Loss-free Resistor Research Articles

Digital Sliding Mode Control of a 3-Phase AC-DC rectifier for Ultra-Fast Charging of EV Battery

This paper describes a digital sliding mode control (SMC) technique applied to a three-phase four-wire rectifier operating at a fixed frequency for ultra-fast charging of electric vehicle (EV) battery. The control algorithm employs three decoupled sliding mode controllers to achieve loss-free resistor (LFR) behavior in each phase for power factor correction (PFC). The design of the sliding mode controller is twofold. The first one is to guarantee convergence of the sliding variable to zero. The equivalent control and the discrete-time dynamic model of the rectifier are obtained by imposing sliding-mode regime in discrete-time. The second one is to stabilize the inner-loop under the obtained control law. Theoretically, the resulting inner-loop is stable with a deadbeat behavior in the inner current loop. The results are validated by numerical simulations using on a 350 kW AC-DC rectifier for EV battery ultra-fast charging applications. The numerical simulation results performed on the switched model implemented in PSIM© software are in close agreement with the theoretical analysis.

Constant Power-Constant Voltage Battery Charging Based on a Loss-Free Resistor Approach

Constant Power-Constant Voltage Battery Charging Based on a Loss-Free Resistor Approach

Series Loss-Free Resistor as Stabilizing Active Damping of Constant-Power Load Systems

Series Loss-Free Resistor as Stabilizing Active Damping of Constant-Power Load Systems

The Virtual Resistor Used in Droop Control of DC Microgrids is a Series Loss-Free Resistor (SLFR)

The recently introduced series loss-free resistor (SLFR) is used to obtain the non-linear differential equations that describe the dynamic response of a DC-DC converter with virtual resistor and input LC filter, employed in the voltage droop control of DC microgrids. The equilibrium point and the stability criteria of the converter are presented. The results of the theoretical analysis are validated via computer simulation of largeamplitude transients for step change of the input voltage, the output current and the voltage reference signal. It is shown that the energy absorbed by the virtual resistor is not converted into heat but returned to the input stage by a power source. Thus, the paradox of the virtual resistor, which causes a voltage drop but does not consume power, is resolved. This is a theoretical study.

Comment on “Series Loss-Free Resistor: Analysis, Realization, and Applications”

In the paper by Barbi (2021), the concept of series loss-free resistor (SLFR) was presented. The SLFR was realized by novel circuitry derived by topological variation of classical noninverting buck–boost converter operated in discontinuous-conduction mode. The purpose of this note is complementing the work of Barbi (2021) by demonstrating that SLFR may also be realized by classical converters employing dedicated current loops. Validation is carried out by realizing the capacitors balancer example by Barbi (2021) by means of a classical noninverting buck–boost converter, demonstrating the results similarity.

Series Loss-Free Resistor: Analysis, Realization, and Applications

An analysis of the transient behavior of dc networks consisting of voltage sources, capacitors, and series loss-free resistors (SLFRs) is presented. The realization of an SLFR was achieved by means of a topological variation of the positive output voltage buck-boost converter operated in discontinuous-conduction mode. It is demonstrated that even simple RC circuits containing SLFRs exhibit behavior that is described by Abel nonlinear differential equations, which do not have an exact analytical solution. Some possible applications of the SLFRs in power electronics, dc microgrids, and renewable energy power systems include loss-free charge and discharge of capacitor banks, voltage equalization of capacitors, and loss-free voltage clamping circuits. The concept of the SLFR can also be applied for voltage control in dc microgrids, employing the droop voltage technique, equalization of power and current in voltage sources associated in parallel (including batteries and dc-dc converters), and also input and output voltage natural balance in input-series output-series association of dc converters. The theoretical analysis results are validated via numerical examples and computer simulation.

Analysis and Design of Self-Oscillating Resonant Converters with Loss-Free Resistor Characteristics

A general approach for the analysis and design of self-oscillating resonant converters is presented in this paper, for a particular class of circuits in which the change of input voltage polarity is caused by the zero-crossings of the input inductor current. The key features of the method are an analytical description in the time-domain of a spiral that eventually converges into an ellipse, and a frequency–domain analysis that explains the behavior of the ellipse as a limit cycle. On a theoretical basis, this class of circuits behaves as loss-free resistors (LFR) because in steady-state the input inductor current is in phase with the first harmonic of the input voltage. The proposed analytical procedure predicts accurately the amplitude and frequency of the limit cycle and justifies the stability of its generation. This accuracy is reflected in the close agreement between the theoretical expressions and the corresponding simulated and measured waveforms. Third and fourth order resonant converters are designed following simple guidelines derived from the theoretical analysis.

