Inverter, system, and inverter DC current estimation method

Abstract

In an inverter, the estimation accuracy of DC current is improved by taking into account the influence of the magnet temperature of the motor rotor. [Solution] An inverter (2) has its DC side connected to a smoothing capacitor (C) and its AC side connected to a motor (3), and converts DC power into AC power to drive the motor (3). A DC current estimator estimates the DC current Idc on the inverter (2) side of the smoothing capacitor (C), or the DC current on the opposite side of the smoothing capacitor (C) from the inverter (2). The DC current estimator estimates a simulated magnet temperature of the rotor of the motor (3) based on the detected coil temperature value or motor current of the motor (3) and the rotation speed of the motor (3), and derives a magnet temperature correction gain based on the simulated magnet temperature. An uncorrected DC current estimate is calculated based on a torque command value, the rotation speed, and the DC voltage. The uncorrected DC current estimate is multiplied by the magnet temperature correction gain to calculate a corrected DC current estimate.

Description

[Technical Field]

[0001] The present invention relates to a method for estimating a DC current in an inverter for an EV (electric vehicle). [Background technology]

[0002] In electric vehicles, the battery's DC power is converted to AC power by an inverter to drive a motor, which rotates the vehicle's wheels. The motor often uses a synchronous motor with a permanent magnet embedded in the rotor. Figure 1 shows a typical example of an inverter configuration. In order to calculate the remaining battery capacity, information on the battery output current while the inverter is operating is required. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2007-159347 Summary of the Invention [Problem to be solved by the invention]

[0004] The remaining battery capacity can be calculated by installing a current sensor in the DC section connecting the battery and the inverter and using the detected value as information on the battery output current. However, in this case, the current sensor increases the size and cost of the inverter.

[0005] As a means for solving this problem, Patent Document 1 discloses a method for estimating the inverter DC current without using a current sensor. Furthermore, by applying this prior art, a method for estimating the inverter DC current based on the motor torque command, rotation speed detection value, etc. can be considered.

[0006] On the other hand, changes in the rotor magnet temperature generally cause the induced voltage to increase or decrease. When the DC voltage input to the inverter is constant, the motor AC voltage increases or decreases due to the influence of the magnet temperature, so the inverter input power changes according to the inverter output power, and the DC current increases or decreases. If this effect is not taken into account, the accuracy of DC current estimation decreases.

[0007] As described above, the challenge for the inverter is to improve the accuracy of estimating the DC current by taking into account the influence of the magnet temperature of the motor rotor. [Means for solving the problem]

[0008] The present invention has been devised in view of the above-mentioned problems in the related art, and one aspect thereof is an inverter having a DC side connected to a smoothing capacitor and an AC side connected to a motor, which converts DC power to AC power to drive the motor, wherein a DC current estimation unit that estimates a DC current on the inverter side of the smoothing capacitor or a DC current on the opposite side of the smoothing capacitor from the inverter estimates a simulated magnet temperature of a rotor of the motor based on a detected coil temperature value of the motor or the motor current and the motor rotation speed, derives a magnet temperature correction gain based on the simulated magnet temperature, calculates a pre-correction DC current estimate based on a torque command value, the rotation speed and a DC voltage, and calculates a post-correction DC current estimate by multiplying the pre-correction DC current estimate by the magnet temperature correction gain.

[0009] In one aspect, the DC current estimation unit includes: a first data table that derives a first magnet temperature estimation value based on the coil temperature detection value; a second data table that derives a magnet temperature rotational speed correction amount based on the rotational speed; a first adder that adds the first magnet temperature estimation value and the magnet temperature rotational speed correction amount to output the simulated magnet temperature; a magnet temperature correction gain table that derives the magnet temperature correction gain based on the simulated magnet temperature; a current calculation unit that calculates the pre-correction DC current estimation value based on the torque command value, the rotational speed, the DC voltage and a loss; and a multiplier that multiplies the pre-correction DC current estimation value by the magnet temperature correction gain to output the corrected DC current estimation value.

[0010] In another aspect, the DC current estimation unit includes a magnet temperature rise table that derives a magnet temperature rise estimated value based on the motor current and the rotational speed, a second adder that adds the motor ambient temperature to the magnet temperature rise estimated value to output the simulated magnet temperature, a magnet temperature correction gain table that derives the magnet temperature correction gain based on the simulated magnet temperature, a current calculation unit that calculates the pre-correction DC current estimated value based on the torque command value, the rotational speed, the DC voltage and a loss, and a multiplier that multiplies the pre-correction DC current estimated value by the magnet temperature correction gain to output the corrected DC current estimated value.

