Pulse Width Modulation Scheme Research Articles

A New Nine-Level Highly Efficient Boost Inverter for Transformerless Grid-Connected PV Application

Transformerless grid-connected multi-level <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">PV</i> (photovoltaic) inverter has the major concern of leakage current and buck behavior of output voltage, hence not suitable for low voltage PV applications. A new <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">9L4x</i> (nine-level quad boost) highly efficient inverter based on the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">SC</i> (switched capacitor) with a <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">CG</i> (common ground) configuration has been proposed in this paper, which provides four times the gain of input voltage. Hence, this inverter is preferable for low voltage <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">PV</i> applications without any boost dc/dc converter intermediate stage. The inverter is designed in such a way that total conducting switches for different level generation is minimum. This technique helps to increase the efficiency of the inverter. Two <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">SC</i> cells are utilized to step-up the input <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">PV</i> voltage and facilitate nine steps in output voltage. The common grounding feature of the proposed inverter topology helps mitigate the leakage current. Additionally, this new inverter can handle reactive power during the grid’s lagging/leading pf (power factor) condition. To regulate the active and reactive grid power, a <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">PR</i> (proportional resonant) controller is designed. The proposed modulation strategy balances the voltages of switched capacitors at their base voltage with allowable ripple. The inverter circuit details, control strategy, <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">PWM</i> (pulse width modulation) scheme, thermal modeling, and loss analysis with component design guidelines are described in detail. Experimental results are presented to validate the effectiveness and feasibility of this proposed inverter.

An Improved Modulation Strategy With Torque Ripple Suppression Method for OEW-PMSM Drives With Common DC Bus

The open-end winding permanent magnet synchronous machine drive with common dc bus has zero sequence loop, which inevitably generates the zero sequence current (ZSC). Due to the existence of the third harmonic flux linkage, ZSC causes the zero sequence torque and augments the torque ripple. In this paper, an improved modulation strategy with torque ripple suppression method is presented. Firstly, to reduce the computation burden, a modified alternate sub-hexagonal center pulsewidth modulation (ASHCPWM) strategy is designed. The switching duration time of two inverters can be obtained by the projection of voltage vector on the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">abc</i> coordinate frame. Secondly, a ZSC suppression method based on the time compensation coefficient is adopted for the modified modulation strategy, which can restrain ZSC and reduce torque ripple. Thirdly, to further reduce torque ripple, a <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">q</i> -axis current injection method is employed in the control scheme. Finally, three methods are presented in simulation and experiments for comparison, namely the deadbeat predictive current control (DPCC) method with conventional ASHCPWM, the DPCC method with sample-averaged zero-sequence current elimination PWM, and the proposed DPCC method with modified ASHCPWM and <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">q</i> -axis current injection. The results test the effectiveness of the proposed method.

A Novel Discrete Hybrid Dual Random SVPWM Scheme for Reducing PMSM Harmonic Intensity

Aiming at suppressing the switching frequen-cy harmonics, a novel discrete hybrid dual random control (DHDRC) technique is proposed in this article. Based on the space vector pulsewidth modulation (SVPWM) strategy, the DHDRC-SVPWM technique is applied to randomize the switching period and pulse position by selecting dual discrete random factors from predefined discrete sequences. Accordingly, the original switching narrowband harmonic energy of SVPWM is extended to a wide range of frequencies. To analyze the harmonic dispersion degree quantitatively, the power spectrum is deduced to assess the performance of the discrete random SVPWM. Then, the connection between the discrete sequence and the harmonic energy distribution is obtained under random variables following a discrete uniform distribution. The obtained results demonstrate that the proposed technique significantly expands harmonic clusters in the frequency domain, thereby reducing the harmonic intensity. The present study provides a reference to investigate random SVPWM and improve electromagnetic interference and noise in power converters.

Space Vector Pulsewidth Modulation Strategy for ANPC-5L Inverter Based on Model Predictive Control

SVPWM strategies for active neutral-point-clamped five-level (ANPC-5L) inverters have multiple control degrees of freedom and control objectives. However, traditional SVPWM strategies are hard to realize optimal control of multiple objectives due to the objectives are coupled with each other. To address this problem, an SVPWM strategy based on model predictive control (MPC) is proposed. In the pulse generation process of the proposed SVPWM, all control degrees of freedom are utilized to achieve optimal control of multiple objectives through MPC. Firstly, voltage vector sequences that meet the requirements of CMV are selected. Then, a cost function is constructed to realize optimal control of the neutral point potential (NPP) and three floating capacitors (FCs) voltage. The proposed strategy has advantages such as high control accuracy and producing low CMV. Finally, the effectiveness of the proposed strategy is validated by a 150kW three-phase ANPC-5L inverter prototype.

