Power conversion device

Abstract

[Problem] To provide a power conversion device that, by using a GND common-type dual inverter, can expand an operation range while performing high-efficiency driving of a motor which has a winding that has an open-end structure. [Solution] The present invention is provided with a control device 6 that controls a primary-side inverter INV1 and a secondary-side inverter INV2 of a power conversion apparatus 1 of a GND common-type dual inverter. The control device 6 executes switching between a high-efficiency operation mode in which the secondary-side inverter INV2 is stopped or the secondary-side inverter INV2 outputs only reactive power, and a high-output operation mode in which the secondary-side inverter INV2 outputs either only active power or active power and reactive power. In the high-output operation mode, the active power output by the secondary-side inverter INV2 is minimized.

Description

Power converter 【0001】 The present invention relates to a power conversion device that applies an AC output to a motor having windings with an open-end structure where both ends are open, using two inverters, a primary inverter and a secondary inverter. 【0002】 For example, when driving an electric compressor used in the air conditioning system of electric vehicles such as electric cars and hybrid vehicles, a three-phase permanent magnet synchronous motor (IPMSM) is used. In a typical three-phase star-connected permanent magnet synchronous motor using an inverter, the switching methods and definitions of the operating range for maximum torque / current control (high-efficiency operation), flux weakening control (high-output operation), and maximum torque / voltage (high-output operation) are well-established, as shown in Figure 13. 【0003】 In Figure 13, the vertical axis represents torque and the horizontal axis represents speed. Maximum torque / current control (high-efficiency operation) is performed in the constant torque operation region at low speeds, flux weakening control (high-power operation) is performed in the operation region at higher speeds, and maximum torque / voltage (high-power operation) is performed in the operation region at even higher speeds (see, for example, Patent Document 1). 【0004】 On the other hand, motors driven by inverters tend to have a narrower high-speed driveable range when the input voltage drops, as the driveable rotational speed decreases, or the output torque at high rotational speeds decreases. In the above-mentioned automotive electric compressors, which drive the compression mechanism with a motor housed within a housing, the required input voltage range was not conventionally wide, but in recent years, the requirements for the driveable range in response to changes in input voltage have become stricter even for electric compressors. 【0005】 However, in electric compressors used in vehicles, the battery of the electric vehicle is used as the DC power source, which can cause the input voltage to drop. When the input voltage drops, the torque that can be output decreases in the high-speed range. 【0006】Therefore, as a method to increase the output voltage to the motor relative to the input voltage, a dual inverter power conversion device has been proposed in which a motor with a so-called open-end winding structure (a motor with the neutral point of the motor exposed outside without being connected) equipped with multiple stator windings that are open at both ends is sandwiched between two inverters, a primary and a secondary inverter, and the differential voltage between the primary and secondary inverters is applied to the motor to drive it (see, for example, Patent Document 2). 【0007】 Patent No. 5925526 Patent No. 7414923 【0008】 In a dual-inverter power converter that drives a motor with an open-end winding structure, there are two inverters, a primary and a secondary, which provides flexibility in how the voltage command value is distributed to the two inverters. 【0009】 Figure 14 shows a typical dual inverter power converter. In Figure 14, M is a motor with the open-ended winding structure described above, INV1 is the primary inverter, and INV2 is the secondary inverter, which sandwich the stator winding of the motor M. 【0010】 A dual inverter power converter with a shared power supply is the simplest type, sharing the primary and secondary power supplies. Because there is only one power supply, the voltage ratings of all semiconductor elements and passive elements (capacitors, etc.) on both the primary and secondary sides must be set according to the power supply voltage, but both the primary and secondary sides can output both active and reactive power. In this method, since a common power supply is used for both the primary and secondary sides, half of the voltage command value will be output by each inverter INV1 and INV2. 【0011】However, in the case of a dual inverter power converter with a shared power supply, there is a path through which zero-sequence current flows, and since this zero-sequence current directly leads to losses, it is necessary to take measures to address the zero-sequence current. Furthermore, since the use of zero-sequence current in a dual inverter power converter with a shared power supply is limited, it is common practice to control it so that the zero-sequence current becomes 0A. By controlling the zero-sequence current to 0A, it was possible to apply the same theory as a three-phase star-connected permanent magnet synchronous motor. 【0012】 Other types of dual-inverter power converters include isolated power supply dual-inverter power converters and floating capacitor dual-inverter power converters. However, isolated power supply dual-inverter power converters require two isolated power supplies, which raises concerns about their size. 【0013】 On the other hand, floating capacitor type dual inverter power converters have the advantage of being able to control the secondary voltage and not allowing zero-sequence current to flow, but they require an additional power supply to drive the switching elements of the secondary inverter. 【0014】 Furthermore, since the power supply for the secondary inverter is a capacitor, it can only supply reactive power. Therefore, the primary inverter outputs active power at the voltage command value, and the secondary inverter outputs reactive power. In addition, any reactive power that cannot be output by the secondary inverter is borne by the primary inverter. 【0015】 This floating capacitor type dual inverter has the advantage of being able to drive the motor while boosting the voltage of the capacitor in the secondary inverter, thus allowing the voltage that can be applied to the motor to be even higher than that of a common power supply type. 【0016】However, the conventional dual-inverter power converters described above all have a large number of components, making it difficult to reduce costs and miniaturize them. In particular, in floating capacitor type dual-inverter power converters, the secondary inverter is at a floating potential, so it is necessary to create a separate power supply (isolated power supply) for driving the gates of the switching elements of the secondary inverter, which has a different reference potential, in addition to the power supply for driving the gates of the switching elements of the primary inverter. This makes it difficult to adopt in equipment with limited board area, such as electric compressors for automobiles, due to the component mounting area and cost. 【0017】 Therefore, the applicant previously proposed a power conversion device as shown in Figure 1. In this method, the positive power line of the power supply common type shown in Figure 14 is separated by the primary inverter INV1 and the secondary inverter INV2, while only the negative power line is made common, and a capacitor is placed on the secondary side, similar to a floating capacitor type. Hereinafter, this type of power conversion device will be referred to as a GND common type dual inverter. In this method, the secondary voltage can be controlled in the same way as the control of a floating capacitor type dual inverter power conversion device. 