DE102011077718A1 - Method for operating an electrical power supply arrangement - Google Patents

Abstract

The invention relates to a method for operating an electrical energy supply arrangement (46), in particular in a motor vehicle (10). The electrical energy supply arrangement (46) has a generator (28) driven by a drive unit (32), in particular an internal combustion engine (32), in which alternating voltages are induced which generate currents. The currents are passed via a rectifier (52) to at least one electrical consumer (38) and / or an electrical storage device (34 '): The torque (t) of the drive unit (32) is kept essentially constant. The speed (d) of the drive unit (32) varies as a function of a load torque generated by the generator (28) on the drive unit (32).

Description

The invention generally relates to a method for operating an electrical power supply arrangement, in particular in a motor vehicle.

State of the art

Electric vehicles driven by an electric machine are known in the art. The electric machine draws its energy from a vehicle battery, the DC voltage taken from the vehicle battery is converted by a pulse inverter into an AC voltage, which is supplied to the electric machine. The range of known electric vehicles is limited by the capacity of the vehicle battery. There are several approaches to increase the limited range. A concept for increasing the range of an electric vehicle consists of range extenders. A range extender is usually an internal combustion engine that drives a generator. This additionally provided by the range extender electrical energy can be used depending on the strategy of the vehicle operation to charge the vehicle battery or be supplied directly to the engine circuit of the vehicle.

From the prior art, the rectification of that of such an internal combustion engine-generator unit is known by means of active power electronics components (IGBT, thyristors, e.g., pulse inverters) or passive power electronics devices (e.g., diodes in a B6 bridge).

Furthermore, the prior art regulates the voltage of the direct current generated by the engine-generator unit, e.g. by controlling the speed of the internal combustion engine known. This known solution has the disadvantage that the desired size of the voltage or the speed determined consuming from the current state of the high-voltage network (battery voltage, current to consumers or output power, SOC, etc.) and the maximum generatable power of the generator must become. Thus, for example, the specification of an always constant setpoint speed or voltage (fixed value control) is not meaningful if the current retrieved power from the vehicle battery exceeds the maximum power of the internal combustion engine-generator unit and thus a drop in the generator speed is inevitable. This case is particularly relevant because common range extender concepts often provide for designing the Range Extener generators with significantly lower horsepower compared to traction engine performance. If the speed (or voltage) is held constant by regulation when, where possible, increased battery power has been obtained, the range extender generator must fully compensate for the recalled battery power, i.e., the range extender generator. that attack moment of the internal combustion engine must follow the change of the retrieved battery power. With larger changes in the retrieved battery power (e.g., at significant vehicle accelerations), this significantly shifts the engine operating point with negative consequences for fuel efficiency. This operation is difficult to achieve due to the limited compared to the generator dynamics of the internal combustion engine.

From the prior art, it is also known to regulate the output power of the engine-generator unit. Also in this solution, the target size for the power to be generated must be determined consuming from the current state of the high-voltage network and the maximum generative power of the generator. A fixed value control would also lead to significant shifts in the engine operating point.

Disclosure of the invention

The disadvantages of the prior art described above can be avoided by the method according to the invention. In the method according to the invention for operating an electrical energy supply arrangement, in particular in a motor vehicle, alternating voltages are induced in a generator driven by a drive unit, in particular an internal combustion engine. These AC voltages generate currents which are conducted via a rectifier to at least one electrical load and / or an electrical storage. A torque of the drive unit is kept substantially constant. In this case, a rotational speed of the internal combustion engine varies depending on a load torque generated by the generator to the internal combustion engine.

It is understood that the generator may be an electric machine of basically any kind that can be operated as a generator. The invention is basically independent of the type the internal combustion engine used (eg Otto, Diesel, Wankel, turbine, watts, .... etc.) or of the medium to be burned (liquid, gas, solid).

