WO2015198789A1

WO2015198789A1 - Alternating current load-driving device

Info

Publication number: WO2015198789A1
Application number: PCT/JP2015/065414
Authority: WO
Inventors: 浅野　勝宏
Original assignee: 株式会社豊田中央研究所
Priority date: 2014-06-27
Filing date: 2015-05-28
Publication date: 2015-12-30
Also published as: JP2016012959A

Abstract

　The present invention is configured so as to be provided with: an inverter for converting DC power from a plurality of DC power sources into AC power and outputting the AC power to an AC load, a multilevel DC output means having a switch for switching the connective relationships between the plurality of DC power sources and the inverter; and an inverter-controlling means for transitioning the inverter to a circulation mode before the switch is switched, switching the switch during the circulation mode, and ending the inverter circulation mode after the switch is switched.

Description

AC load drive

The present invention relates to an AC load driving device including an inverter for driving an AC load.

2. Description of the Related Art An AC load drive system that drives an AC motor by converting DC power from a DC power source (battery) such as a battery into a three-phase AC current by an inverter and supplying the AC motor to the AC motor is widely used. Such an AC load driving system is suitable for driving a load by converting electric energy into mechanical energy by an AC motor, and for braking the load by converting mechanical energy into electric energy (by an AC motor). It is widely adopted as a drive system for electric vehicles and hybrid vehicles.

In such a system, when high-voltage direct current is output from low-voltage alternating current, the ratio of inverter switching loss increases and the ratio of unnecessary harmonic components also increases, reducing efficiency and reducing noise and noise. May increase. Thus, a step-up / step-down converter is provided between the DC power supply and the inverter, and the DC power supply is boosted and supplied to the inverter in accordance with the operating condition of the AC load, thereby improving efficiency and reducing noise and noise. Is used.

However, there is a problem that the buck-boost converter is expensive and the system becomes large. In addition, the efficiency decreases due to switching loss and on-resistance loss in the buck-boost converter.

Therefore, a plurality of DC power supplies are provided, and these DC power supplies are connected in series or in parallel by switches to switch DC voltages in stages, and this multi-level DC power supply is connected to an inverter to drive an AC load. A method has been proposed (see Patent Documents 1 to 3).

JP 2001-198113 A JP 2005-287222 A JP 2007-98981 A

By the way, when the DC voltage from multiple DC power supplies is input to the inverter and the connection relationship of multiple DC power supplies is switched while driving an AC load, the switch is opened with the current flowing through the switch, The switch is closed while a voltage is applied between the terminals.

When a relay with a mechanical contact was used as a switch, an arc was generated at the time of opening and closing, leading to contact welding, increased contact resistance, and reduced life. In order to prevent this, it is necessary to take measures to extinguish the arc at an early stage and to enhance the resistance of the contact to the arc, and it is inevitable that the relay is increased in cost and size. In addition, electromagnetic noise is generated at the time of opening and closing, increasing the risk of malfunction of the electronic device, and there is a risk of increasing the cost and size of the system as a countermeasure.

In addition, when a semiconductor switch is used as a switch, there is a risk that a switching loss may occur during opening and closing, an on-resistance loss may occur during conduction, and the system may increase in cost and size.

One aspect of the present invention is an inverter that converts DC power from a plurality of DC power sources into AC power and outputs the AC power to an AC load, the plurality of DC power sources, and the connection relationship between the plurality of DC power sources and the inverter. Multi-level DC output means having a switch for switching, and before switching the switch, the inverter is shifted to the reflux mode, the switch is switched during the reflux mode, and the inverter is switched to the reflux mode after the switch is switched. And an inverter control means for terminating the operation.

Here, a capacitor is generally provided between the positive electrode and the negative electrode on the input side of the inverter. The inverter control means shifts the inverter to a recirculation mode before switching the switch. During the recirculation mode, the inverter and the plurality of DC power sources are switched to an open mode. During the open mode, the mode is shifted to a capacitor voltage control mode for charging / discharging the capacitor, and when the charging voltage of the capacitor is in a target voltage range, the inverter is shifted to the reflux mode. Further, during the open mode, when the multi-level DC output means is shifted to the switch switching mode so that the target voltage is supplied to the inverter from the plurality of DC power supplies, when the switch switching is completed, that is, When the output of the multilevel DC output means reaches the target voltage, the multilevel DC output means is shifted to the normal output mode. When the switching of the inverter to the recirculation mode and the transition of the multi-level DC output means to the normal output mode are completed, the inverter is shifted to the ON mode in which the plurality of DC power supplies are connected. After shifting to the on mode, the inverter circulation mode is terminated and the normal mode is shifted. The mode transition as described above is suitable. Further, when the inverter and the plurality of DC power supplies are disconnected and shifted to the open mode, or when connected to the on mode, the switch of the multi-level DC output means is used, or the system main relay is used. Is preferred.

