Drive and load system for rotating electrical machine, test bench and electrical load and drive train

Abstract

The invention relates to a drive and load system for a rotary electric machine, the system having a controllable power source connectable to a power supply. A controllable power source is connected to an intermediate circuit having a capacitor for temporarily storing power. Thus, the capacitor acts as an energy storage to stabilize the intermediate circuit voltage. The drive and load system also has a motor inverter connected to the intermediate circuit and converting an intermediate circuit voltage applied to the motor inverter input into a drive current for rotating the electric machine, or feeding a load current from the electric machine back to the intermediate circuit. A closed control loop of the drive and load system, whose actual value input is connected to the motor inverter input, controls the motor inverter input voltage as an actual value to a setpoint USet in a closed loop manner through a controllable power source. According to the invention, the drive and load system has a setpoint output device which is connected to a setpoint input of the closed control loop and sets a current setpoint USet (t) of the closed control loop. The setpoint output means are adapted to determine a setpoint USet (t) of the closed control loop by means of a predefined setpoint curve USet [n (t)] dependent on the speed n (t) of the electric machine.

Description

Field of the Invention

[0001] The present invention relates to a drive and load system for a rotating electric machine, which can be used in a test bench (especially in a motor, transmission, brake or vehicle test bench), in an electrical load system especially for a current generator, or in an electric drive system especially for an electric vehicle. Background Art

[0002] Modern test benches in the automotive industry cover the main areas of motor testing / transmission testing / brake testing. They can be used in any type of development and functional test bench. The scope of use ranges from simple static test benches to high-dynamic test benches with road load simulation (RLS) for driver or vehicle simulation. Statutory emission tests (such as ELR, ESC and ETC, etc.) are other typical applications.

[0003] These test benches use so-called dynamometers, which can drive a test sample (such as an internal combustion engine or an electric motor of an electric vehicle, etc.) and can also apply a load to the test sample. In addition, it is possible that at least one complete vehicle is located on a running drum braked via a dynamometer. Therefore, these dynamometers are especially high-torque drive and load machines composed of an alternating current motor and a motor inverter. In this case, the current supply is provided by a DC voltage, wherein the motor is controlled via a machine-side pulse inverter. Therefore, the motor inverter supplies a predetermined voltage and a time-related current to the electric motor to provide any dynamics of the dynamometer in the drive or load mode. Such modern pulse inverters are equipped with IGBT (Insulated Gate Bipolar Transistor) switching elements so that both the motor and the generator can operate at full current. It is also possible to consider using SiC MOSFET (Metal Oxide Semiconductor Field Effect Transistor) instead of IGBT.

[0004] Although such a pulse inverter equipped with IGBT or MOSFET can achieve high-dynamic control of the electric machine, this flexibility is accompanied by switching losses in the transistors used in the motor inverter. In this case, the switching losses in the IGBT of the motor inverter depend on the pulse frequency (high frequency generates high losses), the current and voltage applied to the intermediate circuit or the DC bus (high voltage generates high losses). The temperature losses in the three-phase AC motor (asynchronous or synchronous) connected to the motor inverter depend on the harmonics of the current. These harmonics strongly depend on the pulse frequency (high frequency generates low amplitude, and then generates low losses) and the amount of the intermediate circuit voltage (DC bus voltage).

[0005] DE 10 2017 220 682 A1 relates to a control device for a rotating AC motor. In this case, a DC motor is controlled in a closed-loop manner based on the midpoint potential to reduce the load on the control central processing unit.

[0006] From DE 10 2019 114 480 A1, a motor control device and a control method for controlling a motor by comparing phase voltage values with pulse width modulation count values are known. This motor control reduces errors in switching processing and improves the accuracy of control.

[0007] EP 3 809 584 A1 relates to a motor control device. In this case, a motor stop signal is delayed based on the time required for a current detector to convert a leakage current into an analog signal. Therefore, incorrect detection of leakage current due to turning on and off power conversion elements can be reduced.

[0008] However, known motor inverter systems all have the problem of generating unnecessary losses in the drive system and the AC motor at low speeds of the AC motor. Summary of the Invention

[0009] Therefore, based on the object of producing a drive and load system for a rotating electrical machine, in this system, magnetic losses in the electrical machine and switching losses in the motor inverter of the drive and load system are reduced.

[0010] This object is achieved by the drive and load system according to claim 1, the test bench according to claim 13, the load system according to claim 14, and the drive system according to claim 15. Advantageous embodiments and further developments of the invention are set forth in the dependent claims.

[0011] According to the invention, a drive and load system for a rotating electrical machine is produced, which has a controllable current source that can be connected to a current supply. The controllable current source is connected to an intermediate circuit, which has a capacitor for intermediate storage of current. Therefore, the capacitor serves as an energy storage for stabilizing the intermediate circuit voltage. The drive and load system further includes a motor inverter connected to the intermediate circuit, which converts the intermediate circuit voltage applied to the motor inverter input into a drive current for the rotating electrical machine or feeds the load current from the electrical machine back to the intermediate circuit. The closed-loop control circuit of the drive and load system (whose actual value input is connected to the motor inverter input) controls the motor inverter input voltage as the actual value to a setpoint U in a closed-loop manner through the controllable current source. Set According to the invention, the drive and load system includes a setpoint output device, which is connected to the setpoint input of the closed-loop control circuit and sets the current setpoint U of the closed-loop control circuit. Set(t). The setpoint output device is adapted to determine the setpoint U of the closed-loop control circuit as a function of the speed n(t) of the electric machine via a predetermined setpoint curve U Set [n(t)], as a function of the speed n(t) of the electric machine, to determine the setpoint U of the closed-loop control circuit Set (t).