Advantages of the invention

In other words, the essence of the invention is the operation of the internal combustion engine in uncontrolled operation under specification of a constant torque. According to the invention, there is no control of the engine speed. The internal combustion engine runs with constant torque, regardless of the currently applied vehicle electrical system voltage or the output power. This allows the use of a cost-effective diode rectifier and the absence of a control with correspondingly complex metrological observations of the controlled variables.

In one embodiment of the method according to the invention, the generator supplies an electrical system of the motor vehicle with a number of consumers and / or a battery with electrical energy. In this case, a generator voltage is applied to the generator. The torque is constant regardless of a current value of the vehicle electrical system voltage.

Especially in the field of electrical vehicle electrical systems so far occur on the disadvantages described above. Therefore, this opens up an essential area of application for the present invention.

According to one embodiment variant of the method according to the invention, the generator supplies electrical energy to an electric drive of the motor vehicle and / or the generator charges a battery.

In this way, e.g. at a low load request, a power surplus of the drive unit via the generator into electrical energy to be converted. This electrical energy can be stored in the vehicle battery and is thus available for a subsequent higher load requirement for the electric drive of the motor vehicle.

In one embodiment of the method according to the invention, the drive unit is operated without regulating the speed.

This means in other words that the drive unit is operated in open-loop mode and is not designed as a much more expensive feedback control system. Thus, a costly control electronics can be avoided.

For example, the rectifier is designed as a passive rectifier. In a passive rectifier, there is no drive and control effort. In one embodiment of the method according to the invention, the electric machine is a PSM (permanent-magnet synchronous machine) machine, which has very high efficiencies due to the loss of exciter pathways.

According to one embodiment of the method according to the invention, the rectifier is designed such that a current flow through the rectifier is blocked when a difference U _A - U _B between a vehicle electrical system voltage U _B and an output voltage U _{A of} the rectifier is negative. As a result, for example, in a start-up phase of the generator in which the difference is generally negative, the speed of the generator can be increased rapidly, because only the inertia of the drive unit to be accelerated.

In one embodiment of the method according to the invention, the rectifier is designed such that the current flow is conducted through the rectifier at a positive difference between the vehicle electrical system voltage U _B and the output voltage U _A.

This allows the current, e.g. vary in response to a load jump.

In one embodiment of the method according to the invention, a constant current is set when the load torque corresponds to the torque.

Due to this equilibrium condition between load torque and torque, the maximum current can be limited without any additional expense.

According to one embodiment of the method according to the invention, the rectifier has diodes which, with a negative difference, block the current via the rectifier and otherwise pass the current.

Diodes are particularly reliable and at the same time inexpensive electrical components.

In one embodiment of the method according to the invention, the rectifier is designed as a B6 diode bridge circuit.

B6 diode bridge circuits are mass-produced, low-cost mass-produced items.

Brief description of the drawings

1 shows in schematic form a motor vehicle with a drive train, comprising an electric induction machine and a device for driving this machine;

2 shows a schematic representation of a power supply arrangement according to the invention;

3a shows a first graph showing the time course of the rotational speed of the reciprocating internal combustion engine;

3b shows a second graph showing the time course of the voltage supplied by the electric machine in a regenerative operation and then rectified; and

3c shows a third graph showing the time course of the current supplied by the electric machine in generator operation and then rectified.

embodiments

In 1 is a motor vehicle shown schematically and generally with 10 designated. The car 10 has a drive train 12 on, in the present case, an electric drive machine 14 for providing drive power. The powertrain 12 is used to drive driven wheels 16L . 16R of the motor vehicle 10 ,

The electric drive machine 14 provides a torque Dm at an output shaft and rotates at an adjustable speed.

The powertrain 12 may be adapted to the motor vehicle 10 solely by means of the electric drive machine 14 to drive (electric vehicle). Alternatively, the electric drive machine 14 Part of a hybrid powertrain 12 be, with the powertrain 12 another, in 1 unspecified drive motor such as an internal combustion engine or the like may include. Furthermore, the powertrain 12 in this case have a gear and the like.

