WO2022153520A1

WO2022153520A1 - Power converter

Info

Publication number: WO2022153520A1
Application number: PCT/JP2021/001401
Authority: WO
Inventors: 翔太朗烏山; 航平恩田
Original assignee: 三菱電機株式会社
Priority date: 2021-01-18
Filing date: 2021-01-18
Publication date: 2022-07-21
Also published as: JP7361955B2; JPWO2022153520A1

Abstract

In order to provide a power converter that can determine the state of deterioration of a switching element, the present invention comprises a first detection resistor (11) connected in parallel to a first switching element (211) provided on the high side, a second detection resistor (12) connected in parallel to a second switching element (212) provided on the low side, a voltage detector (31) that detects the voltage on both ends of the first detection resistor (11) or the second detection resistor (12), and a control circuit (40) that controls the switching operation of the first and second switching elements (211, 212). In a state in which the operation of the first and second switching elements (211, 212) is stopped and the temperatures of the first switching element (211) and the second switching element (212) are higher than the environment temperature, the control circuit (40) determines deterioration in the withstand voltage of the first and second switching elements (211, 212) from the voltage values detected by the voltage detector (31).

Description

Power converter

This application relates to a power conversion device.

In the power converter, the function of power conversion is realized by the operation of turning on / off a plurality of semiconductor switching elements constituting the power converter. Examples of the semiconductor switching element include a voltage-driven semiconductor switching element represented by a MOSFET (Metal-Oxide-Semiconductor Field-Effect Transistor) and an IGBT (Insulated-Gate-Bipolar-Transistor).
Downtimelessness is realized by grasping the deterioration state of the semiconductor switching element and updating the semiconductor switching element before a problem occurs in the power conversion device.

As a device for detecting an abnormality in a power converter, an abnormality detection device that can detect an abnormality in a power converter with a small number of terminal voltage detections and can secure the same abnormality detection accuracy even if the number of phases increases. An abnormality detection device for providing the above is shown in Patent Document 1.
The abnormality detection device shown in Patent Document 1 includes one or more parallel power conversion units, one high-select terminal voltage detection unit having a corresponding detection resistor for one parallel power conversion unit, and one high-select terminal voltage detection unit. , One abnormality detection unit is provided, and in each parallel power conversion unit, the abnormality detection unit detects an abnormality of each power converter included in the parallel power conversion unit based on the voltage at the gathering point.

Japanese Unexamined Patent Publication No. 2019-11720

However, in the proposed technique, the detected voltage value is compared with a predetermined threshold value to determine a failure (abnormality is detected), and the state of deterioration of the semiconductor switching element is determined. Instead, a power conversion device having a function of determining a state of deterioration of a semiconductor switching element is desired.
An object of the present application is to provide a power conversion device having a function of determining a state of deterioration of a semiconductor switching element.

The power conversion device of the present application is connected in parallel to a first detection resistor connected in parallel to a first switching element provided on the high side of the arm and a second switching element provided on the low side of the arm. Switching operation of the first switching element and the voltage detector that detects the voltage value across the first detection resistor and / or the voltage value across the second detection resistor. And a control circuit for controlling the switching operation of the second switching element, the operation of the first switching element and the operation of the second switching element are stopped, and the voltage detector detects the operation. In the control circuit, the withstand voltage of the first switching element deteriorates and / or the withstand voltage of the second switching element is based on the voltage value across the first detection resistor and / or the voltage value across the second detection resistor. It is characterized by judging deterioration.

According to the power conversion device of the present application, it is possible to diagnose the withstand voltage deterioration of the first switching element or the second switching element.

It is a block diagram of the withstand voltage deterioration detection circuit of the power conversion apparatus of Embodiment 1. FIG. It is explanatory drawing which shows the operation when the switching element of the power conversion apparatus of Embodiment 1 is normal. It is explanatory drawing which shows the operation when the withstand voltage of the switching element of the power conversion apparatus of Embodiment 1 deteriorates. It is explanatory drawing which shows the detection method when the withstand voltage of the switching element of the power conversion apparatus of Embodiment 1 deteriorates. It is explanatory drawing which shows the detection method when the withstand voltage of the switching element of the power conversion apparatus of Embodiment 1 deteriorates at the same time up and down. It is a block diagram of the withstand voltage deterioration detection circuit diagram of the power conversion apparatus of Embodiment 2. It is an operation explanatory drawing. It is a block diagram of the withstand voltage deterioration detection circuit diagram of the power conversion apparatus of Embodiment 3. It is a block diagram which shows the hardware structure of the control means used in embodiment.

