A low frequency switching device and a method for minimizing the switching noise caused by back EMF in a low frequency switching device

Abstract

The disclosure relates to a low frequency switching device (1) and method for minimizing switching noise caused by back-EMF in inductive loads. The device comprises a load (3), a switching device (4) driven by a digital logic signal, and a programmable voltage or current source (2) supplying the switching device. The programmable source is configured to output a voltage / current with a curved rising and / or falling edge preceding or trailing polarity switching, the rise and / or fall time being greater than zero. By controlling the edge profile and decaying response frequency equal to the switching frequency, stored inductive energy in the load, cabling, or switching device is substantially depleted before polarity reversal, thereby suppressing voltage spikes, ringing, and electromagnetic noise. The switching device may comprise transistors or relays in an H-bridge configuration, and the programmable source may output rectified signals with sine-wave components. The invention is particularly advantageous for subsea electromagnetic survey systems, where electrodes in seawater form the load, enabling reliable low frequency operation in the range 0.01–100 Hz with reduced interference and improved signal quality.

Description

[0001] A low frequency switching device and a method for minimizing the switching noise caused by back emf in a low frequency switching device

[0002] Technical field

[0003] The present disclosure relates to a low frequency switching device and a method for minimizing the switching noise caused by back emf in a low frequency switching device. More specifically, the disclosure relates to a low frequency switching device and a method for minimizing the switching noise caused by back emf in a low frequency switching device as defined in the introductory parts of the independent claims.

[0004] Background art

[0005] Switching bridges such as an H-bridge is often used in switching devices to reverse polarity potential over a load, such as for example reversing a DC motor's direction. The Flbridge is typically comprising 4 or more power transistors or relays, wherein the switching device comprises a power source, the switching bridge and a load. Further embodiments where such switching devices are use may be in DC-to-AC converters, where a fast switching device can provide an AC source.

[0006] For applications such as running a DC motor there is low vulnerability to system generated Back-EMF signals.

[0007] However, when using such switching devices for providing an EM source system in for example subsea surveillance embodiments, wherein a load consisting of seawater, will also have a series inductive component due to cables connecting source electrodes to the EM source.

[0008] MOSFET H-Bridge drivers are specifically designed to be fast switching devices (nano- to micro-second switching times). One of the main reasons for using this in present disclosure is to reduce MOSFET switching losses i.e. the shortest (fastest) time the MOSFET transitioning between ON and OFF states, and the more efficient the device is the less heat / power is dissipating in the switching devices. The problem with using fast switching devices is that the reactive e.g. inductance components in the device and load will generate a problematic Back EMF signal each time the polarity switches in the switching device. Thus, unwanted voltage spikes will appear.

[0009] These "spikes" will generate wide spectrum EM noise, that can potentially interfere with the EM source electronics, EM receiver electronics, and other electronic systems in proximity to the EM source.

[0010] Further, it is possible that the parasitic components in the load and circuits lead to oscillations or "ringing".

[0011] Both back EMF with unwanted power spikes, and ringing, represents problematic effects that must be mitigated in the field of low frequency EM survey applications. These problematic effects can be for example high energy, wide bandwidth EM noise at switch time.

[0012] Known switching devices such as those disclosed in EP 1771750 Bl (DI), US 2012 / 0229264 Al (D2), US 2011 / 0157942 Al (D3), WO 2011 / 016734 Al (D4), and US 2022 / 0045617 Al (D5) describe low frequency switching devices with programmable sources. However, these documents do not disclose or suggest a programmable voltage or current source configured to deplete stored inductive energy before polarity switching, thereby suppressing back-EMF and eliminating switching noise.

[0013] There is thus a need for improved low frequency switching device with reduced or eliminated Back EMF / power spikes and ringing.

[0014] It is an objective of the present disclosure to mitigate, alleviate or eliminate one or more of the above-identified deficiencies and disadvantages in the prior art and solve at least the above mentioned problem.

[0015] The technical problem addressed by the present disclosure is the generation of back-EMF, voltage spikes, and ringing in subsea electromagnetic survey systems when polarity is switched in a low frequency H-bridge. The solution provided is a programmable voltage or current source with curved rising and / or falling edges, configured such that energy stored in inductive components is substantially depleted oerore polarity switching. This ensures minimal back-EMF and reduced electromagnetic noise.

[0016] According to a first aspect there is provided a low frequency switching device comprising: a load, a switching device, and a digital logic signal configured to drive the switching device, and a programmable voltage or current source for supplying the switching device, wherein the switching device is configured for switching polarity over the load, and the programmable voltage or current source is configured to provide a voltage / current with a programmable curved falling and / or rising edge preceding or trailing the switching device switching polarity over the load wherein the falling and / or rise time > 0.

