Method for braking power tool and power tool

Abstract

The invention relates to a method for braking a power tool, the power tool being a battery operated power tool and the electrical energy released when the power tool is braked being fed back to the power supply of the power tool. The basic idea of the invention is to reduce the braking power when the power supply device has reached its electrical energy absorption limit. This reduction in braking power may be accomplished by shortening the current space vector using a correction factor or by rotating the current space vector in a space vector representation. In a second aspect, the invention relates to a power tool for performing a braking method.

Description

Technical Field

[0001] This invention relates to a method for braking a battery-operated power tool, wherein the electrical energy released when the power tool is braked is fed back to the power tool's power supply device. The basic idea of ​​this invention is to reduce the braking power when the power tool's power supply device has reached its energy absorption limit. This reduction in braking power can be achieved by shortening the current space vector using a correction factor or by rotating the current space vector in its space vector representation. In a second aspect, this invention relates to a power tool for performing a braking method. Background Technology

[0002] In the field of power tools, it is known to slow down power tools to complete work or for safety reasons. The following braking methods are known in particular in the prior art: short-circuit braking, using a brake chopper as a braking resistor, and energy recovery.

[0003] In short-circuit braking, the motor of the power tool is short-circuited. This can be achieved, for example, by simultaneously turning on all the low-side semiconductors of the motor inverter. A relatively high initial short-circuit current can be generated, which then becomes a constant short-circuit current. This short-circuit current generates braking torque in the motor of the power tool, which can be used to decelerate the power tool or its components. A disadvantage of short-circuit braking is that the user has little control over the braking torque or braking time. The level of the short-circuit current is determined solely by the motor parameters. Furthermore, the electronics of the power tool must be able to withstand the relatively high initial short-circuit current at the start of short-circuit braking. If the power tool is not designed to withstand this short-circuit current, it may be damaged.

[0004] When a brake chopper is used as a braking resistor, the motor of a power tool can be braked in a controlled manner, making it act as a generator. The delivered energy can be fed back to the DC link of the power tool's electronics. A power tool can have a brake chopper as a braking resistor, configured to connect a resistor to the DC link, thereby converting the energy in the braking resistor into heat. While using a brake chopper provides more freedom in achieving certain desired braking torque or braking time, a disadvantage is that at least one additional hardware component must be installed in the power tool. This increases the weight and size of the power tool. For example, a larger size can affect the ergonomics or handling of the power tool. Installing a brake chopper often requires other additional electronic components, such as MOSFETs, gate drivers, or wiring, which can further complicate the manufacture or assembly of the power tool. Especially if the brake chopper is designed for high pulse power, the cost of the power tool and the required internal installation space can increase significantly.

[0005] Energy recovery is only possible when a power tool uses a power supply unit with feedback capability. The power tool's motor can brake in a controlled manner during energy recovery, thus becoming a generator. The delivered energy can be fed back to the DC link and from there transferred to the power supply unit. The quality and energy recovery capability of a power tool depend heavily on the power supply unit installed in it. During braking operations, assuming, for example, a constant braking current or a specified braking slope, operating conditions may arise that load the power supply unit, potentially exceeding limits that affect its electrical characteristics (such as voltage or current carrying capacity). This can lead to damage to the power supply unit. To avoid exceeding these limits, the practice known to date in the prior art is to perform braking operations as slowly as possible. However, this is not a good idea, especially when the power tool needs to decelerate rapidly, for example, to quickly and reliably protect the user from injury.

[0006] The purpose of this invention is to overcome the defects and disadvantages of the prior art and to provide a method for slowing down a power tool, as well as a power tool that, firstly, allows for the most effective possible protection for the user of the power tool, and secondly, provides a compact and manageable power tool. Furthermore, the released energy should be fed back to the power supply device as efficiently as possible to provide a power tool that is as resource-efficient as possible and has good battery life.

[0007] This objective is achieved through the subject matter of the independent claim. Advantageous embodiments of the subject matter of the independent claim can be found in the dependent claims. Summary of the Invention

[0008] According to the present invention, a method for braking a power tool, the power tool being a battery-operated power tool, is provided, wherein the electrical energy released when the power tool is braked is fed back to the power supply device of the power tool. The braking method is characterized by the following steps: a) Operate the power tool by specifying a first current value. b) The electrical energy released when the power tool is braked will be fed back to the power tool's power supply device. c) If at least one limit value of the power supply device is exceeded, reduce the braking power of the power tool. d) Continue to operate the power tool at the desired current values, which are calculated based on the reduction of the power tool's braking power and the initial current value.

[0009] This method can be used primarily to minimize braking time, and secondarily to provide compact, manageable power tools. The exceptionally short braking time allows for particularly effective protection of the power tool user from injury. The proposed method advantageously allows for energy recovery with exceptionally high efficiency, i.e., feeding electrical energy back to the power supply unit in the power tool. The proposed method can be termed highly efficient regenerative braking operation without a braking chopper.

[0010] This method advantageously allows the released braking energy to be fed back to the power supply device particularly efficiently. According to the invention, the power tool can be connected to at least one power supply device to be supplied with electrical energy. For example, the power tool may have a receiving area or provide options for connecting one, two, or more power supply devices (such as batteries or rechargeable batteries (“batteries”). According to the invention, the terms “rechargeable battery,” “battery,” and “power supply device” are used synonymously. The electronics and motor of the power tool preferably operate with particularly low power loss at optimal operating points. To achieve this, the power tool can, for example, operate along a characteristic curve with optimized power loss. According to the invention, the description of the power tool operating along a characteristic curve with optimized power loss preferably means that losses during the operation of the power tool can be minimized using the invention. For example, these losses can be iron losses and / or copper losses. According to the invention, the description of the power tool operating along a characteristic curve with optimized power loss can also mean that the power tool operates in a manner optimized in terms of current yield and / or efficiency.

[0011] According to the invention, preferably, the power tool operates along the MTPA characteristic curve in the space vector representation, where MTPA stands for "maximum torque per ampere". This advantageously allows the power tool to operate at an optimal current yield. It has been found that in this way, the power tool can operate with particularly low losses or low power losses. Preferably, in the context of the invention, a maximum desired motor stator current I_S, max is specified, which is also preferably referred to as the maximum motor current I_S, max according to the invention. Thus, according to the invention, the maximum motor current I_S, max can be a first current value. However, if the feedback or feedback power is too high, it may exceed the limits designed to ensure reliable operation of the power supply device. These limits may be related to the voltage and / or current of the power supply device. According to the invention, they are referred to as the limits of the power supply device or "battery limits". According to the invention, preferably, the battery voltage limit is referred to as U_Akku, max, and the battery current limit is referred to as I_Akku, max.

[0012] Alternatively or additionally, the first current value may be the desired motor current I_S, soll. According to the invention, it is preferred to prevent exceeding battery limits by actively controlling the battery voltage and / or battery current. This is achieved by initiating a reduction in the braking power of the power tool, preferably after at least one of the battery limits has been identified as being exceeded. According to the invention, for this purpose, it is provided that desired current values ​​are calculated and output, determined based on the reduction in the braking power of the power tool and the first current value. According to the invention, it is preferred that the desired current values ​​from method step d) of the proposed method are desired current values ​​for the d-axis and q-axis represented by a space vector. Therefore, the desired current values ​​for the d-axis and q-axis may be modified current values ​​or second current values, which can be used to continue the operation of the power tool. Continuing operation of the power tool with modified desired current values ​​(preferably for the d-axis and q-axis represented by a space vector) allows ensuring that the braking power of the power tool is reduced and therefore does not exceed the limits of the power supply device, but the power tool can still brake reliably and quickly.

