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Collaborative control of power converters operating in microgrids with unbalanced single-phase loads is difficult to achieve, considering that the voltages and currents have positive-, negative-, and zero-sequence components. In this paper, a new control scheme for collaborative control of four-leg microgrids is proposed. The main advantage of the proposed methodology is simplicity, because the sharing of the powers produced by the positive-, negative-, and zero-sequence voltage and currents is simple to achieve using the easy to implement and well-known droop control algorithms, i.e., as those based on $P$ – $\omega$ and $Q$ – $v$ droop control. The proposed droop algorithms do not require high bandwidth communication channels and the application of virtual impedances, whose design usually demands extensive simulation work, is not required. Three secondary control systems are also analyzed, discussed, and implemented in this paper to regulate the frequency, voltage, and phase at the point of common coupling (PCC), to achieve a balanced 50-Hz three-phase voltage supply in the PCC during steady-state operation. For these secondary control systems, single-phase phase-locked loop based on quadrature signal generators are implemented. Small signal modeling and design are discussed in this paper. A microgrid prototype of $\approx$ 5 kW, implemented using two power converters of 3 kW (each), is used to experimentally validate the proposed algorithms. [ABSTRACT FROM AUTHOR]

Operating in the high-speed range is necessary for high-performance permanent-magnet synchronous motor (PMSM) drives. However, due to the back electromotive force effect, the PMSM is approaching the voltage limit at field decreasing scope. This paper presents a new flux-weakening scheme along with an improved vector control strategy to alleviate the influence of this problem. Control parameters of the anti-windup proportional and integral (AWPI) controller are optimized off-line in relying on an adaptive velocity particle swarm optimization (AVPSO) algorithm. The AVPSO algorithm considers the summation of AWPI measurement error which is the objective function of the optimization problem without knowing the transfer function of the plant. Hence, the tuned flux-weakening controller with a filter is used to set the flux level without saturating the current controllers. Meanwhile, the other controllers of inner and outer loops award a great dynamic and steady-state performance for the PMSM. In the proposed scheme, the flux-weakening control is not dependent on machine parameters that adapts the flux level automatically and provide a fast transition between the constant torque region and the field-weakening region. Effectiveness and advantages of the proposed scheme are presented in this paper through both simulation and experimental results. [ABSTRACT FROM AUTHOR]

In this paper, to improve the robustness and realize the precision positioning as well as speed control of the servo drive system, an integrated sliding-mode control (ISMC) optimized by differential evolution (DE-ISMC) algorithm is proposed. ISMC guarantees that a motor can reach at given position with given speed, and given speed is set first. ISMC, which is combined with speed regulator and position regulator, is different from the conventional sliding-mode control (SMC) replacing speed regulator. ISMC can guarantee that motor speed is controlled under position control mode, which is a novelty and an advantage of ISMC in this paper. To achieve good control performance of ISMC, parameters of it should be chosen exactly, so DE algorithm is selected to optimize them. The most significant influence factor of DE algorithm is the optimization iteration. Once parameters of ISMC are optimized under convergent iteration, servo system performance reaches given indices in the shortest time. Experimental results indicate that robustness of the servo system is improved; correctness and effectiveness of DE-ISMC are verified. [ABSTRACT FROM AUTHOR]

This paper presents an improved direct torque control (DTC) method for an asymmetrical six-phase induction motor using a two-level six-phase inverter. As is well known, a simple extension of three-phase DTC technique to an asymmetrical six-phase motor, using large vectors only, introduces significant current harmonics of the order 6 n±1 (n = 1, 3, 5,…), which are mapped into the nonflux/torque producing (xy) plane. These harmonics cause only losses in the motor winding as they do not take part in torque production. Hence, a number of different improved DTC techniques have been developed in the past for multiphase motor drives. The paper takes one such DTC method as the starting point and improves it further by using the concept of virtual voltage vectors. Developed vector selection algorithm, based on two virtual voltage vectors, requires the information on position of the flux in the auxiliary (xy) subspace and provides stator current quality commensurate with the currently available best DTC algorithm for six-phase drives. However, use of two virtual voltage vectors enables a substantial reduction of the torque ripple, which is achieved by means of a five-level torque comparator. Extensive experimentation is performed and it is shown that the reduction of the current harmonics is in essence almost the same as in another recently developed DTC scheme, based on the use of a single virtual voltage vector. However, the achieved torque ripple reduction, which is verified experimentally, makes the scheme superior when compared to the existing approaches. At the same time, developed scheme retains qualities of conventional DTC schemes, such as simple structure and fast response. Its additional beneficial feature is the easiness of implementation. [ABSTRACT FROM PUBLISHER]

Accurate and efficient simulation of power electronic systems is challenging due to their hybrid nature consisting of continuous states and discrete events. In this paper, a comprehensive discrete state event-driven (DSED) framework is proposed for offline simulation of such hybrid dynamic systems. Two key elements of the proposed comprehensive DSED simulation framework that contribute to the significant improvements in numerical accuracy and computational efficiency are a flexible adaptive algorithm for flexible integration of continuous states and an event-driven mechanism for efficient locating of discrete events. The proposed DSED simulation framework is applied to a 50-kVA solid-state transformer and a multileg full-bridge Class-D amplifier to verify its accuracy and efficiency by comparisons with experimental waveforms and simulated waveforms of Simulink and PLECS. Up to 100-fold and 10-fold improvements in simulation speed are achieved at the same level of numerical accuracy compared with Simulink and PLECS, respectively. [ABSTRACT FROM AUTHOR]

