基于CAN总线的并联式多逆变器风电并网控制系统

为了实现多逆变器并联风电系统信息交互和同步控制,提出了基于CAN总线的多逆变器并联风电并网系统控制方法。建立了共直流母线并联型拓扑的等效平均模型,利用CAN总线控制各逆变器正弦参考电压的幅值以均分并网功率。采用TMS320F28335实现全数字化并联风电系统设计,并基于55kW永磁风电样机对所提方法进行性能验证。实验表明,CAN总线同步驱动方法保证了多逆变器并联系统的数据交互性和同步性。     

间歇式能源发电系统无功补偿技术的研究

针对间歇式能源发电系统的特点和无功需求,提出了将无功补偿与风力并网发电相结合的设计方案,通过计算得出了间歇式能源发电系统中电缆和变压器无功损耗.本文利用Mat-lab/Simulink搭建了具有无功补偿功能的并网变流器的仿真模型,并采用有功无功解耦控制和SPWM控制方法,补偿系统所需无功以及有效抑制动态电压波动.最后,仿真结果验证了风力并网变流器在向电网提供有功功率的同时也能够提供一定容量的无功功率,提高系统功率因数,有效抑制电网电压波动.     

A Multilevel Modular Converter for a Large, Light Weight Wind Turbine Generator

In an onshore horizontal axis wind turbine, generator and converter are usually in the nacelle on the top of the tower, while the grid step-up transformer is placed at the bottom. Electric power is transmitted down through flexible cables of high current rating which are expensive and can suffer from large I² R loss. An offshore wind turbine usually has to include the step-up transformer in the nacelle. This adds significantly to the mechanical loading of the tower even new designs aim to reduce the transformer size and weight. In either case, a transformer-less, high voltage, high reliability generating unit for nacelle installation would be an attractive technology for large wind turbines. This study presents a power electronic solution based on a permanent magnet generator design. A multilevel cascaded voltage source converter is developed to synthesize a high sinusoidal output voltage. The dc link voltages of inverter modules are balanced by rectifiers fed from isolated generator coils while the inverter switching strategy equalizes the power sharing between the modules. The switching strategy also reduces the low order harmonics to constrain the sizing of the dc link capacitors. The modulating effect between the ac and dc sides of the inverter is taken into account. This paper describes the generator-converter arrangement, analyzes the inverter switching effects and derives the switching strategy which is verified by simulation and laboratory experiment.     

新型共直流母线高压变频器

针对电机叠频试验容易产生较大的有功功率低频波动,在弱电网条件下对电网造成污染导致电网上其他设备无法正常工作,提出了一种新型共直流母线的高压变频器。其整流侧采用移相变压器加二极管整流方案,通过电容串联建立高压直流母线,直流母线储存能量使其不回馈至电网,特别适用于弱电网下的电机叠频试验;逆变侧采用MMC逆变器(Modular Multilevel Converter),通过平衡控制策略达到模块电压平衡,环流抑制的效果。最后应用PSCAD/EMTDC搭建系统的仿真模型,证实了方案的可行性。     

Current Source Inverter Based Grid Connected Hybrid PV-Wind Power Generation Unit

ABSTRACT

This paper presents a current source inverter (CSI)-based hybrid power generation system, which uses wind turbine and photovoltaic cells (PVs). A permanent magnet synchronous generator (PMSG) is connected to the CSI using a diode rectifier and a buck converter that is used to control the speed of the rotor. Another buck converter is used to control the maximum power point tracking of PVs. The operation of proposed system is studied under normal and grid voltage dip conditions. According to new grid codes, most power generating units are supposed to remain connected to the grid during voltage sag conditions and inject reactive current to grid as defined by grid codes. The CSI has fault current limiting capability that makes it appropriate to use in grid-connected applications and during voltage sag conditions in particular. The proposed system tracks the maximum power point of wind turbine and PVs under normal mode and injects required reactive current to the grid during voltage drop. However, incorporation of CSI with the inherent behaviour of wind turbine and PVs causes fault current to be within the tolerable range for power electronic devices. Simulations are carried out by using PSCAD/EMTDC software to verify the proposed system.     

