Improved Modulation Scheme Research Articles

An Improved Modulation Scheme of Isolated Matrix Converter for Common-Mode Voltage Reduction and DC-Bias Current Mitigation

In this paper, an optimized space vector modulation (SVM) method is proposed for the isolated three-phase matrix-type AC/DC converter, where the four-quadrant operation ability of the bidirectional power switch can be fully used. The primary-side transformer current can be eliminated naturally during zero current vectors without extra switching actions. Therefore, the conduction loss of matrix converter (MC) is reduced and the efficiency can be increased. Moreover, the proposed method can avoid the shoot-through operation in MC, and the common-mode voltage can be mitigated effectively. As the zero current vector is kept with the proposed modulation strategy, the current harmonics will not be increased. Thirdly, both the DC-link inductor current and DC-bias current of high-frequency transformer (HFT) are measured through the secondary-side current of HFT. Therefore, the DC-bias current and the saturation of HFT are avoided by closed-loop control with the proposed modulation strategy. The experiments have been carried on a 1-kW laboratory prototype to verify the validity of the proposed modulation scheme.

An Improved Modulation Scheme With Better Performance for Open-Winding Permanent Magnet Synchronous Motors Drives

In order to improve the performance of voltage synthesis of the open-winding permanent magnet synchronous motors (OW-PMSMs) with isolated DC bus when the voltages of two power supplies are not equal, an innovative voltage modulation method is proposed. The novel method is based on the conventional alternate sub-hexagonal center PWM method, but the low-voltage powered inverter is kept at low-potential clamped state throughout a period instead of having the two inverters clamped alternately. In this way, the high-voltage powered inverter expands the range of voltage synthesis, making up for the deviation between the synthesized voltage and the voltage reference when the high-voltage powered inverter is clamped and the low-voltage powered inverter modulates individually. Therefore, compared with the traditional method, a larger total voltage synthesis range is covered so that the capability of voltage synthesis is enhanced, thereby improving the quality of the corresponding torque and the output current. The simulation and experimental validations are presented to certify the effectiveness of the proposed method under different conditions, and the results prove that the new method indeed improves the current performance and reduces torque ripples.

Harmonic Current Control of OW-PMSM for Low-Voltage Traction by Nonlinear Disturbance Rejection With Improved Modulation Scheme

The open-winding permanent magnet synchronous motor (OW-PMSM) has been developed, mostly potential for low-voltage traction in electric vehicles. Yet, both the disturbance from vehicle system under driving and the motor with low-reactance (LR) feature expose the limits of traditional controllers that are prone to great current harmonics. Therefore, the current control for LR OW-PMSM becomes challenging. The main objective of this research is to provide a current harmonic control strategy for LR OW-PMSM by the nonlinear lumped disturbance observer (NLDO) combined with improved space vector modulation (SVM) scheme. The existence of nonlinear, unknown, unmodeled factors has been confirmed by current measurement and harmonic analysis in full operation range, and thus is considered in proposed controllers. The NLDO is designed for all the three axes under the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">dq</i> 0 frame. The SVM algorithm is adjusted to two switching patterns in order to get widened linear voltage modulation range. In addition, in the 3-D voltage space is the possible modulation area investigated. Ultimately, the target LR OW-PMSM has been designed, prototyped, and tested. The proposed NLDO, juxtaposed with ordinary PI and deadbeat controllers, reduces current harmonics on both the motor and inverter sides, possesses high robustness, and is practical for LR motors, according to experimental results.

Simple and Seamless PWM Scheme of Isolated Bidirectional AC–DC Converter for Reducing Voltage Spike

This article proposes an improved modulation scheme based on unipolar sinusoidal pulsewidth modulation for a single-phase single-stage isolated bidirectional ac&#x2013;dc converter. A direct ac&#x2013;ac conversion system connected with a high-frequency transformer typically suffers from high-voltage spikes because of the leakage inductors of the high-frequency transformer and the grid filter inductors, resulting in reduced reliability and large power losses. The proposed modulation scheme can eliminate the high-voltage spikes in bidirectional power flow without the use of additional circuits while realizing zero-voltage switching. In addition, because the proposed method does not require individual gate control of the bidirectional power switches, the generation of gate signals can be simplified using the proposed modulation scheme. A simulation model and a 1.2 kW grid-connected ac&#x2013;dc converter based on silicon-carbide metal&#x2013;oxide&#x2013;semiconductor field-effect transistors are implemented to validate the effectiveness of the proposed modulation scheme.

