该文提出了一种适用于三相准Z源逆变器的二维空间矢量调制策略,其计算简单且能够有效减小准 Z 源网络电感电流纹波(脉动量).该方法将准 Z 源逆变器的输出电压映射在二维坐标系的坐标轴上,依据三相电压的大小关系划分控制域,根据参考电压所在的控制域选择电压矢量和开关状态;并根据电感电流脉动量,将一个开关周期中的直通时间分成六小段,插入在零矢量首尾位置和两个非零矢量之间;以电感电流在直通状态与相邻的非直通状态间的净变化量等于零为目标,计算每段直通作用时间,实现了一个开关周期内电感电流纹波最小.该方法计算简单,且能够有效减小电感电流的脉动量.仿真和实验验证了该方法的有效性.
Inductor Current Ripple Reduction Strategy Based on Two-Domain Space Vector PWM for Qusai-Z Source Inverter
The quasi-Z-source inverter(qZSI)couples an impedance network,consisting of two inductors and two capacitors,between the dc source and the inverter.A shoot-through zero state is inserted into the inverter's switches to boost the DC input voltages up to a higher voltage level.Compared with the DC-DC boost circuitry-based two-stage inverter,the qZSI efficiency can be increased,and cost savings can be achieved.Additionally,the inverter reliability is highly improved,allowing turning on one bridge leg's upper and lower switches simultaneously without damaging the inverter.However,the qZSI must use two large inductors to limit the ripple of the inductor current.Since the size and weight of the qZS network impact the overall volume and weight of the system,large inductors reduce the power density of the entire system.Therefore,it is necessary to minimize the inductor current ripple.One approach is increasing the operating frequency of the inductors.Another approach is modifying the modulation and switching sequence.The former is challenging to maximize the effectiveness because it depends on the switching performance and circuit layout.The latter requires immense computations and hardware resources for two reasons.(1)Two shoot-through references are added to compare with the triangular-carrier wave to generate the shoot-through state.(2)The procedure is complicated due to the difficulty in the location determination of the reference,the calculation of active,zero,and shoot-through times in every sector,and the switching state selection.In addition,the calculations involved in coordinate transformation and triangular functions can result in a high computational burden,potentially leading to delay errors in the system.This paper proposes a new modulation for the three-phase qZSI with minimum inductor current ripple,reducing calculation burden and saving controller resources.Firstly,the two-domain pulse width modulation(2D-PWM)technique performs shoot-through behavior based on the geometric representation of the three-phase output voltage ranges in a two-dimensional Cartesian coordinate system.The generated geometry is the control region,a series of elliptic curves bounded by a cube for the three-phase qZSI.According to the size relationship between va,vb,and vc,the control region of 2D-PWM can be divided into six sections in the coordinate axes.Then,the qZS inductors are charged at the shoot-through state(inductor currents rise)and discharged at active and zero states(inductor currents decrease).The charging current ripple is determined by the shoot-through duty ratio,and the discharging current ripple is determined by the active time and zero time.Therefore,the inductor current ripple can be mitigated by choosing the suitable switching sequence and switching times.The shoot-through state time is divided into six unequal parts in one switching cycle,and the times of the six shoot-through intervals are designed.Consequently,the charging current ripple generated in shoot-through intervals equals the discharging current ripple generated in the nearest non-shoot-through intervals,resulting in reduced inductor current ripple.The maximum inductor current ripple of SVM-6(2.9 A)is 1.61 times larger than that of the proposed 2D-PWM(1.8 A)in the simulation test.In the experimental test,the maximum inductor current ripples of the proposed 2D-PWM and traditional SVM-6 are about 1.1 A and 2.4 A,reduced by 54.1%compared with traditional SVM-6.
Quasi-Z-source inverterspace vector modulationpulse-width modulationinductor current ripple
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