Electrical system testing processes

Abstract

A testing process for an electrical system is described. The electrical system includes a power converter (2) and a direct current (DC) bus (12) having two or more DC bus terminals (14a, 14b, 14c) and at least one DC bus capacitor (16a, 16b). The testing process is a fully automated testing process in which a sequence of various diagnostic tests is executed on the electrical system, wherein each diagnostic test tests either the power converter (2) or the DC bus (12) to determine whether it is responding as expected or operating within normal parameters.

Description

Technology Field

[0001] The present invention relates to a testing process for an electrical system including a power converter, and in particular, to a testing process that does not require the use of any additional testing equipment or components.

[0002] Generally, the testing process includes a sequence of various diagnostic tests designed to test different components of an electrical system. Each diagnostic test can be performed as a series of individual steps. Data obtained during each diagnostic test can be used to check whether the electrical system is responding as expected. Additionally, the data may be recorded or stored so that it can be compared, for example, with data obtained during a future testing process to check for component failure or aging. Background Technology

[0003] Electrical system testing processes are known. However, such known testing processes are typically executed manually (e.g., by engineers) and take a long time to complete—sometimes several days. The testing process also requires the use of additional testing equipment or components to obtain the necessary data.

[0004] Consequently, there is a need for an improved testing process that can be executed more quickly by using only the components of the electrical system that will be used during normal operation.

[0005] The present invention provides an electric system, wherein the electric system is:

[0006] Power converter including the following:

[0007] Two or more direct current (DC) converter terminals, and

[0008] At least one converter leg connected to a DC converter terminal - each converter leg includes an alternating current (AC) terminal that defines the AC phase of a plurality of semiconductor switches and an electrical system and is connectable to each AC terminal of an electrical load - ;

[0009] DC bus including the following:

[0010] Two or more DC bus terminals - each DC bus terminal is connected to a respective DC converter terminal - and

[0011] At least one DC bus capacitor;

[0012] DC voltage supply unit for supplying DC voltage to a DC bus;

[0013] A control unit adapted to control a DC voltage supply and a plurality of semiconductor switches to keep a converter leg in an off state, or to keep it in one of a plurality of on states defining each voltage level of the converter leg;

[0014] At least one voltage sensor connected to a control unit for measuring DC bus voltage; and

[0015] It includes at least one current sensor connected to a control unit for measuring AC current in at least one AC phase of an electrical system;

[0016] The control unit is further adapted to execute a testing process as described below. The testing process is preferably a fully automated testing process (or "automated testing process") in which a sequence of various diagnostic tests is executed on the electrical system without any additional manual intervention. Each diagnostic test is designed to test different components of the electrical system (e.g., power converters, DC buses, sensors, etc.) to determine whether they are responding as expected or operating within normal parameters.

[0017] The testing process can be executed without the need for any additional testing equipment or components. Only components used during the normal operation of the electrical system are utilized. This includes sensors that provide voltage and current measurements to the control unit. If necessary, the electrical system is controlled to generate the electrical conditions required for diagnostic tests to be executed.

[0018] Power Converter:

[0019] A power converter is equipped with two or more DC converter terminals. In one arrangement, the power converter includes a positive DC converter terminal, a negative DC converter terminal, and optionally one or more intermediate DC converter terminals. For example, if the power converter has three voltage levels, the power converter will generally include one intermediate (or midpoint) DC converter terminal. If the power converter has five voltage levels, the power converter will generally include three intermediate DC converter terminals, and so on.

[0020] The power converter comprises at least one converter leg connected to a DC converter terminal. Each converter leg comprises a plurality of semiconductor switches (e.g., IGBTs) that can be arranged in any suitable topology, e.g., 2-level, multi-level neutral point piloted (NPP) or neutral point clamped (NPC), etc., as is known to those skilled in the art. Each converter leg comprises an AC terminal that defines the AC phase of the electrical system.

[0021] In practice, a power converter may be equipped with any appropriate number of converter legs, but three converter legs will be typical. In this arrangement, the power converter will have three AC terminals and therefore three AC phases. The converter legs are generally connected in parallel to the DC converter terminals.

[0022] Each AC terminal can be connected to each AC terminal of an electrical load. The electrical load may be, for example, an electric motor.

[0023] The AC terminal(s) of the power converter can be connected to an electrical load by a suitable switching device. When the switching device is open, the power converter is electrically disconnected from the electrical load. In most testing processes, the switching device is typically closed to ensure that the power converter is electrically connected to the electrical load.

[0024] DC Bus:

[0025] The DC bus has two or more DC bus terminals, each DC bus terminal being connected to a respective DC converter terminal. In one arrangement, the DC bus includes a positive DC bus terminal connected to a positive DC converter terminal and a negative DC bus terminal connected to a negative DC converter terminal. The positive DC bus terminal can define a positive voltage level, and the negative DC bus terminal can define a negative voltage level. The DC bus may optionally include one or more intermediate DC bus terminals. For example, if the power converter has three voltage levels, the DC bus will typically include one intermediate (or intermediate point) DC bus terminal connected to an intermediate (or intermediate point) DC converter terminal and capable of defining the intermediate (or zero) voltage level of the power converter. Voltage levels can be conveniently identified as +1, 0, and -1. If the power converter has five voltage levels, the DC bus will generally include three intermediate DC bus terminals defining the second positive voltage level, the midpoint (or zero) voltage level, and the second negative voltage level of the power converter, respectively, and so on. The voltage levels can be conveniently identified as +2, +1, 0, -1, and -2.

[0026] A DC bus includes at least one DC bus capacitor. A DC bus may include two or more DC bus capacitors connected in series. For example, if a DC bus includes a positive DC bus terminal, a negative DC bus terminal, and an intermediate (or intermediate point) DC bus terminal, the DC bus may include a first DC bus capacitor connected between the positive DC bus terminal and the intermediate DC bus terminal, and a second DC bus capacitor connected between the intermediate DC bus terminal and the negative DC bus terminal. Generally speaking, if a power converter has n voltage levels (where n = 2, 3, 5, etc.), the DC bus will have n DC bus terminals and (n-1) DC bus capacitors, each DC bus capacitor connected between adjacent pairs of DC bus terminals and defining each partial DC bus voltage.

[0027] The partial DC bus voltage across each end of the DC bus capacitor can be measured independently by each voltage sensor.

[0028] Unless otherwise noted, any reference to "DC bus voltage" in this document may be construed as any appropriate DC bus voltage. In particular, in an arrangement where the DC bus comprises two or more DC bus capacitors, the referred DC bus voltage may be a partial DC bus voltage across one or more of the DC bus capacitors, or a total DC bus voltage across the entire DC bus (i.e., across the entire DC bus capacitors connected in series). For example, if the DC bus comprises two DC bus capacitors, the "DC bus voltage" may be as follows:

[0029] - The partial DC bus voltage across the DC bus capacitor connected between the positive DC bus terminal and the intermediate (or midpoint) DC bus terminal, or

[0030] - The partial DC bus voltage across the DC bus capacitor connected between the intermediate (or midpoint) DC bus terminal and the negative DC bus terminal, or

[0031] - The total DC bus voltage across both terminals of the DC bus capacitors, i.e., the DC voltage between the positive and negative DC bus terminals.

[0032] DC voltage supply:

[0033] DC voltage can be supplied to the DC bus from any suitable DC voltage supply.

[0034] In one configuration, the DC voltage can be supplied using a pre-charge circuit. The pre-charge circuit is typically used as a low-voltage power supply to charge the DC bus capacitor before the power converter is enabled for normal operation—for example, in this case, the power converter operates as an inverter to supply power from the DC bus to the electrical load or as an active rectifier to supply power from the electrical load to the DC bus. Therefore, the pre-charge circuit is a common part of electrical systems and can be used for testing processes.

[0035] The precharge circuit can be directly connected to a DC bus. In this arrangement, the precharge circuit can also be connected to an AC power supply and includes a precharge rectifier. The DC voltage supply can be considered as a precharge circuit comprising an AC power supply and a precharge rectifier. The AC power supply may be, for example, a supply network or a utility grid.

[0036] A DC bus may be connected to a second power converter. The second power converter may have two or more DC converter terminals, each connected to a DC bus terminal, and at least one AC terminal connected to an AC power supply. The AC power supply may be, for example, a supply network or a utility grid. During normal operation of the electrical system, the second power converter may operate as a rectifier to supply power from the AC power supply to the DC bus. The second power converter may be, for example, a diode bridge or an active rectifier. If the second power converter can operate as an inverter, it may supply power from the DC bus to the AC power supply. A precharge circuit may be connected to the AC side of the second power converter (for example, to the AC side of the diode bridge). A DC voltage supply may be considered to be the AC power supply, the precharge circuit, and the second power converter. In other words, DC voltage is supplied to the DC bus through the second power converter, which forms part of the electrical system.

[0037] The precharge circuit may include a contactor that can be opened and closed by a control unit. In particular, the control unit may generate open and close commands to operate the contactor. The precharge circuit will supply DC voltage to the DC bus only when the precharge contactor is closed.

[0038] Control Unit:

[0039] Any suitable electronic control unit may be used. The control unit may include a plurality of coordinated control units or controllers, each of which is adapted for a specific control function, for example, to control the switching operation of a semiconductor switch of a power converter by generating a gate drive command, to open and close a specific contact by generating open and close commands, to receive and store sensor measurements, for data processing, to generate a fault signal, etc.

[0040] The control unit will receive data (e.g., measurements from voltage and current sensors and other related measurements or information) and process the data to generate fault signals. The data does not need to be processed in "real time." For some diagnostic tests, it may be desirable to record or store the data, and then perform data processing on the recorded or stored data at a later time, in a separate step, including during the testing process (e.g., between sequential diagnostic tests). Data derived as part of the data processing by the control unit may also be recorded or stored and used to generate fault signals. The data may also be transmitted for remote analysis and diagnosis.

[0041] Data derived from testing processes executed at different times may be compared and analyzed to determine, for example, whether any component of an electrical system is responding differently as a result of aging or internal failure. For example, each testing process may derive an "individual signature" for the electrical system using data containing predetermined measured or determined values. The measured or determined values ​​obtained during the testing process may include, for example, one or more of the following:

[0042] - Response time for closing the switching device between the AC terminal(s) of the power converter and the electrical load,

[0043] - Response time for closing cooling system contacts,

[0044] - Response time to close precharge contacts,

[0045] - Response time for opening and / or closing a switching device,

[0046] - DC bus charging time constant,

[0047] - DC bus internal time constant,

[0048] - Partial DC bus voltage imbalance,

[0049] - DC bus discharge time constant.

[0050] Data obtained during the testing process may include measured or determined values ​​that vary as a function of time, for example, including one or more of the following:

[0051] - DC voltage profile

[0052] - AC current profile, and

[0053] - AC voltage profile.

[0054] (For example, when an electrical system is commissioned) a first testing process may be executed to determine basic individual signatures, and these basic individual signatures may be compared with individual signatures obtained by executing the same testing process on the electrical system in the future (for example, during regular scheduled maintenance or following repairs). It is also possible to compare individual signatures obtained from a subsequent testing process—that is, a testing process executed after the first testing process. In one example, the response time for closing a precharge contact obtained during the testing process may be compared with the corresponding response time obtained during a previous testing process. Taking into account any appropriate tolerance value to allow for measurement errors, etc., if there is a difference between the two response times, this may indicate aging or failure of the precharge contact. In another example, the DC voltage profile obtained during the testing process may be compared with the corresponding DC voltage profile obtained during a previous testing process. For example, if there is a difference between the two profiles, this may indicate aging or failure of the DC bus. It will be easily understood that these examples are intended merely to illustrate the types of comparisons that can be performed, and that in practice, the same type of comparison between data obtained from two or more testing processes running at different times can be performed on any of the obtained data.

