Multi-level DC/AC Converter Voltage Segmentation
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Solution Overview
Problem
Existing DC/AC converters face challenges in efficiently converting low and variable direct current from renewable energy sources into alternating current with high harmonic content, leading to increased complexity, cost, and switching losses due to high voltage requirements for electronic switches.
Innovation Solution
A DC/AC converter with a half-bridge configuration that employs auxiliary switches driven by PWM signals to manage output voltage levels, reducing harmonic content and switching losses by limiting voltage ratings and optimizing switch operation based on output voltage requirements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If a step-up converter is used to convert low direct voltage to high alternating voltage, then the output voltage can reach the required peak value, but the circuit complexity and cost increase due to the additional step-up stage
Solution Approach 1:
The patent segments the voltage conversion function across multiple half-bridge legs, each capable of generating multiple voltage levels (0, +Vdc/2, -Vdc/2). By coordinating the switching of these legs, the system synthesizes high-voltage output without requiring a separate step-up converter, thus reducing circuit complexity while maintaining the required output voltage capability
Solution Approach 2:
The patent transitions from a single-voltage-level conversion approach to a multi-level voltage synthesis approach. Instead of using one converter stage, it employs multiple switching legs that can independently contribute different voltage levels, effectively adding a dimensional aspect to voltage generation and eliminating the need for sequential conversion stages
2Object-generated harmful factors
If a full-bridge converter connected to series DC sources is used, then the harmonic content is reduced, but the electronic switches must be dimensioned for high voltage ratings causing high switching losses
Solution Approach 1:
The patent divides the voltage stress across multiple switches in series within each half-bridge leg. Each switch only needs to block a fraction of the total voltage (Vdc/2), rather than the full high voltage. This segmentation of voltage stress allows using lower-voltage-rated switches, reducing switching losses while maintaining the ability to generate high-voltage output through series connection during specific switching states
Solution Approach 2:
The patent changes the voltage rating parameter of the electronic switches from high voltage to medium voltage by introducing a multi-level topology. The switches are designed to operate at lower voltage levels (Vdc/2) but achieve high-voltage output through the coordinated series connection of multiple switches and the use of capacitive energy storage elements, thereby reducing switching losses
3Loss of energy
If multiple voltage levels are generated using series switch arrangements, then switching losses are reduced, but the device complexity increases due to additional switches and control requirements
Solution Approach 1:
The patent designs each half-bridge leg to be multi-functional, capable of generating multiple voltage levels (0, +Vdc/2, -Vdc/2) and operating in different modes (buck, boost, buck-boost) depending on the switching state. This universality allows the same basic circuit structure to perform multiple functions, reducing the need for additional dedicated components while achieving reduced switching losses through multi-level operation
Solution Approach 2:
The patent employs dynamic switching control where the function of each switch changes over time within the switching cycle. Switches are dynamically turned on and off in specific sequences to achieve different voltage levels and conversion modes. This dynamic operation allows the circuit to adapt its configuration for optimal performance, reducing switching losses while managing complexity through intelligent control rather than additional hardware
Data Source
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AI summary
The multi-level DC/AC converter, comprising: an input (5,7) connectable to a direct voltage source (3), with a first connection (5) and a second connection (7) between which can be applied an input voltage (Vi); a half-bridge with a first controlled switch (21) and a second controlled switch (25) between which is positioned an output (U) of the converter; a first connecting branch (15) between the first controlled switch (21) and the first connection (5) and a second connecting branch (17) between the second controlled switch (25) and the second connection (7); a third controlled switch (59) associated to the first controlled switch (21), connectable in series to the first controlled switch to generate an output voltage exceeding a first limit value (Vi/2); a fourth controlled switch (61) associated to the second controlled switch (25), connectable in series to said second controlled switch to generate an output voltage below a second limit value (-Vi/2).