1- Introduction

2- System architecture

3- Modelling of the WECS

4- Performance analysis of proposed DC nanogrid topology

5- Conclusion

References

Abstract

Wind energy conversion system (WECS) based DC nanogrid topology is proposed in this paper. The WECS topology is based on self-excited induction generator (SEIG) which is cost effective, and has rugged construction and combination of diode bridge rectifier (DBR) with DC-DC converter to implement the maximum power point tracking technique. The combination of diode DBR with DC-DC converter allows simple control structure due to one controllable switch as compared to complex control in the conventional controlled/semi-controlled rectifier with six controllable switches. Further, proposed DC nanogrid topology enhances the SEIG efficiency due to the reduction of harmonic injection on machine side from DBR implementation. The detailed harmonic spectrum analysis is carried out by developing the laboratory scale prototype of DBR based SEIG topology for WECS to justify the selection of DBR instead of the controlled rectifier. Further, to analyze the effect of different types DC-DC converter to make combination with the DBR. Afterwards, the dynamic performance of the proposed DC nanogrid topology is analyzed to understand the selection of the DC-DC converter with DBR for different DC grid voltage conditions.

Introduction

Electricity plays a vital role in energy supply, however, the electricity generation is the single largest source of CO2 emission, which is more than 40% of CO2 emission related to global energy. By the year 2030, global electricity demand is likely to double [1,2]. Hence, climate change mitigation and increasing energy demand motivates for the development of renewable energy resources. The renewable energy resources such as solar and wind energy are distributed in nature which favors the electricity generation and consumption on site. With technological advancement and regulatory changes, the concept of supplying the load locally has led to a concept of nanogrid. Thus, the development of renewable based nanogrid are gaining attention in recent past for providing environment-friendly, sustainable and economical electricity [3]. Further, the development of power electronics has transformed the load profile of end user as the modern appliances operate on DC supply [4]. Having this understanding, the concept of DC nanogrid has been proposed in the literature to elude multiple AC-DC conversion and vice-versa [5]. The DC distribution enables easy control, no issue of frequency, power angle, phase sequence, and power factor. Mashood et al.

This paper proposes the self-reconfigurable batteries topology without DC-DC converter, which is similar to selfreconfigurable batteries, but it can guarantee that the voltage of the battery pack is within the set range when the SOC (state of charge) is from 0 to 100%, even if the voltage will drop with the SOC or some cells will be bypassed. Simply put, when the battery pack is discharged, the batteries whose SOC is high and their voltages satisfy the demand are discharged, and the cell with lower SOC is continuously replaced, and the consistency of the battery pack is ensured while stabilizing the voltage. The topological and control strategy are analyzed in detail. The proposed topology is verified by the battery pack composed of 9 cells in series, the experiment result shows that this topology not only retains the advantages of good equalization of self-reconfiguration batteries but also maintains low voltage fluctuations even without DC-DC converters, besides, without the DC-DC converter, the capacity utilization rate of the battery pack reaches 99.8%, demonstrating the superior performance of the proposed topology.

Introduction

Lithium-ion batteries are widely used in a variety of applications, including electric vehicles, energy storage systems, due to their high energy density, long cycle life and low self-discharge rate [1]. A number of battery cells are usually connected in series in order to supply higher voltage and higher power to the load in a wide range of applications, while significant efforts are made by designers to select the battery cells such that they are as identical/matched as possible, the battery cells will still have mismatches in practice due to manufacturing tolerances, different self-discharge rates, uneven operating temperature across the battery cells, and nonuniform aging process, among others [2]. Such inevitable differences within battery cells will drift apart through cycling and could potentially lead to overcharging or over discharging, it is clear that such non-uniformity limits the battery capacity and may even cause safety issues [3]. Therefore, to properly maintain all cells balanced is of significant importance for enhancing battery life [4–6]. While the passive balancing dissipates the excess energy through resistors in the form of heat, the active balancing equalizes the battery cells by transferring the excess energy between battery cells [7].

In this paper, the effects of random spread spectrum (SS) electromagnetic interference (EMI) on digital communications are addressed. For this purpose, the influence of EMI on a communication channel is described in the framework of information theory in terms of an equivalent channel capacity loss, which is analytically predicted and validated by experimental results. The EMI-induced channel capacity loss for nonmodulated and SS-modulated interference generated by a switching-mode DC-DC power converter are then evaluated for different EMI and channel characteristics so that to compare different scenarios of practical interest.