[0055] Individual signatures obtained during each testing process may be recorded or stored and may also be made available for remote analysis and diagnosis. Data derived from each testing process may be analyzed using any suitable mathematical or computational method known to a person skilled in the art for the general purposes set forth herein.

[0056] Each diagnostic test can be executed sequentially, and if a fault signal is generated, the testing process may be terminated early. In other arrangements, the entire testing process may be executed even if one or more fault signals are generated, except where the fault signal indicates that, for example, a power converter or another component of the electrical system may be damaged. Then, once the testing process is complete, the fault signal can be analyzed.

[0057] The control unit can control the switching operation of a plurality of semiconductor switches of a power converter by generating a gate drive command for each gate driver (i.e., switching each switch between an ON state and an OFF state). The gate drive command can be generated using a pulse width modulation (PWM) control strategy that uses a modulation index and a carrier waveform (e.g., a triangular waveform or a sawtooth waveform). During the testing process, the modulation index can be selected to generate an expected AC current in one or more AC phases of the electrical system.

[0058] Each converter leg can be turned off by a control unit. As used herein, the “off state” of a converter leg refers to a switching state in which the power converter is enabled but all semiconductor switches of the converter leg are turned off (i.e., turned off).

[0059] Each converter leg may be placed in one of a plurality of on states by a control unit. As used herein, the “on state” of a converter leg refers to a switching state in which the semiconductor switch of the converter leg is in an on or off state (i.e., turned on or turned off) to define each voltage level in the AC phase. It can be easily understood that each on state of the converter leg is determined by the individual switching state of the semiconductor switch. In one arrangement in which the power converter has three voltage levels and is operated as an inverter, for example, the first on state will define a positive voltage level (or +1) in the AC phase, the second on state will define a negative voltage level (or -1) in the AC phase, and the third on state will define a zero voltage level (or 0) in the AC phase. For example, during normal operation of the power converter as an inverter, each converter leg will be independently switched between various ON states by a control unit according to an appropriate control scheme (e.g., the PWM control scheme mentioned above) to generate a desired AC output voltage to be supplied to an electrical load. During the testing process, the converter leg may be placed in either an "OFF state" or an "ON state" (first diagnostic test) or operated using an appropriate control scheme (second and third diagnostic tests) as described in more detail below. In other diagnostic tests described below, the converter leg is typically placed in the "OFF state" and the power converter is not enabled.

[0060] The control unit can control the operation of one or more contacts (e.g., contacts of a precharge circuit or a cooling system) by generating respective open and close commands. The control unit can be connected to each contact by any suitable wired or wireless connection. The control unit can control the operation of a switching device by generating respective open and close commands. The control unit can be connected to the switching device by any suitable wired or wireless connection.

[0061] The control unit can control the operation of the optional chopper circuit - see below.

[0062] Sensor:

[0063] Any suitable voltage and current sensors may be used. The voltage and current sensors are connected to the control unit and provide voltage and current measurements, respectively, for use in diagnostic tests. The connection may be appropriately wired or wireless, and the measurements are transmitted to the control unit using any suitable protocol.

[0064] The electrical system may further include at least one voltage sensor connected to a control unit for measuring one or more AC voltages of the electrical system, for example, an AC voltage in at least one AC phase (phase voltage) or an AC voltage between at least two AC phases (line voltage).

[0065] Chopper Circuit:

[0066] The electrical system may optionally include a chopper circuit connected in parallel with the DC bus, the chopper circuit including at least one semiconductor switch connected in series with a resistor to dissipate excess electrical energy from the DC bus as heat.

[0067] Each semiconductor switch (e.g., an IGBT) of the chopper circuit can be controlled by a control unit so that the chopper circuit short-circuits and discharges each DC bus capacitor in a manner known to a skilled person. In particular, each semiconductor switch can be controlled by a control unit to switch between an ON state and an OFF state according to an appropriate control strategy. A gate drive command for each semiconductor switch can be generated using a PWM control strategy that uses a modulation index and a carrier waveform (e.g., a triangular waveform or a sawtooth waveform). During normal operation of the chopper circuit, the modulation index can switch each semiconductor switch between an ON state and an OFF state to create an intermittent short-circuit path between one or more pairs of DC bus terminals. The short-circuit path includes a resistor. The chopper circuit dissipates excess electrical energy in a safe manner that prevents overheating. The chopper circuit can also be operated to discharge the DC bus capacitor, whereby the stored energy is dissipated in the resistor. During the testing process, the modulation index may be selected to generate an expected DC voltage after a period of time when discharging the DC bus, or to discharge the DC bus as quickly as possible by, for example, creating a continuous short-circuit path between one or more pairs of DC bus terminals.

[0068] Testing Process:

[0069] The present invention provides a testing process for an electrical system, wherein the electrical system is:

[0070] Power Converter - The power converter is:

[0071] Two or more DC converter terminals, and

[0072] It includes at least one converter leg connected to a DC converter terminal—each converter leg defines the AC phase of a plurality of semiconductor switches and an electrical system and includes an AC terminal connectable to each AC terminal of an electrical load—and

[0073] A plurality of semiconductor switches can be controlled to keep the converter leg in an off state or to be in one of a plurality of on states defining the respective voltage level of the converter leg - ; and

[0074] DC Bus - DC Bus is:

[0075] Two or more DC bus terminals - each DC bus terminal is connected to a respective DC converter terminal - and

[0076] Includes at least one DC bus capacitor -

[0077] Includes, but;

[0078] The testing process is a fully automated testing process in which a sequence of various diagnostic tests is executed on an electrical system, and each diagnostic test tests either the power converter or the DC bus to determine whether it is responding as expected or operating within normal parameters.

[0079] The testing process is preferably:

[0080] Each converter leg is in an off state or is in the same on state among a plurality of on states, and includes one or more first diagnostic tests, wherein each first diagnostic test includes the following:

[0081] Measuring the DC bus voltage while the DC voltage is supplied to the DC bus for a period of time, and generating a fault signal if the measured DC bus voltage does not exceed the first expected DC bus voltage.

[0082] The testing process is preferably:

[0083] A second diagnostic test is further included, wherein the second diagnostic test includes the following steps:

[0084] Step of measuring DC bus voltage while DC voltage is supplied to the DC bus,

[0085] A step of terminating the supply of DC voltage when the measured DC bus voltage exceeds the first DC bus voltage, and allowing the DC bus voltage to gradually decrease toward the first DC bus voltage,

[0086] When the measured DC bus voltage is substantially the same as the first DC bus voltage, the step of controlling the power converter to provide the expected AC current in at least one AC phase of the electrical system,

[0087] A step of measuring AC current in at least one AC phase of an electrical system, and

[0088] A step of generating a fault signal if the measured AC current is not within the range defined by the corresponding expected AC current plus or minus tolerance value.

[0089] Diagnostic Test No. 0:

[0090] In preparation for the execution of the first diagnostic test, the switching device may be closed to connect the power converter to the electrical load, and any cooling system may be turned on so that the electrical system is properly cooled during the execution of the testing process. The response time of the switching device may be checked as a zero diagnostic test (i.e., a diagnostic test performed prior to the first diagnostic test). In particular, it is possible to measure the time between when a closing signal is initiated by the control unit and when a feedback signal confirming that the switching device is closed is received. If the measured time is greater than the expected response time, a fault signal is generated. The response time for closing the switching device may be recorded or stored. If the cooling system includes one or more contacts controlled by the control unit (e.g., for switching on a pump or similar component), the response time of each contact may also be checked during the zero diagnostic test. In particular, it is possible to measure the time between when a closing signal is initiated by the control unit and when a feedback signal confirming that the contact is closed is received. If the measured time is greater than the expected response time, a fault signal is generated. The response time of the cooling system contact closure can be recorded or stored.

[0091] The zeroth diagnostic test generally corresponds to Step 1 of the exemplary testing process described below.

[0092] Diagnostic Test 1:

[0093] The purpose of the first diagnostic test is to check whether the DC bus is responding as expected.

[0094] The first diagnostic test generally corresponds to steps 2-5 of the exemplary testing process described below.

[0095] During each first diagnostic test, each converter leg of the power converter is controlled to be in an off state or to be in the same on state among multiple on states. For example, if the power converter includes three converter legs, all three converter legs are controlled to be in the same state, i.e., off state or the same on state.

[0096] Preferably, a plurality of first diagnostic tests are executed sequentially with converter legs in different states for each first diagnostic test. For example, if each converter leg of a power converter can be placed in three ON states—in this case, each ON state defines positive, negative, and zero voltage levels in the AC phase—a first diagnostic test may be executed with each converter leg in the OFF state, another first diagnostic test may be executed with each converter leg in the first ON state, another first diagnostic test may be executed with each converter leg in the second ON state, and another first diagnostic test may be executed with each converter leg in the third ON state. There is no fixed sequence for the various states, and it is possible for the control unit to place each converter leg in some or all of the available states in any appropriate sequence or order.

[0097] During each first diagnostic test, a DC voltage is supplied to the DC bus for a period of time to increase the DC bus voltage. As described above, the DC bus voltage may be a partial DC bus voltage across one or more ends of the DC bus capacitor, or a total DC bus voltage across the entire DC bus (i.e., across the entire end of the series-connected DC bus capacitor).

[0098] The duration of time during which the DC voltage is supplied to the DC bus can be, for example, about 100-200 ms. The duration of time must be long enough to allow the DC bus voltage to reach the expected DC bus voltage when the DC bus is operating normally.

[0099] A DC voltage can be supplied by closing the contact of the precharge circuit for a period of time. The response time of the precharge contact can be checked in at least one of the first diagnostic tests. In particular, it is possible to measure the time between when a closing signal is initiated by the control unit and when a feedback signal confirming that the contact is closed is received. If the measured time is greater than the expected response time, a fault signal is generated. The response time of the precharge contact can be recorded or stored.

[0100] If the measured DC bus voltage does not exceed the expected DC bus voltage during a period of time (which may be equal to or shorter than the period during which the DC voltage is supplied to the DC bus), a fault signal is generated. As described above, the measured DC bus voltage may be a partial DC bus voltage across one or more ends of the DC bus capacitor, or the total voltage across the entire DC bus (i.e., across the entire end of the series-connected DC bus capacitor). In one arrangement, the expected DC bus voltage may be based on the measurement of the DC bus voltage at the start of each first diagnostic test ("initial DC bus voltage"). For example, if the measured DC bus voltage does not increase by a certain percentage, for example, at least about 2-3%, compared to the initial DC bus voltage within a period of time, for example, about 15-25 ms, a fault signal may be generated. In another arrangement, the expected DC bus voltage may be a threshold that can be optionally determined by reference to the rated DC voltage. For example, if the measured DC bus voltage does not exceed a certain percentage of the rated DC voltage within a period of time, a fault signal may be generated. These parameters can be selected by referring to the level of stored energy in the DC bus.

