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This paper presents a method for switching reduction in cascaded H-bridge converters. Given the wide applicability of this topology, it would be especially desirable to increase its efficiency with switching losses reduction techniques. Since this type of converter requires voltage balancing methods, several modulation methods consider the possibility of combining the balancing and switching reduction goals together. In this paper, a previously disclosed optimization-based balance method was modified further to consider the switching losses in its objective function. Each commutation was penalized in proportion to the phase current and the module voltage, thus avoiding commutations that would produce the most losses but tolerating low-losses commutations. The structure of the original method was maintained so that the algorithm could be applied with minimal change. The results show that it is possible to reduce the switching up to 14% without any noticeable drawback and up to 22% at the cost of a greater DC-link ripple. It is also possible to selectively reduce the effective switching frequency of only some modules, making it significantly low. This extends the adaptability of the converter, possibly allowing hybrid converters with modules of different transistor technologies.

The conventional DC-link type quasi-Z-source inverter has been known as a buck–boost inverter with a low component voltage rating. This paper proposes an active DC-link type quasi-Z-source inverter by adding one active switch and one diode to the impedance-source network to enhance the voltage gain of the inverter. As a result, the component voltage rating of the inverter is significantly reduced, which is demonstrated through some comparisons between the proposed topology and others. A discontinuous pulse width modulation (DPWM) scheme is proposed to control the inverter, which reduces the number of commutations compared to the traditional strategy. Under this approach, the insertion of a shoot-through state does not cause any extra commutations compared to the conventional voltage-source inverter. Details about control implementation, steady-state analysis, and design guidelines are also presented in this paper. Simulation and a laboratory prototype have been built to test the proposed inverter. Both buck and boost operations of the proposed inverter are implemented to validate the performance of the inverter.

Based on the brushless DC motor system with DC-link small capacitance powered by a single-phase AC power source, a boosting DC-link voltage strategy to reduce the commutation torque ripple of brushless DC motors is proposed in this paper. The control strategy utilizes the special topology of the motor system to boost the DC-link capacitor voltage in a specific zone during the non-commutation period. During the commutation period, the high voltage of the DC-link capacitor is released to meet the voltage requirement of the brushless DC motor during commutation. In order to reduce the commutation torque ripple and ensure the normal operation of the brushless DC motor, each rectifier cycle is divided into three zones according to the characteristics of the periodic change of the rectifier output voltage. Different operation modes are proposed for different zones. In DC-link capacitor boost voltage mode, the DC-link capacitor boosts the voltage to meet the voltage of the motor demand during the commutation period for achieving the purpose of reducing the commutation torque ripple. In this paper, the controller of the brushless DC motor system is designed and the experimental platform is built. The experimental results verified the correctness of the theoretical analysis and the feasibility of the proposed method.

In conventional control methods of brushless DC (BLDC) motor drives, back-electromotive force (EMF) is assumed to be in ideal form and the controller injects rectangular phase current commands to produce the desired constant torque. However, real back-EMF waveform might not be exactly trapezoidal because of non-ideality of magnetic material, design considerations and manufacturing limitations. This makes the generated electromagnetic torque contain ripples in its waveform which is not desirable in motor operation performance especially, in sensitive industries. Moreover, commutation states affect the quality of generated torque by producing torque pulsations because of changes of conducting phases. In this study a control strategy for a four-phase BLDC motor with non-ideal back-EMF to reduce electromagnetic torque ripples is presented. Basis of the proposed method is to inject phase currents considering back-EMF instantaneous magnitude. For this purpose, an on-line back-EMF estimation technique is used to inject appropriate phase currents to compensate non-ideality of back-EMF waveform. Moreover, the estimated back-EMF is also used for commutation torque ripple reduction. The experimental results indicate performance of the proposed control strategy in torque pulsations reduction compared with conventional control method.

This study focused on the efficiency improvement and acoustic noise reduction of brushless DC (BLDC) motors by reducing current harmonics using a novel BLDC commutation method. To achieve these goals, we designed an improved 150° commutation method for a three-phase permanent magnet BLDC motor that can improve the current waveform. Although the 120° commutation method is generally employed for BLDC motors, an improved 150° commutation method is introduced to operate the BLDC with increased efficiency and acoustic noise similar to a brushless AC motor. This study investigated the attributes of various commutation methods, both theoretically and experimentally, to determine the optimal commutation method. The results of this study indicate that the improved 150° commutation method is optimal in terms of harmonic attributes and reduced torque ripple, allowing it to improve motor efficiency and reduce acoustic noise.

