Pulse Width Modulation Scheme Research Articles

High Efficiency Operation of Brushless DC Motor Drive Using Optimized Harmonic Minimization Based Switching Technique

This article presents a new switching technique to minimize losses in a trapezoidal brushless dc motor (BLDCM) drive. Based on the analysis, a pulsewidth modulation (PWM) strategy with selective harmonics elimination (SHE) is projected for motor phase current for dynamic loss minimization of BLdc motor drive system. The proposed control technique uses SHEPWM to optimize PWM to minimize different losses at different loads and motor speeds based on a predefined look-up table. The efficacy of the control methodology is presented using proper simulation results in MATLAB/Simulink environment. The control methodology is also validated with an experimental prototype of 350W BLDCM drive system.

Suppression Strategy for Midpoint Potential Fluctuation of Three-Level Wind Power Converter

With the development of offshore wind power, three-level wind power converters have begun to be widely used in wind farms, but there has always been a problem of low-frequency fluctuations in bus voltage, which will seriously affect the power quality of wind farms. This paper studies a GA-BP neural network optimization control method, injecting zero-sequence components on the basis of the sine pulse width modulation strategy of carrier stacking, and then optimizing the neural network weights and thresholds through genetic algorithm, and the bus capacitor voltage Low-frequency fluctuations are tracked and compensated to improve the predictive ability of the control system. This combination of zero-sequence voltage injection and injection-compensated low-frequency fluctuation components solves the problem of bus voltage fluctuations. Through Matlab/simulink simulation analysis and 1140V wind power converter experimental verification, the verification results show that the bus voltage fluctuation is reduced by 50%, and the grid current waveform is improved. The proposed scheme can well solve some of the influences caused by the fluctuation of the bus voltage in the wind power converter, ensure the operation reliability of the wind power system and improve the operation efficiency of the wind power system.

A Simple Virtual-Vector-Based PWM Formulation for Multilevel Three-Phase Neutral-Point-Clamped DC–AC Converters including the Overmodulation Region

Neutral-point-clamped (NPC) power conversion topologies are among the most popular multilevel topologies in current industrial products and in industrial and academic research. The proper operation of multilevel three-phase NPC DC–AC converters requires the use of specific pulse-width modulation (PWM) strategies that maintain the DC-link capacitor voltage balance and concurrently optimize various performance factors such as efficiency and harmonic distortion. Although several such PWM strategies have been proposed in the literature, their formulation is often complex and/or covers only particular cases and operating conditions. This manuscript presents a simple formulation of the original virtual-vector-based PWM, which enables capacitor voltage balance in every switching cycle. The formulation is presented, for the general case, in terms of basic phase voltage modulating signals, with no reference to space vectors, involving any number of levels and for any operating conditions, including the overmodulation region. The equivalence of the presented formulation to the original PWM strategy is demonstrated through simulation under different scenarios and operating conditions. Thus, this manuscript offers in a one-stop source a simple, effective, and comprehensive PWM formulation to operate multilevel three-phase NPC DC–AC converters with any number of levels in any operating condition.

Modified T-type topology of three-phase multi-level inverter for photovoltaic systems

In this article, a three-phase multilevel neutral-point-clamped inverter with a modified t-type structure of switches is proposed. A pulse width modulation (PWM) scheme of the proposed inverter is also developed. The proposed topology of the multilevel inverter has the advantage of being simple, on the one hand since it does contain only semiconductors in reduced number (corresponding to the number of required voltage levels), and no other components such as switching or flying capacitors, and on the other hand, the control scheme is much simpler and more suitable for variable frequency and voltage control. The performances of this inverter are analyzed through simulations carried out in the MATLAB/Simulink environment on a three-phase inverter with 9 levels. In all simulations, the proposed topology is connected with R-load or RL-load without any output filter.

