ECRES – 3. European Conference on Renewable Energy Systems, Antalya, TURKEY, 07-10 Oct. 2015
DSP CONTROLLED HIGH FREQUENCY BATTERY CHARGER FOR PV GENERATION SYSTEMS Harun Özbay 1, Akif Karafil 2, Selim Öncü 3, Metin Kesler 4 1
Bilecik Seyh Edebali University, Department of Electric, Vocational High School, Gulumbe Campus, 11000, Bilecik, Turkey
2
Bilecik Seyh Edebali University, Department of Energy, Vocational High School, Gulumbe Campus, 11000, Bilecik, Turkey
3
Karabuk University, Department of Electrical & Electronics Engineering, Engineering Faculty, Demir-Celik Campus, 78000, Karabuk, Turkey 4
Bilecik Seyh Edebali University, Department of Computer Engineering, Engineering Faculty, Gulumbe Campus, 11000, Bilecik, Turkey Abstract
This paper presents DSP controlled high frequency battery charger application consisting of a maximum power point tracker (MPPT) and resonant converter to transfer the maximum possible power from PV panels to the battery group. High power density is achieved by using 200 KHz high frequency series resonant converter. Switching losses electromagnetic interference (EMI) size and cost of the circuit are reduced. The efficiency of the battery charger is increased. In the system P&O algorithm is used in order to transfer maximum power from 600W PV panels. The system is simulated in PSIM and the experimental results are compared with simulation results. Keywords: Series resonant converter, MPPT, battery charger, DSP.
1. Introduction Among the renewable energy sources, the solar energy has been more attractive for energy demand recently and has been prompted. Although generating energy using PV panels has many advantageous, the efficiency of the panels is low depending on the environmental factors such as temperature, radiation level, shading, and dirt. Therefore, it becomes important to transfer maximum available power from PV panels. To transfer the maximum possible power dc-dc converter (MPPT) is used between the PV generator and the load [1,2]. Many MPPT techniques have been developed recently in order to determine the maximum power point (MPP). They can be classified into four groups as direct calculation methods, intelligent methods, incremental conductance (IC) methods and perturb and observe (P&O) methods in terms of PV panel dependency, true MPPT, periodic adjustment, tracking speed and complexity. IC and P&O are the most widely used MPPT techniques due to the high accuracy at MPP [3]. The efficiency of the converter with MPPT algorithm decreases due to the switching losses. Resonant converter can be used to eliminate the drawbacks [4]. In literature, some battery charger applications such as low frequency series resonant topology without MPPT algorithm [5], high frequency low power charger with MPPT property [6], PWM controlled fixed frequency charger [7], electric vehicle plug in battery charger [8] have been studied. In addition DSP controlled resonant solar energy-battery charging system [9] and high voltage Li-on battery charger [10] applications are achieved with resonant topologies. However these applications include dc-dc converter system without MPPT algorithm. In the study, high frequency battery charger is designed for 350W 106V PV system. Maximum power transfer is achieved with boost converter and perturb & observe algorithm. In the designed system, boost converter tracks the MPP and battery charge current is controlled by the resonant converter. Both the MPPT and the high frequency dc-dc converter are controlled by TMS320F28335. Proposed system is simulated with PSIM and experimentally tested. Soft switching is maintained from full to low load.
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1
ECRES – 3. European Conference on Renewable Energy Systems, Antalya, TURKEY, 07-10 Oct. 2015
2. PV Generation System and Battery Charger 2.1. MPPT P&O method is one of the most widely used MPPT methods due to its simplicity, practicality and high efficiency. Moreover, the most important advantage of the method is that it is independent from some factors such as PV characteristic, temperature and radiation level in achieving MPP [11,12]. In P&O method, PV panel power is measured and compared with the previous one. The operating point of the converter is changed according to the power measurements [13]. If the power increases, perturbation direction is not changed. Otherwise, perturbation direction is reversed. This process will be applied until MPP is achieved. In P&O MPPT algorithm perturbation direction is determined to achieve MPP according to the power changes [12, 14]. The flow chart of the algorithm is shown in Figure 1. Operating voltage of the PV system is changed with a small increase of ΔV. Therefore, ΔP is also changed. The power of the PV system is compared with the previous one. If the power is higher than the previous one (ΔP>0) and the voltage of the PV system is higher than the previous one (ΔV>0), the duty ratio is increased. If the voltage of the PV system is smaller than the previous than (ΔV