Multiphase Bidirectional Flyback Converter Topology for Hybrid Electric Vehicles

For hybrid electric vehicles, the batteries and the drive dc link may be at different voltages. The batteries are at low voltage to obtain higher volumetric efficiencies, and the dc link is at higher voltage to have higher efficiency on the motor side. Therefore, a power interface between the batteries and the drive's dc link is essential. This power interface should handle power flow from battery to motor, motor to battery, external genset to battery, and grid to battery. This paper proposes a multi-power-port topology which is capable of handling multiple power sources and still maintains simplicity and features like obtaining high gain, wide load variations, lower output-current ripple, and capability of parallel-battery energy due to the modular structure. The scheme incorporates a transformer winding technique which drastically reduces the leakage inductance of the coupled inductor. The development and testing of a bidirectional flyback dc-dc converter for hybrid electric vehicle is described in this paper. Simple hysteresis voltage control is used for dc-link voltage regulation. The experimental results are presented to show the working of the proposed converter.     

具有提升直流环节稳态电压功能的单相全桥 谐振直流环节逆变器

为改善直流电压利用率,提出了一种具有提升直流环节稳态电压功能的单相全桥谐振直流环节软开关逆变器,利用辅助电路中的变压器可以将电能补充到直流母线上等效为电压源的钳位电容,使直流环节稳态电压高于直流电源电压,提高了逆变器输出线电压的基波幅值和直流电压利用率.文中分析了电路的工作状态.在4kW样机上的实验结果表明逆变器的主开关和辅助开关能完成软切换.因此,该拓扑结构对于研发高性能谐振直流环节逆变器具有一定的借鉴意义.     

Solid-state power electronics in the U.S.A.

This article focuses on the conversion and control of large blocks of electric energy by solid-state power devices such as silicon rectifier diodes and thyristors. Power conversion fulfills the important requirement of delivering a desired type of electric energy when the available form is unsuitable. Examples include the energization of dc machines, dc fields, and batteries when the available source is single-phase or polyphase alternating current. Another example relates to variable-speed drives for Induction and synchronous motors when the power source is either dc or fixed-frequency ac. Power control is concerned with varying the level of power delivered to a load, as in on-off switching, or varying the output voltage of a rectifier.     

Development of a low cost fuel cell inverter system with DSP control

In this paper, the development of a low cost fuel cell inverter system is detailed. The approach consists of a three-terminal push-pull dc-dc converter to boost the fuel cell voltage (48V) to /spl plusmn/200 VDC. A four switch [insulated gate bipolar transistor (IGBT)] inverter is employed to produce 120-V/240-V, 60-Hz ac outputs. High performance, easy manufacturability, lower component count, safety and cost are addressed. Protection and diagnostic features form an important part of the design. Another highlight of the proposed design is the control strategy, which allows the inverter to adapt to the requirements of the load as well as the power source (fuel cell). A unique aspect of the design is the use of the TMS320LF2407 DSP to control the inverter. Two sets of lead-acid batteries are provided on the high voltage dc bus to supply sudden load demands. Efficient and smooth control of the power drawn from the fuel cell and the high voltage battery is achieved by controlling the front end dc-dc converter in current mode. The paper details extensive experimental results of the proposed design on Department of Energy (DoE) National Energy Technology Laboratory (NETL) fuel cell.     

Induction-generator-based system providing regulated voltage withconstant frequency

The electrical characteristics of an isolated induction-generator-based system are improved through the association with a voltage-source pulsewidth modulation (PWM) inverter. The electronic converter allows the achievement of a better system behavior in many aspects: voltage regulation, frequency stabilization, and reactive power compensation. The system operation strategy consists of maintaining constant synchronous frequency at the induction generator via an association with a PWM inverter. The system power balance and the generator voltage regulation may be accomplished by two different means: through the rotor speed regulation, or by sending part of the energy stored in the inverter DC side to the grid through a single-phase line, in case the rotor speed is not regulated and a single-phase grid connection is available. The obtained results demonstrated the system is stable, robust, and an effective source of regulated three-phase voltages     

