A dynamic current sharing method for three-phase series capacitor Buck converter

Abstract

The present invention provides a dynamic current-sharing technology based on series capacitor charge balancing and a three-phase series capacitor Buck converter device thereof, belonging to the field of power electronics. This control method ensures that the three-phase series capacitor Buck converter maintains good steady-state accuracy while rapidly responding to sudden changes in load current. This control method simplifies and solves the problem of ensuring that all state variables reach new steady-state values ​​simultaneously at the end of a transient process when implementing charge balancing control in a three-phase series capacitor Buck converter. This control method offers the advantages of a constant switching frequency, independence from converter circuit parameters, zero steady-state error, and rapid load transient response.

Description

Technical Field

[0001] The present invention belongs to the technical field of power electronics, and in particular relates to a dynamic current sharing method based on charge balance of series capacitors and a three-phase series capacitor Buck converter device thereof. Background Art

[0002] Charge balance control (CBC) is a dual-mode control method used to improve the load dynamic response speed of the converter. Its control concept is: use linear control technology to enable the converter to obtain good steady-state performance, and use nonlinear loops during load transients to enable the converter to obtain the best load transient response speed. In the Buck converter, when the load current suddenly jumps up / down, the output voltage begins to decrease / increase because the inductor current cannot suddenly change. When the controller detects that the load current has suddenly jumped up / down, it immediately turns on / off the main switch tube, and the inductor current begins to increase / decrease. When the inductor current is equal to the load current after the jump, the output voltage reaches its valley / peak value. The peak detection circuit is used to detect the moment when the output voltage valley / peak value occurs, and the output voltage valley value v is sampled. valley / peak v peak The output voltage v at the required switching time can be calculated based on the charge balance of the output capacitor. sw , when the output voltage reaches v sw When the output voltage returns to its steady-state value, all state variables of the converter have reached their new steady-state values. The system recovers from the load transient with the shortest recovery time and minimum voltage drop / overshoot, i.e., optimal transient response. The system then switches to the linear controller to handle the error after controller switching and to take charge of the converter's steady-state control.

[0003] When charge balancing control is applied to a Buck converter, only two state variables need to be considered: the inductor current and the output capacitance. However, in some specialized applications, the Buck converter cannot meet these requirements. For example, applications requiring a high step-down ratio, large output current, and fast load transient response result in a very low duty cycle, which reduces system efficiency and dynamic range. The three-phase series capacitor Buck converter, with its high step-down ratio and staggered parallel structure, is well-suited for these applications. However, the converter has a large number of state variables, and all of them must reach their new steady-state values ​​at the end of the load transient.

[0004] Therefore, in order to improve the load dynamic response of the three-phase series capacitor Buck converter, charge balancing control can be used. However, how to make all the state variables of the converter reach a new steady state at the same time becomes a problem to be solved. Summary of the Invention

[0005] In view of the problems existing in the background technology, the purpose of the present invention is to provide a dynamic current sharing control method and device based on series capacitor charge balance. The specific implementation method of the control method is: in the "ON" section of the converter load transient process, the three-phase duty cycle is alternately and evenly distributed, so that the phase current maintains dynamic current sharing during the transient process, and the system is transformed into (i sum ,v o ) is a simplified system of state variables. At the end of the transient process, all state variables of the converter can reach new steady-state values, and there will be no overcharging or overdischarging of the series capacitor and phase current oscillation. At the same time, the converter has the best load transient response.

[0006] To achieve the above object, the technical solution of the present invention is as follows:

[0007] A dynamic current balancing method based on series capacitor charge balance for a three-phase series capacitor Buck converter is characterized in that when the converter is working in a steady state, the output voltage is sampled and a linear controller is used to adjust the output voltage of the converter so that the steady-state working voltage is v s ; By comparing the output voltage with a specific reference value v cmp1 and v cmp2 Compare and judge whether the load current jumps and the polarity of the jump; when the load current jumps, the linear controller switches to the charge balance controller to control the converter; when the load current jumps suddenly, the output voltage decreases, and the charge balance controller switches the converter to the "ON" state first, and the sum of the phase currents i sum Increases when it increases to the new load current i o2 When the output voltage reaches the valley value, the output voltage valley value v is detected and sampled. valley , calculate the output voltage v at the switching moment sw1 , when the output voltage increases to v sw1 When the load current drops suddenly, the output voltage increases, and the charge balance controller switches the converter to the "OFF" state first, and the sum of the phase currents decreases. sum When it decreases to the value corresponding to the new load current i o2 When the output voltage reaches its peak value, the output voltage peak value v is detected and sampled. peak , calculate the output voltage v at the switching moment sw2 , when the output voltage decreases to v sw2 When the output voltage is equal to the specific reference value v cmp1 and v cmp2 Compare and judge whether the converter returns to steady state. When the converter returns to steady state, switch to linear controller to adjust the output voltage of the converter.

