# 3-phase dual parallel-bridge converter with inductive load

The dual parallel bridge converter with suitable examples and sketches are discuss here advanced. dual parallel bridge converter is needed to read.

Dual full-bridge converter uses two nos. of full-bridge converters in series or parallel.  These converters are called β12-pulse convertersβ because there are 12 thyristors, each requiring a separate trigger pulses.

Series-converter gives a higher output voltage and the parallel converter gives higher output current.  Per unit voltage-ripple at the output is lesser for both types.

Dual converter produces an input current having 12-steps, bringing it more towards the sinusoidal shape.  So, THD of input current is lesser.   Because of these reasons, most high power converters prefer dual-bridge arrangement.

## (i)  Dual Ordinary Parallel Converter

Two bridges are operated concurrently with πΌ1 = πΌ2 = πΌ.  The center-tapped inductor absorbs the instantaneous voltage difference between ππ1 and ππ2. In general, dual parallel converter gives, ο· Higher DC current output ο· Higher ripple-frequency in output voltage ο· Lesser THD at the supply side AC current

Mean inductor-voltage is zero and hence,

Ripple in π π has a frequency of  12π π  as in the series converter.  Amplitude of ripple is 50% of that produced by an individual bridge.  Both are desirable outcomes.

πΌπ = πΌπ1 +πΌπ2

Thus, output current is greater. Input current  πΌπ΄ at the utility side is a stepped sine waveform as in the series converter, having only   12π Β±1 π‘π order of harmonics, where π = 1,2,3β¦. (assuming equal current sharing).

• Dual Inverse Parallel Converter

An alternative version of dual parallel converter is obtained when the two bridges are connected in inverse parallel.  In this case, we can give either positive or negative  πΌπ by making  πΌπ2 greater or lesser than πΌπ1, respectively.  So, the load can absorb or regenerate real power, offering true 4-quadrant operation.

Since the mean voltage across the inductor is zero, using KVL,

ππ2 ππππ + ππ1 ππππ = 0

This means the dual inverse-parallel converter should be operated complying the condition  πΌ2 +πΌ1 = 180Β°.

π π ππππ is positive when πΌ2 < 90Β° or negative when πΌ2 > 90Β°.  (πΌ1 is determined by πΌ2).  πΌπ is determined by the load but set by the relative values of πΌπ2 and πΌπ1.  It is positive when πΌπ2 > πΌπ1 or negative when πΌπ2 < πΌπ1 or zero when πΌπ2 = πΌπ1.

The load can either consume or regenerate real power depending on the product  π π πππππΌπ.  Positive product means consuming, negative product means regenerating or zero product means idling.

Contributions to the fundamental component of  πΌπ΄ at utility side by bridge-2 and bridge-1, assuming utility phase-A voltage as ππ΄ = ππ sinππ‘, are:

Using this expression of πΌπ΄,πΉπ’ππ , we can determine the input Displacement Angle and input DisF.  For example, when πΌπ2 = πΌπ1,  πΌπ΄,πΉπ’ππ is 90Β° lagging behind ππ΄, indicating zero DisF.

We can show,

## Assignment:  dual parallel bridge converter

Drive mathematical expressions for  π π ππππ , π·ππ πΉ and associated  π’πs for the following dual full-bridge thyristor converters.  Take a Dd0y1 three-phase transformer to feed two bridges with bridge-2 connected to d-winding and bridge-1 to y-winding.  Each output of the transformer is having equal rms line-voltage ππΏ .  Net internal inductance on d-winding is  πΏπ 2 and that on y-winding is πΏπ 1.  Delay angles for bridge-2 and bridge-1 are  πΌ2 and πΌ1, respectively.

(i) Dual series-bridge converter with constant load current πΌπ with concurrent control. (ii) Dual series-bridge converter with constant load current πΌπ with sequential sub-mode 1 control. (iii) Dual series-bridge converter with constant load current πΌπ with sequential sub-mode 2 control (inverter mode operation). (iv) Dual parallel-bridge converter with constant load current πΌπ with concurrent control and equal sharing of current. (v) Dual inverse-parallel-bridge converter with constant load current πΌπ with bridge-2 current  πΌπ2 and bridge-1 current πΌπ1.

You may use appropriate standard expressions for the relevant cases without internal inductances and modify them to account the effects of  πΏπ 2 and πΏπ 2, giving reasons.

The dual parallel bridge converter with suitable examples and sketches are discuss here advanced. dual parallel bridge converter is needed to read.