Valves
An apparatus ( 10 ) for compressing and expanding a gas includes a chamber ( 22 ), a positive displacement device ( 24 ) moveable relative thereto, first and second valves ( 26, 28 ) activatable to control flow of gas into and out of the chamber ( 22 ), and a controller ( 80 ) for controlling activation of the valves ( 26, 28 ) that selectively switches operation between a compression and an expansion mode with selective switching between modes being achieved by selectively changing the activation timing of at least one of the valves during the first mode. An energy storage system including the device may be operatively coupled via a rotary device for power transmission to an input/output device, whereby the direction and speed of rotation are preserved during switching, and the input/output device may be synchronized to the grid.
1. A method of gas compression and expansion, the method comprising:
receiving a gas in a chamber for which first and second valves are operable to control gas flow into and out of the chamber; and
selectively changing, with a controller, an activation timing of at least one of the first and second valves to selectively switch operation of a positive displacement device moveable relative to the chamber between a compression mode in which the gas received in the chamber is compressed by the positive displacement device and an expansion mode in which the gas received in the chamber is expanded by the positive displacement device, wherein the activation timing is changed during the operation of the positive displacement device in one of the compression and expansion modes.
2. The method according to claim 1 , further comprising:
transmitting, via the positive displacement device being coupled to a rotary device, mechanical power between the positive displacement device and an input/output device; and
selectively switching, via the controller, from one of the compression and expansion modes to the other of the compression and expansion modes of operation whilst the rotary device continues to move in a predetermined direction associated with the one of the compression and expansion modes.
3. The method according to claim 2 , further comprising switching of a grid synchronised motor/generator of the input/output device between operation as a motor and a generator during a switch between the compression and expansion modes, without losing grid synchronisation.
4. The method according to claim 1 , further comprising selectively connecting, via the first and second valves, the chamber to either a high pressure region or a low pressure region.
5. The method according to claim 4 , further comprising allowing only one of the low pressure and high pressure regions to be connected to the chamber at any one time.
6. The method according to claim 1 , further comprising:
opening at least one of the first and second valves when gas pressures on either side of said at least one valve are equal; and
altering, via the controller, a valve closure timing of said at least one valve to selectively switch from the one of the compression and expansion modes to the other of the compression and expansion modes.
7. The method according to claim 6 , further comprising self-opening of at least one of the first and second valves when gas pressures on either side of said at least one valve are equal.
8. The method according to claim 1 , further comprising reversing, upon switching between the compression and expansion modes, functions of the first and second valves such that the gas flows in a reversed direction.