在永磁同步电机的控制中，需要对电机的三相定子施加一定的电压，才能控制电机转动。现在用的较多的是SVPWM（SVPWM的具体原理会在后面另写一篇博客说明），要想产生SVPWM波形，需要控制的三相电压呈如下形式，即A、B、C三相的电压是中间对齐的，这就需要用到stm32定时器的中间对齐模式了。

1、stm32的时钟树

stm32的时钟树如下图所示，简单介绍一下stm32时钟的配置过程。以外部时钟作为时钟源为例。HSE代表外部时钟（假设为8M）、SYSCLK为系统时钟，经过倍频器之后变成168M、SYSCLK经过AHB预分频器（假设分频系数为1）后变成HCLK时钟等于系统时钟SYSCLK，HCLK即AHB外部总线时钟，经过APB预分频器分出APB1时钟（分频系数为2，低速设备SYSCLK/4）与APB2时钟（分频系数为1，高速设备SYSCLK/2）

HSE->SYSCLK->HCLK->APB1、APB2。

针对stm32f427的配置源码如下

1. static void SetSysClock(void)
   
2. {
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3. #if defined (STM32F40_41xxx) || defined (STM32F427_437xx) || defined (STM32F429_439xx) || defined (STM32F401xx)
   
4. /******************************************************************************/
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5. /*            PLL (clocked by HSE) used as System clock source                */
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6. /******************************************************************************/
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7.   __IO uint32_t StartUpCounter = 0, HSEStatus = 0;
   
8.   
   
9.   /* Enable HSE */
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10.   RCC->CR |= ((uint32_t)RCC_CR_HSEON);
    
11. 
    
12.   /* Wait till HSE is ready and if Time out is reached exit */
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13.   do
    
14.   {
    
15.     HSEStatus = RCC->CR & RCC_CR_HSERDY;
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16.     StartUpCounter++;
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17.   } while((HSEStatus == 0) && (StartUpCounter != HSE_STARTUP_TIMEOUT));
    
18. 
    
19.   if ((RCC->CR & RCC_CR_HSERDY) != RESET)
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20.   {
    
21.     HSEStatus = (uint32_t)0x01;
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22.   }
    
23.   else
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24.   {
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25.     HSEStatus = (uint32_t)0x00;
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26.   }
    
27. 
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28.   if (HSEStatus == (uint32_t)0x01)
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29.   {
    
30.     /* Select regulator voltage output Scale 1 mode */
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31.     RCC->APB1ENR |= RCC_APB1ENR_PWREN;
    
32.     PWR->CR |= PWR_CR_VOS;
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33. 
    
34.     /* HCLK = SYSCLK / 1*/
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35.     RCC->CFGR |= RCC_CFGR_HPRE_DIV1;//AHB时钟  
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36. 
    
37. #if defined (STM32F40_41xxx) || defined (STM32F427_437xx) || defined (STM32F429_439xx)      
    
38.     /* PCLK2 = HCLK / 2*/
    
39.     RCC->CFGR |= RCC_CFGR_PPRE2_DIV2;//APB2时钟
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40.    
    
41.     /* PCLK1 = HCLK / 4*/
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42.     RCC->CFGR |= RCC_CFGR_PPRE1_DIV4;//APB1时钟
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43. #endif /* STM32F40_41xxx || STM32F427_437x || STM32F429_439xx */
    
44. 
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45.    
    
46.     /* Configure the main PLL */
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47.     RCC->PLLCFGR = PLL_M | (PLL_N << 6) | (((PLL_P >> 1) -1) << 16) |
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48.                    (RCC_PLLCFGR_PLLSRC_HSE) | (PLL_Q << 24);
    
49. 
    
50.     /* Enable the main PLL */
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51.     RCC->CR |= RCC_CR_PLLON;
    
52. 
    
53.     /* Wait till the main PLL is ready */
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54.     while((RCC->CR & RCC_CR_PLLRDY) == 0)
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55.     {
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56.     }
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57.    
    
58. #if defined (STM32F427_437xx) || defined (STM32F429_439xx)
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59.     /* Enable the Over-drive to extend the clock frequency to 180 Mhz */
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60.     PWR->CR |= PWR_CR_ODEN;
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61.     while((PWR->CSR & PWR_CSR_ODRDY) == 0)
    
62.     {
    
63.     }
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64.     PWR->CR |= PWR_CR_ODSWEN;
    
65.     while((PWR->CSR & PWR_CSR_ODSWRDY) == 0)
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66.     {
    
67.     }      
    
68.     /* Configure Flash prefetch, Instruction cache, Data cache and wait state */
    
69.     FLASH->ACR = FLASH_ACR_PRFTEN | FLASH_ACR_ICEN |FLASH_ACR_DCEN |FLASH_ACR_LATENCY_5WS;
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70. #endif /* STM32F427_437x || STM32F429_439xx  */
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71. 
    
