DE102016221315A1 - Device for controlling an electrical machine - Google Patents

Abstract

The present invention relates to a device 1 for controlling an electrical machine, comprising a field weakening controller 100 for outputting a longitudinal current setpoint I_d_soll at an output 104 of the field weakening controller 100; a cross current regulator 200 for outputting an infinite cross voltage U_q_unlim at a cross current regulator output 202 of the cross current regulator 200; a longitudinal current regulator 300 for outputting a longitudinal voltage U_d_unlim, Ud at a longitudinal current regulator output 302 of the longitudinal current regulator 300; a cross-voltage limiter 400 for outputting a limited cross-voltage U_q, wherein the longitudinal current regulator output 302 is connected to a first input 101 of the field weakening regulator 100, wherein the cross-current regulator output 202 to a second Input 102 of the field weakening controller 100 is connected and wherein the cross-current regulator output 202 is connected to an input 401 of the cross-voltage limiter 400.

Description

Technical part

The present invention relates to a device for regulating and in particular for field-weakened control of an electrical machine.

Technical background

Electrical machines, such as permanent magnet synchronous motors are controlled by means of appropriate controls, which can make particular the speed and power control of the synchronous motors. In a permanent magnet synchronous motors, for example, a constant magnetized rotor, or rotor called synchronously driven by a moving magnetic rotating field in a so-called stator. The field in the rotor is caused by a permanent magnet. For example, such engines, a so-called field-oriented control is used in many cases. The operation of a synchronous motor can be described by two characteristic currents: The field-forming longitudinal flow and the torque-forming cross-flow.

Electric motors can be driven by inverters, whereby a series of modulated width rectangular pulses can be generated by so-called pulse width modulation (PWM) to modulate the energy supplied to the electric motor. For this purpose, the converter may comprise an intermediate circuit, such as a DC intermediate circuit, the intermediate circuit setting the limit of the maximum voltage that can be applied to the stator. The maximum voltage that can be supplied by a converter to an electric machine can be limited by a DC link voltage and PWM settings.

In principle, the torque of a permanent magnet-excited synchronous motor is set via the desired value of the cross current in order to set a desired rotational speed. The manipulated variable of the corresponding cross-flow regulator is the transverse voltage. However, as the speed increases, the voltage induced by the permanent magnet increases. Now a system voltage available to the control or regulation can no longer be sufficient to impress the desired crossflow.

Therefore, it is known to set at high speeds also a negative longitudinal current to the field weakening of the permanent magnet, especially when a voltage ceiling or a limit for the transverse stress has been reached. A longitudinal flow controller can form a corresponding longitudinal voltage component as a manipulated variable. The corresponding longitudinal current setpoint is specified by a corresponding voltage regulator whose input is fed with the difference between the voltage requirement and the maximum available system voltage. Thus, the voltage induced by the permanent magnet is reduced, and higher speeds can be achieved at a given cross-flow.

Since the voltage requirement is limited or limited in terms of a voltage limit, the threshold for entering the field weakening, or the limit at which field weakening occurs, is usually reduced, otherwise no field weakening would occur. For example, a field weakening is already initiated at a voltage requirement of 280 V, although 320 V is available as the maximum voltage. This early initiation of the field weakening unnecessarily increases the motor current and still does not achieve optimum utilization of the motor at high speeds. Furthermore, this lowering of the limit is problematic with a fluctuating DC link voltage.

It is known to use a characteristic curve method in which a longitudinal current setpoint value can be preset as a function of the rotor speed via a characteristic curve. As a result, however, the inverters can not be protected from excessive voltages and, at the same time, an optimum entry into a field weakening can be brought about.

It is thus an object of the present invention to provide a device for controlling an electric machine, which optimizes the field weakening during operation of an electrical machine.

Content of the invention

The above and other objects, which will become apparent from the following description, are achieved by the apparatus for controlling an electric machine of independent claim 1.

In particular, they are achieved by a device for controlling an electrical machine, comprising a field weakening controller for outputting a longitudinal current setpoint at an output of the field weakening controller, a cross-current controller for outputting an unlimited cross-voltage at a cross-current regulator Output of the cross current regulator, a longitudinal current regulator for outputting a longitudinal voltage at a longitudinal current regulator output of the longitudinal current regulator, a cross voltage limiter for outputting a limited cross voltage wherein the longitudinal current regulator output is connected to a first input of the field weakening regulator, the cross current regulator output being connected to a second input of the field weakening regulator, and the cross current regulator output being connected to an input of the cross-voltage limiter is connected.

