Power conversion device and electric power steering device

Abstract

In the power conversion device and the electric power steering device of the present invention, the first offset correction and the second offset correction are switched at a period (T c ) shorter than the electrical angle period of the AC rotating electric machine (1). The first offset correction determines a first offset amount (Vofs1) such that the applied voltage of at least n-2 phases among the phase currents (Iu1, Iv1, Iw1) of the AC rotating electric machine (1) can be detected, and the applied voltage is calculated by equally subtracting the first offset amount (Vofs1) from all voltage commands. The second offset correction determines a second offset amount (Vofs2) whose sign of the average value in the electrical angle period is opposite to that of the average value in the electrical angle period of the first offset amount (Vofs1), and the applied voltage is calculated by equally subtracting the second offset amount (Vofs2) from all the voltage commands.

Description

Technical Field

[0001] The present application relates to a power conversion device and an electric power steering device. Background Art

[0002] Conventionally, for example, in a motor control device used in an electric power steering device, a power conversion device such as an inverter is used.

[0003] For example, Patent Document 1 discloses a power conversion device that can reduce power losses caused by a shunt resistor or a switching element for current detection. In Patent Document 1, the power loss in the shunt resistor is reduced by shifting the three-phase voltage command in the positive direction. In addition, the duty ratio of the maximum phase that cannot be subjected to current detection because the current detection time has not been reached is fixed at 100%, and the current detection accuracy is ensured by performing current detection with the other two phases.

[0004] In addition, for example, Patent Document 2 discloses a power conversion device that reduces the difference in the conduction time of each switching element and reduces the deviation of the heat loss of each switching element by changing the shift direction of the voltage command in the case of left steering and right steering of a vehicle-equipped steering wheel.

[0005] Furthermore, for example, Patent Document 3 discloses a PWM amplifier in which the peak value and the effective value of the input current are small without increasing the circuit scale, and discloses the following technique: by alternately switching the bias signals of the PWM amplifier on the first axis and the PWM amplifier on the second axis in each prescribed period of the triangular wave, the conduction time of the transistors constituting the upper arm or the lower arm is not restricted.

[0006] Prior Art Documents

[0007] Patent Documents

[0008] Patent Document 1: Japanese Patent Laid-Open No. 2009-17671

[0009] Patent Document 2: Japanese Patent Laid-Open No. 2012-161154

[0010] Patent Document 3: Japanese Patent Laid-Open No. 2007-306705

[0011] Patent Document 4: Japanese Patent Laid-Open No. 2012-170277

[0012] Patent Document 5: International Publication WO2016 / 143121A1 Summary of the Invention

[0013] Technical Problem to be Solved by the Invention

[0014] In the power conversion device disclosed in Patent Document 1, in order to reduce the power loss in the shunt resistor, the three-phase voltage command is shifted in the positive direction. By using this method, although the power loss in the shunt resistor can be reduced, the conduction loss in the high-potential-side switching element becomes larger than the conduction loss in the low-potential-side switching element.

[0015] The shunt resistor often has a smaller thermal resistance than the switching element. In addition, even if the thermal resistances are the same, by using a non-contact current detector instead of the shunt resistor, the heat generation caused by the shunt resistor can be suppressed. In this case, in the method of Patent Document 1 where there is a deviation in the heat generation states between the upper arm and the lower arm, even if there is a margin in the temperature of the low-potential-side switching element, due to the temperature rise of the high-potential-side switching element with a large amount of heat generation, the function of overheat protection is limited.

[0016] In addition, in the power conversion device disclosed in Patent Document 2, in the high modulation rate region, there are differences in current detection accuracy depending on the direction of the shift, so there is a problem that noise or vibration deteriorates in a certain winding. In addition, since the shift direction of the voltage command of each winding is switched according to the direction of the steering torque, in the case of a locked steering wheel, if the state of the steering torque in the input fixed direction continues, a heat generation deviation will occur.

[0017] In addition, in the PWM amplifier disclosed in Patent Document 3, the bias signal is switched. However, for example, when current detection is performed by a current detector serially inserted with the low-potential-side switching element, although current can be detected without problems when the bias signal is supplied in the negative direction, when the bias signal is supplied in the positive direction, there is a problem that the number of phases where current cannot be detected increases compared to the case where no bias signal is supplied.

[0018] This application discloses a technology for solving the above problems, and its purpose is to provide a power conversion device and an electric power steering device that eliminate the heat generation deviation while ensuring current detection accuracy.

[0019] Technical means for solving technical problems

[0020] The power conversion device disclosed in this application includes a DC power supply that outputs a DC voltage, and this power conversion device is connected to an AC rotating electric machine having n-phase windings of three or more phases, and is characterized by including:

[0021] A power converter that has a high-potential-side switching element and a low-potential-side switching element, performs switching control on the high-potential-side switching element and the low-potential-side switching element based on on / off signals, and converts the DC voltage into an AC voltage and applies it to the n-phase windings;

[0022] A current detector inserted in series with the high-potential side switching element or the low-potential side switching element to obtain a detected current for each phase; and a control unit that calculates a voltage command based on a current command of the AC rotating machine, and compares an applied voltage obtained by performing a first offset correction and a second offset correction on the voltage command with a carrier signal to output the on / off signal,

[0023] The control unit switches between the first offset correction and the second offset correction at a period shorter than the electrical angle period of the AC rotating machine. The first offset correction determines a first offset amount such that an applied voltage capable of detecting at least n-2 phases of the phase currents of the AC rotating machine is obtained, and the applied voltage is calculated by equally subtracting the first offset amount from all the voltage commands. The second offset correction determines a second offset amount whose average value in the electrical angle period has the opposite sign to the average value in the electrical angle period of the first offset amount, and the applied voltage is calculated by equally subtracting the second offset amount from all the voltage commands.

[0024] Advantageous Effects of the Invention

[0025] According to the power conversion device disclosed in the present application, a power conversion device capable of eliminating the deviation of heat generation while ensuring current detection accuracy can be obtained. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 It is an overall structural diagram of controlling an AC rotating machine using the power conversion device according to Embodiment 1.

[0027] Figure 2 It is an operation explanatory diagram of the on / off signal generator for the power conversion device according to Embodiment 1.

[0028] Figure 3 It is a flowchart for explaining the calculation of the first offset correction in the power conversion device according to Embodiment 1.

[0029] Figure 4A It is a diagram showing three-phase applied voltages with a modulation rate of 85% when determining the first offset amount in the power conversion device according to Embodiment 1.

[0030] Figure 4B It is a diagram showing three-phase applied voltages with a modulation rate of 100% when determining the first offset amount in the power conversion device according to Embodiment 1.

[0031] Figure 5 It is a flowchart for explaining the calculation of the second offset correction in the power conversion device according to Embodiment 1.

[0032] Figure 6A It is a diagram showing a three-phase applied voltage with a modulation rate of 85% when determining the second offset in the power conversion device according to Embodiment 1.

[0033] Figure 6B It is a diagram showing a three-phase applied voltage with a modulation rate of 100% when determining the second offset in the power conversion device according to Embodiment 1.

[0034] Figure 7A It shows Figure 4A and Figure 4B the first offset in Figure 6A and Figure 6B the second offset in

[0035] Figure 7B It shows Figure 4A and Figure 4B the first offset in Figure 6A and Figure 6B the second offset in

[0036] Figure 8 It is a flowchart explaining another operation of the first offset correction in the power conversion device according to Embodiment 1.

