Apparatus for passive common-mode leakage mitigation

Abstract

This application is directed to approaches for addressing technical problems that arise due to common-mode (CM) leakage currents. CM leakage currents may or may not be present depending on grid architecture, and if not addressed, can lead to operational issues relating to electrical safety mechanisms (e.g., nuisance tripping). A circuit topology approach and corresponding methods and circuit operation control instruction programming are proposed where an additional predominantly inductive branch is included as a parallel impedance branch to provide an equivalent parallel CM impedance at the grid frequency.

Description

APPARATUS FOR PASSIVE COMMON-MODE LEAKAGE MITIGATIONCROSS REFERENCE

[0001] This application is a non-provisional of, and claims all benefit, including priority to, US Application No. 63 / 524,373, entitled APPARATUS FOR PASSIVE COMMON-MODE LEAKAGE MITIGATION, filed June 30, 2023, the entirety of which is incorporated herein by reference.FIELD

[0002] Embodiments of the present disclosure relate to the field of grid connected converters, including electric vehicle on-board chargers, and more specifically to approaches for common-mode leakage mitigation, improving safe operation of electrical circuits.INTRODUCTION

[0003] Common-mode (CM) leakage currents, which are defined as the sum of the currents flowing on mains wires towards the load, are an important safety consideration. A return path for this current can include ground I a protective earth (PE) conductor.

[0004] A leakage current travelling along various return paths could also potentially raise a safety hazard, and specifications and standards have been established to limit the amount of potential leakage current before a safety mechanism is tripped. However, this safety mechanism can also have the deleterious effect of causing nuisance tripping during operation when a fault does not exist.

[0005] CM leakage currents can vary depending on grid infrastructure implementation, and for various reasons, different grids in different jurisdictions or countries can have different CM characteristics, depending, for example, on whether one of the grid mains is at ground potential for single-phase connections. The resilience to different grid CM characteristics is a necessary consideration in the design of devices to be deployed across different jurisdictions.SUMMARY

[0006] Common-mode (CM) leakages can arise from grid infrastructure design. While certain grids have ground potentials where the average between terminals is close toground, others have an average with respect to ground and create CM voltages as a result. As noted above, CM voltages can cause safety concerns and thus there are mechanisms that limit the amount of CM that can be present during operation. CM leakage currents may or may not be present depending on grid architecture, and if not addressed, can lead to operational issues relating to electrical safety mechanisms such as nuisance tripping. As described herein, CM leakage currents can occur for various reasons, such as non-idealities in practical real world implementation, and mis-matching due to manufacturing tolerances.

[0007] Approaches are proposed herein for addressing technical problems that arise due to CM leakage currents and specific circuit topologies are proposed that provide a “LCM (leakage current mitigation) circuit I circuit module”. Essentially, the additional circuit components proposed herein are adapted to help reduce safety operation issues associated with CM currents, where, for example, if one were to envisage the circuit as pushing charge, normal operation has “pushing at the top” and “pulling at the bottom” branches of an example circuit. If there is “pushing” at the top and the bottom branches, a CM current situation arises and this CM current could be dangerous for operation.

[0008] A circuit topology approach and corresponding methods and circuit operation control instruction programming are proposed where an additional predominantly inductive branch is included as a parallel impedance branch to provide an equivalent parallel CM impedance at a frequency of interest, e.g., the grid frequency. The branch effectively creates a tailored electrical pathway for mitigating the CM leakage voltage.

[0009] While passive approaches are described in this document, an active commonmode leakage mitigation variation is also proposed as a variant embodiment, where active circuit components monitor the leakage and, using a feedback control loop for example, mitigate the common-mode leakage more accurately (at the cost of greater complexity). The active approach is useful in variations where there are concerns that the device components degrade or diverge in characteristics over time, such as where the components are aged and become deformed, warped, etc., over time and environmental conditions. A benefit of the active variation over the passive variation is that the active variation can also handle changes over time and can more accurately cancel relative to the passive variation, and can also provide an opposite phasor through active electronic control, whereas the passive variation can only include an admittance but it cannot address the resistive component.

[0010] The approaches described herein are adapted to limit the total admittance magnitude. The total admittance magnitude is the difference of the capacitive admittance (from the y-capacitors) and the inductive admittance (from the LCM branch).

[0011] From a passive control perspective, there are two approaches provided. Approach 1 is best used when there is high certainty (e.g., there is reason to expect that the device operates a certain way, such as a same temperature, or elements do not deteriorate significantly over time. Approach 2 is used when there is high uncertainty as noted below (essentially allowing the maximum range of capacitances).

[0012] One approach (Approach 1), resonance, attempts to make that difference as close to zero as possible by matching the inductive admittance to the known capacitive admittance.

[0013] Another approach (Approach 2), used when the capacitive admittance is not known, adapts the inductive admittance close to the total limit, such that the highest range of capacitive admittance is acceptable without causing nuisance tripping.

[0014] The approaches are separate in terms of suitability to specific situations rather than inherent quality. As described herein, if the y-capacitance is known, the resonance method can be used. If it is not known, the approach can be adapted instead to provide a wide range of capacitance values for which the system would work. Practically, either approach can be functional and not necessarily used in specific contexts, for example, it may be decided to always use the “maximization of acceptable capacitance”.

[0015] Structurally, an example LCM filter module can be connected from both grid rails to a ground, the LCM filter module including a first branch having a first capacitor and a first inductor from the live I line terminal to the ground I protective earth conductor, and a second branch having a second capacitor and a second inductor from the ground to the neutral terminal. This variation is described for single phase operation and and an example of three phase operation is described in the following paragraph.

