JP2019106799A - Power converter and rankine cycle system - Google Patents

Abstract

To simultaneously reduce a leakage current in a load connected with a multilevel inverter circuit at a main unit side and a leakage current in a load connected with an inverter circuit at an auxiliary unit side.SOLUTION: A power converter comprises: a converter circuit 3 for generating an intermediate voltage; a multilevel inverter circuit 2 controlled at three levels; an inverter circuit 4 driven at the intermediate voltage; and a controller 5 for controlling an AC voltage output of the multilevel inverter circuit 2 and the inverter circuit 4 and controlling the intermediate voltage according to required voltage of the load connected with the inverter circuit 4. The intermediate voltage controlled by a total voltage of a command voltage of a load connected with the inverter circuit 4 and a drop voltage of the inverter circuit 4 suppresses a voltage change rate of the multilevel inverter circuit 2 and the number of switching to suppress the leakage current. Then the inverter circuit 4 is driven at a low voltage, allowing the load connected with the inverter circuit 4 to suppress the leakage current simultaneously.SELECTED DRAWING: Figure 1

Description

  The present disclosure relates to a power converter and a Rankine cycle system using a multilevel inverter used for drive control of a rotating machine, a power supply device, and the like.

  As a conventional power converter of this type, a three-level inverter has been proposed that generates a neutral point with a pair of serially connected capacitors and switches and outputs three levels (for example, see Patent Document 1) ). FIG. 6 shows the configuration of the conventional power conversion device described in Patent Document 1. As shown in FIG.

  As shown in FIG. 6, in the conventional power converter, positive side bus capacitor 101, negative side bus capacitor 102, and positive and negative DC wires connected in series between positive and negative DC buses and whose neutral point is connected to the second line. The switch elements 103 and 104 connected in series between the busbars, and the balance circuit 107 having the reactor 106 connected between the connection point of the switch elements 103 and 104 and the neutral point 105 are provided. This power converter operates the inverter 108 while balancing the voltage by operating either one of the switch elements 103 or 104 in accordance with the voltage difference between the positive bus capacitor 101 and the negative bus capacitor 102. Is configured to output 3 levels.

JP, 2014-33565, A

  The conventional power conversion device disclosed in Patent Document 1 is controlled to fix the neutral point voltage of the inverter to reduce the leakage current by reducing the common mode component due to the increase in the number of levels. However, when the output voltage is controlled by pulse width modulation based on the voltage controlled to fix the neutral point, the leakage current suppression effect on the main unit side is limited because there is a period for switching the neutral point voltage. At the same time, there is a problem that the accessory side in the power converter does not have the effect of reducing the leakage current.

  In order to solve the conventional problems, the present disclosure relates to a converter circuit that generates an intermediate voltage using a DC voltage supplied from a DC power supply, and to the DC power supply and the converter circuit, which is connected to the DC voltage and the intermediate circuit. A multi-level inverter circuit driven by inputting a voltage and controlled at at least three levels, an inverter circuit connected to the converter circuit and driven by inputting the intermediate voltage, and a predetermined multi-level inverter circuit The first AC voltage is output and the inverter circuit is controlled to output a predetermined second AC voltage, and the intermediate voltage sums the command voltage of the load connected to the inverter circuit and the voltage drop of the inverter circuit. And a controller configured to control the set voltage.

With this configuration, the intermediate voltage generated by the converter circuit is controlled to be the sum of the command voltage of the load connected to the inverter circuit corresponding to the auxiliary device side and the voltage drop of the inverter circuit, and the multilevel inverter circuit At the same time as switching between a DC input voltage and an intermediate voltage to generate an output voltage, the intermediate voltage is supplied as an input voltage of the inverter circuit, and an AC voltage is outputted to the load of the inverter circuit with a minimum necessary intermediate voltage. Can.

  According to the technology according to the present disclosure, since the voltage change rate according to the number of levels is suppressed in the multilevel inverter circuit, the leakage current can be suppressed on the main machine side, and the load connected to the inverter circuit on the auxiliary machine side It is possible to suppress the leakage current by driving with a minimum necessary stable intermediate voltage lower than the DC voltage.

