TW202209788A - Power switch fault detection method for brake circuit and circuit of detectiing the same - Google Patents

Abstract

A fault detection method for a power switch is used to determine whether the power switch coupled to a DC bud on output side of a converting device is faulty. The Method comprises steps: Detecting a bus voltage to provide a voltage signal, and getting at least a detection value according to the voltage signal. Providing a control signal to control the power switch to turn off or turn on alternately. When providing the control signal to control the power switch to turn off, determines that the power switch is short circuit fault when a first detection value is greater than or equal to a first threshold. When providing the control signal to control the power switch to turn on, determines that the power switch is open circuit fault when a second detection value is smaller than a second threshold. When determines that the power switch is close circuit fault or open circuit fault, provides a warning signal or a disable signal.

Description

Power switch fault detection method and detection circuit thereof

The invention relates to a power switch fault detection method and a detection circuit, in particular to a power switch fault detection method and a detection circuit for judging whether a power switch is faulty according to a voltage signal comparison threshold.

Inverter with power conversion system is a common power equipment at present, and its application range is very wide, from small household appliances to large mine grinders and compressors...etc. The use of frequency converters to control the speed of the motor, which brings about a significant improvement in energy efficiency, is one of the main reasons for using frequency converters. Inverter technology is closely related to power electronic systems, including semiconductor switching components, inverter topology, control and simulation technology, and advances in control hardware and firmware...etc.

Among them, the most common type of power conversion system is the motor control applied to the elevator. The front stage uses a power conversion circuit to couple the inverter through a DC link. When the power conversion circuit of the front stage of the inverter is a unidirectional power conversion structure, the braking circuit is usually used to adjust the DC link voltage, so as to avoid the system failure caused by the continuous increase of the DC link voltage when the inverter operates in the power generation mode. However, since damage to the brake circuit usually requires additional hardware to measure, additional costs are required. Or, it is necessary to wait for the components of the braking circuit to heat up to a certain level before it can be known, so that the fault of the braking circuit cannot be dealt with immediately, resulting in the potential risk of damage to the power conversion system.

Therefore, how to design a power switch fault detection method and its detection circuit, such as using the detection bus voltage to compare known control signals to determine whether the power switch is faulty, is a major subject of this study.

In order to solve the above problems, the present invention provides a power switch fault detection method to overcome the problems of the prior art. Therefore, the power switch fault detection method of the present invention determines whether the power switch on the DC bus coupled to the output side of the conversion circuit is faulty, including the following steps: receiving the bus voltage across the DC bus through continuous detection by the control unit to The voltage signal is provided, and at least one detection value is obtained correspondingly according to the voltage signal; the control unit determines whether to provide a control signal to control the power switch to turn off, and if the judgment result is "Yes", it provides a control signal to control the power switch to turn off , and if the judgment result is "No", another control signal is provided to control the power switch to be turned on; when the control unit provides the control signal to control the power switch to be turned off, it compares whether the first detected value is greater than or equal to the first detected value. Threshold value, if the comparison result is "Yes", it is judged that the power switch is a short-circuit fault, and if the comparison result is "No", it is judged that the power switch can be turned off normally; the control unit is providing another control signal to control the power switch When conducting conduction, compare whether the second detection value is less than the second threshold value, if the comparison result is "Yes", it is judged that the power switch is an open-circuit fault, and if the comparison result is "No", it is judged that the power switch is normal. Conduction; and when it is judged that the power switch is a short-circuit fault or an open-circuit fault, a warning signal or a disable signal is provided.

In order to solve the above problem, the present invention provides a power switch fault detection circuit for judging whether the power switch on the DC bus coupled to the output side of the conversion circuit is faulty, and includes: a detection circuit coupled to the DC bus, used to detect the bus voltage of the bus capacitor connected across the DC bus to provide a voltage signal; and a control unit, coupled to the detection circuit, to receive the voltage signal, and obtain a detection value according to the voltage signal; wherein, the power switch is used in In the braking circuit, the braking circuit is coupled between the output side of the conversion circuit and the input side of the frequency conversion circuit, wherein the control unit provides a control signal to control the power switch to be turned on or off, and cooperates with the obtained detection value to perform the power switch fault detection.

The main purpose of the present invention is to provide a power switch fault detection method and a detection circuit. When a known control signal is used to control the power switch to be turned on or off, the control unit is used to obtain a corresponding voltage signal provided by continuously detecting the bus voltage. The detection value is compared with the threshold value, so as to judge whether the power switch is faulty at present, so as to achieve the effect of simple detection circuit and easy operation method.

In order to further understand the technology, means and effect adopted by the present invention to achieve the predetermined purpose, please refer to the following detailed description and accompanying drawings of the present invention. For specific understanding, however, the accompanying drawings are only provided for reference and description, and are not intended to limit the present invention.

