电力电子技术第5版 教学课件 作者 王兆安 chapter07.pptVIP

The most widely used control technique in power electronics Outline 7.1 Basic principles of PWM Basic principles of PWM A list of PWM techniques Triangular-wave sampling Natural sampling Uniform sampling Calculation Calculation based on equal-area criterion Selective harmonics elimination Hysteretic control Space Vector Modulation (SVM, or SVPWM) Random PWM 7.2 Some major PWM techniques Natural sampling Uniform sampling Selective harmonics elimination Some practical issues Synchronous modulation and asynchronous modulation Harmonics in the PWM inverter output voltages Ways to improve DC input voltage utilization and reduce switching frequency Connection of multiple PWM inverters Triangular-wave natural sampling Triangular-wave natural sampling Triangular-wave natural sampling Triangular-wave uniform sampling Selective harmonics elimination PWM (SHEPWM) Frequency relationship between triangular-wave carrier and control signal Harmonics in the PWM inverter output voltages No lower order harmonics The lowest frequency harmonics is wc and adjacent harmonics. wc has the highest harmonic content. Harmonics in the PWM inverter output voltages No lower order harmonics No harmonics at wc. The lowest frequency and highest content harmonics are wc?2wr and 2wc?wr. Ways to improve utilization of DC input voltage and reduce switching frequency Ways to improve utilization of DC input voltage and reduce switching frequency Use 3k order harmonics bias in the modulating signal Connection of multiple PWM inverters Space Vector PWM (SVPWM or SVM) Line-to-Line Voltage Space Vector Switching States for 3-phase Voltage Source Inverter Switching State Vector [pnn] Switching State Vector [ppn] Switching State Vector [ppp] Switching State Vectors Reference Voltage Vector, Vref Definition of High Frequency Synthesis Synthesis of Vref using Switching State Vectors Duty Ratio of Switching State Vectors in SVPWM 7.3 PWM techniques with  feedback control Current hysteretic control V