Method, device and system for discharging the intermediate circuit using the rotor excitation device of a separately excited synchronous machine

Abstract

Method for discharging an intermediate current circuit of power electronics for a separately excited synchronous machine, comprising: energizing a primary coil of an inductive coupling for rotor excitation with a direct current, so that the intermediate current circuit is discharged.

Description

[0001] Electric cars are commonly known to be powered by various electric motor concepts, such as permanent magnet motors, self-excited synchronous motors, or separately excited synchronous motors. These electric motor concepts are operated with high-voltage (HV) systems.

[0002] In general, an HV system requires active discharge of the intermediate circuit or intermediate circuit capacitor in certain driving situations when requested by the vehicle. This is required by various standards for electric vehicles. These driving situations include vehicle standstill, especially in a workshop.

[0003] Active discharge of the DC link capacitor following CAN commands from the vehicle is a standard component of the functional safety concept for electric drive systems. This is necessary, among other things, to ensure that all HV components are de-energized after the vehicle is shut down—i.e., after the HV system has been shut down. For this purpose, at least one HV component of the HV system has a dedicated discharge device as standard. In the current state of the art, this is usually the case in the power electronics of the traction drive.

[0004] The current state of the art provides a dedicated discharge circuit within the power electronics for this purpose. This discharge circuit consists primarily of resistive elements that convert the energy stored in the DC link capacitor into heat. A disadvantage of this solution is the need for sufficient heat dissipation, as the heat dissipation is very high. Simply dissipating heat via the (FR4) circuit board is usually insufficient. Furthermore, the discharge circuit takes up significant space within the power electronics and incurs corresponding costs.

[0005] However, this device is intended exclusively for active discharge, is relatively cost-intensive and requires significant installation space.

[0006] The object is to at least partially eliminate the disadvantages mentioned and to provide an improved method, an improved device and an improved system for discharging the intermediate current circuit using the rotor excitation device of a separately excited synchronous machine.

[0007] This object is achieved by a method according to claim 1. This object is further achieved by power electronics according to claim 4, a separately excited synchronous machine according to claim 9 and a vehicle according to claim 10.

[0008] According to the invention, a method for discharging an intermediate current circuit of power electronics for a separately excited synchronous machine, comprising: energizing a primary coil of an inductive coupling for rotor excitation with a direct current, so that the intermediate current circuit is discharged.

[0009] For a separately excited synchronous motor (SESM) with inductive coupling, which serves to transfer electrical energy to the rotor, energizing the primary coil of the inductive coupling with direct current enables the requested discharge of the intermediate circuit or the intermediate circuit capacitor via an existing switching device, which is required for rotor excitation anyway and generates alternating current. This could make a dedicated discharge device within the power electronics obsolete. The control for the intermediate circuit discharge guarantees torque-free operation during the discharge process, since energizing with direct current does not induce a current in a secondary coil of the inductive coupling, and thus no significant energy transfer takes place via the inductive coupler into the rotor.

[0010] No additional components are required to perform a discharge, thus saving space and costs.

[0011] When energized with direct current, heat is generated in the primary coil, which reduces electrical losses. The primary coil thus acts as an electrical resistance to the direct current.

[0012] There are designs in which energizing the primary coil includes: controlling an inverter with an H-bridge so that two switches of the inverter are closed, whereby the primary coil is energized with the direct current.

[0013] A separately excited synchronous machine with inductive coupling—that is, an inductive energy transfer from power electronics to the rotor—requires a switching device, usually in the form of an H-bridge. The H-bridge is usually part of an inverter. During normal operation, this drives the primary side of the inductive coupler with an alternating voltage, so that the alternating field generated in the magnetic core generates an alternating voltage on the secondary side of the transformer. With the help of passive diode rectification, the direct current for rotor excitation can be provided.

[0014] The inductive coupler is thus a transformer and requires the alternating voltage generated by the H-bridge for energy transfer. In separately excited synchronous machines, the H-bridge is phase-shifted (or pulse-width modulated).

[0015] This switching device is thus used for the active discharge of the intermediate circuit or intermediate circuit capacitor when required by the vehicle's operating strategy. For this purpose, the power semiconductors of the H-bridge are controlled in such a way that the primary side of the inductive coupling is supplied with a direct current, preventing any significant voltage induction in the secondary winding. Consequently, torque-free operation can always be guaranteed during active discharge. The energy stored in the intermediate circuit capacitor is converted into heat in the primary windings and in the switching elements of the H-bridge.

[0016] The switches are closed, for example, via pulse-width modeling, which adjusts the current intensity in the discharge. Adjustment can include regulation and control.

[0017] There are designs in which the energization of the primary coil involves clocking a switch in a control loop using pulse width modulation so that the primary coil is energized with a constant DC voltage, thus protecting the primary coil.

