Pulse width modulation fault management power system

Abstract

A fault management power system (FMPS) and a method thereof can limit the cumulative impact of a repetitive current pulse on a human body during a fault without changing the amplitude of the current pulse. Once a fault is detected, the fault management power system progressively reduces the duration (i.e., ON interval) of the current pulse rather than amplitude to limit the cumulative effect of the current pulse. The fault management power system may step down the pulse width incrementally or step by step, limiting the cumulative effect of the current pulse below a predefined energy level. In some embodiments, the predefined level is a level that can prevent loosening or cause ventricular fibrillation in the human body. The fault management power system advantageously provides a simple and efficient method to limit the energy delivered into the fault without changing the amplitude of the current pulse.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This patent application claims priority to and is incorporated herein by reference from U.S. Provisional Application No. 63 / 352,825, entitled “Pulse Width Modulated Fault Managed Power System,” filed on June 16, 2022. Technical Field

[0003] Embodiments disclosed herein relate generally to fault protection in power supplies and, more particularly, to power supply methods and systems that limit the energy delivered into a fault and that may be combined with Ethernet or other communication protocols using hardwire or fiber optic cables or the like. Background Art

[0004] Supplying power via Ethernet is called Power over Ethernet (PoE) and generally refers to the use of conductor pairs (usually twisted pairs) to send electrical power and data simultaneously. Therefore, devices that can be powered via PoE are called powered devices (PDs), and generally do not require a separate power adapter to power the device. Examples of powered devices include VoIP phones, HD cameras (pan-zoom-tilt cameras), wireless access points (WAPs), network routers, and other devices. As the demand for so-called "smart building" services continues to grow, the number of powered devices is expected to grow exponentially.

[0005] Powered fiber cable (PFC) systems are similar to PoE systems in that both electrical power and data are supplied over a single cable, eliminating (or at least reducing) the need for separate power adapters to power devices. With PFC, data is sent over the optical fiber, while power is typically supplied through a conductive sheath (usually copper) surrounding the optical fiber. Because of the lossless or nearly lossless nature of optical fiber, a typical PFC cable can send data over longer distances than a typical PoE cable.

[0006] In applications such as PoE and PFC, power is typically injected into the cable at between 44 and 57Vdc (typically 48Vdc) and transmitted along the cable as a series of pulses. This voltage level allows for efficient transmission of power along the cable while still being low enough to ensure the safety of the end user. The original industry standard for PoE power source equipment (PSE) allowed for a maximum power level of 30W. The new PoE standard or PoE++ (IEEE 802.3bt) allows for power levels up to 100W. Standards are currently being developed to account for higher power levels.

[0007] As power levels continue to increase in applications such as PoE and PFC, a method is needed to ensure that the amount of energy delivered to the fault is limited. Summary of the invention

[0008] Embodiments disclosed herein relate to methods and systems for supplying power that limit the energy delivered to a fault. The method and system provide a fault management power system (FMPS) that can limit the cumulative effects of repeated current pulses on a human body during a fault without changing the amplitude of the current pulses over time. Once a fault is detected, the fault management power system gradually reduces the duration or width of the current pulses rather than their amplitude to limit the cumulative effect of the current pulses. The fault management power system can gradually reduce the pulse width in increments or steps, and when all of these increments or steps are added together, the cumulative effect of the current pulses over time can be limited to below a predefined level. In some embodiments, the predefined level is below a level that can prevent a let-go or cause ventricular fibrillation in a human.

[0009] In some embodiments, the fault management power system may perform a progressive pulse width reduction based on a predefined number of consecutive current pulses or based on a predefined maximum allowed fault interval. In some embodiments, the fault management power system may also limit the execution of the progressive pulse width reduction sequence to a predefined number of attempts or iterations, after which the system is shut down or otherwise disabled if the fault is not cleared. Such a fault management power system advantageously provides a simple and effective method to limit the energy delivered to a fault without changing the amplitude of the current pulses.

[0010] In general, in one aspect, disclosed embodiments are directed to a fault management power system. The system includes, among other things, a source switch connected to receive a source voltage from a power source, the source switch further connected to a cable line and controllable to connect the power source to the cable line. The system also includes an impedance sensor circuit connected to the cable line, the impedance sensor circuit configured to sense an impedance on the cable line. The system further includes a controller coupled to the source switch and the impedance sensor circuit, the controller configured to receive an impedance sensed by the impedance sensor circuit and detect the presence of a fault on the cable line based on the impedance. The source voltage appears as a current pulse on the cable line, each current pulse having an amplitude and a duration, and the controller is configured to perform a pulse duration reduction on a predefined number of current pulses to limit the cumulative effect of the predefined number of current pulses to below a predefined threshold level without reducing the amplitude of the predefined number of current pulses.

[0011] In general, in another aspect, disclosed embodiments are directed to a method for managing faults in a power system. The method includes, among other things, connecting a power source and a cable line using a source switch, the source switch being configured to receive a source voltage from the power source and being controllable to connect the power source to the cable line, the source voltage appearing as current pulses on the cable line when the power source is connected to the cable line, each current pulse having an amplitude and a duration. The method also includes sensing an impedance on the cable line using an impedance sensor circuit connected to the cable line, and detecting the presence of a fault on the cable line based on the impedance of the cable line using a controller coupled to the impedance sensor circuit and the source switch. The method also includes performing a pulse duration reduction on a predefined number of current pulses using the controller to limit the cumulative effect of the predefined number of current pulses to below a predefined threshold level without reducing the amplitude of the predefined number of current pulses.

