Abstract: This paper proposes a model predictive control based on three voltage vectors for an interior permanent-magnet synchronous motor in a rotating reference frame. The proposed method can obtain the reference voltage vector quickly by predicting only one voltage vector during one sampling period using the characteristics of the deadbeat control. In addition, to obtain better steady-state performance, the optimal vector duration ratios can be obtained from the cost function to minimize the error between the predicted reference voltage vector and the synthesis vector by using the switching sequence relationship of a symmetrical three vector, which is different from applying a single voltage vector in the conventional finite-control-set model predictive control (FCS-MPC). To verify the proposed method, the experimental results are compared with the conventional FCS-MPC and two-vector-based MPC.

Abstract: Conventional model predictive control (MPC) suffers from unfixed switching frequency, heavy computational burden, and cumbersome weighting factors’ tuning, especially for multilevel inverter applications due to a large number of voltage vectors. To address these concerns, this article proposes multiple-voltage-vector (MVV) MPC algorithms with reduced complexity and fixed switching frequency for T-type three-phase three-level inverters. First, MMVs are adopted during each control period, and their execution times are set according to the predefined cost functions. Second, weighting factors for balancing the neutral point (NP) voltage in the cost function are eliminated by utilizing redundant voltage vectors, which simplifies the control implementation. Third, through mapping the reference voltage in the first large sector, the calculation complexity for the execution times of voltage vectors in different large sectors becomes much lower. Finally, main experimental results were presented to validate the effectiveness of the proposed algorithms.

Abstract: This letter proposes a simplified modulation strategy for the open-end winding permanent-magnet synchronous motor (OW-PMSM) system with common dc bus under the open-phase fault condition, with the suppression of the circulating current. Based on the analysis of the voltage distribution of the OW-PMSM under the open-phase fault, a phase-shifted stationary coordinate system is proposed and applied to synthesize the reference voltage. In the proposed modulation process, the duration time of the two selected orthogonal voltage vectors is directly obtained and both sector identification and calculation of trigonometric function can be avoided. Furthermore, the arrangement of switching signals is achieved universally according to the switching states of the selected voltage vectors. Thus, the proposed modulation scheme can be greatly simplified, compared with the conventional strategies. Moreover, the current controller with low bandwidth is applied to suppress the circulating current, considering its effect on the currents in the synchronous rotating coordinate system. The performance of the proposed scheme is validated experimentally in an OW-PMSM system with a common dc bus under the open-phase fault.

Abstract: Model predictive control (MPC) is considered as a promising control strategy for power electronic converters and drive systems due to its merits of simplicity, fast-dynamic response, and multi-variable control flexibility. However, the variable switching frequency and the large computational burden represent serious problems for applying MPC in high-power multi-phase converters and drive systems. This article introduces a low-complexity model predictive current control (MPCC) for five-phase permanent magnet synchronous machine (PMSM) with constant switching frequency based on the deadbeat (DB) principles. To avoid the full enumeration process, the proposed method calculates the reference voltage vector using the DB technique, considering one-step delay compensation. The information of the reference voltage is used to select the best approximation for the reference voltage from the enhanced control set with virtual voltage vectors (V3), which eliminate the third-harmonic phase voltage and phase current components. Moreover, the optimal duty ratio is calculated to fit the selected voltage vector on the reference voltage vector. The proposed control strategy is compared with three existing MPC techniques. The effectiveness of the proposed MPCC strategy is validated using MATLAB simulation and hardware-in-the-loop results.

Abstract: A simple real and reactive power (P-Q) control method based on synchronous reference DQ-axis frame theory for a grid-connected AC microgrid has been proposed in this paper which was validated using real time simulation tool real time digital simulator (RTDS). The proposed control method consisted of two control loops where proportional integral (PI) controllers have been used at the outer real and reactive power control loops to produce reference d-axis and q-axis currents respectively. Then, dq frame currents are controlled in inner closed loop using PI controllers to produce the reference voltage for generating appropriate control signals. The effectiveness of the proposed P-Q controller has been verified for the cases like load change, solar irradiation change and by changing both solar irradiation and load. Outcome of the simulation study has demonstrated the efficacy of the proposed DQ-axis synchronous reference frame based P-Q controller for real-time operation of grid-connected AC microgrid.

