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Sharp LC resonance peak may enlarge inherent harmonics, dominant harmonics of the supply voltage generated by a three-phase diode rectifier, around the resonance frequency, which will intensify fluctuations of the dc-link voltage, and grid currents in motor drives with small dc-link capacitor. In this article, a novel resonance suppression strategy based on inherent harmonics impedance shaping is proposed specially for three-phase input permanent magnet synchronous motor (PMSM) drives with small dc-link capacitor. Instead of increasing the damping of the whole system for resonance suppression, the motor side power disturbance can be reduced by designing the impedance for inherent harmonics around LC resonance frequency based on the new model with the consideration of motor side characteristic. For damping current generation, the angle of the virtual admittance is modified to eliminate the influence of the dc-link voltage sampling delay. Experimental results show the effectiveness of the method on a prototype of electrolytic capacitorless PMSM drive. [ABSTRACT FROM AUTHOR]

It is important to improve the accuracy of rotor position estimation for the high-performance operation of position sensorless permanent magnet synchronous motor (PMSM) drives. To mitigate the position harmonic error caused by the nonideal factors in high-frequency signal injection based methods, an adaptive quasi-proportional-resonant rotor position observer (AQPRO) for sensorless PMSM drives is proposed in this article. The AQPRO can track the estimation error and generate the compensation value, which can realize online suppression for position error. By analyzing the stability and the influence of parameters of the proposed position observer on the suppression performance, a proportional-resonant gain self-tuning strategy is investigated to improve the suppression effect of the position harmonic error for different loads and speeds. The influence of self-tuning regulator parameters is modeled and analyzed in detail. The proposed method does not require offline detection and has a strong suppression ability for different harmonic error components. The effectiveness is verified by experiments on a 2.2-kW PMSM drive platform. [ABSTRACT FROM AUTHOR]

Accurate rotor position estimation is important to ensure the high-performance operation of position sensorless permanent magnet synchronous motor (PMSM) drives. To suppress the estimated rotor position harmonic error (ERPHE) caused by inverter nonlinearities, flux spatial harmonics, and the current measurement error in high-frequency signal injection-based schemes, an adaptive iterative learning control-based online suppression method is proposed in this article. This method constructs a P-type iterative learning rotor position observer with the forgetting factor to obtain the tracking error and generate the compensation value in real time. The stability, the convergence, and the parameter sensitivity of this observer are analyzed in detail. To improve the suppression effect of the ERPHE for different loads and speeds, an iterative learning gain self-tuning strategy is investigated. The proposed method does not require the offline detection and the discrimination of harmonic frequencies, which has strong suppression ability for different harmonic error components. The effectiveness is verified by experiments on a 2.2-kW interior PMSM drive platform. [ABSTRACT FROM AUTHOR]

An integrated zero common-mode voltage (ZCMV) modulation algorithm is developed in this article for dual-parallel neutral-point-clamped (NPC) inverters treated as an integrated system. While the conventional methods achieve CMV elimination with the cost of worse harmonic performance, the proposed method guarantees a ZCMV and better current quality simultaneously by taking advantage of the extra space vectors provided by paralleling. Specially designed switching sequences are developed to maintain a balanced neutral point of dc bus and keep the averaged value of the circulating current to be zero, ensuring the normal function of parallel NPC inverters. In addition, although the switching sequence design is complicated, a simple approach is proposed and implemented on a commonly used digital signal processor. A laboratory prototype is developed to test the system performance under steady-state conditions and dynamic process in grid-connected operation. Compared with the conventional ZCMV modulation, experimental results verify the effectiveness of the integrated modulation in eliminating the CMV, in addition to the dramatically reduced output current distortion. [ABSTRACT FROM AUTHOR]

The overmodulation-based nonlinear voltage extension could increase the maximum output torque of the induction motor (IM) in the field-weakening (FW) region. Since the voltage distortion increases with the deepening of overmodulation degree, the extreme nonlinear voltage extension (six-step voltage) is only worthwhile in maximum torque demand conditions. However, the conventional overmodulation-FW scheme always adopts the six-step voltage regardless of torque demand, leading to severe torque ripple. To solve this problem, the minimum-nonlinear-voltage (MNV) method is proposed to satisfy the torque demand with minimum overmodulation-voltage nonlinearity. The difference between the limiting and the feedback values of the torque current is used for suppressing the nonlinear voltage extension during a nonmaximum torque demand state. The quantitative relation between the torque ripple and torque demand of the MNV method is calculated and compared with that of the conventional six-step-FW method. Analysis shows that the MNV method can eliminate the torque ripples of low and medium torque demand conditions completely and partially, respectively. The effectiveness of the proposed method is verified experimentally on a 3.7 kW IM platform. [ABSTRACT FROM AUTHOR]

