Patent Description:
Conventional power conversion equipment, like frequency converters, are commonly used in a variety of applications in which electrical power must be converted from alternating current (AC) power at a fixed frequency and voltage, supplied by the power grid. For example, variable-frequency drives often must convert fixed frequency and voltage power supplied by the grid into variable frequency - variable voltage source in order to adjust for proper control of AC motors. In many instances, AC power is first converted to direct current (DC) power via an AC-DC converter, and then subsequently converted back to AC power via a DC-AC converter, thereby enabling voltage and frequency of the final AC power output via adjustment in the DC-AC converter.

However, conventional power converters, like frequency converters, can be prone to malfunction due to disconnection of one phase of a three phase or multiphase input, possibly due to a blown fuse in that particular phase or by accidental disconnection of a connection due to a wiring fault. It is important to detect such a disconnection of an input phase and take appropriate and pre-emptive actions to that such a malfunction of the power converter will not cause operational inefficiencies due to avoidable down-time of equipment.

In some instances, it is necessary to conduct routine maintenance or repair of power conversion equipment, which may require that a three phase or multiphase input be disconnected for safety reasons. Even if an AC input is disconnected, residual voltages may be present inside the power converter for a significant period of time and as many as tens of seconds, and an unprepared repairperson may be prone to electric shock caused by such residual voltages.

Document <CIT> describes a sensing circuit for open phase of three-phase power supply. In a voltage sensing circuit, a voltage which is generated due to the potential difference between a terminal P and a terminal N1 is used as an input. When the value of the input becomes a prescribed value or more, a DC voltage sensing signal which is electrically insulated from the input is turned on. When the value of the input is smaller than the prescribed value, the sensing signal is turned off. An open-phase discrimination circuit turns on an open-phase sensing signal as the sensing of an open phase when the detection signal becomes square waves which repeat an ON-OFF operation. In the sensing circuit for the open phase of the three-phase power supply, the voltage sensing circuit can be reduced to one. When the open phase is not generated in the three-phase power supply, a voltage which is input to the voltage sensing circuit becomes a nearly definite voltage, a change with the passage of time in a sensing level is not generated, and the open phase of any one phase from among respective phases of the power supply can be sensed stably.

Document <CIT> describes a motor driving device. If any one of three phases V1-V3 of a three-phase AC power supply lacks, the output becomes equivalent ot a single-phase AC voltage, and the voltage generated at a point becomes a single-phase full-wave rectified voltage. Therefore, a transistor becomes OFF-state in a period of time wherein the base voltage of the transistor goes lower than the voltage generated at the point when any one of the three phases lacks. In the period of time wherein the transistor is in OFF-state, a diode is driven to cause a current to flow through a photo-coupler, and the photo-coupler becomes On-state. As a result, a lower level signal is generated temporarily at the collector of the photo-coupler and a microcomputer forbids a motor to be drive, judging the generation of a lack of phase. Then, the microcomputer informs that the cause of non-operation of the motor is the lack of phase by lighting a diode for display.

Document <CIT> describes an open phase and interruption detection device. There are provided a three-phase AC power supply that outputs AC voltages in Ll, L2, L3 phases, photocouplers that are connected to respective lines between the L1 phase and the L2 phase, the L2 phase and the L3 phase, and the L3 phase and the L1 phase of the three-phase AC power supply, and convert respective line voltages of the L1 phase and the L2 phase, the L2 phase and the L3 phase, and the L3 phase and the L1 phase of the three-phase AC power supply into a pulse detection signal, a light receiving element of the photocoupler that is set to turn on at a predetermined threshold voltage or higher, and a controller that performs an AND operation of each pulse detection signal to generate an AND operation pulse, and determines presence or absence of an open phase and interruption and which of the L1 phase, L2 phase, and L3 phase is the open phase when the open phase is present by each pulse detection signal and the AND calculation pulse. Furthermore, detection signals of respective phase detectors result in pulses as in lower signal graph in <FIG>, which are counted as shown in <FIG> to detect open phase.

In an embodiment, the present disclosure provides a detection circuit comprising a converter configured to convert a multiphase alternating current (AC) input into a direct current (DC) output, a plurality of sensing diodes, each sensing diode being separately electrically connected to one phase of the multiphase AC input, at least one node arranged downstream from the plurality of sensing diodes relative to the multiphase AC input, a power source configured to output a power source voltage to the at least one node and plurality of sensing diodes, a bias resistor connected between the power source and the at least one node, and the power source is a DC power source which has one end connected to a direct current output terminal of the converter, and a mask time generator configured to determine a node voltage at the at least one node and determine whether the node voltage persists for a predetermined mask time period, which is a multiple of the grid voltage period, in order to detect a disconnection of an output phase according to claim <NUM> or <NUM>.

