CN103368538A - Switching frequency range-adjustable digital PWM (pulse-width modulation) device and method - Google Patents

Abstract

The invention relates to a switching frequency range-adjustable digital PWM (pulse-width modulation) device and method and belongs to the technical field of power electronics. The switching frequency range-adjustable digital PWM method disclosed by the invention comprises the following steps of performing cycle calculation according to a pseudo-random code generated by a pseudo-random code generator to obtain a cycle count point; then performing cycle count by a clock, and performing signal modulation calculation according to an input reference wave and the cycle count point to obtain a positive level count point; and finally processing an output PWM pulse signal by pulse generation according to the positive level count point and a cycle count value. According to the method, a switching frequency range can be adjusted so as to avoid the phenomenon that communication signals with specific frequencies are interfered by a switching power supply, and therefore, the requirements of special application occasions on electromagnetic radiation are met. The generation of the PWM signal is realized by adopting a digital mode. Moreover, the method is simple and is convenient to realize and transplant.

Description

The digital pulse width modulation device and method that a kind of switching frequency scope is adjustable

Technical field

The present invention relates to the adjustable digital pulse width modulation device and method of a kind of switching frequency scope, belong to electric and electronic technical field.

Background technology

The pulse-width modulation PWM technology has been widely used in the power electronic technology, and still, the pwm signal of fixed frequency contains a large amount of high order harmonic components near the integral multiple of switching frequency and switching frequency, can cause electromagnetic interference problem.The random PWM modulation technique is that the random signal that certain probabilistic law distributes is joined switching signal, make switching signal become nonperiodic signal, electromagnetic radiation and the electric current and voltage harmonic component of power electronic equipment are evenly distributed in the wider frequency range, thereby suppressed the Conducted Electromagnetic Interference in the switching circuit, improved system EMC.In addition, in electric power system, because the extensive use of carrier communication in electrical network is checked meter, at present there is not unified regulation for carrier frequency, the frequency of Switching Power Supply might cause interference to the carrier communication product, investigation of random PWM can change switching frequency, avoids frequency conflicts and affects carrier communication.

Present existing method is to realize by dsp chip, Chinese invention patent " a kind of power electronic equipment random switching frequency pulse width modulated implementation method " (CN201210083780.1) in, a kind of random switching frequency pulse width modulated implementation method has been described: in the current switch periods, dsp chip utilizes mathematical algorithm to produce a random number, and utilize random number computing cycle register value and comparand register value, adopt counting and the comparison circuit of DSP, output pwm signal.The method is based on the realization of the dsp chip of special use, and pulse generation need to rely on the clock circuit of DSP, and its random algorithm operand is large, and hardware cost is high, can't be applied to the control chip design of Switching Power Supply.

Summary of the invention

The objective of the invention is to propose the adjustable investigation of random PWM device and method of a kind of switching frequency scope, be used for the control chip design of Switching Power Supply, realize that the switching frequency scope is adjustable, to avoid Switching Power Supply to the interference of the signal of communication of characteristic frequency, satisfy the electromagnetic radiation requirement of particular application.

The present invention is for the digital pulse width modulation device that provides a kind of switching frequency scope adjustable is provided, and this modulating device comprises:

The pseudo noise code generation module is used for producing pseudo noise code R (m) zero hour in current switch periods;

The computation of Period module be used for to be calculated the pseudo noise code that produced by the pseudo noise code generation module at the cycle count of the current period C (m) that counts;

The signal modulation module is used for relatively current period reference wave amplitude V _R(m) with pulse-width modulation reference wave input higher limit V _M, according to V _R(m) big or small shared V _MRatio, and the big or small calculative determination current period of C (m) positive level is counted the W (m) that counts;

Pulse generating module is used for current period positive level counting W (m) and the cycle count of current period C (m) size of counting of counting is compared definite output duty cycle, exports the width-modulation pulse in this cycle according to duty ratio

The cycle count of pseudo noise code being calculated as follows of C (m) of counting in the described computation of Period module:

$C\left(m\right)=C_D+\mathrm{ROUND}((C_U-C_D)\·\frac{R\left(m\right)}{(2^M-1)})$

Wherein, C (m) is that the cycle count in m cycle is counted C _DAnd C _URespectively according to switching frequency lower limit f _DWith upper limit f _UHigher limit and lower limit that the cycle count that arranges is counted are when the frequency of cycle count clock CLK is F _kThe time, C _D=F _k/ f _D, C _U=F _K/ f _U, R (m) is pseudo noise code, M is the length of pseudo noise code, the integer after ROUND (x) expression real number x rounds up.

