JP7567651B2 - Switching element drive circuit - Google Patents

Description

The present invention relates to a switching element drive circuit that drives the gate of a switching element.

In switching element drive circuits that drive the gates of switching elements such as IGBTs (insulated gate bipolar transistors) and MOSFETs (metal oxide semiconductor field effect transistors), there is a demand for reducing switching noise, which is electromagnetic noise generated by switching.

In order to reduce the switching noise of a switching element, it is said that it is effective to disperse the frequency of the switching noise. The frequency of the switching noise is affected by the length of the transition time, which is the time it takes for the drain-source voltage of the switching element to reach a voltage amplitude in which it rises from 0, or the time it takes for the drain-source voltage to go from a voltage amplitude to 0.

The following Patent Document 1 discloses an invention for a switching element driver that varies the transition time from Δt-α to Δt+α, with a reference value Δt at the center, by diffusively varying the slew rate, which is the rate of change of the drain-source voltage during the transition time.

Patent No. 5385341

However, the invention of Patent Document 1 has a problem in that the relationship between the change in transition time due to the diffusion of the slew rate and the reduction in switching noise is unclear, and therefore there are frequency bands in which the effect of reducing switching noise cannot be observed depending on how the slew rate is diffused.

The present invention was created in consideration of the above problems, and aims to obtain a switching element drive circuit that controls the slew rate of a switching element based on conditions under which switching noise reduction is effective.

In order to achieve the above object, the switching element drive circuit of the present invention includes a drive signal generation unit (22U) that generates a drive signal to be supplied to a switching element (44U) that has a control terminal and an output terminal, is switched to an on state or an off state in response to supply and stop of supply of a drive signal to the control terminal, and outputs a signal having a waveform that rises and falls in response to supply and stop of supply of the drive signal from the output terminal, a slew rate adjustment unit (32U) that is arranged between the drive signal generation unit and the control terminal and adjusts the slew rate of the signal having a waveform that is output from the output terminal, and a control unit (30U) that controls the slew rate adjustment unit (32U) so that, when the difference between a maximum transition time (t _L ) and a minimum transition time (t _S ) of the transition time when the switching element ( _44U ) transitions to an on state or an off state is proportional to the reciprocal of a specific frequency (f 1 ) of electromagnetic noise generated by switching of the switching element, the slew rate when _the waveform rises and falls changes between the maximum transition time (t _L ) and the minimum transition time (t S ).

By configuring it in this way, switching noise can be reduced by controlling the slew rate of the switching element based on the conditions under which switching noise reduction is effective.

1 is a block diagram showing an example of an inverter including a switching element drive circuit according to an embodiment of the present invention; FIG. 2 is a block diagram showing an example of a configuration of a gate driver provided at the gate of a switching element. FIG. 4 is a block diagram showing an example of a specific configuration of a control unit. FIG. 4 is an explanatory diagram showing an example of a waveform of a drain-source voltage. 11 is an explanatory diagram showing the waveform of a drain-source voltage when the transition time is changed in a diffusive manner. FIG. FIG. 11 is an explanatory diagram showing a change in transition time. FIG. 11 is an explanatory diagram of a diffusion number, which is a number related to the number of times the transition time is changed. 1A is an explanatory diagram of a frequency range to be reduced, a center frequency of the frequency range to be reduced, and a frequency difference which is the difference between the center frequency and a lower limit value of the frequency range to be reduced and also the difference between an upper limit value of the frequency range and the center frequency; and FIG. 1B is a schematic diagram showing the relationship between the center frequency and a specific frequency. 4 is a flowchart showing an example of a process of the switching element drive circuit according to the present embodiment. 1 is a schematic diagram showing an example of a relationship between a center frequency of a frequency range, a specific frequency, and a frequency difference. FIG. 1A is a schematic diagram showing an example of a _Vds waveform when the transition time is changed to five different values, and FIG. 1B is a schematic diagram showing the relationship between the length and shortness of each diffusion time when the transition time is changed in equal increments. FIG. 1A is a schematic diagram showing an example of the relationship between the frequency range, the center frequency, and the specific frequency when m = 2 in formula (4), and FIG. 1B is a schematic diagram showing an example of the relationship between the frequency range, the center frequency, and the specific frequency when m = 1 in formula (4). FIG. 11 is an explanatory diagram of a case where an upper switching element and a lower switching element are turned on and off complementarily, and the operating unit is controlled to change the current value of the drive signal so that the range in which the transition time changes differs between when the upper switching element is turned on or off and when the lower switching element is turned on or off. 11 is an explanatory diagram of a case where the current value of the drive signal is changed by controlling the operation unit so that the transition time changes every half cycle of the electrical angle in the rotating electric machine. FIG. 13 is an explanatory diagram of a case where the current value of the drive signal is changed by controlling the operation unit so that the average transition time of the upper switching element and the average transition time of the lower switching element within a predetermined period become equal. FIG.

