Power system having short circuit protection controller

A power system that supplies electrical power to at least one load is disclosed. The power system may include an electrical power generator, current sensors configured to provide current signals representative of currents output from the electrical power generator to the load, and voltage sensors configured to provide voltage signals representative of voltages output from the electrical power generator to the load. The power system may also include a controller configured to receive the current signals and the voltage signals, compare the current signals and the voltage signals to a predetermined map, determine whether a short circuit exists inside the electrical power generator based on the comparison, and send a command to turn off the electrical power generator when the short circuit exists inside the electrical power generator.

TECHNICAL FIELD

The present disclosure relates generally to a power system, and more particularly, to a power system having a short circuit protection controller.

BACKGROUND

A power system is a network of components used to supply, transmit and/or use electric power. Generally, the power system includes generator sets (gensets), that are self-contained power modules that can be permanently or temporarily connected to an offboard facility, such as a home, a hospital, or a factory, to provide primary, supplemental, and emergency backup power to one or more external loads.

In some situations, an overcurrent condition may occur within the power system. The overcurrent condition may occur due to an overload of the power system, or due to a short circuit within the generator of the power system (an internal short circuit) or a short circuit somewhere outside of the generator of the power system (an external short circuit) of the power system. Certain regulating codes require over current and short circuit protection for power systems both inside and outside of the power system. In addition, the regulating codes require the power system under an overcurrent condition to be able to supply current long enough to allow an overcurrent protection device (e.g., a circuit breaker) closest to the location where an external short circuit exists to trip. This is called selective coordination and is important for providing power to life critical facilities such as hospitals. Selective coordination may require the power system to continue to supply current for several minutes. However, continuing to supply current to a load when the power system has an internal short circuit may greatly increase the risk of fire within the power system, thus increasing the risk of damaging components of the power system other than the ones initially involved in the short circuit. In certain circumstances, there is a risk that the fire may start in as little at 1/10th of a second after the internal short circuit occurs.

U.S. Pat. No. 7,521,822 (the '822 patent) to Lorenz, published on Nov. 13, 2008, discloses a method for protecting gensets from overcurrent. Specifically, the '822 patent discloses a protection technique for a back-up electric power generation system having generator control circuitry. The technique includes receiving sensor signals representative of electric output of an electric power generator, and determining if a shut-down condition exists, as a function of a protection profile pre-determined for the system.

But, the system of the '822 patent may not differentiate internal short circuits from external short circuits. The system of the '822 patent merely keeps current from exceeding an arbitrary time versus current curve chosen to limit insulation aging from excessive heat generation. The system of the '822 patent may not react fast enough to internal short circuits to inhibit damage to the system. In addition, since the system of the '822 patent relies on current measurement outside of the generator, the system may not be able to identify short circuits in the generator itself.

The disclosed power system having a short circuit protection controller is directed to overcoming one or more of the problems set forth above and/or other problems of the prior art.

SUMMARY

In one aspect, the present disclosure is directed to a power system that supplies electrical power to at least one load. The power system may include an electrical power generator, current sensors configured to provide current signals representative of currents output from the electrical power generator to the load, and voltage sensors configured to provide voltage signals representative of voltages output from the electrical power generator to the load. The power system may also include a controller configured to receive the current signals and the voltage signals, compare the current signals and the voltage signals to a predetermined map, determine whether a short circuit exists inside the electrical power generator based on the comparison, and send a command to turn off the electrical power generator when the short circuit exists inside the electrical power generator.

In another aspect, the present disclosure is directed to a system for controlling an electrical power generator that supplies electrical power to at least one load. The system may include one or more memories including instructions, and one or more processors configured to execute the instructions to receive current signals and voltage signals representative of currents and voltages output from the electrical power generator, compare the current and voltage signals to a predetermined map, determine whether a short circuit exists inside the electrical power generator based on the comparison, and send a command to turn off the electrical power generator when the short circuit exists inside the electrical power generator.

In still another aspect, the present disclosure is directed to a computer-implemented method of controlling an electrical power generator that supplies electrical power to at least one load. The method may include receiving current signals and voltage signals representative of currents and voltages output from the electrical power generator, comparing the currents and the voltages to a predetermined map, determining whether a short circuit exists inside the electrical power generator based on the comparison, and sending a command to turn off the electrical power generator when the short circuit exists inside the electrical power generator.

