Bidirectional switch of induction motor, control method thereof and soft turn-off system of induction motor

Abstract

Embodiments of the present disclosure relate to soft turn-off for motor controllers. A bidirectional switch for an induction motor is described. The bidirectional switch can include a first power semiconductor transistor having a first source, a first drain, and a first gate. The bidirectional switch can also include a second power semiconductor transistor having a second source, a second drain, and a second gate. The bidirectional switch can include the second source connected to the first source. The bidirectional switch can include a soft start device including a control circuit configurable to provide a first control signal to the first power semiconductor transistor and a second control signal to the second power semiconductor transistor.

Description

Bidirectional switch for induction motor, its control method and soft shutdown system for induction motor Technical Field

[0001] This disclosure generally relates to soft starters for induction motors. More specifically, this disclosure relates to the use of a controller and a field-effect transistor to control a bidirectional switch. Background Technology

[0002] Soft starters for induction motors typically use thyristors as control switches. These types of devices are gated with pulsed current at a specific firing angle during half a cycle of the power supply voltage. Without a gate pulse, these devices naturally turn off when the next current crosses zero. The firing angle varies throughout the soft-start process based on a control strategy defined to limit the motor's starting current. Summary of the Invention

[0003] Any or all portions of any embodiment disclosed herein may be combined with any other portion of any embodiment.

[0004] In some embodiments of a bidirectional switch for an induction motor, the bidirectional switch includes a first field-effect transistor (FET), wherein the first FET includes a first source, a first drain, and a first gate; a second FET, wherein the second FET includes a second source, a second drain, and a second gate; wherein the second source is connected to the first source; and a soft-start device including control circuitry that can be configured to provide a first control signal to the first FET and a second control signal to the second FET.

[0005] In some embodiments of the bidirectional switch, the control circuit is configured to provide a first control signal and a second control signal such that the first FET and the second FET provide multiple operating modes.

[0006] In some embodiments of the bidirectional switch, multiple modes include a first mode, wherein the first mode provides bidirectional conduction of current; a second mode, wherein the second mode provides unidirectional conduction of current in a first direction; a third mode, wherein the third mode provides unidirectional conduction of current in a second direction; and a fourth mode, wherein the fourth mode provides bidirectional blocking of current conduction.

[0007] In some embodiments of the bidirectional switch, the multiple modes further include a first mode, characterized in that the control circuit provides an enable control signal to both the first FET and the second FET; a second mode, characterized in that the control circuit provides an enable control signal to the first FET and a disable control signal to the second FET; a third mode, characterized in that the control circuit provides a disable control signal to the first FET and an enable control signal to the second FET; and a fourth mode, characterized in that the control circuit provides a disable control signal to both the first FET and the second FET.

[0008] In some embodiments of a bidirectional switch, the control circuit is a voltage-resistance divider or a voltage transformer.

[0009] In some embodiments, the bidirectional switch further includes a trigger angle reference generator, wherein the trigger angle reference generator can be configured to generate a linear ramp descent from a fixed starting angle.

[0010] In some embodiments of a method for controlling a bidirectional switch for an induction motor, the method includes initializing a first field-effect transistor (FET) and a second FET, wherein initialization includes providing a first control signal that sets the first FET to a turn-off state; and providing a second control signal that sets the second FET to a turn-off state; determining a reference firing angle; comparing a measured phase angle with the reference firing angle; and based on the comparison, controlling the first FET or the second FET to enter one of a plurality of modes.

[0011] In some embodiments of the method, multiple modes include a first mode, wherein the first mode provides bidirectional conduction of current; a second mode, wherein the second mode provides unidirectional conduction of current in a first direction; a third mode, wherein the third mode provides unidirectional conduction of current in a second direction; and a fourth mode, wherein the fourth mode provides bidirectional blocking of current conduction.

[0012] In some embodiments of the method, multiple modes further include a first mode characterized by providing an enable control signal to both the first FET and the second FET; a second mode characterized by providing an enable control signal to the first FET and a disable control signal to the second FET; a third mode characterized by providing a disable control signal to the first FET and an enable control signal to the second FET; and a fourth mode wherein a disable control signal is provided to both the first FET and the second FET.

[0013] In some embodiments, the method further includes detecting the falling edge of a turn-on pulse generated by comparing a measured phase angle with a reference trigger angle; and determining the number of return path devices in one or more other phases, wherein the number of return path devices is based on the state of each return path device in the return path devices.

[0014] In some embodiments, the method further includes comparing the measured phase current with a diode threshold current, wherein the comparison includes determining the slope of the measured phase current.

[0015] In some embodiments of the method, the comparison includes performing a comparison of the measured phase angle with a reference firing angle for each half-cycle of the power supply voltage.

[0016] In some embodiments of a system for performing a soft-shutdown of an induction motor, the system includes a soft-start device comprising a first field-effect transistor (FET) including a first source, a first drain, and a first gate; a second FET including a second source, a second drain, and a second gate, wherein the second source is connected to the first source; and control circuitry configured to provide a first control signal to the first FET and a second control signal to the second FET. In other embodiments, the FET may be configured using an insulated-gate bipolar transistor (IGBT) having a common drain, a common collector, or a common emitter.

