Inverter control device

Abstract

To relax vehicle impulses due to recognition error of an estimated speed that is easily generated in a low frequency region of an inverter.SOLUTION: An inverter controller 10 comprises an estimated speed calculation part 11 for estimating a rotor frequency as a rotational frequency of a rotor via calculation; an accelerated / decelerated speed calculation part 13 for calculating an accelerated / decelerated speed as a changing amount of the rotor frequency; an inverter frequency command generation part 12 for generating an inverter frequency command for instructing a frequency of a voltage output by an inverter 20, based on the rotor frequency; and a torque control part 14 for outputting a voltage command to the inverter 20, based on the inverter frequency command. The inverter frequency command generation part 12 controls the inverter frequency command so as to maintain the accelerated / decelerated speed.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to an inverter control device for controlling an inverter mounted on an electric vehicle (railway vehicle).

Background Art

[0002] The main electric motor constituting the inverter main circuit system of an electric vehicle (railway vehicle) generally employs a cage-type three-phase induction motor. The inverter control device can control the applied voltage and rotational speed of the induction motor according to the output command by detecting the rotational speed of the induction motor with a speed sensor (for example, a PG (Pulse Generator) sensor) arranged on the induction motor. However, since the speed sensor is composed of electronic components, maintenance and inspection are required. In addition, when the speed sensor fails, the induction motor often cannot be controlled. Therefore, high-reliability components are adopted for the speed sensor, resulting in high costs.

[0003] Therefore, an inverter control device that employs sensorless control capable of controlling an induction motor without using a speed sensor has become widespread (see, for example, Patent Document 1). Sensorless control not only improves the performance of electric vehicles through high-precision torque control but also has the advantages of cost reduction due to the absence of a speed sensor and increased structural freedom of the induction motor. Therefore, currently, sensorless control is adopted in many railway vehicles.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] In sensorless control, since there is no speed sensor input from the induction motor, the inverter control device must control the inverter while estimating the rotational speed of the induction motor. The secondary magnetic flux and torque of the induction motor are obtained from the primary voltage and current applied to the stator of the induction motor, and the secondary current obtained by the slip generated by the rotation of the rotor due to the primary magnetic flux from the stator. At this time, the rotational speed of the rotor is estimated from the values obtained by coordinate conversion from magnetic flux calculation and torque calculation. However, if a detection error occurs in the voltage or current detected in this series of operations, it causes a large calculation error, and the accuracy of the magnetic flux and torque deteriorates, resulting in the drawback that the induction motor cannot be controlled normally.

[0006] Also, in sensorless control, by recognizing the difference between the inverter frequency that controls the stator and the rotor frequency that controls the rotor, that is, the slip, the exciting current and torque current that become the secondary magnetic flux component are recognized, and the rotational speed of the rotor is estimated as the d-axis current (exciting current) and q-axis current (torque current), and the induction motor is controlled as the output voltage vector of the inverter.

[0007] However, as described above, if a detection error occurs in the induced voltage or current detected by the rotation of the rotor, it causes a calculation error, and it becomes difficult to normally recognize the estimated speed of the vehicle calculated by the secondary magnetic flux component obtained by the slip. In particular, in a situation where the vehicle is about to stop, which is the low-frequency region of the inverter, vehicle impulses may occur due to misrecognition of the estimated speed.

[0008] As a countermeasure for this, in order to accurately capture the secondary magnetic flux component obtained by the slip of the induction motor, it is conceivable to increase the exciting current input to the induction motor to increase the induced voltage of the induction motor. However, if the exciting current is increased for the induction motor, magnetic saturation may occur, the circuit constants of the induction motor may change, and the error in the estimated speed calculation of the vehicle may increase.

[0009] In addition, it is considered that the recognition error of the estimated speed is caused by the detection error of the voltage and current of the induction motor or the change in the equivalent circuit constants due to the temperature change of the induction motor. Further, dead time is required for the control of the induction motor, and a voltage error occurs during this period. The voltage error due to dead time causes distortion in the current and induces vehicle impulses due to torque ripple. To improve these, it is considered that it can be improved by optimizing the equivalent circuit constants of the induction motor by constantly monitoring the induction motor temperature or by optimal control that corrects the voltage error difference due to dead time. However, it is very difficult to establish an algorithm that can handle the entanglement of these complex elements.

[0010] In view of such circumstances, an object of the present invention made is to provide an inverter control device and a program capable of alleviating vehicle impulses caused by recognition errors of the estimated speed that are likely to occur in the low-frequency region of the inverter.

