DE102010021865A1 - Method for controlling synchronous machine e.g. three-phase motor, involves regulating flux-forming current component of motor current such that regenerative energy generated in motor is transformed into heat - Google Patents

Abstract

The method involves determining a stator current space vector, and calculating torque and a flux-forming current component. The flux-forming current component of motor current is regulated such that regenerative energy generated in the motor is transformed into heat. Inverter supply voltage i.e. intermediate supply voltage, is detected and regulated to a predetermined set point. A deviation of direct current voltage is supplied to a linear regulator element at a nominal value. An output signal is used as a reference value for regenerative operation of a synchronous motor (6). Independent claims are also included for the following: (1) a method for braking a synchronous machine (2) an inverter powered synchronous machine comprising a controller.

Description

The invention relates to a method for controlling or decelerating a synchronous machine and a converter-fed synchronous machine.

In modern electric drives increasingly inverter-fed synchronous machines are used. In particular, the embodiment of the synchronous machine with permanent magnets in the rotor allows high system efficiencies, since no ohmic pathogen losses can occur.

As a control system, a field-oriented control is often used, wherein a Statorstromraumzeiger is determined and from a moment-forming and flow-forming current component is determined, these values are subtracted from corresponding setpoints and control units are supplied, which generate a setpoint voltage space pointer as the output, from which in turn drive signals for the circuit breakers of an inverter. The setpoint for the torque-forming current is often determined by means of functional dependence of a torque setpoint and the setpoint of the flow-forming d-current is set to zero in the base speed range.

A negative torque setpoint leads to deceleration at a positive actual speed, that is to say the reduction in magnitude of the actual speed, and a positive torque setpoint leads to deceleration of the synchronous motor operated by field-oriented control when the actual speed is negative. In both regenerative operating cases, mechanical motion / rotational energy is converted into electrical energy. This in turn causes the voltage at the usual DC link capacitor increases. For reasons of safety, this DC link voltage must not exceed a limit value.

In order to keep the DC link voltage below this limit, in practice often two different solution variants are used. In the first variant, known as power feedback, the network-side rectifier is provided with controllable switches that can be controlled via a control unit in a control electronics. This makes it possible to control the power flow between the network and the DC link capacitor. A second common variant is the connection of a braking resistor to the DC link capacitor, wherein between resistor and capacitor sits a controllable switch.

However, both variants have the disadvantage that the costs of the inverter-fed synchronous machine increase due to the additional expenditure on the components.

In order to avoid the disadvantage of increased system costs, a method is required which makes it possible to brake a converter-fed synchronous machine without additional expenditure of components.

In the European patent application EP 0 742 637 A1 a method for decelerating a converter fed synchronous machine is described in which an armature short circuit is cyclically established by one inverter bridge is securely locked and the other inverter bridge is driven by a clocked signal, the frequency of the drive signal z. B. depends on a mechanic-specific characteristic.

In the German patent DE 100 59 173 C1 will the procedure of EP 0 742 637 A1 developed by an electronic circuit, the cyclic armature short circuit is combined in a very advantageous manner with the method of impulse prerence of power semiconductors in case of failure.

In the also German patent DE 103 00 953 B4 A method is presented which makes it possible to decelerate a rotary field machine fed by a power converter by switching from the conventional field-oriented control to a method which determines a target voltage vector by multiplying a detected stator current space pointer with a complex impedance.

All methods have the disadvantage that they can not be combined with a field-oriented control, the braking torque can not be controlled exactly and the resulting DC link voltage is not taken into account.

In the published patent application DE 198 46 079 A1 A method is described of how an AC motor can be decelerated by subtracting the measured intermediate circuit voltage from a reference voltage and supplying it to a control unit, limiting the torque-forming setpoint to the limited output value of the control unit and determining a set value for the flux-forming current component by is subtracted from the setpoint of the torque-forming current component of the maximum allowable moment-forming current component and a second control unit is supplied, wherein the limited output value is used as a flux-forming setpoint.