[0013] In a particularly preferred configuration of the invention, the power tool can operate, for example, with a desired motor current I_S, soll. Furthermore, a maximum motor current I_S, max can be specified, and if it exceeds at least one limit value of the power supply voltage, the braking power of the power tool is reduced. Specifically, the braking power of the power tool is reduced by applying a modified braking angle β_brems to rotate the current space vector I_S, max in the space vector representation such that the length of the current space vector I_S, max remains substantially constant. The rotation of the current space vector I_S, max allows for the determination of modified desired current values, preferably for the d-axis and q-axis of the space vector representation, and in this way, the braking power of the power tool is reduced. In this configuration of the invention, it is preferred that the maximum stator current I_S, max and the braking angle β_brems are used to determine the desired current values, preferably for the d-axis and q-axis of the space vector representation, which are intended to be considered as the basis for the remainder of the deceleration process as output or manipulation variables.

[0014] In one exemplary embodiment, the present invention relates to a method for braking a power tool, the power tool being a battery-operated power tool, wherein electrical energy released when the power tool is braked is fed back to the power tool's power supply device. The method is characterized by the following steps: a) By specifying a first current value, operate the power tool along the MTPA characteristic curve in the space vector representation. b) The electrical energy released when the power tool is braked will be fed back to the power tool's power supply device. c) If at least one limit value of the power supply device is exceeded, reduce the braking power of the power tool. d) Continue to operate the power tool with the desired current values ​​for the d-axis and q-axis, which are represented by a space vector and are calculated based on the reduction of the power tool's braking power and the first current value.

[0015] According to a preferred embodiment of the invention, the correction factor k_Dreh can be determined even if the current space vector I_S,max has been rotated. Preferably, the correction factor k_Dreh can be applied to the angular position of the current space vector I_S,max, and thus achieves a modified braking angle ß_brems for rotating the current space vector I_S,max.

[0016] In another particularly preferred configuration of the invention, the braking power of the power tool can be reduced by determining at least one correction factor k and applying it to the maximum motor current I_S,max. This allows for obtaining a desired reduction in the motor current I_S,red, and then, based on this desired reduction, a modified desired current value, preferably for the d-axis and q-axis represented by a space vector, is determined again, thereby reducing the braking power of the power tool. The desired reduction in the motor current I_S,red can be forwarded to the motor current controller, and thus the motor current can be controlled or set based on the desired reduction in the motor current I_S,red. Preferredly according to the invention, in this configuration, the braking power of the power tool is reduced due to the shortening of the current space vector. In other words, applying the correction factor k to the maximum motor current I_S,max to shorten the current space vector results in an advantageous reduction in the braking power of the power tool.

[0017] In another particularly preferred configuration of the invention, the power tool can be operated by specifying a maximum motor current I_S,max. The braking power of the power tool can be reduced by determining at least one correction factor k and applying it to the maximum motor current I_S,max to obtain a desired reduction in the motor current I_S,red; or by rotating the current space vector I_S,max in its space vector representation such that the length of the current space vector I_S,max remains substantially unchanged. The current space vector I_S,max can preferably be rotated by applying a modified braking angle β_brems to the current space vector I_S,max.

[0018] Rotation of the current space vector I_S,max allows the operating point of the power tool's motor to be set to a lower torque, and therefore also a lower braking power, without reducing the stator current amplitude. This high stator current can then also cause high losses in the inverter, electronics, and / or motor, and thus braking energy can be absorbed and converted into heat. Preferably, even when power absorption is limited, unexpectedly large power losses can be converted in the power tool's electronics, inverter, and / or motor when electrical energy is fed back to the power supply device. This advantageously allows for additional power reduction and even faster braking operation. In particular, applying a modified braking angle β_brems and the resulting rotation of the current space vector I_S,max in the space vector representation allows for regenerative braking operation with high losses to decelerate the power tool; the proposed method initially does not require a braking chopper. Preferably, according to the invention, the braking angle β_brems can also be preferably referred to as the "stator current space vector angle β_brems".

[0019] According to a preferred embodiment of the invention, when the current space vector I_S,max is rotated to reduce braking power, a correction factor is determined or output as a manipulated variable using a battery voltage controller and a battery current controller. This reduction in braking power is preferred, particularly when the power supply device and an optional braking resistor (e.g., a braking chopper) have reached their maximum power absorption. This can advantageously maintain battery limits without damaging the power supply device. In particular, rotation of the current space vector allows for obtaining an operating point with reduced braking torque in the space vector representation. The reduced braking torque can be obtained, in particular, by shortening the current space vector and / or by rotating the current space vector.

[0020] The correction factor k can include different components or be formed by different individual correction factors. For example, a correction factor k_U, red for the battery voltage and / or a correction factor k_I, red for the battery current controller can be specified. In addition to the correction factors k_U, red and k_I, red, the optional duty cycle of the brake chopper can also be considered when calculating the braking angle. In other words, according to the invention, it is preferable that the combined correction factor k_red also includes a portion associated with the duty cycle of the brake chopper. This is particularly true when the power tool has a brake chopper. These correction factors can be combined under the term "correction factor k," and the general term for the correction factors in the block diagram is "k_red." According to the invention, it is preferable that the combined correction factor k_red also includes a portion associated with the duty cycle of the brake chopper. This is particularly true when the power tool has a brake chopper. Therefore, the correction factor k can represent the battery voltage correction factor k_U, red or the battery current correction factor k_I, red or a correction factor that reproduces the duty cycle of the brake chopper. Furthermore, the correction factor k can be a mixed correction factor that includes a portion of or a subset of the correction factors mentioned above.

[0021] If the on-duty cycle is 100% or substantially 100%, the energy absorption capacity of the braking chopper may be limited. To circumvent this limitation caused by the on-duty cycle, according to the invention, it is preferable to use a braking chopper with relatively low resistance. Preferably, the braking chopper may have a resistance in the range of 0.1 ohms to 2 ohms. According to the invention, such a braking chopper or braking resistor is preferably referred to as a "low-resistance braking chopper".

[0022] If the power tool includes a brake chopper, the energy distribution of the proposed braking method can be described as follows: First, the released braking energy is fed back to the power supply device. If the power supply device is no longer able to absorb braking energy or braking power, the remaining excess energy can be directed to the brake chopper. If the brake chopper is no longer able to absorb braking energy or braking power, the braking power of the motor can be reduced by using a lower braking torque.

[0023] Preferably, according to the present invention, the braking angle β_brems can also be preferably referred to as the "stator current space vector angle β_brems". In the context of the present invention, this braking angle β_brems can be calculated as follows: β brems = k red ( β brems, MTPA -β brems, 0 Nm ) + β brems, 0 Nm .

