An electric energy conversion circuit for an aviation electric propulsion power system

Abstract

The present invention relates to the technical field of aviation electric propulsion power systems, and provides an electric energy conversion circuit for an aviation electric propulsion power system, comprising: a DC distribution bus; a DC / DC step-up transformer, whose input end is coupled to the DC distribution bus, for increasing a first DC voltage to a second DC voltage; a DC / AC step-down inverter, whose input end is coupled to the output end of the DC / DC step-up transformer, for converting the second DC voltage into AC; a permanent magnet motor, coupled to the AC, for converting electrical energy into mechanical energy to drive a propeller; the AC voltage is greater than or equal to the first DC voltage; the DC / DC step-up transformer includes an N-stage conversion structure, 1≤N≤3 and N∈Z, wherein the first-stage conversion structure is composed of two first-type conversion units in a two-phase staggered parallel manner; it can provide greater power for the permanent magnet motor of the aviation electric propulsion power system without reducing the power-to-weight ratio.

Description

Technical Field

[0001] The present invention relates to the technical field of aviation electric propulsion power systems, and in particular to an electric energy conversion circuit for aviation electric propulsion power systems. Background Art

[0002] In aircraft electric propulsion systems, propellers are the most efficient actuators and are widely used in model aircraft, fixed-wing electric aircraft, and multi-rotor drones. With the development of heavy-duty cargo drones and manned electric aircraft, electric propulsion systems are moving towards higher torque and greater power, while also requiring high power density and a high power-to-weight ratio.

[0003] In more-electric and all-electric aircraft, according to the current DO-160 standard, the high-power HVDC power distribution bus voltage is 270V. For example, the F35 fighter jet uses this DC distribution bus voltage. For aircraft requiring even higher power, such as the Boeing 787 and Airbus A380, with a distribution power of up to 1MW, a ±270V two-wire HVDC power distribution bus voltage is used, equivalent to 540V DC.

[0004] Despite doubling the DC distribution bus voltage, for electric propulsion power systems where the motor directly drives the propeller, due to the low propeller speed (2000RPM to 5000RPM), it is still technically difficult for the motor and inverter as a whole to achieve a power-to-weight ratio of more than 5kW / kg.

[0005] The power conversion circuit of the traditional permanent magnet aviation electric propulsion power system has an inverter that draws power directly from the DC distribution bus, converts DC power into AC power to control the speed of the permanent magnet motor. The permanent magnet motor rotor directly drives the propeller to rotate, providing thrust or lift for the aircraft.

[0006] At a given speed, a motor's torque is proportional to its power. Limited by the DC bus voltage, achieving higher torque requires increasing the motor's rated current or using multiple motors, connecting their rotors together to drive the propellers. All of these approaches significantly increase the size and weight of the electric propulsion system.

[0007] Therefore, how to develop an electric energy conversion circuit for an aviation electric propulsion system while ensuring that the size and weight of the electric propulsion system do not increase significantly, so as to provide greater power for the permanent magnet motor of the aviation electric propulsion system. Summary of the Invention

[0008] The technical problem to be solved by the present invention is to overcome the defect that the power-to-weight ratio of the above-mentioned existing aviation electric propulsion system will decrease after the power is increased, and provide an electric energy conversion circuit for the aviation electric propulsion power system, which can provide greater power for the permanent magnet motor of the aviation electric propulsion system without reducing the power-to-weight ratio.

[0009] To achieve the above-mentioned objectives, the present invention is implemented through the following technical solutions: an electric energy conversion circuit of an aviation electric propulsion power system, comprising: a DC distribution bus for providing a first DC voltage; a DC / DC step-up transformer, whose input end is coupled to the DC distribution bus, for increasing the first DC voltage to a second DC voltage; a DC / AC step-down inverter, whose input end is coupled to the output end of the DC / DC step-up transformer, for converting the second DC voltage into AC; a permanent magnet motor, coupled to the AC, for converting electrical energy into mechanical energy to drive a propeller; the AC voltage is greater than or equal to the first DC voltage; the DC / DC step-up transformer includes an N-stage conversion structure, 1≤N≤3 and N∈Z, wherein the first-stage conversion structure is composed of two first-type conversion units in a two-phase staggered parallel manner.

[0010] A further preferred embodiment of the present invention is as follows: the first type of conversion unit includes: a resonant tank circuit, comprising at least one resonant inductor and a resonant capacitor; a plurality of switches, each switch having a first terminal, a second terminal and an input terminal for receiving a control signal, the control signal causing the switch to be in an on state or an off state, wherein in the on state, a conduction path is established between the first terminal and the second terminal, and in the off state, the conduction path is eliminated between the first terminal and the second terminal; and a control circuit for generating a first control signal set and applying it to the input terminal of the switch so that the first DC voltage is increased to the second DC voltage through periodic switching of the switch.