[0017] It is thus possible for the stored energy in the inductive components of the load to dissipate during the rise and fall time of the driving voltage. Thus, at the moment the switch switches polarity there is no energy stored in the systems inductive components.

[0018] According to some embodiments, the low frequency switching device further comprises: a microcontroller configured to provide the digital logic signal to drive the switching device.

[0019] According to some embodiments, the low frequency switching device the comprises power transistors or relays, and the power transistors or relays are one of, or a combination of:

[0020] - Metal-oxide-semiconductor-field-effect Transistors, MOSFETs,

[0021] - standard transistors,

[0022] - Insulated Gate Bipolar Transistors, IGBTs,

[0023] - Bipolar Junction Transistors, BJTs, and

[0024] - Static Induction Transistors, SITs.

[0025] - Solid state relays

[0026] - Mechanical relays

[0027] According to some embodiments, the low frequency switching device comprise an H- bridge. A standard H-bridge using power transistors are well known technology and therefore a preferred choice when building an electrical circuit for a circuit which shall deliver a polarity reversed signal.

[0028] According to some embodiments, the curved rising or falling edge of the programmable voltage or current source output is configured as:

[0029] - a falling, towards 0V / 0A, signal-form when preceding the switching device switching polarity across the load, or

[0030] - a rising, from 0V / 0A, signal-form, when trailing the switching device switching polarity across the load.

[0031] According to some embodiments, the programmable output is a controlled voltage or current source.

[0032] According to some embodiments, the programmable voltage or current source is configured with a decaying response signal frequency equal to the switching device switching frequency.

[0033] Thus, the programmable voltage or current is configured with a controlled change, dv / dt or di / dt, before and after the switching device switches, and thereby provide for the energy stored in the inductor relative the switched energy level to be partly or fully discharged during the fall and rise time for the programmable voltage or current.

[0034] According to some embodiments, the low frequency switching device further comprises: an inductor component representing the total inductance in one or more of: load, load cabling, and switching device, and the falling edge of the programmable voltage or current source output is configured to reduce the voltage / current over the switching device such that some or all of a stored energy in the inductor component is depleted before the switching device switch polarity over the load.

[0035] The advantage is thus to obtain zero energy within the cable systems inductance when the switching device switches states.

[0036] According to some embodiments, low frequency is defined by switching frequencies in the range 0,01 - 100 Hz. The ability to obtain no energy storea upon switching time is found to be unique for low frequency switching devices only, and the energy within the cable systems inductance is almost zero at switching time. Compared with, high frequency switching applications wherein the requirement to the rise / fa 11 time is to be much faster and energy stored within the cable systems inductance is much higher at switching time,

[0037] According to some embodiments, the programmable voltage or current source is configured to output a signal comprising falling and rising edge signal components, and the switching device is configured to output a corresponding low frequency, with a corresponding switched signal output with less unwanted harmonics or electromagnetic, EM, noise.

[0038] According to some embodiments, the programmable voltage or current source is configured to output a rectified signal with sine wave components, such that at each 0V state on the programmable voltage or current source output, the switching device switches polarity and produces a signal with sine wave components output.

[0039] An output from the switching device corresponding to a sine wave may be advantageous in certain embodiments.

[0040] According to some embodiments, the load is an Electromagnetic, EM, source system comprising two conducive electrodes and is configured to put a potential difference across the two conductive electrodes, wherein the conductive electrodes are in contact with sea water.

[0041] The load is constituted by the seawater between the conductive electrodes. The seawater is itself conductive, so a current will flow between these electrodes, generating an electric field. The EM source load, consists of conductive seawater (resistive, R), and has a series inductive component (L), the inductance is here due to cables connected between the source electrodes, and an EM source pressure housing, that contains the system electronics.

[0042] According to some embodiments, the EM source system is arrange in a subsea entity being one of a Remotely Operated Subsea vehicle, ROV, Remotely Operated Towed Vehicle, ROTV, an Autonomous Underwater Vehicle, AUV, a subsea vehicle, or a fixed subsea asset.

[0043] According to a second aspect there is provided a method for minimizing the switching noise caused by back EMF in a low frequency switching device, comprising the steps: providing a low frequency switching device according to the first aspect, configuring the output of the programmable voltage or current source for supplying a voltage / current with a programmable curved falling and / or rising edge preceding or trailing the switching device switching polarity over the load wherein the falling and / or rise is greater than 0.