5kW光伏并网发电系统及其仿真研究

随着新能源发电的迅速发展,越来越多的可再生能源被转化为电能并通过并网逆变器输送到电网。利用MATLAB仿真工具箱建立了由光伏阵列输出、Boost升压电路、逆变器、控制器、电网等组成的5 kW光伏并网发电系统的仿真模型,研究了光伏并网系统的特性。采用变结构模糊PID控制器实现5 kW光伏发电系统的MPPT;采样电网电压作为逆变器电流的参考信号,利用滞环比较法控制逆变器,实现系统输出电流与电网电压同频同相,功率因素近似为1。仿真结果表明,系统较好地实现了光伏发电系统的MPPT及安全并网,对实际光伏并网系统的设计有参考意义。     

A novel single-stage full-bridge buck-boost inverter

A novel single-stage full-bridge series-resonant buck-boost inverter (FB-SRBBI) is proposed in this paper. The proposed inverter only includes a full-bridge topology and a LC resonant tank without auxiliary switches. The output voltage of the proposed inverter can be larger or lower than the dc input voltage, depending on the instantaneous duty-cycle. This property is not found in the classical voltage source inverter, which produces an ac output instantaneous voltage always lower than the dc input voltage. The proposed inverter circuit topology provides the main switch for turn-on at ZCS by a resonant tank. The nonlinear control strategy is designed against the input dc perturbation and achieves well dynamic regulation. An average approach is employed to analyze the system. A design example of 500 W dc/ac inverter is examined to assess the inverter performance and it provides high power efficiency above 90% under the rated power.     

多电平单元串联电压源型变频器高压电源瞬时失电连续运行研究

高压变频调速系统现场应用复杂，工艺多样。在重要的大型工业系统中，高压电源系统有双备用，紧急互投等功能，当变频器对大功率的电机供电时，如果高压电源进行切换，将出现0．1S～1．5s左右的失电间隔，要求变频器在失电间隔中能正常工作，且转速波动较小，达到系统在失电期间不出现剧烈振荡。对于多电平单元串联电压源型变频器，当通过对功率单元电容值的加大，PWM输出占空比减小的方法提高失电连续运行性能，其效果均不理想。在经过大量论证后，采用特殊的DSP控制逻辑，并利用旋转系统中的飞轮动能转换，取得实现变频器在高压瞬时失电时保持稳定运行。     

Energy Management Fuzzy Logic Supervisory for Electric Vehicle Power Supplies System

This paper introduces an energy management strategy based on fuzzy logic supervisory for road electric vehicle, combining a fuel cell power source and two energy storage devices, i.e., batteries and ultracapacitors. The control strategy is designed to achieve the high-efficiency operation region of the individual power source and to regulate current and voltage at peak and average power demand, without compromising the performance and efficiency of the overall system. A multiple-input power electronic converter makes the interface among generator, energy storage devices, and the voltage dc-link bus. Classical regulators implement the control loops of each input of the converter. The supervisory system coordinates the power flows among the power sources and the load. The paper is mainly focused on the fuzzy logic supervisory for energy management of a specific power electronic converter control algorithm. Nevertheless, the proposed system can be easily adapted to other converters arrangements or to distributed generation applications. Simulation and experimental results on a 3-kW prototype prove that the fuzzy logic is a suitable energy management control strategy.     

A New Multilevel Conversion Structure for Grid-Connected PV Applications

A novel scheme for three-phase grid-connected photovoltaic (PV) generation systems is presented in this paper. The scheme is based on two insulated strings of PV panels, each one feeding the dc bus of a standard two-level three-phase voltage-source inverter (VSI). The inverters are connected to the grid by a three-phase transformer having open-end windings on the inverter side. The resulting conversion structure performs as a multilevel power active filter (equivalent to a three-level inverter), doubling the power capability of a single VSI with given voltage and current ratings. The multilevel voltage waveforms are generated by an improved space-vector-modulation algorithm, suitable for the implementation in industrial digital signal processors. An original control method has been introduced to regulate the dc-link voltages of each VSI, according to the voltage reference given by a single maximum power point tracking controller. The proposed regulation system has been verified by numerical simulations and experimental tests with reference to different operating conditions.     

