Drive and load system for a rotating electric machine, test stand, and electric load and drive train
Patent Information
- Application Number
- EP2023817067
- Authority / Receiving Office
- EP · EP
- Patent Type
- Applications
- Current Assignee / Owner
- Priority Date
- 2022-12-07
- Filing Date
- 2023-11-29
- Publication Date
- 2025-10-15
Smart Images
Figure 1.1
Abstract
Description
[0001] Drive and load system for a rotating electrical machine, test bench and electrical load and drive train
[0002] The invention relates to a drive and loading system for a rotating electrical machine, which can be used in a test bench, in particular in an engine, transmission, brake or vehicle test bench, in an electrical load train, in particular for a power generator, or in an electrical drive train, in particular for an electric vehicle.
[0003] Modern test benches in the automotive sector cover the essential areas of engine testing, transmission testing, and brake testing. They can be used in all types of development and functional test benches. The application spectrum ranges from simple stationary test benches to highly dynamic test benches with road load simulation for driver or vehicle simulation (Road Load Simulation, RLS). Legal emissions tests such as ELR, ESC, and ETC are other typical applications.
[0004] These test benches utilize so-called dynamometers, which can drive and load a test specimen such as an internal combustion engine or an electric motor of an electric vehicle. Furthermore, it is possible for at least an entire vehicle to rest on running drums that are braked by a dynamometer. These dynamometers are therefore particularly high-torque drive and loading machines consisting of an electric AC motor and a motor inverter. The power supply is provided by direct current, with the motor controlled by a pulse-controlled inverter on the machine side. The motor inverter thus supplies the electric motor with a predetermined voltage and a time-dependent current to provide any desired dynamic response of the dynamometer, either in drive or load mode.Such modern pulse-controlled inverters are equipped with IGBT switching elements (insulated gate bipolar transistors) to enable both motor and generator operation at full current. The use of SiC MOSFETs (metal oxide semiconductor field-effect transistors) instead of IGBTs is also conceivable. Although such IGBT- or MOSFET-equipped pulse-controlled inverters enable highly dynamic control of the electrical machine, this flexibility is accompanied by switching losses of the transistors used in the motor inverter. The switching losses in the IGBTs of the motor inverter depend on the pulse frequency (high frequencies generate high losses), the current, and the voltage applied to the intermediate circuit or DC bus (high voltages generate high losses). The temperature losses in a three-phase AC motor (asynchronous or synchronous) connected to a motor inverter depend on the current harmonics.These harmonics depend strongly on the pulse frequency (high frequencies produce low amplitudes, which in turn produce low losses) and the magnitude of the intermediate circuit voltage (DC bus voltage).
[0005] DE 10 2017 220 682 A1 is directed to a control device for rotating AC electric machines. Here, an electric DC machine is controlled based on a center-point potential in order to reduce the load on the controlling central processing unit.
[0006] DE 10 2019 114 480 A1 discloses a motor control device and a control method, wherein the motor is controlled by comparing the phase voltage value and the pulse width modulation count value. This motor control reduces errors in the switching process and improves control accuracy.
[0007] EP 3 809 584 A1 is directed to a motor control device. Here, a motor stop signal is delayed based on the time required for the current detector to convert the leakage current into an analog signal. Thus, erroneous detection of the leakage current caused by the switching on and off of the power conversion element can be reduced.
[0008] However, the known motor inverter systems all have the problem that unnecessary losses occur in the drive system and the AC machine at low speeds of the AC machine.
[0009] The invention is therefore based on the object of creating a drive and load system for a rotating electrical machine in which the magnetic losses in the electrical machine as well as the switching losses in a motor inverter of the drive and load system are reduced.
[0010] This object is achieved by the drive and loading system according to claim 1, by the test bench according to claim 13, by the loading train according to claim 14, and by the drive train according to claim 15. Advantageous embodiments and further developments of the invention are set forth in the subclaims.
[0011] According to the invention, a drive and load system for a rotating electrical machine is provided, which has a controllable current source connectable to a power supply. The controllable current source is connected to an intermediate circuit having a capacitor for intermediate current storage. The capacitor thus acts as an energy storage device for stabilizing the intermediate circuit voltage. The drive and load system further comprises 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 a rotating electrical machine or feeds a load current from the electrical machine back into the intermediate circuit.A control loop of the drive and load system, whose actual value input is connected to the motor inverter input, regulates the motor inverter input voltage as an actual value to a setpoint Uset using the controllable current source. According to the invention, the drive and load system has a setpoint output device that is connected to the setpoint input of the control loop and sets its current setpoint Uset (t). The setpoint output device is suitable for determining the setpoint Uset (t) for the control loop using a predetermined setpoint curve Uset [n(t)] as a function of the speed n(t) of the electric machine.
[0012] According to the invention, a frequency converter system or a motor inverter system for an electric AC machine is provided, in which the AC machine is preferably controlled by a pulse-controlled inverter having switching elements used in the inverter process. Instead of applying a constant supply voltage to the motor inverter input, the input voltage at the motor inverter is adjusted depending on the speed of the AC machine, with lower voltages preferably being applied to the motor inverter input at lower speeds. This allows switching losses in the switching elements of the motor inverter and / or magnetic losses within the AC machine to be reduced.