With the device according to the invention, any suitable electrical machine can be controlled, and in particular a permanent magnet synchronous motor. The field weakening controller induces a field weakening by injecting a longitudinal current into the electrical machine. In this case, a field-weakening current can be impressed into the stator, whereby the excitation field is weakened in the electric machine to allow higher speeds, for example, at the same voltage.

Characterized in that the longitudinal current regulator output is connected to a first input of the field weakening regulator, wherein the cross-current regulator output is connected to a second input of the field weakening regulator, and wherein the cross-current regulator output to a Input of the cross-voltage limiter is connected, is advantageously achieved that the electric machine is controlled by means of field weakening, only when the unlimited transverse voltage requirement reaches a voltage limit or its physical voltage limit. The longitudinal current setpoint can be generated based on the unlimited cross voltage requirement. The electric machine is used much better than in comparison to the previously conventional methods of the prior art, since the machine is operated up to the voltage limit or the physical voltage limit without field weakening. This allows, in particular, an efficient control of the machine with a fluctuating intermediate circuit voltage or a narrow DC link capacitance. This advantageously achieves that a field weakening is regulated based on a voltage regulation difference, which in turn depends on the unlimited transverse voltage requirement. An artificial lowering of the threshold voltage is not required, so no additional motor currents need to be fed unnecessarily.

The field weakening controller preferably has an integral behavior or a proportional-integral behavior. With such an I-controller behavior, the field weakening controller can be designed as a very accurate regulator, which is advantageous for the output of the longitudinal current setpoint. By means of the PI controller behavior, a control deviation can be effectively avoided with a constant setpoint value.

Preferably, the field weakening controller is configured to calculate the longitudinal current setpoint based on the unlimited cross-voltage and the longitudinal voltage and a maximum voltage derived in particular from a DC link voltage. The maximum voltage can represent a limit of the inverter. In particular, the maximum voltage may be the maximum voltage that can be supplied by a converter of the electric machine, and may be limited by the intermediate circuit voltage and / or PWM settings. Furthermore, the intermediate circuit voltage may represent the physical limit to the optimal entry into the field weakening.

The field weakening controller preferably has a voltage regulator for outputting the longitudinal current setpoint, the field weakening controller having an arithmetic circuit for forming a subtraction voltage, in particular according to the Pythagorean theorem of the unbounded transverse voltage and the longitudinal voltage, and wherein an input of the voltage regulator is connected to an output of a differential element to form a difference between the maximum voltage and the subtraction voltage. Thus, it can be advantageously taken into account that the combination of longitudinal and transverse voltage does not exceed the maximum voltage, and the behavior of the machine remains determined.

Particularly preferably, the field weakening controller is set up to generate the field weakening if the subtraction voltage is greater than the maximum voltage. Thus, the entrance of the Field weakening to be optimally controlled. A field weakening can be initiated if and only if the combination of unlimited longitudinal and transverse stress is greater than the maximum stress.

Preferably, the device further comprises a first multiplier which is connected to an input of the field weakening controller for inputting the maximum voltage, wherein the first multiplier is adapted to multiply the intermediate circuit voltage with a first factor, in particular the factor 1 / √3 for calculating the maximum voltage , Thus, a suitable maximum voltage can be determined as the limit to the optimal entry into the field weakening.

The device preferably also has a second multiplier for outputting an overmodulation voltage, wherein the second multiplier is set up to multiply the intermediate circuit voltage by a second factor, in particular the factor 2/3 for calculating the overmodulation voltage, wherein a limiter value for limiting the cross modulation voltage Voltage through the limiter is dependent on the overmodulation voltage. This limit can be used to ensure that the behavior of the machine remains determined.

Preferably, one or more of the regulators, limiters and multipliers, and in particular preferably all components of the device are formed in one or more FPGAs.

list of figures

• 1 schematisch eine bevorzugte Vorrichtung zur Regelung einer elektrischen Maschine; und
• 2 schematisch einen bevorzugten Feldschwächungsregler.

In the following, the present invention will be described in more detail with reference to the accompanying figure. Showing:

• 1 schematically a preferred device for controlling an electrical machine; and
• 2 schematically a preferred field weakening regulator.

Description of preferred embodiments

1 schematically shows a preferred device 1 for controlling an electric machine, comprising in particular a permanent magnet synchronous motor (not shown). The device 1 includes a rock mitigation regulator 100 , a cross-flow regulator 200 , a longitudinal flow regulator 300 , a transverse voltage limiter 400 , a first multiplier 500 , a second multiplier 600 , a longitudinal voltage limiter 700 , a limiter value regulator 800 and a power amp 900 ,

The device 1 allows control of the speed ω a to the power amplifier 900 connected electrical machine. The rotational speed ω of the electric machine is primarily controlled by a current I, which is supplied to the electric machine. For this purpose, the cross-current controller 200 at the entrance 201 through an adder 204 the difference between the cross-flow setpoint I_q_soll and the actual cross-machine current I_q_is present on the machine is provided.

