FR2791195A1 - Control of electric generator driven by internal combustion engine to match load demand - Google Patents

Abstract

The alternator (3) is driven by an internal combustion engine (2), and delivers power through a rectifier to an electric motor (6). The generator has a controller (4) and an electronic supervisory system (5) controlling the entire system. The speed of the internal combustion engine is regulated by measuring power delivered by the alternator so it matches the power demanded by the load.

Description

l

  Control system of an electric generator group.

  The present invention relates to the control of an electric generator group comprising an alternator associated with its rectifier and a heat engine, intended in particular for an automotive application. This electric generator associated with its control can be used in particular in a hybrid electric vehicle or with electric transmission. However, the invention can also be used to supply any system requiring a source of electrical energy with

outside the automotive field.

  On a series hybrid vehicle, a heat engine drives an alternator which produces electrical energy. This set constitutes a primary source of electrical energy. The battery is a second source of energy. The battery can also be a receiver of electrical energy since it can store electrical energy. The electric motor is the receiver of electric energy which transforms electric power into mechanical power for the advancement of the vehicle. Finally, during braking, the electric motor can transform mechanical energy into electrical energy returned to the battery, this is

regenerative braking.

  Energy flows can pass from the alternator and the battery to the electric motor, from the single alternator to the electric motor, from the single battery to the electric motor, from the electric motor and the alternator to the battery, from the alternator alone to the battery or, from the electric motor alone to the battery, To optimize the criteria of consumption and emission of pollutants, it is necessary for the generator group to travel in the plane of rotation speed of the heat engine- couple, a set of particular points. This set of points constitutes a line of best operating points. And a neighborhood encompassing this line constitutes an area of best operating points. It is then possible to operate the heat engine in its zone of better operating points, to be able to operate entirely electrically, and to recover the energy from the braking of the

  electric motor to the battery.

  Indeed, if the vehicle is fully electric, with the combustion engine off, the batteries are the only source of energy. Therefore, the specification of an all-electric autonomy requires the carrying of a certain amount of energy, which results in a

certain battery mass.

  In serial hybrid mode, with the engine running, the

  batteries are required to meet the driver's request.

  Indeed, the driver's request is an instantaneous request for power at the vehicle wheels. Experience shows that this power varies rapidly compared to the maximum possible speed of variation of the power delivered by an alternator driven by a heat engine. At all times, the battery is called upon to fill or absorb the dips or surplus power delivered by the alternator, so that the sum of the power delivered (in algebraic value) by the battery, and the power delivered by the alternator corresponds to the power absorbed by the electric motor, in accordance with the driver's request. The estimation of the power dips that the battery will have to fill instantly by delivering power, and the power peaks to which the battery will have to respond instantly by absorbing power, implies the power sizing of the battery. This design results in a minimum battery mass to be loaded on the vehicle. The presence of batteries also makes it possible, when the vehicle is in situations where the electric motor requires only little power, to remain in operating zones of interest to the thermal engine: indeed, these are its zones of better efficiency placed at high torque, hence the advantage of being able to produce more power than the electric motor needs: the surplus produced will be stored in the batteries. In addition, the battery or the generator set can supply power to the auxiliaries. In general, since the control of the heat engine is a complex operation, the control strategy consists in operating the heat engine in the vicinity of a fixed point in the plan speed (speed of rotation of the heat engine) - couple. This also makes it possible to make the most of the series hybrid configuration, which allows the thermal engine to operate while avoiding transients, which are harmful in terms of pollutant emissions and consumption. Obviously, this strategy implies that the heat engine delivers almost constant power or varying in a narrow range. Therefore, the power delivered by the alternator hardly follows the variations in power drawn by the electric motor due to the

variation in driver demand.

  The disadvantage of this strategy is the carrying of a relatively high mass of battery, penalizing in terms of cost and performance of the vehicle. Indeed the battery is requested to ensure compliance with the driver's request. So the power sizing of the battery is all the greater, resulting in a

greater battery mass.

  In the state of the prior art, certain vehicles bypass the batteries to achieve a transmission entirely

  electric. The battery can therefore no longer act as a buffer.

