JP5772020B2 - Switching control device - Google Patents

Description

  The present invention relates to a switching control device that provides a switching element with a PWM drive signal in which a dead time period is secured with respect to a PWM control signal.

  Many motor drive devices and power supply devices use PWM control as a means for controlling the magnitude of the output voltage. In the PWM control, the switching element is turned on / off for each carrier frequency to cut off the current, so that noise having the carrier frequency and its harmonic components is generated. For example, if a motor drive device or a power supply device is mounted on a vehicle, radio noise is generated.

  For this, a technique for changing the frequency of PWM control aperiodically or without regularity (Patent Document 1) or a technique for changing the frequency of a current control signal periodically (Patent Document 2) has been proposed. Yes. According to these frequency spread controls, frequency components included in noise are dispersed, and the influence of radio noise can be reduced.

JP 2000-217395 A (FIG. 3) JP 07-099795 (FIG. 2)

  If the command voltage is suddenly raised when starting the motor drive device or the power supply device, an excessive current may flow through the switching element or the motor may fail to start. For this reason, at the time of start-up, soft start is performed so as to gradually increase the command voltage, that is, the duty ratio of PWM control. Further, even during the period before stopping the operation, the command voltage is gradually lowered for the purpose of avoiding a motor free run or a sudden stop. When the frequency spread control as described above is executed in the start-up period and the pre-stop period, the inventors of the present application increase radio noise or increase the heat generation of the filter coil even though the frequency is spread. I discovered that this phenomenon occurs.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a switching control device that can reduce the influence of noise on peripheral devices associated with PWM control including the start-up period and the pre-stop period as much as possible.

  According to a first aspect of the present invention, a PWM control signal is generated based on the command voltage, and a PWM drive signal in which a dead time period is secured for the PWM control signal is given to the switching element. The frequency spreading control means controls the carrier frequency of the PWM control signal to be constant during the start-up period in which the duty ratio of the PWM control signal increases and the pre-stop period in which the duty ratio of the PWM control signal decreases. In a switching operation period other than the start period and the pre-stop period, frequency spread control is performed in which the carrier frequency of the PWM control signal is switched to a plurality of frequencies over time.

  In the PWM control, a dead time period is provided to prevent an arm short circuit, and control is performed so that the switching elements of the upper and lower arms are turned off during the period. On the other hand, when the carrier frequency is changed by frequency spreading control, the pulse width changes even at the same duty ratio. As a result, when frequency spread control is executed in a period with a small duty ratio such as the start period and the pre-stop period, the pulse width becomes smaller than the dead time period when the carrier frequency is increased by the frequency spread control, and the PWM drive signal The pulse may disappear temporarily.

  If this means is adopted, the frequency spread control is stopped in a period where the duty ratio is small, such as the start period and the pre-stop period, and the carrier frequency of the PWM control signal is controlled to be constant. It can be prevented that the period in which the occurrence of the pulse occurs and the period in which the pulse disappears appear repeatedly. As a result, the output voltage also monotonously increases or decreases as the command voltage increases or decreases, so that the output voltage ripple decreases, and the influence of noise on peripheral devices due to PWM control is reduced. Can suppress heat generation.

Specifically, when the highest carrier frequency used in the frequency spread control is fcmax, the frequency spread control means sets the duty ratio of the PWM control signal to be larger than (fcmax × dead time period) in the start-up period. Frequency spread control is started on the condition that the first threshold value is reached. Further, in the pre-stop period, the frequency spread control is stopped on condition that the duty ratio of the PWM control signal is equal to or less than the second threshold value set larger than (fcmax × dead time period).

As described above, the pulse is most easily extinguished when the carrier frequency becomes fcmax. The on-pulse width at this time is 1 / fcmax × duty ratio. Therefore,
When the relationship of 1 / fcmax × duty ratio> dead time period is established, that is, when the duty ratio of the PWM control signal is larger than (fcmax × dead time period), the pulse disappears. The first threshold value and the second threshold value satisfy this conditional expression.

