Control method of bidirectional quasi-parallel resonant converter

Abstract

The invention discloses a control method of a bidirectional quasi-parallel resonant converter, the bidirectional quasi-parallel resonant converter is composed of a main converter and an auxiliary converter, the circuit topology of the main converter selects an LLC resonant converter, the auxiliary converter selects a Buck / Boost converter, and the main converter and the auxiliary converter are connected in an input-parallel output-series mode. The transmission power ratio of the main converter to the auxiliary converter is equal to the output voltage ratio. The main converter works in an open-loop state, the switching frequency is fixed at the resonant frequency, the efficiency of the main converter is highest at the moment, so that the main converter transmits most power, and the auxiliary converter plays a role in closed-loop control of the system voltage. According to the control method disclosed by the invention, firstly, the low-voltage side input voltage is detected, whether the auxiliary converter needs to be started or not is judged, the main converter is ensured to bear most power, and when the low-voltage side input voltage is reduced, a method of adjusting the duty ratio of the auxiliary converter is adopted, so that the voltage closed-loop control of the system is ensured.

Description

TECHNICAL FIELD

[0001] The application relates to a control method of a bidirectional quasi-parallel resonant converter, and belongs to the technical field of power electronic converters. BACKGROUND

[0002] In recent years, wide-bandgap semiconductor devices represented by silicon carbide and gallium nitride have developed rapidly, promoting the development of power electronic converters to high frequency. However, with the increase of switching frequency, the problem of increased switching loss and low efficiency also arises. Soft switching technology can effectively reduce switching loss by realizing zero-voltage turn-on (ZVS) and zero-current turn-off (ZCS).

[0003] LLC resonant converters have attracted attention from academia and industry due to their soft switching and high power density. For LLC resonant converters, PFM control is generally used, but the change of switching frequency will cause the shift of resonant point, and the circulating current and reactive loss of the converter will increase significantly, so it is difficult for the resonant converter to maintain high efficiency under wide input application, and the design of magnetic elements of the resonant converter is also difficult. Therefore, the traditional single-pole LLC resonant converter cannot meet the requirement of maintaining high efficiency under wide input application. In order to solve the contradiction between high efficiency and voltage regulation capability of the resonant converter under wide input application, some scholars improve the control method to expand the gain of the converter. However, it is still difficult to solve the contradiction between the efficiency and the gain of the LLC resonant converter by improving the control method only. SUMMARY

[0004] The application provides a control method of a bidirectional quasi-parallel resonant converter, which can solve the problems and defects in the prior art. First, the low-voltage side input voltage is detected to determine whether the auxiliary converter needs to be started, so that most of the power is borne by the main converter. When the low-voltage side input voltage decreases, the duty cycle of the auxiliary converter is adjusted to ensure the voltage closed-loop control of the system.

[0005] Technical scheme: The application provides a control method of a bidirectional quasi-parallel resonant converter. The bidirectional quasi-parallel resonant converter mainly comprises a main converter and an auxiliary converter, which are connected in parallel input and series output mode. The ratio of the power transmitted by the main converter to the power transmitted by the auxiliary converter is equal to the ratio of the output voltages. The main converter works in an open-loop state, and the switching frequency is fixed at the resonant frequency. At this time, the efficiency of the main converter is the highest, so the main converter transmits most of the power, and the auxiliary converter plays a role in the voltage closed-loop control of the system. The method comprises the following steps: Step Step1: setting the duty cycle of the main converter D m = 0.5, and then entering step Step2; Step Step2: detecting the low-voltage side input voltage UL , main converter output voltage U 1, auxiliary converter output voltage U 2, then enter Step 3; Step 3: set the output voltage reference value of the system U ref , and determine U L whether it is greater than U ref / N , where N is the transformer ratio of the transformer in the main converter; when U L ≥ U ref / N Step 4: set the duty cycle signal Step 4: set the duty cycle signal D a = 0, the auxiliary converter does not work, and all the power is borne by the main converter, and then the control method ends; Step 5: set the initial value D a = 0.5, and calculate the reference voltage of the auxiliary converter U aref , then enter Step 6; Step 6: auxiliary converter closed-loop regulation, then enter Step 7; Step 7: calculate the duty cycle signal D a , and the control method ends.

[0006] The circuit topology of the main converter selects a bidirectional LLC resonant converter, and the auxiliary converter selects a bidirectional double-tube Buck / Boost converter. BRIEF DESCRIPTION OF DRAWINGS

