A ferroresonant transformer is adapted to be connected to a primary power source, an inverter system, and a resonant capacitor. The ferroresonant transformer comprises a core, a main shunt arranged to define a primary side and a secondary side of the ferroresonant transformer, first windings arranged on the primary side of the ferroresonant transformer, second windings arranged on the secondary side of the ferroresonant transformer, and third windings arranged on the secondary side of the ferroresonant transformer. The first windings are operatively connected to the primary power source.

An uninterruptible power supply (UPS) and methods of operation are provided. The UPS includes a transformer configured to receive power from a utility. The transformer includes a primary winding, a secondary winding, and a tertiary winding. The UPS also includes a rectifier coupled to the secondary winding and an inverter coupled to an output of the rectifier, wherein a connection between the rectifier and the inverter defines a DC link. The inverter is configured to output a first regulated voltage configured to be provided to a load. The UPS further includes a voltage-boost converter coupled to the tertiary winding and is configured to output a second regulated voltage to be combined with the first regulated voltage.

A UPS control circuit and a UPS is provided. The UPS includes a rechargeable battery and a UPS control circuit connected with the rechargeable battery. The UPS control circuit includes an input filtering circuit, a rectification circuit, an inversion circuit, a static transfer switch, an output filtering circuit, a control circuit, and a multipurpose DC/DC circuit connected between the rechargeable battery and an output terminal of the rectification circuit. The multipurpose DC/DC circuit is controlled by the control circuit. In a battery mode, the rechargeable battery supplies an input voltage to the inversion circuit via the multipurpose DC/DC circuit. In a mains power mode, the rechargeable battery is charged by an output voltage of the rectification circuit via the multipurpose DC/DC circuit. Therefore, no independent charging circuit is needed to charge the rechargeable battery, causing a simpler circuit structure and a lower cost, and providing greater value to the customer.

A switch-mode power supply that includes a transformer coupled to an alternating current (AC) power source and a direct current (DC) power source, wherein the AC power source is electrically isolated from the DC power source. The switch-mode power supply further includes a first controller configured to regulate a first voltage output from the AC power source, and a second controller configured to regulate a second voltage output from the DC power source when the transformer is not receiving power from the AC output.

The present disclosure provides a method for maintaining continuous power to a critical load. The method comprises providing a source side converter (SSC) configured to provide autonomous grid support including reactive power support during fault conditions and a load side converter (LSC) configured to support the critical load by boosting voltage at load terminals through autonomous injection of reactive current, each coupled to a DC energy storage. The method includes coupling the SSC to an AC source and coupling the LSC to the critical load. The AC source and the critical load are connected via a bypass connection including a ride-through inductor with measurement capability. Under nominal source conditions, the SSC and the LSC are controlled so that a majority of power consumed by the critical load flows through the bypass connection. The method involves monitoring electrical parameters of the bypass connection and compensating for critical load variations using either the SSC or LSC or both based on bypass connection measurements.