Saturable Core Inductors

Abstract

A saturable core inductor (20) includes a magnetic core structure having an unsaturable portion (24A, 24B) and a saturable portion (22A, 22B). The unsaturable core portion includes at least one core body (24A, 24B) arranged to form a closed magnetic circuit having at least one air gap (26A, 26B). The saturable core portion includes a core bridge element (26A, 26B) inserted into each of the at least one air gap (26A, 26B) to form a magnetic bridge across the air gap for closing the magnetic circuit. Each bridge element (26A, 26B) and the core body (24A, 24B) are configured to be unsaturated at a predetermined low current level to provide low current high inductance. Each bridge element (26A, 26B) is configured to fully saturate first as current levels increase and quickly drop inductance from low current high inductance to low inductance, while the air gap (26A, 26B) is configured to prevent the core (24A, 24B) from fully saturating.

Description

Technical Field

[0001] The present invention relates to inductors, and in particular to saturable core inductors for alternating current (AC) applications. Background Art

[0002] Saturable cores have been used in low frequency applications, especially dc-link filter chokes in ac drives. In these applications, the current frequency typically does not exceed the ripple frequency of the current in the dc-link filter choke, which in a 50 Hz supply is about 300 Hz without any significant harmonics above 300 Hz. There, the saturation characteristic is designed to achieve a "one size fits all" design, i.e. the inductance increases as the nominal current decreases. In addition, the input current harmonic distortion at partial load is also greatly reduced. Examples of saturable core dc-link filter chokes are disclosed in US8035470 and US7889040.

[0003] Saturable core inductors are also used in high frequency applications where the current frequency can be several orders of magnitude higher than the current ripple frequency in the dc-link filter choke, such as over 1 kHz or tens of kHz. One such application is the resonant branch in the auxiliary resonant pole commutation (ARCP) topology. ARCP has obvious potential advantages in motor drive applications. By suitable selection of resonant circuit parameters, the output voltage waveform during commutation can be shaped to be motor-friendly. Stress in the motor insulation and bearings is thereby reduced. For example, the basic configuration and operation of ARCP are described in the article "Auxiliary Resonant Pole Commutation Converter" of the IEEE-IAS Reference Conference Proceedings 1990, pages 1228-35, and in US5047913 by RWDe Doncker et al. The ARCP inverter includes a dc-link capacitor connected in series between the negative (N) and positive (P) dc-link rails on the dc-link side of the inverter. At the center tap of the capacitor, called the neutral point (NP), a neutral point voltage or potential U NP. Each main switching device of the inverter is provided with an anti-parallel diode and is associated with a resonant capacitor. In addition, an auxiliary circuit including a resonant inductor and (one or more) auxiliary switching devices is connected between the neutral point and the phase output. The difference between an ARCP inverter and a hard-switching inverter lies in the commutation between states. In ARCP, the commutation is accomplished by an auxiliary circuit in a limited time. The auxiliary circuit is only used when the output needs to be commutated from one voltage rail to another. In order to ensure that the inverter output voltage reaches at least the positive and negative dc rail voltages during each resonant commutation cycle, a boost current is added to the resonant current by appropriately controlling the conduction time of the auxiliary switching devices and the main switching devices. The amount of boost current is controlled by applying a known voltage to a known resonant inductor during a known boost time. The predetermined boost current level in the resonator inductor adds sufficient energy to the resonant operation to ensure that the output voltage attempts to overshoot the corresponding converter anti-parallel diode and clamps the output voltage to the corresponding rail voltage. Ideally, the main switch is turned on and off under zero voltage conditions, and the auxiliary switch(es) are turned on and off under zero current conditions, which reduces switching losses. Therefore, the switching frequency can be increased without considerable loss losses. The low noise of this type of driver is valued in many applications. High switching frequency also supports higher fundamental output frequencies and low distortion, which makes the ARCP topology very attractive for high-speed drive applications.