[0101] During each first diagnostic test, if the AC output current of the power converter exceeds a threshold, for example, about 2% of the rated converter current, a fault signal may be generated.

[0102] At the end of each first diagnostic test, after the contact of the precharge circuit is opened, the DC bus voltage will gradually decrease. The testing process may be switched to another first diagnostic test or a second diagnostic test in which the converter leg is in a different state if the measured DC bus voltage drops below a threshold that can be optionally determined by reference to the rated DC voltage. For example, the testing process may be switched to another first diagnostic test or a second diagnostic test if the measured DC bus voltage drops below a certain percentage of the rated DC voltage, for example, less than about 1.5-2.5% of the rated DC voltage.

[0103] 2nd Diagnostic Test:

[0104] The purpose of the second diagnostic test is to check whether the power converter and sensor are responding as expected.

[0105] The second diagnostic test generally corresponds to steps 6-13 of the exemplary testing process described below.

[0106] When switching to the second diagnostic test, the DC bus voltage may be below a threshold that can be determined optionally by referring to the rated DC voltage. For example, the DC bus voltage may be less than a certain percentage of the rated DC voltage, for example, less than about 1.5-2.5% of the rated DC voltage.

[0107] At the start of the second diagnostic test, DC voltage is supplied to the DC bus to increase the DC bus voltage.

[0108] DC voltage can be supplied by closing the contacts in the precharge circuit.

[0109] In the second diagnostic test, the DC voltage is not supplied to the DC bus for a period of time. Instead, the DC voltage is supplied until the measured DC bus voltage exceeds the first DC bus voltage. The first DC bus voltage may be a threshold that can be optionally determined by reference to the rated DC voltage. For example, the first DC bus voltage may be about 5-15% of the rated DC voltage. The first DC bus voltage must be high enough to allow proper switching operation of the semiconductor switch, but low enough so that the power converter is not damaged if one or more of the semiconductor switches fail during the second diagnostic test.

[0110] If the measured DC bus voltage does not exceed the expected DC bus voltage during a period of time, a fault signal is generated. In one configuration, the expected DC bus voltage may be based on the measurement of the DC bus voltage at the start of the second diagnostic test when the precharge contact is closed ("initial DC bus voltage"). For example, if the measured DC bus voltage does not increase by a certain percentage, for example, at least about 2-3%, compared to the initial DC bus voltage within a period of time, for example, about 15-25 ms, a fault signal may be generated. In another configuration, the expected DC bus voltage may be a threshold that can be optionally determined by reference to the rated DC voltage. For example, if the measured DC bus voltage does not exceed a certain percentage of the rated DC voltage within a period of time, a fault signal may be generated. These parameters may be selected by reference to the level of stored energy in the DC bus.

[0111] The supply of DC voltage is terminated, for example, by opening the contact of the precharge circuit when the measured DC bus voltage exceeds the first DC bus voltage.

[0112] After the contact of the precharge circuit is opened, the DC bus voltage will gradually decrease toward the first DC bus voltage.

[0113] When the measured DC bus voltage is substantially the same as the first DC bus voltage, the power converter is controlled to provide an expected AC current in at least one of the AC phases of the electrical system. The expected AC current may be selected to be a percentage of the rated converter current, for example, about 20-30% of the rated converter current. If the selected expected AC current is too low, the measurement of the AC current may not be reliable; however, the expected AC current must not be selected too high so that the power converter is not damaged in the event of a failure in one or more semiconductor switches during the second diagnostic test. The power converter is also optionally controlled to provide an expected AC voltage in at least one of the AC phases (phase voltage) or an expected AC voltage between two AC phases (line voltage).

[0114] The AC current in at least one of the AC phases of the electrical system is measured by a current sensor. If the measured AC current is not within a range defined by an expected AC current plus or minus tolerance value, for example, within ±50% of the expected AC current, a fault signal is generated. This tolerance value must be selected to ensure reliable detection of the current sensor fault.

[0115] The power converter can be controlled to provide the expected AC current in each AC phase of the electrical system. The AC current in each AC phase is measured by a respective current sensor, and if any of the measured AC currents is not within a range defined by a plus or minus tolerance value of the corresponding expected AC current (i.e., the expected AC current for the same AC phase), for example, within ±50% of the expected AC current, a fault signal is generated.

[0116] At least one AC voltage can be measured by a voltage sensor. At least one AC voltage may be a phase voltage or a line voltage. If the measured AC voltage is not within a range defined by an expected AC voltage plus or minus tolerance value, for example, ±20% of the expected AC voltage, a fault signal is optionally generated. This tolerance value should be selected to ensure reliable detection of voltage sensor faults.

[0117] If the measured DC bus voltage drops below the expected DC bus voltage while the power converter is being controlled, a fault signal may be generated. In one configuration, the expected DC bus voltage may be based on the measurement of the DC bus voltage at the start of power converter control ("initial DC bus voltage"). For example, if the measured DC bus voltage decreases by a certain percentage, for example, about 1.5-2.5%, compared to the initial DC bus voltage, a fault signal may be generated. In another configuration, the expected DC bus voltage may be a threshold that can be optionally determined by reference to the rated DC voltage. For example, if the measured DC bus voltage drops below a certain percentage of the rated DC voltage, a fault signal may be generated. These parameters may be selected to be high enough to manage normal DC bus discharge during the time the power converter is being controlled.

[0118] A fault signal may be generated if, outside of the time when the power converter is being controlled, the AC output current of the power converter exceeds a threshold, for example, about 2% of the rated converter current. For the protection of the power converter, when the power converter is being controlled, a fault signal may be generated if the AC output current of the power converter exceeds a maximum threshold, for example, about 30-35% of the rated converter current—and it is desirable for the testing process to be terminated.

[0119] The semiconductor switches of each converter leg of a power converter can be controlled using a suitable control scheme having a modulation index that generates a sequence of positive and negative current pulses in each AC phase. Each current pulse can be applied over two consecutive time periods of the control scheme, where the AC current is measured at the end of the first time period and at the end of the second time period (when the expected AC voltage in each AC phase is typically zero). In an array of electrical systems having three AC phases, positive current pulses can be applied to one or more AC phases, and negative current pulses can be applied to one or more AC phases simultaneously. This can be repeated for various combinations of positive and negative current pulses. For example, the modulation index can generate a sequence of various current pulse combinations including the following:

[0120] - Positive current pulse in the first AC phase and negative current pulse in the second and third AC phases,

[0121] - Positive current pulse in the second AC phase and negative current pulse in the first and third AC phases,

[0122] - Positive current pulse in the third AC phase and negative current pulse in the first and second AC phases,

[0123] - Negative current pulse in the first AC phase and positive current pulse in the second and third AC phases,

[0124] - Negative current pulse in the second AC phase and positive current pulse in the first and third AC phases,

[0125] - Negative current pulse in the third AC phase and positive current pulse in the first and second AC phases.

[0126] It will be readily recognized that there is no fixed sequence for current pulse combinations, and that it is possible for a control unit to control the power converter to generate some or all of the available current pulse combinations in any appropriate sequence or order.

[0127] Third diagnostic test:

[0128] The testing process may include a third diagnostic test comprising the following steps:

[0129] Step of measuring DC bus voltage while DC voltage is supplied to the DC bus,

[0130] A step of terminating the supply of DC voltage when the measured DC bus voltage exceeds the second DC bus voltage, and allowing the DC bus voltage to gradually decrease toward the second DC bus voltage—where the second DC bus voltage is greater than the first DC bus voltage.

[0131] When the measured DC bus voltage is substantially the same as the second DC bus voltage, the step of controlling the power converter to provide the expected AC current in at least one AC phase of the electrical system,

[0132] A step of measuring AC current in at least one AC phase of an electrical system, and

[0133] A step of generating a fault signal if the measured AC current is not within the range defined by the corresponding expected AC current plus or minus tolerance value.

[0134] The third diagnostic test is preferably performed after the second diagnostic test. However, one or more diagnostic tests may be performed between the second and third diagnostic tests—see below.

[0135] The third diagnostic test generally corresponds to steps 17-24 of the exemplary testing process described below.

[0136] The purpose of the third diagnostic test is to check whether the power converter and sensors are responding as expected. The third diagnostic test is similar to the second diagnostic test, but uses a much higher DC bus voltage, for example, and is run at about 90% of the rated DC voltage rather than about 10%.

[0137] When switching to the third diagnostic test, the DC bus voltage may be below a threshold that can be optionally determined by reference to the rated DC voltage. For example, the DC bus voltage may be less than a certain percentage of the rated DC voltage, for example, less than about 1.5-2.5% of the rated DC voltage. In one configuration, the DC bus voltage is reduced below the threshold by operating an optional chopper circuit—see below.

[0138] At the start of the third diagnostic test, DC voltage is supplied to the DC bus to increase the DC bus voltage.

[0139] DC voltage can be supplied by closing the contacts in the precharge circuit.

[0140] The DC voltage is supplied until the measured DC bus voltage exceeds the second DC bus voltage. The second DC bus voltage may be a threshold that can be optionally determined by reference to the rated DC voltage. For example, the second DC bus voltage may be approximately 85-95% of the rated DC voltage. The second DC bus voltage must be close to the rated DC voltage to indicate normal operation of the electrical system.

[0141] If the measured DC bus voltage does not exceed one or more expected DC bus voltages during each period of time, a fault signal is generated. In one configuration, the expected DC bus voltage may be based on the measurement of the DC bus voltage at the start of the third diagnostic test when the precharge contact is closed ("Initial DC bus voltage"). In another configuration, the expected DC bus voltage may be a threshold that can be optionally determined by referring to the rated DC voltage. For example, a fault signal may be generated if the measured DC bus voltage does not meet the following conditions:

[0142] - Increased by at least about 2-3% during the first period of time (e.g., about 10-30 ms) compared to the initial DC bus voltage, or

[0143] - Exceeding the first threshold (e.g., about 5-15% of the rated DC voltage) within a second period of time, e.g., about 0.5-1.5 seconds, or

[0144] - A third period of time, for example, when the second threshold (e.g., about 85-95% of the rated DC voltage) is exceeded within about 5-15 seconds. In this case, the period of time is calculated from when the DC voltage is supplied to the DC bus, i.e., from when the contact of the precharge circuit is closed. These parameters can be selected by referring to the level of stored energy in the DC bus.

[0145] While a DC voltage is being supplied to the DC bus, a DC bus charging time constant for the DC bus can be determined. For example, the first and second DC bus voltages can be measured at different times, and the time constant is the ratio of the first and second DC bus voltages. It can be calculated based on the fact that it is identical to, where t is the time between measurements, and is the DC bus charging time constant. The first DC bus voltage can be measured about 0.5-1.5 seconds after the DC bus voltage is first supplied to the DC bus, and the second DC bus voltage can be measured about 4-6 seconds after the second DC bus voltage.

[0146] The supply of DC voltage is terminated, for example, by opening the contact of the precharge circuit when the measured DC bus voltage exceeds the second DC bus voltage.

[0147] After the contact of the precharge circuit is opened, the DC bus voltage will gradually decrease toward the second DC bus voltage.

[0148] If the DC bus includes two or more DC bus capacitors, any imbalance in the partial DC bus voltage can be determined after the contacts of the precharge circuit are opened. For example, the partial DC bus voltage across each of the DC bus capacitors can be measured, and the difference between the partial DC bus voltages can be calculated. The difference between the partial DC bus voltages can be recorded or stored.

