Chamnan Limsakul

An impedance model of a PV grid-connected system

PV grid-connected systems are rich in nonlinear behaviors. Their operation depends on several factors such as radiation, switching algorithm and maximum power point tracking (MPPT) algorithm implemented in the grid-connected inverter which give rise to a variety of nonlinear behaviors and uncertainties. This paper proposes a passive impedance network as a model that can capture the system behaviors based on scenarios and data observed on the actual PV grid-connected system. A hardware experimental setup is created to imitate the operating characteristics of a PV grid-connected system such as current and voltage on both dc and ac sides. This work emphasizes on the salient features of the system operation and modeling strategies. Because of nonlinearity in the proposed model, the measured data and the Newton-Raphson iterative method are used to determine the model parameters. The study results show that the impedances in the proposed model have shown negative characteristics similar to that commonly found in power electronic converters. The proposed model may be integrated into a sequential, power solver for determining effects on a distribution system.

A Study of Effects of Stochastic Wind Power and Load to Power System Stability Using Stochastic Stability Analysis Method

The stochastic stability analysis method is proposed in this paper to investigate the small signal stability (SSS) of the single machine infinite bus power system. An induction generator wind turbine model is examined including frequency dependent load. The first integral energy function method is applied based on Lyapunovs stability and the theory of stochastic stability. This proposed method can investigate effects of stochastic wind power and load quantitatively while the general deterministic methods cannot.

Effects of dynamic parameters on measurements of IV curve

In current-voltage characteristic measurements of a PV module, distortions of curves can often be observed when measurements are done under flash tester with different sweeping rates of curve tracing, direction of tracing from short circuit to open circuit (SCOC)or from open circuit to short circuit (OCSC). In our recent work, we observed that dissimilarities of IV curves of a PV module, maximum power and fill factor, can be explained in terms of charging or discharging capacitive current due to voltage dependence of solar cells. This paper describes that measured maximum powers of a PV module are deviated around 2% when measurements are done with varying sweeping rates from 2 ms to 10 ms and directions of tracing of SCOC and OCSC conditions. The results are comparable with time constants of a module obtained by using dynamic characterization. Our methods using square wave inputting signal, both in the dark and in the illumination conditions, can determine not only time constants, but also determine dynamic parameters of a module. We found that the overestimation or underestimation of output powers are obtained when the sweeping rates are not more than time constants, and each time constant is depend on each operating voltage.

Impact of photovoltaic grid-connected power fluctuation on system frequency deviation in contiguous power systems

In this paper, a power system with an automatic generation control (AGC) in two contiguous areas are studied to demonstrate speed deviation of a generator due to photovoltaic (PV) power fluctuation in both time and frequency domains. The system is linearized and modeled in state-space representation. The change of the PV power is defined as the input of the system, and the change of speed deviation is defined as the output of the system. The analysis using a unit step function input illustrates that increased change of PV power can affect the speed deviation of generators. Changed PV power on another side can lower overshoot of the change of speed deviation in the study area. Moreover, the system is excited with the sinusoidal waveform input signal imposed on dc signal, and with the scaled solar irradiance data, respectively. In the case of using sinusoidal waveform input, the results show that the magnitude of change of speed deviation can be a function of amplitude and frequency, but is not a function of biasing. In case of the system which has been inputted by using scaled solar datasets, the changes of the speed deviation are observed when the PV power fluctuation occurs.

A study of impact of wind power to power system stability using stochastic stability index

The stochastic stability index (SSI) is proposed in this paper to investigate the small signal stability (SSS) of the power system incorporating wind power. The SSI is developed using the first integral energy function method based on Lyapunovs stability and the theory of stochastic stability. The model of induction generator wind turbine is modified and applied for the SSS study. This proposed method can investigate impact of stochastic wind power quantitatively while the general deterministic methods cannot.

PV industry growth and module reliability in Thailand

The PV applications in Thailand are now installed more than 1.2 GWp cumulatively. It is due to the National Renewable Energy Program and its targets. In the latest Alternative Energy Development Plan (AEDP), the PV electricity production target has increased from 2 GWp to 3 GWp. With this rapid growth, customers and manufacturers seek for module standard testing. So far over one thousands of PV modules per annum have been tested since 2012. The normal tests include type approval test according to TIS standard, acceptance test and testing for local standard development. For type test, the most module failure was found during damp heat test. For annual evaluation test, the power degradation and delamination of power was found between 0 to 6 percent from its nameplate after deployment of 0 to 5 years in the field. For thin-film module, the degradation and delamination was found in range of 0 to 13 percent (about 5 percent on average) from its nameplate for the modules in operation with less than 5 years. However, for the PV modules at the reference site on campus operated for 12 years, the power degradation was ranging from 10 to 15 percent. Therefore, a long term performance assessment needs to be considered to ensure the system reliability.

Investigation of power values of PV rooftop systems based on heat gain reduction

PV rooftop system can generally be installed to produce electricity for the domestic house, office, small enterprise as well as factory. Such a system has direct useful for reducing peak load, meanwhile it also provides shaded area on the roof and hence the heat gain into the building is reduced. This study aims to investigate the shading effect on reduction of heat transfer into the building. The 49 kWp of PV rooftop system has been installed on the deck of the office building located in the middle of Thailand where the latitude of 14 ° above the equator. The estimation of heat gain into the building due to the solar irradiation throughout a day for one year has been carried out, before and after the installation of the PV rooftop system. Then the Newton’s law of cooling is applied to calculate the heat gain. The calculation and the measurement of the heat reduction are compared. Finally, the indirect benefit of the PV rooftop system installed is evaluated in terms of power value.