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As the inverter-based generation replaces the conventional synchronous generators, it may also need to fill in the missing ancillary service support. One of these ancillary services is dynamic reactive power provision and voltage control. This paper analyzes optimal strategy of reactive and active fault-current support of the inverter-based generation leading to fast voltage recovery of the system. For the purpose of the analysis, new ramping active current controller able to emulate different behavior of active current injection is proposed. By optimizing its parameters for different case studies of the system, the conclusions about optimal behavior of the inverter based generation with respect to system parameters and operating conditions are drawn. It is observed that the optimal combination of active and reactive fault-current is the most sensitive to the dynamic load component penetration levels in the system. With the increasing penetration levels, the significance of active fault-current injection increases. The results show that with higher penetration levels of dynamic load component in the heavy load areas, the ramping down of the inverter-based generation active fault-current results in slower voltage recovery of the system. Following this conclusion, a recommendation on update of current European grid codes is proposed. [ABSTRACT FROM AUTHOR]

To improve the torque accuracy for open-end winding permanent magnet synchronous motor (OEW-PMSM) with common dc bus, it is necessary to eliminate the zero-sequence torque (ZST) caused by zero-sequence current (ZSC) and the third back electromotive force. But the third flux linkage mismatch can enlarge ZSC which causes torque ripple. To deal with the above problem, firstly, a q-axis current injection method combined with deadbeat predictive current control (DPCC) is adopted to inject an extra current into the reference q-axis current. The extra torque generated by this injected current can compensate for ZST. Secondly, to ensure the accuracy of the q-axis injected current, a parameter identification method based on recursive least square (RLS) algorithm with forgetting factor is presented to identify the third flux linkage accurately. The identification value can reduce ZSC and torque ripple under different working conditions. And the accurate q-axis injected current can be obtained to counteract ZST and output accurate torque. Finally, three methods are comparatively analyzed in this paper, namely the traditional DPCC method, the DPCC method with q-axis current injection and the proposed DPCC method based on RLS with forgetting factor. The simulation and experimental results verify the effectiveness of the proposed DPCC method. [ABSTRACT FROM AUTHOR]

This paper presents a simple pulse width modulation algorithm for control of an ultracapacitor based energy storage system used for source and load support applications. As opposed to dual loop control philosophy that is widely used for backup applications, this paper presents a simple single loop current control that is only useful for controlling the ultracapacitor based DC/DC converters used in source and load support applications. The proposed PWM blocking method necessitates the DC/DC converter to operate in five states and takes into consideration the essential operational limits associated with the ultracapacitors. The performance of the proposed algorithm is verified experimentally using a 24 V laboratory prototype setup. Further, the shortcomings of dual loop control when applied to source and load support applications are demonstrated. [ABSTRACT FROM AUTHOR]

Although Switched Reluctnace Motors have many advantages, vibration is known as their most severe drawback acting as an impediment limiting their widespread use in industrial and domestic applications. Through electromechanical relationships, it is shown that the first-order time derivative of applied phase voltage and second-order time derivative of radial force directly affect the amplitude of generated vibration, especially at the beginning of demagnetization instance. Therefore, a set of criteria is stated in this paper meeting which ensures having low vibration intensity. In this paper, three types of demagnetization voltages are proposed which comprehensively meet the stated criteria. These voltages share the same characteristics contributing to the vibration reduction in Switched Reluctance Motor. Two vital parameters of Synchronous Counter and Coefficient are included in the proposed demagnetization voltages which must be meticulously chosen in order to be effective. Noticeable contribution of the proposed methods to the vibration alleviation is validated through simulation and experimental tests conducted under different working conditions. [ABSTRACT FROM AUTHOR]

This paper investigates the effects of the dynamic properties of a photovoltaic generator (PVG) on the stability of a grid-connected current-source inverter (CSI)-based photovoltaic system and presents a simple yet effective active compensator to ensure system stability. A detailed equivalent model of the PVG that considers the dynamic resistance, diffusion capacitance, series inductance, and dc cable resistance and inductance is used, and the effects of these parameters are assessed. It has been found that when the PVG operates in the constant-current region (CCR), the phase margin becomes negative in the control-to-input dynamics, which alters the stability of the dc-link current control. The change in the system dynamics when the operating point of the PVG shifts from the constant-voltage region (CVR) to CCR is verified through a detailed small-signal state-space model of the complete system. Furthermore, an active compensator is proposed to ensure stable dc-link current control operation at all operating points of the PVG. The influence of different control parameters on the integrated system dynamics is examined to determine the range of the control parameters required for stable operation. The performance of the proposed system under utility-grid fault, grid voltage parameter variation, weak grid, and changes in insolation level is also evaluated. Detailed nonlinear time-domain simulation results, using a typical utility-scale CSI-based PV system, validate the analytical results and the effectiveness of the proposed active stabilization under different operating conditions. [ABSTRACT FROM AUTHOR]

In this paper, consideration from the viewpoint of the dq-axis current vector locus is reported on the clues for improving the output of wound-field motor utilizing space harmonic for field excitation. It is experimentally verified by visualizing the vector locus on the dq coordinates. First, voltage equation will be explained, and then the offline parameter estimation will be discussed. Then, visualization of the voltage-limit ellipse and vector locus will reveal clues for performance improvement. [ABSTRACT FROM AUTHOR]

The paper addresses an improved inner current reference calculation to be employed in the control of modular multilevel converters operating during either balanced or unbalanced conditions. The suggested reference calculation is derived based on the AC and DC additive and differential voltage components applied to the upper and lower arms of the converter. In addition, the impacts caused not only by the AC network’s impedances but also by the MMC’s arm impedances are also considered during the derivation of the AC additive current reference expressions. Another issue discussed in this article regards that singular voltage conditions, where the positive-sequence component is equal to the negative one, may occur not only in the AC network but also internally (within the converter’s applied voltages). Several different inner current reference calculation methods are compared and their applicability during the former fault conditions is analyzed. The paper presents a detailed formulation of the inner current reference calculation and applies it to different unbalanced AC grid faults where it is shown that the presented approach can be potentially used to maintain the internal energy of the converter balanced during normal and fault conditions. [ABSTRACT FROM AUTHOR]

