High frequency, high output impedance amplifier for emi active filter applications

Abstract

The invention relates to high frequency, high output impedance amplifiers for EMI active filter applications. A high frequency amplifier for an active EMI filter has a symmetric class B emitter follower output stage driven by a driver stage, with a sense output resistor. In a global voltage feedback loop, the two terminals of the sense resistor are connected through two voltage dividers of the same ratio to the non-inverting input, the inverting input of the driver stage, respectively. The amplifier is configured to provide a high output impedance from 10 kHz and up to 100 MHz, a peak to peak output current of 2-10 Ampere and a low quiescent current of less than 400 mA. The invention includes an EMI filter with such a high frequency current source, for example in a current sense current injection feedback configuration.

Description

Technical Field

[0001] This invention relates to an electromagnetic compatibility filter for suppressing unwanted noise components superimposed on power supply lines. Embodiments of the invention relate to filters placed behind motor drive units on DC power buses in electric vehicles, although this is not the only application of the invention. Background Technology

[0002] Electrical systems in vehicles and industry are becoming increasingly complex, including many components that generate or are susceptible to electromagnetic interference. For example, electric motors are typically driven by electronic inverters, which control the motor's speed and torque by generating waveforms with variable frequency and amplitude. These systems offer high efficiency but generate significant electromagnetic noise.

[0003] Switching power supply converters are used in electric and hybrid vehicles, as well as countless other applications such as driving stationary motors, battery chargers, photovoltaic systems, lighting control, computers, and others. In all these cases, the switching action of the converter is a source of electromagnetic noise, which, if not managed or attenuated, can affect the function of other systems or exceed specification limits.

[0004] Electrical or electronic filters (EMI filters) used to attenuate these unwanted disturbances are used in all branches of electrical engineering to improve reliability and comply with existing specifications. Well-designed filtering systems are crucial to the performance of many complex electrical systems.

[0005] Electric and hybrid vehicles are equipped with different power converters in very confined spaces. This coexistence presents significant electromagnetic problems and necessitates efficient EMI filtering. Shielded cables can be used when filters are insufficient to bring noise levels to acceptable levels, but these significantly increase costs.

[0006] Passive low-pass LC filters are known to be used to attenuate EMI. While passive solutions do offer significant attenuation, they have their limitations. Magnetic components currently used in modern electric vehicles are bulky, expensive, and cumbersome, and are not always suitable for mass production.

[0007] Document US20180269781 discloses an active EMI filter for electric vehicles. Active filters can be more compact than equivalent passive filters, but providing a satisfactory active filter for the large current and wide bandwidth interference generated in electric vehicles is difficult.

[0008] Active filters are known in many variations and topologies. They typically include an output stage that must be fast enough to eliminate noise in the desired frequency band, have dynamics that match the noise level, and have sufficient input and output impedances. Applications in the automotive field present unprecedented demands in terms of speed and output current, requirements that are difficult to meet using known architectures.

[0009] Active power filters inevitably rely on an auxiliary power supply. In some cases, the auxiliary power supply must be bipolar, which may be uneconomical to use.

[0010] The stopband (the frequency range where attenuation is significant) of an active EMI filter will be selected as needed. In most applications (including vehicles), it is expected that the EMI filter should be effective in the frequency band between 1 kHz and tens of MHz (potentially up to 100 MHz or higher). In the following text, this frequency range may be conventionally referred to as "HF" or "high frequency," while the portion of the spectrum below this range and down to 0 may be conventionally referred to as "DC." Summary of the Invention

[0011] The objective of this invention is to provide a filter that overcomes the shortcomings and limitations of the prior art.

[0012] According to the invention, these objectives are achieved by the objectives of the appended claims, and particularly by a high-frequency amplifier for an active EMI filter, the high-frequency amplifier having: a symmetrical emitter follower output stage having two bipolar transistors in a symmetrical complementary pair configuration; an input stage driving the output stage; a sensing resistor through which the output current flows; and a voltage feedback loop for feeding back the voltage measured across the sensing resistor to the input stage. In a preferred configuration (however, this is not the only configuration), the voltage feedback loop is configured to preferably feed back the potential across the sensing resistor to the inverting input and the non-inverting input of the input stage, respectively, via two resistor dividers of equal ratio.

