Share PDF

Search documents:
  Report this document  
    Download as PDF   
      Share on Facebook

A Novel Hybrid Integrated Wind-PV Micro Co-Generation Energy Scheme for Village Electricity

Adel M. Sharaf Mohamed A. H. El-Sayed

Centre of Energy Studies

University of Trinidad and Tobago

Point Lisas Campus, Esperanza Road, Brechin Castle, Couva elsmah@hotmail.cm Mohamed.el-sayed@utt.edu.tt

Abstract-A hybrid wind/PV system for supplying an isolated small community with electrical energy is digitally simulated and presented in this paper. The proposed hybrid renewable green energy scheme has four key subsystems or components to supply the required electric loads. The first subsystem includes the renewable generation sources from PV array and wind turbine. The second is the interface converters used to connect the renewable energy generators to the common DC collection bus, where all generated energy is collected. The third device represents the added inverter between the common collection DC bus and the added AC bus interface to feed all AC loads. The fourth subsystem comprises all controllers including the modulated power filter. The controller main function is to ensure efficient energy utilization and dynamic matching between loads and green energy generation as well as voltage stabilization. The proposed controllers are coordinated dynamic error driven PI regulators to control the interface converters. The integrated hybrid green energy system with key subsystems are digitally simulated using the Matlab/Simulink/Sim-Power software environment and fully validated for efficient energy utilizations and enhanced interface power quality under different operating conditions and load excursions.

I.INTRODUCTION

In remote isolated areas and arid communities such as small islands, diesel generator sets and micro gas turbines are usually the main source of power supply. Fossil fuel for electricity generation has several drawbacks: it is costly due to transportation to the remote areas and it causes global warming pollution and green house gases. The need to provide an economical, viable and environmental safe alternative renewable green energy source is very important. As green renewable energy resources such as wind and Photovoltaic (PV) have gained great acceptance as a substitute for conventional costly and scare fossil fuel energy resources. Stand-alone renewable green energy is already in operation at many places despite solar and wind variations and stochastic nature. Isolated green energy hybrid operation may not be effective or viable in terms of the cost; efficiency and supply reliability unless an effective and robust stabilization of AC- DC interface scheme and maximum energy tracking control strategies are fully implemented [1, 2].

The equivalent quasi-steady state circuit type Volt-Ampere characteristic model of a solar cell consists of a current source in parallel with a diode [3]. The output terminals of the equivalent quasi-steady state circuit model are connected to the load. Ideally the voltage-current equation of the solar source is given by [3]:

 

A k T c

I p h + I 0

I c

 

V c =

 

ln

 

 

R s I C

e

I 0

 

 

 

 

 

Where,

e: electron charge (1.602 × 10-19 C).

k: Boltzmann constant (1.38 × 10-23 J/oK). Ic: cell output current (A).

Iph: photocurrent, function of irradiation level and junction temperature (5 A).

I0: reverse saturation current of diode (0.0002 A). Rs: series resistance of cell (0.001 ).

Tc: reference cell operating temperature (20 °C). Vc: cell output voltage (V).

A: a curve fitting constant(100).

The output DC voltage, current and power of any photovoltaic PV array vary as a function of the solar Insolation/Irradiation level (Sx), junction temperature (Tc), ambient temperature (Ta), and varying electric DC load demand. As a result, the effect of all these varying ambient parameters should be considered while designing any efficient PV power tracking controller, it should be mentioned that the maximum power generated by the PV cell and PV arrays is also function of the solar irradiation level and operating junction/ambient temperature, and should be tracked for better operational performance and maximum energy utilization [4, 5].

The current research deals with the efficient utilization and low impact of PV panels as well as novel control concepts of power matching and decoupled interfacing topologies. Thereby, the interaction of PV source with power system and converters

978-1-4244-4252-2/09/$25.00 ©2009 IEEE

1244

Authorized licensed use limited to: Felix Raja S V. Downloaded on October 11, 2009 at 07:56 from IEEE Xplore. Restrictions apply.

feeding motors, choppers and dynamic controllers are crucial [6-8].