In this paper, it is identified that unstable weak grid connection of voltage source inverters (VSIs) is dominantly caused by the current control. In particular, it is found the proportional gain $ k_p$ of conventional PI controller cannot balance the grid voltage impact and damping capability especially when a very weak grid with short circuit ratio (SCR) $ < $ 1.3 is connected. This issue is solved in this paper by simply restructuring the PI controller as an IP controller for current control. This IP controller will not change the tuning method of current control and make this VSI indeed connect to a very weak grid with rated power injection. [ABSTRACT FROM AUTHOR]

This paper proposes an improved SOC balancing strategy for the modular energy storage system (ESS) based on low bandwidth communication (LBC) technology, aiming at solving the drawbacks of the conventional balancing strategy based on droop control. The proposed control scheme can improve the SOC balancing efficiency and remove the current deviation by using the SOC slope-adjusting and current-shifting approaches simultaneously. The average value of SOC can be derived through the LBC line, and the droop coefficient based on SOC can be controlled in the local control layer. Thus, the SOC of each sub-module can converge to the average SOC value in system dynamic process, and the balancing speed under the condition of low SOC difference between sub-modules can be improved. Furthermore, the current regulation performance in steady and transient states can be enhanced by using the proposed method. At last the effectiveness of the proposed strategy is verified by experimental results. [ABSTRACT FROM AUTHOR]

An improved two-stage model predictive current control (MPCC) for three-phase three-level converters in the paper, which can simultaneously achieve common-mode voltage (CMV) reduction, effective dc-link capacitor voltage control, and decreased computational burden, is proposed. Compared to the other current control strategies, it has the capability of handling multiple control objectives and possesses a simple structure. Furthermore, it greatly reduces the CMV since the peak CMVs of all the candidate voltage vectors are constrained to be less than one sixth of the dc-link voltage. In addition, an optimal two-stage voltage vector selection mechanism is employed in the proposed method. It helps to significantly reduce the computational complexity. Simulation and experimental results are provided to verify the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

This paper analytically derives oscillatory stability criteria of a grid-connected PMSG based on the block diagram model. The derivation reveals the general mechanism about how the condition of grid connection, loading and converter control parameters setting of the PMSG jointly affect the oscillatory stability of the PMSG. It logically explains why the condition of weak grid connection and heavy loading may cause destabilization. In addition, computationally simple and modal-computation free indices are proposed to identify the instability risk caused by the “improper parameters setting” of the control system of grid side converter (GSC) and the phase locked loop (PLL). Following analytical conclusions are obtained: (1) When the PLL is of high-frequency bandwidth, high-frequency oscillations are mainly caused by the PLL or the open-loop modal resonance between the PLL and current control of the GSC. In addition, the low-frequency oscillations may also occur as caused by the power control of the GSC. (2) When the PLL is of low-frequency bandwidth, low-frequency oscillations may be caused jointly by the power control of GSC and the PLL. An example grid-connected wind farm with eighteen similar PMSGs is presented to demonstrate and evaluate the stability criteria derived and analytical conclusions obtained in the paper. [ABSTRACT FROM AUTHOR]

A soft starter is commonly utilized in various industrial induction motor systems to reduce the inrush current during motor startup. The conventional voltage ramp-up method, used in the typical soft starter, gradually increases the voltage over the startup period. However, this method can result in a significant voltage increase as the induction motor approaches its rated speed, resulting in a rapid torque increase compared to the beginning part of the startup phase. This sudden torque increase can potentially cause physical damage to the induction motor system due to a transient current overshoot, which in turn can result in resonance. Additionally, the changes in the parameters of the induction motors can lead to the variations in torque during startup, especially because of the air gap permeance. Therefore, a firing angle control method for the soft starter that maintains a constant torque, facilitating a gradual increase in speed, is desirable. This paper proposes a novel firing angle control method, to achieve a constant torque and a gradual speed increase, using only current feedback. This paper is the first time that a change in air gap permeance is considered and compensated for in controlling the firing angle of the soft starter. The air gap permeance variation is modeled as an effective inertia in the transient response of the induction motor. Experimental results demonstrate that the proposed method effectively reduces rapid torque increases and speed variations compared to the conventional voltage ramp-up method, through its application to a 30kW industrial induction motor system.

Due to the relatively low operational reliability of the MMC valve, it is necessary to establish corresponding test methods to examine the tolerance of the valve to electrical and thermal stresses under engineering requirements through operational tests, to verify its operational reliability. To meet the operational testing requirements for higher voltage and larger current converter valves, an appropriate test topology is required. The paper first analyzes the voltage and current stress characteristics of capacitor components and MMC converter valves in ±800 kV/8 GW Flexible DC transmission system, providing a theoretical basis for the stress of operational testing valve, requiring that to be equivalent to actual operating conditions. Addressing the operational testing demands for high voltage and large current converter valves in the ±800 kV/8 GW flexible DC transmission MMC, a test topology is proposed. This topology can meet the operating conditions of higher voltage and larger current and simultaneously conduct tests on valve segments and modules, significantly improving operational testing efficiency and reducing testing costs. Additionally, a control method applicable to this test topology is proposed, enabling flexible adjustment of DC and AC in the test circuit, thereby enhancing the equivalency of operational tests. In this paper, the proposed topology and control method have enhanced testing efficiency, reduced testing costs, improved testing equivalence, and enhanced the precision of current and capacitor voltage control. Finally, simulations and experiments are constructed to validate the feasibility and effectiveness of the proposed operational test topology and its control method through simulations and experiments.