The positive level counting computing formula of counting is in the described signal modulation module:

$W\left(m\right)=\left\{\begin{array}{cc}\mathrm{ROUND}(C\left(m\right)\·\frac{V_R\left(m\right)}{V_M})& V_R\left(m\right)\≤V_M\\ C\left(m\right)& V_R\left(m\right)>V_M\end{array}\right.$

Wherein W (m) is that the positive level counting in m cycle is counted V _R(m) and C (m) be respectively input reference wave and the cycle count in m cycle and count V _MIt is pulse-width modulation reference wave input higher limit.

The present invention is for the digital pulse width modulation method that also provides a kind of switching frequency scope adjustable is provided, and the step of this digital pulse width modulation method is as follows:

1) in current switch periods zero hour, produces a corresponding pseudo noise code, calculate a cycle count with the current period of this Pseudo-code Correlation C (m) that counts;

2) relatively current period is inputted reference wave amplitude V _R(m) with pulse-width modulation reference wave input higher limit V _M, according to V _R(m) big or small shared V _MRatio, and the big or small calculative determination current period of C (m) positive level is counted the W (m) that counts;

3) current period positive level counting is counted W (m) and the cycle count of current period C (m) size of counting compares definite output duty cycle, exports the width-modulation pulse in this cycle according to duty ratio.

The cycle count of the pseudo noise code C (m) that counts is calculated as follows in the described step 1):

$C\left(m\right)=C_D+\mathrm{ROUND}((C_U-C_D)\·\frac{R\left(m\right)}{(2^M-1)})$

Wherein, C (m) is that the cycle count in m cycle is counted C _DAnd C _URespectively according to switching frequency lower limit f _DWith upper limit f _UHigher limit and lower limit that the cycle count that arranges is counted are when the frequency of cycle count clock CLK is F _kThe time, C _D=F _k/ f _D, C _U=F _K/ f _U, R (m) is pseudo noise code, M is the length of pseudo noise code, the integer after ROUND (x) expression real number x rounds up.

Described step 2) as follows to the process of cycle count to utilizing clock in:

According to the cycle count in m the cycle C (m) that counts, each specific variable signal of corresponding clock CLK, cycle count value d (n) increases 1 counting from 0, until count down to (C (m)-1), corresponding next clock CLK, m end cycle, (m+1) individual cycle begins, d (n) is set to 0, restarts clock CLK is increased 1 counting.

The digital pulse width modulation method that switching frequency scope according to claim 4 is adjustable is characterized in that, described step 2) in the positive level counting computing formula of counting be:

$W\left(m\right)=\left\{\begin{array}{cc}\mathrm{ROUND}(C\left(m\right)\·\frac{V_R\left(m\right)}{V_M})& V_R\left(m\right)\≤V_M\\ C\left(m\right)& V_R\left(m\right)>V_M\end{array}\right.$

Wherein W (m) is that the positive level counting in m cycle is counted V _R(m) and C (m) be respectively input reference wave and the cycle count in m cycle and count V _MIt is pulse-width modulation reference wave input higher limit.

The invention has the beneficial effects as follows: the present invention carries out cycle count according to the pseudo noise code that pseudo-noise code generator produces, and obtains cycle count and counts; Carry out cycle count by clock again, close cycle count according to the input reference wave and count and carry out signal modulation and calculate, obtain the positive level counting and count; Count and cycle count value according to the positive level counting at last, by pulse generation processor output pulse width modulated pulse signal, thereby realize that the switching frequency scope is adjustable, avoided the interference of Switching Power Supply to the signal of communication of characteristic frequency, the electromagnetic radiation requirement of particular application that riveting is sufficient, adopt digital form to realize the generation of pulse-width modulation PEM signal, and method is simple, is convenient to realize and transplant.

Description of drawings

Fig. 1 is the principle assumption diagram of the adjustable investigation of random PWM method of a kind of switching frequency scope of the present invention;

Fig. 2 is the circuit logic diagram of pseudo-noise code generator;

Fig. 3 is the signal waveform schematic diagram of the adjustable investigation of random PWM method of a kind of switching frequency scope of the present invention.