Hereby, the technical content and detailed description of the present invention are described as follows in conjunction with the drawings:

Please refer to FIG. 1 , which is a block diagram of a power conversion system having a power switch fault detection circuit according to the present invention. The power conversion system 100 is applied to, for example, a frequency converter, is coupled between an input power source Vin and a load 200 , and converts the input power source Vin into an output power source Vo to supply power to the load 200 . The power switch failure detection circuit 300 is coupled to the power conversion system 100 and detects whether the power switch Sb in the power conversion system 100 is faulty when the power conversion system 100 is operating. The aforementioned power switch Sb is, for example, disposed in a braking circuit 100A in the power conversion system 100 , which will be described in detail later. The power conversion system 100 basically includes a conversion circuit 12 , a DC bus 14 and a frequency conversion circuit 16 , and the DC bus 14 includes a bus capacitor Cbus, a bus resistor Rb and a power switch Sb. The input side of the conversion circuit 12 receives the input power Vin, and the output side of the conversion circuit 12 is coupled to the input side of the frequency conversion circuit 16 through the DC bus 14 . In detail, the conversion circuit 12 converts the input power Vin into the bus voltage Vbus, and provides the bus voltage Vbus to the frequency conversion circuit 16 through the DC bus 14 . The input side of the frequency conversion circuit 16 receives the bus voltage Vbus, and converts the bus voltage Vbus into the output power Vo, and then the output side of the frequency conversion circuit 16 provides the output power Vo to the load 200 . The bus capacitor Cbus and the bus resistor Rb are coupled in parallel between the output side of the conversion circuit 12 and the input side of the frequency conversion circuit 16 , and the bus resistor Rb is connected in series with the power switch Sb. It should be noted that, when the power conversion system 100 is applied to a frequency converter, the bus voltage Vbus may be a DC link voltage across the bus capacitor Cbus connecting the positive and negative ends of the DC bus 14 . The bus capacitor Cbus stores electrical energy corresponding to the bus voltage Vbus, and when the bus voltage Vbus is greater than or equal to a preset value, the power switch Sb is turned on, so that the stored excess electrical energy is consumed through the bus resistor Rb to the grounding loop. That is, the circuit from the bus resistance Rb and the power switch Sb to the ground terminal constitutes the braking circuit 100A of the aforementioned power conversion system 100 . That is, the braking circuit 100A is constructed on the DC bus 14 and between the output side of the conversion circuit 12 and the input side of the frequency conversion circuit 16 . When the bus voltage Vbus is less than the preset value, the power switch Sb is turned off to avoid energy consumption through the loop of the bus resistor Rb to the ground terminal, resulting in waste of energy or damage to the bus resistor Rb.

The power conversion system 100 further includes an input switch 100B. The input switch 100B may be in the form of a hardware or a loop, and is coupled between the input power source Vin and the input side of the conversion circuit 12 . When the input switch 100B does not receive the disable signal Sd, the input switch 100B is turned on by default, so that the input power Vin can be supplied to the conversion circuit 12 . When the input switch 100B receives the disable signal Sd, the input switch 100B is turned off, so that the input power Vin cannot be supplied to the conversion circuit 12, which can be used for safety protection. It is worth mentioning that, in an embodiment of the present invention, the frequency conversion circuit 16 is a bidirectional conversion circuit. That is, in addition to converting the bus voltage Vbus into the output power Vo, the inverter circuit 16 can also convert the output power Vo into the bus voltage Vbus.

The power switch fault detection circuit 300 includes a detection circuit 32 and a control unit 34 . The detection circuit 32 is coupled to the DC bus 14 and the control unit 34 , and provides a voltage signal Sv to the control unit 34 according to the bus voltage Vbus when the conversion circuit 12 operates. The control unit 34 is coupled to the power switch Sb (ie, coupled to the braking circuit 100A) and the input switch 100B, and can receive the voltage signal Sv provided by the detection circuit 32, and provide a control signal Sc according to the voltage signal Sv to control the power switch Sb to become It is turned on or off to perform fault detection of the power switch Sb on the braking circuit 100A. Specifically, when the power switch Sb has an open-circuit fault and cannot be normally turned on, an alarm needs to be issued to prompt the power conversion system 100 to perform fault handling, or the frequency conversion circuit 16 should be disabled to prevent the frequency conversion circuit 16 from operating, so as to prevent the power conversion system 100 from The failure of the power switch Sb is associated with damage. Wherein, the alarm signal Sw sent by the control unit 34 can directly or indirectly (eg, through other controllers) perform fault handling on the power conversion system 100 . As mentioned above, when the load 200 is in the power generation mode (such as, but not limited to, the power generation mode of the motor), the output power Vo provided by the load 200 is reversely converted into the bus voltage Vbus through the frequency conversion circuit 16, and the bus voltage Vbus is recharged to Bus capacitance Cbus. Therefore, when the load 200 is in the power generation mode, when the power switch Sb cannot be turned on due to an open-circuit fault, the excess recharge energy cannot be discharged through the bus resistor Rb and the loop from the power switch Sb to the ground terminal. As a result, the voltage value of the bus voltage Vbus is gradually increased to be greater than the preset value, thereby increasing the risk of failure of the power conversion system 100 . In some embodiments, the aforementioned bleeder circuit is, for example, the brake circuit 100A.