Therefore, according to the present means, it is possible to suppress the noise at the time of start-up described above, and to start the frequency spread control from an early point when there is no possibility of the disappearance of the pulse according to the set level of the first threshold value. It becomes. Further, according to the set level of the second threshold value, it becomes possible to stop the frequency spread control before the time point when the pre-stop pulse disappears.
According to a second aspect of the present invention, there is provided voltage detecting means for detecting a voltage output from the switching element to the load. The frequency spread control means starts the frequency spread control on the condition that the deviation of the detected voltage with respect to the command voltage is equal to or less than a predetermined convergence determination value during the startup period. Under this condition, since the output voltage approaches the command voltage (for example, the target voltage during steady operation), it is considered that the duty ratio of PWM control is often large enough to prevent the disappearance of the pulse. According to the present means, it is possible to suppress the generation of noise at the time of starting as described above, and to start the spread spectrum control from an early point in time when the possibility of the disappearance of the pulse is reduced, thereby achieving noise dispersion.

1 is a schematic configuration diagram of a motor drive device showing a first embodiment of the present invention. Functional block diagram of the voltage controller Waveform diagram of the main circuit when setting the dead time period Waveform diagram showing carrier frequency, carrier frequency change trend line and load current during spread spectrum control Fig. 1 shows details of carrier frequency during execution of spread spectrum control (1) Diagram showing in detail carrier frequency during execution of spread spectrum control (2) Waveform diagram showing carrier frequency and load current during spread spectrum control Diagram showing a comparison of the waveform during execution of frequency spread control and the waveform during stop of frequency spread control during the start-up period or the period before stoppage The schematic block diagram of the switching power supply device which shows the 2nd Embodiment of this invention

(First embodiment)
Hereinafter, a first embodiment of the present invention will be described with reference to FIGS. FIG. 1 is a schematic configuration diagram of a motor driving device. A motor drive device 1 mounted on a vehicle performs PWM control based on a command signal transmitted from an ECU 2 (Electronic Control Unit), and an applied voltage to a DC motor 4 (load) connected to an output terminal 3 is ECU 2. The voltage follow-up control is executed so as to match the command voltage from.

  The main circuit includes MOS transistors 7 and 8 (switching elements) connected in series between the positive and negative terminals of the battery 5 and a filter 9 provided between the output node 6 and the output terminal 3. The filter 9 is an LC filter including a coil 10 and a capacitor 11. The drive control device 12 (switching control device) includes a voltage control unit 13 and drivers 14 and 15, and outputs PWM drive signals Db 1 and Db 2 to the gates of the MOS transistors 7 and 8.

  FIG. 2 is a functional block configuration diagram of the voltage control unit 13. The command signal transmitted from the ECU 2 is a pulse signal having a fixed period, and its pulse width (duty ratio) corresponds to the command voltage. This duty ratio is different from the duty ratio of PWM control described later. The duty detection unit 16 detects the duty ratio of the command signal, and the command voltage output unit 17 determines the command voltage Vr from this duty ratio.

  The drive control device 12 includes a voltage detection unit 20 (voltage detection means) including a level conversion unit 18 and an A / D converter 19 in order to detect the voltage at the output terminal 3. The level converter 18 divides the output terminal voltage and converts it to a voltage level of a control power supply voltage (for example, 5 V) used in the drive control device 12. The subtracter 21 subtracts the detection voltage V from the command voltage Vr and outputs a voltage deviation ΔV.

  The computing unit 22 generates a command voltage signal Sv in PWM control by performing, for example, proportional integration (PI) computation on the voltage deviation ΔV. The PWM control unit 23 compares the triangular wave signal Sc having the carrier frequency fc given from the frequency spreading control unit 24 with the command voltage signal Sv, and PWM control signals for the upper arm MOS transistor 7 and the lower arm MOS transistor 8. Da1 and Da2 are generated.

  The dead time setting unit 25 generates PWM drive signals Db1 and Db2 in which a dead time period Td is secured for the PWM control signals Da1 and Da2 in order to prevent an arm short circuit. FIG. 3 is a waveform diagram for explaining the influence when the dead time period is set. The waveforms indicate the PWM control signals Da1 and Da2, the mask signal, and the voltage at the output node 6 in order from the top. The PWM control signals Da1 and Da2 before setting the dead time have complementary waveforms whose logic levels are opposite to each other. When the PWM control signal Da1 or Da2 changes from the H level (ON) to the L level (OFF), the mask signal having a width of Td becomes the H level (mask state). As a result, the change to the H level of the PWM drive signal Db2 or Db1 on the other arm side is delayed by Td to prevent an arm short circuit.