Embodiment

Below in conjunction with accompanying drawing the specific embodiment of the present invention is further described.

The embodiment of the digital pulse width modulation device that a kind of switching frequency scope of the present invention is adjustable

The adjustable digital pulse width modulation dress of switching frequency scope comprises pseudo noise code generation module, computation of Period module, signal modulation module and pulse generating module in the present embodiment.Wherein, the pseudo noise code generation module is used for producing pseudo noise code R (m) zero hour in current switch periods, the pseudo noise code generation module adopts m=8 level linear feedback shift register to form, as shown in Figure 2, and the pseudo noise code R (m) of pseudo noise code generation algorithm output M bit.

The computation of Period module be used for to be calculated the pseudo noise code that produced by the pseudo noise code generation module at the cycle count of the current period C (m) that counts, and the formula of computation of Period is:

$C\left(m\right)=C_D+\mathrm{ROUND}((C_U-C_D)\·\frac{R\left(m\right)}{(2^M-1)})$

Wherein, C (m) is that the cycle count in m cycle is counted C _DAnd C _URespectively according to switching frequency lower limit f _DWith upper limit f _UHigher limit and lower limit that the cycle count that arranges is counted are when the frequency of cycle count clock CLK is F _kThe time, C _D=F _k/ f _D, C _U=F _K/ f _U, R (m) is pseudo noise code, M is the length of pseudo noise code, the integer after ROUND (x) expression real number x rounds up, the frequency F of assumption period clock CLK _k=8MHz, the lower limit f of switching frequency _DBe set to 10KHz, upper limit f _UBe set to 12.5KHZ, therefore, the lower limit C that cycle count is counted _D=640, the higher limit C that cycle count is counted _U=800.

The signal modulation module is used for relatively current period reference wave amplitude V _R(m) with pulse-width modulation reference wave input higher limit V _M, according to V _R(m) big or small shared V _MRatio, and the big or small calculative determination current period of C (m) the positive level counting W (m) that counts, its concrete computing formula is as follows:

$W\left(m\right)=\left\{\begin{array}{cc}\mathrm{ROUND}(C\left(m\right)\·\frac{V_R\left(m\right)}{V_M})& V_R\left(m\right)\≤V_M\\ C\left(m\right)& V_R\left(m\right)>V_M\end{array}\right.$

As cycle count value d (n) when equaling 0, according to the input reference wave V in m cycle _R(m) and the cycle count C (m) that counts, carry out the signal modulation and calculate, the positive level that obtains m cycle is counted the W (m) that counts; Suppose pulse-width modulation reference wave input higher limit V _MBe 300, as input reference wave V _R(m)=100, carry out the signal modulation and calculate, the positive level that obtains m cycle is counted the W (m)=225 that counts.

Pulse generating module is used for current period positive level counting W (m) and the cycle count of current period C (m) size of counting of counting is compared definite output duty cycle, exports the width-modulation pulse in this cycle according to duty ratio,

Suppose at W (m)=225 o'clock, 0＜W (m)＜C (m), d (n) from 0 to 224 o'clock, pulse generation is processed and is all exported the positive level signal; When d (n) from 225 to 674, pulse generation is processed and is all exported anti-level signal.Therefore can adjust duty ratio according to the input reference wave, output pwm signal, the signal waveform schematic diagram is as shown in Figure 3.

The embodiment of the digital pulse width modulation method that a kind of switching frequency scope of the present invention is adjustable

The present invention mainly is by producing pseudo noise code, pseudo noise code is carried out computation of Period, cycle count count, carry out cycle count by clock again, and count according to input reference wave and cycle count and to carry out the signal modulation and calculate, process is as follows:

1) in current switch periods zero hour, produces a corresponding pseudo noise code, calculate a cycle count with the current period of this Pseudo-code Correlation C (m) that counts;

2) relatively current period is inputted reference wave amplitude V _R(m) with pulse-width modulation reference wave input higher limit V _M, according to V _R(m) big or small shared V _MRatio, and the big or small calculative determination current period of C (m) positive level is counted the W (m) that counts;

3) current period positive level counting is counted W (m) and the cycle count of current period C (m) size of counting compares definite output duty cycle, exports the width-modulation pulse in this cycle according to duty ratio.

