FIELD OF THE INVENTION

The present invention relates to power electronics. Especially, the invention realtes to an electric power module and an electric power converter (a DC to AC converer) with one or more of such power modules. Especially, the power module is suited for applications where an AC voltage in the MHz range is required such as for powering a heater or dryer. E.g. the power module and a power converter with a plurality of power modules can replace exiting converter solutions based on vacuum tubes.

BACKGROUND OF THE INVENTION

Implementation of a reliable an efficient electric power converter for AC electric power applications in the MHz range and at high power levels in the kW range and voltages in the kV range is challenging.

Currently, for example heaters or dryers for industrial applications are typically powered based on electric power converted to a MHz range (or even GHz range) AC voltage by means of a vacuum tube based converter. Such vacuum tube based converters can handle tens of kW power in the kV voltage range. However, there are several problems with such vacuum tubes: they are inefficient with respect to energy consumption, they are expensive, and only a few manufacturers producing such vacuum tubes exist.

Still, the interconnection of several power modules to allow high power at high voltages is challenging based on power module with electric components with limited current and voltage ratings. This is due to the fact that either current or voltage stress (or both) are put on specific components in at least one of the power modules in the interconnection. Still further, this problem is even further pronounced at high frequencies in the MHz range.

Examples of semiconductor switch based power modules can be seen in WO 2019/210918 Al. OBJECT OF THE INVENTION

It is an object of the present invention to provide a power module and a power converter based on such power module which allows reliable and efficient interconnection to allow DC to AC voltage conversion to generate an AC power output in the MHz frequency range for high power and high voltage applications.

It is a further object of the present invention to provide a power module and a power converter which is simple and easy to implement, and which can be easily scaled according to voltage and power needs.

SUMMARY OF THE INVENTION

In a first aspect, the invention provides a power module arranged to receive a DC electric input signal at first and second connection terminals, and to output an AC electric output signal at third and fourth connection terminals, the power module comprising

- a first capacitor connected, such as directly connected, between the first and second connection terminals,

- a second capacitor connected, such as directly connected, between the third and fourth connection terminals,

- a first inductor connected, such as directly connected, at least to the third connection terminals, such as the first inductor being connected between the first and third connection terminals,

- a second inductor connected, such as directly connected, at least to the fourth connection terminals, such as the second inductor being connected between the second and forth connection terminals, and

- a switch network comprising at least one electrically controllable bidirectional two-quadrant switch, such as one single, two or fourth electrically controllable bidirectional two-quadrant switches, wherein the switch network is connected between at least two of the first, second, third and fourth connection terminals, wherein the at least one one electrically controllable bidirectional two-quadrant switch is arranged for being controlled according to a switching cycle, so as to provide an average voltage of zero across the first inductor over one switching period of the switching cycle, and to provide an average voltage of zero across the second inductor over one switching period.

Such power module has been found and tested to function reliably either alone or interconnected to form a power converter, even at high switching frequencies. The switch(es) can be implemented in for example Gallium Nitride technology, which allows efficient switching at high frequencies, e.g. in the MHz range. Further, at very high switching frequencies, such as more than 5-10 MHz, it has been found that a one-switch version of the power module may be preferred.

It has been found that the power modules can be stacked to provide an AC output at high power level (kW range) and at high voltages (kV range) at a high frequency (MHz range). Especially, the power module is found to be attractive at high frequency AC applications such as industrial heaters or dryers, where the power modules and a power converter based on such power modules can replace existing converters based on vacuum tubes.

The power module is made of simple components which can be selected with limited voltage and current rating. The power module can be implemented as stand-alone module e.g. housing in a casing or package suitable for easy interconnection with other power modules or for easy replacement. Especially, it may be preferred that all the fourth connection terminals are externally accessible, and in some embodiments the two inductors may be connected to respective separate externally acccessible terminals as well, since this allows special interconnections for some applications of the power module.

By using a plurality of interconnected power modules, e.g. identical power modules, a power converter can be built which is scalable with respect to voltage and power requirements. Thus, the power module is suitable for large scale production and still it can be used in a variety of power converter configurations.

In the following, preferred features and embodiments will be described.

Here and in the following "connected" means electrically connected. By "output an AC electric output signal" is meant that the power circuit outputs a stepped voltage waveform which can approximate an AC signal.

The switch network may be implemented by one, two or four electrically controllable bidirectional two-quadrant switches. Especially one, two or four electrically controllable bidirectional two-quadrant switches directly connected between the at least two of the first, second, third and fourth connection terminals.

Especially, the switch network may have only one or two electrically controllable bidirectional two-quadrant switches, such as one or two switches direcly connected between two of the first, second, third and fourth connection terminals. It may be preferred to use one- or two-switch versions, e.g. using Gallium Nitride based switches, in case an AC voltage output is required with a frequency in the MHz range, at least to exceed e.g. 10 MHz.

