Unsteady aerodynamic forces and power requirements of a bumblebee in forward flight

Aerodynamic forces and power requirements in forward flight in a bumblebee （Bombus terrestris） were studied using the method of computational fluid dynamics. Actual wing kinematic data of free flight were used in the study （the speed ranges from 0 m/s to 4.5 m/s; advance ratio ranges from 0-0.66）. The bumblebee employs the delayed stall mechanism and the fast pitching-up rotation mechanism to produce vertical force and thrust. The leading-edge vortex does not shed in the translatory phase of the half-strokes and is much more concentrated than that of the fruit fly in a previous study. At hovering and low-speed flight, the vertical force is produced by both the half-strokes and is contributed by wing lift; at medium and high speeds, the vertical force is mainly produced during the downstroke and is contributed by both wing lift and wing drag. At all speeds the thrust is mainly produced in the upstroke and is contributed by wing drag. The power requirement at low to medium speeds is not very different from that of hovering and is relatively large at the highest speed （advance ratio 0.66）, i.e. the power curve is Jshaped. Except at the highest flight speed, storing energy elastically can save power up to 20%-30%. At the highest speed, because of the large increase of aerodynamic torque and the slight decrease of inertial torque （due to the smaller stroke amplitude and stroke frequency used）, the power requirement is dominated by aerodynamic power and the effect of elastic storage of energy on power requirement is limited.

FORWARD LINK PARTIAL-BALANCE POWER CONTROL ALGORITHM FOR W-CDMA COMMUNICATION

Balance power control is based on the idea of balancing Carrier to Interference Ratio (CIR) of all wireless links. Unbalance power control means that different traffics can achieve different CIR at receivers. This paper proposes a forward link partial-balance power control algorithm, which can provide necessary Quality of Service (QoS) for multimedia traffics in Wideband CDMA(W-CDMA) systems. The proposed algorithm is the integration of grading traffics priority and allocating and adjusting forward link power levels. For higher priority traffics, the unbalance power control is used. Whereas for lower priority traffics, balance power control is adopted. Computer simulation results show that the proposed algorithm can guarantee the special QoS requirements of the traffics with higher priority orders and maximize the CIR of the traffics with lower priority orders.

Bargaining Game Theoretic Power Control in Selfish Cooperative Relay Networks

Wireless cooperative communications require appropriate power allocation （PA） between the source and relay nodes. In selfish cooperative communication networks, two partner user nodes could help relaying information for each other, but each user node has the incentive to consume his power solely to decrease its own symbol error rate （SER） at the receiver. In this paper, we propose a fair and efficient PA scheme for the decode-and-forward cooperation protocol in selfish cooperative relay networks. We formulate this PA problem as a two-user cooperative bargaining game, and use Nash bargaining solution （NBS） to achieve a win-win strategy for both partner users. Simulation results indicate that the NBS is fair in that the degree of cooperation of a user only depends on how much contribution its partner can make to decrease its SER at the receiver, and efficient in the sense that the SER performance of both users could be improved through the game.

A Near Optimal Power Allocation Scheme for Cooperative Relay Networking with NOMA

In this paper, we propose cooperative relay networks with non-orthogonal multiple access in order to design a near-optimal power allocation strategy. Like other next generation wireless technologies, spatially multiplexed transmissions are achieved by relay nodes which enables decode-and-forward relaying of a new superposition code after reception from the source. It is worth noting that, since it is hard to exactly prove the proposed PA scheme, due the fact that it is one kind of the approximate conjectures. Therefore, mathematical and numerical methods have been used to clarify the feasibility of the proposal. Numerical results indicate that it is able to asymptotically achieve the optimal sum rate at the higher signal-to-noise ratio region with the proposed strategy applied instead of negligible performance loss.

Performance for Device-to-Device Communication with Three-Time-Slot Two-Way Amplify-and-Forward Relay Protocol

Multi-hop device-to-device(D2D) communication can significantly improve the system performance. This paper studied the outage performance of D2 D communication assisted by another D2 D user using three-timeslot two-way amplify-and-forward relaying protocol over Rayleigh fading channels. Considering the co-channel interference from cellular user at the D2 D node,the approximate expression for the overall outage probability was derived. Furthermore,a power allocation optimum method to minimize the outage probability was developed,and the closed form expression for the optimal power allocation coefficient at the relay was derived. Simulation results demonstrate accuracy of the derived outage probability expressions. Simulation results also demonstrate that the outage performance can be improved using the proposed optimal power allocation method.

Joint Power Allocation and Beamforming for Cooperative Networks

In this paper, we investigate power allocation problem with the use of transmit beamforming in a dual hop MISO (multiple input single output) relay channel. We consider either amplify and forward (AF) or decode and forward (DF) cooperative protocols at the relay and optimize the power allocated to the relay and the source, under total transmit power constraint, to minimize the bit error rate (BER) of relaying system. Cooperative communication is viewed as a method for increasing diversity gain and reducing end to end path loss. The use of relay can create a virtual antenna array so that it allows users to exploit the advantages of multiple input multiple output (MIMO) techniques. In this work, we solve cooperative ratio, which is defined as the ratio power used for cooperative transmission over the total power. This approach is then compared to an equal power assignment method and its performance enhancement is verified by simulation results.

