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The conventional approach of predictive torque control (PTC) is frequently employed in the control of permanent magnet synchronous motors (PMSMs) driven by a two-level voltage source inverter (2L-VSI). This technique offers low complexity and reduced torque ripples in the low-speed region by minimizing the duty-cycle of the applied voltage vector (VV) compared to the complete utilization of the DC-link voltage. However, it has its limitations, including slow torque dynamics, restricted modulation index (MI), and an inability to select zero VV, which would be useful for minimizing ripples in multilevel VSI drives. Additionally, it can lead to an unbalanced DC link due to the restricted VV selection, especially at low MI. To address these limitations, a modified PTC based on space vector pulse-width modulation approach is proposed for three-level neutral-point-clamped (3L-NPC) VSI-fed PMSM. The proposed 3L-PTC method can reduce torque and flux ripples at low MI, improve dynamic response, and maintain a balanced DC link regardless of operating conditions. Intensive numerical and experimental evaluations are carried out to validate the effectiveness of the proposed 3L-PTC. [ABSTRACT FROM AUTHOR]

The paper presents an improved adaptive iterative learning current control approach for interior permanent magnet synchronous motor (IPMSM) drives, which greatly improves performance in both dynamic and steady-state scenarios. The proposed method includes three control terms: feedback control terms, which stabilize state errors and get them closer to zero; iterative learning control terms, which enhance transient performance by updating the control command signals according to the recorded data (i.e., the preceding input and state errors) so they get closer to zero; and adaptive-terms, which compensate for parameter variations. The proposed method offers a robust dynamic/steady-state response due to the above three terms, when compared to the conventional non-adaptive ILC, i.e., it is sensitive to parameter variations. Simulation and experimental analysis confirm the efficacy of the proposed method using PSIM software tools and an IPMSM test-bed. The proposed method demonstrates improvements in terms of its transient response (i.e., fast settling time with a smaller overshoot) and steady-state response (i.e., less THD along with reduced current ripples) when compared with conventional methods. [ABSTRACT FROM AUTHOR]

Discrete space vector modulation (DSVM) is employed to synthesize large number of voltage vectors (VVs) to improve the steady-state performance of predictive torque control (PTC). However, enumerating all the VVs in the prediction process increases the computation load of the motor drive. To address this issue, this article proposes a unidirectional VV preselection (UVVP) method for optimizing the performance of DSVM-based PTC of ac motors. The proposed UVVP method divides both voltage space vector diagram (VSVD) and flux space trajectory into twelve 30° based sectors to reduce the impact of candidate VVs with negative effects. At each flux position, the UVVP strategy can restrict the nearest candidate VVs in the 30° based VSVD region within the circular flux trajectory. This is achieved by using the speed direction to avoid the candidate VVs, which are in the same flux sector for reverse flux rotation, hence resulting in significant flux and torque ripple reduction. The main benefit of the proposed method is its simplicity since it only requires the flux sector and speed information as well as it can generate the VV enumerations online while ensuring the reduction of computation burden. [ABSTRACT FROM AUTHOR]

Flying capacitors (FCs) are very important in multilevel inverter systems when it comes to synthesizing additional voltage levels for various medium-voltage industrial applications, including renewable energy, motor drives, and power transmission. In particular, they are responsible for forming the five-level output pole voltages in five-level hybrid active neutral-point-clamped (ANPC) topologies. This is only possible when the FCs reach their reference values (i.e., 25% of the DC-link value). When a five-level hybrid ANPC inverter operates in the high-frequency (HF) range, the output three-phase current waveforms are less distorted when compared to the low-frequency (LF) performance. Instantaneously achieving a five-level output pole voltage during HF operation is a challenging task. This is due to the large capacitance of some existing types of FCs. In this study, a novel analysis of the effects of a FC on the performance of a five-level hybrid ANPC inverter is presented with simulation and experimental validations. Film capacitors significantly enhanced system performance when compared to electrolytic capacitors due to their many advantageous features, including the ability to charge and discharge quickly during HF operation. In addition, the total harmonic distortion of the output pole voltage is significantly suppressed. Consequently, the size of the required filter can be reduced. Therefore, the proposed system is highly desirable for various industrial applications. [ABSTRACT FROM AUTHOR]

This article exhibits an output voltage-derivative observer-based output voltage-tracking technique for dc/dc boost converters without current feedback, taking the model-plant mismatches (caused by parameter and load variations) and model nonlinearity into consideration. In contrast to extant passivity-based approaches, the proposed solution includes observers to estimate the output voltage derivative and does not require exact model information, which offers a few features: converter parameter information-free output voltage-derivative observers including the modified disturbance observation algorithm for improving the high-frequency disturbance rejection capability as a replacement of the estimation error integral actions, and the observer-based output voltage and its derivative error stabilizer with a damping adaptation mechanism assigning the desired energy function to the closed-loop system. Experimental verification is provided to demonstrate the practical advantages of the proposed solution using a 3-kW bidirectional converter. [ABSTRACT FROM AUTHOR]