[0007] Figure 1 is the main circuit of the bidirectional quasi-parallel resonant converter in the embodiment of the application; Figure 2 is the main waveform schematic diagram of the bidirectional quasi-parallel resonant converter in the embodiment of the application when working in the forward direction; Figure 3 is the working principle diagram of mode 1 of the bidirectional quasi-parallel resonant converter in the embodiment of the application when working in the forward direction; Figure 4 is the working principle diagram of mode 2 of the bidirectional quasi-parallel resonant converter in the embodiment of the application when working in the forward direction; Figure 5The working principle diagram of mode 3 of the bidirectional quasi-parallel resonant converter in the embodiment of the present application when working in the forward direction; Figure 6 The working principle diagram of mode 4 of the bidirectional quasi-parallel resonant converter in the embodiment of the present application when working in the forward direction; Figure 7 The main waveform schematic diagram of the bidirectional quasi-parallel resonant converter in the embodiment of the present application when working in the reverse direction; Figure 8 The working principle diagram of mode 1 of the bidirectional quasi-parallel resonant converter in the embodiment of the present application when working in the reverse direction; Figure 9 The working principle diagram of mode 2 of the bidirectional quasi-parallel resonant converter in the embodiment of the present application when working in the reverse direction; Figure 10 The working principle diagram of mode 3 of the bidirectional quasi-parallel resonant converter in the embodiment of the present application when working in the reverse direction; Figure 11 The working principle diagram of mode 4 of the bidirectional quasi-parallel resonant converter in the embodiment of the present application when working in the reverse direction; Figure 12 The voltage closed-loop control flow chart in the embodiment of the present application. DETAILED DESCRIPTION

[0008] The present application will be further illustrated below in conjunction with specific embodiments, which should be understood as merely illustrating the present application but not limiting the scope of the present application, and various equivalent modifications of the present application made by those skilled in the art after reading the present application all fall within the scope defined by the claims of the present application.

[0009] The control method of the bidirectional quasi-parallel resonant converter, the implementation of the method is based on two input parallel output series bidirectional converters, one bidirectional LLC resonant converter as the main converter, and the other as the auxiliary converter, the method comprises the following steps: Step 1: setting the duty cycle of the main converter D m = 0.5, and then entering Step 2; Step 2: detecting the low-voltage side input voltage U L , the main converter output voltage U 1, the auxiliary converter output voltage U 2, and then entering Step 3; Step 3: setting the output voltage reference value of the system U ref , and determining U L whether it is greater thanU ref / N wherein N is the transformation ratio of the transformer in the main converter; when U L ≥ U ref / N Step 4 is entered; otherwise, Step 5 is entered; Step Step 4: setting D a =0, the auxiliary converter is not working, and all the power is borne by the main converter, and then the control method ends; Step Step 5: setting the initial value D a =0.5, and calculating the reference voltage U aref of the auxiliary converter, and then Step 6 is entered; Step Step 6: the auxiliary converter is closed-loop regulated, and then Step 7 is entered; Step Step 7: calculating the duty cycle signal D a , and then the control method ends.

[0010] The main converter duty cycle D m =0.5, and the switching frequency is fixed at the resonance frequency.

[0011] The implementation of the method is based on a bidirectional quasi-parallel resonant converter, the bidirectional quasi-parallel resonant converter comprising a main converter and an auxiliary converter, connected in the manner of input parallel and output series; the duty cycle of the ninth switch tube S9 of the auxiliary converter is D a .

[0012] Step Step 5 calculates the reference voltage U aref of the auxiliary converter U aref = U ref - U 1.

[0013] Step Step 7 calculates the duty cycle signal D a , wherein D a = U aref / U L .

[0014] When the bidirectional quasi-parallel resonant converter is operating in the forward direction, one cycle can be divided into four stages, let t i Representing time points, i = 0, 1, 2, 3, 4, specifically as follows: Mode 1 [t0-t1]: such as Figure 3 As shown, the first switch S1 and the fourth switch S4 are simultaneously turned on, while the second switch S2 and the third switch S3 are turned off. The resonant current i Lr Greater than the excitation current i Lm， Energy is transferred from the primary side to the secondary side of the transformer. The anti-parallel diodes of the fifth switch S5 and the eighth switch S8 are turned on. At this time, the magnetizing inductance L m clamped in U 1 / N L r and C r Participating in resonance. The ninth switch, S9, turns on, affecting the inductor L. b Charging, i b Linear increase.

[0015] Mode 2 [t1-t2]: such as Figure 4 As shown, the first switch S1, the second switch S2, the third switch S3, and the fourth switch S4 are all turned off. Lr equals i Lm The primary side of the transformer no longer transfers energy to the secondary side, and the magnetizing inductance L... m No longer clamped, L r C r and L m All three components participate in resonance. The ninth switch, S9, is turned off, and the inductor L... b Discharge, i b Linear decrease.

[0016] Mode 3 [t2-t3]: such as Figure 5 As shown, the second switch S2 and the third switch S3 are simultaneously turned on, while the first switch S1 and the fourth switch S4 are turned off. The anti-parallel diodes of the sixth switch S6 and the seventh switch S7 are turned on, L r and C r Participating in resonance, magnetizing inductance L m Clamped in - U 1 / N L b Continuous discharge.

[0017] Mode 4 [t3-t4]: such as Figure 6 As shown, the first switch S1, the second switch S2, the third switch S3, and the fourth switch S4 are all turned off. Lr =i LmThe primary side of the transformer no longer transfers energy to the secondary side. Magnetizing inductance L m No longer clamped, L r C r and L m All three components participate in resonance. At time t4, the inductor L... b Discharge ends.

