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The back-electromotive force (BEMF) model-based observer is an attractive sensorless control strategy for permanent magnet synchronous motor (PMSM) drives. However, the accuracy of BEMF observer is deteriorated due to the dc offsets caused by current measurement and inverter nonlinearity. To address this problem, the paper proposed a two-degree-of-freedom structure-based backstepping observer (TSBO) for sensorless PMSM drives. First, a two-degree-of-freedom structure is presented to improve the frequency-domain response of the BEMF observer. Second, a second-order complex vector transfer function is inversely introduced into the studied structure to achieve bandpass characteristics. Compared with the conventional BEMF observer, the studied TSBO can achieve dc error suppression without introducing the extra bandpass filter. The studied algorithm is verified by the experimental results on a 4.4kW PMSM platform.

This article reports on the design, modeling, control, and testing of a novel compliant nanopositioning stage driven by a self-developed normal-stressed electromagnetic actuator. To facilitate the parameter selection for the stage to achieve the desired stroke and natural frequency, an analytical model of both the electromagnetic circuit and flexure mechanism is established, which is then systematically verified through finite element analysis. By combining a proportional--integral--differential (PID)-based main controller with a system dynamics inversion-based feedforward compensator, a closed-loop control system for the stage is constructed with the main controller being tuned through Bode's ideal transfer function-based loop-shaping method. The experimental result shows that a stroke of ± 95 μ m and a first natural frequency of 743 Hz are achieved for the designed stage. Finally, taking advantage of the constructed control system, the nanopositioning capability is demonstrated by finely tracking the harmonic and nanostair commands.

The stability problem of low-voltage multi-terminal DC (MTDC) system has drawn lots of interest. This paper focuses on oscillation instability phenomenon of low-voltage MTDC system and analyses the interaction behavior between each voltage-source converter (VSC) and DC network oscillation modal. The typical structure and control strategy of low-voltage MTDC system under master-slave control is first described and its equivalent circuit is established. Then the interaction behavior analytical model is proposed and the source-network and network-load interaction characteristics are studied. Furthermore, a system stability analysis method is built based on the modularized modelling which can solve the problem of how to deal with the complexity of high-order low-voltage MTDC system. The transfer function of the whole system is conveniently established revealing the mechanism of system instability. The proposed method can provide effective stability assessment for low-voltage MTDC system. Finally, the results are verified using electromagnetic transient simulation and validated experimentally using a low-voltage three-terminal DC system test platform with AC 0.4kV/DC 800V. This research can be flexibly promoted to high-order systems for controller design and performance optimization.

Buck-boost inverter with unfolding circuit in a grid-connected mode has numerous advantages but suffers from nonlinear nature and zero-crossing spike, which is difficult to eliminate; it therefore requires an accurate control approach. This paper presents an optimal tuning approach of the digital control system based on a proportional resonant and repetitive controller along with proper pulse-width modulation block. Optimal performance consists in the minimal steady-state error and fast transient response keeping the system in the stable domain in a wide range of operation. It is achieved by a derived set of coefficients of the controller for different operation points. To tune the system, an appropriate transfer function of the plant is developed in the z-domain, taking into account nonlinearity of the system and digital delay. In advance, we present a detailed study of various discretization methods for best coincidence with the simulation and experimental results. Simulation and experimental results confirmed theoretical statements. The proposed approach allows double improvement of the THD of the grid current in most of the operating points.

Vibrations impose negative impacts on the effectiveness and public acceptance of helicopters. Active rotors with trailing-edge flaps have been proved to be an effective way to actively eliminate helicopter vibrations. For the existing control algorithm based on offline system identification, the transfer functions of an active rotor under different flight conditions are pre-requisites to implement closed-loop vibration control. In this study, a three-bladed active rotor with improved trailing-edge flaps is designed, and wind-tunnel tests are conducted to identify the transfer functions of this active rotor using frequency sweep and phase sweep methods. The experimental results demonstrate that these transfer functions are insensitive to the variation of flight speeds: the amplitude of the transfer function varies slightly, while the phase delay almost remains unchanged. In addition, this finding is validated through closed-loop vibration control tests with the active rotor. The transfer function obtained from the hover test results is also applicable to closed-loop vibration control tests under the forward flight conditions. This will dramatically simplify the implementation and operation of an active rotor.

The H₂ finite impulse response (FIR) filtering approach allows for optimal object tracking under harsh industrial conditions. In this brief, we propose a bias-constrained H₂ optimal unbiased FIR (H₂-OUFIR) filter for linear discrete time-invariant systems under bounded disturbances, data errors, and initial errors. The H₂-OUFIR filter is derived using the backward Euler method by minimizing the squared Frobenius norm of the weighted transfer function. A bias-constrained suboptimal H₂ FIR filtering algorithm using a linear matrix inequality (LMI) is also designed. Based on experimental examples of global positioning system (GPS)-based vehicle tracking and video human tracking, it is shown that the batch H₂-OUFIR filter operating on short horizons with full error matrices is able to outperform the Kalman, optimal finite impulse response (OFIR), and unbiased finite impulse response (UFIR) filters.

