Oscillator circuit for inductive energy transfer

Abstract

Oscillator circuit for power electronics, which is a parallel-fed push-pull oscillator circuit with a resonant circuit consisting of at least one inductor (L1) and at least one capacitor (C). 1p ) and is configured with at least one first and one second power transistor (Q1, Q2) which are excited to oscillate via feedback in the resonant circuit, wherein one or more third power transistors (Q3) are arranged in series with the first power transistor (Q1) between the first power transistor (Q1) and the resonant circuit, and one or more fourth power transistors (Q4) are arranged in series with the second power transistor (Q2) between the second power transistor (Q2) and the resonant circuit, wherein the feedback of the first power transistor (Q1) is provided via a first feedback branch (to Q s2) which connects the drain or collector terminal of the second power transistor (Q2) or one of the fourth power transistors (Q4) to the gate or base terminal of the first power transistor (Q1), and the feedback of the second power transistor (Q2) via a second feedback branch (to Q s1 ) which connects the drain or collector terminal of the first power transistor (Q1) or one of the third power transistors (Q3) to the gate or base terminal of the second power transistor (Q2), wherein in each feedback branch a control transistor (Q s1 , Q s2 ) is arranged, by which the slew rate of a gate or base voltage at the respective power transistor (Q1, Q2) is increased during a rise and a fall compared to an arrangement without a control transistor, and wherein one or more third power transistors (Q3) are connected between the connection of the first power transistor (Q1) with the second feedback branch (to Q s1 ) and the resonant circuit, and the one or more fourth power transistors (Q4) are arranged between the connection of the second power transistor (Q2) with the first feedback branch (to Q s2 ) and the resonating circuit.

Description

Technical application area

[0001] The present invention relates to an oscillator circuit for power electronics, in particular for contactless inductive energy transfer, which is designed as a parallel-fed push-pull oscillator circuit with a resonant circuit consisting of at least one inductor and at least one capacitor and with at least two power transistors which are excited to oscillate via feedback in the resonant circuit.

[0002] Contactless power transmission requires power electronics with a high switching frequency and voltage. Depending on the type of reactive power compensation used, different system behaviors are achieved. Particularly with primary-side parallel compensation, the system exhibits intrinsically safe behavior without critical conditions in the event of a short circuit or open circuit on the secondary side. Due to the capacitor connected in parallel to the inductor in this case, an inductor is required to simulate a current source upstream of the power electronics (half-bridge, full-bridge). However, this complicates the switching process in controlled power electronics. State of the art

[0003] To avoid this problem, it is known to use autoresonant switching Royer converters.

[0004] These converters also eliminate the need for control engineering to keep the system in resonance, making such a system very cost-effective to implement.

[0005] For example, German patent DE 20 2007 011 745 U1 discloses a parallel-fed push-pull oscillator circuit in the form of a Royer converter, which features a resonant circuit consisting of an inductor and a capacitor, and at least one first and one second power transistor. These transistors are excited to oscillate via feedback in the resonant circuit. The feedback is symmetrical, applied to the drain or collector of the opposite power transistor. This ensures that even at low operating voltages, a sufficiently high control voltage is available for switching the power transistors. Each feedback branch also includes a control transistor that ensures the gate or base voltage at the respective power transistor rises and falls rapidly. This increased slew rate ensures reliable operation of the power transistors.

[0006] However, such a Royer converter places high demands on the voltage rating of the power transistors used. The voltage across the resonant circuit in such a converter is... - times the input DC voltage. Therefore, the conventional approach for high-power applications with a typical intermediate circuit voltage of 600 to 800 V is no longer applicable, as the required voltage withstand of approximately 1900 V cannot currently be achieved by available power transistors. The use of Royer converters is thus far only possible with low input voltages. Due to the high currents occurring at low input voltages, they are unsuitable or only conditionally suitable for higher power ranges of, for example, 3.6 to 22 kW. For high power ranges, series-compensated systems on the primary side are therefore predominantly used. However, these systems require condition monitoring, as they are not short-circuit and / or open-circuit proof.

