JP7392570B2 - inverter device - Google Patents

Description

The present invention relates to an inverter device, and particularly to an inverter device including a bootstrap capacitor.

Conventionally, an inverter device including a bootstrap capacitor is known (for example, see Patent Document 1).

The motor drive device described in Patent Document 1 is provided with a motor drive DC power source, an upper switching element, and a lower switching element. Further, the connection point between the upper switching element and the lower switching element serves as an output end to the motor. Further, the motor drive device is provided with a bootstrap capacitor for applying a predetermined voltage to the emitter of the upper-stage switching element to turn on the upper-stage switching element. The bootstrap capacitor is charged by turning on the lower switching element before the motor rotates. Furthermore, although it is not specified in Patent Document 1, the conventional motor drive device described in the above motor drive device is provided with a main circuit capacitor for smoothing the voltage of the DC power supply for driving the motor. It is thought that

Here, to restart the motor drive device while the motor is in a free run state (a state in which the motor continues to rotate even though the output from the motor drive device to the motor has stopped). The bootstrap capacitor may be charged. In this case, when the bootstrap capacitor is charged by turning on the lower switching element, an overcurrent flows in the motor drive device (between the motor and the lower switching element) due to the back electromotive voltage from the motor. There are cases. In contrast, although not specified in Patent Document 1, control may be performed to suppress the occurrence of overcurrent by lowering the duty ratio of the lower switching element.

JP2013-198234A

However, in the conventional motor drive device (inverter device) as described in Patent Document 1, when charging the lower switching element by lowering the duty ratio of the lower switching element, during the period when the lower switching element is off, Since regenerative current flows from the motor to the main circuit capacitor, a problem may arise in which the voltage of the main circuit capacitor becomes excessively large. Note that if the voltage of the main circuit capacitor becomes excessively high, the main circuit capacitor may be damaged, or the motor drive device itself may be forced to stop in order to prevent overvoltage of the main circuit capacitor.

This invention was made in order to solve the above-mentioned problems, and one purpose of this invention is to solve the problem of excessive voltage on the main circuit capacitor when charging the bootstrap capacitor during free running of the motor. An object of the present invention is to provide an inverter device that can suppress the increase in size.

In order to achieve the above object, an inverter device according to one aspect of the present invention includes a power supply section that outputs a DC voltage, a main circuit capacitor that smoothes the DC voltage from the power supply section, and a superconductor connected in series with each other. a switching element section including an arm element and a lower arm element, in which a connection point between the upper arm element and the lower arm element is connected to the motor; a bootstrap capacitor that is charged while the lower arm element is turned on; and a control unit that controls the duty ratio of the lower arm element, and when the lower arm element is off, the upper arm element is turned on by the voltage charged in the bootstrap capacitor. In a free run state where the output from the inverter circuit to the motor is stopped and the rotation of the motor continues for a certain period of time without being stopped, the control section controls whether the bootstrap capacitor is being charged , controls charging of the bootstrap capacitor by turning on and off the lower arm element according to the first duty ratio, and changes the duty ratio of the lower arm element from the first duty ratio to the second duty ratio based on the voltage of the main circuit capacitor. By changing the duty ratio to , the bootstrap capacitor is controlled to be charged while controlling to suppress the increase in the voltage of the main circuit capacitor.

In the inverter device according to one aspect of the present invention, as described above, the duty ratio of the lower arm element is changed from the first duty ratio based on the voltage of the main circuit capacitor during charging of the bootstrap capacitor in the free run state. By changing the duty ratio to the second duty ratio, control is performed to charge the bootstrap capacitor while controlling to suppress an increase in the voltage of the main circuit capacitor. Here, if the second duty ratio is smaller than the first duty ratio, by changing (lowering) the duty ratio of the lower arm element from the first duty ratio to the second duty ratio, It is possible to suppress an increase in the current value flowing through the inverter circuit section. As a result, when the bootstrap capacitor is charged during free running of the motor, control is performed to suppress the rise in voltage of the main circuit capacitor based on the voltage of the main circuit capacitor, thereby increasing the current flowing through the inverter circuit. can be suppressed from increasing, and it is also possible to easily suppress the voltage of the main circuit capacitor from becoming excessively large. In addition, if the second duty ratio is larger than the first duty ratio, booting is performed by changing (increasing) the duty ratio of the lower arm element from the first duty ratio to the second duty ratio. The time required to charge the strap capacitor can be shortened. As a result, when charging the bootstrap capacitor while the motor is free-running, control is performed to suppress the rise in voltage of the main circuit capacitor based on the voltage of the main circuit capacitor. The time can be shortened, and the voltage of the main circuit capacitor can be easily prevented from becoming excessively large.

In the inverter device according to the first aspect, preferably, the control unit adjusts the duty ratio of the lower arm element to the first duty based on the voltage of the main circuit capacitor during charging of the bootstrap capacitor in the free run state. By lowering the duty ratio from the first duty ratio to a second duty ratio smaller than the first duty ratio, the bootstrap capacitor is controlled to be charged while performing control to suppress an increase in the voltage of the main circuit capacitor. . Here, during the ON period in which the lower arm element is turned on and off while the bootstrap capacitor is being charged, a short-circuit current flows between the motor and the lower arm element. Energy is stored in the motor coils due to this short circuit current. Further, when the lower arm element is turned off from the on state, the (regenerated) energy stored in the coil of the motor is released to the main circuit capacitor, so that the voltage value of the main circuit capacitor increases. Here, the short-circuit current between the motor and the lower arm element increases as the duty ratio of the lower arm element increases (the longer the time the lower arm element is turned on). Moreover, the energy stored in the coil of the motor depends on the square of the current value between the motor and the lower arm element. Therefore, by reducing the duty ratio of the lower arm element from the first duty ratio to the second duty ratio (lengthening the off period of the lower arm element), the regenerative current from the motor flows to the main circuit capacitor. Even if the main circuit capacitor voltage rises for a longer period of time, the energy stored in the motor coil due to the main circuit capacitor voltage rise will be significantly smaller, preventing the main circuit capacitor voltage from increasing excessively. Can be suppressed.

