Multilevel Converter Flying Capacitor Pre-Charging Using Single DC Link Sensor
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Solution Overview
Problem
Existing multilevel power converters require multiple voltage sensors for pre-charging flying capacitors, increasing costs and complexity due to the need for additional input/output channels and cabling, especially as power ratings increase.
Innovation Solution
A method and system that reduces the number of voltage sensors by using a single voltage measurement device across the DC link to pre-charge and isolate flying capacitors in multilevel converters, applicable to various topologies such as multicell, active neutral point clamped, and nested neutral point piloted converters, thereby decreasing the number of input/output channels and associated wiring.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a voltage sensor is installed on each flying capacitor for pre-charging, then the pre-charging operation can be monitored accurately, but the system complexity and cost increase significantly
Solution Approach 1:
The patent applies universality by making the DC link voltage sensor serve multiple functions: it monitors the overall DC link voltage and enables the controller to calculate individual flying capacitor voltages through voltage division relationships, eliminating the need for dedicated sensors on each capacitor. This multi-functional approach reduces sensor quantity while maintaining measurement capability.
Solution Approach 2:
The patent uses the DC link voltage as an intermediary measurement. Instead of directly measuring each flying capacitor voltage with dedicated sensors, the system measures the DC link voltage and uses computational relationships to derive individual capacitor voltages. This intermediary approach simplifies the measurement system while preserving the ability to monitor each capacitor's state.
2Measurement precision
If multiple voltage sensors are used for each flying capacitor, then precise voltage control is achieved, but the number of input/output channels and cabling increases
Solution Approach 1:
The DC link voltage sensor performs the universal function of enabling voltage monitoring for all flying capacitors. The controller uses the single DC link voltage measurement combined with known voltage division ratios to determine the voltage state of each individual capacitor, thereby achieving comprehensive monitoring with minimal sensing infrastructure.
Solution Approach 2:
The DC link voltage serves as an intermediary that carries information about the state of all flying capacitors. By measuring this single intermediary voltage and applying computational logic based on the converter topology and switching states, the system derives individual capacitor voltages without requiring direct electrical connections to each capacitor.
3Measurement precision
If traditional pre-charge procedure with multiple sensors is used, then each flying capacitor voltage can be directly measured, but the configuration and maintenance costs increase
Solution Approach 1:
The controller is designed with multi-functionality to perform voltage division calculations and determine individual flying capacitor voltages from the single DC link voltage measurement. This computational approach replaces the need for multiple physical sensors, reducing both assembly complexity and maintenance requirements while preserving measurement precision.
Solution Approach 2:
The system uses DC link voltage as an intermediary measurement that simplifies the overall sensing architecture. This approach reduces the number of components that need to be assembled and maintained, lowering configuration and maintenance costs while still providing accurate individual capacitor voltage information through computational derivation.
Data Source
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AI summary
An electrical circuit (160) for a power converter includes a first switching device (132) proximate an AC source (104). The circuit also includes a voltage measurement device (154) proximate a DC link (112) and extends between the AC source and the DC link. The circuit further includes a DC voltage source (152) and a first capacitive device (134). The first capacitive device (134) is positioned between the first switching device (132) and the voltage measurement device (154). The circuit further includes a second switching device (132) positioned between the first capacitive device (134) and the voltage measurement device (154). The circuit also includes a controller (120) operatively coupled to the DC voltage source (152), the voltage measurement device (154), and the switching devices (132). The controller (120) is configured to open the second switching device when a measured voltage signal generated by the voltage measurement device (154) is substantially representative of a reference voltage value.