In some embodiments, the power module comprises a series connection of an output inductor and a bias capacitor, wherein said series connection is connected at one end to the second connection terminal and at the opposite end to the third connection terminal. Especially, an output voltage for connection of an external electric load is provided across the output inductor. In this way the output inductor defines the resonance frequency of the load, and further it serves as a current limiter. Especially, the output inductor and the bias capacitor may be provided external to the power module, e.g. external to a casing for housing all of: the first and second capacitors, the first and second inductors, and the switch network. However, if preferred, the output inductor and the bias capacitor may be arranged inside said casing for housing all of the first and second capacitors, the first and second inductors, and the switch network.

The power module may have at least one externally accessible terminal to allow external control of the switching cycle of the switch network. However, still the power module may comprise a switching controller or switching circuit connected to control switching of the switch network. Alternatively, the switching controller or switching circuit may be provided outside the power module, e.g. outside a casing housing the power module components. Preferably, all of the first, second, third and fourth connection terminal are externally accessible terminals.

In some embodiments the power module has a first externally accessible terminal connected to the first inductor so that the first inductor is connected, such as directly connected, between the first externally accessible terminal and the third connection terminal, and a second externally accessible terminal connected to the second inductor, such as directly connected, between the second externally accessible terminal and the fourth connection terminal. This allows various connections of the inductors to allow interconnection of the power module with further power modules. Especially, the first inductor may be directly connected between the third connection terminals and a first additional externally accessible terminal, and wherein the second inductor is directly connected between the fourth connection terminals and a second additional externally accessible terminal.

Such embodiments with two separate externally accessible terminals connected to the inductors may be preferred for interconnection of a plurality of power modules in parallel, where these additional externally accessible terminals are connected to the input voltage source. Such interconnections may be relevant for both 1- switch, 2-switch as well as 4-switch versions of the power module.

In some embodiments, the first inductor is connected, such as directly connected, between the first and third connection terminals, and the second inductor is connected, such as directly connected, between the second and fourth connection terminals. This provides a simpler power module with a limited number of external terminals, e.g. only the four connection terminals and an additional external terminal to allow control of the switching of the switch network.

The first and second inductors may be magnetically coupled with each other. In some embodiments the first and second inductors are not magnetically coupled with each other.

In some embodiments, the switch network comprises one single electrically controllable bidirectional two-quadrant switch being either directly connected between the first and fourth connection terminals or directly connected between the second and third connection terminals. Preferably, in these one-switch embodiments, the first inductor is connected, such as directly connected, between the first and third connection terminals, and the second inductor is preferably also connected, such as directly connected, between the second and fourth connection terminals.

In some embodiments, the switch network comprises a first electrically controllable bidirectional two-quadrant switch directly connected between the first and fourth connection terminals and a second electrically controllable bidirectional two-quadrant switch directly connected between the second and third connection terminals. Preferably, in these two-switch embodiments, the first inductor is connected, such as directly connected, between the first and third connection terminals, and the second inductor is preferably also connected, such as directly connected, between the second and fourth connection terminals.

In some embodiments, the switch network comprises first, second, third and fourth electrically controllable bidirectional two-quadrant switches being connected to a first node so that the first, second, third and fourth electrically controllable bidirectional two-quadrant switches are connected between the first node and the respective first, second, third, and fourth connection terminals. In these four- switch embodiments, it may be preferred that the first inductor is connected, such as directly connected, between the first and third connection terminals, and the second inductor is preferably also connected, such as directly connected, between the second and fourth connection terminals. Alternatively, in these four-switch embodiments, it may be preferred that the first inductor is connected, such as directly connected, between the third connection terminal and a first externally accessible terminal, and the second inductor also being connected, such as directly connected, between the fourth connection terminal and a second externally accessible terminal. With the inductors connected to the four connection terminals, a simple power module is provided with few external terminals. However, with the inductors accessible with separate external terminals allows a freedom for interconnection of a plurality of power modules, especially for parallel connection of several power modules, where current stress on the inductors can be eliminated by connecting the inductors of all parallel conducted power modules to the input DC voltage.

The at least one electrically controllable bidirectional two-quadrant switch may comprise an IGBT or a MOSFET transistor with diode function enabling bidirectional current flow. Alternatively, the at least one electrically controllable bidirectional two-quadrant switch may be implemented based on SiC or GaN technology, which may be preferred for switching frequencies in the MHz range.

In some embodiments, the switch network is configured to operate at a switching frequency of at least 500 kHz, such as at least 1 MHz, such as 1-3 MHz, such as at least 10 MHz, such as at least 20 MHz, such as at least 30 MHz, such as at least 40 MHz, such as at least 100 MHz. It is to be understood that the power module may be configured for switching frequencies below 500 kHz, such as 1-100 kHz.