[0012] In general, in yet another aspect, the disclosed embodiments are directed to a network. The network includes, among other things, at least one network cable and a fault management power system connected to the at least one network cable, the fault management power system being operable to provide a series of current pulses on the at least one network cable, each current pulse having an amplitude and a duration. The network also includes at least one load connected to the at least one network cable and the fault management power system, the at least one load being powered by the series of current pulses from the fault management power system. The fault management power system is further operable to detect the presence of a fault on the at least one network cable and perform a pulse duration reduction on a predefined number of current pulses to limit a cumulative effect of the predefined number of current pulses to below a predefined threshold level without reducing the amplitude of the predefined number of current pulses. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] The foregoing and other advantages of the disclosed embodiments will become apparent upon reading the following detailed description and referring to the accompanying drawings, in which:

[0014] Figure 1A shows a series of current pulses with reduced amplitude in a fault management power system;

[0015] Figure 1B shows a series of current pulses having the same amplitude but gradually decreasing pulse durations in a fault management power system according to an embodiment of the present disclosure;

[0016] Figure 2 The pulse duration of the fault current limit curve in the fault management power system according to the embodiment of the present disclosure is shown;

[0017] Figure 3A shows a high level view of an exemplary fault management power system according to an embodiment of the present disclosure;

[0018] Figure 3B shows a more detailed view of an exemplary fault management power system according to an embodiment of the present disclosure;

[0019] Figure 4 A method of performing a step-down pulse duration in a fault management power system according to an embodiment of the present disclosure is shown;

[0020] Figure 5A shows an example of a graph showing voltage sensed across conductor(s) such as a power cable over time in relation to a human body model according to an embodiment of the present disclosure;

[0021] Figure 5B shows an example of a graph over time showing voltage sensed across conductor(s) such as a power cable in relation to a human body model according to an embodiment of the present disclosure;

[0022] Figure 6 An example of a point-to-point architecture that may be employed for a fault management power system according to an embodiment of the present disclosure is shown;

[0023] Figure 7 An example of a radial architecture that may be employed for a fault management power system according to an embodiment of the present disclosure is shown;

[0024] Figure 8 An example of a daisy chain architecture that may be employed for a fault management power system according to an embodiment of the present disclosure is shown;

[0025] Fig. 9 An example of a fishbone architecture that can be used to manage a power system in accordance with an embodiment of the present disclosure is shown;

[0026] Fig.10 The embodiment according to the present disclosure is shown Fig. 9 An enlarged partial view of a fishbone architecture with a junction box, a load and associated load-side components, wherein a fault management power system may be employed;

[0027] Fig.11 A fault management power system for a single-pole power configuration with a grounded source, 2-wire cable (shielded) and a single switch is shown in accordance with an embodiment of the present disclosure;

[0028] Fig.12 A fault managed power system for a single pole power configuration with an isolated source, 2-wire cable (shielded) and a single switch according to an embodiment of the present disclosure is shown;

[0029] Fig.13A fault managed power system for a single pole power configuration with an isolated source (no shield), 2-wire cable and a single switch according to an embodiment of the present disclosure is shown;

[0030] Fig.14 A fault management power system for a single-pole power configuration with a grounded source, 2-wire cable (shielded) and dual switches according to an embodiment of the present disclosure is shown;

[0031] Fig.15 A fault management power system for a single-pole power configuration with a grounded source, 2-wire cable (shielded) and dual switches according to an embodiment of the present disclosure is shown;

[0032] Fig.16 A fault managed power system for a single pole power configuration with an isolated source (no shield), 2-wire cable and dual switches according to an embodiment of the present disclosure is shown;

[0033] Fig.17 A fault management power system for a bipolar power configuration with a grounded source, 3-wire cable (shielded) and dual switches according to an embodiment of the present disclosure is shown;

[0034] Fig.18 A fault management power system for a bipolar power configuration with an isolated source, 3-wire cable (shielded) and dual switches according to an embodiment of the present disclosure is shown;

[0035] Fig.19 A fault managed power system for a bipolar power configuration with an isolated source (no shield), 3-wire cabling, and dual switches is shown according to an embodiment of the present disclosure; and

[0036] Fig. 20 An example of sample data of a calibration table, such as a voltage reference (Vref) table, according to an embodiment of the present disclosure is shown. DETAILED DESCRIPTION

[0037] First, it should be understood that the development of practical, real business applications incorporating various aspects of the disclosed embodiments will require many specific implementation decisions to achieve the developer's ultimate goal for the business embodiment. Such specific implementation decisions may include, but are not limited to, compliance with system-related, business-related, government-related, and other restrictions, which may vary depending on the specific implementation, location, and time. Although the work of a developer may be complex and time-consuming in an absolute sense, such efforts are still routine work for those skilled in the art who benefit from this disclosure.

[0038] It should also be understood that the embodiments disclosed and taught herein may be subjected to a variety of modifications and alternative forms. Therefore, the use of singular terms (such as but not limited to "one", etc.) is not intended to limit the number of items. Similarly, any relational terms, such as but not limited to "top", "bottom", "left", "right", "up", "down", "below", "above", "side", etc., and the drawings used in the written description are specifically referenced to the drawings for clarity and are not intended to limit the scope of the present invention.

[0039] As mentioned above, power levels continue to increase in applications such as PoE, PFC, and other applications that power powered devices. For example, the National Electrical Code (NEC) recently released the industry standard ANSI / NFPA 70, which defines new Class 4 power systems. These Class 4 power systems are rated up to 450V with no power restrictions while retaining the safety of PoE systems and lower-level systems. To achieve Class 4 standards, the power system must be able to meet specific safety requirements regarding the delivery of energy into a fault. Specifically, the Underwriters Laboratories standard UL-1400-1 requires that in the event of a fault, the amplitude of the repetitive current pulse must be reduced to limit the cumulative effect of the current pulse over time to below the "let-go" limit (i.e., the voltage and current levels that can prevent let-go as defined by UL-1400-1). Table 1 below lists the reduction in the amplitude of the repetitive current pulse as a percentage or ratio (see UL-1400-1, Table 5).

[0040]

[0041]

[0042] Table 1: Current reduction for repetitive pulses

[0043] In Table 1, the current reduction multiplier Ct(n) specifies the percentage reduction in the amplitude of the first seven current pulses after a fault is detected. It can be seen that the current reduction multiplier Ct(n) starts at 1.00 (100%) and is gradually reduced to 0.10 (10%). This means that the amplitude of the first current pulse (n=1) after the fault is detected is multiplied by 1.00 (no reduction), while the amplitude of the second current pulse (n=2) is multiplied by 0.65 (reduced to 65% of its original level), and the amplitude of the third current pulse (n=3) is multiplied by 0.42 (reduced to 42% of its original level). And so on as shown in the table. After seven pulses, a 3 second timeout interval is applied during which all further current pulses are stopped and it is determined whether the fault has been cleared. If it is determined that the fault has not been cleared, the above amplitude reduction sequence is repeated for an additional seven current pulses. If the fault is still not cleared after a predetermined number of amplitude reduction sequence attempts, the system is shut down or otherwise disabled.

