High-frequency current source for active emi filter, active emi filter and use of active emi filter

Abstract

High frequency current source for active EMI filter, active EMI filter and use of active EMI filter. A high frequency current source having a symmetric bipolar output stage piloted by an active bias network with extended temperature range. The source is configured to provide high impedance at 1 MHz and above. The invention includes such active EMI filter having such high frequency current source, for example in a current sense current injection feedback configuration.

Description

Technical Field

[0001] This invention relates to an active electromagnetic compatibility (EMC) filter for suppressing unwanted noise components superimposed on an electric supply line, and a high-frequency current source for the active EMC filter. Embodiments of the invention relate to filters placed behind motor drive units on a DC power bus in electric vehicles, but this is not the only application of the invention. Background Technology

[0002] Electrical systems in vehicles and industry are becoming increasingly complex and include numerous 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 converters are used in electric and hybrid vehicles, as well as countless other applications such as driving stationary electric motors, battery chargers, photovoltaic systems, lighting control, computers, and more. In all these cases, the switching action of the converter is a source of electromagnetic noise, which, if left unmanaged or attenuated, can affect the function of other systems or exceed regulatory limits.

[0004] Electrical or electronic filters, commonly known as EMI filters, are used in all branches of electrical engineering to attenuate these unwanted disturbances in order to improve reliability and comply with existing specifications. Well-designed filtering systems are essential for the performance of many complex electrical systems.

[0005] Electric and hybrid vehicles are equipped with different power converters in a very compact space. This coexistence presents serious electromagnetic problems and requires effective EMI filtering. Shielded cables can be used when filters are insufficient to bring noise to an acceptable level, but they 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. The magnetic components rated for current levels used in modern electric vehicles are large, expensive, heavy, and 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 high 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 matched to the noise level, and sufficient input and output impedances. Applications in the automotive field present unprecedented requirements in terms of speed and output current that are difficult to meet with known architectures.

[0009] When excellent filter performance is required simultaneously, conventional technical solutions cannot be applied to automotive applications due to stricter space, weight, reliability, and temperature requirements. Therefore, existing technologies are either too bulky or unreliable when operating over the extended temperature ranges required for automotive applications.

[0010] Active power filters rely on an auxiliary power supply. In some cases, the auxiliary power supply must be bipolar, which may not be economically viable.

[0011] The stopband of the active EMI filter will be selected as needed (attenuation is the interval of perceptible frequencies). In most applications, including in vehicles, it is expected that the EMI filter should be effective in the frequency band between 1 kHz and tens of MHz, which may be as high as 30 MHz or 50 MHz. In the following text, this frequency interval may be conventionally indicated as "HF" or "high frequency," while the portion of the spectrum below this interval and down to 0 may be conventionally indicated as "DC." Summary of the Invention

[0012] The purpose of this invention is to provide a filter that overcomes the shortcomings and limitations of the prior art.

[0013] According to the invention, these objectives are achieved by the purposes of the appended claims, and in particular by a high-frequency current source comprising a provided output via an output network having two bipolar transistors in a symmetrical common-emitter configuration connected between an upper power rail having a first potential and a lower power rail having a second potential, an active bias network determining the operating points of the two bipolar transistors, an analog control network receiving the output and generating a DC correction signal fed to the active bias network to stabilize the DC value of the output, and an HF input controlling the high-frequency output current, wherein the analog control network is configured to maintain a DC potential at the output at a predetermined interval between the first and second potentials. The predetermined interval can be limited or set to a predetermined DC potential, wherein the DC potential is maintained at the midpoint of the potential difference between the first and second potentials.

[0014] The active bias network preferably includes temperature-sensitive elements such as a diode array, configured to compensate for the temperature variability of the transistor's characteristics. The current source requires only a single-pole power supply, and the active bias circuitry is configured to maintain the DC output at the midpoint between the upper and lower rails over an extended temperature range, which is particularly useful when the source is used in an EMI filter. At 30 MHz, the output impedance is at least 1 kohm, and 2 kohm is possible with appropriate selection of the output transistor. The maximum output current can be 1 or 2 amps, and the temperature operating range can be extended at least between -40 °C and 125 °C.

[0015] This invention also relates to an active EMI filter, including the aforementioned high-frequency current source, which may have a sensing unit, which may be a current converter, configured to sense a noise signal flowing in the power line from the noise source to the load, and control the high-frequency current source according to the noise signal, injecting the high-frequency output current of the high-frequency current source into the power line through a current injection unit. In many applications, the noise signal will be a common-mode undesired noise current and can be picked up by a current converter on the power line, but this invention is not limited to current-sensing type filters, nor is it limited to feedback filters.

