Noise currents compensator in devices with switching power output stages

0001The invention is directed to a circuit arrangement for Compensation asymmetrical interference currents, which in devices with switching output stages by the transhipment of parasitic Output capacity caused.

0002In particular, in electric drive technology already existed long been a need for power converter equipment with improved speed and especially position control properties with reduced noise. the therefrom Sprung desire for higher allowable clock frequencies the output stages could recently due to improved Power transistors. So-called example. IGBT modules, are generally complied with, however, revealed that at Use of such "fast" power modules due to the steep voltage edges on the active outputs of Converter which there inevitably existing, parasitic Capacity shorten intervals must be recharged. To this end, much higher charging currents are required, which over the device housing and flow from there to the ground potential. This increased interference to the response of trigger protection circuits and affect the quality the mains voltage in the vicinity of the equipment. It is therefore desirable, this flowing to earth interference stay away from the area of ​​a device.

0003For this purpose, for example in the technical article "High Frequency Leakage Current Reduduction Based on a common mode Voltage Compensation Circuit "in the journal IEEE 1996, pages 1961-1967, a passive compensation circuit for the transhipment of the active outputs of a converter power module inevitably present, parasitic Capacities necessary interference disclosed. To this end is at the output terminals of the converter power section a capacitive neutral point formed of a first Winding of a coupling transformer connected to ground is. The other winding of the coupling transformer side also grounded, its free end is a Resistor to the center tap of a capacitive voltage divider connected, the parallel to the intermediate circuit capacitor connect the power converter to the DC voltage rails is. Ideally, this should the coupling transformer appropriate compensation currents from the DC link draining to ground potential of the power converter. This but can only be successful to a limited extent, as a real Coupling transformer naturally not an ideal transmission behavior having. For a good coupling transformer having between primary and secondary side, has its Winding be executed possible streuarm what to elaborate and performs expensive arrangements.

0004Further, in the technical article "Elimination of Common Mode Voltage in Three Phase Sinusoidal Power Converters "by AL Julian, TA Lipo and G. Oriti in IEEE 1996, pages 1968 - 1972, a second compensation circuit for interfering Ground currents to the active outputs of a three-phase inverter disclosed. is in this case parallel to the three-phase bridge circuit the inverter to the DC link voltage Another power transistor branch with two in Series-connected power transistors the common Node via a coupling capacitor to a capacitive star point of the inverter is coupled. The efficiency of such a compensation circuit is extremely limited, as necessary as a result of Withstand voltage of equipment connected to the intermediate circuit voltage Transistor exclusively power semiconductor can be used, the dynamic behavior does not is better than the actual power modules. to earth faults the intermediate circuit voltage exclude certain only clocked can such compensation part are operated, so that the compensation voltage also exclusively at the two intermediate circuit potentials can be preset defined. Such a compensation circuit can meet the requirements of modern power converter with higher clock frequencies do not match, and means also due to the additional power transistor module including the necessary for this drive circuits a significant additional expense.

0005From the disadvantages of prior art compensation circuits resulting the problem initiating the invention, a circuit concept for compensation of the ground final interference on electrical appliances with to provide switched power amplifiers, one for a has good compensation sufficient momentum and also can be constructed with inexpensive components as possible.

0006To solve this problem, the invention provides, in a generic A compensation circuit for detecting and / or Observation of state variables to the device coupled Control and / or regulating circuit from whose output stage for feeding compensation currents to the device housing and / or a ground terminal is coupled. here is one hand, electronically active control or made arrangements which low relatively Effort yet is far more accurate than a passive coupling transformer, and the other part is here not a capacitive made coupling to a virtual star point but after a control or control algorithm certain compensation current is sent directly to the device housing and / or a ground terminal fed.

0007Unlike previous, active compensation circuits, which as power actuators relatively slow power transistors need, preferably, the invention provides the use fast electronics semiconductors in the compensator output stage, which allow a highly dynamic control, so that the environment of such a device compensated is of spikes largely free.

0008To exploit the dynamics of fast electronics semiconductors can, the invention further provides that the compensator output stage is constructed as a push-pull amplifier.

0009To the use of fast (small signal) semiconductors to make possible the compensator output stage should under another aspect of the invention at a low (Small signal) must be connected supply voltage. while the compensation circuit not according to the invention of the high Intermediate circuit voltage is supplied, are as semiconductors highly dynamic small-signal transistors are available, the on the one hand have a much better time performance as power transistors and operated on the other hand not clocked must be, but due to reduced power losses can provide a continuously variable output signal, which optimum dynamics and control quality allowed.

0010The circuit scale can be further reduced by that the compensator output stage with the same supply voltage connected as the control and / or control circuit. These may be the electronically with each controlled device by default existing electronics supply voltage act so that the overhead ideally limited to the few components of the compensation electronics is.

0011Like any amplifier, the compensator output stage primarily an output voltage available, in accordance with their Amplitude, the desired compensation current setting. To this defined to drain to ground, is one terminal of the compensator output level to the device housing and / or a ground terminal directly or via a coupling network connected, defined while the opposite adjustable voltage terminal of the compensator output stage preferably to a reference voltage, eg. an intermediate circuit voltage directly or via a coupling network is. The coupling network is primarily used to voltage fluctuations or even spikes of the power part of the keep Kompensatorelektronik and in the simplest Case consist of one or more capacitors. Also a Coupling transformer, because of its galvanic isolation are used between the primary and secondary winding. It is also possible, by means of further elements, in particular Coils to achieve a desired dynamic.