Variable Voltage Variable Frequency Modular Multilevel AC/AC Converter With High-Frequency Harmonics Filtering Capability

This article proposes a variable voltage variable frequency modular multilevel ac/ac converter (VVVF-MMC) with a high-frequency isolation link, which can realize voltage and frequency conversion simultaneously with insulated-gate bipolar transistors (IGBTs) of the same rated voltage and current level. The parallel connection of multiple modules is realized by coupling reactors, which can realize large-scale voltage and current transformation and save volume. It combines parallel multiplexing and serial multiplexing technology of submodules (SMs) to increase the equivalent switching frequency, thereby canceling nonzero sequence high-frequency voltage and current harmonics, so it has good power quality in the steady-state. Under the improved carrier phase-shifted pulsewidth modulation (CPS-PWM) strategy, the pulse flip circuit can realize soft switching operation, thereby improving energy conversion efficiency. Furthermore, dc capacitor voltage balancing and parallel SM current balancing control strategies are designed. With the strong filtering ability, the proposed ac/ac converter can be used as the onshore converter station of fractional frequency offshore wind power system. Due to the advantages of small size and high efficiency, it also has broad application prospects in distribution networks and electric drive. Simulation and experimental results validate the effectiveness of the proposed converter topology.

A Pulse-Width Modulation Control Approach for the High-Voltage Gain Operation of a Z-Source Neutral-Point Clamped Inverters

This paper deals with a developed pulse-width modulation technique for a Z-source three-level NPC inverter. This technique overcomes the limitation of the boost capability of the Z-source NPC inverter; hence, it may suit applications that involve a high-voltage boosting gain. The proposed modulation strategy is based on the discontinuous pulse-width modulation strategy of the neutral-point clamped inverter. It guarantees an improved current and voltage profile at the output and ensures a high-voltage gain by decoupling control for the shoot-through duty ratio and the modulation index. The effectiveness of the proposed modulation strategy is tested through an intensive simulation. Experimental tests, carried out on the digital development board, demonstrate the feasibility of the proposed control.

Performance Analysis of Modular Multilevel Converter with NPC Sub-Modules in Photovoltaic Grid-Integration

In this article, a three-phase modular multilevel converter (MMC) with three-level neutral point clamped converter (NPC) sub-modules (SMs) along with the placement of transformers in place of arm inductors is proposed for PV grid integration. Compared to the traditional MMCs, the proposed configuration reduces the voltage and power rating for the switches and the requirement of a high capacitor bank. In order to analyze the performance of the proposed converter arrangement, we have implemented four pulse width modulation schemes, such as Sine PWM with phase-level shifted carrier (SPWMLSC), Sine PWM with a phase-shifted carrier (SPWMPSC), Sine with the third harmonic injected level-shifted carrier (STHILSC), and Sine with the third harmonic injected phase-shifted carrier (STHIPSC). The proposed converter was simulated in the MATLAB/Simulink platform. Under normal and faulty operation, the results were presented with their performance indices of voltage and current harmonic distortion and sub-module capacitor voltage ripples at various modulation indices.

A carrierless pulse-width modulation strategy for three-phase cross-switched multilevel inverter using area equalization method

A carrierless pulse-width modulation strategy for three-phase cross-switched multilevel inverter using area equalization method

Nonlinear Adaptive Control with Asymmetric Pressure Difference Compensation of a Hydraulic Pressure Servo System Using Two High Speed On/Off Valves

A hydraulic pressure servo system based on two high-speed on/off valves (HSV) is a discontinuous system due to the discrete flow of HSV when driven by pulse width modulation (PWM) signal. Pressure variation in the testing chamber is determined by the flow rate difference between the charging and discharging HSV. In this paper, a pressure controller consisting of a differential PWM (DPWM) scheme, asymmetric pressure difference compensation (APDC) and nonlinear adaptive control (NAC) is proposed to precisely control the pressure. The DPWM scheme is designed to improve the resolution of the net flow rate into the testing chamber. Furthermore, due to the strong asymmetry between the charging and the discharging process, the APDC method is proposed to design the two initial duty cycles of the DPWM signal which help to balance its charging and discharging ability under different working pressure points. Since the pressure system is a nonlinear, uncertain system due to oil compression and leakage, the NAC is designed to calculate the control duty cycle of the DPWM signal, which is used to overcome the unmodeled dynamic and parameter uncertainties. Comparative experiments indicate that the proposed controller can ensure good pressure tracking performance and enhance system robustness under different working pressure points and tracking frequencies.