[0004] The resonant leg of the ARCPI topology is prone to overvoltage ringing and potential overvoltage on the auxiliary switch, which is mainly caused by the reverse recovery current of the auxiliary diode and the LC resonant circuit. One solution is to use a saturable inductor in series with a conventional cored or coreless resonant inductor. Saturable inductors are designed to provide high inductance at very low current levels, but almost zero inductance above the saturation current. Saturable inductors are used to alleviate the problems caused by the reverse recovery current of the auxiliary diode; reverse current flows in the inductor, and when the diode "cuts off" the current, the energy stored in the inductor must be released. The saturable inductor has high inductance at low currents (the region when the current polarity in the anti-parallel diode is reversed), greatly reducing the rate of change of the auxiliary diode current, causing a delay in the reverse recovery current "cutting off", and reducing the peak energy stored in the inductor (the peak value of the reverse current is reduced).

[0005] The conventional approach to implementing a saturable core is to simply use a toroidal core. Due to the radial symmetry of the shape, the toroid saturates uniformly in the radial dimension. As the current increases, the material in the inner diameter saturates first and finally, at full saturation, the outer ring will also be fully saturated. To minimize eddy current losses in high frequency applications, high resistance ferrite cores or amorphous and nanocrystalline wound cores with film thicknesses of approximately 20 μm are typically employed. In applications where the core material is fully saturated at high frequencies, hysteresis losses become a major issue. The total losses are proportional to the volume of core material that is forced into saturation.

[0006] For applications where the current polarity changes at high frequency, low losses and steep saturation characteristics are required in saturable cores. It is desirable that the drop in inductance relative to the increase in current be very steep. Summary of the invention

[0007] An object of the invention is to provide a saturable core inductor with lower losses and steeper saturation characteristics for high frequency applications. The object of the invention is achieved by a saturable core inductor, the use of a saturable core and an ARCP converter according to the independent claims. Preferred embodiments of the invention are disclosed in the dependent claims.

[0008] One aspect of the present invention is a saturable core inductor comprising

[0009] an inductor wire configured to carry a high frequency AC current,

[0010] A magnetic core structure, the magnetic core structure comprising an unsaturable part and a saturable part,

[0011] wherein the non-saturable portion of the magnetic core structure comprises at least one core body arranged to form a closed magnetic circuit having at least one air gap,

[0012] wherein the saturable portion of the magnetic core structure comprises a core bridge element inserted into each of the at least one air gap to form a magnetic bridge across the air gap for closing the magnetic circuit,

[0013] Wherein each bridge element and at least one core are configured to be unsaturated at a predetermined low current level to provide low current high inductance, and wherein each bridge element is configured to first be fully saturated as the current level increases and thereby quickly drop the inductance from low current high inductance to low inductance, while the remainder of the at least one air gap is configured to prevent the at least one core from being fully saturated.

[0014] In one embodiment, the non-saturable portion of the magnetic core structure includes at least two cores assembled to form a closed magnetic circuit having an air gap between opposite ends of the cores.

[0015] In one embodiment, the magnetic core structure is a toroidal core structure, preferably having two or more cores, more preferably having two semi-toroidal cores.

[0016] In one embodiment, the cross-sectional area of ​​each core bridge element in a plane perpendicular to the magnetic circuit is smaller than the cross-sectional area of ​​at least one core body, so that the core bridge element is fully saturated first and quickly reduces inductance as the AC current level increases, while at least one core body remains unsaturated and defines a low inductance at increasing current levels.

[0017] In one embodiment, the magnetic core structure has an outer periphery and an inner periphery defining a central opening, and each bridge element is configured to extend only a portion of the length of the air gap in a direction from the inner periphery to the outer periphery of the magnetic core structure.

[0018] In one embodiment, each bridge element is inserted into at least one air gap located at the inner periphery of the core structure.

[0019] In one embodiment, the core bridge element is arranged to extend across the entire air gap or across only a portion of the air gap in the direction of the magnetic circuit.

[0020] In one embodiment, the high frequency is above about 1 kHz, preferably above about 10 kHz.

[0021] In one embodiment, the high frequency is a switching frequency of the electrical converter.

[0022] Another aspect of the invention is the use of a saturable core inductor according to an embodiment as a saturable resonant inductor in an auxiliary circuit branch of an ARCP converter.