[0016] Another example of an LCM filter module can be connected to all grid rails and to ground when there are more than two grid rails, such as for three-phase connections. In this example, each grid rail is connected to a branch of the LCM, containing at least one inductor and at least one capacitor. The other end of the branch of the LCM is connectedto the equipotential ground. The three-phase device can operate in single phase situations as well.

[0017] The capacitors act as DC blocking capacitance in series that can be used for DC charging operation. Two implementation variations are contemplated.

[0018] The first resonance approach is described where the y-capacitance branch impedance is matched with the inductive branch. This approach is preferable in situations where the y-capacitance and grid frequency are known.

[0019] The second approach is based on identifying a minimum inductance value such that even if no y-capacitance is present, the CM current drawn by the inductive branch is below a nuisance tripping threshold. This approach is an alternative approach when there is uncertainty in y-capacitance values.

[0020] As noted below, another approach incorporates active circuitry, such as switches, feedback control systems, common mode sensors and a current or voltage source, which may measure CM current from the grid and control the current between the protective earth and line I live terminal to cancel out the CM current from the grid. This may be implemented when variable operating grid frequency is present.

[0021] The LCM filter module can be a physical electronic circuit coupled to an electrical grid, which could potentially be providing the CM current, depending on the implementation. A benefit of the approach proposed herein is that the circuit with the LCM filter module can work flexibly with different grid connections, which may not be known at time of manufacture or initial configuration. Furthermore, an electrical device may be moved between different jurisdictions and it is desirable that the device can be used without further grid adaptations. The electrical grid has at least a line I live terminal and a neutral terminal.

[0022] The electronic circuit (LCM) is adapted for addressing a leakage CM signal from the electrical grid, and the LCM includes a first circuit path connecting the line I live terminal of the electrical grid to a ground I protective earth conductor terminal and a second circuit path connecting the ground I protective earth conductor terminal to the neutral terminal of the electrical grid. The combined CM impedance of the LCM is configured to be locally maximum at or near the grid frequency. Specifically, the combined CM impedance needs to be sufficiently high at the grid frequency to ensure that the CM current, dictated by theratio of the CM voltage caused by the grid and the CM impedance, is sufficiently low to not cause nuisance tripping by protection measures, such as the residual current monitoring devices or ground fault current interrupters that may be present in the circuit.

[0023] Variations of the LCM approach can include different circuit implementations. In some embodiments, the circuit paths have both an inductor and a capacitor in series.

[0024] There are potential single-phase and three-phase implementations that are being contemplated, and in a variation, the system can be further configured to provide local maximums at frequency of interest, e.g., the grid frequency or multiples of the thereof. This can be achieved by the inclusion of additional capacitors or inductors in each branch of the LCM. The combined CM impedance, as a function of the frequency, can be described as a transfer function, whose order is determined by the combined number of linearly independent capacitors and inductors in the circuit. Moreover, an increased transfer function order allows for an increased number of local CM impedance maximums, which can be designed to occur at desired multiples of the grid frequency. In some embodiments, this may include the third, fifth, or seventh multiples (or eleventh or thirteenth) of the grid frequency (grid harmonics can occur at these multiples). Other frequencies of interest are contemplated (that are not necessarily multiples). For example, even higher frequencies can be adapted for, etc.

[0025] From a practical perspective, the LCM and corresponding circuit components and topologies can be adapted for usage for various grid connection applications related to charging energy storage devices, such as batteries, capacitors, among others.

[0026] A potential use case includes adapting the circuits described herein for incorporation into an electrical vehicle drivetrain or charger stages, connecting or otherwise coupling the electric vehicle drivetrain to the grid for charging. For example, the electrical vehicle drivetrain can reside in an electric vehicle. When the electric vehicle connects to the grid, the LCM can be connected as part of an integrated inverter or other grid connection modules to address potential CM leakage currents. The electric vehicle can include an electric automobile, a micromobility device, a ship, a train, an airplane, among others. In some embodiments, corresponding circuit control firmware I software I instruction sets I computer program products are contemplated. Corresponding methods of operation of the circuit are also contemplated. The approach can include the specific steps for manufacturingand / or selection of circuit components. Corresponding software program products are contemplated relating to design and selection of components for usage in practical implementation scenarios.

[0027] A technical contribution of some of the proposed circuits is the capability to operate without the use of expensive I heavy transformers for galvanic isolation that alternative approaches use to address CM leakage.

[0028] As weight and complexity directly impact cost and range of electric vehicles (and thus limit adoption), the proposed approaches are potentially helpful for improving the adoption of cleaner technologies that, if commercialized, would help to resolve or mitigate environmental impacts or to conserve the natural environment or natural resources. By proposing an approach that aids in reducing the complexity and / or weight of charging circuits (compared to alternative designs), the technology aids in energy conservation and furthers the development and adoption of clean technologies that could ultimately yield greenhouse gas emission reduction for enhanced climate resilience and adaptation.

[0029] It is important to note that while the embodiments described herein are described in relation to electric vehicle operation as an illustrative example, it is not limited to only electric vehicles, but the approach can also be used for other circuit use cases where there are ground fault considerations, such as building wide applications, swimming pools, lawn mowers.DESCRIPTION OF THE FIGURES

[0030] In the figures, embodiments are illustrated by way of example. It is to be expressly understood that the description and figures are only for the purpose of illustration and as an aid to understanding.

[0031] Embodiments will now be described, by way of example only, with reference to the attached figures, wherein in the figures:

[0032] FIG. 1 is a block diagram representation of an H60 system with a leakage mitigation module filter, according to some embodiments.

