Carrier-based Modulation Research Articles

Efficiency and Power Loss Distribution in a High-Frequency, Seven-Level Diode-Clamped Inverter

The paper presents efficiency and power loss analysis in a high-frequency, seven-level diode-clamped inverter (7LDCB). The inverter is composed of four-level (4L) diode-clamped branches based on MOSFET transistors and Si Schottky diodes. The range of DC-link voltages enables the operation of the inverter in connection with a single-phase power grid. The tested inverter can be controlled using various modulation concepts that affect its parameters, but also energy losses. Carrier-based modulation, which may be useful in a few applications, is compared to selective modulation based on the state machine (SM-based) algorithm. The article demonstrates the efficiency level of the inverter as well as the influence of the modulation method and switching frequency on the efficiency and loss distribution in semiconductor devices. The article also shows the hardware implementation of a complex modulation algorithm based on selective switching states used to maintain voltage balance on three DC-link capacitors. Redundant switching states allow the generation of the same voltage but with the use of a selected DC-link capacitor. This makes it possible to balance the DC-link voltage with the load current. The article presents experimental results, which show the advantage of using the modulation method with selective switching states. First, it allows for equalizing the loading of DC-link capacitors. The second advantage is a more uniform distribution of losses in semiconductor components.

Analysis of Control Strategy of Arc Plasma Power Supply Inverter Module

The inverter module serves as a critical component in the conversion of electrical energy within arc plasma power sources, exerting a profound influence on the overall performance and stability of the power supply. Consequently, the meticulous design and precise control of the inverter module are of paramount importance in ensuring the effective operation and application of arc plasma power sources. This paper introduces a dual-closed-loop control system, integrating a voltage outer loop with a current inner loop, as the cornerstone of its inverter module design. It also undertook a comprehensive comparative analysis of various voltage-control strategies, encompassing four control methods (PI, PID, PR, QPR) and two modulation techniques (bipolar modulation and unipolar, carrier-based modulation) under diverse operating conditions. Additionally, simulation experiments were conducted on a prototype 10 kW inverter module using the Matlab/Simulink simulation platform, with evaluation criteria including waveform tracking performance, voltage waveform distortion rate, and steady-state error. The results indicate that in low-frequency operating conditions, the voltage-control strategy employing QPR control plus unipolar, carrier-based modulation, and in high-frequency operating conditions, the voltage-control strategy utilizing PI control plus unipolar, carrier-based modulation exhibited superior waveform tracking performance. The waveform distortion rates were measured at below 0.47% and 4.2%, respectively, aligning perfectly with the stringent standards of IEEE 519. This research provides valuable theoretical support and practical guidance for future engineering endeavors in the field of inverters.

Operation of a Hybrid Energy Storage System Based on a Cascaded Multi-Output Multilevel Converter with a Carrier-Based Modulation Scheme

Hybrid Energy Storage Systems (HESSs) have gathered considerable interest due to their potential to achieve high energy and power density by integrating different storage technologies, such as batteries and capacitors, to name a few. Among the various topologies explored for HESSs, the multi-output multilevel converter stands out as a promising option, offering decoupled operation of the AC ports while maintaining an internal balance among the diverse storage units. In this paper, the operation and restrictions of a HESS based on a multi-output multilevel converter with a carrier-based modulation scheme are presented. The study provides compelling evidence of the correct operation of the proposed modulation scheme and highlights its advantages, including simplicity and stability.

An analogous carrier‐based implementation of virtual space vector modulation with low common‐mode voltage and neutral‐point voltage oscillation elimination for three‐level NPC inverter

AbstractBalancing control of neutral‐point voltage (NPV) and reducing common‐mode voltage (CMV) are crucial for a three‐level neutral‐point‐clamped (NPC) inverter. NPV oscillation can be inhibited by constructing virtual vectors and adding adjustment factors to eliminate stochastic disturbances that cause unbalanced NPV. However, the adjustment factors significantly increase computational complexity and introduce a dynamic sector split instead of the traditional static one. Moreover, constructing virtual vectors prompts a considerable rise in CMV. Therefore, this paper proposes a virtual space vector modulation strategy for the NPC inverter that eliminates NPV oscillation and reduces CMV. The study applies the idea of carrier‐based modulation (CBM), which reduces calculation time caused by the novel strategy of adding adjustment factors. A method to determine the maximum adjustment voltage is designed to evaluate NPV regulation ability, which is analysed. The novel method and the basic VSVM are theoretically compared, and it is proved that the novel method has better NPV regulation capability than the basic VSVM under high modulation ratio and high power factors, such as in motors systems.