[0023] Another aspect of the invention is an ARCP converter comprising an auxiliary circuit branch connected between a neutral point and an output node in the ARCP converter, the auxiliary circuit branch comprising a series connection of at least one bidirectional auxiliary switch and a saturable core inductor according to an embodiment of the invention.

[0024] In one embodiment, the bidirectional auxiliary switch includes a pair of switching devices, the paired switching devices being connected back-to-back and provided with anti-parallel diodes.

[0025] In one embodiment, the high frequency is a switching frequency of the bidirectional auxiliary switch, and wherein the AC current is an auxiliary current of the auxiliary circuit branch. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] The present invention will be described in more detail below by means of exemplary embodiments with reference to the accompanying drawings, in which

[0027] In the figure

[0028] Figure 1An exemplary core inductor having a toroidal core structure is shown;

[0029] Figure 2 Shows Figure 1 Magnetic flux density curve of the magnetic core structure;

[0030] Figure 3 An exemplary inductor having a magnetic core structure according to an embodiment is shown;

[0031] Figure 4 Shows Figure 3 Magnetic flux density curve of the magnetic core structure;

[0032] Figure 5 FIG. 1 shows an example of an inductor in a saturable core inductor according to an embodiment of the present invention.

[0033] A graph showing the change in current;

[0034] Figure 6 shows a schematic diagram of an exemplary ARCP inverter;

[0035] Figure 7 shows a diagram illustrating the current pulses in the saturable inductor of the ARCP converter

[0036] Current waveform;

[0037] Figure 8 Another example embodiment is shown when the core bridge element is fully saturated.

[0038] A magnetic flux density curve of a magnetic core structure; and

[0039] Fig. 9 Another core structure is another one when the core bridge element is not saturated.

[0040] Magnetic flux density graph of the core structure. DETAILED DESCRIPTION

[0041] A core inductor includes a magnetic core and a current-carrying inductor wire. The inductor wire may form a coil in which two or more turns of wire are wound around the magnetic core. In the simplest design, a core inductor may include a magnetic core and a current-carrying inductor wire that passes once through the center opening of the magnetic core.

[0042] An exemplary embodiment of the present invention will be described using a ring or annular core as an example of a core structure shape. As used herein, a ring core is substantially the same as a circular ring in shape and performance. For example, the magnetic core structure can have a rectangular shape, a hollow rod, a tube or a cylindrical shape, a combination of two or more core elements of the same or different cross-sectional shapes, such as two C elements, two U elements, a combination of an I element and a C element or a U element, etc.

[0043] In general, a magnetic core is an object of magnetic material with high magnetic permeability that is used to confine and direct the magnetic field in electrical, electromechanical and magnetic devices such as inductors. The magnetic core can be made of ferromagnetic metals such as iron or ferrimagnetic compounds such as ferrites. The high magnetic permeability relative to the surrounding air causes the magnetic field lines to concentrate in the core material. The magnetic field is often generated by a current-carrying coil around the core or a current-carrying wire passing through the core. In alternating current (AC) inductors, the core causes energy losses, called core losses, due to hysteresis and eddy currents.

[0044] Figure 1 An exemplary core inductor 2 is shown, which has a toroidal core structure or a toroidal core structure 6 with a central opening 8, and an inductor wire 4 passing through the central opening 8 of the core structure 6 and configured to carry an inductor current I. The inductor wire 4 can form a coil, in which N turns of wire are wound around the magnetic core 6 through the central opening 8, where N is a positive integer greater than 0. In the simplest design, the current-carrying inductor wire 4 can pass through the central opening 8 of the magnetic core 6 only once. The core structure 6 has an outer periphery with an outer diameter r1, and an inner periphery with an inner diameter r2 and defining the central opening 8. As shown in FIG. Figure 1 As shown by the dotted arrows in , a closed magnetic circuit, i.e., a closed path through which magnetic flux (or magnetic field lines) can flow, is provided inside the core 2. The magnetic flux density B is a measure of the density of magnetic field lines per unit area of ​​the core. As the current I increases, the magnetic flux density B in the core 2 increases. As the current increases, a point is reached at which the magnetic material or core will saturate, i.e., beyond this point, the magnetic flux density B in the core 2 will not increase as the current I increases. When the core is saturated, the inductance of the inductor 2 drops to zero. Due to the radial symmetry of the shape, the toroidal inductor 2 reaches saturation uniformly in the radial dimension. As the current increases, the material near the inner diameter r2 is saturated first and finally fully saturated, and the material at the outer diameter r2 will also be fully saturated. This is in Figure 2 The magnetic flux density graph of the core shown is illustrated in FIG. 1 , which is made of mild steel 1010. The inductor wire 4 is a copper conductor that passes once through the central opening 8. There, the outer ring is not yet fully saturated (slightly lighter grey shading compared to the grey shading near the inner diameter r1).

