Photovoltaic Power Conditioning System Research Articles

Design and control of LCL-type grid-tied PV power conditioning system based on inverter and grid side currents double feedback

ABSTRACT Solar energy as a limitless, clean, and cost-effective energy source could be converted to electrical power by photovoltaic cells. In this paper, a photovoltaic power conditioner, which is connected to the low voltage grid via an LCL filter, is presented. This power conditioning system supplies high-quality current and has high stability against disturbances. Since the generated PV voltage is lower than the grid voltage, a DC-DC converter is utilized. Also, DC voltage is also converted to AC by an LCL-type inverter. To ensure the resonance elimination yielded from the LCL filter, inverter and grid side currents, a double feedback strategy is employed. By considering resonance damping, stability margin, and the grid-connected requirements, a systematic design procedure for the suggested strategy is investigated to ensure the system stability in the low-voltage network. In comparison with the conventional strategies, the suggested strategy gives suitable resonance damping capability, higher marginal stability, and better grid-connected properties. Simulation results of the PV power conditioning system illustrate the accurate performance of the control system, suitable tracking of the PV array maximum power point, and high-quality current injection into the grid.

Multi-input multi-output sliding-mode control of LCL-based grid-connected modified Y-source inverter for power conditioning of photovoltaic generation

A multi-input-multi-output (MIMO) sliding mode controller has been proposed in this paper in order to control a grid-connected photovoltaic (PV) power conditioning system with an LCL filter. In the proposed control approach, nonlinear-control method is used and simultaneous control of both the AC and DC inverter sides is done. Therefore, all the state variables are controlled simultaneously. The proposed sliding mode control (SMC) method provides several advantages, including zero grid current error, easy implementation, and robustness against parameter uncertainties of the investigated system. Hence, the resonance in the inverter output resulting from the LCL filter can be eliminated using SMC with no need for active damping techniques. Applying this approach can bring about maximum power point tracking (MPPT), control of the DC side, and injection of high-quality current into the grid at the AC side of the inverter. Various simulations have been conducted in MATLAB/Simulink for the proposed system.

Multi‐input high step‐up inverter with soft‐switching capability, applicable in photovoltaic systems

In this study, a new multi-input high step-up inverter, based on isolated soft-switching DC-DC converter blocks is proposed. Each of these blocks can provide zero-voltage and zero-current switching for its semiconductors, which improve power efficiency. The interesting feature of this DC-DC converter is using bidirectional switches to generate both positive and negative output voltage levels in each DC-DC block with an appropriate control scheme. Each DC-DC converter operates by simple pulse width modulation control through fixed frequency and has two degrees of freedom, which provide the capability of output voltage regulation or maximum power point tracking. The proposed inverter consists of the cascaded connection of these DC-DC converters at their output terminal. This inverter can operate with high voltage gain, where the output voltage of each DC-DC converter is regulated. Furthermore, it can generate more output voltage levels with less number of DC-DC blocks. All these advantages make the proposed inverter suitable for photovoltaic power conditioning systems. In this study, the theoretical analysis with steady-state waveforms, design constraints, resonant tank analysis and comparison study are given. Then, experimental results of both the proposed inverter and its DC-DC blocks are presented.

RETRACTED: Design and implementation of novel soft switching method based DC-DC converter with non-isolated coupled inductor in solar system using FPGA