Embodiment 1.
Hereinafter, embodiments will be described with reference to the drawings. In the description described below, the same components or the corresponding components are designated by the same reference numerals.
Further, in the following description, the state of the element in which the device does not operate is referred to as "failure", and the case in which the element operates is referred to as "deterioration". In "deterioration", if the test (screening) performed before the device is shipped, it is confirmed that the required specifications, quality, and reliability targets of various tests are satisfied. The target element is.

FIG. 1 shows an example of the configuration of the withstand voltage deterioration detection circuit of the power conversion device according to the first embodiment. The withstand voltage deterioration detection circuit 100 of the power conversion device includes a first switching element 211, a second switching element 212, a first detection resistor 11, a second detection resistor 12, a first voltage detector 31, and a control circuit 40. It has.

The first switching element 211 and the second switching element 212 constitute an inverter of a power conversion device, the first switching element 211 is provided on the high side of the arm, and the second switching element 212 is It is provided on the low side of the arm. The first switching element 211 and the second switching element 212 are connected in series. The first detection resistor 11 is connected in parallel to the first switching element 211, and the second detection resistor 12 is connected in parallel to the second switching element 212.

The first voltage detector 31 is connected in parallel to either the first detection resistor 11 or the second detection resistor 12, and the result of the voltage detected by the first voltage detector 31 is sent to the control circuit 40. Be done. The control circuit 40 gives a signal for driving the first switching element 211 and the second switching element 212.
The control circuit 40 determines the deteriorated state of the first switching element 211 and the second switching element 212. When it is determined that the control circuit 40 has deteriorated, a warning is notified by the notification means 41.

FIG. 1 shows only the first arm 21 in which the first switching element 211 and the second switching element 212 are connected in series because the minimum configuration requirements are described, but the third switching element 221 and the third switching element 221 are shown. The second arm 22 in which the switching elements 222 of 4 are connected in series and the first arm may be connected in parallel. In this case, it becomes an H-bridge circuit. Alternatively, the third arm 23 and the second arm 22 in which the fifth switching element 231 and the sixth switching element 232 are connected in series may be connected in parallel. In this case, it is a three-phase inverter circuit.
Switching elements connected in series (for example, the first switching element 211 and the second switching element 212) alternately repeat on and off. For example, when the first switching element 211 is on, the second switching element 212 is off. Further, when the first switching element 211 is off, the second switching element 212 is turned on.

(Design method of detection resistor)
The resistance values of the first detection resistor 11 and the second detection resistor 12 are designed so that the current value flowing through the detection resistor is larger than the leak current parasitic on the first and second switching elements. Further, the first and second detection resistors use the same resistance value.
Deterioration is determined by the voltage detected by the first voltage detector 31 in a state where the first and second switching elements are stopped.

(Detection method for pressure resistance deterioration)
FIG. 2 shows an example of a change in voltage across the first detection resistor 11 and the second detection resistor 12 when the withstand voltage of the switching element has not deteriorated in order to detect the withstand voltage deterioration according to the first embodiment. Is. By using resistance values equal to the first detection resistor 11 and the second detection resistor 12, if there is no deterioration in the withstand voltage of the switching element, the voltage across the first and second detection resistors is the bus voltage. Converges near the midpoint. Since there are variations in the parasitic withstand voltage leak current and detection resistance value of the switching element, the threshold voltage for detecting deterioration takes a margin of plus or minus several volts from the midpoint of the bus voltage, and if it falls within that margin, switching There is no deterioration in the withstand voltage of the element, and it is judged to be normal.

FIG. 3 is an example of a change in the voltage across the first detection resistor 11 and the second detection resistor 12 when the withstand voltage of the switching element is deteriorated in order to detect the withstand voltage deterioration according to the first embodiment. .. When the withstand voltage of either the first switching element 211 or the second switching element 212 deteriorates, the withstand voltage leak current flowing through the deteriorated switching element becomes large, and the voltage across the first and second detection resistors becomes large. It varies from the midpoint of the bus voltage. Since the switching element has a parasitic withstand voltage leak current, the threshold voltage for detecting deterioration is provided with a margin of plus or minus several volts from the midpoint of the bus voltage, but the first and second detection resistors exceed the provided margin. When the value of the voltage across both ends varies, it is judged that the withstand voltage of the switching element has deteriorated.