Configuration diagram of a power conversion device according to a first embodiment of the present disclosure Control block diagram of first control unit of control device in the first embodiment of the present disclosure Control block diagram of second control unit of control device in the first embodiment of the present disclosure Control block diagram of third control unit of control device in the first embodiment of the present disclosure The figure which shows the operation | movement waveform of each part of the power converter device in Embodiment 1 of this indication. The block diagram of the Rankine cycle system in Embodiment 2 of this indication The figure which shows the operation | movement waveform of each part of the power converter device in Embodiment 2 of this indication. The block diagram of the conventional power converter in patent document 1

<Findings based on the study of the inventor>
In the conventional power conversion device shown in Patent Document 1, only the common mode component of the multilevel inverter output corresponding to the main unit is reduced. That is, only the leakage current in the load connected to the part corresponding to the main machine is reduced. However, the inventor has found that there is a problem that the load connected to the accessory side inside the conventional power conversion device does not have the effect of reducing the leakage current. In this regard, the inventor of the present invention finds that the intermediate voltage generated by the converter circuit is used as both the intermediate voltage of the multilevel inverter circuit corresponding to the main unit and the input voltage of the inverter circuit corresponding to the auxiliary unit. I focused on That is, the load connected to the multilevel inverter circuit is controlled at a voltage change rate according to the number of levels, but at the same time the load connected to the inverter circuit is driven at an intermediate voltage lower than the maximum voltage of the multilevel inverter circuit. Therefore, the voltage change rate of the load connected to the inverter circuit is also suppressed. Therefore, if it is possible to control the intermediate voltage, which fluctuates under the influence of the input / output power of the multilevel inverter circuit and the input / output power of the inverter circuit, to a desired set voltage, both these loads simultaneously The rate of change is suppressed, and leakage current can be suppressed.

  Furthermore, the inventor noted that a constant voltage drop occurs in an actual inverter circuit. That is, if the desired set voltage is set in consideration of the voltage drop of the inverter circuit, the command voltage of the load connected to the inverter circuit can be set to the minimum necessary voltage, and the leakage current on the accessory side Can be further suppressed.

  Based on the above, the inventor of the present invention controls the intermediate voltage so as to be a desired set voltage obtained by summing the command voltage of the load connected to the inverter circuit and the voltage drop of the inverter circuit, and supplies it to the inverter circuit. Then, the power converter which can drive the load connected to the inverter circuit with the necessary minimum stable voltage and reduce the leakage current was examined.

The term "intermediate voltage" as used herein refers to any voltage smaller than the maximum voltage as viewed in absolute value. For example, when the maximum voltage is Vmax, the intermediate voltage is a voltage greater than 0 and less than Vmax. As a typical example, the intermediate voltage can be a sum of the command voltage of the load connected to the inverter circuit and the voltage drop of the inverter circuit in the range of 0 to Vmax.

The first aspect of the present disclosure is
A converter circuit that generates an intermediate voltage using a DC voltage supplied from a DC power supply,
A multi-level inverter circuit connected to the DC power supply and the converter circuit, driven by inputting the DC voltage and the intermediate voltage, and controlled at at least three levels;
An inverter circuit connected to the converter circuit to input and drive the intermediate voltage;
The multilevel inverter circuit outputs a predetermined first alternating voltage and the inverter circuit controls the inverter circuit to output a predetermined second alternating voltage, and the command voltage of the load connected to the inverter circuit by the intermediate voltage A control device that controls a set voltage obtained by summing the voltage drop of the inverter circuit;
To provide a power converter.

  According to the first aspect, the intermediate voltage generated by the converter circuit is controlled to be a sum of the command voltage of the load connected to the inverter circuit and the voltage drop of the inverter circuit, and the multilevel inverter circuit The intermediate voltage is supplied as an input voltage of the inverter circuit while switching with the intermediate voltage to generate an output voltage. As a result, the AC voltage is output to the load of the inverter circuit with the minimum necessary intermediate voltage, so the multilevel inverter circuit can suppress leakage current by suppressing the rate of change in voltage according to the number of levels. The load connected to the inverter circuit can suppress the leakage current by driving with a minimum necessary stable intermediate voltage lower than the DC voltage.

