Switching Frequency Modulation Technique Research Articles

A new generalized floor function based high switching frequency modulation and control technique: Multilevel inverters

SummaryA new generalized floor function (F2) based single carrier pulse width modulation (F2SC‐PWM) technique has been proposed in this paper by considering a single‐phase 9‐level T‐type packed U‐cell (PUC) inverter topology. In literature, the conventional level‐shifted PWM technique requires (level‐1) carriers, and the unipolar phase disposition (UPD) PWM technique requires (level‐1)/2 carriers to produce a particular level of output. To reduce the complexity of control, the authors have developed single‐carrier‐based PWM techniques. However, these are not generalized in a simple manner and are especially applicable only to particular inverter topologies. In this paper, a new F2SC‐PWM technique with a single modulating signal has been introduced that is applicable to any multilevel inverter (MLI) topology. This technique is very simple to implement, and it does not internally require any large number of mathematical operations and if‐else loops. Finally, a laboratory prototype has been used to verify the operation of the 9L‐TPUC topology considering R and RL loads with respect to step change of load, step change of modulation index (MI), and step change of modulation frequecy (MF) via with new proposed control technique (PCT).

Hybrid multilevel inverter using switched capacitor with boosting and self-balancing capability

Switched capacitor based multilevel inverters with boosting capability are emerging as single stage DC–AC conversion in utilizing low voltage DC sources such as solar PV and fuel cell. This paper proposes a single-phase hybrid multilevel inverter topology based on a switched capacitor that is capable of generating 9-levels along with a voltage gain of 2. The components required to construct the basic module of topology are 11 switches, 1 diode and 2 capacitors. The voltage balancing of the switched capacitors is achieved with the help of a modulation strategy, thereby eliminating the need of sensors. The theoretical loss analysis of the inverter is presented and the nearest level control based fundamental switching frequency modulation technique is employed to study the performance of the proposed inverter. The effectiveness of the suggested topology is validated with the help of a prototype built in the laboratory. The superiority of the proposed topology is assessed with the help of comparison with existing topologies.

An improved switched‐ladder bidirectional multilevel inverter: Topology, operating principle, and implementation

AbstractMulti‐level inverters (MLIs) for medium or high power and voltage utilization have acceptable application in industry and are utilized commercially. The performance of MLIs is considerably preferable to traditional two‐level inverters due to their negligible harmonic content, small filter size, utilization of lower‐rated voltage devices, low electromagnetic interference (EMI), and so on. However, in the face of these many advantages, few disadvantages can be expressed such as more device count and a sophisticated control strategy. This paper presents an improved switched‐ladder topology to enhance the performance of multi‐level inverters by improving the above drawbacks. Compared to existing inverter topologies, the proposed extendable diode‐containing bidirectional structure requires fewer switches and driver circuits. The proposed topology is compared with other similar topologies, and its superiority is examined. Fundamental switching frequency modulation technique is utilized to obtain high‐quality output voltage waveforms with lower harmonic contents and reduced switching losses. This converter, despite the use of diodes, can supply the low power factor inductive‐resistive loads, bidirectionally. To demonstrate the performance of the proposed topology, in addition to simulation with the nearest level modulation technique, a prototype of the proposed structure has been implemented and tested. The results display the proper performance of the proposed topology in the real‐time environment.

Analysis and implementation of a new asymmetric double H‐bridge multilevel inverter

AbstractMultilevel inverters (MLI) have become an integral component in many industrial applications including drive systems and distributed generation grid integrated systems. Efficient and cost‐effective MLI topologies are required to enhance the performance of industrial systems. In the present work, an asymmetric double H‐bridge MLI is proposed, which incorporates and enhances the attributes of a modified T‐type converter and produces a superior output voltage waveform with the lesser component requirement. The proposed MLI can generate a 15‐level output. An extendable generalized topology (cascaded) based on the proposed configuration has also been proposed. The topology is compared with recently introduced MLI topologies based on various performance parameters, and results are presented. The output voltage control is achieved using nearest level control which is a low switching frequency modulation technique for lowering the switching losses in the inverter. The hardware is realized, and performance is evaluated under different dynamically changing loading conditions.