Means for Solving the Problems

[0011] To solve the above problems, an inverter control device according to the present invention is an inverter control device that controls an inverter and applies a current to an induction motor to generate slip on the rotor of the induction motor, and includes an estimated speed calculation unit that estimates, by calculation, the rotor frequency that is the rotational frequency of the rotor, an acceleration / deceleration calculation unit that calculates the acceleration / deceleration that is the amount of change in the rotor frequency, an inverter frequency command generation unit that generates an inverter frequency command for instructing the frequency of the voltage output by the inverter based on the rotor frequency, and a torque control unit that outputs a voltage command for instructing the voltage output by the inverter to the inverter based on the inverter frequency command. The inverter frequency command generation unit In the braking operation, when the inverter frequency command exceeds the threshold value, the inverter frequency command is not changed from the frequency calculated based on the rotor frequency estimated by the estimated speed calculation unit, and when the inverter frequency command becomes equal to or less than the threshold value, controls the inverter frequency command regardless of the rotor frequency estimated by the estimated speed calculation unit, so as to maintain the acceleration / deceleration.

[0013] Furthermore, in the inverter control device according to the present invention, when the torque command increases, the inverter frequency command generation unit increases the amount of change in the inverter frequency command, and when the torque command decreases, the inverter frequency command generation unit decreases the amount of change in the inverter frequency command.

[0014] Furthermore, in the inverter control device according to the present invention, the estimated speed calculation unit calculates the magnetic flux vector of the induction motor from the current vector and voltage vector obtained by converting the current and voltage of the induction motor into space vectors, calculates the slip frequency of the induction motor from the magnetic flux vector and the current vector, and calculates the difference between the angular frequency of the magnetic flux vector and the slip frequency as the rotor frequency.

Advantages of the Invention

[0015] According to the present invention, it is possible to mitigate vehicle impulses caused by recognition errors in the estimated speed that are likely to occur in the low-frequency region of the inverter.

Brief Description of the Drawings

[0016]

Figure 1

Figure 2

Figure 3

Embodiments for Carrying Out the Invention

[0017] Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings. Note that frequency and angular frequency can be converted into each other only in terms of units, and either can be used in calculations. Therefore, in this specification, the term "frequency" includes angular frequency.

[0018] Figure 1 shows a configuration example of an inverter main circuit system 1 including an inverter control device according to an embodiment of the present invention. The inverter main circuit system 1 includes an inverter control device 10, an inverter 20, a current detector 30, a voltage detector 40, and an induction motor 50.

[0019] The inverter 20 applies a voltage v corresponding to a voltage command v instructing an output voltage to the induction motor 50, which is input from the inverter control device 10, to the induction motor 50. * to the induction motor 50.

[0020] The current detector 30 detects a current i flowing through the induction motor 50 and outputs a detection result to the inverter control device 10.

[0021] The voltage detector 40 detects a voltage v applied to the induction motor 50 and outputs a detection result to the inverter control device 10.

[0022] The inverter control device 10 controls the inverter 20 and applies a current to the induction motor 50 to generate a slip on the rotor of the induction motor 50. Further, the inverter control device 10 performs sensorless speed control. That is, without using a speed sensor, the rotational frequency of the rotor of the induction motor 50 (hereinafter referred to as "rotor frequency") ω m is obtained by calculation, and torque control of the induction motor 50 is performed according to a torque command T * . The rotor frequency ω m means the estimated speed of the vehicle. By transmitting the torque of the induction motor 50 to the vehicle wheel axle, the vehicle can be accelerated or decelerated. The inverter control device 10 includes an estimated speed calculation unit 11, an inverter frequency command generation unit 12, an acceleration / deceleration calculation unit 13, and a torque control unit 14.

[0023] The estimated speed calculation unit 11 estimates the rotor frequency ω m by calculation and outputs it to the inverter frequency command generation unit 12 and the acceleration / deceleration calculation unit 13. The estimated speed calculation unit 11 uses, for example, the current i detected by the current detector 30 and the voltage v detected by the voltage detector 40 to calculate the rotor frequency ωm Perform the operation.

[0024] Specifically, the estimated speed calculation unit 11 calculates the magnetic flux vector φ2 of the induction motor 50 according to Equation (1). Here, R1 is the primary resistance of the induction motor 50, and L1, L2, and M are the primary self-inductance, secondary self-inductance, and mutual inductance of the induction motor 50, respectively. i is the current vector obtained by converting the detected or estimated current flowing through the induction motor 50 into a space vector. v is the voltage vector obtained by converting the detected or estimated voltage applied to the induction motor 50 into a space vector.

