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 “12-pulse converters” 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 𝛼1 = 𝛼2 = 𝛼.  The center-tapped inductor absorbs the instantaneous voltage difference between 𝑉𝑜1 and 𝑉𝑜2. In general, dual parallel converter gives,  Higher DC current output  Higher ripple-frequency in output voltage  Lesser THD at the supply side AC current

Mean inductor-voltage is zero and hence,

Ripple in 𝑉 𝑜 has a frequency of  12𝑓 𝑠 as in the series converter.  Amplitude of ripple is 50% of that produced by an individual bridge.  Both are desirable outcomes.

𝐼𝑜 = 𝐼𝑜1 +𝐼𝑜2  

Thus, output current is greater. Input current  𝐼𝐴 at the utility side is a stepped sine waveform as in the series converter, having only   12𝑘 ±1 𝑡𝑕 order of harmonics, where 𝑘 = 1,2,3…. (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  𝐼𝑜 by making  𝐼𝑜2 greater or lesser than 𝐼𝑜1, 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, 

𝑉𝑜2 𝑚𝑒𝑎𝑛 + 𝑉𝑜1 𝑚𝑒𝑎𝑛 = 0

This means the dual inverse-parallel converter should be operated complying the condition  𝛼2 +𝛼1 = 180°.

In the steady state,

𝑉 𝑜 𝑚𝑒𝑎𝑛 is positive when 𝛼2 < 90° or negative when 𝛼2 > 90°.  (𝛼1 is determined by 𝛼2).  𝐼𝑜 is determined by the load but set by the relative values of 𝐼𝑜2 and 𝐼𝑜1.  It is positive when 𝐼𝑜2 > 𝐼𝑜1 or negative when 𝐼𝑜2 < 𝐼𝑜1 or zero when 𝐼𝑜2 = 𝐼𝑜1. 

The load can either consume or regenerate real power depending on the product  𝑉 𝑜 𝑚𝑒𝑎𝑛𝐼𝑜.  Positive product means consuming, negative product means regenerating or zero product means idling.

Contributions to the fundamental component of  𝐼𝐴 at utility side by bridge-2 and bridge-1, assuming utility phase-A voltage as 𝑉𝐴 = 𝑉𝑚 sin𝜔𝑡, are:

Using this expression of 𝐼𝐴,𝐹𝑢𝑛𝑑 , we can determine the input Displacement Angle and input DisF.  For example, when 𝐼𝑜2 = 𝐼𝑜1,  𝐼𝐴,𝐹𝑢𝑛𝑑 is 90° lagging behind 𝑉𝐴, indicating zero DisF.  

We can show,

Assignment:  dual parallel bridge converter

Drive mathematical expressions for  𝑉 𝑜 𝑚𝑒𝑎𝑛 , 𝐷𝑖𝑠𝐹 and associated  𝑢𝑇s 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 𝑉𝐿 .  Net internal inductance on d-winding is  𝐿𝑠2 and that on y-winding is 𝐿𝑠1.  Delay angles for bridge-2 and bridge-1 are  𝛼2 and 𝛼1, respectively. 

(i) Dual series-bridge converter with constant load current 𝐼𝑜 with concurrent control. (ii) Dual series-bridge converter with constant load current 𝐼𝑜 with sequential sub-mode 1 control. (iii) Dual series-bridge converter with constant load current 𝐼𝑜 with sequential sub-mode 2 control (inverter mode operation). (iv) Dual parallel-bridge converter with constant load current 𝐼𝑜 with concurrent control and equal sharing of current. (v) Dual inverse-parallel-bridge converter with constant load current 𝐼𝑜 with bridge-2 current  𝐼𝑜2 and bridge-1 current 𝐼𝑜1. 

You may use appropriate standard expressions for the relevant cases without internal inductances and modify them to account the effects of  𝐿𝑠2 and 𝐿𝑠2, giving reasons.

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

Reference

1. Page
2. Page