EP1966879A1

EP1966879A1 - Method and device for operating an electric motor

Info

Publication number: EP1966879A1
Application number: EP06830105A
Authority: EP
Inventors: Matthias Schanzenbach; Juergen Hachtel; Markus Wimmer
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 2005-12-20
Filing date: 2006-11-23
Publication date: 2008-09-10
Also published as: JP2009520453A; US20100270961A1; US8653775B2; WO2007071520A1; DE102005060859A1

Abstract

The invention relates to a method and a device for controlling and/or regulating an electric motor. Such electric motors are used, for example, in motor vehicles, as pump motors. The electric motor is generally provided with electrical power from a battery and/or by means of a generator.The control and regulation is achieved by means of a high frequency pulse width modulation (PWM). The invention is based on a continuous increase in the motor current required for operation of the electric motor on starting up the electric motor by means of the PWM modulation, for example, from a value of 0 upwards.

Description

Method and device for controlling an electric motor

State of the art

The invention is based on a method and a device for operating an electronic motor controlled by pulse width modulation on a DC voltage network according to the independent claims.

Such a method is known from DE 199 44 194 A1, in which the output stage of an electronically commutatable motor is controlled via an electronic control unit by means of pulse-width-modulated signals. Here, the electric motor with

Voltage pulses from a DC power supply supplied in accordance with the predetermined by a setpoint control voltage pulses.

Advantages of the invention

The present invention describes a method and a device for controlling and / or regulating an electric motor. Such electric motors are used for example in motor vehicles in the form of pump motors. It is generally provided to supply the electric motor from a battery and / or by means of a generator with electrical energy. The control and / or regulation takes place by means of a high-frequency pulse width modulation (PWM). The essence of the invention is that during start-up of the electric motor by means of the PWM the motor current necessary for the operation of the electric motor is increased continuously, for example from the value 0. The advantage of such a control of the electric motor is that current peaks can be avoided, which are caused by the occurring during start-up of electric motors large starting currents. Such current peaks can lead to damage to the battery. Furthermore, these current peaks can cause a dynamic voltage dip, which in other consumers who also from the battery and / or the

Generator can be supplied, can lead to failure.

Advantageously, therefore, the current gradient, with which the motor current is continuously increased, limited to a predetermined maximum value.

The maximum value, which can also be designed as a setpoint value, can be predefined as a function of operating parameters of the battery and / or of the generator. Typical operating parameters represent the discharge current of the battery and / or the current increase generated by the generator. In addition, however, the structural design of the generator can be used to specify the maximum value, for example by the

Determination of the maximum achievable current gradient by the generator. The latter is defined as the current that can be generated within a given time by the generator.

In order to limit the increase of the motor current or the current gradient, it can be provided in one embodiment of the invention to limit the rotational speed of the electric motor.

In this case, for example, a maximum target rotational speed can be used, which is predetermined as a function of the battery voltage. Another possibility is to take into account the load torque, which is applied to the electric motor or must be applied by the electric motor, in determining the maximum target speed.

In one embodiment of the invention, it is further provided that the intended for the operation of the electric motor battery or the generator supplies additional electrical consumers with energy. It is prevented by the present invention that it comes at current peaks during startup of the electric motor to a failure of these other consumers. In a development of the invention it can also be provided that the continuous increase of the motor current or the current gradient to which this increase is limited is made dependent on the supply of the further consumers with electrical energy. For example, the power demand for more consumers in one Vehicle such as the heater, the light or an ACC (Adaptive Cruise Control) can be considered to determine the allowable current gradient.

In a specific embodiment of the invention, it is provided that only the electric motor is supplied by the generator with electrical energy, whereas the other electrical consumers are largely supplied by the electrical energy that supplies the battery. It is also conceivable that the separation of the supply takes place only during the start-up phase of the electric motor.