72. 
    
73.     /* Select the main PLL as system clock source */
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74.     RCC->CFGR &= (uint32_t)((uint32_t)~(RCC_CFGR_SW));
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75.     RCC->CFGR |= RCC_CFGR_SW_PLL;
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76. 
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77.     /* Wait till the main PLL is used as system clock source */
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78.     while ((RCC->CFGR & (uint32_t)RCC_CFGR_SWS ) != RCC_CFGR_SWS_PLL);
    
79.     {
    
80.     }
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81.   }
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82.   else
    
83.   { /* If HSE fails to start-up, the application will have wrong clock
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84.          configuration. User can add here some code to deal with this error */
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85.   }
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86. }

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2、stm32定时器的时钟

stm32定时器分为高级定时器（TIM1与TIM8）、通用定时器（TIM2-TIM5、TIM9-TIM14）、基本定时器（TIM6、TIM7）。不同的定时器使用不同的时钟。

其中TIM1、TIM8、TIM10、TIM11使用的是APB2时钟，而其余定时器使用的是APB1时钟。

在stm32手册中有这么一段话

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根据前面RCC配置可以知道TIM1、TIM8、TIM10、TIM11使用的时钟频率为SYSCLK，其他定时器使用的时钟频率为SYSCLK/2

3、stm32定时器1的中间对齐模式

对齐模式的图示如下图所示，可以看到在中心对齐模式下产生的PWM波形的周期比实际计数周期要大1倍，所以假设要使用中间对齐模式，并且需要产生的PWM波频率为20K，那么对应的定时器时基应该设为40K。

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在SVPWM波的产生过程中使用的是定时器1的3对互补的PWM通道，它的配置如下

1. static void TIM1_Configuration(void)
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2. {   
   
3.     TIM_TimeBaseInitTypeDef  TIM_TimeBaseStructure;
   
4.     TIM_OCInitTypeDef  TIM_OCInitStructure;
   
5.     TIM_BDTRInitTypeDef TIM_BDTRInitStructure;
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6.    
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7.     RCC_APB2PeriphClockCmd(RCC_APB2Periph_TIM1, ENABLE);//使能定时器1时钟
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8.    
   
9.     Time1_Period =  (SystemCoreClock / 40000 );//定时器频率为APB2频率的2倍=HCLK 自动重装载为40K，最大值为4200
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10.    
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11.     Limit_Pluse_Max_Value = Time1_Period * 0.95;
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12.    
    
13.   /* TIM1 Peripheral Configuration */
    
14.    
    
15.   TIM_DeInit(TIM1);
    
16. 
    
17.   /* Time Base configuration */
    
18.     //配置定时器的计数方式为中间对齐方式，所以产生的PWM波的频率为20K
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19.   TIM_TimeBaseStructure.TIM_Prescaler = 0x0;
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20.   TIM_TimeBaseStructure.TIM_CounterMode = TIM_CounterMode_CenterAligned1;//TIM_CounterMode_Up;TIM_CounterMode_CenterAligned1
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21.   TIM_TimeBaseStructure.TIM_Period = Time1_Period - 1;//PERIOD;//定时器时基40K
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22.   TIM_TimeBaseStructure.TIM_ClockDivision = 0x0;
    
23.   TIM_TimeBaseStructure.TIM_RepetitionCounter = 0x0;
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24. 
    
25.   TIM_TimeBaseInit(TIM1,&TIM_TimeBaseStructure);
    
26. 
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27.   /* Channel 1, 2,3 and 4 Configuration in PWM mode */
    
28.   TIM_OCInitStructure.TIM_OCMode = TIM_OCMode_PWM1;
    
29.   TIM_OCInitStructure.TIM_OutputState = TIM_OutputState_Enable;
    
30.   TIM_OCInitStructure.TIM_OutputNState = TIM_OutputNState_Enable;                  
    
31.   TIM_OCInitStructure.TIM_Pulse = Time1_Period / 2;//CCR1_Val; //占空比50%
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32.   TIM_OCInitStructure.TIM_OCPolarity = TIM_OCPolarity_High;//TIM_OCPolarity_Low;TIM_OCPolarity_High;
    
33.   TIM_OCInitStructure.TIM_OCNPolarity = TIM_OCNPolarity_High;//TIM_OCNPolarity_Low;TIM_OCNPolarity_High;         
    
34.   TIM_OCInitStructure.TIM_OCIdleState = TIM_OCIdleState_Reset;//TIM_OCIdleState_Set;
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35.   TIM_OCInitStructure.TIM_OCNIdleState = TIM_OCIdleState_Reset;
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36.    
    
