Fabrication and experiment of an electrical generator for sea wave energy - Nguyen Van Hai

Vietnam Journal of Science and Technology 55 (6) (2017) 780-792 DOI: 10.15625/2525-2518/55/6/9116 FABRICATION AND EXPERIMENT OF AN ELECTRICAL GENERATOR FOR SEA WAVE ENERGY Nguyen Van Hai*, Nguyen Dong Anh, Nguyen Nhu Hieu Institute of Mechanics, Vietnam Academy of Science and Technology 264 Doi Can Str., Ba Dinh Dist., Ha Noi *Email: nguyenvanhai1977@gmail.com Received: 30 December 2016; Accepted for publication 5 September 2017 Abstract. This paper presents some results of fabrication and experiment of an electrical generator for sea wave energy. The electrical generator device is fixed on the bottom of the sea and works in the vertical direction of sea waves. The experiment results show that, for the received voltage and current, the power of the electrical generator is up to 300 W and operates stably at about 200 W during experiment at sea. The output voltage is at 220 VAC frequency 50 Hz and is a pure sine wave. Keywords: renewable energy, sea wave energy, electrical generator. 1. INTRODUCTION According to calculations by scientists, the received energy from fossil fuels will become gradually exhausted, and now therefore looking for new energy sources is requisite. For Vietnam, the 2020 target is to become a country in which marine economics will constitute over 50 % of GDP. Therefore, the energy demand supplying for general economics and particular marine economics is very important. The research and fabrication of electrical generators for sea wave energy are necessary. Moreover, the electrical energy received from sea wave energy conversion is friendly to environment, almost endless and is a clean energy source. The sea wave energy is an important energy source of the world as well as Vietnam in the future. In this paper, we present some results of designing, fabrication and experiment of the electrical generator at the sea with the output voltage being 220 VAC frequency 50 Hz and being pure sine wave. The electrical generator can be used for signal buoys of seaway and can supply the electrical power for lighthouses. 2. ANALYSIS OF THE DEVICE MODEL In the world, the research and fabrication of the electrical generators for sea wave energy source have been considered for a long time. The received electrical energy source for wave energy conversion has met some demands of society. Up to now, the electrical generators from sea wave energy have been investigated and fabricated in many countries, for example, Nguyen Van Hai, Nguyen Dong Anh, Nguyen Nhu Hieu 781 Australia, Britain, China, Denmark, Ireland, Italy, Japan, Portugal, Spain, Sweden, South Korea, the United States [1]. The devices models are categorized into two major kinds, the device fixed on the bottom of the sea and the floating device on the sea [1 - 14]. The electrical generator devices fixed on the bottom of the sea usually use the linear generators. In Ref. [2], the device is connected with a buoy on the sea surface by a rope moving in vertical direction under the action of sea waves. The power of this device is about 10 kW. In Ref. [3], Stelzer and Joshi have evaluated buoy heave responses for a wave energy generator based on a linear model. The authors calculated the buoy motion to determine the coupled hydrodynamic and electromagnetic coefficients of the electrical power generator for both regular and irregular waves. In a monograph by Eriksson [5], the author has developed a model of a wave energy converter using linear potential wave theory in order to describe the wave-buoy interaction and effects of modeling parameters on device system dynamics. A significant topic on the optimization of wave energy converter is presented by Cargo et al. [6]. That work is devoted to the investigation of technology of generic point-absorber converter for irregular waves using a hydraulic power take-off unit of wave energy converter. Another detailed research on the optimization