power converters

Abstract

A power converter (1) includes transistors (Q11, Q12); a converter control unit (10) that outputs a gate pulse for controlling the transistors (Q11, Q12); a functional safety control unit (20) that sets a gate drive permission signal to ON and outputs it when the soundness of the gate cutoff function is not determined; a cutoff circuit (31) that outputs a logical AND operation result of the gate pulse and the gate drive permission signal as a drive signal; a gate drive circuit (41) that outputs a gate signal based on the drive signal; and a current detection unit (61) that detects a current flowing through a phase including the transistors (Q11, Q12) and outputs a current value. Based on the current value and the gate signal, the functional safety control unit (20) temporarily sets the gate drive permission signal to OFF during the period when the gate pulse is ON after confirming that the gate signal has changed to ON during a period when current is not flowing through the transistors (Q11, Q12), and determines whether the gate signal has changed to OFF.

Description

Technical Field

[0001] The present invention relates to a power converter having a power conversion transistor. Background Art

[0002] In recent years, driven by the need for energy conservation, power converters such as inverters and servo amplifiers, which provide variable-speed motor drives, have become increasingly common. Meanwhile, because abnormal operation of electrical equipment can sometimes lead to serious accidents, manufacturers are striving to enhance safety features. Furthermore, strict safety standards are established throughout each stage of product development, design, production, maintenance, and disposal to minimize potential human impacts.

[0003] In particular, regarding electrical equipment, there are functional safety standards such as IEC (International Electrotechnical Commission) 61508 and IEC 61800-5-2, which takes into account motor drive systems such as inverters and servo amplifiers.

[0004] To comply with these safety standards, electrical equipment must be equipped with a functional safety system. This system includes safety functions that prevent the equipment from being driven and monitoring functions that detect safety function anomalies. To demonstrate compliance with the safety standards set by these standards, the circuits that comprise the functional safety system must undergo quantitative evaluation using methods such as Failure Modes Effects and Diagnostics Analysis (FMEDA). Furthermore, any circuit changes require ongoing management through impact analysis. Consequently, the larger the circuit scale of a functional safety system, the higher the management cost.

[0005] The STO (Safe Torque Off) function, which shuts off the energy supplied to the motor when the motor is stopped, is provided. This function is implemented by a safety device, for example, which includes a gate drive circuit with a cutoff function between the main circuit and the control device. This device shuts down the gate drive circuit and cuts off the control signal in response to a cutoff command from an independently installed safety function circuit, thereby stopping the power supply to the motor from the main circuit. The main circuit supplies the power to drive the motor, and the control device generates the control signal for controlling the switching devices in the main circuit. As one of the cutoff conditions for the gate drive circuit, the safety function circuit outputs a cutoff command when a cutoff signal, also known as a Safe Torque Off command, is input from the outside.

[0006] However, if the cutoff signal is not always input, it is unclear whether the gate drive circuit operates normally when the cutoff signal is actually input. Attempting to verify the normal operation of the safe torque-off function by simulating the input of a cutoff signal requires stopping the power converter, which reduces the operating efficiency. Another method involves checking the gate drive circuit's response and ensuring its integrity by applying a short cutoff confirmation pulse to the gate signal of the gate drive circuit, to which the transistors of the main circuit cannot respond.

[0007] However, the time width of the confirmation pulse is strictly limited in the following aspects. First, the thickness of the wafer of the switching device used in the main circuit, that is, the transistor, has become thinner, and high-speed cut-off is required in the event of an abnormality. Therefore, it is necessary to speed up the response of the gate drive circuit so that the transistor will respond to a short confirmation pulse. As a result, when the integrity of the safe torque-off function is confirmed, the error in the output voltage from the main circuit increases. Then, the switching speed of the transistor of the new generation switching device such as SiC (Silicon Carbide) has become even faster, and high-frequency switching is performed to utilize this feature. Therefore, it is necessary to speed up the response of the entire gate drive circuit including the cut-off circuit so that the transistor will respond even to a short confirmation pulse. As a result, the error in the output voltage from the main circuit increases because the gate state becomes different from the instruction of the control device due to the cut-off confirmation.

[0008] To address this problem, Patent Document 1 discloses a technology that cuts off the power supply to the gate drive element, i.e., the photocoupler, when the converter control gate pulse is turned off during one on-off cycle of PWM (Pulse Width Modulation) control, monitors the power cut-off state, and confirms the operation of the gate cut-off function, thereby confirming the integrity of the gate cut-off function without affecting the converter control.

[0009] Patent Document 1: Japanese Patent Application Laid-Open No. 2016-127702 Summary of the Invention

[0010] However, the above-mentioned prior art suffers from the problem of being unable to confirm abnormalities on the output side of the gate drive element or the actual state of the gate signal input to the transistor. Furthermore, in order to confirm the operation of the aforementioned gate cutoff function in a short period of time, matching the timing of the converter control gate pulse turning off within a single PWM control on-off cycle, the above-mentioned prior art requires transmitting information on the PWM control on-off timing to the functional safety system, which makes it impossible to maintain the independence of the functional safety system and the converter control system.

[0011] The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to provide a power converter capable of confirming the soundness of the gate cutoff function of a power conversion transistor without affecting normal operation.

[0012] In order to solve the above-mentioned problems and achieve the purpose, the power converter of the present invention is characterized in that it has: two transistors connected in series for use in power conversion; a converter control unit, which outputs a gate pulse for controlling the on and off of the transistor for each transistor; a functional safety control unit, which sets the gate drive permission signal to be turned on and outputs it for each transistor when the soundness of the gate cut-off function of the transistor is not determined; two cut-off circuits, which correspond to each of the two transistors and output the result of a logical AND operation using the gate pulse and the gate drive permission signal as a drive signal; two gate drive circuits, which correspond to each of the two transistors and output the gate signal for driving the transistor to the transistor and the functional safety control unit based on the drive signal; and a current detection unit, which detects the current flowing through the phase including the two transistors and outputs the detection result as a current value to the functional safety control unit. For each transistor, the functional safety control unit, based on the current value and gate signal, temporarily turns off the gate drive enable signal while the gate pulse is on, after confirming that the gate signal has changed to on during a period when current is not flowing through the transistor, to determine whether the gate signal has changed to off.

[0013] Effects of the Invention

[0014] The power converter of the present invention has an effect of being able to confirm the soundness of the gate cutoff function of the power conversion transistor without affecting normal operation. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 This is a diagram showing a configuration example of a power converter according to the first embodiment.

[0016] Figure 2 This is a diagram showing an example of an operation waveform of the power converter according to the first embodiment.

[0017] Figure 3 This is a flowchart showing the operation of the power converter according to the first embodiment.

[0018] Figure 4 This is a diagram showing a configuration example of hardware that realizes the processing circuit of the power converter according to the first embodiment.

[0019] Figure 5 This is a diagram showing a configuration example of a power converter according to the second embodiment.

[0020] Figure 6 FIG1 is a first diagram showing an example of an operation waveform of the power converter according to the second embodiment.

[0021] Figure 7 FIG2 is a second diagram showing an example of an operation waveform of the power converter according to the second embodiment.

[0022] Figure 8 This is a flowchart showing the operation of the power converter according to the second embodiment. DETAILED DESCRIPTION

[0023] Hereinafter, a power converter according to an embodiment of the present invention will be described in detail with reference to the drawings.

[0024] Implementation Method 1

[0025] Figure 1 This figure shows a configuration example of a power converter 1 according to Embodiment 1. The power converter 1 includes a converter control unit 10, a functional safety control unit 20, cutoff circuits 31 and 32, gate drive circuits 41 and 42, gate signal branching units 51 and 52, transistors Q11 and Q12, freewheeling diodes D11 and D12, and a current detection unit 61.

[0026] The converter control unit 10 is a control unit for performing normal power conversion control in the power converter 1. The converter control unit 10 outputs a gate pulse GP11 used for power conversion control, that is, for controlling the gate connection and gate disconnection of the transistor Q11 of the main circuit, to the disconnection circuit 31. Similarly, the converter control unit 10 outputs a gate pulse GP12 used for power conversion control, that is, for controlling the gate connection and gate disconnection of the transistor Q12 of the main circuit, to the disconnection circuit 32. In other words, the converter control unit 10 outputs gate pulses GP11 and GP12 for controlling the on and off of the transistors Q11 and Q12, respectively. In the following description, gate connection is simply referred to as connection, and gate disconnection is simply referred to as disconnection. The main circuit is, for example, an inverter that supplies power to an electric motor (not shown) in the power converter 1, but is not limited to this.

