Showing papers on "Three-phase published in 2021"

Single-Source Three-Phase Multilevel Inverter Assembled by Three-Phase Two-Level Inverter and Two Single-Phase Cascaded H-Bridge Inverters

Abstract: Multilevel inverters (MLIs) with reduced number of switching devices and dc sources have compact size, reduced cost, and higher efficiency. This article proposes a transformer-based single-source MLI with reduced number of components and small size transformers. The proposed topology is a hybrid three-phase MLI assembled by a conventional three-phase two-level inverter (TTI) and two single-phase cascaded H-bridge inverters (CHBIs). The proposed MLI has a low ratio of number of active switches to number of output voltage levels. In order to use only one dc source, the CHBIs are cascaded with the TTI through transformers. An individual nearest level modulation (NLM) has been developed to control voltage of this inverter. Moreover, power distribution between its modules is analyzed. The total power of the transformers is 28% of the inverter rated power. Simulation and experimental results of a 13-kVA prototype verify the efficiency of the proposed arrangement.

New Three-Phase Current Reconstruction for PMSM Drive With Hybrid Space Vector Pulsewidth Modulation Technique

Abstract: Current sensing techniques with reduced number of sensors attract a high interest from industry, for the possibility of cost reduction and sampling mismatch reduction. This article puts forward a new single current sensor (SCS) method for a permanent magnet synchronous motor three-phase current reconstruction, with a novel hybrid pulsewidth modulation (PWM) technique introduced. This method is implemented by changing the position of SCS from dc bus to a current branch, and a modified space vector PWM technique is employed to realize the phase current reconstruction. Compared with traditional SCS control methods, the proposed method can relieve the measurement dead-zones at sector boundary region without introducing extra compensation algorithms. Besides, this method can be realized not only with a single hall-effect current sensor but also a single shunt resistor, which further expands the applications and increases the system reliability as well. This method is also available in other motor control with a two-level three-phase PWM voltage source inverter topology. The accuracy and feasibility of the proposed method is validated by the simulation and experimental results.

Fault-Tolerant Control of Dual Three-Phase PMSM Drives With Minimized Copper Loss

Abstract: In this article, a minimum-copper-loss fault-tolerant control scheme is proposed for open-phase fault and open-switch fault of dual three-phase permanent magnet synchronous motor (DT-PMSM) drives. Both the winding configurations of isolated neutral points and connected neutral points are studied in this article. In conventional minimum-copper-loss fault-tolerant control schemes, the constraints of sinusoidal phase currents result in insufficient copper-loss reduction. Different from them, the current references with the theoretically lowest copper losses are first derived and applied for different fault cases of DT-PMSM drives without using any unnecessary constraints in the proposed fault-tolerant control scheme. Thus, all phase currents in the proposed minimum-copper-loss fault-tolerant control scheme are optimized to be nonsinusoidal waveforms. Besides, the copper losses are further reduced by fully utilizing the remaining healthy switch in the faulty inverter leg for the open-switch fault of DT-PMSM drives with the proposed scheme. It has been theoretically and experimentally proved that the proposed fault-tolerant control scheme can reduce copper losses than all existing fault-tolerant schemes for both open-phase fault and open-switch fault in typical two-level voltage-source-inverter-fed DT-PMSM drives.

Direct Phase-Angle Detection for Three-Phase Inverters in Asymmetrical Power Grids

Abstract: This article introduces a signal reformation-based direct phase-angle detection (DPD-SR) technique for three-phase inverters supporting asymmetrical grids. Asymmetries in three-phase systems may happen because of unbalanced three-phase loads, which can lead to the voltage asymmetry at the terminals of grid-tied inverters. The proposed DPD-SR technique can detect the voltage phase angle under asymmetrical conditions. The DPD-SR technique also offers precise and rapid phase-angle detection through signal reformation and trigonometric functions. In essence, the phase-angle detection is directly derived from the trigonometric properties of the line–line voltages, while signal reformation is implemented to handle asymmetrical voltages. The proposed method measures two line–line voltages and detects the phase angle of a three-phase system under both symmetrical and asymmetrical conditions. Unlike classical phase-locked loop (PLL) techniques, DPD-SR does not need any closed-loop proportional-integral (PI) controller, which significantly reduces the complexity and the delay in detecting the phase angle. In this article, the efficacy of the proposed technique is examined in comparison with the state-of-the-art PLLs under asymmetrical conditions through a set of laboratory experiments. The performance of the phase-angle detection is also tested as part of an inverter feeding an asymmetrical grid.

