Improved Control of DFIG Systems During Network Unbalance Using PI–R Current Regulators

This paper presents a new control strategy for a doubly fed induction generator (DFIG) under unbalanced network voltage conditions. Coordinated control of the grid- and rotor-side converters (GSC and RSC, respectively) during voltage unbalance is proposed. Under an unbalanced supply voltage, the RSC is controlled to eliminate the torque pulsation at double supply frequency. The oscillation of the stator output active power is then compensated by the active power output from the GSC, to ensure constant active power output from the overall DFIG generation system. In order to provide precise control of the positive- and negative-sequence currents of the GSC and RSC, a current control scheme consisting of a proportional integral (PI) controller and a resonant (R) compensator is presented. The PI plus R current regulator is implemented in the positive synchronous reference frame without the need to decompose the positive- and negative-sequence components. Simulations on a 1.5-MW DFIG system and experimental tests on a 1.5-kW prototype validate the proposed strategy. Precise control of both positive- and negative-sequence currents and simultaneous elimination of torque and total active power oscillations have been achieved.      

Single-stage three-phase buck-boost type AC-DC converter with highpower factor

A new control process for single-stage three-phase buck-boost type AC-DC power converters with high power factor, sinusoidal input currents and adjustable output voltage is proposed. This converter allows variable power factor operation, but this work focus on achieving unity power factor. The proposed control method includes a fast and robust input current controller based on a vectorial sliding mode approach. The active nonlinear control strategy applied to this power converter, allows high quality input currents. Given the comparatively slow dynamics of the DC output voltage, a proportional integral (PI) controller is adopted to regulate the converter output voltage. The voltage controller modulates the amplitudes of the current references, which are sinusoidal and synchronous with the input source voltages. Experimental results from a laboratory prototype show the high power factor and the low harmonic distortion characteristics of the circuit     

电网不平衡时的三相PWM整流器控制策略

三相电网不平衡时,电压会存在负序分量。此时,如果对三相电压型PWM整流器采用普通的控制策略进行控制,会使其网侧电流含有大量的谐波,从而无法得到正弦输入电流。文章通过对三相电压型PWM整流器在电网不平衡情况下的建模,分析了网侧电流谐波产生的原因。在此基础上,采用了一种能使其网侧电流正弦化的控制策略,并进行了仿真验证。研究表明,该控制策略有良好的控制能力,可以使得交流侧电流达到正弦。     

New current control concept-minimum time current control in thethree-phase PWM converter

In this paper, a new current controller that guarantees the fastest transient response is proposed. The basic concept is to find the optimal control voltage for tracking the reference current with minimum time under the voltage limit constraint. Though this minimum time control concept is also applicable to all the machine drive systems, this paper focuses on the current regulation in the three-phase pulse width modulation (PWM) converter. In the simulation and experimental results, it is observed that the proposed controller has much less transient time than the conventional synchronous PI regulator and the performance of the DC link voltage control is also greatly improved with the proposed current controller     

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.     

新型三相三线制并联有源滤波器的滑模控制方法

为了提高有源滤波器的谐波补偿效果,设计了一种新型滑模控制器,用于三相三线制并联有源滤波器的参考电流跟踪控制.谐波电流检测方法采用基于瞬时无功功率理论的谐波电流检测方法,能快速、准确的检测出负载电流中的谐波分量.直流侧电压控制方法采用PI控制方法实现.Simulink仿真结果显示,与传统的滞环比较控制方法相比,所设计的新型滑模控制方法能够有效的降低跟踪误差,提高有源滤波器的谐波补偿效果.     

Current control strategy for brushless DC motors based on a commonDC signal

A simplified current controlled modulation technique for brushless DC motors is presented. It is based on the generation of quasi square-wave currents, using only one current controller for the three phases. The advantages of this strategy are: (a) very simple control scheme; (b) the phase currents are kept balanced; (c) the difficult sensing of DC link current in flat plates is avoided; and (d) the current is controlled through only one DC component. These characteristics allow to use the triangular carrier as a current control strategy for the power transistors, which is simpler and better than other options. Computer simulations using power electronic simulator (PSIM), have been developed to show the good characteristics of this solution, and its simplicity. Some experiments with a 15 kW motor-inverter system, show the excellent behavior under steady-state, and transient situations, such as step response and reversal of power     

A grid-interfacing power quality compensator for three-phase three-wire microgrid applications