[0044] Thus, minimizing any energy within the cable systems inductance to be the source of a Back EMF when the switch switches state. This is the case both before and after the switching.

[0045] According to some embodiments, the method comprises the step: deploying the low frequency switching device in a subsea entity wherein the load is an Electromagnetic, EM, source system comprising two conductive electrodes, inserting the subsea entity into seawater, and outputting by the switching device a potential difference across the two conductive electrodes.

[0046] Thus, providing a method for enabling low frequency subsea EM survey applications.

[0047] According to some embodiments, the method further comprises the step: configuring the programmable voltage or current source to output a low frequency signal with switching frequencies in the range 0,01 - 100 Hz.

[0048] Effects and features of the second aspect are to a large extent analogous to those described above in connection with the first aspect. Embodiments mentioned in relation to the first aspect are largely compatible with the the second aspect.

[0049] The present disclosure will become apparent from the detailed description given below. The detailed description and specific examples disclose preferred embodiments of the disclosure by way of illustration only. Those skilled in the art understand from guidance in the detailed description that changes and modifications may be made within the scope of the disclosure.

[0050] Hence, it is to be understood that the herein disclosed disclosure is not limited to the particular component parts of the device described or steps of the methods described since such device and method may vary. It is also to be understood that the terminology used herein is for purpose of describing particular embodiments only, and is not intended to be limiting. It should be noted that, as used in the specification and the appended claim, the articles "a", "an", "the", and "said" are intended to mean that there are one or more of the elements unless the context explicitly dictates otherwise. Thus, for example, reference to "a unit" or "the unit" may include several devices, ana me like. Furthermore, the words "comprising", "including", "containing" and similar wordings does not exclude other elements or steps.

[0051] Terminology

[0052] The term "low frequency" is to be interpreted as a frequency in the range 0, 01 Hz to 100Hz, a frequency optimized for use in Electro Magnetic, EM, subsea surveys.

[0053] The term "signal with sine wave components" is to be interpreted to also comprise any composition of signal forms and frequencies, or sole signal form at a single frequency, that combined will appear as a signal with sine-like decaying or rising waveform components.

[0054] The term "Programmable curved edge" define as a controlled rise / fall profile (e.g., exponential, sinusoidal, polynomial).

[0055] The term "Decaying response signal" define as a signal whose amplitude decreases in phase with the switching frequency.

[0056] Brief of the

[0057] The above objects, as well as additional objects, features and advantages of the present disclosure, will be more fully appreciated by reference to the following illustrative and non-limiting detailed description of example embodiments of the present disclosure, when taken in conjunction with the accompanying drawings.

[0058] Figure 1A shows a typical DCDC source supplying an H-bridge design driving a load.

[0059] Figure IB shows how an H-bridge design embodiment for driving a load according to of the invention of present disclosure.

[0060] Figure 2 shows electrodes arranged on an AUV according to an embodiment of the present disclosure for deploying an electric field into the ambient seawater.

[0061] Figure 3 shows a diagram visualizing how a back EMF will result in power spikes. Figure 4 shows a diagram wherein the oacK t ix / l F, and power, dissipates over time in accordance with a time constant around the time of switching polarity in the switching device in accordance with a prior art embodiment.

[0062] Figure 5 shows a diagram of an example of ringing in a prior art system.

[0063] Figure 6 shows a diagram of a simulation of a prior art system with a 100A source.

[0064] Figure 7 shows a diagram of a controlled voltage source supplying an H-bridge according to an embodiment of the present disclosure.

[0065] Figure 8 shows how the embodiment of Figure 7 creates a minimal Back EMF and ignorable power spikes.

[0066] Figure 9 shows a comparison of a standard H-bridge FFT of energy pulse vs. a 0 energy H-bridge FFT of energy pulse according to an embodiment of the present disclosure.

[0067] Figure 10 shows diagram according to an embodiment of the present disclosure wherein the controlled voltage DC source is programmed to output a rectified sine wave, in this case the output into the load is a pure sinewave containing a no harmonics.

[0068] Figure 11 shows the three H-bridge output scenarios, standard H-bridge output, 0- energy output and sine like output, the two latter according to embodiments of the present disclosure.

[0069] Figure 12 shows the corresponding FFT of each output.

[0070] Figure 13 shows a diagram showing an example according to embodiments of the present disclosure of an analog signal output wherein a dual sine-like wave is output on the EM transmitter, and the transmission starts at 0.5Hz, then after several cycles changes to 4Hz.

