Converter Load Research Articles

An Energy Buffer for Controllable Input Impedance of Constant Power Loads

Power electronic circuits often regulate load power and present a constant power profile to the utility or other electrical source. These constant power loads therefore exhibit a negative incremental input impedance and pose stability challenges when present in either dc or ac systems. This paper presents an energy buffer power converter for a constant power LED lighting load that presents a controllable input impedance to the electrical source. The use of an energy buffer allows the converter to independently control input and output power. The input power is controlled to resemble a resistive load, ensuring that the device exhibits a positive incremental input impedance over short-term input disturbances. Simultaneously, the output power is held constant through high-bandwidth regulation. The control scheme balances the power flow in the long term. Experimental results are presented that demonstrate independence between input and output performance, as well as long-term power balance.

Analysis, Design, and Control of Switching Capacitor Based Buck–Boost Converter

A switching-capacitor-based buck–boost converter (with common ground) for point of load applications is proposed in this paper. It is capable of operating in stand-alone buck or boost mode in addition to its primary operation of performing the buck–boost conversion. The striking feature of the proposed converter is low source current ripple content irrespective of its mode of operation (buck–boost, buck, or boost). First, feasible pulsewidth modulation schemes for the proposed converter are identified and thereafter the corresponding circuit performance analysis, steady-state analysis, and state-space modelling is established. Through steady-state analysis, voltage gain expressions are formulated and equations defining L - C components are derived in terms of their ripple quantities. The state-space models are used to formulate small-signal analysis and to obtain the relevant transfer functions required in the controller design. A voltage-mode/current-mode controller is designed, with a tradeoff in bandwidth, to control the proposed converter and transit it from buck to boost mode or vice versa seamlessly. A 30–55 W , 100 kHz, prototype point of load converter with 36-V input dc source is built to supply power at constant load voltage of either 48 or 28 V. The proposed converters’ effectiveness is demonstrated experimentally in terms of reduced source current ripple along with seamless transition from buck to boost mode and vice versa.

Dynamical effects of memristive load on peak current mode buck-boost switching converter

Abstract When an output load of switching DC-DC converter exhibits the fingerprints of frequency dependent pinched hysteresis loops, the load can be regarded as a memristive load. By substituting a resistive load with the voltage-controlled memristive load emulator, a peak current mode (PCM) memristive buck-boost converter is presented in this paper. Based on the circuit equations under two kinds of switch states, the switched conditions and normalized system model of the PCM memristive buck-boost converter operating at continuous conduction mode (CCM) are derived. Through MATLAB numerical plots, dynamical behaviors of the PCM memristive buck-boost converter are investigated and dynamical effects of the memristive load on the buck-boost converter are thereby uncovered. The results indicate that such a buck-boost converter exhibits complex dynamical behaviors including chaos, period, period-doubling bifurcation, and border collision bifurcation; the memristive load does not affect the bifurcation structures but can make the normal operation region to broaden and cause the average output voltages to drop. Additionally, the enlargement of the memristive effect of the load, the normal operation regions are further expanded and the average output voltages are further reduced. Finally, PSIM simulation model is constructed, upon which circuit simulations effectively confirm the numerical plots.

Implementation of zero current switch turn-ON based buck-boost-buck type rectifier for low power applications

ABSTRACTA single-stage single-switch AC–DC integrated converter is proposed in this paper, as a tight DC voltage regulator with unity input power factor for the fundamental component of the input current. Proposed converter is formed by the integration of buck-boost configuration with a buck converter operated by a single switch. The buck-boost section of the proposed configuration is operated in current discontinuous conduction mode (DCM) to get unity input power factor at the supply terminals and the buck section is operated up to boundary current conduction mode (BCM). The features acquired by the converter operating in complete discontinuous conduction mode (DCM) are unity input power factor, zero-current turn-ON for the Switch, fast and good DC output voltage regulation with extensive conversion range and low voltage stress on the switch. Additionally, the intermediate capacitor voltage stress is independent of converter load variations and so the switch also is subjected to constant peak voltage stress. A comprehensive study is carried out to obtain the necessary design equations. A design model is implemented using simulation and hardware. The results confirm the performance of the proposed configuration.

Discontinuous Control Analysis for Step Down DC-DC Voltage Converters

The DC-DC power converters have extreme importance in contemporary applications. Moreover, the DC-DC power converters are the ideal candidates in numerous applications such as electric and hybrid vehicles, fuel cells and others. They have been extensively researched upon over three decades. The control of these converters has been often implemented using PWM techniques and based on discrete components and integrated circuits. In this paper we propose a systematic approach for the control of step down DCDC converters with variable input voltage based on discontinuous control action. We demonstrate that the proposed algorithm achieves robustness to variations of the converter load and the input voltage without additional sensors

Direct Predictive Current-Error Vector Control for a Direct Matrix Converter

This paper proposes a novel control strategy for matrix converters that is coined “direct predictive current-error vector control.” The proposed control method retains the advantageous features of both a modulation scheme and of a predictive-based controller. The result is a controller that is capable of good dynamic performance and steady-state response with fixed switching frequency operation. Control of load and input currents of a direct matrix converter using the proposed method is demonstrated in this paper by simulation and experimental results.