  Patent application A-EP0678414 describes a solution for overcoming batteries. The disclosed structure can be briefly described as follows. The position of the accelerator pedal, actuated by the driver, is transformed into a power setpoint considering that this position of the pedal represents the proportion of the

  maximum torque at instantaneous speed to be applied to the electric motor.

  By a map, this power setpoint is transformed into an optimal control setpoint and an optimal speed setpoint for the heat engine. A corrector controls the speed of the heat engine to the set speed by improved all-or-nothing actions on command (maximum command if the measured speed is lower than the set point, minimum command if the measured speed is higher than the set point , optimal control if the measured speed is equal to the setpoint). From the speed measured on the heat engine, a supervisor calculates the mechanical power that the heat engine would deliver at this speed with the optimal control, and by subtracting the losses, the supervisor deduces the power actually available for the electric motor. The power setpoint actually applied to the electric motor is the minimum of what the driver requires and what the heat engine can instantly provide. The power absorbed by the electric motor is controlled by this new setpoint by an integrator. In this structure, it is important to note that the alternator is a passive member which transforms into electrical power exactly what the electric motor consumes, the difference with the power supplied by the engine resulting in variations in speed.

of the heat engine.

  However, experience shows that the type of all-or-nothing order

  or all-or-nothing improved used in this patent application A-

  EP0678414 is suitable for maintaining a stabilized state in steady state (non-transient) and introduces variations around the equilibrium position (power, speed, ...). In addition, this type of command involves transients which are harmful in terms of emission of

pollutants and consumption.

  On the other hand, the power delivered by the alternator is regulated by the control between the alternator and the electric motor. What has

  indeed a complex development of the alternator control.

  The invention aims to provide a solution to these problems, by using the electric generator group in the vicinity of its best

  operating point for the power output.

  The object of the invention is therefore to optimize the criteria for

  consumption and emission of pollutants.

  The object of the invention is also to control the electric generator group so that the power delivered by the alternator is as close as possible to the power called by the electric motor while remaining in efficiency zones.

  interesting, that is to say above a minimum power.

  According to the invention, the control system of an electric generator group comprises a heat engine coupled to an alternator, the latter being associated with a rectifier capable of supplying power to an electric motor, a generator control unit, and

  a supervisor, electronic control unit for the whole.

  The system further comprises means for regulating the speed of rotation of the heat engine in a closed loop by action on an alternator control device, and means for measuring the power delivered by the alternator and for regulating this power in a loop closed by action on a thermal engine control device, so that the alternator delivers substantially the

  power required at the input of the electric motor.

  The engine control can for example be a throttle angle control, pump lever angle, a control

  supply or a torque control.

  In a variant of the control system according to the invention, the closed loop on the speed of rotation of the heat engine comprises an open loop by action on a control device of the alternator and a closed loop internal to the alternator to impose

  said rotational speed of the heat engine.

  According to another advantageous variant of the invention, the closed loop on the speed of rotation of the heat engine comprises a means for measuring this speed and a means for comparing this same speed with an alternator control instruction sent by the generator control unit so as to generate a torque or excitation command on said alternator which can be controlled by torque or by

excitation.

  The power, thus regulated in a closed loop according to the invention,

  ensures the accuracy of the alternator's power delivery.

  Similarly, the regulation of the closed-loop speed makes it possible not to degrade the power delivery of the alternator, and to ensure speed

  and the stability of this service.

  According to one embodiment of the invention, the generator control unit preferably comprises two maps in parallel to simultaneously generate an optimal control command for the heat engine and an optimal control command for the alternator, from of a requested power, so as to simultaneously place the engine and the alternator on an operating point included in an area of better operating points. Each map advantageously contains optimal control instructions which have been pre-established on the basis of a reference heat engine. For a given power, each map generates an ideal command setpoint in relation to this requested power so as to control the heat engine or the alternator. By simultaneously positioning the engine speed and the power delivered by the alternator at a point on the given torque plan, the

  Stalling of the engine is prohibited by speed regulation.

  The generator control unit can also include a digital corrector for comparing the power delivered by the alternator with the requested power and for generating a correction of said optimal control command of the thermal engine so as to

  regulate the power delivered by said heat engine.

