Four-switch DC-DC converter suitable for wide input voltage range

Abstract

The invention discloses a four-switch DC-DC converter suitable for a wide input voltage range, and belongs to the field of power electronic converters. The DC-DC converter uses four power semiconductor devices, can realize a buck-boost Buck-Boost function, and is called a four-switch Buck-Boost converter. The converter system comprises a power loop and a control loop, the main power loop comprises four GaN switch tubes, a power magnetic device used for energy exchange and an input and output filter capacitor, and the control loop comprises a current sampling loop and a digital controller loop. The converter mainly adopts three working modes after optimization delay for control, the minimum ripple of input inductive current can be realized, meanwhile, a mathematical model of the converter is combined, the design of control parameters is optimized, very fast dynamic response can be realized, and the working performance of the converter is verified through various experimental waveforms, so that the converter can be widely applied to the field of current control. The system is suitable for various scenes such as wind power, photovoltaic and data centers.

Description

Technical Field

[0001] The present invention belongs to the field of power electronic converters, and specifically relates to a four-switch DC-DC converter that realizes wide input voltage range regulation. Background Art

[0002] Power electronics technology has been developing continuously since its birth, and the application of related technologies has penetrated into all aspects of people's lives. This technology mainly uses power electronic devices to convert and control electric energy, and DC / DC converters play an extremely important role in it. DC / DC converters convert different input voltages into specific input voltages and maintain the stability of the output voltage. However, the input voltage range is not completely controlled by humans. In real life, we often encounter some special situations that make the input voltage of the equipment exceed the normal range. This puts forward a new requirement for DC / DC converters, that is, how to better adapt to this wide input voltage range.

[0003] In fact, in people's daily lives, there are many situations in which the input voltage changes over a wide range. For example, grid voltage fluctuations, changes in the working environment, etc. may cause the input voltage to change significantly. When the input voltage changes over a large range, it may cause the system to oscillate, making the control system parameters originally designed by the engineer no longer applicable, and at the same time reducing the conversion efficiency of the converter.

[0004] Therefore, we need a DC / DC converter that can adapt to a wide input range, and convert the input voltage with a large range of changes into a stable voltage value required by industrial production and life. However, when the input voltage changes in a large range, it is difficult for the DC / DC converter to ensure a relatively ideal efficiency in the full input range: when the input voltage is low, because the required output power is certain, the input current will be large, and the current will flow through the switch tube, resulting in large conduction losses; and when the input voltage is high, it will cause the switching loss of the switch tube to increase. However, with the development of digital control technology, many new control methods and strategies have emerged. These control methods can effectively improve the efficiency of the system and keep the system stable. The wide input voltage range power supply modules produced by mainstream switching power supply manufacturers on the market today usually have an input voltage range of only 1:4, and their control strategy is generally analog control. The efficiency of the entire system is easily affected by changes in input voltage. Therefore, it is of far-reaching significance to study wide input voltage range DC / DC converters and methods to improve the efficiency of such converters. Summary of the invention

[0005] In order to solve the above technical problems, the present invention provides the following technical solutions:

[0006] First, the present invention proposes a three-working mode DC-DC converter. The converter system includes two parts: a power circuit and a control circuit. The main power circuit includes four GaN switching tubes, power magnetic devices for energy exchange, and input and output filter capacitors. The control circuit includes a current sampling circuit and a digital controller circuit.

[0007] The control method of the converter proposed in the present invention is relatively diverse, with three basic working modes: Buck, Boost, and Buck-Boost. Q1 and Q2 are always complementary and turned on, and the duty cycle of Q1 is set to D1; Q3 and Q4 are always complementary and turned on, and the duty cycle of Q4 is set to D2.

[0008] The average voltage across the inductor is given by:

[0009]

[0010] According to the relationship between inductor volt-second balance, the input voltage V in and output voltage V out The basic relationship is as follows:

[0011]

[0012] When Q1 and Q4 are turned on at the same time, the inductor current increases; when Q1 and Q4 are turned off at the same time, the inductor current decreases; when Q1 is turned off and Q4 is turned on, the inductor current remains unchanged; when Q1 is turned on and Q4 is turned off, the inductor current is around V in ≤V out Reduced, at V in >V out When increased.