  The frequency spread control unit 24 (frequency spread control means) switches the carrier frequency fc of the PWM control signals Da1 and Da2 to a plurality of frequencies over time. Further, in order to determine the start period and the pre-stop period or the start timing of the frequency spread control, the duty ratio of the command signal output from the duty detection unit 16, the voltage deviation ΔV output from the subtractor 21 and the command voltage The signal Sv is input. However, only a necessary input may be input according to a determination method of a start period and a pre-stop period described later. The frequency spreading method may be any method as long as the carrier frequency fc is increased or decreased continuously or discretely. Here, an example of frequency spreading will be described with reference to FIGS.

  FIG. 4 shows a carrier frequency fc (the waveform is omitted in the middle), a change trend line schematically showing the increase / decrease tendency of the carrier frequency fc by a straight line, and a load current IL. The waveform following the upper and lower two stages in FIG. 5 and the waveform shown in FIG. 6 continuing thereto show more detailed changes in the carrier frequency fc. The numbers in parentheses shown in FIGS. 5 and 6 represent the number of PWM periods using the carrier frequency fc. FIG. 7 shows the load current IL corresponding to the change of the carrier frequency fc while thinning out the increase / decrease process of the carrier frequency fc.

  The frequency spreading control unit 24 sequentially switches five discrete carrier frequencies fc from f1 (fcmin) to f5 (fcmax). For example, in the upper part of FIG. 5, the carrier frequency fc of f1 is first used for n1 periods of the triangular wave signal Sc, then switched to the carrier frequency fc of f2, and used for n2 periods of the triangular wave signal Sc, and further f3 The carrier frequency fc is switched to that used for n3 periods of the triangular wave signal Sc.

  Once the frequency is increased to f5 and then decreased to f1, the use period of the carrier frequency fc of f1 is decreased from the n1 period to the n1-1 period of the triangular wave signal Sc, and then increased to f5 and then decreased to f2. At that time, the use period of the carrier frequency fc of f2 is decreased from the n2 period of the triangular wave signal Sc to the n2-1 period. Eventually, when the use cycle of the carrier frequency fc of f1 decreases to one cycle of the triangular wave signal Sc as shown in FIG. 6, thereafter, the use cycle of each carrier frequency fc is increased by 1 contrary to the above-described change. To go.

  As a result, as indicated by a change trend line in FIG. 4, in the period in which the use cycle of each carrier frequency fc is sequentially reduced, the up / down change cycle of the carrier frequency fc in five stages is gradually shortened, and eventually each carrier frequency fc. In the period in which the use cycle is increased, the up / down change cycle of the carrier frequency fc in five stages gradually increases. The overall cycle is Tp (fpHz).

  Next, frequency spreading control in the start period and the pre-stop period will be described with reference to FIG. FIG. 8 shows (a) a carrier frequency fc during execution of frequency spread control, (b) a PWM drive signal Db1, and (c) a carrier when frequency spread control is stopped when the PWM duty ratio of PWM control signals Da1 and Da2 is small. The frequency fc and (d) the PWM drive signal Db1 are shown.

  If the command voltage is suddenly raised when starting the motor drive device 1, an excessive current flows through the MOS transistors 7 and 8 because no speed electromotive force is generated in the DC motor 4. For this reason, soft start is performed so as to gradually increase the command voltage during startup. Further, the command voltage is gradually lowered in order to avoid a free run or a sudden stop of the DC motor 4 even during the period before the drive is stopped. That is, the command voltage, that is, the duty ratio of the PWM drive signal Db1 is small in such a start-up period and a pre-stop period.

  When the H level width (ON period) of the PWM control signal Da1 becomes shorter than the dead time period Td, the entire width of the PWM drive signal Db1 is masked, and the H level pulse (ON pulse) of the PWM drive signal Db1 disappears. If the duty ratio of the PWM control signal Da1 is DR (range 0 to 1), the ON period of the PWM control signal Da1 is DR / fc, and thus the pulse disappears under the condition of DR / fc ≦ Td. That is, the smaller the duty ratio or the higher the carrier frequency fc, the easier the pulse disappears.

  In FIG. 8B, it can be seen that the on-pulse of the PWM drive signal Db1 has disappeared in the period when the carrier frequency f4 and f5 are switched from the higher one as a result of performing the frequency spread control. On the other hand, in the period in which the carrier frequencies f1, f2, and f3 are switched from the lowest, the pulse width of the PWM drive signal Db1 is narrowed by Td from the pulse width of the PWM control signal Da1, but the pulse does not disappear.

