Medium Voltage Inverter Power Failure Compensation
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Solution Overview
Problem
Conventional instantaneous power failure compensating apparatuses for medium voltage inverters with a cascade H-bridge structure fail to control DC-link voltage across multiple power cells, leading to inverter shutdown during prolonged power outages, especially in industrial settings with large loads, due to inability to manage parasitic elements and external environmental factors.
Innovation Solution
A method and system for compensating instantaneous power failures in medium voltage inverters by decreasing and maintaining output frequency during power restoration, using a controller to regulate the frequency of power cells connected in series to a motor, allowing for continuous operation by converting mechanical kinetic energy into electric energy, and preventing property damage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional electrolytic condenser capacity is designed for 16 msec operation, then the inverter can operate without interruption during short power failures, but the inverter stops operating when power failure lasts more than 16 msec
Solution Approach 1:
The patent changes the operational parameters of the inverter during power failure conditions. Specifically, it adjusts the output frequency and voltage of the power cells dynamically based on the power cell voltage levels, allowing the inverter to extend its operation beyond the conventional 16 msec limit by adapting to changing conditions rather than maintaining fixed parameters
Solution Approach 2:
The patent introduces dynamic control mechanisms that adjust the inverter's operation in real-time during power failures. The controller modifies output frequency and voltage based on detected power cell voltages, transforming the static 16 msec operation limit into a dynamic, adaptable system that can extend operation duration based on actual power availability and load conditions
2Ease of operation
If feedback reference voltage is used as voltage command for DC-link, then the control system is simple, but DC-link voltage of each power cell differs due to parasitic elements making it impossible to drive the inverter
Solution Approach 1:
The patent implements a feedback mechanism that monitors the actual voltage of each power cell and uses this information to adjust the output frequency and voltage commands. This closed-loop feedback approach compensates for voltage differences caused by parasitic elements, ensuring reliable inverter operation while maintaining reasonable control complexity
Solution Approach 2:
The patent applies different control strategies to different power cells based on their individual voltage levels. Each power cell's output frequency and voltage are adjusted according to its specific voltage condition, allowing the system to accommodate parasitic element variations across different cells while maintaining overall system reliability
3Reliability
If output frequency is decreased during power restoration, then continuous operation is enabled, but the load acceleration time increases
Solution Approach 1:
The patent dynamically adjusts the output frequency based on the operational phase - maintaining reduced frequency during power failure to enable continuous operation, then progressively increasing frequency during restoration to balance continuous operation capability with load acceleration requirements. This dynamic adjustment minimizes time loss while ensuring 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
Enables continuous operation of medium voltage inverters during power failures exceeding 16 ms, enhancing reliability and product quality by effectively managing power restoration and preventing over-current trips, thus overcoming limitations of conventional systems.
Implementation Method 1
configured to convert a mechanical kinetic energy stored in a load to an electric energy in a case an instantaneous power failure occurs
Data Source
AI summary
Provided are a method for compensating instantaneous power failure in medium voltage inverter and a medium voltage inverter system by using the same, the method for compensating instantaneous power failure in medium voltage inverter including a plurality of power cells supplying a phase voltage to a motor by being connected to the motor in series, the method including decreasing an output frequency of the plurality of power cells by as much as a predetermined value at a relevant point where an input voltage of the plurality of power cells is less than a reference value, decreasing the output frequency at a predetermined deceleration gradient, and maintaining the output frequency during restoration of input voltage as long as a predetermined time, in a case the input voltage is restored.