VFD DC Link Power Supply Using Precharged Energy Storage
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Solution Overview
Problem
Existing variable frequency drives (VFDs) face issues with grid disturbances causing voltage dips, leading to insufficient power delivery and loss of controllability, which can result in turbomachine trips, and the implementation of auxiliary power converters or oversizing the VFD and electric machine to address this increases size, weight, and cost.
Innovation Solution
A power supply device with a switch and energy storage device, including an additional impedance, is used to manage DC link voltage during dips, allowing energy storage means to supply the DC link without oversizing, using a method that controls the switch based on voltage thresholds and energy flow to maintain optimal operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If auxiliary power converter is implemented to supply DC link during voltage dips, then power delivery reliability is improved, but device complexity and cost increase
Solution Approach 1:
The energy storage device is integrated directly into the existing DC link structure, merging the energy storage function with the power conversion system. This eliminates the need for a separate auxiliary power converter while maintaining the ability to supply power during voltage dips, thereby improving reliability without increasing device complexity
Solution Approach 2:
The energy storage device serves itself by automatically charging during normal operation and discharging during voltage dips without requiring external control or additional power conversion equipment. This self-service capability reduces system complexity while ensuring continuous power delivery
2Device complexity
If energy storage means are directly connected to DC link without auxiliary power converter, then device complexity is reduced, but energy storage capacity must be oversized increasing size and weight
Solution Approach 1:
The energy storage device is pre-charged to a voltage higher than the maximum DC link voltage during normal operation. This preliminary charging action allows the device to immediately discharge and support the DC link during voltage dips without requiring oversized capacity, thereby reducing weight while maintaining simplicity
Solution Approach 2:
The operating voltage parameter of the energy storage device is changed to be higher than the maximum DC link voltage. This parameter change enables the device to function as both an energy storage element and a voltage support mechanism, reducing the required energy storage capacity and overall device weight
3Reliability
If VFD and electric machine are oversized to maintain torque during voltage dips, then power delivery reliability is improved, but size and cost increase
Solution Approach 1:
The energy storage device acts as an intermediary between the grid and the electric machine during voltage dips. It mediates the power transfer by supplying additional energy to the DC link, allowing the VFD and electric machine to operate at their rated size without requiring oversizing for reliability
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 approach reduces the need for oversized components, minimizing size, weight, and cost while ensuring continuous power delivery during voltage dips, enhancing reliability and efficiency.
Implementation Method 1
loading the energy storage means when the switch is open so that the voltage of the energy storage means is equal to a loading voltage value equal to the sum of the DC maximal value and a voltage threshold
Implementation Method 2
the energy storage device including an additional impedance
Data Source
AI summary
Provided is a power supply device for a variable frequency drive, a drive system and a method for supplying the same, the power supply device includes a switch and an energy storage device having an additional impedance and an energy storage means, a loading means to load the energy storage means when the switch is open so that the voltage of the energy storage means is equal to a loading voltage value equal to the sum of a DC maximal value and a voltage threshold, and maintain the load of the energy storage means when the switch s open so that the voltage of the energy storage means is equal to the loading voltage value, and a control means to close the switch when a DC link voltage of the variable frequency drive is equal or smaller than a DC minimal value minus a predetermined voltage value.