Analysis of Current Ripples in Electromagnetic Actuators with Application to Inductance Estimation Techniques for Sensorless Monitoring

Abstract

Techniques for estimating the plunger position have successfully proven to support operation and monitoring of electromagnetic actuators without the necessity of additional sensors. Sophisticated techniques in this field make use of an oversampled measurement of the rippled driving current in order to reconstruct the position. However, oversampling algorithms place high demands on AD converters and require significant computational effort which are not desirable in low-cost actuation systems. Moreover, such low-cost actuators are affected by eddy currents and parasitic capacitances, which influence the current ripple significantly. Therefore, in this work, those current ripples are modeled and analyzed extensively taking into account those effects. The Integrator-Based Direct Inductance Measurement (IDIM) technique, used for processing the current ripples, is presented and compared experimentally to an oversampling technique in terms of noise robustness and implementation effort. A practical use case scenario in terms of a sensorless end-position detection for a switching solenoid is discussed and evaluated. The obtained results prove that the IDIM technique outperforms oversampling algorithms under certain conditions in terms of noise robustness, thereby requiring less sampling and calculation effort. The IDIM technique is shown to provide a robust position estimation in low-cost applications as in the presented example involving a end-position detection.

A Solution to Ambiguities in Position Estimation for Solenoid Actuators by Exploiting Eddy Current Variations

“…Figure 6 illustrates the response of the current to a PWM voltage for two cases: an actuator without eddy currents (black) and an actuator with eddy currents (blue). In case no eddy currents are present, the response is the classical ripple which has been previously described in the work [26]. Under consideration of eddy currents, cusps in the current response appear.…”

“…Equation (26) resembles the differential equation of the electrical equivalent circuit that is shown in Figure 5. Such a circuit including a parallel resistance which accounts for losses is common in many works such as [23,26,29].…”

“…Equation (26) resembles the differential equation of the electrical equivalent circuit that is shown in Figure 5. Such a circuit including a parallel resistance which accounts for losses is common in many works such as [23,26,29]. Unlike the work [26], parasitic capacitances are not considered since they complicate the mathematical treatment significantly while their influence on the current response is negligible [23,26,33].…”

“…Despite the benefit of increasing the SNR significantly, such techniques require additional sampling and computational effort, thus making their implementation on low-cost actuators difficult. Other approaches [23][24][25][26] are based on the analog processing of the current ripple with the aim of increasing the SNR and decreasing the computational effort, thus allowing the implementation on cost-critical actual inductance towards position variation at the complete speed range. Therefore, a majority of works prefers the evaluation of this parameter.…”

“…The response of the current ripple during a PWM switching voltage transient is exploited for deriving a resistance estimator. For a resource-efficient identification of the differential inductance, the Integrator-Based Direct Inductance Measurement (IDIM) technique, known from prior works [25,26], is presented and summarized. Both parameter information are merged by means of a multilayer perceptron neural network, allowing a unique position estimation by weighting the different information.…”