[0013] Since the switching losses are high at high voltages, whereby the switching losses can be reduced by a corresponding reduction of the input voltage at the motor inverter, and at the same time the voltage requirement of the electrical machine or the electric motor increases with increasing speed, it is advantageous if the setpoint curve Uset [n(t)] is increased stepwise or gradually with increasing speed n.
[0014] Since the required supply voltage of the motor inverter and the electric machine runs into saturation from a certain speed, it is advantageous if the setpoint curve Uset [n(t)] has a constant saturation value llMax from a saturation speed nsat.
[0015] Since a minimum supply voltage value must be present at the motor inverter input at low speeds, it is useful if the setpoint curve Uset [n(t)] has a constant offset value Uoffset as an addend.
[0016] In order to ensure that a certain power buffer or supply voltage buffer is available at the motor inverter input in the event of significant speed changes, it is advantageous if the setpoint curve Uset [n(t)] has a positive lead component b*dn / dt as an addend, which is equal to 0 for speed changes dn / dt < 0.
[0017] In order to simulate the setpoint curve as accurately as possible to the supply voltage actually required at the motor inverter input, with a corresponding safety margin or voltage buffer being added, it is advisable if the setpoint curve Uset [n(t)] is divided into N consecutive speed intervals h to IN and in the x-th speed interval Ix with an associated linear gradient a x runs, where the gradients a x > a x +i >0 applies.
[0018] For a very precise adjustment or fitting of the setpoint curve to the required supply voltage as a function of the speed n, it is particularly advantageous if the setpoint curve Uset [n(t)] in the x-th speed interval l x of N consecutive speed intervals h to IN applies: Uset_x [n(t)] = a x *n(t) + b x *dn / dt + Uottset + Uoeita_x, for n x -iSn <n x , where no=O; a x a gradient factor with ao = 0 and a x > 0; dn / dt is the time derivative of the speed n(t), b x a lead factor with b x = 0 at dn / dt <0, Uoffset an offset value, UDeita_ x a continuity value with U D eita_ x = E?=i and where furthermore: U Se t_ x [n(t)J = U Max for n(t) > n N = n sa t is.
[0019] Furthermore, it is advantageous if the setpoint curve Uset (n) comprises a sum formed from a required supply voltage curve Uzk_min (n) of the motor inverter and the electric machine as well as an offset value Uottset.
[0020] In the event that a required supply voltage curve is measured as a function of the speed, it is advantageous if the required supply voltage curve Uzk_min (n) is an interpolated function of data points from measured required supply voltages and associated speeds n.
[0021] In order to be able to take into account not only the speed n but also the torque M of the electric machine, it is advantageous if the setpoint output device is further suitable for determining a current setpoint Uset (t) for the control loop by means of a predetermined setpoint curve Uset [M(t)] as a function of the torque M(t) of the electric machine.
[0022] For reliable and fast switching behavior with simultaneously high currents of the switching elements in the motor inverter, it is particularly advantageous if the motor inverter comprises a pulse inverter that is equipped with power semiconductor switching elements, in particular IGBTs or SiC MOSFETS.
[0023] In the case of a high-voltage power supply for the drive and load system and generally in test bench applications, it is particularly useful if the controllable power source for a 3-phase high-voltage power supply comprises a frequency converter with a controlled mains rectifier, in particular an Active Front End (AFE) converter with PID control.
[0024] According to the invention, a test bench, in particular an engine, transmission, brake, or vehicle test bench, is further provided, which has the electrical drive and loading system according to the invention. The engine or transmission test bench further comprises an electrical machine connected to the motor inverter, which can be designed as an asynchronous machine or synchronous machine and is adapted to drive or load a test object designed as an electric or internal combustion engine. The test bench further comprises a mechanical shaft connection adapted to connect the shafts of the electrical machine and the test object. Furthermore, the engine or transmission test bench has a torque measuring unit adapted to measure the torque M(t) via a torque measuring flange on the shaft connection and to transmit it to an evaluation unit.Using a speed measurement unit on the engine or transmission test bench, the speed N (t) is measured via a pulse generator on the shaft connection and transmitted to the evaluation unit. The evaluation unit is configured to receive the measured torque M (t) and the measured speed n (t) from the torque measurement unit and the speed measurement unit and to store them for further evaluation of the test process.
[0025] Furthermore, the invention provides an electrical load train, in particular for a power generator, which has the drive and load system according to the invention. The electrical load train has an electrical machine connected to the motor inverter output, which is designed as a power generator machine and sends a generated alternating current to the motor inverter and the controllable power source as a frequency converter in order to feed a frequency-converted current into a power grid. Due to the adaptation of the output voltage applied to the motor inverter input to the speed of the power generator machine, particularly effective power generation can be achieved in electrical power plants in which the generator speed is not or cannot be kept constant. Such a load train would be particularly advantageous, for example, when used in gearless wind turbines.