The one-, two- and four-switch versions of the power module may have different advantages for different applications. However, the one-switch version can be seen as the most simple hardware design with a minimum of components, and with one single switch, and safe operation without "shoot-through" can be provided at a high switching frequency, such as above 30 MHz. However, for lower switching frequencies, the non-zero dead-time due to the turn-on and turnoff time of the switches can be fully acceptable in the two- and four-switch versions.

The power module may comprise a control circuit configured to control the switching cycle of the switch network. However, in some embodiments the control circuit configured to control the switching cycle of the switch network may be provided external to a casing for housing the power module, e.g. by providing at least one externally accessible terminal for external control of the switching of the switch network.

The power module may be configured to receive a DC voltage of at least 1 V, such as at least 10 V, such as at least 100 V, such as at least 300 V, such as at least 500 V, such as at least 1.5 kV, such as 1 V to 1.5 kV, such as 10 V to 500 V, such as 10 V to 200 V, such as 1 V to 100 V. The power module may be configured to generate an AC output voltage of at least 10 V, such as at least 100 V, such as at least 300 V, such as at least 500 V, such as at least 1.5 kV, such as 1 V to 1.5 kV, such as 10 V to 500 V, such as 10 V to 200 V.

The power module may be configured to generate an electric output power of at least 1 W, such as 1-100 W, such as 100 W to 1 kW, such as 1-100 kW, such as at least 100 kW.

In essence, the power module is suited for various voltage ranges, various power ranges and various switching frequencies. Especially, the power module has been found to be suitable for providing an interconnection of several power modules each with limited power and voltage ratings to form a power converter with a high voltage and power capacity. In other words, the power module is suited as the basic module in a modular power converter, such as a modular multi-level power converter.

In a second aspect, the invention provides a power converter comprising two input terminals arranged to receive a DC electric input voltage, and two output terminals arranged to output an AC electric output voltage, the power converter comprising one or more of the power module according to the first aspect. Preferably, the one or more power module is connected between the input and output terminals, such as at least the first or second connection terminal being connected to one of the input terminals and, such as at least the third or fourth connection terminal being connected to one of the otput terminals.

A number of interconnected power modules according to the first aspect are advantageous for building up a power converter which can be scaled to a given power and/or voltage requirement. In this way e.g. a plurality of identical power modules each with limited power and voltage ratings can be used to form a power converter with a higher power and/or voltage rating.

Preferably, the power converter comprises two or more power modules of the power module according to the first aspect, such as two or more identical power modules, wherein the two or more power modules are interconnected between the input and output terminals. Especially, at least one of the two input terminals of the power converter is directly connected to one of the first and second connection terminals of one of the two or more power modules. Especially, at least one of the two output terminals of the power converter is directly connected to one of the third and fourth connection terminals of one of the two or more power modules. The power converter may comprise at least three, such as at least 4, such as at least 6, such as at least 10, power modules of the power module according to the first aspect, wherein the at least three power modules are interconnected between the input and output terminals of the power converter. Specifically, all of the at least three, such as at least 4, such as at least 6, such as at least 10, power modules of the power module according to the first aspect may be identical.

In some embodiments, the power converter comprises two or more power modules connected in series.

In some embodiments, the power converter comprises two or more power modules connected in parallel.

In some embodiments, the power converter comprises an interconnection of two or more power modules connected in series and two or more power modules connected in parallel.

In some embodiments, the power converter comprises three input terminals arranged to receive respective DC electric input voltages, and wherein the at least three power modules are interconnected between the three input terminals and the output terminals. Specifically, in such embodiments, at least three power modules may be connected in series. More specifically, in such embodiments, four or more power modules may be connected in series, such as 4-20 power modules, and wherein each of the power modules are connected to respective input terminals arranged to receive respective DC electric input voltages.

In some embodiments, the power converter according to claim 26 and 28, comprising three sets of power modules, wherein each set of power modules comprises at least first and second power modules connected in parallel, and wherein the three sets of power modules are connected in series. Specifically, the first power module of each of the three sets of power modules are connected to respective ones of the three input terminals.

In some embodiments, the power converter comprises a rectifier circuit arranged to receive an AC voltage, such as a 50 or 60 Hz AC voltage, wherein the rectifier circuit is configured to generate in response a DC voltage to said input terminals of the power converter, such as the power converter being configured to generate an AC voltage on the output terminals with a frequency of at least 500 kHz, such as 1-40 MHz or even higher.

