A method of controlling RF power delivered from a bipolar electrosurgical instrument into a biological tissue. The method comprises controlling the profile of a RF waveform by: setting a maximum voltage limit for a voltage applied across the bipolar electrosurgical instrument； calculating a tissue resistance, the calculating step including a correction for an impedance associated with the RF channel； determining an objective tissue current limit from the calculated tissue resistance and a predetermined power dissipation target； and dynamically adjusting the current limit based on the determined objective tissue current limit. This control method may ameliorate the impact of an increased cable length on the accuracy of control of RF waveforms delivered to the tip of the probe.