[0008] 1. Detection circuit: When v cmp1 =0.98v s , the converter steady-state output voltage is v s When the comparator output is low, the load current jumps up suddenly when the comparator is set; when the comparator is reset, the converter returns to steady state; when v cmp2 =1.02v s , the converter steady-state output voltage is v s When the comparator is set, the output of the comparator is low. When the comparator is set, the load current jumps down suddenly. When the comparator is reset, the converter returns to steady state.

[0009] 2. Charge balance controller: In the "OFF" state, all main switch tubes S a , S b and S c are all in the off state, the sum of the phase currents i sum Decrease.

[0010] 3. Dynamic current sharing method: In the "ON" state, the converter's duty cycle is kept at 1 / 3, and the sum of the phase currents i sum As the load increases, the voltage across the series capacitor remains constant and the phase currents are evenly distributed during load transients.

[0011] 4. Charge balance control, v sw1 and v sw2 The calculation formulas are

[0012]

[0013] A device for dynamic current balancing based on series capacitor charge balance, characterized in that it includes a three-phase series capacitor Buck converter and a control circuit, wherein the three-phase series capacitor Buck converter includes an input power supply V in , Main switch tube S a , S b and S c , synchronous tube D a , D b and D c , series capacitor C B1 and C B2 , phase inductance L a , L b and L c , output capacitor C o , load resistance R L and the output voltage V o , the control circuit includes a sampling / holding circuit, a comparator, a control module and a driving circuit;

[0014] The switch tube S aThe drain and input power supply V in The positive electrode is connected to the source and the series capacitor C B1 The positive terminal and the switch tube S b The drain of the switch tube S b The source and series capacitor C B2 The positive terminal and the switch tube S c The drain of synchronous tube D a The drain and C B1 The negative terminal and phase inductance L a The positive end of the synchronous tube D b The drain and C B2 The negative terminal and phase inductance L b The positive end of the synchronous tube D c The drain and S c The source and phase inductance L c The positive end of the phase inductor L a , L b and L c The negative terminal of the S is connected to the positive terminal of the output capacitor and the load resistor; the negative terminal of the input power supply is connected to the source of all synchronous tubes, the output capacitor and the negative terminal of the load resistor. The gate and source of all switching tubes are connected to the drive signal. a , C B1 , D a and L a The first phase of the converter, S b , C B2 , D b and L b The second phase of the converter, S c , D c and L c It constitutes the third phase of the converter;

[0015] The sample / hold circuit and the load resistor R L Parallel connection for real-time detection of load R L The output voltage, and the output voltage v o Transmitted to the control module; the linear controller receives v o The output voltage is stabilized after sampling feedback; the comparator responsible for transient detection compares the output voltage with the reference value v cmp1 and v cmp2 Comparison is used to determine whether the converter has a sudden change in load current and the polarity of the sudden change; the peak detection circuit is used to detect the output voltage v o The peak value occurs at this moment, and the output voltage is sampled at this moment; the control module is based on the output voltage v o With v cmp1 , v cmp2 and v swThe relationship between the two, that is, the state of each comparator, is used to select the controller and generate the corresponding drive signal; the drive circuit amplifies the drive signal generated by the control module to control the conduction and shutdown of each switch tube in the main circuit. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 This is a circuit structure block diagram of the charge balance control based on the dynamic current sharing method provided by the present invention.

[0017] Figure 2 The present invention provides a load dynamic response (load current jump mutation) of charge balance control based on a dynamic current sharing method.

[0018] Figure 3 The present invention provides a load dynamic response (load current down-jump mutation) of charge balance control based on the dynamic current sharing method.

