Soft start and interphase equalization current control method for interleaved Buck / Boost converter

Abstract

The invention relates to the field of power electronic technology and direct-current converter control, and aims to provide a soft start and inter-phase equalizing current control method for an interleaved Buck / Boost converter. According to the method, a multi-phase interleaved parallel bidirectional Buck / Boost converter is used as rectification and buck-boost equipment; the duty ratio of a switching tube in a Buck / Boost circuit of one phase is firstly changed, so that the output voltage of the circuit of the phase is gradually increased to a target value; enabling the whole Buck / Boost converter to enter a closed-loop mode, setting the duty ratio of the Buck / Boost circuit of the residual phase to be consistent, and gradually adjusting the voltage output of the Buck / Boost converter to a target value; after the soft start of the Buck / Boost converter is completed in this way, each phase of circuit keeps current balance. According to the soft start method, the problems of initial voltage impact and unbalanced current in the soft start process of the interleaved parallel bidirectional Buck / Boost converter are solved, no additional device needs to be added, the system can be ensured to be safe and stable in the soft start process only by a simple control strategy, and inter-phase current balance is realized after the soft start is finished.

Description

Technical Field

[0001] The present invention relates to the fields of power electronics technology and DC converter control, and particularly to a soft start and phase - balanced current control method for interleaved parallel Buck / Boost converters. Background Art

[0002] With the gradual increase in the penetration rate of new - energy power generation, a large number of energy - storage systems are connected to the AC grid through power - electronic devices. For general energy - storage systems, the voltage during the rectification or inversion process by the connected power - electronic devices does not meet the requirements. There is an urgent need for a DC / DC converter that can achieve step - up and step - down functions to cooperate with a grid - connected bidirectional AC / DC converter to ensure the normal and stable operation of power transmission.

[0003] The interleaved parallel bidirectional Buck / Boost converter is optimized based on synchronous rectification and the Buck / Boost circuit. It has a simple and reliable topology, a simple control method, can achieve wide - range input and output, a relatively high power level, and low device energy loss. As the front - stage of an AC / DC converter, it has high reliability and stable output, so it has a wide range of applications.

[0004] When the duty cycle is changed under a certain input voltage in a Buck / Boost converter, it may cause extremely high current surges and damage power - electronic devices. Therefore, a soft - start method is usually required to make the output voltage reach the target voltage.

[0005] In the prior art, the soft - start process of the Buck / Boost converter is usually achieved by adjusting the output - voltage reference value or using an additional current - detection module. The main drawback is the complexity of the soft - start process. For example, in the published literature "A Wide - Input - Range Buck - Boost Converter with Smooth Transition", the solution is to slowly change the output - voltage reference value in the closed - loop state. Another example is in the technical solution of the patent literature "Soft - Start and Current - Limiting Circuit and Method for a Four - Transistor Buck - Boost Converter" (CN115021549A), where the solution is to control the current using a current - limiting unit, but this method also adds extra complexity. The above solutions still have room for further simplification in the soft - start process of the Buck / Boost converter.

[0006] Therefore, the present invention intends to propose a new solution to solve the above problems. Summary of the Invention

[0007] The technical problem to be solved by the present invention is to overcome the deficiencies in the prior art and provide a soft start and phase - balanced current control method for interleaved parallel Buck / Boost converters.

[0008] To solve the technical problem, the solution of the present invention is as follows:

[0009] Provide a soft start and phase - to - phase balanced current control method for an interleaved parallel Buck / Boost converter. Use a multi - phase interleaved parallel bidirectional Buck / Boost converter as the rectification and buck - boost device. First, change the duty cycle of the switching tube in one of the Buck / Boost circuits of a certain phase to gradually increase the output voltage of this phase circuit to the target value. Then, put the entire Buck / Boost converter into the closed - loop mode, and at the same time set the duty cycles of the Buck / Boost circuits of the remaining phases to be the same, so that their voltage outputs are gradually adjusted to the target value. After completing the soft start of the Buck / Boost converter in this way, the current of each phase circuit remains balanced.