【0018】 Furthermore, in a GND-common dual inverter power converter, it is possible to share the power supply for the drive circuit of the secondary inverter INV2, similar to the power supply-common type. This allows the primary inverter INV1 on the power supply side to be constructed with high-voltage components, while the controllable secondary inverter INV2 can be constructed with low-voltage components. The GND-common type, which allows the power supply for the drive circuit of the secondary inverter INV2 to be shared with the primary inverter INV1, offers significant advantages in applications where the power supply voltage fluctuates greatly. 【0019】 In a GND-common dual inverter power converter, the zero-sequence current is used to control the DC link voltage of the secondary inverter, i.e., the secondary voltage. Therefore, it is not always appropriate to control the zero-sequence current to 0A, as is the case with a power-common dual inverter power converter. 【0020】In particular, in operating ranges requiring high output, it becomes necessary to continuously supply a zero-sequence current in order to output active power from the secondary inverter. That is, the power converter of a common-GND dual inverter can output active power from the secondary inverter by supplying a zero-sequence current. 【0021】 Outputting active power through the secondary inverter increases the output degrees of freedom of the voltage vector, enabling high-power operation. On the other hand, allowing zero-sequence current to flow leads to increased losses, so it is desirable to avoid or suppress it as much as possible. However, as in the case of the three-phase star-connected permanent magnet synchronous motor mentioned above, methods for switching between high-efficiency operation and high-power operation modes, and methods for determining the operating range, had not been established. 【0022】 The present invention was made to solve the aforementioned conventional technical problems, and provides a power conversion device that can efficiently drive a motor having an open-end winding structure while expanding the operating range using the above-mentioned common-GND dual inverter. 【0023】 In order to efficiently drive motors with open-end windings over a wide operating range using the above-mentioned GND-common dual inverter power converter, the control device is equipped with a high-efficiency operation mode and a high-output operation mode, which are switched between and executed. 【0024】In other words, the power conversion device of the present invention comprises a primary inverter connected to one end of an open-ended winding of a motor, and a secondary inverter connected to the other end of the winding, and applies the differential voltage between the primary and secondary inverters to the motor, wherein the primary inverter is connected to a DC power supply, the secondary inverter is connected to a capacitor, the negative power lines of the primary and secondary inverters are shared, and the device comprises a control device that controls the primary and secondary inverters, and this control device switches between a high-efficiency operating mode in which the secondary inverter is stopped or outputs only reactive power, and a high-output operating mode in which the secondary inverter outputs only active power or active power and reactive power, and in the high-output operating mode, minimizes the active power output by the secondary inverter. 【0025】 The power conversion device of the second invention is characterized in that, in the above invention, the control device executes a high-efficiency operation mode in the constant torque operation region of the motor and executes a high-output operation mode in the speed operation region higher than the constant torque operation region. 【0026】 The third power conversion device of the present invention is characterized in that, in the present invention, the primary inverter and the secondary inverter are each composed of a plurality of switching elements, the positive input terminal of the primary inverter is connected to the positive power line of the DC power supply, the negative input terminal of the primary inverter is connected to the negative power line of the DC power supply, the output terminal of the primary inverter is connected to one end of the winding, the output terminal of the secondary inverter is connected to the other end of the winding, a capacitor is connected between the positive and negative input terminals of the secondary inverter, the positive input terminal of the secondary inverter is not connected to the positive power line of the DC power supply, and the negative input terminal of the secondary inverter is connected to the negative power line of the DC power supply, and an AC output is generated from the DC power supply by switching each switching element with a control device. 【0027】 The fourth power conversion device of the present invention is a control device in which the dq axis voltage command value V dq refFrom the primary-side voltage vector command value V1 for switching the primary-side inverter ref and the secondary-side voltage vector command value V2 for switching the secondary-side inverter ref An output voltage command generation unit is provided, and in the high-output operation mode, this output voltage command generation unit adjusts the primary-side voltage vector command value V1 ref and the secondary-side voltage vector command value V2 ref so that the effective power output by the secondary-side inverter is minimized. This is the characteristic of this device. 【0028】 In the power conversion device of the fifth invention, in the high-output operation mode, the output voltage command generation unit makes the component of the secondary-side voltage vector command value V2 m in the direction opposite to the phase of the motor current I ref minimized. This is the characteristic of this device. 【0029】 In the power conversion device of the sixth invention, in the high-output operation mode, the output voltage command generation unit operates the phases of the primary-side voltage vector command value V1 ref and the secondary-side voltage vector command value V2 ref within the output limit to execute maximum amplitude output control to minimize the component of the secondary-side voltage vector command value V2 m in the direction opposite to the phase of the motor current I ref This is the characteristic of this device. 【0030】 In the power conversion device of the seventh invention, based on the fifth invention, the output voltage command generation unit makes the primary-side voltage vector command value V1 ref have the same phase as the dq-axis voltage command value V dq ref and makes the secondary-side voltage vector command value V2 ref have a phase opposite to that of the dq-axis voltage command value V dq ref within the output limit to execute secondary-side reverse-phase output control to minimize the component of the secondary-side voltage vector command value V2 m in the direction opposite to the phase of the motor current I ref This is the characteristic of this device. 【0031】The power conversion device of the eighth invention is such that, in the fifth invention, the output voltage command generation unit has a primary side voltage vector command value V1 ref and secondary voltage vector command value V2 ref By manipulating their phases while the output limit is set, the motor current I m The secondary voltage vector command value V2 is in the opposite phase direction to this. ref Maximum amplitude output control that minimizes the component and primary side voltage vector command value V1 ref The dq axis voltage command value V dq ref With the phase the same and the output limit reached, the secondary voltage vector command value V2 ref The dq axis voltage command value V dq ref By making it out of phase, the motor current I m The secondary voltage vector command value V2 is in the opposite phase direction to this. ref It has secondary-side reverse-phase output control that minimizes the component of the motor current I m The secondary voltage vector command value V2 is in the opposite phase direction to this. ref This method is characterized by selecting and executing either maximum amplitude output control that reduces the component, or secondary side inverse phase output control. 