Level Modulation Scheme Research Articles

Hybrid-Level Modulation Scheme for Dual-Bridge Series-Resonant Converter

This paper proposes a hybrid level modulation (HLM) scheme to achieve full load range zero voltage switching (ZVS) over various voltage gains for dual-bridge series-resonant converter. According to the load conditions, HLM includes two parts. At heavy load, a variable-frequency symmetrical level modulation (VFSLM) scheme is offered to ensure the complete commutation of the bridge legs with soft-switching operation. In addition, the optimal root mean square (rms) of the inductor current can be achieved, which further benefits the transfer efficiency. At light load, the switching frequency demanded by VFSLM is much higher than the resonant frequency. So, a dual asymmetric level modulation (DALM) scheme is proposed to prevent devices from hard-switching operation within a moderate range of changes in frequency. Furthermore, the method of identifying control variables with DALM is analyzed for overall efficiency optimization. The developed approach is validated on a 6.6kW on-board-charger whose output voltage varies from 220V to 470V.

Selective Harmonic Mitigation Based on Closest Level Modulation Scheme for Cascaded H-Bridge Multilevel Inverter

Multi-inverters have higher quality output waveform as they have lower total harmonic distortion (THD) but the individual harmonics do not satisfy the Grid Code EN 50160 and CIGRE Code WG 36-05. Therefore, mitigation of these individual harmonics is necessary to satisfy the mentioned codes. In this paper, a novel solution for mitigating individual harmonics has been proposed. The proposed harmonic mitigation technique uses nearest level control (NLC) for reducing individual harmonics in a grid-cascaded H-bridge multilevel inverter (CBH-MLI). The proposed technique involves solving simultaneous non-linear equations in real-time. For this, first non-linear equations have been derived and then proposed individual harmonics mitigation techniques are digitally applied for 7-level and 9-level CHB-MLI. The main advantage of the proposed novel technique is that it is easy to implement in real time due to less computational burden and lower complexity. Further, an experimental setup has been developed to validate the simulation results. From the results it is obtained that individual harmonics has been reduced for 7-level and 9-level CHB-MLI.

A single‐source switched‐capacitor based 13‐level sextuple boost inverter with reduced component count and low THD

AbstractA switched‐capacitor‐based 13‐level inverter with a lesser number of components is presented in this article. The 13‐level single‐phase AC output voltage is achieved with a voltage gain of 6 by including a single DC source, 11 switches, 4 capacitors, and 3 diodes in the proposed converter. The self‐voltage balancing is achieved for various types of load without the need for complex control schemes and auxiliary circuits. The proposed topology does not require a back‐end H‐bridge to generate negative polarity. This leads to a reduction in voltage stresses across the switches. Thus, total standing voltage (TSV) and the overall cost of the proposed topology are reduced as compared to the state‐of‐the‐art topologies reported in the literature. Furthermore, an Improved Nearest Level Modulation (INLM) scheme is used to improve the power quality of the output voltage. Using the proposed scheme, the Total Harmonic Distortion (THD) of the output voltage is reduced to 5.08%. The power loss analysis for various elements of the proposed converter is also included. A comparison with recent topologies in reference to various performance parameters is carried out. In addition to the simulation study, a laboratory prototype is prepared to validate the efficacy of the proposed converter.

Power Quality Improvement in Modular Multilevel Inverter Using for Different Multicarrier PWM

Pulse width modulation (PWM) is a powerful technique employed in analog circuit convert with a microprocessor based digital output. Besides, Pseudo Random Multi Carrier (PRMC) involves in two random PWM strategies to minimize the harmonic order for 9- level cascaded multilevel H-bridge (CHB) inverter and 9-level Modular Multilevel inverter are introduced. The design mainly focuses on the (Pulse Width Modulation) PWM method, in which two nearest voltage levels are approached in estimated output voltage prediction based on the Partial swarm optimization (PSO) algorithm, and it conveys a random variation in the pulse position of output by Pseudo Random Multi Carrier- Pulse Width Modulation (PRMC-PWM). The CHB and the Modular inverters generate low distortion output by using PMRC. The simulation and prototype circuit are developed for the nine level output using sixteen switches and ten with Resistive-Inductive (R-L) load variation condition. The power quality is improved in CHB and Modular inverter (MoI) with minimized harmonics in various modulation index (MI) as varied from 0.1 up to 0.8. The circuit is designed by using a Field Programmable Gate Array (FPGA), Implementing a PSO algorithm for both CHB, and MoI are proposed. The comparisons of results are verified with lower order harmonics and find the best switching angle across the MLI switches. Modular inverter furthermore investigates with PRMC, Random Nearest level (RNL) modulation scheme are presented, and the proposed circuit is along with the respective degree of the output voltage were synthesized in non-linear load by the development of reactive power across a motor load.

