Improved Modulation Technique Research Articles

An improved modulation technique suitable for a three level flying capacitor multilevel inverter

This research paper introduces an innovative modulation technique for controlling a 3-level flying capacitor multilevel inverter (FCMLI), aiming to streamline the modulation process in contrast to conventional methods. The proposed simplified modulation technique paves the way for more straightforward and efficient control of multilevel inverters, enabling their widespread adoption and integration into modern power electronic systems. Through the amalgamation of sinusoidal pulse width modulation (SPWM) with a high-frequency square wave pulse, this controlling technique attains energy equilibrium across the coupling capacitor. The modulation scheme incorporates a simplified switching pattern and a decreased count of voltage references, thereby simplifying the control algorithm.

Improved Triple-Phase-Shift Modulation for Bidirectional CLLC Converters

CLLC resonant converters are an attractive option for battery charging applications due to their bidirectional power flow and high efficiency. Pulse frequency modulation (PFM) is the simple method to drive CLLC converters. However, PFM cannot regulate the output voltage under the light-load condition properly, which leads to high switching and core losses. Phase shift modulation techniques like dual-phase shift (DPS) modulation can overcome this challenge. However, more improvements are demanded due to high circulating currents in phase shift modulations. In this paper, an improved modulation technique based on triple-phase shift (TPS) has been applied in CLLC converters to improve the light-load efficiency. TPS modulation like any other phase-shift modulation, keeps the switching frequency of CLLC converters fixed at the resonant frequency under the light-load condition and regulates the output voltage by its three phase shift parameters. The improved TPS modulation has lower circulating current at the same average output current compared to DPS modulation. Therefore, higher efficiency, smaller peak, and RMS current values can be achieved under the light-load condition. In addition, the proposed TPS modulation has a better flexibility in regulating the output voltage under the light-load condition due to an extra phase shift parameter compared to DPS modulation. The proposed TPS modulation has been analyzed thoroughly in this paper and a proper selection of phase shift values has been explained to improve the efficiency of the converter. Finally, advantages of the improved TPS modulation have been validated by simulation and a 1 kW experimental setup.

A new single‐phase multilevel inverter with improved modulation technique

SummaryThis article proposes a seventeen‐level (17L) inverter with a common leg configuration and an improved modulation technique. The proposed inverter uses only 10 switches, one toroidal core transformer, and one dc source. Therefore, the proposed design offers less control complexity with reduced cost and volume. Additionally, the suggested modulation technique improves the load voltage quality by minimizing the harmonic content. Simulation and laboratory studies are performed to confirm the proficiency of the suggested inverter with a new modulation technique. Further, a thorough comparison with recent transformer‐based circuits is carried out to highlight the benefits of the proposed structure.

Обзор методов модуляции ближайшего уровня на основе MMC

In view of the relevant situation of offshore wind power research, development and construction at home and abroad, as well as the energy crisis facing the world, we have ushered in a new opportunity and outbreak period for the development of new energy. Therefore, higher requirements are placed on the power supply, and the key technology for the design of offshore wind power flexible DC transmission high-power converters is proposed. The Modular Multi-level Converter (MMC) topology can only use a lower switching frequency to obtain higher power Waveform quality. The output voltage waveform can effectively reduce the switching loss and filter capacity and improve the efficiency and economy of the converter. Among them, the method based on Level Modulation (NLM) is usually the preferred method. This paper introduces the topology and working principle of the modular multilevel converter (MMC) in detail and describes the improved modulation method for NLM in detail. The advantages, disadvantages and application occasions of different improved modulation techniques are summarized, which provides a reference for the engineering application of MMC.

