Steady-state Ripple Research Articles

Hilbert–Huang Transform Based Transient Analysis in Voltage Source Converter Interfaced Direct Current System

Due to the rapid discharging of the dc-link capacitors, the short-circuit fault normally results in a fast-growing transient current in the voltage source converter (VSC) based dc power system. Therefore, a fast and sensitive fault detection method is required. In this article, the feasibility of Hilbert-Huang transform (HHT) for fault detection in VSC-based high-voltage direct current systems is analyzed. The instantaneous energy density level is used as the fault detection criterion, which emphasizes the fault characteristics in a predefined frequency range and suppresses the effect of steady-state ripple components. The theory of the proposed HHT-based fault detection method is presented in detail. Its effectiveness is tested on an OPAL-RT based multiterminal dc system and a point-to-point experimental dc system. A response delay within 2 ms after the fault inception is achieved. The comparison with other popular frequency-domain based fault detection methods including the wavelet transform, the short-time Fourier transform, the S transform, and the existing HHT-based analysis, using amplitude frequency coefficient as detection criterion, underlines the performance of the proposed method.

A Low-Ripple Charge Pump With Novel Compensator for Transient-Response Improvement in CMOS Image Sensors

This brief presents a low-ripple, fully-integrated, linear-regulated charge pump with transient-response improvement for CMOS image sensors. A compensator is proposed to accelerate the recovery of the output when an undershoot occurs. The regulated charge pump is designed with 0.11 μm 1-poly 4-metal CMOS process and occupies an area of 0.073 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> . According to the post-layout simulation, the worst steady-state ripple is 0.95 mV <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">PP</sub> and the recovery time (99.9%) of the regulated output is 155 ns when the undershoot is 114 mV. The application of the compensator leads to a 78% decrease on the recovery time. When achieving similar recovery time, the area cost of the proposed topology is reduced by 49% compared to the traditional method of increasing filter capacitance. The total power dissipation of the charge pump is 1.476 mW, and the compensator only consumes 28 μW.

HIL-Assessed Fast and Accurate Single-Phase Power Calculation Algorithm for Voltage Source Inverters Supplying to High Total Demand Distortion Nonlinear Loads

The dynamic performance of the local control of single-phase voltage source inverters (VSIs) can be degraded when supplying to nonlinear loads (NLLs) in microgrids. When this control is based on the droop principles, a proper calculation of the active and reactive averaged powers (P–Q) is essential for a proficient dynamic response against abrupt NLL changes. In this work, a VSI supplying to an NLL was studied, focusing the attention on the P–Q calculation stage. This stage first generated the direct and in-quadrature signals from the measured load current through a second-order generalized integrator (SOGI). Then, the instantaneous power quantities were obtained by multiplying each filtered current by the output voltage, and filtered later by utilizing a SOGI to acquire the averaged P–Q parameters. The proposed algorithm was compared with previous proposals, while keeping the active power steady-state ripple constant, which resulted in a faster calculation of the averaged active power. In this case, the steady-state averaged reactive power presented less ripple than the best proposal to which it was compared. When reducing the velocity of the proposed algorithm for the active power, it also showed a reduction in its steady-state ripple. Simulations, hardware-in-the-loop, and experimental tests were carried out to verify the effectiveness of the proposal.

Applying a modified model predictive current control method to improve surface‐mounted permanent magnet synchronous motor drives performance in transient and steady‐state operations

The performance of the conventional model predictive current control (MPCC) method is not without steady-state ripples in electrical drives. Although some recently proposed MPCC methods have succeeded to mitigate this drawback, they have led to reductions in the dynamic speed response inherent to the conventional MPCC method. An improved MPCC is proposed here which would enhance the conventional MPCC method without any side effect on its merits. In this proposed method, three control strategies are presented for transient- and steady-state operations. The first two strategies are applied to improve motor performance in the steady state, through calculating the voltage vector (VV) and its optimal duration to minimise ripples in both d–q -axis currents. The third strategy is applied in the transient-state operation, where, instead of two VVs, an allowable non-zero VV is applied throughout the control cycle to prevent dynamic response reduction caused by zero VV. The experimental results confirm the effectiveness of this proposed method in reducing torque ripples, flux ripples, and the stator current total harmonic distortion in relation to those obtained by the previous MPCC methods.