The digital implementation of all the control loops of a versatile buck-boost (VBB) dc–dc converter used in a stand-alone photovoltaic application is proposed in this paper to improve existing digital-analog sliding-mode-based implementations. All three control loops: maximum power point tracking (MPPT), fast input voltage regulation, and inner high-bandwidth current control, have been programmed in the same digital signal controller (DSC). A Model Predictive Control (MPC) based algorithm has satisfactorily solved the challenge of implementing the nominal 100 kHz switching frequency current loop. The MPC cost function is distributed throughout the algorithm to achieve three specific goals: the tracking of the reference current (G1), a quasi-constant steady-state switching frequency (G2), and the assurance that the duration of an interval is larger than the time required to calculate it (G3). The third goal requires the current control to toggle between peak- and valley-modes depending on the operating point. The correct fulfillment of these control objectives on the proposed MPC-based algorithm has been validated through simulations and experimental tests performed on a purpose built-prototype. [ABSTRACT FROM AUTHOR]

In this paper, a fault-tolerant control of a symmetrical six-phase induction generator based on a variable structure strategy is experimentally tested and compared with a classical proportional-integral controller. For this, we use a linear feedback sliding mode controller with switched feedback gains in such a way to control the inner current loops of this machine. One main drawback of the classical three-phase induction generator is that it is no longer possible to generate electrical power if only one phase is lost on the stator side. To overcome this issue, we will use a squirrel cage six-phase induction machine that can still operate when at least three phases remain on the stator side. This article proposes to use a variable structure control in order to cope with unbalanced currents and also maintain the generation of power when a loss of the stator's phases occurs. The proposed controller shows its robustness and good regulation performance in healthy and faulty modes. The simulation and experimental tests were carried out with a 24 kW induction machine that represents 1/100 of the electrical power of a real wind turbine. [ABSTRACT FROM AUTHOR]

The power – voltage (P-V) characteristics of photovoltaic (PV) systems exhibit multiple power peaks under partially shaded conditions. Several global maximum power point tracking (GMPPT) algorithms in the literature recognize the irradiance change, only after the convergence of operating point to global peak, or use additional hardware to call GMPPT subroutine at definite time intervals to detect any insolation change, and thus track the global peak. However, during fast changing partial shading conditions, these methods are less effective, as they do not detect any irradiance change during the tracking phase of any shading pattern. This paper proposes a novel modified current control approach that uses current as a parameter to detect the insolation change during the tracking phase and track the global peak under fast changing partial shading conditions without any additional hardware. The proposed technique improves the tracking efficiency by as much as 39%, thus proving to be effective under fast-changing partial shading conditions. The superior tracking performance of the proposed algorithm over the existing techniques in terms of its tracking efficiency, dynamic tracking capability, tracking speed, and convergence to the global peak is demonstrated with extensive simulations using MATLAB/Simulink and experimental results. [ABSTRACT FROM AUTHOR]

Directional, phase-selection, and distance elements of a relay are prone to misoperation in the presence of inverter-based resources (IBRs). To address these problems, modifications of relay elements as well as new control schemes for IBRs have been proposed in the literature. These methods focus mainly on addressing the misoperation of only one of the above relay elements. The available solutions that are based on a new control system focus only on the negative-sequence current loop. Thus, they work only for unbalanced faults. This paper proposes a comprehensive dual current control scheme for IBRs during all types of faults such that all of these relay elements operate correctly. The proposed method controls the IBR to operate as a voltage source behind a virtual impedance in the positive-sequence circuit, and a single impedance in the negative-sequence circuit, thereby emulating the phase angles of a synchronous generator's (SG's) fault current. The proposed method also maximizes the active, and reactive current generation of the IBR during faults, and emulates the incremental sequence current magnitudes of an SG. The proposed method does not require altering the relay elements. Moreover, correct operation of the relay elements is achieved regardless of the fault type, resistance, and location. The effectiveness of the proposed method is verified through not only simulation studies, but also hardware-in-the-loop testing of commercial relays. [ABSTRACT FROM AUTHOR]

This article proposes a novel flux weakening scheme for five-phase PMSM with active harmonic currents injection. The conventional flux weakening control schemes applied in the five-phase PMSM do not consider the voltage limit drop in the fundamental subspace due to the harmonic current controller. Thus, the derivation between the reference current trajectory and actual current trajectory would cause the current distortion when applying deadbeat current controller (DBCC). This article analyses the precise voltage limit circles considering the voltage drop caused by the resistance and harmonic currents control at first. Then, a feed-forward flux weakening control algorithm is designed to optimize the current trajectory online. The gradient descent method is used to ensure the converge speed and stability of the optimized current trajectory. Thirdly, the peak value of phase currents would be clipped by the harmonic currents to prevent the inverter current limit, where a new non-linear harmonic current controller is designed to precisely control the harmonic currents. Finally, the DBCC and modified SVPWM technology are utilized to generate the duty cycle. The proposed improved flux weakening control strategy is successfully implemented in an interior five-phase PMSM, and the performance demonstrate the effectiveness of this strategy. [ABSTRACT FROM AUTHOR]

The penetration of distributed energy resources is drastically increasing in the distribution systems. Inverters are employed to efficiently process the harvested energy of these energy resources. These inverters are commonly operated in parallel with some loads to form a microgrid. The control of these inverters has become a vital component to operate their microgrid. The microgrid formed by the inverters and loads can be operated into two main modes, which are the grid-connected mode and the islanded mode. Any control (operational) scheme for the microgrid should be able to operate these inverters along with their microgrid in these two modes, and it should enable the whole microgrid to have a seamless transition from one mode to another. This paper articulates different control schemes that are employed to operate parallel/several inverters within microgrids or connected to distribution systems. There are serval classifications for these control schemes used for inverters in microgrids. The main focus of this review paper is dedicated to the centralized control (with/without inter-communications) schemes that are developed to operate several parallel inverters within the microgrid to control current, voltage, and power at different operating conditions.

