Isolation bidirectional converter low switching loss unipolar control method

Abstract

The invention discloses a low-switching-loss unipolar control method for an isolated bidirectional converter. The converter is composed of a direct-current source 1, a primary side full-bridge circuit, a transformer, a series resonance circuit, a secondary side full-bridge circuit and a direct-current source 2. According to the control method, the converter can always work at the resonant frequency point of the series resonant circuit, and bidirectional energy regulation and control can be realized only by adjusting the duty ratio of the switching tubes of the primary side full-bridge circuit and the secondary side full-bridge circuit; in addition, the input and output voltage relation of the resonant converter can be independent of the size and direction of the transmitted power, the bidirectional power rapid regulation and control capability is achieved, the large turn-off current brought by PWM modulation can be effectively reduced by adopting the control method, the average switching frequency in one switching period is reduced, the switching loss is further greatly reduced, and the switching efficiency is improved. The power transmission efficiency is improved, and the device is especially suitable for the technical field of high-performance bidirectional electric energy conversion of energy storage, electric automobiles, new energy and the like.

Description

Technical Field

[0001] The invention relates to a low switching loss unipolar control method for an isolated bidirectional converter, belonging to the technical field of power electronic converters, in particular to the technical field of isolated direct current-direct current electric energy conversion. Background Art

[0002] In electric vehicles, energy storage and other systems, bidirectional converters are the key to achieving energy interconnection and management. Bidirectional converters can reduce the volume, weight and cost of the system. In addition, with the popularization and application of solar photovoltaic power generation systems, the market for DC bidirectional converters is even broader. They are efficient, stable and reliable, and can improve the power generation efficiency and reliability of solar photovoltaic power generation systems. How to improve the power transmission efficiency of the converter and find a control method with superior performance, smoothness and stability are the key issues in this field.

[0003] The traditional LLC variable frequency resonant converter can realize soft switching and high frequency of semiconductor devices. However, when the input voltage range is wide and the required voltage regulation range is large, the smaller the excitation inductance is, the greater the circulating current loss of the transformer resonant cavity will be, resulting in reduced efficiency. When it is used in bidirectional applications, there are still problems such as inconsistent transmission characteristics and inability to achieve smooth switching of forward and reverse power transmission. In addition, the traditional DC bidirectional converter is mainly a two-stage architecture. In order to achieve a lighter, more efficient and smaller DC bidirectional converter, the single-stage architecture has more advantages due to its inherent high efficiency and high density.

[0004] In order to improve the voltage regulation range of the resonant converter and reduce the frequency conversion range, the patent "[1] Wu Hongfei. A bidirectional resonant converter and its control method [P]. CN: 201610578503.6, 2016-07-20" proposed a small bidirectional resonant converter that can be used in energy storage systems and photovoltaic power generation. This converter uses fixed-frequency pulse width modulation, which can perform both step-up and step-down conversions, and has the same characteristics in forward and reverse transmission. At the same time, its gain is only related to the duty cycle of the original and secondary sides, and has nothing to do with the load, which can achieve fast power transmission direction. The resonant converter and its control method need to introduce additional inductance to achieve soft switching in a wide gain range, which increases additional power loss and reduces the power density and power transmission efficiency of the converter. At the same time, under this control method, due to the use of PWM modulation, the shutdown current varies with the size of the primary and secondary duty cycle. In most of the gain range, there is a large shutdown current, and zero current shutdown cannot be achieved, which in turn causes a large shutdown loss and greatly reduces the power transmission efficiency. Summary of the invention Purpose of the invention:

