Efficient Modulation Technique for a Four-Leg Fault-Tolerant Neutral-Point-Clamped Inverter

This paper presents a new low-loss modulation technique for the hybrid three-level four-leg converter. The total losses of the converter are reduced by about 18% on average compared to the standard three-leg neutral-point-clamped converter. Furthermore, the low-frequency voltage oscillation in the neutral point is completely cancelled, and the maximum benefit of the dc-link voltage is obtained. All these facts, together with the fault-tolerant ability due to the fourth leg, make this topology very interesting for applications such as wind generation, in which it is important to maximize efficiency and reliability. Some experimental results confirm the good performance of the proposed modulation technique.     

Pulsewidth Modulation Circuits Using CMOS OTAs

This paper presents three pulsewidth modulation modulators using CMOS operational transconductance amplifiers. They consist of a ramp integrator and current-tunable Schmitt triggers. Prototype circuits built using discrete components exhibited that their duty cycles are linearly controllable. Because of their simple structure, the proposed modulators can be easily fabricated in a monolithic integrated circuit.     

Pulsewidth Modulation Control of Brushless DC Motors for Robotic Applications

Pulsewidth modulation (PWM) control of brushless dc motors is implemented with digital servo mechanisms for robotic applications. Under the assumption that the pulse period is much smaller than the motor time-constants, the motor is modeled by a discrete-time transfer function with the pulsewidth playing the role of the control signal. This model enables the application of classical linear control engineering to the design of a digital position servo for the brushless dc steering motors on the CMU Rover. The controller is implemented with a microprocessor and programmable timer to calculate concurrently the actuating signals, time sampling periods, and pulsewidths, as well as to provide commutation. Computer simulation and real-time hardware implementation of the servo demonstrate the efficacy of the approach.     

Feedback Linearization Control of Three-Phase UPS Inverter Systems

In this paper, a feedback linearization technique is proposed to control the output voltage control of three-phase uninterruptible power supply systems. First, a nonlinear model including the output $LC$ filters is derived from the power balance condition between the inverter output terminal and the load side. Then, input–output feedback linearization is applied to the nonlinear model to make it linear. The controller of the linearized model is designed by linear control theory. The tracking control law is obtained with a pole placement technique. It is shown experimentally that the proposed control scheme gives high dynamic responses in response to load variation as well as a zero steady-state error.      

基于闭环控制的高精度三相电源的设计

针对某设备所需的三相电源相位精度要求高的特点,在传统DDS技术的基础之上,设计了一款高度对称的三相电源。该设计采用数字闭环控制模型,利用相位误差自动检测值作为反馈,在DDS模块中增加相位自动修正,以达到高精度稳频和高精度三相对称的目的。     

Characteristic Analysis for Multisampled Digital Implementation of Fixed-Switching-Frequency Closed-Loop Modulation of Voltage-Source Inverter

In this paper, a fixed-switching-frequency closed-loop modulation of a voltage-source inverter (VSI), upon the digital implementation of the modulation process, is analyzed and characterized. The sampling frequency of the digital processor is considered as an integer multiple of the modulation switching frequency. An expression for the determination of the modulation design parameter is developed for smooth modulation at a fixed switching frequency. The variation of the sampling frequency, switching frequency, and modulation index has been analyzed for the determination of the switching condition under closed loop. It is shown that the switching condition determined based on the continuous-time analysis of the closed-loop modulation will ensure smooth modulation upon the digital implementation of the modulation process. However, the stability properties need to be tested prior to digital implementation as they get deteriorated at smaller sampling frequencies. The closed-loop modulation index needs to be considered maximum while determining the design parameters for smooth modulation. In particular, a detailed analysis has been carried out by varying the control gain in the sliding-mode control of a two-level VSI. The proposed analysis of the closed-loop modulation of the VSI has been verified for the operation of a distribution static compensator. The theoretical results are validated experimentally on both single- and three-phase systems.      