Computationally efficient model predictive control of three‐level open‐end winding permanent‐magnet synchronous motor drive

The model predictive current control (MPCC) is popular and widely used method for permanent-magnet synchronous motor (PMSM) and the tuning of weighting factor in classical cost function (CF) of MPCC of PMSM is not required. A three-level inversion-fed open-end winding PMSM (OEW-PMSM) would produce lesser torque and stator flux ripples; however, computation time required for the prediction of control variables is large. This study proposes a control method to three-level inversion-fed OEW-PMSM for reduction of computational time without affecting the performance when compared with conventional MPCC. The proposed method uses a maximum four voltage vectors (VVs) instead of 19 VVs in three-level conventional MPCC. The reduced VVs decrease the number of predictions and computational time for predictions. CF in terms of voltage is used, thereby eliminating the need to predict the currents and faster execution of algorithm is achieved. A higher sampling rate is possible to achieve using the proposed method; thereby, reducing the steady-state ripples in developed torque and stator flux, and improving the percentage total harmonic distortion of stator current. The effectiveness of the presented control method is practically verified after comparing its computational time, steady-state response and dynamic response with that of three-level conventional MPCC.

Fuzzy Logic Speed Control of Permanent Magnet Synchronous Machine and Feedback Voltage Ripple Reduction in Flux-Weakening Operation Region

Voltage feedback flux-weakening control has the advantages of simplicity and robustness against parameter variation. However, due to less voltage control margin in the flux-weakening region, the increased feedback voltage ripple could deteriorate the system performance in the flux-weakening region and may even cause oscillation. In this article, based on a nonsalient permanent magnet synchronous machine, the steady-state feedback voltage ripple in the flux-weakening region are analyzed first. It shows that the feedback voltage ripple caused by the current command ripple could dominate in some flux-weakening regions. Consequently, the speed bandwidth based on the conventional speed proportional-integral (PI) controller in the flux-weakening region can be hardly increased, which leads to poor dynamic performance. In order to obtain both fast speed dynamics and less steady-state ripple, especially in the flux-weakening region, an adaptive fuzzy logic (FLC) speed controller is designed and compared with the conventional speed PI controller. With the adaptive FLC, the dc-link voltage utilization can be increased and better flux-weakening capability can be obtained. Finally, the improved performances are verified by the experimental results.

Architectural Advancement of Digital Low-Dropout Regulators

Digital Low-dropout (DLDO) regulators have been widely utilised for highly-efficient fine-grained power delivery and management in system-on-chips (SoCs) due to their process scalability, ease of integration, and low-voltage operation. However, conventional DLDOs suffer gravely from the power-speed tradeoff, which arises from the use of sampling clocks. To obtain reasonable performance in the undershoot and recovery during load transient states, a large output capacitor is inevitably required in these DLDOs. Moreover, they inherently involve large steady-state voltage ripples and poor power-supply rejection (PSR). These limitations of synchronous DLDOs and their counter measures are thoroughly discussed in this paper. Various design strategies of major building blocks, i.e. comparators and power transistor arrays, are explained in detail with examples. Architectural advances are also expounded including state-of-the-art DLDO architectures such as clock-boosted synchronous, analog-assisted synchronous, asynchornous, event-driven, and hybrid DLDOs. These state-of-the-art DLDOs do not only address the power-speed tradeoff and achieve fast load transient responses, but also can eliminate the use of an output capacitor in some cases. Moreover, some hybrid DLDOs successfully removed the steady state ripples and achieve high PSR. All of these DLDO are compared on basis of their performance metrics and figure-of-merits (FOMs).

Robust Predictive Control of High-Density Cascaded DC Voltage Link Power Converters

Cascaded dc voltage link power converters typically employ a significant amount of energy storage at the intermediate link. The dc bus voltage is assumed to be stiff enough to provide decoupling between the source and load, allowing dynamic regulation functions to be implemented at the load and source terminals independently. In these cases, the size of the dc bus capacitance is dictated by requirements of steady-state ripple voltage, ripple current rating, ride-through considerations, and, more importantly, voltage overshoot during source and load transients. Design tradeoffs in realizing a stable system with acceptable transient performance often place a lower bound in the value of dc bus capacitance. In this paper, a robust predictive controller based on integrated and coupled control at the intermediate dc link, source, and load terminals is presented. The approach permits the use of a small amount of intermediate energy storage compared to conventional decoupled designs. The predictive control aspect of the proposed approach features cost function minimization and accurate duty ratio calculations based on converter model that accounts for small values of dc link capacitance. Although this allows stable operation of the system, it leads to persistent steady state error and transient overshoot voltages. The robust aspect of the proposed approach is based on the theory of variable structure systems. It introduces a capacitor charge restoration function that overcomes the drawbacks of the predictive control by squarely addressing uncertainty of model parameters and operating conditions. The resulting significant reduction in size of the capacitive reactive components opens the prospect of replacing electrolytic capacitors that have a limited life span with film capacitors with much longer life in emerging applications. The proposed approach is presented in a step-by-step manner using a dc-to-dc converter example and further extended to a dc-to-ac inverter case. Extensive computer simulations and experimental results from a laboratory-scale prototype of an example system are used to demonstrate the viability of the proposed controller.