MATPOWER平台下配电网潮流算法的应用及比较

提出了配电网潮流算法在MATPOWER平台下应用的解决方案。同时基于MATPOWER平台,针对辐射状配电网,对牛顿拉夫逊法和前推回代法在收敛性、计算速度、稳定性以及网孔处理能力上进行了细致的研究比较。为配电网潮流计算系统的核心算法选取提供了实验理论依据。

Joint Centralized Power Control and Cell Sectoring for Interference Management in CDMA Cellular Systems in a 2D Urban Environment

The interference reduction capability of cell sectoring and power control algorithms have been considered separately as means to decrease the interference in Code Division Multiple Access (CDMA) cellular systems. In this paper, we present Switched-Beam (SB) and Rotatable Equal Sectoring (RES) techniques for CDMA cellular systems in a 2D urban environment. In the SB technique by using a number of fixed, independent, or directional antennas we increase the downlink capacity of the CDMA systems. Also in the RES method, the equal sectors of the base stations are rotating together to decrease the inter-cell and intra-cell interferences. Also in this paper we use centralized power control to overcome the near-far problem. Simulation results indicate that the proposed techniques considerably increase the capacity of the CDMA cellular systems compared to ordinary Equal Sectoring (ES) method.

分布式电源对配电网潮流计算的影响研究

配电中接入的分布式电源的增多,潮流计算时,传统的前推回代法无法满足精度要求。对系统研究发现,分布式电源的出力和接入位置对配电网的网损有不同的影响,阐述了分布式电源潮流计算模型,并引入了一种带有PV节点无功修正的分布式电源配电网潮流计算方法。通过对IEEE14节点系统进行仿真验证,证明了所提算法的有效性和收敛性。研究结果显示:新提出的方案和技术能够更加高效地解决带有分布式电源的配电网潮流问题。

基于频率超前校正的VSG并联系统有功振荡抑制策略

针对虚拟同步发电机(virtual synchronous generator,VSG)在外界扰动时存在的有功暂态振荡问题,提出一种基于频率超前校正的VSG并联系统有功振荡抑制策略。首先,建立VSG并联系统有功环小信号模型,分析负载功率突变时的VSG有功振荡机理。然后,基于微分超前校正思想并结合VSG有功环控制结构,将有功功率反馈至频率偏差之上,从而增大系统阻尼程度并抑制VSG并联系统有功暂态振荡。接下来,建立改进型VSG并联系统状态空间模型,通过根轨迹分析系统动态响应性能。最后,通过Matlab/Simulink仿真和实验验证了该方案能够有效抑制VSG并联系统有功暂态振荡,并且不影响其稳态有功特性。

Hybrid Relaying Protocol for Joint Power and Subcarrier Allocation for OFDM Based Cognitive Radio Networks

This paper aims to avoid the interference imposed by the secondary user on a primary user in Cognitive Radio Network (CRN). In CRN, the interference from secondary user enforced on primary user mainly depends on spectral interval between primary and secondary systems. Moreover, it also depends on the power allocated to the secondary user. In order to avoid interference imposed by secondary user on primary user, a Hybrid Relaying Protocol for Joint Power and Subcarrier Allocation for Orthogonal Frequency Division Multiplexing (OFDM) based Cognitive Radio Networks is proposed. In hybrid relaying protocol, a secondary user uses amplify and forward (AF) protocol and decode and forward (DF) protocol based on the requirement to maximize network throughput. A greedy algorithm is proposed for the selection of relay to get the optimal solution. Moreover, an efficient hybrid power and subcarrier algorithm is used by considering interference constraint imposed by cognitive network to the primary user.

Outage Probability Analysis for Modified Decode-and-Forward Model over Nakagami-m Fading Channels

This paper proposes a modified decodeand-forward(DAF) protocol with a three-node model,which contains two users and one destination.Each user can be either the source or the relay in different frames.We analyze the four cooperative cases in the first frame and run simulations to obtain the optimal power allocation coefficients in the second frame.The closed-form expression of outage probability is derived over Nakagami-m fading channels.Furthermore,we show that the proposed model has better performance than the non-cooperation system and traditional DAF strategy based on the derived outage probability.

A Novel Method of Auxiliary Power Supply Used in Wide-Range High Voltage Input DC-DC Converter

In high voltage input DC-DC converter, auxiliary winding of isolation transformer is usually used to supply power for control circuit. Due to the wide-range of input voltage, the variable output voltage of auxiliary winding will cause a series of problems, such as variable drive pulse amplitude, increased driver switching devices loss and drive transformer core saturation. This paper analyzes the influence of variable output voltage of auxiliary winding in detail. A novel method is proposed to solve the problem of large variation range of auxiliary winding output voltage, which is adding a buck converter between the auxiliary winding and the control circuit. A dual switch forward convert has been designed with 300 V - 800 V input and 24 V/5 A output. The results show that this method is effective by comparing the different results of using buck converter or not.