V/F control has been widely applied for induction motor drive systems because of its simplicity and reliability. However, sustained oscillation often occurs under light load, which leads to undesirable faults. This paper focuses on the causes of oscillation and proposes an oscillation suppression solution. Based on the small-signal model, an open-loop transfer function of induction motor is derived. The resonant peak, which is related to system parameters such as frequency and inertia, is obtained from the transfer function and leads to the unstable regions. The oscillation effects are discussed in detail. Then, the current feedback compensation method without any motor parameter is proposed to suppress the oscillation by decreasing the resonant peak. The feedback gain is optimized and designed. Finally, three current feedback paths are tested and compared in simulation and experiment. Simulation and experimental results have demonstra-ted the correctness of theoretical analysis and the effectiveness of the proposed methods. And the feedback path from current to voltage in d-axis is the best suppression solution for its wider gain range and higher stability in application.

This paper addresses the interactions among the control loops of voltage-sourced converters (VSCs) embedded in high-voltage direct current(HVDC) systems and the impact of these interactions on the performance of individual control loops. Furthermore, this paper proposes a method to design the individual control loops, rather than the interconnected control system, such that the overall system stability is ensured in the presence of interactions. This paper addresses three aspects of the impact of control loop interactions on the overall control system of the VSC including stability, transient response, and steady-state response. To illustrate the impact of interactions on the VSC small-signal stability, stability regions of the interconnected control loops are obtained and compared against those of the various individual control loops. Then, a novel formulation of the VSC stability criterion is presented, and the small-gain theorem is utilized to determine a range of stabilizing gains for the interconnected control system. Moreover, new indices using the infinity norm are introduced to evaluate the impact of interactions on the transient response of the VSC. Finally, the DC gain of a certain set of transfer functions is used to assess the impact of control loops interactions on the set-point tracking capability of the VSC

The DC distribution power system has drawn widespread attention and rapidly developed in recent years, however, its stability issue is one of the urgent challenges, requiring much attention. In previous stability studies, the line impedance network is often overlooked, which is convenient for geographically centralized systems, but inaccurate for the distributed systems. In this paper, the modeling and stability criteria of these two systems are simultaneously studied. For the distributed systems, firstly, the transfer functions from each input voltage or current disturbance to the bus voltage are derived. On this basis, the sufficient and necessary condition for the system stability is discussed. Subsequently, a bus node impedance criterion (BNIC) is proposed to assess the small-signal stability of the DC distribution power system. For the centralized systems, by ignoring the line impedance network, its small-signal model can be deduced by the distributed system, and the proposed BNIC is proved to be still valid. In addition, some existing impedance-based stability criteria are analyzed and compared with the proposed BNIC. Finally, the correctness and effectiveness of the proposed BNIC is verified by the cases study and experiments.

This paper presents a dedicated robust adaptive neural network control (RANNC) scheme for dynamic positioning (DP) of marine vessels with a prescribed performance under model uncertainties, external disturbances and input saturation. To guarantee that the transient performance is always within the prescribed performance constraints, a novel error transfer function is firstly proposed to transfer the original dynamic positioning system with the constrained error behavior into an equivalent unconstrained one. Next, the RANNC scheme is developed with the backstepping technique, and the method of command filter is introduced to avoid the ”dimension disaster” problem. Considering the ship’s inertial matrix and damping matrix are not constant in practice, the adaptive control technique and RBF neural networks are adopted to design the model adaptive controller, which only requires the actuator matrix rather than a completely accurate model. Moreover, minimal learning parameter technique is introduced to minimize the computational burden triggered by weight update of neural networks. Finally, comparison simulation results are provided to illustrate the performance of the proposed RANNC scheme.

This paper presents design of a robust fractional order proportional-integral (FO-PI) prototype controller for a grid connected photovoltaic (PV) system. The robustness in face of parameter variation is handled by designing a suitable controller considering sensitivity function, gain margin and phase margin for both inner and outer control loops. As FO-PI controller is not yet available in physical form and due to complexity involved in grid-tied PV system, we propose an alternative way of hardware implementation of inner loop FO-PI controller by using fractor through RC ladder network. Firstly, an emulator circuit of the inner current loop comprising the FO-PI controller (including fractor and the proportional gain) along with the transfer function of inverter and filter is developed and the response is verified through a real-time simulator (OPAL-RT). Finally, the FO-PI part of the emulator circuit is interfaced with the PC target to form a hardware-in-loop (HIL) by employing OPAL-RT. The performance of the complete system is verified through OPAL-RT simulator. The result shows the improved robustness by the proposed control design method.

The work focuses on a new mathematical formulation for the transfer function of a pulsating injection-based position observer, as the key point for its correct design. The proposed analysis exploits the modulation/demodulation control theory to derive the transfer function of the whole estimator in the Laplace domain. Magnetic iron saturation effects and cross–saturation between the dq-axes are taken into consideration in the observer design. To test the effectiveness of the new transfer function representation of the observer, it is used to synthesise two different regulators, namely by the direct synthesis and the internal model principle. An extensive experimental stage is included pointing to fully verify the accuracy of the proposed model and the theoretical considerations. A comparison with the existing mathematical model of the observer is also reported to show the improvement achievable in the position estimation by the proposed observer synthesis.