[0013] Because it includes a voltage reference defining the potential difference between the bases of the bipolar transistors, the high-frequency amplifier is configured for operation in Class B (or AB). Preferably, the voltage reference has a negative temperature coefficient for thermal stability and can be implemented using a Vbe multiplier, among other possibilities. Although the amplifier can deliver peak-to-peak currents of 1 A or up to 10 A, its quiescent current is moderate, typically less than 400 mA. The temperature operating range extends at least between -40 ºC and 125 ºC and is sufficient for automotive applications.

[0014] The high-frequency amplifier can operate on a single-pole power supply and has a high output impedance (approximately that of a current source). Typically, the output impedance exceeds 1 kOhm at 100 kHz. Furthermore, the amplifier of this invention has a flat bandwidth (within 3 dB) in the frequency range between 10 kHz and 10 MHz (extendable to 100 MHz through careful design and selection of components).

[0015] Due to the aforementioned characteristics, the amplifier of this invention is an excellent choice for constructing active filters (particularly those with "current injection" topologies). The filter stopband is directly determined by the amplifier's bandwidth and covers most of the switching noise generated by variable frequency motor drivers found in electric or hybrid vehicles. Higher frequencies, if present, can be effectively attenuated by a small passive filter. The filter is preferably configured to attenuate common-mode noise, and sensing of the noise current circulating in the power line can be obtained via a common-mode current transformer.

[0016] The present invention also relates to the use of the above-described active EMI filter on the power bus of electric or hybrid vehicles. Attached Figure Description

[0017] Exemplary embodiments of the present invention are disclosed in the specification and illustrated in the accompanying drawings, in which:

[0018] Figure 1 The diagram schematically illustrates a possible structure for an electric vehicle in which the filter of the present invention can be employed.

[0019] Figure 2 A conventional passive EMI filter is shown.

[0020] Figures 3 to 5 A filter according to the present invention is illustrated schematically. Detailed Implementation

[0021] Figure 1 The main components of the electric vehicle are shown in a very simplified manner. The energy required for traction is stored in a battery pack 45 and can be replenished by a charger 45 or, in the case of a hybrid vehicle, by an internal combustion engine (not shown). The battery pack 25 is connected to a power distribution unit 30, which distributes power to various loads, such as a DC / DC converter 40 for generating 12V voltage for auxiliary equipment (entertainment, lights, onboard computer, etc.) and a heat pump 20 for heating / ear regulation. Importantly, a high-voltage DC bus 15 transmits the battery voltage to a motor drive unit 60, which includes an inverter that generates a multiphase AC waveform suitable for an electric traction motor 70. An EMI filter 50 is inserted at the power supply point of the drive unit 60 on the DC bus 15 to filter out noise generated by the inverter in the drive unit 60.

[0022] Figure 1 The configuration described is just one of many possibilities and is provided only as a non-limiting example of one possible use of the invention. The invention can be used in electric vehicles presenting various configurations, for example, for those not corresponding to… Figure 1 The diagrams illustrate series hybrid, parallel hybrid, and plug-in hybrid configurations. This invention is not limited to automotive applications.

[0023] Figure 1 Two EMI filters 50 are shown: one between battery 25 and charging connector 49, and one on the DC side of motor driver 60. The EMI filters of this invention can be used in other locations without departing from the scope of the invention. Significant locations for the EMI filters are: before and after charger 45; after battery 25; and before DC / DC converter 40. Charging unit 45 can be installed wholly or partially after connector 49. All these variations are included within the scope of the invention as defined in the appended claims.

[0024] Figure 2 A possible structure of a passive EMI filter 51 known in the art is shown. This filter is configured as a two-stage LC filter with two common-mode chokes L1 and L2 and several capacitors (X capacitors C2, C5, C8) connected between the positive and negative power rails or several capacitors (Y capacitors C1, C3, C4, C6, C7, C9) connected between the power rails and the protective ground conductor. Such a filter can be designed to provide effective noise attenuation at the cost of increased size, weight, and manufacturing cost.

[0025] EMC filters can be designed to attenuate differential-mode and / or common-mode noise as needed. Common-mode noise appears simultaneously on all conductors of the power supply bus with the same polarity and is usually dominant. Figure 2 The filter is designed to primarily attenuate common-mode noise.

[0026] Figure 3 A possible structure of the filter 50 according to the invention is shown. It is drawn as a single-wire scheme, and the power line 15 is represented by a single wire. This is a simplification of a practical implementation in which the power line 15 may include several conductors. In an important but non-exclusive implementation, the power line 15 may be an HVDC bus in an electric vehicle including positive and negative rails. The filter may be designed to attenuate differential noise, or preferably, attenuate common-mode noise components.

