Method for increasing the efficiency of a motor in the form of a permanent magnet synchronous machine

Abstract

Method for increasing the efficiency of a motor in the form of a permanent magnet synchronous machine by means of a field-oriented control (33), wherein a setpoint value of the flux-forming current (35, 44) for an operating point on the motor is determined by means of the following steps: a) detecting data of a power change of the motor when the flux-forming current (35, 44) changes according to a predetermined rate of change (9); b) forming a mathematical function (5), wherein the mathematical function (5) establishes a relationship between the data of the power change (3, 4) and the flux-forming current (35, 44) to be set; c) determining a local minimum of the mathematical function (5); d) operating the motor at the local minimum of the mathematical function (5) and repeating the preceding process steps within a first operating time; e) after the first operating time has elapsed: changing the flux-forming current (35, 44) to raise the power change (4) from the local minimum by means of an excitation function and repeating the preceding method steps, wherein in the case of a power change (3, 4) below a predetermined hysteresis, no changes to the flux-forming current (35, 44) are made.

Description

The invention relates to a method according to independent patent claim 1 and to a device for carrying it out.In such methods, in the case of electric motors, for example in the case of permanently excited synchronous machines, or brushless DC motors, the current in specific rotor positions is commutated by means of electrical switching elements, such as transistors. In order for this commutation process to take place at the correct point in time, the current rotor position must be known.For detecting the rotor position, Hall sensors or even sensorless methods are usually used in such motors, for example. Hall sensors are arranged at locations of the armature circumference at which the normal component of the induction is zero and sense the magnetic field generated by the permanent magnetic rotor. If the rotor reaches such a position, for example the slot center of the stator, which also corresponds in each case to the mechanical commutation position, the Hall sensor generates a commutation signal.Due to the inductance of the motor winding, the current does not reach its maximum immediately after the turn-on, but lags behind the applied voltage and is thus delayed by a certain time.In order to compensate for this delay, it is known that, for example, a so-called pre-commutation can be used. The commutation process is started in this case even before the rotor has reached the actual commutation position.In order to improve the efficiency of the motor, methods are known in which a specific angle for pre-commutation is measured as a function of the operating point by means of a field-oriented control and is stored in a look-up table. Based on this angle, the flux-forming current as well as the torque-forming current is impressed during operation of the motor.Methods are also known in which an input power is changed at steady-state operating points by means of a sliding adaptation of the flux-forming current component, or which optimize the pre-commutation angle on the basis of loss models and search approaches.From document US 2012 / 0293106 A1 an electric motor is known, which comprises a permanent magnet rotor and a device for generating a three-phase sinusoidal current for supplying current to the motor, as well as also a microprocessor for carrying out the method steps. In this case, the losses are optimized on the basis of a set voltage vector.Moreover, from the scientific publication of JEONG, Yu-seok [et al.], IEEE Transaction on Industry Applications, Vol. 42, 2006, No. 5, pp. 1222-1229, discloses a method which is suitable for increasing an efficiency of a synchronous machine operated as a motor by means of field-oriented regulation.Furthermore, methods for changing the flux-forming current component are known for optimizing the efficiency of an electric motor, wherein the power of an intermediate circuit is measured and the flux-forming current component is changed on the basis of this information until a minimum efficiency of the motor is obtained.A disadvantage here is that, in order to carry out this method, there must always be a steady-state operating state of the engine, i.e. an operating state of the engine that does not change over time, and there is thus a steady-state dependence.It is therefore an object of the invention to propose a method for optimizing the efficiency of an electrically commutated motor as a function of the operating point, in which method iron losses of the commutation can be compensated independently of the operating state of the motor and thus, in particular, a steady-state dependence of the method is avoided.This object is achieved by means of the independent patent claims. Advantageous and practical refinements are specified in the dependent patent claims.In the sense of the invention, the term field-oriented regulation is to be understood as meaning a regulation concept in which alternating variables, such as alternating voltages and alternating currents, which are assumed to be substantially sinusoidal, are not regulated directly in their instantaneous value over time, but rather in an instantaneous value corrected by the phase angle within the period. For this purpose, the detected change quantities are each transmitted into a coordinate system rotating at the frequency of the change quantities. Within the rotating coordinate system, the alternating variables then result in variables of the same magnitude, to which all conventional methods of control technology can be applied. In other words, in field-oriented regulation, measured variables with a substantially sinusoidal character are transformed into a rotor-fixed coordinate system by using a Clark / Park