On the other hand, when the power switch Sb has a short-circuit fault, it cannot be turned off normally, and the input power supply Vin needs to be disconnected immediately to prevent the bus resistor Rb from being continuously turned on, causing heat or even damage. In detail, when the power switch Sb cannot be turned off due to a fault, the energy will be continuously discharged from the bus resistor Rb, the power switch Sb to the braking circuit 100A of the ground terminal, so that the bus resistor Rb is continuously turned on due to the power switch Sb and heat, which in turn creates the risk of overheating and burning. It is worth mentioning that, in an embodiment of the present invention, the control unit 34 controls the power switch Sb to be turned on or off, and the operation of the frequency conversion circuit 16 is controlled by another controller (not shown), but the control unit 34 The controller (not shown) can also be separated or integrated into one according to actual needs. The detailed fault detection circuit and detection method of the power switch Sb of the braking circuit 100A will be further described later. It is worth mentioning that, in an embodiment of the present invention, the power conversion system 100 is mainly applied to the power control system of the elevator, so the power switch fault detection circuit 300 is mainly applied to the fault of the brake circuit power switch of the elevator system. It is detected, and the load 200 represents may be a motor that pulls the elevator up and down, but it is not limited thereto. For example, any power system with a braking circuit 100A (or a braking resistor connected in series with the power switch) can be used in the power switch fault detection circuit 300 of the present invention for power switch fault detection, and the load 200 can also be other power circuits , the present invention is not limited to this.

Please refer to FIG. 2A and FIG. 2B for the flowchart of the power switch fault detection method of the present invention, and refer to FIG. 1 and FIG. 3 in combination. In the present disclosure, FIG. 2A shows the main process, and FIG. 2B shows the secondary process. Before detecting whether the power switch Sb of the braking circuit 100A is faulty, the control unit 34 can first determine whether the DC bus 14 is no-load (step S100 ). If the determination result of step S100 is "No", this step can be repeated until the DC bus 14 is no-load, so as to reduce the interference condition of the detection, thereby achieving a better detection effect. Specifically, the control unit 34 can know whether the DC bus 14 is no-load by detecting the voltage value of the bus voltage Vbus, detecting the input or output current value of the frequency conversion circuit 16, or being notified by (the controller of) the load 200 or not. . When it is confirmed that the DC bus 14 is no-load, it means that the load 200 and the frequency conversion circuit 16 are in a standby state. At this time, it is a better time to perform fault detection of the power switch Sb of the braking circuit 100A. At this time, the control unit 34 needs to determine the There are relatively few variables, and the detection is carried out in the no-load or standby state, and the fault of the power switch Sb can be detected in advance and properly handled to avoid the damage of other circuit components; however, it should be noted that the present invention can also be used in the load or non-load state. Detecting in the standby state is not limited to this. Then, after the control unit 34 confirms that the DC bus 14 is unloaded, the control unit 34 continuously detects the voltage signal Sv generated by the corresponding bus voltage Vbus through the receiving detection circuit 32 when the conversion circuit 12 operates, and calculates the voltage signal Sv to Correspondingly, at least one detection value Vs is obtained (step S120 ).

Then, the control unit 34 determines whether to provide the control signal Sc to control the power switch Sb to be turned off according to the current voltage signal Sv during the detection (step S200 ). In detail, if the ripple value of the voltage signal Sv is large within a certain period of time, it is possible that the power switch Sb can be normally turned on or has been short-circuited (continuously turned on). For example, the period t2 in FIG. 3 is based on the continuous detection of the bus voltage Vbus. The ripple value of the provided voltage signal Sv is relatively large, so the control unit 34 determines whether the control signal Sc should be changed to detect whether the power switch Sb can be turned off normally at this time. The ripple value of the voltage signal Sv provided by the continuous detection of the bus voltage Vbus during the period t1 is relatively small, it is possible that the power switch Sb can be normally turned off at this time or has an open circuit fault (continuously turned off), so the control unit 34 according to In order to determine whether another control signal Sc should be provided at this time to detect whether the power switch Sb can be turned on normally, such repeated operations can confirm whether the individual off or on functions of the power switch Sb are faulty, and will not be misjudged due to the voltage signal Sv . Therefore, if it is determined as "Yes" in step S200, the control unit 34 determines that the control signal Sc can be provided at this time to control the power switch Sb to be turned off, so as to confirm whether the power switch Sb can be turned off normally (step S210); In step S210, when the control unit 34 provides the control signal Sc to control the power switch Sb to be turned off, the control unit 34 then determines whether the first detection value Vs1 corresponding to the voltage signal Sv is greater than or equal to the first threshold V1 ( Step S220), wherein the first threshold V1 is the ripple value of the voltage signal when the power switch Sb can be normally turned on. When the control unit 34 determines that the control signal Sc is provided to control the power switch Sb to be turned off (the determination in step S200 is “Yes” and the process goes to step S210 ), and the control unit 34 determines the first detection value obtained corresponding to the voltage signal Sv at this time Vs1 is greater than or equal to the first threshold V1, that is, when the judgment in step S220 is "Yes", it means that the power switch Sb is a short-circuit fault at this time (step S240); otherwise, the judgment result in step S200 is "Yes", and The judgment result of step S220 is "No", which means that the power switch Sb can be turned off normally at this time, and can be connected to step S300 shown in FIG. 2B via path (A) at this time, and through steps S300-S340 to additionally confirm the power Whether the conduction function of switch Sb is normal.

