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One main concern of power quality is harmonics because the distorted waveforms of current and voltage have a huge effect on electrical equipment. Due to the continuous increase of grid connected photovoltaic (PV) and nonlinear loads, as a result of the fast development and growth of power electronics application, power quality becomes more important since it introduces harmonics to the power system. This paper presents a power quality study to the isolated northwest grid of Saudi Arabia in presence of PV system and battery storage. Moreover, the study includes nonlinear loads for more analysis regarding harmonics penetration and the design procedure for passive filters to eliminate the harmonics.

Supplying energy at constant frequency and magnitude of voltage is always the objective for any electrical utility. This can only happen in ideal power system but in practice this condition is hard to achieve. Many studies are required for planning and operation of power system in order to assist system performance, reliability and safety. Power quality is one important aspect of power system. It is the concept for many types of power disturbances such as voltage variation, and transient and harmonic distortion. The most unlikely condition for power quality is the harmonic distortion as it is a steady state condition. With high growth of installing grid connected photovoltaic (PV), power quality becomes more important as the DC-AC inverter can affect the quality of the power delivered to the grid due to the switching mechanism responsible for additional harmonics. Moreover, the widespread nonlinear loads due to power electronics applications result in distorted current and voltage in transmission and distribution networks. A solution for this power quality issue can be achieved by using harmonic filters which are designed to reduce the harmonic penetration to the network [

All appliances that use diode rectifiers to convert AC to DC have a nonlinear characteristic that can lead to introduce harmonics. Examples of nonlinear loads include television, computers, fluorescent lamp and adjustable speed drives (ASD) for air condition and heat pump. Harmonic distortion is unwanted phenomena as it can cause additional line losses and interference in communication system. Therefore, analysis of harmonics and nonlinear loads is vital. A common way to analyze and study harmonics is to represent a load by linear model, then adding nonlinearity by using voltage or current harmonic sources [

This paper presents a complete study of power quality for the isolated northwest grid of Saudi Arabia. A detailed PV model with battery storage is modeled and a combination of nonlinear loads is introduced. Also, the paper includes filter design to reduce harmonics. The outline of this paper is as follows. Section 2 shows PV and battery model. Section 3 explains the filter design. Section 4 describes the nonlinear load modeling. Section 5 provides a brief description of the test system. Section 6 shows the simulation results.

_{f} is used to reduce the harmonic produced by the PV system. _{dc} reference given by MPPT and the dc-link voltage is passed through PI compensator whose output provides the d-axis reference current

The PLL is used to synchronize VSC’s output voltage with electric-grid angular frequency in order to make dq- frame transformed variables constant and by regulating

From (1) and (2), controlling the active power is archived by regulating

The control of the dc voltage link is achieved by simply comparing the dc voltage with the reference value. This reference is calculated from MPPT strategy to ensure that the PV works at its maximum output power. The error between these two signals is passed through a PI compensator whose output provide

The current controller is comparing the dq-reference currents with the actual ones to obtain the modulation signals

The state variables of (3) and (4) are

By substituting (5) and (6) into (3) and (4), two control inputs produced which can control

However, the

This paper used the developed battery model in PSCAD [

One way to improve the power quality of power system is to resolve the harmonics issue. This can be done by many approaches described in [_{C} = X_{L} at the tuned frequency (fn) [

For a tuned harmonic (hn) with a capacitor

And to eliminate the hn harmonic, the reactor size should be

The reactance resistor can be calculated as follows

where Q is the quality factor and its typical value is between 30 and 100 [

The increase of nonlinear loads due power electronics applications has introduced more effect on power system quality. Therefore, analysis of nonlinear loads and its affects is important. In power system, one common way to model a nonlinear load is to model it as a load for the fundamental current and as a current source for the harmonics current [

Saudi Arabia grid is divided into four operation areas, West area (WA), East area (EA), South area (SA) and Central Area (CA). Each one has its own control center and operation however they are now under interconnection projects. The WA consists of two parts, the west part and the northwest isolated area which has Tabuk region and its surrounding towns. The grid data was provided from Saudi Electricity Company, Tabuk sector. Line and Peak load data are shown in

H (n) | IHD (%) | ||
---|---|---|---|

Fluorescent lamp | Computer | ASD | |

1 | 100 | 100 | 100 |

2 | 0.3 | 3.3 | 4.12 |

3 | 13.9 | 87.2 | 0.78 |

4 | 0.3 | 5.1 | 1.79 |

5 | 9 | 64.1 | 35.01 |

6 | 0.2 | 1.6 | 0.215 |

7 | 3.3 | 41.1 | 2.62 |

8 | 0 | 0 | 1 |

9 | 3.2 | 17.9 | 0.06 |

10 | 0.1 | 1.1 | 0.73 |

11 | 10.3 | 9.99 | |

12 | 0.3 | 1.2 | 0.03 |

13 | 1.7 | 10.3 | 0.19 |

14 | 0.3 | 0 | 0.48 |

15 | 1.9 | 10.3 | 0.07 |

16 | 0.3 | 0 | 0.52 |

17 | 0.8 | 5.1 | 4.85 |

THD (%) | 18 | 118.3 | 37.3 |

MW respectively.