Performance Improvement of Dual-Buck Inverter With Mitigating Reverse Recovery Characteristics and Supporting Reactive Power

This paper proposes a three-level dual-buck inverter (DBI) that reduces reverse recovery current and compensates reactive power. To reduce the reverse recovery problem of main switching diodes in the DBI, the auxiliary circuit consisting of diodes and coupled inductors is adapted. The auxiliary circuit enables zero-current turn-off of the diodes. The coupled inductor design is also conducted considering not only for unity power factor (PF) but also non-unity PF operations. By utilizing the auxiliary circuit, the reverse recovery and the shoot-through problems in silicon devices can be significantly mitigated so that the efficiency and the reliability of the DBI are much improved. Meanwhile, the pulse-width modulation scheme is also proposed to supply reactive power with the DBI which is a unidirectional inverter. In the proposed modulation method, the duty offset is simply added according to the required PF and the operating region of the DBI. By doing so, traditional current control concepts for bidirectional inverters can be directly applied to the DBI without any modification. By utilizing the proposed techniques, the reliability, efficiency, and utilization of the DBI can be significantly improved. The experimental results with a 3 kVA DBI prototype demonstrate the effectiveness of the proposed DBI.

Active Voltage Balancing Control of a Seven-Level Hybrid Multilevel Converter Topology

The series connection of a standard three-level active neutral-point-clamped (ANPC) inverter and two cascaded H-bridge (CHB) modules comprising the flying capacitors (FCs) instead of the isolated dc voltage sources forms a seven-level hybrid topology that is referred to as improved ANPC (I-ANPC) converter. This article proposes an active voltage balancing technique for control of this hybrid multilevel inverter. The suggested method is based on a set of effortless logic equations that aim to stabilize the FC voltages within the CHB modules at their requisite reference values as well as to control the output voltage of the overall hybrid converter based on the phase-shifted-carrier pulsewidth modulation strategy. The experimental results obtained from a single-phase I-ANPC inverter's prototype are presented to validate the proposed control technique and its simple logic equations.

A Generalized Phase-Shift PWM Extension for Improved Natural and Active Balancing of Flying Capacitor Multilevel Inverters

The emergence of wide bandgap power devices has brought the attention back to the flying capacitor (FC) multilevel inverters with a large number of stages, in an effort to increase the power density by minimizing the passive components. The main challenge that such systems face, particularly the ones based on high-frequency Gallium-Nitride devices and small-value ceramic capacitors, relate to the stringent requirements for precise and fast capacitor balancing. Conventional <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">natural balancing</i> techniques exhibit poor settling times, while most improved natural balancing methods are not easily scalable to more than five levels. The alternative of <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">active balancing</i> normally requires one isolated sensor per FC which increases the overall system cost and footprint, or a single ac-side sensor that is more compact but calls for sophisticated PWMs that again are not available for multiple levels. In this paper we introduce a generalized pulse width modulation (PWM) strategy based on the phase-shift and carrier swapping principles for an arbitrary number of levels. We provide an easy and intuitive method for the extraction of the PWM pattern, the switching states, and their sequence. Simulations were carried out in Matlab/Simulink and experimental tests were conducted on a single-phase 7-level GaN inverter prototype. Not only is the extended PWM advantageous in natural balancing, but it also provides the right zero switching states for ac-side FC sensing in active balancing.

Novel Variable Switching Frequency PWM Strategy for a SiC-MOSFET-Based Electric Vehicle Inverter to Increase Battery Usage Time

In this study, a novel variable switching frequency pulse width modulation (VSFPWM) strategy is proposed to achieve improved electric vehicle inverter efficiency. The silicon carbide (SiC) MOSFET inverter has excellent switching characteristics, thus enabling pulse width modulation control with a high switching frequency. The high switching frequency can reduce the voltage ripples in DC-link capacitors, which enables their use at a reduced capacitance. The switching frequency is typically set to a level that is within the limits of the voltage ripple in the maximum output region. Given that the same switching frequency is applied to the entire operating region, there is a sufficient margin with respect to the limits of the voltage ripple in the low-to-medium output range. The proposed method is designed to consider the real-time minimum switching frequency by considering the voltage ripple of the capacitor during operation under loaded conditions, thereby minimizing the switching loss. In addition, the method is suitable for high-switching frequency control because the calculation time is short. Because it does not require additional hardware, it is easy to apply to the existing inverter. The validity of the proposed method was verified based on simulations and experiments.

