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Since its establishment, Huanfang has been focusing on the manufacture of automotive relays and solenoid switches. It is the drafting unit of the national industry standards for solenoid switches and relays. In recent years, new energy vehicles have developed rapidly around the world. Huanfang has developed specifically for use in new energy vehicles. Circuit control, high-voltage DC contactor for charging piles for new energy vehicles. And apply for a number of patents, and actively develop a new generation of high-voltage DC contactors with world-renowned auto parts suppliers. Do our best to contribute to the green travel of mankind.

The role of high-voltage relays in new energy vehicles

Relay is one of the important parts of new energy vehicles. The main circuit voltage of new energy vehicles is generally greater than 200V, which is much higher than the 12-48V of traditional vehicles. In addition to the low-voltage relays or contactors required by traditional vehicles, new energy The car also needs to be equipped with a special high-voltage DC contactor.

New energy vehicles generally use high-voltage battery packs to provide power for electric vehicles. In order to ensure the normal on and off of the electrical system, a high-voltage DC relay needs to be configured between the battery system and the motor controller of the electric vehicle. When the system stops running, it acts as an isolation. When the system is running, it acts as a connection. When the vehicle is shut down or fails, it can safely separate the energy storage system from the vehicle electrical system and play the role of breaking the circuit. Therefore, the high voltage DC relay is a key safety device for new energy vehicles. Without it, electric vehicles will not be able to start, drive and stop.

1. The application of high-voltage relays in new energy vehicles

According to different models and power systems, the number and scale of relays used in automobiles also vary greatly. On average, each new energy vehicle needs to be equipped with 5-8 high-voltage DC relays-2 main relays, 1 pre-charge relay, 2 fast-charge relays, 2 ordinary charging relays and 1 high-voltage system auxiliary equipment relay.

2. Basic functions of high voltage DC relay

As a key safety component in new energy vehicles, high-voltage DC relays need to have the basic functions of high voltage resistance, load resistance, impact resistance, strong arc extinguishing ability and strong breaking ability.

1. High pressure resistance

The working platform voltage of new energy electric vehicles is relatively high, much higher than the 12V/24V of traditional vehicles. Therefore, the high-voltage DC relays used are required to withstand higher working voltages and reliably close and open under high-voltage loads.

2. Strong load resistance

The rated power of the electric motor of new energy passenger cars and buses is generally above 30KW and 80KW, and the peak value is above 60KW and 160KW. The current will reach about 200A and 300A respectively. Under the dual pressure of product performance and cost, the same volume is required. , The product has a strong load-bearing capability, and at the same time it must have an instantaneous overload capability several times the rated load current; or under the same load-bearing capability, the smaller the product, the better.

3. Impact resistance

High-voltage DC relays for new energy vehicles must not only have the basic function of withstanding higher voltages and carrying sufficient current, but also resist the impact of the huge current of the capacitive load at the moment of closing. This current is generally several times to dozens of load rated current Conventional relays cannot withstand the impact of this instantaneous current. The hazard of this impact current is that it is very easy to cause the relay contacts to stick, the relay contacts to separate and fail, the power supply is cut out of control, and it can cause car crashes in severe cases. Safety accidents are extremely harmful. Therefore, the DC relay products for new energy vehicles should have good impact resistance.

4. Strong arc extinguishing ability

Arc is an inevitable problem during the closing and opening of relay contacts, which greatly reduces the service life of the relay contacts. Some special rapid arc extinguishing methods are adopted to reduce the arc energy, reduce the damage to the relay contacts and extend the service life of the product. Therefore, strong arc extinguishing capability is also the basic characteristic of relays.

5. Strong breaking capacity

The operating conditions of the automobile are complex during operation. In emergency situations, such as the short circuit of the electrical system, the instantaneous current in the loop rises. At this time, the relay is required to smoothly cut off the circuit under the limit high current without contact adhesion or The occurrence of abnormal conditions such as relay explosion, to prevent the safety hazards of battery over-discharge, short circuit, fire or explosion, which requires the relay contacts to have good shock resistance and anti-adhesion capabilities.

Three, the type of high voltage DC relay

From the perspective of application types, vacuum and gas-filled relays are currently the most widely used high-voltage DC relays for new energy vehicles.

Vacuum is the ideal insulation. Since the high-voltage arc is generated by the ionization of the insulating medium, and the vacuum itself has no medium, there is a good isolation between the contacts. The complete vacuum state is only an ideal state, and some impurity oxygen will actually remain. The impurity oxygen will generate copper oxide with the copper electrode in the presence of an arc. The contact resistance will increase and the relay will be at risk of failure.

At present, gas-filled relays are mainly used, and the main arc extinguishing solutions for gas-filled relays are hydrogen and nitrogen. Filling with pure hydrogen and adding a deflection magnet to assist arc extinguishing has better arc extinguishing effect than vacuuming and nitrogen filling. Hydrogen has good insulation properties and is difficult to ionize.