[0010] As a preferred solution of the present invention, the multi - phase interleaved parallel bidirectional Buck / Boost converter refers to a Buck / Boost converter with at least two parallel Buck / Boost circuits.

[0011] As a preferred solution of the present invention, in the topological structure of the multi - phase interleaved parallel bidirectional Buck / Boost converter, it includes a common capacitor arranged at both ends, and at least two parallel Buck / Boost circuits arranged between the capacitors; the Buck / Boost circuits in each phase have the same structure: each includes an inductor and two switching tubes. The inductor and the first switching tube are connected in series and then connected to one side of the capacitors at both ends of the converter; one end of the second switching tube is connected to the mid - point of the inductor and the first switching tube, and the other end is connected to the other side of the capacitors at both ends of the converter.

[0012] As a preferred solution of the present invention, the switching tube is a MOSFET switching tube; the source electrode of the first switching tube and the drain electrode of the second switching tube are connected to one end of the inductor, the other end of the inductor is connected to the positive electrode of the low - voltage - side capacitor; the source electrode of the second switching tube is connected to the positive electrode of the high - voltage - side capacitor, and the drain electrode of the first switching tube, the negative electrode of the low - voltage - side capacitor, and the negative electrode of the high - voltage - side capacitor are connected together and denoted as GND; the high - level of the first switching tube and the second switching tube are complementary, and there is a low - level dead zone.

[0013] As a preferred solution of the present invention, the method specifically includes:

[0014] Select any one of the Buck / Boost circuits in the converter as the first - phase circuit, which is the initial target for soft start. Detect its current value, input voltage value and output voltage value, and calculate the duty cycle of the first switching tube that is simultaneously connected to the capacitors at both ends in this Buck / Boost circuit in each power - frequency cycle, and denote the duty cycle as D.

[0015] In the initial state, the voltage across the first-phase circuit is detected to determine its operating state; if the voltage values of the low-voltage capacitor and the high-voltage capacitor are equal, the first-phase circuit enters the Boost operating mode; otherwise, it enters the Buck mode;

[0016] In the Boost operating mode: The switching transistors in the first-phase circuit conduct complementarily, and the duty cycle D gradually increases from 0, causing the voltage of the high-voltage terminal capacitor to gradually increase to near the preset reference value, ending the soft-start process of the first-phase circuit; the currents of each phase of the Buck / Boost circuit are recorded and written into the PI controller, and the entire Buck / Boost converter enters the closed-loop mode; at the same time, the initial duty cycles of the remaining phases of the Buck / Boost circuit are set to be the same as that in the first-phase circuit, and their voltage outputs are gradually adjusted to the target value;

[0017] In the Buck operating mode: The switching transistors in the first-phase circuit conduct complementarily, and the duty cycle D gradually decreases from 1, causing the voltage of the low-voltage terminal capacitor to gradually increase to near the preset reference value, ending the soft-start process of the first-phase circuit; the currents of each phase of the Buck / Boost circuit are recorded and written into the PI controller, and the entire Buck / Boost converter enters the closed-loop mode; at the same time, the initial duty cycles of the remaining phases of the Buck / Boost circuit are set to be the same as that in the first-phase circuit, and their voltage outputs are gradually adjusted to the target value;

[0018] After the Buck / Boost converter enters the closed-loop mode, the output value of the closed-loop voltage outer loop is the sum of the current values of each phase of the Buck / Boost circuit; there is no current impact during the entire switching process, and the initial duty cycles of the switching transistors in the remaining phases of the Buck / Boost circuit are all the same as that in the first-phase circuit, and the currents of each phase will be automatically balanced.

