Power conversion device and electric power steering device

Abstract

The power conversion device of the present invention is characterized in that when a current detection resistor is connected between the lower-arm switching element of the inverter and the negative-side input terminal, it is set that the conduction resistance between the output terminal of the inverter and the positive-side input terminal is larger than the conduction resistance other than the current detection resistor between the output terminal of the inverter and the negative-side input terminal; when a current detection resistor is connected between the upper-arm switching element of the inverter and the positive-side input terminal, it is set that the conduction resistance between the output terminal of the inverter and the negative-side input terminal is larger than the conduction resistance other than the current detection resistor between the output terminal of the inverter and the positive-side input terminal.

Description

Technical Field

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

[0002] As existing power conversion devices and electric power steering devices, the technology of Patent Document 1 is known. In this document, it is configured to detect current based on the output signal of a current detection resistance element connected in series with a switching element on the negative electrode side of an inverter. Such an inverter is called a "lower arm 3 shunt current detection type inverter". Then, for the purpose of further reducing the cost of the device, an inverter using a current detection method called a "bus 1 shunt current detection type inverter" has also been popularized.

[0003] Compared with inverters using a current detection method using a DC current sensor (DC-CT), these current detection methods are widely popularized in the industry because they are cheaper in terms of the cost for current detection.

[0004] Prior Art Documents

[0005] Patent Documents

[0006] Patent Document 1: Japanese Patent No. 6266161 Summary of the Invention

[0007] Technical Problem to be Solved by the Invention

[0008] In a lower arm 3 shunt current detection type inverter and a bus 1 shunt current detection type inverter, a current detection resistor is mostly inserted between the negative electrode side input terminal of the inverter and the lower arm switching element. As a result, the conduction resistance between the output terminal of the inverter and the negative electrode side input terminal is larger than the conduction resistance between the output terminal of the inverter and the positive electrode side input terminal by the part where the current detection resistor is inserted.

[0009] Through this current detection resistor, when the third harmonic component overlaps with the voltage command value related to the voltage of the inverter, the inter-phase voltage output from the inverter may include a third harmonic component (third voltage error), and the current flowing through the inductive load connected to the output terminal of the inverter may include a third harmonic component with respect to its fundamental wave.

[0010] As a result, for example, when an AC rotating motor is used as the inductive load, a third torque ripple is generated with respect to its fundamental wave, and as a result, problems such as uneven rotation of the AC rotating motor, or vibration or noise of the AC rotating motor occur.

[0011] The present application is proposed to solve the above problems, and its purpose is to provide a power conversion device capable of reducing the influence of the third harmonic caused by the superposition of the third harmonic component.

[0012] Technical means for solving technical problems

[0013] The power conversion device disclosed in the present application includes:

[0014] An inverter having an upper-arm switching element and a lower-arm switching element, which converts a DC voltage into an AC voltage and outputs it to a load;

[0015] A voltage command value calculation unit that calculates a voltage command value for controlling the load to an instructed state; and

[0016] A corrected voltage command value calculation unit that calculates a corrected voltage command value by adding a third-harmonic component, which is a triple-frequency component, to the fundamental-wave component of the voltage command value,

[0017] The inverter converts to an AC voltage according to the corrected voltage command value,

[0018] When a current detection resistor is connected between the lower-arm switching element and the negative-side input terminal of the inverter, it is set that the conduction resistance between the output terminal of the inverter and the positive-side input terminal is larger than the value obtained by dividing the conduction resistance between the output terminal of the inverter and the negative-side input terminal by the current detection resistor other than the current detection resistor,

[0019] When a current detection resistor is connected between the upper-arm switching element and the positive-side input terminal of the inverter, it is set that the conduction resistance between the output terminal of the inverter and the negative-side input terminal is larger than the value obtained by dividing the conduction resistance between the output terminal of the inverter and the positive-side input terminal by the current detection resistor other than the current detection resistor.

[0020] Advantages of the invention

[0021] According to the power conversion device disclosed in the present application, the influence of the third harmonic of the inverter output caused by the superposition of the third-harmonic components can be reduced. Description of the drawings

[0022] Figure 1 It is an overall structure diagram of the power conversion device according to Embodiment 1.

[0023] Figure 2 It is a diagram for explaining the hardware structure of the controller according to Embodiment 1.

[0024] Figure 3 It is a diagram for explaining the behavior of amplitude reduction modulation calculated by the corrected voltage command value calculation unit according to Embodiment 1.

[0025] Figure 4 It is a diagram for explaining the operation of the PWM control unit according to Embodiment 1.

[0026] Figure 5 This is a diagram showing the equivalent circuit of one phase of a three-phase inverter.

[0027] Figure 6 This is a diagram showing the circuit after adding the current detection circuit according to Embodiment 1 to the equivalent circuit of one phase of the three-phase inverter.

[0028] Figure 7 This is a diagram explaining the relationship between the conduction potential of the switching signal of the upper-arm switching element and the conduction potential of the switching signal of the lower-arm switching element according to Embodiment 1.

[0029] Figure 8 This is a diagram showing another circuit after adding the current detection circuit according to Embodiment 1 to the equivalent circuit of one phase of the three-phase inverter.

[0030] Figure 9 This is the overall structure diagram of the power conversion device according to Embodiment 2.

[0031] Figure 10 This is a diagram explaining the behavior of the amplitude reduction modulation calculated by the corrected voltage command value calculation unit according to Embodiment 2.

[0032] Figure 11 is a diagram explaining the relationship between the conduction resistance between the output terminal and the input terminal of the inverter and the torque of the AC rotating motor connected to the inverter.

[0033] Figure 12 This is another diagram explaining the behavior of the amplitude reduction modulation calculated by the corrected voltage command value calculation unit according to Embodiment 2.

[0034] Figure 13 This is a simplified structure diagram of applying the power conversion device to the electric power steering device according to Embodiment 3. Detailed Embodiments

[0035] Hereinafter, preferred embodiments of the power conversion device according to the present application will be described with reference to the accompanying drawings. In addition, the same reference numerals are assigned to the same content and corresponding parts, and their detailed descriptions are omitted. In the following embodiments, the structures with the same reference numerals are also omitted from repeated descriptions.

[0036] Embodiment 1.

[0037] Figure 1 This is the overall structure diagram of the power conversion device 100 of the present application that supplies power to the AC rotating motor 1.

[0038] The AC rotating electric machine 1 includes a stator and a rotor disposed radially inside the stator. In the stator, three-phase windings Cu, Cv, and Cw of U-phase, V-phase, and W-phase are wound. A permanent magnet is provided on the rotor, and it is a permanent magnet type synchronous rotating electric machine. In addition, the AC rotating electric machine 1 may also be a field winding type synchronous rotating electric machine having an electromagnet on the rotor, or an induction motor having no permanent magnet on the rotor. The three-phase windings Cu, Cv, and Cw may be connected in star, or may be connected in delta.

