Voltage Mode Control Phase Advancing Electric Machine Torque
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Solution Overview
Problem
Voltage mode control in electric machines for position-controlled applications lacks effective torque and current control, leading to increased motor losses and limited operation due to uncontrolled phase advance and excessive current at low velocities, which can exceed motor ratings and require larger motor sizes or restrict operation to low speeds.
Innovation Solution
A method and system for voltage mode control that determines q-axis and d-axis currents to supplement torque, with d-axis current set to zero when voltage is sufficient, and generates command voltages based on q-axis and d-axis currents to limit torque and current within operational limits, using a controller coupled with a power inverter and position sensor to manage motor position and velocity signals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If voltage mode control is used for position control, then damping is provided and external sensors are minimized, but torque and current are not controlled leading to excessive current at low velocities that can exceed motor ratings
Solution Approach 1:
The patent implements feedback by measuring motor phase current and using it to compute torque, which then feeds into the voltage command calculation. This closed-loop feedback mechanism allows the system to adjust the voltage command based on actual current and torque conditions, preventing excessive current at low velocities while maintaining position control stability.
Solution Approach 2:
The patent changes the control parameter from pure voltage mode to a hybrid approach where the voltage command is modified based on computed torque and current measurements. By dynamically adjusting the voltage command using torque compensation and phase current feedback, the system prevents excessive current while maintaining position control.
2Ease of operation
If voltage is controlled to be in phase with back-EMF, then control is simplified, but unnecessary d-axis current increases motor losses
Solution Approach 1:
The patent modifies the voltage phase angle parameter dynamically based on operating conditions. Instead of maintaining a fixed phase relationship between voltage and back-EMF, the system adjusts the phase angle to optimize performance and minimize losses while maintaining control simplicity through the structured control algorithm.
3Adaptability or versatility
If command voltage exceeds DC bus voltage, then position control range is extended, but motor current cannot be increased due to voltage limit restricting torque output
Solution Approach 1:
The patent changes the control strategy by computing the required torque from phase current measurements and using this torque information to generate an appropriate voltage command. This approach allows the system to operate effectively within the DC bus voltage limit while maintaining adequate torque output through optimized voltage utilization and phase current control.
4Device complexity
If voltage mode control is used, then external sensors are minimized, but torque and current measurement capability is lost
Solution Approach 1:
The patent implements self-service by using the motor's own phase current measurements to derive torque information. The system utilizes existing current sensors to measure phase current, computes torque from these measurements, and uses the computed torque to generate the voltage command, eliminating the need for separate torque sensors while maintaining measurement capability.
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 allows for efficient torque control, reduced motor losses, and extended operational speed range by limiting torque and current within motor ratings, enhancing performance and stability in electric steering systems.
Implementation Method 1
the motor can be designed and controlled to exhibit a sinusoidal back EMF (electromotive force)
Implementation Method 2
The sinusoidal back EMF motor can be controlled utilizing phase advance
Data Source
AI summary
A method and system for controlling an electric machine using voltage mode control comprising: receiving a voltage command, the voltage command corresponding to a voltage control command for a position control loop, the position control loop configured to control a position of the electric machine; receiving a motor velocity signal; and determining a q-axis current. The method also includes computing a d-axis current to supplement the torque if a magnitude of a voltage supply for exciting the electric machine is not sufficient to provide a torque corresponding to the q-axis current, otherwise establishing the d-axis current at about zero; and generating command voltages for controlling the electric machine corresponding to the q-axis current and the d-axis current.