[0024] parameter β brems, MTPA Preferably, it corresponds to the angle on the MTPA characteristic curve, while the parameter β brems, 0 Nm This corresponds to the current space vector angle used to achieve an operating point where the torque is 0 Nm or substantially 0 Nm. For example, this operating point could be located in the third or fourth quadrant represented by the space vector. The third quadrant should explicitly include the boundary with the second quadrant (the limit at the top of the third quadrant), and the fourth quadrant should explicitly include the boundary with the first quadrant (the limit at the top of the fourth quadrant). Figure 2a As can be seen, the boundary between the third and second quadrants is the intersection of the current-limiting circle K and the 0 Nm characteristic curve represented by the space vector, and preferably, no torque is generated. For example, in... Figure 2b As can be seen, the intersection of the current limiting circle K and the 0Nm characteristic curve can also be located in the fourth quadrant. The maximum stator current I_S,max and the current space vector angle... β brems It can be advantageously used to calculate the desired current values ​​of the d-axis and q-axis, preferably represented by a spatial vector.

[0025] According to the present invention, the braking torque is reduced by the rotational braking angle or the stator current space vector angle β_brems, while the losses in the inverter and / or motor of the power tool continue to absorb the maximum braking power because the motor current amplitude is substantially constant, and therefore the present invention can be used in general to achieve particularly rapid deceleration of the power tool.

[0026] According to the invention, preferably, the length and / or angle of the operating range of the current space vector I_S are limited by a correction factor k, and therefore do not exceed the first limit value U_Akku, max and / or the second limit value I_Akku, max of the power supply device. Preferably, the operating range of the current space vector I_S can be limited by the current limit of the power tool's inverter, particularly by providing a correction factor K that can be applied to the length and / or angle of the current space vector I_S, thereby advantageously ensuring that it does not exceed the voltage and / or current limits of the power supply device. According to the invention, preferably, if electrical energy is recovered into the power supply device of the power tool in an unrestricted manner, the longest current space vector I_S lies on the MTPA characteristic curve, which is preferably limited by the current limit of the power tool's inverter. The operating range of the current space vector I_S can be limited by the current limit of the power tool's inverter, particularly since the current space vector I_S is limited by the limit values ​​U_Akku, max and / or I_Akku, max when it reaches these limit values, and therefore does not exceed the limits of the power supply device.

[0027] According to one configuration of the invention, since at least one correction factor k is determined and applied to the maximum motor current I_S,max, a reduced desired value of the motor current I_S,red is obtained, thus preventing these limits of the power supply device from being exceeded. Advantageously, this allows for active control of the battery voltage and / or battery current, and provides a balanced trade-off between maximum feedback efficiency and battery protection. At least one correction factor k is preferably determined in a controller configured for this purpose; the voltage correction factor k_U,red can be provided by a voltage controller, and the current correction factor k_I,red can be provided by a current controller within the electronics of the power tool. The voltage controller and current controller are preferably the voltage controller and current controller of the power supply device. Preferably, the battery voltage controller is thus configured to determine the battery voltage correction factor k_U,red, and the battery current controller is configured to determine the battery current correction factor k_I,red. The corresponding correction factors k_U,red and k_I,red can preferably take values ​​in the range between 0 and 1. The reduced desired motor stator current I_S,red is preferably output as an output variable in this control or correction process. According to a preferred embodiment of the invention, this reduced desired motor stator current I_S, red is also referred to as the reduced motor current I_S, red. Therefore, a fixed maximum motor current I_S, max can be multiplied by correction factors or reduction factors k_U, red and k_I, red, such that the reduced desired current value I_S, red can be forwarded to the motor current controller. Preferably, a first current value (e.g., the maximum motor current I_S, max) can be multiplied by a battery voltage correction factor k_U, red and / or a battery current correction factor k_I, red to obtain desired current values ​​preferably for the d-axis and q-axis, which, according to the invention, serve as a second current value that can be used to continue operating the power tool.

[0028] The so-called operating range AB of the current space vector I_S is shown in the corresponding space vector representation (see Figure 1 Without limiting energy feedback (i.e., "battery energy recovery"), the longest current space vector I_S is obtained on the MTPA characteristic curve. The current space vector I_S is specifically the stator current space vector, that is, specifically represents the space vector of the stator current of the electric motor of the power tool. According to the invention, preferably, the current space vector I_S is limited by the current limit of the inverter of the power tool's electronics. This current limit of the inverter is also... Figure 1The spatial vector representation depicted is shown, specifically, as circle K. Preferably, when the battery's voltage limit (U_Akku, max) and / or when the battery's current limit (I_Akku, max) is reached, the current spatial vector I_S can be shortened to a degree not exceeding the battery's limit. Preferably, the current spatial vector I_S is shortened by applying at least one correction factor k.

[0029] The term "correction factor k" is a general term for different correction factors. For example, they can be correction factors k_U, red and k_I, red used to limit the maximum motor current I_S, max to a reduced motor current I_S, red. In the context of this invention, at least one correction factor k is applied to the desired value of the maximum motor current. For example, when using a braking chopper, i.e., when electrical energy is fed back not only to the power supply device but also to a braking resistor (preferably referred to as a "braking chopper" according to the invention), another correction factor k_red can limit the duty cycle (duty time). According to the invention, it is preferred that at least one correction factor k is in the range of 0 to 1.

[0030] According to a preferred embodiment of the present invention, at least one correction factor k is composed of a first correction factor k_U, red, a second correction factor k_I, red, and / or a third correction factor k_red, wherein the first correction factor k_U, red is determined by the voltage controller of the power supply device, the second correction factor k_I, red is determined by the current controller of the power supply device, and the third correction factor k_red is used to limit the duty cycle.

[0031] According to the present invention, preferably, at least one correction factor k corresponds to a first correction factor k_U, red determined by the voltage controller of the power supply device, or corresponds to a second correction factor k_I, red determined by the current controller of the power supply device, or corresponds to a third correction factor k_red used to limit the duty cycle.

[0032] The voltage and current controllers of the power supply device are configured to determine corresponding correction factors k_U,red and k_I,red, particularly when a braking chopper is not used. Additionally, the power tool or its electronics may include other controllers. Specifically, if a braking chopper is used in the context of this invention, the power tool or its electronics may include three controllers. For example, a first controller may be provided, preferably in the form of a two-level controller with hysteresis and configured to excite the braking chopper. According to the invention, this first controller is preferably in the form of a comparator with switching hysteresis, preferably including an upper on threshold and a lower off threshold, or characterized by such thresholds. The first controller is particularly designed to compare the DC link voltage or voltage U_Akku of the power supply device with the reference voltage U_Chopper of the braking chopper. The output signal of the first controller may preferably be or be formed as a signal for pulse width modulation (PWM), and the first controller outputs a high-level signal, particularly when the voltage U_Akku of the power supply device is greater than the reference voltage U_Chopper of the braking chopper. In other words, the first controller is configured to output a high-level PWM signal, specifically when U_Akku > U_Chopper. For example, the PWM signal can have a duty cycle, which can be formed by a low-pass filter.

[0033] In an alternative configuration of the invention, the first controller may also be in the form of a PI controller. Preferably, according to the invention, the output variable of the first controller, preferably in the form of a PI controller, is the duty cycle of the braking chopper. Preferably, this duty cycle can be used to generate excitation pulses for the braking chopper. For example, this can be achieved by using a PWM module. In other words, the PWM module can be designed to use the duty cycle output by the PI controller to generate excitation pulses for the braking chopper.