This paper presents the development of improved synergetic current control for the injected current of an inverter in the grid-connected microgrid and the distributed generation system (DGS). This paper introduces new formulas of the macro-variable functions for integral synergetic control (SC) and integral fast terminal SC, which both have an integral term to guarantee zero steady-state error. The proposed integral SC and integral fast terminal SC achieve a seamless performance such as the fast convergence, minimal overshoot, zero steady-state error, and chattering-free operation. To demonstrate the meritorious performance of the proposed scheme for injected current control, it is compared with the performance of a proportional-integral (PI) controller and advanced exponential sliding mode control (SMC). Finally, the practicality of the proposed scheme is justified by experimental results obtained through rapid control prototyping (RCP) using the dSPACE-SCALEXIO platform.

Discrete-time dynamic systems demonstrate quite exciting possibilities from the perspective of control as compared with the continuous-time counterpart. Interesting properties of discrete-time dynamic systems include the possibility to algebraically determine previously unknown system parameters by simply measuring the present inputs and outputs of the system. Additionally, achieving a finite settling time with zero steady-state error is only achievable in discrete-time dynamic systems. Deadbeat current control (DBCC) has been used to achieve a finite settling time, especially in grid-connected inverter applications. However, there is no comprehensive study on reviewing or evaluating existing control approaches, to the authors’ best knowledge. This paper systematically examined the existing methods by paying attention to four key research issues: 1) research evidence indicating the adoption of DBCC in grid-connected inverter applications (GCIAs), 2) the types of deadbeat control approaches adopted in GCIAs, 3) the best approach in terms of stability especially regarding grid-impedance variation, and 4) the barriers that might prevent the wide adoption of DBCC in GCIAs. Finally, this paper presents a hypothesis based on the simulated results on which approach is superior at present to give readers a direction for further research classification on deadbeat control.

Computing-in-memory (CIM) architectures have gained importance in achieving high-throughput energy-efficient artificial intelligence (AI) systems. Resistive RAM (RRAM) is a promising candidate for CIM architectures due to a multiply-and-accumulate (MAC)-friendly structure, high bit density, compatibility with a CMOS process, and nonvolatility. Notwithstanding the advancement of RRAM technology, the reliability of an RRAM array hinders the spread of RRAM applications such that a circuit-technology joint approach is necessary to attain reliable RRAM-based CIM architectures. This article presents a 64-kb hybrid CIM/digital RRAM macro supporting: 1) active-feedback-based voltage-sensing read (RD) to enable 1–8-b programmable vector-matrix multiplication under a low-resistance ratio of the high-resistance state to the low-resistance state in an RRAM array; 2) iterative write with verification to secure a tight resistance distribution; and 3) online RD-disturb detection in the background during CIM. The test chip fabricated in a 40-nm CMOS and RRAM process achieves a peak energy efficiency of 56.67 TOPS/W while demonstrating the eight-bitline hybrid CIM/digital MAC operation with 1–8-b inputs and weights and 20-b outputs without quantization. [ABSTRACT FROM AUTHOR]

Energy-storage-equipped static synchronous compensators (E-STATCOM) are crucial devices in a modern power grid for regulating both the active and reactive power, thereby improving the efficiency and power quality. Current controllers commonly used with E-STATCOM devices include proportional-integral (PI), repetitive, and deadbeat controllers. However, each has application-dependent restrictions and therefore lack the ability to achieve optimal operation. This paper presents a novel hybrid current controller that combines the strengths of the PI, deadbeat, and repetitive controllers. The proposed current controller mitigates cross-coupling effects and provides a wide control bandwidth, thereby ensuring quick, precise, and robust response to system parameter variations. Moreover, the proposed controller provides an efficient disturbance rejection, presenting a holistic solution for enhanced performance of the E-STATCOM. The proposed controller not only overcomes the limitations of individual controllers, but also provides improved current regulation. A comparative analysis of the proposed hybrid controller and a conventional repetitive controller clearly shows the efficiency of the proposed technique. Experimental findings based on a three-phase E-STATCOM demonstrate that the proposed controller significantly minimizes cross-coupling effects and provides approximately $150~\%$ higher bandwidth compared to the conventional controller. In addition, applying the proposed controller shows $3~\%$ and $6~\%$ of total harmonic distortions (THD) during normal system operation and during periodic disturbances, respectively, which is approximately $38~\%$ lower than the THD observed with the conventional controller.

This paper proposes a computationally efficient modulated model predictive current control method for a three-phase neutral-point clamped (NPC) central inverter in the photovoltaic energy system. The proposed control method produces optimal triangular region consisting of optimal voltage vectors through an optimization function analysis. The optimal voltage vectors along with their duty cycles are used in the modulation stage to accomplish constant switching frequency operation, low steady-state errors and fast transient response. The control method accomplishes the system requirements such as the maximum power point tracking, balancing of the DC-link capacitor voltages, grid reactive power control, and grid synchronization. The proposed method is evaluated with a MATLAB/Simulink simulation on an 817 kW system under steady-state and varying solar irradiance conditions. The experimental validation is accomplished with a dSPACE MicroLabBox for a 5 kW system to validate the simulation results.

This paper presents a grid-forming (GFM) voltage-source inverter (VSI) with direct current regulation for a hybrid wind-solar generator, enabling stable operation at very weak grid conditions and under faults. The GFM-VSI interfaces a hybrid wind-solar generator without an intermediate dc-dc conversion to increase the system efficiency. The wind generator comprises a wind turbine with a permanent magnet synchronous generator (PMSG) interfaced by a voltage-source rectifier (VSR). The PMSG-VSR and a solar photovoltaic (PV) array are connected to the GFM-VSI's dc-side. The VSR is responsible for extracting wind power with a power reserve option. The GFM-VSI is implemented to extract solar power with a power reserve capability and support the grid voltage or reactive power. The stable operation of the proposed system is validated under very weak grid conditions, and it is shown that a similar hybrid wind-solar system with grid-following control is unstable under the same weak grid conditions. A complete small-signal state-space model of the proposed hybrid system is developed and analyzed. Nonlinear time-domain simulations and real-time simulation tests verify the model's accuracy and show the proposed system's effective performance under challenging operating scenarios, such as grid uncertainties and faults.