[0011] In one aspect, the DC current estimation unit includes a loss table that stores the loss using the torque command value, the rotation speed, and the DC voltage as parameters, and the loss used in the current calculation unit is a value derived from the loss table based on the torque command value, the rotation speed, and the DC voltage.

[0012] In one aspect, a battery is connected to the smoothing capacitor on the opposite side to the inverter, and the corrected DC current estimate value is used to estimate the remaining capacity of the battery. [Effects of the Invention]

[0013] According to the present invention, it is possible to improve the accuracy of estimating DC current in an inverter by taking into account the influence of the magnet temperature of the motor rotor. [Brief explanation of the drawings]

[0014] [Figure 1] FIG. 2 is a diagram showing an example of the configuration of an inverter. [Figure 2] FIG. 2 is a block diagram showing a DC current estimation unit according to the first embodiment. [Figure 3] FIG. 10 is a block diagram showing a DC current estimation unit according to a second embodiment. [Figure 4] FIG. 10 is a diagram showing the DC current estimation accuracy (difference from actual measurement) relative to magnet temperature. DETAILED DESCRIPTION OF THE INVENTION

[0015] Hereinafter, first and second embodiments of the inverter according to the present invention will be described in detail with reference to FIGS.

[0016] [Example 1] First, the configuration of a typical inverter will be described with reference to Fig. 1. A battery (not shown) is connected between the P terminal and the N terminal. A smoothing capacitor C is also connected between the P terminal and the N terminal.

[0017] Furthermore, the P terminal and N terminal are connected to the DC side of the inverter 2. The inverter 2 includes a first switching element U+ and a second switching element U- connected in series between the P terminal and the N terminal, a third switching element V+ and a fourth switching element V- connected in series between the P terminal and the N terminal, and a fifth switching element W+ and a sixth switching element W- connected in series between the P terminal and the N terminal.

[0018] A motor 3 is connected to the AC side of the inverter 2. Specifically, a motor winding 3U is connected to the connection point between the first switching element U+ and the second switching element U-. A motor winding 3V is connected to the connection point between the third switching element V+ and the fourth switching element V-. A motor winding 3W is connected to the connection point between the fifth switching element W+ and the sixth switching element W-. The motor windings 3U, 3V, and 3W are connected in a star connection.

[0019] Next, a description will be given of DC current estimation in this embodiment 1. Fig. 2 is a block diagram of a DC current estimation unit in this embodiment 1. The DC current estimation unit has a DC current estimation block and a block that calculates a simulated magnet temperature from the coil temperature and rotation speed and corrects the DC current estimation value.

[0020] The first data table 4a derives the first magnet temperature estimate value from the coil temperature detection value, which is, for example, a value obtained by actually measuring the coil temperature of the motor by attaching a coil temperature detector (e.g., a thermistor; not shown) to the coil of the motor.

[0021] The first magnet temperature estimate output from the first data table 4a corresponds to a temperature estimate that depends on the motor copper loss. The first data table 4a is set through a pre-test that measures the temperature of each coil and the magnet temperature under the condition of a constant rotation speed N0. A temperature sensor is attached to the magnet only during the pre-test.

[0022] The second data table 4b calculates the magnet temperature rotation speed correction amount based on the rotation speed. The rotation speed input to the second data table 4b may be either the rotation speed detection value or the rotation speed command value.

[0023] The magnet temperature rotation speed correction output from the second data table 4b is due to the effect of heat generation on the magnet caused by changes in iron loss due to rotation speed. The magnet temperature rotation speed correction calculated from the second data table 4b is used to correct the first magnet temperature estimate. The second data table 4b is set through a pre-test that measures the magnet temperature at each rotation speed under conditions of a constant coil temperature. The difference between the magnet temperature at a constant rotation speed N0 set in the pre-test of the first data table 4a and the magnet temperature at each rotation speed to be tabulated is set as a table value.

[0024] The first adder 7 adds the first magnet temperature estimate value and the magnet temperature rotational speed correction to calculate the simulated magnet temperature.

[0025] Next, a method for calculating the pre-correction current (pre-correction DC current estimate value) will be described. The current calculation unit 5 inputs the torque FB (torque command value), rotation speed (rotation speed detection value), DC voltage (DC voltage detection value), and loss, and calculates the pre-correction current (pre-correction DC current estimate value) using the following equation (1). This estimates the inverter DC current Idc in Figure 1. Pre-correction current = (torque command value × rotation speed detection value / 60 * 2π + loss) / DC voltage detection value... (1) The loss in equation (1) uses the value derived from loss table 6. Loss table 6 derives the loss using the torque command value, rotation speed (detected rotation speed value), and DC voltage (detected DC voltage value) as parameters.

