Power conversion device, power conversion method, and system

Abstract

The power conversion device (1) includes: a power conversion circuit (10) that generates drive power for a motor (3); an instruction generation section (111) that calculates a voltage instruction based on a frequency instruction, an output current from the power conversion circuit (10) to the motor (3), and an estimated value of an inductance of the motor (3); an error calculation section (115) that calculates a phase error based on the voltage instruction, the output current from the power conversion circuit (10) to the motor (3), and the estimated value of the inductance; an instruction correction section (116) that corrects a phase of the voltage instruction based on the phase error; and a PWM control section (117) that controls the power conversion section (10) so that the drive power follows the voltage instruction whose phase is corrected by the instruction correction section (116).

Description

Technical Field

[0001] This disclosure relates to power conversion devices, power conversion methods, and systems. Background Technology

[0002] Patent Document 1 discloses the following control method: using an estimated rotor pole position signal and a rotor speed estimation signal obtained by calculation based on the internal signal of the control device of the IPM motor, the armature rotation magnetic field and rotor speed of the IPM motor are controlled.

[0003] Existing technical documents

[0004] Patent documents

[0005] Patent document 1: Japanese Patent No. 4228651. Summary of the Invention

[0006] The problem that the invention aims to solve

[0007] This disclosure provides an effective power conversion device, power conversion method, and system for improving the robustness of motor control in response to inductance variations at the power supply destination, including the electric motor.

[0008] means for solving problems

[0009] One aspect of this disclosure relates to a power conversion device, comprising: a power conversion unit that generates drive power for a motor; a command generation unit that calculates a voltage command based on a frequency command, an output current from the power conversion unit to the motor, and an estimated value of the motor's inductance; an error calculation unit that calculates a phase error based on the voltage command, the output current from the power conversion unit to the motor, and an estimated value of the inductance; a command correction unit that corrects the phase of the voltage command based on the phase error; and a control unit that controls the power conversion unit to cause the drive power to follow the voltage command whose phase has been corrected by the command correction unit.

[0010] Another aspect of this disclosure relates to a power conversion method that generates drive power for a motor via a power conversion unit. The power conversion method includes: calculating a voltage command based on a frequency command, an output current from the power conversion unit to the motor, and an estimated value of the motor's inductance; calculating a phase error based on the voltage command, the output current from the power conversion unit to the motor, and the estimated value of the inductance; correcting the phase of the voltage command based on the phase error; and controlling the power conversion unit to make the drive power follow the phase-corrected voltage command.

[0011] Another aspect of this disclosure relates to a system comprising: the aforementioned power conversion device; an electric motor; a filter for reducing noise components contained in the output of the power conversion unit; and a step-up transformer for boosting the output of the power conversion unit and supplying it to the electric motor.

[0012] Invention Effects

[0013] According to this disclosure, an effective power conversion device, power conversion method, and system can be provided to improve the robustness of motor control in response to inductance changes at the power supply destination, including the electric motor. Attached Figure Description

[0014] Figure 1 This is a block diagram illustrating the structure of a power conversion device.

[0015] Figure 2 This is a schematic diagram illustrating a fixed coordinate system and a rotating coordinate system.

[0016] Figure 3 This is a graph showing the gain distribution.

[0017] Figure 4 This is a block diagram illustrating the hardware structure of the control circuit.

[0018] Figure 5 This is a flowchart illustrating the power conversion process.

[0019] Figure 6 This is a block diagram representing a modified example of a control circuit.

[0020] Figure 7 This is a flowchart illustrating a variation of the power conversion process.

[0021] Figure 8 This is a schematic diagram illustrating a system with a power conversion device.

[0022] Figure 9 This is a schematic diagram showing a modified example of the control circuit.

[0023] Figure 10 This is a flowchart illustrating a variation of the power conversion process.

[0024] Figure 11 This is a flowchart illustrating the process of deriving control parameters. Detailed Implementation

[0025] Hereinafter, the embodiments will be described in detail with reference to the accompanying drawings. In the description, the same symbols are used to mark the same elements or elements with the same function, and repeated descriptions are omitted.

[0026] Figure 1 The power conversion device 1 shown is a device that performs power conversion between the power source 2 and the motor 3. The power source 2 is, for example, a three-phase AC power source. Specific examples of the power source 2 include a three-phase AC power system, a three-phase AC generator, an uninterruptible power supply, etc.

[0027] The electric motor 3 is a synchronous motor that operates by supplying alternating current (e.g., three-phase alternating current). The electric motor 3 can also be a synchronous motor with salient polarity. Salient polarity means that the inductance of the electric motor 3 relative to the direction of the magnetic poles of the mover is different from the inductance of the electric motor 3 relative to the direction of the current perpendicular to the magnetic poles. Specific examples of synchronous motors with salient polarity include PMA (Permanent Magnet Assistance) motors, IPM (Interior Permanent Magnet) motors, and synchronous reluctance motors. The electric motor 3 can also be a synchronous motor without salient polarity. Specific examples of synchronous motors without salient polarity include SPM (Surface Permanent Magnet) motors.

[0028] The electric motor 3 can be a fixed-coil type with coils on the stator or a movable-coil type with coils on the mover. Furthermore, the electric motor 3 can be either a rotary type or a linear type. The following description focuses on the rotary type of the electric motor 3; therefore, the operating speed of the electric motor 3 will be referred to as the "rotational speed." "Rotational speed" refers to the rotational speed of the electric motor 3.

[0029] The power conversion device 1 includes a power conversion circuit 10 and a control circuit 100. The power conversion circuit 10 (power conversion section) performs power conversion between the power source 2 and the motor 3, generating AC power for driving the motor 3. For example, the power conversion circuit 10 converts AC power (hereinafter referred to as "power source power") from the power source 2 into AC power (hereinafter referred to as "drive power") for driving the motor 3 and supplies it to the motor 3. As an example, the power conversion circuit 10 includes a rectifier circuit 11, a smoothing capacitor 12, an inverter circuit 13, and a current sensor 14. The rectifier circuit 11, for example, is a diode bridge circuit or a PWM converter circuit, converting the power source power into DC power. The smoothing capacitor 12 smooths the DC power.

[0030] The inverter circuit 13 performs the power conversion between the aforementioned DC power and the aforementioned drive power. For example, in the power operation state, the inverter circuit 13 converts DC power into drive power to supply the motor 3, and in the regenerative state, it converts the power generated by the motor 3 into DC power. Furthermore, the power operation state refers to the state in which the motor 3 operates using the drive power supplied from the inverter circuit 13, and the regenerative state refers to the state in which the motor 3 supplies the inverter circuit 13 with the generated power corresponding to the operation.

[0031] For example, the inverter circuit 13 has multiple switching elements 15, and the aforementioned power conversion is performed by switching the multiple switching elements 15 on / off. The switching elements 15 are, for example, power MOSFETs (Metal Oxide Semiconductor Field Effect Transistors) or IGBTs (Insulated Gate Bipolar Transistors), which are switched on / off according to a gate drive signal.

[0032] Current sensor 14 detects the current flowing between inverter circuit 13 and motor 3. For example, current sensor 14 can be configured to detect the current of all three phases (U phase, V phase, and W phase) of three-phase AC, or it can be configured to detect the current of any two phases of three-phase AC. Since the sum of the currents of U phase, V phase, and W phase is zero as long as zero-phase current is not generated, information about the current of all three phases can be obtained even when detecting the current of two phases.

[0033] The structure of the power conversion circuit 10 shown above is just one example. The structure of the power conversion circuit 10 can also be modified as long as it can generate drive power for the motor 3. For example, the rectifier circuit 11 can also be a thyristor converter circuit or a matrix converter circuit that converts AC power to DC power. The power conversion circuit 10 can also be a matrix converter circuit that performs bidirectional power conversion between power supply and drive power without DC conversion. When the power supply is DC power, the power conversion circuit 10 may not have a rectifier circuit 11.

[0034] The control circuit 100 is configured to calculate a voltage command based on a frequency command, an output current from the power conversion circuit 10 to the motor 3, and an estimated value of the inductance of the motor 3; calculate a phase error based on the voltage command, the output current from the power conversion circuit 10 to the motor 3, and an estimated value of the inductance; correct the phase of the voltage command based on the phase error; and control the power conversion circuit 10 such that the drive power follows the phase-corrected voltage command.

