High voltage interlock connector

General requirements for high voltage interlock circuit HVIL

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In the near future, I will pay more attention to the issue of battery high voltage safety. Here are some requirements for high-voltage interlocking. These requirements are general requirements. For these requirements, each manufacturer will have their own different implementation methods. For example, if the barrier/enclosure permits direct access, individuals can only open or remove it using tools or maintenance keys, or there is a method to disconnect the B-level voltage at certain points, such as through an interlock.” Interlock here generally refers to High Voltage Interlock Loop (HVIL), which detects the electrical integrity or connectivity of high-voltage components, wires and connectors through low-voltage circuits, recognizes abnormal disconnection of the circuit, and disconnects the controller at the high-voltage input in time.

When HVIL fails, make sure to safely power off the high-voltage system in an appropriate manner. Before resolving the fault, refrain from powering on the high-voltage system, while simultaneously triggering the corresponding DTC. When disconnecting the high-voltage module from the high-voltage circuit, exercise caution regarding the charging of capacitive loads and high-voltage cables to prevent electric shocks to operators. During normal vehicle operation, prevent electric shocks caused by improper operation, vehicle vibration, product aging, and local heating and arcing caused by line wear.

HVIL Design Requirements

1) The functional safety level of HVIL-related modules in the controller should reach ASIL C

2) HVIL should include a signal generator and 2 signal detection devices

3) It must be able to continuously and real-time monitor the on/off of the entire loop

4) Users cannot open or separate all high-voltage connectors of the HVIL circuit without tools or without doing so unconsciously.

5) All high-voltage connectors of the high-voltage circuit should have mechanical interlocking devices. The high-voltage connectors can only be opened when the HVIL circuit is disconnected first.

6) The HVIL circuit should have a safety redundancy design, that is, the failure of a key component will not seriously affect the misjudgment of the high-voltage circuit monitoring function

7) Under special circumstances, the HVIL circuit can be detected directly through the HCU or BMS, and the high-voltage circuit can be directly disconnected.

 

Diagnostic Function Requirements

The HVIL related controller should diagnose the following faults

1) The circuit is disconnected

2) Short circuit to ground

3) Short circuit to 12V power supply

4) Short circuit

5) The loop impedance becomes larger

Signal Source Requirements

1) HVIL signal source voltage is generally 5V

2) HVIL and 12V power supply are short-circuited, the signal source cannot fail, and it has reverse protection

3) HVIL wiring harness cannot have branch crimp contact points

4) When the voltage of the 12V lead-acid battery drops, such as about 10V. It is also necessary to protect the HVIL signal source to have a stable output.

High Voltage Connector Requirements

1) The high voltage connector needs to integrate the interlock function

2) When the high voltage connector is disconnected, HVIL is disconnected first; when connected, HVIL is connected later, some designs are connected at the same time

3) The contact resistance of the high-voltage connector after joining meets the “Technical Conditions of Automotive Wire Harness Connectors”

4) When the interlocking wiring harness is arranged, it should be led out from the low-voltage interface of the high-voltage components and separated from the high-voltage wiring harness.

5) Usually, connectors are crimped, plugged and unplugged, and they typically have angles of 90° or 180°, often featuring built-in interlocking shorting tabs or pins at the harness end or plug-in end. For example, in a relatively common MSD, the HVIL design (yellow dashed frame) in the picture below employs pins.

Hazard Control Strategy

When HVIL recognizes a danger, the entire controller needs to use safety strategies reasonably according to the driving status and the degree of damage caused by the accident at the time of the incident. Here are some common safety strategies:

1) Failure alarm. Regardless of whether the vehicle is driving or not, when HVIL recognizes a danger, it must issue a warning in some form to remind the driver to deal with it in time

2) Cut off the high voltage. When the vehicle is in a stopped state, when HVIL detects danger, it needs to tell the system controller to disconnect the high voltage.

3) Reduced power operation. When identifying a danger during driving, it is not possible to immediately disconnect the high voltage. First, the control system issues a reminder or alarm to alert the driver of the abnormality. Subsequently, the system reduces the operating power of the motor and the speed of the vehicle, allowing the high-voltage system to operate under a lighter load. This provides the driver with a certain amount of time to pull over and stop, facilitating the next step of failure analysis.

There are many ways to realize HVIL in electrical design, and the realization of each way needs to consider the interrelationship between various high and low voltage devices, and comprehensively consider the overall requirements of the system.

New energy electric vehicle high-voltage system connection relationship

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In order to understand the connection relationship between the various systems of the new energy electric vehicle, a simple logic diagram is now given to deepen the understanding of each system.

High-voltage system components connection logic diagram

New energy electric vehicle high-voltage system connection relationship

New energy electric vehicle high-voltage system connection relationship

It is recommended to look at it for yourself first, think about the logical connection between them, and then look at the following specific introduction.