A new cascaded asymmetrical multilevel inverter based on switched dc voltage sources

Multilevel inverters are now becoming an important element for medium-voltage high-power applications. A low switch count multilevel inverters are currently attracting more attention due to its high efficiency, low cost, and easy control. This paper proposes a new single-phase cascade asymmetrical multilevel inverter topology based on switched dc voltage sources which is capable of achieving a higher number of output levels using fewer number of switches, driver circuits, and dc voltage sources. Other advantages include the inherent generation of negative voltage levels and lower voltage stress across the switches. Three different approaches in selecting the magnitude of the sources for the cascade connection has been included to produce a higher number of voltage levels. Furthermore, the power loss and fault-tolerant analysis of the proposed basic module has also been discussed. To set the benchmark of the proposed multilevel inverter structure, a comparison with several recently proposed topologies is carried out. The comparison has been carried out for the basic module, generalized structure, and cascade connection. The proposed topology gave improved parameters for all three categories. Fundamental switching frequency modulation technique is used to achieve high-quality output voltage waveforms with lower harmonic contents and reduced switching losses. Finally, the operation and performance of the proposed basic module and its cascade connection for two modules are presented together with experimental results in several steady-state and dynamic operating conditions.

Single‐phase hybrid multilevel inverter topology with low switching frequency modulation techniques for lower order harmonic elimination

A new single-phase asymmetrical multilevel inverter (MLI) is presented in this study. The proposed topology generates a staircase output voltage waveform with a maximum number of levels using less number of components compared to several existing and recent topologies. The basic module consists of a combination of two isolated DC sources with ten switches that produce all the possible number of levels. Other advantages of the proposed MLI include improved output voltage performance and a low blocking voltage of the switches. The low switching frequency pulse width modulation (LSF-PWM) technique has been used for the generation of gate pulses. In the LSF technique, selective harmonic elimination (SHE) and fundamental switching frequency PWM techniques have been discussed for the better output voltage waveform. The optimised switching angles with SHEPWM has been calculated using particle swarm optimisation considering the different combination of the elimination of lower order harmonics. Simulation work was carried out using MATLAB/SIMULINK, and a prototype was implemented to validate the proposed MLI module. Simulation and experimental results have been provided in the study to show the performance of the proposed topology with these modulation techniques.

Circulating Current Control for Modular Multilevel Converters With (N+1) Selective Harmonic Elimination—PWM

Modular multilevel converters (MMCs) require control of the circulating current, $i_{\text{circ}}$ , to improve their operation and efficiency. This is particularly important when low switching frequency modulation techniques, such as selective harmonic elimination pulsewidth modulation (SHE-PWM) are applied. This article provides a novel method to control the circulating current along with (N+1) SHE-PWM. Unlike the case of (2N+1) SHE-PWM, explicit redundant levels are not available and, therefore, different modulation indexes, $m_{1}$ and $m_{2}$ , are employed in the upper and lower arms to obtain the desired modulation index $m_{a}$ . Unlike previous (N+1) circulating current methods, the distances between $m_{a}$ , $m_{1}$ , and $m_{2}$ remain constant to not disturb the phase output voltage, with an interchange of $m_{1}$ and $m_{2}$ between the arms used to follow the desired $i_{\text{circ}}$ . The control adjusts the dc component of the circulating current and the energy stored in the SMs to their references, while maintaining the energy balance between the upper and lower arms. Simulation tests and experimental results, obtained from a single-phase laboratory prototype MMC, validate the proposed control technique.

Synchronous random switching frequency modulation technique based on the carrier phase shift to reduce the PWM noise

Pulse width modulation (PWM) technique brings harsh acoustic noise in motor drive system. Thus, synchronous random switching frequency modulation (SRSFM) technique based on carrier phase shift for paralleled three-phase voltage source inverters is proposed in this study to eliminate the PWM noise. The proposed SRSFM technique is able to remove the high-frequency PWM noise more effectively than the conventional random switching frequency PWM; it not only completely eliminates the PWM noise nearby odd-order carrier frequency but also reduces PWM vibration noise around even-order carrier frequency depending on the switching frequency variation range. Furthermore, the SRSFM technique is simple to implement and requires no additional hardware. Finally, the effectiveness of the proposed method is verified by detailed experimental results.