By designing the resistance values of the first detection resistor 11 and the second detection resistor 12 to be larger than the leakage current parasitic on the first and second switching elements, when the withstand voltage of the elements deteriorates. The change in the withstand voltage leak current due to the withstand voltage deterioration of the element is reflected in the voltage across the first detection resistor 11 and the second detection resistor 12, and the withstand voltage deterioration of the element can be detected with high accuracy.

(Operation after detecting deterioration)
When the switching element is determined to be deteriorated, the control circuit 40 notifies the receiver side. For example, the notification means 41 shown in FIG. 1 is provided with an abnormality lamp in the device, and turns on the abnormality lamp when it is determined that the device has deteriorated. The device may be stopped immediately after the abnormality lamp lights up. Further, since the abnormal lamp is lit when the switching element is determined to be deteriorated, the device can operate even if the abnormal lamp is lit. Therefore, the device may be replaced after the next stop opportunity.

Further, when it is determined that the switching element has deteriorated, the operation may be changed so as to temporarily extend the life of the switching element. For example, if the original modulation method of the inverter is three-phase modulation, change to two-phase modulation, lower the switching carrier, or reduce the number of switchings. After the switching element is detected as deteriorated and a warning is displayed, the life of the switching element can be extended by a temporary measure so that the device can be operated without stopping. Since the device operates normally even if the switching element deteriorates, this is a temporary temporary measure aimed at preventing the switching element from failing and the device from going down. After the switching element is notified of deterioration, the device can be operated without downtime by replacing the element or the circuit board after the next device stop.

(Timing to detect deterioration)
In order to detect the deterioration of the element, it is necessary that the voltages across the first and second detection resistors connected in parallel to the first and second switching elements are converged. Therefore, the timing for detecting deterioration is a state in which the operations of the first and second switching elements are stopped. Specifically, it is either when the device is started or stopped, or when the inverter operation is stopped during the operation period of the device.

Since the withstand voltage leak current increases in proportion to the temperature of the element, for example, the junction temperature which is the temperature of the chip joint surface of the element, the withstand voltage deterioration can be determined with the highest accuracy by detecting immediately after the operation of the device is stopped.
Also, since the junction temperature of the switching element is not high when the device is started, the inverter is short-circuited for a short time to raise the junction temperature of the switching element, and when the temperature is higher than the environmental temperature, it should be detected at that timing. The withstand voltage deterioration may be determined with high accuracy. Here, as the temperature of the switching element, the case where the junction temperature, which is the temperature of the chip junction surface of the switching element, is detected at a temperature higher than the environmental temperature is shown, but it does not necessarily have to be the junction temperature, and the switching element Any temperature may be used as long as it is the temperature.

(Detection method for withstand voltage deterioration, detection method for simultaneous upper and lower withstand voltage deterioration)
FIG. 4 is a diagram showing a method for detecting pressure resistance deterioration according to the first embodiment. In the method shown in FIG. 4, the withstand voltage deterioration is detected by the time constant of the voltage across the detection resistor after the switching element is turned off. The voltage value at t2 after a certain period of time from the timing t1 when the switching is turned off is detected. Normality or deterioration is judged by the voltage value of t2. The voltage value for the time of t2 is arbitrarily set, but the voltage of t2 when the withstand voltage deteriorates is extremely low (during deterioration A shown in FIG. 4) or extremely high (during deterioration shown in FIG. 4). B) It becomes a value.

(Advantages of pressure resistance deterioration detection method)
By determining the withstand voltage deterioration of the switching element by the time constant, it is possible to detect even if the withstand voltage of the first switching element 211 and the second switching element 212 shown in FIG. 1 deteriorates at the same time.

