Direct Torque and Predictive Control Strategies in Nine-Phase Electric Drives Using Virtual Voltage Vectors

Abstract

One of the main distinctive features of multiphase machines is the appearance of new degrees of freedom (voltages/currents) that do not exist in their three-phase counterparts. As a direct consequence, control approaches that apply a single switching state during the sampling period cannot achieve zero average-voltage production. In direct torque control (DTC) this implies that-currents are not regulated, whereas in finite-control-set model predictive control (FCS-MPC) an enhanced-current regulation is feasible only at the expense of disturbing the flux/torque production. Aiming to avoid these shortcomings, this work makes use of the concept of synthetic/virtual voltage vectors (VVs) to nullify/limit the-voltage production in order to improve the current regulation in the secondary planes. Two strategies using two and four virtual voltage vectors (2-VV and 4-VV, respectively) are proposed and compared with the standard case that applies a single switching state. Since standard MPC has the capability to indirectly regulatecurrents, the improvements with the inclusion of VVs are expected to be more significant in DTC strategies. Experimental results validate the proposed VVs and confirm the expectations through a detailed performance comparison of standard, 2-VV and 4-VV approaches for DTC and MPC strategies.

Recent Advances in Model Predictive and Sliding Mode Current Control Techniques of Multiphase Induction Machines

“…Fortunately, the implementation of multivector solutions (Gonzalez-Prieto et al, 2018;Xue et al, 2018;Luo and Liu, 2019;Ayala et al, 2020;Gonzalez-Prieto et al, 2020;Aciego et al, 2021;Ayala et al, 2021b;Gonçalves et al, 2021), such as synthesized or virtual voltage vectors (Gonzalez-Prieto et al, 2018;Garcia-Entrambasaguas et al, 2019;, has permitted the minimization of the aforementioned harmonic injection thanks to the use of control actions formed by several switching states per sampling period. To take advantage of MPC features for multiphase electric drives, a significant number of researchers have promoted the development of more competitive multi-vector alternatives (Gonzalez-Prieto et al, 2018;Xue et al, 2018;Garcia-Entrambasaguas et al, 2019;Luo and Liu, 2019;Gonzalez-Prieto et al, 2020;Aciego et al, 2021;Ayala et al, 2021b;Gonçalves et al, 2021), providing phase current with low harmonic content. As a consequence of the evolution of the multi-vector approach, MPC has been able to be reformulated in electric drive regulation techniques (Tenconi et al, 2018).…”

Predictive current control in electrical drives: an illustrated review with case examples using a five‐phase induction motor drive with distributed windings

“…Most of the research work in the field of DTC is applied to five‐ and six‐phase machines, but a recent work aims to extend the method to a higher number of phases [64, 65]. Furthermore, the fault‐tolerant capability of the DTC has been recently addressed for a five‐phase IM drive.…”

Switching-Table-Based Direct Torque Control of Six-Phase Drives With $x-y$ Current Regulation

“…The slow dynamic behavior of the modulation-based DTC is mainly due to PI regulators, which has been investigated by a hybrid two-mode DTC scheme [12]. However, the complexity of the modulationbased DTC schemes, especially for multi-phase drives, has stimulated a prolific research work to tackle the problems of ST-DTC strategy [13]- [22].…”

“…Definition of VVs is a core idea to decrease unwanted stator current harmonics due to uncontrolled x − y subspaces in multi-phase drives, where the VVs are firstly constructed using appropriate actual voltage vectors, then, their duty ratios are calculated offline in such a way that the average volt-seconds in the secondary subspaces to be zero. This context has been frequently highlighted for the non-modulation-based control techniques, i.e., ST-DTC strategy [13]- [22] and FCS-MPC strategy [22], [23]. In this regard, VVs have been synthesized for three-level and two-level VSIs-fed five-phase induction machine in [13] and [14], respectively.…”

“…Such ST-DTC schemes with a modified three-level [17] and five-level [18] hysteresis torque regulators as well as rearranged VVs, to provide a simpler realization, have been addressed for six-phase permanent magnet synchronous machine. Forming VVs for ST-DTC of seven-phase and nine-phase machines has been reported in [21] and [22], respectively. Despite an inevitable decrease in dclink utilization and increase in average switching frequency as consequences of using several actual voltage vectors within every sampling period, ST-DTC and FCS-MPC benefit greatly from VVs in terms of lower harmonic content of the stator currents compared with actual voltage vectors.…”