Inverter driving device

Abstract

To provide an inverter drive device capable of suppressing ringing on a high side and a low side and reducing heat generation of a switching element with a simple and low-cost circuit configuration.SOLUTION: The first slew rate setting part 13 is electrically connected to the signal lines P1 to P6, and sets the slew rates of the drive signals input to the control terminals of the switching elements S1 to S6 to a first predetermined slew rate, and the second slew rate setting part 14 is provided inside the pre-driver 12 and can set the slew rates of the drive signals to a second predetermined slew rate smaller than the first predetermined slew rate. The first slew rate setting part 13 is connected to the signal lines L1 to L6, and sets the slew rates of the drive signals input to the control terminals of the switching elements to to a second predetermined slew rate. The waveform of the drive signal falls according to the first predetermined slew rate at the falling timing, and rises according to the second predetermined slew rate at the rising timing.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to an inverter drive device. [Background technology]

[0002] Generally, inverter drivers are known for driving inverter circuits having multiple current-carrying phases in which semiconductor switching elements are connected in series. In inverter drivers, high-frequency ringing (switching noise) occurs when switching occurs. As an example of conventional technology for suppressing this ringing, Patent Document 1 below discloses a power supply control device equipped with a slew rate control unit configured to control the slew rate of a switch voltage when a high-side switch element is turned on. In this power supply control device, the slew rate control unit detects the ringing level of the switch voltage, and the current capacity of the high-side pre-driver is adjusted according to the detection result, thereby automatically adjusting the ringing. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2023-82752 Summary of the Invention [Problem to be solved by the invention]

[0004] However, the above-mentioned conventional technologies are configured to focus only on the ringing of the switching voltage when the high-side switching element is turned on, making it difficult to suppress the ringing of the switching voltage when the low-side switching element is turned on. Furthermore, the need to constantly monitor the ringing of the switching voltage complicates the circuit configuration, resulting in increased component count and cost. Furthermore, if the slew rate of the switching voltage changes not only when it rises (turns on) but also when it falls (turns off), this can have a significant impact on the heat generation performance of the switching element. Therefore, there is room for improvement in terms of both suppressing ringing (switching noise) and reducing heat generation.

[0005] The present invention has been made in light of the above points, and aims to provide an inverter drive device that can suppress high-side and low-side ringing and reduce heat generation in switching elements using a simple, low-cost circuit configuration. [Means for solving the problem]

[0006] To achieve the above object, one aspect of the present invention provides an inverter drive device including an inverter circuit having a plurality of conduction phases in which semiconductor switching elements are connected in series, and a pre-driver that outputs a rectangular wave drive signal to be input to a control terminal of each semiconductor switching element. The inverter drive device also includes a first slew rate setting unit electrically connected to each signal line connecting an output port of the pre-driver to the control terminal of each semiconductor switching element and configured to set the slew rate of the drive signal to a first predetermined slew rate, and a second slew rate setting unit either provided inside the pre-driver or electrically connected to each signal line and configured to set the slew rate of the drive signal to a second predetermined slew rate smaller than the first predetermined slew rate. The drive signal is configured so that, at its falling edge, its waveform falls according to the first predetermined slew rate set by the first slew rate setting unit, and, at its rising edge, its waveform rises according to the second predetermined slew rate set by the second slew rate setting unit. [Effects of the Invention]

[0007] According to the inverter driving device of the present invention, ringing on the high side and low side can be suppressed and heat generation in the switching elements can be reduced with a simple and low-cost circuit configuration. [Brief explanation of the drawings]

[0008] [Figure 1] 1 is a diagram showing the configuration of a main part of an electric power steering device to which an inverter drive device according to an embodiment of the present invention is applied; [Figure 2] FIG. 2 is a block diagram showing a circuit configuration of the inverter driving device according to the embodiment. [Figure 3] 4 is a graph showing an example of a voltage waveform of a drive signal input to a control terminal of each semiconductor switching element in the inverter drive device according to the embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0009] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An inverter drive device according to an embodiment of the present invention will be described in detail below with reference to the accompanying drawings. In the following embodiment, a case will be described in which the inverter drive device according to the present invention is applied to an electric power steering device that uses torque generated by a motor to assist the force required to operate the steering wheel of a vehicle such as an automobile.

