Bidirectional buck-boost DC conversion device

Abstract

The utility model relates to a bidirectional buck-boost DC conversion device, which aims to solve the technical problem that the current DC conversion device cannot ensure high-efficiency energy transmission in two modes, and is composed of a battery BAT, a pre-charging circuit, a DC EMI, an input capacitor, a Buck-Boost inductor, a half-bridge power semiconductor IGBT and an output capacitor. The pre-charging circuit comprises a relay and a half-bridge power semiconductor IGBT, the relay and the half-bridge power semiconductor IGBT are connected in series through a switch, and the relay and the half-bridge power semiconductor IGBT are connected in series with a battery BAT through wires; the direct current EMI is connected in series with the direct current circuit breaker and the battery BAT through wires; current is output by a DC positive electrode, is connected to the bidirectional converter in series through the output capacitor and is connected with the Buck-Boost inductor in parallel through a wire, the bidirectional half-bridge converter (Buck-Boost converter) and voltage and current double-closed-loop PI control strategy is adopted, the circuit topological structure is simple and high in reliability, and power expansion is easy to achieve through multi-stage parallel connection.

Description

Technical Field

[0001] This utility model relates to the field of DC-DC converters, specifically a bidirectional buck-boost DC-DC converter. Background Technology

[0002] Bidirectional DC-DC converters are an important conversion device in power electronics technology. Their core function is to achieve bidirectional conversion of DC voltage, that is, to convert low voltage to high voltage and vice versa. This feature makes them indispensable in many applications that require bidirectional energy flow, such as energy storage systems, electric vehicles, distributed generation, and renewable energy integration systems.

[0003] According to publicly available patent CN320111, a bidirectional buck-boost DC-DC converter is disclosed. This converter consists of an input DC voltage source module, seven identical power switches (S1-S7), an inductor (L), and a load. Its topology can operate in two modes: boost mode and buck mode. In each different operating mode, only one power switch operates at high frequency, significantly reducing switching losses and improving the converter's conversion efficiency to achieve the desired power conversion. Simultaneously, this converter requires only one magnetic inductor, thus reducing the converter's cost and size. In realizing this invention, the inventors discovered that at least the following problems remain unsolved in the prior art. Currently, there are various topologies of this type of converter on the market, which can be broadly divided into two types:

[0004] 1. Isolated bidirectional DC-DC converters use an isolation transformer + power semiconductor + filter capacitor method for main transformer power conversion, and are mostly used in civil equipment; due to the limitations of transformer technology and power, their conversion power is mostly below 10kW, and the control strategy is relatively complex.

[0005] 2. Non-isolated bidirectional DC-DC converters, which employ an inductor + power semiconductor + filter capacitor approach for main transformer power conversion, are mostly used in industrial equipment. Therefore, a new technical solution needs to be designed to address this issue. Utility Model Content

[0006] The purpose of this invention is to overcome the shortcomings of the existing technology, adapt to the needs of reality, and provide a bidirectional buck-boost DC-DC converter to solve the technical problem that current DC-DC converters cannot guarantee efficient energy transmission in both modes.

[0007] To achieve the objectives of this utility model, the technical solution adopted is as follows: A bidirectional buck-boost DC-DC converter is designed, comprising a battery (BAT), a pre-charge circuit, a DC EMI converter, an input capacitor, a Buck-Boost inductor, a half-bridge power semiconductor IGBT, and an output capacitor. The pre-charge circuit includes a relay and a half-bridge power semiconductor IGBT, which are connected in series via a switch and connected in series with the battery (BAT) via wires. The DC EMI converter is connected in series with a DC circuit breaker and the battery (BAT) via wires. Current is output from the positive terminal of the DC converter and connected in series with the output capacitor, and in parallel with the Buck-Boost inductor via wires. The output capacitor is connected in parallel to the DC EMI circuit with the positive terminal at the top and the negative terminal at the bottom, and connected in series with the positive terminal of the battery (BAT) via the input capacitor, with positive terminals to positive terminals and negative terminals to negative terminals.

[0008] Preferably, the pre-charging circuit is used to charge the input capacitor and the output capacitor to prevent overcurrent when the DC circuit breaker is closed.

[0009] Preferably, the positive terminal of the pre-charge circuit is connected in series with the positive terminal of the battery BAT, the negative terminal of the pre-charge circuit is connected in series with the positive terminal of the DC EMI, and the negative terminal of the DC EMI is connected in series with the negative terminal of the battery BAT.

[0010] Preferably, the DC circuit breaker includes two circuit breakers, which are connected in series with the positive and negative terminals of the battery BAT, respectively.

[0011] Preferably, the relay regulates the input and output voltage values ​​from high voltage to low voltage and vice versa.

[0012] Compared with the prior art, the beneficial effects of this utility model are as follows:

[0013] 1. This utility model adopts a bidirectional half-bridge converter (Buck-Boost converter) + voltage and current dual closed-loop PI control strategy. The circuit topology is simple and highly reliable, and power expansion can be easily achieved through multi-stage parallel connection.

