Abstract this paper is devoted to study the conversion of renewable energy resources into electrical energy in a stand-

alone hybrid power generation system. The hybrid system

consists of a 230 kW wind turbine, a 30 kW micro-turbine and

solar heaters of double-parallel flow. Solar heaters are being

used to partially preheat the air entering the combustion

chamber of the micro-turbine in order to decrease the amount

of fuel consumption. The dynamic behavior and simulation

results are being discussed to extract the maximum energy

obtained from a variable speed wind power generation system.

The hybrid model has been simulated under several wind speed

conditions. A supervisory controller is designed that was able to

manage between the maximum energy captured from the wind

turbine and the generated energy by the microturbine to meet

the load demands and wind power fluctuation due to wind

speed variation. Solar heaters saved amount of fuel on average

15.4 U.S. Dollars/hr monthly according to the data provided in

the year 2013.

I. INTRODUCTION

Renewable energy resources are the primary contributors to

achieve sustainable energy production. Energy crisis,

climate changes such as atmosphere temperature rise due to

the increase of greenhouse gases emission and the Kyoto

Protocol restrictions in generation of these gases, coupled

with high oil prices, limitation and depletion of fossil fuels

reserves make renewable energies more noticeable [1].

Among the renewable energy resources, wind power has

had the fastest growth in the world over the last 20 years [2].

Wind turbine is being integrated with other renewable

resources to meet more load demands. Also, because some

systems depend on renewable resources specially the wind

speed, their reliability in satisfying the load demands

decreases under all conditions. Hence, some studies propose

the combination of a diesel generator as a back up and

wind/solar power generation systems [3, 4]. These hybrid

systems also will reduce the operating costs and

environmental impacts caused by diesel generators.

There has been an increasing interest in using solar air

collectors because of their simple designs, cheap

construction and maintenance costs, their operational

Mostafa Abdel-Geliel is now an associate professor in the Electrical and

Control Engineering Department, Arab Academy for Science technology and maritime transport , Alexandria, Egypt ( e-mail:

maelgeliel@yahoo.com).

Iham Zidane is now a teaching assistant in the mechanical Engineering Department, Arab Academy for Science technology and maritime transport,

Alexandria, Egypt ( e-mail: iham_zidane@hotmail.com).

Sohair Rezeka is now a visiting professor in the mechanical Engineering Department, Arab Academy for Science technology and maritime transport,

Alexandria, Egypt ( e-mail: srezeka@yahoo.com).

simplicity and their availability for local production.

Moreover, they are ecologically friendly. On the other hand,

solar air heaters are limited in their thermal performance due

to the low density, the small volumetric heat capacity and

the small heat conductivity of air [5, 6].

Microturbines are small electricity generators that burn

gaseous and liquid fuels to create high-speed rotation that

turns an electrical generator. The size range for

microturbines available and in development is from 20 to

500 kilowatts [7]. The microturbine can be either one of two

types, namely single- and split-shaft. In the single-shaft

arrangement, the turbine and generator are mounted on the

same shaft. Output frequency of the microturbine is from

about 400 Hz up to several kilo Hertz. It must be converted

to 50 Hz using electronic power converters. In the spilt-shaft

microturbine, the shaft is connected to the generator by a

gearbox and the converters are not needed [8- 10].

This paper presents the dynamic behavior of a stand-alone

hybrid power generation system of wind turbine and micro-

turbine associated with solar heater cell. Micro-turbine, solar

heater and wind turbine models are addressed based on

references [11-13], respectively. Solar heater cells are being

used to preheat the air entering the combustion chamber,

thus decreasing the amount of fuel mass flow rate. A

Supervisory controller is designed to manage between the

maximum energy captured from the wind turbine and the

generated energy by the microturbine to meet the load

demands and wind power fluctuation due to wind speed

variation.

II. PROPOSED SYSTEM DESCRIPTION

The proposed hybrid system is described in Fig. 1. It

consists of a 230 kW wind turbine, a 30 kW microturbine

which drives a high-speed permanent magnet synchronous

machine, solar heaters implemented in order to partially

preheat the air entering the microturbine to decrease the

amount of fuel consumption, and a supervisory controller to

manage the power generated between the wind and hybrid

solar micro-turbine.