【0032】 According to the present invention, in a power conversion device comprising a primary inverter connected to one end of an open-ended winding of a motor and a secondary inverter connected to the other end of the winding, the differential voltage between the primary and secondary inverters is applied to the motor. By using the aforementioned common-GND dual inverter, in which the primary inverter is connected to a DC power supply and the secondary inverter is connected to a capacitor, and the negative power lines of the primary and secondary inverters are shared, the capacitor is charged by the secondary inverter via the motor from the DC power supply, and the AC output is applied to the motor using the voltage charged in this capacitor, thereby expanding the drivable range in response to changes in input voltage. 【0033】Furthermore, in a GND-common dual inverter power converter, as in the third invention, the positive input terminal of the secondary inverter is not connected to the positive power line of the DC power supply, and the negative input terminal of the secondary inverter is connected to the negative power line of the DC power supply. As a result, the secondary inverter does not become floating potential, and the reference voltages of the primary and secondary inverters become the same. 【0034】 This eliminates the need to create a separate gate drive power supply (isolated power supply) for the switching elements of the secondary inverter, in addition to the gate drive power supply (isolated power supply) for the switching elements of the primary inverter. This allows the switching elements of both the primary and secondary inverters to be switched using a common gate drive power supply, thus expanding the drivable range in response to changes in input voltage without the need for a separate boost converter or similar device. 【0035】 Furthermore, since it becomes unnecessary to create a separate power supply for each inverter to drive the gate, the increase in component mounting area can be suppressed, enabling miniaturization and cost reduction. This makes it extremely effective for equipment such as automotive electric compressors, where the input voltage changes significantly, there is a strong demand for cost reduction, and the board area is limited, requiring miniaturization of the power conversion device. 【0036】 In particular, the present invention provides a control device that controls the primary and secondary inverters. This control device switches between a high-efficiency operating mode in which the secondary inverter is stopped or outputs only reactive power, and a high-output operating mode in which the secondary inverter outputs only active power or both active and reactive power. Furthermore, in the high-output operating mode, the active power output by the secondary inverter is minimized. Therefore, for example, as in the second invention, by switching the operating mode to execute the high-efficiency operating mode in the constant torque operating range of the motor and the high-output operating mode in the operating speed range higher than the constant torque operating range, the motor can be driven stably over a wide range of operating conditions. 【0037】Furthermore, in high-power operation mode, the active power output by the secondary inverter is minimized, thereby minimizing the zero-sequence current and suppressing the increase in losses in high-power operation mode, making it possible to achieve efficient motor drive across the entire operating range. 【0038】 In this case, the control device actually receives the dq-axis voltage command value V as in the fourth invention. dq ref Therefore, the primary voltage vector command value V1 for switching the primary inverter. ref The secondary voltage vector command value V2 for switching the secondary inverter. ref An output voltage command generation unit is provided to generate the primary voltage vector command value V1 in the high-power operation mode so that the active power output by the secondary inverter is minimized. ref and secondary voltage vector command value V2 ref Make it generate 【0039】 Furthermore, as in the fifth invention, the output voltage command generation unit, in the high-power operation mode, the motor current I m The secondary voltage vector command value V2 is in the opposite phase direction to this. ref Minimize the component. 【0040】 In that case, for example, as in the sixth invention, the output voltage command generation unit generates the primary side voltage vector command value V1 ref and secondary voltage vector command value V2 ref By manipulating their phases while the output limit is set, the motor current I m The secondary voltage vector command value V2 is in the opposite phase direction to this. ref This performs maximum amplitude output control to minimize the component. This reduces the motor current I that outputs active power. m The secondary voltage vector command value V2 is in the opposite phase direction to this. ref By minimizing this component and reducing the zero-sequence current, it becomes possible to suppress the increase in losses. 【0041】 Furthermore, as in the seventh invention, the output voltage command generation unit generates the primary side voltage vector command value V1 ref The dq axis voltage command value V dqref With the phase the same and the output limit reached, the secondary voltage vector command value V2 ref The dq axis voltage command value V dq ref By making it out of phase, the motor current I m The secondary voltage vector command value V2 is in the opposite phase direction to this. ref The secondary side reverse-phase output control may be implemented to minimize the component of the motor current I that outputs active power. m The secondary voltage vector command value V2 is in the opposite phase direction to this. ref By minimizing this component and reducing the zero-sequence current, it becomes possible to suppress the increase in losses. 【0042】 Furthermore, as in the eighth invention, the maximum amplitude output control and the secondary side inverse phase output control are compared, and the motor current I m The secondary voltage vector command value V2 is in the opposite phase direction to this. ref You can also choose to execute the option that results in a smaller component. 【0043】This is an electrical circuit diagram of a GND-common type dual inverter power converter according to one embodiment of the present invention. This is a block diagram of the control device of the power converter in Figure 1. This is a diagram illustrating the voltage vector of the power converter in Figure 1. This is a diagram showing the state in which the phase of the motor current has changed in Figure 3. This is a diagram illustrating the high-efficiency operation mode performed by the control device of the power converter in Figure 1. This is a diagram showing the state in which the phase of the motor current has changed in Figure 5. This is a diagram illustrating the maximum amplitude output control of the high-output operation mode performed by the control device of the power converter in Figure 1. This is a diagram showing the state in which the phase of the motor current has changed in Figure 7. This is a diagram showing the primary side dq axis voltage, secondary side dq axis voltage, and zero-sequence current in the maximum amplitude output control in Figures 7 and 8. This is a diagram illustrating the secondary side reverse phase output control of the high-output operation mode performed by the control device of the power converter in Figure 1. This is a diagram showing the primary side dq axis voltage, secondary side dq axis voltage, and zero-sequence current in the secondary side reverse phase output control in Figure 10. This is a diagram illustrating the switching method between the high-efficiency operation mode and the high-output operation mode performed by the control device of the power converter in Figure 1. This diagram illustrates the method for switching between high-efficiency operation mode and high-output operation mode when driving a typical three-phase star-connected permanent magnet synchronous motor with an inverter. It also shows the electrical circuit diagram of a conventional dual-inverter power converter. 