Induction Machine Parameter Estimation Standstill
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Solution Overview
Problem
Existing methods for identifying motor parameters of induction motors, especially the main inductance and rotor time constant, are inaccurate in stand-still conditions due to counter torque from connected loads and limitations in voltage measurement accuracy, leading to poor control performance.
Innovation Solution
A method involving two phases of DC magnetization with different current references to measure stator current maximum values during zero voltage vectors, allowing for indirect estimation of main inductance and rotor time constant without rotating the machine, using a voltage source inverter to control the induction machine and determine the magnetizing current magnitude reliably.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If stand-still identification procedure is used, then the machine can be identified without rotating, but the main inductance and rotor time constant cannot be accurately identified
Solution Approach 1:
The patent applies preliminary action by performing DC magnetization of the induction machine before the actual identification measurement. The machine is magnetized with a DC current to establish a known magnetic flux state, then the power semiconductors are switched off and a zero voltage vector is applied. This preliminary magnetization action enables accurate measurement of main inductance and rotor time constant even in stand-still conditions, resolving the contradiction between ease of operation and measurement precision.
2Measurement precision
If voltage measurement accuracy is increased to improve main inductance estimation, then measurement accuracy improves, but the cost and complexity of the voltage converter increases
Solution Approach 1:
The patent replaces direct voltage measurement with an indirect measurement approach using current measurement. Instead of measuring voltage directly (which would require high-precision voltage sensors and complex converter hardware), the method measures the stator current response during zero voltage vector application. The main inductance is calculated from the current decay characteristics, substituting a simple current measurement system for a complex high-precision voltage measurement system.
3Measurement precision
If DC magnetization current is applied to magnetize the machine, then the main inductance can be measured, but the power semiconductors and output phases must be precisely controlled
Solution Approach 1:
The patent employs periodic action by applying DC magnetization current in discrete pulses rather than continuously. The magnetization current is applied for a specific duration, then the power semiconductors are switched off and a zero voltage vector is applied for measurement. This periodic pulsing simplifies the control requirements compared to continuous magnetization, as the system only needs to maintain control during the brief measurement window rather than throughout continuous operation.
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 provides accurate estimates of main inductance and rotor time constant, eliminating inaccuracies and enabling precise control of the induction motor without the need for rotating the machine, improving control performance.
Implementation Method 1
magnetizing the induction machine by providing a first DC magnetization current (im) to the induction machine via the inverter
Implementation Method 2
measuring a first maximum value (imz—max) of a stator current (isd) during the zero voltage vector
Data Source
AI summary
A method and an arrangement are disclosed for identifying one or more parameters of an induction machine when the induction machine is connected to the output phases of a voltage source inverter and the induction machine is in standstill state. The method can include a first phase for magnetizing the machine by providing a first DC magnetization current until the induction machine reaches steady state, the current reference of the inverter having a first value (idc<sub2>—</sub2>ref1). A first maximum value (imz<sub2>—</sub2>max) of the stator current (isd) is measured during a zero voltage vector. In a second phase, the machine is magnetized by providing a second DC magnetization current, the current reference having a second value (idc<sub2>—</sub2>ref2) which is higher than the first reference (idc<sub2>—</sub2>ref1). A second maximum value of (isdz<sub2>—</sub2>max) the stator current is measured during a zero voltage vector, and a parameter of the induction machine is estimated when the measured first and second maximum values are equal.