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Three-phase grid synchronization is one of the main techniques of the three-phase grid connected power inverters used in photovoltaic systems. This technique was used to reach the fast and accurate three-phase grid tied inverter synchronization. In this paper a new synchronization method is presented on the basis of integrating the grid voltage two times (line-to-line or phase voltage). This method can be called “double integral synchronization method” (DISM) as it integrates the grid voltage signals two times to generate the reference signals of three-phase photovoltaic inverter currents. DISM is designed and simulated in this paper to operate in both analog and digital circuits of three-phase photovoltaic inverter system with the same topology. The digital circuit design and dsPIC33FJ256GP710A as a microcontroller (the dsPIC33FJ256GP710A with the Explorer 16 Development Board from microchip) was used practically in this paper to generate and control the sine pulse width modulation (SPWM) technique according to DISM for three-phase photovoltaic inverter system. The main advantage for this method (DISM) is learning how to eliminate the integration constant to generate the reference signals without needing any reference signals or truth table, just the line-to-line or phase voltage of grid.

Due to the continuous rise in energy consumption, the demand for electricity and its efficiency has increased in the world. Some countries have tended to adopt small renewable energy sources linked to power transmission lines with traditional energy sources. Solar energy is one of the most important sources of renewable energy in the world today.

The synchronization is the first item of any closed control system of single or three-phase inverter connected to grid [

This paper focuses on using a new synchronization method to set up the three-phase reference signals of measuring current depending on line-to line or phase voltage of grid without a phase or frequency generation. This method is called double integral synchronization method (DISM).

The double integration method in power electronic or power system is a procedure to set the references value (voltage or current ) in the time[

Double integration is also used in other applications where a solution is needed to avoid a DC integrating constant. Figure

Analog circuit design of DISM.

Digital circuit design of DISM.

The double integral method block diagram (DISM).

The analog circuit is designed for single and three-phase double integral synchronization method. The integration circuits designed and simulated are identical for the first and second integration for single phase. All the signals and equations for three-phase inverter were derived based on Figure

The aim of this work is to design, simulate, and implement new analog and digital circuit to synchronize the generated current from three-phase photovoltaic inverter system with grid without needing any reference signals or truth table (just the line-to-line or phase voltage of grid).

The rest of the paper is organised as follows: Section

The famous synchronization method of output reference signals in electronic and power application is a Phase Locked Loop. The Phase Lock Loop (PLL) is a control system designed to generate the reference output signals related to the input signals for each phase. There are different types of PLL methods in the world of electronic and communication system [

Table

List of related work review.

| | | | | |
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Masoud Karimi-Ghartemani and M. Reza Iravani[ | EPLL | ★★ | ★★ | ★★★ | ★★★ |

| |||||

Houshang Karimi et al[ | QPLL | ★★ | ★★ | ★★★ | - |

| |||||

Shinji Shinnaka[ | RPLL | ★★ | ★★ | ★★★ | - |

| |||||

Kyoung-Jun Lee et al[ | APLL | ★★ | ★★ | ★★★ | ★★★ |

| |||||

H. Shokrollah Timorabadi and F. P. Dawson[ | PPLL | ★★ | ★★★ | ★★★ | ★★★ |

| |||||

Sidelmo M. Silva[ | SFPLL | ★★★ | ★★ | ★★ | ★ |

The integration in mathematics means finding area under the curve or finding the volume of solids for double integral. In a steady state sine wave a double integration corresponds to 180o phase rotation is an inverted signal. So, it can be used as a way to synchronize voltage and current of the grid. The art will be to be able to remove the DC component without introducing a phase shift. The double integration is used in synchronization method of three-phase inverter signals. The double integration method in power electronic or power system is a procedure to set the references value (voltage or current) for slope and deflection at points along the time axis. The double integration block diagram in Figure

The single phase circuit of DISM in Figure

The analog circuit of DISM (a) single phase circuit; (b) three-phase circuit.

VA1, VB1, and VC1 are three-phase output signal of first stage and VA, VB, and VC are three-phase output reference signals.

