{[ promptMessage ]}

Bookmark it

{[ promptMessage ]}

DC_Drive_Converters

# DC_Drive_Converters - 1 2 Electronic power supplies for dc...

This preview shows pages 1–3. Sign up to view the full content.

2. Electronic power supplies for dc motors There are following electronic power supplies used for control of DC motors: 1) Controlled rectifiers, 2) Choppers. 2.1 Controlled rectifiers They are used if there is an AC supply. There are two types of controlled converters: - full converter: all switching devices are controlled devices - semi-converter: if some switching devices are diodes. The output voltage depends on the firing angle α . If the output current is continues the average value of the output voltage of controlled rectifiers is calculated from the following formulae: - single-phase input a) full-converter 2 2 cos out p V V α π = (1) b) semi-converter 2 (1 cos ) out p V V α π = + (2) - Three-phase input a) full-converter 3 6 cos out p V V α π = (3) b) semi-converter 3 6 (1 cos ) 2 out p V V α π = + (4) where V p is the rms of the ac phase voltage. 2.2 Choppers Choppers convert a fixed-voltage dc supply into a variable-voltage dc supply. Output voltage is: on out t V V T = (5) 1

This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document
or out V d V = (6) where: V – input voltage t on – is on-time of the chopper T – is the chopping period d - is the duty ratio of the chopper 3. Open loop control The block diagram of open-loop circuit to control the speed of dc motor is shown in Fig.5. The converters used are controlled rectifiers or choppers. S o l i d - s t a t e c o n v e r t e r t o c o n t r o l t h e a r m a t u r e v o l t a g e D C M o t o r D C v a r i a b l e v o l t a g e L o a d D C o r A C p o w e r s u p p l y I f S o l i d - s t a t e f i e l d c o n t r o l l e r α α Fig.5 Block diagram of open loop control of dc motors 3.1 First quadrant control As an example, a separately excited (or permanent magnet) DC motor is considered. 3.1.1 Six-pulse controlled rectifier The armature winding is connected to a 3-phase line via 3-phase, 6-pulse controlled rectifier as shown in Fig.6. The field winding is separately excited by a single-phase half controlled bridge rectifier. The inductance of field winding is large enough to smooth the current so there is no need for external inductance.
This is the end of the preview. Sign up to access the rest of the document.

{[ snackBarMessage ]}