DETAILED DESCRIPTION

FIG. 1illustrates an exemplary power system100providing electrical power to a load200consistent with certain disclosed embodiments. Power system100may include an electrical power generator110, an engine120, a frame130, a plurality of sensors140a,140b,140c, and140n, and a controller150.

Electrical power generator110may generate alternating current (AC) power at different phases. InFIG. 1, electrical power generator110is shown as a three-phase AC generator that includes three phase windings110a,110b, and110cto generate power at three phases A, B, C. However, the disclosed embodiments are not limited to this configuration, and electrical power generator110may be a two-phase generator, a four-phase generator, or any other multiphase generator. Electrical power generator110may also include a generator neutral connector110nconnected to a neutral point (not shown). Electrical power generator110may be, for example, an AC induction generator, a permanent-magnet generator, an AC synchronous generator, or a switched-reluctance generator. Electrical power generator110may further include a generator field excitation unit112that regulates excitation of phase windings110a,110b, and110cof electrical power generator110. Electrical power generator110may also include a ground fault current transformer (GFCT)114for monitoring the current flowing through all of the leads inside electrical power generator110, i.e., phase windings110a,110b, and110c, and generator neutral connector110n, to ground.

Engine120may drive electrical power generator110to generate the electrical power. Engine120may be, for example, a combustion engine that combusts a mixture of fuel and air to produce the rotating mechanical output. One skilled in the art will recognize that engine120may be any type of combustion engine such as a diesel engine, a gasoline engine, or a gaseous fuel-powered engine.

Frame130may connect engine120to electrical power generator110. At least one of engine120and electrical power generator110may be mounted to frame130.

Sensors140a,140b, and140cmay sense voltages and currents output by electrical power generator110on phases A, B, C, respectively. Each one of sensors140a,140b, and140cmay include a voltage sensor and a current sensor. In addition, sensor140nmay be constructed to sense a neutral current flowing through generator neutral connector110n. Sensors140a,140b,140cand140nmay also transmit current and voltage signals representative of the sensed voltages and currents, respectively, to controller150.

Controller150may be configured to receive the current and voltage signals transmitted from sensors140a,140b,140cand140n, compare the current signals and the voltage signals to a predetermined map, and determine whether a short circuit exists inside electrical power generator110based on the comparison. When the short circuit exists inside electrical power generator110, controller150may be configured to send a command to turn off electrical power generator110.

Controller150may include processor150a, storage150b, and memory150cthat are included together in a single device and/or provided separately. Processor150amay include one or more known processing devices, such as a microprocessor from the Pentium™ or Xeon™ family manufactured by Intel™, the Turion™ family manufactured by AMD™, or any other type of processor that is capable of controlling operations of electrical power generator110and engine120in response to various input. Memory150cmay include one or more storage devices configured to store information used by controller150to perform certain functions related to the disclosed embodiments. Storage150bmay include a volatile or non-volatile, magnetic, semiconductor, tape, optical, removable, nonremovable, or other type of storage device or computer-readable medium. Storage150bmay store programs and/or other information, such as information related to processing data received from one or more sensors, such as a voltage sensor, a current sensor, and a temperature sensor, as discussed in greater detail below. Storage150bmay include one or more data structures, such as, for example, one or more maps, which may include multi-dimensional arrays or lookup tables. The maps may contain data in the form of equations, tables, or graphs. Various other circuits may be associated with controller150, including power supply circuitry, signal-conditioning circuitry, actuator driver circuitry (i.e., circuitry powering solenoids, motors, or piezo actuators), communication circuitry, and other appropriate circuitry.

FIG. 2Ais a graph illustrating voltage waveforms210a,210b, and210cof voltages on the three phases A, B, and C, when electrical power generator110is operating under normal condition, i.e., no short circuit exists inside or outside of electrical power generator110.FIG. 2Bis a graph illustrating voltage waveforms220a,220b, and220cof voltages on the three phases A, B, and C, when electrical power generator110is experiencing a short circuit between phase A and phase B, that is, between phase winding110aand phase winding110b. As can be seen from comparingFIG. 2AtoFIG. 2B, when a short circuit does not exist (FIG. 2A), the phase shifts among voltage waveforms210a,210b, and210care evenly distributed. On the other hand, when a short circuit exists between phase A and phase B (FIG. 2A) there is no phase shift (or a negligible phase shift) between waveforms220aand220b, and the magnitudes of waveforms220aand220bdecrease.