[0037] Figure 9A It is a diagram showing the waveform of the applied voltage when the second offset is applied so that the applied voltage of the maximum phase of the three-phase applied voltage becomes the maximum value of the carrier signal.

[0038] Figure 9B It is a diagram showing the waveform of the applied voltage when the second offset is applied so that the applied voltage of the maximum phase of the three-phase applied voltage becomes the maximum value of the carrier signal.

[0039] Figure 10 It is a flowchart explaining another operation of the first offset correction in the power conversion device according to Embodiment 1.

[0040] Figure 11A It is a waveform diagram of the applied voltage when the maximum value of the applied voltage capable of current detection is 0.4 and the modulation rate is 2√3 / 5 in the power conversion device according to Embodiment 1.

[0041] Figure 11B It is a waveform diagram of the applied voltage when the maximum value of the applied voltage capable of current detection is 0.4 and the modulation rate is 2√3 / 5 in the power conversion device according to Embodiment 1.

[0042] Figure 12AThis is a waveform diagram of the applied voltage when the maximum value of the applied voltage capable of current detection is 0.4 and the modulation rate is 0.7 in the power conversion device according to Embodiment 1.

[0043] Figure 12B This is a waveform diagram of the applied voltage when the maximum value of the applied voltage capable of current detection is 0.4 and the modulation rate is 0.7 in the power conversion device according to Embodiment 1.

[0044] Figure 13 This is a diagram showing the operation timing of the voltage command calculator, offset calculator, and on / off signal generator used in the power conversion device according to Embodiment 1.

[0045] Figure 14 This is an overall structure diagram of controlling an AC rotating electric machine using the power conversion device according to Embodiment 2.

[0046] Figure 15 This is an operation explanatory diagram of the on / off signal generator for the power conversion device according to Embodiment 2.

[0047] Figure 16 This is a flowchart for explaining the operation of the first offset correction in the power conversion device according to Embodiment 2.

[0048] Figure 17A This is a diagram showing the three-phase applied voltage when the modulation rate is 85% for determining the first offset amount in the power conversion device according to Embodiment 2.

[0049] Figure 17B This is a diagram showing the three-phase applied voltage when the modulation rate is 100% for determining the first offset amount in the power conversion device according to Embodiment 2.

[0050] Figure 18 This is a flowchart for explaining the operation of the second offset correction in the power conversion device according to Embodiment 2.

[0051] Figure 19A This is a diagram showing the three-phase applied voltage when the modulation rate is 85% for determining the second offset amount in the power conversion device according to Embodiment 2.

[0052] Figure 19B This is a diagram showing the three-phase applied voltage when the modulation rate is 100% for determining the second offset amount in the power conversion device according to Embodiment 2.

[0053] Figure 20A This is a diagram showing Figure 17A and Figure 17B the first offset amount in Figure 19A and Figure 19BThe figure of the second offset in

[0054] Figure 20B shows Figure 17A and Figure 17B the first offset in Figure 19A and Figure 19B the figure of the second offset in

[0055] Figure 21 is a flowchart illustrating another operation of the first offset correction in the power conversion device according to Embodiment 2.

[0056] Figure 22A is a figure showing the waveform of the applied voltage when the second offset is applied such that the applied voltage of the minimum phase of the three-phase applied voltage becomes the minimum value of the carrier signal.

[0057] Figure 22B is a figure showing the waveform of the applied voltage when the second offset is applied such that the applied voltage of the minimum phase of the three-phase applied voltage becomes the minimum value of the carrier signal.

[0058] Figure 23 is a flowchart illustrating another operation of the first offset correction in the power conversion device according to Embodiment 2.

[0059] Figure 24A is a waveform diagram of the applied voltage when the maximum value of the applied voltage at which current detection can be performed is 0.4 and the modulation rate is 2√3 / 5 in the power conversion device according to Embodiment 2.

[0060] Figure 24B is a waveform diagram of the applied voltage when the maximum value of the applied voltage at which current detection can be performed is 0.4 and the modulation rate is 2√3 / 5 in the power conversion device according to Embodiment 2.

[0061] Figure 25A is a waveform diagram of the applied voltage when the maximum value of the applied voltage at which current detection can be performed is 0.4 and the modulation rate is 0.7 in the power conversion device according to Embodiment 2.

[0062] Figure 25B is a waveform diagram of the applied voltage when the maximum value of the applied voltage at which current detection can be performed is 0.4 and the modulation rate is 0.7 in the power conversion device according to Embodiment 2.

[0063] Figure 26 is a block diagram showing the overall structure of the electric power steering device according to Embodiment 3. Detailed implementation mode

[0064] Hereinafter, embodiments of the present application will be described with reference to the accompanying drawings. In addition, the same or corresponding parts are denoted by the same reference numerals in each figure for description.

[0065] Embodiment 1.

[0066] Figure 1 It is an overall structure diagram for controlling an AC rotating electric machine using the power conversion device according to Embodiment 1.

[0067] In Figure 1 , the AC rotating electric machine 1 is a three-phase AC rotating electric machine in which three-phase windings U1, V1, and W1 are housed in the stator of the rotating electric machine. As the AC rotating electric machine, a permanent magnet synchronous rotating electric machine, an induction rotating electric machine, a synchronous reluctance rotating electric machine, etc. can be cited. However, in the present embodiment, any rotating electric machine can be used as long as it is an AC rotating electric machine having n-phase windings of three phases or more.

[0068] The DC power supply 2 outputs a DC voltage V to the power converter 3 dc . As the DC power supply 2, it includes all devices that output a DC voltage, such as a battery, a DC-DC converter, a diode rectifier, and a PWM rectifier.

[0069] The filter capacitor 4 is connected in parallel with the DC power supply 2 to suppress fluctuations in the bus current and thereby achieve a stable DC current. Although not shown in detail here, in addition to the actual capacitance C, there are also an equivalent series resistance Rc and a lead inductance Lc.

[0070] The power converter 3 uses a buck - boost circuit (inverter) and, based on on / off signals Qup1, Qun1, Qvp1, Qvn1, Qwp1, Qwn1, turns on / off the high - potential - side switching elements Sup1, Svp1, Swp1 and the low - potential - side switching elements Sun1, Svn1, Swn1, thereby performing power conversion on the DC voltage V dc input from the DC power supply 2 and applying a voltage to the three - phase windings U1, V1, W1 of the AC rotating electric machine 1 to make the currents I u1 , I v1 , I w1Power on. Here, the conduction / cutoff signal Qup1 is a signal for turning on / off the high-potential side switching element Sup1 of the power converter 3, and the conduction / cutoff signal Qun1 is a signal for turning on / off the low-potential side switching element Sun1 of the power converter 3. Additionally, the conduction / cutoff signal Qvp1 is a signal for turning on / off the high-potential side switching element Svp1 of the power converter 3, and the conduction / cutoff signal Qvn1 is a signal for turning on / off the low-potential side switching element Svn1 of the power converter 3. Furthermore, the conduction / cutoff signal Qwp1 is a signal for turning on / off the high-potential side switching element Swp1 of the power converter 3, and the conduction / cutoff signal Qwn1 is a signal for turning on / off the low-potential side switching element Swn1 of the power converter 3. After that, among the conduction / cutoff signals Qup1, Qun1, Qvp1, Qvn1, Qwp1, Qwn1, if the value is 1, a signal for turning on the corresponding switching element is output. On the other hand, if the value is 0, a signal for turning off the corresponding switching element is output. As the switching elements Sup1, Svp1, Swp1, Sun1, Svn1, Swn1, switching elements obtained by reversely connecting in parallel a semiconductor switch such as an IGBT, a bipolar transistor, a MOS power transistor, and a diode are used.

