Multi-level multi-step power converter

Abstract

The invention pertains to a multi-level power converter with reduced from electromagnetic interference, decreased power losses, and increased component lifetime The multi-level power converter comprises a high voltage terminal, a low voltage terminal and a plurality of parallel converter legs arranged between the high voltage terminal and the low voltage terminal. Each converter leg comprises a same even number of at least four switching elements that are connected in series between the high voltage terminal and the low voltage terminal, and a midpoint terminal. A first pair of consecutive switching elements of a first converter leg is connected at a shared terminal of the first pair of consecutive switching elements via a balancing inductor having an inductance value to a shared terminal of a second pair of consecutive switching elements, the second pair of consecutive switching elements being located in a second converter leg at a downstream location corresponding to a downstream location of the first pair of consecutive switching elements in the first converter leg. (Fig. 1)

Description

[0001] Multi-level multi-step power converter

[0002] BACKGROUND

[0003] The present invention relates to the field of multi-level multi-step inverters as can e.g. be applied for powering an electric motor such as a permanent magnet motor driving a vehicle wheel.

[0004] Multi-level inverters as e.g. applied to convert a DC power, e.g. received from a battery, to an AC power for powering an electric motor, will typically comprise a plurality of switching elements arranged in multiple parallel branches or legs, each branch or leg comprising a plurality of series connected switches.

[0005] In conventional two-level inverters, it is known from the document “Y. Shen, L. Shillaber, H. Zhao, Y. Jiang and T. Long, "Desynchronizing paralleled GaN HEMTs to reduce light-load switching loss", IEEE Trans. Power Electron., vol. 35, no. 9, pp. 9151-9170, Sep. 2020” that the midpoint of each paralleled half bridge can be connected with a commutation inductor which can desynchronize the paralleled devices at light loads to generate a circulating current flowing through the commutation inductors. The circulating current enables the lagging HEMTs to achieve the zero-voltage switching (ZVS) and allows the leading ones to turn on at a current lower than the load, thereby reducing the total switching loss.

[0006] Known multi-level multi-step inverters, however, may suffer from electromagnetic interference (EMI). In addition, the use of multiple branches or legs in parallel in known inverters may cause excessive losses or lifetime issues for the applied switches.

[0007] SUMMARY

[0008] It is an object of the present invention to at least mitigate one of the aforementioned issues and / or to provide an alternative to the prior art.

[0009] In a first aspect, the invention pertains to a multi-level power converter, comprising a high voltage terminal, a low voltage terminal and a number p of parallel converter legs arranged between the high voltage terminal and the low voltage terminal, p being at least two, wherein:

[0010] • each converter leg comprises a same even number n switching elements, n being at least four; • the switching elements of each converter leg are connected in series in a downstream fashion between the high voltage terminal and the low voltage terminal;

[0011] • each converter leg comprises a midpoint terminal, the midpoint terminal of each converter leg being arranged such that the number of switching elements comprised by a respective converter leg between the high voltage terminal and the midpoint terminal is and the number of switching elements comprised by the respective converter leg between the midpoint terminal and the low voltage terminal is

[0012] • the midpoint terminal of each converter leg is connected via a respective output inductor to a common output terminal;

[0013] • the high voltage terminal and the low voltage terminal form a direct current port, the direct current port being connectable to a direct current power source;

[0014] • the output terminal and the low voltage terminal form an alternating current port, the alternating current port being connectable to an alternating current load; characterized in that:

[0015] • a first pair of consecutive switching elements of a first converter leg, the first pair of consecutive switching elements being located between the high voltage terminal and the midpoint terminal of the first converter leg or between the midpoint terminal of the first converter leg and the low voltage terminal, is connected at a shared terminal of the first pair of consecutive switching elements via a balancing inductor having an inductance value to a shared terminal of a second pair of consecutive switching elements, the second pair of consecutive switching elements being located in a second converter leg at a downstream location corresponding to a downstream location of the first pair of consecutive switching elements in the first converter leg.

[0016] The multi-level power converter is configured to convert power between the direct current port and the alternating current port. To perform power conversion, the multi-level power converter comprises at least two parallel converter legs, wherein each converter leg comprises a same even number of at least four switching elements. The number of levels of the multi-level power converter is + 1, wherein n is the number of switching elements in each converter leg. For example, if the converter legs each comprise 4 switching elements, the number of levels of the multi-level power converter is 3. For another example, if the converter legs each comprise 6 switching elements, the number of levels of the multi-level power converter is 4.

[0017] When placing multiple switching elements in parallel in this fashion, the difference in parasitic drain inductance may cause the switching elements in the parallel branches to switch at different moments. This causes the switching elements to switch a different fraction of the current and thus result in additional losses and lifetime issues. These issues are especially apparent in high-frequency applications where the switching times of the switching elements is short. A short switching time in this application means a switching time in the range of 1-100ns, in particular in the range of 1-10ns.