OPTIMAL POWER ALLOCATION WITH AF AND SDF STRATEGIES IN DUAL-HOP COOPERATIVE MIMO NETWORKS

Dual-hop cooperative Multiple-Input Multiple-Output (MIMO) network with multi-relay cooperative communication is introduced. Power allocation problem with Amplify-and-Forward (AF) and Selective Decode-and-Forward (SDF) strategies in multi-node scenario are formulated and solved respectively. Optimal power allocation schemes that maximize system capacity with AF strategy are presented. In addition, optimal power allocation methods that minimize asymptotic Symbol Error Rate (SER) with SDF cooperative protocol in multi-node scenario are also proposed. Furthermore, performance comparisons are provided in terms of system capacity and approximate SER. Numerical and simulation results confirm our theoretical analysis. It is revealed that, maximum system capacity could be obtained when powers are allocated optimally with AF protocol, while minimization of system's SER could also be achieved with optimum power allocation in SDF strategy. In multi-node scenario, those optimal power allocation algorithms are superior to conventional equal power allocation schemes.

无线电能传输系统最大效率追踪及恒压输出复合控制方法

针对无线电能传输(WPT)系统的传输效率受耦合线圈之间的互感以及负载影响的特点,该文提出一种基于阻抗匹配技术的最大效率追踪及基于前馈PI控制的恒压输出复合控制方法。首先,对双边LCC型WPT系统的参数和传输效率进行分析,通过调整系统参数优化系统的传输效率。其次,在二次侧使用DC-DC变换器采用阻抗匹配的方法实现最大效率追踪,同时在一次侧采用DC-DC变换器利用前馈PI控制器闭环控制负载端电压实现恒压输出。该方法中,效率追踪和电压控制之间相互独立,互不干扰。此外,该方法还通过系统工作时的电路参数来估算线圈间的互感值,并通过线性拟合的方法对该估算互感值进行修正,得到更精确的互感估算值。最后,通过搭建实验平台验证了该方法的可行性和有效性。与PI控制相比,前馈PI控制方法在快速性和抗扰动性上均具有明显优势。

一种适用于介质阻挡放电负载的简易型单极性正向脉冲式供电电源

针对常用的负载谐振型波形连续式的供电电源无法充分发挥介质阻挡放电负载的性能,以及现有脉冲式供电电源拓扑结构比较复杂的不足,提出了一种由1个功率开关管、2个二极管和1个耦合电感构成的单极性正向脉冲式供电电源。通过对该供电电源工作模态的分析得出,该供电电源不仅能为介质阻挡负载提供快速上升的脉冲电压,而且功率器件工作于软开关状态。仿真和实验结果验证了该供电电源的可行性,所提出的单极性正向脉冲式供电电源对现有的介质阻挡放电负载的供电电源的升级改造有一定的借鉴意义。

基于DFS的船舶配电网潮流计算

为提升船舶直流区域辐射型配电网潮流计算的效率与准确性,解决传统前推回代法在复杂网络和多节点情况下的计算问题。提出了一种改进的前推回代法,该方法融入深度遍历(DFS)策略,并优化了节点编号处理过程。通过DFS遍历网络,实现了节点的高效重新编号,并在节点数量较多时构建邻接矩阵,从而加速计算流程。计算结果显示,改进的前推回代法不仅加快了迭代速度,而且确保了计算误差精度。仿真案例中,与传统前推回代法相比,研究提出的方法在节点电压、支路电流和部分节点功率的计算误差上均有减少,同时,迭代次数保持不变的情况下,计算时间显著缩短。因此采用DFS结合节点编号优化的改进前推回代法,能够有效应对船舶配电网的复杂结构和多节点挑战,确保了潮流计算的高效性与准确性,为船舶电力系统的稳定运行提供了有力保障。该方法不仅提高了计算效率,还增强了船舶电力系统潮流分析的可靠性和实用性。

含负载前馈补偿的电流型PWM整流器改进无差拍控制

针对三相电流源型PWM整流器直流侧电压-直流侧电流双闭环控制策略中动态响应速度较慢、参数整定复杂的问题,该文提出一种无差拍预测电流控制与负载功率前馈补偿相结合的改进控制策略。首先,分析三相电流源型PWM整流器在两相静止坐标系中的网侧离散化数学模型,在此基础上,电流内环采用无差拍控制跟踪网侧电流,但由于电感参数与控制延时的影响,将导致网侧电流控制精度及波形质量下降。针对此问题,该文采用改进型无差拍控制策略,并利用根轨迹法对电流内环稳定性能进行分析。在环路设计中,通过在外环上加入负载功率前馈等效电流,加快了系统动态响应,解决了负载突变时直流侧电压超调问题。最后,对传统方案和改进方案进行了对比仿真测试和样机实验,验证了所提控制策略的正确性。