[0027] In the illustrated embodiment, the active filter has a feedback configuration comprising: a current sensing unit 110, which may be a current transformer that reads noise current flowing out of the output as an error signal; an analog signal conditioning stage 120 designed to amplify the error signal in a defined frequency band; and a current source 130 that injects a correction current into the power supply line 15 via a current injection circuit 140.

[0028] The presented filter has a "current sensing / current injection" topology, which senses current and injects a corresponding correction current. However, the invention is not limited to this, and may also include filters that sense noise as voltage disturbances on the power supply line, and / or include voltage sources for injecting voltage on the power supply line, or include filters with output circuitry that is neither a pure current source nor a pure voltage source. The following description introduces a "current sensing unit" at the input of the filter and a "current source" at the output, but these can be replaced by voltage sensors (voltage sources, respectively), or by sensors and sources that are neither purely current nor purely voltage types, without departing from the scope of the invention.

[0029] As is well known, an ideal feedback filter provides attenuation in the closed loop given by Y = X / (1+H), where Y represents the signal at the filter output, X represents the signal at the input, and H is the open-loop gain. In practice, the non-ideal behavior of sensors and electronic circuitry will introduce additional factors. However, the present invention is not limited to this filter topology and may also include, for example, feedforward filters.

[0030] All active filters exhibit a dynamic limitation, namely the maximum current that can be injected back into the power supply line and that relies on the power supply (not shown) for their operation. Their performance is guaranteed within a defined bandwidth, where their operating parameters (e.g., insertion loss) adhere to nominal values. The bandwidth of the filter stage will be determined by considering the noise bandwidth. The amplifier of this invention can operate in an extended bandwidth, for example, between 10 kHz and 10 MHz or up to 100 MHz with a substantially constant gain (within 3 dB).

[0031] An active filter is inserted into the power supply line after the noise source (ultimately with a passive pre-filter stage) and should be able to inject a current of the same strength as the noise current. Demanding applications may have noise amplitudes of 2 A peak-to-peak or higher (up to 10 A peak-to-peak), and the output dynamics of the first active filter stage should match these figures.

[0032] It can be done as follows Figure 4 and 5The filter configured as shown achieves the desired dynamic behavior. In this configuration, the common-mode noise signal sensed by the current transformer 110 is amplified by the gain stage 120 and then presented to the input of the amplifier 130, which is configured to deliver an output current proportional to its input voltage. The current is then injected into the power supply line through a passive decoupling network 140. For good filter performance, it is important that the amplifier 130 approximates an ideal current source with high output impedance or at least an output impedance significantly exceeding the equivalent impedance of the power supply line 15.

[0033] Amplifier 130 in Figure 5 A simplified schematic diagram is shown. It has two bipolar transistors in a symmetrical emitter follower configuration: a PNP transistor 138 with a collector connected to a positive supply voltage V++ and an NPN transistor 139 with a collector connected to ground or a suitable constant supply voltage below V++. The emitters of the transistors are connected via two emitter resistors 194. A sensing resistor is located between the common point of the emitter resistors 194 and the output of the amplifier.

[0034] The bases of the two transistors are offset from each other by a voltage reference 164, which maintains a constant voltage between nodes 'd' and 'c' linked to the transistor bases. It is important to emphasize that this is just one example among many possible arrangements used to determine the appropriate operating points for transistors 138 and 139.

[0035] This stage can be configured to operate in Class B (where the PNP transistor is only active for the negative polarity of the output current and the NPN transistor is active for the positive polarity) or possibly in Class AB (where a small area of ​​Class A operation is around the center point).

[0036] Voltage reference 164 preferably has a negative temperature coefficient that matches the temperature coefficient of Vbe of transistors 138 and 139. This can be achieved, for example, by the drawn Vbe multiplier circuit. The voltage difference between nodes 'd' and 'c' changes with respect to the current flowing from resistor 208 and has the desired temperature coefficient. Without this arrangement, the quiescent current flowing through transistors 138 and 139 would increase with temperature. Other voltage sources can be used instead of Vbe multiplier 164.

[0037] Amplifier 130 generates an output current proportional to its input voltage, which flows through sensing resistor 195 to a load represented in simplified form by network 203. In the voltage feedback loop, the two terminals of sensing resistor 195 are connected to input 166 of the driver stage. Terminal A is connected to the inverting input of operational amplifier 166, while terminal B is connected to the non-inverting input of operational amplifier 166. To avoid confusion, the two wires connecting points AA and BB are omitted. Resistors 210a and 210b form two resistive voltage dividers, which preferably have the same ratio.