A Generalized Methodology to Generate, Amplify and Compensate Multi-Frequency Power for a Single-Inverter-Based MF-MR-S-WPT System

To meet the unique challenges on how to generate, amplify and compensate the multi-frequency (MF) power in MF multi-receiver simultaneous wireless power transfer (MF-MR-S-WPT) systems, this article proposes an innovative and generalized methodology. In proposed methodology, a MF modulation method based on cosine switching frequency modulation (CSFM) technique and a general multi-resonant transmitting tank design method based on circuit synthesis theory are introduced. With the proposed MF modulation method, a standard full-bridge inverter can be used to generate MF power, leading to a simple configuration of transmitting source. Moreover, a modulation degree of freedom can be provided to change the power transfer ratio, achieving power redistribution among receivers though software implementation. With the proposed design method of multi-resonant transmitting tank, the use of complicated multiple harmonic analysis can be avoided and the arbitrary multiple power components at selected resonant frequencies can be effectively amplified and completely compensated. Finally, the effectiveness of proposed methodology is verified theoretically and experimentally.

EMI mitigation in switching power converters combining closed‐loop gate drive and chaotic frequency modulation technique

All switching power converters are characterised by inevitable switching actions with relevant interference emissions. The voltage and current transients of power metal oxide semiconductor field effect transistor (MOSFET)/insulated-gate bipolar transistor are the main sources in switching power converters for both conducted and radiated emissions. In this study, a promising electromagnetic interference (EMI) mitigation method combining the closed-loop gate drive method and the chaotic switching frequency modulation technique is demonstrated for switching power converters. A chaotic pulse-width modulation waveform with Gaussian S-shape switching transients was proposed to achieve remarkable reduced EMI generation at all frequencies. Spectral characteristics of this new switching waveform were investigated by the power spectral density to verify the feasibility of reduced EMI generation. A closed-loop gate controller was presented to shape the switching transients of power MOSFET into the proposed switching waveform. Circuit tests were carried out in both simulations and experiments. The results validated that the proposed method could achieve remarkable EMI mitigation in switching power converters.

Current-Fed Multilevel Converters: An Overview of Circuit Topologies, Modulation Techniques, and Applications

Multilevel converters (MLCs) have emerged as standard power electronic converters in high power as well as quality demanding applications. They are classified into current-fed MLCs and voltage-fed MLCs. Voltage-fed MLCs have widely researched whereas the current-fed MLCs are the recent topic of research. Based on the principle of duality between voltage and current sources, several current-fed MLCs analogous to voltage-fed MLCs have been identified. Current-fed MLCs offer several advantages in terms of high power capability, transformerless operation, short-circuit protection, and excellent quality of output current waveform. The goal of this paper is: 1) to present review of circuit topologies, modulation schemes, and applications of current-fed MLCs; and 2) to review an emerging low-device switching frequency modulation technique known as synchronous optimal pulsewidth modulation for current-fed MLCs. The circuit configuration and advantages of each topology along with various modulation techniques are discussed in detail. Compared to voltage-fed MLCs, the operation of current-fed MLCs need to satisfy additional switching constraints. A survey of classical methods for realization of these operational constraints has been done and a new generalized method has been proposed. Finally, future scope of research has been presented to encourage further development of topologies and modulation techniques for current-fed MLCs.

Modified Synchronous Pulsewidth Modulation of Current-Fed Five-Level Inverter for Solar Integration

Large-scale photovoltaic (LSPV) energy conversion systems have been installed at many places across the world. The essential component of the LSPV system is the dc-ac conversion stage. The usage of multilevel converters is one of the recent advances in the dc-ac conversion stage of the LSPV system to enable transformer-less inversion. Current-fed multilevel inverter has been chosen in this paper as it provides high power inversion with inherent voltage boosting, and thus, avoids the usage of transformer. High power conversion necessitates low device switching frequency operation in order to satisfy thermal constraint of semiconductor devices and also to improve efficiency. However, low device switching frequency operation leads to higher harmonic distortion of inverter output currents. Synchronous optimal pulsewidth modulation (SOP) technique is an emerging low device switching frequency modulation technique that has been successfully implemented for voltage-source multilevel inverters. However, the state-of-the-art SOP technique cannot be directly applied to modulate current-source multilevel inverter topologies due to additional constraints on the switching commutations. Therefore, the purpose of our study was to propose a modified SOP technique to achieve: low device switching frequency and minimal harmonic distortion of inverter output currents. The topology of current-fed five-level inverter was used for demonstrating the performance of proposed technique. A generalized conversion method was introduced in the modified SOP technique for including switching constraints of the current-fed inverter. In addition, a state-sequencing machine was developed by utilizing redundant inverter states to produce equal switching commutation among all semiconductor devices at minimal switching frequency of 350 Hz. The experimental results obtained from the five-level current-source inverter of 1.2 kW demonstrated the effectiveness of the proposed SOP technique.