The electric drive machine 14 is designed multi-phase (in the present case with three phases) and is by means of power electronics 18 driven. The power electronics 18 is with a power supply such as a DC power supply (eg accumulator) 20 of the motor vehicle 10 connected and serves one of the accumulator 20 to convert the DC voltage provided into three alternating currents for the three phases of the electric induction machine. The power electronics 18 has for this purpose a plurality of circuit breakers and is by means of a control unit 22 driven. The control unit 22 can also with the electric drive machine 14 be connected, for example, actual values of the rotational speed and / or rotational position of a rotor of the electric drive machine 14 to obtain. Furthermore, the control unit 22 with the accumulator 20 be connected. Finally, the controller can 22 with a parent or equal controller 24 for controlling further components of the drive train 12 be connected.

In the following 2 the same reference numbers as in 1 used to designate the same or equivalent components. In the 2 schematically shown power supply arrangement according to the invention 46 has a power or drive unit, here as a conventional one-cylinder reciprocating internal combustion engine 32 is trained. The one in a cylinder 48 reciprocating pistons 50 the reciprocating internal combustion engine 32 is over a connecting rod 54 with a crankshaft 30 connected. The piston 50 The task is to transfer the combustion forces into the connecting rod 54 initiate.

The piston internal combustion engine 32 is drivingly with an electric machine 28 coupled to drive the latter. The connection of the electric machine 28 to the crankshaft 30 can be done in different ways. That's how the electric machine works 28 directly or via a coupling with the crankshaft 30 be connected or via a gear or other force and / or positive connection. In the present case, the reciprocating internal combustion engine 32 without the interposition of a gearbox directly to the electric machine 28 connected. The electric machine 28 is designed here as a permanent magnet synchronous machine (PSM). To the electric machine 28 is a rectifier 52 connected here as a B6 diode bridge circuit 52 is executed. The three phases U, V, W of the electric machine 28 are in the B6 diode bridge circuit 52 connected. The B6 diode bridge circuit 52 is a DC link circuit 58 with an inductance 60 and a capacity 62 for smoothing over the B6 diode bridge circuit 52 rectified voltage downstream.

The connections of the accumulator 20 that's here as a traction battery 20 is formed, and a high voltage electrical system 38 are via connecting lines L1, L2, L3, L4 to the terminals of the DC link circuit 58 connected. The high voltage electrical system 38 has a variety of electrical loads and the electric drive machine 14 on.

The PSM machine 28 converts into regenerative operation by passing through the reciprocating internal combustion engine 32 is driven, the torque of the reciprocating internal combustion engine 32 that's from the crankshaft 30 assumes into electrical power. This electrical power is used to charge the accumulator 20 and / or for the supply of a high voltage electrical system 38 of the motor vehicle 10 used. The piston internal combustion engine 32 is thus a range extender, which, unlike an internal combustion engine in a hybrid vehicle, or in contrast to a fuel-supplied internal combustion engine, is not designed to the motor vehicle 10 to drive mechanically. Rather, the driving of the motor vehicle takes place 10 solely by the electric drive machine 14 , The piston internal combustion engine 32 is therefore not with the wheels 16L . 16R of the motor vehicle 10 mechanically coupled.

When connecting electrical loads in the high voltage on-board electrical system 38 of the motor vehicle 10 is caused by the output power increase of the PSM electric machine 28 one on the reciprocating internal combustion engine 32 retroactive braking torque. A control device 56 is adapted to that of the reciprocating internal combustion engine 32 delivered torque t regardless of a current value of the output power of the electric power plant PSM 28 to keep constant.