Linear switched reluctance motors (LSRMs) are highly popular due to their simple and robust structure, affordable pricing, and ability to operate at high efficiency. However, a major drawback of these motors is the high ripple force. In this paper, a novel structure for a linear motor with an exceptionally lightweight rotor and a stator with separate poles is presented, making it suitable for use in electric train systems. The proposed system not only significantly reduces force fluctuations but also enables the distribution of force along the length of the moving vehicle, ensuring smooth motion. Moreover, the reliability of the system is enhanced, as the LSRM can continue its motion even in the presence of a fault in one of the phases. In applications with high speeds, the use of a fast controller seems essential, but conventional fast regulators often lack sufficient precision. To address this issue, a new control system is introduced, utilizing a new 12-vector voltage switching table and a current controller. Unlike conventional control methods, the phases firing angle in the proposed system is not fixed. As a result, acceptable performance at different speeds is achieved through an adaptive real-time turn-on position control.

In the realm of medium-power high-volume applications, Switched Reluctance Motor (SRM) drives hold great advantages over other motors. However, the SRM drive must be optimized to reduce cost without compromising the performance for medium power applications. This paper presents a novel SRM drive utilizing a Miller converter-fed SRM motor with a single current sensor, offering a comprehensive control development procedure encompassing system modeling, design procedures, dynamic simulation, analysis, and experimental validation. The SRM is characterized through finite element analysis (FEA) to derive a MATLAB Simulink simulation model, and the conduction angle is optimized for drive efficiency through parametric simulation studies. The linear SRM model for control design is obtained via small signal analysis. Speed and current controllers are designed using the K-factor method, and the efficacy of the proposed drive is rigorously evaluated across various operating modes in MATLAB Simulink. Additionally, a hardware prototype is developed and the digital control algorithm is implemented on the DSP microcontroller TMS320F28379D based on the designed controllers to further assess drive performance. The results obtained validate the robustness and dynamic performance of the SRM drive across variable speed, variable torque, and constant power modes of operation.

In this paper, a super twisting sliding mode control method (ST-SMC) is proposed for an isolated input series output parallel current source converter (ISOP-CSC). The main idea behind the input series output parallel connection is to share the input voltage and output current among the converter cells. Since the input current of each cell has to be identical, the control strategy should be able to provide an accurate phase angle to each cell at the same time. The decentralized control method requires a current sensor for each cell. Therefore, the controller performance can be affected by faults, measurement errors and noises in the slave cell’s current sensor. To overcome this issue, the proposed ST-SMC method generates the phase shift between the primary side switching signals of the master cell. After that, the generated phase shift value is transferred to the slave modules. Thus, the same phase angle value is used for each cell and the current sensor is only needed for the master cell. Furthermore, the proposed method doesn’t need any voltage sensor. The effectiveness of the proposed control method is investigated by experimental studies that are performed on an ISOP-CSC prototype. The results reveal that the proposed method successfully regulates the input current to reference value under both steady-state and dynamic transition conditions.

In this paper, an innovative control method, namely angle-current dual-loop feedback control, is proposed for use with microstepping motors. This method involves adjusting the stator excitation angle and current simultaneously on the basis of the feedback angle of the sensor on the microstepping motor. The proposed method is expected to enhance the positioning accuracy and energy efficiency of stepping motors. The proposed method was tested by implementing it in a microstepping motor control system, which included a core microcontroller unit circuit, dual-H-bridge pulse width modulation drive circuit, current sensing circuit, and angle sensing encoder readback circuit. An algorithm based on the proposed method was developed, and data sampling, storage, and return communication functions, which are convenient for experimental verification, were included in this algorithm. To verify that the proposed method is superior to traditional open-loop control and excitation angle feedback control, a testing platform was used to measure the differences in positioning accuracy and drive power under the three control methods and biased torsion loads. The results indicate that compared with the other two control methods, the proposed control method improves the positioning accuracy and reduces the power consumption of a stepping motor.

The model predictive control increased its prominence in the field of induction machine drives. However, the performance of this strategy depends on the accuracy of the machine model parameters. In order to overcome this deficiency, this paper proposes a robust model predictive current control employing indirect field-oriented control in stationary reference frame using the stator current and the rotor flux vectors as state and stator voltage vector as the input. The control algorithm combines the classical model predictive control with the deadbeat approach in order to calculate the applied stator voltage vector in two components: one element considers the stator current reference, and another employs the disturbances caused due to the parameter errors, which allows to compensate the parameter mismatches in the plant model. The minimized cost function employs the predicted stator voltage vector to select the voltage vector to be applied to the stator terminals of the motor. The control method performance was verified using an experimental test bench analyzing the system steady-state and dynamic actions. In this way, the results corroborate the proposed controller robustness against parametric variations.