[0026] Furthermore, the invention provides an electric drive train, in particular for an electric vehicle, which has the drive and load system according to the invention, wherein the power supply is a mobile power supply, in particular a rechargeable battery module. This electric drive train further has the electric machine connected to the motor inverter output, which converts the drive current into rotational power and feeds braking power back to the motor inverter, wherein the controllable power source is designed as a DC / DC converter. By adapting the input voltage at the motor inverter input to the speed of the electric machine, the switching losses in the motor inverter and / or the magnetic losses in the AC machine can be reduced, thereby drastically reducing the power consumption of the electric vehicle and thus increasing the range of the electric vehicle.
[0027] The invention is described in detail below with reference to the drawings. They show:
[0028] Fig. 1A is a schematic view of an engine or transmission test bench according to an embodiment of the invention;
[0029] Fig. 1 B is a schematic block diagram of the engine or transmission test bench according to an embodiment of the invention;
[0030] Fig. 2 is a schematic block diagram of an electric drive and load train according to an embodiment of the invention;
[0031] Fig. 3 is a schematic block diagram of an electric drive and loading system according to an embodiment of the invention;
[0032] Fig. 4A shows a circuit structure of a frequency converter with a regulated mains rectifier for controlling an alternating current machine according to the prior art;
[0033] Fig. 4B is a schematic block diagram illustrating the energy flow in a drive or load train according to the prior art;
[0034] Fig. 5A is a schematic block diagram of an electric drive or load train according to the prior art;
[0035] Fig. 5B shows a Un diagram of the necessary supply voltage of a motor inverter as a function of the speed and the fixed supply voltage applied to the motor inverter input in the prior art;
[0036] Fig. 6A is a schematic block diagram of a drive and load train according to an embodiment of the invention;
[0037] Fig. 6B is a Un diagram of the required supply voltage of a motor inverter as a function of the speed and a setpoint curve as a function of the speed according to an embodiment of the invention; and
[0038] Fig. 7 is a flowchart of a drive and loading method according to an embodiment of the invention.
[0039] In the various figures of the drawings, corresponding components are provided with the same reference numerals. Figures 1A and 1B show schematic views of an engine or transmission test bench 1 according to the invention. The engine or transmission test bench 1 according to the invention has a drive and loading system 10 connected to a power supply 80.
[0040] As can be seen in the schematic block diagram of Fig. 1B, the drive and load system 10 according to the invention has a controllable current source 100 connectable to the power supply 80. The controllable current source 100 is connected to an intermediate circuit ZK, which has a capacitor 200 for intermediate current storage and / or as an energy storage device for stabilizing the intermediate circuit voltage. The drive and load system 10 further has a motor inverter 300 connected to the intermediate circuit, which converts the intermediate circuit voltage Uzk applied to the motor inverter input into a drive current for the rotating electrical machine 20 or feeds a load current from the electrical machine 20 back into the intermediate circuit ZK.The drive and load system 10 comprises a control circuit 400, the actual value input of which is connected to the motor inverter input, and which, by means of the controllable current source 100, regulates the motor inverter input voltage Uzk as an actual value to a setpoint Uset.
[0041] Furthermore, the drive and load system 10 has a setpoint output device 500, which is connected to the setpoint input of the control loop 400 and sets its current setpoint Uset(t). The setpoint output device 500 is suitable for determining the current setpoint Uset(t) for the control loop 400 by means of a predetermined setpoint curve Uset[n(t)] as a function of the speed n(t) of the electric machine 200. The determination of the setpoint curve Uset as a function of the speed n is described in more detail below with reference to Figures 5C and 6B. The essential purpose of adjusting the intermediate circuit voltage Uzk at the motor inverter input is to reduce corresponding switching losses in the motor inverter 300 when controlling the electric machine 20, as well as magnetic losses in the AC machine 20.
[0042] As further shown in Figures 1A and 1B, the motor or transmission test bench 1 has the electric machine 20 connected to the motor inverter 300. The electric machine 20 can be designed as an asynchronous or synchronous machine and is adapted to drive or load a test object 30 designed as an electric or internal combustion motor. 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 invention, the asynchronous machine 20 forms the drive and loading device for the test object 30. The asynchronous machine 20 enables high speeds of up to 10,000 rpm and significantly higher and has low mass moments of inertia and overload capacity for high speed dynamics.The asynchronous machine 20 enables both generator and motor operation in two directions of rotation and can be coupled to heavy masses. In combination with the drive and load system 10, the machine 20 can not only brake but also drive, e.g., to simulate downhill travel and gear shifting.
[0043] In the event that the test object 30 is an electric motor, this electric motor 30 can have an alternating current machine 32 and a motor inverter 34. The motor inverter 34 is supplied with power by the drive and load system 10 by connecting the motor inverter 34 to the DC bus or intermediate circuit ZK. A DC / DC converter 600 can optionally be connected between the intermediate circuit ZK and the capacitor 200 in order to level the voltage applied to the intermediate circuit ZK accordingly and adjust it to a desired input voltage at the motor inverter 34. However, it should be emphasized that the DC / DC converter 600 is an optional element of the electrical drive and load system 10 according to the invention.