[0018] A known solution to mitigate the issues described above for single-level power converters is to add an artificial inductance in series with the switching elements of the parallel legs of the single-level power converter. This known solution, however, cannot be readily applied to multi-level power converters because the voltage at the midpoints between pair of switching elements in the parallel converter legs cannot be clamped. Consequently, in the multi-level power converters such a configuration would lead to a problem as during the switching it may occur that a single switching element needs to switch the total current leading to a failure.

[0019] Therefore, in the first aspect of the invention a balancing inductor having an inductance value is provided. The balancing inductor is connected to a shared terminal of a first pair of consecutive switching elements of a first converter leg and to a shared terminal of a second pair of consecutive switching elements of a second converter leg. The first converter leg and the second converter leg are different converter legs of the multi-level power converter. The second pair of consecutive switching elements is located in the second converter leg at a downstream location corresponding to a downstream location of the first pair of consecutive switching elements in the first converter leg. For example, the first pair of switching elements comprises the first switching element and the second switching element downstream from the high voltage terminal in the first converter leg. Then, the second pair of switching elements comprises the first switching element and the second switching element downstream from the high voltage terminal in the second converter leg. For another example, the first pair of switching elements comprises the last switching element and the second-to- last switching element downstream from the high voltage terminal in the first converter leg. Then, the second pair of switching elements comprises the last switching element and the second-to-last switching element downstream from the high voltage terminal in the second converter leg.

[0020] The switching elements of the converter legs are for example gallium nitride high electron mobility transistors.

[0021] The invention ensures that the parallel legs of the multi-level power converter are decoupled. The invention further is a passive solution to the problems identified above since current imbalances between the switching elements and differences in voltage over time on capacitors of the multi-level power converter is avoided. Therefore, the invention does not require additional control logic to avoid current imbalances between the switching elements and / or voltage differences over time on the capacitors of the multi-level power converter. In an embodiment, the inductance value of the balancing inductor is configured to compensate a parasitic drain inductance in the multi-level convertor. Advantageously, this will cause the switching elements to switch at the same time.

[0022] In an embodiment according to the first aspect of the invention, the first converter leg and the second converter leg are directly neighboring converter legs of the multi-level power converter.

[0023] In an embodiment according to the first aspect of the invention, each first pair of consecutive switching elements of the first converter leg is connected at the shared terminal of a respective first pair of consecutive switching elements of the first converter leg via a respective balancing inductor to the shared terminal of a respective second pair of consecutive switching elements of the second converter leg.

[0024] In an embodiment according to the first aspect of the invention, each first pair of consecutive switching elements of all directly neighboring consecutive converter legs is connected at the shared terminal of a respective first pair of connected switching elements via a respective balancing inductor to the shared terminal of a respective second pair of consecutive switching elements.

[0025] In an embodiment according to the first aspect of the invention, the p parallel converter legs are divided in a number of k parallel leg groups each parallel leg group comprising directly neighboring parallel converter legs of the multi-level power converter, k being at least two. All parallel converter legs are comprised in a single parallel leg group. The first converter leg and the second converter leg are comprised in the same parallel leg group.

[0026] In an embodiment according to the first aspect of the invention, the inductance value of the balancing inductor has a value depending on a number of levels nroflevels of the multilevel power converter, an output current lout of the multi-level power converter, a bus voltage Vbus of the multi-level power converter, and a target rate of voltage change over time^^.

[0027] The number of levels of the multi-level power converter (101) is + 1.

[0028] Optionally, in this embodiment, the inductance value of the balancing inductor is determined based on a formula Trise-desired IS a desired bus voltage rise time of the multi-level power converter. TrjSe-switch is a rise time of the switching elements, nrofsteps is p * (nrof levels - 1).

[0029] In an embodiment according to the first aspect of the invention, the inductance value of the balancing inductor is in a range of 10nH-100nH to compensate a parasitic drain inductance in the multi-level convertor in a range of 100pH - 500pH.

[0030] In an embodiment according to the first aspect of the invention, the multi-level converter is a flying-capacitor multi-level power converter.

[0031] In an embodiment according to the first aspect of the invention, the multi-level converter is a neutral-point clamped multi-level power converter.

[0032] In an embodiment according to the first aspect of the invention, the switching elements are gallium nitride high electron mobility transistors.

[0033] In a second aspect, the invention pertains to a method of controlling a multi-level power converter according to the first aspect of the invention, starting in a state where:

[0034] • the switching elements of all converter legs between the high voltage terminal and the midpoint terminal of each converter leg are closed; and

[0035] • the switching elements of all converter legs between the midpoint terminal of each converter leg and the low voltage terminal are opened; the method comprising the steps of:

[0036] • for each converter leg, in turn: o opening, in turn, each switching element of a respective converter leg between the high voltage terminal and the midpoint terminal of the respective converter leg, in upstream order, starting with a switching element closest to the midpoint terminal of the respective converter leg, and ending with a switching element closest to the high voltage terminal;

[0037] • for each converter leg, simultaneously: o closing, simultaneously, each switching element of a respective converter leg between the midpoint terminal of the respective converter leg and the low voltage terminal.

