SE541090C2

SE541090C2 - A power tool for connection to ac mains via at least one residual current protective device

Info

Publication number: SE541090C2
Application number: SE1750749A
Authority: SE
Inventors: Magnus Rosén
Original assignee: Husqvarna Ab
Priority date: 2017-06-14
Filing date: 2017-06-14
Publication date: 2019-04-02
Also published as: WO2018231126A1; AU2018283826A1; SE1750749A1

Abstract

A power tool (PT) for connection to AC mains (20) via at least one residual current protective device (RCCD; PRCD) is disclosed. The power tool has a DC motor (DCM), a power factor correction unit (PFC) for converting AC mains power to DC power at a DC voltage higher than the AC mains voltage, and a motor frequency inverter (MFI) for driving the DC motor with DC power from the power factor correction unit and controlling the torque and/or the number of revolutions per time unit of the DC motor. The power factor correction unit (PFC) is configured to control the conversion of AC power to DC power such that in case of a ground fault (60) which causes residual current (I) in a protective earth line (PE), the residual current will have a waveform (80) lacking a smooth DC component.

Description

A POWER TOOL FOR CONNECTION TO AC MAINS VIA AT LEAST ONE RESIDUAL CURRENT PROTECTIVE DEVICE TECHNICAL FIELD The present invention relates to the technical field of electrical power tools. More specifically, the present invention relates to a power tool for connection to AC mains via at least one residual current protective device, where the power tool has a DC motor, a power factor correction unit for converting AC mains power to DC power at a DC voltage higher than the AC mains voltage, and a motor frequency inverter for driving the DC motor with DC power from the power factor correction unit and controlling the torque and/or the number of revolutions per time unit of the DC motor.

BACKGROUND Well-known examples of power tools are hand-held electrical tools like chainsaws, trimmers, bush cutters, drilling tools, grinding tools, liquid cleaning tools, etc.

Figures 1A-1C generically illustrate a power tool PT being adapted for connection to AC mains 20 so as to supply electrical/motor parts 50 of the power tool PT with electric power. The AC mains 20 is part of an electrical installation 10 at a site and has an AC mains socket 30. The power tool PT has a corresponding plug 40 which is adapted for connection to the AC mains socket 30, as is generally well known.

As seen in Figure 2, the electrical/motor parts 50 of the power tool PT comprises a DC motor DCM. The electrical/motor parts 50 also comprises a power factor correction unit PFC for converting AC mains power to DC power at a DC voltage higher than the AC mains voltage, and a motor frequency inverter MFI for driving the DC motor with DC power from the power factor correction unit and controlling the torque and/or the number of revolutions per time unit of the DC motor.

Electrical safety is of importance for such power tools, and there are standards and regulations which serve to protect an operator from injuries in case of electrical malfunctions. An example of an electrical malfunction is seen in Figures 1A-1C in the form of a ground fault 60 that may cause a potentially dangerous residual current in a protective earth line.

To this end, residual current protective devices (also known as residual current devices (RCD:s)) may be used to provide protection in case of indirect contact with fault current, and/or to provide supplementary protection in case of direct contact. Residual current protective devices may be provided at the electrical installation 10 side, as can be seen in Figures 1A and 1B in the form of a residual current circuit breaker, RCCD.

Alternatively or additionally, residual current protective devices may be provided at the power tool PT side, as can be seen in Figures 1B and 1C in the form of a portable residual current device, PRCD.

A PRCD may be an external device separate from but connected to the power tool 10, as can be seen in Figure 1B, or it may be integrated with the power tool 10, as can be seen in Figure 1C.

Both an RCCD and a PRDC may be used at the same time, as can be seen in Figures 1A and 1B. Alternatively, a single residual current protective device may be used, as can be seen for PRDC in Figure 1C.

Certain regulations dictate that before allowing connecting an electrical equipment to a supply protected by a residual current protective device, the compatibility of the electrical equipment with the residual current protective device must be verified. In particular, operation of a residual current protective device connected in series with an electrical equipment shall not be disturbed by a smooth DC component in the fault current.

According to the regulations, residual current protective devices are categorized in different types, namely types A, B, AC and F. The present inventor has realized that power tools which are based on certain PFC (power factor correction unit) topologies may give rise to fault currents having a smooth DC component, wherein such PFC topologies are unsuitable for use with certain types of residual current protective devices.