[0019] Figure 4 This is the time domain simulation waveform of the load current jump sudden change of the converter under linear control.

[0020] Figure 5 The present invention provides a time domain simulation waveform of a converter that experiences a sudden load current jump under charge balance control based on the dynamic current sharing method.

[0021] Figure 6 This is the time domain simulation waveform of the load current drop mutation of the converter under linear control.

[0022] Figure 7 The present invention provides a time domain simulation waveform of a converter under charge balance control based on a dynamic current sharing method when a load current drop mutation occurs. DETAILED DESCRIPTION

[0023] In order to make the objectives, technical solutions and advantages of the present invention more clear, the present invention is further described in detail below in conjunction with the implementation methods and drawings.

[0024] Figure 1 The circuit structure block diagram of the charge balance control based on the dynamic current sharing method provided by the present invention includes a three-phase series capacitor Buck converter and a control circuit. The three-phase series capacitor Buck converter includes an input power supply V in , Main switch tube S a , S b and S c , synchronous tube D a , D b and D c , series capacitor C B1 and C B2 , phase inductance L a , L b and Lc , output capacitor C o , load resistance R L and the output voltage V o , the control circuit includes a sampling / holding circuit, a comparator, a control module and a driving circuit;

[0025] The switch tube S a The drain and input power supply V in The positive electrode is connected to the source and the series capacitor C B1 The positive terminal and the switch tube S b The drain of the switch tube S b The source and series capacitor C B2 The positive terminal and the switch tube S c The drain of synchronous tube D a The drain and C B1 The negative terminal and phase inductance L a The positive end of the synchronous tube D b The drain and C B2 The negative terminal and phase inductance L b The positive end of the synchronous tube D c The drain and S c The source and phase inductance L c The positive end of the phase inductor L a , L b and L c The negative terminal of the S is connected to the positive terminal of the output capacitor and the load resistor; the negative terminal of the input power supply is connected to the source of all synchronous tubes, the output capacitor and the negative terminal of the load resistor. The gate and source of all switching tubes are connected to the drive signal. a , C B1 , D a and L a The first phase of the converter, S b , C B2 , D b and L b The second phase of the converter, S c , D c and L c It constitutes the third phase of the converter;

[0026] The sample / hold circuit and the load resistor R L Parallel connection for real-time detection of load R L The output voltage, and the output voltage v o Transmitted to the control module; the linear controller receives v o The output voltage is stabilized after sampling feedback; the comparator responsible for transient detection compares the output voltage with the reference value v cmp1 and v cmp2Comparison is used to determine whether the converter has a sudden change in load current and the polarity of the sudden change; the peak detection circuit is used to detect the output voltage v o The peak value occurs at this moment, and the output voltage is sampled at this moment; the control module is based on the output voltage v o With v cmp1 , v cmp2 and v sw The relationship between the two, that is, the state of each comparator, is used to select the controller and generate the corresponding drive signal; the drive circuit amplifies the drive signal generated by the control module to control the conduction and shutdown of each switch tube in the main circuit.

[0027] Figure 2 The figure shows the working principle of the charge balancing control based on the dynamic current balancing method provided by the present invention when the load current suddenly jumps. Before time t0, the linear controller regulates the output voltage of the converter. At time t0, the detection circuit detects the load current jump and switches to the charge balancing controller to control the converter, immediately switching the converter to the "ON" state. In the "ON" state, the duty cycle of the converter remains at 1 / 3. After time t0, the output voltage v o Decrease, the sum of phase current i sum Increase, at time t1 i sum With the new load current i o2 Equal, the output voltage reaches the minimum value, the peak detection circuit detects and samples the output voltage v at this time valley At t2, the output voltage increases to v sw The charge-balancing controller switches the converter to the "OFF" state, turning off all main switches. At time t3, the transient detection circuit detects that the output voltage has recovered, and the linear controller reassumes control of the converter. Throughout the transient process, the phase currents remain evenly distributed, and no oscillation occurs at the end of the transient. The output voltage of the series capacitor remains essentially unchanged, preventing overcharging or overdischarging.

