Method and apparatus for impedance matching in virtual impedance droop controlled power conditioning units

An apparatus for setting a virtual impedance ratio of a power conditioning unit (PCU), comprising:

• a controller, comprising at least one central processing unit, for (i) applying a disturbance to a virtual AC voltage of the power conditioning unit (PCU), the PCU operating in a virtual impedance droop control mode in which the PCU appears, from the perspective of a power grid coupled to the PCU, as a virtual AC voltage source in series with a virtual impedance;
• (ii) measuring the phase of the applied disturbance on the power grid;
• (iii) comparing the measured phase of the applied disturbance on the power grid to the phase of the disturbance;
• and (iv) adjusting, when the measured phase of the applied disturbance on the power grid differs from the phase of the disturbance by more than a threshold amount, a ratio of a resistive impedance of the virtual impedance to an inductive impedance of the virtual impedance.

A system for setting a virtual impedance ratio of a plurality of power conditioning units (PCUs), comprising:

• a plurality of DC power sources;
• and
• the plurality of PCUs coupled to the plurality of DC power sources in a one-to-one correspondence, wherein each PCU of the plurality of PCUs is operating in a virtual impedance droop control mode in which the PCU appears, from the perspective of a power grid coupled to the PCU, as a virtual AC voltage source in series with a virtual impedance, and wherein each PCU of the plurality of PCUs comprises a controller, comprising at least one central processing unit, for (i) applying a tone voltage to a virtual AC voltage of the PCU;
• (ii) measuring the phase of the applied tone voltage on the power grid;
• (iii) comparing the measured phase of the applied tone voltage on the power grid to the phase of the tone voltage;
• and (iv) adjusting, when the measured phase of the applied tone voltage on the power grid differs from the phase of the tone voltage by more than a threshold amount, a ratio of a resistive impedance of the virtual impedance to an inductive impedance of the virtual impedance.