[0007] JP S60-124 121 A describes a drive circuit for a power MOSFET. This circuit includes a rectifier circuit for rectifying the control pulse on the secondary side of the coupling transformer, to which the control pulse is applied. The DC voltage obtained by the rectifier circuit is used as the operating current source for an additionally connected buffer transistor. The buffer transistor is driven by the control pulse, and the power MOSFET is driven by its output.

[0008] US Patent 2,953,754 A describes a self-excited transistor inverter circuit. It proposes an electrical inverter circuit comprising a pair of transistor switches with separate impedance media connected in series with each transistor, so that the reverse voltage is divided between the non-conducting transistor and its associated impedance media.

[0009] Several transistors are used as impedance media, operated as controlled switching devices.

[0010] US 5,763,962 A deals with a driver circuit for a semiconductor switch suitable for switching high voltages. The introductory part of this document points out that the higher voltage rating is achieved by connecting several of the switching transistors in series, which are then driven simultaneously via transformer coupling. The same measure is also discussed in US 3,710,147 A and US 4,394,590 A.

[0011] The object of the present invention is to provide an oscillator circuit for power electronics which has a higher voltage resistance than previously known Royer converters and does not require condition monitoring. Description of the invention

[0012] The problem is solved by the oscillator circuit according to claim 1. Advantageous embodiments of the proposed oscillator circuit are the subject of the dependent claims or can be found in the following description and the exemplary embodiments.

[0013] The proposed oscillator circuit for power electronics, particularly for contactless inductive power transfer, is designed as a parallel-fed push-pull oscillator circuit with a resonant circuit consisting of at least one inductor and at least one capacitor, and with at least one first and one second power transistor, which are excited to oscillate via feedback in the resonant circuit. The proposed oscillator circuit is characterized by the fact that one or more additional power transistors are arranged in series with the first and second power transistors, respectively, between the first and second power transistors and the resonant circuit.The one or more additional power transistors between the first power transistor and the resonant circuit are referred to in this description as third power transistors, and the one or more additional power transistors between the second power transistor and the resonant circuit are referred to as fourth power transistors. The feedback from the first power transistor is provided via a first feedback branch that connects the drain or collector terminal of the second power transistor or one of the fourth power transistors to the gate or base terminal of the first power transistor. The feedback from the second power transistor is provided accordingly via a second feedback branch that connects the drain or collector terminal of the first power transistor or one of the third power transistors to the gate or base terminal of the second power transistor.Each feedback branch contains a control transistor which increases the slew rate of the gate or base voltage at the respective power transistor during a rise and fall compared to an arrangement without such a control transistor.

[0014] The proposed oscillator circuit thus represents a further development of the conventional Royer converter. By adding further power switches or power transistors in series with the first and second power transistors, the voltage rating of the Royer converter is increased. Furthermore, a third and a fourth power transistor are added to the first and second power transistors. However, multiple third or fourth power transistors can also be connected in series with the first or second power transistors, respectively.

[0015] One or more third power transistors are placed between the connection of the first power transistor to the second feedback branch and the resonant circuit, and one or more fourth power transistors are placed between the connection of the second power transistor to the first feedback branch and the resonant circuit. This ensures that when the first or second power transistor is conducting, a low potential is always present at the tap to the respective control transistors, so that the power transistors on the opposite side are accordingly switched off.

[0016] In a further development of the proposed oscillator circuit, balancing capacitors and / or balancing resistors are arranged in parallel with the power transistors to balance the voltage across them. These balancing capacitors act as additional compensation capacitors to the compensation capacitance or the compensation capacitor in the resonant circuit and can also replace it.

[0017] The individual power transistors can be controlled in different ways. In a first advantageous embodiment, the first and one or more third power transistors, and the second and one or more fourth power transistors, are controlled galvanically isolated via transformers by the control transistor located in the first feedback branch or the second feedback branch, respectively.

[0018] In a further embodiment, only the control of one or more third and one or more fourth power transistors is galvanically isolated via transformers. The first and second power transistors are controlled directly via the respective control transistors of the feedback branches using the conventional Royer converter method. In this embodiment, the third power transistors are controlled by the signal from the control transistor in the second feedback branch, and the fourth power transistors are controlled by the control transistor in the first feedback branch.