Direct Harmonic Current Control Scheme for Dual Three-Phase PMSM Drive System

Abstract: The performance of model predictive control mainly depends on the accuracy of model and parameters, such as the back electromotive force (EMF) harmonics in dual three-phase permanent magnet synchronous motors (PMSMs) However, the back EMF harmonics would vary with the operation conditions Thus, the parameter mismatches in the harmonic subspace would be inevitable In this article, a direct harmonic current control scheme is proposed to provide further harmonic current suppression under parameter mismatches in the xy subspace First, deadbeat control concept is applied to calculate the reference voltage in the αβ subspace This reference voltage vector is utilized to generate a group of control sets with different voltage vectors in the xy subspace Then, a slide mode control scheme is provided to deal with the inaccurate parameters in the xy subspace The reference voltage vector in the xy subspace is obtained with this slide mode control scheme without the remaining inductance parameters Third, a two-step modulation method and cost function are discussed to further suppress the harmonic currents The control sets generated by deadbeat control are optimized with the cost function Moreover, a switching pattern with fixed switching frequency is proposed in this section Finally, experimental results verify that proposed control scheme could further suppress the harmonic currents

Closed-Form Asymmetrical Duty-Cycle Control to Extend the Soft-Switching Range of Three-Phase Dual-Active-Bridge Converters

Abstract: The three-phase dual-active-bridge (DAB) converter is a promising topology for high-power dc–dc conversion in dc grids and industrial applications. However, the conventional single-phase-shift modulation shows a limited soft-switching range and large reactive currents under light-load operation especially with large voltage variations. This article proposes an asymmetrical duty-cycle control method for the three-phase DAB to extend the soft-switching range and reduce reactive currents by realizing three-phase triangular- and trapezoidal-current-mode operation. Closed-form solutions of the proposed modulation schemes are derived that enable a simple online calculation of the control parameters. The proposed modulation schemes can substantially reduce losses of both power semiconductor devices and the medium-frequency transformer. Thus, the three-phase DAB converter can realize high efficiency over a wide operation range, especially under light-load conditions. Considering the practical implementation, a compensation method is presented to correct the distorted current waveforms caused by the dead time and ensure the desired soft-switching operation. Besides, the power loss imbalance between top and bottom switches induced by the asymmetrical duty cycle is addressed by an active thermal balancing strategy. The effectiveness of the proposed method is validated by simulation results and experiments on a downscaled converter prototype.

Interleaved Model Predictive Control for Three-Level Neutral-Point-Clamped Dual Three-Phase PMSM Drives With Low Switching Frequencies

Abstract: In this article, the control strategy is studied for the neutral-point-clamped three-level inverter-fed dual three-phase permanent-magnet synchronous motor (PMSM) drive with low switching frequencies. An interleaved finite-control-set model predictive control (MPC) scheme is proposed, where a two-layer MPC is designed to solve the multiobjective optimization problem. The two sets of windings in PMSM are sampled and controlled in an interleaved way so that the control delay and the prediction horizon of the drive system are reduced by half. Moreover, the proposed interleaved control scheme increases the equivalent sampling and control frequency from the perspective of the whole drive system, and thus provides better steady-state performance and dynamic performance. With the switching states of one inverter remaining unchanged, the cross traversal of vector candidate sets between two sets of windings is avoided, and the computational burden can be reduced effectively. Experimental results are given to verify the validity and effectiveness of the proposed interleaved control scheme.