[0012] Thus, according to the present invention, a frequency converter system or a motor inverter system is provided for an alternating current electric machine, in which the alternating current electric machine is preferably controlled by a pulse inverter having switching elements used in the inverter processing. Instead of applying a constant supply voltage to the motor inverter input, the input voltage on the motor inverter is set as a function of the speed of the alternating current electric machine, wherein preferably a lower voltage is applied to the motor inverter input at lower speeds. Thus, the switching losses in the switching elements of the motor inverter and / or the magnetic losses in the alternating current electric machine can be reduced.

[0013] Since the switching losses are high at high voltages, and the switching losses can be reduced by correspondingly reducing the input voltage on the motor inverter, and at the same time the voltage requirement of the electric machine or the electric motor increases with increasing speed, it is advantageous if the setpoint curve U Set [n(t)] increases stepwise or gradually with increasing speed n.

[0014] Since the required supply voltages of the motor inverter and the electric machine enter saturation from a specific speed, it is advantageous if the setpoint curve U Set [n(t)] has a constant saturation value U Sat from the saturation speed n Max .

[0015] Since a minimum supply voltage value must be applied to the motor inverter input at low speeds, it is advantageous if the setpoint curve U Set [n(t)] has a constant offset value U Offset as an addend.

[0016] In order to obtain a specific power buffer or supply voltage buffer at the motor inverter input in the case of large speed variations, it is advantageous if the setpoint curve U Set [n(t)] has a positive lead component b*dn / dt as an addend (which is equal to 0 in the case of a speed change dn / dt < 0).

[0017] In order to simulate the setpoint curve as accurately as possible as the actual required supply voltage at the motor inverter input (with a corresponding safety margin or voltage buffer added), if the setpoint curve U Set [n(t)] is divided into N consecutive speed intervals I1 to I N and in the xth speed interval Ix The associated linear gradient a x extends (where a x > a x+1 > 0 applies to the gradient), which is advantageous.

[0018] In this case, in order to adjust or fit the setpoint curve very precisely to the required supply voltage as a function of the speed n, it is particularly advantageous if the following applies to N consecutive speed intervals I1 to I N the x-th speed interval I x of the setpoint curve U Set [n(t)]: For n x-1 ≤ n < n x , U Set_x [n(t)] = a x * n(t) + b x * dn / dt + U Offset + U Delta_x , where n0 = 0; a x is a gradient factor with a0 = 0 and a x > 0; dn / dt is the time derivative of the speed n(t), b x is a lead factor with b x = 0 when dn / dt < 0, U Offset is an offset value, U Delta_x is the continuity value, and where, additionally, the following applies: For n(t) > n N = n sat , U Set_x [n(t)] = U Max .

[0019] Furthermore, it is advantageous if the setpoint curve U Set (n) includes the sum formed by the required supply voltage curve of the motor inverter and the motor U Zk_min (n) and the offset value U Offset .

[0020] In the case where the required supply voltage curve is measured as a function of the speed, it is advantageous if the required supply voltage curve U Zk_min (n) is an interpolation function for the data points from the measured required supply voltage and the associated speed n.

[0021] In order to be able to take into account the torque M of the motor in addition to the speed n, it is advantageous if the setpoint output device is also adapted to determine the current setpoint U Set [M(t)] of the closed-loop control circuit as a function of the torque M(t) of the motor. Set (t).

[0022] In order to achieve a reliable and fast switching behavior of the switching elements in a motor inverter in the case of high currents, it is particularly advantageous if the motor inverter comprises a pulse inverter equipped with power semiconductor switching elements (in particular IGBTs or SiC MOSFETs).

[0023] In the case of a high-voltage current supply for a drive and load system and generally for test bench applications, it is particularly advantageous if the controllable current source for a three-phase high-voltage current supply comprises a frequency converter with a controlled line rectifier (in particular an active front end (AFE) converter with PID closed-loop control).

[0024] According to the invention, there is also provided a test bench comprising an electric drive and load system according to the invention, in particular a motor, gearbox, brake or vehicle test bench. In this case, the motor or gearbox test bench also has an electric machine connected to the motor inverter, which can be configured as an asynchronous or synchronous machine and is suitable for driving or loading a test specimen designed as an electric motor or an internal combustion engine. The test bench also comprises a mechanical shaft connection, which is suitable for connecting the shafts of the electric machine and the test specimen. Furthermore, the motor or gearbox test bench has a torque measuring unit, which is suitable for measuring the torque M(t) via a torque measuring flange on the shaft connection and for transmitting the torque M(t) to an evaluation unit. The speed N(t) is measured by a speed recording unit of the motor or gearbox test bench via a pulse generator on the shaft connection and is transmitted to the evaluation unit. The evaluation unit is suitable for receiving the measured torque M(t) and the measured speed n(t) from the torque measuring unit and the speed recording unit and for storing them for further evaluation of the test process.

[0025] Furthermore, according to the invention, there is provided an electric load system, in particular for a current generator, comprising a drive and load system according to the invention. In this case, the electric load system has an electric machine connected to the output of the motor inverter, which is configured as a current generator machine and sends the generated alternating current to the motor inverter and to a controllable current source acting as a frequency converter in order to feed the frequency-converted current into the mains supply. Since the output voltage applied to the input of the motor inverter is adjusted according to the speed of the current generator machine, particularly efficient current generation can be achieved in power plants in which the generator speed is not constant or cannot be kept constant. For example, such a load system would be particularly advantageous for use in a gearless wind turbine.

