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1764 IEEE TRANSACTIONS ON POWER ELECTRONICS, VOL. 28, NO. 4, APRIL 2013

Design, Analysis, and Implementation of Solar PowerOptimizer for DC Distribution System

Shih-Ming (Orion) Chen , Student Member, IEEE , Tsorng-Juu (Peter) Liang , Member, IEEE , and Ke-Ren Hu

 Abstract—This paper proposes a high step-up solar power op-timizer (SPO) that efficiently harvests maximum energy from aphotovoltaic (PV) panel then outputs energy to a dc-microgrid.Its structure integrates coupled inductor and switched capacitortechnologies to realize high step-up voltage gain. The leakage in-ductance energy of the coupled inductor can be recycled to re-duce voltage stress and power losses. A low voltage rating andlow-conduction resistance switch improves system efficiency byemploying the incremental conductance method for the maximumpower point tracking (MPPT) algorithm. Because of its high track-ing accuracy, the method is widely used in the energy harvesting of PV systems. laboratory prototypes of the proposed SPO that havean input voltage range of 20 to 40 V and a maximum PV output

power of 400 V/300 W are applied. The highest PV power conver-sion efficiency is 96.7%. The maximum MPPT accuracy is 99.9%,and the full load average MPPT accuracy is 97.8%.

 Index Terms—High step-up voltage gain, maximum power pointtracking (MPPT), solar power optimizer (SPO).

I. INTRODUCTION

FOSSIL fuels continue to be depleted, and their use has been

instrumental to climate change, a problem that grows more

severe each year. A photovoltaic (PV) power generation system,

which uses a renewable resource, has been extensively used in

emergency facilities and in generating electricity for mass use.A conventional PV generation system is either a single- or a

multistring PV array that is connected to one or several cen-

tral PV inverters. Numerous series-connected PV modules are

connected in the PV array to achieve the DC link voltage that

is high enough to be connected to electricity through the DC-

AC inverter. However, the power reduction that is caused by

the shadow effect is an inevitable problem in a centralized PV

system. The use of a microinverter or ac module has recently

been proposed for individual PV panels [1], [2]. Although this

discrete PV power generation solution may partially eliminate

the shadow problem, a microinverter structure constrains the

Manuscript received March 31, 2012; revised June 27, 2012; acceptedAugust 6, 2012. Date of current version October 26, 2012. This work wassupported in part by the financial support from the Bureau of Energy, the Min-istry of Economic Affairs, Taiwan, under Project 101-D0204-2, and in part bythe National Science Council of Taiwan under Project NSC 101-3313-E-006-017 and Project NSC 101-2218-E-006-014. Recommended for publication byAssociate Editor T. Shimizu.

S.-M. (Orion) Chen and T.-J. (Peter) Liang are with the Department of Electrical Engineering, Advanced Optoelectronic Technology Center (AOTC),Green Energy Electronics Research Center (GREERC), National Cheng-Kung University, Tainan 701, Taiwan (e-mail: orion.chen@msa.hinet.net;tjliang@mail.ncku.edu.tw).

K.-R. Hu is with the Richtek Technology Company, Hsinchu 302, Taiwan(e-mail: mimix1986@yahoo.com.tw).

Digital Object Identifier 10.1109/TPEL.2012.2213270

Fig. 1. Configuration of multiple parallel SPO for a dc-microgrid system.

system energy’s harvesting efficiency and entails high costs. A

solar power optimizer (SPO) was developed as an alternative to

maximize energy harvest from each individual PV module. An

SPO is used as a dc–dc converter with maximum power point

tracking (MPPT), which increases PV panel voltage to opti-

mum voltage levels for a dc microgrid connection or through adc–ac inverter for electricity [3]–[6]. Fig. 1 shows a single PV

panel’s energy, which passes through an SPO to a dc micro-

grid system. A 400 V dc-microgrid system was proposed as an

energy-efficient distribution option for data center systems and

telecommunication facilities [7]. The SPO attempts to improve

the use of distributed renewable resources and lower system

cost. It may also potentially improve the efficiency of PV sys-

tems, has an antishadow effect, and can monitor the status of 

PV modules [8]. Moreover, the dc-grid voltage is regulated by

bidirectional inverter and battery tank. In case of low-loading

condition, the redundant energy will store into battery or through

bidirectional inverter to ac grid.

The maximum power point (MPP) voltage range of a singlePV panel ranges from 15 to 40 V and has a power capac-

ity of about 100 to 300 W [9]. An SPO has a high step-up

converter that increases low-input voltage to a sufficient volt-

age level. Various step-up dc–dc converter topologies include a

conventional boost and flyback converters [10], [11], switched-

inductor converter, and switched capacitor converter [12]–[16],

as well as a transformerless switched capacitor types [17], [18],

voltage-lift types [19]–[21], capacitor–diode voltage multipli-

ers [22]–[25], and boost types that are integrated with coupled

inductors [26]–[29]. With increasing voltage gain, recycling the

leakage inductance energy of a coupled inductor will reduce the

voltage stress on the active switch, which enables the coupled

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