[0033] FIG. 2 is an equivalent circuit diagram of FIG. 1 during charging operation, according to some embodiments.

[0034] FIG. 3 is an equivalent circuit diagram of a common-mode model during charging operation, according to some embodiments.

[0035] FIG. 4 is a Bode plot of equivalent common-mode impedance after compensation, according to some embodiments.

[0036] FIG. 5 is a plot of simulation results comparing the uncompensated H60 commonmode current to its compensated counterpart, under unbalanced grid, according to some embodiments.

[0037] FIG. 6 is an image of a leakage mitigation module prototype, according to some embodiments.

[0038] FIG. 7 is an oscilloscope readout showing an uncompensated charging operation under a 120V AC grid, according to some embodiments.

[0039] FIG. 8 is an oscilloscope readout showing compensated charging operation with the prototype of FIG. 6 under a 120V AC grid, according to some embodiments.

[0040] FIG. 9 is a plot of Fourier decomposition of the leakage current flowing through the grid, according to some embodiments.

[0041] FIG. 10 is an oscilloscope readout showing an uncompensated charging operation at 15 A under a 120V AC grid, according to some embodiments.

[0042] FIG. 11 is an oscilloscope readout showing a compensated charging operation with the prototype of FIG. 6 at 15 A under a 120V AC grid, according to some embodiments.

[0043] FIG. 12 is an oscilloscope readout showing an uncompensated charging operation under a 240V AC grid, according to some embodiments.

[0044] FIG. 13 is an oscilloscope readout showing a compensated charging operation with the prototype of FIG. 6 under a 240V AC grid, according to some embodiments.

[0045] FIG. 14 is an oscilloscope readout showing an uncompensated charging operation at 32 A under a 120V AC grid, according to some embodiments.

[0046] FIG. 15 is an oscilloscope readout showing a compensated charging operation with the prototype of FIG. 6 at 32 A under a 120V AC grid, according to some embodiments.

[0047] FIG. 16 is an example of a load control module in three-phase charging application, according to some embodiments.

[0048] FIG. 17 is a schematic diagram of a system for incorporating the LCM circuit into an electric vehicle’s operation under a single phase AC electrical grid.

[0049] FIG. 18 is a schematic diagram of a system for incorporating the LCM circuit into an electric vehicle’s operation under a three-phase AC electrical grid.

[0050] FIG. 19 is a diagram illustrating one potential embodiment of the system in an electric vehicle.

[0051] FIG. 20 is a diagram illustrating one potential embodiment of the system in an electric vehicle.

[0052] FIG. 21 is a workflow diagram illustrating the method for incorporating the LCM circuit to mitigate CM leakage under a single-phase AC grid.DETAILED DESCRIPTION

[0053] Approaches are proposed herein for addressing technical problems that arise due to common-mode (CM) leakage currents and specific circuit topologies are proposed that provide a “LCM circuit I circuit module”. A circuit topology approach and corresponding methods and circuit operation control instruction programming are proposed where an additional predominantly inductive branch is included as a parallel impedance branch to provide an equivalent parallel CM impedance at the grid frequency.

[0054] As described below, CM leakage can arise from grid infrastructure design. While certain grids have ground potentials where the average between terminals is close to ground, others have an average with respect to ground and thus creating CM voltages. Accordingly, several standards and regulation effectively limit the amount of CM current that can occur during operation. I EC 60479 defines the effect of current on humans and livestock. I EC 60990 defines methods for measuring the touch current and current through the protective earth conductor. For electric vehicle charging applications, standards suchas UL 2231 , UL 2202, and IEC 61140 effectively limit the CM current (e.g., to 20 mA, but other values are possible and this value is just an example) during operation. In practice, these limits are enforced by residual current detection (RCD) devices, which cause the system to trip protection systems in the event of excessive CM leakage current, interrupting the charging process.

[0055] An alternative strategy to meet the strict CM leakage current limits is to include galvanic isolation as a conversion step in the on-board or off-board chargers. One common approach of galvanic isolation includes the use of a transformer. This approach has significant drawbacks as an additional conversion step leads to efficiency, mass, volume, and cost penalties. As described in further embodiments below, a proposed improvement in some embodiments herein is the capability to operate without the use of expensive I heavy transformers for galvanic isolation.

[0056] As a result, significant effort is put into designing safe, standard compliant nonisolated electric vehicle chargers.

[0057] One example of such charger is presented in Lehn, Soong et al. (P. Lehn, T. Soong, P. Gray and S. Semsar, "On-board bidirectional ac fast charger for electric vehicles". United States Patent US20200280190A1 , 2018). By not including galvanic isolation, this converter is capable of potential reductions in costs for electric vehicles. Due to the nonisolated nature of the converter, alternative CM leakage mitigation techniques are necessary to avoid nuisance tripping. Specifically, it must be ensured that the switching action of the converter does not generate excessive leakage current and that the grid does not generate excessive leakage current in the event of CM voltage caused by the grid. Lehn, Viana et al. (P. Lehn, C. Viana, S. Semsar and M. Pathmanathan, "Converter Modulation for Reduction of Common-Mode Leakage Current". World Patent WO2021 / 258212A1 , 24 June 2020) details a method to design and operate an electric vehicle charger such that the charger does not generate excessive CM leakage currents caused by the converter modulation- induced CM voltages, typically at frequency much greater than that of the grid. However, Lehn, Viana et al. does not comment on or otherwise address the resilience of the system to CM currents caused by the grid, typically at grid frequency or small multiples thereof. Therefore, these two methods can, in some applications, be combined to eliminate both high frequency and low frequency leakage currents, making the system safe and reliable over the entire frequency spectrum.