Research on internal model control and hybrid modulation strategy of a MW-level direct-drive PMSM for traction drives in electric locomotive

Aiming at the problem of motor control performance degradation caused by the cross-coupling and low switching frequency condition in the high-power direct-drive permanent magnet synchronous motor (PMSM) control system, a robust current control of PMSM based on internal model control (IMC) and hybrid pulse width modulation (PWM) is proposed and applied to the control of a MW-level direct-drive PMSM in electric locomotive traction system. Firstly, combined with the characteristics of the low switching frequency of the electric locomotive inverter, a hybrid PWM strategy is adopted. Secondly, the IMC of PMSM is designed, and the IMC is adopted to solve the problems of more control parameters and cross-coupling of direct-drive PMSM in the d-q axis under low switching frequency, which improves the robustness of the whole locomotive system. Finally, the experiments have been carried out on a 1.2 MW direct-drive PMSM for traction system in electric locomotive, the correctness and effectiveness of IMC and hybrid PWM strategy are verified.

A Modified PWM Scheme to Improve the Power Quality of NPC Inverter Based Solar PV Fed Induction Motor Drive for Water Pumping

This paper proposes a modified modulating signal-based pulse width modulation (PWM) scheme for a neutral point clamped (NPC) inverter-based induction motor drive (IMD) for enhancing the efficiency of solar photovoltaic (PV) fed water-pumping systems. During the previous several decades, the use of sustainable source-based power generation systems has benefited water pumps in household life, irrigation-based activities, and industrial sectors, especially in areas where the electric grid is less available. A critical concern has long been the power quality, speed, and torque of an induction motor used in solar PV-powered water pumping. This paper focuses on the improvement of power performance by minimizing total harmonic distortions (THDs), switching losses and conduction losses, and torque ripples in the induction motor driving the PV-fed water pump by using a modified PWM scheme that generates symmetrical and balanced gate driving signals for the NPC inverter employed in the IMD. The IMD with the suggested PWM switching strategy has been tested in all feasible induction motor operating situations. To demonstrate the effectiveness of the suggested PWM scheme, a performance comparison of the proposed PWM scheme with conventional PWM schemes is performed, and also the IMD with the suggested PWM switching strategy is tested in all feasible induction motor operating situations using the MATLAB/Simulink platform.

Space vector pulse width modulation strategy for modular multilevel converters in power system

AbstractAs a superior modulation strategy, space vector pulse width modulation (SVPWM) provides redundant voltage vectors and adjustable action time, which can achieve multi‐objective control of modular multilevel converter (MMC). An SVPWM strategy suitable for MMC is proposed. The strategy is divided into three stages. In the first stage, the appropriate voltage vector, the action time and the basic sub‐module (SM) input number are quickly calculated to ensure the output quality by equating MMC as a 2‐level inverter. In the second stage, a finite set of the circulating current suppression is established on the basis of the basic SM input number. The optimal SM input number is selected through rolling optimisation. In the last stage, according to the SM voltage sorting and the optimal SM input number, the optimal switching state is determined to realise the SM voltage balance control. The proposed control strategy simplifies the design of the control system, reduces the computational burden and can be easily extended to MMC with any SM number. The simulation and experimental results show that the proposed SVPWM strategy can reduce the circulating current and balance the SM capacitor voltage while ensuring the output quality.

Control of Pneumatic Artificial Muscle Actuated Two Degrees-of-Freedom Robot Using PD-Based Pulse Width Modulation Strategy With Feed-Forward Outer Control Loop

AbstractThis work presents a novel approach for the design and control of a two degrees-of-freedom (DOF) robotic manipulator driven by one pneumatic artificial muscle (PAM) and one passive spring for each of its DOFs. The required air pressure is supplied to the PAMs using fast-switching on/off type pneumatic flow control valves. The proposed control architecture uses a proportional-derivative (PD) controller with a feed-forward term in the outer control loop to correct the position errors using an approximate model of the system dynamics and approximate PAM force-contraction characteristics. An inner pressure regulator loop tracks the reference pressure signals supplied by the outer loop using a pulse width modulation (PWM) scheme to control the pneumatic valves based on the approximated inflation–deflation characteristics for the given pneumatic flow circuit. The proposed controller is unique for PAM actuated robots that simultaneously consider three levels of complications, namely, coupled dynamics of multi-degrees-of-freedom system, non-linearities in the force-contraction characteristics of PAMs, and non-linearities involved in the use of on/off type pneumatic flow control valves. Experiments carried out using a laboratory prototype validate the effectiveness of the proposed control scheme.