[0044] The shafts of the asynchronous machine 20 and the test object 30 are connected to each other via a mechanical shaft connection 40 to create a torque connection between the two machines 20 and 30. The electric machine 20 is thus directly connected to the test object 30 via a measuring flange of a torque measuring unit 50 and the shaft connection 40. An intermediate bearing block is not required because the electric machine 20 is designed for high connectable masses.
[0045] The torque measuring unit 50 is adapted to measure the torque M(t) via the torque measuring flange on the shaft connection 40 and transmit it to an evaluation unit 70. The torque measuring unit 50 is designed as a torque measuring flange with an integrated evaluation unit, enabling dynamically correct measurement directly at the interface to the test object 30. The shaft torque between the asynchronous machine 20 and the test object 30 is recorded via a strain gauge measuring bridge on the rotating flange of the torque measuring unit 50 and transmitted contactlessly to the stator. The signal is transmitted digitally from the rotor to the stator of the asynchronous machine 20. The supply voltage is transmitted from the stationary to the rotating side inductively. By measuring directly on the test object 30, dynamically correct torque measurement is guaranteed.In addition to the torque measuring unit 50, a speed detection unit 60 is also 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 detection by the speed detection unit 60 is carried out using a bearingless, encapsulated hollow shaft encoder, which is mounted on the side facing away from the test object 30. The scanning unit of the speed detection unit 60 is rigidly connected to the shaft 40, i.e. without a coupling. The speed encoder has two separate scanning systems for the drive and load system 10 and the evaluation unit 70 (see Fig. 1 B), thereby enabling redundant speed detection, which enables safe shutdown in the event of a scanning system failure. The number of pulses / revolution is optimally matched to the respective speed range of the asynchronous machine 20.
[0046] The evaluation unit 70 is adapted to receive the measured torque M(t) and the measured speed n(t) from the torque measuring unit 50 and the speed detection unit 60 and to store them for further evaluation of the test process. The evaluation unit 70 can be designed as a test bench controller that functionally covers all areas of modern engine testing.
[0047] As shown in Fig. 1A, in addition to the test bench controller 70, a safety control center 72 can also be provided, which ensures safe shutdown of the connected system / machine when an emergency stop is triggered. The safety control center 72 records the input information of the connected devices and displays the status of the devices. The safety control center 72 is a switching device that enables safe and redundant contact duplication of the emergency stop input signal. When an emergency stop command device is actuated, the safety contacts of the safety switching device open immediately and can thus stop dangerous movements and deactivate other hazards. In addition to the safety control center 72, an optional power supply module 74 can also be provided, which supplies the safety control center 72 and the test bench controller 70 with power. As shown in Fig.2, the drive and load system 10 according to the invention can be used in an electrical drive and load train 2, 3, in particular in an electrical load train 2, for example for a power generator, or in an electrical drive train 3, for example for an electric vehicle.
[0048] First, the electrical load train 2 will be described in more detail. In the load train 2 for a power generator, the electrical machine 20, configured as a power generator machine, is connected to the motor inverter output of the motor inverter 300 and sends a generated alternating current to the motor inverter 300 and the controllable power source 100, which together operate as a frequency converter to feed a frequency-converted current into a power grid 80. The power supply 80 is preferably a three-phase power supply.
[0049] In the electrical load train 2 for a power generator shown in Fig. 2, the controllable power source 100, similar to the engine or transmission test bench 1 shown in Figs. 1A and 1B, is designed as an AC / DC converter, which, in the case of a three-phase power supply, comprises a frequency converter with a regulated mains rectifier, in particular an active front-end (AFE) converter with PID control. Such an active front-end converter with PID control will be discussed in more detail below, particularly with reference to Figs. 4A to 5B.
[0050] An important feature of an AFE converter is that such a controllable power source 100 can, on the one hand, provide an electrical drive current for the motor inverter 300, but can also feed a direct current generated by the power generator 20 and converted by the motor inverter 300 into the grid 80 (see Fig. 4B). Since the drive and load system 10 according to the invention can drastically reduce both switching losses in the motor inverter 300 and magnetic losses in the power generator 20, an electrical load train 2 in which the drive and load system 10 is used is particularly effective and enables high-efficiency power generation.
[0051] The system shown in Fig. 2 can also be used as an electric drive train 3.
[0052] The electric drive train can be used for any electrically powered mobile device, such as an electric vehicle, an electric aircraft, an electrically powered drone, or an electrically powered ship. In this case, the power supply 80 is designed as a mobile power supply, in particular as a battery module. The controllable power source 100, which is designed as a DC / DC converter for this purpose, is connected to this battery module 80.