[0010] FIG. 1 is a diagram showing the configuration of the main parts of an electric power steering device 200 to which an inverter drive device 10 according to this embodiment is applied. 1, an electric power steering device 200 is attached to the front of a vehicle 100. A steering mechanism 210 of the electric power steering device 200 has a steering wheel 201, a steering shaft 202 which is the rotation axis of the steering wheel 201, a pinion shaft 203 provided at the end of the steering shaft 202, a rack bar 204 connected to the pinion shaft 203, and a rack housing 205 which accommodates the rack bar 204.

[0011] In the steering mechanism 210, when the driver of the vehicle 100 rotates the steering wheel 201, the steering torque of the steering wheel 201 is transmitted to the pinion shaft 203 via the steering shaft 202. Then, the rotational motion of the pinion shaft 203 is converted into the linear motion of the rack bar 204, thereby changing the steering angles (in other words, tire angles) of the left and right wheels (front wheels) 110, 110 connected to both ends of the rack bar 204 via tie rods 250.

[0012] In other words, the rotational motion of the steering shaft 202 is converted into linear motion of the rack bar 204 using a rack-and-pinion system in which the pinion shaft 203 meshes with the rack teeth formed on the rack bar 204, thereby changing the steering angle of the wheels (front wheels) 110, 110 in accordance with the rotational operation of the steering wheel 201.

[0013] The steering shaft 202 is provided with an operation angle sensor 206 that detects an operation angle β, which is the rotation angle of the steering shaft 202 , and a steering torque sensor 207 that detects a steering torque TS of the steering wheel 201 .

[0014] The steering mechanism 210 also includes a motor 220, which is a steering actuator that applies a steering torque to the rack bar 204, in other words, that generates a steering force that moves the rack bar 204 in the axial direction. The rotational motion of the motor 220 is transmitted to the rack bar 204 via a transmission mechanism 208 that includes a belt, a ball screw, or the like. The application of the steering torque by the motor 220 is performed to assist the driver's steering operation. The steering torque applied by the motor 220 makes it possible to perform autonomous steering (in other words, automatic steering).

[0015] The motor 220 is a DC motor having a multi-phase winding set, for example, a three-phase brushless DC motor having a motor rotor and a winding set including a U-phase winding, a V-phase winding, and a W-phase winding. The motor 220 is driven by receiving power supply from the inverter drive device 10 according to this embodiment. The inverter drive device 10 includes an inverter circuit 11 and a pre-driver 12.

[0016] The inverter circuit 11 is, for example, a three-phase bridge inverter circuit having six semiconductor switching elements. The inverter circuit 11 controls the power supplied to each winding of the motor 220 by controlling the on / off of each semiconductor switching element in accordance with a drive signal output from the pre-driver 12.

[0017] The pre-driver 12 generates a rectangular wave drive signal for PWM (Pulse Width Modulation) control of the drive current of the motor 220 based on a command torque CT from a microprocessor (MPU) 230 and outputs the signal to the inverter circuit 11.

[0018] The microprocessor 230 acquires a sensor signal relating to the operation angle β of the steering shaft 202 output by the operation angle sensor 206, a sensor signal relating to the steering torque TS output by the steering torque sensor 207, a sensor signal relating to the vehicle speed VS output by the vehicle speed sensor 211 (or wheel speed sensor), and a sensor signal relating to the rotor rotation angle θ of the motor 220 output by the motor rotation angle sensor 209. Based on the acquired various sensor signals, the microprocessor 230 calculates a command torque CT which is a target value of the steering torque (in other words, assist torque) output by the motor 220, and outputs the command torque CT to the pre-driver 12.