of sea wave energy harvesting electromagnetic device is carried out by Marco Trapanese [7]. He studied optimal characteristics of a permanent magnet linear generator using a mathematical model of system including the stochastic features of the model. An approach to the conversion of the power generated by a sea wave power generator integrated in an offshore wind power farm has been proposed by Franzitta et al. [8]. The authors compared two possible ways to connect the generator to the network and to the offshore wind power farm based on a conversion subsystem and a DC-AC converter, respectively. In Ref. [9] by Engstrom et al., a wave energy converter with enhanced amplitude responses is studied based on a theoretical model for passive systems having optimum amplitude response at frequencies coinciding with Swedish west coast conditions. A comprehensive review on the linear generator and related modern devices can be seen in Ref. [10]. In this review Ekstrom et al. have categorized, described and compared different generators for wave energy converters based on technologies of electrical damping circuits and techniques of power output optimization. The electrical generator devices floating on the sea surface consist of the two main types, a vertical-floating type and a horizontal-floating type. The vertical floating electrical generator device consists of an oscillating upper part (the floater) and a bottom-fixed lower part (the basement) with the fixed installed linear generator. The floater is pushed down under a wave crest and moves up under a wave trough. This motion makes the generator work to generate the power about 10÷80 kW [1, 4, 11-14]. The horizontal floating device can be illustrated here, such as a pelamis device that it looks like a snack. The structure of pelamis composes of four cylindrical sections linked by hinged joints, and aligned with the wave direction. The wave- induced motion of these joints is resisted by hydraulic rams, which pump high-pressure oil through hydraulic motors driving three industrial electrical generators. The power of this device is about 750 kW [1, 4, 14]. In Vietnam, several research institutions have fabricated electrical generators for sea wave energy. At Hanoi University of Science and Technology, and the National Research Institute of Mechanical Engineering, the researchers have calculated device models with industrial generating motors installed on fixed frame structures, and the buoy of device floating on the sea surface. The hydraulic diver system will transmit the obtained sea wave energy from the buoy to the generating motor [15]. At Vietnam National University, the researchers have Fabrication and experiment of an electrical generator for sea wave energy 782 fabricated linear electrical generators that operate and float on the sea surface in vertical direction. The initial experimental output voltage on load is received about 1 V [16, 17]. To minimize the influence of sea storms on the device operating at sea, we build an electrical generator model with the generator part fixed on the bottom of the sea with the small and medium power (see Fig. 1). The device works in the vertical direction, and the buoy of device floats on the sea surface. When sea waves act on the buoy, it will transfer the sea wave energy to the generating motor through a rope in the vertical direction and a rotational mechanical structure system [18]. In this study, we use a type of industrial generating motor and a voltage stabilizer with high performance (see Fig. 4 a,b), and fabricate a block DC-AC inverter to generate the output voltage at 220 VAC frequency 50 Hz and pure sine wave. The electrical generator model poses an advantage in that it may be not affected by waves and sea storms impacts because the generator part is fixed on the seabed. 