A total of 21 people have been arrested in connection with the protest. All three officers were later released from hospital.
"A total of three officers were injured at the scene of the protest," police said in a statement.
Organisers Camp for Climate Action earlier said more than 1,000 people were taking part in the two-day protest.
Hundreds of these were peacefully protesting by the front gate, while others were trying to "take down the fences so people can enter the site... and stop the power station," spokeswoman Kate Walker told AFP.
A spokeswoman for German energy giant E.ON, which owns the plant, estimated that around 500 people had gathered there, saying many were peaceful but some were trying to cut the fence with bolt cutters or bring it down with ropes.
"Police officers stationed at the perimeter of Ratcliffe-on-Soar power station are facing groups of protesters, around 50-strong in places, trying to gain entry to the site," a police spokeswoman said.
"A breach of the fence line has now been secured and a number of further arrests have been made," she added.
Walker said at least three people had managed to get through the fence before being arrested.
The protesters targeted the Ratcliffe plant because it is one of the largest producers of carbon dioxide, which contributes to global warming, in Britain.
"We want to take control of Ratcliffe this weekend because we believe its time to start imagining a future without coal," Walker said.
E.ON spokeswoman Emily Highmore told AFP it was "incredibly irresponsible" to break into a working power plant.
She said E.ON was already closing three of its other oil and coal-fired power stations in Britain and had invested in renewable energy, but had a duty to keep providing power to the two million people served by Ratcliffe.
-------------------------------------------------------------------------------------------------------------------------------