DC-Offset Compensation for Three-Phase Grid-Tied SPV-DSTATCOM Under Partial Shading Condition With Improved PR Controller

Abstract: This work deals with a single-stage three-phase grid-connected solar photovoltaic distribution static compensator (SPV-DSTATCOM) under partial shading condition (PSC). During PSC, the SPV-DSTATCOM is connected to the distribution network to solve issues like active current sharing, reactive power control, and harmonic elimination. The conventional Proportional Resonant (PR) controller for SPV-DSTATCOM behaves as a notch filter at resonance frequency with high gain of magnitude and has less DC offset rejection capability. Here, an improved PR based on second-order generalized integrator (IPR-SOGI) control architecture with unity gain at the fundamental frequency and more DC offset rejection capability is presented to address the drawback of the conventional PR controller. The performance of the proposed controller is examined under different loading conditions in steady-state and dynamic conditions. Finally, a comparison between the proposed controller with the conventional PR controller and adaptive PR controller are provided with the experimental validation.

Improved Direct Torque Control Method for Dual-Three-Phase Permanent-Magnet Synchronous Machines With Back EMF Harmonics

Abstract: In this article, we propose a novel switching-table-based direct torque control (ST-DTC) method to eliminate the current harmonics in dual-three-phase permanent-magnet synchronous machines due to the back electromotive force (back EMF) harmonics and voltage vector selection. By employing a novel space voltage vector selection strategy and the optimal action time for different groups of vectors, a novel ST-DTC method is developed. Furthermore, in order to implement standard pulsewidth modulation (PWM) switching sequence, a centralization PWM method for 36 voltage vectors is introduced. The proposed method can effectively reduce the phase current harmonics caused by both back EMF distortion and voltage vector selection, and still reserve the advantages of the conventional ST-DTC, such as fast torque response and simple structure. Its effectiveness is verified by simulations and experiments.

Dynamic-Space-Vector Discontinuous PWM for Three-Phase Vienna Rectifiers With Unbalanced Neutral-Point Voltage

Abstract: Neutral-point (NP) voltage imbalance is an inherent issue of three-level converters The alternating input current distortion is generated by using the conventional discontinuous pulsewidth modulation (DPWM) scheme without NP voltage balance control In this article, the deviation vector between the synthesis vector and the reference vector, which is the fundamental cause of alternating input current distortion under NP voltage unbalance conditions, is revealed Then, by optimizing the subsector division and the switching state sequence, a dynamic-space-vector DPWM (DSV-DPWM) is proposed to eliminate the deviation vector Further, the comparisons of the proposed DSV-DPWM, the conventional DPWM, and an existing triangle carrier-based DPWM (TCB-DPWM), are addressed Finally, a 10-kW prototype was built to verify the effectiveness of the proposed DSV-DPWM scheme Experimental results show that, compared with the conventional DPWM scheme and the TCB-DPWM scheme, both the current THD performance and efficiencies can be significantly improved by the proposed DSV-DPWM scheme under unbalanced NP voltage conditions

Adaptive Hysteresis Current Based ZVS Modulation and Voltage Gain Compensation for High-Frequency Three-Phase Converters

Abstract: This article proposed a systematic approach for the control of three-phase bidirectional zero-voltage switching (ZVS) converters. Combining the adaptive hysteresis-band current control and turn- on delay modifications, ZVS conditions are realized in full line-cycle in all loading conditions like active power, reactive power, light load, and heavy load. The soft-switching resonant period is carefully analyzed, and the current band is designed accordingly, which minimized the additional conduction loss. Meanwhile, a zero-sequence voltage injection control is included in the approach, which compensates the voltage gain by 15% and narrows down the switching frequency variation range. The hardware design approach is also provided including the LCL filter design and a low-cost high-bandwidth high-accuracy current sensor design. A highly integrated 5-kW silicon carbide implemented three-phase ZVS converter prototype with printed circuit board integrated inductors and customized current sensors is designed. All the control is implemented in a single microcontroller unit, which achieves a high electromagnetic compatibility. The designed prototype achieves a total power density of 5.5 kW/L and a peak efficiency of 98.5%. All the analysis and the proposed control approach are experimentally verified on the designed prototype.

