Voltage Tracking Error Research Articles

Current sensorless finite-time control for buck converters with time-varying disturbances

DC–DC buck converters are widely adopted to feed power from renewable energy distributed generators into smart grids. Sliding mode control (SMC) schemes enable such converter systems to inject high-accuracy voltage and current into the connected devices or loads, which are of good robustness in dealing with matched disturbances and model uncertainties. However, the chattering phenomenon, caused by the discontinuous control law, leads to large ripples in output voltage and increases switching losses. Moreover, in current sensor failure cases, conventional state feedback control law is not available for higher control performance. In this research paper, a recursive design based universal finite-time observer (UFTO) is applied to reconstruct the current information and lumped disturbances simultaneously, which provides an active disturbance rejection approach. Then, a non-singular sliding mode control based current sensorless finite-time control strategy is developed for the converter system to improve the transmit behaviours, control accuracy, and fault tolerance ability in the presence of various time-varying disturbances. As compared with traditional PID and existing asymptotical current sensorless approaches, both finite-time convergence property of voltage tracking error and active suppression ability against time-varying disturbances are obtained. A rigorous analysis on robustness stability has been provided for the proposed current sensorless finite-time control method. Experimental results are explored to comprehensively illustrate the feasibility and effectiveness of the proposed strategy.

Analytical synthesis of voltage‐mode even/odd‐nth‐order differential difference current conveyor and fully differential current conveyor II‐grounded resistor and capacitor universal filter structures

SummaryA complete definition of an odd/even‐nth‐order notch or band‐reject filter transfer function is presented. Based on the differences between the input voltage and (i) an nth‐order high‐pass; (ii) a traditional nth‐order notch; and (iii) an nth‐order all‐pass filtering transfer function, a systematic method has been proposed to derive a universal filter structure that can realize voltage‐mode odd/even‐nth‐order low‐pass, band‐pass, high‐pass, all‐pass and traditional notch filters. The intrinsic capability of voltage‐mode addition and subtraction of the two active elements, differential difference current conveyors and fully differential current conveyors, is used to advantage in the aforementioned synthesis procedure. Based upon the definition of an nth‐order notch or band‐reject filter transfer function proposed in this paper, the aforementioned universal one has been further extended to the newly defined nth‐order band rejection filter. The voltage and current tracking errors of the two active elements are compensated by varying the resistances of the proposed filter. Filtering feasibility, stability, component sensitivities, linear and dynamic ranges, power consumption, and noise are simulated using H‐Spice with 0.35 µm process. Compared to some of the recently reported universal biquads, the new one is shown to enjoy the lowest component sensitivities and the best output accuracy for all‐pass signals. Moreover, Monte Carlo and two‐tone tests for intermodulation linearity simulations are also investigated. Copyright © 2014 John Wiley & Sons, Ltd.

Robust Integral Voltage Tracking Control for PEM Fuel Cell Systems Under Varying Operating Current

This paper presents a robust controller design approach for nonlinear PEM fuel cell systems in a linear parameter varying system representation. The magnitude bounds on variations of the elements of system matrices corresponding to variational operating current are identified and addressed during control law construction via numerically tractable linear matrix inequality algorithms. In order to achieve voltage control with diminishing tracking error, integration of the tracking error is considered as an additional state and included in the fuel cell control system design. For a desired magnitude of voltage tracking command, the allowable magnitude constraints on gas flowrate are specified accordingly. The upper bound of the energy ratio between voltage tracking error and command is minimized in terms of \({\mathcal {H}^\infty}\) optimization. In time response simulation based on the parameters of a Ballard 5 kW PEM fuel cell, both constant step and variational sinusoid tracking commands are considered for verification. The situation of a sudden change of load resistance and output current is also included in the simulation study. As demonstrated, the proposed robust controller design can achieve the desired voltage tracking performance for the tracking command and gas flowrates with specified magnitude while the operating current varies within its specified range.

Output-feedback voltage tracking control for input-constrained PEM fuel cell systems

An output-feedback voltage control system for nonlinear PEM fuel cells is presented. For voltage tracking around equilibrium operating points, the controller design minimizes the energy ratio between tracking error and normalized command while hydrogen and oxygen flowrates satisfy specified magnitude constraints and closed-loop poles meet desired placement constraints. Time response simulations based on Ballard 5 kW PEM fuel cell system parameters verify the design. Simulated controllers constructed numerically via the linear matrix inequality algorithm elaborate relationships between designed input flowrate and voltage tracking error. With controller design based on the same nominal input flowrate constraints, the achieved voltage tracking capability is comparable to our published state-feedback design study. To reduce voltage tracking error under fixed external resistance, gas flowrate magnitude constraints must be relaxed, requiring more fuel energy to manipulate the system variables for operation away from equilibrium conditions. Whereas state-feedback designs depend on internal state variables which are not always measurable, output-feedback control using only voltage tracking error as measurement simplifies practical implementation.

