Voltage Boost Circuit for Motor Drive Speed Control
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Solution Overview
Problem
Permanent magnet electric motors, such as those used in electric power steering systems, face limitations in maximum rotational speed and torque production due to back EMF, which restricts their performance, especially when powered by batteries, as they rely on varying current phases and voltages that are constrained by battery voltage.
Innovation Solution
A drive system incorporating a voltage boost circuit and phase advance control, where a push-pull voltage boost circuit with a bifilar wound component and active switches boosts the nominal voltage, and control means adjust the phase of the current relative to the rotor position, allowing for increased torque and speed by optimizing the phase advance angle and voltage boost strategy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If battery voltage is used directly to drive the motor, then the system is simple, but the maximum motor speed is limited by back EMF
Solution Approach 1:
A voltage boost circuit is introduced as an intermediary device between the battery and the motor. This circuit temporarily boosts the battery voltage to a higher level, enabling the motor to overcome back EMF limitations and achieve higher speeds without permanently increasing system complexity
Solution Approach 2:
The voltage boost circuit is controlled dynamically based on motor operating conditions. The control system activates voltage boosting when high speed is required and deactivates it when normal operation suffices, making the system adaptable to different speed requirements
2Speed
If voltage boost circuit is added to increase motor speed, then maximum motor speed increases, but device complexity increases
Solution Approach 1:
The voltage boost circuit is integrated into the existing motor control system, allowing the control unit to perform multiple functions: normal PWM control and voltage boosting. This multi-functionality reduces the need for separate dedicated components and minimizes overall system complexity
3Force
If phase advance control is applied to increase torque at high speed, then torque increases, but battery current increases
Solution Approach 1:
The control system dynamically adjusts the phase advance angle based on motor speed and load conditions. By optimizing this parameter, the system achieves maximum torque with minimum current draw, preventing excessive battery current while maintaining high torque output
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 enhances motor efficiency and power output at higher speeds by increasing the effective torque constant and reducing losses, enabling the motor to operate at higher speeds and produce more torque while maintaining battery current within limits, thus overcoming the constraints imposed by back EMF and battery voltage.
Implementation Method 1
boost means in electric communication with the power input and power output, and controllable to boost the nominal voltage to a higher voltage for application to the winding
Implementation Method 2
Applying suitable voltages across each of the phase windings causes current to flow through the windings, generating a current flux vector in the air gap between the stator and the rotor. This flux interacts with the magnetic field of the rotor to cause the rotor to rotate
Implementation Method 3
as rotor speed increases the back emf that is produced limits the torque that can be produced
Data Source
AI summary
A drive system for a motor having a rotor and a phase winding (a, b, c) comprises; a drive circuit including switch means associated with the winding a, b, c for varying the current passing through the winding; rotor position sensing means arranged to sense the position of the rotor; control means arranged to provide drive signals to control the switch means; a power input for connection to a power supply at a nominal voltage; and boost means in electric communication with the power input and power output, and controllable to boost the nominal voltage to a higher voltage for application to the winding.