A new DC voltage balancing method for cascaded multilevel inverter based statcom

It has been mentioned in the literature that, among the multilevel inverter topologies used for STATCOM applications, the cascaded multilevel topology is the most advantageous and economical one. On the other hand, the main problem of this topology comes out to be the difficulty of sustaining the DC capacitors' mean voltages. This issue is very important for obtaining an output voltage with low THD and having equal device stresses. In this work, a new DC voltage balancing method (Selective-Swapping Algorithm) for cascaded multilevel inverter based STATCOM applications is investigated and the results are given. Moreover, these results are compared with the ones obtained for the other DC voltage equalization methods given in the literature

Multi-DSP and -FPGA-Based Fully Digital Control System for Cascaded Multilevel Converters Used in FACTS Applications

In this paper, a fully digital controller based on multiple digital signal processor (DSP) and field-programmable gate array (FPGA) boards has been proposed for parallel-operated cascaded multilevel converters (CMC) used in flexible AC transmission system (FACTS) applications. The proposed system is composed of a DSP-based master controller in combination with a multiple number of slave DSP boards, FPGA boards, microcontrollers, a programmable logic controller (PLC), an industrial computer, and their peripherals in interaction. Inter-communication of these digital controllers is achieved mainly through fiber-optic links, via synchronous serial data link wherever a high-speed, full duplex communication is needed, and via asynchronous serial communication interface wherever relatively slow communication speed is required. The proposed fully-digital control system has been implemented on a sample 11-level CMC-based 154-kV, +/-50-MVAr transmission type static synchronous compensator (T-STATCOM). Field test results have shown that the proposed fully digital control system provides good transient response and steady-state characteristics for the oveall system including protection and monitoring functions

Multipurpose Platform for Power System Monitoring and Analysis With Sample Grid Applications

This paper is devoted to the design and implementation of a multipurpose platform (MPP) for power system monitoring and analysis. This MPP is a novel device, which combines the abilities of a power quality (PQ) analyzer, an event logger, a synchronized phasor measurement unit, and an interarea oscillation identifier, all in one device. The multiple functions of the proposed MPP can serve the needs of the power system operators (SOs) as a wide-area monitoring system to observe the states and stability of the power system, and as a PQ analyzer to monitor the PQ events and parameters, permanently. Furthermore, the algorithms of flicker and harmonic current contributions at a point of common coupling can be embedded on this MPP, to determine the individual contributions of different loads supplied from the same bus. The operational features of the developed MPP have been tested on the Turkish electricity transmission system and its interfaces with the distribution system by installing 450 MPPs and integrating them with a monitoring and control center. The proposed all-in-one MPP can therefore meet the multiple requirements of the power SOs to serve the needs of modern electricity markets and convert an ordinary electricity system to a smart grid

Electrical Power Quality of Iron and Steel Industry in Turkey

The iron and steel industry has been growing increasingly in Turkey in the last decade. Today, its electricity demand is nearly one tenth of the installed generation capability of 40 GW in the country. In this paper, power quality (PQ) investigations based on the arc furnace installations of the iron and steel plants using field measurements according to the international standard IEC 61000-4-30 are documented. Interharmonics and voltage flicker problems occurring both at the common-coupling points of those plants and at the arc furnace and static var compensator (SVC) systems of the plants themselves are determined with the use of GPS receiver synchronization modules attached to the mobile PQ measurement systems. It has been observed that flicker and interharmonic problems are dominant at the points of common couplings where arc furnace installations are supplied. Based on the field measurements obtained with collaborative work of five arc furnace plants, it is possible to say that contemporary SVC systems cause interharmonic amplification problems around the second harmonic, and novel methods are required to solve this problem

Design and Implementation of a 154-kV +/- 50-Mvar Transmission STATCOM Based on 21-Level Cascaded Multilevel Converter

In this research work, the design and implementation of a 154-kV +/- 50-Mvar transmission static synchronous compensator (T-STATCOM) have been carried out primarily for the purposes of reactive power compensation and terminal voltage regulation and secondarily for power system stability. The implemented T-STATCOM consists of five 10.5-kV +/- 12-Mvar cascaded multilevel converter (CMC) modules operating in parallel. The power stage of each CMC is composed of five series-connected H-bridges (HBs) in each phase, thus resulting in 21-level line-to-line voltages. Due to modularity and flexibility of implemented HBs, each CMC module has reached a power density of 250 kvar/m(3), thus making the mobility of the system implementable. DC-link capacitor voltages of HBs are perfectly balanced by means of the modified selective swapping algorithm proposed. The field tests carried out at full load in the 154-kV transformer substation where T-STATCOM is installed have shown that the steady-state and transient responses of the system are quite satisfactory