Subject matter of the present disclosure will be described in even greater detail below based on the exemplary figures. All features described and/or illustrated herein can be used alone or combined in different combinations. The features and advantages of various implementations will become apparent by reading the following detailed description with reference to the attached drawings, which illustrate the following:.

Aspects of the present disclosure include systems and methods for detecting disconnections of one or more phases of a three phase or multiphase input to an AC-DC section of a power converter. The disclosed systems and methods provide significant performance and safety improvements to AC-DC converters, as electrical disconnections can be more easily detected and diagnosed with more specificity. In some aspects, the present disclosure provides for detection of which input in a three phase power input has experienced an electrical disconnection. In some aspects, the disclosed features provide safety benefits by immediately eliminating the potential for electric shock upon detection of an electrical disconnection. In some aspects, the disclosed features provide safety benefits by discharging residual voltages, thereby decreasing the likelihood of electric shock to a repairperson. Furthermore, by providing a more reliable and accurate electrical input disconnection detection, the present disclosure enables increased automated functionality, such as automatic triggering of redundancy measures, warning and/or alarm systems, and/or downstream protection measures. The embodiments of <FIG> are not according to the invention and are present for illustration purposes only.

<FIG> illustrates a simplified schematic of a frequency converter <NUM>. The frequency converter <NUM> includes a three phase power input <NUM> that passes an alternating current (AC) input, such as an AC input from grid power, to a rectifier section <NUM>. The rectifier section <NUM> converts the AC signal from the three phase power input <NUM> into a direct current (DC) signal. The DC signal is measured as a voltage potential across a DC bus <NUM>, which in some cases includes a capacitor <NUM> (or other circuitry represented herein by capacitor <NUM>). The DC signal from the DC bus <NUM> is then passed on to a three phase inverter <NUM>, which is configured to convert the DC signal into a three phase power output <NUM>. Depending on the use case of the frequency converter <NUM>, the three phase power output <NUM> may be customized for operating a specialized motor or other equipment. Equipment and/or systems utilize a frequency converter <NUM> to convert AC power, such as grid power, to a usable form of AC power for operating equipment as needed.

<FIG> illustrates a more detailed view of the rectifier section <NUM> of the frequency converter <NUM> illustrated in <FIG>. In rectifier section <NUM>, the three phase power input <NUM> of the frequency converter <NUM> is electrically connected to a collection of diodes <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>. Specifically, two diodes of the six diodes <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM> are assigned to each phase of the three phase power input <NUM>, with one set of diodes <NUM>, <NUM>, <NUM> configured to only pass positive downstream current from each phase and a second set of diodes <NUM>, <NUM>, <NUM> configured to pass negative downstream current from each phase. In this manner, a direct current potential is created across the DC bus <NUM> of the frequency converter <NUM>. In the illustrated embodiment, two precharge configurations are included on a positive side of the DC bus, a first precharge contact configuration <NUM> and a second precharge contact configuration <NUM>, which are each essentially the same in structure and may be implemented as alternative configurations. It will be readily understood that precharge circuitry can be implemented on the positive or negative side of the DC bus, although it is customarily drawn on the positive side. Each precharge contact configuration <NUM>, <NUM> includes one precharge contact <NUM>, <NUM> and a precharge resistor <NUM>, <NUM>. Each configuration, regardless of which is used, is configured to limit an inrush of current through rectifier diodes <NUM>, <NUM>, <NUM> during charging of the DC bus capacitor <NUM> when power through the three phase power input <NUM> is initially applied. The resistors <NUM>, <NUM> are configured to limit an inrush current, and when the DC bus capacitor <NUM> is fully charged, the precharge contacts <NUM>, <NUM> are closed under command of a frequency converter controller.