Further advantages will become apparent from the following description of

Embodiments or from the dependent claims.

drawings

Figure 1 shows schematically in a block diagram an inventive device for

Control or regulation of an electric motor. A corresponding circuit diagram is shown in FIG. FIG. 3 shows an equivalent circuit diagram of an electric motor. A comparison of the motor current with and without Stromgradientenbegrenzung is shown in Figure 4. FIGS. 5a to 5c show diagrams for explaining the derivation of the speed limitation.

embodiment

When operating an electric motor, a high power requirement occurs during startup. If the electric motor is powered by a battery with electrical energy, it can be a

Break in the supply voltage supplied by the battery come. This dynamic voltage dip can affect other consumers that are also connected to the battery. Especially when starting an electric (pump) motor in a vehicle, for example in the pressure generation in the context of an electro-hydraulic brake system, such a temporarily lowered supply voltage can lead to problems with other electrical components located in the vehicle. - A -

As a remedy, according to the present invention, the energy supplied to the motor or the supplied motor current is slowly increased, in order to avoid unwanted high current peaks and to protect the electrical system of the vehicle.

FIG. 1 schematically shows a possible device with which a slow or continuous increase of the motor current at the electric motor 180 can be achieved. In this case, a processing unit 110 is provided in a control unit 100, for example in the form of a microprocessor or an ASICS, which evaluates external data and derives therefrom control signals which control or regulate the electric motor 180 and possibly also a generator 190 present in the vehicle.

In this case, operating parameters of the electric motor itself can be detected as external data, which are recorded by means of a suitable means 130 and forwarded to the processing unit 110. In this context, operating parameters can also be understood to mean the pressure ratio in the hydraulic branch before and after a pump motor, which by means of

Pressure sensors or models can be determined. In addition, however, predetermined operating parameters of the electric motor can also be detected as operating parameters, which can optionally be stored directly in a suitable memory on the electric motor or in the control unit. Schematically, such a memory is represented by the block 120.

In order to initiate the continuous increase in the current, it is furthermore necessary for a requirement for starting the electric motor to be detected by a corresponding device 140. This device can also query the required load torque for the electric motor and direct it to the processing unit 110 so that this at the

Control can be considered.

If a generator 190 is present in the vehicle in which the control unit 100 is used, its operating parameters can likewise be used to generate the control signals of the electric motor 180. For this purpose, for example, by means of a suitable

By means of 150 the current operating state of the generator 190 detected. In addition, it is also conceivable that specific structural parameters of the generator 190 can be taken into account, which can be stored in a memory on the generator or in the control unit. As more specific Construction parameters can be understood, for example, as the maximum current flow rate that can be generated by the generator, ie the current that can be generated within a predetermined time.

For controlling the electric motor 180, the state of the battery 160 is also detected and taken into account. It is primarily on the state of charge or the degree of strain of

Target battery through other consumers. However, it is also possible to specifically detect the required supply power of the further consumers by suitable means 170 in order to be able to make a prognosis about the utilization of the battery 160. Such a prognosis can also be incorporated in the control of the electric motor 180, for example when the battery supplies the only supply voltage for the consumers considered.

In a further exemplary embodiment it can also be provided that the generator 190 can likewise be operated as a function of the detected data and / or as a function of the activation of the electric motor 180.

FIG. 2 shows a schematic block diagram in which the control unit 200 controls the electric motor 220 by means of a motor voltage U _M or a motor current I _M. Typically, such control is performed by (high frequency) pulse width modulation. The power supply of the controller 200 and the electric motor 220 is in the present case by a battery 230, which supplies a battery voltage U _Ba t, and a

Generator 210 secured. By combining the battery and the generator, the control unit 200 or the electric motor 220 can be supplied with a higher current I _Zu .

Since the generator and the battery are usually connected in parallel in the vehicle and the generator is readjusted only with a certain current gradient (eg 300 to 1000 A / s), the power is supplied from the battery in a jump-like switching on the motor. These high currents can damage the battery. By specifying a maximum current gradient, ie a defined increase in current in a given time when driving the motor during startup, such damage can be avoided. If, in addition, the current gradient is adapted to the current gradient of the generator, the motor current required for starting the motor can be generated completely by the generator of the vehicle. This spares the battery from high current jumps. About that In addition, in such a control dynamic Spannungsseinbrücke be avoided in the electrical system, since the battery is relieved.