【0044】 The embodiments of the present invention will be described in detail below with reference to the drawings. (1) Power conversion device 1 Figure 1 is an electrical circuit diagram of a GND common type dual inverter power conversion device 1 of an embodiment to which the present invention is applied. The power conversion device 1 of the embodiment converts the DC voltage V of a DC power source (for example, a high-voltage battery of an electric vehicle) 2 dc This converts the DC voltage to a three-phase AC voltage (AC output) and supplies it to the motor M. The motor M in this embodiment consists of a stator with three-phase windings and a rotor with a built-in magnet that rotates inside it, and is a three-phase permanent magnet synchronous motor (Internal Permanent Magnet Synchronous Motor) that drives an electric compressor used in the air conditioning system of electric vehicles such as electric vehicles and hybrid vehicles. Note that the DC voltage V of the DC power supply 2 dc The primary side voltage V of the power converter 1 dc1 This is the DC link voltage of the primary inverter INV1, which will be described later. 【0045】 In this embodiment, the power converter 1 consists of a three-phase primary inverter INV1 consisting of upper and lower arm switching elements 3A to 3F, a three-phase secondary inverter INV2 consisting of upper and lower arm switching elements 4A to 4F, and a control device 6 (Figure 2), etc. In this embodiment, each switching element 3A to 3F and 4A to 4F is composed of an insulated gate bipolar transistor (IGBT) with a MOS structure incorporated into its gate portion. 【0046】 In this invention, the DC voltage V of the DC power supply 2 is controlled by the primary inverter INV1 and the secondary inverter INV2. dc The current is converted into a three-phase AC voltage (AC output), and the difference voltage between inverters INV1 and INV2 is applied to the windings (stator windings) of motor M. Here, the windings of motor M have an open-end structure and are not bundled at the neutral point. 【0047】 (2) Primary Inverter INV1 The primary inverter INV1 has a U-phase half-bridge circuit 9U, a V-phase half-bridge circuit 9V, and a W-phase half-bridge circuit 9W. Each of the phase half-bridge circuits 9U to 9W has the upper arm switching elements 3A to 3C and the lower arm switching elements 3D to 3F, respectively. Furthermore, each of the switching elements 3A to 3F incorporates a freewheeling diode 5 connected in antiparallel. 【0048】 The collector electrodes of the upper arm switching elements 3A to 3C, which are the positive input terminals of the primary inverter INV1, are connected to the positive power supply line 11 (HV+) of the DC power supply 2. On the other hand, the emitter electrodes of the lower arm switching elements 3D to 3F, which are the negative input terminals of the primary inverter INV1, are connected to the negative power supply line 12 (HV-) of the DC power supply 2. In the figure, 13 is a capacitor connected between the positive power supply line 11 and the negative power supply line 12, and constitutes a noise filter. 【0049】In this case, the emitter electrode of the upper arm switching element 3A of the U-phase half-bridge circuit 9U of the primary inverter INV1 is connected to the collector electrode of the lower arm switching element 3D, and the connection point between them (the arm midpoint: the output terminal of the primary inverter INV1) is connected to one end of the U-phase winding of the motor M. 【0050】 Furthermore, the emitter electrode of the upper arm switching element 3B of the V-phase half-bridge circuit 9V and the collector electrode of the lower arm switching element 3E are connected, and their connection point (arm midpoint: output terminal of primary side inverter INV1) is connected to one end of the V-phase stator winding of the motor M. 【0051】 Furthermore, the emitter electrode of the upper arm switching element 3C of the W-phase half-bridge circuit 9W and the collector electrode of the lower arm switching element 3F are connected, and their connection point (arm midpoint: output terminal of primary side inverter INV1) is connected to one end of the W-phase stator winding of the motor M. 【0052】 (3) Secondary Inverter INV2 The secondary inverter INV2 also has three half-bridge circuits 16U, 16V, and 16W corresponding to each of the U, V, and W phases. The neutral points of each phase of the motor M are not bundled together, and the motor M windings are sandwiched between the half-bridge circuits 9U to 9W of the primary inverter INV1 and the half-bridge circuits 16U to 16W of the secondary inverter INV2. 【0053】 The half-bridge circuits 16U to 16W of the secondary inverter INV2 each have upper arm switching elements 4A to 4C and lower arm switching elements 4D to 4F, respectively. Each of the switching elements 4A to 4F also incorporates a freewheeling diode 10 connected in antiparallel. 【0054】 Furthermore, a capacitor C is connected between the collector electrodes of the upper arm switching elements 4A to 4C, which are the positive input terminals of the secondary inverter INV2, and the emitter electrodes of the lower arm switching elements 4D to 4F, which are the negative input terminals of the secondary inverter INV2. 【0055】However, the collector electrodes of the upper arm switching elements 4A to 4C, which are the positive input terminals of the secondary inverter INV2, are not connected to the positive power line 11 of the DC power supply 2, but are disconnected. On the other hand, in this invention, the emitter electrodes of the lower arm switching elements 4D to 4F, which are the negative input terminals of the secondary inverter INV2, are connected to the negative power line 12 of the DC power supply 2. 【0056】 Then, the emitter electrode of the upper arm switching element 4A of the U-phase half-bridge circuit 16U and the collector electrode of the lower arm switching element 4D are connected, and their connection point (arm midpoint: output terminal of secondary inverter INV2) is connected to the other end of the U-phase winding of the motor M. 【0057】 Furthermore, the emitter electrode of the upper arm switching element 4B of the V-phase half-bridge circuit 16V and the collector electrode of the lower arm switching element 4E are connected, and their connection point (arm midpoint: output terminal of secondary inverter INV2) is connected to the other end of the V-phase stator winding of the motor M. 【0058】 Furthermore, the emitter electrode of the upper arm switching element 4C of the W-phase half-bridge circuit 16W and the collector electrode of the lower arm switching element 4F are connected, and their connection point (arm midpoint: output terminal of secondary inverter INV2) is connected to the other end of the W-phase stator winding of the motor M. In other words, the power conversion device 1 of the present invention has the configuration of the GND common type dual inverter system described above. 