The successful integration and stable operation of renewable energy sources in power grids often require the deployment of HVDC (High Voltage Direct Current) systems and FACTS (Flexible AC Transmission Systems), for example for long-distance power transmission, shunt compensation, and/or power flow control. More recently, a new FACTS device for shunt compensation has emerged, namely the E‑STATCOM (Enhanced Static Synchronous Compensator). In addition to providing rapid capacitive or inductive reactive power for voltage regulation, the E‑STATCOM is capable of fast injection and absorption of active power to support grid frequency.

To enable active power exchange, an energy storage system (ESS), in this case based on supercapacitors, is integrated with the STATCOM, thereby providing rapid power generation and absorption capability in the megawatt range. For instance, stored energy can be released instantaneously in response to grid contingencies that cause a high rate of change of frequency (RoCoF). Supercapacitor cells are assembled into modules; modules are connected in series to form racks, and racks are further series connected to create strings. The ESS is completed by connecting multiple strings in parallel.

The design and integration of E‑STATCOMs into power systems requires comprehensive studies. In addition to dynamic performance assessments, electromagnetic compatibility (EMC), lightning, switching transient, converter passivity, and resonance studies are necessary to properly dimension components and to ensure reliable and secure operation of electrical assets. Specialized electromagnetic and power system simulation tools, such as CST and PSCAD/EMTDC, are employed for this purpose. EMC studies for conductive RF require models valid up to 80 MHz, lightning studies require validity up to 1–3 MHz, switching transient studies up to 100 kHz–1 MHz, and converter passivity and resonance studies up to the bandwidth of the control system, typically below 100 kHz.

This paper presents Hitachi Energy’s recent experience in high frequency impedance measurement and modeling of supercapacitor technology for E‑STATCOM integration studies. To estimate stray resistance, inductance, and capacitance in supercapacitor assemblies, detailed three-dimensional (3D) models were analyzed using electromagnetic simulations in CST. Equivalent circuit models incorporating the extracted parameters were subsequently developed in PSCAD/EMTDC, and their frequency responses were compared with those obtained from the 3D CST models.

Furthermore, the frequency responses of the proposed circuit models were validated against laboratory measurements, showing quite good agreement between simulation and measurement results. The validated models were then used to perform EMC, lightning, switching transient, converter passivity, and resonance studies in compliance with applicable standards. The proposed modeling approach is scalable and adaptable to different E‑STATCOM station ratings and physical layouts. Simulated and measured frequency responses, together with selected results from the system‑level studies, are presented and discussed in this paper.