Development and testing midpoint voltage balance algorithms of three-level inverters

Nowadays, the use of inverters is increasing in more and more applications. Environmental awareness is becoming a trend, so more and more people install solar energy systems on their houses, which also require the use of inverters. Higher power levels have led to the emergence of three-level inverters which has opened up new challenges, such as the issue of midpoint voltage balancing. This paper discusses voltage balancing and voltage ripple reduction techniques for three-level inverters with Neutral-Point Clamped (NPC) topology. The balancing is based on injecting zero-sequence voltage component in carrierbased modulation. The viability of the modulation techniques are verified by computer simulation and then tested on hardware.

Three Parts Modulation and Hybrid DC Capacitor Voltage Balancing for a Single-Phase Two-Leg Five-Level NPC Inverter

Capacitor voltage unbalance in NPC multilevel inverters is an inherent challenge and has a severe effect on five and higher-level inverters. Current modulation-based voltage balancing schemes for five-level NPC inverters require a high number of switching, especially at high modulation index operations. Moreover, hardware-based voltage balancing techniques come with a high component count. This paper proposes a unique three-part modulation technique combined with a hybrid voltage balancing approach to reduce switching losses and maintain voltage balancing. The modulation is composed of different carrier-based modulations, while the hybrid balancing scheme combines modulation-based and hardware-based balancing techniques. Comparative switching loss analysis demonstrates a reduction in inverter switching associated with the modulation. While the voltage unbalance characteristics of the modulation are determined considering linear loading conditions. Furthermore, balancing capacity analysis and switching loss reevaluation are used to justify the hybrid balancing performance. The concept verification use Matlab-Simulink simulation and hardware experiments on a five-level single-phase NPC inverter setup operated at different modulation index and power factor conditions.

A Flexible and Decoupled Space Vector Modulation Scheme With Carrier-Based Implementation for Multilevel Converters

This article proposes a novel space vector pulse width modulation (SVPWM) scheme for multilevel converters in <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">abc</i> coordinate system, in which the reference vector is decomposed into an offset vector and a remainder vector that can be synthesized using two-level SVPWM. The switching state satisfying a specific relationship is first selected as the offset vector such that the common-mode components are eliminated and therefore the phase voltages are decoupled. A dynamic reference point mechanism establishes a one-to-one correspondence between all available vector combinations and one unique variable, i.e., the number of level shifts. This feature further facilitates a general approach to determining the optimum switching states to satisfy different control objectives, such as common-mode voltage rejection. Besides, phase decoupling enables the introduction of carrier-based modulation to simplify implementation, where the duty cycle of the zero vector can be flexibly adjusted while the non-zero vectors remain the same to generate an equivalent output. Consequently, two-level SVPWM-based method and carrier-based PWM are combined to exploit their respective strengths. The proposed scheme achieves overmodulation operation, and provides more flexibility, i.e., redundant switching states and adjustable duty cycles, to optimize switching patterns. Simulation and experimental results validate the proposed algorithm.

A Novel Modulation Strategy for Asymmetrical Six-Phase Series-Winding PMSM Based on Predictive Controller

Series-winding (SW) permanent magnet synchronous motors (PMSMs) are of increasing interest and great potential for low-voltage traction in electric vehicles because of their both higher DC voltage utilization and fewer inverter legs. A few studies attempt to promote this topology from three-phase to multi-phase frame. However, the SW topology for asymmetrical multi-phase system has yet to be understood, given the fact that all existing voltage modulation strategies are not applicable. The study presents a feasible, simple carrier-based modulation strategy for this special SW-PMSM with an asymmetrical winding system. A predictive current controller is introduced in the process of modulation since the multi-phase system involves several current control loops. An asymmetrical six-phase PMSM prototype is fabricated for verification. Experimental results show that the novel strategy performs much better than its space-vector-based counterparts. Also, it is capable of suppressing the current distortion within the nonlinear modulation range. Voltage utilization and achievable rotational speed become higher.

A Carrier-Based Low Total Current Ripple Modulation Strategy for Parallel Converters With Leakage Current Attenuation

In order to meet the high performance and low leakage current requirements in high power rating photovoltaic applications, an improved carrier-based modulation (ICBM) for parallel converters is presented in this paper. Different from existing methods which are based on PS-PWM, a proper zero-sequence modulation wave is injected into the three-phase modulation waves to achieve low total current ripple based on the root mean square value analysis of output current ripple. Aside from this, the initial phase shift angles for the carriers in each converter are modified to minimize the excitation source of leakage current, while the quality of total output current is not affected. Furthermore, the proposed ICBM is extended to parallel multilevel converters according to the vector shift principle. By using the proposed ICBM, total current ripple reduction and leakage current attenuation in parallel converters can be achieved simultaneously. Experimental results validated the correctness and effectiveness of the proposed method.