Common-Mode Voltage Suppression Technique for Open-End Winding PMSM System With Five Bridge Arms

To further improve the reliability of the open-end winding permanent magnet synchronous motor (OW-PMSM) and avoid the secondary damage caused by the common-mode voltage (CMV) in the event of bridge-arm failure, a CMV suppression technique is proposed. With the proposed technique, the reference voltages in three-phase stationary coordinate system are optimized to adapt the characteristics of OW-PMSM with five bridge arms. Further, an improved modulation scheme is proposed, in which the CMV is suppressed and the switching actions within every control cycle is reduced. The effectiveness of the proposed technique is validated through experimental results.

Security improved duobinary optical communication scheme through bio‐inspired chaos masking scheme

In optical fibre communication system, improved modulation schemes have been proposed to increase capability and high bit rate transmission. One such technique is optical duobinary modulation, which can able to broadcast high-speed optical signals over bandwidth-limited channels. The conventional modulation schemes employ the non-return-to-zero modulation and return-to-zero modulation technique. These schemes decrease spectrum width and increase the dispersion tolerance. However, the effect of inter-symbol inference presents between the pulses. These techniques give a reduced performance for high bit rate transmissions and transmission over long distances. Hence in this work, the implementation of duobinary modulation improves the performance of optical communication along with the provision of enhanced security through bio-inspired chaos masking scheme. The bio-inspired chaos-masking scheme generates the security key using the spider security pattern generator to provide improved security. The parameters of the proposed technique are analysed for different transmission rates and the performance improvement is validated.

Improved Modulation Schemes for Lattice-Partition-Based Downlink Non-Orthogonal Multiple Access Systems

This letter proposes alternative modulation schemes for a two-user lattice-partition-based non-orthogonal multiple access (NOMA) system, where the NOMA transmission signal is composed of four elements from four amplitude-level groups, respectively, instead of two elements from two amplitude-level groups in the conventional method. Each user’s message is split into most significant bits (MSBs) and least significant bits (LSBs), with the MSBs modulated at one of the higher-level groups and the LSBs modulated at one of the lower-level groups to meet the NOMA principle. Both analysis and simulation results show that the proposed schemes offer higher system capacity than the conventional method.

An Improved Modulation Scheme of Active Commutated Current-Fed Bidirectional dc/dc Converter

Active commutated or naturally clamped techniques have emerged as a new solution to achieve wide range soft-switching and eliminate the necessity of active clamping circuit of current-fed bidirectional dc/dc converter. Multiple typical modulation schemes have been proposed, which include single phase-shift (SPS) modulation, dual phase-shift (DPS) modulation, and discontinuous current SPS (DCSPS) modulation. DCSPS provides the lowest circulating current compared with prior two modulations, but it suffers from the problem of resonance and high peak current at partial loads. This article proposes a DCDPS modulation based on the existing modulations. The duty cycles of the two legs on the high-voltage side are controlled to be unsymmetrical to solve the current resonance problem in DCSPS. Extra phase shift is introduced to achieve much lower circulating current at wide range load conditions. Zero current switching (ZCS) of primary switches and zero voltage switching (ZVS) of secondary switches can be achieved over wide input range and wide load range. A 250-W laboratory converter prototype has been built. Experimental results are presented to validate the analysis and design.