transformation. As a result, the three alternating variables are converted into two constant variables and can be applied to the usual method of control technology.The invention provides a method for increasing the efficiency of a motor in the manner of a permanently excited synchronous machine by means of a field-oriented control system, wherein a setpoint value of the flux-forming current for an operating point on the motor is determined by means of the following steps: a) acquisition of data of a power change of the motor when the flux-forming current changes in accordance with a predetermined change rate; b) formation of a mathematical function, wherein the mathematical function establishes a relationship between the data of the power change and the flux-forming current to be set; c) determination of a local minimum of the mathematical function; d) operation of the motor in the local minimum of the mathematical function and repetition of the preceding method steps within a first operating time; e) after the first operating time has elapsed: changing the flux-forming current in order to raise the power change from the local minimum by means of an excitation function and repeating the preceding method steps, wherein no changes in the flux-forming current are carried out in the event of a power change below a predetermined hysteresis.The method advantageously extends a field-oriented control of an electrically commutated motor by an efficiency control with respect to the flux-forming current of the motor. The method thus optimizes this only when considering the efficiency of the engine. By providing a low flux-forming current, iron losses in the motor can be partially compensated and the efficiency of the motor can be increased, which can save energy expenditure and thus enable more favorable operation of the motor. The method can be used continuously and over the entire running time, both in a steady state, i.e. in a state that does not change over time, and in a non-steady state, i.e. in a state that changes over time, of the engine.A complicated detection of operating point-dependent pre-commutation angles can thus be omitted and the method can be used universally by means of continuous optimization, since it has proven more dynamic as a look-up table and exception treatments can be omitted in dynamic situations. For example, a look-up table cannot take into account any factors that change with the operation of themoto, such as thermal or aging-related parameter changes. By means of the method, effects resulting therefrom can be compensated for, since the optimum is also displaced and this is set independently of the state of the motor. Changes can thus be directly detected and adapted according to the operating points of the motor. It is also advantageous that a complex measurement of the motor is omitted.It is furthermore advantageous that even in the case of incorrectly parameterized sensorless methods, the motor can be operated at the optimum operating point in a steady state and a high tolerance to parameter changes of the motor can be generated during operation.Raising the local minimum by means of an excitation function and subsequently minimizing the power consumption again at a constant operating point by means of changing the flow-forming current advantageously prevents the mathematical function from being stuck in a local minimum in favor of finding a global minimum.It is also provided that when there is a power change below a predetermined hysteresis, no changes are made in the flux-forming current.This can have an advantageous effect on the running smoothness of the engine during operation, which can reduce, inter alia, disturbing noises, oscillations and unnecessary energy losses.In a preferred embodiment variant, it is provided that the method comprises the step: a.1) if the change in the flow-forming current leads to a reduction in the power consumption of the motor:further changing the flux forming current according to the predetermined rate;otherwise: changing the flux forming current according to a rate inverted to the predetermined rate;This makes it possible for the method to always move in a direction optimizing the efficiency of the motor and for the time required for this to be minimized. A drift of the method from the minimum to be achieved can thus be prevented.Furthermore, it is provided that the recorded data are filtered by means of a low-pass filter in order to determine the power change.The acquisition of the data is subject to certain inaccuracies and system-related disturbances and noise. High-frequency changes in the captured data can be suppressed by means of a low-pass filter and a more stable and reliable method sequence can be ensured.It is preferably provided that the power change is detected in a moving coordinate system by means of current pointer information and / or power pointer information.It is advantageous here that no additional measurement effort is thereby generated, since this information is already available for each field-controlled motor.In particular, it is provided that sensor-associated methods, e.g. by means of Hall sensors and / or sensorless methods, are used for detecting the rotor position of the motor.As a result, the motor can be described easily and reliably in a coordinate system dedicated to the motor. The reference system of the control can thus be advantageously described specifically for each motor as a function of its angle of rotation.Furthermore, it is provided that the detection of the power change is carried out by means of direct methods, e.g. by measuring the machine power, and / or indirect methods, e.g. by detecting the motor phase currents.For example, the power can be determined indirectly by detecting the motor phase currents, by detecting the total current of the motor or by the length of the measured current vector. It is especially advantageous to use the variables known from the regulation, such as the torque-forming and