[First embodiment]

The present embodiment will be described below with reference to the drawings. FIG. 1 is a block diagram showing an example of an inverter 10 equipped with a switching element drive circuit according to the present embodiment. The inverter 10 is a three-phase inverter that converts a DC voltage supplied from a DC power source 80, such as an on-board battery, into a three-phase AC voltage, such as U-phase, V-phase, and W-phase, and outputs the voltage to the motor 12.

As shown in FIG. 1, the inverter 10 according to this embodiment includes switching elements 42U, 42V, 42W, 44U, 44V, and 44W such as MOSFETs, and generates the power to be supplied to the coils of the stator of the motor 12 by switching the switching elements 42U, 42V, 42W, 44U, 44V, and 44W on and off. For example, the switching elements 42U and 44U switch the power to be supplied to the U-phase coil, the switching elements 42V and 44V switch the power to be supplied to the V-phase coil, and the switching elements 42W and 44W switch the power to be supplied to the W-phase coil.

The drains of the switching elements 42U, 42V, and 42W are connected to the positive pole (+) of the DC power supply 80, and the sources of the switching elements 42U, 42V, and 42W are connected to the drains of the switching elements 44U, 44V, and 44W. The sources of the switching elements 44U, 44V, and 44W are connected to the negative pole (-) of the DC power supply 80.

Node 46U, which connects the source of switching element 42U and the drain of switching element 44U, is connected to the U-phase coil of motor 12. As an example, when switching element 42U is turned on and switching element 44U is turned off, power from DC power supply 80 is supplied to the U-phase coil of motor 12 via node 46U. At the same time, as an example, when switching element 42W is turned off and switching element 44W is turned on, the current flowing through the U-phase coil flows through the W-phase coil via the neutral point of the coil of motor 12. The current flows to the negative pole (-) of DC power supply 80 via node 46W, which connects the source of switching element 42W and the drain of switching element 44W, and switching element 44W. When the U-phase coil and W-phase coil are energized, a magnetic field is generated in the U-phase coil and W-phase coil.

Node 46V, where the source of switching element 42V and the drain of switching element 44V are connected, is connected to the V-phase coil of motor 12. As an example, when switching element 42V is turned on and switching element 44V is turned off, power from DC power supply 80 is supplied to the V-phase coil of motor 12 via node 46V. At the same time, as an example, when switching element 42U is turned off and switching element 44U is turned on, the current flowing through the V-phase coil flows through the U-phase coil via the neutral point of the coil of motor 12. The current flows to the negative pole (-) of DC power supply 80 via node 46U and switching element 44U. When the V-phase coil and the U-phase coil are energized, a magnetic field is generated in the V-phase coil and the U-phase coil.

As another example, when switching element 42W is turned on and switching element 44W is turned off, power from DC power supply 80 is supplied to the W-phase coil of motor 12 via node 46W. At the same time, as an example, when switching element 42V is turned off and switching element 44V is turned on, the current flowing through the W-phase coil flows through the V-phase coil via the neutral point of the coil of motor 12. The current flows to the negative pole (-) of DC power supply 80 via node 46V and switching element 44V. When the W-phase coil and the V-phase coil are energized, a magnetic field is generated in the W-phase coil and the V-phase coil.

As described above, by switching the switching elements 42U, 42V, 42W, 44U, 44V, and 44W (hereafter abbreviated as "switching elements 42U to 44W") to switch the phase in which a magnetic field is generated in the coils of the motor 12, a so-called rotating magnetic field is generated in the coils of the motor 12, which rotates a rotor (rotor) composed of a permanent magnet or the like. In actual motor rotation control, a three-phase AC-like voltage is generated and applied to the coils of each phase of the motor 12 by PWM (pulse width modulation) control that turns each of the switching elements 42U to 44W on and off in short increments.

As an example, when the switching elements 42U to 44W are n-type MOSFETs, they are turned on by applying a positive voltage drive signal to the gate. As shown in FIG. 1, in this embodiment, each of the switching elements 42U to 44W is connected to a gate driver 20U, 20V, 20W, 22U, 22V, 22W (hereinafter abbreviated as "gate drivers 20U to 22W") that controls the current value of the drive signal. Each of the gate drivers 20U to 22W is also connected to a higher-level control device (not shown) such as a vehicle ECU (Electronic Control Unit). Each of the gate drivers 20U to 22W amplifies the drive signal input from the higher-level control device, and applies the amplified drive signal to the gate of each of the switching elements 42U to 44W by adjusting the current value using a variable resistor.