37.   TIM_OC1Init(TIM1,&TIM_OCInitStructure);
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38. 
    
39.   TIM_OCInitStructure.TIM_Pulse = Time1_Period / 2;//CCR2_Val;//占空比50%
    
40.   TIM_OC2Init(TIM1,&TIM_OCInitStructure);
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41. 
    
42.   TIM_OCInitStructure.TIM_Pulse = Time1_Period / 2;//CCR3_Val;//占空比50%
    
43.   TIM_OC3Init(TIM1,&TIM_OCInitStructure);
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44.    
    
45.    
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46. //   /* Channel 4 Configuration in OC */
    
47. //   TIM_OCInitStructure.TIM_OCMode = TIM_OCMode_PWM2;
    
48. //   TIM_OCInitStructure.TIM_OutputState = TIM_OutputState_Enable;
    
49. //   TIM_OCInitStructure.TIM_OutputNState = TIM_OutputNState_Disable;
    
50. //   TIM_OCInitStructure.TIM_Pulse = 4000;//Time1_Period / 2;            //1500;//PERIOD - 1;
    
51. //   
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52. //   TIM_OCInitStructure.TIM_OCPolarity = TIM_OCPolarity_High;
    
53. //   TIM_OCInitStructure.TIM_OCNPolarity = TIM_OCNPolarity_Low;         
    
54. //   TIM_OCInitStructure.TIM_OCIdleState = TIM_OCIdleState_Reset;
    
55. //   TIM_OCInitStructure.TIM_OCNIdleState = TIM_OCIdleState_Reset;            
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56.   
    
57. //   TIM_OC4Init(TIM1,&TIM_OCInitStructure);   
    
58.    
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59.     /* TIMx->CCMR1的bit3设为1：输出比较寄存器预装载使能 */  // PWM占空比改变只在更新事件时生效
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60.   TIM_OC1PreloadConfig(TIM1,TIM_OCPreload_Enable);//A相
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61.    
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62.     /* TIMx->CCMR1的bit11设为1：输出比较寄存器预装载使能 */ // PWM占空比改变只在更新事件时生效
    
63.   TIM_OC2PreloadConfig(TIM1,TIM_OCPreload_Enable);//B相
    
64.    
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65.     /* TIMx->CCMR2的bit3设为1：输出比较寄存器预装载使能 */  // PWM占空比改变只在更新事件时生效
    
66.   TIM_OC3PreloadConfig(TIM1,TIM_OCPreload_Enable);//C相
    
67. 
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68. //   TIM_OC4PreloadConfig(TIM1,TIM_OCPreload_Enable);//电磁铁
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69.    
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70.   /* Automatic Output enable, Break, dead time and lock configuration*/
    
71.   TIM_BDTRInitStructure.TIM_OSSRState = TIM_OSSRState_Enable;
    
72.   TIM_BDTRInitStructure.TIM_OSSIState = TIM_OSSIState_Enable;
    
73.   TIM_BDTRInitStructure.TIM_LOCKLevel = TIM_LOCKLevel_1;
    
74.   TIM_BDTRInitStructure.TIM_DeadTime = 50;
    
75.   TIM_BDTRInitStructure.TIM_Break = TIM_Break_Disable;//TIM_Break_Enable;
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76.   TIM_BDTRInitStructure.TIM_BreakPolarity = TIM_BreakPolarity_High;
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77.   TIM_BDTRInitStructure.TIM_AutomaticOutput = TIM_AutomaticOutput_Disable;//TIM_AutomaticOutput_Enable;
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78. 
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79.   TIM_BDTRConfig(TIM1,&TIM_BDTRInitStructure);
    
80.    
    
81.     TIM_SelectOutputTrigger(TIM1,TIM_TRGOSource_Update);
    
82.    
    
83.   /* TIM1 counter enable */
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84. //   TIM_Cmd(TIM1,ENABLE);
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85. 
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86.   /* Main Output Enable */
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87.    TIM_CtrlPWMOutputs(TIM1,ENABLE);//由于使用中间对齐模式，PWM频率为20K
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88.    
    
89.   //TIM_ITConfig(TIM1, TIM_IT_Update, ENABLE);//定时器1的溢出中断
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90. }

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