【0059】 (4) Control device 6 Next, Figure 2 shows a block diagram of the control device 6. The control device 6 of this embodiment consists of a microcomputer having a processor, and receives the speed command value ω from the ECU of the electric vehicle. rm ref and secondary voltage command value v dc2 ref Input the current and receive the phase current (motor current I) of motor M from a current sensor (not shown). m The system takes inputs from these inputs and controls the ON / OFF states of the switching elements 3A-3F and 4A-4F of the primary inverter INV1 and secondary inverter INV2 based on these inputs (switching). 【0060】Specifically, the gate voltages applied to the gates of the switching elements 3A to 3F and 4A to 4F are controlled. Further, the control device 6 of the embodiment has a configuration including a speed control unit 21, a dq-axis current control unit 22, a secondary-side voltage control unit 27, a z-axis current control unit 28, an output voltage command generation unit 29, a primary-side modulation unit 24, and a secondary-side modulation unit 26. 【0061】 (4-1) Speed control unit 21 The speed control unit 21 performs PI calculation and q-axis current I q and calculates and outputs the q-axis current command value I q ref according to the relational expression between torque. 【0062】 (4-2) dq-axis current control unit 22 The dq-axis current control unit 22 calculates and outputs the d-axis voltage command value V d ref and the q-axis voltage command value V q ref by PI calculation and non-interference control. In this case, in the dq-axis current control unit 22, basically, the d-axis current command value I d ref and the d-axis current I d (estimated value), the q-axis current command value I q ref and the q-axis current I q (estimated value) to eliminate the deviation in the direction of the d-axis voltage command value V d ref and the q-axis voltage command value V q ref are calculated. These d-axis voltage command value V d ref and the q-axis voltage command value V q ref become the dq-axis voltage command value V dq ref (vector) in the present invention. 【0063】 (4-3) Secondary-side voltage control unit 27 The secondary-side voltage control unit 27 outputs the zero-phase current command value I z ref . This zero-phase current command value I z ref becomes the secondary-side DC link current command value necessary for controlling the secondary-side voltage V dc2 (DC link voltage of the secondary-side inverter). 【0064】 (4-4) z-axis current control unit 28 The z-axis current control unit 28 controls the zero-sequence current I z (Secondary DC link current) is set to zero-sequence current command value I z ref (Secondary DC link current command value) Zero-sequence voltage command value V for control z ref Outputs. 【0065】 (4-5) Output voltage command generation unit 29 Output voltage command generation unit 29 generates the d-axis current I d (Estimated value), q-axis current I q (Estimated value) and the d-axis voltage command value V output by the dq-axis current control unit 22. d ref q-axis voltage command value V q ref The dq-axis voltage command value V consists of the following: dq ref (Vector) and the zero-sequence voltage command value V output by the z-axis current control unit 28 z ref Therefore, the primary voltage vector command value V1 for switching each switching element 3A to 3F of the primary inverter INV1 ref The secondary voltage vector command value V2 is used to switch each of the switching elements 4A to 4F of the secondary inverter INV2. ref It generates and outputs the output voltage. The operation of this output voltage command generation unit 29 will be described in detail later. 【0066】 (4-6) Primary side modulation unit 24 The primary side modulation unit 24 controls the primary side voltage vector command value V1 ref From this, the primary inverter INV1 generates and outputs a primary inverter switching signal (PWM signal) for switching (PWM control) each switching element 3A to 3F. The secondary modulation unit 26 also generates a secondary voltage vector command value V2 ref From there, a secondary inverter switching signal (PWM signal) is generated and output for switching (PWM control) each of the switching elements 4A to 4F of the secondary inverter INV2. 【0067】(5) Operation of the Output Voltage Command Generation Unit 29 Next, the operation of the output voltage command generation unit 29 described above will be explained. In the following explanation, the DC link voltage ratio of the primary inverter INV1 and the secondary inverter INV2 is set to 2:1, and in this embodiment, the DC link voltage of the primary inverter INV1 (primary voltage V dc1 ) to 250V, the DC link voltage of the secondary inverter INV2 (secondary voltage V dc2 Set the voltage to 125V. 【0068】 First, the voltage vector of the power converter 1 of the GND common type dual inverter will be explained. Figure 3 is a diagram illustrating the voltage vector of the power converter 1 of the embodiment. In the figure, the vertical axis is the q-axis voltage V q The horizontal axis is the d-axis, which is voltage V. d Furthermore, the outermost dashed circle C1 represents the linear output range of the power converter 1 of the GND common type dual inverter, the innermost dashed circle C2 represents the linear output range of the primary inverter INV1, and the innermost dashed circle C3 represents the linear output range of the secondary inverter INV2. 【0069】 As mentioned above, since the DC link voltage ratio between the primary inverter INV1 and the secondary inverter INV2 is set to 2:1, the radius of circle C3 is half that of circle C2, and the radius of circle C1 is the sum of the radii of circle C2 and circle C3. 【0070】 Also, I m V is the vector of the current (motor current) of motor M. dq ref This is the vector of the dq axis voltage command values ​​mentioned above, V1 ref V2 is the primary voltage vector command value for switching the primary inverter INV1 mentioned above. ref The secondary voltage vector command value, θ, is used to switch the secondary inverter INV2 as described above. m is the motor current I m This is the phase. 【0071】 The output voltage command generation unit 29 of the control device 6 generates the dq-axis voltage command value V dq ref Therefore, the dq-axis voltage command value V dq refPrimary voltage vector command value V1 for generating (vector) ref and secondary voltage vector command value V2 ref This generates the following. In this case, in order to create a potential difference, the voltage of the secondary inverter INV2 is the opposite of that of the primary inverter INV1, so the secondary voltage vector command value V2 ref A vector with the opposite phase and the primary side voltage vector command value V1 ref The combined vector is the dq-axis voltage command value V dq ref This is the result. Note that Figure 4 shows the motor current I. m This shows the case where the phase changes (d-axis current I d When this flows, the motor current I m (The phase rotates). 【0072】 In this case, the motor current I m When a voltage with the same phase as or opposite phase to the vector is output, active power is output, and when a voltage in the orthogonal direction is output, reactive power is output. In Figures 3 and 4, the primary side voltage vector command value V1 ref is the motor current I m Since it is in the same phase, the primary inverter INV1 outputs only active power. On the other hand, the secondary voltage vector command value V2 ref is the motor current I m Since the phase is perpendicular to the direction of the polarity, the secondary inverter INV2 is in a state where it outputs only reactive power. 【0073】 Here, when the secondary inverter INV2 outputs active power, steady-state powering or regeneration occurs in capacitor C, so in the operating range where high output is required, the secondary voltage V dc2 (The DC link voltage of the secondary inverter) is set to the secondary voltage command value v dc2 ref To keep it in line, a constant zero-sequence current I z It is necessary to flush it. 