Active emc filter

Abstract

The invention describes a circuit arrangement (30) in a feed-forward structure for active EMC filtering of interference signals which are coupled into a load (20) from an EMC source (10). The circuit arrangement (30) comprises a voltage measuring device (VS), a current impressing unit (CI) and a control unit (35). The current impressing unit (CI) comprises a coupling capacitor (36) connected to the transmission line (15), and a controllable voltage source (37). The voltage measuring device (VS) is designed to determine the capacitor voltage (vaf) falling across the coupling capacitor (36) and to supply it to the control unit (35) as a reference variable. Furthermore, the control unit (35) is designed to determine a manipulated variable for the controllable voltage source (37) from the reference variable in a control loop and to supply it to said source for generating a compensation voltage (vafA), wherein the manipulated variable is determined such that the compensation voltage (vafA) is equal and opposite to the capacitor voltage (vaf).

Description

[0001] Description

[0002] Active EMC filter

[0003] The present invention relates to a circuit arrangement in a feedforward structure for the active EMC filtering of interference signals which are coupled from an EMC source into a load which is connected to the EMC source via a transmission line and comprises a voltage measuring device, a current impression unit and a control unit.

[0004] Power systems whose semiconductor switching elements operate with pulse-width modulation cause EMC interference. Electromagnetic compatibility (EMC) describes the ability of a technical device not to interfere with other devices through unwanted electrical or electromagnetic effects or to be interfered with by other devices. To meet specified standards, e.g., N 61800-3 for industrial applications, filters must generally be integrated into a power electronics system. A distinction is made between passive filters and active filters.

[0005] Passive filters require a large volume of space, are heavy, and can cause resonances associated with line impedance. Active filters do not have these disadvantages if they are appropriately controlled. In the past, active EMI filters (AEFs) were controlled by analog control loops. To implement infinite gains and delay compensation, digital control loops are preferred.

[0006] A variety of structures for EMC filters are known, whereby these can be divided into filters with a so-called feedforward structure (FF structure for short) and filters with a so-called feedback structure (FB structure for short). The general topologies are briefly explained below with reference to Figures 1 to 6. In all of the following examples, the EMC interference to be filtered is caused by an EMC source 10, e.g., a converter. The EMC source is also known as an "EMI source." The EMC interference is coupled from the EMC source 10 into a load 20 (the so-called "EMI victim") via a transmission line 15. In order to suppress or eliminate the EMC interference, an active EMC filter 30 is arranged between the EMC source 10 and the load 20.

[0007] Each of the active EMC filters 30 shown in Figures 1 to 6 comprises a sensor 31, an injector 32 and a control loop 33 which, based on sensor signals detected by the sensor 31, controls the injector 32 in such a way that the interference at the load 20 caused by the EMC source 10 is suppressed or eliminated.

[0008] In general, in a feedback structure, sensor 31 records measured values ​​on the load side at a so-called mains connection point of load 20. This is shown in Fig. 1. The measured values ​​are thus recorded by sensor 31 at the point where a disturbance has already been eliminated by the injector 32 of the EMC filter 30, which is arranged on the source side. The control loop 33 must therefore have a very fast amplifier circuit with a high gain. Due to its principle, however, the injector 32 can only counteract the disturbance caused by the EMC source 10 with a delay, so that a new disturbance can be caused by the injector 32. This can cause an increasing disturbance to occur at the load 20. Feedback structures therefore require very fast amplifier circuits to close the control loop and avoid instabilities.

[0009] In a feedforward structure, sensor 31 measures the disturbance at the source, i.e., at the EMC source 10. This is shown in its general form in Fig. 2. This allows an accurate measurement to be made at the disturbance source, the EMC source 10. The feedforward structure uses the disturbance to estimate the counter-feedback signal to be delivered by the injector 32. Since there is no closed control loop, errors can arise due to modeling and nonlinearities.

[0010] To date, there are essentially four different feedback structures, which are illustrated in Figures 3 to 6. In these, the disturbance is measured either in the form of voltage or current and subsequently impressed as current or voltage. In these, the EMC source 10 is represented by a voltage source 11 and an internal impedance 12. The load 20 is represented in these embodiments by an internal impedance 23.

[0011] In the feedback structures of Figures 3 and 4, the sensor 31 is designed as a current measuring device CS. The current measuring device CS detects the current I @20 flowing into the load 20, which is fed to the control circuit 33. In the feedback structures of Figures 5 and 6, the sensor 31 is designed as a voltage measuring device VS. The voltage measuring device VS detects the voltage drop across the load 20, which is fed to the control circuit 33.

