Patent Application
20200052617
This application claims the priority, under 35 U.S.C. ยง 119, of German Patent Application DE 10 2018 006 357.8, filed Aug. 11, 2018; the prior application is herewith incorporated by reference in its entirety.
The present invention relates to a drive circuit for driving an electronically commutated motor, specifically a motor of an electronic household appliance, and specifically such a drive circuit having an EMC filter and a power factor correction filter.
Drive circuits of that type, because of their high-frequency pulse characteristics, generate radio interference, which is propagated by using electromagnetic fields in clear space, and by conduction through power connection lines in the form of high-frequency voltages and currents. Consequently, drive circuits are customarily equipped with an EMC filter, through the use of which the power supply grid is intended to be protected against interference originating from the drive circuit and the connected motor.
German Patent DE 10 2007 058 376 B4, corresponding to U.S. Pat. No. 8,422,251, discloses a switched-mode power supply for an electronic household appliance, which is equipped with an EMC filter. The EMC filter respectively includes a reactance coil in the phase conductor connection and the neutral conductor connection to the power supply grid, a capacitor which is connected in parallel with the AC terminal, and a discharge resistor which is connected in parallel with that capacitor. The phase conductor connection and the neutral conductor connection are further respectively connected to protective ground through a Y-capacitor.
In many cases, drive circuits of that type are further equipped with an active power factor correction (PFC) filter, for example in a step-up converter topology. However, the use of an active PFC filter, as a result of an insulation fault on the above-mentioned capacitive feedback coupling to protective ground, can result in a permanent DC component on protective ground, which can compromise the correct operation of a fault current circuit-breaker.
It is accordingly an object of the invention to provide an improved drive circuit for driving an electronically commutated motor, which overcomes the hereinafore-mentioned disadvantages of the heretofore-known circuits of this general type and which eliminates the above-mentioned disadvantages associated with the use of a conventional EMC filter.
With the foregoing and other objects in view there is provided, in accordance with the invention, a drive circuit for driving an electronically commutated motor including an AC terminal, to which a power supply grid is connectable, a rectifier which is connected on the input side to the AC terminal, an inverter which is connected on the input side to the rectifier and to which the motor phases of the motor are connectable, an intermediate DC voltage circuit between the rectifier and the inverter, and an EMC filter. According to the invention, the EMC filter includes a capacitive feedback coupling having at least one Y-capacitor, which is connected between one pole of the intermediate DC voltage circuit and protective ground and which, overall, incorporates stronger insulation than basic insulation.
Through the use of the at least one Y-capacitor, the capacitively coupled parasitic currents associated with the stray capacitances of the motor phases which are pulsed by the inverter are fed back to protective ground on the intermediate voltage circuit, and consequently are not propagated further outwards into the power supply grid through the AC terminal, where they might cause EMC interference.
Due to the use of stronger insulation than simple basic insulation in the capacitive feedback coupling between one pole of the intermediate DC voltage circuit and protective ground, upon the occurrence of an insulation fault on one part of the stronger insulation, the presence of the remaining fault-free part of the insulation can prevent the occurrence of a DC fault current leakage to protective ground, as a result of which the correct operation of a fault current circuit-breaker can be ensured and/or a simpler and more cost-effective fault current circuit-breaker (e.g. of type A) can be employed, wherein the protection of persons is improved by the remaining part of the insulation or by the correct operation of the fault current circuit-breaker.
Y-capacitors are protective capacitors, which are classified, for example, in IEC standard 60384-1. In that connection, according to the household appliances standard EN 60335, paragraph 3.3, basic insulation constitutes the insulation of live parts for the provision of fundamental protection against electric shock; additional insulation is an independent insulation provided additionally to basic insulation which, in the event of the failure of the basic insulation, ensures protection against electric shock; double insulation constitutes an insulation system including basic insulation and additional insulation; reinforced insulation constitutes the single insulation of live parts which, under the conditions defined in this standard, provides protection against electric shock which is equivalent to double insulation. Thus, for example, stronger insulation than basic insulation can be constituted by double insulation and/or by reinforced insulation. In general, stronger insulation than basic insulation preferably provides at least double the strength of basic insulation.
The capacitive feedback coupling to protective ground can be provided on one pole of the intermediate DC voltage circuit or on both poles of the intermediate DC voltage circuit. In the event of a single-pole capacitive feedback coupling only, this is preferably provided between the positive pole of the intermediate DC voltage circuit and protective ground.
The EMC filter, in addition to the capacitive feedback coupling of one pole of the intermediate DC voltage circuit to protective ground, preferably includes further capacitive, inductive and/or resistive elements.
The invention is not restricted to any specific type of motor. The motor in the motor configuration is in particular an electronically commutated motor such as, for example, a synchronous motor or an asynchronous motor, an AC motor, a three-phase AC motor, or similar.
The inverter of the drive circuit preferably includes an inverter bridge circuit, preferably having a plurality of power switches (e.g. MOSFETs or IGBTs with antiparallel connected diodes). The inverter, correspondingly to the connected motor, is preferably of a multi-phase configuration. The intermediate DC voltage circuit of the drive circuit preferably includes an intermediate circuit capacitor. The rectifier of the drive circuit is preferably configured as a bridge rectifier having a plurality of rectifier diodes.
