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This paper proposes the integration of the auxiliary power module (APM) and nondissipative balancing hardware of a high-voltage battery. The proposed battery-balancing APM is projected to reduce the costs of nondissipative battery balancing by providing two functionalities: balancing of the high-voltage battery cells and charging of the low-voltage battery. This paper proposes two model predictive control strategies that address simultaneous balancing and charging. Both approaches make unbalanced charge available that increases the effective capacity of the high-voltage battery. The monolithic controller solves the balancing and charging problem as a single optimization problem. In contrast, the decoupled controller defines a separate control law for charging to achieve a higher bandwidth, e.g., for systems without dedicated low-voltage battery. The battery-balancing APM concept is validated on a software-in-the-loop and experimental test bench. [ABSTRACT FROM PUBLISHER]

Electric bicycles (EBs) are becoming increasingly popular in some regions such as China and Europe. However, wireless power transfer (WPT) for charging massive EBs poses a challenge related to the cost of WPT system (WPTS), especially in China, where EBs application is so sensitive to the product price. This paper presents an optimization method of the passive components for the S-LCC topology to decrease the cost of the overall system. With the novel method, the number of passive components can be optimized to the minimum and still with constant current and constant voltage outputs. A novel compensation method with an inductor array is also proposed to guarantee an inductive input impedance of WPTS, achieving soft switching and reducing the high switching losses of the high-frequency inverter (HFI). To demonstrate the validity of the proposed methods, an experimental setup is built. The performance of two WPTS indicates that massive EBs can be charged with only one HFI, and the cost of the overall system decreases accordingly. [ABSTRACT FROM PUBLISHER]

This paper addresses the effect of rotor structure on the magnetic adjusting performance of an axial-radial permanent magnetic machine via the comparative performance investigation on the axial-radial flux type permanent magnet machines with three different structures. By using the three-dimensional time stepping finite-element method, the distributions of the air-gap flux density are obtained when the machine operates with different axial magnetomotive force, and the key factor that affects the magnetic adjusting ability is determined. The variation of the magnetic field is investigated, and the back electromotive forces of the three machines with different structures are also studied. Meanwhile, the eddy current distribution and the eddy current loss in machines with different structures during load operation are analyzed. The theoretical claims are verified by both numerical simulations and experimental tests. [ABSTRACT FROM PUBLISHER]

Supporting a wide operating range for industrial-standard backward-compatible transmitters often results in energy inefficiency. This paper describes an energy-efficient voltage-mode-serializing transmitter with an operating range of up to 32 Gb/s. The proposed transmitter uses a programmable internal supply to set the voltage level for various data rates optimally, thus improving overall energy efficiency. Output swing and pre-emphasis levels are largely adjustable while the constant output impedance is maintained using a dedicated control loop. CMOS-logic-based circuits and quarter-rate clocking enhance the energy efficiency over the entire data rate range, while a P-over-N voltage-mode driver is used to achieve a high maximum output swing. Two supply regulators with replicas provide constant pull-up and pull-down impedances of the output driver. The variable output swing, pre-emphasis, and internal supply are realized by using segmented output drivers and replicas. The proposed transmitter, fabricated in a 65-nm CMOS process, occupies an active area of 0.173 mm2. The prototype chip achieves a wide output swing range of 0.4–1.3 Vppd and an energy efficiency of 2.10–3.45 pJ/bit, across a data rate of 5 –32 Gb/s. [ABSTRACT FROM PUBLISHER]

Tap changers are commonly used to maintain the limits in medium-voltage lines. Initially based on electromechanical switches, efforts have been made since the 1990's to reduce maintenance expenses with thyristor-based versions. Among the methods to limit the short-circuiting current in commutating taps, the multiwinding coil has demonstrated, during decades of use in the low-voltage field, to be reliable and cheap. Two previous papers showed that multiwinding changers can be applied to medium-voltage lines up to 34.5 kV, 15 MVA with no parallel or series thyristor association. This paper proposes a new topology, based on a double array of tap switches per phase, allowing for step-up the power from 15 to 36 MVA and insertion in any point of the line with no connection to the head transformer. A comparative cost analysis gives technical and economical results for a typical 10 MVA, 34.5 kV stabilizer demonstrating the advantages of the proposed circuit over the electronic single array topology and the classic mechanical solutions. [ABSTRACT FROM PUBLISHER]

Due to the relatively low output voltage of photovoltaic (PV) source, a high step-up converter with high efficiency is needed when the PV source is connected to the power grid. A novel high step-up converter based on two switched capacitors and a coupled inductor is proposed in this paper. The operating principle is analyzed and the voltage gain is derived. A 100-W prototype is fabricated in the laboratory to verify the theoretical analysis, and the highest efficiency is 96.4%. [ABSTRACT FROM PUBLISHER]

