TWM501048U - Bidirectional DC/DC converter - Google Patents

Description

Bidirectional DC/DC converter

The present invention relates to a DC/DC converter, and more particularly to a bidirectional DC/DC converter for use in a charge and discharge system.

In traditional power conversion systems, the unidirectional DC/DC converter is the most basic power converter and the most widely used power converter. The power converter includes three basic single-ended converters. Grounded, non-isolated buck, boost, and buck-boost converters are often used between a mains supply and a load device; and bidirectional DC/DC conversion It is also widely used in battery charging and discharging systems, such as: uninterruptible power system, battery energy storage system, grid-connected energy storage system, converter-charger, uninterruptible power supply (UPS), car charging On Board Charger, various hybrid power generation systems, microgrid systems, etc. It should be noted that the input voltage is limited by the battery voltage charge and discharge state and there will be great fluctuations, and the voltage instability is quite easy to cause the power equipment. Damage.

A known buck-boost converter has a low-frequency transformer at the output end of the converter to achieve isolation and voltage level conversion, but the method has the problems of large volume, heavy weight, and low efficiency, and the other Known high-frequency transformers are smaller in size and lighter in weight. They use a bidirectional DC/DC converter architecture. Although the control is easy but the input voltage fluctuates with the battery voltage, the average transformer turns will be designed with the lowest battery voltage. At the highest battery voltage, the input voltage is too high, so it is necessary to use high withstand voltage components to increase system cost and high conduction loss; in addition to the above-mentioned bidirectional DC/DC converter architecture, there is a current source push-pull type. The circuit structure has an input terminal having an inductance of a current source. Therefore, a switching buffer circuit is required to reduce the voltage at the moment when the switch is turned off, and a surge is generated in order to improve the efficiency of the leakage energy to make the switch zero voltage switching (ZVS). Although it is further combined with a clamp circuit, it is also faced with high voltage applications, and there is still a switching voltage. Therefore, a known DC/DC converter series-connected buck-boost converter can solve the problem of large battery voltage variation and high voltage application, and it is necessary to increase the primary circuit in series, but it will reduce the working efficiency and Increase manufacturing costs.

For example, China's invention patent No. I397250 "bidirectional full-bridge zero-voltage-zero current DC/DC converter" (hereinafter referred to as the previous case) mainly includes an input inductor, a transformer, a load device, and a number of first switching components. And a plurality of second switching elements; the input inductor mainly converts an input voltage into a DC input current, the transformer includes a primary side winding and a secondary side winding, and the load device is connected to the power output end of the discharging, the number first The switching element includes a parasitic capacitance and a parasitic diode, and is connected to the primary winding of the transformer to utilize the characteristics of the resonant circuit, so that switching between turning on and off at zero voltage and zero current, the second switching element also includes a parasitic capacitor and a parasitic diode are connected to the secondary winding of the transformer, and the AC power supply provided by the transformer is continuously flowed through the power supply, and the input inductor is respectively transmitted through a resonant capacitor, a capacitor and the first switching component And connecting the second switching element, through the above structure, the main switch in the circuit structure is turned on and off Both operate in a zero voltage-zero current state to reduce conduction losses.

It can be seen from the above prior art that the input voltage of the conventional bidirectional DC/DC converter is limited by the battery voltage charging and discharging state and has a large fluctuation. Therefore, it is necessary to use a high withstand voltage component to increase the system cost and the conduction loss is high. Even if the switching off-chip is reduced by the switching buffer circuit, there is still a problem that the switching voltage is too high. If the series-connected buck-boost converter reduces the working efficiency and increases the manufacturing cost, the circuit structure of the previous case saves cost and reduces the conduction. Loss, but still not applicable to battery charging and discharging systems, especially when the input voltage varies widely due to battery voltage charging and discharging, not only to stabilize the output voltage, but also to switch all zeros to reduce conduction loss. Under the current needs of the prior art, there is indeed a need to further propose a better solution under the need of cost savings and improved conversion efficiency.

In view of the above-mentioned deficiencies of the prior art, the main object of the present invention is to provide a bidirectional DC/DC converter for use in a charging and discharging system having a battery connected between two DC power sources for bidirectional discharge/charging, The output voltage is stabilized and the input voltage can be varied widely to improve voltage conversion efficiency and reduce power loss.