In principle, this is a cascaded rule structure, where the inner loop must always be faster than the outer loop. The disadvantage here is the low maximum control dynamics of the outer control loop and the associated danger of overshoot of the DC link voltage as a result Braking torque request realized via the fastest control circuit, the stator current control circuit. Particularly with small capacitance values of the DC link capacitor, the described problem is intensified.

task

The invention is therefore an object of the invention to develop a method for controlling or decelerating a synchronous machine, which allows a controlled braking an inverter-fed synchronous machine, with a regenerative power supply and a braking resistor can be saved and the DC link voltage is safely kept below a certain threshold and with a field-oriented control can be combined.

According to the invention the object is achieved in the method for controlling a synchronous machine according to claim 1, in the method for braking a synchronous machine according to the in claim 9 and in the inverter-fed synchronous machine according to the features indicated in claim 15.

Important features of the invention in the method for braking a synchronous machine are that
a nominal mechanical power is calculated from a torque setpoint and a mechanical angular velocity,
wherein this mechanical target power is limited in the generator case to a power whose value is at most as large as the maximum allowable power loss of the inverter-fed synchronous machine,
wherein a limited setpoint torque is determined from this limited mechanical target power and the mechanical angular speed,
wherein this limited target torque is converted by means of functional dependency into a setpoint value for the torque-forming q-current component,
wherein the difference between desired value and an actual value of the intermediate circuit energy are supplied to a DC link energy control unit,
the intermediate circuit energy control unit having as its output a power which is multiplied by the reciprocal of the ohmic resistance and thus the square of a desired leakage current is determined,
wherein the squared of the desired leakage current, the square of the torque-forming q-current component is subtracted, then limited to the lower limit of zero and is determined by pulling the square root of the setpoint of the flow-forming d-current.

The advantage here is that the generator target power is limited so that their amount is at most as large as the maximum allowable power loss, which can be ensured in combination with a DC link regulator that the DC link energy remains below a system-specific limit.

Another advantage of the method according to the invention is that the deceleration of the inverter-fed synchronous machine can be performed with the maximum allowable power. This can be significantly higher than the maximum continuous power loss of the inverter-fed synchronous machine.

Furthermore, it is advantageous that the limited target torque depends directly on the mechanical angular velocity, which means that the braking torque at desired or maximum braking power directly and without delay is correspondingly larger when the amount of the actual speed decreases, which means a constant braking power.

Furthermore, it is advantageous that the path of action of the power loss has the square of the desired leakage current as the initial value from which the square of the moment-forming current component, which depends directly on the nominal torque, is subtracted, whereby the square of the nominal value for the flux-forming d-current can be determined , In this way, it is possible that exactly the power loss is realized in the inverter-fed synchronous machine was desired.

Furthermore, it is advantageous that the limitation of the square of the nominal value of the flow-forming d-current component to the lower limit of zero allows the square root to be drawn and thus only losses due to d-current can be realized if the desired loss setpoint is greater than or equal to zero , This is the case when the desired losses are greater than the losses caused by the torque-generating q-current component.

In an advantageous embodiment of the invention, the desired power loss is pre-controlled by a value is added to the output value of the Zwischenkreisenergiereglers, which is proportional to the amount of the limited mechanical target power.

The advantage here is that thus can be better prevented that the DC link energy increases due to a change in the torque setpoint.

In a further advantageous embodiment of the invention, the value of the ohmic resistance is tracked over the temperature.

The advantage here is that the ohmic power loss is known in more detail.

In a further advantageous embodiment of the invention, the maximum permissible current I _max is limited by a thermal protection model so that the protection of motor and inverter is guaranteed.

The advantage here is that during braking the amount of maximum allowable current (I _max ) can be selected according to the maximum allowable overload limits of inverter and motor, the thermal protection is ensured by the thermal protection model. This makes a deceleration process possible at the physical limits of the inverter-fed synchronous machine.

In a further advantageous embodiment of the invention, the output value of the DC link energy regulator is divided into different active paths, that both the power loss and the regenerative power can be influenced.

The advantage here is that when reaching the current limit, which connected and no further increase in the ohmic power loss is possible, an increase in the DC link energy can be prevented that the limited regenerative target power is reduced in amount.

Important features in the synchronous machine for carrying out the aforementioned method are that the synchronous machine is fed by a converter having control electronics, comprising a controller, wherein the control electronics drive signals for semiconductor switch of an inverter of the inverter, wherein the synchronous machine can be fed from the inverter ,

Further advantages emerge from the subclaims. The invention is not limited to the combination of features of the claims. For the skilled person, further meaningful combination possibilities of claims and / or individual claim features and / or features of the description and / or figures, in particular from the task and / or posing by comparison with the prior art task arise.