Design and control of grid-connected solar-wind integrated conversion system with DFIG supplying three-phase four-wire loads

Abstract: This paper describes the architecture and control of an autonomous hybrid solar-wind system (AHSWS) powered distributed generation system supplying to a 3ϕ-4 wire system. It includes a nonlinear controlling technique for maximum power point tracking (MPPT) used in doubly fed induction generator dependent wind energy translation scheme and solar photovoltaic system (SPVS). In the hybrid model, the DC/DC converter output from the PV system is explicitly coupled with the DC-link of DFIG's back-to-back converter. An arithmetical model of the device is developed, derived using a suitable d-q reference frame. The grid-voltage-oriented vector regulation is required to manage the GSC to keep the steady-state voltage of the DC bus and to adjust reactive power on the grid side. Also, the stator-voltageoriented control scheme offers a stable function of DFIG to regulate the RSC on the stator edge for reactive and active power management in this approach. DC/DC converter is being used to maintain the maximum power from SPVS. A Perturb & Observe method is used for tracing maximum power in an SPVS. The simulation designs of 4.0kW DFIG and 4.5kW solar array simulator are built-in SIMPOWER software kit of MATLAB, it is shown to achieve optimum efficiency under various mechanical and electrical circumstances. It can produce rated frequency and voltage in both scenarios.

Improved Interleaved Discontinuous PWM for Zero-Sequence Circulating Current Reduction in Three-Phase Paralleled Converters

Abstract: Interleaving is widely used in paralleled converters to enhance the output current quality, but subsequent circulating currents could lead to harmonic distortion and extra power losses. This article proposes an improved interleaved discontinuous pulsewidth modulation (IIDPWM) method to reduce zero-sequence circulating currents (ZSCC) in paralleled converters with common dc and ac bus. For two-paralleled converters, optimal vector sequences are selected considering minimal common-mode voltage (CMV) differences, the NTVs principle, and power losses. Furthermore, a novel carrier-based scheme is presented to implement the proposed strategy in a general case with any number of paralleled units. The 180 $^\circ$ carrier phase shift between two unclamped phase legs in discontinuous PWM is first applied for ZSCC reduction. Compared to existing works, the proposed strategy shows a practical value achieving good overall performance in ZSCC, output currents, switching losses, ease of use and scalability. Simulation and experimental results verified the effectiveness of the proposed IIDPWM strategy.

A Common-Mode Voltage Reduction Method Using an Active Power Filter for a Three-Phase Three-Level NPC PWM Converter

Abstract: This article proposes a common-mode (CM) voltage reduction method using an active power filter (APF) and common-mode transformer (CMT) for a grid-connected three-phase three-level neutral-point-clamped (NPC) AC-DC pulsewidth modulation (PWM) converter. The CM voltage can be caused by switching operations of converters and the CM voltage should be reduced because it is one of the main causes of electromagnetic interference (EMI) noises. In this article, the CM voltage of the three-phase converter with the proposed APF is analyzed to explain the CM voltage reduction using the proposed APF. Based on this analysis, the application of a specific PWM method to the three-phase converter for an optimal reduction of the CM voltage is described. Besides, the APF circuit design and its switching method are proposed considering practical problems such as the self-resonance of inductors and the effect of the dead-time on the CM voltage. To prove the effectiveness of the proposed APF on the CM voltage reduction, experimental results for the CM voltage and current are presented in this article. Furthermore, EMI noise measurement results are shown to verify the performance of the noise reduction capability of the proposed APF.

Fault-tolerant Hybrid Current Control of Dual Three-phase PMSM with One Phase Open

Abstract: A fault-tolerant hybrid current control is proposed for dual 3-phase permanent magnet synchronous machines (PMSMs) with one phase open in this paper. The maximum torque control, minimum copper loss control, and single 3-phase mode control are unified in the proposed method, which is a combination of single 3-phase mode control and maximum torque control with different percentages. When the percentage of single 3-phase mode control (k) varies from 0% to 100%, the hybrid current control transitions from maximum torque control (k=0%), to minimum copper loss control (k=50%), and then to single 3-phase mode (k=100%). Therefore, the hybrid current control can be switched among the aforementioned three control methods easily and smoothly. Meanwhile, it can be a mixed-mode with a tradeoff between the maximum torque control and minimum copper loss control, such as the minimum copper loss control for a given torque within the full torque range, which can be achieved by changing k. The smoothness of transition among the maximum torque control, minimum copper loss control, and single 3-phase mode control is verified by experimental results on a prototype machine.