[0013] When the converter reaches steady state, the increase in inductor current is equal to the decrease in inductor current in each switching cycle. in ≤V out , the inductor current will increase only when Q1 and Q4 are turned on at the same time, so the inductor current ripple is determined by the overlapping on-time Tolp_on of Q1 and Q4. in >V out , the inductor current will only decrease when Q1 and Q4 are turned off at the same time, and the inductor current ripple is determined by the overlapping off-time Tolp_off of Q1 and Q4. Shortening the overlapping on-time Tolp_on or off-time Tolp_off can reduce the inductor current ripple.

[0014] When V in ≤V out During the time when Q4 is turned off or Q1 and Q4 are turned on at the same time, the change in the inductor current is the inductor current pulsation, and the corresponding inductor voltages are V in -Vout and V in .

[0015] When V in >V out When Q1 is turned on or Q1 and Q4 are turned off at the same time, the change in the inductor current is the inductor current pulsation, and the corresponding inductor voltages are V in -V out and -V out .

[0016] The expression of inductor current ripple is as follows:

[0017]

[0018] The average value of the inductor current is:

[0019]

[0020] By integrating the inductor current within one cycle, the effective value of the inductor current can be obtained:

[0021]

[0022] The three-mode control strategy implemented in the present invention introduces a buck-boost mode in a voltage interval near the switching point. Assuming the length of the interval is 2ΔV, 200-ΔV and 200+ΔV are two new switching points. When Vin<200-ΔV and Vin>200+ΔV, the FSBB converter operates in Boost mode and Buck mode respectively, and when Vin is in the interval [200-ΔV, 200+ΔV], the FSBB converter operates in Buck-Boost mode. Therefore, we call it a three-mode control method.

[0023] In order to increase the direct power ratio in Buck-Boost mode, we should try to increase D1 and reduce D2. Therefore, we can choose to let D1 work at a fixed maximum duty cycle Dm and only control D2 to adjust the output voltage of the converter. Then D2 can be expressed as:

[0024]

[0025] When Vin changes within the interval [200-ΔV, 200+ΔV], the maximum and minimum values ​​of D2 are:

[0026]

[0027]

[0028] The duty cycle of the switching power supply is designed to vary between 0.1 and 0.9, so ΔV=10 and Dm=0.85 are determined. The input voltage range corresponding to the Buck-Boost mode is [190V, 210V], and the corresponding range of D2 is [0.1, 0.2].

[0029] At the same time, the inductor current pulsation of the converter under three-mode control can be obtained as:

[0030]

[0031] The effective value of the inductor current is:

[0032]

[0033] In this way, the expression of the effective value of the inductor current is converted into a formula related to the inductance, frequency, and working range. By optimizing the selection of these parameters, a three-working mode DC-DC converter with optimized delay and efficiency can be obtained, which is further explained below through the accompanying drawings and implementation methods. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 A circuit topology diagram of a wide input DC-DC converter with three working modes provided by an embodiment of the present invention;

[0035] Figure 2 A converter gain surface diagram provided by an embodiment of the present invention;

[0036] Figure 3 A current variation diagram of the Boost working mode provided by an embodiment of the present invention;

[0037] Figure 4 A current conversion diagram of the Buck working mode provided by an embodiment of the present invention;

[0038] Figure 5 A diagram of power conversion efficiency in three working modes provided by an embodiment of the present invention;

[0039] Figure 6 A parameter range definition diagram for the Buck-Boost working mode provided by an embodiment of the present invention;

[0040] Figure 7 A closed-loop control circuit diagram provided for an embodiment of the present invention;

[0041] Figure 8 A converter simulation circuit diagram provided by an embodiment of the present invention;

[0042] Fig. 9 A small signal modeling diagram of a converter provided in an embodiment of the present invention;

[0043] Fig.10 A control flow chart of a converter operation mode provided by an embodiment of the present invention;

[0044] Fig.11 Buck mode simulation waveform diagram provided by the embodiment of the present invention;

[0045] Fig.12 Buck-Boost mode simulation waveform diagram provided by an embodiment of the present invention;

[0046] Fig.13 This is a Boost mode simulation waveform diagram provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0047] like Figure 1 As shown, it is a power circuit topology diagram of an embodiment of the present invention. The main power circuit uses four power semiconductor switching devices, usually MOS tubes or GaN tubes, wherein GaN tubes are usually used in occasions with lower voltage levels. The four switching devices are symmetrically distributed on both sides of the power inductor and should generally be of the same model. The switching tubes Q1 and Q2 are located on the input filter capacitor C1 side, and the switching tubes Q3 and Q4 are located on the output filter capacitor C2 side. The switching devices on both sides each form a half-bridge structure, and the whole can be regarded as a special H-bridge circuit structure.