[0017] In some embodiments of the system, the control circuit is configured to provide a first control signal and a second control signal such that the first FET and the second FET provide multiple operating modes.

[0018] In some embodiments of the system, multiple modes include a first mode, wherein the first mode provides bidirectional conduction of current; a second mode, wherein the second mode provides unidirectional conduction of current in a first direction; a third mode, wherein the third mode provides unidirectional conduction of current in a second direction; and a fourth mode, wherein the fourth mode provides bidirectional blocking of current conduction.

[0019] In some embodiments of the system, the multiple modes also include a first mode, characterized in that the control circuit provides an enable control signal to both the first FET and the second FET; a second mode, characterized in that the control circuit provides an enable control signal to the first FET and a disable control signal to the second FET; a third mode, characterized in that the control circuit provides a disable control signal to the first FET and an enable control signal to the second FET; and a fourth mode, characterized in that the control circuit provides a disable control signal to both the first FET and the second FET.

[0020] In some embodiments of the system, the control circuit is a resistive voltage divider or a voltage transformer.

[0021] In some embodiments, the system further includes a trigger angle reference generator, wherein the trigger angle reference generator can be configured to generate a linear ramp descent from a fixed starting angle.

[0022] In some embodiments of the system, the control circuitry can also be configured to perform operations including: comparing the measured phase current with the diode threshold current; and determining the slope of the measured phase current.

[0023] In some embodiments of the system, the control circuitry can also be configured to perform a comparison of the measured phase current with a reference firing angle for each half-cycle of the power supply voltage. Attached Figure Description

[0024] Referring to the accompanying drawings, which form part of this disclosure, and illustrating embodiments in which the systems and methods described herein can be practiced.

[0025] Figure 1A depicts a soft starter for an induction motor that uses a thyristor-controlled switch;

[0026] Figure 1B depicts a fully controlled soft-start device (“soft-start device”) according to aspects of this disclosure.

[0027] Figure 2 illustrates examples of various operating modes of a soft-start device according to aspects of this disclosure;

[0028] Figure 3 illustrates an example of a timing diagram using diode mode according to aspects of this disclosure;

[0029] Figure 4 illustrates an example of a process for controlling a soft-start device according to some aspects of this disclosure;

[0030] Figure 5 illustrates an example of a control circuit that implements the process of Figure 4 according to some aspects of this disclosure;

[0031] Figure 6 illustrates an example of a control circuit using a resistor divider for soft shutdown according to some aspects of this disclosure;

[0032] Figure 7 illustrates an example of a control circuit for soft shutdown using a voltage transformer according to some aspects of this disclosure.

[0033] Figure 8 illustrates an example of a soft-shutdown control circuit for a three-phase four-wire load according to some aspects of this disclosure; and

[0034] Figure 9 illustrates simulation results comparing motor winding voltages with and without control circuitry for soft shutdown according to some aspects of this disclosure.

[0035] The same reference numerals may refer to the same or similar parts from beginning to end. Detailed Implementation

[0036] In the field of induction motors and highly inductive loads, performing shutdown operations presents challenges because even very small current levels, such as less than 10 amps, can cause excessive voltage across the soft starter, exceeding safe operating limits and potentially damaging or destroying the device or its components. Furthermore, the motor windings may experience corresponding overvoltages, increasing stress on the winding insulation and other motor components. The soft starter described herein reduces the starting current to a sufficient level to avoid interference with the power grid or the motor startup process by limiting the current conduction time. Moreover, the elimination of overvoltages improves the reliability of the control circuitry and the motor.

[0037] Soft-start devices can be implemented using fully controllable power semiconductor devices (e.g., SiC MOSFETs), particularly one or more source-to-source (or emitter-to-emitter) series connections for the MOSFETs to form a bidirectional switch. Soft-start devices include control circuitry and decision algorithms to operate the fully controllable power semiconductor device to control the bidirectional switch, thereby achieving zero-current turn-off based on the independent control state of the semiconductor device without the need for precise current sensing.

[0038] In a non-limiting example, the control circuitry and decision-making algorithm can control the supply voltage applied to a three-phase load (e.g., a motor load powered by a soft starter) using fully controllable power semiconductor devices, and extend the number of operations (e.g., tens of millions of operations) of the FET / IGBT-based control switches and MOVs due to reduced stress under normal operation. Stress reduction can also be achieved in the motor winding insulation during direct online / soft-start motor startup. The disclosed soft-start device can utilize fully controllable semiconductor devices such as SiC MOSFETs and GaN FETs, which enable low losses and small size for solid-state circuit breakers, contactors, and circuit breakers (i.e., circuit breaker + contactor) and other event-switching applications.