The second aspect of the present disclosure is in addition to the first aspect,
The converter circuit is
Generate a plurality of said intermediate voltages,
The inverter circuit is
Drive by inputting any one of the plurality of intermediate voltages,
To provide a power converter.

  According to the second aspect, an appropriate voltage is selected from the plurality of intermediate voltages, the voltage adjustment range of the converter circuit can be limited, and the voltage supply to the inverter circuit can be further stabilized.

The third aspect of the present disclosure is
The power converter of the first aspect or the second aspect;
A pump for pumping a working fluid, an evaporator for heating the working fluid, an expander for expanding the working fluid, and a Rankine cycle flow path in which a condenser for condensing the working fluid is annularly connected in this order, the pump A Rankine cycle device comprising: a motor connected to the motor; and a generator connected to the expander to generate and output a third AC voltage.
A power supply device which receives the third alternating voltage output from the generator, converts it into a direct voltage, and outputs the direct voltage;
Have
The power supply device
Operates as the DC power supply that supplies the DC voltage to the converter circuit and the multilevel inverter circuit,
The inverter circuit is
Converting the input intermediate voltage into the second AC voltage and supplying the second AC voltage to the motor;
Provide Rankine cycle system.

  According to the third aspect, the intermediate voltage generated by the converter circuit is used as both the intermediate voltage of the multilevel inverter circuit and the input voltage of the inverter circuit. A load such as a commercial power source connected to the multilevel inverter circuit, for example, has a voltage change rate suppressed according to the number of levels, and at the same time, a motor connected to the inverter circuit is a load of the inverter circuit. Since these two loads are driven at the minimum necessary intermediate voltage, the voltage change rate is suppressed at the same time, and the leakage current can be suppressed.

  Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. The present invention is not limited to the following embodiments.

Embodiment 1
FIG. 1 is a configuration diagram of a power conversion device 1 according to a first embodiment of the present disclosure. In FIG. 1, a power conversion device 1 includes a multilevel inverter circuit 2, a converter circuit 3 for generating an intermediate voltage, an inverter circuit 4 connected to input and drive an intermediate voltage, and a multilevel inverter circuit 2 and a converter circuit. A controller 5 is provided to control the inverter 3 and the inverter circuit 4. A DC power supply is connected to the power conversion device 1. The DC power supply supplies a DC voltage to converter circuit 3 and multilevel inverter circuit 2. In FIG. 1, the DC power supply is disposed outside the power conversion device 1, but may be disposed inside the power conversion device 1.

  Multilevel inverter circuit 2 has three levels, and includes switching elements 6a to 6h (for example, IGBTs (Insulated Gate Bipolar Transistors) or MOSFETs (metal-oxide-semiconductor field-effect transistors)) and diodes 7a to 7d. It is done.

  The capacitor 8a is disposed for smoothing a direct current voltage, the capacitor 8b is disposed for shaping an alternating current waveform, and the capacitor 8c is disposed for smoothing an intermediate voltage. The inductors 9a and 9b are disposed together with the capacitor 8b for waveform shaping of the AC output.

  Here, the output of the multilevel inverter circuit 2 is supplied to a general load. Converter circuit 3 includes switching elements 6i and 6j and an inductor 9c. The inverter circuit 4 includes switching elements 6k to 6p, and the motor 10 is connected as a load.

  Moreover, the arrow extended from the control apparatus 5 in FIG. 1 has shown the drive signal with respect to each circuit, and its signal quantity.

  FIGS. 2A to 2C are diagrams showing examples of control blocks of the first control unit 51, the second control unit 52, and the third control unit 53, which are included in the control device 5. FIG. The control device 5 controls the converter circuit 3 such that an intermediate voltage that fluctuates under the influence of the input / output power of the inverter circuit 4 and the input / output power of the multilevel inverter circuit 2 becomes a desired set voltage. Here, the desired set voltage is controlled to be the sum of the command voltage for driving the motor 10 connected to the inverter circuit 4 and the voltage drop of the inverter circuit 4. Control device 5 includes a first control unit 51 that is a control block that controls inverter circuit 4 shown in FIG. 2A, and a second control unit 52 that is a control block that controls multilevel inverter circuit 2 that is shown in FIG. And a third control unit 53 which is a control block for controlling the converter circuit 3 shown in FIG. 2C.