<FIG> illustrates an alternate rectifier section <NUM> of the frequency converter <NUM> illustrated in <FIG>. The alternate rectifier section <NUM> includes a third precharge configuration <NUM> that may be implemented as an alternative to the first and second precharge contact configurations <NUM>, <NUM>. In the third precharge configuration <NUM>, a three phase power input <NUM> passes an AC signal to upper diodes <NUM>, <NUM>, <NUM>, with each phase of the three phase power input <NUM> being passed to a separate upper diode <NUM>, <NUM>, <NUM>. The upper diodes <NUM>, <NUM>, <NUM> are configured to allow only positive downstream current from the three phase power input <NUM>. The third precharge configuration <NUM> then passes current from each of the diodes to a precharge resistor <NUM>. The alternate rectifier section <NUM> also includes lower diodes <NUM>, <NUM>, <NUM> that are configured to pass negative downstream current from the three phase power input <NUM> toward a negative side of the DC bus capacitor <NUM>. Three silicon-controlled rectifiers (SCRs) <NUM>, <NUM>, <NUM> are included downstream of the three phase power input <NUM> and the upper diodes <NUM>, <NUM>, <NUM>, with one SCR <NUM>, <NUM>, <NUM> assigned to each phase of the three phase power input <NUM>. The third precharge configuration <NUM>, via the upper diodes <NUM>, <NUM>, <NUM> and precharge resistor <NUM>, limit the charging current of the DC bus capacitor <NUM>. When the DC bus capacitor <NUM> is substantially charged, the SCRs <NUM>, <NUM>, <NUM> are gated on under the control of a frequency converter controller.

<FIG> illustrates an input phase loss detection circuit <NUM> according to an embodiment of the present disclosure. The detection circuit includes sensing diodes <NUM>, <NUM>, <NUM>, a DC power supply (Vcc) <NUM>, a bias resistor (R) <NUM>, and a mask time generator. In the illustrated detection circuit <NUM>, three sensing diodes <NUM>, <NUM>, <NUM> are included, each being electrically connected downstream of one phase of a three phase power input <NUM>. In the illustrated embodiment, the three phase power input <NUM> includes a first phase <NUM>, a second phase <NUM>, and a third phase <NUM>. The first phase <NUM> is connected to two diodes, diode (D1) <NUM> and diode (D4) <NUM>. The first phase <NUM> is also connected to sensing diode (DS_a) <NUM>. The second phase <NUM> is connected to two diodes, diode (D3) <NUM> and diode D6 <NUM>. The second phase <NUM> is also connected to sensing diode (DS_b) <NUM>. The third phase <NUM> is connected to two diodes, diode (D5) <NUM> and diode (D2) <NUM>. The third phase <NUM> is also connected to sensing diode (DS_c) <NUM>. Upper diodes <NUM>, <NUM>, <NUM> are configured to allow positive downstream current to flow and to form a positive DC voltage <NUM>. Lower diodes <NUM>, <NUM>, <NUM> are configured to allow negative downstream current to flow and form a negative DC base voltage <NUM>. The sensing diodes <NUM>, <NUM>, <NUM> are high voltage, low current sensing diodes and are electrically connected to form a node <NUM>. The node <NUM> is then electrically connected to mask time generator <NUM> and bias resistor <NUM>.

The detection circuit <NUM> is configured to sense and respond to a variety of scenarios based on function of the three phase power input <NUM> and the upper and lower diodes <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>. When power is received via three phase power input <NUM>, one or more of the lower diodes <NUM>, <NUM>, <NUM> conduct electricity during some portion of a period of the AC input, the period for an AC input of <NUM> being <NUM> milliseconds (ms) and the period for an AC input of <NUM> being <NUM>. When one or more of the lower diodes <NUM>, <NUM>, <NUM> are properly conducting, the voltage at node <NUM> is at or near the base voltage <NUM>, which is indicative of a logic state of <NUM> (zero) at the node <NUM>. This is because a current path between the DC power supply <NUM>, the bias resistor <NUM>, one or more of sensing diodes <NUM>, <NUM>, <NUM>, and one or more of lower diodes <NUM>, <NUM>, <NUM> exists. When the AC power input is not received via the three phase power input <NUM>, all three lower diodes <NUM>, <NUM>, <NUM> are off and the node <NUM> is at a voltage potential equal to the voltage provided by the DC power supply <NUM>. This causes a logic state of <NUM> (one) at node <NUM>, because there is no current flow path from the DC power supply <NUM> through sensing diodes <NUM>, <NUM>, <NUM>.

When there is a substantial electrical load on a DC bus (between the positive DC voltage <NUM> and the negative DC base voltage <NUM>), the diodes <NUM>, <NUM>, 434conduct for about <NUM> electrical degrees each and in sequence. Thus, one of the three diodes <NUM>, <NUM>, 434is always conducting at a given time, and node <NUM> will therefore be held at a logical state of <NUM>. At partial loads or at very small loads on the DC bus, such as a load caused by a power input being connected while a unit is in a "standby mode," for example, the duration during which each diode <NUM>, <NUM>, 434conducts becomes smaller and smaller, but is never zero. Therefore, in a so-called "standby mode," the diodes <NUM>, <NUM>, 434may only conduct for about <NUM>-<NUM> electrical degrees. As a result, the node <NUM> stays at a logical state of <NUM> for most of the time, but periodically falls to a logical state of <NUM> for a very short time during each input power supply period. Thus, a mask time generator <NUM>, as described in greater detail hereafter, is required to monitor the node <NUM> and declare an input disconnected only when node <NUM> is persistently at a logical state of <NUM> for a sufficiently long period of time, which may be a period of time that is a multiple of the grid voltage period to ensure input phase loss detection has not been mis-detected.