[0005] The purpose of the present invention is to provide a low switching loss unipolar control method for an isolated bidirectional converter in view of the deficiencies in the prior art. The control method can make the converter always operate at the resonant frequency point of the series resonant circuit. The duty cycle of the switch tubes of the primary full-bridge circuit (10) and the secondary full-bridge circuit (30) can be adjusted to achieve bidirectional energy regulation. The input-output voltage relationship of the resonant converter can be made independent of the size and direction of the transmitted power and have the ability of bidirectional power rapid regulation. The control method of the present invention can also effectively reduce the large turn-off current caused by PWM modulation, reduce the average number of switches in a switching cycle, and thus significantly reduce the switching loss and improve the power transmission efficiency. Technical solution:

[0006] The purpose of the present invention is achieved through the following technical solutions:

[0007] The isolated bidirectional converter consists of a DC source 1 (U dc1 ), primary full-bridge circuit (10), transformer (T), series resonant circuit (20), secondary full-bridge circuit (30), DC source 2 (U dc2 ), the primary full-bridge circuit (10) is composed of a first switch tube (S 1 ), the second switch tube (S 2 )、The third switch tube (S 3 )、The fourth switch tube (S 4 ), the series resonant circuit (20) is composed of a resonant inductor (L r ) and the resonant capacitor (C r ), the secondary full-bridge circuit (30) is composed of a fifth switch tube (S 5 )、The sixth switch tube (S 6 )、The seventh switch tube (S 7 )、The eighth switch tube (S 8 ) is composed of a DC source 1 (U dc1 ) is connected to the positive electrode of the first switch tube (S 1 ) and the third switch tube (S 3 ) of the drain, the first switch tube (S 1 ) is connected to the source of the second switch tube (S 2 ) drain, the third switch tube (S 3 ) is connected to the source of the fourth switch tube (S 4 ) of the drain, the second switch tube (S 2 ) and the fourth switch tube (S 4 ) are connected to the source of DC source 1 (U dc1 ) is the negative electrode, the first switch tube (S 1 ) is connected to the primary winding (N p ) of the same name, the third switch tube (S3 ) is connected to the primary winding (N p ), and the same-name end of the secondary winding of the transformer (T) is connected to the resonant inductor (L) of the series resonant circuit (20) r ), the non-same-name end of the secondary winding of the transformer (T) is connected to the resonant capacitor (C r ) at one end, the resonant inductor (L r ) is connected to the fifth switch tube (S 5 ) and the source of the sixth switch tube (S 6 ) of the drain, the resonant capacitor (C r ) is connected to the seventh switch tube (S 7 ) and the source of the eighth switch tube (S 8 ) of the drain, the fifth switch tube (S 5 ) and the seventh switch tube (S 7 ) are connected to the source of the sixth switch tube (S 6 ) and the eighth switch tube (S 8 ) of the drain, the seventh switch tube (S 7 ) is connected to the drain of DC source 2 (U dc2 ) positive terminal, the eighth switch tube (S 8 ) is connected to the source of DC source 2 (U dc2 ) negative terminal; the first switch tube (S 1 ) and the second switch tube (S 2 ) is complementary turned on, the third switch tube (S 3 ) and the fourth switch tube (S 4 ) are complementary turned on, the first switch tube (S 1 ) and the third switch tube (S 3 ) have equal duty cycles, are switched on 180 degrees in an alternating pattern, and the first switch tube (S 1 ), the second switch tube (S 2 )、The third switch tube (S 3 )、The fourth switch tube (S 4 ) is equal to and greater than or equal to the resonant frequency of the series resonant circuit, and the fifth switch tube (S 5 )、The sixth switch tube (S 6 )、The seventh switch tube (S 7 )、The eighth switch tube (S 8 ) duty cycle is always kept at 0.5, and the fifth switch tube (S 5 ) and the sixth switch tube (S 6 ) is complementary turned on, the seventh switch tube (S 7 ) and the eighth switch tube (S 8) is complementary turned on, the fifth switch tube (S 5 ) and the seventh switch tube (S 7 ) are turned on 180 degrees in an alternating manner, and the fifth switch tube (S 5 )、The sixth switch tube (S 6 )、The seventh switch tube (S 7 )、The eighth switch tube (S 8 ) is equal to the switching frequency of the switch tube of the primary full-bridge circuit (10), wherein the first switch tube (S 1 )、The fourth switch tube (S 4 ), the fifth switch tube (S 5 )、The eighth switch tube (S 8 ) of the driving signal, the high level center is aligned, and the second switch tube (S 2 )、The third switch tube (S 3 )、The sixth switch tube (S 6 )、The seventh switch tube (S 7 )’s high level center alignment of the driving signal;