[0071] Figure 14 shows a diagram showing the FFT output, according to the example in figure

[0072] 13 with no unwanted harmonics.

[0073] Detailed description The present disclosure will now be aescnoea with reference to the accompanying drawings, in which preferred example embodiments of the disclosure are shown. The disclosure may, however, be embodied in other forms and should not be construed as limited to the herein disclosed embodiments. The disclosed embodiments are provided to fully convey the scope of the disclosure to the skilled person.

[0074] Figure 1A shows a block diagram of a typical H-bridge design driving a load. The invention according to present disclosure will use a modified version of this typical H-bridge switching device as shown in figure IB. The invention is not limited to using an H-bridge switching device, but may be implemented in different ways using different types of power transistors or relays.

[0075] An H-bridge is essentially a high powered digital circuit, that is, the bridge is driven by a digital logic signal, that then inputs into a circuit comprising power transistors, that act digitally in that they are either ON or OFF. MOSFET H-Bridge drivers are specifically designed to be fast switching devices with nano to micro second switching times. One of the main reasons is to reduce MOSFET switching losses i.e. the fastest time the MOSFET is transitioning between ON and OFF states, the more efficient the device; reducing heat / power dissipation in the switching devices. Such H-bridge embodiments are designed for use in driving digital motors and the like, wherein the issue of Back EMF, power spikes and ringing are of no concern.

[0076] Back EMF, spikes and ringing caused by sensor systems is of great concern in subsea EM surveys, and must be minimized and / or eliminated to enable acceptable survey data quality.

[0077] Using a traditional H-Bridge for powering an EM source system in a subsea survey will require introduction of significant resources related to filtering and screening of the inductive components of the system.

[0078] If a system as shown in figure 2 where an AUV operating in seawater is equipped with such an unprotected H-bridge system as illustrated in figure 1A, it would be the source of severe Back EMF, ringing and power spikes. An EM source system as shown, puts a potential difference (Voltage) across 2 conductive electrodes, the seawater is itself conductive, so a current will flow between these electrodes, generating an electric field. In practice this current is typically 20A, but can be any value.

[0079] The EM source load, consists of conductive seawater (resistive, R), and has a series inductive component (L), the inductance is due to cables connected between the source electrodes, and an EM source pressure housing, that contains the system electronics.

[0080] Measurement shows that this unwanted inductance for about 10m of cable is typically in the region of 20uH. The equivalent seawater resistance is for example about 0.6 Ohms. Longer cable lengths will increase this inductance linearly (20m cable = 40uH).

[0081] Inductors store energy as a magnetic field, and this stored energy will try to maintain a constant current across its windings.

[0082] However the H-bridge voltage will fully reverse polarity in around 1-2 micro seconds when it switches polarity over the load. In this example the inductor will try to maintain current flow, by generating a "back EMF". This back EMF gives rise to a voltage spike, that will gradually decay over 5 time constants. During this time, all, or most, of the energy stored in the inductor is dissipated. The time constant can be expressed as: T = L / R = 20uH / 0.6 Ohms = 33uS, thus 5*T=166US.

[0083] Figure 3 shows a scenario where the power source in the upper diagram provide a constant 12 V source over the switching device according to figure 1A. This scenario highlight the problem area with using traditional switching devices with constant power / current sources. The switching device with the H-bridge is set up to provide a switched source current of + / - 20A though the load as seen in the second from the top diagram of figure 3.

[0084] It is then possible to estimate the Energy stored in the inductor to be: W =1 / 2* L * l2=1 / 2* 20u * 400 = 4 mJ

[0085] Back EMF (VL ) = L dl / dt, and if the bridge switches in 2uS

[0086] = 20u * 40 / 2u = 400V (Will be practically limited in a real circuit) The Power pulse may thus be estimated using the stored energy of 4mJ from above, and if the bridge switches state in say 2uS, this will result in a:

[0087] J (Joule) = Watt / sec= 400W pulse.

[0088] Figure 4 illustrates how this inductor driven power spike and Back EMF dissipates over the time constant.

[0089] It is important to note that the situation may be even a lot worse than shown. This is because parasitic components (small capacitance and inductance in PCB tracks, and within the MOSFET switching devices) can lead to oscillations or "ringing" as exemplified in figure 5.

[0090] The above examples considers an 20A source, BUT, an important point really worth noting, is that all of the above will scale by output current2

[0091] Energy stored is given by1* L * I2

[0092] Thus, for a 100A source this will give:1* 20u * 1002= 100 mJ

[0093] It then follows that the energy stored will be 25 times more for 5 times more current.

[0094] The 100A simulation is shown in figure 6.

