Average Switching Frequency Research Articles

Total Frequency Spread: A New Metric to Assess the Switching Frequency Spread of FCS-MPC

This work proposes a metric to assess the spread of the switching frequency profile of power converters, focusing on Finite Control Set-Model-Predictive-Control (FCS-MPC)-based converters, and analyses the effect of the filter sizing, sampling period, and cost function on the switching frequency spread. An algorithm that estimates the instantaneous switching frequency is the basis of the proposed metric. The literature review shows that only two metrics, THD and average switching frequency, are used to assess the switching frequency of FCS-MPC, but the findings of this research show that both are insufficient to characterize FCS-MPC. The main contribution of this paper is that now researchers can quantitatively assess the switching frequency spread of FCS-MPC through the proposed metric.

Efficient RF-PA Two-Chip Supply Modulator Architecture for 4G LTE and 5G NR Dual-Connectivity RF Front End

This article presents a two-chip supply modulation architecture for efficient RF power amplification using a fully switched-mode supply modulator (SM) and a linear-assisted hybrid SM to support simultaneous transmission on long-term evolution (LTE) and 5G bands. The designed fully switched-mode SM consists of a fast switching buck converter and a slow switching buck converter, and it achieves 88.2% peak efficiency and a low receiver (RX) band noise of −140 dBm/Hz at the SM output. The fully switched-mode SM tracks the envelope of LTE 5-/10-/20-MHz signals with the average switching frequencies of 50/70/120 MHz, respectively. The ET-PA measured using the fully switched-mode SM and LTE band-3 power amplifier module integrated duplexer (PAMiD) saves the dc power consumption of 320 mW at a 23-dBm output power compared to an average power tracking (APT)-PA. The designed 5G new radio (NR) SM consisting of a class-AB linear amplifier (LA) and an interleaved three-level buck–boost converter provides a 160-MHz 3-dB bandwidth to track the envelope of a 100-MHz NR signal. The measured peak SM efficiency is 84.1% at a 3.53-W output power. The measured ET-PA with 5G NR SM and 5G n77 PAMiD achieves an ACLR of −36.9 dBc at a 27.45-dBm output power with a 6-dB peak-to-average-power ratio DFT-spread-OFDM NR 100-MHz quadrature phase shift keying (QPSK) signal. It saves the dc power consumption of 950 mW at a 27-dBm output power compared to APT-PA. An optimal RF power amplifier (RF-PA) supply deployment using the two SMs efficiently supports multiple RF-PA loads while satisfying the dual-transmission requirements of E-UTRAN new radio dual-connectivity (EN-DC) and 5G 100-MHz ET operation. The fully switched-mode SM is implemented in a 130-nm CMOS process, and the die size is 4.0 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> . The 5G NR SM is implemented in a 90-nm CMOS process, and the die size is 6.75 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> .

Dual Active Bridge Based Reduced Stage Multiport DC/AC Converter for PV-Battery Systems

Standalone power systems are significant for electrifying the remote areas where extending the grid connectivity is not feasible, either economically or logistically. Solar Photovoltaic (PV) systems with battery backup are among the most popular candidates to serve as an energy source in standalone systems. This article presents a novel multiport converter (MPC) for PV-battery systems powering standalone loads. The proposed converter is a reduced stage power converter based on current fed dual active bridge (CF-DAB) topology. CF-DAB offers galvanic isolation and a high voltage ratio without sacrificing efficiency. Switching losses are further reduced by a modified modulation scheme that reduces the average switching frequency of some of the switches. The proposed converter performs the functions of tracking maximum power point of the solar panel and regulating the load voltage while using fewer power conversion stages. This is done by sharing components among the various stages performing maximum power point tracking, voltage boosting, and dc/ac conversion. A small-signal model of the proposed MPC required for its closed-loop control is also proposed, which can also be utilized for other CF-DAB-based converters. A lab prototype of the proposed MPC has been fabricated and its operation has been validated under various static and dynamic conditions.