[0038] In a third aspect, the invention pertains to a multi-level power converter system, comprising:

[0039] • a multi-level power converter according to the first aspect of the invention; • a controller, connected to the multi-level power converter and configured to control the switching elements of the converter legs of the multi-level power converter by applying the method according to the second aspect of the invention.

[0040] In a fourth aspect, the invention pertains to an electric vehicle, comprising:

[0041] • a multi-level power converter system according to the third aspect of the invention;

[0042] • a battery, connected to the direct current port of the multi-level power converter of the multi-level power converter system;

[0043] • an electric motor, connected to the alternating current port of the multi-level power converter of the multi-level power converter system.

[0044] BRIEF DESCRIPTION OF DRAWINGS

[0045] The invention is described below with reference to the figures. These figures serve as examples to illustrate the invention, and will not be construed as limiting the scope of the claims. In the different figures, like features are indicated by the like reference numerals.

[0046] In the figures:

[0047] Fig. 1 schematically shows a multi-level power converter according to a first embodiment of the first aspect of the invention.

[0048] Fig. 2 schematically shows a multi-level power converter according to a second embodiment of the first aspect of the invention.

[0049] Fig. 3 schematically shows a multi-level power converter according to a third embodiment of the first aspect of the invention.

[0050] Fig. 4 schematically shows a multi-level power converter according to a fourth embodiment of the first aspect of the invention.

[0051] Fig. 5 schematically shows a multi-level power converter according to a fifth embodiment of the first aspect of the invention.

[0052] Fig. 6 schematically shows a multi-level converter system according to an embodiment of the third aspect of the invention.

[0053] Fig. 7 schematically shows an electric vehicle according to an embodiment of the fourth aspect of the invention.

[0054] DETAILED DESCRIPTION

[0055] Fig. 1 schematically shows a multi-level power converter 101 according to a first embodiment of the invention. The multi-level power converter 101 is a flying-capacitor multi-level power converter. The multi-level power converter 101 comprises a high voltage terminal 102, a low voltage terminal 103, and two parallel converter legs 104a and 104b. The parallel converter legs 104a and 104b are arranged between the high voltage terminal 102 and the low voltage terminal 103. Each parallel converter leg 104a-b comprises four switching elements. As an example, the switching elements 105a-d are arranged and connected in series with each other in the parallel leg 104a in downstream fashion between the high voltage terminal 102 and the low voltage terminal 103. Switching element 105a is the first switching element downstream from the high voltage terminal in the parallel leg 104a, switching element 105d is the last switching element downstream from the high voltage terminal in the parallel leg 104b.

[0056] Switching elements 105a-d are for example gallium nitride high electron mobility transistors.

[0057] The converter leg 104a comprises a midpoint terminal 106a. The converter leg 104b comprises a midpoint terminal 106b. The number of switching elements arranged between the high voltage terminal 102 and the midpoint terminal 106a-b in each converter leg 104a- 104b is half of the total number of switching elements comprised in each converter leg 104a- 104b. The number of switching elements arranged between the midpoint terminal 106a-b and the low voltage terminal 103 in each converter leg 104a-104b is half of the total number of switching elements comprised in each converter leg 104a-104b. For example, in parallel leg 104a, two switching elements 105a-105b are arranged between the high voltage terminal 102 and the midpoint terminal 106a, and the two switching elements 105c-105d are arranged between the midpoint terminal 106 and the low voltage terminal 103.

[0058] The midpoint terminal 106a-b of each converter leg 104a-b is connected, via a respective output inductor 107a-b, to a common output terminal 108.

[0059] The high voltage terminal 102 and the low voltage terminal 103 form a direct current port 112, connected to a direct current power source 113. For example, the direct current power source 113 is a battery. The output terminal 108 and the low voltage terminal 103 form an alternating current port 114, connected to an alternating current load 115. For example, the alternating current load 115 is an electric motor of an electric vehicle such as a car or a freight truck or a boat.

[0060] The converter leg 104a comprises two pairs of consecutive switching elements 109a-b. The pair of consecutive switching elements 109a is arranged between the high voltage terminal 102 and the midpoint terminal 106a. The pair of consecutive switching elements 109b is arranged between the midpoint terminal 106a and the low voltage terminal 103. The pair of consecutive switching elements 109a comprises switching elements 105a and 105b. The pair of consecutive switching elements 109b comprises switching elements 105c and 105d. Similarly, converter leg 104b comprises two pairs of consecutive switching elements 109c-d. The pair of consecutive switching elements 109c is arranged between the high voltage terminal 102 and the midpoint terminal 106b. The pair of consecutive switching elements 109d is arranged between the midpoint terminal 106b and the low voltage terminal 103. The pair of consecutive switching elements 109c comprises switching elements at a downstream location in the converter leg 104b corresponding to the downstream location of switching elements 105a-105b in the converter leg 104a. The pair of consecutive switching elements 109d comprises switching elements at a downstream location in the converter leg 104b corresponding to the downstream location of switching elements 105c-105d in the converter leg 104a. In other words, the consecutive pair of switching elements 109c is located in the converter leg 104b at a downstream location corresponding to a downstream location of the pair of consecutive switching elements 109a in the converter leg 104a. Similarly, the consecutive pair of switching elements 109d is located in the converter leg 104b at a downstream location corresponding to a downstream location of the pair of consecutive switching elements 109b in the converter leg 104a.