If the node <NUM> has a logic state that is "low," then this indicates that one or more of the lower diodes <NUM>, <NUM>, <NUM> are conducting, and that therefore the rectifier system is connected to the three phase power input and receiving AC power. If the node <NUM> has a logic state that is "high," then this indicates that all of the lower diodes <NUM>, <NUM>, <NUM> are not conducting at that instant and, therefore, a possibility that the rectifier system is disconnected from the three phase power input <NUM> or from an AC power input.

The mask time generator <NUM> increases certainty that a "high" logic state at node <NUM> is due to disconnection of the AC power supply. The mask time generator has a generator output <NUM> configured to indicate a rectifier logic state. Specifically, the mask time generator <NUM> outputs a rectifier logic state that is "high" to indicate that the AC power input is disconnected when node <NUM> is in a "high" state for a predetermined period of time, referred to herein as a mask time. This assures, for instance, that a measured condition of the lower diodes <NUM>, <NUM>, <NUM> being disconnected from an AC input power (corresponding to a logic state of "high" at node <NUM>) persists for at least the mask time. In some embodiments, the mask time is between approximately one to five times the period of the AC power input. For example, the mask time may be from <NUM> to <NUM> for a <NUM> AC power input, and from <NUM> and <NUM> for a <NUM> AC input. The logic state, in the form of a signal, may be passed via the generator output <NUM> from mask time generator <NUM> to a frequency converter controller, which may be programmed to take necessary action depending on the signal. For example, the frequency converter controller may initiate a warning or alert through a user interface (UI) or alarm to indicate that AC power input disconnect has been detected. It will be readily appreciated that the frequency converter controller may be further configured to initiate a variety of tasks, outputs, or actions based on the logic state of the generator output <NUM>, such initiating redundancy features, initiating safety procedures to make a disconnected system more safe for maintenance or repair, communicating the generator output logic status with further local and/or remote systems, and the like. In some embodiments, the mask time generator <NUM> may be implemented as a microcontroller, using field programmable gate arrays (FPGAs), and/or using discrete analog and digital integrated circuits (ICs). In some embodiments, the mask time generator <NUM> is implemented inside a microcontroller already included in a frequency converters for carrying out basic frequency converter operations.

<FIG> illustrates a detection circuit <NUM> according to an embodiment of the present disclosure that is configured for more detailed input phase loss detection. Like the detection circuit <NUM> of <FIG>, the detection circuit <NUM> illustrated in <FIG> includes a three phase power input <NUM> with each of three phases <NUM>, <NUM>, <NUM> being connected to respective upper diodes <NUM>, <NUM>, <NUM> and lower diodes <NUM>, <NUM>, <NUM> of a rectifier diode circuit. The detection circuit <NUM> also similarly includes sensing diodes <NUM>, <NUM>, <NUM> arranged on each of the phases <NUM>, <NUM>, <NUM>. In the illustrated embodiment, however, each sensing diode <NUM>, <NUM>, <NUM> is associated with a separate node <NUM>, <NUM>, <NUM>, and thereby separate bias resistors <NUM>, <NUM>, <NUM> and separate mask time generators <NUM>, <NUM>, <NUM>. Specifically, a first sensing diode <NUM> associated with a first phase <NUM> is electrically connected to a first node <NUM>, which in turn is connected to a first bias resistor <NUM> and a first mask time generator <NUM> that outputs a first generator output <NUM>. A second sensing diode <NUM> associated with a second phase <NUM> is electrically connected to a second node <NUM>, which in turn is connected to a second bias resistor <NUM> and a second mask time generator <NUM> that outputs a second generator output <NUM>. A third sensing diode <NUM> associated with a third phase <NUM> is electrically connected to a third node <NUM>, which in turn is connected to a third bias resistor <NUM> and a third mask time generator <NUM> that outputs a third generator output <NUM>. Each of the bias resistors <NUM>, <NUM>, <NUM> are electrically connected to a DC power supply <NUM> that produces a base voltage <NUM>.