Performance Investigation of Deadbeat Predictive Controllers for Three-Level Neutral Point Clamped Inverter

This article aims to improve the performance of the deadbeat (DB) predictive controller for a three-level neutral point clamped (NPC) inverter. The effect of the number of effective vectors considered for the cost function evaluation on steady-state and dynamic performance is investigated. To do that, three DB predictive controllers with different numbers of effective vectors, namely, 19 vectors-based, six vectors-based, and three vectors-based DB, are compared beside the conventional current-based model predictive control (MPC). The neutral-point (NP) voltage is balanced using the redundant vectors. Simulations and experimental tests are performed to evaluate the performance of the competing MPC algorithms in terms of four main criteria, namely: NP voltage balancing error, total harmonic distortion (THD), the computational effort required, average switching frequency, power loss, and sensitivity to parameters mismatch. Compared to conventional MPC, the experimental results show that the three vectors-based DB predictive controller has the best steady-state and dynamic performance with a reduction of computational burden up to 60% and a reduction of the current THD up to 72%.

Improve Performance of Induction Motor Drive using Weighting Factor approach-based Gravitational Search Algorithm

ABSTRACT The weighting factor adjustment limits the extensive application of conventional model predictive torque control in practice. In this paper, a model predictive torque control strategy with gravitational search algorithm (GSA) is proposed. The detail of an adaptive torque variable is introduced to control the flux linkage of the induction motor, and a modified value function is constructed by using electromagnetic torque and image torque. The proposed model uses two control variables to replace the torque and flux variables in the conventional model predictive torque control and improve the control efficiency. The simulation and experimental results show that the proposed method achieves a fast dynamic performance compared to the conventional model and reduces the average switching frequency. Besides, the system has high response speed, high accuracy, stability, and a certain application value.

Bandwidth-Increased Ripple-Mitigating Scheduling Algorithm for Dynamically Reconfigurable Batteries

Modular cascaded circuits offer attractive qualities in reconfigurable battery applications, including improved fault tolerance and flexibility. In contrast to conventional hard-wired dc battery packs, however, cascaded topologies, such as modular multilevel circuits (MMC) with serial or serial and parallel connectivity, load modules with substantial low-frequency current ripple, which generates additional loss and can accelerate battery aging. Recent studies reveal that low-frequency ripple can cause noticeable battery aging, whereas high frequencies are insignificant, presumably mainly as they can be absorbed by the dielectric electrode capacitance, and reduce heating associated with lower high-frequency battery impedance. Previous MMC–battery control methods solely focus on state-of-charge and thermal balancing of individual modules, while the few existing methods for suppressing ripple tend to form low-frequency patterns in the modules’ load, which increase battery cycling as well as loss. This paper presents a ripple-oriented high-bandwidth control technique that minimizes low-frequency components in the module load spectrum and improves battery treatment, while maintaining the average switching frequency. The control method takes limitations related to module data acquisition into account and enhances the feedback bandwidth using observers. It works with a wide range of topologies including modules with series connectivity only as well as series/parallel. The measurements in the laboratory verify the shift of the module load from the 10 – 100 Hz range to ~5 kHz and a reduction of battery losses by up to 20 %.

An improved long‐horizon model predictive control for DFIG in WECS with variable sampling‐time

This paper presents an improved finite-control-set model predictive control (MPC) strategy for the doubly fed induction generator (DFIG). The MPC-based controller's main drawback is high computational burden, which requires a long time to perform online optimization. In this regard, real-time implementation becomes impossible in some cases. Thereupon, this paper suggests a variable sampling time in the prediction process to achieve a balance between the prediction horizon and computational burden. In other words, compared to the conventional MPC-based techniques, longer horizon is predicted with fewer samples. In this method, there are two sampling times including a fixed sampling time for the system discretization structure, and a variable sampling time used in the prediction process. The proposed technique also utilizes a comparative incremental algorithm to prevent checking all possible control inputs over the objective function in order to reduce the computational time further. In addition, a penalty term, which includes the number of switch changes, is added to the cost function to reduce the switching frequency. Both the simulation and experimental results show that the proposed MPC can significantly improve the DFIG control system's performance by increasing the accuracy of tracking response and reducing the computational time. The experimental test is carried out by the hardware in loop system by using TMS320F28338 and PC-Lab card. The computational delay caused by the digital signal processor and other influential factors are compensated by using the prediction plus prediction approach. The results confirm that the proposed controller has a lower overshoot and power ripple compared to the vector controller and direct torque controller. It also reduces the computational time up to 40% and reduces the average switching frequency by 12% in comparison to the conventional MPC.