A Modulation Method to Realize Sinusoidal Line Current for Bidirectional Isolated Three-Phase AC/DC Dual-Active-Bridge Converter Based on Matrix Converter

Abstract: A high-frequency link three-phase ac/dc converter based on matrix converter is widely studied because of its small size of passive components, and some modulation methods have been proposed. However, these methods have not achieved zero-voltage-switching (ZVS) and sinusoidal line currents under bidirectional operation with PQ control. This article presents a new modulation method to realize ZVS and sinusoidal line currents under bidirectional operation by accurate control parameters (duty cycle and phase shift) for high-frequency link bidirectional three-phase ac/dc dual-active-bridge (DAB) converter. The converter can realize ZVS by phase-shift-modulation similarly to the dc/dc DAB converter. The line currents have nonlinear characteristics to phase shift and duty cycle. Therefore, the proposed method uses a nonlinear mathematical model to determine the accurate duty cycle and phase shift in order to realize sinusoidal line currents. The accurate duty cycle and phase shift are determined by real-time numerical calculation. Experimental results employing a 1-kW laboratory prototype verify the capability to control active and reactive power with sinusoidal line current. It is confirmed that the proposed method can realize the sinusoidal line current with total harmonic distortion of less than 4% under the bidirectional operating condition at the rated power.

A Narrow-Rail Three-Phase Magnetic Coupler With Uniform Output Power for EV Dynamic Wireless Charging

Abstract: For the EV dynamic wireless charging system, the conventional single-phase magnetic couplers with alternately arranged magnetic poles, such as I-type, S-type, and N-type, have both the advantage of narrow power supply rail and the disadvantage of large output power fluctuation. Although the conventional three-phase meander-type magnetic coupler uses the traveling wave magnetic field to ensure uniform output, a wide transmitter is required in order to provide a large air gap. This article proposes a narrow-rail three-phase magnetic coupler, which realizes the advantages of the above two kinds of couplers by integrating the narrow rail with uniform output power in one coupler. The magnetic field distribution and the working principle of the proposed coupler are illustrated and the receiver structure and the transmitter coil's winding method are optimized. Moreover, the effect of the interphase mutual inductance between different phases in transmitter coils on the system is analyzed. Finally, an experimental prototype was built for the verification. The experimental results showed that the fluctuation of output voltage was within ±2.5% during the dynamic charging process.

Dual Reference Frame Based Current Harmonic Minimization for Dual Three-Phase PMSM Considering Inverter Voltage Limit

Abstract: This article proposes an optimized current harmonic minimization (CHM) approach for dual three-phase permanent magnet synchronous machines (PMSMs) with consideration of inverter voltage limit. The current harmonic model is derived to analyze the dominant current harmonic components in dual three-phase PMSM drives. Dual reference frame (DRF) model is proposed to convert the current harmonics into dc components in the new DRFs, and PI controllers are employed to control voltages to minimize the dc components. This article will prove that current harmonics can be minimized by using the DRF model. Since CHM requires additional voltages, inverter voltage limit must be considered especially at high speeds. Hence, inverter voltage limit is considered to derive the theoretical control strategy, in which minimal copper loss is selected as the design objective to reduce current harmonic with limited voltage. The proposed approach is supported by theoretical analysis and proof, and it does not require inverter voltage and machine parameters. Moreover, the proposed approach is compared with an existing method to show the performance improvement and evaluated with extensive tests on a laboratory prototype under both steady-state and transient conditions.

Harmonic Linearization and Investigation of Three-Phase Parallel-Structured Signal Decomposition Algorithms in Grid-Connected Applications

Abstract: In practice, because of different factors, the supply voltage (especially in the distribution level) almost always has some degrees of imbalance and harmonic pollution. With increasing the level of these power quality issues in recent years, their monitoring and compensation using custom power devices have received much attention. In addition, modern power converter based renewable energy sources are expected to provide some ancillary services to mitigate these power quality issues. These tasks and requirements often involve using a signal processing tool for the online detection of the fundamental sequence components and harmonics of the voltage and/or current signals. The typical choice for this purpose is the discrete Fourier transform as it offers a fast computational speed. It, however, may not be a very attractive solution for applications where the selective extraction of a few frequency components is required as it demands a high computational effort. In such scenarios, using time-domain signal decomposition algorithms is more desirable. Generally speaking, these algorithms are nonlinear feedback control systems, which include two or more dynamically interactive frequency-adaptive filters tuned to concerned frequency components. The complex structure of these algorithms, however, makes them complicated to analyze, especially for those who are not experienced in this field. This article aims to address this difficulty by developing harmonic models for these algorithms and investigating them. To this end, three case studies are considered. Through a harmonic linearization procedure, developing harmonic models for them is shown. The accuracy of these models is then investigated, and performing the harmonic stability analysis using them is demonstrated.