Further, in this case, preferably, the control unit preliminarily controls the duty ratio of the lower arm element from the first duty ratio to the second duty ratio while charging the bootstrap capacitor in the free run state. It is configured to perform control to lengthen the charging time of the set bootstrap capacitor. With this configuration, although the charging efficiency of the bootstrap capacitor decreases by the reduction in the duty ratio of the lower arm element, control is performed to lengthen the preset charging time of the bootstrap capacitor. It is possible to prevent the charging period from ending before the bootstrap capacitor is fully charged.

Further, in the inverter device according to the first aspect, preferably, the control unit turns on and off the lower arm element according to the first duty ratio while charging the bootstrap capacitor in the free run state, thereby increasing the voltage of the main circuit capacitor. When the voltage exceeds the first threshold voltage, the voltage of the main circuit capacitor can be reduced by changing the duty ratio of the lower arm element from the first duty ratio to the second duty ratio when charging the bootstrap capacitor. It is configured to perform control to charge the bootstrap capacitor while performing control to suppress the increase. With this configuration, the duty ratio of the lower arm element can be controlled simply by comparing the first threshold voltage with the voltage value of the main circuit capacitor. Compared to the case where the duty ratio of the lower arm element is controlled based on the calculated rate of change by calculating the rate of change, the control by the control unit can be simplified (the control load can be reduced).

In this case, preferably, the control unit changes the voltage of the main circuit capacitor from a state equal to or higher than the first threshold voltage to a state lower than the first threshold voltage while charging the bootstrap capacitor in the free run state. In this case, the control is performed to return the duty ratio of the lower arm element from the second duty ratio to the first duty ratio. With this configuration, the duty ratio of the lower arm element can be returned to its original state in conjunction with the return of the voltage of the main circuit capacitor to its original state. Thereby, when the first duty ratio is larger, the bootstrap capacitor can be charged more quickly. Furthermore, when the first duty ratio is smaller, the value of current flowing through the inverter circuit section can be reduced.

Further, in the inverter device according to the first aspect, preferably, the inverter circuit section further includes a voltage detection section that detects the voltage value of the main circuit capacitor, and the control section is configured such that the , by changing the duty ratio of the lower arm element from the first duty ratio to the second duty ratio based on the voltage value of the main circuit capacitor detected by the voltage detection section, the increase in the voltage of the main circuit capacitor is suppressed. It is configured to perform control to charge the bootstrap capacitor while performing control to suppress the charge. With this configuration, the duty ratio of the lower arm element can be controlled based on the detected value of the voltage detection section, so that control to suppress the increase in voltage of the main circuit capacitor can be accurately performed.

Further, in the inverter device according to the first aspect, preferably, the inverter circuit section further includes a current detection section that detects a current value flowing between the switching element section and the motor, and the control section is configured to turn on/off the lower arm element. When the control is stopped, the lower arm element is turned on with a duty ratio of 1 to perform initial charging of the bootstrap capacitor, and during initial charging, an overcurrent is flowing due to the current detection unit. Based on this detection, the duty ratio of the lower arm element is lowered from 1 to the first duty ratio to charge the bootstrap capacitor, and the lower arm element is controlled to charge the bootstrap capacitor based on the voltage of the main circuit capacitor. By changing the duty ratio from a first duty ratio to a second duty ratio, the bootstrap capacitor is charged while performing control to suppress a rise in voltage of the main circuit capacitor. There is. With this configuration, by reducing the duty ratio of the lower arm element based on the detected value of the current detection unit, the current flowing between the switching element unit and the motor is suppressed from becoming an overcurrent, and the main It is possible to suppress the voltage of the circuit capacitor from becoming excessively large.

In the inverter device according to the first aspect, preferably, the switching element section includes a multi-phase upper arm element and a multi-phase lower arm element, and the bootstrap capacitor is connected to each of the multi-phase upper arm elements. The control unit uniformly sets the duty ratio of each of the lower arm elements of the multiple phases based on the voltage of the main circuit capacitor while charging the bootstrap capacitors of multiple phases in a free run state. The battery charger is configured to charge each of the plurality of bootstrap capacitors by changing the duty ratio from the first duty ratio to the second duty ratio. With this configuration, it is possible to prevent the voltage of the main circuit capacitor from becoming excessively large in an inverter device that supports multiple phases. Furthermore, by uniformly changing the duty ratio of each of the lower arm elements of the multiple phases from the first duty ratio to the second duty ratio, it is possible to prevent the charging states of the bootstrap capacitors of the multiple phases from becoming different from each other. Can be suppressed.

According to the present invention, as described above, when charging the bootstrap capacitor during free running of the motor, it is possible to suppress the voltage of the main circuit capacitor from becoming excessively large.

FIG. 1 is a diagram showing the configuration of an inverter device according to a first embodiment. FIG. 3 is a diagram for explaining a method of charging a bootstrap capacitor in the inverter device according to the first embodiment. FIG. 7 is a diagram showing the current flowing from the motor when the lower arm element according to the first and second embodiments is on. FIG. 7 is a diagram showing the current flowing from the motor when the lower arm element according to the first and second embodiments is off. FIG. 3 is a diagram schematically representing a chopper circuit formed by a back electromotive voltage of a motor according to the first and second embodiments. FIG. 7 is a diagram for explaining the operation of the lower arm element when the voltage value of the main circuit capacitor becomes equal to or higher than the second threshold voltage according to the first and second embodiments. FIG. 6 is a diagram for explaining the operation of the lower arm element when the voltage value of the main circuit capacitor becomes smaller than the first threshold voltage according to the first and second embodiments. FIG. 3 is a diagram showing the configuration of an inverter device according to a second embodiment. FIG. 7 is a diagram for explaining a method of charging a bootstrap capacitor in an inverter device according to a second embodiment.

DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments embodying the present invention will be described based on the drawings.

[First embodiment]
The configuration of an inverter device 100 according to the first embodiment will be described with reference to FIGS. 1 to 7.

(Configuration of inverter device)
As shown in FIG. 1, the inverter device 100 includes an inverter circuit section 10. The inverter circuit section 10 includes a power supply section 1 that outputs a DC voltage. The power supply unit 1 includes a three-phase output AC power supply 1a and a rectification unit 1b that converts an AC voltage from the AC power supply 1a into a DC voltage.

Inverter circuit section 10 includes a main circuit capacitor 2 that smoothes the DC voltage from power supply section 1 . The main circuit capacitor 2 is charged with DC voltage from the power supply section 1. Further, the inverter circuit section 10 includes a voltage detection section 2a that detects the voltage value Edc of the main circuit capacitor 2.

Inverter circuit section 10 includes switching element section 3 . The switching element section 3 includes an upper arm element 3a and a lower arm element 3b that are connected in series with each other. Each of the upper arm element 3a and the lower arm element 3b is provided for each of multiple phases (R phase, S phase, and T phase). Note that the upper arm element 3a and the lower arm element 3b are bipolar transistors.

Further, an upper diode element 3c is connected in parallel to each of the three upper arm elements 3a. Furthermore, a lower diode element 3d is connected in parallel to each of the three lower arm elements 3b. Note that the anode side of the upper diode element 3c is connected to the emitter side of the upper arm element 3a. Further, the anode side of the lower diode element 3d is connected to the emitter side of the lower arm element 3b.

Further, a connection point A between the upper arm element 3a and the lower arm element 3b is connected to the motor 101. That is, each of the three connection points A provided for each phase is connected to the motor 101.

The inverter circuit section 10 also includes a bootstrap capacitor 4 that is charged while the lower arm element 3b is turned on. The positive side of the bootstrap capacitor 4 is connected to the base side of the upper arm element 3a. Further, the negative side of the bootstrap capacitor 4 is connected to the emitter side of the upper arm element 3a. As a result, the upper arm element 3a is turned on by the voltage charged in the bootstrap capacitor 4 while the lower arm element 3b is turned off. Specifically, bootstrap capacitor 4 turns on upper arm element 3a by applying a predetermined voltage to the base and emitter of upper arm element 3a.

Note that when the lower arm element 3b is on and the upper arm element 3a is off, a closed circuit is formed by the power supply 6a, which will be described later, the bootstrap capacitor 4, and the lower arm element 3b. , the bootstrap capacitor 4 is charged by the power supply 6a.

The inverter circuit section 10 includes a base drive section 5a of the upper arm element 3a and a base drive section 5b of the lower arm element 3b. The positive side of the bootstrap capacitor 4 is connected to the base drive section 5a. The base drive section 5a is provided corresponding to each of the three-phase upper arm elements 3a. Furthermore, the base drive section 5b is provided corresponding to each of the three-phase lower arm elements 3b. Further, the operation (opening/closing) of each of the base drive section 5a and the base drive section 5b is controlled by a control section 8, which will be described later. Although FIG. 1 is simplified and shows that signals are transmitted from the control unit 8 to the base drive units 5a and 5b of one phase, in reality, signals are transmitted to the base drive units of each of the three phases. 5a and the base drive unit 5b.

The inverter circuit section 10 is also provided with one base voltage power source 6a. The power source 6a is input to the base drive section 5a of each phase and the base drive section 5b of each phase. Then, the voltage of the power source 6a is input to the bases of the upper arm element 3a and the lower arm element 3b via the base drive unit 5a and base drive unit 5b operated (opened and closed) by the control unit 8, which will be described later. Note that a diode 6b whose anode side is connected to the power source 6a is provided between the power source 6a and each of the base drive units 5a of each phase.

The inverter circuit section 10 includes a current detection section 7 that detects the value of the current flowing between the switching element section 3 and the motor 101. The current detection unit 7 is configured to detect current values between the three connection points A and the motor 101. Note that the current detection unit 7 may be configured to detect the respective current values between two of the three connection points A and the motor 101. This is because the sum of the AC current values of the three phases is always 0, so the current value of one of the three phases can be detected (calculated) from the detected values of the remaining two phases without directly measuring it. This is because it is possible.

The inverter device 100 also includes a control section 8 that controls the duty ratios of the upper arm element 3a and the lower arm element 3b. Specifically, the control unit 8 controls the on/off of the upper arm element 3a and the lower arm element 3b (controls the duty ratio) by transmitting a pulse signal to each of the base drive unit 5a and the base drive unit 5b. It is configured as follows.

(Control regarding restart of inverter device)
Here, control related to restarting the inverter device 100 will be explained with reference to FIGS. 2 to 7.