Abstract DC-DC converter is a basic element for stand-alone photovoltaic power conditioning system. Here, a new topology called an ANFIS (Adaptive Neuro-Fuzzy Inference System) controller based soft switched DC/DC converter with non-isolated coupled inductor has been simulated and presented for improving the power of stand-alone PV system. Both AC analysis and voltage gain is calculated for the proposed converter along with the presence of gain analysis. The steady state/dynamic performance of the non-isolated coupled inductor based converter have been analyzed using MATLAB simulation. The topology has been developed to reduce the input current ripple and to enhance the operating power conversion efficiency. To improve the dynamic response of the converter, Proportional, Integral and Derivative (PID) controller is implemented. However, the linear controllers are influenced by the system parameters of the converters; it results in reduced voltage regulation for wide variations in system parameters. Hence to over rid the limitations of analog controllers and to improve the closed-loop performance of the proposed converter, a simple ANFIS controller is proposed. Consequently, its performance of the proposed controller is compared and analyzed with PID and FL (Fuzzy Logic) controller. It is seen that the implementation of the proposed controller improves the efficiency of the system and also reduces the voltage drop across the switching operation to enhance the operating power conversion efficiency. From the analysis, it is concluded that the proposed converter improves the voltage regulation of the proposed converter. Steady state error, peak time, peak overshoot and THD are used to evaluate the performance of the proposed system. A 200 W, 100 kHz prototype model is developed and demonstrated. Finally, Experimental results are carried out to validate the efficiency of this method using FPGA – Spartan6. From the observed results, it can be revealed that the suggested converter is a feasible alternative to PV applications.

PV power conditioning system using a three‐phase multilevel pulse width modulation inverter employing cascaded Scott transformers

Voltage source inverters (VSIs) are power converters that are considered essential in grid connected photovoltaic (PV) generators. There are several types of topologies for these converters. However, from the point of view of high-quality AC output voltage, multilevel inverters are considered the most adequate. Under this context, this study proposes a new structure for the three-phase DC−AC conversion stage for a grid-connected PV system. It consists of two four-leg two-level voltage source inverters that are connected to two PV generators. These inverters are associated with two Scott transformers. The secondary windings of the transformer are connected in a way that allows a series connection. Due to this, a multilevel operation will be achieved. The performance of the proposed power conditioning system will be verified through simulation and experimental results.

Unit-Minimum Least Power Point Tracking for the Optimization of Photovoltaic Differential Power Processing Systems

Recently, the module integrated converter and differential power processing (DPP) architecture were introduced to enable the photovoltaic (PV) power conditioning system to maintain the optimal operating condition of PV cells, such as maximum power point tracking (MPPT), even under partial shading conditions. However, the DPP architecture was found to have more room to optimize the performance of the systems, by the application of an extra extremum-seeking control, the so-called least power point tracking (LPPT) method that was introduced last year. The main idea is that most of the power from the PV modules is processed through the main-string high-efficiency nonisolation converter, and only a minimal fraction of the power that changes depending on the PV-string current is transferred through the low-efficiency bidirectional isolated DPP converters. This paper suggests a second version of the LPPT method, called unit-minimum power-distributing LPPT, which improves the first version of LPPT, called total-minimum centralized power-distributing LPPT. Instead of minimizing the total power of DPPs, the proposed LPPT minimizes the power of the DPP converter unit, which is the largest among them. Then, the system size and cost can be reduced by the proposed LPPT method, which enables the multiple DPP converters to have smaller power capacity and losses than those of the previous LPPT method. The real-time extremum-seeking algorithm employs a perturb-and-observe method, which comes from the conventional MPPT one, while the optimization process directs minimal extremity, not maximal. The peak system efficiency achieved with a 400-W prototype DPP system employing the LPPT algorithm is 96.7%.

Three-stage control architecture for cascaded H-Bridge inverters in large-scale PV systems – Real time simulation validation

