Hi Sharath, PPM is equivalent to mg per litre, here goes the calculation.
NPK 5:15:30 means that your fertilizer is 5 % N, 15 % P and 30 % K and the remaining 50 % is binding material which ideally should be inert.
1 gram (g) is 1000 milligram (mg)
therefore 1 g fertilizer contains 50 mg N, 150 mg P and 300 mg K.
Now, PPM stands for parts per million,
i.e a solution with a concentration of 1 ppm has 1 part of the solute in a million parts of solvent.
therefore a 1ppm fertilizer solution is a solution of 1mg fertilizer in 1 million mg of water,
1 million mg of water is 1000 g which is 1 litre.
So if you dissolve 1 g of your fertilizer in 1 litre of water you will have 50 ppm N, 150 ppm P and 300 ppm K.
I usually fertilize my plants with a balanced fertilizer which is 200 ppm of each NPK ( 1g 20:20:20 in 1 litre water.)