Space Vector PWM Based DTC Scheme With Reduced Common Mode Voltage for Five-Phase Induction Motor Drive

In multiphase induction motor drives, lowering the common-mode voltage (CMV) reduces motor insulation degradation and the existence of destructive bearing current. For this investigation, a five-phase two-level voltage source inverter (FPTL-VSI) fed five-phase induction motor (FPIM) drive is used. FPTL-VSI produces increased CMV, which cannot be totally removed. Moreover, CMV can be reduced by 80% in contrast to its peak-to-peak value with suitable selection of small and large voltage vectors in a space vector pulsewidth modulation (SVPWM) scheme. Direct torque control (DTC) combined with the SVPWM scheme can accomplish such reduced CMV performance at constant switching frequency. To provide better speed and torque control, two virtual vector (VV) based SVPWM-DTC (DTC1 and DTC2) methods are proposed in this study. Over a wide range of modulation index, the influence of each voltage VV on motor drive speed and torque response is investigated. The proposed DTC1 and DTC2 schemes are validated under steady-state and dynamic conditions over a wide range of speed fluctuations using a high-power laboratory prototype of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$3.8\,\text{{k}W}$</tex-math></inline-formula> FPIM drive. The efficacy of the proposed DTC1 and DTC2 is compared to the current literature by evaluating the effectiveness of CMV and the switching frequency.

A Modified Variable Switching Frequency Spread-Spectrum PWM Technique With Reduced Torque Ripple for a Vector-Controlled PMSM Drive

The discrete tonal bands introduced in an AC machine’s stator current spectrum by constant switching frequency pulse width modulation schemes, have adverse impacts on the vibration, the acoustic noise, and the electromagnetic interference. Spreading the harmonic spectrum and reducing the magnitude of dominant harmonics is one solution to this problem. Ripples in the electromagnetic torque developed is another major concern in AC drives. Inspired by these factors, this study proposes two novel variable switching frequency schemes for a vector-controlled PMSM drive to disperse the frequency spectrum with a significant reduction in torque ripple. The modulation techniques use linear and trapezoidal variation of sub-cycle sampling period; <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T_s</i> during their implementation. Further, these methods would be able to eliminate the difficulty in compensator design, which is a major problem with other variable switching frequency schemes. The presented strategies achieve a maximum of 27 % reduction in torque ripple, 51.8 % reduction in dominant harmonics, and a dispersion index of 1.63, demonstrating their competency as promising variable switching frequency schemes. The suggested techniques also show excellent torque ripple reduction capability in comparison with latest spread-spectrum techniques in literature. The proposed techniques are implemented in simulation using MATLAB/Simulink and are experimentally validated using WAVECT-FPGA controller on a 1.07 kW, surface-mounted PMSM drive.

Single-Source Cascaded Multilevel Inverter With Voltage-Boost Submodule and Continuous Input Current for Photovoltaic Applications

Cascaded multilevel inverter (CMI) produces a step-up output voltage by series-connection of several submodules (SMs) supplied by isolated dc sources, which can be implemented by photovoltaic (PV) sources. The unbalanced power provided by different PV sources may however distort the output voltage. To use a single dc source while retaining the voltage boosting, this article proposes a novel CMI based on a four-switch SM. It is conditioned by an input inductor, which discharges with boosted voltages across the SMs. Furthermore, a continuous input current is achieved by the inductor. The proposed inverter can be extended to higher voltage-level operations using capacitors to supply its extended SMs. To avoid switched-capacitive charging, a two-phase configuration where capacitors are directly charged by the inductive input current is presented. The voltages of capacitors are well balanced at the same average value and feature a similar ripple. The operating principles and pulsewidth modulation scheme of the two-phase inverter are described. Theoretical analysis, calculations, and comparisons with the prior-art CMIs illustrate the superiorities of the proposed inverter. Simulation and experimental results agree well with each other and verify the feasibility of the proposed inverter for PV power applications.

