Sensorless PMSM Startup Using DC Link Voltage Feedback
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Solution Overview
Problem
The challenge of starting a synchronous machine with a permanent magnet rotor without a position sensor or speed control, particularly during low-speed operations, is the inability to regulate torque effectively, leading to potential overcurrent and overvoltage issues due to negative torque and kinetic energy buildup in the DC link, which can damage the system if the DC link capacitance is insufficient.
Innovation Solution
A method involving vector current control with a controller that adjusts a rotating reference current vector based on a predetermined speed profile, dynamically correcting the speed profile to prevent negative torque and minimize transient processes by using different controller parameters depending on DC link voltage conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If purely controlled startup methods are used without position sensors, then device complexity is reduced and cost is lowered, but torque regulation capability is lost leading to potential overcurrent and overvoltage issues
Solution Approach 1:
The patent implements feedback by monitoring DC link voltage during startup and using this information to dynamically adjust the speed profile. The controller continuously compares the actual DC link voltage with a reference value and modifies the acceleration profile accordingly, creating a closed-loop control system that prevents overcurrent and overvoltage without requiring position sensors.
Solution Approach 2:
The patent dynamically changes the speed profile parameters based on DC link voltage conditions. When DC link voltage exceeds the reference value, the controller reduces the acceleration rate or adjusts the speed trajectory to prevent negative torque and energy feedback. This adaptive parameter adjustment enables torque regulation without position sensing.
2Reliability
If high DC link capacitance is used to prevent overvoltage, then system reliability is improved, but device complexity and cost increase
Solution Approach 1:
The patent uses DC link voltage feedback to enable minimal capacitance design. By continuously monitoring the voltage and adjusting the speed profile in real-time, the system prevents energy feedback that would cause overvoltage, allowing the use of smaller capacitance values while maintaining reliability.
Solution Approach 2:
The control system serves itself by using the DC link voltage information to automatically adjust its own operating parameters (speed profile). This self-regulation prevents the need for large passive energy storage elements, as the active control compensates for energy fluctuations.
3Device complexity
If fixed speed profile is used during startup, then control simplicity is maintained, but negative torque occurs causing energy feedback and potential damage
Solution Approach 1:
The patent transforms the static speed profile into a dynamic one that adapts to real-time conditions. The speed profile is no longer fixed but is continuously modified based on DC link voltage feedback, enabling the system to respond to rotor position and load variations without requiring position sensors.
Solution Approach 2:
The patent takes preliminary anti-action by proactively adjusting the speed profile before negative torque can occur. By monitoring DC link voltage trends and preemptively modifying the acceleration profile, the controller prevents the conditions that lead to negative torque and energy feedback rather than reacting after the problem occurs.
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 controlled startup with minimal DC link capacitance, preventing overcurrent and overvoltage while ensuring positive torque and stable rotor alignment, even with low-capacitance DC links, thereby enhancing system safety and reducing costs.
Implementation Method 1
These methods evaluate the voltage induced back into the stator coils by the rotor's magnetic field, the so-called back-EMF (electromagnetic force).
Implementation Method 2
synchronous machine with a permanent magnet rotor and a stator
Data Source
Figure 1~2
Figure 3
Figure 4
AI summary
The invention relates to a method for starting a synchronous machine (1) supplied by a frequency converter with a voltage intermediate link, with a permanent magnet rotor (3) and a stator (2), without a position sensor, in which, for a controlled start-up of the synchronous machine (1), a vectorial current control (5) with at least one first current controller (11) setting a first current component (id) of the stator current sets a reference current space vector (I) rotating according to a predetermined, increasing speed profile (nstart), which has a magnitude predetermined at least by a setpoint (Idref) of the first current controller (11) and a defined angular position (ϕ) in a coordinate system (d, q) rotating with the reference current space vector (I) relative to a stationary reference system (α, β) of the stator (2).The DC link voltage (Udc) is measured during startup and compared to a reference value (Udcmax), or a derived value thereof. A speed correction value (n+) is added to the speed curve if the DC link voltage (Udc) exceeds the reference value (Udcmax). This protects a compact DC link from overvoltage during startup.