The detection circuit <NUM> operates in a similar manner to that of the detection circuit <NUM> of <FIG>, except that the logical state of each node <NUM>, <NUM>, <NUM> corresponding to a state of each lower diode <NUM>, <NUM>, <NUM>, respectively, can be individually detected by separate corresponding mask time generators <NUM>, <NUM>, <NUM>. Thus, the detection circuit <NUM> enables detection of individual failures or disconnects of each phase <NUM>, <NUM>, <NUM> as opposed to detection overall of all three phases <NUM>, <NUM>, <NUM> together. In some embodiments, the detection circuit <NUM> also enables detecting failure of a fuse for an individual phase based on detection of a failure within the individual phase. Because the logical sate of each node <NUM>, <NUM>, <NUM> represents the operational state of each respective lower diode <NUM>, <NUM>, <NUM>, each respective mask time generator <NUM>, <NUM>, <NUM> can also provide more detailed information to a frequency converter controller configured to receive each generator output <NUM>, <NUM>, <NUM>. The frequency converter controller may thus process or communicate more detailed status data to provide more detailed status reports, initiate more detailed diagnostic, redundancy, or safety measures, or the like. In some embodiments, the frequency converter controller may be configured to reduce output power and/or current capacity of an inverter when operating upon detecting via the detection circuit that the system is operating on a single-phase supply.

The detection circuit <NUM> may be more readily understood by the following hypothetical scenario that is illustrative only, and represents only one of numerous scenarios that may be encountered and properly handled by the detection circuit <NUM>. The three phase power input <NUM> may be properly connected to AC input power and each phase <NUM>, <NUM>, <NUM> may likewise be properly and normally functioning. However, the connection between diode (D4) <NUM> and the first phase <NUM> may be lost due to, for example, fatigue of a physical connection point. The detection circuit <NUM> would detect a logical state of "high" at node <NUM>, corresponding to a disconnection of the first phase <NUM>, and a logical state of "low" at nodes <NUM>, <NUM> indicating nominal performance of the second and third phases <NUM>, <NUM>. The first mask time generator <NUM> may output a logical state of "high" to first generator output <NUM> upon determining that the logical state of "high" at node <NUM> persists beyond a predetermined time period. The second and third mask time generators <NUM>, <NUM> would output logical states of "low" to each of the second and third generator outputs <NUM>, <NUM>, respectively. A frequency converter controller would then receive each of the first, second, and third generator outputs. Based on the "high" state of the first generator output <NUM>, the frequency converter controller may update a UI to indicate that the first phase <NUM> is disconnected or trigger a warning or alarm indicating disconnection of the first phase <NUM>. Depending on other conditions, the frequency converter controller may determine that initiating redundancy or safety measures may be necessary. For example, the frequency converter controller may disconnect the entire electrical system or sub-system from AC power to allow safe handling and repair of diodes or fuses connected to the first phase. In some embodiments, the frequency converter controller may also initiate communication or action based on a "low" state of the nominally operating phases, such as displaying a monitoring status to a UI.

By improving the level of detail of disconnect detection, the detection circuit <NUM> provides a variety of advantages over conventional systems. For example, maintenance or repair time and cost may be reduced, as workers are able to more quickly identify failure points and perform maintenance or repair work accordingly. Contingency operations that were previously not possible to implement in conventional systems may also be implemented by the frequency converter controller. For example, upon detecting that a single phase has failed or disconnected, the frequency converter controller may reduce the load on remaining operational phases to ensure that the power demands of the system do not cause a spike in power drawn by other parts of the rectifier, which may cause damage to the remaining parts of the rectifier.

<FIG> illustrates a detection circuit <NUM> according to an embodiment of the present disclosure. The detection circuit <NUM> operates in a similar manner to the detection circuit <NUM> of <FIG>, but sensing diodes <NUM>, <NUM>, <NUM> are instead arranged to prevent upstream current flow towards the three phase power input <NUM>. The sensing diodes <NUM>, <NUM>, <NUM> are electrically connected downstream via a node <NUM>, which is also electrically connected to a mask time generator <NUM> and a bias resistor <NUM>. A power supply (Vcc) <NUM> is also included downstream of both the bias resistor <NUM> and upper diodes <NUM>, <NUM>, <NUM>. The mask time generator <NUM> is configured to output a generator output <NUM>. The general logical states and operation of the detection circuit <NUM> are similar to that of the detection circuit <NUM> of <FIG>, but instead of comparing the voltage at node <NUM> to base voltage <NUM>, the voltage at node <NUM> is compared against positive voltage <NUM>, the voltage of power supply <NUM> is referenced against positive voltage <NUM>, and the detection circuit is configured to detect disconnection of upper diodes <NUM><NUM>, <NUM> instead of lower diodes <NUM>, <NUM>, <NUM>. For example, when one or more of the upper diodes <NUM>, <NUM>, <NUM> are properly conducting, the voltage at node <NUM> is at or near the positive voltage <NUM>, which is indicative of a logic state of <NUM> (zero) at the node <NUM>. The mask time generator <NUM> is likewise configured to determine, based on the logical state of the node <NUM>, whether there is a disconnection of the system from an AC power input and output a logical state via generator output <NUM> accordingly.