A Low-Noise, Positive-Input, Negative-Output Voltage Generator for Low-to-Moderate Driving Capacity Applications

In this paper, a generic, low-noise, negative-voltage generator with wide tuning range and moderate driving capacity is presented. The highly integrated solution, incorporating a fully-integrated charge-pump and a regulator block, requires only one off-chip capacitor that can be shared with the supply decoupling capacitors. The fully integrated charge-pump operation is analyzed quantitatively, and a closed-form expression of its output impedance is derived. Powered from a single 3.3-V dc input, the output has a tuning range from -4.4 to +2.1 V for biasing applications, while the design supports a maximum load current of 250, 550, and 800 μA for the regulated output voltage at -3.0, -1.5, and 1.5 V, respectively. The measured steady-state ripple is under 3 mV <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">PP</sub> , while the noise voltage at the charge-pump operating frequency harmonics is below 130 μV <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">rms</sub> and the noise floor is under 5 μV <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">rms</sub> . The design is also the application verified with a gallium nitride power amplifier, thus further confirming its low-noise performance. Implemented in CMOS 180-nm process, the prototype chip occupies an area of 0.55 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> .

Performance Analysis of Brush Less DC Motor Drive Using Fractional Order Controller with PSO Algorithm

Background: This paper investigates the detailed study on the performance of Brushless DC (BLDC) motors with sudden application of loads, by using different control techniques. The increasing trend of usage of accurate control, high torque, low noise and higher efficiency for Electric Vehicles has appealed the attention Researcher in BLDC motors. So, BLDC motors can act a substitute for the conventional motors like Switched Reluctance motors, Induction Motors etc. Methods: A Fractional Order Propositional-Integral Derivative (FOPID) controller has been proposed in this paper. The parameters FOPID controller is tuned with Particle Swarm (PSO) algorithm based on Integral Absolute Time Error (IATE) rule. A comparative analysis has been carried out in this paper by simulating the BLDC motor in MATLAB/Simulink and conducting experimental setup in the laboratory. Results: The results reveal that the performance of FOPID controller is better regarding settling time, steady state error and ripple factor in the speed response with sudden load application. Conclusion: In reference to the analysis, it can be summarized that the best tuned Fractional Order PID can perform better than the PID. The digital controller isimplemented using ccs-studio and tested in the DSPms320f28335 board.

A New Control Method Based on DTC and MPC to Reduce Torque Ripple in SRM

This paper proposes a new control strategy to reduce torque ripple in a switched reluctance motor (SRM). The flux linkage in this paper is related to model predictive flux control (MPFC). In addition, the torque hysteresis remained in the system is similar to direct torque control (DTC) and direct instantaneous torque control (DITC). The candidate voltage vectors (VVs) are selected from the torque hysteresis and the cost function is designed for the flux linkage minimization to select the best VV from candidate VVs. The advantages, as well as the improvement prospects for these methods, are discussed in details. Performance for torque ripple in steady state and the robustness in the transient state are evaluated in this paper under the simulation and experimental results, and also the possibility and some advice for model predictive control (MPC) applied to an SRM are indicated. The experimental result for the new method is carried out on a three-phase 12/8 poles SRM with the analysis of torque ripple compared to a DTC and DITC.