This paper proposes a grid-interfacing power quality compensator for three-phase three-wire microgrid applications with consideration of both the power quality of the microgrid and the quality of currents flowing between the microgrid and utility system. It is proposed that two inverters connected in shunt and series are used for each distributed generation (DG) system in the microgrid. In each inverter, both positive- and negative-sequence components are controlled to compensate for the effects caused by the unbalanced utility grid voltages. Specifically, the shunt inverter is controlled to ensure balanced voltages within the microgrid and to regulate power dispatches among parallel-connected DG systems, while the series inverter balances the line currents by injecting appropriate voltage components. A current-limiting algorithm is also proposed and integrated within the inverter control schemes to protect the microgrid from large fault currents during utility voltage sags. The proposed compensator has been tested in simulations and experimentally using a laboratory hardware prototype.     

多单片机直流电源控制板设计

介绍了一种以单片机控制晶闸管触发脉冲为核心的直流电源控制板系统,该系统实现了晶闸管触发脉冲信号的同步产生、移相、驱动以及系统过压／过流保护等功能。用户可通过键盘来设置直流电源的输出,八段数码管显示实际输出电压／电流值;在硬件与软件的配合设计下,该系统实现了智能化三相交流电的相序判断、同步脉冲形成、断线检测、脉冲编码计算、输出数据采样、软启动控制及比例控制等功能。     

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     

电容中点式有源电力滤波器数学模型及电流复合控制策略

三相四线并联型有源电力滤波器通常可用来补偿非线性负载所引起的谐波和无功电流,以及负载不平衡引起的负序或零序电流。本文描述了电容中点型三相四线有源电力滤波器在abc及dq0坐标系下的数学摸型,并由此给出了dq0同步旋转坐标系下的一种系统控制策略。由于有源电力滤波器指令为快速变化的交流谐波信号,传统的PI控制由于带宽有限,稳态精度较差。因此,提出了基于PI控制和重复控制并联的电流复合控制策略,利用重复控制对于周期扰动信号无差跟踪的特点来提高稳态精度,同时,PI控制又能保证良好的动态性能。仿真和实验结果验证该控制策略的可行性和有效性。     

FPGA电流型PMSM变频驱动器及开路故障保护

电流源逆变器(CSI)随着反阻断IGBT器件的成功开发,在电动汽车等大功率变频调速领域前景广大。FPGA作为控制器,其时序控制能力强大,适合用来实现基于电流型空间矢量脉宽调制(SVPWM)技术的永磁同步电机(PMSM)变频驱动器。该系统通过采用最小直流链电流命令产生法和合理的死区开关状态设置,有效减小直流和开关损耗。系统为应对开路故障引起直流链电感产生瞬间高压打坏开关器件的现象,设置由双向TVS管和功率电阻构成的电感电压箝位环节,并监测直流链电流值,一旦低于限值则实现保护性停机。实际系统使用Xilinx公司FPGA开发板,基于电流源逆变器转子参考框下交流侧的理论模型,建立了一套数字化闭环调速策略,实测定子电流THD值及功率因数均达到良好效果。     

A Novel Control Scheme for Current-Source-Converter-Based PMSG Wind Energy Conversion Systems

A novel control scheme for permanent-magnet synchronous generator is proposed in this paper, where a current-source converter is employed as the bridge between the generator and the grid for high-power wind energy conversion systems. In these medium voltage (2.3-13.8 kV) level applications, current-source converters not only have inherent advantages, but also present some challenges for controller design due to the DC link choke and filter capacitors. The control strategy is developed to achieve better performances with improved dynamic response. By maintaining the grid-side converter modulation index at the highest possible level, the proposed control scheme reduces the DC link current to a minimum value to reduce converter conduction loss. The systempsilas dynamic performance is further improved by adopting generator-side power feedforward. Simulation and experimental results are provided to verify the proposed control scheme.     

Three phase bridge current controller with single sensor

Control of phase currents in a three-phase voltage source inverter bridge is important for electric drives and unity power factor converters. To reduce equipment costs and overcome unequal sensor errors, the use of a single DC link current sensor is important. A new technique is described which uses redundant bridge switching states to allow current control with a DC link current sensor     

基于DSP的三相光伏并网逆变器控制系统设计与实现

三相电压型光伏并网逆变器,直接控制其三相电流较困难.同步旋转坐标下基于PWM技术的PI控制方法动态响应快,且可实现对指令的无静差跟踪,但是d、q两相直流电流之间还存在耦合关系,不利于控制设计,同时还存在电网电压的影响,为了消除这些影响,运用了前馈解耦控制算法,结合空间矢量SVPWM给出了逆变器的电流控制策略.浮点数字信...     