[0034] The power tool or its electronics may have a second controller for monitoring the limits of the power supply device. These limits may be related to, for example, voltage and / or current; accordingly, they are preferably referred to as U_Akku, max or I_Akku, max. According to the invention, it is particularly preferred that the second controller is configured to control the current of the power supply device (i.e., the "battery current") to the limit value I_Akku, max. Preferably, the second controller outputs a reference voltage U_Chopper for braking the chopper as a manipulated variable, which can then be controlled to its maximum value or limit value U_Akku, max to ensure that the maximum permissible "battery voltage" is not exceeded, i.e., the voltage of the power supply device.

[0035] The power tool or its electronics may have a third controller for limiting the duty cycle. The third controller may be specifically designed to control the duty cycle to a desired value D_Soll, which is at most approximately 95% of the on-time duty cycle of the brake chopper. The third controller may output a correction or reduction factor k_red as an output variable, which, like the other two correction factors k_U,red and k_I,red, is in the range of 0 to 1. Preferably, according to the invention, the correction factor k_red is preferably referred to as the "third correction factor". Preferredly according to the invention, the third correction factor k_red is multiplied by the maximum desired motor stator current I_S,max. This advantageously allows obtaining or determining the reduced desired motor stator current I_S,red.

[0036] Power tools or their electronics may have a limiting device for the rate of change of motor current. The limiting device is preferably configured to provide a smooth transition from driving the power tool or its components to decelerating it. According to the invention, the limiting device may also preferably be referred to as a "motor current rate of change limiter". Preferably, according to the invention, the limiting device prevents the desired motor stator current from jumping to the maximum motor stator current I_S,max by allowing only the maximum rate of change of the desired motor stator current. The rate of change is preferably indicated in the physical unit "amperes per second" (i.e., amperes / second or A / s). The limiting device may be provided as an optional component on the power tool. The limiting device can then be... Figures 3 to 6 The block diagram is shown as an additional box that allows for a particularly smooth transition from drive to deceleration.

[0037] The proposed braking method is described based on field-oriented control (FOC). However, according to the invention, it is also preferred to implement the method using block commutation. In the language of space vector representation, Figure 2a and Figure 2b The operating range of the current or stator current space vector is shown in the figure.

[0038] Power tools may include a braking chopper, which absorbs the electrical energy released when the power tool is braked. The braking method using a braking chopper is an energy recovery method that utilizes the braking chopper for efficient regenerative braking operation. According to the invention, it is preferred that the stator current I_S be shortened only when at least one of the limiting values ​​of the power supply device (e.g., U_Akku, max and / or I_Akku, max) has reached its applicable limit. According to the invention, it is also preferred that the stator current I_S be shortened when the duty cycle of the braking chopper's on-time has reached its limit.

[0039] The use of a braking chopper is advantageous, particularly when the power absorption of a power supply device is limited, for example, due to exceeding the critical limit of the power supply device. According to the invention, preferably, in addition to the power supply device, the braking chopper can also absorb electrical energy released when the power tool is braked. Preferably, the power supply device can absorb a basic amount of electrical energy, and the braking chopper can be provided as an optional element on the power tool to absorb additional electrical energy that the power supply device can no longer absorb due to possible technical limitations. This advantageously allows for the provision of higher braking power. It has been found that when a braking chopper is provided, the power supply device has less impact on braking torque and braking time than a braking process without a braking chopper. According to the invention, preferably, the maximum power loss within the braking chopper is limited by design. In particular, the limit is reached when the duty cycle of the braking chopper, especially the on-time duty cycle, is 100% or substantially 100%. According to the invention, the duty cycle or on-time duty cycle can also preferably be referred to as duty degree D. If such a duty cycle or on-time duty cycle is reached at 100% or substantially 100%, then according to the invention it is preferable to reduce the braking power by reducing the motor current, and in particular reducing the desired motor stator current I_S,red. This is especially true because, in this case, the power supply device and the braking chopper have already reached their maximum power absorption.

[0040] In an exemplary embodiment of the invention, the power tool can be operated by specifying a maximum motor current I_S,max, particularly a maximum desired motor stator current I_S,max. In this case, a first correction factor k_U,red can be determined by the voltage controller of the power supply device, and / or a second correction factor k_I,red can be determined by the current controller of the power supply device; these correction factors can be applied to the maximum motor current I_S,max. This allows for a reduced desired value of the motor current I_S,red, which can also be converted into a second current value for continued operation of the power tool, particularly desired current values ​​for the d-axis and q-axis in the space vector representation. According to the invention, preferably, the reduced desired value of the motor current I_S,red is forwarded to the motor current controller, and thus the motor current can be controlled or set based on the reduced desired value I_S,red. This method reduces braking power by shortening the stator current space vector on the MTPA characteristic curve in the space vector representation. In particular, correction factors can be applied to reduce the value of the maximum motor current I_S,max to the reduced desired value of the motor current I_S,red.

[0041] In another exemplary embodiment of the invention, the power tool can determine at least one correction factor k, which is applied to the maximum motor current I_S,max, to obtain a reduced expected value I_S,red of the motor current. The reduced expected value I_S,red of the motor current can be forwarded to the motor current controller, and thus the motor current can be controlled or set based on the reduced expected value I_S,red. This method also reduces braking power by shortening the stator current space vector on the MTPA characteristic curve in the space vector representation. Specifically, at least one correction factor can be applied to reduce the value of the maximum motor current I_S,max to the reduced expected value I_S,red of the motor current.

[0042] According to a preferred embodiment of the invention, the power tool stops with a braking time ranging from 2 to 4 seconds. Decelerating the power tool with a braking time between 2 and 4 seconds (s) particularly protects parts and components in the power tool's transmission system. According to a preferred embodiment of the invention, the braking torque of the power tool can be set such that a braking time between 2 and 4 seconds can be achieved.

[0043] If a recoil event is detected in the power tool, according to the invention, it is preferable that the tool stop with a braking time of less than 1.5 seconds, preferably less than 1 second, and most preferably less than 0.5 seconds. This allows the tool to decelerate as quickly as possible to optimally protect the user from injury. According to the invention, the expression "stopped power tool" or "stopped tool" means bringing the tool to a standstill. However, according to the invention, the expression "stopped power tool" or "stopped tool" can also mean that the tool loses a large portion of its rotational energy, and the tool now continues to rotate only at speeds less dangerous to the user. According to the invention, the expression "a large portion of its rotational energy" preferably means that more than 50% of the tool's rotational energy is converted into another form of energy and / or fed back to the power supply device. It is particularly preferred according to the invention that, in the context of the proposed braking method, more than 60%, 70%, 80%, 90%, or 95% of the tool's rotational energy is converted into another form of energy and / or fed back to the power supply device. Preferably, the power tool can decelerate with a braking time of less than 1.5 seconds, preferably less than 1 second, and most preferably less than 0.5 seconds, causing the machine tool to lose a large portion of its rotational energy. According to the invention, this preferably means that the power tool loses more than 50%, preferably more than 60%, 70%, 80%, 90%, or 95% of its rotational energy, and that more than 50%, preferably more than 60%, 70%, 80%, 90%, or 95% of the rotational energy is converted into another form of energy and / or fed back to the power supply device. Of course, all intermediate values ​​between 50% and 100%, as indicated by the expression "large portion of rotational energy," are also possible; that is, for example, greater than 53%, greater than 66.66%, greater than 75%, greater than 87.5%, or greater than 93.76%.