[0008] The isolated bidirectional converter has N switching cycles (1) to (N) forming a cycle, and has N working modes, wherein the control method of any Kth (K is a natural number greater than or equal to 1 and less than or equal to N) working mode is as follows:

[0009] The converter adjusts the first switch (S) in the Kth switching cycle (K) in the cycle. 1 ) to adjust the output voltage and power of the bidirectional resonant converter;

[0010] When K=1, the first switch (S 1 ) has a duty cycle less than or equal to 0.5, and then the first switch tube (S 1 ) has a duty cycle of 0;

[0011] When K=2, the first switch (S 1 ) has a duty cycle less than or equal to 0.5, and the first switch tube (S 1 ) has a duty cycle of 0.5, and then the first switch tube (S 1 ) has a duty cycle of 0;

[0012] 3<K≤N, the first switch tube (S 1 ) has a duty cycle less than or equal to 0.5, and the first switch tube (S 1) has a duty cycle of 0.5, and the first switch tube (S 1 ) has a duty cycle of 0;

[0013] The technical solution of the present invention is essentially different from the existing technical solution in that, under the present control method, the converter always operates at the resonant frequency point of the series resonant circuit, and bidirectional energy regulation can be achieved by simply adjusting the duty cycle of the switch tubes of the primary full-bridge circuit (10) and the secondary full-bridge circuit (30). The input-output voltage relationship of the resonant converter can also be made independent of the magnitude and direction of the transmitted power, and the converter has the ability to quickly regulate power in both directions. The control method of the present invention can also effectively reduce the large turn-off current caused by PWM modulation, reduce the average number of switches in a switching cycle, and thus significantly reduce the switching loss, thereby improving the power transmission efficiency.

[0014] The present invention has the following beneficial effects:

[0015] (1) The control method of the present invention can effectively reduce the large turn-off current caused by PWM modulation, reduce the average number of switches in a switching cycle, and thus significantly reduce switching losses and improve power transmission efficiency;

[0016] (2) The converter operates at the resonant frequency of the series resonant circuit, which can achieve soft turn-on of all switches over a wide voltage and load range, thereby reducing switching losses.

[0017] (3) The overall voltage regulation range of the converter is relatively wide. The voltage and current of the isolated bidirectional converter can be regulated over a wide range simply by adjusting the duty cycle of the switch tube, and a smooth DC voltage output can be achieved under any load condition. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] In order to more clearly illustrate the technical solution of the present invention, the following is a brief introduction to the drawings required for use in the embodiments;

[0019] Attached Figure 1 The schematic diagram of the isolated bidirectional converter with the resonant cavity on the secondary side;

[0020] Attached Figure 2 The schematic diagram of the isolated bidirectional converter with the resonant cavity on the primary side;

[0021] Attached Figure 3 It is the driving waveform diagram of the Kth working mode;

[0022] Attached Figure 4A comparison diagram of the average number of switching times of the switch tube of the primary full-bridge circuit (10) in one switching cycle when the input voltage, output voltage and load are the same, using the control method described in this patent and using the control method described in the patent "[1] Wu Hongfei. A bidirectional resonant converter and its control method [P]. CN: 201610578503.6, 2016-07-20";

[0023] Attached Figure 5 The figure is a comparison chart of the efficiency of multiple power test points when the output voltage is 250V using the control method described in this patent and the control method described in the patent "[1] Wu Hongfei. A bidirectional resonant converter and its control method [P]. CN: 201610578503.6, 2016-07-20" under the condition of the same input voltage and load. DETAILED DESCRIPTION

