The conventional finite control set-model predictive control (FCS-MPC) suffers from poor robustness against model mismatches. This paper presents an improved FCS-MPC with a reconstructed mathematical ...model to predict current variations without using a lookup table (LUT) or motor parameters. The model coefficients and current variations related to different voltage vectors can be updated during each control period. As a result, the prediction error is significantly reduced at low switching frequency when compared with the prior LUT-based model-free predictive current control (MFPCC). Additionally, the tracking accuracy of the proposed method at high speeds is improved due to the elimination of approximation error. Furthermore, a simple scheme is developed to suppress neutral-point-potential drift without knowledge of the dc-bus capacitor. Simulation and experimental tests, along with comparisons with prior arts carried out on a three-level inverter-fed surface-mounted permanent magnet synchronous motor drive, confirm the superiority of the proposed method.
In order to reduce switching loss of neutral point clamped three-level inverter (NPC TLI), generally discontinuous pulsewidth modulation (DPWM) is used. But it can result in dc offset and ac ripple ...on neutral point (NP) voltage. So a novel pulse sequence DPWM (NPSDPWM) is proposed to reduce switching loss and control NP voltage simultaneously in this paper. NP voltage is controlled by choosing proper clamping modes. To avoid unexpected switching action during changing clamping mode, an improved pulse sequence is also presented. The switching loss and NP voltage ripple of NPSDPWM, traditional and proposed DPWM in previous literature are compared, respectively. The experimental results show that NPSDPWM has well NP voltage control ability and the switching losses are reduced effectively.
Due to the less number of switching devices, a coupled eight-switch converter is an attractive topology for reducing cost in photovoltaic generation systems. Nevertheless, the medium vectors are ...absent in an eight-switch converter compared to the conventional three-level topology, resulting in an undesired performance for leakage current suppression and neutral point voltage (NPV) balancing with existing methods. To overcome such limitations, this article proposes a modulation method without the medium vectors for leakage current suppression and NPV balancing for eight-switch converters. In order to mitigate the leakage current, except for using the low common-mode voltage (CMV) vectors to reduce the amplitude of the CMV, two pairs of sequences are further designed to lower the transitions of the CMV. Simultaneously, the average switching frequency is reduced and the NPV balance can be achieved by changing between sequences. The effectiveness of the proposed method is verified by simulations and experiments.
Summary
In this paper, a three‐phase single‐stage grid‐connected photovoltaic (PV) system with active power filtering capability by means of a three‐level T‐type inverter is presented. The system is ...intended to fulfill many functions: harmonic mitigation, unity power factor operation, maximum power extraction from PV source, and so on. For the proposed system to achieve these tasks with a good dynamic performance, a new control strategy based on the fuzzy logic controller is developed. Fuzzy control has three main stages and each one requires many settings or selection of parameters. A new approach of setting the scaling factors which considerably affect the system's response is proposed. Furthermore, a methodology to properly set the fuzzy rules is suggested. The electrical power chain of the system comprises a farm of a PV source, three‐level T‐type inverter space vector pulse width modulation controlled, inductor filter, non‐linear load, and the utility grid. To evaluate the performance of the proposed control, a processor‐in‐the‐loop is performed as a hardware verification of the inverter control algorithm using a low‐cost STM32F4 discovery board, while the power circuit plant is modeled in the host computer using Matlab/Simulink. The obtained results are very satisfactory and confirm the role of each component, especially in terms of maximum power tracking, power quality, unity power factor operation, and control robustness.
A three‐phase single‐stage grid‐connected photovoltaic (PV) system with active power filtering capability by means of a three‐level T‐type inverter is presented in this work.
The system is intended to fulfill many functions simultaneously: harmonic mitigation, unity power factor operation, maximum power extraction from PV source, and so on.
A processor‐in‐the‐loop was performed to evaluate the performance of the system as a hardware verification of the inverter control algorithm using a low‐cost STM32F4 discovery board, while the power circuit plant is modeled in the host computer using Matlab/Simulink.
This study presents an improved maximum boost control (MBC) method for three-level impedance source inverter. This technique offers removal of sixth frequency component from the inductor current ...present in the existing MBC technique of ZSI (Impedance Source Inverter). In addition, the proposed technique reduces the common mode voltage to 1/6
th
of dc bus voltage. The conventional zero vectors of three-level switching diagram are suitably modified and implemented for the case of 3L-CDBCZSI (three level controlled diode bridge clamped based impedance source inverter). It offers increased switching frequency of impedance network and reduces the size of passive components. On the basis of the proposed technique, the merits offered by 3L-CDBCZSI are highlighted and compared with T-type and diode clamped based ZSI. Simulation and experimental results are presented to verify the correctness of the proposed method.