Figure 2 is a block diagram showing an example of the configuration of gate driver 22U provided at the gate of switching element 44U. As described above, gate drivers 20U to 22W are provided for each of switching elements 42U to 44W, but gate driver 22U will be explained as a representative example and explanations of the other gate drivers will be omitted.

2, the gate driver 22U includes a terminal voltage detection unit 24U that detects the output terminal voltage (drain-source voltage V _ds ), which is the voltage at the output terminal of the switching element 44U, in association with time information, a detection processing unit 28U that converts the detection signal of the terminal voltage detection unit 24U into a signal in a format that can be processed by a control unit 30U described later, a control unit 30U that performs control calculation of a drive signal to be applied to the gate of the switching element 44U based on a transition time target value input from a higher-level control device and the output of the detection processing unit 28U, and an operation unit 32U that changes the gate drive capability. The terminal voltage detection unit 24U detects the time information using, for example, a control clock of the control unit 30U.

The detection processing unit 28U is a circuit that includes a type of A/D converter that converts the detection signal of the terminal voltage detection unit 24U, for example, into a digital signal that can be processed by the control unit 30U when the detection signal is an analog signal.

Operation unit 32U is a variable resistor that changes its resistance under control of control unit 30U to change the current value of the drive signal applied to the gate of switching element 44U. Operation unit 32U includes variable resistor 32UO, which changes the current value of the positive voltage drive signal applied to the gate of switching element 44U, and variable resistor 32UF, which changes the current value of the negative voltage drive signal applied to the gate of switching element 44U.

A drive signal is input to the operation unit 32U from a higher-level control device via an amplifier 34U and a complementary MOS 36U, which is a type of inversion circuit. The drive signal input from the higher-level control device is amplified by the amplifier, and then the positive and negative sides are inverted by the complementary MOS 36U. Depending on the positive and negative states of the drive signal input from the higher-level control device, the complementary MOS 36U may be omitted.

Figure 3 is a block diagram showing an example of a specific configuration of the control unit 30U. The control unit 30U is a type of computer, and includes a CPU (Central Processing Unit) 30UB, a ROM (Read Only Memory) 30UA, a RAM (Random Access Memory) 30UC, and an input/output port 30UD.

In the control unit 30U, the CPU 30UB, ROM 30UA, RAM 30UC, and input/output port 30UD are connected to each other via various buses such as an address bus, a data bus, and a control bus. The input/output port 30UD is connected to various input/output devices such as the detection processing unit 28U, the operation unit 32U, and the higher-level control device 400.

ROM 30UA is installed with a calculation program that calculates a voltage slew rate (hereinafter abbreviated as "slew rate") based on a transition time target value, and a control command program that generates commands to operate operation unit 32U based on the calculated slew rate. In this embodiment, CPU 30UB executes the calculation program to calculate the slew rate. CPU 30UB also generates commands to operate operation unit 32U using the control command program. RAM 30UC is a storage unit that temporarily stores data, and holds, for example, data input from detection processing unit 28U.

Next, various functions that are realized by the CPU 30UB of the control unit 30U executing the calculation program and the control command program will be described. By the CPU 30UB executing the calculation program and the control command program, the CPU 30UB functions as a calculation unit 300A that calculates the slew rate and a control command unit 300B that generates commands to operate the operation unit 32U, as shown in FIG. 3.

4 is an explanatory diagram showing an example of the waveform of the drain-source voltage _Vds output from the source of the switching element. As shown in Fig. 4, in one PWM period _Ts , the drain-source voltage _Vds changes from 0 to a voltage amplitude A at transition time _tr , maintains the state of voltage amplitude A during on-time _Ton , and changes from voltage amplitude A to 0 at transition time _tf .

Although the transition times t _r and t _f have different definitions as described above, in this embodiment, the transition times t _r and t _f are equal to each other.

The slew rate SR is the rate of change of the drain-source voltage V _ds during transition time t _r , and is therefore A/t _r .

4, the drain-source voltage V _ds is a trapezoidal wave, but under the condition of t _r = t _f , it can be expressed as a combination of sine waves by Fourier transform as shown in the following formula (1). In the following formula (1), |sin(π·t _r ·f)/π·t _r ·f| is a factor that depends on the slew rate SR.