An Improved Low Switching Frequency Modulation Scheme for a Symmetric CCS-Multilevel Inverter

In this paper, a low switching frequency modulation scheme is proposed for the symmetrical configuration of cross-connected sources-based multilevel inverter (CCS-MLI). The proposed scheme, named modified nearest level modulation (mNLM), is an improvement over the conventional nearest level modulation (NLM) scheme for MLI. The implementation of mNLM, compared to the NLM, has shown a considerable reduction in total harmonic distortion (THD) at the ac output of MLI. The mNLM works through variations in the switching angles of the MLI. By suitably varying the switching angles, the THD content is brought to the minimum. An algorithm for the same is also proposed which enables the mNLM to be implemented on other MLI topologies. Simulation is carried out in MATLAB/Simulink environment and it is also extended to a hardware prototype. The effectiveness of the proposed modulation scheme is also seen in terms of improved inverter parameters such as rms voltage, rms current and generated power.

Online Capacitance Estimation of Submodule Capacitors for Modular Multilevel Converter With Nearest Level Modulation

This letter proposes an online capacitance estimation method for the modular multilevel converter. In the prevalent methods, the inherent second-order circulating current or the injected low-frequency current/voltage component is utilized to calculate the submodule (SM) capacitance. In this letter, the relationship between the voltage variation of an SM capacitor in one fundamental period and the driving signals switching angle under the nearest level modulation scheme is revealed. The voltage variation of each SM capacitor is a direct component and has no relationship with the second-order harmonic current and voltage ripples. Accordingly, an online capacitance estimation method for HVdc applications is proposed by simply monitoring the SM capacitor voltage variations at fundamental frequency. In the proposed scheme, neither the current/voltage injection nor the inherent circulating current is required, which reduces the estimation complexity. The recursive least squares algorithm is also adopted to guarantee the accuracy of the estimation method. Effectiveness of the proposed online capacitor estimation method is verified by the experimental results.

RETRACTED: A modified nearest level modulation scheme for symmetric and asymmetric configurations of cascaded H-bridge inverter

The switching angles play a vital role in varying the total harmonics distortion in the operation of a multilevel inverter. This paper proposes a modified nearest level modulation scheme to be empl...

An Improved Harmonics Mitigation Scheme for a Modular Multilevel Converter

Modular Multilevel Converters (MMC) are gaining importance because of their flexible structure, re-configurable property, and simplicity of operation. The operation of MMC at a low-switching frequency (LSF) helps in enhancing the performance of the converter. This paper proposes an improved harmonics mitigation scheme for a Multilevel DC-Link Inverter (MLDCLI), which is a variant of MMC. The proposed scheme is a modified version of the conventional Nearest Level Modulation (NLM) scheme, termed as modified Nearest Level Modulation (mNLM) Scheme. The proposed scheme is effective compared to NLM because of the choice of the switching angles obtained by the use of the algorithm proposed. The MLDCLI topology is operated for twelve different configurations, and mNLM is implemented on all the configurations. Using MATLAB software, the simulation results are validated, and the same is extended to a hardware prototype. The simulation and experimental results of NLM and mNLM schemes are compared. The effectiveness of the proposed scheme is evident by the reduced voltage THD, increased rms voltage, increased rms current, and increased output power.

A Discrete-Time Low-Frequency-Ratio Nearest Level Modulation Strategy for Modular Multilevel Converters With Small Number of Power Modules

There has been increased usage of modular multilevel converters (MMCs) in the medium-voltage traction drives for increased efficiency and reduced switching losses. One of the disadvantages of utilizing the conventional nearest level modulation (NLM) scheme is the poor performance of output voltage distortion and dynamic response. The control design of low-frequency ratio for the MMC system with a small number of power modules should, therefore, be considered due to the industrial operation requirements. This paper focuses on the voltage state switching mechanism of a discrete-time low-frequency-ratio NLM strategy. A five-segment voltage state allocation guideline based on voltage state smooth transition is analyzed in the discrete-time domain. The proposed strategy features a linearly synthesized output voltage by means of simple arithmetic calculations to determine the switching sequences and the duration times. The overall strategy benefits from reduced dv/dt in the rising/falling edges of the output voltage and the unnecessary switching actions are highly constrained. The simulation analysis and the experimental results validate the proposed modulation strategy and establish its effectiveness.