[0011] A further preferred solution of the present invention is that the first type of conversion unit also includes an energy storage capacitor.

[0012] A further preferred solution of the present invention is that the control circuit causes the switch to be in an on state in half a cycle and in an off state in half a cycle through the first control signal set.

[0013] A further preferred solution of the present invention is that in two first-type conversion units connected in parallel with two phases, the phase difference between the control signal received by the switch on one phase and the control signal received by the switch on the other phase is half a cycle.

[0014] A further preferred solution of the present invention is that the switch is switched in a zero current on-state and zero current off-state manner during the switching process.

[0015] A further preferred solution of the present invention is that the resonant inductor is a distributed inductance of the line.

[0016] A further preferred solution of the present invention is that in the two first-type conversion units connected in parallel with two phases, the resonant inductors on the two phases are coupled inductors.

[0017] A further preferred embodiment of the present invention is that the control circuit is also used to generate a third control signal set when the propeller decelerates, and the switches in the DC / DC step-up transformer and the DC / AC step-down inverter receive the third control signal set to enable energy to flow in both directions.

[0018] A further preferred solution of the present invention is that the switches in the DC / AC step-down inverter receive the third control signal set to enable bidirectional energy flow.

[0019] In summary, the present invention has the following beneficial effects: The power conversion circuit of the aviation electric propulsion power system of the present invention doubles the voltage of the DC distribution bus by adding a DC / DC step-up transformer. Moreover, for motors below 1000V, increasing the motor terminal voltage does not significantly increase the insulation requirements of the motor. Compared with increasing the rated current of the motor, increasing the rated voltage of the motor is a more effective way to increase the torque. The circuit added to this structure does not significantly increase the weight, and therefore does not reduce the power-to-weight ratio. In addition, the conversion structure of the DC / DC step-up transformer of the present invention adopts a first-class conversion unit with two phases interleaved in parallel, which can significantly reduce the required filter capacitance value. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 It is a principle block diagram of the electric energy conversion circuit of the aviation electric propulsion power system described in Example 1.

[0021] Figure 2 This is a circuit schematic diagram of the electric energy conversion circuit of the aviation electric propulsion power system described in Example 1.

[0022] Figure 3 This is a circuit diagram of the DC / DC step-up transformer described in Example 1 when the step-up ratio is reduced to 1.

[0023] in:

[0024] 100, DC distribution bus; 200, DC / DC step-up transformer; 210, resonant tank circuit; 220, control circuit

[0025] 300, DC / AC step-down inverter; 400, permanent magnet motor; 500, propeller. DETAILED DESCRIPTION

[0026] The present invention will be further described in detail below with reference to the accompanying drawings.

[0027] This embodiment is merely an explanation of the present invention and is not a limitation of the present invention. After reading this specification, those skilled in the art may make non-creative modifications to this embodiment as needed, but as long as they are within the scope of the claims of the present invention, they are protected by patent law.

[0028] like Figure 1-3 As shown, this embodiment shows an electric energy conversion circuit of an aviation electric propulsion power system, including a DC distribution bus 100, a DC / DC step-up transformer 200, a DC / AC step-down inverter 300, a permanent magnet motor 400 and a propeller 500.

[0029] The DC distribution bus is used to provide a first DC voltage. The first DC voltage provided by the DC distribution bus is 270V or 540V. This embodiment uses 540V as an example for description.

[0030] A DC / DC step-up transformer, having an input coupled to the DC distribution bus, is configured to step up a first DC voltage to a second DC voltage of 540 V or 1080 V. The DC / DC step-up transformer comprises an N-stage conversion structure, where 1 ≤ N ≤ 3 and N∈Z, wherein a first-stage conversion structure comprises two first-type conversion units connected in two-phase interleaved parallel fashion.

[0031] The specific number of conversion stages used in a DC / DC step-up transformer depends on the DC distribution bus voltage and the final output voltage. For example, if the DC distribution bus voltage is 270V, boosting it to 1080V requires a four-fold voltage increase, necessitating at least two conversion stages. In this embodiment, boosting from 540V to 1080V only doubles the voltage, so N = 1, resulting in only one conversion stage.

[0032] The first type of conversion unit includes a resonant tank circuit 210, multiple switches, a control circuit and an energy storage capacitor.

[0033] A resonant tank circuit includes a resonant inductor and a resonant capacitor. The resonant inductor Lr and the resonant capacitor Cr are connected in series to form a resonant tank circuit, i.e., a resonant cavity. However, in other embodiments, the resonant tank circuit can also be an equivalent circuit in which the resonant inductor Lr and the resonant capacitor Cr are connected in series. The resonant inductor can also be the distributed inductance of the circuit.