[0019] FIG. 2 is a block diagram showing the circuit configuration of the inverter driving device 10 according to this embodiment. 2, the inverter driving device 10 includes the above-mentioned inverter circuit 11 and pre-driver 12, a first slew rate setting unit 13 electrically connected to each signal line connecting them, and a second slew rate setting unit 14 provided inside the pre-driver 12. Specific configuration examples of each unit of the inverter driving device 10 will be described in detail below.

[0020] Inverter circuit 11 has a U-phase arm, a V-phase arm, and a W-phase arm connected in parallel between a system power supply 120 mounted on vehicle 100 and ground GND. In the U-phase arm, a high-side semiconductor switching element S1 and a low-side semiconductor switching element S2 are connected in series. A node between each of the semiconductor switching elements S1 and S2 is connected to a U-phase winding (not shown) of motor 220. In the V-phase arm, a high-side semiconductor switching element S3 and a low-side semiconductor switching element S4 are connected in series. A node between each of the semiconductor switching elements S3 and S4 is connected to a V-phase winding (not shown) of motor 220. In the W-phase arm, a high-side semiconductor switching element S5 and a low-side semiconductor switching element S6 are connected in series. A node between each of the semiconductor switching elements S5 and S6 is connected to a W-phase winding (not shown) of motor 220.

[0021] Each of the semiconductor switching elements S1 to S6 constituting the inverter circuit 11 is a semiconductor element having an externally controllable control terminal, such as a metal oxide semiconductor metal field effect transistor (MOSFET) or an insulated gate bipolar transistor (IGBT). In this embodiment, each of the semiconductor switching elements S1 to S6 is an N-channel MOSFET, and includes parasitic diodes D1, D2, D3, D4, D5, and D6 formed between the drain and source during the manufacturing process. The parasitic diodes D1 to D6 have their anodes connected to ground GND and their cathodes connected to the system power supply 120, and allow current to flow from ground GND to the system power supply 120. A capacitor C1 for smoothing the power supply voltage is connected in parallel with the inverter circuit 11 between the system power supply 120 and ground GND.

[0022] The pre-driver 12 has six output ports P1, P2, P3, P4, P5, and P6 corresponding to the semiconductor switching elements S1 to S6 of the inverter circuit 11. Six signal lines L1, L2, L3, L4, L5, and L6 connect the output ports P1 to P6 of the pre-driver 12 to the control terminals (gate terminals) of the semiconductor switching elements S1 to S6, respectively. Resistance elements R1, R2, R3, R4, R5, and R6 constituting the first slew rate setting unit 13 are inserted on the signal lines L1 to L6, respectively.

[0023] The pre-driver 12 receives a command torque CT calculated by the microprocessor 230. The pre-driver 12 generates a rectangular wave drive signal for PWM control of the drive current of the motor 220 based on the command torque CT from the microprocessor 230. In this embodiment, the pre-driver 12 includes a current adjustment circuit 12A that adjusts the current value of the drive signal output from each of the output ports P1 to P6.

[0024] The current adjustment circuit 12A has a function as a second slew rate setting unit 14. The current adjustment circuit 12A is configured to be able to select from a plurality of current adjustment modes in which the current values ​​of the drive signals output from the output ports P1 to P6 of the pre-driver 12 are different from one another. In this embodiment, the plurality of current adjustment modes are switched in synchronization with the rising and falling timings of the waveform of the drive signal.

[0025] The slew rate of the drive signals output from the output ports P1 to P6 of the pre-driver 12 to the signal lines L1 to L6 and input to the control terminals of the semiconductor switching elements S1 to S6 of the inverter circuit 11 via the resistor elements R1 to R6 varies depending on the current value of the drive signal and the resistance value of the resistor elements R1 to R6. The slew rate of the drive signal is an index that represents the rate of change of voltage over time at the rising and falling edges of a square wave.

[0026] For example, assuming that the current adjustment circuit 12A as in this embodiment is not provided inside the pre-driver 12 and the current value of the drive signal output from each output port P1 to P6 of the pre-driver 12 is constant at a predetermined reference value, the slew rate of the drive signal input to the control terminal of each semiconductor switching element S1 to S6 becomes a first predetermined slew rate determined according to the resistance value (fixed value) of each resistance element R1 to R6.

