Inverter Phase Disconnection for Zero-Sequence Current Control
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Classic multi-phase electric motor systems experience significant current ripples due to magnetic couplings, leading to parasitic currents that do not contribute to the rotating magnetic field, and result in increased switching losses in the inverter.
Innovation Solution
The method involves selectively disconnecting and reconnecting phases of the electric motor in a controlled manner, using an inverter to manage phase currents and voltages, thereby reducing zero sequence currents and switching losses by altering the impedance and phase connections based on measured current vectors and angular sectors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If phases are continuously connected to the voltage source to maintain motor operation, then the motor produces continuous torque, but significant current ripples appear due to zero sequence current
Solution Approach 1:
The patent applies periodic disconnection of phases synchronized with the current vector rotation. At specific angular positions during each rotation cycle, one or more phases are disconnected from the voltage source and then reconnected, creating a periodic action pattern that eliminates zero sequence current at critical moments while maintaining overall continuous motor operation and torque production.
Solution Approach 2:
The patent implements preliminary anti-action by disconnecting phases in advance of when zero sequence current would naturally occur. The control system predicts the rotation position of the current vector and proactively disconnects phases before harmful current ripples can develop, preventing the harmful effect rather than reacting to it after occurrence.
2Object-generated harmful factors
If phases are disconnected to reduce current ripples, then zero sequence current is reduced, but motor torque may be affected
Solution Approach 1:
The periodic disconnection is timed to occur at angular positions where the current vector orientation naturally minimizes torque impact. By synchronizing phase disconnection with specific rotational positions, the system maintains torque production during connected phases while eliminating zero sequence current during disconnected phases, achieving both goals through coordinated periodic action.
Solution Approach 2:
The system performs preliminary action by preparing the phase disconnection sequence in advance based on predicted current vector position. This ensures that phase disconnection occurs at optimal moments that minimize torque disruption while maximizing zero sequence current reduction, balancing both requirements through advance planning and execution.
3Ease of operation
If conventional switching is used to control phase voltages, then the inverter can regulate motor operation, but switching losses increase
Solution Approach 1:
The patent reduces switching losses by implementing periodic phase disconnection that minimizes the frequency of switching operations. Instead of continuous high-frequency switching required in conventional control, the system disconnects phases periodically at lower frequency, significantly reducing the number of switching events and associated energy losses while maintaining adequate voltage control capability.
Solution Approach 2:
The patent extracts the harmful switching operations from the continuous control process. By removing phases from active switching during specific intervals, the system eliminates unnecessary switching losses while retaining essential voltage control functionality during connected phases, effectively separating the control function from the loss-generating switching action.
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 effectively reduces unwanted current ripples and switching losses, while maintaining motor torque efficiency by strategically disconnecting phases during specific angular sectors, thereby enhancing the overall performance of the electric motor system.
Implementation Method 1
a control device for controlling an inverter so that the latter makes a switched connection of phases to a voltage source so as to rotate a current vector
Implementation Method 2
in a conventional multi-phase machine, the magnetic couplings between the phases oppose a very low impedance to this zero sequence current, so that significant current ripples appear
Data Source
Figure 1~3
Figure 4~5
Figure 6~7
AI summary
The invention relates to a method comprising the switched connection of the phases to a voltage source in such a way as to turn the current vector defined by the phase currents (iu, iv,iw ). Said method also comprises, during at least one turn of the current vector, for each of one or more phases: on part of the turn, the disconnection of the phase from the voltage source in order to place the phase in an open circuit and cancel the corresponding phase current (iu, iv,iw ), and, on the other part of the revolution, the switched connection of the phase to the voltage source.