Optimal Low Switching Frequency Pulsewidth Modulation of Current-Fed Three-Level Converter for Solar Power Integration

Large-scale photovoltaic energy conversion systems have been installed at many places across the world and they handle higher power levels. In high power conversion, low device switching frequency operation is preferred in order to satisfy the thermal constraints of semiconductor devices and also to improve efficiency. However, low device switching frequency operation leads to higher total harmonic distortion (THD) of the converter output currents. Synchronous optimal pulsewidth modulation (SOP) is an emerging low device switching frequency modulation technique, which has been successfully implemented for voltage source inverters without compromising on THD. The goal of our research is to propose, analyze, and implement a modified SOP technique for current source inverter topologies. The additional switching constraints for these inverter topologies have been included in the modified SOP technique. The experimental results obtained from a low-power prototype demonstrated its effectiveness.

A Survey of Low Switching Frequency Modulation Techniques for Medium-Voltage Multilevel Converters

Multilevel converters (MLCs) have emerged as standard power electronic converters for medium-voltage high-power industrial applications. Owing to dominating device switching losses in high-power applications, it is preferable to use low device switching frequency (LDSF) modulation techniques. Then, it is possible to achieve higher device utilization, higher converter efficiency, and reduced cooling requirements. However, there exists a tradeoff between device switching frequency and harmonic distortion of converter output currents. Therefore, the main challenge for LDSF modulation techniques is to minimize the harmonic distortion of the output currents. The goal of this paper is to provide a review of various LDSF modulation techniques proposed in the literature and also discuss in detail about one of the emerging LDSF control techniques known as synchronous optimal pulsewidth modulation. Finally, challenges to LDSF modulation techniques for emerging multilevel topologies and future trends in applications of MLCs are discussed to motivate further research, to enhance the proposed LDSF techniques, and to explore for new alternatives.

Fundamental Switching Frequency Optimal Pulsewidth Modulation of Medium-Voltage Cascaded Seven-Level Inverter

Multilevel converters (MLCs) emerged as standard solutions for medium voltage (MV) high-power industrial ac drives. MV drives require low device switching frequency operation due to the higher switching losses of semiconductor devices. However, low device switching frequency operation leads to an increase in the harmonic distortion of machine stator currents. Therefore, there is a need to implement low switching frequency modulation technique for MLCs, which does not compromise on the harmonic distortion of machine currents. The goal of this paper is to propose a new optimal pulsewidth modulation technique for a cascaded seven level (7L) inverter such that the maximum device switching frequency is limited to the rated fundamental frequency (50/60 Hz) and all power semiconductor devices operate at identical switching frequency. Optimal switching patterns were determined offline assuming steady-state conditions. Later, switching angles for each semiconductor device are determined and stored in an FPGA controller. A low-power prototype of the 7L cascade inverter has been developed to demonstrate the proposed modulation technique. The experimental results demonstrated that the proposed optimal modulation technique maintains the quality of machine stator currents while the device switching frequency is limited to the rated fundamental frequency.

Dimmable electronic ballasts by variable power density modulation technique

Dimming can be accomplished commonly by switching frequency and pulse density modulation techniques and a variable inductor. In this study, a variable power density modulation (VPDM) control technique is proposed for dimming applications. A fluorescent lamp is operated in several states to meet the desired lamp power in a modulation period. The proposed technique has the same advantages of magnetic dimming topologies have. In addition, a unique and flexible control technique can be achieved. A prototype dimmable electronic ballast is built and experiments related to it have been conducted. As a result, a 36WT8 fluorescent lamp can be driven for a desired lamp power from several alternatives without modulating the switching frequency.

