Three-Level Inverter Circuit with Bridge Polarity Inversion
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Solution Overview
Problem
Existing DC/AC inverter devices with multi-level circuits face challenges in reducing switching loss due to the high number of switches required, which increases complexity and cost.
Innovation Solution
A three-level inverter circuit with a bridge circuit and an intermediate voltage output circuit, where the front-stage switches are PWM-controlled at a carrier frequency and the rear-stage switches are switching-controlled at the power supply frequency, reducing the number of switches and switching loss.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a multi-level circuit with five levels is used to generate sine wave voltage, then the output voltage quality is improved, but the number of switches increases to 2(n-1) = 8 switches, causing switching loss to increase
Solution Approach 1:
The inverter circuit is divided into two separate stages: a three-level inverter circuit (front stage) and a bridge circuit (rear stage). The front stage generates a three-level voltage waveform, and the bridge circuit converts it to a five-level sine wave output. This segmentation allows each stage to use fewer switches while achieving the overall five-level output quality.
Solution Approach 2:
The three-level inverter circuit acts as an intermediary between the DC power supply and the final five-level AC output. It generates an intermediate three-level voltage that is then processed by the bridge circuit to achieve the desired five-level sine wave output, reducing the direct switching requirements.
2Measurement precision
If each switch operates at carrier frequency to control the multi-level circuit, then the output waveform quality is improved, but switching loss increases due to high-frequency switching
Solution Approach 1:
Different switching frequencies are applied to different parts of the circuit. The front-stage switches operate at carrier frequency (e.g., 20 kHz) to generate the three-level waveform, while the rear-stage bridge switches operate at lower power supply frequency (e.g., 50 Hz or 60 Hz) to perform polarity inversion. This local differentiation reduces overall switching loss while maintaining waveform quality.
3Adaptability or versatility
If a five-level inverter circuit is implemented, then the system interconnection capability is improved, but device complexity increases due to multiple switches and capacitors
Solution Approach 1:
The complex five-level inverter function is segmented into two simpler circuits: a three-level inverter circuit with fewer switches and capacitors, and a bridge circuit that performs polarity inversion. This segmentation reduces the overall device complexity while maintaining the capability for system interconnection.
Solution Approach 2:
The bridge circuit serves multiple functions: it converts the three-level output from the front stage into a five-level output, performs polarity inversion, and enables system interconnection. This multi-functionality reduces the need for additional dedicated components, simplifying the overall device.
Data Source
AI summary
A three-level inverter circuit includes first to fourth front-stage switches connected in series, and a floating capacitor connected between a connection point of the first and second front-stage switches and a connection point of the third and fourth front-stage switch elements, and outputs an intermediate voltage of a DC power supply through a connection point of the second and third front-stage switches. A bridge circuit includes first, second, third, and fourth rear-stage switches which are bridge-connected to first to fourth terminals. The first terminal thereof is connected to a connection point of the second front-stage switch and the third front-stage switch and a second terminal thereof is connected to the second input terminal.