Consider the following statements regarding Voltage Source Converters (VSC):
1. They use self-commutating devices like IGBT.
2. They can independently control active and reactive power.
3. They require strong AC system for operation.
Which options stated above is/are correct?
Answer & step-by-step solution
The key distinction is commutation. LCC relies on the AC system for commutation and consumes reactive power; VSC uses self-commutating devices and synthesized AC voltage, giving flexible P/Q control and better weak-grid capability. Key relation: Conceptually, active power is strongly related to converter voltage-angle difference, while reactive power is strongly related to voltage-magnitude difference (subject to network/converter limits).
Exam focus: VSC keyword pair: self-commutated + independent/flexible P-Q control. Common trap: Transferring the “strong AC system required” limitation from LCC to VSC.
Statement-wise Verification
- Statement 1 - Correct.
They use self-commutating devices like IGBT.
Modern VSC-HVDC uses turn-on/turn-off controllable semiconductor valves (classically IGBT-based; modern MMC implementations use IGBT submodules or equivalent self-commutating devices). - Statement 2 - Correct.
They can independently control active and reactive power.
By controlling converter voltage magnitude and phase, VSC can regulate active and reactive power substantially independently within converter limits. - Statement 3 - Incorrect.
They require strong AC system for operation.
Requiring a strong AC system is a major limitation of LCC-HVDC, not VSC; VSC is well suited to weak grids, offshore networks and black-start/passive-network support.
Core Concept
The key distinction is commutation. LCC relies on the AC system for commutation and consumes reactive power; VSC uses self-commutating devices and synthesized AC voltage, giving flexible P/Q control and better weak-grid capability.
Formula / Key Relationship
Conceptually, active power is strongly related to converter voltage-angle difference, while reactive power is strongly related to voltage-magnitude difference (subject to network/converter limits).
Step-by-Step Check
Device technology, control capability and weak-grid behavior independently give truth set {1,2}. Option B.
Why the Other Options Are Wrong
Option A is incorrect because it includes incorrect statement(s) 3 and omits correct statement(s) 1. Option C is incorrect because it omits correct statement(s) 2. Option D is incorrect because it includes incorrect statement(s) 3.
Answer-Key Verification Note
The uploaded provisional key marks D . After independent technical verification, the defensible answer is B . This discrepancy is stated explicitly rather than silently copying the provisional key.
Exam Shortcut / Approach
VSC keyword pair: self-commutated + independent/flexible P-Q control.
Common Mistake
Transferring the “strong AC system required” limitation from LCC to VSC.
Quick Revision
Self-Commutation and P-Q Control is linked with VSC-HVDC, HVDC Transmission and Power Systems. VSC keyword pair: self-commutated + independent/flexible P-Q control.
वोल्टेज सोर्स कन्वर्टर (VSC) के संबंध में निम्नलिखित कथनों पर विचार कीजिए:
1. ये IGBT जैसे स्व-कम्यूटेटिंग डिवाइस उपयोग करते हैं।
2. ये सक्रिय और प्रतिक्रियाशील शक्ति को स्वतंत्र रूप से नियंत्रित कर सकते हैं।
3. इन्हें संचालन के लिए मज़बूत AC प्रणाली चाहिए।
ऊपर बताए गए कौन-से विकल्प सही हैं?
उत्तर और चरणबद्ध हल
B — केवल 1 और 2। VSC स्व-कम्यूटेटिंग IGBT उपयोग करता है और P तथा Q को स्वतंत्र रूप से नियंत्रित करता है, इसलिए कमज़ोर या निष्क्रिय AC नेटवर्क को भी पोषित कर सकता है। 'मज़बूत AC प्रणाली आवश्यक' LCC की सीमा है, VSC की नहीं।
विस्तृत हल (मूल भाषा में)
Statement-wise Verification
- Statement 1 - Correct.
They use self-commutating devices like IGBT.
Modern VSC-HVDC uses turn-on/turn-off controllable semiconductor valves (classically IGBT-based; modern MMC implementations use IGBT submodules or equivalent self-commutating devices). - Statement 2 - Correct.
They can independently control active and reactive power.
By controlling converter voltage magnitude and phase, VSC can regulate active and reactive power substantially independently within converter limits. - Statement 3 - Incorrect.
They require strong AC system for operation.
Requiring a strong AC system is a major limitation of LCC-HVDC, not VSC; VSC is well suited to weak grids, offshore networks and black-start/passive-network support.