Introduction

Electromagnetic interference (EMI) from switching-mode power converters and digital equipment can be easily coupled to susceptible communication blocks within the same module or integrated circuit, due to parasitic coupling through the power distribution network, through the package and/or through the silicon substrate and can be a threat to the operation of present-day information and communication technology (ICT) electronic systems inducing malfunctions ranging from the degradation of the bit error rate (BER) up to the complete failures [1]–[6]. As a consequence, EMI needs to be carefully controlled in the very first design stages at architectural and integrated circuit level to assure the proper operation of complex systems with no penalty in terms of costs, time-tomarket and performance, and also in order to meet the more and more stringent Electromagnetic Compatibility (EMC) regulations [7]–[10]. In this context, several techniques have been devised to address EMI at circuit and architectural level [11]–[14]. In particular, the techniques based on the frequency modulation of critical switching signals, generally known as SpreadSpectrum (SS) techniques, have been extensively proposed as simple, low cost solutions to mitigate EMC problems and are widely employed in practice [13]. Spread-spectrum techniques have been introduced as a mean to reduce the peak value of EMI spectrum since the middle of 1990s with specific reference to switching power converters and digital clocked equipment [15], [16].

I- Introduction

II- Fundamental Assumptions

III- Inductor Voltage Equation

IV- First-Order Converters

V- Second-Order Converters

References

Abstract

The paper describes a theory to synthesize nonisolated DC-DC converters. It uses the fundamental flux balance equation across the inductors of a converter as a starting point in this synthesis process. The flux balance equations are the linear equations of the input voltage, capacitor voltages and duty cycle (D). The coefficients of these linear equations can be selected from a finite set of choices. These choices define the converter topologies which are subsequently used to synthesize a converter. The synthesis procedure applies to a converter of multiple order. All the possible converters are identified for a first order topology. In the case of second-order converters, all the choices of the flux balance equation are defined. Based on these choices three new quadratic topologies are derived and verified to demonstrate the effectiveness of the theory. The procedure to synthesize a converter from a given voltage conversion ratio is also outlined.

INTRODUCTION

Non-isolated DC-DC converters are the basic building blocks for power processing in renewable applications, data centers, and various consumer electronics devices, etc. Buck, Boost, and Buck-boost topologies are the three major topologies which are manipulated to obtain other non-isolated topologies [1-17]. With increasing novel areas of application, there is a need to look for DC-DC converters with a given voltage conversion characteristic. For example, quadratic buck (Q buck) converter provides a very low output to input conversion ratio at a relatively higher duty-cycle [12-13], which makes it suitable for bias voltage derivation when input DC is very high. Mostly, converter topologies are invented intuitively or by combining the existing basic topologies of buck, boost, and buck-boost converter. However, a systematic procedure to synthesize a converter topology from the required voltage conversion ratio is scarce. This paper presents a thorough review of the prior attempts to generalize DC-DC converter synthesis process and subsequently proposes a method to synthesize the exhaustive set of DC-DC converters of a given order. While many DC-DC converters have been invented over the past few decades, there has been a constant drive among the researchers to find a unifying link among the different DC-DC converter topologies and find a generalized converter synthesis theory. Many such approaches such as graph-theoretic approach with duality principle [1], [2], converter switching cell theory [3], [4], [5], [6], analytical synthesis theory [7], [8], and converter synthesis with layer and graft schemes [9-11], etc., are presented in the literature. The graph-theoretic approach was used in [1] to establish a relation between basic Pulse Width Modulated (PWM) converters [1-7, 18-22].