A Three-Phase Hybrid Multilevel Inverter With Enhanced Pulse-Width Modulation Strategy

This paper presents a three-phase hybrid multilevel inverter (MLI) with enhanced pulse-width modulation (PWM) strategy. The proposed hybrid MLI is developed based on the series connection of half-bridge and full-bridge for its level generation together with the T-type inverter for its polarity generation. The level and polarity generation circuits operate at high and fundamental frequencies respectively. An enhanced PWM strategy has been proposed to reduce the computational complexity and solve the high-frequency switching transitions issue in the existing hybrid MLI modulation method. The proposed MLI can produce 11 levels of line output voltage with reduced dc sources requirement. The detailed analyses which have been performed include the circuit configuration, operating principles and modeling, PWM signals generation, output voltage characteristics, dynamic response, harmonics content, power loss analysis and voltage stress of power switches. The results obtained from simulation and experiments verified the operating principle and functionality of the proposed hybrid MLI.

Model-Free Predictive Current and Disturbance Rejection Control of Dual Three-Phase PMSM Drives Using Optimal Virtual Vector Modulation

Model-based predictive current control (MBPCC) relies heavily on adequate system modeling and accurate parameters. The detailed models of dual three-phase permanent magnet synchronous motors (PMSMs) contain mutual cross-coupling dynamics which make it difficult to extract accurate parameters. Also, some of the physical parameters of PMSMs are generally nonlinear functions of current and rotor position. In this article, a model-free predictive current control (MFPCC) based on an ultralocal model and an extended state observer is proposed for an asymmetrical dual three-phase (ADTP) PMSM. The MFPCC method is shown to provide superior current regulation when compared to the standard MBPCC approach under uncertain parameter conditions. Furthermore, the harmonic currents and the current ripple in the ADTP PMSM drive have been regulated to near-zero values by using optimized voltage vectors comprised of virtual vectors and null vectors. A generalized center-aligned pulsewidth modulation (PWM) scheme is presented to facilitate the synthesis of the optimal virtual voltage vectors for implementation on a low-cost digital signal processing platform. The performance improvements of the MFPCC with optimal virtual vector modulation are verified and compared with the conventional MBPCC method in both simulations and experiments on a surface-mount type dual three-phase PMSM.

Hybrid Active Modulation Strategy for Three-Level Neutral-Point-Clamped Converters in High-Speed Aerospace Drives

In the aircraft electric starter/generator system, the three-level neutral-point-clamped converters play a crucial role in driving turbofan engines and delivering onboard electrical power. However, the conventional pulsewidth modulation (PWM) strategies face the challenge of capacitor voltage deviation, large common-mode voltage (CMV), and extra switching losses. Regarding the characteristics of the studied wide-speed range aerospace drives, the modulation scheme needs to be designed according to its operating conditions. To tackle the above demerits, a hybrid active modulation approach is, hence, proposed in this article. By the coordinate-based PWM, the nearest-three-vector is used in the startup process as the neutral-point (NP) voltage balance can be realized with fewer switching intervals; when the drives run in generation mode, an enhanced carrier-based virtual-space-vector modulation technique is involved, which aims to eliminate NP voltage fluctuation, suppress CMV, and simplify the modulation process. With the help of bias-offset injection in the time and voltage domain, capacitor voltages can be effectively kept at a balanced state even though the imbalance exists. The validity of the presented algorithm is proved by simulation and experimental results obtained from a 45 kW, 32 kr/min aircraft starter/generator test rig.