In one embodiment, the predetermined map may be a baseline table that includes current and voltage values representative of electrical power generator110operating under normal condition, i.e., there is no short circuit inside or outside of electrical power generator110. Currents and voltages output from electrical power generator110may be measured and compared to the baseline table to determine whether there is a short circuit inside electrical power generator110. The current and voltage values included in the baseline table may be predetermined based on experimental results of operating electrical power generator110, or a similar generator, when it is known that there are no short circuits, for example. The baseline table may include a time series of current values for each of the three phases A, B, and C, a time series of neutral current values, and a time series voltage values for each of the three phases A, B, and C. For example, the time series of voltage values on each of the three phases A, B, and C may be determined according waveforms210a,210b, and210cof the voltages on each of the three phases A, B, and C as shown inFIG. 2A.

FIG. 3illustrates an exemplary short circuit detection method that may be performed according to one embodiment. The method may be implemented by processor150aof controller150, for example, by executing instructions stored in storage150b, memory150c, or elsewhere. First, controller150may receive current signals and voltage signals (step310). The current signals may be representative of currents output from electrical power generator110on each of the three phases A, B, and C and a neutral current flowing through generator neutral conductor110nat a certain time point. The voltage signals may be representative of voltages output from electrical power generator110on each of the three phases A, B, and C and voltage output from electrical power generator110to generator neutral conductor110nat the time point. Controller150may compare the currents to corresponding current values at the same time point in the baseline table, and determine whether one or more of the currents significantly increase relative to the corresponding current values in the baseline table (step320). For example, controller150may determine whether a difference between one or more of the currents and the corresponding current values in the baseline table exceeds a first threshold, which may be determined based on the characteristics of the entire power system100. When none of the currents significantly increases relative to the corresponding current values in the baseline table (step320, No), controller150may compare the voltages to corresponding voltage values in the same time period in the baseline table, and determine whether one or more of the voltages significantly differ from their expected values (step330). For example, controller150may determine whether one or more of the voltages significantly differ from the corresponding voltage values in the baseline table. Controller150may determine whether a difference between a voltage and the corresponding voltage value in the baseline table exceeds a second threshold, which may be determined based on the characteristics of the entire power system100. In certain embodiments, when a voltage exceeds 1.73 (or approximately the square root of 3) times the corresponding voltage value in the baseline table, controller150may determine that the voltage significantly differs from its expected value. When one or more of the voltages significantly differ from the corresponding voltage values (step330, Yes), controller150may determine that an internal short circuit exists, i.e., a short circuit exists inside electrical power generator110(step340). In such case, controller150may send out a command to stop generator field excitation unit112of electrical power generator110(step350). Controller150may also send out a short circuit alarm signal (step360). When none of the voltages is significantly different from where it should be (step330, No), the process goes back to step310where the current signals and the voltages signals are received. When one of the currents significantly increases relative to the corresponding current values in the baseline table (step320, Yes), controller150may determine that an external short circuit exists, i.e., a short circuit exists outside of electrical power generator110(step370). In such case, controller150may implement an external overcurrent procedure in accordance with the selective coordination requirement specified in the regulation code (step380). In certain embodiments, controller150may complete one iteration of the steps described above every 1/10th of a second or less.

In other embodiments, the predetermined map may be a fault table that includes current and voltage trend indicators predetermined when electrical power generator110is operating under various fault conditions as illustrated inFIGS. 4A-4F.FIG. 4Aillustrates one of the fault conditions when a short circuit402between phase A and ground exists at location I420, that is, inside electrical power generator110.FIG. 4Billustrates another fault condition when a short circuit404exists at location I420inside electrical power generator110and between phase A and phase B. Although not illustrated in the figures, the short circuit at location I420may be a short circuit between phase B and ground, or between phase C and ground, or between phase B and phase C, or between phase C and phase A.

FIGS. 4C and 4Dillustrate fault conditions when short circuits exist at location II430, that is, outside of electrical power generator110and in a location upstream of sensors140a,140b,140cand140n. InFIG. 4C, short circuit406is between phase A and ground. InFIG. 4D, short circuit408is between phase A and phase B. Similarly, the short circuit at location II430may be a short circuit between phase B and ground, or between phase C and ground, or between phase B and phase C, or between phase C and phase A.