The hybrid energetic system (HES) is generally an energy system operating simultaneously several sources with different capacities and proprieties. It is principally based on renewable energy sources (RES) and distributed generators DG. Their distributed production should meet an increasingly variable demand. The RES depend strongly on meteorological conditions, thereby they cannot be considered as a continuous energy supply and therefore behave as passive generator. To balance between consumption and generation the RES should be coupled with other sources and storage systems. Diversifying the energy sources is now a real issue. Hybridizing the RES with the storage system and DG as cogeneration system can meet the distributed production requirements allowing the RES intensive integration. The HES ensure a long-term energetic availability and it is able to deliver a subscribed power when the RES act as active generators. The HES can be shown as a supply system consisting of small distributed energy systems [1-2]. However, the DGs and the storage technologies life cycle should be respected. To take full advantages of the HES a distributed energy management (DEM) is necessary. It deals with the simultaneous operation of the different generators, the storage system and DGs constraints, and the variable load demand. Furthermore; other requirements should be satisfied in the DEM, as voltage limit control, the produced energy cost, the system effectiveness, the energy quality improvement, the energy flexible use and the environmental issue. Thanks to DEM, the HES can produce and consume effectively depending on the capacity of each generator and the loads’ needs. The HES studied in this paper consists of PV generator and wind turbine as a RES and battery as storage technology system. This configuration can lead to prematurely lose battery life, because of the quickly battery charge and discharge. Many studies have dealt with the effective battery use [3-4]. Linking a hybrid generator to the RES and the battery as the Fuel cell (FC)-electrolyser combination generator is the HES suggested in this paper. A custom role for power electronics is the development of HES, by meeting the distributed production constraints. Several studies have brought more interest to HES control containing DGs, RES and storage technologies. The Fuzzy logic and neural networks [5] were the subjects of many studies regarding the HES control, but the complexity and the difficulty in their implementation and comprehension can be their main inconvenient. Furthermore, these approaches can make the system non-scalable which conflicting with the distributed generation and therefore the future energy networks. This paper proposes a distributed energy management system based on the bus voltage control allowing simultaneously a flexible energy generation and consumption depending on the capacity of each generator and the variable demand by the bias of multi-agent system (MAS).

In this paper, a novel PWM carrier synchronization method is proposed for distributed DC–DC converters in DC-Microgrids. The synchronization method is based on carrier frequency extraction from DC-bus voltage ripple. In addition, an advanced phase shift control algorithm for the synchronized carriers is implemented to reduce the DC bus voltage ripple contents. A DC-Microgrid encompassing different distributed energy resources with their DC–DC converters is modeled using Matlab\Simulink to test the proposed synchronization method and control algorithm. Then, a small power scale experimentaltestbed is built in order to validate the simulation results. The simulation and the experimental results demonstrated that the proposed method and algorithm are very promising to minimize DC-bus ripple contents in DC-Microgrid applications. © 2018 Elsevier B.V. All rights reserved.

Introduction

The new trend in future power generation systems is developing toward Distributed Generators (DGs), which means that energy conversion systems are situated close to energy consumers and large units are substituted by smaller ones [1]. The integration of these DGs, energy storage systems, and distributed electric loads through the point of common coupling is called a Microgrid (MG) [2]. MGs can be configured into DC (DCMG) and AC (ACMGs) based on the power electronics interface circuits that will be used [3]. Recently, there has been a general upsurge of interest in using DCMGs being described as flexible, intelligent, and active power networks [4]. In addition, they are able to improve system reliability, efficiency, and security leading to promote and increase the renewable energy sources integration [5].In DCMGs, a DC–DC boost converter is a key element to interface DGs to the MG’s DC-bus [6]. Various DC–DC boost converters topologies have been studied in Refs. [7–12]. DCMGs along with their DC–DC boost converters still face numerous challenges such as ripple contents of the MG DC- bus voltage and current [13]. Indeed, voltage and current ripple are among the various phenomena that contribute to a reduction in lifespan of power sources and energy storage devices interfaced to the DC-bus [14,15]. Multi-Phase Interleaved Boost Converters (MP-IBCs) are introduced in applications such as electric vehicles to interface different DC power sources to a common DC bus achieving low ripples contents in the input current and the output voltage [16,17]. The pulse width modulation (PWM) signals ofthese converters are generated based on multiple carriers with the same frequency and different phase angles. The synchronization of these multiple PWM carriers are quite easy since all the PWM modulators are driven from the same controller and hence the same oscillator [18]. In addition, the phase angles can be easily considered as 360/N where N is the number of converters as mentioned in Ref. [19]. In applications such as DCMGs, each DG along with its converter has its own local controller (LC) and hence its own oscillator which makes the PWM carriers synchronization is a big challenge. This challenge is related to the frequency drift of each oscillator due to temperature and component tolerance. This drift will create a continuous change in the phase shift angle between PWM carriers of each converter [20,21]. To ensure the most accurate synchronization process, it should be taking into account clock drift and start latency by using the available real-time system integration [22]. InRef. [23], a theoretical study has been presented for DC-bus voltage ripple minimization of distributed DC–DC converters based on phase shifting theory. However, there is no experimental study to validate that theory. In this article, a simulation study as well as an experimental investigation for the aforementioned study is presented. The proposed method is investigated based on extracting the carrier frequency information from the DC-bus voltage ripples to generate a very accurate and stable time reference in order to generate synchronized PWM carriers for DC–DC converters. One of the DCMGs converters will be chosen by the Microgrid energy management center (MGEMC) to work as a master converter. This converter will be responsible to regulate the carrier frequency of the DC-bus. The other converters, slave converters, interfaced to the DC-bus will receive the carrier frequency component based on measurements from the bus ripples and will synchronize their local frequency to this carrier. Following the synchronization process, LC based on DC-bus voltage measurements will run its phase shift control algorithm (PSCA) in order to deliver the optimum phase angle of PWM carriers and minimize the DC-bus ripple.

