Constant Switching Frequency Operation Research Articles

An abc Reference Frame Hysteresis Current Controller for Grid Connected Converter With Constant Switching Frequency Operation

An <i>abc</i> Reference Frame Hysteresis Current Controller for Grid Connected Converter With Constant Switching Frequency Operation

Dual-frequency transmitter configuration for shallow surface electromagnetic detection

In shallow surface electromagnetic detection, the square wave scheme is generally used in conventional transmission systems. Based on frequency-domain electromagnetic sounding theory, high-frequency measurement helps to improve vertical resolution. However, long grounded cable inductance produces severe reactive power suppression at high frequency transmission frequencies, which will reduce detection. To further improve detection accuracy and efficiency, a dual-frequency transmitter configuration is proposed in this article for shallow surface detection. The transmitter simultaneously powers two LC series resonant circuits for the detection of shallow and deep area. Dual-frequency control strategy is adopted, with both bridge arms being provided with constant switching frequency operation. According to the equivalent model of the transmission system, the control of the load branches is independent of each other. The LC series resonant circuit guarantees a wide passband to match long cable inductance that cannot be accurately estimated in advance. Simulations and experimental tests were carried out using this transmitter configuration and control technique. The simulation and experimental results are in general agreement, verifying the feasibility and effectiveness of the proposed dual-band transmitter configuration.

A new integral-synergetic controller for direct reactive and active powers control of a dual-rotor wind system

This paper proposes a new integral-synergetic controller for direct reactive and active powers control (DARPC) for a grid-connected doubly-fed induction generators (DFIGs) in dual-rotor wind power generation applications. The proposed DARPC strategy employs integral-synergetic control (ISC) to regulate the reactive and active powers of the DFIG-based variable speed dual-rotor wind turbine systems. The proposed ISC technique is the contribution of this work, where this strategy is a development of synergetic control and simplicity and robustness are the most prominent features. The main advantages of the proposed ISC-DARPC technique are ease of implement, good dynamic response, simple structure, and constant switching frequency operation. The Matlab software is used to validate the design of the ISC-DARPC technique, and the obtained results are compared with traditional DARPC. In addition, the ISC-DARPC technique is able to fully minimize ripples in both torque and active power during grid voltage imbalance or parametric changes on the DFIG.

An Advanced Shunt Active Power Filter (SAPF) for Non-ideal Grid Using Predictive DPC

The usage of power electronic converters and other non-linear devices is very common in this modern era because of their flexibility in control. However, they inject harmonics into the power system. To deal with the problem, the use of filters has become almost inevitable. Active power filters controlled by direct power control (DPC) have overtaken this responsibility from the passive filters because of their numerous advantages. To deal with the real-world power system grid which is far from the idealized character of being balanced and sinusoidal, the proposed method uses the extended pq theory integrated with the dual second-order generalized integrator (D-SOGI) for the correct estimation of the all-important instantaneous powers. In contrast, the conventional pq theory is used in the existing works, which doesn’t hold in a non-ideal grid. In addition to that, here, for the selection of the switching vector, an advanced and more accurate predictive DPC method which is specifically designed to operate in a non-ideal grid, replaces the static look-up tables used in the previous works. Further, to make the filter designing easier, the proposed method focuses on constant switching frequency operation eliminating the problems arising from variable switching frequency used in literature. The proposed technique is tested in MATLAB/Simulink environment and the real-time system to validate its feasibility.

Wind characteristics analysis and application of ontrol strategy for wind system based on direct power control

This study analyses yearly and seasonal wind speed data recorded over eight years using Weibull distribution function and the direct power control application of a wind chain. The wind potential evaluation was carried out based on empirical model. Results show that, during the warm months the wind speed is uniform, constant and stable. In addition, it has been found that the use of a control strategy was necessary for extracting the optimum power. For this purpose, the second part of this work presents a direct power control (DPC) technique in order to adjust the produced active and reactive powers. The application and performance evaluation of the proposed control system implemented within the d-q reference framework has been exposed and discussed. The system modeling and the control diagram are built under MATLAB software. According to simulation results, the forward power control provides almost sinusoidal input waveform current, constant switching frequency operation, unity power factor regulation and also provides powers decoupling. As shown by simulation results, the suggested control method is efficient.