Emulation of Loss Free Resistor for Single-Stage Three-Phase PFC Converter in Electric Vehicle Charging Application

In this article, the modular three-phase ac-dc converter using single-phase isolated Ćuk rectifier modules for charging of electric vehicles is discussed. The converters are designed and analyzed for the continuous conduction mode (CCM). This article is based on a new concept of adaptive sliding-mode-based loss-free resistor (ASLFR). ASLFR is a control scheme, which allows dual aim of power factor correction along with tight voltage regulation; hence, the adopted topology serves as a fitting single-stage solution for balanced three-phase systems. Complete theory is developed for the application, and the effectiveness of the scheme is well-established. Various studies to confirm the robustness of the system to any load and line variation are carried out. Moreover, a qualitative analysis is also made to show the expediency of the proposed ASLFR. Simulation as well as experimental studies are claimed theoretically.

Modelling and Control of Modular DC-Nanogrids Based on Loss-Free Resistors

This paper proposes a modular photovoltaic (PV) dc-Nanogrid (dc-NG) architecture for residential applications. The proposed architecture is based on the Loss-Free Resistor (LFR) concept. The dc distribution bus is supplied by PV panels, ac utility and a storage battery. The storage battery is connected to the main dc bus through a dc-dc bidirectional converter (BDC). This battery has also an important role to ensure uninterruptible power supply to the critical loads and controls the power flow in the dc-NG. A mathematical model of the system is first derived and a stability analysis is carried out showing that the stability is guaranteed under certain mild conditions. Numerical simulations of a case study for two PV panels corroborate the theoretical predictions which have been finally confirmed by experimental measurements.

An Electrolytic Capacitorless Modular Three-Phase AC–DC LED Driver Based on Summing the Light Output of Each Phase

The proposal of this paper is a modular three-phase ac–dc light-emitting diode (LED) driver for high-power luminaires based on LEDs that uses each phase to control an independent LED load removing in the process both the electrolytic capacitor and the second stage to increase both the lifetime and the efficiency. The driving of each LED load is done by means of a dc–dc converter operating as a loss-free resistor responsible for controlling the current across it. Furthermore, each dc–dc converter needs to achieve power factor correction (PFC) to comply with the restrictive IEC 61000-3-2 class C requirements, hence, achieving unity power factor and low total harmonic distortion. Taking advantage of the light properties, the output of the LED driver will be the sum of the light of each of the phases. Therefore, a theoretical study will be carried out to observe the feasibility of removing the electrolytic capacitor while guaranteeing a flicker-free behavior of the LED luminaire, even if the current of each string is pulsating at twice the mains frequency. This particular performance under high output current and voltage ripples requires reevaluating the well-known limits between the conduction modes in PFC converters. In addition, the theoretical analysis also discusses and proposes control methods for the LED driver, which thanks to its modularity can easily scale in power to drive high-power luminaires. In order to validate the theoretical analysis, a prototype has been built comprised three PFC boost converters disposing of their electrolytic capacitors. The designed prototype operates in the full range of the European three-phase line voltage, which varies between 380 and 420 V, and supplies an output light of 42.000 lm at a maximum power of 300 W while achieving an electrical efficiency of 97.5%.

Analysis of Sliding-Mode Controlled Impedance Matching Circuits for Inductive Harvesting Devices

A sea-wave energy harvesting, articulated device is presented in this work. This hand-made, wooden device is made combining the coil windings of an array of three single transducers. Taking advantage of the sea waves sway, a linear oscillating motion is produced in each transducer generating an electric pulse. Magnetic fundamentals are used to deduce the electrical model of a single transducer, a solenoid-magnet device, and after the model of the whole harvesting array. The energy obtained is stored in a battery and is used to supply a stand-alone system pay-load, for instance a telecom relay or weather station. To maximize the harvested energy, an impedance matching circuit between the generator array and the system battery is required. Two dc-to-dc converters, a buck-boost hybrid cell and a Sepic converter are proposed as impedance adaptors. To achieve this purpose, sliding mode control laws are introduced to impose a loss free resistor behavior to the converters. Although some converters operating at discontinuous conduction mode, like the buck-boost converter, can exhibit also this loss free resistor behavior, they usually require a small input voltage variation range. By means of sliding mode control the loss free resistor behavior can be assured for any range of input voltage variation. After the theoretical analysis, several simulation and experimental results to compare both converters performance are given.

