RELIANCE ELECTRIC INVERTRON DBU Dynamic Braking Unit

RELIANCE ELECTRIC INVERTRON DBU dynamic braking unit: precise control of braking energy to ensure stable operation of the drive system

In industrial variable frequency drive systems, processes such as rapid deceleration of the motor, lowering of potential loads (such as lifting heavy objects from a crane), or stopping of a centrifuge will cause the motor to operate in a generating state, converting mechanical energy into electrical energy and feeding it back to the DC bus of the frequency converter. If this regenerated energy cannot be consumed in a timely manner, it will cause a sharp increase in DC bus voltage, threaten the safety of power devices, trigger overvoltage faults (such as the "HU" fault of GV3000), or force the frequency converter to automatically extend the deceleration time. The Dynamic Braking Unit (DBU) is a key component designed to address this issue. The INVERTRON DBU series guides excess DC bus energy to external braking resistors through intelligent control, safely dissipating it in the form of thermal energy to ensure the stability and reliability of the drive system during four quadrant operation. This article will comprehensively analyze the working principle, technical details, selection calculation, installation points, and advanced diagnostic functions of DBU.

The core function and working principle of DBU

A frequency converter with a diode rectifier bridge can only transmit energy unidirectionally on its DC bus, making the system essentially operate in two quadrants (forward and reverse electric). When the motor is in regenerative braking mode, energy cannot be fed back to the grid and can only accumulate in the DC bus capacitor, resulting in a voltage rise.

The core of DBU is an IGBT (Insulated Gate Bipolar Transistor) switching circuit controlled by an intelligent gate driver. It monitors the DC bus voltage (UDC) in real-time. When the UDC exceeds the preset "on" threshold (such as approximately DC 750V when set to 460V line voltage), the internal regulator of the DBU (initially a BUA type hysteresis regulator, later upgraded to a BUC type PWM regulator) will drive the IGBT to conduct at high frequency (BUC is 1kHz), connecting the DC bus to the external braking resistor. The braking resistor consumes energy, causing a decrease in UDC. When UDC is below the "turn off" threshold (such as DC 720V), IGBT turns off and stops consuming energy. Through this "switch" or "PWM" control, the DBU maintains the bus voltage within a safe range, allowing the inverter to quickly stop according to the set deceleration slope or stably control the potential load.

INVERTRON DBU offers four power levels and two configurations:

Basic models: DBU-50 (37kW), DBU-100 (75kW), DBU-200 (150kW)

Built in diagnostic card types: DBU-50-DIS, DBU-100-DIS, DBU-200-DIS

High power type (standard built-in diagnostic): DBU-400 (300kW)

Analysis of Key Specifications and Technical Parameters

Choosing and applying DBU requires a thorough understanding of its electrical and mechanical parameters.

Electrical specifications:

Maximum braking current (Imax): From 50A for DBU-50 to 400A for DBU-400, it defines the peak processing capability of the unit.

Minimum value of braking resistance: To ensure that the IGBT inside the DBU does not overcurrent, a resistor with a resistance value not less than the specified value must be used. The resistance value varies depending on the line voltage jumper setting (415V or 460V). For example, DBU-100 requires a resistance of ≥ 7.2 Ω at 460V.

Braking power:

Continuous braking power: The power that can be continuously consumed for a long time under a 460V bus voltage (such as 18kW for DBU-100).

Short term braking power: The peak power allowed to be processed in a short period of time (such as 75kW for DBU-100 at 460V). This corresponds to the power at which the maximum current Imax flows through the minimum allowable resistance.

Allowable load characteristics: To prevent thermal overload, the load of DBU during a 10 minute cycle must be limited within the current time area of "Imax x x 2.5 minutes". DBU-400 allows 400A current to last for 110 seconds/10 minutes.

Line voltage selection (key setting): The blue jumper plug (position: 460V/415V) on the regulator card under the DBU cover plate is crucial. It determines the operating voltage threshold of DBU.

Factory default: For safety reasons, set to 460V (corresponding to UDC activation point~750V).

415V system: Used for GV3000 frequency converters with line voltage ≤ 415V, or INVERTRON VTI/VCI/VGI 415V type (with a maximum allowable bus voltage of DC 720V), the jumper must be changed to 415V (corresponding to UDC turn-on point~680V).

The consequences of incorrect settings: Using 460V settings in a 415V system can cause the DBU to act too late, and the bus voltage may have triggered the inverter overvoltage fault before reaching 750V.

Environment and Machinery: Operating temperature range of 0-40 ° C (rated below 40 ° C), protection level IP20. During installation, it is necessary to ensure that the heat sink is vertical and there is at least 100mm space above and below for natural air convection (DBU-400 with fan, requires forced air cooling, air volume 158m ³/h).