Continuing from the above, when the determination in step (S200) is “No”, the control unit 34 determines that another control signal Sc should be provided to control the power switch Sb to be turned on at this time, so as to confirm whether the power switch Sb can be normally turned on (step S200). S300). After the control unit 34 provides the control signal Sc to control the power switch Sb to be turned on, the control unit 34 then determines whether the second detection value Vs2 corresponding to the voltage signal Sv is smaller than the second threshold V2 (step S320 ). When the control unit 34 determines that the control signal Sc is provided to control the power switch Sb to be turned on (the determination in step S200 is “NO” and the process proceeds to step S300 ), and the control unit 34 determines the second detection value obtained corresponding to the voltage signal Sv at this time Vs2 is less than the second threshold V2, that is, when the determination in step S320 is "Yes", it means that the power switch Sb is in an open circuit fault (step S340), wherein the second threshold is the voltage signal when the power switch Sb can be normally turned off the ripple value. When the determination in the aforementioned step S320 is "No", it means that the power switch Sb can be normally turned on. At this time, it can be connected to the step S210 shown in FIG. 2B via the path (B), and the power is confirmed through the steps S210-S240. Whether the shutdown function of switch Sb is normal. Furthermore, when the control unit 34 determines that the power switch Sb is a short-circuit fault (step S240 ) or an open-circuit fault (step S340 ), the control unit 34 can issue a warning signal Sw to make the power conversion system 100 perform fault handling, or directly provide a disable function. The signal Sd disables the frequency conversion circuit 16 so that the frequency conversion circuit 16 does not operate (step S400 ). It is worth mentioning that, in addition to the aforementioned methods and steps for alternately detecting the turn-off and turn-on functions of the power switch Sb via the path (A) and path (B), in an embodiment of the present invention, steps S200 to S240 are also Correspondingly, the two groups of steps S300 to S340 can be interchanged, that is, in the spirit of the present invention, it is only necessary to provide a plurality of control signals Sc in turn to control the power switch Sb to be turned on or off, and to continuously detect the bus voltage to provide the voltage signal, and correspondingly obtain the detection value according to the voltage signal, and use the control unit 34 to compare the current detection value with the first threshold or the second threshold to assist in judging whether the fault is or not. The replacement of the above steps is only for detection The difference in the sequence of the open-circuit fault and the short-circuit fault can completely confirm whether the turn-off and turn-on functions of the power switch are normal, without affecting the final judgment.

Please refer to FIG. 3 for a schematic diagram of the bus voltage waveform when the power switch is turned on and off according to the present invention, and refer to FIGS. 1 to 2 in combination. When the control unit 34 provides the control signal Sc to control the power switch Sb to be turned off (period t1 ), the ripple of the bus voltage Vbus is relatively small, and its waveform can be regarded as a substantially smooth straight line. When the bus voltage Vbus rises to be greater than or equal to the preset value Vd ((time period t2, for example, but not limited to, the load 200 is in the power generation mode), the control unit 34 provides the control signal Sc to control the power switch Sb to be turned on, so that The excess energy of the bus voltage Vbus is discharged by the braking circuit 100A formed by the bus resistor Rb, the power switch Sb and the ground terminal. At this time, the ripple of the bus voltage Vbus is relatively large, and its waveform has a roughly fixed frequency with a certain amplitude range Therefore, the main purpose of the present invention is to provide a power switch Sb fault detection method and a detection circuit, and utilize the control unit 34 to provide the control signal Sc to control the power switch Sb to be turned on or off, so the time control signal Sc is The control unit 34 provides and is known to perform threshold comparison according to the voltage signal Sv provided by the bus voltage Vbus obtained again and the detected value corresponding to the voltage signal Sv to determine whether the power switch Sb is faulty, which is easy to compare. Yes, in order to achieve the effect of simple detection circuit and easy operation, wherein, the aforementioned bus resistor Rb and power switch Sb are constructed in the braking circuit 100A.

It is worth mentioning that, in an embodiment of the present invention, the input power source Vin may be a three-phase input power source or a single-phase input power source. When the power switch Sb is turned on, the ripple frequency of the bus voltage Vbus corresponds to the frequency of the input power Vin. When the input power Vin is single-phase, the frequency of the input power Vin is usually 60Hz. Therefore, if the conversion circuit 12 is a full-bridge rectifier, the ripple frequency of the bus voltage Vbus is 120 Hz. Similarly, if the input power Vin is three-phase and the conversion circuit 12 is a full-bridge rectifier, the ripple frequency of the bus voltage Vbus is 360 Hz. In addition, if the conversion circuit 12 is a half-bridge rectifier, the ripple frequency of the bus voltage Vbus is 60 Hz and 180 Hz respectively when the above-mentioned single-phase input power and three-phase input power are respectively used.