[0095] These "spikes" will generate wide spectrum EM noise, that will interfere with the EM source electronics, EM receiver electronics, and other electronic systems in proximity to the EM source.

[0096] There are standard and well known techniques to deal with the worst of these effects, but there is a lot of pitfalls and drawbacks and problem areas include, but is not limited to:

[0097] Optimizing circuitry by a lot of "trial and error" o usually the end result is a compromise of volume (for filters) vs effectiveness vs design time

[0098] Good filtering & decoupling components require large components o especially for high output current Design changes to the drive e.g. changing onage MOSFETs, may require a new filtering strategy o specially for controlling oscillations

[0099] Changing the load changes performance o the load inductance is the main issue, so changing this value will change load characteristics potentially requiring a redesign of the filtering strategy o An EM transmitter mounted on an electronically sensitive subsea platform presents many design challenges, in particular generating high energy, wide bandwidth EM noise at switch time.

[0100] Thus there are multiple problem areas that needs to be solved when designing the power supply to switching devices used in subsea EM source systems.

[0101] The first aspect of this disclosure shows a low frequency switching device 1 comprising: a load 3, a switching device 4, and a digital logic signal configured to drive the switching device, and a programmable voltage or current source 2 for supplying the switching device 4, wherein the switching device 4 is configured for switching polarity over the load 3, and the programmable voltage or current source 2 is configured to provide a voltage / current with a programmable curved falling 20 and / or rising 21 edge preceding or trailing the switching device switching polarity over the load wherein the falling (21) or rise (20) time > 0.

[0102] By increasing the rise and fall time of the output driving voltage it is possible to obtain zero energy within the systems inductance. For the embodiment shown in figure 2 this means to obtain zero energy within the cable systems 7 inductance from the electronics in the programmable voltage or current source 2 to the electrode plates 11,12 in the seawater when the switching device switches states.

[0103] This possibility, as it was discovered, is unique for low frequency switching devices, and particularly for H-bridge applications, as in EM survey applications with a required frequency bandwidth of 0.01-100 Hz. The system and method will not work for high frequency H-bridge applications which the H-bridge was designed to serve, for which the DCDC source's rise / fa II time need to be much faster than for low frequency applications. It was shown that it is possible to use existing components / circuitry with no additional hardware changes required except for the firmware / hardware controlling the voltage or current source 2. Then no additional filtering of the switching device is required, resulting in

[0104] No additional space needed for filters

[0105] No transients

[0106] No resonance

[0107] No switching noise

[0108] The low frequency switching device 1 will work equally well on any switching device, and particularly well on any H-bridge. It is only the switching device / H-bridge output frequency that limits the frequency bandwidth of the system, which is why it can be uniquely applied to subsea low frequency EM applications.

[0109] One of the major advantages is that all output energy is directed to the application load and no energy is "wasted" by generating unwanted harmonics.

[0110] It is within the inventive concept of present disclosure understood that the low frequency switching device 1 comprising power transistors or relays 5, and the power transistors or relays 5 are one of, or a combination of, but not limited to:

[0111] - Metal-oxide-semiconductor-field-effect Transistors, MOSFETs,

[0112] - standard transistors,

[0113] - Insulated Gate Bipolar Transistors, IGBTs,

[0114] - Bipolar Junction Transistors, BJTs, and

[0115] - Static Induction Transistors, SITs.

[0116] - Solid state relays

[0117] - Mechanical relays

[0118] There are a multitude of ways to control the power transistors or relays of the switching device, such as from a microcontroller configured for controlling the switching device. In the embodiments of present disclosure such a microcontroller may be configured to control both the power transistors of the switching device as well as the output from the voltage or current source. Thus, also being able to, if required, to synchronize the power transistors with the output current or voltage of the source. Other options are to use control logic, being HW or SW driven, to control the power transistors or relays of the switching device. In one embodiment of present disclosure me IOW frequency switching device 1 further comprises a microcontroller configured to provide the digital logic signal configured to drive the switching device.

[0119] In one advantageous embodiment the low switching device 3 comprise an H-bridge. the advantage is that H-bridge is a de facto standard, which is the simplest way to achieve switching according to present disclosure. Other equivalent designs may be used, but will most probably mean more complex designs.