[0053] High-voltage DC / DC converters, which can ensure traction voltage stabilization in the electric drive train 3, are preferred for an electric car. For this purpose, so-called non-isolating DC / DC converters are used, which combine buck converters with boost converters to form a buck-boost converter, enabling bidirectional energy transfer from the accumulator module 80 to the electric motor 20, as well as feed-in of current to the accumulator module 80. The described components of an electric drive train for an electric vehicle are well known to those skilled in the art and are the subject of lectures (see lecture notes “Power Electronics in Vehicles and Drive Trains,” Winter Semester 2021 / 2022, Prof. Dr.-Ing. Martin März, Chair of Power Electronics (LEE), Friedrich-Alexander University Erlangen-Nuremberg).
[0054] During a drive, the electric machine 20 connected to the motor inverter output converts the drive current from the controllable power source 100 into rotational power, and during a braking operation, the electric machine 20 feeds the braking power back to the motor inverter 300. The controllable power source 100, designed as a DC / DC converter, feeds the generated current, which was converted into direct current by the motor inverter 300 and stored in the capacitor 200 (42V-side intermediate circuit capacitor), back into the accumulator module 80 after the high-voltage has been reduced or converted accordingly, for example to an operating voltage (14V) of the traction battery 80.By using the drive and load system 10 according to the invention, which reduces switching losses in the motor inverter 300, the electric drive train 3 for an electric vehicle can operate particularly effectively, whereby the range of an electric vehicle having this drive train 3 can be increased.
[0055] The following describes how the drive and load system 10 according to the invention works in comparison to a conventional drive and load system. Fig. 4A shows an exemplary circuit configuration of a conventional drive and load system 10' for a rotating electrical machine 20'. Such a drive and load system 10' is also referred to as a frequency converter with a regulated mains rectifier. Such converters have active power switches 110' at the input, which are configured here as a bridge consisting of six power transistors, IGBTs, or power MOSFETs. Although this requires greater control complexity, it offers several advantages, such as energy recovery into the grid, for example, when motor-driven masses need to be braked.Furthermore, a pulse-controlled inverter enables almost sinusoidal current consumption from the grid, which exhibits significantly fewer low-frequency harmonics, as well as fast switching between motor and generator operation. On the grid side, input-side clocking and potential resonance peaks can be sufficiently dampened using special filters. A PID-controlled AFE frequency converter, for example, 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., 2020 IEEE 21st Workshop on Control and Modeling for Power Electronics (COMPEL), November 9-12, 2020, DOI: 10.1109 / COM-PEL49091.2020.9265801.
[0056] The frequency converter 10' shown in Fig. 4A consists of a line-side pulse-controlled inverter (active front end) 100' and a machine-side pulse-controlled inverter 300' (inverter). The inverters 100' and 300' convert the line voltage, which is constant in amplitude and frequency (50 or 60 Hz), from the power supply 80' into a system with variable voltage and frequency. Both power sections are equipped with IGBT switching elements 110' (insulated gate bipolar transistors) or MOSFETs, in particular SiC MOSFETs. In general, all types of power semiconductor switching elements are encompassed by the invention, as long as they can switch high currents reliably and quickly. This enables both motor and generator operation at full current.
[0057] Fig. 4B illustrates the power flow in the system. The field-oriented vector control of the machine-side frequency converter 300' (corresponding to the motor inverter 300 according to the invention) enables excellent control dynamics and very smooth running across the entire speed range. The line-side pulse-controlled inverter 100' (corresponding to the controllable current source 100 according to the invention) is operated with a power factor cos (p = 1). With this setting, no fundamental reactive power occurs. The line currents are almost sinusoidal. The standard line filter reduces the pulse-frequency harmonics to a minimum.
[0058] Fig. 5A shows a drive and load system 10' for a rotating electrical machine 20' according to the prior art, which, as in Fig. 4A, can be designed as a frequency converter with a regulated mains rectifier or as an AFE converter or active front-end converter. The goal of this drive and load system 10' is to provide a defined supply voltage for the motor inverter 300' directly at the supply input of the motor inverter 300'. To ensure that voltage drops across the intermediate circuit ZK and the capacitor 200' are compensated for at high supply currents, a control circuit 400' is used in the frequency converter 100' with a regulated mains rectifier, the actual value input of which is connected to the motor inverter input and which, by means of the controllable current source 100', regulates the motor inverter input voltage as an actual value to a setpoint Uset.As supply voltage Uzk at the input of the motor inverter 300' according to the state of the art, a supply voltage is selected which ensures sufficient power even at high loads and maximum speeds.
[0059] This constant supply voltage Uzk as alternating voltage Uzk[VAC] and as direct voltage Uzk[VDC] are shown in Fig. 5B as dashed lines and do not depend on the speed of the electric machine 20. In the example shown in Fig. 5B, this supply voltage Uzk is set to 500 V. However, the required supply voltage Ukl of the electric machine 20' or AC electric machine 20' increases with increasing speed to a maximum peak supply voltage and then remains constant. The intermediate circuit voltage or the DC bus voltage applied to the input of the motor inverter 300' is regulated according to the prior art independently of the speed such that a required supply voltage is provided over the entire speed range for the electric machine 20 and additional reserves are available for dynamic processes (especially for speeds above the peak supply voltage).