First, when the motor 101 is normally operated by the inverter device 100 (see the first state "operating" in FIG. 2), the voltage value Edc of the main circuit capacitor 2 is constant. Here, it is assumed that the inverter device 100 is stopped (see the state "stopped" in FIG. 2) based on the occurrence of a predetermined alarm factor or the like. A case where a predetermined alarm factor or the like occurs is, for example, a case where the voltage value Edc of the main circuit capacitor 2 decreases. In this case, the output from the inverter circuit unit 10 (inverter device 100) to the motor 101 is stopped. At this time, the motor 101 enters a free run state in which the rotation of the motor 101 is not stopped and continues for a certain period of time (see the motor speed in the "stop" state in FIG. 2). The free run state means a state in which the motor 101 is rotating only by inertia force or external force. A free-run state occurs when the fan or pump is being turned by an external force, or when a momentary power outage occurs during operation and the output is cut off. Further, while the inverter device 100 is stopped, the charge of the bootstrap capacitor 4 decreases.

Next, when the alarm factor etc. are canceled and normal operation is possible, if there is a command to operate, the inverter device 100 resumes operation regardless of whether the motor 101 is in a free running state. Specifically, the inverter device 100 resumes operation without tripping immediately after a power outage due to functions such as instantaneous power failure recovery. Tripless means that an emergency stop is not required due to abnormal voltage.

When restarting the inverter device 100, the control unit 8 first performs control to charge the bootstrap capacitor 4 in a free run state. Charging of the bootstrap capacitor 4 in the free run state will be described in detail below. Note that while the bootstrap capacitor 4 is being charged, the on/off states of the three-phase lower arm elements 3b are the same. That is, while the bootstrap capacitor 4 is being charged, the duty ratio (on/off) of the three-phase lower arm element 3b is uniformly controlled by the control unit 8.

Specifically, the control unit 8 turns on the lower arm element 3b with a duty ratio of 1 from a state where the on/off control of the lower arm element 3b is stopped (a state where the off state is maintained). The controller is configured to control the initial charging of the bootstrap capacitor 4 (see period T1 in the state "waiting for bootstrap charging" in FIG. 2). This increases the charging of the bootstrap capacitor 4. Note that during the period of the state "waiting for bootstrap charging" in FIG. 2, the three upper arm elements 3a are maintained in the off state.

Here, when the three-phase lower arm element 3b is turned on, the R phase, S phase, and T phase of the motor 101 are short-circuited to each other, and a large current (overload) is generated between the motor 101 and the lower arm element 3b. Current) (see dashed arrow in FIG. 3) flows. Note that this current flows due to an induced electromotive force generated because the motor 101 is rotating in a free run state. Further, this current is a short circuit current between the RST phases. Note that in FIG. 3, elements unnecessary for the explanation are omitted for the sake of simplification.

In this case, an excessively large current (see the output current during period T1 in FIG. 2) is generated in the inverter circuit section 10. Then, the control unit 8 changes the duty ratio of the lower arm element 3b from 1 to a first duty ratio (for example 0.5) to charge the bootstrap capacitor 4 (see period T2 in the state "waiting for bootstrap charging" in FIG. 2). Note that the control unit 8 performs control to reduce the duty ratio of the lower arm element 3b from 1 to the first duty ratio when the current value detected by the current detection unit 7 becomes I1 or more.

Here, by turning on and off the lower arm element 3b at the first duty ratio, a period in which the lower arm element 3b is turned off occurs. When the lower arm element 3b is off (the state shown in FIG. 4), regenerative current from the motor 101 flows to the main circuit capacitor 2 through the upper diode element 3c connected in parallel with the upper arm element 3a. As a result, the voltage value Edc of the main circuit capacitor 2 increases. Note that during the period T2, the lower arm element 3b is turned on and off with a duty ratio smaller than 1, so a current with a current value I2 smaller than I1 flows through the inverter circuit section 10.

Further, when the lower arm element 3b is on (the state shown in FIG. 3), a boost chopper circuit (see FIG. 5) is configured between the motor 101 and the inverter circuit section 10. Here, E and L in FIG. 5 represent the back electromotive force of the motor 101 and the inductance within the motor 101, respectively. Further, TR and D in FIG. 5 represent the lower arm element 3b and the upper diode element 3c, respectively. Further, C in FIG. 5 represents the main circuit capacitor 2.

As shown in FIG. 5, while TR (lower arm element 3b) is on, current flows through the paths E, L, and TR. Thereafter, when TR is turned off, the energy stored in L is released and C is charged. The voltage generated at C at this time is larger than E because the voltages of E and L are added. Moreover, the energy stored in L depends on the square of the current value flowing in L while TR (lower arm element 3b) is on.

Here, in the first embodiment, as shown in FIG. 2, the control unit 8 changes the duty ratio of the lower arm element 3b from the first duty ratio to the second duty ratio based on the voltage of the main circuit capacitor 2. (for example, 0.25), the bootstrap capacitor 4 is charged while performing control to suppress the increase in voltage of the main circuit capacitor 2 (period T3 of the state "waiting for bootstrap charging" in FIG. 2). ). That is, by lowering the duty ratio of the lower arm element 3b, the current value flowing through L (see FIG. 5) caused by the increase in the voltage value Edc of the main circuit capacitor 2 decreases (reduced from I2 to I3) and L The energy stored in the is reduced. On the other hand, by lowering the duty ratio of the lower arm element 3b, the time during which the current from the motor 101 flows through the main circuit capacitor 2 increases, but the voltage value of the main circuit capacitor 2 decreases by the amount of energy stored in L. The increase in Edc is suppressed. This is because the energy stored in L depends on the square of the current value flowing through L, and the magnitude of the current value has a large effect on energy. Note that each of the first duty ratio and the second duty ratio is a preset value.

Specifically, the control unit 8 controls the bootstrap capacitor 4 when the voltage of the main circuit capacitor 2 becomes equal to or higher than the first threshold voltage E1 by turning the lower arm element 3b on and off according to the first duty ratio. It is configured to perform control to change (reduce) the duty ratio of the lower arm element 3b from the first duty ratio to the second duty ratio during charging. The first threshold voltage E1 is a preset value. For example, the first threshold voltage E1 is about 400V.