In large-scale PV power stations, Cascaded H-Bridge (CHB) inverter based PV power conditioning systems are recommended over a conventional Two-Level Inverter based systems since CHB operates at medium voltage levels and provides better power quality. An insulated-gate bipolar transistor (IGBT) based H-bridge along with the auxiliaries such as DC link capacitors, breakers, contactors, bypass switch, voltage and current transducers is the fundamental power module of a CHB inverter. In this paper, the procedure for selection of components for Basic building block is presented. Due to a higher number of H-Bridge modules in a large-scale system, it is difficult to control the system with a single controller card. In this work, a control architecture for three-phase CHB based PV power conditioning systems is proposed in which the controls are distributed into three different stages. With the proposed control architecture, independent Maximum power point tracking (MPPT) controls of each PV array is carried out at module level itself. Carrying out MPPT controls at module level helps in improving the computational speed and in maintaining modularity. Hardware requirements of individual processor cards also minimized with the proposed control architecture. In this work, functionalities of each controller card namely module level control card, phase-level control card and master controller cards are explained in detail. Detailed interfacing and signal exchange between H-Bridge modules and the other controller cards are also presented. Controller-in-loop simulations are carried out with the help of Real-Time Simulator to validate the functionalities of each controller card. Real-Time simulation results are presented to verify the operation of the system with the proposed control architecture. Performance and dynamic response of MPPT controls for sudden changes in irradiance inputs on PV arrays are studied. Operation of the system during unequal irradiance inputs on the PV arrays is also analyzed. Current sharing between PV Inverter and grid to feed a fixed load for different values of irradiance inputs is explained through the presented results.

Single-Phase Transformerless PV Power Conditioning Systems with Low Leakage Current and Active Power Decoupling Capability

Single-Phase Transformerless PV Power Conditioning Systems with Low Leakage Current and Active Power Decoupling Capability

Domestic Technical Standards and Performance Test of Photovoltaic PCS for Renewable Energy

This paper describes domestic technical standard of Photovoltaic(PV) PCS(Power Conditioning Systems)-Characteristics of the utility interface. This standard tests utility compatibility and personnel safety and equipment protection of PV inverter performance functions. Especially utility compatibilit...

A PV Power Conditioning System Using Nonregenerative Single-Sourced Trinary Asymmetric Multilevel Inverter With Hybrid Control Scheme and Reduced Leakage Current

A power conditioning system (PCS) using multiple module-integrated converters and a single sourced 27-level asymmetric cascaded H-bridge multilevel inverter (MLI) without regeneration for photovoltaic (PV) applications is proposed. A newly suggested hybrid-switching closed-loop strategy is proposed to enable the use of a 27-level inverter in PV systems. The suggested hybrid-switching strategy implements fundamental line-frequency switching in the main H-bridge to ensure a high efficiency and low leakage current operation. Furthermore, high-frequency switching is used in the auxiliary H-bridge cells to achieve a higher bandwidth control loop. A cost-effective unidirectional single-ended 1-kW dc–dc module based on a boost coupled inductor and charge-pump circuits is proposed to achieve a single PV source per module for a multistring configuration. To couple the unidirectional converters with the central inverter, a jumping element in the hybrid switching strategy is introduced to enable an optimal nonregenerative operation. The proposed PCS with the control scheme is analyzed and verified using hardware results in a grid connected mode of operation.

The Design of a Grid-connected Photovoltaic Power Conditioning System

In view of the grid-connected photovoltaic power system’s function of load shifting to the power network and to achieve the coordinated control of inverter and battery management system, this paper designed a grid-connected photovoltaic power conditioning system (PCS) with function of bi-directional conversion. The function of the PCS is set, the control strategy and technology indexes is also given out. The research improves the solar energy utilization efficiency of the grid photovoltaic power generation, and makes the function of load shifting to the power network coming true without interference, so as to achieve the purpose of saving energy.

Three-level three-phase transformerless inverter with low leakage current for photovoltaic power conditioning system

This paper presents a three-level three-phase transformerless inverter with low leakage current for photovoltaic (PV) power conditioning systems (PCS). The proposed PCS consists of a three-level step-up converter and a modified three-phase T-type inverter and is developed for a corner grounded delta system. By connecting the grounded S-phase directly to the midpoint of the input and the dc-link capacitors, the common mode voltage is fixed to a constant value and leakage current is suppressed. The three-level step-up converter not only lowers switching and conduction losses with reduced voltage stress but also guarantees balancing of the dc-link capacitor voltages using a simple control algorithm. As the modified three-phase T-type inverter has only two legs, the number of components is reduced and power loss is minimized. The direct nominal voltage compensation control algorithm enables the PCS to obtain high grid power quality. The proposed PCS is theoretically analyzed in detail, and experimental and simulation results are applied to a 10kW prototype to evaluate its performance.