0012To measure the common mode interference current can eg. A the Leads of the device or the connection lines to the consumer induction coil surrounding be used also can be disposed in the ground line, a current transformer. Finally, it is also possible that output currents indirectly to determine from the output voltages and therefrom in turn to calculate the effluent to ground share.

0013Further features, details and advantages on the basis of Invention will become apparent from the following description of some preferred embodiments of the invention, and reference to the drawing. In the drawing:<dl tsize="7"><dt>Fig. 1</dt><dd>A basic block diagram of a first embodiment the invention;</dd><dt>FIG. 2</dt><dd>a concretization of the embodiment of Fig. 1; as</dd><dt>Fig. 3</dt><dd>another embodiment of the invention.</dd></dl>

00141 shows at 1 the power section of a Drehstromumrichters indicated. One recognizes the intermediate circuit capacitor C1, of the intermediate circuit voltage U0 between the two intermediate circuit rails 2, 3 stabilized. Coupled with the power Rectifier is in the representation of Figure 1 omitted. Further, an output stage 4 of the inverter shown. This is the usual form of two series-connected power transistors T1, T2, which in Collectively, the intermediate circuit potentials 2, 3 each connect. Each power transistor T1, T2 is a freewheeling diode D1, D2 connected in antiparallel. To the power loss reduce, the transistors T1, T2 are clocked operated and only switched alternately, so that there are no cross-shorts intermediate circuit voltage U0 can form. Thus, the potential at the active fluctuates Output 5 of this inverter branch 4 between the negative Intermediate circuit potential 2 and the positive intermediate circuit potential 3. To these high voltage jumps from a connected Consumers keep at least partially, is a smoothing reactor 6 connected to the output. 5 Still formed through between the active output 5 and the the throttle 6 smoothed in the waveform output terminal 7 and the potential of the metallic instrument housing 8 parasitic Capacitances Cp1, Cp2 from. As a result of the use of IGBT power transistors T1, T2 possible clock frequencies of about 20 kHz arise particularly on the active Output 5, but also to the pre-smoothed output 7 relative steep voltage edges, which in the parasitic capacitances Cp1, Cp2 recharge currents with high current peaks according to drag that to the housing 8 and from there via a ground line 9 desisted to ground 10th

0015These disturbing ground currents can network side protection circuits affect or trigger installed around equipment and therefore by law with respect to their Maximum values ​​were regulated. There are, therefore, countermeasures necessary despite the clocked power output stages 4 to the ground potential 10 effluent to zero to regulate. This is the purpose, the inventive compensating circuit is 11. The core of this compensation circuit a control or regulating circuit 12, the input side, 13 for detecting and / or monitoring of the ground potential 10 flowing interference current to the power unit 1, the grounding line 9 and / or coupled to the control part of the device and is selected from the thus provided information the actual value of the effluent to ground potential 10 determines interference current, in particular calculated, or estimates. This information is based on a control algorithm G (jw) is a controller output signal 14 generated with which the compensator output stage is driven 15th These consists of a push-pull amplifier with two series-connected Transistors TC1, TC2, the common node 16 the active output of Kompensatorschaltkreises 11 represents that of a coupling network 17 with a Transfer function H (jw) to the metal housing 8, optionally also with a heat sink and / or ground terminal is coupled for feeding a compensation current. Of the Control algorithm, G (jw) is optimized such that the compensation current the magnitude caused by the performance Part 1 Total noise current equivalent but opposite has signed, so that the power unit 1 as Störstromquelle the compensation circuit 11 as Störstromsenke is assigned, and the effluent to ground potential 10 Current total to zero.

0016For optimal control is also a highly dynamic Kompensatorausgangs actuator 15 necessary. here are therefore fast small signal transistors TC1, TC2 used such as those offered in the most varied designs. This is possible because as a supply voltage for the compensation circuit 11 a low auxiliary voltage Uh used is their negative potential 18 to the negative intermediate circuit potential 2 is connected. In the ideal case, it is This is required for the control of the unit 1, 8 provided electronic voltage. The coupling network 17 may be constructed of various reactances eg. one or more capacitors and / or coils. also it is possible, here an electrically isolated coupling transformer to use, the secondary winding for example. coupled to the housing 8 or to the ground line 9 may be connected.

0017The simplest realization of the feedback network 17 is in Figure 2 is reproduced and consists of a coupling capacitor CK1, the active output 16 of the compensator circuit 11 connects to the device housing. 8 This keeps one hand Voltage peaks of the compensator 11 and has from on the other hand a defined transmission behavior of the control or regulation algorithm G (jw) to produce the desired Compensation current can be controlled.

00183 shows a different coupling of the compensation circuit 11 drawn. Here is the negative potential 19 the electronics supply voltage Uh directly to the housing 8 connected to here the necessary compensation current directly feed, so that the current flowing to the ground potential 10 Current to zero can be compensated. The compensation currents are in this case from the recharge currents of coupling capacitors CK1, won Ck2 whose common circuit node to the active output 16 of the compensator output stage 15 is connected, while the respective free terminals of the coupling capacitors CK1, Ck2 to the negative or positive Intermediate circuit potential 2, 3 are connected. To the polar To achieve compensation currents, the compensator output stage can antiparallel 15 corresponding semiconductor devices be switched.