Patent Description:
It is known for a transport refrigeration system (TRS) to include an electrical apparatus comprising at least one electrical load that requires a supply of electrical power for operation. The supply of electrical power for operating the electrical load may be derived from, for instance, an electrical generator which is mechanically coupled to a prime mover of a vehicle in which the transport refrigeration system is incorporated. Otherwise, the supply of electrical power for operating the electrical load may be derived from a power supply external to the vehicle (sometimes referred to as "shore power"), from an electrical energy storage device, such as a battery, or from another source such as a solar cell or array of solar cells on the vehicle or the TRS.

Generally, at least one electrical conductor is provided for coupling the electrical load to the remainder of the electrical apparatus. However, the electrical coupling(s) to the electrical load are typically subject to deterioration and/or degradation in use due to, for example, the effect of vibrations originating from other parts of the TRS and/or a vehicle in which the TRS is incorporated and/or corrosion due to exposure to the atmosphere or contaminants. Eventually, the electrical coupling(s) may become degraded or otherwise compromised. A variety or risks may arise from such degradation or compromise of the electrical couplings, such as excessive heat generation within the electrical apparatus and/or transmission of electrical currents to other parts of the transport refrigeration system and/or to a user of the transport refrigeration system.

It is desirable to provide an electrical apparatus for a transport refrigeration system which is able to effectively detect if the electrical coupling(s) to an electrical load are in a degraded or compromised condition.

<CIT> describes a method for managing energy to a transport climate control system from a vehicle electrical system. The vehicle electrical system includes a vehicle power network and an auxiliary power network connected to a transport climate control load network via a DC regulated bus. The method includes monitoring a vehicle voltage of the vehicle power network and determining whether the vehicle power network requires holdover assistance based on the vehicle voltage.

According to a first aspect, there is provided an electrical apparatus for a transport refrigeration system, the electrical apparatus comprising: a rectifier configured to output a supply voltage, the rectifier being a synchronous rectifier; a DC-DC converter having an input electrically coupled to an output of the rectifier; and a controller, characterised in that the controller is configured to: monitor the supply voltage output by the rectifier by monitoring a signal received from a voltage sensor of the rectifier; and monitor a voltage received by the DC-DC converter at the input of the DC-DC converter by monitoring a signal received from a voltage sensor of the DC-DC converter; determine whether a trigger criterion has been met based on a comparison of the supply voltage and the voltage received by the DC-DC converter at the input of the DC-DC converter; and cause the electrical apparatus to enter an error handling mode in response to a determination that the trigger criterion has been met.

The controller being configured to cause the electrical apparatus to enter the error handling mode may include the controller being configured to: deactivate the rectifier.

The controller being configured to cause the electrical apparatus to enter the error handling mode may include the controller being configured to: cause an alert to be provided on an interface to the transport refrigeration system.

The controller may be configured to determine that the trigger criterion has been met if a difference between the voltage outputted by the rectifier and the voltage received by the DC-DC converter is greater than a trigger threshold.

Further, the controller may be configured to determine that the trigger criterion has been met if: a difference between the voltage output by the rectifier and the voltage received by the DC-DC converter has been greater than a secondary trigger threshold throughout a predetermined trigger period; and a start of the predetermined trigger period is set as being a time when the difference between the voltage output by the rectifier and the voltage received by the DC-DC converter is greater than a primary trigger threshold.

The primary trigger threshold may be greater than the secondary trigger threshold. Alternatively, the primary trigger threshold may be equal to the secondary trigger threshold. The predetermined trigger period may be equal to or greater than <NUM> second or equal to or greater than <NUM> seconds.

The rectifier may be configured to: monitor the voltage output by the rectifier using the voltage sensor of the rectifier; and maintain the voltage output by the rectifier within an output voltage tolerance range of an output voltage target value.

It may be that: the output voltage target value is between <NUM> V and <NUM> V; the output voltage tolerance range is between <NUM> V and <NUM> V; the primary trigger threshold is equal to or greater than <NUM> V; and/or the secondary trigger threshold is at least <NUM> V less than the primary trigger threshold.

The controller may be further configured to: record a number of trigger events, each trigger event corresponding to the trigger criterion being met; increment the number of recorded trigger events in response to a determination that the trigger criterion has been met; and cause the electrical apparatus to exit the error handling condition according to the number of recorded trigger events.