The regulation of the current takes place by regulating a voltage. For this purpose, the cross-flow controller 200 at its output an unlimited transverse voltage requirement U_q_unlim, which may be for example 500 volts. In order to protect the inverters of the machine, if necessary, the unlimited transverse voltage requirement U_q_unlim by a cross-voltage limiter 400 limited as described below. The resulting, possibly limited cross-flow U_q is sent to the output stage 900 provided, which controls the machine by means of space vector modulation.

The unlimited cross-voltage requirement U_q_unlim is between the output 202 of the cross-current regulator 200 and the entrance 401 of the cross voltage limiter 400 tapped and the field weakening controller 100 at the entrance 102 fed.

Furthermore, the field weakening controller 100 a maximum voltage U_max at input 103 fed. The maximum voltage U_max is based on an intermediate circuit voltage U_z. The maximum voltage U_max is in this case by a first multiplier 500 calculated by dividing the intermediate circuit voltage U_z by a first factor, in particular the factor 1 / √3 multiplied. If, due to a high speed specification ω _, the unlimited transverse voltage requirement U_q_unlim is for example 500 volts, but the maximum voltage U_max is only 320 volts, the motor is operated by impressing a longitudinal current in field weakening.

Furthermore, by means of a second multiplier 600 calculated an overmodulation voltage U_max ', wherein the second multiplier 600 the intermediate circuit voltage U_z with a second factor, in particular the factor 2 / 3 multiplied. The overmodulation voltage U_max 'becomes an input of a limiter value controller 800 supplied to calculate a limiter value U_q_max for limiting the cross voltage.

The field weakening controller 100 gives at the exit 104 the longitudinal current setpoint I_d_soll off. From this longitudinal current setpoint I_d_soll is in the adder 304 the longitudinal current actual value I_d_act is subtracted and the difference becomes the longitudinal current regulator 300 provided. The longitudinal current actual value I_d_ist corresponds to the longitudinal current actually present on the machine.

The longitudinal current regulator 300 calculated on the basis of the difference between the longitudinal current setpoint I_d_soll and the longitudinal current actual value I_d_is an initially unlimited longitudinal voltage requirement U_d_unlim. The unlimited longitudinal voltage requirement U_d_unlim is from the output 302 of the longitudinal current regulator 300 to the entrance 101 of the field weakening controller 100 provided. Furthermore, the unlimited longitudinal voltage requirement U_d_unlim may optionally be in a downstream longitudinal voltage limiter 700 be limited, so that the amount of the longitudinal voltage requirement does not exceed the overmodulation voltage U_max '. For this purpose, the overmodulation voltage U_max ', by the second multiplier 600 was generated, including the longitudinal voltage limiter 700 fed.

Finally, the resulting longitudinal stress U_d of the longitudinal voltage limiter 700 to the control module 900 provided, to which also the transverse voltage U_q is provided. Based on the longitudinal voltage U_d and the transverse voltage U_q the electric machine is driven.

In addition, the resulting longitudinal voltage U_d also the limiter value controller 800 fed. Thus, the limiter value controller 800 from the overmodulation voltage U_max 'and the longitudinal voltage U_d calculate a limiter value U_q_max for limiting the cross voltage. This ensures that the transverse voltage as well as the longitudinal voltage are each small enough so that a certain regulation is ensured. The limiter value U_q_max can be calculated as follows: $$\text{U}\_\text{q}\_\text{Max}={\left(\text{U}\_{\text{Max}}^{\text{'}2}-\text{U}\_{\text{d}}^{\text{2}}\right)}^{\text{0}\text{, 5}}$$

As in 2 illustrated in detail, includes the field weakening controller 100 an arithmetic circuit 130 which calculates a subtraction voltage U_unlim. This is done in particular according to the theorem of Pythagoras from the unlimited cross-voltage U_q_unlim, which is at the entrance 102 is applied, and the unlimited longitudinal voltage U_d_unlim, the input 101 is applied. The subtraction voltage U_unlim can be calculated as follows: $$\text{U}\_\text{unlim}={\left(\text{U}\_\text{q}\_{\text{unlim}}^2+\text{U}\_\text{d}\_{\text{unlim}}^{\text{2}}\right)}^{\text{0}\text{, 5}}$$

$$\left|\text{U}\_\text{unlim}\right|>\left|\text{U}\_\text{max}\right|$$

The of the arithmetic circuit 130 formed subtraction voltage U_unlim is a difference element 120 which subtracts the subtraction voltage U_unlim from the maximum voltage U_max that is present at the input 103 is applied. In this case, for the field weakening: $$\text{U}\_\text{unlim}-\text{U}\_\text{Max}>\text{O}$$

