US Patent 7031176 Inverter

In a system for the conversion between DC power and AC power, including a buffercapacitor and a controllable converting arrangement, said conversion is controlled by a power control quantity that in turn depends on a first component assuring a balance between DC power and AC power and a second component indicating a change in energy stored in the buffer capacitor on a predetermined sampling time instant in the cycle of the voltage ripple on the buffer capacitor.