the flux-forming current, since additional current measurements can be dispensed with as a result. This allows rapid access to the required information on the one hand, and on the other hand, these can thus be generated favorably with reduced outlay on measurement technology.Furthermore, it is provided that the method for increasing the efficiency takes place continuously over the entire life cycle of the permanently excited synchronous machine. This advantageously makes possible uninterrupted optimization.Furthermore, the invention provides a device for carrying out an above-described method comprising at least one speed regulator, at least one efficiency regulator, and at least two current regulators and at least one control unit for carrying out arithmetic operations.Further details of the invention are described in the drawings on the basis of schematically illustrated exemplary embodiments.This shows FIG. 1 shows a flow chart of the method, and FIG. 2 shows a schematic structure of an apparatus for carrying out the method.FIG. 1 shows a flow diagram of the method.With reference to FIG. 1, a possibility for implementing the method by means of a step function 8 is described below.First, data of a power change of a motor when the flow-forming current changes are acquired 1. The data are then filtered 2 by means of a low-pass filter in order not to allow possible measurement uncertainties or noise to influence the method.If the change in the flux-forming current results in a decrease in the power consumption of the motor 3, the change in the flux-forming current is continued according to the predetermined rate of change, otherwise the change in the flux-forming current is continued according to a rate inverted from the predetermined rate of change 4.A mathematical function is now formed 5, which establishes a relationship between the data of the power change and the flux-forming current to be set.A local minimum of the mathematical function is then determined and the motor is operated in this local minimum within a predetermined time 6.After the predetermined time 6, the local minimum of the mathematical function is raised by means of an excitation function, for example a step function 8, and the preceding method steps are repeated. Raising the minimum thereby prevents the method from locking down in a local minimum and enables a global minimum to be found.In other words, when using a step function 8 as an optimization algorithm, the motor can be optimized based on the dimensioning of the power change. Since the measurement of the current or the power is very volatile and measurement inaccuracies can additionally occur, the data for the detection of the power change 1 are prefiltered by means of a low-pass filter.The filtered data are passed to an optimum pre-commutation tracking, not designated in more detail, which can be executed with a slower time constant than the control system. The optimal pre-commutation tracking then calculates the difference between the current measurement value and the last measurement value and accordingly provides a larger or a smaller flow-forming current component.If the change in the flux-forming current component leads to a reduction in the power consumption at the motor, the change in the flux-forming current component is continued at the same rate. If, on the other hand, there is a greater power consumption at the motor, the rate of change is inverted.Continuous optimization thus leads to a local minimum of performance in the long term.FIG. 2 shows a schematic structure of a flow chart for carrying out the method comprising a speed control 20, a current control designed as a field-oriented control 33, and an upstream efficiency control 42.The interaction of rotational speed information 21, 48, a first PI controller 22, a reset time 23, a gain 24, and setpoint value information 25 transferred to the current controller 33 is shown within the rotational speed controller 20.The interaction of current information 47, 46 whose magnitude produces a current vector 42 and voltage information 43, 44 whose magnitude produces a voltage vector 45 is shown within the efficiency control 42. Current vector 41 is converted with voltage vector 45 to a power vector 40, which represents the current power information at the motor. The minimum of the power indicator corresponds to the optimum of the power of the motor per operating point. Based on the change in the power pointers 40, optimal pre-commutation tracking 39 then sets a flow-forming stream, which is represented as stream information 38. This is changed until a local minimum is reached. If the working point changes, the local minimum also changes. The stream information is then transferred to the field-oriented control 33.The field-oriented control 33 shows the interaction of the setpoint value information 25 obtained from the speed control, the current information 38 obtained from the efficiency control 42, and the respectively associated current information 26, 37 and the respectively associated PI controllers 27, 36. A torque-forming current component 28 is then transformed by means of a Clark / Park transformation with a flux-forming current component 35 into three-phase current components 30, 31, 32, which can be used to drive the motor.List of reference numbers:1 Detection of the power change 2 Low-pass filter 3 Power change less than 4 Power change greater than 5 Mathematical function 6 after predetermined time 7 otherwise 8 Step function 9 Change of the flux-forming current 20 Speed control 21, 48 Speed information 22, 27, 36 PI controller 23 Adjusting time 24 Amplification 25 Setpoint value information 26, 37, 38, 46, 47 Current information 28, 43 Torque-forming current component 29, 34 Clark / Park transformation 30, 31, 32 Three-phase current components 33 Field-oriented control 35, 44 Flux-forming current component 39 Optimum pre-commutation tracking 40 Power vector 41 Current vector 42 Efficiency control 45 Voltage vector