See for instance Figure 3A which illustrates one kind of PFC topology that includes a common full-bridge rectifier arrangement, extensively used in applications where voltage increase and stabilization are not needed. As is seen in Figures 3B and 3C, the typical load current ILmay give rise to a pulsating DC waveform in the residual current Idcaused by a ground fault, and hence reduce the sensitivity of residual current protective devices of type AC. Accordingly, a combination of a PFC being based on a common full-bridge rectifier arrangement and a residual current protective device of type AC may not be acceptable.

In application where it is desired or necessary to increase and stabilize the voltage of the DC link, the common full-bridge rectifier arrangement in Figure 3A is typically combined with a single-way rectifier, as is shown in Figure 4A. This combined arrangement is advantageous when there are large variations in the AC input voltage and may increase the power output from the electrical motor with an increased supply voltage when using step-up from the available AC mains voltage. As is seen in Figures 4B and 4C, the typical load current ILof the single-way rectifier may give rise to a strong smooth DC component 70 in the residual current Idcaused by a ground fault, and hence reduce the sensitivity of residual current protective devices of types A, F and AC. Accordingly, a PFC being based on the circuitry in Figure 4A in combination with the circuitry in Figure 3A may not be used with a residual current protective device of type A, F or AC.

On the other hand, combinations of the circuitry in Figure 3 A or Figure 4 A with residual current protective devices of type B will be suitable and acceptable. This is so, since residual current protective devices of type B are triggered by all waveforms of residual current occurring from the circuitry shown in Figures 3A and 4A.

Flowever, residual current protective devices of type B are not readily available with the high sensitivity required for some applications, for example hand-held tools with liquid circuits for cooling and/or dust cleaning.

Also, a residual current protective device of type B is an expensive and bulky part, making it a non-favorable choice for emerging technology products like power tools for construction, drilling and cutting.

The present inventor has realized that there is room for improvements in this field.

SUMMARY An object of the present invention is therefore to provide one or more improvements in the field of technical field of electrical power tools of the kind described above.

The present inventor has invented, after insightful consideration, a new way of implementing power factor correction and motor frequency inverter stages that avoid a smooth DC component in a residual current caused by a ground fault.

Accordingly, an aspect of the present invention is a power tool for connection to AC mains via at least one residual current protective device, where the power tool comprises a DC motor, a power factor correction unit for converting AC mains power to DC power at a DC voltage higher than the AC mains voltage, and a motor frequency inverter for driving the DC motor with DC power from the power factor correction unit and controlling the torque and/or the number of revolutions per time unit of the DC motor. According to the invention, the power factor correction unit comprises a semibridgeless totem-pole boost converter and is configured to control the conversion of AC power to DC power such that in case of a ground fault which causes residual current in a protective earth line, the residual current will have a waveform lacking a smooth DC component, advantageously a pulsating DC waveform.

The invention combines the arrangement of semi-bridgeless totem-pole boost converter topology with the motor frequency inverter in such a way that the residual current waveform can be controlled not to cause a smooth DC component in case of a residual current flow. The clamping mechanism inherent to the semi-bridgeless totempole boost converter will, with dedicated digital control, create a pulsating DC component in case of contact with the live circuit. Thereby, compatibility also of lowcost portable residual current protective devices is assured.

Embodiments of the invention are defined by the appended dependent claims and are further explained in the detailed description section as well as on the drawings.

It should be emphasized that the term “comprises/comprising” when used in this specification is taken to specify the presence of stated features, integers, steps, or components, but does not preclude the presence or addition of one or more other features, integers, steps, components, or groups thereof. All terms used in the claims are to be interpreted according to their ordinary meaning in the technical field, unless explicitly defined otherwise herein. All references to "a/an/the [element, device, component, means, step, etc]" are to be interpreted openly as referring to at least one instance of the element, device, component, means, step, etc., unless explicitly stated otherwise. The steps of any method disclosed herein do not have to be performed in the exact order disclosed, unless explicitly stated.

BRIEF DESCRIPTION OF THE DRAWINGS Objects, features and advantages of embodiments of the invention will appear from the following detailed description, reference being made to the accompanying drawings.

Figure 1 A is a schematic block diagram of a power tool adapted for connection to AC mains being part of an electrical installation at a site so as to supply electrical/motor parts of the power tool with electric power, the drawing showing use of a first residual current protective device at the electrical installation side and a second residual current protective device being integrated in the power tool.

