This paper describes a new maximum-power-point-tracking (MPPT) method focused on low-power (<; 1 W) photovoltaic (PV) panels. The static and dynamic performance is theoretically analyzed, and design criteria are provided. A prototype was implemented with a 500-mW PV panel, a commercial boost converter, and low-power components for the MPPT controller. Laboratory measurements were performed to assess the effectiveness of the proposed method. Tracking efficiency was higher than 99.6%. The overall efficiency was higher than 92% for a PV panel power higher than 100 mW. This is, in part, feasible due to the low power consumption of the MPPT controller, which was kept lower than 350 μW. The time response of the tracking circuit was tested to be around 1 s. Field measurements showed energy gains higher than 10.3% with respect to a direct-coupled solution for an ambient temperature of 26°C. Higher gains are expected for lower temperatures.

This paper presents an absolute capacitive angular-position sensor with a contactless rotor. The sensor is mainly composed of three parts: the capacitive sensing element, a signal processor, and a microcontroller. The electrically floating rotor can be either conductive or dielectric. For the dielectric material, we chose plastic, and for the conductive rotor, we chose aluminum. The sensing element has a redundant structure, which reduces mechanical nonidealities. The signal processor has a multicapacitance input and a single output, which is a period-modulated square-wave voltage. The microcontroller acquires output data from the processor and sends them to a PC, which calculates the rotor position. Theoretical analysis, supported by experimental results, show that the sensitivity to mechanical nonidealities of the sensing element is higher in the case of a conductive rotor. The resolution of the capacitive angular-position sensor over the full range (360°) was better than 1". The measured nonlinearity was ± 100" and ± 300" for the dielectric and the conductive rotor, respectively.

This paper proposes a closed-loop maximum power point tracker (MPPT) for subwatt photovoltaic (PV) panels used in wireless sensor networks. Both high power efficiency and low circuit complexity are achieved. A microcontroller (μC) driven by a fast clock was used to implement an MPPT algorithm with a low processing time. This leads to a maximum central-processing-unit duty cycle of 6% and frees the μC to be used in the remaining tasks of the autonomous sensor, such as sensing, processing, and transmitting data. In order to reduce power consumption, dynamic power management techniques were applied, which implied the use of predictive algorithms. In addition, the measurement and acquisition of the output current and voltage of the PV panel, which increase circuit complexity, was avoided. Experimental measurements showed power consumptions of the MPPT controller as low as 52 μW for a 2.7-mW PV power and up to 388 μW for a 94.4-mW PV power. Tracking efficiency was higher than 99.4%. The overall efficiency was higher than 90% for a PV panel power higher than 20 mW. Field measurements showed an energy gain 15.7% higher than that of a direct-coupled solution.

This paper analyzes the effects of power-supply interference on direct sensor-to-microcontroller interfaces based on measuring the charging/discharging time of an RC circuit that includes the sensor. Power-supply interference becomes a source of trigger noise that affects the measurement of the charging/discharging time and, hence, the measurement of the sensor resistance or capacitance. The measurement uncertainty increases proportionally to the amplitude of the interference and depends on its frequency. Such interference effects are smaller when measuring the discharging time and can be further reduced by placing an additional resistor in the interface circuit. Experimental data obtained from a PIC microcontroller agree with the theoretical predictions