[0039] The rotor includes a rotation detection circuit 2 for detecting the rotation angle of the rotor. The rotation detection circuit 2 uses a resolver, an encoder, an MR (Magneto Resistive) sensor, or the like. The output signal of the rotation detection circuit 2 is input to the controller 7.

[0040] The DC power supply 3 outputs a power supply voltage Vdc to the inverter 6. As the DC power supply 3, any device may be used as long as it outputs the power supply voltage Vdc, such as a battery, a DC-DC converter, a diode rectifier, or a PWM rectifier. A voltage sensor for detecting the power supply voltage Vdc is provided in the DC power supply 3, and the output signal of the voltage sensor may be input to the controller 7. The controller 7 may perform control using the detected power supply voltage Vdc.

[0041] The circuit breaker 4 has a function of cutting off the DC power supply 3 and the inverter 6, and cuts off when an abnormality occurs anywhere in the power conversion device 100 composed of the inverter 6 and the controller 7, and has a function of protecting the DC power supply 3. As the circuit breaker 4, an electromagnetic contactor or a semiconductor switching element (MOSFET (Metal Oxide Semiconductor Field Effect Transistor), IGBT (Insulated Gate Bipolar Transistor), bipolar transistor, thyristor) may be used. The circuit breaker 4 has a resistance Rdc.

[0042] The capacitor 5 is connected in parallel to the inverter 6 to stabilize the DC voltage Vdc input to the inverter 6. Therefore, it is connected in parallel to the DC power supply 3 via the circuit breaker 4. As a reason for connecting the capacitor 5 to the side closer to the inverter 6 with respect to the circuit breaker 4, the purpose of inserting the capacitor 5 is to stabilize the voltage input to the inverter 6 and to absorb the variable part of the voltage drop represented by the product of the resistance Rdc and the output current Idc of the DC power supply 3. The capacitor 5 has a positive terminal Cp and a negative terminal Cn.

[0043] The inverter 6 is provided with three sets of series circuits (branches) corresponding to each of the three phases. The series circuits are obtained by connecting in series the switching element SP on the positive side (hereinafter referred to as the upper arm), which is connected to the positive side terminal Cp of the capacitor 5 (substantially equal to the positive side input terminal of the inverter 6), and the switching element SN on the negative side (hereinafter referred to as the lower arm), which is connected to the negative side terminal Cn of the capacitor 5 (substantially equal to the negative side input terminal of the inverter 6). Then, the connection points of the two switching elements in the series circuit of each phase are connected to the windings of the corresponding phase.

[0044] Specifically, in the series circuit of the U phase, the upper arm switching element SPu of the U phase and the lower arm switching element SNu of the U phase are connected in series, and the connection point of the two switching elements is connected to the winding Cu of the U phase. In the series circuit of the V phase, the upper arm switching element SPv of the V phase and the lower arm switching element SNv of the V phase are connected in series, and the connection point of the two switching elements is connected to the winding Cv of the V phase. In the series circuit of the W phase, the upper arm switching element SPw of the W phase and the lower arm switching element SNw of the W phase are connected in series, and the connection point of the two switching elements is connected to the winding Cw of the W phase.

[0045] IGBTs with anti-parallel diodes, MOSFETs, bipolar transistors with anti-parallel diodes, etc. are used as the switching elements. The gate terminals of the respective switching elements SPu to SNw are connected to the controller 7 via a gate drive circuit or the like. The respective switching elements SPu to SNw are turned on or off by the switching signals GPu to GNw output from the controller 7.

[0046] The current detection circuit 8 is configured to detect the currents flowing through the lower arm switching elements SNu, SNv, and SNw of the three phases. The current detection circuit 8 has shunt resistors 8u, 8v, and 8w connected in series with the lower arm switching elements SNu, SNv, and SNw of each phase. That is, the shunt resistor 8u of the U phase is connected in series on the negative side of the lower arm switching element SNu of the U phase, the shunt resistor 8v of the V phase is connected in series on the negative side of the lower arm switching element SNv of the V phase, and the shunt resistor 8w of the W phase is connected in series on the negative side of the lower arm switching element SNw of the W phase. The potential differences VRu, VRv, and VRw across the shunt resistors 8u, 8v, and 8w of each phase are input to the controller 7.

[0047] In addition, in the present embodiment, the current detection circuit 8 is configured to detect the currents flowing through the lower arm switching elements SNu, SNv, and SNw of the three phases, but the current detection circuit 8 may also be configured to detect the currents flowing through the lower arm switching elements of any two phases. In this case, since the sum of the winding currents of the three phases is zero, the controller 7 can also calculate the current of the remaining one phase based on the current detection values of the two phases. For example, if the current detection circuit 8 detects the currents Iur and Ivr of the U phase and the V phase, the controller 7 can also calculate the current Iwr of the W phase by Iwr = -Iur - Ivr.

[0048] The controller 7 controls the AC rotating electric machine 1 via the inverter 6. As Figure 1 shown, the controller 7 includes a rotation detection unit 31, a current detection unit 32, a current coordinate conversion unit 33, a current command value calculation unit 35, a dq-axis voltage command value calculation unit 361, a voltage coordinate conversion unit 362, a corrected voltage command value calculation unit 363, a PWM control unit 37, etc. Each function of the controller 7 is implemented by a processing circuit included in the controller 7. Specifically, as Figure 2 shown, as the processing circuit, it includes an arithmetic processing device 90 (computer) such as a CPU (Central Processing Unit), a storage device 91 that exchanges data with the arithmetic processing device 90, an input circuit 92 that inputs external signals to the arithmetic processing device 90, and an output circuit 93 that outputs signals from the arithmetic processing device 90 to the outside, etc.

[0049] As the arithmetic processing device 90, it may include an ASIC (Application Specific Integrated Circuit), an IC (Integrated Circuit), a DSP (Digital Signal Processor), an FPGA (Field Programmable Gate Array), various logic circuits, and various signal processing circuits, etc. In addition, as the arithmetic processing device 90, it may also include a plurality of arithmetic processing devices of the same type or different types to share and execute each process. As the storage device 91, it may include a RAM (Random Access Memory) configured to be able to read and write data from the arithmetic processing device 90, a ROM (Read Only Memory) configured to be able to read data from the arithmetic processing device 90, etc. The input circuit 92 is connected to various sensors and switches such as a rotation detection circuit 2 and a current detection circuit 8, and includes an A / D converter that inputs the output signals of these sensors and switches to the arithmetic processing device 90. The output circuit 93 is connected to electrical loads such as a gate drive circuit that drives a switching element to conduct and turn off, and includes a drive circuit that outputs a control signal from the arithmetic processing device 90 to these electrical loads.