[0027] The functional safety control unit 20 is a control unit in the power converter 1 that performs functional safety control. As described in the background section, functional safety control refers to the control of a functional safety system that includes a safety function that prevents driving force from being applied to electrical equipment and a monitoring function that monitors for abnormalities in the safety function. In this embodiment, functional safety control involves the control of the function that safely stops the power converter 1. Specifically, it involves the control of the execution of gate cutoff and the integrity check of the gate cutoff function. The functional safety control unit 20 outputs a gate drive enable signal SAF11 for functional safety control to the cutoff circuit 31 and a gate drive enable signal SAF12 for functional safety control to the cutoff circuit 32. During normal operation, the functional safety control unit 20 turns on and outputs the gate drive enable signals SAF11 and SAF12. Here, normal operation refers to the state in which the power converter 1 is not executing gate cutoff or the integrity check of the gate cutoff function. Operations other than normal operation refer to the state in which the power converter 1 is executing gate cutoff or the integrity check of the gate cutoff function. As described above, the functional safety control unit 20 turns on and outputs the gate drive enable signal SAF11 to the transistor Q11 when the integrity of the gate cutoff function of the transistor Q11 is not determined. The functional safety control unit 20 turns on and outputs the gate drive enable signal SAF12 to the transistor Q12 when the integrity of the gate cutoff function of the transistor Q12 is not determined.

[0028] When both the gate pulse GP11 output from the converter control unit 10 and the gate drive enable signal SAF11 output from the functional safety control unit 20 are on, corresponding to transistor Q11, the cutoff circuit 31 turns on and outputs a drive signal for driving the gate drive circuit 41. Specifically, the cutoff circuit 31 is an AND circuit that performs a logical AND operation using the gate pulse GP11 and the gate drive enable signal SAF11, and outputs the result of the logical AND operation as the drive signal. Similarly, the cutoff circuit 32 turns on and outputs a drive signal for driving the gate drive circuit 42 when both the gate pulse GP12 output from the converter control unit 10 and the gate drive enable signal SAF12 output from the functional safety control unit 20 are on, corresponding to transistor Q12. Specifically, the cutoff circuit 32 is an AND circuit that performs a logical AND operation using the gate pulse GP12 and the gate drive enable signal SAF12, and outputs the result of the logical AND operation as the drive signal.

[0029] Because the cutoff circuit 31 performs the above-described operation, the functional safety control unit 20 can disconnect the output of the cutoff circuit 31 by turning off the gate drive enable signal SAF11 for the cutoff circuit 31. That is, the functional safety control unit 20 can disconnect the gate pulse GP11 used for normal power conversion control, output from the converter control unit 10, in the power converter 1, and place the transistor Q11 in the gate-off state. Similarly, because the cutoff circuit 32 performs the above-described operation, the functional safety control unit 20 can disconnect the output of the cutoff circuit 32 by turning off the gate drive enable signal SAF12 for the cutoff circuit 32. That is, the functional safety control unit 20 can disconnect the gate pulse GP12 used for normal power conversion control, output from the converter control unit 10, in the power converter 1, and place the transistor Q12 in the gate-off state.

[0030] The gate drive circuit 41 corresponds to the transistor Q11 and outputs a gate signal for driving the transistor Q11 based on the drive signal output from the cutoff circuit 31. That is, the gate drive circuit 41 drives the transistor Q11 according to the drive signal output from the cutoff circuit 31. Specifically, the gate drive circuit 41 turns the gate signal on and outputs it when the drive signal is on, and turns the gate signal off and outputs it when the drive signal is off. Similarly, the gate drive circuit 42 corresponds to the transistor Q12 and outputs a gate signal for driving the transistor Q12 based on the drive signal output from the cutoff circuit 32. That is, the gate drive circuit 42 drives the transistor Q12 according to the drive signal output from the cutoff circuit 32. Specifically, the gate drive circuit 42 turns the gate signal on and outputs it when the drive signal is on, and turns the gate signal off and outputs it when the drive signal is off.

[0031] The gate signal branching unit 51 branches the gate signal output from the gate drive circuit 41 to the transistor Q11. The gate signal branching unit 51 outputs one of the branched gate signals to the transistor Q11 and feeds the other of the branched gate signals back to the functional safety control unit 20 as the gate signal FBQ11. Similarly, the gate signal branching unit 52 branches the gate signal output from the gate drive circuit 42 to the transistor Q12. The gate signal branching unit 52 outputs one of the branched gate signals to the transistor Q12 and feeds the other of the branched gate signals back to the functional safety control unit 20 as the gate signal FBQ12.

[0032] Here, due to the necessity of controlling the operation of transistor Q11, the current value of the gate signal output from gate drive circuit 41 to transistor Q11 is greater than the current value of the drive signal output from cutoff circuit 31 to gate drive circuit 41. Therefore, if gate signal branching section 51 simply branches the gate signal, a large current would flow through functional safety control unit 20 as gate signal FBQ11. Therefore, gate signal branching section 51 branches the gate signal output from gate drive circuit 41 to transistor Q11 so that the current value of gate signal FBQ11 fed back to functional safety control unit 20 is less than or equal to a specified current value. To ensure the current required to control the operation of transistor Q11, cutoff circuit 31 may also slightly increase the current value of the drive signal before outputting it, taking into account the current amount branched by gate signal branching section 51 to functional safety control unit 20. Similarly, due to the need to control the operation of transistor Q12, the current value of the gate signal output from gate drive circuit 42 to transistor Q12 is greater than the current value of the drive signal output from cutoff circuit 32 to gate drive circuit 42. Therefore, if gate signal branching section 52 simply branches the gate signal, a large current would flow through functional safety control unit 20 as gate signal FBQ12. Therefore, gate signal branching section 52 branches the gate signal output from gate drive circuit 42 to transistor Q12 so that the current value of gate signal FBQ12 fed back to functional safety control unit 20 is less than or equal to a specified current value. To ensure the current required to control the operation of transistor Q12, cutoff circuit 32 may also slightly increase the current value of the drive signal before outputting it, taking into account the amount of current branched from gate signal branching section 52 to functional safety control unit 20. Furthermore, the power converter 1 may prevent a large current from flowing into the functional safety controller 20 by adjusting the input impedance of the transistors Q11 and Q12 and the functional safety controller 20 , thereby preventing the gate signal branching units 51 and 52 from having the above-mentioned function.

[0033] It can also be said that in power converter 1, gate drive circuit 41 outputs a gate signal to transistor Q11 and functional safety control unit 20 via gate signal branching unit 51. Similarly, gate drive circuit 42 outputs a gate signal to transistor Q12 and functional safety control unit 20 via gate signal branching unit 52.

[0034] The transistor Q11 is a switching device included in the main circuit and performs power conversion in the power converter 1. The power conversion transistor Q11 used for power conversion is turned on and off according to the gate signal output from the gate drive circuit 41. Specifically, the transistor Q11 is gate-on when the gate signal is on, and is gate-off when the gate signal is off. Similarly, the transistor Q12 is a switching device included in the main circuit and performs power conversion in the power converter 1. The power conversion transistor Q12 used for power conversion is turned on and off according to the gate signal output from the gate drive circuit 42. Specifically, the transistor Q12 is gate-on when the gate signal is on, and is gate-off when the gate signal is off. In this embodiment, the transistors Q11 and Q12 will not be gate-on at the same time.

[0035] The freewheeling diode D11 is a diode connected in parallel with the transistor Q11. Similarly, the freewheeling diode D12 is a diode connected in parallel with the transistor Q12.

[0036] The current detection unit 61 detects the current I1 flowing through the phase including the transistors Q11 and Q12. The current I1 flowing through the phase is the current flowing through the connection line between the power converter 1 and the motor (not shown) supplied with power by the power converter 1. Specifically, the current detection unit 61 detects the current I1 flowing through the transistor Q11, or the freewheeling diode D11, or the transistor Q12, or the freewheeling diode D12. The current detection unit 61 outputs the detection result, i.e., the detected current I1, to the functional safety control unit 20 as a feedback signal, i.e., the current value FBI1. The current I1 is expressed as Figure 1 The direction of the arrow shown is assumed to be positive, and the Figure 1 The arrows shown are in the opposite direction of the flow, which is negative. Figure 1 In the example, when the current I1 flows through the transistor Q11 or the freewheeling diode D12, the current I1 is positive, and when the current I1 flows through the freewheeling diode D11 or the transistor Q12, the current I1 is negative.