The controller may be configured to deactivate the rectifier and then reactivate the rectifier following a predetermined rest period if the number of recorded trigger events is fewer than an event number threshold greater than one. The predetermined rest period may be equal to or greater than <NUM> minute. The predetermined rest period may be equal to or greater than <NUM> minutes. The predetermined rest period may be equal to or greater than <NUM> minutes.

It may be that the controller is configured to deactivate the rectifier and prevent reactivation of the rectifier until an unlock signal is received from an interface to the transport refrigeration system if the number of recorded trigger events is equal to an event number threshold greater than one. The event number threshold may be equal to or greater than three.

The controller may be configured to: set the number of recorded trigger events to zero if the trigger criterion has not been met throughout a predetermined probationary period. The predetermined probationary period may be equal to or greater than <NUM> hour. The predetermined probationary period may be equal to or greater than <NUM> hours.

According to a second aspect there is provided a transport refrigeration system comprising an electrical apparatus in accordance with the first aspect.

<FIG> shows a vehicle <NUM> comprising a transport refrigeration system <NUM>. In the example of <FIG>, the transport refrigeration system <NUM> forms a part of an over-the-road refrigerated semi-trailer having a structure <NUM> supporting (or forming) at least one climate-controlled compartment <NUM> which is configured to be cooled and/or heated by a TRU <NUM>. The structure <NUM> includes a chassis. The vehicle <NUM> comprises an electrical apparatus <NUM> which includes various components disposed within an under-chassis box <NUM>. In some examples, one or more components of the electrical apparatus <NUM> may be integrated or incorporated into the TRU <NUM>. The structure <NUM> supports the TRU <NUM> and the under-chassis box <NUM>. The vehicle <NUM> further comprises a tractor unit <NUM> removably couplable to the trailer.

<FIG> schematically shows a diagram of an example TRU <NUM> suitable for use within the vehicle <NUM> and the transport refrigeration system <NUM> of <FIG>. The TRU <NUM> comprises a vapour-compression refrigeration circuit <NUM>. The vapour-compression refrigeration circuit <NUM> includes an evaporator <NUM> which is configured to receive heat from the climate-controlled compartment <NUM> of the transport refrigeration system <NUM> and a condenser <NUM> which is configured to reject heat to a thermal sink <NUM> (e.g., ambient air outside of the climate-controlled compartment <NUM>). For these purposes, the vapour-compression refrigeration circuit <NUM> also includes a compressor <NUM> and an expansion valve <NUM>. Accordingly, the vapour-compression refrigeration circuit <NUM> may be controlled to cause heat to be removed from the climate-controlled compartment <NUM>. The vapour-compression refrigeration circuit <NUM> may be controlled by any number of suitable control methods, as will be apparent to those skilled in the art. The TRU <NUM> also comprises a plurality of fans <NUM>, <NUM>. In the example of <FIG>, a first fan <NUM> is associated with (e.g. located in proximity to) the condenser <NUM> for improving heat transfer at one or more surfaces of the condenser <NUM>, and a second fan <NUM> is associated with (e.g. located in proximity to) the evaporator <NUM> for improving heat transfer at one or more surfaces of the evaporator <NUM>.

<FIG> shows a diagram of an example electrical apparatus <NUM> suitable for use with a transport refrigeration system <NUM> comprising a transport refrigeration unit (TRU) <NUM>. The electrical apparatus <NUM> may be incorporated within a mobile climate-controlled module including a climate-controlled compartment, such as the transport refrigeration system <NUM> and the climate-controlled compartment <NUM> shown in <FIG>. Accordingly, the electrical apparatus <NUM> is generally configured for use in transit. The electrical apparatus <NUM> comprises a rectifier <NUM>, a DC-DC converter <NUM>, a power distribution unit (PDU) <NUM>, a DC subsystem <NUM>, a plurality of motors <NUM>, <NUM>, an external interface <NUM> and a controller <NUM>. In use, the rectifier <NUM> functions as a voltage source, whereas the DC-DC converter <NUM> functions as a load. Hence the rectifier <NUM> may be described as a voltage source <NUM> and the DC-DC converter <NUM> may be described as a load <NUM>. The external interface <NUM> may be user interface capable of providing visual, audible and/or tactile information to a user. The controller <NUM> is generally configured to operate the electrical apparatus <NUM> in accordance with the method described below with reference to <FIG>.

