Grid connectable inverter with ripple control signal rejection

Abstract Power inverters that are connected to the grid and which tend to shunt the grid's ripple control signal will have an adverse effect upon the ripple control system as they may attenuate the control signal below the relay sensitivity of devices such as hot water heaters. In order to address this problem there is provided a switch mode device having an output terminal for connection to an electrical network conveying a first signal of predetermined frequency and a second signal of a frequency falling within a predetermined range, the switch mode device being configured to produce a signal at the predetermined frequency at the output terminal and including: a processor coupled to a current sensor for sensing current through the terminal and arranged to cause switching of output switches coupled to said terminal; and a memory storing a firmware product including instructions for execution by the processor, to determine the second signal, and instructions to cause the processor to operate the output switches to apply an anti-phase version of the second signal to the terminal. +Dc Source - C1 L 1 L2 point of Coupling -Dc Source Figure 4 Network voltatge (235 V rms typical) + Ripple control signal 1-12V rms Current Coupling impedance (0.15 Ohm @ 50 Hz) Inverter measurement (approaches infinity as the current at 281 Hz is reduced towards zero @ 281 Hz)) Figure 5