[0035] For example, the control circuit 100, as a functional structure (hereinafter referred to as a "functional block"), includes an instruction generation unit 111, a voltage calculation unit 112, a phase calculation unit 113, a current acquisition unit 114, an error calculation unit 115, an instruction correction unit 116, and a PWM control unit 117. Since each functional block is a component of the control circuit 100, the processing performed by each functional block is equivalent to the processing performed by the control circuit 100.

[0036] The instruction generation unit 111 calculates the voltage instruction based on the frequency instruction, the output current from the power conversion circuit 10 to the motor 3, and an estimated value of the inductance of the motor 3. The frequency instruction is an instruction that determines the target value of the frequency of the driving power. The frequency instruction can be the target value of the driving power frequency itself, or a value that indirectly determines the target value. For example, the frequency instruction can also be the target value of the rotational speed (synchronous speed) of the motor 3. The estimated value refers to a value not based on real-time measured results. The estimated value can be a design value not based on actual measurements, or a value calculated through simulation. Alternatively, the estimated value can be a value measured beforehand. The voltage instruction is, for example, the target value of the voltage output from the power conversion circuit 10 to the motor 3.

[0037] For example, the instruction generation unit 111 includes an induced voltage calculation unit 121 and a voltage instruction calculation unit 122 as further subdivided functional blocks. The induced voltage calculation unit 121 calculates the induced voltage (hereinafter referred to as the "induced voltage target value") corresponding to the frequency instruction according to a predetermined instruction distribution. For example, the instruction distribution is predetermined such that the induced voltage target value changes by an amount proportional to the change in the frequency instruction. Alternatively, the instruction distribution may be determined so that the induced voltage target value is constant if the frequency instruction is above a predetermined upper limit.

[0038] The voltage command calculation unit 122 uses the target value of the induced voltage calculated by the induced voltage calculation unit 121 to calculate the voltage command based on the equivalent circuit of the motor 3. For example, the voltage command calculation unit 122 calculates the voltage command vector in a coordinate system (hereinafter referred to as the "rotating coordinate system") that rotates synchronously with the frequency command. The rotating coordinate system rotates relative to the coordinate system (hereinafter referred to as the "fixed coordinate system") that is fixed on the stator of the motor 3.

[0039] As a concrete example of a fixed coordinate system, the αβ coordinate system can be cited. The origin of the αβ coordinate system is located at the rotational center axis of the mover of the motor 3. The α-axis is a coordinate axis whose direction is aligned with, for example, the direction of the magnetomotive force generated by the current flowing through one of the three-phase windings of the stator. The β-axis is a coordinate axis perpendicular to the α-axis and the rotational center axis of the mover of the motor 3.

[0040] As a concrete example of a rotating coordinate system, we can give the following: Figure 2 The γδ coordinate system is shown. The origin of the γδ coordinate system is located at the rotation center axis of the mover of motor 3. The γδ coordinate system is a coordinate system that rotates synchronously with the frequency of the output voltage. For example, during startup, the γ axis coincides with the α axis of the fixed coordinate system, i.e., the αβ coordinate system described later, and rotates synchronously with the startup and frequency commands. The δ axis is a coordinate axis perpendicular to the γ axis and the rotation center axis of the mover of motor 3. Various quantities related to control are calculated based on the γδ coordinate system.

[0041] In contrast, there is a dq coordinate system that is fixed and rotates on the mover (rotor) of the motor 3. The origin of the dq coordinate system is located at the rotation center axis of the mover of the motor 3. The d-axis is a coordinate axis with the magnetic pole direction of the mover of the motor 3 (from the S pole of the permanent magnet towards the N pole) as the positive direction. The q-axis is a coordinate axis perpendicular to the d-axis and the rotation center axis of the mover of the motor 3.

[0042] For example, the voltage command calculation unit 122 calculates the γ-axis voltage command Vγ, which is the γ-axis component of the voltage command vector V, and the δ-axis voltage command Vδ, which is the δ-axis component of the voltage command vector V. The voltage command calculation unit 122 performs non-interference compensation on the induced voltage target value based on the output current from the power conversion circuit 10 to the motor 3, the winding voltage drop of the winding resistance of the motor 3, and the estimated values ​​of the rotational speed and inductance of the motor 3, and calculates the γ-axis voltage command Vγ and the δ-axis voltage command Vδ.

[0043] As an example, the voltage command calculation unit 122 calculates the γ-axis voltage command Vγ and the δ-axis voltage command Vδ using the following formula.

[0044] Vγ=R·iγ-ω·Lδ·iδ……(1)

[0045] Vδ=ω·Lγ·iγ+R·iδ+E……(2)

[0046] In equations (1) and (2), iγ is the γ-axis component of the output current vector (hereinafter referred to as "γ-axis current"). iδ is the δ-axis component of the output current vector (hereinafter referred to as "δ-axis current"). R is the winding resistance of motor 3. ω is the rotational speed of the mover, derived based on the frequency command. Lγ is the inductance of motor 3 relative to the γ-axis current (hereinafter referred to as "γ-axis inductance"). Lδ is the inductance of motor 3 relative to the δ-axis current (hereinafter referred to as "δ-axis inductance"). E is the target value of the induced voltage, for example, determined based on the frequency command using the set V / f mode.

[0047] The voltage command calculation unit 122 uses the γ-axis current iγ and δ-axis current iδ calculated by the current acquisition unit 114 (described later) as the γ-axis current iγ and δ-axis current iδ for calculating the γ-axis voltage command Vγ and δ-axis voltage command Vδ. Alternatively, the voltage command calculation unit 122 may use one of the γ-axis current iγ and δ-axis current iδ used for calculating the γ-axis voltage command Vγ and δ-axis voltage command Vδ as the value calculated by the current acquisition unit 114, and use the other as a predetermined command value.

[0048] For example, the voltage command calculation unit 122 may use the delta-axis current iδ, which is used to calculate the γ-axis voltage command Vγ and the delta-axis voltage command Vδ, as the value calculated by the current acquisition unit 114, and use the γ-axis current iγ as a predetermined command value. In this case, the command generation unit 111 may also have a current command generation unit 123. The current command generation unit 123 generates the command value of the γ-axis current iγ. The current command generation unit 123 may also generate a negative γ-axis current iγ as a command for reluctance power (power caused by salient polarity). The current command generation unit 123 may also generate the γ-axis current iγ based on the frequency command. For example, the current command generation unit 123 may increase the absolute value of the γ-axis current iγ based on the increase of the frequency command. In addition, increasing the absolute value of the γ-axis current iγ according to the increase of the frequency command also includes the following cases: within the specified range of the frequency command, the absolute value of the γ-axis current iγ is increased according to the increase of the frequency command, and the absolute value of the γ-axis current iγ is kept constant in other ranges.

[0049] Return to Figure 1 The voltage calculation unit 112 calculates the absolute value of the voltage command generated by the command generation unit 111. For example, the voltage calculation unit 112 calculates the square root of the sum of the squares of the γ-axis voltage command Vγ and the δ-axis voltage command Vδ calculated by the voltage command calculation unit 122 as the absolute value of the voltage command vector V.

[0050] The phase calculation unit 113 calculates the phase of the voltage command in the fixed coordinate system. For example, the phase calculation unit 113 calculates the phase angle of the voltage command vector V relative to the α-axis of the αβ coordinate system. For example, based on the frequency command, the phase calculation unit 113 calculates the phase angle θf of the γδ coordinate system relative to the αβ coordinate system (e.g., the phase angle of the γ-axis relative to the α-axis) , and based on the γ-axis voltage command Vγ and the δ-axis voltage command Vδ, calculates the phase angle θv of the voltage command vector V in the γδ coordinate system (the phase angle of the voltage command vector V relative to the γ-axis) , and sums the phase angle θf and the phase angle θv to calculate the phase angle θ of the voltage command vector V relative to the α-axis (refer to...). Figure 2 ).

[0051] The current acquisition unit 114 acquires current information from the current sensor 14. For example, the current acquisition unit 114 performs a three-phase to two-phase conversion and a rotating coordinate conversion on the current information acquired from the current sensor 14, and calculates the γ-axis current iγ and the δ-axis current iδ. This rotating coordinate conversion requires the phase of the rotating coordinate system relative to the fixed coordinate system. For example, the current acquisition unit 114 uses the phase angle θf calculated by the phase calculation unit 113 for the rotating coordinate conversion.

