Inverter Supply Research Articles

Operation Modes Analysis and Limitation for Diode-Assisted Buck–Boost Voltage Source Inverter With Small Voltage Vector

Diode-assisted buck-boost voltage source inverter (VSI) boosts the dc source voltage by introducing diode-assisted capacitor network. With parallel capacitive charging and series capacitive discharging, the new topology extends voltage regulation range and avoids extreme duty ratio of switching devices in the front boost circuit. As for the unique structure, various novel pulse-width modulation strategies are provided to obtain the linear voltage gain with regard to the chopped intermediate dc-link voltage of the inverter bridge in one switching time period. It provides a competitive solution for high voltage gain applications. However, when the inverter supplies inductive or capacitive load with extreme low load power factor, the unidirectional current flow of the diode may limit the application of the converter utilizing small voltage vectors for ac output voltage extension. As a result, diode-assisted buck-boost VSI exhibits new operation mode that has not been discussed before. This paper makes a detailed circuit analysis of the relationship between the undesired operation condition and load power factor. Then, a simple approach to totally eliminate the undesired limitation by replacing the diodes with controlled switching devices is provided. Finally, the related simulations and experiments are implemented to verify all the theoretical findings and solutions.

A simplified control strategy for single-phase UPS inverters

Abstract Though there are many strategies to control single-phase uninterruptible power supply (UPS) inverters, they suffer from some drawbacks, the main being complexity. This paper proposes a simple dual-loop controller for the single-phase UPS inverter with the LC filter. The suggested control scheme uses the capacitor current as the feedback signal in the inner current loop. No fictitious phase generation or reference frame transformations are required, and simple proportional gains are employed as both voltage and current regulators. A feedforward of the derivative of the output voltage is also proposed, which significantly improves the performance of the closed loop control system. Then, based on the model of the inverter with the proposed control strategy, a simple and systematic design procedure is presented. Finally, the theoretical achievements are supported by extensive simulations.

Offset-Free Model Predictive Control for Output Voltage Regulation of Three-Phase Inverter for Uninterruptible Power Supply Applications

This paper proposes an offset-free model predictive control (MPC) method for output voltage regulation of the three phase inverter for an uninterruptible power supply (UPS) application. A use of a disturbance observer (DOB) is made to estimate the unknown disturbance caused by the load current and a plant-model mismatch. The proposed MPC optimizes the one step ahead cost function. The online computation considering the input constraint of the inverter system is very simple. It is shown that the closed-loop system is globally asymptotically stable in the presence of input constraints and that the integral action in the DOB eliminates the steady state errors caused by a plant-model mismatch. The effectiveness of the closed-loop system is experimentally shown under a use of resistive load.

Analysis of Losses and Thermal in Induction Motors

This paper presents an investigation into the losses and thermal characteristics of induction motors operated from pulse width-modulated (PWM) voltage supply in comparison to that operated from sinusoidal voltage supply. It was concluded that due to the abundant harmonics in the PWM waveforms, significant losses are induced in the motor by the inverter supply. The temperature ascends correspondingly. Experiments were conducted with no load and with load conditions. The losses and thermal characteristics were calculated using finite element analysis (FEA) and validated by the experiments.

Per-phase vector control strategy for a four-leg voltage source inverter operating with highly unbalanced loads in stand-alone hybrid systems

This paper proposes a new per-phase vector (dq) control scheme for a four-leg grid-forming inverter operating in a three-phase four-wire hybrid stand-alone power system (mini-grid). The challenge is to provide balanced output voltages to highly unbalanced loads, very common in such systems, with a fast dynamic response. By using dq control in a per-phase basis one avoids the use of slow filter-based symmetrical components calculators (SCCs) while achieving zero error, i.e. voltage balancing, in steady-state. Further improvement in the dynamic response is achieved by using fictive axis emulation for obtaining the orthogonal current components required for the per-phase dq control. Simulation and experimental results are provided, to demonstrate the good performance of the system. It works very well, even when the grid-forming inverter supplies active power in two phases and absorbs in the other one, due to the presence of a single-phase PV inverter in the hybrid mini-grid.

New Control Strategy for High-Frequency Digital Inverter Power Supply

The inverter power supply system has strong nonlinearity and parameter variability, especially in the non-linear loads, conventional control technology is difficult to achieve effective control and get the ideal control effect. Aiming at the control requirements of single-phase high-frequency induction heating inverter supply power control applications, uses a novel multiple and composite control technologies to achieve rapid power modulation control of inverter. The components and design principles of proposed control system were introduced in detail. The inverter power system model based on the new control strategy has been built, and inverter prototype used for high-frequency induction heating was designed. The experimental results show that the proposed control method to obtain better dynamic characteristics than the conventional control technologies, and has good advantages of system steady-state accuracy, robustness and control qualities, which has wide range of application.