[0039] Referring now to Figure 1A, which depicts a soft starter for an induction motor using a thyristor-controlled switch. The device is gated with a pulsed current at a specific firing angle during half a cycle of the supply voltage. Then, in the absence of a gate pulse, the device naturally turns off at the next current zero crossing. The firing angle varies throughout the soft-start duration based on a control strategy defined to limit the motor's starting current. However, in the event of a downstream fault, this uncontrolled turn-off of the thyristor cannot be used to limit the fault current.

[0040] Figure 1B depicts a fully controlled soft-start device (“soft-start device”) according to aspects of this disclosure. For example, a fully controlled soft-start device can be a field-effect transistor, such as a silicon carbide field-effect transistor (SiC MOSFET). SiC MOSFETs can be used to combine motor control functions and fault protection functions of a motor controller / starter.

[0041] As shown in Figure 1B, a fully controlled soft starter provides rapid interruption of fault current, thereby reducing the need for additional protection devices between the soft starter and the load. A fully controlled soft starter also provides frequent start and stop of motors or frequent on / off control of general loads.

[0042] Because induction motors are highly inductive loads, even performing a turn-off operation at very small current levels can cause the voltage across the soft-start device to exceed the safe operating range. The motor windings may also experience corresponding overvoltages, leading to increased stress on the winding insulation. The accuracy of this zero-current-to-turn-off (ZCTO) operation depends on the precision of the current sensor and the control electronics in the circuit. In some cases, the current sensor's range may be very high when it also controls the starting current. Current sensors used to control the starting current are typically low-sensitivity and therefore have reduced accuracy near zero-crossing at low currents.

[0043] Other examples of soft-start devices may include insulated gate bipolar transistors (IGBTs), junction gate field-effect transistors (JFETs), or gallium nitride (GaN) FETs.

[0044] As shown in Figure 1B, the soft-start device 102 includes a first field-effect transistor (FET) 110 and a second FET 120. The first FET 110 includes a first source 112, a first drain 114, and a first gate 116. The soft-start device 102 also includes a second FET 120. The second FET 120 includes a second source 122, a second drain 124, and a second gate 126.

[0045] Although not shown in Figure 1B, and as described elsewhere herein, the soft-start device 102 may include control circuitry configured to provide independent control of the first FET 110 and the second FET 120. The control circuitry provides an independent control signal to each of the first FET 110 and the second FET 120 to allow alternating conduction of current through the diodes of the soft-start device 102. The alternating conduction of the diodes of the soft-start device 102 stops conduction at diode current reversal (zero crossing). Controlled conduction based on diode current reversal provides reliable operation of both the soft-start device 102 and the metal-oxide-switched varactor (MOV).

[0046] Figure 2 illustrates examples of various operating modes of a soft-start device according to aspects of this disclosure. The soft-start device includes control circuitry for a back-to-back FET (e.g., SiC MOSFET) four-quadrant switching configuration. The back-to-back FET configuration provides soft shutdown for solid-state circuit breakers, contactors, and plug-and-play motor controllers. As described with respect to Figure 1B, the back-to-back FET configuration provides current interruption while the current reverses instantaneously at its practically zero state (i.e., zero-crossing and diode current reversal).

[0047] Soft-start devices use diode current reversal control FETs to prevent dangerous overvoltages across the soft-start device (e.g., component semiconductor) and excessive energy consumption of auxiliary components (e.g., MOVs in parallel with the semiconductor) that clamp the voltage in the event of an overvoltage.

[0048] Soft-start devices can use control circuitry to selectively turn off one or more FETs to commutate current to a freewheeling diode (e.g., a body diode or FET). Because the soft-start device commutates current to one or more freewheeling diodes, the current is not abruptly interrupted but continues until the natural current reverses. After the current carried by one or more freewheeling diodes is exhausted by the diode's reverse recovery, the soft-start device can turn off one or more other FETs (e.g., using control circuitry). Turning off one or more other FETs results in complete current interruption and circuit isolation. Further details regarding the operating modes of soft-start devices are described below.

[0049] In the two modes labeled diode mode in Figure 2, one of the two semiconductor devices is selected to be low. Therefore, conduction occurs via an anti-parallel diode to form these unidirectional conduction modes. In diode mode, conduction will naturally stop at zero current, where the typical natural current reversal of an AC system occurs. Therefore, these modes can be used to achieve the desired natural zero-current turn-off during soft-start operation.

[0050] In the first mode 202, current conduction is provided in both directions. For example, both FETs (G1 and G2) are both selected high. Therefore, the channels of both devices conduct, and the soft starter behaves like a resistor to allow conduction in both directions.

[0051] The second mode 204 and the third mode 206 provide a directional current conduction, as depicted by the current flowing through the corresponding diode in each mode. For example, in the second mode 204, one of the two FETs (G1 or G2) is selected low (and for the third mode 206, the opposite FET is selected low). Current is conducted through the anti-parallel diode, making the second mode 204 and the third mode 206 unidirectional conduction modes. In the second mode 204 and the third mode 206, similar to an AC system, conduction will naturally stop at zero current at the point of natural current reversal. Therefore, the second mode 204 and the third mode 206 can be used to achieve the desired natural zero-current turn-off during soft-start operation and reduce the need for high-precision current sensors.