[0058] An example of a non-galvanic-isolated charger is presented in Lehn, Soong et al. (P. Lehn, T. Soong, P. Gray and S. Semsar, "On-board bidirectional ac fast charger for electric vehicles". United States Patent US20200280190A1 , 2018). By not including galvanic isolation, this converter is capable of potential reductions in costs for electric vehicles. However, due to the non-isolated nature of the converter, alternative CM leakage mitigation techniques are necessary to avoid nuisance tripping. Specifically, it must be ensured that the switching action of the converter does not generate excessive leakage current and that the grid does not generate excessive leakage current in the event of CM voltage caused by the grid.

[0059] The apparatus disclosed herein introduces the passive CM leakage mitigation module, designated by the term LCM. The aforementioned module reduces (e.g., potentially minimizes) the CM leakage current caused by grid CM voltages. The module can, for example, be established entirely of passive components, leading to a minimal design complexity and price increase. Other variations are possible. The module can be practically provided in the form of an improved circuit on a circuit board or other circuit housing. In some embodiments, the module can be added as a retrofit circuit or coupled onto other circuits to provide the LCM capabilities.

[0060] The electric vehicle presented in Lehn, Soong et al., herein referred to as Allpurpose Powertrain (APT), consists of an active inlet interface, acting as a grid active frontend, connected to a split-battery pack, connected to the dual inverter. During charging operation, the inlet interface operates as an unfolder stage, while the dual inverter otherwise controls the charging voltage waveform. The zero-sequence inductance of the machine is used as the filtering inductance for the resulting charging converter.

[0061] FIG. 1 presents a block diagram representation of the system with the proposed LCM filter 101.

[0062] The equivalent charging model can be achieved by applying the method described in Brovont et al. (A. D. Brovont and S. D. Pekarek, "Derivation and Application of Equivalent Circuits to Model Common-Mode Current in Microgrids," IEEE Journal of Emerging and Selected Topics in Power Electronics, pp. pp. 297 - 308, 2016.).

[0063] The equivalent model is shown in FIG. 2, in which:

[0064] Ls201 represents the leakage inductor of one of the machine phase-windings;

[0065] Cy204 represents the y-capacitance connecting each rail of each half-battery;

[0066] Cw206 represents the total parasitic capacitance from each stator winding to ground, lumped in a t-model;

[0067] vin208 represents the voltage at the vehicle inlet, which could be, for instance, a sinusoidal grid;

[0068] vii210 represents the voltage synthesized by the top portion of the inlet interface, referred to as inlet interface 1, as a function of its duty-cycle, dii, explicitly, viil batldui,’ (1)

[0069] vii2212 represents the voltage synthesized by the inlet interface 2, vii2= Vbat2dii2,

[0070] 214 represents the zero-axis voltage synthesized by the inverter 1,= batl ^Yd=a ^il’ where a, b, c, represent the phases of the inverter, and dtlrepresents the associated duty-cycle;

[0071] v2216 represents the zero-axis voltage synthesized by the inverter 2, v2=

[0072] o 218 represents the distribution of the difference of potential with respect to ground, between the two live conductor connections. For instance, a value of o = 0.5 represents a balanced grid, as observed in North America’s 240 V system, whereas a value of a = 1 represents a line-and-neutral grid, where the bottom live conductor in FIG. 2 is connected to ground;

[0073] GND 220 labels earth ground;

[0074] CGND 222 labels chassis ground I equipotential bond node (e.g., on the chassis); and

[0075] PE 224 labels the protective earth conductor.

[0076] If the process described in Brovont et al. is applied once more to the circuit shown in FIG. 2, the CM equivalent circuit of the charger would be acquired.

[0077] FIG. 3 showcases the resulting model.

[0078] In FIG. 3, viiiCm302 represents the aggregate CM voltage produced by the inlet interface,

[0079] whereas vcm304 represents the aggregate CM voltage produced by the inverter,

[0080] If the approach proposed in Lehn, Viana et al. is followed, both CM voltages produced by the vehicle, it can be ensured that viiiCm= vcm= 0. Under these conditions, the only CM voltage defining the current circulating through the PE conductor is the one produced by the AC grid. Note that this voltage cannot be addressed via the H60 design, since it is caused by off-board components. Thus, a better approach is to increase the CM impedance of the system. Furthermore, note that that increasing the CM impedance of the system is the core rationale behind including galvanic isolation in the design.

[0081] However, in the present case, once the on-board CM voltages are ensured to be zero, the frequency of the remaining CM voltage is known to be the grid frequency. Thus, a potential approach is to include a parallel impedance branch to increase the grid-line CM impedance.

[0082] Assuming the CM mitigation in Lehn, Viana et al. is used, the grid CM voltage source is connected directly to the parallel combination of the y-capacitance and the EV motor CM impedance, which is Zmotor cm= —sLs+ — . In practical applications, however,’ 12 3sCwthe machine winding-to-chassis parasitic capacitance is expected to be negligible, and the y-capacitance connected to the inverter is expected to dominate. Therefore, the impedance seen by the CM voltage produced by the grid can be approximated as ZCM= -1— .

[0083] The proposed solution consists of including a predominantly inductive path at the grid, from all rails to ground. The equivalent parallel CM impedance, at the grid frequency, between this additional inductive branch and the originally present y-capacitance path is increased.