The longitudinal control of the platoon of connected and automated vehicles (CAVs) has gained extensive attention in recent transportation research. A majority of existing results are based on linearized third-order vehicular models, under the premise that a complete priori knowledge of vehicle dynamics is available. This article focuses on a general class of third-order nonlinear CAVs with parametric uncertainty and unknown external disturbance which cannot be linearized. A vehicle-to-vehicle (V2V) communication-based cooperative adaptive backstepping control scheme is proposed, in which unknown parameters and disturbance bounds are estimated on-line. Since the transfer function of linear systems cannot be applied to nonlinear systems to guarantee string stability, asymmetric time-varying constraints are employed to prevent the spacing errors from growing up. A realistic example is considered to verify the feasibility of the control algorithm.

The power oscillation damper (POD) in the doubly-fed induction generator (DFIG) is to damp the low- frequency oscillation (LFO) in the power systems. But the POD will introduce the LFO to the DFIG and intensify the oscillation of the latter. In this paper, open-loop subsystems of the DFIG with the POD and the rest part of power system are derived to describe the interaction between them. The balanced truncation method is applied to reduce the transfer function of the DFIG and derive the analytical description to the oscillation of the DFIG. Considering the impact of the POD on the DFIG, the constraint to the DFIG is newly incorporated in the optimization model to the POD parameters, with the aim to alleviate the oscillation of both the DFIG and the power system. The simulation results verify the accuracy of the reduced model of the DFIG, and validate the control effect of the optimized design to the POD of the DFIG.

Due to the nonlinear time-periodic nature, precise impedance modeling of power-converter-based single-phase ac systems is complex. Small-signal modeling for the systems with a fixed operating point is easy, but the extension of the same procedure to the systems with time-periodic trajectory is still challenging. In this article, a recursive single-input single-output (SISO) impedance modeling framework for single-phase rectifiers is presented, which can greatly simplify both the modeling procedure and the resulting impedance model. A general linear-time periodic modeling method is proposed by extending the linear-time invariant modeling method, where frequency-coupling effects are modeled by the transfer function vector rather than the transfer function matrix, so the modeling complexity is reduced. Furthermore, based on the idea of mathematical induction, an analytical and accurate recursive SISO impedance model is derived. The resulting recursive SISO impedance model can characterize the frequency-coupling dynamics of arbitrary order with a low computation burden. Experiments validate the accuracy of the recursive SISO impedance modeling method.

This article classifies, describes, and critically compares different modeling techniques and control methods for dual-active-bridge (DAB) dc–dc converters and provides explicit guidance about the DAB controller design to practicing engineers and researchers. First, available modeling methods for DAB including reduced-order model, generalized average model, and discrete-time model are classified and quantitatively compared using simulation results. Based on this comparison, recommendations for suitable DAB modeling method are given. Then, we comprehensively review the available control methods including feedback-only control, linearization control, feedforward plus feedback, disturbance-observer-based control, feedforward current control, model predictive current control, sliding mode control, and moving discretized control set model predictive control. Frequency responses of the closed-loop control-to-output and output impedance are selected as the metrics of the ability in voltage tracking and the load disturbance rejection performance. The frequency response plots of the closed-loop control-to-output transfer function and output impedance of each control method are theoretically derived or swept using simulation software PLECS and MATLAB. Based on these plots, remarks on each control method are drawn. Some practical control issues for DAB including dead-time effect, phase drift, and dc magnetic flux bias are also reviewed. This article is accompanied by PLECS simulation files of the reviewed control methods.

The Cuk inverter operating in continuous conduction mode (CCM) is susceptible to grid disturbances and its transfer function has two right-half plane zeros, which cause a large phase lag. To improve the output-tracking precision in the grid-connected environment, a repetitive controller with linear phase-lead compensation has been developed for the Cuk inverter. However, this controller requires heavy computational burden and memory space; these problems become more severe as the converter operates at a higher switching frequency. This paper proposes to use a down-sampled repetitive controller (DRC) for Cuk CCM inverter to alleviate these problems. The down-sampling technique itself can significantly reduce the computational burden and memory space of RC. On the contrary, its control accuracy becomes very low, particularly for the Cuk CCM inverter. Unlike conventional module integrated inverters (MIIs), the Cuk CCM inverter must adopt a fractional-order phase-lead compensation algorithm to compensate for the effect of the large phase lag in the down-sampled environment. To clarify the inevitable usage of DRC with a fractional-order phase-lead compensation for Cuk CCM inverter, the DRC is classified into four types, this paper provides its detailed design guideline based on stability analysis of the overall control system and also presents design examples for representative MIIs. Experiments using a 300-W prototype Cuk inverter validate that the proposed control approach achieves acceptable output-tracking accuracy. The total computation time and memory space with the DRC decrease by 76.0% and 80.0% compared to those with the conventional RC while the output-tracking accuracy with the DRC decreases by 0.42%.

