Abstract
In this paper, a nonlinear observer is proposed for the estimation of the current ripple in a ferrite-core inductor working in partial saturation, mounted on a boost converter. The estimator is based on a recently proposed nonlinear inductance model, which expresses the inductance as a function of the inductor current, taking into account also the non-negligible effects of the core temperature. The proposed observer is implemented on a low-cost microcontroller and tested, both offline and online, on a real boost converter with different operating conditions. The offline tests show a satisfactory estimation accuracy both during the electrical (fast) and thermal (slow) transients. Due to the high microcontroller latency, some delays and inaccuracies occur during electrical transients in the online tests. This work suggests that, in order to exploit the observer for control purposes, the target architecture should be a high-performance microcontroller, a system-on-chip, or a field programmable gate array, where parallelism can be exploited to speed-up the computations. The proposed implementation can be instead suitable for switch-mode power supply (SMPS) monitoring purposes.
Highlights
Switch-mode power supplies (SMPSs) are employed in all modern devices and systems using electrical energy: in consumer, industrial, aerospace, automotive, lighting, and other areas.Their use is expected to grow due to the increase of more electric vehicles in all transportation areas
The first tests were performed both offline, in order to assess the accuracy of the estimator if computation delays were neglected, and online, where the estimator ran on the microcontroller together with the boost converter
The proposed observer achieved a relative percent error below 10% in estimating the current ripple at steady-state and during the slow thermal transients, when the inductor worked in saturation and observers based on the classical linear inductor would fail
Summary
Switch-mode power supplies (SMPSs) are employed in all modern devices and systems using electrical energy: in consumer, industrial, aerospace, automotive, lighting, and other areas. Their use is expected to grow due to the increase of more electric vehicles in all transportation areas. The frequency and duty cycle of the PWM signal are imposed by a control system, such that the converter output voltage is maintained at a reference value and the current flowing through the inductor does not exceed safety limits, independently of variations in the input voltage and load current. The simplest control strategy is the voltage mode control, where the difference between the output voltage and the reference value is used as input for the controller, e.g., a proportional-integral regulator. The main drawback of this approach is that it has a slow response to load current variations, and good closed-loop performances are difficult to achieve [1,2]
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