Table 1 shows examples of different operating points, resulting in the typical operation of the power supply arrangement according to the invention 46 result. The rows of Table 1 contain the various steady-state speed values for the specified onboard electrical system loads, while the columns of Table 1 represent the steady state speeds for the indicated torques t of the reciprocating internal combustion engine 32 include. PL \ IG torque t 1.7 A (1Nm) 17A (10Nm) 36 A (20Nm) 58A (30Nm) 86 A (40Nm) 1.3 kW 5480 5850 6260 6680 7530 2.5 kW 5475 5845 6255 6675 7520 13 kW 5440 5810 6215 6630 7470 111 kW 5130 5500 5850 6280 7060 Table 1

So for example, the piston internal combustion engine 32 operated with a constant torque of 40 Nm, in the unloaded case (1.3 kW), a speed of 7530 rpm is established. If, on the basis of this situation, the vehicle electrical system load is increased to eg 13 kW (for example because the driver accelerates the motor vehicle), the speed drops to 7470 rpm. The voltage dip thus leads to a speed reduction of 60 1 / min (corresponds to about 1%).

This small stroke of speed over the load is an important point for the invention.

The speed d of the reciprocating internal combustion engine 32 and the electric machine 28 are identical. A gear ratio stage is adapted to the design of the electrical machine 28 Not necessary. The absolute speed ratios depend on the selected engine topology and dimensioning. The values assumed here are only examples of the one-cylinder piston internal combustion engine 32 ,

The implementation of the torque-controlled operation is always possible, even and especially when the electric machine 28 not the power of the electric drive machine 14 can muster.

Regarding the influence of the state of charge of the accumulator 20 It should be noted that an accumulator 20 for an electric vehicle is typically operated in the range of 20 to 80% state of charge. This results in a method according to the invention to a voltage fluctuation of about 0.4 V. Based on the voltage at maximum state of charge (SoC, State of Charge), this corresponds to a change of about 10%. During a charging process from 20% SoC to 80% SoC, the speed of the internal combustion engine will increase accordingly by about 10%.

The following is with reference to the 3a to 3c a typical scenario for the use of the inventive power supply arrangement 46 clarified. The 3a to 3c is based on the same time scale.

In the method according to the invention, the piston internal combustion engine is initially at the time t = 0 32 approached with constant torque t. Initially, the diodes block the B6 diode bridge circuit 52 against the vehicle electrical system voltage. Therefore, no current flows first I. Accordingly, the current I in the third graph according to 3c at the time t = 0 the value of 0. Since at the time t = 0 no current flows, there is no load torque on the electrical PSM machine 28 at. In other words, this means that the reciprocating internal combustion engine 32 With constant torque t only the mass inertia accelerates. The speed d of the reciprocating internal combustion engine 32 begins to steeply rise from time t = 0, as through the first left slope section 68 in 3a described.

At the time t = t ₀ reaches that of the electric machine 28 supplied and via the B6 diode bridge circuit 52 rectified voltage U the level of the electrical high voltage electrical system 38 , As a result, the diodes of the B6 diode bridge circuit begin 52 to conduct and the current I begins at time t0 starting from the value 0 increase. This increase of the current I is in the third graph through the third left rising section 70 played. The speed d of the reciprocating internal combustion engine 32 After the time t _{0, it} initially continues to increase until the current flow leads to a load torque which compensates for the driving torque t. This achieves a stationary operating point. After reaching the steady-state operating point, the voltage U initially remains constant over a period of time, as through the second, left parallel section 72 in 3b is reproduced. Likewise, in this period remains the speed d of the reciprocating internal combustion engine 32 (as through the first left parallel section 74 in 3a described) and the current I (as through the third left parallel section 76 in 3c described) temporally constant.

At time t ₁ leads a load jump in the high voltage on-board electrical system 38 for lowering the vehicle electrical system voltage U. The abrupt drop in the vehicle electrical system voltage U is due to the falling section 78 of the second graph in 3b described. Since the speed d of the reciprocating internal combustion engine 32 or the electric machine 28 is constant at this time, the difference between that of the electric machine increases 28 generated voltage U and the vehicle electrical system voltage, resulting in an increase of the electric machine 28 supplied current I takes place. This sudden increase in current is due to the wave-like peak section 80 described in the third graph. The peak section 80 shows a local maximum 82 , which means, in other words, that the current I first rises sharply. wherein the increase gradually weakens until the current I reaches its maximum value. After passing through the maximum 82 the current I decreases until a constant value is reached.