Modulation for the AVC-HERIC Inverter to Compensate for Deadtime and Minimum Pulsewidth Limitation Distortions

With the superiority in leakage current suppression, the active voltage clamping highly efficient and reliable inverter concept (AVC-HERIC) has become a promising candidate in low- and medium-power photovoltaic systems. In addition, the high power density and low system costs have been attained in the AVC-HERIC due to the removal of the isolation transformers. However, to maintain high efficiency and good power quality under reactive power injection, prior-art modulation methods for the AVC-HERIC should be modified. In this paper, a simple modulation scheme is proposed for the AVC-HERIC, which ensures bidirectional current flow at any time. An improved modulation scheme is implemented according to the reference voltage polarity, and it is integrated into the proposed scheme to enable flexible reactive power injection. Moreover, the improved modulation scheme can maintain the same high efficiency as adopting the unipolar pulsewidth modulation strategy. More importantly, the deadtime and minimum pulsewidth limitation distortions are compensated effectively by the proposed modulation, leading to a good power quality. Simulations and experimental tests are performed on a 3-kW AVC-HERIC, and the results verify the effectiveness of the proposed modulation.

An Improved Modulation Scheme of Current-Fed Bidirectional DC–DC Converters For Loss Reduction

Current-fed bidirectional dc–dc converters have attracted much attention in battery energy storage system applications due to their zero-voltage-switching performances and greater degree of control freedom. However, high efficiency cannot be achieved for both light and heavy load ranges with the present modulation schemes for a current-fed bidirectional dc–dc converter, especially with low battery voltages. A new modulation scheme is proposed to improve the conversion efficiency over a wide load range and with variations in the battery voltage. The relationship between the duty cycle of the secondary full bridge and the phase-shift angle was investigated to lower the power losses with the wide load variations. Based on the operation mode analysis, the control loop with the proposed pulse wide modulation plus phase-shift modulation scheme was developed. Comparisons of the switch conduction loss and the core loss in the series inductor for the previous modulation schemes and the proposed modulation scheme were carried out. The results show that lower power losses occur with the proposed scheme. The experimental results verify the theoretical analysis and effectiveness of the proposed modulation scheme on loss reduction.

Improved Modulation Scheme for Loss Balancing of Three-Level Active NPC Converters

The three-level neutral point-clamped (NPC) converter has attracted much attention in high-power medium-voltage applications, but it is well-known that the NPC topology suffers from unequal power loss distribution among its semiconductor devices. The power loss unbalance problem becomes especially severe when the converter is operating at low fundamental frequencies. To overcome the loss unbalance problem of the NPC converter, the active NPC (ANPC) technique was introduced. However, it is demonstrated in this paper that in many cases, the conventional modulation method for the ANPC converter only marginally relieves the loss unbalance problem. This paper proposes a new modulation scheme (named the adaptive doubled frequency modulation) for the three-level ANPC converter, which significantly improves the power loss and thermal sharing among the semiconductor devices. The basic idea of the proposed scheme is adaptively adjusting the duty cycles of the switching states for every switching cycle, so as to optimize the power loss distribution. Simulation and experimental results verify this new method.

A Theoretical Survey of the Spreading Modulation of the New GPS Signals (L1C, L2C, and L5)

In this paper a survey of the spreading modulation of the new GPS signals (L1C, L2C, and L5) is considered. The new signals seem to offer several improvements which range from higher power, better code selection, and improved modulation schemes which offer receiver designers the opportunity to obtain unmatched performance in many ways such as in the case of a maximum likelihood GPS receiver. For example the Multiplexed Binary Offset Carrier (MBOC) spreading modulation has been recommended by the GPS-GALILEO Working Group on interoperability and compatibility because the MBOC(6,1,1/11) power spectral density is a mixture of BOC(1,1) spectrum and BOC(6,1) spectrum, that would be used by GALILEO for its Open Service (OS) signal at L1 frequency, and also by GPS for its modernized L1 Civil (L1C) signal. It is suggested that a number of different time waveforms can produce the MBOC(6,1,1/11) spectrum, allowing flexibility in implementation and maintaining interoperable waveforms for GALILEO and GPS. On the other hand, the timemultiplexed BOC (TMBOC) implementation interlaces BOC(6,1) and BOC(1,1) spreading symbols in a regular pattern, whereas composite BOC (CBOC) uses multilevel spreading symbols formed from the weighted sum of BOC(1,1) and BOC(6,1) spreading symbols, interplexed to form a constant modulus composite signal. New L1C provides a number of advanced features, which includes 75% of the power in a pilot component for enhanced signal tracking, advanced Weil-based spreading codes, an overlay code on the pilot that provides data message synchronization, support for improved reading of clock and ephemeris by combining message symbols across messages, advanced forward error control coding, and data symbol interleaving to combat fading. The resulting design offers receiver designers the opportunity to obtain a greatly improved performance in many ways. In this paper we perform a theoretical survey of the new signals and suggest a new code spreading modulation scheme which could provide even further improvements to the new GPS III signals.