[0026] Furthermore, according to the present invention, there is provided an electric drive train, particularly for an electric vehicle, comprising a drive and load system according to the present invention, wherein the current supply is a mobile current supply, particularly a battery module. The electric drive train further comprises an electric machine connected to the output of a motor inverter, which converts drive current into rotational power and feeds back braking power to the motor inverter, wherein a controllable current source is configured as a DC / DC converter. By adjusting the input voltage at the input of the motor inverter according to the speed of the electric machine, the switching losses in the motor inverter and / or the magnetic losses in the AC electric machine can be reduced, which greatly reduces the current consumption of the electric vehicle and thus increases the range of the electric vehicle. Description of the Drawings

[0027] The present invention will be described in detail hereinafter with reference to the drawings, in which:

[0028] Figure 1A A schematic view of a motor or transmission test bench according to an exemplary embodiment of the present invention is shown;

[0029] Figure 1B A schematic block diagram of a motor or transmission test bench according to an exemplary embodiment of the present invention is shown;

[0030] Figure 2 A schematic block diagram of an electric drive and load system according to an exemplary embodiment of the present invention is shown;

[0031] Figure 3 A schematic block diagram of an electric drive and load system according to an exemplary embodiment of the present invention is shown;

[0032] Figure 4A A circuit configuration of a frequency converter with a controlled line rectifier for controlling an AC electric machine according to the prior art is shown;

[0033] Figure 4B A schematic block diagram for illustrating the energy flow in a drive or load system according to the prior art is shown;

[0034] Figure 5A A schematic block diagram of an electric drive or load system according to the prior art is shown;

[0035] Figure 5B A U-n diagram of the required supply voltage of a motor inverter as a function of speed according to the prior art and a fixed supply voltage applied to the input of the motor inverter are shown;

[0036] Figure 6A A schematic block diagram of a drive and load system according to an exemplary embodiment of the present invention is shown;

[0037] Figure 6Bshows a U-n diagram of the required supply voltage of a motor inverter as a function of speed and a setpoint curve as a function of speed according to an exemplary embodiment of the present invention; and

[0038] Figure 7 shows a flowchart of a driving and loading method according to an exemplary embodiment of the present invention.

[0039] In the respective figures of the drawings, components corresponding to each other have the same reference numerals. Detailed Description

[0040] Figure 1A and Figure 1B shows a schematic view of a motor or transmission test bench 1 according to the present invention. The motor or transmission test bench 1 according to the present invention has a drive and load system 10, and the drive and load system 10 is connected to a current supply 80.

[0041] As can be seen in the schematic block diagram view of Figure 1B the drive and load system 10 according to the present invention has a controllable current source 100 that can be connected to the current supply 80. The controllable current source 100 is connected to an intermediate circuit ZK, and the intermediate circuit ZK has a capacitor 200 for intermediate storage of current and / or as an energy storage for stabilizing the intermediate circuit voltage. The drive and load system 10 further includes a motor inverter 300 connected to the intermediate circuit. The motor inverter 300 converts the intermediate circuit voltage U Zk applied to the motor inverter input into a drive current for the rotating electrical machine 20, or feeds the load current from the electrical machine 20 back into the intermediate circuit ZK. The drive and load system 10 includes a closed-loop control circuit 400. The actual value input of the closed-loop control circuit 400 is connected to the motor inverter input, and the closed-loop control circuit 400 controls the motor inverter input voltage U Zk as an actual value to a setpoint U Set .

[0042] In addition, the drive and load system 10 includes a setpoint output device 500. The setpoint output device 500 is connected to the setpoint input of the closed-loop control circuit 400 and sets the current setpoint U Set (t) of the closed-loop control circuit 400. The setpoint output device 500 is adapted to determine the current setpoint U Set [n(t)] of the closed-loop control circuit 400 as a function of the speed n(t) of the electrical machine 200 through a predetermined setpoint curve U Set (t). The setpoint curve U Figure 6B as a function of speed n will be described in detail below with reference to FIGS. 5C and SetDetermination. In this case, the intermediate circuit voltage U at the input of the motor inverter is set. Zk The main purpose is to reduce the corresponding switching losses in the motor inverter 300 and the magnetic losses in the AC motor 20 when controlling the motor 20.

[0043] As Figure 1A and Figure 1B further shown in, the motor or transmission test bench 1 includes a motor 20 connected to the motor inverter 300. The motor 20 can be configured as an asynchronous machine or a synchronous machine and is suitable for driving or applying a load to a test specimen 30 designed as an electric motor or an internal combustion engine.

[0044] The asynchronous machine 20 is designed as a squirrel-cage machine, which is characterized by a wide speed range, high dynamics, and robustness. In the motor or transmission test bench 1 according to the present invention, the asynchronous machine 20 constitutes a driving and loading device for the test specimen 30. The asynchronous machine 20 can achieve speeds of up to 10,000 rpm and significantly higher speeds, and has a low mass moment of inertia and overload capacity for high-speed dynamics. The asynchronous machine 20 can operate as both a generator and a motor in both rotational directions and can be coupled to a high quality. In combination with the drive and load system 10, the machine 20 can not only brake but also drive, for example, to simulate downhill driving and gear shifting.

[0045] In the case where the test specimen 30 is an electric motor, the electric motor 30 can include an AC motor 32 and a motor inverter 34. In this case, the motor inverter 34 is supplied with current by the drive and load system 10 because the motor inverter 34 can be connected to the DC bus or the intermediate circuit ZK. Here, the DC / DC converter 600 can optionally be interconnected with the intermediate circuit ZK and the capacitor 200 to correspondingly level the voltage applied to the intermediate circuit ZK and set it to the desired input voltage on the motor inverter 34. However, it should be emphasized that the DC / DC converter 600 is an optional element of the electric drive and load system 10 according to the present invention.