$$\left|\text{U}\_\text{unlim}\right|>\left|\text{U}\_\text{Max}\right|$$

For the field weakening, the subtraction voltage U_unlim is therefore greater than the maximum voltage U_max. If the current voltage requirement exceeds the maximum voltage U_max, a corresponding longitudinal current setpoint can be generated to initiate the field weakening. In this case, the resulting difference between the maximum voltage U_max and the subtraction voltage U_unlim is applied to the voltage regulator 110 for calculating the corresponding longitudinal current setpoint I_d_soll provided.

Otherwise, if the maximum voltage U_max has not been exceeded, no field weakening is necessary, and the machine is preferably operated only by means of the transverse voltage. The difference between the maximum voltage U_max and the subtraction voltage U_unlim is then positive.

If, however, the maximum voltage U_max is less than the subtraction voltage U_unlim, ie the machine is to be operated in field weakening, the resulting difference is the maximum voltage U_max and the subtraction voltage U_unlim of the output 123 of the differential element 120 to an entrance 111 a voltage regulator 110 which calculates and outputs a longitudinal current command value I_d_soll. The longitudinal current setpoint I_d_soll is located at an output 104 of the field weakening controller 100 at.

If the subtraction voltage U_unlim increases due to a higher speed specification or because of increasing load torques over the maximum voltage U_max, the voltage actually output by the space vector modulation remains limited, whereas in the field weakening controller 100 the unlimited values are used. As a result, the machine no longer goes into field weakening too soon, but at the exact moment when the voltage requirement reaches its physical limit. Thus, the utilization of the machine is significantly improved.

Claims (7)

Device (1) for controlling an electrical machine, comprising a. a field weakening controller (100) for outputting a longitudinal current command value (I_d_soll) at an output (104) of the field weakening controller (100); b. a cross current regulator (200) for outputting an infinite cross voltage (U_q_unlim) at a cross current regulator output (202) of the cross current regulator (200); c. a longitudinal current regulator (300) for outputting a longitudinal voltage (U_d_unlim, Ud) at a longitudinal current regulator output (302) of the longitudinal current regulator (300); d. a cross voltage limiter (400) for outputting a limited cross voltage (U_q); e. wherein the longitudinal current regulator output (302) is connected to a first input (101) of the field weakening regulator (100); f. wherein the cross-current regulator output (202) is connected to a second input (102) of the field weakening regulator (100); and G. wherein the cross current regulator output (202) is connected to an input (401) of the cross voltage limiter (400). Device after Claim 1 wherein the field weakening controller (100) has an integral behavior or a proportional-integral behavior. Device according to one of the preceding claims, wherein the field weakening controller (100) is arranged, the longitudinal current setpoint (I_d_soll) based on the unlimited cross-voltage (U_q_unlim) and the longitudinal voltage (U_d_unlim, U_d) and one in particular from a DC link voltage (U_z) derived maximum voltage (U_max) to calculate. Device after Claim 3 , a. wherein the field weakening controller (100) comprises a voltage regulator (110) for outputting the longitudinal current command value (I_d_soll), b. wherein the field weakening controller (100) has an arithmetic circuit (130) for forming a subtraction voltage (U_unlim), in particular according to the set of Pythagoras from the unbounded cross voltage (U_q_unlim) and the longitudinal voltage (U_d_unlim, Ud), and c , wherein an input (111) of the voltage regulator (110) is connected to an output (123) of a differential element (120) to form a difference between the maximum voltage (U_max) and the subtraction voltage (U_unlim). Device after Claim 4 wherein the field weakening controller (100) is arranged to generate the field weakening when the subtraction voltage (U_unlim) is greater than the maximum voltage (U_max). Device according to one of the preceding claims, further comprising - a first multiplier (500), which is connected to an input (103) of the field weakening controller (100) for inputting the maximum voltage (U_max), - wherein the first multiplicator (500) is arranged, multiply the DC link voltage (Uz) by a first factor, in particular the factor 1 / √3, to calculate the maximum voltage (U_max). Apparatus according to any one of the preceding claims, further comprising a second multiplier (600) for outputting an overmodulation voltage (U_max '), - wherein the second multiplier (600) is arranged to multiply the intermediate circuit voltage (U_z) with a second factor, in particular the factor 2/3 for the calculation of the overmodulation voltage (U_max '), - Wherein a limiter value (U_q_max) for limiting the transverse voltage (U_q) by the limiter (400) of the overmodulation voltage (U_max ') is dependent.

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