[0016] The present invention also relates to the use of the above-described active EMI filter on the power bus of an electric or hybrid vehicle. 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] Figure 3 A filter according to the present invention is illustrated schematically.

[0021] Figure 4 and 5 Two possible configurations of the active filter of the present invention are shown.

[0022] Figure 6 This is a simplified schematic diagram of a common-emitter output stage with a bias network, and

[0023] Figure 7 This is a simplified schematic diagram of the control network used to stabilize the operating point of the filter. Detailed Implementation

[0024] Figure 1The 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 that distributes power to various loads, such as a DC / DC converter 40 for generating 12V voltage for auxiliary equipment (entertainment, lighting, onboard computers, etc.), and a heat pump 20 for heating / ear regulation. Importantly, a high-voltage DC bus 15 transmits the battery voltage to an electric 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 on the DC bus 15 at the power point of the drive unit 60 to filter out noise generated by the inverter in the latter.

[0025] Figure 1 The configuration described is merely 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 exhibiting various structures, and these configurations, for example, do not correspond to... Figure 1 The diagram illustrates series hybrid, parallel hybrid, and plug-in hybrid configurations. This invention is not limited to automotive applications.

[0026] 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 mounted wholly or partially after connector 49. All such variations are included within the scope of the invention as defined by the appended claims.

[0027] Figure 2 A possible structure of a passive EMI filter 51 known in the art is shown. The filter is configured as a two-stage LC filter having two common-mode chokes L1 and L2 and several capacitors connected between the positive and negative power rails (X capacitors C2, C5, C8) or between the power rails and the protective ground conductor (Y capacitors C1, C3, C4, C6, C7, C9). Such a filter can be designed to provide effective noise attenuation at the expense of increased size, weight, and manufacturing cost.

[0028] Depending on the requirements, EMC filters can be designed to attenuate differential-mode and / or common-mode noise. Common-mode noise occurs simultaneously with the same polarity on all conductors of the power bus and often dominates. Figure 2 The filter is designed to primarily attenuate common-mode noise.

[0029] Figure 3 A possible structure of the filter 50 according to the invention is shown. It is drawn as a unifilar scheme, and the power line 15 is represented by a single wire. This is a simplification of a practical implementation where 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.

[0030] In the illustrated embodiment, the active filter has a feedback configuration including a current sensing unit 110, which may be a current converter that reads the noise current flowing out of the output as an error signal, an analog signal conditioning stage 120 that is designed to amplify the error signal in a defined frequency band, and a current source 130 that inserts a correction current into the power line 15 through a current injection circuit 140.

[0031] The proposed filter has a "current sensing / current injection" topology that senses current and injects a corresponding correction current. However, the invention is not limited to this case and may also include filters that sense noise as voltage disturbances on the power line, and / or include voltage sources that inject voltage on the power line, or 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, or sensors and sources that are neither purely current nor purely voltage types, without departing from the scope of the invention.

[0032] As is 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's output, X represents the signal at the input, and H is the open-loop gain. In practice, the non-ideal behavior of the sensor will introduce additional factors, and so on. However, the invention is not limited to this filter topology and may also include, for example, feed-forward filters.

[0033] All active filters exhibit a dynamic limit, which is the maximum current that can be injected back onto the power line and depends on the power supply (not shown) used for their operation. Their performance is guaranteed within a defined bandwidth, where their operating parameters (e.g., insertion loss) respect nominal values. The bandwidth of the filter stage will be determined taking into account the noise bandwidth. In typical automotive applications, a bandwidth of at least 1 MHz is required.

[0034] An active filter is inserted after the noise source onto the power line (ultimately leading to a passive pre-filter stage) and should be able to inject a current with the same strength as the noise current. Demanding applications may have noise amplitudes of 2 A peak-to-peak or greater, and the output dynamics of the first active filter stage should match these figures.

[0035] The required dynamic behavior can be achieved through, for example Figure 4 The filter configuration shown is used to obtain the current. In this configuration, the current source 130 has a common-emitter network 132, the operating point of which is determined by a bias network 134 and a PI (proportional-integral) control network 136 to stabilize the DC component of the output. Importantly, the active filter of the present invention has a unipolar power supply, rather than a more complex bipolar power supply with positive and negative voltage rails.