[0149] If the measured DC bus voltage is substantially the same as the second DC bus voltage, the power converter is controlled to provide the expected AC current in at least one of the AC phases of the electrical system. The expected AC current may be selected to be a percentage of the rated converter current, for example, about 20-30% of the rated converter current. If the selected expected AC current is too low, the measurement of the AC current may not be reliable; however, the expected AC current must not be selected too high so that the power converter is not damaged in the event of a failure in one or more semiconductor switches during the second diagnostic test. The power converter is also optionally controlled to provide the expected AC voltage in at least one of the AC phases (phase voltage) or the expected AC voltage between two AC phases (line voltage).

[0150] The AC current in at least one of the AC phases of the electrical system is measured by a current sensor. If the measured AC current is not within a range defined by an expected AC current plus or minus tolerance value, for example, within ±50% of the expected AC current, a fault signal is generated. This tolerance value must be selected to ensure reliable detection of the current sensor fault.

[0151] The power converter can be controlled to provide the expected AC current in each AC phase of the electrical system. The AC current in each AC phase is measured by a respective current sensor, and if any of the measured AC currents is not within a range defined by a plus or minus tolerance value of the corresponding expected AC current (i.e., the expected AC current for the same AC phase), for example, within ±50% of the expected AC current, a fault signal is generated.

[0152] At least one AC voltage can be measured by a voltage sensor. At least one AC voltage may be a phase voltage or a line voltage. If the measured AC voltage is not within a range defined by an expected AC voltage plus or minus tolerance value, for example, ±20% of the expected AC voltage, a fault signal is optionally generated. This tolerance value should be selected to ensure reliable detection of voltage sensor faults.

[0153] If the measured DC bus voltage drops below the expected DC bus voltage while the power converter is being controlled, a fault signal may be generated. In one configuration, the expected DC bus voltage may be based on the measurement of the DC bus voltage at the start of power converter control ("initial DC bus voltage"). For example, if the measured DC bus voltage decreases by a certain percentage, for example, about 1.5-2.5%, compared to the initial DC bus voltage, a fault signal may be generated. In another configuration, the expected DC bus voltage may be a threshold that can be optionally determined by reference to the rated DC voltage. For example, if the measured DC bus voltage drops below a certain percentage of the rated DC voltage, a fault signal may be generated. These parameters may be selected to be high enough to manage normal DC bus discharge during the time the power converter is being controlled.

[0154] A fault signal may be generated if, outside of the time when the power converter is being controlled, the AC output current of the power converter exceeds a threshold, for example, about 2% of the rated converter current. For the protection of the power converter, when the power converter is being controlled, a fault signal may be generated if the AC output current of the power converter exceeds a maximum threshold, for example, about 30-35% of the rated converter current—and it is desirable for the testing process to be terminated.

[0155] If a DC bus includes two or more DC bus capacitors, DC bus voltage imbalance can be measured. This can be performed, for example, after the DC voltage supply has been terminated and before the power converter is controlled. Each partial DC bus voltage can be measured, and the measurements can be compared to verify whether the partial DC bus voltages are sufficiently balanced. A positive or negative imbalance may indicate that a particular DC bus capacitor is aging faster than any of the other DC bus capacitors.

[0156] An internal DC bus time constant for the DC bus can be determined. For example, the first and second DC bus voltages can be measured at different times, and the time constant is the ratio of the first and second DC bus voltages. It can be calculated based on the fact that it is identical to, where t is the time between measurements, and is the internal time constant of the DC bus. The first DC bus voltage can be measured approximately at the time when the power converter stops controlling, and the second DC bus voltage can be measured after about 20-40 seconds.

[0157] The semiconductor switches of each converter leg of the power converter can be controlled using an appropriate control scheme having a modulation index that generates a sequence of positive and negative current pulses in each AC phase—see the description above for the second diagnostic test. However, it will be readily understood that the modulation index used during the third diagnostic test will be different due to the higher DC bus voltage.

[0158] 4th Diagnostic Test:

[0159] If the electrical system includes an optional chopper circuit, the testing process may include a fourth diagnostic test executed between the second and third diagnostic stages, that is, before the DC bus voltage is significantly increased to the second DC bus voltage.

[0160] The purpose of the fourth diagnostic test is to check whether the optional chopper circuit is responding as expected.

[0161] The fourth diagnostic test generally corresponds to steps 14-16 of the exemplary testing process described below.

[0162] The fourth diagnostic test includes the following steps:

[0163] A step of operating a chopper circuit for a period of time to provide an expected DC bus voltage,

[0164] After a period of time, a step of measuring the DC bus voltage, and

[0165] A step of generating a fault signal if the measured DC bus voltage is not within the range defined by the expected DC bus voltage plus or minus tolerance value, or if the DC bus voltage is not reduced by a predetermined percentage compared to the initial DC bus voltage.

[0166] In an array in which a DC bus comprises two or more series-connected DC bus capacitors, the chopper circuit may be operated to discharge each DC bus capacitor separately while the stored energy is dissipated in the resistor. Accordingly, the testing process may include one or more fourth diagnostic tests, wherein for each fourth diagnostic test, the chopper circuit is operated to discharge each DC bus capacitor. For example, if the DC bus includes a first DC bus capacitor connected between a positive DC bus terminal and an intermediate DC bus terminal, and a second DC bus capacitor connected between an intermediate DC bus terminal and a negative DC bus terminal, a fourth diagnostic test may be performed by operating a chopper circuit to create an intermittent short-circuit path between a positive DC bus terminal and an intermediate DC terminal to discharge the first DC bus capacitor, and then measuring the partial DC bus voltage across the first DC bus capacitor, and another fourth diagnostic test may be performed by operating a chopper circuit to create an intermittent short-circuit path between a negative DC bus terminal and an intermediate DC terminal to discharge the second DC bus capacitor, and then measuring the partial DC bus voltage across the second DC bus capacitor.

[0167] At least one semiconductor switch of the chopper circuit can be switched between an ON state and an OFF state according to an appropriate control strategy, for example, a PWM control strategy using a modulation index selected to result in an expected value of the DC bus voltage. The control unit can control the switching operation of at least one semiconductor switch by generating a gate drive command for each gate driver based on the control strategy (i.e., switching each switch between an ON state and an OFF state). The modulation index can be calculated based on parameters such as a desired reduction in the DC bus voltage, the total DC bus voltage, the capacitance of the DC bus capacitor, the resistance of the chopper circuit resistor, the minimum ON-time of the semiconductor switch, the frequency of the carrier waveform, etc.

[0168] The expected value of the DC bus voltage may be based on the measurement of the DC bus voltage at the start of the fourth diagnostic test ("Initial DC Bus Voltage"). If the measured DC bus voltage ("End DC Bus Voltage") is not within the range defined by the expected DC voltage plus or minus tolerance value, for example, within ±1% of the expected DC bus voltage, a fault signal may be generated.

[0169] When the DC bus voltage is not reduced by a predetermined percentage, for example, about 2-4%, compared to the initial DC bus voltage as a result of operating the chopper circuit for a predetermined period of time, a fault signal may be generated.

[0170] 5th Diagnostic Test:

[0171] The testing process may include a fifth diagnostic test executed after the third diagnostic test.

[0172] The fifth diagnostic test generally corresponds to steps 25-26 of the exemplary testing process described below.

[0173] After the third diagnostic test is completed, the switching device between the AC terminal(s) of the power converter and the electrical load is preferably opened to electrically disconnect the power converter from the electrical load. The response time of the switching device can be checked. In particular, it is possible to measure the time between when the open signal is initiated by the control unit and when the feedback signal confirms that the switching device is open. If the measured time is longer than the expected response time, a fault signal is generated. The response time of the switching device opening can be recorded or stored.

[0174] The fifth diagnostic test includes the following steps:

[0175] The step of operating a chopper circuit to discharge DC bus capacitor(s) until the DC bus voltage becomes less than the third DC bus voltage, and

[0176] A step of generating a fault signal if the measured DC bus voltage does not drop below the expected DC bus voltage during a period of time.

[0177] The purpose of the fifth diagnostic test is to check whether the optional chopper circuit is responding as expected.

[0178] During the fifth diagnostic test, it is desirable for the chopper circuit to operate to discharge the DC bus capacitor(s) as quickly as possible. The third DC bus voltage may be a predetermined percentage of the rated DC voltage, for example, about 1.5-2.5% of the rated DC voltage.

[0179] In one configuration, the expected DC bus voltage may be based on the measurement of the DC bus voltage at the start of the fifth diagnostic test when the chopper circuit is operated ("initial DC bus voltage"). For example, if the measured DC bus voltage does not decrease by a certain percentage compared to the initial DC bus voltage within a period of time, a fault signal may be generated. In another configuration, the expected DC bus voltage may be a threshold that can be optionally determined by reference to the rated DC voltage. For example, if the measured DC bus voltage drops below a certain percentage of the rated DC voltage (e.g., about 3-7% of the rated DC voltage) within a period of time, e.g., about 0.5-1.5 seconds, a fault signal may be generated.

[0180] A DC bus discharge time constant for a DC bus can be determined. For example, the first and second DC bus voltages can be measured at different times, and the time constant is the ratio of the first and second DC bus voltages. It can be calculated based on the fact that it is identical to, where t is the time between measurements, and is the internal time constant of the DC bus. The first DC bus voltage can be measured when the DC bus voltage reaches about 50-70% of the rated DC voltage, and the second DC bus voltage can be measured when the DC bus voltage reaches about 5-15% of the rated DC voltage.

[0181] After the fifth diagnostic test is completed, any cooling system may be turned off. This generally corresponds to step 27 of the exemplary testing process described below. Brief explanation of the drawing

[0182] FIG. 1 is a schematic diagram of an electrical system according to the present invention; FIG. 2 is a flowchart illustrating individual steps of a testing process according to the present invention; FIG. 3 is a diagram illustrating various parameters and fault conditions for individual steps of the testing process; FIG. 4 is a diagram illustrating a modulation index for controlling an inverter; and Figure 5 is a diagram illustrating a modulation index for controlling a chopper circuit. Specific details for implementing the invention

[0183] Referring to FIG. 1, an electric system according to the present invention includes an inverter (2). The inverter (2) includes three direct current (DC) converter terminals (4a, 4b, and 4c). Three converter legs (not shown) are connected to the DC converter terminals (4a, 4b, and 4c). Each converter leg (not shown) includes a plurality of semiconductor switches (e.g., IGBTs) arranged with a suitable topology, such as a 3-level NPP and an alternating current (AC) terminal defining the AC phase of the electric system. In the following description, the AC phases are identified by the letters U, V, and W, respectively. Accordingly, the inverter (2) includes three AC terminals (6) connected to an electric motor (8) via a switching device (10).

[0184] DC converter terminals (4a, 4b, and 4c) are connected to a DC bus (12). The DC bus (12) includes a positive DC bus terminal (14a), a negative DC bus terminal (14b), and an intermediate or intermediate point DC bus terminal (14c). A first DC bus capacitor (16a) is connected between the positive DC bus terminal and the intermediate DC bus terminals (14a and 14c), and a second DC bus capacitor (16b) is connected between the negative DC bus terminal and the intermediate DC bus terminals (14b and 14c).

