## 1 Introduction
Installing flexible, reactive power compensation devices at the points of common coupling for new energy plants and within hybrid distribution grids can enhance power transmission capacity, reduce power loss in electrical equipment, and improve system performance [29]. The Static Synchronous Compensator (STATCOM) is a versatile and advanced device for power quality control, providing continuous and dynamic reactive power support superior to that of the Static Var Compensator (SVC). It also offers a substantial improvement in mitigating harmonic distortions [30]. With its continuous reactive power regulation capability, rapid dynamic response, and significant reductions in harmonic content, STATCOM has seen increased application in power systems, establishing itself as a prominent topic of research in power quality management [31]. To facilitate reactive power compensation in high-voltage transmission and distribution networks, some researchers have suggested integrating a cascaded H-bridge converter or modular multilevel converter (MMC) with STATCOM [32; 33]. However, both approaches still involve relatively high switching frequencies (around 1000 Hz), and reducing the switching frequency necessitates a sufficient number of submodules in series, complicating equipment redundancy. To reduce the switching frequency and harmonic impact of STATCOM, a solution combining a cascaded H-bridge RMVSC with STATCOM has been proposed [15]. This solution reduces the number of switching devices and auxiliary capacitors needed for RMVSC, simplifies the complexity of the reinjection circuit, and, since the H-bridge acts as a common intermediate circuit, allows the rated current and voltage of the switches to be designed for only half of the equipment rated voltage. Consequently, this approach significantly reduces the cost of the reinjection circuit. While this design supports high voltage by adjusting the number of H-bridges, it still presents some drawbacks, such as the requirement for large capacitors on the dc side to act as support elements, which can be problematic in high-voltage, high-power applications. The paper leverages the principles of submodule operation and reinjection multilevel conversion technology to propose a novel submodule series RMVSC topology. This topology is capable of fulfilling all RMVSC functionalities while allowing for the scaling of device voltage and capacity by adjusting the number of series-connected submodules. This approach eliminates the need for large capacitors as dc voltage support components, thereby reducing equipment size and cost and enhancing the system's dynamic response capability. The proposed topology exhibits several advantages, including strong modularity, low switching frequency, and high output power quality. When applied as a STATCOM, the RMVSC demonstrates continuous, bidirectional reactive power regulation and superior dynamic performance. This paper provides an in-depth analysis of the novel RMVSC topology and its operational principles, including the design of a cyclic drive pulse sequence to maintain submodule voltage balance within a specified range in the reinjection circuit. Additionally, a reactive power compensation control strategy tailored to this device is proposed. The feasibility and effectiveness of the new topology and control strategy are validated through simulation. The rest of this paper is organized as follows: Section 2 outlines the working principle of the RMVSC, detailing the operation of the devices and the harmonic elimination mechanism. Section 3 designs a cyclic pulse sequence for the RMVSC to achieve capacitor voltage balancing. Section 4 applies the RMVSC as a STATCOM based on its excellent performance and designs an appropriate control strategy for this application. In Section 5, simulations verify the effectiveness of the proposed modulation and control strategies. Finally, the conclusion is presented in Section 6.