Further, when the control unit 34 provides the control signal Sc according to the voltage signal Sv to control the power switch to turn off Sb, the ripple of the bus voltage Vbus should be relatively small. However, if the control unit 34 provides the control signal Sc according to the voltage signal Sv to control the power switch Sb to be turned off, the first detection value Vs1 obtained according to the voltage signal Sv detected at that time is greater than or equal to the first valve When the value is V1, it means that the ripple of the bus voltage Vbus is larger. Therefore, the control unit 34 can determine that the power switch Sb is faulty (short-circuit fault), and the control unit 34 can issue a warning signal Sw and/or provide a disable signal Sd to turn off the input switch 100B to ensure safety . Alternatively, the control unit 34 can also notify the controller (not shown) of the power conversion system 100 so that the controller provides the disable signal Sd to the input switch 100B. On the other hand, when the control unit 34 provides the control signal Sc to control the power switch Sb to be turned on according to the voltage signal Sv, the ripple of the bus voltage Vbus should be relatively large. However, if the control unit 34 provides the control signal Sc according to the voltage signal Sv to control the power switch Sb to be turned on, the second detection value Vs2 obtained according to the voltage signal Sv detected at that time is smaller than the second threshold value V2 , which means that the ripple of the bus voltage Vbus is small. Therefore, the control unit 34 can determine that the power switch Sb is faulty (open-circuit fault) at this time, and can also issue a warning signal Sw to make the power conversion system 100 perform fault handling and/or provide a disable signal Sd to turn off the input switch 100B for safety. It is worth mentioning that, in an embodiment of the present invention, both the disable signal Sd and the warning signal Sw are one of various signals provided by the control unit 34 for troubleshooting when the power switch Sb fails, and can be controlled by the control unit 34 They are respectively sent to the input switch 100B and the controller (not shown) of the power conversion system 100, but the present invention is not limited to this. Alternatively, the control unit 34 directly sends the aforementioned signal to the controller of the power conversion system 100, and then the controller uniformly forwards the signal and handles the status.

Please refer to FIG. 4 for a circuit diagram of a power conversion system having a power switch fault detection circuit according to the present invention, and refer to FIGS. 1 to 3 in combination. In an embodiment of the present invention, the input power Vin is three-phase, and the conversion circuit 12 is configured as a three-phase full-bridge rectifier according to the type of the input power Vin, which includes three sets of rectifier bridge arms formed by series-connected diodes. The frequency conversion circuit 16 is correspondingly configured as a three-phase frequency conversion circuit, which includes three groups of frequency conversion bridge arms connected in series by switches. The detection circuit 32 uses a voltage divider circuit formed by connecting two voltage divider groups R1 and R2 in series. The detection circuit 32 is coupled between the positive and negative terminal nodes of the DC bus 14 , and the voltage divider group R1 is connected to the voltage divider. The nodes between the piezoelectric groups R2 are coupled to the control unit 34 . The bus voltage Vbus is divided by the voltage dividing groups R1 and R2 to generate a voltage signal Sv, and the voltage signal Sv is provided to the control unit 34 . It should be noted that the detection circuit 32 is connected in parallel with the bus capacitor Cbus and the braking circuit 100A on the DC bus 14, and the voltage across the detection circuit 32 should be the same. Therefore, the location of the detection circuit 32 can be adjusted according to the requirements, and is not limited. this invention. After receiving the voltage signal Sv, the control unit 34 generates and provides the control signal Sc to the driving circuit 36 according to the judgment of the voltage signal Sv, so that the control unit 34 drives the power switch Sb to be turned off or turned on through the driving circuit 36 . The control signal Sc can also be fed back to the control unit 34 (not shown) by means of feedback coupling, so that the control unit 34 can actively know that the specific control signal Sc is used to control the power by receiving the control signal Sc provided by itself. The switch Sb is turned on or the power switch Sb is controlled to be turned off.

It is worth mentioning that, in an embodiment of the present invention, if the input power Vin is single-phase, and the output power Vo is also single-phase, the structure of the conversion circuit 12 and the frequency conversion circuit 16 can be adjusted accordingly. To repeat. In addition, in one embodiment of the present invention, the detection circuit 32 uses a voltage divider circuit to achieve the effects of simple operation and simple component structure, but the structure of the detection circuit 32 is not limited to the voltage divider circuit. For example, but not limited to, the detection circuit 32 can also be constituted by a structure of a resistor connected in series with a capacitor. Therefore, any detection circuit structure capable of correspondingly generating the voltage signal Sv for the control unit 34 to determine according to the bus voltage Vbus should be included in the scope of this embodiment.

Please refer to FIG. 5A , which is a schematic diagram of sampling the bus voltage waveform when the power switch is turned on and off according to the present invention, and refer to FIGS. 1 to 4 in combination. Taking the input power Vin as a three-phase, the conversion circuit 12 as a three-phase full-bridge rectifier, and the detection circuit 32 as a voltage divider circuit as an example, the voltage signal Sv is a proportionally reduced signal value of the bus voltage Vbus, and in When the power switch Sb is turned on, the ripple waveform of the voltage signal Sv oscillates at a frequency of approximately 360 Hz. As shown in the figure, the small circles are a plurality of sampling points Ps set by the control unit 34 according to a specific interval (time difference) in the waveform of the voltage signal Sv. The distance between the sampling points Ps is preferably the same, but the Adjust to different spacings according to actual needs. Further, the control unit 34 can set a plurality of sampling points Ps according to the sampling frequency, and the sampling frequency can be determined according to the number of phases of the input power Vin, and the conversion circuit 12 is a full-bridge rectifier or a half-bridge rectifier. Specifically, since the input power Vin can be three-phase or single-phase, and the conversion circuit 12 can be a full-bridge or half-bridge rectifier, for example, but not limited to, the sampling frequency must be at least higher than 1000 Hz, when the input power is three-phase , and when the conversion circuit 12 is a full-bridge rectifier, for example, each 360Hz cycle includes about 2.78 sampling points (1000/360).