[0185] The diode bridge (18) includes three DC converter terminals (20a, 20b and 20c) and three AC terminals (22) connected to the DC bus (12).

[0186] The AC terminal (22) is connected to the AC power supply unit (24) through the main transformer (26).

[0187] A precharge circuit (28) is connected between the AC power supply unit (24) and the AC terminal (22) of the second power converter. The precharge circuit (28) includes a precharge transformer (30) and a contactor (32). The precharge circuit (28) and the diode bridge (18) together define a DC power supply unit for supplying DC voltage to the DC bus (12) when the contactor (32) is closed.

[0188] The first voltage sensor (34a) is connected between the positive DC bus terminal and the intermediate DC bus terminals (14a and 14c), and the second voltage sensor (34b) is connected between the negative DC bus terminal and the intermediate DC bus terminals (14b and 14c). The first voltage sensor (34a) is connected to the control unit (36) and measures the positive partial DC bus voltage across the first DC bus capacitor (16a). The second voltage sensor (34b) is connected to the control unit (36) and measures the negative partial DC bus voltage across the second DC bus capacitor (16b). The positive partial DC bus voltage is V below. DC+ Identified as and the negative part DC bus voltage is V below DC- It is identified as. The total DC bus voltage (i.e., the sum of the two partial DC bus voltages) is V below. DC It is identified as.

[0189] The current sensor (38) is connected to the control unit (36) and measures the AC current in each AC phase. The individual AC current for each AC phase is I below. U , I V and I W It is identified as.

[0190] A third voltage sensor (40) is connected to the control unit (36) to measure the AC voltage. In particular, the third voltage sensor (40) measures a first AC line voltage between phases U and V, and a second AC line voltage between phases V and W. The first AC line voltage is U below. UV Identified as and the second AC line voltage is U below VW It is identified as.

[0191] The chopper circuit (42) is connected to the DC bus (12). Although not illustrated, the chopper circuit (42) includes a semiconductor switch (e.g., an IGBT) and a resistor for dissipating excess electrical energy of the DC bus as heat. The chopper circuit can discharge the first and second DC bus capacitors (16a and 16b) separately. In other words, the chopper circuit (42) can be operated to discharge only the first DC bus capacitor (16a) while the second DC bus capacitor (16b) remains charged, or vice versa. The chopper circuit (42) can also be operated to discharge the first and second DC bus capacitors (16a and 16b) simultaneously.

[0192] The electrical system also includes a cooling system (44) having a contactor (46).

[0193] The control unit (36) can control the precharge contactor (32) to open and close. In particular, the control unit (36) can generate a closing signal to close the precharge contactor (36) so that a DC voltage is supplied to the DC bus (12) through the precharge circuit (28) and the diode bridge (18). When the precharge contactor (32) is closed, the precharge contactor can generate a feedback signal and provide it to the control unit (36). The control unit (36) can generate an opening signal to open the precharge contactor (36). In FIG. 1, the command signal for the precharge contactor (32) is identified by a dashed line labeled "Precharge Cmd".

[0194] The control unit (36) can also control the cooling system contactor (46) to be opened and closed. In particular, the control unit (36) can generate a closing signal to close the cooling system contactor (46) so that, for example, one or more pumps are started to circulate the coolant. When the cooling system contactor (46) is closed, the cooling system contactor can generate a feedback signal and provide it to the control unit (36). The control unit (36) can generate an opening signal to open the cooling system contactor (46). In FIG. 1, the command signal for the cooling system contactor (46) is identified by a dashed line labeled "Cooling Cmd".

[0195] The control unit (36) can control the switching device (10) to be opened and closed. In particular, the control unit (36) can generate a closing signal to close the switching device (10) so that the AC terminal (6) of the inverter (2) is connected to the electric motor (8). When the switching device (10) is closed, the switching device can generate a feedback signal and provide it to the control unit (36). The control unit (36) can generate an opening signal to open the switching device (10) to disconnect the inverter (2) from the electric motor (8). When the switching device (10) is open, the switching device can generate a feedback signal and provide it to the control unit (36). In FIG. 1, the command signal for the switching device (10) is identified by a dashed line labeled "switch Cmd".

[0196] The control unit (36) can generate a gate drive command to control the switching operation of the semiconductor device of each converter leg (not shown) of the inverter (2). The gate drive command can be generated using a control strategy, for example, a pulse width modulation (PWM) control strategy using a modulation index and a carrier waveform. During normal operation of the inverter (2), the control strategy can be used to induce a desired AC current waveform at the AC terminal (6) by switching each converter leg (not shown) between various voltage levels. The inverter (2) shown in FIG. 1 has three voltage levels, namely a positive voltage level (or +1), a negative voltage level (or -1), and an intermediate (or zero) voltage level (or 0). However, it will be readily recognized that the inverter (2) may appropriately have two voltage levels or five or more voltage levels. Generally speaking, when a power converter has n voltage levels (where n = 2, 3, 5, etc.), the DC bus will have n DC bus terminals and (n-1) DC bus capacitors, each DC bus capacitor connected between adjacent pairs of DC bus terminals and defines each partial DC bus voltage.

[0197] Each converter leg (not shown) can be turned off by the control unit.

[0198] Each converter leg (not shown) can be placed in one of a plurality of ON states by a control unit. As described above, each ON state of the converter leg is determined by the individual switching state of the semiconductor switch, which is ultimately determined by a gate drive command. In an arrangement where the power converter has three voltage levels and is operating as an inverter, for example, the first ON state will define a positive voltage level in the AC phase, the second ON state will define a negative voltage level in the AC phase, and the third ON state will define a zero voltage level in the AC phase.

[0199] In FIG. 1, the gate drive command for the inverter (2) is "G Inv Identified by dashed lines labeled as "

[0200] The control unit (36) can generate a gate drive command to control the switching operation of the semiconductor device in the chopper circuit (42). The gate drive command can be generated using a control strategy, for example, a pulse width modulation (PWM) control strategy using a modulation index and a carrier waveform. The gate drive command can switch the semiconductor switch of the chopper circuit (42) between the ON and OFF states to create an intermittent short path between the DC bus terminals (14a and 14c) and / or between the DC bus terminals (14b and 14c). The gate drive command can also keep the semiconductor switch of the chopper circuit (42) in the ON state to create a continuous short path. The short path includes a resistor to dissipate the discharged energy as heat. The resistor is appropriately selected for a particular electrical system.

[0201] In FIG. 1, the gate drive command for the chopper circuit (42) is "G Chp+ / - Identified by dashed lines labeled as "

[0202] Although FIG. 1 illustrates a single control unit, it will be easily understood that multiple separate but coordinated control units may be used.

[0203] An example of a fully automated testing process (or "automated testing process" or "reduced power test") will now be described with reference to FIGS. 2 through 5. A testing process of an electrical system may be initiated by a user or engineer to validate hardware components of the electrical system, such as, for example, DC link capacitors, semiconductor switches of an inverter, current and voltage sensors, and chopper circuits. The testing process may be used to check the health of various components—that is, to determine whether the electrical system is operating normally. The testing process allows any data, such as time constants, current and voltage profiles, to be stored or recorded and / or analyzed. Data derived from testing processes executed at different times may be compared and analyzed to determine, for example, whether any component of the electrical system is responding differently as a result of aging or internal failure.

[0204] Data obtained during the testing process may be displayed to a user or engineer, for example, on a suitable display panel or monitor. The generated failure may also be displayed.

[0205] Figure 2 is a flowchart identifying the individual steps (i.e., steps 1-27) of the testing process.

[0206] FIG. 3 illustrates various parameters and failure states for individual steps of the testing process. In particular, FIG. 3 illustrates the following for each of steps 1-27:

[0207] - DC voltage profile having individual profiles for the following:

[0208] o Total DC voltage (V DC ),

[0209] o Positive partial DC voltage profile (V DC+ ) and

[0210] o Negative part DC voltage profile (V DC- ),

[0211] - Individual AC current profiles for phases U, V, and W, respectively (I U , I V and I W ),

[0212] - Individual AC voltage profiles (U UV and U VW ),

[0213] - A command ("Cooling Cmd") for controlling the operation of a cooling system, in particular, for controlling the opening and closing of a cooling system contactor (46) - wherein the cooling system contactor (46) is closed when the command is high and opened when the command is low - ,

[0214] - A command ("Precharge Cmd") for controlling the opening and closing of the precharge contactor (32) - where the precharge contactor (32) is closed when the command is high and opened when the command is low - ,

[0215] - A command ("Inverter Cmd") for controlling the operation of the inverter (2) - where the inverter (2) is controlled when the command is high and is off or not enabled when the command is low - ,

[0216] - A command ("Chopper Cmd") for controlling the operation of the chopper circuit (42) - where the chopper circuit (42) is controlled to discharge the DC link when the command is high - and

[0217] - A command ("switch Cmd") for controlling the opening and closing of the switching device (10) - where the switching device (10) is closed when the command is high and opened when the command is low - .

[0218] During the testing process, except when the inverter (2) is being controlled in steps 7-12 and 18-23, if the AC output current of the inverter exceeds a threshold, for example, about 2% of the rated converter current, a fault signal is generated. When a specific fault signal is generated, the testing process may be stopped, which may result in damage to the electrical system.

[0219] Step 1: Closure of switching device and start of cooling system

[0220] The switching device (10) is closed by the control unit (36) to connect the AC terminal (6) of the inverter (2) to the electric motor (8). The closing response time of the switching device (10) is checked. In particular, the time between the initiation of the closing signal by the control unit (36) and the reception of a feedback signal confirming that the switching device (10) is closed is measured. If the measured time is greater than the expected response time, a fault signal is generated. The response time for the switching device closing is recorded or stored.

[0221] The cooling system (44) is started so that the electrical system is properly cooled while the testing process is executed. The contactor (46) is closed by the control unit (36). The response time of the contactor (46) is checked. In particular, the time between the initiation of the closing signal by the control unit (36) and the reception of a feedback signal confirming that the contactor (46) is closed is measured. If the measured time is greater than the expected response time, a failure signal is generated. The response time of the cooling system contactor closure is recorded or stored.

[0222] When the switching device (10) is closed and the cooling system (44) is started, the testing process can proceed to step 2. If the switching device (10) is not closed or the cooling system is not started (for example, due to a failure), the testing process will stop normally.

[0223] Step 2: Pre-charge using an inverter in the off state

[0224] The inverter (2) is turned off by the control unit (36), that is, each semiconductor switch of the three converter legs is turned off (or turned off).

[0225] The precharge contactor (32) is closed by the control unit (36) so that a DC voltage is supplied to the DC bus (12) through the precharge circuit (28) and the diode bridge (18). The partial DC bus voltage is increased as shown in FIG. 3.

[0226] The response time of the precharge contactor (32) is checked. In particular, the time between the initiation of a closing signal by the control unit (36) and the reception of a feedback signal confirming that the contactor (32) is closed is measured. If the measured time is greater than the expected response time, a failure signal is generated. The response time of the precharge contactor is recorded or stored. The response time of the precharge contactor may also be checked at any one of steps 3-5 described below.

[0227] Positive part DC bus voltage (V DC+ ) is measured by the first voltage sensor (34a) and the negative partial DC bus voltage (V DC- ) is measured by the second voltage sensor (34b).