A Flyback-Assisted Single-Sourced Photovoltaic Power Conditioning System Using an Asymmetric Cascaded Multilevel Inverter

This paper proposes a power conditioning system (PCS) for distributed photovoltaic (PV) applications using an asymmetric cascaded multilevel inverter with a single PV source. One of the main disadvantages of the cascaded multilevel inverters in PV systems is the requirement of multiple isolated DC sources. Using multiple PV strings leads to a compromise in either the voltage balance of individual H-bridge cells or the maximum power point tracking (MPPT) operation due to localized variations in atmospheric conditions. The proposed PCS uses a single PV source with a flyback DC-DC converter to facilitate a reduction of the required DC sources and to maintain the voltage balance during MPPT operation. The flyback converter is used to provide input for low-voltage H-bridge cells which processes only 20% of the total power. This helps to minimize the losses occurring in the proposed PCS. Furthermore, transient analyses and controller design for the proposed PCS in both the stand-alone mode and the grid-connection mode are presented. The feasibility of the proposed PCS and its control scheme have been tested using a 1㎾ hardware prototype and the obtained results are presented.

A new approach in maximum power point tracking for a photovoltaic array with power management system using Fibonacci search algorithm under partial shading conditions

This paper deals with maximum power point tracking (MPPT) of a photovoltaic (PV) system under partially shaded conditions and active power support to the grid with power quality improvement at the point of common coupling (PCC). The overall system also provides an efficient power management among the various power sources, i.e., photovoltaic system, battery, and grid. The proposed MPPT algorithm is based on two important aspects, i.e., power versus voltage characteristic curve of the PV array under normal as well as partial shading conditions and a modified Fibonacci search algorithm. The PV power conditioning system is connected to the grid through an inverter and a DC-link capacitor. The inverter works both as a DC–AC converter for the PV system and as an active power filter for compensation of harmonics and reactive power. This system is cost-effective as a single inverter is used for both power quality improvement and power flow control from the PV system to the grid. Under unavailability of main AC supply, the operation is switched over to the standalone mode in which the PV system along with the battery is used to meet the load power demand. The performances of the above system are verified by simulation studies in MATLAB/SIMULINK environment and on a real time experimental prototype system using dSPACE controller.

독립형 태양광 인버터의 병렬 운전 기법

In this paper, a parallel operating technique for the stand alone photovoltaic (PV) power conditioning system (PCS) is proposed. The proposed parallel operating technique can increase the power rating of the system easily. Also, it provide three-phase connection function. The proposed technique does not separated master and slave system. Also, it does not use the separated synchronization line. Therefore, the PCS can supply continuous power even if one of the PCS breaks down. This technique is composed of a phase locked loop (PLL) control, droop control, current limit control and etc. Experimental result obtained on 2-kW prototype to verify the proposed technique.

Three-level single-ended primary-inductor converter for photovoltaic power conditioning systems

The two-level single-ended primary-inductor converter (SEPIC) has been used for photovoltaic (PV) power conversion. The two-level SEPIC, however, has high switching losses because of high switch voltage stress. To reduce the switching losses, a three-level SEPIC is proposed. The three-level SEPIC has low switching losses by reducing the switch voltage stress. It improves power efficiency by using a lower-voltage-rated switch, which has better switching performance compared to the switch in the two-level SEPIC. In this paper, the operation of the three-level SEPIC is explained. The control strategy is described to perform the maximum power point tracking (MPPT). The capacitor voltage balance control is also addressed. The experimental results for a 1.0kW prototype system are discussed for a PV power conditioning system. The three-level SEPIC achieves high efficiency of 96.2% for a 1.0kW output power, improving power efficiency by 1.3% compared to the two-level SEPIC.