Computation-Efficient Solution to Open-Phase Fault Tolerant Control of Dual Three-Phase Interior PMSMs With Maximized Torque and Minimized Ripple

Abstract: For dual three-phase interior permanent magnet synchronous machines (DT-IPMSMs), open-phase fault (OPF) can result in significant average torque reduction and harmonics in the output torque and speed, which prevent the machines from a reliable and safe operation. Indeed, these adverse effects are mainly due to significant harmonics in the stator currents caused by OPF. This article investigates fault-tolerant control (FTC) of DT-IPMSM under OPF and proposes a computation-efficient FTC solution to maximize the average torque and minimize the fault-induced torque and speed ripples. In the proposed FTC, the open-phase model is first derived, and optimal stator currents are then derived to achieve maximized average torque and minimized fault-induced torque harmonics. The computation efficiency enables the proposed solution, the capability of FTC, under both the steady-state and transient conditions. Moreover, the proposed FTC can eliminate the harmonic current components in the torque contributing frame and, thus, reduce the harmonic losses, and nonlinear inductance maps are employed to consider magnetic saturation. The proposed FTC is compared with existing methods and evaluated with experiments on a laboratory DT-IPMSM under various operating conditions.

Novel Three-Phase Multilevel Inverter With Reduced Components for Low- and High-Voltage Applications

Abstract: In this article, a novel multilevel topology for three-phase applications, having three-level and hybrid N -level modular configurations, enabling low-, medium-, and high-voltage operations, is presented. The proposed topology has several attractive features, namely reduced component count, being capacitor-, inductor-, and diode-free, lowering cost, control-complexity, and size, and can operate in a wide range of voltages and powers. Selected simulation and experimental results are presented to verify the performance of the proposed topology. Further, the overall efficiency of the topology and loss distribution in switches are studied. Finally, the key features of the proposed topology in terms of component count, blocking voltage, and dc-link requirements are highlighted via a comparative study.

High Efficiency Three Phase Interleaved Buck Converter for Fast Charging of EV

Abstract: The electric vehicles (EVs) is the future of transportation to match the demand of the increasing population by reducing dependency on fossil fuels. The EVs are inefficient today due to the requirement of the long charging hour. Therefore, a fast charger is essential for EVs to fulfill the high mileage demand and to reduce time of charging of electric vehicles leading to better performance as compared to EVs today. In a fast-charging station, high power is required to charge the vehicles in a short time, which varies with the charge level of the battery. The proposed work is on a three- phase Interleaved buck converter for fast charging operation. However, the fast charging operation cannot be applied for complete (0-100)% SOC level of the battery, this may reduce the battery life. The algorithm is proposed to operate the phases of interleaved buck converters based on the SOC level of the battery. In the proposed method the operation of the converter below 20% and above 80% SOC level is not at a fast- charging level. The proposed interleaved converter phases (one for low, two for medium, and three for high) are selected for operating the converter at various power levels also maintains high efficiency. Additionally, the converter is operating in constant voltage mode in the fast charging region (20%- 80% SOC). The Coulomb Counting Method is implemented to estimate the SOC level. The preliminary analysis and simulation results are included in this paper.

Current-Fed Isolated Three-Phase Matrix-Type Grid Inverter With Soft-Switching Capability

Abstract: The grid inverters play an important role in renewable energy systems, transferring the DC power to the AC grid. Galvanic isolation is usually needed between the DC source and the grid due to safety reasons and grounding leakage current mitigation. In this paper, a soft-switching isolated grid inverter is proposed based on the current-fed matrix-type configuration. The topology of this converter is composed of a current-fed H-bridge on the side of DC source and a direct matrix converter on the grid side, which are linked by a high-frequency transformer (HFT). The current-fed H-bridge on the primary-side can smooth the DC-source current and control the DC-source current directly. The avoidance of DC-link energy-storage element in the single-stage matrix converter can prolong the system's life. A space-vector-modulation based soft-switching scheme is proposed for the matrix converter on the grid side and a model-based commutation method is adopted in the current-fed H-bridge on the DC side. With the proposed modulation methods, the soft switching can be realized for all devices in the converter. Finally, a laboratory prototype of the proposed converter has been built to verify the effectiveness of the proposed method experimentally.