Abstract: In this article, a computation-efficient model predictive control (MPC) is proposed to eliminate common-mode voltages (CMVs) of three-phase five-level active neutral-point-clamped (3P-5L-ANPC) converters. Originated from the CMV analysis of the 3P-5L-ANPC with all possible 125 possible voltage vectors, only 19 voltage vectors that generate zero CMV are adopted as the candidate voltage vectors for the MPC. The best voltage vector from the candidate voltage vectors is selected to track the current references. Then, appropriate switching combinations of the selected best voltage vector are determined to effectively balance the flying and dc-link capacitor voltages without any additional hardware components. Furthermore, the proposed MPC only chooses five candidate voltage vectors involving in MPC optimization according to the location of the reference voltage vector, which significantly alleviates the computational burden. Finally, the effectiveness of the proposed MPC in terms of the steady-state and dynamic performances is validated by simulated and experimental results.

Abstract: In significant cases, the generated voltage needs to be step-up with high conversion ratio by using the DC-DC converter as per the requirement of the load. The drawbacks of traditional boost converter are it required high rating semiconductor devices and have high input current ripple, low efficiency, and reverse recovery voltage of the diodes. Recently, the family of Multilevel Boost Converter suggested and suitable configuration to overcome the above drawbacks. In this article, hybrid DC-DC non-isolated and non-inverting Nx Interleaved Multilevel Boost Converter (Nx-IMBC) is analyzed in Continuous Conduction Mode (CCM) and Discontinuous Conduction Mode (DCM) with boundary condition and investigated in detail. The Nx-IMBC circuit combined the features of traditional Interleaved Boost Converter (IBC) and Nx Multilevel Boost Converter (Nx-MBC). The modes of operation, design of Nx-IMBC and the effect of the internal resistance of components are presented. The comparison study with various recent DC-DC converters is presented. The experimental and simulation results are presented with or without perturbation in input voltage, output power and output reference voltage which validates the design, feasibility, and working of the converter.

Abstract: DC microgrid is becoming popular because of its high efficiency, high reliability and connection of distributed generation with energy storage devices and dc loads. The main objective in the dc microgrid is to keep the dc bus voltage constant and equalise per unit current sharing among converters. The conventional droop control is used to equalise per unit current sharing similar to reactive power sharing in an ac microgrid. Nevertheless, the problem in conventional droop control is that equal current leads to a reduction of dc bus reference voltage and voltage regulation becoming unequal across each node due to unequal line resistance drop. The proposed controller works on adaptive droop and voltage shifting technique, which equalises the current sharing whether line resistances are similar or not and controls each output voltage to follow the respective bus reference voltage. The isolated dc–dc converters are used to simulate and validate the proposed control technique.

Abstract: To enhance the steady-state performance of the virtual-vector-based model predictive current control (VV-MPCC) for a five-phase flux-switching permanent magnet motor, an improved multi-vector-based MPCC (MV-MPCC) method with geometric solution is proposed and investigated in this article. The desired voltage is employed to preselect voltage vector candidates and provide a guidance for the geometric division of a sector. According to the link between the reference voltage and the division, the optimal voltage vectors are determined and their duty ratios are obtained by projection method. Compared to the conventional MV-MPCC method using derivative method, the proposed geometric MV-MPCC method employs the desired voltage to quickly determine the voltage vectors and the corresponding duty ratio, which not only alleviates computational burden but also favors for more intuitive implementation. Finally, the effectiveness of the proposed method is verified by experiments.

Abstract: This paper presents a new global maximum power point tracking (GMPPT) technique for the photovoltaic (PV) array under uniform as well as non-uniform solar irradiance. The proposed method uses the I–V characteristic of the PV array to track the global peak. The proposed intelligent technique is based on the computation of settling time of the PV voltage to track the reference voltage given by the GMPPT algorithm. The computed settling time information is used to distinguish between the current source region and voltage source region of the PV array operating point. Thus, it is possible to identify the change in the region of operation, which is utilized to detect the presence of the local peak. After all local peaks are tracked, the GMPPT algorithm sets the reference operating voltage corresponding to the global peak. The given algorithm skips the settling of PV voltage to reference voltage when the operating voltage lies in the current source region during the global peak tracking. This helps in fast tracking of global peak. Furthermore, it does not require any complex mathematical operations like division which makes the proposed algorithm simple to implement. The performance of the proposed algorithm is further verified using both MATLAB/Simulink and experimental results.

