Bi-directional multi-port inverter with high frequency link transformer
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.
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The field of this invention is power electronics and electrical power conversion. Electronic power inverters are devices for converting direct current (DC) power, usually from a storage battery, into alternating current (AC) power for household appliances. Some inverters also convert power from an AC source to charge the storage battery used by the inverter. Devices capable of power transfer in either direction, DC-to-AC or AC-to-DC are commonly referred to as inverter/chargers or bi-directional inverters. Inverters are also used in renewable and distributed energy systems to convert DC power from photovoltaic panels, fuel cells or wind turbines into power that can be delivered into the utility grid. There is a growing demand for an inverter product with this capability that can also charge storage batteries and support AC loads when the utility grid is not available. Residential systems with both renewable energy sources and energy storage components typically use a battery-centric topology. This is because the battery provides a stable voltage and high peak power capabilities. In these systems, the renewable energy source interfaces to the battery through a DC-to-DC converter or charge controller to provide the required matching and regulation functions. The battery is in turn connected to a DC-to-AC inverter, to support the system loads, and to a battery charger. Additional energy sources as well as DC loads would also logically tie in at the storage battery connection point. With the present state of technology, this arrangement typically provides the most cost effective and highest performance system solution. There are a number of inherent limitations with this approach. (i) The storage battery voltages are relatively low compared to the AC voltages that the inverter produces. A common power conversion method is to convert the low DC battery voltage into a low AC voltage and then use a transformer to convert to a higher AC voltage. This approach requires a heavy, expensive, and typically inefficient, low frequency transformer. (ii) The conversion efficiency from the renewable energy source to the battery to the utility grid is low because of the additive losses from each successive power conversion stage. (iii) Higher voltage, higher efficiency, lower cost photovoltaic series “string” arrays are not practical because of the photovoltaic/battery voltage disparity. (iv) Individual power converters in battery-centric systems are usually autonomous. It is advantageous for all power converters to act in concert in order to achieve optimum battery life and to better support the system loads.
SUMMARY OF INVENTIONThe invention is a multi-port power electronics topology, with a high frequency transformer as the common power “conduit” and interface point for all ports. This invention would allow for energy systems that are high-frequency-transformer-core-centric as opposed to battery-centric. This invention mitigates essentially all of the limitations of battery-centric energy systems. The underlying power converter concept used for this invention was originally invented by William McMurry and disclosed in U.S. Pat. No. 3,517,300 in 1970. Since then, others have expanded the potential capabilities of these power converters but with less-than-novel or with technically obvious variations on the original McMurry invention. The invention disclosed herein involves a number of novel power circuit topologies that allow much greater port flexibility and provide enhanced performance. The invention allows a port to perform as a boost or buck converter when sourcing power into the high frequency transformer, a capability that has not been previously established. These added capabilities allow applications to be served that would otherwise not have been practical. Also, the invention allows each non-battery port to “see” only the reflected battery characteristics at the transformer interface so that the operation of all non-battery ports are independent and non-interactive. The preferred embodiment of the invention is intended for residential electrical energy systems. There are three ports; a bi-directional battery port that allows a storage battery to source energy to the transformer or sink energy from the transformer to charge the battery, a bi-directional AC port that allows the transformer to source energy to loads and also to sink or source energy from a utility grid at unity power factor, and a renewable energy port that sources energy into the transformer and is capable of controlling the operating point of the renewable energy source and the amount of power delivered into the transformer. Products developed using this invention will be (i) lighter because transformers operating at ultrasonic frequencies are much smaller than line frequency transformers (ii) lower cost because of the smaller transformer and the system-integrated power conversion approach and (iii) more efficient because of fewer power conversion stages and the lower core and copper losses associated with high frequency transformers. These advantages are had without sacrificing the isolation properties of a transformer.
Claims
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. The power conversion system of claim 1, wherein the third switching circuit is a hybrid switch having first and second switch poles and comprises:
- first and second series MOSFET devices connected in parallel with first and second series IGBT devices between the first and second switch poles;
- a gate driver for driving the first and second series MOSFET devices through a first node between the first and second series MOSFET devices, and through a second node between the first and second series IGBT devices.
