Topology and control of a new line commutated converter-modular multilevel converter hybrid bipolar high-voltage direct current transmission system

Abstract

Summary This paper presents a new line commutated converter (LCC) and modular multilevel converter (MMC)‐based hybrid bipolar high‐voltage direct current (HVDC) transmission system. In the proposed circuit, each polar consists of one 12‐pulse LCC (12P‐LCC) and 1 MMC; meanwhile, the two 12P‐LCCs and the 2 MMCs locate diagonally. In each polar, the 12P‐LCC regulates DC voltage, while the MMC regulates the transmitted active and reactive power. Moreover, the MMC functions as an alternating current active power filter and a DC active power filter at the same time. Therefore, the 11th and 13th alternating current harmonics and the 12th DC current harmonic can be suppressed by the MMC without any other filters. It saves both footprint and cost of the system. In addition, the performance of this proposed system is almost the same as that of the MMC‐HVDC, while the footprint and cost are smaller than those of both the LCC‐HVDC and MMC‐HVDC systems. It means that the proposed system combines the benefits of both the MMC‐HVDC system and the LCC‐HVDC system. At last, the topology and control strategies of the proposed system are verified by the Power Systems Computed‐Aided Design/Electromagnetic Transients including DC simulations.

Key technologies for flexible interconnection in urban power grid and pilot demonstration

“…In Equation 13, t c is fault clearing time, and t d is fault recovery time. Besides, t lim = 10 seconds, U lim = 0.8 p.u.…”

“…There are some previous theoretic works on this subject, including mathematical model, topology, and control strategy of MMC, calculation methods of static security analysis, total supply capability, as well as reliability model of SP‐DCLink . The previous work focuses on 1 aspect, such as the control of MMC or operation of SP‐DCLink.…”

Non‐characteristicharmonic resonance in line commutated converters‐high‐voltage direct current terminals: A practical case study

“…L 1 can be determined by filter tuning frequency (5) once R is known. Therefore, the problem is basically a single-variable optimization problem, which tries to find R that satisfies harmonic mitigation performance (7) and the damping performance (9). There are many methods to solve the optimization problem.…”

“…However, the inherent non‐linear feature of power converters makes it generate abundant harmonics. For example, the widely adopted 12‐pulse HVDC converters, 6‐10 ideally, inject 12 k ± 1 order harmonics into the system, where k is an integer. These harmonics are regarded as the characteristic harmonics of this HVDC terminal.…”

Power losses minimization for modular multilevel converter s with second‐order and fourth‐order harmonic circulating current injection

“…The modular multilevel converter (MMC), which was first proposed by A. Lesnicar and R. Marquardt 1‐2 , was developed in 2003. Recently, the MMC has drawn significant attention from the power electronic industry and academia due to its advantages such as modularity, high efficiency, high‐quality waveforms and flexible expandability 3‐4 . The MMC has been widely adopted in the applications of the high voltage direct current transmission systems 5 .…”