Its concrete implementation process is as follows:

Step 1: in current switch periods zero hour, be that cycle count value d (n) equals at 0 o'clock, produce a corresponding pseudo noise code, employing m=8 level linear feedback shift register in the present embodiment forms pseudo-noise code generator and produces pseudo noise code, the pseudo noise code R (m) of pseudo noise code generation algorithm output M bit.

Step 2: the cycle to the pseudo noise code R (m) that produces calculates, the cycle count that obtains m the cycle C (m) that counts, and the formula of concrete computation of Period is:

$C\left(m\right)=C_D+\mathrm{ROUND}((C_U-C_D)\·\frac{R\left(m\right)}{(2^M-1)})$

The frequency F of assumption period clock CLK _k=8MHz, the lower limit f of switching frequency _DBe set to 10KHz, upper limit f _UBe set to 12.5KHZ, therefore, the lower limit C that cycle count is counted _D=640, the higher limit C that cycle count is counted _U=800, the pseudo noise code R (m) that the output of pseudo noise code generation algorithm is 8 is such as 55; According to above-mentioned computation of Period formula, the cycle count that obtains m the cycle C (m)=675 that counts.

Step 3: in current pulse-width modulation generating period, according to cycle count clock CLK, cycle count value d (n) increases 1 from 0 and count down to 674, then again counts since 0 at next cycle d (n).

Step 4: as cycle count value d (n) when equaling 0, according to the input reference wave V in m cycle _R(m) and the cycle count C (m) that counts, carry out the signal modulation and calculate, the positive level that obtains m cycle is counted the W (m) that counts; The formula that the signal modulation is calculated is:

$W\left(m\right)=\left\{\begin{array}{cc}\mathrm{ROUND}(C\left(m\right)\·\frac{V_R\left(m\right)}{V_M})& V_R\left(m\right)\≤V_M\\ C\left(m\right)& V_R\left(m\right)>V_M\end{array}\right.$

As cycle count value d (n) when equaling 0, according to the input reference wave V in m cycle _R(m) and the cycle count C (m) that counts, carry out the signal modulation and calculate, the positive level that obtains m cycle is counted the W (m) that counts; Suppose pulse-width modulation reference wave input higher limit V _MBe 300, as input reference wave V _R(m)=100, carry out the signal modulation and calculate, the positive level that obtains m cycle is counted the W (m)=225 that counts;

Count count W (m) and cycle count value d (n) according to positive level, the output pulse width modulated pulse signal is processed in pulse generation.According to step 4, W (m)=225 o'clock, 0＜W (m)＜C (m), d (n) from 0 to 224 o'clock, pulse generation is processed and is all exported the positive level signal; When d (n) from 225 to 674, pulse generation is processed and is all exported anti-level signal.Therefore can adjust duty ratio according to the input reference wave, output pwm signal, the signal waveform schematic diagram is as shown in Figure 3.

The higher limit C that counts by cycle count in the step 1 of the present invention and 2 _DWith lower limit C _USetting, at one stroke dynamically adjust pulse width modulation cycle by pseudo noise code, to realize that switching frequency is at lower limit f _DWith upper limit f _UInterior change at random, so that switching noise even random distribution of similar white noise in this frequency band, thereby reduce the switching noise of certain single frequency, cycle count value d (n) equivalence that step 3 simultaneously of the present invention produces is the modulation sawtooth waveforms of pulse-width modulation, realizes input reference wave data V by step 4 and 5 _{R (m)}Digital Modulation, output pulse width pulse pwm signal.The present invention has realized that the switching frequency scope is adjustable, avoid the interference of Switching Power Supply to the characteristic frequency signal of communication, satisfied the electromagnetic radiation requirement of particular application, and adopted digital form to realize, method is simple, is convenient to realize in the Switching Power Supply control chip and transplant.

Claims (7)

1. the digital pulse width modulation device that the switching frequency scope is adjustable is characterized in that, this modulating device comprises:

The pseudo noise code generation module is used for producing pseudo noise code R (m) zero hour in current switch periods;

The computation of Period module be used for to be calculated the pseudo noise code that produced by the pseudo noise code generation module at the cycle count of the current period C (m) that counts;

The signal modulation module is used for relatively current period reference wave amplitude V _R(m) with pulse-width modulation reference wave input higher limit V _M, according to V _R(m) big or small shared V _MRatio, and the big or small calculative determination current period of C (m) positive level is counted the W (m) that counts;

Pulse generating module is used for current period positive level counting W (m) and the cycle count of current period C (m) size of counting of counting is compared definite output duty cycle, exports the width-modulation pulse in this cycle according to duty ratio.