[0045] In conventional inductors, magnetic saturation is not a desired feature. However, in certain applications, saturable core inductors can be used, whose magnetic core is intentionally driven into saturation under certain conditions.

[0046] One aspect of the present invention is a saturable core inductor for high frequency alternating current (AC) applications where high inductance is required at low current levels and core power losses need to be minimized due to high operational frequencies. The volume and saturation characteristics of the core material determine the hysteresis losses that occur during the operational AC cycle. The higher the unit loss, the greater the high frequency losses.

[0047] One aspect of the invention is a core structure having a portion that saturates at low flux levels and a portion that remains unsaturated. The volume of the saturable portion is proportional to the hysteresis losses that occur at high operational frequencies. The core structure allows limiting the volume of the saturable core while maintaining a desired inductance to current ratio.

[0048] The high frequency may be above 1 kHz, preferably above 10 kHz.

[0049] Figure 3 An exemplary inductor 20 having a magnetic core structure according to aspects of the present invention is shown. The exemplary notched structure is an annular notched structure having two cores 24A and 24B having air gaps 26A and 26B between their opposite ends. The cores 24A and 24B having air gaps 26A and 26B are primarily used as portions of the core structure that remain unsaturated at desired current and flux levels. Additional core elements 22A and 22B are inserted into the air gaps 26A and 26B to provide a local bridge for the magnetic flux passing through the air gaps 26A and 26B between the opposite ends of the cores 24A and 24B. The core elements 22A and 22B are referred to herein as core bridge elements. The core bridge element 22A has a cross-sectional area in a plane perpendicular to the magnetic circuit that is much smaller than the cross-sectional area of ​​the core. The magnetic field lines (magnetic flux) are choked or throttled to pass through this limited area, which causes the high magnetic flux density in the core bridge elements 22A and 22B to be already at a low current level, while the low magnetic flux density in the magnetic core 24A and 24B is at the same low current level. The core bridge elements 22A and 22B are also saturated at a low saturation current level, and the core 24A and 24B remain unsaturated at this low saturation current level. Therefore, the core bridge elements 22A and 22B form part of the core structure, which is saturated at a low current level and thus saturated at a low flux level. The volume of the saturable part of the core structure can be limited to a very small amount, which causes very small core losses. In other words, when the core bridge elements 22A and 22B are unsaturated, they provide a high inductance of the inductor 20. When the core bridge elements 22A and 22B are saturated, the inductance of the inductor 20 is limited by the air gaps 26A and 26B, and the core 24A and 24B, resulting in an inductance value lower than the high inductance. Basically, the saturated core bridge elements 22A and 22B act like air.

[0050] Figure 4 Shows Figure 3 An exemplary magnetic flux density curve diagram of a magnetic core structure of FIG. 1, wherein the core bodies 24A and 24B and the core bridge elements 22A and 22B are made of low carbon steel 1010, that is, Figure 2The materials used in the examples shown are the same. The flux density graph indicates the degree of saturation of different areas of the core. In this example, the outer diameter of the annular core structure is about 60 mm, the air gap is about 5 mm, and the width of the bridge is 4 mm. It can be easily seen that as the current increases, the core bridge elements 22A and 22B saturate first. Once this occurs, the appropriately sized air gaps 26A and 26B have prevented the cores 24A and 24B from being completely saturated. If one compares Figure 2 and Figure 4 The reduction in hysteresis loss is evident from the size of the dark area (saturated high flux density area) in the two graphs shown in . Figure 2 , conventional core 2 is almost completely dark (saturated), while only core bridge elements 22A and 22B are fully saturated in inductor 20. It should be understood that the shapes, dimensions, and material selections in these graphs are for illustration purposes only.