[0052] The error calculation unit 115 calculates the phase error of the voltage command based on the voltage command, the output current from the power conversion circuit 10 to the motor 3, and the estimated value of the inductance. The phase error is the angular error between the γδ coordinate system and the dq coordinate system.

[0053] For example, the error calculation unit 115 calculates the induced voltage vector based on the voltage command vector, the output current vector from the power conversion circuit 10 to the motor 3, the winding resistance of the motor 3, and the estimated value of the inductance, and calculates the phase error based on the phase of the induced voltage vector. For example, the error calculation unit 115 calculates the phase angle of the induced voltage vector in the γδ coordinate system relative to the δ axis as the phase error. As an example, the error calculation unit 115 takes the rotation direction of the γδ coordinate system relative to the αβ coordinate system as the positive direction and calculates the phase error using the following formula.

[0054] Δθ=-tan -1 (εd / εq)……(3)

[0055] εd=Vγ-R·iγ+ω·Lδ·iδ......(4)

[0056] εq=Vδ-ω·Lγ·iγ-R·iδ......(5)

[0057] In equations (3), (4) and (5), Δθ is the phase error, εd is the γ-axis component of the induced voltage vector, and εq is the δ-axis component of the induced voltage vector.

[0058] As illustrated above, the principle that the phase angle of the induced voltage vector in the γδ coordinate system relative to the δ axis can be used as the phase error is explained below. When the γ axis coincides with the d-axis, which is the positive direction of the magnetic poles of the mover of motor 3, the induced voltage would normally only be generated in the δ-axis direction. However, when the γ axis and d-axis are not aligned, the induced voltage vector tilts relative to the δ axis, resulting in this error. Therefore, it can be said that the phase angle of the induced voltage vector relative to the δ axis represents the aforementioned phase error. Furthermore, this phase error is mainly due to errors in the estimation of the inductance. In particular, in synchronous reluctance motors, compared to permanent magnet motors, the error in estimating the inductance tends to be larger because the variation in the inductance corresponding to the output current is greater.

[0059] Alternatively, the current acquisition unit 114 can also use the phase angle calculated by the phase calculation unit 113 plus the phase error Δθ to perform the rotational coordinate transformation.

[0060] The command correction unit 116 corrects the phase of the voltage command based on the phase error calculated by the error calculation unit 115. For example, the command correction unit 116 may also correct the phase of the voltage command by adding the correction amount based on the phase error calculated by the error calculation unit 115 to the phase calculated by the phase calculation unit 113 (hereinafter referred to as "the phase before correction"). Hereinafter, the phase of the corrected voltage command will be referred to as "the phase after correction". The command correction unit 116 may also calculate the above-mentioned correction amount (hereinafter referred to as "the correction amount based on proportional calculation") by multiplying the phase error calculated by the error calculation unit 115 by a predetermined proportional gain.

[0061] The command correction unit 116 can also correct the phase of the voltage command based on the integral value of the phase error. For example, the command correction unit 116 can also calculate the correction amount based on the integral value of the phase error calculated by the error calculation unit 115. The command correction unit 116 can also multiply the integral value of the phase error calculated by the error calculation unit 115 by a predetermined proportional gain to calculate the correction amount (hereinafter referred to as "correction amount based on integral operation"). The command correction unit 116 can also add the correction amount based on proportional operation and the correction amount based on integral operation to the phase before correction to calculate the corrected phase.

[0062] The command correction unit 116 can also calculate the corrected phase by adding the correction amount calculated as described above, after applying low-pass filtering, to the phase before correction. Alternatively, the command correction unit 116 can apply low-pass filtering to the corrected phase to correct the phase of the voltage command.

[0063] The PWM control unit 117 (control unit) controls the power conversion circuit 10 to make the drive power follow the voltage command whose phase has been corrected by the command correction unit 116. Making the drive power follow the voltage command means making the voltage in the drive power follow the voltage command. For example, the PWM control unit 117 switches the on / off state of multiple switching elements 15 of the inverter circuit 13 to output a voltage consistent with the voltage command determined based on the absolute value calculated by the voltage calculation unit 112 and the corrected phase calculated by the command correction unit 116 to the motor 3.

[0064] The control circuit 100 may also be configured to change the estimated value of the inductance based on the value of the output current from the power conversion circuit 10 to the motor 3. For example, the control circuit 100 may also have an inductance storage unit 131 and an inductance estimation unit 132.

[0065] The inductor storage unit 131 stores the aforementioned inductance distribution. As described above, the inductance distribution is a distribution representing the relationship between the value of the output current and the value of the inductance. The inductance distribution is set such that the inductance varies according to the value of the output current. The inductance distribution is set such that at least the inductance corresponding to the first output current value and the inductance corresponding to the second output current value are different from each other.

[0066] The inductor storage unit 131 can also store the inductance distribution of the γ-axis inductor Lγ and the inductance distribution of the δ-axis inductor Lδ, respectively. In addition, the inductor storage unit 131 can also store the inductance distribution that varies according to the value of the γ-axis current iγ or the δ-axis current iδ for the γ-axis inductor Lγ and the δ-axis inductor Lδ, respectively.

[0067] Furthermore, the inductance storage unit 131 can also store the three-dimensional inductance distribution that varies according to the values ​​of the γ-axis current iγ and the δ-axis current iδ for the γ-axis inductance Lγ and the δ-axis inductance Lδ, respectively. The inductance storage unit 131 can store the inductance distribution as a function or as a point sequence of data.

[0068] The inductance estimation unit 132 derives an estimated value of the inductance based on the output current value (e.g., γ-axis current iγ, δ-axis current iδ) acquired (calculated) by the current acquisition unit 114 and the inductance distribution stored in the inductance storage unit 131. For example, the inductance estimation unit 132 derives the inductance value corresponding to the output current value from the inductance distribution as the estimated value of the inductance. When the inductance distribution is point data, the inductance estimation unit 132 can derive the inductance value corresponding to the output current value through interpolation of the point data.

[0069] When the control circuit 100 has an inductance storage unit 131 and an inductance estimation unit 132, the voltage command calculation unit 122 calculates the voltage command based on the estimated value of the inductance derived from the inductance estimation unit 132. The error calculation unit 115 calculates the phase error based on the estimated value of the inductance derived from the inductance estimation unit 132.

[0070] The control circuit 100 may also include a distribution generation unit 134. The distribution generation unit 134 generates an inductance distribution based on user input at least two points specifying the inductance distribution and stores it in an inductance storage unit 131. Each of the aforementioned at least two points includes a combination of the output current value and the inductance distribution value. The user input is input from the user of the power conversion device 1, for example, via an input device 300 described later. The distribution generation unit 134 may also automatically set the inductance distribution based on the stored data, while changing the estimated inductance value, corresponding to the output current, the estimated inductance value, and the phase error, thereby reducing the phase error.

[0071] The control circuit 100 can also be configured to suppress the phase correction of the voltage command by the error calculation unit 115 when the rotational speed of the motor 3 is a second speed higher than the first speed, compared to when the rotational speed of the motor 3 is a first speed. For example, the control circuit 100 also includes a gain storage unit 141 and a gain calculation unit 142. The gain storage unit 141 stores a gain distribution in which the gain is smaller when the rotational speed of the motor 3 is a second speed higher than the first speed, compared to the gain when the rotational speed of the motor 3 is the first speed. The first speed and the second speed can be any speed as long as the second speed is higher than the first speed.

[0072] Figure 3 This is a graph showing the gain distribution. Figure 3 In the diagram, the horizontal axis represents the frequency of the driving power. Since the frequency of the driving power is approximately proportional to the rotational speed of motor 3, it can also be said that the horizontal axis represents the rotational speed of motor 3. The vertical axis represents the magnitude of the gain. Figure 3 In this circuit, when the frequency of the driving power is below a specified frequency threshold ft, the gain is constant. If the frequency exceeds the frequency threshold ft, the gain decreases as the frequency increases (i.e., as the rotational speed of motor 3 increases).

[0073] In this distribution, the gain is smaller when the frequency is greater than the frequency threshold ft (when the rotational speed of motor 3 is the second speed) than the gain is smaller when the frequency is less than the frequency threshold ft (when the rotational speed of motor 3 is the first speed). For example, the gain K1 corresponding to a frequency f1 that is smaller than the frequency threshold ft is smaller than the gain K2 corresponding to a frequency f2 that is greater than the frequency threshold ft. The gain storage unit 141 can store the gain distribution as a function or as a point sequence of data.