[0024] The technical solution of the present invention is described in detail below with reference to the accompanying drawings;

[0025] Figure 1 , 2 The circuit schematic diagram is shown in which the resonant cavity is placed on the secondary side and the primary side respectively. The control method of the present invention is applicable to both circuits. Figure 1 As an example, the isolated bidirectional converter consists of a DC source 1 (U dc1 ), primary full-bridge circuit (10), transformer (T), series resonant circuit (20), secondary full-bridge circuit (30), DC source 2 (U dc2 ), the primary full-bridge circuit (10) is composed of a first switch tube (S 1 ), the second switch tube (S 2 )、The third switch tube (S 3 )、The fourth switch tube (S 4 ), the series resonant circuit (20) is composed of a resonant inductor (L r ) and the resonant capacitor (C r ), the secondary full-bridge circuit (30) is composed of a fifth switch tube (S 5 )、The sixth switch tube (S 6 )、The seventh switch tube (S 7 )、The eighth switch tube (S 8 ) is composed of a DC source 1 (U dc1 ) is connected to the positive electrode of the first switch tube (S 1 ) and the third switch tube (S 3 ) of the drain, the first switch tube (S 1 ) is connected to the source of the second switch tube (S 2 ) drain, the third switch tube (S 3 ) is connected to the source of the fourth switch tube (S4 ) of the drain, the second switch tube (S 2 ) and the fourth switch tube (S 4 ) are connected to the source of DC source 1 (U dc1 ) is the negative electrode, the first switch tube (S 1 ) is connected to the primary winding (N p ) of the same name, the third switch tube (S 3 ) is connected to the primary winding (N p ), and the same-name end of the secondary winding of the transformer (T) is connected to the resonant inductor (L) of the series resonant circuit (20) r ), the non-same-name end of the secondary winding of the transformer (T) is connected to the resonant capacitor (C r ) at one end, the resonant inductor (L r ) is connected to the fifth switch tube (S 5 ) and the source of the sixth switch tube (S 6 ) of the drain, the resonant capacitor (C r ) is connected to the seventh switch tube (S 7 ) and the source of the eighth switch tube (S 8 ) of the drain, the fifth switch tube (S 5 ) and the seventh switch tube (S 7 ) are connected to the source of the sixth switch tube (S 6 ) and the eighth switch tube (S 8 ) of the drain, the seventh switch tube (S 7 ) is connected to the drain of DC source 2 (U dc2 ) positive terminal, the eighth switch tube (S 8 ) is connected to the source of DC source 2 (U dc2 ) negative terminal;

[0026] like Figure 3 As shown, the first switch tube (S 1 ) and the second switch tube (S 2 ) is complementary turned on, the third switch tube (S 3 ) and the fourth switch tube (S 4 ) are complementary turned on, the first switch tube (S 1 ) and the third switch tube (S 3 ) have equal duty cycles, are switched on 180 degrees in an alternating pattern, and the first switch tube (S 1 ), the second switch tube (S 2 )、The third switch tube (S 3 )、The fourth switch tube (S 4) is equal to and greater than or equal to the resonant frequency of the series resonant circuit, and the fifth switch tube (S 5 )、The sixth switch tube (S 6 )、The seventh switch tube (S 7 )、The eighth switch tube (S 8 ) duty cycle is always kept at 0.5, and the fifth switch tube (S 5 ) and the sixth switch tube (S 6 ) is complementary turned on, the seventh switch tube (S 7 ) and the eighth switch tube (S 8 ) is complementary turned on, the fifth switch tube (S 5 ) and the seventh switch tube (S 7 ) are turned on 180 degrees in an alternating manner, and the fifth switch tube (S 5 )、The sixth switch tube (S 6 )、The seventh switch tube (S 7 )、The eighth switch tube (S 8 ) is equal to the switching frequency of the switch tube of the primary full-bridge circuit (10), wherein the first switch tube (S 1 )、The fourth switch tube (S 4 ), the fifth switch tube (S 5 )、The eighth switch tube (S 8 ) of the driving signal, the high level center is aligned, and the second switch tube (S 2 )、The third switch tube (S 3 )、The sixth switch tube (S 6 )、The seventh switch tube (S 7 )’s high level center alignment of the driving signal;