[0060] This can lead to unnecessarily high DC link voltages or DC bus voltages in a lower speed range, which are then accompanied by corresponding switching losses, as already described above. This particularly affects permanent magnet (PM) motors, which are used in the high-speed range and therefore require comparatively low rated voltages at the operating point of the rated speed. Such a standard control of a DC link voltage to a constant input voltage value Uzk is shown in Fig. 5A. As can be seen from Fig. 5B, in the low speed range, the provided supply voltage Uzk is significantly higher than the required supply voltage in this speed range.However, in a motor inverter 300' comprising a pulse-controlled inverter, this is associated with unnecessarily high switching losses at low speeds n, especially if this pulse-controlled inverter is equipped with power semiconductor switching elements such as IGBTs or MOSFETS, in particular SiC MOSFETs.
[0061] Fig. 6A shows a drive and load system 10 according to an embodiment of the invention, which can be used for a rotating electrical machine 20. In the drive and load system 10 according to the invention, in addition to the controllable current source 100, the intermediate circuit ZK with the capacitor 200, the motor inverter 300 and the control loop 400, a setpoint output device 500 is also provided, which is connected to the setpoint input of the control loop 400 and sets its current setpoint Uset (t), wherein the setpoint output device is suitable for determining the current setpoint Uset (t) for the control loop by means of a predetermined setpoint curve Uset [n(t)] as a function of the speed n(t) of the electrical machine.The goal of the setpoint curve Uset [n(t)] is to approximate as closely as possible the required supply voltage curve of the AC motor 20, while providing a certain safety margin, offset, or voltage reserve. Since the voltage reserve is proportional to the charge stored in capacitor 200, this voltage reserve also corresponds to an energy reserve for the electric machine 20.
[0062] In Fig. 6B, the setpoint curves Uset(n) are again shown as alternating voltage Uzk[VAC] and corresponding direct voltage Uzk[VDC] (corresponds to Uzk[VAC]*Sqrt[2]) as dashed lines. Since the required supply voltage Uzk_min or, equivalently in Fig. 6B, the required supply voltage or motor terminal voltage Uki is lower at low speeds of the alternating current machine 20 than at high speeds, it is advantageous according to the invention if the setpoint curve Uset(n) has a smaller setpoint voltage value at lower speeds than at high speeds. The setpoint curve Uset(n) is therefore preferably increased in steps or gradually with increasing speed n. In this case, according to the invention, the setpoint curve Uset(n) can, from a certain saturation speed n satt (here at approximately 14,000 revolutions per minute) have a constant saturation value UMax (here Uiviax = 500 V). Furthermore, it is advantageous to have certain voltage reserves for dynamic processes and to have a constant offset value Uonset as an addend to the setpoint curve. This ensures that the setpoint voltage never falls below the required supply voltage.
[0063] The intermediate circuit voltage or DC bus voltage at the intermediate circuit ZK is therefore calculated based on the speed n and the speed gradient dn / dt. In order to keep a certain lead voltage as a reserve during acceleration, the setpoint curve U- set [n(t)] can have a positive lead component b*dn / dt as an addend, which is 0 for speed changes dn / dt < 0 = 0. The setpoint of the DC bus voltage or intermediate circuit voltage Uzk is therefore only calculated based on the current speed n(t) if the speed gradient or the time derivative of the speed dn / dt is less than 0. The voltage setpoint Uzk at the intermediate circuit ZK or the setpoint of the DC bus voltage is therefore only provided with a positive lead component if the time derivative of the speed dn / dt > 0.This leads to a pre-control of the intermediate circuit voltage Uzk, which is important for fast positive speed gradients dn / dt, since otherwise, in the case of high speed changes or accelerations, the DC bus voltage or intermediate circuit voltage cannot follow the voltage requirement of the machine quickly enough and the electric machine 20 cannot be supplied with sufficient power.
[0064] As further shown in Fig. 6B, the setpoint curve Uset [n(t)] can be divided into N consecutive speed intervals I1 to In. In the exemplary embodiment shown in Fig. 6B, the setpoint curve Uset shows a first gradient in a first speed range up to approximately 4,000 revolutions per minute, then transitions into a second speed range between 4,000 revolutions per minute and 14,000 revolutions per minute with a second gradient, and then transitions to a saturation value UMax from 14,000 revolutions onwards. Furthermore, it is preferred if these corresponding gradients transition from high gradients to low gradients in the different intervals, as this is best adapted to the actual curve of the required supply voltage. It is therefore expedient if the setpoint curve is divided into n consecutive speed intervals I1 to In and in the x-th speed interval Ix with an associated linear gradient a xruns, where the gradients a x > a x +i > 0. Although Fig. 6B shows only two speed intervals (from 0 to 4,000 revolutions per minute and from 4,000 revolutions per minute to 14,000 revolutions per minute) with two different slopes, the number N of speed intervals can also consist of 10 intervals or even 100 intervals. However, in order to keep the 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.