Introduction to the principle of high voltage relay:

A simple understanding of high-voltage relay is an automatic switch that uses a smaller current to control a larger current. It plays the role of automatic adjustment, safety protection, and conversion circuit in the circuit. The main purpose of the high-voltage relay control is to ensure the normal power-on and power-off of the battery system. When the car starts, the high-voltage relay is turned on and the high-voltage relay is turned off when the car is stopped. The high-voltage relay control belongs to the automotive electronic and electrical system, and its failure form may cause harm to the life safety of the driver. Therefore, it should be developed in accordance with the ISO26262 standard to meet the functional safety requirements.

The high-voltage relay status monitoring is mainly to judge whether the working state of the high-voltage relay meets the control requirements by checking the contact state of the high-voltage relay, and avoid applying electrical load to the high-voltage circuit when the high-voltage relay is open, and the high-voltage circuit has a large electrical load. In case of disconnecting the high voltage relay. The contact detection of the high-voltage relay can accurately find the adhesion of the high-voltage relay, prevent the high-voltage circuit components from being damaged by misoperation in the case of the high-voltage relay, and operate the high-voltage relay reasonably (open/close) to extend the service life of the relay. The high-voltage relay contact detection method adopts the high-voltage relay with auxiliary contact detection, and the auxiliary contact detection circuit can also be designed separately to judge the opening/closing status of the high-voltage relay contact by detecting the voltage of the two sections of the high-voltage relay.

Two typical technical routes of high voltage relays (ceramic sealing and epoxy sealing)

Ceramic sealing, this technical route is represented by Panasonic; the other is epoxy sealing, which is represented by TE.

Why do HVDC relays need inflatable bodies? What is the principle of gas arc extinguishing? Why is the ceramic package (Panasonic) filled with hydrogen and the epoxy package (TE) is filled with nitrogen? The main difference between DC and AC is that DC does not cross zero. Once an arc is formed, it will not extinguish by itself, but will continue to burn, which is fatal to the contacts! And what is the nature of arc? It is the escape of electrons under the force of an electric field, and it is an extreme discharge. Therefore, there are two methods of arc extinguishing, one of which is to increase the contact gap (the essence of magnetic blowing arc extinguishing is to use the Lorenz force to change the path of the arc, which can be understood as increasing the contact gap, if only physically Enlarge the contact gap, instead of magnetic blowing out the arc, the corresponding relay magnetic gap should also be large, then under the same load capacity, the volume and weight are unimaginable), another method is to have a gap between the contacts This kind of substance can block the path of electrons. The best way that can be thought of is an inflatable body. Inflation is very particular. The first requirement is that the gas is very active. When the gas is active, it is easier to collide with the electrons escaping from the arc, thereby producing a blocking effect and easier to take away heat. The second requirement is that the molecular structure of the gas itself is very stable, and its own electrons are not easy to escape. According to the above two requirements, it is natural to think that hydrogen is the preferred gas for arc extinguishing. The molecular weight of hydrogen is the smallest and most active among all gases, and the molecular structure is stable enough. So this is the technical route of Panasonic, Hongfa, etc., because they are taking the route of ceramic packaging. Why is TE not charged with hydrogen, but with nitrogen, because they are epoxy resin encapsulated. Hydrogen is the best arc-extinguishing gas, but it has a small molecular weight and must be sealed so that it does not leak. Epoxy resin cannot do it, so nitrogen is the second choice.

At present, Huanfang Electric has two series of ceramic sealed high voltage relays and epoxy resin sealed high voltage contactors

Primary selection of high voltage relay:

1. Understand the initial needs of customers: such as rated voltage, rated current, peak charge and discharge current, peak current duration, seismic performance, working environment requirements, altitude, vehicle operating simulation conditions, etc.;

2. Common parameters of high-voltage relays: contact parameters, normally open contacts, normally closed contacts, performance parameters, insulation resistance, withstand voltage, working current, working voltage, mounting hole size, mounting hole size, etc.;

3. First select the matching model according to the rated voltage. Most high-voltage relays have a wide voltage range and can match most application scenarios. This is just a reference;

4. According to the rated current, continue to narrow the range to select the model, choose a high-voltage relay that is larger than the rated current and close to it, such as a rated current of 200A, such as a manufacturer's rated current of 200A high-voltage relay, the specification is a rated current of 250A relay, temporarily select 250A;

5. Estimate the expected service life based on the peak current provided by the customer;

6. Estimate the short-circuit current according to the electrical performance of the battery pack, estimate the short-circuit current according to the estimated short-circuit current, and estimate the failure time of the high-voltage relay according to the circuit current;

7. A more important step: compare the failure time of the high voltage relay with the failure time of the fuse in the case of a short circuit. The failure time of the relay in the case of a short circuit is longer than the failure time of the fuse. You can compare it yourself or let the company do the comparison.