Sliding‐mode control of a boost converter under constant power loading conditions

The cascade connection of two dc-dc switching converters for constant power supply is studied. The source converter is of boost type while the load converter is of buck type. The natural unstable behaviour of the cascade connection for both on and off states of the boost converter is counteracted by a sliding-mode control strategy that combines unstable trajectories to generate a stable one for the regulated boost converter dynamics. Experimental results using an electronic load to emulate a buck converter-based constant power load are in good agreement with the theoretical predictions. A similar agreement is later obtained when a buck converter with a dynamic behaviour close to an instantaneous constant power load is employed instead of the electronic load.

Interval Robust Controller to Minimize Oscillations Effects Caused by Constant Power Load in a DC Multi-Converter Buck-Buck System

Multi-converter electronic systems are becoming widely used in many industrial applications; therefore, the stability of the whole system is a big concern to the real-world power supplies applications. A multi-converter system comprised of cascaded converters has a basic configuration that consists of two or more converters in series connection, where the first is a source converter that maintains a regulated dc voltage on the intermediate bus while remaining are load converters that convert the intermediate bus voltage to the tightly regulated outputs for the next system stage or load. Instability in cascaded systems may occur due to the constant power load (CPL), which is a behavior of the tightly regulated converters. CPLs exhibit incremental negative resistance behavior causing a high risk of instability in interconnected converters. In addition, there are other problems apart from the CPL, e.g., non-linearities due to the inductive element and uncertainties due to the imprecision of a mathematical model of dc-dc converters. Aiming to effectively mitigate oscillations effects in the output of source converter loaded with a CPL, in this paper, an interval robust controller, by linear programming based on Kharitonov rectangle, is proposed to regulate the output of source converter. Several tests were developed by using an experimental plant and simulation models when the multi-converter buck-buck system is subjected to a variation of power reference. Both simulation and experimental results show the effectiveness of the proposed controller. Furthermore, the performance indices computed from the experimental data show that the proposed controller outperforms a classical control technique.

Virtual Resistor-Based Integrated DC Bus Voltage Conditioner for Stability Improvement of Cascaded Power Converters

A bidirectional integrated bus voltage conditioner (IBVC) for an isolated phase-shifted full bridge (PSFB) dc/dc converter is proposed to reduce the dc bus voltage oscillations in a cascaded power converter system, where a load converter is controlled tightly with high-control bandwidth. In the proposed method, unlike conventional dc bus voltage stabilization methods for which auxiliary switches are used, the multiplexing utilization of the full bridge switches at the primary side of a PSFB is adopted. In this paper, to improve the dc bus voltage stability, an equivalent virtual resistor is implemented by applying the duty cycle regulation for both legs of the PSFB. The effectiveness of the proposed method on the dc voltage stabilization is examined through simulations and experiments. The achieved results reveal that the dc bus voltage stability is significantly improved with the proposed method.

An Optimal Voltage-Level Based Model Predictive Control Approach for Four-Level T-Type Nested Neutral Point Clamped Converter With Reduced Calculation Burden

Four-level T-type nested neutral point clamped (NNPC) converter is a newly developed multilevel voltage source converter for higher power density systems in low and medium voltage applications. The T-type NNPC converter can operate over a wide range of voltages and own less proportion of components compared with other four-level topologies, which makes it attractive among multilevel converters. In this paper, an optimal voltage-level based model predictive control (OVL-MPC) with reduced calculation burden is proposed for the T-type NNPC converter. The main objectives of this paper are to achieve the T-type NNPC converter load current control and the flying capacitors voltages balancing while remaining computationally feasible. In our proposed method, the output voltage levels are considered as the control options rather than the switching states in the conventional MPC scheme. Meanwhile, a simplified capacitor voltage balancing approach is employed to regulate the voltages of the capacitors at their desired values without punishing the computational complexity. The contribution of this paper lies in the following two aspects: first, the finite control set is decreased in the optimization processes. Second, a simplified capacitor voltage balancing strategy is introduced for the T-type NNPC converter. The performance of the proposed OVL-MPC approach for the T-type NNPC converter under steady-state, transient-operation, and unbalance mode are verified by the simulation results.