[0044] Figure 1A A sequence of reduced amplitudes of the above series of seven current pulses 100 is shown, and this type of current pulse is commonly found in power systems that supply power to powered devices. As shown, each current pulse in the series of current pulses 100 has the same pulse width or duration as the first current pulse, Td(n)=Td(1). This pulse duration is simply the nominal / standard pulse duration used in the power system to supply power to powered devices. However, the amplitudes of the current pulses are not exactly the same. Each current pulse has an amplitude multiplied by the current reduction multiplier I(n)=I(1)*Ct(n), as specified by UL-1400-1. This results in the cumulative effect of the series of current pulses 100 over time being limited to a predefined energy level, which for UL-1400-1 means below a level that can prevent loosening or cause ventricular fibrillation in humans.

[0045] Figure 1B An alternative approach for limiting the cumulative effect of a series of current pulses 100 over time that may be used by the fault management power system disclosed herein is shown. Figure 1B In the example above, instead of reducing the amplitude of the current pulse when a fault is detected, the fault management power system here gradually reduces the duration of the current pulse using the current reduction multiplier Ct(n) specified in Table 1, Td(n)=Td(1)*Ct(n). This enables the fault management power system to achieve the same result, namely limiting the cumulative effect of a series of current pulses 100 over time, but without reducing the amplitude of the current pulse (I(n)=I(1)).

[0046] It should be understood that although Figure 1BThe pulse width reduction scheme depicted in has the advantage of meeting the requirements of UL-1400-1, but the fault management power system herein is not limited thereto. Those of ordinary skill in the art will appreciate that within the scope of the present disclosure, changes and modifications may be made as required by a particular system or application. For example, instead of seven current pulses, there may be less than seven current pulses (e.g., six, five, etc.), or more than seven current pulses (e.g., eight, nine, etc.) may be used by appropriately adjusting the current reduction multiplier Ct(n). Similarly, instead of applying a different current reduction multiplier value to each current pulse, the same current reduction multiplier value may be applied to two or more consecutive current pulses by using an appropriately modified Ct(n). In fact, the fault management power system herein may apply the same current reduction multiplier value (i.e., a constant value) to all current pulses in a series of current pulses 100 by using an appropriately selected multiplier (e.g., 50%). In addition, a stepwise reduction of the current reduction multiplier Ct(n) may be achieved using an appropriate equation (e.g., via curve fitting or similar techniques) rather than using a specific multiplier value.

[0047] Figure 2 A graph 200 is shown illustrating how the pulse width reduction scheme of the fault management power system herein can be used to limit the cumulative effects of repetitive current pulses, as required by UL-1400-1. In graph 200, the vertical axis represents current (DC or AC rms) in milliamperes (mA) and the horizontal axis represents current duration in seconds. Both axes are displayed on a logarithmic scale (i.e., a log-log graph). Line 202 shows the fault current limit specified by UL-1400-1, which is intended to limit the cumulative effects of repetitive current pulses to levels below that which can prevent loosening or cause ventricular fibrillation in a human. Line 202 represents two current curves, one for DC and one for AC, which completely overlap when the fault event lasts less than 100ms, but separate when the fault event lasts longer.

[0048] exist Figure 2In the example of , the fault management power system provides power in the form of current pulses having a nominal or standard pulse duration of 0.004 seconds (Td=4ms) and a nominal or standard amplitude of 300mA (I=300mA). The line labeled n=1 represents the first current pulse after the fault is detected, while the line labeled n=2 represents the second current pulse, and so on. It can be seen that the fault management power system in this article uses the current reduction multiplier Ct(n) listed in Table 1 to gradually reduce the duration or width of the second current pulse to 2.6ms, the duration or width of the third current pulse to 1.68ms, and the duration or width of the fourth current pulse to 1.08ms, and so on. This gradually reduced pulse width causes the cumulative effect of the repetitive current pulses to be limited to the level defined by line 202, thereby providing an equivalent-current-time exposure given in the requirements of UL-1400-1. Note that although there is a seventh current pulse, it is not explicitly shown here due to the size limitations of the figure.

[0049] Reference now Figure 3A , shows a high-level diagram of an exemplary fault management power system 300 that can perform the step-by-step pulse width reduction discussed above when a fault is detected. The power system 300 in this example is primarily composed of upstream components or source-side components ("source"). For example, there is an AC / DC or DC / DC converter 301 configured to receive electrical power from an AC or DC power source, a filter 302 (such as a pi filter) configured to provide noise filtering of the electrical power, and a switch 303 (such as a solid-state switch) configured to connect / disconnect electrical power. The power system 300 further includes a crowbar circuit 304 configured to selectively implement a short circuit at the output of the power system 300, and a line impedance sensor 305 configured to output a line impedance, which can then be used to detect a leakage current indicative of a fault. Optionally, a leakage sensor 306 can be provided to directly detect a leakage current indicative of a fault. An optional communication circuit 307 can also be provided to implement power line communication (PLC) via the power system 300.

[0050] An electrical power cable 308 is connected between the above-mentioned source-side components and one or more downstream or load-side components ("Fx"). The electrical power cable 308 is configured to deliver a DC current / voltage (e.g., a DC steady-state current) from the source to the load-side components. The load-side components in this embodiment include a filter 309 similar to the source-side filter 302, whereby the two filters 302, 309 are configured to isolate the power cable 308 from the source-side power supply and the load-side load, thereby providing a noise-free DC current / voltage on the cable to a DC / DC or DC / AC converter 310, which converts the power into a form that can be used by the load.

[0051] The controller 312 is used to implement various functions and operations described herein, including but not limited to controlling the operation of one or more components of the power system 300, performing or implementing fault detection, and managing the supply of power / energy from the power source to or on the cable 308. To this end, the controller 312 is equipped with a pulse width signal modulation module (PWSM) 314, or is programmed to execute a pulse width signal modulation module (PWSM) 314, etc., which is configured to perform the step-by-step pulse width reduction sequence described herein. Any suitable programmable controller or microcontroller can be used to implement the controller 312 and the pulse width signal modulation module 314, including, for example, part number STM32L476RG, which is a programmable microcontroller with an integrated A / D converter and embedded and external storage / memory available from ST Microelectronics.

