在直流减速电机控制中，最常用的方法就是通过PWM来控制直流电机的转速。在控制小车走直线的过程中，需要两者的转速一置（如果要走得很直，还需要在短时间内保证两者的行程大致相当，这可以用PID算法来控制）。因此，在检测到两者转速不一样时，需要动态调整其中一个或两个轮子的PWM的点空比（简单点的就以一个轮为基准，调整另外一个轮子即可；如果以一个固定的标准的话，需要调整两个轮子的PWM占空比）。

 1 程序第一步：设置GPIO，略（输出PWM的管脚用Mode_AF_PP即可）
 2 
 3 程序第二步：设置定时器，（保证产生两路PWM即可，我用的是TIM4）
 4 
 5 void TIM4_Configuration(void)
 6 {
 7 TIM_TimeBaseInitTypeDef   TIM_TimeBaseInitStructure;
 8 TIM_OCInitTypeDef TIM_OCInitStructure;
 9 
10 //时间基初始化
11 TIM_TimeBaseInitStructure.TIM_Period=144;   //18K/144=125Hz,这个是电机PWM的频率
12 TIM_TimeBaseInitStructure.TIM_Prescaler=4000; //72000000/4000=18K
13 TIM_TimeBaseInitStructure.TIM_ClockDivision=TIM_CKD_DIV1;
14 TIM_TimeBaseInitStructure.TIM_CounterMode=TIM_CounterMode_Up;
15 TIM_TimeBaseInitStructure.TIM_RepetitionCounter=0x0000;
16 
17 TIM_TimeBaseInit(TIM4,&TIM_TimeBaseInitStructure);
18 
19 //输出比较模式设置,用于4路PWM输出
20 TIM_OCInitStructure.TIM_OCMode=TIM_OCMode_PWM2; //输出PWM
21 TIM_OCInitStructure.TIM_OutputState=TIM_OutputState_Enable; //使能正向通道
22 TIM_OCInitStructure.TIM_OutputNState=TIM_OutputState_Disable; //失能反向通道
23 TIM_OCInitStructure.TIM_Pulse=PWM_L;    //左轮DIR的占空比
24 TIM_OCInitStructure.TIM_OCPolarity=TIM_OCPolarity_Low; //输出极性为低电平
25 TIM_OCInitStructure.TIM_OCNPolarity=TIM_OCPolarity_High;//互补输出极性为高电平
26 TIM_OCInitStructure.TIM_OCIdleState=TIM_OCIdleState_Set;
27 TIM_OCInitStructure.TIM_OCNIdleState=TIM_OCNIdleState_Reset;
28 
29 TIM_OC1Init(TIM4,&TIM_OCInitStructure);    //PWM_L初始化
30 TIM_OC1PreloadConfig(TIM4,TIM_OCPreload_Disable); //改变点空比后,立即产生效应
31 
32 TIM_OCInitStructure.TIM_Pulse=PWM_R;    //左轮PWM的占空比
33 TIM_OC2Init(TIM4,&TIM_OCInitStructure);    //PWM_R初始化
34 TIM_OC2PreloadConfig(TIM4,TIM_OCPreload_Disable); //改变点空比后,立即产生效应
35 
36 //使能定时器4
37 TIM_Cmd(TIM4,ENABLE);
38 TIM_CtrlPWMOutputs(TIM4,ENABLE);

程序第一步：设置GPIO，略（输出PWM的管脚用Mode_AF_PP即可）

程序第二步：设置定时器，（保证产生两路PWM即可，我用的是TIM4）

void TIM4_Configuration(void)

{

TIM_TimeBaseInitTypeDef TIM_TimeBaseInitStructure;

TIM_OCInitTypeDef TIM_OCInitStructure;

//时间基初始化

TIM_TimeBaseInitStructure.TIM_Period=144; //18K/144=125Hz,这个是电机PWM的频率

TIM_TimeBaseInitStructure.TIM_Prescaler=4000; //72000000/4000=18K

TIM_TimeBaseInitStructure.TIM_ClockDivision=TIM_CKD_DIV1;

TIM_TimeBaseInitStructure.TIM_CounterMode=TIM_CounterMode_Up;

TIM_TimeBaseInitStructure.TIM_RepetitionCounter=0x0000;

TIM_TimeBaseInit(TIM4,&TIM_TimeBaseInitStructure);

//输出比较模式设置,用于4路PWM输出

TIM_OCInitStructure.TIM_OCMode=TIM_OCMode_PWM2; //输出PWM

TIM_OCInitStructure.TIM_OutputState=TIM_OutputState_Enable; //使能正向通道

TIM_OCInitStructure.TIM_OutputNState=TIM_OutputState_Disable; //失能反向通道

TIM_OCInitStructure.TIM_Pulse=PWM_L; //左轮DIR的占空比

TIM_OCInitStructure.TIM_OCPolarity=TIM_OCPolarity_Low; //输出极性为低电平

TIM_OCInitStructure.TIM_OCNPolarity=TIM_OCPolarity_High;//互补输出极性为高电平

TIM_OCInitStructure.TIM_OCIdleState=TIM_OCIdleState_Set;

