How do diodes work in energy feedback systems?

一, Technical characteristics of diodes: the physical basis for energy feedback
A diode is a PN junction structure formed by a P-type semiconductor and an N-type semiconductor, and its core characteristics include:

Unidirectional conductivity: Conducts when forward biased (with a conduction voltage of approximately 0.6-0.7V for silicon transistors and 0.2-0.5V for Schottky diodes), and turns off when reverse biased (with only microampere level reverse leakage current present).
Fast switching capability: The reverse recovery time of Schottky diodes is close to zero, and the reverse recovery time of silicon carbide (SiC) diodes can be shortened to less than 10 nanoseconds.
Voltage and current resistance characteristics: Industrial grade diodes can withstand thousands of volts and have transient current resistance capabilities exceeding hundreds of amperes.
These characteristics enable it to perform three core functions in energy feedback systems:

Rectification: The initial process of converting alternating current into direct current to achieve energy feedback;
Continuous current: In motor drive or inverter circuits, it provides a current path for inductive loads to prevent voltage spikes;
Protection: Isolate reverse voltage to prevent impact on power side equipment during energy feedback process.
二, Typical application scenarios: from new energy vehicles to industrial energy storage
1. New energy vehicle braking energy recovery system
During the braking process of electric vehicles, the wheel hub motor switches from driving mode to generating mode, producing three-phase alternating current. At this point, the diode rectifier bridge (usually composed of 6 diodes) converts AC power into DC power, which is then boosted by an inverter and charged into the power battery. The working logic is as follows:

Energy management strategy: The brake controller dynamically adjusts the recovery intensity based on the battery SOC (remaining charge). When SOC>80%, cancel energy recovery; When SOC<70%, full power recovery occurs.
Diode selection requirements: Use Schottky diodes or SiC diodes with low forward voltage drop to reduce conduction losses. For example, after using SiC Schottky diodes in a certain car model, the braking recovery efficiency increased by 3% and the range increased by 5 kilometers.
Thermal management design: Under high current conditions, the diode packaging should adopt a low thermal resistance TO-247 or DFN8 × 8 structure, combined with a liquid cooling system to ensure a junction temperature of ≤ 150 ℃.
2. Energy feedback unit for industrial frequency converters
During the deceleration phase of equipment such as elevators and cranes, the motor is in a generating state, and the generated electrical energy is fed back to the DC bus capacitor through a diode rectifier bridge. If there is excess energy, the IGBT and diode combination in the IPM (Intelligent Power Module) is used to invert DC power into AC power and feed it back to the grid. Its technological highlights include:

Efficient rectification: using fast recovery diodes (FRD) or SiC diodes, the reverse recovery time is shortened to 1/10 of traditional silicon tubes, and the switching loss is reduced by 70%.
Grid synchronization control: By using phase-locked loop (PLL) technology, the feedback current and grid voltage are synchronized in frequency and phase, with a power factor of ≥ 0.99.
Protection mechanism: TVS (transient voltage suppression) diode clamps voltage spikes to prevent damage to equipment caused by lightning strikes or overvoltage.
3. Bidirectional converter for energy storage power station
In the scenario of power grid peak shaving, the energy storage system achieves charge discharge switching through bidirectional DC/DC converters. The diode plays a dual role in this process:

Charging mode: As a rectifier component, it converts AC power into DC power and stores it in the battery;
Discharge mode: As a freewheeling diode, it provides a current path for the inverter circuit to ensure smooth energy output.
Taking a 20 foot container energy storage system as an example, its BMS (Battery Management System) uses 1600-1800 TVS and Schottky diodes for battery balancing, overvoltage protection, and anti reverse connection. After adopting Trench Schottky diodes, the system efficiency increased by 0.4%, and the annual power savings of a single box exceeded 1000 kWh.