The current error is hard to avoid for finite control set model predictive current control (FCS-MPCC) in nine-phase open-end winding permanent magnet synchronous motors. To overcome this problem, an online virtual voltage vector (V $^{3}$) synthesis strategy is proposed in this article. First, a group of V $^{3}$ s without harmonic voltage components are designed as the basic vectors for online synthesis. Then, two adjacent basic V $^{3}$ s and a zero vector are used to synthesize a new V $^{3}$ , which can output arbitrary amplitude and phase angle in the fundamental space. The two basic V $^{3}$ s are directly selected from the located sector of the predicted reference voltage vector (RVV), and their duration ratio can be simply calculated according to the angle of the RVV in the sector. In this way, the zero error is realized between the new V $^{3}$ and RVV. Moreover, an online pulse generation algorithm corresponding to the new V $^{3}$ is proposed, which can calculate the symmetrical pulse sequences in real-time for the multiphase OW drive system without the space vector modulator. Finally, experimental results have verified the effectiveness and superiority of the proposed strategy, in comparison to existing FCS-MPCC in multiphase OW motor drive systems. [ABSTRACT FROM AUTHOR]

This article investigates a decoupled vector current control strategy for grid-tied single-phase nine-level Packed E-Cell (PEC) inverters for vehicle-to-grid (V2G) technologies. The control design is based on a loop shaping approach, where performance specifications such as desired closed-loop bandwidth, closed-loop stability, robustness to pure time-delays in control loops/process, and decoupling between direct ($d$) and quadrature ($q$) axis of control signals are specified in the frequency domain. The control design problem is formulated as a convex optimization problem whose solution results in a multivariable controller in the $dq$ framework. The effectiveness of the proposed control strategy in terms of robust stability, current tracking, and improved total harmonic distortion is evaluated by experimental and simulation results under several case studies. The results also show that the designed controller provides the desired transient response as well as decoupling between the $dq$ output currents. [ABSTRACT FROM AUTHOR]

The data-driven control paradigm allows overcoming conventional troubles in the controller design related to model identifications procedures. Raw data are directly exploited in the control input selection by forcing the future plant dynamics to be coherent with previously collected samples. This article focuses, in particular, on the data-enabled predictive control algorithm. A relevant disadvantage of this algorithm is the fact that the complexity of the online control program grows with the dimension of the dataset. This issue becomes particularly relevant when considering embedded applications, such as the control of synchronous motor drives, characterized by challenging real-time constraints. This work proposes a systematic approach for dramatically reducing the complexity of such algorithms. Such methodology enables real-time feasibility of the constrained version of this control structure, which was previously precluded. Simulations and experimental results are provided to validate the method, considering the current control of an interior permanent magnet motor as test-case. [ABSTRACT FROM AUTHOR]

This article proposes a decoupled fault-tolerant model predictive current control for a dual three-phase permanent magnet synchronous motor with harmonic compensation. The harmonics caused by nonsinusoidal back electromotive force can be well controlled under the open-circuit fault scenario by designing a harmonic closed-loop scheme. First, a decoupled predictive model and fault-tolerant voltage vectors are deduced based on a reduced-dimension matrix, which can eliminate the coupling issues between the harmonic and fundamental subspaces. Afterward, a uniform harmonic-free virtual vector is constructed by rearranging the irregular voltage vectors. More importantly, a virtual null vector is designed in the scheme, where the virtual null vector is effective in the harmonic subspace and has no components in the fundamental subspace. So, the harmonics can be further controlled without affecting torque and flux generation. Extensive experimental results verify the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

In a single-phase charging system of electric vehicles, the current control performance of the single-phase ac–dc factor correction (PFC) converter with a deadbeat predictive current control (DPCC) method is affected by the distorted grid voltage, parameter dependence, and control delay. To tackle these problems, a modified DPCC method is proposed in this article. By introducing a phase adjustment parameter θc, which can be directly calculated according to the required power factor, into the grid voltage feedforward of the current loop, an improved input current control performance with lower harmonic components and higher power factor can be achieved when the converter operates at unity power factor. At the same time, compared with the traditional method, a reactive power compensation function is added in the modified DPCC and a deadtime compensation method is adopted in the modulation. Finally, a 7.8-kW single-phase PFC converter prototype is built to verify the feasibility and effectiveness of the proposed control method. [ABSTRACT FROM AUTHOR]

Two-stage ac–dc converters have hard-switched ac–dc stage followed by soft-switched dc–dc stage. Since devices in the ac–dc stage are switched at low frequency (typically 10–20 kHz), bandwidth of current control loop of this stage is limited (typically less than 2 kHz). This low bandwidth current loop fails to reject current harmonic disturbances arising due to distorted grid voltages, thus necessitating multiple harmonic compensation loops or complex control algorithms for meeting IEEE Std 519-2014. Lack of soft-switching prohibits devices of the ac–dc stage from being switched at a frequency above 100 kHz and thereby attain a bandwidth of around 10 kHz for natural rejection of grid current harmonics. This article proposes an integrated three-phase bidirectional isolated ac–dc converter, where soft-switching operation is extended to devices in ac–dc stage as well. Thus, high bandwidth current loop can be achieved without reduction in efficiency. The proposed modulation scheme decouples ac–dc and dc–dc operations using xor logic. An iterative procedure for design of resonant tank is provided. The integration also leads to 25% fewer devices. Experiments carried out on a 5-kW prototype demonstrate that a low current total harmonic distortion, complying with IEEE standard, can be achieved with good efficiency, even under distorted grid voltages. [ABSTRACT FROM AUTHOR]

Pulsewidth modulated (PWM) current-source converters (CSCs) have been attractive for high-power adjustable-speed machine systems with low carrier ratios. However, the high-order nonlinear model of CSC-fed machine systems, the distinct digital delay from the low carrier ratios, and the cross-coupling caused by coordinate transformation bring great challenges to design of high-performance stator current controller for such kind of machine systems. Firstly, this article derives the discrete-time complex-vector model for the CSC-fed permanent-magnet ac (PMAC) machine system with low carrier ratios considering the distinct digital delay and cross-coupling effect mentioned above. On that basis, the stator current controller is proposed with the modified controller parameters and the compensation technique to improve both dynamic performance and stability of the CSC-fed PMAC machine systems with low carrier ratios. The theoretical analysis and controller design process have been presented in detail to provide a guide for the model derivation and controller design. The experiments on a laboratory prototype are conducted to verify the effectiveness of the developed modeling and controller. [ABSTRACT FROM AUTHOR]