[0048] like Figure 2 As shown, the gain of the converter is only related to D1 and D2. And D1 and D2 can be controlled independently, so the FSBB converter has two control degrees of freedom, D1 and D2, and has multiple control schemes, which is conducive to the optimal design and control of the converter. Figure 2 The relationship between the gain and duty cycle of the FSBB converter is given. When the duty cycles D1 and D2 vary between 0.1 and 0.9, the gain range of the converter is 0.111~9.

[0049] In order to study the inductor current under different switching states, it is necessary to assume that the switching frequency of Q1 and Q4 is the same. The change of the inductor current in one switching cycle is as follows: Figure 3 and Figure 4 shown.

[0050] Figure 5The curve of the direct power ratio of the converter changing with the input-output voltage relationship is given. For DC / DC converters, direct power transmission can reduce device stress, reduce energy storage during power transmission, and improve efficiency. When the converter transmission power is constant, the ratio of direct power to output power Pdirect / Po is called the direct power ratio. Since the power transmission mode of Buck converter and Boost converter depends on whether the circuit is in the on-state of the switch tube, their direct power ratio can be expressed by the duty cycle D. The direct power ratios of Buck and Boost are D and 1-D respectively, while the direct power ratio of Buck-Boost is 0 because there is no direct power transmission in the whole stage.

[0051] Furthermore, it can be seen from the relationship curve that the direct power ratio of both the Buck converter and the Boost converter is large when the input and output voltages are close. When the output voltage is constant, the wider the input voltage range, the smaller their direct power ratio and the lower the efficiency. The direct power ratio of the Buck-boost converter is always 0, which makes it difficult to achieve high efficiency.

[0052] Figure 6 The parameter interval current waveform diagram in the Buck-Boost working mode. According to the voltage value across the inductor at this time, it can be concluded that the pulsation value of the inductor current in the Buck-Boost mode is:

[0053]

[0054] Under the dual-edge modulation strategy, the four-switch Buck-Boost converter working in the Buck-Boost working mode, in order to minimize the inductor current ripple value, we set the duty cycle D1 to be 0.85, and from the gain relationship between the output voltage and the output voltage, we can get:

[0055]

[0056] It can be concluded that the inductor current ripple value in Buck-Boost working mode is:

[0057]

[0058] The inductor current ripple rate in Buck-Boost mode is:

[0059]

[0060] We hope that the ripple rate of the inductor current is less than 50%, so we can calculate the inductor value in the Buck-Boost working mode, that is:

[0061]

[0062] like Figure 7 The system block diagram shown is a voltage negative feedback closed-loop system control block diagram of a four-switch Buck-Boost converter. The voltage divider in the system block diagram is a sampling circuit that samples and conditions the output voltage. The voltage after the voltage divider is compared with the reference voltage preset by the controller to generate an error voltage, which will be sent to the compensation network we designed. After the error signal is corrected by the compensation network, it will generate the control voltage signal we need. The control voltage signal will be compared with the pulse width modulator to generate a PWM modulation signal. Finally, the PWM modulation signal controls the on and off of the switch tube of the four-switch Buck-Boost converter through the drive circuit to control the output voltage to ensure that the output voltage can be closed-loop regulated.

[0063] PSIM is a professional simulation software in the field of power electronics. Figure 8 That is, a circuit simulation model built using PSIM is used to verify the control method proposed in the present invention.

[0064] The converter loop control parameters should be designed according to the mathematical model. Fig. 9 The converter small signal modeling provided by the present invention is based on the inductor current i L (t) and capacitor voltage v C (t) as two independent state variables, the input voltage v in (t) as input variable, output voltage v o (t) and input current v in (t) as the output variable.

