Reduced Switching Frequency Research Articles

A look-up table-based model predictive torque control of IPMSM drives with duty cycle optimization

Model Predictive Control (MPC) is an effective method of driving motors and power converters due to its quick response, integrity, and multivariable control adaptability. A model-predictive torque control (MPTC) technique for permanent magnet synchronous motors (IPMSMs), which is computationally efficient and of low complexity, is presented in this paper. The proposed technique designs a lookup table that is independent of flux angle and torque deviation. For each control instant, this technique has to evaluate four voltage space vectors (VSV) from the lookup table, resulting in a substantial reduction in switching frequency and computational burden without compromising the performance. A maximum torque per ampere (MTPA) technique generates reference currents. The controller’s complexity is minimized by eliminating the flux weighting factor from the cost function, saving time on offline weighting factor adjustments. Moreover, duty cycle optimization is performed using the mean torque control technique to minimize torque and flux ripples. The proposed method has been experimentally validated using a real-time simulator hardware in loop (HIL) with a TMS320F28335 floating-point digital signal processor on a prototype IPMSM drive. Furthermore, the proposed MPTC scheme is compared to conventional MPTC and direct torque control (DTC).

New Random PWM Method at Constant Switching Frequency and Maximum Harmonic Reduction Created With a Flexible FPGA-Based Test Bench

It has been shown that the converters that integrate random PWM produce a spread spectrum in their harmonic emission, shortening the emission peaks. On the converter’s input side, the reduction minimizes electromagnetic interference EMI. On the output side of the converter, the reduction manages to smooth the voltage and current ripple in the load. We have built a flexible test bench (FTB) developed with FPGA to generate most of the proposed random PWM modes for converters. The conducted harmonic voltage emission of these modes, both on the input side of the converter and on the load side, has been measured and compared in a DC-DC Buck converter. FTB also has the ability to create new random PWM modes. Of the random modes, the ones that produce the greatest peak reductions are those with variable switching frequency. However, variable frequency modes lead to load feedback problems. A new random PWM method has been developed that significantly reduces the amplitude of the emission peaks but keeps the switching frequency constant.

A Novel Space Vector PWM Technique With Duty Cycle Optimization Through Zero Vectors for Dual Three-Phase PMSM

In this paper, a novel space vector pulse width modulation (SVPWM) technique with duty cycle optimization through zero vectors for dual three-phase (3-ph) permanent magnet synchronous machines (PMSMs) is proposed. Dual 3-ph PMSMs can be optimally controlled in vector space decomposition, which allows controls of the fundamental component and main low-frequency harmonics separately in two orthogonal subspaces, i.e., αβ and xy subspaces. However, the space voltage vector modulations of voltage references in two subspaces are not independent, because each voltage vector possesses its unique and fixed spatial location in two subspaces. Therefore, many SVPWM techniques intend to extend the modulation capability by designing the voltage vector selection principle, but the duty cycle saturation determines the limit of phase voltage regardless of the voltage vector selection principle. Therefore, a simple SVPWM technique with duty cycle optimization by adjusting dwell times of zero vectors is developed to offer a reasonable modulation capability with reduced switching frequency and no complex voltage vector selection principle. The linear modulation range is explained as well. Finally, the experimental results validate the performance of the proposed SVPWM technique through voltage injection and closed-loop current control.

An Adaptive DC-Link Voltage Control of a Multifunctional SPV Grid-Connected VSI for Switching Loss Reduction

In the proposed method in this article, to minimize the burden on the switches of the multifunctional grid-connected voltage-source inverter (MFGCVSI), the voltages of dc-link split capacitors are adjusted according to power injection from the MFGCVSI. The MFGCVSI is used to control the active power injection from solar photovoltaic (SPV) power generation to the main grid and loads, load reactive power compensation, harmonic mitigation, and main grid current total harmonic distortion within 5 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\%$</tex-math></inline-formula> . In such a case, the voltages of split capacitors depend on the rated power injection from the MFGCVSI. The power generated from the SPV system and the loads that are connected at the point of common coupling vary with respect to time. It is observed that the selection of rated dc-link voltages during low power injection from the MFGCVSI leads to additional switching stress and higher switching losses. Therefore, to reduce the burden on inverter switches and switching losses, the reference dc voltage is reduced under low power injection from the MFGCVSI. A model predictive controller with a multiconstraint technique is used in the proposed method for balancing the dc-link capacitor voltages and average switching frequency reduction. The proposed method is validated through simulation and hardware setup.