[0050] Then, included in the controller 7 Figure 1Each function is implemented by the arithmetic processing unit 90 executing software (program) stored in a storage device 91 such as a ROM and cooperating with other hardware of the controller 7 such as the storage device 91, the input circuit 92, and the output circuit 93. In addition, setting data such as gains and thresholds used by the rotation detection unit 31, the current detection unit 32, the current coordinate conversion unit 33, the current command value calculation unit 35, the dq-axis voltage command value calculation unit 361, the voltage coordinate conversion unit 362, the corrected voltage command value calculation unit 363, the PWM control unit 37, etc. are stored in the storage device 91 such as a ROM as part of the software (program). Hereinafter, each function of the controller 7 will be described in detail.

[0051] The rotation detection unit 31 detects the magnetic pole position (rotation angle of the rotor) θ of the rotor based on the output signal of the rotation detection circuit 2. The magnetic pole position of the rotor is set to the direction of the N pole of the permanent magnet provided in the rotor. In addition, the rotation detection unit 31 may be configured to estimate the rotation angle (magnetic pole position) based on current information obtained by overlapping a harmonic component on the current command value without using a rotation sensor (so-called sensorless method).

[0052] The current detection unit 32 detects the currents Iur, Ivr, and Iwr flowing through the windings of the three phases based on the output signal of the current detection circuit 8. That is, the potential differences VRu, VRv, and VRw across the shunt resistors 8u, 8v, and 8w of each phase are divided by the resistance values of the shunt resistors 8u, 8v, and 8w to detect the currents Iur, Ivr, and Iwr of the respective phase windings.

[0053] Since the current detection circuit 8 detects the current flowing through the lower arm switching elements SNu, SNv, and SNw, the current detection unit 32 detects the current at the timing when the lower arm switching element is turned on. In addition, in the PWM control unit 37 described later, the lower arm switching elements SNu, SNv, and SNw are turned on in each carrier period Tc. Accordingly, the current detection unit 32 detects the currents Iur, Ivr, and Iwr of the three-phase windings based on the output signal of the current detection circuit 8 in a period that is the first natural number A times the carrier period Tc, that is, the current detection period TIdt (= A × Tc) when the lower arm switching elements SNu, SNv, and SNw are turned on. In the present embodiment, the current detection circuit 8 detects the current at the timing of each current detection period TIdt when the carrier CA reaches the peak.

[0054] Each time current is detected, the current coordinate conversion unit 33 converts the three-phase current detection values Iur, Ivr, and Iwr into the d-axis current detection value Idr and the q-axis current detection value Iqr in the d-axis and q-axis coordinate systems. The d-axis and q-axis coordinate systems are two-axis rotating coordinate systems that rotate synchronously with the magnetic pole position of the rotor. The d-axis is determined as the direction of the magnetic pole position θ (N pole), and the q-axis is determined as the direction that is 90 degrees ahead of the d-axis in the electrical angle. Specifically, the current coordinate conversion unit 33 performs three-phase to two-phase conversion and rotating coordinate conversion on the three-phase current detection values Iur, Ivr, and Iwr based on the magnetic pole position θ, and converts them into the d-axis current detection value Idr and the q-axis current detection value Iqr.

[0055] The current command value calculation unit 35 calculates the d-axis and q-axis current command values Ido and Iqo based on the torque command value T_ref, the power supply voltage Vdc, the rotational angular velocity ω, etc. According to known current vector control methods such as maximum torque current control, maximum torque voltage control, field weakening control, and Id = 0 control, etc., the d-axis and q-axis current command values Ido and Iqo are calculated. For example, when performing Id = 0 control, the current command value Ido on the d-axis is set to zero (Ido = 0), and the current command value Iqo on the q-axis is set to the value obtained by multiplying the torque command value T_ref by a conversion coefficient. The torque command value T_ref can be calculated within the controller 7 or transmitted from an external control device.

[0056] The dq-axis voltage command value calculation unit 361 performs current feedback control that changes the d-axis voltage command value Vdo and the q-axis voltage command value Vqo through PI (Proportional-Integral) control, etc., so that the d-axis current detection value Idr approaches the d-axis current command value Ido and the q-axis current detection value Iqr approaches the q-axis current command value Iqo. In addition, feedforward control can also be performed to prevent interference between the d-axis current and the q-axis current.

[0057] The voltage coordinate conversion unit 362 performs fixed coordinate conversion and two-phase to three-phase conversion on the d-axis and q-axis voltage command values Vdo and Vqo based on the magnetic pole position θ, and converts them into the three-phase voltage command values Vuoc, Vvoc, and Vwoc after coordinate conversion. The three-phase voltage command values Vuoc, Vvoc, and Vwoc after this coordinate conversion are sine waves.

[0058] The corrected voltage command value calculation unit 363 applies amplitude reduction modulation to the sine-wave three-phase voltage command values Vuoc, Vvoc, and Vwoc after coordinate conversion while maintaining the line voltage. This amplitude reduction modulation reduces the amplitude of the three-phase voltage command values. Then, the final three-phase voltage command values, that is, the corrected voltage command values Vuo, Vvo, and Vwo, are calculated.

[0059] Specifically, as shown in Equation (1-1), the corrected voltage command value calculation unit 363 determines the minimum value Vmin and the maximum value Vmax of the three-phase voltage command values Vuoc, Vvoc, and Vwoc after coordinate conversion, multiplies the sum of the minimum value Vmin and the maximum value Vmax by 0.5 to calculate the offset voltage Voff, and subtracts the offset voltage Voff from the three-phase voltage command values Vuoc, Vvoc, and Vwoc after coordinate conversion to calculate the three-phase voltage command values Vuo, Vvo, and Vwo.

[0060]

[0061] The operation of the amplitude reduction modulation of Equation (1-1) is shown in Figure 3 The upper graph shows the three-phase voltage command values Vuoc, Vvoc, and Vwoc after coordinate conversion. The three-phase voltage command values Vuoc, Vvoc, and Vwoc after coordinate conversion exceed the range from -Vdc / 2 to +Vdc / 2, resulting in voltage saturation. On the other hand, the three-phase voltage command values Vuo, Vvo, and Vwo after the amplitude reduction modulation in the lower graph are within the range from -Vdc / 2 to +Vdc / 2, preventing the occurrence of voltage saturation.