This study introduces a novel bidirectional hybrid T-type converter configuration named the single-capacitor unit-based hybrid T-type converter (SCU-HTC). This innovative architecture employs a ...single capacitor, leading to a 50% reduction in total capacitor count when compared to conventional T-type inverters. The design operates in two primary modes: buck mode and normal mode. In buck mode, the single capacitor's voltage is maintained at half of the DC link voltage, resulting in lower output voltage magnitude and improved total harmonic distortion. This outcome is distinct from standard T-type inverters. Conversely, during normal mode, the topology functions either as a three-phase two-level inverter or a three-phase three-level inverter. To facilitate seamless operation in both buck and normal modes, a new switching strategy is proposed. This strategy ensures balanced capacitor voltage, enhancing the stability of the DC link voltage. The proposed architecture also exhibits power factor correction (PFC) capabilities. Unlike many PFCs that struggle with maintaining unity power factor (UPF) across various power levels, often necessitating additional circuitry and control complexity, the suggested topology for rectifier mode offers sensor-less self-balancing that consistently upholds UPF. Notably, this topology also effectively addresses issues related to capacitor voltage balance. Experimental validation of the proposed concept underscores its viability.
Capacitor voltage imbalance is a significant problem for three-level inverters. Due to the mid-point modulation of these inverter topologies, the neutral point potential moves up or down depending on ...the neutral point current direction creating imbalanced voltages among the two capacitors. This imbalanced capacitor voltage causes imbalanced voltage stress among the semiconductor devices and causes increase output voltage and current harmonics. This paper introduces a modified voltage balancing strategy using two-level space vector modulation. By decomposing the three-level space vector diagram into two-level space vector diagram and redistributing the dwell times of the two-level zero space vectors, the modified voltage balancing method ensures minimal NP voltage ripple. Compared to the commonly used NP voltage control method (using 3L SVM 9), the proposed modified NP voltage control method offers a slightly higher neutral-point voltage ripple and output voltage harmonics but, it has much lower switching loss, code size and execution time.
Multilevel inverters (MLIs) are playing a pivotal role in the power sector with potential applications, such as interfacing renewable energy sources with the grid and several industrial drive ...applications. MLIs with a smaller number of switching devices are more promising due to their compact size, reduced cost, and higher efficiency compared with their traditional counterparts. This paper, therefore, presents a new three-phase seven-level inverter. This topology is a combination of two cascade-connected two-level voltage-source inverters (VSIs) and H-bridge cells with flying capacitors (FCs). This paper presents the operating principle and the balancing technique for the dc-link capacitors and FCs. The generation of various output voltage levels and the limitation of the sinusoidal pulsewidth modulation control for FC voltage balancing is also presented. The number of components in the proposed circuit configuration and their voltage ratings are considerably lower compared with the recently proposed topologies. The behavior of the proposed circuit configuration is first assessed with simulation studies and is then tested with a laboratory prototype. The simulation and experimental results validate the effectiveness of the proposed topology and the voltage balancing technique.
As a modulation technology for low electromagnetic interference, random pulsewidth modulation has been increasingly applied to inverter power supply for three-phase motors. This article proposes a ...random triangular carrier wave space vector pulse width modulation (RTCW-SVPWM) strategy with dual random parameters, which are subject to a uniform distribution. In this strategy, the shape of the triangular carrier wave changes with random carrier frequency and random pulse center position while the duty cycle of the pulse is the same as that in the conventional SVPWM. 2-D Fourier analysis is used to describe the basic principle of the harmonic dispersion effects in the proposed strategy. The simulation and experimental results show that the dominant harmonics of the output voltage at the integral multiples of the carrier frequency are scattered to their sidebands. Therefore, the prominent harmonic peaks can be greatly attenuated and the harmonics in the high-frequency band are evenly distributed.
Transformerless three-level inverters have many advantages over two-level inverters in photovoltaic (PV) systems. However, in transformerless systems, except for the inherent unbalanced neutral ...voltage of the three-level inverter, the leakage current also needs to be limited strictly. Concerning the defects of the conventional common-mode voltage (CMV) suppression methods, an improved LMSVM (ILMSVM) method is proposed. Unlike the conventional CMV suppression method, the ILMSVM method no longer just abandons the high CMV small vectors to limit the range of CMV to ±1/<inline-formula> <tex-math notation="LaTeX">6U_{\mathrm {dc}} </tex-math></inline-formula>, but limits CMV variation to <inline-formula> <tex-math notation="LaTeX">\Delta 1/6U_{\mathrm {dc}} </tex-math></inline-formula> in all switching cycles. So, high CMV small vectors also can be used in some sequence to help controlling neutral point (NP) while keeping leakage current well suppressed. Moreover, medium vector sequences are also used as an independent control sequence to help achieving bidirectional control on NP potential. Compared with LMP/NSVM strategy, the ILMSVM method has advantages in regulating NP potential, and leakage current spikes of the LMP/NSVM method are also eliminated. In comparison with the conventional SVPWM (CSVPWM) method, leakage current in the ILMSVM method is also well restrained. Simulations and experiment results verify that the ILMSVM method can well restrain leakage current and maintain good control of NP in comparing with LMP/space vector modulation (SVM) method and CSVPWM method.
