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TMS320F280039C:SFRA和Compensation Designer使用問題

Andy
Prodigy 230 points
Part Number: TMS320F280039C
Other Parts Discussed in Thread: SFRA

你好，我在使用SFRA和Compensation Designer測試目前電路的回授係數，有些問題想詢問一下:

1.我是使用BuckBoost的電路，我在使用SFRA掃描時應該要在開迴路的Buck、等電壓還是Boost的模式下去掃描呢?

2.Compensation Designer中ISR Freq就是PWM的切換頻率嗎?

3.我使用2P2Z的補償，我發現我補償後Folg_cf和Gain Margin、Phase Margin都為NA，卻顯示Stable Loop，而實際測試閉迴路的輸出是穩定的

當我把KDC調高，Folg_cf和Gain Margin、Phase Margin都有值，也顯示為Stable Loop，但是實際測試閉迴路的輸出是不穩定的，想請問有值的情況下不是應該比NA的情況穩定嗎?

4.為什麼Folg_cf、Gain Margin和Phase Margin都為NA卻顯示Stable Loop?

5.我在無載的情況下測試閉迴路的輸出都是穩定的，補償曲線如下圖，但是當我加載1A後輸出就不穩定的跳動導致電源也進入CC模式，這部分和補償也有關係嗎?我應該要再怎麼調整

6.SFRA中Plant Mode是閉迴路的意思嗎?

  • 0
    TI__Guru* 81380 points

    Hi Andy,

    您的问题我们已经升级到英文论坛了，有答复尽快给您。

  • 0 回复 Cherry Zhou
    TI__Guru* 81380 points

    Hi，

    我们的专家可能会稍晚答复您，英文论坛的链接给您贴在下面：

    e2e.ti.com/.../4685205

  • 0 回复 Cherry Zhou
    TI__Guru* 81380 points

    Hi,

    您可以看下以下答复：

    Andy 说：
    1.我是使用BuckBoost的電路，我在使用SFRA掃描時應該要在開迴路的Buck、等電壓還是Boost的模式下去掃描呢?

    The question is a little bit vague. The SFRA ifself is independent of which mode you would like to measure. This depends on which condition you would like to test the bandwidth.

    Andy 说：
    2.Compensation Designer中ISR Freq就是PWM的切換頻率嗎?

    No, it is different. The ISR frequency is the control loop freq. It is different from switching frequency.

    Andy 说：
    3.我使用2P2Z的補償，我發現我補償後Folg_cf和Gain Margin、Phase Margin都為NA，卻顯示Stable Loop，而實際測試閉迴路的輸出是穩定的

    Are you using our reference design? or you implement the SFRA by yourself inside your own project? This usually happens when the curve is not typical. It may mean you have a very large buffer to make the system stable.

    Andy 说：
    6.SFRA中Plant Mode是閉迴路的意思嗎?

    The question is not clear for me. when running closed loop, SFRA is measuring the "open loop transfer function". When running open loop. SFRA is measuring plant model. 

    详情请见英文论坛答复。

  • 0 回复 Cherry Zhou
    Prodigy 230 points
    Cherry Zhou 说：
    The question is a little bit vague. The SFRA ifself is independent of which mode you would like to measure. This depends on which condition you would like to test the bandwidth.

    我只需要讓程式動作就可以了嗎?假如我在Buck下掃描，回授穩定後，在Buck、等電壓和Boost都可以穩定嗎?

    Cherry Zhou 说：
    No, it is different. The ISR frequency is the control loop freq. It is different from switching frequency.

    那麼ISR頻率的值我要如何決定呢?

    Cherry Zhou 说：
    Are you using our reference design? or you implement the SFRA by yourself inside your own project? This usually happens when the curve is not typical. It may mean you have a very large buffer to make the system stable.

    我是使用你們的設計；但是我嘗試調整參數讓Flog_cf、Gain Margin和Phase Margin在一定範圍值內，而非NA且顯示穩定的迴圈，但實際輸出卻不穩定，我可以怎麼做，Stable Loop可以當作我是否穩定的指標嗎?

    Cherry Zhou 说：
    The question is not clear for me. when running closed loop, SFRA is measuring the "open loop transfer function". When running open loop. SFRA is measuring plant model

    我在使用SFRA時，如果要量測閉迴路Open Loop/Plant Mode Select要選擇Open Loop，如果要量測開迴路要選擇Plant嗎?

  • 0 回复 Andy
    TI__Guru* 81380 points

    请看以下答复：

    Andy 说：
    我只需要讓程式動作就可以了嗎?假如我在Buck下掃描，回授穩定後，在Buck、等電壓和Boost都可以穩定嗎?

    Yes, most probably if your control function is the same since SFRA is integrated with your control function. 

    Andy 说：
    那麼ISR頻率的值我要如何決定呢?

    This depends on the control method and topology. For Buckboost, I think you can use the same freq as switching freq if possible to achieve the best performance. 

    Andy 说：
    我是使用你們的設計；但是我嘗試調整參數讓Flog_cf、Gain Margin和Phase Margin在一定範圍值內，而非NA且顯示穩定的迴圈，但實際輸出卻不穩定，我可以怎麼做，Stable Loop可以當作我是否穩定的指標嗎?

    yes, if it shows stable loop, this can be a indicator of stability because this is based on the basic control theory.

    Andy 说：
    我在使用SFRA時，如果要量測閉迴路Open Loop/Plant Mode Select要選擇Open Loop，如果要量測開迴路要選擇Plant嗎?

    if you want to measure the open loop transfer function, you need to select open loop and running under closed loop operation. If you want to measure the plant transfer function, you need to select plant and running under open loop operation.

  • 0 回复 Cherry Zhou
    Prodigy 230 points
    Cherry Zhou 说：
    if you want to measure the open loop transfer function, you need to select open loop and running under closed loop operation. If you want to measure the plant transfer function, you need to select plant and running under open loop operation.

    下圖分別是是我操作在閉迴路下選擇開迴路掃描和操作在開迴路下選擇開迴路掃描的曲線，結果看起來是在開迴路下選擇開迴路掃描的曲線比較接近User Guide的曲線，而操作在閉迴路掃描會有不穩定的抖動，我如何能夠獲得和User Guide一樣穩定的曲線呢?

    閉迴路:

    開迴路:

    User Guide:

  • 0 回复 Andy
    TI__Guru* 81380 points

    Hi,

    您这边是否可以登录E2E？如果可以的话，建议您可以直接在英文论坛和工程师进行交流，这样可以避免传达上可能会出现的错误。