1、为每极磁通量;K 为电动机结构参数。所以直流电动机的转速控制方法可分为两类:对励磁磁通进行控制的励磁控制法和对电枢电压进行控制的电枢控制法。其中励磁控制法在低速时受磁极饱和的限制,在高速时受换向火花和换向器结构强度的限制,并且励磁线圈电感较大,动态响应较差,所以这种控制方法用得很少。现在,大多数应用场合都使用电枢控制法。绝大多数直流电机采用开关驱动方式。开关驱动方式是使半导体功率器件工作在开关状态,通过脉宽调制PWM 来控制电动机电枢电压,实现调速。上图是利用开关管对直流电动机进行 PWM 调速控制的原理图和输入输出电压波形。图中,当开关管MOSFET 的栅极输入高电平时,开关管导通,直流电动
2、机电枢绕组两端有电压Us。t1 秒后,栅极输入变为低电平,开关管截止,电动机电枢两端电压为0。t2 秒后,栅极输入重新变为高电平,开关管的动作重复前面的过程。这样,对应着输入的电平高低,直流电动机电枢绕组两端的电压波形如图中所示。电动机的电枢绕组两端的电压平均值Uo 为S SSO U UTtt tt UU = =+= 11 21 0式中为占空比,=t1/T占空比表示了在一个周期 T 里,开关管导通的时间与周期的比值。的变化范围为01。由此式可知,当电源电压Us 不变的情况下,电枢的端电压的平均值Uo 取决于占空比的大小,改变值就可以改变端电压的平均值,从而达到调速的目的,这就是PWM调速原理。
3、PWM 调速方法:在 PWM 调速时,占空比是一个重要参数。以下3 种方法都可以改变占空比的值:(1)定宽调频法:这种方法是保持t1 不变,只改变t2,这样使周期T(或频率)也随之改变。(2)调宽调频法:这种方法是保持t2 不变,只改变t1,这样使周期T(或频率)也随之改变。(3)定频调宽法:这种方法是使周期T(或频率)保持不变,而改变t1 和t2。前两种方法由于在调速时改变了控制脉冲的周期(或频率),当控制脉冲的频率与系统的固有频率接近时,将会引起震荡,因此这两种方法用得很少。目前,在直流电动机的控制中,主要使用定频调宽法图中 PWM 输入对应ICETEKF2812-A 评估板上P4 外扩插
4、座第26 引脚的PWM11 信号,DSP 将在此引脚上给出PWM 信号用来控制直流电机的转速;图中的DIR 输入对应ICETEKF2812-A 评估板上P1 外扩插座第6 引脚的P4 信号,DSP 将在此引脚上给出高电平或低电平来控制直流电机的方向。从DSP 输出的PWM 信号和转向信号先经过2 个与门和1 个非门再与各个开关管的栅极相连。控制原理当电动机要求正转时,PWM11 给出高电平信号,该信号分成3 路:第1 路接与门Y1的输入端,使与门Y1 的输出由PWM 决定,所以开关管V1 栅极受PWM 控制;第2 路直接与开关管V4 的栅极相连,使V4 导通;第3 路经非门F1 连接到与门Y2
5、 的输入端,使与门Y2 输出为0,这样使开关管V3 截止;从非门F1 输出的另一路与开关管V2 的栅极相连,其低电平信号也使V2 截止。同样,当电动机要求反转时,PWM5 给出低电平信号,经过2 个与门和1 个非门组成的逻辑电路后,使开关管V3 受PWM 信号控制,V2 导通,V1、V4 全部截止。4程序编制程序中采用定时器中断产生固定频率的 PWM 波,在每个中断中根据当前占空比判断应输出波形的高低电平。主程序用轮询方式读入键盘输入,得到转速和方向控制命令。在改变电机方向时为减少电压和电流的波动采用先减速再反转的控制顺序。实验设计及调试:(1)对实验内容和实验原理进行分析,理出完成实验的设计
6、思路。通过C语言编程改变pwm波的占空比,将此pwm波从I/O口输出到直流电动机,从而改变其转速,通过引脚上给出高电平或低电平和逻辑电路来控制直流电机的方向。(2)列出设计所需的特殊环节1.pwm初始化2.电机使能3.键盘实时监测4.中断调用(3)画出设计流程图。(4)调试程序#include DSP281x_Device.h / DSP281x Headerfile Include FileDSP281x_Examples.h / DSP281x Examples Include File/ Prototype statements for functions found within th
7、is file.interrupt void cpu_timer0_isr(void);void Delay(unsigned int nTime);void Gpio_select(void);void error(int);void program_stop();void Gpio_PortA(void);void Gpio_PortB(void);void Gpio_PortF(void);void Gpio_PortDEG(void);char ConvertScanToChar(unsigned char cScanCode);void RefreshLEDArray(); / 刷新
8、显示void SetLEDArray(int nNumber); / 修改显示内容#define T46uS 0x0d40#define SCANCODE_0 0x70#define SCANCODE_1 0x69#define SCANCODE_2 0x72#define SCANCODE_3 0x7A#define SCANCODE_4 0x6B#define SCANCODE_5 0x73#define SCANCODE_6 0x74#define SCANCODE_7 0x6C#define SCANCODE_8 0x75#define SCANCODE_9 0x7D#define S
9、CANCODE_Del 0x49#define SCANCODE_Enter 0x5A#define SCANCODE_Plus 0x79#define SCANCODE_Minus 0x7B#define SCANCODE_Mult 0x7C#define SCANCODE_Divid 0x4A#define SCANCODE_Num 0x77#define CTRGR *(int *)0x108000#define CTRLCDCMDR *(int *)0x108001#define CTRKEY *(int *)0x108001#define CTRLCDCR *(int *)0x108
