Hybrid Pulse Width Modulation Strategy Research Articles

Performance Characteristics of a Newly Developed Asymmetric Seven-Level Inverter Utilizing Various Hybrid Pulse Width Modulation Strategies

This study unveils a notable breakthrough in inverter technology, holding promise for substantial improvements in voltage quality and the attenuation of harmonic distortions within power systems. This study concentrates on the design and implementation of a novel Seven-Level Asymmetric Inverter (NSLAI) by incorporating various hybrid Pulse Width Modulation (PWM) techniques. The primary goal is to improve the output voltage magnitude while decreasing the Total harmonics compared to conventional PWM methods. The investigation introduces a novel Seven-Level Asymmetric Inverter (NSLAI) with innovative Hybrid Pulse Width Modulation (PWM) strategy. The purpose of this study is to investigate the distinct features of a recently developed asymmetric seven-level inverter, with a focus on exploring its characteristics through the implementation of diverse hybrid pulse width modulation strategies. Hybrid PWM methodology intricately centers on enhancing voltage quality and achieving better harmonious spectral characteristics. The gate signal producing approach for this suggested PWM technology incorporates a hybrid PWM methodology that combines trapezoidal and sinusoidal waveforms, as well as a standard triangular carrier signal enabling NSLAI. The hybrid version of PWM practices is deliberately used to generate switching signals for the NSLAI. An intensive evaluation of numerous indicators of effectiveness across multiple modulation indexes leads in the demonstrating of quantitative findings that compare the unique Hybrid PWM practice with established PWM tactics. Notably, the hybrid reference Carrier Overlapping strategy has emerged as a leading approach surpassing conventional pulse width modulation techniques. It achieves a significantly higher fundamental Root Mean Square voltage output and remarkably lower percentage of Total Harmonic Distortion values compared to all within the hybrid reference Variable Frequency strategy. The principal analytical tool used in the modeling investigation is MATLAB-SIMULINK. This study marks a watershed moment in the development of inverters, claiming significant improvements in battery power quality and distortion caused by harmonics avoidance across power systems, as evidenced by extensive simulation and prototype-based discoveries.

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.

Hybrid Pulse-Width Modulation Strategy With Reduced High-Frequency Common-Mode Voltage to Lower RMS Motor Leakage Current for a Three-Level Neutral Point Clamped Converter

Hybrid Pulse-Width Modulation Strategy With Reduced High-Frequency Common-Mode Voltage to Lower RMS Motor Leakage Current for a Three-Level Neutral Point Clamped Converter

Symmetrical Cascaded Switched-Capacitor Multilevel Inverter Based on Hybrid Pulse Width Modulation

Multilevel inverters have been widely used in various industrial applications such as renewable energy generation and electric vehicles. An improved circuit of symmetrical cascaded switched-capacitor multilevel inverter is proposed so that the reactive power is absorbed by its power supply instead of capacitors. Then, a special hybrid pulse width modulation strategy combing level-shifted pulse width modulation (LS-PWM) and phase-shifted pulse width modulation (PS-PWM) was developed for the inverter. With this modulation algorithm, the power between cascaded units is automatically balanced, and the voltage of the capacitor in each unit is also automatically balanced to the dc input voltage. In addition, the optimized capacitor voltage ripple makes it possible to use a smaller capacitor to produce a better output voltage waveform. Theoretical analysis, simulation and experimental results show that the equivalent switching frequency of the cascaded multilevel inverter is twice the original frequency so that the output voltage harmonics are only distributed near even multiples of the carrier frequency.

An Optimized Hybrid PWM Strategy for Five Level NPC VSI With Unequal DC-Links in a PV System

This article presents an optimized hybrid pulsewidth modulation (PWM) strategy for five-level neutral point clamped (5L-NPC) inverter with unequal dc-link capacitor voltages fed by differential power processing (DPP)-based photovoltaic (PV) system. The generation of balanced output from the 5L-NPC inverter with the unequal dc-link capacitor voltages becomes necessary in a PV system. The unequal dc-link capacitor voltages cause low order harmonics in inverter output voltage. A hybrid PWM strategy combining the advantages of space-vector PWM (SVPWM) and the nearest level modulation (NLM) methods is proposed to address the issues associated with unequal dc-link capacitor voltages in a five-level NPC inverter. The proposed hybrid PWM is optimized to achieve balanced output voltage with less total harmonic distortion at fundamental frequency. In-depth theoretical analysis of sector identification algorithm and dwell time computation for the proposed optimized hybrid PWM method are described. Simulation and experimental results are illustrated for several combinations of unequal dc-link capacitor voltages to validate the functionality and performance of the proposed optimized hybrid PWM method.

