Abstract: A zero-sequence current balancer for a controlling zero-sequence current in a three-phase power system includes a zig-zag transformer coupled to the three-phase power system, an inverter coupled to an output of the zig-zag transformer, and at least one of: (i) a clamp device operating as a normally open switch, the clamp device being provided in between the output of the zig-zag transformer and a neutral conductor (which may be grounded) and being connected in parallel with the inverter, and (ii) a load-break switch provided between the output end of the zig-zag transformer and an input of inverter. A controller is structured and configured to detect a fault condition in the three-phase power system, and in response cause at least one of the closing of the clamp device or the opening of the load-break switch in order to protect the system.

Abstract: A zero-sequence current balancer for a controlling zero-sequence current in a three-phase power system includes a cascade multilevel modular inverter (CMMI) coupled to the three-phase power system, wherein the CMMI has a plurality of modules, each module having a module capacitor, and a real power injector circuit provided between the three-phase power system and the CMMI, wherein the real power injector circuit is structured and configured to cause real power to injected into and/or absorbed from the CMMI to regulate a voltage of one or more of the module capacitors.

Abstract: A zero-sequence current balancer for a controlling zero-sequence current in a three-phase power system includes a cascade multilevel modular inverter (CMMI) coupled to the three-phase power system, wherein the CMMI has a plurality of modules, each module having a module capacitor, and a real power injector circuit provided between the three-phase power system and the CMMI, wherein the real power injector circuit is structured and configured to cause real power to injected into and/or absorbed from the CMMI to regulate a voltage of one or more of the module capacitors.

Abstract: In a three-phase, four-wire electrical distribution system, a zig-zag transformer and at least one Cascade Multilevel Modular Inverter (CMMI) is coupled between the distribution system and the neutral. A controller modulates the states of the H-bridges in the CMMI to build an AC waveform. The voltage is chosen by the controller in order to control an equivalent impedance that draws an appropriate neutral current through the zig-zag transformer. This neutral current is generally chosen to cancel the neutral current sensed in the line. In other embodiments, the chosen neutral current may be based on a remotely sensed imbalance, rather than on a local value, determined by the power utility as a critical load point in the system. The desired injection current is then translated by the controller into a desired zero-sequence reactive impedance, based on measurement of the local terminal voltage, allowing the controller to regulate the current without generating or consuming real power.