This article analyzes the admittance-dissipativity of dual-sequence current control for grid-connected voltage-source converters (VSCs). The output admittance model of dual-sequence current control is first developed in the stationary reference frame by using complex vectors. Impacts of digital filters used within current control and voltage-feedforward (VFF) control loops, and of the delay compensation at the fundamental frequency, are then evaluated. It is found that the cascaded use of sequence-decomposition filter (SDF) and the low-pass filter (LPF) in the VFF control loop adds a nondissipative region in the output admittance, and the fundamental-frequency delay-compensation further worsens the dissipativity. An analytical design method for the LPF is then developed to mitigate the nondissipative region, which lowers the instability risks and improves the stability robustness of dual-sequence current control under different grid conditions. Lastly, simulations and experimental results corroborate theoretical analyses.

By employing the properties of centered realizations, we devise a modified version of the dual Riccati equation approach to optimal $\mathcal {H}_{2}$ control for differential-algebraic systems that is guaranteed to be more computationally efficient and numerically accurate than other methods from literature. Moreover, we show that if the optimal controller has an improper transfer function matrix, then all controllers which ensure a finite $\mathcal {H}_{2}$ norm will share this property.

In this letter we are considering the problem of fixed structure controller synthesis and system identification for large scale systems. The systems considered are referred to as decomposable systems and can be seen as resulting from the interconnection of a large number of identical subsystems. Combining recent results from nonsmooth controller synthesis with the special structure of decomposable systems, we show that the computational complexity of the controller synthesis and system identification procedure scale linearly with the size of the system. Employing results from robust control, the computational complexity of the controller synthesis can be reduced further, however, at the cost of additional conservatism. Using numerical examples we demonstrate that the proposed method can reduce the conservatism compared to existing LMI methods for full order decomposable controllers.

We consider the output-feedback state consensus problem for a homogeneous multi-agent system consisting of one leader agent and $N$ follower agents. The dynamics of each of these agents is governed by a single-input single-output regular linear system (RLS), with the input to the leader agent being zero at all times. The transfer function of this RLS has all its poles in the closed left-half of the complex-plane, with only a finite number of them lying on the imaginary axis. Each follower agent can access the relative output of all its neighboring agents and some of the follower agents can access the relative output of the leader. The communication graph associated with the exchange of relative outputs is directed. Under this setting, we first establish that a controller solves the above leader-follower consensus problem if and only if it can simultaneously stabilize $N$ regular linear systems. We then adapt a recently developed frequency-domain technique to construct a stable finite-dimensional output-feedback controller which solves the simultaneous stabilization problem, and hence the consensus problem. We demonstrate the efficacy of our controller design technique using a numerical example.

In this article, we consider a feedback interconnection, which consists of a networked multi-agent system with its distributed controller and two sets of external input signals. Assuming that the agents are identical, and the dynamics of each agent and its local controller are represented by transfer functions, the well-posedness condition, internal stability and input-output stability of the feedback interconnection are investigated. A controller is designed by solving a Diophantine equation, and a gain for the network is selected using root-locus of a unity feedback system to achieve input-output stability. The developed results are demonstrated with a numerical example.

The double-sided LCC compensation is widely used in the inductive power transfer systems. However, there is no simple and accurate small-signal equivalent circuit model for this resonant converter. Based on the extended describing function method, this paper proposed an full-order (17th-order) equivalent circuit model to accurately predict the small-signal behaviors. For simplification, the full-order model is gradually simplified to a ninth-order model and finally to a fifth-order model. The input to output transfer function are analytically derived for the first time. Both SIMPLIS-based simulation and experimental results are presented to justify the effectiveness of the model, and the model is accurate up to one-fifth of the switching frequency.

For the digitally controlled buck converters, the nonlinearity and time periodicity, caused by the pulsewidth modulator (PWM) and sample and hold, make the accurate frequency-domain analysis intractable. In this article, based on the harmonic transfer function (HTF) approach, a precise small-signal continuous-time modeling for the digitally controlled Buck converter operating in continuous-conduction mode (CCM) under constant-frequency voltage-mode control is presented. The sideband components on the closed-loop control are embedded in the model. Thus, this model is accurate within the full frequency domain region, which breaks the limit of Nyquist frequency. Furthermore, by overcoming the barrier of infinite series introduced by the sideband effects, the analytical loop gain expression is derived, which contributes to accurate stability assessment and reduction of computation burden. In addition, the proposed exact small-signal model has explained the reasons why different information injection points lead to different measured loop gains. Simulations and experimental results are conducted to verify the effectiveness of the proposed method.

This article presents a modified equivalent-input-disturbance (MEID) approach that actively rejects exogenous disturbances. A dynamic compensator is newly introduced in a conventional equivalent-input-disturbance (EID) estimator to further suppress the disturbances. The mechanism of the MEID approach to improving disturbance rejection is analyzed based on the transfer characteristic from the EID to the output of the system, and a stability condition of the MEID control system is presented and is used to design the parameters of the system. A comparison with the conventional EID approach and the disturbance-observer method through experiments demonstrates the validity of the presented method.