One important characteristic of modular multilevel converter (MMC) is the existence of circulating current, which consists of a dc component and a series of undesirable even-order (predominantly second-order) harmonics. However, only the dc part of the circulating current is required for power balance, the ac harmonics are unwanted. These undesirable harmonics should be suppressed to reduce device stress and power losses. Most state-of-the-art circulating current suppression techniques employ separate controllers to generate the arm reference voltage for circulating current suppression. This paper proposes an alternate approach, eliminating the need of any additional control loop. Generation of undesirable circulating current is prevented inherently in the modulation stage. Reduced switching frequency sorting algorithm based modulation framework is employed to ensure reduced switching loss. Suitability of the proposed method is validated by experiments performed on a three-phase laboratory prototype of MMC. Steady state and transient operation of the MMC in grid-connected condition is studied. [ABSTRACT FROM AUTHOR]

This paper presents a transistor open-circuit fault diagnosis method based on an average model and post-fault reconfiguration algorithms for a grid-tied single-phase inverter that transfers power bi-directionally. The transistor open-circuit fault occurrence is detected by comparing the average bridge arm pole-to-pole voltage deviation and threshold first. Then, the exact faulty transistor is identified by developed algorithms based on post-fault reconfiguration of control (PFRC) and of utilizing redundant leg (PFRUR). These two fault identification algorithms are suitable for different situations. Compared with the PFRUR, the PFRC can identify the faulty transistor without the help of redundant leg, but the identification time is longer. For inverters equipped with redundant leg already, the PFRUR can achieve faster identification speed so that inverters in reliability-oriented applications can return to normal operation after fault with short interruption. With average model, this method only requires existing signals sampled for control, thus it can be embedded in system easily without adding extra sensors and diagnosis circuits. The sampling frequency can be as low as switching frequency. Furthermore, this method is suitable for both inverters with L or LCL filters. Finally, experiments are carried out on a 550-W/10-kHz grid-tied single-phase inverter to verify the effectiveness. [ABSTRACT FROM AUTHOR]

This paper further develops the concept of very large size flash-memory-based pulsewidth-modulated (PWM) algorithms for three-phase inverters. Such algorithms differ from the conventional counter-based implementation, and they follow a preprogrammed optimal PWM pattern that is read from a very large size memory with magnitude and phase as coordinates. Any sequence of states is thus possible within a PWM sampling interval. A novel digital structure has been built around the newly released flash memory integrated circuits. The paper demonstrates the feasibility of operation at any PWM sampling frequency up to 20 kHz when using gigabit-size flash memory integrated circuits along any low-cost microcontroller with an SPI peripheral. To empower the concept, a multioptimal PWM has been proposed and implemented on a 2-Gbit memory table. The harmonics of the phase currents are reduced by more than 40% while a constant PWM sampling frequency is maintained in order to comply with the conventional vector control methods for grid or motor applications. [ABSTRACT FROM AUTHOR]

Rotor position estimated with high-frequency (HF) voltage injection methods can be distorted by voltage errors due to inverter nonlinearities, motor resistance, and rotational voltage drops, etc. This paper proposes an improved HF square-wave voltage injection algorithm, which is robust to voltage errors without any compensations meanwhile has less fluctuation in the position estimation error. The average position estimation error is investigated based on the analysis of phase harmonic inductances, and deduced in the form of the phase shift of the second-order harmonic inductances to derive its relationship with the magnetic field distortion. Position estimation errors caused by higher order harmonic inductances and voltage harmonics generated by the SVPWM are also discussed. Both simulations and experiments are carried out based on a commercial PMSM to verify the superiority of the proposed method and the investigations in this paper. [ABSTRACT FROM AUTHOR]

A robust field-weakening method for direct-torque-controlled (DTC) synchronous reluctance motors is presented in this paper. The proposed algorithm achieves smooth transition between the constant torque and field-weakening regions. Maximum torque per ampere is utilized below base speed, while both the current and voltage limits of the drive system are satisfied in the field-weakening region. The proposed method is robust to the variations in the machine dq -axis inductances. This ensures the system stability during field-weakening operation, especially along the maximum torque per flux trajectory. The proposed algorithm is incorporated into the duty ratio regulation-based DTC to achieve high-performance torque and flux control in the field-weakening region. Experimental results included in this paper confirm the veracity of the proposed method. [ABSTRACT FROM AUTHOR]

At present, virtual flux voltage oriented control strategy is one of the widely used control strategies without grid voltage sensor. To solve the dc bias resulting from voltage vector integration in vector calculation of virtual flux and further avoid the steady-state error, a virtual flux observer with negative feedback resonant filter is presented in this paper based on virtual flux principle and a delay compensation algorithm is also proposed to solve the delay of virtual flux. In addition, the control system diagram of the pulsewidth modulated rectifier without grid voltage sensor is brought forth. Then, simulation system and experimental platform are both established to simulate and test the rectifier. Eventually, the correctness and feasibility of the proposed algorithm are verified through the analysis of simulation and experimental results. [ABSTRACT FROM AUTHOR]

Maglev trains attracted to suspend above tracks without mechanical contact is a promising type of track transportation. Suspension choppers with levitation magnets resembling wheels of traditional trains or tires of automobiles are responsible for levitation and support of maglev trains. With successful launch of the first Chinese medium/low-speed maglev line, lifetime prediction of power devices in suspension choppers becomes a crucial topic. This paper analyzes the lifetimes under two typical daily mission profiles of suspension choppers. Using look-up tables of IGBT/diode losses, a widely usedRCthermal network is established. A test rig is built to measure the IGBT/diode transient case temperature and extract the thermal impedance of a heat sink. Therefore, the junction temperatures under these typical mission profiles are estimated. Using comprehensive equations to describe solder behavior, the stress–strain curves under different temperature profiles can be plotted by means of Clech's algorithm. Finally, an energy-based approach is utilized for lifetime evaluation. The daily mission profile where maglev trains operate without landing during operation hours is expected to survive much longer. [ABSTRACT FROM AUTHOR]