[0120] It is further shown as one embodiment of present disclosure is exemplified in figure 7 wherein the top diagram is output of the controlled voltage source which never goes below 0, and the bottom diagram is the H-bridge output current. Here it is demonstrated how: the controlled voltage source supplying the H-bridge does not maintain a constant voltage, but over a time, preferably longer or equal to the resistorinductor time constant, provide a voltage / current with a programmable curved falling (20) and / or rising (21) edge when activated it can be provided with an approximate sine response until the required DC voltage is reached before switching time, the source voltage or current follows a decaying signal with sine wave components response from DC down to 0V o This controlled voltage source response is provided with the same frequency, and in phase with the H-bridge switching frequency

[0121] At H-bridge switch time, the energy stored in the inductor, is now at 0J o Series inductance gains, and depletes energy on sinussignal-curve with sine wave components is substantially or completely discharged in time for the switch time

[0122] At 0V the h-bridge switches polarity

[0123] Rise time of the voltage or current source is the same or slower than the time constant influenced change pattern of the output, 5T, until all Back EMF is dissipated.

[0124] - The process repeats The falling response from DC down to uv or rising back to maximum source output level does not need to be formed as a sine wave, but, the best way to eliminate noise, or at least reduced the magnitude considerable, is providing it as a signal-curve with sine wave components. In practice it will be an approximation of a sine wave form.

[0125] It is thus provided a curved rising or falling edge of the programmable voltage or current source 2 output which may be configured as:

[0126] - a falling, towards 0V / 0A, signal-form when preceding, or

[0127] - a rising, from 0V / 0A, signal-form when trailing, the switching device 4 switching polarity across the load 3.

[0128] In this example the waveform is approximately 0.5Hz, and shows a signal-curve with sine wave components rise / fall time 0.1 seconds.

[0129] In figure 8 it is shown how such a scenario provides an H-bridge output of + / -20A (top diagram), no voltage spikes (middle diagram), and the energy being stored in the inductor ( 4mJ) during the DC state discharges gently to OmJ upon which time the switching device changes polarity. No power spikes are generated during the polarity change of the switching device (H-bridge), and power never exceeds 400mW. The absence of no voltage or power spikes means that no electrical noise is radiated from the output, and there is thus no need for transient management.

[0130] With respect to figure 8:

[0131] The top diagram of figure 8 shows the output current (as in figure 7)

[0132] The bottom diagram of figure 8 shows a 1 second switch time, the energy stored in the inductor being discharged to a 0 energy state at switch time (lsecond into the simulation). This eliminates any switching noise, as was seen with a standard H-bridge configuration

[0133] Figure 7 and figure 8 thus highlights depletion of inductive energy before switching.

[0134] As shown in figure 9 it can be seen a plot showing an FFT (Fast Fourier Transform) of energy pulse comparison of a standard H-bridge shown in the upper diagram vs the 0 energy bridge according to present disclosure shown in the lower diagram. As is clearly shown, there is a significant improvement in noise performance across all frequencies, such as 200dB improvement at 100Hz.

[0135] AS discussed above the programmable voltage or current source 2 is a controlled voltage DC source, but the invention according to present disclosure is not limited to controlled voltage DC source converters, and any type of programmable source may be used.

[0136] The programmable voltage or current source 2 is advantageously configured with a decaying response signal frequency equal to the switching device 4 switching frequency.

[0137] It is seen in these embodiments that the low frequency switching device comprises of an inductive component representing the total inductance in one or more of the load 3, the load cabling 6, and the switching device 4. The falling edge of the programmable voltage or current source 2 output is configured to delay and substantially reduce the voltage / current over the switching device 4 such that some or all of a stored energy in the inductor component is depleted before the switching device 4 switch polarity over the load 3. The rising edge of the programmable voltage or current source 2 output is configured to delay the rising voltage / current over the switching device 4, preferably aligned with the dissipation over 5 time constants of the back EMF energy stored in the inductor. These delayed fall and rise times prevent and / or reduce voltage and power spikes and ringing to appear.

[0138] The falling and / or rising edge is configured such that energy stored in inductive components of the load, load cabling, and / or switching device is substantially depleted before polarity switching, thereby minimizing back-EMF, voltage spikes and switching noise. Typically substantially depleted means reducing stored inductive energy in the inductive components to <10% of its steady-state value before switching.

[0139] This back EMF gives rise to a voltage spike, that will gradually decay over 5 time constants. During this time, all, or most, of the energy stored in the inductor is dissipated.

[0140] The low frequency is defined by switching frequencies in the range 0,01 - 100 Hz, but it is also seen that the invention may be successful in cancelling out voltage and energy spikes in lower and higher frequencies, as long as the time constant of the circuit is large enough to reduce the back EMF of the inductance when device switches its state. If the time constant is greater than 5 T, it is possible to achieve close to 0 energy when switching device switch state, thus eliminating switching noise. If the time constant is less than 5 the output may be the source of increasing voltage and power spikes, and possibly ringing.