[0071] The control unit 5 includes a voltage command calculator 6, an offset calculator 7, and a conduction / cutoff signal generator 8. The voltage command calculator 6 calculates the three-phase voltage command V u1 、V v1 、V w1 applied to the three-phase windings U1, V1, W1 of the drive AC rotating motor 1, and outputs it to the offset calculator 7. As a calculation method of the three-phase voltage command V u1 、V v1 、V w1 , the current command of the AC rotating motor 1 is set as a control command, and current feedback control that calculates the three-phase voltage command V u1 、V v1 、V w1 through proportional-integral control is used, so that the deviation of the currents I u1 、I v1 、I w1 flowing through the three-phase windings U1, V1, W1 detected by the current detector 9 described later becomes zero. Since this control is a well-known technique, detailed description is omitted.

[0072] The offset calculator 7 calculates the three-phase applied voltage V u1 、V v1 、V w1 , and calculates the three-phase applied voltage V u1c, V v1 c, V w1 c. In the first offset correction, a first offset amount Vofs1 is determined such that an applied voltage enabling current detection of at least one of the three-phase currents is obtained. The first offset amount Vofs1 is subtracted from the three-phase voltage command V u1 , V v1 , V w1 to obtain the three-phase applied voltage V u11 c, V v11 c, V w11 c. In the second offset correction, a second offset amount Vofs2 is determined. The average value in the electrical angle period of the second offset amount Vofs2 has a sign opposite to that of the average value in the electrical angle period of the first offset amount Vofs1. The second offset amount Vofs2 is subtracted from the three-phase voltage command V u1 , V v1 , V w1 to obtain the three-phase applied voltage V u12 c, V v12 c, V w12 c. Then, the three-phase applied voltage V u11 c, V v11 c, V w11 c obtained by the first offset correction or the three-phase applied voltage V u12 c, V v12 c, V w12 c obtained by the second offset correction is output as the three-phase applied voltage V u1 c, V v1 c, V w1 c.

[0073] Hereinafter, the three-phase voltage commands V u1 , V v1 , V w1 are arranged in descending order and set as the three-phase voltage command V max1 of the maximum phase (hereinafter referred to as the maximum phase V max1 ), the three-phase voltage command V mid1 of the intermediate phase (hereinafter referred to as the intermediate phase V mid1 ), and the three-phase voltage command V min1 of the minimum phase (hereinafter referred to as the minimum phase V min1 ). The three-phase applied voltage V u1 c, V v1 c, V w1 c obtained by the offset correction is arranged in descending order and set as the corrected three-phase applied voltage V max1 c of the maximum phase (hereinafter, referred to as the maximum phase V max1 c), the corrected three-phase applied voltage V mid1 c of the intermediate phase, and the corrected three-phase applied voltage Vmin1 c (hereinafter referred to as the minimum phase V min1 c) will be described.

[0074] The conduction / cutoff signal generator 8 outputs conduction / cutoff signals Qup1, Qun1, Qvp1, Qvn1, Qwp1, Qwn1 based on the three-phase applied voltages V u1 c, V v1 c, V w1 c, and outputs conduction / cutoff signals Qup2, Qun2, Qvp2, Qvn2, Qwp2, Qwn2 based on the second three-phase applied voltages V u2 c, V v2 c, V w2 c.

[0075] Figure 2 is an operation explanatory diagram of the conduction / cutoff signal generator 8. In Figure 2 , the label Cl is a carrier signal, and it has a minimum value of -0.5V at time t1 and time t3 dc , and has a maximum value of 0.5V at time t2 dc with a period T c of a triangular wave. The carrier signal Cl is compared with the three-phase applied voltage V u1 c. If the three-phase applied voltage V u1 c is larger, then "Qup1 = 1 and Qun1 = 0" is output. If the three-phase applied voltage V u1 c is smaller, then "Qup1 = 0 and Qun1 = 1" is output. Similarly, the carrier signal Cl is compared with the three-phase applied voltage V v1 c. If the three-phase applied voltage V v1 c is larger, then "Qvp1 = 1 and Qvn1 = 0" is output. If the three-phase applied voltage V v1 c is smaller, then "Qvp1 = 0 and Qvn1 = 1" is output. Similarly, the carrier signal Cl is compared with the three-phase applied voltage V w1 c. If the three-phase applied voltage V w1 c is larger, then "Qwp1 = 1 and Qwn1 = 0" is output. If the three-phase applied voltage V w1 c is smaller, then "Qwp1 = 0 and Qwn1 = 1" is output. In addition, the detection timing t s represents the timing of current detection.

[0076] The current detector 9 is serially provided on each phase of the low-potential side switching elements Sun1, Svn1, Swn1 of the power converter 3, and detects the currents I u1 , I v1 , I w1 .

[0077] Here, the time required for the current detector 9 to detect the current (the lower limit value of the energization time of the current detection resistance element determined in consideration of the ringing convergence time included in the detection waveform, or the conversion time of the analog / digital converter, and the time required for sampling / holding) is set as t. i . In Figure 2 , in order to accurately detect at the detection timing t of the current detector 9 s , it is necessary that no switching from 0 to 1 and from 1 to 0 of the on / off signals Qup1, Qun1, Qvp1, Qvn1, Qwp1, Qwn1 of the power converter 3 occurs during the period from t s - t i to t s . If such switching occurs, noise is mixed into the detected currents I u1 , I v1 , I w1 , resulting in vibration or noise generated by the AC rotating machine 1.

[0078] In order to accurately detect when the detection timing t s is set within t i / 2 from time t2, taking the maximum phase V max1 c as the maximum value of the three-phase applied voltages V u1 c, V v1 c, V w1 c, the following formula (1) needs to be satisfied. Here, it is within t i / 2 because if it is set after this, it will be affected by the noise generated due to the switching of the on / off signal from 0 to 1 or from 1 to 0 after time t2.

[0079] [Mathematical formula 1]

[0080]

[0081] According to formula (1), when the detection timing t s is set within t i / 2 from time t2, the applied voltage V max c of the maximum phase can be set to the maximum. If the following formula (2) is satisfied, the currents of the three phases can be detected at the detection timing t s . In addition, for the time t i , the convergence time of the current interference caused by the influence of the switching noise of other phases can also be considered. In this case, by avoiding the switching within the time t i centered on the detection timing, high-precision currents can be detected not only in the maximum phase but also in all phases.

[0082] As Figure 2 shown, preferably, by updating the conduction / cutoff signal at the trough of the carrier signal Cl, a conduction / cutoff signal that is substantially symmetric about the peak of the carrier signal Cl can be achieved, and it is possible to determine whether current detection can be performed by applying a voltage once. In addition, in the case where the conduction / cutoff signal is updated at the peak of the carrier signal Cl, it is possible to determine whether current detection can be performed by considering two applied voltages sandwiching the peak of the carrier signal Cl.

[0083] [Mathematical formula 2]

[0084]

[0085] In the current detector 9 inserted in series with the low-potential side switching elements Sun1, Svn1, and Swn1, the ratio of the maximum value of the applied voltage at which current detection can be performed to the DC voltage (hereinafter referred to as the maximum applied voltage ratio) is set to K m In the case of m V dc (hereinafter referred to as the maximum applied voltage) or less, current detection can be performed with high precision. Here, K m satisfies the following formula (3).