A flux-weakening control algorithm with an improved stator flux linkage command's adjustment part of interior permanent magnet synchronous motors is proposed in this paper. The current commands are derived from lookup tables, which consider variation of motor parameters. The merits of this algorithm are the maximization of torque and high torque stability. Experimental results are demonstrated to verify the effectiveness of the proposed algorithm. [ABSTRACT FROM AUTHOR]

In this paper, we propose model predictive control methods to reduce the common-mode voltage of three-phase voltage source inverters (VSIs). In the reduced common-mode voltage-model predictive control (RCMV-MPC) methods proposed in this paper, only nonzero voltage vectors are utilized to reduce the common-mode voltage as well as to control the load currents. In addition, two nonzero voltage vectors are selected from the cost function at every sampling period, instead of using only one optimal vector during one sampling period. The two selected nonzero vectors are distributed in one sampling period in such a way as to minimize the error between the measured load current and the reference. Without utilizing the zero vectors, the common-mode voltage controlled by the proposed RCMV-MPC algorithms can be restricted within ±Vdc/6. Furthermore, application of the two nonzero vectors with optimal time sharing between them can yield satisfactory load current ripple performance without using the zero vectors. Thus, the proposed RCMV-MPC methods can reduce the common-mode voltage as well as control the load currents with fast transient response and satisfactory load current ripple performance compared with the conventional model predictive control method. Simulation and experimental results are included to verify the effectiveness of the proposed RCMV-MPC methods. [ABSTRACT FROM AUTHOR]

In this paper, an immune algorithm (IA)-based dead-time elimination PWM control strategy is proposed. For existing dead-time elimination applications, one of the major problems is the dead-time control around the zero-current-crossing points. To deal with this problem, this paper proposes a different PWM control method which first restricts the control sequence to a specified level around the zero-crossing zone. Also, the proposed method can improve the current waveform quality by using the IA approach and three-level control strategy. Compared with conventional dead-time elimination methods, this technique has the features of simple hardware requirement and adaptive control. Moreover, this control strategy effectively eliminates the effect of dead-time, while at the same time significantly reducing the total harmonic distortion of output current and improving the amplitude of output RMS value in different modulation indexes and loads conditions. To verify the analysis, an experimental platform based on DSP and field-programmable gate array is built. The simulation and experimental results are given to demonstrate the effectiveness and feasibility of this new method. [ABSTRACT FROM AUTHOR]

This paper presents a simple controller integrating a new reactive current reference algorithm for enhancing the transient performance of static synchronous compensator (STATCOM). A multilevel cascaded inverter with separated dc capacitors which is driven by carrier-based pulse width modulation is used to implement the STATCOM. The voltage across each dc-link capacitor is regulated by the rotated switching swapping scheme. In this paper, the STATCOM is controlled to provide both reactive power (VAR) compensation and grid power factor correction at the point of common coupling with a dynamically varying reactive load system. The proposed algorithm enhances the transient performance of the closed-loop system with only proportional controller and minimizes the STATCOM reactive current ripples. STATCOM based on a five-level cascaded inverter is presented in this paper and the performance of the proposed controller is investigated through various simulation studies using MATLAB/Simulink software for both steady state and transient conditions. A laboratory prototype is also developed to verify the simulation results where a good match between simulation and experimental results is achieved. [ABSTRACT FROM AUTHOR]

Power electronics are increasingly important in new generation vehicles as critical safety mechanical subsystems are being replaced with more electronic components. Hence, it is vital that the health of these power electronic components is monitored for safety and reliability on a platform. The aim of this paper is to develop a prognostic approach for predicting the remaining useful life of power electronic components. The developed algorithms must also be embeddable and computationally efficient to support on-board real-time decision making. Current state-of-the-art prognostic algorithms, notably those based on Markov models, are computationally intensive and not applicable to real-time embedded applications. In this paper, an isolated-gate bipolar transistor (IGBT) is used as a case study for prognostic development. The proposed approach is developed by analyzing failure mechanisms and statistics of IGBT degradation data obtained from an accelerated aging experiment. The approach explores various probability distributions for modeling discrete degradation profiles of the IGBT component. This allows the stochastic degradation model to be efficiently simulated, in this particular example ~1000 times more efficiently than Markov approaches. [ABSTRACT FROM AUTHOR]

This paper presents a novel on-line inertia identification method with a load torque observer to optimize the speed loop PID parameters of a servo system. The proposed inertia identification algorithm in this paper adopts the fixed-order recursive empirical frequency-domain optimal parameter estimation to improve the speed loop performance. A load torque observer is employed in order to obtain a more precise value of inertia. Then, the method of speed loop PI parameters optimization with the identified inertia and load torque is deduced in frequency domain. Compared with the recursive least square algorithm, the effectiveness of the proposed method is demonstrated by the simulation and experimental results. [ABSTRACT FROM AUTHOR]

This paper proposes a single power-conversion ac-dc converter with high power factor and high efficiency. The proposed converter is derived by integrating a full-bridge diode rectifier and a series-resonant active-clamp dc-dc converter. To obtain a high power factor without a power factor correction circuit, this paper proposes a novel control algorithm. The proposed converter provides single power-conversion by using the novel control algorithm for both power factor correction and output control. Also, the active-clamp circuit clamps the surge voltage of switches and recycles the energy stored in the leakage inductance of the transformer. Moreover, it provides zero-voltage turn-on switching of the switches. Also, a series-resonant circuit of the output-voltage doubler removes the reverse-recovery problem of the output diodes. The proposed converter provides maximum power factor 0.995 and maximum efficiency of 95.1% at the full load. The operation principle of the converter is analyzed and verified. Experimental results for a 400 W ac-dc converter at a constant switching frequency of 50 kHz are obtained to show the performance of the proposed converter. [ABSTRACT FROM AUTHOR]