Figure 1. The Proposed System Schematic

Modeling and Simulation of a Hybrid Power Generation System of

Wind turbine, Micro-turbine and Solar Heater Cells

Mostafa Abdel-Geliel*, Iham F. Zidane **, Mohammed Anany, Sohair F. Rezeka ***

A. Wind Turbine Model

This model is a 230 kW wind turbine. The wind turbine

is driving a 480 V, 275 kVA induction generator. The wind

turbine used has no pitch control. The wind turbine uses a 2-

D Lookup Table to compute the turbine power output as a

function of wind speed. This is shown in the following

equation

Pwmech = 0.5 Ab v3 CPwt (1)

where, Pwmech is wind turbine power, is air density, Ab is Area Swept by Turbine Blades, v is Wind Speed and Cpwt

is Power Coefficient [13].

The induction generator converts the mechanical power

generated from the wind turbine and converts it into

electrical power. This induction generator is an isolated type

(self exited) in which excitation takes place by a terminal

capacitor and a diesel generator of 480 V and 300 kVA to

adjust the operation and the frequency fluctuation [13].

B. Micro-turbine Model

The microturbines are a smaller version of heavy-duty

gas turbines which are compact in size and components. A

block diagram of the simplified single shaft microturbine

along with its control is shown in Fig. 2. This consists of

fuel, speed and temperature control along with the

combustor and turbine dynamics. The turbine torque (T) is

expressed as

T= 1.3 (Wf - 0.23) + 0.5 (1 - N) (2)

The exhaust gas temperature (Tex ) is expressed as

Tex=TR - 700 (1 - Wf) + 550 (1 - N) (3)

where, TR is reference temperature of the micro-turbine, Wf

is per unit fuel demand signal and N is per unit speed.

Figure 2. Micro-Turbine Control Block Diagram

The simplified single shaft gas turbine including all its

control systems is implemented in MATLAB /SIMULINK.

This turbine model was proposed by W I Rowen [11].

Speed Control: It operates on the speed error formed between a reference speed and the rotor

speed of the Micro-Turbine Generator (MTG)

system. It is the primary means of control for the

microturbine under different load conditions. It is a

lead-lag transfer function [14]. Also, a PID control

is being used. The PID gains were adjusted using

continuous cycling Ziegler-Nichols.

Temperature Control: It limits the gas turbine output at a predetermined firing temperature,

independent of variation in ambient temperature or

fuel characteristics.

Fuel Control: The output of low value selector represents the least amount of fuel required for that

particular operating point. For the current case, the

output of the selector is limited and multiplied by

0.77 and offset by no load fuel flow value as

illustrated in Fig. 4 to ensure the continuous

combustion process. The fuel flow controls are

represented by a series of blocks including the

valve position and flow dynamics.

Combustor and Exhaust Delay: combustor delay is the time lag associated with the compressor

discharge volume and the exhaust delay is due to

the transport of gas from the combustion system

through the turbine.

C. Solar Heater Model

This model represents the solar air heaters of double

parallel flow configuration. Fig. 3 shows the structure of this

configuration. Based on the local energy balances, algebraic

expressions for the efficiency factor (F) and the overall heat loss coefficient (UL), as well as air temperature distributions

along the collectors were obtained. In addition, the

expressions of the mean temperatures of the two air streams

and of the absorber plate were determined. The heat transfer

coefficients involved in the energy balances were estimated.

The useful energy gain (Qu) is expressed in terms of the air

inlet temperature to the collector (Ti) which is generally a

known parameter in the applications [12]. It is expressed as

Qu = Ac Fr [S - UL (Ti Ta)] (4)

The output air temperature (To) from the collector is

expressed as

To = Ta + [S/ UL] + [Ti Ta (S/UL)] exp [(Ac F UL) / (m Cp)] (5)

The instantaneous efficiency for double flow solar heaters

() is expressed by as

= 0.54 [4.56 (Ti Ta ) / S] (6)

where, S is solar irradiance absorbed by the collector, Fr is

collector heat removal, , m is mass flow rate of air, Ta is

environment temperature, Ac is collector dimensions and Cp

is specific heat of air.

Figure 3. Solar Heaters Structure

D. Hybrid Solar Micro-turbine Model

The solar heaters model is being integrated with the

micro-turbine model to simulate a hybrid solar micro-turbine

model as shown in Fig. 4. The fuel used in the micro-turbine

is Methane.

The average inlet temperature to the collector during the

twelve months is being calculated according to the following

equation:

Ti = Ta (P2 / P1 ) 0.4/1.4

(7)

The amount of mass flow rate after using the solar

heater (mf2) is expressed as

mf2 = mf1 [ Cpair m (To - Ta) ] / HVMethane (8)

where, P1 is atmospheric pressure, P2 is air compression

pressure, mf1 is fuel mass flow rate before using solar heater,

and HVMethane is lower heating value of methane.