[0025]

Equation

[0026] Note that instead of the voltage v, the voltage command v * output by the inverter control device 10 may be used. In that case, the inverter main circuit system 1 may not be provided with the voltage detector 40.

[0027] The angular frequency ω of the magnetic flux vector φ2 c is the d-axis component of the magnetic flux vector φ2, which is φ 2d and the q-axis component of the magnetic flux vector φ2, which is φ 2q and is expressed by Equation (2).

[0028]

Equation

[0029] Also, the estimated speed calculation unit 11 uses the magnetic flux vector φ2 and the current vector i corresponding to the current detected by the current detector 30 to calculate the slip frequency ω sc of the induction motor 50 according to Equation (3).

[0030]

Equation

[0031] Then, as shown in Equation (4), the estimated speed calculation unit 11 calculates the difference between the angular frequency ω of the magnetic flux vector φ2 c and the slip frequency ω sc as the rotor frequency ω m of the induction motor 50.

[0032]

Equation

[0033] The acceleration / deceleration calculation unit 13 calculates the acceleration / deceleration dω m which is the change amount of the rotor frequency ω obtained by the estimated speed calculation unit 11, and outputs it to the inverter frequency command generation unit 12. m

[0034] Based on the rotor frequency ω m obtained by the estimated speed calculation unit 11, the inverter frequency command generation unit 12 generates an inverter frequency command ω i * that indicates the frequency of the voltage output by the inverter 20, and outputs it to the torque control unit 14. The inverter frequency command generation unit 12 includes a slip frequency command calculation unit 121, an addition unit 122, and an open brake frequency command calculation unit 123.

[0035] Based on the input torque command T * and the secondary magnetic flux command φ2 * the slip frequency command calculation unit 121 generates a slip frequency command ω s * using the following Equation (5), and outputs it to the addition unit 122.

[0036]

Equation

[0037] The addition unit 122 adds the rotor frequency ω m calculated by the estimated speed calculation unit 11 and the slip frequency command ω s ​* Add them to generate the inverter frequency command ω i * and output it to the open brake frequency command calculation unit 123.

[0038] In the open brake operation, the open brake frequency command calculation unit 123 controls the inverter frequency command ω i * generated by the addition unit 122 to maintain the acceleration / deceleration dω m input from the acceleration / deceleration calculation unit 13, and outputs it to the torque control unit 14. Details will be described later.

[0039] The torque control unit 14 inputs the torque command T * the secondary flux command φ2 * the current i detected by the current detector 30, and the inverter frequency command ω i * generated by the open brake frequency command calculation unit 123. Based on these inputs, the torque control unit 14 generates a voltage command v * to instruct the voltage output by the inverter 20 so that the torque of the induction motor 50 follows the torque command T * and outputs it to the inverter 20.

[0040] In FIG. 1, an example is shown in which the torque command T * and the secondary flux command φ2 * are input to the torque control unit 14, but it is not limited to this. For example, the torque control unit 14 may calculate the secondary flux command φ2 * based on the input torque command T * .

[0041] Next, the control of the inverter control device 10 will be described. FIG. 2 is a state transition diagram showing the control of the inverter control device 10 in the brake operation. The inverter control device 10 determines whether the inverter frequency command ω i * output by the addition unit 122 is equal to the open brake start frequency ω STWhen it exceeds, it operates in the normal operation mode (state A). The inverter control device 10 has the inverter frequency command ω output by the addition unit 122 i * When it becomes equal to or less than the open brake start frequency ω ST it operates in the open brake mode (state B). The open brake start frequency ω ST is predetermined, for example, 3 Hz.

[0042] FIG. 3 is a diagram for explaining the control of the open brake frequency command calculation unit 123. In the normal operation mode (that is, when the inverter frequency command ω i * exceeds the open brake start frequency ω ST ), the open brake frequency command calculation unit 123 outputs the inverter frequency command ω input from the addition unit 122 i * to the torque control unit 14 without changing it. In the open brake mode (that is, when the inverter frequency command ω i * becomes equal to or less than the open brake start frequency ω ST ), the open brake frequency command calculation unit 123 performs open-loop control so as to maintain the acceleration / deceleration rate dω i * at the start of the open brake mode and outputs it to the torque control unit 14. That is, in the open brake mode, the open brake frequency command calculation unit 123 decreases the inverter frequency command ω m at the same rate as in the immediately preceding normal operation mode. i * That is, in the open brake mode, the open brake frequency command calculation unit 123 decreases the inverter frequency command ω