[0018] The switches can be adjusted to protect the primary coil, for example, from excessive discharge current or excessive discharge voltage of the direct current. The current can be regulated for this purpose.

[0019] More precisely, the inverter's H-bridge can be controlled as a two-quadrant controller. One switch is pulse-width modulated, one switch is permanently closed, and two switches are permanently open. This results in a constant current in the primary coil through primary current control and no feedback into the intermediate circuit.

[0020] During the on phase of pulse width modulation, the current flows through the clocked switch, the primary coil, and the closed switch. During the off phase of pulse width modulation, the current flows through the primary coil, the closed switch, and a diode that is antiparallel to one of the open switches.

[0021] In pulse width modulation, the on and off phases alternate repeatedly, whereby a change in the pulse width changes the ratio of the on phase to the off phase.

[0022] A control loop that has a direct current as a reference variable, a pulse width of the pulse width modulation as a manipulated variable and a current flowing at the primary coil, or a variable correlated with it, as a controlled variable, can regulate the direct current at the primary coil to a constant value by means of the pulse width modulation, whereby the constant value does not overload the primary coil and thus damage it.

[0023] According to the invention, a power electronics system for a separately excited synchronous machine comprises: an inductive coupling for rotor excitation with a primary coil and an intermediate current circuit, wherein the primary coil is designed to be supplied with a direct current for discharging the intermediate current circuit.

[0024] The separately excited synchronous machine can be designed as described above.

[0025] There are embodiments further comprising an inverter with an H-bridge which is configured to close two switches so that the primary coil is energized with the direct current.

[0026] The inverter with H-bridge can be designed as described above.

[0027] There are designs in which the inverter is further configured to clock a switch by means of pulse width modulation in a control loop so that the primary coil is supplied with a constant DC voltage.

[0028] As already explained above, the primary coil can be protected from excessive discharge current or discharge voltage by controlling it using the inverter.

[0029] There are embodiments further comprising: a controller designed to control the H-bridge so that the primary coil is energized with the direct current.

[0030] This control can, for example, be a microcontroller in the inverter.

[0031] There are designs in which the inductive coupling including the primary coil is designed to be cooled by oil cooling of the separately excited synchronous machine.

[0032] The inductive coupling is coupled to the rotor of the separately excited synchronous machine. If the rotor is oil-cooled, this also applies to the inductive coupling. Thus, the heat generated by discharging using the primary coil, which acts as an electrical resistance, is dissipated via the oil cooling of the separately excited synchronous machine.

[0033] According to the invention, a drive system comprising a separately excited synchronous machine with the power electronics according to an above embodiment, which is designed to carry out the method according to an above embodiment.

[0034] The processes can then be executed by the microcontroller in the inverter as soon as a discharge is requested via a CAN interface. This determines the driving situation in the CAN (Computer Area Network), and decides whether a discharge should be performed. The inverter's microcontroller then receives the command to discharge the intermediate circuit and switches the H-bridge accordingly.

[0035] According to the invention, a vehicle with the separately excited synchronous machine according to the above embodiment.

[0036] A vehicle can be any vehicle with an electric drive or actuator. This vehicle can move, for example, on land, on (in) water, in the air, or in space. The vehicle can be used to transport loads, goods, or people.

[0037] Embodiments of the invention will now be described by way of example and with reference to the accompanying drawings, in which: Fig. 1 an embodiment of an inductive coupling of a separately excited synchronous machine; Fig. 2 an embodiment of an inverter and a separately excited synchronous machine; Fig. 3 an inverter and a synchronous machine with active discharge circuit; Fig. 4 an inverter and a separately excited synchronous machine with active discharge circuit; Fig. 5 a flowchart of a method for discharging an intermediate circuit of power electronics for a separately excited synchronous machine; Fig. 6 an extension for the flow diagram of a method for discharging an intermediate circuit of a power electronics system for a separately excited synchronous machine; and Fig. 7 an embodiment of a vehicle with a separately excited synchronous machine with the power electronics.

[0038] Fig. 1 shows an embodiment of an inductive coupling of a separately excited synchronous machine.

[0039] The inductive coupling 100 includes parts of the inverter 110, a transformer 120, a passive rectifier 130 and the rotor winding 220.

[0040] The box of inverter 110 depicts an H-bridge consisting of four switches S1 to S4, each configured with an anti-parallel diode. The direct current applied to the H-bridge is modeled via switches S1 to S4 and energizes a primary coil 121 of transformer 120. If energy is to be transferred to a secondary coil 122 of the transformer via transformer 120, the primary coil is energized by continuously switching switches S1 to S4 in pairs. This generates an alternating current in secondary coil 120, rectified by diodes D1 to D4 in passive rectifier 130, and thus energizes rotor winding 220. Inverter 110 and primary coil 121 are assigned to static part 150, while secondary coil 122, rectifier 130, and rotor winding 220 are assigned to rotating part 160.