In some embodiments, the power converter comprises a series connection of an output inductor and a bias capacitor, and wherein the output terminals of the power converter are connected to respective terminals of the output inductor. Specifically, said series connection of the output inductor and the bias capacitor may be connected at one end to one of the first, second, third, and fourth connection terminals of the power module and at the opposite end said series connection of the output inductor and the bias capacitor being connected to another one of the first, second, third, and fourth connection terminals of the power module. Specifically, said series connection may be connected at one end to one of the first, second, third, and fourth connection terminals of a first one of two or more power modules, and at the opposite end said series connection of the output inductor and the bias capacitor is connected to one of the first, second, third, and fourth connection terminals of another one of the two or more power modules.

In some embodiments, the power converter comprises a control circuit configured to control switching of the switch network of the power module or all of the switch networks of the two or more power modules. Specifically, the control circuit may be configured to control switching so as to provide a multilevel AC electric output voltage, such as 3-10 levels of AC electric output voltages. Specifically, the control circuit may be configured to control switching of the switch network of the power module or all of the switch networks of the two or more power modules so as to generate an AC voltage at the output terminals having a frequency of at least 500 kHz, such as at least 1 MHz, such as 1-3 MHz, such as at least 10 MHz, such as the switch network (SWN) is configured to operate at a switching frequency of at least 20 MHz, such as at least 30 MHz, such as at least 40 MHz, such as at least 100 MHz.

In some embodiments, the power converter comprises at least first and second power modules each comprising the four-switch version of the power module of the first aspect, wherein a first power module has its first inductor connected between the first and third connection terminals and its second inductor connected between the second and fourth connection terminals, and wherein the first and second connection terminals of the first power module are connected to respective first and second input terminals of the power converter,

- wherein the second power module has its first inductor connected between the first input terminal of the power converter and its third connection terminal and its second inductor connected between the second input terminal of the power converter and its fourth connection terminal, and

- wherein the third and fourth connection terminals of the first power module are connected, such as directly connected, to the respective first and second connection terminals of the second power module. Specifically, a series connection of an output inductor and a bias capacitor may be connected at one end to the third connection terminal of the second power module and at the opposite end to the second input terminal of the power converter.

In some embodiments, the power converter comprises at least first and second power modules each comprising the two-switch version of the power module of the first aspect, wherein both of the first and second power modules have their respective first inductors connected between their respective first and third connection terminals and their respective second inductors connected between their respective second and fourth connection terminals. Specifically, the first and second connection terminals of the first power module are connected, such as directly connected, to the respective first and second input terminal of the power converter, wherein the the third and fourth connection terminals of the first power module are connected, such as directly connected, to the respective first and second connection terminals of the second power module, and wherein the third and fourth connection terminals are connected, such as directly connected, to the respective first and second output terminals of the power converter.

In some embodiments, the power converter comprises at least first and second power modules each comprising the one-switch version of the power module of the first aspect, wherein both of the first and second power modules have their respective first inductors connected between their respective first and third connection terminals and their respective second inductors connected between their respective second and fourth connection terminals. Specifically, the first and second connection terminals of the first power module may be connected, such as directly connected, to the respective first and second input terminal of the power converter, wherein the the third and fourth connection terminals of the first power module are connected, such as directly connected, to the respective first and second connection terminals of the second power module. Specifically, a series connection of an output inductor and a bias capacitor may be connected at one end to the third connection terminal of the second power module and at the opposite end to the second input terminal of the power converter. In a special embodiment, in both of the first and second power modules, the one single electrically controllable bidirectional two-quadrant switch is directly connected between the first and fourth connection terminals. In another special embodiment, in the first power module, the one single electrically controllable bidirectional two- quadrant switch is directly connected between the first and fourth connection terminals, and wherein in the second power module, the one single electrically controllable bidirectional two-quadrant switch is directly connected between the second and third connection terminals.

In some embodiments, the power converter comprises first, second, third and fourth power modules each comprising the one-switch version of the power module of the first aspect, wherein all of the first, second, third and fourth power modules have their respective first inductors connected between their respective first and third connection terminals and their respective second inductors connected between their respective second and fourth connection terminals. Especially, the first and second power modules may be connected to form a first parallel connection, wherein the third and fourth power modules are conneceted to form a second parallel connection, and wherein the first and second parallel connections are connected in series. Specifically, the first connection terminal of the first power module may be connected to, such as via an input inductor, to a first input terminal of the power converter, and wherein the fourth connection terminal of the fourth power module is connected to a first output terminal of the power converter. Specifically, the fourth connection terminal of the second power module may be connected, such as directly, to a the first connection terminal of the third power module.

The power converter may be arranged to receive a DC input voltage of 1 V to 100 V, or of 100 V to 1.5 kV, such as of 1.5 kV or more.

The power converter may be arranged to output an AC voltage of 100 V to 1.5 kV, or 1.5 kV to 100 kV.

