Design and application of passive filters for improved power quality in standalone PV system
Authors:   , Dlamini Sandile 
Published: September 2024

Harmonic components have developed in power systems due to the non-linear properties of the circuit components utilized in power electronics-based products and their rapid application. Power systems rely on fundamental quantities like sinusoidally varying voltage and current, which oscillate at a frequency of 50 Hz. The standard restrictions of IEEE-519-1992 were utilized as a benchmark in this study. To generate the best output, the total harmonic distortion (THD) should be decreased below the limit, even for certain individual harmonic numbers, and reflect the power factor output. Using the results of the simulation and projections for each mitigation strategy, the THDI can be reduced below the IEEE-519 standard whilst also providing cost and electrical advantages. Analysed and modelled is the PV system, which comprises solar panels, a DC-DC converter, a DC-AC inverter, and a non-linear load. Passive filters are an effective solution for improving power quality in standalone photovoltaic (PV) systems. This dissertation provides an overview of the design and application of passive filters for this purpose. Firstly, an introduction to PV systems and the power quality issues associated with them was preferred. Next, different types of passive filters, namely LC filters, LCL filters and LLCL filters, are discussed along with their advantages and disadvantages, and the design considerations for these filters, including the selection of filter components and the calculation of filter parameters. The application of passive filters in standalone PV systems was then discussed, including their implementation in DC-DC converters and Z-Source inverters and, the design of PWM controllers such as the constant boost control method and simple boost control method. The analysis of the outcome of the engineered systems was conducted according to the IEEE standard and SANS 10142 Standard to protect the connected equipment within the off-grid network. The outcomes pertain to the single-phase stand-alone/off-grid photovoltaic system and the single-phase Z-Source inverter. The Z-Source inverter is equipped with two distinct methods for PWM control, namely the constant boost control method and the simple boost control method. All three designs incorporate three passive filters, namely the LC filter, the LCL filter and the LLCL filter. The results were obtained from the network consisting of three distinct designs. LLCL demonstrates superior performance as a passive filter, substantiating its position as the optimal choice. The optimal outcomes of a single-phase off-photovoltaic (PV) network can be achieved using LC, LCL and LLCL filters, with corresponding percentages of 2.99%, 2.45% and 1.71% respectively. Unfiltered was 89.05%, which is not good for the equipment connected to the network. The Z-Source showcases the capability of voltage amplification to an infinite level, rendering it highly effective in minimizing total harmonic distortion. This research investigation further demonstrated the efficacy of the Z-Source Inverter with Constant Control Boost Method and Simple Boost Control Method, achieving unfiltered total harmonic distortion levels of 38.85% and 44.96% respectively. The Z-Source inverter, when combined with the Constant Boost Control method and Simple Boost Control method, exhibits various filter configurations such as LC, LCL, and LLCL filters. In the context of the constant boost control and simple boost control methods, it is imperative to assess the total harmonic distortion percentage of voltage and current for LC, LCL, and LLCL configurations. The constant boost control voltage (LC, LCL, LLCL) and current total harmonic distortion (LC, LCL, LLCL) are measured at 4.177%, 2.655%, 1.951%, and 2.958%, 2.09%,1.465% correspondingly. The voltage-based boost control methods, namely LC, LCL and LLCL, exhibit total harmonic distortion levels of 2.345%, 1.920% and 0.211%, respectively. Similarly, the current-based boost control methods, LC, LCL and LLCL, demonstrate total harmonic distortion levels of 2.346%, 1.921%, 0.211%, and 2.346%, 1.921%, 0.211%, respectively. Finally, the dissertation wrapped up by exploring the potential of passive filters for enhancing power quality in standalone PV systems. The thesis offers a comprehensive investigation of the design and implementation of passive filters in standalone PV systems, providing valuable insights for engineers and researchers in the field. It enhances understanding and utilization of these imperative devices.