Further, in the capacitor voltage control mode, the circulation mode is temporarily stopped, the AC load is subjected to power running control or regenerative control to charge / discharge the capacitor, and the charging voltage of the capacitor is set to a target voltage, that is, the multi-level DC output. It is preferable that the inverter is made to recirculate again so that the voltage after the switch switching of the means is quickly followed and the state is maintained when the voltage converges near the target voltage. In the recirculation mode, the current continuously flows due to the magnetic energy accumulated in the AC load, but since the external energy supply to the AC load is lost, the current value gradually decreases and eventually becomes zero. Become. Similarly, the generated torque gradually decreases and eventually becomes zero. However, in the case of a PM motor, an induced voltage generated by a magnet is generated at each terminal of the AC load. Therefore, in the reflux mode, that is, when the upper arm switch is closed or the lower arm switch is closed, AC Each terminal of the load is short-circuited, and a short-circuit current that generates brake torque begins to flow. For this reason, it is preferable to open the switch that has been closed in the reflux mode and converge the current to zero at the timing when switching from driving to braking, that is, when the torque current component switches from positive to negative. By performing such control, generation of braking torque can be avoided.

A capacitor connected between a positive electrode and a negative electrode on the input side of the inverter; and a system main relay between the inverter and the multi-level DC output means. Furthermore, it is preferable to connect a series connection circuit of a system sub relay, an inductor, and a resistor in parallel with the system main relay. Here, when the charging voltage of the capacitor cannot be converged to the vicinity of the target voltage in the capacitor voltage control mode, the inverter is shifted to the circulation mode, and in the circulation mode, the system main relay is opened and the system sub It is preferable to charge the capacitor with the relay closed. The resistance R of the resistor, the inductance L of the inductor, and the capacitance C of the capacitor satisfy a critical braking condition (R ² = 4 L / C) so that the capacitor is quickly charged without vibration. It is preferable to set to.

According to the present invention, stress such as arc generation is not applied to the switch. Therefore, it is possible to provide an AC load driving device that suppresses the increase in size and cost of the device.

It is a figure which shows the structure of the alternating current load drive system in 1st Embodiment. It is a figure which shows the structure of the alternating current load drive system in embodiment of this invention. It is a figure which shows the effect | action of the multilevel DC output means in embodiment of this invention. It is a flowchart explaining the switching process of DC power supply in 1st Embodiment. It is a timing chart explaining the switching process of the direct-current power supply in 1st Embodiment. It is a figure which shows the structure of the alternating current load drive system in 2nd Embodiment. It is a figure which shows the effect | action of the multilevel DC output means in 2nd Embodiment. It is a flowchart explaining the switching process of DC power supply in 2nd Embodiment. It is a timing chart explaining the switching process of the direct-current power supply in 2nd Embodiment. It is a figure which shows the structure of the alternating current load drive system in 3rd Embodiment. It is a flowchart explaining the switching process of the DC power supply in 3rd Embodiment. It is a timing chart explaining the switching process of the direct-current power supply in 3rd Embodiment.

<First Embodiment>
The AC load driving system 100 in the first embodiment includes an AC load driving device 102, a DC power supply 104, and an AC load 106 as shown in FIG. The AC load driving system 100 converts DC power from the DC power source 104 into AC power by the inverter 10 included in the AC load driving device 102 and supplies the AC power to the AC load 106 for driving.

The AC load 106 can be a three-phase motor generator including three-phase coils u, v, and w, for example. The three-phase motor generator can be mounted on a hybrid vehicle or an electric vehicle.

The AC load driving device 102 includes an inverter 10, a multi-level DC output means 20, and an inverter control means 30.

