Current-Dependent Inductance Determination in Polyphase Machines
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Solution Overview
Problem
Existing methods for determining current-dependent inductances in polyphase electrical machines are unreliable and require offline measurement of saturation characteristics, which are not feasible during operation.
Innovation Solution
A method involving pulse width modulation to generate phase voltages, apply a single voltage pulse during a PWM cycle to induce current changes in the torque- or field-forming axes, measure the changes, and calculate current-dependent inductances, allowing for real-time identification of differential inductances at various operating points.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If offline measurement of saturation characteristics is used, then reliability of inductance determination is improved, but operational feasibility deteriorates
Solution Approach 1:
The patent applies preliminary action by pre-calculating saturation characteristics during an initialization phase before actual operation. The system performs offline measurements once during commissioning, stores the saturation data in lookup tables, and then uses this pre-prepared information during real-time operation without requiring additional measurements. This resolves the contradiction by ensuring reliability through preliminary offline measurement while maintaining operational feasibility through efficient use of pre-stored data.
Solution Approach 2:
The patent implements dynamics by transitioning from static offline measurement to dynamic real-time determination. The system uses pulse width modulation to dynamically inject test signals during operation and calculates inductances based on current operating conditions. This allows the inductance determination to adapt to changing operational states while maintaining reliability through continuous updates based on actual measured values rather than relying solely on pre-stored static data.
2Measurement precision
If multiple voltage pulses are applied during PWM cycles, then measurement accuracy is improved, but processing time increases
Solution Approach 1:
The patent applies partial action by using a single voltage pulse per PWM cycle instead of multiple pulses. The system determines inductances by applying one test voltage pulse during each PWM period and measuring the resulting current change. This single pulse provides sufficient measurement data for calculating both differential series inductances and differential parallel inductances, achieving adequate measurement accuracy while minimizing the time loss associated with multiple repeated measurements.
3Reliability
If current levels are varied repeatedly to map saturation characteristics, then completeness of inductance data is improved, but operational disruption increases
Solution Approach 1:
The patent implements periodic action by systematically varying current levels through repeated PWM cycles with different amplitude settings. The control unit executes multiple PWM periods sequentially, each with progressively increased current amplitude, allowing the system to map saturation characteristics across the full operating range. This periodic variation ensures complete inductance data coverage while maintaining operational continuity by performing measurements in structured intervals rather than causing random operational disruptions.
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 reliable and accurate ascertainment of saturation characteristics and current-dependent inductances during operation, improving control calculations and reducing the need for pre-measured static tables.
Implementation Method 1
generating phase voltages for the polyphase electrical machine by means of a pulse width modulation such that currents of predefined current level flow through stator windings of the electrical machine
Data Source
AI summary
A method ascertains current-dependent inductances of a polyphase electrical machine. The method generates phase voltages for the polyphase electrical machine by means of a pulse width modulation such that currents of predefined current level flow through stator windings of the electrical machine. During a number of cycles of the pulse width modulation, the method generates a voltage pulse such that a change of current is brought about in a torque-forming axis of the polyphase electrical machine and/or in a field-forming axis of the polyphase electrical machine. The method measures the change of current, and ascertains the current-dependent inductances on the basis of the change of current.