ELECTRIC HAND TOOL MACHINE

Description

[0001] The present invention relates to an electric hand-held power tool with a brushless DC motor and a control unit for field-oriented control of the DC motor based on a current request signal and a voltage setpoint derived from the current request signal. The hand-held power tool is designed to provide a system voltage for supplying the brushless DC motor.

[0002] Hand-held power tools of the type mentioned above are generally known from the prior art. The d / q transformation has proven useful as a spatial vector representation for the design of such field-oriented control systems. Accordingly, it is used to describe the present invention.

[0003] DE 10 2008 042978 A1 describes a method for determining the phase currents of a multiphase electrical machine connected to a converter. The method comprises performing current control, which generates one or more control signals for the converter based on the actual phase currents output of the electrical machine and on specified target phase currents; determining phase voltages based on an intermediate circuit voltage present at the converter's input and on the control signals; and determining the actual phase currents based on the determined phase voltages.

[0004] EP 2 760 124 A2 describes a power tool comprising a brushless motor, a battery voltage detection unit for detecting the voltage of a battery supplying energy to drive the brushless motor, a rotation position detection unit for detecting the rotational position of the brushless motor, and a control unit for controlling a drive output supplied to the brushless motor. The control unit regulates a current input angle and / or a lead angle supplied to the brushless motor so that, during control of the drive output to the brushless motor, the rotational speed or conduction current of the brushless motor approaches or reaches a target value, the target value being based at least partially on a battery voltage detected by the battery voltage detection unit.

[0005] The object of the present invention is to provide an electric hand-held power tool which provides a basis for improved speed control of the brushless DC motor.

[0006] The task is solved by setting up the control unit to adjust the current request signal taking into account a voltage difference between the system voltage and the voltage setpoint.

[0007] The invention incorporates the understanding that, in field-oriented control systems, so-called windup effects can occur in the typically intended integral component of the control unit at the voltage limit, i.e., when the maximum available system voltage is identical to or even higher than the voltage setpoint. Because the control unit can no longer induce current in the windings of the brushless DC motor due to the high back-induced voltage, any residual errors, which in reality cannot be corrected, are integrated into the integral component of the control unit. This leads to an undesirable, delayed response of the brushless DC motor when the voltage limit is exceeded.

[0008] By configuring the control unit to adjust the current request signal based on a voltage difference between the system voltage and the voltage setpoint, the foundation for avoiding the windup effect is laid. In particular, the controller design can be optimized without using certain motor parameters that would otherwise require measuring the brushless DC motor. It has proven advantageous to calculate the voltage difference using a differential block integrated into the control unit.

[0009] In a particularly preferred embodiment, the control unit is configured to take the voltage difference into account variably. In other words, the control unit is specifically configured so that, for voltage differences of varying magnitudes greater than zero, a constant value is not used to adjust the current request signal. This facilitates particularly efficient control of the brushless DC motor.

[0010] In a particularly preferred embodiment, the control unit is configured to consider the system voltage and / or the voltage setpoint in transformed form. It has proven advantageous to calculate the voltage setpoint as the square root of the sum of the squares of the d-voltage setpoint and the q-voltage setpoint (d / q transformation). This can be achieved, for example, by means of a setpoint transformation block included in the control unit. It has also proven advantageous to consider the system voltage with a factor of 1 / √3 (3-phase system). This is preferably achieved by means of a system transformation block included in the control unit.

[0011] In a particularly preferred embodiment, the control unit is configured to amplify the voltage difference, in particular by means of a proportional-integral controller. Furthermore, the control unit is configured to adjust the current request signal solely by means of a negative control variable that directly or indirectly represents the voltage difference. It has proven advantageous for the control unit to include a limiting block for this purpose. Adjustment of the current request signal can be implemented by an adding block included in the control unit.

[0012] In a further particularly preferred embodiment, the control unit is configured to determine the voltage setpoints between a current controller of the control unit and the brushless DC motor. This has the advantage that the use of certain motor parameters, which would require complex measurements of the brushless DC motor, can be avoided.

