防止llc進入容性工作狀態(tài)的控制方法english(lastest)

1、Avoiding capacitive-mode operation by a new LLC Resonant Converter control method Author: Yong Peng(+86-18688784669), Jun LiuAbstract: in this paper, a novel control method for LLC converter is proposed to avoid capaciti

2、ve-mode operation, which is implemented by DSP controller. The real-time input voltage and output voltage is being monitored, a minimum frequency limit is calculated with the values of them. The LLC resonant converter is

3、 constantly operating above the minimum frequency limit to avoid capacitive-mode operation. The higher reliability is achieved by this control method. Index Terms: avoiding capacitive-mode operation, LLC converter contro

4、l method, DSP controller.1. IntroductionLLC converter is being widely used in power supply industry for its noticeable merits. Hence, the reliability of which is getting more and more attentions. Going into capacitive-mo

5、de operation is a primary risk to its reliability [1]. As it showed in Fig 1, when it goes into capacitive-mode operation, the resonant current Ir leads to input voltage, the resonant current Ir flows in the body diode o

6、f low side MOSFET Q2 before high side MOSFET Q1 turns on. The reverse recovery current of body diode of low side MOSFET Q2 is inevitable, when high side MOSFET Q1 turns on. Sometimes, a fixed minimum frequency limit can

7、effectively keep LLC resonant converter from capacitive operation. However, a fixed minimum frequency is not a guaranteed success to avoid capacitive-mode operation, the shoot-through occurs in conditions, such as startu

8、p, overload, dynamic load, etc. Hence, to avoid high reverse recovery current, which may causes MOSFET failure, MOSFETs with fast recovery diode are required in LLC converter.Fig 1 LLC Resonant ConverterIn this paper, a

9、novel LLC resonant converter control method that can avoid capacitive-mode operation is proposed. This paper is organized as follows: section 2 is theoretical analysis of how to avoid capacitive-mode operation, section 3

10、 presents the experimental performance of this control method. Concl-usions is presented in section 4.2. theoretical analysis of how to avoid capacitive-mode operationFig 2 Simplified Model of LLCAccording to the simplif

11、ied model of LLC converter, which showed in Fig 2, the impedance of which can be expressed as below：Equation 1 G(ω ? j) =1Cr ? ω ? j + Lr ? ω ? j +Lm ? ω ? j ? RLm ? ω ? j + RNormalizing Equation 1 with , and λ =LrLm f

12、 = ω. Lr ? Cr Q =, the imaginary part of the impedance can be expressed 1R ?LrCrby ： Equation 2LrCr ? (f ?1f +λ ? fλ2 + Q2 ? f2 )To avoid capacitive-mode operation, the resonant current should not lead the input voltage.

13、 This means the imaginary part of the impedance should not be negative:Equation 3 f ?1f +λ ? fλ2 + Q2 ? f2 ≥ 0Rearranging Equation 3 as below：enough for engineering applications.Proposed control method: to avoid capaciti

14、ve-operation, the real-time input voltage and output voltage is being monitored, a minimum frequency limit is calculated with the values of them. The operating frequency is being limited by the corresponding minimum f

15、requency limit for different . N ? VoVinWhen , the minimum frequency limit is the resonant N ? VoVin 1the minimum frequency limit is calculated by f ≥λ1 + λ - (VinN ? Vo)2.when the operating frequency is being pushed be

16、yond the minimum frequency by the output voltage control loop, it will be limited by DSP controller itself. So the detailed control method is given below:3. EXPERIMENTAL RESULTSThe experiments were carried on a 3KW fu

17、ll bridge LLC resonant converter, whose input voltage is 393V and output voltage is 53.3V. All the resonant tank parameters are showed in table 1.Fig5 shows the circuit diagram of the 3KW full bridge LLC resonant convert

18、er. Plus, the response time of over current protection of it is less than 200μs.Table 1Components ValueResonant inductor 25 μHTransformer magnetizing inductor 150μHResonant capacitor 66 nFInput voltage 393 VOutput volt

19、age 53.3VOutput current 56.3AFig 5 3KW full bridge LLC resonant converterFor the purpose of comparison, the performance of conventional control strategy with fixed minimum operating frequency limit has been tested duri

20、ng shut off and short circuit. The Fig5 and Fig 7shows the capacitive operation under shut off and short circuit conditions before the new control method implemented.Fig6 and Fig 8shows the performance of the new control