Fault-tolerant deadbeat model predictive current control for a five-phase PMSM with improved SVPWM

The main drawbacks of traditional finite set model predictive control are high computational load, large torque ripple, and variable switching frequency. A less complex deadbeat (DB) model predictive current control (MPCC) with improved space vector pulse-width modulation (SVPWM) under a single-phase open-circuit fault is proposed. The proposed method predicts the reference voltage vector in the α-β subspace by employing the deadbeat control principle on the machine predictive model; thus, the exhaustive exploration procedure is avoided to relieve the computational load. To perform the constant switching frequency operation and achieve better steady-state performance, a modified SVPWM strategy is developed with the same conventional structure, which modulates the reference voltage vector. This new approach is based on a redesigned and adjusted post-fault virtual voltage vector space distribution that eliminates the y-axis harmonic components in the x-y subspace and ensures the generation of symmetrical PWM pulses. Meanwhile, the combined merits of the DB, MPCC, and SVPWM methods are realized. To verify the effectiveness of the proposed control scheme, comparative experiments are performed on a five-phase permanent magnet synchronous motor (PMSM) drive system.

Analysis of Current Error Space Phasor for a Space Vector-Modulated Indirect Matrix Converter

AC motor drives fed from current-controlled power electronic converters are popular on account of their superior steady-state and transient performance. Hysteresis control is a popular current control technique, which needs modifications to compensate for its demerits. Appraisal of current error as a space phasor for implementing the hysteresis controller is one such modification. Current error space phasor (CESP)-based hysteresis controller for voltage source inverters-fed motor drives are capable of achieving superior dynamic performance. With the modified hysteresis current controller, the drive operates at a constant switching frequency and ensures an optimal switching vector selection. This article presents the analysis of CESP for a space vector-modulated indirect matrix converter (IMC). The modified algorithm for space vector modulation of IMC accommodates for the variations in dc-link voltage since CESP is input voltage dependent. The boundary for the hysteresis current controller is calculated from the computed values of CESP. The time-varying nature of the hysteresis boundary ensures a constant switching frequency operation for IMC. Thus, a CESP-based hysteresis controller is proposed for the vector control of the IMC-fed permanent magnet synchronous machine (PMSM) drive. Experimental results are presented for validating the performance of the proposed controller.

Study on an Improve Finite‐Control‐Set ‐Model Predictive Control (FCS‐MPC) Strategy for a T‐Type Rectifier with Direct Power Control Strategy

Model predictive control has been wildly used in the modern power electronic converter with the advantages of the multi‐objective optimization, no additional modulator is required and small grid current harmonic. However, the switching operation is not constant and higher sampling frequency must be required. A novel direct power control using model predictive control (DPC‐MPC) strategy is presented in this paper, which achieve the optimal vector prediction scheme with constant switching frequency operation. The calculation process is greatly simplified due to the optimal voltage vector generated directly, then, it applied to the control of a three‐phase three‐level T‐type grid converter. A cost function is first built to balance the neutral‐point‐potential voltage. After then, the cost function is updated by considering the delay caused by the calculation, sampling and gate driver. Finally, a comprehensive comparative study with the conventional DPC‐MPC strategy is introduced to verify the superiority of the presented DPC‐MPC. The simulation and experimental results show that the steady and the transient performance of the grid current with the proposed DPC‐MPC control strategy are effectively improved. © 2021 Institute of Electrical Engineers of Japan. Published by Wiley Periodicals LLC.

Modulated predictive current control for a two‐level grid‐connected converter with over‐modulation capability

Modulated model predictive control (M2PC) approaches have been widely investigated owing to their improved steady-state performance and constant switching frequency operation. However, most of these methods either increase control complexity or cannot obtain optimal solutions under certain operating conditions such as lower modulation index and near the boundary of linear and over-modulation regions. To overcome these limitations, this study proposes a new modulated predictive current control technique based on a novel virtual vector synthesis. The optimal duty cycle is obtained by solving the optimisation problem defined by the cost function. To minimise the tracking error of the input current, a simple non-linearity compensation method for the converter is also demonstrated. The experimental results confirm that the proposed technique significantly reduces the steady-state error of the controlled objective and the ripples in the input current without sacrificing the transient performance compared to other existing M2PC methods.

Symmetrical Six-Phase Induction Motor-Based Integrated Driveline of Electric Vehicle With Predictive Control

In this article, an integrated driveline for electric vehicle (EV) is developed by using a symmetrical six-phase induction motor (IM). In propulsion mode, predictive torque control (PTC) is proposed to improve the dynamic performance similarly in charging mode, predictive current control is implemented. The conventional PTC (C-PTC) in propulsion mode generates xy-subspace flux and provides variable switching frequency with a high computational burden. Modified PTC (M-PTC) with only torque and flux as a constraint variable with constant switching frequency operation is implemented. In this method, xy-subspace is eliminated by using synthetic voltage vectors, and the computational burden is also reduced by adopting stator flux monitoring in dq-subspace. The switching sequence with the minimum transition while a digital signal processor (DSP) implementation is feasible due to redundancy in synthetic voltage vectors. In the charging mode, the same high rating driveline inverter is utilized as a rectifier. In this mode, stator windings are reconfigured to provide grid interfacing inductance, while the rotor is maintained in stationary position due to transfer of excitation from torque producing (dq) plane to nontorque producing (xy) plane. This controller also provides a constant switching frequency operation. The comparative analysis, along with experimental results, is provided to validate the effective predictive control during both operating modes.

