Control of a Cascade STATCOM With Star Configuration Under Unbalanced Conditions

A control scheme for star-connected cascade static synchronous compensators (STATCOMs) operating under unbalanced conditions is proposed. The STATCOM is assumed to be connected to an equivalent three-phase star-connected power supply. By selecting the line-to-neutral voltages of the equivalent power supply, zero average active power in each phase can be obtained under unbalanced compensation currents or unbalanced supply voltages. Furthermore, to implement a separate control for the three-phase dc-link voltages, the average active power in each phase can also be adjusted to a target value determined by the dc-link voltage control loop. Then, by forcing the converter neutral voltage to be equal to the counterpart of the equivalent power supply, the STATCOM can be decoupled into three single-phase systems and the line-to-neutral voltage of the equivalent power supply can be used as the input voltage to the corresponding phase leg. Accordingly, reference current tracking and dc-link voltage maintaining can be simultaneously achieved under unbalanced conditions. The valid operating range of the star-connected cascade STATCOM under unbalanced conditions is also analyzed. The proposed control scheme has been tested using the power systems computer-aided design/electromagnetic transient in dc system (EMTDC) simulation results and the experimental results based on a 30-kVAr cascade STATCOM laboratory prototype are proposed.      

Four-wire current-regulated PWM voltage converter

Shunt active power filters are connected in parallel with the electricity supply network. If the AC mains has a neutral conductor, it is desirable to compensate the mains harmonic currents zero-sequence components. This can be achieved with a four-wire pulsewidth modulation voltage converter connected to the AC mains. In this case, the three-phase and the neutral AC currents must be controlled. A generalization of the space-vector-based current controller in the αβo coordinate system is presented in this paper. With this current controller, all the current harmonic systems of positive, negative, and zero sequence can be injected by the converter and, thus, compensated on the AC mains. The system is also useful to compensate unbalanced currents of fundamental frequency. A useful benefit of this system is that it is possible to control the converter four-wire currents with equal hysteresis errors. Simulation and experimental results are presented     

基于PMBus和VID技术的电源电路设计

针对高速嵌入式系统对自动调节输出电压的电源系统的需求,本文采用PMBus总线为电源芯片之间,电源芯片和控制器之间的通信提供标准,通过重点分析基于PMBus总线的数字可编程电源的内部结构和电压识别的技术实现方法,设计了一支持电压识别(VID)技术的带两路独立电压输出的数字可编程电源系统。经PMBus总线进行配置后,该电源系统可以满足高速嵌入式系统的多种电压需求,取得了良好的效果。     

FPGA最小系统的数字电源设计

文章介绍了一种FPGA最小系统的数字电源设计方法。FPGA最小系统的数字电源包括FPGA端口电压、内核电压、EEPROM配置芯片内核电压等部分。对数字电源产生、软启动、上电时序控制进行了设计改进,可以有效避免数字电源设计不合理造成的FPGA最小系统工作不稳定的设计隐患,对于稳定可靠的FPGA最小系统设计具有重要意义。     

Grid current regulation of a three-phase voltage source inverter with an LCL input filter

Many grid connected power electronic systems, such as STATCOMs, UPFCs, and distributed generation system interfaces, use a voltage source inverter (VSI) connected to the supply network through a filter. This filter, typically a series inductance, acts to reduce the switching harmonics entering the distribution network. An alternative filter is a LCL network, which can achieve reduced levels of harmonic distortion at lower switching frequencies and with less inductance, and therefore has potential benefits for higher power applications. However, systems incorporating LCL filters require more complex control strategies and are not commonly presented in literature. This paper proposes a robust strategy for regulating the grid current entering a distribution network from a three-phase VSI system connected via a LCL filter. The strategy integrates an outer loop grid current regulator with inner capacitor current regulation to stabilize the system. A synchronous frame PI current regulation strategy is used for the outer grid current control loop. Linear analysis, simulation, and experimental results are used to verify the stability of the control algorithm across a range of operating conditions. Finally, expressions for ""harmonic impedance" of the system are derived to study the effects of supply voltage distortion on the harmonic performance of the system.     

Voltage Unbalance Mitigation in Low Voltage Distribution Networks with Photovoltaic Systems

This paper proposes a technique to mitigate the voltage unbalance issue caused by the high penetration of photovoltaic(PV) systems into the low voltage distribution networks(LVDN) using a single phase energy storage system(ESS).The ESS comprises a bi-directional power flow inverter and a battery bank.The system is capable of absorbing the excess power and delivering power to the network in order to keep the voltage unbalance factor(VUF) below the statutory limit of 1%.Investigations are carried out in the experimental small-scale energy zone(SSEZ).The experimental results demonstrate that the ESS is capable of mitigating the VUF of the network.     

