Half Bridge Inverter with Inductive Load

Half Bridge Inverter with Inductive Load

Operation of Half Bridge Inverter with Inductive Load :

Let us divide the operation into four intervals. We start will explanation from the second time interval t₁ to t₂, because at negative the beginning of this interval transistor S₁ will start at conducting. Refer Figure E for better understanding.

Interval II (t₁ –  t₂) :

S₁ is turned on at instant t₁, the load voltage is equal to + V / 2 and the positive load current increases generally. At Instant the load current reaches the peak value. The thyristor S₁ is turned off at this instant. Due to the same polarity of load voltage and load current the energy is stored by the load. Refer Figure A.

Figure A

Figure B

Interval III (t₂ – t₃) :

Due to inductive load the load current direction will be maintained same even after S₁, is turned off. The self induced voltage across the load will be negative. The load current flows through lower half of the supply and D₂ as shown in Figure B. In this interval the stored energy in load is fed back to the lower half of the source and the load voltage is clamped to – V / 2.

Interval IV (t₃ – t₄) :

At the instant t₃,  the load current goes to zero, indicating that all the stored energy has been returned back to the lower half of supply. At instant t₃,S₂ is turned on. This will produce a negative load voltage v₀
 = – V /
2 and a negative load current load current reaches a negative peak at the end of this interval ( See (Figure C).

Figure C

Figure D

Interval I (t₄ to t₅) or (0 to t₁) :

• Thyristor S₂ is turned off at instant t₄. The self induced voltage in the inductive load will maintain the load current. 
• The load voltage changes its polarity to become positive V / 2. load current remains negative and the energy stored in the load is returned back to the upper half of the dc source ( see Figure D).
• At t₅, the load current goes to 0 and S₁ can be turned on again. The cycle of operation repeats.

Note : The output voltage waveform remains square with purely resistive or Rl type of load. 

• Conduction period of the thyristors depends upon the load power factor. For purely inductive load, a thyristor conducts only for T₀ / 2 or 90°. Depending on the load power factor, the conduction period of a thyristor wil vary between 90° to 180° (180° for purely resistive load). 

Waveforms of Half Bridge Inverter with Inductive Load :

• The voltage and current waveforms for RL load are at shown in Figure E.

Figure E