Constant current source Inverter

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Discussion Overview

The discussion revolves around the concept of Constant Current Source Inverters (CSI), focusing on their operation, the role of inductors in maintaining current, and the characteristics of current sources in electrical circuits. Participants seek clarification on the basic principles and applications of CSIs, as well as the theoretical underpinnings related to inductance and current stabilization.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • Some participants express confusion about the basic concept of a Constant Current Source Inverter and request explanations and diagrams for better understanding.
  • One participant explains that a CSI is a type of thyristor inverter that requires a constant current source to keep the thyristors in conduction mode until load voltage causes commutation.
  • Another participant discusses the analogy between capacitors stabilizing voltage and inductors stabilizing current, suggesting that inductors serve a similar purpose in current circuits.
  • There is a discussion about the limitations of inductors as current sources, noting that they cannot behave as ideal current sources indefinitely and only maintain current for a limited time based on stored energy.
  • Some participants highlight that the term "constant current" in this context is relative and only applies over short time frames, particularly during switching events in the inverter operation.
  • One participant references an external source that describes power inductors maintaining steady current, prompting questions about the duration of this maintenance and its implications.
  • A later reply clarifies that while inductors can smooth out noise in a current source, they can only maintain current for a limited duration when the source is intermittent.

Areas of Agreement / Disagreement

Participants generally agree on the basic function of inductors in stabilizing current, but there is no consensus on the specifics of how constant current is maintained over time or the implications of this behavior in practical applications. The discussion remains unresolved regarding the ideal characteristics of current sources and the limitations of inductors.

Contextual Notes

Participants note that the concept of "constant current" is context-dependent and varies with time frames, particularly in relation to switching events. There are also references to external materials that may not fully clarify the discussed concepts, indicating potential gaps in understanding.

ESMAT 1995
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i was reading about CSI and the first paragaph said "A constant current source is assumed here, which may be realized by using an inductance of suitable value, which must be high, in series with the current limited dc voltage source. " and it says nothing else about it , so clearly it's a basic concept, but i have no idea how that works, so can anyone explain to me please?
the link to the PDF
http://www.nptel.ac.in/courses/Webcourse-contents/IIT%20Kharagpur/Power%20Electronics/PDF/L-39%28NKD%29%28PE%29%20%28%28EE%29NPTEL%29%20.pdf
 
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Welcome to the PF. :smile:
ESMAT 1995 said:
clearly it's a basic concept, but i have no idea how that works,
Me neither. What's a Current Source Inverter? Can you post a scan of the page you are reading, along with any schematic diagrams?
 
berkeman said:
Welcome to the PF. :smile:

Me neither. What's a Current Source Inverter? Can you post a scan of the page you are reading, along with any schematic diagrams?
sure, i will edit the post adding the link to the PDF
 
Are you familiar with the use of a capacitor to stabilise a voltage? Well an inductor does the same thing but for currents rather than voltages.
 
CSI is the name of a general thyristor (SCR) inverter, DC to AC converter. This inverter need a constant current source to "force" the thyristors to stay in conduction mode, until the voltage in the load forces the commutation.

The typical design is just a traditional rectifier, with a large inductance in the DC link.
 
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Windadct said:
CSI is the name of a general thyristor (SCR) inverter, DC to AC converter. This inverter need a constant current source to "force" the thyristors to stay in conduction mode, until the voltage in the load forces the commutation.

The typical design is just a traditional rectifier, with a large inductance in the DC link.
So how is this "constant current" provided?
thanks by the way for this great reference
 
CWatters said:
Are you familiar with the use of a capacitor to stabilise a voltage? Well an inductor does the same thing but for currents rather than voltages.
i am familiar to the use of inductors as a filter for ripples, is that what you mean?
 
Yes. Inductors don't "like" changing currents. They try and maintain an established current if the source is removed (at least they do for as long as they have sufficient energy stored in them).

Compare with a soothing capacitor, they try and maintain a voltage when the source is removed.
 
  • #10
PS an inductor can't behave like an ideal current source any more than a capacitor can behave like an ideal voltage source. The inductor only has to provide current for awhile as Windadct describes.
 
  • #11
Keep in mind - Constant Current in this case only need to be considered in the a relatively small time frame, clearly this is not a "Constant Current" over time period over much more than one cycle, or anywhere near a second. But in the time frame of a switching event needed to make the inverter work, it is not anything close to an IDEAL Current Source. In the link, the energy source for the system,is a traditional voltage source, with the addition of the inductor, the source for the Inverter behaves as constant current.
 
  • #12
Windadct said:
Keep in mind - Constant Current in this case only need to be considered in the a relatively small time frame, clearly this is not a "Constant Current" over time period over much more than one cycle, or anywhere near a second. But in the time frame of a switching event needed to make the inverter work, it is not anything close to an IDEAL Current Source. In the link, the energy source for the system,is a traditional voltage source, with the addition of the inductor, the source for the Inverter behaves as constant current.
so i started reading a little in that reference but it could take me months before i can truly understand what's going on, but i found this link too on future electronics describing power inductors as " A power inductor maintains a steady current in an electrical circuit with a varying current and/or voltage."
Did he mean that it will maintain for a very short period of time or is that another case?
http://www.futureelectronics.com/en/inductors/power-inductors.aspx
 
  • #13
ESMAT 1995 said:
Did he mean that it will maintain for a very short period of time..

Yes and no.

Suppose you have a current source of 5A with some noise on it (+/- 0.1A). Putting an inductor in series will reduce the noise so the output is a constant 5A. It can do that indefinitely.

On the other hand if you have an intermittent source that delivers 5A for awhile and then switches off, the inductor will try to maintain 5A after it switches off but it can only do that until it runs out of stored energy.
 

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