DE102010021865B4 - Method for controlling or braking a synchronous machine and a converter-fed synchronous machine - Google Patents

Abstract

Method for controlling a synchronous machine, namely a synchronous motor, wherein the synchronous machine can be fed by an inverter or converter, characterized in that the intermediate circuit energy (Wact) is recorded and regulated to a predeterminable setpoint (WSoll), the stator current space vector is determined and from this torque-forming and a flow-forming current component (iq_Soll, id_Soll) is determined, whereby the flow-forming current component of the motor current is regulated to such a target value (id_Soll) that generator-generated energy is converted into heat in the motor, with the deviation of the intermediate circuit energy (Wact) from its Setpoint (WSoll) is fed to a linear controller element and the output signal is used as a setpoint (id_Soll) for the flow-forming current component in the generator operation of the synchronous machine.

Description

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

Converter-fed synchronous machines are increasingly being used in modern electric drives. In particular, the embodiment of the synchronous machine with permanent magnets in the rotor enables high system efficiencies because no ohmic excitation losses can occur.

A field-oriented control system is often used as a control system, whereby a stator current space vector is determined and from this a torque-forming and flux-forming current component is determined, these values being subtracted from corresponding setpoints and control units being fed, which generate a target voltage space vector as an output variable, from which control signals are in turn for the circuit breakers of an inverter. The setpoint for the torque-forming current is often determined by means of a functional dependency from a torque setpoint and the setpoint of the flux-forming d-current is set to the value zero in the basic speed range.

A negative torque setpoint leads to braking when the actual speed is positive, i.e. a reduction in the amount of the actual speed, and a positive torque setpoint leads to braking of the synchronous motor operated by means of field-oriented control when the actual speed is negative. In both generator operating cases, mechanical kinetic/rotational energy is converted into electrical energy. This in turn causes the voltage on the usual intermediate circuit capacitor to increase. For protection reasons, this intermediate circuit voltage must not exceed a limit value.

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

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

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

In the European patent application EP 0 742 637 A1 A method for braking a converter-fed synchronous machine is described in which an armature short circuit is cyclically produced by safely blocking one inverter bridge and controlling the other inverter bridge by a clocked signal, the frequency of the control signal depending, for example, on a mechanics-specific characteristic curve.

In the German patent specification DE 100 59 173 C1 will be the procedure of EP 0 742 637 A1 further developed by using an electronic circuit to combine the cyclic armature short circuit in a very advantageous manner with the process of pulse blocking of power semiconductors in the event of a fault.

In the patent specification, which is also German DE 103 00 953 B4 A method is presented that makes it possible to brake an induction machine fed by a power converter by switching from the usual field-oriented control to a method that determines a target voltage vector by multiplying a detected stator current space vector by a complex impedance.

All methods have the disadvantage that they cannot be combined with field-oriented control, the braking torque cannot be controlled precisely and the resulting intermediate circuit voltage is not taken into account.

In the disclosure document DE 198 46 079 A1 describes a method of how an AC motor can be braked by subtracting the measured intermediate circuit voltage from a reference voltage and supplying it to a control unit, whereby the torque-forming setpoint is limited to the limited output value of the control unit and a setpoint for the flux-forming current component is determined by The maximum permitted torque-forming current component is subtracted from the setpoint of the torque-forming current component and fed to a second control unit, the limited output value of which is used as the flow-forming setpoint.

In principle, this is a cascaded rule structure, with the inner rule The control loop must always be faster than the outer control loop. The disadvantage here is the low maximum control dynamics of the outer control loop and the associated risk of the intermediate circuit voltage overshooting as a result of a braking torque requirement that is implemented via the fastest control loop, the stator current control loop. The problem described increases in particular with small capacitance values of the intermediate circuit capacitor.

From the DE 195 09 974 C2 The closest prior art is a method for braking an AC motor.

From the DE 10 2007 022 515 A1 a method and a device for operating a control unit for controlling an electrical machine are known.

From the DE 10 2005 034 635 A1 a wind turbine generator is known.

From the DE 101 06 944 A1 a method for temperature control of an electrical machine is known.

Task

The invention is therefore based on the object of developing a method for regulating or braking a synchronous machine, which enables controlled braking of a converter-fed synchronous machine, whereby a mains regeneration and a braking resistor can be saved and whereby the intermediate circuit voltage is safely kept below a certain limit value can be combined with a field-oriented control.

According to the invention, the object is achieved in the method for controlling a synchronous machine according to the features specified in claim 1, in the method for braking a synchronous machine according to the features specified in claim 9 and in the converter-fed synchronous machine according to the features specified in claim 13.