[0019] As an alternative to control via transformers, active driver circuits can also be used in the latter configurations, e.g. using high-side gate driver ICs or gate driver ICs with bootstrapping.

[0020] In the preferred embodiment, the oscillator circuit is designed such that, as in the Royer converter of DE 20 2007 011 745 U1, a constant voltage is applied to the base or gate of each control transistor, which determines the maximum gate or base voltage applied to the power transistors.

[0021] Field-effect transistors such as IGBTs, MOSFETs, or JFETs are preferably used as power transistors. However, the power transistors that can be used are not limited to these types.

[0022] The proposed oscillator circuit makes it advantageous to implement primary-side parallel compensated inductive power transmission systems that can be supplied with mains voltage 230 / 400 V without an additional buck converter. Brief description of the drawings

[0023] The proposed oscillator circuit is explained in more detail below using exemplary embodiments in conjunction with the drawings. These show: Fig. 1 an example of an oscillator circuit in the form of an autoresonant Royer converter according to the state of the art; Fig. 2 a comparison of the power paths of the conventional Royer converter (A) and the proposed oscillator circuit (B) ; Fig. 3 an example of the balancing of the voltages in the proposed oscillator circuit; Fig. 4 Two examples of the control of the power transistors in the proposed oscillator circuit; Fig. 5 an abstract representation of one of the two control inputs of the oscillator circuit; Fig. 6 an example of the gate voltage at JFET and MOSFET in an embodiment of the proposed oscillator circuit; Fig. 7 an example of driving a MOSFET as a power transistor in the proposed oscillator circuit; and Fig. Figure 8 shows a representation of the voltages across a power transistor in the proposed oscillator circuit. Ways to implement the invention

[0024] Fig. Figure 1 shows an example of a conventional Royer converter, according to the state of the art, for contactless inductive energy transfer. Energy transfer occurs via the inductance L1 of the resonant circuit to the inductance L2 of the secondary side. The primary-side parallel compensation is achieved via the compensation capacitor C. 1p carried out. The throttle L DR It serves to simulate a current source. The circuit has two power transistors, Q1 and Q2, which are connected via feedback in a resonant circuit consisting of the capacitor C. 1pand the inductor L1 is excited to oscillate. The feedback is symmetrical, occurring via the drain terminal of the opposite power transistor, as can be seen from the Fig. As can be seen in Figure 1. A control transistor Q is present in each feedback branch. s1 or Q s2 These control transistors ensure that the gate voltage at the respective power transistor Q1 or Q2 rises and falls rapidly. This generates clean switching edges for the power transistors, thus guaranteeing their reliable operation.

[0025] Such a Royer converter is in the Fig. 2A again in a simplified representation compared to an embodiment of the proposed oscillator circuit in Fig. 2B is shown. In a conventional Royer converter, the voltage U1 at the resonant circuit is the - times the input DC voltage U IN,DC. As a result, the conventional Royer converter is no longer suitable for high-performance applications with high input voltages of, for example, 600 to 800 V, since the required voltage rating of approximately 1900 V cannot be achieved by the currently available power transistors.

[0026] In the present invention, the voltage rating of a conventional Royer converter is increased by connecting additional power transistors in series or by incorporating them into the circuit. This is exemplified by the proposed oscillator circuit of the Fig. Figure 2B illustrates this. By adding the two additional power transistors Q3 and Q4 in series with the power transistors Q1 and Q2, the voltage rating of the circuit is increased. The tap to the control transistors Q s1 and Q s2 It is preferably located directly above the lowest power transistors Q1 and Q2. This is shown in the diagram. Fig. 2 is only indicated for clarity. This procedure ensures that a low potential is always achieved. For the circuit to function correctly, a low potential at the tap to Q is required when the power transistor Q1 or Q2 is conducting. s1 or Q s2This is necessary so that the power transistors on the opposite side block accordingly. This is a problem with the conventional Royer circuit at high currents, because a significant voltage drop occurs due to the resistance of the power transistor in the conducting state. Voltages on the order of the threshold voltage lead to a less than ideal blocking of the other side. This problem is solved by using multiple power switches. Furthermore, the voltage stability of the oscillator circuit is also increased by using multiple power switches or power transistors in series. Instead of the single additional power transistor Q3 or Q4 shown on each side, two or more power transistors can also be arranged in series with the existing power transistors.