Assessment of Total Harmonic Distortion in Buck-Boost DC-AC Converters using Triangular Wave and Saw-Tooth based Unipolar Modulation Schemes

This paper presents an assessment of the levels of total harmonic distortion (THD) in buck-boost DC-AC converters using triangular wave and saw-tooth unipolar based-modulation schemes. This paper seeks to identify a better technique for mitigating the total harmonic distortion on buck-boost DC-AC converters under unipolar carrier-based modulation schemes. This was achieved by subjecting the buck-boost DC-AC converter under triangular wave-based and saw-tooth based-unipolar modulation schemes. The voltage and current output of the buck- boost DC-AC converter under each scheme was analysed using a power GUI Fast Fourier Transform (FFT) analytical tool resident in the MATLAB Simulink environment unlike with the conventional scheme of computing the percentage of THD. The test system was obtained by a combination of DC-DC buck-boost converter, H-bridge based-insulated unipolar gate transistors, and a logic control unit. It was realized that THD of 0.2865%, peak output voltage of 294.1V and current of 9.805A were obtained by using the saw-tooth based-unipolar modulation scheme, whereas a THD of 0.1479%, peak output voltage of 297.4V and current of 9.53A were obtained by using the triangular wave based-bipolar modulation scheme on the same Buck-boost DC-AC converter circuit. The results imply a high power factor utilization and low power loss in the triangular wave based-unipolar modulation scheme compared to the saw-tooth based-unipolar modulation technique for improving the performance characteristics of the buck-boost converter system. This study showed that power drives and heavy load machines based-power electrical loads are required to use the saw-tooth based-unipolar modulation (STBUM) scheme for high current and low THD%, whereas sensitive power electrical loads such as hospital equipment and communication industries based-power electronic devices are required to use the triangular wave-based unipolar modulation (TWBUM) scheme due to low current and THD%.

Duty-Ratio-Based Direct Torque Control With Enhanced Harmonic Current Suppression for Dual-Three-Phase Permanent Magnet Motor

This article proposes a new duty-ratio-based direct torque control (DR-DTC) with enhanced harmonic current suppression for a dual-three-phase permanent magnet (DTP-PM) motor. First, a new virtual voltage vector construction method based on the carrier-based modulation technique is proposed. Twelve virtual voltage vectors with null average voltage values in two harmonic subspaces are constructed. The sequences of the constructed virtual voltages can be calculated directly in the natural coordinate system. In addition, the whole sequences are standard symmetrical, which can be easily generated by a digital controller. After that, an online harmonic current compensation method is investigated. Additional controllers compensate for the harmonic currents induced by the back electromotive force and nonlinear factors. Since the virtual voltage vectors have null average voltage values in two harmonic subspaces and the online harmonic current compensation method is designed, the proposed DR-DTC can be introduced to the DTP-PM motor with a single neutral point and two neural points. With the proposed strategy, the capability of harmonic current suppression can be significantly improved, and the processes of virtual voltage construction can be simplified. In addition, the advantages of the conventional DR-DTC can be inherited. Finally, experiments are carried out to validate the feasibility of the proposed strategy.

Bidirectional H8 AC–DC Topology Combining Advantages of Both Diode-Clamped and Flying-Capacitor Three-Level Converters

A three-level bidirectional ac–dc converter with H8 topology is proposed to combine the advantages of both neutral-point clamped and flying-capacitor (FC) three-level converters for medium-voltage (MV) ac–dc solid-state transformer (SST) applications. The innovative H8 converter features self-balanced capacitor voltage, common-mode voltage elimination, and small capacitance of the FCs. The proposed carrier-based modulation enables the H8 converter to operate under both active and reactive power conditions. A 10-kVA ac–dc converter prototype with 1.7-kV SiC MOSFETs and 3.3-kV SiC diodes verifies the feasibility and advantages of the proposed topology and the modulation method. The capacitance of the FCs in the H8 converter is reduced by 45 times compared to that of the FC converters. The H8 converter efficiency is tested up to 99% at 2-kV dc voltage. The proposed H8 converter is suitable for the next-generation PV inverter, grid-forming inverter, MV fast charger, and SST applications.

