Patent Description:
In general, current sensing in high current circuits presents a challenge in space flight applications. For instance, resistors are impractical in high current applications due to size and power dissipation, and Hall Effect sensors require electronics that are sensitive to radiation effects. Thus, a solution for current sensing in a high radiation environment is needed for space applications. <CIT> relates to a system for measuring current in a conductor.

According to one or more embodiments, an integrated magnetic sensor is provided in claim <NUM>.

The figure depicts a circuit according to one or more embodiments.

Embodiments herein relate to a radiation hardened magnetic current sensor and, more particularly, to a compact integrated magnetic current sensor for current sensing in a high radiation environment, such as space applications. In this regard, embodiments of the compact integrated magnetic current sensor herein provide a wide-band current sensor (e.g., direct current (DC) to ~<NUM> megahertz (MHz) bandwidth) to provide a control system current feedback.

<NUM> depicts a wiring diagram of a circuit <NUM>, which is an example of the integrated magnetic current sensor according to one or more embodiments. The circuit <NUM> can be use in one or more applications, including space applications and applications with respect to surviving a nuclear event. For example, as an astronaut changes between tasks, the astronaut switches power between different devices on a spacecraft to implement a next task (e.g., power is switched to solid state electronic circuitry designed for a next task). As power is switched, a built in current limiting feature is employed to avoid power failures or short circuits. To achieve this, current being provided needs to be sensed. As such, in one embodiment, the circuit <NUM> is employed to magnetically detect/sense the current when the power switch is engaged.

Also, as another example, the circuit <NUM> can be used with respect to a thrust vector controller (e.g., a motor drive) that drives three phases of a motor. Because it is desirable to sense the current in all three phases of the motor, the circuit <NUM> is employed to magnetically detect/sense the current in all three phases of the motor.

In one or more embodiments, the circuit <NUM> includes an electrical wire network interconnecting electrical components. As shown in FIG. <NUM>, the circuit <NUM> includes one or more of the following electrical components: terminals <NUM>, <NUM>, and <NUM>; transformers <NUM> and <NUM> with primary windings <NUM>, <NUM>, and secondary windings <NUM>, <NUM>, and <NUM> therein; diodes <NUM> and <NUM>; a reference or "ground" connection <NUM> which may be a common location or locations that are connected to common reference potential; a bidirectional current source <NUM>; a capacitor <NUM>; a voltage source <NUM>; operational amplifiers <NUM> and <NUM>; and resistors <NUM>, <NUM>, <NUM>, <NUM>, and <NUM>. The circuit <NUM> is configured to detect or sense current over a range of frequencies from DC to several megahertz (MHz).

The circuit <NUM> is configured to accurately measure electric current over a wide bandwidth (including DC and extending to several megahertz (MHz)). This is achieved utilizing transformers having primary and secondary windings. When utilizing techniques such as keeping the transformer in a state of excitation from an alternating current (AC) power supply, very low frequency components (e.g., DC) flowing in the primary winding of the transformer can be measured in the secondary winding. These transformers also add the benefit of electrical isolation from the circuit being measured. The current to be sensed is supplied via terminals <NUM>, <NUM> and flows through the primary windings <NUM>, <NUM> of transformers <NUM>, <NUM>. In one or more embodiments, the current flowing through terminals <NUM> and <NUM> can be in any direction (e.g., flowing from <NUM> to <NUM> or flowing from <NUM> to <NUM>). The first transformer <NUM> is utilized to sense current having both a DC and AC component in a waveform when applied to the terminals <NUM> and <NUM>. Typically, the DC component cannot be measured by a transformer because a voltage is not induced in the secondary winding of the transformer with a DC current. To account for this, the secondary winding <NUM> is excited by a voltage source <NUM> which supplies a constant AC voltage in the form of a square wave across the secondary winding <NUM> of the first transformer <NUM> and resistor <NUM>. Resistor <NUM> can be referred to as a current sense resistor. The voltage supplied from the voltage source <NUM> is in the form of an AC square wave which provides a positive voltage for the first half of a duty cycle and a negative voltage for the second half of the duty cycle in the range of, for example, +15V to -15V. When a current having both a DC component and an AC current is flowing through terminals <NUM> and <NUM>, there will a voltage offset field included in the secondary winding <NUM> and the sense resistor <NUM> that is caused by the DC current flowing through the primary winding <NUM>. A proportional voltage will be present in the capacitor <NUM>. The voltage waveform across capacitor <NUM> will be for lower frequencies including DC. That is to say, the DC offset and lower frequencies current will be shown in the capacitor <NUM>. Lower frequency current values include frequency of around <NUM> kilohertz and lower. In one or more embodiments, as mentioned above, the current flow can be in the "reverse" direction from terminal <NUM> to <NUM>. In this case, the DC offset will not move the mean amplitude of the square wave voltage supplied from the power supply <NUM> higher than zero; but, instead will offset the mean amplitude to be lower than zero.