The inverter 10 includes transistors T11 to T16 and diodes D11 to D16. Two transistors T11 to T16 are arranged in pairs so as to form an upper arm on the source side and a lower arm on the sink side with respect to the positive electrode bus and the negative electrode bus, respectively. Each of the three-phase coils u, v, w is connected. If the on-time ratio of the paired transistors T11 to T16 is controlled while a voltage is applied to the positive and negative buses of the inverter 10, a rotating magnetic field is generated by the three-phase coils u, v, and w of the AC load 106. And the AC load 106 can be rotationally driven. Open / close control of the transistors T11 to T16 is performed by an inverter control signal S1 from the inverter control means 30.

The DC power supply 104 includes a plurality of DC power supplies 104a to 104n. The multi-level DC output means 20 includes a switch that switches a mutual connection relationship between the plurality of DC power sources 104 a to 104 n and a connection relationship with the inverter 10.

For example, as shown in FIG. 2A, by configuring the multilevel DC output means 20 as switches SW1 to SW6, the connection of the four DC power supplies 104a to 104d is switched, and different input voltages are applied to the inverter 10. Can be applied. Note that the configuration of the multi-level DC output means 20 is not limited to this, and any configuration that can apply different voltages to the inverter 10 by switching the mutual connection relationship of a plurality of DC power sources.

The switch of the multi-level DC output means 20 is switched by a switch switching signal S2 from the inverter control means 30. FIG. 2B shows the relationship between the state of each switch and the output of the multilevel DC output means 20. By providing the multi-level DC output means 20, it becomes possible to input a multi-stage DC voltage obtained by switching the connection relation of the plurality of DC power sources 104a to 104n to the inverter 10, and appropriately depending on the required output The AC load 106 can be driven with a simple voltage waveform.

For example, currents Iu, Iv, and Iw flowing through the three-phase coils u, v, and w of the AC load 106 are detected by a current sensor and input to the inverter control unit 30. The switch switching signal S2 can be output to the means 20 to adjust the voltage input to the inverter 10. Further, the control signal S3 can be input from the outside to the inverter control means 30, and the switch switching signal S2 can be output to the multi-level DC output means 20 in accordance with the control signal S3 to adjust the voltage input to the inverter 10. . The control signal S3 may be a signal related to the output required for the AC load 106, such as a signal indicating the accelerator opening of the vehicle, a signal indicating the amount of depression of the brake, a signal indicating the gear ratio of the transmission, or the like. Good.

Hereinafter, the switch switching sequence of the multilevel DC output means 20 will be described with reference to the flowchart of FIG. 3 and the timing chart of FIG. The switching sequence of the multilevel DC output means 20 is started in response to a change in the required output to the AC load 106. Before the start of the switching sequence, a DC voltage is applied from the DC power supply 104 to the inverter 10 via the multi-level DC output means 20, and AC power that has been subjected to cross-flow conversion is supplied to the AC load 106.

In step S10, a process for shifting the inverter 10 to the reflux mode is performed. The inverter control means 30 switches from the normal mode in which the inverter 10 is cross-flow converted to the reflux mode by the inverter control signal S1.

The reflux mode is a state where current is circulated between the inverter 10 and the AC load 106. For example, all the transistors Tr11, 13 and 15 in the upper arm are closed, and all the transistors Tr12, 14 and 16 in the lower arm are opened, so that the circulation mode via the upper arm of the inverter 10 is set. it can. Further, for example, all the transistors Tr11, 13, and 15 in the upper arm are opened, and all the transistors Tr12, 14, and 16 in the lower arm are closed, thereby setting the circulation mode through the lower arm of the inverter 10. be able to.

By setting the inverter 10 to the reflux mode, an open loop state in which no current flows between the multilevel DC output means 20 and the AC load 106 is established. In addition, when the AC load 106 is a PM motor, an induced voltage generated by a magnet is generated at each terminal of the AC load 106, so that the state of the recirculation mode, that is, the upper arm switch is closed or the lower arm switch is closed. In the state, a short-circuit current that generates brake torque begins to flow. Therefore, before the torque current component is switched from positive to negative, the switch that has been closed by the circulation mode is opened to avoid the occurrence of braking torque. Also in this case, the multilevel DC output means 20 and the AC load 106 are in an open loop state in which no current flows.

In step S12, the multi-level DC output means 20 performs a process of shifting to a switch switching mode in which the voltage input from the DC power supply 104 to the inverter 10 is changed. In the switch switching mode, the inverter control means 30 changes the connection relationship of the plurality of DC power sources 104a to 104n so that an input voltage corresponding to the output of the AC load 106 is input to the inverter 10 by the switch switching signal S2. The relationship between the switch state and the output of the multilevel DC output means 20 is shown in FIG. Here, for example, the output 104a means the output voltage of the DC power supply 104a, and the other is the same.