[0038] The inventors have discovered that this configuration can provide high output impedance due to feedback, which is desirable in active EMI filters.

[0039] The combination of an emitter follower symmetry stage 193, an active gain stage 166, a sense resistor 195, and voltage feedback provides a voltage-controlled high-frequency amplifier whose output approximates a current source. This amplifier has been found to be well-suited for implementing active EMI filters in various industrial sectors, particularly in automotive applications. While this system is more complex than other known HF sources, this complexity brings several significant advantages, including:

[0040] • High output impedance over a wide frequency range, such as 2 kΩ at 100 kHz (value depends on component selection).

[0041] • Stable operating point over an extended temperature range (e.g., between -40 ºC and 125 ºC).

[0042] Single power supply

[0043] High current capability, up to 10A peak-to-peak.

[0044] • Low quiescent current, typically less than 400 mA.

[0045] Reference symbols in the attached figure

[0046] 15 power supply lines, DC bus

[0047] 20 Heat Pump

[0048] 25 battery packs

[0049] 30 power distribution units

[0050] 40 DC / DC converter

[0051] 45 Charger

[0052] 48 Charging cable

[0053] 49 Connectors

[0054] 50 EMC Filter

[0055] 51 Passive Filter

[0056] 60 motor drive units

[0057] 65 Noise Sources

[0058] 70 motors

[0059] 75 Load, Damaged Equipment

[0060] 100 ECU

[0061] 101 Active Filter Stage (Power Stage)

[0062] 110 Current detection, current transformer

[0063] 120 Preamplifier, Signal Conditioning

[0064] 130 Current Amplifier

[0065] 137 NPN transistor

[0066] 138 NPN transistors

[0067] 139 PNP transistor

[0068] 140 Current Injection

[0069] 164 Voltage reference, Vbe multiplier

[0070] 166 gain stages

[0071] 193 Complementary Pairs

[0072] 194 Emitter Resistor

[0073] 195 Sensing Resistor

[0074] 203 Equivalent impedance of power supply line

[0075] 208 resistor.

Claims

1. A high frequency amplifier for an active EMI filter, comprising: A symmetric emitter follower output stage for providing an output current, having two bipolar transistors in a symmetric complementary pair configuration and configured as current sources to generate an output current; an input stage driving the output stage; a sense resistor through which the output current flows; a voltage feedback loop for feeding back a voltage measured across the sense resistor to the input stage, the amplifier comprising a voltage reference defining a potential difference between the bases of the bipolar transistors, wherein the voltage reference has a negative temperature coefficient.

2. The high frequency amplifier of claim 1, wherein the voltage feedback loop is configured for feeding back a potential across the sense resistor to an inverting input of the input stage, a non-inverting input of the input stage, respectively.

3. The high frequency amplifier of claim 1, wherein the voltage reference is a Vbe multiplier.

4. The high frequency amplifier of claim 1, wherein the voltage reference is configured for operating in class B or AB, and a quiescent current of the high frequency amplifier is less than 400 mA.

5. The high frequency amplifier of claim 1, having a single pole power supply.

6. The high frequency amplifier of claim 1, having an output dynamic range between 1 A peak to peak and 10 A peak to peak, a bandwidth of at least 10 MHz or a bandwidth in the interval 10 kHz - 100 MHz, and an output impedance of at least 1000 Ohms at 100 kHz.

7. The high frequency amplifier of claim 1, having a temperature operating range extending between -40 °C and 125 °C.

8. An active EMI filter comprising: a sensing unit configured to sense a noise signal circulating in a power supply line from a noise source to a load; the high frequency amplifier of claim 1, driven by the noise signal, thereby generating an output current; a current injection unit injecting the output current into the power supply line, wherein an output impedance of the output stage exceeds an equivalent impedance of the power supply line.

9. The active EMI filter of claim 8, comprising: a sensing unit configured to sense a noise signal circulating in a power supply line from a noise source to a load, a high frequency current source controlled in dependence of the noise signal, a current injection unit injecting a high frequency output current of the high frequency current source into the power supply line.

10. The active EMI filter of claim 8, wherein the noise signal is common mode.

11. The active EMI filter of claim 8, wherein the sensing unit is a current transformer coupled to a noise current on the power supply line.

12. Use of the active EMI filter of claim 8 on a power supply bus of an electric or hybrid vehicle.

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