# Current Sensorless MPPT Control for PV Systems Based on Robust Observer
## 1 Introduction  
The utilization of solar energy as an alternative for electrical energy generation has shown a great improvements in recent decades. This is motivated by a global interest in developing green energy sources with a lower environmental impact in contrast with the traditional schemes based on fossil fuels. Nowadays, due to technological development related to photovoltaic (PV) systems, the associated system costs lowered and the efficiency of panels and components increased. These developments have given rise to the generation of PV systems for a broad range of applications from low power domestic use to large generation sites for industrial usage. In order to make the most from the available solar energy, a PV system requires maximum power point tracking (MPPT) techniques that allow the system to operate in optimal conditions, guaranteeing the extraction of maximum power at every instant. There are several MPPT techniques with different characteristics that range from the most common schemes as the Perturb and Observe (PO) algorithm [1], incremental conductance (INC) [2] or fractional open circuit voltage, to novel and more complex approaches as artificial neural networks [3], genetic algorithms [4], fuzzy logic [5], among others. However, nowadays the most commonly used MPPT schemes are still the first ones due to its ease of implementation and capability to operate without knowledge about PV system characteristics requiring only voltage and current measurements. Hence, the system requires voltage and current sensors to perform MPPT operation which increases the overall system cost and reduces its reliability by possible sensor faults. The voltage of the PV array can be measured in a simple way using a potential divider arrangement for non-isolated measurement. On the other hand, the current measurement shows more difficulties, where Shunt resistors or Hall effect sensors are commonly used. The Shunt resistor based sensors obtain the current value in terms of voltage by means of voltagedrops across them. Hence, a heat power dissipation exists across this type of sensor because of Joule's effect which affects the measurement, so it requires low tolerance, high precision and low temperature drift resistance [6; 7]. Further, to perform the current measurement in a proper scale it is necessary to increase the value of shunt resistance which will also increase the heat dissipation. Moreover, when low values of PV arrangement current are measured the sensor provides an almost undetectable output which needs to be amplified increasing the number of components and overall system cost. On the other hand, Hall effect sensors use measurements of the magnetic field generated by the current of interest. Therefore, this type of current sensor is easily affected by external magnetic fields [8; 9]. So, the precision of current measurements from Hall effect sensors is affected by the conductor and sensor position [10]. Conventional MPPT controllers using Hall Effect sensors, include additional circuitry, like signal conditioning buffers and amplifier circuits to filter out the high frequency components caused by the converter switching. However, this increases the cost and complexity of the PV system. Thus, elimination of the current sensor can be a convenient option to provide some key benefits in PV systems as cost reduction, low maintenance and more reliability, particularly when working with systems using multi-level or cascaded topologies [11]. In the related literature one can find different current sensorless schemes that allows the system to dispense with the use of a current sensor. In [12], a current sensorless method is presented which is based on the estimation of the PV current by shorting the two terminals of the PV system. However, such technique will decrease the life of the components connected to the PV terminals and also the PV panel itself. A sensorless MPPT scheme based on Internet of Things is proposed in [13] using public domain solar irradiation data from Internet.