In step S14, a process for returning the inverter 10 to the normal mode is performed. The inverter control means 30 switches the inverter 10 from the recirculation mode to the normal mode in which the cross flow is converted by the inverter control signal S1.

Thus, the DC voltage changed by switching the switch of the multilevel DC output means 20 in step S12 is applied to the inverter 10, and the AC load 106 can be driven by the AC voltage obtained by orthogonally converting the DC voltage. .

Thus, the inverter 10 is set to the reflux mode, and the connection of the plurality of DC power sources 104a to 104n is changed by the multi-level DC output means 20 during the reflux mode, so that it is not necessary to use the step-up / step-down converter. In addition, it is possible to perform opening / closing in a state where no current flows through the switch of the multilevel DC output means 20 and no voltage is applied. Therefore, no arc is generated at the contact point when the switch is opened and closed, and it is possible to avoid contact welding, increase in contact resistance, and decrease in switch life.

Further, a relay having an inexpensive mechanical contact can be applied as a switch of the multi-level DC output means 20, and the AC load driving device 102 can be reduced in cost and size. Further, since it is not necessary to use a semiconductor switch as the switch, it is not necessary to consider the switching loss when the switch is opened and closed, and the on-resistance loss when conducting.

In addition, when the switch of the multi-level DC output means 20 is opened and closed, spike-like high voltage and electromagnetic noise are not generated, so there is no fear of inducing malfunction of the electronic device, increasing the cost for noise countermeasures and the device Can be avoided.

Further, since no inrush current is generated when the switch of the multi-level DC output means 20 is opened and closed, there is no possibility of causing deterioration of the DC power supply 104, the inverter 10, the AC load 106 and the like.

Furthermore, when the AC load drive system 100 is applied to a hybrid vehicle, an electric vehicle, or the like, the input voltage is switched by the multilevel DC output means 20 in accordance with the output of the AC load 106, and therefore the frequency is accelerated and decelerated. It is about the same as the frequency. Therefore, even if a relay having a mechanical contact or a semiconductor switch is used as a switch, the life as a switch is sufficiently secured.

If the switch opening / closing time is about several tens of milliseconds, the input voltage of the inverter 10 can be changed according to the change in the required output to the AC load 106 without giving the driver a sense of incongruity such as torque loss. it can.

<Second Embodiment>
In 2nd Embodiment, as shown to Fig.5 (a), the capacitor | condenser 12 which smoothes an input voltage is provided in the input side of the inverter 10 of the alternating current load drive device 102. FIG. By providing the capacitor 12, noise generated between the positive bus and the negative bus of the inverter 10 can be removed. A system main relay 16 is provided between the multilevel DC output means 20 and the inverter 10. By opening the system main relay 16, the multilevel DC output means 20 and the inverter 10 can be disconnected so that an excessive capacitor charging current does not flow when the multilevel DC output means 20 is switched. The function of the system main relay 16 can be provided in the multilevel DC output means 20.

Hereinafter, the switching sequence of the multilevel DC output means 20 in the present embodiment will be described with reference to the flowchart of FIG. 6 and the timing chart of FIG.

Before the switching sequence is started, a DC voltage is applied from the DC power source 104 to the inverter 10 via the multi-level DC output means 20, and the input voltage smoothed by the capacitor 12 is orthogonally converted by the inverter 10 and applied to the AC load 106. It is assumed that it is being supplied.

In step S20, the inverter 10 is shifted to the reflux mode. This process is the same as step S10 in the first embodiment.

In step S22, the system main relay 16 is shifted to the open mode. In the case where the function of the system main relay 16 is included in the multilevel DC output means 20, the inverter control means 30 switches the switch of the multilevel DC output means 20 by the switch switching signal S2 and the DC power supply 104. The inverter 10 is disconnected, and the mode is shifted to the open mode in which no DC current is input from the DC power supply 104 to the inverter 10.

