Bi-directional multi-port inverter with high frequency link transformer

Abstract

This invention is a multi-port power converter where all ports are coupled through different windings of a high frequency transformer. Two or more, and typically all, ports have synchronized switching elements to allow the use of a high frequency transformer. This concept and type of converter is known. This invention mitigates a number of limitations in the present art and adds new capabilities that will allow applications to be served that would otherwise not have been practical. A novel circuit topology for a four-quadrant AC port is disclosed. A novel circuit topology for a unidirectional DC port with voltage boost capabilities is disclosed. A novel circuit topology for a unidirectional DC port with voltage buck capabilities is disclosed. A novel circuit for a high efficiency, high frequency, bi-directional, AC semiconductor switch is also disclosed.

1. A power converter apparatus comprising three or more ports, a transformer and a control circuit where one end of each port is connected to a distinct winding on a common transformer core and where the remaining end of each port is connected to a load or power source and where each port comprises an arrangement of capacitive or inductive energy storage elements and semiconductor switches where individual semiconductor switches are commanded on and off by said control circuit in a synchronous manner with semiconductor switches in other ports and where said power converter apparatus is further defined, as having one port dedicated to a storage battery, designated for reference herein as the battery port, having characteristics different from all other ports, specifically, semiconductor switches in the battery port operate in a free-running mode and provide frequency and phase references that are followed by synchronous switches in all remaining ports and the interface at the battery port transformer winding is that of a low impedance AC voltage source or sink, whereas the interface at the transformer windings of all other ports is that of a high impedance AC current source or sink and where these two distinct port types, battery and non-battery, enable energy transfer into or out of all non-battery ports simultaneously and in an autonomous manner in terms of energy transfer and where the net energy into or out of all non-battery ports charges or discharges the storage battery, respectively, via the battery port. 
     
     
       2. A power conversion method using a transformer comprising a first winding, a second winding, and a third winding, a first switching circuit coupled to the first winding and to first terminals coupled to a photovoltaic array, the first switching circuit including a buck regulator providing unidirectional energy flow from the photovoltaic array to the transformer, a second switching circuit coupled to the second winding and to second terminals for connection to a battery, and a third switching circuit coupled to the third winding and to third terminals for connection to an AC power source connected to a utility grid or to a load, the method comprising:
 controlling the first, second and third switching circuits by switching the first, second and third switching circuits at a frequency much greater than a frequency of the utility grid such that at least some of the time, the first, second, and third switching circuits are all active, with switching of the first, second and third switching circuits being synchronized with respect to each other and such that when the second switching circuit is active to provide energy from the battery, a voltage across the battery is provided to the second winding; and   selectively activating the buck regulator to cause unidirectional energy to flow from the photovoltaic array to the transformer such that when the first switching circuit is active no energy flows from the transformer back to the photovoltaic array, wherein the buck regulator includes a capacitor and a parallel-connected diode connected across the photovoltaic array, a unidirectional semiconductor switch, and an inductor connected in series with the first winding, wherein the selectively activating causes current from the photovoltaic array to be converted to a corresponding voltage at the capacitor of the buck regulator and then converted to a corresponding current via the inductor of the buck regulator and provided to the first winding.   
     
     
       3. The power conversion method of claim 2, comprising switching the third switching circuit in accordance with a varying duty cycle so as to produce a line-frequency power waveform. 
     
     
       4. The power conversion method of claim 2, comprising controlling the first switching circuit so as to supply power to the transformer. 
     
     
       5. The power conversion method of claim 2, comprising controlling the second switching circuit so as to, at one time, supply power to the transformer and to, at another time, be supplied power from the transformer. 
     
     
       6. The power conversion system of claim 2, comprising controlling the third switching circuit so as to perform boost regulation. 
     
     
       7. The power conversion method of claim 2, comprising controlling the third switching circuit so as to, at one time, supply power to the transformer and to, at another time, be supplied power from the transformer. 
     
     
       8. The power conversion method of claim 2, comprising coupling the battery coupled to the second terminals. 
     
     
       9. The power conversion method of claim 2, comprising coupling the third terminals to the load or to the utility grid. 
     
     
       10. The power conversion method of claim 2, wherein the frequency of the switching of the first, second and third switching circuits is at an ultrasonic frequency or greater.