Minimum DC-Link Capacitance for Single-Phase Applications With Power Factor Correction

This letter presents the calculation of the minimum dc-link capacitance in power factor correction single-phase systems employing hysteretic current-mode control for low total harmonic distortion. The proposed design can be applied to the cascade connection of converters in which the source converter can be modeled as a loss-free resistor and the load converter can be characterized as a constant power load. The value of the minimum capacitance is obtained as a function of voltage and frequency of the mains, maximum power transferred to the load converter, and desired dc-link voltage. The resulting capacitance is ten times smaller than the one obtained by the conventional design. The theoretical predictions are verified by means of simulations and experiments.

Adaptive Sliding Mode Based Loss-Free Resistor for Power-Factor Correction Application

The emulation of virtual resistance finds various applications in the power processing industry. This paper proposes a novel notion of adaptive sliding mode based loss free resistor (ASLFR). This is achieved by allowing the input power of the power-out power-in ( POPI ) system to vary, in order to accommodate the load demands. In this paper, the concept is illustrated for power-factor correction (PFC) applications. The ASLFR is used to achieve the dual purpose of harmonics-free rectification along with excellent system response under load and line transients. The scheme serves itself as an efficient single-stage PFC solution. A generic mathematical formulation of the scheme is presented, which can be used for different converters. Then on, a boost topology, operating in continuous conduction mode, is chosen to demonstrate theoretical developments and to showcase the effectiveness of the scheme. The robustness of the proposed controller to any line or load variation is established. A fast voltage recovery with almost no undershoot/overshoot is achieved at transients by using the proposed controller. Additionally, a qualitative analysis is provided to demonstrate the expediency of the proposed ASLFR. The theoretical claims are well supported by simulation as well as experimental results.

A Loss-Free Resistor-Based Versatile Ballast for Discharge Lamps

This paper presents a versatile ballast for discharge lamps, whose operation is based on the notion of a loss-free resistor (LFR). The ballast consists of two stages: (1) a boost converter operating in continuous conduction mode (CCM) and exhibiting an LFR behavior imposed by sliding-mode control; and (2) a resonant inverter supplying the discharge lamp at high frequencies. Thanks to this mode of operation, the power transferred to the lamp is regulated by the LFR input resistance, allowing successful ignition, warm-up, nominal, and dimming operation of a range of discharge lamps, with no need for complex regulation schemes based on lamp models. The versatility of the ballast has been experimentally proven for both conventional and electrodeless discharge lamps. Tests include induction electrodeless fluorescent (IEFL), high-pressure sodium (HPS) vapor, and metal-halide lamps.

Multicell Three-Phase AC–DC Driver for HB-LED Lighting Applications

High-brightness light-emitting diodes (HB-LEDs) are becoming omnipresent across all aspects of illumination products, due to their incredible characteristics such as efficiency, reliability, long lifetime, controllability, etc. This paper proposes power conversion topologies to drive medium to high power HB-LEDs in three-phase power grids when these connections are available. For that reason, an evaluation of several drivers for medium to high power HB-LEDs in three-phase power grids is done. Moreover, a new topology is proposed, which complies with IEC 1000-3-2 Class C requirements, achieves high power factor, low total harmonic distortion, and the capability to have a flicker free behavior while disposing of the bulk capacitor and having galvanic isolation. The HB-LED driver is based on a modular approach with several cells working together with their inputs connected to the three-phase network and their outputs connected in parallel generating a dc output. Each one of these cells is a dc–dc converter operating as a loss free resistor. In order to validate the concept, a prototype has been built by the use of flyback converters operating in discontinuous conduction mode. Furthermore, it operates in the full range of the European three-phase line voltage, which varies between 380 and 420 V, and it supplies an output voltage of 48 V with maximum power of 90 W.

LED Driver Based on Input Current Shaper Without Electrolytic Capacitor

This paper presents a high-power-factor light-emitting diode (LED) driver implemented by using an input current shaper technique. A flyback converter operating in DCM is placed between the main rectifier and dc bus, in order to increase the conduction angle of the rectifier diodes and to decrease the current harmonics injected to the mains. A buck converter performs the LED power control stage, which is integrated with the flyback by sharing the same active switch, thus presenting reduced component count. The use of a flyback converter operating as a loss-free resistor provides reduced power processing, increasing the converter's overall efficiency. The two-stage configuration allows bus capacitor reduction, owing to the effect of low frequency filtering provided by the second stage. In this way, electrolytic capacitors can be avoided, thus increasing reliability of the LED driver. An analysis of the effects of the bus voltage ripple caused by the capacitance reduction is performed. The driver also presents dimming capability. Analysis and design example of the proposed converter are presented. Experimental results of the proposed converter supplying an LED luminaire of $\text{50}\, \text{V}/\text{2.1}$ A LEDs are shown. The prototype presented high power factor, ${\text{PF}} = \text{0.97}$ , harmonic distortion of input current satisfying the IEC 61000-3-2 requirements, THD = 22.3%, and high efficiency, $\eta = \text{91.1}\% $ .