[0019] As a preferred embodiment of the present invention, in the Boost operating mode, the duty cycle D of the switching transistors in the first-phase circuit is calculated according to the following formula:

[0020]

[0021] where T sum represents a linear growth amount, and its growth rate is determined by the time of the soft-start process and the control interruption time T s ; within one cycle, T sum =T sum +k*T s ; k is the soft-start time coefficient.

[0022] As a preferred embodiment of the present invention, in the Buck operating mode, the duty cycle D of the switching transistors in the first-phase circuit is calculated according to the following formula:

[0023] D = 1 - T sum

[0024] Among them, T sum represents a linear growth quantity, and its growth rate is determined by the time of the soft start process and the control interruption time T s . Within one cycle, T sum = T sum + k * T s ; k is the soft start time coefficient.

[0025] As a preferred solution of the present invention, assume that the target voltage output by the Buck / Boost converter is V ref . In the Boost mode, when the output voltage V2 of the high-voltage side capacitor satisfies V2 > (0.95 * V ref ), the soft start process ends, and the Buck / Boost converter will enter the closed-loop state; in the Buck mode, when the output voltage V1 of the low-voltage side capacitor satisfies V1 > (0.95 * V ref ), the soft start process ends, and the Buck / Boost converter will enter the closed-loop state.

[0026] Compared with the prior art, the advantages of the present invention are:

[0027] 1. The present invention first adjusts the voltage of a certain phase Buck / Boost circuit in the multi-phase interleaved parallel Buck / Boost converter, ensuring the safety and stability of the system during the soft start process without increasing additional control quantities and without affecting the output waveform; then the Buck / Boost converter is put into closed-loop operation, keeping the duty cycles of each phase Buck / Boost circuits consistent, so as to ensure the balance of the currents of each phase after the soft start ends.

[0028] 2. The present invention solves the problems of initial voltage impact and uneven current during the soft start process of the interleaved parallel bidirectional Buck / Boost converter through the soft start method, providing reliable support for the boost connection of the energy storage system to the AC / DC converter bus.

[0029] 3. The present invention does not require additional devices, and only needs a simple control strategy to ensure the safety and stability of the system during the soft start process and achieve the balance of the inter-phase currents after the soft start ends. Brief Description of the Drawings

[0030] Figure 1 is a schematic diagram of the main circuit topology of the Buck / Boost converter in the present invention;

[0031] Figure 2 is a flowchart of the soft start and inter-phase current balance control of the Buck / Boost converter in the present invention. Detailed Embodiments

[0032] The present invention will be further described below in conjunction with the accompanying drawings and embodiments.

[0033] Figure 1 Shown in the figure is a schematic diagram of the interleaved parallel bidirectional Buck / Boost main circuit topology of the present invention. Each phase of the Buck / Boost circuit in the main circuit consists of an inductor and two switching tubes, and these three components are used to connect to other phases to jointly form a Buck / Boost converter with an interleaved parallel structure.

[0034] In the topology of this Buck / Boost converter, there are common capacitors provided at both ends, namely a low-voltage capacitor and a high-voltage capacitor. There should be at least two phases of Buck / Boost circuits connected in parallel between the capacitors, and the specific number of phases can be determined according to the actual engineering current magnitude. The Buck / Boost circuits in each phase have the same structure: they all include an inductor and two switching tubes. The inductor and the first switching tube are connected in series and then connected to one side of the capacitors at both ends of the converter; one end of the second switching tube is connected to the midpoint of the inductor and the first switching tube, and the other end is connected to the other side of the capacitors at both ends of the converter.

[0035] As an optional example, the switching tubes in each phase of the Buck / Boost circuit are MOSFET switching tubes. The source of the first switching tube and the drain of the second switching tube are connected to one end of the inductor, and the other end of the inductor is connected to the positive electrode of the low-voltage side capacitor; the source of the second switching tube is connected to the positive electrode of the high-voltage side capacitor, and the drain of the first switching tube, the negative electrode of the low-voltage side capacitor, and the negative electrode of the high-voltage side capacitor are connected together and denoted as GND; the high levels of the first switching tube and the second switching tube are complementary, and there is a low-level dead zone.