PWM-Based Optimal Model Predictive Control for Variable Speed Generating Units

This article investigates the dc-link voltage control of an active rectifier that is supplied by a variable speed permanent magnet synchronous generator. This configuration is commonly encountered in gearless wind energy conversion systems as well as in variable speed generating units. The proposed control strategy uses an optimal voltage vector based modulated model predictive control (MPC) to achieve direct power control. The studied scheme combines the advantages of finite control set MPC and control techniques that use pulsewidth modulator. The fast dynamics of the former are obtained during large transients, and the constant switching frequency operation, of the latter, is ensured in steady state. At each sampling instant, all the switching states are evaluated and the two adjacent states that give minimum error in the controlled variables are selected. The duty cycle of each of these vectors is computed through linear combination and appropriately limited for overmodulation. Simulations and cosimulation results presented in this article show interesting results. The control strategy has been developed on a field-programmable gate array control platform and experimental results at steady state are shown, with the aim to demonstrate the computational feasibility of the control strategy.

Constant Switching Frequency Control for CRM Buck PFC Converter

Critical conduction mode (CRM) buck power factor correction (PFC) is widely used in low-power applications because of its several advantages. However, the switching frequency is dependent on the electrical angle of the input voltage, and the variation range of the switching frequency is large, especially at high input voltages. This makes the conducted electromagnetic interference (EMI) spectra appearing great differences and complicates the design of the EMI filter. For this issue, a novel constant frequency control scheme is proposed by varying the on-time of the switch. Compared with the original control, the proposed method realizes a constant switching frequency operation in a line cycle. Consequently, the design of the power devices especially the magnetic components can be simplified. Meanwhile, a higher efficiency and a lower output voltage ripple are achieved. The proposed strategy also yields a higher PF at low input voltages and a lower PF at high input voltages. A 120-W prototype with 90–264-VAC input and 90-V output is built in the lab. The experimental waveforms of input voltage, input current, inductor current, and output voltage ripple, the measured input current harmonic contents, the PF and efficiency curves regarding the input voltage, and the common-mode (CM) and differential-mode (DM) noises’ spectra of the converter are presented to show the validity of the proposed scheme.

Novel Current Controller Based on MPC With Fixed Switching Frequency Operation for a Grid-Tied Inverter

In this paper, a novel controller based on the predictive technique has been introduced for a neutral-point-clamped grid-tied inverter. The aim of the developed method is to achieve a constant system switching frequency operation. The proposed method generates the voltage vector by nullifying the derivative of the cost function of a finite-set model predictive controller. The developed controller takes in action of injecting the desired grid current while a closed-loop space vector modulator regulates the capacitors voltages. A comparative study with a similar model predictive algorithm with constant switching frequency (MPC-CSF) is introduced and discussed in terms of computational complexity. Experimental results are provided to verify the performance and robustness of the new method over MPC-CSF with its ability of injecting a very low total harmonic distortion to the grid with almost unity power factor during normal and transient operations.

Bidirectional Power Converter for Solar Grid Interface Applications: An Experimental Investigation

Switching control of a current controlled grid integrated inverter using three-level neutral point clamped (NPC) inverter is investigated in this paper. The proposed scheme uses both the hysteresis current control (HCC) and carrier based switching schemes to improve the low switching frequency operation. To overcome the problems associated with current control techniques a simple carrier injection method is proposed in this paper. This current control method uses a high frequency triangular carrier injected to the current tracking error. The triangular carriers are chosen with minute amplitude comparable with current tracking error. This will enhance the switching frequency and stabilize the NPC inverter. This will ensure constant switching frequency operation of the grid interface inverter (GII). A comprehensive modeling of GII is carried out to study the stability of the system. A comparative study of switching frequency stabilization is presented. To verify the proposed current controller a prototype setup is developed. Analytical studies with experimental results of the proposed techniques are presented to show the superiority of results.

ZVS Modulation Scheme for Reduced Complexity Clamp-Switch TCM DC–DC Boost Converter

DC–DC boost converter zero-voltage-switching (ZVS) modulation schemes such as triangular current mode (TCM) offer a highly efficient operation but suffer from large switching frequency variations, which are complicating the EMI filter design and the digital control. As a solution, a tri-state boost converter operated in ZVS mode, referred to as clamp-switch TCM (CL-TCM) operation can be introduced, which allows to limit the switching frequency variation significantly. This paper presents two variations of the CL-TCM boost converter with reduced number of active switches in the circuit, which are suitable for high input-to-output voltage conversion ratios. In addition, the ZVS modulation schemes, its limitations, the converter design and the controller implementation are presented and analyzed in detail for both converter topologies. The timing calculations for the switching signals are provided for two operating modes, either offering a minimized switching frequency variation and minimized RMS inductor current or a constant switching frequency operation, which in turn comes at the expense of an increased RMS inductor current. The ZVS operation and the operating modes are experimentally verified using a hardware prototype.