In this paper, the design and development of a novel interleaved tri-state boost converter (ITBC), which produces lower ripple and exhibits better dynamic response, is discussed. Boost converters are frequently connected in parallel and operate in an interleaving mode for the reduction of ripple content in source current and in output voltage. In this way, interleaved boost converter (IBC) is conceived, which improves the power handling capabilities and increases the overall system rating. It also has the advantage of reduction of the ripple content in source current and output voltage, but when control-to-output transfer function of IBC is derived under continuous conduction mode of operation, then a right-half-plane (RHP) zero appears in the transfer function. Due to the presence of RHP zero, IBC has nonminimum phase problem, which deteriorates the dynamic performance. The tri-state boost converter (TBC) is the best choice for RHP zero elimination, but due to the extra freewheeling mode, ripple content will also be increased. The proposed converter is a parallel combination of two TBC and operates in an interleaving mode. Therefore, the proposed converter has both of the advantages of TBC and IBC. The performance analyses of ITBC, TBC, and IBC have been studied based on simulation and experimental results. From the comparative analysis, it is observed that ITBC is performed better than other two converters. The ripple comparisons between three converters have also been done. It is found that the ripple content in ITBC is slightly greater than IBC but is less than TBC. [ABSTRACT FROM PUBLISHER]

This paper proposes a multiloop framework for current control of grid-connected voltage source inverters (VSIs) with LCL output filter. The discrete-time model is of third-order with a nonminimum phase zero when controlling the grid side current. This poses some difficulties on the design of most types of controllers. Motivated by this problem, the inner loop is implemented by a discrete-time sliding mode control law to ensure the tracking of the converter side current. This can be achieved regardless the grid impedance and voltage, making the converter to behave like a current source inverter with a capacitive+inductive (CL) filter. Thus, the problem of current control falls from a third-order system to a second-order system. Several types of controllers can be designed to implement the outer loop based on the equivalent CL circuit. In this work, a resonant controller with a virtual resistor was applied. Simulations and experimental results are presented to validate the proposal. [ABSTRACT FROM PUBLISHER]

This paper proposes a new phase current reconstruction scheme without using null switching states for interior permanent magnet synchronous motor (IPMSM) sensorless control. The phase currents are independently reconstructed and no additional test voltage pulses are required. First, the principle of the basic phase current reconstruction for IPMSM drive system is analyzed in detail. Then, an independent phase current reconstruction scheme without using null switching states is proposed. The current reconstruction dead zone is divided into six sectors, and each sector is split into three parts with corresponding vector synthesis methods. Meanwhile, the null switching states, V000 and V111, are removed from the proposed scheme. In this case, the zero vector is synthesized by the other available vectors. Finally, the reconstructed three-phase currents are utilized for high frequency sine-wave voltage injection-based position estimation. The effectiveness of the proposed scheme is verified by experimental results on a 5 kW IPMSM motor prototype, which shows that the reconstructed phase currents track the actual currents accurately under different working conditions. [ABSTRACT FROM PUBLISHER]

In-circuit frequency response measurement of power converters enables verification of the control loop and periodic measurement during normal operation of the converter. This enables addition of diagnostics and monitoring functions without additional cost. The disturbance injected for frequency response measurement causes output of the converter to be disturbed, which is undesirable during normal converter operation. This paper presents an auto injection control algorithm by which the disturbance amplitude is controlled while maintaining good measurement fidelity. A voltage source inverter is selected as a case study to test the proposed algorithm, in which both current and voltage loop are verified using in-circuit frequency response analysis measurement. [ABSTRACT FROM PUBLISHER]

Adding the auxiliary switches to the conventional H-bridge inverter is an effective way to eliminate the leakage current for transformerless PV systems, such as H5, H6, etc. Inspired by the newly developed embedded-switch H6 topology, a novel embedded-switch inverter (ESI) is proposed in this paper for three-phase transformerless PV systems. First, the operation principle and characteristics of the proposed ESI are analyzed. Second, the common-mode model of the three-phase ESI is established, based on which the main factors that affect the leakage current are discussed. The finding reveals that the switching states with conventional modulation strategy result in high-frequency common-mode voltage, which is the source of leakage current. In order to solve the problem, a new modulation strategy is presented for ESI to eliminate the high-frequency leakage current. Finally, the time-domain simulation and the experimental tests are carried out. The results verify the effectiveness of the proposed solution. [ABSTRACT FROM AUTHOR]

This paper proposes a novel autonomous control scheme for equal load current distribution between $n$ parallel-connected, LCL-based, three-phase online uninterruptible power supply (UPS) modules. The control is based on regulating the reference voltage of the filter's capacitor of each inverter as a function of its own output current. The control is achieved without exchanging information between the inverters. The load voltage is maintained fixed at the specified reference value. The control method is fast, precise, and robust against load variations. The validity of the proposed method is verified experimentally and by simulation on a system of two parallel inverters under different load conditions, including step-load and nonlinear load. [ABSTRACT FROM AUTHOR]

The traditional generating set is usually comprised of a classical, wound-field, salient-pole, or cylindrical rotor synchronous generator, excited by a separate smaller machine, via a rotating, uncontrolled diode rectifier. The effects of the commutation processes of the diode bridge are often overlooked and neglected. However, due to the uncontrolled nature of this process, the rectified voltage available at the main generator's rotor terminals can be significantly lower than the expected value. This is especially true for low-to-medium power rated systems. In this paper, a detailed investigation of these aspects is done and an accurate voltage drop prediction model is then proposed. The model is validated with finite-element analysis and with experimental results for a particular low–medium rated generating system in the 400 kVA power range. The validated tool is then integrated into an innovative design tool, which first performs an analytical presizing procedure and then utilizes a genetic algorithm approach to identify an optimal excitation system design, aimed at minimizing the voltage drop ensuing from the diode commutations, with minimum impact on the overall efficiency. [ABSTRACT FROM AUTHOR]