The comparison of the load of a motor startup with and without Stromgradientenbegrenzung is shown in Figure 4. Plotted is the motor current I _M required for starting the motor over time t. The curve according to FIG. 420 shows the motor current I _M without current limitation with a very high current peak shortly after the start of the startup. The dashed curve according to FIG. 400, on the other hand, shows a continuous course, which after a certain time, like the course according to FIG. 420, also changes into a constant power requirement for the operation of the motor.

In a further embodiment, different current gradients may be set, which are required depending on the hydraulic power requirement of an existing in the vehicle ESP controller.

Since the electric motor typically additionally has a speed control, the setting of the maximum current gradient can be carried out by specifying a setpoint speed. The maximum setpoint speed used in this way is calculated in accordance with a particular exemplary embodiment

>

The maximum setpoint speed can be derived as follows:

As can be seen from an equivalent circuit diagram of an electric motor (see FIG. 3), the motor voltage U _{M can be divided} into different partial voltages U _R (assignment to the ohmic resistance

300 of the motor), Ui _n d (assignment to the inductive resistor 320 of the motor) and V> Q _W (assignment to the regenerative component 340 of the motor) are split.

The system equations of the motor can be derived from the stress balance and the spin set and read: _τ dω _

L = U - Ri - Kω dt (i.i)

The states here are the armature current i and the rotational speed ω. The parameters are the inductance L, the moment of inertia J, the motor constant K and the resistance R. The inputs of the system are the manipulated variable supply voltage U and the load torque Ti _oad . The load torque depends on the pressure applied to the pump elements and the

Rotation speed. As a first approximation, the speed dependency can be neglected. Thus, the load torque is composed of a constant friction component and a pressure-dependent load component: ^~ / Where p is the pressure-side and p _ds _ss represents the suction pressure, which values can for example be taken from HIM (hydraulic model of the ESP) or directly detected by pressure sensors. Thus, the load torque can be assumed to be known.

In the following, the supply voltage U is calculated so that the desired

Set speed. The basis for this is the theory of flat systems. If one selects the speed ω y ^{= ω} , (i.2) as the output, one obtains a relationship between the armature current i and the rotational acceleration _{y = ώ} = I (κi -τ _load ) through the first derivative and insertion into the system equations (1.1) ) → i = l (jώ + τ _load )

J ^κ . (1.3)

On further derivation, the supply voltage U occurs:

_y = ώ = - (U - Ri - Kω) + ^ JL J (1.4)

By dissolving after U you get

JL RJ R L

U = - ώ + - ώ + Kω + - T loa, d + - T ^L , load

^KKK . (1.5) This equation can be simplified because of the small influence of the inductance. By inserting the desired values, one thus obtains a control _which moves the system along the desired trajectory ω _d :

U ^d = - ^ ώ _{d +} K ω _{d +} ^ T _load ^{κ κ} . (1.6)

The first term takes into account the inertia of the motor, the second the voltage induced by rotation and the third the required voltage due to the load torque.

Planning the target trajectory

The scan of the controller is 5ms. Therefore, both the supply voltage U and the desired trajectory ω _d (t) can be modified in these time steps. In a first step, the trajectory is planned over a sampling cycle. This is shown in FIG. 5a.

At time j, the desired speed at time j + 1 is thus selected so that both control value limitations are met and the current gradient does not exceed the required maximum. The calculation of the new setpoint value ω _d ^{J + 1} will be discussed in more detail below. For this, the calculation of the control is necessary first.

Calculation of the scheme

To control the setpoint speed, a linear PI controller is used. Thus, the controller component is composed of proportional and integral component. In discretized notation, the general controller equations can be written as follows:

U ^ ₁ = k _p (ω i -ω i _eas ) + k _I £ (ω _d -ω i _as )

1 = 1 u?