In step S24, the inverter 10 is shifted to the capacitor voltage control mode. The capacitor voltage control mode is a mode in which the capacitor 12 is charged and discharged by performing power running control or regenerative control of the AC load 106. The inverter control means 30 controls the open / close state of the transistors Tr11 to Tr16 by the inverter control signal S1, controls the voltage of the capacitor 12 by discharging or charging the capacitor 12 by powering or regenerating the AC load 106. By setting the capacitor voltage control mode, the capacitor 12 can be charged and discharged to adjust the charging voltage (terminal voltage). Power running control can be realized, for example, by driving an AC load and converting electrical energy into kinetic energy. The regenerative control can be realized, for example, by converting inertial energy of the AC load 106 into an energy source and converting it into electric energy by a generator operation. The regenerative control can be continued by driving the AC load 106 as a generator with an external engine or the like, for example.

In step S26, it is determined whether or not the charging voltage of the capacitor 12 has entered the target voltage range. The inverter control means 30 receives the input of the charging voltage of the capacitor 12 measured by the voltage sensor 14, and shifts the process to step S28 if the charging voltage of the capacitor 12 is within the target voltage range, and enters the target voltage range. If not, the capacitor voltage control mode is continued.

Here, the target voltage range is set in the vicinity of the target voltage to be output from the multilevel DC output means 20 after the switch of the multilevel DC output means 20 is switched in step S30 described later. Further, the target voltage is determined based on the voltage required for the AC load 106 at that time.

For example, the target voltage ± ΔV is set to the target voltage after the switch of the multilevel DC output means 20 changed in step S30 described later. ΔV is a voltage that does not cause an arc at the switch contact, and is set to, for example, a minimum arc voltage or less based on the specifications of the switch.

In step S28, a process for shifting the inverter 10 to the reflux mode is performed. This process is the same as step S10 in the first embodiment. In addition, when the AC load 106 is a PM motor, an induced voltage generated by a magnet is generated at each terminal of the AC load 106, so that the state of the recirculation mode, that is, the upper arm switch is closed or the lower arm switch is closed. In the state, a short-circuit current that generates brake torque begins to flow. Therefore, in the recirculation mode state in the second embodiment, the braking torque is generated by opening the switch that has been closed by the recirculation mode at the timing when the torque current component switches from positive to negative. To avoid. Also in this case, the multilevel DC output means 20 and the AC load 106 are in an open loop state in which no current flows. This process is the same as step S10 in the first embodiment.

Further, steps S30 to S34 are performed in parallel with steps S24 to S28. In step S30, the multi-level DC output means 20 performs a process of shifting to a switch switching mode for changing the voltage input from the DC power supply 104 to the inverter 10. This process is the same as step S12 in the first embodiment. In step S32, the process waits until the switch switching is completed. When the output is stabilized, the process proceeds to the normal output mode in step S34. In step S36, the process waits until the inverter 10 is switched to the reflux mode and the multi-level DC output means 20 is shifted to the normal output mode. When it is confirmed that the inverter 10 is completed, the system main relay 16 is checked in step S38. To the on mode.

In step S40, a process for returning the inverter 10 to the normal mode is performed. This process is the same as step S14 in the first embodiment.

As described above, in the present embodiment, when the capacitor 12 is provided on the input side of the inverter 10, the excessive capacitor 12 is switched in accordance with the switch of the multilevel DC output means 20 or the system main relay 16. In order to prevent the charging / discharging current from flowing, the capacitor voltage control mode can be charged and discharged in advance to the target voltage.

<Third Embodiment>
In the second embodiment, the mode in which the AC load 106 is subjected to power running control or regenerative control to control the voltage of the capacitor 12 has been described. However, as shown in FIG. A system sub-relay 18 may be provided to control the voltage of the capacitor 12 with power from the DC power source 104.

The system main relay 16 is provided between the multilevel DC output means 20 and the inverter 10 on the positive bus side of the inverter 10. The system main relay 16 can open and close the connection between the multilevel DC output means 20 and the inverter 10. The system sub relay 18 is provided in parallel with the system main relay 16 between the multilevel DC output means 20 and the inverter 10 on the positive bus side of the inverter 10. The system sub relay 18 is connected in series with the resistor 11 and the inductor 13.

The capacitor 12 can be charged / discharged from the DC power source 104 via the resistor 11 and the inductor 13 by closing the system sub relay 18 while the system main relay 16 is open.

Hereinafter, the switching sequence of the multilevel DC output means 20 in the present embodiment will be described with reference to the flowchart of FIG. 9 and the timing chart of FIG.