[0012] The control circuit 33 generates a control variable from the measured current I @20 or from the voltage V@20 across the load 20, which is sent to the injector 32 to generate a (compensation) current I an ti or a (compensation) voltage V anti is supplied. In the feedback structures of Figures 3 and 6, the injector 32 has a voltage impressing unit VI which applies the voltage V antiat the terminals of the EMC source 10. In the feedback structures of Figures 4 and 5, the injector 32 is designed as a current injection unit CI, which injects the current I into the transmission line 15. anti memorizes .

[0013] From a technical point of view, it is easier to measure a voltage on the load side and to inject a voltage on the source side, as shown in Fig. 6. One problem here is the coupling network for the voltage V to be injected. anti . To date, this has generally been achieved with the aid of a 32T transformer, as shown schematically in Fig. 7. For this purpose, a primary coil of the 32T transformer is located in the transmission line 15 between the EMC source 10 and the load 20. In addition, a decoupling capacitor Cdec is connected to the terminals of the EMC source 10 between the EMC source 10 and the primary coil of the 32T transformer. The voltage V anti, which is generated by the injector 32, is applied via an impedance Z anti impressed into a secondary coil of the 32T transformer. A disadvantage of this structure is that the voltage V anti with changing frequencies. Suitable transformers are difficult to produce, especially at high frequencies and high currents.

[0014] It is an object of the invention to provide a circuit arrangement which enables a simpler reduction of EMC interference emanating from an EMC source.

[0015] This object is achieved by a circuit arrangement according to the features of claim 1. Advantageous embodiments emerge from the dependent claims.

[0016] A circuit arrangement in a feedforward structure for active EMC filtering of interference signals which are coupled into a load from an EMC source is proposed, wherein the load is connected to the EMC source via a transmission line. The circuit arrangement arranged between the EMC source and the load comprises a voltage measuring device, a current impression unit and a control unit. The current impression unit comprises a coupling capacitor connected to the transmission line and a controllable voltage source. The voltage measuring device is designed to determine the capacitor voltage drop across the coupling capacitor and to feed it to the control unit as a reference variable.The control unit is designed to determine a manipulated variable for the controllable voltage source from the reference variable in a control loop and to supply it to generate a compensation voltage, wherein the manipulated variable is determined in such a way that the compensation voltage is equal to and opposite to the capacitor voltage.

[0017] The present circuit arrangement enables voltage measurement with current injection in a feedforward topology. Because the capacitor voltage drop across the coupling capacitor is measured rather than the EMC voltage remaining at the load, the control loop can be simplified, allowing the requirements for feedforward control with a slow operational amplifier to be met with a single controller structure.

[0018] This is made possible by reducing the interference voltage component to 0 V at the source-side coupling point of the current injection unit, which means that no more (interference) current flows into the load. Current compensation is thus achieved by the coupling capacitor. By eliminating a transformer coil, improved frequency response can be achieved. A further advantage is that, thanks to the controllable voltage source, only the interference component needs to be eliminated.

[0019] The coupling capacitor and the controllable voltage source are advantageously connected in series. The series circuit comprising the coupling capacitor and the controllable voltage source is connected between the coupling point of the transmission line and a reference potential.

[0020] According to a further advantageous embodiment, the voltage measuring device is designed as a first voltage measuring device for measuring the capacitor voltage drop across the coupling capacitor. According to this embodiment, only the first voltage measuring device is required to filter out interference signals.

[0021] According to a further embodiment, it can be provided that the control unit is designed to increase the manipulated variable in a control loop compared to the reference variable over a predetermined frequency range with a gain of exactly 1. This can be done, for example, by a very slow gain adjustment of a higher-level control loop. The time requirements for this control loop are moderate and can be implemented with inexpensive hardware. For this purpose, a second voltage measuring device is provided which records the total voltage across the series connection of the coupling capacitor and the controllable voltage source and makes it available to the control unit in the higher-level control loop as a reference variable. The higher-level control loop represents a feedback loop.

[0022] In another embodiment, it is provided that the voltage measuring device is designed to calculate the capacitor voltage occurring across the coupling capacitor from a first measuring voltage and a second measuring voltage. The first measuring voltage can be provided by the second voltage measuring device, which detects the total voltage across the series connection of the coupling capacitor and the controllable voltage source. The second measuring voltage can be provided by a third voltage measuring device, which detects the voltage across the controllable voltage source. The first and the second measuring voltage can then be subtracted from one another by means of an adder.

[0023] The design of the EMC filter has the advantage over other control methods that no knowledge of the EMC filter's environment is required. The result is a plug-and-play solution that can be connected to any EMC source, such as a converter, and compensates for EMC interference without special parameterization.