This paper applies the adaptive gradient descent method to the second-order generalized integrator (SOGI) filter in order to find an online estimation algorithm for the grid frequency, which leads to the proposal of three possible estimators. One of them is identical to the frequency-locked loop algorithm reported in the literature, which proves that it should be understood as a gradient descent estimation algorithm and not as a “frequency locked loop.” The proposed gradient descent estimators are simple and suitable to be implemented into a digital processor with small computational burden. However, due to the SOGI characteristics, the estimators show to be especially sensitive to subharmonic and dc-offset voltage distortion. These problems are removed adopting a cascaded double SOGI approach, which strongly increases the rejection capability to harmonics and enhances the response to voltage sags. Simulation and experimental results are provided to validate the proposed contribution. [ABSTRACT FROM PUBLISHER]

A new analytical electro-thermal model of a multichip power module is described in this paper. The proposed model is intended to be used during in-service conditions inside a motor drive for remaining useful lifetime calculation, in combination with a thermal cycle counting algorithm. The model allows fast calculations of the chips temperature, based on simple analytical expressions of averaged total power losses, and mathematical formulations of thermal impedances using the Foster network representation. The proposed model is computationally efficient, since it does not require the switching instants information, but only the used pulse width modulation (PWM) technique, which is advantageous for embedding in terms of reducing computation resources and time. Finally, a comparison between the proposed model results and experimental measurements is conducted at different operating points of the motor drive, and under two different switching modes; the third harmonic injection PWM for output frequencies below 20 Hz and the discontinuous PWM for frequencies above 20 Hz. The results obtained are very satisfactory in terms of mean temperature levels and temperature swings for frequencies from 1 to 50 Hz. [ABSTRACT FROM AUTHOR]

This paper presents a novel loss minimization technique for induction motor driven elevator systems (IMDES) to determine an energy optimum velocity pattern. The objective function consists of a differential equation relating total power losses in the induction motor to its rotor speed. The constraints are provided in terms of velocity and acceleration governed by passenger comfort. Since the velocity and acceleration are state variables, Pontryagin's minimum principle is used to determine the most optimum trajectory by forming an appropriate Hamiltonian function. Boundary conditions are specified and used to obtain the coefficients of the rotor speed equation. As the velocity is optimized, the total travel time is not fixed and treated as a variable. A fixed-point iterative procedure is used to estimate the travel time. Additional loss minimization is incorporated by optimizing the machine flux for the constrained portion of the velocity pattern. An algorithm for implementing the optimization scheme is explained in detail. The theoretical claims are supported with analytical and experimental results. Proposed technique is developed for IMDES, but it can be easily adapted to other drive applications as well. [ABSTRACT FROM AUTHOR]

Photovoltaic power plants (PVPPs) typically operate by tracking the maximum power point (MPP) in order to maximize the conversion efficiency. However, with the continuous increase of installed grid-connected PVPPs, power system operators have been experiencing new challenges, such as overloading, overvoltages, and operation during grid-voltage disturbances. Consequently, constant power generation (CPG) is imposed by grid codes. An algorithm for the calculation of the photovoltaic panel voltage reference, which generates a constant power from the PVPP, is introduced in this paper. The key novelty of the proposed algorithm is its applicability for both single- and two-stage PVPPs and flexibility to move the operation point to the right or left side of the MPP. Furthermore, the execution frequency of the algorithm and voltage increments between consecutive operating points are modified based on a hysteresis band controller in order to obtain fast dynamic response under transients and low-power oscillation during steady-state operation. The performance of the proposed algorithm for both single- and two-stage PVPPs is examined on a 50-kVA simulation setup of these topologies. Moreover, experimental results on a 1-kVA PV system validate the effectiveness of the proposed algorithm under various operating conditions, demonstrating functionalities of the proposed CPG algorithm. [ABSTRACT FROM AUTHOR]

The race to increase the efficiency and reduce the power losses in transmission systems has resulted in the substantial growth of high-voltage direct current (HVDC) transmission systems. Moreover, the interconnection of these transmission systems significantly increases their reliability. However, the control of these meshed grids is a key problem that usually is managed through the control of the VSCs in those grids, but the control of the VSC can be complemented with a reconfiguration algorithm. This paper proposes the use of the particle swarm optimization algorithm, in order to reconfigure meshed HVDC transmission systems and reduce losses. The proposed algorithm has been tested in the CIGRE benchmark grid, which comprises of several offshore wind farms that generate energy sent to the grid through several HVDC transmission lines. The results show that as the energy generation changes due to wind changes, the grid topology must be reconfigured in order to achieve the maximum efficiency. Doing this reconfiguration, power savings around 18–19% could be achieved. [ABSTRACT FROM PUBLISHER]

Modular power converters are expected to play a major role in medium- and high-voltage/power applications. Normally, each module processes the same amount of power; however, this does not take into consideration that different modules can have a different remaining useful lifetime. This paper proposes the concept of power routing for cascaded H-bridge (CHB) converters, with the purpose of delaying the failure of the system. A third-harmonic injection into the duty cycles allows extending the imbalance capability of the structure, keeping the CHB operational even if some power paths are completely unloaded. Analytic investigation in conjunction with simulation and experimental measurements demonstrate the power routing by means of the proposed method. [ABSTRACT FROM PUBLISHER]