PMDC generators are usually preferable due to their reliability, durability, low cost, low voltage characteristics, positive coefficient of conversion between electrical and mechanical parts, sizing and design flexibility. A permanent magnet direct current (PMDC) generator converts mechanical energy provided by wind kinetic energy to electrical power provided by a spinning rotor by means of magnetic coupling. The parameters and symbols which were used in simulating the system are given in Appendix of the paper. The armature coil of the DC generator is represented by an inductance (Lm) in series with resistance (Rm) in series with an induced voltage (Em). A differential equation for the equivalent circuit is derived by using Kirchhoff’s voltage law around the electrical loop.

E=Ke.ω

(2)

E-V=RI+L[dI/dt]

(3)

PMDC generator Load Equations can be expressed by:

TT = PT / ω

(4)

TG=KTI

(5)

TT-TG=J[dω/dt]+Bω

(6)

Where ω is the generator angular velocity, TG is the generator torque, TT is the wind turbine torque, KT is the torque constant and J, B are the generator inertia and friction coefficients.

An effective approach is to ensure renewable energy diversity and effective utilization by combining these different renewable energy sources to form a coordinated and hybrid integrated energy system. Hybrid green energy system is a valid alternative solution for small scale micro-grid electrification for remote rural and isolated village/island where the utility grid extension is both costly and geographically difficult. Hybrid renewable green energy system incorporates a combination of several diverse renewable energy sources such as photovoltaic, wind energy and possibly wave and fuel cell sources. A system using such diverse combination has the full advantage of supply diversity, capacity and system stability that may offer the strengths of each type that complement others [3, 4]. The main objective of hybrid green energy scheme is to provide supply security for remote communities. Hybrid integrated green energy systems are also pollution free, and can provide electricity at comparatively viable and economic advantages to micro grid or diesel generator set utilized in village/island electricity.

II- LAYOUT OF THE STUDIED GREEN ENERGY

SYSTEM

The paper presents a hybrid dual wind/PV system for supplying an isolated community with electrical energy. In order to obtain electricity from the hybrid green system at an economical price, its topology and control design must be optimized in terms of coordinated operation and layout configuration. Many topologies are currently available for hybrid green system configurations, depending on the use of interface converters based on common DC/common AC bus interface architecture.

Solar panels can be connected in parallel or in series to obtain required photovoltaic power rating power rating. The power obtained by this way is DC in nature and it should be converted to AC for some AC type loads. Therefore, DC to AC converters are required for such load types. Electrical energy is not only required during day time, but also at night. This key requirement puts forwards the possible use of other renewable green energy sources, such as wind energy, tidal/wave and fuel cells in hybrid micro co-generation schemes [8,9].

The wind energy scheme with PMDC generator could be directly connected to the common DC bus through DC-DC- Chopper to convert the kinetic energy in wind to DC electrical energy [4,5]. In hybrid green energy power system, wind and solar are fully used as the main energy sources to supply the hybrid DC and AC type loads. Fig. (1) shows the general architecture of the proposed hybrid green energy

Fig.(1) Hybrid Integrated (Wind-PV) Green

Energy Scheme for Village Electricity

scheme with common DC/ common AC collection bus interface. The scheme uses a primary common DC bus collection with an added secondary common AC bus for feeding any AC loads. The proposed hybrid green energy scheme is digitally simulated for different operation conditions

1245

Authorized licensed use limited to: Felix Raja S V. Downloaded on October 11, 2009 at 07:56 from IEEE Xplore. Restrictions apply.

and load excursions. The proposed control scheme comprises novel multi-loop coordinated dynamic error driven controllers with supplementary regulation loops to control the different subsystems [6,7]. Figure (2) shows the multi loop coordinated error driven hybrid green energy scheme controller.

III- COORDINATED ERROR DRIVEN TRI-LOOP

CONTROLLER

Figure (2) shows the general four regulator coordinated control structure. The hybrid system was digitally simulated and validated using MATLAB/Simulink –SimPower software environment in order to test the controller performance for interfacing devices of PV panels and wind generator under changing weather conditions and load disturbances. The simulation results show that the effects of the change in solar radiation and ambient temperature are compensated by controlling the DC-DC chopper, which interfaces the PV panel to the common DC bus.

Fig. (2) Structure of Coordinated error driven multi-loop controller

The main controller comprises the following four regulators:

(1)DC-DC converter regulator for PV array.

