Vehicle with an electric motor and two partial electrical systems

Abstract

Vehicle with an N-phase electric machine, with a first sub-system (BN1) and with a second sub-system (BN2), wherein the electric machine comprises a rotor and a stator system (1), the first sub-system comprises an inverter (2), the stator system is assigned to the inverter, and the electric machine can be operated with an inverter controller according to the principle of field-oriented control, such that the stator system is configured in a star connection, the star point is connected to the second sub-system or can be connected to the second sub-system via a star point switch (5), the inverter controller comprises a current controller and a star point controller, the current controller regulates phase currents of the stator system, and the star point controller regulates a star point current.

Description

The invention relates to a vehicle with an N-phase electric machine, with a first partial electrical system and with a second partial electrical system, wherein the electric machine comprises a rotor and a stator system, the first partial electrical system comprises an inverter, the stator system is assigned to the inverter, and the electric machine can be operated with an inverter controller according to the principle of field-oriented control. Typically, components in a vehicle that consume electrical energy are supplied by an electrical system with a nominal voltage of 14 volts. A secondary 12-volt energy storage device, which functions as either an energy source or an energy sink in the electrical system depending on the operating situation, and a 14-volt generator are designed to provide an electrical power output of 2-3 kW in the vehicle. Especially when several consumers with increased power requirements are integrated into the vehicle's electrical system, the system can have two sub-systems. A DC-DC converter then transfers electrical power between these two sub-systems. The electric machine, which in a vehicle with an electrified powertrain can also be operated as a motor, functions as either an electrical energy source or sink within the vehicle, as does at least one energy storage device in each sub-system. Such an electrical system topology is described, for example, in German patent application DE 102 44 229 A1. DE 10 2011 003 372 A1 discloses a drive system and a corresponding method for an automobile. The system comprises a first voltage source, a power electronics unit with a plurality of power switching devices connected to the first voltage source, and an electric motor with a plurality of windings connected to the plurality of power switching devices. The electric motor has a neutral node connecting the plurality of windings. A second voltage source is connected to the neutral node of the electric motor and to the first voltage source. It is an object of the invention to describe an improved vehicle with a multi-phase electric machine, with a first partial electrical system and with a second partial electrical system, wherein the electric machine comprises a rotor and a stator system, the first partial electrical system comprises an inverter, the stator system is assigned to the inverter, and the electric machine can be operated with an inverter controller according to the principle of field-oriented control. This problem is solved by a vehicle according to claim 1. Advantageous embodiments and further developments of the invention are set out in the dependent claims. According to the invention, the stator system is configured in a star connection, the star point is connected to the second sub-system or can be connected to the second sub-system via a star point switch, and the inverter controller comprises a current controller and a star point controller. This means that the neutral point of the electric machine can be connected to the potential of the second sub-network via the neutral switch, or is permanently connected. This allows current to flow through the neutral point, which is referred to as neutral current. The neutral current is thus introduced into the machine as an additional degree of freedom, provided it is connected to the second sub-network via the neutral switch. The control principle of the electric machine is extended by adding a neutral controller to the inverter controller, which regulates the electric machine and includes a current controller for the stator system. The neutral controller allows the current through the neutral point to be regulated. The second sub-network can be formed, for example, by electrical loads or, alternatively or additionally, by another stator system in a star or delta connection of an electric machine.An intermediate circuit capacitor may also be associated with the inverter. According to a preferred embodiment of the invention, at least a number of N-1 phase currents can be measured from the number N phase currents of the stator system, the measured phase currents can be transformed via an extended Clarke-Park transformation into a field-oriented current phasor with a flux-forming component, with a torque-forming component and with a zero-current