When such generation and extinction of pulses are repeated, the ripple voltage of the output voltage, and hence the ripple current of the load current IL, increases, and a large fluctuation occurs in the starting torque and braking torque of the DC motor 4, causing torque ripple and noise. Therefore, radio noise increases on the contrary, although the frequency is spread. Further, the AC loss generated in the coil 10 and the like of the filter 9 is expressed by (ripple current effective value ² × (ACR−DCR)) (where ACR: equivalent resistance representing iron loss, DCR: DC resistance). A phenomenon occurs in which heat generation in the coil 10, the DC motor 4, etc. increases.

  Therefore, the frequency spread control unit 24 stops the frequency spread control as shown in FIG. 5C in the period where the duty ratio is small such as the start period and the period before stop, and the carrier frequency of the PWM control signals Da1 and Da2 fc is controlled to be constant. As for the carrier frequency fc at this time, it is most preferable that the condition of DR / fc> Td is satisfied in the entire period of the starting period or the period before stopping as shown in FIG.

  However, when the duty ratio DR increases monotonously during the start period and decreases monotonously during the pre-stop period, the condition DR / fc> Td is satisfied in at least a part of the start period or the pre-stop period. In this case, it is possible to prevent the occurrence of the starting torque or the braking torque during the period and the repeated generation and disappearance of the pulse. Note that the carrier frequency used in the start-up period may be different from the carrier frequency used in the pre-stop period.

  Next, a method for determining the activation period will be described. As a first determination method, the frequency spread control unit 24 determines start-up when the duty ratio of the command signal output from the duty detection unit 16 rises from 0, and the voltage deviation ΔV is equal to or less than a predetermined convergence determination value. When it becomes, it determines with the starting period having been complete | finished and starts frequency spreading | diffusion control. In the start-up period, the command voltage Vr output from the command voltage output unit 17 gradually increases, and feedback control is performed while maintaining the voltage deviation ΔV so that the output terminal voltage V follows it.

  Therefore, the time when the voltage deviation ΔV is equal to or less than the convergence determination value is the time when the command voltage Vr reaches the target voltage and the output terminal voltage V is also set to the target voltage, that is, the time when the start-up period ends. In general, in order to output a target voltage used in a steady state, it is considered that a duty ratio DR that satisfies DR> fc · Td is required, and thus the above-described pulse disappears.

  As a second determination method, when the highest carrier frequency used in the frequency spread control is fcmax (= f5), the frequency spread control unit 24 increases the duty ratio of the command signal output from the duty detection unit 16 from 0. The activation start is determined. Then, referring to the command voltage signal Sv, when the duty ratio of the PWM control signal Da1 becomes equal to or larger than the first threshold value Dt1 set larger than fcmax · Td, it is determined that the start-up period has ended and the frequency spread Start control.

  Further, the frequency spread control unit 24 refers to the command voltage signal Sv, and when the duty ratio of the PWM control signal Da1 becomes equal to or less than the second threshold value Dt2 set larger than fcmax · Td, It is determined that it has entered, and the frequency spread control is stopped. According to the second determination method, since the condition of DR / fc> Td is satisfied in the start period and the pre-stop period, the above-described pulse disappears.

  As described above, the motor drive device 1 controls the voltage applied to the DC motor 4 by PWM controlling the MOS transistors 7 and 8 constituting the upper and lower arms with a dead time period. In this case, the carrier frequency fc is switched to five levels by the frequency spreading control unit 24 in order to reduce the noise level by dispersing the frequency component of the switching noise accompanying the PWM control.

  In the present embodiment, since the frequency spread control is stopped and the carrier frequency fc is controlled to be constant while the duty ratio is small, such as the start period and the pre-stop period, the spread of the carrier frequency fc is performed regardless of the existence of the dead time period. During the period Tp, it is possible to prevent the period during which the pulse is generated at the output node 6 and the period during which the pulse disappears from appearing repeatedly.

  As a result, as the command voltage Vr increases or decreases, the output voltage applied to the DC motor 4 monotonously increases or decreases, so that the ripple of the output voltage decreases, and in addition to the steady operation period, the start period and the pre-stop period The noise associated with PWM control (for example, noise to a radio as a peripheral device in the vehicle) can be reduced. By reducing the ripple of the output voltage, the ripple amount of the load current IL is also reduced, so that the heat generation of the main circuit components such as the coil 10 and the MOS transistors 7 and 8 and the DC motor 4 as the load can be suppressed.

