Pump system

1 . A pump system, comprising:

a first pump having a first inlet and a first outlet;

a second pump having a second inlet and a second outlet, wherein the second pump is arranged in parallel with the first pump, and the first inlet and the second inlet are for fluidically coupling to one or more fluid reservoirs;

a control system coupled to the first pump and the second pump for controlling the operation of the first pump and the second pump simultaneously,

wherein the control system is configured to:

measure a value of a first pressure head at the first outlet;

measure a value of a second pressure head at the second outlet;

control the first pump to achieve a required output; and

control the second pump by providing a demand for the second pump to achieve a measured value of the second pressure head which equals the measured value of the first pressure head.

2 . The pump system according to claim 1 , further comprising a fluid chamber downstream of the first outlet and the second outlet and to be fed by both the first pump and the second pump, and wherein the control system is further configured to:

measure a third pressure head at the fluid chamber; and

control the first pump by providing a demand for the first pump to achieve a measured value of the third pressure head which equals a required value of the third pressure head.

3 . The pump system according to claim 2 , wherein the control system includes a first proportional and integral controller for setting the demand to the first pump, wherein the first proportional and integral controller has as inputs the measured value of the third pressure head and the required value of the third pressure head.

4 . The pump system according to claim 1 , wherein the control system includes a second proportional and integral controller for setting the demand to the second pump, wherein the second proportional and integral controller has as inputs the measured value of the second pressure head and the required value of the second pressure head.

5 . The pump system according to claim 3 , wherein first and/or second proportional and integral controllers each have a lag-lead filter to achieve pole-zero cancellation.

6 . The pump system according to claim 1 , further comprising a first non-return valve between the first outlet and the fluid chamber, and a second non-return valve between the second outlet and the fluid chamber.

7 . The pump system according to claim 1 , wherein the first pump and the second pump are substantially identical.

8 . The pump system according to claim 1 , further comprising a plurality of the second pumps each arranged in parallel with the first pump, wherein each second pump has a respective second outlet and a respective second inlet, each second inlet for fluidically coupling to the fluid reservoir(s), wherein the control system is coupled to each of the second pumps for controlling the second pumps simultaneously, and wherein the control system is further configured to:

measure a value of a respective second pressure head at each respective second outlet; and

control each of the second pumps by providing a demand for the respective second pump to achieve a measured value of the respective second pressure head which equals the measured value of the first pressure head.

9 . The pump system according to claim 1 , wherein the first and second pumps are each rotary pumps.

10 . The pump system according to claim 9 , wherein the first and second pumps are each centrifugal pumps.

11 . A fluid delivery system comprising:

the pump system according to claim 1 ; and

a fluid reservoir fluidically coupled to the first inlet and the second inlet.

12 . The fuel system comprising the fluid delivery system according to claim 11 , wherein the fluid reservoir is a liquid fuel tank and the pump system is for delivering liquid fuel to a combustor.

13 . The fuel system according to claim 12 , wherein the fuel system is an aircraft fuel system and the liquid fuel tank is a liquid hydrogen fuel tank for feeding to an aircraft propulsion engine.

14 . A method of operating a pump system, the pump system comprising a first pump having a first inlet and a first outlet, a second pump having a second inlet and a second outlet, wherein the second pump is arranged in parallel with the first pump, wherein the first inlet and the second inlet are fluidically coupled to one or more fluid reservoirs, the method comprising:

measuring a value of a first pressure head at the first outlet;

measuring a value of a second pressure head at the second outlet;

controlling the first pump to achieve a required output; and

controlling the second pump by providing a demand for the second pump to achieve a measured value of the second pressure head which equals the measured value of the first pressure head such that the first pressure head and the second pressure head are the same in steady-state.

15 . A pump system, comprising:

a first pump having a first inlet and a first outlet;

a second pump having a second inlet and a second outlet, wherein the second pump is arranged in parallel with the first pump, and the first inlet and the second inlet are for fluidically coupling to one or more fluid reservoirs;

a control system coupled to the first pump and the second pump for controlling the operation of the first pump and the second pump simultaneously,

wherein the control system is configured to:

measure a value of a first pressure head at the first outlet;

measure a value of a second pressure head at the second outlet;

control the first pump to achieve a required output; and

control the second pump by providing a demand for the second pump based on a calculated pressure discrepancy between the measured value of the first pressure head and the measured value of the second pressure head, to achieve a measured value of the second pressure head which equals the measured value of the first pressure head.