交流变频调速系统仿真建模及谐波特性分析

随着电力电子技术的发展,交流变频调速系统以其强大的优势逐渐取代传统的直流调速传动,其在给人们生产生活带来方便和效率的同时,也造成了电力系统谐波污染加重的问题。因此,设计了一种开环正弦脉宽调制（sinusoidal pulse width modulation,SPWM）控制的交流变频调速系统并搭建仿真模型,实现了对系统中变频器输出电压频率和幅值及电机转速的灵活控制。对系统网侧电压和电流进行了谐波特性分析,结果表明：网侧电压的波形比较理想、畸变很小,而电流波形畸变严重;且随着变频器输出频率的增加,电压波形畸变程度有所加剧,电流畸变程度有所减轻。     

Power calibrator using switched mode voltage source

The paper is focused on a sophisticated switched mode power supply with a pure sinusoidal output voltage waveform with frequency (40-65 Hz) and voltage range (30-500 V). In order to cope with stringent voltage (10.2%) and distortion constraint (THD<0.7%) in a modern calibration system, traditional inverter design with an output LC filter is upgraded with a feedback-feedforward control principle. The paper presents the voltage source topology, analyzes its steady-state response and gives its comprehensive evaluation. Using a simple sensor that is capable to detect a small voltage asymmetry at the presence of a high AC component (500 VRMS), the parasitic DC component is limited below 5 mV. Experimental results demonstrate exceptional voltage accuracy (<0.2%) and low total harmonic distortion (THD)     

基于状态空间的PWM逆变器数字PI双环控制技术研究

主要研究了数字控制的实际应用情况以及脉宽调制(PWM)正弦波逆变器的特点,包括电流内环电压外环的双闭环控制。在建立逆变器控制系统状态空间模型的基础上,详细分析了外环为输出电压,内环为电感电流加负载电流前馈控制对应的控制策略的稳定性和动态响应。先对控制系统直接离散化,再利用极点配置的方法进行系统参数设计。从响应速度、外特性、稳定性方面进行了具体分析,结果说明在离散域里双环控制逆变器具有较好的动态响应速度和输出外特性。最后通过实验验证和仿真波形分析,证明这种双环控制技术能满足各项性能指标要求。     

Soft-switching flyback inverter with enhanced power decoupling for photovoltaic applications

A novel single-phase flyback inverter for photovoltaic applications is proposed to achieve low-frequency ripple current reduction on the DC busbar and to draw sinusoidal current into the AC grid. Based on capacitive idling techniques, the proposed circuit topology is derived from a single-ended primary-inductance converter and two-switch flyback inverter to obtain soft-switching operation for all of the active switches. Compared with a buck-boost inverter and other flyback inverter topologies for AC photovoltaic module systems, no extra active switches are used in the proposed inverter to realise both soft-switching and enhanced power decoupling with only four active switches. Peak-current mode control method is employed in the control schemes to ensure pure sinusoidal current with unity power factor on the AC grid. Laboratory experimental results based on a 500 W prototype are provided to verify the effectiveness of the proposed inverter     

Study on the new control scheme of class-E inverter for IH-jar application with clamped voltage characteristics using pulse frequency modulation

A new control scheme of Class-E inverter for induction heating jar applications with clamped voltage characteristics using pulse frequency modulation (PFM) is introduced. To reduce the voltage stress of a switch, the proposed PFM control scheme does not need any auxiliary circuit. It can decrease the voltage stress of a switch through the modulation of switching frequency. The Class-E inverter using the proposed control scheme has the advantages of not only the same output power when it is compared with an active clamped class-E (ACCE) inverter, but also zero-voltage-switching, which are characteristics of conventional Class-E and ACCE inverter. The control principles of the proposed method are explained in detail and its validity is verified through experimental results     