The power converter may be arranged to convert electric power of 1 W to 100 W, or 100 W to 1 kW, or 1 kW to 100 kW, or 100 kW to 1 MW, or 1 MW to 10 MW, or above 10 MW.

The power module or power modules in the power converter may be based on a switch network or switch networks implented with Gallium Nitride (GaN) technology.

In the power converter, the switch network or switch networks of the power module or power modules may be operated to provide an AC voltage at the output terminals with a frequency of 500 kHz to 50 MHz, such as 2-40 MHz. Specifically, the power converter may be configured for generating an AC voltage at the output terminals having a voltage of 3-10 kV. More specifically, the power converter may be configured for generating an AC voltage at the output terminals up to a power of 50 kW or more.

In a third aspect, the invention provides a device comprising the power converter according to the second aspect, wherein the device comprises at least one electrically power consuming component connected to receive electric power from the output terminals of the power converter. Especially, the device may comprise a heating machine connected to receive electric power from the power converter. Especially, the device may comprise a drying machine connected to receive electric power from the power converter.

In a fourth aspect, the invention provides use of the power module of the first aspect.

In a fifth aspect, the invention provides use of the power converter according to the second aspect.

In a sixth aspect, the invention provides use of the device according to the third aspect.

The use of the fourth, fifth or sixth aspects may especially be for producing or performing a process on one or more of: 1) wood, 2) furniture, 3) fiberglass, 4) a pharmaceutical substance, 5) a chemical substance, 6) a silicon or ceramic, 7) foam, 8) a textile, 9) a dairy product, 10) a vulcanized product, and 11) food. Specific application examples within the food industry are: boiling/heating, bakeries, defrosting, pasteurization, sterilization, and disinfestation.

Especially, in the mentioned industrial application areas, the power module or power converter of the first and second aspects can be used to provide AC power for heating and drying applications, and here these converter solutions can replace existing vacuum tube technologies and thus improve energy efficiency, lower component costs and provide a modern alternative to the old vacuum tube technology with only few providers.

In a seventh aspect, the invention provides a method for converting a DC electric signal to an AC electric signal, the method comprising

- providing at least one power module according to the first aspect,

- connecting the first and second connection terminals of at least one of the at least one power module to receive the DC electric signal, and

- operating the switch network of the at least one power module according to a switching scheme, so as to generate the AC electric signal based on an electric output from at least one of the at least one power module. Feathres and embodiments of the mentioned aspects of the present invention may each be combined with each other. These and other aspects of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter.

BRIEF DESCRIPTION OF THE FIGURES

The present invention and in particular preferred embodiments thereof will now be disclosed in more detail with regard to the accompanying figures. The figures show ways of implementing the present invention and are not to be construed as being limiting to other possible embodiments falling within the scope of the attached claim set.

FIG. la and lb show a power module module embodiment based on two capacitors, two inductors, and a switch network of one or more electrically controllable switches interconnected between four connection terminals, and a graph illustrating an example of switching timing of the switch network, FIG. 2a, 2b, 2c show two interconnected four-switch versions of the power module, and graphs illustrating switching timing,

FIG. 3a, 3b shows a two-switch version of the power module and graphs illustrating switching timing,

FIG. 4 shows two interconnected two-switch versions power modules,

FIG. 5a, 5b shows a one-switch version of the power module and a graph illustrating switching timing,

FIG. 6a, 6b, 6c shows an in-phase parallel connection of two one-switch versions of the power module, and graphs illustrating switching timing,

FIG. 7a, 7b, 7c shows an out of phase parallel connection of two one-switch versions of the power module, and graphs illustrating switching timing,

FIG. 8a shows an example of a combination of two sets of power modules connected in series, where each set of power modules has two power modules connected in parallel,

FIG. 8b, 8c, illustrate specific circuits with one-switch versions of the power module for implementation of the embodiment of FIG. 8a,

FIG. 9 shows a block diagram of an example of interconnecting power modules for connection to a grid supply, FIG. 10 shows a block diagram of another example of interconnecting power modules for connection to a grid supply,

FIG. 11 illustrates preferred power, voltage and switching frequency ranges for embodiments of the power module compared to other cells,

FIG. 12 illustrates a device embodiment, and

FIG. 13 illustrates steps of a method embodiment.

DETAILED DESCRIPTION OF EMBODIMENTS

FIG. la shows a basic power module according to the invention. The power module has two capacitors CAP1, CAP2, two inductors LI, L2, and a switch network SWN of one or more electrically controllable bidirectional two-quadrant switches. These components are interconnected between four connection terminals A, B, C, D. Capacitor CAP1 is connected between the connection terminals A, B, and capacitor CAP2 is connected between the connection terminals C, D. Inductor LI is connected in this embodiment between connection terminals A, C, and inductor L2 is connected between the second and forth connection terminals B, D. Especially, the two inductors LI, L2 may be magnetically coupled.