To improve the control performance for grid-tied power converters, the fundamental frequency and harmonics of the grid voltage should be quickly and accurately estimated even under distorted voltage condition. This paper introduces a straightforward discrete adaptive filter to observe fundamental and harmonic sequence components of the grid voltage. The proposed filter possesses a simple and straightforward implementation. Based on the newly developed filter, frequency error transmission was analyzed when the frequency of the input voltage was unequal to the center frequency of the filter. Consequently, a frequency estimation loop was designed to adapt to the frequency variation for the filter. Compared to previous algorithms, the proposed algorithm has a better dynamic performance rating for frequency estimation, robust stability, and a simpler implementation. The effectiveness of the algorithm is verified by simulations and laboratory experiments. [ABSTRACT FROM PUBLISHER]

Predictive torque control (PTC) is based on the prediction of motor torque and stator flux for all possible voltage vectors of power converter. These predictions are derived from a mathematical model of the motor that depends on the motor parameters. But, these parameters may not match with their actual values. These parametric uncertainties lead to inaccurate predictions of torque and stator flux and affect the performance of the predictive algorithm. This paper presents a modified PTC for a permanent magnet synchronous motor to reduce the torque ripple at the presence of parametric uncertainty by improving the prediction accurateness. Simulation and experimental results are provided to show the effect of the proposed method. [ABSTRACT FROM PUBLISHER]

In this paper, a comprehensive and practical method of implementing speed range extended maximum torque per ampere (MTPA) control for permanent magnet synchronous machine (PMSM) is presented. The inverter-based method of measuring PMSM parameters, including winding resistance and d- and q-axis flux linkages, is introduced. The nonlinearities of the inverter, including voltage amplitude error and voltage phase shift, are identified and compensated, which improves the accuracy of the characterized flux linkage. The extended MTPA current references are obtained by employing nonlinear optimization algorithm, and the results are verified analytically on the current plane. MTPA control is applied on the PMSM experimentally in the entire speed range. Current transition, torque control accuracy, and efficiency performance are measured in the entire torque–speed range. [ABSTRACT FROM PUBLISHER]

To improve the performance of sensorless induction motor (IM) drives, an adaptive speed and flux estimation method based on the multiple-model extended Kalman filter (EKF) with Markov chain for IMs is proposed in this paper. In this algorithm, the multiple model EKF for speed and flux estimation is established, and the transition of the models obeys the Markov chain and the estimation value is obtained by mixing the outputs of different models in different weightings, and the calculation of the weighting is researched. Simultaneously, the transition probability can be continuously self-tuned by the residual sequence, the prior information is modified by the posterior information, and the more accurate transition among the models is obtained. Therefore, the proposed method improves the model adaptability to the actual systems and the environmental variations, and reduces the speed estimation error. The correctness and the effectiveness of the proposed method are verified by the simulation and experimental results. [ABSTRACT FROM PUBLISHER]

This paper presents an effective closed-loop control approach for a stepper motor. The proposed approach consists of motor parameter identification, closed-loop current control, closed-loop position control, and damping control. The presented implementation achieves accurate position, high torque, and smooth speed. By using an improved proportional-integral current control algorithm, this approach not only guarantees the current tracking performance but also increases the bandwidth during the speed response. The advanced position controller achieves both high torque and the synchronous condition of the motor after a loss of synchronism occurs. In addition, this method applies an effective speed damping method to remove resonance at low speed and reduce vibration at high speed. All the proposed algorithms were implemented on an industrial test-bench. The experimental results demonstrate the validity of the proposed approach for practical applications. [ABSTRACT FROM PUBLISHER]

This paper presents a novel system for producing the optimum power output from photovoltaic (PV) arrays using dynamic cell reconfiguration. The proposed approach is the first in the literature that creates strings using individual substrings that have been characterized and categorized ensuring maximum power extraction for a given irradiance profile. This optimized and decentralized PV architecture can produce significantly more power than a static equivalent (by an average of 22.6%) and also outperforms the sophisticated alternative known as an irradiance equalized dynamic photovoltaic array (IEq-DPVA) by an average of 13.7% for the relevant tests carried out. This paper identifies the hardware requirements to produce such a system and it describes an algorithm that performs the optimized-string reconfiguration strategy. Finally, a simulator programmed in MATLAB is used to compare the performance of the optimized-string DPVA against an IEq-DPVA in a series of flexibility tests. [ABSTRACT FROM AUTHOR]

Photovoltaic (PV) source simulators serve as a convenient tool for the dynamic evaluation of solar power conditioning systems and maximum power point tracking algorithms. High efficiency and fast transient response time are essential features of any PV source simulator. This paper proposes a new type of PV source simulator that incorporates the advantages of both analog and digital-based simulators. The proposed system includes a three-phase ac–dc dual boost rectifier cascaded with a three-phase dc–dc interleaved buck converter. The selected power stage topology is highly reliable and efficient. Moreover, the multiphase converter helps improve system transient response though producing low output ripple which makes it adequate for PV source simulators. The simulator circuitry emulates precisely the static and the dynamic characteristics of actual PV generators under different load and environmental conditions. Additionally, the system allows the creation of the partial shading and bypass diodes effect on PV characteristics. The paper investigates the dynamic performance of a commercial solar power inverter using the proposed PV source simulator in steady-state and transient conditions. Closed-loop output impedance of the proposed PV source simulator has been measured and verified at different operating regions. The impedance profile-–magnitude and phase-–matches the output impedance of actual PV generators. Mathematical modeling and experimental validation of the proposed system is thoroughly presented based on a 2.0 kW hardware prototype. The proposed simulator efficiency, including the active-front-end rectifier and the converter stages, peaks at 96.7%. [ABSTRACT FROM AUTHOR]