The rectifier <NUM> has an input side <NUM> (i.e., an input <NUM>) and an output side <NUM> (i.e., an output <NUM>). The input side <NUM> of the rectifier <NUM> is configured to receive a plurality of alternating current voltages from a multi-phase power supply <NUM>, and the output side <NUM> of the rectifier <NUM> is configured to output a direct-current supply voltage. The rectifier <NUM> is a synchronous rectifier (i.e., an active rectifier). Accordingly, each side <NUM>, <NUM> of the rectifier <NUM> comprises a plurality of power switching components. Each power switching component may include, for example, an insulated gate bipolar transistor (IGBT), a junction-gate field-effect transistor (JFET), a thyristor, and/or a metal-oxide-semiconductor field-effect transistor (MOSFET). In particular, each power switching component may include a gate turn-off thyristor (GTO) and/or an integrated gate-commutated thyristor (IGCT). The power supply <NUM> may comprise an electrical generator which is mechanically coupled to a prime mover (e.g., an internal combustion engine) of a vehicle in which the transport refrigeration system <NUM> is incorporated (e.g., the vehicle <NUM> of <FIG>). The electrical generator may also be mechanically coupled to, or may also comprise, an electric motor. The electric motor may be couplable to a power supply external to the vehicle (e.g., a "shore" power supply), such that the electrical generator is operable when the vehicle <NUM> is stationary (e.g., not in transit) and/or when the prime mover is not operating.

The rectifier <NUM> comprises a voltage sensor <NUM> configured to monitor an output voltage Vr output by the output side <NUM> of the rectifier <NUM>. The rectifier <NUM> is configured to monitor the output voltage Vr using the voltage sensor <NUM>, and to maintain the voltage Vr within a predetermined output voltage tolerance range of an output voltage target value by appropriately controlling the plurality of power switching components of each side <NUM>, <NUM> of the rectifier <NUM>. This may be described as self-regulating functionality, and so the rectifier <NUM> may be described as a self-regulating rectifier <NUM>. Preferably, the output voltage target value is between <NUM> V and <NUM> V and the output voltage tolerance range is between <NUM> V and <NUM> V. However, those skilled in the art will appreciate that other output voltage target values and/or output voltage tolerances ranges may be used. By way of example, the output voltage target value may be between <NUM> V and <NUM> V (e.g., <NUM> V) and/or the output voltage tolerance range may be between <NUM>% and <NUM>% of the output voltage target value.

The DC-DC converter <NUM> has an input side <NUM> (i.e., an input <NUM>) and an output side <NUM> (i.e., an output <NUM>). The DC-DC converter <NUM> is generally configured to convert an input DC voltage at a first magnitude received at the input side <NUM> of the DC-DC converter <NUM> to an output DC voltage at a second magnitude for supply from the output side <NUM> of the DC-DC converter <NUM>. A ratio of the first magnitude to the second magnitude may be referred to as a conversion ratio of the DC-DC converter <NUM>. The DC-DC converter <NUM> may comprise a forward-type converter (e.g., a buck converter, a split-pi converter, a half-bridge converter or a full-bridge converter) and/or a flyback-type converter (e.g. a boost converter, a buck-boost converter, a Ćuk converter, or a SEPIC converter).

The DC-DC converter <NUM> comprises a voltage sensor <NUM> configured to monitor the input voltage Vl received at the input side <NUM> of the DC-DC converter <NUM>. The DC-DC converter <NUM> is configured to monitor the input voltage Vl using the voltage sensor <NUM> (i.e., the DC-DC converter monitors the first magnitude) and to vary the conversion ratio of the DC-DC converter <NUM> based on the monitored input voltage Vl, so as to control the voltage supplied from the output side <NUM> of the DC-DC converter <NUM> (i.e., the second magnitude) to the DC subsystem <NUM> and thereby facilitate proper operation of the DC subsystem <NUM>, which is described in further detail below. This may be described as self-regulating functionality, and hence the DC-DC converter <NUM> may be described as a self-regulating DC-DC converter <NUM>.

