Current Converter Fault Voltage Characterization for Three-Phase Machines
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Solution Overview
Problem
Existing methods for determining and compensating for incorrect voltage in power converters, such as frequency converters, are inaccurate due to current-dependent influences like switching delays and voltage drops, which complicate parameter identification and voltage regulation in induction machines.
Innovation Solution
A method that determines the incorrect voltage by measuring the resistance from a target voltage jump and actual current jump in a high current range, using a current-dependent correction element to adjust the target voltage, and characterizes the voltage behavior with a fault voltage characteristic curve to improve accuracy and compensation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the output voltage is increased stepwise to determine machine parameters, then parameter identification can be performed, but the current-dependent fault voltage causes measurement inaccuracy
Solution Approach 1:
The system uses the machine's own step response current measurement to determine the fault voltage, eliminating the need for separate voltage measurement instruments. The controller measures the current resulting from stepwise voltage increases and calculates the fault voltage characteristic curve using the relationship Ufault = Utarget - R * Iactual, where the machine itself provides the measurement data needed for compensation.
Solution Approach 2:
The system changes the operating parameters by applying stepwise voltage increases and measuring the corresponding current responses at different operating points. By varying the target voltage and measuring the resulting current changes, the system builds a fault voltage characteristic curve that captures the current-dependent behavior, enabling accurate compensation across the operating range.
2Measurement precision
If current-dependent influences like switching delays and voltage drops are considered, then voltage compensation accuracy improves, but the system complexity increases
Solution Approach 1:
The system extracts the fault voltage characteristic from the overall system behavior by measuring only the current response to stepwise voltage changes. Instead of trying to measure or control each individual current-dependent influence (switching delays, voltage drops), the system separates and characterizes the combined fault voltage effect, which simplifies the compensation approach while maintaining accuracy.
Solution Approach 2:
The system implements feedback by using the measured actual current to calculate and compensate for the fault voltage. The controller continuously determines the fault voltage based on the relationship between target voltage and measured current, then uses this information to adjust the voltage commands, creating a closed-loop compensation mechanism that accounts for current-dependent influences.
3Reliability
If the fault voltage is compensated using a characteristic curve, then the output voltage matches the target voltage more closely, but additional measurement and calculation steps are required
Solution Approach 1:
The system performs preliminary characterization by determining the fault voltage characteristic curve during commissioning or parameter identification. Once this characteristic is established, it can be stored and reused for compensation during normal operation, avoiding the need to perform time-consuming measurements during each operating phase while maintaining high voltage 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
This approach simplifies the determination of resistance and reduces inaccuracy in voltage compensation, ensuring the output voltage closely matches the target voltage by accounting for current-dependent factors, enhancing the precision of parameter identification and control in induction machines.
Implementation Method 1
The resistance is determined from a target voltage step and a corresponding actual current step within a sufficiently high current range
Data Source
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AI summary
The invention relates to a method for determining an error voltage of a current converter to which a load, in particular in the form of a three-phase machine such as an asynchronous machine, is connected, is determined and if necessary compensated, wherein an output voltage on the current converter is increased stage-by-stage or step-by-step and which is measured here as a current adjusting a step response. The invention further relates to a three-phase machine, for example in the form of an asynchronous machine having power electronics comprising a current converter and in the form of a compensation device for compensating the error voltage of the current converter. The invention further relates to a method for operating and/or controlling such a three-phase machine, in which the error voltage of the current converter is determined and compensated. According to the invention, the error voltage is determined from the current measured as a step response and from a resistance of the load, wherein said resistance is determined from a target voltage jump and from a simultaneously measured actual current jump in a relatively high current range of at least 30% of at least 50% of the rated current of the end stage of the current converter.