[0027] The isolated bidirectional converter has N switching cycles (1) to (N) forming a cycle, and has N working modes, wherein the control method of any Kth (K is a natural number greater than or equal to 1 and less than or equal to N) working mode is as follows:

[0028] The converter adjusts the first switch (S) in the Kth switching cycle (K) in the cycle. 1 ) to adjust the output voltage and power of the bidirectional resonant converter;

[0029] When K=1, the first switch (S 1 ) has a duty cycle less than or equal to 0.5, and then the first switch tube (S 1 ) has a duty cycle of 0;

[0030] When K=2, the first switch (S 1) has a duty cycle less than or equal to 0.5, and the first switch tube (S 1 ) has a duty cycle of 0.5, and then the first switch tube (S 1 ) has a duty cycle of 0;

[0031] 3<K≤N, the first switch tube (S 1 ) has a duty cycle less than or equal to 0.5, and the first switch tube (S 1 ) has a duty cycle of 0.5, and the first switch tube (S 1 ) has a duty cycle of 0;

[0032] like Figure 4 As shown, under the conditions of the same input voltage, output voltage and load, the average number of switching times of the switch tube of the primary full-bridge circuit (10) in one switching cycle is compared between the control method of the present patent and the control method of the patent "[1] Wu Hongfei. A bidirectional resonant converter and its control method [P]. CN: 201610578503.6, 2016-07-20". Since K≤N, the average number of switching times of the switch tube of the primary full-bridge circuit (10) in one switching cycle using the control method of the present patent is less than or equal to that using the control method of the cited patent.

[0033] like Figure 5 As shown, under the same input voltage and load, when the output voltage is 250V, the efficiency of the control method of this patent is compared with the control method of the patent "[1] Wu Hongfei. A bidirectional resonant converter and its control method [P]. CN: 201610578503.6, 2016-07-20" at different power points. The efficiency of the control method of this patent is higher than that of the control method of the cited patent within the tested power range.

[0034] The above description is only a preferred example of the present invention and is not intended to limit the present invention. For ordinary technicians in this technical field, under the premise that the corresponding technical solution does not essentially deviate from the principle of the present invention, several improvements and modifications can be made, which should be regarded as within the protection scope of the present invention.