3. MODELLING OF THE ELECTRICAL GENERATOR The electrical generator device is fabricated for converting sea wave energy into electrical energy. This requires a system that can convert the vertical slow motion of buoy to a high speed rotating motion at the input of generating motor. The main structures of device include circular cylinder-shaped buoy, rope, piston-rack, gearbox, generating motor, block of 12 VDC voltage stabilizer, DC-AC inverter and protection system with the generating voltage being 220 VAC frequency 50 Hz and pure sine wave, as shown in Fig. 1. Figure 1. Schematic illustration of an electrical generator for sea wave energy. The governing equation of buoy associated with piston-rack, as shown in Fig. 1, can be written as follows [7, 8]: ),0()(2 2 zgzskdt gdz mggzszbgSdt gzd m −−−−−= γρ (1) where m is total mass of the buoy and the piston-rack, zg= zg(t) is the vertical coordinate describing the position of the buoy at time t; ρ is the water density, g is the acceleration gravity, Sb is the bottom area of the buoy, zs is the vertical coordinate describing the sea level from the Nguyen Van Hai, Nguyen Dong Anh, Nguyen Nhu Hieu 783 seabed; the damping constant γ is the sum of the fluid damping (γf) and the electrical generator damping (γeg), i.e. γ=γf+γeg; ks is the spring constant, z0 is the rest position. The Eq. (1) will be solved to find optimal parameters in order use for designing and fabrication of the device. For simplicity, the sea wave can be modeled as a harmonic fluctuation about the rest position z0 ,0)sin( ztHsz += ω (2) where H and ω are the wave amplitude and frequency, respectively. Substituting Eq. (2) into Eq. (1) and then solving for zg, we obtain ),sin( 000 ϕωχρ ρ ++ + +− = t gSk zgSmgzk z bs bs g (3) where the amplitude χ and phase constant φ0 are determined as follows , )( 2222 ωγωρ ρχ +−+ = mgSk HgS bs b (4) .tan 20 ωρ γωϕ mgSk bs −+ −= (5) The average of power Pgm extracted from the wave by the converter in a period is given by [2]: , 1 0 2 ∫= T geggm dtzT P ɺγ (6) in which the damping coefficient of fluid, γf, is assumed to be very small in comparison with the electrical generator damping γeg [19], and can be neglected. The output electrical power P received from an electrical generator is determined as follows: ,gmPP η= (7) where η is a power performance value of the electrical generator. It is seen that the amplitude χ can be considered as a function of the frequencyω , i.e. )(ωχχ = , therefore the electrical power P is also a function of the frequency ω . The power simulation results for the present device are shown in Fig. 2 with parameters ρ = 1020 kg/m3, g = 9.81 m/s2, m = 30 kg, Sb = 0.5024 m2, ks = 2100 N/m, z0 = 5.5 m, and γeg = 3400 Ns/m. Fig. 2 portrays the power curves depending on the frequency of sea wave with various values of the wave amplitude, H1 = 0.4 m, H2 = 0.5 m, H3 = 0.6 m, and H4 = 0.7 m. 0 10 20 30 40 50 60 70 0 500 1000 1500 2000 Frequency (rad/s) Po w e r (W ) H=0.4 m H=0.5 m H=0.6 m H=0.7 m Figure 2. Power of the output electrical generator versus frequency. Fabrication and experiment of an electrical generator for sea wave energy 784 For the linear model of the buoy motion (Eq.1), it is seen that the obtained power will be extended in all range of frequency if the wave amplitude increases. In the sea experimental test of device, the sea wave amplitude value is estimated at about 0.4m÷0.5m; the sea wave frequency arises primarily at 1.472 rad/s (see Fig. 6). The range of received power belongs to interval 199W÷311W. At various frequencies, the corresponding power values of the electrical generator are received as shown in Fig. 2. 