[0028] where v sw The calculation formula is

[0029] v sw =(1-D o )v valley +D o v s (1)

[0030] And D o The expression is

[0031]

[0032] Figure 3The figure shows the working principle of the charge balancing control based on the dynamic current balancing method provided by the present invention when the load current suddenly jumps. Before time t0, the linear controller regulates the output voltage of the converter. At time t0, the detection circuit detects the load current jump and switches to the charge balancing controller to control the converter, immediately switching the converter to the "OFF" state and turning off all the main switches. After time t0, the output voltage v o Increase, the sum of phase current i sum Decrease, at time t1 i sum With the new load current i o2 The output voltage reaches its maximum value, and the peak detection circuit detects and samples the output voltage v at this time. peak At t2, the output voltage decreases to v sw , the charge balancing controller switches the converter to the "ON" state, and the converter maintains a duty cycle of 1 / 3 until time t3, when the transient detection circuit detects that the output voltage has recovered and the linear controller takes over control of the converter again. During the entire transient process, the phase currents always maintain equal flow, and there will be no oscillation at the end of the transient process. The output voltage of the series capacitor remains basically unchanged, and there will be no overcharge or overdischarge. Where v sw The calculation formula is

[0033] v sw =D o v peak +(1-D o )v s (3)

[0034] Figure 4-Figure 7 The control method of the present invention is simulated in the time domain using Simulink simulation software. The method is applicable to a three-phase series capacitor Buck converter.

[0035] The simulation conditions are: output voltage V in =48V, output voltage reference value V ref =3.3V, phase inductance L a =L b =L c =5.6uH, series capacitor C B1 =2.2uF, C B2 =4.7uF, switching frequency f=500kHz.

[0036] Figure 4 This is the simulation waveform when the load current jumps from 4A to 20A. The waveforms in the figure are as follows from top to bottom: (a) voltage v1 and v2 of the series capacitor; (b) phase current i La ,i Lb and i Lc (c) The sum of the phase currents isum and the output current i o (d) Output voltage v o . Figure 4 The simulation did not use the charge balancing controller, but only the linear controller. When the load current suddenly increased, the output voltage dropped by 328mV and recovered in 130µs. This indicates that the output voltage recovery time is long due to phase current oscillation.

[0037] Figure 5 The simulation conditions and Figure 4 The same waveforms are simulated in the time domain when the load current jumps from 4A to 20A. However, with the charge balancing controller activated, we can see that the phase currents remain evenly distributed during the transient, and no phase current oscillation occurs after the transient. In this case, the voltage drop caused by the sudden increase in output current is reduced to 254mV, and the recovery time is shortened to 32.6µs.

[0038] Figure 6 and Figure 7 This is the simulation waveform when the load current suddenly changes downward, and the load current suddenly jumps from 23A to 2A. Figure 6 The simulation waveform is the result of not enabling charge balance control. Figure 6 In the example, the voltage overshoot is 397mV and the recovery time is 100us. Figure 7 The simulation waveform is the result of enabling charge balance control. Figure 7 In the transient process, the voltage overshoot is 272.5mV, the recovery time is 29us, and the phase current maintains a balanced flow throughout the transient process, and no phase current oscillation occurs at the end of the transient process.

[0039] Comparison of the four sets of results above shows that while linear control can ensure good steady-state accuracy for the converter, it cannot guarantee a rapid recovery from load transients due to the controller's bandwidth when the load current changes suddenly. This results in large voltage overshoots / drops and long recovery times. The charge balancing control based on the dynamic current sharing method proposed in this invention not only ensures good steady-state accuracy for the converter, but also allows it to quickly reach a new steady-state when a load transient occurs. By ensuring phase current balance during the transient process, all state variables can simultaneously reach their new steady-state values ​​at the end of the transient process.

[0040] The above description is only a specific embodiment of the present invention. Any feature disclosed in this specification, unless otherwise stated, can be replaced by other equivalent or alternative features with similar purposes; all disclosed features, or all steps in the methods or processes, except for mutually exclusive features and / or steps, can be combined in any way.