Specifically, the control unit 8 changes the duty ratio of the lower arm element 3b from the first duty ratio to the second duty ratio based on the voltage value Edc of the main circuit capacitor 2 detected by the voltage detection unit 2a. (lower) control. That is, the control unit 8 compares the voltage value Edc detected by the voltage detection unit 2a with the first threshold voltage E1, and when the voltage value Edc becomes equal to or higher than the first threshold voltage E1, the lower arm Control is performed to change (reduce) the duty ratio of the element 3b from the first duty ratio to the second duty ratio.

As shown in FIG. 6, if the voltage of the main circuit capacitor 2 becomes equal to or higher than the second threshold voltage E2 while the bootstrap capacitor 4 is being charged in the free run state, the inverter circuit section 10 is forced to be stopped. In this case, the lower arm element 3b is fixed in the off state. The second threshold voltage E2 is greater than the first threshold voltage E1. Specifically, the second threshold is, for example, about 420V. Further, the second threshold voltage E2 is a preset value. Note that the main circuit capacitor 2 has a withstand voltage (for example, about 450 V) that is higher than the second threshold voltage E2.

Further, in the first embodiment, as shown in FIG. 7, the control unit 8 controls the voltage of the main circuit capacitor 2 from being equal to or higher than the first threshold voltage E1 while the bootstrap capacitor 4 is being charged in the free run state. When the voltage changes to a state lower than the first threshold voltage E1, the duty ratio of the lower arm element 3b is controlled to return from the second duty ratio to the first duty ratio. Specifically, during the period T4 in FIG. 7, the voltage (Edc) of the main circuit capacitor 2 is equal to or higher than the first threshold voltage E1, so the lower arm element 3b is turned on and off at the second duty ratio. Further, during the period T5 in FIG. 7, the voltage (Edc) of the main circuit capacitor 2 is lower than the first threshold voltage E1, so the lower arm element 3b is turned on and off at the first duty ratio. Note that if the voltage (Edc) of the main circuit capacitor 2 becomes smaller than the first threshold voltage E1 and then becomes equal to or higher than the first threshold voltage again, the duty ratio of the lower arm element 3b becomes the first duty ratio. The duty ratio is then changed to the second duty ratio again.

Further, in the first embodiment, as shown in FIG. 2, the control unit 8 changes the duty ratio of the lower arm element 3b from the first duty ratio to the second duty ratio while the bootstrap capacitor 4 is being charged in the free run state. When the duty ratio is lowered, the charging time of the bootstrap capacitor 4, which is set in advance, is controlled to be extended. Specifically, the charging time is set in advance in accordance with the time required for charging when the bootstrap capacitor 4 is charged while the duty ratio of the lower arm element 3b remains 1. Then, when the duty ratio of the lower arm element 3b is changed to the first duty ratio and the second duty ratio, the control unit 8 performs control to lengthen the charging time in accordance with the changed duty ratio. .

For example, assume that the preset charging time is 10 seconds, and charging is performed for 1 second with the duty ratio of the lower arm element 3b being 1. After that, if the duty ratio is changed to 0.5, charging will take 9 seconds remaining when the duty ratio is 1, so 18 seconds, which is twice 9 seconds (1/0.5 = 2), will remain for charging. It's time. In addition, when the duty ratio is changed to 0.25, using the same idea as above, the remaining charge capacity based on the charging time when the duty ratio is 1 and 0.5 is used for charging. The time required is calculated. For example, after charging for 1 second when the duty ratio is 1 and charging for 8 seconds when the duty ratio is 0.5, the duty ratio becomes 0.25 because the battery is half fully charged. If changed, the remaining charging time will be 20 seconds (10 x 1/2 x 1/0.25 = 20).

After the charging of the bootstrap capacitor 4 is completed (after the calculated charging time has elapsed), the motor 101 operates normally (see the state "operating" after the state "waiting for bootstrap charging" in FIG. 2). ) will be resumed.

[Effects of the first embodiment]
In the first embodiment, the following effects can be obtained.

In the first embodiment, as described above, the control unit 8 charges the bootstrap capacitor 4 by turning on and off the lower arm element 3b according to the first duty ratio while charging the bootstrap capacitor 4 in the free run state. The increase in the voltage of the main circuit capacitor 2 is controlled by controlling the voltage of the main circuit capacitor 2 and changing the duty ratio of the lower arm element 3b from the first duty ratio to the second duty ratio based on the voltage of the main circuit capacitor 2. It is configured to perform control to charge the bootstrap capacitor 4 while performing suppression control. As a result, when the bootstrap capacitor 4 is charged during free running of the motor 101, control is performed to suppress the increase in the voltage of the main circuit capacitor 2 based on the voltage of the main circuit capacitor 2, so that the inverter circuit section It is possible to suppress the current value flowing through the main circuit capacitor 10 from increasing, and it is also possible to easily suppress the voltage of the main circuit capacitor 2 from becoming excessively large.