4. FABRICATION OF THE ELECTRICAL GENERATOR 4.1. Structural design The structure of device is designed in two parts: the buoy of device floating on the surface of sea which is designed in the circular cylinder shape and the generator part fixed on the bottom of the sea. Mechanical structures and a generating motor are installed inside the casing of circular cylinder-shaped device, as shown in Fig. 3. The main parameters of the electrical generator are presented in Table 1. The buoy of device is connected to a piston shaft of the electrical generator by a rope. a. The electrical generator b. Inner of the electrical generator Figure 3. Main structural components of the electrical generator. The buoy and the casing of device are fabricated from stainless steel sheets with 3mm in depth. The piston-rack, pinion and inner mechanical structures are also fabricated from stainless steels. Table 1. The main parameters of the electrical generator. Parameters Value Parameters Value Buoy radius (mm) 400 Piston length (mm) 400 Buoy height (mm) 420 Rack length (mm) 450 Device casing height (mm) 750 Pinion diameter (mm) 60 Device casing diameter (mm) 500 Gearbox ratio 1:30 4.2. Generating motor and voltage stabilization In this model, we use a generating motor that it is the AC three-phase type permanent magnet motor, and the 12 VDC voltage stabilizer with the input voltage received from AC three- phase voltage of the generating motor. These equipments were imported from American WindBlue Power Company (see Fig. 4) [20]. Nguyen Van Hai, Nguyen Dong Anh, Nguyen Nhu Hieu 785 Figure 4. The generating motor and 12 VDC voltage stabilizer. The power of generating motor can grow to 1500 W (see Fig. 4c). The output voltage from the 12 VDC voltage stabilizer is connected to the input of DC-AC inverter to generate the voltage at 220 VAC frequency 50 Hz and in a pure sine wave form. 4.3. DC-AC inverter and protection system The main structures of DC-AC inverter and protection system (as shown in Fig. 5) include DC-DC converter circuit block, oscillating circuit block, DC-AC converter and protection circuit block, and filter circuit block [21, 22]. The main function blocks in the scheme are described as follows: - The DC-DC converter circuit block: the function of this circuit block is to convert a low voltage 12 VDC to high voltage 330 VDC with the maximum input current up to 180 A. In this circuit block, we use 5 ferrite transformers of 400 W-type power, transistor couples of type IRF 1404 (such as Q1&Q2, Q3&Q4, Q5&Q6, Q7&Q8, Q9&Q10), and an oscillating circuit generating an alternating current at frequency 33 kHz using the IC TL494C. The input and output values of ferrite transformer are calculated and designed based on input 12 VDC voltage and output 330 VDC voltage. After calculation, the input and output parameters of ferrite transformer are given in Table 2. Three geometric parameters of the size 15 mm × 15 mm × 50 mm are obtained (i.e. width × length × high, respectively). Table 2. Input and output parameters of the ferrite transformer. Parameters Value Parameters Value Primary turns (turns) 4 Secondary turns (turns) 110 Maximum primary current (A) 36 Maximum secondary current (A) 1.3 Primary wire diameter (mm) 3 Secondary wire diameter (mm) 0.58 - The oscillating circuit block: we use the PIC16F716 which generates two antiphase AC signals at frequency 50 Hz. Two antiphase signals will be connected to two H-bridges hafts for voltage multiplexing at the DC-AC converter. a. The generating motor b. The 12VDC voltage stabilizer c. The voltage and current characteristics versus rotation speed of the generating motor Fabrication and experiment of an electrical generator for sea wave energy 786 C28 4.7u C28 393 - + U19A LM324 3 2 1 4 11 S L2 294SN 13 LS2 R10-E1Y2-V52 6 5 7 9 8 10 1 4 TP1 TP2 - + U12A LM324 3 2 1 4 11 U11 PI C 16 LC 74 /F P VD D VS S R E0 VD D R E1 R E2 R A0 R A1 R A2 R A3 R A4 R A5 R D 1 R D 0 R C 3 R C 2 R C 1 R C 0 R A7 O SC 1 R A6 O SC 2 VS S R D 7 R D 6 R D 5 R D 4 R C 7 R C 6 R C 5 R C 4 R D 3 R D 2 R E3 R B0 R B1 R B2 R B3 R B4 R B5 R B6 R B7 R55 2.2K R44 3.3K R52 3.3K 5VDC 3 3 0 V D C Q20 A1013 R59 1.8K V 12 V 12 D15 4148 R32 22R Y2 20M R33 3.3K U1 IR4427 OUT3 RST4 VCC 8GND1 CV 5 TRG2 THR 6 DSCHG 7 Q1 IRF140 R1 R T13 1 5 4 8 R2 R Q2 IRF140 R3 R R4R D16 4148D28 D29 - + U21A LM339 7 6 1 3 12 5VDC R34 22R Ap chuan Sensor R43 1K R35 3.3K R41 2.2R D34 4148 12VDC D17 4148 R45 1K R36 22R R37 3.3K D26 D27 VCC R46 1K