[0041] A discharge of the intermediate circuit (not shown) can be carried out via the H-bridge with switches S1 to S4 and the primary coil 121 by applying a direct current to the primary coil.

[0042] For example, switch S1 is clocked using pulse width modulation, switch S4 is permanently closed, and switches S2 and S3 are permanently opened, causing a direct current to flow through switches S1 and S4 and primary coil 121, but no feed-back into the intermediate circuit occurs during the off phase of pulse width modulation. A direct current is generated via the primary coil by regulating the primary current using pulse width modulation of switch S1.

[0043] The primary coil 121 induces no current in the secondary coil 122, and no significant electrical energy is transferred to the rotating part 160 and thus to the rotor, thus ensuring torque-free operation. The primary coil 121 functions merely as an electrical resistor and converts electrical energy into heat, thereby discharging the intermediate circuit. The switches S1, S4, and the diodes of the H-bridge also contribute to the conversion of electrical energy into heat.

[0044] In the on-phase of the pulse width modulation, the switch S1 is closed and current flows from the intermediate circuit via the switch S1 into the upper contact of the primary coil 121, through the primary coil 121 into the switch S4, which is permanently open, and back into the intermediate circuit.

[0045] In the off-phase of the pulse width modulation, the switch S1 is opened and the circuit consisting of the diode at switch S2, the primary coil 121 and the switch S4 is short-circuited, whereby the current introduced in the on-phase - through the inductance of the primary coil 121 - flows in the circuit and is not fed back into the intermediate circuit.

[0046] In pulse width modulation, the on and off phases alternate repeatedly, whereby a change in the pulse width changes the ratio of the on phase to the off phase.

[0047] A control loop that has a direct current as a reference variable, a pulse width of the pulse width modulation as a manipulated variable and a current flowing at the primary coil, or a variable correlated with it, as a controlled variable, can regulate the direct current at the primary coil to a constant value by means of the pulse width modulation, whereby the constant value does not overload the primary coil and consequently does not damage it.

[0048] An oscillating circuit between the primary coil and the intermediate circuit capacitor cannot occur because S4 is permanently closed.

[0049] Fig. 2 shows an embodiment of an inverter and a separately excited synchronous machine.

[0050] The drive system 1 comprises the inverter 110 and a separately excited synchronous machine 200.

[0051] The inverter includes the microcontroller 111, the power stage 112, and the H-bridge 113. The microcontroller 111 controls the power stage 112 and the H-bridge 113 using pulse width modulation and thus determines the strength and orientation of the magnetic fields of the stator and the rotor.

[0052] The separately excited synchronous machine 200 comprises the stator winding 210, the rotor winding 220 and the transformer 120 with the rectifier 130.

[0053] The microcontroller 111 sends control signals to the switches (S1 to S4 in Fig. 1) of the H-bridge 113, for example using pulse width modulation PWM.

[0054] There may be a discharge of the intermediate circuit (not shown) - as with reference to Fig. 1 - be carried out.

[0055] Fig. 3 shows an inverter and a permanent magnet synchronous machine with active discharge circuit.

[0056] In contrast to the separately excited synchronous machine from Fig. 2, the drive system 1 comprises the synchronous machine 300 without the transformer 120 and rectifier 130. As a result, the rotor of the synchronous machine 300 in the illustrated reference 320 has either short-circuited windings or permanent magnets. As a result, the illustrated synchronous motor 300 is either a self-excited synchronous machine or a permanent magnet synchronous motor.

[0057] In addition to the inverter from Fig. 2, the inverter 110 has an active discharge circuit 114. This is used in the prior art to discharge the intermediate circuit and is Fig. 1 and Fig. 2 is replaced by the control of the H-bridge 113 for energizing the primary coil of the transformer 120 with direct current.

[0058] Fig. 4 shows an inverter and a separately excited synchronous machine with active discharge circuit.

[0059] The drive system 1 in Fig. 4 corresponds to the system of Fig. 2 with the addition that the inverter 110 has an active discharge circuit 114. This is used in the prior art to discharge the intermediate circuit and is Fig. 1 and Fig. 2 is replaced by the control of the H-bridge 113 for energizing the primary coil of the transformer 120 with direct current.

[0060] However, a discharge of the intermediate circuit (not shown) - as with reference to Fig. 1 - can be carried out in parallel with a discharge using active discharge circuit 114. Thus, the active discharge circuit 114 can be designed with a lower discharge and heat dissipation capability, thereby saving costs and space.

[0061] Fig. 5 shows a flowchart of a method for discharging an intermediate circuit of a power electronics system for a separately excited synchronous machine.