[0084] The CM equivalent circuit of the system can be understood as the parallel combination of a branch formed by the total y-capacitance in the system and the equivalent impedance of the series combination of LLCM102, CLCM104, and RLCM. As a result of these two branches being combined in parallel, the total admittance of the system can be computed as the sum of the complex admittances of the system. Since the impedance magnitude, as a function of the frequency, is determined by the inverse of the admittance magnitude, as a function of the frequency, having a high impedance can equivalently be understood as having a low admittance magnitude.

[0085] The admittance of a predominantly capacitive electric branch, as a complex number, lies in the opposite semicircle as the admittance of a predominantly inductive electric branch. It is, therefore, possible to combine a predominantly capacitive electric branch in parallel with a predominantly inductive electric branch to obtain a total admittance that is much smaller than that of each individual branch.

[0086] The solution proposed in this text leverages this effect, wherein the inverter, as a result of its y-capacitances, defines a predominantly capacitive branch, for the purposes of the CM equivalent model. The added LCM filter 101 defines a predominantly inductive branch, particularly so that the combined CM admittance is high.

[0087] The CM impedance of the system can be shown to be:

[0088] which, in turn, can be simplified as:

[0089] The CM impedance of the system has three important critical frequencies. Firstly, DC is completely rejected since the impedance ZCM(o) = 0) = oo. This can be seen mathematically from the fact that the denominator of the impedance transfer function has a pole at zero. From a physical standpoint, this can be understood by the fact that all current paths include a capacitor, which behaves as an open circuit connection at DC.

[0090] Secondly, at the frequency

[0091] the system has approximately zero impedance. This is because the DC blocking capacitor, CLCM, resonates with the inductor LLCM. This frequency should be ensured to be significantly below the grid frequency.

[0092] Thirdly, at the frequency

[0093] The CM impedance can be shown to be infinity. This means that at that frequency, the system completely rejects the CM voltage produced by the grid. Another interpretation is that the current drawn by the inductive branch is equal and opposite to that drawn by the aggregate y-capacitance of H60.

[0094] With this design objective, two approaches can be taken.

[0095] The first approach consists of matching the y-capacitance branch impedance with the inductive branch. This strategy should lead to approximately zero CM current.

[0096] This approach is to be preferred if the y-capacitance of the system, as well as the operating grid frequency, is well known. During the implementation of this approach, the following steps are taken:

[0097] As the first step, a DC blocking capacitor, CLCM104 is chosen, based on price and availability. This capacitor prevents a low impedance path between the grid mainsconnecting point and the equipotential bond of the vehicle, connected to the chassis. The equipotential bond node can be different metallic components of the chassis. A wide range of capacitance values can be appropriate, as the inductance chosen accommodates for the desired value of capacitance. In some deployments, the value of the capacitance may be chosen to be around one hundred times the sum of the y-capacitances.

[0098] As the second step, the inductance value for LLCM102 is determined by ensuring that tt>2where o)inrepresents the input voltage angular frequency, specifically:

[0099] The second steps ensures that the combined CM admittance of the system is low at the grid frequency.

[0100] As a third step, the low impedance critical frequencyis computed. If the result is well below the grid frequency, the design is acceptable. If, however, the frequency is close or above the grid frequency, the capacitance of CLCM104 needs to be increased and steps 1 and 2 should be repeated, defining an iterative process. Failing to perform this step could cause start up transients when the grid is connected to the system. These transients may lead to currents sufficiently high to trip protection systems, ultimately interrupting the charging process and nullifying the efforts to address nuisance tripping.

[0101] As a fourth step, the current rating of the inductor is defined by:

[0102] where Vin208 represents the magnitude of the grid input voltage. This is the current that traverses the inductor during regular operation. Therefore, failure to appropriately rate the inductors 102 can cause the inductors 102 to overheat and ultimately malfunction. The current rating is designed with some margin of safety.

[0103] This approach aims to produce the lowest CM current, given a set system, assuming the grid frequency and y-capacitance are known with a high level of accuracy, andthat the LCM components can be defined with low tolerance. The low current results from the high CM impedance magnitude or, equivalently, from the low CM admittance magnitude.

[0104] A second approach consists of substituting the second step of the first approach by specifying the minimum inductance value such that, even if no y-capacitance is present, the CM current drawn by the inductive branch is sufficiently below the GFCI threshold to not trip the protection. This can be conducted by providing a circuit with the specifications as described.

[0105] In this case, the inductance of LLCM102 can be defined as:

[0106] where Vinis the input voltage magnitude, whereas Icm,max represents the desired CM current flowing through the inductive branch, i.e., the maximum CM current flowing the circuit, which occurs when the y-capacitance of the system is zero. In general, the compensated current is given by:

[0107] Explicitly, this approach can be understood as following a sequence of four steps as detailed below.

[0108] As the first step, a DC blocking capacitor, CLCM104 is chosen, based on price and availability. This capacitor prevents a low impedance path between the grid mains connecting point and the equipotential bond of the vehicle, connected to chassis. A wide range of capacitance values can be appropriate, as the inductance chosen based on equation (8) accommodates for the desired value of capacitance. In some deployments, the value of the capacitance may be chosen to be around one hundred times the sum of the y- capacitances.

[0109] As the second step, the inductance value, LLCM102 is determined in equation (11). This formula is designed so that any non-zero amount of y-capacitance below that which is equivalent to twice the admittance of the LCM branch leads to a sufficiently low CM current to prevent leakage-current-induced nuisance tripping. Only if the capacitance is twice aslarge as what is necessary to cause the admittance of the LCM branch, nuisance trip occurs. For many applications, this is a very wide range of capacitances that is sufficient to enable a nuisance tripping-free implementation, i.e. , to enable the LCM designer to be sufficiently confident that the unknown y-capacitance falls within the acceptable range.