[0052] In the fourth mode 208, the soft-start device blocks current conduction in both directions. For example, both FETs (G1 and G2) are selected to low level. Therefore, the channels of both devices are blocked, and the soft-start device behaves like an open circuit, thus preventing bidirectional conduction.

[0053] Figure 3 illustrates an example of a timing diagram using a diode mode according to aspects of this disclosure. For example, Figure 300 illustrates the timing diagram of pulse 302 for the first FET, pulse 306 for the second FET, and phase current 304.

[0054] Figure 4 illustrates an example of a process for controlling a soft-start device according to some aspects of this disclosure. In this example process, the soft-start device includes two field-effect transistors Q1 and Q2, and control circuitry. In one example, Q1 and Q2 may be the transistors described with respect to Figures 1-3.

[0055] In block 402, process 400 involves gating both field-effect transistors Q1 and Q2 to turn off. For example, control circuitry may provide a low signal to the gate of each of Q1 and Q2. On one hand, the operation of block 402 involves initializing field-effect transistors Q1 and Q2.

[0056] In block 404, process 400 involves determining a reference firing angle for comparison with the measured phase angle. In one example, the control circuitry may set the reference firing angle to a predetermined value or adjust the reference firing angle based on environmental, performance, and circuit characteristics (e.g., tolerances, motor specifications, etc.).

[0057] In block 406, process 400 involves comparing the measured phase of the power supply voltage with a reference firing angle. In one example, the soft-start device may perform a modulo operation of the measured phase angle relative to 180°. For each half-cycle of the power supply voltage, the soft-start device may perform a comparison of the measured phase angle with the reference firing angle. In another example, the soft-start device may compare the measured phase with the reference firing angle as a binary comparison, or by calculating the difference and determining the absolute value of the difference.

[0058] In block 408, process 400 involves turning on the first FET Q1 and the second FET Q2. As previously described, enabling both Q1 and Q2 puts the soft-starter in a first mode, and the soft-start device provides bidirectional current conduction. For example, both FETs (G1 and G2) are selected to a high level. Therefore, the channels of both Q1 and Q2 conduct, and the soft-starter behaves like a resistor to allow bidirectional conduction. From block 408, process 400 proceeds in parallel to blocks 410 and 412.

[0059] In block 412, the soft-start device can detect the falling edge of the turn-on pulse generated by the phase comparison. For example, the soft-start device can detect that the turn-on pulse generated at block 408 is transitioning from a high logic value to a low logic value. When the soft-start device detects the falling edge, process 400 can move to block 414.

[0060] In block 414, the soft-start device can determine whether any return path device in other phases is in the ON state. For example, in a three-phase motor circuit, the soft-start device can determine whether to turn off device Q1 in phase A depends on whether an enable control signal (gate-on signal) is being provided to device Q2 in phases B and C. As described with respect to block 412, the check of the return path device is performed when a falling edge is detected.

[0061] In an example of a three-phase load without a neutral connection, it is necessary to determine whether any return path devices are on, because current cannot begin to flow unless devices in at least two phases are off. During motor soft-start operation, the check of return path devices may occur at the beginning of the soft-start period, when the firing angle is high. In this example, if only current-based turn-off conditions are used, the devices in the first phase will remain on until the next half-cycle when the second phase switch is turned on.

[0062] For example, when the reference angle is 150° 0 At that time, the semiconductor devices in the second phase will reach 30 in the first phase during the second half of the cycle. 0 It will only be switched on at that time. The semiconductor devices in the first phase will be kept in the on state until 30% of the next half-cycle. 0 This will result in high inrush current. When the firing angle is higher than 120°... 0 At this time, high inrush currents may be observed. To compensate, the soft-start device detects the state of semiconductor devices in other phases, allowing the soft-start device to turn off semiconductor devices in other phases at the end of a half-cycle to achieve a high trigger angle. In another example, this turn-off condition will not be met for trigger angles less than 120°. From block 414, process 400 can proceed to block 416.

[0063] In box 410, the soft-start device can compare the phase current with the diode threshold currents (e.g., IDiode- and IDiode+). The soft-start device can apply different comparison conditions to FETs Q1 and Q2 in each phase. In the example shown in Figure 4, the comparison condition for Q1 can be... And the slope is greater than 0, so the comparison condition for Q2 can be... And the slope is less than 0. Soft-start devices can use additional conditions on the slope to ensure that turn-off determination only occurs at the end of each current half-cycle. From block 410, process 400 can proceed to block 416.

[0064] In block 416, the soft-start device can determine whether to turn off Q1 or Q2 based on one or both of the conditions analyzed in blocks 410 and blocks 412-414. In one example, the soft-start device can send a disable (e.g., logic low) signal to turn off one of the field-effect transistors Q1 or Q2.