[0037] The functional safety control unit 20 monitors the gate signal FBQ11 fed back from the gate signal branch unit 51, the gate signal FBQ12 fed back from the gate signal branch unit 52, and the current value FBI1 output from the current detection unit 61. Specifically, the functional safety control unit 20 monitors the gate signal output from the gate drive circuit 41 to the transistor Q11, the gate signal output from the gate drive circuit 42 to the transistor Q12, and the current I1 flowing through the transistor Q11 or the freewheeling diode D11, the transistor Q12 or the freewheeling diode D12.

[0038] Next, a description will be given of a mechanism for checking the soundness of the gate cutoff function in the power converter 1. In the first embodiment, the gate cutoff function is a function for setting the gates of the transistors Q11 and Q12 to an OFF state when some abnormality is detected in the power converter 1.

[0039] In power converter 1, current I1 flows through transistor Q11 or freewheeling diode D12 when current I1 is positive, and through freewheeling diode D11 or transistor Q12 when current I1 is negative. When current I1 flows through freewheeling diode D11, even if transistor Q11 is gate-on, current I1 does not flow through transistor Q11 and continues to flow through freewheeling diode D11. Therefore, even if transistor Q11 is gate-on while current I1 is flowing in a negative direction, current I1 does not flow through transistor Q11, thus unaffecting the output voltage intended to be generated by the original converter control. Similarly, when current I1 flows through freewheeling diode D12, even if transistor Q12 is gate-on, current I1 does not flow through transistor Q12 and continues to flow through freewheeling diode D12. Therefore, even if the gate of transistor Q12 is turned on while current I1 is flowing in the positive direction, current I1 does not flow through transistor Q12 , and thus power converter 1 is not affected by the output voltage to be generated by the original converter control.

[0040] Since the current value FBI1 is fed back from the current detection unit 61, the functional safety control unit 20 can detect whether the current I1 is flowing in a positive or negative direction based on the current value FBI1. In addition, since the gate signal FBQ11 is fed back from the gate signal branch unit 51, the functional safety control unit 20 can detect the state of the gate signal given to the transistor Q11. Therefore, the functional safety control unit 20 first detects the period when the current I1 is flowing in a negative direction based on the current value FBI1 fed back from the current detection unit 61. Even during the period when the current I1 is flowing in a negative direction, the converter control unit 10, regardless of the operation of the functional safety control unit 20 and others, outputs the gate pulse GP11 by appropriately turning it on or off in order to control the operation of the equipment connected to the power converter 1.

[0041] As described above, since the functional safety control unit 20 turns on and outputs the gate drive enable signal SAF11, the converter control unit 10 turns on the gate pulse GP11, causing the cutoff circuit 31 to turn on and output the drive signal to the gate drive circuit 41. As a result, the gate drive circuit 41 turns on the gate signal based on the on drive signal from the cutoff circuit 31 and outputs it to the transistor Q11. The gate signal branching unit 51 branches the on gate signal output from the gate drive circuit 41 to the transistor Q11 and feeds the gate signal FBQ11 back to the functional safety control unit 20. The functional safety control unit 20 can detect that the gate signal output from the gate drive circuit 41 is on by feeding back the gate signal FBQ11 from the gate signal branching unit 51.

[0042] The functional safety control unit 20 turns off the gate drive enable signal SAF11 while the current I1 is flowing in a negative direction and the gate signal output from the gate drive circuit 41 is on. Since the gate drive enable signal SAF11 output from the functional safety control unit 20 is off, the cutoff circuit 31 turns off the drive signal to the gate drive circuit 41 and outputs it. Based on the off drive signal from the cutoff circuit 31, the gate drive circuit 41 turns off the gate signal and outputs it to the transistor Q11. The gate signal branching unit 51 branches the off gate signal output from the gate drive circuit 41 to the transistor Q11 and feeds the gate signal FBQ11 back to the functional safety control unit 20.

[0043] The functional safety control unit 20 can detect that the gate signal output from the gate drive circuit 41 is off by feedback from the gate signal FBQ11 from the gate signal branch unit 51. Thus, since the gate signal to the transistor Q11 is turned off by turning the gate drive enable signal SAF11 off, the functional safety control unit 20 can determine that the gate cutoff function is functioning properly. The functional safety control unit 20 turns the gate drive enable signal SAF11 off while the current I1 is flowing in a negative direction and the gate signal output from the gate drive circuit 41 is on. If the gate signal output from the gate drive circuit 41 is no longer off as detected by feedback from the gate signal FBQ11 from the gate signal branch unit 51, the functional safety control unit 20 determines that the gate cutoff function is malfunctioning.

[0044] Figure 2 : is a diagram showing an example of an operation waveform of the power converter 1 according to the first embodiment. Figure 2In the figure, the current value I1 is the current I1 detected by the current detection unit 61, and is the current value FBI1 fed back from the current detection unit 61 to the functional safety control unit 20. The Q11 gate pulse is the gate pulse GP11 output from the converter control unit 10. The Q11 gate drive enable signal is the gate drive enable signal SAF11 output from the functional safety control unit 20. The Q11 gate drive circuit output is the gate signal output from the gate drive circuit 41 to the transistor Q11, and is the gate signal FBQ11 fed back from the gate signal branch unit 51 to the functional safety control unit 20. In addition, the description of the signals associated with the transistor Q12, namely the gate pulse GP12, the gate drive enable signal SAF12, and the gate signal FBQ12, is omitted.

[0045] The functional safety control unit 20 determines that the gate cutoff function is normal if, after confirming that the gate signal FBQ11, the gate signal output from the gate drive circuit 41, has turned on while the current I1 is flowing in a negative direction, the functional safety control unit 20 temporarily turns off the gate drive enable signal SAF11 while the gate pulse GP11 is on, causing the gate signal FBQ11, the gate signal output from the gate drive circuit 41, to turn off. Under the same conditions as above, if the functional safety control unit 20 cannot detect that the gate signal FBQ11, the gate signal output from the gate drive circuit 41, has turned off, the functional safety control unit 20 determines that the gate cutoff function is abnormal.

[0046] Here, the functional safety control unit 20 does not know the duration for which the converter control unit 10 turns on and outputs the gate pulse GP11. However, if information is pre-set regarding the minimum duration for which the gate pulse GP11 remains on when the converter control unit 10 turns on the gate pulse GP11, the functional safety control unit 20 can perform the above-mentioned operation by temporarily turning off the gate drive enable signal SAF11 during the minimum duration for which the gate pulse GP11 remains on, i.e., turning it on again after turning it off. Furthermore, the functional safety control unit 20 can also select the shortest on-period as the minimum on-period for which the gate pulse GP11 remains on, from among the periods during which the gate signal FBQ11 fed back from the gate signal branch unit 51 is on, while the power converter 1 is operating for a specified period. Alternatively, when the power converter 1 supplies power to an electric motor (not shown), the power converter 1 generally does not drastically change the control content midway to ensure smooth operation of the motor. In the functional safety control unit 20, if the on-period of the previous gate pulse GP11 is greater than or equal to a predetermined period, a certain degree of on-period can be expected to be ensured during the on-period of the next gate pulse GP11, for example, even if the on-period is shorter than the previous period. Therefore, based on the on-period of the previous gate pulse GP11, the functional safety control unit 20 may temporarily turn off the gate drive enable signal SAF11 during the on-period of the next gate pulse GP11, for which a certain degree of on-period can be expected.

[0047] As described above, in the power converter 1, the functional safety control unit 20 temporarily turns off the gate drive enable signal SAF11 based on the current value FBI1 and the gate signal FBQ11 during a period in which the current I1 flows in a negative direction, that is, during a period in which the current I1 does not flow through the transistor Q11 and the gate signal is on, and determines the soundness of the gate cutoff function for the transistor Q11 by whether the gate signal to the transistor Q11 changes to off.

[0048] The operation of the power converter 1 will be described using a flowchart. Figure 3This is a flowchart illustrating the operation of the power converter 1 according to Embodiment 1. In the power converter 1, the functional safety control unit 20 determines whether the direction of the current I1 is negative, that is, whether the current value FBI1 fed back from the current detection unit 61 is negative (step S11). If the current value FBI1 is positive (step S11: No), the functional safety control unit 20 performs the operation of step S11 again. If the current value FBI1 is negative (step S11: Yes), the functional safety control unit 20 checks whether the gate signal output from the gate drive circuit 41 to the transistor Q11 is on, that is, whether the gate signal FBQ11 fed back from the gate signal branch unit 51 is on (step S12). If the gate signal FBQ11 is off (step S12: No), the functional safety control unit 20 performs the operation of step S11 again.

