Discussion on “Mitigation of Fault Induced Delayed Voltage Recovery (FIDVR) by PV-STATCOM”

Abstract

The authors of [1] presented a novel controller for PV-STATCOM. The theory posits dynamic modulation of PV inverters’ active/reactive power through non-unitary power factor operation. The proposed approach is applied to mitigate the effects of fault-induced delayed voltage recovery (FIDVR) experienced in power systems with high penetration of solar PVs and induction motor loads. The structure of the proposed control algorithm is based on 4 modes: 1) normal operation, 2) active power control, 3) reactive power control, and 4) ramp-up active power process. The methodology is tested and comprehensively validated on a radial distribution network (RDN) for numerous scenarios of LLL-G faults, X/R ratios, and night-time operation. For clarity, the authors’ insights on the following technical points are appreciated: 1)The authors meticulously adhered to many standards (IEEE std. 1547-2018, German grid code - BDEW and NERC) to formulate the PV-STATCOM and RDNs’ operational constraints. As per the IEEE std. 1547-2018, the PV inverter design is recommended to be oversized by 11% to address numerous operational challenges [2]. Did the authors consider this standard for the solar farm placed at Bus 3 of the RDN as depicted in Fig. 1? 2)In [Section IV-A (3 and 4)], the authors introduced the values of variables “$k_2$” and “$k_1$” as 1.1 and 0.96 that were used in Mode 2 and Mode 3 for active and reactive power control of the PV-STATCOM respectively as depicted in Fig. 2. What is the selection criteria and/or the range(s) of these variables? Will these values be the same under different RDN scenarios or different RDN networks (for instance, IEEE 34 feeder test system)? 3)In [Section VII], the authors comprehensively presented in-depth analytical case studies for the proposed PV-STATCOM. Most of these studies considered only a single solar farm. Practically, the active-reactive power coordination strategies through PV inverters mostly consider high PV penetration (at each bus) in RDNs [3]. Therefore, how will the proposed PV-STATCOM framework coordinate with more than one solar farm? 4)In [Section VII-E], the author validated the economical dominance of the proposed PV-STATCOM over conventional STATCOM in terms of equivalent size. Nevertheless, the operation of PV inverters as STATCOM negatively affects the inverter lifetime and hence impacts their economical significance [4]. In this respect, is the inverter of the PV-STATCOM economically dominant for long-term operation as well? 5)In [Section VII-G], the authors presented 5 cases to study the voltage recovery rate of the proposed PV-STATCOM based on different fault locations. These faults are LLL-G (for 100 ms) induced at various distances from the substation and the PV solar farm, high voltage side, and low voltage side of the 138/12.6 kV transformer. Considering these 5 cases, will the obtained recovery time be different if the PV-STATCOM was placed at different bus of the study system considered. In other words, is the placement of PV-STATCOM optimal? 6)Finally, the authors proposed a novel application of PV-STATCOM in the field of PV-integrated power network. Voltage stability requirement is one of the key parameters that affects the permissibility of integrating high-scale, inertia-less, and unpredictable PVs in a power network [5]. Therefore, with the proposed PV-STATCOM configuration, what is the maximum achievable hosting capacity of the RDN under consideration?