[0110] As a third step, the low impedance critical frequencyis computed. If the result is well below the grid frequency, the design is acceptable. If, however, the frequency is close or above the grid frequency, the value of the capacitance CLCM104 needs to be increased and steps 1 and 2 should be repeated, defining an iterative process. Failing to perform this step could cause start up transients when the grid is connected to the system. These transients may lead to currents sufficiently high to trip protection systems, ultimately interrupting the charging process and nullifying the efforts to address nuisance tripping.

[0111] As the fourth step, the current rating of the inductor is defined by equation (9). This is the current that traverses the inductor during regular operation. Therefore, failure to appropriately rate the inductor can cause the inductor to overheat and ultimately malfunction. The current rating is designed with some margin of safety.

[0112] This approach allows for the maximum amount of uncertainty in the y-capacitance values. Equation (11) defines an approach that is appropriate for low certainty y- capacitance optimal for values of Cy> —

[0113] The proposed solution is verified through simulation using the H60 Simulink model and control algorithm with values LLCM= 40 H, CLCM= 1 F, RLCM= 100 fl. The results are shown in FIG. 5 with the compensated result 502 showing significant improvement over the uncompensated counterpart 504.

[0114] The proposed circuit is constructed for experimental prototype 600 as shown in FIG. 6. The inductor is formed by the series combination of two Hammond Manufacturing 154E inductors 602 totalling 40 H of nominal inductance and a nominal resistance of 3.2 / cfl. A 1 nF class Y capacitor 604 is used.

[0115] Two charging operating modes are tested. Under a 120 VrmsAC grid with 100 Vdcat each power supply, the grid is unbalanced, and therefore causes some leakage current at 60 Hz. First, the system is operated without the proposed compensation hardware. Theuncompensated result 702 is shown in FIG. 7, where a strong 60 Hz component can be observed in the leakage current. This leakage current is the property that causes safety concerns. The appearance of such a significant leakage current represents safety issues for practical applications. Moreover, even if alternative protective measures are included, such as residual current monitoring devices or ground fault current interrupters are present, this current would cause nuisance tripping. A sufficiently large expected occurrence of nuisance tripping, such as those caused by unmitigated CM leakage current, may preclude the launch of a commercial product such as an electric vehicle.

[0116] Next, the test is repeated with the proposed LCM connected to the AC grid inlet. The compensated results 802 are shown in FIG. 8, where a significant 60 Hz component reduction can be observed. This reduction demonstrates the adequate mitigation of the CM leakage current challenges. Therefore, it is demonstrated that the technique presented herein enables safe and reliable operation of non-isolated leakage current, in a clear contrast with the result 702 that does not use the proposed technique, shown in FIG. 7.

[0117] The current is decomposed into its frequency harmonics in FIG. 9 without the visual noise included as the rest of the spectrum content. The difference between the uncompensated current 902 and compensated current 904 at 60 Hz illustrates the reduction. The data used to produce this image is the output voltage of the toroidal current sensor embedded in the charging connection of TB1. The magnitude of the 60 Hz component on the uncompensated case is defined as 1 p.u. A reduction of 71.88 % is achieved using the prototype LCM 600.

[0118] Further experiments are conducted to demonstrate efficacy at different operating points and to verify that the added hardware does not interfere with the circuit operation in other charging scenarios. FIG. 10 and FIG. 11 show the charging operation with 15 A of grid current.

[0119] Operation at 240 V is shown in FIGS. 12-15. In this case, the grid already produces near zero leakage current. Thus, the tests are conducted to show that the hardware does not cause any adverse effects.

[0120] The passive CM leakage current mitigation network can be deployed for three- phase applications as well as single-phase applications. An example three-phaseembodiment 1600 is presented in FIG. 16. In some embodiments designed for three-phase applications, the three-phase LCM 1601 is comprised of three identical branches 1610a, 1610b, and 1610c containing at least one inductor 1602 and one capacitor 1604.

[0121] In some embodiments, which may be implemented when the amount of uncertainty in the y-capacitance values are large, such as when dealing with variable circuit performance, active circuitry including switches and a current or voltage source may be included. The active circuitry may be used to control the current between the two conductors to cancel out the potential CM leakage current. The active components incorporated into the LCM 100 may include a CM sensor which measures the common mode current from the grid. In response to the CM current measured by the CM sensor, one or more switches may be actuated to control the flow of current from a current or voltage source. The current or voltage source may be placed within the system seen in FIG. 1 between PE and the inductor along the branch connected to the live conductor connection. In this embodiment, the capacitor CLCM seen in FIG. 1 would be replaced by the current or voltage source.

[0122] The one or more switches may be controlled to release a flow of current from the current or voltage source which will cancel out the CM current, which may include both capacitive and resistive current. The flow of current released from the current or voltage source may act as a phasor having an opposite direction which may zero out the CM current.

[0123] In a further embodiment, the active circuitry may operate under a feedback loop, in which the CM sensor may measure the CM current between the PE and live conductor connection at pre-determined intervals. The reading from the CM sensor may be compared by a feedback component within a power electronic system to generate an actuator control signal for the one or more switches. The one or more switches may control the voltage or current provided from a current or voltage source to cancel out the CM current. In some embodiments, the switch may be a gallium nitride switch. In some embodiments, the feedback component will compare the CM sensor reading against a reference point of zero, such that the feedback loop will iteratively control the current or voltage source until the CM leakage current is zeroed.