[0065] It is useful if the setpoint curve Uset [n(t)] in the x-th speed interval l x of N consecutive speed intervals h to IN applies:
[0066] Uset x [n(t)l = a x *n(t) + b x *dn / dt + Uoffset + U De ita_ x , for n x .i <n<n x
[0067] Where: no=O; a x is a gradient factor with ao = 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 at dn / dt <0,
[0068] Uoffset is an offset value,
[0069] Uoeita x is a continuity value with UDeita_ x = i=iai-i(nt ~ n^),
[0070] In addition:
[0071] Uset x [n(t)l = Uiviax for n(t) > n N = n sa t is.
[0072] However, it is also possible to approximate (fit) the setpoint curve Uset [n(t)] as a root function of the required supply voltage and to provide it with an offset value:
[0073] Furthermore, the lead component b*dn / dt can be included: Other functions such as a logarithmic function are also conceivable in order to adapt the setpoint curve Uset [n(t)] as precisely as possible to the curve of the required supply voltage as a function of the speed, so that the same voltage reserve Uoffset + b*dn / dt is available at each speed:
[0074] Uset [n(t)l = e*log[f*n(t) A g+1] + b*dn / dt + Uoffset
[0075] The slope factor a is advantageously in a 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. The offset value Uoffset is advantageously in a 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 in a 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 in a 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 in a 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 in a 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 expediently in a 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 expediently in a range from 0.1 to 100, or from 0.5 to 50, or from 1 to 10. The voltage values in volts are related to the alternating voltage values Uzk[VAC], as shown in Figs. 5B and 6B.
[0076] In the event that the required supply voltage can be either measured or simulated as a function of the speed, the setpoint curve Uset (n) can also comprise a sum formed from a minimum supply voltage curve Uzk_min (n) of the motor inverter 300 and the electric machine 20, as well as an offset value Uoffset. In this case, the required supply voltage curve Uzk_min (n) can be an interpolated function of data points from measured required supply voltages and associated speeds n. The interpolating function can be one of the functions described above, which is appropriately fitted to the data set. The setpoint curve Uzk_s et (n) can further comprise at least one speed interval Ix between speed 0 and speed nsat, in which the setpoint curve exhibits a step-like, a continuously increasing, a linearly increasing, a root-shaped increasing, or a logarithmically increasing component. The setpoint curve can be any desired monotonically increasing function. The setpoint curve can be any desired continuous and monotonically increasing function.
[0077] In addition to regulating the voltage as a function of the speed, the invention also provides that the setpoint output device 500 is further suitable for determining the current setpoint Uset (t) for the control loop by means of a predetermined setpoint curve Uset [n(t), M(t)] as a function of the torque M(t) of the electric machine 20. Regulating the intermediate circuit voltage solely as a function of the torque M(t) is not possible. However, it is expedient according to the invention if, in addition to evaluating the speed n(t), the torque M(t) is used as a further influencing variable on the setpoint Uset [n(t), M(t)] of the intermediate circuit voltage.
[0078] Fig. 7 shows a flowchart of a method for operating a drive and load system 10 for a rotating electrical machine 20. The method 1000 comprises a first step S1010 of providing a controllable current source 100 that can be connected to a power supply. In a further step S1020, an intermediate circuit ZK connected to the controllable current source 100 is provided, which intermediate circuit has a capacitor 200 for intermediate current storage. 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 a rotating electrical machine 20 or feeds a load current from the electrical machine 20 back into the intermediate circuit ZK.In a further step S1040, a control loop 400 is provided, the actual value input of which is connected to the motor inverter input and which, by means of the controllable current source 100, regulates the motor inverter input voltage as an actual value to a setpoint Uset. In a still further step S1050, a setpoint output device 500 is provided, which is connected to the setpoint input of the control loop and sets its current setpoint Uset(t). In a step S1060, the current setpoint Uset(t) for the control loop 400 is determined as described above using a predetermined setpoint curve Uset[n(t)] as a function of the speed n(t) of the electric machine.The control or regulation of the DC bus voltage or intermediate circuit voltage, depending on the speed and the speed gradient, leads to a reduction of losses, in particular switching losses and magnetic losses, which occur in the motor inverter 300 and the electric machine 20. These magnetization losses occur in the machine and in any installed choke (on the grid and motor sides), whereby the magnetization losses of the motor-side chokes can also be reduced.
[0079] This is particularly true for high-speed PM synchronous motors. Thus, during operation in a test bench, the thermal load at low speeds and full load can be reduced, 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. According to the invention, a DC bus voltage of a drive system is regulated based on the machine speed and the speed gradient so that switching losses at low speeds are compensated by applying a lower voltage.Thus, magnetic losses in the AC machine and, if applicable, in installed motor chokes and 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 can be increased according to the invention.