Harmonics Minimization in PUC Type Solar Multilevel Converter with Multicarrier Switching Schemes

This paper presents the power quality investigation of a seven-level three-phase packed U-cell (PUC) converter with multicarrier switching schemes. This system is grid-connected, and each phase has two solar PV arrays of different voltages. Various modulation schemes are available for switching the multilevel converter, and level-shifted multicarrier pulse width modulation is widely used for easy implementation. A new modified carrier-based modulation technique is introduced for solar PV array fed PUC inverter. The main aim is to reduce the harmonic content in the seven-level output voltage. It also increases the magnitude of the fundamental component of the converter voltage. The comparison of the presented technique shows its advantages over other existing modulation schemes. Closed-loop control is implemented with the inclusion of a modified switching scheme for switching the three-phase PUC converter. The proportional resonant controller provides excellent dynamic performance to feed the power into the grid. Modeling and simulation of the system are done in MATLAB/Simulink. Furthermore, obtained simulation results verify the effectivity of the switching scheme towards minimizing total harmonic distortion. The overall system is validated in the real-time simulator for steady-state and dynamic environmental conditions.

Pre- and Post-Fault Operations of Six-Phase Electric-Drive-Reconstructed Onboard Charger for Electric Vehicles

The concept of electric-drive-reconstructed onboard charger (EDROC) potentially opens the door to harness the existing drivetrain in electric vehicle (EV) to do the job of battery charger, thus performing a remarkable value in commerce. In this article, the pre- and post-fault operations of an EDROC are studied, which incorporates an asymmetrical six-phase permanent magnet synchronous machine (ASPMSM) drive. At first, the decomposed currents of the machine in healthy and faulty cases are solved and their trajectories are depicted, indicating that a rotating field will exist if an open-phase fault (OPF) occurs. Afterward, a rotating field cancellation scheme based on the minimum copper loss criterion is proposed by rearranging stator currents, with two constraints under consideration that are responsible for generating pulsating field and balanced grid currents, respectively. Following this, a control scheme shared for both pre- and post-fault conditions is proposed, where the carrier-based modulation without any zero-sequence signal injection is employed. Finally, the proposed rotating field cancellation scheme is verified by experimental results.

Integrated Three-Level Dual-Phase Inverter

In view of reducing the number of inverter legs that provide dual-phase, three-level output voltages (as may be needed in an uninterruptible power supply), and that also provide a wide range of output frequencies (as needed in an advanced motor drive system with wide speed ranges), a three-level, dual-phase inverter topology is presented in this paper. Its three-level attribute was based on the F-type inverter topological concept, and its dual-output feature was based on the common representation of the inverter-leg concept. The proposed inverter could deliver single- and three-phase voltages to corresponding one- and three-phase loads, in common or different frequency modes of operation. A boundary between these modes of operation was established for the proposed inverter. An additional possibility of either operation in the one-phase or the three-phase system was offered by the inverter configuration. A modified carrier-based sinusoidal pulse-width modulation scheme is presented for the control of the inverter topology. The performances of the dual-phase inverter are given in the simulation results and demonstrated with a hardware prototype.

A Novel Single DC Source Three-Phase Wye Packed U-Cell (Y-PUC) Converter

A new configuration of three-phase Wye Packed U-cells (Y-PUC) with a single DC source is proposed in this paper. In fact, this configuration represents a single DC source modular three-phase PUC converter. The DC source on PUC topology is replaced by a flying capacitor to obtain a suitable submodule. Moreover, the modularity of the Y-PUC configuration makes it an appropriate alternative for MMC applications. Furthermore, the proposed structure is an advantageous configuration for high voltage applications such as high voltage direct current (HVDC) transmission lines with the capability of DC fault handling. All PUC topologies such as PUC5, PUC7, PUC9, PUC15 can be replaced in the modules of this proposed single-phase and three-phase configuration to multiply the load voltage levels for improving the output waveform. Active voltage balancing technique through carrier-based modulation is applied. System modeling and operating sequences are developed. Simulation and experimental results are presented and discussed to validate the performance of the proposed structure.