1. Power Battery

Power battery is an energy supply device in electric vehicles, which needs to provide energy for all systems of the vehicle. When the power is consumed, you also need to charge him. Therefore, its energy flow has both outflow and inflow.

2. High voltage distribution box (PDU)

PDU can be considered as a place for power transfer and distribution, and each component in the high-voltage system needs it for power distribution. Such as high-pressure compressor, PTC, motor controller, etc.

3. service switch

The service switch is located between the power battery and the PDU, which is a necessary component. When the power battery is repaired, it can be used to cut off the high-voltage power of the vehicle to ensure the safety of repairs.

MSD Connectors 500A Waterproof IP67 2 Pin Orange Plastic Plug

 

high-voltage service switch

4. Motor controller and drive motor

The motor controller converts the high-voltage direct current from the PDU into three-phase alternating current and supplies it to the drive motor.

The drive motor converts electrical energy into mechanical energy to provide power for the vehicle to travel. At the same time, the drive motor can also convert the mechanical energy (such as braking efficiency) generated during driving into electrical energy, and finally send it to the power battery to supplement the electrical energy.

5. Fast charging port

The power of the fast charging port is high-voltage direct current, which can be directly sent to the power battery for charging through the PDU without processing.

6. Slow filling

The power of the slow charging port is high-voltage alternating current, which needs to be converted through the OBC unit in the two-in-one controller, or OBC (there is no two-in-one controller, OBC and DC/DC are separated). The converted high-voltage direct current is charged through the PDU to charge the power battery.

7. DC/DC

In order to achieve the electric balance of the whole vehicle, the power battery needs to provide the power supply of the electric appliances of the whole vehicle, and at the same time, it can charge the battery. However, the power of the power battery is high-voltage electricity, so it is necessary to convert high-voltage direct current into low-voltage direct current through a DC/DC device.

 

The composition and role of high-voltage systems in new energy electric vehicles

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This article mainly introduces the composition and role of high-voltage systems in new energy electric vehicles

The composition of the high-pressure system

In the new energy electric vehicle, the parts with high voltage of the whole vehicle include power battery, drive motor, high-voltage distribution box (PDU), electric compressor, DC/DC, OBC, PTC, high-voltage wiring harness, etc., these components It forms the high-voltage system of the whole vehicle, in which the power battery, the drive motor, and the high-voltage control system are the three major components of the new energy electric vehicle.

1.Battery pack and power battery management system BMS

Different from traditional fuel vehicles, the power source of new energy electric vehicles is the power battery, not the engine. Because pure electric vehicles use electric energy directly, they do not need to burn the fuel and discharge the emissions into the atmosphere like traditional fuel vehicles. Therefore, in order to reduce environmental pollution, the development of new energy vehicles is actively supported by the state.

The voltage of the new energy power battery is generally 100~400V, and its output current can reach 300A. The capacity of the new energy power battery directly affects the mileage of the vehicle, and also directly affects the charging time and charging efficiency. Lithium-ion power batteries are currently the mainstream. Affected by current technology, most current cars use lithium-ion power batteries.

new energy electric vehicles

new energy electric vehicles

2.Drive motor and motor controller MCU

The motor controller MCU converts high-voltage direct current to alternating current, and performs signal interaction with other modules on the vehicle to achieve effective control of the drive motor. The drive motor converts electrical energy into mechanical energy to drive the car. Unlike traditional fuel vehicles, which convert the chemical energy of fuel combustion into mechanical energy, the engine has a higher working efficiency, which can reach more than 85%. Therefore, compared with traditional vehicles, its energy utilization rate is higher and can reduce the waste of resources.

3.High voltage distribution box

The high-voltage power distribution box is a power distribution device for the high-voltage power of the entire vehicle, similar to the electrical fuse box in the low-voltage circuit system. The high-voltage fuse box PDU (Power Distribution Unit) is composed of many high-voltage relays and high-voltage fuses. There are related chips inside it to realize signal communication with related modules to ensure the safety of high-voltage electricity for the whole vehicle.

high-voltage power distribution box

high-voltage power distribution box

4.Car charger OBC

On Board Charge is a device that converts alternating current to direct current. Because the battery pack is a high-voltage direct current power supply, when using alternating current for charging, the alternating current cannot be directly stored by the battery pack. Therefore, an OBC device is required to convert the high-voltage alternating current to high-voltage direct current to charge the power battery.

5. DC/DC

In new energy vehicles, DC/DC is a device that converts high-voltage direct current to low-voltage direct current. There is no engine in new energy vehicles, and the source of electricity for the whole vehicle is not all generators and batteries, but power batteries and batteries. Since the rated voltage of the vehicle’s electrical appliances is low voltage, a DC/DC device is required to convert high-voltage direct current to low-voltage direct current, so as to maintain the balance of vehicle power consumption.