[0065] Figure 5 illustrates an example of a control circuit 500 that implements the process of Figure 4 according to some aspects of this disclosure. The operations performed by the control circuit 500 are described with respect to the operations performed in the various boxes of Figure 4.

[0066] Figure 6 illustrates an example of a control circuit 600 for soft shutdown using a resistive voltage divider according to some aspects of this disclosure. For example, the voltage sensing circuit of Figure 6 implements a resistive voltage divider and a Zener diode to generate a bipolar supply voltage for a differential amplifier and an analog isolator. In this example, the fully differential output of the analog isolator is used to generate a neutral point voltage to be sensed by an instrumentation amplifier line to the neutral point voltage.

[0067] Figure 7 illustrates an example of a control circuit 700 for soft shutdown using a voltage transformer according to some aspects of this disclosure. For example, the voltage detection circuit can also be implemented using a delta-to-star three-phase voltage transformer. In this example, because the shutdown decision of one or more FETs is based on measurements from other phases, the measured voltage and current of each phase can be used as a common control ground.

[0068] Figure 8 illustrates an example of a control circuit 800 for soft shutdown of a three-phase four-wire load according to some aspects of this disclosure. In this configuration, measurements and analyses of each phase can be performed independently due to access to the neutral connection. Therefore, the circuit shown in Figure 8 is used for one phase of a three-phase system. In this particular example, the control circuit includes a trigger angle reference generator that generates a linear ramp-down from a fixed starting angle. The trigger angle reference generator can be used in applications of open-loop buck soft-start types. The circuit can be modified according to application requirements.

[0069] Figure 9 depicts simulation results 900 comparing motor winding voltages with and without control circuitry for soft shutdown according to some aspects of this disclosure. For example, simulation result 900 shows a comparison of voltages across phase windings of motors with and without the soft shutdown control circuitry described herein. First graph 902 shows the voltage using a soft-start device as disclosed herein. Second graph 904 shows the voltage without implementing a soft-start device as disclosed herein. Third graph 906 shows the current when using a soft-start device as disclosed herein.

[0070] Figures 902 (first), 904 (second), and 906 (third) clearly illustrate that the motor phase windings experience significant overvoltages in the absence of the soft-start device disclosed herein. Similar overvoltages can be observed in the control circuit connected in series with the phase windings. By implementing the soft-start device disclosed herein, the overvoltages are eliminated, thereby improving the reliability of the control circuit and the motor.

[0071] While various aspects of the invention have been detailed and described in the accompanying drawings and the foregoing description, such description is to be considered illustrative or exemplary, and not restrictive. The invention is not limited to the disclosed embodiments.

[0072] By studying the accompanying drawings, the disclosure, and the dependent claims, those skilled in the art can understand and implement other variations to the disclosed embodiments in practicing the claimed invention. It should be understood that changes may be made in detail, particularly in terms of the construction materials used and the shape, size, and arrangement of components, without departing from the scope of this disclosure. This specification and the described embodiments are exemplary, and the true scope and spirit of this disclosure are indicated by the appended claims.

[0073] aspect:

[0074] The following describes various aspects. Any aspect or any part thereof may be combined with any other aspect or any part thereof.

[0075] Aspect 1. A bidirectional switch for an induction motor, the bidirectional switch comprising:

[0076] First power semiconductor transistor,

[0077] The first power semiconductor transistor includes a first source, a first drain, and a first gate;

[0078] Second power semiconductor transistor,

[0079] The second power semiconductor transistor includes a second source, a second drain, and a second gate;

[0080] Wherein the second source is connected to the first source; and

[0081] A soft-start device includes a control circuit configured to provide a first control signal to a first power semiconductor transistor and a second control signal to a second power semiconductor transistor, wherein the soft-start device is three-phase; and wherein the control circuit generates the first control signal and the second control signal based on the following:

[0082] The falling edge of the turn-on pulse is detected by comparing the measured phase angle with a reference trigger angle.

[0083] Determine the number of return path devices in one or more other phases, wherein the number of return path devices is based on the state of each return path device; and

[0084] The measured phase current is compared with the diode threshold current, wherein the comparison includes determining the slope of the measured phase current.

[0085] Aspect 2. The bidirectional switch according to aspect 1, wherein the control circuit is configured to provide the first control signal and the second control signal, such that the first power semiconductor transistor and the second power semiconductor transistor provide multiple operating modes.

[0086] Aspect 3. The bidirectional switch according to any one of Aspects 1 to 2, wherein the multiple modes include:

[0087] First mode,

[0088] The first mode provides bidirectional current conduction;

[0089] Second mode,

[0090] The second mode provides unidirectional conduction of current in the first direction;

[0091] The third mode,

[0092] The third mode provides unidirectional conduction of current in the second direction; and

[0093] Fourth mode,

[0094] The fourth mode provides bidirectional blocking of current conduction.

[0095] Aspect 4. The bidirectional switch according to any one of Aspects 1 to 3, wherein the plurality of modes further includes:

[0096] The first mode is characterized in that the control circuit provides an enable control signal to both the first power semiconductor transistor and the second power semiconductor transistor.