[0044] The power tool or its tool decelerates by the proposed braking method, in which the braking power of the power tool decreases when at least one limit value of the power supply device is exceeded, and the power tool continues to operate with desired current values, particularly for the desired current values ​​of the d-axis and q-axis in spatial vector representation, calculated based on the reduction of the braking power of the power tool and a first current value. The rotational energy loss suffered by the power tool due to deceleration can advantageously be fed back to the power tool's power supply device, and thus this energy can later be used again to further supply energy to the power tool. In other words, the power tool's power supply device can be at least partially recharged by the proposed braking method by feeding back the rotational energy released when the power tool or its tool is braked (i.e., recovering it into the power tool's power supply device). According to the invention, it is particularly preferred that the tool or power tool does not necessarily stop completely, i.e., does not necessarily come to a complete stop, but only that the power tool loses or loses a large portion of its rotational energy. Therefore, the braking time t_down preferably does not end when the tool is stationary, but rather when the tool's speed n has reached, for example, less than 70%, preferably less than 63%, 55%, 45%, 32%, 22%, or even lower percentages of the original speed n_max. Thus, the time period before the power tool is actually stationary is advantageously no longer important.

[0045] The braking time t_down (i.e., the time period required for the power tool to stop or come to a standstill) is limited by time values ​​t2 and t3. Preferably, the power tool or its tool begins to decelerate at time t2, and the tool of the power tool comes to a standstill at time t3. The tool coming to a standstill is synonymous with the tool rotating at 0% of its original speed n_max. However, if the tool is to lose only or a large portion of its rotational energy, the speed of the tool is preferably reduced to a percentage or value less than 70%, preferably less than 63%, 55%, 45%, 32%, 22%, or lower of the original speed n_max. According to the invention, the corresponding end time of the braking time t_down is thus preferably referred to as t3_70%, t3_63%, t3_55%, t3_45%, t3_32%, or t3_22%. For example, the braking time t_down may end at the time value t3_22%, which corresponds to a speed of 22% of the original speed n_max of the power tool. Therefore, the time value t3_22% and the velocity value of 22% of the tool's original velocity n_max form a value pair, which can be represented in a graph of velocity n versus time t and, together with other value pairs, form the curve n(t). This graph is in Figure 7 and Figure 8As shown in the figure. According to the present invention, preferably, the rotational energy E of the tool and the velocity n have the following relationship: E = 1 / 2 J (2 π n / 60) 2 , Here, the letter J represents the moment of inertia of the power tool. This means that if the tool's speed n decreases by 50%, only 25% of the original rotational energy E remains. Therefore, in this example, if the tool's speed n decreases to half its original value, the rotational energy E decreases by 75%.

[0046] If the power tool detects a recoil event, according to the present invention, it is preferable that the power tool stops with a braking time of less than 1.5 seconds, preferably less than 1 second, and most preferably less than 0.5 seconds, wherein the braking time t_down is preferably characterized not only by the power tool being stationary. Rather, the braking time may also end when the power tool is rotating at a speed of less than 70%, preferably less than 63%, 55%, 45%, 32%, or 22% of the tool's original speed n_max. Preferably, the time period before the power tool is actually stationary is no longer important for this choice of the end of the braking time t_down t3_x % . The letter x in the expression "t3_x %" preferably represents any percentage value between 0 and 70% of the tool's original speed n_max.

[0047] The term "recoil event" describes a sudden and unexpected force occurring between a power tool and the substrate to be processed. For example, the tool itself or the power tool may move unexpectedly while processing the substrate, potentially posing a risk to the user of the power tool. Such a recoil event can occur, for instance, when the tool becomes stuck or jammed in the substrate (e.g., in a cutting gap). Furthermore, recoil can occur if the substrate to be processed has non-uniform material properties (e.g., reinforcing steel in concrete), or if a blunt tool is used. In all these cases, it is desirable for the tool to stop as quickly as possible, i.e., to come to a complete stop. This invention enables such rapid deceleration by achieving a braking time of less than 1.5 seconds after the recoil event is detected.

[0048] The rapid deceleration of a power tool is preferably also represented by a particularly low ratio of braking time to acceleration time, which is less than 1. This is because, according to the invention, it is quite particularly preferred that the ratio of braking time t_down to acceleration time t_up is less than 1. According to the invention, this preferably means that braking time t_down is less than acceleration time t_up. In the case of recoil, the ratio of braking time t_down to acceleration time t_up can even be less than 0.7, particularly preferably less than 0.5. According to the invention, such a ratio less than 0.5 preferably means that braking time t_down is less than half of acceleration time t_up. According to the invention, the term "acceleration time t_up" preferably represents the time period required for the power tool to reach its maximum speed n_max from a standstill. If time t0 is assigned to the power tool being at a standstill and time t1 is assigned to the first time the maximum speed is reached, then the time period associated with "acceleration time t_up" extends between time t0 and t1. According to the invention, the term "braking time t_down" preferably refers to the time period required for a power tool to reach a standstill from its maximum speed n_max (at which point the tool no longer rotates, i.e., the speed n is "0", n = 0 revolutions per minute (rpm)). If time t3 is assigned to the power tool being at a standstill and time t2 is assigned to the start of deceleration, then the "braking time t_down" period extends between time t2 and t3. The power tool can be used during the time period between t1 and t2, for example, by operating the power tool at different speeds. According to the invention, it is preferred that the power tool includes a speed controller to adjust the speed. Preferably, a short braking time during "normal" braking and when a recoil event is detected can be achieved by the proposed braking method, i.e., because the rotational energy stored in the power tool can be fed back, for example, to the power tool's power supply device, and because the power tool's braking power decreases when the power tool's power supply device has reached its energy absorption limit.

[0049] According to the invention, it is preferable to use a sensor device to detect recoil events. In other words, the power tool may include a sensor device configured to reliably, quickly, and accurately detect recoil events or other emergency situations. It is also preferable according to the invention to use existing electronics or electronics present in the power tool for detecting recoil events. This can be done, for example, by evaluating the operating parameters of the power tool (such as current, motor and / or spindle speed, acceleration, or electrical energy), information about which is already available or known in the power tool, in order to detect the onset of a recoil event. According to the invention, it is also preferable to provide sensing devices, such as sensors, on the power tool to determine and evaluate the operating parameters in order to reliably and quickly detect recoil events or other emergency situations.

[0050] In a second aspect, the present invention relates to a power tool for performing the proposed method. The terminology, definitions, and technical advantages introduced for the braking method are preferably applied to the power tool with necessary modifications. The motor of the power tool is a brushless motor capable of delivering power greater than 1.8 kilowatts (kW). Preferably, the power tool can be a brushless control electrical unit with braking functionality. For example, the power tool can take the form of an electrically operated cutting grinder. According to the invention, it is particularly preferred that the power tool is a battery-operated cutting grinder having a cutting disc as a tool. The power tool can be connected to at least one power supply device so that electrical energy is supplied by the power supply device. At least one power supply device of the power tool can, for example, deliver a voltage greater than 20 volts (V). A voltage between 21 V and 22 V is particularly preferred. The power tool can also have two or more power supply devices. If the power tool has more than one power supply device, the electrical energy released when the power tool is braked can be fed back to the first power supply device and / or the second power supply device. This energy recovery can be performed substantially simultaneously, sequentially, or according to a specially designed algorithm.