[0124] The inclusion of active components may provide a benefit when variable circuit performance is expected. For example, when the system is implemented within an electric vehicle, deterioration over time of circuitry components may be expected, such as thedeterioration of the capacitors leading to the plates losing their shape. Further, environmental conditions may lead to components, such as the battery, expanding or contracting. These events may lead to variable performance within the electrical system (i.e., changes in capacitance, battery performance, etc.) which may include parasitic capacitance and resistive current. Active circuitry may address this uncertainty within circuit performance through the use of the feedback components and current or voltage source which can iteratively zero-out the resistive and capacitive current in real time.

[0125] A potential use case of the LCM includes adapting the proposed circuits described herein in various embodiments for incorporation into an electrical vehicle 1900. The electrical vehicle is adapted for providing mobility solutions for users, and can be useful for reducing or limiting climate effects. The electrical vehicle can be connected to an AC grid for AC charging capability, and in some embodiments, can include an integrated inverter that can be used, depending on the use case, for bi-directional charging (e.g., vehicle to grid, and / or grid to vehicle).

[0126] The vehicle 1900 has an energy storage device (e.g., battery 1906, but can also be a capacitor or a hyper-capacitor), a motor 1904 (e.g., electric traction motor), and an inverter 1902 (e.g., devices used to manage electric drive systems, supplying power to operate the electric motor) as shown in FIG. 19. The vehicle 1900 can be coupled to an AC grid for charging the electrical vehicle. As noted above, a LCM circuit module is proposed for use as it may assist with addressing CM leakage currents.

[0127] The combined system 1800 in FIG. 18 could potentially include a drivetrain 1802, battery 1812, motor 1810, battery 1812, auxiliary battery 1814, or headlights and air conditioning 1808, connecting to the electric vehicle and to a three-phase AC electrical grid 1820 or a single-phase AC electrical grid 1720 (FIG. 17). When the electric vehicle 1900 connects to the grid, the LCM circuit 1804 can be connected as part of an integrated inverter 1806 or other grid connection modules to address potential CM leakage currents. During charging, the LCM circuit 1804 interoperates with the APT inverter package, which can include the inlet interface and the dual inverter to charge various energy storage devices, such as the battery 1812 and the auxiliary battery 1814.

[0128] The system could potentially be implemented in an electric automobile, a micromobility device, a ship, a train, an airplane, among others. Similar approaches can betaken in respect of electrical vehicles as they extend to different usage scenarios. In some embodiments, the system could be implemented in personal or industrial building infrastructure where a residual current device is required or implemented to protect against current imbalances stemming from leakage current. In a further embodiment, the system could be implemented in smaller electric devices such as lawnmowers, fluid pumps, air conditioners, HVAC units and the like.

[0129] In some embodiments, corresponding circuit control firmware I software I instruction sets I computer program products are contemplated. The circuit may passively operate once it is provided (e.g., during manufacturing). In operation (e.g., during grid connection for charging), problems associated with leakage currents can be addressed. Bidirectional operation is also considered, and the device can help with leakage current issues that can occur in either direction (either vehicle to grid or grid to vehicle). Software can be utilized during the manufacturing process for design and corresponding instruction sets for implementing the software are contemplated.

[0130] Corresponding methods of operation are also contemplated. As shown in FIG. 20, steps 2002-2012 are shown in respect of the first approach in workflow diagram 2000. As shown in FIG. 21 , steps 2102-2112 are shown in respect of the second approach in workflow diagram 2100.

[0131] Applicant notes that the described embodiments and examples are illustrative and non-limiting. Practical implementation of the features may incorporate a combination of some or all aspects, and features described herein should not be taken as indications of future or existing product plans. Applicant partakes in both foundational and applied research, and in some cases, the features described are developed on an exploratory basis.

[0132] Although the embodiments have been described in detail, it should be understood that various changes, substitutions and alterations can be made herein without departing from the scope. Moreover, the scope of the present application is not intended to be limited to the particular embodiments of the process, machine, manufacture, composition of matter, means, methods and steps described in the specification.

[0133] As one of ordinary skill in the art will readily appreciate from the disclosure, processes, machines, manufacture, compositions of matter, means, methods, or steps,presently existing or later to be developed, that perform substantially the same function or achieve substantially the same result as the corresponding embodiments described herein may be utilized. Accordingly, the embodiments are intended to include within their scope such processes, machines, manufacture, compositions of matter, means, methods, or steps.

[0134] As can be understood, the examples described above and illustrated are intended to be exemplary only.

Claims

WHAT IS CLAIMED IS:

1. An electronic circuit coupled to an electrical grid, the electrical grid having at least a line I live terminal and a ground terminal, the electronic circuit adapted for addressing a leakage common-mode signal from the electrical grid, the electronic circuit comprising: a first circuit path connecting the line I live terminal of the electrical grid to a ground I protective earth conductor terminal; and a second circuit path connecting the ground I protective earth conductor terminal to the neutral terminal of the electrical grid; wherein a combined common-mode impedance is configured to be locally maximum at or near either the grid frequency or a multiple of the grid frequency.

2. The electronic circuit of claim 1 , wherein at least one of the first circuit path or the second circuit path is a circuit branch including at least one inductor and at least one capacitor.

3. The electronic circuit of claim 1 , wherein the first circuit path is a circuit branch including a capacitor and an inductor connected in series between the line I live terminal to the ground I protective earth conductor terminal.

4. The electronic circuit of claim 1 , wherein the second circuit path is a circuit branch including a capacitor and an inductor connected in series from the ground I protective earth conductor terminal to the neutral terminal.