Abstract: This paper proposes an extended-state-observer-based distributed robust secondary voltage and frequency control for an autonomous microgrid (MG) with inverter-based distributed generators (DGs) considering the uncertainties from models and measurement noise. The MG is considered as a multi-agent system where each DG is defined as an agent and its controller only requires its own information and the information of its neighbors, but each DG obtains noisy measurements of the states of itself and its neighbors easily due to stochastic noise. Therefore, in this paper, an extended state observer is employed to estimate the accurate state information of each DG, which is significantly influenced by measurement noise. Furthermore, the distributed controllers based on a fast terminal sliding mode surface and an adaptive super-twisting algorithm are designed to track the voltage reference and to fasten the convergence rate against disturbances and uncertainties caused by parameter perturbation. Moreover, the distributed frequency controllers are also designed to restore the frequency and to guarantee the accurate active power sharing without power information of DGs. Finally, the effectiveness of the propose control strategy is illustrated by the simulation of an autonomous MG in MATLAB/Simulink.

Abstract: Digital power management systems allow power converters to operate with multiple changes in voltage reference. This asks for a new paradigm that shifts from achieving faster response to achieving best efficiency during multiple transients, with transient being eventually time constrained. State-space-based design of the control system fits perfectly this goal, since it is a time-domain design tool. It can further be enhanced with a linear quadratic regulator (LQR) optimization, configured with converter loss equation as cost function. The LQR mathematics guarantees a solution to the algebraic Riccati equation that produces the best system efficiency for the converter system during multiple transients. This article documents the design of the LQR control system having converter loss as a cost function and demonstrates the advantages of this method. The closed-loop control software yields very simple, running with a 250 kHz sampling frequency capability on a general use Microchip microcontroller platform. While a loss reduction of 2.5% is demonstrated by experiment in our setup, the advantage depends on the actual system work profile.

Abstract: Nearest-level control (NLC) is a popular technique used in modular multilevel converters (MMCs) with a large number of submodules (SMs) owing to the NLC's flexibility and ease of implementation. However, in medium-voltage applications, MMCs contain a relatively low number of SMs, and the drawbacks of the NLC methods emerge, wherein the poor quality of output voltages and currents result in high total harmonic distortion, large ripples in SM capacitor voltages, and unsuppressed circulating currents. Several NLC methods have been proposed to handle these problems, but they do not satisfy all the control objectives simultaneously. This paper proposed a modified NLC capable of enhancing the output quality of MMCs with low number of SMs without deteriorating the control objectives. Unlike previously reported NLC methods, instead of directly calculating the numbers of SMs from the upper and lower arm voltage references, the difference and total number of SMs are obtained from the output voltage reference and circulating current control, respectively. Hence, the numbers of SMs in the upper and lower arms are acquired by simply solving a system of first-order two-variable equations. The simulated and experimental results for a single-phase MMC system were used to verify the appropriateness and effectiveness of the proposed modified NLC method.

Abstract: This paper introduces an efficient strategy to improve the voltage quality of sensitive loads with the optimal utilization of a dynamic voltage restorer (DVR). Traditional control strategies mainly focus on the voltage compensation stage to reduce the voltage rating of the DVR or minimize the required capacity of the energy storage device. In addition, the phase jump correction in the early stage of the compensation has attracted more attention as well. In reality, phase jump issues may occur in the initial and final stages of compensation, and they must be avoided for most loads, but few works focus on how a DVR can smoothly exit the system after the fault elimination. With the main objective of mitigating the phase jump in the load side voltage while improving the overall sag compensation time, this paper demonstrates that: 1) based on energy-optimized compensation strategies, the proposed approach aims at completing the smooth transition of the transient process during the voltage compensation and recovery stages and ensuring effective linkage from the former to the latter and 2) the mode operation boundaries in the two stages are derived and compared, and the updated procedure of a new injected reference voltage is activated to prevent the system from going outside its operating limits. Furthermore, the operation logic and the overall control scheme are elaborated, which ensure that the proposed approach preserves superior controllability to provide flexible voltage support. Finally, a combination of simulation and experimental results is used to validate the performance of the proposed method.