Frequency response analysis (FRA) has recently been developed as a widely accepted tool for power transformer winding mechanical deformation diagnosis, and has proven to be effective and powerful in many cases. However, there still exist problems regarding the application of FRA. FRA is a comparative method in which the measured FRA signature should be compared with its fingerprint. Small differences of FRA signatures in certain frequency bands might be produced by external disturbance, which hinders fault diagnosis. Additionally, the existing correlation coefficient indicator recommended by power industry standards cannot reflect key information of signatures, namely the extreme points. This paper proposes an improved FRA based on binary morphology and extreme point variation. Binary morphology is first introduced to extract the certain frequency bands of signatures with significant difference. A composite indicator of extreme point variation is adopted to realize the diagnosis of fault level. A ternary diagram is constructed by the area proportions of the binary image to identify winding faults, which has a potential to realize cluster analysis of fault types. [ABSTRACT FROM AUTHOR]

The parallel three-phase grid-connected converters sharing dc and ac bus can increase the system power level effectively. However, the zero sequence circulating current (ZSCC) will occur inevitably under space vector pulse width modulation or discontinuous pulse width modulation (DPWM). In this paper, the mechanism and the mathematical model of ZSCC are studied. Then, a hybrid PWM (HPWM) strategy is proposed to suppress the ZSCC based on the same zero sequence voltage injected, which is dependent on the common grid information. The dc voltage utilization of HPWM can be extended compared with sinusoidal PWM (SPWM). The number of parallel modules can be infinity theoretically by using HPWM. It is noted that there is no internal commutation among modules (expect the dq current reference). Finally, the feasibility and the effectiveness of the proposed method are verified by experiments. [ABSTRACT FROM AUTHOR]

Traditional model predictive control cost functions, when utilizing long prediction horizons ( $N\geq 10$) in power inverter applications, have demonstrated harmonic performances approaching that of schemes based on offline-generated optimal pulse patterns. However, long prediction horizons often prohibitively increase computational load. A different approach to maximizing harmonic performance is taken in this paper. It is shown that shaping the output voltage spectra using a simple feedback mechanism can significantly reduce the length of the required prediction horizon, facilitating a feasible computational load. When a short-horizon cost function is augmented by the feedback mechanism an excellent tradeoff between harmonic performance and switching loss is achieved, even with a prediction horizon of one. It is also shown that the feedback mechanism can be used to improve input reference tracking. Experimental verification of the proposed modulator is performed on a two-level three-phase inverter. [ABSTRACT FROM AUTHOR]

Active ripple decoupling technique of the single-phase inverter is a popular topic to minimize the dc-link capacitance. However, the existing control methods are based on tracking sinusoidal or predetermined voltage waveforms of the compensation capacitor, assuming the inverter outputs are pure sinusoidal voltage and current. Therefore, the performance of existing methods degrades when the inverter output voltage and current are not purely sinusoidal. Furthermore, the limited dynamic performance threatens the safety of dc-link capacitor when the load changes. This happens, because the inrush ripple power is injected into dc link with small capacitance and the dc-link voltage will suddenly rise up when the ripple power is not buffered during transients. In this paper, a direct instantaneous power predictive control is proposed for the decoupling circuit to buffer ripple power of the single-phase inverter, which combines instantaneous ripple power control with model predictive control to overcome the issues above. The proposed method tracks the instantaneous ripple power rather than voltage or current waveforms. In this way, it can fully buffer all ripple powers in the system even for distorted output voltage and current of the inverter and enables the full utilization of storage capacitor. In addition, model predictive control makes the proposed method have fast dynamic and perfectly compensate ripple power during transients and steady states. The buck-type active ripple decoupling circuit is chosen to implement the proposed method after comparing with another typical decoupling topology. The proposed method is also compared with conventional method using proportional-integral-resonant regulator to track the predetermined capacitor voltage waveform. Experimental tests verify the theoretical analysis and the proposed control method. [ABSTRACT FROM AUTHOR]

In this paper, a single-phase multilevel ac/ac converter with reduced number of power semiconductor devices is proposed. For the simple case of a three-level converter, only three bidirectional switches and two capacitors are required. The proposed converter provides a highly sinusoidal and regulated output voltage with a simple topology. The efficiency is high because in each state of operation only one semiconductor conducts. The converter can be easily extended to any desired levels in the output voltage to even more reduce the output total harmonics distortion. Another advantage of the proposed converter is that by increasing the voltage levels, the stress on the switches will decrease. The proper performance of the proposed converter is confirmed through extensive simulation and experimental tests. [ABSTRACT FROM PUBLISHER]

To achieve precise voltage value for modern model-based motor control strategies, an accurate voltage distortion compensation method for voltage source inverters is proposed in this paper. The voltage distortion principles of a mosfet-based inverter and an IGBT-based inverter are analyzed and compared. A graphical solution of compensating voltage error is proposed, all the voltage distortion factors are considered. A current observer is designed to overcome time delay, achieve precise current in each switching period for compensation. The proposed method is of high precision, intuitive, and easy to implement. The effectiveness of the proposed method is verified by experiments. [ABSTRACT FROM PUBLISHER]