This paper proposes a diagnostic and fault-tolerant method for an open-fault condition in dual inverters with open-end winding interior permanent magnet synchronous motors (OEW-IPMSMs). Certain switch pairs show similar behavior in the output current in an open-fault condition due to the structural characteristics of the two-level dual inverter. This work presents a method for detecting open-fault conditions and ensuring a fault-tolerant operation. The proposed method is applied in dual inverters with isolated voltage sources for driving OEW-IPMSM. In the event of an open-fault condition, a pair of switches containing the faulty switch is identified based on the stator current. Subsequently, the switch with the open-fault condition is determined, and fault-tolerant control for a faulty switch is immediately performed through a single-mode operation using zero-voltage vectors. The effectiveness of the proposed detection and tolerant control method is confirmed through simulation and experimental results. [ABSTRACT FROM AUTHOR]

In this study, discrete space vector modulation (DSVM) is used to achieve the flux and torque ripple reduction of finite set model predictive torque control (FS-MPTC) fed by a three-level neutral point clamped inverter (3L-NPCI). In the proposed DSVM, the synthesis of voltage vectors (VVs) can be controlled and implemented online, thereby eliminating the need for a VV lookup table. In addition, a simple and efficient preselection VV strategy is presented to reduce the number of candidate VVs in the prediction stage. The problem of capacitor voltage imbalance in 3L-NPCI is easily solved without including it as a control objective in the cost function. Thus, the complexity of tuning multiple weighting factors can be reduced. Hence, the proposed PTC-DSVM algorithm is simple and is capable of minimizing torque/flux ripples. It can also achieve a fast torque dynamic performance while maintaining balanced capacitor voltages. The effectiveness of the proposed method is verified through experimental results. [ABSTRACT FROM AUTHOR]

Three-level neutral-point-clamped (3L-NPC) voltage source inverters are widely used in many low- and medium-power applications. However, the 3L-NPC inverter has an inheritance issue of the neutral-point (NP) voltage unbalancing due to the deviation of dc-link capacitor voltages causing distortions for the output waveform quality. Generally, discontinuous pulsewidth modulation (DPWM) is used to diminish the stress on power transistors and prolong their lifespan, however; it is not capable of solving the issue of NP voltage unbalancing. Therefore, this article proposes a simple voltage balancing control based on DPWM with a hysteresis NP voltage band. The balancing control method is only activated once the capacitance voltage error exceeds the hysteresis band by generating a momentary offset on the opposite direction of the DPWM offset. In this way, both top and bottom capacitance voltages will converge within a predefined error band. Various hysteresis error bands are investigated by analyzing the power losses, total harmonic distortions, and common mode voltage. The advantages of this proposed method are its simplicity and ease of control while maintaining the features of DPWM. The effectiveness of the proposed method is validated using simulation and experimental results. [ABSTRACT FROM AUTHOR]

Switched-capacitor-based multilevel inverters have been gaining increasing attention in recent years in view of their voltage-boosting capability and capacitor self-balancing properties. However, the existing topologies, which comprise frontend switched-capacitor cells and a backend H-bridge, result in longer discharging duration in some of their switched-capacitors. In addition, the adoption of backend H-bridge introduces common-mode voltage and necessitates multiple dc sources for voltage level extension. To resolve these problems, this article proposes a novel topology comprises a T-type inverter and n cascaded switched-capacitor cells. It requires only a single dc source and it manages to mitigate the common-mode voltage by connecting the neutral of ac output to the mid-point of dc link. All switched-capacitors in the proposed topology are ensured to be charged for at least half of the fundamental period to alleviate the capacitor voltage ripples and current spikes. The operation of the proposed topology is analyzed and experimental results are presented for validation. [ABSTRACT FROM AUTHOR]

This study proposes a modified modulation scheme based on the phase-shifted pulse-width modulation (PS-PWM) method to improve the output performance and reduce the switching loss in cascaded H-bridge multilevel inverters. The PS-PWM method is one of the most popular modulation schemes. However, it generates significant switching loss, which can lead to the failure of power semiconductor switches. Various studies have proposed modulation schemes to reduce switching loss. The clamped discontinuous PWM (DPWM) method achieves the best switching loss reduction performance in comparison with other modulation schemes. However, the clamped DPWM method has low output characteristics, such as total harmonic distortion. The proposed modulation scheme achieves the same switching loss reduction and improved output performance by modifying the dwell time order. The proposed evenly clamped DPWM method was compared with the conventional clamped DPWM method through simulations and experiments. [ABSTRACT FROM AUTHOR]

Constant frequency torque controller-based direct torque control (CFTC-DTC) is emerging as a powerful control strategy for a high-performance control of alternating-current motor drives. Compared to DTC, the CFTC-DTC has less torque and flux ripples with a fixed switching frequency. Nevertheless, it has a limitation of the torque-loop bandwidth, as it uses the sampling frequency from a digital signal processor to generate a triangular-based carrier. The switching frequency of the control system is determined by the carrier frequency of the CFTC. The frequency limitation of CFTC leads to sector-flux droop, which causes a distortion in the motor phase current and aggravation in the torque and speed waveforms at low speed regions. In this article, we propose a modification of the frequency carriers of the CFTC-DTC of induction motors to increase the switching frequency and torque loop bandwidth by replacing the triangular-carrier-based waveform with a ramp-carrier-based waveform. The proposed method is verified by simulation and experimental results showing its excellent performances in steady- and transient-state operations. [ABSTRACT FROM AUTHOR]