  The first control unit 51 of FIG. 2A operates as follows. The deviation between the commanded rotational speed (rpm_ref) of the motor 10 and the actual rotational speed (rpm_t) is input to the proportional integral controller, and the q-axis current command (Iq_ref) is calculated. The deviation between the calculated q-axis current command and the actual q-axis current (Iq_t) is calculated, and the q-axis voltage command (Vq_ref) is calculated based on the calculated deviation. In addition, zero is input to the d-axis voltage command (Vd_ref). The q-axis voltage command and the d-axis voltage command that have been input are three-phase converted by the two-phase / three-phase converter, and the modulation signal generator detects the intermediate voltage that is the input voltage of the inverter circuit 4 (Vc_t) And the modulation rate is calculated. The drive signal is generated by comparing the calculated modulation factor with a carrier wave (for example, a triangular wave operating with a cycle sufficiently earlier than the rotational frequency of the motor 10) to generate a drive signal, and switch the switching elements 6k-6p. Do.

  The second control unit 52 of FIG. 2B operates as follows. The modulation factor command (the result of dividing the output voltage command by the voltage detection value of the capacitor 8a) (m_ref) of the output is input. The input modulation rate command inputs a determination signal to the driver circuit (Dri) so as to control the switching elements 6a and 6c on / off according to the result of comparison with the carrier wave (carry1). Further, the input modulation rate command inputs a determination signal to the driver circuit (Dri) so that the switching elements 6b and 6d are respectively controlled to be turned on / off according to the result of comparison with the carrier wave (carry 2). Further, the sign inversion signal of the input modulation rate command is generated, and the switching elements 6e and 6g are controlled to be turned on / off according to the result of comparing the inverted modulation rate command and the carrier wave (carry1). Each signal is input to the driver circuit (Dri). Further, the determination signal is input to the driver circuit (Dri) so that the switching elements 6f and 6h are controlled to be turned on / off according to the result of comparison between the inverted modulation factor command and the carrier wave (carry2). Each driver circuit outputs a drive signal instructing switching to each corresponding switching element based on the determination signal.

  The third control unit 53 of FIG. 2C operates as follows. The square root of the sum of the squares of the q-axis voltage command (Vq_ref) and the d-axis voltage command (Vd_ref) in the modulation factor generation of the output of the inverter circuit 4 is calculated to generate a vector sum. The command voltage is limited through the limiter with the maximum value as the voltage detection value (Vpn_t) of the capacitor 8a and the minimum value as the zero voltage. The doubled voltage (Vdev) of the voltage drop (corresponding to Vce for IGBT and Vds for MOSFET) of the voltage drop of switching elements 6k to 6p of inverter circuit 4 is added to the restricted command voltage, and capacitor 8c The deviation from the actual voltage (Vc_t) is calculated. The calculated deviation is input to a proportional integral controller (PI) to calculate a charge current command value (Ic_ref). The deviation between the calculated current command and the actual current detection value (Ic_t) is input to the proportional integral controller to calculate the command voltage (Vc_ref), and dividing by the voltage detection value (Vpn_t) of the capacitor 8a allows charging. The modulation factor command (m_pnc) of the switching element 6i on the side is calculated. A determination signal is input to the driver circuit (Dri) so as to control the switching element 6i according to the comparison result of the obtained modulation factor command with the carrier wave (carry 3). In addition, the switching element 6j has a driver circuit (Dri) for determining the determination signal so that switching is performed by the inverted signal of the switching element 6i when the actual voltage detection value (Vc_t) of the capacitor 8c is higher than the command voltage (Vc_ref). Enter in Each driver circuit outputs a drive signal instructing switching to each corresponding switching element based on the determination signal. In this manner, switching element 6i that controls charging of capacitor 8c and switching element 6j that controls discharging of capacitor 8c are respectively switching controlled, and the intermediate voltage generated by converter circuit 3 is converted to an inverter circuit. Control can be performed so as to be the sum of the command voltage of the load (corresponding to the motor 10 in the case of the present embodiment) connected to 4 and the voltage drop of the inverter circuit 4.