This paper shows a synchronization technique of power converters based on a limit cycle oscillator (LCO) and a frequency-locked loop (FLL), which makes the system frequency adaptive. The proposed technique LCO-FLL offers a high degree of immunity and robustness against swells, sags, harmonics, and phase-frequency shift. Furthermore, the LCO-FLL has the advantage of performing the synchrony with the grid from any initial condition set for LCO, ensuring an acceptable transient onto the synchronization process. Other advantages of the proposed scheme are that it does not require a phase-locked loop or trigonometric functions and it gives useful information to estimate the positive- and negative-sequence components in a three-phase system with a highly polluted grid scenario. In this paper, a local stability analysis of the LCO-FLL is presented. The behavior and performance of the proposed technique are compared with synchronization techniques by means of experimental results. Furthermore, a three-phase application of the synchronization technique is evaluated experimentally. [ABSTRACT FROM PUBLISHER]

Inverter-based distributed generation (DG) system is becoming an attractive solution for high penetration of renewable energy sources to the main grid. DG system should be able to supply power to the local loads whenever necessary even in case of utility power outage. Thus, the inverters in DG systems are expected to operate in both grid-connected and islanded mode, where they are acting as a current source for the ac grid and a voltage-source for the load, respectively. Transition between modes of operation is nontrivial and can cause deviations in voltage and current, because of mismatch in frequency, phase, and amplitude between the inverter output voltage and the grid voltage. Thus, it is necessary to have seamless transition between grid-connected and islanded mode. This paper presents a new control strategy with seamless transfer characteristics for a grid-connected voltage-source inverter using model predictive control (MPC) framework. The main objectives of the proposed predictive controller are: 1) decoupled power control in grid-connected mode, which enables the proposed power electronics interface to provide ancillary services such as reactive power compensation; 2) load voltage control in islanded mode; and 3) seamless transition between modes of operation through proposed synchronization and phase adjustment algorithm. The proposed controller features simplicity to implement since only one cost function should be minimized for all modes of operation, and hence no ambiguity in the control algorithm that could cause mode transition problems. An autotuning strategy for weight factors in MPC cost function is proposed to simplify the weight factor tuning strategy. The stability analysis of the proposed controller is provided. Simulation and experimental results validate the expected performance and effectiveness of the proposed control strategy. [ABSTRACT FROM PUBLISHER]

Dead-time insertion increases noise and torque pulsation in motors under open-loop constant V/f control, and it results in instability in motors under sensorless field-orientated control or direct torque control at low speed, degrading performance of motor drive systems. In order to overcome the drawback of dead-time insertion, a novel current-detection-independent dead-time compensation technique based on terminal voltage A/D conversion is proposed in this paper. Both current polarity and compensation time can be extracted from the sampled terminal voltage. Experiments on an induction motor rated at 210 V, 2.2 kW demonstrated the proposed technique can significantly improve the performance of the fixed compensation, online compensation, and even the feedback compensation method. The proposed scheme does not rely on current sensors, and thus can be applied to both open-loop and closed-loop motor drive systems. When combined with the fixed compensation method, the performance of the proposed technique is even comparable with the feedback compensation method within a large frequency range, making it very attractive for open-loop constant V/f drives where current sensors are not available. [ABSTRACT FROM PUBLISHER]

The paper presents an innovative concept of applying a combination of well-known selective harmonic elimination (SHE) and selective harmonics mitigation (SHM) methods to shape a spectrum of catenary current harmonics, generated by a traction drive system equipped with a voltage source inverter. Application of this method allows for reducing distorting influence of a modern rolling stock supplied by a 3 kV dc catenary on the railway signaling, command, and control systems. The efficiency of the proposed method is independent of synchronization of a vehicle's inverters and of load balance of traction motors, which makes it more reliable than as it is proposed in the literature. Results of computer simulations were presented and compared with laboratory measurements. The obtained dc-link current spectrum using the proposed SHE/SHM method was compared with spectra received using synchronized and unsynchronized sinusoidal pulse-width modulations (SPWMs). Based on the conducted tests, it was shown that the proposed method of control, which was implemented in a laboratory drive system, is effective in reducing dc side current harmonics in a frequency range of 1300–3100 Hz, which is used by track circuits on railway lines, e.g., in Poland. The technique proposed by the authors allows taking into account any restrictions arising from the technical nature of low-frequency traction drives. [ABSTRACT FROM PUBLISHER]

Silicon carbide (SiC) power devices have been investigated extensively in the past two decades, and there are many devices commercially available now. Owing to the intrinsic material advantages of SiC over silicon (Si), SiC power devices can operate at higher voltage, higher switching frequency, and higher temperature. This paper reviews the technology progress of SiC power devices and their emerging applications. The design challenges and future trends are summarized at the end of the paper. [ABSTRACT FROM AUTHOR]

In this paper, two topologies are presented for the enhanced-boost quasi-Z-source inverters (qZSI), namely continuous input current configuration and discontinuous input current configuration of enhanced-boost qZSI with two-switched impedance networks. Similar to enhanced-boost impedance-source inverters (ZSIs), these proposed inverter topologies possess very high boost voltage inversion at low shoot-through duty ratio and high modulation index to provide an improved quality output voltage. Compared to enhanced-boost ZSIs with two-switched Z-source impedance networks, these proposed inverter topologies share common ground with source and bridge inverter, overcome the starting inrush problem, and draw continuous input current and the lower voltage across the capacitors. Moreover, the input ripple current is negligible. This paper presents the operating principles and analysis of continuous input current configuration enhanced-boost qZSI with two-switched impedance networks and compares with ZSI, switched inductor ZSI, DA/CA-qZSI, and enhanced-boost ZSIs. The theoretical analysis is done and is validated through simulation and experimental results. [ABSTRACT FROM PUBLISHER]

