Permanent Magnet Synchronous Motor Soft-Start Without Encoders
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Solution Overview
Problem
Existing solutions for starting permanent magnet synchronous machines on a soft starter require encoder systems, which increase costs and reduce availability, making them unattractive for high-efficiency motors, and existing sensorless methods are not applicable to thyristor controllers.
Innovation Solution
A method that determines the initial rotor position and optimal ignition angle in advance, allowing the motor to be accelerated with maximum torque during the first firing of thyristors, enabling the calculation of the electrical angle from induced voltages without additional hardware, using existing sensors in the soft starter.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If an encoder system is used to determine rotor position and speed for soft starter control, then the machine can be started up on a rigid network with a soft starter, but the cost and system complexity increase significantly
Solution Approach 1:
The patent extracts the position detection function from the encoder system and implements it through sensorless methods using only the existing current sensors in the soft starter. The rotor position is determined by analyzing the back-EMF voltages induced in the stator windings during the starting process, eliminating the need for additional encoder hardware while maintaining soft starter compatibility
Solution Approach 2:
The system uses its own existing current sensors to detect the back-EMF voltages and determine rotor position without requiring external sensing devices. The soft starter's built-in sensors serve dual purposes: both for current control and for position detection, making the system self-sufficient
2Device complexity
If sensorless methods are used to eliminate encoders, then cost and complexity are reduced, but existing sensorless methods cannot be applied to thyristor-based soft starters
Solution Approach 1:
The patent changes the operating parameters and control strategy specifically for thyristor-based soft starters. Instead of using pulse-controlled inverters with PWM techniques, the method utilizes the natural commutation characteristics of thyristors and analyzes back-EMF during the thyristor conduction and blocking periods. The rotor position is determined by evaluating the voltage equations during the blocking time when thyristors are off, adapting sensorless control to the specific hardware topology
Solution Approach 2:
The patent performs preliminary determination of the initial rotor position and optimal ignition angle before the main starting process. By analyzing the back-EMF voltages during the first thyristor firing and using the known electrical angle from the soft starter, the system pre-calculates the optimal firing angles for subsequent commutations, enabling smooth operation without encoders
3Productivity
If the machine is started with maximum torque acceleration, then the starting time is reduced, but the induced voltages may be too low to measure accurately during thyristor blocking time
Solution Approach 1:
The patent implements a feedback mechanism where the measured back-EMF voltages during thyristor blocking time are continuously evaluated to determine rotor position and speed. The control system uses this feedback information to adjust the firing angles and ensure that the induced voltages remain measurable throughout the starting process, balancing acceleration torque with measurement accuracy
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
Enables efficient and cost-effective startup of permanent magnet synchronous machines on a soft starter without encoders, achieving energy efficiency class IE4 operation by maximizing torque and accurately determining the electrical angle from induced voltages, thus eliminating the need for additional sensors.
Implementation Method 1
the induced voltages can therefore be measured with sufficient accuracy during the blocking time of the thyristors due to the principle. The electrical angle of the motor can then be determined from the induced voltages
Data Source
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AI summary
In order to achieve the energy efficiency class IE4 defined in IEC standard 60034, it is necessary to operate permanent-magnet synchronous machines directly from the supply system. Since this is not readily possible, soft-starting devices come into consideration as cost-effective solutions. The problem of transmitter-free running up can be split into two component problems: determining the initial rotor angle and running up the machine. The present invention describes a (rotary) transmitter-free starting method with which the motor can be started using a soft-starting device.