Control Techniques for CRM-Based High-Frequency Soft-Switching Three-Phase Inverter Under Unbalanced Grid Conditions

This article presents control techniques for the critical conduction mode(CRM) based high-frequency soft-switching three-phase inverter under unbalanced grid conditions. The soft-switching technique with silicon carbide (SiC) power devices allows the inverter to operate at hundreds of kHz with high efficiency and high power density. To extend the soft-switching technique to more practical cases, behaviors of the inverter under unbalanced grid conditions, specifically voltage sag, are investigated. During the voltage sag, the ac voltage at the grid becomes unbalanced. This requires unbalanced ac current reference to avoid output active power oscillation. With the unbalanced grid voltage and the ac current reference, the inverter loses the soft-switching capability. Continuous conduction mode (CCM) operation occurs where discontinuous conduction mode (DCM) operation is intended leading to large turn- <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">on</small> loss. To eliminate the CCM issue, two improved modulation techniques are proposed by using <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">off</small> -time extension in the CRM phase and by skipping pulses in the DCM phase. This article discusses how the CCM operation arises and details the proposed control methods. The performance of the proposed control is validated experimentally under a variety of grid imbalance cases with an SiC-based three-phase inverter prototype.

Enhanced Level-Shifted Modulation for a Three-Phase Five-Level Modified Modular Multilevel Converter (MMC)

The rapid growth of the penetration level of renewable energy sources (RESs) in low-voltage (LV) networks increases the research interest in more efficient, compact, reliable, and easily expandable energy conversion systems. The long commutation loops of the existing LV multilevel converters (MLCs), such as active neutral point clamped (ANPC) converters, lead to high-voltage overshoots induced during switching due to the significant parasitic inductance. Modular multilevel converters (MMCs) are gaining an increased interest due to their modularity, flexibility, and short commutation loops also for some LV applications. However, several issues related to the number of components, dc capacitor requirements, and the added complexity need to be considered. This article aims to reduce the five-level modified MMC capacitance requirements where the upper and lower submodules (SMs) are connected in parallel. This reduction has been achieved using an improved modulation technique by minimizing the insertion time of the SMs that require higher capacitance. The proposed modulation is effective in reducing the inner SMs’ capacitor voltage ripple at lower modulation indices. Instead, the circulating current injection of the second harmonics effectively reduces the voltage ripple at higher modulation indices. Thus, maximum reduction in the total capacitance requirement for the entire operating range of modulation index can be achieved by a proper combination of the two solutions. Simulation and experimental results on a laboratory-scaled prototype verify the validity of the proposed solution.

Voltage boosting capability of three phase current source inverter for standalone system

This paper presents a three-phase current source inverter (CSI) topology with voltage boosting capability for standalone system. Current source inverter (CSI) and voltage source inverter (VSI) are two competitive options to be used as an interfacing unit between variable dc input resource and ac output fed into on-grid, off-grid and industrial used. Among the two topologies, VSI is widely used due to its variable controllable output voltage and ability to operate steadily with open loop V/Hz control. Yet, it suffers circuit complexity due to the need of extra converter stage to meet the required output. On the other hand, CSI has an advantage of voltage boosting capability and better quality of output waveshape, thus no extra converter stage is needed. Most of research works were focusing on studying the suitability and practicality of CSI, along with the advancement using silicon carbide-based power switches and improved modulation techniques to minimize the harmonics suffer by CSI. There is lack of research in investigating the boosting capability particularly on how high CSI able to boost the fundamental output and its impact to overall performance in both open and closedloop standalone system. Thus, this work is intended to highlight in detail the boosting capability of CSI and compare with VSI based on the several circuity and operational features. To support the work, three modulators are implemented namely sinusoidal pulse width modulation (SPWM), third harmonic injection PWM (THIPWM) and space vector modulation (SVM). A dedicated synchronous frame proportional-integral (PI) control in used in closed-loop condition. Result shows that CSI topology able to boost the fundamental output voltage by 52% to 58% by using smaller modulation index as compared to VSI. Interestingly, CSI able to achieve comparable quality and harmonic minimization of output voltage and current as in VSI but with smaller PI control gain. All works are analyzed and verified using MATLAB/Simulink platform.

