【作者】 于玮；

【导师】 徐德鸿；

【作者基本信息】 浙江大学 ， 电力电子与电力传动， 2009， 博士

【摘要】 不间断电源(UPS)具有提供持续、稳定、不间断供电的优点,UPS并联系统由于具有N+X冗余性,可扩展性,高可靠性以及容易维护等优点越来越广泛地应用于重要负载的供电以及停电保护中。针对本文所研究的在线式UPS结构和应用场合,提出UPS系统工作于经济模式的一种解决方案以及市电掉电的快速检测方法,当输入市电不正常时保证系统在最短的时间内从旁路供电切换到逆变供电,在市电恢复正常以后重新切换到旁路工作。实现了经济模式下UPS系统工作状态的可靠切换。针对整流性负载和电动机负载,由于这些冲击性负载启动瞬间的电流非常大,为了保证在这种类型负载下UPS正常工作且负载不断电,本文提出了一种突加冲击性负载的控制策略。本文重点研究了UPS并联均流控制,通过比较瞬时电流均流控制,平均功率均流控制和下垂均流控制三种控制方式的优缺点,采用有功功率和无功功率控制输出电压的幅值和相角,实现负载电流的均分。在空载和小功率负载下由于输出电流很小,带来很大的采样误差和功率计算误差,大大影响了并联系统的均流控制精度和稳定性。为了精确计算系统输出的有功功率和无功功率,本文提出了一种改进的有功功率和无功功率计算方法,即采用输出滤波电感电流代替输出电流计算UPS输出功率,通过选取电感电流的采样时刻实现轻载和空载情况下功率的精确计算,提高整个UPS系统的均流特性和稳定性,并通过试验证实了该方法的正确性。本文基于N台UPS逆变器并联等效电路推导了平均功率均流控制策略。由于有功功率和无功功率均流控制不能消除直流环流,不控的直流环流能够使直流母线电压不对称,导致过压保护,本文在有功功率和无功功率均流控制的基础上加入电感电流直流分量控制,从而有效的抑制直流环流。实际系统中,由于存在检测误差,有功环流、无功环流和直流环流会产生误调节问题。为了避免在空载和轻载情况下由于误调节引起环流导致直流母线电压升高,本文提出了一种改进的均流控制方法。由于UPS并联系统功率控制环节调节速度比较慢,当系统存在扰动时,由功率器件参数不一致和输出连接线阻抗差异导致的等效内阻抗差异会对并联系统中UPS逆变器输出电压的幅值和相角控制产生影响,降低并联系统的均流特性。为了进一步提高系统的均流特性,本文在电压电流双环控制的外部加入了虚拟阻抗环路,详细分析了虚拟阻抗对UPS逆变器非理想情况产生环流的抑制作用,并就虚拟阻抗对UPS逆变器电源调整率和负载调整率的影响进行详细分析。本文推导了基于平均功率控制的UPS并联系统的小信号模型,建立仿真模型,具体分析了功率调节器控制参数对并联系统动态均流特性的影响。基于均流控制方式的理论分析,研制了10-40KVA的三相四线UPS并联系统,通过试验验证了理论分析的正确性。实验证明运用该均流控制方法UPS并联系统取得了良好的均流效果。更多还原

【Abstract】 UPS (uninterruptible power supply) has been widely used in various applications, providing power supply to critical load. Nowadays, paralleled UPS systems become more and more attractive for their merits on reliability, redundancy, expandability, and maintenance.This paper proposes a control strategy of the economical operation mode of DSP controlled online UPS. When the grid is abnormal, UPS switches to inverter working mode. Until the grid is normal again, then UPS back to bypass working mode. The proposed control strategy realizes the reliable working mode change of UPS system. When putting the rectified and motor load into UPS system, the initiation current is very large. In order to ensure the normal operation of UPS in these conditions, a control strategy is proposed.The most important part of this paper is load-sharing control strategy. Through comparing the current-sharing control strategies of instant current control with current sharing bus, output droop control scheme, active and reactive power control scheme, the active and reactive power control scheme is used to achieve the load-sharing.Averaged power control method needs to calculate UPS output active and reactive powers accurately for control of the phase and amplitude of output voltage. In light or no load conditions, UPS output current is very small; the sampling value contains many measured errors, which will affect the active and reactive power calculation accuracy. This paper suggests an improved power calculation method of using the UPS output filter inductor current instead of the output current when calculating the UPS output active and reactive powers. The sampling time of the inductor current is chosen to ensure high accuracy of the power calculation. Theory analysis and experimental results of power calculation is presented.Based on the equivalent circuit of N paralleled UPS inverters, an averaged power control strategy is proposed. Because the pure active and reactive power sharing control can not guarantee the DC current sharing among the paralleled UPS system. Hence, a combination of the power control and the filter DC circulation current control is proposed. In actual UPS systems, there exist error regulations of active, reactive and DC circulation current because of detecting error. To solve these problems, an improved load-sharing control strategy is proposed in this paper. In paralleled UPS system, because the active and reactive power control loops are quite slow, when there are disturbances in the paralleled systems, the device parameters variation, UPS output impedance mismatch have influence on the control precision of the UPS output voltage amplitude and phase. In order to increase the control precision of the output power control loop of paralleled UPS system and further minimize the circulation current, an intermediate droop control loop to program a virtual resistance is added to the output voltage and inductor current double loop controller. The influence of virtual resistance on circulation current caused by none idea situation of UPS inverter is analyzed. Also the influence of virtual resistance on load regulation and source regulation of UPS inverter is analyzed.The small signal model of two paralleled UPS inverters based on averaged power load-sharing control strategy is derived; the influence of active and reactive power controller PI parameters on the transition characteristics of paralleled UPS systems is analyzed.Using above mentioned control strategies, the load-sharing quality and stability of paralleled UPS system can be greatly increased. The related experimental results are presented to verify this control method with digital controlled three-phase four-wire 10-40KVA paralleled UPS systems.更多还原