3. A power conversion system comprising:
- 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 for connection to a DC power source;
- a buck regulator coupled to the first winding and having a diode, inductor and a switch;
- a second switching circuit coupled to the second winding and to second terminals for connection to an electrical power storage device; and
- a third switching circuit coupled to the third winding and to third terminals for connection to an AC power source or load,
- a boost circuit coupled to the third winding and having an inductor and a switch; and
- a control circuit for controlling the first, second and third switching circuits 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.
4. The power conversion system of claim 3, wherein the control circuit is configured to switch the third switching circuit so as to produce a line-frequency power waveform.
5. The power conversion system of claim 3, wherein the first switching circuit is configured to perform boost regulation.
6. The power conversion system of claim 3, wherein the first switching circuit comprises:
- a first semiconductor switch coupled to one of the first terminals and to one end of the first winding;
- a second semiconductor switch coupled to the one of the first terminals and to another end of the first winding; and
- a third semiconductor switch coupled to the one of the first terminals, and coupled through a diode to a center tap of the first winding.
7. The power conversion system of claim 6, wherein the first switching circuit comprises an inductor coupled to another one of the first terminals and to the diode so as to conduct current from the first terminal through the diode.
8. The power conversion system of claim 6, wherein the first, second and third semiconductor switches are unidirectional semiconductor switches.
9. The power conversion system of claim 3, wherein the second switching circuit comprises first, second, third and fourth semiconductor switches arranged in an H-bridge configuration.
10. The power conversion system of claim 9, wherein the first, second, third and fourth semiconductor switches are unidirectional semiconductor switches.
11. The power conversion system of claim 3, wherein the third switching circuit is configured to perform boost regulation.
12. The power conversion system of claim 3, wherein the third switching circuit comprises:
- a first semiconductor switch coupled to one of the third terminals and to one end of the third winding;
- a second semiconductor switch coupled to the one of the third terminals and to another end of the third winding; and
- a third semiconductor switch coupled on one side thereof to another one of the third terminals and to a center tap of the third winding, and coupled on another side thereof to the one of the third terminals through an inductor.
13. The power conversion system of claim 12, wherein the first, second and third semiconductor switches are bidirectional.
14. The power conversion system of claim 3, comprising one of a photovoltaic array, a DC generator and a fuel cell coupled to the first terminals.
15. The power conversion system of claim 3, comprising a battery coupled to the second terminals.
16. The power conversion system of claim 3, wherein the third terminals are coupled to a utility grid.
17. A power conversion system comprising:
- 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 for connection to a DC power source;
- a second switching circuit coupled to the second winding and to second terminals for connection to an electrical power storage device; and
- a third switching circuit coupled to the third winding and to third terminals for connection to an AC power source or load;
- a boost circuit having an inductor and a switch; and
- a control circuit for controlling the first, second and third switching circuits 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, wherein the first switching circuit comprises:
- a first semiconductor switch coupled to one of the first terminals and to one end of the first winding;
- a second semiconductor switch coupled to the one of the first terminals and to another end of the first winding; and
- a third semiconductor switch coupled to another one of the first terminals, and coupled through an inductor to a center tap of the first winding.
18. The power conversion system of claim 17, wherein the first switching circuit comprises a diode coupled to the one of the first terminals and to the inductor so as to conduct current flowing through the inductor and through one of said first and second semiconductor switches.
19. The power conversion system of claim 17, wherein the first, second and third semiconductor switches are unidirectional semiconductor switches.
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Type: Grant
Filed: Sep 5, 2008
Date of Patent: Nov 30, 2010
Assignee: Xantrex Technology Inc. (Livermore, CA)
Inventor: Richard T. West (San Luis Obispo, CA)
Primary Examiner: Albert W Paladini
Assistant Examiner: Daniel Cavallari
Attorney: Nixon Peabody LLP
Application Number: 12/205,743
International Classification: H02J 1/00 (20060101);