Calculation of Iron Losses in Inverter-fed Induction Motors based on Time-stepping FEM

This paper presents a method for calculating iron losses in three-phase induction motors under the inverter supply through the field-circuit coupled time-stepping finite element method (FEM). Iron losses are calculated by using the three-term iron losses separated model and modifying the loss coefficients obtained by the iron losses curves which are provided by the manufacturer under the sinusoidal supply. Simulation results by the presented method are verified by the measured results with an error lower than 5%, confirming the validity of the proposed method. Finally, iron losses distribution of the inverter-fed three-phase induction prototype motor is shown.

Evaluating performances of electric machines supplied by the sinusoidal and pulse width modulated voltages

PurposeMany authors reported the decrease of performances when electric machines and electromagnetic devices were supplied by pulse width modulated (PWM) voltages. However, these statements are rarely supported by measurements performed under fair conditions. The aim of this paper is to compare the performances of a single‐phase transformer and a three‐phase permanent magnet synchronous motor (PMSM) supplied by sinusoidal and PWM voltages and to find a way to evaluate the decrease of performances when PWM voltages are applied.Design/methodology/approachIn order to perform a fair comparison between performances of the tested objects supplied by sinusoidal and PWM voltages, an experimental system was built. It contains a single‐phase and a three‐phase linear rectifier for supply with sinusoidal voltages and an H‐bridge inverter and a three‐phase inverter for supply with PWM voltages. The tests and measurements were performed on a single‐phase transformer and three‐phase PMSM, where different constant loads and different modulation frequencies were used. The test conditions were identical for the supply by sinusoidal and PWM voltages. The measured data, used for the evaluation of performances, were the input and output power and the time behaviours of currents and voltages together with their THDs.FindingsThe results presented in the paper clearly show that the efficiency of the singe‐phase transformer and three‐phase PMSM decreases with the increasing level of voltage THD. To properly determine the THD of PWM voltage, the sampling frequencies above 1 MHz and special equipment are normally required. However, if the modulation frequency is not too high, also the current THD, which can be easily determined, can be used to evaluate the decrease of efficiency in the case of supply by PWM voltages.Originality/valueThe results presented in the paper clearly show that the efficiency of the singe‐phase transformer and three‐phase PMSM decreases with the increasing level of voltage THD.

Comparison of Permanent Magnet Linear Synchronous Motor Characteristics Fed by SPWM Inverter and Sinusoid Voltage Source

Permanent Magnet Linear Synchronous Motor (PMLSM) characteristics are deteriorated seriously by amount of time and space harmonics, which are arisen respectively from the inverter comprised array switches, the motor teeth-slots and distributed windings. The paper presents field-circuit coupled adaptive time-stepping finite element method to comparison research on PMLSM characteristics fed by SPWM voltage inverter and sinusoid supply. The co-simulation is used with the status space functions and time-step finite element functions. The simulation results of PMLSM fed by SPWM voltage source inverter and S-VS were compared and analyzed.

A Robust Fuzzy Sliding Mode Controller Synthesis Applied on Boost DC-DC Converter Power Supply for Electric Vehicle Propulsion System

The development of electric vehicles power electronics system control comprising of DC-AC inverters and DC-DC converters takes a great interest of researchers in the modern industry. A DC-AC inverter supplies the high power electric vehicle motors torques of the propulsion system and utility loads, whereas a DC-DC converter supplies conventional low-power, low-voltage loads. However, the need for high power bidirectional DC-DC converters in future electric vehicles has led to the development of many new topologies of DC-DC converters. Nonlinear control of power converters is an active area of research in the fields of power electronics. This paper focuses on a fuzzy sliding mode strategy (FSMS) as a control strategy for boost DC-DC converter power supply for electric vehicle. The proposed fuzzy controller specifies changes in the control signal based on the surface and the surface change knowledge to satisfy the sliding mode stability and attraction conditions. The performances of the proposed fuzzy sliding controller are compared to those obtained by a classical sliding mode controller. The satisfactory simulation results show the efficiency of the proposed control law which reduces the chattering phenomenon. Moreover, the obtained results prove the robustness of the proposed control law against variation of the load resistance and the input voltage of the studied converter.

Experimental determination and numerical evaluation of core losses in a 150‐kVA wound‐field synchronous machine

The losses in the laminated core of a 150-kVA wound-field synchronous machine are investigated with calorimetric measurements and a numerical iron-loss model for steel laminations. Both grid supply and pulse-width modulated inverter supply with 1 kHz and 6 kHz switching frequencies are studied. The effect of rotor lamination material on total core losses is studied by measuring and simulating the machine with three prototype rotors, the first one being stacked of insulated 0.5-mm Fe–Si sheets and the last two of uninsulated 1-mm and 2-mm steel sheets, respectively. At no load, the losses in the frame of the machine are shown to be extremely significant with voltages above the rated one. The results on load operation show that the additional inverter-induced core losses are significantly larger with the thicker sheets. The rotor eddy-current loss is the most affected component because of loading and the distorted supply voltage. However, unlike expected and predicted by the model, the differences in the losses between the 1-mm and 2-mm rotors are negligible in no-load operation and relatively small also at load operation.