The main technical means for achieving the above purpose is that the bidirectional DC/DC converter comprises: a first full bridge switching unit, which is mainly composed of first to fourth switches and forms two first nodes and Two second nodes, the two first nodes are connected to a first DC power source; a transformer having a primary side winding and a secondary side winding, the primary side winding system and the first full bridge switching unit a second node is connected; a resonant unit having two first ends and two second ends, the two first ends being connected to the secondary winding of the transformer and receiving power to generate resonance; a second full bridge switching unit, It is mainly composed of fifth to eighth switches, and forms two third nodes and two fourth nodes, wherein the two fourth nodes are connected to the second ends of the resonant unit, the two third The node is connected to a second DC power source; and a frequency conversion control module is respectively connected to the first to fourth switches of the first full bridge switching unit and the fifth to eighth switches of the second full bridge switching unit.

The novel mainly detects the state of each DC power source by the variable frequency control module, and operates the first full bridge switching unit and the second full bridge switching unit according to the state of the continuous power source, and reduces the switching losses by zero voltage switching. The variable frequency control module adjusts the voltage gain ratio by changing the working frequency and receiving the control signal to adapt to the large change of the input voltage, and performs a boost discharge mode or a step-down by controlling the first and second full bridge switching units. The charging mode provides bidirectional power conversion, which can achieve the purpose of improving voltage conversion performance and reducing power loss.

Regarding the first preferred embodiment of the novel bidirectional DC/DC converter, the DC/DC converter is mainly used in a charging and discharging system with a battery, especially when the output voltage is still varied when the input voltage is widely varied. Maintaining a steady state, as shown in FIG. 1 , comprising a first DC power source Vdc1, a second DC power source Vdc2, a first full bridge switching unit 10, a transformer 20, a resonant unit 30, and a second full In the embodiment, the first DC power source Vdc1 is composed of a chargeable and dischargeable battery, and the second DC power source Vdc2 is used for a converter (in the figure). Not shown) connection.

The first full bridge switching unit 10 is mainly composed of first to fourth switches S1 to S4, and forms two input first nodes n11 and n12 and two output second nodes n21 and n22. The first nodes n11, n12 are connected to the first DC power source Vdc1; wherein the two second nodes n21, n22 are respectively connected by the series node of the first and second switches S1, S2 and the third and fourth switches S3 And a series node of S4, wherein the two first nodes are respectively composed of parallel nodes of the first and third switches S1 and S3 and the second and fourth switches S2 and S4; in this embodiment, the first full bridge The first to fourth switches S1 to S4 of the switching unit 10 can be respectively a power transistor, and the power transistor system refers to a reinforced metal oxide field field transistor (Metal-Oxide-Semiconductor Field-Effect Transistor, MOSFET). ).

The transformer 20 has a primary winding N1 and a secondary winding N2. The primary winding N1 is connected to the two second nodes n21 and n22 of the first full bridge switching unit 10; in this embodiment, the transformer 20 further There is a magnetizing inductance Lm. When the number of turns of the winding of the transformer 20 is higher, the higher the value of the magnetizing inductance Lm, the larger the current generated.

The resonant unit 30 has two first ends and two second ends. The two first ends are connected to the secondary winding N2 of the transformer 20 and receive a DC power supply to generate resonance. In this embodiment, the resonant unit 30 is mainly composed of a resonant inductor Lr and a resonant capacitor Cr. The first ends of the resonant unit 30 are formed by the resonant inductor Lr and one end of the resonant capacitor Cr. The second ends of the resonant unit 30 are composed of the resonant inductor Lr. The other end of the resonant capacitor Cr is formed.

The second full bridge switching unit 40 is mainly composed of fifth to eighth switches S5 to S8, and forms two input third nodes n31 and n32 and two output fourth nodes n41 and n42. The second nodes n41 and n42 for the two outputs are connected to the second terminals of the resonating unit 30, and the two third nodes n31 and n32 are connected to the second DC power source Vdc2; wherein the second node N31 and n32 are respectively composed of series nodes of the fifth and sixth switches S5 and S6 and series nodes of the seventh and eighth switches S7 and S8, and the second and fourth nodes are respectively connected by the fifth and seventh switches S5 and S7. The sixth and eighth switches S6 and S8 are connected in parallel.

