Multilevel Regenerative Drive DC Link Neutral Point Management
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Solution Overview
Problem
Conventional elevator systems face challenges during utility voltage sags or power losses, leading to potential shutdowns and passenger safety issues, as they struggle to manage power demands and neutral point stability in regenerative drive systems.
Innovation Solution
A multilevel regenerative drive system with a DC link that includes independent or shared neutral points, utilizing insular-gate bipolar transistors and various topologies such as T-type and neutral-point-clamped configurations, along with unipolar and bipolar pulse width modulation modes, to manage power components and reduce acoustic noise and thermal imbalances.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If conventional systems draw more current from the power supply during voltage sags, then power delivery to the motor is maintained, but the drive shuts down to avoid damaging components
Solution Approach 1:
A DC capacitor bank is introduced as an intermediary energy storage device between the power supply and the drive components. During voltage sags, the capacitor bank supplies additional energy to maintain power delivery to the motor without requiring the drive to draw excessive current from the unstable power supply, thereby preventing shutdown while avoiding component damage.
Solution Approach 2:
The DC capacitor bank is pre-charged during normal operating conditions to store energy in advance. When voltage sags occur, this pre-stored energy acts as a cushion, immediately supplementing power delivery without causing harmful current spikes to the drive components, thus maintaining both power delivery and operational reliability.
2Loss of energy
If multilevel topologies are used in the converter and inverter, then power management efficiency is improved, but neutral point stability and thermal balancing become more difficult to manage
Solution Approach 1:
The DC link is segmented into multiple independent DC capacitor banks instead of a single unified capacitor. Each capacitor bank is associated with specific phases and has its own neutral point, allowing independent control and management. This segmentation enables separate regulation of each neutral point, simplifying the management of neutral point stability and thermal balancing while maintaining the efficiency benefits of multilevel topologies.
Data Source
AI summary
A regenerative drive device and a method for configuring the DC link of a regenerative drive device are disclosed. The multilevel regenerative drive device may include an inverter having a plurality of power components and a converter having a plurality of power components. The multilevel regenerative drive device may also include a direct current (DC) link bridging the inverter and the converter, the DC link including a capacitor, an inverter neutral point, and a converter neutral point independent of the inverter neutral point. Alternatively, the inverter neutral point and the converter neutral point may be connected.