[0046] The shafts of the asynchronous machine 20 and the test specimen 30 are connected to each other via a mechanical shaft connection 40 to produce a torque connection between the two machines 20 and 30. Thus, the motor 20 is directly connected to the test specimen 30 via the measuring flange of the torque measuring unit 50 and the shaft connection 40. No intermediate bearing housing is required because the motor 20 is designed for high couplable mass.

[0047] The torque measurement unit 50 is adapted to measure the torque M(t) via a torque measurement flange on the shaft connection 40 and transmit it to the evaluation unit 70. The torque measurement unit 50 is designed as a torque measurement flange with an integrated evaluation unit, which enables a dynamically correct measurement directly at the interface with the test specimen 30. The shaft torque between the asynchronous machine 20 and the test specimen 30 is recorded via the DMS measurement bridge on the rotating flange of the torque measurement unit 50 and transmitted contactlessly to the stator. The signal transmission from the rotor to the stator of the asynchronous motor 20 is digital. The feed voltage transmission from the stationary side to the rotating side is inductive. The direct measurement of the test specimen 30 ensures a dynamically correct torque measurement. In addition to the torque measurement unit 50, a speed recording unit 60 is provided, which is adapted to measure the speed n(t) via a pulse generator on the shaft connection 40 and transmit it to the evaluation unit 70. The speed recording of the speed recording unit 60 is performed using a bearingless, encapsulated hollow shaft encoder, which is mounted on the side facing away from the test specimen 30. The scanning unit of the speed recording unit 60 is rigidly connected to the shaft 40, i.e., there is no coupling. The speed sensor has two separate scanning systems for the drive and load system 10 as well as the evaluation unit 70 (see Figure 1B ), which enables redundant speed recording and thus enables a safe shutdown in the event of a failure of one of the scanning systems. The number of pulses / revolutions is optimally matched to the corresponding speed range of the asynchronous machine 20.

[0048] The evaluation unit 70 is adapted to receive the measured torque M(t) and the measured speed n(t) from the torque measurement unit 50 and the speed recording unit 60 and store them for further evaluation of the test process. In this case, the evaluation unit 70 can be designed as a test bench controller, which functionally covers all areas of modern motor testing.

[0049] As Figure 1A shown, in addition to the test bench controller 70, a safety center 72 can be provided, which ensures a safe shutdown of the connected systems / machines when an emergency stop is triggered. The safety center 72 records the input information from the connected devices and displays the status of the devices. The safety center 72 is a switching device that enables safe and redundant contact replication of the emergency stop input signal. When the emergency stop command device is actuated, the safety contacts of the safety switching device immediately open, so that dangerous movements can be stopped and other hazards can be cut off. In addition to the safety center 72, an optional feed module 74 can be provided, which supplies current to the safety center 72 and the test bench controller 70.

[0050] As Figure 2As shown, the drive and load system 10 according to the present invention can be used in electric drive and load systems 2, 3, particularly in an electric load system 2 for a current generator, for example, or in an electric drive system 3 for an electric vehicle, for example.

[0051] First, the electric load system 2 will be described in more detail. In the load system 2 for a current generator, a motor 20 configured as a current generator machine is connected to the motor inverter output of a motor inverter 300, and the generated alternating current is sent to the motor inverter 300 and a controllable current source 100, and the motor inverter 300 and the controllable current source 100 operate together as a frequency converter to feed the frequency-converted current into the mains supply 80. In this case, the current supply 80 is preferably a three-phase high-voltage current supply.

[0052] In Figure 2 the shown electric load system 2 for a current generator, the controllable current source 100 is configured as an AC / DC converter similar to Figure 1A and Figure 1B the shown motor or gearbox test bench 1. In the case of a three-phase high-voltage current supply, the AC / DC converter includes a frequency converter with a controlled line rectifier, particularly an active front end (AFE) converter with a PID closed-loop control. Such an active front end converter with a PID closed-loop control will be discussed in more detail below, particularly with reference to Figures 4A to 5B .

[0053] An important property of the AFE converter is that this controllable current source 100 provides an electric drive current to the motor inverter 300 on the one hand, but can also feed the direct current generated by the current generator 20 and converted by the motor inverter 300 into the line 80 (see Figure 4B ). Since the drive and load system 10 according to the present invention can greatly reduce both the switching losses in the motor inverter 300 and the magnetic losses in the current generator machine 20, the electric load system 2 using the drive and load system 10 is particularly effective and can generate current with high efficiency.

[0054] Figure 2 The shown system can also be used as an electric drive system 3. In this case, the electric drive system can be used for any electrically operated mobile device, such as an electric vehicle, an electric aircraft, an electrically operated drone, or an electrically operated ship, etc. In this case, the current supply 80 is configured as a mobile current supply, particularly as a battery module. The controllable current source 100 configured as a DC / DC converter for this purpose is then connected to the battery module 80.

[0055] In the electric drive system 3 for an electric vehicle, a high-voltage DC / DC converter that can ensure the stability of the traction voltage in the electric drive system 3 is preferred. For this purpose, a so-called non-isolated DC / DC converter combines a buck converter and a boost converter into a buck-boost converter in such a way that bidirectional energy transfer from the battery module 80 to the electric motor 20 and current feeding back into the battery module 80 are made possible. The described components of the electric drive system for an electric vehicle are well known to those skilled in the art and are the subject of a lecture (in this regard, see the lecture notes "Power electronics in a vehicle and drive train" published by Professor Dr.-Ing. Martin of the Chair of Power Electronics (LEE), Friedrich-Alexander University Erlangen-Nuremberg, in the winter semester 2021 / 2022). The theme of the lecture notes is "Power electronics in a vehicle and drive train".