Sliding mode control (SMC) was first proposed for variable structures in the early 1950s in the former Soviet Union [1– 3]. Since then, variable structure systems and their control methods have been used in a broad range of different applications, such as non-linear discrete models; and multiinput/multi-output, large scale, and stochastic systems. The main control goal for variable structure systems is to improve the closed-loop stability. In recent years, nonlinear controllers have been largely replaced by linear controllers for DC-DC power converters, using feedback linearization [4], adaptive back stepping control [5], non-active based control [6], and SMC [7] to regulate the output voltage. Robust SMC has attracted consider-able attention because of the simplicity of implementation, relatively low volume calculations, and the controller can be practically implemented using basic analog circuits rather than digital processors. Applying sufficient controller power switches, the power converter is tuned so the output voltage tracks the reference value (Vref). The effects of parasitic elements were not considered in the modeling phase. For example, the voltage drop across the power switch, semiconductor diode, and output capacitor equivalent series resistance in dynamic and steady state equations governing the behavior of the converter were neglected. The proposed method was simulated in MATLAB / Simulink, and the controller, buck converter, boost, buck/boost, and fly back responses were determined. The proposed sliding mode control can cover the operating range of load variations, input voltage, and other parameters to provide robust and steady output voltage.

High conversion gain dc-dc power converters have recently seen an increased demand in variety of power electronics applications. In fact, the main reasons behind this increased attention have three folds. Firstly, fast deployment of Renewable Energy (RE) based power systems has intensified the need for high conversion gain power converters. This is due to the low voltage generation inherent in most RE sources such as Photovoltaic (PV) modules and fuelcells, where stepping up the low input voltage (e.g., 20 V – 40 V) to higher voltage levels (e.g., 200 V – 400 V) is required in order to have a properly function grid-forming or grid-feeding converter [1], [2]. Secondly, prevalence of applications demanding higher voltage levels for better performance, from few hundreds of Volts such as for Light Emitting Diode (LED) in lightning [3] up to few kilovolts in pulsed power applications [4]. Lastly, one of the most relevant is the possibility of distributing electrical energy more efficiently at higher dc voltage levels (e.g., 380 V400 V or even higher). This is the case in applications such as telecommunication and dc power systems where electrical energy can be transferred with higher efficiency, reliability and power quality [5], [6]. Conventionally, the boost and buck-boost topologies can be employed in order to step-up the output voltage. However, practically achieving conversion gains of beyond six due to presence of parasitic elements is not feasible [2]. Moreover, operating at high duty cycles compromise the boost converter efficiency as small turn-off times which may incline Electromagnetic Interference (EMI) and ripple current levels, indicating a requirement for larger magnetic components [2], [7]. Another derivation of a buck-boost topology suitable for high voltage applications is the flyback converter [4], [8], [9]. Although this topology is well employed for high voltage applications with low parts count, it is only suitable for very low power levels (i.e., < 300 W). This is due to the high dc magnetization current requirement of its flyback transformer, which increases the size of the transformer and consequently the losses for higher power levels under continuous conduction mode operation [8]. From this standpoint, many research efforts have been devoted towards developing high voltage gain power converters without imposing extreme duty ratio. In general, the demanded performance can be obtained through utilizing coupled-inductor, switched inductors and switched capacitor cells [7], [10]-[16] and/or employing multi-cell configurations [4], [17]-[21]. All these attempts are made in order to overcome the existing technological limits (i.e., power switch breakdown voltage and limited power ratings) and to reach the required output voltage level with minimum duty ratio (i.e., obtaining better efficiency). However, in many practical situations, in order to obtain the required voltage gain and reduce voltage stress across the power switch many switched-cells are typically required. Furthermore, using an impedance network is also considered as another topological variant. The impedance network based power converters. known as Z-source, is initially proposed for dc-ac inverter operation [22], but it can be modified to operate as a high voltage gain dc-dc converter [23]. Recently, with the aim of reducing start-up inrush current and improving the voltage gain of conventional Z-source converter, a variety of modified impedance networks have been introduced. These modifications can be summarized as switched inductor, extended boost, switched inductor quasi Z-source and enhanced boost [24]-[29].While using the aforementioned topologies a high voltage gain with small duty cycle (D) is achievable, but the demerits of the aforementioned topologies are high parts counts (i.e., diodes, inductors and capacitors) and particularly the conduction of most diodes in (1-D) of the switching period, which lead to high power loss and low efficiency.