A novel converter topology for multiple individually regulated outputs

Power supply voltages in digital systems have reduced considerably in recent years, and often digital components requiring different voltages are present on the same board. This has increased the demand for multiple output power distribution systems with tight individual load voltage regulation. This paper presents a power distribution system having a central power supply that acts as a controlled current source whose output is connected to individual loads on a time shared basis. All the magnetics are concentrated in the converter acting as the current source. The current source can be realized by a current controlled buck, buck-boost, or single-ended primary inductance converter (SEPIC). First, a comparative analysis of buck, buck-boost, and SEPIC based implementation of the current source is carried out. Next, a buck-based current source implementation with constant frequency pulse-width modulation control for the output voltages is described. Detailed component and control design, simulations, and experimental results for a 100-W prototype are presented.     

A quick response peak detector for variable frequency three-phasesinusoidal signals

An instantaneous peak detector for three-phase variable frequency sinusoidal signals is proposed. The three-phase characteristic is fully used in the proposed detector to achieve instantaneous response and frequency independence characteristics. A very simple hardware implementation circuit is also presented for minimizing the number of analog computational components. Moreover, the proposed detector possesses excellent linearity and low sensitivity to small voltage unbalance and harmonic distortion. Because of its promising accuracy and transient response, it can be used in many systems such as the voltage regulator of an uninterruptible power supply (UPS), an automatic line voltage regulator, or electric generators, etc., to improve the system transient performance. Theoretical analysis, hardware implementation, and some experimental results are also detailed in this paper     

MC34063A在嵌入式宽电压输入中的应用

电源是电子系统中重要的组成部分,电源的稳定性直接影响到整个系统的性能和使用寿命。嵌入式系统中的核心电压多为+5 V,而使用环境往往不能随时提供+5 V电压。为了使嵌入式系统具有更广泛的适应性,在此根据MC34063A芯片的原理,介绍了一种依据此芯片进行的降压型宽电压输入电源电路的设计。通过计算电路外围器件的参数,完成具体电路的设计;最后对系统的几个重要性能指标进行了测试,测试结果验证了该宽电源输入电路具有良好的稳定性和实用性。相对于其他方式的宽电压,该设计具有更广范的适应性以及精确性。     

Coordinated Control of DFIG's Rotor and Grid Side Converters During Network Unbalance

This paper proposes a coordinated control of the rotor side converters (RSCs) and grid side converters (GSCs) of doubly-fed induction generator (DFIG) based wind generation systems under unbalanced voltage conditions. System behaviors and operations of the RSC and GSC under unbalanced voltage are illustrated. To provide enhanced operation, the RSC is controlled to eliminate the torque oscillations at double supply frequency under unbalanced stator supply. The oscillation of the stator output active power is then cancelled by the active power output from the GSC, to ensure constant active power output from the overall DFIG generation system. To provide the required positive and negative sequence currents control for the RSC and GSC, a current control strategy containing a main controller and an auxiliary controller is analyzed. The main controller is implemented in the positive (dq)⁺ frame without involving positive/negative sequence decomposition whereas the auxiliary controller is implemented in the negative sequence (dq)^- frame with negative sequence current extracted. Simulation results using EMTDC/PSCAD are presented for a 2 MW DFIG wind generation system to validate the proposed control scheme and to show the enhanced system operation during unbalanced voltage supply.     

风光互补并网发电系统的PSCAD仿真设计

针对目前单一式离网型新能源发电系统的发电不稳定性及能源溢出浪费等问题,提出了一种风电与光电相结合的互补式并网发电系统的设计理念。利用风能与太阳能二者较强的互补性,解决传统单一式发电系统昼夜间歇性供电问题。同时,该发电系统采用并网式结构,可以将溢出的多余能源回馈给电网系统,实现系统发电量的有效利用,保证供电系统的长期稳定...     