Figure IB is a schematic block diagram of a power tool adapted for connection to AC mains being part of an electrical installation at a site so as to supply electrical/motor parts of the power tool with electric power, this drawing showing use of a first residual current protective device at the electrical installation side and a second residual current protective device which is separate from the power tool.

Figure 1 C is a schematic block diagram of a power tool adapted for connection to AC mains being part of an electrical installation at a site so as to supply electrical/motor parts of the power tool with electric power, this drawing showing use of a single residual current protective device integrated in the power tool.

Figure 2 is a schematic block diagram of the major components of the electrical/motor parts of the power tool.

Figures 3A-3C illustrate a common full-bridge rectifier arrangement for a power factor correction unit of the power tool, and also how a typical load current may give rise to a pulsating DC waveform in the residual current Idat the occurrence of a ground fault.

Figures 4A-4C illustrate another common kind of power factor correction unit topology, where a common full-bridge arrangement is combined with a single-way rectifier, and also how a typical load current may give rise to a strong smooth DC component in the residual current Idat the occurrence of a ground fault.

Figures 5A-5C illustrate a preferred embodiment of the invention, where the power factor correction unit of the power tool comprises a semi -bridgeless totem-pole boost converter, and also that a typical load current will not give rise to a strong smooth DC component in the residual current Idat the occurrence of a ground fault, but rather a pulsating DC waveform.

Figures 6A and 6B illustrate the typical residual currents at the motor frequency inverter, caused by ground faults, with a rectifier arrangement for a power factor correction unit according to the prior art, and with a semi-bridgeless totem-pole boost converter for a power factor correction unit according to the embodiment in Figure 5A, respectively.

Figure 7 is a diagram illustrating in more detail a power factor correction unit implemented with semi-bridgeless totem-pole boost converter topology.

Figures 8A and 8B illustrate the power factor correction unit implemented as an interleaved 3-phase semi-bridgeless totem-pole boost converter topology, and an associated timing diagram.

Figure 9 is a principal PID regulator diagram for the power factor correction unit implemented with semi-bridgeless totem-pole boost converter topology, the PID regulator functionally typically being implemented in program code executed by a processor.

Figures 10A and 10B are principal signal diagrams of the PID regulator functionality in Figure 9.

DETAILED DESCRIPTION OF EMBODIMENTS Embodiments of the invention will now be described with reference to the accompanying drawings. The invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. The terminology used in the detailed description of the particular embodiments illustrated in the accompanying drawings is not intended to be limiting of the invention. In the drawings, like numbers refer to like elements.

As has already been explained previously in this document, Figure 1A is a schematic block diagram of a power tool PT adapted for connection to AC mains 20 being part of an electrical installation 10 at a site so as to supply electrical/motor parts the form of a residual current circuit breaker, RCCD, is provided at the electrical installation side. A second residual current protective device in the form of a portable residual current device, PRCD, is integrated in the power tool PT. A ground fault 60 may occur at the electrical/motor parts 50 of the power tool 10.

Figure 1B is a similar diagram, showing the power tool PT for connection to the AC mains 20 of the electrical installation 10, except that the second residual current protective device PRCD is an external device separate from the power tool PT.

Figure 1C, too, is a similar diagram, showing once more the power tool PT for connection to the AC mains 20 of the electrical installation 10. Here, however, the residual current protective device PRCD being integrated in the power tool PT is the only residual current protective device used.

As has been explained previously in this document, Figure 2 shows the main components of the electrical/motor parts 50 of the power tool PT. A DC motor DCM is one of these main components, forming the very heart of the power tool. The DC motor DCM may advantageously be a three-phase, brushless DC motor (BLDC).

Alternatively, it may, for instance, be a permanent magnet synchronous motor (PMSM).

The electrical/motor parts 50 of the power tool PT also comprises a power factor correction unit PFC. The purpose of the power factor correction unit PFC is to convert AC mains power from the AC mains 20 to DC power at a DC voltage higher than the AC mains voltage.

Moreover, the electrical/motor parts 50 of the power tool PT comprises a motor frequency inverter MFI for driving the DC motor DCM with DC power from the power factor correction unit PFC and controlling the torque and/or the number of revolutions per time unit of the DC motor DCM.