Claims

1. A low switching loss unipolar control method for an isolated bidirectional converter is characterized by: The isolated bidirectional converter consists of a DC source 1 (U dc1 ), primary full-bridge circuit (10), transformer (T), series resonant circuit (20), secondary full-bridge circuit (30), DC source 2 (U dc2 ), the primary full-bridge circuit (10) is composed of a first switch tube (S1), a second switch tube (S2), a third switch tube (S3), and a fourth switch tube (S4), and the series resonant circuit (20) is composed of a resonant inductor (L r ) and the resonant capacitor (C r ), the secondary full-bridge circuit (30) is composed of a fifth switch tube (S5), a sixth switch tube (S6), a seventh switch tube (S7), and an eighth switch tube (S8), wherein the DC source 1 (U dc1 ) is connected to the drain of the first switch tube (S1) and the third switch tube (S3) of the primary full-bridge circuit (10), the source of the first switch tube (S1) is connected to the drain of the second switch tube (S2), the source of the third switch tube (S3) is connected to the drain of the fourth switch tube (S4), and the sources of the second switch tube (S2) and the fourth switch tube (S4) are connected to the DC source 1 (U dc1 ), the source of the first switch tube (S1) is connected to the primary winding (N) of the transformer (T) p ), the source of the third switch tube (S3) is connected to the primary winding (N) of the transformer (T) p ), and the same-name end of the secondary winding of the transformer (T) is connected to the resonant inductor (L) of the series resonant circuit (20) r ), the non-same-name end of the secondary winding of the transformer (T) is connected to the resonant capacitor (C r ) at one end, the resonant inductor (L r ) is connected to the source of the fifth switch tube (S5) and the drain of the sixth switch tube (S6) of the secondary full-bridge circuit (30), and the resonant capacitor (C r ) is connected to the source of the seventh switch tube (S7) of the secondary full-bridge circuit (30) and the source of the eighth switch tube (S s ), the sources of the fifth switch tube (S5) and the seventh switch tube (S7) are connected to the drains of the sixth switch tube (S6) and the eighth switch tube (S8), respectively, and the drain of the seventh switch tube (S7) is connected to the DC source 2 (U dc2 ) positive terminal, the source of the eighth switch tube (S8) is connected to the DC source 2 (U dc2 ) negative terminal; The first switch tube (S1) and the second switch tube (S2) of the primary full-bridge circuit (10) are complementary turned on, the third switch tube (S3) and the fourth switch tube (S4) are complementary turned on, the first switch tube (S1) and the third switch tube (S3) have equal duty cycles, are turned on 180 degrees in an alternating manner, the switching frequencies of the first switch tube (S1), the second switch tube (S2), the third switch tube (S3) and the fourth switch tube (S4) are equal and are greater than or equal to the resonant frequency of the series resonant circuit, the duty cycles of the fifth switch tube (S5), the sixth switch tube (S6), the seventh switch tube (S7) and the eighth switch tube (S8) of the secondary full-bridge circuit (30) are always kept at 0.5, the fifth switch tube (S5) and the sixth switch tube (S6) are complementary turned on, the seventh switch tube (S7) and the eighth switch tube (S8) are complementary turned on, the fifth switch tube (S s ) and the seventh switch tube (S7) are turned on alternately by 180 degrees, the switching frequencies of the fifth switch tube (S5), the sixth switch tube (S6), the seventh switch tube (S7) and the eighth switch tube (S8) are equal to the switching frequency of the switch tube of the primary full-bridge circuit (10), wherein the high level centers of the driving signals of the first switch tube (S1), the fourth switch tube (S4), the fifth switch tube (S5) and the eighth switch tube (S8) in each switching cycle are aligned, and the high level centers of the driving signals of the second switch tube (S2), the third switch tube (S3), the sixth switch tube (S6) and the seventh switch tube (S7) are aligned; The isolated bidirectional converter has N switching cycles (1) to (N) forming a cycle, and has N working modes, wherein the control method of any Kth (K is a natural number greater than or equal to 1 and less than or equal to N) working mode is as follows: The converter adjusts the output voltage and power of the bidirectional converter by adjusting the duty cycle of the first switch tube (S1) in the Kth switching cycle (K) in the cycle; When K=1, the duty cycle of the first switch tube (S1) in the first switching cycle (1) is less than or equal to 0.5, and the duty cycle of the first switch tube (S1) in the subsequent N-1 switching cycles (2) to (N) is equal to 0; When K=2, the duty cycle of the first switch tube (S1) in the second switching cycle (2) is less than or equal to 0.5, the duty cycle of the first switch tube (S1) in the previous switching cycle (1) is equal to 0.5, and the duty cycle of the first switch tube (S1) in the subsequent N-2 switching cycles (3) to (N) is equal to 0; When 3<K≤N, the duty cycle of the first switch tube (S1) in the Kth switching cycle (K) is less than or equal to 0.5, the duty cycle of the first switch tube (S1) in the first K-1 switching cycles (1) to (K-1) is equal to 0.5, and the duty cycle of the first switch tube (S1) in the subsequent NK switching cycles (K+1) to (N) is equal to 0.

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