Further, in the first embodiment, as described above, the control unit 8 sets the duty ratio of the lower arm element 3b to the first value based on the voltage of the main circuit capacitor 2 while the bootstrap capacitor 4 is being charged in the free run state. By lowering the duty ratio from 1 to a second duty ratio smaller than the first duty ratio, control is performed to charge the bootstrap capacitor 4 while performing control to suppress an increase in the voltage of the main circuit capacitor 2. It is composed of Here, during the ON period during which the lower arm element 3b is turned on and off while the bootstrap capacitor 4 is being charged, a short-circuit current flows between the motor 101 and the lower arm element 3b. Energy is stored in the coil of motor 101 due to this short circuit current. Furthermore, when the lower arm element 3b is turned off from the on state, the (regenerative) energy stored in the coil of the motor 101 is released to the main circuit capacitor 2, so the voltage value Edc of the main circuit capacitor 2 increases. It gets expensive. Here, the short circuit current between the motor 101 and the lower arm element 3b increases as the duty ratio of the lower arm element 3b increases (the longer the time that the lower arm element 3b is turned on). Furthermore, the energy stored in the coil of the motor 101 depends on the square of the current value between the motor 101 and the lower arm element 3b. Therefore, by reducing the duty ratio of the lower arm element 3b from the first duty ratio to the second duty ratio (lengthening the off period of the lower arm element 3b), the regenerative current from the motor 101 is reduced to the main circuit capacitor 2. Even if the time for the voltage of the main circuit capacitor 2 to rise by flowing to It is possible to suppress the voltage from becoming excessively large.

Further, in the first embodiment, as described above, the control unit 8 changes the duty ratio of the lower arm element 3b from the first duty ratio to the second duty ratio while charging the bootstrap capacitor 4 in the free run state. When the charging time of the bootstrap capacitor 4 is lowered to 1, the preset charging time of the bootstrap capacitor 4 is extended. As a result, while the charging efficiency of the bootstrap capacitor 4 is reduced by the amount that the duty ratio of the lower arm element 3b is reduced, control is performed to lengthen the preset charging time of the bootstrap capacitor 4. It is possible to prevent the charging period from ending before the bootstrap capacitor 4 is fully charged.

Further, in the first embodiment, as described above, the control unit 8 controls the main circuit capacitor 2 by turning on and off the lower arm element 3b according to the first duty ratio while charging the bootstrap capacitor 4 in the free run state. By changing the duty ratio of the lower arm element 3b during charging of the bootstrap capacitor 4 from the first duty ratio to the second duty ratio when the voltage becomes equal to or higher than the first threshold voltage E1, It is configured to perform control to charge the bootstrap capacitor 4 while performing control to suppress an increase in the voltage of the main circuit capacitor 2. As a result, the duty ratio of the lower arm element 3b can be controlled simply by comparing the first threshold voltage E1 and the voltage value Edc of the main circuit capacitor 2, so that, for example, the voltage value Edc of the main circuit capacitor 2 Compared to the case where the rate of change of is calculated and the duty ratio of the lower arm element 3b is controlled based on the calculated rate of change, the control by the control unit 8 can be simplified (the control load can be reduced). can.

Further, in the first embodiment, as described above, while charging the bootstrap capacitor 4 in the free-run state, the control unit 8 changes the voltage of the main circuit capacitor 2 from a state equal to or higher than the first threshold voltage E1 to a first threshold voltage E1. When the voltage changes to a state lower than the threshold voltage E1, the duty ratio of the lower arm element 3b is controlled to return (increase) from the second duty ratio to the first duty ratio. Thereby, the duty ratio of the lower arm element 3b can be returned to the original state in conjunction with the return of the voltage of the main circuit capacitor 2 to the original state. Thereby, the bootstrap capacitor 4 can be charged more quickly.

Further, in the first embodiment, as described above, the control unit 8 controls the voltage value Edc of the main circuit capacitor 2 detected by the voltage detection unit 2a while charging the bootstrap capacitor 4 in the free run state. , by changing the duty ratio of the lower arm element 3b from the first duty ratio to the second duty ratio, control is performed to charge the bootstrap capacitor 4 while performing control to suppress an increase in the voltage of the main circuit capacitor 2. is configured to do so. Thereby, the duty ratio of the lower arm element 3b can be controlled based on the detected value of the voltage detection section 2a, so that control to suppress the increase in voltage of the main circuit capacitor 2 can be performed more accurately.

Further, in the first embodiment, as described above, the control unit 8 is configured to control the initial charging of the bootstrap capacitor 4 by turning on the lower arm element 3b with a duty ratio of 1. has been done. Further, the control unit 8 reduces the duty ratio of the lower arm element 3b from 1 to the first duty ratio based on the fact that the current detection unit 7 detects that an overcurrent is flowing during the initial charging. The device is configured to perform control to charge the bootstrap capacitor 4 using the power supply voltage. Further, the control unit 8 increases the voltage of the main circuit capacitor 2 by changing the duty ratio of the lower arm element 3b from the first duty ratio to the second duty ratio based on the voltage of the main circuit capacitor 2. It is configured to perform control to charge the bootstrap capacitor 4 while performing control to suppress. As a result, the duty ratio of the lower arm element 3b is reduced based on the detected value of the current detection section 7, thereby suppressing the current flowing between the switching element section 3 and the motor 101 from becoming an overcurrent. It is possible to suppress the voltage of the circuit capacitor 2 from becoming excessively large.

Further, in the first embodiment, as described above, the control unit 8 controls the lower arm elements of the plural phases based on the voltage of the main circuit capacitor 2 while charging the bootstrap capacitors 4 of the plural phases in the free run state. 3b is uniformly changed from the first duty ratio to the second duty ratio to control charging of each of the plurality of bootstrap capacitors 4. Thereby, in the inverter device 100 that supports multiple phases, it is possible to suppress the voltage of the main circuit capacitor 2 from becoming excessively large. Furthermore, by uniformly changing the duty ratio of each of the lower arm elements 3b of the plural phases from the first duty ratio to the second duty ratio, the states of charge of the bootstrap capacitors 4 of the plural phases become different from each other. can be suppressed.

