This project addresses the problem of high arm currents in Modular Multilevel Converters (MMCs) used in high voltage direct current (HVDC) transmission systems. Conventional converters face challenges with high output levels, leading to circulating currents. To solve this, a new control scheme is proposed that reduces the peak of arm currents by optimizing the second harmonic current. This enhancement improves the power handling capacity of the converter by approximately 24.3%. The control scheme includes a Circulating Current Optimizing Controller (CCOC) which ensures the proper magnitude and alignment of the second harmonic current, making the system more efficient and reliable.
Figure (1) Circulating current optimisation controller; Laboratory prototype of MMC
High voltage direct current (HVDC) transmission systems face a challenge with conventional voltage source multilevel converters, where the varying currents through sub-module capacitors cause circulating currents dominated by even harmonic components. This leads to inefficiencies and limits the power handling capacity of the system.
- High Efficiency and Reliability: HVDC transmission systems are highly efficient and reliable, attracting significant interest and investment.
- Modular Structure: MMCs are built with a modular structure, allowing for scalability and adaptability to different voltage levels.
- Reduced Peak Arm Current: The proposed control scheme reduces the peak arm current, enhancing the power handling capacity of the converter by nearly 24.3%.
- Circulating Current Optimization: The CCOC ensures the magnitude of the second harmonic current is optimized and orthogonal to the fundamental current, improving overall system performance.
- Minimized Harmonic Distortion: MMCs produce low total harmonic distortion, making them suitable for a wide range of high voltage applications.
- Improved Semiconductor Device Utilization: With the optimized control scheme, semiconductor devices can handle higher power levels without requiring higher ratings, leading to cost efficiencies.
- Versatile Application: The invention can be applied in various high voltage applications, including HVDC, FACTS, and high/medium power drives, making it versatile and widely applicable.
The prototype features a Circulating Current Controller (CCC) integrated into a Modular Multi-level Converter (MMC). This CCC receives the circulating current, which contains an undesirable Second Harmonic Current (SHC), from the MMC's upper and lower arms. It then converts this current into a rotating frame (dq frame) to simplify analysis. A PI controller is used to compare the transformed circulating current against a reference, generating an error signal. This error signal drives the PI controller to precisely adjust both the magnitude of the SHC to a predefined optimal value and its phase to be orthogonal to the fundamental current, thereby minimizing the overall arm current peak in the MMC.
A Hardware prototype has been developed, and all the simulations and hardware studies have been successfully performed.
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HVDC systems are vital for long-distance power transmission and interconnecting different power grids. By improving MMC performance, this technology contributes to more robust, reliable, and efficient national and international power grids, reducing transmission losses and blackouts. Enhanced efficiency translates to lower operational costs for power utilities, which can eventually lead to more stable or even reduced electricity prices for consumers.
HVDC, Drives, FACTS, Power Electronics, Renewable Energy, Electrical Engineering Renewable Energy Integration.
Geography of IP
Type of IP
201821021181
503667