[0062] In Figure 3 when looking at the waveform of the offset voltage Voff in the middle graph, it becomes a third harmonic component that varies at three times the frequency of the fundamental wave of the voltage command values Vuoc to Vwoc. The offset voltage Voff is targeted at the third harmonic component that varies at three times the frequency of the voltage command values Vuoc, Vvoc, and Vwoc.

[0063] The PWM control unit 37 controls the on / off of the switching elements by comparing each of the three-phase voltage command values Vuo, Vvo, and Vwo with the carrier wave CA that oscillates at the carrier period Tc. The carrier wave CA is set as a triangular wave that oscillates around 0 with an amplitude of half of the power supply voltage Vdc / 2 during the carrier period Tc.

[0064] As Figure 4 shown, when the carrier wave CA is lower than the voltage command values Vuo, Vvo, and Vwo, the PWM controller 37 turns on the switching signals GPu, GPv, and GPw of the upper arm switching elements SPu, SPv, and SPw ( Figure 4 in Figure 4 the voltage VGp), and when the carrier wave CA is higher than the voltage command values Vuo, Vvo, and Vwo, the PWM controller 37 turns off the switching signals GPu, GPv, and GPw of the upper arm switching elements SPu, SPv, and SPw (

[0065] On the other hand, when the carrier wave CA is lower than the voltage command values Vuo, Vvo, and Vwo, the switching signals GNu, GNv, and GNw for turning off the lower-arm switching elements SNu, SNv, and SNw ( Figure 4 in which the voltage is 0), while when the carrier wave CA is higher than the voltage command values Vuo, Vvo, and Vwo, the switching signals GNu, GNv, and GNw for turning on the lower-arm switching elements are turned on ( Figure 4 in which the voltage is VGn). In addition, for each phase, a short-circuit prevention period (dead time) for turning off both the upper-arm and lower-arm switching elements can be set between the conduction period of the upper-arm switching elements SPu, SPv, and SPw and the conduction period of the lower-arm switching elements SNu, SNv, and SNw.

[0066] The switching signal mentioned here is a signal for controlling the switching element. If it is an IGBT, it is the potential signal of the gate G with the emitter E as the reference potential. If it is a MOSFET, it is the potential signal of the gate G with the source S as the reference potential. Here, the conduction potentials VGp of the switching signals GPu, GPv, and GPw of the upper-arm switching elements SPu, SPv, and SPw and the conduction potentials VGn of the switching signals GNu, GNv, and GNw of the lower-arm switching elements SNu, SNv, and SNw are both set to the values required to turn on the switching elements, and the relationship between the two is "VGn > VGp", and the reason will be described later.

[0067] As Figure 4 shown, in the interval B centered on the peak vertex of the carrier wave CA, the lower-arm switching signals GNu, GNv, and GNw of all three phases are turned on, and in this interval B, the current detection circuit 8 can detect the current flowing through the three-phase windings. In the present embodiment, as described above, the current detection unit 32 is configured to detect the current at the timing of the peak vertex of the carrier wave CA.

[0068] Next, the advantages of setting "VGn > VGp" will be described in detail when the shunt resistors 8u, 8v, and 8w are connected between the lower-arm switching elements SNu, SNv, and SNw and the negative-side input terminal of the inverter 6.

[0069] Figure 5 is the equivalent circuit of one phase of the inverter 6. The potential of the positive-side input terminal is Vp, and the potential of the negative-side input terminal is Vn. Among them, according to the DC voltage Vdc, Vp - Vn = Vdc. The on-resistance of the lower-arm switching element SN is set to Rn, and the on-resistance of the upper-arm switching element SP is set to Rp.

[0070] The output terminal is connected in the middle of the upper-arm switching element SP and the lower-arm switching element SN, and its potential is set to the output terminal potential Vout.

[0071] Here, if the ratio (duty ratio) of the conduction of the upper-arm switching element SP with respect to the period Tc of the PWM carrier is D, the potential Vout of the output terminal is given by the following formula.

[0072] Vout = D × (Vp - Rp × i) + (1 - D) × (Vn - Rn × i) Equation (1-2)

[0073] Here, if Vn = 0 and Vp = Vdc, Equation (1-2) becomes as follows.

[0074] Vout = D × Vdc + D × (Rn - Rp) × i - Rn × i Equation (1-3)

[0075] Similarly, if the ratios of the conduction of the upper-arm switching elements SPu and SPv with respect to the period Tc of the PWM carrier are Du and Dv, the U-phase terminal voltage Vout_u and the V-phase terminal voltage Vout_v are expressed by the following equations.

[0076] Vout_u = Du × Vdc + (1 - Du) × (Rn - Rp) × iu - Rn × iu Equation (1-4)

[0077] Vout_v = Dv × Vdc + (1 - Dv) × (Rn - Rp) × iv - Rn × iv Equation (1-5)

[0078] Here, when the offset voltage Voff is superimposed, if the change part of the ratios of the conduction of the upper-arm switching elements SPu and SPv with respect to the period Tc of the PWM carrier due to the superimposed offset voltage Voff is ΔD, the following equations are obtained.

[0079] Vout_u = (Du + ΔD) × Vdc + (1 - (Du + ΔD)) × (Rn - Rp) × iu - Rn × iu Equation (1-6)

[0080] Vout_v = (Dv + ΔD) × Vdc + (1 - (Dv + ΔD)) × (Rn - Rp) × iv - Rn × iv Equation (1-7)

[0081] Here, when the on-resistance Rn and the on-resistance Rp are made equal (Rn = Rp), the phase-to-phase voltage Vout_uv between the U-phase and the V-phase is as follows.

[0082] Vout_uv = Vout_u - Vout_v = (Du - Dv) × Vdc - Rn × (iu - iv) Equation (1-8)

[0083] Since the inter-phase voltage Vout_uv does not include the varying part ΔD, the influence of the superimposed offset voltage Voff does not appear in the inter-phase voltage. Therefore, since the current of the AC rotating machine 1 flows based on the inter-phase voltage, the influence of the superimposed offset voltage Voff does not appear in the current flowing through the AC rotating machine 1.

[0084] According to the above content, as Figure 5 shown, the conduction resistance Rn between the output terminal and the negative-side input terminal of the inverter is preferably equal to the conduction resistance Rp between the output terminal and the positive-side input terminal of the inverter.

[0085] Generally, the conduction resistance depends on the conduction potential of the switching signal of the input switching element. The higher the conduction potential, the more the conduction resistance tends to decrease. Therefore, when trying to improve the inverter efficiency, the conduction potential can be increased and the conduction resistance can be reduced.