[Second embodiment]
Next, the configuration of the inverter device 200 according to the second embodiment will be described with reference to FIGS. 8 and 9. In the inverter device 200 of the second embodiment, unlike the first embodiment, the duty ratio of the lower arm element 3b is reduced when the voltage value Edc of the main circuit capacitor 2 becomes equal to or higher than the first threshold voltage E1. When the voltage value Edc becomes equal to or higher than the first threshold voltage E1, the duty ratio of the lower arm element 3b is increased. Note that configurations similar to those in the first embodiment are illustrated with the same reference numerals as those in the first embodiment, and description thereof will be omitted.

(Configuration of inverter device)
As shown in FIG. 8, the inverter device 200 includes a control section 18 that controls the duty ratio of the upper arm element 3a and the lower arm element 3b.

(Control regarding restart of inverter device)
Control regarding restart of inverter device 200 will be described with reference to FIG. 9.

In the second embodiment, as shown in FIG. 9, the control unit 18 causes the voltage of the main circuit capacitor 2 to reach the first threshold by turning on and off the lower arm element 3b with a first duty ratio (for example, 0.5). When the voltage exceeds E1, the increase in the voltage of the main circuit capacitor 2 is suppressed by increasing the duty ratio of the lower arm element 3b from the first duty ratio to the second duty ratio (for example, 0.75). The controller is configured to perform control to charge the bootstrap capacitor 4 while performing control to charge the bootstrap capacitor 4 (see period T13 in the state "waiting for bootstrap charging" in FIG. 9).

In this case, by increasing the duty ratio of the lower arm element 3b, the current value flowing through L (see FIG. 5) due to the increase in the voltage value Edc of the main circuit capacitor 2 increases (increases from I2 to I13). Energy stored in L increases. On the other hand, by increasing the duty ratio of the lower arm element 3b, the time during which the current from the motor 101 flows through the main circuit capacitor 2 is reduced. In other words, a decrease in the time during which the current from the motor 101 flows through the main circuit capacitor 2 has a greater effect on the voltage value Edc of the main circuit capacitor 2 than an increase in the energy stored in L. Therefore, by increasing the duty ratio of the lower arm element 3b to the second duty ratio, an increase in the voltage value Edc of the main circuit capacitor 2 is suppressed.

Note that the other configurations of the second embodiment are the same as those of the first embodiment.

(Effects of the second embodiment)
In the second embodiment, the following effects can be obtained.

In the second embodiment, as described above, the control unit 18 sets the duty ratio of the lower arm element 3b to the first value based on the voltage of the main circuit capacitor 2 while charging the bootstrap capacitor 4 in the free run state. By increasing the duty ratio to the second duty ratio, control is performed to charge the bootstrap capacitor 4 while performing control to suppress a rise in the voltage of the main circuit capacitor 2. As a result, when the bootstrap capacitor is charged during free running of the motor 101, control is performed to suppress the increase in the voltage of the main circuit capacitor 2 based on the voltage of the main circuit capacitor 2, so that the bootstrap capacitor 4 The time required for charging the main circuit capacitor 2 can be shortened, and the voltage of the main circuit capacitor 2 can be easily prevented from becoming excessively large.

Further, in the second embodiment, as described above, the control unit 8 controls the voltage of the main circuit capacitor 2 from the state where the voltage is equal to or higher than the first threshold voltage E1 to the first threshold voltage E1 while the bootstrap capacitor 4 is being charged in the free run state. When the voltage changes to a state lower than the threshold voltage E1, the duty ratio of the lower arm element 3b is controlled to be returned (reduced) from the second duty ratio to the first duty ratio. Thereby, the duty ratio of the lower arm element 3b can be returned to the original state in conjunction with the return of the voltage of the main circuit capacitor 2 to the original state. Thereby, the bootstrap capacitor 4 can be charged more quickly. Thereby, the value of the current flowing through the inverter circuit section 10 can be reduced.

Note that other effects of the second embodiment are similar to those of the first embodiment.

[Modified example]
Note that the embodiments disclosed this time should be considered to be illustrative in all respects and not restrictive. The scope of the present invention is indicated by the claims rather than the description of the embodiments described above, and further includes all changes (modifications) within the meaning and range equivalent to the claims.

For example, in the first and second embodiments described above, an example was shown in which the duty ratio of the lower arm element 3b is changed when the voltage value Edc of the main circuit capacitor 2 becomes equal to or higher than the first threshold voltage E1. The invention is not limited to this. For example, the duty ratio of the lower arm element 3b may be changed based on the rate of increase in the voltage value Edc of the main circuit capacitor 2.

Further, in the first and second embodiments described above, an example was shown in which control is performed to set the duty ratio of the lower arm element 3b to 1 during the initial charging of the bootstrap capacitor 4, but the present invention is not limited to this. For example, the duty ratio of the lower arm element 3b may be set to the first duty ratio (duty ratio smaller than 1) from the time of initial charging.

Further, in the first and second embodiments described above, an example was shown in which the inverter device 100 (200) is configured to handle three-phase alternating current, but the present invention is not limited to this. For example, the inverter device may be configured to handle single-phase alternating current. Further, the inverter device may be configured to handle alternating current of three or more phases (for example, six phases).

Further, in the first and second embodiments described above, an example was shown in which control is performed to lengthen the charging time of the bootstrap capacitor 4 when the duty ratio of the lower arm element 3b is decreased. Not limited to. Even when the duty ratio of the lower arm element 3b changes, the charging time of the bootstrap capacitor 4 may be maintained at the preset charging time without changing.

Further, in the first and second embodiments described above, when the voltage of the main circuit capacitor 2 changes from a state higher than the first threshold voltage E1 to a state lower than the first threshold voltage E1, the lower arm element 3b Although an example has been shown in which control is performed to return the duty ratio from the second duty ratio to the first duty ratio, the present invention is not limited to this. If the voltage of the main circuit capacitor 2 exceeds the first threshold voltage E1, the duty ratio of the lower arm element 3b may be maintained at the second duty ratio until the main circuit capacitor 2 is completely charged. good.

