Constant Switching Frequency Research Articles

MTPA Associated DTC Methodologies for Enhanced Performance and Energy Savings in Electric Vehicle Mobility With Induction Motor Drive

This article presents two new energy-saving control methodologies for induction motor (IM)-based electric vehicles (EVs) that exploit advantages from both direct torque control (DTC) and maximum torque per ampere (MTPA) control. While the first variant implements IM control through hysteresis controllers, the second variant employs a modulator to achieve constant switching frequency. For both variants, a flux observer is carefully designed to minimize the effects of IM parameter variations. Detailed torque ripple and power loss characteristics of IM drive controlled with the envisaged MTPA-DTC variants are also presented. The proposed techniques clearly show a reduction in current drawn by the EV system in comparison with the existing techniques. The IM drive is tested for fast acceleration and also the European Union (EU) Urban Drive Cycle to assess the advantages offered by the proposed control techniques. Advantages obtained, such as simple and fast implementation, high dynamic performance, reduced stator current, power loss leading to improved IM efficiency, and reduced steady-state torque ripple followed by energy savings obtained in the EV, are presented in the article, which can greatly benefit EV applications.

Generalized Predictive Direct Power Control With Constant Switching Frequency for Multilevel Four-Leg Grid Connected Converter

This article proposes a novel generalized predictive direct power control (PDPC) with a constant switching frequency for a multilevel four-leg (4L) grid connected converter (GCC) diode clamped converter (DCC). A new predictive power model for 4L-GCC is developed in which the proposed PDPC can operate with a constant switching frequency without any modulation stage. During each switching period, four appropriate switching vectors are selected and applied using precalculated switching times. Moreover, these appropriate switching vectors are selected only from one sector, and a new proposed approach to calculate the switching times is proposed and generalized for any level of 4L-DCC. The proposed PDPC for the multilevel 4L-GCC can ensure better active and reactive powers control, lower grid current harmonics, better compensation of grid neutral current and reactive power, and accurate balancing of the dc capacitor voltages. The presented results demonstrate the effectiveness of the proposed control strategy.

Optimal Periodic Variable Switching PWM for Harmonic Performance Enhancement in Grid-Connected Voltage Source Converters

Variable switching frequency PWM (VSFPWM) modulation can be advantageously implemented in industrial applications, such as renewable energy, motor drives, and uninterrupted power supply (UPS) systems, to reduce the injected current harmonic amplitudes, to suppress audible noise, and to improve semiconductor power efficiency. In this article, the usage of periodic VSFPWM methods in a voltage source converter (VSC) is proposed, analyzed, and benchmarked in terms of harmonic spectrum spreading, following the IEEE-519 current harmonic standard for the connection to the distribution grid. Particular attention is paid to the influence of VSFPWM on the ac filter design. First, the analytical model of the voltage harmonic spectrum generated by a three-phase three-wire two-level VSC implementing several periodic VSFPWM methods is derived. Subsequently, a design guideline for the commonly used <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LCL</i> filter in the grid-tied VSC application is proposed, which minimizes the size requirement of the necessary components. The voltage spectrum models of the proposed VSFPWM method and the optimal switching profiles are verified by MATLAB/Simulink simulations and a 5-kW three-phase two-level VSC hardware demonstrator. The study shows that the ac filter power density for the studied VSFPWM methods can be greatly increased when compared with the conventional and widely employed constant switching frequency continuous PWM strategies.

Constant and Green Mode Operation Technique in Flyback and Push-Pull DC-DC Converter

Abstract: The high frequency switching causes switching losses and reduces the efficiency of converters. Therefore, operating the DC-DC converters with lower frequencies at light loads reduces the switching losses significantly. Variable frequency switching is generally defined as Green mode operation. The green mode control method is obtained from high efficiency over the entire load range. This method is also called variable frequency control and it changes the switching frequency according to the load condition. At full load conditions, the controller increases the switching frequency to decrease switching ripple and ripple-related conduction loss. When the load decreases, the controller decrease switching frequency to diminish switching loss and increase switch life cycle. In this paper, the flyback and push-pull converter topologies are simulated using MATLAB/Simulink and the results obtained from the variable switching converter are compared with the results obtained from constant switching frequency. Keywords: Green Mode Operation, Flyback Converter, Push-Pull Converter, Variable Switching Frequency, Constant Switching Frequency.