In one or more embodiments, the cross-coupled diodes <NUM>, <NUM> and capacitor <NUM> act as a peak rectifier that outputs a DC voltage equal to the peak value of the applied AC signal (e.g., the signal value across resistor <NUM>). This peak voltage value is proportional to the measured low frequency current applied to primary winding <NUM> and includes a DC offset. This peak voltage value is then applied to an input of a summing amplifier. A summing amplifier is a type of operational amplifier circuit configuration that is used to combine the voltages present on two or more inputs into a single output voltage. The summing amplifier includes resistor <NUM> and resistor <NUM> which act as two inputs for operational amplifier (op-amp) <NUM> and feedback resistor <NUM>. The output of the summing amplifier is a voltage that is proportional to the current flowing through terminals <NUM> and <NUM>, in either direction. The voltage across resistor <NUM> is present based on a high frequency current flowing through primary winding <NUM> inducing a voltage across secondary winding <NUM>. This will be described in greater detail below. The output terminal <NUM> includes the output voltage of the summing amplifier as described above. This terminal <NUM> can be connected to a controller or any other device that can be utilized to determine the current flow measured by terminals <NUM> and <NUM>. The controller determining the current value from terminal <NUM> can be implemented by executable instructions and/or circuitry such as a processing circuit and memory. The processing circuit can be embodied in any type of central processing unit (CPU), including a microprocessor, a digital signal processor (DSP), a microcontroller, an application specific integrated circuit (ASIC), a field programmable gate array (FPGA), or the like. Also, in embodiments, the memory may include random access memory (RAM), read only memory (ROM), or other electronic, optical, magnetic, or any other computer readable medium onto which is stored data and algorithms as executable instructions in a non-transitory form.

In one or more embodiments, the second transformer <NUM> with primary winding <NUM> and secondary winding <NUM> act as a current transformer that is configured to sense higher frequency (AC) current flowing through the terminals <NUM> and <NUM>. This higher frequency current is the current sensed over and above the current sensed at secondary winding <NUM> (greater than around <NUM> kilohertz). When current flows through primary winding <NUM>, a voltage is induced in secondary winding <NUM>. This voltage is present across resistor <NUM> and is later summed at the summing amplifier where this voltage across <NUM> is added to any corresponding voltage across capacitor <NUM> through the summing resistors <NUM> and <NUM>.

In one or more embodiments, the first transistor <NUM> and second transistor <NUM> can include separate magnetic cores. The magnetic cores can each be made up of a ferrite material, for example. When a current is applied to the terminals <NUM> and <NUM>, the DC component in the current can saturate the ferrite material used in the magnetic core of the second transformer <NUM> ultimately corrupting the signal. Once this core is magnetized, it will contain hysteresis and the accuracy will degrade unless the core is demagnetized. In one or more embodiments, to account for the above described issue, the circuit <NUM> includes a bi-directional current source <NUM> which is controlled by the output of operational amplifier (op-amp) <NUM>. The positive input of the op-amp <NUM> is the voltage across capacitor <NUM> and the negative input is ground <NUM>. A mentioned above, when a DC component of a current flows through primary winding <NUM>, a DC offset field occurs in the magnetic core. This offset field can be counter acted by the bi-directional current source <NUM> which can supply an equal current through the secondary winding <NUM> in the opposite direction of the current flowing through primary winding <NUM>. This has the effect of biasing the magnetic field to avoid saturating the magnetic core to allow for operation of the high frequency current detection through primary winding <NUM> and secondary winding <NUM>. The direction of the current through the secondary winding <NUM> is controlled by the op-amp <NUM>. When a positive voltage (e.g., positive DC offset) is across <NUM> when current is flowing from terminal <NUM> to <NUM>, the bi-directional current source <NUM> supplies current in the opposite direction. When a negative voltage (e.g., negative DC offset) is at the positive input of op-amp <NUM>, the op-amp controls the bi-directional current source <NUM> in the opposite direction to counter act the DC offset field in the magnetic core.