<FIG> illustrates a detection circuit <NUM> according to an embodiment of the present disclosure. The detection circuit <NUM> operates in a similar manner to the detection circuit <NUM> of <FIG>, but sensing diodes <NUM>, <NUM>, <NUM> are include instead and are arranged to prevent upstream current flow towards the three phase power input <NUM>. The first phase <NUM> is electrically connected with a first sensing diode <NUM>, which connects subsequently to first node <NUM> and then to first bias resistor <NUM>. The first node <NUM> is also connected to first mask time generator <NUM>, which is configured to output to a first generator output <NUM>. The second phase <NUM> is electrically connected with a second sensing diode <NUM>, which connects subsequently to second node <NUM> and then to second bias resistor <NUM>. The second node <NUM> is also connected to second mask time generator <NUM>, which is configured to output to a second generator output <NUM>. The third phase <NUM> is electrically connected with a third sensing diode <NUM>, which connects subsequently to third node <NUM> and then to third bias resistor <NUM>. The third node <NUM> is also connected to third mask time generator <NUM>, which is configured to output to a third generator output <NUM>. The first, second, and third bias resistors <NUM>, <NUM>, <NUM> are configured to electrically connect to a power supply <NUM>.

Instead of detection of the conduction state of individual lower diodes <NUM>, <NUM>, <NUM>, the detection circuit <NUM> is configured to detect the conduction state of individual upper diodes <NUM>, <NUM>, <NUM> and/or individual corresponding phases <NUM>, <NUM>, <NUM>. The logical states of each node <NUM>, <NUM>, <NUM> is similar to those of the detection circuit <NUM>, but the reference voltage for the power supply and for determining a "high" versus "low" state is the positive voltage <NUM>, not base voltage <NUM>.

It will be readily appreciated that the detection circuits of <FIG> and <FIG>, in addition to having structural, operational, and logical similarities to the detection circuits of <FIG> and <FIG>, respectively, also have many of the same features, advantages, and applications as those previously described herein.

<FIG> illustrates a detection and residual voltage discharge system <NUM> including a detection circuit <NUM>, frequency converter controller <NUM>, discharge resistor <NUM>, and switch <NUM>. The detection circuit <NUM> may include a detection circuit according to any detection circuit disclosed in the present disclosure, including the detection circuits illustrated in <FIG>. As described above with regard to <FIG> and <FIG>, prior art systems may include capacitors <NUM> (or other components which behave electrically like capacitors) across a DC bus. This is a potential safety hazard, as the capacitor <NUM> may carry a charge after the three phase power input <NUM> stops receiving AC power, or even after other conventional isolation measures are taken. In fact, in some cases full discharge of the capacitor <NUM>, and therefore the power conversion system, can take tens of seconds, and in some cases more than <NUM> seconds, subverting the expectation of an unwary worker and creating a substantial safety hazard.

In the illustrated embodiment, the detection circuit <NUM> outputs one or more status signals to the frequency converter controller <NUM>, which is configured to control the open/close state of switch <NUM>. Upon detection by the detection circuit <NUM> of a phase disconnection, the frequency converter controller <NUM> may, in addition to shutting down the power conversion system or otherwise isolating it from AC power, close switch <NUM>, thereby immediately discharging the capacitor <NUM> by providing an electrical connection between positive reference voltage <NUM> and negative reference voltage <NUM> via discharge resistor <NUM>. This is particularly advantageous as a safety feature, as automated and immediate discharge of remaining voltage in the power conversion system can be performed well before a worker performing maintenance, repair, or debugging can interact with the system after a shutdown.

Although descriptions above describe the discharge as "immediate," it will be readily understood that discharge is immediate in the sense that it is safe, but that discharge is never instantaneous in real-world applications. Accordingly, the discharge time can be determined approximately by obtaining the product of the resistance of the discharge resistor <NUM> and the capacitance of the capacitor <NUM>, and multiplying the product by four. The value of the resistance of the discharge resistor <NUM> and therefore be adjusted or selected based on a discharge time requirement set forth by a desired safety protocol or standard.