Core Concept
The key distinction is commutation. LCC relies on the AC system for commutation and consumes reactive power; VSC uses self-commutating devices and synthesized AC voltage, giving flexible P/Q control and better weak-grid capability.
Formula / Key Relationship
Conceptually, active power is strongly related to converter voltage-angle difference, while reactive power is strongly related to voltage-magnitude difference (subject to network/converter limits).
Step-by-Step Check
Device technology, control capability and weak-grid behavior independently give truth set {1,2}. Option B.
Why the Other Options Are Wrong
Option A is incorrect because it includes incorrect statement(s) 3 and omits correct statement(s) 1. Option C is incorrect because it omits correct statement(s) 2. Option D is incorrect because it includes incorrect statement(s) 3.
Answer-Key Verification Note
The uploaded provisional key marks D . After independent technical verification, the defensible answer is B . This discrepancy is stated explicitly rather than silently copying the provisional key.
Exam Shortcut / Approach
VSC keyword pair: self-commutated + independent/flexible P-Q control.
Common Mistake
Transferring the “strong AC system required” limitation from LCC to VSC.
Quick Revision
Self-Commutation and P-Q Control is linked with VSC-HVDC, HVDC Transmission and Power Systems. VSC keyword pair: self-commutated + independent/flexible P-Q control.
વોલ્ટેજ સોર્સ કન્વર્ટર (VSC) અંગે નીચેનાં વિધાનો ધ્યાનમાં લો:
1. તે IGBT જેવાં સ્વ-કમ્યુટેટિંગ ડિવાઇસ વાપરે છે.
2. તે સક્રિય અને પ્રતિક્રિયાશીલ પાવરને સ્વતંત્ર રીતે નિયંત્રિત કરી શકે છે.
3. તેને સંચાલન માટે મજબૂત AC પ્રણાલી જોઈએ.
ઉપર જણાવેલા કયા વિકલ્પો સાચા છે?
જવાબ અને પગલાવાર ઉકેલ
B — ફક્ત 1 અને 2. VSC સ્વ-કમ્યુટેટિંગ IGBT વાપરે છે અને P તથા Qને સ્વતંત્ર રીતે નિયંત્રિત કરે છે, તેથી નબળા કે નિષ્ક્રિય AC નેટવર્કને પણ પોષી શકે છે. 'મજબૂત AC પ્રણાલી જરૂરી' એ LCCની મર્યાદા છે, VSCની નહીં.
વિગતવાર ઉકેલ (મૂળ ભાષામાં)
Statement-wise Verification
- Statement 1 - Correct.
They use self-commutating devices like IGBT.
Modern VSC-HVDC uses turn-on/turn-off controllable semiconductor valves (classically IGBT-based; modern MMC implementations use IGBT submodules or equivalent self-commutating devices). - Statement 2 - Correct.
They can independently control active and reactive power.
By controlling converter voltage magnitude and phase, VSC can regulate active and reactive power substantially independently within converter limits. - Statement 3 - Incorrect.
They require strong AC system for operation.
Requiring a strong AC system is a major limitation of LCC-HVDC, not VSC; VSC is well suited to weak grids, offshore networks and black-start/passive-network support.
Core Concept
The key distinction is commutation. LCC relies on the AC system for commutation and consumes reactive power; VSC uses self-commutating devices and synthesized AC voltage, giving flexible P/Q control and better weak-grid capability.
Formula / Key Relationship
Conceptually, active power is strongly related to converter voltage-angle difference, while reactive power is strongly related to voltage-magnitude difference (subject to network/converter limits).
Step-by-Step Check
Device technology, control capability and weak-grid behavior independently give truth set {1,2}. Option B.
Why the Other Options Are Wrong
Option A is incorrect because it includes incorrect statement(s) 3 and omits correct statement(s) 1. Option C is incorrect because it omits correct statement(s) 2. Option D is incorrect because it includes incorrect statement(s) 3.
Answer-Key Verification Note
The uploaded provisional key marks D . After independent technical verification, the defensible answer is B . This discrepancy is stated explicitly rather than silently copying the provisional key.
Exam Shortcut / Approach
VSC keyword pair: self-commutated + independent/flexible P-Q control.
Common Mistake
Transferring the “strong AC system required” limitation from LCC to VSC.
Quick Revision
Self-Commutation and P-Q Control is linked with VSC-HVDC, HVDC Transmission and Power Systems. VSC keyword pair: self-commutated + independent/flexible P-Q control.
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