10、002#define CTRCLKEY *(int *)0x108002#define CTRLCDLCR *(int *)0x108003#define CTRLCDRCR *(int *)0x108004#define CTRLA *(int *)0x108005#define CTRLR *(int *)0x108007Uint16 var1 = 0;Uint16 var2 = 0;Uint16 var3 = 0;Uint16 test_count = 0;Uint16 Test_flag = 0;Uint16 Test_var = 0;Uint16 Test_status32;Uint
11、16 PASS_flag = 0;unsigned int uWork;int jishu=0;unsigned int uWork,nCount=0,uN,uN1,nCount1,nDir;unsigned int uPort8000;unsigned int nScreenBuffer1024;unsigned char ledbuf8,ledx8;unsigned char ledkey108= 0x00,0x00,0x7C,0x82,0x82,0x82,0x7C,0x00, 0x00,0x00,0x00,0x84,0xFE,0x80,0x00,0x00, /1 0x00,0x00,0x
12、84,0xC2,0xA2,0x92,0x8C,0x00, /2 0x00,0x00,0x44,0x92,0x92,0x92,0x6C,0x00, 0x00,0x00,0x30,0x28,0x24,0xFE,0x20,0x00, 0x00,0x00,0x4E,0x92,0x92,0x92,0x62,0x00, 0x00,0x00,0x7C,0x92,0x92,0x92,0x64,0x00, 0x00,0x00,0x02,0xC2,0x32,0x0A,0x06,0x00, 0x00,0x00,0x6C,0x92,0x92,0x92,0x6C,0x00, 0x00,0x00,0x4C,0x92,0x
13、92,0x92,0x7C,0x00;void main(void) /int nCount=0; char cKey,cOldKey; unsigned int nScanCode,nKeyCode; unsigned int nSpeed;/ Step 1. Initialize System Control:/ PLL, WatchDog, enable Peripheral Clocks/ This example function is found in the DSP281x_SysCtrl.c file. InitSysCtrl();/ Step 2. Initalize GPIO
14、: / This example function is found in the DSP281x_Gpio.c file and/ illustrates how to set the GPIO to its default state./ InitGpio(); / Skipped for this example / Step 3. Clear all interrupts and initialize PIE vector table:/ Disable CPU interrupts DINT;/ Initialize the PIE control registers to thei
15、r default state./ The default state is all PIE interrupts disabled and flags/ are cleared. / This function is found in the DSP281x_PieCtrl.c file. InitPieCtrl(); StopCpuTimer0();/ Disable CPU interrupts and clear all CPU interrupt flags: IER = 0x0000; IFR = 0x0000;/ Initialize the PIE vector table w
16、ith pointers to the shell Interrupt / Service Routines (ISR). / This will populate the entire table, even if the interrupt/ is not used in this example. This is useful for debug purposes./ The shell ISR routines are found in DSP281x_DefaultIsr.c./ This function is found in DSP281x_PieVect.c. InitPie
17、VectTable();/ Interrupts that are used in this example are re-mapped to/ ISR functions found within this file. EALLOW; / This is needed to write to EALLOW protected registers PieVectTable.TINT0 = &cpu_timer0_isr; EDIS; / This is needed to disable write to EALLOW protected registers/ Step 4. Initiali
18、ze all the Device Peripherals:/ This function is found in DSP281x_InitPeripherals.c/ InitPeripherals(); / Not required for this example /InitCpuTimers(); / For this example, only initialize the Cpu Timers CpuTimer0.RegsAddr = &CpuTimer0Regs; / Initialize timer period to maximum: /CpuTimer0Regs.PRD.a