Before the switching sequence is started, the system main relay 16 is closed and the system sub-relay 18 is opened, and a DC voltage is applied from the DC power source 104 to the inverter 10 via the multi-level DC output means 20. It is assumed that the smoothed input voltage is orthogonally transformed by the inverter 10 and supplied to the AC load 106.

In step S50, the inverter 10 is shifted to the reflux mode. This process is the same as step S10 in the first embodiment.

In step S52, the inverter control means 30 opens the system main relay 16 by the switch switching signal S4. As a result, both the system main relay 16 and the system sub relay 18 are in an open state (open mode).

In step S54, the inverter 10 is shifted to the capacitor voltage control mode. This process is the same as step S24 in the second embodiment.

In step S56, it is determined whether or not the charging voltage of the capacitor 12 has entered the target voltage range. The inverter control means 30 receives the input of the charging voltage of the capacitor 12 measured by the voltage sensor 14, and shifts the process to step S58 if the charging voltage of the capacitor 12 is within the target voltage range, and the target voltage range. If not, the process proceeds to step S72. The target voltage range may be set similarly to the second embodiment.

In step S72, it is determined whether or not the capacitor voltage control mode has continued for a reference time or longer. The inverter control unit 30 shifts the process to step S74 when the capacitor voltage control mode is continued for the reference time or longer, and continues the capacitor voltage control mode when the capacitor voltage control mode is continued for less than the reference time.

In step S74, a process for returning the inverter 10 from the capacitor voltage control mode to the reflux mode is performed. This process is the same as step S10 in the first embodiment.

In step S76, the system sub relay 18 is shifted to the on mode. The inverter control means 30 closes the system sub relay 18 by the switch switching signal S4. As a result, the system main relay 16 is in an open state (open mode) and the system sub-relay 18 is in a closed state (on mode).

In this state, DC power is supplied from the DC power source 104 to the inverter 10 through the multi-level DC output means 20, the system sub relay 18, the resistor 11, and the inductor 13. At this time, if there is a potential difference between the charging voltage of the capacitor 12 and the DC voltage output from the multilevel DC output means 20, the capacitor 12 is charged / discharged via the resistor 11 and the inductor 13.

At this time, by appropriately setting the capacitance C of the capacitor 12, the resistance value R of the resistor 11, and the inductance L of the inductor 13, the time constant of the charging circuit of the capacitor 12 can be adjusted, and the capacitor 12 is charged and discharged. In addition, the occurrence of ripples and the like can be suppressed during charging, and at the same time, the capacitor 12 can be charged and discharged rapidly. For example, if the critical braking condition (R ² = 4 L / C) is set, the capacitor 12 is quickly charged and discharged without vibration. Charging may be performed until the charging voltage of the capacitor 12 falls within the target voltage range, or may be performed until the charging time exceeds the reference time.

In step S78, the system sub relay 18 is shifted to the off mode. Inverter control means 30 opens system sub-relay 18 (open mode) by switch switching signal S4.

Thereby, the charge / discharge state of the capacitor 12 via the system sub relay 18 is released.

On the other hand, when the process proceeds from step S56 to step S58, the inverter 10 is returned from the capacitor voltage control mode to the reflux mode. This process is the same as step S10 in the first embodiment. In addition, when the AC load 106 is a PM motor, an induced voltage generated by a magnet is generated at each terminal of the AC load 106, so that the state of the recirculation mode, that is, the upper arm switch is closed or the lower arm switch is closed. In the state, a short-circuit current that generates brake torque begins to flow. Therefore, in the recirculation mode state in the third embodiment, the braking torque is generated by opening the switch that has been closed by the recirculation mode at the timing when the torque current component switches from positive to negative. To avoid. Also in this case, the multilevel DC output means 20 and the AC load 106 are in an open loop state in which no current flows. This process is the same as step S10 in the first embodiment.

Further, steps S60 to S64 are performed in parallel with the loop of steps S54 to S58 and steps S54 to S78. In step S60, the multilevel DC output means 20 performs a process of shifting to a switch switching mode for changing the voltage input from the DC power supply 104 to the inverter 10. This process is the same as step S12 in the first embodiment. In step S62, the process waits until the switch switching is completed. When the output is stabilized, the process proceeds to the normal output mode in step S64.

In step S66, the system sub-relay 18 is set in the off mode, the inverter 10 is set in the reflux mode, and the multi-level DC output means 20 is set in the normal output mode. In step S68, the system main relay 16 is shifted to the on mode.