Discrete pulse modulation strategies for high-frequency invertersystems

High-performance, high-frequency inverter systems for UPS (uninterruptible power system) applications cannot be easily realized using conventional hard-switched PWM inverter topologies. Adoption of typical soft-switched inverters such as the resonant DC link inverter, require the use of discrete pulse modulation strategies. New controller structures are necessary to cope with stringent voltage regulation and distortion constraints in the presence of unbalanced and nonlinear loads. A controller that utilizes a load current feedforward strategy with a cost function current regulator to achieve excellent transient performance characteristics is presented. Voltage regulation is ensured using a synchronous frame regulator. Detailed simulation and experimental results verifying the concepts are presented. Although this work focuses on soft-switching inverters, the control concepts can be applied to conventional hard-switching inverters as well     

A soft-switched, high-frequency resonant rectifier andcharacteristics of the controlled system

In this paper, a high frequency and soft-switched AC/DC rectifier employing a series-type resonant circuit is proposed to obtain the sinusoidal AC line current. Using the proposed rectifier, the high power factor and low harmonic currents are obtained in the AC line. Furthermore, several advantages such as the high power density and wide output voltage range can also be available. To regulate the output voltage of the proposed circuit, the digital proportional-integral (PI) controller is used whose sampling time corresponds to the zero-crossing point of the AC line voltage. Including this controller, the model for the closed-loop system is developed in order to examine the stability and dynamic characteristics. With this model, the gain of the PI-controller is determined by the pole assignment technique and the closed-loop dynamics is investigated by the root locus plots. A good agreement is made between the simulated and experimental results     

A high-performance sensorless indirect stator flux orientation control of induction motor drive

A new method for the implementation of a sensorless indirect stator-flux-oriented control (ISFOC) of induction motor drives with stator resistance tuning is proposed in this paper. The proposed method for the estimation of speed and stator resistance is based only on measurement of stator currents. The error of the measured q-axis current from its reference value feeds the proportional plus integral (PI) controller, the output of which is the estimated slip frequency. It is subtracted from the synchronous angular frequency, which is obtained from the output integral plus proportional (IP) rotor speed controller, to have the estimated rotor speed. For current regulation, this paper proposes a conventional PI controller with feedforward compensation terms in the synchronous frame. Owing to its advantages, an IP controller is used for rotor speed regulation. Stator resistance updating is based on the measured and reference d-axis stator current of an induction motor on d-q frame synchronously rotating with the stator flux vector. Experimental results for a 3-kW induction motor are presented and analyzed by using a dSpace system with DS1102 controller board based on the digital signal processor (DSP) TMS320C31. Digital simulation and experimental results are presented to show the improvement in performance of the proposed method.     

A comparison of high-power converter topologies for the implementation of FACTS controllers

This paper compares four power converter topologies for the implementation of flexible AC transmission system (FACTS) controllers: three multilevel topologies (multipoint clamped (MPC), chain, and nested cell) and the well-established multipulse topology. In keeping with the need to implement very-high-power inverters, switching frequency is restricted to line frequency. The study addresses device count, DC filter ratings, restrictions on voltage control, active power transfer through the DC link, and balancing of DC-link voltages. Emphasis is placed on capacitor sizing because of its impact on the cost and size of the FACTS controller. A method for the dimensioning the DC capacitor filter is presented. It is found that the chain converter is attractive for the implementation of a static compensator or a static synchronous series compensator. The MPC converter is attractive for the implementation of a unified power flow controller or an interline power flow controller, but a special arrangement is required to overcome the limitations on voltage control.     

不平衡电网电压下三相PWM整流器控制策略的研究

在不平衡电网电压下三相电压型PWM整流器的优越性能受到了很大的影响,其原因是由于直流电压产生了奇次谐波以及交流的电流产生了偶次谐波。三相PWM整流器直流侧电压的二次谐波以及在交流侧电流所产生的负序分量都将对整流器负载性能产生影响,同时还将影响直流侧电容寿命。文章提出一种新型不平衡观测器及其控制策略可有效地对不平衡电压进行补偿。通过此控制策略可同时抑制直流侧电压的2次谐波以及减小网侧电流的不平衡度。分析及仿真结果证明了此控制策略的有效性。