19、ll = musicnCount0*450; CpuTimer0Regs.PRD.all = 0x3000; / Initialize pre-scale counter to divide by 1 (SYSCLKOUT): CpuTimer0Regs.TPR.all = 0; CpuTimer0Regs.TIM.all = 0; CpuTimer0Regs.TPRH.all = 0; / Make sure timer is stopped: CpuTimer0Regs.TCR.bit.TSS = 1; CpuTimer0Regs.TCR.bit.SOFT = 1; CpuTimer0Re
20、gs.TCR.bit.FREE = 1; / Reload all counter register with period value: CpuTimer0Regs.TCR.bit.TRB = 1; CpuTimer0Regs.TCR.bit.TIE = 1; / Reset interrupt counters: CpuTimer0.InterruptCount = 0; / Step 5. User specific code, enable interrupts:/ Enable CPU INT1 which is connected to CPU-Timer 0: IER |= M_
21、INT1;/ Enable TINT0 in the PIE: Group 1 interrupt 7 PieCtrlRegs.PIEIER1.bit.INTx7 = 1;/ Enable global Interrupts and higher priority real-time debug events: EINT; / Enable Global interrupt INTM ERTM; / Enable Global realtime interrupt DBGM CTRGR=0x80; / 初始化ICETEK-CTR CTRGR=0x0; CTRLR=0; / 关闭东西方向的交通灯
22、 CTRLR=0x40; / 关闭南北方向的交通灯 CTRLR=0xC0; CTRGR=0x81; uPort8000=CTRCLKEY; Gpio_PortA(); Gpio_PortB(); nSpeed=T46uS; uN=60; nCount=nCount1=0; nDir=0; cKey=cOldKey=0; StartCpuTimer0(); /启动定时器 while (1) nScanCode=*(int *)0x108001; / 读扫描码 nScanCode&=0x0ff; / 低8位 uPort8000=*(int *)0x108002; /Delay(5); if ( n
23、ScanCode!=0 ) if ( nScanCode=9 ) break; else cKey=nScanCode; if ( cKey!=0 & cOldKey!=cKey ) cOldKey=cKey; switch ( cKey ) case 1: uN=10; break; case 2: uN=50; case 3: case 4: uN=70; case 5: uN=80; case 6: uN=100; case 7: uN1=uN; uN=60; / 降速 Delay(128); GpioDataRegs.GPADAT.bit.GPIOA4 = 1; /CpuTimer0R
24、egs.PRD.all = nSpeed; /CpuTimer0Regs.PRD.all = 182*50; nDir=0; Delay(128); uN=uN1; break; case 8: GpioDataRegs.GPADAT.bit.GPIOA4 = 0; Delay(128); /CpuTimer0Regs.PRD.all=nSpeed; nDir=1; /Delay(4); CTRGR=0; interrupt void cpu_timer0_isr(void) CpuTimer0.InterruptCount+; / Acknowledge this interrupt to
25、receive more interrupts from group 1 PieCtrlRegs.PIEACK.all = PIEACK_GROUP1; CpuTimer0Regs.TCR.bit.TIF = 1; GpioDataRegs.GPBSET.bit.GPIOB4=1; GpioDataRegs.GPBDAT.bit.GPIOB4=( nCount1uN )?1:0; nCount1+; nCount1%=100;void Delay(unsigned int nDelay) int ii,jj,kk=0; for ( ii=0;iinDelay;ii+ ) for ( jj=0;
26、jj64;jj+ ) /RefreshLEDArray(); kk+; void RefreshLEDArray() int i; for ( i=0;i8;i+ ) CTRGR=ledxi; CTRLA=ledbufi;void Gpio_PortA(void)/ GPIO Test #2:/ Configure Upper 8 bits of Port as inputs and lower 8 bits as outputs / Loop back bits 7:0 to bits 15:8/ Dont set any input qualifier var1= 0x0000; / sets GPIO Muxs as I/Os var2= 0x00FF; / sets GPIO 15-8 DIR as inputs, 7-0 DIR as outputs var3= 0x0000; / Don Gpio_select(); test_count =
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