[0051] A cutting disc is a disc-shaped tool of a cutting-type grinding machine, which can be slowed down and brought to a stop using the proposed braking method. The cutting disc can have a diameter greater than, for example, 230 mm. For example, the cutting disc can have a diameter of 300 mm, 250 mm, or 400 mm, but is not limited to this. For example, the weight of the cutting disc can be in the range of 200 to 2500 grams, i.e., between 0.2 and 2.5 kg. For example, the weight of the cutting disc can be 210 g, 530 g, 550 g, 930 g, 1270 g, 1280 g, 1720 g, or 2450 g, but is not limited to this. For example, the cutting disc can be a diamond cutting disc or an abrasive cutting disc with bonded abrasive particles. A diamond cutting disc is preferably characterized by having a steel core with a diamond section.

[0052] According to the present invention, the motor of the power tool can preferably be controlled using field-oriented control or block commutation. In a preferred configuration of the invention, it is preferable that the braking angle β_brems can be modified to reduce the braking power of the power tool and rotate the current space vector I_S,max in the space vector representation. If block commutation is used to control the motor of the power tool, it is also preferable according to the present invention to modify the commutation angle to reduce the braking power of the power tool. In a preferred configuration, these commutation angles are modified in such a way that the resulting commutation block lags. The power tool may include a brake chopper configured to absorb electrical energy released when the power tool is braked. In addition to the power supply device, the brake chopper is specifically configured to absorb additional electrical energy that the power supply device can no longer absorb due to limited power absorption.

[0053] The following describes exemplary embodiments of the present invention, specifically a braking method using energy recovery, which utilizes a braking chopper for efficient regenerative braking operation, such as... Figure 4 The diagram illustrates this. In this configuration of the invention, the PWM signal for the braking chopper can be generated as follows, specifically provided by a first controller (e.g., a two-level controller). The first controller may include or may be formed from a comparator. The comparator is configured to compare the output voltage u_Akku with the output manipulated variable of the battery current controller U_Chopper.

[0054] If the battery voltage u_Akku (with hysteresis considered if necessary) is greater than the reference voltage U_Chopper, a high level can be output on the PWM signal U_GatedriverinputPWM. Otherwise, a low level is output. According to the present invention, preferably, the battery current ripple, battery voltage ripple, and / or the resulting switching frequency are adjusted over the hysteresis width.

[0055] According to a preferred embodiment of the invention, the duty cycle of the PWM signal is determined by a low-pass filter, preferably an RC low-pass filter. For example, a PID controller can be used as a controller for the battery current or the duty cycle.

[0056] For example, if a power tool is to be braked with a relatively cold and fully charged rechargeable battery (“battery”), initially, the battery preferably has a high cell voltage due to its high fill level and a high cell internal resistance due to the low temperature. When electrical energy is fed back to the power supply device, the battery voltage can rise rapidly and thus reach the voltage limit U_Akku, max of the power supply device within a short time. The proposed braking method involves advantageously limiting the voltage to this limit value U_Akku, max. According to the invention, it is preferred that the power supply device operates within the region of the voltage limit U_Akku, max during prolonged braking operations.

[0057] For example, if a power tool is to be braked with a relatively warm and essentially half-full battery, the voltage limit U_Akku, max is not reached. Instead, in this case, it is preferable to actively limit the battery current to the limit value through control.

[0058] Further advantages will become apparent from the following description of the drawings. The drawings, description, and claims contain many combinations of features. Those skilled in the art will also be able to consider these features individually and combine them to produce other useful combinations. Attached Figure Description

[0059] In the accompanying drawings, identical and similar parts are indicated by the same reference numerals.

[0060] In the attached diagram: Figure 1 The possible operating range of the stator current space vector in the space vector representation during efficient regenerative braking operation is shown; Figure 2a , Figure 2b The possible operating range of the stator current space vector in the space vector representation during highly lossy regenerative braking operation is shown; Figure 3 A possible "energy recovery" block diagram is shown, in which efficient regenerative braking operation is achieved without a braking chopper; Figure 4 A possible "energy recovery" block diagram is shown, in which efficient regenerative braking operation is achieved with a braking chopper; Figure 5 A possible "energy recovery" block diagram is shown, in which extremely lossy regenerative braking operation is achieved without a braking chopper; Figure 6 A possible "energy recovery" block diagram is shown, in which extremely lossy regenerative braking operation is achieved with a braking chopper. Figure 7A schematic graph of speed versus time is shown to illustrate braking and acceleration times; Figure 8 A schematic graph of speed versus time is shown to illustrate braking and acceleration times; Figure 9 A schematic representation of a preferred configuration of the proposed power tool is shown. Detailed Implementation

[0061] Figure 1 A possible spatial vector representation depicting the operation of the power tool 10 is shown. Specifically, Figure 1 The possible operating range AB of the stator current space vector I_S in this space vector representation during efficient regenerative braking operation of the power tool 10 is shown. The x-axis of the space vector representation shows the value of the current I_d flowing through the motor 12 of the power tool 10. Figure 8 The power tool 10 is shown schematically.

[0062] The y-axis, represented by the space vector, shows the I_q value of the current flowing through the motor 12 of the power tool 10. The value I_q represents the torque component of the current, while the value I_d represents the current component that forms the field.

[0063] Figure 1 The four quadrants 1, 2, 3, and 4, representing spatial vectors, are shown. Quadrant 1 is characterized by a negatively increasing torque. M and generator operation G. The second quadrant (2) is characterized by a positively increasing torque. M and motor operation M. The third quadrant (3) is characterized by negatively increasing torque. M and motor operation M. The fourth quadrant (4) is characterized by positively increasing torque. M and generator operation G. In Figure 1 As shown in Figure 2, the rising or falling torque hyperbola is represented by the dashed arrows. The torque hyperbola is preferably formed from operating points having the same torque. Figure 1 Circle K is shown, representing the current limit of the inverter of power tool 10. Circle K, or the inverter's current limit, has equal portions located in the four quadrants 1, 2, 3, and 4 of the space vector representation, meaning that the center of circle K coincides with the intersection of the y-axis and x-axis of the space vector representation. The operating range AB of the stator current space vector I_S is shown in the third quadrant 3 of the space vector representation. Figure 1 In the space vector representation shown, the operating range AB of the stator current space vector I_S coincides with the MTPA characteristic curve of the power tool 10. Therefore, the motor 12 of the power tool 10 advantageously operates at an efficiency-optimized operating point, where heat loss is minimized.

[0064] The 0 Nm characteristic curve N, which extends substantially parallel to the y-axis representing the space vector, extends through the first quadrant 1 and the fourth quadrant 4. Furthermore, a second 0 Nm characteristic curve N2 is obtained that extends along or coincides with the x-axis (and is therefore not shown). Figure 1 The spatial vector depicted illustrates the power tool 10 or its operation, for which, due to the determination of at least one correction factor k and its application to the maximum motor current I_S,max of the power tool 10, the braking power of the power tool 10 is reduced, resulting in a desired reduction in the motor current I_S,red. This corresponds to the efficient regenerative braking operation of the power tool 10.