In this paper, novel remedial direct torque control (DTC) schemes are proposed for open-circuit faults in T-type neutral-point-clamping (T-NPC) three-level asymmetric six-phase permanent-magnet synchronous motor (PMSM) drives. First, a simplified space vector modulation (SVM) is designed and applied for DTC-controlled asymmetric six-phase drive, in such a way that both good current harmonic performance and fast dynamic response are available. Based on the SVM-DTC scheme, a remedial strategy is proposed for the open-circuit faults in phase windings. The key is to derive the relationship between the stator fluxes and the stator voltages of all phases under faulty condition. Then, a derived perturbation term is compensated for normal voltage references, and the fault-tolerant scheme is, thus, implemented without changing control structure of normal condition. The remedial DTC schemes are also studied and proposed for open-switch faults in T-NPC six-phase drives. The modulation methods are redesigned for the faults in half-bridge switches and NPC switches. The experiments are carried out on a laboratory prototype to verify the validity and performance of the proposed fault-tolerant control schemes. [ABSTRACT FROM PUBLISHER]

Large transient inrush fault current in a synchronverter during a short-circuit fault can potentially damage the inverter and cause grid instability. It is therefore important to study the characteristics of and the way to restrain the inrush fault current. This paper investigates the characteristics of the synchronverter inrush fault current and proposes a new control method based on mode switching to protect synchronverters. First, an ideal voltage source inverter instantaneous inrush current calculation method for a grid symmetrical short circuit is discussed. Then, based on the inertia of synchronverter, the approximate calculation of the synchronverter instantaneous inrush current is described. The results show that the synchronverter's inrush current mainly consists of a gradually attenuated periodic component and a dc component when the phased voltage symmetry is lost. In our proposed new control approach, the synchronverter switches to the hysteresis controller to limit the output current quickly while staying connected to the grid, and supporting the grid voltage simultaneously. Simulation and experiment results verify the validity of the theoretical analysis. [ABSTRACT FROM PUBLISHER]

The detection and classification of power quality (PQ) disturbances have become a pressing concern due to the increasing number of disturbing loads connected to the power line and the susceptibility of certain loads to the presence of these disturbances; moreover, they can appear simultaneously since, in any real power system, there are multiple sources of different disturbances. In this paper, a new dual neural-network-based methodology to detect and classify single and combined PQ disturbances is proposed, consisting, on the one hand, of an adaptive linear network for harmonic and interharmonic estimation that allows computing the root-mean-square voltage and total harmonic distortion indices. With these indices, it is possible to detect and classify sags, swells, outages, and harmonics–interharmonics. On the other hand, a feedforward neural network for pattern recognition using the horizontal and vertical histograms of a specific voltage waveform can classify spikes, notching, flicker, and oscillatory transients. The combination of the aforementioned neural networks allows the detection and classification of all the aforementioned disturbances even when they appear simultaneously. An experiment under real operating conditions is carried out in order to test the proposed methodology. [ABSTRACT FROM PUBLISHER]

Neutral-point (NP)-clamped three-level inverter, which is a widely used topology of multilevel converters, suffers from the NP voltage drift as its main technical drawback. The nearest-three-virtual-vector (\NTV^2) modulation method can control the NP voltage balance for any load over the full range of inverter output voltage. However, compared with the nearest-three-vector (NTV) modulation method, \NTV^2 increases the switching frequency. This paper combines \NTV^2 with NTV, and the two methods are used alternately in a fundamental cycle. The duty-cycle coefficients of the redundant small vectors are analyzed to explore the intervals where NTV can control the NP voltage balance in a fundamental cycle. The proportional parameter, which represents the combination of the two methods in hybrid space vector pulsewidth modulation, can be selected to achieve a high-performance NP balance control and low switching frequency. The steady- and transient-state behaviors of the proposed strategy are analyzed in this paper. The experimental results verify the validity of the proposed strategy. [ABSTRACT FROM PUBLISHER]

To reduce stored capacitor energy in modular multilevel converters (MMCs), previous papers propose injection of harmonics in the arm circulating currents and zero-sequence voltages. While this approach is effective, previously utilized combinations of injected harmonics significantly increase converter current ratings. In contrast, the optimization approach developed in this article identifies harmonics that simultaneously achieve capacitor energy optimization and reduced overrating of converter currents. In addition, the proposed approach eliminates the possibility of convergence to local minima, which is a significant improvement on previously proposed nonconvex optimization approaches. Experimental verification of the proposed approach is performed on a low-voltage three-phase modular multilevel converter. [ABSTRACT FROM AUTHOR]

This paper proposes an alternative strategy of finite-control-set model-predictive torque control (MPTC) to reduce the computational burden and the torque ripple and decouple the switching frequency from the controller sampling time. An improved discrete space-vector modulation (DSVM) technique is utilized to synthesize a large number of virtual voltage vectors. The deadbeat (DB) technique is used to optimize the voltage vector selection process, avoiding enumerating all the feasible voltage vectors. With this proposed method, only three voltage vectors are tested in each predictive step. Based on the improved DSVM method, the three candidate voltage vectors are calculated by using a novel algebraic way. This new strategy has the benefits of both the MPTC method and the DB method. The effectiveness of the proposed strategy is validated based on a test bench. [ABSTRACT FROM PUBLISHER]