[0061] The switching elements comprised in the pairs of consecutive switching elements 109a-d are connected in series, and thus have a shared terminal where the connection between the switching elements is made. For example, the pair of consecutive switching elements 109a has a shared terminal 110a; the pair of consecutive switching elements 109d has a shared terminal 110d.

[0062] Each pair of consecutive switching elements 109a-b of the converter leg 104a is connected at a shared terminal 110a-110b of the pair of consecutive switching elements 109a-b via a respective balancing inductor 111a-d to a shared terminal of a respective pair of consecutive switching elements 109c-d of the converter leg 104b located at the downstream location corresponding to the downstream location of the pair of consecutive switching elements 109a-b in the converter leg 104a. For example, the pair of consecutive switching elements 109a is connected at its shared terminal 110a via balancing inductor 111a to the shared terminal 110c of the pair of consecutive switching elements 109c. The pair of consecutive switching elements 109b is connected at its shared terminal 110b via balancing inductor 111b to the shared terminal 110d of the pair of consecutive switching elements 109d.

[0063] A capacitor may be connected to the converter leg 104a via the shared terminals 110a and 110b as shown in Fig. 1.

[0064] Fig. 2 schematically shows a multi-level power converter according to a second embodiment of the invention.

[0065] The second embodiment of the invention schematically shown in Fig. 2 is identical to the first embodiment of the invention schematically shown in Fig. 1 , with the difference that the multilevel power converter 101 is a neutral-point clamped multi-level power converter. Fig. 3 schematically shows a multi-level power converter according to a third embodiment of the invention.

[0066] The third embodiment of the invention schematically shown in Fig. 3 is identical to the first embodiment of the invention schematically shown in Fig. 1 , with the difference that the multilevel power converter 101 comprises an additional converter leg 104c.

[0067] In this embodiment, each first pair of consecutive switching elements 109a-f of all directly neighboring consecutive converter legs 104a-c is connected at a shared terminal 110a-f of a respective first pair of connected switching elements 109a-f via a respective balancing inductor 111a-d to the shared terminal 110a-f of a respective second pair of consecutive switching elements 109a-h. A second pair of consecutive switching elements 109a-f connected in such a manner to a first pair of consecutive switching elements 109a-f is located in a second converter leg 104a-c at a downstream location corresponding to a downstream location of the first pair of consecutive switching elements 109a-f in a first converter leg 104a-c, wherein the first converter leg 104a-c and the second converter leg 104a-c are directly neighboring.

[0068] Converter legs 104a and 104b are directly neighboring. Converter legs 104b and 104c are directly neighboring. However, converter legs 104a and 104c are not directly neighboring. The pair of consecutive switching elements 109a of the converter leg 104a is connected at its shared terminal 110a via balancing inductor 111 a to the shared terminal 110c of the pair of consecutive switching elements 109c of the converter leg 104b. Similarly, the pair of consecutive switching elements 109b of the converter leg 104a is connected at its shared terminal 110b via balancing inductor 111 b to the shared terminal 110d of the pair of consecutive switching elements 109d of the converter leg 104b.

[0069] The pair of consecutive switching elements 109c of the converter leg 104b is connected at its shared terminal 110c via balancing inductor 111c to the shared terminal 110e of the pair of consecutive switching elements 109e of the converter leg 104c. Similarly, the pair of consecutive switching elements 109d of the converter leg 104b is connected at its shared terminal 110d via balancing inductor 111d to the shared terminal 110f of the pair of consecutive switching elements 109f of the converter leg 104c.

[0070] Therefore, this embodiment demonstrates how the invention is scaled to an increasing number of parallel converter legs of the multi-level power converter. The invention is scalable to an arbitrary number of parallel converter legs of the multi-level power converter.

[0071] Fig. 4 schematically shows a multi-level power converter according to a fourth embodiment of the invention.

[0072] The fourth embodiment of the invention schematically shown in Fig. 4 is identical to the first embodiment of the invention schematically shown in Fig. 1 , with the difference that the parallel converter legs 104a-b of the multi-level power converter 101 comprise six switching elements instead of four. For example, converter leg 104a comprises switching elements 105a-f. Half of the switching elements 105a-f is arranged in the converter leg 104a between the high voltage terminal 102 and the midpoint terminal 106a; the other half of the switching elements 105a-f is arranged in the converter leg 104a between the midpoint terminal 106a and the low voltage terminal 103. In other words, three switching elements 105a-c are arranged in the converter leg 104a between the high voltage terminal 102 and the midpoint terminal 106a, and three switching elements are arranged in the converter leg 104a between the midpoint terminal 106a and the low voltage terminal 103. Six switching elements are similarly arranged in the converter leg 104b. Thus, the multi-level power converter of the fourth embodiment comprises four levels. The multi-level power converter of the first embodiment comprises three levels.