[0027] In this case, if the resistance value of each of the resistor elements R1 to R6 is increased to make the rising waveform of the drive signal gentler in order to suppress ringing (switching noise) when each of the semiconductor switching elements S1 to S6 is turned on, the falling waveform will also become gentler. If the falling waveform becomes gentler, the ON time of each of the semiconductor switching elements S1 to S6 becomes longer, which will have a greater impact on the heat generation performance of the inverter circuit 11. In other words, it is difficult to design the resistance values ​​of each of the resistor elements R1 to R6 so that both ringing suppression and heat reduction are achieved, and this requires a lot of work, such as evaluation of the actual device.

[0028] Therefore, in the inverter driving device 10 according to this embodiment, a current adjustment circuit 12A capable of selecting from a plurality of current adjustment modes is provided inside the pre-driver 12, separate from the respective resistance elements R1 to R6. Then, by switching the current adjustment mode selected by the current adjustment circuit 12A in synchronization with the rising and falling timing of the waveform of the drive signal, it is possible to achieve both suppression of ringing and reduction of heat generation.

[0029] Specifically, the multiple current regulation modes selectable by the current regulation circuit 12A in this embodiment include first and second current regulation modes. The first current adjustment mode is a mode in which the current value of the drive signal output from each output port P1 to P6 of the pre-driver 12 is adjusted to the aforementioned reference value so that the slew rate of the drive signal input to the control terminal of each semiconductor switching element S1 to S6 is set to the first predetermined slew rate by each resistance element R1 to R6.

[0030] The second current adjustment mode is a mode in which the current values ​​of the drive signals output from the output ports P1-P6 of the pre-driver 12 are adjusted to a value different from the reference value, so that the slew rates of the drive signals input to the control terminals of the semiconductor switching elements S1-S6 via the resistor elements R1-R6 are set to a second predetermined slew rate that is smaller than the first predetermined slew rate. The adjustment amount of the current value in the second current adjustment mode is set in advance taking into account the resistance values ​​of the resistor elements R1-R6, the line lengths of the signal lines L1-L6, etc.

[0031] That is, in this embodiment, the slew rate of the drive signal input to the control terminal of each semiconductor switching element S1 to S6 changes depending on the current adjustment mode selected by the current adjustment circuit 12A. The current adjustment circuit 12A switches between a plurality of current adjustment modes, selecting the first current adjustment mode at the timing of the falling edge of the waveform of the drive signal and selecting the second current adjustment mode at the timing of the rising edge. The rising and falling edge timings of the waveform of the drive signal are determined according to the rectangular waveform of the drive signal corresponding to PWM control generated by the pre-driver 12 based on the command torque CT from the microprocessor 230.

[0032] By switching the current adjustment mode by the current adjustment circuit 12A in the pre-driver 12 as described above, the slew rate of the drive signal input to the control terminal of each semiconductor switching element S1 to S6 is set to a first predetermined slew rate determined according to the resistance value of each resistor element R1 to R6 at the timing of the falling edge, and is set to a second predetermined slew rate determined according to the current value adjusted by the second current adjustment mode at the timing of the rising edge.

[0033] FIG. 3 is a graph showing an example of the voltage waveform of the drive signal input to the control terminal of each of the semiconductor switching elements S1 to S6 in this embodiment. In the graph of Fig. 3, the horizontal axis represents time t and the vertical axis represents the voltage (gate voltage) Vg of the drive signal. In the example of Fig. 3, the voltage waveform of the drive signal rises at timing t0 and falls at timing t3. The rising slew rate SRr of this voltage waveform of the drive signal is set to a second predetermined slew rate determined in accordance with the current value adjusted by the second current adjustment mode in the current adjustment circuit 12A in the pre-driver 12. The falling slew rate SRf is set to a first predetermined slew rate determined in accordance with the resistance values ​​of each of the resistance elements R1 to R6.