In the following the invention will be explained in more detail with reference to figures and an embodiment.

1 shows a synchronous motor 006 the one with an inverter 004 is connected, wherein the inverter 004 with an electronic unit / control electronics 005 , with a DC link capacitor 003 and with a rectifier 002 is connected and where the rectifier 002 with an electrical alternating voltage network 001 connected is.

The synchronous motor 006 is designed as a three-phase motor, the mounted on the stature windings are referred to as stator windings and mounted on its opposite the stature of the motor rotatably mounted rotor permanent magnets or has an excitation field winding which is traversed by the formation of magnetic poles of direct current.

2 shows how the inventive method 001 in a field-oriented control 100 operated synchronous machine 401 can be integrated. The stator windings of the synchronous machine 401 are with an inverter 201 connected, wherein at least two of the three stator currents are detected by measurement 301 and a current vector is determined whose components z. B. in the stator-fixed coordinate system with the two axis names α and β can be displayed. In a transformation unit 106 the current vector represented in the stator coordinate system, which can also be called a current space vector, is transformed into the field coordinate system using a so-called field angle. The axes of the field coordinate system, also referred to below as the dq coordinate system, point in the direction of the moment-forming q-current component and in the direction of the flux-forming d-current component. The field angle can be determined with the help of a encoder angle 402 be determined 107 or by a model 108 whose input variables z. B. the current space pointer of the actual current in Statorkoordinaten and the Sollspannungsraumzeiger are determined. Are both units 107 . 108 To determine the field angle, an angle must be selected 109 , Often, by means of a speed calculation unit 111 determined by differentiation or a model, an angular velocity z. B. is required by a parent speed control unit.

The control unit of the flow-forming d-current component 103 , which preferably has a P- and an I-channel, becomes the difference between d-current setpoint and d-current actual value 101 supplied wherein the manipulated variable of the control unit is a voltage.

The control unit of the torque-generating q-power component 104 , which preferably has a P- and an I-channel, becomes the difference between the q-current setpoint and the q-current actual value 102 supplied, wherein the manipulated variable of the control unit is a voltage.

In another transformation unit 105 becomes that of the stator current control units 103 . 104 outputted Sollspannungsraumzeiger transformed by the field coordinate system using the field angle in the stator fixed αβ coordinate system.

Another unit 110 determined from the Sollspannungsraumzeiger, shown in the stator fixed αβ coordinate system, using the voltage at the DC link capacitor, the drive signals for the power semiconductors in the inverter 201 ,

The inventive method 001 , has as input values the setpoint and the actual value of the intermediate _{circuit energy} , the torque setpoint and the mechanical angular velocity and as output values the setpoint values for the two stator current _regulators (i _{d_soll} , I _{q_soll} ).

ermittelt werden, wobei die Ermittlung des Istwertes der Zwischenkreisenergie inThe setpoint and actual value of the DC link energy can according to

be determined, wherein the determination of the actual value of the DC link energy in

2 in the block with the label 002 is carried out.

3 shows a first embodiment of the present invention, wherein in a first inventive step, the maximum possible mechanical target power (P _{mech_soll_begrenzt} ) is calculated by the vorgebare by a parent system, target torque (M _soll ) with the mechanical angular velocity (ω _mech ) is multiplied and then limited to a negative, valid for the generator case, power _{limit value} (-P _{v_max} = -I _max ² · R) is limited.

If the maximum possible ohmic losses are taken into account in this regenerative limit value, it is ensured that the amount of the limited mechanical nominal power is smaller than the maximum possible total power loss, which u. a. still includes friction and iron losses.

In a further method step according to the invention, the limited mechanical nominal power is divided by the mechanical angular velocity and limited one target _torque (M _{soll_begrenzt} ) determined, which is converted taking into account a functional dependence in a target value of the torque-forming q-current.

In an advantageous embodiment, it is recognized that the mechanical power must also be zero at zero mechanical angular velocity, which in turn means that the previous limit was not engaged and when intercepting the division by zero, the original torque reference to the target current determination (determination of a q-current setpoint via functional dependency) can be passed on.

