C8051Fxxx单片机在小型电机PWM控制中的应用

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"silicon单片机PWM马达驱动程序示例" 本文档主要介绍了使用Silicon Laboratories的C8051Fxxx系列微控制器进行小型电机控制，特别是通过PWM（脉宽调制）技术来驱动马达。PWM是一种常见的马达控制技术，通过改变信号的占空比来调整电机的转速和扭矩，从而实现精细的控制。首先，文档提到了小型电机在各种应用中的广泛使用，包括汽车、打印机、复印机、纸张处理设备、工厂自动化、测试设备、机器人、空间及军事等领域。小型电机通常分为直流电机（DC）、无刷直流电机（BLDC）和步进电机（Stepper motors）三类，其产量与功率大小成反比，小功率电机的生产数量远超大功率电机。针对大型离线电机（Off-line motors）如交流感应电机或无刷直流电机，专门的电机控制DSP（数字信号处理器）被设计出来，但这些器件往往成本较高，不适合用于小型电机控制系统。而C8051F3xx系列微控制器则因其小巧的封装形式和丰富的功能，成为小型电机控制的理想选择。 C8051F3xx系列微控制器具有多个对电机控制非常有用的特性。除了标准的8051定时器外，还可能包括高速的模拟到数字转换器（ADC）、模拟比较器、内置的PWM模块等。这些特性使得微控制器能够实时采集电机的反馈信号，如电流、电压，并根据这些信息精确调整PWM输出，以控制电机的速度和位置。在实际应用中，通过编写适当的控制程序，可以实现以下功能： 1. **初始化设置**：配置微控制器的PWM引脚，设置PWM的周期和占空比，以及相应的中断服务程序。 2. **速度控制**：通过改变PWM的占空比来调整电机的转速，占空比越高，电机转速越快；反之，转速越慢。 3. **方向控制**：通过切换PWM信号的极性来改变电机的旋转方向。 4. **电流控制**：通过ADC测量电机电流，确保不超过设定的限制，防止过载。 5. **保护机制**：当检测到异常情况如过热、过载或短路时，自动停止PWM输出，保护电机和系统安全。此外，文档AN191可能还包括了具体的编程示例，指导用户如何利用C8051Fxxx系列单片机的库函数和API来实现这些功能。开发者可以通过这些示例快速上手，进行马达驱动程序的开发。总结来说，Silicon的C8051Fxxx系列微控制器以其高效能和低成本的优势，为小型电机的PWM控制提供了理想的解决方案。结合提供的软件示例，工程师能够有效地设计和实现各种小型电机控制系统，满足不同应用的需求。

AN191

10 Rev. 1.0

High-Voltage ICs may be used to provide a simple, low

parts count, cost-effective gate drive. Dead-time is

required to prevent cross-conduction and increased

power losses. The switching time is limited by the

performance of the power transistors and the circuit

parasitics. The dead-time must also account for any

mismatch in the turn-on and turn-off delay of the

system. High-voltage ICs are available with built in

dead-time for little or no additional cost.

The IR2103S is a 600 V half-bridge gate driver with a

fixed dead-time of 520 ns and 3 V compatible inputs.

The IR2104S provides the same features plus an active

low shut-down that disables both outputs. The shut-

down feature is very useful in more complex systems

for both start-up and fault protection.

This example provides simple open loop V/Hz control

for AC Induction motors using the C8051F300 MCU.

The MCU reads the value of a speed control

potentiometer and generates the three-phase sine

wave PWM required to drive the power transistors.

Three PCA modules configured for 8-bit PWM are used

to generate three-phase PWM. The three-phase PWM

waveforms are shown in Figure 8.

Figure 8. Three-Phase PWM

PCA0 outputs CEX0, CEX1, and CEX2 are enabled by

writing 0xC0 to the XBR1 SFR. The XBR0 SFR is

cleared to not skip any pins. This configures the PCA0

outputs on P0.0, P0.1, and P0.2. The first three outputs

P0.0–P0.2 are configured as push-pull outputs by

writing 0x07 to the P0MDOUT SFR. P0.6 is configured

as input for the analog speed control. When the

crossbar is enabled this will enable the three outputs.

All three PCA modules are configured for 8-bit PWM

mode by writing 0x42 to their respective capture/

compare mode registers. The PWM high times are

initialized to 50%.

At startup, P0.0–P0.2 will be initially pulled high by the

weak pullups by default. Pulldown resistors are used

force the output low at start-up. This turns on the lower

transistors and charges the bootstrap supply used for

the high-side gate drive. The PCA is initialized before

the crossbar is enabled. When the crossbar is initialized

a 50% waveform will appear on outputs P0.0 through

P0.2.

The main loop reads the ADC using averaging and

stores the value in the global variable

Volts. All sine

wave generation and updating is done using interrupts.

Timer T0 is configured for 16-bit counter mode 1. The

timer uses the 24.5 MHz SYSCLK divided by four. The

timer is started and TF0 is set to a 1 to force an initial

interrupt.

The Timer Interrupt Service Routine

Timer_ISR() is

used to generate a periodic interrupt with a period of

about 1 ms. After setting up the next interrupt, the

Timer_ISR() will call the Update() function.