The benefits of implementing a damper winding in salient-pole synchronous generators are widely known and well consolidated. It is also well known that such a winding incurs extra losses in the machine due to a number of reasons. In order to improve the overall efficiency and performance of classical salient-pole, wound field synchronous generators that employ the traditional damper cage, an improved amortisseur winding topology that reduces the inherent loss is proposed and investigated in this paper. This is essential in order to meet modern power quality requirements and to improve the overall performance of such “classical” machines. The new topology addresses the requirements for lower loss components without compromising the acceptable values of the output voltage total harmonic distortion and achieves this by having a modulated damper bar pitch. As vessel for studying the proposed concept, a 4-MVA salient-pole synchronous generator is considered. A finite element model of this machine is first built and then validated against experimental results. The validated model is then used to investigate the proposed concept with an optimal solution being achieved via the implementation of a genetic algorithm optimization tool. Finally, the performance of the optimized machine is compared to the original design both at a steady state and transient operating conditions. [ABSTRACT FROM PUBLISHER]

The traditional flux-switching permanent-magnet machines (FSPMMs) with radial lamination have serious partial magnetic saturation for their nonlinear magnetic path, where the maximal flux density is usually more than 2.0 T occurring at the edges/tips of stator teeth or rotor poles. In this case, the core loss of FSPMMs becomes evident especially beyond the rated speed, which leads to decrease of output power, torque/power density, and efficiency. To overcome these problems, an axially laminated flux-switching permanent-magnet machine (ALFSPMM) with high grain-oriented silicon steel stator and rotor cores is proposed. The detailed fabrication procedures are presented in this paper. The theoretical characteristics of the ALFSPMM, such as back electromotive force, self-/mutual inductance, and cogging torque are calculated by the two-dimensional finite-element method (FEM). The influence of misalignment between the stator core and the rotor shaft (a common issue in motor manufacturing) is investigated by the FEM. Experimental measurements of the prototype machine are presented to validate the FEM calculation. In addition, a simple low-cost method to measure the cogging torque is also presented in this paper. [ABSTRACT FROM AUTHOR]

Distributed secondary control plays an important role in dc microgrids, since it ensures system control objectives, which are power sharing and dc-bus voltage stability. Previous studies have suggested using a control architecture that utilizes a parallel secondary bus voltage and current sharing compensation. However, the parallel controllers have a mutual impact on each other, which degrades the transient performance of the system. This paper reports on an alternative distributed secondary control architecture and controller design process, based on small-signal analysis to alleviate the mutual effect of the current sharing and bus voltage compensation, and to improve the transient response of the system. Experimental results confirm the improved transient performance in the current sharing control and dc-bus voltage stability utilizing the proposed control architecture. [ABSTRACT FROM PUBLISHER]

This paper presents a new family of hybrid Z-source boost dc–dc converters intended for photovoltaic applications, where the high step-up dc–dc converters are demanded to boost the low-source voltages to a predefined grid voltage. Because the boost capabilities of the traditional Z-source networks are limited, the proposed converters are composed of combine traditional Z-source networks in different ways to enhance the boost abilities of the traditional Z-source networks. The new version of the proposed Z-source converters is termed as hybrid Z-source boost dc–dc converters to satisfy the traditional benefits of Z-source networks with stronger voltage boost abilities which can also be applied to dc–ac, ac–ac, and ac–dc power conversions. The performances of the proposed converters are compared with other Z-source networks behaviors. The simulation and experimental results of the proposed converters are validated at different operating conditions. [ABSTRACT FROM PUBLISHER]

Multilevel converter topologies for open-end stator winding medium-voltage (MV) induction motor drives have been researched from the last two decades. In this paper, a dual $n$ -level modular multilevel converter (MMC) topology has been proposed for open-end stator winding MV induction motor drives. The control requirements of the proposed system are low device switching frequency, minimal harmonic distortion of machine stator currents, elimination of common-mode voltages in machine stator windings, and maintaining floating capacitor voltages around their nominal value. Based on these requirements, an emerging modulation technique for MV induction motor drives known as synchronous optimal pulsewidth modulation has been developed for the proposed dual $n$L-MMC topology. The laboratory measurements from a dual three-level MMC fed 1.5-kW open-end stator winding induction motor drive demonstrate the performance of proposed technique. [ABSTRACT FROM PUBLISHER]

Leakage current reduction of the single-phase transformerless cascaded H-bridge PV inverter is investigated in this paper. The high-frequency common-mode loop model of a typical single-phase cascaded H-bridge PV system is established. Based on the model, the main factors that affect the leakage current are discussed. The reason why the typical single-phase cascaded H-bridge inverter fails to reduce the leakage current is explained. In order to solve the problem, a cascaded topology based on the H5 inverter is presented, along with a new modulation strategy, which can ensure that the stray capacitor voltage is free of high-frequency components. In this way, the leakage current can be effectively reduced. Finally, a prototype with TMS320F28335DSP + XC3S400FPGA digital control is built. The performance tests of cascaded H-bridge and the proposed topologies are carried out. The experimental results verify the effectiveness of the proposed solution. [ABSTRACT FROM AUTHOR]