(2)DC-AC inverter regulator to interface DC –Bus with the grid

(3)MPFC regulator for ripple minimization of AC-Bus.

 

 

1

 

 

-K-

Vr

 

 

 

 

1

Gain 1

1

 

 

 

Vdc

 

10 e-3s+1

 

 

 

1

 

 

 

 

 

Transfer Fcn 2

 

 

 

 

Gain 3

 

 

1

 

 

 

10e-3s+1

1

 

 

 

2

 

-K-

Transfer Fcn 3

 

 

 

 

 

 

 

 

Gain 5

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Idc

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

1

 

 

 

 

 

 

 

 

0.5

 

 

Gain 4

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

10 e-3s+1

 

 

 

 

 

 

 

 

 

 

 

Transfer Fcn 1

 

 

 

 

Gain 2

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

PI

 

 

 

 

 

 

Signal(s)Pulses

 

1

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Out 1

 

Saturation

 

 

 

 

 

 

Discrete

 

 

 

 

 

 

 

PWM Generator 1

 

PI Controller

Transport

Delay 1

Fig. (3-a) DC-DC Converter Regulator for PV-array

The DC-DC converter regulator compensates for any dynamic oscillations in DC-bus voltage together with the regulator of the PMDC generator voltage. The inverter and modulated power filter regulate the AC-Bus. The loop weighing factors are assigned to ensure loop time scaling and dominant control action. In each regulator the total error signal is the summation of the separate control loops and is fed into PI controller. The total error signal to ensure maximum power utilization of the multi-loop is driven through PI controller that is used to compensate the dynamic total error in order to provide control signal, which is then converted to degrees as phase angles. This phase angles are then sent to the Pulse Width Modulated (PWM) generator through saturation to adjust the sequence of the two IGBT/Diode switch triggering. The adaptive control scheme is able to guarantee the tracking of a time-varying trajectory with minimum steady state error.

 

 

1

 

 

 

-K-

Vr

 

 

1

Gain 1

 

 

 

 

 

 

 

Wwnd

 

 

 

 

 

 

 

1

 

 

 

1

Gain 3

 

 

 

 

 

 

 

10 e-3s+1

 

 

 

 

Transfer Fcn 2

 

 

2

-K -

 

 

 

 

 

 

 

Iwnd

 

1

 

 

 

Gain 4

10e-3s+1

-K -

 

 

 

 

 

 

 

Transfer Fcn 1

Gain 2

 

 

 

 

 

 

 

 

PI

Signal(s)Pulses

 

 

 

 

 

 

 

Discrete

Saturation

 

 

 

PI Controller

PWM Generator 1

 

 

Transport

 

 

 

 

 

 

 

Delay 1

 

 

(4)DC-DC converter regulator for PMDC wind generator.

 

 

 

1

 

 

 

Out 1

Figure (3 a-d) shows the detailed regulators mentioned above.

Fig. (3-b) DC-DC Converter Regulator of Wind Driven PMDC Generator

 

 

 

1246

Authorized licensed use limited to: Felix Raja S V. Downloaded on October 11, 2009 at 07:56 from IEEE Xplore. Restrictions apply.

 

 

 

 

1

 

 

 

 

Out1

 

 

RMS

 

 

 

 

RMS

 

2

 

 

 

 

 

1

 

 

Out 2

 

 

 

 

1

10e-3s+1

 

 

 

 

.5

 

 

Vac

 

 

 

Transfer Fcn 2

 

 

 

 

 

 

 

 

-K-

Gain 2

 

 

 

 

 

 

 

Gain 4

 

 

 

 

Transport

 

 

 

 

Delay 1

 

 

 

 

 

.5

 

 

 

 

Gain 3

 

 

 

 

 

PI

Signal(s)Pulses

 

1

 

Discrete

Saturation

 

|u|

PWM Generator 1

 

 

 

 

PI Controller

 

 

10 e-3s+1

 

 

 

Transfer Fcn 3

Abs

 

 

 

 

 

 

 

 

 

Scope 1

 

Fig. (3-c) DC-AC Inverter Regulator to Interface Common DC-Bus with Grid

 

 

 

 

1

 

 

 

 