[0097] The second mode is characterized in that the control circuit provides an enable control signal to the first power semiconductor transistor and a disable control signal to the second power semiconductor transistor.

[0098] The third mode is characterized in that the control circuit provides a disable control signal to the first power semiconductor transistor and an enable control signal to the second power semiconductor transistor; and

[0099] The fourth mode is characterized in that the control circuit provides a disable control signal to both the first power semiconductor transistor and the second power semiconductor transistor.

[0100] Aspect 5. A bidirectional switch according to any one of Aspects 1 to 4, wherein the control circuit is a voltage, resistance divider or a voltage transformer.

[0101] Aspect 6. The bidirectional switch according to any one of Aspects 1 to 5 further includes:

[0102] Trigger angle reference generator,

[0103] The trigger angle reference generator can be configured to generate a linear ramp descent from a fixed starting angle.

[0104] Aspect 7. A method for controlling a bidirectional switch for an induction motor, the method comprising:

[0105] Initializing the first power semiconductor transistor and the second power semiconductor transistor, wherein the initialization includes:

[0106] Provide the first control signal,

[0107] The first control signal sets the first power semiconductor transistor to the off state; and

[0108] Provide a second control signal,

[0109] The second control signal sets the second power semiconductor transistor to the off state;

[0110] Determine the reference trigger angle;

[0111] The measured phase angle is compared with the reference firing angle; and

[0112] Based on the comparison, the first power semiconductor transistor or the second power semiconductor transistor is controlled to one of a variety of modes.

[0113] Aspect 8. The method according to aspect 7, wherein the plurality of modes includes:

[0114] First mode,

[0115] The first mode provides bidirectional current conduction;

[0116] Second mode,

[0117] The second mode provides unidirectional conduction of current in the first direction;

[0118] The third mode,

[0119] The third mode provides unidirectional conduction of current in the second direction; and

[0120] Fourth mode,

[0121] The fourth mode provides bidirectional blocking of current conduction.

[0122] Aspect 9. The method according to any one of Aspects 7 to 8, wherein the plurality of modes further comprises:

[0123] The first mode is characterized by providing an enable control signal for both the first power semiconductor transistor and the second power semiconductor transistor;

[0124] The second mode is characterized by providing an enable control signal to the first power semiconductor transistor and a disable control signal to the second power semiconductor transistor;

[0125] The third mode is characterized by providing a disable control signal to the first power semiconductor transistor and an enable control signal to the second power semiconductor transistor; and

[0126] The fourth mode is characterized by providing a disable control signal to both the first power semiconductor transistor and the second power semiconductor transistor.

[0127] Aspect 10. The method according to any one of aspects 7 to 9, further comprising:

[0128] The detection involves the falling edge of a turn-on pulse generated by comparing the measured phase angle with a reference trigger angle; and

[0129] Determine the number of return path devices in one or more other phases, wherein the number of return path devices is based on the state of each return path device in the return path devices.

[0130] Aspect 11. The method according to any one of Aspects 7 to 10 further includes comparing the measured phase current with a diode threshold current, wherein the comparison includes determining the slope of the measured phase current.

[0131] Aspect 12. The method according to any one of Aspects 7 to 11, wherein the comparison comprises performing the comparison of the measured phase angle with the reference trigger angle for each half-cycle of the power supply voltage.

[0132] Aspect 13. A system for performing soft shutdown of an induction motor, the system comprising:

[0133] Soft starter devices, including:

[0134] First power semiconductor transistor,

[0135] The first power semiconductor transistor includes a first source, a first drain, and a first gate;

[0136] Second power semiconductor transistor,

[0137] The second power semiconductor transistor includes a second source, a second drain, and a second gate.

[0138] Wherein the second source is connected to the first source; and

[0139] The control circuit can be configured to provide a first control signal to the first power semiconductor transistor and a second control signal to the second power semiconductor transistor.

[0140] Aspect 14. The system according to aspect 13, wherein the control circuit is configured to provide the first control signal and the second control signal such that the first power semiconductor transistor and the second power semiconductor transistor provide multiple operating modes.

[0141] Aspect 15. The system according to any one of Aspects 13 to 14, wherein the plurality of modes includes:

[0142] First mode,

[0143] The first mode provides bidirectional current conduction;

[0144] Second mode,

[0145] The second mode provides unidirectional conduction of current in the first direction;

[0146] The third mode,

[0147] The third mode provides unidirectional conduction of current in the second direction; and

[0148] Fourth mode,

[0149] The fourth mode provides bidirectional blocking of current conduction.

[0150] Aspect 16. The system according to any one of aspects 13 to 15, wherein said plurality of modes further comprises:

[0151] The first mode is characterized in that the control circuit provides an enable control signal to both the first power semiconductor transistor and the second power semiconductor transistor.

[0152] The second mode is characterized in that the control circuit provides an enable control signal to the first power semiconductor transistor and a disable control signal to the second power semiconductor transistor.