[0086] [Mathematical formula 3]

[0087]

[0088] For example, when the period T c is 50 μs and the time t i required for the current detector 9 to detect current is 4.9 μs, when the modulation rate K at which the maximum phase V max1 c can be made 0.4 V dc or less is 90% or less, three-phase detection can be performed. In the region where the modulation rate K exceeds 90%, the maximum phase V max1 c is 0.4 V dc or more, so two phases other than the maximum phase can be detected, and the remaining one phase can be estimated from the two detectable phases by a known method.

[0089] Hereinafter, the case where the maximum applied voltage ratio K m is 0.4 will be described as an example.

[0090] First, the operation of the first offset correction will be described.

[0091] Figure 3 is a flowchart for explaining the operation of the first offset correction. In Figure 3 , in step S120, the three-phase voltage commands V u1 , V v1 , Vw1 Substitute the maximum phase V in descending order max1 , the intermediate phase V mid1 , the minimum phase V min1 .

[0092] In step S121, it is determined whether the modulation rate K is 90% or less. If true ("yes"), step S122 is executed. If false ("no"), step S123 is executed. Additionally, for example, as shown in Patent Document 4 Figure 8 , it is also possible to use the difference between the maximum phase V max1 and the minimum phase V min1 for determination.

[0093] In step S122, the first offset Vofs1 is determined such that the maximum phase V max c of the three-phase applied voltage is 0.4V or less for current detection dc .

[0094] In step S123, it is determined whether the difference between the voltage command of the maximum phase and the voltage command of the intermediate phase is less than 0.1V dc . If true ("yes"), step S124 is executed. If false ("no"), step S125 is executed.

[0095] In step S124, in order to maximize the time from the switch of the maximum phase to the detection timing t s , the first offset Vofs1 is determined such that the minimum phase V min c of the three-phase applied voltage is -0.5V dc .

[0096] In step S125, in order to stop the switch of the maximum phase, the first offset Vofs1 is determined such that the maximum phase V max c of the three-phase applied voltage is 0.5V dc . At this time, the three-phase applied voltage with a modulation rate K of 85% is as shown in Figure 4A , and the three-phase applied voltage with a modulation rate K of 100% is as shown in Figure 4B . In all regions, a detection current of two or more phases can be obtained.

[0097] According to the modulation rate K, sometimes only one phase can be detected in a part, but the first offset Vofs1 can be set to a value that obtains a detection current of at least one phase or more.

[0098] By making the modulation rate K less than or equal to the third specified value K3 that satisfies the following formula (4), the applied voltage of the maximum phase can be made less than or equal to the maximum applied voltage, and a detection current of at least one phase or more can be obtained in all regions. Additionally, in Figure 4A and Figure 4B , the dashed line a represents the three-phase applied voltage Vu11 c, the single-dot dash line b represents the three-phase applied voltage V v11 c, the solid line c represents the three-phase applied voltage V w11 c.

[0099] [Mathematical formula 4]

[0100]

[0101] In addition, when the modulation rate K is greater than the third specified value K3, by making the applied voltage of the maximum phase the maximum applied voltage K m V dc hereinafter, or the maximum value of the carrier signal Cl, it is possible to detect one or more phases of current with high accuracy. When the modulation rate is large, the applied voltage of the intermediate phase may sometimes be greater than the maximum applied voltage K m V dc and less than the maximum value of the carrier signal Cl. However, for example, as in Patent Document 5, by setting two detection timings, it is possible to detect one or more phases of current with high accuracy and to estimate the remaining two phases.

[0102] Next, the operation of the second offset correction will be described. Figure 5 is a flowchart for explaining the operation of the second offset correction.

[0103] In Figure 5 in step S130, the three-phase voltage commands V u1 、V v1 、V w1 are substituted into the maximum phase V max1 、the intermediate phase V mid1 、the minimum phase V min1 in descending order.

[0104] In step S131, it is determined whether the modulation rate K is 90% or less. If true ("yes"), step S132 is executed. If false ("no"), step S133 is executed.

[0105] In step S132, according to step S122, the second offset Vofs2 is determined so that the minimum phase V min c of the three-phase applied voltage is -0.4V dc .

[0106] In step S133, it is determined whether the difference between the voltage command of the intermediate phase and the voltage command of the minimum phase is less than 0.1V dc , if true ("yes"), step S134 is executed. If false ("no"), step S135 is executed.

[0107] In step S134, according to Figure 3In step S124, determine the second offset Vofs2 such that the maximum phase V of the three-phase applied voltage max c is 0.5 V dc .

[0108] In step S135, according to Figure 3 In step S125, determine the second offset Vofs2 such that the minimum phase V of the three-phase applied voltage min c is -0.5 V dc . At this time, the three-phase applied voltage with a modulation rate K of 85% is as Figure 6A shown, and the three-phase applied voltage with a modulation rate K of 100% is as Figure 6B shown. Additionally, in Figure 6A and Figure 6B , the dashed line a represents the three-phase applied voltage V u12 c, the dash-dotted line b represents the three-phase applied voltage V v12 c, and the solid line c represents the three-phase applied voltage V w12 c.

[0109] Next, the heat generation amounts of the high-potential side switching element Sup1 and the low-potential side switching element Sun1 of the U1 phase will be described.

[0110] If the conduction time ratio of the conduction time of the high-potential side switching element Sup1 with respect to the time of one cycle of the carrier signal Cl is set as D u1 , and the on-resistance of the switching element is set as R on , then the heat generation amount P up1 of the high-potential side switching element Sup1 and the heat generation amount P un1 of the low-potential side switching element Sun1 are given by the following equation (5).

[0111] [Mathematical formula 5]

[0112]

[0113] Here, the current I u1 and the three-phase voltage command V u1 are given by the following equation (6). In equation (6), I uvw represents the phase current amplitude, V uvw represents the phase voltage amplitude, and γ represents the phase difference between the phase voltage and the phase current, that is, the power factor angle.

[0114] [Mathematical formula 6]

[0115]

[0116] When the three-phase applied voltage V obtained by the offset arithmetic unit 7 u1When Vc is represented by the following formula (7), if the offset determined according to the first offset Vofs1 and the second offset Vofs2 is set as f(θ), the conduction time ratio D of the conduction time of the high-potential side switching element Sup1 with respect to the time of one cycle of the carrier signal Cl u1 is given by the following formula (8).

[0117] [Mathematical formula 7]

[0118] V u1 c = V u1 -f(θ)…(7)

[0119]

[0120] If formula (6) and formula (8) are substituted into formula (5), the calorific value P up1 and P un1 are as shown in the following formula (9).

[0121] [Mathematical formula 8]

[0122]

[0123] In order to make the calorific value of the high-potential side switching element Sup1 within one cycle of the electrical angle equal to the calorific value of the low-potential side switching element Sun1, it is only necessary for the following formula (10) to hold.

[0124] [Mathematical formula 9]

[0125]

[0126] That is to say, since the offset f(θ) starting from the first offset Vofs1 and the second offset satisfies the following formula (11), the calorific value of the high-potential side switching element Sup1 and the calorific value of the low-potential side switching element Sun1 can be equal.

[0127] [Mathematical formula 10]

[0128]

[0129] Figure 7A and Figure 7B shows Figure 4A and Figure 4B the first offset Vofs1 of Figure 6A and Figure 6B the second offset Vofs2 of Figure 7A andFigure 7B Among them, the dashed line d represents the second offset Vofs2, and the solid line e represents the first offset Vofs1.

[0130] In addition, the operation flowchart of the first offset correction can be as Figure 8 shown and replace Figure 3 step S122.