In this paper, an adaptive current controller is proposed for variable speed brushless direct current (BLDC) motor drives to minimize the output torque ripples caused by parametric and periodically varying uncertainties. Phase-to-phase non-ideal back-electromotive force (back-EMF) in BLDC motor changes periodically with respect to the shaft angle, and hence the period of these signals alters depending on the rotor frequency. To address these problems, the uncertain current dynamics of the BLDC motor is reformulated by transforming the time variable, then the periodic adaptive controller employing the instantaneous estimation values of the unknown periodic signal is developed to achieve the torque ripple reduction. The periodic estimation of the non-ideal back-EMF waveform is achieved considering the switching between conduction and commutation periods. Also, the update rules based on direct adaptation for parametric uncertainties are derived, and thus, hybrid differential-periodic adaptation rules are obtained considering the switching phenomenon. Asymptotic convergence of the phase currents to the reference values is proven by an appropriate Lyapunov-Krasovskii function depending on the angular position. Comprehensive numerical simulation studies have been successfully carried out to verify the performance and the effectiveness of the proposed controller for variable speed applications.

The flow-matching problem of hydraulic systems is an important factor affecting the working performance and energy saving of hydraulic systems. According to the different flow-matching mechanisms, the flow-matching technology of hydraulic systems can be divided into three categories: positive flow-control technology, negative flow-control technology, and load-sensitive control technology. In this paper, the working mechanism of flow-matching technology and the cause of energy loss are analyzed, and the research results of flow matching are introduced from two aspects of energy saving and consumption reduction and system performance improvement. In the direction of energy saving and consumption reduction, the purposes of energy saving and consumption reduction are achieved by means of multi-way valve commutation, independent inlet and outlet control, parallel replacement of shuttle valve by a cylinder piston rod controlled by pilot pressure, change of hydraulic resistance of a pressure compensating valve, improvement of the power regulation range of a hydraulic pump, and potential energy recovery. In the direction of system performance, by means of flow-forecasting system pressure change, applying flow unsaturation real-time control idea, and combining electronic control technology with load-sensitive technology, the pressure drop during transmission process and the transmission signal lag are reduced, the speed regulation interval is enlarged, fine-tuning characteristics are improved, and the response speed is increased. The research results indicate that improving the structure and the control strategy of hydraulic systems and improving the flow-matching degree of a system to achieve global matching will be a future development trend.

Multilevel three-phase inverters are increasingly popular due to their ability to generate high-quality output voltage with harmonic distortion lower than traditional inverters. They are used in various applications, including grid-connected renewable energy systems, motor drives, and power transmission systems, to improve efficiency and reduce costs. The control quality of grid-connected multilevel inverters depends on various factors such as the modulation technique, switching frequency, and control strategy. A good control system can achieve a balance between output current harmonics and switching losses, improving the efficiency and performance of the inverter. This paper suggests a technique for reducing current harmonics of grid-connected multilevel three-phase inverters using variable frequency carriers, without any corresponding increase of the number of switching commutations. The effectiveness of the suggested method has been confirmed through simulation results, which were compared to those obtained from the method of phase opposite disposition modulation using fixed frequency carriers.

A novel hybrid control strategy for reducing torque ripple in permanent magnet brushless direct current motors has been developed by combining the deterministic nature of direct torque control and the adaptive nature of fuzzy logic control. Direct torque control using space vector pulse width modulation has been developed. This technique ensures the near-sinusoidal nature of the stator and rotor current. The impact of commutation ripple corresponding to the sinusoidal current is reduced compared to square wave current in conventional direct torque control. Further, the fuzzy logic controller provides adaptive modulation in space vector to mitigate the torque ripple. The response of the proposed method has been analyzed in the time domain as well as in the frequency domain. Experimental results establish a significant reduction in torque ripple and minimization of high-frequency components. A comparative study with conventional direct torque control methods has also been presented.

This study presents an improved switching-table-based direct torque control method for three-phase permanent magnet synchronous machine drives. The instantaneous variation rates of stator flux and torque of each converter output voltage vector are analysed. It is found that large steady-state error of torque response exists because of the difference in the decreasing and increasing variation rates. A novel and simple on-line band-shifted torque regulator is proposed to reduce this steady-state error of torque response. The experimental results verify that the proposed method can significantly reduce the steady-state error of torque response with the extra bonus of slight reduction of both the torque ripple and average commutation frequency, while preserve the merits of the conventional direct torque control, that is, simple structure, good robustness and excellent transient response.