Parallel Converter Control for Split DC Bus Voltage Balance
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Solution Overview
Problem
In power conversion devices with an inverter having a DC side divided into two by capacitors, voltage unbalance between capacitors can lead to complications in control and reduced efficiency, particularly due to the need for cooperative operation of the DC-DC converter and balance circuit.
Innovation Solution
A power conversion device configuration that includes two converters and capacitors connected in series, where each converter individually controls the DC voltage of its corresponding capacitor to maintain voltage balance without a balance circuit, thereby simplifying control and reducing power loss.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If a balance circuit is added to eliminate voltage difference between capacitors, then voltage balance is improved, but device complexity increases
Solution Approach 1:
The patent extracts the voltage balance function from a separate balance circuit and integrates it into the existing DC-DC converter control system. By removing the need for a dedicated balance circuit and incorporating balance control within the converter's existing control architecture, the invention eliminates voltage unbalance while reducing overall device complexity.
Solution Approach 2:
The DC-DC converter is designed to perform multiple functions simultaneously: it regulates the DC bus voltage and also maintains voltage balance between the series-connected capacitors. This multi-functionality eliminates the need for a separate balance circuit, as the converter's control system handles both voltage regulation and balance maintenance through integrated control logic.
2Speed
If responsiveness of DC bus voltage control and balance circuit control are made equivalent, then control speed is improved, but voltage fluctuations increase
Solution Approach 1:
The patent implements dynamic control where the responsiveness of the balance function is adjusted based on operating conditions. The control system dynamically prioritizes DC bus voltage regulation over capacitor voltage balance during transient states, and focuses on balance maintenance during steady-state operation. This dynamic adjustment prevents control interference and voltage fluctuations while maintaining both control functions effectively.
3Loss of energy
If power loss in balance circuit is reduced by optimizing control operation, then efficiency is improved, but control complexity increases
Solution Approach 1:
The DC-DC converter serves itself by simultaneously performing DC bus voltage regulation and capacitor voltage balance maintenance through its existing control system. This self-service approach eliminates the need for a separate balance circuit that would incur power losses, while the control logic remains integrated and manageable within the converter's existing control architecture.
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 effectively suppresses voltage unbalance between capacitors without complicating control or reducing efficiency, ensuring stable operation of the power conversion device.
Implementation Method 1
a first converter (20A) to receive an input voltage from a power source (10) and output a first DC voltage (V1) to a first capacitor (C1), a second converter (20B) to receive an input voltage common to the first converter and output a second DC voltage (V2) to a second capacitor (C2)
Data Source
AI summary
A first capacitor and a second capacitor are connected in series through a neutral point on the DC side of an inverter. A first converter receives an input voltage from a power source and outputs a first DC voltage to the first capacitor. A second converter receives a common input voltage and outputs a second DC voltage to the second capacitor. A control circuit controls the first converter such that the first DC voltage is controlled in accordance with a preset first voltage command value and controls the second converter such that the second DC voltage is controlled in accordance with a second voltage command value set equivalent to the first voltage command value.