FIG. 5 shows an example of changes in the voltage across the first detection resistor 11 and the second detection resistor 12 when the switching element is normal and when the switching element deteriorates at the same time. When the upper and lower switching elements deteriorate at the same time, the withstand voltage leak currents flowing through the switching elements become almost equal, so the voltage across the first detection resistor 11 and the second detection resistor 12 is within the margin provided from the midpoint of the bus voltage. Fits in. Therefore, the voltage detection method shown so far cannot detect when the upper and lower elements are deteriorated at the same time or similarly. On the other hand, even if the upper and lower switching elements deteriorate at the same time, the time for convergence to the midpoint voltage changes, so that the deterioration can be detected by the time constant.

(Disadvantages of pressure resistance deterioration detection method)
On the other hand, when determining the deterioration of the switching element from the time constant of the switching element, the detection timing is restricted. Deterioration of the element cannot be judged by the time constant unless the switching element is stopped from the operating state. That is, it is necessary to detect the deterioration of the switching element at the timing when the device enters the stop mode from the operating state or at the timing when the device enters the stopped state from the operating state.

(More accurate detection method of withstand voltage deterioration)
The first voltage detector 31 holds the initially detected voltage (initial voltage). The first voltage detector 31 detects the voltage each time the device stops operating. At this time, the initial voltage is compared with the latest detected voltage. If the latest detected voltage is within the range of the initial voltage and a margin of several V, it is judged to be normal, and if it exceeds the margin, it is judged that the withstand voltage of the element has deteriorated.
In the method of determining that the margin is exceeded from the midpoint of the bus voltage, it is necessary to set the deterioration range in consideration of the variation in the withstand voltage leak of the switching element and the variation in the detection resistance. The detection accuracy of is likely to deteriorate. On the other hand, in the method of determining the deterioration from the difference from the initial voltage, the voltage considering the variation is first stored and the initial voltage value is compared with the measured repression, so that the withstand voltage deterioration can be detected with higher accuracy.

(Detection method when vertical withstand voltage deteriorates at the same time)
FIG. 6 shows a circuit diagram for detecting deterioration when the withstand voltage of the elements connected in series deteriorates at the same time. As shown in FIG. 6, in addition to the detection circuit shown in FIG. 1, the circuit in which the third detection resistor 13 and the detection switching element 14 are connected in series is either the first detection resistor or the second detection resistor. The configuration is connected to one side. Although the third detection resistor 13 is used this time, the on-resistance of the detection switching element 14 may be used instead of the third detection resistor 13.

The detection switching element 14 is turned on before or after the detection of the voltage across the first or second detection resistor. When only one of the switching elements is deteriorated, it can be detected from the variation between the voltage across the first or second detection resistor and the midpoint potential with the detection switching element 14 turned off in the same manner as described above. To detect when the withstand voltage of the switching element deteriorates at the same time, the detection switching element 14 is turned on. The combined resistance changes when the third detection resistor and the first or second detection resistor are connected in parallel. As a result, a difference is generated in the resistance value when both the upper and lower switching elements are normal and when they are deteriorated, and detection becomes possible.

(Example of circuit when actually using)
FIG. 7 is an example of a circuit when connected to a circuit actually used. As shown in FIG. 7, the first to sixth switching elements include a first arm 21 in which the first switching element 211 and the second switching element 212 are connected in series, and the third switching elements 221 and the fourth. It is composed of a second arm 22 in which the switching element 222 is connected in series, and a third arm 23 in which the fifth switching element 231 and the sixth switching element 232 are connected in series, and the first arm 21 and the second arm 22 It has an inverter configuration in which the third arm 23 is connected in parallel.

Series connection terminals of the first switching element 211 and the second switching element 212, series connection terminals of the third switching element 221 and the fourth switching element 222, and the fifth switching element 231 and the sixth switching element. The series connection terminal of 232 is connected to the motor 50. The withstand voltage deterioration detection circuit is connected to at least one of the first arm 21, the second arm 22, or the third arm 23. Since each arm is connected via a motor, if a sufficiently long time can be secured after the first to sixth switching elements stop switching, a method for detecting withstand voltage deterioration can be incorporated into one arm. , Deterioration can be diagnosed.

