Current Source Modular Multilevel Converter: Detailed Analysis and STATCOM Application

Abstract

Multilevel current source converters are a smart choice for the high power applications with low voltage and high current requirements. This paper presents the detailed analysis of a current source modular multilevel converter (CSMMC) and its application as a STATCOM. Various properties of CSMMC are correlated with the voltage source modular multilevel converter (VSMMC). Submodule inductance selection method and a sorting based algorithm for inductor current balancing are proposed for CSMMC. The validity of the inductance selection method and the inductor current balancing algorithm are confirmed by the simulation of a three phase CSMMC using PSCAD/EMTDC. The carrier phase shifted sinusoidal pulse width modulation is used as the switching technique. The performance of a converter is analyzed with both interleaved and non-interleaved carrier signals for the upper and lower arms. Results show that CSMMCs and corresponding VSMMCs have analogous features. Hence, the development on VSMMCs can be used for reference to CSMMCs and vice versa. Furthermore, the control designs for CSMMC based STATCOM are presented and verified using simulations. The obtained results of the proposed STATCOM show that the steady state and transient performance of the system are quite satisfactory. This makes the CSMMC suitable for HVDC and FACTS applications.

Current-Fed Multilevel Converters: An Overview of Circuit Topologies, Modulation Techniques, and Applications

“…The topologies of single-rating inductor, multi-rating inductor, and paralleled H-bridge current-fed MLC topologies are obtained from classical voltage-fed MLCs by using principle of duality. These topologies are suitable for applications such as active filter [18], power converters for grid connected photo-voltaic (PV) panels [19], fuel-cell power grid integration [20], wind energy conversion [21], SMES [14], [22], ac motor drives [23] and HVDC applications [24]. A detailed discussion about various current-fed MLCs including emerging topologies is given next.…”

“…8(b) and these cells are inserted or bypassed in each arm of the converter to control the output current. A detailed analysis and operation of the current source MMC can be referred from [24].…”

“…Mukesh and Anshuman Shukla has proposed inductance selection method on current-fed MMC which ensures the minimization of inductor ripple current [24] and thereby it reduces the circulating current.…”

“…For MMC topology the cell inductors act as storage element and the size of the submodule inductor L SM is decided by the amount of energy need to be stored in the submodule. The value can be calculated as [24],…”

“…However the limitation of LCC is large capacitor and filter banks and lack of restoring the system without relying on external energy sources. In [24], a current source MMC converter has been studied for STATCOM operation under different operating conditions such as capacitive mode, inductive mode and also with dc short circuit fault. The dynamic response showed at each condition, current-fed MMC proves that it can tolerate dc short circuit fault.…”