Line-commuted converter-based high-voltage direct current (LCC-HVDC) has undergone extensive development in power systems. Commutation failure (CF) in LCC-HVDC poses a considerable threat to the safe and stable operation of power systems. The coupling of electrical quantities, including DC current, DC voltage, AC voltage, and extinction angle (EA) of an inverter station, is a critical factor that makes CF difficult to suppress effectively. Existing methods adopt preset fixed control parameters and a single control target. The demand of CF recovery typically cannot be satisfied. Control even becomes the driving force of subsequent CF (SCF). Accordingly, a new concept of a fault security region (FSR) in an inverter station under the effects of multi-electrical quantities is proposed. The security range under the coupling effects of electrical quantities is described by the active power and exchanged reactive power of the inverter station. EA, active power, and exchanged reactive power are coordinated through the adaptive regulation of DC current. Thus, SCF can be prevented under the condition that the effect of varying active power and reactive power of LCC-HVDC on a power system is balanced. First, the coupling characteristics of multi-electrical quantities of the inverter station are analyzed. Second, the modeling method for the FSR in the inverter station is proposed. Third, an adaptive current control method is developed by analyzing the evolution characteristics of the FSR. Moreover, a calculation method for the DC current order value is presented. Finally, the effectiveness of the proposed method is verified using the CIGRE HVDC standard system. [ABSTRACT FROM AUTHOR]

A demand-customized selective wireless power transfer system is proposed in this article. Multiple receivers can be recognized based on their positions and the magnetic field in the powering area can be controlled and regulated accordingly. For authorized receivers, the system can simultaneously deliver power to meet different output requirements for different electrical appliances, while for unauthorized ones, they can be shut down independently for energy security, even when they are also in the powering area. Compared to the traditional calculation models for multi-input multi-output systems, the proposed current control algorithm uses a piecewise optimization procedure to simplify the iteration and improve control flexibility. Hybrid-frequency pacing is adopted as the control strategy to further reduce the output fluctuation and raise the system efficiency. An experimental prototype with a 3 × 3 transmitter matrix is established. The system can successfully power two receivers with the same sizes for four different power requirement scenarios, which validates the selectivity and the controllability of the proposed system. [ABSTRACT FROM AUTHOR]

In this article, a novel point of view on grid-forming control with current controlled power electronic converters is presented. A control concept based on the emulation of the combined effect of a virtual synchronous condenser and a parallel-connected virtual current source is proposed. It combines the positive effects of virtual synchronous generator control, such as the provision of inertia, voltage support, the possibility of islanded operation, and good control performance in weak grids, with the benefits of vector current control, such as fast current limitation, improved synchronization properties, and fast setpoint tracking. The proposed control concept is simply a modification of standard vector current control. Therefore, it can be implemented easily on all control platforms with minor software changes. The control method is verified with analytical models, time-domain simulations, and experimental results. [ABSTRACT FROM AUTHOR]

In this article, a sliding mode control (SMC) is applied to regulate the delivered power of a symmetrical six-phase induction generator. For this, the SMC strategy associated to the field-oriented control strategy is used in order to adjust the inner current loops of a squirrel cage six-phase induction generator (SC6PIG). In this way, the control algorithm switches between positive and negative feedback according to the position of the operating point in the phase plane. This technique guarantees the robustness of the SC6PIG in case of the loss of one to three stator phases or machine converter legs. The switching line slope and the initial operating point have been set so that the system starts with a negative feedback, then it continuously switches back and forth to positive feedback in order to maintain the desired trajectory of the system. The simulation and experimental results demonstrate the effectiveness and the robustness of this technique since the delivered power of the SC6PIG presents the same dynamics in healthy or faulty modes with one to two phase losses. [ABSTRACT FROM AUTHOR]

Due to ever-increasing power demand and high renewable energy penetration, the power system's harmonics and voltage unbalancing have become significant power quality issues. In this aspect, because of the multifunctioning ability of the power electronic converters, the grid-connected power electronic converter-based distributed generations are expected to provide desired compensation whenever required. Especially in a weak grid environment, the compensation draws more attention due to constricted coupling between the voltage and current at the point of common coupling as a consequence of high grid impedance. Therefore, this article presents a feedback-based flexible compensation strategy for a weak-grid-tied distributed generation (DG) to enhance the compensation of harmonics and voltage unbalance in the system. The main uniqueness of the proposed work is to seamlessly embed a flexible harmonic loop with a fundamental current control loop for achieving three control targets: voltage harmonic compensation, DG line current harmonic rejection, and voltage unbalance compensation. Achieving control targets require voltage feedback and no need to measure nonlinear load current. In order to execute flexible harmonic compensation (i.e., from voltage harmonic compensation to DG line current harmonic rejection) through the harmonic loop, the proposed strategy generates a harmonic reference from voltage feedback and inherent current feedback. The delay introduced by the harmonic compensators is accurately compensated distinctly to improve the performance of the harmonic loop. The voltage unbalance compensation is achieved through the fundamental current control loop by improving the fundamental positive sequence voltage and decreasing negative sequence components concurrently. To enhance the flexibility between two different targets (i.e., flexible harmonic compensation and voltage unbalance compensation), the harmonic and unbalanced compensations are executed on an individual target basis, subjected to the converter's maximum current and system voltage constraints. The proposed compensation strategy offers better harmonic suppression and voltage unbalance compensation than conventional methods. Because it exactly acts upon modulation signals and directly regulates sequence components and voltage harmonics. Furthermore, the proposed control's detailed design and stability analysis is presented, and its superiority is validated through simulations and real-time experimentations. [ABSTRACT FROM AUTHOR]