[0043] Conventionally, in the low frequency region of the inverter 20, an error occurs in the rotor frequency ω estimated by the estimated speed calculation unit 11 m , and as a result, an error occurs in the inverter frequency command ω i *Errors may also occur. The inverter control device 10 according to the present invention includes an open brake frequency command calculation unit 123 and an acceleration / deceleration calculation unit 13. The acceleration / deceleration calculation unit 13 calculates the acceleration / deceleration dω m in advance in a region where the accuracy of ω m is high. Then, in a speed range where the accuracy of the rotor frequency ω m cannot be maintained (a region below the open brake start frequency ω ST ), instead of directly using the inverter frequency command ω i * generated by the adder 122, the open brake frequency command calculation unit 123 controls the inverter frequency command ω m so as to maintain the acceleration / deceleration dω i * . This makes it possible to mitigate vehicle jerks caused by recognition errors of the estimated speed that are likely to occur in the low-frequency region of the inverter 20.

[0044] Also, in order to adjust the stop position, the torque command T * may be changed in the low-speed range. When the torque command T * changes during the open brake mode control, if the open brake frequency command calculation unit 123 decreases the inverter frequency command ω i * at a constant rate, there is a risk of vehicle jerks occurring. Therefore, in the open brake mode, as shown by the dashed-dotted line in FIG. 3, when the torque command T * increases in the negative direction (the absolute value of the torque command T * increases), the open brake frequency command calculation unit 123 increases the change amount of the inverter frequency command ω i * . Also, as shown by the dotted line in FIG. 3, when the torque command T * decreases in the negative direction (the absolute value of the torque command T * decreases), the open brake frequency command calculation unit 123 decreases the change amount of the inverter frequency command ω i * .

[0045] For example, as shown in FIG. 3, when the inverter frequency command ω i * is lower than the open brake start frequency ω ST , the torque command T * at that time is memorized as the reference torque command T ST . During the open brake control, when there is a change in the torque command T * , the inverter frequency command ω ST is increased or decreased according to the ratio with the reference torque command T i * .

[0046] By operating the open brake frequency command calculation unit 123 in this way, the inverter control device 10 can control the inverter 20 in accordance with the movement of the vehicle, and even when the torque command T * changes in the low frequency region of the inverter 20, it is possible to suppress vehicle impulses.

Industrial Applicability

[0047] The present invention is useful for an electric vehicle that performs speed sensorless control.

Explanation of Signs

[0048] 1 Inverter main circuit system 10 Inverter control device 11 Estimated speed calculation unit 12 Inverter frequency command generation unit 13 Acceleration / deceleration calculation unit 14 Torque control unit 20 Inverter 30 Current detection unit 40 Voltage detection unit 121 Slip frequency command calculation unit 122 Addition unit 123 Open brake frequency command calculation unit

Claims

1. An inverter control device that controls an inverter and applies current to an induction motor to generate slip in the rotor of the induction motor, comprising: An estimated speed calculation unit that estimates, by calculation, the rotor frequency that is the rotational frequency of the rotor; An acceleration / deceleration calculation unit that calculates the acceleration / deceleration that is the amount of change in the rotor frequency; An inverter frequency command generation unit that generates an inverter frequency command for instructing the frequency of the voltage output by the inverter based on the rotor frequency; A torque control unit that outputs a voltage command for instructing the voltage output by the inverter to the inverter based on the inverter frequency command, wherein, in a braking operation, when the inverter frequency command exceeds a threshold value, the inverter frequency command generation unit does not change the inverter frequency command from the frequency calculated based on the rotor frequency estimated by the estimated speed calculation unit, and when the inverter frequency command becomes equal to or less than the threshold value, the inverter frequency command generation unit controls the inverter frequency command to maintain the acceleration / deceleration regardless of the rotor frequency estimated by the estimated speed calculation unit. The inverter control device is characterized by this.

2. The inverter control device according to claim 1, wherein the inverter frequency command generation unit increases the amount of change in the inverter frequency command when the torque command increases, and decreases the amount of change in the inverter frequency command when the torque command decreases.

3. The estimated speed calculation unit according to claim 1 or 2, wherein the estimated speed calculation unit calculates the magnetic flux vector of the induction motor by using the current vector and voltage vector obtained by converting the current and voltage of the induction motor into space vectors, calculates the slip frequency of the induction motor from the magnetic flux vector and the current vector, and calculates the difference between the angular frequency of the magnetic flux vector and the slip frequency as the rotor frequency.

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