【0074】 In other words, the power converter 1 of the GND common type dual inverter has a zero-sequence current I zBy flowing this current, it becomes possible to output active power from the secondary inverter INV2. The output of active power from the secondary inverter INV2 increases the output degrees of freedom of the voltage vector, enabling high-power operation. 【0075】 However, zero-sequence current I z Since releasing it leads to increased losses, it is desirable to avoid or minimize it as much as possible. 【0076】 Therefore, in this invention, a high-efficiency operation mode and a high-output operation mode (high-efficiency operation and high-output operation shown in Figure 2) are provided in the output voltage command generation unit 29, and these operation modes are switched and executed depending on the operating area. That is, in this embodiment, the operation mode selection unit 30 of the output voltage command generation unit 29 switches between a high-efficiency operation mode in which the secondary inverter INV2 is stopped or outputs only reactive power with the secondary inverter INV2, and a high-output operation mode in which the secondary inverter INV2 outputs only active power or active power and reactive power with the secondary inverter INV2, thereby achieving a wide operating range and high efficiency. In the following description, the secondary inverter INV2 will be operated in high-efficiency operation mode. 【0077】 (5-1) High-efficiency operation mode Figures 5 and 6 show the voltage vectors of the high-efficiency operation mode and the operating range of each operation mode. Note that Figure 6 shows the motor current I m This shows the case where the phase changes (d-axis current I d When this flows, the motor current I m (The phase rotates). In each figure, circle X1 is the output range for the high-power operation mode, and is basically the same as the linear output range C1 of the GND common type dual inverter power converter 1 described above. Also, oval X2 is the output range for the high-efficiency operation mode, and is the linear output range of the primary side inverter INV1 described above, with the secondary side voltage vector command value V2 ref The d-axis voltage V d It will be a shifted (expanded) shape in that direction. 【0078】 In this high-efficiency operation mode, the output voltage command generation unit 29 generates the motor current I m Refer to the secondary voltage vector command value V2 ref Motor current Im The phase is set to be in a direction orthogonal to the secondary side inverter INV2, and the secondary side voltage vector command value V2 is the orthogonal component. ref It continues to output only reactive power. That is, the primary voltage vector command value V1 is set so that the secondary inverter INV2 outputs only reactive power. ref and secondary voltage vector command value V2 ref Distribute it. 【0079】 In this case, the secondary inverter INV2 outputs only reactive power, so the steady zero-sequence current I z No current flows, zero-sequence current I z This minimizes losses due to [unspecified factor]. However, in this high-efficiency operating mode, the motor current I m Secondary voltage vector command value V2 in a direction perpendicular to the direction. ref Because it can only output and the output voltage vector is limited, the dq-axis voltage command value V is limited to the range of the ellipse X2. dq ref It is not possible to output the region between the oval X2 and the circle X1. In other words, the region between the oval X2 and the circle X1 cannot be output, and the entire linear output range C1 of the power converter 1 of the GND common type dual inverter cannot be output. 【0080】 (5-2) High-Power Operation Mode Therefore, the output voltage command generation unit 29 switches the operation mode to the high-power operation mode when high power is required in the operation range. In the following explanation, we will describe the high-power operation mode in which the secondary inverter INV2 outputs active power and reactive power. 【0081】 The high-power operation mode allows for the output of dq-axis voltage command values ​​V, which cannot be output in the high-efficiency operation mode. dq ref This applies when outputting the following. In high-power operation mode, the dq-axis voltage command value V dq ref Prioritizing the output of the secondary voltage vector command value V2, the secondary inverter INV2 also outputs active power. ref Outputs. 【0082】 Furthermore, in high-power operation mode, the secondary inverter INV2 outputs active power, so the secondary voltage V dc2To control the DC link voltage of the secondary inverter, a constant zero-sequence current I z It is necessary to flow this zero-sequence current I. z To minimize this, the primary voltage vector command value V1 is set so that the active power output from the secondary inverter INV2 is minimized. ref and secondary voltage vector command value V2 ref Distribute it. 【0083】 Furthermore, in high-power operation mode, the secondary voltage vector command value V2 of the secondary inverter INV2 ref Since no restrictions are imposed, the entire output range X1 of the power converter 1 of the GND-common type dual inverter becomes the operating range. 【0084】 This high-power operation mode uses a primary voltage vector command value V1 ref and secondary voltage vector command value V2 ref Due to the high degree of freedom in output, multiple output methods are possible. In this embodiment, we will describe two of these methods: maximum amplitude output control and secondary side inverse phase output control. 【0085】 (5-2-1) Maximum Amplitude Output Control Figures 7 and 8 show the case of maximum amplitude output control. Note that Figure 8 shows the motor current I m This shows the case where the phase changes (d-axis current I d When this flows, the motor current I m (The phase rotates). Maximum amplitude output control is performed using the primary voltage vector command value V1 of the primary inverter INV1, as shown in each figure. ref The length is extended to the output limit circle C2, and the secondary voltage vector command value V2 of the secondary inverter INV2 ref With the length extended to the output limit circle C3, each vector command value V1 ref , V2 ref By manipulating the phase, the dq-axis voltage command value V dq ref The following are combined and output. As can be seen from each figure, the secondary voltage vector command value V2 ref is the motor current I m The phase is not perpendicular to the direction, but rather at a larger angle than the perpendicular direction. 【0086】 At that time, the output voltage command generation unit 29 generates the motor current I m The secondary voltage vector command value V2 is in the opposite phase direction to this. ref The component (the vector component shown by arrow Y1 in Figures 7 and 8) is minimized. In practice, the dq-axis voltage command value V dq ref Draw a circle with the same radius as circle C3, centered on the tip of the arrow, and measure the dq-axis voltage command value V to the intersection point where this circle and circle C2 intersect, whichever intersection point results in a smaller vector component of arrow Y1. dq ref Draw an arrow from the tip, and an arrow in the opposite phase to it, and the secondary voltage vector command value V2 ref This will result in the active power output by the secondary inverter INV2 being minimized, and the zero-sequence current I z This minimizes losses. 【0087】 Figure 9 shows the d-axis voltage V of the primary inverter INV1 when switching from high-efficiency operation mode to high-power operation mode and performing maximum amplitude output control in this high-power operation mode. d1 and q-axis voltage V q1 And the d-axis voltage V of the secondary inverter INV2 d2 and q-axis voltage V q2 And, zero-sequence current I z (I z res This indicates that... 【0088】 In high-efficiency operation mode, as mentioned above, the zero-sequence current I z It is approximately 0A. On the other hand, in high-power operation mode, the zero-sequence current I z While some noise is present, its increase is kept to a minimum. 