This brief presents a high current-efficiency rail-to-rail class-AB op-amp with dual-loop control. Based on the conventional folded cascode op-amp with gain-boost, a dual-loop control strategy consisting of a gain-boost loop and an adaptive output stage current control loop is proposed to achieve bidirectional large load driving capability and high DC gain. Furthermore, the adaptive output stage current control loop achieves class-AB operation with symmetric separate signal paths to the output transistors and high reconfigurability. In addition, the implementation of the constant transconductance ($\text{g}_{\mathrm{ m}}$) rail-to-rail input and slew rate (SR) enhancement circuit is adopted to widen the input voltage range and improve the large-signal transient response. The proposed op-amp is fabricated in a 0.18- $\mu \text{m}$ 5 V CMOS process with an active area of about 0.25*0.27 mm2. Measured results show the proposed op-amp achieves over 122 dB DC gain, 1 MHz gain-bandwidth, and 2.1 V/ $\mu \text{s}$ SR under bidirectional load conditions (100pF and 10k $\boldsymbol{\Omega }$). At 1.5 V and 5.5 V supplies, positive current-efficiency (CE+) are 15 and 1780, negative current-efficiency (CE−) are 37 and 1658, power consumptions are 59.2 $\mu \text{W}$ and 225.5 $\mu \text{W}$ , respectively. [ABSTRACT FROM AUTHOR]

Wireless control of modular multilevel converter (MMC) submodules can benefit from different points of view, such as lower converter cost and shorter installation time. In return for the advantages, the stochastic performance of wireless communication networks necessitates an advanced converter control system immune to the losses and delays of the wirelessly transmitted data. This article proposes an advancement to the distributed control of MMCs to be utilized in wireless submodule control. Using the proposed method, the operation of the MMC continues smoothly and uninterruptedly during wireless communication errors. The previously proposed submodule wireless control concept relies on implementing the modulation and individual submodule-capacitor-voltage control in the submodules using the insertion indices transmitted from a central controller. This article takes the concept as a basis and introduces to synthesize the indices autonomously in the submodules during the communication errors. This new approach allows the MMC continue its operation when one, some, or all submodules suffer from communication errors for a limited time. The proposal is validated experimentally on a laboratory-scale MMC. [ABSTRACT FROM AUTHOR]

To optimize the current-control performance of the linear permanent magnet synchronous motor (LPMSM) drive system, a robust continuous time model-based predictive control for the LPMSM drive systems is proposed in this article. Since the current regulation technology is fundamental for obtaining the precise thrust of the LPMSM, a continuous time model-based predictive control is utilized in the current loop to achieve a fast dynamic response and accurate tracking accuracy. However, the predictive control is a model-based scheme, thus, the model uncertainties and parameter variations will influence the accuracy of stator current. To solve this problem, an augmented internal model disturbance observer is proposed to estimate the lumped disturbances and then compensate to the forward channel. First, the internal model equation of the current loop is constructed by the internal model control principle. Then, a new augmented matrix is constructed by introducing the error variables of the actual current and the internal model current. The observer control law is designed by the state feedback theory, and the observer parameters are optimized by pole assignment method. Finally, the experimental results demonstrate the correctness and effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

This article develops a solid-state transformer (SST), which integrates PV panels and EV chargers together through the open-dc modular multilevel converter (MMC). Different from the well-known MMC, which has a common dc link, the discussed MMC is open-circuited at the dc link so that it should be analyzed from the three-phase viewpoint. The developed SST performs like two parallel-connected cascaded converters, and they are operated with opposite power flow directions. Compared with the conventional SST solution using two separate cascaded H-bridge (CHB) converters, the developed SST has relatively low component count so that it is expected to be of superiority in cost, footprint, and even power density. In addition, the usage of zero sequence voltage in the CHB converter can be replaced by circulating currents in the open-dc MMC so as to greatly reduce the risk of overmodulation. After the thorough power flow analysis on the open-dc MMC and the corresponding controller design, the developed SST is capable of freely working at any operating points with PV panels and EV chargers. Moreover, the developed SST takes the unbalanced grid conditions into account, which is another key contribution of this article. Finally, the balanced and unbalanced operations of the developed SST are both confirmed by the laboratory test results, and furthermore, the dynamic performance of the developed SST considering the time-variant characteristics of PV panels and EV chargers is also demonstrated through the PLECS simulation platform. [ABSTRACT FROM AUTHOR]

The LLC resonant converter is typically adopted in battery charging applications due to its excellent performance in terms of efficiency, power density, and wide input/output voltage regulation. However, this converter is a complex high-order system characterized by a strong nonlinear behavior, featuring large variations of the small-signal gain/phase and pole location depending on the operating point. Consequently, these features pose substantial challenges in designing a closed-loop controller and providing constant dynamical performance over a wide operating range. Therefore, this article proposes a digital multiloop control strategy for LLC resonant converters ensuring constant closed-loop bandwidth and excellent disturbance rejection performance across the complete converter operating region. The control scheme consists of two cascaded voltage and current loops. To design and tune these controllers, a simplified LLC dual first-order small-signal model is proposed. The system nonlinear behavior affecting the current control loop is counteracted by a real-time controller gain adaptation process, which ensures constant control bandwidth. In particular, the adaptive gain values are provided by a static switching frequency lookup table obtained experimentally. Moreover, the steady-state switching frequency value is fed forward at the output of the current loop regulator, providing a further dynamical performance enhancement. The proposed control strategy and the controller design procedure are verified both in simulation and experimentally on a 15-kW LLC converter prototype. The results demonstrate the superior reference tracking and disturbance rejection performance of the proposed control strategy with respect to a state-of-the-art solution based on a proportional–integral regulator. [ABSTRACT FROM AUTHOR]

Power electronics converters are equipped with current controls that protect the converter from over-currents. This protection introduces non-differentiable equations into the power flow problem. The conventional Newton's method is not suitable in that conditions. This letter proposes a fixed-point iteration to overcome this difficulty. The technique is derivative-free, and hence, it can naturally include the saturation given by the converters’ current protection. Exact conditions for convergence and uniqueness of the solution are demonstrated using Banach's fixed point theorem. Numerical experiments in Matlab complement the analysis. [ABSTRACT FROM AUTHOR]