Half-Bridge Modular Switched-Capacitor Multilevel Inverter With Hybrid Pulsewidth Modulation

In order to explore a single-phase microinverter with boosting ability, simple structure, low-cost, and high power density, a new structure of a multilevel inverter (MLI) is proposed in this article. With this structure, two half-bridge modular switched-capacitor circuits are arranged on both left- and right-sides of a dc source. Circuit configuration of this MLI can be bilaterally symmetrical and this benefits to modular design and the voltage stress reduction of inverting bridges. Additionally, in order to reduce voltage ripple of capacitors and total harmonic distortion of output voltage simultaneously, a hybrid pulsewidth modulation strategy is developed to improve the performance of this MLI. As a result, capacitors of this MLI can be replenished repeatedly when they are taken as voltage sources to generate different voltage levels. Circuit configuration, operation principle, modulation, power loss, and voltage ripple are analyzed in detail. Both simulation and experimental results are provided to demonstrate the effectiveness of the proposed MLI and modulation strategy.

Hybrid Pulse Width Modulation Strategy of a High-Frequency Link Three-Phase Four-Leg Matrix Converter Based on Compensation Theory

A high-frequency link (HFL) three-phase four-leg matrix converter (MC) can output three-phase balanced voltage for unbalanced load conditions. It is an inverter with great development potential. This paper presents a hybrid pulse width modulation (HPWM) strategy for a four-wire matrix converter based on the fourth bridge leg compensation method. Firstly, the rear-stage topology of a high-frequency link three-phase four-leg matrix converter is decoupled into two sets of ordinary three-phase four-wire inverters. Then the compensation strategy is applied to separate the fourth bridge leg from the coupling of the ordinary inverter and realize its independent control. Under the theory of compensation, the fourth bridge leg plays a role in compensating the deviation of the neutral point potential when the load is unbalanced, the fourth bridge leg does not need to work when the load is balanced. Finally, the fourth bridge leg modulation wave obtained by the compensation method is combined with the front three bridge leg modulation waves to perform the coupling control using the hybrid pulse width modulation strategy. It has changed the problem that the previous hybrid pulse width modulation strategy cannot be directly applied to the four-wire matrix converter. This strategy is simple to control, without adding any auxiliary commutation detection circuitry, can effectively solve the inherent commutation problem in the bidirectional switch tube of the four-wire matrix converter. It simplifies the complexity of the system, reduced control cost, and high switching loss caused by high switching frequency. The fast adjustment function of compensation strategy makes the dynamic response performance of system under load fluctuation state more prominent, the harmonic distortion rate is smaller. The perfect combination of two strategies allows the high-frequency link three-phase four-leg matrix converter with any form of load to give full play to its structural advantages. The related work verifies the feasibility and effectiveness of the modulation method and control logic.

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.

Modified hybrid modulation strategy with power balance control for H‐bridge hybrid cascaded seven‐level inverter

Compared with the traditional cascaded H-bridge multi-level inverters, the hybrid cascaded multi-level inverters have been receiving attention because they can generate more levels with the same number of power cells. However, with the general hybrid pulse width modulation (PWM), the output power distribution between the high-voltage and low-voltage H-bridge cells is extremely uneven in low amplitude modulation, and it may appear that the high-voltage cell feeds power into the low-voltage cell in some modulation ratio intervals causing the low-voltage cell capacitor voltage boost. To avoid this problem, a method of a modified hybrid PWM strategy with power balance control is proposed. It has achieved the output power balance of H-bridge cells in full amplitude modulation, the occurrence of the phenomena of extremely uneven output power distribution between the high- and low-voltage cells in low amplitude modulation is avoided, and the performance of the inverter is improved. Simulation and experimental results verify the correctness and feasibility of the proposed strategy.

A Hybrid PWM Strategy for Three-Level Inverter With Unbalanced DC Links

The dc links of the three-level neutral-point-clamped (3L-NPC) converter are needed to work in imbalanced state in some special fields, and a hybrid pulsewidth modulation (PWM) strategy in this case is studied in this paper. The proposed strategy is a combination of the space-vector PWM and carrier-based modulation (CBM) method. The characteristic of the revised space-vector diagram (RSVD) with unbalanced dc links is studied from a new perspective, and based on it, a novel sector distribution method is proposed to identify the utilized switching sequences. Instead of calculating the durations of the adopted space vectors in the asymmetrical and complicated RSVD, the proposed strategy adopts the CBM with well-calculated injected zero-sequence voltage (IZSV) to produce the pulses directly. The IZSV calculating methods to realize the asymmetric control of dc-link voltages for both the continuous and discontinuous PWM are studied in detail. Simulated and experimental results are given to validate the effectiveness.