The PDU <NUM> is generally configured to act as an interface between various electrical components of the electrical apparatus <NUM>. The PDU <NUM> may comprise at least one short-circuit protection device, such that the PDU is able to rapidly decouple components of the electrical apparatus <NUM> if a fault current develops within the electrical apparatus <NUM>. The input side <NUM> of the DC-DC converter <NUM> and the output side <NUM> of the rectifier <NUM> are each electrically coupled to the PDU <NUM>. Accordingly, the input side <NUM> of the DC-DC converter <NUM> is electrically coupled to the output side <NUM> of the rectifier <NUM> via the PDU <NUM> via suitable electrical couplings (e.g., insulated conductors).

The plurality of motors <NUM>, <NUM> are also coupled to the PDU <NUM>. Therefore, the plurality of motors <NUM>, <NUM> are coupled to the output side <NUM> of the rectifier <NUM> via the PDU <NUM>. In the example of <FIG>, the plurality of motors <NUM>, <NUM> are connected in parallel with each other. However, in other examples, the plurality of motors <NUM>, <NUM> may be connected in series. Each motor <NUM>, <NUM> is configured to drive a mechanical device. By way of example, the mechanical device may be a fan, a pump or a compressor of the transport refrigeration system <NUM>. In particular, each motor <NUM>, <NUM> is configured to drive a respective fan <NUM>, <NUM> associated with the vapour-compression refrigeration circuit <NUM> of the TRU <NUM>.

The DC subsystem <NUM> may include at least one load, at least one voltage source, or a combination of one or more loads and/or one or more voltage sources. In particular, the DC subsystem <NUM> may include a battery (which may function as either a load or a voltage source depending on whether the battery is being charged or discharged). The DC subsystem <NUM> may have an operating voltage, which may correspond to a nominal voltage or a rated voltage of the battery, if present. In use, the DC-DC converter <NUM> converts the voltage supplied from the PDU <NUM> (that is, a voltage having the first voltage magnitude) to a voltage for supply to the DC subsystem <NUM> at the operating voltage of the DC subsystem <NUM> (that is, a voltage having the second voltage magnitude).

In the example described above with reference to <FIG>, the electrical apparatus <NUM> includes a PDU <NUM> electrically coupled to the rectifier <NUM> and the DC-DC converter <NUM>. In other examples, it may be that the rectifier <NUM> is directly electrically coupled to the DC-DC converter <NUM>. In such examples, the electrical apparatus <NUM> may not include the plurality of motors <NUM>, <NUM>.

<FIG> is a flowchart which shows an example method <NUM> of operating the electrical apparatus <NUM>. As discussed above, the method <NUM> is generally implemented by the controller <NUM>. The method <NUM> comprises a process of monitoring (at block <NUM>) the voltage output by the rectifier <NUM> (at block 302A) and the voltage received by the DC-DC converter <NUM> (at block 302B). In particular, the controller <NUM> is configured to monitor the voltage output by the rectifier <NUM> (at block 302A) by monitoring a signal received from the rectifier output voltage sensor <NUM>, and to monitor the voltage received by the DC-DC converter <NUM> (at block 302B) by monitoring a signal received from the converter input voltage sensor <NUM> described above. During initialisation (e.g., startup) of the electrical apparatus <NUM>, the method <NUM> may include waiting until a predetermined delay period has elapsed before the process of monitoring (at block <NUM>) the voltage output by the rectifier <NUM> (at block 302A) and the voltage received by the DC-DC converter <NUM> (at block 302B) is commenced in order to allow the electrical apparatus <NUM> to stabilise before the method <NUM> continues as described below. The predetermined delay period may be, for instance, at least <NUM> minute.

The method <NUM> also comprises a process of evaluating (at block <NUM>) a trigger criterion. In response to a determination (in block <NUM>) that the trigger criterion has not been met, the method <NUM> returns to the process of monitoring the voltages (at block <NUM>) and the process of evaluating (at block <NUM>) the trigger criterion such that the trigger criterion is repeated until a determination (in block <NUM>) is made that the trigger criterion has been met. In response to a determination (in block <NUM>) that the trigger criterion has been met, the method <NUM> continues to a process of causing (at block <NUM>) the electrical apparatus <NUM> to enter an error handling mode. The processes represented by blocks <NUM> and <NUM> are described in further detail below with reference to <FIG> and <FIG>, respectively.