[0153] The third mode is characterized in that the control circuit provides a disable control signal to the first power semiconductor transistor and an enable control signal to the second power semiconductor transistor; and

[0154] The fourth mode is characterized in that the control circuit provides a disable control signal to both the first power semiconductor transistor and the second power semiconductor transistor.

[0155] Aspect 17. The system according to any one of Aspects 13 to 16, wherein the control circuit is a resistive voltage divider or a voltage transformer.

[0156] Aspect 18. The system according to any one of aspects 13 to 17 further includes:

[0157] Trigger angle reference generator,

[0158] The trigger angle reference generator can be configured to generate a linear ramp descent from a fixed starting angle.

[0159] Aspect 19. The system according to any one of aspects 13 to 18, wherein the control circuitry is further configured to perform operations including:

[0160] The measured phase current is compared with the diode threshold current; and

[0161] Determine the slope of the measured phase current.

[0162] Aspect 20. The system according to any one of Aspects 13 to 19, wherein the control circuit is further configured to perform the comparison of the measured phase current with the reference firing angle for each half-cycle of the power supply voltage.

[0163] The terminology used herein is intended to describe embodiments and is not intended to be limiting. Unless otherwise expressly stated, the terms “a,” “an,” and “the” also include the plural forms. When used in this specification, the terms “comprising” and / or “including” specify the presence of the stated features, integrals, steps, operations, elements, and / or components, but do not exclude the presence or addition of one or more other features, integrals, steps, operations, elements, and / or components.

Claims

1. A bidirectional switch for an induction motor, the bidirectional switch comprising: A first power semiconductor transistor, wherein the first power semiconductor transistor includes a first source, a first drain, a first gate, and a first body diode; A second power semiconductor transistor, wherein the second power semiconductor transistor includes a second source, a second drain, a second gate, and a second body diode; wherein the second source is connected to the first source; And a soft-start device, including control circuitry configured to provide a first control signal to a first power semiconductor transistor and a second control signal to a second power semiconductor transistor, wherein the soft-start device is for a three-phase load; and wherein the control circuitry is configured to generate the first control signal and the second control signal based on one of the three phases: comparing a measured phase angle of a power supply voltage with a reference trigger angle; detecting the falling edge of a turn-on pulse generated to the first power semiconductor transistor and the second power semiconductor transistor by comparing the measured phase angle with the reference trigger angle; Determine the number of return path devices in one or more phases of other phases in the on and off states, wherein the number of return path devices is based on the state of each return path device in the return path devices. The measured phase current is compared with the diode threshold current, wherein the comparison includes determining the slope of the measured phase current; wherein the phase current through the first power semiconductor transistor is switched to the first body diode by turning off the first power semiconductor transistor, and the phase current through the second power semiconductor transistor is switched to the second body diode by turning off the second power semiconductor transistor, so as to control the conduction of the alternating current at zero crossings.

2. The bidirectional switch of claim 1, wherein the control circuit is configured to provide the first control signal and the second control signal such that the first power semiconductor transistor and the second power semiconductor transistor provide multiple operating modes.

3. The bidirectional switch according to claim 2, wherein the multiple operating modes include: First mode, wherein the first mode provides bidirectional conduction of current; A second mode, wherein the second mode provides unidirectional conduction of current in a first direction; A third mode, wherein the third mode provides unidirectional conduction of current in a second direction; and a fourth mode, wherein the fourth mode provides bidirectional blocking of current conduction.

4. The bidirectional switch according to claim 3, wherein the multiple operating modes further include: The first mode is characterized in that the control circuit provides an enable control signal to both the first power semiconductor transistor and the second power semiconductor transistor; the second mode is characterized in that the control circuit provides an enable control signal to the first power semiconductor transistor and a disable control signal to the second power semiconductor transistor; the third mode is characterized in that the control circuit provides a disable control signal to the first power semiconductor transistor and an enable control signal to the second power semiconductor transistor; and the fourth mode is characterized in that the control circuit provides a disable control signal to both the first power semiconductor transistor and the second power semiconductor transistor.

5. The bidirectional switch according to claim 1, wherein the control circuit includes a resistive voltage divider or a voltage transformer.

6. The bidirectional switch according to claim 1, further comprising: A reference trigger angle generator, wherein the reference trigger angle generator can be configured to generate a linear ramp descent from a fixed starting angle.