The waveform of each part when it is made to operate | move by the said structure is shown in FIG. (A) shows the voltage of capacitor 8b (ie the output voltage of multilevel inverter circuit 2) and the waveform of the output current of multilevel inverter circuit 2, (b) shows the waveform of the voltage of capacitors 8a and 8d, (c) shows the multilevel The waveform of the voltage between the output lines of the inverter circuit 2, (d) shows the waveform of the change in rotational speed of the motor 10, and (e) shows the waveform of the phase current of the motor 10. From the waveforms shown in (b) and (d), the voltage of the capacitor 8d is controlled so that the voltage of the capacitor 8d rises because the q-axis voltage command increases with the increase of the rotational speed of the motor 10. From the waveform of (c), the output line voltage of the multilevel inverter circuit 2 is modulated according to the fluctuation of the intermediate voltage so as to supply a sine wave voltage to the general load. Further, from the waveform of (e), in the motor 10, a substantially sinusoidal phase current is supplied.

  According to this configuration, the voltage generated by the converter circuit 3 is supplied as the intermediate voltage of the multilevel inverter circuit 2 and at the same time is supplied as the drive voltage of the inverter circuit 4 and the intermediate voltage is generated. The level inverter circuit 2 can generate output voltages at multiple levels. At the same time, since the intermediate voltage is controlled to a voltage obtained by adding the voltage drop of the inverter circuit 4 to the command value of the output voltage of the inverter circuit 4, the inverter circuit 4 can be driven with the minimum necessary voltage. it can.

  Therefore, the load connected to the multilevel inverter circuit 2 reduces the voltage change by switching the intermediate voltage lower than the voltage of the DC power supply when the voltage utilization is low and the voltage amplitude is small. At the same time, the load connected to the inverter circuit 4 (in the case of the present embodiment, the motor 10 corresponds) is driven by a voltage (voltage of the capacitor 8d) lower than the voltage of the capacitor 8a connected to the multilevel inverter circuit 2. It will be done. For this reason, the voltage change rate is simultaneously suppressed for the outputs to the two loads connected to this power conversion device, and the leakage current in each load can be suppressed.

  Although multilevel inverter circuit 2 has a three-level configuration in the present embodiment, the number of other levels (for example, five levels) may be employed.

  The multilevel inverter circuit 2 has a diode clamp type three level inverter configuration, but may have another configuration (for example, NPC (Neutral Point Clamped) configuration using RBIGBT (Reverse Blocking Insulated Gate Bipolar Transistor)).

  Further, in the present embodiment, an example in which converter circuit 3 generates one intermediate voltage as shown in FIG. 1 is shown, but a plurality of circuits having the configuration of converter circuit 3 shown in FIG. By appropriately controlling each to generate a desired intermediate voltage, it is possible to suppress the voltage change width of the capacitor 8c by generating a plurality of intermediate voltages and to control to a more suitable voltage. In this case, inverter circuit 4 is driven by inputting any one of a plurality of intermediate voltages, and multilevel inverter circuit 2 connects switching elements 6 in series in multiple stages according to the number of generated intermediate voltages. To drive. As a result, an appropriate voltage can be selected from a plurality of intermediate voltages in accordance with the load connected to the inverter circuit, and multilevel inverter circuit 2 is multileveled in accordance with the number of intermediate voltages generated. can do.

  Furthermore, although the concrete control block of each part inside control device 5 was shown in Drawing 2A-Drawing 2C, it is an example in this indication, and it is not limited to this.

  In addition, although the multi-level inverter circuit 2, the converter circuit 3, and the inverter circuit 4 use MOSFETs, other power devices (such as IGBTs) may be used. All are not limited to this.