D33 DIODE D18 4148 R38 22R R39 3.3K C20 105 C18 225 D32 4148 U6 7815 IN1 O U T 3 GND 2 U4 IR2110 LO 1 HO 7 HIN10 SHDN11 LIN12 13 VSS COM2 VB 6 VC C 3 VD D 9 VS 5 R22 10K DD C23 225 Q11 40N60 3 2 1 C21 105 R23 10K Q12 40N60 3 2 1 Q3 IRF140 R54 1M R5 R R6R R58 18k Q4 IRF140 R7 R R8R Q13 40N60 3 2 1 VCC T7 1 4 5 6 7 8 2 3 Q14 40N60 3 2 1 C7 104 Q15 40N60 3 2 1 Q5 IRF140 R9 R R10R Q6 IRF140 R11 R Q16 40N60 3 2 1 R12 R T14 TRANSFORMER ISOLATED 1 5 4 8 5VDC VCC T8 1 4 5 6 7 8 2 3 VCC D30 D31 T9 1 4 5 6 7 8 2 3 D11 4148 Y1 20M R24 22R - + D21 DB102 1 2 3 4 T10 1 4 5 6 7 8 2 3 Q7 IRF140 R13 R R50 22R Q8 IRF140 R14 R C8 104 VCC + C9 2200uF T11 1 4 5 6 7 8 2 3 D19 DIODE C22 104 R49 10K S L1 294SN 13 D22 D23 C10 104 + C11 470uF 3 3 0 V D C D1 Q17 40N60 3 2 1 Q18 40N60 3 2 1 R19 15 0K 1 1 2 2 D2 C16 22n R47 10K R51 330R D3 D4 U5 7805 IN 1 OUT 3 G N D 2 C17 22n R20 15 0K 1 1 2 2 C25 33 U7 16F716 GND 5 VDD 14 OSC2/CLKOUT15 M C LR 4 OSC1/CLKIN16 R A0 17 R A1 18 R A2 1 R A3 2 R A4 /T O C KI 3 RB0/INT 6 RB1 7 R B2 8 R B3 9 R B4 10 R B5 11 R B6 12 R B7 13 C1 0.1uF D5 D6 R25 3.3K D7 D8 DIODE C29 10u R40 2.2R C12104 + C13 10uF D9 D10 DIODE R48 1K 3 3 0 V D C + C2 330uF D24 D25 Q9 IRF140 R15 R C26 33 R16 R L 22 0u H Q10 IRF140 U20 TL494C VCC12 IN1+1 IN1-2 IN2+16 IN2-15 C1 8 C2 11 COMP3 DTC4 OC13 E1 9 E2 10 CT5 VREF14 RT6 R17 R R56 5.6K R18 R C27 103 VCC 3 3 0 V D C 3 3 0 V D C 3 3 0 V D C VDK + C3 330uF U8 IR2110 LO 1 HO 7 HIN10 SHDN11 LIN12 13 VSS COM2 VB 6 VC C 3 VD D 9 VS 5 D12 4148 R26 22R R27 3.3K U9 521 1 2 4 3 Q19TIP41C D13 4148 R28 22R R29 3.3K + C6 470uF + C4 330uF R42 1K U10 521 1 2 4 3 D20 R21 0.15R1 1 2 2 C14104 + C15 10uF + C5 330uF D14 4148 R30 22R R31 3.3K DD 12VDC AQ R58 470R 220V AC Q21 A1013 S L3 294SN 13 R57 10K C24 104 Figure 5. Schematic illustration of DC-AC inverter and protection system. - The DC-AC converter and protection circuit block: The DC-AC converter circuit block is designed using the IGBT 40N60A, the first H-bridge half (including ICs named Q11, Q12, Q13, Q14) and the second H-bridge half (including ICs named Q15, Q16, Q17, Q18). The output AC voltage obtained from full H-bridge is transmitted through a filter circuit block in order to filter all distortions of voltage. The protection circuit is designed using the microchip PIC 16LC74/FP to control the operation of system based on conditions of the overload, overheating, high and low voltages. If one of which occurs, the protection circuit will shut-down and turn off the electrical generator in order to protect the system. - The filter circuit block: this block uses the LC filter to process all voltage distortions. The LC filter is designed based on the output voltage of DC-AC converter and minimum reactive power of the filter. The output voltage is received at 220 VAC frequency 50 Hz and is pure sine wave. The LC filter must satisfy the following condition [23]: Nguyen Van Hai, Nguyen Dong Anh, Nguyen Nhu Hieu 787 , 12 ff c CL =ω (8) where ωc is the corner frequency of filter, Lf is the filter inductance, Cf is the filter capacitance. The inductance value Lf can be determined by: , 2 0If DV L S out f ∆ = (9) where D is constant, Vout is the output voltage, fs is the switching frequency, ∆I0 is the output current ripple. By combining Eqs. (8) and (9), we get the filter inductance value at 4.1 mH and the filter capacitance value at 330 µF. 4.4. Operational description of device system Sea waves are random in nature and can be considered as a combination of an infinite number of waves with different frequencies and amplitudes. The change of sea waves in frequency and amplitude will affect to the operation of device system [6, 24]. When sea waves act on the buoy, it will transfer the energy of sea waves to the generator part fixed on the bottom of the sea by rope in the vertical direction (see Fig. 1). Both of piston-rack and the gearbox are used to convert the received vertical slow motion of buoy to the high speed rotating motion with the ratio 1:30. The obtained