CIRCUIT ARRANGEMENT WITH ACTIVE RECTIFIER CIRCUIT AND ITS APPLICATION IN A SYNCHRONOUS MACHINE

Abstract

The present invention relates to a circuit arrangement having an active rectifier circuit, in particular on a secondary side of an inductive energy transmission path. The circuit arrangement has a half or full bridge of power transistors for rectifying an AC voltage induced in an input inductor of the circuit arrangement. The power transistors are connected to the input inductor in such a way that an auxiliary voltage is split off from the induced AC voltage for switching the power transistors. As a result, even large currents, which result in a low output voltage, can be transmitted without endangering the operation of the rectifier circuit.

Claims

1. Circuit arrangement having an active rectifier circuit, in particular on the secondary side of an inductive energy transmission path, with a half or full bridge of power transistors (Q.sub.1, Q.sub.2) for rectifying an AC voltage induced in an input inductor (L.sub.2) of the circuit arrangement, and with a resonant circuit formed by a parallel circuit of the input inductor (L.sub.2) and a first capacitor (C.sub.2,p), characterized in that the power transistors (Q.sub.1, Q.sub.2) are connected to the input inductor (L.sub.2) such that an auxiliary voltage for switching the power transistors (Q.sub.1, Q.sub.2) is split off from said resonant circuit.

2. (canceled)

3. Circuit arrangement according to claim 2, characterized in that a first power transistor (Q.sub.1) establishes a switchable electrical connection between a first side of the input inductor (L.sub.2) and a first pole of an output terminal, a second power transistor (Q.sub.2) establishes a switchable electrical connection between a second side of the input inductor (L.sub.2) and the first pole of the output terminal, a drain terminal of a first control transistor (Q.sub.S1) is connected to a drain terminal of the first power transistor (Q.sub.1) and a source terminal of the first control transistor (Q.sub.S1) is connected to a gate terminal of the second power transistor (Q.sub.2), a drain terminal of a second control transistor (Q.sub.S2) is connected to a drain terminal of the second power transistor (Q.sub.2) and a source terminal of the second control transistor (Q.sub.S2) is connected to a gate terminal of the first power transistor (Q.sub.1), a centre tap of the input inductor (L.sub.2) or both sides of the input inductor (L.sub.2) of the resonant circuit is/are connected to a second pole of the output terminal via respective chokes (L.sub.DR2), and gate terminals of the first and second control transistors (Q.sub.S1, Q.sub.S2) are connected to at least one side of the input inductance (L.sub.2) of the resonant circuit via at least one resistor (R.sub.0) and a diode (R.sub.f) and connected to the first pole of the output terminal via a parallel circuit consisting of a second capacitor (C.sub.0) and a Zener diode (R.sub.Z).

4. Circuit arrangement according to claim 3, characterized in that the gate terminals of the first and second control transistors (Q.sub.S1, Q.sub.S2) are each connected via a resistor (R.sub.0) and a diode (R.sub.f) to both sides of the input inductor (L.sub.2) of the resonant circuit.

5. Circuit arrangement according to claim 3, characterized in that the gate terminals of the first and second power transistors (Q.sub.1, Q.sub.2) in each case are connected to the first pole of the output terminal either via a series circuit of another Zener diode (R.sub.z1, R.sub.z2) and another diode (R.sub.d1, R.sub.d2) or via a bidirectional Zener diode, wherein the further Zener diode (R.sub.z1, R.sub.z2) prevents a current from flowing from the gate terminal of the respective power transistors (Q.sub.1, Q.sub.2) to the first pole until the Zener voltage is reached, and the further diode (R.sub.d1, R.sub.d2) prevents a current flowing from the first pole to the gate terminal of the respective power transistors (Q.sub.1, Q.sub.2).

6. Circuit arrangement according to claim 3, characterized in that the control transistors (Q.sub.S1, Q.sub.S2) are MOSFETs.

7. Circuit arrangement according to claim 3, characterized in that the power transistors (Q.sub.1, Q.sub.2) are MOSFETs.

8. A method for the use of the circuit arrangement according to claim 1 on a rotor of a synchronous machine, comprising: performing an inductive energy transmission to the rotor via the input inductor (L.sub.2) of the circuit arrangement.