Sensorless torque and flux control of induction motor fed by photovoltaic system

This paper presents a new direct torque and flux control method for induction motor fed from Photovoltaic (PV) System. The proposed strategy is based on Stator Field Orientation with deadbeat torque and flux control. The deedbeat control approach is based on establishing the voltage vector necessary to supply the motor and reach the electromagnetic torque and flux references at the end of a sampling period T. In order to create the voltage shape and frequency to control the induction motor, the inverter is supplied by a DC voltage extracted from a PV system. Model Reference Adaptive System and Luenberger Observer are designed to determine the stator flux and rotor speed. Extensive simulation work was carried out, which demonstrated that the proposed strategy is capable of reducing the torque and flux ripples and maintaining a constant switching frequency.

A Hybrid Model Predictive Control for a Seven-Level Hybrid Multilevel Converter With Independent Low-Frequency and High-Frequency Stages

This article puts forward a hybrid model predictive control (H-MPC) that enables the decoupling of low- and high-frequency stages in a seven-level hybrid multilevel converter (7L-HMC). It first uses the sign pattern of the reference voltage vector to determine switching states of the low-frequency stage. Next, the reference vector is shifted to the internal hexagon of the original space vector diagram, which is thereby converted to a 120&#x00B0; oblique coordinate system, where the adjacent vectors can be rapidly selected. Then, the optimal current tracking is primarily safeguarded by the duty cycle optimization of the three adjacent vectors. Finally, an optimized symmetric switching sequence minimizing the dc voltage deviation over one control iteration is selected through the assessment of possible switching sequences that are subject to the chosen vectors with optimal duty cycles. The proposed H-MPC method can reduce both the current ripple and computational burden while achieving a constant switching frequency. Comprehensive simulation and experimental comparisons on an all-silicon-carbide 7L-HMC prototype verify the effectiveness of the proposed H-MPC.

A Passive Variable Switching Frequency SPWM Concept and Analysis for DCAC Converter

Variable switching frequency sinusoidal pulsewidth modulation (VSFSPWM) method does well in many aspects such as lower harmonic peak and losses compared with constant switching frequency sinusoidal pulsewidth modulation (CSFSPWM) for DCAC converters. This article presents a passive VSFSPWM (PVSFSPWM) method for spectrum improvement, filter inductor reduction, and losses reduction, obtaining similar output current quality as that of the CSFSPWM method. Because the PVSFSPWM method does not need any feedback information compared with the model-predictive-based method, it is an open-loop method and is called the passive method. In order to obtain the law of harmonic distribution, the mathematical expression of harmonic spectrum distribution is derived. The required filter inductor under the same current ripple and the losses between CSFSPWM and PVSFSPWM methods have been compared. Simulation and experimental results show that the PVSFSPWM method achieves excellent performance in EMI suppression, inductance, and losses reduction without impairing the output quality.

Fixed switching frequency and three level inverter to improve the performance of sensorless PMSM

The vector control drive system is a very important method to get high dynamic performance. To increase the reliability and decrease the cost of this system, the sensorless speed control is used. Here sensorless speed control conventional model reference adaptive system was studied. It was studied due to have many advantages. Although it has many advantages, but also, it has some drawbacks. These drawbacks an increase in the torque ripples, an increase in distortion of the stator currents, fluxes and motor speed. The aim of this paper is beating the drawbacks of the chosen system through simulation only. Three level inverter with space vector modulation constant switching frequency is used to overcome these drawbacks. To show the effect of the proposed system, it was compared to the conventional system. The conventional system here uses the two-level inverter with space vector modulation. To show the advantages of the constant switching frequency, the three-level inverter was used without keeping the constant switching frequency. The comparison held among the conventional model, the improved model which using the three-level inverter only and proposal model (the three-level inverter which using constant switching frequency). In the conventional model, the reference currents and the estimating currents compared to generate the reference voltage of the space vector modulation. In proposal model, the stator fluxes were estimated and compared to the reference stator fluxes to generate the same voltage of the space vector modulation through keeping the switching time constant. The simulation results proved that importance of the proposed model to improve the drawbacks of the conventional model reference adaptive system.

