Digital quasi-random modulated SFAVM PWM in an AC-drive system

A main research topic in PWM-VSI inverter-driven electrical machines is to reduce the generated acoustic noise which often is dominated by a multiple of the switching frequency in the inverter. This paper proposes a modulation scheme for reducing the acoustic noise effect from an AC machine which can be implemented digitally for low and high performance systems. The scheme is based on a stator flux asynchronous vector modulation (SFAVM) imposed by a digital band limited PWM white noise generator for varying the switching frequency randomly. The white noise generator can be used for 8, 16 and 32 bit microcontrollers. The modulation strategy is tested in a 1 kVA high performance 16 bit microprocessor controlled AC drive system. Voltage-spectra on the line-to-line voltage and the acoustic noise spectra are presented and show that the new modulation strategy can decrease the noise effect. The stator-flux-polygon and the line current are measured and demonstrate the random modulation strategy. Finally, the total sound pressure level from the AC machine is investigated with fixed switching frequencies and with different randomly modulated frequency spans. It is concluded that a properly chosen fixed switching frequency has the lowest total sound pressure level. However, the random modulation strategy distributes the noise frequencies and the noise is more comfortable and less annoying     

Analysis, design, and implementation of a random frequency PWMinverter

Random pulse width modulation (RPWM) approaches can make the harmonic spectrum of inverter output voltage be continuously distributed without affecting the fundamental frequency component, and thus the acoustic noise and mechanical vibration of an inverter-fed AC motor drive are greatly reduced. However, the analysis and design of the RPWM mechanisms are generally not so trivial for practical engineers that their applications are limited. In this paper, a random frequency PWM (RFPWM) inverter and its practical design procedure are presented. First, the effects of the attributes of a random signal on the inverter output harmonic spectrum distribution characteristics are analyzed using an intuitive concept, then based on which, the quantitative design. Simulink simulation and implementation of the proposed RFPWM inverter are introduced. The proposed RFPWM inverter is employed to power an indirect field-oriented induction motor drive. The simulated and measured results indicate that the uniform random distribution of inverter output harmonic spectrum and thus smaller acoustic noise and mechanical vibration are obtained by the proposed RFPWM scheme     

Elimination of common-mode voltage in three-phase sinusoidal powerconverters

This paper presents an active solution to a common-mode voltage created by typical three-phase inverters. It is shown that the addition of a fourth leg to the bridge of a three-phase inverter eliminates the common-mode voltage to ground created by the modulation of the inverter. An appropriate four-phase LC filter is inserted between the inverter and the load in order to create sinusoidal output line-to-line voltage. A simple modification of the modulation strategy is implemented for the four-phase inverter to achieve a three-phase wye-output neutral-to-ground voltage which is equal to zero at all times for an ideal inverter. The modulation strategy thereby completely eliminates the common-mode potential produced by traditional modulation techniques with traditional three-phase inverter topologies     

High-efficiency and low acoustic noise drive system using open-winding AC motor and two space-vector-modulated inverters

The combining of the outputs of two inverters using interphase reactors is a widely used method for supplying large AC drives rated at more than several thousands kilowatts. Certain drawbacks are associated with this method, such as high acoustic noise and high losses due to the interphase reactors. To overcome these problems, the authors propose a new high-efficiency drive system using an open-winding motor and two space-vector-modulated inverters. This configuration consists of a three-level inverter with switching at once every cycle and a two-level inverter of about 1-kHz switching frequency, connected, respectively, to the opposite terminals of the open-winding AC motor. With the proposed configuration, good current waveforms, high efficiency, and low acoustic noise can be obtained.     