As the most common and practical topology of the power converters, DC-DC converters have the advantages on simple structure, low cost and high conversion efficiency. DC-DC converters have been widely used in household appliances, electrical industries, aerospace and other fields [1-5]. Today, pulse width modulation (PWM) is widely adopted in DC-DC converters. In addition, the traditional linear modeling and stability analysis methods are usually used for DC-DC converters, such as the average state space method [6]. But as the rapid development of power electronic technologies, the requirements of power electronic systems or equipment on stability, reliability and electrical performance have become stricter and stricter. The traditional linear modeling and analysis methods more and more cannot satisfy these requirements due to the nonlinearity of power converters [7]. In recent decades, the nonlinear behaviors of the power converters have been gradually revealed [8, 9]. The application of nonlinear theories in the field of power electronics has become a hot topic and received wide attention both at home and abroad [10-14]. At present, the common nonlinear analysis methods include analytical method [15, 16], phase plane method [17], switch signal flow graph method [18, 19], describing function method [20, 21], etc. The analytical method solves the state-space averaged equations directly, which is suitable for the one or secondorder system. But, the analytical method is very complicated for the high order systems [22]. The phase plane method is a graphic analysis method, and it transforms the movement of the first or second order system to a trajectory about position and velocity in phase plane, which is intuitive but also disabled for the high order systems [23]. The switch signal flow graph method is a nonlinear graphical modeling method, by which, the switching process can be equivalent as two linear branches in turn-on or turn-off periods [18, 19]. But the dedicated graphic computer simulation software is needed for the analysis. The three methods mentioned above all use the concept of averaging for system modeling and analysis, which can neither reflect the frequency characteristic of the nonlinear link nor be used in high order system.

Currently, studies on Integrated Power System (IPS) for ships are increasing to integrate several modules such as Power Generation Modules (PGM), Power Distribution Modules (PDM), Power Conversion Modules (PCM), Energy Storage Modules (ESM), Propulsion Motor Modules (PMM) and Power Control Modules (PCON) in order to operate IPS efficiently [1]. DC zonal distribution in the shipboard power system is more advantageous compared to AC radial distribution owing to its difficulties in isolating the fault. Hence, an integrated power system with DC zonal distribution is the hot topic for researchers and the best option for shipboard power system [2]. The energy storage system in next-generation shipboard power supplies is batteries, ultra capacitor, fuel cell, etc. The Shipboard power system is given in figure 1. All Electric Ship (AES) is the best way to power all the loads in the ship from the common electric platform [3]. IPS in all-electric ships will reduce the cost and provides flexibility in the system. Nowadays, submarines are incorporated with Medium Voltage DC (MVDC) integrated power system. DC-DC converter plays a vital role to supply power to the loads in the ship with MVDC shipboard power system. The presence of DC-DC converter can affect the power quality and stability of the system. So, PCM is designed to provide appropriate system stability [4]. Power electronic converter integrates the renewable energy sources and energy storage systems to the electric grid. Thus, it is necessary to work on the power electronic equipment to interface all the loads to the sources in the future AES. Reduced Redundant Power Processing is introduced and used for PFC voltage regulator to improve its efficiency [5]. Prevention of reprocessing of power processed by one converter entirely by another converter is called Reduced Redundant Power Processing (RRPP). This technique is also used to derive quadratic step down DC-DC converters [6]. The attractive feature of this method is to avoid the power reprocessing and to improve the efficiency of the converter [7, 8]. A family of the quadratic step-up DC-DC converters is derived based on RRPP by avoiding the cascade connection in [9]. However, it is observed that in this case, the conversion ratio is quite low. The conversion ratios of the four derived topologies in [9] are equal to the voltage gain of the quadratic boost converter or lesser than QB converter. Modeling of the converters derived using RRPP is carried out in [10, 11], and its dynamic behavior is analyzed. Derivation of the high gain DC-DC converter using RRPP technique is not yet reported in the literature. The primary intent of this learning is to derive a topology using this method for high voltage applications. In this article, we derived four topologies (type I-IV) with RRPP based on I-IIA configuration in [5], and we analyzed the performance of all the topologies. Finally, we observed that type-IV topology is superior compared to other *For correspondence topologies. Type-IV topology is compared with the other high gain converter reported in the literature to prove its superiority.

