DC Link Voltage Boost for Transient High-Speed VFD Motors
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Solution Overview
Problem
Existing variable frequency drive systems are limited by the maximum DC link voltage, which restricts high-speed performance and torque, particularly during transient operations such as acceleration and deceleration, due to the reduced power available at high speeds.
Innovation Solution
A system and process that transiently boosts the DC link voltage using an energy storage system, such as a battery bank, capacitor bank, or flywheel, directly connected to the DC link, to increase the available voltage for short-term high-speed operation of electric motors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the DC link voltage is limited to its maximum rated value, then the system operates reliably within design specifications, but the motor cannot achieve high-speed/high-torque transient operation
Solution Approach 1:
The energy storage system is pre-charged to a voltage higher than the maximum DC link voltage during normal operation. When transient high-speed operation is required, the pre-charged energy storage system immediately discharges to boost the DC link voltage, enabling the motor to achieve high torque at high speed without waiting for voltage buildup.
Solution Approach 2:
The system dynamically adjusts the DC link voltage based on operational requirements. During normal operation, the DC link voltage is maintained at its maximum rated value for reliability. During transient high-speed operation, the DC link voltage is temporarily boosted above the maximum rated value by the energy storage system, and then returned to the rated value after the transient period.
2Power
If the DC link voltage is boosted for high-speed operation, then the motor achieves higher torque and speed performance, but the DC link voltage exceeds its maximum rated value
Solution Approach 1:
The energy storage system operates in periodic charge-discharge cycles. During normal operation, it charges to maintain a voltage higher than the maximum DC link voltage. During transient high-power demand, it discharges to boost the DC link voltage. After the transient period, it recharges to restore its energy reserve, creating a periodic action pattern that enables sustained high-performance operation.
Solution Approach 2:
The energy storage system acts as an intermediary between the rectifier and the inverter. It buffers the DC link voltage, absorbing excess energy during normal operation and releasing energy during transient high-power demands, thereby mediating the voltage fluctuations and enabling the motor to achieve higher power output without directly modifying the rectifier or inverter circuits.
3Productivity
If an energy storage system is added to the variable frequency drive, then transient high-speed performance is improved, but the system complexity increases
Solution Approach 1:
The energy storage system is electrically connected in parallel with the DC link, merging its energy capacity with the existing drive system. This configuration allows the energy storage system to supplement the DC link voltage during transient operations without requiring separate control circuits or complex modifications to the rectifier and inverter, thereby improving productivity while minimizing the increase in device complexity.
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
The DC link voltage boost enables the electric motor to operate at higher voltages, matching acceleration and deceleration performance, thereby enhancing high-speed performance and torque capabilities.
Implementation Method 1
A rectifier-fed variable frequency drive controlled motor system includes an energy storage system that stores electrical energy
Implementation Method 2
a rectifier connected to the AC power supply and adapted to convert the polyphase AC voltage into a DC voltage
Implementation Method 3
an inverter module connected to the DC link so as to convert the DC voltage to an alternating current
Data Source
AI summary
A process for transiently increasing performance of an electric motor includes boosting a DC link voltage of a rectifier-fed variable frequency drive of the electric motor by using an energy storage system. The energy storage system delivers power directly to a DC link of the variable frequency drive. The energy storage system can be at least one of a battery bank, capacitor bank and a flywheel. Feedback from the DC link is delivered to a DC link controller.