Multilevel cascade voltage source inverter with seperate DC sources

Abstract

A multilevel cascade voltage source inverter having separate DC sources is described herein. This inverter is applicable to high voltage, high power applications such as flexible AC transmission systems (FACTS) including static VAR generation (SVG), power line conditioning, series compensation, phase shifting and voltage balancing and fuel cell and photovoltaic utility interface systems. The M-level inverter consists of at least one phase wherein each phase has a plurality of full bridge inverters equipped with an independent DC source. This inverter develops a near sinusoidal approximation voltage waveform with only one switching per cycle as the number of levels, M, is increased. The inverter may have either single-phase or multi-phase embodiments connected in either wye or delta configurations.

Description

FIELD OF THE INVENTIONThe present invention relates to a multilevel voltage source inverter with separate DC sources, and more particularly to a multilevel voltage source inverter with separate DC sources including an apparatus and a method for use in flexible AC transmission system (FACTS) applications such as compensating reactive power and voltage balancing.BACKGROUNDWith long distance electrical power transmission and load growth, active control of reactive power (VAR) is indispensable with regard to stabilizing power systems and maintaining supply voltages. Static VAR generators (SVGs) using voltage-source inverters have been widely accepted as the next generation of reactive power controllers for power systems replacing conventional VAR compensators such as Thyristor Switched Capacitors (TSCs) and Thyristor Controlled Reactors (TCRs).Delivering power from a power generating station to the ultimate power consumers over long transmission lines can be very costly for an electric ...

AI Technical Summary

Benefits of technology

Accordingly, it is an object of the present invention to provide a new and improved multilevel cascade voltage source inverte

Problems solved by technology

Delivering power from a power generating station to the ultimate power consumers over long transmission lines can be very costly for an electric utility.

The major problem of using this transformer coupling approach resides in the transformer as a function of harmonic neutralizing magnetics.

(a) is the most expensive equipment in the system;

(b) produces approximately 50% of the total system losses;

(c) occupies approximately 40% of the system layout; and

(d) causes difficulties in system control due to DC magnetizing and surge overvoltage problems resulting from saturation of the transformers on the transient state.

These clamping diodes not only increase the cost of the system but also cause packaging / layout problems and introduce parasitic inductances into the system.

Thus, for practicality, the number of levels of a conventional multilevel diode clamped inverter is typically limited to seven or nine levels.

In addition, control is very complicated and higher switching frequency is required to balance the voltages between each capacitor in the inverter.

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