Modelling and Simulation of Grid-tied Inverter for Interfacing Solar Power Supply to Distribution Networks

• Author(s): Ijomah, O. P. ; Iloh, J. P. I. ; Okonkwo, I. I.
• Paper ID: 1703049
• Page: 247-256
• Published Date: 31-12-2021
• Published In: Iconic Research And Engineering Journals
• Publisher: IRE Journals
• e-ISSN: 2456-8880
• Volume/Issue: Volume 5 Issue 6 December-2021

Abstract

A. Materials The materials used are Solar panel, Maximum power point tracker, Boost converter, Voltage source converter, Voltage source control main controller, Harmonic filter, Transformers, distribution unit (utility grid). These materials where virtually deployed in Matlab/ Simulink environment where simulations where carried out. The software tools are Matlab/ Simulink. B. Method The software tools are Matlab/ Simulink. The block diagram of the proposed grid tied inverter is shown in Fig. 1. Fig. 1 Block diagram of a proposed grid tied inverter Description of the Proposed Grid-Tied Inverter: The grid tied inverter must match the phase of the grid and maintain the output voltage, the same as the grid voltage at any instant. If the inverter’s output is higher than the utility voltage, the grid tied inverter will be overloaded. If it is lower, the grid tied inverter sinks current rather than sourcing it. Its phase angle is within one degree of the AC power grid. The output voltage and current are perfectly lined up. It is also designed to quickly disconnect from the grid if the utility grid goes down. In this dissertation, there is an additional coupling inductor (Lgrid) between the grid tied inverter and mains that acts as a shim that absorbs the extra voltage, it also reduces the current harmonics generated by the pwm. A 100-kW PV array is connected to an 11-kV grid via a DC-DC boost converter and a three-phase three-level Voltage Source Converter. Maximum Power Point Tracking (MPPT) is implemented in the boost converter by means of a Simulink model using the 'Incremental Conductance + Integral Regulator' technique. There are some that use average models for the DC-DC and VSC converters. The detailed model contains the following components: PV array which delivers a maximum of 100 kW at 1000 W/m2 sun irradiance. 5 KHz DC-DC boost converter increasing voltage from PV natural voltage (273 V DC at maximum power) to 500 V DC. Switching duty cycle is optimized by a MPPT controller that uses the 'Incremental Conductance + Integral Regulator' technique. This MPPT system automatically varies the duty cycle in order to generate the required voltage to extract maximum power. 3-level 3-phase Voltage Source Control. The VSC converts the 500Vdc link voltages to 240 Vac and keeps unity power factor. The VSC control system uses two control loops: an external control loop which regulates DC link voltage to +/- 250 V and an internal control loop which regulates Id and Iq grid currents (active and reactive current components). Id current reference is the output of the DC voltage external controller. Iq current reference is set to zero in order to maintain unity power factor. Vd and Vq voltage outputs of the current controller are converted to three modulating signals Uabc ref used by the PWM Generator. The control system uses a sample time of 100 microseconds for voltage and current controllers as well as for the PLL synchronization unit. Pulse generators of Boost and VSC converters use a fast sample time of 1 microsecond in order to get an appropriate resolution of PWM waveforms. 10-kvar capacitor bank filtering harmonics produced by VSC. 100-kVA 260V/11kV three-phase coupling transformer. Utility grid (11kV distribution feeder + 33kV equivalent transmission system). The 100-kW PV array uses 330 Sun Power modules (SPR-305E-WHT-D). The array consists of 66 strings of 5 series-connected modules connected in parallel. Hence, The Power Output of the PV = 66 x 5 x 305.2 W = 100.7 kW. The 'Module' parameter of the PV Array block allows the designer to choose from among various array types of the NREL System Advisor Model. The manufacturer specifications for one module are: Number of series-connected cells = 96 Open-circuit voltage: Voc = 64.2 V Short-circuit current: Isc = 5.96 A Voltage and current at maximum power: Vmp = 54.7 V, Imp= 5.58 A The PV array block menu allows the designer to plot the I-V and P-V characteristics for one module and for the whole array. The PV array block has two inputs for varying sun irradiance (input 1 in W/m2) and temperature (input 25?). The irradiance and temperature profiles are defined by a Signal Builder block which is connected to the PV array inputs. The Simulink model of the proposed grid-tied inverter is shown in Fig. 2. Fig. 2 The model of the proposed grid tied inverter C. Photovoltaic Cell The detailed parameters of the photovoltaic array block diagram are done in the module depending on the type of the PV cell choose in the MATLAB from National renewable energy laboratory (NREL). The block parameters are shown in Fig. 3.

Keywords

Distributed network, Grid-tied, Inverter, Photovoltaic, Power system

Citations

IRE Journals:
Ijomah, O. P. , Iloh, J. P. I. , Okonkwo, I. I. "Modelling and Simulation of Grid-tied Inverter for Interfacing Solar Power Supply to Distribution Networks" Iconic Research And Engineering Journals Volume 5 Issue 6 2021 Page 247-256

IEEE:
Ijomah, O. P. , Iloh, J. P. I. , Okonkwo, I. I. "Modelling and Simulation of Grid-tied Inverter for Interfacing Solar Power Supply to Distribution Networks" Iconic Research And Engineering Journals, 5(6)