Proposed Pulse Width Modulation Strategy Research Articles

Mathematical Modeling and Analysis of Capacitor Voltage Balancing for Power Converters with Fewer Switches

The multilevel inverter (MLI) has been developed as a powerful power conversion scheme for several processes, including renewable energy, transmission systems, and electric drives. It has become popular across medium- to high-power operations due to its many advantages, including minimum harmonic content, low switching losses, and reduced electromagnetic interference (EMI). In this paper, the capacitor voltage balancing technique-based pulse width modulation (PWM) has been proposed. The proposed PWM strategy offers several advantages, such as high-quality output waveforms with reduced harmonic distortion, improved efficiency, and better control over the output voltage. The Xilinx ISE 10.1 software was used for synthesizing, and the VHDL code was written for the proposed method. MATLAB software was used to simulate and hardware was used to verify the proposed system. The SPARTAN 3E FPGA was used for the generation of the PWM. This paper developed a 2 kW single-phase 15-level inverter that created an AC wave from the DC input voltage, with a total harmonic distortion (THD) of 8.02%, which was less than the THD achieved from other conventional MLI. The results indicate that MLI topologies with low total harmonic currents, fewer switches, and higher output voltage levels are better stabilized during load disturbance circumstances.

THE ANALYSIS OF REDUCTION IN SWITCHING LOSS WITH FEEDFORWARD CONTROL IN GRID-TIED MICRO GRID SYSTEM

This paper proposes the simplified pulse widthmodulation (PWM ) strategy in the bidirectionalac/dc single-phase converter with the feed-forwardcontrol scheme. In this, the number of switching ofthe proposed simplified PWM strategy is reduced toone-fourth to that of the unipolar & bipolar PWM.The feed-forward control scheme is used to achievebetter performance of the ac/dc converter in both therectifier & inverter mode as compared with theconventional dual-loop control scheme. Thesimplified PWM strategy with feed-forward controlscheme has higher efficiency than that of the unipolarPWM & bipolar PWM strategies. Also, the totalharmonic distortion is less in this PWM strategy. Thesimulation & experiments are carried out to verify thevalidity of the proposed PWM strategy & controlscheme. The proposed simplified PWM strategy withthe proposed feedforward control scheme has lowertotal harmonic distortion than the bipolar PWM andhigher efficiency than both unipolar and bipolarPWMs. Furthermore, the proposed simplified PWMoperated in the inverter mode also has largeravailable fundamental output voltage VAB than boththe unipolar and bipolar PWMs. A prototype systemis constructed and the control scheme is implementedusing FPGA Spartan-3E XC3S250E. Both simulationand experimental results verify.

Modified PWM Scheme to Reduce Reverse Conduction Loss in GaN-Based Independently Controlled Multiple Output Flyback Converter

The recently proposed independently controlled multiple output flyback converter (ICMOFC) scheme improves cross-regulation by utilizing gallium nitride (GaN) switches with negative gate turn- <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">off</small> voltage. The highly inefficient reverse conduction (RC) of negative gate biased GaN devices leads to significant RC loss in the existing ICMOFC scheme. To mitigate this problem, this letter proposes a new pulsewidth modulation (PWM) scheme. The RC loss reduction is achieved by reducing the RC duration and RC current. The effectiveness of the proposed PWM strategy is analytically and experimentally verified using a 40-W dual output flyback converter. The results demonstrate a peak efficiency improvement of 1.26% over the existing ICMOFC scheme. Furthermore, the scheme also achieves high power density (51 W/in <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$^{3}$</tex-math></inline-formula> ) and excellent cross-regulation (0.2%).