[0073] Converter leg 104a comprises four pairs of consecutive switching elements: two pairs of consecutive switching elements 109a-b are located between the high voltage terminal 102 and the midpoint terminal 106a. Two pairs of consecutive switching elements 109c-d are located between the midpoint terminal 106a and the low voltage terminal 103. Similarly, converter leg 104b comprises four pairs of consecutive switching elements: two pairs of consecutive switching elements 109e-f are located between the high voltage terminal 102 and the midpoint terminal 106b. Two pairs of consecutive switching elements 109g-h are located between the midpoint terminal 106b and the low voltage terminal 103.

[0074] Thus, in converter leg 104a, the pair of consecutive switching elements 109a comprises switching elements 105a and 105b. The pair of consecutive switching elements 109b comprises switching elements 105b and 105c. The pair of consecutive switching elements 109c comprises switching elements 105d and 105e. The pair of consecutive switching elements 109d comprises switching elements 105e and 105f.

[0075] Each first pair of consecutive switching elements 109a-d of the converter leg 104a is connected at a respective shared terminal 110a-d via a respective balancing inductor 111a-d to the shared terminal 110e-h of a respective second pair of consecutive switching elements 109e-f of the converter leg 104b. The second pair of consecutive switching elements 109e-f is located in the converter leg 104b at a downstream location corresponding to the downstream location of the first pair of consecutive switching elements 109e-f in the converter leg 104a.

[0076] Therefore, this embodiment demonstrates how the invention is scaled to an increasing number of levels of the multi-level power converter. The invention is scalable to an arbitrary number of levels of the multi-level power converter.

[0077] Fig. 5 schematically shows a multi-level power converter according to a fifth embodiment of the invention. The fifth embodiment of the invention schematically shown in Fig. 5 is identical to the first embodiment of the invention schematically shown in Fig. 1 , except for the differences described below.

[0078] In this embodiment, the multi-level power converter 101 comprises four parallel converter legs 104a-d. The converter legs 104a-d are divided in two parallel leg groups 501 a-b. The parallel leg groups 501 a-b each comprise two directly neighbouring converter legs 104a-d. The parallel leg group 501a comprises converter legs 104a-b and the parallel leg group 501b comprises converter legs 104c-d.

[0079] Within each parallel leg group 501 a-b, each first pair of consecutive switching elements 109a-h of a first converter leg 104a-d is connected at a shared terminal 110a-110h of a respective first pair of consecutive switching elements 109a-h of the first converter leg 104a-d via a respective balancing inductor 111a-d to a shared terminal 110a-110h of a respective second pair of consecutive switching elements 109a-h of the second converter leg 104a-d. The first converter leg 104a-d and the second converter leg (104a-d) are comprised in the same parallel leg group 501 a-b.

[0080] For example, within parallel leg group 501a, the pair of consecutive switching elements 109a of the converter leg 104a is connected at shared terminal 110a via a balancing inductor 111a to shared terminal 110c of the pair of consecutive switching elements 109c of the converter leg 104b. Similarly, within parallel leg group 501b, the pair of consecutive switching elements 109e of the converter leg 104c is connected at shared terminal 110e via a balancing inductor 111c to shared terminal 110g of the pair of consecutive switching elements 109g of the converter leg 104d.

[0081] Therefore, groups of consecutive switching elements 109a-109h that are not comprised in converter legs 104a-d that are comprised in the same parallel leg group 501 a-b are not connected via a balancing inductor 111a-111d.

[0082] In this embodiment, the number of required components is reduced.

[0083] Fig. 6 schematically shows a multi-level converter system 601 according to an embodiment of the third aspect of the invention.

[0084] The multi-level converter system 601 comprises a multi-level power converter 101 according to the first aspect of the invention. For example, the multi-level power converter 101 is a multi-level power converter 101 according to one of the embodiments of the first aspect of the invention as schematically shown in Figs. 1-5.

[0085] Further, the multi-level converter system (601) comprises a controller 602, connected to the multi-level power converter 101 and configured to control the switching elements 105a- 105d of the converter legs 104a-b of the multi-level power converter 101 by applying the method according to the second aspect of the invention. Fig. 7 schematically shows an electric vehicle 701 according to an embodiment of the fourth aspect of the invention.

[0086] The electric vehicle 701 comprises a multi-level power converter system 601 according to the third aspect of the invention. For example, the electric vehicle 701 comprises a multi-level power converter system 601 according to one of the embodiments of the first aspect of the invention as schematically shown in Fig. 6.

[0087] Further, the electric vehicle comprises a battery 702, connected to the direct current port 112 of the multi-level power converter 101 of the multi-level power converter system 601.

[0088] Further, the electric vehicle comprises an electric motor 703, connected to the alternating current port 114 of the multi-level power converter 101 of the multi-level power converter system 601.