FIGS. 4E and 4Fillustrate fault conditions when short circuits exists at location III440, that is, outside of electrical power generator110and in a location downstream of sensors140a,140b,140cand140n. InFIG. 4E, short circuit410exists between phase A and ground. InFIG. 4F, short circuit412exists between phase A and phase B. Similarly, the short circuit at location III440may be a short circuit between phase B and ground, or between phase C and ground, or between phase B and phase C, or between phase C and phase A.

FIG. 5illustrates an exemplary fault table500that may be used in certain embodiments. Fault table500includes current and voltage trend indicators predetermined when electrical power generator110is operating under various fault conditions and when there is no load. There are four different types of trend indicators in fault table500. An upwards arrow “↑” indicates that a current or a voltage increases in a certain degree from its expected value. For example, when a measured voltage or current value exceeds 1.73 (or approximately the square root of 3) times its expected value, the voltage increases and the trend indicator of the voltage is “↑”. An indicator “↑s” indicates that a current or a voltage slightly increases from its expected value. For example, when a measured voltage is more than its expected value, but less than 1.73 times its expected value, the trend indicator of that particular voltage is “↑s”. A downwards arrow “↓” indicates that a current or a voltage decreases in a certain degree from its expected value. Again, in one example, the trend indicator may be the downward arrow “↓” when a measured voltage or current value is 1.73 (or approximately the square root of 3) time less than its expected value. A left right arrow “” indicates that the current or a voltage remain constant in a certain degree. For example, when a difference between a current and its expected value is less than a threshold (e.g., 1.73), the current is constant and the trend indicator of the current is “”. A number “0” indicates that a current or a voltage is zero. Although there are only five types of trend indicators in fault table500ofFIG. 5, additional indicators may be included. For example, a trend indicator “↑↑” may be used to indicate that a measured value greatly increases (e.g., more than 5 times its expected value).

Fault table500may include a plurality of rows each representing a unique fault condition. For example, the first row of table represents a condition in which a short circuit between phase A and ground exists at location I, which is illustrated inFIG. 4A. Each row of fault table500may include trend indicators of voltage differences between phase A and phase B, between phase B and phase C, between phase C and phase A, between phase A and generator neutral conductor110n, between phase B and generator neutral conductor110n, between phase C and generator neutral conductor110n, and between generator neutral conductor110to ground, and of currents flowing on phase A, phase B, phase C, and through generator neutral conductor110n, as well as a ground fault current. In this example, fault table500illustrated inFIG. 5is determined when there is no load. Alternatively, a load may be connected between a pair of phases A, B, and C, or between one of phases A, B, and C, and ground. Different fault tables may be composed based on different locations of the load.

In this embodiment, currents and voltages output from electrical power generator110may be measured and compared to their expected values to determine their respective trends, and the determined trends of the currents and voltages are compared to the corresponding trend indicators in each of the rows in fault table500to determine whether there is a matching row, and when there is matching row, to determine the type and location of a short circuit based on a location of the matching row. In one embodiment, a row is determined to be a matching row when all of the determined trends within that row are the same as their corresponding trend indicators in a row of fault table500. In addition, in this disclosure, the values of the voltages and currents are root mean square (RMS) values over a certain period, e.g., a generator cycle.

Short circuits cause two changes in the electrical power produced by electrical power generator110. First, a voltage between shorted components will drop to near zero as required by Kirchhoff's voltage law. When a short circuit exists inside electrical power generator110and between one of phases A, B, and C and ground, the voltage difference between that phase and generator neutral conductor110nwill be nearly zero. For example, according toFIG. 5, in the first row of fault table500(short circuit exists at location I and between phase A and ground), the voltage A-N is zero. Similarly, when a short circuit exists inside electrical power generator110and between two of phases A, B, and C, the voltage difference between the two phases will be zero. For example, according toFIG. 5, in the fourth row of fault table500(short circuit exists at location I and between phase A and phase B), the voltage A-B is zero. On the other hand, when the short circuit exists outside of electrical power generator110and between two of phases A, B, and C, the voltage difference between the phase voltages will also drop as described, but the amount of the voltage difference that stays above zero will be higher due to the resistance in the remaining circuit of electrical power generator110that excludes the components that are shorted. Second, current measured along the electrical path that includes the components (phase windings110a,110b,110c, or neutral connector110n) that experiencing short circuit will increase as required by Kirchhoff's current law. However, Ohms law requires that the amount of current passing though other circuits that connect the same elements will have to decrease.

