PWM-CSI induction motor drive with phase angle control

The authors describe a pulse-width-modulated current-source inverter drive system using an induction motor. Its dominant feature is that it provides adequate control of either torque or speed over a wide range without requiring a shaft position or speed sensor. The capacitor-loaded current-source invertor system has the advantages of simplicity, low switching frequency, four-quadrant operation, overcurrent protection, and low harmonic content in the motor current and voltage. The choice of maximum value for the capacitor depends on the degree of nonlinearity that can be tolerated in the torque-stator current relation, whereas its minimum value depends on the need for a low impedance path for inverter current harmonics. The control strategy is based on the concept of controlling the stator phase angle of the induction motor. The stator voltage is sensed, and the current-source inverter is used to inject current into the motor with the desired phase angle     

High Performance IM Drive by Coordinate Control Using a Controlled Current Inverter

An induction motor drive which can replace a high performance dc motor drive in steel and paper mill applications has long been desired. The authors have brought this into reality by accurate coordinate control of a combination of a caged rotor induction motor and controlled current inverter. The concept of the improved coordinate control is that the exciting current and torque current are controlled independently by controlling slip and stator current vector. This is achieved by a coordinate transformation of the electrical quantities of an induction motor. A generalized coordinate control system and a method of compensating for variations in flux and torque resulting from a difference between actual constants and controller constants are described.     

Quick regulation of sinusoidal output current in PWMconverter-inverter system

An induction motor drive system composed of a current output-type power converter and a current source inverter with sinusoidal input and output voltage/current is presented. Pulsewidth modulation (PWM) strategies with GTOs are applied to the converter and the inverter sections from the point of view of reduction of the current harmonics and suppression of the motor torque pulsations. A simple method for quick regulation of the AC output current amplitude is presented and applied to the PWM inverter section. To demonstrate the improvement in the current response of the inverter, a slip frequency/current regulation of an induction motor is considered. The experimental results of steady-state and dynamic operations of the motor are shown. The merits and demerits of this control method are discussed     

Controlled-Power-Angle Synchronous Motor Inverter Drive System

This paper describes a controlled-power-angle synchronous motor inverter system which provides drive characteristics similar to those of an induction motor inverter system. The system consists of a conventional synchronous motor with a shaft-position sensor which controls the firing of thyristors in an inverter. This paper investigates the steady-state properties and control strategies for the controlled-angle synchronous motor inverter system. Some experimental results are presented and compared with theoretical predictions.     

Analysis and Comparison of Two Types of Square-Wave Inverter Drives

The application of adjustable frequency static inverters to induction motor speed control has resulted in a diversity of inverter designs. In this paper, the state-variable formulation is applied to the analysis of two widely used drive systems incorporating square-wave inverters with 180° and 120° firing logic. Measured characteristics of an actual drive system are included, and the results are compared to an analytical solution. Steady-state speed-torque curves for each inverter supplying three markedly different types in induction motors are given. Performance of the two inverter drives are compared by a thorough investigation of typical operating points.     

6 Kv/1250 Kw绕线式电机的新型串级调速装置

对风机和水泵类负载，串级调速是一种高性价比的节能调速方法。介绍了新型的6kV／1250kW绕线式电动机的软开关升压型串级调速装置，它采用IGBT软开关升压电路结合晶闸管逆变器来实现转差功率的回馈并实现电动机的连续调速。由于升压开关频率为2kHz，逆变触发角固定，使得装置具有逆变功率因数高、升压电感体积小、效率高等优点。装置结合内馈绕线式电动机构成风机、水泵类负载的调速系统，具有极高的性价比。     

Current regulated PWM-CSI induction motor drive system without aspeed sensor

This paper deals with a current source inverter-induction motor drive system without a speed sensor, and the speed estimation with only sense of the motor voltage is investigated. The input DC link current which is kept constant by a pulsewidth modulated (PWM) converter with sinusoidal input current is supplied to the PWM inverter. The inverter output current with sinusoidal wave is directly regulated by employing the modulation index control of the PWM strategy. The motor is driven by a slip frequency/current regulation control. The motor speed is estimated by using the measured voltage and current, or using the measured voltage and the estimated current. The filter capacitor which is installed in the inverter circuit is taken into consideration for the current estimation. A digital signal processor is employed for calculation. As the PWM pulse of the inverter is calculated by an online real-time system, the quick regulation of the sinusoidal output current is achieved. The experiments show that the high performance steady state behavior and the acceleration/deceleration characteristics with smooth drives and low noise of the motor is obtained     

System Design Method for a Load Commutated Inverter-Synchronous Motor Drive

In a thyristorized load commutated inverter synchronous motor drive system, the inverter relies on the back EMF of the synchronous motor to provide the reverse voltage for commutation. The level of the back EMF is a function of both the synchronous motor's field current and rotational speed. The inverter operating frequency is determined by the motor speed and number of pole pairs. For a fixed thyristor firing angle, an increase inmthe level of armature current decreases the available thyristor turn-off time due to overlap of the incoming and outgoing thyristor. This overlap time is a function of the commutating reactance of the synchronous motor. These factors, field current, motor speed, inverter frequency, and armature current, together with a thyristor turnoff time specification, set a maximum limit on the value of motor commutating reactance. The motor designer and inverter designer must perform a tradeoff study of these factors to arrive at a satisfactory drive system. The results are presented of an analysis that allows the synchronous motor reactance to be specified based on the other given parameters of the inverter-synchronous motor drive system. Test data are provided from a 20-kVA 500-1000 Hz load commutated inverter/ inductor type synchronous motor drive system. The effects of motor speed and field excitation on the operating condition of the drive are discussed.     