Variable Switching Frequency PWM for Three-Phase Four-Wire Split-Capacitor Inverter Performance Enhancement

Three-phase, four-wire, split-capacitor inverters, thanks to their capability to deal with unbalanced systems, are currently employed in photovoltaic installations, electric vehicles battery chargers, active power filters, and many other grid-tied applications. The minimization of ac output current ripple and switching losses positively impacts the inverter's efficiency, volume, weight, and cost optimization. For this reason, a novel variable switching frequency driving strategy independently tunable on each phase is proposed in this article. Taking advantage of phase current ripple prediction, a proper variable switching frequency strategy is applied for obtaining a flat current ripple profile. Having tuned the driving strategy parameters, it is possible to optimize and compare individual metrics such as the maximum peak-to-peak value of the current ripple, current ripple rms, average switching frequency, and switching losses. By applying the proposed modulation method, a significant inverter performance enhancement has been obtained. Converter efficiency is improved without introducing detrimental effects on the current harmonic quality. Analytical derivations are expressed as a modulating index function and the power factor for balanced and unbalanced systems. All the theoretical developments are verified throughout numerical simulations and experimental tests.

Model predictive current control with lower switching frequency for permanent magnet synchronous motor drives

The model predictive current control (MPCC) technique has been an effective alternative for motor drive applications requiring fast dynamic response. However, the conventional MPCC suffers from high switching losses due to high switching frequency of the inverter. This study proposes a low average switching frequency MPCC method based on boundary-constrained quadratically extrapolated current trajectory for a permanent magnet synchronous motor drive. First, a quadratic function-based current prediction model is constructed to obtain the current trajectory in the long-term future. Second, the boundary constraint is designed to obtain the prediction horizon which is changing in real-time in order to ensure the validity of the predicted current trajectory. Finally, the cost function established according to the value of the prediction horizon is used to reduce the average switching frequency. In comparison with the conventional MPCC method, the proposed method can significantly reduce the switching frequency of the inverter. In the meantime, fast dynamic response and high steady-state performance of the conventional MPCC method are preserved. Both simulation and experimental results of the proposed method and the conventional MPCC method are presented to verify the feasibility and advantages of the proposed method.

Model Predictive Current Control Based on Virtual Voltage Vector Method for Parallel Three-Level Inverters

The parallel three-level neutral-point clamp (3L-NPC) inverters are widely solicited today to satisfy the higher power demand by using low-rated switching devices in industrial applications such as renewable power generation. With the 3L-NPC in parallel, the zero-sequence circulating current (ZSCC) occurs in the closed circuit and decreases the performances of the current response if the two 3L-NPCs share the same dc bus with no galvanic isolation at the ac side. From the analysis of the ZSCC equivalent circuit, the virtual voltage vectors are proposed and exploited by the finite control set model predictive control (FCS-MPC) for mitigating the ZSCC and improving the current accuracy. In order to keep the neutral-point balance and reduce the switching loss, the differential capacitor voltage and the average switching frequency are considered in the proposed MPC. An experimental platform based on the Simulink-Real-Time system is presented for further verification of the effectiveness of the proposed method. The simulation and the experimental results obtained under the proposed strategy show that the ZSCC is reduced to near zero, and the current response provided has lower THD.

Six-Leg Three-Phase AC–DC–AC Converter With Shared Legs

This article proposes a six-leg three-phase ac-dc-ac converter with three of its legs shared between grid and load sides. The proposed converter presents double of voltage generation capability at load side compared with grid side and it is suitable for operation with the same grid and load frequency. Pulsewidth modulation (PWM) and control strategy are presented. Analysis of dc-link voltage requirement, current in the shared legs, and design of passive devices are carried out. The proposed converter is compared with conventional topologies considering harmonic distortion, average switching frequency, average converter current, and semiconductor losses. Operating with the same voltage amplitude at grid and load, the proposed converter presents lower conduction losses than the conventional ones. Besides that, for operation with load voltage twice the amplitude of grid voltage, the converter presented the lowest switching and conduction losses compared with the conventional converters. Finally, experimental results are shown for validation purposes.

