A Review of Multilevel Inverter Topology and Control Techniques <s> D. Other Multilevel Inverter Structures <s> Multilevel voltage source converters are emerging as a new breed of power converter options for high-power applications. The multilevel voltage source converters typically synthesize the staircase voltage wave from several levels of DC capacitor voltages. One of the major limitations of the multilevel converters is the voltage unbalance between different levels. The techniques to balance the voltage between different levels normally involve voltage clamping or capacitor charge control. There are several ways of implementing voltage balance in multilevel converters. Without considering the traditional magnetic coupled converters, this paper presents three recently developed multilevel voltage source converters: (1) diode-clamp, (2) flying-capacitors, and (3) cascaded-inverters with separate DC sources. The operating principle, features, constraints, and potential applications of these converters are discussed. <s> BIB001 </s> A Review of Multilevel Inverter Topology and Control Techniques <s> D. Other Multilevel Inverter Structures <s> A new control algorithm for a power converter-based device that is capable of alleviating the problems of harmonic interference and voltage regulation on radial distribution lines is introduced. It comprises a relocatable converter in series with a passive filter and is known as the Power Quality Manager. Simulation results based on an existing 88-kV line are presented. Experimental results are presented, based on a three-phase 200-VA scaled model of the existing 88-kV system. It is a cost-effective and flexible solution to improving power quality. <s> BIB002 </s> A Review of Multilevel Inverter Topology and Control Techniques <s> D. Other Multilevel Inverter Structures <s> Publisher Summary ::: This chapter demonstrates the state of the art of multilevel power converter technology, discussing fundamental multilevel converter structures and modulation paradigms. A multilevel converter not only achieves high power ratings but also enables the use of renewable energy sources. A multilevel converter has several advantages over a conventional two-level converter that uses high switching frequency pulse width modulation (PWM). Multilevel converters produce smaller CM voltage and can draw input current with low distortion. Existing multilevel converters such as diode-clamped and capacitor-clamped multilevel converters can be derived from the generalized converter topology called P2 topology. To reduce the number of separate dc sources for high-voltage, high-power applications with multilevel converters, diode clamped or capacitor-clamped converters can be used to replace the full-bridge cell in a cascaded converter. Two multilevel converters can be connected in a back-to-back arrangement, and then the combination can be connected to the electrical system in a series-parallel arrangement. <s> BIB003
Besides the three basic multilevel inverter topologies previously discussed, other multilevel converter topologies have been proposed BIB003 , however, most of these are "hybrid" circuits that are combinations of two of the basic multilevel topologies or slight variations to them. Additionally, the combination of multilevel power converters can be designed to match with a specific application based on the basic topologies.  Generalized Multilevel Topology The generalized converter topology called P2 topology proposed by Peng  , as illustrated in Fig. 5 . The basic 2P cell is conjoined in cascade to develop this inverter. The topology can balance each voltage level by itself regardless of load characteristics, active or reactive power conversion and without any assistance from other circuits at any number of levels automatically. Thus, the topology provides a complete multilevel topology that embraces the existing multilevel converters in principle BIB003 ,  .  Mixed-Level Hybrid Multilevel Inverter The configuration has mixed-level hybrid multilevel units because it embeds multilevel cells as the building block of the cascade inverter. To reduce the number of separate DC sources for high-voltage, high-power applications with multilevel inverters, diode-clamped or capacitor-clamped inverters could be used to replace the full-bridge cell in a cascaded inverter. Fig. 6 shows the 9-level cascade inverter integrating a 3-level diode-clamped inverter as the cell BIB003 . The original CHBMI requires four separate DC sources for one phase leg and twelve for a three-phase inverter BIB003 ,  . The advantage of the topology lies in less separate DC sources requirements, while the disadvantage of this topology is the complexity in its control strategy due to its hybrid structure.  Back-To-Back Diode-Clamped Inverter Two multilevel inverters can be connected in a backto-back procedure and then the arrangement can be connected to the electrical system in a series-parallel plan as shown in Fig. 7 . Both the current needed from the utility and the voltage supplied to the load can be controlled at the same time simultaneously. This seriesparallel active power filter has been referred to as a universal power conditioner when used on electrical distribution systems and as a universal power flow controller when applied at the transmission level BIB001 , BIB002 . 