[0052] Figure 3B Shown with Figure 3A 3. The power system 320 in the figure mainly includes a power supply 322, a switch S1, an upstream filter 324 (such as a low-pass filter), resistors R1 and R2, a switch S2, a capacitor C1, a diode D1, a switch S3, a line impedance sensor 340, an isolation switch S4, a current sensor for sensing current (such as Isense), a power cable 350, a blocking diode D2, a downstream filter 360 (such as a low-pass filter), a power converter 370 (such as a DC / DC or DC / AC converter), and one or more loads 380. The power system 320 may also include one or more controllers 390, at least one of which is equipped with or programmed to execute a pulse width signal modulation (PWSM) module 392 therein, for controlling the various components of the system 320 and controlling, implementing or causing the various operations and functions described herein. As described above, components upstream between power supply 322 and cable 350 may generally be referred to as source-side components, while components downstream of cable 350 or between cable 350 and load 380 may generally be referred to as downstream or load-side components or ("Fx").

[0053] The power supply (or power source) or input power source 322 can be an AC power supply or a DC power supply. When AC power supply is adopted, the power system 320 can also include a power converter, such as an AC / DC converter, to supply DC electric power on the cable 350. In various embodiments, when DC power supply is adopted, the power system 320 can further include a power converter, such as a DC / DC converter. The power supply / input power 322 can provide a system voltage Vs.

[0054] Switch S1 is a switch operable to connect or disconnect the power supply 322 with components downstream of the source (including the cable 350). Switch S1 can be a mechanical switch or other switch that can be operated to an open position to disconnect the power supply 322 from these components and can be operated to a closed position to connect the power supply 322 to these components. Switch S1 can be manually operated or automatically operated. In other embodiments, switch S1 can be located on the line side (source side) of the AC / DC power source instead.

[0055] The upstream filter 324 and the downstream filter 360 may be low-pass filters, such as pi filters (also known as π filters), which may employ LC components (or circuits). The filters 320, 360 may be configured to isolate the cable 350 from source-side / upstream noise and load-side / downstream noise to achieve noise-free DC current / voltage delivery on the cable 350. In this example, the upstream filter 324 may also include one or more freewheeling diodes D3 and Zener diodes Dz, and the downstream filter 360 may include one or more freewheeling diodes D4.

[0056] Resistors R1 and R2 can be configured to provide a voltage Vin, which can be a scaled system voltage corresponding to the applied (operating) system voltage of the source circuit. In this example, the voltage Vin can be equal to Vs*(R2 / (R1+R2)) or the voltage V S It can be equal to Vin*((R1+R2) / R2).

[0057] Switch S2 may be an electronic switch operable to quickly disconnect the power supply provided by power source 322 from cable 350 and connect the power supply provided by power supply 322 to cable 350. In this example, switch S2 may be a solid-state switch.

[0058] In various embodiments, a pulse generator (or generating circuit) may be provided or implemented on or by the source by operating switch S2, and the pulse generator (or generating circuit) may be controlled to generate (multiple) electrical pulses, for example, by opening switch S2 for a short time (e.g., 500us) and then turning off the switch. The pulse generator may be configured to generate electrical pulses, such as a voltage Vp (or current) that may be supplied to cable 350. In various embodiments, electrical pulses (e.g., voltage pulses) may be generated to have a pulse frequency within a frequency range filtered out by filters 320, 360. For example, the frequency may be a high frequency, and the amplitude of the voltage may be small enough (e.g., within a touch-safe range). In addition, in some embodiments, switch S2 may be controlled to generate (multiple) electrical pulses, for example, by opening switch S2 for a short time (e.g., 500us) and then turning off the switch. Although a pulse generator or its circuit may be implemented by the operation of switch S2, it should be understood that, according to embodiments, other pulse generating circuits may be incorporated into the source to generate (multiple) electrical pulses as needed.

[0059] Switch S3 may be an electronic switch that may be operated as a short-circuit source or source-side component to quickly interrupt and block the supply of power from power supply 322 to cable 350. In this example, switch S3 may be a crowbar circuit that quickly shorts (or in other words, cuts) the supply line if, for example, the voltage and / or current exceeds a predefined threshold (i.e., in the event of a fault).

[0060] The line impedance sensor 340 can sense or measure electrical energy on the cable 350. The sensor 340 can include an impedance sensor and a frequency selective filter, such as a pi filter. In various embodiments, the impedance sensor combined with the pi filter can provide a tank circuit (also referred to herein as an "impedance sensor tank circuit") that can output an amplified voltage measurement value (Vm or Vout) that can correspond to an impedance difference on the cable 350 or a leakage current on the cable 350. The sensor measurement can be used to detect the occurrence or existence of a fault or a fault signal associated therewith (e.g., a human touch or other fault on the cable 350). In this example, the impedance sensor 340 can include a resistor Rc and an RC circuit (or component), and the filter can be a pi filter, which can include an LC circuit (or component). In this example, the capacitor in the impedance sensor of the sensor 340 and the inductor in the pi filter can form a tank circuit for tuning a desired frequency or range to measure and detect electrical disturbances, such as electrical disturbances caused by (multiple) fault signals on the cable 350. In one embodiment, an impedance sensor may be used in conjunction with pi filter components, such as an inductor and capacitor primarily proximate to the impedance sensor, to provide a tank circuit.

[0061] In various embodiments, the tank circuit may be configured to measure a frequency signal within a pulse frequency range of the generated electrical pulses to facilitate detecting electrical disturbances on the power cable.

[0062] The switch S4 can be an isolation switch that can be operated to connect or disconnect the source from (multiple) components (also referred to as circuits) located downstream of the source. In various embodiments, the switch S4 can be operated to isolate the source circuit from (multiple) components downstream (such as power cable 350, (multiple) loads, and (multiple) load-side components (such as downstream filters, etc.)). For example, the source circuit can be isolated when performing an open circuit test (e.g., testing in an open circuit state) when measuring a reference voltage for calibration purposes, as described herein.

[0063] The current sensor can be used to sense the current on the cable (eg, Isense). The current sensor can be used to detect leakage current or other current signal(s) on the cable, including fault signal(s).

[0064] The power cable 350 may be an electrical cable, which may include one or more conductors (e.g., conductors, conductive lines, conductive wires, etc.). In various embodiments, the cable may be a 2-wire (twisted) cable, a 3-wire (twisted) cable, etc. The cable may be shielded or unshielded.

[0065] The converter 370 may be a power converter, such as a DC / DC converter or a DC / AC converter. The type of converter depends on a variety of factors, including the application, the load, and so on.

