Grid Synchronization in a 3-Phase Inverter using Double Integration

Method

FAHEEM FAROOQ1, KAMRAN HAFEEZ1,*, BAYAN MAHDI SABBAR2,

MOHANNAD JABBAR MNATI3

COMSATS University Islamabad,

PAKISTAN

conventional fossil fuel-based energy sources. These sources are connected to the utility grid using a suitable

synchronization method. It requires accurate information on grid voltage magnitude and phase angle. But the

presence of harmonics, DC Offset, and voltage unbalances makes the synchronization process more

non–ideal grid conditions and also tested on grid-connected 3-phase Inverter.

Inverter,Harmonics.

Received: April 14, 2023. Revised: February 16, 2024. Accepted: April 19, 2024. Published: May 14, 2024.

Due to the expansion in consumption of electrical

parallel inverters. To achieve parallel operation, of

inverters, its parameters; a) voltage magnitude b)

phase c) frequency must be synchronized to grid

parameters, [3]. An increase in network diversity

and connection of various types of DS makes the

synchronization process more challenging. As grid

voltage contains disturbances like DC Offset and

harmonics its waveforms are distorted and the

synchronization process is also affected, [4]. Many

synchronization techniques are discussed in the

Figure 1, [7]. These methods include zero crossing

detector (ZCD) [8], discrete Fourier transform

(DFT) [9], adaptive notch filtering (ANF) [10],

Phase locked loop (PLL) [11] and Kalman filter

[12]. There are several performance parameters

detected from the literature including; unbalanced

in a single-phase system, [14]. A de-coupled double

synchronous reference frame (DDSRF-PLL) is

proposed for the grid synchronization during non-

ideal grid conditions but problems of the DC-off set

is not solved. The SRF-PLL technique is sensitive to

grid voltage unbalanced waveforms and also has a

100 Hz problem, [15]. An enhanced-PLL (E-PLL)

and dual-EPLL (DE-PLL) methods are developed

for solving grid voltage disturbances but these

techniques can be affected by harmonics, [16], [17].

The moving average filter (MAF) is used in the

structure of SRF-PL to counter-unbalance and

harmonic in the voltage signals. However, it has a

connected Inverter using double integration is

proposed in [20], that considered steady state

conditions only.

Fig. 1: Synchronization techniques

the DIM method in a 3-phase grid tied Inverter

under distorted grid conditions. In this paper

from transients, as nonlinear feedback always

remains active.It only synchronizes giving a current

or voltage reference. Therefore the proposed method

works well during non-ideal grid conditions. A PI in

the feedback will result in a high pass filter. The low

pass will make it a compensator integrating low and

high frequencies,

The SRF-PLL and DIM techniques are further

discussed in this section

and q-axis corresponds to phase angle information

of any one of the phases. This structure of PLL is

called Synchronous Reference Frame (SRF- PLL) or

d-q PLL. The phase angle  makes a feedback loop;

the proportional integral (PI) controller is in a

forward path to secure the d-axis component 

aligned with the q-axis component, [21].

value (voltage or current) over time as shown in

equation (1), [22].

Where  grid voltage and requirement is to remove

DC constant of integration.

Let’s consider the grid voltage in equation (2)

applied to synchronize grid voltage or grid current.

A block diagram of single-phase digital DIM is

distorted grid conditions.A comparison between

(g)

(h)

Conventional SRF-.PLL does not perform well

during harmonics and an additional filter is

signal with 5th, 7th, and 11th harmonics in it.

Figure 6(b-f) shows the output of SRF-PLL

synchronize with 5th, 7th and 11th harmonics in

the input, phase angle of SRF-PLL, frequency

error signal and FFT analysis of input and output

PLL. Figure 6(g-h) shows output of DIM

synchronized with input DC offset signal at t=

0.005s and FFT analysis gives its THD value of

0.28%.

(a)

(b)

(c)

(d)

(e)

(f)

SRF-PLL. (f) Output FFT analysis SRF-PLL. (g)

DIM

The 3-phase input signal is included with

voltage unbalances with voltage magnitudes of 0.9,

0.8 and 1.2 % of Vm phase voltage. Figure 7(a-h),

shows the simulation results of SRF-PLL and DISM

with voltages unbalances in input signal as shown in

Figure 7(a) Whereas, Figure 7(b-f) shows the

output of PLL synchronize with the input phase

voltage unbalance signal, phase angle of PLL,

voltages unbalance at t= 0.005s and FFT analysis

gives THD value of 0.02%.

(c)

(d)

(e)

(f)

SRF-PLL. (c) Phase angle SRF- PLL. (d) frequency

and output DIM. (h) Output FFT analysis DIM

The 3-phase input signal is added with

frequency unbalances using unequal frequencies of

0.95, 0.97 and 1.03 times of fundamental frequency.

Figure 8(a-h), exhibits the simulation results of

SRF-PLL and DIM with frequencies unbalances in

the input signal as shown in Figure 8(a) Whereas,

Figure 8(b-f) shows the output of PLL synchronized

with input signal having un balance frequencies,

(b)

(c)

(e)

Fig. 8: SRF-PLL and DIM 3-Phase Frequency

Frequency and error signal SRF- PLL. (e) Input FFT

analysis SRF-PLL. (f) Output FFT analysis SRF-

PLL. (g) Input and output of DIM. (h) Output FFT

analysis DIM

The results comparison between SRF-PLL and

DIM during distorted grid conditions are given in

Table 2.

Table 2. ResultsSRF-PLL and DIM

3-phase Inverter is synchronized with a grid voltage

using SRF-PLL and DIM methods under ideal and

distorted grid conditions as shown in Figure 9, [25].

The control system developed for SRF-PLL and

inverter in a natural reference frame is shown in (9).













DIM with grid-connected 3-phase inverter during

d) shows FFT analysis SRF-PLL and DIM.

connected 3-phase inverter during harmonics.