The PSCAD software is used to build and simulate the grid with a detailed PV model and Battery storage. A peak loading condition for a summer day, 07/16/2013, with a total load of 720 MW is selected for the simulation. Bus 5 has been selected as a slack bus due to its largest capacity. The PV Farm is connected to bus 6 because it has enough land that can accommodate two PV farms connected in parallel with a total capacity of 40 MW, 20 MW each. The battery is assumed to have a capacity of 50% of the total PV Power. A harmonic current source is used to represent the nonlinear loads; the harmonic injection based on

From Bus | To Bus | R (Ohm/Km) | X (Ohm/Km) | Bus | Peak Load (MW) |
---|---|---|---|---|---|

1 | 2 | 0.0493 | 0.2408 | 1 | 106 |

1 | 4 | 0.0493 | 0.2408 | 2 | 94 |

2 | 3 | 0.047 | 0.25 | 3 | 55 |

2 | 5 | 0.0773 | 0.4682 | 4 | 62 |

2 | 7 | 0.08606 | 0.5062 | 5 | 11 |

3 | 10 | 0.0493 | 0.2408 | 6 | 37 |

4 | 5 | 0.0773 | 0.4682 | 7 | 60 |

4 | 6 | 0.093 | 0.452 | 8 | 67 |

4 | 8 | 0.0493 | 0.2408 | 9 | 134 |

4 | 9 | 0.047 | 0.25 | 10 | 12 |

5 | 6 | 0.094 | 0.458 | 11 | 33 |

5 | 7 | 0.0794 | 0.4671 | 12 | 43 |

5 | 12 | 0.08 | 0.47 | ||

6 | 9 | 0.0493 | 0.2408 | ||

6 | 11 | 0.149 | 0.497 | ||

10 | 8 | 0.0493 | 0.2408 |

the low voltage side 13.8 KV. At each bus the load is divide into 80% linear load and 20% nonlinear load. The nonlinear loads that used are ASD, to represent air condition and heat pump, fluorescent lamp and a personal computer with percentage of 18%, 1% and 1% respectively. All loads at each bus has the same procedure therefore the highest load at bus 9 is selected to show the result of including the nonlinear loads, ^{2} with initial SOC of 70% for the battery. ^{2} at 25 second and 30 second. The THD of the PV current injected to the grid for all penetration stages is within the acceptable limits. It is oscillating around 2.5% as observed from

One advantage of the Battery model in PSCAD is that, it allows the user to define the characteristic charge and discharge curves. And since the PV farm output power is high and so the dc voltage link,it is hard to find a battery with such voltage level therefore a characteristic charge and discharge curve of lead acid battery has

Bus No. | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 |
---|---|---|---|---|---|---|---|---|---|---|---|---|

THD% for load current | 2.11 | 1.96 | 2.03 | 2.18 | 5.87 | 2.33 | 1.90 | 1.97 | 1.98 | 5.63 | 1.83 | 2.49 |

<20 | <20 | <20 | <20 | 50 < 100 | 20 < 50 | <20 | <20 | <20 | 50 < 100 | <20 | <20 | |

IEEE limit % for 132 KV level | 2.5% | 2.5% | 2.5% | 2.5% | 6% | 4% | 2.5% | 2.5% | 2.5% | 6% | 2.5% | 2.5% |

been scaled up to match the DC link voltage and defined in the battery model. For the control scheme, the reference current for the battery can be obtained based on the DC link voltage and the amount of power to be stored. Since the battery assumed to have 50% of the PV power, the battery reference current is calculated as follows

From

This paper presents a power quality study for the northwest grid of Saudi Arabia in presence of PV and battery storage. Different PV power penetrations with battery storage are introduced and the THD of PV current is within the acceptable limit for all penetration stages. Also, nonlinear load has been included for more analysis and it shows that the harmonic impact of introducing such loads has been solved by designing passive filters. It also discusses the passive filter design producer.