Novel SVPWM for Open Winding PMSM Drives With Simultaneous Common Mode Voltage Control and Full Frequency Zero Sequence Current Suppression

Zero sequence voltage (ZSV) can cause zero sequence current (ZSC), while variation of common mode voltage (CMV) can cause bearing current in an open winding (OW) permanent magnet synchronous machine (PMSM) fed by common dc -bus dual two-level inverters. This article proposes a novel space vector pulsewidth modulation (SVPWM) strategy for simultaneously eliminating CMV variation and suppressing full frequency ZSC harmonics in either linear or over modulation region by optimal selection of switching combinations. The proposed SVPWM can reduce large ZSV ripples and number of switching actions in the conventional CMV control method for the common dc -bus OW drive. Thus, high-frequency ZSC harmonics and switching frequency can be significantly reduced in both linear and over modulation regions. Moreover, the proposed SVPWM can suppress large low-frequency ZSC harmonics induced by the conventional method in over modulation region. The superior performances of CMV variation elimination and full frequency ZSC suppression in the proposed SVPWM are verified by experiments.

An Active Power Decoupling-Integrated Reduced-Switch Current-Fed Switched Inverter

In recent literature, high-gain dc–ac inverters are employed in grid-connected photovoltaic (PV) systems. These inverters can have several features, such as shoot-through immunization and buck/boost capabilities achieving a wide range of operations with reliability and minimum distortion. One such example is the single-phase reduced-switch current-fed switched inverter (RSCFSI). This article proposes the enhanced boost control-based pulsewidth modulation (EBC-PWM) strategy for RSCFSI to improve the inverter’s dc–ac gain. Being a single-phase inverter, RSCFSI suffers from the double-line frequency ripple problem. However, a low-frequency (LF) ripple analysis reveals that the RSCFSI is also plagued with fundamental frequency ripple, which poses additional challenges for the active power decoupling (APD) integration and corresponding closed-loop controllers. Although both LF ripples can be alleviated using markedly large passive elements, the power density and reliability of the inverter worsen. In this article, an APD-integrated RSCFSI (APDRSCFSI) is introduced as a solution that deflects the aforementioned LF ripple energy to an auxiliary capacitor without adding more active switches. As a result, the inverter can employ smaller passive elements. In addition, the EBC-PWM strategy is also extended for APDRSCFSI, improving its dc–ac voltage gain and voltage stress. A closed-loop control technique that combines output voltage control and APD functionality is also illustrated. A hardware prototype is used to corroborate the advantages of APDRSCFSI.

Transmission of Power and Signal Multiplex for Electric Vehicles Using Cascaded Multilevel Inverters

Abstract: P&amp;SMT, or power and signal multiplex transmission, is a method for transmitting communication signals using power electronic circuits. A three-phase cascaded multilevel inverter-based P&amp;S MT system is recommended in this investigation. By allowing communication signals to be transmitted without utilizing a Controller Area Network bus, the proposed solution can lower the wiring expense of the existing electric vehicle (EV) communication system. The system's architecture enables battery balancing discharge and motor speed management for EVs. In a simulation system proposed in MATLAB/Simulink, both power and communication signals are effectively conveyed using the combined pulse width modulation scheme and frequency shift keying approach. The maximum signal rate of the proposed system is established at 600 bits per second by analyzing the bit error rate of the sent signal.

Boundary-Based Hybrid Control Algorithm for Switched Boost Converter Operating in CCM and DCM

It is essential to have enhanced efficiency for the DC-DC converters operating in continuous conduction mode (CCM) and discontinuous conduction mode (DCM). This requires a hybrid controller designed using pulse width modulation (PWM) and pulse frequency modulation (PFM) schemes. This paper fixates on a boundary-based hybrid control algorithm for the second-order DC-DC converter - the switched boost converter. The proposed algorithm works in PWM control scheme for CCM operation, whereas DCM operation uses PFM control scheme. The boundary conditions are defined by the load current, output voltage, and switching frequency. Here, an attempt is carried out to have the advantages of both the control schemes. The boost converter is represented by the switched system operating in three modes. Violating transition guards condition orchestrates the switching among these modes. A supervisor detects the CCM and DCM operations, and subsequently switches between PWM and PFM control scheme. Extensive circuit-level simulations are carried out in MATLAB to show the efficacy of the suggested algorithm under the fluctuating line, load, and set-point.

Modular three phase asymmetrical cascaded multilevel inverter with lower number of switches

ABSTRACT This paper introduces a modular circuit for three-phase asymmetrical multilevel inverter, which is composed of series basic unit cells. It requires fewer number of switches as compared to conventional MLI circuits. Carrier-based pulse width modulation scheme is used to generate switching pulses circuit switches. The proposed circuit is compared with conventional MLI circuit. In order to verify the superiority of proposed circuit, a single phase 4-level inverter and three phase 7-level inverter are simulated in MATLAB/Simulink environment and hardware porotype is also demonstrated using dSPACE 1104 real-time controller.