[0034] Specifically, the rise-through rate SRr can be expressed as, for example, the ratio of the voltage change amount ΔVg (= |Vth(ON) - Vth(OFF)|) to the required time ΔTr (= t2 - t1) for the voltage Vg of the drive signal to rise from exceeding the OFF threshold Vth(OFF) to the ON threshold Vth(ON) of each semiconductor switching element S1 to S6 (SRr = ΔVg / ΔTr). Similarly, the fall-through rate SRf can be expressed as the ratio of the voltage change amount ΔVg = |Vth(OFF) - Vth(ON)| to the required time ΔTf (= t5 - t4) for the voltage Vg of the drive signal to decrease from below the ON threshold Vth(ON) to the OFF threshold Vth(OFF) (SRf = ΔVg / ΔTf).

[0035] As shown in FIG. 3, the voltage waveform of the drive signal input to the control terminals of each semiconductor switching element S1 to S6 gently rises according to a substantially constant through rate SRr (second predetermined through rate) when the second current adjustment mode is selected by the current adjustment circuit 12A at the rising timing. This makes it possible to suppress the ringing generated when each semiconductor switching element S1 to S6 turns on (transitions from the OFF state to the ON state). Then, at the falling timing, when the first current adjustment mode is selected by the current adjustment circuit 12A, it falls more steeply than when rising according to the through rate SRf (first predetermined through rate) (SRr < SRf). This makes it possible to suppress the heat generation of the elements by shortening the ON time of each semiconductor switching element S1 to S6.

[0036] As described above, in the inverter driving device 10 according to this embodiment, the first slew rate setting unit 13 is electrically connected to each of the signal lines L1 to L6 that connect each of the output ports P1 to P6 of the pre-driver 12 to the control terminals of each of the semiconductor switching elements S1 to S6 of the inverter circuit 11, and the second slew rate setting unit 14 is provided inside the pre-driver 12. Then, at the falling timing of the drive signal input to the control terminal of each of the semiconductor switching elements S1 to S6, the waveform falls in accordance with the first predetermined slew rate (SRf) set by the first slew rate setting unit 13, and at the rising timing, the waveform rises in accordance with the second predetermined slew rate (SRr) set by the second slew rate setting unit 14, which is smaller than the first predetermined slew rate.

[0037] The inverter drive device 10 described above can suppress ringing and reduce heat generation in both the high-side semiconductor switching elements S1, S3, and S5 and the low-side semiconductor switching elements S2, S4, and S6 that make up the inverter circuit 11. Furthermore, unlike the conventional technology described above, it is not necessary to constantly monitor the ringing of the switch voltage; instead, it is sufficient to determine the timing of the rise and fall of the drive signal waveform, resulting in a simple and low-cost circuit configuration. By using the inverter drive device 10 described above to supply power to the motor 220 of the electric power steering device 200, the electric power steering device 200 can be operated stably.

[0038] Furthermore, in the inverter drive device 10 according to this embodiment, the first slew rate setting unit 13 is configured by resistor elements R1 to R6 inserted on the signal lines L1 to L6, and the first predetermined slew rate is determined according to the resistance value of each of the resistor elements. The first slew rate setting unit 13 configured by such resistor elements R1 to R6 can be realized at even lower cost, and the resistance values ​​of the resistor elements R1 to R6 can be easily designed with a relatively small number of steps, mainly taking into consideration the reduction of heat generation.

[0039] Furthermore, in the inverter drive device 10 according to this embodiment, the second slew rate setting unit 14 is provided inside the pre-driver 12 and is composed of a current adjustment circuit 12A that adjusts the current value of the drive signal. It is relatively easy to adjust the output current value of the pre-driver 12 internally, and the second slew rate setting unit 14 can be realized simply and at low cost.

