IEEE TRANSACTIONS ON INDUSTRIAL ELECTRONICS, VOL. 54, NO. 2, APRIL 2007 733 Zero-Steady-State-Error Input-Current Controller for Regenerative Multilevel Converters Based on Single-Phase Cells Pablo Lezana, Member, IEEE, César A. Silva, Member, IEEE, José Rodríguez, Senior Member, IEEE, and Marcelo A. Pérez, Member, IEEE Abstract—Multicell converters are one of the alternative topolo- gies for medium-voltage industrial drives. For an application requiring regenerative capability, each power cell must be con- structed with a three- or single-phase pulsewidth-modulation (PWM) rectifier as front end. The choice of single-phase PWM rectifiers for the input of the cells results in a reduced number of power switches and a simpler input transformer than the three- phase equivalent. However, its control is not as straightforward. This paper proposes the use of higher order resonant controllers in the classical control structure of the single-phase PWM rectifier. This ensures zero steady-state tracking error of the reference cur- rent at fundamental frequency. A detailed description of the design criteria for the position of the zeros and poles of the controller is given. Experimental results showing the good performance of the single-phase input cells and its proposed control are included. Index Terms—Multilevel converter, pulsewidth-modulation (PWM) rectifiers, resonant controller. I. I NTRODUCTION T HE use of medium-voltage variable-speed drives based on voltage-source converters has become increasingly wide- spread in the last ten years. A wealth of multilevel topologies has been developed to achieve the medium-voltage range using available semiconductors [principally, the insulated-gate bipo- lar transistor (IGBT)] [1]. These topologies also allow for lower distortion of the output ac voltage of the converter. One of the alternatives of multilevel topologies is known as a multicell converter [2] and is based on the series connection of several single-phase inverters per output phase. The classical multicell converter [2], using diodes to obtain a dc-link voltage of each output inverter, is not able to regenerate power from the load. To achieve regeneration, the use of three- and single-phase pulsewidth-modulation (PWM) rectifiers has been proposed [3], [4]. These PWM rectifiers produce good- Manuscript received January 21, 2006; revised December 18, 2006. Abstract published on the Internet January 14, 2007. This work was supported in part by the Universidad Técnica Federico Santa María, in part by the Chilean Research Council (Conicyt) under Grant Fondecyt 1050357, in part by the Millennium Nucleus on Industrial Electronics and Mechatronics P04048-F (MIDEPLAN), and in part by the postgraduate support program of the Fundación Andes under Grant C-14055. The authors are with the Departamento de Electrónica, Universidad Técnica Federico Santa María, 239-0123 Valparaíso, Chile (e-mail: pablo.lezana@ usm.cl; cesar.silva@usm.cl; jrp@elo.utfsm.cl; marcelo.perez@usm.cl). Digital Object Identifier 10.1109/TIE.2007.891994 quality input-current waveforms in addition to their regenera- tive capability; this allows operation at high power factor (very near unity). The use of the three-phase PWM rectifier as the front end of the cells has some operational advantages but requires more semiconductors, sensors, and a more complex input transformer than the single-phase alternative. Another important difference between the three- and single- phase front-end alternatives is the way in which the current con- trol is implemented. In three-phase PWM rectifiers, the current control is normally performed in a synchronous rotating frame, converting measured ac currents into dc values. This allows the use of conventional proportional–integral (PI) controllers for the current control, achieving zero stationary error [5]. This technique is not directly applicable in single-phase systems, resulting in steady-state reference tracking error if PI current controllers are used. This tracking error affects the current amplitude and phase, deteriorating the power factor. The use of resonant controllers in stationary frames have been proposed for the control of ac currents with zero steady- state tracking error [6]–[8]. In [6], a proportional + pure resonant element is proposed for current control of three- and single-phase PWM rectifiers. In [7], the derivation of a resonant controller through the frequency transformation of a standard PI controller is proposed for current control of inverters. Both techniques result in infinite controller gain at the resonant fre- quency, hence achieving zero steady-state current tracking error at this frequency without coordinate rotations. Nevertheless, in both cases, the proposed resonant controllers are somehow derived from PI structures, resulting in restrictions on the zero locations, and fail to take full advantage of the design flexibility of resonant biproper controllers. This paper proposes new controller designs for the single- phase voltage PWM rectifiers of a multicell inverter for the classical cascade control structure. These controller designs consist of a resonant biproper controller for the inner current loop with unrestricted zero locations and an external voltage loop closed with a modified PI. The voltage controller includes the dc-link voltage filter to give a clean sinusoidal reference for the inner current loop. This configuration ensures a good- quality input-current waveform and, hence, high-power-factor operation. A detailed discussion of the controller design criteria and experimental results that shows their good performance is presented. 0278-0046/$25.00 © 2007 IEEE