Switching Frequency Effects on the Efficiency and Harmonic Distortion in a Three-Phase Five-Level CHBMI Prototype with Multicarrier PWM Schemes: Experimental Analysis

The current climatic scenario requires the use of innovative solutions to increase the production of electricity from renewable energy sources. Multilevel Power Inverters are a promising solution to improve the penetration of renewable energy sources into the electrical grid. Moreover, the performance of MPIs is a function of the modulation strategy employed and of its features (modulation index and switching frequency). This paper presents an extended and experimental analysis of three-phase five-level Cascaded H-Bridges Multilevel Inverter performance in terms of efficiency and harmonic content considering several MC PWM modulation strategies. In detail, the CHBMI performance is analyzed by varying the modulation index and the switching frequency. For control purposes, the NI System On Module sbRIO-9651 control board, a dedicated FPGA-based control board for power electronics and drive applications programmable in the LabVIEW environment, is used. The paper describes the modulation strategies implementation, the test bench set-up, and the experimental investigations carried out. The results obtained in terms of Total Harmonic Distorsion (THD) and efficiency are analyzed, compared, and discussed.

Generic Analysis Framework for Modular Multilevel Converter HVDC with Multi-Infeed Line-Commutated Converter HVDC System

This paper proposes a generic analysis framework for a grid supporting modular multilevel converter (MMC)-high voltage DC (HVDC) in a multi-infeed of line commutated converter (LCC) and MMC (MILM) system. MMC-HVDC can support the grid by compensating for the exact reactive power consumptions within the MMC-HVDC system and the varying power system conditions in the MILM system. Maximum active/reactive power capability (MPQC) curve and PQ loading curve comparison process is introduced to properly design a grid supporting MMC-HVDC. While the MPQC curve presents the maximum PQ range of the MMC-HVDC system based on the submodule capacitance value and the modulation index, the PQ loading curve presents the reactive power requirement from the power system that MMC-HVDC needs to compensate. Finally, the comparison of these two curves yields the proper value of submodule capacitance and the modulation index for sufficiently supporting the MILM system. The proposed framework is validated with detailed PSCAD/EMTDC simulation; it demonstrated that it could be applied to various power system conditions.

Modulation Technique for Modified Active Quasi-Z-Source Inverter with Common-Mode Voltage Reduction

In Z-source topologies, a high-amplitude common-mode voltage can occur when shoot-through states are inserted. In this study, a new space vector pulse-width modulation for an active quasi-Z-source topology is proposed to operate at a high modulation index and reduce the common-mode voltage to one-third of the DC-link voltage. Moreover, the quality of the output voltage is improved by operation with a high modulation index and decreasing the switching loss of the H-bridge switches. The detailed operating principles of the active quasi-Z-source topology using the proposed space vector modulation (SVM) method are presented. A simulation model was built, and an experimental prototype was verified to correct the theoretical analysis.

Large Tunable 16-Tupled Millimeter Wave Generation Utilizing Optical Carrier Suppression With a Tunable Sideband Suppression Ratio

Coping up with the rising bandwidth demands for 5G ultra-high speed applications, utilizing millimeter (MM) wave spectrum for data transmission over the radio over a fiber-based system is the ideal approach. In this study, a highly conversant and spectrally pure photonic generation of a 16-tupled MM wave signal using a series-connected DD-MZM with a lower modulation index, a splitting ratio, and a wider tunable range is presented. A 160-GHz MM wave is generated through a double sideband optical carrier suppression technique having an optical sideband suppression ratio (OSSR) of 69 dB and a radio frequency sideband suppression ratio (RSSR) of 40 dB. However, the OSSR and the RSSR are tunable with values greater than 15 dB when the modulation index (M.I.) varies from 2.778 to 2.873, ±8° phase drift, and a 15-dB enhancement in the OSSR with a wider nonideal parameter variation range giving acceptable performance can be seen in the model as compared with previous research works.

Three-Level Unidirectional Rectifiers under Non-Unity Power Factor Operation and Unbalanced Split DC-Link Loading: Analytical and Experimental Assessment

Three-phase three-level unidirectional rectifiers are among the most adopted topologies for general active rectification, achieving an excellent compromise between cost, complexity and overall performance. The unidirectional nature of these rectifiers negatively affects their operation, e.g., distorting the input currents around the zero-crossings, limiting the maximum converter-side displacement power factor, reducing the split DC-link mid-point current capability and limiting the converter ability to compensate the low-frequency DC-link mid-point voltage oscillation. In particular, the rectifier operation under non-unity power factor and/or under constant zero-sequence voltage injection (i.e., when unbalanced split DC-link loading occurs) typically yields large and uncontrolled input current distortion, effectively limiting the acceptable operating region of the converter. Although high bandwidth current control loops and enhanced phase current sampling strategies may improve the rectifier input current distortion, especially at light load, these approaches lose effectiveness when significant phase-shift between voltage and current is required and/or a constant zero-sequence voltage must be injected. Therefore, this paper proposes a complete analysis and performance assessment of three-level unidirectional rectifiers under non-unity power factor operation and unbalanced split DC-link loading. First, the theoretical operating limits of the converter in terms of zero-sequence voltage, modulation index, power factor angle, maximum DC-link mid-point current and minimum DC-link mid-point charge ripple are derived. Leveraging the derived zero-sequence voltage limits, a unified carrier-based pulse-width modulation (PWM) approach enabling the undistorted operation of the rectifier in all feasible operating conditions is thus proposed. Moreover, novel analytical expressions defining the maximum rectifier mid-point current capability and the minimum peak-to-peak DC-link mid-point charge ripple as functions of both modulation index and power factor angle are derived, the latter enabling a straightforward sizing of the split DC-link capacitors. The theoretical analysis is verified on a 30 kW, 20 kHz T-type rectifier prototype, designed for electric vehicle ultra-fast battery charging. The input phase current distortion, the maximum mid-point current capability and the minimum mid-point charge ripple are experimentally assessed across all rectifier operating points, showing excellent performance and accurate agreement with the analytical predictions.

The Three-Carrier Quasi Switched Boost Inverter Control Technique

This paper presents a carrier modulation technique to control the three-phase, two-level quasi switched boost inverter. This PWM algorithm uses three carrier waves, the first of which is for the inverter while the others are for the booster. The boost factor depends on the short circuit interval on the DC/DC booster and the inverter. When the short circuit interval on the DC boost is twice that on the inverter, the modulation index can be enlarged. The new algorithm is analyzed, calculated, simulated, and tested. The analysis and calculation results show that the proposed technique can reduce the voltage on the DC link capacitor compared to a conventional approach. It can reach 22.16% when the ratio of the DC source voltage to the effective reference voltage is 0.5. The modulation index can extend to 29% under these conditions and the current ripple in the boost inductor can be reduced by 4.8%. The simulation and experimental results also show similarities, thereby confirming the analysis and calculation.