[0013] In a particularly preferred embodiment, the system voltage is provided by means of a battery pack. It has proven advantageous if the system voltage is preferably between 12 and 36 volts, in particular 12 volts, 22 volts, or 36 volts. The system voltage can correspond to the open-circuit voltage of the battery pack.

[0014] It has proven advantageous if the control unit is set up to adjust the current request signal solely by taking into account a voltage difference between the system voltage and the voltage setpoint.

[0015] Further advantages will become apparent from the following description of the figures. The figure illustrates a particularly preferred embodiment of the present invention.

[0016] The characters, the description, and the claims contain numerous features in combination.

[0017] The expert will expediently consider the features individually and combine them into meaningful further combinations.

[0018] In the figure, identical and similar components are numbered with the same reference symbols. It shows: Figure 1 shows a preferred embodiment of an electric hand-held power tool. Example implementation:

[0019] Figure 1shows - in a highly schematic representation - an electric hand tool 100.

[0020] The hand-held power tool 100 is equipped with a brushless DC motor 10. The hand-held power tool 100 is further designed to provide a system voltage Vdc to supply the DC motor 10. This is done using a battery pack 30, which, for example, has a supply voltage of 22 volts.

[0021] The hand-held power tool 100 is also equipped with a control unit 20 for field-oriented control of the DC motor 10. As the Figure 1As can be seen, the control unit 20 is shown after a d / q transformation. Based on a current request signal Is, which can originate, for example, from a speed controller (not shown here), voltage setpoints Vd and Vq for the brushless DC motor 10 are derived in a forward branch 29 (in a manner known from the prior art). The voltage setpoints Vd and Vq each originate from a current controller 21 included in the control unit 20. The current controllers 21 are implemented as PI controllers by way of example. Instead of a PI controller, the current controller 21 can also be a PID controller (proportional-integral-derivative controller), which consists of the components of a P element, an I element, and a D element.

[0022] The control unit 20 has a feedback branch 28 which is connected to Figure 1The control unit 20 is characterized by a dotted box. It is configured to determine the voltage setpoints Vd and Vq between a current regulator 29 of the control unit 20 and the DC motor 10. The voltage setpoints Vd and Vq are then fed into a setpoint transformation block 22 to account for these values ​​in transformed form. In the setpoint transformation block 22, a transformed voltage setpoint Vs is calculated as the square root of the sum of the squares of the d-voltage setpoint Vd and the q-voltage setpoint Vq.

[0023] The control unit 20 additionally includes a system transformation block 23, in which the system voltage Vdc, provided by the battery pack 30 (for example, 22 volts), is transformed into a transformed system voltage value Vsmax. This is done by multiplying the system voltage Vdc by the factor 1 / √3 (3-phase system). The transformed system voltage value Vsmax is the maximum phase voltage actually available for the brushless DC motor 10, i.e., after the current regulators 21. In this example, this is 12.7 volts.

[0024] According to an alternative embodiment, not shown in the figures, the hand-held power tool 100 does not have a battery pack 30 as a power supply. In this case, the hand-held power tool 100 is equipped with a power cable to connect it to a mains voltage for electrical power supply. The system voltage Vdc provided can be measured via a mains voltage in the intermediate circuit when the hand-held power tool 100 is supplied with electrical power.

[0025] For hand tool machine 100 without a battery pack 30 and with a power cable, the system voltage Vdc can also be generated by a rectified intermediate circuit voltage and / or via a PFC optimized intermediate circuit voltage.

[0026] The control unit 20 is configured to adjust the current request signal Is taking into account a voltage difference VA between the system voltage Vdc and the voltage setpoint Vd, Vq. In the exemplary embodiment of the Figure 1To calculate a voltage difference VA, the transformed system voltage value Vsmax is subtracted from the transformed voltage setpoint Vs in a differential block 24. In the exemplary embodiment shown here, a transformed voltage setpoint Vs of 20 volts is requested after the current controllers 21 based on the instantaneous current request signal Is. Since only 12.7 volts can be provided in this example, the differential block 24 determines a voltage difference VA of -7.3 volts. This is fed via an amplifying PL controller 25 to a limiting block 26, which is configured to adjust the current request signal Is only by a negative control variable. Accordingly, the control unit 20 has an adding block 27. Here, the current request signal Is is reduced by 20 amperes as an example.

