State Variable Determination in Multi-Phase Synchronous Machines
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Solution Overview
Problem
Existing methods for determining the state variable of a three-phase synchronous machine in a multi-phase power network are unreliable, particularly in detecting torque limits, due to errors in current sensor measurements and redundant calculations that fail to detect critical torque exceedances, posing safety risks.
Innovation Solution
The method determines the state variable by using the current space vector corresponding to the maximum torque-forming current component, eliminating the need for angle of rotation calculations and directly checking the plausibility of current values using Kirchhoff's first law, thereby minimizing error accumulation and ensuring reliable torque detection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If current values from all n phases are recorded and used for plausibility check, then reliability of state variable determination is improved, but device complexity increases due to additional sensors and calculation channels
Solution Approach 1:
The patent applies partial action by recording current values from only n-1 phases (instead of all n phases) for the state variable determination. The nth phase current is not directly measured but can be calculated from the other n-1 phases using Kirchhoff's current law, reducing the number of current sensors needed while maintaining reliability through plausibility checks.
Solution Approach 2:
The patent uses the sum of all n phase currents as an intermediary for plausibility checking. By calculating the sum of currents from n-1 measured phases and comparing it with the negative of the nth phase current (derived from Kirchhoff's law), the system verifies measurement consistency without requiring direct measurement of all phases, thus reducing device complexity while improving reliability.
2Measurement precision
If redundant calculation channels are used to detect errors, then measurement precision is improved, but productivity decreases due to additional calculation operations
Solution Approach 1:
The patent performs plausibility checks using a simplified approach: it calculates the sum of n-1 measured phase currents and compares this with the negative of the nth phase current. This partial verification approach provides sufficient error detection capability without requiring multiple redundant calculation channels, thus maintaining productivity while achieving the necessary measurement precision.
Solution Approach 2:
The patent extracts only the essential plausibility check (sum of currents equals zero according to Kirchhoff's law) from the full set of possible verification operations. By focusing on this single critical check rather than implementing multiple redundant calculation channels, the system achieves adequate measurement precision without the productivity loss that would result from extensive redundant calculations.
3Manufacturing precision
If angle of rotation calculations are performed for torque determination, then manufacturing precision is improved, but loss of time increases due to additional calculation steps
Solution Approach 1:
The patent extracts and eliminates the angle of rotation calculation step from the torque determination process. Instead of calculating torque using the full formula that requires angle measurements, the system directly uses the sum of phase currents (which is zero under normal conditions) as a plausibility indicator. This removes the time-consuming angle calculation while maintaining the essential safety function of detecting abnormal conditions.
Solution Approach 2:
The patent applies partial action by performing only the necessary current summing operation for plausibility checking rather than the complete torque calculation that would require angle of rotation measurements. This partial verification approach provides sufficient safety assurance without the time loss associated with full torque calculations, enabling faster error detection.
Data Source
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AI summary
To reliably determine a state variable (G) of a three-phase synchronous machine (1) supplied with electrical current from a multiphase power grid (2) with n phases (U,...,N), where n ≥ 3, the current values of at least n-1 phase currents (Iu,...,In-1) from at least n-1 phases (U,...,N-1) of the multiphase power grid (2) are recorded. The state variable (G) is then determined using these at least n-1 current values (Iu,...,In-1), whereby the current values of all n phase currents (Iu,...,In) from the n-phase multiphase power grid (2) are recorded and the n phase currents (Iu,...,In) are correlated. The result of combining all n phase currents (Iu,...,In) is used for a plausibility check of the n-1 phase currents (Iu,...,In-1) used to determine the state variable (G).