A NOVEL CONTROL STRATEGY FOR HYBRID AC/DC MICRO GRID SYSTEMS BY T.NAVEEN S.NEELIMA P.S SUBRMANYAM Asst.professor Assos.professor Professor, DEPARTMENT OF E.E.E, V.B.I.T

LAY OUT KEY WORDS OBJECTIVES GRID CO ORDINATION EXISTING SYSTEM PROPOSED SYSTEM HYBRID AC/DC POWER SYTEMS SIMULATION RESULTS CONCLUSION REFERENCES SCOPE FOR FUTURE WORK

KEY WORDS Hybrid AC/DC power systems: The combination of AC/DC networks connected to a grid Micro grid : Collects power from various small energy sources and connects it to grid. AC micro grids: facilitate connection of renewable power sources to conventional ac systems dc power from photovoltaic (PV) panels or fuel cells - converted into ac using dc/dc boosters and dc/ac inverters to connect to ac grid. AC/DC/AC converters: commonly used as drives to control the speed of ac motors in industrial plants.

OBJECTIVES To reduce the processes of multiple dc–ac–dc or ac–dc–ac conversions in an individual ac or dc grid. To have stable operation in grid-tied or autonomous mode. To implement Grid coordination and control algorithms To achieve smooth power transfer between ac and dc links for stable system operation under various generation and load conditions. To maintain stable operation for grid switching from one operating condition to another.

GRID CO ORDINATION The coordination -control schemes among various converters to harness maximum power from renewable power sources . Minimization of power transfer between ac and dc networks. Stable operation of both ac and dc grids under variable supply and demand conditions in both grid and islanding modes. Avoids multiple reverse conversions in individual ac or dc grids which cause additional power loss .

EXISTING SYSTEM Individual AC/DC grids. Requires multiple reverse conversions. For long distance transmission HVDC is required. Poor quality of electricity. Less reliable. Difficult to interface for DC loads. Less operational efficiency. Interfacing of different sources is difficult

PRPOSED SYSTEM A hybrid system with minimal reverse conversions. Co ordination-control schemes for optimal operation under all conditions. Improved operational efficiency. Integration of various AC/DC sources with energy storage systems. DC micro grids to integrate various distributed generators.

A HYBRID AC/DC MICROGRID:

GRID OPERATION The hybrid grid can operate in two modes. GRID-TIED MODE : The main converter provides stable dc bus voltage Required power is exchanged between the ac and dc buses. The boost converter and WTG are controlled to provide the maximum power. Converter acts as an inverter or converter based on total power generation Isolated Mode Power is not balanced by the utility grid. MPPT on or MPPT off based on system power constraints.

CONSIDERED HYBRID GRID Forty kW PV arrays connected to dc bus through a dc/dc boost converter. A capacitor Cpv to suppress high frequency ripples of the PV output voltage. A 50 kW wind turbine generator (WTG) with doubly fed induction generator (DFIG) is connected to an ac bus. The rated voltages for dc and ac buses are 400 V and 400 V rms respectively. A three phase bidirectional dc/ac main converter with R-L-C filter connects the dc bus to the ac bus through an isolation transformer.

Modeling of PV Panel The current output of the PV panel is modeled by the following three equations Fig. 3. Equivalent circuit of a solar cell.

MODELING OF WIND TURBINE GENERATOR Power output Pm from a WTG is determined from following equation Where ρ is air density, A is rotor swept area, Vω is wind speed, and is the power coefficient, which is the function of tip speed ratio and pitch angle . The voltage equations of an induction motor in a rotating d-q coordinate are as follows

COMPACT REPRESENTATION OF HYBRID GRID

The main converter operates bidirectional A. Grid-Connected Mode Boost converter tracks the MPPT of the PV array by regulating its terminal voltage. The dc/dc converter of the battery can be controlled as the energy buffer in this technique The main converter operates bidirectional Variable characteristic of wind and solar sources are compensated . Buck or boost operations are performed accordingly.

CONTROL STRATEGIES FOR GRID-CONNECTED MODE The control block diagram for boost converter and main converter

B. Isolated Mode The converter may operate in the MPPT on or MPPT off based on power balance The dc-link voltage is maintained by either the battery or the boost converter based on system operating condition State of charging battery is observed Net power is calculated and compared with reference Powers under various conditions balanced as follows:

CONTROL STRATEGIES FOR ISOLATED MODE

Operation of main converter in grid connected mode Grid-Connected Mode simulation circuit and results Operation of main converter in grid connected mode

Terminal voltage of the solar panel

PV output power VS solar irradiation

Ac side voltage and current of the main converter with variable solar irradiation level and constant DC load

Ac side voltage and current of the main converter with constant solar irradiation level and variable DC load.

DC bus voltage transient response

Dynamic response of main converter in isolated connected mode Isolated Mode simulation circuit and results Dynamic response of main converter in isolated connected mode

Battery charging current (upper) for the normal case ISOLATED MODE: Battery charging current (upper) for the normal case

Battery SOC for the normal case

Output power of the DFIG

AC side voltage VS current

DC bus voltage transient response in isolated mode.

DC bus voltage when MPPT is mode.

PV output when MPPT is on

Battery current when MPPT is on mode

SCOPE FOR FUTURE WORK The future objective of constructing a smart gird is to provide reliable high quality electric power in eco friendly and sustainable way. With the advancement in power electronics technology plays a most important role to interface different sources and loads to a smart grid. Robust control can be applied to meet the uncertainties in controller design due to uncertain parameters or disturbances in the renewable energy sources The hybrid grids can be implemented for some small customers want to install their own PV systems on the roofs Feasible for some small isolated industrial plants with both PV system and wind turbine generator as the major power supply.

REFERENCES [1] R. H. Lasseter, “Micro Grids,” in Proc. IEEE Power Eng. Soc. Winter Meet., Jan. 2002, vol. 1, pp. 305–308. [2] Y. Zoka, H. Sasaki, N. Yorino, K. Kawahara, and C. C. Liu, “An interaction problem of distributed generators installed in a Micro Grid,” in Proc. IEEE Elect. Utility Deregulation, Restructuring. Power Technol., Apr. 2004, vol. 2, pp. 795–799. [3] R. H. Lasseter and P. Paigi, “Micro grid: A conceptual solution,” in Proc. IEEE 35th PESC, Jun. 2004, vol. 6, pp. 4285–4290. [4] C. K. Sao and P. W. Lehn, “Control and power management of converter fed Micro Grids,” IEEE Trans. Power Syst., vol. 23, no. 3, pp. 1088–1098, Aug. 2008. [5] T. Logenthiran, D. Srinivasan, and D.Wong, “Multi-agent coordination for DER in Micro Grid,” in Proc. IEEE Int. Conf. Sustainable Energy Technol., Nov. 2008, pp. 77–82. [6] M. E. Baran and N. R. Mahajan, “DC distribution for industrial systems: Opportunities and challenges,” IEEE Trans. Ind. Appl., vol. 39, no. 6, pp. 1596–1601, Nov. 2003.

THAN Q…