component, wherein the neutral point current is three times the zero-current component. A permanent electrical connection is understood to mean a current path that is neither open nor openable. This means, for example, that diodes may be incorporated into the current path. Accordingly, the electric machine can be controlled according to the field-oriented control principle, which is well-known to those skilled in the art of electrical machines. In a three-phase electric machine, for example, two phase currents of the stator system are measured and transformed into two rotor-fixed current quantities via a two-dimensional Clarke-Park transformation. These two rotor-fixed current quantities represent a flux-generating current component and a torque-generating current component. The transformation is performed by a control unit, such as a control device. According to the preferred embodiment, two phase currents and the neutral point current are measured, or alternatively, the three phase currents are measured. When measuring the three phase currents, they are subjected to an extended three-dimensional Clarke-Park transformation, which cleverly modifies the two-dimensional Clarke-Park transformation known to those skilled in the art. In addition to the flux-generating current component and the torque-generating current component, a zero-current component is obtained. This zero-current component is one-third of the neutral-point current, i.e., the current flowing through the neutral point of the electrical machine. In general, i.e., in any multi-phase electrical machine, a total number of current measuring points is provided via current measuring devices, which corresponds at least to the number N of phases of the electrical machine. Furthermore, it is particularly advantageous if the inverter controller has the flux-generating current component as a controlled variable, the torque-generating current component as a controlled variable, the zero-current component as a setpoint, a first setpoint current for the flux-generating current component as a setpoint, a second setpoint current for the torque-generating current component as a setpoint, a star point setpoint current for the star point current as a setpoint, and outputs a first stator control voltage associated with the flux-generating current component as a manipulated variable, a second stator control voltage associated with the torque-generating current component as a manipulated variable, and a third stator control voltage associated with the zero-current component as a manipulated variable. The third stator control voltage is directly related to the neutral point current due to the relationship between the zero-sequence current component and the neutral point current. Therefore, the third stator control voltage should be considered the control variable of the neutral point controller, while the first and second stator control voltages serve as control variables of the current controller for the stator system. According to a particularly preferred embodiment of the invention, the current controller and the star point controller are essentially designed as Pl controllers. The design of the current controller and the star point controller as robust PL controllers is particularly advantageous due to the control loop, which describes the relationship between the quantities of the electrical machine such as speed, output torque, input torque, angular position of the rotor relative to the stator, magnetic fluxes through the stator and rotor, as well as phase voltages and phase currents. Alternatively, control loops with dynamics and accuracy comparable to PI controllers, but with equally low complexity, such as PID controllers or controllers with feedforward control, can also be used. According to a further embodiment of the present invention, the N-phase electric machine is designed as a 3-phase electric machine and the inverter comprises six inverter switches arranged in three half-bridges for the three phases of the stator system, and the inverter switches the phase voltage for each of the phases in a switching cycle according to the principle of pulse width modulation, wherein the first stator control voltage, the second stator control voltage and the third stator control voltage can be transformed into the phase voltages of the stator system to be switched by an extended inverse Clarke-Park transform. The phase voltages to be switched are determined by a modified inverse Clarke-Park transform, where the modification of the inverse Clarke-Park transform corresponds to the modification of the Clarke-Park transform to an extended Clarke-Park transform. The resulting phase voltages can be switched by the inverter using pulse-width modulation. This means the phase voltage is set by switching the respective half-bridge center to the higher potential of the first sub-network for a specific switching time. This is achieved by opening the inverter switch between the half-bridge center and the lower potential of the first sub-network and closing the other switch of the half-bridge. The ratio of the switching time to the clock time is directly proportional to the phase