<FIG> is a flowchart which shows an example implementation of the process of evaluating the trigger criterion, as represented by block <NUM> in <FIG>. In general, the trigger criterion relates to whether an anomaly is present in the electrical coupling(s) between the rectifier <NUM> and the DC-DC converter <NUM>.

The process of evaluating the trigger criterion comprises an action of calculating (at block <NUM>) a difference ΔV between the voltage Vr output by the rectifier <NUM> and the voltage Vl received by DC-DC converter <NUM>. The process of evaluating the trigger criterion then continues to an action of comparing (at block <NUM>) the voltage difference ΔV (as calculated in block <NUM>) to a primary trigger threshold ΔVt<NUM>. The primary trigger threshold ΔVt<NUM> is selected as a value of the difference between the voltage Vr outputted by the rectifier <NUM> and the voltage Vl received by DC-DC converter <NUM> which is indicative of the electrical coupling(s) between the rectifier <NUM> and the DC-DC converter <NUM> being in a compromised or degraded condition.

If it is determined that the voltage difference ΔV does not exceed the primary trigger threshold ΔVt<NUM> as a result of the comparison (at block <NUM>), the process continues to an action of determining (at block <NUM>) that the trigger criterion has not been met, and the method <NUM> continues as described above with respect to <FIG>.

In some examples, if it is determined that the voltage difference ΔV meets or exceeds the primary trigger threshold ΔVt<NUM> as a result of the comparison (at block <NUM>), the process may directly continue to an action of determining (at block <NUM>) that the trigger criterion has been met. That is to say that the method <NUM> includes determining (at block <NUM>) that the trigger criterion has been met if the difference ΔV between the voltage Vr output by the rectifier <NUM> and the voltage Vl received by DC-DC converter <NUM> is equal to or greater than the primary trigger threshold ΔVt<NUM>.

In other examples, if it is determined that the voltage difference ΔV exceeds the primary trigger threshold ΔVt<NUM> as a result of the comparison (at block <NUM>), the process may continue to an action of beginning (at block <NUM>) timing of a predetermined trigger period before continuing to an action of comparing (at block <NUM>) the voltage difference ΔV (as calculated in block <NUM>) to a secondary trigger threshold ΔVt<NUM>. Subsequently, if it is determined that the voltage difference ΔV exceeds the secondary trigger threshold ΔVt<NUM> as a result of the comparison (at block <NUM>), the process continues to an action of determining (at block <NUM>) whether timing of the predetermined trigger period has ended (i.e., whether the predetermined trigger period has elapsed).

If it is determined (at block <NUM>) that timing of the predetermined trigger period has not yet ended, the process returns to the action of comparing (at block <NUM>) the voltage difference ΔV (as calculated in block <NUM>) to the secondary trigger threshold ΔVt<NUM> such that the voltage difference ΔV is repeatedly compared to the secondary trigger threshold ΔVt<NUM> until a determination (in block <NUM>) is made that the timing of the predetermined trigger period has ended. If and when it is subsequently determined (in block <NUM>) that the predetermined trigger period has ended, the process continues to the action of determining (at block <NUM>) that the trigger criterion has been met. Otherwise, if it is found that the voltage difference ΔV does not exceed the secondary trigger threshold ΔVt<NUM>, as a result of the comparison (at block <NUM>), the process continues to the action of determining (at block <NUM>) that the trigger criterion has not been met such that if the voltage difference ΔV is determined (at block <NUM>) to be equal to or less than the secondary trigger threshold ΔVt<NUM> at any point during timing of the predetermined trigger period, the process results in a determination (at block <NUM>) that the trigger criterion has not been met and the method <NUM> continues as shown and described above with respect to <FIG>.

Accordingly, in such examples, the method <NUM> includes determining (at block <NUM>) that the trigger criterion has been met only if the difference ΔV between the voltage Vr output by the rectifier <NUM> and the voltage Vl received by DC-DC converter <NUM> has been greater than the secondary trigger threshold ΔVt<NUM> throughout the predetermined trigger period, with a start of the predetermined trigger period being set as the time when the difference ΔV between the voltage Vr output by the rectifier <NUM> Vr and the voltage Vl received by DC-DC converter <NUM> was determined (at block <NUM>) as being greater than the primary trigger threshold ΔVt<NUM>.