[0027] In a further development of the proposed oscillator circuit, balancing capacitors C are used to balance the voltage. S and symmetry resistors R S parallel to the circuit breakers Q1 to Q n (n = number of power transistors present). This is schematically shown for the two power transistors Q1 and Q3 in the Fig. Figure 3 shows the balancing capacitors C. S They act as additional compensation capacitors to the compensation capacitor C. 1p Furthermore, these balancing capacitors can replace the compensation capacitor C. 1p substitute.

[0028] The power transistors can be controlled in different ways. In one configuration, as exemplified in Fig. As indicated by 4A, the upper and lower power transistors Q1 and Q3 respectively are controlled by means of one or more transformers L. GDTthrough the signal of the control transistor Q s2 This galvanically isolated control also applies to all other power transistors that may be connected in series with Q1. Similarly, power transistor Q2 and any power transistors connected in series with it are controlled by the signal from control transistor Q via one or more transformers. s1 targeted.

[0029] In a further advantageous embodiment, only the upper power transistors Q3 and Q4 (and any additional series-connected power transistors) are driven by transformers, while the lower power transistors Q1 and Q2 are driven by the conventional Royer converter method, as is the case for power transistors Q1 and Q3 in the Fig. 4B is indicated. In this example, the control of the additional power switches (here: Q3) on the left side of the circuit is galvanically isolated by means of the transformers L.GDT through the signal of the control transistor Q s1 , the activation of the power transistor Q1 by the signal from the control transistor Q s2 Accordingly, the additional power switches on the right side of the circuit are galvanically isolated by transformers via the signal from the control transistor Q. s2 and the power transistor Q2 directly through the signal of the control transistor Q s1 targeted.

[0030] As an alternative to control via transformers, active driver circuits can also be used for control.

[0031] In the design of the Fig. 4B uses a JFET as an example of power transistor Q3. The control signal of Q s1 is tapped, as is described in the Fig. 5 is shown. It is important to consider the design of the Fig. 4B It is also possible to tap the control signal for the additional power switches Q3, Q4, ... from the other control transistor, e.g. at Q s2 for Q3 and at Q s1 for Q4.

[0032] The design of the Fig. 4B offers the advantage that at the time of commutation, the upper circuit breakers Q3 to Q n are conductive and therefore behave transparently. The conventional Royer circuit is therefore not affected by the additional components in this training. The switching behavior is, for example, in Fig. Figure 6 shows the gate voltage at JFET Q3 and MOSFET Q1 ( Fig. Figure 4B) shows the relationship between the MOSFET and the voltage over time. It is evident that the MOSFET is unaffected at the commutation point. The measurement data were adjusted so that the respective threshold voltage is 0 V.

[0033] As an alternative to the JFET, the additional power transistors Q3 to Q can be used for the additional power transistors Q3 to Q3. nA MOSFET with bias voltage from a series-connected voltage source V can also be used. Fig. Figure 7 shows an example of how to control the MOSFET, which uses a JFET as an additional power transistor Q3 in the configuration of the Fig. 4B replaced. The SR terminal corresponds to the source terminal of the Q control switch. s1 GR2 corresponds to the gate terminal of power transistor Q3. SR2 is the source terminal of Q3.

[0034] Fig. Figure 8 finally shows the halved voltage load on the power transistors due to the proposed oscillator circuit. The halved voltages U are shown in the figure. MOSFET,DS or U JFET,DS via the individual power transistors, e.g. Q1 and Q3, as well as the resonant circuit voltage U LC shown, which falls below Q1 and Q3.