[0131] In Figure 8 step S122a, by setting the applied voltage of the minimum phase V min1 to the minimum value of the carrier signal Cl, the time from the switch of the maximum phase V max1 to the detection timing t s can be maximized, thereby improving the current detection accuracy.

[0132] In addition, the second offset can be applied so that the applied voltage of the maximum phase V max1 of the three-phase applied voltage becomes the maximum value of the carrier signal Cl. At this time, Figure 9A and Figure 9B show the waveforms of the applied voltage in the case where the maximum applied voltage ratio K m is 0.4 and the modulation rate K is 0.7. Figure 9A Among them, the dashed line f represents the three-phase applied voltage V u12 c, the dash-dotted line g represents the three-phase applied voltage V v12 c, and the solid line h represents the three-phase applied voltage V w12 c. In addition, in Figure 9B among them, the dashed line i represents the three-phase applied voltage V u11 c, the dash-dotted line j represents the three-phase applied voltage V v11 c, and the solid line k represents the three-phase applied voltage V w11 c.

[0133] In addition, since the electrical angle that changes in the carrier period is larger when the modulation rate K is high, the time staying in the region where the difference between the voltage commands of the maximum phase and the intermediate phase is small is short. Therefore, in addition to Figure 3 step S123, the operation flowchart of the first offset correction can be as Figure 10 shown.

[0134] When the modulation rate K is greater than the third specified value K3 provided by the maximum applied voltage ratio K m + 0.5, by setting it to the maximum value of the carrier signal Cl, the switch of one phase can be stopped. Therefore, the current detection error caused by the switching noise of other phases can be suppressed, and the current of more than one phase can be detected with high precision. In addition, by reducing the conditional branch, the processing load can be reduced.

[0135] In addition, when the modulation rate K is low, the amplitude of the voltage command is small, and there is a degree of freedom in the selection of the first offset. Therefore, when the modulation rate K is equal to or less than the first specified value K1, the first offset can be set to zero. In order to perform current detection with high precision, the applied voltage of the maximum phase needs to be at the maximum applied voltage K m V dc or less. Therefore, the first specified value K1 only needs to satisfy the following formula (12). By also setting the second offset to zero, the heat generation can be equalized. At this time, the ratio of the maximum applied voltage K m is 0.4, and the waveform of the applied voltage when the modulation rate K is 2√3 / 5 is as shown in Figure 11A and Figure 11B . The three-phase applied voltages V u11 c, V v11 c, V w11 c obtained by the first offset correction are equal to the three-phase applied voltages V u12 c, V v12 c, V w12 c obtained by the second offset correction. In addition, in Figure 11A , the dotted line l represents the three-phase applied voltage V u12 c, the dash-dotted line m represents the three-phase applied voltage V v12 c, and the solid line n represents the three-phase applied voltage V w12 c. In addition, in Figure 11B , the dotted line o represents the three-phase applied voltage V u11 c, the dash-dotted line p represents the three-phase applied voltage V v11 c, and the solid line q represents the three-phase applied voltage V w11 c.

[0136] [Mathematical formula 11]

[0137]

[0138] In addition, when it is desired to fix the offset so that the modulation rate K is equal to or less than the second specified value K2, the first offset is calculated based on the second specified value K2 as shown in the following formula (13). That is, the first offset is determined regardless of the modulation rate K at that time.

[0139] [Mathematical formula 12]

[0140]

[0141] The second offset is determined such that the sum of the second offset and the first offset is zero, and is therefore represented by the following formula (14).

[0142] [Mathematical formula 13]

[0143]

[0144] For high-precision current detection, the applied voltage of the largest phase needs to be at the maximum applied voltage K m V dc or less. Therefore, the second specified value K2 only needs to satisfy the following formula (15).

[0145] [Mathematical formula 14]

[0146]

[0147] At this time, Figure 12A and Figure 12B show the waveform of the applied voltage when the maximum applied voltage ratio K m is 0.4 and the modulation rate K is 0.7. As shown in formula (14), by making the offset constant, the low-order variation of the neutral point voltage can be suppressed. In particular, in a structure that detects faults or abnormalities based on the obtained neutral point voltage or the average value of the three-phase voltages, the determination accuracy of this structure with suppressed neutral point voltage variation is excellent. In addition, in Figure 12A , the dotted line l represents the three-phase applied voltage V u12 c, the dash-dot line m represents the three-phase applied voltage V v12 c, and the solid line n represents the three-phase applied voltage V w12 c. In addition, in Figure 12B , the dotted line o represents the three-phase applied voltage V u11 c, the dash-dot line p represents the three-phase applied voltage V v11 c, and the solid line q represents the three-phase applied voltage V w11 c.

[0148] In addition, when the thermal resistance of the high-potential side switching elements Sup1, Svp1, Swp1 is different from the thermal resistance of the low-potential side switching elements Sun1, Svn1, Swn1, or when the on-resistance of the high-potential side switching elements Sup1, Svp1, Swp1 is different from the on-resistance of the low-potential side switching elements Sun1, Svn1, Swn1, etc., use the constant K based on this situation pn Let it be the second offset so that the following formula (16) holds.

[0149] [Mathematical formula 15]

[0150]

[0151] Figure 13 is a diagram showing the operation timing of the voltage command calculator 6, the offset calculator 7, and the on / off signal generator 8. Here, Qup1(m - 1), Qun1(m - 1), Qvp1(m - 1), Qvn1(m - 1), Qwp1(m - 1), Qwn1(m - 1) are based on the three-phase applied voltage V obtained by the first offset correctionu1 (m - 1)c, V v1 (m - 1)c, V w1 ON / OFF signal of (m - 1)c

[0152] At timing t(m), since the applied voltage for performing the first offset correction for current detection can be output, the m-th I is detected, so u1 (m), I v1 (m), I w1 (m) is used to calculate the three-phase voltage command V u1 (m), V v1 (m), V w1 (m). Based on the three-phase voltage command V u1 (m), V v1 (m), V w1 (m), the three-phase applied voltage V is calculated by the second offset correction u1 (m)c, V v1 (m)c, V w1 (m)c

[0153] At timing t(m + 1), the applied voltage for the second offset correction for equalizing the heat generation is output. Therefore, without performing current detection, based on the previous three-phase voltage command V u1 (m), V v1 (m), V w1 (m), the three-phase applied voltage V is calculated by the first offset correction u1 (m + 1)c, V v1 (m + 1)c, V w1 (m + 1)c. Alternatively, a three-phase voltage command with a phase advanced by the rotational change amount of the AC rotating machine 1 with respect to the previous three-phase voltage command V u1 (m), V v1 (m), V w1 (m) can be used

[0154] At timing t(m + 2), the applied voltage for the first offset correction for current detection can be output. Therefore, by detecting the (m + 2)-th I u1 (m + 2), I v1 (m + 2), I w1 (m + 2) is used to calculate the three-phase voltage command V u1 (m + 2), V v1 (m + 2), V w1 (m + 2). Based on the three-phase voltage command V u1 (m + 2), V v1 (m + 2), V w1 (m + 2), the three-phase applied voltage V is calculated by the second offset correctionu1 (m + 2)c, V v1 (m + 2)c, V w1 (m + 2)c.

[0155] That is, when outputting the applied voltage generated by the first offset correction capable of current detection, the voltage command is calculated based on the detected phase currents. When outputting the applied voltage generated by the second offset correction for equalizing the heat generation without considering whether current detection is possible, the voltage command is not updated. Thus, while obtaining highly accurate detected current, equalization of heat generation is achieved, and by stopping the calculation based on low-accuracy detected current, the processing load can be suppressed.