[0024] The invention is explained in more detail below with reference to exemplary embodiments in the drawing. In the drawing: Fig. 1 shows a schematic representation of an active EMC filter in a feedback structure;

[0025] Fig. 2 is a schematic diagram of an active EMC filter in feedforward structure;

[0026] Fig. 3 is a schematic diagram of an active EMC filter with current measurement and voltage injection in feedback structure (FB CSVI AEF);

[0027] Fig. 4 is a schematic diagram of an active EMC filter with current measurement and current injection in feedback structure (FB CSCI AEF);

[0028] Fig. 5 is a schematic diagram of an active EMC filter with voltage measurement and current injection in feedback structure (FB VSCI AEF);

[0029] Fig. 6 is a schematic diagram of an active EMC filter with voltage measurement and voltage impression in feedback structure (FB VSVI AEF);

[0030] Fig. 7 is a schematic diagram showing a known technical implementation of a voltage injection;

[0031] Fig. 8 shows a first embodiment of an active EMC filter according to the invention;

[0032] Fig. 9 shows a second embodiment of an active EMC filter according to the invention with a higher-level control loop; and

[0033] Fig. 10 shows a third exemplary embodiment of an active EMC filter according to the invention with indirect determination of a capacitor voltage drop across a coupling capacitor. The variants of an active EMC filter shown in Figures 8 to 10 for filtering interference signals which are coupled into a load 20 from an EMC source, such as a converter with clocked power semiconductor switches, are based on a voltage measurement with current injection in a feedforward structure. The feedforward structure estimates the signal to be counter-coupled based on the interference measured as voltage. At the same time, the proposed EMC filter implements a closed control loop in order to eliminate the errors from modeling and non-linearities which have previously resulted in feedforward structures.However, the closed control loop inherent in a feedback structure does not require fast amplifier circuits to close the control loop, unlike conventional structures.

[0034] Figures 8 to 10 each show, on the right-hand side, a schematic EMC source 10, which is represented by a voltage source 11 and an internal impedance in the form of an inductance 12. The EMC source 10 is coupled to a load 20 via a transmission line 15. The load 20 is represented by a voltage source 21 and a network simulation 22, which is implemented as a Line Impedance Stabilization Network (LISN). A current injection unit CI is connected to a coupling point A on the load side of the transmission line 15.

[0035] The current injection unit CI comprises a coupling capacitor 36 connected to the transmission line 15 and a controllable voltage source 37 connected in series thereto, which is coupled to a reference potential. A voltage resulting from the capacitor voltage v is coupled into the network (transmission line 15) via the coupling capacitor 36. af and a voltage generated by the voltage source 37. The voltage generated by the voltage source 37 is referred to below as compensation voltage v afA The level of the compensation voltage v afA is determined as follows . A voltage measuring device VS , which is represented in Fig . 8 by a first voltage measuring device 38 , detects the capacitor voltage v dropping across the coupling capacitor 36 af. This is fed to a control unit 35 of a control loop as a reference variable. The control unit 35 is designed to calculate from the reference variable v af to determine a control variable u for the controllable voltage source 37. From this, the controllable voltage source 37 generates the compensation voltage v afA , which is dimensioned such that the compensation voltage v afA the capacitor voltage v af is equal and opposite in amount.

[0036] As a result, a voltage of 0 V is generated at the coupling point A of the transmission line 15, from which an interference current i emanating from the EMC source c as compensation current i af flows into the current injection unit CI . As a result, the current i emanating from the coupling point A n into the load 20 to 0 ( i n = 0 ) . Current compensation is thus achieved by the current injection unit CI and its coupling capacitor 36 .

[0037] This design enables improved frequency response compared to the transformer arrangement shown in Fig. 7. A further advantage is that the controllable voltage source 37 only needs to eliminate the interference component of the interference signal emanating from the EMC source 10. By controlling the controllable voltage source 37, the desired compensation of the capacitor voltage v dropping across the coupling capacitor 36 is then achieved. af , causing a disturbance current i n can be eliminated .

[0038] For the EMC filter 30 to operate as intended, it is advisable to ensure that the gain of the control loop, which is implemented by the control unit 35 in conjunction with the current injection unit CI, is exactly 1 over the frequency range under consideration. This can be achieved by a very slow gain adjustment of a higher-level control loop. This is shown in Fig. 9.

[0039] In this embodiment, a second voltage measuring device 39 is provided, which detects the total voltage across the current injection unit CI, i.e., the series circuit comprising coupling capacitor 36 and controllable voltage source 37. The corresponding voltage signal is fed to the higher-level control loop 35GC of the control unit 35. This ensures that the control loop 35G described in connection with Fig. 8 has a gain of 1. The time requirements for the higher-level control loop 35GC are moderate and can be implemented using inexpensive hardware in a manner familiar to those skilled in the art.