Then, the control unit 34 obtains at least one detection value by calculating the values of the plurality of sampling points Ps. The detection value may represent the peak-to-peak value of the voltage value of the voltage signal Sv, which is mainly based on the difference of the voltage values as the judgment condition. Alternatively, the detected value may represent the slope between at least two sampling points Ps in the voltage signal Sv timing sequence, which is mainly based on the difference in ripple when the power switch Sb is turned on or off as the judgment condition. Alternatively, the detected value may represent the voltage change rate between at least two sampling points Ps of the voltage signal Sv, that is, the voltage drop rate or the voltage rise rate, which is mainly based on the change of the voltage value within a specific period as the judgment condition. Various implementations for obtaining the detection value will be described below, in order to determine whether the power switch is faulty or not based on the waveform, but is not intended to limit the present invention.

Specifically, in the embodiment where the detected value represents the peak-to-peak value of the voltage signal Sv, the control unit 34, for example, but not limited to, extracts two sampling points Ps with the largest voltage difference in a suitable period. Then, the voltage values of the two sampling points Ps are subtracted to obtain the voltage difference (that is, the detection value), and the absolute value of the voltage difference is compared with the first threshold value and the second threshold value to determine whether the power switch Sb is faulty . When the power switch Sb is a short-circuit fault, it cannot be turned off normally, and the absolute value of the voltage difference is greater than or equal to the first threshold; or when the power switch Sb is an open-circuit fault, it cannot be normally turned on, and the absolute value of the voltage difference at this time If it is less than the second threshold, the above conditions can determine that the power switch Sb is faulty.

In the embodiment where the detected value represents the slope between at least two sampling points Ps of the voltage signal Sv, the control unit 34, for example, but not limited to, subtracts the voltage values of the two sampling points Ps respectively, and then calculates the time difference between the two sampling points. Slope (ie, detection value). If the time difference is fixed, when the slope is relatively sloping, the ripple of the voltage signal Sv is larger and the change rate is larger, and when the slope is relatively gentle, the ripple of the voltage signal Sv is smaller and the change rate is smaller. Then, the control unit 34 determines whether the power switch Sb is faulty by comparing the absolute value of the slope between the sampling points Ps of the voltage signal Sv with the first threshold and the second threshold. When the power switch Sb is a short-circuit fault, the absolute value of the slope is greater than or equal to the first threshold value, or when the power switch Sb is an open-circuit fault, the absolute value of the slope is less than the second threshold value, the above conditions can be judged that the power switch Sb is faulty .

In the embodiment in which the detected value represents the voltage change rate between at least two sampling points Ps of the voltage signal Sv, that is, the voltage drop rate or the voltage rise rate, the control unit 34, for example, but not limited to, extracts the voltage signal Sv respectively in time sequence The voltage value of the two sampling points Ps is divided by the difference between the two points and the voltage value of the first sampling point Ps, and then multiplied by the percentage to calculate the voltage drop rate or voltage rise rate between the two sampling points Ps (that is, the detection value). The voltage rise rate can be used, for example, but not limited to, (voltage value after rise - voltage value before rise)/voltage value before rise*100%, and the voltage drop rate can be used, for example, but not limited to, (voltage value before fall -Voltage value after drop)/Voltage value before drop*100%. When the voltage falling rate or the voltage rising rate is high, it means that the ripple of the voltage signal Sv has a large change rate, and when the voltage falling rate or the voltage rising rate is low, it means that the ripple of the voltage signal Sv has a small change rate. Also smaller. Then, the control unit 34 determines whether the power switch Sb is faulty according to the absolute value of the voltage drop rate or the absolute value of the voltage rise rate and the first threshold and the second threshold. When the power switch Sb is a short-circuit fault, the absolute value of the voltage drop rate or the absolute value of the voltage rise rate is greater than or equal to the first threshold, or when the power switch Sb is an open-circuit fault, the absolute value of the voltage drop rate or the voltage rise rate The absolute value of is less than the second threshold, and the above conditions can all determine that the power switch Sb is faulty.

It is worth mentioning that, in an embodiment of the present invention, the above-mentioned detection value sampling and calculation method is only an implementation method that is easier to implement and has a smaller error rate, but it is not limited to only obtain detection in the above-mentioned method. value. That is to say, the sampling point and calculation method for obtaining the detection value which can determine whether the power switch Sb is faulty or not after calculation, such as the value of the voltage and time of the sampling point Ps, should be included in the scope of this embodiment. In addition, in an embodiment of the present invention, the control unit 34 can also set a sampling period Ts (eg, the sampling period Ts shown in FIG. 5A ) for the voltage signal Sv, and only perform the sampling period Ts in the set sampling period Ts A plurality of sampling points Ps are set. As the aforementioned control signal Sc may be a known condition, including the time point of switching the switch, it is not necessary to monitor the sampling point all the time to cause redundant sampling in practice. Therefore, the control unit 34 can only provide the control signal Sc to control the power The voltage value of the voltage signal Sv is sampled only during the critical period when the switch Sb is turned on or off, so as to save energy consumption and improve efficiency.