High-Speed Drive Circuit with Separate Source Terminal for 600 V / 40 A Normally-off SiC-JFET

When using JFETs with a threshold voltage lower than 2 V in a power supply system or inverter system, a high-speed drive circuit capable of precisely controlling the gate current and a mounting method are important to reduce the switching loss. In this paper, a drive circuit of a normally-off SiC-JFET with a separate source terminal is proposed and the effects are evaluated. By dividing the common source inductance and applying the speed-up capacitor, the turn-on time and turn-on energy losses can be decreased by 40% and 60%, respectively. A speed-up capacitor larger than 100 nF greatly decreases the rising time (tr) and turn-on energy losses. By applying the developed normally-off SiC-JFETs and proposed gate driver to PFC circuits and DC/DC circuits, a highly efficient power supply will be achieved.

Starting Phenomena and Temperature-rise under vvvf Supply of Three-Phase Squirrel-Cage ac Traction Motor of Electric Locomotive

In three-phase squirrel-cage ac traction motor, temperature-rise calculation during variable-voltage and variable-frequency starting is of vital importance and has to be predicted and critically examined. Under voltage source inverter supply with PWM, the generation of harmonics by inverter supply reduces the output during starting due to higher harmonic losses, thereby reducing the starting tractive effort in kN on locomotive wheel. Stator and rotor temperature-rises during starting have been determined for average acceleration torque in segmental zone (calculated from variable acceleration) which have been presented in the paper with both copper and aluminium alloy rotor bars.

Basic Investigation of High-efficiency Power Control between Frequency-controlled Inverter Power Supply and Spot Welding Load

We developed a frequency-controlled inverter power supply for spot welding machines. The welding currents reached 10 kA or higher, while impedance at the weld was extremely small, at 1 mΩ or less. These conditions demanded welding power supplies capable of providing low voltage at high current. To develop such a power supply, we investigated how to control the welding current using an inverter power supply by installing an internal transformer with a large winding ratio. However, due to issues concerning the global environment and energy conservation, inverter power supplies require increasingly higher efficiency. One method of improving efficiency is to match the impedance between the inverter power supply and the load. The leakage impedance of the inverter transformer, however, is dependent on frequency and current. In addition, the extremely low load (1 mΩ or less) makes such impedance matching difficult to implement. This paper presents the results of an investigation into high-efficiency power control between an inverter power supply with an internal transformer (with a large winding ratio) and a load of no more than 1 mΩ. The results confirmed that inverter output power that maximized frequency and matching were possible.

Power flow management algorithm for photovoltaic systems feeding DC/AC loads

In this paper, a power flow management algorithm for photovoltaic system feeding DC and AC loads is presented. PV being a major energy source enables the DC loads to be connected directly to the DC bus. A grid connected PV system involves one power source (PV array), one power sink (load) and two power sources/sink (utility and battery), and hence a power flow management system is required to balance the power flow among these sources. A unique control algorithm is developed for selecting the operating mode of the bidirectional converter by sensing the battery voltage. The bidirectional converter has three modes of operation namely, the rectifier mode, inverter mode and the voltage control mode. In both the rectifier and inverter modes of operation, the converter current is controlled by employing a hysteresis current controller and unity power factor is achieved in both the cases. In voltage control mode, the converter regulates the inverter voltage and supplies the reactive power to the grid. Detailed simulation studies are carried out on a single phase bidirectional converter in MATLAB/Simulink environment. The viability of the scheme has been ascertained by performing experimental studies on a laboratory prototype. The control strategy is digitally implemented on an Altera Cyclone II FPGA board and the algorithm is verified for different modes of operation by varying the load and the relevant results are presented.

MODELING OF EDDY CURRENT LOSS AND TEMPERATURE OF THE MAGNETS IN PERMANENT MAGNET MACHINES

The eddy current loss in the magnets of permanent magnet (PM) motors in a hybrid electric vehicle (HEV) and plug-in HEV is usually not taken into consideration in traditional motor design and analysis. However, due to the high conductivity of the rare-earth magnet, neodymium-iron-boron (NdFeB), and slot/tooth harmonics, there is eddy current loss generated inside the magnets. This loss may not attribute very much to the efficiency of the motor, but the temperature-rise inside the magnets caused by this loss can lead to the unpredictable deterioration of the magnets, such as the degradation of performance and potential demagnetization. In addition, the output voltage of pulse-width-modulated (PWM) inverter contains abundant high frequency harmonics, which induce excessive loss in the magnets. The excessive heat in PM motor induced by the eddy current loss combined with other losses can degrade the performance of the machine. This paper presents the modeling and analysis of eddy current loss in surface-mounted-magnets PM synchronous motors (SPMSM) and interior-magnets PM synchronous motors (IPMSM), operated by PWM inverter supply. Analytical methods are implemented, in conjunction with time-stepped finite-element analysis (FEA) for the calculation of eddy current loss in the magnet. Based on the calculated losses in the machines, simplified analytical models are developed as thermal circuits with network of interconnected nodes, thermal resistances and heat sources representing the heat processes within the SPMSM and IPMSM, to predict the temperature of the magnets. The predicted machine temperatures are found to be consistent with the experimental measurement.