Review of recent advancements of direct torque control in induction motor drives – a decade of progress

Since the invention of direct torque control (DTC) in later 1980s for alternating current (AC) motor drives, it has undergone many modifications to improve the control strategy. This study provides a comprehensive review of recent advancements of DTC of induction motor (IM) for the past one decade. Strategies adopted to improve the performance of DTC based on switching table, constant switching frequency operation, intelligent control, sensorless control and predictive control are extensively discussed with its key results and algorithms.

Analysis and Experiments on a Single-Inductor Half-Bridge LED Driver With Magnetic Control

This paper presents the analysis and experiments of a variable inductor (VI) based LED driver for dc grid lighting applications. The proposed driver requires only a series inductor and a transformer as major components to drive the LED lamp from a half-bridge inverter. By introducing a VI as the series inductor, the LED current can be controlled independently from any other parameter, which makes it possible to drive and regulate several LED branches from the same half-bridge output. Other advantages of the proposed converter include inherent open-circuit and short-circuit protections, zero-voltage switching for the bridge transistor and zero-current switching for the output rectifier diodes, simple dynamics, possibility of analog and pulse width modulation dimming, constant switching frequency operation, and high efficiency. The converter is thoroughly analyzed and modeled for both steady-state and dynamic operation. As another novelty of this paper, the dynamic response of the VI has been studied and taken into account to obtain the complete transfer function of the VI-controlled system. In addition, some housekeeping issues that usually arise when dealing with VI, e.g., how to drive the VI bias winding, are solved in this work. Experimental results provided from a 50 W laboratory prototype demonstrate the correctness of the performed analysis and the good possibilities of the proposed converter.

Time-Varying and Constant Switching Frequency-Based Sliding-Mode Control Methods for Transformerless DVR Employing Half-Bridge VSI

This paper presents time-varying and constant switching frequency based sliding-mode control (SMC) methods for three-phase transformerless dynamic voltage restorers (TDVRs) which employ half-bridge voltage source inverter. An equation is derived for the time-varying switching frequency. However, since the time-varying switching frequency is not desired in practice, a smoothing operation is applied to the sliding surface function within a narrow boundary layer with the aim of eliminating the chattering effect and achieving a constant switching frequency operation. The control signal obtained from the smoothing operation is compared with a triangular carrier signal to produce the pulse width modulation signals. The feasibility of both SMC methods has been validated by experimental results obtained from a TDVR operating under highly distorted grid voltages and voltage sags. The results obtained from both methods show excellent performance in terms of dynamic response and low total harmonic distortion (THD) in the load voltage. However, the constant switching frequency-based SMC method not only offers a constant switching frequency at all times and preserves the inherent advantages of the SMC, but also leads to smaller THD in the load voltage than that of time-varying switching frequency-based SMC method.

Sliding Mode Fixed Frequency Current Controller Design for Grid-Connected NPC Inverter

In this paper, a fixed-frequency pulsewidth modulation (PWM) based on sliding-mode current controller is designed and applied to a utility interface three-phase/wire/level neutral-point-clamped inverter. The proposed design methodology of the sliding-mode control is based on a constant switching frequency operation and on Gao’s reaching law that allows chattering compensation. The aim of the controller is to inject a controlled active power from renewable energy sources into the grid while controlling the power factor and minimizing supply current harmonics. Moreover, the dc-link voltages across the split capacitors are controlled with a simple proportional–integral (PI) regulator. Experimental results show the advantages of the proposed control algorithm in terms of fast dynamic response, low voltage ripple on the dc bus, low current Total Harmonic Distortion, and robustness toward external perturbations from the dc and ac sides; moreover, a comparison with a PWM–PI current controller is presented.

Grid connected three‐phase multiple‐pole multilevel unity power factor rectifier with reduce components count

This study presents a simple design and cost-effective rectifier topology based on five-level multiple-pole structure. Better efficiency and low grid current total harmonic distortion is achieved with the constant low switching frequency operation. The proposed rectifier topology consists two set of VIENNA rectifiers to form a five-level input characteristic which is known as five-level/multiple-pole multilevel unity power rectifier (5L-M2UPFR). Observer techniques are designed for the proposed in-phase quantities carrier-based average current control scheme for the rectifier. Hence, unity power and input current shaping is achieved with the reduced sensor measurements. In addition to that, a proportional+resonance controller is implemented in the grid voltage observer to achieve dynamic response and better tracking under unbalanced grid condition.