A constant air flow rate control of blower for residentialapplications

This paper presents a technique to control a blower for residential applications at constant air flow rate using an induction motor drive. The control scheme combines a variable volt/hertz ratio inverter drive and an average motor current regulation loop to achieve control of the motor torque-speed characteristics, consequently controlling the air flow rate of the blower which the motor is driving. The controller is simple to implement and practical for commercialization. It is also reliable, since no external pressure or air flow sensor is required. Both a theoretical derivation and an experimental verification for the control scheme are presented in this paper     

Improved current source GTO inverter-fed induction motor driveswith PWM-controlled thyristor converter

An improved current-source GTO (gate turn-off) inverter system for driving an induction motor at high frequency was developed. This system is composed of an inverter using GTOs and a PWM (pulsewidth-modulated)-controlled thyristor rectifier. The energy rebound circuit in the inverter is used to turn off the thyristors in the rectifier and to apply PWM control techniques. This circuit plays an important role in the treatment of reactive power in a load. The capacitors connected to the AC input terminal to improve PWM control also function as a filter. Thus, the waveforms of the input voltage and current become almost sinusoidal. Principles and circuit operations of the rectifier section are described in detail. The current-source GTO inverter is used to drive a 5.5 kW induction motor. The experimental waveform and characteristics for the tested motor drives are given. It is shown that the harmonic components of the input voltage and current are eliminated or reduced by using the PWM control technique without spoiling the inherent characteristics of the current-source GTO inverter     

电网瞬时停电保持变频器母线电压的新方法

工业现场中,变频器带大惯性负载运行时,有时会遇到电网瞬时停电的情况,由于负载惯性大,电网瞬时停电再来电后,电机不能立即起动运行.针对这种情况,提出了一种新的解决方法:瞬时停电后,变频器有规律地降频运行,使异步电动机进入微发电状态,电机与变频器构成一个自治系统,以维持变频器母线电压.来电后,变频器从当前运行频率处,再恢复到额定运行状态.对所提出的方案,在山东新风光电子科技发展有限公司生产的JD-BP32变频器上进行了试验,试验结果验证了控制方案的正确性.     

A DSP-based modified slip energy recovery drive using a 12-pulse converter and shunt chopper for a speed control system of a wound rotor induction motor

This paper introduces a modified slip energy recovery drive system for speed control of a wound rotor induction motor offering improvement of drive performance, particularly line power factor and overall system efficiency. A 12-pulse line commutated thyristor converter operating in an inverter mode in conjunction with an additional IGBT shunt chopper is employed to transfer slip energy back to ac mains supply via three phase transformers. This approach offers motor speed control by varying the duty cycle of the chopper instead of changing the inverter firing angle. As a consequence, supply power factor can be improved. The servo state feedback designed by linear quadratic regulator (LQR) with observer is also included in order to keep motor speed to be constant over a certain range of operating conditions by using the estimated dc link current derived from motor speed. The advantage of this technique is absence of current transducers for current feedback control loop. The overall control system is implemented on DSP, DS1104’TMS320F240 controller board. Experimental results are illustrated in order to validate performance of the proposed system.     

High-performance direct torque control of an induction motor

A novel direct torque control method for an induction motor is presented which is quite different from field-oriented control. Improving the torque response of a large-capacity induction motor using two sets of three-phase inverters and an open-data induction motor is of special concern. Instantaneous voltage vectors applied by an inverter have redundancy characteristics which provide some flexibility for selecting the inverter switching modes. By using this switching freedom, control is achieved according to the following priorities: (1) high-speed torque control; (2) regulation of the primary flux; (3) decreasing the zero phase sequence current; and (4) minimization of the inverter switching frequency. Simulations and experiments have been carried out to verify the feasibility of this priority control, accompanied by comparisons with another control scheme. Torque frequency-response corner frequencies above 2000 Hz have been experimentally measured, and time constants of 4 ms have been achieved for rotor-speed step responses from -500 to 500 r/min. The peak transient torque during the step change is about 20 times the rate torque     

A fast-response current controller for microprocessor-based SCR-DCmotor drives

An LSI firing circuit, in conjunction with a high-speed digital signal processor (DSP), has been developed to adjust the thyristor firing angle between 0 and 180° for both positive and negative current control in a dual antiparallel-connected three phase power converter connected to a DC motor. A fast-response current controller is obtained by using feedforward techniques and a variable-structure proportional-integral (PI) compensator to produce an optimal current response under both continuous and discontinuous current conduction. Theoretical derivations and practical results of a predictive control strategy are shown. The main objective of this control scheme is to analyze the mathematical behavior of the system and use this knowledge to advantage in the control of armature current     

