【单选题】【消耗次数：1】
带二极管整流器的SPWM变频器是以正弦波为逆变器输出波形，是一系列的（）矩形波。
①
幅值不变，宽度可变
②
B幅值可变，宽度不变
③
幅值不变，宽度不变
④
D幅值可变，宽度可变
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