A new generalized cascade multilevel converter topology and its improved modulation technique

SummaryIn this paper, a basic unit for the nine‐level converter is firstly presented. Then, a new developed basic unit topology for the multilevel converter is proposed. This topology comprises several bidirectional and unidirectional switches along with dc voltage sources. In order to increase the number of generated levels, a cascade topology based on the series connection of developed basic units is studied. Due to the extensive nature of the presented cascade multilevel converter, the optimization analysis is presented for generating the maximum number of levels with minimum numbers of IGBTs, drivers, dc voltage sources, and voltage on switches. All required mathematical analysis consisting of switching losses, conduction losses, and voltage on switches is illustrated. In order to indicate the merits of the proposed multilevel converter, comparison results are provided. It is shown that the presented topology uses the least numbers of power electronic components. Also, the voltage on the switches in the presented cascade topology is low. For controlling the switches, a modified triangular carrier signal for dual pulse generation is proposed. The performance of the proposed multilevel converter is proven with experimental results of a typical 25‐level converter.

Improvement in Performance of Series Z-Source Inverter with an Application as Solar PV Fed Water Pump

For a stand-alone solar pump, Z-source inverter (ZSI) is being preferred because of its single-stage power conversion capability with buck-boost ability. As compared to traditional ZSI, series Z-source inverter (SZSI) reduces the voltage stress on capacitor and inrush current of the inductor significantly. In this paper, modes of operation of the SZSI for an induction motor load are explained. When an induction motor runs at a low power factor, an additional mode exists. In this mode, high-magnitude pulses appear on the DC link voltage if the decoupling capacitor is not used with an unidirectional source like solar photovoltaic (PV). In addition, an improved modulation technique is proposed to improve the performance of SZSI. This paper presents a performance of SZSI with solar photovoltaic as a source and an induction motor coupled with the centrifugal pump as a load. Simulation results show the performance of the proposed scheme. Experimental and simulation results demonstrate the validity of analysis. Therefore, SZSI is a promising topology for the solar PV stand-alone system.

PAPR reduction performance of bat algorithm in OFDM systems

The progression in technology requires improved modulation techniques for wideband digital communication systems. Orthogonal frequency division multiplexing is efficacious systems to fulfill high-speed data transmissions needs. However, high peak-to-average power ratio (PAPR) is one of the significant limitations on the performance and power efficiency of OFDM systems. Due to industrial and scientific relevance, the assessment of the PAPR reduction has become popular subject in the current decade. This study presents the combination of bat algorithm with partial transmit sequence scheme as an efficient PAPR reduction method with an alleviated computational load. A set of simulations with different partial transmit sequence schemes are performed to comparatively evaluate the PAPR reduction performance of the partial transmit sequence based on bat algorithm scheme in OFDM system. The simulation results elucidate that BA-PTS scheme can provides better PAPR reduction performance with less computational load.

Suppression of residual intensity modulation induced error in resonator fiber optic gyroscopes with improved modulation technique

The carrier-suppressed phase modulation effectively suppresses backscattering induced noise in resonator fiber optic gyroscopes (RFOGs), but also introduces residual intensity modulation (RIM) induced error when determining the resonance line center. This paper proposes an improved modulation technique to suppress backscattering induced noise while reducing the zero offset induced by the RIM effect on the demodulation curve. The improved modulation technique is that the left and right working points are periodically located at the source frequency by the PZT to obtain the output signal of the RFOG, and the light waves are modulated by a triangular wave with the Y-branch modulator without demodulation. Theoretical analysis shows that the improved modulation technique can effectively reduce the RIM induced error. The experimental results show that the improved modulation technique can effectively suppress the backscattering induced noise while reducing the RIM induced error, and a gyro bias stability of 56°/h has been carried out.