9. A method for the use of the circuit arrangement according to claim 3 on a rotor of a synchronous machine, comprising: performing an inductive energy transmission to the rotor via the input inductor (L.sub.2) of the circuit arrangement, and forming the one or multiple chokes (L.sub.DR2) by rotor windings of the rotor.

10. A rotor of a synchronous machine comprising the circuit arrangement according to claim 1, wherein an inductive energy transmission to the rotor is performed via the input inductor (L.sub.2) of the circuit arrangement.

11. A rotor of a synchronous machine comprising the circuit arrangement of claim 3, wherein an inductive energy transmission to the rotor is performed via the input inductor (L.sub.2) of the circuit arrangement, and wherein one or multiple chokes (L.sub.DR2) are formed by rotor windings of the rotor.

Description

SHORT DESCRIPTION OF THE DRAWINGS

[0013] The proposed circuit arrangement is explained in more detail below based on exemplary embodiments in conjunction with the drawings. In these:

[0014] FIG. 1 shows an example of a circuit arrangement with active rectifier circuit in the form of a Royer converter according to the prior art;

[0015] FIG. 2 shows a first example of a design of the proposed circuit arrangement;

[0016] FIG. 3 shows a second example of a design of the proposed circuit arrangement;

[0017] FIG. 4 shows another example of a design of the proposed circuit arrangement;

[0018] FIG. 5 shows an example of the design of an inductive energy transmission path in which the proposed circuit arrangement can be used.

WAYS TO IMPLEMENT THE INVENTION

[0019] An advantageous embodiment of the proposed circuit arrangement is based on a circuit known, for example, from DE 202007011745 U1. FIG. 1 shows this circuit of the prior art, which uses a so-called Royer converter. The Royer converter has two MOSFET power transistors Q.sub.1, Q.sub.2, which connect a side of the input inductor L.sub.2 to a pole of the DC voltage terminal in a switchable manner. The two MOSFET power transistors Q.sub.1, Q.sub.2 are driven via two MOSFET control transistors Q.sub.S1, Q.sub.S2. For this purpose, the drain terminal of one of the control transistors is connected to the drain terminal of the first power transistor Q.sub.1 and the source terminal of this control transistor Q.sub.S1 is connected to the gate terminal of the second power transistor Q.sub.2 via a resistor R.sub.g2. The drain terminal of the other control transistor Q.sub.S2 in turn is connected to the drain terminal of the second power transistor Q.sub.2, and the source terminal is connected to the gate terminal of the first power transistor Q.sub.1 via a resistor R.sub.g1, as shown in FIG. 1. The voltage for the gates of the two control transistors Q.sub.S1, Q.sub.S2 is tapped at the DC link voltage U.sub.2,DC by means of a Zener diode R.sub.Z in this circuit. A centre tap on the input inductor L.sub.2 is connected to the second pole of the DC voltage terminal via a choke L.sub.DR2. The input inductor L.sub.2 is compensated in parallel via the capacitor C.sub.2,p connected in parallel. The two poles of the DC voltage terminal are connected via a series circuit of a resistor R.sub.0 and a parallel circuit of a capacitor C.sub.0 and the Zener diode R.sub.Z. In addition to operating as an inverter, this circuit can also be operated as an active rectifier. In both cases, the choke L.sub.DR2 can be designed either as a component with a centre tap on the input inductor (coil L.sub.2), as shown in FIG. 1, or in the form of two chokes without centre tap in the coil L.sub.2.

[0020] When using this circuit as an inverter, it is necessary to first have a supply voltage present at the gates, such that the circuit can start to oscillate in an autoresonant manner. Otherwise, the control transistors Q.sub.S1, Q.sub.S2 are closed, such that the power transistors Q.sub.1, Q.sub.2 cannot transition into a conducting state. In the case of operation as rectifier, the diodes, which are not shown in FIG. 1 but are present in the power transistors Q.sub.1 and Q.sub.2, become active. This allows the circuit to first work passively as a rectifier before a DC link voltage is applied at output U.sub.2,DC a short time later, which in turn supplies the control transistors Q.sub.S1 and Q.sub.S2, such that the circuit now operates as an active rectifier. The time span until the circuit operates as an active rectifier lasts a few oscillations and is therefore tolerable by the passive components. However, as described above, only a very low output voltage U.sub.2,DC is present at the DC voltage terminal at a very high current, which output voltage is not sufficiently high at every operating point to reliably switch the gates. This is only possible with a design of the circuit arrangement according to the present invention.