This article presents a new hybrid-mode pulse-frequency-modulation control method for an LLC resonant converter. In the proposed control method, the primary-side resonant current sensing signal of the current-mode control variable is combined with a ramp signal of the voltage-mode control variable to determine an operating frequency. Then, the proposed control method mainly modulates the ramp signal in accordance with the output load condition. Therefore, the control-to-output voltage transfer function has both the current - mode control and voltage-mode control characteristics that provide fast frequency response and stable output voltage regulation in a light-load condition. In addition, since the ramp signal is also used for slope compensation of the resonant current sensing signal, an external slope compensation circuit is not required. A small-signal ac modeling and loop analysis of the proposed method verify the advantages. The proposed control method is implemented into a field programmable gate array (FPGA) board with an analog front-end board. An experiment is carried out on a 288-W LLC resonant converter. The result shows that the proposed control method provides fast dynamic performance and stable operation under a light-load condition without an additional slope compensation circuit.

The grid impedance ratio X/R (GIR) and the short circuit ratio (SCR) are the indexes that widely applied to the stability analysis of power systems integrated with voltage source converters (VSC). Based on the assumption that GIR is large enough, the impacts of grid resistances are neglected in most studies. In this paper, the impact mechanisms of grid impedance are analyzed by single-input and single-output (SISO) transfer functions under different GIR conditions. It is found that the decrease of GIR has both “enhancement effect” and “reduction effect” on SISO transfer function magnitudes, while the “reduction effect” is stronger than the “enhancement effect”. When GIR f0/fpll, ∞), the interaction behaves between the grid impedance and phase-locked loop (PLL), and it mainly has impacts on the magnitude-frequency curve. When GIR 0, f0/fpll), the interaction behaves among the phase of grid impedance, PLL and current loop, and it mainly has impacts on the phase-frequency curve. Simulations are carried on Matlab to verify the effectiveness of the proposed analysis.

This letter aims to investigate the robust stability of an interval fractional-order plant with an interval time delay by a general form of fractional-order controllers. Based on a simple graphical procedure, necessary and sufficient criteria are proposed to analyze the robust stability of an interval fractional-order plant. Then, the idea of “robust stability testing function” is extended to analyze the robust stability of the considered type of systems. Besides, an upper frequency bound is provided which is useful for the simulation purposes and it helps to reduce the computational cost. Finally, two examples are presented to verify the usefulness of the obtained results.

This note proposes a novel architecture of integral sliding mode control, in which a special “ideal control” part is introduced. This part incorporates a fairly general form of internal model to deal with regular (i.e., modeled) persistent disturbances. A key property of this architecture is a complete separation of the internal model from the design of the “discontinuous” component of the controller. In particular, the latter component is designed for systems whose dimension coincides with that of the plant, even if the internal model is infinite dimensional.

This study presents the control of the nonlinear model of a continuous stirred tank reactor (CSTR) through different control structures. The structures considered are single feedback configuration (SFC), cascade control configuration (CCC) and sliding mode control (SMC). To design the controllers, the dynamic behaviour of CSTR with a recirculating jacket heat transfer system is modelled into a third order unstable transfer function. Efforts have been made for the first time to control the CSTR also through parallel control configuration (PCC). Model matching technique in low frequency region has been used to design the controllers of SFC, CCC and PCC. The SMC controller parameters are obtained using root-locus technique and by minimizing the performance index. To analyse the performance of CSTR in these structures, simulations are conducted using the nonlinear model equations of the CSTR. The performance is also compared with recently reported work. It is observed that CSTR has been satisfactorily controlled using these structures and the best performance has been obtained using CCC.

This paper proposes a new method to estimate the electrical parameters of five-phase induction motors based on the response to a step voltage applied to the stator with the rotor at standstill. The first part of the method consists of the identification of the parameters of the dynamic model expressed in terms of transfer functions including the fundamental and third-harmonic components of the airgap induction. The second part consists of an open-phase test proposed to estimate the stator leakage inductances of each circuit separately. Further, the impact of iron saturation on the parameters is discussed through Finite Element analysis of a case study. The accuracy of the proposed method is experimentally assessed through the analysis of the behavior of a 4.5-kW motor running in a closed loop under Rotor Field-Oriented Control. The theoretical and practical results suggest that the method can also be applied to self-commissioned drives, given that the estimation proceeds under null torque and speed. The prominent advantages of the proposed method are (i) the possibility of tracking the saturation effects on the parameters, (ii) the tests are easy to execute, and (iii) few sensors are required.

The asymptotic stability of the electric vehicle-to-grid (V2G) system with actuator faults (AFs) is studied in this article. When control signals transmit from controllers to actuators, AFs may affect control laws and destroy the asymptotic stability of the V2G system. Thus, the asymptotic stability of the V2G system with AFs is worked out by the proposed methods in two steps. First, the effects of AFs are analyzed that break or reduce passivity of the V2G system. Second, structure and energy features of the V2G system with AFs are applied to stabilize the system asymptotically. The proposed methods not only avoid applying the observer of traditional fault-tolerant control (FTC) methods to design control laws but also avoid switching from one control law to traditional FTC control law. Finally, the validity and advantages of the proposed methods are shown in examples.

