Method and device for compensating for a drop in the output voltage of a motor vehicle generator

Abstract

Method for compensating for a dip in the output voltage of a motor vehicle generator (11) caused by the addition of a load or a change in speed by means of a generator regulator (1) which provides a control signal (s) with a duty cycle that increases the excitation current of the motor vehicle generator (10) to a switching transistor (6), wherein, after the occurrence of the voltage dip, in a first step the duty cycle of the control signal is abruptly increased by a difference amount (B1, B2) and the control signal (s) with the increased duty cycle is supplied to the switching transistor (6), and in a subsequent second step the compensation speed is limited, wherein, after the occurrence of the voltage dip, parameters describing the instantaneous operating point of the motor vehicle generator (11) are recorded and, in the first step, an operating point-dependent adjustment of the difference amount is made.where different difference amounts are assigned to different working points.

Description

[0001] The invention relates to a method and a device for compensating for a drop in the output voltage of a motor vehicle generator. State of the art

[0002] The electrical system of a motor vehicle is powered by a generator, whose output voltage is regulated to a predetermined value, for example, 14V, by a generator regulator. Adding loads or changing the vehicle's speed can cause a drop in the electrical system voltage. The generator regulator compensates for this voltage drop, thereby increasing the torque required by the drivetrain or engine. When a load is added, a higher torque is needed to drive the generator. This regulation is achieved by increasing the excitation current in the generator's rotor. This increase is brought about by increasing the duty cycle of a PWM signal set by the generator regulator. The change in the magnetic field resulting from the excitation current increases the voltage induced in the stator.

[0003] In the event of a rapid correction of a voltage dip, the torque-determining excitation current also rises accordingly. Particularly at low speeds, the motor often cannot generate the required torque quickly enough. In this case, the generator brakes the motor, which can lead to stalling.

[0004] To prevent such engine stalling, it is already known to limit the response rate of a generator controller in the lower speed range. This so-called load response function limits the rate of change of the duty cycle when it needs to be increased due to a voltage dip. This also affects the rate of change of torque to the same extent, giving the engine more time to respond to the increased torque demands. However, a disadvantage of this approach is that it results in a corresponding delay in the response to the voltage dip. The voltage dip lasts for a longer period.

[0005] If only small loads are switched on, and the duty cycle therefore only needs to be increased slightly, then the torque is also only increased slightly, which is generally not critical for the motor. To avoid having to accept the slow compensation of a voltage dip caused by the load response function, even with such small load changes, it is already known to first increase the duty cycle by a predetermined value, also known as the "blind zone," so that a rapid response to the voltage dip occurs, and only then increase it further at the rate of increase limited by the load response function.

[0006] The "blind zone" is defined as the duty cycle delta within which rapid adjustment can occur. In modern controllers, the blind zone is either set to a fixed value or can be switched between two values. The resulting possible loads that can be quickly adjusted, as well as the resulting possible torque changes, are not constant but depend on the generator's operating point. Reasons for this dependence include, for example, the temperature-dependent properties of the excitation winding (resistance and inductance) and the disproportion between the excitation current and the generator current, caused by the saturation behavior of the rotor's iron core.

[0007] From DE 199 05 984 A1, a control device for a motor vehicle alternator is known. The alternator is driven by an internal combustion engine and charges a battery after rectifying the output voltage it generates. This control device includes a voltage regulator that maintains a constant battery charging voltage and a device that gradually increases the alternator's generator current after an electrical load is switched on. The amount of the increase in a control current of a circuit breaker, used to control the alternator's excitation current, is set according to the alternator's power generation conditions. This increase occurs immediately after the electrical load is switched on but before the gradual excitation control device is activated.In particular, the increase in the control current of the circuit breaker for controlling the alternator's excitation current is set as a function of the alternator's generator current such that the increase is higher for high generator currents and lower for low generator currents. Alternatively, the increase in the control current of the circuit breaker for controlling the excitation current is set so that it is proportional to the excitation current value before the electrical load is switched on. This ensures that, when using the same control device for generators with different generator power capacities, the output current of the alternator in question, which represents a single and immediate response to the switching on of a load before the activation of the control circuit for a gradual excitation that gradually increases the generator current, is kept essentially constant.