This paper proposes a power conversion system (PCS) to utilize the differential pressure (DP) energy in district heating systems with reduced DC-link voltage variation. A differential pressure control valve (DPCV) is usually used to regulate pressure for heat transmission to remote areas in district heating systems. However, there is a high probability of malfunctions and failures of the DPCV, due to cavitation, since high-pressure fluids are used in district heating systems. Therefore, a PCS for utilizing DP energy in the district heating system replacing the DPCV is proposed in this paper. In addition, the DC-link voltage of the PCS greatly fluctuates when a sudden change occurs in a hydraulic turbine. It is effectively relieved by using the feed-forward control method. The effectiveness of the PCS for utilizing the DP energy in district heating systems with reduced DC-link voltage variation is verified by simulation and experimental results. [ABSTRACT FROM AUTHOR]

In this article, a simple overmodulation method is proposed for achieving fast direct torque control with a constant torque-switching controller (CTSR-DTC) in induction machines. The conventional overmodulation method applied to CTSR-DTC focuses on attaining and maintaining the voltage vector with the largest tangential component to the locus of the stator flux. The selected voltage vector is held during the transient state and fed into the switching table. Nevertheless, unlike a classical DTC, the CTSR activates both zero- and active-voltage vectors owing to the nature of its operation. As a result, the optimized active voltage during an overmodulation cannot be maintained throughout the complete torque transient owing to an interruption by the zero-voltage vectors. To overcome this problem, the proposed method modifies the CTSR output to eliminate the zero-voltage vectors only during a transient state. Consequently, a full exploitation of the overmodulation is achieved, and hence an excellent torque dynamic response can be obtained when torque is demanded. Simulation and experimental results are provided to validate the effectiveness of the proposed overmodulation strategy. [ABSTRACT FROM AUTHOR]

This paper proposes the predictive control with the discrete space-vector modulation (DSVM) for Vienna rectifier connecting to the permanent magnet synchronous generator (PMSG) of the wind turbine system (WTS). Since Vienna rectifier has the special operation principle, Vienna rectifier generates only the feasible eight voltage vectors, which can be a candidate vector for the predictive control, depending on the sign of the input currents. In the proposed predictive control, the feasible voltage vectors are extended from 8 to 19 consisting the 8 original voltage vectors and 11 virtual voltage vectors by using the DSVM for improving the current quality related to the torque ripple, vibration, and noise, and the neutral-point voltage balance with low voltage ripple is guaranteed by using the offset value calculated based on the model of two dc-link capacitors in Vienna rectifier. The scheme for reducing calculation burden is applied in selecting the candidate vector. In addition, the limited operation range for the maximum torque per ampere control of PMSG connected to Vienna rectifier is analyzed. The performance of the proposed predictive control with DSVM for Vienna rectifier with PMSGs is verified in simulation and experiment. [ABSTRACT FROM AUTHOR]

The integration of switched-capacitor techniques into multilevel inverters (MLIs) with a dc source string contributes to the boosting of voltage gain, renders it particularly attractive in reducing the number of input dc sources in the series string. However, the recent two-stage MLI topologies suffer from high voltage stress across the backend H-bridge. Addressing this concern, an improved topology, namely the one-switched-capacitor integrated MLI (1SCI-MLI) is proposed in this paper. An extended topology of 1SC-MLI is also established by appropriate incorporation of another switched-capacitor circuit. The two proposed topologies are endowed with voltage boosting capability. They also feature low switch count and low number of dc sources. More importantly, they resolve the high voltage stress problem in the existing counterparts. Their corresponding operational analysis and comparisons with recent MLI topologies are discussed. Simulation and experimental results from a laboratory prototype are presented to validate the effectiveness of the proposed topologies. [ABSTRACT FROM AUTHOR]

The conventional three-level active-neutral-point-clamped (ANPC) inverter requires high dc-link voltage at least twice the peak of ac output. To reduce the dc-link voltage, a recent topology that enhanced the voltage gain from half to unity has been presented. In this letter, an alternative ANPC topology is established by using two T-type inverters. Two floating capacitors with self-voltage balancing capability are integrated to achieve a voltage-boosting gain of 1.5. In addition, the proposed topology is capable of generating seven voltage levels. Its operation is validated through circuit analysis followed by experimental results of a prototype. [ABSTRACT FROM AUTHOR]

This paper proposes the new clamping angle control (CAC) pulse width modulation (PWM) method to restore its maximum linear modulation range of voltage source inverters (VSIs) reduced by the duty ratio limitation in hardware implementation, which makes the VSIs to operate nonlinearly in the high modulation range. The deadtime and the bootstrap gate driver circuit mainly cause this duty ratio limitation in practice. In particular, the bootstrap gate driver circuit is used in many industrial applications by avoiding the additional power supply to apply the gate-source voltage of power switches, and therefore making the VSIs to be small size with the low cost. First, the proposed CACPWM method is theoretically analyzed. Then, it is applied in the high modulation range to overcome the limitation of the duty ratio due to the use of the bootstrap gate driver circuit. Thereafter, its practical effectiveness is verified by both simulation and experimental tests. Also, the resulting harmonic distortions are compared with those by the conventional PWM methods. [ABSTRACT FROM AUTHOR]