[0074] The gain calculation unit 142 calculates the gain based on the rotational speed of the motor 3 and the gain distribution. The gain calculation unit 142 can also calculate the gain based on the frequency command and the gain distribution. Since the rotational speed of the motor 3 is approximately proportional to the frequency command, calculating based on the frequency command is equivalent to calculating based on the rotational speed of the motor 3. For example, the gain calculation unit 142 calculates the gain corresponding to the frequency command in the gain distribution. When the gain distribution is point data, the gain calculation unit 142 can also calculate the gain corresponding to the frequency command by interpolating the point data.

[0075] When the control circuit 100 has a gain storage unit 141 and a gain calculation unit 142, the command correction unit 116 can also correct the phase of the voltage command by multiplying the gain calculated by the gain calculation unit 142 by a correction amount based on the phase error. Additionally, the control circuit 100 may also have a gain generation unit (not shown) that generates a gain distribution based on user input, etc., and stores it in the gain storage unit 141. The gain generation unit can be configured to automatically generate a gain distribution based on stored data.

[0076] Figure 4 This is a block diagram illustrating the hardware structure of the control circuit 100. For example... Figure 4 As shown, the control circuit 100 includes at least one processor 191, a memory 192, a storage device 193, and a switch control circuit 194. The storage device 193 has a computer-readable storage medium, such as a hard disk. The storage medium can be a removable medium such as non-volatile semiconductor memory, a disk, or an optical disk. The storage device 193 stores a program for causing the control circuit 100 to perform the following steps: calculating a voltage command based on a frequency command, an estimated value of the output current from the power conversion circuit 10 to the motor 3, and an estimated value of the inductance of the motor 3; calculating a phase error based on the voltage command, the output current, and the estimated value of the inductance; correcting the phase of the voltage command based on the phase error; and controlling the power conversion circuit 10 so that the drive power follows the phase-corrected voltage command.

[0077] Memory 192 temporarily stores the program loaded from memory 193 and the calculation results of processor 191. Processor 191 executes the program in cooperation with memory 192, thereby forming the aforementioned functional blocks. Switch control circuit 194 generates the aforementioned gate drive signal according to instructions from processor 191 and outputs it to inverter circuit 13. Input / output port 195 performs electrical signal input and output between current sensor 14, display device 200, and input device 300 according to instructions from processor 191.

[0078] Display device 200 and input device 300 serve as the user interface of power conversion device 1. Display device 200 includes, for example, an LCD monitor for displaying information to the user. Input device 300 includes, for example, a keyboard for acquiring user input. Display device 200 and input device 300 can be integrated, such as a so-called touch panel. Display device 200 and input device 300 can be located in external devices connected to power conversion device 1, or they can be assembled within power conversion device 1.

[0079] Furthermore, the control circuit 100 is not limited to having its functions configured through a program. For example, the control circuit 100 may be configured with at least some of its functions using dedicated logic circuits or ASICs (Application Specific Integrated Circuits) that integrate these.

[0080] [Electrical Conversion Process]

[0081] Below, as an example of a power conversion method for generating drive power for the motor 3 via the power conversion circuit 10, the control process of the power conversion circuit 10 performed by the control circuit 100 is illustrated. This process includes: calculating a voltage command based on a frequency command, the output current from the power conversion circuit 10 to the motor 3, and an estimated value of the inductance of the motor 3; calculating a phase error based on the voltage command, the output current from the power conversion circuit 10 to the motor 3, and an estimated value of the inductance of the motor 3; correcting the phase of the voltage command based on the phase error; and controlling the power conversion circuit 10 so that the drive power follows the phase-corrected voltage command.

[0082] For example, control circuit 100 repeats a predetermined control cycle. Figure 5 The steps S01 to S08 are shown. In step S01, the induced voltage calculation unit 121 calculates the target value of the induced voltage corresponding to the frequency command according to a predetermined command distribution.

[0083] In step S02, the inductance estimation unit 132 derives an estimated value of the inductance based on the value of the output current (e.g., γ-axis current iγ, δ-axis current iδ) acquired (calculated) by the current acquisition unit 114 in the previous control cycle and the inductance distribution stored in the inductance storage unit 131.

[0084] In step S03, the voltage command calculation unit 122 adds or subtracts voltage drop, speed electromotive force, etc., to the induced voltage target value calculated in step S01 to generate a voltage command. For example, the voltage command calculation unit 122 calculates the γ-axis voltage command Vγ and the δ-axis voltage command Vδ based on the γ-axis current iγ and δ-axis current iδ calculated by the current acquisition unit 114 in the previous control cycle, the winding resistance of the motor 3, the rotational speed of the motor 3 derived from the frequency command, the estimated value of the inductance of the motor 3 derived in step S02, and the induced voltage target value.

[0085] In step S04, the voltage calculation unit 112 calculates the absolute value of the voltage command generated in step S03, and the phase calculation unit 113 calculates the phase of the voltage command in the fixed coordinate system. For example, the phase calculation unit 113 calculates the phase angle θf of the γδ coordinate system relative to the αβ coordinate system based on the frequency command, calculates the phase angle θv of the voltage command vector V in the γδ coordinate system based on the γ-axis voltage command Vγ and the δ-axis voltage command Vδ, and adds the phase angle θf and the phase angle θv to calculate the phase angle θ of the voltage command vector V relative to the α axis.

[0086] In step S05, the command correction unit 116 corrects the phase of the voltage command based on the phase error Δθ calculated by the error calculation unit 115 in the previous control cycle. For example, the command correction unit 116 adds a correction amount based on the phase error to the phase calculated in step S03 (the phase before correction) to correct the phase of the voltage command. In step S05, the gain calculation unit 142 calculates the gain based on the frequency command and the gain distribution. The command correction unit 116 may also correct the phase of the voltage command using a correction amount obtained by multiplying the gain calculated by the gain calculation unit 142 by the correction amount based on the phase error.

[0087] In step S06, the PWM control unit 117 starts controlling the power conversion circuit 10 so that the drive power follows the voltage command whose phase was corrected in step S05 (the corrected voltage command mentioned above).

[0088] In step S07, the current acquisition unit 114 acquires the current information output from the power conversion circuit 10 to the motor 3 according to the corrected voltage command from the current sensor 14, performs three-phase to two-phase conversion and rotating coordinate conversion on the acquired current information, and calculates the γ-axis current iγ and the δ-axis current iδ. The current acquisition unit 114 can use the phase angle θf calculated in step S04 for the above-mentioned rotating coordinate conversion, or it can use the phase angle calculated in step S04 plus the phase error Δθ to obtain the phase angle for the above-mentioned rotating coordinate conversion.

[0089] In step S08, the error calculation unit 115 calculates the phase error of the voltage command based on the voltage command calculated in step S03 (the voltage command before correction mentioned above), the output current (γ-axis current iγ and δ-axis current iδ) calculated in step S07, and the estimated value of the inductance derived in step S02. The output current obtained (calculated) in step S07 is also used in step S02 of the next control cycle. The phase error estimation result from step S08 is used in step S05 of the next control cycle.

[0090] Thus, one control cycle is completed. In one control cycle, step S02 (inductance estimation) can also be performed before step S01 (calculating the target value of the induced voltage). Alternatively, step S02 can be performed after step S07 (acquiring current information). In this case, in step S03 (voltage command calculation), the voltage command calculation unit 122 generates a voltage command based on the inductance estimate derived by the inductance estimation unit 132 in the previous control cycle.

[0091] Step S08 (calculating phase error) can be performed before step S05 (correcting phase). In this case, in step S05, the error calculation unit 115 calculates the phase error based on the voltage command calculated in the previous control cycle and the output current calculated in the previous control cycle.

[0092] [Variation Example]

[0093] Figure 6 This is a block diagram representing a modified example of a control circuit. Figure 6 The control circuit 100A shown differs from the control circuit 100 in its structure for calculating voltage commands based on frequency commands. The control circuit 100A replaces the command generation unit 111 in the control circuit 100 with a command generation unit 151 and adds a speed estimation unit 152.