By determining that the trigger criterion has been met only when the difference ΔV between the voltage Vr output by the rectifier <NUM> and the voltage Vl received by DC-DC converter <NUM> was initially greater than the primary trigger threshold ΔVt<NUM> and subsequently has been greater than the secondary trigger threshold ΔVt<NUM> throughout the predetermined trigger period, a probability that the trigger criterion will be determined to have been met by the method <NUM> when an anomaly is not present in the electrical coupling(s) between the rectifier <NUM> and the DC-DC converter <NUM> (which may be referred to as a false positive determination) can be reduced. The inventors have found that a predetermined trigger period of at least <NUM> second, and preferably at least <NUM> seconds, is particularly effective at reducing the probability of false positive determinations that the trigger criterion has been met.

Preferably, the primary trigger threshold is greater than the secondary trigger threshold. This accounts for possible transients (e.g. temporary or short-lived voltage spikes) in the measured voltage Vr output by the rectifier <NUM> and the measured voltage Vl received by the DC-DC converter <NUM>, and therefore increases a probability that the trigger criterion will be determined to have been met by the method <NUM> when an anomaly is present in the electrical coupling(s) between the rectifier <NUM> and the DC-DC converter <NUM> (which may be referred to as a true positive determination) without significantly increasing the probability of a false positive determination that the trigger criterion has been met, despite possible measurement errors. For instance, if the output voltage target voltage of the rectifier <NUM> is between <NUM> V and <NUM> V and the output voltage tolerance range of the rectifier <NUM> is between <NUM> V and <NUM> V, the primary trigger threshold may be equal to or greater than <NUM> V (e.g., equal to or greater than <NUM> V) and the secondary trigger threshold may be at least <NUM> V (e.g., at least <NUM> V) less than the primary trigger threshold. The inventors have found that use of these numerical values is particularly effective at reducing false positives arising from transients in the measured voltages Vr and Vl.

<FIG> is a flowchart which shows an example implementation of the process of causing the electrical apparatus <NUM> to enter and then exit an error handling mode, as represented by block <NUM> in <FIG>. The error handling mode may be a first error handling mode (as represented by block <NUM>) or a second error handling mode (as represented by block <NUM>). Generally, the second error handling mode includes various error handling actions which are more disruptive to operation of the transport refrigeration system <NUM> than the first error handling mode. Consequently, the method <NUM> is adapted so that the second error handling mode is generally only selected when there is a high probability that the electrical coupling(s) between the rectifier <NUM> and the DC-DC converter <NUM> are in a substantially compromised condition and/or in a rapidly degrading or deteriorating condition.

The process includes selecting whether to enter the first error handling mode or the second error handling mode based on a number n of recorded trigger events, with each trigger event corresponding to a unique instance of the trigger criterion being met (as determined at block <NUM>). To this end, the process includes an action of recording (at block <NUM>) a number n of trigger events, for example in a memory of or associated with the controller <NUM>. During initialisation (e.g., startup) of the electrical apparatus <NUM>, the number of recorded trigger events may be set to zero, so that n = <NUM> or the number of recorded trigger events may be set as being equal to a last known value for n stored in the memory of or associated with the controller <NUM>. Recording (at block <NUM>) the number of trigger events includes incrementing (i.e., increasing by one) the number of recorded trigger events each time the trigger criterion is determined (at block <NUM>) to have been met. The action of recording (at block <NUM>) the number of trigger events may also include setting the number of recorded trigger events to zero if the trigger criterion has not been met throughout a predetermined probationary period. In general, the predetermined probationary period may be defined based on a set of characteristics of the electrical coupling(s) between the rectifier <NUM> and the DC-DC converter <NUM>. In particular, the predetermined probationary period may be equal to or greater than <NUM> hour or equal to or greater than <NUM> hours. Consequently, a series of isolated determinations (at block <NUM>) that the trigger criterion has been met across a relatively long period of time will not lead to the controller <NUM> causing the electrical apparatus <NUM> to enter the second error handling mode. Such isolated determinations may be made as a result of conditions arising from, for example, the transport refrigeration system <NUM> being in transit. Additionally or alternatively, such isolated determinations may be made during relatively rare transient events within the electrical apparatus <NUM> and/or as a result of high levels of electrical noise (occurring, e.g., as a result of electromagnetic interference) within the electrical coupling(s) between the rectifier <NUM> and the DC-DC converter <NUM>.