Magnetic noise reduction technique for an AC motor driven by a PWMinverter

A technique for reducing magnetic noise from an AC motor driven by a pulsewidth modulation (PWM) inverter is proposed. In this technique, the meaningless magnetic noise is converted into selected information. The technique can be adopted independently of the inverter rated output power. The relationship between carrier waveform frequency in PWM control and harmonics contained in the motor current is first clarified by a harmonics analysis. Then a hardware circuit configuration and carrier frequency control software in a microcomputer are introduced. Using a musical melody as the selected information, the effect of this control is experimentally confirmed. It is shown that the desired sound can be obtained from the AC motor, and the motor voltage and motor current waveforms are not affected by such control     

Random switching techniques for inverter control

New techniques which dramatically reduce acoustic noise by randomising the inverter switching frequency for inverter control are presented. It is shown that the proposed techniques combine the advantages of conventional pulsewidth modulation (PWM) techniques based on regular-sampling techniques and random PWM techniques     

Improved PWM Control Strategy for Inverters and Induction Motor Drives

This paper develops a novel pulse-width modulation (PWM) strategy for application in uninterruptible power supply (UPS) and ac motor drive systems. The voltage/current harmonic spectra and other properties of this PWM scheme are thoroughly investigated. This modulation strategy is compared with other modulation techniques, especially with the commonly used sinusoidal modulation scheme, from the standpoints of simplicity, inverter switching losses, motor losses, and other output performance features. This novel modulation scheme produces an acceptable motor curent waveform while keeping the number of inverter commutations low. Implementation of this scheme is quite simple in hardware-based as well as microprocessor-based systems.     

Reduction of vibration and acoustic noise in induction motor drivenby three phase PWM AC chopper using static induction transistors

A three-phase pulse-width-modulated (PWM) chopper that uses a static induction transistor (SIT) to chop the three-phase AC voltage with a 20 kHz carrier frequency and control an induction motor is proposed. Harmonic components in the voltage and current waveforms do not appear in the audio frequency band with this method. When each terminal of the motor is connected to a 4 μF capacitor, the terminal voltage and line current waveforms are almost sinusoidal. The motor speed is controlled by changing the on-time width of the gate signal. The power spectrum of the chopper-driven motor is calculated using a fast Fourier transform and measured. The results are used to reduce vibration and acoustic noise in the motor, which is confirmed by measurement     

Application of parallel connected NPC-PWM inverters with multilevelmodulation for AC motor drive

The neutral point clamped (NPC)-PWM inverters have been put into practical use for large capacity AC motor drives, because of their many advantages. With the increase in use, still larger capacity inverters are also expected. In this paper, a parallel connected NPC-PWM inverter is applied for AC motor drive. The conventional modulation techniques are extended to improve the inverter characteristics. To determine an optimum modulation for controlling the parallel connected NPC-PWM inverter, various modulation techniques are devised and discussed, whose results are verified by experiment     

A novel prediction method of acoustic magnetic noise based oninduction motor's NHCC function

When an induction motor is driven by a pulsewidth modulation (PWM) inverter, acoustic magnetic noise caused by harmonics of the induction motor input is a serious environmental problem. In this paper, a novel prediction method of acoustic magnetic noise is proposed. Acoustic magnetic noise emitted from an induction motor is considered as the function of harmonic components of induction motor current. The acoustic magnetic noise versus harmonic current characteristic (NHCC) function is defined. This NHCC function describes the response of acoustic magnetic noise to a single-frequency harmonic current. Based on the NHCC function, acoustic magnetic noise can be predicted very easily and accurately, simply by the calculation of harmonic components of the induction motor current. By making use of this method, the difficulties of the conventional prediction method, such as the complex calculations of magnetic force, mechanical resonant frequencies, and sound radiation efficiency can be avoided. This novel method can be used as a tool for environmental noise management and evaluation of low-acoustic magnetic noise characteristics of different inverter PWM control methods     

基于升降压斩波电路的三相DC/AC逆变器研究

为了解决常用的逆变器所带来的问题,我们提出一种新型的带升降压功能的三相DC/AC变换器拓扑,并介绍了其工作原理。借助于PSIM仿真软件,对单相和三相电路进行了仿真研究,提出了由单相组成三相电压输出的构成方法。在列出仿真参数的前提下,给出了负载电压,负载电流以及调制给定电压和逆变器输出电压的仿真结果。仿真结果表明三相DC/AC逆变器可以实现50 kHz高频功率变换下宽输入电压范围工频逆变输出,证明了理论分析的正确性。     