In step S70, the inverter 10 is returned to the normal mode. This process is the same as step S14 in the first embodiment.

As described above, the capacitor 12 can be charged / discharged by switching the charge / discharge circuit by the system main relay 16 and the system sub relay 18. Therefore, even if the capacitor 12 is not fully charged / discharged when the inverter 10 is regeneratively controlled to charge / discharge the capacitor 12, the capacitor 12 can be appropriately charged / discharged. Thereby, when the multilevel DC output means 20 and the inverter 10 are directly connected by the system main relay 16, the difference between the output voltage of the multilevel DC output means 20 and the charging voltage of the capacitor 12 can be reduced. Further, it is possible to prevent an excessive charge / discharge current from flowing through the switch contact and the capacitor 12.

In the first to third embodiments, the switches constituting the system main relay, the system sub relay, and the multi-level DC output means may be any switching device that can be turned on and off from the outside, and have, for example, mechanical contacts. An electromagnetic relay, a semiconductor switch, or the like can be used.

When configured with an electromagnetic relay having a mechanical contact, switching is performed in a state of zero voltage and zero current, which is preferable because there is no arc and switching loss and no on-resistance loss occurs during conduction. In addition, even when constituted by a semiconductor switch or the like, although an on-resistance loss during conduction occurs, the switching loss is eliminated because zero voltage and zero current switching is performed. Since the on-mode is instantaneous for the system sub-relay, it is preferable that the on-resistance loss during conduction is negligible, and the system sub-relay is configured with a semiconductor switch that has less operation delay and good controllability.

10 inverter, 11 resistor, 12 capacitor, 13 inductor, 14 voltage sensor, 16 system main relay, 18 system sub relay, 20 multi-level DC output means, 30 inverter control means, 100 AC load drive system, 102 AC load drive device, 104 (104a-104n) DC power supply, 106 AC load.

Claims

AC load driving device,
An inverter that converts DC power from a plurality of DC power sources into AC power and outputs it to an AC load;
The plurality of DC power supplies;
Multi-level DC output means having a switch for switching the connection relationship between the plurality of DC power supplies and the inverter;
Before switching the switch, the inverter is shifted to the recirculation mode, the switch is switched during the recirculation mode, and the inverter control means for terminating the recirculation mode of the inverter after the switch is switched;
Is provided.
The AC load driving device according to claim 1,
A capacitor connected between the positive and negative electrodes on the input side of the inverter;
A system main relay between the inverter and the multi-level DC output means,
The inverter control means includes
Before switching the system main relay, the inverter is shifted to the reflux mode,
During the recirculation mode, the system main relay is opened to shift to the open mode in which the inverter and the plurality of DC power sources are disconnected,
During the open mode, transition to a capacitor voltage control mode for charging and discharging the capacitor,
When the charging voltage of the capacitor is in the target voltage range, the inverter is shifted to the reflux mode,
During the open mode, the switch of the multi-level DC output means is switched so that the target voltage is supplied from the plurality of DC power supplies to the inverter in parallel with the capacitor voltage control mode and the reflux mode,
After the target voltage is output from the multi-level DC output means and the inverter has completed the transition to the circulation mode, the system main relay is transitioned to the on mode, and after the transition to the on mode is completed, the circulation mode of the inverter is terminated. Let
The AC load driving device according to claim 2,
In the capacitor voltage control mode, the circulation mode is temporarily stopped, and the AC load is charged / discharged by power running control or regenerative control,
Thereafter, the inverter is set to the reflux mode again.
The AC load driving device according to claim 2,
A capacitor connected between the positive and negative electrodes on the input side of the inverter;
A system sub-relay connected in series with an inductor and a resistor connected in parallel with the system main relay between the inverter and the multi-level DC output means;
With
In the capacitor voltage control mode, when the capacitor cannot be set within the target voltage range, the inverter is shifted to the circulation mode, and the system main relay is in an open state and the system sub-relay during the circulation mode. Is closed to charge the capacitor.
The AC load driving device according to claim 3,
A capacitor connected between the positive and negative electrodes on the input side of the inverter;
A system sub-relay connected in series with an inductor and a resistor connected in parallel between the inverter and the multi-level DC output means;
With
In the capacitor voltage control mode, when the capacitor cannot be set within the target voltage range, the inverter is shifted to the circulation mode, and the system main relay is in an open state and the system sub-relay during the circulation mode. Is closed to charge the capacitor.