Multilevel Drive DC Bus Neutral Point Control
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Solution Overview
Problem
Elevator systems with regenerative drives face challenges in managing acoustic noise, efficiency, neutral point stability, and thermal balancing.
Innovation Solution
A control system and method that utilize unipolar and bipolar modulation in multilevel regenerative drives to maintain neutral point current at zero amperes and distribute output voltage across the DC bus, connecting auxiliary power supplies to unevenly loaded portions and applying modulation techniques to converters and inverters to achieve balanced neutral point and thermal stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If regenerative drives are used to generate electricity during elevator operation, then energy efficiency is improved, but neutral point stability and thermal balancing become challenging to manage
Solution Approach 1:
The control system continuously monitors the neutral point current and adjusts the duty cycle signals in real-time to maintain stability. The controller receives feedback about the actual neutral point current and modifies the switching signals to keep the current at zero, ensuring stable operation while maintaining regenerative energy conversion.
Solution Approach 2:
The system dynamically changes the duty cycle parameters of the converter and inverter based on operating conditions. By adjusting the duty cycle signals for upper and lower arms of each phase, the system maintains neutral point current at zero while adapting to varying load conditions and maintaining energy efficiency.
2Use of energy by moving object
If regenerative drives are used to generate electricity during elevator operation, then energy efficiency is improved, but thermal balancing becomes challenging to manage
Solution Approach 1:
The control system monitors thermal conditions and adjusts duty cycle signals to distribute thermal stress evenly across converter and inverter components. By balancing the power distribution and switching patterns, the system prevents localized overheating while maintaining regenerative energy conversion efficiency.
3Stability of the object's composition
If duty cycle signals are adjusted to maintain neutral point current at zero amperes, then neutral point stability is improved, but control complexity increases
Solution Approach 1:
The control system performs multiple functions simultaneously: it maintains neutral point stability, balances thermal distribution, optimizes energy conversion, and manages auxiliary power supplies through a single integrated controller. This multi-functionality reduces the need for separate control circuits while achieving multiple objectives.
4Adaptability or versatility
If the DC bus is unevenly loaded, then power distribution flexibility is improved, but voltage balance across upper and lower portions deteriorates
Solution Approach 1:
The control system dynamically adjusts the duty cycle signals in response to uneven loading conditions. When the upper or lower DC bus portions become unevenly loaded, the controller modifies the switching patterns to redistribute power and maintain equal voltage across both portions, enabling flexible power distribution while preserving voltage balance.
Data Source
AI summary
A regenerative drive (30) and method for providing power from such to at least one auxiliary power supply (41, 43) is disclosed. The drive may include a converter (32) and an inverter (34) connected by a DC bus (33), and a controller (54) configured to apply at least one of unipolar modulation and bipolar modulation to the converter (32) and the inverter (34), and to provide about half of the output voltage across the upper portion (130) of the DC bus (33) and about half of the output voltage across the lower portion (136) of the DC bus (33), when the upper and lower portions (130, 136) of the DC bus (33) are unevenly loaded. A first auxiliary power supply (41) may be connected to one of the upper and lower portions (130, 136) of the DC bus (33) and may receive power from the multilevel regenerative drive (30).