TIM_OCInitStructure.TIM_OCNIdleState=TIM_OCNIdleState_Reset;

TIM_OC1Init(TIM4,&TIM_OCInitStructure); //PWM_L初始化

TIM_OC1PreloadConfig(TIM4,TIM_OCPreload_Disable); //改变点空比后,立即产生效应

TIM_OCInitStructure.TIM_Pulse=PWM_R; //左轮PWM的占空比

TIM_OC2Init(TIM4,&TIM_OCInitStructure); //PWM_R初始化

TIM_OC2PreloadConfig(TIM4,TIM_OCPreload_Disable); //改变点空比后,立即产生效应

//使能定时器4

TIM_Cmd(TIM4,ENABLE);

TIM_CtrlPWMOutputs(TIM4,ENABLE);

 1 程序第三步：
 2 
 3 在SysTick中断中，读取两个轮子的速度（具体的方法是：每0.1秒读一次，并以此人作为速度的依据），并比较，如果以右轮为基准，则调整左轮的PWM占空比。涉及到关键语句是：TIM_SetCompare1（）；
 4 
 5 u16 COUN1=0;
 6 u16 COUN2=0;
 7 
 8 volatile u16 Dist_L=0;    //左轮行程脉冲数
 9 volatile u16 Dist_R=0;   //右轮行程脉冲数
10 void SysTick_Handler(void)
11 {
12 
13 COUN1=TIM1->CNT;    //左轮在0.1秒里脉冲数
14 COUN2=TIM2->CNT;   //右轮在0.1秒里脉冲数
15 Dist_L=Dist_L+COUN1; //左轮行程脉冲数
16 Dist_R=Dist_R+COUN2; //右轮行程脉冲数
17 if( (COUN1-COUN2)>2)
18 {
19       PWM_L= TIM_GetCapture1(TIM4);
20      TIM_SetCompare1(TIM4, PWM_L - 4);
21 }
22    else if ( (COUN2-COUN1)>2)
23    {
24        PWM_L= TIM_GetCapture1(TIM4);
25        TIM_SetCompare1(TIM4, PWM_L + 4);
26    }
27 
28   TIM_SetCounter(TIM1, 0);
29   TIM_SetCounter(TIM2, 0);
30 
31 }
32 
33 关于TIM_SetCompareX（；）这个函数，还是有很多用途的，其中另外一个用途，就是用于产生不同频率的PWM，具体程序如下：
34 
35 u16 capture = 0;
36 
37 extern vu16 CCR1_Val;
38 extern vu16 CCR2_Val;
39 extern vu16 CCR3_Val;
40 extern vu16 CCR4_Val;
41 
42 void TIM2_IRQHandler(void)
43 {
44 
45 /* TIM2_CH1 toggling with frequency = 183.1 Hz */
46 if (TIM_GetITStatus(TIM2, TIM_IT_CC1) != RESET)
47 {
48      TIM_ClearITPendingBit(TIM2, TIM_IT_CC1 );
49 capture = TIM_GetCapture1(TIM2);
50 TIM_SetCompare1(TIM2, capture + CCR1_Val );
51 }
52 
53 /* TIM2_CH2 toggling with frequency = 366.2 Hz */
54 if (TIM_GetITStatus(TIM2, TIM_IT_CC2) != RESET)
55 {
56      TIM_ClearITPendingBit(TIM2, TIM_IT_CC2);
57 capture = TIM_GetCapture2(TIM2);
58     TIM_SetCompare2(TIM2, capture + CCR2_Val);
59 } 
60 
61 /* TIM2_CH3 toggling with frequency = 732.4 Hz */
62 if (TIM_GetITStatus(TIM2, TIM_IT_CC3) != RESET)
63 {
64     TIM_ClearITPendingBit(TIM2, TIM_IT_CC3);
65 capture = TIM_GetCapture3(TIM2);
66     TIM_SetCompare3(TIM2, capture + CCR3_Val);
67 }
68 
69 /* TIM2_CH4 toggling with frequency = 1464.8 Hz */
70 if (TIM_GetITStatus(TIM2, TIM_IT_CC4) != RESET) 
71 {
72     TIM_ClearITPendingBit(TIM2, TIM_IT_CC4);
73 capture = TIM_GetCapture4(TIM2);
74     TIM_SetCompare4(TIM2, capture + CCR4_Val);
75 }
76 
77 }