Dual active bridge (DAB) DC-DC converters have several advantages, such as bidirectional power flow, high power density, easy implementation of zero-voltage switching, convenient access to cascading and parallelism. As a result, these converters are widely used in the distributed generation systems [1–3], DC-micro-grid systems [4], electric vehicle charging systems [5–8], energy storage systems [9, 10], and power electronic transformers in railway locomotive applications [11, 12]. In applications mentioned above, it is significant to achieve robust dynamic performances of DAB DC-DC converters under challenging circumstances, such as input voltage fluctuation, output load disturbance, and etc. Various advanced control schemes have been proposed to enhance the dynamic response. Firstly, dynamic characteristics of DAB DC-DC converters were analyzed by the small-signal modeling and the discrete-time average modeling methods [13–15]. A feed-forward compensation strategy [16], which feedbacks the load current to the control system, was used to improve transient response of DAB DC-DC converters in the load disturbance conditions. However, a table lookup is essential for the feed-forward strategy, which makes it less applicable in complex operation conditions. Besides, a model-based phase-shift (MPS) control was also developed to improve dynamic response under load disturbance [17, 18]. Meanwhile, high efficiency is another critical requirement for DAB DC-DC converters. Switching strategies utilizing off-line computation have capability in minimizing power losses [19, 20]. However, consecutive optimal control cannot be realized by these strategies. Reducing current stress and power reflow in a DAB DC-DC converter can increase efficiency as well [21]. Extended phase shift (EPS) control, which is able to largely improve efficiency by reducing current stress, was introduced in [4]. However, when EPS control was adopted to DAB DC-DC converters, there usually exists slow dynamic response issues. Direct power control (DPC) scheme is a popular active solution to enhance dynamic performance of AC-DC or DC-AC converters [22, 23]. It is well known for its strong abilities to improve dynamic and static performances of power converters. However, there are few reports about the DPC scheme applied in DAB DC-DC converters so far. By combing EPS control with DPC control, a hybrid scheme EPS-DPC is proposed in this paper. The EPS-DPC scheme unites high efficiency of EPS and great dynamic performance of DPC. As a result, the DAB DC-DC converter using EPS-DPC has advantages in both high efficiency and outstanding dynamic performance. The paper is organized as follows. SPS and EPS control schemes are introduced and compared in detail in Section 2. In Section 3, EPS-DPC control is proposed, and its derivation from combination of EPS and DPC is included as well. Theoretical comparison of dynamic response performance in EPS and SPS was demonstrated in Section 4.

