Innovation Solution
A multi-level AC/DC and DC/DC conversion circuit design that calculates the duty ratio of synchronous rectification switches based on input and output voltages, switching cycle, and interval time, eliminating the need for additional detection circuits and enhancing reliability and reducing costs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If synchronous rectification switch is turned off early to prevent negative current, then circuit reliability is improved, but greater losses are generated reducing efficiency
Solution Approach 1:
The control module calculates and determines the turn-off time of the synchronous rectification switch before the actual switching operation occurs. By using the formula Toff = Ts - Ton - (1-D)×Ts/(N-1), the system proactively sets the optimal turn-off moment based on pre-known parameters (switching cycle Ts, main switch conduction time Ton, duty ratio D, and level number N), preventing both early and late turn-off scenarios and thus resolving the contradiction between reliability and energy losses.
2Productivity
If zero-current detecting function is added to accurately control turn-off time, then efficiency is improved, but cost and circuit complexity are increased
Solution Approach 1:
The invention extracts and eliminates the need for complex zero-current detection circuits and sampling systems by using a purely calculation-based approach. The control module directly computes the turn-off time using basic circuit parameters (Ts, Ton, D, N) through a mathematical formula, removing the disturbing elements of current detection hardware while maintaining accurate timing control, thus improving efficiency without adding complexity.
Solution Approach 2:
The system uses its own inherent parameters (switching cycle, conduction time, duty ratio, and level configuration) to self-determine the optimal turn-off time without external detection aids. The control module serves itself by calculating Toff from internally known quantities, eliminating the need for separate detection circuits and making the system self-sufficient.
3Measurement precision
If zero-crossing detection circuit is added to control turn-off time, then turn-off accuracy is improved, but cost and layout difficulty are increased
Solution Approach 1:
The invention replaces physical detection circuits (zero-crossing detectors, current sensors, sampling hardware) with a mathematical calculation system. Instead of using electrical circuits to detect and measure current zero-crossings, the control module uses a formula-based approach (Toff = Ts - Ton - (1-D)×Ts/(N-1)) to compute the exact turn-off time, substituting complex electrical measurement systems with simpler computational logic.
4Reliability
If synchronous rectification switch is clamped by flying capacitor, then switch protection is provided, but switch may be broken when current is too large
Solution Approach 1:
The control module calculates and sets the optimal turn-off time before the synchronous rectification switch experiences dangerous current levels. By determining Toff = Ts - Ton - (1-D)×Ts/(N-1) in advance, the system proactively turns off the switch at the precise moment when current becomes negative, preventing excessive current buildup that could damage the switch or overload the flying capacitor, thus maintaining both protection and strength.
Data Source
AI summary
In the present disclosure, the multi-level AC/DC conversion circuit and the multi-level DC/DC conversion circuit calculate the duty ratio of synchronous rectification switch according to the input voltage, the output voltage, the interval time of turning on the main switch, the switching cycle and the duty ratio of main switch, thereby eliminating the need for additional zero-current detecting function or zero-crossing detection circuit in conventional AC/DC conversion circuits. Accordingly, for the multi-level AC/DC conversion circuit and the multi-level DC/DC conversion circuit of the present disclosure, the cost is reduced, and the reliability is enhanced.