三相电压型逆变器优化控制策略研究

三相电压型逆变器控制中,适当提高系统开关频率可以优化输出电压波形,但同时会带来系统开关损耗的增加,且死区时间增加从而使得死区效应影响变大。提出一种基于两相调制SVPWM的优化无死区控制方案,两相调制SVPWM算法可以减少开关损耗,提高电压利用率,优化无死区控制可以从根本上消除死区带来的不良影响。通过MATLAB/SIMULINK仿真对该方法进行了验证。     

Voltage-Balance Compensator for a Carrier-Based Modulation in the Neutral-Point-Clamped Converter

This paper presents an optimal voltage-balancing compensator for a specific modulation technique applied to a neutral-point-clamped converter. The technique uses two modulation signals per phase, and it is called double-signal pulsewidth modulation. It completely eliminates low-frequency oscillations in the neutral-point voltage. However, it does not provide natural voltage balancing; therefore, a compensation loop is required. The proposed control generates a feedback compensation signal that correctly modifies the three-phase modulation signals. The optimal compensation signal is calculated by a dynamic limiter according to the intrinsic limitations of the system related to the variability range of the modulation signals. It significantly improves the voltage balancing under all operating conditions of the converter. In addition, this compensation strategy does not increase the switching frequencies of the power devices. The algorithm is tested and verified using both simulation and experimentation.      

一种高性能的三相逆变电源波形控制策略

恒频恒压(CVCF)逆变电源的输出电压波形质量是衡量其性能的重要指标之一。文章采用一种重复控制和双闭环控制相结合的电压波形控制策略,以重复控制器提高逆变电源输出电压的稳态精度,减小总谐波畸变率;以双闭环控制器达到较快的动态响应速度。该方案在一台采用TMS320F240DSP控制芯片的50Hz三相PWM逆变器上得到验证。     

Closed-Loop Control of a Manipulator Arm Using a Wrist Force Sensor

Robot force sensing and force control have been researched for several years, producing a variety of sensing methods and control strategies. Most of the published work has been theoretical in nature, with little emphasis on the practical problems encountered in the implementation of a system. This paper describes the interfacing of a 6-axis wrist force sensor to a manipulator and the design and implementation of a control system incorporating the sensor as a feedback device (in addition to existing position control).     

Continuous-Time Sigma–Delta Modulator With an Embedded Pulsewidth Modulation

A new Continuous-Time (CT) sigma-delta modulator (SDM) based on the well-known asynchronous SDM is proposed in this paper. To this end, the flash quantizer and the digital-to-analog converter (DAC) in a multibit (MB) CT-SDM clocked at a rate f_max are replaced by a single-bit (SB) comparator with hysteresis clocked at a higher rate f_s and a SB-DAC, respectively. By proper selection of the hysteresis in the comparator and the ratio F = f_s/f_max, the performances of both modulators are shown to be equivalent. The comparator with hysteresis and the loop filter produce, in the modulator output, a limit cycle of frequency /max which is modulated by the input signal. Therefore, the modulator output can be considered to be a pulsewidth (PW) modulated signal with a frequency approximately equal to /max, and the proposed modulator is called a PW-SDM. Despite the high sampling rate of the comparator output, the integrators and the SB-DAC of the proposed modulator have the same speed requirements as those of the equivalent conventional MB-SDM. On the other hand, in the proposed modulator there are not MB (analog-to-digital or digital-to-analog) converters. Therefore, for a given set of specifications, the proposed PW-SDM is expected to consume less power and area than its equivalent conventional MB modulator.     

三相并网逆变器的双环控制策略研究

由于对高频谐波的抑制效果明显好于L型滤波器,因此LCL滤波器在电流源控制的并网逆变器中应用越来越广泛。而针对该类型的并网逆变器的控制策略更为复杂,为了简化控制策略一种基于电流双环的并网控制方案被提出来。与电压电流的双环控制器设计方法不同,设计电流双环控制器参数时除了考虑内外环控制器的相互影响以外,还需要考虑双环控制器带来的降阶和少自由度问题。因此本文在介绍基于高阶极点配置的电流双环控制器设计方法的基础上,重点分析在电流双环控制带来的少自由度的情况下如何合理的设计控制器参数。实验结果表明,根据该方案设计的控制器参数能够使三相并网逆变器安全、可靠运行且具有较快的动态响应速度。     

Selective Harmonic Elimination PWM Control Scheme on a Three-Phase Four-Leg Voltage Source Inverter