Design of Electric Vehicle Battery Charger With Reduced Switching Frequency Variation

This article presents the design of an electric vehicle (EV) battery charger isolation stage for minimizing switching frequency variation with the proposed duplex control. Traditionally, the realization of an EV charger with a resonant power conversion stage involves extreme frequency variation in the constant voltage (CV) mode resulting in switching losses, imposes severe constraints on the optimal design of magnetics, and presents control complexities due to secondary resonance and degraded pulsewidth modulation resolution. In this context, reported hybrid control strategies are complex and entail the simultaneous variation of control variables. In order to simplify control complexity and design constraints, the EV charger isolation stage with the quadruple rectifier and employing the proposed duplex control is presented with notable frequency reduction. Furthermore, the effect of high-frequency transformer nonidealities on the soft-switching range is delineated. The proposed duplex control contributes to the efficiency enhancement of the EV charger over a comprehensive range during CV charging, ensures soft switching, and prevents secondary resonance. It also offers continuous resonant current to overcome the underutilization of the transformer arising from high-frequency distortions. To validate the presented analysis, a 1.25-kW hardware prototype is designed and tested in the laboratory, and experimental results are presented.

Low–Harmonic Control Strategy of a Dual Three–Phase Synchronous Reluctance Motor Based on Three–Vector Synthesis

Dual three–phase synchronous reluctance motors (DTP–SynRM) have the advantages of simple structure, high power density, fast dynamic response, and small torque ripple, and have broad application prospects in flywheel batteries. However, the synchronous reluctance motor has no permanent magnet, and the inductance value will change with the current change in actual operation. Direct torque control (DTC) is more suitable for the control strategy of dual three–phase synchronous reluctance motors because of its low dependence on motor parameters. However, traditional direct torque control uses a large vector control motor within one control period, which can not suppress the inherent 5th and 7th current harmonics in the motor. A new harmonic suppression method is proposed in this paper: that is, using a low harmonic vector to replace a large vector in traditional direct torque control, which can be synthesized by adjusting the action time and order of three adjacent large vectors within one control period. Through this improvement, torque control can have a harmonic suppression effect. The three vector synthesis method can make full use of the existing space voltage vector, and to adapt to different working conditions, two synthesis methods of switching frequency reduction and constant torque response are proposed. An improved direct torque control strategy is obtained by optimizing the design of the switch table using a new vector synthesis method. Finally, the suppression effect of traditional DTC and improved DTC on current harmonics is compared and analyzed. The results show that the direct torque control with low harmonic vector can suppress the harmonic current in x–y subspace, and the current harmonic content is greatly reduced.

Improved Pulse Edge Independent Distribution Method for High PAPR High Bandwidth Envelope Tracking Power Supply

Envelope tracking (ET) power supply provides the power amplifier (PA) with a dynamic supply voltage that tracks the envelope of the input signal to the PA, and the final PA efficiency can be greatly improved. With the ever-advancing tracking bandwidth, the switching frequencies of ET power supplies are pushed to be very high and even difficult to be implemented. To address this issue, the pulse edge independent distribution (PEID) method has been proposed. Based on the idea of alternatively working by sets, the control pulses for the multilevel converter are broken into independent rising and falling edges, and rematching them with optimized new sequences can achieve a 1/ <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$n$ </tex-math></inline-formula> ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$n \in N$ </tex-math></inline-formula> ) ratio of the switching frequency over envelope bandwidth. However, each increase of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$n$ </tex-math></inline-formula> by 1 means that a whole set of voltage cells is added, leading to a great increase in system complexity and cost, especially for high peak-to-average power ratio (PAPR) applications. Besides, due to the irregular and aperiodic feature of the real communication envelope, the PEID control logic may suffer from surplus and imbalance in switching frequency reduction. Thus, this article proposes an improved PEID method. Assisted by the digital control platform, the control logic is redesigned, which can realize a balanced distribution of the rising and falling edges for arbitrary envelopes. Moreover, it can extend the domain of the “ <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$n$ </tex-math></inline-formula> ” to noninteger, achieving a more subtle resolution of PEID. On this basis, an evaluation function is constructed taking into account the efficiency, voltage-cell quantities, and switching frequency. With the desired weighted coefficients, an optimized comprehensive performance can be achieved. A prototype with 2–27-V output voltage range, 10- and 20-MHz tracking bandwidths, and 8.5-dB PAPR is fabricated and tested in the lab. The experimental results validate the proposed method.

