Active discharge circuit and method for hydrogen fuel cell system

Abstract

This invention belongs to the field of fuel cell technology and discloses an active discharge circuit and method for a hydrogen fuel cell system. The DC / DC converter includes two or more boost circuits connected in parallel. Each boost circuit has an inductor and a controllable switch connected to an anti-parallel diode. At least one boost circuit has two controllable switches, one upper and one lower, with the lower controllable switch grounded. During discharge, at least one boost circuit operates in boost mode, and at least one boost circuit operates in buck mode. The boost ratio of the output and input voltages is maintained constant through current control. This invention achieves shorter discharge time and simplifies the circuit topology.

Description

Technical Field

[0001] The present invention belongs to the technical field of fuel cells, and in particular relates to an active discharge circuit and method for a hydrogen fuel cell system. Background Art

[0002] In new energy vehicles powered by hydrogen fuel cells, the main DC / DC converter is used to output the energy of the hydrogen stack to the DC bus. When the system stops working, there is a certain amount of residual hydrogen (residual hydrogen) in the stack. The DC / DC converter needs to release the energy of the residual hydrogen reaction within a certain period of time to avoid damage to the stack caused by the residual hydrogen.

[0003] At present, the main method to release the residual energy (residual hydrogen) of the battery stack is to discharge through resistors, and release the residual hydrogen energy through resistor heating. Resistor discharge has the following two defects: on the one hand, the discharge time is long. Taking a 500-ohm discharge resistor as an example, if the average voltage of the battery stack during the discharge process is 70V, then the time required to discharge 50 coulombs of electricity is about 50 / (70 / 500) = 357 seconds; on the other hand, the resistor heats up severely, which can easily damage the resistor and cause the discharge function to fail. Summary of the invention

[0004] An object of the embodiments of the present invention is to provide an active discharge circuit and method for a hydrogen fuel cell system, which can shorten the discharge time and simplify the circuit topology.

[0005] The embodiment of the present invention is implemented as follows:

[0006] An active discharge circuit for a hydrogen fuel cell system. The hydrogen fuel cell system has a stack, the negative output end of the stack is grounded, and includes: a DC / DC converter, an input capacitor and an output capacitor. The input capacitor is connected across the two output ends of the stack. One end of the DC / DC converter is connected to the positive output end of the stack, and the other end is connected to the negative output end of the stack through the output capacitor. The DC / DC converter includes two or more boost circuits connected in parallel. The boost circuit has an inductor and a controllable switch tube connected to an anti-parallel diode. At least one boost circuit has an upper and a lower controllable switch tube, wherein the lower controllable switch tube is grounded. During discharge, at least one boost circuit works in a boost mode, and at least one boost circuit works in a buck mode, and the boost ratio of the output input voltage is maintained unchanged through current control.

[0007] The output capacitor voltage is maintained at 1-8 times the input capacitor voltage, but does not exceed the maximum limit voltage of the output capacitor.

[0008] The lower controllable switch tube in the boost BOOST circuit is controlled to work in a PWM mode, and the upper controllable switch tube is disconnected, so that the boost BOOST circuit works in a boost mode.

[0009] The upper controllable switch tube in the boost circuit is controlled to work in a PWM mode, so that the boost circuit works in a buck mode.

[0010] The active discharge circuit for a hydrogen fuel cell system further includes a current loop corresponding to the number of boost circuits for controlling the current size of each circuit, and a voltage loop for controlling the output capacitor voltage.

[0011] An active discharge method for a hydrogen fuel cell system, the hydrogen fuel cell system has a stack, the negative output end of the stack is grounded, and includes: a DC / DC converter, an input capacitor and an output capacitor, the input capacitor is connected across the two output ends of the stack, one end of the DC / DC converter is connected to the positive output end of the stack, and the other end is connected to the negative output end of the stack through the output capacitor, the DC / DC converter includes two or more boost circuits connected in parallel, the boost circuit has an inductor and a controllable switch tube connected to an anti-parallel diode, at least one boost circuit has an upper and a lower controllable switch tube, wherein the lower controllable switch tube is grounded; during discharge, at least one boost circuit works in a boost mode, and at least one boost circuit works in a buck mode, and the boost ratio of the output input voltage is maintained unchanged through current control.

[0012] The output capacitor voltage is maintained at 1-8 times the input capacitor voltage, but does not exceed the maximum limit voltage of the output capacitor.

[0013] The lower controllable switch tube in the boost BOOST circuit is controlled to work in a PWM mode, and the upper controllable switch tube is disconnected, so that the boost BOOST circuit works in a boost mode.

[0014] The upper controllable switch tube in the boost circuit is controlled to work in a PWM mode, so that the boost circuit works in a buck mode.

[0015] The active discharge method for a hydrogen fuel cell system also includes a current loop corresponding to the number of boost circuits for controlling the current size of each circuit, and a voltage loop for controlling the output capacitor voltage.