In one configuration of the invention, the capacitive feedback coupling of the EMC filter includes a series-connected configuration of at least two Y-capacitors, each of which is provided with at least basic insulation. In the event of an insulation fault on one of the two Y-capacitors, the capacitive feedback coupling still includes one Y-capacitor with intact insulation, so that any DC fault current leakage to protective ground can be prevented, and the protection of persons is improved.
In a further configuration of the invention, the capacitive feedback coupling of the EMC filter is constituted by a Y-capacitor having double insulation or reinforced insulation. In the event of an insulation fault on one part of the double or reinforced insulation of the Y-capacitor, the capacitive feedback coupling still includes intact insulation, so that any DC fault current leakage to protective ground can be prevented, and the protection of persons is improved.
In one configuration of the invention, the EMC filter further includes a resistive and/or inductive attenuator disposed in series with the capacitive feedback coupling between the pole of the intermediate DC voltage circuit and protective ground.
In one configuration of the invention, the EMC filter is connected between the AC terminal and the rectifier.
In a further configuration of the invention, the drive circuit further includes a power factor correction filter (PFC filter), which is connected between the rectifier and the intermediate DC voltage circuit, and is preferably a PFC filter configured in a step-up converter topology.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a drive circuit for driving an electronically commutated motor, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.
Understanding of the above-mentioned and further characteristics and advantages of the invention will be clarified by the following description of a preferred and non-limiting exemplary embodiment, with reference to the attached drawing.
The single FIGURE is a partially schematically represented circuit layout of a drive circuit with a connected motor, according to one exemplary embodiment of the invention.
Referring now in detail to the single FIGURE of the drawing, there is seen an exemplary drive circuit 10 according to the invention for driving an electronically commutated motor 12. In the example shown in
The input side of the intermediate DC voltage circuit 14 is connected to an AC terminal 22 through a rectifier 20. The drive circuit 10 can be connected through the AC terminal 22 to a power supply grid 24. In the example shown in
As represented in the FIGURE, a power factor correction (PFC) filter 26 is preferably further connected between the rectifier 20 and the intermediate DC voltage circuit 14. In this example, the PFC filter 26 is configured in a step-up converter topology, and specifically incorporates an inductance L7, a switch M7 and a rectifier diode D7.
The drive circuit 10 further includes a non-illustrated control device, for example in the form of a microcontroller, which actuates the power switches M1 to M6 of the inverter 16 and the switch M7 of the PFC filter 26 by using corresponding control signals.
The drive circuit 10 moreover incorporates an EMC filter 28 which, in the present exemplary embodiment, is connected between the rectifier 20 and the AC terminal 22. In the exemplary form of embodiment according to the FIGURE, this EMC filter 28 incorporates a first inductance L1 in the phase conductor connection to the phase conductor L of the power supply grid 24, a second inductance L2 in the neutral conductor connection to the neutral conductor N of the power supply grid 24, two capacitors C3, C6 for the capacitive coupling of the phase conductor L with the neutral conductor N, and two capacitors C4, C5 for the coupling of the phase conductor L or the neutral conductor N to the protective ground PE. In other forms of embodiment of the invention, the EMC filter 28 can also incorporate other and/or further capacitive, inductive or resistive elements.
As is illustrated in the FIGURE, the EMC filter 28 according to the invention further incorporates a capacitive feedback coupling 30 between one pole of the intermediate DC voltage circuit 14 (in this case the positive pole, represented by the intermediate circuit voltage U+HV) and the protective ground PE. In the exemplary embodiment according to
Through the use of the capacitive feedback coupling 30 of the two Y-capacitors C1 and C2 shown in the FIGURE, the capacitively coupled parasitic currents I associated with the stray capacitances C8, C9, C10 of the motor phases U, V, W, which are pulsed by the inverter 16, are fed back to the protective ground PE on the intermediate voltage circuit 14, and consequently are not propagated further outwards into the power supply grid 24 through the AC terminal 22, where they might cause EMC interference.
A fault current circuit-breaker 34 is preferably provided between the AC terminal 22 and the power supply grid 24. Due to the use of a capacitive feedback coupling 30 having stronger overall insulation than simple basic insulation, it can be achieved that, even in the event of an insulation fault on the feedback coupling 30, at least part of the insulation remains intact. Specifically in the case of drive circuits 10 having a PFC filter 26 in a step-up converter topology, it can thus be prevented that, in the event of an insulation fault on the feedback coupling 30, a critical DC fault current leakage to the protective ground PE occurs on the intermediate DC voltage circuit 14. Due to the use of a drive circuit 10 according to the invention having an EMC filter 28 with capacitive feedback coupling 30, a more cost-effective type A fault current circuit-breaker can thus be advantageously used. By way of comparison, in conventional drive circuits, the EMC filter of which incorporates a capacitive feedback coupling having only a single Y-capacitor with simple basic insulation between one pole of the intermediate DC voltage circuit and protective ground, more expensive type B fault current circuit-breakers, for example, are employed, the trip characteristics of which are not adversely affected by DC fault currents.
The following is a summary list of reference numerals and the corresponding structure used in the above description of the invention:
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2018 006 357.8 | Aug 2018 | DE | national |