[0065] Figure 2a and Figure 2b The spatial vector representation of the highly lossy regenerative braking operation of the power tool 10 is shown. Figure 1 Unlike the method shown in Figure 2, the braking method involves rotating the current space vector I_S,max in the space vector representation by applying a modified braking angle β_brems, such that the length of the current space vector I_S,max remains substantially unchanged, and the braking power of the power tool 10 is reduced. The current space vector I_S,max is initially in the third quadrant 3 of the space vector representation, but due to… Figure 2a The rotation within the space vector eventually occurs at the boundary between the second quadrant (2) and the third quadrant (3). The current space vector I_S,max is initially in the third quadrant (3) as represented by the space vector, but due to... Figure 2b The rotation ultimately places it in the fourth quadrant 4. The braking angle β_brems is also shown in the fourth quadrant 4, represented by a space vector. The rotated current space vector I_S,max in the fourth quadrant 4 intersects the circular region K representing the current limit of the inverter of the electronic device of the power tool 10. The intersection of the rotated current space vector I_S,max and the circular region K in the exemplary embodiment of the invention depicted in FIG2 coincides with the intersection of the circular region K and the 0 Nm characteristic curve N. Therefore, the operating range AB is limited to the operating point between the state "maximum braking torque" and "no braking torque, i.e., 0 Nm".

[0066] It should be noted that Figures 3 to 6 The block diagram shown illustrates a braking method involving the use of field-oriented control to operate motor 12 in a power tool 10. The proposed method can, of course, also be implemented in the power tool 10, in which block commutation is used to control motor 12. Motor 12 of the power tool 10 is preferably a brushless motor capable of delivering power exceeding 1800 watts (W).

[0067] Figure 3A possible "energy recovery" block diagram is shown, in which efficient regenerative braking operation of the power tool 10 is achieved without the braking chopper 18. Figure 3 In the described braking method, the battery voltage controller 20 is configured to output a correction factor k_U, red for the voltage of the power supply device 14, while the battery current controller 22 is configured to output a correction factor k_I, red for the current of the power supply device 14. Furthermore, a speed controller 30 is provided to control the speed n of the power tool 10. The desired current value, which can be forwarded to the motor current controllers 34 and 36, can be obtained as an output variable or manipulated variable of the braking method. The desired current value can preferably be a desired current value for the d-axis and q-axis represented by a space vector. The motor current controllers 34 and 36, particularly the d-current controller 34 and q-current controller 36, forward their control commands to pulse width modulation (PWM).

[0068] Figure 4 A possible "energy recovery" block diagram is shown, in which efficient regenerative braking operation of the power tool 10 is achieved with a braking chopper 18. Figure 4 The block diagram shown depicts the process from... Figure 3 The block diagrams shown therein include the known battery current controller 22, speed controller 30, and motor current controllers 34 and 36. Furthermore, Figure 4 A duty cycle controller 28 is shown, which, according to the invention, may also be referred to as a "third controller," and is used to limit the duty cycle to a desired value D_soll, for example, 95%. The output value of the third controller is a correction factor k_red, which is between a value of 0 and a value of 1. This correction factor k_red can be multiplied by the current I_S,max to obtain a reduced desired motor stator current I_S,red.

[0069] also, Figure 4 The block diagram illustrates a two-level controller 24 with hysteresis, which, according to the invention, is preferably referred to as a "first controller." This first controller 24 is preferably used to excite a braking resistor 18, referred to as a "braking chopper." The first controller 24 can, for example, be in the form of a comparator with switching hysteresis and is configured to compare a DC link voltage with a reference voltage. The DC link voltage can also preferably be referred to as the battery voltage u_Akku, while Figure 4 The reference voltage in the circuit is referred to as "U_Chopper". The first controller 24 outputs a PWM signal as its output signal. If the battery voltage is greater than the reference voltage, i.e., u_Akku > u_Chopper, then the PWM signal outputs a high level. The duty cycle of the PWM signal can be, for example, determined by... Figure 4The low-pass filter 32 shown is formed. According to the present invention, values ​​or variables that change over time are represented by lowercase letters, while constant values ​​or variables (such as limit values ​​or other specified values) are represented by uppercase letters.

[0070] Figure 5 A possible "energy recovery" block diagram is shown, in which highly lossy regenerative braking operation of the power tool 10 is achieved without the braking chopper 18. Similar to... Figure 3 The block diagram, Figure 5 The braking method described herein involves output correction factors k_U, red and k_I, red, which can be combined to form a common correction factor k_red. Figure 5 The correction factor k_red used is preferably generated by a combination of the voltage and current correction factors k_U, red and k_I, red. Figure 5 The correction factor k_red in the configuration of the present invention shown (where the braking chopper 18 is preferably not used) does not have a portion attributable to the duty cycle of the braking chopper 18.

[0071] Specifically, the correction factor k_U,red can be determined by the battery voltage controller 20, and the correction factor k_I,red can be determined by the battery current controller 22. The correction factors k_U,red and k_I,red can be used to calculate a combined correction factor k_red, which can be used to calculate the stator current space vector angle or braking angle β_brems. This is achieved by subtracting the angles β_brems, MTPA and β_brems, 0 Nm and multiplying them by the combined correction factor k_red. β_brems, 0 Nm can be added back to the product, thus obtaining the braking angle β_brems. The parameter β_brems, MTPA preferably represents the angle on the MTPA characteristic curve, while the parameter β_brems, 0 Nm corresponds to the stator current space vector angle in the fourth quadrant 4 of the space vector representation or to the stator current space vector angle on the x-axis between the second quadrant 2 and the third quadrant 3, at which no torque is generated. In the fourth quadrant 4, the parameter β_brems, 0 Nm is preferably obtained from the intersection of the current limit circle K and the 0 Nm characteristic curve N. The braking angle β_brems and the current I_S, max can be used to calculate the expected values ​​of d and q that can be forwarded to the d current controller 34 and the q current controller 36.

[0072] Figure 6 A possible "energy recovery" block diagram is shown, in which highly lossy regenerative braking operation of the power tool 10 is achieved with the braking chopper 18. Figure 6 The block diagram shown broadly illustrates Figure 4 and Figure 5 A combination of elements in a diagram.

[0073] Figure 7 A schematic graph showing the speed n of the motor 12 of the power tool 10 relative to time t is provided to illustrate the braking time t_down and acceleration time t_up. It shows the possible response of speed n, with an interruption between time t1 and t2. During the time interval between time t0 and t1, the speed n of the power tool 10 increases so as to reach its maximum value n_max at time t1. According to the invention, this time interval between the limit t1 and t2 is referred to as the acceleration time t_up. From the maximum speed value n_max, the power tool 10 can be brought to a stop by a deceleration operation. In the case of a power tool in normal operation, this braking operation can be performed according to… Figure 7 The dashed lines in the diagram represent the braking time, and it can, for example, take longer than the acceleration time t_up. In this case, the ratio of braking time to acceleration time can be greater than 1 because the braking time t_down is greater than the acceleration time t_up. Figure 7 In the curve of speed n versus time t shown, the braking time t_down is limited by times t2 and t3.

[0074] According to a preferred configuration of the present invention, the braking of the power tool 10 has a... Figure 7 The response of the two solid lines in the diagram. Deceleration during normal deceleration is indicated by the right solid line, with a braking time t_down ranging from 2 to 4 seconds. In this case, the ratio of braking time to acceleration time can be less than 1, i.e., braking time t_down is less than acceleration time t_up. After detecting recoil, the power tool 10 or its tool 16 can decelerate in less than 1.5 seconds. Such rapid or recoil braking operations are caused by... Figure 7 The solid line on the left indicates this. In this case, the ratio of braking time to acceleration time can be less than 0.7, preferably less than 0.5, that is, the braking time t_down is significantly less than the acceleration time t_up. For example, the braking time t_down can be less than 70% of the acceleration time t_up, preferably less than 50%.