A selective harmonic elimination (SHE) control strategy on a three-phase four-leg inverter is reported in this paper. The control signals of the four legs are calculated as follows: 1) control signals of three legs are mathematically expressed using Fourier-based equations on line-to-line basis as conventional SHE technology, which eliminates lower order nontriplen harmonics, and 2) the fourth leg produces the harmonics that are equal to the lower triplen harmonics produced by the other legs. The inverter has almost symmetric three-phase output voltage with unbalanced load because the fourth leg provides a low-impedance path for the triplen harmonics. The switching-to-fundamental frequency ratio is only 13 and 27 (per unit) p.u. for the three legs and the fourth leg in the proposed prototype, which is with the total harmonic distortion of output voltage lower than 4%. Selected solutions for the switching angles are presented and verified by simulation and experimentation in order to confirm the effectiveness of the proposed scheme.     

A Comprehensive Study of a Hybrid Modulation Technique for the Neutral-Point-Clamped Converter

This paper presents a hybrid modulation technique for the three-level neutral-point-clamped converter. A modulation strategy, based on two modulation signals per phase, was presented previously. This strategy completely removes the low-frequency voltage oscillations that appear at the neutral point (NP) in some operation conditions. However, it also has a major drawback: it significantly increases the switching losses of the converter. The proposal in this paper combines such a modulation strategy with sinusoidal pulsewidth modulation (SPWM). The main characteristic of this hybrid modulation is the reduction in switching losses at the cost of some low-frequency voltage oscillations at the NP. The amplitude of these oscillations can be controlled by varying the combination of the two strategies. The performance of the hybrid modulation is analyzed and compared with the original strategies. Power losses and oscillation amplitudes on the dc-link capacitors are evaluated. Experimental results show how the hybrid modulation performs by balancing the dc-link capacitors.      

不平衡负载条件下三相四桥臂逆变器的控制

三相四桥臂逆变器具备外接三相不平衡负载的能力。为改善逆变器系统在严重不平衡负载情况下输出电压的对称性,文中提出一种新颖的控制策略——旋转坐标系下的PIR-P双环控制。当系统接不平衡负载时,电压外环的PI控制器保证系统的动态性能,谐振控制器保证其稳态精度。最后在旋转坐标系下对系统分别采用PI-P和PIR-P两种双闭环控制器情形作对比仿真。结果表明系统在严重不平衡负载情况下,输出电压负序不平衡度由2.41%减小到0.129%,零序不平衡度由2.25%减小到0.032%。     

基于重复控制与电压双闭环控制的逆变器设计

文章提出了一种基于重复控制与电压双闭环控制相结合的单极倍频SPWM正弦波逆变器控制方案,详尽阐明了单极倍频SPWM控制方式的工作原理,并给出了逆变系统的数学模型,在此基础之上研究了重复控制与电压双闭环控制相结合的控制方案。实验结果表明：这种逆变器输出电压只有较小的谐波含量,同时具有良好的动态特性。     

利用CPLD设计逆变器的控制电路

CPLD作为近几年兴起的一种优秀的可编程逻辑器件。其众多的优点非常符合逆变器控制电路设计的需要。结合CPLD的功能和特点，分析了CPLD在逆变器控制电路中的典型应用，并由此说明CPLD的使用可以极大地改善传统逆变器控制电路的设计。     

用可编程序控制器变频器实现三相异步电动机闭环速度控制的教学实验

本文介绍了用可编程序控制器、变频器实现三相异步电动机闭环速度控制的教学实验的系统组成,主要的实验内容以及在教学中的应用。     

Comparison of Three-Phase Modulation with Two-Phase and Four-Phase Modulation

For a constant added noise density at high signal-to-noise ratios and for the same error rate, three-phase PSK requires about 0.75 dB less energy per bit than two-phase or four-phase PSK. However, at very low signal-to-noise ratios, three-phase PSK requires about 0.74 dB more energy per bit of channel capacity than two-phase or four-phase PSK.     

数字化三相大功率逆变波形内模控制方法

针对三相逆变电源数学模型在旋转αβ坐标系下的特点,提出了基于神经网络内模原理的逆变波形控制方案.用神经网络预估器作为逆变器的内部模型,用神经网络辨识预估逆变器正模型及其逆模型,在线修正、补偿内部模型与被控逆变器之间的模型失配.仿真和实验结果表明,该方案控制下系统稳压精度高,有较快的动态响应.