In this case, however, the fact must be taken into account that the supply voltage U belonging to the instant j is output only at the instant j + 1 and therefore the setpoint trajectory is shifted by one sampling cycle. This situation is illustrated in FIG. 5b. Therefore, the current speed is compared with the set speed of the last cycle in the controller. This results in the following equation for the controller:

U ^ = (k _p + - ^C ₁ W - ^O) L.) + ^! (3.1)

Control and regulation

The manipulated variable U is composed of feedforward control U _d and control U _H :

R T R

U = U _d + U _PI = - ώ _d + K ω _d + -T _load + U _PI ^{κ κ} . (3.2)

Here, the speed and spin used in the control still have to be set. The rotational acceleration is determined by linear interpolation of the target speed at the time j and j + 1 ω _d ⁺¹ - ω _d ω _d =

.DELTA.t (3.3) This results in the manipulated variable U ⁺¹ j + 1 by the time

It should be noted that only the control component depends on the new target variable ω _d ^{J + 1} . This equation is used below to prevent manipulated variable restrictions

Compliance with manipulated variable restrictions

The speed control receives a setpoint speed from higher-level functions. However, it can not be guaranteed that it can be performed by the pump. Therefore, the target speed at the next time (j + l) should be modified so that

Manipulated variable restrictions are met and therefore the speed can be achieved by the pump. In the following, by (3.4) an upper bound (d ⁺¹ _max and lower Barrier (d ⁺¹ _mm calculated for the setpoint speed within which the manipulated variable restrictions are complied with The setpoint speed is limited by the barriers:

The two bounds can be calculated by (3.4). By solving (3.4) for C ^ ⁺¹ and using the maximum stress you get the upper bound:

By inserting the minimum voltage U = U _mm , the lower barrier is obtained.

By (4.1) - (4.3) can thus be ensured that manipulated variable restrictions are met. However, very large current gradients can still occur. The

Limitation of current gradients will be described below.

Limitation of the stoma gradient

a. Limitation of motor current gradient

From the torque balance (1.1), the current can be expressed in the time m as a function of the load torque and the spin.

¹ = - 1 ^T load + ^Jω ) ^κ . (5.1)

To limit the current gradient, the change in the current between the sampling steps is decisive. By (5.1) the current change can be determined depending on the load torque change and the rotational acceleration change:

.DELTA.i ^{j + 1} = i ^{j i +} ^j = -i - ^ ^{(j + i} ώ -ώ 'H- ^ fc -TU)

^KK (5.2) By inserting the maximum permissible current change Δi _max one thus obtains the maximum

Spin: ώ ^ = γΔi _{max +} ώ ^J -ifc -T ₁ i _ad )

It should be noted that the load torque change due to the unknown load torque at time j + 1 is approximated by the load torque change of the last cycle. Thus, by linear approximation of the spin acceleration, a further condition for the new setpoint speed ω _d ^{J + 1 is obtained} :

, ω ^{J + 1} -ω ^J ^Δt (5.4) ω, ^{J + 1} = ω ^J + Δtώitl

The new setpoint speed is thus subject to the restriction (4.1) of the restriction ω ^{d J + 1} <ω ^{> J + 1} . (5.6) Under nominal conditions (no model error, ideal load moment estimation) condition (5.6) can therefore be used to maintain the permitted motor current gradient. It should be noted that both model errors and faulty load moment estimates can lead to deviations.

b. Limit battery current gradient

Decisive for the on-board load is not directly the motor current i _mot , but the battery current i _bat required by the PWM generator. FIG. 5c shows the PWM generator with its interfaces.

Due to the smoothing of the battery current through filters and the high clock frequency, it is assumed that averaged DC voltages. The motor voltage is calculated as a function of the PWM duty cycle and the battery voltage:

U _mot = PWM U _bat _ _{(5 7)} Considering the power balance of the PWM generator

^ bat bat ^ mot mot is obtained for the battery current i _bat = i _mot PWM _ For the current gradient of the battery voltage the following applies: i _bat = L _t PWM + i _mot PWM or written with differences follows

Δi £ = Δi ^ _t PWM ^J + i ^ _ot ΔPWM ^{J + 1} _ _{(5 g)}

The motor current of the last cycle i _mot ^J and the PWM ^J can be calculated from known quantities of the last cycle:

U ¹ - Kωi

^ mot

R

U ¹

PWM ^] = ^■ ^Uba "(5.10)

The motor current difference can be expressed using the equation of motion as follows

