Variable-frequency drive

About: Variable-frequency drive is a research topic. Over the lifetime, 837 publications have been published within this topic receiving 5691 citations. The topic is also known as: VFD.

Anti-surge speed control

Abstract: The present invention relates to a method and control system to control the speed of a centrifugal compressor operating within a vacuum pressure swing adsorption process to avoid an operation at which surge can occur and directly driven by an electric motor that is in turn controlled by a variable frequency drive. In accordance with present invention an optimal speed for operation of the compressor is determined at which the compressor will operate along a peak efficiency operating line of a compressor map thereof. This speed is adjusted by a feed back speed multiplier when the flow or other parameter referable to flow through the compressor is below a minimum and a feed forward multiplier during evacuation and evacuation with purge steps that multiplies the feed back multiplier to increase speed of the compressor and thereby avoid surge.

An ANOVA-Based Fault Diagnosis Approach for Variable Frequency Drive-Fed Induction Motors

Abstract: In this article, an analysis of variance (ANOVA)-based fault diagnosis approach using experimental data is proposed for variable frequency drive (VFD)-fed induction motors Line-to-neutral voltages at the motor terminal and the stator currents, measured from two identical 025 HP three-phase squirrel-cage induction motors fed by a voltage source inverter-based low-voltage VFD under healthy and faulty cases, are evaluated Harmonic spectra of the measured voltage and current are obtained by Discrete Fast Fourier Transform (DFFT) Through the coherence and magnitude consistency analysis, the fundamental and 5th harmonic of the stator current are chosen as “signature frequency components” ANOVA along with the multiway analysis are then applied to signature frequency components, their mean and standard deviation are identified as “fault signatures”; and the p -value from the inter-group analysis of the mean and standard deviation is used to classify faults To facilitate fault diagnosis for untested motor operating conditions, formulas to calculate fault signatures are derived by surface fitting using tested data

Sensorless Start-up and Control of Permanent Magnet Synchronous Motor with Long Tieback

Abstract: The master thesis is a further investigation of the start-up procedure of a permanent magnet synchronous motor operated by variable frequency drive without position feedback via a long cable and transformers; as proposed in the specialization project, fall of 2013. The challenge is how to avoid large saturation in the transformers and motor while achieving the maximum possible starting torque with high cable resistance. In order to model and simulate the electrical system, the simulation software Simulink is used. A theoretical review is conducted in order to understand how to model system components, and how to start-up a permanent magnet synchronous motor while avoiding saturation in the transformer. Using the attained theoretical background, two permanent magnet synchronous motor Simulink models (with and without damper windings), an accurate pump load Simulink model, and three scalar control schemes which includes transmission system components for their control algorithms have been produced. In addition, a vector control scheme using field oriented control and extended Kalman filter for position estimation has been evaluated. A study case comprising of a permanent magnet synchronous motor operated by a variable frequency drive without position feedback via a long cable and transformers has been defined. The purpose of the study case is to study the defined control schemes, the permanent magnet synchronous motor's start-up procedure, and the electrical system's steady state behaviour. This include investigation of input parameter effects on the start-up procedure. The simulation results using the implemented pump load Simulink model shows that accurate load modelling affects the start-up procedure, as additional torque is required due to more rotational friction components. The simulation results of the study case show that the three proposed scalar control methods all are able to start-up the motor successfully, regardless of the initial rotor position. However, stability is not guaranteed at certain speed ranges due to the rise of small system disturbances. It has been shown that stability all through out the entire applied frequency range can be guaranteed by adding damping to the system. This is can be done by either adding transmission system components, motor damper windings, or a stabilization loop via frequency modulation.\pe It has been shown that cable length and applied frequency determines the accuracy of the transmission system voltage drop compensation algorithms of the proposed scalar control schemes. Increase in applied frequency and cable length increases the inaccuracy of the voltage drop compensation algorithms due to the ignored cable capacitance. Assuming that the maximum allowed voltage deviation from the required motor voltage during steady state is 0.1 pu, the longest cable length that can be used with the proposed scalar control schemes is 40 km. An exception is the open-loop scalar control scheme using constant voltage boosting, which can be used for cable lengths up to 20 km, due to its inaccurate calculation assumptions. Additionally, it has been shown that the breakaway torque and the reference frequency ramp slope used by the controllers directly affect the torque oscillations during start-up. Additional torque oscillations can be experienced if the breakaway torque is too high or if the reference frequency ramp slope is too low due to the lack of torque build up, which consequently makes the start-up time higher. The vector controller gave the best performance during load step tests due to its precise control of the rotor field. However, due to the requirement of rotor position feedback, position estimation is required. The investigated position estimation technique, extended Kalman filter is able to estimated speed and position with very little error. However, the initial rotor position is required by the extended Kalman filter algorithm in order to predict states properly. Simulation results show that the vector control scheme offers the lowest possible start time due to its high performance. However, due to the requirement of initial rotor position of the sensorless vector controller, it can not be used during start-up, due to inaccuracies of predicting rotor position at zero speed. This leaves either the partial and delayed open-loop scalar control scheme or the closed-loop scalar control scheme to be the most viable start-up control schemes; as both control schemes offer comparably low start-up times, start-up currents and voltage boosting; which will consequently affect the dimensioning of the transformer. The vector controller can then be implemented after the start-up procedure using the selected scalar control scheme, in order to obtain the optimal controller performance.

Remote Monitoring and Control of VFD fed Three Phase Induction Motor with PLC and LabVIEW software

Abstract: In today’s competitive market, industries are facing the growing demands-for improving process efficiencies, comply with the environmental-regulations-and to meet corporate financial objectives. The dynamic industrial manufacturing market, intelligent and low cost industrial automation systems-are required to improve their productivity and efficiency. There is a need for cost effective wireless automation system-which are secured and flexible. So in this regard the present work aims at remote monitoring and control of electrical parameters such as speed, current of Variable Frequency Drive (VFD) fed-three phase Induction Motor with Programmable -Logic Controller (PLC) and LabVIEW software. The LabVIEW Graphical User Interface (GUI) act like server communicates with the remote authorized client and can access motor parameters via Transmission Control Protocol/Internet Protocol (TCP/IP). A hardware setup and an algorithm has been developed in PLC and Arduino module for acquisition of current and speed data of three phase Induction Motor. The speed and rotational directional control of induction motor is achieved through PLC programming. Object linking and Embedding for Process Control (OPC) server is used as an-interface to communicate PLC with LabVIEW software.

A new sinusoidal input-output three-phase full-bridge direct power converter

Abstract: A direct power converter based variable frequency drive with three-level input/output waveforms is presented. The proposed drive generates common-mode free output voltages while drawing sinusoidal input currents. Like the conventional matrix converter, the input and output quantities are controlled simultaneously with one controller. Unlike the conventional matrix converter, the circuit always provides a freewheeling path for the load and source currents, thus eliminating the clamp circuit. Further, zero voltage switching (ZVS) of the front-end is naturally achieved. Functional operation of the converter is demonstrated using a hardware prototype. The drive is evaluated for the output common-mode voltage as well as its performance to load and source transients. Extension of the presented drive to an open-end winding drive with enhanced voltage gain is also discussed in context of previous research.