1.国网浙江省电力有限公司宁波供电公司;2.重庆大学 自动化学院
TM743
国网浙江省电力有限公司科技项目(B311NB210005)。
1.State Grid Ningbo Electric Power Supply Company,Ningbo;2.College of Automation,Chongqing University
SS型Buck-WPT(Buck-wireless power transfer)系统由Buck电路和基本的SS型无线电能传输电路组成。该电路系统因为结构简单、控制方式简单、控制效果明显等优点在感应式无线电能传输方面得到应用广泛。然而，在实际情况下，该电路的动态特性较差，并不能满足一些时变系统对快速性较高的要求。例如，该类系统在启动时会存在较强震荡和较大超调,系统负载改变时稳定状态会发生改变且存在明显抖动，系统极限空载时原边谐振电流会增大且该电流值远大于安全工作范围等。针对这类动态特性问题，本文提出了一种基于可控电感的SS型 Buck-WPT系统。首先可控电感的工作原理出发，分析了其电感值可调的方法并在COMSOL中建立仿真模型验证了其电感值可控的特性。接着对SS型Buck-WPT系统进行了数学建，将SS型WPT系统作为Buck电路的特殊负载，推导SS型Buck-WPT系统状态空间方程。同时研究了其三维空间内相轨迹的降维描述方法，将该系统用二维相轨迹描述系统运行过程。然后，通过分析启动阶段相轨迹运行规律，改进前级Buck电路。将传统Buck电路中的电感换成可控电感，运用其电感值可调的特性来控制系统开通阶段的运行轨迹，使系统在一个开关周期内无超调快速进入稳态；当系统负载改变时，不仅系统的输出电压会改变，而且改变的过程是一个不断抖动来回反复的过程。为此，利用PI算法对系统进行恒流控制。通过可控电感控制系统相轨迹，使副边输出能无抖动的快速进入稳态，保证输出电压不变；针对SS型谐振网络的Buck-WPT系统中空载时出现的大电流问题，提出了将可控电感串联接入原边谐振网络的方法。实时检测原边谐振电流的值，一旦该值超过正常工作范围就快速增大感值增大。减小了原边谐振电流而达到空载时维持原边谐振电流处于安全值以下的目的。最后，为了验证上诉方法在优化SS型Buck-WPT系统的动态特性的有效性，特在Simulink中搭建仿真电路。经过分析发现，该方法能够减小当工作条件改变时带来的系统抖动。而且能在不改变系统响应速度的前提下减小超调，优化系统动态性能，增强系统抗负载扰动力。对提高系统带负载能力有明显效果。
The SS Buck-WPT system composed with Buck and basic SS-type wireless power transfer circuit has been widely used in inductive wireless power transmission because of its superiority in structure, control methods and effect. However, this kind of system can"t meet the requirements of time-varying system in responsiveness due to its poor dynamic characteristics. For example, the system in filed applications has large overshoot and oscillation when starting up, alteration on system stability for the various load resistance and sharp fluctuation of primary resonance current under light condition. To address those dynamic problem, a SS-type Buck-WPT system based on controllable inductance was proposed in this paper. First of all, controllable inductance was analyzed in detail to figure out the principle of adjustable inductance and modeled in COMSOL to verify the conclusion. Then the Mathematical modeling analysis of SS Buck-WPT system was carried out. Taking SS WPT system as the load of Buck, the system state space equation was derived. And the system was described with two-dimensional phase trajectories by reducing dimensionality. Then the phase trajectory operation law during start-up was proposed and pre-Buck circuit was improved by changing conventional inductor to controllable one and controlling the inductor via to make system get in stable in one turn-on without any overshoot; The output voltage will be different that goes back and forth once load changes. So, the PI algorithm is used to keep current constant, so that the phase trajectory runs as expected, and the output of secondary returns to the steady state quickly with the real-time control of inductance ; For the excessive primary resonant current, the controlled inductance cascaded with SS in primary to maintain it’s current within permissible values by adjust inductance automatically. To validate the performance of proposed method, the prototype is set up in Simulink. The results show that this strategy has better effect on system dynamic performance and loads tolerance compared with traditional one.