output voltage of the generating motor is not stable because the characteristics of voltage and current depend on the rotation speed of the motor (see Fig. 4c). In our device system, the 12 VDC voltage stabilizer is an important part to stabilize and control the output voltage of the generating motor at 12 VDC (see Fig. 4b) [8, 11]. The DC-AC inverter is used to convert the voltage 12 VDC into the voltage 220 VAC frequency 50 Hz and pure sine wave. The voltage 220 VAC frequency 50 Hz is also the output voltage of the electrical generator. The performance of device is partly considered in the next section from our experimental calculation and measurement. 5. EXPERIMENT RESULTS The electrical generator device for sea wave energy has operated for a long time in the Hon Dau sea, Hai Phong province, Viet Nam. At the experiment site, the sea wave amplitude is about 0.4÷0.5 m. This wave amplitude range is received from the Hon Dau Hydro-Meteorological Monitoring Station. The sea wave frequency is about 1.472 rad/s (see Fig. 6), it is obtained from DASIM measurement equipment with Futek pressure sensor of America mounted on the buoy hull. 2 4 6 8 10 12 0 0.1 0.2 0.3 0.4 X: 1.472 Y: 0.3143 Frequency (rad/s) Pr e ss u re (P SI ) Figure 6. The sea wave pressure exerting on the buoy. a. The sea wave pressure versus time b. Pressure spectrum of sea wave Fabrication and experiment of an electrical generator for sea wave energy 788 In Fig. 6, the received average pressure value is about 0.31 psi (i.e. 0.021 atm in SI unit) and maximum value is 0.74 psi (i.e. 0.05 atm). The obtained pressure value information will be used for the purpose of fabrication of buoy and device casing. The output voltage received is efficient with power up to 300 W. In this experiment, we use equipments to measure and analyze voltage and current as Picoscope USB oscilloscope 2204A of England, Gwinstek digital clamp meter of Taiwan, Kyoritsu digital clamp meter of Japan, voltage meter Sanwa CD800a of Japan, voltage meter Klein tools MM2000 of America. The measurement results received from the electrical generator during experiment at Hon Dau sea are given in Table 3. The DC-AC inverter - protection system circuit board is shown in Fig. 7. Table 3. Measurement results received from input and output of DC-AC inverter. Load power P (W) Voltage UDC (VDC) Current IDC (A) Voltage UAC (VAC) Current IAC (A) Performance ACDC −η (%) 100 12 9.92 224 0.45 84.67 140 12 13.47 223 0.61 84.15 200 12 20.33 223 0.92 84.09 300 12 29.5 221 1.35 84.27 In Table 3, we use normal loads with a 40 W incandescent lamp and three 100 W incandescent lamps. The quantities UDC and IDC are voltage and current received at the output of the 12 VDC voltage stabilizer. UAC and IAC are voltage, current received at the output of the DC- AC inverter and protection system. The performance ACDC −η is determined from the voltage and current at the input and output of the DC-AC inverter through the experimental measurement. The measured values in Table 3 show that the load power of the electrical generator works from 100 W to 300 W, and operates stably at 200 W during the experiment. Fig. 8 shows the voltage and current characteristic curves versus output loads at the experiment site. In Fig.1, the piston-rack of device receives the sea wave energy from the buoy through a rope. This energy is transmitted to the generating motor through the pinion and gearbox system. In practice, the input sea wave signals are random, the voltage and current at the output of the generating motor are not stable. The 12 VDC voltage stabilizer of device is used in order to stabilize the received electrical power from the generating motor output at 12 VDC voltage. The DC-AC inverter converts the received 12 VDC voltage at the 12 VDC voltage stabilizer output to the 220 VAC voltage and 50 Hz frequency (it is also the output voltage of the electrical Figure 7. The DC-AC inverter and protection system circuit board. Figure 8. The