Resonance inverter

Abstract

A resonant inverter (10) that is particularly favorable with regard to its electromagnetic compatibility (EMC), especially for supplying power to an electric drive motor in a motor vehicle, comprises two switches (SLS, SHS) connected to a phase output (OPH) for each phase provided, and an auxiliary branch (14) connected to the phase output (OPH) which includes an inductor (LAUX), wherein each of the two switches (SLS, SHS) has at least one adjustable snubber capacitance (CSNL, CSNH).

Description

[0001] The present invention relates to a resonant inverter, also called an ARCP (“Auxiliary Resonant Commutated Pole”) inverter. State of the art

[0002] US 5642273 A discloses a resonant inverter for a motor, using a single semiconductor switch for resonant snubber branches equipped with inductors. The proposed circuit topology requires few components overall.

[0003] US2013 / 293008 A1 discloses resonant inverters for an electrical power supply for a radiation source and techniques to actively add a snubber capacitance to a resonant inverter at currents above a threshold value.

[0004] US2013 / 0049654 A1 discloses an inverter for a motor in a motor vehicle, wherein a half-bridge has snubber branches, each with a resistor, a capacitor and a switching element, wherein the snubber branches are connected in parallel to each other.

[0005] US 6 205 040 B1 discloses a three-point or multi-point inverter with snubber capabilities.

[0006] WO 2021 / 221680 A1 reveals possibilities for dynamically changing the capacitance values ​​of capacitors. Disclosure of the invention

[0007] Battery electric vehicles are often equipped with drive motors in the form of three-phase machines.

[0008] Inverters are used to convert the direct current from the battery into the multi-phase alternating current required by such three-phase machines.

[0009] Due to their high efficiency, inverter topologies such as the "Auxiliary Resonant Commutated Pole" (ARCPI) inverter, which is also referred to as a resonant inverter in the following, can be used.

[0010] Such resonant inverters can comprise one half-bridge per output phase. Each half-bridge has at least one snubber capacitor. An inductive auxiliary branch is also connected to the phase output, and thus to the contact point of the half-bridge. This inductive auxiliary branch can be switched on or off as needed, for example, by means of semiconductor switches.

[0011] Depending on the phase current at the phase output and the direction of commutation, a resonant inverter operates in two different modes. In a so-called CSC mode, the inductive auxiliary branch is not used. In a so-called ACSC mode, however, the inductive auxiliary branch is utilized.

[0012] In particular, due to the CSC mode, resonant inverters often exhibit insufficient electromagnetic compatibility (EMC).

[0013] The object of the present invention is therefore to offer a resonant inverter with improved EMC.

[0014] The problem is solved by a resonant inverter, particularly for supplying power to an electric drive motor in a motor vehicle. The resonant inverter comprises two switches connected to a phase output for each provided phase, and an auxiliary branch connected to the phase output which includes an inductor, wherein each of the two switches has at least one adjustable snubber capacitance.

[0015] This surprisingly simple solution is based, among other things, on the idea that adjusting the snubber capacitance can improve the EMC performance of the resonant inverter.

[0016] This is based on the further idea that EMC also depends on the strength of the phase current at the phase output. In particular, higher phase currents have so far led to a deterioration of EMC. Among other things, commutation times can be shortened. Voltage waveforms, especially voltage rises, become increasingly linear with increasing phase currents. High-frequency components occur more frequently.

[0017] The proposed resonant inverter now offers the possibility of adjusting the snubber capacitance using the adjustable snubber capacitance. Higher snubber capacitances can increase the period of oscillations. Commutation, and thus the maximum voltage transconductance, can therefore be reduced. Increasing the snubber capacitance can thus counteract the negative effects of higher phase currents.

[0018] Accordingly, the proposed resonant inverter allows the snubber capacitance to be adjusted depending on, for example, the phase current at the phase output. EMC can thus be improved overall by continuously adjusting the snubber capacitances to the respective phase currents.

[0019] This allows the advantages of resonant inverters, such as very high efficiencies, to be retained.