A Cascaded Multi-level Inverter Topology with Improved Modulation Scheme

This article proposes a single-phase, cascaded multilevel inverter topology. Each of the cascaded unit cells is made up of a main inverting H-bridge leg and a level-clamping half-bridge circuit. The single-carrier, multilevel pulse-width modulation scheme is employed to generate gating signals fort he power switches. The modulation scheme is hybridized to enable the output voltage of the proposed inverter configuration, inherit the features of switching-loss reduction from fundamental pulse-width modulation, and good harmonic performance from multiple sinusoidal pulse-width modulation. A sequential switching scheme is embedded with the already employed hybrid modulation to overcome unequal switching losses among the power devices. A simple base pulse-width modulation circulation scheme is also introduced in this work to get resultant sequential switching hybrid pulse-width modulation circulation that balances power dissipation among the power modules. The proposed inverter configuration was subjected to a resistor-inductor load, and the respective numbers of output voltage level were synthesized. Fast Fourier transform (FFT) analyses of the output voltage waveforms were carried out. Analysis of the conduction power losses in the power semiconductor switches of the proposed inverter topology is given. Simulations and experiments are carried out on a 3.07-kW rated prototype of the proposed inverter for a resistor-inductor load.

An Improved Modulation Scheme for Voltage Balancing in Modular Multilevel Converter

AbstractWith the continuous development of power electronic technology toward the high voltage and high-power conversion, the Modular Multilevel Converter (MMC) has attracted research attention. Since a large number of capacitors, voltage balancing problem becomes one of the key technologies of the MMC. To resolve the voltage balancing problem, this paper presents a novel voltage balancing modulation scheme, which control the instantaneous power of each sub-module timely by adjusting carriers offset in PWM, and the respective capacitor voltage could be stabilized at a set value. Simulation results based on MATLAB/SIMULINK environment are provided to testify to the effectiveness of the proposed method.

Improved Modulation Schemes for Indirect Z-source Matrix Converter With Sinusoidal Input and Output Waveforms

Z-source energy conversion is a recent concept introduced for adding voltage-boost functionality to the traditional buck-only dc-ac inverter. The same concept can equally be extended to the indirect ac-ac matrix converter, where only a single Z-source impedance network needs to be inserted to its intermediate dc link. The topology formed is, thus, quite straightforward. Its modulation is, however, nontrivial if advantages like buck-boost flexibility, minimum commutation count, ease of implementation, and sinusoidal input and output quantities are to be attained simultaneously. This capability is now pursued through unveiling related modulation theories, so as to better present the indirect Z-source matrix converter as an attractive alternative for ac-ac buck-boost energy conversion. Findings presented have already been verified in simulation and experiment.

Parallel Optical Interconnects Over Multimode Waveguides Using Mutually Coherent Channels and Direct Detection

We present an approach for parallel optical interconnect channels using a single light source and a single multimode waveguide. Parallel transmission is achieved by exploiting the modal diversity of the multimode waveguide, thus improving the channel density, compared to other optical interconnect schemes. The proposed system facilitates packaging and requires relatively simple components, which can be integrated using silicon technology. The performance of such a system is analyzed for different modulation schemes. Based on the analysis, improved modulation schemes that reduce the system error probability are suggested.

Pulsewidth Modulated Inverter Motor Drives with Improved Modulation

The performance of inverter drives, which use the pulsewidth modulated (PWM) technique to control motor applied voltage and frequency, are critically influenced by the choice of the modulation policy used in the control circuits. This paper deals with practical inverter drives for squirrel cage induction motors and presents some basic considerations on modulation requirements. The advantages and limitations of popular modulation methods are discussed, and an improved modulation scheme, which allows us to extend the practical speed range of PWM ac drives, is presented.