This study devises an advanced single-loop output voltage control method for DC/DC converters incorporating a model-free filter, active damping, and nonlinearly designed feedback terms. The resultant output-feedback controller ensures the order reduction property and reduces both the dependence level of the system model and the number of feedback loops. There are two main features that differentiate this from extant results. First, a model-free first-order pole-zero cancellation (PZC) filter extracts the time derivative component from the output voltage measurement according to the first-order dynamics by the order reduction property without any converter model information. Second, an active damping controller forming a modified proportional-integral-derivative structure tracks the output voltage to its desired trajectory along the first-order low-pass filter dynamics by the order reduction property from the PZC, which is independent of the current feedback. Experimental evidence obtained from an actual feedback system adopting a 3-kW prototype DC/DC converter validates the effectiveness of the proposed technique, which demonstrates the capability of the current sensor fault tolerance. [ABSTRACT FROM AUTHOR]

This paper proposes an improved offset selection method for discontinuous-pulse-width-modulation (DPWM)-based back-to-back converters to reduce dc-link current ripple. DPWM is introduced to power converters to diminish the stress on power transistors and prolong their lifespan. However, when using the DPWM method, the dc-link current ripple is increased in nonswitching regions of the power transistors. Moreover, in DPWM-based back-to-back converters, the dc-link current ripple reaches its maximum when the two transistors of both inverters are clamped in opposite directions. Therefore, the dc-link capacitors endure more stress, resulting in decreased life duration. To overcome this issue, the switching method should consider the clamping periods, when the current ripple increases. This can be achieved by modifying the DPWM offset, so that the clamping states of both converters are matched. The effectiveness of the proposed method is confirmed by both simulation and experimental results. [ABSTRACT FROM PUBLISHER]

In this paper, a level-shift-based voltage modulation method for dual inverters used to drive open-end winding interior permanent magnet synchronous motors is presented. Notably, the conventional level-shift-based voltage modulation method used for dual inverters presents a disadvantage, since the differential mode voltage (DMV) significantly increases compared with that in the basic control method of dual inverters. This defect can be attributed to the fact that the conventional level-shift-based voltage modulation method uses a voltage vector combination that generates the maximum DMV peak value. To address this problem, the proposed method reduces the DMV by explicitly switching the voltage vectors that generate a large DMV. In this paper, the DMV generation process in a dual-inverter system is analyzed. Moreover, the DMV tendencies of the conventional and proposed methods are divided into operating regions according to the modulation index, which are further analyzed. The effectiveness and performance of the proposed voltage modulation method for a dual inverter are verified based on simulation and experimental results. [ABSTRACT FROM AUTHOR]

This study presents an optimal design for a 1 kW switched reluctance generator (SRG) for wind‐power applications. The design of the SRG is optimised to increase efficiency and reduce the volume of the generator compared with a basic model designed using the D2L method. To begin the optimisation, Latin hypercube sampling is employed to extract samples of the design variables for the design of experiment. The Kriging method of approximation modelling is used to interpolate the non‐linear characteristics for the optimal design. Finally, a genetic algorithm is utilised to optimise the original design model for efficiency and reduced volume. The optimal design of the SRG uses the shape parameters of the basic model. Design variables are selected to be at their maxima. The designed optimal model is compared with the basic model and prototype to verify the results. [ABSTRACT FROM AUTHOR]

The nongenerative-boost type rectifier, which is called the Vienna rectifier, is advantageous in terms of efficiency and current total harmonic distortion. Therefore, the Vienna rectifier is used in grid-connected applications such as telecommunication systems and wind turbine systems. Owing to the structural characteristics of the Vienna rectifier, various switching methods exist. Among these methods, a carrier-based discontinuous pulse-width modulation (CB-DPWM) method guarantees high efficiency compared to continuous pulse-width modulation methods; moreover, it is simple compared to a DPWM method based on space vectors. In this paper, the performance of the CB-DPWM method, its applicable region depending on the power factor and modulation index (Ma ), and its efficiency are analyzed in detail. Then, based on the analysis, a neutral-point voltage balancing method for the CB-DPWM method is proposed. The effectiveness and performance of the proposed neutral-point voltage balancing method are verified by simulation and experiment. [ABSTRACT FROM AUTHOR]

A three-level converter is used as the power converters of wind turbine systems because of their advantages such as low-current total harmonic distortion, high efficiency, and low collector–emitter voltage. Interior permanent magnet synchronous generators (IPMSGs) have been chosen as the generator in wind turbine systems owing to their advantages of size and efficiency. In wind turbine systems consisting of the three-level converter and the IPMSG, fault-tolerant controls for an open-circuit fault of switches should be implemented to improve reliability. This paper focuses on the open-circuit fault of outer switches (Sx1 and Sx4) in three-level rectifiers (both neutral-point clamped and T-type) that are connected to the IPMSG. In addition, the effects of Sx1 and Sx4 open-circuit faults are analyzed, and based on this analysis, a tolerant control is proposed. The proposed tolerant control maintains normal operation with sinusoidal currents under the open-circuit fault of outer switches by adding a compensation value to the reference voltages. The effectiveness and performance of the proposed tolerant control are verified by simulation and experiment. [ABSTRACT FROM AUTHOR]

