Power Switching Circuit for Permanent Magnet Machine Speed Control
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
The existing integrated starter generator (ISG) systems for internal combustion engines face inefficiencies in power generation due to the need for shunt-control at high speeds, which leads to heating issues and insufficient power at low speeds, and the inability to control DC bus voltage effectively, risking battery overcharging.
Innovation Solution
A system comprising a central processing unit, a series power switching circuit, a bus decoupling power switch, and a bridge switching circuit that selectively connects the voltage bus to the machine or battery, allowing voltage amplification at low speeds and shunt-control at high speeds, using MOSFETs, IGBTs, or SCRs to manage power flow efficiently.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If shunt-control is used to reduce DC bus voltage at high speeds, then DC bus voltage remains within permissible limits, but power generation efficiency decreases due to heating of stator coil and MOSFET bridge
Solution Approach 1:
The patent applies dynamics by making the control method adaptive to operating conditions. The system dynamically switches between shunt-control and series-control modes based on machine speed. At high speeds, shunt-control is used to limit DC bus voltage, while at low speeds, series-control is activated to improve efficiency. This dynamic adaptation resolves the contradiction by applying the appropriate control strategy for each operating regime.
Solution Approach 2:
The patent changes the control parameter from fixed shunt-control to variable control mode selection. By monitoring machine speed and switching between control modes, the system optimizes the balance between voltage safety and efficiency. The control parameter transitions from a static approach to a dynamic one that adapts to changing operating conditions.
2Reliability
If machine characteristics are chosen for shunt-control at high speeds, then DC bus voltage is controlled, but at low speeds the back-emf is insufficient to supply required power to battery and electrical loads
Solution Approach 1:
The system dynamically adjusts control mode based on machine speed. At low speeds, series-control is activated to boost the insufficient back-emf and supply adequate power to the battery and electrical loads. At high speeds, the system switches to shunt-control to maintain DC bus voltage within safe limits. This dynamic adaptation ensures both voltage control and sufficient power supply across the entire operating range.
Solution Approach 2:
The control system acts as an intermediary that mediates between the machine's natural back-emf characteristics and the power requirements of the battery and loads. By introducing series-control at low speeds, the system compensates for insufficient back-emf, and by switching to shunt-control at high speeds, it prevents overvoltage conditions.
3Power
If shunt-control is performed at low operating speeds, then power is available to battery and loads, but cranking current is unduly increased
Solution Approach 1:
The system dynamically selects control mode based on speed to minimize harmful effects. Series-control is applied at low speeds to provide adequate power while avoiding the need for excessive cranking current. The system transitions to shunt-control at high speeds where voltage limiting becomes necessary. This dynamic approach optimizes power delivery while minimizing harmful cranking current.
4Device complexity
If a single control mode is used for all speeds, then system complexity is reduced, but either efficiency is lost at high speeds or power is insufficient at low speeds
Solution Approach 1:
The control system is made dynamic by implementing speed-based mode switching. The system monitors machine speed and automatically transitions between series-control and shunt-control modes. This dynamic approach maintains relatively simple control logic while achieving high overall efficiency by applying the optimal control mode for each operating regime.
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 enables efficient power generation at low speeds, reduces heating, and ensures safe operation by optimizing the electric machine characteristics, allowing shunt-control only at high speeds, thereby maintaining high average efficiency and reducing fuel consumption and thermal failures.
Implementation Method 1
In a permanent magnet machine, the back-emf generated at the machine terminals is proportional to speed of rotation of the machine
Implementation Method 2
the MOSFET bridge used for driving the electric machine acts as a bridge rectifier, resulting in formation of a rectified DC voltage in the DC voltage bus
Implementation Method 3
a series power switching circuit connected between the machine and a battery, and a bridge switching circuit connected between the voltage bus and the machine, the bridge switching circuit configured to amplify voltage generated by the machine
Data Source
AI summary
A system for controlling electrical power generated by a permanent magnet machine coupled to an internal combustion engine includes a central processing unit configured to determine speed of the machine, and compare the machine speed with a predetermined range of machine speeds, a series power switching circuit connected between the machine and a battery, a bus decoupling power switch connected between a voltage bus and the battery, and a bridge switching circuit connected between the voltage bus and the machine and configured to amplify voltage generated by the machine if the machine speed is less than a predetermined value or fall within a predetermined range thereby charging the battery with amplified voltage even at lower machine speeds. The central processing unit selectively connects the bridge switching circuit with the battery by actuating the bus decoupling switch and/or the series power switching circuit depending upon the machine speed.