A Combined Frequency Converter for Soft Acceleration of Induction Electric Drives with Heavy Starting Conditions

The usability of a thyristor frequency converter with a supplementary controlled series compensator for soft starting of induction motors with high torque of inertia of actuating mechanisms is considered as an alternative to transistor converters. It is shown that the supplemental device, in the form of a transistor–capacitor convertor, can be considered as an adjustable capacitor, the equivalent capacitance of which can be varied from very large values (to a maximum of infinitely large) to some fixed minimum value. The voltage of an adjustable series capacitor provides the desired switching conditions of thyristor inverter, and the capacitive reactance ensures the compensation of reactive power consumed by the induction motor and thyristor inverter, reducing the current load of the motor and converter. The addition of a thyristor current converter with a controlled series compensator of reactive power in the form of a transistor–capacitor unit makes it possible to carry out a soft start of induction motors similar to the starting modes of synchronous machines. Simulation results confirming the achievement of the desired effect are presented. It is shown that the supplemental device in the form of transistor–capacitor converter is a robust system well adaptable to various conditions of electric-drive operation. The functional equivalence of a transistor frequency converter and thyristor frequency converter with a supplemental transistor–capacitor unit with a substantially lower cost of the latter makes possible a new mechanism for soft starting of powerful electric drives with induction motors under conditions of high torques of inertia of actuating mechanisms.     

Excitation Control of a Brushless Synchronous Motor

A simple system is presented for controlling the excitation of a brushless synchronous motor independently of the motor speed or load angle. The system comprises a pulsewidth modulated (PWM) inverter provided with controllable pulsenumber. Experimental measurements of the induced rotor excitation shows that a wide range of excitation control is obtainable by simply varying the pulsenumber of the output waveform of the inverter while keeping the fundamental frequency of the inverter unaltered. An approximate formula for the rotor current is also given which confirms the dependence of the rotor current upon the pulsenumber.     

Optimal Efficiency Drive of a Current Source Inverter Fed Induction Motor by Flux Control

When an induction motor is driven under light loads, the efficiency can be substantially improved by reducing the air-gap flux of the motor. The air-gap flux can be indirectly controlled by adjusting the stator current and slip frequency in the case of a current source inverter induction motor drive system. The relationship between the stator current and the slip frequency for an optimal efficiency control is derived, and the control loop is suggested. By this method, ten percent or more improvement in the efficiency is obtained at a quarter of the full load. Generally, the reduced air-gap flux may result in undesirable dynamic responses. The small signal analysis is used in order to estimate the transient characteristics. The experimental results indicate a stable operation and a good dynamic response.     

A Current Source GTO Inverter with Sinusoidal Inputs and Outputs

With the application of gate turn-off thyristors (GTO's) and PWM control techniques, a current source inverter capable of producing sinusoidal input/output (I/O) voltages and currents has been developed. The sinusoidally modulated current is fed to the GTO's in the rectifier and inverter sections. The overvoltage-absorption capacitors connected to the ac input and output terminals function as a filter and, consequently, the waveforms of the input/output voltages and currents become sinusoidal. Because the PWM control utilizes the high-speed switching characteristics of the GTO's, the dc link current smoothing reactor and the overvoltage absorption capacitors are greatly reduced. The dc link voltage in the rectifier section is controlled to adjust the ac motor current. This is accomplished by using the firing angle shift method in conjunction with the method involving varying the width of the bypass gate pulses, which put the rectifier section into a bypass state. The current source GTO inverter is used to drive an 11-kW induction motor. As a result, excellent acceleration and deceleration characteristics are obtained, which verifies that the new current source inverter is quite suitable for driving an ac motor at variable speeds.     

基于dsPIC的预冷水泵电机变频调速的控制

通过对空分预冷系统情况的分析,阐述了变频调速的节能原理,介绍dsPIC30F4012型微处理器的特点及其在交流变频调速控制系统中的应用。使用IPMPS21865型智能功率模块作为逆变器主电路,应用Matlab／Simulink强大的仿真能力建立交流异步电机控制系统的仿真模型,经仿真实验验证了其简单有效、具有良好的动态性能。     

变频空调负荷虚拟同步机化改造及其参与微网互动调控

为了提高微网系统运行的安全稳定性,充分发掘海量空调负荷资源的可调潜力,从而增强负荷响应自主性,在对空调压缩机电机控制电路改造的基础上,提出了一种变频空调负荷虚拟同步机群参与微网调频的控制方法。首先对变频空调压缩机电机进行负荷虚拟同步机控制改造,建立其控制模型;然后将空调压缩机电机进行聚合等值,便于其参与微网互动调控;接着建立了变频空调负荷虚拟同步机群参与微网互动的控制架构;最后提出变频空调负荷参与微网一次和二次调频的策略,并通过对变频空调负荷虚拟同步机群控制仿真,验证了负荷虚拟同步机化改造能够有效提升空调负荷参与调频的能力。