It is recalled that Figures 3A-3C and particularly Figures 4A-4C, which were described in the Background section of this document, illustrate the disadvantage of prior art power factor correction unit topologies in that a ground fault 60 may give rise to a strong smooth DC component in the residual current Id, wherein this in turn makes the prior art power factor correction unit topologies incompatible with some types of residual current protective devices.

In comparison, Figures 5A-5C illustrate an advantageous embodiment of the invention, where the power factor correction unit PFC of the power tool PT comprises a semi-bridgeless totem-pole boost converter SBTPB. The semi-bridgeless totem-pole boost converter SBTPB of the power factor correction unit PFC is configured to control the conversion of AC power to DC power such that in case of a ground fault 80 which causes residual current IGFin a protective earth line PE, the residual current will have a waveform 80 lacking a smooth DC component. This can be seen in Figure 5C.

More specifically, as can be seen in Figure 5C, the semi-bridgeless totem-pole boost converter SBTPB of the power factor correction unit PFC is configured to control the conversion of AC power to DC power such that the residual current IGFin case of a ground fault 60 will have a pulsating DC waveform 80. This is in contrast to the strong smooth DC component in the residual current Idcaused by a ground fault 60 in the prior art (see Figures 4A-C).

The difference is contrasted even more clearly in Figures 6A and 6B. Figure 6A illustrates the typical residual current IGFat the motor frequency inverter, caused by a ground fault for a power factor correction unit with a prior art rectifier arrangement as previously described. As can be seen in Figure 6A, the residual current IGFhas a waveform 70 containing a strong, smooth 50 mA DC component.

Figure 6B on the other hand illustrates the typical residual current IGFat the motor frequency inverter, caused by a ground fault 60 for a power factor correction unit with a semi-bridgeless totem-pole boost converter SBTPB for a power factor correction unit PFC according to the embodiment in Figure 5A. As can be seen in Figure 6B, the residual current IGFhas a waveform 80 lacking a strong smooth DC component (i.e., 0 mA) and instead exhibiting a pulsating DC waveform.

As can be seen in Figure 5A, the semi-bridgeless totem-pole boost converter SBTPB comprises half-wave rectifier circuitry HWR and totem-pole voltage boost converter circuitry TPB.

The left-hand side of Figure 7 illustrates the half-wave rectifier circuitry HWR of the semi-bridgeless totem-pole boost converter SBTPB in more detail. The half-wave rectifier circuitry HWR comprises first and second inputs 100-1, 100-2 for connection to first and second AC mains lines L, N, respectively.

The half-wave rectifier circuitry HWR further comprises a half-wave diode bridge comprising first and second diodes 110-1, 110-2 (see Figure 8 A). The half-wave diode bridge is configured for converting an input AC mains voltage waveform into a half-wave waveform where every second half of each waveform period is equal to the input AC mains voltage waveform and every other half of each waveform period is set to zero voltage.

Moreover, the half-wave rectifier circuitry HWR comprises first and second outputs 120-1, 120-2 for outputting the half-wave waveform from the half-wave diode bridge.

The right-hand side of Figure 7 illustrates the totem-pole voltage boost converter circuitry TPB of the semi-bridgeless totem-pole boost converter SBTPB in more detail. The totem-pole voltage boost converter circuitry TPB of the semibridgeless totem-pole boost converter SBTPB comprises an AC side connected to the first and second outputs 120-1, 120-2 of the half-wave rectifier circuitry HWR, as well as a DC side connected to the motor frequency inverter MFI.

As seen in Figure 8 A, a first pair of power transistor 130-1 and anti-parallel diode 132-1 form an upper converter leg between the AC side and the DC side, whereas a second pair of power transistor 130-2 and anti-parallel diode 132-2 form a lower converter leg.

An inductor 140 is connected between the AC side and a mid-point between the upper converter leg and lower converter leg, and a capacitor 150 is connected between the upper converter leg and lower converter leg at the DC side.

As can be seen at the bottom of Figure 7, the semi-bridgeless totem-pole boost converter SBTPB further comprises a controller 90 for controlling the first and second pairs of power transistors 130-1, 132-1 and anti-parallel diodes 130-1, 132-1 of the totem-pole voltage boost converter circuitry TPB to produce a pulse width modulated PWM voltage waveform.