[0014] 2. This utility model applies a bidirectional half-bridge converter (Buck-Boost converter) to a battery energy storage system, realizing the function of a battery manager. By reasonably setting the energy management strategy of the EMS, the output and load of the energy storage battery system can be managed, which can effectively extend the battery life and reduce maintenance costs. Attached Figure Description

[0015] Figure 1 This is a circuit connection diagram of the components of this utility model;

[0016] Figure 2This is a schematic diagram illustrating the working principle of this utility model. Detailed Implementation

[0017] The present invention will be further described below with reference to the accompanying drawings and embodiments:

[0018] Example 1: A bidirectional buck-boost DC-DC converter, comprising a battery BAT, a pre-charge circuit, a DC EMI converter, an input capacitor, a Buck-Boost inductor, a half-bridge power semiconductor IGBT, and an output capacitor. The pre-charge circuit includes a relay and a half-bridge power semiconductor IGBT, which are connected in series via a switch and connected in series with the battery BAT via wires. The DC EMI converter is connected in series with a DC circuit breaker and the battery BAT via wires. Current is output from the positive terminal of the DC converter and connected in series with the output capacitor, and in parallel with the Buck-Boost inductor via wires. The output capacitor is connected in parallel with the DC EMI circuit (positive at the top and negative at the bottom) and connected in series with the positive terminal of the battery BAT via the input capacitor, with positive to positive and negative to negative.

[0019] The pre-charging circuit is used to charge the input and output capacitors to prevent overcurrent when the DC circuit breaker is closed.

[0020] The positive terminal of the pre-charge circuit is connected in series with the positive terminal of the battery BAT, the negative terminal of the pre-charge circuit is connected in series with the positive terminal of the DC EMI, and the negative terminal of the DC EMI is connected in series with the negative terminal of the battery BAT.

[0021] The DC circuit breaker includes two circuit breakers, which are connected in series with the positive and negative terminals of the battery BAT, respectively.

[0022] The relay regulates the input and output voltage values ​​from high voltage to low voltage and vice versa.

[0023] DC EMI circuit: Eliminates interference from incoming AC power;

[0024] DC circuit breaker: A protective device for DC circuits, mainly used to disconnect overload current and short-circuit current in the circuit;

[0025] Charging: The current is output from the DC positive terminal, passes through the output capacitor to the bidirectional converter, and then flows to the inductor L to step down the voltage. This process is the charging process. The current passes through the capacitor with the positive terminal on top and the negative terminal on the bottom. The DC EMI is used to eliminate the interference of the AC current. Then it passes through the input capacitor and finally flows into the positive terminal of the battery bat, with the positive terminal to the positive terminal and the negative terminal to the negative terminal.

[0026] Discharge: The current is output from the positive terminal of the battery (bat), boosted by the relay and output through the input capacitor, and then the AC interference is eliminated by the DC EMI. The current then flows through the capacitor (at this time, the capacitor is negative at the top and positive at the bottom) through the Buck-Boost inductor discharge process, and finally flows out of the bidirectional rheostat to the DC positive terminal.

[0027] A bidirectional Buck-Boost converter consists of a battery (BAT) input, a pre-charge circuit, a DC EMI circuit, an input capacitor, a Buck-Boost inductor, a half-bridge power semiconductor (IGBT), and an output capacitor, etc. (e.g.) Figure 1 As shown in the diagram, the pre-charge circuit is used to charge the input and output capacitors and prevent overcurrent when the DC circuit breaker closes. The bidirectional Buck-Boost converter, in boost mode, boosts the energy in the battery to DC voltage through the Boost circuit; in buck mode, it steps down the energy in the high-voltage DC to the battery voltage through the Buck circuit, realizing bidirectional energy transfer.

[0028] Working principle, such as Figure 2 As shown:

[0029] 1) Q2 is off, Q1 is controlled by PWM, the circuit operates in Buck mode, and electrical energy flows from left to right, V2 <V1 ;

[0030] 2) Q1 is cut off, Q2 is controlled by PWM, the circuit works in Boost mode, the power flows from right to left, V1>V2.

[0031] In actual operation, the driving PWM of Q1 and Q2 is controlled by DSP. DSP samples the input voltage, inductor current, and output voltage and combines them with relevant input and output requirements to perform PWM control on the converter using a voltage and current dual closed-loop PI control strategy.

[0032] A bidirectional buck-boost DC-DC converter is mainly used in battery energy storage systems. The energy storage batteries in this system have two states: charging and discharging, which perfectly matches the boost and buck modes in the bidirectional Buck-Boost converter.

[0033] The following is a solution for applying a bidirectional Buck-Boost converter to an energy storage system, which consists of a lithium battery pack, a Buck-Boost converter, a power storage converter (PCS), and an energy storage system (EMS).

[0034] The lithium battery pack is responsible for storing or releasing energy, the Buck-Boost converter is responsible for bidirectional conversion of DC energy, the energy storage converter (PCS) is responsible for the conversion between DC and AC power, and the EMS is responsible for energy management and scheduling.