Double integration synchronization circuit diagram in Figure

According to (11), (12), and (13) and the three-phase analog circuit in Figure

Analog simulation result (45, 50, and 55) Hz: (a) three-phase output signals (first integral); (b) three-phase output signals (inverse of double integral).

Figures 3 (a1), (b1), and (c1) present the simulation results of the first integral. These figures present the output signals of three phases according to the input voltage with frequencies 45, 50, and 55 Hz, respectively. The phase shift between the input and output signal of the first integral is

Figures 3 (a2), (b2), and (c2) present the simulation results of the inverse of the double integral method following the second integration of the phase shift between the output and input signal which is (

The digital circuit block diagram of DISM in Figure

The digital block diagram of DISM: (a) single phase; (b) three-phase.

Figure

Phase shift delay between input and output.

| | |
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35 | 400 | lagging |

40 | 200 | lagging |

45 | 75 | lagging |

50 | 0 | = |

55 | 50 | leading |

60 | 75 | leading |

65 | 100 | leading |

70 | 100 | leading |

MATLAB/Simulink results of three-phase DISM (45, 50, and 55) Hz: (a) sine wave input signal; (b) square wave input signal.

The single phase bode blot diagram for the first and second stage of DISM in Figure

Bode plot diagram of single phase DISM: (a) 45Hz; (b) 50 Hz; (c) 55 Hz.

In order to verify the feasibility of the DISM of three-phase PWM, a DISM for digital circuit is shown in Figure

dsPIC33FJ256GP710A with the Explorer 16 Development Board from microchip as a microcontroller.

Three-phase DC-AC inverter for photovoltaic application designed in the laboratory.

Three-phase LC filter and three-phase load.

DC power supply circuit.

Three-phase voltage and current measuring circuits.

Three-phase hardware experimental setup of DISM.

The dsPIC33FJ256GP710A microcontroller is used in this paper to control the full system of three-phase photovoltaic inverter. This type of controller is used for its high speed, especially in the applications of industrial applications that require accuracy and very high speed in control. This type has been used in industrial applications due to the low power consumption. Main pin terminals and the salient features are observed in Table

Specifications of dsPIC33FJ256GP710A.

| | | | | | | | | | |
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dsPIC33FJ256GP710A | 100 | 256 | 30 | 9 | 8 | 8 | ＇＇2 ADC, 32 ch | 2 | 2 | 85 |

Figure

SPWM experimental results of digital circuit DISM: (a) three-phase SPWM (line-to-line voltage); (b) three-phase SPWM (phase voltage).

According to [

Grid voltage and output voltage of three-phase photovoltaic inverter with digital circuit of DISM. (a) Phase A; (b) phase B; (b) phase C. Note: Ch1 for inverter output voltage and Ch2 for grid voltage.

This article has presented an alternative method to generate the reference signals of current for three-phase photovoltaic inverter. This method is called double integral synchronization method DISM. DISM is very important to synchronize the PWM for three-phase photovoltaic inverter depending on line-to-line voltage. Main advantage for this method in power electronics is to synchronize the grid voltage without needing any type of reference to compare the results. Analog and digital circuit were designed, implemented, and simulated by using MTLAB/Simulink. The Analog and Digital simulation circuits work successfully with good results. The final digital circuit was designed and implemented in the laboratory to generate the PWM depending on DISM to control the three-phase photovoltaic inverter. The dsPIC33FJ256GP710A with the Explorer 16 Development Board from microchip as a controller to generate the sinusoidal pulse width modulation was programed by C language and using a MPLAB X IDEV3.65 software compiler for programing.

The future of this work is to compare the double integral synchronization method with deferent type and techniques of phase looked loop (PLL) for single and three-phase grid–tide inverter application.

The data used to support the findings of this study are available from the corresponding author upon request.

The authors declare that there are no conflicts of interest regarding the publication of this paper.

The first author, Mohannad Jabbari Mnati, has a scholarship from The Ministry of Higher Education and Scientific Research/IRAQ and acknowledges Special Research of Ghent University for the financial support during this work.