Abstract: For the open-winding permanent-magnet synchronous generator system with a common dc bus, in order to improve the steady-state control performance of conventional prediction control and simultaneously reduce the calculation burden, a zero-sequence current suppression method based on the prediction of three-dimensional reference voltage is proposed in this article. First, the voltage vector used by prediction control is extended from the plane to the three-dimensional (3-D) space. The voltage vectors of two converters are analyzed and predicted under the 3-D space. Moreover, to improve steady-state performance, two voltage vectors are applied in one control period, and the voltage selection principle that determines candidate vectors is presented. Finally, experimental results test the effectiveness of this method.

Abstract: The phase-shifted-carrier (PSC) technique is preferred for multilevel converters in medium-voltage applications with low submodule (SM) number. This technique can elevate the equivalent switching frequency resulting in low total harmonic distortions. However, for half-/full-bridge hybrid modular multilevel converter (MMC) with boosted modulation index, the conventional PSC method is invalid due to the asymmetric voltage reference wave. The SM capacitor voltages deviate from the rated value and harmonics below equivalent switching frequency appear in the arm and equivalent ac voltages. This paper introduces an improved PSC technique with a capacitor sorting algorithm to overcome this problem. The negative part of the reference wave is turned over and then multiplied by a correction factor. The angular displacement for triangular carriers between the upper and lower arms is determined by the parity of the half-bridge number per arm. With the proposed method, the capacitor voltages are balanced and the ac voltage of MMC has the lowest harmonic distortion. Double-Fourier analysis for the proposed technique is carried out, and harmonic characteristics are revealed. The experimental results validate the correctness and feasibility of the improved PSC technique for hybrid MMC with boosted modulation index and asymmetric reference wave.

Abstract: Hierarchical linear control scheme is widely used in ac microgrids. However, its transient response is slow and parameter tuning is time-consuming. Finite Control Set-Model Predictive Control (FCS-MPC) strategy has desired dynamic performance. Nevertheless, it requires an additional sensor to measure the inductor current. This article aims to mitigate these problems by introducing an improved FCS-MPC strategy for paralleled Voltage Source Inverters (VSIs). A capacitor current estimator is employed to reduce the extra current sensor in each VSI. The proposed control scheme consists of two loops: voltage reference generation loop and voltage tracking loop. The voltage reference generation loop achieves accurate load power sharing using virtual impedance-based droop control. Thus, communication is unnecessary among parallel VSIs. The voltage tracking loop utilizes a modified FCS-MPC block with capacitor current estimator to regulate the VSI output voltage. In order to verify the concept of the proposed control strategy, an ac microgrid consisting of two paralleled VSIs is implemented in dSPACE DS1202 hardware-in-the-loop platform. Then a single VSI hardware prototype is implemented and tested experimentally. The proposed method has the merits of good extensibility, low system cost and compact structure. Its steady-state performance is competitive with hierarchical linear control, while the transient response is significantly improved.

Abstract: The Grey Wolf Optimizer (GWO) algorithm is a metaheuristic optimization method based on the hunting made by wolves in nature. In this work, the GWO algorithm was proposed for tuning a Proportional-Integral-Derivative (PID) controller parameters for a DC-DC boost converter. DC-DC boost converters are electronic devices widely used for voltage regulation in renewable energies applications, these devices need a controller, commonly a PID controller which needs to be correctly tuned to reduce the error between the reference voltage and the system output voltage. Classical PID controller tuning methods require a mathematical formulation or an empirical system response analysis, bioinspired optimization algorithms are an alternative for system design. This paper presents a performance comparative analysis between the proposed GWO algorithm, Particle Swarm Optimization (PSO) and Genetic Algorithm (GA). The simulation was carried out using MATLAB/Simulink environment, then the tuned PID controller performance was evaluated using the system response analysis to variable load conditions and Root Mean Squared Error (RMSE) between reference and output voltage. Results showed that the proposed GWO algorithm has a lower RMSE compared to PSO and GA, and therefore, it could be an effective method for optimal PID controllers for power converters applications.

