Control system and method for controlling a multi-stage hybrid flying capacitor converter

Abstract

A control system and corresponding method for controlling a multi-level hybrid flying capacitor (MLHFC) converter. The control system includes: a controller configured to control the output of the MLHFC converter; a feedback region detector configured to detect a change in the feedback region of the MLHFC converter; and a controller adjuster configured to adjust the control system in response to the detected change to counteract instability.

Description

Technical Field

[0001] The present invention relates to a control system and method for controlling a multi-level hybrid flying capacitor (MLHFC) converter. Background Art

[0002] The present disclosure relates to flying capacitor instability detection and correction in a multi-level hybrid flying capacitor (MLHFC) converter.

[0003] Reliable control of the MLHFC converter ensures that the flying capacitor of the MLHFC converter is properly balanced under all conditions and prevents the flying capacitor voltage from drifting. Instability of the flying capacitor may cause the converter components to be subjected to full output voltage or full input voltage, which may be higher than the maximum rated voltage of the component. This may lead to reduced service life, performance, reliability, and ultimately permanent damage to the power stage of the converter.

[0004] Flying capacitor balancing is usually achieved by adaptively adjusting the duty cycle of the switch control signal in different switching phases. The fundamental problem with this approach is that the feedback signal from the duty cycle change to the flying capacitor voltage change depends on system parameters such as load current, input voltage, output voltage, switching frequency and inductance value. Therefore, there are different feedback regions. This is not good for the control law because the feedback may accelerate the flying capacitor voltage drift instead of compensating for it.

[0005] The voltage mode control (VMC) method overcomes the flying capacitor instability using techniques such as dual edge modulation. This technique cannot be applied to other control methods such as current mode control (CMC) and sliding mode control (SMC). CMC and SMC have better dynamic performance and overcurrent protection compared to VMC and are therefore usually the preferred methods. Therefore, it is important to have a flying capacitor instability detection and correction solution that is applicable to various control schemes. Summary of the invention

[0006] According to one aspect of the present invention, a control system for controlling a multi-level hybrid flying capacitor (MLHFC) converter is disclosed, the control system comprising: a controller configured to control the output of the MLHFC converter; a feedback region detector configured to detect changes in the feedback region of the MLHFC converter; and a controller regulator configured to adjust the control system in response to the detected changes to offset instability.

[0007] According to another aspect of the present invention, a method for controlling a multi-level hybrid flying capacitor (MLHFC) converter by a control system is disclosed, the method comprising: controlling the output of the MLHFC converter by a controller; detecting a change in the feedback region of the MLHFC converter by a feedback region detector; and adjusting the control system by a controller adjuster in response to the detected change to offset instability. BRIEF DESCRIPTION OF THE DRAWINGS

[0008] Figure 1A and Figure 1B A schematic diagram of a control system and a multi-level hybrid flying capacitor (MLHFC) converter according to aspects of the present disclosure is shown.

[0009] Figure 2A and Figure 2B The present invention illustrates the integration of known control systems with various aspects of the present disclosure. Figure 1A and Figure 1B The waveforms are compared with those of the disclosed control system.

[0010] Figure 3 A flow chart is shown of a method 300 of controlling a MLHFC converter by a control system according to aspects of the present disclosure. DETAILED DESCRIPTION

[0011] The present disclosure relates to a control system that balances the flying capacitor voltage by detecting the feedback area without any additional measurements or assumptions, and then adapting the feedback sign accordingly.

[0012] Figure 1A and Figure 1B A schematic diagram of a control system 100 and a multi-level hybrid flying capacitor (MLHFC) converter 10 is shown in accordance with aspects of the present disclosure.

[0013] The MLHFC converter 10 may be any MLHFC converter. For example, the converter 10 may be a boost converter, a buck converter, a buck / boost converter, etc. The topology of the MLHFC converter 10 may have any number of flying capacitors, levels, and phases. For example, the MLHFC converter 10 may include a single flying capacitor and have three levels. Alternatively, the MLHFC converter 10 may include a plurality of flying capacitors, in which case each flying capacitor corresponds to a corresponding pair of feedback region detectors 120 and controller regulators 130 as described below.

[0014] The control system 100 includes a controller 110, a feedback region detector 120, and a controller regulator 130. At least one of the feedback region detector 120 and the controller regulator 130 may be part of the controller 110, or alternatively, at least one of the feedback region detector 120 and the controller regulator 130 may be separate from the controller 110.

