WO2017183209A1

WO2017183209A1 - Power conversion device

Info

Publication number: WO2017183209A1
Application number: PCT/JP2016/062852
Authority: WO
Inventors: 覚寺島; 清江口
Original assignee: 三菱電機株式会社
Priority date: 2016-04-22
Filing date: 2016-04-22
Publication date: 2017-10-26

Abstract

The purpose of the present invention is to obtain a power conversion device capable of detecting the state of a capacitor without providing a voltage monitoring circuit. This power conversion device is provided with: a series circuit 10, wherein one end is connected to a positive electrode of a first direct current power supply 1, the other end is connected to a negative electrode of the first direct current power supply 1, and a first switching element, a second switching element, and a shunt resistor 9 are connected in series in this order; an output unit 11 connected between the first switching element and the second switching element; a first drive circuit that on/off drives the first switching element; a second drive circuit which, complementarily with respect to the first switching element, on/off drives the second switching element; a second direct current power supply 6, i.e., a power supply for the second drive circuit; and a capacitor 7 to be charged by means of the second direct current power supply 6 when the second switching element is turned on. The state of the capacitor 7 is detected using a current of the shunt resistor 9.

Description

Power converter

The present invention relates to a power conversion device capable of detecting the state of a capacitor provided.

In the drive circuit of the conventional power converter, the upper arm switching element and the lower arm switching element are connected in series on both sides of the first DC power supply, and the capacitor used as the drive power supply for the upper arm switching element is connected to the second through the diode. The capacitor is charged when the lower arm switching element is turned on, and the capacitor charge is consumed when the upper arm switching element is turned on. Such a circuit is called a bootstrap circuit.

According to Patent Document 1, which is an example of the prior art, a technique is disclosed in which the voltage of the capacitor of the bootstrap circuit is monitored by a voltage monitoring circuit and switching is stopped when the voltage drops.

Japanese Patent Laid-Open No. 3-150075

However, according to the above prior art, there is a problem that a new voltage monitoring circuit is required to detect the state of the capacitor in the bootstrap circuit.

The present invention has been made in view of the above, and an object of the present invention is to obtain a power conversion device that can detect the state of a capacitor in a bootstrap circuit during charging without providing a voltage monitoring circuit.

In order to solve the above-described problems and achieve the object, the present invention has one end connected to the positive electrode of the first DC power supply and the other end connected to the negative electrode of the first DC power supply. A series circuit in which an element, a second switching element, and a shunt resistor are connected in series in this order; an output unit connected between the first switching element and the second switching element; A first driving circuit for driving on / off of one switching element; a second driving circuit for driving on / off of the second switching element; and the second driving circuit complementary to the first switching element. A second DC power source that is a power source of the first drive circuit, a capacitor that is a power source of the first drive circuit that is charged by the second DC power source when the second switching element is turned on, and the shunt resistor A power converter and a control unit for detecting a state of the capacitor using a current flowing through the.

The power converter according to the present invention has an effect that the state of the capacitor in the bootstrap circuit can be detected during charging without providing a voltage monitoring circuit.

1 is a circuit diagram showing a configuration of a power conversion device according to a first embodiment; The figure which shows the on-off pattern of the upper arm switching element and the lower arm switching element at the time of charge of the power converter device shown in FIG. The figure which shows the current pathway at the time of charge of the power converter device shown in FIG. The circuit diagram which shows the structure of the power converter device concerning Embodiment 2. FIG. The figure which shows the on-off pattern of the upper arm switching element and the lower arm switching element at the time of charge of the power converter device shown in FIG. The circuit diagram which shows the structure of the power converter device concerning Embodiment 3. FIG.

Hereinafter, a power converter according to an embodiment of the present invention will be described in detail with reference to the drawings. Note that the present invention is not limited to the embodiments.

