F280049 EPWM：PWM变频率后第一个PWM周期输出不准确

Yankai Ma

Prodigy 40 points

你好，

调试中遇到一个PWM的问题，PWM变频后（同时也更新了comp值）第一个PMW周期的输出不准确，配置代码如下，ctr=0时从shadow中load period和compare值。帮忙看一下是哪里的问题，谢谢。

// =============================================== //

// === Configure Time Base Submodule Registers === //

// =============================================== //

// Enable TBPRD shadow load (Default is load on CTR=0)

// PWM frequency = 1 / period

// No phase shift

// Initialize counter to 0

// Counter continues to increment during emulation stop

// Configure counter for up-down count mode

// Set prescalers: clock divider = 1, HS clock divider = 1

EPWM_setPeriodLoadMode(base, EPWM_PERIOD_SHADOW_LOAD);

EPWM_selectPeriodLoadEvent(base, EPWM_SHADOW_LOAD_MODE_COUNTER_ZERO);

EPWM_setTimeBasePeriod(base, LLC_PERIOD_INIT_TICKS);

EPWM_setTimeBaseCounter(base, 0);

EPWM_setEmulationMode(base, EPWM_EMULATION_STOP_AFTER_NEXT_TB);

EPWM_setTimeBaseCounterMode(base, EPWM_COUNTER_MODE_DOWN);

EPWM_setClockPrescaler(base, EPWM_CLOCK_DIVIDER_1, EPWM_HSCLOCK_DIVIDER_1);

// === Action Qualifier SubModule for LLC - PH1/2/3, PRI === //

EPWM_setActionQualifierShadowLoadMode(base, EPWM_ACTION_QUALIFIER_A, EPWM_AQ_LOAD_ON_CNTR_ZERO);

EPWM_setActionQualifierShadowLoadMode(base, EPWM_ACTION_QUALIFIER_B, EPWM_AQ_LOAD_ON_CNTR_ZERO);

EPWM_setActionQualifierAction(base, EPWM_AQ_OUTPUT_A, EPWM_AQ_OUTPUT_LOW, EPWM_AQ_OUTPUT_ON_TIMEBASE_PERIOD);

EPWM_setActionQualifierAction(base, EPWM_AQ_OUTPUT_A, EPWM_AQ_OUTPUT_HIGH, EPWM_AQ_OUTPUT_ON_TIMEBASE_DOWN_CMPA);

EPWM_setActionQualifierAction(base, EPWM_AQ_OUTPUT_A, EPWM_AQ_OUTPUT_HIGH, EPWM_AQ_OUTPUT_ON_TIMEBASE_ZERO);

EPWM_setActionQualifierAction(base, EPWM_AQ_OUTPUT_B, EPWM_AQ_OUTPUT_LOW, EPWM_AQ_OUTPUT_ON_TIMEBASE_PERIOD);

EPWM_setActionQualifierAction(base, EPWM_AQ_OUTPUT_B, EPWM_AQ_OUTPUT_HIGH, EPWM_AQ_OUTPUT_ON_TIMEBASE_DOWN_CMPB);

EPWM_setActionQualifierAction(base, EPWM_AQ_OUTPUT_B, EPWM_AQ_OUTPUT_HIGH, EPWM_AQ_OUTPUT_ON_TIMEBASE_ZERO);

// ===================================================== //

// === Configure Counter Compare Submodule Registers === //

// ===================================================== //

// Set initial CMPA value

// Set initial CMPB value

// Enable CMPA shadow load on CTR = 0

// Enable CMPB shadow load on CTR = 0

EPWM_setCounterCompareShadowLoadMode(base, EPWM_COUNTER_COMPARE_A, EPWM_COMP_LOAD_ON_CNTR_ZERO);

EPWM_setCounterCompareShadowLoadMode(base, EPWM_COUNTER_COMPARE_B, EPWM_COMP_LOAD_ON_CNTR_ZERO);

EPWM_setCounterCompareValue(base, EPWM_COUNTER_COMPARE_A, LLC_PERIOD_INIT_TICKS >> 1);

EPWM_setCounterCompareValue(base, EPWM_COUNTER_COMPARE_B, LLC_PERIOD_INIT_TICKS >> 1);