Modeling, Dynamics, Bifurcation Behavior and Stability Analysis of a DC–DC Boost Converter in Photovoltaic Systems

A study of a DC–DC boost converter fed by a photovoltaic (PV) generator and supplying a constant voltage load is presented. The input port of the converter is controlled using fixed frequency pulse width modulation (PWM) based on the loss-free resistor (LFR) concept whose parameter is selected with the aim to force the PV generator to work at its maximum power point. Under this control strategy, it is shown that the system can exhibit complex nonlinear behaviors for certain ranges of parameter values. First, using the nonlinear models of the converter and the PV source, the dynamics of the system are explored in terms of some of its parameters such as the proportional gain of the controller and the output DC bus voltage. To present a comprehensive approach to the overall system behavior under parameter changes, a series of bifurcation diagrams are computed from the circuit-level switched model and from a simplified model both implemented in PSIM© software showing a remarkable agreement. These diagrams show that the first instability that takes place in the system period-1 orbit when a primary parameter is varied is a smooth period-doubling bifurcation and that the nonlinearity of the PV generator is irrelevant for predicting this phenomenon. Different bifurcation scenarios can take place for the resulting period-2 subharmonic regime depending on a secondary bifurcation parameter. The boundary between the desired period-1 orbit and subharmonic oscillation resulting from period-doubling in the parameter space is obtained by calculating the eigenvalues of the monodromy matrix of the simplified model. The results from this model have been validated with time-domain numerical simulation using the circuit-level switched model and also experimentally from a laboratory prototype. This study can help in selecting the parameter values of the circuit in order to delimit the region of period-1 operation of the converter which is of practical interest in PV systems.

Interleaved Digital Power Factor Correction Based on the Sliding-Mode Approach

This study describes a digitally controlled power factor correction (PFC) system based on two interleaved boost converters operating with pulsewidth modulation (PWM). Both converters are independently controlled by an inner control loop based on a discrete-time sliding-mode (SM) approach that imposes loss-free resistor (LFR) behavior on each cell. The switching surface implements an average current-mode controller so that the power factor (PF) is high. The SM-based digital controller is designed to operate at a constant switching frequency so that the interleaving technique, which is recommended for ac–dc power conversion systems higher than 1 kW, can be readily applied. An outer loop regulates the output voltage by means of a discrete-time proportional–integral (PI) compensator directly obtained from a discrete-time small-signal model of the ideal sliding dynamics. The control law proposed has been validated using numerical simulations and experimental results in a 2-kW prototype.

Model-based maximum power point tracking for wind generators

A model-based maximum power point tracking solution for wind systems is presented in this paper. The strategy uses the Loss-free resistor concept and a generator model, which relates the load impedance required to produce the maximum power depending on the generator rotor speed. The strategy performance is validated through simulation and the emulation of a multi-machine wind generation system. With the proposed strategy, it is possible to extract the maximum power of each generator and, therefore, the maximum power of the generation system.

Design of AC–DC PFC High-Order Converters With Regulated Output Current for Low-Power Applications

AC-DC power factor corrector circuits used in low-power applications have to overcome important power quality problems related to crest and power factors as well as total harmonic distortion (THD), and in many cases, they have to exhibit a high degree of output regulation. The design of efficient drivers for low-power applications using high-order converters is considered in this paper. Power factor correction is achieved by imposing a loss-free resistor behavior to SEPIC and Ćuk converters by means of an internal loop based on sliding-mode control, which requires a hysteretic comparator for its implementation. However, with a constant hysteresis width, the system exhibits harmful harmonic distortion in the input line current waveform so that a variable hysteresis window is used instead to avoid this distortion near the zero crossings of the input current. The subsequent analysis of the ideal sliding dynamics around the equilibrium point allows the design of an outer control loop to regulate the output current. Mathematical analysis, numerical simulations, and experimental results are presented to demonstrate the functionality of the proposed technique obtaining a significant improvement in terms of decreasing the THD. A dimmable LEDs driver supplying an HBLEDs string with a wide range of output current regulation illustrates the design.