Important features of the invention in the method for braking a synchronous machine are that
A mechanical target power is calculated from a torque setpoint and a mechanical angular velocity,
whereby in the generator case this mechanical target power is limited to a power whose value is at most as large as the maximum permitted power loss of the converter-fed synchronous machine,
whereby a limited target torque is determined from this limited mechanical target power and the mechanical angular velocity,
whereby this limited target torque is converted into a target value for the torque-forming q-current component using functional dependency,
whereby the difference between the setpoint and an actual value of the intermediate circuit energy is supplied to a DC link energy control unit,
wherein the intermediate circuit energy control unit has a power as an output variable, which is multiplied by the reciprocal of the ohmic resistance and thus the square of a target loss current is determined,
whereby the square of the torque-forming q-current component is subtracted from the square of the target loss current, then limited to the lower limit of zero and the target value of the flux-forming d-current is determined by taking the square root.

The advantage here is that the regenerative target power is limited so that its amount is at most as large as the maximum permitted power loss, which, in combination with a DC link energy controller, can ensure that the DC link energy remains below a system-specific limit value.

A further advantage of the method according to the invention is that the braking process of the converter-fed synchronous machine can be carried out with the maximum permitted power. This can be significantly higher than the maximum continuous power loss of the converter-fed synchronous machine.

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

It is also advantageous that the effective path of the power loss has the square of the target loss current as an initial value from which the square of the torque-forming current component, which depends directly on the target torque, is subtracted, whereby the square of the target value for the flux-forming d-current can be determined . This makes it possible to achieve exactly the power loss that was desired in the converter-fed synchronous machine.

It is also advantageous that limiting the square of the setpoint value of the flow-forming d-current component to the lower limit of zero enables the square root to be taken and so that losses due to d-current are only realized if the desired loss setpoint is greater than/equal to zero. This is exactly the case when the desired losses are greater than the losses caused by the torque-forming q-current component.

In an advantageous embodiment of the invention, the target power loss is pre-controlled by adding a value to the output value of the intermediate circuit energy controller, which is proportional to the amount of the limited mechanical target power.

The advantage here is that it can be even better prevented that the intermediate circuit energy increases as a result of a change in the torque setpoint.

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

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

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 the motor and converter is guaranteed.

The advantage here is that during the braking process, the amount of the maximum permissible current (I _max ) can be selected according to the maximum permissible overload limits of the converter and motor, with thermal protection being guaranteed via the thermal protection model. This makes it possible to brake at the physical limits of the converter-fed synchronous machine.

In a further advantageous embodiment of the invention, the output value of the intermediate circuit energy controller is divided into different effective paths so that both the power loss and the regenerative power can be influenced.

The advantage here is that when the current limit is reached, which means that no further increase in the ohmic power loss is possible, an increase in the intermediate circuit energy can be prevented by reducing the amount of the limited regenerative target power.

Important features of the synchronous machine for carrying out the aforementioned method are that the synchronous machine is fed by a converter which has control electronics comprising a controller, the control electronics having control signals for semiconductor switches of an inverter of the converter,
whereby the synchronous machine can be fed from the inverter.

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

The invention is explained in more detail below using illustrations and an exemplary embodiment.

1 shows a synchronous motor 006 which is connected to an inverter 004, wherein the inverter 004 is connected to an electronic unit/control electronics 005, to an intermediate circuit capacitor 003 and to a rectifier 002, and wherein the rectifier 002 is connected to an electrical alternating voltage network 001.

The synchronous motor 006 is designed as a three-phase motor, the windings attached to the stator being referred to as stator windings and permanent magnets being mounted on its rotor, which is rotatably mounted relative to the stator of the motor, or which has an excitation field winding through which direct current flows to form magnetic poles.

2 shows how the method 001 according to the invention can be integrated into a synchronous machine 401 operated by means of field-oriented control 100. The stator windings of the synchronous machine 401 are connected to an inverter 201, with at least two of the three stator currents being detected by measurement 301 and a current vector being determined, the components of which can be represented, for example, in the stator-fixed coordinate system with the two axis designations α and β. In a transformation unit 106, the current vector represented in the stator coordinate system, also referred to as a current space vector, is transformed into the field coordinate system using a so-called field angle. The axes of the field coordinate system, hereinafter also referred to as the dq coordinate system, point in the direction of the torque-forming q-current component and in the direction of the flux-forming d-current component. The field angle can be adjusted using a sensor Angle 402 can be determined 107 or by a model 108, the input variables of which are, for example, the current space vector of the actual current in stator coordinates and the target voltage space vector. If both units 107, 108 are present for determining the field angle, an angle must be selected 109. An angular velocity is often determined by means of a speed calculation unit 111 through differentiation or via a model, which is required, for example, by a higher-level speed control unit.

