Veerapol Monyakul

High efficiency battery management system for serially connected battery string

This article presents an approach for balancing serially connected battery strings with high efficiency energy transferred. The efficiency of this balancing process is accomplished by channeling an excess energy through a DC Link Bus rather than done serially. Using this proposed technique with converter which was 80 percent efficiency, the equalized efficiency of balancing process is increased more than the conventional techniques at least 12.80 percent. By applied this proposed technique to the charge equalized system, the unbalance charging problem can be eliminated. The validity of this approach can be supported by computer simulation and experimental result.

A microcontroller based islanding detection for grid connected inverter

This paper presents the development of a microcontroller based islanding detection for grid connected inverter with very simple under/over voltage and under/over frequency islanding detection algorithms. The system based on a microcontroller from Microchip Technology Inc. PIC family. A PIC microcontroller searches the under/over voltage and under/over frequency from utility grid and processed the value of voltage and frequency for turned on-off relay between grid connected inverter and utility grid.

CPLD-based islanding detection for mini grid connected inverter in renewable energy

This paper presents the development of a CPLD-based islanding detection for mini grid connected inverter in renewable energy with very simple under/over voltage and under/over frequency islanding detection algorithms. The system was implemented on a single XC9572 complex programmable logic device (CPLD) chip using schematic based and VHDL based synthesis model The CPLD monitor the under/over voltage and under/over frequency of utility grid and processed the value of voltage and frequency for turned on-off relay between mini grid connected inverter and utility grid.

Charge equalized module for serially connected VRLA battery string using quasi-resonant flyback converter

This article present charge equalized module using quasi-resonant flyback converter with DC-link bus strategy. With this technique, turn on switching loss is decrease by 71 percent. Switching at low voltage and operating at low dv/dt, the electromagnetic interferences are also decline. By applied this proposed technique to the charge equalized system, the unbalance charging problem can be eliminated. The validity of this approach can be supported by computer simulation and experimental result.

FPGA-based islanding detection for grid connected inverter

This paper presents the development of a FPGA based islanding detection for grid connected inverter with simple under/over voltage and under/over frequency islanding detection algorithms. The design is based on the Xilinx chip XC4005E field programmable gate array (FPGA). The FPGA is used for all system logic function. This allows software development, testing, implementation and modification of logic circuitry without hardware modification. The FPGA monitor the under/over voltage and under/over frequency of utility grid and processed the value of voltage and frequency for turned on-off relay between grid connected inverter and utility grid. The results are provided to demonstrate the effectiveness of the design.

The high efficiency charge equalized system for serially connected VRLA battery string using synchronous flyback converter

This article presents a high efficiency charge equalized system for balancing energy in serially connected battery strings using synchronous flyback converter. The efficiency of this synchronous flyback converter is 80.1 percent. By applying this proposed converter along with DC Link Bus technique in charge equalized system, the unbalance charging problem can be eliminated. The validity of this approach can be supported by experimental result.

Modeling of Photovoltaic Grid Connected Inverters Based on Nonlinear System Identification for Power Quality Analysis

Photovoltaic systems are attractive renewable energy sources for Thailand because of high daily solar irradiation, about 18 MJ/m2/day. Furthermore, renewable energy is boosted by the government incentive on adders on electricity from renewable energy like solar PV, wind and biomass, introduced in the second half of 2000s. For PV systems, domestic rooftop PV units, commercial rooftop PV units and ground-based PV plants are appealing. Applications of electricity supply from PV plants that have been filed total more than 1000 MW. With the adder incentive, more households will be attracted to produce electricity with a small generating capacity of less than 10 kW, termed a very small power producer (VSPP). A possibility of expanding domestic roof-top grid-connected units draw our attention to study single phase PV-grid connected systems. Increased PV penetration can have significant [1-2] and detrimental impacts on the power quality (PQ) of the distribution networks [3-5]. Fluctuation of weather condition, variations of loads and grids, connecting PV-based inverters to the power system, requires power quality control to meet standards of electrical utilities. PV can reduce or improve power quality levels [6-9]. Different aspects should be taken into account. In particular, large current variations during PV connection or disconnection can lead to significant voltage transients [10]. Cyclic variations of PV power output can cause voltage fluctuations [11]. Changes of PV active and reactive power and the presence of large numbers of single phase domestic generators can lead to long-duration voltage variations and unbalances [12]. The increasing values of fault currents modify the voltage sag characteristics. Finally, the waveform distortion levels are influenced in different ways according to types of PV connections to the grid, i.e. direct connection or by power electronic interfaces. PV can improve power quality levels, mainly as a consequence of increase of short circuit power and of advanced controls of PWM converters and custom devices. [13] Grid-connected inverter technology is one of the key technologies for reliable and safety grid interconnection operation of PV systems [14-15]. An inverter being a power

