PRIORITY CLAIM TO RELATED APPLICATIONS

This application is a U.S. national stage filing under 35 U.S.C. § 371 from International Application No. PCT/NZ2018/050039, filed on 28 Mar. 2018, and published as WO2018/182432 on 4 Oct. 2018, which claims the benefit under 35 U.S.C. 119 to New Zealand Application No. 730582, filed on 28 Mar. 2017, the benefit of priority of each of which is claimed herein, and which applications and publication are hereby incorporated herein by reference in their entirety.

BACKGROUND

As the uptake of battery powered devices continues to grow around the world, effective charging techniques, which are safe, reliable and convenient, have become a major point of discussion. Traditionally, conductive charging techniques (hard-wired chargers, where a physical connection between a battery and an external energy source, most likely the utility grid) have been used, however these techniques are inconvenient for users, and often raise concerns over user safety and reliability, especially at higher power levels and during harsh weather conditions. Consequently, there has been a shift towards wireless chargers, which are inherently safer, more convenient and lack any physical contacts. Inductive Power Transfer (IPT), which has been used in a wide variety of applications, including powering automated guided vehicles (AGV); materials handling; charging of portable electronic devices and powering biomedical devices and Electric Vehicle (EV) charging, is currently the preferred technology for implementing wireless chargers. This preference is mainly due to the high galvanic isolation and flexibility offered by IPT based wireless chargers while still being able to achieve efficiencies comparable to wired chargers.

The current uptake in IPT charging is highlighted by the introduction of specifications, standards and guidelines for IPT based chargers, which intends to ensure interoperability between various systems. For example, portable communication or computing devices may require multiple different plug arrangement. Another example of particular relevance is electric vehicle (EV) charging in which wire charging techniques suffer from reliability and safety issues at high power levels. To minimise safety concerns for EV's, minimal user input is preferred to initiate the charging process therefore there has been a shift towards wireless charging techniques. Standards such as SAE J2954, provides specification guidelines on the implementation of wireless chargers for EV's. SAE J2954 specifies wireless charging through inductive power transfer (IPT), which is currently the preferred technology for wireless power applications.

IPT systems are capable of transferring very high levels of power through a safe and reliable inductive link. This has led to numerous industrial applications in the past 20 years including factory automation, clean room applications and monorail systems. Furthermore, the inherent safety provided by this technology has also led to many biomedical applications, see for example, G. A. Covic and J. T. Boys, “Modern Trends in Inductive Power Transfer for Transportation Applications,” IEEE Journal of Emerging and Selected Topics in Power Electronics, vol. 1, pp. 28-41, 2013.

The majority of IPT based EV chargers reported to date only allow unidirectional power flow, typically from the utility grid to the EV battery. However, the recent introduction of bidirectional IPT (BD-IPT) technologies not only improves system efficiency and flexibility, but also enables Vehicle to Grid/Grid to Vehicle (V2G/G2V) services. These services, which are expected to become an integral part of future EV charging infrastructure, include the absorption of power variances produced by renewable energy sources, reactive power injection for grid voltage regulation and harmonics absorption for improved power quality. Overall, such services can further enhance the use of renewable energy sources, while also providing an additional revenue stream for EV owners.

Wide-bandgap devices, such as silicon-carbide or gallium-nitride devices, provide the possibility to operate IPT systems at higher frequencies and higher voltages. Furthermore, wide bandgap devices have much lower on state resistances and negligible reverse recovery losses when compared to silicon devices. Thus, IPT systems can benefit from improved power density and efficiency with these devices. More specifically, operating at higher voltages will allow for lowered current in magnetic couplers, hence reducing resistive losses and unwanted heating effects. A higher driving voltage also opens up opportunities to drive multiple series connected couplers or even elongated tracks, which will be beneficial in high power applications such as fast charging and in-motion charging. Existing IPT systems, which utilise conventional switch-mode power converters, lack the capability to utilise wide bandgap devices to their full voltage rating.

This limitation can be mainly attributed to limited supply and output voltages found in typical applications. Increasing the operating voltage of these systems can be a simple, yet expensive solution. For example, additional power converters can be used to boost/buck supply/load voltages, however an increased component count and reduced efficiency lead to an undesired solution.

SUMMARY

An exemplary embodiment includes:A converter comprising:a bridge circuit having a first leg and a second leg, each leg including a high switch and a low switch, the high switches being connected to a first energy source and the low switches being connected to ground;a coupling network(s) having a first connection between the switches of the first leg and a second connection between the switches of the second leg; anda second (or multiple secondary) energy source(s) connected between the coupling network(s) and ground, whereinthe coupling network may comprise a first inductive element connected between the second energy source and the switches of the first leg, and a second inductive element connected between the second energy source and the switches of the second leg.