Architecture of a Network-in-the-Loop Environment for Characterizing AC Power-System Behavior

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> This paper describes the method by which a large hardware-in-the-loop environment has been realized for three-phase ac power systems. The environment allows an entire laboratory power-network topology (generators, loads, controls, protection devices, and switches) to be placed in the loop of a large power-network simulation. The system is realized by using a real-time power-network simulator, which interacts with the hardware via the indirect control of a large synchronous generator and by measuring currents flowing from its terminals. These measured currents are injected into the simulation via current sources to close the loop. This paper describes the system architecture and, most importantly, the calibration methodologies which have been developed to overcome measurement and loop latencies. In particular, a new “phase advance” calibration removes the requirement to add unwanted components into the simulated network to compensate for loop delay. The results of early commissioning experiments are demonstrated. The present system performance limits under transient conditions (approximately 0.25 Hz/s and 30 V/s to contain peak phase- and voltage-tracking errors within 5<formula formulatype="inline"><tex Notation="TeX">$^{\circ}$</tex> </formula> and 1%) are defined mainly by the controllability of the synchronous generator. </para>

High-performance flux-based two-degrees-of-freedom uninterruptible power supply

A three-phase flux-based two-degrees-of-freedom uninterruptible power supply with improved voltage regulation performance is presented. The proposed AC supply is controlled using an outer P+resonant voltage regulation loop to nullify voltage tracking errors and compensate for unbalanced voltages. Within this outer voltage loop is a flux-based two-degrees-of-freedom inner current regulation loop for the fast compensation of dynamic load changes and other external disturbances. This inner current regulator originates from the combined use of classical two-degrees-of-freedom control theory and a hysteretic flux modulation technique. By integrating the individual advantages of P+resonant compensators, two-degrees-of-freedom control and flux modulation, the proposed AC supply can achieve both precise steady-state tracking and a fast transient response. Theory and experimental results are presented to validate the performance of the proposed AC supply.

Current-Mode High Output Impedance Multifunction Filters Employing Minimum Number of FTFNs

In this study, five current-mode FTFN-based multifunction filters are proposed, which realize the same transfer functions in ideal case. All circuits employ two capacitors and three resistors. For each circuit R-C:C-R transformation increases the number of realization possibilities to ten. The proposed topologies simultaneously realize three basic filtering functions using minimum number of FTFNs and provide high output impedances that enable easy cascading in current mode. Sensitivity analysis of the filters show that they have low passive sensitivities, \omega_0, Q and \omega_0/Q of the filters are insensitive to current tracking errors, furthermore \omega_0 of the filters are insensitive to voltage tracking errors of the FTFNs. The proposed circuits do not require component matching condition except for notch and allpass responses and permit independent adjustment of \omega_0 without disturbing \omega_0/Q. Experimental and simulation results are given to verify the theoretical analyses.

A new four terminal floating nullor based single-input three-output current-mode multifunction filter

In this study, a new circuit configuration to realise a current-mode multifunction filter is presented. The circuit uses four four terminal floating nullors (FTFNs) and six passive components, four of them are grounded and can simultaneously realise low-pass, band-pass and high-pass filter functions without changing the circuit topology and elements. It does not require any parameter matching condition and has the possibility of independent adjustment of ω 0 without disturbing ω 0/ Q. Sensitivity analysis of the filter shows that it has low passive sensitivities and ω 0, Q and ω 0/ Q of the filter are insensitive to current tracking errors, furthermore ω 0 of the filter is insensitive to voltage tracking errors of the FTFNs. All outputs of the multifunction filter exhibit high output impedances so that the synthesised current-mode filters can be cascaded without additional buffers. The theoretical results are verified by PSPICE simulations.

A new CCII-based sinusoidal oscillator providing fully independent control of oscillation condition and frequency

In this paper, a new CCII-based double-resistance controlled sinusoidal oscillator employing grounded resistors and capacitors is presented. The oscillator topology provides fully independent control of oscillation conditions and oscillation frequency, and suitability for VLSI realization due to including only grounded passive elements. The circuit exhibits low active and passive sensitivities; voltage and current tracking error effects on the current conveyors can easily be eliminated with careful design. Moreover, a methodology for determination of linear operation conditions of the oscillator is studied. For the proposed oscillator circuits, the maximum output signal level not causing clipping and the slew-rate-limiting problem is determined using a simple formula. Theoretical results are confirmed with both PSPICE simulations and experimental results.

New current conveyor based active-gyrator implementation

An active-gyrator circuit employing one positive type and one negative type second generation current conveyors is presented. The circuit uses a minimum number of passive components which are all grounded and no element matching conditions are imposed. The circuit is compared with the existing ideally equivalent topology considering voltage and current tracking errors and loading effects.

Novel second-order current mode filters using CCIIs

Two new current mode active-RC networks using the second generation current conveyer (CCII) devices are presented. The circuits provide high-Q bandpass (BP)/lowpass(LP) filter characteristics; the highpass(HP) response may also be obtained with suitable design. Current mode sine wave signal generation (Q→α) is possible by tuning a grounded resistor. With non-ideal CCIIs the design equations are slightly altered owing to CCII port current and voltage tracking errors (ei,v). 3

Insensitive current mode realization of third-order Butterworth characteristics using current conveyors

An active-RC realization scheme of a third-order Butterworth function in the current mode, using the second-generation current conveyor (CC II) active elements and with all equal-valued passive components, is proposed. With nonideal CC II's, some of the coefficients of the function are altered owing to the finite port current and voltage tracking errors of the device. The network parameters are practically insensitive to the device errors.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

The single CCII biquads with high-input impedance

Two new configurations for the design of single second-generation current conveyor (CCII) biquad (SCB) filters with high-input impedance are presented. They can synthesize low-pass, bandpass, high-pass, all-pass, and notch filtering functions with a single CCII connected to five passive one-port RC elements. The active and passive sensitivities are calculated in order to determine the suitable domain for filtering applications. The quality factor and natural frequency of the proposed SCBs are insensitive to the voltage tracking error of the CCII. Experimental results that confirm the theoretical analysis were obtained. The circuits studied show the versatility of the CCIIs.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>