Optimum Design of MMC-Based ES-STATCOM Systems: The Role of the Submodule Reference Voltage

Abstract

In recent years, the combination of battery energy storage systems and static synchronous compensators in a single device, known as ES-STATCOM, has been studied by both academia and industry. The modular multilevel converter (MMC) is an interesting candidate for ES-STATCOM realization. The integration of batteries based on dc/dc converter presents advantages in terms of design flexibility. However, there is a gap in the literature in terms of design and cost-optimization of ES-STATCOM systems. To fill this void, this paper provides a methodology to support engineers to design and perform cost-optimization of ES-STATCOM systems. Both capital expenditures (CAPEX) and operational expenditures (OPEX) due to energy losses and battery replacement are taken into account. The methodology identifies what is the optimum submodule voltage reference which minimizes the ES-STATCOM total cost for a given target of operating time. A lifetime model is employed to predict if battery replacement is required. This model computes the battery capacity fade caused by the operation mission profile considering both calendar and cycling aging mechanisms. The case study is based on a 25 MVA/75 MWh ES-STATCOM connected to a 34.5 kV grid, which provides ancillary services for a photovoltaic (PV) power plant. Different rated blocking voltages are assumed for the semiconductor devices. Moreover, different maximum and minimum allowed state-of-charge (SOC) are adopted in the converter design. The proposed methodology can also be used to find the optimum combination of the battery and IGBT part-numbers based on a given initial set.

Self-aligned hybrid carrier-based PWM for modular multilevel converters

“…Figure 2 explains the operation principle of an upper arm MMC in case of N=2 and M=3 while Table 1 illustrates the switching states and output voltages of an SM with three parallel cells. As noticeable from (8), the voltage of SM will be synthesized depending on the switching state of the cells contained in that SM. In the case of M parallel-connected cells, the number of voltage levels for the SM voltage will be M + 1 between 0 to 𝑣 𝑐𝑎𝑝 .…”

“…Nowadays, a popular and high converter topology is the modular multilevel converter (MMC), which was initially introduced in [1]. The modular multilevel converter has become a significant and desirable option despite the availability of a variety of topologies, not only for high voltage direct current (HVDC) applications [2]- [5] but also for static compensator (STATCOM) [6]- [8] or motor drives applications [9]- [12]. The reason for this is because MMC provides greater flexibility, reliability, performance, and output quality as compared to conventional multilevel converters.…”

Optimization-Based Methodology to Design the MMC's Sub-Module Capacitors

“…M ODULAR multilevel converters (MMC) have attracted the attention of the industrial community in several areas such as Onshore and Offshore High Voltage Direct Current (HVDC) transmission, variable frequency, reactive power compensation (STATCOM), etc., in the past decades [1]- [3]. In HVDC applications, MMCs have become the preferred choice among the different Voltage Source Converters (VSCs) due to its improved efficiency, reduced AC voltage harmonic content and easier scalability to higher voltage levels [4], [5].…”