Second Embodiment
FIG. 4 is a block diagram of the Rankine cycle system 21 according to the second embodiment of the present disclosure. The Rankine cycle system 21 is configured using the power conversion device 1 and the Rankine cycle device 11. In FIG. 4, the same components as those in FIGS. 1 to 3 are denoted by the same reference numerals, and the description thereof will be omitted. FIG. 4 shows, as an example, a Rankine cycle system 21 that operates as a power generation device that generates power using, for example, exhaust heat discharged by combustion gas in a factory for the Rankine cycle device 11.

  The Rankine cycle device 11 includes a pump 12, a motor 10 as a power source for driving the pump 12, an evaporator 13 as a heat exchanger for absorbing thermal energy of combustion gas, and a working fluid by expanding a working fluid. , The generator 15 connected to the expander 14, and the working fluid discharged from the expander 14 by heat exchange with the cooling water or the like to cool the working fluid. A condenser 16, a bypass valve 17 capable of appropriately changing the opening degree and adjusting the flow rate of the working fluid, and a temperature sensor 18 measuring the inlet temperature of the expander 14 are provided. The pump 12, the evaporator 13, the expander 14, and the condenser 16 are annularly connected by a plurality of pipes in this order to form a Rankine cycle flow path. The bypass valve 17 is disposed on a flow path that bypasses the expander 14. In addition, the power conversion device 1 includes a three-phase converter circuit 19 that converts alternating current power generated by the generator 15 into direct current power. Three-phase converter circuit 19 is connected to supply this DC power to capacitor 8a. Furthermore, the power conversion device 1 includes a brake circuit 20 that consumes power when a surplus is generated in the DC power output from the three-phase converter circuit 19. Further, the motor 10 of the Rankine cycle device 11 is driven by the inverter circuit 4 of the power conversion device 1. As in the first embodiment, control device 5 controls a first control unit 51 that controls inverter circuit 4, a second control unit 52 that controls multilevel inverter circuit 2, and a third control that controls converter circuit 3. And a fourth control unit 54 that controls the three-phase converter circuit 19 and a fifth control unit 55 that controls the brake circuit 20 in the present embodiment.

  In the first embodiment, the DC power supply is connected to the power conversion device 1. However, in the second embodiment, the three-phase converter circuit 19 is a DC power supply that is a power supply device. Supply DC voltage to In FIG. 4, the three-phase converter circuit 19 operating as the power supply device is disposed inside the power conversion device 1, but may be disposed outside the power conversion device 1. Similarly, in FIG. 4, the brake circuit 20 is disposed inside the power conversion device 1, but may be disposed outside the power conversion device 1.

  The operation in the above configuration will be described below. At start-up, power is received from a separate power source (e.g., the illustrated DC power source). The received power causes the converter circuit 3 to generate an intermediate voltage, and controls the motor 10 to be driven.

  On the other hand, the expander 14 is controlled to hold the stop until the indicated value of the temperature sensor 18 exceeds the predetermined temperature. The bypass valve 17 controls the degree of opening based on the temperature of the temperature sensor 18. Thereby, the flow rate of the working fluid in the path of the bypass valve 17 is adjusted.

  After start-up, when the temperature of the working fluid reaches a predetermined temperature condition due to thermal energy absorption by the evaporator 13, the stop control of the expander 14 is canceled and control is performed to start or start power generation. Holding of the stop of the expander 14 is controlled by the three-phase converter circuit 19. The operation of the three-phase converter circuit 19 is controlled by the controller 5.

  Thereafter, the generated power rises, and by exceeding the necessary power of the inverter circuit 4, the voltage of the capacitor 8a rises. On the other hand, the multilevel inverter circuit 2 operates so that the voltage of the capacitor 8a becomes substantially constant, thereby outputting power to the general load.

  Also, when the general load is interrupted or changed to a light load, the supply voltage rises and the output of the multilevel inverter circuit 2 is suppressed, the brake circuit 20 starts switching, and is consumed internally. Works to do. The operation of the brake circuit 20 is controlled by the controller 5.