With the variation of parameters, the performance of the buck-boost converters may degrade due to the nonlinear phenomenon such as Neimark-Sacker bifurcation, period doubling bifurcation, even chaos. In this paper, a method to suppress the bifurcation and improve system stability through improving the control principle is indicated. By changing the control principle of the conventional OCC, the proposed one-cycle energy balance control method achieve the one-cycle control by keeping the energy balance of the circuit in each switching cycle. Then the poles of system transfer function are adjusted and the parameter stability range is extended, which achieve the objective of suppressing the bifurcation. Furthermore, such adjustments do not increase the order of the transfer function, thus there is no increase in the computational complexity. Compared with the conventional OCC method, the theoretical analysis based on the sampled-data model demonstrates the ability of the proposed method to suppress the bifurcation and extend the parameter range. Further simulation and experimental results also validate the theoretical analysis.

DC Motor is an essential element for many applications in the field of automation, robotics, and many others. They are important for many engineers to understand its behaviours and characteristics. However, controlling any system is still a challenge because of their abnormal behavior. In this paper, we are applying techniques to understand the behavior of servo system. Several groups of researchers conducted experiments based on a standard first-order model of a DC Motor using first principles modeling to derive the parameters. However, not much highlighting is identified on how well these models match up the actual data. In this paper, a deeper understanding has been taken place to gain some familiarity in testing and measurements by exploring a special arrangement in a laboratory called Quanser QUBE-Servo. In addition to this, signals monitoring on the live-mode has the advantage of gaining conceptual knowledge in the experimental test, analysis, and verification of the system. On the other hand, solving differential equations numerically using powerful software such as LabVIEW which endorses the comprehension of the system operation. In general, this report discusses a simple technique to study the DC motor transient response, read the angular position of the encoder by interface data acquisition device used with LabVIEW software.

Duty-cycle control is a widely used control method of resonant converters. In this article, the existing model of duty-cycle controlled resonant converters is found to have discrepancy compared with the simulation and experimental results. The reason behind is investigated, showing the phase change in the output voltage of the inverter bridge caused by the duty-cycle perturbation was ignored in the existing model. The phase change law is highly dependent on the duty-cycle scheme used, which is further determined by the forms of the carriers and the switching sequences of the resonant converters. With this consideration, improved models of both full-bridge and half-bridge resonant converters with different duty-cycle control schemes are rederived. It is revealed that different duty-cycle control schemes lead to different phase curves of the duty-cycle-to-output-voltage transfer functions, therefore care should be taken when selecting the appropriate duty-cycle control scheme. In the end, a series-series compensated wireless power transfer system is built to verify the validity of the proposed models.

It is commonly believed that observer-based compensation is an effective way for disturbance rejection. A less talked about fact is that such disturbance rejection control technique may also degrade control performance. In this article, we present a typical cross-coupling system to reveal this problem and, more importantly, propose a new design principle of conditional disturbance negation (CDN) to eliminate its potential drawbacks of disturbance observer-based compensation. Qualitative analysis is first given for a general form of such cross-coupling systems, indicating the necessity of CDN. The analysis and control design principle of CDN is then exemplified through two applications. A numerical linear application produces abundant quantitative results through the powerful transfer function and frequency domain tools. A more complex nonlinear flexible air-breathing hypersonic vehicle application shows how conventional compensation deteriorates the couplings between rigid and flexible modes, and validates the effectiveness of CDN through comprehensive model analysis and simulation results. The proposed CDN design principle also arouses awareness of the importance of: 1) understanding the characteristics of the plant to be controlled and 2) recognizing the critical role the information plays in engineering practice.

The proportional-integrator (PI) controller in the synchronous reference frame (dq-frame) and the proportional-resonant (PR) controller in the stationary reference frame (αβ-frame) are two typical linear current control schemes for three-phase voltage source converters. It is generally believed that the plant model is mathematically uncoupled in αβ-frame. Hence, the decoupling control required to attenuate the axis cross-coupling effect in dq-frame is regarded as not necessary in αβ-frame. However, detailed analysis with complex coefficient transfer functions reveals differences in the control performance between the fully decoupled PI control scheme in dq-frame and the PR control scheme in αβ-frame. When regulating sinusoidal currents in αβ-frame, the α-axis and β-axis current references are strongly correlated with each other, which implies a cross-coupling effect equivalent to that of dq-frame. In analogy to the dq-frame decoupling control, cross-coupling terms can be employed together with the conventional PR control scheme. It can bring the benefit of improving the transient response of current tracking and reducing the sensitivity of the resonant controller to frequency variation, especially for low-switching-frequency applications with limited current control bandwidth. Furthermore, the cross-coupling terms based on reference current feed-forward are proposed to improve the performance of both positive- and negative-sequence current control. Experimental results are shown to validate the analysis and the performance of the proposed control scheme.