An Intelligent Maximum Power Point Tracking Algorithm for Photovoltaic System

This work comprehensively demonstrates the performance analysis of Fuzzy Logic Controller (FLC) with Particle Swarm Optimization (PSO) Maximum Power Point Tracker (MPPT) algorithm on a stand-alone Photovoltaic (PV) applications systems. A PV panel, DC-DC Boost converter and resistive load was utilized as PV system. Three different MPPT algorithms were implemented in the converter. The result obtained from the converter was analyzed and compared to find the best algorithm to be used to identify the point in which maximum power can be achieve in a PV system. The objective is to reduce the time taken for the tracking of maximum power point of PV application system and minimize output power oscillation. The simulation was done by using MATLAB/Simulink with DC-DC Boost converter. The result shows that FLC method with PSO has achieved the fastest response time to track MPP and provide minimum oscillation compared to conventional P&O and FLC techniques.

Efficiency Estimation of Hybrid Electrotechnical Complex for Non-Sinusoidal Signals Level Correction in Autonomous Power Supply Systems for Oil Fields

Actuality of highest harmonics hybrid compensation in currents and voltages was gained to improve efficiency of oil fields power supply equipment. A positive effect is achieved due to implementation of active and passive filters in centralized and autonomous power supply systems with high percentage of non-linear loads. There was an observed structure of the hybrid electrotechnical complex based on a parallel active filter and two passive filters that were set for elimination of the 5th and 7th current harmonics that were generated by non-linear load represented as a power converter. This scheme was adapted for the use with a frequency-controlled electric drive due to adjustment of the parallel filter DC link and non-linear load of the frequency converter. There were developed mathematical and computer simulation models of the observed hybrid electrotechnical complex with the common DC link for the conditions of autonomous power supply at the oil field object. The control system of the autonomous electrotechnical complex hybrid part was develop. It contains phase converters and a dead space width disposal variable of relay controllers during generation of control pulses. Analyses of non-sinusoidal level adjustment efficiency of voltage and current signals were conducted after simulation of the hybrid electrotechnical complex. The calculations of technical-and-economic indices and efficiency usage were performed taking into account implementation of the hybrid electrotechnical complex into industrial power supply systems. The obtained results prove that the developed hybrid electrotechnical complex with the common DC link for the autonomous power supply of oil fields in the DG networks is efficient, reliable and can be installed in the existing power supply systems.

Active stabilisation design of DC–DC converters with constant power load using a sampled discrete‐time model: stability analysis and experimental verification

Instabilities of cascade converters with an LC filter in between in power electronic systems have been known, and many answers have been proposed. The load converters are tightly regulated, acting as constant power loads (CPLs). Average models are generally utilised to study the behavior of the converters. For embedded applications, the weight and the volume should be reduced. Consequently, in this case, the limitations of the average method are reached when the cut-off frequency of the LC input filter is close to the switching frequency. Then, other tools are necessary to study this type of system. To overcome this problem, a discrete-time model was developed to study the behavior of the system, taking into account the switching effect. The aim was to enlarge the power range of the stability zone for a DC system composed of a DC-DC boost converter as a source converter, which was connected to the power load via an LC input filter. For this purpose, a stabilisation expression is integrated in the command of the source converter. The stability analysis by the eigenvalues of the system is described using the proposed model. Simulation and experimental results are discussed to verify the proposed stabiliser in different cases.

Simulation of 8x8 Heavy Duty Truck for Evaluating Effects of Torque Converter Characteristics on Vehicle Performance

This paper investigates the powertrain system of an 8x8 heavy duty vehicle through the integration of two couple of diesel engine with automatic transmission as power sources for evaluating the vehicle performance. The primary goal of this paper is to show the effects of torque converter selection on acceleration performance and fuel consumption of the vehicle. To achieve this goal, powertrain system simulation carried out by using two different torque converter individually according to Heavy Duty Urban Dynamometer Driving Schedule (HD-UDDS) drive cycle. Torque converter alternatives (design 1 and design 2) are chosen considering operational area in moment characteristics of the engine. A mathematical model of powertrain system is implemented based on longitudinal dynamics of vehicle motion in HD-UDDS cycle. Required moments on torque converter during the motion of test cycle are compared for converter alternatives and loading condition of vehicle. Fuel consumption results are also compared by using fuel consumption data and required power in the engine. Results demonstrate that the increase in acceleration performance and traction ability of vehicle can be obtained by selection of torque converter correctly.DOI: http://dx.doi.org/10.5755/j01.mech.24.2.18887

DC bus voltage stability improvement using disturbance observer feedforward control

The constant power load (CPL) property of a load converter with tight control results in DC bus voltage oscillations in interconnected power converter systems. In this paper, a disturbance observer (DOB) feedforward compensation scheme is proposed to stabilize the DC bus voltage of a cascaded power converter. An equivalent DC link voltage control model and a disturbance observer are used to reconstruct the dynamic changes of the DC bus current to correct the inner current loop reference of the load converter. Simulation and experimental results show that the proposed method is effective in stabilizing the DC bus voltage.