7. A method for controlling a bidirectional switch for an induction motor, wherein the bidirectional switch comprises: A first power semiconductor transistor, the first power semiconductor transistor including a first source, a first drain, a first gate and a first body diode; and a second power semiconductor transistor, the second power semiconductor transistor including a second source, a second drain, a second gate, and a second body diode, the second source being connected to the first source, wherein the method includes: initializing a first power semiconductor transistor and a second power semiconductor transistor in one phase for a three-phase load, wherein the initialization includes: providing a first control signal, wherein the first control signal sets the first power semiconductor transistor to a turn-off state; and providing a second control signal, wherein the second control signal sets the second power semiconductor transistor to a turn-off state; controlling the first power semiconductor transistor or the second power semiconductor transistor to one of multiple operating modes in one of the three phases, wherein the first power semiconductor transistor or the second power semiconductor transistor is controlled based on: the phase angle of the measured power supply voltage being compared with a reference... The process includes: comparing the firing angle; detecting the falling edge of the turn-on pulse generated to the first and second power semiconductor transistors by comparing the measured phase angle with the reference firing angle; determining the number of return path devices in the on and off states of one or more other phases, wherein the number of return path devices is based on the state of each of the return path devices; and comparing the measured phase current with the diode threshold current, wherein the comparison includes determining the slope of the measured phase current; wherein the phase current through the first power semiconductor transistor is commutated to the first body diode by turning off the first power semiconductor transistor, and the phase current through the second power semiconductor transistor is commutated to the second body diode by turning off the second power semiconductor transistor, to control the conduction of the AC current at zero crossings.

8. The method according to claim 7, wherein the plurality of operating modes include: A first mode, wherein the first mode provides bidirectional conduction of current; a second mode, wherein the second mode provides unidirectional conduction of current in a first direction; A third mode, wherein the third mode provides unidirectional conduction of current in a second direction; and a fourth mode, wherein the fourth mode provides bidirectional blocking of current conduction.

9. The method according to claim 8, wherein the plurality of operating modes further comprises: The first mode is characterized in that an enable control signal is provided to both the first power semiconductor transistor and the second power semiconductor transistor; The second mode is characterized by providing an enable control signal to the first power semiconductor transistor and a disable control signal to the second power semiconductor transistor; the third mode is characterized by providing a disable control signal to the first power semiconductor transistor and an enable control signal to the second power semiconductor transistor; and the fourth mode is characterized by providing disable control signals to both the first power semiconductor transistor and the second power semiconductor transistor.

10. The method of claim 7, wherein the comparison comprises: The comparison between the measured phase angle and the reference trigger angle is performed for each half-cycle of the power supply voltage.

11. A system for performing a soft shutdown of an induction motor, the system comprising: A soft-start device includes: a first power semiconductor transistor, wherein the first power semiconductor transistor includes a first source, a first drain, a first gate, and a first body diode; a second power semiconductor transistor, wherein the second power semiconductor transistor includes a second source, a second drain, a second gate, and a second body diode, wherein the second source is connected to the first source; and control circuitry configured to provide a first control signal to the first power semiconductor transistor and a second control signal to the second power semiconductor transistor, wherein the soft-start device is for a three-phase load; and wherein the control circuitry is configured to generate the first control signal and the second control signal based on one of the three phases: comparing a measured phase angle of a power supply voltage with a reference firing angle; detecting the phase angle by comparing the measured phase angle with... The falling edge of the turn-on pulse generated to the first power semiconductor transistor and the second power semiconductor transistor is generated by comparing the reference firing angle; the number of return path devices in the on and off states of one or more other phases is determined, wherein the number of return path devices is based on the state of each return path device; and the phase current of the measured phase is compared with the diode threshold current, wherein the comparison includes determining the slope of the measured phase current; wherein the phase current through the first power semiconductor transistor is commutated to the first body diode by turning off the first power semiconductor transistor, and the phase current through the second power semiconductor transistor is commutated to the second body diode by turning off the second power semiconductor transistor, to control the conduction of the AC current at zero crossings.

12. The system of claim 11, wherein the control circuit is configured to provide the first control signal and the second control signal such that the first power semiconductor transistor and the second power semiconductor transistor provide multiple operating modes.

13. The system according to claim 12, wherein the plurality of operating modes include: A first mode, wherein the first mode provides bidirectional conduction of current; a second mode, wherein the second mode provides unidirectional conduction of current in a first direction; A third mode, wherein the third mode provides unidirectional conduction of current in a second direction; and a fourth mode, wherein the fourth mode provides bidirectional blocking of current conduction.

14. The system of claim 13, wherein the plurality of operating modes further includes: The first mode is characterized in that the control circuit provides an enable control signal to both the first power semiconductor transistor and the second power semiconductor transistor; the second mode is characterized in that the control circuit provides an enable control signal to the first power semiconductor transistor and a disable control signal to the second power semiconductor transistor; the third mode is characterized in that the control circuit provides a disable control signal to the first power semiconductor transistor and an enable control signal to the second power semiconductor transistor; and the fourth mode is characterized in that the control circuit provides a disable control signal to both the first power semiconductor transistor and the second power semiconductor transistor.

15. The system of claim 11, wherein the control circuit comprises a resistive voltage divider or a voltage transformer.

16. The system of claim 11, further comprising: A reference trigger angle generator, wherein the reference trigger angle generator can be configured to generate a linear ramp descent from a fixed starting angle.

17. The system of claim 16, wherein the control circuitry is further configured to perform the comparison of the measured phase current with the reference firing angle for each half-cycle of the power supply voltage.

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