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

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

In a further transformation unit 105, the target voltage space vector output by the stator current control units 103, 104 is transformed from the field coordinate system into the stator-fixed αβ coordinate system using the field angle.

A further unit 110 determines the control signals for the power semiconductors in the inverter 201 from the target voltage space vector, shown in the stator-fixed aß coordinate system, using the voltage at the intermediate circuit capacitor.

The method 001 according to the invention 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 setpoints for the two stator current controllers ( _{id_soll} , i _{q_soll} ).

$$W_{ist}=\frac{1}{2}\cdot C\cdot U_{z\_mess}^2$$

ermittelt werden, wobei die Ermittlung des Istwertes der Zwischenkreisenergie in 2 im Block mit der Beschriftung 002 durchgeführt wird. 3 zeigt eine erste Ausführungsform der vorliegen Erfindung, wobei in einem ersten erfindungsgemäßen Verfahrensschritt die maximal mögliche mechanische Sollleistung (P_{mech_soll_begrenzt}) berechnet wird, indem das, von einem übergeordneten System vorgebare, Solldrehmoment (M_soll) mit der mechanischen Winkelgeschwindigkeit (ω_mech) multipliziert wird und anschließend auf einen negativen, für den generatorischen Fall gültigen, Leistungsgrenzwert (-P_{v_max}=-I_max ²*R) begrenzt wird.The setpoint and actual value of the DC link energy can be set according to $$W_{sOll}=\frac{1}{2}\cdot C\cdot U_{\mathrm{e.g}\_sOll}^2$$

$$W_{ist}=\frac{1}{2}\cdot C\cdot U_{\mathrm{e.g}\_mess}^2$$

can be determined, whereby the actual value of the intermediate circuit energy is determined in 2 is carried out in the block labeled 002. 3 shows a first embodiment of the present invention, wherein in a first method step according to the invention the maximum possible mechanical target power (P _{mech_soll_limited} ) is calculated by multiplying the target torque (M _target ) specified by a higher-level system with the mechanical angular velocity (ω _mech ). and then limited to a negative power limit value (-P _{v_max} =-I _max ² *R) that is valid for the generator case.

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

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

In an advantageous embodiment, it is recognized that the mechanical power must also be zero at a mechanical angular velocity of zero, which in turn means that the previous limit was not engaged and when the division by zero is intercepted, the original torque setpoint is sent to the setpoint 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 current actual value of the intermediate circuit energy is subtracted from the setpoint 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, the control value of the control unit being a power (P _R ). . If no sign inversion is carried out in the DC link energy control unit, this must be carried out separately, for example by multiplying by the value minus one, whereby the result is referred to as the power loss setpoint (P _{v_soll} ).

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

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

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

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

In a further process step, the output variable of the intermediate circuit energy controller (P _R ) is multiplied by a factor of 0.5 and limited to the positive limit value of zero and the negative limit value (-P _{mech_max} ) and this limited value (ΔP _mech ) is limited mechanical target power (P _{mech_soll_limited} ) is deducted. Since the change in the mechanical target power (ΔP _mech ) due to the limitation assumes a maximum value of zero, the braking torque cannot be increased in the generator case (P _{mech_soll_limited} <0), which in turn means that the power flow into the intermediate circuit via this path does not increase can be. However, the DC link controller can use this path to shift the target power towards motor operation, which means that energy is taken from the DC link.

The second effective path of the manipulated variable of the intermediate circuit energy controller goes to the target power loss, with a change in the target power loss (ΔP _v ) being formed by the part of the first path that cannot 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 (P _R ) specified by the controller can be achieved within the valid current limits.

The target power loss (P _{v_soll} ) is formed by subtracting the limited mechanical target power (P _{mech_soll_limited} ) from the desired change in power loss (ΔP _v ). This ensures efficient pre-control.

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

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

In an advantageous embodiment, the determined setpoint of the flux-forming d-current is given a negative sign, so that it has a field-weakening effect, which increases the voltage reserve of the underlying current control algorithms.