The process then continues to an action of comparing (at block <NUM>) the number n of recorded trigger events to an event number threshold nt. If the number n of recorded trigger events is not equal to (e.g., is fewer than) the event number threshold nt, the process includes causing the electrical apparatus to enter the first error handling mode (see block <NUM>). On the other hand, if the number n of recorded trigger events is equal to (e.g., is not fewer than) the event number threshold nt the process includes causing the electrical apparatus to enter the second error handling mode (see block <NUM>). The event number threshold nt is generally an integer greater than one. Preferably, the event number threshold nt may be equal to or greater than three. This ensures that the electrical apparatus <NUM> only enters the second error handling mode when a significant number of trigger events have been recorded and thus when there is a high probability that the electrical coupling(s) between the rectifier <NUM> and the DC-DC converter <NUM> are in a substantially compromised condition and/or in a rapidly deteriorating or degrading condition.

Both the first error handling mode (represented by block <NUM>) and the second error handling mode (represented by block <NUM>) include an action of deactivating (at blocks <NUM> and <NUM>, respectively) the rectifier <NUM>. The rectifier <NUM> being deactivated means that the output side <NUM> of the rectifier <NUM> does not output a direct-current supply voltage.

Optionally, the first error handling mode (see block <NUM>) also includes an action of causing (at block <NUM>) an alert to be provided on an external interface (e.g., the external interface <NUM> described above with respect to <FIG>) to the electrical apparatus <NUM> or the transport refrigeration system <NUM>, the alert being indicative of the electrical apparatus <NUM> having been entered into the first error handling mode.

The first error handling mode (see block <NUM>) further includes an action of beginning (at block <NUM>) timing of a predetermined rest period before continuing to an action of determining (at block <NUM>) whether timing of the predetermined rest period has ended (i.e., whether the predetermined rest period has elapsed).

If it is determined (at block <NUM>) that timing of the predetermined rest period has not yet ended, the process returns to the action of determining (at block <NUM>) whether timing of the predetermined rest period has ended and continues thereafter in a loop until a determination (in block <NUM>) is made that the timing of the predetermined rest period has ended. If and when it is determined (at block <NUM>) that timing of the predetermined rest period has ended, the process continues to an action of reactivating (at block <NUM>) the rectifier <NUM> and the electrical apparatus <NUM> is then caused to exit the first error handling mode. The method <NUM> then returns to the process of monitoring the voltages (at block <NUM>) and then the process of evaluating (at block <NUM>) the trigger criterion, as shown by <FIG>. If the first error handling mode (see block <NUM>) includes the action of causing (at block <NUM>) an alert to be provided on the interface, the process also continues to an action of causing (at block <NUM>) the alert to be removed from the interface if it is determined (at block <NUM>) that timing of the predetermined rest period has ended.

The predetermined rest period may be equal to or greater than <NUM> minute. Optionally, the predetermined rest period may be equal to or greater than <NUM> minutes or equal to or greater than <NUM> minutes. Use of a predetermined rest period in the manner described herein allows any transient conditions (e.g., excessive vibration originating from a vehicle <NUM> in which the transport refrigeration system <NUM> is incorporated or localised contamination from substances such as water) to dissipate before the rectifier is reactivated and the electrical apparatus <NUM> is caused to exit the first error handling mode. In addition, use of the predetermined rest period allows any heat which has been generated in the electrical coupling(s) between the rectifier <NUM> and the DC-DC converter <NUM> to dissipate before the electrical apparatus <NUM> is caused to exit the first error handling mode. Further, use of the predetermined rest period may facilitate resetting of measurement circuits associated with the voltage sensor(s) of the rectifier <NUM> and/or the DC-DC converter <NUM> prior to the electrical apparatus <NUM> being caused to exit the first error handling mode and the method <NUM> returning to the process of monitoring (at block <NUM>) the voltage output by the rectifier <NUM> (at block 302A) and the voltage received by the DC-DC converter <NUM> (at block 302B).

The second error handling mode (see block <NUM>) also includes an action of causing (at block <NUM>) an alert to be provided on the interface to the electrical apparatus <NUM> or the transport refrigeration system <NUM>, the alert being indicative of the electrical apparatus <NUM> having been entered into the second error handling mode. In particular, the interface may be a user interface, and the alert may inform a user that the electrical apparatus <NUM> has been entered into the second error handling mode. The alert may also instruct the user to carry out, or instruct the user to arrange for the carrying out of, remedial work on the electrical apparatus <NUM>.