Noise Reduction of a Three-Phase Reactor by Optimization of Gaps Between Cores Considering Electromagnetism and Magnetostriction

To reduce the noise of a reactor connected to an inverter power supply, we have already proposed an improved one-phase reactor, in which the hard materials are chosen as the insulators inserted in the gaps between the cores, and gaps are added in the yokes, using a three-dimensional (3-D) coupled magnetic field and vibration analyses taking account of both the electromagnetism and magnetostriction. The effectiveness was shown by experiment. In this paper, the design method is improved and applied to a three-phase reactor. First, the method of determining the optimal hardness of insulators inserted in gaps, so that both the displacements by electromagnetism and magnetostriction are canceled with each other, is proposed. In this method, the optimal hardness of gaps can be represented using a simple equation involving the lengths of the iron cores and the gaps, and a parameter concerned with magnetostriction. Moreover, the method of adding gaps in the yokes without changing the balance and reluctance of a three-phase reactor is also proposed. It is shown that the displacements of the reactor improved by using the proposed methods can be reduced to be 1/25 of the ordinary reactor in the 3-D coupled magnetic field and mechanical analyses taking account of both the electromagnetism and magnetostriction and laminated structure of the iron cores.

Research on Operating Performance for Hybrid Rotor Synchronous Motor

This paper with an open-loop V/f control mode of inverter supply, searched for the causes of the oscillation using small signal analysison the axially-laminated anisotropic (ALA) rotor and hybrid rotor (ALA-SPM two-part) motor, and analyzed operating performance of themotors with inertial damper on the same shaft. Results show that the negative electromagnet damping coefficient can be the key point toresult in the oscillation; the electromagnet damping coefficient can increase with the increasing new variable k, the fraction length of SPMpart, the maximum load of the motors and the stability can be improved. The stability of the system and the dynamic performance can bebetter with reasonable viscous damping coefficient of inertial damper, the motors can adequately develop their output torque capability,and improve operating performance. Ill. 11, bibl. 11, tabl. 3 (in English; abstracts in English and Lithuanian).http://dx.doi.org/10.5755/j01.eee.113.7.603

Optimal tuning of linear controllers for power electronics/power systems applications

This paper presents a new method for tuning various linear controllers such as Proportional–Integral (PI), Proportional–Integral–Derivative (PID) and Proportional–Resonant (PR) structures which are frequently used in power electronics and power system applications. The linear controllers maintain a general structure defined by the Internal Model Principle (IMP) of control theory. The proposed method in this paper is twofold. The first perspective uses the well-known concept of the Linear Quadratic Regulator (LQR) to address the problem as a regulation problem. The Q matrix of the LQR design is then finely adjusted in order to assure the desired transient response for the system. The second perspective redefines the LQR in order to add capability to address the optimal tracking problem and is then generalized to systems with more than two states. These methods are then applied to two specific examples, one in an uninterruptible power supply (UPS) inverter system and the other one in a distributed generation (DG) system. In these examples, the tuning of PR and PI controllers is studied in great detail. These proposed design methods provide an easy and algorithmic procedure without jeopardizing stability or robustness. These tuning methods can also be utilized for linear state-space realization of any power converters. Both examples are supported via simulation and the results, which confirm analytical derivations, are presented and discussed.

Voltage Doubler를 이용한 4-스위치 3상 BLDC 전동기 구동 알고리즘

Over the years, traditionally, six-switch three-phase inverters have been widely utilized for variable speed alternating current motor drives. Recently, some efforts have been made on the application of four-switch three phase inverter for uninterruptible power supply and variable speed drives. This is due to some advantages of the four-switch three phase inverter over the conventional six-switch three-phase inverters such as reduced price due to reduction in number of switches, reduced switching losses, reduced number of interface circuits to supply logic signals for the switches, simpler control algorithms to generate logic signals, less chances of destroying the switches due to lesser interaction among switches, and less real-time computational burden. However such as slow di/dt and speed limitation, are the inherent characteristics and main drawbacks of the four-switch configuration. Those problems can be overcome in conjugation with Voltage-doublers which has additional advantage, such as unity power factor correction.