voltage to be set. Thus, the phase voltage is set over the average time of a clock cycle. According to another variant of the invention, when the star point switch is closed and the star point current is flowing from the star point to the second sub-system, the electric machine transfers electrical power from the first sub-system to the second sub-system. This means that if a neutral point current is specified and set for the electric machine, corresponding to a current flow from the neutral point to the second part of the vehicle electrical system, the electric machine acts as a buck converter. According to another variant of the invention, when the star point switch is closed and the star point current is flowing from the second sub-system to the star point, the electric machine causes a transfer of electrical power from the second sub-system to the first sub-system. This means that if a neutral point current is specified and set for the electric machine, corresponding to a current flow from the second sub-network to the neutral point, the electric machine acts as a boost converter. Furthermore, with the neutral point switch closed, a neutral point current can be set by specifying the neutral point set current and adjusting the neutral point control voltage, which corresponds to a current flow from the second sub-system to the neutral point or from the neutral point to the second sub-system. Thus, the electric machine acts as a bidirectional power controller. This applies to both rotating and stationary rotors. A preferred embodiment of the invention is described below with reference to the accompanying drawing. Further details, preferred embodiments, and further developments of the invention will be derived from this. Specifically, Fig. 1 schematically shows a vehicle with two partial electrical systems, an electric motor, and a star-point switch. The embodiment according to Fig. 1 shows an exemplary N-phase machine as a three-phase electrical machine with a rotor and a stator system (1). The three phases are designated (u, v, w). An inverter (2) and a DC link capacitor (3) are associated with the electrical machine. The electrical machine, the inverter, and the DC link capacitor are components of a first partial electrical system (BN1) of a vehicle. This partial electrical system also includes at least one first electrical energy storage device (3'), which may be designed as an electrochemical energy storage device. The electric machine, which can be operated both as a generator and as an electric motor, is controlled by the inverter according to the field-oriented control (FOR) principle, which is well known to those skilled in the art. For this purpose, the inverter is preferably designed as a bridge inverter, meaning that each phase of the electric machine is assigned an electrical half-bridge of the inverter. A half-bridge consists of two switches connected in series, with the switch assigned to the higher electrical potential being designated as the high-side switch (HS1, HS2, HS3) and the switch assigned to the lower electrical potential being designated as the low-side switch (LS1, LS2, LS3). As an alternative to a bridge converter, a multilevel converter can also be used. Without limiting this generality, however, we will continue to assume a bridge converter. The vehicle also has a second sub-network (BN2), which includes, for example, a second electrical energy storage device (4) with an optional intermediate circuit capacitor (12) and electrical consumers (13). The second sub-network can have various embodiments. These embodiments have in common that the lower potential of the second sub-network corresponds to the lower potential of the first sub-network. There is no electrical connection between the higher potential of the second sub-network and the higher potential of the first sub-network. However, the star point (1a) of the electric machine is permanently electrically connected to the higher potential of the second sub-network or can be electrically connected via a switch called the star point switch (5). In further embodiments of the second sub-network, it comprises a stator, which can preferably be connected in a star configuration, or alternatively in a delta configuration. The star point (1a) can then be connected to the star or delta connection of the second sub-network, or via the star point switch. The phase currents of the electric machine (Iu, Iv, Iw) are measurable. The measured phase currents are subjected to the following transformation: where and βel denotes the electric angle of the rotor and Zp the number of pole pairs of the electric machine. The result of the transformation from (equation 1) is a field-oriented current vector (Id, Iq, I0), where the component Id corresponds to a flux-forming component and the component Iq to a moment-forming component. With respect to the components Id and Iq, the transformation corresponds to a Clarke-Parke transformation known to those skilled in the art; that is, a 2x2 matrix of the 3x3 matrix from Equation 1 corresponds to the Clarke-Parke matrix. This matrix is ​​cleverly extended to a 3x3 matrix in Equation 1 such that the