利用脉冲位宽调制技术和一级滤波电路实现正弦波输出

利用PWM和RC滤波电路输出正弦波

1、初始化硬件

(1)时钟

• 使能RCC，选择外部高速晶振
  
• 将HCLK配置为最大的84MHz

(2)PWM

• 使能TIM1，将PWM设为20KHz，将死区设置为25ns
  
• 注意：为防止开关不同步导致的短路，需要设置“死区”

PWM频率计算公式：\(频率 = \frac{计时器频率}{(预分频 + 1) \times (重装载值 + 1)}\)
此时计时器频率为84MHz，预分频数值为0，重装载值为4199，所以PWM频率为20KHz

(3)TIM

• 将TIM2的时钟源设置为内部时钟，重装载值设置为4199
  
• 使能TIM2中断
  

(4)代码部分

• 在主循环外部对TIM进行初始化

  /* USER CODE BEGIN 2 */HAL_TIM_Base_Start_IT(&htim2);//开启定时器2中断HAL_TIM_PWM_Start (&htim1,TIM_CHANNEL_1);//开启四路pwm波HAL_TIMEx_PWMN_Start (&htim1,TIM_CHANNEL_1);/* USER CODE END 2 */

2、写入代码

(1)启用TIM

  /* USER CODE BEGIN 2 */HAL_TIM_Base_Start_IT(&htim2);//开启定时器2中断HAL_TIM_PWM_Start (&htim1,TIM_CHANNEL_1);//开启四路pwm波HAL_TIMEx_PWMN_Start (&htim1,TIM_CHANNEL_1);

(2)中断回调

• 在主函数外侧定义中断回调

/* USER CODE BEGIN PM */
uint16_t spwmcnt=0;//数组计数值：0~399；
float M=0.8;//调制比M：0~1int spwm_group[400]={33,99,165,231,297,362,428,494,559,624,690,755,819,884,948,1013,1076,
1140,1203,1266,1329,1392,1454,1515,1577,1638,1698,1758,1818,1877,1936,1994,2052,
2110,2166,2223,2278,2333,2388,2442,2495,2548,2600,2652,2703,2753,2802,2851,2899,
2946,2993,3039,3084,3129,3172,3215,3257,3298,3339,3378,3417,3455,3492,3528,3564,
3598,3632,3664,3696,3727,3757,3786,3814,3841,3868,3893,3917,3940,3963,3984,4005,
4024,4042,4060,4076,4092,4106,4119,4132,4143,4153,4163,4171,4178,4184,4190,4194,
4197,4199,4200,4200,4199,4197,4194,4190,4184,4178,4171,4163,4153,4143,4132,4119,
4106,4092,4076,4060,4042,4024,4005,3984,3963,3940,3917,3893,3868,3841,3814,3786,
3757,3727,3696,3664,3632,3598,3564,3528,3492,3455,3417,3378,3339,3298,3257,3215,
3172,3129,3084,3039,2993,2946,2899,2851,2802,2753,2703,2652,2600,2548,2495,2442,
2388,2333,2278,2223,2166,2110,2052,1994,1936,1877,1818,1758,1698,1638,1577,1515,
1454,1392,1329,1266,1203,1140,1076,1013,948,884,819,755,690,624,559,494,
428,362,297,231,165,99,33,-33,-99,-165,-231,-297,-362,-428,-494,-559,
-624,-690,-755,-819,-884,-948,-1013,-1076,-1140,-1203,-1266,-1329,-1392,-1454,-1515,-1577,
-1638,-1698,-1758,-1818,-1877,-1936,-1994,-2052,-2110,-2166,-2223,-2278,-2333,-2388,-2442,-2495,
-2548,-2600,-2652,-2703,-2753,-2802,-2851,-2899,-2946,-2993,-3039,-3084,-3129,-3172,-3215,-3257,
-3298,-3339,-3378,-3417,-3455,-3492,-3528,-3564,-3598,-3632,-3664,-3696,-3727,-3757,-3786,-3814,
-3841,-3868,-3893,-3917,-3940,-3963,-3984,-4005,-4024,-4042,-4060,-4076,-4092,-4106,-4119,-4132,
-4143,-4153,-4163,-4171,-4178,-4184,-4190,-4194,-4197,-4199,-4200,-4200,-4199,-4197,-4194,-4190,
-4184,-4178,-4171,-4163,-4153,-4143,-4132,-4119,-4106,-4092,-4076,-4060,-4042,-4024,-4005,-3984,
-3963,-3940,-3917,-3893,-3868,-3841,-3814,-3786,-3757,-3727,-3696,-3664,-3632,-3598,-3564,-3528,
-3492,-3455,-3417,-3378,-3339,-3298,-3257,-3215,-3172,-3129,-3084,-3039,-2993,-2946,-2899,-2851,
-2802,-2753,-2703,-2652,-2600,-2548,-2495,-2442,-2388,-2333,-2278,-2223,-2166,-2110,-2052,-1994,
-1936,-1877,-1818,-1758,-1698,-1638,-1577,-1515,-1454,-1392,-1329,-1266,-1203,-1140,-1076,-1013,
-948,-884,-819,-755,-690,-624,-559,-494,-428,-362,-297,-231,-165,-99,-33,
};void HAL_TIM_PeriodElapsedCallback(TIM_HandleTypeDef *htim)  //中断回调函数 20k
{if(htim==&htim2){__HAL_TIM_SET_COMPARE(&htim1, TIM_CHANNEL_1, (4200.f + M*spwm_group[spwmcnt]) / 2.0f);//频率算错了，20kHz频率改变200次20000 / 200 = 50Hz的正弦波，因此占空比整体除2spwmcnt++;if(spwmcnt==400)spwmcnt=0;	}
}
/* USER CODE END PM */

(3)验证

• 先关闭中断，设定一个固定比较值，用示波器观察PWM波周期是否符合要求，确认无误后，可进行后续步骤

I 验证的代码部分

• 在主循环外侧写入以下内容：

	__HAL_TIM_SET_COMPARE(&htim1, TIM_CHANNEL_1, 1000);//设置固定比较值为1000/* USER CODE END 2 */

II 示波器采样结果

• PWM通道
  
• PWM互补通道
  

3、滤波电路

• 在完成验证后，可重新开启中断，并删除验证部分代码

(1)计算规格

• 已知方波频率为20kHz，所以RC滤波电路的截止频率\(f_c\)应该为10kHz ~ 2kHz
• 根据\(f_c = \frac{1}{2\pi \times R \times C}\)以及手头得器件进行选择

由于我实验室没有合适的零件，所以选择2个10Ω的电阻串联等效，1个2.2\(\mu F\)的电容和1个1.0\(\mu F\)的电容并联等效

由公式得，截止频率为\(f_c = \frac{1}{2\pi \times 10 \Omega \times 2 \times (2.2 \mu + 1.0 \mu)} = 2,486.79 Hz\)

(2) 搭建滤波电路

• 依照下图进行搭建，电阻侧接信号源，电容接地
  
  

3、测试信号

• 将示波器鳄鱼夹处夹在电容接地端，笔头接入电容与电阻之间，便能看到正弦波信号
  
• 分别测量PWM输出通道和PWM互补通道得滤波信号，可得到一对互补的正弦波信号
  

4、注意事项

电容

• 如果是使用的点解电容，请注意电容极性与电流方向匹配

采样接地端

• 请注意将示波器表笔的接地端直接接在电容接地端，若接入开发板的接地端可能会受到其他信号的干扰

接入开发板总地线的效果，可见干扰明显增大

死区

• 注意将TIM模块设置为"生成互补PWM"模式时，要开启死区保护电路，防止短路