Current-Sensorless MPPT with DC-DC Boost Converter for Photovoltaic Battery Chargers Gamal M. DOUSOKY 1, 2
Emad M. AHMED 2
Masahito SHOYAMA 2
1)
Electrical Engineering Department, Minia University, EGYPT Electrical Engineering Department, Kyushu University, JAPAN E-mails:
[email protected],
[email protected],
[email protected] 2)
Abstract— This paper proposes a simple current-sensorless MPPT with dc-dc boost converter for Photovoltaic battery chargers. The proposed tracker eliminates the use of the current sensor by using only the voltage sensor: The current sensor is substituted with a new quantity that employs both of the input voltage and the duty ratio of the converter. An empirical observation is used to develop a theoretical prove for this quantity. Then, the proposed tracker is designed in MATLAB Simulink and implemented using a fixed-point DSP. Moreover, a breadboard circuit has been built-up for testing the use of the proposed tracker with a dc-dc boost converter operating in continuous conduction mode. Experimental results show that the proposed tracker attains good dynamic and steady-state performances comparable to that obtained with the conventional MPPTs. A substantial part of the manufacturing cost and complexity burdens of MPPTs involves the use of current sensors. Considering this investigation saves cost, decreases complexity, and increases the efficiency and the power density of the MPPTs.
I.
INTRODUCTION
Maximum Power Point Tracker (MPPT) is an essential part of any photovoltaic (PV) system. Research trend in MPPTs is generally moves into two main directions: improving the performance of the tracker [1]-[4], and reducing its cost and complexity [5]-[8]. Therefore, a satisfying tradeoff between both directions has to be made to ensure good performance at a reasonable cost. In most of tracking algorithms, two sensors are necessary for periodic measurement of voltage and current. Hence, the PV power can be calculated and subsequently maximized, as shown in Fig.1. This paper proposes a current-sensorless tracker that eliminates the use of the current sensor, by using only the voltage sensor. Getting rid of the current sensor has many merits such as saving cost, decreasing complexity, and increasing the efficiency and the power density of the tracker. Digital control is a flexible and attractive hardware design option, becoming lower cost, and getting faster. These competitive tools have made the application of many sophisticated control algorithms possible in this field [9][11]. The implementation of the proposed tracker has been
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Fig.1 Schematic diagram of the conventional INR MPPT for PV battery charger. accomplished by a fixed-point Digital Signal Processor (DSP). This paper is organized as follows: Section II describes the main concepts of the incremental resistance maximum power point tracker (INR) MPPT. Section III introduces the proposed current sensor-less maximum power point tracker based on battery charging PV system. Section IV addresses digital simulation results using MATLAB SIMULINK. Experimental setup and results are presented in section V. Then conclusions are summarized in section VI. II.
CONVENTIONAL INCREMENTAL RESISTANCE (INR) MPPT
Incremental-conductance (INC) method [12]-[13] is based on the fact that the slope of the PV array power curve versus voltage is zero at the MPP. The INC MPPT algorithm usually has a fixed iteration step size determined by the requirements of the accuracy at steady state and the response speed of the MPPT. Thus, a tradeoff between dynamic and steady-state responses has to be investigated at the corresponding design. The primary rules for INR MPPT algorithm can be deduced by duality from the INC MPPT as follows [4]: the power curve of the PV module shows that the derivative of the PV module power PPV is positive before reaching the
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a) Basic circuit
Fig. 2 Basic fundamentals of the incremental resistance MPPT MPP, zero at the MPP, and negative after passing the MPP as shown in Fig. 2. The derivation of PPV is given in (1), which leads to the actuating error (e) in (2).
dPPV d (VPV * I PV ) dVPV = = * I PV + VPV dI PV dI PV dI PV
⇒e=
dVPV VPV + dI PV I PV
(1) b) Waveforms
Fig. 3 Basic dc-dc boost converter.
(2)
Therefore tracking the maximum power point is achieved by applying the following rule: e≥0
⇒
e