This paper proposes a power predictive control (PPC) method for three-phase pulse width modulated rectifiers without a proportional-integral controller. The proposed PPC method calculates the optimized voltage vector by analyzing the relationship between the virtual flux, active power, converter voltage, and filter parameters. Thus, an overshoot does not occur and the fast and accurate power control becomes possible. The predictive algorithm computes the power error that would be produced by applying each vector and selects the one that contributes the minimum error. The simulation and experimental results prove that the proposed method provides an excellent steady-state performance and quick dynamic response. [ABSTRACT FROM PUBLISHER]

The purpose of neutral-point voltage balancing algorithms in the three-level neutral-point clamped (3L-NPC) topology is to eliminate the voltage unbalance of top- and bottom-side dc-link voltages (neutral-point voltage). These algorithms are divided into dc unbalance and ac unbalance compensation methods. The dc unbalance causes distortion of output currents; therefore, this problem has to be solved. The ac unbalance implies that there is an ac ripple in the top- and bottom-side dc-link voltages. In applications using 3L-NPC topology, a large dc-link capacitor value is required to mitigate this ac unbalance problem. As a result, the size and the cost of applications become large and expensive. In this paper, a compensation method for mitigating the ac unbalance of the neutral-point voltage is proposed, which causes the dc-link capacitor value to be small, when a carrier-based pulse width modulation method is applied. The proposed method compensates the ac unbalance of the neutral-point voltage by adding an optimal compensation value to the reference duty signals. This compensation value is calculated simply by currents and reference duty signals. The calculation process of the optimal compensation value is discussed, and the effectiveness of the proposed method is verified with simulations and experiments. [ABSTRACT FROM PUBLISHER]

The Vienna rectifier, which is a nongenerative-boost type rectifier, is used in many applications such as telecommunication systems and wind turbine systems. The Vienna rectifier has a special operating requirement. Many switching methods considering this requirement were proposed. These methods generally take into account the Vienna rectifier's operation with the unity power factor because the Vienna rectifier aims to provide the power to the load. However, as the applications for the Vienna rectifier are diversified, control requirements have been suggested, including the dc-link voltage balance control and the novel control under severely unbalanced grids. In this paper, we propose a carrier-based pulse-width modulation (CB-PWM) method for Vienna rectifier operation with a variable power factor. The proposed CB-PWM method adds the compensation voltage to the three-phase reference voltages, depending on the power factor, to maintain the sinusoidal input currents of the Vienna rectifier. The performance and effectiveness of the proposed CB-PWM method are verified by simulation and experiment. [ABSTRACT FROM AUTHOR]

This paper suggests a cascade output voltage regulation strategy for dc/dc boost converters that embeds a robust inner-loop current controller against parameter variations. The contributions of this paper are divided into two parts. The first contribution is to present a simple and robust inner-loop current controller despite parameter uncertainties, guaranteeing the stability of the whole closed-loop system including the first-order internal dynamics. The second contribution is to show that an outer-loop proportional–integral regulator can stabilize the output voltage error without relying on any parameter information. Simulations and experiments using a 3-kW dc/dc boost converter showed that the proposed method offers satisfactory closed-loop performance in the presence of parameter uncertainties. [ABSTRACT FROM PUBLISHER]

This paper proposes a simple and effective method to reduce torque ripples for the torque predictive control (TPC) of permanent-magnet synchronous motors (PMSMs). The conventional TPC analyzes the relationship among the electrical torque, stator flux, and stator voltage using the magnitude of the stator voltage vector of PMSMs to obtain the angle of the reference voltage vector and accurately control the torque. In addition, the stator-flux control uses the hysteresis method. However, the voltage vector that can be chosen in an inverter is limited because the conventional TPC fixes the magnitude of the reference voltage vector, and thus, a large torque ripple is generated in the low-speed region. The proposed TPC does not fix but varies the magnitude of the reference voltage vector using both the torque and flux error information. Therefore, it not only has the fast dynamic of a direct torque control but also can reduce effectively the torque ripple. The proposed method is proven by the simulation and experimental results, and the proposed algorithm provides an excellent steady-state response and fast dynamics. [ABSTRACT FROM AUTHOR]

This paper presents a control scheme for the dynamic performance improvement of an AC/DC converter using the model predictive direct power control (MPDPC) with a duty cycle. In the MPDPC, the active and reactive power is simultaneously controlled with a single cost function. If either of the two control targets has a large power variation, the control weight is concentrated on one side, which causes mutual interference. Because of such mutual interference, the control dynamics of the AC/DC converter deteriorates. Due to the control weight being concentrated on one side using the single cost function, even if the control dynamics of the other side decreases, the dynamic performance of the system is improved by reconfiguring the cost function that has the weighting factor to minimize the decline of the system dynamics that is caused by the mutual interference. The effectiveness of the proposed control scheme is verified by comparing its results with those of the conventional MPDPC. The results are obtained through the simulations and experiments. [ABSTRACT FROM PUBLISHER]

Three-level topologies are widely used in back-to-back converters of wind turbine generation (WTG) systems. In comparison with a conventional two-level topology, three-level topologies have more advantages, particularly for the high power. Neutral-point clamped (NPC) and T-type are typical three-level topologies. An open-switch fault of a three-level rectifier that is connected to a permanent-magnet synchronous generator (PMSG) leads to the current distortion and torque vibration in WTG systems. Furthermore, WTG systems can break down in the worst case. Therefore, a tolerance control for open-switch faults is required to improve the reliability of WTG systems. WTG systems by applying the tolerance control can be stopped safely and prevent additional problems. Depending on the situation, it can keep the operation of WTG systems under open-switch fault. The effects of outer open-switch faults of three-level rectifiers are analyzed by considering PMSG specifications in this paper. Moreover, a tolerance control for outer open-switch faults of the NPC and T-type three-level rectifiers are proposed with existing tolerance controls for inner open-switch faults. The proposed tolerance control is to inject the exact $d$-axis current value to eliminate current distortion. The simulation and experiment are conducted to prove the feasibility of the proposed tolerance control and to identify its performance. [ABSTRACT FROM PUBLISHER]