Model Predictive Direct Power Control for Virtual-Flux-Based VSR With Optimal Switching Sequence

Three-phase voltage-source rectifier (VSR) has been widely used in energy, industry and other fields in the past few years. Model predictive control with optimal switching sequence (OSS-MPC) has further reduced output current THD and ripples with a constant switching frequency, compared with the conventional model predictive control (MPC). However, in practical application, the AC side voltage is often in a distorted state, which causes a distorted AC side current and a dramatic increase of THD. To overcome the drawback mentioned before, based on the analysis of OSS-MPC and combined with virtual flux oriented direct power control strategy, a virtual-flux-based model predictive direct power control strategy with optimal switching sequence (VF-OSS-MPDPC) is proposed in this paper. This control strategy for VSR combines the advantages of virtual-flux, low-pass filtering characteristics and optimal switching sequence model predictive control, which has high prediction accuracy and the AC current THD are greatly reduced under distorted AC voltage. The proposed control strategy can realize a constant switching frequency in steady-state operation without a modulator, which reduces the complexity of control strategy and the difficulty of AC side filter design. The proposed VF-OSS-MPDPC is validated through simulation and experiment compared with OSS-MPC, which proves the correctness and effectiveness of the proposed control strategy.

Space Vector PWM Based DTC Scheme With Reduced Common Mode Voltage for Five-Phase Induction Motor Drive

In multiphase induction motor drives, lowering the common-mode voltage (CMV) reduces motor insulation degradation and the existence of destructive bearing current. For this investigation, a five-phase two-level voltage source inverter (FPTL-VSI) fed five-phase induction motor (FPIM) drive is used. FPTL-VSI produces increased CMV, which cannot be totally removed. Moreover, CMV can be reduced by 80% in contrast to its peak-to-peak value with suitable selection of small and large voltage vectors in a space vector pulsewidth modulation (SVPWM) scheme. Direct torque control (DTC) combined with the SVPWM scheme can accomplish such reduced CMV performance at constant switching frequency. To provide better speed and torque control, two virtual vector (VV) based SVPWM-DTC (DTC1 and DTC2) methods are proposed in this study. Over a wide range of modulation index, the influence of each voltage VV on motor drive speed and torque response is investigated. The proposed DTC1 and DTC2 schemes are validated under steady-state and dynamic conditions over a wide range of speed fluctuations using a high-power laboratory prototype of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$3.8\,\text{{k}W}$</tex-math></inline-formula> FPIM drive. The efficacy of the proposed DTC1 and DTC2 is compared to the current literature by evaluating the effectiveness of CMV and the switching frequency.

An Ultra-Low Quiescent Current Tri-Mode DC-DC Buck Converter With 92.1% Peak Efficiency for IoT Applications

An ultra-low quiescent current tri-mode DC-DC buck converter is presented in this paper, which is able to handle a 100,000X load range. In pulse width modulation (PWM) and pulse frequency modulation (PFM) mode, adaptive on-time (AOT) V² control is utilized to achieve seamless mode transition and constant switching frequency in PWM mode. A deep green mode (DGM) is proposed for light load, where both the switching loss and the power of control circuitry are minimized. By reducing the comparator current, a delay-based hysteresis window adaptive to load current is generated, reducing the switching frequency and the loss. Meanwhile, the average current of zero current detector (ZCD) and AOT controller are reduced significantly by dynamic biasing. As a result, the efficiency of the converter is improved while maintaining a reasonable output ripple. The proposed converter is implemented in a 0.18μ m BCD technology. Experimental results show that the converter can provide a 1.6 V output from a 2.7 to 4.7V input for 1μ A to 100 mA load, while consuming only 490nA quiescent current. The proposed converter achieves a 92.1% peak efficiency and efficiency can be maintained above 80% in a load range of 20μ A to 60 mA.

