Patent Description:
Mechanical circuit breakers have been used for years to protect electrical components from short circuits or over current conditions, e.g., an electrical fault. However, a time lag between the occurrence of an electrical fault and a mechanical circuit breaker actually breaking the circuit exists due to the slow response time of the breaker's mechanical components. Moreover, as system ratings rise lag times of a mechanical circuit breaker also rise.

As such, there has been a move towards solid state circuit breakers (SSCBs). SSCBs utilize electronic switches, which have no moving parts, in place of mechanical switches. The electronic switches enable the SSCB to respond to an electrical fault much more quickly than a mechanical circuit breaker and, thereby, provide more responsive protection to electrical circuit components.

An increase in electrical subsystems within aerospace and automotive applications has made circuit protection a top priority in these sectors and SSCBs have become a preferred choice to provide this protection. However, due to the weight and volume constraints (e.g., many electrical components in a small space) present in aerospace and automotive applications, current density within an electrical subsystem must be high. Accordingly, the weight and volume of every electrical component is of concern including the weight and volume of an SSCB.

In <CIT> there is disclosed a current detector which includes a semiconductor relay and a control circuit for controlling the semiconductor relay. The semiconductor relay includes a switching element which is arranged on a bus bar between a high-voltage battery and a high-voltage load. The semiconductor relay further comprises a detection unit that detects a physical quantity related to a flowing current.

The present invention is directed to a current sensor that has numerous applications and is particularly suited to, for example, a solid state power control system or, its equivalent, a solid state circuit breaker (SSCB) system whose weight and volume is reduced by eliminating a high weight, high volume current detector relied upon by an SSCB. The function of the current detector is replaced by utilizing an existing busbar as a current measurement shunt resistor. The busbar, in combination with a voltage measurement of the voltage between first and second voltage detection points on the busbar and thermal properties of the busbar, are used to provide current monitoring for the SSCB system.

in a first aspect, the present invention is a solid state circuit breaker system as it is defined in claim <NUM>. The solid state circuit breaker system includes a parallel configuration of an electronic switching module and an electronic energy absorbing module, a voltage sensor, a temperature sensor and a controller. The parallel configuration is connected between a voltage source, via a busbar, and a load. The voltage sensor detects a difference in voltage between a first location on the busbar and a second location on the busbar. The temperature sensor indicates a temperature of the busbar. The controller determines the current flowing to the parallel configuration based on the difference in voltage and based on the electrical resistance of the busbar based on the following equation: <MAT> where:.

In a second aspect the present invention is a method of determining an over current fault to activate a solid state circuit breaker that is coupled between a power supply, via a busbar, and a load, as it is defined in claim <NUM>.

Whenever appropriate, terms used in the singular also will include the plural and vice versa. The use of "a" herein means "one or more" unless stated otherwise or where the use of "one or more" is clearly inappropriate. The use of "or" means "and/or" unless stated otherwise. The use of "comprise," "comprises," "comprising," "include," "includes," and "including" are interchangeable and not intended to be limiting. The term "such as" also is not intended to be limiting. For example, the term "including" shall mean "including, but not limited to.

Efforts continue to expand the functionality and use of electrical systems in automobile, aircraft and other applications where the volume and/or weight of the electrical system are constrained. For example, high voltage and high current electrical systems are being proposed for future aircraft ranging from <NUM> V AC to <NUM> V DC, and above. Accordingly, the volume and/or weight of an electrical system's power converter plays an important role in efficient and effective power management as does the volume and/or weight of the circuit breaker that protects electrical components supplied by the converter. Volume and weight constraints affect selection of every electrical component within an electrical system. As such, any possibility to reduce weight or volume of an electrical component is highly desirable.

Reduction in weight and volume within volume-constrained and/or weight-constrained electrical systems has, at least in-part, been achieved by replacing mechanical circuit breakers with solid state circuit breakers (SSCBs). SSCBs replace the traditional moving parts of an electromechanical circuit breaker with power electronics and software algorithms that control power and can interrupt a current within microseconds. In order to operate, SSCBs rely on a component that can be used to measure and monitor current flow. Typically, a current sensor, such as a hall effect sensor, provides the current monitoring ability external to the SSCB. However, the current sensor adds significant weight, takes up significant space and reduces current density. An alternative solution provides for the addition of a shunt resistor external to the SSCB that is used to monitor current flow. However, an external shunt resistor is typically a power resistor that is high in weight, subjects the electrical system to power dissipation and may, itself, require additional cooling.

<FIG> depicts a simplified diagram of an SSCB system <NUM> with an external current sensor <NUM>. As shown, a power source S1 is coupled, via a first busbar <NUM>, through the current sensor <NUM> to the SSCB <NUM>, which is coupled to a second busbar <NUM> and positioned ahead of a load <NUM>; the load <NUM> is represented by inductor L and resistor R. The SSCB <NUM> includes an electronic switching module <NUM> in parallel with an electronic energy absorbing module <NUM> controlled by a controller <NUM> receiving input from the current sensor <NUM>. The switching module <NUM> carries the current through normal operation. However, when a fault occurs (e.g., the current sensor <NUM> indicates an over current) the controller <NUM> directs the switching module <NUM> to open/trip while the current stored in the line is dissipated by the energy absorbing module <NUM> thereby protecting the load <NUM>.

