Zero-sequence Signal Injection Research Articles

Pre- and Post-Fault Operations of Six-Phase Electric-Drive-Reconstructed Onboard Charger for Electric Vehicles

The concept of electric-drive-reconstructed onboard charger (EDROC) potentially opens the door to harness the existing drivetrain in electric vehicle (EV) to do the job of battery charger, thus performing a remarkable value in commerce. In this article, the pre- and post-fault operations of an EDROC are studied, which incorporates an asymmetrical six-phase permanent magnet synchronous machine (ASPMSM) drive. At first, the decomposed currents of the machine in healthy and faulty cases are solved and their trajectories are depicted, indicating that a rotating field will exist if an open-phase fault (OPF) occurs. Afterward, a rotating field cancellation scheme based on the minimum copper loss criterion is proposed by rearranging stator currents, with two constraints under consideration that are responsible for generating pulsating field and balanced grid currents, respectively. Following this, a control scheme shared for both pre- and post-fault conditions is proposed, where the carrier-based modulation without any zero-sequence signal injection is employed. Finally, the proposed rotating field cancellation scheme is verified by experimental results.

Carrier-Based Modulated Model Predictive Control Strategy for Three-Phase Two-Level VSIs

The implementation of finite-control-set model predictive control (FCS-MPC) in voltage source inverters (VSIs) can make the system suffer from poor current harmonics performance, which may complicate the design of the required AC filter. To overcome this shortcoming, a carrier-based modulated model predictive control (CB-MMPC) strategy is proposed in this paper. This method enables the utilization of existing PWM modulation techniques with FCS-MPC, where a modulation waveform with zero-sequence signal injection is generated and compared to a triangular carrier wave, while optimizing the selection of the switching states. As it is shown, the studied CB-MMPC strategy not only considerably improves the current total harmonic distortion (THD) but also attains the performance of fast current dynamic response and robustness as the traditional FCS-MPC. Herein, the detailed implementation of the CB-MMPC control strategy is given, while considering its application to the current feedback control loop of a three-phase three-wire two-level VSI modulated at constant switching frequency. Finally, PLECS circuit simulation and a 3-kW VSI prototype are used to verify the superiority and the effectiveness of the presented CB-MMPC strategy. This is also benchmarked to the FCS-MPC and dead-beat based controllers.

Optimal Neutral-Point Voltage Balancing Algorithm for Three-Phase Three-Level Converters With Hybrid Zero-Sequence Signal Injection and Virtual Zero-Level Modulation

This article presents an optimal carrier-based voltage balancing scheme for three-phase three-level converters. The proposed scheme utilizes two available degrees of freedom, i.e., zero-sequence signal injection and virtual zero-level modulation (VZM), to eliminate the low-frequency neutral-point voltage oscillation. It is universally effective over the full power factor and modulation index range and easy to implement in digital controllers. The hybrid algorithm combines the merits of both approaches, which offers the optimal performance regarding controllability, switching device power losses, and output harmonics. The main drawbacks of VZM, i.e., the increased switching loss and high-frequency harmonics due to additional switching transitions, have been minimized in the proposed scheme. The performance of the proposed scheme is evaluated through simulation and experiment.

Topology, Efficiency Analysis, and Control of a Four-Level $\pi$ -Type Converter

This paper provides a comprehensive analysis for a four-level $\pi $ -type converter for low-voltage applications. This topology is a kind of reduced device-count neutral-point-clamped multilevel converter and formed by only six switches in each phase leg. The line (phase-to-phase) output voltage can have seven levels and the output harmonics are much lower than that of a standard two-level converter. The switching states and their associated output voltage levels have been analyzed. A generalized averaged analytical power loss model of this converter has also been developed to investigate the loss distribution among the power devices as well as the efficiency. The four-level $\pi $ -type converter has a higher efficiency when the switching frequency is above 5 kHz compared with two-level and three-level converters with the power devices used in this paper. The reduced output harmonics, hence reduced filtering requirement together with improved efficiency and cooling (heat sink) requirement, offer a higher density alternative to the two-level converter. A simplified level shifted carrier-based modulation method with dynamic optimal zero-sequence signal injection has been employed to modulate the converter and to control dc-link neutral-point voltages. This paper has experimentally validated the predicted four-level $\pi $ -type converter efficiency and the neutral-point voltage balancing control with a back-to-back configuration under high modulation indices and unity power factor. The neutral-point voltage balance region has been plotted and experimentally verified.

Investigation on Zero-Sequence Signal Injection for Improved Harmonic Performance in Split-Phase Induction Motor Drives

In three-phase induction motor drives, addition of certain zero-sequence signal which divides the null vector time equally between the two zero states is known to improve the harmonic performance over sinusoidal modulation. Similarly, in split-phase induction motor (SPIM) drives also, addition of such a zero-sequence signal to each set of three-phase sinusoidal modulating waves leads to reduction in total harmonic distortion (THD) in a motor current. However, the above method known as double zero-sequence injection pulse width modulation (DZIPWM) is significantly inferior to four-dimensional 24-sector space vector pulse width modulation (4D24SEC PWM) in terms of THD. This paper investigates and attempts to determine the zero-sequence signal, if any, whose injection could result in a harmonic performance comparable to that of 4D24SEC PWM. Such a zero-sequence signal is determined and is shown to be quite different from that used in DZIPWM. The analytical findings are used to propose a computationally efficient, carrier-based approach to implement the 4D24SEC PWM, whose implementation is otherwise highly resource intensive. The feasibility, computational efficiency, and accuracy of the proposed approach are demonstrated and validated on a 6-kW split-phase motor drive, controlled from a field programmable gate array platform. This paper enables good harmonic performance of the split-phase drive with low computational effort and resources.