[0049] If gate signal FBQ11 is on (step S12: Yes), the functional safety control unit 20 temporarily turns off gate drive enable signal SAF11 while gate signal FBQ11 is on (step S13). By temporarily turning off gate drive enable signal SAF11, the functional safety control unit 20 checks whether the gate signal output from gate drive circuit 41 to transistor Q11 has turned off, that is, whether the gate signal FBQ11 fed back from gate signal branch unit 51 has turned off (step S14). If gate signal FBQ11 has turned off (step S14: Yes), the functional safety control unit 20 determines that the gate cutoff function is functioning properly (step S15). Specifically, when the functional safety control unit 20 temporarily turns the gate drive enable signal SAF11 off and then back on again, and successfully confirms a change from on to off to on in the gate signal FBQ11 fed back from the gate signal branch unit 51 in response to the change in the gate drive enable signal SAF11, the functional safety control unit 20 determines that the gate cutoff function is normal. If the gate signal FBQ11 does not change to off (step S14: No), the functional safety control unit 20 determines that the gate cutoff function is abnormal (step S16). The functional safety control unit 20 may also determine that the gate cutoff function is abnormal if the gate signal FBQ11 changes to off when the gate drive enable signal SAF11 is off, but does not change to on when the gate drive enable signal SAF11 is turned on again. If the functional safety control unit 20 determines that the gate cutoff function is abnormal, it turns off the gate drive enable signals SAF11 and SAF12 (step S17).

[0050] Here, as Figure 2As shown, if an abnormality is detected during the determination of the integrity of the gate cutoff function of transistor Q11, the functional safety control unit 20 may be unable to turn off the gate signal FBQ11, the feedback signal, that is, the gate signal output from the gate drive circuit 41 to transistor Q11, even if the gate drive enable signal SAF11 is turned off. However, by turning off the gate drive enable signal SAF12 for transistor Q12, the functional safety control unit 20 can turn off the gate signal output from the gate drive circuit 42 to transistor Q12. In this case, the functional safety control unit 20 can issue an alert to the user of the power converter 1, etc., indicating that an abnormality has been detected in the integrity of the gate cutoff function. Alternatively, the functional safety control unit 20 can execute control such as cutting off the power supply to the converter control unit 10 and stopping the output of gate pulses GP11 and GP12 from the converter control unit 10 to stop the operation of the power converter 1. Thus, the functional safety control unit 20 can turn off the gates of both transistors Q11 and Q12.

[0051] While the functional safety control unit 20 has been described as determining the integrity of the gate cutoff function for transistor Q11, the functional safety control unit 20 also operates in the same manner as it determines the integrity of the gate cutoff function for transistor Q12. When determining the integrity of the gate cutoff function for transistor Q12, the functional safety control unit 20 temporarily turns off the gate drive enable signal SAF12 while the current I1 is flowing in a positive direction and the gate of transistor Q12 is on, and then checks whether the gate signal FBQ12 has been turned off.

[0052] As described above, for transistor Q11, the functional safety control unit 20 temporarily turns off the gate drive enable signal SAF11 while the gate pulse GP11 is on, after confirming that the gate signal FBQ11 has turned on, based on the current value of current I1 and the gate signal FBQ11, during a period when no current is flowing through transistor Q11. Similarly, for transistor Q12, the functional safety control unit 20 temporarily turns off the gate drive enable signal SAF12 while the gate pulse GP12 is on, after confirming that the gate signal FBQ12 has turned on, based on the current value of current I1 and the gate signal FBQ12, during a period when no current is flowing through transistor Q12. Furthermore, if the functional safety control unit 20 determines that the gate cutoff function of one transistor is abnormal, it turns off the gate drive enable signals SAF11 and SAF12 for both transistors Q11 and Q12.

[0053] Next, the hardware configuration of power converter 1 implementing Embodiment 1 will be described. In power converter 1, cutoff circuits 31 and 32 are electrical circuits that form AND circuits. Gate drive circuits 41 and 42 amplify the current values of the drive signals output from cutoff circuits 31 and 32. Gate signal branching units 51 and 52 branch gate signals. Current detection unit 61 is a sensor. Transistors Q11 and Q12 and freewheeling diodes D11 and D12 are semiconductor elements. Converter control unit 10 and functional safety control unit 20 are implemented by processing circuits. Figure 4 1 is a diagram showing a configuration example of hardware that realizes a processing circuit of the power converter 1 according to the first embodiment. Figure 4 A configuration example is shown in which the converter control unit 10 and the functional safety control unit 20 are implemented by a processing circuit 90 including a processor 91 and a memory 92 .

[0054] Processor 91 is a CPU (Central Processing Unit). Processor 91 may also be an arithmetic device, a microprocessor, a microcomputer, or a DSP (Digital Signal Processor). Memory 92 is, for example, a volatile or nonvolatile semiconductor memory such as RAM (Random Access Memory), ROM (Read Only Memory), flash memory, EPROM (Erasable Programmable Read Only Memory), or EEPROM (registered trademark) (Electrically Erasable Programmable Read Only Memory).

[0055] The memory 92 stores a program for operating as the converter control unit 10 and the functional safety control unit 20. The processor 91 reads and executes the program, thereby realizing the converter control unit 10 and the functional safety control unit 20. In addition, the program for operating as the converter control unit 10 and the functional safety control unit 20 stored in the memory 92 can be provided to the user in a state of being written on a recording medium such as a CD (Compact Disc)-ROM or a DVD (Digital Versatile Disc)-ROM, or can be provided via a network. In addition, the processor 91 outputs data such as calculation results to the volatile memory of the memory 92. Alternatively, the processor 91 saves the data by outputting data such as calculation results to an auxiliary storage device via the volatile memory of the memory 92.

[0056] Figure 4This is an example of hardware in which the converter control unit 10 and the functional safety control unit 20 are implemented using a general-purpose processor 91 and memory 92. However, the converter control unit 10 and the functional safety control unit 20 may also be implemented using a dedicated processing circuit in place of the processor 91 and memory 92. Here, the dedicated processing circuit may be a single circuit, a composite circuit, an ASIC (Application Specific Integrated Circuit), an FPGA (Field Programmable Gate Array), or a combination thereof. Furthermore, the converter control unit 10 and the functional safety control unit 20 may be partially implemented using the processor 91 and memory 92, while the remaining portion may be implemented using a dedicated processing circuit.

[0057] As described above, according to this embodiment, in power converter 1, functional safety control unit 20 determines the period during which current I1 is not flowing through transistor Q11 based on current value FBI1 from current detection unit 61, and determines the period during which the gate signal to transistor Q11 is on based on gate signal FBQ11 from gate signal branching unit 51. During the period during which current I1 is not flowing through transistor Q11, while the gate signal to transistor Q11 is on, functional safety control unit 20 temporarily turns off gate drive enable signal SAF11 and determines the integrity of the gate cutoff function for transistor Q11 by determining whether the gate signal to transistor Q11 changes to off. Similarly, functional safety control unit 20 determines the period during which current I1 is not flowing through transistor Q12 based on current value FBI1 from current detection unit 61, and determines the period during which the gate signal to transistor Q12 is on based on gate signal FBQ12 from gate signal branching unit 52. When the gate signal to transistor Q12 is on while current I1 is not flowing through transistor Q12, functional safety control unit 20 temporarily turns off gate drive enable signal SAF12. The robustness of the gate cutoff function for transistor Q12 is determined by whether the gate signal to transistor Q12 has turned off. This allows functional safety control unit 20 to verify the robustness of the gate cutoff function for power conversion transistors Q11 and Q12 without affecting the normal operation of power converter 1.

[0058] Furthermore, the functional safety control unit 20 can verify the integrity of the gate cutoff function for transistors Q11 and Q12 of the main circuit without using short-duration confirmation pulses that would render the main circuit unresponsive. Furthermore, the functional safety control unit 20 can monitor the output conditions of the gate drive circuits 41 and 42, thereby enabling integrity verification, including the status of the gate signals actually input to transistors Q11 and Q12. Furthermore, the functional safety control unit 20 operates independently without receiving information such as control timing from the converter control unit 10, thereby maintaining the independence of the converter control unit 10 and the functional safety control unit 20. Furthermore, the functional safety control unit 20 can verify the integrity of the gate cutoff function without stopping the operation of the power converter 1 and without affecting the output voltage intended to be generated through the original converter control, thereby improving the reliability of the power converter 1.

[0059] Implementation Method 2

[0060] In the first embodiment, power converter 1 determines whether the gate cutoff function is normal for one branch of two transistors Q11 and Q12, i.e., one transistor pair. In the second embodiment, a case will be described in which the power converter determines whether the gate cutoff function is normal for multiple branches of multiple transistor pairs.