General Modulation Strategy for Seven-Phase Inverters With Independent Control of Multiple Voltage Space Vectors

This paper focuses on the analysis of a seven-phase voltage-source inverter for high-performance motor drives. The problem of the modulation strategy of the inverter is solved by combining the multiple space vector representation with traditional carrier-based pulsewidth modulation. This approach leads to the definition of a general modulation strategy that can be usefully utilized in multimotor drives, as well as in multiphase motor drives for improving the torque density. The inverter output voltage capability is investigated, showing that the proposed modulation strategy is able to fully exploit the dc input voltage either in sinusoidal or nonsinusoidal operating conditions. The results obtained in the analytical investigation are confirmed by experimental tests.     

A novel control scheme for the multilevel rectifier/inverter

A novel three-level pulsewidth modulation (PWM) rectifier/inverter is proposed: this single-phase three-level rectifier with power factor correction and current harmonic reduction is proposed to improve power quality. A three-phase three-level neutral point clamped (NPC) inverter is adopted to reduce the harmonic content of the inverter output voltages and currents. In the adopted rectifier, a switching mode rectifier with two AC power switches is adopted to draw a sinusoidal line current in phase with mains voltage. The switching functions of the power switches are based on a look-up table. To achieve a balanced DC-link capacitor voltage, a capacitor voltage compensator is employed. In the NPC inverter, the three-level PWM techniques based on the sine-triangle PWM and space vector modulation are used to reduce the voltage harmonics and to drive an induction motor. The advantages of the adopted th-ree-level rectifier/inverter are (1) the blocking voltage of power devices (T1, T2, S_a1-S_c4) is clamped to half of the DC-link voltage, (2) low conduction loss with low conduction resistance due to low voltage stress, (3) low electromagnetic interference, and (4) low voltage harmonics in the inverter output. Based on the proposed control strategy, the rectifier can draw a high power factor line current and achieve two balance capacitor voltages. The current harmonics generated from the adopted rectifier can meet the international requirements. Finally, the proposed control algorithm is illustrated through experimental results based on the laboratory prototype.     

Design and implementation of vector-controlled induction motordrives using random switching technique with constant sampling frequency

Recent results have shown that random switching techniques reduce electromagnetic interference, annoying acoustic noise, and other undesirable effects. However, to incorporate random switching techniques into digital-controlled induction motor drives, it requires dynamic adjustment of the gains of controllers. This paper presents details of the design and implementation of induction motor drives using a new random switching technique. It is shown, and confirmed by experimental results in this paper, that the sampling frequency of inverter control is constant, and therefore it is not required to adjust the gains of controllers dynamically. The details of controller design of the random switching inverter-controlled vector drives are fully explored, including the controller design in the discrete-time domain and the effect of the random technique on the speed response. Moreover, the advantages and disadvantages of inverter-controlled vector drives using random switching techniques are highlighted by experimental results     

A comparison of passband and baseband transmission schemes for HDSL

Using an ideal decision feedback equalizer (DFE), the SNR of quadrature amplitude modulation (QAM) and baseband pulse amplitude modulation (PAM) in the presence of self near-end crosstalk is computed for a large sample of loops within a carrier serving area (CSA). When baud-space feedforward filters are used, PAM has 1-2 dB more SNR than QAM, where the type of PAM is the 2B1Q line code. However, when using fractionally spaced feedforward equalizers (FSEs), the SNRs of 2B1Q and QAM are almost equal for loops at the extreme range of a CSA. Four- and 16-state trellis-coded modulation is applied to PAM and QAM. Coded and uncoded PAM and QAM are simulated with parallel decision feedback estimation. Viterbi receivers and coding gains are computed. QAM has up to 1 dB higher coding gains that PAM. However, the higher coding gains of QAM do not compensate for the lower SNR of uncoded QAM, and coded QAM has worse performance than coded PAM in the presence of self near-end crosstalk. The error rates of PAM and QAM with impulse noise are computed using a collection of measured impulse noise events. Results indicate that QAM has a lower error rate than PAM in the presence of impulse noise     