This paper deals with the design methodology for cascaded multilevel converter (CMC)-based transmission-type STATCOM (T-STATCOM) and the development of a ±12 MVAR, 12 kV line-to-line wye-connected, 11-level CMC. Sizing of the CMC module, the number of H-bridges (HBs) in each phase of the CMC, ac voltage rating of the CMC, the number of paralleled CMC modules in the T-STATCOM system, the optimum value of series filter reactors, and the determination of busbar in the power grid to which the T-STATCOM system is going to be connected are also discussed in this paper in view of the IEEE Std. 519-1992, current status of high voltage (HV) insulated gate bipolar transistor (IGBT) technology, and the required reactive power variation range for the T-STATCOM application. In the field prototype of the CMC module, the ac voltages are approximated to sinusoidal waves by the selective harmonic elimination method (SHEM). The equalization of dc-link capacitor voltages is achieved according to the modified selective swapping (MSS) algorithm. In this study, an L-shaped laminated bus has been designed and the HV IGBT driver circuit has been modified for the optimum switching performance of HV IGBT modules in each HB. The laboratory and field performances of the CMC module and of the resulting T-STATCOM system are found to be satisfactory and quite consistent with the design objectives. [ABSTRACT FROM AUTHOR]

This paper investigates the problem of low-frequency voltage oscillations that appear at the neutral point (NP) of a three-level neutral-point-clamped (NPC) converter. Starting with a detailed analysis of their origin, the paper derives the minimum amplitude of these oscillations that can be achieved by nearest-vector (NV) modulation strategies. It then proves that the criterion of the direction of dc-link capacitor imbalance, which is commonly adopted by NV strategies for performing the task of capacitor balancing, poses a barrier in achieving this minimum. A new criterion is proposed instead, together with an algorithm that incorporates it into existing NV strategies. For the case of NPC inverters operating as motor drives, the resulting reduction in the amplitude of NP voltage oscillations ranges from 30% to 50%. The approach has the advantage of avoiding the significant increment in switching losses and output voltage harmonic distortion, caused by other methods. Simulations in MATLAB-Simulink are used to illustrate its operation and verify that it offers the claimed benefit. [ABSTRACT FROM AUTHOR]

A digitally controlled low-dropout voltage regulator (LDO) that can perform fast-transient and autotuned voltage is introduced in this paper. Because there are still several arguments regarding the digital implementation on the LDOs, pros and cons of the digital control are first discussed in this paper to illustrate its opportunity in the LDO applications. Following that, the architecture and configuration of the digital scheme are demonstrated. The working principles and design flows of the functional algorithms are also illustrated and then verified by the simulation before the circuit implementation. The proposed LDO was implemented by the 0.18-μm manufacturing process for the performance test. Experimental results show that the LDO's output voltage Vout can accurately perform the dynamic voltage scaling function at various Vout levels (1/2, 5/9, 2/3, and 5/6 of the input voltage V\bf DD) from a wide V\bf DD range (from 1.8 to 0.9 V). The transient time is within 2 μs and the voltage spikes are within 50 mV when a 1-μF output capacitor is used. Test of the autotuning algorithm shows that the proposed LDO is able to work at its optimal performance under various uncertain conditions. [ABSTRACT FROM AUTHOR]

In this paper, a novel voltage-based charge balance control algorithm is presented, which is suitable for both digital and analog implementations for buck converter to achieve near-optimal dynamic performance. First, this paper presents a new derivation of practical charge balance equations based on simplified differential equations. This deviation is applicable to both fast input voltage and load step transients. The final algorithm does not require complex calculations and accurate knowledge of the output filter LC parameter. Second, the proposed voltage-based charge balance controller does not require accurate current sensor or fast analog-to-digital converter. Instead, to detect the critical time instant when the inductor current equals the new load current, a practical extreme voltage detector is introduced to capture the output voltage peak/valley information. Third, this algorithm is simple to be implemented by either low-cost digital signal processing devices (such as microcontroller unit) or analog circuits. Both digital and analog experimental prototypes are built to verify the feasibility and advantages of the new method. [ABSTRACT FROM AUTHOR]

Synchronous-frame proportional-integral (PI) curr-ent control is the most popular solution in industrial permanent-magnet synchronous motor (PMSM) drive systems. However, due to the nonlinearities from large parameter uncertainties and complex operating conditions, it is challenging to select the parameters of the PI controller with satisfactory performance by trial-and-error. To this end, this paper presents an uncertainty-and-disturbance-estimator-based current control scheme for PMSM drives, which has a simple structure and is robust to machine parameter perturbations. Meanwhile, it is interesting that the controller parameters (proportional and integral gains) are simply expressed in the desired closed-loop bandwidth and the approximate lumped disturbance bandwidth. A simple dual-loop tuning algorithm is also proposed to select the appropriate controller parameters, and trial-and-error can be largely avoided. Finally, the efficacy of the proposed control method is fully supported by comparative experimental validation with the synchronous-frame PI control on a dSPACE DS1103-based PMSM drive prototype. [ABSTRACT FROM AUTHOR]

The recently-developed nested neutral-point clamped (NNPC) converter is a four-level converter for medium-voltage high-power applications. It has some merits such as operating over wide voltage ranges (2.4–7.2 kV) without switching devices in series and less diodes or capacitors when compared with classical four-level topologies. But it has severe voltage balancing problems under low output frequency conditions when conventional space vector modulation (SVM) or sinusoidal pulse width modulation (SPWM) is applied, which limits its wide applications. In order to solve this issue, a space virtual-vector modulation (SVVM) along with a voltage balance control (VBC) algorithm is proposed in this paper. It helps reduce the voltage ripples greatly and maintain them within an acceptable region under low output frequency conditions. Therefore, it guarantees even voltage stresses among switching devices and extends the NNPC converter's applications. Principles of the proposed SVVM and VBC algorithms are elaborated in detail, and the voltage balancing performance is investigated and compared with the cases where conventional SVM and SPWM with the same VBC are applied. The relationship curves between voltage ripples and flying capacitance, output power, and output frequency have been explored and compared for both conventional SVM and proposed SVVM. Simulation and experimental results are presented to verify the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