[0086] In the present embodiment, making the conduction resistances Rp and Rn consistent helps to reduce the influence of the offset voltage Voff superimposed on the inter-phase voltage. Therefore, by setting the conduction potentials VGp and VGn of the switching signals input to the upper-arm switching element SP and the lower-arm switching element SN to be equal, as a result, the conduction resistances Rp and Rn become equal.

[0087] Next, consider the case of adding the current detection circuit 8 having a resistor R connected in series with the lower-arm switching element SN in Figure 6 compared with Figure 5 . (It can be considered as the equivalent circuit of one phase of the inverter 6 in Figure 1 ). In this case, by setting the conduction resistance Rn between the output terminal and the negative-side input terminal of the inverter in Figure 5 to be Rn + R in Figure 6 , the same discussion can be made.

[0088] For Figure 6 , for the U-phase terminal voltage Vout_u and the V-phase terminal voltage Vout_v after superimposing the offset voltage Voff, in equations (1-6) and (1-7), it is only necessary to replace the conduction resistance Rn with Rn + R. Therefore, it becomes the following formula.

[0089] Vout_u = (Du + ΔD) × Vdc + (1 - (Du + ΔD)) × (Rn + R - Rp) × iu - (Rn + R) × iu Equation (19)

[0090] Vout_v = (Dv + ΔD) × Vdc + (1 - (Dv + ΔD)) × (Rn + R - Rp) × iv - (Rn + R) × iv Equation (1-10)

[0091] Here, as before, if the on-resistance Rn = Rp, the line-to-line voltage Vout_uv between the U-phase and V-phase is as follows.

[0092] Vout_uv = Vout_u - Vout_v = (Du - Dv) × Vdc - ΔD × R × (iu - iv) - (Rn + R) × (iu - iv) Equation (1-11)

[0093] As can be seen from Equation (1-11), the line-to-line voltage Vout_uv includes the variable part ΔD. Therefore, the influence of the superimposed offset voltage Voff appears in the line-to-line voltage Vout_uv. This is because, as Figure 3 shown, the third harmonic is superimposed as the offset voltage Voff. Therefore, the third harmonic is superimposed on the line-to-line voltage, resulting in a third torque ripple in the torque of the AC rotating machine 1.

[0094] Therefore, as described above, in the present embodiment, the relationship between the conduction potential VGp of the switching signal GP of the upper-arm switching element and the conduction potential VGn of the switching signal GN of the lower-arm switching element satisfies "VGn > VGp". That is, it becomes the relationship shown in the Figure 7 curve graph. Figure 7 shows the characteristics when the conduction potential VG is VG = VGn, VG = VGp, and VG = 0, where VGn > VGp > 0. Figure 7 In, the horizontal axis represents the drain-source voltage Vds, and the vertical axis represents the drain current Id.

[0095] Figure 7 In the saturation region, the flatter the slope of the curve graph, the greater the on-resistance. That is, as Figure 7 shown, the on-resistances Rn and Rp are respectively represented by

[0096] Rn = ΔVds_n / ΔId_n Equation (1-12)

[0097] Rp = ΔVds_p / ΔId_p Equation (1-13)

[0098] to represent.

[0099] As a result, the on-resistance Rp between the output terminal of the inverter and the positive-side input terminal is greater than the on-resistance Rn between the output terminal of the inverter and the negative-side input terminal. In a more ideal case, the conduction potential VGp of the switching signal GP of the upper-arm switching element and the conduction potential VGn of the switching signal GN of the lower-arm switching element are set to satisfy Rp = Rn + R. Thus, Equations (1-9) and (1-10) respectively become as shown below.

[0100] Vout_u = (Du + ΔD) × Vdc - (Rn + R) × iu Equation (1-14)

[0101] Vout_v = (Dv + ΔD) × Vdc - (Rn + R) × iv Equation (1-15)

[0102] Compared with Equation (1-9) and Equation (1-10), the second term on the right side can be cancelled out. As a result, the inter-phase voltage Vout_uv is as follows.

[0103] Vout_uv = Vout_u - Vout_v = (Du - Dv) × Vdc - (Rn + R) × (iu - iv) Equation (1-16)

[0104] Therefore, the inter-phase voltage does not include the variable part ΔD, so the influence of the superimposed offset voltage Voff does not appear in the inter-phase voltage. Since the current of the AC rotating electrical machine 1 flows based on the inter-phase voltage, the influence of the superimposed offset voltage Voff does not appear in the current flowing through the AC rotating electrical machine 1.

[0105] Therefore, in Figure 6 the inverter shown, it is desirable that the conduction resistance Rn between the output terminal and the negative-side input terminal of the inverter and the conduction resistance Rp between the output terminal and the positive-side input terminal of the inverter ideally satisfy "Rp = Rn + R". However, considering that the conduction potential VG of the switching signal may change to some extent, and Rp and Rn may change in the thermal characteristics of the switching element, inconsistent situations may also occur in actual applications. In this case, it is set to satisfy "Rp > Rn". Specifically, by setting the conduction resistance Rp between the output terminal and the positive-side input terminal of the inverter to be greater than the conduction resistance Rn other than the current detection resistor R between the output terminal and the negative-side input terminal of the inverter, even if the third harmonic voltage is superimposed as the offset voltage Voff, the influence appearing in the third harmonic of the inter-phase voltage can be reduced, and as a result, the effect of suppressing the third torque ripple of the AC rotating electrical machine 1 is achieved.

[0106] Therefore, the difference between the conduction resistance Rn between the output terminal and the negative-side input terminal of the inverter and the conduction resistance Rp between the output terminal and the positive-side input terminal of the inverter is corrected, so that the influence of the third harmonic caused by the superimposition of the third harmonic component can be reduced.

[0107] In addition, the setting of the above conduction potential can be performed by the conduction command signal of the switching element (if the switching element is a MOSFET or IGBT, it is the gate voltage; if the switching element is a bipolar transistor, it is the base current). If the value of the conduction command signal is made smaller, the conduction resistance increases.

[0108] The above has described the inverter with the shunt current detection method for the lower arm 3. However, this embodiment is also applicable to the inverter with the shunt current detection method for the bus bar 1. The reason is that even in the inverter with the shunt current detection method for the bus bar 1, the conduction resistance between the output terminal of the inverter and the negative-side input terminal is also "Rn + R", and the conduction resistance between the output terminal of the inverter and the positive-side input terminal is Rp. Therefore, the conduction resistance between the output terminal of the inverter and the negative-side input terminal is large. Thus, similar to this embodiment, by setting to satisfy "Rp > Rn", even if a third harmonic voltage is superimposed as the offset voltage Voff, the influence occurring in the third harmonic of the inter-phase voltage can be reduced, and as a result, the effect of suppressing the third torque ripple of the AC rotating electric machine 1 can be obtained.