Asymmetrical PWM Scheme to Widen the Operating Range of the Three-Phase Series-Capacitor Buck Converter

The three-phase series-capacitor (3P-SC) buck converter is analyzed extensively in this study for high-voltage step-down applications with a wide input voltage range. This structure is attractive due to its high step-down conversion ratio and inherent current balancing. However, the inductor currents of the 3P-SC converter become unbalanced when the duty cycle exceeds 1/3. This results in significant stress and reduces the utilization of switching devices. This article proposes an asymmetrical pulsewidth modulation (PWM) scheme for the 3P-SC converter to overcome the limitations of the conventional PWM scheme. By using the proposed switching scheme, the duty cycle can be increased to one while retaining the high conversion ratio and current balancing functionality. Thereafter, the proposed asymmetrical PWM strategy is generalized for multiphase series-capacitor (nP-SC) converters. Finally, to validate the performance of the proposed PWM strategy, a 1.2-kW prototype 3P-SC converter is fabricated and tested.

Vector-Splitting Method to Reduce Common-Mode Voltages in Two-Level Inverters for Grid Connection

This article proposes a new pulsewidth modulation (PWM) strategy to reduce common-mode voltages (CMVs) in grid-connected two-level inverters. Reduction of CMVs is an important issue in the field of distributed energy resources (DERs) because CMVs at a high switching frequency cause ground leakage currents that lead to safety issues in the applications of DERs. In the proposed PWM strategy, each reference vector is split into two vectors during the PWM period. The peak-to-peak magnitude of CMV is reduced by one-third as the split vectors are synthesized without using zero vectors. The influence of the dead-time and its compensation in the proposed method are also described. Our proposed method can be easily implemented with carrier-based PWM. Simulation and experimental results are presented to verify the performance of the proposed strategy.

PWM Strategy for MW-Scale “SiC+Si” ANPC Converter in Aircraft Propulsion Applications

In this article, an improved pulsewidth modulation (PWM) strategy is introduced for three-level active neutral point clamped converters based on a hybrid configuration of silicon carbide (SiC) mosfets and silicon (Si) insulated gate bipolar transistor (IGBTs). Compared with the conventional PWM strategies in the literature, this proposed PWM strategy enables the SiC switches only to interface with small commutation loops, thus the turn-off voltage overshoots caused by the parasitic loop inductance and high <b xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">di</b> / <b xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">dt</b> are much lower. Soft switching is achieved across all the IGBTs, and the switching losses of the converter only dissipate from the SiC mosfets, leading to high efficiency of the converter. Also, with this improved PWM strategy, the conduction loss at zero voltage output of this converter is reduced due to the turn-on of two parallel conduction paths. Furthermore, this proposed PWM strategy can protect the body diodes of the SiC mosfets from conducting large load current. All these advantages with the proposed PWM strategy are experimentally verified in a megawatt-scale three-phase three-level “SiC+Si” hybrid active neutral point clamped inverter developed for electric aircraft propulsion applications.

A Temporary Overvoltages Mitigation Strategy for Grid-Connected Photovoltaic Systems Based on Current-Source Inverters

Temporary overvoltages (TOVs) typically caused by short-circuit faults and switching events can impose considerable damage on power system equipment. Furthermore, the penetration of distributed generations into the utility grids may intensify the problem arising from the TOVs. Despite recent research advancements, the TOV problems with current-source inverter (CSI)-based photovoltaic (PV) systems have not been investigated comprehensively. This paper proposes a combination of virtual impedance and modified switching strategy for grid-connected CSI-based PV systems. The virtual impedance-based control damps current and voltage oscillations. On the other hand, the proposed pulse width modulation strategy restricts power injection during the fault conditions. Simulation results confirm that the proposed approach effectively mitigates the TOV without controller mode switching between the standard and fault conditions.