Some regulated power supply apparatus using the Morgan circuit

The SCR chopper circuit has a very wide range of application in regulating a dc power, and its merits are universally appreciated. Because of its merits, the circuit is most suitable for a nonfailure power source that supplies power from a set of rectifier-batteries to a communication equipment or any other electronic equipment, which requires a dc power source of several output voltages. For such purposes, the output voltage of the circuit should be smooth, accurately regulated, and should respond quickly; at the same time, the efficiency must be high and reliability excellent. This paper offers, firstly, some improvements on the Morgan circuit in order to make it peculiarly suitable for different kinds of practical applications; namely, the smoothing filter is made as small as possible to make the response of the circuit rapid, while the efficiency is kept high. Secondly, data, obtained through the analysis of the operation in the case of the small filter, are presented. Thirdly, the paper shows, as the result of such analysis, that if a saturable current transformer (SCT) is designed properly, the circuit will behave as a self-regulating constant voltage power source. Lastly, it proposes a practical application which has a suitable protecting circuit composed of some simple circuit elements providing against the failure of commutation which causes a severe overvoltage and overcurrent to the load.     

新型箝位式压电电机的设计研究

针对传统箝位式压电电机在谐振态下工作时,方波振动的箝位部分结构设计复杂问题,提出一种新型箝位式压电电机。该电机箝位部分与驱动部分均由同频正弦电压驱动实现正弦振动,通过定子对动子的箝位接触,实现动子单向输出运动。相较于传统箝位式压电电机和超声电机,该电机的定子结构设计无需采用模态简并,结构设计难度降低。利用有限元仿真确定定、动子结构参数,制造样机并搭建实验平台。对箝位部分分别采用正弦波与方波做激励,再对驱动部分进行波形对比,表明正弦波亦能达到预期效果。实验结果表明:准静态时,激励电压频率为250Hz、电压峰峰值Vp-p为10V时,步进距离为0.5μm,步进速度0.13mm/s;谐振态时,激励电压频率为540Hz、电压峰峰值Vp-p为70V时,步进距离为32μm,步进速度16.9mm/s;该电机可兼顾低频高分辨率和高频高速输出以实现跨尺度工作。     

Capacitor voltage balancing in multilevel flying capacitor inverters by rule-based switching pattern selection

A rule-based scheme is investigated for capacitor voltage balancing in a multilevel flying capacitor inverter (MFCI). Without using voltage feedback, the scheme determines the best switching pattern for maintaining nil mean current in all capacitors, hence minimising the capacitor voltage fluctuation. The method is developed to work with the selective harmonic elimination (SHE) technique for sinusoidal voltage generation applied to control static VAR compensators. The method has been designed using a four-cell five-level MFCI as an example. The selected pattern has been shown to give superior performance in load-voltage total-harmonies distortion level and mean capacitor voltage fluctuation. The method is validated experimentally for this form of MFCI     

带逆变负载的柴油机组稳定性分析及性能测试

柴油机组加载电力电子非线性负载时会发生低频振荡现象导致输出波形畸变失真。为确定系统稳定性条件,将逆变负载作为研究对象,结合同步发电机-整流器系统分析基础,建立柴油机组逆变负载等效电路模型,对该系统稳定性条件做出假设,并通过实验验证假设的正确性,对该系统的性能进行测试,同时指出存在的问题和不足。     

基于自抗扰控制的微电网三相不平衡问题研究

当微电网中三相负载呈现不平衡状态时,会导致三相输出电压不平衡,若采用三相四桥臂逆变器,则可解决此问题。但在dq0旋转坐标系下,三相四桥臂逆变器输出电压和输出电流会相互耦合。同时若系统中出现负载不平衡工况,直接采用开环控制,因不平衡负载导致输出电压中含有二倍频扰动,所以负载端输出电压仍然处于不平衡状态。针对上述2个问题,建立了三相四桥臂逆变器对应的数学模型,推导被控对象开环传递函数,对三相不平衡问题进行了深入分析。同时根据系统模型信息,设计二阶自抗扰控制器,目的是对dq轴电压、电流进行解耦,同时可以减少测量原件的个数。并针对由不平衡负载产生的二倍频扰动引入比例谐振控制器,最后通过Matlab/Simulink仿真,验证了该解决方案的有效性。     

Eighteen-sided polygonal voltage space-vector-based PWM control for an induction motor drive