[0109] In the above description, in order to satisfy "Rp > Rn", it has been described that "VGn > VGp" is satisfied in the relationship between the conduction potential VGp of the upper arm switch signal GP and the conduction potential VGn of the lower arm switch signal GN. However, in the case where the current detection resistor R is connected between the lower arm switching element and the above-mentioned negative-side input terminal, by satisfying "Rp > Rn", even if a third harmonic voltage is superimposed as the offset voltage Voff, the influence occurring in the third harmonic of the inter-phase voltage is reduced. Therefore, for example, the upper arm switching element and the lower arm switching element can be selected such that at the conduction potential of the same switching signal, the conduction resistance of the upper arm switching element is greater than the conduction resistance of the lower arm switching element, so that "Rp > Rn" is satisfied even in the state of "VGn = VGp".

[0110] Generally, the performance of a switching element is determined by its conduction resistance. The lower the conduction resistance, the higher the efficiency of the inverter, and thus it is considered better. However, here, since it is desired that the conduction resistance of the upper arm switching element be greater than the conduction resistance of the lower arm switching element, therefore, compared with the lower arm switching element, a lower-grade (greater conduction resistance) product can be deliberately used for the upper arm switching element to satisfy "Rp > Rn". Thereby, even if a third harmonic voltage is superimposed as the offset voltage Voff, the influence occurring in the third harmonic of the inter-phase voltage can be reduced, and as a result, the effect of suppressing the third torque ripple of the AC rotating electric machine 1 can be obtained.

[0111] That is, typified by the MOSFET, the performance of the power switching element depends on the conduction resistance. The higher the conduction resistance, the lower the performance (cheaper). Therefore, by using the upper arm switching element with a high conduction resistance, on the basis of reducing the price of the power switching element, the influence of the third harmonic can be reduced.

[0112] In addition, with respect to Figure 1 , such as Figure 8Similar to the case where the equivalent circuit of one phase is shown, it is also considered that the current detection circuit 8 is configured to be connected in series to the switching elements SPu, SPv, and SPw to detect the current flowing through the three-phase upper-arm switching elements SPu, SPv, and SPw. In this case, in order to ideally satisfy "Rn = Rp + R" and realistically satisfy "Rp < Rn", the relationship between the conduction potential VGp of the upper-arm switching signal GP and the conduction potential VGn of the lower-arm switching signal GN is set to "VGn < VGp". Alternatively, the switching elements can be selected such that the on-resistance Rn of the lower-arm switching element is greater than the on-resistance Rp of the upper-arm switching element under the state of the same conduction potential. That is, by setting the conduction resistance between the output terminal of the inverter and the negative-side input terminal to be greater than the conduction resistance other than the current detection resistor between the output terminal of the inverter and the positive-side input terminal, even if a third-harmonic voltage is superimposed as the offset voltage Voff, the influence appearing in the third harmonic of the inter-phase voltage can be reduced, and as a result, the effect of suppressing the third torque ripple of the AC rotating electric machine 1 is achieved.

[0113] Furthermore, in the structure having the current detection resistor R between the lower-arm switching element and the negative-side input terminal, the imbalance between the conduction resistance between the output terminal of the inverter and the negative-side input terminal and the conduction resistance between the output terminal of the inverter and the positive-side input terminal can be reduced by inserting at least one resistor R1 between the upper-arm switching element and the positive-side terminal Cp of the capacitor 5. Thereby, even if a third-harmonic voltage is superimposed as the offset voltage Voff, the influence appearing in the third harmonic of the inter-phase voltage can be reduced, and as a result, the effect of suppressing the third torque ripple of the AC rotating electric machine 1 is obtained.

[0114] Furthermore, in the structure having the current detection resistor R between the upper-arm switching element and the positive-side input terminal, the imbalance between the conduction resistance between the output terminal of the inverter and the positive-side input terminal and the conduction resistance between the output terminal of the inverter and the negative-side input terminal can be reduced by inserting at least one resistor R2 between the lower-arm switching element and the negative-side terminal Cp of the capacitor 5. Thereby, it can also be configured that even if a third-harmonic voltage is superimposed as the offset voltage Voff, the influence appearing in the third harmonic of the inter-phase voltage can be reduced, and as a result, the effect of suppressing the third torque ripple of the AC rotating electric machine 1 is obtained.

[0115] In addition, the on-resistance Rp described in this specification can be considered to include the wiring resistance from the positive-side input terminal of the upper-arm switching element to the positive-side terminal Cp of the capacitor 5 on the basis of the on-resistance of the upper-arm switching element, but does not include the resistance Rdc of the circuit breaker 4. Further, the on-resistance Rn described in this specification can be considered to include the wiring resistance from the negative-side input terminal of the lower-arm switching element to the negative-side terminal Cn of the capacitor 5 on the basis of the on-resistance of the lower-arm switching element. Thus, the "on-resistance between the output terminal of the inverter and the positive-side input terminal" can be regarded as the on-resistance from the positive-side terminal Cp of the capacitor 5 to the output terminals (Out_u, Out_v, Out_w), and the "on-resistance between the output terminal of the inverter and the negative-side input terminal" can be regarded as the on-resistance from the negative-side terminal Cn of the capacitor 5 to the output terminals (Out_u, Out_v, Out_w). At this time, if the wiring resistance from the terminal of the capacitor to the switching element is sufficiently smaller than the on-resistance of the switching element, it can be ignored and the on-resistances of the upper- and lower-arm switching elements can be considered.

[0116] In the present embodiment, the AC rotating electric machine 1 is described as a load connected to the inverter 6. However, any load that can be regarded as a current source from the perspective of the inverter 6 is acceptable. Therefore, as long as it is a three-phase inductive load, such as the AC rotating electric machine, it is acceptable.

[0117] Embodiment 2.

[0118] By Figure 9 the power conversion device according to Embodiment 2 will be described. The difference between Embodiment 2 and Embodiment 1 is the corrected voltage command value calculation unit 363a.

[0119] As shown in the following formula (2-1), the corrected voltage command value calculation unit 363a determines the maximum value Vmax of the three-phase voltage command values Vuoc, Vvoc, and Vwoc after coordinate conversion, subtracts the maximum value Vmax from Vdc / 2 to calculate the offset voltage Voff, and subtracts the offset voltage Voff from the three-phase voltage command values Vuoc, Vvoc, and Vwoc after coordinate conversion to calculate the three-phase corrected voltage command values Vuo, Vvo, and Vwo.