[0061] Figure 5 : This is a diagram showing a structural example of a power converter 1a according to Embodiment 2. The power converter 1a includes a converter control unit 10a, a functional safety control unit 20a, cutoff circuits 31 to 34, gate drive circuits 41 to 44, gate signal branch units 51 to 54, transistors Q11, Q12, Q21, Q22, freewheeling diodes D11, D12, D21, D22, and current detection units 61 and 62. In Embodiment 2, the power converter 1a includes a plurality of transistors Q11, Q12, Q21, Q22, i.e., a plurality of branches. In addition, the power converter 1a includes a plurality of cutoff circuits 31 to 34, a plurality of gate drive circuits 41 to 44, and a plurality of gate signal branch units 51 to 54 corresponding to each of the plurality of transistors Q11, Q12, Q21, Q22. In addition, the power converter 1a includes a plurality of current detection units 61 and 62 corresponding to each of the plurality of branches. In addition, in Embodiment 2, as Figure 5 The power converter 1a is described as an example in which the power converter 1a includes four transistors Q11, Q12, Q21, and Q22, that is, two pairs of transistors forming two branches. However, the power converter may also include three or more branches.

[0062] The converter control unit 10a is a control unit for performing normal power conversion control in the power converter 1a. The converter control unit 10a outputs a gate pulse GP11 for power conversion control, i.e., for controlling the on / off operation of the main circuit transistor Q11, to a disconnection circuit 31. Furthermore, the converter control unit 10a outputs a gate pulse GP12 for power conversion control, i.e., for controlling the on / off operation of the main circuit transistor Q12, to a disconnection circuit 32. Furthermore, the converter control unit 10a outputs a gate pulse GP21 for power conversion control, i.e., for controlling the on / off operation of the main circuit transistor Q21, to a disconnection circuit 33. Furthermore, the converter control unit 10a outputs a gate pulse GP22 for power conversion control, i.e., for controlling the on / off operation of the main circuit transistor Q22, to a disconnection circuit 34. The main circuit may be, for example, an inverter in the power converter 1a that supplies power to an electric motor (not shown), etc., but is not limited thereto.

[0063] The functional safety control unit 20a is a control unit in the power converter 1a that performs functional safety control. The functional safety control unit 20a outputs a gate drive enable signal SAF11 for functional safety control to the cutoff circuit 31, a gate drive enable signal SAF12 for functional safety control to the cutoff circuit 32, a gate drive enable signal SAF21 for functional safety control to the cutoff circuit 33, and a gate drive enable signal SAF22 for functional safety control to the cutoff circuit 34. The functional safety control unit 20a turns on the gate drive enable signal SAF11 for transistor Q11 when the integrity of the gate cutoff function of transistor Q11 is not being determined. The functional safety control unit 20a turns on the gate drive enable signal SAF12 for transistor Q12 when the integrity of the gate cutoff function of transistor Q12 is not being determined. The functional safety control unit 20a turns on the gate drive enable signal SAF21 for transistor Q21 when the integrity of the gate cutoff function of transistor Q21 is not being determined. The functional safety control unit 20 a turns on and outputs the gate drive permission signal SAF22 for the transistor Q22 when the soundness of the gate cutoff function of the transistor Q22 is not determined.

[0064] When both the gate pulse GP21 output from the converter control unit 10a and the gate drive enable signal SAF21 output from the functional safety control unit 20a are on, corresponding to transistor Q21, the cutoff circuit 33 turns on and outputs a drive signal for driving the gate drive circuit 43. Specifically, the cutoff circuit 33 is an AND circuit that performs a logical AND operation using the gate pulse GP21 and the gate drive enable signal SAF21, and outputs the result of the logical AND operation as the drive signal. Similarly, the cutoff circuit 34 turns on and outputs a drive signal for driving the gate drive circuit 44 when both the gate pulse GP22 output from the converter control unit 10a and the gate drive enable signal SAF22 output from the functional safety control unit 20a are on, corresponding to transistor Q22. Specifically, the cutoff circuit 34 is an AND circuit that performs a logical AND operation using the gate pulse GP22 and the gate drive enable signal SAF22, and outputs the result of the logical AND operation as the drive signal. Note that the operations of the cutoff circuits 31 and 32 are the same as those of the cutoff circuits 31 and 32 in the first embodiment.

[0065] Because the cutoff circuit 33 operates as described above, the functional safety control unit 20a can turn off the output of the cutoff circuit 33 by turning off the gate drive enable signal SAF21 for the cutoff circuit 33. Specifically, the functional safety control unit 20a can cut off the gate pulse GP21 for normal power conversion control outputted from the converter control unit 10a in the power converter 1a, thereby turning off the gate of the transistor Q21. Similarly, because the cutoff circuit 34 operates as described above, the functional safety control unit 20a can cut off the output of the cutoff circuit 34 by turning off the gate drive enable signal SAF22 for the cutoff circuit 34. Specifically, the functional safety control unit 20a can cut off the gate pulse GP22 for normal power conversion control outputted from the converter control unit 10a in the power converter 1a, thereby turning off the gate of the transistor Q22. Furthermore, the operation of the functional safety control unit 20a for the cutoff circuits 31 and 32 is the same as the operation of the functional safety control unit 20 for the cutoff circuits 31 and 32 in the first embodiment.

[0066] The gate drive circuit 43 corresponds to the transistor Q21 and outputs a gate signal for driving the transistor Q21 based on the drive signal output from the cutoff circuit 33. That is, the gate drive circuit 43 drives the transistor Q21 according to the drive signal output from the cutoff circuit 33. Specifically, the gate drive circuit 43 turns on the gate signal and outputs it when the drive signal is on, and turns off the gate signal and outputs it when the drive signal is off. Similarly, the gate drive circuit 44 corresponds to the transistor Q22 and outputs a gate signal for driving the transistor Q22 based on the drive signal output from the cutoff circuit 34. That is, the gate drive circuit 44 drives the transistor Q22 according to the drive signal output from the cutoff circuit 34. Specifically, the gate drive circuit 44 turns on the gate signal and outputs it when the drive signal is on, and turns off the gate signal and outputs it when the drive signal is off. Furthermore, the operations of the gate drive circuits 41 and 42 are the same as those of the gate drive circuits 41 and 42 in the first embodiment.

[0067] The gate signal branching section 53 branches the gate signal output from the gate drive circuit 43 to the transistor Q21. The gate signal branching section 53 outputs one of the branched gate signals to the transistor Q21 and sets the other of the branched gate signals as the gate signal FBQ21, which is a feedback signal to the functional safety control unit 20a, and feeds it back to the functional safety control unit 20a. Similarly, the gate signal branching section 54 branches the gate signal output from the gate drive circuit 44 to the transistor Q22. The gate signal branching section 54 outputs one of the branched gate signals to the transistor Q22 and sets the other of the branched gate signals as the gate signal FBQ22, which is a feedback signal to the functional safety control unit 20a, and feeds it back to the functional safety control unit 20a. Furthermore, the operations of the gate signal branching sections 51 and 52 are the same as those of the gate signal branching sections 51 and 52 in the first embodiment.

[0068] Similar to gate signal branching units 51 and 52, gate signal branching unit 53 branches the gate signal output from gate drive circuit 43 to transistor Q21 so that the current value of gate signal FBQ21 fed back to functional safety control unit 20a is less than or equal to a predetermined current value. To ensure the current required for controlling the operation of transistor Q21, cutoff circuit 33 may also slightly increase the current value of the drive signal before outputting it, taking into account the current amount branched from gate signal branching unit 53 to functional safety control unit 20a. Furthermore, gate signal branching unit 54 branches the gate signal output from gate drive circuit 44 to transistor Q22 so that the current value of gate signal FBQ22 fed back to functional safety control unit 20a is less than or equal to a predetermined current value. To ensure the current required for controlling the operation of transistor Q22, cutoff circuit 34 may also slightly increase the current value of the drive signal before outputting it, taking into account the current amount branched from gate signal branching unit 54 to functional safety control unit 20a. Furthermore, the power converter 1 a may prevent a large current from flowing into the functional safety control unit 20 a by adjusting the input impedance of the transistors Q21 and Q22 and the functional safety control unit 20 a , thereby preventing the gate signal branching units 53 and 54 from having the above-mentioned function.