[0015] The controller 110 is configured to control the output of the MLHFC converter 10, and the controller 110 is independent of the controller architecture. The MLHFC converter 10 may be a three-level flying capacitor boost converter 10. The controller 110 may be configured to perform sliding mode control (SMC), current mode control (CMC), voltage mode control (VMC), proportional integral derivative (PID) control, hysteresis control, nonlinear control, etc. The controller 110 may use a flying capacitor balancing loop, and the flying capacitor balancing loop may be part of the controller 110, or alternatively, the flying capacitor balancing loop may be separate from the controller 110. In the example shown, the controller 110 is configured to perform CMC and flying capacitor balancing using a flying capacitor balancing loop 110A. The CMC controller 110 shown is used for a single capacitor three-level MLHFC converter 10, and the flying capacitor balancing loop 110A maintains a flying capacitor voltage V Cfly The CMC controller 110 is briefly described below. The controller 110 and the flying capacitor balancing loop 110A configured to perform CMC are known, and further detailed description is omitted for the sake of brevity.

[0016] The feedback region detector 120 is configured to monitor the flying capacitor voltage V Cfly Characteristics and control signal S of the control system 100 Cfly The characteristics of the MLHFC converter 10 are used to detect the change of the feedback region. Using the CMC controller 110 shown, the flying capacitor voltage V Cfly The characteristic is the sign of the derivative of the flying capacitor voltage of the MLHFC converter 10 The characteristic of the control signal is the sign of the derivative of the control signal of the control system 100 Since the flying capacitor voltage V Cfly To achieve its balance, no additional hardware is required. In addition, in a digital controller, all control signals are readily available and can be further processed.

[0017] The feedback region detector 120 is configured to detect when the sign of the derivative of the flying capacitor voltage and the sign of the derivative of the control signal The feedback region detector 120 detects a change in the feedback region from the negative feedback region (NFB) to the positive feedback region (PFB) when the feedback region is not equal. Alternatively, the feedback region detector 120 is configured to detect a change in the feedback region from the negative feedback region (NFB) to the positive feedback region (PFB) when the sign of the derivative of the flying capacitor voltage is and the sign of the derivative of the control signal When they are equal, the change in feedback area from PFB to NFB is detected.

[0018] The controller adjuster 130 is configured to adjust the feedback region by inverting the control signal S of the controller 110 when the feedback region detector 120 detects a change in the feedback region. Cfly The control system 100 is adjusted to counteract the instability caused by the changed feedback region by adjusting the sign of the control signal V to counteract the instability caused by the changed feedback region. The change of the feedback region of the MLHFC converter 10 can be from NFB to PFB or from PFB to NFB. As an example configuration, the controller regulator 130 includes an inverter 132 and a multiplexer 134, and the multiplexer selects the inverted version of the control signal output by the inverter 132 in response to the selection signal from the feedback region detector 120 to invert the sign of the flying capacitor balance. Therefore, the flying capacitor voltage V can be balanced without switching between controllers or adopting a special modulation scheme. Cfly .

[0019] Instabilities may be caused by changes in the operating point of the MLHFC converter 10. Additionally, instabilities may be caused by changes in parameters of the MLHFC converter 10. Since such instabilities may be counteracted, the feedback region detector 120 and the controller regulator 130 are configured to operate independently of the parameters of the MLHFC converter 10, which may include load current, input voltage, output voltage, switching frequency, and / or inductance.

[0020] The control system 100 is also independent of the control method. Figure 1B A controller 110 is shown configured to perform CMC to determine the state of the MLHFC converter switches.

[0021] The control signal that indicates the switching decision is provided by the following equation:

[0022]

[0023] Then by evaluating S CMC Obtaining a control signal c that determines the state of the control switch of the MLHFC converter 10 CMC .

[0024] Here, a constant frequency implementation is used. To this end, a constant clock signal generated by a finite state machine (FSM) controls the signal cCMC Set to 1, and in S CMC >0, the control signal c CMC Reset to 0. The FSM is used to select the appropriate MLHFC converter switch group.

[0025] For the boost converter, the flying capacitor voltage is stabilized at Typically, the flying capacitor voltage is stabilized at a fraction of the output voltage. Cfly The control signal is used to achieve flying capacitor voltage balancing. As a first step, assuming operation in the default NFB, the sign is determined by the FSM. This results in the two sub-phases being composed of S CMC >0 The timing of resetting the SR latch in the controller 110 is different, for example, if the flying capacitor is charged in the first sub-phase of controlling the first switch group, the flying capacitor will be discharged in the second sub-phase of controlling the second switch group. Therefore, the duty cycles of the two switch groups are modified in opposite directions, resulting in a balanced flying capacitor voltage V Cfly .