This paper presents an adaptive observer (AO)-based model predictive control (MPC) for a multilevel flying capacitors inverter (FCI). The proposed system consists of a midpoint dc-link three-cell four-level FCI feeding an RL load. Using the actual load current, the proposed AO estimates accurately the capacitors’ voltages, which are fed to the MPC algorithm by means of a hybrid model considering both discrete and continuous variables. For real-time constraints, sufficient conditions are given to guarantee the practical stability of the proposed AO-based MPC. Theoretical analysis and experimental results are given to show that the proposed method is stable for all system configurations and has good performances even during disturbances (load change, input change, and parameters variations). [ABSTRACT FROM AUTHOR]

Compensation of nonlinear effects generated by dead-time and semiconductors voltage drop has been widely studied in the literature about two-level converters. This paper takes a closer look at those analyses for multilevel converters, specifically for a cascaded H-bridge (CHB) converter modulated with phase-shifted pulse width modulation. The interaction between the cells is analyzed for a generic $n$ -cell converter, from which a general expression for the distortion generated by the nonlinearities has been obtained. Based on this expression, a compensation signal for the overall converter is calculated on each sample time, which is a fraction of the triangular carrier used to modulate each cell, thus significantly improving the quality of the output voltage signals. Experimental validation of the proposed compensation method is presented using a three-phase four-cell CHB converter prototype of 5.5 kW. [ABSTRACT FROM AUTHOR]

This paper presents new look-up table methods for a three-level ac/dc converter supplied from the grid. The nonlinear direct power control (DPC) method, by reason of its drawbacks resulting from the omission of grid inductance voltage drop, has been improved in the DPC-\updelta $5\times2$ method by rotating the orientation of coordinates by angle \updelta, i.e., the angle between grid voltage vector and set converter voltage vector. The other proposed development involves further improvement of the DPC-\updelta $5\times2$, into which a new optimal division of the current error plane is introduced. The new optimal voltage vector assignment allows us to choose a converter voltage vector using the modified error current vector. The proposed look-up table methods have been tested and compared applying the following criteria: current error, total harmonic distortion (THD) of input current, average transistor switching frequency, and response time on step changes of set current. The experimental results validate the proposed control schemes and show good system performances that were verified according to above criteria. [ABSTRACT FROM AUTHOR]

This paper describes the development of a 50-kV 100-kW cathode power supply (CPS) for the operation of a 30-kW 95-GHz gyrotron. For stable operation of the gyrotron, the requirements of CPS include low output voltage ripple and low arc energy less than 1% and 10 J, respectively. Depending on required specifications, a three-phase series-parallel resonant converter (SPRC) is proposed for designing CPS. In addition to high-efficiency performance of SPRC, three-phase operation provides the reduction of the output voltage ripple through a minimized output filter component that is closely related to the arc energy. For allowing symmetrical resonant current from three-phase resonant inverter, the high-voltage transformers are configured as star connection with floated neutral node. This facilitates balanced voltage on each secondary winding. In addition, distinctive design of the high-voltage rectifier is introduced, taking into consideration the effective series stacking of diodes by means of the parallel resonant capacitor. In particular, the implementation of the high-voltage part including transformer and rectifier is presented in detail. For providing high power density and high reliability, effective methods for winding the high-voltage transformer and stacking rectifier diodes are discussed. Finally, the developed CPS achieves 95.5% of maximum efficiency, 0.92 of maximum power factor, 500 W/liter of power density, 0.6% of output voltage ripple, with 8.3-J arc energy. [ABSTRACT FROM AUTHOR]

A new single-phase \uppi-\texttype 5-level inverter using 3-terminal switch-network (3TSN) is proposed in this paper. The topology is considered as a variant of T-type 3-level structure or dual-buck inverter with coupled inductors. This new inverter is suitable for multilevel power inversion with low dc-bus voltage. The merit of the proposed topology is to apply only four active power switches to achieve 5-level operation. Other benefits include double frequency operation of output inductor and equal division of the current that flows through power switches and filter inductor. Hence, it leads to high efficiency and low harmonics. These characteristics allow improvement of losses distribution and volume reduction of output filter inductor. The operation scenario with sinusoidal pulsewidth modulation (SPWM) is described in details. Meanwhile, the magnetic analysis and design are studied and discussed. Finally, a prototype is built to verify the theoretical analysis and demonstrate the benefits of the proposed topology. [ABSTRACT FROM AUTHOR]

This paper presents a small-signal analysis of an islanded microgrid composed of two or more voltage-source inverters connected in parallel. The primary control of each inverter is integrated through an internal current and voltage loops using proportional resonant compensators, a virtual impedance, and an external power controller based on frequency and voltage droops. The frequency restoration function is implemented at the secondary control level, which executes a consensus algorithm that consists of a load-frequency control and a single time delay communication network. The consensus network consists of a time-invariant directed graph and the output power of each inverter is the information shared among the units, which is affected by the time delay. The proposed small-signal model is validated through simulation results and experimental results. A root locus analysis is presented that shows the behavior of the system considering control parameters and time delay variation. [ABSTRACT FROM PUBLISHER]

This paper investigates the distributed finite-time restoration of inverter voltage and frequency terms in an islanded ac microgrid. Formulating networked inverters of ac microgrids as a cooperative multiagent system, the voltage and frequency restoration can be cast as synchronization problems, while the active power sharing can be viewed as a consensus problem. One popular distributed control approach is the neighbor-based linear consensus protocol, where the consensus at the frequency and voltage set points is achieved over an infinite-time horizon with an exponential convergence. To achieve accelerated convergence and better disturbance rejection properties, a distributed finite-time control protocol, based on feedback linearization approach, is proposed for voltage restoration, which synchronizes the voltage term at each inverter to the reference value in finite time period. Then, a finite-time control protocol for both frequency restoration and active power sharing problems is proposed to synchronize the microgrid frequency to the nominal value, and share the active power among inverters based on their ratings in a finite time. Rigorous Lyapunov proofs are provided to establish the upper bounds on the convergence times. Numerical simulation studies verify the effectiveness of the proposed control protocols. [ABSTRACT FROM PUBLISHER]