2. the adjustable digital pulse width modulation device of switching frequency scope according to claim 1 is characterized in that, the cycle count of pseudo noise code being calculated as follows of C (m) of counting in the described computation of Period module:

$C\left(m\right)=C_D+\mathrm{ROUND}((C_U-C_D)\·\frac{R\left(m\right)}{(2^M-1)})$

Wherein, C (m) is that the cycle count in m cycle is counted C _DAnd C _URespectively according to switching frequency lower limit f _DWith upper limit f _UHigher limit and lower limit that the cycle count that arranges is counted are when the frequency of cycle count clock CLK is F _kThe time, C _D=F _k/ f _D, C _U=F _K/ f _U, R (m) is pseudo noise code, M is the length of pseudo noise code, the integer after ROUND (x) expression real number x rounds up.

3. the adjustable digital pulse width modulation device of switching frequency scope according to claim 1 and 2 is characterized in that, the positive level counting computing formula of counting is in the described signal modulation module:

$W\left(m\right)=\left\{\begin{array}{cc}\mathrm{ROUND}(C\left(m\right)\·\frac{V_R\left(m\right)}{V_M})& V_R\left(m\right)\≤V_M\\ C\left(m\right)& V_R\left(m\right)>V_M\end{array}\right.$

Wherein W (m) is that the positive level counting in m cycle is counted V _R(m) and C (m) be respectively input reference wave and the cycle count in m cycle and count V _MIt is pulse-width modulation reference wave input higher limit.

4. the digital pulse width modulation method that the switching frequency scope is adjustable is characterized in that, the step of this modulator approach is as follows:

1) in current switch periods zero hour, produces a corresponding pseudo noise code, calculate a cycle count with the current period of this Pseudo-code Correlation C (m) that counts;

2) relatively current period is inputted reference wave amplitude V _R(m) with pulse-width modulation reference wave input higher limit V _M, according to V _R(m) big or small shared V _MRatio, and the big or small calculative determination current period of C (m) positive level is counted the W (m) that counts;

3) current period positive level counting is counted W (m) and the cycle count of current period C (m) size of counting compares definite output duty cycle, exports the width-modulation pulse in this cycle according to duty ratio.

5. the adjustable digital pulse width modulation method of switching frequency scope according to claim 4 is characterized in that, the cycle count of the pseudo noise code C (m) that counts is calculated as follows in the described step 1):

$C\left(m\right)=C_D+\mathrm{ROUND}((C_U-C_D)\·\frac{R\left(m\right)}{(2^M-1)})$

Wherein, C (m) is that the cycle count in m cycle is counted C _DAnd C _URespectively according to switching frequency lower limit f _DWith upper limit f _UHigher limit and lower limit that the cycle count that arranges is counted are when the frequency of cycle count clock CLK is F _kThe time, C _D=F _k/ f _D, C _U=F _K/ f _U, R (m) is pseudo noise code, M is the length of pseudo noise code, the integer after ROUND (x) expression real number x rounds up.

6. according to claim 4 or the adjustable digital pulse width modulation method of 5 described switching frequency scopes, it is characterized in that described step 2) in as follows to the process of cycle count to utilizing clock:

According to the cycle count in m the cycle C (m) that counts, each specific variable signal of corresponding clock CLK, cycle count value d (n) increases 1 counting from 0, until count down to (C (m)-1), corresponding next clock CLK, m end cycle, (m+1) individual cycle begins, d (n) is set to 0, restarts clock CLK is increased 1 counting.

7. the adjustable digital pulse width modulation method of switching frequency scope according to claim 6 is characterized in that described step 2) in the positive level counting computing formula of counting be:

$W\left(m\right)=\left\{\begin{array}{cc}\mathrm{ROUND}(C\left(m\right)\·\frac{V_R\left(m\right)}{V_M})& V_R\left(m\right)\≤V_M\\ C\left(m\right)& V_R\left(m\right)>V_M\end{array}\right.$

Wherein W (m) is that the positive level counting in m cycle is counted V _R(m) and C (m) be respectively input reference wave and the cycle count in m cycle and count V _MIt is pulse-width modulation reference wave input higher limit.

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