In some embodiments, the frequency converter controller <NUM> is optional, and detection circuit <NUM> may be configured to directly control the switch <NUM> rather than passing a signal to the frequency converter controller <NUM>. In some embodiments, the discharge resistor <NUM> is not a single resistor per se, but one or more components which electrically behave as a resistor.

In some embodiments, the detection and residual voltage discharge system <NUM> may be modified by eliminating the discharge resistor <NUM> and thereby utilizing a precharge resistor <NUM> or <NUM> to instead serve the function of discharge resistor <NUM> as described above. In such embodiments, it is important to ensure that before the switch <NUM> is turned on by the frequency converter controller <NUM>, a precharge contact <NUM> or <NUM> is opened. In this case, the discharge time would be the same as the charge time. The discharge resistor <NUM> cannot be omitted if the precharge scheme of alternate rectifier section <NUM> (Option <NUM>) from <FIG> is used.

<FIG> illustrates a power conversion system <NUM> including a shared DC bus connections <NUM>, <NUM> between a first frequency converter <NUM> and a second frequency converter <NUM>. Each of the first and second frequency converters <NUM>, <NUM> are configured to receive AC power via a three phase power input <NUM>. First fuses <NUM> are included, with one fuse on each phase of the three phase power input <NUM> to protect the first frequency converter <NUM>. Likewise, second fuses <NUM> are included, with one fuse on each phase of the three phase power input <NUM> to protect the second frequency converter <NUM>. In some embodiments, circuit breakers may be used in place of fuses <NUM>, <NUM>. In some embodiments, one or more AC reactors may be included between the three phase power input <NUM> and the inputs to each frequency converter. The first and second frequency converters <NUM>, <NUM> each include a rectifier section <NUM>, <NUM>, a three phase inverter <NUM>, <NUM>, and a DC bus capacitor <NUM>, <NUM> between a positive DC bus reference <NUM>, <NUM> and a negative DC bus reference <NUM>, <NUM>. The positive DC bus references <NUM>, <NUM> are connected via a first shared DC bus connection <NUM> and the negative DC bus references <NUM>, <NUM> are connected via a second shared DC bus connection <NUM>. Each frequency converter <NUM>, <NUM> is configured to supply output voltage to a separate downstream system, such as an AC motor.

Configurations such as those illustrated in <FIG> are sometimes referred to as "common AC-common DC" configurations. While only two frequency converters <NUM>, <NUM> are included in the illustrated power conversion system <NUM>, it will be readily appreciated that more than two frequency converters may be included by simply connecting additional rectifier sections via fuses to the three phase power input <NUM> and ensuring a common shared connection between positive and negative DC bus references. The main advantage of the illustrated configuration and similar configurations, is that regenerative energy from one system, such as an AC motor electrically connected to one of the frequency converters, can be consumed by other motors due to the shared DC bus connections. For example, regenerative energy produced by a motor connected to the three phase inverter <NUM> of the first frequency converter <NUM> may be transmitted via shared DC connections <NUM>, <NUM> to power the motor connected to the three phase inverter <NUM> of the second frequency converter <NUM>. However, when just one or more input phases to any frequency converter <NUM>, <NUM> is/are compromised, the remaining rectifier circuits of one or more of the frequency converters <NUM>, <NUM> may suffer an overload, because remaining operative rectifier sections will draw additional power to compensate. Furthermore, detection of which phase out of the shared phases has disconnected is not possible in conventional common AC-common DC systems. Thus, detection circuits such as those described in the present disclosure can be used in each frequency converter to ensure appropriate protections are carried out in the even that just one more of the input phases fails or is disconnected. In some embodiments, appropriate protections comprise displaying or otherwise communicating that a disconnection has occurred. In some embodiments, appropriate protections may comprise adjusting output power, such as reducing output power of a frequency converter that would otherwise be overloaded.

It will be readily understood that embodiments of the present disclosure may be applied, and their relative advantages realized, by implementing detection circuits in power conversion equipment using active front end or line converter front end circuits, rather than the passive rectifier circuits illustrated in the Figures or described in exemplary embodiments. Regardless of the AC-DC conversion topology used in a particular power conversion system, the disclosed embodiments provide detection circuits that help detect disconnections and thereby improve the functionality and safety of conventional power conversion systems. It will also be readily understood that while exemplary embodiments described herein primarily refer to a three phase power input, that the disclosed detection circuits may be readily modified to accommodate any multi-phase power input.