A reduced switching frequency capacitor voltage balancing control for modular multilevel converters

Modular multilevel converter (MMC) is one of the most promising topologies in high/medium-voltage applications, but high switching losses impair system economy and reliability. For the high-voltage MMC with the nearest level modulation (NLM), there is usually high frequency and uncertain switching actions among submodules (SMs) in each arm, due to the traditional sorting based capacitor voltage balancing control method, which brings additional power losses. In order to solve this problem, the SM switching process and the capacitor voltage sequence of a MMC arm is analyzed, and then a method to predict the capacitor voltage convergence in the next control cycle is proposed in this paper. Based on the predicted voltage sequence, an improved capacitor voltage balancing method is proposed, which can significantly reduce the additional switching loss and improve the operating efficiency of the converter system. MATLAB/simulink simulation and RT-LAB based HIL test results verify the proposed method under different operating conditions.

Voltage-Sourced Converter Fed High-Speed Switched Reluctance Motor Drive System With Energy Feedback and Near-Unity Power Factor

The diode bridge rectifier fed asymmetric half-bridge converter (AHBC) is conventionally employed to drive switched reluctance motors (SRMs), which leads to poor grid-side power quality. In the proposed system, a topology made up of a voltage-sourced converter and an AHBC is employed to drive the high-speed SRM. Stable SRM operation can be obtained by manipulating the active power flowing to motor side, and on the basis of that, the grid-side power quality is enhanced by directly manipulating input reactive power. Predictive deadbeat control with disturbance observer is employed to follow the power references, thereby achieving controllable speed, energy feedback, near-unity grid-side power factor, and low grid-side current distortion simultaneously. Additionally, an improved asymmetric modulation method is developed for switching frequency reduction. Experiments are carried out to test the proposed drive system in steady and dynamic conditions. Performance comparisons validate the improvement of the proposed high-speed SRM drive system.

Low Switching Frequency SPWM Strategies for Open-Winding Machine With Low Current Harmonics

In this article, two novel sinusoidal pulsewidth modulation (SPWM) strategies with simple implementation are proposed for an open-winding machine fed by isolated dc-bus dual two-level three-phase inverters to reduce switching frequency and current harmonics. The proposed strategies utilize zero sequence voltage injection and unbalanced reference voltage distribution to generate discontinuous PWM with low current harmonics and less switching action. Two different zero sequence voltages are introduced in this article corresponding to two proposed PWM strategies with different switching actions in a PWM cycle. The novelty of this article is low current harmonics and less switching actions in a PWM cycle compared with the conventional SPWM strategy. Moreover, compared with the subhexagonal center PWM strategy, the proposed SPWM strategies have advantages of easy implementation and half switching commutations with the same current harmonic characteristics. The superiority of the proposed SPWM strategies is validated by simulation and experiment results.

Multifunctional Control of Wind-Turbine Based Nano-Grid Connected to Distorted Utility-Grid

This paper proposes a multifunctional control strategy and associated control algorithms for distributed wind-turbine (WT) based nano-grids connected to a distorted utility-grid. The contribution is on a new strategy with innovative control algorithms to coordinate multiple converters for a multitasking operation of the nano-grids. The novelty is on a unique control design with feasibilities: maximizing the generated power from WT, maintaining power quality in both <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ac</i> - and <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">dc</i> -sides under critical conditions of the power grid, and improving power quality against distortion from local nonlinear loads under a reduced switching frequency. A robust fast-dynamic predictive control method is developed for current controllers to fulfil the multifunction. Unconstrained deadbeat control inputs are derived in twofold targets: ensuring fast dynamic response and significantly reducing both the computation and switching frequency for finite predictive control. The control system is applied on a permanent-magnet synchronous generator (PMSG) WT-based nano-grid connected to a distorted utility-grid. An OPAL-RT-based real-time platform is used for comparative studies among the proportional integration (PI) control, finite predictive control (FS-MPC), and proposed control method. The performance verification exhibits the power quality improvement in both the nano- and utility-grids under critical conditions via high-performed regulation of currents, voltages, reactive power, and rotor-speed of the PMSG-WT.