[0075] Figure 8A schematic graph of the speed n of the motor 12 of the power tool 10 relative to time t is also shown to illustrate the braking time t_down and the acceleration time t_up. The inventors have recognized that at reduced speeds, the rotating cutting disc 16 now possesses only very little rotational energy, and therefore poses less risk to the user of the power tool 10. Therefore, in the context of this invention, it may be sufficient that the tool 16 of the power tool 10 does not come to a complete stop, but rather that the braking operation ends, for example, before the tool 16 of the power tool 10 rotates at a speed n less than 70%, preferably less than 63%, 55%, 45%, 32%, or 22% of its original speed n_max. Of course, for example, the tool 16 of the power tool 10 may also rotate at an even lower percentage of its original speed n_max before decelerating to a stop. The end of the braking time t_down is then defined accordingly by the end time t3_70%, t3_63%, t3_55%, t3_45%, t3_32%, or t3_22%. Of course, all intermediate values ​​between 70% and 0% are also possible, such as 67%, 57.5%, 43.33%, 2.56%, etc. In this configuration of the invention, it is preferable that the tool 16 of the power tool 10 loses a larger share of its rotational energy, which is fed back to the power supply device 14 of the power tool 10. Since a large share of rotational energy is removed, the tool 16 of the power tool 10 can decelerate sharply, so that the rotating cutting disc 16 no longer poses a danger to the user of the power tool 10. If the braking time t_down does not end first when the tool 16 of the power tool 10 is stationary, but ends when the tool 16 of the power tool 10 is rotating only at less than 70%, preferably less than 63%, 55%, 45%, 32%, or 22% of the original speed n_max of the tool 16, the time period before the tool of the power tool is actually stationary is advantageously no longer important, because the braking time t_down or its end t3 is defined by reaching this lower speed.

[0076] According to the invention, it is also preferable to bring the power tool 10 or its tool 16 to a stop with a decreasing gradient having different slopes.

[0077] Figure 8 The graph of velocity n versus time t specifically shows a constant straight line representing the values ​​of 90% and 10% of the maximum velocity n_max. The value of 90% of the maximum velocity n_max forms a value pair with the associated time value t1_90%, which lies on the curve n(t). Similarly, the value of 10% of the maximum velocity n_max forms a value pair with the associated time value t3_10%, which also lies on the curve n(t).

[0078] Figure 9A schematic representation of a preferred configuration of the proposed power tool (10) is shown. The power tool 10 has a motor 12, which is preferably in the form of a brushless motor. The power tool 10 may have a tool 16, which may be, for example, in the form of a disc cutting tool. Figure 9 The power tool 10 depicted is preferably a cutting grinder, which can be used for cutting in a substrate such as concrete. The tool 16 of the power tool 10 may be surrounded by a blade guard (not shown in the figures) to protect the user of the power tool 10 from flying debris and sparks. The power tool 10 may be connected to at least one power supply device 14 to supply electrical energy to the power tool 10. Of course, the power tool 10 may also have two or more power supply devices 14. In the context of this invention, electrical energy can be fed back to at least one power supply device 14, particularly when the power tool 10 decelerates. Furthermore, the power tool 10 may have one or more handles (not shown in the figures) that the user of the power tool 10 can use to transport the power tool 10 or guide it during operation.

[0079] List of reference numerals 1. The first quadrant of spatial vector representation 2. The second quadrant of spatial vector representation 3. The third quadrant of spatial vector representation 4. The fourth quadrant of spatial vector representation 10 Power Tools 12 motors 14 Power Supply Units 16 tools 18-speed brake chopper Voltage controller for 20 power supply units 22 Current controller for power supply devices 24 First Controller 26 Second Controller 28. The third controller, especially the duty cycle controller 30 speed controller 32 Low-pass filter 34-day current controller 36q Current Controller M motor operation G Generator Operation I_d torque I_q torque M is increasing in torque. M negative increase torque The circular region serves as the current limit for the inverter. Operating range of AB stator current space vector N 0 Nm characteristic curve MTPA (Maximum Torque Per Ampere) Characteristic Curve β_brems Braking angle PWM pulse width modulation n speed t represents time.

Claims

1. A method for braking a power tool (10), which power tool (10) is a battery-operated power tool, and the electrical energy released when the power tool (10) is braked is fed back to a power supply device (14) of the power tool (10), characterized in that the following method steps: a) operating the power tool (10) by specifying a first current value, b) feeding back the electrical energy released when the power tool (10) is braked to the power supply device (14) of the power tool (10), c) reducing the braking power of the power tool (10) if at least one limit value of the power supply device (14) is exceeded, d) continuing to operate the power tool (10) at desired current values, which are calculated on the basis of the reduction in the braking power of the power tool (10) and the first current value.

2. The method as claimed in claim 1, characterized in that the power tool (10) is operated along a characteristic curve with optimized power loss.

3. The method as claimed in claim 1 or 2, characterized in that the power tool (10) is operated along a MTPA characteristic curve in a space vector representation.

4. The method as claimed in claim 3, characterized in that the desired current values are desired current values for a d-axis and a q-axis of the space vector representation.

5. The method as claimed in one of the preceding claims, characterized in that the braking power of the power tool (10) is reduced by the following method steps: e) rotating the current space vector I_S, max in the space vector representation by applying a modified braking angle β_brems, such that the length of the current space vector I_S, max remains substantially unchanged.

6. The method as claimed in one of claims 1 to 4, characterized in that the braking power of the power tool (10) is reduced by the following method steps: f) determining at least one correction factor k, and g) applying the at least one correction factor k to the maximum motor current I_S, max, as a result of which a reduced desired value I_S, red of the motor current is obtained.

7. The method as claimed in claim 6, characterized in that the at least one correction factor k is in the value range between 0 and 1.

8. The method as claimed in claim 6 or 7, characterized in that the at least one correction factor k consists of a first correction factor k_U, red, which is determined by a voltage controller of the power supply device, a second correction factor k_I, red, which is determined by a current controller of the power supply device, and / or a third correction factor k_red for limiting the duty cycle.

9. The method as claimed in one of the preceding claims, characterized in that the power tool (10) comprises a braking chopper (18), which absorbs the electrical energy released when a tool (16) of the power tool (10) is braked.

10. The method as claimed in one of the preceding claims, characterized in that The control of the motor (12) of the power tool (10) comprises field-oriented control or block commutation.

11. The method according to one of the preceding claims, characterized in that the tool (16) of the power tool (10) is stopped with a braking time in the range from 2 to 4 seconds.

12. The method according to one of the preceding claims, characterized in that the tool (16) of the power tool (10) is stopped with a braking time of less than 1.5 seconds, preferably less than 1 second, most preferably less than 0.5 seconds when the braking occurs after a kickback event has been detected.

13. The method according to one of the preceding claims, characterized in that the ratio of the braking time t down to the acceleration time t up is less than 1.

14. A power tool (10) for performing the method according to one of the preceding claims, characterized in that the motor (12) of the power tool (10) is a brushless motor.

15. The power tool (10) according to claim 14, characterized in that the power tool (10) comprises a braking chopper (18) configured to absorb electrical energy released when the tool (16) of the power tool (10) is braked.

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