In this work, fractional order proportional integral derivative controller (FOPIDC) is proposed and implemented for speed control of electric machines using nature-inspired metaheuristic optimization algorithm (MOA) named as flower pollination algorithm (FPA). Investigations are performed by considering the second-order transfer function of D.C Motor. FOPIDC constants K P , K I , K D , λ , and μ are optimized by considering FPA. The desired response of the electric machine is obtained by using tuned parameters of FOPIDC. After that, FOPIDC response using FPA is compared with PIDC response using FPA in the sense of time-domain specifications and performance indices (PI) like ‘integral of square error (ISE), integral of time-weighted square error (ITSE), integral of absolute error (IAE) and integral of time-weighted absolute error (ITAE)’. Finally, the desired response of electric machine using FPA based FOPIDC is compared with desired response of electric machine using firefly algorithm (FA) and particle swarm optimization (PSO) algorithm based FOPIDC.

The feedback control may cause the system to oscillate or even collapse due to its unreasonable parameters, so the stability analysis with considering the control parameters is very important. The traditional frequency-domain stability analysis method based on the small-signal modeling has limitations in the inverter stability analysis due to the existing power frequency and the complexity of the transfer functions. In this article, a time-domain stability analysis method for a grid-connected inverter with proportional-resonance (PR) control is first proposed based on Floquet theory. Meanwhile, a transfer function decomposition construction method is first proposed to obtain the time-domain model of the PR control in this article, which makes the traditional frequency-domain control be analyzed in the time domain. Furthermore, the comparison of calculation cost between the proposed stability analysis method based on the Floquet theory and the traditional frequency-domain stability analysis method is given. Finally, the simulation and experimental results prove the correctness and effectiveness of the proposed time-domain stability analysis method for the grid-connected inverter with the PR control. Therefore, this article provides a new way of the stability analysis for the grid-connected inverter.

Low-frequency oscillations have been reported in several weak-grids-connected voltage-source-converter(VSC) systems. Although efforts have been devoted to understand the parametric and sensitivity impact of the VSC controller gains, a general formulation of the oscillation mechanism is still missing. Using transfer function dynamic modelling approach, we find that the outer loop active power control's bandwidth mainly determines the oscillation frequency. The PLL introduces a large phase lag around the frequency of the PLL bandwidth in weak grids conditions which decreases the oscillation damping. A simple but effective PI+Clegg integrator (CI) compensator is proposed to replace the standard outer loop active power controller compensating the PLL's phase delay and increase the oscillation damping. The results are verified in a real time digital simulator.

Formulating a fractional-order controller and then implementing it in real-world environment is a challenging task for control professionals. Therefore, this paper proposes a simple, analytical and robust fractional-order controller synthesis scheme using Bode ideal transfer function in internal model control (IMC) paradigm. The controller acquires a PI form followed by a fractional-order integrator. The main advantage of the proposed scheme is that only two tuning parameters are required for satisfying the desired gain crossover frequency and phase margin. The properties of the proposed scheme are examined on the basis of tracking and disturbance rejection attributes. The effectiveness of the proposed method is verified through simulations of linear and nonlinear systems, and it is further experimentally validated on QUBE-Servo 2 set-up to control the velocity of DC motor. The proposed scheme exhibits satisfactory tracking and disturbance rejection performance when compared with integer-order and fractional-order PI controllers.

Uphill and downhill roads are prevalent in mountainous areas and freeways. Despite the advancements of vehicle-to-vehicle (V2V) communication technology, the driving field of vision could be still largely limited under such a complex road environment, which hinders the sensors from accurately perceiving the speed of front vehicles. As such, a fundamental question for autonomous traffic management is how to control traffic flow associated with the velocity uncertainty of preceding vehicles? This paper aims to answer this question by devising a cooperative control method for autonomous traffic to stabilize the traffic flow under such a complex road environment. To this end, this paper first develops a traffic flow model accounting for the uncertainty of preceding vehicle’s velocity on gradient roads and further devises a new self-delayed feedback controller based on the velocity and headway differences between the current time step and historical time step. The sufficient condition where traffic jams do not occur is derived from the perspective of the frequency domain via Hurwitz criteria and $$H_{\infty }$$ norm of transfer functions. The Bode diagram reveals that the robustness of the closed-loop traffic flow model can be significantly enhanced. Simulation results show that the key parameters (control gain coefficient and delay time) of the designed controller contribute to the stability of traffic flow, which is consistent with the theoretical analysis conclusion.

A new model diminution technique is proposed for the reduction of complexity of higher order linear dynamical systems. In this proposed method, a generalized pole clustering technique is used for obtaining the denominator polynomial of the lower order plant and the numerator polynomial is evaluated by applying the Pade approximation technique. The generalized pole clustering algorithm promises the preservation of stability and dominant poles of the actual system in the reduced order plant. The performance error indices such as integral square error (ISE), integral absolute error (IAE), integral time weighted absolute error (ITAE) and relative integral square error (RISE) are used to validate the proposed technique. By using the transfer function of the simplified order plant, the PID and lead/lag compensators are designed by using a moment matching algorithm. This controller is applied to the original large scale system and the response of the closed loop system is matching with the response of the desired reference model.