This paper describes an alternative to connect power converters to a direct-current network with an inductor circuit. The circuit allows the connection of converters through a coil and avoids short-circuit currents with different instantaneous values of voltage output. A description of the calculation and the choice of components together with a real implemented example in a dc network within Smart City project (Endesa Utility) is presented. [ABSTRACT FROM PUBLISHER]

This paper presents a new control scheme for the enhancement of the low-voltage ride-through (LVRT) capability of doubly fed induction generators. The LVRT capability is provided by extending the range of operation of the controlled system to include typical postfault conditions. Controllers are designed simultaneously for both the rotor- and grid-side converters using a linear quadratic output-feedback decentralized control strategy. The nonlinear terms in the power system model are represented in this paper by an uncertain term derived from the Cauchy remainder of the Taylor series expansion. A genetic algorithm is used to calculate the bound on the uncertainty. The robust controller resulting from this design provides acceptable performances to enhance voltage and transient stability margins and thereby to limit the oscillations, the peak value of the rotor current, and the dc-link voltage fluctuations. The performance of the designed controller is demonstrated under different operating conditions by large-disturbance simulations on a test system. [ABSTRACT FROM PUBLISHER]

Many different topologies based on the multilevel converter approach have been presented in the last decades. In order to obtain improved output waveforms, several modulation techniques have been developed for such converters. Some of those modulation schemes can be directly applied to almost any multilevel converter, while others require significant adaptation in order to be implemented in certain specific converters. This paper presents the implementation of a phase-disposition level-shifted pulsewidth modulation to the recently introduced hybrid multicell converter (HMC). The HMC uses a flying capacitor module on each cell to generate a positive variable dc-link voltage. The variable dc link is inverted at fundamental switching frequency by an H-bridge to generate the cell output voltage. It is desirable to use PD-PWM for its well-known high-performance waveforms. In this paper, a state-machine decoder is developed to balance the floating capacitor voltages and to equalize the supplied power for the series-connected cells of the HMC when using a PD-PWM pattern. Experimental results obtained from a 10-kW prototype are presented, confirming the good-quality waveforms of the HMC modulated with PD-PWM and the adequate balance of all floating capacitors. [ABSTRACT FROM PUBLISHER]

In this paper, an immune algorithm (IA) is developed for optimization of the harmonic performance of a three-phase inverter under the space-vector pulsewidth-modulation (SVPWM) control strategy. The presented algorithm employs the immune approach as the search method for finding the best optimal control vectors and action time of the three-phase inverter. As a result, the optimal control vectors and action time are calculated to minimize the objective function of the weighted total harmonic distortion of the output voltage waveforms. In addition, an experimental platform based on DSP and field-programmable gate array is built. This paper provides a detailed performance analysis of the method with comparison to the conventional SVPWM. The simulation and experimental results verify the superiority of the best control sequences generated by IA compared with the existing conventional control strategies. [ABSTRACT FROM PUBLISHER]

A new pulse width modulation (PWM) strategy which is an alternative approach of the discontinuous PWM (DPWM) for a three-level neutral-point-clamped (NPC) inverter is developed and presented in this paper. The proposed PWM scheme not only takes advantage of the special properties available in NPC inverters, but also reduces the switching loss of the inverter along with an inherent neutral point (NP) voltage control. Based on a circuit-level decoupling concept, the NPC inverter can be decoupled into two three-level Buck converters in every defined operating section, and thereby the controller design can be simplified. The salient features of the proposed scheme, as compared with the existing carrier-based DPWM strategies, are: 1) its reduced computational processing time, 2) its capability to balance the dc-link voltage without any additional control, and 3) its reduced complexity, e.g., only one carrier wave needed for pulse width modulating. Same as a space-vector modulation, the maximum modulation index, 1.1547, can be attainable by the proposed scheme. Moreover, compared to conventional continuous sinusoidal PWM, using this technique proposed here, the switching losses of the devices can be reduced by one third. In order to explain the operation of this topology properly, the decoupling principle including the driving signal synthesis and the NP potential variation are analyzed in detail in this paper. Finally, the viability and performance of the proposed modulation scheme are shown through simulation and experimental results in a laboratory prototype. [ABSTRACT FROM PUBLISHER]

A new approach for modulation of an 11-level cascade multilevel inverter using selective harmonic elimination is presented in this paper. The dc sources feeding the multilevel inverter are considered to be varying in time, and the switching angles are adapted to the dc source variation. This method uses genetic algorithms to obtain switching angles offline for different dc source values. Then, artificial neural networks are used to determine the switching angles that correspond to the real-time values of the dc sources for each phase. This implies that each one of the dc sources of this topology can have different values at any time, but the output fundamental voltage will stay constant and the harmonic content will still meet the specifications. The modulating switching angles are updated at each cycle of the output fundamental voltage. This paper gives details on the method in addition to simulation and experimental results. [ABSTRACT FROM PUBLISHER]