The second error handling mode (see block <NUM>) further includes an action of determining (at block <NUM>) whether an unlock signal has been received by the controller <NUM>. The alert which is caused (at block <NUM>) to be provided to the interface may also inform a user that the electrical apparatus <NUM> will not be permitted to exit the second error handling mode until an unlock input which is indicative of a specific command to exit the second error handling mode is provided to the interface. When the unlock input is provided to the interface, the unlock signal is provided to the controller <NUM> from the interface.

If it is determined (at block <NUM>) that the unlock signal has not yet been received, the process returns to the action of determining (at block <NUM>) whether the unlock signal has been received and continues thereafter in a loop until a determination (in block <NUM>) is made that the unlock signal has been received. If and when it is determined (at block <NUM>) that the unlock signal has been received, the process continues to an action of reactivating (at block <NUM>) the rectifier <NUM> as well as to an action of causing (at block <NUM>) the alert to be removed from the interface. The electrical apparatus <NUM> is then caused to exit the second error handling mode and the method <NUM> returns to the process of monitoring the voltages (at block <NUM>) and then the process of evaluating (at block <NUM>) the trigger criterion, as shown by <FIG>. In this way, the method <NUM> includes preventing the rectifier <NUM> from being reactivated (at block <NUM>) and the electrical apparatus <NUM> from exiting the second error handling mode unless and until the unlock signal is determined (in block <NUM>) to have been received.

In summary, the conditions under which the method <NUM> includes causing the electrical apparatus <NUM> to reactivate the rectifier <NUM> and then exit the respective error handling mode differs according to whether the electrical apparatus <NUM> has been caused to enter the first error handling mode or the second error handling mode (and, therefore, differs according to the number n of recorded trigger events).

Operation of the electrical apparatus <NUM> in accordance with the methods disclosed herein ensures that the electrical coupling(s) between the rectifier <NUM> and the DC-DC converter <NUM> being in a compromised condition and/or in a deteriorating or degraded condition may be effectively detected without requiring additional (e.g., dedicated) sensor devices to be included within the electrical apparatus <NUM> for this purpose, as was employed in a previously-considered electrical apparatus. Therefore, a part count (e.g., a complexity), an installation mass and/or size of the electrical apparatus <NUM> may be minimised.

It should be understood that the processes and actions described with respect to <FIG> may be performed in any suitable order, and/or that the specific content of each process and/or action may be varied while still achieving the desired control outcomes described above.

The controller(s) described herein may comprise a processor. The controller and/or the processor may comprise any suitable circuity to cause performance of the methods described herein and as illustrated in the drawings. The controller or processor may comprise: at least one application specific integrated circuit (ASIC); and/or at least one field programmable gate array (FPGA); and/or single or multi-processor architectures; and/or sequential (Von Neumann)/parallel architectures; and/or at least one programmable logic controllers (PLCs); and/or at least one microprocessor; and/or at least one microcontroller; and/or a central processing unit (CPU), to perform the methods and or stated functions for which the controller or processor is configured.

Claim 1:
An electrical apparatus (<NUM>) for a transport refrigeration system (<NUM>), the electrical apparatus comprising:
a rectifier (<NUM>) configured to output a supply voltage, the rectifier being a synchronous rectifier;
a DC-DC converter having (<NUM>) an input (<NUM>) electrically coupled to an output (<NUM>) of the rectifier; and
a controller (<NUM>), characterised in that the controller is configured to:
monitor (302A) the supply voltage output by the rectifier by monitoring a signal received from a voltage sensor (<NUM>) of the rectifier; and
monitor (302B) a voltage received by the DC-DC converter at the input of the DC-DC converter by monitoring a signal received from a voltage sensor (<NUM>) of the DC-DC converter;
determine (<NUM>) whether a trigger criterion has been met based on a comparison (<NUM>) of the supply voltage and the voltage received by the DC-DC converter at the input of the DC-DC converter; and
cause (<NUM>) the electrical apparatus to enter an error handling mode (<NUM>, <NUM>) in response to a determination that the trigger criterion has been met.