Embodiment 1 FIG.
FIG. 1 is a circuit diagram showing a configuration of the power conversion apparatus according to the first embodiment of the present invention. 1 includes a DC power source 1 that is a first DC power source, an upper arm switching element 2 that is a first switching element, a lower arm switching element 3 that is a second switching element, An upper arm side driving circuit 4 that is a first driving circuit, a lower arm side driving circuit 5 that is a second driving circuit, a DC power source 6 that is a second DC power source, a capacitor 7, and a diode 8, A shunt resistor 9. Further, the upper arm switching element 2, the lower arm switching element 3, and the shunt resistor 9 are connected in series in this order to form a series circuit 10.

The power converter 12 includes a control unit (not shown) that controls the first drive circuit and the second drive circuit. This control unit is realized by, for example, a CPU (Central Processing Unit).

Although only one series circuit 10 is shown in FIG. 1, a plurality of series circuits are actually provided. That is, two series circuits are provided when outputting single-phase alternating current, and three series circuits are provided when outputting three-phase alternating current. The upper arm side drive circuit 4 outputs a control signal to the gate of the upper arm switching element 2 to drive the upper arm switching element 2 on and off. The lower arm side drive circuit 5 outputs a control signal to the gate of the lower arm switching element 3 to drive the lower arm switching element 3 on and off in a complementary manner to the upper arm switching element 2. The DC power supply 6 is a power supply for the lower arm drive circuit 5, and the positive electrode of the DC power supply 6 is connected to the anode of the diode 8 and the lower arm drive circuit 5. The capacitor 7 is a power source for the upper arm side drive circuit 4, one end is connected to the upper arm side drive circuit 4 and the cathode of the diode 8, and the other end is connected to the upper arm side drive circuit 4, the upper arm switching element 2, and the lower arm. It is connected between the switching element 3. When the lower arm switching element 3 is turned on, it is charged by the DC power source 6. The diode 8 is connected in series with the DC power supply 6 and the capacitor 7. The shunt resistor 9 is connected in series to the upper arm switching element 2 and the lower arm switching element 3 to detect an output current. The series circuit 10 has one end connected to the positive electrode of the DC power supply 1 and the other end connected to the negative electrode of the DC power supply 1. The output unit 11 is connected between the upper arm switching element 2 and the lower arm switching element 3.

1 converts the DC voltage from the DC power source 1 into AC and generates an output current by alternately turning on and off the upper arm switching element 2 and the lower arm switching element 3. The upper arm side drive circuit 4 turns on and off the upper arm switching element 2 by a PWM (Pulse Width Modulation) signal comparing the carrier wave and the phase voltage command. The lower arm side drive circuit 5 turns on and off the lower arm switching element 3 by a PWM signal that compares the carrier wave and the phase voltage command.

When the upper arm switching element 2 is turned on, the electric charge of the capacitor 7 is consumed as a gate power source, and the voltage of the capacitor 7 drops. Further, when the lower arm switching element 3 is turned on, the capacitor 7 is charged and the voltage of the capacitor 7 rises. The upper arm switching element 2 and the lower arm switching element 3 are repeatedly turned on and off in a complementary manner, that is, alternately, and the same voltage fluctuation is repeated every one output frequency cycle. When the output is restarted after the output is stopped, that is, when the power conversion device 12 is started, the capacitor 7 is charged.

FIG. 2 is a diagram showing an on / off pattern of the upper arm switching element 2 and the lower arm switching element 3 when the power conversion device 12 shown in FIG. 1 is charged.

In FIG. 2, all of the upper arm switching element 2 and the lower arm switching element 3 are turned on all at once. However, the present invention is not limited to this, and the upper arm switching element 2 and the lower arm switching element are switched on. The timing for turning on the element 3 may be shifted for each phase. However, as shown in FIG. 2, it is possible to shorten the start-up time by matching the timing of turning on the upper arm switching element 2 of each phase and matching the timing of turning on the lower arm switching element 3 of each phase. Is preferable.