Uplink Time Scheduling With Power Level Modulation Scheme in Wireless Powered Communication Networks

In this paper, we propose an uplink scheduling scheme via downlink signal design for wireless powered communication networks (WPCNs). Although harvest-then-transmit protocols and related optimal resource allocation problems were studied, explicit methods of transmitting the scheduling information have not been considered in prior works. For uplink scheduling, we propose a design of the downlink energy signal with a power level modulation, which conveys the scheduling information to users. Hybrid-access point allocates different power levels to the subslots of the downlink energy signal, and the users recognize their uplink subslot lengths from their corresponding downlink subslots' power levels. The scheduling can be optimized based on the user channel state with respect to the sum rate. We formulate the sum throughput maximization problem for the proposed scheme, which is shown to be a convex optimization problem. We also study the proposed scheme in a noisy environment. The solution to the problem provides the optimal downlink and uplink slot lengths. The numerical results confirm that the throughput of the proposed WPCN scheme outperforms that of the conventional schemes. The improvement is shown even in imperfect synchronization scenario.

Effect of Higher Level Modulation Schemes on Strictly Bandlimited Intensity Modulated Channels

Effect of Higher Level Modulation Schemes on Strictly Bandlimited Intensity Modulated Channels

SATELLITE TELECOMMAND MODEM

With the increasing interest in nano, micro and small satellites, need arises for miniaturization of satellite systems for small size, low weight, low cost designs and short development periods. For the operation and maintenance of a satellite in the designated orbit, a reliable commanding system is mandatory. This paper presents the work carried out in designing and developing a telecommand modem for use with student satellites. To transmit low bit rate command data, PSK/PM a two level modulation scheme is adopted. The architecture and the simulation and test results of the hardware realized on an FPGA are provided.

Investigation and Analysis of SNR Estimation in OFDM system

Estimation of signal to noise ratio (SNR) of received signal and to transmit the signal effectively for the modern communication system. The performance of existing non-data-aided (NDA) SNR estimation methods are substantially degraded for high level modulation scheme such as M-ary amplitude and phase shift keying (APSK) or quadrature amplitude modulation (QAM).In this paper SNR estimation proposed method which uses zero point auto-correlation of received signal per block and auto/cross- correlation of decision feedback signal in orthogonal frequency division multiplexing (OFDM) system. Proposed method can be studied into two types; Type 1 can estimate SNR by zero point auto-correlation of decision feedback signal based on the second moment property. Type 2 uses both zero point auto-correlation and cross-correlation based on the fourth moment property. In block-by-block reception of OFDM system, these two SNR estimation methods can be possible for the practical implementation due to correlation based the estimation method and they show more stable estimation performance than the earlier SNR estimation methods.

SNR Estimation in OFDM System by the Correlation of Decision Feedback Signal

In the channel-varying environment, it is very important to estimate the signal to noise ratio (SNR) of received signal and to transmit the signal effectively for the modern communication system. The performance of existing non-data-aided SNR estimation methods are substantially degraded for high level modulation scheme such as M-ary amplitude and phase shift keying or quadrature amplitude modulation. In this paper, we propose a SNR estimation method which uses zero point auto-correlation of received signal per block and auto/cross-correlation of decision feedback signal in orthogonal frequency division multiplexing (OFDM) system. Proposed method can be studied into two types; Type 1 can estimate SNR by zero point auto-correlation of decision feedback signal based on the second moment property. Type 2 uses both zero point auto-correlation and cross-correlation based on the fourth moment property. In block-by-block reception of OFDM system, these two SNR estimation methods can be possible for the practical implementation due to correlation based the estimation method and they show more stable estimation performance than the previous SNR estimation methods. Also, we mathematically derive the SNR estimation expression according to computational difference of auto/cross-correlation. Finally, Monte Carlo simulations are used to verify the proposed method.