Control of Reduced Switches Count and Classical Multilevel Inverters: a Comparison

Multilevel inverter has appeared as one of the important topologies in the area of high power and medium voltage because it can efficiently realize lower harmonics with reduced switching frequency. These Multilevel inverters (MLI) improve the energy quality shaped by producing many voltage levels. However, improving the quality of the output voltage of a multilevel inverter requires many switches, which tend to weigh down the structure and make it complex to control. This work deals with a comparison in terms of the spectral content of two configurations of thirty-one-level inverters for injection into the electrical grid. The first configuration is a classical cascaded H-bridge and the second one is a reconfigured Packed U-Cell (PUC) multilevel inverter. The classical configuration requires sixteen switches while the second uses only ten ones. The control technique based on the half-height modulation was performed and the Total Harmonic Distortion (THD) is calculated for each topology. For the PUC, we got a THD equal to 2.61% while we got 2.72% for the cascaded H-bridge. These results obtained in the MATLAB/Simulink environment, show that the reconfigured structure of the PUC inverter is a good candidate for injection into the electrical network.

Three-Dimension Space Vector Based Finite Control Set Method for OW-PMSM With Zero-Sequence Current Suppression and Switching Frequency Reduction

The zero-sequence current (ZSC) of open-end winding permanent magnet synchronous motor (OW-PMSM) with common dc bus mainly comes from zero-sequence voltage (ZSV) and third harmonic back electromotive force, so the ZSV levels of voltage vectors in model predictive control (MPC) need to be considered to suppress the ZSC. Different from the conventional MPC methods for OW-PMSM, which usually select the optimal voltage vector under αβ0 coordinate system, this article proposes a three-dimension space vector (TDSV) based MPC method under ABC three-phase coordinate system for OW-PMSM with ZSC suppression and switching frequency optimization strategy. Benefiting from the three-phase voltages decoupling feature of OW-PMSM, TDSVs in ABC coordinate system are regularly distributed in a space cube. A simple optimal TDSV selection method is proposed based on subcubes division. TDSV contains the predicted α-,β-,0 -axis voltages information, so ZSC suppression is achieved automatically. Furthermore, utilizing the switch states redundancy feature of dual-inverter system, a cost function is designed to optimize the switch states change and reduce the switching frequency without affecting the optimal TDSV selection. The performance and switching frequency reduction effect of the proposed method are verified and compared with the existing methods through experiments.

Analytical Model to Study Turn-OFF Soft Switching Dynamics of SiC MOSFET in a Half-Bridge Configuration

Switching transients of SiC MOSFET are fast compared to its Si counterpart. Fast switching transient reduces switching loss but may induce prolonged oscillations, spurious turn-on, high device stress, and electromagnetic interference (EMI)-related issues, etc. In soft switched converters, use of external drain source capacitance can reduce these adverse effects along with the reduction in switching loss. However, the selection of external drain source capacitance is not straightforward. A large external capacitance reduces switching loss, (dv/dt), (di/dt), and transient over-voltage but may also result in higher dead-time loss and reduced switching frequency. This article presents an analytical model that captures the soft turn-off switching dynamics of SiC MOSFET using parameters obtained from device datasheet along with the values of external circuit parasitics. Unlike linear approximation, a nonlinear channel current model is used along with a comprehensive model of transfer capacitance. The effect of external gate drain capacitance is also considered. This leads to a better estimation of switching transition time, actual loss, (dv/dt), (di/dt), and transient over voltage. Also, a method to select an optimal value of external drain source capacitance is presented. The proposed model is validated through behavioral simulation and experiment for two 1.2-kV discrete SiC MOSFETs.

A Sliding Mode SVPWM Method for a HTS Shunt Active Power Filter

A sliding mode controller based on SVPWM strategy (SMC-SVPWM) is proposed for three-phase voltage-source-converter-based shunt active power filter. Superconducting magnetic energy storage is used to improve the filtering performance. A sliding mode controller (SMC) is amended to determine the space region of the current error vector for improving dynamic response speed. SVPWM is utilized to select the optimal voltage vector to mitigate the chattering of the SMC and reduce switching frequency. The feasiblity of the proposed SMC-SVPWM method is verified by a series of simulation results and a comparative analysis between the SMC-SVPWM and conventional control methods under various loads.