5 is an explanatory diagram showing the waveform of the drain-source voltage _Vds when the transition times are changed in a diffusive manner such as _tr1 , _tr2 , and _tr3 ( _tr2 > _tr1 > _tr3 ). As shown in FIG. 5, the _Vds waveform includes extracted waveforms 1, 2, and 3 related to the transition times _tr1 , _tr2 , and _tr3 , respectively. Each of the extracted waveforms 1, 2, and 3 is observed every three times the PWM period _Ts . Therefore, the factor depending on the slew rate SR in _Equation (1) is the sum of the terms related to the transition times _tr1 , _tr2 , and _tr3 divided by 3, which is the period in which the waveforms related to the transition times _tr1 , _tr2 , and _tr3 appear. As a result, when the transition time is spread into three transition times t _r1 , t _r2 , and t _r3 , the waveform of the drain-source voltage V _ds is expressed by the following equation (2).

Similarly, when the transition time is spread to n, the waveform of the drain-source voltage V _ds is expressed by the following equation (3).

6 is an explanatory diagram showing the change in transition time. In this embodiment, the shortest minimum transition time _tS and the longest maximum transition time _tL are provided, and the transition time is changed between _tS and _tL , for example, every time one switching element 44U is turned on and off by PWM control. In FIG. 6, the transition time is changed to n+2 times, such as _tS , _t1 , _t2 , _t3 , ..., _tn , _tL , between _tS and _tL . In this embodiment, changing the transition time as shown in FIG. 6 is called diffusion of the transition time.

The diffusion of transition times changes the frequency and phase of the switching noise generated by the switching of the switching elements. This change causes switching noise waveforms with different frequencies and phases to interfere with each other, weakening them through interference, and reducing the intensity of the switching noise.

The transition time changes according to the slew rate of the switching element, and the slew rate changes according to the current value of the drive signal applied to the gate of the switching element. For example, if the current value of the drive signal is increased, the slew rate increases and the transition time shortens. Conversely, if the current value of the drive signal is decreased, the slew rate decreases and the transition time lengthens. In this embodiment, as described below, the transition time is spread out by controlling the current value of the drive signal.

FIG. 7 is an explanatory diagram of the diffusion number, which is a number related to the number of times the transition time is changed. The diffusion number is the number of times the transition time is changed between the minimum transition time t _S and the maximum transition time t _L. Specifically, as shown in FIG. 6, when the transition time is changed to n+2 times between t _S and t _L , such as t _S , t ₁ , t ₂ , t ₃ , ..., t _n , t _L , the diffusion number is n. In this embodiment, the difference between the maximum transition time t _L and the minimum transition time t _S is set as the diffusion width ΔT. In addition, when the transition time is changed in an equal difference, the time difference which is the equal difference is set as the diffusion step Δt. In this embodiment, since a transition time different from t _S and t _L is set at least once between the transition time t _S and t _L , the diffusion number n is a natural number equal to or greater than 1.

FIG. 8A is an explanatory diagram of a frequency range 106 to be reduced, a center frequency _fm of the frequency range 106 to be reduced, and a frequency difference Δf which is the difference between the center frequency _fm and the lower limit value of the frequency range to be reduced and also the difference between the upper limit value of the frequency range and the center frequency _fm .

The center frequency _fm is a desired frequency of the switching noise to be reduced by the diffusion of the transition time. The frequencies of the switching noise for which the reduction of the switching noise by the diffusion of the transition time according to the present embodiment is effective are limited to a noise reduction frequency range 104 as shown in Fig. 8(A). At frequencies outside the noise reduction frequency range 104, destructive interference does not occur, and the waveforms of the frequencies corresponding to the least common multiples of the frequencies changed by the diffusion of the transition time overlap each other, resulting in constructive interference, which may result in the switching noise not being reduced.

Figure 8 (A) shows a spectrum 100 of switching noise when transition time spreading is not performed, and a spectrum 102 of switching noise when transition time spreading is performed. Due to the diffusion of transition time, the level of switching noise in spectrum 102 is reduced compared to spectrum 100 in which transition time spreading is not performed, but the frequency range in which the level is effectively reduced is a range centered on frequency range 106.

In this embodiment, the center frequency f _m of the frequency range 106 to be reduced is defined as a desired frequency, and a specific frequency f ₁ , which is a frequency at which weakening due to interference occurs and a switching noise reduction effect can be expected, is calculated from the center frequency f _m using the following formula (4) from the center frequency f _m . In formula (4), m is an arbitrary order that is a natural number equal to or greater than 1. FIG. 8B is a schematic diagram showing the relationship between the center frequency f _m and the specific frequency f _1. As shown in FIG. 8B, weakening due to interference also occurs at frequencies near the specific frequency f _1, resulting in a switching noise reduction effect. As will be described later, when m=1 in the following formula (4), the center frequency f _m and the specific frequency f ₁ coincide with each other.