【0089】 (5-2-2) Secondary Side Reverse Phase Output Control Next, Figure 10 shows the case of secondary side reverse phase output control. In secondary side reverse phase output control, as shown in this figure, the primary side voltage vector command value V1 of the primary side inverter INV1 ref The length is the dq axis voltage command value V dq ref The output is extended to circle C2, which is the output limit, in the same phase, and the dq axis voltage command value V dq ref The difference is the dq axis voltage command value Vdq ref The secondary voltage vector command value V2 of the secondary inverter INV2, which is in the opposite phase to the secondary side inverter. ref In this case as well, the secondary voltage vector command value V2 ref is the motor current I m The phase is not perpendicular to the direction, but rather at an angle greater than the perpendicular direction. 【0090】 In this case as well, the secondary voltage vector command value V2 ref Since the amplitude can be minimized, the motor current I m The secondary voltage vector command value V2 is in the opposite phase direction to this. ref The component (the vector component shown by arrow Y1 in Figure 10) can be minimized. Therefore, the active power output by the secondary inverter INV2 is minimized, and the zero-sequence current I z This minimizes losses. 【0091】 Figure 11 shows the d-axis voltage V of the primary inverter INV1 when switching from high-efficiency operation mode to high-power operation mode and performing secondary-side reverse-phase output control in this high-power operation mode. d1 and q-axis voltage V q1 And the d-axis voltage V of the secondary inverter INV2 d2 and q-axis voltage V q2 And, zero-sequence current I z (I z res This indicates that... 【0092】 In high-efficiency operation mode, as mentioned above, the zero-sequence current I z It is approximately 0A. On the other hand, in high-power operation mode, the zero-sequence current I z Although some flow occurs, it can be seen that its increase is kept to a minimum in this case as well. 【0093】 (5-3) Switching between high-efficiency operation mode and high-output operation mode The operation mode selection unit 30 of the output voltage command generation unit 29 in the embodiment switches between the high-efficiency operation mode and the high-output operation mode as described above, according to the operating region, as shown in Figure 12. In Figure 12, the vertical axis is torque and the horizontal axis is speed, and the operation mode selection unit 30 executes the high-efficiency operation mode in the constant torque operating region at low speeds, and executes the high-output operation mode in the operating region at higher speeds. 【0094】 As described in detail above, in the present invention, by making the power conversion device 1 a GND common type dual inverter, the capacitor C is charged by the secondary inverter INV2 via the motor M from the DC power supply 2, and the AC output is applied to the motor M using the voltage charged to the capacitor C by the secondary inverter INV2, thereby expanding the drivable range in response to changes in input voltage. 【0095】 Furthermore, in the GND-common dual inverter power converter 1, the positive input terminal of the secondary inverter INV2 is not connected to the positive power line 11 of the DC power supply 2, and the negative input terminal of the secondary inverter INV2 is connected to the negative power line 12 of the DC power supply 2. As a result, the secondary inverter INV2 does not become a floating potential, and the reference voltages of the primary inverter INV1 and the secondary inverter INV2 are aligned. 【0096】 This eliminates the need to create a separate gate drive power supply (isolated power supply) for the switching elements 4A to 4F of the secondary inverter INV2, in addition to the gate drive power supply (isolated power supply) for the switching elements 3A to 3F of the primary inverter INV1. This allows the switching elements 3A to 3F of the primary inverter INV1 and the switching elements 4A to 4F of the secondary inverter INV2 to be switched using a common gate drive power supply, thus expanding the drivable range in response to changes in input voltage without the need for a separate boost converter or the like. 【0097】 Furthermore, since it becomes unnecessary to create a separate gate drive power supply for each inverter INV1 and INV2, the increase in component mounting area can be suppressed, enabling miniaturization and cost reduction. This makes it extremely effective for equipment such as automotive electric compressors, where the input voltage changes significantly, there is a strong demand for cost reduction, and the board area is limited, requiring miniaturization of the power conversion device. 【0098】In particular, the present invention provides a control device 6 that controls the primary inverter INV1 and the secondary inverter INV2. This control device 6 switches between a high-efficiency operation mode in which the secondary inverter INV2 outputs only reactive power and a high-output operation mode in which the secondary inverter INV2 outputs both active and reactive power. Furthermore, in the high-output operation mode, the active power output by the secondary inverter INV2 is minimized. As shown in the embodiment, by executing the high-efficiency operation mode in the constant torque operation region of the motor M and the high-output operation mode in the operating speed region higher than the constant torque operation region, the motor can be driven stably over a wide range of operating conditions. 【0099】 Furthermore, in high-power operation mode, the active power output by the secondary inverter INV2 is minimized, so the zero-sequence current I z By minimizing this, it is possible to suppress the increase in losses in high-power operation modes and achieve efficient motor drive across the entire operating range. 【0100】 In addition, in this embodiment, the control device 6 is given the dq-axis voltage command value V dq ref Therefore, the primary voltage vector command value V1 for switching the primary inverter INV1 ref And the secondary voltage vector command value V2 for switching the secondary inverter INV2. ref An output voltage command generation unit 29 is provided to generate the primary voltage vector command value V1 in the high-power operation mode so that the active power output by the secondary inverter INV2 is minimized. ref and secondary voltage vector command value V2 ref The output voltage command generation unit 29 generates the motor current I in high-power operation mode. m The secondary voltage vector command value V2 is in the opposite phase direction to this. ref By minimizing this component, it becomes possible to appropriately suppress the increase in losses. 【0101】 In that case, as described above, the output voltage command generation unit 29 generates the primary side voltage vector command value V1 refand secondary voltage vector command value V2 ref By manipulating their phases while the output limit is set, the motor current I m The secondary voltage vector command value V2 is in the opposite phase direction to this. ref By implementing maximum amplitude output control that minimizes the component of the motor current I, the motor current that outputs active power will be reduced. m The secondary voltage vector command value V2 is in the opposite phase direction to this. ref Minimize the component of zero-sequence current I z This minimizes the increase in losses, thereby preventing further growth. 