[0008] From JP 07-1 11 799 A, a generator driven by an internal combustion engine is known. This generator comprises a current generation parameter acquisition device for acquiring a parameter representing the generator's field current, and a current generation quantity control device for controlling the generator's field current according to the parameter acquired by the current generation parameter acquisition device. The generator is equipped with a first field current limiting device for gradually increasing the current generation quantity, while the field current is limited based on parameters acquired by the current generation parameter acquisition device during idling operation in an open control mode.The idle speed fluctuation control device is equipped with a second field current limiting device to gradually increase the generated current more slowly than the gradual increase rate of the generated current by the first field current limiting device, while the generator's field current is limited based on the parameter detected by the current generation parameter detection device during idle operation in feedback control mode. The JP exhibits no blind zone.

[0009] DE 102 34 088 A1 relates to a method for influencing the load response function of a separately excited three-phase generator driven by an internal combustion engine. The three-phase generator comprises an excitation circuit and a rotor circuit. The load response function serves to minimize the effects of the three-phase generator on the internal combustion engine when high-power consumers are connected to the vehicle's electrical system, which includes an energy storage device. The load response curve is determined based on the voltage in the vehicle's electrical system and takes into account the operating state and driving situation of the vehicle driven by the internal combustion engine. Furthermore, voltage regulation of the generator can be achieved, whereby both its load response behavior and its voltage can be controlled via an input on the generator.

[0010] DE 195 23 302 A1 relates to a method for controlling the excitation of a generator driven by a diesel engine and which supplies at least one electric motor via at least one drive converter, wherein the excitation of the generator is controlled according to the characteristic curve depending on the current generator load in order to quickly detect and control short-term load changes on the drive. Disclosure of the invention

[0011] In contrast, a method with the features specified in claim 1 and a device with the features specified in claim 7 have the advantage that the selection of the difference by which the duty cycle of the control signal is increased is made depending on the current operating point. This adaptation of the blind zone to the current operating point advantageously leads to predictable and clearly defined generator behavior, which can be optimized for the respective operating points of the engine. This allows, for example, the minimization of more complex functions in the control unit for reacting to torque changes in the drivetrain caused by the generator.

[0012] Further advantages of the invention are that the different operating points do not always have constant conditions, such as constant changes in torque or constantly rapidly regulated voltage dips, but rather different conditions can exist; for example, different operating points can be assigned to different changes in torque.

[0013] An embodiment of the invention is explained in more detail below with reference to the drawing. It shows Fig. 1. A circuit diagram illustrating a device for compensating for a drop in the output voltage of a motor vehicle generator caused by the connection of a load. Fig. 2 diagrams to illustrate a known procedure and Fig. 3 diagrams illustrating a method according to the invention.

[0014] The Fig. Figure 1 shows a circuit diagram illustrating a device for compensating for a dip in the output voltage of a motor vehicle generator caused by the connection of a load. The device shown comprises a generator unit 11, the vehicle's electrical system 12, and detector means 13. The generator unit 11 includes a generator regulator 1 and a generator unit 10, which provides a DC supply voltage for the vehicle's electrical system 12 at its output.

[0015] The generator unit 10 comprises a generator 2 and a rectifier assembly 9. The generator 2 contains an excitation winding 5 and phase windings (not shown) which are connected, for example, in a star or delta configuration. The generator 2 provides alternating voltages at its phase voltage terminals U, V, and W, which are supplied to the downstream rectifier assembly 9. Alternatively, a different number of phases or phase voltage terminals can be provided.

[0016] The rectifier arrangement 9 contains three branches, each of which has a series connection of two diodes or other suitable components and is assigned to one of the phase voltage terminals of the generator.

[0017] The phase voltage terminal U of generator 2 is connected to the junction between diodes D1 and D4 of the first rectifier branch. The phase voltage terminal V of generator 2 is connected to a junction between diodes D2 and D5 of the second rectifier branch. The phase voltage terminal W of generator 2 is connected to a junction between diodes D3 and D6 of the third rectifier branch.

[0018] The cathodes of diodes D4, D5, and D6 are connected together. The output DC voltage of the generator unit 10 is provided there and passed on to the vehicle electrical system 12. The anodes of diodes D1, D2, and D3 are also connected together and are grounded.

[0019] The phase voltage connection W of generator 2 is further connected via a connection X of generator regulator 1 to the control unit 7 of generator regulator 1 and via a resistor R3 and a ground connection 3 of generator regulator to ground 4.

[0020] The generator regulator 1 has an operating voltage terminal B+ as well as additional terminals DF, D-, and X. Furthermore, the generator regulator contains a control unit 7, which is equipped with evaluation logic. The control unit 7 is designed to provide a PWM control signal s to a switching transistor 6. The control unit 7 is also connected to the operating voltage terminal B+ and to ground 4 via the ground connection 3. Additionally, the control unit 7 is connected to terminal X of the generator regulator 1 to receive a phase voltage signal derived from the phase voltage terminal W of the generator 2.