[0020] A simple way to provide electronically different snubber capacitances can be achieved if the adjustable snubber capacitance comprises at least two individual snubber capacitances, for example using capacitors.

[0021] It is particularly conceivable that, with the exception of a base capacitance, each of the adjustable snubber capacitances can be switched on or off by a separate switch. If the snubber capacitances, especially the capacitors, are connected in parallel, the adjustable snubber capacitance can be increased stepwise by adding one of the snubber capacitances at a time. If the phase current is known, the required snubber capacitance can be set directly by selecting the relevant capacitors and their corresponding switches.

[0022] The resonant inverter can be configured to add at least one additional snubber capacitance before resonant commutations in ACSC mode and non-resonant commutations in CSC mode, so that EMC can be improved.

[0023] The resonant inverter can be configured to add an additional snubber capacitance to only one of the two switches at a time.

[0024] Preferably, the switch across which there is no voltage drop can be selected to add the additional capacitance under "zero-voltage switching" (hereinafter: ZVS) conditions, and thus with particularly low switching losses. The snubber capacitance can therefore be switched "softly".

[0025] Losses can be avoided by switching snubber capacitances on or off when the resonant inverter is set up to switch on a snubber capacitance under ZVS conditions.

[0026] Accordingly, further energy savings can be achieved if the resonant inverter is set up to switch off an added snubber capacity again under ZVS conditions after a subsequent commutation.

[0027] Further features and advantages of the invention will become apparent from the following detailed description of an embodiment of the invention with reference to the figures of the drawing, which show details essential to the invention, as well as from the claims.

[0028] The individual features can be implemented individually or in any combination in various versions of the invention. The schematic drawing illustrates exemplary embodiments of the invention, which are explained in more detail in the following description. Brief description of the drawings

[0029] They show: Fig. 1 a circuit topology of a resonant inverter and Fig. 2 diagrams showing the effect of different snubber capacities. Embodiments of the invention

[0030] To facilitate understanding of the invention, the same reference numerals are used for corresponding elements in the following description of the figures.

[0031] Fig. Figure 1 shows a circuit topology of a resonant inverter 10. The resonant inverter 10 is single-phase. By replicating the circuit topology of the resonant inverter 10 shown here, a multi-phase resonant inverter, for example a three-phase resonant inverter, can also be built analogously.

[0032] The resonant inverter 10 can, for example, be used to supply power to an electric drive motor in an electrically powered motor vehicle.

[0033] It features a half-bridge with two switches SHS and SLS, which are connected to each other at its phase output OPH. At phase output OPH, it provides an output current IPH.

[0034] Auxiliary branch 14 also branches off from the phase output OPH. Auxiliary branch 14 has an inductor LAUX. The auxiliary branch 14 can be switched on or off via two opposing semiconductor switches SAUX,P and SAUX,N with associated freewheeling diodes DAUX,P and DAUX,N. Its terminal opposite the phase output OPH is connected to a center point 12.

[0035] The midpoint 12 corresponds to a mean voltage potential of +UDC / 2 or -UDC / 2 relative to a negative or positive potential UN or UP, respectively.

[0036] The switches SHS and SLS of the half-bridge can be, for example, MOSFETs or IGBTs. They can be SiC-based. Freewheeling diodes DHS and DLS, respectively, are connected in parallel to the switches SHS and SLS.

[0037] Furthermore, each switch SHS and SLS has adjustable snubber capacitances CSNH and CSNL, respectively. Each of the adjustable snubber capacitances CSNH and CSNL has a base capacitance CSNH0 and CSNL0, respectively.

[0038] In parallel to the basic capacitors CSNH0 and CSNL0, additional capacitors are connected as supplementary snubber capacitors. Each of these additional capacitors is connected in series with an associated switch, allowing them to be individually switched on or off. In principle, a large number of such additional capacitors, along with their associated switches, can be connected in parallel to the basic capacitors CSNH0 and CSNL0. Fig. Figure 1 shows two additional capacitances per switch SHS and SLS as examples. In the case of switch SHS, the additional snubber capacitance CSNH1 is connected in series with a switch SSNH1, and the additional snubber capacitance CSNH2 is connected in series with a switch SSNH2. Fig. Figure 1 shows the following: In the SLS switch, the additional snubber capacity CSNL1 is connected in series with a switch SSNL1 and the additional snubber capacity CSNL2 with a switch SSNL2.