[0021] In this context, FIG. 2 shows an example of the proposed circuit arrangement with an active rectifier circuit, which represents a modification of the circuit known from the prior art according to FIG. 1. The modification primarily concerns the generation of the supply voltage for switching the MOSFET power transistors Q.sub.1, Q.sub.2, which in the present patent application is also referred to as auxiliary voltage. In the proposed circuit arrangement, this voltage is generated via the resonant circuit consisting of the input inductor L.sub.2 and the parallel capacitor C.sub.2,p. The voltage in the resonant circuit at its peak value is a multiple of the DC link voltage, i.e. the voltage U.sub.2,DC at the output terminal of the active rectifier (voltage across R.sub.2,DC). As virtually no energy is required for driving the gate, the peak value of the voltage in the resonant circuit can be used to switch the gates. In order not to cause any additional effects on the circuit, a balanced circuit was used on both sides of the capacitor or capacitance C.sub.2,p in the present examples. It is also possible to implement only one tap.

[0022] For the tap in the resonant circuit, an additional diode R.sub.f is required in addition to the resistor R.sub.0, as the supply voltage of the control transistors Q.sub.S1, Q.sub.S2 can under no circumstances become lower than the gate threshold voltage of the control transistors Q.sub.S1, Q.sub.S2 when switching off U.sub.2,DC and before the end of the oscillation or during the negative half-waves of the resonant circuit voltage. On the other hand, due to the non-conductive state of the power transistors Q.sub.1 and Q.sub.2, the voltage increase in the input inductor L.sub.2 would destroy at least one of the two transistors. The diode R.sub.f prevents this state by preventing the discharge of the capacitor C.sub.0 parallel to the Zener diode when switching off the supply or output voltage U.sub.2,DC.

[0023] FIG. 3 shows a modification of the proposed circuit arrangement shown in FIG. 2, in which no centre tap on the input inductor L.sub.2 is performed, but in which the two sides of this inductor are connected to the second pole of the output terminal via two separate chokes L.sub.DR2,a, L.sub.DR2,b. When this circuit arrangement is used on the rotor of a synchronous machine, the rotor winding is formed by these two chokes. This is then a split rotor winding, e.g. for a multipolar machine. The series resistor of the rotor winding has been dispensed with; the resistances are shown here as the equivalent resistance R.sub.2,DC. In the case of the example shown in FIG. 2, the choke L.sub.DR2 only forms one rotor winding.

[0024] FIG. 4 shows another example of a design of the proposed circuit arrangement. In this example, in contrast to the embodiment shown in FIG. 2, the respective gates of the first and second power transistor Q.sub.1, Q.sub.2 are connected to the first pole of the output terminal via two opposing diodes. The two diodes are a Zener diode R.sub.z1 or R.sub.z2, which blocks the direction of the current from the gate to the first pole, on the one hand. The second diode R.sub.d1 or R.sub.d2 blocks the opposite direction of the current. A corresponding embodiment is of course also advantageous for the circuit arrangement shown in FIG. 3.

[0025] The two Zener diodes R.sub.z1 or R.sub.z2 are used to protect the respective gates from excessive voltage. It makes sense to install this Zener diode if the resonant circuit voltage is greater than that present at the control transistor Q.sub.S1 as a gate voltage. In this case, the capacitance between drain and source at Q.sub.S1, as well as the capacitance between gate and source at Q.sub.2, forms a capacitive voltage divider. As a result, the permissible gate voltage may be exceeded. The Zener diode prevents this from happening. If the gates of the MOSFET control transistors Q.sub.S1 and Q.sub.S2 are not supplied with a constant voltage as usual, but are charged by the resonant circuit, it takes a certain time period of several oscillations until the gates of these control transistors are put into the conductive state by the resonant circuit. Within this time period, the body diode of the MOSFET power transistors is intended to conduct the current. However, in the absence of the diode R.sub.d1 or R.sub.d2, a further current flow is possible through the Zener diode and the body diode of the control transistor. In this case, a parallel circuit of two diodes is achieved. Power MOSFETs usually have very poor body diodes with high forward voltages, which is why it is possible that the current flows from the first pole via the Zener diode R.sub.z2 and the body diode of the first control transistor Q.sub.S1. In this case, the components are destroyed because they are not designed for this current. Due to the additional diode R.sub.d1 or R.sub.d2, this current flow is prevented. In practice, bidirectional Zener diodes can also be used, whereby the two diodes are embodied in one housing.