  This digital corrector is preferably a regulation system favoring speed when the setpoint is far from the power delivered by the alternator, in order to quickly satisfy the user and to correct the deviations caused by disturbances. When the setpoint is close to the power delivered by the alternator, the regulation system favors stability and precision in order to best follow the line of the best operating points and avoid violent transient phenomena which are penalizing in terms of consumption and

resignation.

  According to one embodiment, the system includes a means of observing a drift on the correction of the optimal control command of the heat engine so as to calculate in real time new operating points included in a zone of better

operating points.

  The alternator output power must be capable of being output, despite variations in the characteristics of the components, disturbances, and variations in operating parameters. The closed-loop power and speed regulation contributes to ensuring robustness, insofar as the power and speed instructions of the two closed loops define a point which can be reached for the group

electric generator.

  If, as a result of the drift in the characteristics of the elements included in the system, due for example to the natural aging of materials, these set points can no longer be reached, the

  control calculates new setpoints in real time, preventing

  reducing the problem, thanks to the observation of the drift on the correction of the

thermal motor.

  In other words, if the power can no longer be reached at the speed level imposed by the alternator, the engine control will go into saturation. But before, the control will have detected that the engine control is drifting towards saturation, when it should remain in the zone of better operating points. The alternator speed setpoint will be corrected to achieve power at

a higher diet level.

  In a preferred embodiment, the supervisor integrates a means of calculating the power requested from a setpoint of

  user and the instantaneous speed of the electric motor.

  The generator control unit may also include an internal model of the heat engine for filtering instructions sent to the alternator control device so as to slow down the dynamics of the alternator. Such a device ensures a satisfactory compromise between the power response and the response

  regime, thus improving the power response of the system.

  According to another embodiment of the invention, the alternator comprises an electronic system so as to respond faithfully to a command instruction generated by the control unit

generator.

  The alternator is advantageously able to respond quickly to a speed setpoint by limiting as much as possible the effects due for example to the static error or to the oscillations in order to ensure the

system stability.

  According to an advantageous embodiment, the generator control unit also comprises a filtering means for filtering setpoints sent to the engine control device so as to eliminate setpoint variations that are too rapid with respect to

the inertia of the heat engine.

  According to another advantageous variant of the invention, the control system comprises a battery connected to the input of the electric motor to make up the difference between the power demanded by the electric motor and that supplied by the alternator when it is desired that the operating point representing the speed of rotation of the heat engine and the output power of the alternator remains within a range

  close better operating points.

  We can therefore keep the battery for fully electric operation, but the on-board mass can be reduced compared to the mass which should be carried on a vehicle whose generator set is not optimally controlled. This reduction is possible if one chooses to limit the operating range or the dynamic range of the electric generator group and only plays the battery attenuated buffer role. As a result, it no longer fully absorbs or supplies peaks and troughs of power, difference between the power demanded

  by the electric motor and that supplied by the alternator.

  The invention further provides a method of controlling an electric generator consisting of a heat engine mechanically coupled to an alternator intended to supply power to an electric motor in which a power demand is determined from a set point of the user and the speed of rotation of the heat engine, then filtering said requested power so as to obtain a lower dynamic power setpoint. These two steps are

  advantageously carried out by a supervisor block.

  First, an optimal control setpoint for the heat engine is determined from this power setpoint and from a map. A second control setpoint for the heat engine is then determined from the optimal control setpoint for the heat engine and a corrective value depending on the power supplied by the alternator and the power setpoint. Next, a low-pass filtering of the second control setpoint for the heat engine is carried out. A third control instruction for the heat engine is obtained. Then we deliver this third

  setpoint, to an engine control unit.

  At the same time, an optimal control setpoint for the alternator is determined from the power setpoint and a second map. Then, a second control setpoint for the alternator is determined from the optimal control setpoint and a corrective value dependent on the power supplied by the alternator, the power setpoint and the first two control setpoints for the engine. Filtering of the second control setpoint for the alternator is then carried out so as to slow down the dynamics of the alternator. A third control instruction for the alternator is then obtained. Then we issue this third instruction to

  an alternator control unit.

  All of the above filters are given by way of example, any type of signal processing system can advantageously be used. Mention may preferably be made of signal processing systems such as an internal model, a second order filter or even a system

ramp limitation.

  Other advantages and characteristics of the invention

  will appear on examining the detailed description of a fashion example

  implementation in no way limiting, and the accompanying drawings, in which: - Figure 1 is a schematic view of the entire system

  on a hybrid electric vehicle.