[0016] In the embodiment of the present invention, the residual hydrogen of the fuel cell stack is released through the controllable internal loss of the DCDC system, rather than being released through the commonly used resistance heating. Since the internal inductance and switch of the DCDC system itself have a good heat dissipation design, it can support long-term discharge and avoid the serious disadvantage of resistance discharge heating; the residual hydrogen of the fuel cell stack is released through the controllable internal loss of the DCDC system, and the size of the internal loss depends on the current passing through the device. Under large current, the energy of the internal loss is much greater than the commonly used resistance heating loss, and the discharge time can be greatly shortened; the residual hydrogen of the fuel cell stack is released through the controllable internal loss of the DCDC system, and the size of the internal loss depends on the current passing through the device. By controlling this current, the speed and time of the residual hydrogen release can be basically controlled, so that the applicability of discharge is greatly broadened. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 It is a topological diagram of an active discharge circuit for a hydrogen fuel cell system in an embodiment of the present invention. DETAILED DESCRIPTION

[0018] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0019] The present invention is used for releasing the residual hydrogen energy of a hydrogen fuel cell, and mainly achieves the purpose of energy discharge through the internal energy loss of a DC / DC converter; the present invention includes:

[0020] (1) The DC / DC converter topology is mainly composed of multiple boosts;

[0021] (2) In the multi-channel BOOST topology of the DC / DC converter, at least one channel has two controllable upper and lower switches;

[0022] (3) The DC / DC converter receives the active discharge command sent by the stack system controller, controls the IGBT switch, makes several (at least one) of the multiple inputs work in the boost mode, and the other several (at least one) work in the buck mode, and maintains the output input voltage boost ratio unchanged through current control, while controlling the inductor current of each input, so that energy is lost in the inductor, IGBT switch (controllable switch tube) and other components. Since the DC / DC converter itself has a targeted heat dissipation design for the inductor and IGBT module, heat dissipation will not become a problem for the release of residual hydrogen. In addition, the IGBT switch and inductor can withstand a large current, and the system loss is proportional to the inductor current and the switch current. By increasing the current flowing through the inductor and the switch tube, the system loss can be greatly increased, thereby greatly shortening the discharge time.

[0023] The specific implementation of the present invention is described in detail below in conjunction with specific embodiments:

[0024] like Figure 1 As shown, an active discharge circuit for a hydrogen fuel cell system, the hydrogen fuel cell system has a stack, the negative output end of the stack is grounded, including: a DC / DC converter, an input capacitor Cin and an output capacitor Cout, the input capacitor is connected across the two output ends of the stack, one end of the DC / DC converter is connected to the positive output end of the stack, and the other end is connected to the negative output end of the stack through the output capacitor, the DC / DC converter includes two or more boost BOOST circuits connected in parallel, the boost BOOST circuit has an inductor and a controllable switch tube (IGBT switch) connected to an anti-parallel diode, at least one boost BOOST circuit has two upper and lower controllable switch tubes, wherein the lower controllable switch tube is grounded; during discharge, at least one boost BOOST circuit works in a boost mode, at least one boost BOOST circuit works in a buck mode, and the output input voltage boost ratio is maintained unchanged through current control. Maintaining a stable voltage is to ensure that the input and output voltages will not enter overvoltage protection.

[0025] The output capacitor voltage is maintained at 1-8 times the input capacitor voltage, but does not exceed the maximum limit voltage of the output capacitor, which is generally about 5 times.

[0026] The lower controllable switch tube in the boost BOOST circuit is controlled to work in a PWM mode, and the upper controllable switch tube is disconnected, so that the boost BOOST circuit works in a boost mode.

[0027] The upper controllable switch tube in the boost circuit is controlled to work in a PWM mode, so that the boost circuit works in a buck mode.

[0028] The active discharge circuit for a hydrogen fuel cell system further includes a current loop corresponding to the number of boost circuits for controlling the current size of each circuit, and a voltage loop for controlling the output capacitor voltage. The current loop and the voltage loop are part of the software control algorithm and are ultimately executed through PWM.

[0029] An active discharge method for a hydrogen fuel cell system, the hydrogen fuel cell system has a stack, the negative output end of the stack is grounded, including: a DC / DC converter, an input capacitor and an output capacitor, the input capacitor is connected across the two output ends of the stack, one end of the DC / DC converter is connected to the positive output end of the stack, and the other end is connected to the negative output end of the stack through the output capacitor, the DC / DC converter includes two or more boost circuits connected in parallel, the boost circuit has an inductor and a controllable switch connected to an anti-parallel diode, at least one boost circuit has two upper and lower controllable switch tubes, wherein the lower controllable switch tube is grounded; during discharge, at least one boost circuit works in a boost mode, at least one boost circuit works in a buck mode, and the output input voltage boost ratio is maintained unchanged through current control. Maintaining a stable voltage is to ensure that the input and output voltages will not enter overvoltage protection.

[0030] The output capacitor voltage is maintained at 1-8 times the input capacitor voltage, but does not exceed the maximum limit voltage of the output capacitor.

[0031] The lower controllable switch tube in the boost BOOST circuit is controlled to work in a PWM mode, and the upper controllable switch tube is disconnected, so that the boost BOOST circuit works in a boost mode.

[0032] The upper controllable switch tube in the boost circuit is controlled to work in a PWM mode, so that the boost circuit works in a buck mode.