[0094] The command generation unit 151 calculates the voltage command based on the frequency command, the output current from the power conversion circuit 10 to the motor 3, and an estimated value of the inductance of the motor 3. The command generation unit 151 includes a speed control unit 153, a current control unit 154, and a voltage command calculation unit 155.

[0095] The speed control unit 153 calculates the current command based on the deviation between the target rotational speed of the motor 3 and the rotational speed of the motor 3 (hereinafter referred to as "speed deviation"). For example, the speed control unit 153 performs proportional calculation, proportional / integral calculation, or proportional / integral / differential calculation on the aforementioned speed deviation to calculate the current command. The target rotational speed is, for example, the target rotational speed of the rotating magnetic field generated by the alternating current according to the frequency command. The current command is the target output current value from the power conversion circuit 10 to the motor 3.

[0096] The current control unit 154 calculates the correction voltage based on the deviation between the target output current value and the output current value acquired by the current acquisition unit 114 (hereinafter referred to as "current deviation"). For example, the speed control unit 153 performs proportional calculation, proportional / integral calculation, or proportional / integral / derivative calculation on the aforementioned current deviation to calculate the correction voltage.

[0097] The voltage command calculation unit 155 calculates the voltage command based on the correction voltage calculated by the current control unit 154. For example, the voltage command calculation unit 155 calculates a voltage vector that has been non-interference compensated for by treating the γ-axis component as zero and the δ-axis component as the product of the rotational speed and the speed electromotive force constant of the motor 3, based on the output current from the power conversion circuit 10 to the motor 3, the rotational speed of the motor 3, and the estimated value of the inductance of the motor 3. The voltage command vector is then calculated by adding the correction voltage vector to this voltage vector.

[0098] The above calculations performed by the voltage command calculation unit 155 are, for example, represented by the following formula.

[0099] Vγ=Eγ-ω·Lδ·iδ……(6)

[0100] Vδ=Eδ+ω·(Lγ·iγ+Φ)......(7)

[0101] In equations (6) and (7), Φ is the velocity electromotive force coefficient, Eγ is the γ-axis component of the correction voltage, and Eδ is the δ-axis component of the correction voltage.

[0102] The error calculation unit 115 calculates the phase error of the voltage command based on the voltage command vector, the correction voltage vector, the output current vector from the power conversion circuit 10 to the motor 3, and the estimated value of the inductance. For example, the error calculation unit 115 calculates the induced voltage vector used to calculate the phase error using the following formula.

[0103] εγ=Vγ-Eγ+ω·Lδ·iδ......(8)

[0104] εδ=Vδ-ω·Lγ·iγ-Eδ......(9)

[0105] The speed estimation unit 152 estimates the rotational speed of the motor 3 based on the phase error calculated by the error calculation unit 115. The speed control unit 153 calculates the current command by using the deviation between the target value of the rotational speed of the motor 3 and the rotational speed of the motor 3 estimated by the speed estimation unit 152 as the speed deviation.

[0106] Figure 7 This is a flowchart illustrating the control process of the power conversion circuit 10 performed by the control circuit 100A. The control circuit 100A repeats the process at a predetermined control cycle. Figure 7 The steps S11 to S21 are shown. In step S11, the speed control unit 153 calculates the current command based on the deviation between the target value of the rotational speed of the motor 3 and the rotational speed of the motor 3 estimated by the speed estimation unit 152 in the previous control cycle (the speed deviation mentioned above).

[0107] In step S12, the current control unit 154 calculates the correction voltage based on the deviation between the target output current value and the output current calculated by the current acquisition unit 114 in the previous control cycle (the aforementioned current deviation). In step S13, similar to step S02, the inductance estimation unit 132 derives an estimated value for the inductance.

[0108] In step S14, the voltage command calculation unit 155 calculates the voltage command based on the correction voltage calculated in step S12. For example, the voltage command calculation unit 155 calculates the voltage command based on the output current calculated by the current acquisition unit 114 in the previous control cycle, the rotational speed of the motor 3, the correction voltage calculated in step S12, and the estimated value of the inductance of the motor 3 derived in step S13.

[0109] In step S15, similar to step S04, the voltage calculation unit 112 calculates the absolute value of the voltage command, and the phase calculation unit 113 calculates the phase of the voltage command in the fixed coordinate system. In step S16, similar to step S05, the command correction unit 116 corrects the phase of the voltage command based on the phase error Δθ calculated by the error calculation unit 115 in the previous control cycle. In step S17, similar to step S06, the PWM control unit 117 starts controlling the power conversion circuit 10 to make the drive power follow the corrected voltage command.

[0110] In step S18, similar to step S07, the current acquisition unit 114 acquires the current information output from the power conversion circuit 10 to the motor 3 according to the corrected voltage command from the current sensor 14, performs three-phase two-phase conversion and rotating coordinate conversion on the acquired current information, and calculates the γ-axis current iγ and the δ-axis current iδ.

[0111] In step S19, similar to step S08, the error calculation unit 115 calculates the phase error of the voltage command based on the voltage command before correction calculated in step S14, the output current calculated in step S18, and the estimated value of the inductance derived in step S13. In step S21, the rotational speed of the motor 3 is estimated based on the phase error calculated in step S19.

[0112] The output current calculated in step S18 is also used in step S13 of the next control cycle. The phase error estimation result from step S19 is used in step S16 of the next control cycle. The rotational speed estimation result of motor 3 from step S21 is used in step S11 of the next control cycle.

[0113] Thus, one control cycle is completed. In one control cycle, step S13 (estimating inductance) can also be performed before steps S11 (calculating target current value) and S12 (calculating correction voltage). Alternatively, step S13 can be performed after step S18 (acquiring current information). In this case, in step S14 (calculating voltage command), the voltage command calculation unit 155 calculates the voltage command based on the estimated inductance value derived by the inductance estimation unit 132 in the previous control cycle, based on the correction voltage.

[0114] Step S19 (calculating phase error) can also be performed before step S16 (correcting phase). In this case, in step S19, the error calculation unit 115 calculates the phase error based on the voltage command calculated in the previous control cycle and the output current calculated in the previous control cycle. Step S21 (estimating speed) can also be performed before step S11 (calculating target current value). In this case, in step S21, the rotational speed of the motor 3 is estimated based on the phase error calculated in the previous control cycle.

[0115] As illustrated in the above variation, the command generation unit of the control circuit can be configured to calculate the voltage command based on the frequency command, the output current from the power conversion circuit 10 to the motor 3, and the estimated value of the inductance of the motor 3. The calculation method can be appropriately modified.

[0116] (Effects of this implementation method)

[0117] As described above, the power conversion device 1 includes: a power conversion circuit 10 that generates drive power for the motor 3; a command generation unit 111 that calculates a voltage command based on a frequency command, an output current from the power conversion circuit 10 to the motor 3, and an estimated value of the inductance of the motor 3; an error calculation unit 115 that calculates a phase error based on the voltage command, the output current from the power conversion circuit 10 to the motor 3, and an estimated value of the inductance; a command correction unit 116 that corrects the phase of the voltage command based on the phase error; and a PWM control unit 117 that controls the power conversion circuit 10 so that the drive power follows the voltage command whose phase has been corrected by the command correction unit 116.

[0118] To ensure that the phase of the voltage command follows the operation of the motor 3, information about the inductance of the motor 3 is sometimes used. In this case, if the error in the estimated value of the inductance increases due to changes in inductance, the phase error of the voltage command becomes larger, potentially preventing the desired power (e.g., torque) from being obtained. In contrast, according to this power conversion device 1, the phase error is calculated based on the voltage command, output current, and the estimated value of the inductance, and the phase of the voltage command is corrected based on the phase error. Therefore, it is effective in improving the robustness of the control of the motor 3 against changes in the inductance of the power supply target including the motor 3.

[0119] The error calculation unit 115 can also calculate the induced voltage vector based on the voltage command, the output current from the power conversion circuit 10 to the motor 3, and the estimated value of the inductance, and calculate the phase error based on the phase of the induced voltage vector. In this case, the phase error can be calculated more appropriately.