Abstract: This paper presents a self-biased subthreshold CMOS voltage reference for low-power and low-voltage applications. To achieve near-zero line sensitivity and high PSRR, a compensation structure utilizing the drain-induced-barrier-lowering (DIBL) effect is proposed to sink a supply dependent current from the output branch of a self-biased CMOS reference, which cancels the bias current’s dependence on the supply voltage due to the DIBL effect. Fabricated in a 0.18- $\mu \text{m}$ CMOS technology, the measurement results demonstrate that the proposed circuit could operate under a minimum supply voltage of 0.34 V and generate a reference voltage of 147 mV, while consuming only 48 pW power. The PSRRs measured at 1 Hz and 10 kHz are −70.6 dB and −50.2 dB, respectively. For 39 measured samples, the mean line sensitivity is 0.019%/V in a supply voltage range from 0.34 to 1.8 V, and the average temperature coefficients before and after trimming are 64.81 and 10.06 ppm/°C in 0 ~ 100 °C temperature range, respectively. The total area of the voltage reference circuit is 0.0332mm2.

Abstract: Grid-connected inverter (GCI) has become the main interface for integrating modern power units, such as distributed energy resources, electric vehicles, microgrids and high voltage direct-current transmission systems. To proceed in this direction, this study presents a novel voltage support control strategy to enhance the reliability and stability of the GCI during unbalanced grid fault conditions. The proposed control strategy simultaneously achieves multiple objectives during grid faults; regulating phase voltages magnitude within pre-defined safety limits, increasing the difference between positive sequence (PS) and negative sequence (NS) voltages, eliminating both active–reactive power oscillations and the DC-link voltage oscillations. Reducing active power oscillations ensure an adjustable control for the DC-link voltage oscillations which result in third-order current harmonic component at the grid side. One of the main contributions to previous studies, reference for reactive power is computed online based on resistive–inductive grid impedance model and reference voltage sequences for the grid support. Another important contribution to existing studies is to supply both the active and reactive powers to the utility grid and load. Detailed mathematical analyses are performed to theoretically describe the behaviour of the proposed control strategy. A comprehensive set of results is presented to confirm the theoretical solutions.

Abstract: Electric vehicles (EVs) and hybrid EVs need stacked lithium-ion (Li-ion) cells to achieve the required high voltage (HV). Cell monitoring and balancing in a stackable battery system is necessary to compensate for accumulative discharge mechanisms and keep the individual cells in the same state of charge. In this article, an integrated circuit consisting of a 12-bit successive approximation register (SAR) analog-to-digital converter is designed to measure, monitor, and balance Li-ion cell voltages with a measured accuracy of $\pm$ 7 mV. These stacked cells are compared simultaneously with a reference voltage to balance the cells. Balancing switches for charging/discharging of the cells are integrated within the circuit to support a balancing current of up to 100 mA, which reduces the number of external components for balancing significantly. The circuit supports both active and passive balancing. A synchronous voltage mode level shifting circuit is implemented for communication between the stacked integrated circuits (ICs) to eliminate external components. Internal linear drop outs (LDOs) (3 and 5 V) power most of the blocks in the IC. The design is fabricated in HV 0.35 $\mu$ m complementary metal oxide semiconductor (CMOS) technology and found to consume a quiescent current of 17 $\mu$ A.

Abstract: This article investigates the nonlinear behavior of the conventional voltage feedback flux-weakening control, i.e., the voltage magnitude feedback control on the nonsalient permanent magnet synchronous machine, and proposes an adaptive control parameter tuning method for the voltage feedback controller. Due to less voltage margin in the flux-weakening region, the current dynamic performance is degraded. This issue is more serious when the system operates in the overmodulation region and could affect the system's stability. Based on the designed voltage feedback controller, the system performance in the flux-weakening and overmodulation regions is further improved by utilizing the current and voltage reference modifiers. Consequently, the system can operate well in both linear and overmodulation regions with the specified scaling factor, which is beneficial to general-purpose applications. The viability of the proposed method is demonstrated by the experimental results.