Claims

1. A dynamic current sharing method based on series capacitor charge balance in a three-phase series capacitor Buck converter, characterized in that: When the converter is working in steady state, the output voltage is sampled and the linear controller is used to adjust the output voltage of the converter so that the steady state working voltage is v s ; Through the output voltage and reference value v cmp1 and v cmp2 Compare and judge whether the load current jumps and the polarity of the jump; when the load current jumps, the linear controller switches to the charge balance controller to control the converter; when the load current jumps suddenly, the output voltage decreases, and the charge balance controller switches the converter to the "ON" state first, and the sum of the phase currents i sum Increase, when it increases to the new load current i o2 When the output voltage reaches the valley value, the output voltage valley value v is detected and sampled. valley , calculate the output voltage v at the switching moment sw1 , when the output voltage increases to v sw1 When the load current drops suddenly, the output voltage increases, and the charge balance controller switches the converter to the "OFF" state first. The sum of the phase currents i sum When it decreases to the value corresponding to the new load current i o2 When the output voltage reaches its peak value, the output voltage peak value v is detected and sampled. peak , calculate the output voltage v at the switching moment sw2 , when the output voltage decreases to v sw2 When the converter is switched to "ON" state, the output voltage is compared with the reference value v cmp1 and v cmp2 Compare and judge whether the converter returns to steady state. When the converter returns to steady state, switch to linear controller to adjust the output voltage of the converter. In the "OFF" state, all main switches are in the off state, and the sum of phase currents i sum In the "ON" state, the duty cycle of the converter is kept at 1 / 3, and the sum of the phase currents i sum As the load increases, the voltage across the series capacitor remains constant and the phase currents are evenly distributed during load transients.

2. The dynamic current sharing method according to claim 1, when v cmp1 =0.98v s , the converter steady-state output voltage is v s When the comparator output is low, the load current jumps up suddenly when the comparator is set, and the converter returns to steady state when the comparator is reset; when v cmp2 =1.02v s , the converter steady-state output voltage is v s When the comparator is set, the load current jumps down suddenly. When the comparator is reset, the converter returns to steady state.

3. The dynamic current sharing method according to claim 1, wherein sw1 and v sw2 The calculation formulas are 4. A device using the dynamic current sharing method based on series capacitor charge balance according to any one of claims 1 to 3, characterized in that: It includes a three-phase series capacitor Buck converter and a control circuit. The three-phase series capacitor Buck converter includes an input power supply V in , main switch tube S a , S b and S c , synchronous tube D a , D b and D c , series capacitor C B1 and C B2 , phase inductance L a , L b and L c , output capacitor C o , load resistance R L and the output voltage V o , the control circuit includes a sampling / holding circuit, a comparator, a control module and a driving circuit; The switch tube S a The drain and input power supply V in The positive electrode is connected to the source and the series capacitor C B1 The positive terminal and the switch tube S b The drain of the switch tube S b The source and series capacitor C B2 The positive terminal and the switch tube S c The drain of synchronous tube D a The drain and C B1 The negative terminal and phase inductance L a The positive end of the synchronous tube D b The drain and C B2 The negative terminal and phase inductance L b The positive end of the synchronous tube D c The drain and S c The source and phase inductance L c The positive end of the phase inductor L a , L b and L c The negative end of the output capacitor and the positive end of the load resistor are connected; the negative end of the input power supply is connected to the source of all synchronous tubes, the output capacitor and the negative end of the load resistor; the gate and source of all switching tubes are connected to the drive signal; S a , C B1 , D a and L a The first phase of the converter, S b , C B2 , D b and L b The second phase of the converter, S c , D c and L c It constitutes the third phase of the converter; The sample / hold circuit and the load resistor R L Parallel connection for real-time detection of load R L The output voltage, and the output voltage v o Transmitted to the control module; the linear controller receives v o The output voltage is stabilized after sampling feedback; the comparator responsible for transient detection compares the output voltage with the reference value v cmp1 and v cmp2 Comparison is used to determine whether the converter has a sudden change in load current and the polarity of the sudden change; the peak detection circuit is used to detect the output voltage v o The peak value occurs at this moment, and the output voltage is sampled at this moment; the control module is based on the output voltage v o With v cmp1 , v cmp2 and v sw The relationship between the two, that is, the state of each comparator, is used to select the controller and generate the corresponding drive signal; the drive circuit amplifies the drive signal generated by the control module to control the conduction and shutdown of each switch tube in the main circuit.

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