An Averaged-Value Model of an Asymmetrical Hybrid Multi-Level Rectifier

Abstract

The development and the validation of an averaged-value mathematical model of an asymmetrical hybrid multi-level rectifier is presented in this work. Such a rectifier is composed of a three-level T-type unidirectional rectifier and of a two-level inverter connected to an open-end winding electrical machine. The T-type rectifier, which supplies the load, operates at quite a low switching frequency in order to minimize inverter power losses. The two-level inverter is instead driven by a standard sinusoidal pulse width modulation (SPWM) technique to suitably shape the input current. The two-level inverter also plays a key role in actively balancing the voltage across the DC bus capacitors of the T-type rectifier, making unnecessary additional circuits. Such an asymmetrical structure achieves a higher efficiency compared to conventional PWM multilevel rectifiers, even considering extra power losses due to the auxiliary inverter. In spite of its advantageous features, the asymmetrical hybrid multi-level rectifier topology is a quite complex system, which requires suitable mathematical tools for control and optimization purposes. This paper intends to be a step in this direction by deriving an averaged-value mathematical model of the whole system, which is validated through comparison with other modeling approaches and experimental results. The paper is mainly focused on applications in the field of electrical power generation; however, the converter structure can be also exploited in a variety of grid-connected applications by replacing the generator with a transformer featuring an open-end secondary winding arrangement.

Multi-Level Open End Windings Multi-Motor Drives

“…Moreover, the main inverter operates at the fundamental frequency in order to achieve low switching power losses, while the active filter is PWM operated. Finally, the DC bus voltage of the two-level inverter is remarkably lower than that of the main inverter [30][31][32][33][34][35][36]. The proposed MMD OW configuration features a higher global efficiency and lower current THD than an equivalent PWM operated multi-level inverter for multi-motor drives [37], exploiting a specific control strategy combining low switching frequency modulation on the MLI and high frequency PWM on the TLI.…”

“…In practice, power devices and motors power losses in the TLI would cause a progressive discharge of the floating capacitor of the TLI DC-bus. Being floating, such a capacitor can only be charged by diverting to it a small quantity of the active power delivered by the MLI to the motors [32][33][34][35][36][37][38][39][40][41][42][43][44]. As shown in the control scheme of Figure 6, this is achieved by slightly modifying the TLI reference voltages.…”

A Polynomial Synthesis Approach to Design and Control an LCL-Filter-Based PWM Rectifier with Extended Functions Validated by SIL Simulations

“…The proposed approach has a significant conceptual advantage over other approaches in that it uses only the linear part of the averaged model to design the LCL filter and tune the controller by concatenating the same polynomial synthesis. On the other hand, most of the existing works use dq transformations, double control loops, or nonlinear controllers, as can be seen in [20]. In straightforward terms, this paper formulates that a fourth-order system is controlled by using the third-order linear part.…”

Multi-Level Multi-Input Converter for Hybrid Renewable Energy Generators

“…A different approach is proposed in this paper, where a particular kind of multipleinput multi-level converter (MMC) is exploited to connect photovoltaic and wind generators to an energy storage system and a three-phase ac grid. It is based on an open-end winding configuration, the asymmetrical hybrid multi-level inverter (AHMLI), whose applications on both motor drives and grid-connected generators are discussed in [22,23] and which has also been successfully exploited to reduce the overvoltage caused by long cables in PWM motor drives [24] as well as to realize a high-speed Gen-set [25,26]. In the present HRES application, the AHMLI topology encompasses an open-end winding three-phase transformer (OWT) whose primary winding operates in an open-end configuration.…”