[0069] Transistor Q21 is a switching device included in the main circuit and performs power conversion in the power converter 1a. The power conversion transistor Q21 used for power conversion is turned on and off according to the gate signal output from the gate drive circuit 43. Specifically, transistor Q21 is gate-on when the gate signal is on and gate-off when the gate signal is off. Similarly, transistor Q22 is a switching device included in the main circuit and performs power conversion in the power converter 1a. The power conversion transistor Q22 used for power conversion is turned on and off according to the gate signal output from the gate drive circuit 44. Specifically, transistor Q22 is gate-on when the gate signal is on and gate-off when the gate signal is off. In this embodiment, transistors Q21 and Q22 do not enter the gate-on state at the same time. In addition, the operation of transistors Q11 and Q12 is the same as the operation of transistors Q11 and Q12 in embodiment 1.

[0070] The freewheeling diode D21 is a diode connected in parallel with the transistor Q21. Similarly, the freewheeling diode D22 is a diode connected in parallel with the transistor Q22. The functions of the freewheeling diodes D11 and D12 are the same as those of the freewheeling diodes D11 and D12 in the first embodiment.

[0071] The current detection unit 62 detects the current I2 flowing through the phase including the transistors Q21 and Q22. The current I2 flowing through the phase is the current flowing through the connection line between the power converter 1a and the motor (not shown) supplied with power by the power converter 1a. Specifically, the current detection unit 62 detects the current I2 flowing through the transistor Q21 or the freewheeling diode D21 or the transistor Q22 or the freewheeling diode D22. The current detection unit 62 outputs the detection result, i.e., the detected current I2, to the functional safety control unit 20a as a feedback signal, i.e., the current value FBI2. Regarding the current I2, it is expressed as Figure 5 The direction of the arrow shown is assumed to be positive, and the Figure 5 The arrows shown are in the opposite direction of the flow, which is negative. Figure 5 In the example, when current I2 flows through transistor Q21 or freewheeling diode D22, current I2 is positive, and when current I2 flows through freewheeling diode D21 or transistor Q22, current I2 is negative. The operation of current detection unit 61 is the same as that of current detection unit 61 in the first embodiment.

[0072] The functional safety control unit 20a monitors the gate signal FBQ11 fed back from the gate signal branch unit 51, the gate signal FBQ12 fed back from the gate signal branch unit 52, the gate signal FBQ21 fed back from the gate signal branch unit 53, the gate signal FBQ22 fed back from the gate signal branch unit 54, the current value FBI1 output from the current detection unit 61, and the current value FBI2 output from the current detection unit 62. Specifically, the functional safety control unit 20a monitors the gate signal output from the gate drive circuit 41 to the transistor Q11, the gate signal output from the gate drive circuit 42 to the transistor Q12, the gate signal output from the gate drive circuit 43 to the transistor Q21, the gate signal output from the gate drive circuit 44 to the transistor Q22, the current I1 flowing through the transistor Q11 or the freewheeling diode D11, the transistor Q12 or the freewheeling diode D12, and the current I2 flowing through the transistor Q21 or the freewheeling diode D21, the transistor Q22 or the freewheeling diode D22.

[0073] Next, a mechanism for checking the health of the gate cutoff function in the power converter 1a will be described. In the second embodiment, the gate cutoff function is a function for setting the gates of the transistors Q11, Q12, Q21, and Q22 to an OFF state when some abnormality is detected in the power converter 1a.

[0074] In power converter 1a, current I1 flows through transistor Q11 or freewheeling diode D12 when current I1 is positive, and through freewheeling diode D11 or transistor Q12 when current I1 is negative. When current I1 flows through freewheeling diode D11, even if transistor Q11 is gate-on, current I1 does not flow through transistor Q11 and continues to flow through freewheeling diode D11. Therefore, even if transistor Q11 is gate-on while current I1 is flowing in a negative direction, current I1 does not flow through transistor Q11. Therefore, power converter 1a is not affected by the output voltage intended to be generated through the original converter control. Similarly, when current I1 flows through freewheeling diode D12, even if transistor Q12 is gate-on, current I1 does not flow through transistor Q12 and continues to flow through freewheeling diode D12. Therefore, even if the gate of transistor Q12 is turned on while current I1 is flowing in the positive direction, current I1 does not flow through transistor Q12 , and thus power converter 1 a is not affected by the output voltage to be generated by the original converter control.

[0075] Since the current value FBI1 is fed back from the current detection unit 61, the functional safety control unit 20a can detect whether the current I1 is flowing in a positive or negative direction based on the current value FBI1. In addition, since the gate signal FBQ11 is fed back from the gate signal branch unit 51, the functional safety control unit 20a can detect the state of the gate signal given to the transistor Q11. Therefore, the functional safety control unit 20a first detects the period when the current I1 is flowing in a negative direction based on the current value FBI1 fed back from the current detection unit 61. Even during the period when the current I1 is flowing in a negative direction, the converter control unit 10a, regardless of the operation of the functional safety control unit 20a and others, appropriately turns on or off the gate pulse GP11 and outputs it in order to control the operation of the equipment connected to the power converter 1a.

[0076] As described above, during normal operation, the functional safety control unit 20a turns on and outputs the gate drive enable signal SAF11. Therefore, the converter control unit 10a turns on the gate pulse GP11, causing the cutoff circuit 31 to turn on and output the drive signal to the gate drive circuit 41. As a result, the gate drive circuit 41 turns on the gate signal based on the on drive signal from the cutoff circuit 31 and outputs it to the transistor Q11. The gate signal branching unit 51 branches the on gate signal output from the gate drive circuit 41 to the transistor Q11 and feeds the gate signal FBQ11 back to the functional safety control unit 20a. The functional safety control unit 20a can detect that the gate signal output from the gate drive circuit 41 is on by feeding back the gate signal FBQ11 from the gate signal branching unit 51.

[0077] The functional safety control unit 20a turns off the gate drive enable signal SAF11 while the current I1 is flowing in a negative direction and the gate signal output from the gate drive circuit 41 is on. Since the gate drive enable signal SAF11 output from the functional safety control unit 20a is off, the cutoff circuit 31 turns off the drive signal to the gate drive circuit 41 and outputs it. Based on the off drive signal from the cutoff circuit 31, the gate drive circuit 41 turns off the gate signal and outputs it to the transistor Q11. The gate signal branching unit 51 branches the off gate signal output from the gate drive circuit 41 to the transistor Q11 and feeds the gate signal FBQ11 back to the functional safety control unit 20a.

[0078] The functional safety control unit 20a can detect that the gate signal output from the gate drive circuit 41 is off by feedback from the gate signal FBQ11 from the gate signal branch unit 51. Thus, since the gate signal to the transistor Q11 is turned off by turning the gate drive enable signal SAF11 off, the functional safety control unit 20a can determine that the gate cutoff function is functioning properly. The functional safety control unit 20a turns the gate drive enable signal SAF11 off while the current I1 is flowing in a negative direction and the gate signal output from the gate drive circuit 41 is on. If the gate signal output from the gate drive circuit 41 is no longer off as detected by feedback from the gate signal FBQ11 from the gate signal branch unit 51, the functional safety control unit 20a determines that the gate cutoff function is malfunctioning.

[0079] Furthermore, while the current I1 is flowing in a positive direction and the gate of the transistor Q12 is on, the functional safety control unit 20a turns off the gate drive enable signal SAF12 and checks whether the gate signal FBQ12 is turned off, thereby determining the soundness of the gate cutoff function of the transistor Q12.

[0080] Similarly, in power converter 1a, current I2 flows through transistor Q21 or freewheeling diode D22 when current I2 is positive, and through freewheeling diode D21 or transistor Q22 when current I2 is negative. When current I2 flows through freewheeling diode D21, even if transistor Q21 is gate-on, current I2 does not flow through transistor Q21 and continues to flow through freewheeling diode D21. Therefore, even if transistor Q21 is gate-on while current I2 is flowing in a negative direction, current I2 does not flow through transistor Q21. Therefore, power converter 1a is not affected by the output voltage intended to be generated through the original converter control. Similarly, when current I2 flows through freewheeling diode D22, even if transistor Q22 is gate-on, current I2 does not flow through transistor Q22 and continues to flow through freewheeling diode D22. Therefore, even if the gate of transistor Q22 is turned on while current I2 is flowing in the positive direction, current I2 does not flow through transistor Q22 , and thus power converter 1 a is not affected by the output voltage to be generated by the original converter control.