The structure and functionality of the controller 90 are illustrated in Figures 8A, 8B, 9, 10A and 10B. Generally, the controller 90 implements three PID regulators as program code executed by a processor such as a CPU or DSP to manage closed-loop input and output control. In boost control, one PID regulator is provided for each phase P, Q and R, as can be seen in Figures 8A and 8B. Accordingly, the semi-bridgeless totem-pole boost converter SBTPB comprises one instance of the half-wave rectifier circuitry HWR and the totem-pole voltage boost converter circuitry TPB for each phase of the DC motor DCM.

The average output voltage is regulated to a pre-set value with an outer loop PID regulator. The input current envelope is regulated with an inner loop PID regulator, sensing the average current of converter phases. For rapid input voltage or output load current changes, the PID regulator is assisted by either a by-passed hysteric regulator or gain scheduling to be able maintain the output voltage and input current within acceptable ranges.

The PFC inductor current during each switching cycle should have an average value proportional to the instantaneous value of rectified AC line voltage. The sample and conversion start of the analog-digital converter, ADC, is aligned with a timer and scan schedule to give the average of the lower leg currents of the three phases. The lower leg could be either switch or rectifier current envelope depending on a L>N : L When L>N, the high side switch is disabled and the low side switch is active with the PWM duty cycle. Current sense shunt resistors measure the switch portion of the totem pole current. The current of the three phases P, Q and R is presented to the analog-digital converter ADC. The reconstructed input current IINis calculated from the sum of the phases Ip, IQand IR.

When L The relative phasing of the phases P, Q and R is close to 120°. This reduces the switching frequency ripple seen at input and output filters. The pulse width modulation duty factors are equally controlled for the phases P, Q and R. Typically the inductances are not equal, so the current sharing is proportional to the inductor initial tolerance and permeability temperature coefficient.

Thermal balance is important for reducing the temperature difference of the inductors. Flence, use of moderately swinging inductance will reduce the inductance deviation between phases.

If the diode/inductor current decays to zero before the next cycle switch on occurs, as should happen at very light load, the boost modelling function calculate the adjusting factor DZC to get the true input inductor current.

At very low load, i.e. the motor DCM is not running, the PWM frequency multiplier should be 1. Calculation frequency is able to generate the low duty factor necessary for low output current.

The proportional output voltage regulator is by-pass paired with a state regulation lane to improve output voltage and input current regulation at input voltage or load fast variations, input voltage brown-out, phase drop-out, cycle drop-out and voltage recovery. Alternatively, gain scheduling may be used to stabilize the output voltage and input current.

As regards PWM frequency spread spectrum for EMI footprint reduction, the following it noticed. Frequency hop should be scattered with a PRND sequence of 1024 flat distributed frequencies. The hop rate should be synchronized with 1/fFOC. Nonsynchronous scatter or non-scatter (without frequency spread spectrum) may be considered.

PFC acquisition and calculation frequency should be within 20-50 kHz. An ideal range is 30-40 kHz.

PWM frequency could be multiplied with a factor 1, 2, 3..., and should be within 20-300 kHz. An ideal range is 30-40kHz/150-250kHz.

Main interrupt for acquisition and calculation is shared with FOC/motor function. Consideration might be taken of the multiplication factor for the mutual optimization of FOC and PFC acquisition, calculation and efficiency.

As can be understood from the above descriptions of Figures 5A-5C, 6B, 7, 8A-B, 9 and 10A-B, the advantages of removing the smooth DC component of the prior art have been made possible by implementing the power factor correction unit PFC as a semi-bridgeless totem-pole boost converter SBTPB which, advantageously, comprises a half-wave rectifier circuitry HWR and a totem-pole voltage boost converter circuitry TPB. This will increase and stabilize the incoming voltage supply to feed the motor frequency inverter MFI. No smooth DC component will appear thanks to the half-wave rectifier HWR; the residual current IGFin case of a ground fault 60 will have a pulsating DC waveform 80 and therefore provide compatibility at least with residual current protective devices of types A and F (in addition, of course, to residual current protective devices of type B).

The presented approach will also assure compliance with the regulatory requirement to protect an upstream residual current protective device from being disturbed by a downstream smooth DC component. If a ground fault occurs at the motor frequency inverter MFI, the reduced DC offset of the current waveform will ensure sufficient sensitivity residual current protective device, thereby reducing the trip current and creating a safety margin for this particular hazard.