[0089] As required, this document describes detailed embodiments of the present invention. However it must be understood that the disclosed embodiments serve exclusively as examples, and that the invention may also be implemented in other forms. Therefore specific constructional aspects which are disclosed herein should not be regarded as restrictive for the invention, but merely as a basis for the claims and as a basis for rendering the invention implementable by the average skilled person. Furthermore, the various terms used in the description should not be interpreted as restrictive but rather as a comprehensive explanation of the invention. The word "a" used herein means one or more than one, unless specified otherwise. The phrase "a plurality of' means two or more than two. The words "comprising" and "having" do not exclude the presence of more elements. Reference figures in the claims should not be interpreted as restrictive of the invention. Particular embodiments need not achieve all objects described. The mere fact that certain technical measures are specified in different dependent claims still allows the possibility that a combination of these technical measures may advantageously be applied.

[0090] Embodiments and further embodiments of the present invention may be expressed in words as set out in the following clauses:

[0091] Clause 1. A multi-level power converter (101), comprising a high voltage terminal (102), a low voltage terminal (103) and a number p of parallel converter legs (104a-d) arranged between the high voltage terminal (102) and the low voltage terminal (103), p being at least two, wherein:

[0092] • each converter leg (104a-d) comprises a same even number n switching elements (105a-f), n being at least four;

[0093] • the switching elements (105a-f) of each converter leg (104a-d) are connected in series in a downstream fashion between the high voltage terminal (102) and the low voltage terminal (103); • each converter leg (104a-d) comprises a midpoint terminal (106a-d), the midpoint terminal (106a-d) of each converter leg (104a-d) being arranged such that the number of switching elements (105a-f) comprised by a respective converter leg (104a-d) between the high voltage terminal (102) and the midpoint terminal (106a-d) is and the number of switching elements (105a-f) comprised by the respective converter leg (104a-d) between the midpoint terminal (106a-d) and the low voltage terminal (103) is n.

[0094] 2 ’

[0095] • the midpoint terminal (106a-d) of each converter leg (104a-d) is connected via a respective output inductor (107a-d) to a common output terminal (108);

[0096] • the high voltage terminal (102) and the low voltage terminal (103) form a direct current port (112), the direct current port (112) being connectable to a direct current power source (113);

[0097] • the output terminal (108) and the low voltage terminal (103) form an alternating current port (114), the alternating current port (114) being connectable to an alternating current load (115); characterized in that:

[0098] • a first pair of consecutive switching elements (109a-h) of a first converter leg (104a-d), the first pair of consecutive switching elements (109a-h) being located between the high voltage terminal (102) and the midpoint terminal (106a-d) of the first converter leg (104a-d) or between the midpoint terminal (106a-d) of the first converter leg (104a-d) and the low voltage terminal (103), is connected at a shared terminal (110a-f) of the first pair of consecutive switching elements (109a-h) via a balancing inductor (111a-d) having an inductance value to a shared terminal (110a-f) of a second pair of consecutive switching elements (109a-h), the second pair of consecutive switching elements (109a-h) being located in a second converter leg (104a-d) at a downstream location corresponding to a downstream location of the first pair of consecutive switching elements (109a-h) in the first converter leg (104a-d).

[0099] Clause 2. Multi-level power converter (101) according to clause 1 , wherein:

[0100] • the first converter leg (104a-d) and the second converter leg (104a-d) are directly neighboring converter legs (104a-d) of the multi-level power converter (101).

[0101] Clause 3. Multi-level power converter (101) according to any one of the preceding clauses, wherein: each first pair of consecutive switching elements (109a-h) of the first converter leg (104a- d) is connected at the shared terminal (110a-f) of a respective first pair of consecutive switching elements (109a-h) of the first converter leg (104a-d) via a respective balancing inductor (111a-d) to the shared terminal (110a-f) of a respective second pair of consecutive switching elements (109a-h) of the second converter leg (104a-d).

[0102] Clause 4. Multi-level power converter (101) according to clause 2 and clause 3, wherein:

[0103] • each first pair of consecutive switching elements (109a-h) of all directly neighboring consecutive converter legs (104a-d) is connected at the shared terminal (110a-f) of a respective first pair of connected switching elements (109a-h) via a respective balancing inductor (111a-d) to the shared terminal (110a-f) of a respective second pair of consecutive switching elements (109a-h).

[0104] Clause 5. Multi-level power converter (101) according to any one of clauses 1-3, wherein:

[0105] • the p parallel converter legs (104a-d) are divided in a number of k parallel leg groups (501 a-b), each parallel leg group (501 a-b) comprising directly neighboring parallel converter legs (104a-d) of the multi-level power converter (101), k being at least two;

[0106] • all parallel converter legs (104a-d) are comprised in a single parallel leg group (501 a-b);

[0107] • the first converter leg (104a-d) and the second converter leg (104a-d) are comprised in the same parallel leg group (501 a-b).

[0108] Clause 6. Multi-level power converter (101) according to any one of the preceding clauses, wherein: the inductance value of the balancing inductor (111a-d) has a value depending on a number of levels (nroflevels) of the multi-level power converter (101), an output current (lout) of the multi-level power converter (101), a bus voltage (VbUS) of the multi-level power converter (101), and a target rate of voltage change over time (^^); wherein the number of levels of the multi-level power converter (101) is + 1.