Reverse-voltage protection methods for CMOS circuits

A number of circuit configurations for protection of CMOS circuits against erroneous connections to the surrounding world (e.g. reversal of the supply voltage) are suggested and analyzed. It is found that protection against any permutation of input connections, output connections, and supply voltage connections can be obtained. The design objective is to prevent permanent damage to the chip regardless of how it is connected. It has been found both analytically and experimentally that this design goal can be achieved     

一种简单优质的双端可调功率直流稳压电源的设计与分析

根据优质直流稳压电源应具有的特点,介绍了采用ＰＩ调节器和共射极连接方式下的晶体管来构成一款简单优质的双端可调功率直流稳压电源的方法,分析了电源的特性,给出了设计实例：其最大输出电流为５Ａ,最大输出电压为５０Ｖ,电压调整率为０．０１２％,负载调整率为０．０４％,纹波抑制比为８４ｄＢ。     

液晶电视3D显示技术的探讨与设计

随着3D显示技术的飞快发展和产品线的逐渐成熟,家用3D电视已经逐步取代普通的2D电视成为广大消费者的首要选择,在种类繁多的显示系统中,快门式3D液晶显示系统以其立体效果突出、画面分辨率高、液晶模组成本低等优势得到了市场的广泛认可。本文主要研究快门3D液晶电视背光源设计和驱动,包括电源设计、软件控制和LED光源的控制三大部分,其中硬件设计包括升压模块的设计和恒流源的设计,软件控制包含背光灯条电流、占空比以及时序的控制。3D LED串并联通过调节各个灯条的亮度、延时以及电压大小实现对LED背光扫描时序的控制。     

Performance of a single-stage UPS system for single-phasetrapezoidal-shaped AC-voltage supplies

A high-performance single-stage UPS system for single-phase AC power supply systems is presented. The topology generates a trapezoidal-shaped load voltage that is synchronized with the AC supply; therefore, a small DC-link capacitor is required. This feature leads to a high-input power factor (0.94 at nominal voltage), and due to the single-stage structure, high efficiency (93% at nominal voltage) is also achieved. Moreover, in both cases the supply current spectrum presents low-order harmonics, all of which satisfy IEC 555. The high performance is validated using both resistive (linear) and diode RC (nonlinear) loads. The dynamic performance of the UPS system is also analyzed under different transient conditions. Specifically, the supply to battery, battery to supply transition, load transient, and supply/battery-voltage transients are performed. They show a transfer time of 500 μs (from AC supply to battery) and overvoltages of at most 15%. The dynamic and static evaluations are performed on a 1 kVA UPS system. The design guidelines for the key components and control parameters are also included     

Discrete time modeling and control of the voltage source converterfor improved disturbance rejection

A new voltage source converter control approach is presented, based on multivariable z-domain control techniques. Using time-averaging theory in the synchronous reference frame, a linear time-varying model of the converter is developed. The new model may be directly employed as an efficient simulation tool and used as a basis for developing discrete time inverter controls. Application of digital control techniques results in current step tracking in one switching period, with zero overshoot. While DC load fluctuations are rapidly compensated through nonlinear feedforward, AC system voltage disturbances are rejected through a positive and negative sequence bias estimation scheme. As a result, the converter may operate at its current limit under even severe AC voltage unbalance and only a balanced AC current will flow, thus ensuring full protection of the semiconductor devices in all three converter legs. Experimental results validate both the time-varying simulation model as well as the proposed control design     

一种用于微波系统的输入电压控制电路

随着射频技术的不断发展,微波系统对功率密度、可靠性的重视程度不断提高。以氮化镓为基础的微波功率器件的应用取得了很大的进步,对微波系统的供电时序也提出了更高要求。根据微波系统对脉冲电压及电源时序控制的要求,设计了一种电压控制电路,实现直流输入电压的脉冲输出和上电、掉电时序的控制,并通过实验电路对设计原理进行了验证。     

便携式可充电多路输出电源设计

针对锂电池输出电压以及使用周期的局限性问题,设计了基于升压稳压芯片MC33063、降压稳压芯片TPS62046和锂电池充电管理芯片CN3065的便携式可充电多路输出电源。给出了整个设计系统框图及硬件电路,在多种不同电源供电系统、能源转换效率、便携以及清洁能源利用等方面做了探索。试验证明该多路输出电源运转正常、转换效率较高、充电性能优越,能用于多种常用设备的供电,能快速地与多种便携设备进行对接供电,是未来便携式电源发展的主要方向。     

Control of series active power filters compensating for source voltage unbalance and current harmonics

In this paper, a novel control scheme compensating for source voltage unbalance and current harmonics in series-type active power filter systems combined with shunt passive filters is proposed, which focuses on reducing the delay time effect required to generate the reference voltage. Using digital all-pass filters, the positive voltage sequence component out of the unbalanced source voltage is derived. The all-pass filter can give a desired phase shift and no magnitude reduction, unlike conventional low-or high-pass filters. Based on this positive-sequence component, the source phase angle and the reference voltage for compensation are derived. This method is easier to implement and to tune controller gains. In order to reduce the delay time effect in the voltage control loop, the reference voltage is predicted a sampling period ahead. The validity of the proposed control scheme has been verified by experimental results.