Furthermore, the diffusion width ΔT of the transition time is defined by the specific frequency f ₁ and the diffusion number n as shown in the following formula (5). As shown in formula (5), the diffusion width ΔT, which is the difference between the maximum transition time t _L and the minimum transition time t _S , is proportional to the reciprocal of the specific frequency f _1. As shown in formula (5), the diffusion width ΔT is a quotient of the value obtained by adding 1 to the diffusion number n as the dividend and the value twice the specific frequency f ₁ as the divisor.

In this embodiment, the operation unit 32U is controlled so that the slew rate during the transition time changes, and the current value of the drive signal is changed, thereby changing the transition time between the minimum transition time _tS and the maximum transition time _tL . The slew rate increases when the current value of the drive signal applied to the gate of the switching element is increased, and decreases when the current value of the drive signal is decreased. The correlation between the current value of the drive signal and the slew rate is determined, for example, through experiments using an actual device.

Furthermore, the spreading number n is defined by the following formula (6): The spreading number n is a quotient of twice the frequency difference Δf as the dividend and the difference between the specific frequency f ₁ and the frequency difference Δf as the divisor.

The frequency difference Δf is defined by the following equation (7):

The specific frequency f ₁ is expressed as the following equation (8) from the above equation (5), and the frequency difference Δf is expressed as the following equation (9).

Fig. 9 is a flow chart showing an example of the process of the switching element drive circuit according to this embodiment. The process shown in Fig. 9 is started, for example, when power is supplied to the motor 12. Specifically, the process is started when a command to start the process associated with the power supply to the motor 12 is input from the upper control device 400. Then, in step 100, a transition time is set. The transition time to be set is between the minimum transition time _tS and the maximum transition time _tL, including the minimum transition time _tS and the maximum transition time _tL , and specifically, is set based on the transition time target value input from the upper control device 400.

In step 102, a target slew rate corresponding to the set transition time is calculated. As described above, the slew rate is the amount of change in the drain-source voltage _Vds during the transition time, so the target slew rate is a value obtained by dividing the voltage amplitude A by the transition time.

In step 104, the current value of the drive signal is calculated. In this embodiment, it is assumed that the correlation between the slew rate and the current value of the drive signal is known in advance. In step 104, the current value of the drive signal is set based on this correlation.

In step 106, a drive signal is generated according to the current value of the drive signal set in step 104 and applied to the gate of switching element 44U.

In step 108, the inter-terminal voltage detection unit 24U detects the change over time in the drain-source voltage _Vds , which is the output terminal voltage of the switching element 44U.

In step 110, the actual slew rate is calculated based on the time-series change in the drain-source voltage V _ds detected in step .

In step 112, the actual slew rate is compared with the target slew rate calculated in step 102 to determine whether the difference between the actual slew rate and the target slew rate is within a predetermined threshold range. As an example, if the difference between the target slew rate and the actual slew rate is about 10% of the target slew rate, a positive determination is made in step 112. If the difference between the actual slew rate and the target slew rate is within the predetermined threshold range in step 112, the procedure proceeds to step 114, and if the difference between the actual slew rate and the target slew rate exceeds the predetermined threshold range, the procedure proceeds to step 102.

In step 114, it is determined whether or not to end the process. The process shown in FIG. 9 ends, for example, when the power supply to the motor 12 is stopped. In step 114, when a command to stop the process is input from the upper control device 400 in conjunction with the stopping of the power supply to the motor 12, it is determined that the process is to be ended and the process ends.

If the process is not terminated in step 114, the procedure proceeds to step 116.

In step 116, it is determined whether the transition time is to be changed. Specifically, for example, it is determined whether a new transition time target value has been input from the upper control device 400, and if a new transition time target value has been input, the procedure proceeds to step 118, and if a new transition time target value has not been input, the procedure proceeds to step 106.

In step 118, a new transition time is set and the procedure proceeds to step 102. Then, a series of steps are executed from calculating the target slew rate in step 102 to determining whether the difference between the target slew rate and the actual slew rate in step 112 is within a predetermined threshold range.