If you replace the spin of the j + 1 cycle by the corresponding one

Difference approximation is obtained

Ai ^{J + ι} = - ω ^J \ + - AT = ω ⁷ ω ^J ω ^J + - K At K KAt KAt KK ^{ki k} *. (5.12)

The change in the PWM is calculated from the quotient of the supply voltage U to the battery voltage U _ba t:

U ^{J +} 1 APWM ^{J +} ¹ = PWM ^{J +} ¹ -PWM ¹ = PWM ¹ . ^Uba "(5.13)

The calculation of the supply voltage U has already been derived above (see (3.4)):

In order to prevent repercussions of the regulation on the trajectory planning, the rule portion is neglected in this case. Put this into the change of the PWM: APWM ^{J + 1} = - - ⁺ - ^ - PWM ^] = - ^ ω ^{J + 1} + - ^ - PWM ^J

U construction U b, au ^k " ^kl (5.15)

By substituting (5.12) and (5.15) into (5.9) one obtains

AC (5.16)

Or resolved according to the speed C ^ ⁺¹ :

If one sets the maximum permissible value for the battery current change, one obtains the associated setpoint speed:

(5.18)

Claims

claims

1. A method for controlling and / or regulating an electric motor, wherein it is provided that

- The electric motor (180, 220) from a battery (130, 230) and / or a generator (150, 190, 210) is supplied with electrical energy and

- For controlling and / or regulating a high-frequency pulse width modulated voltage is applied to the electric motor, characterized in that the at start-up of the electric motor for operating the electric motor from the battery and / or the generator supplied motor current (I _M ) is continuously increased.

2. The method according to claim 1, characterized in that the increase of the motor current is limited to a predetermined desired value in a predetermined time.

3. The method according to claim 2, characterized in that the desired value as a function of operating parameters

- Of the generator and / or - the battery is specified, in particular, it is provided that the desired value in dependence

- From the generated current increase of the generator and / or

- Is specified by the discharge of the battery.

4. The method according to any one of claims 2 or 3, characterized in that the electric motor for limiting the current gradient at most with a predetermined Target speed (ω / ⁺¹ ) is operated, in particular, it is provided that the

Target speed depending on

- the battery voltage, and / or

- Given the load torque on the electric motor.

5. The method according to any one of the preceding claims, characterized in that it is provided that further consumers (160) are supplied by the battery and / or the generator with electrical energy, wherein the continuous increase in dependence on the supply of further consumers with electrical Energy is provided.

6. The method according to claim 5, characterized in that a supply of the further consumer is effected by the battery, whereas a supply of the electric motor takes place at least during the start-up phase by the generator.

7. Device for controlling and / or regulating an electric motor, wherein

- The electric motor (180, 220) by means of a battery (130, 230) and / or a generator (150, 190, 210) is supplied with electrical energy and

- Means (100, 200) for controlling and / or regulating the electric motor by means of a voltage applied to the electric motor high-frequency pulse width modulated voltage, characterized in that the means at the start of the electric motor for the operation of the electric motor from the

Battery and / or the motor current supplied to the generator (I _M ) continuously increased.

8. The device according to claim 7, characterized in that the means limits the increase of the motor current in a predetermined time to a predetermined desired value.

9. Apparatus according to claim 8, characterized in that the means the desired value in dependence - of operating parameters of the generator and / or

- Specifies the battery, which is provided in particular that - the desired value as a function of the generated current increase of the generator and / or

- Is specified by the discharge of the battery.

1 O.Vorrichtung according to any one of claims 8 or 9, characterized in that the electric motor for limiting the current gradient at most with a predetermined

Target speed (ω / ⁺¹ ) is operated, in particular, it is provided that the target speed in dependence of

- the battery voltage, and / or

- Given the load torque on the electric motor.

11. Device according to one of claims 7 to 10, characterized in that it is provided that further consumers (160) are supplied by the battery and / or the generator with electrical energy, wherein the continuous increase in dependence on the supply of other consumers is provided with electrical energy, wherein it is provided in particular that a supply of further consumers by the battery takes place, whereas a supply of the electric motor takes place at least during the start-up phase by the generator.