The present invention provides an SSCB system <NUM> that utilizes an existing pre-calibrated busbar for current monitoring thereby eliminating the need for an external current sensor or an external shunt resistor. <FIG> depicts a simplified diagram of the SSCB system <NUM> of the present invention. As shown, a power source S1 is coupled, via a first busbar <NUM> (absent a current sensor) to the SSCB <NUM>, which is coupled to a second busbar <NUM> and positioned ahead of a load <NUM>; the load <NUM> is represented by an inductor L and a resistor R. An added voltage sensor <NUM> measures the difference in voltage between a first location V1 and a second location V2 on the first busbar <NUM> while an added temperature sensor T1 detects the temperature of the first busbar and/or detects the temperature of the atmosphere surrounding the first busbar <NUM> (e.g., the ambient temperature). A controller <NUM> is in communication with the voltage sensor <NUM>, the temperature sensor T1 and the SSCB <NUM>.

The first busbar <NUM> comprises a pre-calibrated busbar having a known resistance, a known variation in resistance with respect to temperature and known dimensions. The pre-calibrated busbar is fabricated from copper or any other material having good electrical conductivity.

The voltage sensor <NUM> comprises an operational amplifier (op-amp) or another suitable electrical component or circuit capable of determining the voltage difference between first and second locations, V1 and V2, on the first busbar <NUM> and capable of producing an output representative of that difference. The temperature sensor T1 comprises a thermocouple, resistance thermometer (RTD), thermistor or any suitable electronic component or circuit capable of obtaining a temperature and producing an output representative of that temperature.

The SSCB <NUM> includes a parallel electronics configuration comprising an electronic switching module <NUM> in parallel with an electronic energy absorbing module <NUM>; the parallel electronics configuration is controlled by the controller <NUM>.

The electronic switching module <NUM> generally includes a main switch such as a thyristor, a gate turn-off thyristor (GTO), integrated gate commutated thyristor (IGCT), insulated gate bipolar transistor (IGBT), metal oxide semiconductor field effect transistor (MOSFET) or other appropriate electronic switch. The electronic switching module <NUM> can be a single switch or a combination of series and/or parallel switches. Further, the electronic switching module <NUM> can also be a unidirectional switch or a bidirectional switch that has current blocking capabilities. The electronic switching module <NUM> can additionally include auxiliary switches and passive elements.

The electronic energy absorbing module <NUM> generally comprises a varistor, zener diode, resistor, transient-voltage suppression diode (TVS) or other appropriate electronic energy absorbing component.

The controller <NUM> generally comprises a field programmable gate array (FPGA), digital signal processing (DSP) based controller or other suitable controller.

In normal operation, the electronic switching module <NUM> carries the current. However, when an over current fault occurs (e.g., the current exceeds the rated amperage capacity of the load on the circuit) as described further herein, the controller <NUM> instructs the switching module <NUM> to open/trip and the current stored in the line is dissipated by the energy absorbing module <NUM> thereby protecting the load <NUM>.

Over current fault detection, and current monitoring in general, is achieved through use of the existing first busbar <NUM> (e.g., the pre-calibrated busbar) as a current measurement shunt resistor. More specifically, the electrical and thermal properties of the existing first busbar <NUM> are used to determine current (and determine the presence of the over current fault) without adding an additional external current sensor or an additional external shunt resistor. Rather, additional elements include the voltage sensor <NUM> and the temperature sensor T1 which, in the present context, are smaller electrical components that have a combined weight and volume less than that of an external current sensor or an external shunt resistor. The signal from the voltage sensor <NUM>, representing the difference in voltage between locations V1 and V2 on the first busbar <NUM>, and the signal from the temperature sensor T1, representing the temperature of the first busbar <NUM>, are provided to the controller <NUM> which uses the signals to calculate/determine current flowing to the SSCB <NUM>. More specifically, current is determined by the controller <NUM>, as programmed, according to Equation (<NUM>) below: <MAT> Where:.

The current determined by the controller <NUM>, through Equation (<NUM>), is monitored by the controller <NUM> to determine if a rated amperage capacity of the load <NUM> is exceeded. When the controller <NUM> determines that the rated amperage capacity is exceeded an over current situation is occurring and the controller <NUM> directs the electronic switching module <NUM> to trip creating an open circuit. As such, the solid state circuit breaker system <NUM> of the present invention provides the same functionality as one utilizing a current sensor without the weight and volume imposed by an added external current sensor or added external shunt resistor.

It should be noted that, while the present invention is directed to a specific application (e.g., a solid state circuit breaker or an equivalent interchangeable device such as a solid state power controller) of current measurement utilizing a pre-calibrated busbar with voltage and temperature detection, the current measurement technique can also be utilized in other electronic applications as appreciated by one skilled in the art. For example, the current measurement technique utilizing a pre-calibrated busbar with voltage and temperature detection could also be used with converters, distribution devices, controllers, etc..

Claim 1:
A solid state circuit breaker system (<NUM>), comprising:
a parallel configuration comprising an electronic switching module (<NUM>) connected in parallel with an electronic energy absorbing module (<NUM>), the parallel configuration connected between a voltage source, via a busbar (<NUM>), and a load (<NUM>);
a voltage sensor (<NUM>) detecting a difference in voltage between a first location (V1) and a second location (V2) on the busbar (<NUM>);
a temperature sensor (T1) indicating a temperature of the busbar (<NUM>);
a controller (<NUM>) determining the current flowing to the parallel configuration based on the difference in voltage and the electrical resistance of the busbar (<NUM>) based on the following equation: <MAT> where:
I = determined current
V = difference in voltage detected between the first location (V1) and the second location (V2); <MAT> where:
R = electrical resistance of the busbar (<NUM>);
r = electrical resistivity of the busbar material;
t = temperature of the busbar (<NUM>) provided by the temperature sensor (T1);
l = length of the busbar (<NUM>) between the first location (V1) and the second location (V2);
A = area of the busbar (<NUM>) between the first location (V1) and the second location (V2).