The

Update() function updates the three PWM duty

cycles based on a sampled sine wave. The value of

theta is calculated based on the relationships illustrated

in Equation 1. First the global variable

Volts is copied

to the local variable

omega. The variable omega is scaled

so that a value of 0x04 corresponds to a sine frequency

of about 1 Hz. The value of

omega is integrated by

adding

omega to the global variable Sum. Sum is a 16-bit

unsigned int data type. The upper byte of

Sum is copied

into

theta.

Equation 1

The 8-bit variable theta is passed to the sineWave()

function. The value returned from the sineWave()

function is stored in PCA0CPH0. This sets the duty

cycle of CEX0. The other two PWMs are updated using

theta plus 0x55 and theta plus 0xAA. This generates

three sine modulate PWM signals 120º apart.

θωtd

∫

θΣω=

theta = Sum / 256

V∝

Sum = Sum + omega

AN191

Rev. 1.0 11

The sineWave() function uses the sine[] look-up table

containing 256 signed 8-bit values. The

sine[] value

corresponding to

theta is multiplied by the Volts

variable. The most significant byte of the product stored

in an 8-bit variable. An offset of 0x80 is added to the

output value to provide a sine wave centered about

50%.

Example 6—PWM using High-Speed

Output Mode

The 8-bit PWM mode of the PCA provides sufficient

resolution for most small motor drive applications. The

PWM frequency is normally chosen to be just above the

audible range. The optimum PWM frequency for small

motors is in the range of 16 to 24 kHz. Integral-

Horsepower AC Induction motors often employ lower

switching frequencies to reduce switching losses. The

24 kHz frequency is suitable for most small motor

drives.

The 8-bit PWM frequency can be set to 8, 24, or 96 kHz

when operating from a system clock frequency of

24.5 MHz. An 8-bit PWM frequency of 16.0 or 19.1 kHz

may be obtained by using T0 overflow as the PCA clock

source.

Some applications may require more resolution than 8

bits. Higher resolution may be required to achieve

speed regulation of better than 1% using DC or BLDC

motors. AC Induction motor systems that require

greater than 100 to 1 speed range may also require

higher resolution.

Higher resolutions and arbitrary PWM frequencies can

be obtained by using the high-speed output (HSO)

mode of the programmable counter array to generate a

PWM signal. The HSO mode can be used to generate

PWM waveforms with up to 16-bit resolutions and 40 ns

edge timing. This corresponds to an effective resolution

of 10.25 bits or 0.0816% at 20.0 kHz.

The trade-off is that the software latency limits the

minimum high-time and low-time. The MCU must have

sufficient time to interrupt the current process and write

the new values to the output compare registers before

the next edge is scheduled to occur. The latency can be

minimized by assigning the PCA0 to high priority,

caching the edge timing data, and using an alternate

expends a significant portion of its available processing

capability servicing the frequent PCA interrupts.

The software for Example 6 reads the value of the

speed control potentiometer and outputs a 20.0 kHz

PWM waveform on P0.0. The system clock, ADC, and

port initialization are identical to Example 1. The

PCA0_Init() function configures the PCA to use the

system clock and configures Module 0 for high-speed

output mode. The PCA initialization also schedules the

first PCA interrupt.

Two global variables

NextEdge and cycle are used by

the PCA0 Interrupt service routine.

NextEdge is used to

cache the edge timing data one edge ahead of time to

reduce latency. The global bit

cycle is used to keep

track of which edge is to occur next. Since the HSO

mode will toggle the output, a software flag bit is

required. Using a flag bit is more robust than polling the

output pin state because it is independent of compare

matching.

The preprocessor macro LATENCY is set to a value

just greater than the update latency to provide reliable

operation. Preprocessor macro calculations are used to

calculate PERIOD and HTSPAN. The high-time span

HTSPAN is the PERIOD minus two times LATENCY.

The main loop polls the ADC using averaging. The

value from the ADC is multiplied by the desired high-

time span HTSPAN. The product is then incremented

by adding LATENCY. The final result is then stored in a

global variable

HiTime. Temporary variables x and y

are used to calculate the intermediate values. The

scaling operation requires a

long int data type. The

final result is 16-bits. The global variable

HiTime should

not be used for intermediate calculations. The interrupt

service routine might pickup the new value at any time

and would use nonsensical values for the PWM. The

PCA0 interrupt is also temporarily disabled during the

HiTime update to ensure that an interrupt does not

occur until both bytes have been updated.

The PCA interrupt service routine

PCA0_ISR() first

updates the PCA0CPx0 registers and then clears the

PCA0 Module 0 capture/compare flag CCF0. Once the

flag has been cleared, it is safe for the next interrupt to

occur. Depending on the state of the

cycle bit, the

NextEdge is incremented by HiTime or Period minus

HiTime.

A comparison of the HSO PWM is shown versus the 8-

bit PWM in Figure 9. The frequency for the HSO PWM

is exactly 20 kHz and the minimum high time is 1.8 µs.

The frequency for the 8-bit PWM is 24 kHz and the

minimum high-time is 160 ns.

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