1936 IEEE TRANSACTIONS ON INDUSTRIAL ELECTRONICS, VOL. 60, NO. 5, MAY 2013 Phase-Disposition PWM Implementation for a Hybrid Multicell Converter Pablo Lezana, Member, IEEE, Roberto Aceitón, and César Silva, Member, IEEE Abstract—Many different topologies based on the multilevel converter approach have been presented in the last decades. In order to obtain improved output waveforms, several modulation techniques have been developed for such converters. Some of those modulation schemes can be directly applied to almost any multilevel converter, while others require significant adaptation in order to be implemented in certain specific converters. This paper presents the implementation of a phase-disposition level-shifted pulsewidth modulation to the recently introduced hybrid multicell converter (HMC). The HMC uses a flying capacitor module on each cell to generate a positive variable dc-link voltage. The variable dc link is inverted at fundamental switching frequency by an H-bridge to generate the cell output voltage. It is desirable to use PD-PWM for its well-known high-performance waveforms. In this paper, a state-machine decoder is developed to balance the floating capacitor voltages and to equalize the supplied power for the series-connected cells of the HMC when using a PD-PWM pattern. Experimental results obtained from a 10-kW prototype are presented, confirming the good-quality waveforms of the HMC modulated with PD-PWM and the adequate balance of all floating capacitors. Index Terms—Hybrid multicell, modulation, multilevel. I. I NTRODUCTION N OWADAYS, multilevel converters are a well-established technology [1]–[3], mostly based on the classical topolo- gies: neutral point clamped [4], cascade multicell [5], [6], and the flying capacitor (FC) [7]. However, in recent years, many new multilevel [8]–[10] and hybrid topologies [11]–[20] have emerged. The hybrid topologies merged two or more classical topolo- gies in order to improve the output waveforms, reduce the number of semiconductors, reduce the losses, reduce the supply requirements, etc. However, the modulation process for these new topologies is not always straightforward as additional considerations about voltage balance, loss distribution, and circulating power must be taken into account [20]–[26]. This work is focused on the modulation of a new hybrid mul- ticell converter (HMC) recently introduced in [15]. This topol- ogy is based on the series connection of macrocells which are composed by an FC converter that generates a variable dc-link voltage and an H-bridge that applies this voltage to the load Manuscript received October 14, 2011; revised April 12, 2012 and September 19, 2012; accepted November 8, 2012. Date of publication November 16, 2012; date of current version January 30, 2013. This work was supported by the Chilean Research Council (CONICYT) under Grant FONDECYT 1100697. P. Lezana and C. Silva are with the Departamento de Ingeniería Eléctrica, Universidad Técnica Federico Santa María, Valparaíso 1680, Chile (e-mail: pablo.lezana@usm.cl; cesar.silva@usm.cl). R. Aceitón is with the Power Electronics Group, Technical University of Dresden, 01069 Dresden, Germany (e-mail: roberto.aceiton@tu-dresden.de). Digital Object Identifier 10.1109/TIE.2012.2228139 with positive or negative polarity. This topology presents some interesting capabilities for medium-voltage applications such as the following: the voltage doubling effect produced by the low- frequency commutated H-bridges and lower losses compared with conventional topologies with similar performances [15]. In [15], the HMC topology is modulated with a simple phase-shifted pulsewidth modulation (PWM) (PS-PWM) scheme, showing that, by using this modulation, the floating capacitor of the HMC topology reaches the balanced operation. Nevertheless, it is well known that benefits are obtained by using phase-disposition PWM (PD-PWM) patterns over PS-PWM [27]. The problem of using PD-PWM directly in the HMC arises from the fact that it does not balance the floating capacitor voltages in FC converters. This problem has been addressed for conventional FC converters in [28] by using a state-machine decoder (SMD) to implement a rotation between the redundant states in order to reach the desired balance while the PD-PWM patterns are applied to the load. In this paper, a solution based on the approach proposed in [28] is developed for the HMC topology. Due to the hybrid na- ture of the converter (multiple macrocells connected in series), additional restrictions related to the power sharing between the cells are identified, which demand that closer attention be paid to the selection of the redundant switching states used by the SMD. It is important to note that, once those considerations have been made in the design of the SMD, its implementation is very similar to that proposed for a conventional FC [28]. Additionally, the use of the SMD allows the output H-bridges of the macrocells to commutate at zero voltage, in a simple and reliable way. A brief description and the main characteristics of the HMC are provided in Section II. Details about the SMD design and the zero voltage commutation (ZVC) scheme are presented in Section III, and finally, experimental results for a 10-kW HMC prototype are presented in Section IV. The experimental results show the voltage balancing capability of the proposed modula- tion and the good quality of the output waveforms produced. II. HMC The HMC is a new modular multilevel topology proposed in [15]. Each macrocell of the HMC is based on the combi- nation of an FC and an H-bridge inverter, as shown in Fig. 1. The converter’s operating principle is based on the multilevel dc-link concept, previously introduced in [14]. The macrocell multilevel dc-link voltage v m is implemented by the FC con- verter, which is handled by the output H-bridge to generate the cell output signal v oc . 0278-0046/$31.00 © 2012 IEEE