[0228] If one (or both) of the partial DC bus voltages does not exceed the expected partial DC bus voltage, a fault signal is generated. Specifically, the measured positive partial DC bus voltage (V DC+If the precharge contactor (32) is closed and the voltage does not increase by at least about 2.5% compared to the initial positive partial DC bus voltage within about 20 ms, a fault signal is generated and / or the measured negative partial DC bus voltage (V DC- A fault signal is generated if the precharge contact (32) is closed and does not increase by at least about 2.5% compared to the initial negative partial DC bus voltage within about 20 ms.

[0229] The initial partial DC bus voltage is measured when the precharge contact (32) is closed.

[0230] When the AC output current of the inverter (2) exceeds a threshold, for example, about 2% of the rated converter current, a fault signal is generated.

[0231] After a period of time, for example, about 150 ms, the precharge contactor (32) is opened by the control unit so that the supply of DC voltage to the DC bus (12) is stopped.

[0232] After the precharge contact (32) is opened, the partial DC bus voltage will gradually decrease as shown in FIG. 3. The testing process may be switched to step 3 when the total DC bus voltage drops below a threshold. In particular, when the measured total DC bus voltage drops to less than about 2% of the rated DC voltage, the testing process may be switched to step 3.

[0233] If the duration of Step 2 exceeds approximately 180 seconds, a failure signal is generated.

[0234] Step 3: Pre-charge using an inverter in the first ON state

[0235] The inverter (2) is placed in a first ON state by the control unit (36), that is, each semiconductor switch of the three converter legs is placed in an ON state or an OFF state as needed to place each converter leg in a zero switching state (turned on or turned off). In the zero switching state, the AC terminal of each converter leg is connected to the intermediate DC bus terminal (14c).

[0236] The precharge contactor (32) is closed by the control unit (36) so that a DC voltage is supplied to the DC bus (12) through the precharge circuit (28) and the diode bridge (18). The partial DC bus voltage is increased as shown in FIG. 3.

[0237] If one (or both) of the partial DC bus voltages does not exceed the expected partial DC bus voltage, a fault signal is generated. Specifically, the measured positive partial DC bus voltage (V DC+ ) when the precharge contactor (32) is closed and within about 20 ms the initial positive partial DC bus voltage is not increased by at least about 2.5% and / or the measured negative partial DC bus voltage (V DC- If the precharge contact is closed and the voltage does not increase by at least about 2.5% compared to the initial negative partial DC bus voltage within about 20 ms, a fault signal is generated.

[0238] The initial partial DC bus voltage is measured when the precharge contact (32) is closed.

[0239] When the AC output current of the inverter (2) exceeds a threshold, for example, about 2% of the rated converter current, a fault signal is generated.

[0240] After a period of time, for example, about 150 ms, the precharge contactor (32) is opened by the control unit so that the supply of DC voltage to the DC bus (12) is stopped.

[0241] After the precharge contact (32) is opened, the partial DC bus voltage will gradually decrease as shown in FIG. 3. The testing process may be switched to step 4 when the total DC bus voltage drops below a threshold. In particular, when the measured total DC bus voltage drops to less than about 2% of the rated DC voltage, the testing process may be switched to step 4.

[0242] If the duration of Step 3 exceeds approximately 180 seconds, a failure signal is generated.

[0243] Step 4: Pre-charge using an inverter in the second ON state

[0244] The inverter (2) is placed in a second ON state by the control unit (36), that is, each semiconductor switch of the three converter legs is placed in an ON state or an OFF state as needed to place each converter leg in a positive switching state (turned on or turned off). In the positive switching state, the AC terminal of each converter leg is connected to the positive DC bus terminal (14a).

[0245] The precharge contactor (32) is closed by the control unit (36) so that a DC voltage is supplied to the DC bus (12) through the precharge circuit (28) and the diode bridge (18). The partial DC bus voltage is increased as shown in FIG. 3.

[0246] If one (or both) of the partial DC bus voltages does not exceed the expected partial DC bus voltage, a fault signal is generated. Specifically, the measured positive partial DC bus voltage (V DC+ ) when the precharge contactor (32) is closed and within about 20 ms the initial positive partial DC bus voltage is not increased by at least about 2.5% and / or the measured negative partial DC bus voltage (V DC-If the precharge contactor (32) is closed and the voltage does not increase by at least about 2.5% compared to the initial negative partial DC bus voltage within about 20 ms, a fault signal is generated.

[0247] The initial partial DC bus voltage is measured when the precharge contact (32) is closed.

[0248] When the AC output current of the inverter (2) exceeds a threshold, for example, about 2% of the rated converter current, a fault signal is generated.

[0249] After a period of time, for example, about 150 ms, the precharge contactor (32) is opened by the control unit so that the supply of DC voltage to the DC bus (12) is stopped.

[0250] After the precharge contactor (32) is opened, the partial DC bus voltage will gradually decrease as shown in FIG. 3. The testing process may be switched to step 5 if the total DC bus voltage drops below a threshold. In particular, if the measured total DC bus voltage drops to less than about 2% of the rated DC voltage, the testing process may be switched to step 5.

[0251] If the duration of Step 4 exceeds approximately 180 seconds, a failure signal is generated.

[0252] Step 5: Pre-charge using an inverter in the third ON state

[0253] The inverter (2) is placed in a third ON state by the control unit (36), that is, each semiconductor switch of the three converter legs is placed in an ON state or an OFF state as needed to place each converter leg in a negative switching state (turned on or turned off). In the negative switching state, the AC terminal of each converter leg is connected to the negative DC bus terminal (14b).

[0254] The precharge contactor (32) is closed by the control unit (36) so that a DC voltage is supplied to the DC bus (12) through the precharge circuit (28) and the diode bridge (18). The partial DC bus voltage is increased as shown in FIG. 3.

[0255] If one (or both) of the partial DC bus voltages does not exceed the expected partial DC bus voltage, a fault signal is generated. Specifically, the measured positive partial DC bus voltage (V DC+ ) when the precharge contactor (32) is closed and within about 20 ms the initial positive DC bus voltage is not increased by at least about 2.5% and / or the measured negative partial DC bus voltage (V DC- If the precharge contact is closed and the voltage does not increase by at least about 2.5% compared to the initial negative DC bus voltage within about 20 ms, a fault signal is generated.

[0256] The initial partial DC bus voltage is measured when the precharge contact (32) is closed.

[0257] When the AC output current of the inverter (2) exceeds a threshold, for example, about 2% of the rated converter current, a fault signal is generated.

[0258] After a period of time, for example, about 150 ms, the precharge contactor (32) is opened by the control unit so that the supply of DC voltage to the DC bus (12) is stopped.

[0259] After the precharge contact (32) is opened, the total DC bus voltage will gradually decrease as shown in FIG. 3. The testing process may be switched to step 6 when the total DC bus voltage drops below a threshold or after a period of time.

[0260] If the duration of Step 5 exceeds approximately 180 seconds, a failure signal is generated.

[0261] Step 6: Precharge Contact Closure

[0262] The precharge contactor (32) is closed by the control unit (36) so that a DC voltage is supplied to the DC bus (12) through the precharge circuit (28) and the diode bridge (18). The partial DC bus voltage is increased as shown in FIG. 3.

[0263] The DC voltage is the measured total DC bus voltage (V DC It is supplied until it exceeds the first total DC bus voltage. The first total DC bus voltage is a threshold of about 10% of the rated DC voltage.

[0264] If one (or both) of the measured partial DC bus voltages does not exceed the expected partial DC bus voltage for a period of time, a fault signal is generated. The expected partial DC bus voltage is based on the measurement of the partial DC bus voltage at the beginning of step 6 when the precharge contactor (32) is closed ("initial partial DC bus voltage"). In particular, the measured positive partial DC bus voltage (V DC+ ) within one period of time, for example, about 20 ms, compared to the initial positive partial DC bus voltage, it is not increased by a certain percentage, for example, at least about 2.5%, and / or the measured negative partial DC bus voltage (V DC- If, within one period of time, for example, about 20 ms, the initial negative portion DC bus voltage is not increased by a certain percentage, for example, at least about 2.5%, compared to the initial negative portion DC bus voltage, a fault signal is generated.

[0265] The precharge contactor (32) is opened to terminate the supply of DC voltage when the measured total DC bus voltage exceeds the first total DC bus voltage.

[0266] After the precharge contactor (32) is opened, the total DC bus voltage will gradually decrease toward the first total DC bus voltage as shown in FIG. 3.

[0267] If the duration of step 6 exceeds approximately 20 seconds, a fault signal is generated.

[0268] Step 7-12: Inverter firing

[0269] Measured total DC bus voltage (V DC When ) is substantially the same as the first total DC bus voltage, the inverter (2) is controlled by the control unit (36) to provide the expected AC current in the AC phase of the electrical system. The expected AC current is selected to be some percentage of the rated converter current, for example, about 25% of the rated converter current.

[0270] While the inverter (2) is being controlled, the AC current in the AC phase of the electrical system is measured by the current sensor (38) and the AC voltage is measured by the voltage sensor (40).

[0271] If one (or both) of the measured partial DC bus voltages falls below the expected partial DC bus voltage while the inverter (2) is being controlled, a fault signal is generated. The expected partial DC bus voltage is based on the measurement of the partial DC bus voltage at the start of inverter control ("initial partial DC bus voltage"). In particular, the measured positive partial DC bus voltage (V DC+ ) is reduced by a predetermined percentage, for example, about 2%, compared to the initial positive partial DC bus voltage and / or the measured negative partial DC bus voltage (V DC+ A fault signal is generated when the initial negative partial DC bus voltage is reduced by a predetermined percentage, for example, about 2%. The partial DC bus voltage can be measured at the start of each pulse sequence.

[0272] The semiconductor switches of each converter leg of the inverter are controlled using an appropriate control scheme having a modulation index that generates a sequence of positive and negative current pulses in each AC phase. The modulation index is illustrated in FIG. 4. Modulation index (m U , m V and m W ) is indicated for each AC phase (i.e., each AC phase for controlling the semiconductor switch of each corresponding converter leg). The controller (36) will synchronize the inverter command signal with the positive ramp of the carrier waveform, and each current pulse is applied over two consecutive time periods of the control scheme, the AC current being measured at the end of the first time period and at the end of the second time period (when the expected AC voltage in each AC phase is typically zero).

[0273] In Fig. 4, various measurement times are indicated by solid arrows, and the measurement value is I U1 , I U2 ..., I U12 , I V1 , I V2 , ..., I V12 , I W1 , I W2 , ..., I W12 , U UV1 , U UV2 , ... , U UV12 and U VW1 , U VW2 , ..., U VW12 It is indicated by a point labeled as such. AC current and voltage measurements from the current and voltage sensors (38, 40) are recorded and analyzed in step 13. AC current measurements are instantaneous, and AC voltage measurements are averaged.

[0274] Generally, positive current pulses can be applied to one or more AC phases, and negative current pulses can be applied to one or more AC phases simultaneously. This can be repeated for various combinations of positive and negative current pulses.

[0275] In step 7, the modulation index generates a positive current pulse in the U phase and negative current pulses in the V and W phases.

[0276] In step 8, the modulation index generates a positive current pulse in the V phase and negative current pulses in the U and W phases.

[0277] In step 9, the modulation index generates a positive current pulse in the W phase and negative current pulses in the U and V phases.

[0278] In step 10, the modulation index generates a negative current pulse in the U phase and a positive current pulse in the V and W phases.