Minimization of DC-Link Capacitance and Improved Operational Performance of a 5-Level Hybrid Multilevel DC-Link Inverter

This study analyzes a single-phase hybrid multilevel dc-link (MLDCL) inverter, in which a dc-link with two capacitors is integrated into a single dc source. When controlled under the conventional modulation scheme, the MLDCL inverter synthesizes a five-level output voltage. As the capacitor-voltage balancing depends on the fundamental period, the output voltage may contain unsolicited low-order harmonics. Moreover, in the conventional scheme, this inverter requires large dc-link capacitors. To avoid these problems, the present paper develops a simple phase-shifted pulse-width modulation scheme based on redundant switching states, which controls the MLDCL inverter and balances the capacitor voltage within each carrier period. The proposed modulation scheme also minimizes the dc-link capacitance by a factor of the frequency modulation ratio while reducing the total harmonic distortion of the output voltage and current. Unlike the conventional method, the proposed scheme considerably reduces the capacitor-voltage ripples and can be regulated by increasing the carrier frequency, thereby reducing the voltage stress on the switches and improving the reliability of the inverter. The feasibility of the proposed scheme over the conventional scheme is confirmed in a comparative study. Finally, the steady-state and dynamic performances of the proposed strategy are demonstrated in simulations and validated in experiments.

Open-Circuit Fault Detection and Isolation Method for Five-Level PUC Inverter Based on the Wavelet Packet Transform of the Radiated Magnetic Field

This article proposes a noninvasive open-switch fault detection method based on the analysis of the high-frequency signals. The faulty power switch is detected by metering the emitted near-field above a new topology using the wavelet packet transform and considering a complex control algorithm. The proposed method is tested on a single-phase five-level packed U-cell (PUC5) inverter. The latter is controlled using the finite-control set model predictive control (FCS-MPC) technique that generates the gate signals with a variable switching frequency. Moreover, unlike the conventional pulsewidth modulation strategy, the switching pattern provided by the FCS-MPC technique is not known in advance. Despite these complexities, the proposed fault detection method proves its high performance and effectiveness. Experimental studies are carried out on a single-phase PUC5 inverter using the real-time controller (OP4510) from OPAL-RT and prove the capability of this method to properly identify the faulty switch in this multilevel topology.

Hybrid PWM Techniques for a DCM-232 Three-Phase Transformerless Inverter with Reduced Leakage Ground Current.

Pulse Width Modulation (PWM) strategies are crucial for controlling DC–AC power converters. In particular, transformerless inverters require specific PWM techniques to improve efficiency and to deal with leakage ground current issues. In this paper, three hybrid PWM methods are proposed for a DCM-232 three-phase topology. These methods are based on the concepts of carrier-based PWM and space vector modulation. Calculations of time intervals for active and null vectors are performed in a conventional way, and the resulting waveforms are compared with a carrier signal. The digital signals obtained are processed using Boolean functions, generating ten signals to control the DCM-232 three-phase inverter. The performance of the three proposed PWM methods is evaluated considering the reduction in leakage ground current and efficiency. The proposed modulation techniques have relevant performances complying with international standards, which make them suitable for transformerless three-phase photovoltaic (PV) inverter markets. To validate the proposed hybrid PWM strategies, numerical simulations and experimental tests were performed.

A New Multicarrier Sinusoidal Pulse Width Modulation (SPWM) Strategy based on Rooted Tree Optimization (RTO) Algorithm for Reducing Total Harmonic Distortion (THD) of Switched-Capacitor Nine-level Inverter in Grid-connected PV systems

This paper proposed a new strategy of sinusoidal pulse width modulation (SPWM) technique to control three-phase nine-level switched-capacitor inverter (9LSCI) in grid-connected PV systems. The main advantage of this inverter is high voltage gain, achieved by switching the capacitors in series and parallel to boost up the output voltage using low voltage input. To improve the quality of solar energy for injection into the electrical grid, a rooted tree optimization (RTO) algorithm is used to get optimum values of initial angles of multi carriers SPWM technique, giving the lowest possible values of the total harmonic distortion (THD). The design also can maximize the efficiency of the multi-level inverter by minimizing its size using fewer components and a single DC source and reducing the rate of THD. The higher effectiveness and accuracy of the suggested RTO-SPWM technique was tested and verified in comparison to existing classical SPWM technique from the performance of PV-grid systems that it can effectively reduce the total harmonic distortion to 0.16 %.