[0051] In this example, different parts of the magnetic core structure are made of the same core material. Alternatively, different parts of the magnetic core structure can be made of different core materials. In particular, a core material with a low saturation flux density in the core bridges 22A and 22B and another core material with a higher saturation flux density in the core bodies 24A and 24B of the core structure can be advantageous.

[0052] Figure 5 is an exemplary graph showing the variation of inductance with current I in a saturable core inductor according to an embodiment of the present invention. At low current levels, the small volume of material introduced into the magnetic circuit by the core bridge elements 22A and 22B is an effective part of the magnetic circuit and reduces the effective air gap, thereby increasing the inductance presented by the inductor. The inductance has its maximum value Lmax substantially at the zero crossing of the high-frequency current I. As the current level increases, the small volume of material of the core bridge elements 22A and 22B saturates and increases the effective air gap, thereby reducing the inductance. The structure and materials of the other parts of the magnetic circuit are designed to keep the inductance sufficiently close to the target value Lmin when the core bridge elements are saturated. The behavior of the inductance in a function of current is substantially similar for positive and negative values ​​of current.

[0053] In an embodiment, the magnetic core structure may include more than two cores, more than two air gaps, and a core bridge inserted into each air gap.

[0054] As described above, the size of the core bridge 22A and 22B is designed to have a cross-sectional area in the magnetic circuit direction (circumferential direction of the toroidal coil) that is smaller than the cross-sectional area of ​​the core body 24A and 24B. In an embodiment, the size of the core bridge element 22A or 22B can be designed to be smaller in the direction from one side to the opposite side of the core structure, for example, in a direction perpendicular to the Figure 3 and Figure 4In the direction of the plane xy in the middle, only a portion of the length of the air gap 26A or 26B is covered. In an embodiment, the dimensions may be a combination of these. In an embodiment, the cross-sectional shape of the core bridge element 22A or 22B may be rectangular, circular, or other geometric shapes. The size or volume of the bridge element may preferably be substantially less than 50% of the size or volume of the corresponding air gap, but is not limited thereto.

[0055] The core bridge element 22A or 22B may preferably be inserted into the air gap 26A or 26B at or near the inner periphery of the magnetic core structure. This is particularly advantageous in an annular or ring-shaped magnetic core structure, where the cores 24A and 24B saturate first from the inner periphery.

[0056] In an embodiment, the core bridge element 22A or 22B may extend beyond the air gap 26A or 26B.

[0057] In an embodiment, the core bridge element 22A or 22B may be sized to contact the opposite ends of the cores 24A and 24A, i.e., for example, at Figure 3 and Figure 4 The y-axis direction in FIG. 2 extends through the entire air gap 26A or 26B.

[0058] In an embodiment, the core bridge element 22A or 22B may be sized so that it does not contact one or both of the opposite ends of the cores 24A and 24A, i.e., between the core bridge element and one or both of the opposite ends of the cores 24A and 24A, e.g. Figure 3 and Figure 4 In the y-axis direction, there may be smaller air gaps or intermediate materials.

[0059] In an embodiment, two or more core bridge elements may be inserted into each air gap 26A or 26B.

[0060] One aspect of the present invention is the use of a saturable core inductor according to an embodiment of the present invention in an auxiliary circuit branch of an ARCP converter.

[0061] One aspect of the invention is an auxiliary circuit branch connected between a neutral point and an output node in an ARCP converter, the auxiliary circuit branch comprising a series connection of a bidirectional auxiliary switch, an inductor and a saturable core inductor according to an embodiment of the invention.