[0156] By switching between the first offset correction and the second offset correction in the carrier period, the waste time from the detected current to the reflected applied voltage can be suppressed to the minimum, and thus improvement in current detection accuracy and equalization of heat generation can be achieved without deteriorating the control response.

[0157] Embodiment 2.

[0158] Next, the power conversion device according to Embodiment 2 will be described.

[0159] Figure 14 It is the overall structure diagram for controlling an AC rotating electric machine using the power conversion device according to Embodiment 2. The current detector 9a of the power conversion device according to Embodiment 2 is different from that of the power conversion device of Embodiment 1.

[0160] The current detector 9a is serially provided on each phase of the high-potential side switching elements Sup1, Svp1, Swp1 of the power converter 3 to detect the currents I flowing through the three-phase windings u1 , I v1 , I w1 .

[0161] Figure 15 It is the operation explanatory diagram of the conduction / turn-off signal generator for the power conversion device according to Embodiment 2, and is a diagram corresponding to that of Embodiment 1 Figure 2 .

[0162] In Figure 15 , in order to accurately detect at the detection timing t of the current detector 9a s , it is necessary that there is no switching from 0 to 1 and from 1 to 0 of the conduction / turn-off signals Qup1, Qun1, Qvp1, Qvn1, Qwp1, Qwn1 of the power converter 3 during the period from t s - t i to t s . If such switching occurs, then in the detected currents I u1 , Iv1 and I w1 Noise is mixed in, resulting in vibration or noise generated by the AC rotating motor 1

[0163] In the current detector 9a inserted in series with the high-potential side switching elements Sup1, Svp1, and Swp1, the ratio of the minimum applied voltage at which current detection can be performed to the DC voltage (hereinafter referred to as the minimum applied voltage ratio) is set to K S When the applied voltage is K S V dc (hereinafter referred to as the minimum applied voltage) or more, current detection can be performed with high precision. Here, K S Satisfies the following formula (17).

[0164] [Mathematical formula 16]

[0165]

[0166] For example, in the period T c Is 50 μs, and the time t required for the current detector 9a to detect the current i Is 4.9 μs, when the minimum phase V min1 c is -0.4 V dc When the modulation rate K is 90% or less, three-phase detection can be performed. In the region where the modulation rate K exceeds 90%, the minimum phase V min1 c is less than -0.4 V dc , so two phases other than the minimum phase can be detected, and the remaining one phase can be estimated from the two detectable phases by a known method. As Figure 15 Shown, preferably, by updating the on / off signal at the peak of the carrier signal Cl, an on / off signal that is substantially symmetric about the valley of the carrier signal Cl can be achieved, and it is possible to determine whether current detection can be performed with a single applied voltage. In addition, when updating the on / off signal at the valley of the carrier signal Cl, it is possible to determine whether current detection can be performed by considering the two applied voltages sandwiching the valley of the carrier signal Cl

[0167] Hereinafter, the case where the minimum applied voltage ratio K S Is -0.4 will be described as an example

[0168] Figure 16 Is a flowchart for explaining the operation of the first offset correction in the power conversion device according to Embodiment 2 Figure 16 Compared with that of Embodiment 1 Figure 3 It is different from step S122b to step S125b

[0169] In step S122b, a first offset is determined such that the minimum phase V of the three-phase applied voltage min c is -0.4V at which current detection can be performed dc or more.

[0170] In step S123b, it is determined whether the difference between the voltage command of the intermediate phase and the voltage command of the minimum phase is less than 0.1V dc . If true ("yes"), step S124b is executed; if false ("no"), step S125b is executed.

[0171] In step S124b, the time from the switch of the minimum phase to the detection timing t s is maximized, and thus the first offset is determined such that the maximum phase V of the three-phase applied voltage max c is 0.5V dc .

[0172] In step S125b, in order to stop the switch of the minimum phase, the first offset is determined such that the minimum phase V of the three-phase applied voltage min c is -0.5V dc . At this time, the three-phase applied voltage with a modulation rate K of 85% is as Figure 17A shown, and the three-phase applied voltage with a modulation rate K of 100% is as Figure 17B shown. In all regions, detection currents of two or more phases can be obtained. Depending on the modulation rate K, sometimes only one phase can be detected, but the first offset Vofs1 can be a value that obtains a detection current of at least one phase or more.

[0173] That is, by making the modulation rate K below a third specified value K3 that satisfies the following formula (18), the applied voltage of the minimum phase can be made above the minimum applied voltage, and detection currents of at least one phase or more can be obtained in all regions. Additionally, in Figure 17A and Figure 17B , the dashed line a represents the three-phase applied voltage V u11 c, the dash-dotted line b represents the three-phase applied voltage V v11 c, and the solid line c represents the three-phase applied voltage V w11 c.

[0174] [Mathematical formula 17]

[0175]

[0176] Furthermore, in the case where the modulation rate K is greater than the third specified value K3, by making the applied voltage of the minimum phase the minimum applied voltage K S V dc or more, or the minimum value of the carrier signal Cl, currents of one phase or more can be detected with high precision.

[0177] Figure 18 It is a flowchart for explaining the operation of the second offset correction. Figure 18 Compared with that of Embodiment 1 Figure 5 from step S132b to step S135b are different.

[0178] In step S132b, according to Figure 16 step S122b, the second offset is determined such that the maximum phase V of the three-phase applied voltage max c is 0.4V dc .

[0179] In step S133b, it is determined whether the difference between the voltage command of the maximum phase and the voltage command of the intermediate phase is less than 0.1V dc , if true ("yes"), step S134b is executed, if false ("no"), step S135b is executed.

[0180] In step S134b, according to Figure 16 step S124b, the second offset is determined such that the minimum phase V of the three-phase applied voltage min c is -0.5V dc .

[0181] In step S135b, according to Figure 16 step S125b, the second offset is determined such that the maximum phase V of the three-phase applied voltage max c is 0.5V dc . At this time, the three-phase applied voltage with a modulation rate K of 85% is as Figure 19A shown, and the three-phase applied voltage with a modulation rate K of 100% is as Figure 19B shown. In addition, in Figure 19A and Figure 19B , the dashed line a represents the three-phase applied voltage V u12 c, the single-dot chain line b represents the three-phase applied voltage V v12 c, and the solid line c represents the three-phase applied voltage V w12 c.

[0182] Figure 20A and Figure 20B show Figure 17A the first offset and Figure 19A the second offset of Figure 17B the first offset and Figure 19B the second offset of

[0183] The signal with a phase shift of 180 deg by inverting the sign of the first offset coincides with the second offset, satisfies Equation (11), and can equalize the heat generation of the high-potential-side switching elements Sup1, Svp1, and Swp1 and the low-potential-side switching elements Sun1, Svn1, and Swn1 within one cycle of the electrical angle. In Figure 20A and Figure 20B the dashed line d represents the second offset Vofs2, and the solid line e represents the first offset Vofs1.

[0184] In addition, the operation flowchart of the first offset correction can be as shown in Figure 21 and used as step S122c to replace Figure 16 step S122b.