In wind turbine generation (WTG) systems, a back-to-back converter with a neutral-point-clamped (NPC) topology is widely used because this topology has more advantages than a conventional two-level topology, particularly when operating at high power. There are 12 switches in the NPC topology. An open-switch fault in the NPC rectifier of the back-to-back converter leads to the distortion of the input current and torque vibration in the system. Additionally, an open-switch fault in the NPC inverter of the back-to-back converter causes the distortion of the output current. Furthermore, the WTG system can break down in the worst case scenario. To improve the reliability of WTG systems, an open-switch fault detection method for back-to-back converters using the NPC topology is required. This study analyzes effects of inner and outer open-switch faults of the NPC rectifier and inverter and describes a novel open-switch fault detection method for all possible open-switch faults in the back-to-back converter. [ABSTRACT FROM AUTHOR]

Multilevel converter topologies are widely used in applications of wide-power range. The T-type topology, which is one of many three-level topologies, has an advantage in terms of efficiency compared to the neutral-point-clamped (NPC) type. In applications using the T-type topology, interest in reliability has been increased recently. Therefore, the open-switch fault detection method and tolerance control for T-type rectifiers, which are different from those of T-type inverters, are necessary to improve the reliability of applications. When the open-switch fault of switches connected to a neutral point occurs, an NPC-type rectifier cannot restore distorted input currents; however, a T-type rectifier is able to eliminate input current distortion completely. In this paper, an open-switch fault detection method is proposed and can find a position of the open-switch fault. Moreover, two tolerance controls based on space vector modulation are proposed and their characteristics are analyzed. The effectiveness and performance of the proposed open-switch fault detection method and two tolerance controls are verified by simulations and experiments. [ABSTRACT FROM PUBLISHER]

This paper proposes a new diagnosis method of an open-switch fault and fault-tolerant control strategy for T-type three-level inverter systems. The location of the faulty switch can be identified by the average of the normalized phase current and the change of the neutral-point voltage. The proposed fault-tolerant strategy is explained by dividing into two cases: the faulty condition of half-bridge switches and neutral-point switches. The performance of the T-type inverter system improves considerably by the proposed fault-tolerant algorithm when a switch fails. The proposed method does not require additional components and complex calculations. Simulation and experimental results verify the feasibility of the proposed fault diagnosis and fault-tolerant control strategy. [ABSTRACT FROM AUTHOR]

The original direct power control (DPC) is known to give a fast response under transient conditions. However, active power, reactive power, and current pulsations occur in steady-state operation. The variable structure control (VSC) method for a doubly-fed-induction-generator-based wind turbine system is presented, using the principles of an active and reactive power controller known as modified DPC and where VSC and space-vector modulation are combined to ensure high-performance operation. The VSC scheme is designed following the modified DPC philosophy, which provides robust and fast power controls without frame transformation and the current controller that is used in the conventional field-oriented control drive. Simulation and experimental results demonstrate that the proposed methods preserve the effectiveness and robustness during variations of active and reactive power, rotor speed, and converter dc-link voltage. [ABSTRACT FROM PUBLISHER]

This paper presents a new direct torque controlled space vector modulated method to improve the sensorless performance of matrix converter drives using a parameter estimation scheme. The flux and torque error are geometrically combined in a new flux leakage vector to make a stator command voltage vector in a deadbeat manner. A new sensorless method of estimating the rotor speed, flux, stator resistance, and rotor resistance is derived and verified with experimental results. Common terms in the error dynamics are utilized to find a simpler error model involving some auxiliary variables. Using this error model, the state estimation problem is converted into a parameter estimation problem assuming the rotor speed is constant. The proposed adaptive schemes are determined so that the whole system is stable in the sense of Lyapunov. The effectiveness of the proposed algorithm is verified by experiments. [ABSTRACT FROM AUTHOR]

This paper presents a new sensorless vector control system for high-performance induction motor drives fed by a matrix converter with nonlinearity compensation. The nonlinear voltage distortion that is caused by commutation delay and ON-state voltage drop in the switching devices is corrected by a new matrix converter model. A reduced-order extended Luenberger observer is employed to bring better response in the whole speed operation range, and a method to select the observer gain is presented. Experimental results are shown to illustrate the performance of the proposed system. [ABSTRACT FROM AUTHOR]

A stable sensorless controller for DTC of induction motor fed by three-level inverter using the Radial Basis Function Network (RBFN) is presented in this paper. The torque ripple can be drastically reduced and low speed performance can be obtained in the DTC system for high performance induction motor drives. However, speed control performance is still influenced by the lumped uncertainties of the system such as parameter variations, external load disturbances, and unmodeled dynamics which make it difficult to obtain an exact mathematical model. In this paper, the lumped uncertainties are estimated on-line by the RBFN. Simulations as well as experimental results are shown to illustrate the performance of the proposed system. [ABSTRACT FROM AUTHOR]

Presents a torque ripple reduction technique of direct torque control (DTC) for high power induction motors driven by three-level inverters with the inverter switching frequency limited around 0.5-1 kHz level. Principle of DTC for three-level inverter; Details of torque ripple reduction algorithm; Schematic diagram of the proposed control strategy.