Bidirectional Three-Phase DC–AC Converter With Embedded DC–DC Converter and Carrier-Based PWM Strategy for Wide Voltage Range Applications

A bidirectional three-phase dc–ac converter with embedded dc–dc converter for bidirectional storage interface is proposed in this paper. With the help of the embedded dc–dc converter, the voltage of the storage battery can vary in a wide range. To minimize the power rating and power losses of the embedded dc–dc converter, a simple carrier-based pulsewidth modulation (PWM) strategy with zero-sequence injection is proposed. By adopting the proposed PWM strategy, only a small ratio of total power needs to be processed by the embedded dc–dc converter, while most of the power is only processed by the three-phase dc–ac stage within a single conversion stage. As a result, quasi single-stage power conversion is achieved to improve the conversion efficiency of the overall dc–ac power system. Principles, characteristics, and implementations of the proposed three-phase dc–ac converter and its PWM strategy are analyzed in detail. The feasibility and effectiveness of the proposed solutions are verified with experimental results.

Hybrid PWM Strategy for Power Efficiency Improvement of 5-Level TNPC Inverter and Current Distortion Compensation Method

This paper proposes a pulse width modulation (PWM) strategy for improving the efficiency of a 5-level H-bridge T-type neutral point clamped (TNPC) inverter. In the case of the proposed PWM strategy, unlike the conventional PWM strategy in which both of the switching legs of the H-bridge inverter operate at a high frequency, one switching leg of the inverter operates at a low frequency. As the switching frequency is lowered, the switching loss is reduced, this improving the efficiency of the system. The duty references for the switching legs and the operating principle of the inverter are described in detail. The proposed PWM strategy, however, causes distortion of the output filter inductor current. The cause of the distortion has been analyzed and a compensation method is proposed to mitigate the distortion of the current. The effect of the proposed PWM strategy can be predicted through the loss calculation of the inverter for each modulation strategy. Furthermore, current distortion mitigation obtained by compensation method is confirmed through the simulation. In order to verify the effectiveness of the proposed strategy, a 2 kW H-bridge TNPC inverter prototype is implemented and tested. The simulation and experimental results show that the efficiency of the inverter is improved when the proposed PWM strategy is applied.

A Carrier-Based PWM Strategy Providing Neutral-Point Voltage Oscillation Elimination for Multi-Phase Neutral Point Clamped 3-Level Inverter

General pulse width modulation (PWM) model for multi-phase neutral point (NP) clamped (NPC) 3-level inverter (3LI) is described. A novel PWM strategy for $N$ -phase NPC 3LI with unconditional NP voltage balance is proposed as well as its carrier-based realization, in which PWM sequences are generated by comparing a single carrier wave with double modulation waves. The proposed PWM strategy is consistent with the principle of virtual space vector PWM (VSVPWM). However, the mechanism of NP voltage balance under the proposed PWM strategy is based on precisely calculating and executing level 1 action time of each phase, which may be influenced by some non-ideal factors. To avoid that, an active NP voltage control for the proposed PWM strategy is put forward. Then 3-phase and 5-phase NPC 3LIs are built as examples to verify the correctness of the proposed PWM strategy. Finally, the experimental results indicate that the proposed PWM strategy has better NP voltage control abilities.

A Dual Three-Level Inverter Based Open-end Winding Induction Motor Drive with Averaged Zero-Sequence Voltage Elimination and Neutral-Point Voltage Balance

Two three-level inverters driving an open-end winding induction motor can generate equivalent voltage waveforms as a single five-level inverter-based drive. In addition, it can bring in benefits such as reduced dc-link voltage, less number of devices, and fault-tolerant capability, which is favored in high-power motor drive applications. The main challenge with this type of configuration is the appearance of large zero-sequence current circulating between the two inverters, which generates extra losses in the switching devices and the motor as well as affects the normal operation of the machine. Another challenge is to balance the dc-link neutral point voltage of the two three-level inverters. This paper has proposed a simplified decoupled space-vector pulsewidth-modulation (PWM) strategy to eliminate the averaged zero-sequence voltage in each switching cycle by the placement of redundant vectors of each individual inverter using a time shift. Neutral point voltage balance is further achieved by adjusting the time duration of the redundant vectors. In this paper, it is shown that it is possible to operate this kind of drive configuration with a single dc power supply and achieve averaged zero-sequence voltage elimination and neutral-point voltage balancing at the same time. Experimental results of a 5.5-kW dual three-level inverter drive using the proposed PWM strategy are presented, which validates the control method and drive configuration.