Another exemplary embodiment includes:

A converter comprising:a bridge circuit having a first leg and a second leg, each leg including a high switch and a low switch, the high switches being connected to a first energy source and the low switches being connected to ground;a coupling network(s) having a first connection between the switches of the first leg and a second connection between the switches of the second leg; anda second (or multiple secondary) energy source(s) connected between the coupling network(s) and ground, wherein:the converter is a boost active bridge converter that includes a capacitor, the capacitor being the first energy source; andthe converter includes a DC energy source having a positive terminal electrically located between the first leg and the second leg, wherein the DC energy source is the second energy source.Another embodiment includes:

A converter comprising:a bridge circuit having a first leg and a second leg, each leg including a high switch and a low switch, the high switches being connected to a first energy source and the low switches being connected to ground;a coupling network(s) having a first connection between the switches of the first leg and a second connection between the switches of the second leg; anda second (or multiple secondary) energy source(s) connected between the coupling network(s) and ground, whereinthe converter is controlled so that there is a difference in DC voltage on the first leg relative to the second leg, wherein the first leg in combination with the second leg converts AC power to DC power or visa-versa.

The first energy source may comprise a capacitor. A separate energy source, for example a capacitor may be provided connected between each high switch and ground.

A third energy source may be connected in parallel with the coupling network (directly or through another coupling network). The third energy source may comprise an AC energy source.

The coupling network comprises one or more inductors (or capacitors) arranged to interface the second (or third) energy source effectively with the first and second legs.

The coupling network may comprise a first inductive element connected between the second energy source and the switches of the first leg, and a second inductive element connected between the second energy source and the switches of the second leg. The first and second inductive elements may be coupled. A third inductive element may be connected between the first and second inductive elements and the second energy source.

A controller is provided to control the switches of the boost active bridge. The controller is also configured to control the duty cycle and/or phase of the switches. The controller may have one or more input control variables as inputs for controlling the switches. Control of the duty cycle of the switches can control two output variables of the converter. The two output parameters can comprise the voltage of each first energy source and the magnitude of the fundamental voltage across the third energy source.

Alternatively, the controller may control the energy transfer between each source to optimise the operation (efficiency and power transfer) of the converter.

The controller may control the duty cycle of the legs symmetrically.

In another aspect the invention may broadly be said to consist in a dual bridge converter comprising two converters according to the preceding statement wherein the AC energy sources are coupled to each other.

In one example the coupled AC energy sources provide isolation.

In one example the AC sources are loosely coupled. The loose coupling allows inductive power transfer between the converters.

In another aspect the invention broadly provides an IPT converter comprising:

a bridge circuit having a first leg and a second leg, each leg including a high switch and a low switch, the high switches being connected to a first energy source and the low switches being connected to ground,

a coupling network(s) having a first connection between the switches of the first leg and a second connection between the switches of the second leg,

a second energy source connected between the coupling network and ground (directly or through a another coupling network), and

a magnetic coupler connected in parallel with the coupling network(s).

The first energy source may comprise a capacitor. A separate energy source, for example, a capacitor may be provided connected between each high switch and ground.

The magnetic coupler includes a coil which may be series or parallel tuned. The magnetic coupler may comprise a primary apparatus or a secondary (pick-up) apparatus, or may be configured for bi-directional power transfer.

In another aspect the invention broadly provides an IPT system comprising at least one converter according to the preceding statement.

In another aspect the invention broadly provides a method of controlling a boost active bridge converter, the method comprising the steps of:

controlling the bridge switches to alternately apply current from a first energy source to a coupling network which couples the converter to a second energy source, and

controlling the duty cycle of the or selected bridge switches to control the voltage across a third energy source connected in parallel with the coupling network.

The energy flow between first, second and third energy sources can be bi-directional.

The concept can be extended with multiple legs, for example to supply a three-phase system.

In another aspect the invention broadly provides a converter comprising:

an H bridge having a DC side and an AC side,

a first energy source connected to the DC side,

a coupling network connected to the AC side, and

a second energy source connected to the coupling network.

In one example the coupled AC energy sources provide isolation.

In one example the AC sources are loosely coupled. The loose coupling allows inductive power transfer between the converters.

Additionally, if the secondary converter is capable of bidirectional power flow, the grid current can also be controlled to deliver power to the grid.

In another aspect the invention broadly provides an IPT system (50) comprising at least one converter according to the preceding statement.

This functionality enables Vehicle to Grid (V2G) services such as, voltage/frequency regulation, and reactive power/harmonics compensation.

As used herein the term “and/or” means “and” or “or”, or both.

As used herein “(5)” following a noun means the plural and/or singular forms of the noun.

The term “comprising” as used in this specification means “consisting at least in part of”. When interpreting statements in this specification which include that term, the features, prefaced by that term in each statement, all need to be present, but other features can also be present. Related terms such as “comprise” and “comprised” are to be interpreted in the same manner.

It is intended that reference to a range of numbers disclosed herein (for example, 1 to 10) also incorporates reference to all rational numbers within that range (for example, 1, 1.1, 2, 3, 3.9, 4, 5, 6, 6.5, 7, 8, 9 and 10) and also any range of rational numbers within that range (for example, 2 to 8, 1.5 to 5.5 and 3.1 to 4.7).

The entire disclosures of all applications, patents and publications, cited above and below, if any, are hereby incorporated by reference.

The disclosed subject matter also provides method or system which may broadly be said to consist in the parts, elements and features referred to or indicated in this specification, individually or collectively, in any or all combinations of two or more of those parts, elements or features. Where specific integers are mentioned in this specification which have known equivalents in the art to which the invention relates, such known equivalents are deemed to be incorporated in the specification.

Other aspects of the invention may become apparent from the following description which is given by way of example only and with reference to the accompanying drawings.