  The frequency spread control unit 24 determines that the start-up period has ended when the voltage deviation ΔV is equal to or less than the convergence determination value (first determination method). Frequency spread control can be started from the time of settling. As a result, the PWM noise can be reduced by starting the frequency spread control at an early point when the possibility of the extinction of the pulse is lowered.

  Further, the frequency spread control unit 24 determines that the start-up period has ended when the duty ratio of the PWM control signal Da1 becomes equal to or greater than the first threshold value Dt1 set to be larger than fcmax · Td (second Determination method). Thereby, irrespective of the magnitude of the target voltage, the frequency spread control can be started from an early point in time when there is no possibility of the disappearance of the pulse. This second determination method can also be employed in the pre-stop period, and the same effect can be obtained.

(Second Embodiment)
FIG. 9 is a schematic configuration diagram of a switching power supply device 31 showing a second embodiment of the present invention. The same components as those in FIG. The switching power supply device 31 is a series regulator that steps down the input voltage Vin and generates an output voltage Vout. The drive control device 32 (switching control device) includes a voltage control unit 33 and drivers 14 and 15, and outputs PWM drive signals Db 1 and Db 2 to the gates of the MOS transistors 7 and 8.

  The voltage control unit 33 includes a command voltage generation unit (not shown) that generates the command voltage Vr, but the command voltage is based on a command signal given from the outside such as the ECU 2 as in the first embodiment. It may be configured to generate Vr. The operation of the voltage control unit 33 is the same as the operation of the voltage control unit 13 described above. According to this embodiment, the same operation and effect as those of the first embodiment can be obtained.

(Other embodiments)
As mentioned above, although preferred embodiment of this invention was described, this invention is not limited to embodiment mentioned above, A various deformation | transformation and expansion | extension can be performed within the range which does not deviate from the summary of invention.

The frequency spreading control unit 24 may include a protection function for starting the frequency spreading control when it is not possible to determine that the activation period has ended when a predetermined time limit has elapsed from the start of activation.
The main circuit may be any circuit that performs PWM control of the switching power supply while ensuring a dead time period. Therefore, an inverter circuit such as an H bridge for driving a DC motor or other load or a three-phase bridge for driving a brushless DC motor, various chopper circuits, various switching power supply circuits, or the like may be used.

The command voltage may be given from the outside as shown in the first embodiment, or may be generated inside the switching control device as shown in the second embodiment.
The duty ratio of the PWM control signal in the start-up period does not need to increase monotonously, and may include a period in which the duty ratio increases in part. Similarly, the duty ratio of the PWM control signal in the pre-stop period need not be monotonously decreased, but may include a period during which the duty ratio decreases in part.

The frequency spread control may be any one that changes the carrier frequency fc of PWM control, and the spread method is not limited to that shown in FIGS.
The switching element is not limited to a MOS transistor, and may be a bipolar transistor or an IGBT.

  In the drawings, 4 is a DC motor (load), 7 and 8 are MOS transistors (switching elements), 12 and 32 are drive control devices (switching control devices), 20 is a voltage detection unit (voltage detection means), and 24 is frequency spread. It is a control unit (frequency spreading control means).

Claims (2)

In a switching control device that generates a PWM control signal based on a command voltage and applies a PWM drive signal that secures a dead time period to the PWM control signal to a switching element,
In the start-up period in which the duty ratio of the PWM control signal increases and the pre-stop period in which the duty ratio of the PWM control signal decreases, the carrier frequency of the PWM control signal is controlled to be constant, except for the start-up period and the pre-stop period in the switching operation period, with a frequency spread control means for performing frequency spreading control for switching a plurality of frequency over time the carrier frequency of the PWM control signal,
When the highest carrier frequency used in the frequency spread control is fcmax, the frequency spread control means is configured such that the duty ratio of the PWM control signal is set to be larger than (fcmax × dead time period) in the start-up period. The frequency spread control is started on condition that the threshold value is 1 or more, and the duty ratio of the PWM control signal is set to be larger than (fcmax × dead time period) in the period before the stop. A switching control device characterized in that the frequency spread control is stopped on condition that the threshold value is not more than a threshold value . Voltage detecting means for detecting a voltage output from the switching element to a load;
2. The frequency spread control means starts the frequency spread control on the condition that a deviation of the detected voltage with respect to the command voltage is equal to or less than a predetermined convergence determination value during the start-up period. The switching control device described.

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