A Modified Variable Switching Frequency Spread-Spectrum PWM Technique With Reduced Torque Ripple for a Vector-Controlled PMSM Drive

The discrete tonal bands introduced in an AC machine’s stator current spectrum by constant switching frequency pulse width modulation schemes, have adverse impacts on the vibration, the acoustic noise, and the electromagnetic interference. Spreading the harmonic spectrum and reducing the magnitude of dominant harmonics is one solution to this problem. Ripples in the electromagnetic torque developed is another major concern in AC drives. Inspired by these factors, this study proposes two novel variable switching frequency schemes for a vector-controlled PMSM drive to disperse the frequency spectrum with a significant reduction in torque ripple. The modulation techniques use linear and trapezoidal variation of sub-cycle sampling period; <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T_s</i> during their implementation. Further, these methods would be able to eliminate the difficulty in compensator design, which is a major problem with other variable switching frequency schemes. The presented strategies achieve a maximum of 27 % reduction in torque ripple, 51.8 % reduction in dominant harmonics, and a dispersion index of 1.63, demonstrating their competency as promising variable switching frequency schemes. The suggested techniques also show excellent torque ripple reduction capability in comparison with latest spread-spectrum techniques in literature. The proposed techniques are implemented in simulation using MATLAB/Simulink and are experimentally validated using WAVECT-FPGA controller on a 1.07 kW, surface-mounted PMSM drive.

Investigations on Variable and Constant Switching Frequency Hysteresis Controller for VSI fed IM drive

Investigations on Variable and Constant Switching Frequency Hysteresis Controller for VSI fed IM drive

A Random Pulse Position-Based Selective Noise Cancellation Modulation Method for SVPWM Driven PMSMs

Permanent magnetsynchronous motors (PMSMs) are usually driven by the SVPWM technique, which leads to annoying sideband noise near the switching frequency. Traditional random modulation techniques increase the possibility of resonance with the motor structure. This study proposes a novel random pulse position modulation-based strategy to eliminate the current harmonics and electromagnetic noise at a specific frequency. The proposed method adopts a constant switching frequency. A unique design between the pulse position and duty ratio cancels the current harmonics and acoustic noise at the selected frequency. The results show that resonance can be avoided effectively if the chosen frequency is close to the natural frequency. It is concluded that the proposed method is beneficial at lower fundamental frequencies. The techniques can substitute classic random modulation techniques with variable switching frequency in the low speed applications.

Investigations on variable and constant switching frequency hysteresis controller for VSI fed IM drive

In various current controlled-pulse width modulated (CC-PWM) techniques which are extensively employed in high performance drives, hysteresis current control (HCC) offer significant simple implementation and good dynamic response. However, conventional HCC have drawbacks, such as, limit cycle oscillations, overshoot in current error, generation of sub-harmonic components in the current, and non-optimum switching of inverter voltage vectors which can create variable switching frequency. This work proposes a new constant switching current error space phasor (CESP)-based hysteresis controller with a simple online computation of the boundary and phase voltage harmonic spectrum similar to voltage controlled bus clamping PWM (VC-BCPWM)-based VSI fed induction motor drive. The error boundary computed using voltage and current errors in the present sampling interval is used for identifying next vector to be switched. The current controller using CESP approach is simulated using MATLAB Simulink and experimentally verified on 2.2 kW IM drive.

Constant-Current, Constant-Voltage Operation of a Dual-Bridge Resonant Converter: Modulation, Design and Experimental Results

To meet the requirements of charging the mainstream rechargeable batteries, in this work, a dual-bridge resonant converter (DBRC) is operated as a battery charger. Thanks to the features of this topology, the required high efficiency can be achieved with a wide range of battery voltage and current by using different modulation variables. Firstly, a typical charging process including constant-voltage stage and constant-current stage is indicated. Then, two different modulation methods of the DBRC are proposed, both of which can realize constant-voltage charging and constant-current charging. Method I adopts phase-shift modulation with constant switching frequency while Method II adopts varying frequency modulation. Furthermore, as guidance for practical application, the design principles and detailed design procedures of the DBRC are customized for the two modulation methods respectively in order to reduce the switching loss and conduction loss. Consequently, the full soft-switching operation with low rms tank current is achieved under the two modulation methods, which contributes to the high efficiency of the whole charging process. At last extensive simulation and experimental tests on a lab prototype converter are performed, which prove the feasibility and effectiveness of the proposed modulation strategies.