[0021] Furthermore, the information in the Fig. The device shown in Figure 1 comprises an excitation circuit. This circuit runs from the operating voltage terminal B+ of the generator regulator 1 via the switching transistor 6 of the generator regulator, the terminal DF of the generator regulator, the excitation winding 5, the terminal D- of the generator regulator, and the ground connection 3 to ground 4. A freewheeling diode 8 is connected between the terminals D- and DF of the generator regulator 1, or an active freewheeling circuit with a switching transistor is used.

[0022] The control unit 7, which is connected to the operating voltage terminal B+ and via terminal X to the phase voltage terminal W of the generator 2, controls the switch 6 with the control signal s in such a way that an excitation current flows through the excitation winding 5, which depends both on the DC voltage present at the operating voltage terminal B+ and temporarily on the phase voltage supplied to it via terminal X.

[0023] If a drop in the output voltage of the vehicle alternator occurs in such a device due to the connection of a load in the vehicle's electrical system, this is detected by the regulator control unit 7. The regulator control unit is designed in such a way that it compensates for the voltage drop when it occurs. This happens as follows:

[0024] After the load is applied, the controller 7 acquires the parameter values ​​of the signals supplied to it by the detectors 13. These signals correspond to parameters that describe the current operating point of the vehicle generator 2, allowing the controller to determine the current operating point of the vehicle generator from the parameter values ​​it receives. These parameters, whose values ​​allow conclusions to be drawn about the current operating point of the vehicle generator, include rotational speed and temperature. The rotational speed is the generator speed and / or the engine speed. The temperature is the generator temperature and / or the controller temperature and / or the engine compartment temperature and / or the ambient temperature.Other parameters describing the current operating point of the vehicle include, for example, the generator load and / or the excitation current and / or the duty cycle and / or the battery voltage and / or the generator voltage. The controller already has information on the excitation current and the duty cycle. Information on other parameters, whose values ​​allow conclusions to be drawn about the current operating point of the vehicle generator, is supplied to the controller by the detectors 13.

[0025] Once the controller has determined the current operating point of the vehicle alternator from the aforementioned parameters, it selects an operating-point-dependent value corresponding to this operating point by which the current duty cycle of the control signal s is increased. This is done to initiate optimal regulation of the voltage dip that has occurred at this operating point. In a first step, a control signal s with the increased duty cycle is applied to the switching transistor 6. This also increases the excitation current flowing through the excitation winding 5, which in turn leads to an increase in the output voltage of the alternator.

[0026] To select the operating point-dependent amount by which the instantaneous duty cycle of the control signal s is increased, the controller 7 addresses a memory 14 in which a characteristic map is stored, in which a difference amount is assigned to a large number of operating points.

[0027] Subsequently, in a second step, the controller generates the control signal s in such a way that the settling speed is limited, thus performing a load response function.

[0028] Consequently, in the present invention, after a voltage dip occurs due to the connection of a load, the instantaneous operating point of the vehicle generator is first determined, and the duty cycle of the control signal s supplied to the switching transistor 6 is increased by an operating point-dependent differential amount. Then, in a second step, the response speed is limited in accordance with a load response function.

[0029] The Fig. Figure 2 shows diagrams to illustrate a well-known procedure. In the Fig. 2a shows the duty cycle of the control signal s plotted against time, in which Fig. 2b The load L of the generator over time. At time t1, a first load is switched on, and at time t2, a second load is switched on. Both load switching operations cause a drop in the output voltage provided by the generator.

[0030] From the Fig. Figure 2a shows that at time t1, the duty cycle of the control signal s is first increased abruptly by an amount B and then, in a second step, continues to increase slowly according to a load response function to compensate for the voltage dip. The duty cycle then remains unchanged until time t2. At time t2, the duty cycle of the control signal s is again first increased abruptly by an amount B and then, again in a second step, continues to increase slowly according to a load response function to compensate for the further voltage dip. The amount by which the duty cycle of the control signal s is abruptly increased, i.e., the blind zone B, is the same for both load connections and is independent of the generator's current operating point at the time the respective load connection occurs.The duration of the load response function, which lasts until the respective voltage drop is regulated, differs in the illustrated embodiment.