[0018] When the bidirectional quasi-parallel resonant converter operates in reverse, one cycle can be divided into four stages, let t i Representing time points, i = 0, 1, 2, 3, 4, specifically as follows: Mode 1 [t0-t1]: such as Figure 8 As shown, the fifth switch S5 and the eighth switch S8 are turned on simultaneously, while the sixth switch S6 and the seventh switch S7 are turned off. At this time, i Lr When the voltage is negative, the anti-parallel diodes of the first switch S1 and the fourth switch S4 conduct, and energy is transferred from the secondary side of the transformer to the primary side. The tenth switch S... 10 Turn on, for inductor L b Charging, i b Linear increase.

[0019] Mode 2 [t1-t2]: such as Figure 9 As shown, the fifth switch S5, the sixth switch S6, the seventh switch S7, and the eighth switch S8 are all turned off. Lr The value is still negative. The anti-parallel diodes of the first switch S1 and the fourth switch S4 are turned on, and the tenth switch S1... 10 Off, inductor L b Discharge, i b Linear decrease.

[0020] Mode 3 [t2-t3]: such as Figure 10 As shown, the sixth switch S6 and the seventh switch S7 are turned on simultaneously, while the fifth switch S5 and the eighth switch S8 are turned off. At this time, i Lr When the signal is positive, the anti-parallel diodes of the second switch S2 and the third switch S3 conduct, transferring energy from the secondary side of the transformer to the primary side, and the inductor L... b Continuous discharge.

[0021] Mode 4 [t3-t4]: such as Figure 11 As shown, the fifth switch S5, the sixth switch S6, the seventh switch S7, and the eighth switch S8 are all turned off. Lr The current is still positive. The anti-parallel diodes of the second switch S2 and the third switch S3 are turned on. At time t4, the inductor L... b Discharge ends.

[0022] In the examples of the present application, the bidirectional quasi-parallel resonant converter, the working principle analysis: the essence is to connect a main converter and an auxiliary converter in parallel input, output series connection, the output voltage value of the main converter U 1 and the output voltage value of the auxiliary converter U 2, the voltage relationship satisfies:

[0023] The forward voltage gain and the reverse voltage gain of the system of (1) and (2) can be represented as:

[0024] If the transformer ratio N is determined, only by adjusting the duty cycle of the auxiliary converter, the gain of the whole system can be controlled. The main converter has good soft switching characteristics and high transmission efficiency, and the switching frequency is fixed near the resonance point, which is similar to a DC transformer, and the efficiency is the highest, so most of the power is transmitted by the main converter, but it can only realize fixed ratio voltage conversion, and loses the voltage regulation capability. The control method disclosed by the present application judges whether to enable the auxiliary converter and controls the duty cycle of the auxiliary converter D a , on the one hand, it ensures that the main converter transmits most of the power, and on the other hand, it ensures the closed-loop control of the output voltage of the system.

Claims

1. A control method for a bidirectional quasi-parallel resonant converter, characterized in that, The bidirectional quasi-parallel resonant converter mainly consists of a main converter and an auxiliary converter. The method includes the following steps: Step 1: Set the duty cycle D of the main converter m =0.5, then proceed to Step 2; Step 2: Detect the low-voltage side input voltage U L First, determine the output voltage U1 of the main converter and the output voltage U2 of the auxiliary converter, then proceed to step 3. Step 3: Set the system's output voltage reference value U ref And determine U L Is it greater than U? ref / N, where N is the turns ratio of the transformer in the main converter; when U L ≥U ref If / N, proceed to step 4; otherwise, proceed to step 5. Step 4: Set the air ratio signal D a =0, the auxiliary converter does not work, all power is borne by the main converter, and then the control method ends; Step 5: Set the initial value D a =0.5, and calculate the reference voltage U of the auxiliary converter. aref Then proceed to Step 6; Step 6: Auxiliary converter closed-loop adjustment, then proceed to Step 7; Step 7: Calculate the duty cycle signal D a Then the control method ends.

2. The control method for the bidirectional quasi-parallel resonant converter according to claim 1, characterized in that, The main converter uses a bidirectional LLC resonant converter as its circuit topology, and the auxiliary converter uses a bidirectional dual-transistor Buck / Boost converter.

3. The control method for the bidirectional quasi-parallel resonant converter according to claim 1, characterized in that, The duty cycle D of the main converter m =0.5, the switching frequency is fixed at the resonant frequency.

4. The control method for the bidirectional quasi-parallel resonant converter according to claim 1, characterized in that, The control method is implemented based on a bidirectional quasi-parallel resonant converter, which includes a main converter and an auxiliary converter, connected in parallel input and series output configuration; the duty cycle of the ninth switch S9 in the auxiliary converter is D. a .

5. The control method for the bidirectional quasi-parallel resonant converter according to claim 1, characterized in that, Step 5 involves calculating the reference voltage U of the auxiliary converter. aref for U aref = U ref - U1.

6. The control method for the bidirectional quasi-parallel resonant converter according to claim 1, characterized in that, Step 7 calculates the duty cycle D of the ninth switch S9. a for D a = U aref / U L 。

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