Continuous-time switched systems with switching frequency constraints: Path-complete stability criteria

We propose a novel Lyapunov construction for continuous-time switched systems relying on a graph theoretical Lyapunov construction. Starting with a finite family of continuously differentiable functions, suitable inequalities involving these functions and the vector fields defining the switched system are encoded in a direct and labeled graph. We then provide sufficient conditions for (asymptotic) stability subject to constrained switching times, by relying on the path-completeness of the chosen graph. The analysis is first carried out under the hypothesis of constant switching frequency. Then, the results are generalized to dwell time setting. In the case of linear dynamics, the graph formalism allows us to interpret the existing results on dwell time stability in a unified language. Some numerical examples illustrate the usefulness of the conditions.

Study on speed sensorless system of permanent magnet synchronous motor based on improved direct torque control

The traditional direct torque control system of permanent magnet synchronous motor has many problems, such as large torque ripple and variable switching frequency. In order to improve the dynamic and static performance of the control system, a new torque control idea and speed sensorless control scheme are proposed in this paper. First, by deriving the equation of torque change rate, an improved torque controller is designed to replace the torque hysteresis controller of the traditional direct torque control. The improved direct torque control strategy can significantly reduce the torque ripple and keep the switching frequency constant. Then, based on the improved direct torque control and considering the sensitivity of the stator resistance to temperature change, a speed estimator based on the model reference adaptive method is designed. This method realizes the stator resistance on-line identification and further improves the control precision of the system. The performance of the traditional direct torque control and the improved direct torque control are compared by simulation and experiment under different operating conditions. The simulation and experimental results are presented to support the validity and effectiveness of the proposed method.

Finite‐control‐set model predictive control with a constant switching frequency for single‐phase grid‐connected photovoltaic inverter

Taking the advantage of easy implementation in the discrete digital control system, the finite-control-set model predictive control (FCS-MPC) is widely used in multi-phase or multi-level power converters. As the smallest independent operation unit in photovoltaic (PV) distributed power generation systems, the PV inverter has the most direct influence on the power quality. However, the lack of switching states and output voltage levels restricts the development of FCS-MPC in single-phase PV inverters. In order to improve the quality of the PV inverter output current, a constant switching frequency FCS-MPC (CFS-FCS-MPC) method is proposed for single-phase grid-connected PV inverter in this paper, which can thus reduce output current ripples and lower harmonics. Compared with the conventional FCS-MPC method, the proposed CFS-FCS-MPC method synthesizes the switching state with a nonzero and a zero switching state in one sampling period. In addition, an optimum allocation of switching states and execution time for the synthesized switching state is presented. Experimental results have verified the effectiveness of the proposed CSF-FCS-MPC method for the output current, achieving lower current ripples and higher current quality with a constant switching frequency.

Multi-carrier switching strategy for high-bandwidth potential balancing control of multilevel inverters

&lt;span lang="EN-US"&gt;This paper confers on investigation of a direct torque control (DTC) of induction motor drive by 3 level neutral point clamp (NPC) multilevel inverter. The imbalance problem may deteriorate the electric drive performances which might cause a short circuit condition. Various balancing control strategies were proposed, however, most of them employed complex space vector modulation (SVM) and hysteresis-based controller that generates variable switching frequencies. The proposed method will offer a reliable balancing control strategy with a constant switching frequency, and moreover, it will provide excellent electric drive performances. This research proposed a new multi carrier switching modulation strategy that establish a high-band-width control for neutral point potential in the NPC inverter. Potency of the proposed high-bandwidth potential balancing strategy is validated through the MATLAB/SIMULINK environment.&lt;/span&gt;