Out1

 

 

RMS

 

 

 

 

RMS

 

2

 

 

 

 

 

1

 

 

Out 2

 

 

 

 

1

10e-3s+1

 

 

 

 

.5

 

 

Vac

 

 

 

Transfer Fcn 2

 

 

 

 

 

 

 

 

-K-

Gain 2

 

 

 

 

 

 

 

Gain 4

 

 

 

 

Transport

 

 

 

 

Delay 1

 

 

 

 

 

.5

 

 

 

 

Gain 3

 

 

 

 

 

PI

Signal(s)Pulses

 

1

 

Discrete

Saturation

 

|u|

PWM Generator 1

 

 

 

 

PI Controller

 

 

10e-3s+1

 

 

 

Transfer Fcn 3

Abs

 

 

 

 

 

 

 

 

 

Scope 1

 

Fig. (3-d) Modulated Power Filter Regulator at the common AC-Bus

IV. DIGITAL SIMULATION RESULTS

The unified AC-DC system was digitally simulated using MATLAB/Simulink/SimPower software environment to validate the coordinated controller effectiveness under varying wind speed and load excursions. The unified system model is subjected to a number of load excursions and wind speed variations. The system static DC load is increased by 33.3% at t= 8 s and the wind speed is also increased by 50% at t=10 s for a period of two seconds before returning to its rated value. This system is controlled using the described two basic dynamic independent controllers regulating the operation of the

electronic interface converters, namely DC-DC choppers and switching stages of the DC-AC inverter which are coordinated for regulated DC and AC-bus voltage control and voltage stabilization in case of sudden load excursions and wind speed changes.

Figures (4- 6) show the digital simulation of the unified system dynamic responses of DC-bus voltage, PMDC generator speed and AC-bus voltage using multi-loop dynamic error driven PI control strategy. The PV voltage and current are drawn in Figures (7, 8). The digital simulation using the Matlab/Simulink/Simpower Software Environment indicated that the excursions in system loads and wind speed are compensated by the error driven controller of the DC-DC choppers, DC-AC inverter and modulated power filter. In addition the simulation results validate the robustness of the novel coordinated hybrid Wind/PV scheme. It is clearly shown that the proposed dynamic error driven error PI controller can ensure maximum utilization and voltage stabilization with acceptable steady state error. Moreover, the common DC and AC bus current is ripple free with minimum inrush currents and ripple excursion. The multi-loop control strategy can be further modified to ensure combined voltage stabilization and loss reduction in different green energy powered systems.

V- CONCLUSIONS

The paper presents a novel coordinated hybrid Wind/PV green energy utilization scheme for Village/Island micro-grid electricity generation. The hybrid renewable scheme utilized a multi-loop/ multi regulator error driven coordinated controller to ensure effective energy utilization, common DC and AC bus stabilization, enhanced power quality and near maximum energy utilization under varying operating conditions and load excursions. The unified DC-AC system is digitally simulated and validated using the Matlab/Simulink/Sim-power Software environment. The sample study system comprises a PMDC wind driven generator, PV array source with all interface, DC- DC converters, DC-AC inverter and modulated power filter compensator for AC bus stabilization. The operation of the novel error driven controller scheme for green renewable energy utilization is fully validated under sudden DC load excursions and wind speed variation. A novel modulated power filter compensator was used as a voltage stabilization at the AC common bus. Novel dynamic error driven regulators were utilized to ensure a stable common DC and AC bus interfaces with minimum current ripple and near maximum utilization.

REFERENCES

[1]I. Altas, A. Sharaf, “Novel maximum power fuzzy logic controller for photovoltaic solar energy systems”, Renewable Energy, vol. 33, pp 388- 399, 2008.

1247

Authorized licensed use limited to: Felix Raja S V. Downloaded on October 11, 2009 at 07:56 from IEEE Xplore. Restrictions apply.

[2]A. Sharaf, R. Chhetri, “A novel dynamic capacitor compensator/green plug scheme for 3-phase 4-wire utilization loads”, Proceeding IEEE-CCECE conference, Ottawa, Ontario, Canada 2006.