In a further method step according to the invention, the actual value of the intermediate circuit energy is subtracted from the nominal value of the intermediate circuit energy and fed to a control unit for the intermediate circuit energy, which preferably has a P channel and an I channel, wherein the control value of the control unit is a power (P _R ) , If no sign inversion is performed in the control unit of the DC link energy, this must be done separately by B. multiplied by the value minus one, wherein the result is referred to as a power dissipation target value (P _{v_soll} ).

In a further method step according to the invention, the desired power loss (P _{v_setpoint} ) is divided by the ohmic resistance value, whereby the square of a desired leakage current is determined, wherein in an advantageous embodiment the ohmic resistance value is tracked over the temperature.

In a further method step according to the invention, the square of the determined target leakage current is subtracted from the square of the torque-forming desired q-current, whereby the square of a d-current nominal value is determined, which is limited to the lower limit of zero, and finally, by pulling the square root, a nominal value for the d-current is formed.

4 shows a second embodiment of the present invention, which is based on the first embodiment.

In this case, when limiting the mechanical target power (P _{mech_soll} ), an upper limit value (P _{mech_max} ) is used, which is based on the maximum desired or permissible motor power.

In a further method step, the output of the intermediate circuit energy regulator (P _R ) multiplied by the factor 0.5 and the positive limit of zero and the negative limit value (-P _{mech_max} ) is limited and this limited value (ΔP _mech ) is deducted from the limited mechanical nominal power (P _{mech_soll_begrenzt} ). Since the change of the nominal mechanical power (ΔP _mech ) through the limitation takes on the maximum value of zero, in the regenerative case (P _{mech_soll_begrenzt} <0), the braking torque can not be increased, which in turn means that the power _{flow into the DC bus} does not increase over this path can be. However, the DC link controller can shift the setpoint power in the direction of motor operation via this path, which means that energy is drawn from the DC link.

The second path of action of the manipulated variable of the intermediate circuit energy regulator is based on the desired power loss, wherein a change in the desired power loss (ΔP _v ) is formed by the part of the first path which can not be realized due to the limitation (ΔP _mech - 0.5 · P _R ) Half the controller output power (0.5 · P _R ) is subtracted. This ensures that the value specified by the controller (P _R ) can be realized within the valid current limits.

The desired power loss (P _{v_soll} ) is formed by _{subtracting from the desired} change of the power loss (ΔP _v ) the limited mechanical target power (P _{mech_soll_begrenzt} ). This realizes efficient precontrol.

In a further method step _according to the invention, the desired power loss (P _{v_setpoint} ) is limited to the positive limit value (I _max ² * R) and the negative limit value of zero, which ensures that no additional artificial losses are generated during motor operation.

In contrast to the first embodiment, the square of the d-current setpoint (I _{d_setpoint} ² ) is limited not only to the lower limit of zero, but also to the upper limit of the maximum allowed current square (I _max ² ).

In an advantageous embodiment of the determined setpoint of the flow-forming d-current is provided with a negative sign, so that this acts field weakening, which increases the voltage reserve of the subordinate current control algorithms.

LIST OF REFERENCE NUMBERS

M _shall

Torque setpoint

M should be _limited

limited torque setpoint

ω _mech

mechanical angular velocity

P _{mech_soll}

mechanical nominal power

P _{mech_soll_begrenzt}

limited mechanical target power

P _{mech_max}

maximum permitted mechanical power

W _should

Setpoint of the energy stored in the voltage intermediate circuit

W _is

Actual value of the energy stored in the voltage intermediate circuit

U _{z_soll}

Setpoint of the voltage of the DC link capacitor

U _{z_ist}

Actual value of the voltage of the DC link capacitor

P _R

Manipulated variable of the intermediate circuit energy regulator

ΔP _mech

Change in mechanical nominal power caused by the intermediate circuit regulator

ΔP _v

Change request of the power loss

P _{v_soll}

Setpoint of the power loss

P _{v_soll_begrenzt}

limited setpoint of the power loss

P _{v_max}

maximum permitted power loss

I _max

maximum permitted amount of electricity

I _{v_soll}

Setpoint of the power loss current

I _{q_soll}

Setpoint of the torque-generating current

I _{d_soll}

Setpoint of the flow-forming current

I _{d_soll_begrenzt}

limited setpoint of the flux-forming current

R

ohmic resistance

C

Capacitance value of the DC link capacitor

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• EP 0742637 A1 [0008, 0009]
• DE 10059173 C1 [0009]
• DE 10300953 B4 [0010]
• DE 19846079 A1 [0012]