Input-output pairing effectively minimizes the loop interaction in MIMO processes and avoids integral instability. In this article, a modified Relative Normalized Gain Array is proposed for the Inp...

Robotic dexterous operation is a long-term challenging problem. Although recent advances in robotic hand have successfully realized some complex operations, its high dexterity and high precision control are still challenges for robotic hands to replace the human hand. Here, this letter developed a tendon-sheath transmission-based robotic hand with decoupling joint design and high-precision closed-loop control strategy. Firstly, the designed hand is introduced, and the nonlinear joint transmission model is established. Then, the transfer function of the joint is established based on the dynamic model, and an adaptive controller with neural network compensation is designed to realize the high-precision joint control. The simulation and experiment results show that it is feasible to apply the tendon-sheath transmission method to the robotic hand, and the proposed closed-loop control strategy can significantly improve the joint control accuracy. This research opens new prospects for the novel tendon-sheath driving method applied in the design of robotic hand, which is expected to have a long-term impact for the design and control of dexterous hand.

The modeling results and industrial tests of a typical automatic control system (ACS) and the proposed invariant cascade ACS are presented. The advantages of structural-parametric optimization methods for creating high-quality control systems for heat-and-power processes have been substantiated. The following algorithm for forming a block diagram of a high-quality invariant cascade SAR is proposed. At the beginning, the structure of the optimal transfer function of the stabilizing regulator is determined as the product of the inverse transfer function of the leading section of the object by a given transfer function of the open system of the internal circuit in the form of an ideal integrating link with one calculated parameter of dynamic tuning, which allows optimally working out both internal disturbances and the task of the stabilizing regulator. Then, the parameters of the dynamic adjustment of the corrective regulator are calculated for optimal processing of the extreme external disturbance. Next, an equivalent external perturbation is isolated without its direct measurement using a complete model of the inertial section of the object. At the same time, the obtained difference between the main adjustable value and the model output is fed to the input of an equivalent external perturbation compensation device implemented in the form of a differentiator, which makes it possible to increase the accuracy and speed of the invariant SAR compared to the standard one. To ensure high quality control over the entire range of load changes, the parameters of the dynamic adjustment of the invariant SAR and the model of the inertial section are adjusted in the load function.

Pt100 is a resistance temperature detector characterized by a relatively linear resistance/temperature relationship in a narrow temperature range. However, the Pt100 sensor shows a certain degree of static transfer function nonlinearity of 4.42 % in the range between −200 °C and 850 °C, which is unacceptable for some applications. As a solution to this problem, a mixed-mode linearization method based on a special dual-stage piecewise linear ADC design is proposed in this paper. The first stage of the proposed dual-stage piecewise linear ADC is performed with a low-complex and low-power flash ADC of a novel sequential design. The novelty of the proposed sequential design is reflected in the fact that the number of employed comparators is equal to the flash ADC resolution. The second stage is performed with a delta-sigma ADC with a differential input and differential reference. Using the 6-bit flash ADC of novel design and the 24-bit delta-sigma ADC, the nonlinearity error is reduced to 2.6·10−3 %, in the range between −200 °C and 850 °C. Two more ranges are examined, and the following results are obtained: in the range between 0 °C and 500 °C, the nonlinearity error is reduced from 1.99 % to 5·10−4 %, while in the range between −50 °C and 150 °C, the nonlinearity error is reduced from 0.755 % to 2.15·10−4 %.

Droop-based converter plays an important role in future multi-terminal DC (MTDC) system due to its control flexibility, which imposes a great challenge on the stability of the DC grid. Traditional input impedance and eigenvalue analysis methods fail to build the mathematical relationship between the system operating points and the related critical parameters that keep the system stable. The main objective of the paper is to examine the DC side stability of the single grid-connected VSC with the single input single output (SISO) method. The transfer function between the small perturbation of DC-link voltage and DC current at the end of transmission line is firstly constructed considering the control impacts of droop-based converter and the dynamics of DC networks. Based on SISO model, the stability criteria of single VSC converter under different control modes is further proposed by using the classical Routh Judgement. In addition, the sufficient stabilizing conditions and DC side stability boundary are accordingly obtained based on the derived stability criteria. It is worth mentioning that, a critical operation index, namely, DC power transfer limit (DCPTL) is firstly defined for the droop-based converter operating as an inverter, and DC system instability might occur when the transmitted power exceeds this limit. Finally, numerical simulation results of two-terminal HVDC system validate the accuracy of the proposed stability analysis and the criteria for the droop-based converter.

This paper presents an improved equivalent-input-disturbance (EID) approach to deal with exogenous disturbances. A high-order filter is newly used to construct an improved EID estimator. The parameters of the filter are selected to improve the disturbance-rejection performance without changing the bandwidth of an EID-based control system. The stability and disturbance-rejection mechanism of the system are analyzed using the transfer function from the EID to the output. The high-order filter is designed using the loop-shaping method. Simulation results of a rotational control system demonstrate the validity of the approach and superiority over other methods.