COMPARATIVE STUDY OF SINGLE-PHASE PWM RECTIFIER CONTROL TECHNIQUES

In this study, 2.5 kW single-phase pulse-width modulated rectifier is simulated with three different control techniques to investigate the performance of controllers. Rectifier simulation is performed in Matlab / Simulink environment by using hysteresis current control, sinusoidal pulse width modulation and voltage oriented control techniques. In the performance comparison of the control techniques, considering the switching frequencies, the total harmonic content of the current drawn from the grid, the phase difference between the grid voltage and the grid current, and the DC bus voltage regulation at the output are considered as comparison criteria. The switching frequency is set to 35 kHz in sinusoidal pulse width modulation and voltage oriented control techniques. Since the switching frequency is variable in the hysteresis current control technique, the average and instantaneous switching frequency are calculated for different hysteresis band values. In the results with the technique, the switching frequency varies between 18.52 kHz and 47.6 kHz, while the average switching frequency is 34.6 kHz. As a result, the total harmonic distortion of the grid current with hysteresis current control, sinusoidal pulse width modulation and voltage oriented control techniques is 3.69%, 1.12% and 1.82%, respectively. The synchronization with the grid voltage is achieved with all techniques, and the DC voltage is regulated with active power.

RPWM selective voltage harmonic elimination method for single‐phase five‐level MPUC inverter based on cell division

The conventional selective harmonic elimination method of random pulse width modulation (RPWM) is only suitable for the two-level inverter. Furthermore, when the harmonics below 6 kHz are selectively eliminated, it is easy to cause a low average switching frequency of the inverter, which leads to the increase of load current distortion rate. This paper proposes an RPWM selective voltage harmonic elimination method for a single-phase five-level MPUC (modified packed U-cells) inverter based on cell division. The MPUC inverter is supposed to be divided into three series cells, and the carrier stacking strategy is used to realize the coordinated control between each cell. In the process of RPWM, the average switching frequency can be controlled within a certain range by selecting the random number. This method is divided into normal mode and master–slave mode. In the normal mode, the selective harmonic elimination is realized by the method of cancelling the front and back terms of Fourier series in each cell. In the master–slave mode, the master cell is mainly used for fundamental power output, and the slave cell is mainly used for RPWM selective harmonic elimination. The effectiveness of the proposed method is verified by the simulation and experimental results.

A Variable Switching Frequency PWM Method for Indirect Matrix Converters

A variable switching frequency PWM technique (VSF-PWM) for indirect marix converter(IMC) is proposed in this paper. The maximum peak-to-peak value of the three-phase current ripples in each switching cycle can be calculated by analyzing the output current-error vector trajectory of IMC on a-b-c plane and projecting it onto the three-phase coordinate axis. Then the switching frequency is adjusted in real-time according to change of the maximun peak-to-peak value of the current ripples. Compared with the constant switching frequency PWM method (CSF-PWM), the proposed method can reduce the average switching frequency and the swithing loss. Meanwhile, the switching sequence of the traditional SVPWM is modified, which can achieve zero current commutation in rectifier of IMC, and makes the commutation frequency controllable. Simulation results prove that with the proposed method, the distribution range of output current harmonic spectrum is expended and the spikes in the spectrum are eliminated, which will be effective in suppressing the EMI of the converter output and noise of the load.

An Improved Hybrid Frequency Pacing Modulation for Wireless Power Transfer Systems

Zero voltage switching (ZVS) techniques are widely utilized to increase efficiency and reduce electromagnetic interference of wireless power transfer (WPT) systems. Hybrid frequency pacing (HFP) is an excellent modulation method for WPT systems because it can achieve full-load range ZVS without changing the current frequency or adding auxiliary components. Another advantage of HFP is the average switching frequency reduction as decreasing output voltage so that it further reduces switching losses. This article provides an insight into the characteristics of HFP and points out that a large output ripple occurs under some reference conditions. To improve HFP, this article proposes an improved HFP (iHFP) method to minimize output ripple by optimally arranging the hybrid frequencies pulse sequence, but the implementation process of iHFP becomes more complicated. The reason for the unavoidable complicated calculation of HFP is the quantization error. In this viewpoint, this article proposes a modified sigma-delta modulation method with the quantization noise-shaping property for iHFP. As a consequence, the same pulse sequence can be generated by this simple modulator without complex calculations. Experimental results show that iHFP and Σ-Δ iHFP can reduce more than 60% voltage fluctuations compared with HFP. Under 0.2% input reference resolution, 66%-93% computational time reduction is achieved in going from HFP to Σ-Δ iHFP.

