DC Link AC to AC Converters

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DC Link AC to AC Converters In a dc link type AC to AC converter the ac source is first converted into a dc voltage or a dc current source by a diode rectifier circuit. The dc source is then converted into an ac source of the desired specifications: amplitude, frequency, and phase. The intermediate dc stage is called the dc link or the dc bus. The output voltage in the dc link converter may have a different amplitude, a different frequency and a different number of phases than the input voltage
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  DC Link AC to AC Converters In a dc link type AC to AC converter the ac source is first converted into a dc voltage or adc current source by a diode rectifier circuit. The dc source is then converted into an acsource of the desired specifications: amplitude, frequency, and phase. The intermediatedc stage is called the dc link or the dc bus. The output voltage in the dc link converter may have a different amplitude, a different frequency and a different number of phasesthan the input voltage source, as illustrated in Figure 1. The output frequency need not bean integer multiple or a fraction of the source frequency, and it can be higher or lower than the source frequency.  Figure 1 . Block diagram of an ac-to-ac converter The input energy in the dc-link converter is collected at one frequency and delivered tothe load at a different frequency. Hence, the ac components of power at the input and theoutput may not be the same. An inductor, a capacitor or their combination (a resonanttank), placed in the dc link stores the instantaneous difference between the input andoutput energies.In the following sections, we will discuss two basic types of ac-ac converters, namely, thevoltage-link and the current-link ac-ac converters. 1.DC current-link ac-to-ac converter A dc current-link converter is shown in Figure 2. A large inductor is the intermediatestorage element. The ac-dc converter at the front end sees a large inductive load. The dc-ac inverter at the load end sees a current source. The load is an ac source or an ac sink vo,which may represent an induction motor, a synchronous motor, or another ac sourceconnected as part of an ac source in a dc transmission bus. The control parameter in theac-dc converter and the inverter are the delay angle α and pulse width δ, respectively. Thedc output voltage 1 o v of the ac-to-dc converter is α π   cos2 1  so V v = AC-DCConverter 1-øor 3-ø acsupplyDC-ACConverter DClink 1-ø or 3-ø acload  Figure 2 . DC current-link converter. 2.DC voltage-link ac-ac converter The dc voltage-link Ac-ac converter is shown in Figure 3. A large capacitor is theintermediate storage element. The ac-dc converter sees a large capacitive load. The dc-acconverter sees a voltage source. The load is an ac source or sink v o in series with aninductor. The ac source or sink may represent an induction motor or a synchronousmotor. The dc voltage output 1 o v is α π   cos2 1  so V v = Figure 3 . DC current-link converter.1-øor 3-ø acsupply1-ø or 3-ø acloadDC-link inductanceAC-DCConverter DC-ACConverter 1-øor 3-ø acsupply1-ø or 3-ø acloadDC-link capacitor AC-DCConverter AC-DCConverter 
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