In the process shown in FIG. 9, it is determined whether the difference between the actual slew rate and the target slew rate is within a predetermined threshold range, but this is not limiting. For example, an actual transition time, which is the actual transition time, may be calculated in step 110, and it may be determined whether the difference between the transition time set in step 100 and the calculated actual transition time is within a predetermined threshold range.

The process shown in FIG. 9 sets the number of diffusions n, the specific frequency f ₁ , the diffusion width _ΔT , which is the difference between the maximum transition time t _L and the minimum transition time t _{S, and the frequency difference Δf, based on the center frequency f m of the frequency range 106 in which the switching noise is to be reduced, using the relationships of the above-mentioned formulas (4) to (9)} . The number of diffusions n, the specific frequency f ₁ , the diffusion width ΔT, which is the difference between the maximum transition time t _L and the minimum transition time t _S, and the frequency difference Δf have a close and inseparable relationship with each other, as shown in each of the formulas (4) to (9). In this embodiment, the transition time can be set in various ways, provided that the relationships of the formulas (4) to (9) are satisfied. Hereinafter, a description will be given with reference to FIGS. 10 to 15.

FIG. 10 is a schematic diagram showing an example of the relationship between the center frequency f _m of the frequency range 106A, the specific frequency f ₁ , and the frequency difference Δf. In this embodiment, the specific frequency f ₁ is set from the center frequency f _m by equation (4), and the spreading number n and the frequency difference Δf are determined by equations (6) and (7). As an example, the spreading number n is set as an arbitrary natural number, and the frequency difference Δf is calculated by equation (7) based on the set spreading number n and the specific frequency f ₁ calculated by equation (4). Then, the spreading width ΔT, which is the difference between the maximum transition time t _L and the minimum transition time t _S, is determined by equation (5). Alternatively, the frequency difference Δf may be set arbitrarily within a range that does not contradict equations (4) to (9), and the spreading number n may be calculated by equation (6) based on the set frequency difference Δf and the specific frequency f ₁ calculated by equation (4).

FIG. 11(A) is a schematic diagram showing an example of a _Vds waveform when the transition time is changed to five, and FIG. 11(B) is a schematic diagram showing the relationship between the length and shortness of each diffusion time when the transition time is changed in equal increments. As shown in FIG. 11(B), the transition time is changed to five from the minimum transition time _tS2 to the maximum transition time _tL2 at equal diffusion intervals Δt with the average transition time _tave as the center value. Then, the five transition times are randomly applied as shown in FIG. 11(A), thereby reducing the level of switching noise. Since the frequency of switching noise correlates with the transition time, random diffusion of the transition time causes weakening due to interference between switching noise waveforms with different frequencies and phases, thereby reducing the strength of the switching noise.

FIG. 12(A) is a schematic diagram showing an example of the relationship between a frequency range 106B, a center frequency _fm , and a specific frequency _f1 when m=2 in the above formula (4), and FIG. 12(B) is a schematic diagram showing an example of the relationship between a frequency range 106C, a center frequency _fm , and a specific frequency f1 when m= ₁ in the above formula (4).

As shown in FIG. 12A, when m=2 in equation (4), f ₁ =f _m /3, and from equation (7) above, the frequency difference Δf ₃ is given by equation (10) below.

Furthermore, as shown in FIG. 12B, when m=1 in equation (4), f ₁ =f _m , and from equation (7) above, the frequency difference Δf ₁ is given by equation (11) below.

As shown in equations (10) and (11), when the diffusion number n is the same, the frequency difference Δf ₁ when m = 1 is three times larger than the frequency difference Δf ₃ when m = 2. As a result, the frequency range 106C when m = 1 is three times larger than the frequency range 106B when m = 2, and the frequency range in which switching noise can be reduced is expanded.

Figure 13 is an explanatory diagram of a case where, for example, the upper switching element 42U and the lower switching element 44U are turned on and off complementarily, and the current value of the drive signal is changed by controlling the operation unit 32U so that the range in which the transition time changes differs between when the switching element 42U is turned on or off and when the switching element 44U is turned on or off.

13 shows a case where the upper switching element 42U and the lower switching element 44U are complementarily turned on and off at each half-period of the electrical angle of the motor 12 where the waveform of the motor phase current is inverted when the motor 12 is driven. In this case, the diffusion width ΔT is different between the turn-on or turn-off of the switching element 42U and the turn-on or turn-off of the switching element 44U. As a result, the waveform of the output terminal voltage (V _ds ) changes as shown in the lower part of FIG.

In FIG. 13, for example, the transition time in section 110 where switching element 42U is turned on by PWM control varies from a minimum transition time ta-Δt to a maximum transition time ta+Δt around a central value ta, and the diffusion width ΔT in this case is 2Δt.