voltage and current characteristic curves versus output loads. Nguyen Van Hai, Nguyen Dong Anh, Nguyen Nhu Hieu 789 generator). In Table 3, the received average performance of the DC-AC inverter is determined as follows %.295.84 4 27.8409.8415.8467.84 = +++ = − ACDCη (10) In the general case, the performance of the electrical generator is determined by the relation between the real input sea wave signals and the output power signals of the electrical generator. This relation needs to carry out many experiments for statistical calculations. In our experiment, we use the Picoscope USB oscilloscope 2204 A and the software of signal processing to analyze the output voltage obtained from the electrical generator. In Fig. 9, it is observed that the output voltage wave on the 200 W load in time and in frequency is received at 220 VAC ± 1.25 % frequency 50 Hz ± 0.06 % and is a pure sine wave. 0.01 0.02 0.03 0.04 0.05 0.06 0.07 -3 -2 -1 0 1 2 3 Time (s) Vo lta ge (V AC ) x 10 0 0 50 100 150 200 250 300 0 0.5 1 1.5 2 2.5 X: 49.97 Y: 2.223 Frequency (Hz) Am pl itu de (V ) x 10 0 Figure 9. Output voltage wave on the 200 W load of the electrical generator for sea wave energy. Figures 10 and 11 demonstrate several pictures of field experiments of the electrical generator for sea wave energy in the Hon Dau sea, Hai Phong province, Viet Nam. Figure 10. The transport of device on the HQ1788 Ship for experiment process. a. Preparing for experiment setup at the Hon Dau Port b. Uploading experiment device components onto the HQ1788 Ship c. Moving the device to experiment site d. Experimental preparation b. Spectrum of output load voltage a. Output load voltage versus time Fabrication and experiment of an electrical generator for sea wave energy 790 Figure 11. Measurement, storing and analysis of voltage and power from the electrical generator by the Picoscope USB oscilloscope 2204A connecting computer on the HQ1788 Ship. 6. CONCLUSIONS In present paper, we show some results in fabrication and experiment of the electrical generator for sea wave energy. The device works in the vertical direction of sea waves, its generator part is fixed on the bottom of the sea in order to overcome the impact of sea storms as it operates at the sea. The output power of the device is generated up to 300 W and operates stably at 200 W during experiment at the sea. In the framework of experimental study of our fabricated device, the received average performance of the DC-AC inverter from 12 VDC voltage to 220 VAC voltage is about 84.295 %. The output voltage is received at 220 VAC frequency 50 Hz and is pure sine wave. In the general case, the performance value of the electrical generator will be investigated in the next works with the real input sea wave signals. From our experiment results, we realize that the fabrication model is reasonable and efficient. For the obtained electrical power of device, the electrical generator for sea wave energy can be used for the signal buoy of the seaway and can supply the electrical power for the lighthouse. Moreover, at the top of buoy of device has a signal lamp and a 30 W solar panel. The solar panel is also extra energy source to assure that the signal lamp always operates for the time at which the sea is calm. The experiment results have also been used for analyzing the model structure in order to improve the device, and for enhancing power of the electrical generator to meet the needs of the electrical energy at island sea regions. Acknowledgement. The authors express deep thanks to the reviewers for their helpful comments and suggestions. This research was supported by Vietnam Academy of Science and Technology (VAST), project VAST01.10/16-17. a. Testing power of device b. Measurement of output current and voltage c. Buoy of device d. Analysis of output voltage and power The experiment loads Nguyen Van Hai, Nguyen Dong Anh, Nguyen Nhu Hieu 791 REFERENCES 1. Falcão A. F. 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