[0279] In step 11, the modulation index generates a negative current pulse in the V phase and a positive current pulse in the U and W phases.

[0280] In step 12, the modulation index generates a negative current pulse in the W phase and a positive current pulse in the U and V phases.

[0281] To protect the inverter (2), if the AC output current of the inverter (2) exceeds a maximum threshold, for example, about 33% of the rated converter current during steps 7-12, a fault signal is generated - and the testing process is preferably terminated.

[0282] If the duration of any of steps 7-12 exceeds about 0.05 seconds, a fault signal is generated.

[0283] Step 13: Data Collection and Analysis

[0284] Measurement data collected during steps 7-12 is analyzed in step 13.

[0285] If any of the measured AC currents is not within the range defined by the plus or minus tolerance value of the corresponding expected AC current (i.e., expected AC current for the same AC phase), for example, within ±50% of the expected AC current, a fault signal is generated. In particular, for each phase, the current is checked at the end of the first time period and at the end of the second time period. As mentioned above, the expected AC current is selected to be approximately 25% of the rated converter current.

[0286] If the AC voltage measured by the voltage sensor (40) is not within the range defined by the expected AC voltage plus or minus tolerance value, for example, within ±20% of the expected AC voltage, a fault signal is optionally generated.

[0287] Once the analysis is complete, the testing process can be switched to step 14.

[0288] If any measurement data is missing, a fault signal is generated.

[0289] If the duration of step 13 exceeds approximately 0.1 seconds, a fault signal is generated.

[0290] Steps 14 and 15: Start the chopper

[0291] In step 14, the chopper circuit (42) is operated to discharge the first DC bus capacitor (16a) for a period of time and a positive partial DC bus voltage ("V DC+_End The initial positive partial DC bus voltage ("V DC+_Initial") is measured when the chopper circuit (42) is first operated. The chopper circuit (42) is operated to create an intermittent short-circuit path between the first DC bus terminal and the intermediate DC bus terminals (14a and 14c) to dissipate the stored energy of the first DC bus capacitor (16a) of the chopper resistor.

[0292] In step 15, the chopper circuit (42) is operated to discharge the second DC bus capacitor (16b) for a period of time and the negative partial DC bus voltage (V DC-_End The initial negative portion DC bus voltage ("V DC-_Initial ") is measured when the chopper circuit (42) is first operated. The chopper circuit (42) is operated to create an intermittent short-circuit path between the second DC bus terminal and the intermediate DC bus terminals (14b and 14c) to dissipate the stored energy of the second DC bus capacitor (16b) of the chopper resistor.

[0293] In each of steps 14 and 15, each semiconductor switch of the chopper circuit (42) is switched between an on state and an off state according to an appropriate control strategy, for example, a PWM control strategy using a modulation index selected to result in a predicted value of the partial DC bus voltage. The modulation index is selected to reduce each partial DC bus voltage by about 3%. The modulation index can be calculated based on parameters such as the desired reduction in the partial DC bus voltage, the total DC bus voltage, the capacitance of the DC bus capacitor, the resistance of the chopper circuit resistor, the minimum on-time of the semiconductor switch, the frequency of the carrier waveform, etc.

[0294] The modulation index is exemplified in Fig. 5.

[0295] FIG. 5 shows the positive and negative partial DC voltages (V) during steps 14 and 15 as the DC bus capacitors (16a and 16b) discharge. DC+ and V DC-) illustrates how each is reduced. FIG. 5 also shows a modulation index (m) for discharging the first and second DC bus capacitors (16a and 16b). Chp+ and m Chp- A gate drive command (G) for switching each semiconductor switch of the chopper circuit (42) between the on and off states to provide the expected reduction in the triangular carrier waveform and the partial DC bus voltage. Chp+ and G Chp- ) city.

[0296] If the duration of step 14 exceeds approximately 0.1 seconds, a fault signal is generated.

[0297] If the duration of step 15 exceeds approximately 0.1 seconds, a fault signal is generated.

[0298] Step 16: Data Collection

[0299] A check is performed to ensure that data has been collected from steps 14 and 15.

[0300] Positive part DC bus voltage (V DC+ ) is the initial measurement of the positive partial DC bus voltage ("V DC+_Initial If it is not reduced by about 3% compared to "), a fault signal is generated.

[0301] Negative part DC bus voltage (V DC- ) Initial measurement of the negative part of the DC bus voltage ("V DC-_Initial If it is not reduced by about 3% compared to "), a fault signal is generated.

[0302] The chopper circuit (42) is operated to discharge the first and second DC bus capacitors (16a and 16b) until the total DC bus voltage drops to less than about 2% of the rated DC voltage. Then, the testing process can be switched to step 17.

[0303] If the duration of step 16 exceeds approximately 1 second, a fault signal is generated.

[0304] Step 17: Precharge Contact Closure

[0305] When transitioning to step 17, the total DC bus voltage is below a threshold determined based on the rated DC voltage. In particular, the total DC bus voltage is less than a certain percentage of the rated DC voltage, for example, less than about 2% of the rated DC voltage.

[0306] The precharge contactor (32) is closed by the control unit (36) so that a DC voltage is supplied to the DC bus (12) through the precharge circuit (28) and the diode bridge (18).

[0307] The DC voltage is the measured total DC bus voltage (V DC ) is supplied until it exceeds the second total DC bus voltage. The second total DC bus voltage is a threshold determined based on the rated DC voltage. Specifically, the second total DC bus voltage is approximately 90% of the rated DC voltage.

[0308] If one (or both) of the measured partial DC bus voltages does not exceed one or more expected partial DC bus voltages during each period of time, a fault signal is generated. In particular, a fault signal is generated in the following cases:

[0309] - Partial DC bus voltage of the measured positive amount (V DC+ )this:

[0310] o Not increased by at least about 2.5% during the first period of time (e.g., about 20 ms) compared to the initial positive partial DC bus voltage measured when the precharge contactor (32) is closed at the start of step 17, or

[0311] o Not exceeding the first threshold (e.g., about 10% of the rated DC voltage) within a second period of time, e.g., about 1.0 second, or

[0312] o Not exceeding the second threshold (e.g., about 90% of the rated DC voltage) within a third period of time, for example, about 10 seconds - where the period of time is calculated from when the DC voltage is supplied to the DC bus, i.e., when the precharge contactor (32) is closed - , and / or

[0313] - Measured negative part DC bus voltage (V DC- )this:

[0314] o Not increased by at least about 2.5% during the first period of time (e.g., about 20 ms) compared to the initial negative partial DC bus voltage measured when the precharge contactor (32) is closed at the start of step 17, or

[0315] o Not exceeding the first threshold (e.g., about 10% of the rated DC voltage) within a second period of time, e.g., about 1.0 second, or

[0316] o The second threshold (e.g., about 90% of the rated DC voltage) is not exceeded within a third period of time, for example, about 10 seconds - where the period of time is calculated from when the DC voltage is supplied to the DC bus, i.e., when the precharge contactor (32) is closed - .

[0317] While DC voltage is being supplied to the DC bus, a DC bus charging time constant for the DC bus is determined. The first DC bus voltage is measured approximately 1 second after the precharge contactor (32) is closed, and the second DC bus voltage is measured approximately 5 seconds after. The time constant is the ratio of the first DC bus voltage to the second DC bus voltage. It is calculated based on the fact that it is identical to, where t is the time between measurements, and is the DC bus charging time constant. The DC bus charging time constant is recorded or stored.

[0318] The precharge contactor (32) is opened to terminate the supply of DC voltage when the measured total DC bus voltage exceeds the second total DC bus voltage.

[0319] After the precharge contactor (32) is opened, the total DC bus voltage will gradually decrease toward the second total DC bus voltage.

[0320] Any imbalance in the partial DC bus voltage is determined after the precharge contactor (32) is opened. In particular, the positive and negative partial DC bus voltages (V across the first and second DC bus capacitors (16a, 16b) DC+ and V DC- ) can be measured and the difference between them is calculated. The difference between the partial DC bus voltages is recorded or stored. Positive or negative imbalances can indicate whether one of the DC bus capacitors is aging faster than the other.

[0321] If the duration of step 17 exceeds approximately 20 seconds, a fault signal is generated.

[0322] Step 18-23: Start the inverter

[0323] Measured total DC bus voltage (V DC When the second total DC bus voltage is substantially equal to about 90% of the rated DC voltage, the inverter (2) is controlled by the control unit (36) to provide the expected AC current in the AC phase of the electrical system. The expected AC current is selected to be some percentage of the rated converter current, for example, about 25% of the rated converter current.

[0324] While the inverter (2) is being controlled, the AC current in the AC phase of the electrical system is measured by the current sensor (38).

[0325] If one (or both) of the measured partial DC bus voltages falls below the expected partial DC bus voltage while the inverter (2) is being controlled, a fault signal is generated. The expected partial DC bus voltage is based on the measurement of the partial DC bus voltage at the start of inverter control ("initial partial DC bus voltage"). In particular, the measured positive partial DC bus voltage (V DC+ ) is reduced by a predetermined percentage, for example, about 2%, compared to the initial positive partial DC bus voltage and / or the measured negative partial DC bus voltage (V DC- When the initial negative portion DC bus voltage is reduced by a predetermined percentage, for example, about 2%, a fault signal is generated.

[0326] The semiconductor switches of each converter leg of the inverter are controlled using an appropriate control scheme having a modulation index that generates a sequence of positive and negative current pulses in each AC phase. This modulation index is similar to that described above with reference to FIG. 4, but will take into account a much higher DC bus voltage.

[0327] Generally, positive current pulses can be applied to one or more AC phases, and negative current pulses can be applied to one or more AC phases simultaneously. This can be repeated for various combinations of positive and negative current pulses.

[0328] In step 18, the modulation index generates a positive current pulse in the U phase and negative current pulses in the V and W phases.

[0329] In step 19, the modulation index generates a positive current pulse in the V phase and negative current pulses in the U and W phases.

[0330] In step 20, the modulation index generates a positive current pulse in the W phase and negative current pulses in the U and V phases.

[0331] In step 21, the modulation index generates a negative current pulse in the U phase and a positive current pulse in the V and W phases.

[0332] In step 22, the modulation index generates a negative current pulse in the V phase and a positive current pulse in the U and W phases.

[0333] In step 23, the modulation index generates a negative current pulse in the W phase and a positive current pulse in the U and V phases.

[0334] To protect the inverter (2), if the AC output current of the inverter (2) exceeds a maximum threshold, for example, about 33% of the rated converter current during steps 17-22, a fault signal is generated - and the testing process is preferably terminated.

[0335] If the duration of any of steps 18-23 exceeds about 0.05 seconds, a fault signal is generated.

[0336] Step 24: Data Collection and Analysis

[0337] Measurement data collected during steps 18-23 is analyzed in step 24.

[0338] If any of the measured AC currents is not within the range defined by the plus or minus tolerance value of the corresponding expected AC current (i.e., expected AC current for the same AC phase), for example, within ±50% of the expected AC current, a fault signal is generated. In particular, for each phase, the current is checked at the end of the first time period and at the end of the second time period. As mentioned above, the expected AC current is selected to be approximately 25% of the rated converter current.

[0339] If the AC voltage measured by the voltage sensor (40) is not within the range defined by the expected AC voltage plus or minus tolerance value, for example, within ±20% of the expected AC voltage, a fault signal is optionally generated.