[0062] The discharge method 2 begins with step S100. In step S100, it is determined that a signal transmitted by the CAN (2 in Fig. 6) determines the driving situation in which a discharge of the intermediate circuit is to be carried out. This can be done in the CAN or microcontroller (111 in Fig. 2). Once the detection has been made in the CAN, a command to discharge the intermediate circuit is sent to the inverter (110 in Fig. 2) transmitted.

[0063] In step S200, the microcontroller (111 in Fig. 2) the switches (S1 to S4 in Fig. 1) the H-bridge of the inverter (110 in Fig. 1 and Fig. 2) so that the primary coil is supplied with direct current. For example, two switches (S1 and S4 in Fig. 1) closed so that a direct current can flow.

[0064] In step S300, the switches are opened again, for example, when the remaining charge in the intermediate circuit is detected, wherein the remaining charge is low enough so that the discharge is detected as completed.

[0065] Fig. 6 shows an extension for the flow diagram of a method for discharging an intermediate circuit of a power electronics for a separately excited synchronous machine.

[0066] The discharge method 2' relates to an extension for step S200 of Fig. 5. If a discharge is to take place after step 100, control by means of pulse width modulation of the switch (S1 from Fig. 1) with a closed switch (S4 from Fig. 1) and two open switches (S2 and S3 from Fig. 1) to supply, for example, a constant direct current to the primary coil (121 from Fig. 1) as described with reference to Fig. 1 has already been explained.

[0067] In step S300, the switches are opened again, for example when the remaining charge in the intermediate circuit is detected, wherein the remaining charge is low enough so that the discharge is detected as completed and the control is thus terminated.

[0068] Fig. 7 shows an embodiment of a vehicle with a separately excited synchronous machine with the power electronics.

[0069] The vehicle 400 comprises the system 1 according to Fig. 2 and a CAN 3. The vehicle 400 can be any vehicle with an electric drive or an electric actuator. This vehicle 400 can move, for example, on land, on (in) water, in the air, or in space. The vehicle 400 can be used to transport loads or goods or people. The CAN 3 records the driving situation of the vehicle 400, which is as in Fig. 5 forms the basis for the decision to discharge the intermediate circuit. Reference symbol 1 drive system 2, 2' discharge process 3 Computer Area Network (CAN) 100 inductive coupling 110 inverters 111 microcontrollers 112 power level 113 H-bridge 114 active discharge circuit 120 transformer 121 Primary coil 122 Secondary coil 130 rectifiers 150 static part 160 rotating part 200 separately excited synchronous machines 210 Stator winding 220 rotor winding 300 (self-excited / permanent magnet) synchronous machine 310 Stator winding 320 short-circuited winding / permanent magnets 400 vehicles S1, S2, S3, S4 switches D1, D2, D3, D4 diodes PWM pulse width modulation

Claims

[1] Method (2) for discharging an intermediate circuit of a power electronics system for a separately excited synchronous machine (200), comprising: Energizing a primary coil (121) of an inductive coupling (100) for rotor excitation with a direct current so that the intermediate circuit is discharged. [2] Method (3) according to claim 1, wherein energizing the primary coil (121) comprises: Controlling an inverter (110) with an H-bridge (113) so that two switches (S1, S4) of the inverter (110) are closed, whereby the primary coil (121) is supplied with the direct current. [3] Method (3') according to one of the preceding claims, wherein the energizing of the primary coil (121) comprises that a switch (S1) is clocked by means of pulse width modulation in a control loop such that the primary coil (121) is energized with a constant DC voltage such that the primary coil (121) is protected. [4] Power electronics (110) for a separately excited synchronous machine 200, comprising: an inductive coupling (100) for rotor excitation with a primary coil (121), and an intermediate circuit, wherein the primary coil (121) is designed to be supplied with a direct current to discharge the intermediate circuit. [5] Power electronics according to one of the preceding claims, further comprising an inverter (110) with an H-bridge (113) which is configured to close two switches (S1, S4) so that the primary coil (121) is supplied with the direct current. [6] Power electronics according to one of claims 4 or 5, wherein the inverter (110) is further configured to clock a switch (S1) by means of pulse width modulation in a control loop such that the primary coil (121) is supplied with a constant DC voltage. [7] Power electronics according to one of claims 4 to 6, further comprising: a controller (111) designed to control the H-bridge (113) so that the primary coil (121) is supplied with the direct current. [8] Power electronics according to one of the preceding claims, wherein the inductive coupling (100) including the primary coil (121) is adapted to be cooled by an oil cooling of the separately excited synchronous machine (200). [9] Drive system (1) comprising a separately excited synchronous machine (200) with the power electronics according to one of claims 4 to 8, which is designed to carry out the method (3, 3') according to one of claims 1 to 3. [10] Vehicle (400) with the drive system (1) according to claim 9.

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