Flexible System Architecture of Stand-Alone PV Power Generation With Energy Storage Device

A standalone photovoltaic (PV) system with energy storage requires a complex control architecture to take into account the various operating modes. In many cases, a supervisory controller is necessary to manage the change of the control architecture according to the applied mode. This paper presents a flexible architecture of a PV power conditioning system with energy storage. The proposed conditioning unit contains a boost converter (BC), a single-phase inverter, and a bidirectional dc/dc converter connected to the PV side of the BC. The BC regulates the dc-link bus-voltage. The bidirectional dc/dc converter endures battery bank charge/discharge control and PV maximum power point tracking (MPPT). Such architecture guarantees nonchange in controller configuration when the storage disconnects. Therefore, the previously needed supervisory controller is eliminated. A system control strategy based on sliding-mode control (SMC) ensures a reliable output voltage regulation such as fast dynamic response, small steady-state error, and low total harmonic distortion (THD) under step changes and nonlinear loads. The controller structure, the dynamic behavior, and the design procedures are introduced. Finally, the validity of the proposed module with control strategy is verified through hardware experiments on a 500-W prototype test bed with a single TMS320F28335 DSP module.

A New Low-Cost Centralized MPPT Controller System for Multiply Distributed Photovoltaic Power Conditioning Modules

In this paper, an integrated maximum power point tracking (MPPT) controller system using a ZigBee wireless communication module is proposed for multimodal power converters as a concept of an intelligent photovoltaic (PV) module of PV power conditioning systems. The proposed scheme can integrate all information under a single host controller to realize low-cost manufacturing. It can also simplify the monitoring and supervision processes through machine-to-machine communications for the smart-grid. The voltage and current information for each module are periodically sampled and transferred to the central inverter (or another host server) through the ZigBee module. After the transmission process, the MPPT control algorithm derives each of the PV voltage reference parameters to return to each PV module accordingly. The technical benefits of the proposed approach is the configuration of a PV-controller system composed of a single digital-signal processor (DSP), low-cost analog controllers, and some mandatory communication peripherals used to monitor the distributed multimodules. Also, the method is quite desirable for supervision and monitoring of the overall system due to its centralized control structure. For the experimental validation of the proposed MPPT control, multiple ZigBee (XBee-PRO series) modules, as well as a DSP, dual-module solar simulators, and a couple of 50 W dc–dc power conversion hardware prototypes were utilized.

비절연형 양방향 탭인덕터 부스트 플라이백 컨버터

This paper proposes a new bidirectional DC–DC converter with high efficiency. The proposed converter is composed of a flyback and a tapped-inductor boost converter to satisfy extreme operating conditions with low cost. The outputs are connected in series to achieve a high-voltage step-up. In the reverse direction, the proposed converter has an extreme step-down voltage. In this study, the proposed converter was employed with a 100 W hardware prototype. To design the controller, a small-signal transfer function of the proposed converter is derived. For PV power conditioning systems, a maximum power point tracking method is applied with perturb and observe method. To verify the operation of the bidirectional power flow, the current controller is applied. All of the controllers are employed with a digital signal processor.

Power Conditioning for a Small-Scale PV System with Charge-Balancing Integrated Micro-Inverter

The photovoltaic (PV) power conditioning system for small-scale applications has gained significant interest in the past few decades. However, the standalone mode of operation has been rarely approached. This paper presents a two-stage multi-level micro-inverter topology that considers the different operation modes. A multi-output flyback converter provides both the DC-Link voltage balancing for the multi-level inverter side and maximum power point tracking control in grid connection mode in the PV stage. A modified H-bridge multi-level inverter topology is included for the AC output stage. The multi-level inverter lowers the total harmonic distortion and overall ratings of the power semiconductor switches. The proposed micro-inverter topology can help to decrease the size and cost of the PV system. Transient analysis and controller design of this micro-inverter have been proposed for stand-alone and grid-connected modes. Finally, the system performance was verified using a 120 W hardware prototype.