[0056] During driving, the electric motor 20 connected to the output of the motor inverter thus converts the drive current from the controllable current source 100 into rotational power, and during braking operation, the electric motor 20 feeds the braking power back to the motor inverter 300. The controllable current source 100 configured as a DC / DC converter feeds the current generated, which has been converted into direct current by the motor inverter 300 and stored in the capacitor 200 (42V side intermediate circuit capacitor), back into the battery module 80 after the high-voltage has been reduced or converted accordingly to, for example, the operating voltage (14V) of the traction battery 80. By using the drive and load system 10 according to the invention, which reduces the switching losses in the motor inverter 300, the electric drive system 3 for an electric vehicle can be operated particularly efficiently, whereby the range of the electric vehicle including the drive system 3 can be increased.

[0057] Now, the operating mode of the drive and load system 10 according to the invention will be discussed below in comparison with a conventional drive and load system.

[0058] Figure 4AShows a conventional drive and load system 10' for a rotating electrical machine 20' as an exemplary circuit configuration. Such a drive and load system 10' is also designated as a frequency converter with a controlled line rectifier. This converter includes an active power switch 110' at the input, which is here designed as a B6 bridge consisting of six power transistors, IGBTs or power MOSFETs. Although this requires more control effort, it still offers many advantages, such as feeding energy back into the line if, for example, braking a mass driven by the motor is required. In addition, the pulse inverter enables an almost sinusoidal current consumption from the line (which has significantly fewer low-frequency harmonics), as well as a rapid switch between motor and generator operation. On the line side, the input-side clock and possible resonance peaks can be sufficiently suppressed by a specific filter 120'. For example, the AFE frequency converter with PID closed-loop control is described in the paper "Dynamic Model of Active Front-End Converters with 2DOF-PI Controllers for DC Bus Voltage Control" by Anup Thapa et al., published in the 2020 IEEE 21st Workshop on Control and Modeling for Power Electronics (COMPEL) (November 9 - 12, 2020) (DOI: 10.1109 / COMPEL49091.2020.9265801).

[0059] Figure 4A The shown frequency converter 10' consists of a line-side pulse inverter 100' ("active front end") and a machine-side pulse inverter 300' ("inverter"). The inverters 100', 300' convert the line voltage, which is constant in amplitude and frequency (50 or 60 Hz) from the current supply 80', into a system with variable voltage and frequency. Both of these power elements are equipped with IGBT (Insulated Gate Bipolar Transistor) switching elements 110' or MOSFETs, in particular SiC MOSFETs. In general, the present invention encompasses all types of power semiconductor switching elements as long as they are able to switch high currents reliably and quickly. This enables both the motor and the generator to operate at full current.

[0060] In this case, Figure 4BIllustrates the power flow in the system. The field-oriented vector closed-loop control of the machine-side frequency converter 300' (corresponding to the motor inverter 300 according to the present invention) achieves excellent closed-loop control dynamics and very good concentricity over the entire speed range. The main-line side pulse inverter 100' (corresponding to the controllable current source 100 according to the present invention) operates at a power factor cosφ = 1. In this setting, no fundamental reactive power is generated. The main-line current is almost sinusoidal. The default-installed main-line filter reduces the pulse frequency harmonics to a minimum.

[0061] Figure 5A Shows a drive and load system 10' for a rotating electrical machine 20' according to the prior art, which can be configured respectively as a frequency converter with a controlled main-line rectifier or as an AFE converter or active front-end converter, as Figure 4A shown. The purpose of this drive and load system 10' is to directly provide the supply voltage defined for the motor inverter 300' at the supply input of the motor inverter 300'. To ensure compensation of the voltage drop via the intermediate circuit ZK and the capacitor 200' in the case of high supply currents, a closed-loop control circuit 400' is used in the frequency converter 100' with a controlled main-line rectifier. The actual value input of this closed-loop control circuit 400' is connected to the motor inverter input, and this closed-loop control circuit 400' controls the motor inverter input voltage as the actual value to the setpoint U in a closed-loop manner through the controllable current source 100' Set . According to the prior art, the supply voltage is selected as the supply voltage U at the input of the motor inverter 300' Zk , which ensures sufficient power even at high loads and maximum speeds.

[0062] This constant supply voltage U as the AC voltage Uzk [VAC] and as the DC voltage Uzk [VDC] zk is shown as a dashed line in Figure 5B and is independent of the speed of the electrical machine 20. In the example shown in Figure 5B , this supply voltage U Zk is set to 500V. However, the required supply voltage Ukl of the electrical machine 20' or the AC electrical machine 20' increases to the maximum peak supply voltage with increasing speed and then remains constant. According to the prior art, the intermediate circuit voltage or the DC bus voltage applied to the input of the motor inverter 300' is controlled in a closed-loop manner independently of the speed, so that the required supply voltage is provided for the electrical machine 20 over the entire speed range, and additional reserves are available for dynamic processing (especially for speeds above the peak supply voltage).

[0063] This can lead to an unnecessarily high intermediate circuit voltage or DC bus voltage in the lower speed range, followed by corresponding switching losses, as already described at the beginning. This applies in particular to permanent magnet (PM) machines, which are used in the high speed range and therefore require a relatively low nominal voltage at the operating point of the nominal speed. Figure 5A shows such a standard closed-loop control of the intermediate circuit voltage to a constant input voltage value U Zk From Figure 5B it can be seen that the supply voltage U Zk provided in the low speed range is significantly higher than the supply voltage required in this speed range. However, in a motor inverter 300' including a pulse inverter, this is associated with unnecessarily high switching losses at low speed n, especially in the case where the pulse inverter is equipped with power semiconductor switching elements (such as IGBTs or MOSFETs, especially SiC MOSFETs).