  - Figure 2 is a block diagram of the control strategy

of the system.

  FIG. 1 shows, in the case of a vehicle with electric transmission, a heat engine 2 driving an alternator 3 to produce the electric power requested by a supervisor 5 to supply a power unit comprising an electric motor 6

  at the request of the driver acting on the position of a pedal 15.

  O10 A battery 13 can be connected to the input of the electric motor 6 in the

case of a series hybrid vehicle.

  The ax position of the pedal 15 represents the driver's wish. This position a is transmitted to the supervisor 5 which is the electronic member ensuring the overall control of the system. The supervisor 5 is therefore able to receive information coming from the pedal, but it also has a bidirectional connection with the electric motor 6 and a second bidirectional connection with a generator control unit 4. The electric motor 6 is mechanically coupled to the two driving wheels 16 and 17 of the vehicle. This electric motor 6 is electrically coupled to the alternator 3 using two electric cables 18 and 19 on which there is a current sensor 14 and a voltage sensor 11 so as to measure the power delivered by the alternator 3. A control member 8 linked to the alternator 3 allows communication between the alternator 3 and the generator control unit 4. The alternator 3 is mechanically coupled to the heat engine 2 using a shaft drive 20. A tachometer 12 is used to measure

  the speed of rotation (speed) of the heat engine 2.

  The connection between the heat engine 2 and the generator control unit 4 is made using three sensors. A first sensor, control member 7 of the heat engine 2, makes it possible to receive the instructions arriving from the generator control unit 4. A second fault sensor 9 makes it possible to inform the generator control unit 4 of the state of operation of the control member 7. These two sensors

  are connected to a power supply control 2a of the heat engine 2.

  Finally a third temperature sensor 10 is capable of communicating to the generator control unit 4 the state of overheating of the engine.

thermal 2.

  The generator control unit 4 can communicate with the supervisor 5, the heat engine 2 and the alternator 3. It receives power instructions from the supervisor 5 and according to the information it has at its inputs, it makes it possible to generate control instructions at its outputs to the heat engine 2 and the alternator 3. This generator control unit 4 is described more

in detail in Figure 2.

  In fact, FIG. 2 shows by way of example a possible architecture of the system control. We find the supervisor 5 and

  the control unit 4 which are also illustrated in FIG. 1.

  The supervisor 5 comprises a computer 21 having as input data the position a of the pedal 15 and a speed value R of the electric motor 6. This computer 21 makes it possible to calculate a power demanded in reference power Pcl 1 which is then filtered using a filter 22 also present in the supervisor 5. The power Pc l, corresponding to an ideal instantaneous power at the input of the electric motor 6 (Powerplant), or at the output of the alternator 3 The output of filter 22 is a power setpoint Pc2 which is transmitted to

  the generator control unit 4.

  Using maps 23 and 24 respectively, Pc2 is transformed into an optimal speed setpoint Nc 1 sent to the alternator 3 1 5 and into an optimal control setpoint Ic i sent to the heat engine 2, thus defining the best operating point for the power to be produced at the output of the alternator 3. The operating point which will actually be achieved finally will be in the vicinity of this ideal point, the control ensuring a correction to take into account the disturbances and constraints of the organs of the alternator 3 and of the motor

thermal 2.

  The measured power Pm at the output of the alternator 3 is compared with the power setpoint Pc2 in a digital corrector 25 to generate a correction Dc. This digital corrector 25 is based on a conventional corrector. To facilitate the adjustment phases, one can choose a proportional-integral corrector for example, in order to obtain a quick response without static error. With a corrector 25 having the characteristics of a proportional-integral corrector, the objectives can be achieved by developing several sets of parameters for the proportional gain and for the integral gain, depending on the value of the difference between the measurement and the setpoint. For example, when the setpoint is far from the measured power Pm, a very large proportional gain and a small integral gain are chosen to quickly compensate for the difference without unnecessarily saturating the integral term, and when the setpoint is close to the measured power Pm , we choose a small proportional gain and an integral gain large enough to ensure the elimination of the static error without affecting the stability. However, if the heat engine 2 induces significant delays, it is possible to modify the corrector

  proportional-integral in proportional-integral-derivative.