In this embodiment, the fifth to eighth switches S5 to S8 of the second full bridge switching unit 40 may be respectively a power transistor, and the common rate crystal system refers to an enhanced metal oxide half field effect transistor (Metal). - Oxide-Semiconductor Field-Effect Transistor, MOSFET); further, a filter capacitor Co is disposed between the two third nodes n31, n32 of the second full-bridge switching unit 40 and the second DC power source Vdc2 to filter impurities. The filter capacitor Co is connected in parallel with the second DC power source Vdc2.

The variable frequency control module 50 is respectively connected to the first to fourth switches S1 to S4 of the first full bridge switching unit 10 and the fifth to eighth switches S5 to S8 of the second full bridge switching unit 40. The module 50 detects the state of the second DC power source Vdc2, and operates the first full bridge switching unit 10 and the second full bridge switching unit 40 according to the second DC power source Vdc2, and reduces the losses of the switches S1~S8 by zero voltage switching. The variable frequency control module 50 adjusts the voltage gain ratio by changing the operating frequency and receiving the control signal to adapt to the fluctuation of the input voltage over a wide range, and controls the first full bridge switching unit 10 and the second full bridge switching unit. 40 performs a boost discharge mode or a buck charge mode to provide bidirectional power conversion, and the above method can achieve the purpose of improving voltage conversion performance and reducing power loss.

Referring to FIG. 2, the main technical content of the two-way DC/DC converter of the present invention is substantially the same as that of the first preferred embodiment. However, the variable frequency control module 50 in this embodiment. Mainly composed of a controller 51, an oscillator 52, a first trigger unit 53, a first driving unit 54, a second trigger unit 55 and a second driving unit 56; wherein the controller 51 is The first trigger unit 53 is connected to the oscillator 52 and the first driving unit 54 respectively. The second trigger unit 55 is also connected to the oscillator 52 and the second driving unit 56, respectively. The first driving unit 52 is respectively connected to the first to fourth switches S1 to S4 of the first full bridge switching unit 10, and the second driving unit 56 is respectively connected to the fifth to eighth of the second full bridge switching unit 40. Switch S5~S8 are connected.

Through the above configuration, the controller 51 can be used to detect the current signal of the second DC power source Vdc2 and receive a control signal, and control the direction of the power flow through the positive and negative values of the control signal, and the controller 51 outputs an output signal. Vcon is transmitted to the oscillator 52 for controlling the oscillation frequency thereof, and the oscillator 52 outputs a two positive/inverted signal of approximately 50% duty cycle to the first and second trigger units 53, 55, and according to the first, The second triggering unit 53 and 55 change the enabling state, so that the first and second driving units 52 and 54 respectively drive the first full bridge switching unit 10 and the second full bridge switching unit 40 to operate on the first DC power source. Vdc1 (chargeable and dischargeable battery) performs boost discharge/buck charge mode;

In this embodiment, the voltage (battery voltage) of the first DC power source Vdc1 may be 136V~200V, the voltage (output voltage) of the second DC power source Vdc2 is 380V, and the controller 51 refers to a current controller. (Current Controller), the oscillator 52 is referred to as a Voltage Control Oscillator (VCO); the second DC power source Vdc2 is being operated by the frequency conversion control module 50 changing the operating frequency and receiving the control signal. In the step-down charging mode, a range of operating voltage conversion ratio M=1~1.47 can be achieved under various powers, and the first DC power supply Vdc1 can also be converted to another working voltage by frequency conversion in the boost discharge mode. The ratio of M=1~0.68.

Referring to FIG. 3, the main technical content of the present invention is substantially the same as that of the second preferred embodiment. However, the variable frequency control module 50 in this embodiment is the same as the third preferred embodiment of the present invention. Further, a pulse width modulation module 57 and a determination module 58 are further provided, and the oscillator 52 is connected to the first trigger unit 53 through the determination module 58. The pulse width modulation module is further connected. 57 is connected to the oscillator 52 and the determining module 58 respectively; the pulse width modulation module 57 receives the output signal Vcon transmitted by the controller 51, and simultaneously receives the oscillator 52 to generate a synchronized sawtooth wave. The signal (Vramp), when the oscillation frequency of the oscillator 52 reaches a high frequency, the oscillator 52 limits the oscillation frequency to a fixed frequency, and the determining module 58 is based on the output signal of the oscillator 52, the pulse width modulation. The PWM signal of the module 57 is controlled to control the first trigger unit 53 so that the switching frequency is not increased when the power is low, the switching loss is prevented from being too large, and the switching frequency is lowered and the voltage gain is adjustable, and the voltage is also taken into account. Conversion and Low switching loss.