(Other effects (short circuit detection))
The control circuit 40 monitors the gate signal that drives the switching element output by the control circuit 40. The drain voltage of the switching element detected from the first voltage detector 31 is compared with the gate signal output by the control circuit 40, and a short-circuit failure of the switching element is detected from the contradiction between the gate signal and the drain voltage. For example, when the switching element is normal and the gate signal is output as an off signal, the drain voltage of the switching element becomes the bus voltage. On the other hand, when the switching element has a short failure, the drain voltage of the switching element becomes zero even if the gate signal outputs an off signal. In this way, a short-circuit failure of the switching element is detected from the contradiction between the gate signal and the drain voltage.
In order to detect a short circuit in the switching element, the device must be in an operating state. When a short-circuit failure of the switching element is detected, the abnormality lamp of the device is turned on and the device is stopped promptly.

(Other effects (dead time correction))
Generally, a switching element has a time required for turn-on to switch from an off state to an on state (turn-on time ton) and a time required for turn-off to switch from an on state to an off state (turn-off time toff). As the gate resistance value of the switching element increases, the turn-on time ton and the turn-off time toff increase. Further, the turn-on time ton and the turn-off time ton increase or decrease depending on the variation in the electrical characteristics of the first switching element 211 and the second switching element 212 and the operating conditions such as the junction temperature.

When controlling the output voltage of the half-bridge circuit by pulse width modulation (PWM) or the like, the first switching element 211 and the second switching element 212 are alternately turned on, but the first switching element 211 and the second switching When the on and off states of the element 212 are switched at the same time, both the first switching element 211 and the second switching element 212 are turned on at the same time, so that an arm short circuit occurs.
To prevent arm short-circuiting, the gate-on-off command signal is gate-on-off so that the other gate-on-off command signal does not turn on until a certain amount of time has passed after one gate-on-off command signal was turned off. The timing of the off command signal is controlled.

The dead time is set based on the worst conditions that take into account the variation in the characteristics of switching elements and all operating conditions when designing and developing electric power equipment. The shorter the dead time is, the more preferable it is because it affects the output voltage waveform and the output current waveform of the inverter. That is, the inverter outputs AC voltage and current by pulse width modulation, and the increase / decrease of the output voltage is set by the increase / decrease of the ratio of the on / off time of the pulse width modulation. Therefore, when the dead time becomes a size that cannot be ignored with respect to the synchronization of the pulse width modulation, the off time of the switching element increases and the output voltage decreases.

When performing PWM control, if the ratio of the actual dead time td to one carrier cycle becomes large, the output voltage drops and the output voltage waveform and output current waveform deviate from the ideal values. This needs to be done by software on a controller (microcontroller or DSP (Digital Signal Processor), etc.) that generates a gate-on / off command signal.
Also in this circuit, the voltage of the first voltage detector 31 is detected, and the control circuit 40 creates a dead time as short as possible so that the arm short circuit of the element does not occur (dead time correction is performed).

As an effect of dead time correction, it is possible to avoid an arm short circuit or suppress a surge voltage of a switching element. Further, when the switching element is a MOSFET, in addition to reducing the conduction loss during the dead time period, it is possible to improve the controllability in the motor control by improving the execution pulse width accuracy.
(Type of switching element)
The switching element is a semiconductor switching element such as SiC (Silicon Carbide) -MOSFET, GaN (Gallium Nitride), Si-MOSFET, or IGBT.

The controller, switch control circuit, booster controller, and high-voltage controller described in the embodiment are composed of a processor 200 and a storage device 201 as shown in FIG. 8 as an example of hardware. Although the storage device is not shown, it includes a volatile storage device such as a random access memory and a non-volatile auxiliary storage device such as a flash memory. Further, an auxiliary storage device of a hard disk may be provided instead of the flash memory. The processor 200 executes the program input from the storage device 201. In this case, a program is input from the auxiliary storage device to the processor 200 via the volatile storage device. Further, the processor 200 may output data such as a calculation result to the volatile storage device of the storage device 201, or may store the data in the auxiliary storage device via the volatile storage device.

Although the present application describes various exemplary embodiments and examples, the various features, embodiments, and functions described in one or more embodiments are applications of a particular embodiment. It is not limited to, but can be applied to embodiments alone or in various combinations.
Therefore, innumerable variations not illustrated are envisioned within the scope of the techniques disclosed herein. For example, it is assumed that at least one component is modified, added or omitted, and further, at least one component is extracted and combined with the components of other embodiments.