Anti-collision zone division based hazard avoidance guidance for asteroid landing with constant thrust

Future asteroid landing and sample return missions will seek for landing sites with high scientific value, such as hazardous terrains, which means that the spacecraft needs the ability of autonomous hazard avoidance. Nowadays, the guidance algorithm based on artificial potential function plays an increasingly important role in hazard avoidance, but the local minimum problem makes that the spacecraft cannot reach the desired target landing point in some complex terrains. In this paper, a novel hazard avoidance guidance method which improves the traditional artificial potential function is developed. This method focuses on the impact zone analysis of hazards and defines anti-collision zone. In addition, a new repulsive potential function in logarithmic form is designed with continuity and fast numerical change rate in the anti-collision zone on this basis, and the problem of spacecraft falling into local minimum zone in complex terrains can be effectively avoided. Considering the practical application of constant thrust engine, the hazard avoidance control law with constant thrust sliding mode is designed to reduce switching frequency and fuel consumption. The performance of the proposed guidance law is verified through a set of simulations, as well as the global stability of the control system under uncertainty and perturbation conditions.

Enhanced control technique for a sensor-less wind driven doubly fed induction generator for energy conversion purpose

The current paper is concerned with introducing a predictive polar flux control (PPFC) scheme for a variable speed wind driven doubly fed induction generator (DFIG) without speed sensor. The operation of the designed PPFC is based on the power angle regulation. The adaptation process is performed through studying the relation between the generator’s torque and the power angle between the stator and rotor flux vectors. A robust observer is designed based on the back-stepping theory to estimate the rotor speed, stator currents, rotor flux and stator and rotor resistances. Furthermore, an effective maximum power point tracking (MPPT) scheme is designed to achieve the optimal wind power exploitation. To recognize the operation of the schemed PPFC, a discursive performance evaluation is performed for the modeled control scheme and the classic predictive torque control (PTC) scheme. The achieved results report that the DFIG’s performance is effectively enhanced with the proposed PPFC in comparison with the PTC technique. The improved dynamics are observed through the ripples reduction and reduced switching frequency. In addition, the designed observer has successfully managed in estimating the specified variables with high precision.

Multilevel Inverter: A Survey on Classical and Advanced Topologies, Control Schemes, Applications to Power System and Future Prospects

In recent years, multilevel inverters (MLIs) have emerged to be the most empowered power transformation technology for numerous operations such as renewable energy resources (RERs), flexible AC transmission systems (FACTS), electric motor drives, etc. MLI has gained popularity in medium- to high-power operations because of numerous merits such as minimum harmonic contents, less dissipation of power from power electronic switches, and less electromagnetic interference (EMI) at the receiving end. The MLI possesses many essential advantages in comparison to a conventional two-level inverter, such as voltage profile enhancement, increased efficiency of the overall system, the capability of high-quality output generation with the reduced switching frequency, decreased total harmonic distortions (THD) without reducing the power of the inverter and use of very low ratings of the device. Although classical MLIs find their use in various vital key areas, newer MLI configurations have an expanding concern to the limited count of power electronic devices, gate drivers, and isolated DC sources. In this review article, an attempt has been made to focus on various aspects of MLIs such as different configurations, modulation techniques, the concept of new reduced switch count MLI topologies, applications regarding interface with renewable energy, motor drives, and FACTS controller. Further, deep insights for future prospective towards hassle-free addition of MLI technology towards more enhanced application for various fields of the power system have also been discussed. This article is believed to be extremely helpful for academics, researchers, and industrialists working in the direction of MLI technology.

Soft-Switching Current-Source Rectifier Based Onboard Charging System for Electric Vehicles

In this article, a novel soft-switching current-source rectifier (CSR) based bidirectional on-board charger (OBC) system is proposed for electric vehicles (EVs) comprising multiple battery sets. Besides the CSR's inherent advantages of higher-quality input voltage waveforms, enhanced short-circuit-current tolerant capability and long lifetime of dc choke, the cascaded configuration of dc choppers can implement the higher dc-link voltage with multiple low-voltage battery sets, and the low-voltage devices can be used. With the auxiliary resonant circuit in dc link, the soft-switching operation can be achieved for all power switches in the proposed power conversion circuits. Moreover, the high dv/dt caused by high-speed switching silicon carbide devices can be reduced with the capacitor in the auxiliary circuit. The collaborative operation strategy is proposed for the CSR and the dc choppers, which enables reduction of switching frequency of dc choppers and current ripple in dc link simultaneously. The experimental results are presented to verify the performance of the proposed the OBC system.

Stabilizing Switching Law for Reducing Switching Frequency in Switched Linear Systems

Stabilizing Switching Law for Reducing Switching Frequency in Switched Linear Systems