[0036] Based on this Buck / Boost converter, the present invention proposes a soft start and inter-phase balanced current control method for the interleaved parallel Buck / Boost converter.

[0037] This method gradually increases the output voltage of a certain phase of the Buck / Boost circuit to a given value by changing the duty cycle of the switching tube in it, and after reaching the target value, the Buck / Boost converter enters the closed-loop mode for normal operation. At the same time, signals are sent to the Buck / Boost circuits of the remaining phases to keep the duty cycle the same as the aforementioned one, and gradually adjust the output voltage to the target value, thereby completing current balance and enabling the Buck / Boost converter to operate normally. In this process, the balanced characteristics and duty cycle stability characteristics of the interleaved parallel Buck / Boost buck-boost circuit are utilized to ensure the safety and stability of the system during the soft start process without adding additional control quantities and without affecting the output waveform, and the currents of each phase are balanced after the soft start ends.

[0038] Since the open-loop state of the Buck / Boost converter is a second-order system, there is a specific frequency that causes current and voltage surges in the system at this frequency. Therefore, this type of topology converter requires closed-loop control. In the interleaved parallel topology, since the soft-start process is equivalent to an open-loop process, and there is an overshoot problem of the specific frequency voltage during the open-loop process. Therefore, the present invention innovatively proposes to use only one phase of the Buck / Boost circuit as the switching circuit for soft start during the soft-start process, while the other phases remain in the off state. After entering the closed-loop state, it is necessary to put into use the Buck / Boost circuits of other phases to maintain the balance of the currents of each phase.

[0039] For the convenience of understanding, the following takes a control cycle as an example to illustrate. The flowchart of soft start and current balance control is as Figure 2 shown, and its specific implementation steps are as follows:

[0040] 1. Select any one phase of the Buck / Boost circuit in the converter and denote it as the first-phase circuit as the initial target for soft start; detect its current value, input voltage value, and output voltage value, and calculate the duty cycle of the first switch tube that is connected to both ends of the capacitor in this Buck / Boost circuit in each power frequency cycle, and denote the duty cycle as D. In the initial stage of soft start, only the switch tubes in the first-phase circuit are put into operation.

[0041] 2. In the initial state, detect the voltage access value at both ends of the first-phase circuit to determine the working state of the circuit. Use V1 and V2 as the voltage values at both ends of the circuit, where V1 is the voltage value of the low-voltage capacitor and V2 is the voltage value of the high-voltage capacitor. In the initial state, if V1 = V2, the first-phase circuit works in the Boost mode; if V2 > 0 and V1 = 0, the first-phase circuit works in the Buck mode.

[0042] 3. When the first-phase circuit works in the Boost mode: The two switch tubes in the first-phase circuit conduct complementarily, and the duty cycle D gradually increases from 0, so that the high-voltage terminal capacitor is gradually increased to be close to the preset reference value, and the soft-start process of the first-phase circuit ends; record the currents of each phase of the Buck / Boost circuit and write them into the PI controller, and the entire Buck / Boost converter enters the closed-loop mode; at the same time, set the initial duty cycles of the other phases of the Buck / Boost circuit to be the same as those in the first-phase circuit, and gradually adjust their voltage outputs to the target values.

[0043] In the Boost mode, the duty cycle D of the first switch tube is calculated according to the following formula:

[0044]

[0045] where, T sumRepresents a linear growth quantity, and its growth rate is determined by the time of the soft start process and the control interruption time T s and within one cycle, T sum = T sum + k * T s , where k is the soft start time coefficient.