[0036] The three stages—common-emitter network 132, bias network 134, and PI control network 136—are designed to work in coordination and act as a high-frequency voltage-controlled current source. Although significantly more complex than conventional solutions, the circuit of this invention has proven advantageous because it provides high output impedance at high frequencies (thus approximating an ideal current source), good stability, an extended temperature range, and is extremely suitable for building active EMC filters in automotive applications.

[0037] Current output stage 132 in Figure 4 China and in Figure 6 A simplified schematic diagram is shown. It has two bipolar transistors in a symmetrical common-emitter configuration: a PNP transistor 138 with its emitter connected to a positive power supply 185 via a resistor Re of an appropriate value, and an NPN transistor 139 with its emitter similarly connected to a negative power supply 180, which may be ground. The output 175 of the current stage 132 is at the collector of the transistor. The bases of the two transistors are coupled to the HF input signal AC via an active bias network 134, which is described further.

[0038] The stage can be configured to operate in class A, where both transistors are always in the active region, or in class AB, where the PNP transistor is active only for the positive polarity of the output current and the NPN transistor is active for the negative one, with a small area of ​​class A operation around the center point.

[0039] The inventors have discovered that common-emitter provides high output impedance, which is desirable, but cannot be satisfactorily achieved alone in active EMI filters. Because the output is AC-coupled, the load impedance becomes very high at low frequencies. Therefore, the DC gain tends to be much higher than the AC gain. This causes a drift in the output DC voltage (preferably at a distance equal to the power rails Vcc and Vee) because the transistor is only imperfectly matched. This instability is particularly dangerous in EMI filters because current sources may end in saturation, injecting distorted waveforms into the system and thus additional noise at high frequencies. To overcome this, the present invention features a control network 136 that feeds back the DC value at the output to a correction node 172 (labeled "e") and maintains the output voltage fixed to a reference value. The control network 136 can implement P / I control based on integrators and gain stages, such as... Figure 7 As shown in the simplified diagram, other configurations are possible. The input resistor Rin of integrator 156 can have a value between 10 kΩ and 10 MΩ to avoid the output of loading stage 132 and control the integration time constant.

[0040] Integrator 156 is a low-pass filter and will be designed not to interfere with the high-frequency behavior of the filter. Preferably, the cutoff frequency of the integrator will be much lower than the desired low cutoff frequency of the EMI filter, for example, one decibel below. To determine this idea, if the active EMI filter is intended to attenuate noise between 10 kHz and 1 MHz, then the cutoff frequency of the control network should be at most 1 kHz. Proportional stage 166 increases the accuracy of control.

[0041] Since the control network 136 operates at low frequency and power, the integrator stage 156 and the gain stage 166 can be implemented using suitable operational amplifiers. CMOS operational amplifiers exhibit very low input bias current and are available in the single-supply rail-to-rail type. They can be advantageously used in this application.

[0042] The output of gain stage 166 is the offset DC voltage injected into bias correction node 172 of bias network 134.

[0043] exist Figure 4 and 6The visible active bias network 134 is designed to maintain the DC bias of the common-emitter network at the desired operating point across all temperature ranges of interest and to correct for the different characteristics of PNP and NPN transistors. It includes a voltage reference 164, which maintains a constant voltage across nodes “d” and “e” across all temperature ranges of interest. A diode array 154 introduces a negative temperature coefficient, so the potential between nodes “c” and “d” changes with temperature. This causes a temperature-dependent change in the base voltage of the transistors when the voltage drops across R1 and R2 remain equal, which counterbalances the temperature characteristics of transistors 138 and 139. Additionally, by applying a voltage at correction node 172, the potentials at nodes “c” and “d” can shift towards Vcc or Vee, thus increasing the base potential of one transistor and decreasing the base potential of the complementary transistor, or vice versa. This specific design of the bias active circuit, together with the feedback control unit 136, ensures appropriate DC operating voltages for all nodes (a, b, c, d, e, and output) regardless of temperature.

[0044] exist Figure 4 In the topology, the control network 136 directly feeds back the DC signal 124 at a specific correction node e of the active bias network k134, and in doing so, keeps the operating point of the transistor stable within the temperature range of interest. This schematic diagram illustrates a preferred technical solution, but is not the only possibility of the invention. Figure 5 As shown, the operating point can also be controlled by feeding back the DC correction signal through the pre-gain stage 120 instead of directly feeding it back to the active bias network 134. In this variant, the pre-gain stage 120 generates an input signal 126 for the bias network 134, which combines the HF signal sensed by the current converter 110 and the DC correction signal 124.