[0026] If an operation in the PFB is detected, the core of the control system 100 is the feedback area detection and S Cfly Subsequent adaptive adjustment of the sign of (inverting the sign selected by the FSM). In this embodiment, the feedback region is detected as follows.

[0027] First, detect the sign of the slope of the flying capacitor voltage

[0028] Secondly, the sign of the slope of the flying capacitor balance control signal is detected.

[0029] Then, the feedback region (FB) of the correction is determined by the following equation:

[0030]

[0031] If NFB is detected, the feedback sign selected by the FSM is used, since the operation is assumed to be in the default negative feedback region NFB. Otherwise, if PFB is detected, the S determined by the FSM is inverted. Cfly The feedback region detector 130 may be implemented as a digital circuit or an analog circuit.

[0032] Figure 2A and Figure 2B The known control system is shown with Figure 1A and Figure 1B The control system 100 compares the waveforms. More specifically, Figure 2AA comparison of converter waveforms during a load change is shown, with a known control system on the left and control system 100 on the right. Figure 2B A comparison of control system waveforms during this load change is shown, again with the known control system on the left and the control system 100 on the right.

[0033] First consider the known control system during load change, namely Figure 2A The converter waveform on the left and Figure 2B Load changes result in different feedback areas.

[0034] More specifically, for the MLHFC converter 10, the load current is stepped back to 0.5A after it drops from 0.5A to 1mA for transient response. It can be observed that the difference in duty cycle and flying capacitor voltage V Cfly This is the typical operating region considered when designing the flying capacitor balancing loop and analyzing the stability of the MLHFC converter 10. As can be seen from the figure, the flying capacitor balancing in the known system achieves the flying capacitor voltage V under this load condition. Cfly Adjust to the desired value However, at load current I L After dropping to 1mA, the feedback region changes. Cfly (i.e., the control signal responsible for balancing) is negative, but the flying capacitor voltage V Cfly As a result, the MLHFC converter 10 loses output voltage regulation and the flying capacitor voltage V Cfly drift, and the stress on the switch increases. Furthermore, it can be seen that after the load is increased back to 0.5A, regulation and flying capacitor balance are restored, indicating that the balance is as expected by NFB.

[0035] Now compare the control system 100 disclosed in the present application during load changes, i.e. Figure 2A The converter waveform on the right and Figure 2B Control signal on the right. Again, load changes result in different feedback regions.

[0036] Regardless of the load current i load In any case, the disclosed control system 100 can achieve output voltage regulation and balanced flying capacitor voltage V Cfly To simplify the understanding of the waveform on the right, the circled numbers below represent the circled numbers in the waveform shown. First, the default configuration S for NFB is still Cfly The sign of the load current i load After decreasing from 0.5A to 1mA, ② the flying capacitor voltage V CflyInitially increase, ③ while flying capacitor balance control signal S Cfly The feedback area detector 120 is fed back through S Cfly The slope of the integral④(i.e. ) and the slope of the flying capacitor voltage⑤(i.e. ) is different from the sign of the feedback region. Because the feedback region detector 120 has detected that the MLHFC converter 10 is in the wrong feedback region and is losing balance, the feedback sign should be reversed. Cfly The feedback sign is reversed, and the flying capacitor voltage Balance again Place.

[0037] When the load current i load When increasing back to 0.5A, similar behavior can be observed. First, ⑨ is still configured for PFB S Cfly The symbol of S Cfly The sign of the integral slope ⑩ and the flying capacitor voltage V Cfly The slope The flying capacitor voltage V Cfly is losing balance, so S Cfly The feedback sign of is reversed again, This causes the flying capacitor voltage to balance.

[0038] Figure 3 A flow chart is shown of a method 300 of controlling a MLHFC converter 10 by a control system according to aspects of the present disclosure.

[0039] At step 310 , the controller 110 controls the output of the MLHFC converter 10 .

[0040] At step 320 , the feedback region detector 130 detects a change in the feedback region of the MLHFC converter 10 .

[0041] At step 330 , the controller regulator 120 adjusts the control system 100 in response to the detected changes to counteract the instability.