Further, in the first and second embodiments described above, an example was shown in which each of the upper arm element 3a and the lower arm element 3b is a bipolar transistor, but the present invention is not limited to this. For example, each of the upper arm element 3a and the lower arm element 3b may be a MOSFET (Metal Oxide Semiconductor Field Effect Transistor) or an IGBT (Insulated Gate Bipolar Transistor).

Further, in the first and second embodiments described above, an example was shown in which the duty ratio of the lower arm element 3b is changed to a preset value based on the voltage of the main circuit capacitor 2, but the present invention does not change this. Not limited. The amount of change in the duty ratio of the lower arm element 3b may be calculated based on the current value, etc., and may be changed at any time. In this case, the control section may be configured to be able to both increase and decrease the duty ratio of the lower arm element 3b.

1 Power supply section 2 Main circuit capacitor 2a Voltage detection section 3 Switching element section 3a Upper arm element 3b Lower arm element 4 Bootstrap capacitor 7 Current detection section 8, 18 Control section 10 Inverter circuit section 100, 200 Inverter device 101 Motor A Connection point E1 1st threshold voltage Edc voltage value (main circuit capacitor voltage value)

Claims (8)

A power supply section that outputs a DC voltage, a main circuit capacitor that smoothes the DC voltage from the power supply section, and an upper arm element and a lower arm element that are connected in series with each other, the upper arm element and the lower arm element. an inverter circuit section including a switching element section whose connection point is connected to the motor; and a bootstrap capacitor that is charged while the lower arm element is turned on;
a control unit that controls a duty ratio of the lower arm element,
The upper arm element is configured to be turned on by the voltage charged in the bootstrap capacitor while the lower arm element is off,
The control unit is configured to control a first operation while charging the bootstrap capacitor in a free run state in which rotation of the motor continues for a certain period of time without being stopped while output from the inverter circuit unit to the motor is stopped. Control is performed to charge the bootstrap capacitor by turning on and off the lower arm element with a duty ratio of 1, and the duty ratio of the lower arm element is set to the first duty ratio based on the voltage of the main circuit capacitor. An inverter device configured to perform control to charge the bootstrap capacitor while performing control to suppress an increase in voltage of the main circuit capacitor by changing the duty ratio from 1 to a 2nd duty ratio. The control unit changes the duty ratio of the lower arm element from the first duty ratio to the first duty ratio based on the voltage of the main circuit capacitor during charging of the bootstrap capacitor in the free run state. Claim 1: The second duty ratio is lowered to the second duty ratio, thereby controlling the bootstrap capacitor to be charged while suppressing a rise in the voltage of the main circuit capacitor. The inverter device described in . The control unit is configured to perform a preset duty ratio when the duty ratio of the lower arm element is decreased from the first duty ratio to the second duty ratio while charging the bootstrap capacitor in the free run state. The inverter device according to claim 2, wherein the inverter device is configured to perform control to lengthen the charging time of the bootstrap capacitor. The control unit is configured to cause the voltage of the main circuit capacitor to become equal to or higher than a first threshold voltage by turning on and off the lower arm element according to the first duty ratio while charging the bootstrap capacitor in the free run state. In this case, the increase in voltage of the main circuit capacitor is suppressed by changing the duty ratio of the lower arm element from the first duty ratio to the second duty ratio when charging the bootstrap capacitor. The inverter device according to claim 1, wherein the inverter device is configured to perform control to charge the bootstrap capacitor while performing control to charge the bootstrap capacitor. When the voltage of the main circuit capacitor changes from a state equal to or higher than the first threshold voltage to a state lower than the first threshold voltage while charging the bootstrap capacitor in the free run state, The inverter device according to claim 4, wherein the inverter device is configured to perform control to return the duty ratio of the lower arm element from the second duty ratio to the first duty ratio. The inverter circuit section further includes a voltage detection section that detects a voltage value of the main circuit capacitor,
The control section adjusts the duty ratio of the lower arm element to the first voltage value based on the voltage value of the main circuit capacitor detected by the voltage detection section during charging of the bootstrap capacitor in the free run state. Claim 1, wherein the bootstrap capacitor is controlled to be charged while controlling to suppress a rise in voltage of the main circuit capacitor by changing the duty ratio to the second duty ratio. 5. The inverter device according to any one of items 5 to 5. The inverter circuit section further includes a current detection section that detects a current value flowing between the switching element section and the motor,
The control unit includes:
control for initially charging the bootstrap capacitor by turning on the lower arm element with a duty ratio of 1 from a state in which on/off control of the lower arm element is stopped;
Based on the current detection unit detecting that an overcurrent is flowing during the initial charging, the duty ratio of the lower arm element is reduced from 1 to the first duty ratio, and the bootstrap capacitor is and control to charge the
Control for suppressing a rise in the voltage of the main circuit capacitor by changing the duty ratio of the lower arm element from the first duty ratio to the second duty ratio based on the voltage of the main circuit capacitor. The inverter device according to any one of claims 1 to 6, wherein the inverter device is configured to control charging the bootstrap capacitor while performing the control. The switching element section includes the upper arm element of multiple phases and the lower arm element of multiple phases,
A plurality of the bootstrap capacitors are provided corresponding to each of the upper arm elements of the plurality of phases,
The control unit uniformly controls the duty ratio of each of the lower arm elements of the plurality of phases based on the voltage of the main circuit capacitor while charging the bootstrap capacitor of the plurality of phases in the free run state. The inverter according to any one of claims 1 to 7, wherein the inverter is configured to charge each of the plurality of bootstrap capacitors by changing the duty ratio from the second duty ratio to the second duty ratio. Device.

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