Figure 4. Hybrid Micro-turbine Solar Heaters Simulink

E. Permanent Magnet synchronous Machine (PMSM)

The Hybrid Solar Micro-turbine system drives a high

speed PMSM for conversation of mechanical energy to

electrical energy. The PMSM model used is a 2 pole with a

non-salient rotor. The machine output power is 30 kW and

its terminal line-to-line voltage is 480 V at 100 000 rpm.

The dynamic equations of PMSM expressed in the rotor

reference frame (dq frame) [15] a follow:

Electrical Equations:

(11)

Mechanical Equations:

where, Lq and Ld are q and d axis inductances, iq and id are q

and d axis currents, R is Resistance of the stator windings, vq

& vd are q and d axis voltages, r is Angular velocity of the rotor, is Flux induced by the permanent magnets in the stator windings, P is Number of pole pairs, Te is

Electromagnetic torque, J is combined inertia of rotor and

load, F is Combined viscous friction of rotor and load, is Rotor angular position and Tm is Shaft mechanical torque.

F. Power Conditioning Circuit

The high frequency AC power generated by the PMSM

is rectified to DC and then inverted back to 50 Hz AC, after

elimination of harmonics using LC filter. The IGBT inverter

operated through Pulse Width Modulation (PWM) at a 2

kHz carrier frequency and sample time of 10s [16]. The load current is regulated by a PI current regulator (designed

based on Zeigler-Nichols) after transforming it from abc to

dq and from dq to abc. The output of the current regulator is

a vector containing the three modulating signals used by the

PMW generator to generate the gate pulses. The harmonics

generated by the inverter around multiples of 2 kHz are

filtered by the LC filter [16]. Inductors are designed

according to the current ripple and the filter should be

damped to avoid resonance, since the current harmonics

generated by the rectifier or inverter can cause saturation of

the inductors or filter resonance [17]. The values for LC

filter configuration with inductance 2mH and capacitive load

value 3kVar [16].

G. Supervisory Control

The supervisory control is designed to adjust the

operation of micro turbine in active or passive mode. in

addition to determine the amount of its required power by

controlling the wind turbine frequency based on the

operation state shown in Fig. 5, where f is the wind turbine

frequency, fo is the nominal frequency (50Hz), fmax is the maximum allowable tolerance in frequency (0.2 Hz) and Pmt is the micro turbine power (secondary power).

Figure 5. Micro-turbine Operation State

The designed controller uses a standard three-phase Phase

Locked Loop (PLL) system to measure the system

frequency. The measured frequency is compared to the

Passive

(Pmt=0) Active

(Pmt>0)

& f fo

reference frequency (50 Hz) to obtain the frequency error.

The Frequency error is then manipulated by a Proportional-

Integral controller to produce an output signal representing

the required hybrid micro-turbine power solar heater cells.

The PI gains were adjusted using continuous cycling

Ziegler-Nichols. This supervisory control is represented in

Fig. 6. Fig. 7 represents the simulated model for the whole

system with its supervisory control.

Figure 6. Supervisory Control

Figure 7. Hybrid Power Generation system simulink

III. SIMULATION AND RESULTS

MATLAB Simulink 7.12.0 is used to evaluate the performance of the proposed hybrid model. This

mathematical model is presented in the previous sections.

The wind speed input has been changed during the

simulation to study the response of the hybrid power

generation model. Firstly, the micro-turbine model has been

tested to insure that it is capable to produce the amount of

power required which is 30 kW. Secondly, the solar heater

cells were added to the micro-turbine. This hybrid model has

been evaluated. A comparison between the amount of fuel

consumed before and after modification has been studied.

Finally the hybrid solar micro-turbine model was integrated

with the wind turbine model.

A. Micro-turbine Model

A study for the micro-turbine was held to monitor the

amount of torque and per unit speed produced. The speed

controller, shown in Fig. 2 and simulated in Fig.4, is PID

controller that is tuned to obtain a good performance of

micro-turbine speed and torque. Fig. 8 and Fig. 9 show the

amount of torque and per unit speed respectively. The

figures show a good performance from the micro-turbine

producing the rated mechanical power required.

Figure 8. Micro-turbine Torque

Figure 9. Micro-turbine PU Speed

B. Enhanced Fuel Consumption Using Solar Heater Cells

Approach

The average solar irradiance on the tilted plane of the

collector and average environment temperature were

collected during the twelve months in Alexandria, Egypt

[18, 19]. The average collector efficiency and average inlet

temperature during the twelve months were calculated

according to Eq (6) and Eq (7) respectively. Fig. 10

represents the average solar irradiance absorbed by the

heater collector according to the instantaneous efficiency.

This model has shown a good impact on saving the

amount of fuel consumption monthly. Fig. 11 shows the

amount of fuel and money saved monthly. As shown in Fig.