FIG. 3 is a diagram showing a current path when the capacitor 7 is charged in the power conversion device 12 shown in FIG. At the time of charging, as shown in FIG. 2, first, the upper arm switching element 2 is turned on for a time T1 that is a discharge completion time, and the capacitor 7 is discharged so that the voltage of the capacitor 7 approaches 0V. Thereafter, the lower arm switching element 3 is turned on for a time T2 that is a charging completion time to charge the capacitor 7. However, when the voltage of the capacitor 7 is discharged, it is not necessary to turn on the upper arm switching element 2 for T1 time.

Here, two methods for estimating the lifetime, which is an example of the state of the capacitor 7, will be described. In the first estimation method of the lifetime of the capacitor 7, first, the current flowing through the capacitor 7 during charging is obtained by the following equation (1).

In the above equation (1), the current i is the current value of the current flowing through the shunt resistor 9, the voltage Vr is the voltage value applied across the shunt resistor 9, and the resistor R is the resistance value of the shunt resistor 9. is there. The electric charge Q of the capacitor 7 is obtained by integrating the current obtained by the above equation (1).

In the above equation (2), the charge Q at the time of product shipment is stored as the charge Q1 at the time of shipment. When the capacitor 7 deteriorates, the current and time at the time of charging decrease and the charge Q of the capacitor 7 decreases, so that the charge Q2 accumulated at the time of charging after the deterioration becomes smaller than the shipping charge Q1. When this is expressed using the life coefficient K, it is as the following formula (3). However, K <1.

Thus, it is possible to estimate the life by the life coefficient K.

Next, in the second method for estimating the lifetime of the capacitor 7, first, the voltage Vc applied across the capacitor 7 during charging is measured. The voltage Vc is expressed by the following equations (4) and (5).

Here, in the above formulas (4) and (5), the voltage Vc is the voltage of the capacitor 7, the voltage Vm is the voltage of the DC power supply 6, the capacitance C is the capacitance of the capacitor 7, and the resistor R is a shunt. The resistance value of the resistor 9, the voltage ΔV is the total voltage value of the forward voltage of the diode 8 and the ON voltage of the lower arm switching element 3, and the current i is the current in the current path indicated by the dotted line in FIG. Value. Substituting the above equation (4) into equation (5), the current i (t), which is the theoretical current value t seconds after the start of the time T2 when the lower arm switching element 3 is turned on, is given by the following equation (6): expressed.

For the current i (t) that is the theoretical current value, the current at the time of product shipment is stored as the current i1 (t) at the time of shipment. When the capacitor 7 deteriorates, the current and time during charging decrease, and the current i2 (t) that flows during charging after deterioration becomes smaller than the current i1 (t) at the time of shipment. When this is expressed using a life coefficient K <1, the following equation (7) is obtained.

Thus, it is possible to estimate the life by the life coefficient K. In the present embodiment, the controller detects the state of the capacitor represented by the estimation of the lifetime of the capacitor from the current flowing through the shunt resistor 9.

Conventionally, the life of a capacitor in a bootstrap circuit is detected using a voltage monitoring circuit that requires an operational amplifier and an isolated power supply, and such a voltage monitoring circuit must be newly provided in each phase. As a result, the manufacturing cost of the power conversion device has increased. In the present embodiment, the current value of the current flowing through the shunt resistor 9, the voltage value applied across the shunt resistor 9, and the resistance value of the shunt resistor 9 are measured, or the current flowing through the capacitor 7 and the supply source. By measuring the voltage of the DC power supply 6, the lifetime of the capacitor 7 in the bootstrap circuit can be detected. Therefore, a conventional voltage monitoring circuit that requires an operational amplifier and an insulated power supply is not required, so that the power conversion device can be reduced in size and manufacturing cost can be reduced.

