CHP Generator Starter with VFD Bypass for Inrush Current Control
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Solution Overview
Problem
CHP units face challenges in starting due to high inrush current requirements, which strain the grid and lead to inefficiencies and reduced reliability, and existing solutions like soft starters and continuous-use VFDs are either inefficient or complex and costly.
Innovation Solution
A starter system that uses a variable frequency drive (VFD) to reduce the frequency of power to the generator during startup, allowing a bypass relay to connect the generator directly to the grid once started, thereby limiting inrush current and increasing efficiency by reducing the VFD's operational time and complexity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If a soft starter is used to reduce inrush current, then the current load is reduced, but the torque provided by the generator is also reduced and the generator operates inefficiently causing rapid heating
Solution Approach 1:
The patent applies dynamics by making the VFD operational status changeable - it is active during startup to provide controlled frequency and voltage, then bypassed during normal operation. This dynamic configuration allows the system to optimize performance for each operational phase, resolving the contradiction between current limitation and generator efficiency.
Solution Approach 2:
The VFD operates periodically - activated during the startup phase to control inrush current and then deactivated/bypassed during normal operation. This periodic action allows the system to benefit from current limiting only when necessary, maintaining generator efficiency during prolonged operation.
2Use of energy by moving object
If a continuous-use VFD is used to limit inrush current, then the starting current is controlled, but the VFD consumes significant energy, dissipates heat, and requires extensive heat exchange systems increasing size and complexity
Solution Approach 1:
The VFD is activated only during the startup phase and then bypassed during normal operation. This periodic operation eliminates the need for continuous heat dissipation systems, reducing the overall system size and complexity while maintaining effective inrush current control during the critical startup period.
Solution Approach 2:
The patent extracts the VFD from the permanent system configuration by introducing a bypass relay that removes the VFD from the circuit after startup. This extraction eliminates the need for continuous operation of the VFD and its associated heat management infrastructure.
3Speed
If the generator is started directly with high inrush current, then the startup is fast, but the grid connection is strained and may exceed allowable limits
Solution Approach 1:
The VFD is activated before the generator starts to pre-control the frequency and voltage supplied to the generator. This preliminary action smooths the startup process, limiting inrush current while maintaining adequate startup speed, and prevents grid connection strain.
Solution Approach 2:
The VFD changes the frequency and voltage parameters supplied to the generator during startup, initially providing reduced frequency to limit inrush current while still enabling generator rotation and startup, then transitioning to normal parameters once the generator is running.
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 solution limits inrush current, increases overall efficiency, reduces heat generation and the need for extensive heat dissipation, and extends the service life of the generator and starter system, while maintaining efficiency during both startup and normal operation.
Implementation Method 1
a variable frequency drive operable to receive power from the grid, to reduce the frequency of the power, and to provide the reduced-frequency power to the generator to start the generator
Implementation Method 2
a bypass relay configured to bypass the variable frequency drive, allowing direct connection between the grid and the generator after the generator has started
Data Source
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AI summary
A starter system for start up of a combined heat and power unit comprising a generator which is connectable to the grid. The starter system comprises a variable frequency drive, VFD, operable to receive power from the grid. The VFD reduces the frequency of the power, and provides the reduced-frequency power to the generator to start the generator. The starter system further comprises a bypass relay configured to bypass the VFD. The bypass relay allows direct connection between the grid and the generator after the generator has started. The variable frequency drive is configured to operate temporarily during start up of the combined heat and power unit.