In this article, a novel 20-MHz high-frequency high-performance dc–dc resonant converter is analyzed, which owns the characteristics of soft-switching, low voltage stress, and small volume. The numerical analysis is conducted in time domain and the resonant parameters can be accurately calculated based on the corresponding expressions. A full resonant rectifier stage is adopted without using choke inductors, and the value and volume of inductors can be greatly reduced. A 12-V input, 5 V/5 W output prototype is proposed in the laboratory and the experimental results verify the feasibility of the proposed converter and numerical design methodology. [ABSTRACT FROM AUTHOR]

The instability issue is an important concern in the reduced dc-link capacitance motor drive system, which is caused by the interaction of the LC resonance and the negative impedance of the constant power load (CPL). Harmonics of the grid current also need to be concerned to meet the requirement of the application standards. In this paper, the impedance model of the drive system is established considering the dc-link voltage fluctuation, which is applied to evaluate the drive system stability. The grid current harmonics issue could also be analyzed by the grid input impedance model. A novel grid current feedback based stabilization control method is proposed to stabilize the drive system, which could formulate the Nyquist plot of the drive system. Besides, the grid current harmonics could also be suppressed effectively by adopting the proposed stabilization control method. Experimental results are performed to verify the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

In distributed generation, grid-connected and islanded modes are essential, but usually they have different control cores to satisfy their respective control targets. Transferring between the cores may therefore lead to prominent disturbances, if the cores are complex and noticeably different in structures. To introduce seamlessness, some techniques have been recommended, but they usually lack unification of control blocks for the front dc–dc converter and rear dc–ac inverter. Moreover, when connected to the grid, some seamless techniques do not control the grid current directly. Hence, its dynamics may be slow, in addition to distortion caused by grid-voltage harmonics. When islanded, most techniques also use two control loops to regulate a drooped voltage across local loads. This double-loop structure works fine, but it has more state variables to change during a transfer of modes, which may not be as seamless. An alternative technique has thus been proposed here, whose purpose is to identify a simple unified control core, which will remain unchanged during the mode transfer. The transfer may then be viewed as a normal change of power reference, instead of an internal change of control structure. Hence, seamless operation may be ensured, as it is tested in simulations and experiments. These tests have additionally shown that the proposed scheme can regulate the grid current directly when connected to the grid, without compromising the droop-voltage regulation when islanded. [ABSTRACT FROM AUTHOR]

DC-link electrolytic capacitor critically affects the lifetime of the motor drive system. This paper proposes an inverter power control strategy based on dc-link voltage regulation for the electrolytic capacitor-less interior permanent magnet synchronous motor drive system. The dc-link electrolytic capacitor is replaced by a small film capacitor and the power factor correction circuit is also eliminated. Hence, the inverter power should be regulated effectively to achieve high input power factor and low grid current harmonics. The inverter power control loop based on proportional resonant (PR) controller is established to regulate the inverter power into sinusoidal wave. The PR controller can be designed to achieve a high gain at the desired frequency and the parameters are easy to design due to the simple structure. In addition, a power compensation method based on the dc-link voltage regulation is used to diminish the error of inverter power control, which does not depend on the precise calculation and is easy to realize. The effectiveness of the proposed method is demonstrated by the experimental results on an air conditioner. The input power factor can reach 0.992 and the harmonics of grid current are considerably lower than the requirement of EN61000-3-2 standard. [ABSTRACT FROM PUBLISHER]

The papers in this special section are devoted to the topic of solutions for power quality management. Although the power quality problems, such as, reactive and harmonic currents, distortion and fluctuations in the supply voltage, are not new to power system and power electronics researchers, the ever changing landscapes in the power generation and distribution systems have given rise to additional power quality challenges. The growing interest in the smart grid concepts, vehicle to grid operation, inverter based large scale photovoltaic (PV) and wind integration, distributed generators (DGs) as ancillary service provider, multilevel inverters for high power applications and so on is making the power quality aspects more prevalent. [ABSTRACT FROM PUBLISHER]

For the purpose of improving the performance of sensorless interior permanent magnet synchronous motor (IPMSM) drives, an enhanced electromotive-force (EMF)-based position observer adopting second-order generalized integrator (SOGI) to eliminate the harmonic error is proposed. The inverter nonlinearities and flux spatial harmonics that give rise to the harmonic error of position estimation are analyzed. A harmonic decoupling network consisting of multiple SOGIs based adaptive filters is adopted to achieve the multiple selective EMF harmonic elimination (MSEHE). The application of the frequency-locked loop ensures the SOGI resonance frequency adaptive, which is critical for the variable-speed operation in IPMSM drive applications. Using the SOGI-MSEHE in the position tracking estimator, the low-order harmonics in the estimated EMF can be effectively eliminated, contributing to cancelling the position estimation harmonic error. The effectiveness of the proposed enhanced position observer is verified by the experimental results at a 2.2-kW IPMSM sensorless drive. [ABSTRACT FROM PUBLISHER]