The increased current I has an increased braking torque result, which in turn reduces the speed d of the reciprocating internal combustion engine 32 leads to a new stationary operating point. This lowering of the speed d is by the sloping section 84 described in the first graph.

The overshoot in stream I depends on system parameters (such as rotational inertia and the like). Whether the accumulator 20 is unloaded or loaded in the respective operating states is not relevant.

At time t _{2 there} is a sudden decrease in the on-board network load. Due to the associated voltage increase in the electrical system (which is represented by the first right slope section), the diodes of the B6 diode bridge circuit 52 go back into the blocking operation, ie, that no more machine power flows. As a result, no braking torque is built up and there is a through the first right slope section 86 illustrated increase in the speed d of the reciprocating internal combustion engine 32 similar to their retraction. The three functions of the voltage U, the speed d and the current I rise again in response to the voltage drop and after a time reach a maximum value which is kept constant over time. Whether the diodes of the B6 diode bridge circuit 52 go back to the blocking state depends on the amount of voltage dip at time t ₂ and the parameters. In the present case, the diodes block the B6 diode bridge circuit 52 between the time t ₂ and a later time t ₃

Between the times t ₀ and t ₁ , the accumulator 20 while the latter is discharged in the period between t ₁ and t ₃ .

The diodes of the B6 diode bridge circuit 52 lock between the times 0 and t ₀ and between the times t ₂ and t ₃ .

Claims (11)

Method for operating an electrical power supply arrangement ( 46 ) in particular in a motor vehicle ( 10 ) with one of a drive unit ( 32 ), in particular an internal combustion engine ( 32 ), powered generator ( 28 ), in which AC voltages are generated which generate currents, the currents being fed via a rectifier ( 52 ) to at least one electrical consumer ( 38 ) and / or an electrical memory ( 20 ), wherein a torque (t) of the drive unit ( 32 ) is kept substantially constant at least temporarily and a rotational speed (d) of the drive unit ( 32 ) depending on one by the generator ( 28 ) generated load torque on the drive unit ( 32 ) varies. Method according to claim 1, wherein the generator ( 28 ) a traction battery ( 34 ' ) and / or a vehicle electrical system ( 36 ' ) of the motor vehicle ( 10 ) supplied with at least one consumer, wherein at the generator ( 28 ) a vehicle electrical system voltage (U) is applied and wherein the torque (t) is kept constant regardless of the current value of the vehicle electrical system voltage (U). Method according to one of claims 1 or 2, wherein the generator ( 28 ) provides electrical energy to an electric drive of the motor vehicle and / or a battery. invites. Method according to one of claims 1 to 3, wherein the drive unit ( 32 ) is operated without controlling the speed (d). Method according to one of claims 1 to 4, wherein the rectifier ( 52 ) as a passive rectifier ( 52 ) is trained. Method according to one of claims 1 to 5, wherein the generator ( 28 ) is a permanent magnet synchronous machine (PSM). Method according to one of claims 1 to 6, wherein the rectifier ( 52 ) is designed such that a current flow through the rectifier ( 52 ) is blocked when a difference U _A - U _B between a vehicle electrical system voltage U _B and an output voltage U _{A of} the rectifier ( 14 ) is negative. Method according to claim 7, wherein the flow of current through the rectifier ( 52 ) is passed through at a positive difference between the vehicle electrical system voltage U _B and the output voltage U _A. Method according to one of claims 1 to 8, wherein a constant current is set when the load torque corresponds to the torque (t). Method according to one of claims 7 to 9, wherein the rectifier ( 52 ) Has diodes which, with a negative difference, the current through the rectifier ( 52 ) and otherwise pass the current. Method according to one of claims 1 to 10, wherein the rectifier ( 52 ) as a B6 bridge ( 52 ) is trained.

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