Auxiliary power supply systems in traction vehicles are like air brakes, cooling system, air pressures, fans, etc., supplied from a standard 3×400 VAC on-board power grid. The grid is generated by a structure of dedicated converters which usually also provides battery charging functionality. The design of such auxiliary power supply has to respect the fact that the catenary voltage of nominal value 600 VDC or 750 VDC may vary in the range of 400 VDC – 950 VDC. Also the outputs, either the power grid or battery charger, must be isolated in order to maintain high level safety of the vehicle. The soft switching DC-DC converters in these systems with improved efficiency are reasonable solution rather than using hard switching topologies. The Power electronics transformer (PET) converter is presented in [1, 2], based on half bridge topology. The PET converter has improved power density and better efficiency over conventional converter [3]. Then researchers concentrated on efficient usage of fuel cell and solar cells based full bridge and half-bridge resonant converters [4]. Consequently, in [5], the peak gain approximation made on full bridge topology using LLC, which is used for low power applications with higher resonant frequency. A hybrid series resonant, full bridge converter [6] achieved the zero voltage switching (ZVS) turn-on and turn-off operations by means of simple series resonant elements such as a series inductor and additional snubber capacitors. However, the converter has poor efficiency, due to its conduction losses. A high power density, compact LLC resonant converter [7] with buck converter principle, operated at higher switching frequency, doubled resonant frequency and incorporated with a passive integration was used to integrate L-L-C-T components. The discontinuous conduction mode (DCM) based phase modulated series resonant full bridge converter [8] with an analytical approach effectively derived the critical load resistance by defining the continuous conduction mode (CCM) and DCM boundary conditions. To simplify the transformer, a self-sustained oscillator controller (SSOC) is used and it leads to increase the value of mutual inductance in a resonant full bridge converter [9]. An isolated resonant boost converter with synchronous rectifier [10] and achieved 93.3% efficiency at 1.5 kW. Nevertheless, it has a poor efficiency and expensive. An LLC FB step-down converter [11] achieved 94% efficiency at 67 kHz switching frequency under 500 W output power. The present paper deals with a high efficiency resonant DCDC converter and it is compared with the conventional hard switched full bridge topology. In this paper, we obtained a ZVZCS turn on and ZCS turn off of all the power switches, and also it improved the overall system efficiency.

Despite the reduction of solar installation cost by a ratio of 10 during the last 20 years, still conversion efficiency of PV panels remains an important parameter to take into account when designing solar system for residential applications [1]. Therefore, an efficient MPPT algorithm plays a key role to harvest optimum available power especially in large solar installations. Several MPPT algorithms have been elaborated in the literature. Among them, perturb and observe (P&O) and incremental conductance (INC) are practically favorable as the awareness of PV panel characteristics is not required. Moreover, their procedures to find MPP are independent of temperature and irradiation values that their measurements need expensive sensors [2,3]. Principally, P&O and INC are inherently perturbative methods that produce reference voltage or current to be tracked by a subsequent controller. The PI controller has been widely used in MPPT operations [4,5]; however, continuous evolution in microprocessor technology facilitates implementing advanced controllers for efficiency enhancement of MPPT algorithm. The ability of Fuzzy logic [6,7], neural network [8] and genetic algorithm [9] has been investigated in MPPT modules. This paper deals with predictive technique that is lately well adopted for various applications. Indeed, model predictive controller (MPC) is a competitive alternative to address the growing industrial concerns regarding to performance and efficiency issues. It can also formulate inherent nonlinearity in power electronic systems with operational constraints. Moreover, its realization in state matrix can be easily extended to multivariable systems [10]. Basically, MPC solves an optimization problem within a moving time horizon in order to generate future actions for optimal operation of a plant. In fact, at each sampling time, MPC reconstructs instant operating model of the plant, predicts future states and optimizes current dynamic while taking into account the future states. Real time modification is a desirable property in practice that can compensate inevitable modeling errors [11]. In power electronics, MPC were emerged with finite control set (FCS) appearance. Actually the pulse activation nature of switching converters allowed defining FCS-MPC that evaluates cost function in only possible switching states. A low complexity optimization algorithm is solved and simply the minimum cost is selected among predetermined states at each sampling time. FCS-MPC has been investigated in most applications of power converters [12–14], and especially in PV systems [15–18]. Despite numerous reports in this area, the applicability of FCS-MPC is yet a challenge. It works with variable switching frequency which leads to a widespread harmonics spectrum for voltage/current waveforms. This is a fundamental limitation that hinders filter design [19,20], increases switching losses, makes unwanted resonances, and consequently reduces system performance in terms of power quality [21]. However, the switching frequency could be regulated by including some more terms in the cost function, it would add the complexity and consequently the computation burden to the FCS-MPCs while distracting control effort from main target of the reference tracking [22,23]. Moreover, none-zero steady state error is reported in [24,25]. Furthermore, the computational burden increases exponentially in multilevel converters with high number of switching states [26].