[0062] A dc-ac or ac-dc converter, also referred to as an inverter or rectifier, converts power from dc to ac or from ac to dc at a desired voltage and frequency. In addition, a dc-dc converter, such as a dc chopper, converts power from a dc to dc power system. Although embodiments are described using inverters and inverter systems as examples, the present invention is equally applicable to rectifiers and rectifier systems and dc-dc converters. Inverters and rectifiers can be completely similar in structure, and control operations can be similar, with the difference being the direction of power flow. When the converter operates as an inverter (dc / ac converter), it converts power from a dc system to an ac system, i.e., the ac side of the converter is referred to as the output side, and the dc side is considered the input side. When the converter operates as a rectifier (ac / dc converter), it converts power from an ac system to a dc system, i.e., the ac side of the converter is considered the input side, and the dc side is considered the output side. Furthermore, the ac / dc and dc / dc converters are connected in a back-to-back configuration between two ac systems, i.e. the dc sides are connected together, with one of the converters operating in rectifier mode and the other in inverter mode, depending on the power flow direction. Since the power flow can vary, the operating mode of the converter can vary during operation.

[0063] It should be understood that the saturable core inductor according to an embodiment of the present invention is generally applicable to auxiliary resonant circuits in any type of ARCP inverter and its derivatives and variations, regardless of the specific design, configuration and operating variations of the basic ARCP inverter. The basic configuration and operation of ARCP are described in the article "Auxiliary Resonant Commutated Pole Converter" of the IEEE-IAS Reference Conference Proceedings 1990, pages 1228-35, and US5047913 of RWDe Doncker et al. ARCP inverters can be implemented using various topologies, the performance of which is substantially similar. A schematic diagram of an exemplary ARCP inverter INV is shown in FIG. Figure 6 , and described herein to facilitate understanding of the operation and configuration of embodiments of the present invention in relation to an exemplary basic ARCP. This is not intended to limit embodiments of the present invention to the exemplary ARCP described and illustrated.

[0064] Figure 6 The exemplary ARCP inverter INV shown may be a bridge inverter including a DC-link 20 and a power section 70. The DC-link may include a DC-link 20 including a first dc-link rail 22, a second dc-link rail 24, a first dc-link capacitor C coupled to the first dc-link rail 22 and a dc-link midpoint referred to as a neutral point NP. d1, and a second DC-link capacitor C coupled to the second DC-link rail 24 and the neutral point NP d2 During operation, the first dc-link rail 22 is at a first voltage, the so-called positive (P) dc-link potential, and the second dc-link rail 24 is at a second voltage, lower than the first dc voltage, the so-called negative (N) dc-link potential, and the DC-link midpoint NP is at a midpoint voltage, the so-called neutral point voltage U NP Across the dc-link capacitor C connected in series between the dc-link rails 22 and 24 d1 and C d2 The voltages U1 and U2 are provided at both ends. The neutral point voltage or potential U NP can basically correspond to the voltage U dc In other words, U NP =U dc / 2.

[0065] Figure 6 The exemplary half-bridge power section 70 shown in FIG. 7 may include a pair of main or power switching devices S1 and S2 coupled in parallel to the DC link rails 22 and 24 of the DC link 20. The rails. The first main switching device S1 may have a first terminal electrically coupled to the positive dc-link rail 22 and a second terminal electrically coupled to the output node 110. The second main switching device S2 may have a first terminal coupled to the output node 110 and a second terminal coupled to the negative dc-link rail 24. A first anti-parallel diode D1 is connected across the first main switching device S1 between the positive dc-link rail 22 and the output node 110, and a second anti-parallel diode D2 is connected across the second main switching device S2 between the output node 110 and the negative dc-link rail 24. In addition, a first resonant capacitor C1 is operably connected in parallel with the first main switching device S1 (i.e., directly or via an additional component, such as an active or passive damping circuit connected in series with the resonant capacitor), and a second resonant capacitor C2 is operably connected in parallel with the second main switching device S2. More generally, there may be one or more resonant capacitors connected in such a manner that at least one terminal of the resonant capacitor(s) is connected to one of the dc-link rails (P, NP, N) and another terminal(s) is operatively connected to the phase output node 110. The first master switching device S1 is operable to respond to a slave control and drive circuit (such as Figure 6The second main switch device S2 is operable to be turned on and off in response to the control signal(s) G1 received from the inverter-specific ARCP switch controller 80 shown in FIG. 1 , thereby respectively connecting and disconnecting the dc-link rail 22 and the output node 110. The second main switch device S2 is operable to be turned on and off in response to the control signal(s) G2 received from the control and driver circuit (such as the ARCP switch controller 80), thereby respectively connecting and disconnecting the dc-link rail 24 and the output node 110.