Abstract: We present the electrical and radiation characterisation of the most recent prototype of the bPOL12V DCDC converter, a stacked assembly of two ASICs inside a QFN32 package. The use of a reference voltage generator chip in 130nm CMOS on top of the ASIC integrating the control system and power train enables improved radiation tolerance and the trimming of the output voltage during the production phase. Prototype samples have been exposed to X-rays, proton and neutron irradiations, as well as subject to long-term electrical stress to evaluate their reliability in the application. The results confirm that only a few minor modifications are required to achieve production readiness.

Abstract: With the photovoltaic (PV) penetration increases in dc microgrid, the traditional PV converters with maximum power point tracking (MPPT) control, which are equivalent to current sources, can hardly meet the needs of coordinated operation. The PV converter should operate in both MPPT and constant voltage control (CVC) modes. When the operation mode changes, the PV converter needs to switch between current and voltage sources. Inevitably, the bus voltage instability would be caused. This paper presents a novel switching strategy for the smooth and seamless operation of the PV converter between MPPT and CVC modes. The PV converter under these two modes is always controlled as a voltage source, and its control variables are both the output voltage of PV arrays. When its operation mode changes from MPPT to CVC, a small offset signal based on DC bus voltage would be introduced to the reference voltage of inner loop of the PV converter, so as to shift the maximum power point (MPP) voltage. Meanwhile in the voltage inner loop, a double integral sliding mode controller (DISMC) is used to improve the performance and anti-interference ability of the PV converter. This method unifies MPPT and bus voltage adjustment strategy without any communication and changing any hardware structure and control parameters. When mode switching occurs, only the reference value of voltage inner loop would be slightly adjusted near the maximum photovoltaic power point, so the seamless transition for PV converter between the two modes can be ensured. Finally, the effectiveness of the mode seamless switching control strategy is demonstrated by the simulation and experimental tests.

Abstract: This work offers a simple and efficient model predictive voltage control strategy with a two-step prediction for improved output voltage control of single-phase inverter used for stand-alone renewable energy systems. The single-phase inverter with output LC filter is used to provide a sinusoidal output voltage, regardless of the arbitrary consumer load profiles. The suggested control algorithm uses the discrete-time model of the inverter and LC filter for two-step prediction of the output voltage for each possible switching state. Then, the control algorithm selects the switching state which minimizes the error between the output voltage and its reference without using any inner controllers or modulators. An accurate extrapolation methodology with reduced computational burden is used to predict the dynamic changes in the output voltage reference. The switching frequency reduction is also attained by considering a simple constraint in the suggested algorithm. Simulation results are presented to verify the feasibility and excellent performance of the suggested controller under linear and nonlinear load conditions, compared to a conventional voltage control strategy based on PI regulators and PWM. Furthermore, experimental tests using a dSPACE system with DS1104 controller have been done to confirm the simulations results.

Abstract: This paper proposes a maximum power point tracking (MPPT) and voltage regulation method based on model predictive control (MPC) for the two-stage grid-tied photovoltaic (PV) system, which can achieve MPPT and output voltage regulation of a PV system simultaneously. The MPPT algorithm based on MPC is implemented in a DC-DC boost converter. The reference voltage at maximum power point is obtained by dual step Incremental Conductance (I&C) algorithm under the rapidly varying illumination intensity, and the MPPT controller only needs to minimize one cost function of PV current, without pulse width modulation (PWM) module. To inject the generated PV power into the grid with high quality, this paper designs voltage regulation controller based on MPC to maintain the output voltage of the PV system at the desired value. The MPC controller outputs the optimal duty signal with the input and state constraints in the inner loop, and the PI controller in the outer loop is designed to improve the dynamic performance. The proposed method based on MPC was demonstrated using the SimPower systems tool in MATLAB/Simulink. Analysis and simulation results for the PV system show possible improvements on the closed-loop performance such as fast response and low overshoot.