Please refer to FIG. 5B is a schematic diagram of the waveform of the control unit judging the fault of the power switch when the control signal controls the power switch to be turned off according to the present invention, and FIG. 5C is a schematic diagram of the waveform of the control unit judging the fault of the power switch when the control signal of the present invention controls the power switch to be turned on. Refer to Figures 1~5A for coordination. In the embodiment of FIG. 5B , it is assumed that the power switch Sb is a short-circuit fault, and the absolute value of the difference obtained by calculating the peak-to-peak value of the voltage value of the voltage signal Sv is used as the detection value. In this embodiment, the first detection is used. The value Vs1 indicates. Therefore, when the control unit 34 determines to provide a control signal to the power switch Sb to control the power switch Sb to turn off according to the bus voltage corresponding to the voltage signal Sv is less than the preset value (time T1 ), the power switch Sb has a short-circuit fault at this time. , will maintain the on state, so it cannot be turned off smoothly. Therefore, even after time T1, the ripple of the voltage signal Sv is still relatively large, and its waveform still oscillates at a frequency of approximately 360 Hz, resulting in the first detection value Vs1 several times during the period from time T1 to time T2 Detection (eg, sampling points Ps1, Ps1, Ps3), the results are all greater than or equal to the first threshold V1. At this time, the control unit 34 determines that the power switch Sb is a short-circuit fault and cannot be turned off, and provides a warning signal Sw at time T2, for example. The first threshold V1 is the ripple value of the voltage signal Sv when the power switch Sb can be normally turned on. The ripple values are sampled in a peak-to-peak manner, for example.

It is worth mentioning that, in an embodiment of the present invention, if only the voltage difference between the two sampling points Ps1 and Ps2 is used to determine whether the power switch Sb is faulty, it may be caused by insufficient sampling points Ps and noise. The control unit 34 makes a wrong judgment due to factors such as interference or low resolution. Therefore, in order to obtain the accuracy of the judgment by the control unit 34, the resolution can be increased according to actual requirements (ie, the sampling frequency can be increased), or more sampling points can be used (eg, the sampling point Ps3 can be increased) for accurate judgment. When more sampling points are used for judgment, the control unit 34 can delay the time for providing the warning signal Sw.

In the embodiment of FIG. 5C , it is assumed that the power switch Sb is an open-circuit fault, and the absolute value of the difference obtained by calculating the peak-to-peak voltage value of the voltage signal Sv is also used as the detection value. In this embodiment, the second detection value is used. The measured value Vs2 is marked. Therefore, when the control unit 34 determines to provide another control signal to the power switch Sb to control the power switch Sb to turn on according to the bus voltage corresponding to the voltage signal Sv is less than the preset value (time T1 ), the power switch Sb has an open circuit fault at this time. , will remain in the off state, so it cannot be turned on smoothly. After the time T1, the ripple of the voltage signal Sv is still small, and its waveform is still a substantially smooth straight line, so that the result of the second detection value Vs2 from the time T1 to the time T2 is still smaller than the second threshold value V2 , so the control unit 34 determines that the power switch Sb is an open-circuit fault and cannot be turned on. Apart from this, the rest of the waveforms and the control judgment methods are the same as those in the embodiment of FIG. 5B , and will not be repeated here.

To sum up, the embodiments of the present invention have the following advantages and effects:

1. The power switch fault detection circuit of the present invention can directly measure the state of the power switch when the frequency conversion circuit is no-load or standby, so that the fault can be dealt with immediately when the power switch fails without waiting for the components (such as but Not limited to the power switch or bus resistance) heating can be known, wherein the power switch can be applied to the braking circuit, for example;

2. The power switch fault detection circuit of the present invention can directly measure the bus voltage and compare the known control signals to evaluate the state of the power switch without adding additional hardware to measure the state of the power switch or the power conversion system. Output power, which can reduce the cost of system construction; and

3. When the known control signal is used to control the power switch to be turned on or off, use the control unit to compare the voltage signal ripple when the power switch is normally turned on or off according to the detected value corresponding to the bus voltage at that time. The threshold value defined by the value is used to judge whether the power switch is faulty at that time, which can make the operation simple and fast.

However, the above descriptions are only the detailed descriptions and drawings of the preferred embodiments of the present invention, but the features of the present invention are not limited thereto, and are not intended to limit the present invention. The scope of the patent shall prevail, and all embodiments that are consistent with the spirit of the scope of the patent application of the present invention and similar variations thereof shall be included in the scope of the present invention. Anyone who is familiar with the art in the field of the present invention can easily think Changes or modifications can be covered by the following patent scope of the present case.

