Cause and solving method of elevator inverter voltage

Frequency converter in the process of commissioning and use often encounter a variety of problems, including overvoltage phenomenon is most common.

After the overvoltage, frequency converter in order to prevent internal circuit damage, overvoltage protection will, cause the inverter to stop running, cause the device to not work properly. So steps must be taken to eliminate overvoltage, prevent the occurrence of failure. Due to the different applications of frequency converter and motor, cause of overvoltage is not the same, so you should take corresponding countermeasures under the circumstances.

Overvoltage and regenerative braking

So-called over-voltage converter, is due to various reasons causing the inverter voltage exceeding the rated voltage, focus inverter DC voltage on the DC bus. Normal working hours, inverter for three-phase full-wave rectified DC voltage average. If 380V voltage calculation, the average DC voltage Ud=1.35U line =513V.

In voltage occurs, the DC bus capacitor will be charging, voltage up to 700V, (varies by model) frequency converter overvoltage protection. Overvoltage caused by two main reasons: power supply voltage and the voltage. Power supply voltage is the power supply voltage is too high the DC bus voltage exceeds the rated value. Today most up to 460V inverter input voltage and, therefore, caused by power supply overvoltage is very rare.

Issues discussed in this paper are recycled over voltage. Regenerated voltages for the following main reasons: when the GD2 (flywheel torque) inverter when load deceleration deceleration time set too short; motor under the influence of external forces (wind machine, drawing machine) or the potential load (elevators, cranes) down. For these reasons, the motor speed actual speed higher than the inverter instruction, that is, speed than the synchronous speed of the rotor, the slip of the motor is negative, rotor rotating in the opposite direction of the magnetic field and the motor when cutting, the electromagnetic torque for hindered rotation of the direction of braking torque. So the motor actually is in a power state, the kinetic energy of the load is "renewable" electricity.

Renewable energy by the freewheeling diodes on inverter inverter DC energy storage capacitor charge causes DC bus voltage to rise, which is recycled over voltage. Due to overvoltage during torque contrast with original torque, torque and regeneration process of overvoltage is regenerative braking process. In other words, eliminating the renewable energy also improves brake torque. If renewable energy is limited, due to 20% of the frequency converter and the motor itself has regenerative braking capability, this energy will be consumed were converters and motors. If this part of the energy of more than the consumption capacity of the inverter and the motor, DC circuit the capacitor will be charging, frequency converter overvoltage protection function, operation stops. To avoid this from happening, this energy must be disposed of in a timely manner, but also enhances the braking torque, this is the aim of regenerative braking.

Over voltage prevention measures

Due to the different causes of overvoltage and take countermeasures is not the same. Stops overvoltage phenomenon produced in the process, if the parking time or location without special requirements, you can extend the inverter deceleration time or free parking to solve. Free parking which is inverter disconnect the main switch, motor free sliding stops.

If have certain requirements for parking or parking place, you can use DC brake (DC brake). DC braking function is the Motor reducer to a certain frequency, into direct current in the stator winding to form a static magnetic field. Motor rotor winding cutting the field and produce a braking torque, load the kinetic energy into electrical energy in the form of heat consumption in the motor rotor, therefore this type of brake, known as dynamic braking. DC braking process actually contains a regenerative braking and braking in two processes. Only regenerative braking 30-60% this method of braking efficiency, braking torque is smaller. Because of the energy consumed in the motor may overheat the motor, so the brake time should not be too long. And DC braking start frequency, braking time and brake voltage are manually set, regenerated voltage level cannot be adjusted automatically, thus DC overvoltage of brakes cannot be used for normal operation, can only be used when parking brake.

Deceleration (from high to low speed, but does not stop) due to load the GD2 (flywheel torque) of overvoltage arising excessive, prolonged deceleration time can be taken to deal with it. In fact, this method is using the principle of regenerative braking, prolonged deceleration time only controls the load voltage to the inverter charging speed, regenerative braking capacity of the inverter itself 20% rational utilization. For those due to external forces (including the potential delegation) and the motor load in the regeneration State, due to its normal operation in brake State renewable energy is too high by the inverter itself cannot be consumed, making it impossible to use DC braking or prolonged deceleration time approaches.

Regenerative braking compared with DC brake with high braking torque and the braking torque according to the size of the load the required braking torque (that is, the level of renewable energy) braking unit automatic control by frequency converter. Regenerative braking is best used in the process of working to provide load brake torque.