[0034] Multiple switches, each switch having a first terminal, a second terminal, and an input terminal for receiving a control signal (including a first control signal set and a second control signal set, and if necessary, an additional control signal set can be added according to different working modes), wherein the control signal causes the switch to be in an on state or an off state, wherein in the on state, a conduction path is established between the first terminal and the second terminal, and in the off state, the conduction path is eliminated between the first terminal and the second terminal.

[0035] Multiple switches within the first type of conversion unit are controlled by a first control signal set and a second control signal set to form one or more sub-circuit loops, and wherein the one or more sub-circuit loops of the first control signal set are different from the one or more sub-circuit loops of the second control signal set.

[0036] Each of the one or more sub-circuit loops includes at least one resonant tank circuit; and at least one of the one or more sub-circuit loops includes at least one energy storage capacitor (non-resonant capacitor).

[0037] Each of the one or more energy storage capacitors facilitates clamping a voltage across the first terminal and the second terminal of the switch when the switch is in the off state.

[0038] The control circuit 220 is configured to generate a first and second control signal set and apply the set to the input of the switch, so that the first DC voltage is increased to a second DC voltage by periodically switching the switch. In this embodiment, the switch switches in a zero-current-on and zero-current-off manner during the switching process.

[0039] In this embodiment, each first-class conversion unit has four switches, and the two first-class conversion units have a total of eight switches. Specifically, the switches are all 1200V SiC MOSFETs, namely Q11, Q12, Q13, Q14, Q21, Q22, Q23, and Q24. The first terminal of switch Q11 is coupled to the second terminal of switch Q12, the first terminal of switch Q12 is coupled to the second terminal of switch Q13, and the first terminal of switch Q13 is coupled to the second terminal of switch Q14. The first terminal of switch Q21 is coupled to the second terminal of switch Q22, the first terminal of switch Q22 is coupled to the second terminal of switch Q23, and the first terminal of switch Q23 is coupled to the second terminal of switch Q24.

[0040] like Figure 2 As shown, in the conversion structure of the DC / DC boost transformer, Q11, Q12, Q13 and Q14 are located in the upper phase, while Q21, Q22, Q23 and Q24 are located in the lower phase.

[0041] In the upper phase, a resonant inductor Lr1 and a resonant capacitor Cr1 are connected in series in the resonant tank circuit. The other end of the resonant inductor Lr1 is coupled to the connection point between switches Q12 and Q11, while the other end of the resonant capacitor Cr1 is coupled to the connection point between switches Q14 and Q13. The connection point between switches Q13 and Q12 is coupled to the first output terminal of the DC distribution bus, and the first terminal of switch Q14 is coupled to the second output terminal of the DC distribution bus.

[0042] In the lower phase, a resonant inductor Lr2 and a resonant capacitor Cr2 are connected in series in the resonant tank circuit. The other end of the resonant inductor Lr2 is coupled to the connection point between switches Q22 and Q21, while the other end of the resonant capacitor Cr2 is coupled to the connection point between switches Q24 and Q23. The connection point between switches Q23 and Q22 is coupled to the first output terminal of the DC distribution bus, and the first terminal of switch Q24 is coupled to the second output terminal of the DC distribution bus.

[0043] In the two first-type conversion units connected in parallel with two phases, the resonant inductors on the two phases are coupled inductors. Furthermore, one end of the energy storage capacitor C1 is coupled to the connection point between switches Q13 and Q12 (also the connection point between switches Q23 and Q22), and the other end of the energy storage capacitor C1 is coupled to the second output terminal of the DC distribution bus. One end of the energy storage capacitor C2 is coupled to the connection point between switches Q11 and Q21, which serves as the output terminal of the DC / DC step-up transformer, and the other end of the energy storage capacitor C2 is coupled to the second output terminal of the DC distribution bus (ground).

[0044] It can be seen that the two first-class conversion units connected in parallel with the two phases mentioned above have the same structure, but there is a phase difference between the control signal sets received by the switches in the two first-class conversion units. The phase difference between the control signal received by the switch on one phase and the control signal received by the switch on the other phase is half a cycle. If the control signal set is a signal with a period of 2π, then the control signal set on the second phase is the control signal set on the first phase after being phase-shifted by π. The specific control method is the existing technology and will not be described in detail here. Please refer to the Chinese patent No. 208063044, Figure 7 of which shows a circuit diagram of a 2-phase 4 to 1STC topology with full-wave output rectification, including 4 conversion structures, and the conversion structure of this embodiment is modified on the basis of it, and is only one conversion structure. Therefore, the control process involving the switches in the conversion structure is similar and is omitted.