Reference symbol list

Msoll

Torque setpoint

Mset_limited

limited torque setpoint

ωmech

mechanical angular velocity

PMmech_should

mechanical target power

PMech_set_limited

limited mechanical target power

PMech_max

maximum permitted mechanical power

Wsoll

Setpoint of the energy stored in the intermediate voltage circuit

Wist

Actual value of the energy stored in the intermediate voltage circuit

Uz_should

Setpoint of the voltage of the intermediate circuit capacitor

Uz_ist

Actual value of the voltage of the intermediate circuit capacitor

PR

Controlling variable of the DC link energy controller Change in the mechanical caused by the DC link energy controller

ΔPmech

target performance

ΔPv

Request to change the power loss

Pv_set

Setpoint of the power loss

Pv_set_limited

limited setpoint of power loss

Pv_max

maximum permitted power loss

Imax

maximum permitted amount of electricity

Iv_should

Setpoint of the power loss current

lq_soll

Setpoint of the torque-generating current

Id_should

Setpoint of the flow-forming current

Id_should_limited

limited setpoint of the flow-forming current

R

ohmic resistance

C

Capacitance value of the intermediate circuit capacitor

Claims (13)

Method for controlling a synchronous machine, namely a synchronous motor, wherein the synchronous machine can be fed by an inverter or converter, characterized in that the intermediate circuit energy (W _is ) is detected and regulated to a predeterminable setpoint (W _setpoint ), the stator current space vector is determined and from this a torque-forming and a flow-forming current component (i _{q_Soll,} i _{d_Soll} ) is determined, the flow-forming current component of the motor current being regulated to such a target value (i _{d_Soll} ) that generator-generated energy is converted into heat in the motor, whereby the deviation the intermediate circuit energy (W _is ) is fed to its setpoint (W _Soll ) to a linear controller element, and the output signal is used as the setpoint ( _{id_Soll} ) for the flow-forming current component in the generator operation of the synchronous machine. Procedure according to Claim 1 , characterized in that the intermediate circuit voltage (U _{z_act} ), in particular the voltage supplying the inverter, is detected and regulated to a predefinable setpoint (U _{z_Soll} ) by determining the setpoint for the flux-forming d-current component from the deviation from the setpoint becomes. Method according to at least one of the preceding claims, characterized in that the linear controller element is a PI element. Method according to at least one of the preceding claims, characterized in that the deviation of the flow-forming current component from its setpoint value (I _{d_Soll} ) is fed to a linear controller element, in particular a PI element, and the output signal is used as a control value, in particular where the output signal is the component of the voltage space vector to be set by the inverter is 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 (I _{q_Soll} ), in particular wherein the desired value corresponds to a predeterminable braking torque. Method according to at least one of the preceding claims, characterized in that the setpoint (I _{q_Soll} ) for the torque-forming current component is determined from a current-dependent characteristic curve, in particular wherein the characteristic curve describes a dependence of the torque on the motor current. Method according to at least one of the preceding claims, characterized in that a temperature value is formed for the synchronous machine by means of a thermal model and, when a critical temperature value is exceeded, an action is carried out, such as issuing warning information, displaying 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 excited, in particular the rotor has permanent magnets for generating a permanent magnetic field, in particular even when the synchronous machine is de-energized Method for braking a synchronous machine, namely a converter-fed synchronous motor, characterized in that the intermediate circuit energy is detected and regulated to a predeterminable setpoint (W _setpoint ), with a mechanical one consisting of a torque setpoint (M _setpoint ) and a mechanical angular velocity ( _ωmech ). Target power is calculated, with this mechanical target power being limited in the generator case to a power whose Value is at most as large as the maximum permitted power loss of the converter-fed synchronous machine, a limited target torque being determined from this limited mechanical target power (P _{mech_soll} ) and the mechanical angular velocity, this limited target torque being converted into a target value (i _{q_Soll} ) by means of functional dependency the torque-forming q-current component is converted, with the difference between the target and an actual value (W _target , W _actual ) of the intermediate circuit energy being fed to an intermediate circuit energy control unit, the intermediate circuit energy control unit having as an output variable a power that corresponds to the reciprocal of the ohmic Resistance (R) is multiplied and thus the square of a target loss current is determined, whereby the square of the torque-forming q-current component is subtracted from the square of the target loss current, then limited to the lower limit of zero and by taking the square root, the target value of the flux-forming d-current is deducted. Current is determined, whereby the value of the ohmic resistance (R) is tracked over the temperature, with a thermal protection model limiting the maximum current I _max so that protection of the motor and inverter is guaranteed. Method according to at least one of the preceding claims, characterized in that the target power loss (P _{v_Soll} ) is pre-controlled by adding a value to the output value of the intermediate circuit energy controller, which is proportional to the amount of the limited mechanical target power (P _{mech_soll} ). Method according to at least one of the preceding claims, characterized in that the output value of the intermediate circuit energy controller is divided into different effective paths so 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 carried out by supplying the setpoint and actual value (U _{z_Soll} , U _{z_act} ) of the intermediate circuit voltage to a control unit. 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 controller, the control electronics having control signals for semiconductor switches of an inverter of the converter, the synchronous machine being made of can be fed to the inverter.

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