In addition, in FIG. 13, for example, the transition time in section 112 where switching element 44U is turned on by PWM control varies from a minimum transition time ta-2Δt to a maximum transition time ta+2Δt around a central value ta, and the diffusion width ΔT in such a case is 4Δt.

As shown in FIG. 13, by making the diffusion width ΔT different between section 110 and section 112, even if the diffusion number n of the transition time in each of gate drivers 20U and 22U is set to, for example, n=1, the transition time of the entire switching elements 42U and 44U constituting the U phase of inverter 10 is changed to five, from ta-2Δt to ta+2Δt, and substantially the same switching noise reduction effect can be expected as when the diffusion number n is set to n=3.

Therefore, by setting the transition time shown in FIG. 13, the control load of the gate drivers 42U and 44U is reduced by suppressing the diffusion number in each of the gate drivers 42U and 44U, and the frequency of the switching noise generated is diffused to enhance the effect of weakening the interference between switching noises, thereby reducing the switching noise.

In FIG. 13, the transition time is changed to ta-Δt, ta, and ta+Δt in section 110, and to ta-2Δt, ta, and ta+2Δt in section 112, but it is also possible to change the transition time to ta-2Δt, ta, and ta+2Δt in section 110, and to ta-Δt, ta, and ta+Δt in section 112.

Figure 14 is an explanatory diagram of a case where the current value of the drive signal is changed by controlling the operation unit 32U so that the transition time changes every half cycle of the electrical angle in the motor 12. In the example shown in Figure 14, the upper switching element 42U and the lower switching element 44U have different diffusion widths, and the operation unit 32U is controlled so that the slew rate changes every half cycle of the electrical angle.

In FIG. 14, for example, in section 114A where switching element 42U is turned on, the transition time is ta, in section 116A where switching element 44U is turned on, the transition time is ta-2Δt, in the following section 114B it is ta-Δt, in section 116B it is ta+2Δt, in section 114C it is ta+Δt, and in section 116C it is ta. Therefore, in a series of controls from section 114A to section 116C, the transition time is changed to five, but in each of sections 114A to 116C, the operation unit 32U is controlled so that each switching element switches at one transition time, thereby reducing the control load.

As a result, it is possible to reduce the control load of each gate driver 42U, 44U, and to diffuse the frequency of the switching noise generated, thereby enhancing the effect of weakening the interference between switching noises, and thus reducing the switching noise.

Figure 15 is an explanatory diagram of a case where the current value of the drive signal is changed by controlling the operation unit 32U so that the average transition time of the upper switching element 42U and the average transition time of the lower switching element 44U within a specified period are equal.

In FIG. 15, for example, the transition time in section 118 where switching element 42U is turned on by PWM control varies from a minimum transition time ta-Δt to a maximum transition time ta+Δt around a central value ta, and the average transition time in this case is ta.

In addition, in FIG. 15, for example, the transition time in section 120 where switching element 44U is turned on by PWM control varies from a minimum transition time ta-2Δt to a maximum transition time ta+2Δt around a central value ta, and the average transition time in such a case is ta.

In FIG. 15, the transition time is changed to ta-Δt, ta, and ta+Δt in section 118, and to ta-2Δt, ta, and ta+2Δt in section 120, but it is also possible to change the transition time to ta-2Δt, ta, and ta+2Δt in section 118, and to ta-Δt, ta, and ta+Δt in section 120.

In this way, by making the average transition time of the upper switching element 42U and the average transition time of the lower switching element 44U within a specified period equal, it is possible to prevent uneven heating of each of the switching elements 42U and 44U, and to protect the circuit of the inverter 10.

As described above, according to this embodiment, the transition time is diffused to change the frequency and phase of the switching noise generated by the switching of the switching elements, and the switching noise waveforms are weakened by interference with each other, thereby reducing the intensity of the switching noise.

To diffuse the transition time, the slew rate of the switching element is diffused, but if the correlation between the change in transition time and the reduction in switching noise is not clear, the effect of reducing switching noise is small even if the transition time is diffused. However, in this embodiment, as shown in formulas (4) to (9), the transition time of the switching element is controlled based on the close and inseparable relationship between the diffusion number n, the specific frequency f ₁ , the diffusion width ΔT which is the difference between the maximum transition time t _L and the minimum transition time t _S , and the frequency difference Δf which indicates the frequency range effective in reducing switching noise.

As a result, it becomes possible to control the slew rate of the switching element based on the conditions under which switching noise reduction is effective.