  The waveforms of the respective parts when operated by the above configuration are shown in FIG. FIG. 5 shows the behavior after the voltage of the capacitor 8a after start-up is increased and stabilized to the voltage of the DC power supply. (A) is the waveform of the output voltage to the general load and the output current from the multilevel inverter circuit 2, (b) is the waveform of the generated power from the generator 15, (c) is the waveform of the voltage of the capacitors 8a and 8c, (D) is the waveform of the output line voltage of the multilevel inverter circuit 2, (e) is the waveform of the rotational speed change of the motor 10 that drives the rotor of the generator 15 and the pump 12, (f) is the phase current of the motor 10 (G) shows the waveform of the phase current of the generator 15, respectively. From the waveform of each part, in (a), the output voltage to the load and the output current become a sine wave stable output. From the waveforms shown in (b) and (e), it can be seen that the generated power rises as the rotation speed of the generator 15 rises. From the waveform of (c), the voltage of the capacitor 8c is controlled to increase because the q-axis voltage command increases with the increase of the rotational speed of the motor 10 driving the pump 12. From the waveform of (d), the output line voltage of the multilevel inverter circuit 2 is modulated according to the fluctuation of the intermediate voltage so as to supply a sine wave voltage to the general load. Further, from the waveforms of (f) and (g), the phase current of the motor 10 and the phase current of the generator 15 are energized in a substantially sinusoidal manner.

  According to this configuration, the voltage generated by the converter circuit 3 is supplied as the intermediate voltage of the multilevel inverter circuit 2 and at the same time is supplied as the drive voltage of the inverter circuit 4 and the intermediate voltage is generated. The level inverter circuit 2 can generate output voltages at multiple levels. At the same time, since the intermediate voltage is controlled to a voltage obtained by adding the voltage drop of the inverter circuit 4 to the command value of the output voltage of the inverter circuit 4, the inverter circuit 4 can be driven with the minimum necessary voltage. it can.

  Therefore, the load connected to the multilevel inverter circuit 2 reduces the voltage change by switching the intermediate voltage lower than the voltage of the DC power supply when the voltage utilization is low and the voltage amplitude is small. At the same time, the motor 10 for driving the pump 12 connected to the inverter circuit 4 is driven with a voltage (voltage of the capacitor 8 d) lower than the voltage of the capacitor 8 a connected to the multilevel inverter circuit 2. For this reason, the motor 10 is driven with the necessary minimum voltage, and the leakage current can be suppressed along with the suppression of the voltage change rate. Similarly, for the general load connected to multi-level inverter circuit 2 as well, the output voltage is generated at a plurality of levels so that the rate of voltage change is suppressed, and the leakage current in the general load can be simultaneously suppressed. .

  In particular, in the case where the working fluid is circulated as a liquid refrigerant by the pump 12 as in the second embodiment and the working motor 10 is disposed inside the pump 12, the liquid refrigerant is The windings of the motor 10 may be immersed in the liquid refrigerant depending on the filling amount of the liquid refrigerant, so the parasitic capacitance may be increased due to the dielectric constant of the liquid refrigerant, and the leakage current may be increased.

According to the present embodiment, in order to suppress the increase in the leakage current, the motor 12 is driven with the minimum voltage necessary for driving the pump 12, so that the leakage current can be suppressed. At the same time, since this low voltage is also supplied as an intermediate voltage of multilevel inverter circuit 2, the output voltage to the general load is multileveled, and it becomes possible to reduce the rate of voltage change. Leakage current can be reduced.

  Although the Rankine cycle apparatus 11 according to the present embodiment recovers the exhaust heat from the combustion gas of the factory, the present invention is not limited to this. It may not be the combustion gas from the factory, as long as the medium can recover heat by the Rankine cycle.

  Although FIG. 4 shows the state where the motor 10 is disposed outside the pump 12, the motor 10 may be disposed inside the housing of the pump 12. The pump mechanism and the motor mechanism may be collectively referred to as a pump.

  Moreover, although the state which arrange | positions the generator 15 in the exterior of the expander 14 was shown in FIG. 4, you may arrange | position the generator 15 inside the housing | casing of the expander 14. FIG. The expansion mechanism and the power generation mechanism may be collectively referred to as an expander.

