Ⅰ型中性点钳位(neutral point clamped,NPC)三电平变流器作为中大容量新能源发电系统的核心设备,其调制策略直接影响变流器的能量转换效率、谐波特性和运行控制特性等.鉴于Ⅰ型三电平变流器的传统空间矢量脉宽调制(space vector pulse width modulation,SVPWM)策略在实施过程中包含大量三角函数运算,基于三相静止坐标系进行调制算法的大小扇区判断和矢量作用时间计算等,并通过归纳整理,按照单调制波双载波的载波化思路,获得了适用于全扇区的三相统一的占空比函数.借助该占空比函数,变流器的数字控制器仅需通过简单的关系运算和数值计算,便可获得变流器功率管的控制信号,省去了大量三角函数计算,节约了硬件资源.此外,将SVPWM与正弦波脉宽调制(sinusoidal pulse width modulation,SPWM)+3次谐波注入调制算法进行对比,从调制波层面,揭示了这2种调制算法之间的内在差异.最后,通过仿真验证了该算法的有效性.
Three-Level SVPWM Carrier Algorithm of Type Ⅰ NPC Based on Unified Duty Cycle Function of Whole Sector
As the core equipment of medium and large-capacity new energy power generation system,the modulation algorithm of the type Ⅰ neutral point clamped(NPC)three-level(3L)converter can directly affect the energy conversion efficiency,harmonic characteristics and operation control characteristics of the converter.In view of that lots of trigonometric function computation is included in the implementation process of the traditional space vector pulse width modulation(SVPWM)strategy of type Ⅰ NPC 3L converter,this paper executes the sector-area location identifications of the reference voltage vector and the active time calculations of the voltage vector adopted in the modulation algorithm based on the three-phase stationary coordinate system.By induction and reorganization,the three-phase unified duty ratio function available for all sectors is obtained according to the carrier-based idea of single modulated wave with dual-carrier.With the duty ratio function,the digital controller of the converter can obtain the control signals of the power switches by simple relational operations and numerical calculations,which avoids a lot of trigonometric function calculations and saves hardware resources.In addition,the SVPWM and sinusoidal pulse width modulation(SPWM)+3rd harmonic injection modulation algorithms are compared,and the intrinsic differences between the two modulation algorithms from the perspective of the modulated waves are revealed.Finally,the effectiveness of the proposed algorithm is verified by software simulation.
three-levelcarrier-based SVPWMSPWM+3rd harmonic injectionthree-phase stationary coordinate systemunified duty ratio function
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