Typical algorithms of multidimensional space-vector pulsewidth modulation (SVPWM) divide (n –1) dimensional space into (n–1)/2 subplanes with decoupling matrix or symmetrical component approach. However, the determination of effective sectors and appropriate space voltage vectors takes a heavy computing burden. Taking the five-phase inverter as example, the relationship between the operation time of branch switches and the dwell times of active space vectors in the SVPWM method is analyzed in this paper. Then, the branch space voltage vector (BSVV) corresponding to the individual active branch voltage is defined and the synthesis of other active space voltage vectors using BSVVs is given. Furthermore, only the BSVVs are chosen as the base vectors to synthesize the reference voltage vector, and a novel SVPWM algorithm is present. The operation time of branch switch is deduced, and the equivalence of the normalized load-phase voltages and operation times of branch switches is emphasized and used to analyze the simulation results. The zero-sequence voltage vector is also included in the algorithm as a parameter and its effects on the dwell time of the BSVVs, the modulation index and the common-mode voltage are explicated. Finally, the extension to an n-phase system is discussed. The algorithm eliminates the selection of sectors and proper active space vectors, and can effectively control the dwell time of switches of multiphase inverter. Experimental results proved the feasibility and effectiveness of the algorithm. [ABSTRACT FROM AUTHOR]

One of the most important issues in the operation of a photovoltaic (PV) system is extracting maximum power from the PV array, especially in partial shading condition (PSC). Under PSC, P–V characteristic of PV arrays will have multiple peak points, only one of which is global maximum. Conventional maximum power point tracking (MPPT) methods are not able to extract maximum power in this condition. In this paper, a novel two-stage MPPT method is presented to overcome this drawback. In the first stage, a method is proposed to determine the occurrence of PSC, and in the second stage, using a new algorithm that is based on ramp change of the duty cycle and continuous sampling from the P–V characteristic of the array, global maximum power point (MPP) of array is reached. Perturb and observe algorithm is then re-activated to trace small changes of the new MPP. Open-loop operation of the proposed method makes its implementation cheap and simple. The method is robust in the face of changing environmental conditions and array characteristics, and has minimum negative impact on the connected power system. Simulations in Matlab/Simulink and experimental results validate the performance of the proposed methods. [ABSTRACT FROM AUTHOR]

This paper presents a generalized algorithm to eliminate spikes of common-mode voltages (CMV) caused by dead-time effect for common-mode voltage reduction pulse width modulation (CMVRPWM). The characteristics of the CMV spikes for the popular CMVRPWM strategies (AZSPWM1, NSPWM, CRLO-CMVRPWM, and SLO-CMVRPWM) are studied and compared by analyzing the extreme switch pulse patterns. The proposed CMV spikes elimination method directly adjusts the injected zero-sequence voltages instead of the durations of the adopted voltage space vectors to avoid the overlaps of the adjacent dead time periods. The CMV spikes can be eliminated regardless of the output voltages in the dead time periods; thus, the signs of phase currents are not needed to detect and overcome the problem caused by the resolution of the current sensors when the phase currents approach to zero. In addition, an effective method by online selecting low or high active pulses for the three legs is proposed to ensure that at most one leg switches between adjacent carrier periods. The proposed method is generalized and effective for all the CMVRPWM with symmetrical switch pulse patterns and no simultaneous switching problem. The simulation and experimental results validate the effectiveness. [ABSTRACT FROM AUTHOR]

An active power compensator (APC) based on single-phase back-to-back power converter is proposed in this paper to solve problems of power quality of electric railway power supply system. This system adopts a single-phase feeding connection, which is called cophase power supply scheme. In this scheme, APC connects the balance transformer between feeding phase for power supply and another phase for compensation. It has some characteristics, such as active power balancing, reactive power compensating, and harmonics filtering. In order to achieve these characteristics, the control scheme requires seven combination models. In this paper, a multifunctional control algorithm is proposed to realize every conceivable model. A cophase system with APC based on field programmable gate array (FPGA) and YNvd balance transformer is also designed and evaluated. The experimental results obtained from this prototype illustrate that the compensating ability is extremely high in steady-state and dynamic responses, and the power quality of a substation with distorted loads can be improved integrally. [ABSTRACT FROM PUBLISHER]

Power-electronic converters are intrinsically nonlinear. This paper proposes a Lyapunov approach to analysis and design of a class of nonlinear systems arising from power-electronic converters. The system has a bilinear term as the product of the state and the input—the duty cycle, which is subject to strict constraint (or saturation). The nonlinearities and the input saturation are considered in this paper by using piecewise-quadratic Lyapunov functions and by describing the system with a piecewise-linear differential inclusion. The problems considered include controller design for robust stability, and estimation of stability region and tracking domain. These analysis and design problems are converted into numerically efficient optimization algorithms involving linear-matrix inequalities (LMIs). A buck–boost dc–dc converter is used to demonstrate the proposed methods. The optimization results show that a simple state-feedback law can be constructed to achieve practically global stabilization and tracking, which is theoretically confirmed by the Lyapunov approach. An experimental buck–boost converter is constructed to verify the tracking of a square reference varying almost between the upper and the lower limit. [ABSTRACT FROM PUBLISHER]

This paper presents an online procedure for the automatic search of the maximum-torque-per-ampere operating region for a synchronous reluctance motor. The algorithm is based on a signal-injection method with a random-based perturbation pattern applied to a common direct-torque-controlled drive. Among motor parameters, only the stator resistance is required to perform the automatic procedure. Simulations and experimental results are presented in the paper, demonstrating the benefits of the proposed algorithm. The solution is easily extended to any ac drive. [ABSTRACT FROM PUBLISHER]

