Variable-Flux Motor Drive System Torque Control
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Solution Overview
Problem
Conventional permanent-magnet synchronous motor drive systems face inefficiencies and increased inverter size due to high current demands at low speeds, leading to heat and cooling issues, and the need for high withstand voltage in inverters, which complicates torque control and reliability.
Innovation Solution
A variable-flux motor drive system that employs a combination of fixed and variable magnets, allowing flux adjustment via magnetizing currents from the inverter, with a control system to manage torque and flux to optimize efficiency and reduce transient torque and overheating.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If permanent magnet synchronous motor is used to reduce loss and size, then motor efficiency is improved, but inverter current capacity must be increased leading to larger inverter size
Solution Approach 1:
The patent applies dynamics by making the motor flux dynamic rather than fixed. The control system varies the motor flux according to operating conditions (speed, torque requirements) to optimize the balance between motor performance and inverter current capacity, thereby reducing inverter size while maintaining efficiency.
Solution Approach 2:
The patent changes the flux parameter of the motor dynamically through control of the stator current. By adjusting the flux magnitude and orientation based on operating conditions, the system optimizes torque production efficiency while limiting peak current demands on the inverter.
2Loss of energy
If permanent magnet synchronous motor is used for high efficiency, then motor loss is reduced, but inverter size increases due to larger current capacity requirements
Solution Approach 1:
The control system dynamically adjusts motor flux based on real-time operating conditions, enabling the motor to operate efficiently across different loads and speeds while keeping peak current demands within manageable limits for the inverter.
Solution Approach 2:
The system varies flux parameters (magnitude and angle) through controlled stator current to optimize torque production efficiency while preventing excessive current requirements that would increase inverter complexity and capacity.
3Speed
If field-weakening control is carried out to handle high induced voltage, then speed range is extended, but superposed excitation current deteriorates efficiency
Solution Approach 1:
The patent optimizes field-weakening control by carefully managing the excitation current parameters. The control system adjusts the flux reduction magnitude and rate to achieve the necessary speed extension while minimizing the negative impact on efficiency through optimized current superposition.
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 improves torque accuracy, reduces inverter size and heat, and enhances overall efficiency by dynamically controlling flux, thereby addressing the limitations of conventional PM motor drive systems.
Implementation Method 1
a variable magnet (53) whose magnetic material has a variable flux density Br2 according to a magnetizing current from the inverter (1)
Implementation Method 2
a fixed magnet (54) whose magnetic material has a fixed flux density Br1 and a variable magnet (53) whose magnetic material has a variable flux density Br2
Data Source
AI summary
A variable-flux motor drive system including a permanent-magnet motor including a permanent magnet, an inverter to drive the permanent-magnet motor, and a magnetize device to pass a magnetizing current for controlling flux of the permanent magnet. The permanent magnet is a variable magnet whose flux density is variable depending on a magnetizing current from the inverter. The magnetize device passes a magnetizing current that is over a magnetization saturation zone of magnetic material of the variable magnet. This system improves a flux repeatability of the variable magnet and a torque accuracy.