[0120] The power conversion device 1 further includes: an inductance storage unit 131 that stores the inductance distribution that varies with the value of the output current; and an inductance estimation unit 132 that derives an estimated value of the inductance based on the value of the output current from the power conversion circuit 10 to the motor 3 and the inductance distribution. The command generation unit 111 can calculate a voltage command based on the estimated value of the inductance derived by the inductance estimation unit 132, and the error calculation unit 115 can calculate a phase error based on the estimated value of the inductance derived by the inductance estimation unit 132. In this case, the inductance distribution that varies with the value of the output current can be stored in advance, and the estimated value of the inductance can be derived based on the inductance distribution. Therefore, the error amplification of the estimated value of the inductance is suppressed by changes in the value of the output current. Thus, the robustness of the control of the motor 3 is more effectively improved for changes in the inductance at the power supply destination, including the motor 3.

[0121] The power conversion device 1 may also include a distribution generation unit 134 that generates an inductance distribution based on user input at least two points specifying the inductance distribution. In this case, by having the user set an inductance distribution suitable for the actual motor, the error in the estimated inductance can be suppressed more reliably.

[0122] The command correction unit 116 can also correct the phase of the voltage command based on the integral value of the phase error. In this case, the phase of the motor 3 can be corrected more quickly.

[0123] The power conversion device 1 also includes: a gain storage unit 141 that stores a gain distribution that is smaller than the gain when the motor 3 operates at a first speed compared to the gain when the motor 3 operates at a second speed, where the second speed is higher than the first speed; and a gain calculation unit 142 that calculates the gain based on the motor 3's operating speed and the gain distribution. The command correction unit 116 can also correct the phase of the voltage command by multiplying the gain calculated by the gain calculation unit 142 by a correction amount based on the phase error. If the motor 3's operating speed increases, the room for increasing the absolute value of the voltage command vector (hereinafter referred to as "voltage amplitude") decreases. Therefore, it is difficult to adjust the voltage amplitude appropriately in conjunction with the phase correction of the voltage command. Therefore, the correction of the voltage command's phase can actually reduce the power of the motor 3. In contrast, according to the structure that reduces the correction gain of the phase error when the motor 3's operating speed is high, the reduction in the power of the motor 3 accompanying the phase correction of the voltage command can be suppressed.

[0124] The electric motor 3 can be a salient-polarity synchronous motor, and the command generation unit 111 can also calculate a voltage command for generating drive power corresponding to the salient-polarity synchronous motor. In a salient-polarity synchronous motor, the change in inductance is larger with respect to changes in output current compared to a non-salient-polarity synchronous motor. Therefore, when the electric motor 3 is a salient-polarity synchronous motor, it is more beneficial to improve the robustness of the control of the electric motor 3 in response to changes in inductance.

[0125] 〔system〕

[0126] The following is an example of a system equipped with a power conversion device 1. Figure 8 This is a schematic diagram illustrating a system equipped with power conversion device 1. Figure 8 The system PS1 shown is used to extract water from pits dug in resource exploration or civil engineering, and includes a power conversion device 1, an electric motor 3, a filter 4, a step-up transformer 5, and an electric submersible pump 6.

[0127] Filter 4 is positioned between power conversion circuit 10 and motor 3. Here, "positioned between power conversion circuit 10 and motor 3" means electrically positioned between them. Filter 4 reduces the noise component in the output of power conversion circuit 10. Here, "output of power conversion circuit 10" refers to the output power of power conversion circuit 10, which includes output voltage and output current. For example, filter 4 has an input section (primary side) connected to power conversion circuit 10 and an output section (secondary side) connected to step-up transformer 5, outputting power (reduced noise component from the power input from power conversion circuit 10 to the input section) from the output section to step-up transformer 5. A specific example of filter 4 is an LC filter with a coil and a capacitor. Since filter 4 is electrically connected between power conversion circuit 10 and motor 3, the current sensor 14 detects the output current from power conversion circuit 10 to filter 4.

[0128] A step-up transformer 5 is located between the filter 4 and the motor 3. "Between the filter 4 and the motor 3" means that electricity passes between them. The step-up transformer 5 boosts the output of the filter 4 and supplies it to the motor 3. "Boosting the output" means increasing the output voltage. For example, the step-up transformer 5 has an input section (primary side) connected to the filter 4 and an output section (secondary side) connected to the motor 3. It boosts the output from the filter 4 to the input section and outputs it to the motor 3. The step-up transformer 5 can be a YY transformer with a star connection on both the primary and secondary sides, a Δ-Δ transformer with a delta connection on both the primary and secondary sides, a Y-Δ transformer with a star connection on the primary side and a delta connection on the secondary side, or a Δ-Y transformer with a delta connection on the primary side and a star connection on the secondary side.

[0129] The step-up transformer 5 boosts the output of the filter 4 to compensate for the voltage drop in the circuit (e.g., cable) from the step-up transformer 5 to the motor 3. The length of the circuit from the step-up transformer 5 to the motor 3 is, for example, 1 to 10 km. The electric submersible pump 6 is driven by the motor 3. The electric submersible pump 6 is installed in a pit excavated for resource exploration or civil engineering, and uses the driving force provided by the motor 3 to discharge the water accumulated in the pit to the outside.

[0130] In system PS1, the inductance at the destination of the power supplied from the power conversion circuit 10 varies greatly not only from the inductance of the motor 3, but also from the characteristics of the filter 4, the characteristics of the step-up transformer 5, and the characteristics of the circuit from the power conversion circuit 10 to the motor 3 (e.g., length, degree of bending), as well as other external conditions of the motor 3. Therefore, the aforementioned improvement in robustness is more beneficial.

[0131] Furthermore, the phase of the output current generated by the power conversion circuit 10 changes due to the filter 4 and the step-up transformer 5, etc., before reaching the motor 3. Correspondingly, as... Figure 9 As shown, the control circuit 100 may also have a compensation value storage unit 161 and a current correction unit 162.

[0132] The compensation value storage unit 161 stores at least a phase compensation value for compensating for the phase change of the current in the step-up transformer 5 (the phase difference between the current on the primary side and the current on the secondary side). The phase compensation value may include a first phase compensation value for compensating for the phase change of the voltage in the step-up transformer 5. In the step-up transformer 5, the phase difference between the current after removing the excitation current from the primary side current and the current on the secondary side is equal to the phase difference between the voltage on the primary side and the voltage on the secondary side. Therefore, compensating for the phase change of the voltage in the step-up transformer 5 is equivalent to compensating for at least a portion of the phase change of the current in the step-up transformer 5. The compensation value storage unit 161 may also store a second phase compensation value for at least compensating for the phase change of the current in the filter 4. The first and second phase compensation values ​​are derived in advance through actual machine testing or simulation. For example, the first phase compensation value is determined based on the phase difference between the voltage and current generated between the primary and secondary sides of the step-up transformer 5, and the second phase compensation value is determined based on the magnitude of the excitation current on the primary side of the step-up transformer 5 and the fundamental component of the current supplied to the capacitor of the feed filter 4.

[0133] The current correction unit 162 corrects the output current detected by the current sensor 14 based on the phase compensation value. The current correction unit 162 can correct the output current detected by the current sensor 14 based on a first phase compensation value and a second phase compensation value. For example, the current correction unit 162 adds or subtracts the first phase compensation value and the second phase compensation value from the phase of the output current, such that the phase of the output current detected by the current sensor 14 is close to (e.g., substantially consistent with) the phase of the current flowing through the secondary side of the step-up transformer 5 (e.g., the output current from the step-up transformer 5 to the motor 3). For example, the current correction unit 162 corrects the output current vector calculated by the current acquisition unit 114 based on the first phase compensation value and the second phase compensation value. Furthermore, the current correction unit 162 can also be configured to correct the magnitude of the output current (e.g., multiply by the inverse ratio of the transformation ratio) based on the transformation ratio (the ratio of the secondary side voltage to the primary side voltage) in the step-up transformer 5. In addition, the current correction unit 162 can also correct the angle for the rotational coordinate transformation based on the first phase compensation value and the second phase compensation value before the current acquisition unit 114 performs the above-mentioned rotational coordinate transformation, thereby correcting the output current vector calculated by the rotational coordinate transformation.

[0134] The voltage command calculation unit 122 can calculate the voltage command based on the frequency command, the output current from the power conversion circuit 10 to the motor 3 (the output current detected by the current sensor 14), the estimated value of the inductance, and the phase compensation value. For example, the voltage command calculation unit 122 calculates the voltage command based on the frequency command, the output current corrected by the current correction unit 162 according to the phase compensation value, and the estimated value of the inductance. Except for the fact that it is based on the output current corrected by the current correction unit 162 according to the phase compensation value, the voltage command calculation method of the voltage command calculation unit 122 is the same as the method described above.