[0033] The active discharge method for a hydrogen fuel cell system also includes a current loop corresponding to the number of boost circuits for controlling the current size of each circuit, and a voltage loop for controlling the output capacitor voltage. The current loop and the voltage loop are part of the software control algorithm and are ultimately executed through PWM.

[0034] Figure 1 In the topology, there are four parallel inputs, each of which includes an inductor and two IGBT switches (including anti-parallel diodes). In the active discharge function, two of them (such as L1 and L2 branches) are selected to work in the boost mode (the lower tubes Q1_D and Q2_D work in PWM mode, and the upper tubes Q1_U and Q2_U are disconnected), and the other two (such as L3 and L4 branches) work in the buck mode (the upper tubes Q3_U and Q4_U work in PWM mode, and the lower tubes Q3_D and Q4_D are disconnected), and the Cout voltage (Vout) is maintained at about 5 times the Cin voltage (Vin), but not exceeding the maximum limit voltage of Cout.

[0035] The example topology is only a special case of the present invention. Its scope of application is not limited to four-way parallel input, but is applicable to systems with multiple inputs (at least 2 inputs). The present invention does not require that each of the multiple inputs include two upper and lower switching tubes, but only requires that at least one input has two controllable switching tubes.

[0036] The present invention also includes a plurality of current loop controls for controlling the current magnitude of each branch; and a voltage loop control for controlling the voltage on the output capacitor Cout.

[0037] The discharge current of residual hydrogen in a hydrogen fuel cell depends on the resistance loss on the inductor, the IGBT switching loss and the loss of other components. The loss is proportional to the current flowing through the device.

[0038] In the embodiment of the present invention, the active discharge circuit and method described in the present invention can release the residual hydrogen energy to near zero in a short time, and does not rely on other components of the system except DC / DC.

[0039] In an embodiment of the present invention, at least one of the multi-channel BOOST in the DC / DC converter topology has two controllable upper and lower switching tubes, wherein the upper tube is used for BUCK step-down mode control, so that the current can flow from the output to the input, thereby ensuring the stability of the output voltage; the present invention includes multiple current loop controls for controlling the current size of each branch; by controlling the branch current size, the losses of the inductor and the switch tube are basically controllable, and thus the discharge current of the battery stack is controllable; the present invention includes a voltage loop control for controlling the voltage size on the output capacitor Cout; by controlling the output voltage, the system can operate within a controllable range.

[0040] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. An active discharge circuit for a hydrogen fuel cell system, the hydrogen fuel cell system having a stack, the negative output terminal of the stack being grounded, characterized in that: include: A DC / DC converter, an input capacitor and an output capacitor, wherein the input capacitor is connected across the two output terminals of the battery stack, one end of the DC / DC converter is connected to the positive output terminal of the battery stack, and the other end is connected to the negative output terminal of the battery stack through the output capacitor, the DC / DC converter includes two or more boost circuits connected in parallel, the boost circuit has an inductor and a controllable switch connected to an anti-parallel diode, at least one boost circuit has an upper and a lower controllable switch, wherein the lower controllable switch is grounded; during discharge, the lower controllable switch in the boost circuit is controlled to work in a PWM mode, and the upper controllable switch is disconnected, so that the boost circuit works in a boost mode; the upper controllable switch in the boost circuit is controlled to work in a PWM mode, so that the boost circuit works in a buck mode, and the output-input voltage step-up ratio is maintained unchanged through current control; The invention also includes a current loop corresponding to the number of boost circuits for controlling the current size of each path, and a voltage loop for controlling the output capacitor voltage.

2. The active discharge circuit for a hydrogen fuel cell system according to claim 1, characterized in that: The output capacitor voltage is maintained at 1-8 times the input capacitor voltage, but does not exceed the maximum limit voltage of the output capacitor.

3. An active discharge method for a hydrogen fuel cell system, the hydrogen fuel cell system having a stack, the negative output terminal of the stack being grounded, characterized in that: include: A DC / DC converter, an input capacitor and an output capacitor, wherein the input capacitor is connected across the two output terminals of the battery stack, one end of the DC / DC converter is connected to the positive output terminal of the battery stack, and the other end is connected to the negative output terminal of the battery stack through the output capacitor, the DC / DC converter includes two or more boost circuits connected in parallel, the boost circuit has an inductor and a controllable switch connected to an anti-parallel diode, at least one boost circuit has an upper and a lower controllable switch, wherein the lower controllable switch is grounded; during discharge, the lower controllable switch in the boost circuit is controlled to work in a PWM mode, and the upper controllable switch is disconnected, so that the boost circuit works in a boost mode; the upper controllable switch in the boost circuit is controlled to work in a PWM mode, so that the boost circuit works in a buck mode, and the output-input voltage step-up ratio is maintained unchanged through current control; The invention also includes a current loop corresponding to the number of boost circuits for controlling the current size of each path, and a voltage loop for controlling the output capacitor voltage.

4. The active discharge method for a hydrogen fuel cell system according to claim 3, characterized in that: The output capacitor voltage is maintained at 1-8 times the input capacitor voltage, but does not exceed the maximum limit voltage of the output capacitor.

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