11 1st detection resistor, 12 2nd detection resistor, 13 3rd detection resistor, 14 detection switching element, 21 1st arm, 22 2nd arm, 23 3rd arm, 31 1st voltage detector, 40 control circuit, 41 notification means, 50 motor, 100 withstand voltage deterioration detection circuit, 211 first switching element, 212 second switching element, 221 third switching element, 222 fourth switching element, 231 fifth switching Element, 232, 6th switching element

Claims

A first detection resistor connected in parallel to a first switching element provided on the high side of the arm and a second detection resistor connected in parallel to a second switching element provided on the low side of the arm. A voltage detector that detects the voltage value across the first detection resistor and / or the voltage value across the second detection resistor, the switching operation of the first switching element, and the second switching element. The operation of the first switching element and the operation of the second switching element are stopped, and both ends of the first detection resistor detected by the voltage detector are provided. The control circuit is characterized in that the withstand voltage deterioration of the first switching element and / or the withstand voltage deterioration of the second switching element is determined based on the voltage value and / or the voltage value across the second detection resistor. Power conversion device.
The resistance value of the first detection resistance and the resistance value of the second detection resistance are the leak current in which the current value flowing through the first detection resistance and the second detection resistance is parasitic on the first switching element. The power conversion device according to claim 1, wherein the leakage current is set to be larger than the leakage current parasitic on the second switching element.
The power conversion device according to claim 1 or 2, wherein the resistance value of the first detection resistor and the resistance value of the second detection resistor are set to the same value.
Any one of claims 1 to 3, wherein the control circuit includes a notification means for notifying when the first switching element and / or the second switching element determines that the withstand voltage has deteriorated. The power converter according to the section.
The control circuit has a voltage value across the first detection resistor detected by the voltage detector in a state where the temperature of the first switching element and the temperature of the second switching element are higher than the environmental temperature. / Or claims 1 to 4 characterized in that the withstand voltage deterioration of the first switching element and / or the withstand voltage deterioration of the second switching element is determined based on the voltage value across the second detection resistor. The power conversion device according to any one of the above items.
The state in which the operation of the first switching element and the second switching element is stopped is one of when the power conversion device is started, stopped, and when the inverter operation is stopped while the device is in operation. The power conversion device according to any one of claims 1 to 5.
The control circuit stores the initial voltage of the voltage detector, and based on the initial voltage and the latest voltage change detected by the voltage detector, the first switching element and / or the second switching element. The power conversion device according to any one of claims 1 to 6, wherein the withstand voltage deterioration of the switching element is determined.
The first switching element and / or the second switching element of the first switching element and / or the second switching element based on the time when the voltage detected by the voltage detector converges after the operation of the first switching element and the second switching element is stopped. The power conversion device according to any one of claims 1 to 7, wherein the withstand voltage deterioration is determined.
The detection switching element and the third detection resistor connected in series are connected in parallel to either the first detection resistor or the second detection resistor, and the detection switching element is the same. The voltage value across the first detection resistor or the voltage across the second detection resistor is turned on before or after the detection, and the voltage values both before and after the detection switching element is turned on are measured by the voltage detector. The power conversion device according to any one of claims 1 to 7, wherein the power conversion device is made to be detected by.
The first switching element and the second switching element constitute an inverter, a motor is connected to the AC output of the inverter, and the first detection resistor and the second detection resistor are connected to at least one phase of the inverter. The power conversion device according to any one of claims 1 to 9, further comprising a detection resistor and the voltage detector.
When the first switching element or the second switching element is determined to be deteriorated, the modulation method of the inverter is changed, and the first switching element or the second switching element determined to be deteriorated changes the modulation method of the inverter. The power conversion device according to claim 10, further comprising performing at least one of measures of stopping the operation, displaying a warning, or lowering the carrier of the inverter.
The voltage detector is characterized in that it detects even while the inverter is operating, detects a discrepancy between the drain voltage detected during the operation of the inverter and the gate signal of the control circuit, and detects a short circuit of the inverter. The power conversion device according to any one of claims 1 to 11.
One of claims 1 to 11, wherein the voltage detector detects the voltage even while the inverter is operating, and the control circuit corrects the dead time based on the voltage detected by the voltage detector. The power conversion device according to item 1.
The power conversion device according to any one of claims 1 to 13, wherein the switching element is made of a SiC semiconductor or a GaN semiconductor.