[0109] Clause 7. Multi-level power converter (101) according to clause 6, wherein: the inductance value of the balancing inductor (111a-d) is determined based on a formula

[0110] Tnse-desired is a desired bus voltage rise time of the multi-level power converter (101);

[0111] Trise-switch is a rise time of the switching elements (105a-f); nrofsteps is p * (nrof levels — 1). Clause 8. Multi-level power converter (101) according to any one of the preceding clauses, wherein:

[0112] • the inductance value of the balancing inductor (111 a-d) is in a range of 10nH-1 OOnH to compensate a parasitic drain inductance in the multi-level convertor (101) in a range of 100pH - 500pH.

[0113] Clause 9. Multi-level power converter (101) according to any one of the preceding clauses, wherein the multi-level converter (101) is a flying-capacitor multi-level power converter.

[0114] Clause 10. Multi-level power converter (101) according to any one of the preceding clauses, wherein the multi-level converter (101) is a neutral-point clamped multi-level power converter.

[0115] Clause 11. Multi-level power converter (101) according to any one of the preceding clauses, wherein a capacitor is connected to the first converter leg (104a) via shared terminals (110a-f) to form a parallel connection.

[0116] Clause 12. Multi-level power converter (101) according to any one of the preceding clauses, wherein the switching elements (105a-105d) are gallium nitride high electron mobility transistors.

[0117] Clause 13. Method of controlling a multi-level power converter (101) according to any one of clauses 1-12, starting in a state where:

[0118] • the switching elements (105a-105d) of all converter legs (104a-b) between the high voltage terminal (102) and the midpoint terminal (106a-b) of each converter leg (104a-b) are closed; and

[0119] • the switching elements (105a-105d) of all converter legs (104a-b) between the midpoint terminal (106a-b) of each converter leg (104a-b) and the low voltage terminal (103) are opened; the method comprising the steps of:

[0120] • for each converter leg (104a-b), in turn: o opening, in turn, each switching element (105a-105d) of a respective converter leg (104a-b) between the high voltage terminal (102) and the midpoint terminal (106a- b) of the respective converter leg (104a-b), in upstream order, starting with a switching element (105a-105d) closest to the midpoint terminal (106a-b) of the respective converter leg (104a-b), and ending with a switching element (105a- 105d) closest to the high voltage terminal (102);

[0121] • for each converter leg (104a-b), simultaneously: o closing, simultaneously, each switching element (105a-105d) of a respective converter leg (104a-b) between the midpoint terminal (106a-b) of the respective converter leg (104a-b) and the low voltage terminal (103). Clause 14. Multi-level power converter system (601), comprising:

[0122] • a multi-level power converter (101) according to any one of clauses 1-11 ;

[0123] • a controller (602), connected to the multi-level power converter (101) and configured to control the switching elements (105a-105d) of the converter legs (104a-b) of the multilevel power converter (101) by applying the method according to clause 13.

[0124] Clause 15. Electric vehicle (701), comprising:

[0125] • a multi-level power converter system (601) according to clause 13;

[0126] • a battery (702), connected to the direct current port (112) of the multi-level power converter (101) of the multi-level power converter system (601); • an electric motor (703), connected to the alternating current port (114) of the multi-level power converter (101) of the multi-level power converter system (601).

Claims

CLAIMS1. A multi-level power converter (101), comprising a high voltage terminal (102), a low voltage terminal (103) and a number p of parallel converter legs (104a-d) arranged between the high voltage terminal (102) and the low voltage terminal (103), p being at least two, wherein:• each converter leg (104a-d) comprises a same even number n switching elements (105a-f), n being at least four;• the switching elements (105a-f) of each converter leg (104a-d) are connected in series in a downstream fashion between the high voltage terminal (102) and the low voltage terminal (103), and wherein the downstream fashion is defined as a direction from the high voltage terminal towards the low voltage terminal;• each converter leg (104a-d) comprises a midpoint terminal (106a-d), the midpoint terminal (106a-d) of each converter leg (104a-d) being arranged such that the number of switching elements (105a-f) comprised by a respective converter leg (104a-d) between the high voltage terminal (102) and the midpoint terminal (106a-d) is and the number of switching elements (105a-f) comprised by the respective converter leg (104a-d) between the midpoint terminal (106a-d) and the low voltage terminal (103) is n.2 ’• the midpoint terminal (106a-d) of each converter leg (104a-d) is connected via a respective output inductor (107a-d) to a common output terminal (108);• the high voltage terminal (102) and the low voltage terminal (103) form a direct current port (112), the direct current port (112) being connectable to a direct current power source (113);• the output terminal (108) and the low voltage terminal (103) form an alternating current port (114), the alternating current port (114) being connectable to an alternating current load (115); characterized in that:• a first pair of consecutive switching elements (109a-h) of a first converter leg (104a-d), the first pair of consecutive switching elements (109a-h) being located between the high voltage terminal (102) and the midpoint terminal (106a-d) of the first converter leg (104a-d) or between the midpoint terminal (106a-d) of the first converter leg (104a-d) and the low voltage terminal (103), is connected at a shared terminal (110a-f) of the first pair of consecutive switching elements (109a-h) via a balancing inductor (111a-d) having an inductance value to a shared terminal (110a-f) of a second pair of consecutive switching elements (109a-h), the second pair of consecutive switching elements (109a-h) being located in a second converter leg (104a-d) at a downstreamlocation corresponding to a downstream location of the first pair of consecutive switching elements (109a-h) in the first converter leg (104a-d).

