STATIC SYNCHRONOUS GENERATORS

摘要

The invention is concerned with a device and a method for controlling an inverter associated with a power source, which typically will be a distributed power source. The role of an inverter is to modulate the electrical power output, e.g. to provide a three phase AC electrical output at suitable voltage, where the output is to be supplied to a conventional power distribution, grid. The invention involves modelling the behaviour of a synchronous electrical generator. Variables represent the angular position and rotational speed of the virtual rotor (14) of this virtual synchronous generator. The torque electromagnetically exerted on the rotor is calculated from a measured inverter output current, and from a variable representing excitation current in the rotor. Allowing for this and for a notional drive torque applied to the virtual rotor (which in the physical analogue would be supplied by some prime mover such as an engine), as well as for the virtual inertia of the rotor, the angular speed of the virtual rotor is calculated, Using the angular position and rotational speed of the virtual rotor, and allowing for the aforementioned excitation current, it is possible to obtain the cmf induced in stators of the virtual generator. On this basis a control signal is generated which causes the inverter to produce an AC output corresponding to that which would be provided by the virtual synchronous generator. A synchronous generator must be regulated, as too must the virtual synchronous generator of the present invention. To this end, the invention provides a feedback loop in which deviation of the rotational speed of the virtual generator rotor from a reference angular speed is detected and is used to adjust the virtual drive torque, thereby to regulate the rotational speed of the rotor and hence the frequency of the AC output and the real power supplied by it.