[0064] Figure 6A Now shown is a drive and load system 10 according to an exemplary embodiment of the present invention, which can be used for a rotating electric machine 20. In addition to a controllable current source 100, an intermediate circuit ZK having a capacitor 200, a motor inverter 300, and a closed-loop control circuit 400, the drive and load system 10 according to the present invention further provides a setpoint output device 500, which is connected to the setpoint input of the closed-loop control circuit 400 and sets the current setpoint U Set (t) of the closed-loop control circuit 400, where the setpoint output device is adapted to determine the current setpoint U Set of the closed-loop control circuit as a function of the speed n(t) of the electric machine by a predetermined setpoint curve U Set (t). In this case, the purpose of the setpoint curve U Set [n(t)] is to approximate the process of the required supply voltage of the AC motor 20 as closely as possible, while providing a specific safety margin, offset, or voltage reserve. Since the voltage reserve is proportional to the charge stored in the capacitor 200, this voltage reserve also corresponds to the energy reserve for the electric machine 20.

[0065] In Figure 6B the setpoint curve U Set (n) is again shown as the AC voltage Uzk[VAC], and the corresponding DC voltage Uzk[VDC] (corresponding to Uzk[VAC]*Sqrt[2]) is shown as a dashed line. Since the required supply voltage U Zk_min or equivalently the required supply voltage or motor terminal voltage U Figure 6B in kl is lower at low speeds of the AC motor 20 than at high speeds, therefore according to the present invention, if the setpoint curve USet (n) It is advantageous to have a smaller setpoint voltage value at low speeds than at high speeds. Thus, the setpoint curve U Set (n) preferably increases stepwise or gradually as the speed n increases. According to the invention, in this case, the setpoint curve U Set (n) can have a constant saturation value U satt (here about 14,000 revolutions per minute) from a specific saturation speed n Max (here U Max = 500 V). Furthermore, it is advantageous if there is a specific voltage reserve for dynamic processing and the setpoint curve has a constant offset value U Offset as an additional part. This ensures that the setpoint voltage never falls below the required supply voltage.

[0066] Therefore, the intermediate circuit voltage or DC bus voltage at the intermediate circuit ZK is calculated based on the speed n and the speed gradient dn / dt. To maintain a specific leading voltage as a reserve during the acceleration process, the setpoint curve U Set [n(t)] can have a positive leading component b*dn / dt as an additional part, which is 0 for dn / dt < 0 in the case of a speed change. Thus, if the speed gradient or the time derivative of the speed dn / dt is less than 0, the DC bus voltage or the setpoint of the intermediate circuit voltage U Zk is calculated only based on the current speed n(t). Therefore, if the time derivative of the speed is dn / dt > 0, the voltage setpoint U Zk at the intermediate circuit ZK or the setpoint of the DC bus voltage has only a positive leading component. This results in a leading control of the intermediate circuit voltage U Zk , which is important for a rapid positive speed gradient dn / dt, because otherwise the DC bus voltage or the intermediate circuit voltage cannot follow the voltage requirements of the machine fast enough in the case of a high speed change or acceleration and cannot supply sufficient power to the motor 20.

[0067] As Figure 6B further shown, the setpoint curve U Set [n(t)] can be divided into N consecutive speed intervals I1 to I n . In the exemplary embodiment shown in Figure 6B , the setpoint curve U Set shows a first gradient in a first speed range up to about 4,000 revolutions per minute and then switches to a second speed range between 4,000 revolutions per minute and 14,000 revolutions per minute with a second gradient, so as to then switch to the saturation value U MaxIn addition, it is preferred if these respective gradients switch from a high gradient to a low gradient in different intervals, as this is most suitable for the actual process of the required supply voltage. Thus, if the setpoint curve is divided into n consecutive speed intervals I1 to I n and in the x-th speed interval I x extends with an associated linear gradient a x where a x >a x+1 >0 applies to the gradient.

[0068] Although only two speed intervals with two different gradients are shown in Figure 6B (from 0 to 4000 revolutions per minute and from 4000 revolutions per minute to 14000 revolutions per minute), the number N of speed intervals can also consist of 10 intervals or even 100 intervals. However, to keep the closed-loop control simple, it is preferred if N is less than 1000, or less than 500, or less than 200, or less than 100, or less than 90, or less than 80, or less than 70, or less than 60, or less than 50, or less than 40, or less than 30, or less than 20, or less than 10, or less than 9, or less than 8, or less than 7, or less than 6, or less than 5, or less than 4, or less than 3, or equal to 2, or equal to 1.

[0069] In this case, it is advantageous if the following applies to the setpoint curve U N in the x-th speed interval I x of the N consecutive speed intervals I1 to I Set [n(t)]:

[0070] For n x-1 ≤n<n x , U Set_x [n(t)] = a x *n(t)+b x *dn / dt+U Offset +U Delta_x ,

[0071] where the following applies:

[0072] n0 = 0;

[0073] a x is a gradient factor with a0 = 0 and a x >0;

[0074] dn / dt is the time derivative of the speed n(t),

[0075] b x is an advance factor with b x = 0 when dn / dt < 0,

[0076] U Offset is the offset value,

[0077] U Delta_x is the continuity value of.

[0078] In addition, the following applies:

[0079] For n(t) > n N = n sat U Set_x [n(t)] = U Max .