This paper proposes performance improvement of hydraulic turbine generation system (HTGS) using a subdivided finite set model predictive current control (SFS-MPCC). Recently, the differential pressure control valve (DPCV) is replaced by HTGS because of the frequent breakdown in DPCV caused by cavitation in the district heating systems. The HTGS consists of the hydraulic turbine, permanent magnet synchronous generator (PMSG), back-to-back (BTB) converter, and three-phase grid. Especially, BTB converter is composed of a generator-side inverter, DC-link capacitor, and grid-side inverter. In the generator-side inverter, a model predictive current control (MPCC) has been widely used because of its many advantages, such as robustness from parameter variation, fast dynamic response, and unnecessariness of gain tuning. The conventional MPCC uses only eight voltage vectors; thus, it makes a large current ripple, which is directly related to torque ripple. Therefore, to reduce the current and torque ripple, SFS-MPCC, which uses subdivided voltage vectors is proposed. An additional algorithm to reduce the calculation time is proposed because the subdivided voltage vectors increase the calculation time excessively. The effectiveness of the proposed SFS-MPCC is demonstrated by simulation and experimental results. [ABSTRACT FROM AUTHOR]

This paper derives an advanced multi-loop speed feedback system equipped with model-free pole-zero cancellation (PZC) filters for the position and current measurements of servo drives. The proposed feedback system does not necessitate an exact system model, and it renders the transfer function of each loop in a first-order low-pass filter form by involving active damping terms. Furthermore, the PZC filters output the desired speed and current information for each of the loops along the first-order convergent system, independent of the system model. An experimental platform involving a 500 W brushless DC motor, with a digital signal processor as a controller, validates the practical improvement of the proposed feedback system. [ABSTRACT FROM AUTHOR]

This paper presents a hardware implementation for the reliable design of a full silicon carbide (SiC) inverter-fed motor drive system. SiC MOSFETs have been widely used in various applications due to their low switching losses, high voltage capabilities, and high-temperature operation capability. However, SiC MOSFETs are vulnerable to the overvoltage and overcurrent caused by the high switching frequencies and faults of parasitic inductance. The high speed of switching transitions causes high dv/dt, which leads to insulation failures of motor windings. In addition, the high di/dt, according to the parasitic inductance, can destroy the switching devices under short-circuit faults. A gate driver with desaturation protection is required to prevent short-circuit faults, and a passive filter should be installed to reduce the dv/dt to within prescribed values. This paper presents an optimized design process for a full SiC inverter-fed motor drive system with improved reliability. The effectiveness and validity of the process are verified through experimental results under various conditions. [ABSTRACT FROM AUTHOR]

This paper proposes a novel current feedback-free speed regulation method for servo systems subject to system parameter and load uncertainties. The proposed solution has two features. First, the position measurement from the rotary encoder constitutes the speed and acceleration estimates for control loops through a position filter with nonlinearly-structured design parameters and without dependence on the system parameters. Second, the proposed controller only requires nominal system parameter information, and stabilizes both the speed and acceleration loops using only position measurements by injecting active damping terms, which leads to pole-zero cancellation. A prototype servo system was built using a 500 W brushless DC-motor-based dynamo. The prototype experimentally validates the effectiveness of the proposed solution in terms of speed tracking and regulation tasks. [ABSTRACT FROM AUTHOR]

This article proposes a dynamic characteristic improvement of phase-shift full-bridge center-tapped (PSFB-CT) converter using a model predictive control (MPC) method. The PSFB-CT converter is widely used for low-voltage dc–dc converters in electric vehicles. In general, its output voltage is a control object which is usually controlled using a proportional–integral control-based output voltage controller and current controller. However, it has a disadvantage such as undesirable dynamic characteristic of the PSFB-CT converter and the necessity of gain tuning. Especially, if the gain of the PI control is increased to improve the dynamic characteristic of the PSFB-CT converter, an overshoot of the output voltage can occur. In this article, the advanced voltage control using the MPC method is proposed to improve the dynamic characteristic of the PSFB-CT converter without overshoot of the output voltage. As a result, the proposed method has advantages with not only fast dynamic characteristic but also robustness from a sudden change of load impedance. The effectiveness of the proposed MPC method was proved by the simulation and experimental results. [ABSTRACT FROM AUTHOR]

Abstract: Capacitance of a coaxial line terminated by a gap is investigated. An electrostatic boundary-value problem of the coaxial line terminated by a gap is rigorously solved based on the Fourier sine transform, mode matching technique, and superposition. The capacitance of the coaxial line is represented in a fast-convergent series and computed in terms of the gap geometry and the gap permittivity. [Copyright &y& Elsevier]