[0081] Since the current value FBI2 is fed back from the current detection unit 62, the functional safety control unit 20a can detect whether the current I2 is flowing in a positive or negative direction based on the current value FBI2. In addition, since the gate signal FBQ21 is fed back from the gate signal branch unit 53, the functional safety control unit 20a can detect the state of the gate signal given to the transistor Q21. Therefore, the functional safety control unit 20a first detects the period when the current I2 is flowing in a negative direction based on the current value FBI2 fed back from the current detection unit 62. Even during the period when the current I2 is flowing in a negative direction, the converter control unit 10a, regardless of the operation of the functional safety control unit 20a and others, appropriately turns on or off the gate pulse GP21 and outputs it in order to control the operation of the equipment connected to the power converter 1a.

[0082] As described above, during normal operation, the functional safety control unit 20a turns on and outputs the gate drive enable signal SAF21. Therefore, the converter control unit 10a turns on the gate pulse GP21, causing the cutoff circuit 33 to turn on and output the drive signal to the gate drive circuit 43. As a result, the gate drive circuit 43 turns on the gate signal based on the on drive signal from the cutoff circuit 33 and outputs it to the transistor Q21. The gate signal branching unit 53 branches the on gate signal output from the gate drive circuit 43 to the transistor Q21 and feeds the gate signal FBQ21 back to the functional safety control unit 20a. The functional safety control unit 20a can detect that the gate signal output from the gate drive circuit 43 is on by feeding back the gate signal FBQ21 from the gate signal branching unit 53.

[0083] The functional safety control unit 20a turns off the gate drive enable signal SAF21 while the current I2 is flowing in a negative direction and the gate signal output from the gate drive circuit 43 is on. Since the gate drive enable signal SAF21 output from the functional safety control unit 20a is off, the cutoff circuit 33 turns off the drive signal to the gate drive circuit 43 and outputs it. Based on the off drive signal from the cutoff circuit 33, the gate drive circuit 43 turns off the gate signal and outputs it to the transistor Q21. The gate signal branching unit 53 branches the off gate signal output from the gate drive circuit 43 to the transistor Q21 and feeds the gate signal FBQ21 back to the functional safety control unit 20a.

[0084] The functional safety control unit 20a can detect that the gate signal output from the gate drive circuit 43 is off by feedback from the gate signal FBQ21 from the gate signal branch unit 53. Thus, since the gate signal to the transistor Q21 is turned off by turning the gate drive enable signal SAF21 off, the functional safety control unit 20a can determine that the gate cutoff function is functioning properly. The functional safety control unit 20a turns the gate drive enable signal SAF21 off while the current I2 is flowing in a negative direction and the gate signal output from the gate drive circuit 43 is on. If the gate signal output from the gate drive circuit 43 is no longer off as detected by feedback from the gate signal FBQ21 from the gate signal branch unit 53, the functional safety control unit 20a determines that the gate cutoff function is malfunctioning.

[0085] In addition, the functional safety control unit 20a sets the gate drive enable signal SAF22 to off during the period when the current I2 flows in the positive direction and the gate of the transistor Q22 is turned on, and confirms whether the gate signal FBQ22 becomes off, thereby determining the soundness of the gate cutoff function for the transistor Q22.

[0086] Figure 6 FIG1 is a first diagram showing an example of an operation waveform of the power converter 1 a according to the second embodiment. Figure 7 FIG2 is a second diagram showing an example of an operation waveform of the power converter 1 a according to the second embodiment. Figure 6 An example of a case where an abnormality occurs in the gate cutoff function of the transistor Q21 is shown. Figure 7 An example of a case where an abnormality occurs in the gate cutoff function of the transistor Q11 is shown. Figure 6 and Figure 7 In the figure, the current value I1 is the current I1 detected by the current detection unit 61, and is the current value FBI1 fed back from the current detection unit 61 to the functional safety control unit 20a. The current value I2 is the current I2 detected by the current detection unit 62, and is the current value FBI2 fed back from the current detection unit 62 to the functional safety control unit 20a. The Q11 gate pulse is the gate pulse GP11 output from the converter control unit 10a. The Q11 gate drive enable signal is the gate drive enable signal SAF11 output from the functional safety control unit 20a. The Q11 gate drive circuit output is the gate signal output from the gate drive circuit 41 to the transistor Q11, and is the gate signal FBQ11 fed back from the gate signal branch unit 51 to the functional safety control unit 20a. The Q21 gate pulse is the gate pulse GP21 output from the converter control unit 10a. The Q21 gate drive enable signal is the gate drive enable signal SAF21 output from the functional safety control unit 20a. The Q21 gate drive circuit output is the gate signal output from the gate drive circuit 43 to the transistor Q21, and is the gate signal FBQ21 fed back from the gate signal branching unit 53 to the functional safety control unit 20a. Furthermore, description of the gate pulse GP12, gate drive enable signal SAF12, and gate signal FBQ12, signals associated with the transistor Q12, is omitted. Furthermore, description of the gate pulse GP22, gate drive enable signal SAF22, and gate signal FBQ22, signals associated with the transistor Q22, is omitted.

[0087] The functional safety control unit 20a determines that the gate cutoff function is normal if, after confirming that the gate signal FBQ11, the gate signal output from the gate drive circuit 41, has turned on while the current I1 is flowing in a negative direction, the gate drive enable signal SAF11 is temporarily turned off while the gate pulse GP11 is on. This causes the gate signal FBQ11, the gate signal output from the gate drive circuit 41, to turn off. Under the same conditions as above, the functional safety control unit 20a determines that the gate cutoff function is abnormal if it cannot detect that the gate signal FBQ11, the gate signal output from the gate drive circuit 41, has turned off. Similarly, the functional safety control unit 20a determines that the gate cutoff function is normal if, after confirming that the gate signal FBQ21, which is output from the gate drive circuit 43, has turned on while the current I2 is flowing in a negative direction, the gate drive enable signal SAF21 is temporarily turned off while the gate pulse GP21 is on. This causes the gate signal FBQ21, which is output from the gate drive circuit 43, to turn off. Under the same conditions as above, the functional safety control unit 20a determines that the gate cutoff function is abnormal if it cannot detect that the gate signal FBQ21, which is output from the gate drive circuit 43, has turned off.

[0088] Here, the functional safety control unit 20a does not know the duration for which the converter control unit 10a turns on and outputs the gate pulses GP11 and GP21. However, if information is pre-set regarding the minimum duration for which the gate pulses GP11 and GP21 remain on when the converter control unit 10a turns on the gate pulses GP11 and GP21, the functional safety control unit 20a can perform the above-described operation by temporarily turning off the gate drive enable signals SAF11 and SAF21 during the minimum duration for which the gate pulses GP11 and GP21 remain on, i.e., turning them off and then turning them on again. Furthermore, the functional safety control unit 20a can also select the shortest on-period from among the periods during which the gate signals FBQ11 and FBQ21, as fed back from the gate signal branch units 51 and 53, as the minimum on-period for which the gate pulses GP11 and GP21 remain on, while the power converter 1a is operating for a specified period. Alternatively, the functional safety control unit 20a may temporarily turn off the gate drive enable signals SAF11 and SAF21 during the on-period of the next gate pulse GP11 and GP21, based on the on-period of the previous gate pulse GP11 and GP21, when it is expected that a certain degree of on-period can be ensured.

[0089] As described above, in power converter 1a, functional safety control unit 20a, based on current value FBI1 and gate signal FBQ11, temporarily turns off gate drive enable signal SAF11 while current I1 is flowing in a negative direction, i.e., while current I1 is not flowing through transistor Q11, and the gate signal is on. The robustness of the gate cutoff function for transistor Q11 is determined by whether the gate signal to transistor Q11 has changed to OFF. Similarly, functional safety control unit 20a, based on current value FBI2 and gate signal FBQ21, temporarily turns off gate drive enable signal SAF21 while current I2 is flowing in a negative direction, i.e., while current I2 is not flowing through transistor Q21, and the gate signal is on. The robustness of the gate cutoff function for transistor Q21 is determined by whether the gate signal to transistor Q21 has changed to OFF.