Offline Compensation Method for Current Scaling Gains in AC Motor Drive Systems With Three-Phase Current Sensors

Abstract: This article proposes an offline compensation method for current scaling gains in the AC motor drive systems with three-phase current sensors. Many articles have been presented about the current scaling gain compensations of inverters. Most of them can be adopted during rotations. Those were studied for two-phase current sensing. Applications, such as elevators and hoist cranes, generally measure three-phase currents directly using three current sensors in preparation for a fault in any one of them. In this article, we present a compensation method for a three-phase current sensing system. This article analyzes the effect of current scaling gain errors on the neutral current that is calculated with measured stator currents. Based on the analysis, a compensation strategy for the current scaling gains is presented. The proposed method is applicable only at a standstill. It can be used for initial commissioning since it works at a standstill regardless of whether the rotor is locked or not. The experiments that demonstrate the validity of the proposed method were carried out in an elevator system as well as a laboratory. The proposed method is simple to be implemented and it requires no additional hardware.

Three-Phase Multilevel Inverter Using Selective Harmonic Elimination with Marine Predator Algorithm

Abstract: In this paper, the marine predator algorithm (MPA) is proposed for solving transcendental nonlinear equations in a selective harmonic elimination technique using a multilevel inverter (MLI). It proved its suitability and supremacy over the other selective harmonic (SHE) techniques used in recent research as it has good precision, high probability of convergence, and improving quality of output voltage. The optimum values of switching angles from MPA are applied to control a three-phase 11-level MLI using cascaded H-bridge (CHB) topology to control the fundamental component and cancel the low order harmonics for all values of modulation index from 0 to 1. Analytical and simulation results demonstrate the robustness and consistency of the technique through the MATLAB simulation platform. The results obtained from simulation show that the MPA algorithm is more efficient and accurate than other algorithms such as teaching-learning-based optimization (TLBO), flower pollination algorithm (FPA), and hybrid particle swarm optimization with gray wolf optimization (PSOGWO). A prototype for a three-phase seven-level cascaded H-bridge inverter (7L-MLI-CHB) experimental setup is carried out. The output of this experimental test validated and supported the results obtained from the simulation analysis. The model of power loss of three-phase 7L-MLI-CHB using the silicon metal-oxide-semiconductor field-effect transistor (MOSFET) is obtained according to the modulation technique. Conduction and switching losses are calculated based on the experimental manufacturer data from the Si-MOSFET using the thermal model of Piecewise Linear Electrical Circuit Simulation (PLECS). Losses and output power are measured at different modulation index values based on the MPA algorithm. Finally, a design of heatsink volume is presented for this design at different temperatures.

A Modified DPWM With Neutral Point Voltage Balance Capability for Three-Phase Vienna Rectifiers

Abstract: Compared with continuous pulsewidth modulation (PWM), discontinuous PWM (DPWM) is a preferred solution in high-frequency Vienna-type rectifiers due to its inherent characteristics of less commutation number and higher efficiency. In this article, redundant clamping modes at the same subsector with opposite effects on the neutral point (NP) voltage are presented. Then, a modified DPWM (MDPWM) scheme is proposed to regulate the NP voltage by using redundant clamping modes. Thus, the NP voltage can be controlled in each switching period to lower the NP voltage fluctuation. The implementation of the proposed MDPWM is given with variable power factors analysis. Further, the switching loss comparison of conventional space vector PWM (SVPWM), hybrid DPWM (HDPWM), and proposed MDPWM is presented as well. A simulation model was built to verify the proposed NP voltage balance with different modulation indices and variable power factors. Finally, a 10-kW prototype is built to evaluate the proposed MDPWM scheme at conversion efficiency and current total harmonic distortion (THD). Experimental results and analysis show that comparing conventional SVPWM and HDPWM, the efficiency of MDPWM is the highest. The THD of DPWM is slightly higher than that of SVPWM, and it is only 2.5% at rated output power.