Online Torque-Flux Estimation-Based Nonlinear Torque and Flux Control Scheme of IPMSM Drive for Reduced Torque Ripples

In order to have direct and better control of reducing the torque/flux ripples of interior permanent magnet synchronous motor (IPMSM), this paper presents an online torque and flux estimation-based nonlinear torque and flux control (NTFC) scheme of IPMSM drive considering motor electromagnetic developed torque and stator air-gap flux linkage as virtual state variables. For conventional nonlinear controller, the d-q-axis currents (id, iq) are considered as state variables that indirectly controls the torque/flux which may not be suitable for high-performance drives. On the other hand, conventional direct torque and flux control (DTFC) scheme suffers from significant torque ripples. The proposed work overcomes the major drawback of both the conventional nonlinear and DTFC schemes through the significant reduction in torque ripples. Stability of the proposed drive is also demonstrated through Lyapunov's stability criterion and global asymptotic stability is assured through the application of criterion supported by Barbalat's lemma. Reduced torque ripples and robustness of the proposed NTFC scheme is validated through comparative simulation and experimental results with classical nonlinear controller and DTFC-based IPMSM drive. The proposed NTFC scheme achieves the lowest possible torque ripples in steady state at different operating conditions.

Developing a Digital Sliding Mode Controller to Improve the Performance of a Non-Linear Converter

This paper studies the control of the non-linear, time-varying Buck/Buck converter that operates in continuous mode by using the digital sliding mode technology. The main goal is to meet the final objective of achieving acceptable performance and to overcome the system nonlinearity, or in other words, to track the output voltage during load and source diversity. The simulation procedure is based on a small signal state-space model of the Buck/Boost converter in canonical form to achieve the desired operation by using a pulse width modulator to make the system into a stable state, i.e. error signal is zero. This simulation model is preformed in MATLA/SIMULINK to verify the dynamic performance under different operation conditions. All results of the simulation show that this proposed technique both enhances the regulation of the voltage and eliminates the steady-state ripple.

Generalized Multiple-Vector-Based Model Predictive Control for PMSM Drives

Model predictive control (MPC) is emerging as a powerful control method for the high performance control of permanent magnet synchronous motor (PMSM) drives due to its merits of simple principle, quick response, and flexibility to handle multiple variables and constraints. However, conventional MPC applies only one voltage vector during one control period to minimize the cost function, which produces relatively high steady-state ripples and high computational burden due to the enumeration-based predictions. Introducing duty cycle control into MPC can improve its steady-state performance, but the control complexity is further increased. This paper proposes a generalized multiple-vector-based MPC for PMSM drives, which unifies the prior MPC methods in one frame with much lower complexity and computational burden by eliminating the enumeration-based predictions and complex calculations in conventional MPC methods. This is achieved by reconstructing the three-phase duties obtained from the classical deadbeat control with modulator, which also reveals the inherent relationship between deadbeat control and the proposed MPC methods. The presented experimental results confirm the effectiveness of the proposed method.

Constant switching frequency model predictive control for permanent magnet linear synchronous motor

Aim: This paper proposes constant switching frequency model predictive control (CSF-MPC) for a permanent magnet linear synchronous motor (PMLSM) to improve the steady state and dynamic performance of the drive system.&#x0D; Methods: The conventional finite control set model predictive control (FCS-MPC) can be combined with a pulse width modulation (PWM) modulator due to an effective cost function optimization algorithm which is from the idea of dichotomy. In the algorithm, all the voltage vectors in the constrained vector plane are dynamically selected and calculated through iteration. The whole system including control algorithm and mathematical model of PMLSM is built and tested by simulation using MATLAB/Simulink. Besides, the control algorithm is tested in the FPGA controller through FPGA-in-the-Loop test.&#x0D; Results: With the modern digital processors or control hardware such as digital signal processors (DSPs) or field programmable gate arrays (FPGAs), the algorithm can be easily executed in less than 10-micro second. This is very proper for industrial applications. The proposed control algorithm is implemented on FPGA and tested by FPGA-in-the-Loop method. The proposed control algorithm can improve the performance of drive system greatly.&#x0D; Conclusion: The proposed CSF-MPC for PMLSM not only keeps the same dynamic transient performance as FCS-MPC but also greatly decreases the torque ripple in steady state. Furthermore, CSF-MPC is also robust to parameter variations. Simulation and FPGA-in-the-Loop results illustrate that CSF-MPC has an attractive performance for PMLSM drives.