100: Power Conversion System

100A: Brake circuit

100B: Input switch

12: Conversion circuit

14: DC bus

16: Frequency conversion circuit

200: load

300: Power switch fault detection circuit

32: Detection circuit

34: Control unit

36: Drive circuit

Cbus: bus capacitance

R1, R2: divider group

Rb: bus resistance

Sb: Power switch

Vin: input power

Vo: output power

Vbus: bus voltage

Sv: voltage signal

Sc: control signal

Sw: warning signal

Sd: Disable signal

Vd: Default value

Vs: detection value

V1: The first threshold

V2: The second threshold

Ps, Ps1~Ps3: sampling point

Ts: sampling period

T1, T2: time

t1, t2: time period

(A), (B): Path

(S100)~(S400): Steps

1 is a block diagram of a power conversion system with a power switch fault detection system according to the present invention;

2A and 2B are flowcharts of a power switch fault detection method according to the present invention;

3 is a schematic diagram of the bus voltage waveform when the power switch of the present invention is turned on and off;

4 is a circuit diagram of a power conversion system with a power switch fault detection circuit according to the present invention;

5A is a schematic diagram of sampling a bus voltage waveform when the power switch of the present invention is turned on and off;

5B is a schematic diagram of the waveform of the control unit judging the power switch failure when the control signal controls the power switch to be turned off according to the present invention; and

5C is a schematic diagram of the waveform of the control unit judging the power switch failure when the control signal controls the power switch to be turned on according to the present invention.

(A), (B): Path

(S100)~(S400): Steps

Claims (9)

A power switch fault detection method for judging whether a power switch on a DC bus coupled to an output side of a conversion circuit is faulty, comprising the following steps: receiving a voltage signal provided by continuously detecting the bus voltage across the DC bus by a control unit, and correspondingly obtaining at least one detection value according to the voltage signal; The control unit judges whether to provide a control signal to control the power switch to turn off according to the voltage signal, if the judgment result is "Yes", it provides the control signal to control the power switch to turn off, and if the judgment result is "No" ”, another control signal is provided to control the power switch to be turned on; When the control unit provides the control signal to control the power switch to be turned off, it compares whether a first detection value corresponding to the voltage signal is greater than or equal to a first threshold value, if the comparison result is "Yes" ”, it is judged that the power switch is a short-circuit fault, and if the comparison result is “No”, it is judged that the power switch can be turned off normally; When the control unit provides the other control signal to control the power switch to be turned on, it compares whether a second detection value corresponding to the voltage signal is smaller than a second threshold value, if the comparison result is "Yes" then determine that the power switch is an open-circuit fault, and if the comparison result is "No", determine that the power switch can be normally turned on; and When it is judged that the power switch is a short-circuit fault or an open-circuit fault, a warning signal or a disable signal is provided. The power switch fault detection method according to claim 1, wherein the step of correspondingly obtaining the at least one detection value according to the voltage signal comprises: setting a plurality of sampling points on the voltage signal; and The detection value is obtained by calculating the plurality of sampling points. The power switch fault detection method according to claim 2, wherein the step of obtaining the detection value by calculating the plurality of sampling points comprises: obtaining a peak-to-peak value corresponding to the bus voltage by calculating the plurality of sampling points, A voltage slope corresponding to the bus voltage is obtained by calculating the plurality of sampling points, or a voltage change rate corresponding to the bus voltage is obtained by calculating the plurality of sampling points. The power switch fault detection method as claimed in claim 1, further comprising: Before the step of detecting to obtain the voltage signal, determine whether the DC bus is no-load, if the determination result is "No", repeat this step until the DC bus is no-load, so as to reduce the interference condition of detection. The power switch fault detection method according to claim 1, wherein after the step of judging that the power switch can be normally turned off, further comprising providing the other control signal to detect whether the power switch can be normally turned on; and After the step of judging that the power switch can be normally turned on, the step further includes providing the control signal to detect whether the power switch can be normally turned off. A power switch fault detection circuit for judging whether a power switch on a DC bus coupled to an output side of a conversion circuit is faulty, and comprising: a detection circuit coupled to the DC bus for detecting a bus voltage across a bus capacitor of the DC bus to provide a voltage signal; and a control unit, coupled to the detection circuit, for receiving the voltage signal, and obtaining a detection value according to the voltage signal; Wherein, the power switch is applied to a braking circuit, and the braking circuit is coupled between the output side of the conversion circuit and the input side of a frequency conversion circuit, Wherein, the control unit provides at least one control signal to control the power switch to be turned on or off, and cooperates with the obtained detection value to perform fault detection of the power switch. The power switch failure detection circuit as claimed in claim 6, wherein the input side of the conversion circuit is coupled to an input power source through an input switch. The power switch fault detection circuit of claim 7, wherein the control unit samples the voltage signal according to a sampling frequency to obtain the detection value, and the sampling frequency corresponds to the conversion circuit being a full-bridge rectifier or a half-bridge rectifier, and whether the input power is three-phase or single-phase is determined. According to the power switch failure detection circuit of claim 7, the control unit is coupled to the input switch, and when the control unit determines that the power switch is faulty, the control unit provides a disable signal to turn off the input switch.

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