DiSortNet: A Network Protocol With Distributed Sorting for Modular Multilevel Converters

Several authorsinvestigated the use of internal digital communication networks in Modular Multilevel Converters. The first works in this area keep a centralized control scheme, but they struggle to reach the fast cycle times required for achieving goodcontrol performance, specially as the number of cells increases. To reduce the network cycle time, some authors adopted a partly decentralized control scheme. However, those proposals restrict the capacitorbalancing to a closed-loop strategy and the use of carrier-based modulation. This work introduces DiSortNet, a novel Ethernet-based ring network protocol that achieves low cycle times while preserving the centralized control scheme and its modulation flexibility. DiSortNet emerges from a communications-control co-design approach, which main feature is the distributed sorting of capacitor voltages. We show that distributed sorting implies a marginal degradation in the balancing of capacitor voltages while bounding the network payload and reducing the cycle time. Implementation-wise, using FPGA-based network interfaces, DiSortNet achieves half the cycle-time obtained with EtherCAT in a network with 86 nodes and less than half for larger networks, reaching 157 μs with 300 nodes.

A Unified Controller for Multi-State Operation of the Bi-Directional Buck–Boost DC-DC Converter

DC grid interfaces for supercapacitors (SCs) are expected to operate with a wide range of input voltages with fast dynamics. The class-C DC-DC converter is commonly used in this application because of its simplicity. However, it does not work if the output voltage (V2) becomes smaller than the input voltage (V1). The non-isolated bi-directional Buck–Boost DC-DC converter does not have this limitation. Its two half-bridges provide a means for controlling the power flow operating in the conventional dual-state mode, as well as multi-state, tri, and quad modes. These can be used for mitigating issues such as the Right Half Plane (RHP) zero that has a negative impact on the dynamic response of the system. Multi-state operation typically requires multi-variable control, which is not easy to realize with conventional PI-type controllers. This paper proposes a unified controller for multi-state operation. It employs a carrier-based modulation scheme with three modulation signals that allows the converter to operate in all four possible states and eight different modes of operation. A mathematical model is developed for devising a multi-variable control scheme using feedback linearization. This allows the design of control loops with simple PI controllers that can be used for all multi-state modes under a wide range of operating conditions with the same performance. The proposed scheme is verified by means of simulations.

A New Carrier-Based Pulse Width Modulation Technique for an Indirect Matrix Converter

In this work, a new carrier-based pulse width modulation (CPWM) scheme is built for three-to-three phase indirect matrix converter (IMC). In the existing CPWM schemes, the control schemes of the source side converter of the IMC are developed based on either sector based complex calculations or over-modulation operation to obtain the required performance. In the new CPWM scheme, the simplified modulation equations for the source side converter of the IMC are proposed which provide the required performance without resorting to the sector based duty cycle calculations or over-modulation operation. The source and load side converter stages of the IMC are modulated with the standard CPWM principles of the conventional inverter and rectifier topologies in the present work. This work also compares the new CPWM scheme with the SVPWM scheme based on the mathematical calculations which proves that the new CPWM scheme requires less mathematical operations as compared to SVPWM scheme. The simulation and experimental results for both modulation schemes are presented which proves that the new CPWM scheme provides the equivalent input and output performances to those of the SVPWM scheme. The control devices DSP (TMS320F28335) and FPGA (Spartan-6) are used to implement the CPWM and SVPWM schemes.

Analysis of Harmonic Distortion Reduction through Modular Multi-Level Inverter using Nearest Level Modulation (NLM) Control Strategy

The research paper presents the control strategy to reduce THD (Total Harmonic Distortions) losses by the implementation of the Nearest Level Modulation control technique in a Modular Multilevel Converter. Modular Multilevel Converter is found one of the leading technologies in Power Electronics &amp; Control, its applications are very common in HVDC systems, FACTS (Flexible Alternating-current Transmission system), Variable frequency drives and Electric vehicles as well. The power quality of MMC is better and has lesser THD in comparison to conventional converters like 2-level converters with carrier-based modulation techniques. The MMC has been designed with high scalability and has high voltage and power capacity. Sub-module is an integral part of MMC which is built up as an identical and controllable part of it. This converter is also called a controllable voltage source (VSC). Researchers aim to come up with a detailed review of control methods and necessary operations applied to MMC-based systems for HVDC, particularly focusing to control the total harmonic distortions. Power converters use many modulation techniques, but the existing techniques contribute to a great part in switching losses. MMC up to 49 levels, by implementing the Nearest Level Modulation (NLM) technique, is robust and has less complexity for the systems like MMC-HVDC, and the levels control the total harmonic distortions. In this research paper, the reduction of THD by increasing the voltage levels in MMC is comprehensively evaluated. The simulation results in MATLAB/Simulink are used to examine and confirm the proposed control strategy for stable operation of MMC for HVDC application.