一种用于提高风电变流器中功率器件寿命的混合空间矢量调制方法

A Hybrid Modulation Method for Improving the Lifetime of Power Modules in the Wind Power Converter

空间矢量调制可分为连续脉宽调制(continuous pulse width modulation,CPWM)和不连续脉宽调制(discontinuous pulse width modulation,DPWM)。与CPWM相比,当变流器采用DPWM时,器件开关损耗较低,使得结温波动较低。DPWM策略被用于变流器,虽然可以提高功率器件的寿命,但是将导致电能质量问题。因此文中结合DPWM和CPWM策略的优点,提出了一种功率器件混合调制方法,该调制方法根据风电场中风速的概率分布切换不同的调制策略。为考虑长时间风速对器件寿命的影响,文中提出了一种适用于不同调制方法的结温数值计算方法。以1.2MW直驱风机系统为例,结合一年的风速和气温快速计算不同调制序列下器件的结温,进而评估了器件的寿命消耗,并且分析了不同调制序列对器件寿命消耗的影响。结果表明,与CPWM和DPWM相比,当采用混合调制方法时,器件年寿命消耗不仅得到大幅降低,而且风机系统并网的电能质量几乎不受影响。

Pulse width modulation （PWM） techniques can be generally classified into continuous pulse width modulation （CPWM） and discontinuous pulse width modulation （DPWM）. The switching loss of power devices in DPWM converters is lower than that in CPWM converters. Lower loss can reduce the junction temperature fluctuation in converters of wind turbine generator system （WTGS） and may prolong the lifetime of power devices. However, employing DPWM scheme under all WTGS operation conditions will lead to power quality concern. So a new hybrid modulation scheme which combines the CPWM and DPWM methods for WTGS converters was presented. In the presented hybrid modulation method, different modulation schemes are switched according to the probability distribution of the wind speed in the wind site. To consider the effect of the long-term mission profiles of WTGS on devices lifetime, a junction temperature calculation method of power devices, which is suitable for different modulation methods, was also proposed. A 1.2MW power converter was regarded as a case study, junction temperature of power device under different modulation sequences was quickly calculated considering the actual wind speed and air temperature, and then lifetime consumption of power devices was evaluated. The results show that in contrast to CPWM and DPWM, lifetime consumption of devices in wind power converter employing the proposed hybrid modulation method is greatly reduced,and the power quality of the power converters can be guaranteed in all operation conditions, which may not be achieved with DPWMs.