Cascaded Multilevel Converter-Based Transmission STATCOM: System Design Methodology and Development of a 12 kV +/- 12 MVAr Power Stage

This paper deals with the design methodology for cascaded multilevel converter (CMC)-based transmission-type STATCOM(T-STATCOM) and the development of a +/- 12MVAR, 12 kV line-to-line wye-connected, 11-level CMC. Sizing of the CMC module, the number of H-bridges (HBs) in each phase of the CMC, ac voltage rating of the CMC, the number of paralleled CMC modules in the T-STATCOM system, the optimum value of series filter reactors, and the determination of busbar in the power grid to which the T-STATCOM system is going to be connected are also discussed in this paper in view of the IEEE Std. 519-1992, current status of high voltage (HV) insulated gate bipolar transistor (IGBT) technology, and the required reactive power variation range for the T-STATCOM application. In the field prototype of the CMC module, the ac voltages are approximated to sinusoidal waves by the selective harmonic elimination method (SHEM). The equalization of dc-link capacitor voltages is achieved according to the modified selective swapping (MSS) algorithm. In this study, an L-shaped laminated bus has been designed and the HV IGBT driver circuit has been modified for the optimum switching performance of HV IGBT modules in each HB. The laboratory and field performances of the CMC module and of the resulting T-STATCOM system are found to be satisfactory and quite consistent with the design objectives

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

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

Converter and Output Filter Topologies for STATCOMs

This chapter reviews different converter topologies and output filter configurations used in STATCOM applications. The output voltage and harmonic control of a STATCOM is obtained by individual control of each switch in the STATCOM. Several converter topologies can be considered for STATCOMs. The multi-pulse converters are developed using the most widely known 6-pulse configurations. The variations of multi-pulse converters such as 12-pulse, 24-pulse and 48-pulse that are built by combining 6-pulse converters via phase-shifting isolation transformers are introduced in terms of control methods and structures in this chapter. On the other hand, the multilevel converters are considered to be used in recent STATCOM topologies as an alternative to the multi-pulse configurations, owing to their multi MVA switching capability that is inherited from series or parallel connection of converter cells. The diode clamped, flying capacitor, and cascaded H-bridge configurations of multilevel converters, that are the most widely known topologies, are comprehensively introduced in this chapter. The multilevel converter topologies provide several advantages such as harmonic elimination, lower electromagnetic interference, better output waveforms, and increased power factor correction (PFC) capabilities together. Furthermore, each switch can be controlled individually to robustly tackle the unbalanced load operations even in higher switching frequencies relatively to the multi-pulse configuration. The related subsections propose control and operation properties of converters besides introducing the main topological issues. The filtering requirements of STATCOM are particularly considered in this chapter where the passive and active filters are introduced in detail. The passive filters designed with reactive components such as individual L and C or their combinations as LC or LCL are surveyed according to design and analytical criteria. Besides, active power filters (APFs) that provide several feedback control methods increasing the efficiency and controllability are discussed in the following part. The control methods of STATCOM converters are introduced in a separate section where the recent control approaches and analytical calculations required are presented in detail. The block diagrams of the industrial STATCOM applications are also discussed