[0066] The one or more controllers 390 and their pulse width signal modulation (PWSM) modules 392 may be configured to implement various functions and operations described herein, including, but not limited to, controlling the operation of one or more components of the power system 320, performing or implementing fault detection, and managing the supply of electrical power / energy from a source to or on the cable 350. The one or more controllers 390 may include internal memory or may be communicatively coupled to an external memory. The memory may store executable instructions or programs for controlling the operation of the controllers (including the functions and operations described herein), data for implementing the fault management power methods and systems, including system variables (e.g., counters, operating parameters, reference tables such as voltage reference tables, etc.), and any other data described herein.

[0067] The above-mentioned fault management power system 320 of FIG3 is provided as an example only. The fault management power system can be modified, such as adopting one or more switches, upstream and / or downstream power converters, one or more sensors (e.g., (multiple) impedance sensors, (multiple) current leakage sensors, or other sensors to detect faults caused by human contact with the cable or other types of faults on the power system), different types of cables and architectures, etc. The fault management power system may also include a communication device that can be incorporated upstream and downstream of the power cable to implement power line communication (PLC) through the fault management power system or a power distribution system including the fault management power system.

[0068] For example, in an embodiment, the fault management power system 320, via its one or more controllers 390, can be configured to detect electrical disturbances on the power cable 350 corresponding to the occurrence of a fault caused by human body contact with the cable 350 (or its conductive wires) or other faults on the cable 350 based on measurements from the sensor 340 when electrical pulses or DC current / voltage and electrical pulses are supplied to the power cable 350, and in response to detecting such a fault, perform the above-mentioned step-by-step pulse width reduction sequence.

[0069] Figure 4 4 is a flow chart illustrating a method 400 that can be used by or with embodiments of the fault management power system of the present invention to perform a stepwise pulse width reduction upon detection of a fault, thereby limiting the cumulative effect of the current pulses to below a predefined energy level. Specifically, the method 400 can be performed by one or more controllers of the disclosed fault management power system and a pulse width signal modulation module therein in conjunction with one or more sensors and circuits of the fault management power system.

[0070] The method 400 generally begins at box 402, where a pulse counter (n=1) is initialized and a reset counter (R=1) is also initialized. The pulse counter (n) is used to track the number of consecutive current pulses that appear on the power cable after a fault is detected, while the reset counter (R) is used to track the number of consecutive attempts or iterations of step-wise pulse width reduction that have been performed. At box 404, a nominal / standard current pulse duration Td(1) is obtained, for example, from a predefined location in a storage / memory of one or more controllers of the fault management power system. Alternatively, where applicable, the nominal / standard current pulse duration (Td) can be determined as needed, for example, by measuring the time between the rising and falling edges of one or more current pulses in the system in a manner known to those skilled in the art prior to initiating the method 400.

[0071] At box 406, any leakage current that may be present on the cable is measured, for example, using an impedance sensor as described above or other techniques known to those skilled in the art. At box 408, it is determined whether the leakage current exceeds a predefined threshold, which indicates that a fault exists, such as due to contact with a human body. If the determination at box 408 is yes, indicating that a fault has been detected, then at box 410, the maximum allowable pulse duration of the first current pulse (n=1) after the fault is detected is determined. In some embodiments, determining the maximum allowable pulse duration is performed by applying the current reduction multiplier Ct(n) in Table 1 to the pulse duration, Td(n)=Td(1)*Ct(n).

[0072] At block 412, a source switch (e.g., a solid-state switch) is controlled to turn off a source voltage of the fault management power system to quickly cut off a current pulse at or before (i.e., close to) the expiration of the maximum allowed pulse duration of the previous block. At block 414, a crowbar (e.g., a crowbar circuit) is turned on to achieve a short circuit on the cable, thereby quickly cutting off the current pulse at or before (i.e., close to) the expiration of the maximum allowed pulse duration.

[0073] At box 416, determine whether the pulse counter has reached a predefined pulse counter limit. In some embodiments, the pulse counter limit can be seven current pulses (i.e., pulse counter limit = 7), although different limits can certainly be used depending on the requirements of a particular system or application. If the pulse counter has not yet reached the pulse counter limit, then at box 418, wait for the inter-pulse time interval to allow the start of the next current pulse in a series of current pulses to arrive (or simulate the arrival of the next current pulse). At box 420, disconnect the crowbar to eliminate the short circuit on the cable, and turn on the source switch to restore the source voltage of the system. At box 422, the pulse counter is incremented by one to track the number of pulses that have occurred on the cable since the fault was detected. Thereafter, return to box 406 to measure any leakage current or otherwise detect that a fault may still exist on the cable.

[0074] On the other hand, if the pulse counter has reached the pulse counter limit at box 416, it is determined at box 424 whether the reset counter has reached the predefined reset counter limit. In some embodiments, the reset counter limit can be three attempts or iterations (reset counter limit = 3), although of course different limits can be used depending on the requirements of a particular system or application. If the reset counter has not yet reached the reset counter limit, wait for a timeout interval at box 426 to allow the fault to be cleared. In some embodiments, the timeout interval can be three seconds, but of course different timeout intervals can be used. At box 428, the crowbar circuit is disconnected and the source voltage is turned back on. At box 430, the reset counter is incremented by one, and the pulse counter is set back to its initial value. From here, the method returns to box 406 again to measure any leakage current or otherwise detect faults that may still exist on the cable.

[0075] If the reset counter has reached the reset counter limit at box 424, it indicates that the fault has not been cleared and may cause serious problems, and therefore, for safety purposes, it is necessary to shut down or otherwise disable the system. Therefore, at box 432, the series relay (e.g., isolation switch S4) is opened to isolate the power source from the cable and downstream equipment. In addition to opening the series relay, the switch connecting the power system to the power source (i.e., switch S1) can also be opened to further isolate the power source. Thereafter, at box 434, a manual reset of the system is performed and then the system is restarted.

[0076] As described above, various embodiments of the fault management power system disclosed herein operate with a series of current pulses (i.e., a pulse train), each current pulse having an amplitude and a duration. To this end, in some embodiments, the fault management power system herein can be configured as a pulse system that inherently supplies the source voltage as a pulse train on the cable. In other embodiments, the fault management power system herein can be configured as a system that produces a DC source voltage that, when a fault is detected, is then supplied with a pulse train about Figure 4 The current is modulated in the manner discussed in method 400 (eg, using a source switch (switch S2) and a crowbar circuit (switch S3)) to produce current pulses having gradually decreasing durations.