2. Multi-level power converter (101) according to claim 1 , wherein:• the first converter leg (104a-d) and the second converter leg (104a-d) are directly neighboring converter legs (104a-d) of the multi-level power converter (101).

3. Multi-level power converter (101) according to any one of the preceding claims, wherein:• each first pair of consecutive switching elements (109a-h) of the first converter leg (104a- d) is connected at the shared terminal (110a-f) of a respective first pair of consecutive switching elements (109a-h) of the first converter leg (104a-d) via a respective balancing inductor (111a-d) to the shared terminal (110a-f) of a respective second pair of consecutive switching elements (109a-h) of the second converter leg (104a-d).

4. Multi-level power converter (101) according to claim 2 and claim 3, wherein:• each first pair of consecutive switching elements (109a-h) of all directly neighboring consecutive converter legs (104a-d) is connected at the shared terminal (110a-f) of a respective first pair of connected switching elements (109a-h) via a respective balancing inductor (111a-d) to the shared terminal (110a-f) of a respective second pair of consecutive switching elements (109a-h).

5. Multi-level power converter (101) according to any one of claims 1-3, wherein:• the p parallel converter legs (104a-d) are divided in a number of k parallel leg groups (501 a-b), each parallel leg group (501 a-b) comprising directly neighboring parallel converter legs (104a-d) of the multi-level power converter (101), k being at least two;• all parallel converter legs (104a-d) are comprised in a single parallel leg group (501 a-b);• the first converter leg (104a-d) and the second converter leg (104a-d) are comprised in the same parallel leg group (501 a-b).

6. Multi-level power converter (101) according to any one of the preceding claims, wherein:• the inductance value of the balancing inductor (111 a-d) has a value depending on a number of levels (nroflevels) of the multi-level power converter (101), an output current (lout) of the multi-level power converter (101), a bus voltage (VbUS) of the multi-level power converter (101), and a target rate of voltage change over time (^^); wherein the number of levels of the multi-level power converter (101) is + 1.

7. Multi-level power converter (101) according to claim 6, wherein: the inductance value of the balancing inductor (111a-d) is determined based on a formulaTnse-desired is a desired bus voltage rise time of the multi-level power converter (101);Trise-switch is a rise time of the switching elements (105a-f); nrofsteps is p * (nrof levels — 1).

8. Multi-level power converter (101) according to any one of the preceding claims, wherein: • the inductance value of the balancing inductor (111 a-d) is in a range of 10nH-1 OOnH to compensate a parasitic drain inductance in the multi-level convertor (101) in a range of 100pH - 500pH.

9. Multi-level power converter (101) according to any one of the preceding claims, wherein the multi-level converter (101) is a flying-capacitor multi-level power converter.

10. Multi-level power converter (101) according to any one of the preceding claims, wherein the multi-level converter (101) is a neutral-point clamped multi-level power converter.

11. Multi-level power converter (101) according to any one of the preceding claims, wherein:• the switching elements (105a-105d) are gallium nitride high electron mobility transistors.

12. Method of controlling a multi-level power converter (101) according to any one of claims 1-11 , starting in a state where:• the switching elements (105a-105d) of all converter legs (104a-b) between the high voltage terminal (102) and the midpoint terminal (106a-b) of each converter leg (104a-b) are closed; and• the switching elements (105a-105d) of all converter legs (104a-b) between the midpoint terminal (106a-b) of each converter leg (104a-b) and the low voltage terminal (103) are opened; the method comprising the steps of:• for each converter leg (104a-b), in turn: o opening, in turn, each switching element (105a-105d) of a respective converter leg (104a-b) between the high voltage terminal (102) and the midpoint terminal (106a- b) of the respective converter leg (104a-b), in upstream order, starting with a switching element (105a-105d) closest to the midpoint terminal (106a-b) of therespective converter leg (104a-b), and ending with a switching element (105a- 105d) closest to the high voltage terminal (102);• for each converter leg (104a-b), simultaneously: o closing, simultaneously, each switching element (105a-105d) of a respective converter leg (104a-b) between the midpoint terminal (106a-b) of the respective converter leg (104a-b) and the low voltage terminal (103).

13. Multi-level power converter system (601), comprising:• a multi-level power converter (101) according to any one of claims 1-11;• a controller (602), connected to the multi-level power converter (101) and configured to control the switching elements (105a-105d) of the converter legs (104a-b) of the multilevel power converter (101) by applying the method according to claim 13.

14. Electric vehicle (701), comprising:• a multi-level power converter system (601) according to claim 13;• a battery (702), connected to the direct current port (112) of the multi-level power converter (101) of the multi-level power converter system (601);• an electric motor (703), connected to the alternating current port (114) of the multi-level power converter (101) of the multi-level power converter system (601).

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