Common-Mode Voltage Reduction of Three-Level Four-Leg PWM Converter

This paper presents a carrier-based pulsewidth modulation (PWM) method that reduces the common-mode voltage (CMV) of a three-level four-leg converter. Based on an analysis of space vector PWM (SVPWM) and sinusoidal-PWM switching patterns, the fourth-leg pole voltage of a three-phase converter, known as the “f pole voltage,” is manipulated to reduce the CMV. To synthesize the f pole voltage for the suppression of the CMV, positive and negative pole voltage references of the f leg are calculated. In addition, the offset voltage to prevent distortion of the a, b, and c phase voltages regarding the neutral point is deduced. The proposed PWM strategy can be easily implemented in the software of a DSP-based converter control. The three-level four-leg converter with the proposed PWM algorithm results in a remarkable reduction in the peak-to-peak value of the CMV. From the simulation and the experimental results, the peak-to-peak value of the CMV when using the proposed PWM method is 33% compared to that when using the SVPWM method, while the number of CMV transitions during the switching period in the proposed PWM method is only 25% of that when using the SVPWM method.

Pulse‐width modulation control strategy for high efficiency LLC resonant converter with light load applications

LLC resonant converters, generally adopting frequency modulation control, can hardly achieve high efficiency under both heavy and light load conditions. Especially under light load conditions, the high-switching frequency seriously degrades converter's efficiency. This study propose a new pulse-width modulation (PWM) control strategy for LLC resonant converters under light load applications on the premise of no change in the main circuit structure. The voltage gain of the converter is regulated by varying duty ratio instead of increasing switching frequency and therefore zero-current switching for rectifier diodes can be realised under light load conditions. With the proposed PWM control strategy, the gain is not affected by the load variations and an optimal design of the magnetic components is possible, therefore the efficiency is further improved by reducing both the switching losses and the losses in magnetic components. Experimental results demonstrate the effectiveness of the proposed PWM strategy by increasing the efficiency of LCC resonant converter, especially under light load conditions.

Simplified PWM Strategy for Neutral-Point-Clamped (NPC) Three-Level Converter

A novel simplified pulse width modulation(PWM) strategy for neutral point clamped (NPC) three-level converter is proposed in this paper.The direct output voltage modulation is applied to reduce the calculation time. Based on this strategy, several optimized control methods are proposed. The neutral point potential balancing algorithm is discussed and a fine neutral point potential balancing scheme is introduced. Moreover, the minimum pulse width compensation and switching losses reduction can be easily achieved using this modulation strategy. This strategy also gains good results even with the unequal DC link capacitor. The modulation principle is studied in detail and the validity of this simplified PWM strategy is experimentally verified in this paper. The experiment results indicated that the proposed PWM strategy has excellent performance, and the neutral point potential can be balanced well with unequal DC link captaincies.

A Novel Reduced Switching Loss Bidirectional AC/DC Converter PWM Strategy With Feedforward Control for Grid-Tied Microgrid Systems

This paper presents a novel simplified pulse width modulation (PWM) strategy for the bidirectional ac/dc single-phase converter in a microgrid system. Then, the operation mechanism of the novel simplified PWM is clearly explained. The number of switchings of the proposed simplified PWM strategy is one-fourth that of the conventional unipolar PWM and bipolar PWM. Based on the novel simplified PWM strategy, a feasible feedforward control scheme is developed to achieve better rectifier mode and inverter mode performance compared with the conventional dual-loop control scheme. The proposed simplified PWM strategy with the proposed feedforward control scheme has lower total harmonic distortion than the bipolar PWM and higher efficiency than both unipolar and bipolar PWMs. Furthermore, the proposed simplified PWM operated in the inverter mode also has larger available fundamental output voltage VAB than both the unipolar and bipolar PWMs. A prototype system is constructed and the control scheme is implemented using FPGA Spartan-3E XC3S250E. Both simulation and experimental results verify the validity of the proposed PWM strategy and control scheme.