[0046] For example, gradually increase the duty cycle D of the first switching tube from 0 to 0.9, so that the high-voltage terminal capacitor voltage V2 is increased from 1 times the low-voltage terminal capacitor voltage to nearly 10 times the low-voltage terminal capacitor voltage. When the output voltage V2 satisfies V2 > (0.95 * V ref ), the soft start process ends, the Buck / Boost converter enters the closed-loop mode, and at the same time, the switching tubes of the remaining phases work normally, and the initial duty cycle is the same as the duty cycle D of the first switching tube in the first-phase circuit.

[0047] 4. When the first-phase circuit operates in the Buck mode, the two switching tubes in the circuit conduct complementarily, and the duty cycle D gradually decreases from 1, so that the voltage of the low-voltage terminal capacitor is gradually increased to nearly the preset reference value, ending the soft start process of the first-phase circuit; record the currents of each phase of the Buck / Boost circuit and write them into the PI controller, and the entire Buck / Boost converter enters the closed-loop mode; at the same time, set the initial duty cycle of the remaining phases of the Buck / Boost circuit to be the same as that in the first-phase circuit, so that its voltage output is gradually adjusted to the target value.

[0048] In the Buck mode, the duty cycle D of the first switching tube is calculated according to the following formula:

[0049] D = 1 - T sum

[0050] where, T sum Represents a linear growth quantity, and its growth rate is determined by the time of the soft start process and the control interruption time T s and within one cycle, T sum = T sum + k * T s , where k is the soft start time coefficient.

[0051] For example, gradually decrease the duty cycle D of the first switching tube from 1 to nearly 0, so that the low-voltage terminal capacitor voltage V1 is gradually increased from 0 to nearly the high-voltage terminal capacitor voltage V2. When the output voltage V1 satisfies V1 > (0.95 * V ref ), the soft start process ends, the Buck / Boost converter enters the closed-loop mode, and at the same time, the switching tubes of the remaining phases work normally, and the initial duty cycle is the same as the duty cycle D of the first switching tube in the first-phase circuit.

[0052] 5. After the entire Buck / Boost converter enters the closed-loop mode, the output value of the closed-loop voltage outer loop is the sum of the current values of each phase of the Buck / Boost circuit. There is no current impact during the entire switching process, and the initial duty cycles of the switching transistors in the remaining phases of the Buck / Boost circuit are the same as those in the first phase circuit, and the currents of each phase will be automatically balanced.

[0053] The specific embodiments of the present invention have been described above. It should be understood that the present invention is not limited to the above specific embodiments, and those skilled in the art can make various deformations or modifications within the scope of the claims, which does not affect the essence of the present invention.

Claims

1. A soft start and inter-phase balanced current control method for an interleaved parallel Buck / Boost converter, characterized in that, A multiphase interleaved bidirectional Buck / Boost converter is used as a rectifier and buck-boost device. By first changing the duty cycle of the switching tube in one of the Buck / Boost circuits, the output voltage of this phase circuit is gradually increased to the target value. Then, the entire Buck / Boost converter enters the closed-loop mode, and at the same time, the duty cycles of the Buck / Boost circuits of the remaining phases are set to be the same, so that their voltage outputs are gradually adjusted to the target value. After the soft start of the Buck / Boost converter is completed in this way, the current balance of each phase circuit is maintained.

2. The method according to claim 1, wherein The multiphase interleaved bidirectional Buck / Boost converter refers to a Buck / Boost converter with at least two parallel Buck / Boost circuits.

3. The method according to claim 1 or 2, characterized in that, In the topology of the multiphase interleaved bidirectional Buck / Boost converter, it includes a common capacitor at both ends, and at least two parallel Buck / Boost circuits between the capacitors; each Buck / Boost circuit in each phase has the same structure: it includes an inductor and two switching tubes. The inductor and the first switching tube are connected in series and then connected to one side of the capacitors at both ends of the converter; one end of the second switching tube is connected to the midpoint of the inductor and the first switching tube, and the other end is connected to the other side of the capacitors at both ends of the converter.