11 the average amount of fuel saved monthly in Liter/hrs is

21.7. According to ONTARIO [20], the natural gas average

price for the year 2013 is 70.9 cents/ liter. This means the

average amount saved is 15.4 U.S. Dollars/hr monthly.

Figure10. Absorbed Solar Irradiance

60

70

80

90

100

110

120

130

140

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

Ab

sorb

ed S

ola

r Ir

rad

ian

ce W

/m

Figure 11. Average Amount of Fuel Saved

C. Hybrid Power Generation System

This section shows the results of the simulated hybrid

wind turbine, micro-turbine and solar heater cells power

generation system. The wind speed has been changed to

study how the system would response to supply the amount

of power required which is 230 kW. The minimum amount

of power generated from the wind turbine must be 200 kW;

otherwise the amount of load demanded will be reduced to

maintain a frequency of 50 Hz. Therefore, the minimum

wind speed must be 9.8 km/hr according to the wind turbine

characteristics. The maximum amount of power produced is

230 kW produced by a wind speed of 10.5 km/hr. This wind

speed range (9.8 10.5 km/hr) is found in the winter season in Alexandria, Egypt [21], so the model is simulated in

winter. A sample of study was taken at wind speed 10.4

km/hr to show the system response. Fig. 12 shows the

amount of power produced by the wind turbine in the steady

state, which is 220 kW on average.

Figure12. Average Amount of Wind Power

Fig. 13 shows the average amount of power supplied by

the hybrid solar micro-turbine system (10 kW) to

compensate the power shortage of wind turbine to the whole

power generation system. The figure shows a good

performance from the hybrid solar micro-turbine system. It

produced this amount of power at a constant per unit speed

of PMSM which is shown in Fig. 14. Fig. 15 shows the

capacitor DC voltage of the inveter at wind speed 10.4

km/hr.

Figure13. Average Amount of Hybrid solar Micro-turbine

Fig. 16 shows the amount of load demanded which is

230 kW on average. This figure proves that the system could

afford the required power consumption.

Figure15. DC Voltage of The Capacitor

Figure16. Main Load Demand

To study the robustness of the controller of hybird

system, the behavior of each component are observed as the

wind speed varies including the two extreme values within

1.5 seconds, as shown in Fig. 17. Fig. 18 shows the

supervisory control response when changing the values of

wind speed to maintain the same load power demand.

Morover, the frequency response is almost constant (50 Hz)

as in Fig. 19. The per unit PMSM speed and the capaciitor

DC voltage, they had the same values as shown in Fig. 14

and Fig. 15.

10

12

14

16

18

20

22

24

26

28

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

Fuel Saved litre/hr Money Saved Dollars/hr

Figure 14. PMSM Per Unit Speed

Figure 17. Wind Speed Values

Figure 18. Load, Wind Turbine and Microturbine Powers

Figure 19. System Frequency

IV. CONCLUSION

The integration of a hybrid solar micro-turbine and a

wind turbine, which work together to provide the sufficient

load demand required, was proposed. A detailed simulation

model is implemented in MATLAB Simulink 7.12.0 using SIMPOWER systems library. The thermal behavior of the

solar heater and its effect on the amount of the fuel

consumed are analyzed and discussed. Different controller

are designed specially speed controller for micro-turbine and

a supervisory controller to manage the power flow. The

hybrid model has been simulated under several wind speed

conditions. Results showed the good performance and the

amount of annual fuel savings of the hybrid solar micro-

turbine model. According to the data provided in the year

2013, the amount saved on average is 15.4 U.S. Dollars/hr

monthly. In addition, results showed that the hybrid power

generation system could maintain the same load demand

with accepted frequency response during the wind speed

fluctuation.

APPENDIX

Micro-Turbine Specifications:

Rated Power = 30 kW, Air Fuel Ratio = 30:1, Rated Air

Mass Flow Rate = 0.018 kg/s, Rated Fuel Mass Flow Rate =

0.0006 kg/s, Air Compression Ratio = 5 bar.

Micro-turbine Model Parameters:

Combustor Delay = 0.01 s, Exhaust Delay = 0.04 s.

Solar Model Parameters:

F= 0.82, Fr = 0.74, UL = 5.93W/m2K, Air Density = 1kg/s,

Collector Dimensions = 2.0 x 0.9 m2.

PMSM Parameters:

Number of Poles = 2, Maximum Speed = 100 krpm,

Moment of Inertia = 1e-5 kgm2, Stator Resistance = 0.08,

d&q Inductance= 286 H, Rated Power = 30 kW.

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