[0090] Here, as Figure 6 As shown, when an abnormality is detected in the determination of the soundness of the gate cutoff function of the transistor Q21, the functional safety control unit 20a may not be able to turn off the gate signal FBQ21 as the feedback signal, that is, the gate signal output from the gate drive circuit 43 to the transistor Q21, even if the gate drive enable signal SAF21 is turned off. However, the functional safety control unit 20a can turn off the gate signal output from the gate drive circuit 41 to the transistor Q11, the gate signal output from the gate drive circuit 42 to the transistor Q12, and the gate signal output from the gate drive circuit 44 to the transistor Q22 by turning off the gate drive enable signals SAF11, SAF12, and SAF22 for the transistors Q11, Q12, and Q22. Similarly, as Figure 7As shown, if an abnormality is detected during the determination of the integrity of the gate cutoff function of transistor Q11, the functional safety control unit 20a may not be able to turn off the gate signal FBQ11, which serves as the feedback signal, i.e., the gate signal output from the gate drive circuit 41 to transistor Q11, even if the gate drive enable signal SAF11 is turned off. However, by turning off the gate drive enable signals SAF12, SAF21, and SAF22 for transistors Q12, Q21, and Q22, the functional safety control unit 20a can turn off the gate signal output from the gate drive circuit 42 to transistor Q12, the gate signal output from the gate drive circuit 43 to transistor Q21, and the gate signal output from the gate drive circuit 44 to transistor Q22. In such a case, the functional safety control unit 20a can issue an alarm to the user of the power converter 1a, etc., to the effect that an abnormality has been detected in the soundness of the gate cut-off function, or can execute control such as cutting off the power supply to the converter control unit 10a and stopping the output of gate pulses GP11, GP12, GP21, and GP22 from the converter control unit 10a when it is desired to stop the operation of the power converter 1a.

[0091] While the functional safety control unit 20a has been described as determining the soundness of the gate cutoff function for transistor Q11, the functional safety control unit 20a also operates in the same manner when determining the soundness of the gate cutoff function for transistor Q12. To determine the soundness of the gate cutoff function for transistor Q12, the functional safety control unit 20a temporarily turns off the gate drive enable signal SAF12 while current I1 is flowing in a positive direction and the gate of transistor Q12 is on, and then checks whether the gate signal FBQ12 is off. Furthermore, while the functional safety control unit 20a has been described as determining the soundness of the gate cutoff function for transistor Q21, the functional safety control unit 20a also operates in the same manner when determining the soundness of the gate cutoff function for transistor Q22. To determine the soundness of the gate cutoff function for transistor Q22, the functional safety control unit 20a temporarily turns off the gate drive enable signal SAF22 while current I2 is flowing in a positive direction and the gate of transistor Q22 is on, and then checks whether the gate signal FBQ22 is off.

[0092] As described above, the functional safety control unit 20a turns on and outputs multiple gate drive enable signals when the integrity of the gate cutoff function for each of the multiple transistors is not being determined. Based on the current value and the gate signal, the functional safety control unit 20a temporarily turns off the gate drive enable signal while the gate pulse is on, after confirming that the gate signal has turned on for each transistor during a period when no current is flowing through the transistor. The gate drive enable signal is then temporarily turned off while the gate pulse is on, thereby determining whether the gate signal has turned off.

[0093] In the second embodiment, the power converter 1a determines the gate cutoff function of the transistors Q11, Q12, Q21, and Q22 in the same manner as described above. Figure 3 The power converter 1 according to the first embodiment shown has the same method for determining the gate cutoff function of the transistor Q11. Figure 8 This is a flowchart showing the operation of the power converter 1 a according to the second embodiment. Figure 8 The operations shown in the flowchart are performed after the method for determining the gate cutoff function of the transistors Q11 , Q12 , Q21 , and Q22 in the power converter 1 a is implemented. Figure 8 The flowchart shown becomes Figure 3 Although the operation of step S17 in the flowchart shown is repeated, in the power converter 1a, the functional safety control unit 20a continuously monitors the gate cutoff function when the gate cutoff function of all transistors is normal (step S21: Yes). If the gate cutoff function of one or more transistors is abnormal (step S21: No), the functional safety control unit 20a turns off all gate drive enable signals SAF11, SAF12, SAF21, and SAF22 (step S22). As described above, when one or more transistors in the gate cutoff function of each of the plurality of transistors Q11, Q12, Q21, and Q22 are determined to have a gate cutoff function abnormality, the functional safety control unit 20a turns off the gate drive enable signals SAF11, SAF12, SAF21, and SAF22 corresponding to each of the plurality of transistors Q11, Q12, Q21, and Q22.

[0094] In the second embodiment, the hardware configuration of the power converter 1 a is the same as the hardware configuration of the power converter 1 in the first embodiment.

[0095] As described above, according to this embodiment, in the power converter 1a, the functional safety control unit 20a determines the period during which the current I1 is not flowing through transistors Q11 and Q12 based on the current value FBI1 from the current detection unit 61, determines the period during which the current I2 is not flowing through transistors Q21 and Q22 based on the current value FBI2 from the current detection unit 62, and determines the period during which the gate signal is on based on the gate signals FBQ11, FBQ12, FBQ21, and FBQ22 from the gate signal branching units 51 to 54. When the gate signal to transistor Q11 is on while the current I1 is not flowing through transistor Q11, the functional safety control unit 20a temporarily turns off the gate drive enable signal SAF11 and determines the integrity of the gate cutoff function for transistor Q11 by determining whether the gate signal to transistor Q11 has changed to off. Similarly, when current I1 is not flowing through transistor Q12 and the gate signal to transistor Q12 is on, the functional safety control unit 20a temporarily turns off gate drive enable signal SAF12. The integrity of the gate cutoff function for transistor Q12 is determined by whether the gate signal to transistor Q12 has changed to off. Similarly, when current I2 is not flowing through transistor Q21 and the gate signal to transistor Q21 is on, the functional safety control unit 20a temporarily turns off gate drive enable signal SAF21. The integrity of the gate cutoff function for transistor Q21 is determined by whether the gate signal to transistor Q21 has changed to off. Similarly, when current I2 is not flowing through transistor Q22 and the gate signal to transistor Q22 is on, the functional safety control unit 20a temporarily turns off gate drive enable signal SAF22. The integrity of the gate cutoff function for transistor Q22 is determined by whether the gate signal to transistor Q22 has changed to off. Thus, the functional safety control unit 20a can check the soundness of the gate cutoff function of the power conversion transistors Q11, Q12, Q21, and Q22 without affecting the normal operation of the power converter 1a.

[0096] The structures shown in the above embodiments are merely examples and may be combined with other known technologies, or the embodiments may be combined with each other. Part of the structure may be omitted or modified without departing from the spirit of the invention.

[0097] Description of the label

[0098] 1, 1a power converter, 10, 10a converter control unit, 20, 20a functional safety control unit, 31-34 cut-off circuit, 41-44 gate drive circuit, 51-54 gate signal branch unit, 61, 62 current detection unit, D11, D12, D21, D22 freewheeling diodes, Q11, Q12, Q21, Q22 transistors.

Claims

1. A power converter, characterized in that: have: Two transistors connected in series used in power conversion; a converter control unit configured to output a gate pulse for controlling the on / off switching of each of the transistors; a functional safety control unit configured to turn on and output a gate drive permission signal for each of the transistors when the integrity of the gate cutoff function of the transistor is not determined; two cutoff circuits that correspond to each of the two transistors and output a result of a logical AND operation using the gate pulse and the gate drive enable signal as a drive signal; two gate drive circuits corresponding to each of the two transistors and outputting gate signals for driving the transistors to the transistors and the functional safety control unit based on the drive signal; as well as a current detection unit that detects the current flowing through the phase including the two transistors and outputs the detection result as a current value to the functional safety control unit; For each of the transistors, based on the current value and the gate signal, after confirming that the gate signal has changed to on during a period when current is not flowing through the transistor, the functional safety control unit temporarily sets the gate drive enable signal to off during a period when the gate pulse is on, and determines whether the gate signal has changed to off.

2. The power converter according to claim 1, wherein: When the functional safety control unit determines that the gate cutoff function of one of the transistors is abnormal, the functional safety control unit turns off the gate drive enable signals for the two transistors.

3. The power converter according to claim 1, wherein: having a plurality of branches consisting of two of the transistors connected in series, A plurality of the cutoff circuits and a plurality of the gate drive circuits are provided corresponding to each of the plurality of transistors. The current detection unit is provided corresponding to each of the plurality of branches. The converter control unit outputs the plurality of gate pulses for controlling on and off of each of the plurality of transistors. The functional safety control unit sets the plurality of gate drive enable signals to on and outputs them corresponding to each of the plurality of transistors when the soundness of the gate cutoff function of the transistor is not determined. For each of the transistors, based on the current value and the gate signal, during a period when no current flows through the transistor, after confirming that the gate signal has changed to on, the gate drive enable signal is temporarily set to off during a period when the gate pulse is on, and determines whether the gate signal has changed to off.

4. The power converter according to claim 3, wherein: When the functional safety control unit determines that the gate cutoff function of one or more transistors is abnormal, the functional safety control unit turns off the gate drive enable signal for each of the plurality of transistors.

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