[0340] The internal time constant of the DC bus is determined for the DC bus. For example, the first and second DC bus voltages may be measured at different times, and the time constant is the ratio of the first and second DC bus voltages. It is calculated based on the fact that it is identical to, where t is the time between measurements, and is the internal DC bus time constant. The first DC bus voltage is measured approximately at the time the power converter stops control, and the second DC bus voltage is measured after about 30 seconds. The internal DC bus time constant is recorded or stored.

[0341] At the start of step 24, the switching device (10) is opened to disconnect the inverter (2) from the electric motor (8). The switching device (10) is opened by the control unit (36). The opening response time of the switching device (10) is checked. In particular, the time between the initiation of the opening signal by the control unit (36) and the reception of a feedback signal confirming that the switching device (10) is opened is measured. If the measured time is greater than the expected response time, a fault signal is generated. The response time for the opening of the switching device is recorded or stored.

[0342] If any measurement data is missing, a fault signal is generated.

[0343] If the duration of step 24 exceeds approximately 35 seconds, a failure signal is generated.

[0344] Step 25: Start the Chopper

[0345] The chopper circuit (42) is operated to discharge the first and second DC bus capacitors (16a, 16b) as quickly as possible until the total DC bus voltage becomes less than the third total DC bus voltage, for example, about 2% of the rated DC voltage. The chopper circuit (42) is operated to create a continuous short-circuit path (i.e., having the same modulation index as 1) between the first DC bus terminal and the intermediate DC bus terminals (14a and 14c), and between the second DC bus terminal and the intermediate DC bus terminals (14b and 14c).

[0346] If the measured total DC bus voltage does not drop below the expected total DC bus voltage during a period of time, a fault signal is generated. In particular, if the measured total DC bus voltage drops below a certain percentage of the rated DC voltage (e.g., about 5% of the rated DC voltage) within a period of time, for example, about 1.0 second, a fault signal is generated.

[0347] The DC bus discharge time constant for the DC bus is determined. The first DC bus voltage is measured when the DC bus voltage reaches approximately 60% of the rated DC voltage, and the second DC bus voltage is measured when the DC bus voltage reaches approximately 10% of the rated DC voltage. The time constant is the ratio of the first DC bus voltage to the second DC bus voltage It is calculated based on the fact that it is identical to, where t is the time between measurements, and is the internal DC bus time constant. The DC bus discharge time constant is recorded or stored.

[0348] If the duration of step 24 exceeds approximately 2 seconds, a fault signal is generated.

[0349] Step 26: Data Collection

[0350] A check is performed to ensure that data from Step 25 has been collected.

[0351] Next, the testing process can be transitioned to step 27.

[0352] If the duration of step 26 exceeds approximately 0.5 seconds, a fault signal is generated.

[0353] Step 27: Stop the cooling system

[0354] In step 27, the cooling system is stopped by opening the cooling system contactor (46).

[0355] If the duration of step 27 exceeds approximately 70 seconds, a failure signal is generated.

Claims

Claim 1 In a testing process for an electrical system, the electrical system comprises: a power converter (2) comprising: two or more direct current (DC) converter terminals (4a, 4b, 4c), and at least one converter leg connected to the DC converter terminals—each converter leg comprising an AC terminal (6) that defines the alternating current (AC) phase of the electrical system and is connectable to each AC terminal of an electrical load (8), and a plurality of semiconductor switches— wherein the plurality of semiconductor switches are controllable to keep the converter leg in an off state or to be in one of a plurality of on states that define each voltage level of the converter leg; The DC bus (12) comprises: two or more DC bus terminals (14a, 14b, 14c) - each DC bus terminal (14a, 14b, 14c) is connected to each DC converter terminal (4a, 4b, 4c) - and at least one DC bus capacitor (16a, 16b); wherein the testing process is a fully automated testing process in which a sequence of different diagnostic tests is executed on the electrical system, and each diagnostic test tests one of the power converter (2) and the DC bus (12) to determine whether it responds as expected or operates within normal parameters, and the testing process further comprises: one or more first diagnostic tests in which, for each first diagnostic test, each converter leg is in an off state or is in the same on state among the plurality of on states, and each first diagnostic test is characterized by: while a DC voltage is supplied to the DC bus (12) for a period of time, the DC bus A testing process for an electrical system comprising measuring a voltage and generating a fault signal if the measured DC bus voltage does not exceed a first expected DC bus voltage. Claim 2 A testing process for an electrical system according to claim 1, wherein the plurality of first diagnostic tests are executed sequentially with the converter legs in different states for each first diagnostic test. Claim 3 A testing process for an electrical system according to claim 1 or 2, wherein the electrical system further comprises a pre-charge circuit (28) having a contactor (32), and at least one first diagnostic test further comprises: closing the pre-charge contactor (32) for a period of time to supply the DC voltage to the DC bus (12), checking the response time of the pre-charge contactor (32) by measuring the time between the initiation of a closing signal and the reception of a feedback signal confirming that the pre-charge contactor is closed, and generating a fault signal if the measured time is greater than the expected response time. Claim 4 A testing process for an electrical system according to claim 1 or 2, further comprising a second diagnostic test, wherein the second diagnostic test comprises: a step of measuring a DC bus voltage while a DC voltage is supplied to the DC bus; a step of terminating the supply of the DC voltage when the measured DC bus voltage exceeds a first DC bus voltage and causing the DC bus voltage to gradually decrease toward the first DC bus voltage; a step of controlling the power converter (2) to provide an expected AC current in at least one AC phase of the electrical system when the measured DC bus voltage is substantially equal to the first DC bus voltage; a step of measuring the AC current in the at least one AC phase of the electrical system; and a step of generating a fault signal when the measured AC current is not within a range defined by a corresponding expected AC current plus or minus tolerance value. Claim 5 A testing process for an electrical system according to claim 4, wherein the second diagnostic test further comprises: controlling the power converter (2) to provide an expected AC voltage in at least one of the AC phases or between two of the AC phases; measuring the AC voltage in at least one of the AC phases or between two of the AC phases; and generating a fault signal if the measured AC voltage is not within a range defined by a corresponding expected AC voltage plus or minus tolerance value. Claim 6 A testing process for an electrical system according to claim 4, wherein the second diagnostic test further comprises generating a fault signal when the DC bus voltage measured while the power converter is being controlled drops below the expected DC bus voltage. Claim 7 A testing process for an electrical system, wherein, in any one of the four claims, the second diagnostic test further comprises controlling the power converter (2) using a control scheme having a selected modulation index. Claim 8 A testing process for an electrical system, wherein, in any one of claim 4, a third diagnostic test is further included, said third diagnostic test comprises: a step of measuring a DC bus voltage while a DC voltage is supplied to the DC bus; a step of terminating the supply of the DC voltage when the measured DC bus voltage exceeds a second DC bus voltage and causing the DC bus voltage to gradually decrease toward the second DC bus voltage—wherein the second DC bus voltage is greater than the first DC bus voltage; a step of controlling the power converter (2) to provide an expected AC current in at least one AC phase of the electrical system when the measured DC bus voltage is substantially equal to the second DC bus voltage; a step of measuring the AC current in the at least one AC phase of the electrical system; and a step of generating a fault signal when the measured AC current is not within a range defined by a corresponding expected AC current plus or minus tolerance value. Claim 9 A testing process for an electrical system according to claim 1 or 2, wherein the electrical system further comprises a chopper circuit (42) connected to the DC bus (12), and the testing process further comprises: a fourth diagnostic test, wherein the fourth diagnostic test comprises: operating the chopper circuit (42) for a period of time to provide an expected DC bus voltage; measuring the DC bus voltage after the period of time; and generating a fault signal if the measured DC bus voltage is not within a range defined by the expected DC bus voltage plus or minus tolerance value, or if the DC bus voltage has not decreased by a predetermined percentage compared to the initial DC bus voltage. Claim 10 A testing process for an electrical system according to claim 9, wherein the fourth diagnostic test comprises operating the chopper circuit (42) using a control scheme having a selected modulation index. Claim 11 A testing process for an electrical system according to claim 9, further comprising a fifth diagnostic test, wherein the fifth diagnostic test comprises: operating the chopper circuit (42) to discharge the DC bus capacitor(s) (16a, 16b) until the DC bus voltage becomes less than the third DC bus voltage, and generating a fault signal if the measured DC bus voltage does not drop below the expected DC bus voltage for a period of time. Claim 12 A testing process for an electrical system according to claim 1 or 2, wherein the electrical system further comprises a switching device (10), and each AC phase of the electrical system is connectable to each AC terminal of the electrical load (8) by the switching device (10), and the testing process further comprises a zero diagnostic test performed prior to any of other diagnostic tests, wherein the zero diagnostic test comprises: a step of closing the switching device (10) to connect the power converter (2) to the electrical load (8), a step of checking the response time of the switching device (10) by measuring the time between the initiation of a closing signal and the reception of a feedback signal confirming that the switching device (10) is closed, and a step of generating a fault signal if the measured time is greater than the expected response time. Claim 13 In claim 12, the electrical system further comprises a cooling system (44) including a contactor (46), and the zero diagnostic test further comprises: a step of closing the cooling system contactor (46); a step of checking the response time of the cooling system contactor (46) by measuring the time between the initiation of a closing signal and the reception of a feedback signal confirming that the cooling system contactor (46) is closed; and a step of generating a fault signal if the measured time is greater than the expected response time. A testing process for an electrical system. Claim 14 In an electrical system, the power converter (2) comprises: two or more DC converter terminals (4a, 4b, 4c), and at least one converter leg connected to the DC converter terminals (4a, 4b, 4c) - each converter leg includes an AC terminal (6) that defines the AC phase of the electrical system and is connectable to each AC terminal of an electrical load (8) and a plurality of semiconductor switches; the DC bus (12) comprises: two or more DC bus terminals (14a, 14b, 14c) - each DC bus terminal (14a, 14b, 14c) is connected to each DC converter terminal (4a, 4b, 4c) - and at least one DC bus capacitor (16a, 16b); a DC voltage supply unit (24, 28, 18) for supplying a DC voltage to the DC bus (12); to keep the converter leg in an off state, or of the converter leg A control unit (36) adapted to control the DC voltage supply (24, 28, 18) and the plurality of semiconductor switches to place each voltage level in one of a plurality of ON states; at least one voltage sensor (34a, 34b) connected to the control unit (36) to measure the DC bus voltage;and includes at least one current sensor (38) connected to the control unit (36) to measure AC current in at least one AC phase of the electrical system, wherein the control unit (36) is also adapted to execute a testing process which is a fully automated testing process in which a sequence of different diagnostic tests is executed on the electrical system, each diagnostic test tests one of the power converter (2) and the DC bus (12) to determine whether it is responding as expected or operating within normal parameters, and the test process adapted to be executed by the control unit (36) further includes one or more first diagnostic tests in which, for each first diagnostic test, each converter leg is in an off state by the control unit (36) or is in the same on state among the plurality of on states, wherein each first diagnostic test measures the DC bus voltage by the at least one voltage sensor (34a, 34b) while a DC voltage is supplied to the DC bus (12) for a period of time, and the measured DC bus voltage is a first expected DC bus voltage An electrical system that includes generating a fault signal when not exceeded.; Claim 15 delete

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