resulting zero-current component (I0) corresponds to one-third of the neutral-point current (IStern). The 3x3 matrix forms the basis of the so-called extended Clarke-Parke transformation. This means that measuring the three phase currents via the transformation from equation 1 and tripling the zero-current component leads to the neutral point without actually measuring it. For a three-phase machine, and by cleverly extending the 2×2 Clarke-Parke matrix to an extended 3×3 Clarke-Parke matrix, this results from the following relationships within the electrical machine: The star current is formed by the sum of the phase currents according to: Each of the phase currents is a sinusoidal current with the offset I0, where the offset is regulated uniformly across the phases, or uniform distribution is a control objective (stator current controller see below): The star current is thus derived from the junction rule as follows: The sum of the three sinusoidal currents of equal amplitude, each offset by 120° (corresponding to the stator configuration of the 3-phase machine), is zero. Equality of the amplitudes ÎU,V,W is also a control objective in field-oriented control and a key element for the symmetry of the stator system. Thus, ISsternzu simplifies to: The Clarke-Park transformation from equation 1 leads to: which, by substituting equation 1a, leads to: Trigonometric transformation results in which it is shown that the determination of the zero-current component by equation 1 corresponds to a measurement of the neutral point current. The boundary condition of the Clarke-Park transformation is usually ISstern = 0 A. Therefore, for the extended Clarke-Park transformation: 1 / 3 · ISstern = 1 / 3 · (Iu + Iv + Iw) = I0. The additional degree of freedom provided by the extended Clarke-Park transformation compared to the Clarke-Park transformation continues to be used in a clever way. An electric machine is assigned a controller that has input and output variables as well as setpoints. As with a field-oriented control system known to those skilled in the art, the setpoints for the electric machine are a flux-generating setpoint current (I*d) and a torque-generating setpoint current (I*q). The specification of these setpoints results from an operating strategy of the electric machine and essentially follows from a torque requirement for the electric machine. This is not the subject of this document. The flux-generating current (Id) and the torque-generating current (Iq) serve as the control variables corresponding to the setpoint variables (I*d) and (I*q). The controller outputs a first stator control voltage (Ud) and a second stator control voltage (Uq) as manipulated variables. The part of the controller that outputs the first and second stator control voltages is called the stator current controller. The stator current controller is extended by an additional controller, referred to as a star point controller. The setpoint is a star point setpoint current (I*star), where the star point current (IStern) serves as a controlled variable. The star point controller also outputs a third stator control voltage (U0) as a further manipulated variable of the system. This establishes a significant advantage of the system shown in Fig. 1, since a targeted neutral current can be set between the neutral point and the second sub-network via the connection of the neutral point (1a). The degree of freedom of the system shown in Fig. 1, resulting from the electrical connection of the neutral point (1a) to the second sub-network compared to an electrically isolated stator system, is taken into account in the control of the electric machine by extending the Clarke-Park matrix and introducing the zero-current component. The additional degree of freedom is taken into account in the control loop by implementing, in addition to the stator current controller from the FOR known to those skilled in the art, the additional star point controller with a setpoint for the star point current. The rotor-fixed control voltages Ud,Uq and U0 obtained from the stator current regulator and the star point regulator are converted via an inverse transformation into the stator-fixed voltage quantities Uq,Uv and Uw for each phase, which can be adjusted via the inverter (2) on the electrical machine in the respective clock cycle. The inverse transformation is called the extended inverse Clarke-Park transformation and transforms the obtained control voltages according to the following formula: This means that the inverse Clarke-Park transform specifies the phase voltages to be set in the respective clock cycle. The 3x3 matrix from equation 2 is the inverse transformation matrix of the 3x3 matrix from equation 1. The stator-fixed voltage quantities obtained from equation 2 can be adjusted via the inverter (2) by applying the voltage UZk of the intermediate circuit (3) using a method known to those skilled in the art, e.g., the method of pulse width modulation by setting corresponding switching times of the high-side switch and the low-side switch of the respective half-bridge belonging to the phase. This allows the neutral point current of the electric machine