JP2005185052A - Pwm driver - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce radio noise and to suppress heat generation from a semiconductor switching element by varying the inclination time of a trapezoidal wave signal depending on a duty ratio in a PWM driver for controlling power supplied to a vehicle mounted motor based on a pulse width modulated trapezoidal wave signal. <P>SOLUTION: A PWM signal generating section 5 generates a PWM signal having a duty ratio set at a duty ratio setting section 4. A trapezoidal wave signal generating section 6 generates a trapezoidal wave signal where a rising part and a falling part of the PWM signal are inclined at an inclination time set at an inclination time setting section 7. A load driving section 8 controls the gate voltage of an MOSFET 9 so that a voltage fed to a motor 3 has a trapezoidal waveform. The inclination time setting section 7 sets a long inclination time in the vicinity of a 50% duty ratio where radio noise is large and sets a short inclination time in the range of the other duty ratio. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a PWM drive device that controls electric power supplied to a load such as an in-vehicle motor based on a trapezoidal wave signal subjected to pulse width modulation.

A technique for controlling electric power supplied to a load such as an in-vehicle motor by PWM (pulse width modulation) is known. This technology generates a large amount of noise due to a sudden change in load current, and may adversely affect an in-vehicle radio or the like. In order to reduce such noise generation, a PWM signal is converted from a square wave to a trapezoidal wave to eliminate a sudden change in load current (or load voltage) (Patent Documents 1 to 3). 3).
JP 2001-54298 A JP 2000-138570 A JP-A-9-204230

  The longer the trapezoidal wave slope time (the slope time of the trapezoidal wave rise time and the slope time of the fall part) and the slower the slope, the more noise generation can be reduced. However, semiconductor switching elements such as MOSFETs are active regions. Since the operating time becomes longer, switching loss increases, and heat generation of the semiconductor switching element increases.

  If the slope time of the trapezoidal wave is set to be long, the upper side of the trapezoid cannot be formed when the duty ratio is small, and the lower side of the trapezoid cannot be formed when the duty ratio is large. In other words, the duty range in which the trapezoidal wave can be formed is limited by the inclination time.

  When a motor that drives a fan or the like is operated by PWM control, noise (radio noise) mixed into the in-vehicle radio increases when the duty ratio is in a specific range (for example, when the duty ratio is approximately 50%). There is. Therefore, if the slope time of the trapezoidal wave is set long with priority given to the reduction of radio noise, unnecessary heat generation occurs in the semiconductor switching element in the range of the duty ratio where generation of radio noise is small.

  The present invention has been made to solve such a problem, and by varying the slope of the trapezoidal wave according to the duty ratio, it is possible to perform power control with a trapezoidal wave signal over a wide range of the duty ratio. An object of the present invention is to provide a PWM drive device. Also, in the duty ratio range where radio noise generation is large, the slope of the trapezoidal wave is made gentler and the generation of radio noise is further reduced. An object of the present invention is to provide a PWM drive device that reduces switching loss of a switching element and suppresses heat generation.

  In order to solve the above problems, a PWM driving apparatus according to the present invention includes a PWM signal generation unit that generates a PWM signal that is pulse-width modulated at a predetermined modulation period, and a slope time of a trapezoidal wave signal based on the duty ratio of the PWM signal. A trapezoidal wave generated by a trapezoidal wave signal generating unit, a trapezoidal wave signal generating unit that generates a trapezoidal wave signal in which the rising and falling parts of the PWM signal are tilted by the inclination time, And a load driving unit that controls electric power supplied to the load based on the signal.

  The ramp time setting unit sets the ramp time to a long value when the duty ratio of the PWM signal is a preset value or a preset range, and the duty ratio of the PWM signal is set to a preset value or preset. If it is larger than the range, the slope time is set to a shorter value or the slope time is set to a shorter value as the duty ratio becomes larger, and the duty ratio of the PWM signal is set to a preset value or a preset range. If it is small, the inclination time is set to a short value, or the inclination time is set to a shorter value as the duty ratio becomes smaller.

  The load is an in-vehicle motor.

  The PWM drive device according to the present invention can vary the slope time of the trapezoidal wave signal according to the duty ratio of the PWM signal. Therefore, in the region where the duty ratio is small, the upper side of the trapezoidal wave can be secured by setting the inclination time shorter as the duty ratio becomes smaller. In the region where the duty ratio is large, the lower side of the trapezoidal wave can be secured by setting the inclination time shorter as the duty ratio becomes larger. Thereby, power control by a trapezoidal wave signal can be performed over a wide range of the duty ratio.