[0039] A control (in Fig. (1 not shown) of the resonant inverter 10 switches on at least one of the additional snubber capacitances CSNH1, CSNH2, CSNL1 and / or CSNL2 using the respective associated switches SSNH1, SSNH2, SSNL1 and / or SSNL2, each before resonant commutations in ACSC modes and non-resonant commutations in CSC modes.

[0040] The selection of additional snubber capacitances, and thus the setting of the effective snubber capacitance, can be determined, for example, based on the phase current IPH drawn from a load, particularly an electric motor, via the phase output OPH. The controller activates additional snubber capacitances CSNH1, CSNH2, CSNL1, and / or CSNL2 only at one of the two switches SHS or SLS. After subsequent commutation, the respective additional snubber capacitances CSNH1, CSNH2, CSNL1, and / or CSNL2 are deactivated. The controller activates or deactivates the snubber capacitances CSNH1, CSNH2, CSNL1, and / or CSNL2 under ZVS conditions.

[0041] Fig. Figure 2 shows diagrams illustrating the effect of different effective snubber capacitances. It can be seen that with increasing effective snubber capacitance of the adjustable snubber capacitances CSNH, CSNL, voltage peaks of the output voltage ULS, measured between the phase output OPH and the negative voltage potential UN, decrease and phase durations can increase. Correspondingly, voltage slew rates du / dt decrease.

[0042] In total, the resonance inverter can handle 10 (see Fig. 1) thereby exhibiting improved frequency response and thus improved EMC. QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0000] US 5642273 A

[0002] US 2013 / 293008 A1

[0003] US 2013 / 0049654 A1

[0004] US 6 205 040 B1

[0005] WO 2021 / 221680 A1

[0006]

Claims

[1] Resonance inverter (10), in particular for supplying power to an electric drive motor in a motor vehicle, comprising each provided phase - two switches (SLS, SHS) connected to a phase output (OPH), and - an auxiliary branch (14) connected to the phase output (OPH), comprising an inductor (LAUX), - where each of the two switches (SLS, SHS) has at least one adjustable snubber capacity (CSNL, CSNH). [2] Resonance inverter according to the previous claim, characterized by , that the adjustable snubber capacity (CSNL, CSNH) each comprises at least two individual snubber capacities (CSNH0, CSNH1, CSNH2, CSNL0, CSNL1, CSNL2). [3] Resonance inverter according to any of the preceding claims, characterized by, that with the exception of a basic capacity (CSNH0, CSNH1) each snubber capacity of the adjustable snubber capacity (CSNL, CSNH) can be switched on or off by a separate switch (SSNH1, SSNH2, SSNL1, SSNL2). [4] Resonance inverter according to any of the preceding claims, characterized by , that the resonant inverter is set up to add at least one additional snubber capacity (CSNH1, CSNH2, CSNL1, CSNL2) before resonant commutations in ACSC mode and non-resonant commutations in CSC mode. [5] Resonance inverter according to any of the preceding claims, characterized by , that the resonant inverter (10) is set up to add an additional snubber capacitance (CSNH1, CSNH2, CSNL1, CSNL2) to only one of the two switches (SLS, SHS) at a time. [6] Resonance inverter according to any of the preceding claims, characterized by, that the resonant inverter (10) is set up to switch on an additional snubber capacity (CSNH1, CSNH2, CSNL1, CSNL2) under ZVS conditions. [7] Resonance inverter according to any of the preceding claims, characterized by , that the resonant inverter (10) is configured to switch off an additional snubber capacity (CSNH1, CSNH2, CSNL1, CSNL2) after a subsequent commutation under ZVS conditions.

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