[0066] Figure 6 The exemplary half-bridge power section 70 of the ARCP inverter shown also includes an auxiliary circuit branch including a saturable core resonant inductor L connected in series between the neutral point NP and the output node 110. sat and bidirectional auxiliary switch S aux1 It should be understood that the resonant inductor and the auxiliary switch may be located in any order in the ARCP circuit without affecting the present invention. aux1 The auxiliary switch S is operable to be turned on and off in response to a control signal received from a control and drive circuit (such as the ARCP switch controller 80), thereby connecting and disconnecting the neutral point and the output node 110, respectively. aux1 It can work like a bidirectional thyristor: it can be triggered to conduct, and if or before the current tries to reverse its direction, it will turn off. aux1 It can be implemented with pairs of common switching devices connected back-to-back, for example in a common emitter or common collector configuration, and provided with anti-parallel diodes. Figure 6 An exemplary auxiliary switch S is shown. aux1 The exemplary auxiliary switch includes a first auxiliary switch device S connected in series with a common emitter. a1 and the second auxiliary switching device S a2 , connected across the first auxiliary switch device S a1 The first anti-parallel diode D at both ends a1 and across the second auxiliary switching device S a2 The second anti-parallel diode D a2 To initiate new output commutation, in response to a signal from a control and drive circuit (such as Figure 6 The ARCP switch controller 80 shown receives a control signal G a1 and G a2 , two auxiliary switching devices S a1 and S a2 Depending on the conduction state of the main switching devices S1 and S2, the two anti-parallel diodes D a1 and D a2One of the two can be forward biased and start conducting current. In this case, the auxiliary current I a The auxiliary switching device in the auxiliary circuit is preferably turned on and turned off at zero current. When the first auxiliary switching device S a1 is turned on and the second switching device S a2 When turned off, the auxiliary current I a1 will flow through S in one direction a1 and D a2 When the first auxiliary switching device S a1 is turned off and the second switching device S a2 When turned on, the auxiliary current Ia will flow in the opposite direction through S a2 and D a1 The auxiliary circuit branch is only used when the output node 110 needs to be commutated from one voltage rail to another. The auxiliary circuit operates by generating current pulses that, in combination with the resonant capacitor, are used to convert the output voltage on the output node 110.

[0067] Saturable core resonant inductor L sat To relieve the diode D a1 and D a2 The reverse recovery current causes problems; the reverse current in the saturable core resonant inductor L sat When the diode “cuts off” the current, the saturable core resonant inductor L sat The energy stored in the saturable core resonant inductor L sat At low current (this is diode D a1 or D a2 The high inductance in the region where the current polarity is reversed greatly reduces the auxiliary current d Ia / dt changes, which delays the reverse recovery current “cut-off” and also reduces the current stored in the inductors L1 and L sat In the ARCP converter, the saturable core resonant inductor L sat The current pulses in can have different magnitudes and different directions, such as Figure 7 Schematically shown. The interval between current pulses may typically be 1 microsecond ... 1000 microseconds. Saturable core resonant inductor L sat The current is generally about zero, although non-idealities of the circuit components may also cause small leakage currents through the inductor between pulses. The waveform of the inductor current pulse may have linear and sinusoidal portions. Typically, subsequent inductor current pulses are in opposite directions, but in special cases they may be in the same direction.

[0068] The switching frequency of the ARCP topology can reach tens of kHz. When the core material reaches full saturation at high frequencies, hysteresis losses become a major problem. Using the saturable core inductor according to an embodiment of the present invention as the saturable core resonant inductor L in the ARCP topology sat This results in a significant reduction in core loss. According to an embodiment of the present invention, the saturable core resonant inductor L sat It preferably includes an unsaturable core portion and a saturable core, thereby having a high inductance value at low current levels and a lower inductance at higher (normal) current levels. In some applications, there may be a resonant inductor L with a saturable core. sat Another non-saturable resonant inductor L1 is connected in series, such as Figure 6 shown.

