HVDC Light System Control Strategy Research Based On MMC

In recent years, the Light HVDC base on voltage source converter is a hot issue in the field of transmission and distribution, However, this transmission is a new technology, related to some technical problems remain to be resolved, especially HVDC system in power level and harmonic control.Traditional HVDC system using converter technology is still two level or three level transform technique, but the lack of two level transform technique mainly between the harmonic and power devices are pressure problems, the lack of three transform technology mainly for the midpoint potential fluctuations, especially in low system power factor at run time, the midpoint potential becomes more controllable.For the lack of traditional converter technology, Siemens is the first to propose a new modular multi-level converter, the converter technology is relatively traditional two-level three-level converter, the transmission voltage levelhigher and lower harmonics, very suitable for DC transmission system. Domestic of the system is also less, part of the literature of the HVDC converter technology system is divided to two parts for the device-level control and system-level control device level modular multi-level balance control and modulation algorithm, the system-level power decoupling control of the transmission system of the DC converter. For the balance control device level, some of the literature describes the idea of a sort based on capacitive voltage, but did not give a reasonable mathematical proof, on the modulation algorithm in the device level, some described in the literature based on the recent level of approximation modulation algorithm, the algorithm in the level number is lower, larger output harmonic and undesirable. For system-level control section, it is rare in the literature on modular multi-level converter-based HVDC system control strategy analysis.With the modular multi-level converter HVDC Transmission System Research, as well as practical engineering significance, This paper first carried out a detailed analysis of the modular multi-level converter topology and operating principle.and applicationDC transmission system, device and system-level two levels of study, and obtained the complete control algorithm based on the modular multi-level converters of DC transmission system. Which, for the balance of the device-level control and modulation algorithms, this paper put forward a reasonable carrier phase modulation, optimization method, this method combined with the balance control of the sub-module, and not only reflect a better effect of capacitor voltage balance, and output lower harmonic content; for system-level control, power decoupling control of the converter DC transmission system technology. The PSCAD/EMTDC simulation software for the simulation results show the feasibility and effectiveness of the control strategy analysis.