Novel resonant pole inverter for brushless DC motor drive system

The brushless dc motor (BDCM) has been widely used in industrial applications because of its low inertia, fast response, high power density, high reliability, and maintenance-free reputation. It is usually supplied by a hard-switching pulse width modulation inverter, which normally displays relative low efficiency since the power losses across the switching devices are high. In order to reduce the losses, many soft switching inverters have been designed. However, these inverters have such disadvantages as high device voltage stress, large dc link voltage ripple, discrete pulse modulation, and complex control scheme. This paper introduces a novel resonant pole inverter, which is unique to a BDCM drive system, and is easy to implement. The inverter possesses the advantages of low switching power loss, low inductor power loss, low device voltage stress, and simple control scheme. The operation principle of the inverter is analyzed. Simulation and experimental results are proposed to verify the theoretical analysis.     

High power thyristor-battery drive for high peak, low average power pulser

High power thyristors are employed with a battery to provide constant voltage to a quarter-megawatt dc load for 1/2 second, in order to operate a sonar transducer at a pulse repetition period of 10 seconds. Despite the heavy pulse power and the low duty cycle, the power drawn from the mains is maintained almost constant at approximately 12.5 kilowatts, with less than 5 percent variation over a power pulse cycle. The system utilizes a battery for energy storage, in conjunction with a phase-controled ac line to charge the battery at essentially constant current. The availability of high power thyristors for a high frequency inverter-type dc to dc converter makes the entire concept feasible, as the battery voltage drops substantially during the pulse. The inverter is pulse-width-controlled during the output power pulse, to maintain the dc output voltage constant within 3 percent during the power pulse. Basic circuits are described for providing the high peak power to the load, and maintaining virtually constant average power drain from the source over the entire cycle.     

Permanent Magnet Synchronous Generator Cascade for Wind Turbine Application

This paper proposes an energy conversion system for a wind turbine comprising a grid connected permanent magnet synchronous generator and a 20% rated series converter located in its star point. It models the complete system and focuses on the series converter control whose primary function is the active damping of the generator. In addition, this paper addresses the topic of the dc bus voltage control and the dc capacitance sizing of the series converter. Finally, it validates the performance of the proposed system by means of system simulation.     

Solid State Voltage and Frequency Controller for a Stand Alone Wind Power Generating System

This paper deals with the voltage and frequency controller of a wind turbine driven isolated asynchronous generator. The proposed voltage and frequency controller consists of an insulated gate bipolar junction transistor based voltage source converter along-with battery energy storage system at its dc link. The proposed controller is having bidirectional active and reactive powers flow capability by which it controls the system voltage and frequency with variation of consumer loads and the speed of the wind turbine. It is also having capability of harmonic elimination and load balancing. The proposed electro-mechanical system along with its controller is modeled and simulated in MATLAB using Simulink and power system block-set toolboxes. Performance of the proposed controller is presented to demonstrate voltage and frequency control of a wind turbine driven isolated asynchronous generator along with harmonic elimination and load balancing.     

A new power converter for fuel cells with high system efficiency

This paper presents a new high-efficiency grid-connected single-phase converter for fuel cells. It consists of a two-stage power conversion topology. Since the fuel cell operates with a low voltage in a wide voltage range (25?V–45?V) this voltage must be transformed to around 350–400?V in order to be able to invert this dc power into ac power to the grid. The proposed converter consists of an isolated dc–dc converter cascaded with a single-phase H-bridge inverter. The dc–dc converter is a current-fed push-pull converter. The inverter is controlled as a standard single-phase power factor controller with resistor emulation at the output. Experimental results of converter efficiency, grid performance and fuel cell dynamic response are shown for a 1?kW prototype. The proposed converter exhibits a high efficiency in a wide power range (higher than 92%) and the inverter operates with a near-unity power factor and a low current THD.