Series Power-Cell VFD Layout for High-Voltage Pump Drives
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Solution Overview
Problem
The withstand-voltage capacity of existing power modules in VFD systems is limited, leading to mismatched input voltages from power supply facilities, necessitating voltage-reduction transformers, which increase volume, weight, and harmonic pollution, and risk motor damage due to heat and cable complications.
Innovation Solution
A VFD system utilizing multiple power cells connected in series to reduce voltage requirements, incorporating a phase-shifting transformer for electromagnetic isolation and harmonic reduction, and providing bypass and bypath functions to prevent shutdowns and ensure continuous operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If voltage-reduction transformer is used to match input voltage, then voltage compatibility is improved, but volume and weight increase
Solution Approach 1:
The patent divides the power module into multiple series-connected units (first power module, second power module, third power module) to share the voltage stress. Each module handles a portion of the total voltage, eliminating the need for a voltage-reduction transformer and reducing system weight and volume.
Solution Approach 2:
The patent changes the voltage handling parameter of individual power modules by connecting them in series. This allows the system to accept high-voltage input (e.g., 10kV or above) without requiring voltage transformation, directly improving voltage compatibility while avoiding transformer weight.
2Adaptability or versatility
If voltage-reduction transformer is used to match input voltage, then voltage compatibility is improved, but device complexity increases
Solution Approach 1:
The patent extracts and removes the voltage-reduction transformer from the system by implementing series-connected power modules that can directly handle high-voltage input. This simplifies the system architecture by eliminating unnecessary transformation stages and reducing overall device complexity.
3Device complexity
If series-connected power modules are used to handle high voltage, then transformer elimination is achieved, but power loss increases
Solution Approach 1:
The patent segments the power handling function across multiple series-connected modules, which enables direct high-voltage connection without transformers. Although series connection increases cable voltage stress, the elimination of transformer losses and improved power factor compensation reduces overall energy loss.
Solution Approach 2:
The patent implements active power factor compensation using a capacitor bank controlled by a microcontroller. The system continuously monitors power factor and adjusts capacitor switching to maintain optimal values, reducing reactive power losses and improving overall energy efficiency despite series connection losses.
4Reliability
If bypass function is implemented for power module protection, then reliability is improved, but device complexity increases
Solution Approach 1:
The patent implements a bypass circuit with controllable switch and capacitor that activates when a power module fails. The microcontroller detects module failures and preemptively switches bypass paths to maintain continuous operation, preventing total system shutdown and improving reliability.
Solution Approach 2:
The patent introduces a capacitor bank as an intermediary energy storage element that can supply power during module failures. The capacitor acts as a buffer, allowing the system to maintain operation while transitioning to bypass mode, thereby improving reliability without requiring complex real-time replacement mechanisms.
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 system adapts to higher voltage power supplies, reduces cable power loss and diameter, simplifies site layout, and ensures reliable operation by preventing shutdowns and harmonic pollution, while allowing direct connection to large power facilities.
Implementation Method 1
incorporating a phase-shifting transformer for electromagnetic isolation and harmonic reduction
Data Source
AI summary
The techniques disclosed herein reduce the withstand-voltage requirement on single power cell of a VFD (variable-frequency drive) system, and prevent the VFD system from stopping due to the damage of individual power cell in the VFD system. The VFD system includes: a motor; and a plurality of power cells connected in series for supplying electric power from a power supply facility to the motor after the electric power is subjected to voltage regulation and/or frequency conversion, so as to drive the motor to operate and generate a driving force.