[0185] In Figure 21 step S122c, by setting the applied voltage of the maximum phase V of the three-phase applied voltage as the maximum value of the carrier signal Cl, the time from the switching of the minimum phase V to the detection timing t can be maximized, thereby improving the current detection accuracy. In addition, the second offset can be applied so that the applied voltage of the minimum phase V becomes the minimum value of the carrier signal Cl. At this time, max1 the waveforms of the applied voltages in the case where the minimum applied voltage ratio K is -0.4 and the modulation ratio K is 0.85 are shown in min1 and s . In addition, in min1 the dashed line f represents the three-phase applied voltage V Figure 22A and Figure 22B c, the dash-dotted line g represents the three-phase applied voltage V S c, and the solid line h represents the three-phase applied voltage V Figure 22A c. In addition, in u12 the dashed line i represents the three-phase applied voltage V v12 c, the dash-dotted line j represents the three-phase applied voltage V w12 c, and the solid line k represents the three-phase applied voltage V Figure 22B c. In addition, in u11 the dashed line i represents the three-phase applied voltage V v11 c, the dash-dotted line j represents the three-phase applied voltage V w11 c.

[0186] In addition, since the electrical angle that varies in the carrier period is larger when the modulation ratio K is high, the residence time in the region where the difference between the voltage commands of the maximum phase and the intermediate phase is small is short. Therefore, in addition to Figure 16 step S123b, the operation flowchart of the first offset correction can be as shown in Figure 23 .

[0187] When the modulation ratio K is greater than 0.5 - K SIn the case of the provided third specified value K3, by setting it to the minimum value of the carrier signal Cl, the switching of one phase can be stopped. Therefore, current detection errors caused by switching noise in other phases can be suppressed, and currents of one or more phases can be detected with high precision. In addition, by reducing conditional branches, the processing load can be reduced.

[0188] In addition, when the modulation rate K is low, the amplitude of the voltage command is small, and there is freedom in the selection of the first offset. Therefore, when the modulation rate K is equal to or less than the first specified value K1, the first offset can be set to zero. In order to perform current detection with high precision, the applied voltage of the minimum phase needs to be at the minimum applied voltage K S V dc or higher. Therefore, the first specified value K1 only needs to satisfy the following formula (19). By also setting the second offset to zero, the heat generation can be equalized. At this time, the minimum applied voltage ratio K S is 0.4, and the waveform of the applied voltage when the modulation rate K is 2√3 / 5 is as shown in Figure 24A and Figure 24B . The V u11 c, V v11 c, V w11 c obtained through the first offset correction is equal to the V u12 c, V v12 c, V w12 c obtained through the second offset correction. In addition, in Figure 24A , the dashed line l represents the three-phase applied voltage V u12 c, the dash-dotted line m represents the three-phase applied voltage V v12 c, and the solid line n represents the three-phase applied voltage V w12 c. In addition, in Figure 24B , the dashed line o represents the three-phase applied voltage V u11 c, the dash-dotted line p represents the three-phase applied voltage V v11 c, and the solid line q represents the three-phase applied voltage V w11 c.

[0189] [Mathematical formula 18]

[0190]

[0191] In addition, when the modulation rate K is equal to or less than the second specified value K2, as shown in the following formula (20), the first offset is calculated based on the second specified value K2. That is, the first offset is determined regardless of the modulation rate K at that time.

[0192] [Mathematical formula 19]

[0193]

[0194] The second offset is determined such that the sum of the second offset and the first offset is zero, and is thus represented by the following equation (21).

[0195] [Mathematical formula 20]

[0196]

[0197] In order to perform current detection with high precision, the applied voltage of the minimum phase needs to be at least the minimum applied voltage K S V dc or more. Therefore, the second specified value K2 only needs to satisfy the following equation (22).

[0198] [Mathematical formula 21]

[0199]

[0200] At this time, Figure 25A and Figure 25B show the waveform of the applied voltage when the minimum applied voltage ratio K S is -0.4 and the modulation rate K is 0.7. As shown in equation (21), by making the offset constant, low-order fluctuations of the neutral point voltage can be suppressed. In particular, in a configuration where a fault or abnormality is detected based on the obtained neutral point voltage or the average value of the three-phase voltages, the determination accuracy of this configuration with suppressed neutral point voltage fluctuations is excellent. In addition, in Figure 25A , the dashed line l represents the three-phase applied voltage V u12 c, the dash-dot line m represents the three-phase applied voltage V v12 c, and the solid line n represents the three-phase applied voltage V w12 c. In addition, in Figure 25B , the dashed line o represents the three-phase applied voltage V u11 c, the dash-dot line p represents the three-phase applied voltage V v11 c, and the solid line q represents the three-phase applied voltage V w11 c.

[0201] As described above, in the power conversion device according to Embodiment 2, the same effects as those of Embodiment 1 can also be obtained.

[0202] Embodiment 3.

[0203] Next, Embodiment 3 will be described. In Embodiment 3, an example in which the power conversion device described in Embodiment 1 or Embodiment 2 is applied to an electric power steering device mounted on a vehicle will be described.

[0204] Figure 26 is a block diagram showing the overall structure of the electric power steering device according to Embodiment 3.

[0205] In Figure 26In this case, the electric power steering apparatus 10 includes a drive device 11 which is shown as a device integrally including the power conversion device described in Embodiment 1 or Embodiment 2 and the AC rotating electric machine 1 controlled by the power conversion device.

[0206] When the driver of the vehicle generates a steering torque on the steering mechanism of the vehicle by the steering wheel 12, the torque sensor 13 detects the steering torque and outputs it to the drive device 11. Further, the vehicle speed sensor 14 detects the traveling speed of the vehicle and outputs it to the drive device 11.

[0207] Based on the steering torque input from the torque sensor 13 and the traveling speed input from the vehicle speed sensor 14, the drive device 11 generates an auxiliary torque for assisting the steering torque of the steering system from the AC electric machine 1 and supplies it to the steering mechanism of the front wheels 15 of the vehicle. The drive device 11 may also be configured to generate the auxiliary torque based on inputs other than the torque sensor 13 and the speed sensor 14.

[0208] Accordingly, the power conversion device according to Embodiment 1 or Embodiment 2 can be applied to the control device of an electric power steering apparatus that causes the AC rotating electric machine 1 to generate a torque for assisting the steering torque of the steering system. Thereby, an electric power steering apparatus having a steering system with good overheat protection performance, less torque ripple, and less noise can be obtained. Further, instead of using a torque sensor, a known method of estimating the steering torque based on the applied voltage or rotational speed or the like may be used. Further, instead of using a vehicle speed sensor, a known method of performing control based on the estimated road surface reaction force or the like may be used.

[0209] Although this application describes various exemplary embodiments and examples, the various features, aspects, and functions described in one or more embodiments are not limited to the application of a particular embodiment and can be applied singly or in various combinations to the embodiments.

[0210] Therefore, countless unillustrated variations can be conceived within the technical scope disclosed in this application. For example, it is assumed to include cases where at least one component is deformed, added, or omitted, and cases where at least one component is extracted and combined with the components of other embodiments.

[0211] Reference Numeral Explanation

[0212] 1 AC rotating electric machine, 2 DC power supply, 3 power converter, 4 filter capacitor, 5 control unit, 6 voltage command calculator, 7 offset calculator, 8 on / off signal generator, 9 current detector, 10 electric power steering device, 11 drive device, 12 steering wheel, 13 torque sensor, 14 vehicle speed sensor, 15 front wheel, U1, V1, W1 three-phase windings, Qup1, Qun1, Qvp1, Qvn1, Qwp1, Qwn1 on / off signals, Qup2, Qun2, Qvp2, Qvn2, Qwp2, Qwn2 on / off signals, Sup1, Svp1, Swp1 high-potential side switching elements, Sun1, Svn1, Swn1 low-potential side switching elements, Vofs1 first offset, Vofs2 second offset, V u1 V v1 V w1 Three-phase voltage command, V u1 Vc, V v1 Vc, V w1 Vc, V u12 Vc, V v12 Vc, V w12 Vc three-phase applied voltage, Cl carrier signal.