[0135] The error calculation unit 115 can calculate the phase error based on the voltage command, the output current from the power conversion circuit 10 to the motor 3 (the output current detected by the current sensor 14), the estimated value of the inductance, and the phase compensation value. For example, the error calculation unit 115 can calculate the phase error based on the frequency command, the output current corrected by the current correction unit 162 according to the phase compensation value, and the estimated value of the inductance. Except for the fact that it is based on the output current corrected by the current correction unit 162 according to the phase compensation value, the method for calculating the phase error of the error calculation unit 115 is the same as the method described above.

[0136] Thus, the voltage command calculation unit 122 calculates a voltage command considering the phase compensation value, and the error calculation unit 115 calculates a phase error considering the phase compensation value. Therefore, in the command correction unit 116, the voltage command is corrected to suppress the influence of phase changes in the output current of the filter 4 and the step-up transformer 5. The command correction unit 116 can also be configured to correct the voltage command based on both the phase error calculated by the error calculation unit 115 and the phase compensation value. For example, when the wiring methods of the primary and secondary sides of the step-up transformer 5 are different, a phase difference may sometimes occur between the voltage and current on the primary and secondary sides of the step-up transformer 5. For example, when the step-up transformer 5 is a Δ-Y transformer, the phase of the secondary voltage leads the phase of the primary voltage by 30°, and the phase of the secondary current leads the phase of the primary current by 30°. In this case, if phase changes caused by other factors are ignored, the first phase compensation value is 30°. The current correction unit 162 adds 30° to the phase of the output current detected by the current sensor 14. Furthermore, the command correction unit 116 adds the phase error calculated by the error calculation unit 115 to the phase of the voltage command generated by the voltage command calculation unit 122, and then subtracts 30°. Further, the command correction unit 116 can also be configured to correct the magnitude of the voltage command based on the transformation ratio in the step-up transformer 5 (for example, by multiplying it by the inverse ratio of the transformation ratio).

[0137] Furthermore, regarding the step-up transformer 5, there are cases where specifications such as the phase difference between the primary and secondary voltages, the correct transformation ratio including tap changes, and the excitation current are unclear. In such cases, for example, by generating a voltage command from the voltage on the primary side of the step-up transformer 5, control of the motor 3 connected to the secondary side of the step-up transformer 5 can be achieved. At this time, in equations (1) and (2) that determine the voltage command, the winding resistance R, γ-axis inductance Lγ, and δ-axis inductance Lδ of the motor 3 are used as motor constants, and values ​​set in advance as design values ​​for the motor are used. Regarding the target value of the induced voltage E, a voltage lower than the rated voltage of the inverter is set. In this state, the voltage command is determined by equations (1) and (2), and a second phase compensation value that at least compensates for the phase change caused by the filter 4 is set in the compensation value storage unit 161.

[0138] Under the above conditions, since the target value of induced voltage E, winding resistance R, γ-axis inductance Lγ, and δ-axis inductance Lδ are not values ​​converted to the primary winding side, even if the operation is as is, loss of synchronism may occur depending on the load conditions. Therefore, during trial operation, the target value of induced voltage E and the second phase compensation value are adjusted. By adjusting, E, R·iγ, -ω·Lδ·iδ, ω·Lγ·iγ, and R·iδ in equations (1) and (2) are closer to the correct values, thereby enabling the determination of the voltage command on the primary side of the step-up transformer 5 that does not lose synchronism within the operating range of the motor 3.

[0139] Figure 10 This is a flowchart illustrating the power conversion process when the control circuit 100 also includes a compensation value storage unit 161 and a current correction unit 162. For example... Figure 10 As shown, the control circuit 100 executes steps S31, S32, S33, S34, S35, S36, S37, S38, and S39. In step S31, similar to step S01, the induced voltage calculation unit 121 calculates the target value of the induced voltage corresponding to the frequency command according to a predetermined command distribution. In step S32, similar to step S02, the inductance estimation unit 132 derives an estimated value of the inductance based on the value of the output current acquired by the current acquisition unit 114 in the previous control cycle and the inductance distribution stored in the inductance storage unit 131.

[0140] In step S33, the voltage command calculation unit 122 calculates the γ-axis voltage command Vγ and the δ-axis voltage command Vδ based on the output current corrected by the current correction unit 162 in the previous control cycle, the winding resistance of the motor 3, the rotational speed of the motor 3 derived from the frequency command, the estimated value of the inductance of the motor 3, and the target value of the induced voltage. In step S34, similar to step S04, the voltage calculation unit 112 calculates the absolute value of the voltage command, and the phase calculation unit 113 calculates the phase of the voltage command in the fixed coordinate system. In step S35, similar to step S05, the command correction unit 116 corrects the phase of the voltage command based on the phase error calculated by the error calculation unit 115 in the previous control cycle. The command correction unit 116 can also correct the phase of the voltage command based on the phase error calculated by the error calculation unit 115 and the phase compensation value. Furthermore, the command correction unit 116 can further correct the magnitude of the voltage command based on the inverse ratio of the transformer ratio in the step-up transformer 5.

[0141] In step S36, similar to step S06, the PWM control unit 117 starts controlling the power conversion circuit 10 to make the drive power follow the voltage command (the corrected voltage command) whose phase and magnitude were corrected in step S34. In step S37, the current acquisition unit 114 acquires the current information output from the power conversion circuit 10 to the filter 4 according to the corrected voltage command from the current sensor 14, and performs three-phase two-phase conversion and rotating coordinate conversion on the acquired current information to calculate the γ-axis current iγ and the δ-axis current iδ. In step S38, the current correction unit 162 corrects the output current calculated in step S36 based on the phase compensation value, for example, by rotational conversion. In step S39, the error calculation unit 115 calculates the phase error based on the frequency command, the output current corrected by the current correction unit 162 according to the phase compensation value, and the estimated value of the inductance. Thus, one cycle of control is completed. The control circuit 100 repeats the above process with a predetermined control cycle. Furthermore, the above description illustrates the process by which the current correction unit 162 corrects the phase of the output current vector after the current acquisition unit 114 calculates it, but it is not limited to this. For example, the current correction unit 162 may also correct the output current vector calculated by the rotational coordinate transformation by correcting the angle used for the rotational coordinate transformation before the current acquisition unit 114 performs the aforementioned rotational coordinate transformation.

[0142] Return to Figure 9The power conversion device 1 may also include a tuning control unit 163, a tuning unit 164, and a parameter storage unit 165 instead of the inductance estimation unit 132. The tuning control unit 163 applies a tuning voltage from the power conversion circuit 10 to the motor 3 when the power conversion circuit 10 is connected to the motor 3 without passing through the filter 4 and the step-up transformer 5. The tuning unit 164 derives at least one control parameter, including an estimated value of the inductance, based on the tuning current and tuning voltage flowing between the power conversion circuit 10 and the motor 3 according to the applied tuning voltage. The parameter storage unit 165 stores the control parameter derived by the tuning unit 164.

[0143] Furthermore, the estimated inductance derived from the tuning unit 164 includes the inductance of the circuit from the power conversion circuit 10 to the motor 3 and the inductance of the motor 3 itself. In addition to the estimated inductance, at least one control parameter may also include an estimated value of the resistance of the motor 3. The estimated resistance of the motor 3 includes the resistance of the circuit from the power conversion circuit 10 to the motor 3 and the resistance of the windings of the motor 3 itself.

[0144] When the power conversion device 1 also includes a tuning control unit 163 and a tuning unit 164, the voltage command calculation unit 122 can calculate the voltage command based on the frequency command, the output current corrected by the current correction unit 162, and at least one control parameter. The error calculation unit 115 can calculate the phase error based on the voltage command, the output current corrected by the current correction unit 162, and at least one control parameter. According to this structure, the voltage command is generated and the phase error is calculated based on the control parameters that are tuned to match the characteristics of the system PS1 other than the filter 4 and the step-up transformer 5, thus enabling more appropriate correction of the voltage command.