[0031] From the Fig. As shown in Figure 2b, the portion of the load that is quickly regulated across the blind zone at time t1, i.e., before the load response function takes effect, has the value Δ1, and the portion of the load that is quickly regulated has the value Δ2, where Δ1 is greater than Δ2. This is because the generator is at a different operating point at time t1 than at time t2.

[0032] The Fig. Figure 3 shows diagrams illustrating a method according to the invention. Fig. Figure 3a shows the duty cycle of the control signal s plotted against time. Fig. 3b The load L of the generator over time. At time t1, a first load is switched on, and at time t2, a second load is switched on. Both load switching operations cause a drop in the output voltage provided by the generator.

[0033] From the Fig. Figure 3a shows that at time t1, the duty cycle of the control signal s is first increased abruptly by an amount B1 and then, in a second step, continues to increase slowly in accordance with a load response function to compensate for the voltage dip. The duty cycle then remains unchanged until time t2. At time t2, the duty cycle of the control signal s is first increased abruptly by an amount B2 and then, in a second step, continues to increase slowly in accordance with a load response function to compensate for the further voltage dip. The amount by which the duty cycle of the control signal s is increased abruptly, i.e., the blind zone, differs between the two load connections. A blind zone B1 is used when the load is connected at time t1, and a blind zone B2 is used when the load is connected at time t2, with B1 being greater than B2 in the illustrated embodiment.The choice of the blind zone was made depending on the operating point present at the time of the respective load connection, as described above in connection with the . Fig. As explained in section 1. The duration of the load response function, which lasts until the respective voltage drop is regulated, also varies in this embodiment.

[0034] From the Fig. 3b shows that the quickly regulated portion of the switched-on load at time t1 and the quickly regulated portion of the switched-on load at time t2 each have the value Δ, i.e., they are identical.

Claims

[1] Method for compensating for a dip in the output voltage of a motor vehicle generator (11) caused by the addition of a load or a change in speed by means of a generator regulator (1) which provides a control signal (s) having a duty cycle and increasing the excitation current of the motor vehicle generator (10) to a switching transistor (6), wherein, after the occurrence of the voltage dip, in a first step the duty cycle of the control signal is abruptly increased by a difference amount (B1, B2) and the control signal (s) with the increased duty cycle is supplied to the switching transistor (6), and in a subsequent second step the compensation speed is limited, wherein, after the occurrence of the voltage dip, parameters describing the instantaneous operating point of the motor vehicle generator (11) are recorded and, in the first step, an operating point-dependent adjustment of the difference amount is carried out.where different difference amounts are assigned to different working points. [2] Method according to claim 1, characterized by , that the parameters describing the instantaneous operating point of the motor vehicle generator (11) include a rotational speed and a temperature. [3] Method according to claim 2, characterized by , that the parameters describing the instantaneous operating time of the motor vehicle generator (11) include the generator speed and / or the engine speed. [4] Method according to claim 2 or 3, characterized by , that the parameters describing the instantaneous operating point of the motor vehicle generator (11) include the generator temperature and / or the controller temperature and / or the engine compartment temperature and / or the ambient temperature. [5] Method according to any one of claims 2-4, characterized by, that the parameters describing the instantaneous operating point of the vehicle generator (11) include the load of the vehicle generator (11) and / or the excitation current and / or the duty cycle and / or the battery voltage and / or the generator voltage. [6] Method according to any one of the preceding claims, characterized by , that the difference amount (B1, B2) is taken from a stored characteristic map in which a difference amount (B1, B2) is assigned to a large number of operating points. [7] Device for compensating for a dip in the output voltage of a motor vehicle generator (11) caused by the addition of a load or a change in speed, comprising a generator controller (1) which provides a control signal (s) having a duty cycle that increases the excitation current of the motor vehicle generator (11) to a switching transistor (6), wherein, after the occurrence of the voltage dip, the generator controller (1) in a first step abruptly increases the duty cycle of the control signal (s) by a differential amount and supplies the control signal (s) with the increased duty cycle to the switching transistor (6), and in a subsequent second step limits the compensation rate, wherein the device comprises detector means (13) which, after the occurrence of the voltage dip, detect parameters describing the instantaneous operating point of the motor vehicle generator, wherein the detector means are connected to the generator controller (1),wherein the generator controller is designed to determine the operating point of the vehicle generator by evaluating the detector signals provided by the detector means and, in the first step, to make an operating point-dependent adjustment of the differential amount, whereby different differential amounts are assigned to different operating points. [8] Device according to claim 7, characterized by , that it has a memory (14) in which a characteristic map is stored in which a difference amount is assigned to a plurality of operating points.

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