A Universal Multiple-Vector-Based Model Predictive Control of Induction Motor Drives

Conventional finite control set-model predictive control (FCS-MPC) applies single voltage vector within each control period. This leads to relatively high steady-state ripples and requires fast sampling rate. Additionally, enumeration-based optimal vector selection is computationally intensive. Recently, double-vector-based schemes have been proposed to improve the steady-state performance of FCS-MPC. However, they are usually complicated in vector selection and duty ratio calculation. In this paper, a universal multiple-vector-based MPC (UMV-MPC) is proposed, which achieves the same performance as the state-of-the-art double-vector-based MPC, but executes in a much more efficient and universal way. Unlike conventional FCS-MPC, enumerating process and state predictions for candidate voltage vectors are not required in the proposed UMV-MPC to select the best voltage vectors. In UMV-MPC, the optimal vectors and duty ratios are directly constructed from deadbeat control (DBC) based on space vector modulation (SVM), which is easy to follow and quick to use. The proposed UMV-MPC is not only more efficient than prior methods, but also reveals the inherent relationship between double-vector-based MPC and DBC with SVM. A comparative study of UMV-MPC and prior double-vector-based MPC is carried out in this paper. The theoretical analysis as well as simulation and experimental tests on a 2.2-kW induction motor drive are demonstrated to validate the effectiveness of the proposed UMV-MPC.

Digital LDO modelling techniques for performance estimation at early design stage

This work studies the transient responses and steady-state ripples of digital low dropout (LDO) voltage regulators. Simulation models as well as closed-form expressions are provided for estimating the LDO output settling behaviour after load current or reference voltage changes. Estimation equations for the magnitude and frequency of LDO output steady-state ripples are also presented. The accuracy of the developed models is verified by comparing estimation data with results obtained from circuit simulations. The use of the developed estimation equations in design space exploration is also demonstrated.

Adaptive Fuzzy Control System for a Squirrel Cage Induction Motor

A fuzzy adaptive method is designed and implemented in order to improve the response of a scalar fuzzy control system for the speed of an induction motor. The adaptive method determines the set of output membership functions used in the difuzzification process of a typical fuzzy rule based control system. The universe, domain and distribution of the controller's output membership functions are defined at the beginning of every control cycle, thus having a dynamic generation of the set of output membership functions. In this paper, this method is applied to an induction motor in order to control its speed. The experimental results are compared to those obtained with a non-adaptive fuzzy controller, showing an improvement in torque, stator currents and voltages as well as some dynamic parameters such as steady state ripple.

MPPT of Photovoltaic Systems Using Sensorless Current-Based Model Predictive Control

Variability in the solar irradiance level and ambient temperature of photovoltaic (PV) systems necessitates the use of maximum power point tracking (MPPT) of PV systems to ensure continuous harvesting of maximum power. This paper presents a sensorless current (SC) MPPT algorithm using model predictive control (MPC). The main contribution of this paper is the use of model-based predictive control principle to eliminate the current sensor that is usually required for well-known MPPT techniques such as perturb and observe (P&O). By predicting the PV system states in horizon of time, the proposed method becomes an elegant, embedded controller that allows faster response and lower power ripple in steady state than the conventional P&O technique under rapidly changing atmospheric conditions. This becomes possible without requiring expensive sensing and communications equipment and networks for direct measurement of solar irradiation changes. The performance of the proposed SC-MPC-MPPT with reduced load sensitivity is evaluated on the basis of industrial European Efficiency Test, EN 50530, that assesses the performance of PV systems under dynamic environmental conditions. The proposed control technique is implemented experimentally using dSPACE DS1007 platform to verify the simulation results.

Active torque ripple reduction based on an analytical model of torque

The vibration caused by torque ripple may degrade the performance of drivetrain, thus the reduction of torque ripple are necessary for hybrid electrical vehicle/electrical vehicle application, while an analytical description of torque will be the basis. In this study, two-dimensional Fourier series supplemented by polynomial fitting is introduced to reconstruct the numerical solution of magnetic coenergy (MCE) from finite element analysis. An analytical torque model, which can describe torque ripple precisely at all working points, is derived from the reconstructed MCE. On the basis of the torque model, the expressions of harmonic currents used to reduce torque ripple are obtained. The proposed expression also satisfies the principle of maximum torque per ampere. Then, a feedforward torque controller based on the expression of harmonic currents is introduced. Meanwhile, a feedback torque controller based on a torque observer is developed as a comparison. The results of simulation and experiments show that both two controllers can reduce the torque ripple in steady state, but the feedforward torque controller has obviously better effects when motor speed increases. Furthermore, the feedforward torque controller is also beneficial to decline torque ripple during transient process of torque response.