[0141] In figure 10 it is exemplified that the programmable voltage or current source 2 is configured to output a signal comprising falling and rising edge signal components, and the switching device 4 is configured to output a corresponding low frequency output with corresponding switched signal output and substantially no unwanted harmonics or electromagnetic, EM, noise. The falling and rising edge signal components may be formed as portions of a sine wave, or a signal with a rounded falling or rising form correspondingly.

[0142] In an even further embodiment as seen in the figure the programmable voltage or current source 2 is configured to output a rectified signal with sine wave components, such that at each 0V state on the programmable voltage or current source 2 output, the switching device 4 switches polarity and produces a sine like wave output.

[0143] In this manner it is proven that it is possible to reduce output switching noise by programming a controlled voltage DC source to output a signal-curve with sine wave components at h-bridge switch time. And further extending this line of execution of the inventive concept of present enclosure it is shown by programming the controlled voltage DC source such that the H-bridge outputs an analog signal, for example a signal-curve with sine wave components, instead of a typical square wave, this may have some specific EM advantages, in particular the ability to focus output energy to a very specific frequency (or frequencies), with no unwanted harmonics.

[0144] The top diagram of figure 10 it is shown the controlled voltage DC source converter response, in this case, programmed to output a rectified signal with sine wave components. At each 0V on the controlled voltage DC source, the H-bridge switches polarity, and a signal with corresponding sine wave components is produced. If the controlled voltage DC source supplies a 20A rectified signal with sine wave components, the bridge output is a + / -20A signal.

[0145] Figure 11 shows a comparison of 3 time series scenarios, where the upper diagram shows a standard H-bridge output, the middle diagram a 0 energy output according to the invention of the present disclosure, and the lower diagram a signal with sine wave output also according to the invention of the present disclosure. Figure 12 show the FFT of each output respectively. In terms of unwanted harmonics, the signal with sine wave -being the best performing signal, and the standard H-bridge output being the worst. The 0 energy and analog output sources have less harmonic energy.

[0146] According to present disclosure with the zero energy method of running the source, the noise in the generated signal is reduced. It is also an advantage to focus energy at one frequency in for example a sine wave. In embodiments with this source there is only need for one specific output frequency in region of 0.01 - 100 Hz. This is achieved with this zero energy switching.

[0147] A further example embodiment of an analog output is shown in figure 13 and figure 14. In this case a dual sine wave is output on the EM transmitter. A transmission starts at 0.5Hz, then after several cycles changes to 4Hz. Looking at the FFT for this example, in figure 14, it is clearly shown that unwanted harmonics and ringing is absent.

[0148] The embodiment shown in figure 2 wherein the load 4 is an Electromagnetic, EM, source system the low comprises two conducive electrodes 11,12 and is configured to put a potential difference across the two conductive electrodes 11,12, wherein the conductive electrodes 11,12 are in contact with sea water 15.

[0149] The EM source system may advantageously be arranged in a subsea entity, the subsea entity being one of a Remotely Operated Subsea vehicle, ROV, Remotely Operated Towed Vehicle, ROTV, an Autonomous Underwater Vehicle, AUV, a subsea vehicle, or a fixed subsea asset. Fixed subsea assets may include, but not be limited to: seawater used in nuclear power stations, pipelines, water de-salination systems, and corrosion detection systems.

[0150] The second aspect of this disclosure shows a method for minimizing the switching noise caused by back EMF in a low frequency switching device 1, comprising the steps: providing a low frequency switching device according to the first aspect, and configuring the output of the programmable voltage or current source for supplying a voltage / current with a programmable curved falling and / or rising edge preceding or trailing the switching device switching polarity over the load wherein the falling and / or rise time > 0. The curved falling and / or rising edge is a continuous derivative in theory, and in practice it is voltage / current steps wherein the voltage / current source sets the premises for the steps.

[0151] The method may further comprise the steps: deploying the low frequency switching device 1 in a subsea entity wherein the load is an Electromagnetic, EM, source system comprising two conductive electrodes 11,12, inserting the subsea entity 10 into seawater, and outputting by the switching device 4 a potential difference across the two conductive electrodes 11,12.

[0152] In one embodiment the method comprises configuring the programmable voltage or current source 2 to output a rectified signal with sine wave components.

[0153] The method may further comprise the step of configuring the programmable voltage or current source 2 to output a low frequency signal with switching frequencies in the range 0,01 - 100 Hz.