[0120]

[0121] The waveforms of each part in this case are as Figure 10 shown. Figure 10Among them, the upper section shows the three-phase voltage command values Vuoc, Vvoc, and Vwoc after coordinate conversion. The second section from the top is the offset voltage Voff, which varies at three times the frequency with respect to the voltage command value and becomes the third harmonic component. The third section from the top is the three-phase corrected voltage command values Vuo, Vvo, and Vwo. Then, the lowermost section is the voltage command values between phases Vuo - Vvo, Vvo - Vwo, and Vwo - Vuo. It can be seen that the maximum value among the instantaneous values of the three-phase corrected voltage command values Vuo, Vvo, and Vwo is consistent with the upper limit value Vdc / 2 that the inverter can output.

[0122] In an inverter adopting the lower-arm 3-shunt current detection method, the corrected voltage command value is obtained through the operation of Equation (2-1). That is, the third harmonic component (Voff) is calculated, and modulation (hereinafter referred to as "upper solid two-phase modulation") for calculating the corrected voltage command value is performed by adding the third harmonic component so that the maximum value in the corrected voltage command value is consistent with the upper limit value (Vdc / 2) that the inverter can output.

[0123] For reference Figure 4 the advantages of applying upper solid two-phase modulation will be described. Vmax in Equation (2-1) is always consistent with Vdc / 2 (equivalent to Figure 10 the maximum value among the instantaneous values of the three-phase corrected voltage command values Vuo, Vvo, and Vwo is consistent with the upper limit value Vdc / 2 that the inverter can output), and the phase consistent with Vmax does not switch during the period Tc of the carrier wave CA (GP is always on, and GN is always off). Therefore, as seen in other modulations, it has the advantage of not generating the switch of the Vmax phase in interval B. Regarding this point, it can be known that in Figure 10 among the upper-section corrected voltage command values Vuo, Vvo, and Vwo, the phase with the maximum instantaneous value is always Vdc / 2. Not generating a switch in interval B also means not generating a switch near the current detection timing. It can be said that upper solid two-phase modulation is an excellent modulation method in terms of current detection accuracy.

[0124] However, in Figure 9 the lower-arm 3-shunt current detection method inverter shown, the on-resistance between the output terminal of the inverter and the negative-side input terminal is "Rn + R", and the on-resistance between the output terminal of the inverter and the positive-side input terminal is Rp. Therefore, due to the imbalance of the on-resistance, observing Figure 11A the waveform of the torque T in the lowermost section, for the fundamental components of the corrected voltage command values Vuo, Vvo, and Vwo (or, the fundamental components of the currents Iu, Iv, and Iw flowing through the AC rotating machine 1 in the second section), the pulsation of the three-times frequency component can be confirmed to be superimposed.

[0125] Therefore, in the present embodiment, while maintaining the current detection accuracy which is an advantage of the upper solid-state two-phase modulation, in order to reduce the third harmonic component caused by the imbalance of the on-resistance, as described in detail in Embodiment 1, the on-resistance Rp between the output terminal of the inverter and the positive-side input terminal is set to be larger than the on-resistance Rn between the output terminal of the inverter and the negative-side input terminal (excluding the current detection resistance element) (Rp > Rn). Figure 11B The waveforms of each part when the on-resistance is set in such a way that Rp > Rn. If we focus on the torque T in the third segment, it can be seen that compared with Figure 11A the third harmonic component can be reduced.

[0126] As described above, based on the upper solid-state two-phase modulation, in combination with the lower-arm 3 shunt current detection method, by setting the on-resistance Rp between the output terminal of the inverter and the positive-side input terminal to be larger than the on-resistance Rn between the output terminal of the inverter and the negative-side input terminal (excluding the current detection resistance element) (Rp > Rn), while preventing switching noise (chirping sound, the noise mixed into the A / D value when the switching moment and the current A / D moment are close) from being mixed into the current detection value, it is possible to achieve a remarkable effect of suppressing the third harmonic component of the torque generated by the AC rotating machine 1.

[0127] The lower-arm 3 shunt current detection method inverter has been described above. This embodiment is also applicable to the bus-1 shunt current detection method inverter. The reason is that even in the bus-1 shunt current detection method inverter, the on-resistance between the output terminal of the inverter and the negative-side input terminal is "Rn + R", and the on-resistance between the output terminal of the inverter and the positive-side input terminal is Rp. Therefore, the on-resistance between the output terminal of the inverter and the negative-side input terminal is larger. Thus, even if this embodiment is applied to the bus-1 shunt current detection method inverter, the same effect can of course be obtained.

[0128] In addition, when the current detection circuit 8 is configured as in Figure 8 such a way that SPu, SPv, and SPw are connected in series to detect the current flowing through the three-phase upper-arm switching elements SPu, SPv, and SPw (upper-arm 3 shunt current detection method), in order to avoid the current detection timing being close to the switching moment, the corrected voltage command value calculation unit 363a performs the following calculation.

[0129]

[0130] The waveforms of each part in this case are as shown in Figure 12As shown. The upper part shows the three-phase voltage command values Vuoc, Vvoc, and Vwoc after coordinate conversion. The second part from the top is the offset voltage Voff, which is known to vary at three times the frequency relative to the voltage command value, becoming the third harmonic component. The third part from the top is the three-phase corrected voltage command values Vuo, Vvo, and Vwo. Then, the lowermost part is the voltage command values between phases Vuo - Vvo, Vvo - Vwo, and Vwo - Vuo. It can be seen that the minimum value among the instantaneous values of the three-phase corrected voltage command values Vuo, Vvo, and Vwo in this figure is consistent with the lower limit value "-Vdc / 2" that the inverter can output (lower solid two-phase modulation).

[0131] In this case, the conduction resistance between the output terminal of the inverter and the negative input terminal is Rn, and the conduction resistance between the output terminal of the inverter and the positive input terminal is "Rp + R". Therefore, if "Rp = Rn", due to the imbalance of the conduction resistance, the torque of the AC rotating motor 1 will generate a third harmonic. Therefore, by providing a conduction resistance to satisfy Rp < Rn, the third harmonic component can be reduced.

[0132] Thus, by combining the upper-arm three-shunt current detection method with the lower solid two-phase modulation, the conduction resistances of the upper and lower arms are made consistent, thereby being able to suppress the deterioration of the third harmonic torque ripple during lower solid two-phase modulation.

[0133] Embodiment 3

[0134] Next, the electric power steering device 200 according to Embodiment 3 will be described. In Embodiments 1 and 2, the power conversion device 100 was described, but an electric power steering device can also be configured by generating a torque for assisting the steering torque by the power conversion device 100. In Embodiment 3, the differences compared to Embodiments 1 and 2 are the steering wheel 901, the front wheels 902, the gear 903, the torque detector 904, and the motor torque target value calculation unit 905. In the following description, the points different from Embodiments 1 and 2 will be described.