Stabilization and Performance Preservation of DC–DC Cascaded Systems by Diminishing Output Impedance Magnitude

DC–DC cascaded systems are vulnerable to instability and dynamic performance deterioration. These problems arise due to the nonideality in the source converter output impedance and to the negative input impedance of the load converter. Any overlap in magnitude between these two impedances will destabilize the voltage at the dc bus. Thus, we introduce a method to diminish the magnitude of source-converter output impedance such that the source converter will act as an ideal voltage source. As a consequence, the dynamic performance of the source and load converters will be intact, leading to ensuring the bus voltage stability. In addition, the controller is independent of the number of converters that form the load subsystem. To validate the proposed method, an experimental cascaded system was analyzed, simulated, and experimentally tested. Collectively, all of the outcomes proved the effectiveness of the proposed method.

Harmonic Comparison of Three Phase Direct Matrix Converter for Reactive Load with Balance and Unbalance Supply Voltage

<span lang="EN-IN">This paper presents harmonic analysis of matrix converter using different control technique for balance and Unbalance three phase input voltage of reactive load. Since Matrix converter is subject to affected either by external disturbance or by load conditions. Due to this the supply voltage becomes unbalance. This cause improper switching of matrix converter results higher harmonics. This harmonics are harmful to the quality of the output power. The switching sequence of the matrix converter is controlled by vector control method. Different control technique is proposed in this paper to get optimized result with reduced harmonic for unbalanced and balance input voltage using PID, Fractional Order PID (PI<sup>λ</sup>Dδ) controller (FOPID), Particle Swarm Optimization (PSO)FOPID. PID control technique result are compared with other optimization technique for best optimum output. The FOPID controller is used to compensates the current and also improvise the quality of energy by reducing the harmonic content. The simulations and hardware results will be presented and interpreted. The effectivess of the proposed system is proven with the results is shown in this paper which produce a better steady state lesser transient rather than the conventional PID method.</span>

Speed control with incremental algorithm of minimum fuel consumption tracking for variable speed diesel generator

This paper presents a model of a diesel-combustion-engine-based variable speed generation unit driving a permanent magnet generator loaded by a power converter. Variable speed operation of the internal combustion engine facilitates fuel saving when the load profile changes, but it requires a power conditioning unit such as an electronic converter. Power converter operation is well known from wind energy conversion systems, in which variable speed operation increases their efficiency. The paper presents modeling and speed control of an exemplary diesel engine, and control of output voltage and current of the power electronics converter loading the generator. Special attention has been paid to elaboration of the methods of minimum specific fuel consumption points tracking for the given load. Incremental algorithms can find minimum specific fuel consumption in the case in which the details of fuel consumption curves are not exactly known. The incremental algorithm has been adopted from wind energy conversion systems and partly modified to avoid torque peaks during incremental step changes of reference speed. The concept has been validated in a simulation using data of a real model of an internal combustion engine through a three-dimensional approximation of fuel consumption characteristics.

Third‐order boost converter

A third-order boost point of load converter capable of giving higher voltage gain, identical/similar to fifth-order converters, is proposed. In view of the lower order and higher boosting feature, the converter is more suitable to interface the given low voltage source to a high-voltage dc point of load or to a dc-bus. Furthermore, the proposed converter dynamics is simpler as its control-to-output transfer function is free from right half s -plane zeros. Component design expressions are formulated through a steady-state analysis. The boosting factor of the proposed converter is higher than the traditional boost and other reported fourth-order boost converters. The transfer functions are formulated from the state-space model and then a digital controller is designed in the z-domain. The proposed converter features are demonstrated through analysis and then compared with sample experimental observations.

Effect of load current harmonics on vibration of three-phase generator

Almost all today electrical loads are considered non-linear such as switch mode power supply (SMPS) for powering computer and mobile phone or variable speed drive (VSD) for driving home and industrial electric motors. These loads generate ac non-sinusoidal current containing a lot of harmonics as indicated by its high total harmonics distortion (THD) figure. Current harmonics bring negative effects into all electrical power system components, including three-phase generator. This paper provides analysis of load current harmonics effects on vibration of three-phase generator. Three different laboratory experiments have been conducted i.e. three-phase linear resistive loading, non-linear loading with a three-phase ac/dc converter and non-linear loading with three single-phase capacitor filtered ac/dc converters. Results show that the higher load current harmonics content the higher is vibration of the three-phase generator. Non-linear loading with a three-phase ac/dc converter that generate about 24.7% THD gives an increase of 4.3% and 5.5% in average of vertical and horizontal vibrations of the three-phase generator respectively. Further, non-linear loading with three single-phase capacitor filtered ac/dc converters that generate THD as high as 74.9% gives significant increase of 28.1% and 23.6% in average of vertical and horizontal vibrations respectively.