The power module arranged to receive a DC electric input signal VCAP1 at first and second connection terminals A, B, and to output an AC electric output signal VCAP2 at third and fourth connection terminals C, D. As such, the power module can be used as a DC to AC power converter.

In some embodiments, a series connection of an output inductor (not shown) and a bias capacitor (not shown) may be connected to provide a load circuit, where an electric output voltage to a load is provide across such output inductor.

FIG. lb illustrates swithcing timing of the one or more electrically controllable switches of the switch network SWN is arranged for being controlled according to a switching cycle, so as to provide an average voltage <V1> of zero across the first inductor LI over one switching period of the switching cycle, and to provide an average voltage <V2> of zero across the second inductor L2 over one switching period. Such power module is simple to implement from basic components, e.g. all housing in a casing with connection terminals A, B, C, D externally accessible on an exterior part of the casing. In some embodiments, one end of the inductors LI, L2 are also connected to respective externally accessible terminals, so as to allow special external interconnections of these terminals. Preferably, an externally accessible terminal is also provided for control of switching of the switch network SWN, with a switch control circuit being either internally or externally provided.

The power module has been found to be attractive compared to a basic class E cell, since in the basic class E configuration, the voltage rating of the switch puts a limit to the voltage handling capacity of the converter, since only a parallel connection of class E modules can be used to increase power. However, the power modules according to the invention can be series connected and thus the voltage handling of such power converter with series connected power modules is the sum of the voltage ratings of switches. E.g. 10 kV is possible with 20 power modules in series each with 500 V voltage rated switches. Still further, when series connecting power modules, the capacitance of the switches provide an effective capacitance which allows higher operating frequencies.

With various implementations of the switch network SWN, using one, two or four switches, the power module has been found to form a flexible building block in modular power converters. Various ways of interconnecting power modules to form a power converter will be shown in the following.

FIG. 2a illustrates two four-switch power modules connected in parallel to convert an input DC voltage VCAP1 to an output voltage Vout across an output inductor Lout connected in series with a bias capacitor CBIAS. Note that as an alternative, the basic interconnection shown in FIG. 2a could be used as well with two one- switch or two two-switch arrangements, or a mix of a one-switch and a two- switch arrangement.

The first power module has a switch network with four electrically controllable bidirectional two-quadrant switches si, s2, s3, s4 connected to a first node so that these four switches si, s2, s3, s4 are connected between the first node and respective connection terminals Cl, A2, DI, B2. The inductor LI is connected between connection terminals Cl, A2 and inductor L2 is connected between connection terminals DI, B2. The second power module has four switches s5, s6, s7, s8 connected to a common node as in the first power module similar to the first power module. The second power module has its connection terminals C2, D2 directly connected to the respetive connection terminals A2, B2 of the first power module. However, the inductors L3, L4 of the second power module are directly connected to the input terminals, i.e. to connection terminals Cl, DI, rather than to the connection terminals C2, D2 of the second module. Hereby, it is possible to add several four-switch power modules in parallel without any current stress building up in the inductors of the power modules away from the input terminals.

FIG. 2b, 2c illustrate switch timing related to the configuration of FIG. 2a.

With respect to details regarding switching timing, the skilled person will know how to implement switching control based on FIG. 2b, 2c. The same applies to switching timing diagrams for the embodiments that will be explained also in the following. Further, reference is made to WO 2019/210918 Al for description of various aspects of switching timing.

FIG. 3a illustrates a two-switch power module where the switch network comprises two elecronically controllable bidirectional two-quadrant switches si, s2. One switch si is directly connected between two connection terminals A, D and the other switch s2 is directly connected between the connection terminals B, C. Inductor LI is connected between the connection terminals A, C, and the inductor L2 is connected between the connection terminals B, D.

Compared to four-swicth power modules, the two-switch power module is simpler, and for switching frequencies of more than such as 14 MHz, it has been found difficult to operate a four-switch version due to the small dead-time available for the switches to safely turn on and off to avoid "shoot-through". This problem is reduced with the two-swich version, which can operate at switching frequencies above 14 MHz.

FIG. 3b illustrates timing for the two-switch power module of FIG. 3a. FIG. 4 illustrates an example of a power converter with an interconnection of two two-switch power modules, namely where two identical two-switch power modules each with two switches si, s2 and s3, s3 are directly connected via their connection terminals, namly by direct connection of connection terminals Cl, A2 and of connection terminals DI, B2.

FIG. 5a illustrates a one-switch version of the power module version. Here, the switch network has one single electrically controllable bidirectional two-quadrant switch si, and in the illustrated version, this switch si is directly connected between connection terminals A, D. Inductor LI is connected between connection terminals A, C and inductor L2 is connected between connection terminals B, D.