[0077] Figure 5A An example of a graph 500 is shown showing a variation over time of a voltage sensed on a conductor (e.g., a power cable) in relation to a human body model (HBM) for detecting leakage current due to a fault according to an embodiment of the present disclosure. In this example, the voltage Vc may be the voltage of a sensing capacitor (e.g., the capacitor of the impedance sensor 140 of FIG. 1 ) associated with a startup phase. Similarly, Figure 5B5 shows an example of a graph 550 showing the variation of a voltage sensed on a conductor (s) (e.g., a power cable) over time in relation to a human body model (HBM) according to an embodiment of the present disclosure. In this example, the voltage Vout may be a sensor (e.g., Figure 3B The impedance sensor energy storage circuit) outputs the voltage.

[0078] exist Figure 5A The graph of 500 and Figure 5B On the graph 550 of FIG. 5 , sensed voltage curves for different human body models (e.g., different resistances) are shown, which can reflect different types of human contact with the cable, such as the part of the body in contact with the cable, the amount of body contact with the cable, line-to-line human contact, line-to-ground human contact, etc. The HBM can be pre-determined for different human contact scenarios, including no touch / contact scenarios. The HBM can be used as a proxy for actual human testing to test fault detection, such as human contact with the cable, based on the measurement of the gas characteristics of the monitored cable. Based on the sensor measurements, other voltage models can also be used to detect other types of faults on the power cable.

[0079] For example, a DC fault management power system may employ filters on the source and load (or Fx) sides, as described herein, to provide a "noise-free" DC voltage or current on the interconnecting cable line. The introduction of a fault (e.g., human contact, etc.) may generate a disturbance pulse that may be measured by a sensor. The sensor may output a voltage or other electrical measurement that may correspond to an impedance change on the monitored cable or a leakage current on the monitored cable. For example, the peak value of the pulse may be proportional to the leakage current. The presence of a pulse at Vc or Vout may indicate that a human body has contacted one or more conductors of a cable connecting the source side / upstream and load side / downstream filters. The filter may be a low-pass filter, such as a π filter, or other low-pass filter for filtering out noise (such as high-frequency noise or signals). In response to detecting the occurrence of such a fault, the fault management power system may use a switch (or the like) to interrupt or block the power supply (e.g., voltage, current, etc.) through the cable. In various embodiments, fast shut-down and short-circuiting may enable the fault management power system to meet the anti-electric shock / fire protection requirements and other safety requirements of a Class 4 power system.

[0080] Figures 6 to 10Various power distribution architectures are shown that can employ the fault management power methods and systems described herein. In general, these different architectures include one or more sources, one or more downstream components (load-side components or Fx), and (multiple) power cables connecting the sources and (multiple) load-side components. As described herein, the source and downstream components may include upstream and downstream filters to isolate the cables from noise (e.g., filter out any noise within the desired frequency range from the upstream power supply and the downstream (multiple) loads), and the source may include a pulse generating circuit and an impedance sensor to measure electrical activity on the power cable. For example, (multiple) controllers may use the measurement results of the sensor to detect the occurrence of a fault, such as contact between a human body and a cable or other faults. In response to detecting the occurrence of a fault, one or more switches are used to interrupt the power supply to one or more power cables (or block) the cable. These example architectures will be described in more detail below.

[0081] Figure 6 6 shows an example of a point-to-point architecture 600 in which a fault management power system (as described herein) may be employed according to an embodiment of the present disclosure. Figure 6 As shown, architecture 600 includes a source, (multiple) downstream components, and a power cable connected between the source and (multiple) downstream components. The power cable can deliver electrical energy from a single source to a single group of downstream components or Fx. The supplied electrical energy can be a unipolar voltage (e.g., 450 volts) or a bipolar voltage (e.g., ±225 volts).

[0082] Figure 7 1 shows an example of a radial architecture 700 in which a fault management power system (as described herein) may be employed according to an embodiment of the present disclosure. Figure 7 As shown, the architecture 700 includes a single source that can supply power to multiple groups (multiple) of downstream components or Fx (and their associated loads) through respective power cables. A fault management power subsystem can be implemented between the source and each group (multiple) of downstream components or Fx. The power provided can be a unipolar voltage (e.g., 450 volts) or a bipolar voltage (e.g., ±225 volts).

[0083] Figure 8 8 shows an example of a daisy chain architecture 800 in which a fault management power system (as described herein) may be employed according to an embodiment of the present disclosure. Figure 8 As shown, the architecture 800 includes a single source that can supply power to multiple groups (multiple) of downstream components or Fx (and their associated loads). (Multiple) downstream components or Fx groups are connected in series through power cables. The power supplied can be a unipolar voltage (e.g., 450 volts) or a bipolar voltage (e.g., ±225 volts).

[0084] Fig. 9900 according to an embodiment of the present disclosure, in which a fault management power system (as described herein) may be employed. Fig. 9 As shown, the source is connected to one or more series of junction boxes, which in turn are connected to multiple groups of downstream components or Fx (e.g., a pair (multiple) of downstream components or Fx groups). The supplied power can be a unipolar voltage (e.g., 450 volts) or a bipolar voltage (e.g., ±225 volts). Data can be transmitted by power line communication on the fishbone architecture, for example, using frequencies that are not filtered out by upstream or downstream filters or frequencies within the frequency range of detecting faults. Fig.10 The architecture 1000 shows Fig. 9 A magnified partial view of the fishbone architecture.

[0085] Figures 11 to 19 Various examples of cable configurations are shown that can be used for fault management power methods and systems (as described herein). In addition to upstream and downstream filters, (multiple) switches, power cables, and (multiple) power converters, the fault management power systems in these examples can also include additional upstream components that can be incorporated into the source side. These components can include pulse generation circuits and impedance sensors to measure electrical activity on the power cables. For example, the controller can use the sensor's measurements to detect the occurrence of a fault, such as human contact with the cable or other faults. In response to detecting the occurrence of a fault, one or more switches are used to interrupt (or prevent) the power supplied to one or more cables. These exemplary fault management power systems will be described in further detail below.

[0086] Fig.11 FIG. 1 shows a fault management power system 1100 using a unipolar power configuration according to an embodiment. Fig.11 As shown, the power system 1100 may include: a source including an upstream grounded source, an upstream power converter (e.g., an AC / DC converter), an upstream filter, and a single switch; a power cable; and (multiple) downstream components, including a downstream filter and a downstream power converter (e.g., a DC / DC converter or a DC / AC converter) connected to a load. In this example, the power cable is a 2-wire (twisted pair) cable with a shield. As shown, the power cable includes conductors, such as lines L1, L2, and a shield s. The upstream switch is connected between the upstream filter and the conductor L1.