An inverter scheme with 18-sided polygonal voltage space-vector structure is proposed for induction motor drive applications. An open-end winding configuration is used for the drive scheme. The motor is fed from one end with a conventional two-level inverter and from the other end with a three-level inverter, realised by cascading two conventional two-level inverters. The inverters are fed with asymmetrical DC-link voltages. A simple linear PWM control scheme up to 18-step mode is proposed, based only on the motor reference phase amplitudes. The proposed scheme gives an increased modulation range with the elimination of the 5th, 7th, 11th and 13th-order harmonics, for the entire modulation range, when compared with any conventional schemes. The absence of low-order harmonics gives nearly sinusoidal currents throughout the modulation range, and makes PWM control of voltage very simple, with low inverter switching frequencies, especially in the extreme modulation range.     

Analytical evaluation of DC capacitor RMS current and voltage ripple in neutral-point clamped inverters

The sizing of the DC-link capacitor in a three-level inverter is based on the RMS current flowing through it. This paper analyses the DC-link capacitor RMS current in a neutral-point clamped (NPC) inverter and expresses the same as a function of modulation index, line-side current amplitude and power factor. Analytical closed-form expressions are derived for the capacitor RMS current for single-phase half-bridge, single-phase full-bridge and three-phase three-leg topologies of a three-level inverter. The worst-case capacitor current stress is determined for each topology based on the analytical expressions. Further, analytical expressions are derived for the RMS values of low-frequency and high-frequency capacitor currents. These expressions are then used to estimate voltage ripple across the DC capacitor for sinusoidally modulated three-phase NPC inverter. The analytical expressions for the RMS current and voltage ripple are validated experimentally over a wide range of operating points.     

Single-phase induction motor drive system using z-source inverter

Employing conventional three-phase inverter in variable speed single-phase drive suffers from limited maximum output voltage applied to motor or voltage utility factor (VUF). In this study, a z-source inverter (ZSI) has been used to drive a single-phase induction motor (SPIM). By the proposed topology, VUF and consequently torque speed characteristic of the single-phase motor is improved. The equations for employing ZSI in SPIM drive and modulation method are described. Results of two simulations using conventional inverter and ZSI are presented. The results show that using ZSI leads to an increase in motor electromagnetic torque compared to conventional three-phase inverter due to improved VUF. The experimental results confirm the theory and simulation.     

Zero-voltage-switching DC/AC inverter

A novel zero-voltage-switching (ZVS) DC/AC inverter is proposed. The proposed inverter can not only provide output voltage that is higher or lower than DC input voltage but can also use the pulse-width modulation (PWM) control technique. Furthermore, in the proposed inverter, besides operating at constant frequency, all semiconductor devices operate at soft-switching without additional voltage stress and current stress. A design example of 1000 W ZVS-PWM buck-boost inverter is examined to assess the inverter performance     

Three-phase soft-switched pwm inverter for motor drive application

A novel soft-switched inverter topology in which three mutually coupled inductors at a time are involved in the resonance process is proposed. By the introduction of magnetic coupling between three resonant inductors, the zero-voltage instants for the inverter can be generated by one auxiliary switch. Also, the resonant energy can be recycled, and the maximum voltage stress on the auxiliary circuit diode components is confined to the DC-link clamp voltage level. The DC link can be clamped to 1.1-1.3 times the DC-source value. This is unlike the soft-switched inverter in which two mutually coupled inductors are at a time are involved in a resonance process, wherein the clamping diode experiences voltage stress of the order of 11 per unit when clamping the DC-link voltage at 1.1 per unit. The proposed inverter also provides pulse-width modulated operation. An analysis of this novel quasi-resonant DC-link inverter topology is presented to reveal its soft-switching characteristics. Simulation and laboratory experiments are performed to validate the analysis.     

A 1.2-V 0.25-/spl mu/m clock output pixel architecture with wide dynamic range and self-offset cancellation

A 10T/pixel CMOS digital pixel sensor with clock count output, ultra low supply voltage, and wide dynamic range is presented. The pixel fabricated by a standard 0.25-/spl mu/m CMOS logic process comprises a reset transistor, a photo-diode, a comparator, and an inverter with pixel size of 9.4/spl times/9.4 /spl mu/m/sup 2/ and 24% fill factor. The amplified logarithmic output response similar to the light response of human eye is demonstrated in this work. The pixel can operate at a supply voltage as low as 1.2 V without affecting its output characteristics. The dynamic range of this cell limited by either the subsequent analog-to-digital circuit resolution or the rising and falling time of output clock is higher than 90 dB with an 8-bit resolution.     