[0040] Additionally, in the inverter drive device 10 according to this embodiment, the current adjustment circuit 12A selects a first current adjustment mode at the timing of the falling edge, in which the current value of the drive signal is adjusted to a reference value, and selects a second current adjustment mode at the timing of the rising edge, in which the current value of the drive signal is adjusted to a value different from the reference value. With this current adjustment circuit 12A, the first and second current adjustment modes are switched in synchronization with the timing of the rising and falling edges of the drive signal, so that the slew rate of the drive signal can be reliably set to a first predetermined slew rate at the timing of the falling edge and to a second predetermined slew rate at the timing of the rising edge, thereby making it possible to effectively suppress both ringing and heat generation.

[0041] Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and various modifications and changes are possible based on the technical concept of the present invention.

[0042] For example, in the above-described embodiment, an example has been described in which power from the inverter circuit 11 is supplied to the motor 220 of the electric power steering device 200. However, the inverter drive device according to the present invention is effective as a power supply source for various motors mounted on a vehicle other than the motor 220 of the electric power steering device 200.

[0043] In the above-described embodiment, an example has been described in which the second slew rate setting unit 14 (current adjustment circuit 12A) is provided inside the pre-driver 12. However, the second slew rate setting unit 14 may be electrically connected to each of the signal lines L1 to L6 that connect each of the output ports P1 to P6 of the pre-driver 12 to the control terminals of each of the semiconductor switching elements S1 to S6. [Explanation of symbols]

[0044] 10... inverter drive device, 11... inverter circuit, 12... pre-driver, 12A... current adjustment circuit, 13... first slew rate setting unit, 14... second slew rate setting unit, 100... vehicle, 110... wheel, 120... system power supply, 200... electric power steering device, 220... motor, 230... microprocessor, L1 to L6... signal line, R1 to R6... resistive element, P1 to P6... output port, S1 to S6... semiconductor switching element, SRf... falling slew rate (first predetermined slew rate), SRr... rising slew rate (second predetermined slew rate)

Claims

1. an inverter circuit having a plurality of conduction phases in which semiconductor switching elements are connected in series; a pre-driver that outputs a rectangular wave drive signal to be input to a control terminal of each semiconductor switching element, a first slew rate setting unit electrically connected to each signal line connecting an output port of the pre-driver and a control terminal of each semiconductor switching element, the first slew rate setting unit setting a slew rate of the drive signal to a first predetermined slew rate; a second slew rate setting unit that is provided inside the pre-driver or electrically connected to each of the signal lines and that is capable of setting the slew rate of the drive signal to a second predetermined slew rate that is smaller than the first predetermined slew rate; The drive signal is configured such that, at the timing of a fall, the waveform falls in accordance with the first predetermined slew rate set by the first slew rate setting unit, and, at the timing of a rise, the waveform rises in accordance with the second predetermined slew rate set by the second slew rate setting unit.

2. 2. The inverter drive device according to claim 1, The inverter driving device, wherein the first slew rate setting unit is configured by a resistive element inserted on each of the signal lines, and the first predetermined slew rate is determined according to a resistance value of the resistive element.

3. 2. The inverter drive device according to claim 1, The inverter driving device, wherein the second slew rate setting unit is provided inside the pre-driver and is configured by a current adjustment circuit that adjusts a current value of the drive signal.

4. 4. The inverter drive device according to claim 3, the current adjustment circuit is configured to be able to select a plurality of current adjustment modes in which the current values ​​of the drive signal are different from one another; the plurality of current adjustment modes include a first current adjustment mode in which a current value of the drive signal is adjusted to a reference value so that the first slew rate setting unit sets the slew rate of the drive signal to the first predetermined slew rate, and a second current adjustment mode in which the current value of the drive signal is adjusted to a value different from the reference value so that the slew rate of the drive signal is set to the second predetermined slew rate, The inverter drive device is configured such that, at the timing of a falling edge, the first current regulation mode is selected in the current regulation circuit, causing the waveform to fall in accordance with the first predetermined slew rate, and, at the timing of a rising edge, the second current regulation mode is selected in the current regulation circuit, causing the waveform to rise in accordance with the second predetermined slew rate.

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