OFDM 시스템에서 Decision Feedback 신호의 상관 관계를 이용하는 SNR 추정

채널의 상태가 변하는 전송 환경에서 수신된 신호에 대한 잡음비를 추정하여, 보다 효율적으로 신호를 전송하는 것은 현대 통신 시스템에서 중요한 기술이다. 기존 NDA(Non-Data-Aided) SNR 추정 방법은 M진 APSK 또는 같은 고차원 신호의 SNR 추정 성능이 떨어진다. 본 논문에서는 OFDM 시스템에서 블록 단위 수신 신호의 영점 자기 상관과 decision feedback 신호의 자기 상관 및 상호 상관을 이용하는 SNR 추정 방법을 제안한다. 본 논문에서 제안한 방법은 decision feedback 신호의 2차 모멘트인 영점 자기 상관을 이용하여 SNR을 추정하는 Type 1 방식과 4차 모멘트 성질을 갖고 있는 영점 자기 상관과 상호 상관을 이용한 Type 2 방식이다. 이 두가지 SNR 추정 방식은 OFDM 시스템에서 블록 단위 수신을 할 때, 신호의 상관 관계에 기반을 두고 있어 SNR 추정 방법의 실용적인 구현이 가능하게 하고, decision feedback 신호를 사용함으로써 QAM 신호에서도 종전의 SNR 추정 방식들보다 비교적 안정적인 추정 성능을 보인다. 또한, decision feedback 신호를 사용할 때 자기 상관과 상호 상관의 오차에 따른 SNR 추정 식을 수식적으로 유도한다. 그리고 Monte Carlo 시뮬레이션을 통해 제안한 SNR 추정 방법의 성능을 확인한다. In the channel-varying environment, it is very important to estimate the signal to noise ratio(SNR) of received signal and to transmit the signal effectively for the modern communication system. The performance of existing non-data-aided (NDA) SNR estimation methods are substantially degraded for high level modulation scheme such as M-ary APSK or QAM. In this paper, we propose a SNR estimation method which uses zero point auto-correlation of received signal per block and auto-/cross- correlation of decision feedback signal in OFDM system. Proposed method can be studied into two Types; Type 1 can estimate SNR by zero point auto-correlation of decision feedback signal based on the second moment property. Type 2 uses both zero point auto-correlation and cross-correlation based on the fourth moment property. In block-by-block reception of OFDM system, these two SNR estimation methods can be possible for the practical implementation due to correlation based the estimation method and they show more stable estimation performance than the previous SNR estimation methods. Also, we mathematically derive the SNR estimation expression according to computational difference of auto-/cross-correlation. Finally, Monte Carlo simulations are used to verify the proposed method.

Experimental study of the CPT magnetometer worked on atomic energy level modulation

We have set up a coherent population trapping (CPT)-based atomic magnetometer experimental system worked with 87Rb atoms, and with this system experimentally investigated the behaviour of a CPT magnetometer prototype proposed by us, which worked with the atomic energy level modulation scheme. Through systematical comparison with generally used microwave frequency modulation scheme, the experimental results reveal that the energy level modulation scheme not only extends the detection range, but also improves the sensitivity of magnetic field detection.

Enhancement of Data Throughput in the AMC-Employed DS-CDMA Systems through Suppression of Channel Frequency Selectivity by a MTMR Antenna System

SUMMARY In this paper, a new algorithm for MTMR adaptive array antenna (AAA) system combined with analog-type transmit power control (TPC) is proposed for DS-CDMA systems in order to employ high level modulation schemes like 64 QAM in wireless multimedia services. A conventional AAA system considering the strongest path as a target path cannot work effectively when angular dispersion between the strongest path and other delayed paths is large, that is, beam selectivity is so small due to severe frequency selective multipath fading. So, in order to solve such a beam selectivity problem, a beam directivity control scheme using a path manipulation technique is introduced for the BS and MS AAA combining in this paper, along with analog-type TPC. It utilizes virtual delay profiles which are modified from the measured complex delay profile and selects a desired path giving the maximum DUR with an optimized weight vector for BS and MS beamforming. We will show through computer simulation that the proposed scheme is very effective in enhancing the data throughput at the downlink of wideband DS-CDMA systems as compared with the conventional system.

Frequency reuse scheme for cellular OFDM systems

A new frequency reuse scheme for coherent orthogonal frequency division multiplexing (OFDM) cellular systems using high level modulation schemes, whereby both data and pilot parts can have different frequency reuse factors, is described. The capacity increase is investigated by simulations.

Performance analysis of various 16 level modulation schemes under Rayleigh fading

The average bit error rate (BER) performances of 16 square/star QAM and 16 CPSK/DPSK under Rayleigh fading are theoretically analysed and compared. 16 star QAM is inferior to 16 square QAM, which achieves the best performance, by ∼4 dB in the required average Eb/N0; however, when compared with differentially encoded square QAM, the performance inferiority is less than 2 dB.