Claims
Patent claims 1. A drive and load system (10) for a rotating electrical machine (20), comprising a controllable current source (100) connectable to a power supply (80); an intermediate circuit (ZK) connected to the controllable current source (100) and having a capacitor (200) for intermediate current storage; a motor inverter (300) connected to the intermediate circuit (ZK), which converts the intermediate circuit voltage applied to the motor inverter input into a drive current for the rotating electrical machine (20) or feeds a load current from the electrical machine (20) back into the intermediate circuit (ZK); a control circuit (400), the actual value input of which is connected to the motor inverter input, and which, by means of the controllable current source (100), controls the motor inverter input voltage as an actual value to a setpoint Uset;a setpoint output device (500) which is connected to the setpoint input of the control loop (400) and sets its current setpoint Uset (t), characterized in that the setpoint output device (500) is suitable for determining the current setpoint Uset (t) for the control loop (400) by means of a predetermined setpoint curve Uset [n(t)] as a function of the speed n(t) of the electrical machine (20); 2. Drive and load system (10) according to claim 1, characterized in that the setpoint curve Uset [n(t)] is increased stepwise or gradually with increasing speed n.
3. Drive and load system (10) according to claim 1 or 2, characterized in that the setpoint curve Uset [n(t)] has a constant saturation value llMax starting from a saturation speed nsat.
4. Drive and load system (10) according to one of the preceding claims, characterized in that the setpoint curve Uset [n(t)] has a constant offset value Uoffset as an addend.
5. Drive and load system (10) according to one of the preceding claims, characterized in that the setpoint curve Uset [n(t)] has as addends a positive lead component b*dn / dt, which is equal to 0 for speed changes dn / dt<0.
6. Drive and load system (10) according to one of the preceding claims, characterized in that the setpoint curve Uset [n(t)] is divided into N successive speed intervals h to IN and in the x-th speed interval l x with an associated linear gradient a x runs, where the gradients a x > a x+i >0 applies.
7. Drive and load system (10) according to one of the preceding claims, characterized in that for the setpoint curve Uset [n(t)] in the x-th speed interval l x of N consecutive speed intervals h to IN applies: Uset x [n(t)] = a x *n(t) + b x *dn / dt + Uoffset + U De ita_ x , for n x .i <n<n x , where no=O; a x a gradient factor with ao = 0 and a x > 0; dn / dt is the time derivative of the speed n(t), b x a lead factor with b x = 0 at dn / dt <0, Uoffset an offset value, Uoeita x a continuity value with UDeita_ x = i=i at-i(. n i ~ n^), and where furthermore: Uset_ x [n(t)] = UM 3X for n(t) > n N = n sa t is.
8. Drive and load system (10) according to one of the preceding claims, characterized in that the setpoint curve Uset (n) comprises a sum which is formed from a required supply voltage curve Uzk_min (n) of the motor inverter (300) and the electric machine (20) and an offset value Uoffset. Drive and load system (10) according to claim 8, characterized in that the required supply voltage curve Uzk_min (n) is an interpolated function of data points from measured required supply voltages and associated rotational speeds n. Drive and load system (10) according to one of the preceding claims, characterized in that the setpoint output device (500) is further suitable for determining a current setpoint Uset (t) for the control loop by means of a predetermined setpoint curve Uset [n(t), M(t)] as a function of the torque M(t) of the electric machine (20).Drive and load system (10) according to one of the preceding claims, characterized in that the motor inverter (300) comprises a pulse inverter which is equipped with power semiconductor switching elements, in particular IGBTs or MOSFETS. Drive and load system (10) according to one of the preceding claims, characterized in that the controllable current source (100) in the case of a 3-phase power supply (80) comprises a frequency converter with a controlled mains rectifier, in particular an active front-end (AFE) converter with PID control.Test bench (1), in particular an engine, transmission, brake or vehicle test bench, with an electrical drive and loading system (10) according to one of the preceding claims, an electrical machine (20) connected to the motor inverter (300) and adapted to drive or load a test object (30) designed as an electric or internal combustion engine; a mechanical shaft connection (40) adapted to connect the shafts of the electrical machine (20) and the test object (30); a torque measuring unit (50) adapted to measure the torque M(t) via a torque measuring flange on the shaft connection (40) and to transmit it to an evaluation unit (70);. a speed detection unit (60) adapted to measure the speed n(t) via a pulse generator on the shaft connection (40) and transmit it to the evaluation unit (70); and the evaluation unit (70) adapted to receive the measured torque M(t) and the measured speed n(t) from the torque measuring unit (50) and the speed detection unit (60) and to store them for further evaluation of the test process. An electrical load train (2) comprising a drive and load system (10) according to one of claims 1 to 11, the electrical machine (20) connected to the motor inverter output, configured as a current generator, and transmitting a generated alternating current to the motor inverter (300) and the controllable current source (100) as a frequency converter in order to feed a frequency-converted current into a power grid (80).Electric drive train (3), with a mobile power supply (80), in particular an accumulator module; a drive and load system (10) according to one of claims 1 to 11, the electric machine (20) connected to the motor inverter output, which converts the drive current into rotational power and feeds braking power back to the motor inverter (300), wherein the controllable current source (100) is designed as a DC / DC converter.