Abstract: A method and system for detecting the negative sequence of three phase grid-connected inverter systems utilizes, for example, computer hardware and/or computer software to remove a direct current component from a direct-axis current feedback for a three phase current of the inverter system to yield a pure alternating current waveform signal. A first low pass filter eliminates high frequency noise from the alternating current waveform signal while passing a negative sequence signal. The filtered signal is rectified to an absolute value, and a second low pass filter flattens the rectified signal to an output signal that is indicative of the magnitude of the negative sequence current.

Abstract: A method and system for detecting the negative sequence of three phase grid-connected inverter systems utilizes, for example, computer hardware and/or computer software to remove a direct current component from a direct-axis current feedback for a three phase current of the inverter system to yield a pure alternating current waveform signal. A first low pass filter eliminates high frequency noise from the alternating current waveform signal while passing a negative sequence signal. The filtered signal is rectified to an absolute value, and a second low pass filter flattens the rectified signal to an output signal that is indicative of the magnitude of the negative sequence current.

Abstract: An inverter circuit (10) has a plurality of voltage source inverters (VSI) coupled in parallel. Each of the voltage source inverters are coupled to a load (14). A synch signal source (12) generates a square wave from a fundamental operating frequency. The square wave generated by the synch signal source (12) is coupled to each voltage source inverter (VSI). Each voltage source inverter VSI has a timer counter (22), a microprocessor (26), and an inverter (32). The timer counter (22) is preferably a triangle wave generator that corresponds to the time since a rising edge of a synch signal (18) The microprocessor (26) samples the cyclic output signal (24) and determines a phase angle for the voltage source inverter. The phase angle and the voltage magnitude are provided to the inverter (32). The inverter (32) provides an output signal to the load that has the same phase angle as the outputs of the other phase inverters.

Abstract: A method for transmitting phase angle information between inverters in a parallel connected inverter system to synchronize the phase angles of the inverters includes transmitting a common phase angle signal to server inverters. The common phase angle signal is a function of the phase angle of a master inverter. The common phase angle signal is indicative of the absolute phase angle of the master inverter when the phase angle of the master inverter is equal to a phase angle value associated with a new phase cycle. The common phase angle signal is indicative of an incremental phase angle change of the phase angle of the master inverter in a given time period while the phase angle of the master inverter is different from the value associated with a new phase cycle. The server inverters control their phase angles in accordance with the common phase angle signal such that the phase angles of the master inverter and the server inverters are synchronized.