The capacitor CR connected across the switch si is an optional separate component, which can added in order to limit voltage and to adjust frequency.

Such one-switch power module is very simple and has the potential of operating at a very high switching frequency, such as above 40 MHz.

FIG. 5b illustrates the related switching timing to the one-switch configuration of FIG. 5a.

FIG. 6a shows an interconnection of two identical one-switch versions of the power module to provide an in-phase parallel configuration. The two one-switch power modules are connected by connection of their connection terminals Cl, A2 and DI, B2. In input voltage is received a connection terminals Al, B2 of the first power module, and an output voltage Vout is provided across an output inductor Lout connected in series with a bias capacitor CBIAS, wherein this serie connection is connected at one end to connection terminal C2 and the opposite end to connection terminals Bl.

FIG. 6b, 6c illustrate switching timing related to the configuration of FIG. 6a.

FIG. 7a illustrates an alterantive to the configuration of FIG. 6a, namely with two different one-switch power modules being interconnected to form an out of phase configuration. In the first power module switch si is connected between connection terminals Al, DI, and in the second power module switch s2 is connected between connection terminals C2, B2. The two power modules are directly interconnected by connection terminals Cl, A2 and D2, B2.

FIG. 7b, 7c illustrate switching timing related to the configuration of FIG. 7a, see e.g. FIG. 6b, 6c for comparison.

FIG. 8a illustrates a power converter configuration with a combination of two sets of power modules, namely two sets of parallel connected power modules PM1, PM2 and PM3, PM4. These two sets are then series connected and here shown connected to two input voltages vin/2.

An input inductor Lin is connected between one terminal of the input voltages vin/2 and input to the first set of power modules PM1, PM2.

A load circuit is conneceted across the input of the two sets of power modules PM1, PM2 and PM3, PM4, and this load circuit has a series connection of a bias capacitor CBIAS and an output inductor Lout, where the output inducot Lout is specifically in this case connected to ground. The output voltage Vout from the power converter is provided across the output inductor Lout.

FIG. 8b and 8c illustrate a preferred implementation of the configuration of FIG. 8a, namely by means of four one-switch power modules, in fact a each set of two one-switch power modules are similar to the embodiment shown in FIG. 7a.

FIG. 8b shows the first set of two one-switch power modules PM1, PM2 of FIG. 8a, i.e. an out of phase parallel connection of two one-switch power modules.

Connection terminal Al of the first power module is connected to the input voltage, via the input inductor Lin (see FIG. 8a), whereas connection terminals D2 of the second power module forms an output to the following two power modules PM3, PM4. The two modules are directly connected via their connection terminals Cl, A2 and DI, B2.

FIG. 8c shows the second set of two one-switch power modules PM3, PM4 of FIG.

8a, i.e. an out of phase parallel connection of two one-switch power modules. The output voltage from the first set of power modules PM1, PM2 (see FIG. 8a) is received at connection terminals A3 of the first power module, whereas connection terminal D4 of the second power module provides an output, in this case connection terminal D4 is specifically connected to ground.

The power converter shown in FIG. 8a, 8b, 8c has the potential of operating at a switching frequency of such as 10-40 MHz, e.g. with switches s2, s2, s3, s4 implemented with Gallium Nitride technology.

FIG. 9 shows a block diagram of a series/parallel connection of power modules PM1-PM9, preferably one-switch power modules, which is fed from a grid supply. Three sets of power modules each comprises three power modules PM1-PM3, PM4-PM6, PM7-PM9 connected in parallel. Each of the three sets of power modules PM1-PM3, PM4-PM6, PM7-PM9 are then connected in series. The first power module PM1, PM4, PM7 of each of the three sets of power modules PM1- PM3, PM4-PM6, PM7-PM9 are connected to respective ones of the three input terminals provided by a rectifier circuit connected to an AC grid, such as a 50 or 60 Hz AC voltage. The rectifier circuit is configured to generate respective DC voltages to input terminals of each set of power modules PM1-PM3, PM4-PM6, PM7-PM9.

Especially, the power converter of FIG. 9 may be configured to generate an AC voltage on the output terminals with a frequency of at least 500 kHz, and at an output voltage which is such as 5-100 times higher than the received DC voltage(s).

FIG. 10 shows a block diagram of an alternative to the embodiment of FIG. 9, namely a pure series connection of power modules PM1-PM8, e.g. one-switch power modules, based on DC voltages received from a rectifier circuit fed from an AC grid voltage. Hereby, all power modules PM1-PM8 will have equal voltage and current stress, thus providing an optimal utilization of the power modules PM1- PM8 which may then be identical power modules with limited voltage and power ratings. FIG. 11 serves to illustrate power, voltage and switching frequency application ranges for the power modules PM of the present invention with Gallium Nitride (GaN) based switches. Two power module versions, namely a 1-switch and 4- switch versions are compared with prior art technology, namely a class E push- pull configuration with 1,7 kV Silicon Carbide (SiC) based switches.