[0080] However, the setpoint curve U Set [n(t)] can also be approximated (fitted) to the root function of the required supply voltage and an offset value is provided for it:

[0081]

[0082] In addition, an anticipatory component b*dn / dt can also be included:

[0083]

[0084] Other functions (such as logarithmic functions, etc.) can also be envisaged to adjust the setpoint curve U Set [n(t)] to the process of the required supply voltage as a function of speed as precisely as possible, so that the same voltage reserve U Offset + b*dn / dt can be obtained at any speed:

[0085] U Set [n(t)] = e*log[f*n(t)^g + 1] + b*dn / dt + U Offset

[0086] In this case, the gradient factor a is advantageously in the range from 0.001 V / rpm to 1 V / rpm, or from 0.005 V / rpm to 0.5 V / rpm, or from 0.01 V / rpm to 1 V / rpm. In this case, the offset value U OffsetAdvantageously located in the range from 1 V to 1000 V, or from 5 V to 500 V, or from 10 V to 200 V, or from 10 V to 100 V. The lead factor b is advantageously located in the range from 1 V·s / rpm to 10 MV·s / rpm, or from 10 V·s / rpm to 1 MV·s / rpm, or from 100 V·s / rpm to 100 kV·s / rpm. The parameter c is advantageously located in the range from 0.1 V to 100 V, or from 0.5 V to 50 V, or from 1 V to 10 V. The parameter d is advantageously located in the range from 0.1 min / rev to 100 min / rev, or from 0.5 min / rev to 50 min / rev, or from 1 min / rev to 10 min / rev. The parameter e is advantageously located in the range from 0.1 V to 100 V, or from 0.5 V to 50 V, or from 1 V to 10 V. The parameter f is advantageously located in the range from 0.1 min / rev to 100 min / rev, or from 0.5 min / rev to 50 min / rev, or from 1 min / rev to 10 min / rev. The parameter g is advantageously located in the range from 0.1 to 100, or from 0.5 to 50, or from 1 to 10. In this case, the voltage value given in volts is related to the AC voltage value Uzk [VAC] as Figure 5B and Figure 6B shown.

[0087] In the case where the required supply voltage can be measured or simulated as a function of speed, the setpoint curve U Set (n) can also include the sum formed by the minimum supply voltage curve U Zk_min (n) of the motor inverter 300 and the motor 20 and the offset value U Offset . In this case, the required supply voltage curve U Zk_min (n) can be an interpolation function of the data points from the measured required supply voltage and the associated speed n. In this case, the interpolation function can be one of the above functions, which is correspondingly fitted to the data set. Furthermore, the setpoint curve U Zk_Set (n) can have at least one speed interval I Sat between speed 0 and speed n x , in which speed interval I x , the setpoint curve has a component with a stepwise increase, continuous increase, linear increase, root-shaped increase or logarithmic increase. The setpoint curve can be any monotonically increasing function. The setpoint curve can be any constant and monotonically increasing function.

[0088] In addition to controlling the voltage in a closed-loop manner as a function of speed, according to the present invention, it is also provided that the setpoint output device 500 is further adapted to determine the current setpoint U for the closed-loop control circuit through a predetermined setpoint curve U Set [n(t), M(t)], as a function of the torque M(t) of the motor 20.Set (t). It is not possible to control the intermediate circuit voltage in a closed loop manner solely as a function of the torque M(t). However, according to the present invention, it is advantageous if, in addition to the evaluation of the speed n(t), the torque M(t) is also used as a further influencing variable for the setpoint U Set of [n(t), M(t)].

[0089] Figure 7 FIG. depicts a flowchart of a method for operating a drive and load system 10 for a rotating electric machine 20. Thus, method 1000 includes a first step S1010 of providing a controllable current source 100 that can be connected to a current supply. In a further step S1020, an intermediate circuit ZK connected to the controllable current source 100 is provided, which has a capacitor 200 for intermediate storage of current. In a further step S1030, a motor inverter 300 connected to the intermediate circuit ZK is provided, which converts the intermediate circuit voltage applied to the motor inverter input into a drive current for the rotating electric machine 20 or feeds the load current from the machine 20 back to the intermediate circuit ZK. In a further step S1040, a closed-loop control circuit 400 is provided, whose actual value input is connected to the motor inverter input, and which controls the motor inverter input voltage as an actual value to a setpoint U Set in a closed loop manner via the controllable current source 100. In a further step S1050, a setpoint output device 500 is provided, which is connected to the setpoint input of the closed-loop control circuit and sets the current setpoint U Set (t) of the closed-loop control circuit. In step S1060, as described above, the current setpoint U Set for the closed-loop control circuit 400 is determined as a function of the speed n(t) of the electric machine by a predetermined setpoint curve U Set (t).

[0090] The control or closed-loop control of the DC bus voltage or the intermediate circuit voltage depending on the speed and the speed gradient enables a reduction in the losses occurring in the motor inverter 300 and the electric machine 20, in particular switching losses and magnetic losses. These magnetization losses occur in the machine and in the chokes that may be installed (on the line side and on the motor side), and the magnetization losses of the motor-side choke can also be reduced.

[0091] This applies in particular to high-speed PM synchronous motors. Thus, during operation on a test bench, the thermal load can be reduced at low speed and full load, since at the operating point only a low supply voltage corresponding to the actually required supply voltage is applied to the input of the motor inverter 300. Thus, according to the invention, the DC bus voltage of the drive system is controlled in a closed-loop manner based on the machine speed and the speed gradient in such a way that the switching losses at low speed are compensated for by applying a lower voltage. Thus, the magnetic losses in the AC machine and possibly in the motor choke installed, as well as the switching losses in the IGBT switching elements or SiC MOSFETs or generally power semiconductor switching elements or power transistors of the drive system, can be reduced, and the efficiency of the drive and load system 10 according to the invention can be increased.