5. The electrical circuit of claim 1 , wherein the first and second circuit path each have a capacitor and an inductor connected in series.

6. The electronic circuit of claim 2, wherein at least one of the first circuit path and the second circuit path connects between a main inlet terminal lead to the ground I protective earth conductor terminal.

7. The electronic circuit of claim 1 , wherein the ground I protective earth conductor terminal is a chassis.

8. The electronic circuit of claim 1 , wherein the electronic circuit includes only passive electronic components.

9. The electronic circuit of claim 1 , wherein the electronic circuit includes active electronic components within the first circuit path.

10. The electronic circuit of claim 9, wherein the active electronic components include a current or voltage source, at least one switch and a common noise sensor located between the line I live terminal and the ground I protective earth conductor terminal.11 . The electronic circuit of claim 10, wherein the at least one switch controls the flow of current from the current or voltage source to cancel out capacitive and resistive common mode current.

12. The electronic circuit of claim 11 , wherein the active electronic components include a feedback component which iteratively controls the at least one switch based on inputs from the common noise sensor.

13. The electronic circuit of claim 1 , wherein the electronic circuit is utilized with singlephase grid connections, wherein either or both grid rails are each connected to a branch of the electronic circuit which is further connected to ground or to an equipotential bond node of the system.

14. The electronic circuit of claim 1 , wherein the electronic circuit is utilized with three- phase grid connections, wherein all three grid rails are each connected to a branch of the electronic circuit which is further connected to ground through the ground I protective earth conductor terminal or to an equipotential bond node.

15. The electronic circuit of claim 14, wherein the electrical circuit contains three identical branches each containing at least one inductor and at least one capacitor.

16. The electronic circuit of claim 1 , wherein one or more additional capacitors or capacitance is utilized to adapt the combined common-mode impedance to be locally maximum at or near the multiple of the grid frequency.

17. The electronic circuit of claim 1 , wherein the electronic circuit is a circuit stage component of a converter circuit for a drivetrain that is a portion of an electric vehicle charger.

18. The electronic circuit of claim 17, wherein the electric vehicle charger resides onboard the electric vehicle.

19. The electronic circuit of claim 18, wherein the electronic vehicle charger includes an integrated inverter.

20. The electronic circuit of claim 1 , wherein the electronic circuit is a circuit stage component of a converter circuit for a residual current device.21 . A method for operating an electronic circuit coupled to an electrical grid, the electrical grid having at least a line I live terminal and a ground terminal, the electronic circuit adapted for addressing a leakage common-mode signal from the electrical grid, the electronic circuit comprising: a first circuit path connecting the line I live terminal of the electrical grid to a ground I protective earth conductor terminal; and a second circuit path connecting the ground I protective earth conductor terminal to the neutral terminal of the electrical grid; wherein a combined common-mode impedance is configured to be locally maximum at or near either the grid frequency or a multiple of the grid frequency.

22. The method of claim 21 , wherein at least one of the first circuit path or the second circuit path is a circuit branch including at least one inductor and at least one capacitor.

23. The method of claim 21 , wherein the first circuit path is a circuit branch including a capacitor and an inductor connected in series between the line I live terminal to the ground / protective earth conductor terminal.

24. The method of claim 21 , wherein the second circuit path is a circuit branch including a capacitor and an inductor connected in series from the ground I protective earth conductor terminal to the neutral terminal.

25. The method of claim 21 , wherein the first and second circuit path each have a capacitor and an inductor connected in series.

26. The method of claim 22, wherein the at least one of the first circuit path and the second circuit path connects between a main inlet terminal lead to the ground I protective earth conductor terminal.

27. The method of claim 21 , wherein the ground I protective earth conductor terminal is a chassis.

28. The method of claim 21 , wherein the electronic circuit includes only passive electronic components.

29. The method of claim 21 , wherein the electronic circuit includes active electronic components within the first circuit path.

30. The method of claim 29, wherein the active electronic components include a current or voltage source, at least one switch and a common noise sensor located between the line I live terminal and the ground I protective earth conductor terminal.31 . The method of claim 30, wherein the at least one switch controls the flow of current from the current or voltage source to cancel out capacitive and resistive common mode current.

32. The method of claim 31 , wherein the active electronic components include a feedback component which iteratively controls the at least one switch based on inputs from the common noise sensor.

33. The method of claim 21 , wherein the electronic circuit is utilized with single-phase grid connections, wherein either or both grid rails are each connected to a branch of the electronic circuit which is further connected to ground or to an equipotential bond node of the system.

34. The method of claim 21 , wherein the electronic circuit is utilized with three-phase grid connections, wherein all three grid rails are each connected to a branch of the electronic circuit which is further connected to ground or to an equipotential bond node of the system.

35. The method of claim 34, wherein the electrical circuit contains three identical branches each containing at least one inductor and at least one capacitor.

36. The method of claim 21 , wherein one or more additional capacitors or capacitance is utilized to adapt the combined common-mode impedance to be locally maximum at or near the multiple of the grid frequency.

37. The method of claim 21 , wherein the electronic circuit is a circuit stage component of a converter circuit for a drivetrain that is a portion of an electric vehicle charger.

38. The method of claim 37, wherein the electric vehicle charger resides on-board the electric vehicle.

39. The method of claim 38, wherein the electronic vehicle charger includes an integrated inverter.

40. The method of claim 21 , wherein the electronic circuit is a circuit stage component of a converter circuit for a residual current device.

41. A non-transitory computer readable medium, storing machine readable instructions, which when executed by a processor, cause the processor to perform a method according to any one of claims 21-40.

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