[0045] The combination of a common-emitter symmetric stage 132, an active bias network 134, and a control network 136 provides a voltage-controlled high-frequency current source, which has been found well-suited for implementing active EMI filters in various industrial sectors, particularly for automotive applications. This system is more complex than many known HF sources, but this complexity yields several important advantages, including:

[0046] • High output impedance over a wide frequency range, such as 2 kΩ at 30 MHz (the value depends on the choice of transistor).

[0047] • Stable operating point over an extended temperature range, for example, between -40 °C and 125 °C.

[0048] Single power supply

[0049] High current capacity, up to 5A peak-to-peak.

[0050] • Stable output voltage at the midpoint between the power rails.

[0051] Reference symbols in the attached figure

[0052] 15 power supply lines, DC bus

[0053] 20 heat pump

[0054] 25 battery pack

[0055] 30 power distribution units

[0056] 40 DC / DC converter

[0057] 45 charger

[0058] 48 charging cable

[0059] 49 connector

[0060] 50 EMC Filter

[0061] 51 passive filter

[0062] 60 motor drive unit

[0063] 65 noise sources

[0064] 70 electric motor

[0065] 75 load, victim equipment

[0066] 91a positive power supply, input (source side)

[0067] 91b positive power supply, output (load side)

[0068] 92A negative power supply, input (source side)

[0069] 92b negative power supply, output (load side)

[0070] 100 ECU

[0071] 101 Active Filter Stage (Power Stage)

[0072] 110 Current sensing, current converter, sensing unit

[0073] 120 amplifier, signal conditioning

[0074] 122 HF input signal

[0075] 124 DC input signal

[0076] 126 HF and DC input signals

[0077] 130 Current Source

[0078] 132 common emitter network

[0079] 134 bias network

[0080] 136 control network

[0081] 140 Current Injection

[0082] 154 diode array

[0083] 156 Integrator

[0084] 164 voltage reference

[0085] 166 gain level

[0086] Input of 171 common emitter network

[0087] 172 bias correction input

[0088] Output of 175 common emitter network

[0089] 180 ground or negative power supply

[0090] 185 positive power supply

Claims

1. A high-frequency current source for an active EMI filter, comprising: - The output provided by the output network has two bipolar transistors in a symmetrical common-emitter configuration connected between an upper power rail with a first potential and a lower power rail with a second potential. The output network includes a PNP transistor with an emitter connected to the upper power rail with the first potential via a resistor Re and an NPN transistor with an emitter similarly connected to the lower power rail with the second potential. - An active bias network determines the operating points of the two bipolar transistors, and an analog control network receives the output and generates a DC correction signal fed to the active bias network to stabilize the DC value of the output. The active bias network includes a temperature-sensitive element configured to compensate for the temperature variability of the transistor characteristics to stabilize the DC value. -HF input controls the high-frequency output current, wherein the analog control network is configured to maintain a DC potential at the output with a predetermined interval between the first and second potentials. The analog control network includes an integrator stage and a gain stage, wherein the integrator stage is configured as a low-pass filter, and the gain stage is connected to the correction node of the active bias network to keep the operating points of the two bipolar transistors stable within the temperature range of interest.

2. The high-frequency current source according to claim 1, wherein the temperature-sensitive element is a diode array.

3. The high-frequency current source of claim 1, wherein the analog control network is configured to maintain the DC potential at the output at the midpoint of the potential difference between the first and second potentials.

4. The high-frequency current source according to any one of claims 1-3, having a single-pole power supply.

5. The high-frequency current source according to any one of claims 1-3, having an output impedance of at least 1 kohm at 30 MHz, an output capability of at least 1 A peak-to-peak, and a temperature operating range extending at least between -40 °C and 125 °C.

6. An active EMI filter, comprising the high-frequency current source according to claim 1.

7. The active EMI filter of claim 6, comprising a sensing unit configured to sense a noise signal flowing in the power line from a noise source to a load, control a high-frequency current source based on the noise signal, and inject a high-frequency output current from the high-frequency current source into the power line via a current injection unit.

8. The active EMI filter of claim 6 or 7, wherein, The noise signal is common-mode.

9. The active EMI filter according to claim 6, wherein, The sensing unit is a current converter for noise current coupled to the power line.

10. Use of the active EMI filter according to claim 6 or 7 on the power bus of an electric or hybrid vehicle.

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