[0065] During the conduction period of the switch tube Q1, the equation can be listed as follows:

[0066]

[0067]

[0068]

[0069] During the off period of the switch tube Q1, the equation can be listed as follows:

[0070]

[0071]

[0072]

[0073] Substitute the following expression:

[0074]

[0075] Can be obtained:

[0076]

[0077]

[0078] From the static operating point equation:

[0079]

[0080] Substituting in:

[0081]

[0082] Take the switching cycle average value of the state equation:

[0083] Introduce a small signal disturbance:

[0084]

[0085] Assuming that the steady-state DC component is much larger than the AC disturbance and ignoring the second-order AC term, we can get:

[0086] Changing to a scalar equation gives:

[0087]

[0088] By performing Laplace transform on the above formula, we can get the transfer function in Buck mode:

[0089] Similarly, there is a transfer function in Boost mode:

[0090]

[0091] The transfer function in Buck-Boost mode is:

[0092]

[0093] Through the transfer function of small signal modeling, the closed loop parameters are designed, and the three working modes are controlled by the digital controller, such as Fig.10 This is the control flow chart of the digital controller. When the control program enters an interrupt, the controller will determine the voltage sampling value input through the sampling circuit. If the voltage sampling value is within the corresponding working mode range, the controller will enter the corresponding working mode and output the corresponding PWM control signal. Otherwise, the controller will enter the fault mode and will not output any signal to the outside.

[0094] like Figures 11 to 13Shown are the simulation circuit waveforms of the three working modes under this control method. The waveforms are input voltage, output voltage, inductor current, and main switch drive. It can be seen from the waveforms that the converter can smoothly switch between the three working modes, and greatly reduce the delay of the controller and improve work efficiency.

[0095] This example uses the PSIM simulation model and small signal mathematical modeling to test and verify the three-mode switching of the converter. By adding a delay interval, the problems of smooth switching and working delay between modes are solved, and the high efficiency and high frequency of the converter are achieved. It is suitable for wide input range DC-DC converter application scenarios.

[0096] The above content is a further detailed description of the present invention in combination with specific implementation methods, but it cannot be determined that the specific implementation method of the present invention is limited to the above description. For ordinary technicians familiar with the technical field to which the present invention belongs, several simple deductions or substitutions made without departing from the concept of the present invention should be regarded as falling within the scope of protection of the present invention.

Claims

1. A four-switch DC-DC converter with a wide input voltage range, characterized by: Four power semiconductor devices are used to achieve the buck-boost function of stepping up and down voltage, which is called a four-switch buck-boost converter. The converter system consists of two parts: the power circuit and the control circuit. The main power circuit includes four GaN switch tubes, power magnetic devices for energy exchange, and input and output filter capacitors. The control circuit includes a current sampling circuit and a digital controller circuit.

2. The four-switch DC-DC converter according to claim 1, wherein: The main power circuit uses four power semiconductor switching devices, usually MOS tubes or GaN tubes. GaN tubes are usually used in occasions with lower voltage levels. The four switching devices are symmetrically distributed on both sides of the power inductor and should generally be of the same model. The switching tubes Q1 and Q2 are located on the input filter capacitor C1 side, and the switching tubes Q3 and Q4 are located on the output filter capacitor C2 side. The switching devices on both sides each form a half-bridge structure, and the whole can be regarded as a special H-bridge circuit structure.

3. The special H-bridge structure as claimed in claim 2, characterized in that: The connection is made through the power inductor L1, wherein the switching devices Q1 and Q2 on the input side are complementary turned on, and the switching devices Q3 and Q4 on the output side are complementary turned on. The switching devices Q1 and Q3 are main devices. The phase difference and the switching period between the main devices Q1 and Q3 will affect the power transmission of the circuit, and the switching frequency will affect the input current ripple on the power inductor L1.

4. The main devices Q1 and Q3 according to claim 3, characterized in that: The phase difference and switching period between Q1 and Q3 are determined by the feedforward circuit of the input voltage. The three working modes include Buck, Boost, and Buck-Boost, which are determined by the output voltage V o With input voltage V in It is determined by the relationship between the three voltage levels, namely, boost, buck, and buck-boost.

5. The feedforward circuit according to claim 4, characterized in that: It is an op amp sampling circuit built to detect the relationship between input voltage and output voltage. The voltage needs to be added to the voltage closed loop to ensure the stability of the converter system. The sampling circuit detects the input voltage value, and inputs it to the digital controller after analog-to-digital conversion. The digital controller calculates and outputs the PWM wave to the driver of the switching device to control the switch tube to open and close. The principle of mode switching of the digital controller is: convert the expected output voltage into a digital quantity and store it in the comparator. When the input voltage digital conversion value is lower than the expected output voltage value, the controller outputs the Boost mode PWM wave; when the input voltage digital conversion value is higher than the expected output voltage value, the controller outputs the Buck mode PWM wave; when the input voltage digital conversion value is in the dead zone around the expected output voltage value, the controller outputs the Buck-Boost mode PWM wave.

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