[0026] The values ​​in loss table 6 are set through a preliminary test in which the DC current Idc is measured for each combination of the parameters of torque command value, rotation speed (detected rotation speed value), and DC voltage (detected DC voltage value), and the loss (= inverter input power - motor shaft output) is calculated from the inverter input power (= DC voltage x Idc) and motor shaft output. Note that this preliminary test is performed with a temperature sensor attached to the magnet, and under the condition that the magnet temperature is kept at a constant value (Tmg0).

[0027] Next, the magnet temperature compensation gain will be explained. The magnet temperature compensation gain table 8 outputs a compensation gain based on a simulated magnet temperature. The magnet temperature compensation gain table 8 is set based on a pre-test in which the inverter DC current is actually measured at the magnet temperature Tmg under the conditions of a constant torque command value, detected rotation speed value, and detected DC voltage value. This pre-test is performed by placing the motor 3 in a constant temperature bath and varying the magnet temperature Tmg.

[0028] The compensation gain in magnet temperature compensation gain table 8 is Idc(Tmg) / Idc(Tmg0). Here, Idc(Tmg) indicates the DC current actually measured when the magnet temperature was Tmg in the compensation gain pre-test, and Idc(Tmg0) indicates the DC current actually measured when the magnet temperature was Tmg0 in the compensation gain pre-test (the magnet temperature set to a constant value in the loss table 6 pre-test). Magnet temperature compensation gain table 8 inputs a simulated magnet temperature (Tmg) and outputs compensation gain Idc(Tmg) / Idc(Tmg0) from the DC current Idc(Tmg) at the simulated magnet temperature (Tmg) and the DC current Idc(Tmg0) at magnet temperature Tmg0.

[0029] The multiplier 9 multiplies the pre-correction current (pre-correction DC current estimated value) by the correction gain Idc(Tmg) / Idc(Tmg0) and transmits the result as the post-correction current (post-correction DC current estimated value) to the outside of the inverter.

[0030] Figure 4 shows the difference between the pre-correction DC current estimated value (× without magnet temperature correction), which is the input to multiplier 9, and the actual value of the corrected DC current estimated value (● with magnet temperature correction), which is the output of multiplier 9. The horizontal axis of Figure 4 represents magnet temperature (°C), and the vertical axis represents the accuracy of the DC current estimated value (%).

[0031] As shown in Fig. 4, when magnet temperature correction is not applied, the accuracy of DC current estimation deteriorates as the magnet temperature increases. When magnet temperature correction is applied, accurate current estimation is possible regardless of the magnet temperature.

[0032] As described above, according to the first embodiment, in the calculation of the DC current estimated value to be transmitted to the outside of the inverter, the estimation accuracy of the DC current estimated value can be improved by correcting the influence of the magnet temperature of the motor rotor. Furthermore, when the DC current estimated value is used to calculate the remaining capacity of the battery, the estimation accuracy of the remaining capacity of the battery can be improved.

[0033] [Example 2] The simulated magnet temperature calculated in the first embodiment may be calculated using a magnet temperature rise table for each operating region and operating time.

[0034] The copper loss of the motor caused by the magnet temperature rise is roughly proportional to the square of the motor current. As mentioned above, the iron loss of the motor is related to the rotation speed. Therefore, the magnet temperature rise table 10 uses the motor current (inverter output AC current) and rotation speed as parameters and outputs an estimated magnet temperature rise value.

[0035] The magnet temperature rise table 10 is set based on a preliminary test in which the magnet temperature rise is actually measured under conditions in which the motor current and rotation speed are varied.

[0036] The simulated magnet temperature is calculated by adding the motor ambient temperature to the magnet temperature rise estimate in a second adder 11. The motor ambient temperature is actually measured by a temperature sensor. This simulated magnet temperature is input to the magnet temperature correction gain table 8.

[0037] Other configurations are the same as in Example 1. By calculating an estimated magnet temperature rise value using magnet temperature rise table 10 and estimating a simulated magnet temperature by adding the estimated magnet temperature rise value and the motor ambient temperature, it is possible to obtain the same effect as in Example 1.