[0069] Example. The outer diameter of the annular core structure is 58 mm (r1 = 29 mm), the inner diameter is 26 mm (r2 = 13 mm), and the axial length is 13 mm (in the direction perpendicular to the xy plane). The size of the air gap is 1.5 mm. The material of the core is metallic glass, and the material of the core bridge element is FeNiZnV (ferrite). The dimensions of the core bridge element are: width 4 mm (x-axis), height 1.5 mm (y-axis), and length 13 mm (in the direction perpendicular to the xy plane). Figure 8 An exemplary magnetic flux density graph of the provided magnetic core structure is shown when the core bridge element is fully saturated. The power line extends across the air gap. The inductor current is 1600A and the saturation inductance is 115nH. Fig. 9 An exemplary magnetic flux density graph of the provided magnetic core structure is shown when the core bridge element is not saturated. The electric field lines extend through the core bridge element. The inductor current is 1A and the unsaturated inductance is 8.3μH.

[0070] The description and the related drawings are intended to illustrate the principles of the present invention by way of example only. Based on this description, various alternative embodiments, variations and changes will be apparent to those skilled in the art. The present invention is not limited to the examples described herein, but the present invention may be varied within the scope and spirit of the appended claims.

Claims

1. A saturable core inductor comprising An inductor conductor configured to carry a high frequency AC current, The core structure includes an unsaturable part and a saturable part. wherein the non-saturable portion of the magnetic core structure comprises at least one core body, the at least one core body being arranged to form a closed magnetic circuit having at least one air gap, wherein the saturable portion of the magnetic core structure comprises a core bridge element inserted into each of the at least one air gap to form a magnetic bridge across the air gap for the closed magnetic circuit, Wherein each bridge element and the at least one core are configured to be unsaturated at a predetermined low current level to provide a low current high inductance, and wherein each bridge element is configured to first be fully saturated as the current level increases and thereby quickly reduce the inductance from the low current high inductance to a low inductance, while the remainder of the at least one air gap is configured to prevent the at least one core from being fully saturated.

2. The inductor of claim 1, wherein the non-saturable portion of the magnetic core structure comprises at least two cores assembled to form the closed magnetic circuit having an air gap between opposite ends of the cores.

3. The inductor according to claim 1, wherein the magnetic core structure is a toroidal core structure, preferably having two or more cores, more preferably having two semi-toroidal cores.

4. The inductor of claim 1 , wherein in a plane perpendicular to the magnetic circuit, each core bridge element has a cross-sectional area that is smaller than the cross-sectional area of ​​the at least one core body, so that the core bridge element is fully saturated first and then rapidly reduces the inductance as the AC current level increases, while the at least one core body remains unsaturated and defines the low inductance at increasing current levels.

5. The inductor of claim 1, wherein the core structure has an outer periphery and an inner periphery defining a central opening, and each bridge element is configured to extend only a portion of the length of the air gap in a direction from the inner periphery to the outer periphery of the core structure. 6 . The inductor of claim 5 , wherein each bridge element is inserted into the at least one air gap at the inner periphery of the core structure. 7 . The inductor of claim 1 , wherein the core bridge element is arranged to extend across the entire air gap or across only a portion of the air gap in the direction of the magnetic circuit.

8. The inductor of claim 1, wherein the high frequency is above about 1 kHz or above about 10 kHz.

9. The inductor of claim 1, wherein the high frequency is a switching frequency of an electrical converter.

10. Use of the inductor according to any one of claims 1 to 9 as a saturable inductor in an auxiliary circuit branch of an ARCP converter.

11. An ARCP converter comprising an auxiliary circuit branch connected between a neutral point and an output node in the ARCP converter, the auxiliary circuit branch comprising a series connection of at least one bidirectional auxiliary switch and a saturable core inductor according to any one of claims 1-9.

12. The ARCP converter of claim 11, wherein the bidirectional auxiliary switch comprises a pair of switching devices connected back-to-back and provided with anti-parallel diodes.

13. The ARCP converter of claim 11 or 12, wherein the high frequency is a switching frequency of the bidirectional auxiliary switch, and wherein the AC current is an auxiliary current of the auxiliary circuit branch.

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