DC/DC device

DC/DC device

 

6. OBC and DC/DC two-in-one controller

Affected by the layout of the whole vehicle, many cars now combine the two components of OBC and DC/DC into one component. This component is usually called a two-in-one controller. Its function is actually the two components of OBC and DC/DC. Combination of functions.

7.  Electric compressor

The compressor of the traditional car is attracted by the electromagnetic clutch of the compressor, which prompts the engine to drive the compressor to operate. An electric vehicle has no engine, and its compressor is directly driven by a high-voltage power source. In order to distinguish it from the compressor of the traditional car, the air-conditioning compressor on the electric car is called an electric compressor here.

8. PTC heater

The heat source of the air conditioning heating system on traditional vehicles is the heat of the coolant introduced into the engine after cooling. This does not exist in new energy vehicles. Therefore, a special heating device is required. This device is called an air conditioner PTC. The function of PTC (Positive Temperature Coefficient) is heating. When the temperature is low, the battery pack needs heat to work normally. At this time, the battery pack PTC is required to preheat the battery pack.

9. High voltage wiring harness

The high-voltage wiring harness connects the various components of the high-voltage system as a medium for high-voltage power transmission. Different from the low-voltage wiring harness system, these wiring harnesses are equipped with high-voltage electricity, which greatly affects the stability of the high-voltage system of the vehicle. The safety of high-voltage wiring harness design is our main consideration.

 

High voltage interlock connector in BMS

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The high-voltage interlock function is also an important function on the BMS, and other high-voltage controllers will also have this function, such as VCU, etc.; its function is to detect the connection status of the High Voltage Interlock Connector in the high-voltage circuit and identify the high-voltage connector is not connected Or accidental disconnection failure;

As shown in the figure below, the loop of the red line in the figure is the high-voltage interlocking loop, which connects all the relevant high-voltage connectors in the system in series and detects their connection status at the same time.

 

High Voltage Interlock Loop

High voltage interlock connector

The realization of HVIL firstly depends on the structure of the connector itself. The high voltage connector integrates the HVIL interface internally. As shown in the figure below, in addition to its own high-voltage and high-current interface, the high-voltage connector also integrates an HVIL interface; the principle is very simple. The HVIL interface has two PIN pins. When the high-voltage connector is plugged in, the two PINs become short-circuited. ; When the high-voltage connector is disconnected, these two PIN pins are open. The HVIL function is realized by detecting the on-off of these two PIN pins.

HVIL connector

HVIL connector

Similarly, the high-voltage maintenance switch (MSD) also integrates the HVIL interface, as shown in the figure below.

There is a time difference between the HVIL interface in the high-voltage connector and the high-voltage high-current interface when it is inserted or unplugged, as shown in the figure below; when the connector is inserted, the high-voltage terminal contacts first, and the HVIL terminal contacts later, the time difference is Δt1; When the device is pulled out, the HVIL terminal is disconnected first, and the high-voltage terminal is disconnected afterwards. The time difference is Δt2; in this way, the HVIL terminal can ensure that the high-voltage terminal has been reliably connected or the accidental disconnection can be predicted in advance.

high-voltage maintenance

high-voltage maintenance

The above two time differences are generally related to the speed of insertion or removal. I have probably tested it before. Δt1 is about 1s, and Δt2 is about 100ms. The time is not very accurate, but the magnitude is about the same.

Next, a brief introduction to the HVIL detection circuit is generally divided into two types, the DC source scheme and the PWM scheme. As shown in the figure below, the left picture is a simplified diagram of the DC source scheme, and the right picture is a simplified diagram of the PWM scheme. In the left picture, an external DC source is applied to the entire HVIL loop, and the high-voltage connector state is diagnosed by detecting the voltage at V1\V2; in the same way, in the right picture, a controllable switch is introduced, the same Still detect the voltage at V1\V2, but by controlling the switch, two sets of values can be obtained to identify more states;

high-voltage maintenance

high-voltage maintenance

The actual HVIL detection circuit is more complicated. First, determine the type of fault to be detected, and then design the detection circuit according to the type of fault; the types of faults include open circuit, short circuit to ground, short circuit to power, and larger loop impedance.

The high-voltage interlock diagnosis is an important safety mechanism that falls into the safety goal of the BMS. Once a fault is diagnosed, the BMS must enter a safe state. Among them, the whole vehicle scene needs to be subdivided. The safety status is completely different in different scenes; for example, the charging scene, the driving scene, and the startup scene.

to sum up:

This article briefly introduces the concept of HVIL. In most cases, the HVIL circuit is a system circuit. It traverses all the main high-voltage interfaces, and the detection range is defined by the OEM. The difficulty of the HVIL function lies in the processing strategy after the failure is found, which is also the core.