This paper introduces a novel phase-interleaving algorithm for asymmetric multiterminal power converters. Using a variable phase interleaving (VI), the first harmonic of the dc-link current and voltage can be thoroughly eliminated even under the situation where the input voltage and current of each converter differ. This means that the cost and size of the dc-link capacitor can be significantly reduced compared to when the standard (symmetric) interleaving algorithm is used. The VI-algorithm does not require any additional hardware and has only slight influence on the control loop of the converters when compared to the standard solution, which simplifies the integration of this algorithm. As a concrete application, the VI-algorithm is integrated into a photovoltaic inverter with three independent input converters. This paper also provides a method for determining the required dclink capacitance through a worst-case analysis. Furthermore, a performance comparison between edge-aligned fixed interleaving, center-aligned fixed interleaving and VI and is given. [ABSTRACT FROM AUTHOR]

Abstract-In this paper, an optimization-based control algorithm for the compensation of steady-state load under distorted supply voltages is presented. For balanced and sinusoidal supply voltages, load compensation using shunt active filter produces perfect harmonic cancellation (PHC) and unity power factor (UPF) source currents. However, when the supply voltages are distorted, compensation for PHC will not provide UPF, as the harmonics in the supply voltages are not utilized for delivering the average power. In the same way, to achieve UPF source currents, the compensated source currents should have the same harmonics, unbalance, shape, and be in phase with the respective supply voltages, thereby violating the perfect harmonic cancellation objective. Hence, there should be an optimal operation between these two important compensation characteristics. The optimization-based control algorithm presented in this paper gives the best power factor while satisfying the constraints such as total harmonic distortion limits and average power balance of source currents. It is also flexible to adopt different compensation characteristics based upon the supply voltage conditions. MATLAB and its optimization toolbox are used for simulation studies and solving the nonlinear optimization problem, respectively. The algorithm is validated by using a prototype of digital signal processor (TMS320F2812PGFA)-based shunt active power filter. Detailed experimental results are presented. [ABSTRACT FROM AUTHOR]

The instantaneous reactive power (IRP) p-q theory is one of the major theoretical tools for the development of algorithms for generating reference signals for control of switching compensators, commonly known as active harmonic or power filters. This paper presents results of study on how the supply voltage harmonics affect the reference signal that is generated using the IRP approach. According to this approach, the compensator should also compensate, apart from the IRP, the alternating component of the instantaneous active power of the load. The paper, however, demonstrates that in the presence of the supply voltage harmonics, an ideal, unity-power-factor load has an instantaneous active power with a nonzero alternating component. According to the IRP-based approach, it should be compensated, and this requires that a distorted current be injected into the distribution system. Thus, the conclusion of the IRP p-q theory that the instantaneous active power of ideally compensated loads should be constant is generally no true. The Currents' Physical Components (CPC) power theory is the main theoretical tool for the presented analysis. [ABSTRACT FROM AUTHOR]

This paper deals with a crucial aspect in the control of grid-connected power converters, i.e., the detection of the fundamental-frequency positive-sequence component of the utility voltage under unbalanced and distorted conditions. Specifically, it proposes a positive-sequence detector based on a new decoupled double synchronous reference frame phase-locked loop (DDSRF-PLL), which completely eliminates the detection errors of conventional synchronous reference frame PLL's (SRF-PLL). This is achieved by transforming both positive- and negative-sequence components of the utility voltage into the double SRF, from which a decoupling network is developed in order to cleanly extract and separate the positive- and negative-sequence components. The resultant DDSRF-PLL conducts then to a fast, precise, and robust positive-sequence voltage detection even under unbalanced and distorted grid conditions. The paper presents a detailed description and derivation of the proposed detection method, together with an extensive evaluation using simulation and experimental results from a digital signal processor-based laboratory prototype in order to verify and validate the excellent performance achieved by the DDSRF-PLL. [ABSTRACT FROM AUTHOR]

Cascaded multilevel inverters can be implemented through the series connection of single-phase modular power bridges. This paper presents details on how these bridges should be implemented and operated to synchronize their pulse-width-modulation (PWM) carriers, fundamental references and sampling instances to implement a network-controlled cascaded inverter with distributed PWM computation and overall optimal system performance. The paper begins by detailing the development and control of an integrated power bridge, designed with its own digital signal processor and associated control circuitry. Details describing the networked control algorithm and signal protocol needed for synchronizing the multiple power bridges through a dynamically fast data communication network, are then presented to achieve optimum harmonic cancellation and reduced common-mode voltage. The practicality and performance of the presented modular implementation concepts have been confirmed through the close match between simulation and experimental results obtained using a modular cascaded five-level inverter prototype. [ABSTRACT FROM AUTHOR]

This paper focuses on the development of maximum wind power extraction algorithms for inverter-based variable speed wind power generation systems. A review of existing maximum wind power extraction algorithms is presented in this paper, based on which an intelligent maximum power extraction algorithm is developed by the authors to improve the system performance and to facilitate the control implementation. As an integral part of the max-power extraction algorithm, advanced hill-climb searching method has been developed to take into account the wind turbine inertia. The intelligent memory method with an on-line training process is described in this paper. The developed maximum wind power extraction algorithm has the capability of providing initial power demand based on error driven control, searching for the maximum wind turbine power at variable wind speeds, constructing an intelligent memory, and applying the intelligent memory data to control the inverter for maximum wind power extraction, without the need for either knowledge of wind turbine characteristics or the measurements of mechanical quantities such as wind speed and turbine rotor speed. System simulation results and test results have confirmed the functionality and performance of this method. [ABSTRACT FROM AUTHOR]