Inverter, system, and DC current estimation method for inverter

Abstract

An inverter 2, a DC side of which is connected to a smoothing capacitor C and an AC side of which is connected to a motor 3, converts DC power into AC power to drive the motor 3. A DC current estimation unit estimates a DC current Idc on a side of the inverter 2 of the smoothing capacitor C or a DC current on the opposite side of the smoothing capacitor C from the inverter 2. The DC current estimation unit estimates a simulated magnet temperature of the rotor of the motor 3 on the basis of the coil temperature detection value of the motor 3 or the motor current and the rotation speed of the motor 3, and derives a magnet temperature correction gain on the basis of the simulated magnet temperature. A pre-correction DC current estimation value is calculated on the basis of a torque command value, the rotation speed, and a DC voltage. The pre-correction DC current estimation value is multiplied by the magnet temperature correction gain to calculate a post-correction DC current estimation value. In the inverter, the estimation accuracy of the DC current is improved in consideration of an effect of the magnet temperature of the motor rotor.

Description

Inverter, system, and inverter DC current estimation method

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

[0002] In electric vehicles, the DC power from the battery 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. Information on the battery output current while the inverter is operating is required to calculate the remaining battery capacity.

[0003] Japanese Patent Application Laid-Open No. 2007-159347

[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, a method for estimating the inverter DC current without using a current sensor is disclosed in Patent Document 1. 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.

[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.

[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.

[0014] Fig. 1 is a diagram showing an example of the configuration of an inverter. Fig. 2 is a block diagram showing a DC current estimation unit of Example 1. Fig. 3 is a block diagram showing a DC current estimation unit of Example 2. Fig. 4 is a diagram showing DC current estimation accuracy (difference from actual measurement) with respect to magnet temperature.

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

[0016] 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 the 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 from the detected coil temperature value, which is, for example, a value obtained by actually measuring the coil temperature of the motor using a coil temperature detector (e.g., a thermistor; not shown) attached to the coil of the motor.

[0021] The first magnet temperature estimate output from the first data table 4a corresponds to a temperature estimate dependent on the motor copper loss. The first data table 4a is set by a pre-test that measures the coil temperature 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 a magnet temperature rotation speed correction amount based on the rotation speed. The rotation speed input to the second data table 4b may be either a rotation speed detection value or a 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 with 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 by a pre-test that measures the magnet temperature at each rotation speed under a constant coil temperature condition. 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) will be described. The current calculation unit 5 inputs the torque FB (torque command value), rotation speed (detected rotation speed value), DC voltage (detected DC voltage 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 FIG. 1. Pre-correction current = (torque command value × detected rotation speed value / 60 * 2π + loss) / detected DC voltage value (1) The loss in equation (1) uses the value derived from loss table 6. The 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 DC current Idc is measured for each combination of parameters: torque command value, rotation speed (detected rotation speed value), and DC voltage (detected DC voltage value), and loss (= inverter input power - motor shaft output) is calculated from inverter input power (= DC voltage × 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 described. 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 correction gain in magnet temperature correction 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 preliminary test of the correction gain, and Idc(Tmg0) indicates the DC current actually measured when the magnet temperature was Tmg0 in the preliminary test of the correction gain (the magnet temperature set to a constant value in the preliminary test of loss table 6). The magnet temperature correction gain table 8 inputs a simulated magnet temperature (Tmg), and outputs the correction gain Idc(Tmg) / Idc(Tmg0) from the DC current Idc(Tmg) at the simulated magnet temperature (Tmg) and the DC current Idc(Tmg0) at the magnet temperature Tmg0.

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

[0030] Figure 4 shows the difference between the pre-correction DC current estimate (× without magnet temperature correction), which is the input to multiplier 9, and the actual measurement value of the corrected DC current estimate (● 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 estimate (%).

[0031] As shown in Figure 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 estimate value to be transmitted to the outside of the inverter, the estimation accuracy of the DC current estimate value can be improved by correcting for the influence of the magnet temperature of the motor rotor. Furthermore, when the DC current estimate 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] Second Embodiment 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 motor's copper loss caused by magnet temperature rise is roughly proportional to the square of the motor current. As mentioned above, the motor's iron loss 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 to output 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). Therefore, 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 of 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.

[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 to AC power to drive the motor, wherein a DC current estimation unit that estimates the DC current on the inverter side of the smoothing capacitor or the DC current on the opposite side of the smoothing capacitor from the inverter estimates a simulated magnet temperature of the motor's rotor based on a detected coil temperature value or motor current of the motor and the motor's 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 DC voltage, and calculates a post-correction DC current estimate by multiplying the pre-correction DC current estimate by the magnet temperature correction gain.

2. The inverter according to claim 1, wherein the DC current estimation unit comprises: 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 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.

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

4. An inverter according to claim 2 or 3, characterized in that 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.

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

6. 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, 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 the motor's rotor based on the motor's coil temperature or motor current and the motor's 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 DC voltage, and calculates a post-correction DC current estimate by multiplying the pre-correction DC current estimate by the magnet temperature correction gain.

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