The trend indicators within fault table500illustrated inFIG. 5are determined based on experimental analysis in one embodiment of the present disclosure. However, the present disclosure is not limited to those precise trend indicators or arrangement of trend indicators in fault table500. Various other changes and modifications may be made to fault table500for different embodiments without departing from the scope or spirit of the present disclosure.

FIG. 6illustrates an exemplary short circuit protection method that may be implemented by processor150aof controller150, according to certain embodiments. First, controller150may receive current signals and voltage signals (step610). The current signals and the voltage signals may be received from sensors140a,140b,140c,140n, and ground fault current transformer (GFCT)114. The current signals may be representative of RMS currents output from electrical power generator110on each of the three phases A, B, and C and a neutral current flowing through generator neutral conductor110nover a generator cycle. The voltage signals may be representative of RMS voltages output from electrical power generator110on each of the three phases A, B, and C and voltage output from electrical power generator110to generator neutral conductor110nover a generator cycle.

Controller150may calculate voltage differences between each pair of the three phases A, B, and C and between each of the three phases A, B, and C and generator neutral conductor110nbased on the voltage signals (step620). Controller150may compare the currents and the voltage differences to their respective expected values to determine their respective trends (step630). For example, the currents and the voltage differences may be compared to a baseline table that includes the expected values of the currents and the voltage differences.

Controller150may compare the trends of the currents and the voltage differences to their corresponding trend indicators in each row of fault table500, and determine whether there is a matching row of trend indicators in fault table500(step640). Controller150may determine that there is a matching row, i.e., that the measured current and voltage trends match a row in fault table500, if all of the measured trends are the same as their corresponding trend indicators in that particular row of fault table500. On the other hand, controller150may determine that there is not a matching row, i.e., that the measured and current voltage trends to not match a row in fault table500, if one or more of the measured trends are different than their corresponding trend indicators in the rows of fault table500.

When there is a matching row (step640, Yes), controller150may determine that there is a short circuit (step650). In addition, based on a location of the matching row within fault table500, controller150may determine a type and a location of the short circuit within power system100(step660). For example, when the matching row is the fourth (4th) row of fault table500, controller150may determine that the short circuit exists inside electrical power generator110and between phase A and phase B. On the other hand, when the matching row is the eleventh (11th) row of fault table500, controller150may determine that the short circuit exists outside of electrical power generator110, upstream of sensors140a,140b,140cand140n, and between phase B and phase C. In this way, controller150may determine the short circuit type (between one of the three phases A, B, and C and ground or between a pair of the three phases A, B, and C), and the short circuit location (inside electrical power generator110, or outside of electrical power generator110and upstream of sensors140a,140b,140cand140n, or outside of electrical power generator110and downstream of sensors140a,140b,140cand140n).

When the short circuit exists inside electrical power generator110, controller150may send out a command to stop generator field excitation unit112of electrical power generator110, and may send out a short circuit alarm signal. When the short circuit exists outside of electrical power generator110, controller150may implement an external overcurrent procedure in accordance with the selective coordination requirement described in the regulation code. When there is no matching row in fault table500(step640, No), the process returns to step610where current signals and the voltages signals are received.

In some embodiments, when the currents and the voltage differences match the corresponding current and voltage difference values in more than one of the plurality of table entries of the fault table, controller150may use Bayesian inference and probability distribution based on previous measurement results to determine which one of the various fault conditions has the highest probability.

In one embodiment, an outside synchronization signal may be used to determine the direction of the current measured by sensors140a,140b,140c, and140n. For example, controller150may receive the outside synchronization signal, and use the outside synchronization signal to determine whether the currents on the three phases A, B, and C and the neutral current are flowing into electrical power generator110or flowing out of electrical power generator110.

INDUSTRIAL APPLICABILITY

The disclosed power system with the short circuit protection controller may help to reduce damages to an electrical power generator. In particular, the disclosed power system with the short circuit protection controller may quickly determine a location of a short circuit, and may immediately halt the operation of the electrical power generator when the short circuit exists inside the electrical power generator. In this way, effective short circuit protection may be provided while the electrical power generator may still meet the requirement of selective coordination.