// =============================================== //

// === Configure Dead-Band Submodule Registers === //

// =============================================== //

// Active high complementary PWMs - Set up the deadband

// Enable rising edge delay

// Enable falling edge delay

// RED polarity is active high

// FED polarity is active low (inverted)

// Enable shadow load on CTR = 0 for RED count

// Enable shadow load on CTR = 0 for FED count

EPWM_setDeadBandControlShadowLoadMode(base, EPWM_DB_LOAD_ON_CNTR_ZERO);

EPWM_setRisingEdgeDeadBandDelayInput(base, EPWM_DB_INPUT_EPWMA);

EPWM_setFallingEdgeDeadBandDelayInput(base, EPWM_DB_INPUT_EPWMB);

EPWM_setDeadBandDelayMode(base, EPWM_DB_RED, true);

EPWM_setDeadBandDelayMode(base, EPWM_DB_FED, true);

EPWM_setDeadBandDelayPolarity(base, EPWM_DB_RED, EPWM_DB_POLARITY_ACTIVE_HIGH);

EPWM_setDeadBandDelayPolarity(base, EPWM_DB_FED, EPWM_DB_POLARITY_ACTIVE_LOW);

EPWM_setRisingEdgeDelayCountShadowLoadMode(base, EPWM_RED_LOAD_ON_CNTR_ZERO);

EPWM_setFallingEdgeDelayCountShadowLoadMode(base, EPWM_FED_LOAD_ON_CNTR_ZERO);

EPWM_setRisingEdgeDelayCount(base, red);

EPWM_setFallingEdgeDelayCount(base, fed);

下图是PWM的实际输出，红框内的周期不是所设置的变频周期，比期望的周期时间长：

4 年多前

0 Green Deng 4 年多前

TI__Guru** 101655 points

一般来说，出现这个问题考虑：
1、PWM的TBCTL的PRDLD寄存器，看是否是Shadow模式
2、比较器模块的动作时间。比如PWM模块的计数器从0开始计时，然后到了上升阶段的CMPA开始动作置1，到了下降阶段的0置零，这样的话，会有小于半个周期的延迟。

0 Yankai Ma 4 年多前回复 Green Deng

Prodigy 40 points

Hi，

用仿真器读取寄存器的值，可以确定PWM的TBCTL寄存器中的PRDLD是Shadow模式。

关于比较器模块动作时间的问题，哪个文档中有介绍半个周期的延迟吗，这是所说的半个周期是值PRD/2吗？有没有规避延迟的方法？

0 Green Deng 4 年多前回复 Yankai Ma

TI__Guru** 101655 points

似乎没有这样的文档，这个是根据PWM计数器的计数原理推测出来的。
我再咨询一下其他同事这个问题，确认一下问题所在并尽量给出解释和解决方案。

0 Green Deng 4 年多前回复 Yankai Ma

TI__Guru** 101655 points

我查看了上面的EPWM配置和输出波形，基于AQ配置，我怀疑当从影子寄存器加载TBPRD时恰好错过了CTR = TBRPD事件，因为此处使用的计数器模式为DOWN模式。因此，输出不会在整个周期内都保持为低电平，并导致导通时间延长（也就是之前说的会有小于半个周期的延迟）。是否尝试过使用UP模式？

如果应用程序特别需要DOWN计数模式，那么这里提供的一项建议是如下修改动作限定符配置：

EPWM_setActionQualifierAction(base, EPWM_AQ_OUTPUT_A, EPWM_AQ_OUTPUT_LOW,  EPWM_AQ_OUTPUT_ON_TIMEBASE_ZERO);
EPWM_setActionQualifierAction(base, EPWM_AQ_OUTPUT_A, EPWM_AQ_OUTPUT_HIGH, EPWM_AQ_OUTPUT_ON_TIMEBASE_DOWN_CMPA);
EPWM_setActionQualifierAction(base, EPWM_AQ_OUTPUT_B, EPWM_AQ_OUTPUT_LOW,  EPWM_AQ_OUTPUT_ON_TIMEBASE_ZERO);
EPWM_setActionQualifierAction(base, EPWM_AQ_OUTPUT_B, EPWM_AQ_OUTPUT_HIGH, EPWM_AQ_OUTPUT_ON_TIMEBASE_DOWN_CMPB);

即使TBPRD动态变化，这样设置也应该将输出置为低电平。