[0042] The control system 100 enables industrial use of the MLHFC converter 10 in existing or future systems by eliminating the flying capacitor imbalance that causes converter instability. The control system 100 disclosed herein has many advantages. The flying capacitor balance is maintained under all conditions. There is no need to measure the inductor current to detect the feedback region. There is no need to know the converter parameters, operating conditions or feedback region boundaries. The control system 100 is independent of the control scheme (VMC, CMC, SMC, etc.). And the same control system 100 can be used in all feedback regions, that is, for all load conditions. The control system 100 allows the use of low-rated components in the power stage, thereby providing a smaller silicon footprint for the same conductance of the switch, thereby ultimately reducing costs.

[0043] The control system 100 may include any suitable circuit elements, such as bipolar transistors, metal oxide semiconductor field effect transistors (MOSFETs), and the like.

[0044] The techniques of this disclosure may also be described in the following examples.

[0045] Example 1. A control system for controlling a multi-level hybrid flying capacitor (MLHFC) converter, the control system comprising: a controller configured to control the output of the MLHFC converter; a feedback region detector configured to detect changes in the feedback region of the MLHFC converter; and a controller regulator configured to adjust the control system in response to the detected changes to offset instability.

[0046] Example 2. The control system of Example 1, wherein the instability is caused by a change in an operating point of the MLHFC converter.

[0047] Example 3. The control system of any combination of Examples 1-2, wherein the instability is caused by a parameter change of the MLHFC converter.

[0048] Example 4. The control system of any combination of Examples 1 to 3, wherein the change of the feedback region of the MLHFC converter is from a negative feedback region to a positive feedback region or from a positive feedback region to a negative feedback region.

[0049] Example 5. A control system according to any combination of Examples 1 to 4, wherein the controller adjuster is configured to adjust the control system by inverting the sign of a control signal of the controller.

[0050] Example 6. The control system according to any combination of Examples 1 to 5 further includes: multiple pairs of feedback region detectors and controller regulators, wherein the MLHFC converter includes multiple flying capacitors, each flying capacitor in the multiple flying capacitors corresponds to a corresponding pair of feedback region detectors and controller regulators.

[0051] Example 7. The control system of any combination of Examples 1 to 6, wherein the controller is controller architecture independent.

[0052] Example 8. A control system according to any combination of Examples 1 to 7, wherein the controller comprises a sliding mode controller (SMC), a current mode controller (CMC), a voltage mode controller (VMC), a proportional integral derivative (PID) controller, a hysteresis controller, or a nonlinear controller.

[0053] Example 9. The control system of any combination of Examples 1 to 8, wherein the controller comprises a current mode controller (CMC).

[0054] Example 10. A control system according to any combination of Examples 1 to 9, wherein the feedback region detector is configured to detect a change in the feedback region by monitoring characteristics of a flying capacitor voltage of the MLHFC converter and characteristics of a control signal of the controller.

[0055] Example 11. A control system according to any combination of Examples 1 to 10, wherein the characteristic of the flying capacitor voltage is the sign of a derivative of the flying capacitor voltage of the MLHFC converter, and wherein the characteristic of the control signal is the sign of a derivative of a control signal of the controller.

[0056] Example 12. A control system according to any combination of Examples 1 to 11, wherein the controller adjuster is configured to adjust the control system by inverting the sign of a control signal of the controller.

[0057] Example 13. A control system according to any combination of Examples 1 to 12, wherein the feedback region detector is configured to: detect a change in the feedback region from a negative feedback region to a positive feedback region when the sign of the derivative of the flying capacitor voltage is not equal to the sign of the derivative of the control signal, and detect a change in the feedback region from a positive feedback region to a negative feedback region when the sign of the derivative of the flying capacitor voltage is equal to the sign of the derivative of the control signal.

[0058] Example 14. A control system according to any combination of Examples 1 to 13, wherein the controller regulator is configured to adjust the control system by reversing the sign of the control signal of the controller when the feedback region detector detects a change in the feedback region from the negative feedback region to the positive feedback region or from the positive feedback region to the negative feedback region.

[0059] Example 15. The control system of any combination of Examples 1 to 14, wherein the feedback region detector is configured to operate independently of parameters of the MLHFC converter, wherein the parameters include load current, input voltage, output voltage, switching frequency, and inductance.

[0060] Example 16. The control system of any combination of Examples 1-15, wherein the MLHFC converter is a boost converter.

[0061] Example 17. The control system of any combination of Examples 1-16, wherein the MLHFC converter is a buck converter.

[0062] Example 18. A method for a control system to control a multi-level hybrid flying capacitor (MLHFC) converter, the method comprising: controlling the output of the MLHFC converter by a controller; detecting a change in the feedback region of the MLHFC converter by a feedback region detector; and adjusting the control system by a controller regulator in response to the detected change to offset instability.