An Improved Modulation Technique With Minimum Switching Actions Within One PWM Cycle for Open-End Winding PMSM System With Isolated DC Bus

Due to the application of dual inverters in the structure of open-end winding permanent-magnet synchronous machine system with isolated dc bus, the double number of switching devices are employed and thus the switching actions within one pulsewidth modulation (PWM) period are relatively high. To reduce the switching actions, an improved modulation technique is proposed in this letter. In the proposed technique, the reference voltages in the synchronous coordinate system are transferred to the three-phase stationary frame through Park transformation and thus the duration time corresponding to the three-phase windings can be directly obtained. On this basis, by synchronously adjusting the duration time of three phases, the maximum one can be adjusted to be the control period while their resultant voltage remains constant. Furthermore, the switching actions are assigned to the switching devices based on the polarity of duration time for each phase, with the principle of keeping the switching device on one side clamped. The novelty of the proposed technique is that it can be universally applied to minimize the number of switching actions within one PWM cycle for any kind of voltage ratio of the system without sector identification. The experimental validation of the proposed scheme is given to validate its effectiveness.

Single‐phase hybrid‐H6 transformerless PV grid‐tied inverter

Transformerless inverter for grid-tied photovoltaic (PV) system has been widely used due to lower cost, higher efficiency and lighter weight. Various transformerless inverter topologies have been proposed to meet the safety requirement of low leakage current and obtain the reactive power capability. To get better performance, a novel transformerless hybrid-H6 inverter with an improved modulation technique is proposed in this study. By adopting the improved modulation technique, two symmetry paths are realised to share the current during the freewheeling mode. Thus, without paralleling any additional capacitors to the switch, the inverter can reduce the influence of junction capacitance on common mode voltage naturally which results in mitigating the leakage current issue. Thanks to the dead time reduction through the improved modulation, the qualities of output waveforms are improved. Moreover, reactive power control is achieved without any modification of the inverter structure. Finally, a 1 kW prototype is simulated and tested to verify the theoretical analysis of this study. Not only the reactive power capability is obtained for the proposed inverter, but also the small common mode voltage fluctuation is achieved at the same time. In addition, the total harmonic distortion of the current is decreased by more than 1.7%.

Improved modulation strategy for single phase grid connected transformerless PV inverter topologies with reactive power generation capability

In this study, several recently published topologies are analyzed for reactive power generation capability. It has been found that some of the topologies with their conventional modulation strategies are not suitable for reactive power applications. These are not able to generate zero voltage states during negative power flow. As a result, current is distorted and PV inverter injects current with high total harmonic distortion (THD) into the grid. In order to overcome these problems, modified modulation technique is proposed to achieve reactive power capability without having distortion in injected grid current. It provides path for current to flow in order to generate zero voltage states during negative power flow. With improved modulation strategies, reactive power generation is achieved in inverter topologies without any alteration on the converter structures. The controller software of these topologies is only required to be updated for reactive power generation. The implementation and generation of the proposed improved modulation techniques are straightforward and it can easily be realized. Moreover, single phase transformerless inverter topologies are classified for first time on the basis of reactive power handling capability. In order to verify the theoretical explanations, simulations have been carried out in Matlab/Simulink environment and validated through an experimental setup.

New Multilevel Converter Based on Cascade Connection of Double Flying Capacitor Multicell Converters and Its Improved Modulation Technique

This paper proposes a new multilevel converter based on the cascade connection of double flying capacitor multicell (DFCM) converters, as multilevel modules, to decrease the voltage diversity of the flying capacitors. Furthermore, a new switching pattern based on the phase-shifted pulse-width modulation technique is proposed to reduce the voltage ripple across the flying capacitors. Moreover, the proposed modulation technique reduces the rms value of the current flowing through flying capacitors. This results in an increase in the life time of flying capacitors and a decrease in the capacitance of the flying capacitors, to keep the same amount of the ripple, meaning a reduction in the physical size of the converter. In addition, this paper presents an analytical approach to calculate the average and rms currents of the insulated gate bipolar transistors (IGBTs)/diodes in the DFCM converter in a closed-form expression. The derived closed-form equations to calculate the average and rms currents of the IGBTs/diodes are utilized to investigate the conduction power losses in a DFCM converter and the proposed multilevel converter. Numerical results of the derived closed-form equations match the simulation results well, which validates the derived equations. Furthermore, simulation results and experimental measurements of the proposed multilevel power converter, configured by cascading two two-cell five-level DFCM converters, are presented to validate the performance of the proposed converter as well as the suggested modulation technique.