Claims

1. A power conversion device includes a DC power supply that outputs a DC voltage. The power conversion device is connected to an AC rotating electric machine having an n-phase winding with three or more phases, characterized in that, Comprising: A power converter having a high-potential side switching element and a low-potential side switching element, which performs switching control on the high-potential side switching element and the low-potential side switching element based on on / off signals, converts the DC voltage into an AC voltage and applies it to the n-phase winding; A current detector inserted in series with the high-potential side switching element or the low-potential side switching element to obtain the detected current of each phase; And A control unit that calculates a voltage command based on a current command of the AC rotating motor, and compares an applied voltage obtained by performing a first offset correction and a second offset correction with respect to the voltage command with a carrier signal to output the on / off signal, The control unit switches between the first offset correction and the second offset correction at a period shorter than the electrical angle period of the AC rotating motor, The first offset correction determines a first offset amount such that an applied voltage capable of detecting at least n-2 phases of the phase currents of the AC rotating motor is obtained, and calculates the applied voltage by equally subtracting the first offset amount from all the voltage commands, The second offset correction determines a second offset amount whose average value in the electrical angle period is opposite in sign to the average value in the electrical angle period of the first offset amount, and calculates the applied voltage by equally subtracting the second offset amount from all the voltage commands, When the control unit outputs the applied voltage generated by the first offset correction, it calculates the voltage command based on the detected phase currents, When outputting the applied voltage generated by the second offset correction, the voltage command is not updated.

2. The power conversion device according to claim 1, wherein The first offset correction determines the first offset amount such that an applied voltage that maximizes the number of detectable phases of the phase currents is obtained.

3. The power conversion device according to claim 2, wherein The sum of the average value of the first offset amount in the electrical angle period and the average value of the second offset amount in the electrical angle period is zero.

4. The power conversion device according to claim 1, wherein The sum of the average value of the first offset amount in the electrical angle period and the average value of the second offset amount in the electrical angle period is zero.

5. The power conversion device according to any one of claims 1 to 4, wherein The switching period between the first offset correction and the second offset correction is the period of the carrier signal.

6. The power conversion device according to any one of claims 1 to 4, wherein The current detector is inserted in series with the low-potential side switching element, and the ratio of the maximum value of the applied voltage when the applied voltage enables current detection to the DC voltage is defined as K m , and the DC voltage is defined as V dc , when under the above circumstances, at K m V dc when current detection can be performed below, The first offset correction determines the first offset amount such that it becomes the applied voltage below K. m V dc ​ 7. The power conversion device according to claim 6, wherein When the modulation rate is equal to or less than a first specified value based on the range in which current detection can be performed, the first offset amount is set to zero.

8. The power conversion device according to claim 7, wherein The first specified value satisfies the following formula, [Mathematical formula 22] where K1 is the first specified value of the modulation rate, K m is the ratio of the maximum value of the applied voltage capable of current detection to the DC voltage, i.e., the maximum applied voltage ratio.

9. The power conversion device according to claim 6, wherein When the modulation rate is equal to or lower than a second specified value based on the range where current detection is possible, the first offset is given by the following formula: [Mathematical formula 23] where K2 is the second specified value of the modulation rate, and V dc is the DC voltage of the DC power supply.

10. The power conversion device according to claim 9, characterized in that: The second specified value satisfies the following formula: [Mathematical formula 24] where K2 is the second specified value of the modulation rate. K m is the ratio of the maximum value of the applied voltage capable of current detection to the DC voltage, i.e., the maximum applied voltage ratio.

11. The power conversion device according to claim 6, characterized in that: When the modulation rate is equal to or lower than a third specified value based on the range where current detection is possible, the first offset correction determines the first offset such that the applied voltage calculated according to the voltage command of the smallest phase of the three-phase applied voltage is equal to the minimum value of the carrier signal.

12. The power conversion device according to claim 11, characterized in that: The third specified value satisfies the following formula: [Mathematical formula 25] where K3 is the third specified value of the modulation rate. K m is the ratio of the maximum value of the applied voltage that can perform current detection to the DC voltage, that is, the maximum applied voltage ratio.

13. The power conversion device according to claim 6, characterized in that: When the modulation rate is greater than the third specified value based on the range where current detection is possible, the first offset correction determines the first offset such that the applied voltage calculated according to the voltage command of the largest phase of the three-phase applied voltage becomes the maximum value of the carrier signal.

14. The power conversion device according to claim 6, characterized in that: When the modulation rate is greater than a third specified value based on the range in which current detection can be performed, the first offset correction determines the first offset amount such that the applied voltage calculated according to the voltage command of the maximum phase of the three-phase applied voltage is the K m V dc Hereinafter, or becomes the maximum value of the carrier signal.

15. The power conversion device according to any one of claims 1 to 4, characterized in that: The current detector is inserted in series with the high-potential side switching element, and a ratio of a minimum value of the applied voltage at which current detection can be performed to the DC voltage is defined as K S , and the DC voltage is defined as V dc , when in the above case, at K S V dc or more, current detection can be performed The first offset correction determines the first offset amount such that the applied voltage becomes the applied voltage of S V dc or more.

16. The power conversion device according to claim 15, characterized in that: When the modulation rate is equal to or lower than a first specified value based on the range where current detection is possible, the first offset is set to zero.

17. The power conversion device according to claim 16, characterized in that: The first specified value satisfies the following formula: [Mathematical formula 26] where K1 is the first specified value of the modulation rate. K S is the ratio of the minimum value of the applied voltage capable of current detection to the DC voltage, i.e., the minimum applied voltage ratio.

18. The power conversion device according to claim 15, characterized in that: When the modulation rate is equal to or lower than a second specified value based on the range where current detection is possible, the first offset is given by the following formula: [Mathematical formula 27] where K2 is the second specified value of the modulation rate, and V dc is the DC voltage of the DC power supply.

19. The power conversion device according to claim 18, characterized in that: The second specified value satisfies the following formula: [Mathematical formula 28] where K2 is the second specified value of the modulation rate. K S is the ratio of the minimum value of the applied voltage capable of current detection to the DC voltage, i.e., the minimum applied voltage ratio.

20. The power conversion device according to claim 15, characterized in that: When the modulation rate is equal to or lower than a third specified value based on the range where current detection is possible, the first offset correction determines the first offset such that the applied voltage calculated according to the voltage command of the largest phase of the three-phase applied voltage is equal to the maximum value of the carrier signal.

21. The power conversion device according to claim 20, characterized in that: The third specified value satisfies the following formula: [Mathematical formula 29] where K3 is the third specified value of the modulation rate. K S is the ratio of the minimum value of the applied voltage capable of current detection to the DC voltage, that is, the minimum applied voltage ratio.

22. The power conversion device according to claim 15, characterized in that: When the modulation rate is greater than a third specified value based on the range capable of current detection, the first offset correction determines the first offset amount such that the applied voltage calculated according to the voltage command of the minimum phase of the three-phase applied voltage becomes the minimum value of the carrier signal.

23. The power conversion device according to claim 15, wherein: When the modulation rate is greater than a third specified value based on the range in which current detection can be performed, the first offset correction determines the first offset amount such that the applied voltage calculated based on the voltage command of the smallest phase of the three-phase applied voltage is the above-mentioned S V dc or more, or becomes the minimum value of the carrier signal.

24. An electric power steering device, characterized in that, Comprising: The power conversion device according to any one of claims 1 to 23; And A drive device including an AC rotating electric machine controlled by the power conversion device.

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