[3]H. Fargali, F. Fahmy, M. A. El-Sayed, “Control and optimal sizing of PV- Wind powered rural zone in Egypt” Al-Azhar Engineering 10 th International conference, Cairo, Dec. 24-26, 2008.

[4]A. M. sharaf, G. Wang, “Voltage stabilization of standalone wind energy conversion system using active power compensator”, International journal of global energy issues, vol.26 No. 3-4, pp. 417-429, 2006.

[5]Wind power in power systems, edited by T. Ackermann, John Wiley &Sons, 2005

[6]E. Muljadi and C.P. Butterfield, “Dynamic Model for Wind Farm Power Systems,” Global Wind Power Conference, Chicago, Illinois, March/April 2004.

[7]I. H. Altas, A. M. Sharaf, “ A photo-voltaic array simulation model for Matlab-Simulink GUI Environment”, International Conference on Clean Electrical Power, ICCEP’07, May 21-23 Capri, Itelay, 2007.

[8]Naik, R.; Mohan, N.; Rogers, M.; Bulawka, A.; A novel grid interface, optimized for utility-scale applications of photovoltaic, wind-electric, and

fuel-cell

systems

Power Delivery, IEEE Transactions on Volume 10,

Issue 4, Oct. 1995

Page(s):1920 – 1926.

 

[9]J.J. Brey, A. Castro, E. Moreno and C. Garcia, "Integration of Renewable Energy Sources as an Optimized Solution for Distributed Generation," 28th Annual Conference of the Industrial Electronics Society 2002, vol. 4, 5-8 Nov. 2002,

[10]Adel M. Sharaf, Mohamed A. H. El-Sayed,” Dynamic Control of Fuel Cell Powered Water Pumping Station”, Accepted for presentation at International Conf. on Renewable Energies and Power Quality (ICREPQ) Valencia, Spain 15-17 April 2009.

[11]A.M. Sharaf, Mohamed S. EL-Moursi” Novel FACTS Controllers for Voltage Stabilization of Renewable Energy (Wind /Small Hydro) Schemes” Journal of Energy Technology and Policy (IJETP), 2006

Appendix for Simulated System Parameters

PV- Array:

Vpv = 200 V DC

Ppv= 10 kW

PMDC wind driven generator parameters:

Ra = resistance of armature winding=0.1 

La = inductance of armature winding=5 mH

Km=voltage constant= 1.273 V/rad

Kt =torque constant = 1.273 Nm/A

Jm =moment of inertia=0.75 kgm2

Bm=Viscous constant=0.14 Vs/rad

Va=nominal armature voltage=240 V

Static DC-Bus Load parameters:

DC Heating Load = 10 kW

DC Lighting Load =5 kW

Static AC-Bus Load parameters:

AC load

= 10 kW

Modulated Filter at AC Bus:

C1=C2 = 85 µf

Rf= 0.05 

Lf= 0.1 H

PI controller parameters:

PV and Wind DC-DC Chopper Regulators : Kp =5 and KI =1

Inverter and Modulated Power Filter Compensator : Kp =4.5 and KI =1.25

Fig.(4) Common DC bus voltage dynamic Response under varying DC loading and Wind Conditions (increased static load by 33.3% at t=6 s, decrease wind speed by 50% at t=10 s for 2 s)

1248

Authorized licensed use limited to: Felix Raja S V. Downloaded on October 11, 2009 at 07:56 from IEEE Xplore. Restrictions apply.

Fig.(5) Speed Dynamic Response of Wind Driven PMDC Generator under varying DC-loading and Wind Conditions (increased static load by 33.3% at t=6 s, decrease wind speed by 50% at t=10 s for 2 s)

Fig. (7) Dynamic Response of the PV array voltage under varying DC-loading and Wind Conditions (increased static load by 33.3% at t=6 s, decrease wind speed by 50% at t=10 s for 2 s)

Fig (6) Common AC bus voltage Dynamic Response at Inverter Interface using interface inverter

Fig. (8) Dynamic Response of the PV array Generated Current under varying DC-loading and Wind Conditions (increased static load by 33.3% at t=6 s, decrease wind speed by 50% at t=10 s for 2 s)

1249

Authorized licensed use limited to: Felix Raja S V. Downloaded on October 11, 2009 at 07:56 from IEEE Xplore. Restrictions apply.