  In addition, in the vicinity of 50% duty, where radio noise is large, the slope of the trapezoidal wave is moderated to reduce the generation of radio noise. Heat generation of the element can be suppressed.

  Hereinafter, the best mode for carrying out the invention will be described based on examples.

  FIG. 1 is a block diagram of a PWM drive device according to the present invention. A PWM drive device 1 shown in FIG. 1 receives power supplied from a vehicle-mounted battery 2 and operates a vehicle-mounted motor 3 by PWM control. The motor 3 drives a radiator fan, a condenser fan, a blower fan for air conditioning, and the like.

  The PWM drive device 1 includes a duty ratio setting unit 4 that sets a duty ratio based on a command signal, a PWM signal generation unit 5 that generates a PWM signal having a duty ratio set by the duty ratio setting unit 4, and a PWM signal. The trapezoidal wave signal generation unit 6 that generates a trapezoidal wave signal with the rising and falling portions of the trapezoid tilted, and the slope times of the rising and falling portions of the trapezoidal wave signal generated by the trapezoidal wave signal generation unit 6 An inclination time setting unit 7 that is set based on the ratio, and a load driving unit 8 that controls the voltage supplied to the motor 3 that is a load based on the trapezoidal wave signal generated by the trapezoidal wave signal generating unit 6 to have a trapezoidal waveform. It consists of.

  The load drive unit 8 includes a MOSFET 9 as a semiconductor switching element connected in series to the motor 3, a load voltage detection circuit 10 that detects a motor voltage (load voltage) supplied to the motor 3, and a load voltage detection circuit 10. A trapezoidal wave drive that compares the detected motor voltage (load voltage) with the trapezoidal wave signal generated by the trapezoidal wave signal generator 6 and feedback-controls the gate voltage of the MOSFET 9 so that the motor voltage (load voltage) becomes a trapezoidal wave. Circuit 11.

  The PWM signal generation unit 5 includes a counter (not shown) that advances in a cycle shorter than the cycle of the PWM signal, and outputs a PWM signal having a duty ratio designated with reference to the count value of the counter at a predetermined modulation cycle. Output. The PWM signal generator 5 may have an analog circuit configuration that generates a PWM signal by comparing a triangular wave or sawtooth carrier signal with a command signal using a voltage comparator.

  FIG. 2 is a circuit configuration diagram showing a specific example of the trapezoidal wave signal generator. The trapezoidal wave signal generator 6 includes a current discharge type constant current circuit 61 capable of changing a constant current value, a current suction type constant current circuit 62 capable of changing a constant current value, and a charge / discharge changeover switch. The circuit 63, the capacitor 64, and an upper limit voltage limiting circuit 65 that limits the upper limit of the voltage generated at both ends of the capacitor 64 with a predetermined value.

  The charge / discharge changeover switch circuit 63 is in a switching state indicated by a dotted line in the period when the logic level of the PWM signal is at the H level, and charges the capacitor 64 via the current discharge type constant current circuit 61. As a result, the voltage across the capacitor 64 increases linearly with a time constant determined by the constant current value and the capacitor capacity. The charging / discharging changeover switch circuit 63 is in a switching state indicated by a solid line in the period when the logic level of the PWM signal is L level, and discharges the electric charge of the capacitor 64 via the current sink type constant current circuit 62. As a result, the voltage across the capacitor 64 decreases linearly with a time constant determined by the constant current value and the capacitor capacity.

  Here, if the constant current values of the constant current circuits 61 and 62 are increased, the time constants of charging and discharging are increased, and the slope times of the rising and falling portions of the trapezoidal waveform are shortened. If the constant current values of the constant current circuits 61 and 62 are reduced, the time constants for charging and discharging are reduced, and the ramp times of the rising and falling portions of the trapezoidal waveform are lengthened.

  The ramp time setting unit 7 shown in FIG. 1 uses each constant current circuit 61 in the trapezoidal wave signal generation unit 6 as a ramp time setting signal using a constant current value designation signal corresponding to the ramp time set based on the duty ratio. 62.

  The trapezoidal wave signal generator 6 may have a configuration in which the constant current value used for charging / discharging is fixed and the slope time of the rising and falling parts of the trapezoidal waveform is changed by changing the capacitance of the capacitor. In this case, the ramp time setting unit 7 supplies the capacitance value designation signal corresponding to the ramp time to the trapezoidal wave signal generation unit 6 as the ramp time setting signal.