The utilization of three-level T-type (3L T-type) inverters in finite set-model predictive control (FS-MPC) of grid-connected systems yielded good performance in terms of current ripples and total harmonic distortions. To further improve the system's performance, discrete space vector modulation (DSVM) was utilized to synthesize a higher number of virtual voltage vectors. A deadbeat control (DBC) method was used to alleviate the computational burden and provide the optimum voltage vector selection. However, 3L inverters are known to suffer from voltage deviation, owing to the imbalance of the neutral-point voltage. We have proposed a simplified control strategy for balancing the neutral point in the FS-MPC with DSVM and DBC of grid-connected systems, not requiring a weighting factor or additional cost function calculation. The effectiveness of the proposed method was validated using simulation and experiment results. Our experimental results show that the execution time of the proposed algorithm was significantly reduced, while its current quality performance was not affected. [ABSTRACT FROM AUTHOR]

Open- and short-circuit faults are the most severe issues that affect the stability and reliability of power conversion systems. The space vector modulation (SVM) technique is widely used to control power converters. However, conventional SVM is incapable of controlling the system effectively when such faults occur. Considering these, this article proposes a modified SVM that is capable of tolerating the extreme cases of faults (including multi open-/short-circuit faults) simultaneously. An innovative fault tolerance method is proposed to tolerate multifaults in hybrid active neutral point converters (HANPCs). Furthermore, new voltage reference signals are created in addition to calculating voltage offset and inserting modified switching sequences. A descriptive performance analysis of the modified SVM technique is applied under healthy and faulty conditions. Correspondingly, the effects of the total harmonic distortion of the system performance are also highlighted and explained. The results reveal that the proposed control strategy can effectively maintain healthy and safe operation under faulty conditions without the need for additional parts or alteration of the topology configuration. In addition, the proposed method can be applied to HANPCs without special requirements to withstand high voltage levels. The effectiveness of the proposed method is verified by simulation and experimental results. [ABSTRACT FROM AUTHOR]

This paper analyzes the influence of a DC-link capacitor under open-switch failures in hybrid active neutral point clamped (ANPC) inverters that consist of Si-IGBTs and SiC-MOSFETs. Open-switch failures cause the current harmonic distortion of DC-link capacitors. This distorted current affects the capacitor loss increase, which in turn affects the lifetime decrement of the DC-link capacitor. These influences of open-switch failures on inverter operation have not been discussed despite the fact that they lead to secondary failures of the system. In this paper, the influence of open-switch failure is analyzed based on the current harmonics of the DC-link capacitor, which experiences the highest failure rate. Simulation and experimental results demonstrate the effects of various open-switch failure scenarios on DC-link capacitors in terms of current harmonics and lifetime. [ABSTRACT FROM AUTHOR]

Recent developments in power electronics technologies have resulted in a need for fast responses and dynamic control. However, existing control schemes are still limited to the available digital signal processors (DSPs) and their associated high prices. The field-programmable gate array (FPGA) offers fast performance and high control flexibility by providing a reconfigurable computing speed. However, it has some implementation limitations in standalone systems. In this regard, this paper presents a hardware setup for a three-level hybrid active neutral point inverter (HANPC) using a FPGA and a DSP. A unique method using digital and analog modulation is designed in this study using Vivado software. The proposed method depends on receiving analog reference signals from the DSP and then performing all the required processes using the FPGA. Direct pulse width modulation is generated to control the HANPC without changing the hardware configuration of the main topology. The implemented hardware is based on a 15 kW HANPC topology that is mainly controlled by a Digilent Zybo-Z7-20 FPGA. The effectiveness of the proposed system was verified by experimental results. [ABSTRACT FROM AUTHOR]

This article proposes a method to eliminate abnormal output voltages generated in three-level hybrid active neutral-point clamped (ANPC) inverters. The hybrid ANPC inverter is a topology in which silicon (Si) devices are replaced with silicon-carbide (SiC) devices in part from the conventional ANPC topology. The hybrid ANPC inverters have the advantages of high switching frequency and low power switching loss due to the SiC devices. In this hybrid ANPC inverter, abnormal output voltages occur when the polarity of the output pole voltage is changed from positive to negative. The cause of the abnormal voltages is the switching time difference between the Si and SiC devices, and it is various from a few nanoseconds to a few microseconds. These abnormal output voltages need to be eliminated as it leads to degraded output power quality in the hybrid ANPC inverters. The proposed switching method effectively eliminates the abnormal output voltages and reduces output current distortion. The performance of the proposed method is verified using a prototype of the new three-level hybrid ANPC inverter type through both simulations and experiments. [ABSTRACT FROM AUTHOR]

This article presents a dc-link capacitor lifetime improvement method for three-level photovoltaic hybrid active neutral-point clamped inverters in full modulation index range. The capacitors are one of the components with vulnerable reliability in a power conversion system. The dc-link capacitor current ripples lead to temperature rise and wear-out failure of the capacitors. The accumulated thermo-mechanical damages from the temperature rise reduce the capacitor lifetime and reliability of the system. The proposed modulation method suppresses effectively the dc-link capacitor current ripple to improve the capacitor lifetime. In this article, the proposed method is discussed via a comparison with conventional space-vector pulsewidth modulation in full modulation index range. The modulation index range is divided into two regions, namely medium-vector modulation and hybrid modulation region. The capacitor lifetime is evaluated by the capacitor lifetime model according to the modulation methods and modulation regions. The effectiveness of the proposed modulation method is verified through simulation and experimental results. [ABSTRACT FROM AUTHOR]