Hybrid Space Vector Modulation Strategy for Torque Ripple Minimization in Three-Phase Four-Switch Inverter-Fed PMSM Drives

Three-phase four-switch (TPFS) inverters are generally applied as cost-reduction topologies for permanent-magnet synchronous motor (PMSM) drives because of their reduced number of switching devices. However, undesirable torque ripples are produced by the inverter-fed PMSMs due to the application of nonsinusoidal voltages. Because the torque ripples are strongly influenced by the employed pulse width modulation (PWM) strategy, two commonly used switching sequences in TPFS inverter-fed PMSM drives are fully investigated based on the root mean square value of the torque ripples, in which the effects of the different equivalent zero vectors on the torque ripples are presented. Then, a hybrid space vector modulation (SVM) strategy is proposed to minimize the torque ripples by alternatively using the two equivalent zero vector synthesis approaches during a fundamental period. The sector division of the proposed hybrid SVM strategy is determined by the location of the stator current vector, which is quite different from the methods used in other SVM methods. Then, a simplified sector identification method is proposed to reduce the computational burden. The experimental results demonstrate that the proposed hybrid PWM strategy can effectively reduce torque ripples in TPFS inverter-fed PMSM drives.

Hybrid Pulse Width Modulation Strategy for Wide Speed Range in IPMSM with Low Cost Drives

The control performance of hybrid PWM inverter using a phase current measurement is presented in this paper. The hybrid PWM technique consists of space vector pulse width modulation (SVPWM) and six-step voltage control operation. The SVPWM is performed to reduce the harmonic components in the low speed region, and the six-step modulation is applied to increase the maximum speed of the IPMSM in the high speed region. Therefore, it is possible to obtain a great performance in both the low speed range and high speed range. However, the six-step modulation cannot be completely implemented, since the inverter that includes the lag-shunt sensing method has an immeasurable current region. In this paper, a quasi-six-step modulation using a modified voltage vector is proposed. The validity and usefulness of the proposed PWM technique is verified by MATLAB/Simulink and experimental results.

Space-Vector-Based Hybrid PWM Strategy for Reduced DC-Link Capacitor Current Stress in the Post-Fault Grid-Connected Three-Phase Rectifier

A hybrid pulse width modulation (PWM) strategy for the postfault grid-connected three-phase rectifier is proposed in this paper to achieve a reduced current stress on the dc-link capacitors. The capacitor current per sampling period is investigated, which consists of the effective duty ratio-based currents and the ineffective duty ratio-based currents. The currents introduced by the ineffective duty ratio are highly dependent on the allocation of the ineffective duty ratio. Therefore, this degree of freedom of the ineffective duty ratio allocation can be utilized to minimize the capacitor current. Then, the effect of the ineffective duty ratio allocation on the amplitudes of the capacitor current is analyzed. Based on this analysis, the optimized ineffective duty ratio allocations are proposed, where the ineffective duty ratios are flexibly allocated with respect to the vector angle of the ac current. Furthermore, a novel distribution of the vector plane is developed for the proposed hybrid space vector modulation (HBSVM) strategy. Moreover, the root-mean-square (RMS) values of the capacitor current are used to evaluate the performance of the proposed hybrid PWM strategy. The analytical results demonstrate that the proposed HBSVM strategy results in the reduced capacitor current RMS, which avoids a failure of the dc-link capacitors. Finally, the experimental results validate the effectiveness of the proposed HBSVM strategy.

Application of the One-Cycle Control Technique to a Three-Phase Three-Level NPC Rectifier

The three-phase three-level neutral-point-clamped (NPC) topology is widely employed in rectifiers, active power filters, and electric machine drives. This paper proposes an alternative control strategy for the NPC topology based on the one-cycle control technique and the hybrid pulsewidth modulation strategy. Optimal unbalanced load compensation is achieved with the proposed scheme, of which the principal advantages are simplicity, robustness, and low cost. Experimental results confirm the feasibility of the proposed controller.

New PWM switching strategy for microprocessor controlled inverter drives

A new high-voltage suboptimal (HVSO) pulse-width modulation (PWM) switching strategy is presented which can be used at high fundamental PWM voltages to achieve a smooth, transient-free, low harmonic distortion, transition from the PWM to quasisquare-wave mode. The design philosophy underlying the development of the new HVSO strategy is aimed at reproducing the special features and desirable characteristics of the optimised PWM strategy, using a simple and efficient microprocessor implementation. The full theoretical development of the new HVSO strategy is presented; and experimental results, from a microprocessor controlled PWM inverter drive, are provided which confirm this theoretical development. It is shown that the new HVSO strategy is superior to all existing PWM strategies, and can be implemented simply and efficiently on a microprocessor controller with only minor modifications to the existing PWM microprocessor implementations. In addition, a new hybrid PWM strategy is proposed and demonstrated, which combines the HVSO strategy with a previously developed suboptimal strategy. It is shown that this new hybrid PWM strategy can be used to cover the complete voltage/frequency range of the drive system up to and including the quasisquare wave mode, with minimised total harmonic distortion.