Claims

[1] Oscillator circuit for power electronics, which is a parallel-fed push-pull oscillator circuit with a resonant circuit consisting of at least one inductor (L1) and at least one capacitor (C) 1p ) and is configured with at least one first and one second power transistor (Q1, Q2) which are excited to oscillate via feedback in the resonant circuit, wherein one or more third power transistors (Q3) are arranged in series with the first power transistor (Q1) between the first power transistor (Q1) and the resonant circuit, and one or more fourth power transistors (Q4) are arranged in series with the second power transistor (Q2) between the second power transistor (Q2) and the resonant circuit, wherein the feedback of the first power transistor (Q1) is provided via a first feedback branch (to Q s2) which connects the drain or collector terminal of the second power transistor (Q2) or one of the fourth power transistors (Q4) to the gate or base terminal of the first power transistor (Q1), and the feedback of the second power transistor (Q2) via a second feedback branch (to Q s1 ) which connects the drain or collector terminal of the first power transistor (Q1) or one of the third power transistors (Q3) to the gate or base terminal of the second power transistor (Q2), where each feedback branch contains a control transistor (Q s1 , Q s2 ) is arranged, by which the slew rate of a gate or base voltage at the respective power transistor (Q1, Q2) is increased during a rise and a fall compared to an arrangement without a control transistor, and wherein one or more third power transistors (Q3) are connected between the connection of the first power transistor (Q1) with the second feedback branch (to Q s1 ) and the resonant circuit, and the one or more fourth power transistors (Q4) are arranged between the connection of the second power transistor (Q2) with the first feedback branch (to Q s2 ) and the resonating circuit. [2] Oscillator circuit according to claim 1, characterized by , that balancing capacitors (C) are connected in parallel to the power transistors (Q1, Q2, Q3, Q4). S ) and / or balancing resistors (R S ) are arranged to balance a voltage applied to the power transistors (Q1, Q2, Q3, Q4). [3] Oscillator circuit according to claim 1 or 2, characterized by , that the control of the first (Q1) and the one or more third power transistors (Q3) is galvanically isolated via transformers (LGDT ) through the first feedback branch (to Q) s2 ) arranged control transistor (Q s2 ) and the control of the second (Q2) and the one or more fourth power transistors (Q4) galvanically isolated via transformers (L GDT ) through the second feedback branch (to Q) s1 ) arranged control transistor (Q s1 ) take place. [4] Oscillator circuit according to claim 1 or 2, characterized by , that the control of the first (Q1) and the one or more third power transistors (Q3) via driver circuits by the one in the first feedback branch (to Q s2 ) arranged control transistor (Q s2 ) and the control of the second (Q2) and the one or more fourth power transistors (Q4) via driver circuits by the one in the second feedback branch (to Q s1 ) arranged control transistor (Q s1 ) take place. [5] Oscillator circuit according to claim 1 or 2, characterized by , that the control of one or more third power transistors (Q3) is galvanically isolated via one or more transformers (L GDT ) through the second feedback branch (to Q) s1 ) arranged control transistor (Q s1 ) and the galvanically isolated control of one or more fourth power transistors (Q4) via one or more transformers (L GDT ) through the first feedback branch (to Q) s2 ) arranged control transistor (Q s2 ) take place. [6] Oscillator circuit according to claim 1 or 2, characterized by , that the control of one or more third power transistors (Q3) via driver circuits by the second feedback branch (to Q s1 ) arranged control transistor (Q s1) and the control of one or more fourth power transistors (Q4) via driver circuits by the one in the first feedback branch (to Q s2 ) arranged control transistor (Q s2 ) take place. [7] Oscillator circuit according to claim 1 or 2, characterized by , that the control of one or more third power transistors (Q3) is galvanically isolated via one or more transformers (L GDT ) through the first feedback branch (to Q) s2 ) arranged control transistor (Q s2 ) and the galvanically isolated control of one or more fourth power transistors (Q4) via one or more transformers (L GDT ) through the second feedback branch (to Q) s1 ) arranged control transistor (Q s1 ) take place. [8] Oscillator circuit according to claim 1 or 2, characterized by, that the control of one or more third power transistors (Q3) via driver circuits by the one in the first feedback branch (to Q s2 ) arranged control transistor (Q s2 ) and the galvanically isolated control of one or more fourth power transistors (Q4) via driver circuits by the second feedback branch (to Q s1 ) arranged control transistor (Q s1 ) take place. [9] Oscillator circuit according to any one of claims 1 to 8, characterized by , that at the gate or base of each control transistor (Q s1 , Q s2 ) a constant voltage is applied.

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