This paper introduces a multi-granularity locking model (MGL) for concurrency control in object-oriented database system briefiy, and presents a MGL model formally. Four lockingscheduling algorithms for MGL are propos...This paper introduces a multi-granularity locking model (MGL) for concurrency control in object-oriented database system briefiy, and presents a MGL model formally. Four lockingscheduling algorithms for MGL are proposed in the paper. The ideas of single queue scheduling(SQS) and dual queue scheduling (DQS) are proposed and the algorithm and the performance evaluation for these two scheduling are presented in some paper. This paper describes a new idea of thescheduling for MGL, compatible requests first (CRF). Combining the new idea with SQS and DQS,we propose two new scheduling algorithms called CRFS and CRFD. After describing the simulationmodel, this paper illustrates the comparisons of the performance among these four algorithms. Asshown in the experiments, DQS has better performance than SQS, CRFD is better than DQS, CRFSperforms better than SQS, and CRFS is the best one of these four scheduling algorithms.展开更多
通常风电场位于大电网的末端,并网端口电压的大幅波动将引起锁相环不同程度的暂态响应,使并网系统无法呈现预期的控制性能,甚至出现暂态不稳定的现象。考虑锁相环的暂态特性以及线路参数对大功率直驱风电系统中LCL型并网变换器电流控制...通常风电场位于大电网的末端,并网端口电压的大幅波动将引起锁相环不同程度的暂态响应,使并网系统无法呈现预期的控制性能,甚至出现暂态不稳定的现象。考虑锁相环的暂态特性以及线路参数对大功率直驱风电系统中LCL型并网变换器电流控制性能的影响,提出了一种基于多目标函数的电流环PI控制器参数设计方法。首先,建立了并网电流控制系统的精确静态模型。在此基础上,通过对系统响应特性的幅值裕度、相位裕度和静态误差的分析,得到了满足上述要求的PI控制器参数取值范围。随后,建立了受锁相环性能影响的并网电流控制系统的暂态模型,进一步对已有的PI参数取值区间进行优化,得到了性能更优的控制器参数组合。最后,基于典型参数下1.5 MW的LCL型并网变流器进行了仿真分析,在10 k W的直驱式风力发电并网变流器样机上进行了实验验证。结果表明,该方法可全面改善并网电流控制的动静态响应特性以及对电网环境的适应能力。展开更多
文摘This paper introduces a multi-granularity locking model (MGL) for concurrency control in object-oriented database system briefiy, and presents a MGL model formally. Four lockingscheduling algorithms for MGL are proposed in the paper. The ideas of single queue scheduling(SQS) and dual queue scheduling (DQS) are proposed and the algorithm and the performance evaluation for these two scheduling are presented in some paper. This paper describes a new idea of thescheduling for MGL, compatible requests first (CRF). Combining the new idea with SQS and DQS,we propose two new scheduling algorithms called CRFS and CRFD. After describing the simulationmodel, this paper illustrates the comparisons of the performance among these four algorithms. Asshown in the experiments, DQS has better performance than SQS, CRFD is better than DQS, CRFSperforms better than SQS, and CRFS is the best one of these four scheduling algorithms.
文摘通常风电场位于大电网的末端,并网端口电压的大幅波动将引起锁相环不同程度的暂态响应,使并网系统无法呈现预期的控制性能,甚至出现暂态不稳定的现象。考虑锁相环的暂态特性以及线路参数对大功率直驱风电系统中LCL型并网变换器电流控制性能的影响,提出了一种基于多目标函数的电流环PI控制器参数设计方法。首先,建立了并网电流控制系统的精确静态模型。在此基础上,通过对系统响应特性的幅值裕度、相位裕度和静态误差的分析,得到了满足上述要求的PI控制器参数取值范围。随后,建立了受锁相环性能影响的并网电流控制系统的暂态模型,进一步对已有的PI参数取值区间进行优化,得到了性能更优的控制器参数组合。最后,基于典型参数下1.5 MW的LCL型并网变流器进行了仿真分析,在10 k W的直驱式风力发电并网变流器样机上进行了实验验证。结果表明,该方法可全面改善并网电流控制的动静态响应特性以及对电网环境的适应能力。