[0040] The design of the EMC filter 30 described in Figures 8 and 9 has the advantage over the control methods described above that no knowledge of the filter's environment is required. The EMC filter presented here represents a plug-and-play solution that can be connected to any EMC source, e.g., a converter. Parameterization to compensate for EMC interference is not required.

[0041] Fig. 10 shows a further embodiment variant in which the capacitor voltage v dropping across the coupling capacitor 36 afis not measured directly. Instead, this voltage is calculated from a first voltage measurement and a second voltage measurement. The first measurement voltage is provided by the second voltage measuring device 39, which corresponds to the total voltage across the series connection of coupling capacitor 36 and controllable voltage source 37. A third voltage measuring device 40 provides the second measurement voltage, which detects the voltage across the controllable voltage source 37. The first and the second measurement voltage are fed to an adder 35D of the control unit 35, one of the two measurement voltages being inverted beforehand. The difference voltage is fed to the control loop 35G. The higher-level control loop 35GC of the control device 35 also directly receives the second measurement voltage determined by the second voltage measuring device 39.

[0042] Reference symbol list

[0043] 10 EMC source

[0044] 11 Voltage source

[0045] 12 Internal impedance

[0046] 15 Transmission line

[0047] 20 load

[0048] 21 Voltage source

[0049] 22 Network Simulation (LISN)

[0050] 30 Circuit arrangement for active EMC filtering

[0051] 31 Sensor

[0052] 32 injectors

[0053] 33 control loop

[0054] 35 Control unit

[0055] 35G control loop

[0056] 35GC higher-level control loop

[0057] 35D adder

[0058] 36 Coupling capacitor

[0059] 37 controllable voltage source

[0060] 38 first voltage measuring device

[0061] 39 second voltage measuring device

[0062] 40 third voltage measuring device

[0063] VS voltage measuring device

[0064] CS current measuring device

[0065] VI Voltage impression unit

[0066] CI current impression unit i c Current of the EMC source v c Voltage of the EMC source i n Current of load i a f compensation current v afA Compensation voltage

[0067] C a f Capacitance of the coupling capacitor v a f capacitor voltage

Claims

Patent claims 1. Circuit arrangement (30) in a feedforward structure for active EMC filtering of interference signals which are coupled from an EMC source (10) into a load (20) which is connected to the EMC source (10) via a transmission line (15), comprising: a voltage measuring device (VS); a current impressing unit (CI); a control unit (35); wherein the current impressing unit (CI) comprises a coupling capacitor (36) connected to the transmission line (15) and a controllable voltage source (37); the voltage measuring device (VS) is designed to measure the capacitor voltage (v af ) and to supply it to the control unit (35) as a reference variable; the control unit (35) is designed to determine a control variable for the controllable voltage source (37) from the reference variable in a control loop and to supply it to the controllable voltage source (37) to generate a compensation voltage (v afA), whereby the manipulated variable is determined in such a way that the compensation voltage (v afA ) of the capacitor voltage (v af ) is equal and opposite in magnitude.

2. Circuit arrangement according to claim 1, characterized in that the coupling capacitor (36) and the controllable voltage source (37) are connected in series.

3. Circuit arrangement according to claim 1 or 2, characterized in that the voltage measuring device (VS) is designed as a first voltage measuring device (38) to measure the capacitor voltage dropping across the coupling capacitor.

4. Circuit arrangement according to one of the preceding claims, characterized in that the control unit (35) is designed to control the manipulated variable in a control loop (35G) compared to the reference variable over a given frequency range with a gain of exactly one.

5. Circuit arrangement according to claim 3 or 4, characterized in that a second voltage measuring device (39) is provided which detects the total voltage across the series circuit of coupling capacitor (36) and the controllable voltage source (37) and provides it to the control unit (35) in a higher-level control loop (35GC) as a reference variable.

6. Circuit arrangement according to claim 5, characterized in that the higher-level control loop is a feedback loop.

7. Circuit arrangement according to one of the preceding claims, characterized in that the voltage measuring device (VS) is designed to calculate the capacitor voltage drop across the coupling capacitor from a first measuring voltage and a second measuring voltage.

8. Circuit arrangement according to claim 7, characterized in that the first measuring voltage is provided by the second voltage measuring device (39), which detects the total voltage across the series circuit of the coupling capacitor (36) and the controllable voltage source (37).

9. Circuit arrangement according to claim 7 or 8, characterized in that the second measuring voltage is provided by a third voltage measuring device (40) which detects the voltage across the controllable voltage source (37).

Images