A Novel Three-Phase Transformerless Cascaded Multilevel Inverter Topology for Grid-Connected Solar PV Applications

Abstract: Nowadays, multilevel inverters (MLIs) are gaining huge popularity for high power transformerless PV applications. Among the traditional MLIs, the cascaded H-bridge (CHB) MLI accommodates lower voltage rated input dc sources, which reduce the voltage stress across the devices. However, the CHB MLI requires multiple PV sources as separate dc-link voltage sources, which create more paths for leakage currents. Therefore, it is a challenging task to deal with the leakage currents in the case of CHB MLIs. In this article, a novel three-phase transformerless inverter topology for grid-connected solar PV application is introduced. This proposed that the inverter topology has six switches per phase, and it has the combined advantages of dc-bypass and ac-bypass circuit configurations. A new modulation strategy is developed for the proposed topology; it is based on a sine triangle pulsewidth modulation technique combined with the dedicated logic functions. The gate pulses for all switches are provided by using these dedicated logic functions. The switching pulses obtained from the dedicated logic functions control all the inverter switches so that the variation of common-mode voltage (CMV) is constant during the inverter operation. This results in reduced leakage current throughout the operation of the inverter. The theoretical analysis, simulations, and experimental results are presented to validate the proposed topology concept for a 3-kVA grid-connected system. Both the simulation and experimental results show that the proposed solution can well attenuate the leakage current; all the results are presented in the article.

Three-Phase Step-Up Multilevel Inverter With Self-Balanced Switched-Capacitor

Abstract: This article presents a new three-phase multilevel inverter with boosting capability for low-voltage applications like electric vehicles and renewable energy sources. This inverter is fed by a single dc voltage source and each phase involves two low-voltage transistors, two high-voltage transistors, two diodes, and two capacitors. Except that the two high-voltage transistors withstand twice the dc input voltage, all other components are rated to the dc input voltage. With phase-disposition pulsewidth modulation, the two types of high- and low-voltage transistors operate in low and high switching frequencies, respectively. This is very beneficial for reducing switching losses and selecting semiconductor switches. The two capacitors are connected in parallel and series alternately with the dc source resulting in high ac output voltage with multiple levels, self-balanced capacitor voltages as well as low voltage ripples. The topology, operation principle, capacitors’ voltage ripples and power loss are analyzed in detail. Both simulation and experimental results are provided to demonstrate the feasibility of the proposed inverter.

Disturbance Observer-Based Finite-Time Control for Three-Phase AC/DC Converter

Abstract: For three-phase AC/DC converters, load disturbances and parameter uncertainties cause large fluctuations of the DC-link voltage, even resulting in system instability. In order to cope with this problem, the disturbance observer-based finite-time control (DOFTC) is put forward in this paper, where the finite-time disturbance observer (FTDO) is designed to fast and accurately estimate disturbances. Subsequently, the stability of the AC/DC converter closed-loop system is analyzed and theoretically proved. Finally, experimental results verify the effectiveness of the DOFTC strategy, where good dynamic and steady-state performance is achieved under load disturbance and parameter uncertainties. Compared with the enhanced state observer-based sliding mode control (ESO-SMC) and adaptive control method, the proposed DOFTC method not only reduced the fluctuations of the DC link voltage by at least 55% but also improved the transient response.

Integrated Magnetics Design for a Three-Phase Differential-Mode Rectifier

Abstract: In this article, the design methodology of integrated magnetics (IM) for a three-phase differential-mode Ĉuk rectifier (DMCR) is outlined The design and optimization of the IM are so achieved such that the inductor current ripple, total harmonic distortion of the input current, and magnetics loss are optimized without compromising the stability of the DMCR The optimization and design of the IM are conducted using the Maxwell and SaberRD software tools, and subsequently, the results are compared with a plurality of other IM structures for performance comparison Finally, the experimental hardware for the DMCR comprising the optimized IM is fabricated to validate its performance and compare it with a DMCR fabricated solely using discrete magnetics