Claims

1. A drive and load system (10) for a rotating electrical machine (20), comprising: A controllable current source (100) which can be connected to a current supply (80); An intermediate circuit (ZK) which is connected to the controllable current source (100), the intermediate circuit (ZK) having a capacitor (200) for intermediate storage of current; A motor inverter (300) which is connected to the intermediate circuit (ZK), the motor inverter (300) converting the intermediate circuit voltage applied to the motor inverter input into a drive current for the rotating electrical machine (20) or feeding back a load current from the electrical machine (20) to the intermediate circuit (ZK); Closed-loop control circuit (400), the actual value input of the closed-loop control circuit (400) is connected to the motor inverter input, and the closed-loop control circuit (400) controls the motor inverter input voltage as the actual value to the setpoint U in a closed-loop manner through the controllable current source (100) Set ; A setpoint output device (500) is provided, which is connected to the setpoint input of the closed-loop control circuit (400) and sets the current setpoint U of the closed-loop control circuit (400) Set (t). Characterized in that The setpoint output device (500) is adapted to determine the current setpoint U Set [n(t)] of the closed-loop control circuit (400) as a function of the speed n(t) of the electric machine (20). Set (t).

2. The drive and load system (10) according to claim 1, characterized in that, The setpoint curve U Set [n(t)] increases stepwise or gradually as the speed n increases.

3. The drive and load system (10) according to claim 1 or 2, characterized in that, The setpoint curve U Set [n(t)] starts from the saturation velocity n Sat and has a constant saturation value U Max .

4. The drive and load system (10) according to any one of the preceding claims, characterized in that, The setpoint curve U Set [n(t)] has a constant offset value U as an addend Offset .

5. The drive and load system (10) according to any one of the preceding claims, characterized in that, the setpoint curve U Set [n(t)] has a positive leading component b*dn / dt as an additive term, and the positive leading component b*dn / dt equals 0 when the speed change dn / dt < 0.

6. The drive and load system (10) according to any one of the preceding claims, characterized in that, The setpoint curve U Set [n(t)] is divided into N consecutive speed intervals I1 to I N , and in the x-th speed interval I x extends with an associated linear gradient a x , where a x > a x+1 > 0 applies to the gradient.

7. The drive and load system (10) according to any one of the preceding claims, characterized in that, The following applies to the x-th speed range Ix of N consecutive speed ranges I1 to IN N in the setpoint curve U x in Set [n(t)]: For n x-1 ≤ n < n x ,U Set_x [n(t)] = a x *n(t) + b x *dn / dt + U Offset + U Delta_x , where n0 = 0; a x is a gradient factor with a0 = 0 and a x > 0; dn / dt is the time derivative of the velocity n(t), b x is a leading factor with b x = 0 when dn / dt < 0, U Offset is an offset value, U Delta_x is the continuity value of, and Wherein, the following additionally applies: for n(t) > n N = n sat , U Set_x [n(t)] = U Max .

8. The drive and load system (10) according to any one of the preceding claims, characterized in that, The setpoint curve U Set (n) includes the required supply voltage curve U Zk_min (n) of the motor inverter (300) and the electric machine (20) and an offset value U Offset formed as a sum.

9. The drive and load system (10) according to claim 8, characterized in that, Required supply voltage curve U Zk_min (n) is an interpolation function for the data points from the measured required supply voltage and the associated speed n.

10. The drive and load system (10) according to any one of the preceding claims, characterized in that, The setpoint output device (500) is also adapted to determine the current setpoint U Set [n(t), M(t)] of the closed-loop control circuit as a function of the torque M(t) of the electric machine (20). Set (t).

11. The drive and load system (10) according to any one of the preceding claims, characterized in that, The motor inverter (300) includes a pulse inverter which is equipped with power semiconductor switching elements, in particular IGBTs or MOSFETs.

12. The drive and load system (10) according to any one of the preceding claims, characterized in that, In the case of a three-phase high-voltage current supply (80), the controllable current source (100) includes a frequency converter with a controlled line rectifier, in particular an active front-end converter with PID closed-loop control, i.e. an AFE converter.

13. A test bench (1), in particular a motor, gearbox, brake or vehicle test bench, comprising: The electric drive and load system (10) according to any one of the preceding claims, An electric machine (20) connected to the motor inverter (300), the electric machine (20) being adapted to drive or load a test specimen (30) designed as an electric motor or an internal combustion engine; A mechanical shaft connection member (40) which is adapted to connect the shafts of the electric machine (20) and the test specimen (30); A torque measurement unit (50) which is adapted to measure a torque M(t) via a torque measurement flange on the shaft connection member (40) and transmit the torque M(t) to an evaluation unit (70); A speed recording unit (60) which is adapted to measure a speed n(t) via a pulse generator on the shaft connection member (40) and transmit the speed n(t) to the evaluation unit (70); And An evaluation unit (70) which is adapted to receive the measured torque M(t) and the measured speed n(t) from the torque measurement unit (50) and the speed recording unit (60) and store the torque M(t) and the speed n(t) for further evaluation of the test process.

14. An electrical load system (2), comprising: The drive and load system (10) according to any one of claims 1 to 11, An electric machine (20) connected to the motor inverter output, the electric machine (20) being configured as a current generator and sending the generated alternating current to the motor inverter (300), and a controllable current source (100) as a frequency converter to feed the frequency-converted current to the line supply (80).

15. An electric drive system (3), comprising: A mobile current supply (80), in particular a battery module; The drive and load system (10) according to any one of claims 1 to 11, An electric machine (20) connected to the output of a motor inverter, the electric machine (20) converting the drive current into rotational power and feeding the braking power back to the motor inverter (300). Among them, The controllable current source (100) is configured as a DC / DC converter.

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