[0035] The bidirectional Buck-Boost converter accepts power dispatch from the EMS to charge and discharge the energy storage battery. The bidirectional Buck-Boost converter automatically achieves real-time power matching and regulation between voltage, current, and power through a dual closed-loop PI control strategy.

[0036] The bidirectional Buck-Boost converter supports multi-stage parallel connection, which can realize system expansion within a certain range; the multi-stage parallel connection function allows battery packs with different voltages and capacities to be connected to the system at the same time, realizing the function of a battery manager;

[0037] By rationally setting the energy management strategy of EMS, the output and load of the energy storage battery system can be managed, which can effectively extend the battery life and reduce maintenance costs.

[0038] It should be noted that the key technical specifications of the bidirectional buck-boost DC-DC converter are as follows:

[0039] 1) Rated power: 20kW, with two power modules connected to the energy storage battery pack respectively, each power module having a rated power of 10kW;

[0040] 2) Input voltage: 400~800V;

[0041] 3) Output voltage: (Input voltage +30V) ~ 850V (output voltage is dynamically adjusted according to input voltage);

[0042] 4) Input and output voltage ripple: 0.5%;

[0043] 5) Input and output current ripple: 2%;

[0044] Main circuit parameter design

[0045] 1) Switching frequency: 20kHz;

[0046] 2) Current: The maximum current flowing through the power device is...

[0047] Imax = Pn / Udc_min

[0048] = 12000 / 400

[0049] = 30A

[0050] 3) Inductor Design

[0051] The sensitivity value is calculated according to the following formula:

[0052] L≥U i_n ×D / (f sw ×I ripple )

[0053] =400×0.5 / (20×103 ×18)

[0054] =0.555mH

[0055] In the formula: Ui_n is the rated input voltage of the converter, D is the duty cycle corresponding to this rated input voltage, fsw is the switching frequency of the converter, and Iripple is the maximum ripple current. Therefore, the reactor parameters are selected as 0.6mH / 30A.

[0056] 4) Output filter capacitor design

[0057] In Boost mode, the size of the output filter capacitor is calculated according to the following formula:

[0058] C≥Io_max×Dmax / (fsw×ΔUo(pp))

[0059] =39×0.5 / (20×10 3 (×800×0.5%)

[0060] =244uf

[0061] In the formula, C is the capacitance of the input and output side capacitors, Uo is the output side voltage, Dmax is the switching time corresponding to the maximum duty cycle condition, and ΔUo(pp) is the peak-to-peak value of the output side ripple voltage.

[0062] In Buck mode, the output filter capacitor size is calculated using the following formula:

[0063]

[0064]

[0065] =5.2uF.

[0066] In addition, all components designed in this utility model are general standard parts or components known to those skilled in the art. Their structure and principle can be learned by those skilled in the art through technical manuals or conventional experimental methods. Those skilled in the art can fully implement them, so there is no need to elaborate. The content protected by this utility model does not involve improvements to the internal structure and method.

[0067] The embodiments disclosed herein are preferred embodiments, but are not limited thereto. Those skilled in the art can readily grasp the spirit of this utility model based on the above embodiments and make different extensions and variations. However, as long as they do not depart from the spirit of this utility model, they are all within the protection scope of this utility model.

Claims

1. A bidirectional buck-boost DC-DC converter, characterized in that, It consists of a battery (BAT), a pre-charge circuit, a DC EMI converter, an input capacitor, a Buck-Boost inductor, a half-bridge power semiconductor IGBT, and an output capacitor. The pre-charge circuit includes a relay and a half-bridge power semiconductor IGBT, which are connected in series via a switch. The relay and the half-bridge power semiconductor IGBT are also connected in series with the battery (BAT) via wires. The DC EMI converter is connected in series with a DC circuit breaker and the battery (BAT) via wires. Current is output from the positive terminal of the DC converter and connected in series with the output capacitor to the bidirectional converter. It is also connected in parallel with the Buck-Boost inductor via wires. The output capacitor is connected in parallel with the positive terminal on top and the negative terminal on the bottom to the DC EMI circuit. It is also connected in series with the input capacitor to the positive terminal of the battery (BAT), with positive terminals to positive and negative terminals to negative.

2. The bidirectional buck-boost DC-DC converter as described in claim 1, characterized in that, The pre-charging circuit is used to charge the input and output capacitors to prevent overcurrent when the DC circuit breaker is closed.

3. The bidirectional buck-boost DC-DC converter as described in claim 1, characterized in that, The positive terminal of the pre-charge circuit is connected in series with the positive terminal of the battery BAT, the negative terminal of the pre-charge circuit is connected in series with the positive terminal of the DC EMI, and the negative terminal of the DC EMI is connected in series with the negative terminal of the battery BAT.

4. The bidirectional buck-boost DC-DC converter as described in claim 1, characterized in that, The DC circuit breaker includes two circuit breakers, which are connected in series with the positive and negative terminals of the battery BAT, respectively.

5. The bidirectional buck-boost DC-DC converter as described in claim 1, characterized in that, The relay regulates the input and output voltage values ​​from high voltage to low voltage and vice versa.

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