A single phase photovoltaic inverter control for grid connected system

This paper presents a control scheme for single phase grid connected photovoltaic (PV) system operating under both grid connected and isolated grid mode. The control techniques include voltage and current control of grid-tie PV inverter. During grid connected mode, grid controls the amplitude and frequency of the PV inverter output voltage, and the inverter operates in a current controlled mode. The current controller for grid connected mode fulfills two requirements – namely, (i) during light load condition the excess energy generated from the PV inverter is fed to the grid and (ii) during an overload condition or in case of unfavorable atmospheric conditions the load demand is met by both PV inverter and the grid. In order to synchronize the PV inverter with the grid a dual transport delay based phase locked loop (PLL) is used. On the other hand, during isolated grid operation the PV inverter operates in voltage-controlled mode to maintain a constant amplitude and frequency of the voltage across the load. For the optimum use of the PV module, a modified P&O based maximum power point tracking (MPPT) controller is used which enables the maximum power extraction under varying irradiation and temperature conditions. The validity of the proposed system is verified through simulation as well as hardware implementation.     

The design and development of a small infant ventilator using a systems analysis approach

A mechanical infant ventilator which has been systems engineered is described; it is simple to operate, and yet, at the same time can provide a range of adjustments such that it may be used on newly born infants (including premature births) and on small infants of up to 6 months of age.

The machine is designed specifically for medium batch production, operates on simple mechanical principles and provides four direct reading controls which do not interact. The controls are sequentially arranged in a logical manner so that they can be easily set and adjusted by nursing staff once the initial settings have been determined.

The output has a half sinusoidal wave form and the inspired gases are humidified by means of an ultrasonic nebuliser; expiratory resistance meanwhile is provided by a solenoid operated valve.

Power can be supplied by either mains current or from a low voltage source and the total weight of the equipment is only 10 kg (approx.). Consequently, the ventilator is portable and can be used either in an ambulance or in a hospital ward.

The laboratory performance of the ventilator is described and comparative studies with similar ventilators are shown and discussed. The ventilator fully met its design specification and maintained its sinusoidal output even at low volumes, high respiratory rate and maximum ratios of inspiration of expiration.     

Off-diagonal impedance in amorphous wires and its application to linear magnetic sensors

We investigated the magnetic-field behavior of the off-diagonal impedance in Co-based amorphous wires under sinusoidal (50 MHz) and pulsed (5 ns rise time) current excitations. For comparison, we measured the field characteristics of the diagonal impedance as well. In general, when an alternating current is applied to a magnetic wire, the voltage signal is generated not only across the wire but also in a pickup coil wound on it. These voltages are related to the diagonal and off-diagonal impedances, respectively. We demonstrate that these impedances have a different behavior as functions of axial magnetic field: the diagonal impedance is symmetrical, whereas the off-diagonal one is antisymmetrical with a near-linear portion within a certain field interval. For the off-diagonal response, the dc bias current is necessary to eliminate circular domains. In the case of the sinusoidal excitation without a dc bias current, the off-diagonal response is very small and irregular. In contrast, the pulsed excitation, combining both high- and low-frequency harmonics, produces the off-diagonal voltage response without additional biasing. This behavior is ideal for a practical sensor circuit design. We discuss the principles of operation of a linear magnetic sensor based on a complementary metal-oxide-semiconductor transistor circuit.     

Series inverter without gate control

In commonly used inverters, the ac power is supplied to the load by the switching of gate-driven thyristors. The gating signals are supplied by an external triggering circuit. The inverter presented by the authors does not have a separate triggering circuit. The self-excited sinusoidal oscillations are obtained by using the capacitor voltage of the series ringing circuit as a gating signal. This type of inverter is very simple and useful if the load condition falls within the stable range of operation. The paper describes the circuit and it presents the analytical limits of stable operation. Experimental results are compared with analytical results.