to be set according to the target value I*star. This applies regardless of whether the electric machine is operating in generator or motor mode, or is at standstill or idling. The precise adjustment of the neutral point current is particularly advantageous in vehicles, for example, with a nominal voltage of 48 volts for the first sub-system and 12 volts for the second: The 12-volt sub-system can be supplied with electrical power via the neutral point current. This eliminates the need for a separate generator in the 12-volt sub-system. Most importantly, a DC-DC converter is not required for power transfer between the two sub-systems. Electrical power can be transferred bidirectionally between the two sub-systems via the direction of the neutral point current.In other words, the electric machine takes over the function of a DC-DC converter with a minimal number of components. This saves weight, costs, and installation space. Furthermore, the two sub-systems can be mutually supported by adjusting the neutral current; that is, voltage stabilization can be achieved through the adjustable neutral current. The distribution of energy flows within the vehicle is also highly flexible, for example, during recuperation. If, for instance, no recuperation power can be absorbed by the 48-volt sub-system, it can be diverted to the 12-volt system. This increases the recuperation potential. According to another embodiment, a different reference system can be selected for control by the stator current controller and the neutral point controller, for example, by measuring any selection of two phase currents and additionally the neutral point current Istern instead of the three phase currents (Iu, Iv, Iw). The transformation into quantities as suitable as possible for the control effort is then carried out via a correspondingly modified extended Clarke-Park transform and a correspondingly modified extended inverse Clarke-Park transform. Similarly, a corresponding adjustment of Equation 1 and Equation 2 is necessary in an analogous manner if the electrical machine has a different number of phases than N=3, as in the first embodiment. For a 5-phase machine with N=5, five current measurements (e.g., measurement of the five phase currents) are performed, and the matrix for the Clarke-Park transform and the matrix for the inverse Clarke-Park transform are each designed as a 5x5 matrix. In the illustrated embodiments, the inverter is a component of a power electronic unit that includes the stator current controller, the neutral point controller, and current measuring devices for phase current measurement. Phase current measurement can be performed, for example, using Hall sensors or shunt resistors. Subsequent conversion of the analog measurement signals into digitally processable signals is preferably carried out by analog-to-digital conversion in a microcontroller of the power electronic unit. The stator current controller and the neutral point controller are preferably implemented as a microcontroller or an FPGA. According to the described embodiments, the neutral point of the electric machine is optionally connected via the neutral switch. This is particularly advantageous. With a permanent, fixed connection of the neutral point to the second sub-system and with a regulated neutral current, the electric machine reaches the so-called field weakening range earlier, i.e., at a lower speed. The earlier onset of field weakening means that at a given speed, the machine is able to deliver less torque than with a non-electrically connected neutral point. Opening the neutral switch interrupts the neutral current and increases the torque available at that specific speed. In an electric machine with a non-electrically connected neutral point, i.e., in an electric machine conventionally operated via space vector modulation, the zero vectors are uniformly distributed, and it is possible to operate the voltage of each phase at a maximum value. The voltage at the neutral point then fluctuates around the value UZk / 2. Uniformly distributed zero vectors in FOR (Full Range Automation) are known to those skilled in the art and mean that the zero times, i.e., times at which either all phases are switched to the higher potential or all phases to the lower potential, are distributed as symmetrically as possible within a switching cycle. If the neutral point is permanently connected to the second electrical system, the neutral point voltage fluctuates around the voltage value UBn / 2, where the voltage UBnden describes the voltage value of the intermediate circuit (12). This has the disadvantage that the speed (the so-called rated speed), at which field weakening begins towards higher speeds, decreases towards lower speeds. Thus, the electric machine cannot be optimally utilized with respect to the available torque. The zero-times cannot be freely distributed. This resulted in a reduction of the maximum phase voltage and therefore a shift of the rated speed to lower machine speeds. Opening the star point switch prevents the shift of the rated speed to lower machine speeds and thus the reduction of the mechanical power available from the machine.