[0135] Figure 13 is a diagram showing the structure of the electric power steering device according to Embodiment 3. In Figure 13In this case, the driver rotates the steering wheel 901 to the left and right to steer the front wheels 902. The torque detector 904 detects the steering torque of the steering system and outputs the detected torque to the motor torque target value calculation unit 905. The motor torque target value calculation unit 905 calculates the target value T_ref of the motor torque, which is a control command to be output to the AC rotating motor 1, based on the detected torque of the torque detector 904 in order to make the AC rotating motor 1 generate a torque T for assisting the steering torque of the steering system. The target value T_ref is input to the current command value calculation unit 35 of the controller 7 constituting the power conversion device 100, and the AC rotating motor 1 is controlled via the inverter 6 according to the target value T_ref. The AC rotating motor 1 generates a torque for assisting the steering torque via the gear 903.

[0136] Such an electric power steering device focuses on quietness, device cost, and device size. First, from the viewpoints of device cost and device size, it is more advantageous to use current detectors of the "lower arm 3 shunt current detection method inverter" and the "bus bar 1 shunt current detection method inverter". However, since these methods insert a resistor in the conduction path of the inverter, an imbalance occurs in the conduction resistances of the upper arm switching element and the lower arm switching element due to the insertion. This effect occurs when an offset voltage (third harmonic component) is added to the voltage command value, and a third harmonic torque ripple is generated from the AC rotating motor 1. Therefore, in the present embodiment, as described in Embodiment 1, by making the conduction resistance Rp between the output terminal and the positive input terminal of the inverter larger than the conduction resistance Rn between the output terminal and the negative input terminal (excluding the current detection resistance element) of the inverter (Rp > Rn), the influence of this problem is reduced.

[0137] In addition, the "upper arm 3 shunt current detection method" can also achieve the same effect. That is, as described in Embodiment 1, by making the conduction resistance Rn between the output terminal and the negative input terminal of the inverter larger than the conduction resistance Rp between the output terminal and the positive input terminal (excluding the current detection resistance element) of the inverter (Rn > Rp), the influence of this problem can be reduced.

[0138] As described above, the electric power steering device requires quietness. Further, due to low voltage (12V) and high current (e.g., 100A), and due to the difference in the conduction resistances of the upper and lower legs of the three-phase inverter, voltage pulsation becomes current pulsation, which easily causes torque pulsation and becomes noise. If the power conversion devices described in Embodiments 1 and 2 are applied to the electric power steering device, it is possible to achieve both an increase in voltage utilization rate based on the superposition of third harmonic components and quietness.

[0139] Although this application describes various exemplary embodiments and examples, the various features, methods, and functions described in one or more embodiments are not limited to the application of a specific embodiment and can be applied individually or in various combinations to the embodiments.

[0140] Therefore, it can be considered that countless unillustrated variations are also included in the technical scope disclosed in the specification of 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.

[0141] Reference Numeral Explanation

[0142] 1: AC rotating electric machine, 2: Rotation detection circuit, 6: Inverter, 7: Controller, 8: Current detection circuit, 31: Rotation detection unit, 32: Current detection unit, 33: Current coordinate conversion unit, 35: Current command value calculation unit, 37: PWM control unit, 100: Power conversion device, 200: Electric power steering device, 361: dq-axis voltage command value calculation unit, 362: Voltage coordinate conversion unit, 363, 363a: Corrected voltage command value calculation unit, 901: Steering wheel, 902: Front wheels, 903: Gear, 904: Torque detector, 905: Motor torque target value calculation unit.

Claims

1. A power conversion device, characterized in that, Comprising: An inverter having an upper-arm switching element and a lower-arm switching element, which converts a DC voltage into an AC voltage and outputs it to a load; A voltage command value calculation unit that calculates a voltage command value for controlling the load to a commanded state; And A corrected voltage command value calculation unit that calculates a corrected voltage command value by adding a third-harmonic component, which is a three-times frequency component, to the fundamental wave component of the voltage command value, and the inverter converts to the AC voltage according to the corrected voltage command value. When a current detection resistor is connected between the lower-arm switching element and the negative-side input terminal of the inverter, it is set that the conduction resistance between the output terminal and the positive-side input terminal of the inverter is larger than the conduction resistance other than the current detection resistor between the output terminal and the negative-side input terminal of the inverter. When a current detection resistor is connected between the upper-arm switching element and the positive-side input terminal of the inverter, it is set that the conduction resistance between the output terminal and the negative-side input terminal of the inverter is larger than the conduction resistance other than the current detection resistor between the output terminal and the positive-side input terminal of the inverter.

2. The power conversion device according to claim 1, characterized in that When the current detection resistor is connected between the lower-arm switching element and the negative-side input terminal, the conduction resistance of the upper-arm switching element is made larger than the conduction resistance of the lower-arm switching element.

3. The power conversion device according to claim 1 or 2, characterized in that When the current detection resistor is connected between the lower-arm switching element and the negative-side input terminal, the conduction command signal to the upper-arm switching element is made smaller than the conduction command signal to the lower-arm switching element.

4. The power conversion device according to claim 2 or 3, characterized in that The corrected voltage command value calculation unit calculates the third-harmonic component so that the maximum value in the corrected voltage command value coincides with the upper limit value that the inverter can output.

5. The power conversion device according to claim 4, characterized in that The inverter is a three-phase inverter, and the current detection resistor is inserted between the lower-arm switching element of each phase and the negative-side input terminal.

6. The power conversion device according to claim 1, characterized in that When the current detection resistor is connected between the upper-arm switching element and the positive-side input terminal, the conduction resistance of the lower-arm switching element is made larger than the conduction resistance of the upper-arm switching element.

7. The power conversion device according to claim 1 or 2, characterized in that When the current detection resistor is connected between the upper-arm switching element and the positive-side input terminal, the conduction command signal to the lower-arm switching element is made smaller than the conduction command signal to the upper-arm switching element.

8. The power conversion device according to claim 6 or 7, characterized in that The correction voltage command value calculation unit calculates the third harmonic component such that the minimum value in the correction voltage command value is consistent with the lower limit value that the inverter can output.

9. The power conversion device according to claim 8, wherein: The inverter is a three-phase inverter, and the current detection resistor is inserted between the upper arm switching element of each phase and the positive side input terminal.

10. An electric power steering device, characterized in that, Comprising: The power conversion device according to any one of claims 1 to 9; And a driving force transmission mechanism, wherein the load of the driving force transmission mechanism is an AC rotating electric machine, and the driving force of the AC rotating electric machine is transmitted to a steering device of a vehicle.

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