基于PLC与变频器的交流电机调速系统的探究

变频器是利用电力半导体器件的通断作用将电压和频率不变的工频交流电源转化成电压和频率可调的交流电源,供给交流电动机实现软启动、变频调速等功能的电能变换控制装置。变频器交流调速系统具有良好的调速性能,而且运行效率高、可靠性强、节能效果也较为理想,是全球范围内公认较为先进的调速系统。而PLC是一种程序系统,把二者结合在一起,可实现变频器交流电机调速控制系统的自动化、科技化、智能化的控制。本文将设计探究基于PLC的变频器多段速控制,通过总体方案确定功能要求,选择软硬件,完成输入输出分配及接线端子的连接,最后通过变频器的参数设定和PLC的程序设计完成交流电机多段速控制的操作。     

High efficiency, unity power factor VVVF drive system of aninduction motor

A high-efficiency, unity-power-factor VVVF (variable voltage, variable frequency) drive scheme for an induction motor is presented. A unity-power-factor PWM (pulsewidth modulated) converter regulates DC voltage. An inverter circuit with the magnetic flux control PWM method generates VVVF PWM waveforms. The modulation factor of the inverter PWM control with controllable DC link DC voltage is studied. As a result, the distortion factor and the switching frequency are reduced by over-modulation with low DC link voltage. A high-efficiency and unity-power-factor VVVF induction motor drive has been achieved using the control strategy     

A voltage control strategy for current-regulated PWM inverters

Alternative voltage control strategies for current-regulated PWM inverters are analyzed, including previously established feedforward and feedforward/feedback controllers and a newly proposed decoupling feedback control strategy. The steady-state and dynamic characteristics of each of these control methods are illustrated and compared for a selected inverter design. It is shown that the feedforward controller exhibits steady-state error and an undesirable overshoot of the output voltages during startup. The addition of a feedback loop eliminates the steady-state error and reduces the overshoot; however, the natural response is underdamped regardless of the choice of feedback gains. A decoupling feedback control strategy that eliminates the disadvantages of the feedforward and feedforward/feedback controllers is described. Using the decoupling feedback controller, it is possible to eliminate the steady-state error and place the closed-loop poles wherever desired. Moreover, if the closed-loop poles are selected appropriately, it is possible to eliminate the overshoot of the output voltages during startup transients     

Random vibration test control of inverter-fed electrodynamic shaker

The random vibration control of an inverter-fed electrodynamic shaker is presented in this paper. First, the dynamic model of the shaker is found and a current-controlled pulsewidth modulation inverter is designed and implemented. The feedback controller is augmented with a command feedforward controller and a disturbance feedforward controller to let the armature exciting current have low harmonic content and possess excellent waveform tracking performance. Then, an acceleration controller and its random vibration command are arranged. In the proposed acceleration control scheme, a command feedforward controller and a robust disturbance feedforward controller are also employed to let the shaker have close random acceleration command waveform tracking control performance, and the performance be insensitive to the system parameter variations. It follows that the acceleration control with desired frequency response in a vibration test could be achieved through properly setting the command signal. The effectiveness of the proposed control scheme is verified by simulation and measured results     

A new optimized space-vector modulation strategy for acomponent-minimized voltage source inverter

This paper presents a new space-vector modulation strategy suitable for a low-cost pulse-width-modulation (PWM) voltage-source (VS) inverter employing only four switches, four diodes, and a split-capacitor bank in the DC link. The work is motivated by the need for an efficient and flexible modulation method, which is optimized with respect to minimum machine-torque ripple. The modulation strategy is named space-vector modulation for four-switch inverter (SVMFSI), and it is realized by planning the switching patterns between four active voltage vectors on the basis of a desired flux trajectory for the stator-flux vector in the AC machine. The strategy is implemented in a single 8-bit microcontroller as a double-sided modulation strategy. Simulations of the machine-torque ripple are performed at a switching frequency of 4 kHz and indicate a torque ripple of 14% at nominal load. Finally, selected results are verified experimentally on a 1.5-kVA prototype B4 inverter. The test results indicate high-quality output-voltage spectra with no low-order voltage harmonics and a harmonic-loss factor (HLF) of 1.12% at unity modulation index