  The correction Dc is then added to the optimal command setpoint Icl by the accumulator 28, to give a new optimal command setpoint Ic2 whose variations are attenuated, for example by a first order filter 29, in order to reject the transients too rapids which have no influence on the output of the heat engine 2 due to its inertia, but which are harmful in terms of emission of pollutants and consumption. The generator control unit 4 sends the control instruction Ic3 thus obtained to the control member 7 of the heat engine 2. Dc must be interpreted as a variation around the optimal control of the engine

  thermal 2 to regulate the power delivered by this motor.

  Simultaneously with the supply control 2a of the heat engine 2, the alternator 3 is controlled as follows: The mapping 23 transforms the power setpoint Pc2 into an optimal control setpoint Nc l intended for the control member 10 of the alternator 3. But, given the natural aging of the elements constituting the system, the control may require operating points which cannot be reached in the torque regime. A corrector 26 is therefore introduced in order to overcome this problem, thereby ensuring the robustness of the system which remains capable of delivering the desired power, even if the characteristics of the elements

vary widely.

  The command Ic2 of the heat engine 2 is compared to the ideal setpoint Icl determined by the mapping 24 to generate a difference using the corrector 26. We also take into account the measured power Pm and the power setpoint Pc2 which we delivers at the input of said corrector 26. Above a certain power and a certain positive deviation, the output signal of the corrector 26 is a positive speed setpoint dN, to be added in the accumulator 27 to the setpoint of optimal speed Ncl to move the operating point to a zone of points which can be reached. Below a certain negative deviation, the output signal from the corrector 26 is a negative speed setpoint dN, to be subtracted in the accumulator 27 from the optimal speed setpoint Ncl to bring the operating point back to a zone of

best operating points.

  To ensure correct operation of the corrector 26, the engine control is not a saturated variable, so as to be able to generate a non-zero difference, even when the setpoint corresponds to% of the variation range of the engine control. 2.

  The accumulator 27 finally supplies, from the speed setpoint

  optimal Ncl a new speed setpoint Nc2.

  The speed setpoint Nc2 is then transformed into a control setpoint Nc3 by the block 30 which is an internal model of the heat engine 2 aimed at changing the speed of the heat engine controlled by the alternator with dynamics compatible with the

  system power response constraints.

  Indeed, to obtain rapid variations of the speed, the alternator controls the absorbed torque, and therefore indirectly the power output. Concretely, if the alternator is too reactive, a rapid increase in speed, corresponding to a request for an increase in power, can result in a fall, see a

  transient cancellation of the power delivered by the alternator.

  Conversely, a very rapid reduction in speed, corresponding to a request for a reduction in power, can result in a

  transient increase in power delivered by the alternator.

  The model 30 can consist of a first order filter and a pure delay which will be calibrated by testing the traction chain on

  power slots with maximum amplitude of driver demand.

  In the case of a first-order filter, the parameter to be set is the time constant: starting from zero, this must be increased until the excess power on a falling slot, or the dip on an up slot, either canceled or brought to an acceptable level. If the time constant is too strong, the evolution of the engine speed will be too slow, and the power response will be slowed down. Controlling the alternator 3 in speed ensures the stability of the assembly, because experience shows that the measured speed is worth, with very good precision, the speed imposed, due to the high reactivity of the alternator 3 relative to the heat engine 2. As a result, the speed setpoint is limited in model 30 so as not to cause the system to stall or overspeed. This control method can be used if there is an alternator controllable in speed, that is to say having an internal closed loop to impose a chosen speed. In the case where this option does not exist, that is to say in the case of a torque or excitation command for example, it is possible to reduce to the previous case by defining an external closed loop by l of the diet and

  comparison with the setpoint speed by a proportional corrector-

  integral to generate the command in torque or in excitation.

  In general, the invention can be applied to any system consisting of an electric generator group based on a heat engine used to power an electric system, with optimization of the operating point of the electric generator group according to the power requested. . In the case of the series hybrid, the invention makes it possible to minimize the charges and discharges of the batteries, making it possible to reduce the

  mass of on-board batteries and improve their lifespan.