[0145] Figure 11 This is a flowchart illustrating the process of deriving control parameters. This process is... Figure 10 Before the power conversion process illustrated, the power conversion circuit 10 is connected to the motor 3 without passing through the filter 4 and the step-up transformer 5. When this process is performed, the calculation of the inductance estimate in step S32 can be omitted during the power conversion. Figure 11 As shown, the control circuit 100 first executes steps S41, S42, and S43. In step S41, the tuning control unit 163 causes the power conversion circuit 10 to begin applying a tuning voltage. In step S42, the current acquisition unit 114 acquires information about the tuning current flowing between the power conversion circuit 10 and the motor 3 according to the application of the tuning voltage. In step S43, the tuning control unit 163 confirms whether a predetermined tuning period has elapsed.

[0146] If it is determined in step S43 that no tuning period has elapsed, the control circuit 100 returns the process to step S41. If it is determined in step S43 that a tuning period has elapsed, the control circuit 100 executes step S44. In step S44, the tuning unit 164 derives at least one control parameter based on the tuning current and tuning voltage flowing between the power conversion circuit 10 and the motor 3 according to the applied tuning voltage, and stores it in the parameter storage unit 165. The control parameter deriving process is now complete.

[0147] Like system PS1, the structure with filter 4 and step-up transformer 5 can also be applied to systems where the drive object of motor 3 is different from that of electric submersible pump. For example, it is beneficial for systems where the voltage drop in the circuit between power conversion circuit 10 and motor 3 cannot be ignored.

[0148] The implementation methods have been described above, but this disclosure is not limited to the above implementation methods, and various changes can be made without departing from its spirit.

[0149] Symbol Explanation

[0150] 1. Power conversion device; 3. Electric motor; 4. Filter; 5. Step-up transformer; 6. Electric submersible pump; 10. Power conversion circuit (power conversion unit); 14. Current sensor; 111, 151. Command generation unit; 115. Error calculation unit; 116. Command correction unit; 117. PWM control unit (control unit); 131. Inductance storage unit; 132. Inductance estimation unit; 134. Distribution generation unit; 141. Gain storage unit; 142. Gain calculation unit; 161. Compensation value storage unit; 162. Current correction unit; 163. Tuning control unit; 164. Tuning unit.

Claims

1. A power conversion device, comprising: The power conversion unit generates the drive voltage used to drive the electric motor; The current acquisition unit acquires information indicating the output current flowing to the motor according to the drive voltage; The phase calculation unit calculates the phase of the rotating coordinate system relative to the fixed coordinate system, so that the rotating coordinate system rotates synchronously with the frequency command; The instruction generation unit calculates the voltage instruction in the rotating coordinate system based on the frequency instruction, the output current, and the inductance of the motor, regardless of the operating speed of the motor. The error calculation unit calculates the phase error of the rotating coordinate system based on the voltage command, the output current, and the inductance. The command correction unit corrects the phase of the rotating coordinate system by adding the phase error to the calculated phase of the rotating coordinate system. as well as The control unit controls the power conversion unit to generate the driving voltage that corresponds to the voltage command and the phase of the corrected rotating coordinate system.

2. The power conversion device according to claim 1, wherein, The error calculation unit calculates the induced voltage vector in the rotating coordinate system based on the voltage command, the output current, and the inductance. This induced voltage vector is generated in response to the operation of the motor. The phase error is calculated based on the phase of the induced voltage vector.

3. The power conversion device according to claim 2, wherein, The error calculation unit calculates the phase error based on the relationship between the phase of the rotating coordinate system and the phase of the induced voltage vector.

4. The power conversion device according to claim 3, wherein, The error calculation unit calculates the phase error based on the relative phase of the induced voltage vector with respect to the rotating coordinate system.

5. The power conversion device according to claim 1, wherein, It also includes an inductance estimation unit for estimating the inductance of the motor; The instruction generation unit calculates the voltage instruction based on the estimated inductance, and The error calculation unit calculates the phase error based on the estimated inductance.

6. The power conversion device according to claim 5, wherein, It also includes an inductance storage unit that stores an inductance distribution representing the relationship between the inductance and the output current, such that the inductance changes according to changes in the output current. The inductance estimation unit estimates the inductance based on the output current and the inductance distribution.

7. The power conversion device according to claim 6, wherein, It also includes a distribution generation unit that generates the inductance distribution based on user input containing at least two different datasets, each dataset containing a combination of the inductance value and the output current value.

8. The power conversion device according to any one of claims 1 to 7, wherein, The command correction unit corrects the phase of the rotating coordinate system based on the integral value of the phase error.

9. The power conversion device according to any one of claims 1 to 7, wherein, It also includes a gain calculation unit that calculates the gain based on the operating speed of the motor and a stored gain distribution, wherein the stored gain distribution represents the inverse relationship between the gain and the operating speed, and the gain decreases as the operating speed increases. The command correction unit corrects the phase of the rotating coordinate system based on the phase error and the calculated gain.

10. The power conversion device according to any one of claims 1 to 7, wherein, The instruction generation unit calculates the voltage instruction in a manner that reduces the deviation between the driving force generated by the electric motor and the target driving force.

11. The power conversion device according to claim 10, wherein, The electric motor is a synchronous motor with salient polarity, and The instruction generation unit calculates the voltage instruction based on the frequency instruction, the output current, the inductance, and the salient polarity.

12. The power conversion device according to any one of claims 1 to 7, further comprising: The compensation value storage unit stores phase compensation values, which compensate for the phase difference between the output current and the input current to the motor. The instruction generation unit calculates the voltage instruction based on the frequency instruction, the output current, the inductance, and the phase compensation value. The error calculation unit calculates the phase error based on the voltage command, the output current, the inductance, and the phase compensation value.

13. The power conversion device according to claim 12, further comprising: A current sensor detects the output current; as well as The current correction unit corrects the detected output current based on the phase compensation value. The instruction generation unit calculates the voltage instruction based on the frequency instruction, the corrected output current, and the inductance. The error calculation unit calculates the phase error based on the voltage command, the corrected output current, and the inductance.

14. The power conversion device according to claim 13, wherein, The command correction unit corrects the phase of the rotating coordinate system based on the phase error and the phase compensation value.

15. The power conversion device according to claim 14, wherein, The phase compensation value includes a first phase compensation value, which is used at least to compensate for a first phase difference between a first input current input to the transformer and a first output current output from the transformer to the motor.

16. The power conversion device according to claim 15, wherein, The phase compensation value also includes a second phase compensation value, which is used at least to compensate for the second phase difference between the second input current input to the filter and the second output current output from the filter to the motor.

17. A system comprising: The power conversion device according to any one of claims 1 to 16; The electric motor; A filter is connected between the power conversion unit and the motor to reduce noise contained in the drive voltage; as well as A step-up transformer is connected between the power conversion unit and the motor to increase the drive voltage.

18. The system of claim 17, further comprising: An electric submersible pump, driven by the electric motor.

19. A power conversion method, comprising: The control power conversion circuit generates a drive voltage based on voltage commands; Obtain current information representing the output current flowing from the power conversion circuit to the motor according to the drive voltage; Calculate the phase of the rotating coordinate system relative to the fixed coordinate system so that the rotating coordinate system rotates synchronously with the frequency command; The phase error of the rotating coordinate system is calculated based on the voltage command, the output current, and the inductance of the motor. The voltage command is updated based on the frequency command, the output current, and the inductance, regardless of the operating speed of the motor. The phase of the rotating coordinate system is corrected by adding the phase error to the calculated phase of the rotating coordinate system. as well as The power conversion circuit is controlled to generate the drive voltage corresponding to the updated voltage command and the phase of the corrected rotating coordinate system.

20. A non-transitory storage device storing instructions that, in response to execution by a processing device, cause the processing device to perform the following actions: The control power conversion circuit generates a drive voltage based on voltage commands; Obtain current information representing the output current flowing from the power conversion circuit to the motor according to the drive voltage; Calculate the phase of the rotating coordinate system relative to the fixed coordinate system so that the rotating coordinate system rotates synchronously with the frequency command; The phase error of the rotating coordinate system is calculated based on the voltage command, the output current, and the inductance of the motor. The voltage command is updated based on the frequency command, the output current, and the inductance, regardless of the operating speed of the motor. The phase of the rotating coordinate system is corrected by adding the phase error to the calculated phase of the rotating coordinate system. as well as The power conversion circuit is controlled to generate the drive voltage corresponding to the updated voltage command and the phase of the corrected rotating coordinate system.

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