[0045] The advantage of using two-phase interleaved parallel connection is that, for example, the current in the rightmost switch (switch Q11) of the first phase is a sinusoidal half-wave for half of its cycle and zero for half of its cycle. Similarly, the current in the rightmost switch (switch Q21) of the second phase is zero for half of its cycle and a sinusoidal half-wave for half of its cycle. Because the interleaved parallel connection creates a repeating sinusoidal half-wave current, the required filter capacitor value can be significantly reduced (compared to a case where the half-cycle is a sinusoidal half-wave and zero for half of its cycle).

[0046] After being stepped up by the DC / DC step-up transformer, the voltage passes through a multi-level circuit to reduce the output current ripple before being sent to the input of the DC / AC step-down inverter. The DC / AC step-down inverter converts the second DC voltage into AC power and then sends the AC power from its output to the permanent magnet motor, which converts electrical energy into mechanical energy to drive the propeller.

[0047] In this embodiment, the propeller is not always in the high-power and high-speed operating mode. When the propeller speed needs to be less than or equal to half of the rated speed, the control circuit in this embodiment further generates a third control signal set. The switches in the DC / DC step-up transformer and the DC / AC step-down inverter receive the third control signal set to enable bidirectional energy flow. That is, the switches in the DC / DC step-up transformer receive the third control signal set to switch states, disconnecting some of the switches to open the resonant tank circuit (see the disconnected switches). Figure 3 The dotted line portion) reduces the voltage step-up ratio of the DC / DC step-up transformer to 1.

[0048] It should be noted that the third control signal set generated by the control circuit here includes switch control signals in the DC / AC buck inverter, or the switch control signals in the DC / AC buck inverter are generated separately by another control circuit.

Claims

1. An electric energy conversion circuit for an aviation electric propulsion power system, characterized in that: include: A DC distribution busbar, configured to provide a first DC voltage, wherein the first DC voltage is 270 V or 540 V; a DC / DC step-up transformer, an input end of which is coupled to the DC distribution bus, for stepping up a first DC voltage to a second DC voltage, wherein the second DC voltage is 540V or 1080V; a DC / AC step-down inverter, the input end of which is coupled to the output end of the DC / DC step-up transformer, for converting the second DC voltage into AC power; a permanent magnet motor coupled to the AC power to drive the propeller; and when the propeller speed is less than or equal to half the rated speed, energy can flow in both directions through the DC / AC step-down inverter and the DC / DC step-up transformer; The DC / DC step-up transformer includes an N-stage conversion structure, where 1≤N≤3 and N∈Z, wherein the first-stage conversion structure is composed of two first-type conversion units connected in two-phase interleaved parallel, and the first-type conversion unit includes a coupled inductor; in the two first-type conversion units connected in two-phase interleaved parallel, the phase difference between the control signal received by the switch on one phase and the control signal received by the switch on the other phase is half a cycle.

2. The electric energy conversion circuit according to claim 1, characterized in that: The first type of transformation unit includes: a resonant tank circuit comprising at least one resonant inductor and a resonant capacitor; A plurality of switches, each having a first terminal, a second terminal, and an input for receiving a control signal, wherein the control signal causes the switch to be in an on state or an off state, wherein in the on state, a conduction path is established between the first terminal and the second terminal, and in the off state, the conduction path is eliminated between the first terminal and the second terminal; and a control circuit for generating a set of control signals and applying them to the input of the switch to cause a first DC voltage to be increased to a second DC voltage by periodic switching of the switch.

3. The electric energy conversion circuit according to claim 2, characterized in that: The first type of conversion unit also includes an energy storage capacitor.

4. The electric energy conversion circuit according to claim 2, characterized in that: The control circuit enables the switch to be in an on state during a half cycle and in an off state during a half cycle through the control signal set.

5. The electric energy conversion circuit according to claim 2, characterized in that: The switch is switched in a zero-current-on and zero-current-off manner during the switching process.

6. The electric energy conversion circuit according to claim 2, characterized in that: The resonant inductor is the distributed inductance of the line.

7. The electric energy conversion circuit according to claim 2, characterized in that: In the two first-type conversion units connected in parallel with two phases, the resonant inductors on the two phases are coupled inductors.

8. The electric energy conversion circuit according to claim 2, characterized in that: The control circuit is further configured to generate a third control signal set when the propeller decelerates, and switches in the DC / DC step-up transformer and the DC / AC step-down inverter receive the third control signal set to enable bidirectional energy flow.

9. The electric energy conversion circuit according to claim 8, characterized in that: When the rotation speed of the propeller is lower than or equal to half of the rated rotation speed, the switch in the DC / DC step-up transformer receives the third control signal set to switch the state so that the step-up ratio of the DC / DC step-up transformer is reduced to 1.

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