Claims (8)

  1. Control system of an electric generator group comprising: - an electric motor (6); - a heat engine (2) coupled to an alternator (3) associated with a rectifier; - a generator control unit (4), and   - a supervisor (5), an electronic control unit for the assembly-   corn; characterized in that it further comprises means for regulating the speed of rotation of the heat engine (2) in closed loop by action on a control device (8) of the alternator (3), and means for measuring the power (Pm) delivered by the alternator (3) and to regulate this power in closed loop by action on a control device (7) of the heat engine (2), so that the alternator (3) delivers   substantially the power required at the input of the electric motor (6).   2. Control system according to claim 1, characterized in that the closed loop on the speed of rotation of the heat engine (2) comprises an open loop by action on a control device (8) of the alternator (3) and an internal closed loop at   the alternator to impose said speed of rotation of the heat engine.   3. Control system according to claim 1, characterized in that the closed loop on the speed of rotation of the heat engine (2) comprises means for measuring this speed and means for comparing this same speed with a setpoint of alternator command sent by the generator control unit (4) so as to generate a torque or excitation command on said alternator (3)   can be ordered as a couple or as an excitement.   4. Control system according to any one of   previous claims, characterized in that the unit of   generator control (4) comprises two maps (23,24) in parallel to simultaneously generate an optimal control command for the heat engine (Icl) and an optimal control command for the alternator (Nc 1), from a requested power Pc 1, so as to simultaneously place the heat engine (2) and the alternator (3) on an operating point included in an area of best operating points. 5. Control system according to claim 4, characterized in that the generator control unit (4) comprises a digital corrector (25) for comparing the power Pm delivered by the alternator with the requested power Pcl and for generating a correction Dc on said optimal control command of the heat engine (2) of   so as to regulate the power delivered by said heat engine.   6. Control system according to claim 5, characterized in that it comprises a means of observation (26) of a drift on the correction (Ic2) of the optimal control setpoint (Ic 1) of the heat engine. so as to calculate in real time new operating points included in an area of better operating points. 7. Control system according to claim 4, characterized in that the supervisor (5) integrates a means of calculating the requested power Pcl from a user setpoint and the speed of   instantaneous rotation (R) of the electric motor.   8. Control system according to any one of   previous claims, characterized in that the unit of   generator control (4) includes an internal model (30) of the heat engine for filtering instructions sent to the generator control device so as to slow down the dynamics of the generator. 9. Control system according to any one of   previous claims, characterized in that the alternator (3)   includes an electronic system to respond faithfully to a   control setpoint generated by the generator control unit.   10. Control system according to any one of   previous claims, characterized in that the unit of   generator control (4) includes filtering means (29) for filtering setpoints sent to the engine control device so as to eliminate excessively rapid setpoint variations by   compared to the inertia of the heat engine.   11 1. Control system according to any one of   previous claims, characterized in that it comprises a   battery (13) connected to the input of the electric motor (6) to make up the difference between the power required by the electric motor and that supplied by the alternator (3) when it is desired to limit the operating point representing the speed of combustion engine rotation and alternator output power over a narrow range of better operating points.   12. Method for controlling an electric generator consisting of a heat engine (2) mechanically coupled to an alternator (3) intended to supply power to an electric motor (6), characterized in that: - a power is determined requested Pcl from a user setpoint and the engine speed, we filter said requested power Pcl so as to obtain a lower dynamic power setpoint Pc2, - an optimal control setpoint Ic is determined 1 for the heat engine from the power setpoint Pc2 and from a map, a new control setpoint Ic2 for the heat engine is determined from the setpoint Ic 1 and a corrective value Dc depending on the power output by the alternator and the power setpoint Pc2, a low-pass filtering of the new setpoint Ic2 is then carried out, then this filtered Ic2 setpoint (Ic3) is delivered to a control member of the heat engine, in parallel, an optimal control setpoint Ncl for the alternator is determined from the power setpoint Pc2 and from a second mapping, a new control setpoint Nc2 for the alternator is determined from the setpoint Ncl 1 and a corrective value dN depending on the power delivered by the alternator, the power setpoint Pc2 and the control setpoints for the motor Icl and Ic2, then the new setpoint Nc2 is filtered so as to slow down the dynamics of the alternator, then we deliver this   filtered Nc2 setpoint (Nc3) to a generator control unit.