The invention has been described above in detail with reference to embodiments thereof. However, as is readily understood by those skilled in the art, other embodiments are equally possible within the scope of the present invention, as defined by the appended claims.

Claims

1. A power tool (PT) for connection to AC mains (20) via at least one residual current protective device (RCCD; PRCD), the power tool comprising: a DC motor (DCM); a power factor correction unit (PFC) for converting AC mains power to DC power at a DC voltage higher than the AC mains voltage; and a motor frequency inverter (MFI) for driving the DC motor with DC power from the power factor correction unit and controlling the torque and/or the number of revolutions per time unit of the DC motor; characterized in that the power factor correction unit (PFC) comprises a semi-bridgeless totem-pole boost converter (SBTPB) and is configured to control the conversion of AC power to DC power such that in case of a ground fault (60) which causes residual current (IGF) in a protective earth line (PE), the residual current will have a waveform (80) lacking a smooth DC component.

2. The power tool (PT) as defined in claim 1, wherein the power factor correction unit (PFC) is configured to control the conversion of AC power to DC power, such that the residual current (IGF) in case of a ground fault (60) will have a pulsating DC waveform (80).

3. The power tool (PT) as defined in claim 1 or 2, wherein the semi-bridgeless totem-pole boost converter (SBTPB) comprises: half-wave rectifier circuitry (HWR); and totem-pole voltage boost converter circuitry (TPB).

4. The power tool (PT) as defined in claim 3, wherein the half-wave rectifier circuitry (HWR) of the semi-bridgeless totem-pole boost converter (SBTPB) comprises: first and second inputs (100-1, 100-2) for connection to first and second AC mains lines (L, N), respectively; a half-wave diode bridge comprising first and second diodes (110-1, 110-2) and configured for converting an input AC mains voltage waveform into a half-wave waveform where every second half of each waveform period is equal to the input AC mains voltage waveform and every other half of each waveform period is set to zero voltage; and first and second outputs (120-1, 120-2) for outputting the half-wave waveform from the half-wave diode bridge.

5. The power tool (PT) as defined in claim 4, wherein the totem-pole voltage boost converter circuitry (TPB) of the semi-bridgeless totem-pole boost converter (SBTPB) comprises an AC side connected to the first and second outputs (120-1, 120-2) of the halfwave rectifier circuitry (HWR), a DC side connected to the motor frequency inverter (MFI); a first pair of power transistor (130-1) and anti-parallel diode (132-1) forming an upper converter leg between the AC side and the DC side; a second pair of power transistor (130-2) and anti-parallel diode (132-2) forming a lower converter leg; an inductor (140) connected between the AC side and a mid-point between the upper converter leg and lower converter leg; and a capacitor (150) connected between the upper converter leg and lower converter leg at the DC side.

6. The power tool (PT) as defined in claim 5, wherein the semi-bridgeless totem-pole boost converter (SBTPB) further comprises a controller (90) for controlling the first and second pairs of power transistors (130-1, 132-1) and anti-parallel diodes (130-1, 132-1) of the totem-pole voltage boost converter circuitry (TPB) to produce a pulse width modulated (PWM) voltage waveform.

7. The power tool (PT) as defined in any preceding claim, wherein the DC motor (DCM) is a three-phase, bmshless DC motor, BLDC, or a permanent magnet synchronous motor, PMSM.

8. The power tool (PT) as defined in claim 7, wherein the semi-bridgeless totem-pole boost converter (SBTPB) comprises one instance of the half-wave rectifier circuitry (HWR) and the totem-pole voltage boost converter circuitry (TPB) for each phase of the DC motor (DCM).

9. The power tool (PT) as defined in any preceding claim, the power tool (PT) being adapted for connection to an AC mains socket (30) at a site (10) having an electrical installation which comprises a residual current circuit breaker device (RCCD).

10. The power tool (PT) as defined in any preceding claim, the power tool (PT) having a plug (40) and being adapted for connection to an AC mains socket (30) via a portable residual current device (PRCD) connected between the plug (40) and the DC motor (DCM), power factor correction unit (PFC) and motor frequency inverter (MFI) of the power tool (PT).

11. The power tool (PT) as defined in any of claims 1-9, the power tool (PT) comprising an integrated portable residual current device (PRCD).