  Furthermore, although FIG. 4 shows an example in which the general load is arranged on the output side of the multilevel inverter circuit 2, it may be connected to a commercial power supply to operate as a grid-connected inverter.

  Further, in the case where the multilevel inverter circuit 2 is a grid-connected inverter, the multilevel inverter circuit 2 may be operated as a converter without receiving a separate DC power supply at the time of start-up to receive power from a commercial power supply.

  In the present specification, the desired set voltage means a preset voltage. The preset voltage means not only pointing to a specific voltage value but also an arbitrary voltage (that is, a voltage in a preset range) included in a preset predetermined range. Also includes.

  As described above, in the power conversion device according to the present disclosure, the load connected to the multilevel inverter circuit suppresses the voltage change rate according to the number of levels, and at the same time a pump drive motor connected to the inverter circuit is necessary. Since it drives with the minimum low voltage, the voltage change rate is simultaneously suppressed at the output to two loads connected to the power conversion device, and the leakage current due to switching in each load can be suppressed. .

  The power conversion device according to the present disclosure uses a multilevel inverter circuit as a power converter for a main unit (for example, an inverter for a large fan or a grid-connected inverter that outputs generated power to a power system). Can be applied to applications such as connecting to a load for accessories (for example, a motor with a large ground capacity).

DESCRIPTION OF SYMBOLS 1 power converter 2 multilevel inverter circuit 3 converter circuit 4 inverter circuit 5 control device 6a switching element 6b switching element 6c switching element 6d switching element 6e switching element 6f switching element 6g switching element 6h switching element 6i switching element 6j switching element 6k switching Element 6 l Switching Element 6m Switching Element 6n Switching Element 6p Switching Element 7a Diode 7b Diode 7c Diode 7d Diode 8a Capacitor 8b Capacitor 8c Capacitor 8c Capacitor 9a Inductor 9b Inductor 9c Inductor 10 Motor 11 Rankine Cycle Device 12 Pump 13 Evaporator 14 Bulge Stretcher 15 Generator 16 Condenser 17 Bypass valve 18 Temperature sensor 19 Three-phase converter circuit 20 Brake circuit 21 Rankine cycle system 51 1st control unit 52 2nd control unit 53 3rd control unit 54 4th control unit 55 5th control Part 101 Positive bus capacitor 102 Negative bus capacitor 103 Switch element 104 Switch element 105 Neutral point 106 Reactor 107 Balance circuit 108 Inverter

Claims (3)

A converter circuit that generates an intermediate voltage using a DC voltage supplied from a DC power supply,
A multi-level inverter circuit connected to the DC power supply and the converter circuit, driven by inputting the DC voltage and the intermediate voltage, and controlled at at least three levels;
An inverter circuit connected to the converter circuit to input and drive the intermediate voltage;
The multilevel inverter circuit outputs a predetermined first alternating voltage and the inverter circuit controls the inverter circuit to output a predetermined second alternating voltage, and the command voltage of the load connected to the inverter circuit by the intermediate voltage A control device that controls a set voltage obtained by summing the voltage drop of the inverter circuit;
Power converter comprising: The converter circuit is
Generate a plurality of said intermediate voltages,
The inverter circuit is
Drive by inputting any one of the plurality of intermediate voltages,
The power converter device according to claim 1. A power converter according to claim 1 or 2;
A pump for pumping a working fluid, an evaporator for heating the working fluid, an expander for expanding the working fluid, and a Rankine cycle flow path in which a condenser for condensing the working fluid is annularly connected in this order, the pump A Rankine cycle device comprising: a motor connected to the motor; and a generator connected to the expander to generate and output a third AC voltage.
A power supply device which receives the third alternating voltage output from the generator, converts it into a direct voltage, and outputs the direct voltage;
Have
The power supply device
Operates as the DC power supply that supplies the DC voltage to the converter circuit and the multilevel inverter circuit,
The inverter circuit is
Converting the input intermediate voltage into the second AC voltage and supplying the second AC voltage to the motor;
Rankine cycle system.

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