According to the present embodiment, the state of the capacitor in the bootstrap circuit, for example, the lifetime can be detected during charging without providing a voltage monitoring circuit. In addition, when the capacity of the capacitor 7 is less than the allowable value, for example, when the configuration is such that an alarm is output when the capacity is 80% or less of the capacity value at the time of shipment, the upper arm is not operated when the capacity is not detected. It is possible to prevent the loss of the switching element 2 from increasing and generating heat and failure.

Embodiment 2. FIG.
FIG. 4 is a circuit diagram showing a configuration of the power conversion apparatus according to the second embodiment of the present invention. The power converter 12a shown in FIG. 4 differs from the power converter 12 shown in FIG. 1 in that a shunt resistor 20 is provided instead of the shunt resistor 9. The shunt resistor 20 is connected between the lower connection point of the

series circuits

21, 21 a, 21 b that are inverter circuits and the DC power supply 1, and the output current during normal operation is derived from the bus current flowing through the shunt resistor 20. It is possible to ask. The series circuit 21 includes a U-phase upper arm switching element 2 and a U-phase lower arm switching element 3, and the upper arm switching element 2 and the lower arm switching element 3 are connected to the output unit 11. The series circuit 21a includes a V-phase upper arm switching element 2a and a V-phase lower arm switching element 3a, and the upper arm switching element 2a and the lower arm switching element 3a are connected to the output unit 11a. The series circuit 21b includes a W-phase upper arm switching element 2b and a W-phase lower arm switching element 3b, and the upper arm switching element 2b and the lower arm switching element 3b are connected to the output unit 11b. Note that the voltage applied to the shunt resistor 20 is the voltage Vr.

FIG. 5 is a diagram showing an on / off pattern of the upper

arm switching elements

2, 2a, 2b and the lower

arm switching elements

3, 3a, 3b when the power conversion device 12a shown in FIG. 4 is charged. In the power conversion device 12a shown in FIG. 4, when the lower

arm switching elements

3, 3a, 3b are simultaneously turned on during charging, the charging current flows at the same time, so that it is difficult to detect the life. Therefore, as shown in FIG. 5, by providing a U-phase charging period, a V-phase charging period, and a W-phase charging period, and by shifting the timing at which the lower

arm switching elements

3, 3a, 3b of each phase are turned on, The charging current can be passed through the shunt resistor 20 in order.

In FIG. 5, the upper

arm switching elements

2, 2a, 2b are turned on all at once. However, the present invention is not limited to this, and the timing at which the upper

arm switching elements

2, 2a, 2b are turned on is also included. It may be shifted. However, as shown in FIG. 5, it is preferable to match the timings at which the upper

arm switching elements

2, 2a, 2b are turned on because the startup time can be shortened.

In the present embodiment, as in the first embodiment, the lifetime is detected by using the equations (3) and (7) in the first embodiment based on the current flowing for each phase.

Embodiment 3 FIG.
FIG. 6 is a circuit diagram showing a configuration of the power conversion device according to the third embodiment of the present invention. The power converter 12b shown in FIG. 6 includes a current limiting resistor 30 between the branch point to the lower arm side drive circuit 5 of the DC power source 6 and the diode 8, and the shunt resistor 9 is not provided in FIG. Different from the power converter 12 shown.

In the power converter 12b shown in FIG. 6, the output current during normal operation is detected by using a current detector insulated from the inverter output to the motor output. At this time, since the charging current of the bootstrap circuit does not flow to the current detector, it is obtained by measuring the voltage Vr = Vs−Vm across the current limiting resistor 30. Here, the voltage Vs is a voltage value from the negative electrode of the DC power supply 6 to the anode side of the diode 8 of the current limiting resistor 30, and the voltage Vm is a power supply voltage value of the DC power supply 6. Since the voltages Vs and Vm have a common common, they can be simultaneously measured by an AD (Analog to Digital) converter.

In the present embodiment, as in the first embodiment, the life of the capacitor, which is an example of the state of the capacitor, using the equations (3) and (7) in the first embodiment by the current flowing in each phase. Perform detection.