10... inverter, 12... motor, 22U... gate driver, 30U... control unit, 32U... operation unit, 42U, 44U... switching element, 106, 106A, 106B, 106C... frequency range, ΔT... diffusion width, Δf, Δf ₁ , Δf ₂ ... frequency difference, SR... slew rate V _ds ... drain-source voltage, f ₁ ... specific frequency, f _m ... center frequency, n... diffusion number, t _L ... maximum transition time, t _S ... minimum transition time, t f, tr... transition time

Claims (8)

a drive signal generating unit (22U) that generates a drive signal to be supplied to a switching element (44U) that is provided with a control terminal and an output terminal, is switched to an on state or an off state in response to supply and stop of supply of a drive signal to the control terminal, and outputs a signal having a waveform that rises and falls in response to supply and stop of supply of the drive signal from the output terminal;
a slew rate adjustment unit (32U) disposed between the drive signal generation unit and the control terminal and configured to adjust a slew rate of a signal having a waveform output from the output terminal;
a control unit (30U) for controlling the slew rate adjustment unit (32U) to adjust the slew rates at the rising and falling edges of the waveform so that the transition time when the switching element (44U) transitions to an on state or an off state changes between a maximum transition time (tL) and a minimum transition time (tS) by a number of _{diffusion times} (n);
Including,
The difference (ΔT) between the maximum transition time (t _L ) and the minimum transition time (t _S ) is a quotient obtained by dividing a value including the diffusion number (n) by a divisor and a value including a specific frequency (f ₁ ) of electromagnetic noise generated by switching of the switching element.
Switching element drive circuit. The specific frequency (f ₁ ) is a quotient obtained by subtracting 1 from twice the order expressed as a natural number, with the central frequency (f _m ) of the electromagnetic noise to be reduced as the dividend and the divisor being the value obtained by subtracting 1 from twice the order expressed as a natural number,
A spreading number (n), which is the number of times the transition time is changed between the minimum transition time (t _S ) and the maximum transition time (t _L ), is a quotient obtained by dividing by a dividend a value twice the frequency difference (Δf), which is the difference between the center frequency (f _m ) and the lower limit of the frequency range (106) to be reduced and is also the difference between the upper limit of the frequency range and the center frequency (f _m ), and a divisor a difference between the specific frequency (f ₁ ) and the frequency difference (Δf);
The difference (ΔT) between the maximum transition time (t _L ) and the minimum transition time (t _S ) is a quotient obtained by adding 1 to the spreading number (n) as a dividend and doubling the specific frequency (f ₁ ) as a divisor,
2. The switching element drive circuit according to claim 1, wherein the control unit (30U) controls the slew rate adjustment unit (32U) so that the transition time changes between the minimum transition time (t _S ) and the maximum transition time (t _L ) by a number of diffusion numbers (n). The specific frequency _f1 is expressed by the following equation (1) using the center frequency _fm and the order m:
The spreading number n is expressed by the following formula (2) using the frequency difference Δf and the specific frequency f ₁ :
3. The switching element drive circuit according to claim 2, wherein a difference ΔT between the maximum transition time t _L and the minimum transition time t _S is expressed by the following formula (3) using the spreading number n and the specific frequency f ₁ .


4. The switching element drive circuit according to claim 2 or 3, wherein the control unit (30U) controls the slew rate adjustment unit (32U) so that the transition time changes at equal intervals between the minimum transition time (t _S ) and the maximum transition time (t _L ) according to the number of diffusions (n) for each switching of the switching element (44U). 5. The switching element drive circuit according to claim 2, wherein the order is 1, and the specific frequency (f ₁ ) and the center frequency (f _m ) are the same. The switching elements (42U, 44U) are configured such that an upper stage switching element (42U) and a lower stage switching element (44U) are turned on and off complementarily,
The control unit (30U) controls the slew rate adjustment unit (32U) so that the range in which the transition time changes is different when the upper stage switching element (42U) is turned on or off and when the lower stage switching element (44U) is turned on or off. A switching element drive circuit as described in any one of claims 1 to 5. The switching elements (42U, 44U) generate a voltage to be applied to a winding of a rotating electric machine (12) by switching,
7. The switching element drive circuit according to claim 6, wherein the control unit (30U) controls the slew rate adjustment unit (32U) so that the transition time changes for each half period of an electrical angle of the rotating electric machine (12). The switching element drive circuit according to claim 6 or 7, wherein the control unit (30U) controls the slew rate adjustment unit (32U) so that the average transition time of the upper switching element (42U) within a predetermined period is equal to the average transition time of the lower switching element (44U).