Pulsewidth Modulation of Z-Source Inverters With Minimum Inductor Current Ripple

This paper proposes the pulsewidth modulation (PWM) strategy of Z-source inverters (ZSIs) with minimum inductor current ripple. In existing PWM strategy with single-phase shoot-through, the shoot-through time interval is divided into six equal parts, therefore the three phase legs bear the equal shoot-through time interval. In this manner, the allotment and arrangement of the shoot-through state is easy to realize, but the inductor current ripple is not optimized. This causes to use relatively large inductors. In the proposed PWM strategy, the shoot-through time intervals of three phase legs are calculated and rearranged according to the active state and zero state time intervals to achieve the minimum current ripple across the Z-source inductor, while maintaining the same total shoot-through time interval. The principle of the proposed PWM strategy is analyzed in detail, and the comparison of current ripple under the traditional and proposed PWM strategy is given. Simulation and experimental results on the series ZSI are shown to verify the analysis.

Analysis of PWM Strategy for Reduction of Conducted Electromagnetic Interference in an Adjustable-Speed AC Motor Drive

This paper presents various pulse width modulation (PWM) strategies capable of reducing conducted electromagnetic interference (EMI) generated in PWM voltage-source inverter systems. EMI problems caused by both conducted and radiated noise emissions have become a great concern in electrical/electronic systems. Thus, their effects are currently considerably taken into account in circuit design phase in order to restrict or reduce these severe problems. The proposed PWM strategy, which is one of different traditional and/or novel reduction techniques to solve such a problem, is chosen as an EMI reduction method and studied herein. The simulated results show that active vector PWM strategy seems to be a good alternative for inverter system. The impact of dead time of PWM signals is also investigated and discussed.

PMモータ駆動に適した変形台形波変調信号

In this paper, a new modulating signal for pulse width modulation (PWM) inverter system suitable for Permanent Magnet synchronous motor (PMSM) drive is proposed. The PMSM with the sinusoidal electromotive force (EMF) driven by the non-sinusoidal PWM voltage generates a torque ripple. And, the torque ripple is similarly generated in PMSM with the trapezoidal EMF driven in the sinusoidal PWM voltage. The new PWM strategy makes a great improvement of the characteristics in the three-phase PWM inverter for the PMSM. The proposed PWM strategy can reduce torque ripple more than sinusoidal PWM method. Although the output voltage waveform is a non-sinusoidal waveform, the motor driven by the proposed modulating signal produces approximately constant torque. By using the proposed modulating signal, the amplitude of the fundamental component is increased more than that of a conventional sine wave inverter. The usefulness of the proposal method was confirmed by a theoretical analysis, the simulation by modeling the system, and the experiments.

Minimum-loss strategy for three-phase PWM rectifier

In this paper, the conduction and switching losses of a voltage-fed three-phase pulsewidth modulation (PWM) rectifier are analyzed for various PWM schemes. On the basis of this result, a novel PWM strategy which minimizes the loss of a three-phase PWM rectifier is developed. This minimization result is derived from the following two factors: (1) less switching frequency ratio; and (2) the absence of switching in the vicinity of peak input current. As a result, it is anticipated that the switching loss of the rectifier is reduced by 46%, compared with continuous space-vector PWM rectifiers, and 20% compared with conventional discontinuous space-vector PWM rectifiers. Moreover, the proposed PWM scheme can produce the highest available output voltage because it is based on the concept of the voltage space vector. The effectiveness of the proposed PWM strategy is verified by experiments.