A Digitally Controlled Low-EMI SPWM Generation Method for Inverter Applications

This paper presents a digitally controlled way of generating the sinusoidal signal with less memory consumption. Moreover, this paper also presents a new switching frequency modulation technique. This technique utilizes the concept of spread spectrum frequency modulation that is used to suppress the electromagnetic interference (EMI) caused by high switching frequencies. Measurement results at the output sine pulse-width generation show that when the spread spectrum technique was applied to the conventional triangular wave and the fundamental, second, and third harmonics of switching frequency were reduced, respectively, by 12.8, 11.2, and 16.4 dB trading off with the slight increase in total harmonic distortion (THD) of 0.092% from a THD of 2.34%. While in the inverter output, there was a 14-dB reduction in EMI peak in exchange to 0.12% increase in THD from a THD of 2.57%.

EMI reduction by means of switching frequency modulation with variable delay in power supplies

In this article, a new model to predict the amplitude reduction of the interference harmonics in power supplies with parallel topology is presented when the switching frequency modulation with variable delay (VDFM) technique is applied. The VDFM method consists of combining the interleaving and switching frequency modulation (SFM) techniques. The new model presented has been evaluated in a multichannel buck converter, operating with different numbers of converters when a triangular modulation profile is used. Theoretical study and experimental results show the influence of the number of converters and the modulation parameters with regard to electromagnetic interference reduction. From the new model presented, it is possible to predict the value of modulation parameters and the numbers of converters in order to satisfy the required attenuation regarding the electromagnetic compatibility directives, when a triangular modulation profile is used.

Examination of Different Spread Spectrum Techniques for EMI Suppression in dc/dc Converters

Examination of different switching frequency modulation techniques (SFMT) for electromagnetic interference (EMI) suppression in dc/dc power converters is presented. The techniques under investigation are sinusoidal (with modulating frequencies 2 kHz and 5 kHz), pseudo-random (with uniform and normal probability distributions of modulating signal) and pseudo-chaotic SFMT. All the techniques are applied to digitally-controlled buck converter of Microchip dsPICDEM SMPS Buck Development Board. Free-wheeling diode voltage of the buck converter operating at switching frequency of 300 kHz and exposed to switching frequency deviation ranging from 0 to 60 kHz is analyzed in order to show effectiveness of such techniques in terms of EMI attenuation. Concerning with possible undesirable side effects in the form of excessive output voltage ripples, the experiments are accompanied by output voltage control of the converter. Analysis of the results obtained reveals that there is need for trade-off between EMI attenuation and output voltage ripples. The pseudo-chaotic SFMT shows the best results from the standpoint of this trade-off. Pseudo-random SFMT with uniform probability distribution of modulating signal gives better EMI attenuation than the other techniques, but output voltage ripples are also larger. That is why this technique can be used for applications, where high EMI attenuation by use of small switching frequency deviations is of primary importance. Ill. 6, bibl.12 (In English; summaries in English, Russian and Lithuanian).

Conducted EMI Reduction in Power Converters by Means of Periodic Switching Frequency Modulation

Spread spectrum clock generation techniques were originally developed to reduce electromagnetic interference (EMI) in communications and microprocessor systems working in the range of hundreds of megahertz. Nowadays, the switching frequency of power converters has been increasing up to values that make worthy the application of such switching frequency modulation techniques to reduce EMI emissions in power converters. Although random modulations have been applied before to power converters, periodic patterns can provide some advantages. First, theoretical principles of frequency modulation using three periodic patterns for the modulating function are presented. The influence of some important modulation parameters on the EMI reduction is analyzed and some considerations about the EMI filters design are also presented. The effectiveness of such methods in terms of EMI reduction is demonstrated theoretically and confirmed with experimental results obtained from tests carried out on two converters. The first one is a 2.5 W buck converter that can be switched up to 1 MHz and the second one is a 600 W boost converter switching at 40 kHz. In both cases, attenuations obtained in conducted EMI are evaluated. Finally, special attention has been paid to input current and output voltage ripple in order to evaluate possible undesired side-effects produced by this technique.