Claims (15)

A method for controlling a synchronous machine, in particular a synchronous motor, in particular wherein the synchronous machine by an inverter and / or inverter is fed, characterized in that the Statorstromraumzeiger is determined and from a moment-forming and a flow-forming current component is determined, wherein the flow-forming current component of the motor current on a setpoint value is controlled so that regenerated energy generated in the engine is converted into heat. Method according to at least one of the preceding claims, characterized in that the intermediate circuit voltage, in particular therefore the voltage supplying the inverter, is detected and regulated to a predefinable desired value, in particular, by determining the desired value for the flow-forming d-current component from the deviation from the desired value. Method according to at least one of the preceding claims, characterized in that the deviation of the intermediate circuit voltage is fed to its setpoint a linear regulator member, in particular a PI member, and the output signal is used as the setpoint for the flow-forming current component, in particular in the generator mode of the synchronous machine, especially not in engine operation. Method according to at least one of the preceding claims, characterized in that the deviation of the flow-forming current component from its setpoint to a linear controller element, in particular a PI element, is supplied and the output signal is used as a control value, in particular wherein the output signal, the proportion of the inverter to in the direction of the flow-forming current component. Method according to at least one of the preceding claims, characterized in that the torque-forming current component is regulated to a desired value, in particular wherein the desired value corresponds to a predetermined braking torque. Method according to at least one of the preceding claims, characterized in that the desired value for the moment-forming current component is determined from a current-dependent characteristic, in particular wherein the characteristic describes a dependence of the torque on the motor current. Method according to at least one of the preceding claims, characterized in that by means of a heat model for the synchronous machine, a temperature value is formed and when a critical temperature value, an action is performed, such as issuing a warning information, displaying a warning information, switching off the synchronous machine and / or the inverter , Triggering a brake and / or reducing the braking torque. Method according to at least one of the preceding claims, characterized in that the synchronous machine is permanently energized, in particular therefore the rotor has permanent magnets for generating a permanent magnetic field, in particular in the de-energized state of the synchronous machine Method for decelerating a synchronous machine, in particular a converter-fed synchronous motor, characterized in that a nominal mechanical power is calculated from a torque setpoint and a mechanical angular velocity, wherein this mechanical target power is limited in the generator case to a power whose value is at most as large as the maximum allowable power loss of the inverter-fed synchronous machine, wherein a limited setpoint torque is determined from this limited mechanical target power and the mechanical angular speed, wherein this limited target torque is converted by means of functional dependency into a setpoint value for the torque-forming q-current component, wherein the difference between desired value and an actual value of the intermediate circuit energy are supplied to a DC link energy control unit, the intermediate circuit energy control unit having as its output a power which is multiplied by the reciprocal of the ohmic resistance and thus the square of a desired leakage current is determined, wherein the squared of the desired leakage current, the square of the torque-forming q-current component is subtracted, then limited to the lower limit of zero and is determined by pulling the square root of the setpoint of the flow-forming d-current. Method according to at least one of the preceding claims, characterized in that the desired power loss is precontrolled by a value is added to the output value of the Zwischenkreisenergiereglers, which is proportional to the amount of the limited mechanical target power. Method according to at least one of the preceding claims, characterized in that the value of the ohmic resistance is tracked over the temperature. Method according to at least one of the preceding claims, characterized in that a thermal protection model, the maximum current I _max limited so that protection of the motor and inverter is guaranteed. Method according to at least one of the preceding claims, characterized in that the output value of the DC link energy regulator is divided into different paths of action, that both the power loss and the regenerative power can be influenced. Method according to at least one of the preceding claims, characterized in that the control of the intermediate circuit energy is effected in that a control unit of the setpoint and actual value of the intermediate circuit voltage is supplied. Inverter-fed synchronous machine for carrying out a method according to at least one of the preceding claims, characterized in that the synchronous machine is fed by a converter which has control electronics comprising a regulator, the control electronics having drive signals for semiconductor switches of an inverter of the converter, wherein the synchronous machine can be fed from the inverter.

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