Synchronous Motor Control via Q-Axis Voltage Limiting
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Solution Overview
Problem
Existing control methods for permanent magnet and synchronous reluctance motors face challenges in reducing machine terminal voltage while maintaining current control, especially at high speeds, due to limitations in d-axis current control techniques and voltage regulation, particularly in weak flux machines.
Innovation Solution
A method and system for controlling synchronous machines, including generating d-axis and q-axis current commands, producing modified current commands to limit terminal voltage, and using a field-weakening voltage loop to adjust voltage commands, ensuring stable current regulation across non-linear operation regions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If d-axis current control techniques are used to field weaken the back EMF in strong magnet flux PM machines, then the magnet flux and magnet back EMF are reduced, but the control becomes unstable at high speeds with large demagnetizing current due to d-axis flux sign reversal
Solution Approach 1:
Instead of using d-axis current control to reduce back EMF, the patent inverts the approach by using q-axis current control with a modified current command that directly limits the machine terminal voltage. This alternative control path avoids the instability caused by d-axis flux sign reversal while achieving the same back EMF reduction effect.
Solution Approach 2:
The patent changes the control parameter from d-axis current to q-axis current with voltage limiting. By modifying the current command in the q-axis and applying voltage limits, the system achieves back EMF reduction without encountering the flux reversal problem that plagues d-axis current control at high speeds.
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 solution effectively reduces machine terminal voltage while retaining current control at high speeds, improving operational stability and efficiency by modifying current commands and using feedback loops to correct for parameter mismatches and voltage limitations.
Implementation Method 1
The AC motors used in vehicle applications are typically controlled via a voltage source inverter such that the motor phase currents are sinusoidal.
Implementation Method 2
At higher speeds, the PM machine, without voltage control, produces a machine flux, or a back EMF, that may increase beyond the DC bus voltage.
Implementation Method 3
In PM machines, the magnet flux cannot be inherently reduced, thus a demagnetizing current is typically applied to reduce the magnet or total flux of the PM machine.
Implementation Method 4
A field weakening voltage loop is typically used to correct the errors between the model and the actual machine parameters for a stable machine operation.
Data Source
AI summary
Methods and systems are provided for controlling synchronous machines. The method comprises generating a d-axis current command and a q-axis current command, producing a modified current command from the q-axis current command, converting the d-axis current command to a first voltage command, converting the modified current command to a second voltage command, and supplying the first and second voltage commands to the synchronous machine. The modified current command limits a terminal voltage generated by the permanent magnet machine.