[0063] Example 19. The method of Example 18, wherein the change of the feedback region of the MLHFC converter is from a negative feedback region to a positive feedback region or from a positive feedback region to a negative feedback region.

[0064] Example 20. The method of any combination of Examples 18-19, wherein the detecting by the feedback region detector comprises monitoring a characteristic of a flying capacitor voltage of the MLHFC converter and a characteristic of a control signal of the controller.

[0065] Although the foregoing has been described in conjunction with exemplary embodiments, it should be understood that the term "exemplary" merely means an example, rather than the best or optimal. Therefore, the present disclosure is intended to cover alternatives, modifications, and equivalents that may be included within the scope of the present disclosure.

[0066] Although specific embodiments have been illustrated and described herein, it will be appreciated by those skilled in the art that various alternative and / or equivalent implementations may be substituted for the specific embodiments shown and described without departing from the scope of the present disclosure. The present disclosure is intended to cover any adaptations or modifications to the specific embodiments discussed herein.

Claims

1. A control system for controlling a multi-stage hybrid flying capacitor MLHFC converter, the control system comprising: a controller configured to control an output of the MLHFC converter; a feedback region detector configured to detect a change in a feedback region of the MLHFC converter by monitoring a characteristic of a flying capacitor voltage of the MLHFC converter and a characteristic of a control signal of the controller, wherein the change in the feedback region of the MLHFC converter is from a negative feedback region to a positive feedback region or from a positive feedback region to a negative feedback region; as well as A controller adjuster is configured to adjust the control system in response to the detected changes to counteract the instability.

2. The control system according to claim 1, wherein: The instability is caused by variations in the operating point of the MLHFC converter.

3. The control system according to claim 1, wherein: The instability is caused by parameter variations of the MLHFC converter.

4. The control system according to claim 1, wherein: The controller adjuster is configured to adjust the control system by inverting the sign of a control signal of the controller.

5. The control system according to claim 1, further comprising: Multiple pairs of feedback area detectors and controller regulators, The MLHFC converter includes a plurality of flying capacitors, each of the plurality of flying capacitors corresponds to a corresponding pair of feedback region detectors and controller regulators.

6. The control system according to claim 1, wherein: The controller is controller architecture independent.

7. The control system according to claim 6, wherein: The controller includes a sliding mode controller SMC, a current mode controller CMC, a voltage mode controller VMC, a proportional integral derivative PID controller, a hysteresis controller or a nonlinear controller.

8. The control system according to claim 1, wherein: The controller includes a current mode controller CMC.

9. The control system according to claim 1, wherein: The characteristic of the flying capacitor voltage is the sign of a derivative of the flying capacitor voltage of the MLHFC converter, and wherein the characteristic of the control signal is the sign of a derivative of a control signal of the controller.

10. The control system according to claim 9, wherein: The controller adjuster is configured to adjust the control system by inverting the sign of a control signal of the controller.

11. The control system according to claim 9, wherein: The feedback region detector is configured to: When the sign of the derivative of the flying capacitor voltage is not equal to the sign of the derivative of the control signal, a change in the feedback region from a negative feedback region to a positive feedback region is detected, and When the sign of the derivative of the flying capacitor voltage is equal to the sign of the derivative of the control signal, a change in the feedback region from the positive feedback region to the negative feedback region is detected.

12. The control system according to claim 11, wherein: The controller adjuster is configured to adjust the control system by reversing the sign of the control signal of the controller when the feedback region detector detects a change in feedback region from the negative feedback region to the positive feedback region or a change in feedback region from the positive feedback region to the negative feedback region.

13. The control system according to claim 1, wherein: The feedback region detector is configured to operate independently of parameters of the MLHFC converter, wherein the parameters include load current, input voltage, output voltage, switching frequency, and inductance.

14. The control system according to claim 1, wherein: The MLHFC converter is a boost converter.

15. The control system according to claim 1, wherein: The MLHFC converter is a step-down converter.

16. A method for controlling a multi-stage hybrid flying capacitor (MLHFC) converter by a control system, the method comprising: The output of the MLHFC converter is controlled by a controller; Monitoring the characteristics of the flying capacitor voltage of the MLHFC converter and the characteristics of the control signal of the controller by a feedback region detector to detect the change of the feedback region of the MLHFC converter, wherein the change of the feedback region of the MLHFC converter is from a negative feedback region to a positive feedback region or from a positive feedback region to a negative feedback region; as well as The control system is adjusted by a controller regulator in response to the detected changes to counteract the instability.

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