Claims

Method for increasing the efficiency of a motor in the manner of a permanently excited synchronous machine by means of a field-oriented controller (33), wherein a setpoint value of the flux-forming current (35, 44) for an operating point at the motor is determined by means of the following steps: a) acquisition of data of a power change of the motor when the flux-forming current (35, 44) changes in accordance with a predetermined rate of change (9); b) formation of a mathematical function (5), wherein the mathematical function (5) establishes a relationship between the data of the power change (3, 4) and the flux-forming current (35, 44) to be set; c) determination of a local minimum of the mathematical function (5); d) operation of the motor in the local minimum of the mathematical function (5) and repetition of the preceding method steps within a first operating time; e) after the expiration of the first operating time: changing the flux-forming current (35, 44) in order to raise the power change (4) from the local minimum by means of an excitation function and repeating the preceding method steps, wherein no changes of the flux-forming current (35, 44) are carried out in the case of a power change (3, 4) below a predetermined hysteresis.The method of claim 1 comprising the step of: a.1) if the change in the flux forming current (9) results in a decrease in power consumption of the motor: further changing the flux forming current (9) according to the predetermined rate; otherwise: changing the flux forming current (9) according to a rate inverted to the predetermined rate;Method according to Claim 1 characterised in that the recorded data for determining the power change (3, 4) are filtered by means of a low-pass filter (2).Method according to at least one of the preceding claims, characterized in that the power change (3, 4) in a moving coordinate system is detected by means of current pointer information (41) and / or power pointer information (40).Method according to at least one of the preceding claims, characterized in that sensor-associated methods, for example by means of Hall sensors and / or sensorless methods, are used for detecting the rotor position of the motor.Method according to at least one of the preceding claims, characterized in that the power change (3, 4) is detected by means of direct methods, for example by measuring the machine power, and / or indirect methods, for example by detecting the motor phase currents.Method according to at least one of the preceding claims, characterized in that the method for increasing the efficiency is carried out continuously over the entire life cycle of the permanently excited synchronous machine.Device for carrying out a method according to one of the preceding claims, comprising at least one speed control (20), at least one efficiency control (42), and at least one current control, in particular a field-oriented control (33), and at least one control unit for carrying out arithmetic operations.

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