[0087] Fig.12 FIG. 1 shows a fault management power system 1200 using a unipolar power configuration according to an embodiment. Fig.12As shown, the power system 1200 may include: a source including an upstream isolation source, an upstream power converter (e.g., an AC / DC converter), an upstream filter, and a single switch; a power cable; and (multiple) downstream components, including a downstream filter and a downstream power converter (e.g., a DC / DC converter or a DC / AC converter), which are connected to a load. In this example, the power cable is a 2-wire (twisted pair) cable with a shield. As shown, the power cable includes conductors, such as lines L1, L2, and a shield s. The upstream switch is connected between the upstream filter and the conductor L1.

[0088] Fig.13 FIG. 1 shows a fault management power system 1300 using a unipolar power configuration according to an embodiment. Fig.13 As shown, the power system 1300 may include: a source including an upstream isolation source, an upstream power converter (e.g., an AC / DC converter), an upstream filter, and a single switch; a power cable; and (multiple) downstream components, including a downstream filter and a downstream power converter (e.g., a DC / DC converter or a DC / AC converter) connected to a load. In this example, the power cable is a 2-wire (twisted pair) without shielding. As shown, the power cable includes conductors, such as lines L1 and L2. The upstream switch is connected between the upstream filter and conductor L1.

[0089] Fig.14 FIG. 1 shows a fault management power system 1400 using a unipolar power configuration according to an embodiment. Fig.14 As shown, the power system 1400 may include: a source including an upstream grounded source, an upstream power converter (e.g., an AC / DC converter), an upstream filter, and a dual switch; a power cable; and (multiple) downstream components, including a downstream filter and a downstream power converter (e.g., a DC / DC converter or a DC / AC converter) connected to a load. In this example, the power cable is a 2-wire (twisted pair) cable with a shield. As shown, the power cable includes conductors, such as lines L1, L2, and a shield s. Upstream and downstream filters are provided to conductors L1 and L2. The upstream dual switch is connected between the upstream filter and their corresponding conductors (e.g., L1 and L2), and can be operated to connect or disconnect the conductors to the power supply provided by the source or its components.

[0090] Fig.15 FIG. 1 shows a fault management power system 1500 using a unipolar power configuration according to an embodiment. Fig.15As shown, the power system 1500 may include: a source including an upstream isolation source, an upstream power converter (e.g., an AC / DC converter), an upstream filter, and a dual switch; a power cable; and (multiple) downstream components, including a downstream filter and a downstream power converter (e.g., a DC / DC converter or a DC / AC converter) connected to a load. In this example, the power cable is a 2-wire (twisted) cable with a shield. As shown, the power cable includes conductors, such as lines L1, L2, and a shield s. Upstream and downstream filters are provided to conductors L1 and L2. The upstream dual switch is connected between the upstream filter and their corresponding conductors (e.g., L1 and L2), and can be operated to connect or disconnect the conductors to the power supply provided by the source or its components.

[0091] Fig.16 FIG. 1 shows a fault management power system 1600 using a unipolar power configuration according to an embodiment. Fig.16 As shown, the power system 1600 may include: a source including an upstream isolation source, an upstream power converter (e.g., an AC / DC converter), an upstream filter, and a dual switch; a power cable; and (multiple) downstream components, including a downstream filter and a downstream power converter (e.g., a DC / DC converter or a DC / AC converter) connected to a load. In this example, the power cable is a 2-wire (twisted pair) without shielding. As shown, the power cable includes wires, such as lines L1 and L2. The upstream and downstream filters are provided to conductors L1 and L2. The upstream dual switch is connected between the upstream filter and their corresponding conductors (e.g., L1 and L2), and can be operated to connect or disconnect the conductors to the power supply provided by the source or its components.

[0092] Fig.17 FIG. 1 shows a fault management power system 1700 using a bipolar power configuration according to an embodiment. Fig.17 As shown, the power system 1700 may include: a source including an upstream grounded source, an upstream power converter (e.g., an AC / DC converter), an upstream filter, and a dual switch; a power cable; and (multiple) downstream components, including a downstream filter and a downstream power converter (e.g., a DC / DC converter or a DC / AC converter) connected to a load. In this example, the power cable is a 2-wire (twisted pair) cable with a shield, and the upstream power converter can provide bipolar power. As shown, the power cable includes wires, such as lines L1, L2 and a neutral line N, and a shield s. The upstream and downstream filters are provided to conductors L1 and L2. The upstream dual switch is connected between the upstream filter and their corresponding conductors (e.g., L1 and L2), and can be operated to connect or disconnect the conductors to the power supply provided by the source or its components.

[0093] Fig.18FIG. 1 shows a fault management power system 1800 using a bipolar power configuration according to an embodiment. Fig.18 As shown, the power system 1800 may include: a source including an upstream isolation source, an upstream power converter (e.g., an AC / DC converter), an upstream filter, and a dual switch; a power cable; and (multiple) downstream components, including a downstream filter and a downstream power converter (e.g., a DC / DC converter or a DC / AC converter) connected to a load. In this example, the power cable is a 2-wire (twisted pair) cable with a shield, and the upstream power converter can provide bipolar power. As shown, the power cable includes conductors, such as lines L1, L2 and a neutral line N, and a shield s. Upstream and downstream filters are provided to conductors L1 and L2. The upstream dual switch is connected between the upstream filter and their corresponding conductors (e.g., L1 and L2), and can be operated to connect or disconnect the conductors to the power supply provided by the source or its components.

[0094] Fig.19 FIG. 1 shows a fault management power system 1900 using a bipolar power configuration according to an embodiment. Fig.19 As shown, the power system 1900 may include: a source including an upstream isolation source, an upstream power converter (e.g., an AC / DC converter), an upstream filter, and a dual switch; a power cable; and (multiple) downstream components, including a downstream filter and a downstream power converter (e.g., a DC / DC converter or a DC / AC converter) connected to a load. In this example, the power cable is a 2-wire (twisted pair) cable, unshielded, and the upstream power converter can provide bipolar power. As shown, the power cable includes conductors, such as lines L1 and L2 and a neutral line N. The upstream and downstream filters are provided to the conductors L1 and L2. The upstream dual switch is connected between the upstream filter and their corresponding conductors (e.g., L1 and L2), and can be operated to connect or disconnect the conductors to the power supply provided by the source or its components.