[0038] The DC current estimated value in Examples 1 and 2 is the DC current Idc on the inverter 2 side of the smoothing capacitor C, as shown in Fig. 1. There is almost no difference between (1) the effective value of the DC current Idc on the inverter 2 side of the smoothing capacitor C (hereinafter referred to as the inverter DC current) and (2) the effective value of the DC current on the battery side (opposite the inverter) of the smoothing capacitor C (hereinafter referred to as the battery DC current), so there is no problem in estimating the remaining battery capacity by regarding (1) the inverter DC current Idc as (2) the battery DC current.

[0039] Furthermore, if it is absolutely necessary to use the estimated value of (2) the battery DC current, (1) the inverter DC current Idc can be replaced with (2) the battery DC current when calculating the input power in the pre-test for creating the loss table 6 in the first embodiment.

[0040] The application of the DC current estimated in the present invention is not limited to estimating the remaining battery capacity, but may be used for other purposes, and may also be applied to systems other than electric vehicles.

[0041] Although the present invention has been described in detail above only with respect to the specific examples, it will be apparent to those skilled in the art that various modifications and variations are possible within the scope of the technical concept of the present invention, and it is natural that such modifications and variations fall within the scope of the claims. [Explanation of symbols]

[0042] C...smoothing capacitor, 2...inverter, 3...motor, 4a...first data table, 4b...second data table, 5...current calculation unit, 6...loss table, 7...first adder, 8...magnet temperature compensation gain table, 9...multiplier, 10...magnet temperature rise table, 11...second adder

Claims

1. An inverter having a DC side connected to a smoothing capacitor and an AC side connected to a motor, which converts DC power into AC power to drive the motor, a DC current estimation unit that estimates a DC current on the inverter side of the smoothing capacitor or a DC current on the opposite side of the smoothing capacitor from the inverter, an inverter comprising: an inverter estimating a simulated magnet temperature of a rotor of the motor based on a coil temperature detection value or a motor current of the motor and a rotation speed of the motor; deriving a magnet temperature correction gain based on the simulated magnet temperature; calculating a pre-correction DC current estimate based on a torque command value, the rotation speed and a DC voltage; and multiplying the pre-correction DC current estimate by the magnet temperature correction gain to calculate a post-correction DC current estimate.

2. The DC current estimation unit a first data table for deriving a first magnet temperature estimate based on the coil temperature detection value; a second data table for deriving a magnet temperature rotation speed correction amount based on the rotation speed; a first adder that adds the first magnet temperature estimate value and the magnet temperature rotational speed correction value to output the simulated magnet temperature; a magnet temperature correction gain table that derives the magnet temperature correction gain based on the simulated magnet temperature; a current calculation unit that calculates the pre-correction DC current estimation value based on the torque command value, the rotation speed, the DC voltage, and a loss; a multiplier that multiplies the uncorrected DC current estimation value by the magnet temperature correction gain and outputs the corrected DC current estimation value; 2. The inverter according to claim 1, further comprising:

3. The DC current estimation unit a magnet temperature rise table that derives a magnet temperature rise estimate value based on the motor current and the rotation speed; a second adder that adds the motor ambient temperature to the magnet temperature rise estimate value and outputs the simulated magnet temperature; a magnet temperature correction gain table that derives the magnet temperature correction gain based on the simulated magnet temperature; a current calculation unit that calculates the pre-correction DC current estimation value based on the torque command value, the rotation speed, the DC voltage, and a loss; a multiplier that multiplies the uncorrected DC current estimation value by the magnet temperature correction gain and outputs the corrected DC current estimation value; 2. The inverter according to claim 1, further comprising:

4. The DC current estimation unit a loss table storing the loss using the torque command value, the rotation speed, and the DC voltage as parameters; 4. The inverter according to claim 2, wherein the loss used in the current calculation unit is a value calculated from the loss table based on the torque command value, the rotational speed, and the DC voltage.

5. a battery is connected to the smoothing capacitor on the opposite side of the inverter; 2. A system for estimating a remaining capacity of the battery using the corrected DC current estimated value according to claim 1.

6. 1. A DC current estimation method for an inverter having a DC side connected to a smoothing capacitor and an AC side connected to a motor, the inverter converting DC power into AC power to drive the motor, comprising: a DC current estimation unit that estimates a DC current on the inverter side of the smoothing capacitor or a DC current on the opposite side of the smoothing capacitor from the inverter, a magnet temperature correction gain based on the simulated magnet temperature; a torque command value, the rotation speed, and a DC voltage; and a DC current estimation value before correction by multiplying the magnet temperature correction gain by the torque command value.

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