Variable switching frequency PWM for quasi‐Z‐Source inverter based on DC current ripple prediction

AbstractHerein, a variable switching frequency pulse width (VSFPWM) modulation strategy for quasi‐Z‐source inverter (qZSI) based on a recently proposed modulation method, named as ZSVM8, is proposed. The formulae of quasi‐Z‐source inverter inductor current ripple of ZSVM8 are deduced in detail, and a prediction model for the current ripple is obtained. Combining with the VSFPWM technique, an improved modulation method named ZSVM8 VSFPWM is proposed to further reduce the switching times without increasing the maximum inductor current ripple. As a result, the switching losses can be reduced compared with the conventional ZSVM8. Besides, ZSVM8 VSFPWM also suppresses electromagnetic interference noise, such as current EMI and common‐mode voltage. Simulations and hardware experimental results are implemented to verify the efficacies of the proposed modulation method.

Optimized Synchronous Pulse Width Modulation Strategy Based on Discontinuous Carriers

This article proposes a new technique called optimized discontinuous carrier pulse width modulation (ODCPWM), whose main objective is to solve the issue of significant output voltage harmonics of conventional synchronous carrier modulation at low carrier wave ratios. Based on the symmetry principle, the fundamental wave period is divided into regions; the carriers in adjacent regions are flipped, and the carrier width is changed symmetrically in each region to generate an unequal-width optimized discontinuous carrier pulse width modulation. In addition, using the weighted total harmonic distortion (WTHD) of the line voltage as an evaluation index, an optimized multi-mode PWM strategy is proposed to satisfy the system to operate stably in the whole speed range. The experimental results verify the effectiveness of the proposed strategy. The results show that ODCPWM proposed in this article can eliminate harmonics and multiples of three harmonics in line voltage harmonics. The VWTHD is lower, which improves the quality of the output waveform and makes the system operation more stable and reliable. The proposed multi-mode PWM strategy is smooth and shock-free during switching.

A Simplified PWM Strategy for Open-Winding Flux Modulated Doubly-Salient Reluctance Motor Drives With Switching Action Minimization

In this article, a simplified pulsewidth modulation (PWM) strategy is proposed for open-winding flux modulated doubly-salient reluctance motor (FMDRM) drives for switching action minimization and common-mode voltage (CMV) reduction. Conventionally, the open-winding converter topology is utilized to achieve the zero-sequence current flow path and dc-biased sinusoidal current excitation for the FMDRM, where the switching actions of power switches are doubled compared to the conventional modular three-phase converter, leading to higher switching losses. Different from the conventional space vector PWM scheme, the reference voltages of converter legs are directly calculated by the reference phase voltages in the proposed PWM scheme. In addition, a rotor-position-based sector division method is proposed to deal with the sector imbalance caused by the distorted back electromotive force (back EMF). Furthermore, different leg voltage clamping methods are respectively developed in odd and even sectors for switching action minimization, which can achieve voltage stress balance and CMV reduction. With the proposed scheme, the switching actions in each switching cycle can be reduced by half, which effectively increases the system efficiency of the FMDRM drive. Experiments are carried out on a three-phase 12/8 FMDRM prototype to verify the effectiveness of the proposed scheme.

A Hybrid Discontinuous PWM Strategy for Current Ripple and Neutral-Point Fluctuation Reduction of Parallel Vienna Rectifier

Generally, discontinuous pulsewidth modulation (DPWM) strategy used in single Vienna rectifier will result in large current ripple and neutral-point fluctuation. When applied in interleaved rectifier, the issue of neutral-point voltage still exists. Besides, the input current around zero-crossing point is distorted due to the characteristics of unidirectional topology. Hence, a novel hybrid DPWM (H-DPWM) strategy for parallel Vienna rectifier is proposed in this article to reduce the distortion, current ripple, and neutral-point fluctuation. In this article, the characteristics of current ripple and neutral-point fluctuation with traditional DPWM (T-DPWM) are clarified at first. Then, the quantitative analyses on current ripple and neutral-point fluctuation with T-DPWM, classical space vector modulation, and optimized DPWM (O-DPWM) are presented in detail. To solve the issue of current distortion, the H-DPWM is proposed based on O-DPWM. Furthermore, the switching losses of these modulations are evaluated. At last, the analyses and performance of the proposed H-DPWM are verified by the experiments.