New control method of a robust NPC converter for renewable energy sources grid connection

This paper presents a new control strategy for the three-level, neutral point clamped (NPC), voltage source converter. The converter can be used in many high-power renewable energy systems such as direct drive wind turbines and hybrid generating units. The developed control algorithm proposes an improved solution to balance DC bus intermediate voltages using space vector modulation (SVM) techniques. It aims to guarantee fault ride-through (FRT) capabilities of renewable energy plants equipped with multilevel converters. Since the main attention of this paper is the grid side converter control, the energy generating system was simplified to an equivalent variable current source. The grid side converter is connected to the grid through an LCL filter. Two controllers were developed to achieve grid currents regulation. The first controller is based on PI-regulation. In the second case, linear quadratic Gaussian (LQG) control is investigated. The control of DC bus voltage is achieved by PI-regulation. Performances of the two controllers and the improved modulation technique are compared and evaluated in terms of accordance with the grid connection requirements (GCR) including, low voltage ride-through capabilities, frequency variation and reactive power control.

A New Lighting Communication System for Audio Signal with White LED

Light Emitting Diode (LED) is expected as the lighting source of next generation because they are long life, small size, and low power consumption, etc. In previous paper, we proposed a simple visible-light transmission system for sound using white LED. However, the flicker of light is sensed if the transmitted sound signal has the low frequency component. In this study, we propose improved modulation technique to overcome the flicker. LED can transmit audio signal while it is used for lighting source. We verified that it is possible to communicate with the received luminous flux of 1.1×10-5 lm without flicker. We also evaluated the effects of interference by plural LEDs.

Improved modulation techniques for wireless communications: raised cosine filtered FQPSK-FQPSK(RC)

An improved spectrally efficient modem scheme is proposed for wireless communications. This new scheme is based on nonlinear base band processor, with additional filtering to reduced the spectral spreading. Its spectral efficiency is improved up to 20%, comparing with GMSK. Additional filtering is a square root of raised cosine filter with a varying between 0.2 and 0.5. The performance of this technique has been evaluated in both AWGN and Rayleigh fading channels. This new spectral efficient modem is as robust as GMSK in interference limited fading environment and increases the capacity 20%.

Improved modulation techniques for PWM-VSI drives

PWM-VSI based AC motor drives have two main problems. The inverter is nonlinear which causes instability problems in some specific working points of the AC machine and it emits acoustic noise due to the switching frequency. Nonlinearities like dead-time in the inverter, load dependent DC-link voltage ripple and the voltage drop across the switches are modeled and compensated by improved modulation techniques in order to obtain an almost ideal inverter. Different feedback and feedforward techniques are proposed. The acoustic noise is reduced by using a random modulation strategy. Measurements show a significant improvement by using feedforward and feedback techniques for linearizing the inverter. An improvement in reduction of the acoustic noise emission is also achieved by using random modulation. It is concluded that a combination of a random modulation strategy and feedforward/feedback techniques gives an almost ideal AC motor drive system.

The development of a real-time waveform generation and capture system for the evaluation of modulation schemes on satellite links

The performance of a satellite communications link is largely defined by the modulation and forward error correction coding scheme used. The ultimate performance is defined by the theoretical Shannon capacity but practical schemes currently fall far short of this limit. To aid the search for improved modulation techniques, a test facility has been developed which will allow potentially advantageous schemes to be evaluated via a satellite link, without the need to develop dedicated modem hardware. The facility has been constructed using a virtual memory computer which handles the generation and capture of analogue waveforms in real time. The generalized design allows the transfer function of a satellite channel with a bandwidth up to 200 kHz to be assessed and so provides for the testing of an arbitrary waveform modulation scheme within this bandwidth limit.