<FIG>, <FIG>, <FIG>, and <FIG> illustrate experimental data obtained by measuring the voltage across the DC bus of AC-DC converters under varying conditions. <FIG> and <FIG> illustrate DC bus voltage measurements of an AC-DC converter with no phase disconnections when an associated power converter is under a <NUM>% load and a <NUM>% load, respectively. Specifically, <FIG> illustrates a graph of DC bus voltage measurement <NUM> across the DC bus of an AC-DC converter. The power converter, of which the AC-DC converter is a part, is under a <NUM>% load. The DC bus voltage measurement is plotted as a voltage <NUM> in volts against time <NUM> in seconds. <FIG> likewise illustrates a similar graph of a DC bus voltage measurement <NUM> in a power converter that is under a <NUM>% load. <FIG> and <FIG> illustrate DC bus voltage measurements of an AC-DC converter in a similar manner to <FIG> and <FIG>, except that the AC-DC converter in which the DC bus voltage is measured has a disconnected input phase. <FIG> illustrates a graph of DC bus voltage measurement <NUM> across the DC bus of an AC-DC converter in which one input phase is disconnected. The associated power converter is under a <NUM>% load. <FIG> likewise illustrates a similar graph of a DC bus voltage measurement <NUM> in a power converter that is under a <NUM>% load. The voltage measurements illustrated in <FIG>, <FIG>, <FIG>, and <FIG> were obtained using a 400V, <NUM> AC power input.

In some conventional systems, the disconnection of a phase is determined by monitoring the voltage at the DC bus. As illustrated in <FIG>, the variation in voltage of a DC bus voltage when all input phases are connected and the system is under a <NUM>% load is in the range of approximately <NUM> volts. In comparison, the variation in voltage of a DC bus when there is a phase disconnection and the system is under <NUM>% load is in the range of approximately <NUM> voltage, as shown in <FIG>. Thus, a system that includes a controller configured to monitor DC bus voltage may determine that disconnection has occurred when the voltage variation increases beyond an acceptable threshold for a given load. However, an advantage of the detection circuits disclosed in the present disclosure is readily apparent when comparing the graphs of <FIG> and <FIG>. Whereas the difference in voltage variation between <FIG> and <FIG> is immediately apparent, the difference in voltage variation between the graphs in <FIG> and <FIG> is not significantly reduced. Thus, a controller may not be able to reliably discern when a disconnection has occurred (as in <FIG>) at certain loads, particularly at lower loads. Embodiments of the present disclosure eliminate the need to rely solely on such software-based monitoring methods and also eliminate the need for more expensive voltage sensors that may be required for reliably discerning between fully operational and disconnection-related DC bus voltages. Embodiments of the present disclosure thus provide a more reliable and cost-effective detection alternative. Furthermore, in a common AC-common DC configuration, because DC bus reference voltages are shared over shared connections, if one rectifier is partially or fully disconnected, the second or other rectifiers may interfere with DC bus measurements or maintain DC bus voltages without significant voltage ripple, but with increased current stress on remaining active rectifier diodes. Embodiments of the present disclosure thus also increase the reliability of frequency conversion systems by reducing the likelihood of current overload on active rectifier diodes when one or more phase inputs have become disconnected.

Embodiments of the present disclosure including a controller are understood to include a processor and a memory, the processor configured to carry out instructions stored on the memory. For example, in some embodiments, the controller can be a microcontroller configured to monitor the generator output signal of one or more mask time generators and, depending on the received signal from the generator output, further pass on a serial or digital output signal. In some embodiments, the controller is a larger processor with additional peripherals or connected subsystems. For example, the controller may be part of a personal computing device, tablet, or other smart device configured to communicate with a power converter either wirelessly or via a wired serial communication port. It will be readily understood that the controller can thus be configured or adjusted to perform various functions based on received generator output signals, allowing for customized redundancy, safety, or protective measures to be implemented in a frequency converter system.

Claim 1:
A detection circuit comprising:
a converter (<NUM>) configured to convert a multiphase alternating current (AC) input (<NUM>) into a direct current (DC) output;
a plurality of sensing diodes (<NUM>, <NUM>, <NUM>), each sensing diode being separately electrically connected to one phase (<NUM>, <NUM>, <NUM>) of the multiphase AC input;
at least one node (<NUM>) arranged downstream from the plurality of sensing diodes relative to the multiphase AC input;
a power source (<NUM>) configured to output a power source voltage to the at least one node and plurality of sensing diodes;
a bias resistor (<NUM>) connected between the power source (<NUM>) and the at least one node (<NUM>), and the power source is a DC power source which has one end connected to a direct current output terminal of the converter; and
a mask time generator (<NUM>) configured to determine a node voltage at the at least one node and determine whether the node voltage persists for a predetermined mask time period, which is a multiple of the grid voltage period, in order to detect a disconnection of an input phase.