(a) Technical Field
The present invention relates to an induction heating device for a fuel cell system. More particularly, it relates to an induction heating device for a fuel cell system, which can to rapidly heat coolant during cold start-up, control the power consumption depending on the voltage of a fuel cell stack, and ensure the insulation resistance by separating a heating unit, which is in contact with the coolant, from the outside.
(b) Background Art
A conventional fuel cell system comprises a fuel cell stack for generating electricity and heat in the form of reaction products via an electrochemical reaction. In a fuel cell system, the chemical energy of a fuel is converted into electrically energy. Typically, fuel cell systems include, for example, a hydrogen supply system for supplying hydrogen as fuel to the fuel cell stack, an oxygen (air) supply system for supplying oxygen-containing air as an oxidant required for the electrochemical reaction in the fuel cell stack, and a thermal management system (TMS) for removing reaction heat from the fuel cell stack to the outside of the fuel cell system, controlling operation temperature of the fuel cell stack, and performing water management function.
A fuel cell stack is consists of a plurality of unit cells. Each of these unit cells have an anode, a cathode and an electrolyte (electrolyte membrane). Hydrogen is supplied to the anode (“fuel electrode”) and oxygen-containing air is supplied to the cathode (“air electrode” or “oxygen electrode”).
The hydrogen supplied to the anode is dissociated into hydrogen ions (protons, H+) and electrons (e−) by a catalyst disposed in an electrode/catalyst layer. The hydrogen ions and electrons are transmitted to the cathode through the electrolyte membrane and a separator, to respectively. At the cathode, the hydrogen ions and electrons transmitted from the anode react with the oxygen-containing air supplied to the cathode to produce water. Electrical energy generated by the flow of the electrons is supplied to a load (e.g., a motor for driving a fuel cell vehicle) requiring the electrical energy through a current collector of an end plate.
The role of the thermal management system for the fuel cell system is particularly important in order to prevent the temperature of the fuel cell stack from increasing during operation of the fuel cell system and improve cold startability.
The conventional configuration of a thermal management system will be described with reference to FIG. 4 below. In FIG. 4, a water pump 16 is provided in a coolant circulation line 14, which is connected between a coolant outlet of a fuel cell stack 10 and an inlet of a radiator 18. The conventional thermal management system also has a coolant heating device 20 and a reservoir which are sequentially connected in the coolant circulation line 14.
Here, the coolant circulating through the coolant circulation line 14 functions as a cooling medium that cools the fuel cell stack 10 during operation and functions as a heating medium that is rapidly heated by the coolant heating device 20 and supplied to the fuel cell stack 10 to rapidly thaw the fuel cell stack 10 during cold start-up.
In conventional designs, the coolant heating device 20 includes a heater for heating the coolant. The heater is used to increase the temperature of the coolant, achieve more rapid temperature stabilization of the coolant during start-up of the vehicle, and reduce the to remaining voltage of the fuel cell stack during shutdown of the vehicle.
In FIG. 4, the conventional coolant heating device 20 has a structure, in which cartridge resistance heaters 24 are connected to a power unit provided in a housing 22, through which the coolant passes. However, this structure has the following disadvantages. First, there should be a predetermined distance between each of the heaters 24, which are high density heating elements. Thus, the volume of the housing 22 is significantly increased in conventional designs. Therefore, it is difficult to ensure a space for mounting the heating device which has such a large volume in a compact vehicle such as a fuel cell vehicle. Moreover, the complicated structure increases the manufacturing cost and reduces the assemblability and maintainability of this system. Furthermore, the cartridge resistance heaters are in direct contact with the coolant, and thus it is necessary to ensure the cartridge resistance heaters are insulated accordingly.
In addition, the cartridge resistance heaters penetrating the housing are typically sealed with O-rings, and thus when the temperature of the heaters is increased, the coolant may leak due to deformation of the O-rings, thus destroying the insulation.
FIG. 5 is a schematic diagram showing a conventional cold start-up system for a fuel cell. Referring to FIG. 5, a plurality of resistors R1, R2 and R3 and a plurality of switches L1, L2 and L3 are connected to a fuel cell stack 10 such that the resistance values are controlled step by step using the resistors R1, R2 and R3. As a result, it is possible to prevent the voltage of the fuel cell stack from dropping below a lower limit, thus enabling the cold start-up.
In detail, the plurality of resistors R1, R2 and R3 having different resistance values are connected in parallel to both ends of the fuel cell stack 10, and the plurality of switches L1, L2 and L3 for switching the circuit are connected to the resistors R1, R2 and R3, respectively, to change the resistance values applied to the both ends of the fuel cell stack 10 by on/off control of the switches L1, L2 and L3 such that the voltage of the fuel cell stack 10 is controlled between a predetermined lower limit for achieving cold start-up and an upper limit during cold start-up.
However, to control the power of the fuel cell stack during cold start-up, this system requires a heater at each resistor and a relay for controlling the heater, which imposes various limitations to the overall system.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.