[0154] The devices of present disclosure is particularly advantageous when used in subsea electromagnetic survey systems, where suppression of switching noise is critical for data quality.

[0155] The person skilled in the art realizes that the present disclosure is not limited to the preferred embodiments described above. The person skilled in the art further realizes that modifications and variations are possible within the scope of the appended claims.

[0156] Additionally, variations to the disclosed embodiments can be understood and effected by the skilled person in practicing the claimed disclosure, from a study of the drawings, the disclosure, and the appended claims.

Claims

AMENDED CLAIMS received by the International Bureau on 30 March 2026 (30.03.2026)1. A low frequency switching device (1) comprising:- a load (3),- a switching device (4),- a digital logic signal configured to drive the switching device (4), and- a programmable voltage or current source (2) for supplying the switching device (4), wherein the switching device (4) is configured for switching polarity across the load (3), and the programmable voltage or current source (2) is configured to provide a voltage / current with a programmable curve comprising:- a falling, towards 0V / 0A, signal-form when preceding, or- a rising, from 0V / 0A, signal-form, when trailing, the switching device (4) switching polarity across the load (3), wherein the falling and / or rising edge is configured such that energy stored in inductive components of the load, load cabling, and / or switching device is substantially depleted before polarity switching, thereby minimizing back-EMF, voltage spikes and switching noise.

2. The low frequency switching device (1) according claim 1, wherein the programmable voltage or current source (2) is configured with a decaying response signal having a frequency equal to the switching device (4) switching frequency.

3. The device (1) according to claim 1 or 2, wherein the programmable voltage or current source (2) is a controlled voltage source.

4. The device (1) according to one of the preceding claims, wherein the switching device (4) comprises power transistors (5) or relays selected from:- Metal-oxide-semiconductor-field-effect Transistors, MOSFETs,- standard transistors,- Insulated Gate Bipolar Transistors, IGBTs,- Bipolar Junction Transistors, BJTs, and- Static Induction Transistors, SITs,- Solid state relays,- Mechanical relays, and is driven by a microcontroller in an H-bridge configuration.

5. The low frequency switching device (1) according to any of the preceding claims, wherein low frequency is defined by switching frequencies in the range 0,01 - 100 Hz.

6. The device (1) according to any of the preceding claims, wherein: the programmable voltage or current source (2) is configured to output a signal comprising rising and falling edge signal components such that the switching device (4) outputs a corresponding low frequency signal with reduced harmonics and electromagnetic, EM, noise.

7. The device (1) according to claim 6, wherein the programmable voltage or current source (2) is configured to output a rectified signal with sine-wave components, such that at each 0V state the switching device (4) switches polarity and produces a signal with sine wave components.

8. The device (1) according to any of the preceding claims, wherein the load (4) is an Electromagnetic, EM, source system comprising two conducive electrodes (11, 12) in contact with sea water (15).

9. The device (1) according to claim 8, wherein the EM source system is arrange in a subsea entity selected from a Remotely Operated Subsea vehicle, ROV, Remotely Operated Towed Vehicle, ROTV, an Autonomous Underwater Vehicle, AUV, a subsea vehicle, or a fixed subsea asset.

10. A method for minimizing switching noise caused by back EMF in a low frequency switching device (1) the method being performed by a device comprising a load (3), a switching device (4) configured to switch polarity across the load (3), a digital logic signal configured to drive the switching device (4), and a programmable voltage or current source (2) supplying the switching device (4), the method comprising:- operating the programmable voltage or current source (2) to provide a voltage or current having a programmable curved falling and / or rising edge preceding or trailing a polarity switching of the switching device (4); and- controlling the falling and / or rising edge such that energy stored in inductive components of the load (3), load cabling, and / or switching device (4) is substantially depleted before the switching device (4) switches polarity, thereby minimizing back EMF, voltage spikes and switching noise.11.The method according to claim 10, further comprising: deploying the device (1) in a subsea entity wherein the load is an Electromagnetic, EM, source system comprising two conductive electrodes (11,12) in contact with seawater.12.The method according to claim 10 or 11, further comprising: configuring the programmable voltage or current source (2) to output a rectified sine-wave signal.13.The method according to any one of claim 10 to 12, further comprising: configuring the programmable voltage or current source (2) to output a low frequency signal with switching frequencies in the range 0,01 - 100 Hz.

14. Use of a low frequency switching device (1) according to any one of claims 1-9 in a subsea electromagnetic survey system, wherein the device is employed to minimize switching noise caused by back-EMF when generating an electric field between conductive electrodes (11, 12) in contact with seawater (15).

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