In operation, transformers <NUM> and <NUM> detect an electric current between the terminals <NUM> and <NUM> and generate, with other components of the circuit <NUM>, a signal proportional to that current. This signal can be outputted at terminal <NUM>, as an analog output or a digital output. The signal can include voltage and amperage components. The signal (e.g., the voltage and amperage components) can, in turn, be then used for control purposes, used to display a measured current, and/or stored for further analysis.

In some embodiments, the transformers <NUM> and <NUM> utilize a common magnetic core or separate magnetic cores. The magnetic core(s) can be, for example, a low permeability magnetic core enclosed around a current carrying conductor that provides a concentrated magnetic field proportional to the high frequency current through the conductor. In other embodiments, the transformers <NUM> and <NUM> utilize magnetic core(s) that are a high permeability magnetic core.

The diodes <NUM> and <NUM> are two-terminal electronic components (e.g., a semiconductor diode with a p-n junction connected to two electrical terminals) that have low (e.g., near zero) resistance in one direction, high (e.g., approaching infinite) resistance in the other direction, and conduct current primarily in one direction (e.g., asymmetric conductance).

The grounds <NUM> can be any electrical ground (e.g., a reference point built into the circuit <NUM>) that is a baseline when measuring other electrical currents. The grounds <NUM> can be a return path for the circuit <NUM> and/or allow any spikes in electricity to be directed away from the circuit <NUM>.

The bidirectional current source <NUM> is an electrical source component that both charges and discharges at once. In an example operation, a current of the bidirectional current source <NUM> flows primarily in one direction and then in the other. In operation, the current of the bidirectional current source <NUM> is driven by (can be change with respect to) an output of the operational amplifier <NUM>.

The capacitor <NUM> is a passive electronic device with two terminals that stores electrical energy in an electric field providing an effect known as capacitance.

The operational amplifiers <NUM> and <NUM> (a. op-amp or opamp) are direct current (DC) coupled high-gain electronic voltage amplifiers with a differential input and a single-ended output. The operational amplifiers <NUM> and <NUM> produce an output potential (e.g., relative to the grounds <NUM> and <NUM>) that is larger than a potential difference between its input terminals (e.g., positive '+' and negative '-' terminals).

The resistors <NUM>, <NUM>, <NUM>, <NUM>, and <NUM> are a passive two-terminal electrical components that implement electrical resistance to reduce current flow, adjust signal levels, to divide voltages, bias active elements, and/or terminate transmission lines.

The technical effects and benefits of embodiments herein include a method of current sensing without adding an element to the circuit being sensed i.e. resistor etc. That is, the path of the conductor being senses is not broken. technical effects and benefits of embodiments herein also include that the electronics (e.g., components of the circuit <NUM>) associated with the compact integrated magnetic current sensor are available in radiation hardened packages.

Claim 1:
An integrated magnetic current sensor comprising:
a first transformer (<NUM>) comprising a first magnetic core, a first primary winding and a first secondary winding;
a voltage source (<NUM>) configured to supply a first alternating current (AC) voltage to the first secondary winding;
a second transformer (<NUM>) comprising, a second magnetic core, a second primary winding, a second secondary winding, and a third secondary winding, wherein the first primary winding and the second primary winding are connected in series;
a bi-directional current source (<NUM>) configured to bias a magnetic field in the second magnetic core by supplying a current to the second secondary winding responsive to a sense current flowing through the first primary winding and the second primary winding; characterized by
a first operational amplifier (<NUM>) configured to operate the bi-directional current source;
wherein biasing the magnetic field in the second magnetic core comprises operating, by the first operational amplifier, the bi-directional current source to supply the current to the second secondary winding in a direction that is opposite a direction of the sense current flowing through the first primary winding.