Comparison of Hysteresis Based PWM Schemes ΔΣ-PWM and Direct Torque Control

This paper presents the differences and similarities of ΔΣ-PWM as a hysteresis-based PWM scheme with direct torque control (DTC) using simulation models. The variable switching frequency caused by the hysteresis element is examined with regard to its instantaneous values. The comparison is based on an equal maximum switching frequency as a design criterion. With this first assumption, the variation of the instantaneous switching frequency is higher when using DTC because of the temporary prioritization of one inverter leg. Besides the lower variation, ΔΣ-PWM shows a higher average switching frequency. Because the switching frequency is related to the torque ripple, the usage of ΔΣ-PWM results in a smaller torque ripple. Due to the dependence of torque ripple on switching frequency, a second comparison is carried out based on the same average switching frequency. In this comparison the ΔΣ-PWM shows higher torque ripple than DTC.

Multi-objective model predictive control of grid-connected three-level inverter based on hierarchical optimization

In order to solve the problem of weighting factors selection in the conventional finite-control-set model predictive control for a grid-connected three-level inverter, an improved multi-objective model predictive control without weighting factors based on hierarchical optimization is proposed. Four control objectives are considered in this strategy. The grid current and neutral-point voltage of the DC-link are taken as the objectives in the first optimization hierarchy, and by using fuzzy satisfaction decision, several feasible candidates of voltage vectors are determined. Then, the average switching frequency and common-mode voltage are optimized in the second hierarchy. The average ranking criterion is introduced to sort the objective functions, and the best voltage vector is obtained to realize the coordinated control of multiple objectives. At last, the effectiveness of the proposed strategy is verified by simulation results.

Five‐level class‐D amplifier employing fourth‐order continuous‐time sigma‐delta modulator

A new closed-loop multi-level Class-D amplifier employing a fourth-order ‘continuous-time sigma-delta modulator’ is proposed and analysed. The proposed amplifier is intrinsically linear and it has approximately the fixed ‘total harmonic distortion plus noise’ against the input frequency. The corresponding circuit is designed and simulated in 180 nm technology (3.3 V), while the post-layout model of the power stage is employed. A total harmonic distortion plus noise of 0.0016%, the quiescent current of 2.6 mA, the maximum efficiency of 94%, the average switching frequency of 400∼500 kHz and an excellent ‘power supply reject ration’ of 120 dB are achieved.

Cascaded Multioutput Multilevel Converter: Modulation and Operating Limits

This article presents the modulation and operating limits of the modified cascaded multioutput multilevel converter. A phase-disposition pulsewidth modulation strategy is developed to apply the optimal state that leads to a minimized device switching. A Hamming distance-based cost function is adopted to evaluate the number of device transitions. The cost function is further modified to identify the optimal state from a number of feasible states. Moreover, the operating limits of the converter are analyzed for the safe and valid operation of the converter. Simulation and experiment results validate the theoretical analysis, and the converter is operational under a wide range of operation points. The proposed optimal state modulation strategy is shown to be effective in reducing the average device switching frequency.

The Effect of Different Decision-Making Methods on Multi-Objective Optimisation of Predictive Torque Control Strategy

Abstract Today, a clear trend in electrification process has emerged in all areas to cope with carbon emissions. For this purpose, the widespread use of electric cars and wind energy conversion systems has increased the attention and importance of electric machines. To overcome limitations in mature control techniques, model predictive control (MPC) strategies have been proposed. Of these strategies, predictive torque control (PTC) has been well accepted in the control of electric machines. However, it suffers from the selection of weighting factors in the cost function. In this paper, the weighting factor associated with the flux error term is optimised by the non-dominated sorting genetic algorithm (NSGA-II) algorithm through torque and flux errors. The NSGA-II algorithm generates a set of optimal solutions called Pareto front solutions, and a possible solution must be selected from among the Pareto front solutions for use in the PTC strategy. Unlike the current literature, three decision-making methods are applied to the Pareto front solutions and the weighting factors selected by each method are tested under different operating conditions in terms of torque ripples, flux ripples, cur-rent harmonics and average switching frequencies. Finally, a decision-making method is recommended.