Claims

Vehicle with an N-phase electric machine, with a first partial electrical system (BN1) and with a second partial electrical system (BN2), wherein the electric machine comprises a rotor and a stator system (1), the first partial electrical system comprises an inverter (2), the stator system is assigned to the inverter, and the electric machine can be operated with an inverter controller according to the principle of field-oriented control, characterized in that: - the stator system is configured in a star connection, - the neutral point is connected to the second partial electrical system or can be connected to the second partial electrical system via a neutral point switch (5), wherein there is no electrical connection between the higher potential of the second partial electrical system (BN2) and the higher potential of the first partial electrical system (BN1), - the inverter controller comprises a current controller and a neutral point controller, - the current controller regulates phase currents of the stator system.and- the star point controller regulates a star point current, wherein in the controlled system the additional degree of freedom resulting from the electrical connection of the star point (1a) with the second sub-network compared to an electrically isolated stator system is taken into account in the control of the electric machine by extending the Clarke-Park matrix and introducing the zero-current component, by implementing the additional star point controller with a setpoint for the star point current alongside the stator current controller from the field-oriented control, wherein the extended Clarke-Park matrix of the 3x3 matrix from [ I d I q I 0 ] = 2 / 3 ⋅ [ cos ( β el ) cos ( β el − 120 ° ) cos ( β el − 120 ° ) − sin ( β el ) − sin ( β el − 120 ° ) − sin ( β el − 120 ° ) 1 2 1 2 1 2 ] ⋅ [ IUIVIW ], corresponds, where: I u , I v , I w the measurable phase currents of the electrical machine are, β el denotes the electrical angle of the rotor, and I d , I q , I 0 is a field-oriented current phasor, where the component I d a flow-forming component, component I q a moment-generating component and component I 0 which corresponds to the zero current component, and wherein the rotor-fixed control voltages U obtained from the stator current regulator and the star point regulator d ,U q and U 0 via an inverse transformation according to [ UUUVUW ] = [ cos ( β el ) − sin ( β el ) 1 cos ( β el − 120 ° ) − sin ( β el − 120 ° ) 1 cos ( β el + 120 ) − sin ( β el + 120 ° ) 1 ] ⋅ [ U d U q U 0 ] into the stator-fixed voltage quantities U u ,U v and U w for each phase, which can be adjusted via the inverter (2) on the electrical machine in the respective clock cycle. Vehicle according to claim 1, characterized in that - the vehicle comprises measuring means for measuring a number of at least N-1 phase currents and the neutral point current or the vehicle comprises measuring means for measuring a number of at least N phase currents, and - the vehicle has a control unit comprising the inverter controller. Vehicle according to claim 2, characterized in that the measuring means N measures currents (Iu, Iv, Iw) of the electric machine, and the control unit transforms the measured currents (Iu, Iv, Iw) via an extended Clarke-Park transformation into a field-oriented current phasor (Id, Iq, I0) with a flux-forming component (Id), with a torque-forming component (Iq) and with a zero-current component (I0), wherein the neutral point current (IStern) is three times the zero-current component. Vehicle according to claim 3, characterized in that: - the inverter controller has the flux-generating component as a controlled variable, - the inverter controller has the torque-generating component as a controlled variable, - the inverter controller has the zero-current component as a controlled variable, - the inverter controller has a first setpoint current (I*d) for the flux-generating component as a setpoint, - the inverter controller has a second setpoint current (I*q) for the torque-generating component as a setpoint, - the inverter controller has a star point setpoint current (I*star) as a setpoint, - the inverter controller outputs a first stator control voltage (U*d) as a manipulated variable, - the inverter controller outputs a second stator control voltage (U*q) as a manipulated variable, and - the inverter controller outputs a third stator control voltage (U*0) as a manipulated variable. Vehicle according to claim 4, characterized in that the current controller and the star point controller are essentially designed as PI controllers. Vehicle according to claim 4, characterized in that: - the N-phase electric machine is designed as a 3-phase electric machine, - the inverter comprises six inverter switches (HS1, HS2, HS3, LS1, LS2, LS3), - the six inverter switches are arranged in three half-bridges for the three phases of the stator system, - the first stator control voltage, the second stator control voltage and the third stator control voltage can be transformed into phase voltages (Uu, Uv, Uw) of the stator system by an extended inverse Clarke-Park transform, and - the inverter switches the phase voltage for each of the phases in a switching cycle according to the principle of pulse width modulation. Vehicle according to one of claims 2 to 6, characterized in that, with the star point switch closed, the electric machine transfers electrical power from the first sub-system to the second sub-system and acts as a buck converter when the star point current (IStern) is in the direction of current from the star point to the second sub-system. Vehicle according to one of claims 2 to 6, characterized in that, with the star point switch closed, the electric machine transfers electrical power from the second sub-system to the first sub-system and acts as a boost converter when the star point current (IStern) is in the direction of the current from the second sub-system to the star point. Vehicle according to one of claims 4 to 8, characterized in that - by specifying the star point set current and adjusting the star point control voltage, a star point current (IStern) can be set, and - the electric machine acts as a unidirectional or bidirectional power controller when the star point switch is closed.

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