In summary, the novel bidirectional DC/DC converter is mainly operated by the inverter control module 50 according to the power state and the control signal, and the first full bridge switching unit 10 and the second full bridge switching unit 40 are operated at the same time. The voltage switching switch reduces the loss, and the variable frequency control module 50 can adjust the voltage gain ratio to adapt to the large change of the input voltage, and control the first and second full bridge switching units 10, 40 to perform boost discharge/buck charging. Bi-directional power conversion is provided, which can achieve the purpose of improving voltage conversion performance and reducing power loss.

10‧‧‧First full bridge switching unit
20‧‧‧Transformers
30‧‧‧Resonance unit
40‧‧‧Second full bridge switching unit
50‧‧‧Inverter control module
51‧‧‧ Controller
52‧‧‧ oscillator
53‧‧‧First trigger unit
54‧‧‧First drive unit
55‧‧‧Second trigger unit
56‧‧‧Second drive unit
57‧‧‧ Pulse Width Modulation Module
58‧‧‧Judgement module

1 is a circuit diagram of a first preferred embodiment of the present invention. Figure 2 is a circuit diagram of a second preferred embodiment of the present invention. Figure 3 is a circuit diagram of a third preferred embodiment of the present invention.

10‧‧‧First full bridge switching unit

20‧‧‧Transformers

30‧‧‧Resonance unit

40‧‧‧Second full bridge switching unit

50‧‧‧Inverter control module

Claims (10)

A bidirectional DC/DC converter comprising: a first full bridge switching unit, which is mainly composed of first to fourth switches, and forms two first nodes and two second nodes, the two a node is connected to a first DC power source; a transformer having a primary side winding and a secondary side winding, the primary side winding being connected to two second nodes of the first full bridge switching unit; The system has two first ends and two second ends, the two first ends are connected to the secondary winding of the transformer and receive power to generate resonance; and a second full bridge switching unit, mainly by the fifth to eighth switches Forming and forming two third nodes and two fourth nodes, wherein the two fourth nodes are connected to two second ends of the resonant unit, and the two third nodes are connected to a second DC power source; The variable frequency control module is respectively connected to the first to fourth switches of the first full bridge switching unit and the fifth to eighth switches of the second full bridge switching unit. The bidirectional DC/DC converter according to claim 1, wherein the resonant unit is mainly composed of a resonant inductor and a resonant capacitor, and the first ends of the resonant unit are composed of the resonant inductor and one end of the resonant capacitor. The second ends of the resonant unit are formed by the resonant inductor and the other end of the resonant capacitor. The bidirectional DC/DC converter of claim 2, wherein a filter capacitor is disposed between the two third nodes of the second full bridge switching unit and the second DC power source. The bidirectional DC/DC converter according to claim 3, wherein the variable frequency control module is mainly composed of a controller, an oscillator, a first trigger unit, a first driving unit, a second trigger unit, and a a second driving unit, the controller is connected to the oscillator, the first triggering unit is respectively connected to the oscillator, the first driving unit, and the second triggering unit is respectively connected to the oscillator, the second driving unit. The two-way DC/DC converter of claim 4, the variable frequency control module further includes a pulse width modulation module and a determination module, wherein the oscillator passes through the determination module and the first trigger unit The pulse width modulation module is connected to the oscillator and the determination module. The bidirectional DC/DC converter of claim 5, wherein the first to fourth open relationships of the first full bridge switching unit are respectively a power transistor, and the fifth to eighth of the second full bridge switching unit The open relationship is a power transistor. A bidirectional DC/DC converter as claimed in claim 6, the controller being a current controller. A bidirectional DC/DC converter as claimed in claim 7, the oscillator being a voltage controlled oscillator. The bidirectional DC/DC converter of claim 8, wherein the respective power transistors of the first full bridge switching unit and the second full bridge switching unit respectively refer to an enhanced MOS field effect transistor. The bidirectional DC/DC converter according to any one of claims 1 to 9, wherein the first DC power source is constituted by a chargeable and dischargeable battery, and the second DC power source is connected to a current transformer.