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Here, a new bi‐directional hybrid modular non‐isolated DC–DC converter is proposed where it consists of a boost converter (BC) fed from the high‐voltage (HV) side. At the BC output stage, a certain number of half bridge submodules (HB‐SMs) is connected across the BC switch. During the turn‐on period of BC switch, the HB‐SMs are connected sequentially to the low‐voltage (LV) side, which results in charging/discharging their capacitors from/into the LV side. While, during the turn‐off period, the LV side is bypassed and the HB‐SMs capacitors are connected in series across the BC output stage, which results in discharging/charging them into/from the HV side. The power flow is controlled in both directions by controlling the duty cycle. The proposed configuration provides self‐balancing operation thanks to the sequential connection of HB‐SMs capacitors, and it also provides the ability to operate with high conversion ratios. Illustration and analysis of the proposed converter and its closed‐loop controller are presented. A full design of the values and ratings of the involved components are presented. Simulation study for a 2.5 MW (25 kV/10 kV) DC–DC converter is presented. Finally, experimental results for a downscaled prototype are presented for validation. [ABSTRACT FROM AUTHOR]

In this study, a new transformerless wind energy conversion system to integrate high‐power multi‐phase permanent magnet wind generators to medium‐voltage local grids is presented. The proposed converter topology consists of multi‐half‐bridge modules with a high ac–direct current (dc) boosting capability. Each phase of an open winding multi‐phase generator is connected to the ac side of a half‐bridge module, whereas the dc sides of the half‐bridge modules are connected in series forming the high‐voltage dc‐link output. The proposed architecture facilitates the employment of semiconductor switches with a relatively low‐voltage rating, which equals the dc‐link voltage divided by the number of generator phases. A detailed analysis of the proposed architecture along with the required closed‐loop control is presented. The proposed architecture is simulated under different operating conditions using a typical 2 MW system, while the experimental validation is carried out using a low‐scale prototype converter. [ABSTRACT FROM AUTHOR]

This study proposes a new architecture of flywheel energy storage system (FESS) which can be implemented at generating unit (GU) level (e.g. wind turbine) or scaled up for application in grid‐side converter (GSC) stations of a multi‐terminal direct current (MTDC) system. The proposed architecture suppresses DC voltage leaps under grid faults, and performs power levelling duty at grid connection points. When implemented at GU level, the proposed FESS features a doubly‐fed induction machine (DFIM) – the flywheel machine – where its six stator winding terminals are connected in series between the grid and the GSC. The flywheel converter is of partial power rating, and is connected to the DFIM rotor. When employed at an MTDC GSC station, several submodules are connected to build an FESS station. The study proposes the control concept and the general topology of the FESS station. The performance parameters of the system are tested under normal and abnormal operating conditions. Results and analyses indicate smooth dynamic operation, the economic advantage and the improved fault ride‐through capability because of the proposed system. [ABSTRACT FROM AUTHOR]