Solar Power Optimizer for DC Distribution System

GRD Journals- Global Research and Development Journal for Engineering | Volume 2 | Issue 4 | March 2017 ISSN: 2455-5703

Solar Power Optimizer for DC Distribution System Leander J. Ataide Student Department of Electrical and Electronics Engineering Goa College of Engineering, Farmagudi

Aditi A. Desai Assistant Professor Department of Electrical and Electronics Engineering Goa College of Engineering, Farmagudi

Abstract Solar Power Optimizer (SPO) for DC Distribution System comprises of a high step-up solar power optimizer (SPO) which efficiently harvests maximum energy from a photovoltaic (PV) panel, energy is output to a dc-micro grid. It integrates coupled inductor and switched capacitor technologies to realize high step-up voltage gain. The leakage inductance energy of the coupled inductor can be recycled to reduce power losses and voltage stress. A low low-conduction resistance and voltage rating switch improves system efficiency by employing the fuzzy logic method for the (MPPT) maximum power point tracking algorithm. It has high tracking accuracy, hence the method is widely used to harvest energy of PV systems. The reduction in power caused by the existing shadow effect on PV panels is an unavoidable problem in a centralized PV system. The use of a micro inverter or ac module has recently been proposed for individual PV panels.

Keywords- SPO, PV array, MPPT, Micro grid, Fuzzy Controller

I. INTRODUCTION Fossil fuels continue to be depleted, and their use has played a major role in climate change, a problem that grows severely each year. Photovoltaic (PV) power generation systems, which use a renewable resource, has been extensively used in generating electricity and in emergency facilities for mass use. A number of series-connected PV modules are connected in the PV array to obtain the DC link voltage that is high enough to be connected to the grid through the DCAC inverter [3]-[4]. Though, reduction in power caused by the shadow effect is an un avoidable nature in a centralized PV system. The use of a micro inverter or ac module has recently been proposed for individual PV panels. The discrete PV power generation solution partially eliminates the shadow problem, but a micro inverter structure constrains the system energy’s harvesting efficiency and entails high costs. The SPO improves the use of distributed renewable resources and lowers the system cost. It potentially improves the efficiency of PV systems, has an anti-shadow effect, and monitors the status of PV modules. So also the dc-grid voltage is regulated by bidirectional inverter and battery tank. [9-12] during low-loading condition, the redundant energy is stored into battery or is fed through bidirectional inverter to ac grid. A solar power optimizer (SPO) was developed as an alternative to maximize energy harvest from each individual PV module. [13-17].

A switched capacitor with voltage lift technique is used to construct dc/dc converters of small size and has a numerous advantages. An SPO has a high step-up converter that increases low-input voltage to a sufficient voltage level. Various step-up dc– dc converter topologies include a conventional boost and flyback converters, capacitor–diode voltage multipliers switched inductor converter, and switched capacitor converter, as well as a transformer less voltage-lift techniques and switched capacitor techniques.

Switched-inductor cells for voltage lift techniques are proposed to improve the boost capabilities of the transformer less DC-DC converters and designed as integrated cells and inserted into all the basic converters [20]. A high step-up DC/DC converter is needed to boost low input voltage to high voltage output with a voltage multiplier and a coupled inductor. A step-up dc-dc converter with a negative-to-positive voltage conversion pathway for the negative dc-voltage source has the ability to boost the voltage significantly using the switched capacitor and coupled inductor techniques. The voltage on the active switch is clamped, and the energy stored in the leakage inductor is recycled and the conversion efficiency is improved [21]. The secondary side voltage of the coupled inductor is rectified using a voltage multiplier and low duty cycle boost voltage is obtained. [22],[23]. A high stepup dc-dc converter for fuel cell energy conversion utilizing a multiple-winding coupled inductor with voltage doubler to achieve high step-up voltage gain can practically be achieved for low-input-voltage power conversion process.

The converter achieves a high step-up voltage-conversion ratio and the leakage inductance energy of the coupled inductor is recycled efficiently to the load this explains the module's high-efficiency performance [24].

II. SOLAR POWER OPTIMIZER FOR DC SYSTEM The dc–dc converters with high voltage ratio are required in many industrial applications. The conventional boost converters cannot provide such a high dc voltage gain, even for an extreme duty cycle. A conventional PV generation system is either a single- or a multi string PV array that is connected to one or several central PV inverters. The use of an ac module or micro inverter has been

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Solar Power Optimizer for DC Distribution System (GRDJE/ Volume 2 / Issue 4 / 011)

proposed earlier for individual PV panels. Although this discrete PV power generation solution may partially eliminate the shadow problem, a micro inverter structure constrains the system energy’s harvesting efficiency and entails high costs.

Fig. 1: Configuration of multiple parallel SPO for a dc-micro grid system

Figure 1 shows an assembly of PV panels, which are individually connected to SPO to a dc micro grid system. The SPO attempts to improve the use of distributed renewable resources and lower system cost. The dc-grid voltage is regulated by bidirectional inverter and battery tank. “Power optimizers only deploy minimal electronics on the rooftop to control the MPPT and DC to DC conversion, a centrally located inverter is used at the end of the string. This allows installers to reduce hardware, slash costs and improve reliability. By eliminating any string design constraints that would decrease the size of a PV system, power optimizers allow designers to install more modules on the rooftop. For end-users, the system output equates to lower electricity bills. For installers, this implies increased revenues.”

A solar power optimizer is a DC-DC converter used to maximize the energy harvested from solar photovoltaic systems.