[0026] In principle, the active rectifier circuit of the proposed circuit arrangement can be realised not only as a half-bridge, as shown in FIG. 2 to 4, but also as a full bridge, which then means that only a voltage slightly higher than the output voltage of the active rectifier is available for switching the MOSFET power transistors. The proposed circuit arrangement can be used very advantageously in the secondary sides of inductive energy transmission paths, in particular when using such an energy transmission path between the stator and the rotor of a synchronous machine.

[0027] FIG. 5 schematically shows an example of the design of an inductive energy transmission path. On the primary side, the input voltage U.sub.1,DC is converted into an AC voltage U.sub.1 via the inverter 1, which AC voltage is transmitted to the secondary side via the coil system 3 consisting of the primary coil L.sub.1 and the secondary coil L.sub.2. The primary coil L.sub.1 and secondary coil L.sub.2 have a parallel compensation 2, 4. The AC voltage U.sub.2 induced in the secondary coil L.sub.2 is rectified via the rectifier 5 and is provided as the DC voltage U.sub.2,DC. Therein, the proposed circuit arrangement with active rectifier circuit can replace the secondary coil L.sub.2 as input impedance together with the parallel compensation 4 and the rectifier 5.

[0028] At low magnetic couplings between the two coils L.sub.1, L.sub.2, a low pass is created due to the LC resonant circuit. This means that almost no harmonics are present in the system. If only the fundamental wave is considered, sinusoidal currents and voltages exist in the system, depending on the compensation. Thus, so-called conversion factors or form factors for current and voltage result at the inverter and rectifier. The conversion factors are influenced by the design, i.e. whether a half or full bridge is used. If parallel compensation is used on the secondary side, the voltage factor for a full bridge is as follows:

[00001]$U_{2,\mathrm{DC}}=\frac{2.Math.\sqrt{2}}{\pi }.Math.U_2$

[0029] This means that the output or DC link voltage is about 0.9 times the resonant circuit voltage U.sub.2. Correspondingly, the current acts inversely, such that the power remains constant in total. For a half-bridge, as shown in the examples of FIG. 2 to 4, this results in a factor of approximately 0.45 times. In addition, if the peak value is considered instead of the effective value, the formula is

U.sub.2=π.Math.U.sub.2,DC

[0030] This voltage increase in the resonant circuit is used by the proposed circuit arrangement to generate the gate voltage at the control transistors for switching the power transistors of the active rectifier circuit. Thus, even at higher currents and thus very low output voltage, a voltage value can be generated that is sufficiently high for switching the power transistors.

[0031] The proposed circuit arrangement having an active rectifier circuit is particularly advantageous at output voltages U.sub.2,DC<20 V. In this case, the voltage U.sub.2,DC across the resistor R.sub.2,DC, e.g. the rotor resistance, is smaller than the nominal gate voltage of the MOSFET power transistors Q.sub.1 and Q.sub.2. Active switching is therefore no longer possible with the rectified voltage. Typical gate voltages of power MOSFETs are in the range of 10-20 V, wherein the contact resistance of the MOSFETs usually decreases steadily with increasing gate voltage. High losses usually occur below 10 V; the gate of a MOSFET usually cannot be exposed to voltages higher than 20 V without being damaged. The proposed active rectifier circuit can still offer advantages in the voltage range of 20 V≤U.sub.2,DC<100 V, as lower output voltages are often present in the partial load range.

LIST OF REFERENCE SIGNS

[0032] 1 Inverter [0033] 2 Parallel compensation [0034] 3 Coil system [0035] 4 Parallel compensation [0036] 5 Rectifier