[0027] The described feedback branch 28 takes the voltage difference VA into account variably (and does not substitute it with a constant equivalent voltage that is independent of a specific amount of the voltage difference VA).

[0028] Out of Figure 1 It becomes apparent that the higher the voltage setpoint Vs corresponding to the respective current request signal Is, the higher the voltage difference VA. This "degree of overvoltage" is amplified by the PL controller 25 and—being a negative value—subtracted from the current request signal Is in the adding block 27. This reduces the current request. The result is a smaller voltage difference VA for the next control cycle of the control unit. The control unit repeats this process until the voltage difference VA reaches 0 volts and the voltage setpoints Vd and Vq resulting from the current request signal Is are, for example, 12.7 volts.

[0029] Again Figure 1 It can also be seen that the control unit 20 is configured to adjust the current request signal Is solely by considering a voltage difference VA between the system voltage Vdc and the voltage setpoint Vd, Vq. In other words, the adder block 27 has only two inputs. Reference symbol list

[0030] 10 Brushless DC motor 20 Control unit 21 Current controller 22 Setpoint transformation block 23 System transformation block 24 Differential block 25 PI controller 26 Limiting block 27 Adder block 28 Feedback branch 29 Forward branch 30 Battery pack 100 Electric hand tool IS Current request signal VA Voltage difference Vd Voltage setpoint Vdc System voltage Vq Voltage setpoint Vs Transformed voltage setpoint Vsmax Transformed system voltage value

Claims

1. Electric hand-held power tool (100), having a brushless DC motor (10) and a control unit (20) for field-oriented control of the DC motor (10) on the basis of a current requirement signal (IS) and a voltage setpoint value (Vd, Vq) derived from the current requirement signal, wherein the hand-held power tool (100) is further designed to provide a system voltage (Vdc) for powering the DC motor (10), wherein the control unit (20) is configured to adjust the current requirement signal (IS) while taking into account a voltage difference (VA) between the system voltage (Vdc) and voltage setpoint value (Vd, Vq), wherein the control unit (20) is configured to subtract the voltage setpoint value (Vd, Vq) from a system voltage value (Vdc) in order to obtain the voltage difference (VA), characterized in that the control unit (20) is configured to adjust the current requirement signal (IS) only by a negative manipulated variable which indirectly or directly represents the voltage difference (VA).

2. Hand-held power tool (100) according to Claim 1, characterized in that the control unit (20) is configured to take into account the voltage difference (VA) in a variable manner.

3. Hand-held power tool (100) according to Claim 1 or 2, characterized in that the control unit (20) is configured to take into account the system voltage (Vdc) and / or the voltage setpoint value (Vd, Vq) in transformed form.

4. Hand-held power tool (100) according to one of the preceding claims, characterized in that the control unit (20) is configured to amplify the voltage difference (VA) by means of a PI controller (25).

5. Hand-held power tool (100) according to one of the preceding claims, characterized in that the control unit (20) is configured to ascertain the voltage setpoint values (Vd, Vq) between a current controller (29) of the control unit (20) and the DC motor (10).

6. Hand-held power tool (100) according to one of the preceding claims, characterized in that the control unit (20) is configured to adjust the current requirement signal (IS) exclusively while taking into account a voltage difference (VA) between the system voltage (Vdc) and voltage setpoint value (Vd, Vq).

7. Hand-held power tool (100) according to one of the preceding claims, characterized in that the system voltage (Vdc) is provided by means of a rechargeable battery pack (30), and the system voltage is preferably between 12 and 36 volts.

8. Hand-held power tool (100) according to one of the preceding claims, characterized in that the hand-held power tool is designed as a cordless screwdriver.