[0095] Fig. 20 An example of sample data of a calibration table such as a voltage reference (Vref) table according to an embodiment of the present disclosure is shown. As shown, the calibration table can include a positive reference voltage table or array and a negative reference voltage table or array. These calibration measurements can be performed by a sensor, and the sensor measurement results can be used to detect the condition of an electrical or power system. In various embodiments, the sensor can be or include an impedance sensor or an RC circuit, and the reference voltage can be a measurement of a capacitor on the sensor, which can be in an open circuit state (e.g., an open circuit test) when the source / source circuit is in an open circuit state. As described herein, the reference value can be scaled for performing condition detection, such as contact of a power cable or other faults on an electrical or power system.

[0096] While particular aspects, implementations and applications of the present disclosure have been illustrated and described, it will be understood that the disclosure is not limited to the precise construction and composition herein and that various modifications, changes and variations may be evident in light of the foregoing description without departing from the scope of the invention as defined in the appended claims.

Claims

1. A fault management power system, comprising: a source switch connected to receive a source voltage from a power source, the source switch also connected to the cable line and controllable to connect the power source to the cable line; an impedance sensor circuit connected to the cable, the impedance sensor circuit being configured to sense impedance on the cable; as well as a controller coupled to the source switch and the impedance sensor circuit, the controller configured to receive the impedance sensed by the impedance sensor circuit and detect the presence of a fault on the cable line based on the impedance; wherein the source voltage manifests itself as current pulses on the cable line, each current pulse having an amplitude and a duration, and wherein the controller is configured to perform pulse duration reduction on a predefined number of current pulses to limit a cumulative effect of the predefined number of current pulses to below a predefined threshold level without reducing the amplitude of the predefined number of current pulses.

2. The fault management power system of claim 1, wherein the predefined threshold level is below a level that can prevent loosening or cause ventricular fibrillation in a human.

3. The fault management power system of claim 1 , wherein the controller is configured to perform pulse duration reduction on the predefined number of current pulses by detecting whether there is a fault on the cable line for each current pulse, determining a maximum allowable pulse duration for each current pulse, and controlling the source switch to disconnect the power source from the cable line when the maximum allowable pulse duration expires or is close to expiration in response to detecting the presence of a fault on the cable line.

4. The fault management power system of claim 3, further comprising a crowbar circuit coupled to the controller and connected to the cable line, wherein the controller is configured to turn on the crowbar circuit in response to detecting a fault on the cable line when a maximum allowable pulse duration of each current pulse expires or is close to expiration. 5 . The fault managed power system of claim 3 , wherein the controller is configured to determine a maximum allowed pulse duration for each current pulse by applying a current reduction multiplier to the duration of each current pulse.

6. The fault management power system of claim 5, wherein the current reduction multiplier is one of: a step-down multiplier, or a constant value.

7. The fault management power system of claim 3, wherein the controller is configured to shut down or otherwise disable the fault management power system after performing a predefined number of iterations of decreasing the pulse duration.

8. A method of managing faults in a power system, the method comprising: connecting a power source and a cable line using a source switch, the source switch being configured to receive a source voltage from the power source and being controllable to connect the power source to the cable line, the source voltage appearing as current pulses on the cable line when the power source is connected to the cable line, each current pulse having an amplitude and a duration; sensing impedance on the cable line using an impedance sensor circuit connected to the cable line; detecting the presence of a fault on the cable line based on the impedance of the cable line using a controller coupled to the impedance sensor circuit and the source switch; as well as Pulse duration reduction is performed on a predefined number of current pulses using the controller to limit a cumulative effect of the predefined number of current pulses below a predefined threshold level without reducing an amplitude of the predefined number of current pulses.

9. The method of claim 8, wherein the predefined threshold level is below a level that would prevent loosening or cause ventricular fibrillation in a human.

10. The method of claim 8, wherein the controller performs the pulse duration reduction for the predefined number of current pulses by detecting whether there is a fault on the cable line for each current pulse, determining a maximum allowable pulse duration for each current pulse, and controlling the source switch to disconnect the power source from the cable line when the maximum allowable pulse duration expires or is close to expiration in response to detecting the presence of a fault on the cable line.

11. The method of claim 10, further comprising connecting a crowbar circuit to the cable line, and in response to detecting a fault on the cable line, turning on the crowbar circuit using the controller at or near the expiration of a maximum allowed pulse duration of each current pulse.

12. The method of claim 10, wherein the maximum allowed pulse duration of each current pulse is determined by the controller by applying a current reduction multiplier to the duration of each current pulse.

13. The method of claim 12, wherein the current reduction multiplier is one of: a step-down multiplier, or a constant value.

14. The method of claim 10, further comprising shutting down or otherwise disabling the fault management power system using the controller after performing a predefined number of attempts to reduce the pulse duration.

15. A network comprising: at least one network cable; a fault management power system connected to the at least one network cable and operable to provide a series of current pulses on the at least one network cable, each current pulse having an amplitude and a duration; as well as at least one load connected to the at least one network cable and the fault management power system, the at least one load being powered by a series of current pulses from the fault management power system; Wherein, the fault management power system is further operable to detect the presence of a fault on the at least one network cable and perform a pulse duration reduction on a predefined number of current pulses to limit the cumulative effect of the predefined number of current pulses to below a predefined threshold level without reducing the amplitude of the predefined number of current pulses.

16. The network of claim 15, wherein the predefined threshold level is below a level that would prevent disengagement or cause ventricular fibrillation in a human.

17. A network according to claim 15, wherein the fault management power system performs pulse duration reduction on the predefined number of current pulses by detecting whether there is a fault on the network cable for each current pulse, determining a maximum allowable pulse duration for each current pulse, and shutting off each current pulse at or near the expiration of the maximum allowable pulse duration when a fault is detected on the network cable.

18. The network of claim 17, wherein the fault management power system is further operable to, in response to detecting the presence of a fault on the network cable, switch off each current pulse upon or near expiration of a maximum allowed pulse duration of each current pulse.

19. A network according to claim 17, wherein the maximum allowed pulse duration of each current pulse is determined by applying a current reduction multiplier to the duration of each current pulse.

20. The network of claim 19, wherein the current reduction multiplier is one of: a step-down multiplier, or a constant value.

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