4. The method according to claim 1, wherein The switching tube is a MOSFET switching tube; the source electrode of the first switching tube and the drain electrode of the second switching tube are connected to one end of the inductor, and the other end of the inductor is connected to the positive electrode of the low-voltage side capacitor; the source electrode of the second switching tube is connected to the positive electrode of the high-voltage side capacitor, and the drain electrode of the first switching tube, the negative electrode of the low-voltage side capacitor, and the negative electrode of the high-voltage side capacitor are connected together and denoted as GND; the high levels of the first switching tube and the second switching tube are complementary, and there is a low-level dead zone.

5. The method according to any one of claims 1 to 4, characterized in that, This method specifically includes: Select any one of the Buck / Boost circuits in the converter as the first-phase circuit, which is the initial target of soft start; detect its current value, input voltage value, and output voltage value, and calculate the duty cycle of the first switching tube that is connected to the capacitors at both ends in this Buck / Boost circuit in each power frequency cycle, and denote the duty cycle as D. In the initial state, detect the voltage access at both ends of the first-phase circuit to determine its working state; if the voltage values of the low-voltage capacitor and the high-voltage capacitor are equal, the first-phase circuit enters the Boost working mode; otherwise, it enters the Buck mode. In the Boost working mode: the switching tubes in the first-phase circuit conduct complementarily, and the duty cycle D gradually increases from 0, so that the high-voltage side capacitor is gradually increased to be close to the preset reference value, and the soft start process of the first-phase circuit ends; record the currents of each Buck / Boost circuit and write them into the PI controller, and the entire Buck / Boost converter enters the closed-loop mode; at the same time, set the initial duty cycles of the remaining Buck / Boost circuits to be the same as those in the first-phase circuit, so that their voltage outputs are gradually adjusted to the target value. In the Buck operating mode: The switching transistors in the first-phase circuit conduct complementarily, and the duty cycle D gradually decreases from 1, causing the voltage of the low-voltage terminal capacitor to gradually increase to approach the preset reference value, ending the soft-start process of the first-phase circuit; Record the currents of each phase of the Buck / Boost circuit and write them into the PI controller, and the entire Buck / Boost converter enters the closed-loop mode; At the same time, set the initial duty cycle of the remaining Buck / Boost circuits in each phase to be the same as that in the first-phase circuit, so that their voltage outputs are gradually adjusted to the target value; After the Buck / Boost converter enters the closed-loop mode, the output value of the closed-loop voltage outer loop is the sum of the current values of each phase of the Buck / Boost circuit; There is no current impact during the entire switching process, and the initial duty cycle of the switching transistors in the remaining Buck / Boost circuits in each phase remains the same as that in the first-phase circuit, and the currents in each phase will be automatically balanced.

6. The method according to claim 5, characterized in that In the Boost operating mode, calculate the duty cycle D of the switching transistor in the first-phase circuit according to the following formula: Among them, T sum represents a linear growth amount, and its growth rate is determined by the time of the soft start process and the control interruption time T s . Within one cycle, T sum = T sum + k * T s ; k is the soft start time coefficient.

7. The method according to claim 5, wherein In the Buck operating mode, calculate the duty cycle D of the switching transistor in the first-phase circuit according to the following formula: D = 1 - T sum Among them, T sum represents a linear growth amount, and its growth rate is determined by the time of the soft start process and the control interruption time T s . In one cycle, T sum = T sum + k * T s ; k is the soft start time coefficient.

8. The method according to claim 5, wherein Assume that the target voltage output by the Buck / Boost converter is V ref ; in Boost mode, when the output voltage V2 of the high-side capacitor satisfies V2 > (0.95 * V ref ), the soft-start process ends, and the Buck / Boost converter will enter the closed-loop state; in Buck mode, when the output voltage V1 of the low-side capacitor satisfies V1 > (0.95 * V ref ), the soft-start process ends, and the Buck / Boost converter will enter the closed-loop state.

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