According to the present embodiment, the state of the capacitor in the bootstrap circuit, for example, the lifetime can be detected during charging without providing a voltage monitoring circuit and a shunt resistor. In addition, when the capacity of the capacitor 7 is less than the allowable value, for example, when the configuration is such that an alarm is output when the capacity is 80% or less of the capacity value at the time of shipment, the upper arm is not operated when the capacity is not detected. It is possible to prevent the loss of the switching element 2 from increasing and generating heat and failure.

In the first to third embodiments, when the capacity of the capacitor 7 is equal to or less than the allowable value, as an example, a configuration that outputs an alarm when the capacity is 80% or less of the capacity value at the time of shipment is exemplified. Other configurations may alert the user. As an example, it may be configured to output a warning signal to the controller and stop the activation, or a power converter may be provided with a display unit and a warning message displayed on the display unit. In any configuration, the user can recognize that the capacitor 7 should be replaced, and can prevent a failure of the power conversion apparatus due to the deterioration of the capacitor 7.

In the first to third embodiments, the capacitor state is detected by a CPU (Central Processing Unit) (not shown) that realizes a control unit of the power conversion device.

The configuration described in the above embodiment shows an example of the contents of the present invention, and can be combined with another known technique, and can be combined with other configurations without departing from the gist of the present invention. It is also possible to omit or change the part.

1,6 DC power supply, 2, 2a, 2b upper arm switching element, 3, 3a, 3b lower arm switching element, 4 upper arm side drive circuit, 5 lower arm side drive circuit, 7 capacitor, 8 diode, 9, 20 shunt Resistance, 10, 21, 21a, 21b series circuit, 11, 11a, 11b output unit, 12, 12a, 12b power converter, 30 current limiting resistor.

Claims

One end is connected to the positive electrode of the first DC power supply, the other end is connected to the negative electrode of the first DC power supply, and the first switching element, the second switching element, and the shunt resistor are connected in series in this order. A series circuit,
An output connected between the first switching element and the second switching element;
A first driving circuit for driving on and off the first switching element;
Complementary to the first switching element, a second drive circuit for driving the second switching element on and off; and
A second DC power source that is a power source of the second drive circuit;
A capacitor that is a power source of the first drive circuit and is charged by the second DC power source when the second switching element is turned on;
And a control unit that detects a state of the capacitor using a current flowing through the shunt resistor.
A plurality of series circuits each having one end connected to the positive electrode of the first DC power supply, and a first switching element and a second switching element connected in series in this order;
A shunt resistor having one end connected to the other end of each of the plurality of series circuits and the other end connected to the negative electrode of the first DC power supply;
An output connected between the first switching element and the second switching element;
A first driving circuit for driving on and off the first switching element;
Complementary to the first switching element, a second drive circuit for driving the second switching element on and off; and
A second DC power source that is a power source of the second drive circuit;
A capacitor that is a power source of the first drive circuit and is charged by the second DC power source when the second switching element is turned on;
And a control unit that detects a state of the capacitor using a current flowing through the shunt resistor.
One end is connected to the positive electrode of the first DC power supply, the other end is connected to the negative electrode of the first DC power supply, and the first switching element, the second switching element, and the shunt resistor are connected in series in this order. A series circuit,
An output connected between the first switching element and the second switching element;
A first driving circuit for driving on and off the first switching element;
Complementary to the first switching element, a second drive circuit for driving the second switching element on and off; and
A second DC power source that is a power source of the second drive circuit;
A capacitor that is a power source of the first drive circuit and is charged by the second DC power source when the second switching element is turned on;
A current limiting resistor for limiting a charging current when the second switching element is on;
And a control unit that detects a state of the capacitor using a current flowing through the current limiting resistor.
In the detection of the state of the capacitor, at startup, the first switching element is turned on for a discharge completion time to discharge the capacitor, and the second switching element is turned on for a charge completion time to charge the capacitor. The power conversion device according to any one of claims 1 to 3, wherein the power conversion device is performed.