Solar modules are connected in series in an array; to produce optimal power when all the modules are performing well. As temperature changes, or leaves, snow or shade partially cover modules, the output decreases, modules heat up and drag down the performance of the other modules. This causes the array to lose power. Power optimizers can be used to reduce this drawback.

Power optimizers are DC-DC converters attached to the module individually. Maximum output is drawn from the modules by allowing each module to function at its maximum power point (MPP). This enables the entire array to yield more energy. Power optimizers for solar applications, can be similar to micro inverters, in the sense that both systems attempt to isolate individual panels in order to improve overall system performance. A power optimizer integrated with the solar panel or a solar module to form a smart module. A micro inverter essentially combines a power optimizer with a small inverter in a single case that is used on every panel, while for the power optimizer a centralized inverter is used for the entire array. The advantage of using this hybrid approach is lesser overall system costs and reduced electronics.

III. CONTROL OF PROPOSED SOLAR POWER OPTIMIZER Figure 2 shows the circuit for the proposed SPO. Its structure is based on a high step-up dc–dc converter with an MPPT control circuit. The converter includes a coupled inductor T1 with primary winding N1, which is similar to the input inductor of a conventional boost converter capacitor C1, and diode D1 recycle leakage inductance energy from N1. Secondary winding N2 is connected to capacitors, C2 and C3, and also two diodes D2 and D3. The Rectifier diode D4 is connected to the output capacitor C0 and the load R. The duty ratio is modulated by the MPPT algorithm, which uses a Fuzzy controller that is used in the proposed SPO. The Controller detects the PV module voltage VPV to determine the increase and decrease in the duty cycle of the dc converter. The proposed converter has the following features 1) It is a voltage conversion ratio efficiently increased by using the switched capacitor and coupled inductor technique.

2) The floating active switch S isolates the PV panel’s energy during non-operating conditions, thereby preventing any potential electric hazard to humans or facilities. The MPPT control algorithm exhibits high-tracking efficiency. Therefore, it is widely used in the energy harvesting of PV systems.

3) The leakage inductance energy of the coupled inductor can be recycled to increase efficiency, and the voltage spike on the active switch is restrained.

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Solar Power Optimizer for DC Distribution System (GRDJE/ Volume 2 / Issue 4 / 011)

Fig. 2: Circuit diagram of the proposed solar power optimizer

The operating principles include Continuous Conduction Mode (CCM) and Discontinuous Conduction Mode (DCM) with typical waveform of several major components in CCM operation during one switching period. To simplify the circuit investigation of the proposed converter, the following assumptions are made.

1) All the components used in optimizer circuit are ideal, except for the leakage inductance of coupled inductor T 1 is taken into account. On-state resistance Rds (ON) and all the parasitic capacitances of main switch S are disregarded, as are the forward voltage drops of diodes D1 to D4.

2) Capacitors C1 to C3 and C0 are sufficiently large that the voltages across them are considered constant, 3) The equivalent series resistance (ESR) of capacitors C1 to C3 and C0, as well as the parasitic resistance of coupled inductor T1, is neglected 4) Turns ratio n of coupled inductor is equal to N2/N1.

IV. DESIGN Symbol

Table 1: PV Module Design Requirement Description Value

Pmax

Nominal power

36 W

Voc

Open ckt voltage

21V

Isc

Short circuit current

2.1A

Rs

Series resistance of pv cell

0.9 Ω

Rsh

Parallel resistance of pv cell

1000 Ω

Tamb

Ambient Temperature

25 deg C

Q

Electron charge

1.602*10^-19C

Eg

Energy of band gap

1.1eV

G

Solar insolation

1000W/m2

N

Diode ideality factor

1.50

Α

Temperature coefficient of s/c current

0.65*10-3 A/K

Β

Temperature coefficient of o/c voltage

-160mV/K

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Solar Power Optimizer for DC Distribution System (GRDJE/ Volume 2 / Issue 4 / 011)

V. SIMULATION AND RESULTS Simulation is a very powerful tool in industry applications as well as in academics. Simulation is one of the best ways to study the system or circuit behavior without damaging it. It is important to understand the concept of simulation and learn its use in various applications. The tools for performing the simulation in various fields are available in the market for engineering professionals.

Many industries are spending a considerable amount of time and money in performing simulations before manufacturing their product. In research and development (R&D) work, the simulation plays a very important role. It should be noted that in computer simulation, power electronics and hardware prototypes in the laboratory are complimentary to each other. However computer simulation must not be considered as a substitute for hardware prototype using MATLAB tool.

Fig. 3: Closed loop control of SPO using MPPT controller using MATLAB

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Solar Power Optimizer for DC Distribution System (GRDJE/ Volume 2 / Issue 4 / 011)

Fig. 4: Output voltage of boost converter

The output voltage of the 36Wp pv module is fed as input to the boost converter. The input to the boost converter is 14 V d.c. Fig 4 shows the output voltage of the boost converter. The converter produces a boost of about 10 times the input voltage. The output from the boost is 137 V d.c

Fig. 5: Output current

VI. CONCLUSION The high step-up SPO uses the coupled inductor with an appropriate turn’s ratio design and switched-capacitor technology to achieve a high-voltage gain that is 10 times higher than the input voltage. The proposed circuit elements are designed using related equations, developed using the functional component blocks of Simulink library. The Simulation is successfully done by closed loop Fuzzy Logic controller. The closed loop system is simulated and the results are presented.

ACKNOWLEDGEMENT The author would like to thank his guide Prof. Aditi A. Desai for her support and insights in the subject.

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Solar Power Optimizer for DC Distribution System (GRDJE/ Volume 2 / Issue 4 / 011)

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