  FIG. 3 is a diagram showing the relationship between the duty ratio and the inclination time. As shown in FIG. 3 (a) or FIG. 3 (b), the relationship between the duty ratio and the inclination time is such that the inclination time increases when the duty ratio is 50%, and the inclination time increases as the duty ratio deviates from 50%. I try to shorten it. As shown in FIG. 3C, the inclination time may be increased when the duty ratio is in the range of 40 to 60%, and the inclination time may be decreased as the duty ratio deviates from 40 to 60%. As shown in FIG. 3D, the inclination time may be changed stepwise for each predetermined range of the duty ratio.

ここで、ｔは傾斜時間、ｋは係数、Ｄｕｔｙはデューティ比（単位％）、ｎは任意の整数である。 The inclination time setting unit 7 may be configured to include a correspondence table between the duty ratio and the inclination time, or may be configured to obtain the inclination time based on a previously registered arithmetic expression. For example, by obtaining the inclination time t based on the arithmetic expression shown in Expression 1, the inclination time becomes longer at a duty ratio of 50%, and the inclination time can be shortened as the duty ratio deviates from 50%. .

Here, t is an inclination time, k is a coefficient, Duty is a duty ratio (unit%), and n is an arbitrary integer.

  FIG. 4 is a waveform diagram of a trapezoidal wave signal. FIG. 4A shows an example of a trapezoidal wave signal with a duty ratio of 50%, and FIG. 4B shows an example of a trapezoidal wave signal with a duty ratio of 80%. FIG. 4 (c) shows an example of a trapezoidal wave signal with a duty ratio of 20%. As shown in FIG. 4A, when the duty ratio is 50%, the slope is moderated by setting the slope time t of the rising and falling portions longer. By making the slope of the trapezoidal wave signal gentle, the change in the voltage supplied to the motor 3 becomes gentle, the generation of harmonics is reduced, and the level of radio noise is reduced.

  As shown in FIG. 4B, when the duty ratio is large, the slope is made steep by setting the slope time t of the rising portion and the falling portion short. Thereby, the L level section of the trapezoidal wave signal can be secured. As shown in FIG. 4C, when the duty ratio is small, the slope is made steep by setting the slope time t of the rising part and the falling part short. Thereby, the H level section of the trapezoidal wave signal can be secured. By shortening the tilt time t, the time during which the MOSFET 9 operates in the active region is shortened, and the heat generation of the MOSFET 9 can be suppressed.

  As described above, the PWM drive device 1 according to the present embodiment controls the power supplied to the motor 3 as a load based on the trapezoidal wave signal subjected to pulse width modulation. Since the ramp time setting unit for setting the ramp time of the falling portion based on the duty ratio of the PWM signal is provided, the ramp time is set long when the duty ratio at which the radio noise level is high is near 50% ( Reduce the generation of radio noise by making the slope of the trapezoidal wave signal gentle, and improve the switching efficiency by setting the slope time short (making the slope of the trapezoidal wave signal steep) in other duty ratio ranges Heat generation of the MOSFET 9 can be suppressed.

It is a block block diagram of the PWM drive device which concerns on this invention. It is a circuit block diagram which shows one specific example of a trapezoidal wave signal generation part. It is a figure which shows the relationship between a duty ratio and inclination time. It is a wave form diagram of a trapezoid wave signal.

Explanation of symbols

1 PWM drive device 2 Battery 3 Motor (load)
4 Duty ratio setting unit 5 PWM signal generating unit 6 Trapezoidal wave signal generating unit 7 Inclination time setting unit 8 Load driving unit 9 MOSFET (semiconductor switching element)
10 Load voltage detection circuit 11 Trapezoidal wave drive circuit

Claims (3)

  A PWM signal generation unit that generates a PWM signal that is pulse-width modulated at a predetermined modulation period; a ramp time setting unit that sets a ramp time of a trapezoidal wave signal based on a duty ratio of the PWM signal; and a rise of the PWM signal A trapezoidal wave signal generation unit that generates a trapezoidal wave signal in which the part and the falling part are inclined at the inclination time, and the power supplied to the load is controlled based on the trapezoidal wave signal generated by the trapezoidal wave signal generation unit A PWM drive device comprising a load drive unit.   The ramp time setting unit sets the ramp time to a long value when the duty ratio of the PWM signal is a preset value or a preset range, and the duty ratio of the PWM signal is the preset value. Alternatively, if it is larger than a preset range, the slope time is set to a short value or the slope time is set to a shorter value as the duty ratio increases, and the duty ratio of the PWM signal is set to the preset value. 2. The PWM according to claim 1, wherein if the value is smaller than a value or a preset range, the slope time is set to a short value or the slope time is set to a shorter value as the duty ratio becomes smaller. Drive device. The PWM drive apparatus according to claim 1, wherein the load is a vehicle-mounted motor.

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