Comparison between FPGA-Based and dsPIC-Based islanding detection for grid connected inverter in a photovoltaic system

This paper presents the comparison between FPGA-based and dsPIC-based islanding detection for grid connected inverter in photovoltaic (PV) system with under/over voltage and under/over frequency islanding detection algorithms. The comparison is based on the XC4005E field programmable gate array (FPGA) and the dsPIC30F2010 high-performance digital signal controller. The prototypes of the FPGA and the dsPIC are monitor the grid voltage and grid frequency at the point of common coupling (PCC) between the grid connected inverter, the local load and the distribution transformer and processed the value of voltage and frequency for turned off the relay between the grid connected inverter and the utility grid. The results of study, the prototypes can turn off the relay when the voltage is change under 200 V or over 240 V and frequency is change under 48 Hz or over 52 Hz. The FPGA-based is turn off the relay faster than the dsPIC-based but the cost of design and implement is higher.

Low-Voltage-Stress AC-Linked Charge Equalizing System for Series-Connected VRLA Battery Strings

This paper presents a low voltage-stress AC-linked charge equalizing system for balancing the energy in a serially connected, valve-regulated lead acid battery string using a modular converter that consists of multiple transformers coupled together. Each converter was coupled through an AC- linked bus to increase the overall energy transfer efficiency of the system and to eliminate the problem of the unbalanced charging of batteries. Previous solutions are based on centralized and modularized topologies. A centralized topology requires a redesign of the hardware and related components. It also faces a high voltage stress when the number of batteries is expanded. Modularized solutions use low-voltage-stress, double-stage, DC-linked topologies which leads to poor energy transfer efficiency. The proposed solution uses a low-voltage stress, AC-linked, modularized topology that makes adding more batteries easier. It also has a better energy transfer efficiency. To ensure that the charge equalization system operates smoothly and safely charges batteries, a small intelligent microcontroller was used in the control section. The efficiency of this charge equalization system is 85%, which is 21% better than other low-voltage-stress DC-linked charging techniques. The validity of this approach was confirmed by experimental results.

Distributed Generation and Islanding – Study on Converter Modeling of PV Grid-Connected Systems under Islanding Phenomena

Thailand government has launched a 15-year (2008-2022) strategic plan on new and renewable energy. Possible electricity generated from solar photovoltaic has been estimated with a potential of 50,000 MW, whereas at present the cumulative installed wattage is only 32 MW. Under the Plan, numbers of measures and incentives are provided for participation of private very small power producers (VSPP) generating and selling the electricity into the utilities. Most VSPPs generate electricity from renewable sources such as mini-hydro, biogas and biomass, wind and solar. Examples of measures and incentives are the Renewable Portfolio Standard (RPS) for the generating utility and independent power producers (IPP), a feed in tariff with an extra adder, soft loans and tax reduction. The past decade in Thailand has seen shifts from PV used in the public market through government demonstration projects to the consumer market, installations of PV VSPPs and domestic roof-top grid connected PV units gain momentum. With the government incentive more households will be attracted to produce electricity from solar PV and wind energy. As domestic roof sizes are limited, PV roof-top grid-connected units will be of small capacity, less than 10 kW. It is this possible large expansion of market for thousands of small PV rooftop grid-connected units or wind systems in Thailand, and eastern Asia, that draws our attention to the study of single phase distributed generator grid-connected systems. Our focus will be on the anti-islanding protection, which is of concerns to Thai electrical utilities. In order to know the behavior and the effect of anti-islanding techniques, the converter modeling of PV grid-connected systems under islanding phenomena is studied. The approach of modeling is to model a dc-ac full bridge switching converter PV grid-connected system under islanding phenomena using two mathematical modeling techniques. One corresponds to a state-space averaging technique (no linearization) and the other a piecewise technique. The former technique applies a state-space averaging technique (no10