SINGLE PHASE GRID CONNECTED CURENT SOURCE INVERTER: MITIGATION OF OSCILLATING POWER EFFECT ON THE GRID CURRENT A. Darwish*, A.K. Abdelsalam †, A.M. Massoud ~ , and S. Ahmed* * Texas A&M University at Qatar, Electrical and Computer Engineering Department, Qatar † Arab Academy for Science, Technology and Maritime Transport, Electrical Engineering Department, Egypt ~ Qatar University, Electrical Engineering Department, Qatar Correspondence author email: ahmed.abdel-salam@ieee.org Keywords: Single phase current source inverter (CSI), DC- link oscillating power, Proportional Resonant controller (PR). Abstract Although voltage source inverters (VSIs) are the most common DC-AC grid-tied converters, current source inverters (CSIs) are considered to be promising candidate, thanks to their low THD voltages/currents and inherent short-circuit proof. The natural oscillating power at the DC-link creates the main CSI’s single phase application challenge. Hardware based solutions to this problem exhibits additional cost, components and size. Traditional software based solutions detect the oscillating power effect from a second harmonic component in the DC-link current; hence modify the carrier signal to mitigate the oscillation effect on the grid current. Those solutions are characterised mainly by excessive computational burden in addition to poor tracking. In this paper, a Proportional Resonant (PR) controller, tuned at the third harmonic, is utilized to minimize the oscillating power effect from the grid side, and hence acts as a harmonic cancellator (HC). The proposed technique features: (i) simple implementation, (ii) easy tuning, and (iii) superior steady- state elimination. In addition to simulation, experimental setup is implemented to validate the proposed technique effectiveness. 1 Introduction Exponential growth of renewable energy based distributed power generation (DG) is remarked in the last decade. Hence, DGs are now considered as a potential player in the worldwide power generation market [1-2]. Microgrid concept has been proposed as a solution to the conundrum of integrating several power generation units without disturbing the utility [3-5]. Single phase grid connected inverters are the main DG power electronic based block as they represent the generation-grid link for the energy flow. Although voltage source inverters (VSIs) are common and widely utilized, current source inverters (CSIs) feature increasing attention because of their advantages, like inherent current short-circuit proof, simplified filtering requirement, boosting-up capability, and low THD for their output voltage [6-9]. Despite of these merits, single phase inverters suffer from natural oscillating power characteristic which appears as a second order harmonic in the inverter’s DC side and consequently reflected, in the inverter’s grid current, as a remarkable third order harmonic. Several techniques have been proposed to mitigate the oscillating power effect. Classical addition of a third order harmonic signal of the reference was the first trial with a main disadvantage of being open-loop [10]. The technique was improved by feedback control to the added a third order harmonic signal [11]. Mitigation from the DC side by removing the second order harmonic from the controlled DC- link current was introduced with the disadvantage of poor- tracking and sluggish response [12]. A hardware based solution by the addition of parallel resonant circuit to the DC- link inductor was presented but with extra cost, size and complex tuning limitations [13]. Selective harmonic elimination (SHE) based techniques has been introduced as a solution either by calculating the required firing angles for variable modulation indexes [14-15] or injecting predetermined harmonics to vary the carrier signal [16-17]. However, SHE techniques are based on the assumption that the DC link current must be ripple-free and the elimination is effective at particular indexes. The modification of the carrier signal on a pulse amplitude modulation (PAM) base offered a significant improvement in the oscillating power effect mitigation with efficient and simple-implementation technique. The PAM varies the carrier signal with the second order harmonic oscillations in the DC-link current to indirectly mitigate its reflect on the grid current [18-19]. Further mitigation improvement was achieved by nonlinear pulse width modulation (NPWM) which is based on extracting the second order harmonic component from the DC-link current using high computational operations like band-pass filter, low-pass filter, phase-shifter block, and various division operations [20]. Proportional resonant (PR) controllers gained a large popularity in the last decade in current regulation of grid-tied systems [21] especially due to their capability of eliminating steady-state errors when regulating sinusoidal signals as they offer infinite gate at their tuned frequencies [22-24]. Superior performance of PR controllers opens the gate to their expansion in several applications ranging from accurate grid