As illustrated, prior art class E push-pull is limited to 0-10 kW, 1-3 kV and with a limited switching frequency of a maximum of 6.76 MHz. 4-switch versions of the power module may be capable of handling 0-50 kW, 3-10 kV at switching frequencies of up to 27 MHz. The 1-swich power modules are capable of handling 0-50 kW, 3-10 kV at switching frequencies up to 40 MHz. The 1-switch circuits shown in FIG. 6a, 7a, 8a-8c have all been tested in laboratory tests, and these test have confirmed these capabilities of the 1-switch power modules.

FIG. 12 illustrates a device embodiment, namely a device comprising a power converter PCNV with two power modules PM1, PM2 according to the invention, and where the power converter PCNV receives an input DC supply voltage and converts the DC voltage to an output AC voltage, preferably an AC voltage level being higher voltage than the DC voltage level, and preferably at a frequency of such as 1-40 MHz. The AC voltage generated is supplied to a power consuming component HT, here indicates as a heater HT, such as a heater HT consuming such as 1-50 kW for industrial heating or drying applications, or the like. It is to be understood that the power converter PCNV may be used to provide AC power to a large variety of power consuming components in many different applications.

The power converter PCNV may be integrated with the power consuming component HT, or it may be provided in a separate casing, separate from the power consuming component HT.

The power converter PCNV according to the invention is capable of generating AC voltages at frequencies of 0.5-40 MHz at such as l-10kV, up to a power level of at least 50 kW. As such, the power converter PCNV can be used to replace industrial vacuum tubes. FIG. 13 illustrate steps of a method embodiment, namely a method for converting a DC electric signal to an AC electric signal. First, the method comprises providing P_PM at least one power module according to the first aspect of the invention, sue as 1-10 identical power modules based on the described one-, two- or four-switch versions. Next, connecting C_DC the first and second connection terminals of at least one of the power module(s) to receive the DC electric signal. Next, operating O_SWN the switch network, of the at least one power module according to a switching scheme, such as by providing an output of a switch control circuit to the switch network, so as to generate the AC electric signal based on an electric output from at least one of the at least one power module. The method may further comprise powering a power consuming device, such as a heater or a dryer of the like.

To sum up, the invention provides a power module arranged to receive a DC electric input signal at first and second connection terminals (A, B), and to output an AC electric output signal at third and fourth connection terminals (C, D). A set of capacitors (CAP1, CAP2) are connected between respective sets of connection terminals (A, B, C, D). Two inductors (LI, L2) are connected at least to respective connection terminals (C, D), such as the first inductor (LI) being connected between on set of connection terminals (A, C), and the second inductor (L2) being connected between another set of connection terminals (B, D). A switch network (SWN) with at least one electrically controllable bidirectional two-quadrant switch (si), is connected between at least two of the four connection terminals (A, B, C, D). The at least one witch (si) is arranged for being controlled according to a switching cycle, so as to provide an average voltage (VI) of zero across the first inductor (LI) over one switching period of the switching cycle, and to provide an average voltage (V2) of zero across the second inductor (L2) over one switching period. The power module is simple, and can be implemented with only one single switch per module. A DC to AC power converter can be build of a number of interconnected power modules, and such power converter can be designed to provide an AC output voltage in the kV range at a power in the kW range, at a frequency of up to such as 40 MHz.

Although the present invention has been described in connection with the specified embodiments, it should not be construed as being in any way limited to the presented examples. The scope of the present invention is set out by the accompanying claim set. In the context of the claims, the terms "comprising" or "comprises" do not exclude other possible elements or steps. Also, the mentioning of references such as "a" or "an" etc. should not be construed as excluding a plurality. The use of reference signs in the claims with respect to elements indicated in the figures shall also not be construed as limiting the scope of the invention. Furthermore, individual features mentioned in different claims, may possibly be advantageously combined, and the mentioning of these features in different claims does not exclude that a combination of features is not possible and advantageous.

List of reference symbols used in Figures

A, B, C, D Connection terminals

Al, A2, A3, A4 Connection terminals

Bl, B2, B3, B4 Connection terminals

Cl, C2, C3, C4 Connection terminals

DI, D2, D3, D4 Connection terminals

CAP1, CAP2, CAP3, CAP4 Capacitors

CAP4, CAP6, CAP7, CAP8, CBIAS Capacitors sl, s2, s3, s4, ...s8 Switches (electrically controlled)

LI, L2, L3, L4, ...L8, Lin, Lout Inductors vin, vout, vl, v2, v3, v4, VBIAS Voltages VCAP1, VCAP2, VCAP3, VCAP4 Voltages