【0102】 Furthermore, as mentioned above, the output voltage command generation unit 29 generates the primary side voltage vector command value V1 ref The dq axis voltage command value V dq ref With the phase the same and the output limit reached, the secondary voltage vector command value V2 ref The dq axis voltage command value V dq ref By making it out of phase, the motor current I m The secondary voltage vector command value V2 is in the opposite phase direction to this. ref Even if secondary-side reverse-phase output control is implemented to minimize the component of the motor current I that outputs active power, m The secondary voltage vector command value V2 is in the opposite phase direction to this. ref Minimize the component of zero-sequence current I z This minimizes the increase in losses, thereby preventing further growth. 【0103】 In this embodiment, the secondary inverter INV2 is configured to output only reactive power in high-efficiency operation mode. However, the system is not limited to this configuration, and the secondary inverter INV2 may be stopped in high-efficiency operation mode. In that case, the motor current I m The current will flow through the freewheeling diode 10. 【0104】 Furthermore, although the high-power operation mode was described in the embodiment as an example in which the secondary inverter INV2 outputs both active and reactive power, it is not limited to this, and in the high-power operation mode, the secondary inverter INV2 may output only active power. 【0105】Furthermore, in high-power operation mode, the aforementioned maximum amplitude output control and secondary side inverse phase output control may be switched and executed. In that case, the operation mode selection unit 30 of the output voltage command generation unit 29 compares the calculated value by maximum amplitude output control and the calculated value by secondary side inverse phase output control, and determines the motor current I m The secondary voltage vector command value V2 is in the opposite phase direction to this. ref The system will select and execute the option that results in a smaller component (Y1). 【0106】 Furthermore, although the switching element described in the examples consists of an IGBT, a MOSFET may also be used. In addition, the specific configurations and numerical values ​​shown in the examples are not limited to those and can be modified without departing from the spirit of the present invention. 【0107】 1 Power converter 2 DC power supply 3A-3F, 4A-4F Switching element 6 Control device 11 Positive power line 12 Negative power line 21 Speed ​​control unit 22 dq axis current control unit 24 Primary modulation unit 26 Secondary modulation unit 27 Secondary voltage control unit 28 Z axis current control unit 29 Output voltage command generation unit 30 Operating mode selection unit C Capacitor INV1 Primary inverter INV2 Secondary inverter M Motor

Claims

1. A power conversion device comprising a primary inverter connected to one end of an open-ended winding of a motor, and a secondary inverter connected to the other end of the winding, wherein the differential voltage between the primary inverter and the secondary inverter is applied to the motor, wherein the primary inverter is connected to a DC power supply, the secondary inverter is connected to a capacitor, the negative power lines of the primary inverter and the secondary inverter are shared, and the device comprises a control device for controlling the primary inverter and the secondary inverter, wherein the control device switches between a high-efficiency operating mode in which the secondary inverter is stopped or outputs only reactive power, and a high-output operating mode in which the secondary inverter outputs only active power or active power and reactive power, and in the high-output operating mode, minimizes the active power output by the secondary inverter.

2. The power conversion device according to claim 1, characterized in that the control device executes the high-efficiency operation mode in the constant torque operation region of the motor and executes the high-output operation mode in the operation region at a speed higher than the constant torque operation region.

3. The power conversion device according to claim 1, wherein the primary inverter and the secondary inverter are each composed of a plurality of switching elements, the positive input terminal of the primary inverter is connected to the positive power line of the DC power supply, the negative input terminal of the primary inverter is connected to the negative power line of the DC power supply, the output terminal of the primary inverter is connected to one end of the winding, the output terminal of the secondary inverter is connected to the other end of the winding, the capacitor is connected between the positive and negative input terminals of the secondary inverter, the positive input terminal of the secondary inverter is not connected to the positive power line of the DC power supply, the negative input terminal of the secondary inverter is connected to the negative power line of the DC power supply, and the power conversion device according to claim 1 is characterized in that it generates an AC output from the DC power supply by switching each of the switching elements with the control device.

4. The power conversion device according to claim 1, wherein the control device has an output voltage command generation unit that generates a primary voltage vector command value for switching the primary inverter and a secondary voltage vector command value for switching the secondary inverter from a dq axis voltage command value, and the output voltage command generation unit generates the primary voltage vector command value and the secondary voltage vector command value such that the active power output by the secondary inverter is minimized in the high-power operation mode.

5. The power conversion device according to claim 4, characterized in that the output voltage command generation unit minimizes the component of the secondary voltage vector command value in a direction opposite in phase to the motor current in the high-power operation mode.

6. The power conversion device according to claim 5, characterized in that the output voltage command generation unit performs maximum amplitude output control by manipulating the phases of the primary voltage vector command value and the secondary voltage vector command value with the primary voltage vector command value and the secondary voltage vector command value as output limits, thereby minimizing the component of the secondary voltage vector command value that is in the opposite phase to the motor current.

7. The power conversion device according to claim 5, characterized in that the output voltage command generation unit performs secondary reverse-phase output control, which minimizes the component of the secondary voltage vector command value that is in the opposite phase to the motor current by setting the primary voltage vector command value to be in the same phase as the dq-axis voltage command value and to the output limit, and setting the secondary voltage vector command value to be in the opposite phase to the dq-axis voltage command value.

8. The power conversion device according to claim 5, wherein the output voltage command generation unit has a maximum amplitude output control that minimizes the component of the secondary voltage vector command value in the opposite phase to the motor current by manipulating the phases of the primary voltage vector command value and the secondary voltage vector command value while setting them to output limits, and a secondary reverse phase output control that minimizes the component of the secondary voltage vector command value in the opposite phase to the motor current by setting the primary voltage vector command value to the same phase as the dq axis voltage command value and setting it to output limits, and setting the secondary voltage vector command value to the opposite phase to the dq axis voltage command value, and is characterized in that it selects and executes the maximum amplitude output control or the secondary reverse phase output control that reduces the component of the secondary voltage vector command value in the opposite phase to the motor current.

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