Frequency converter

FRA30 (FRA40)

FRA30(FRA40) contains all the functions necessary for modern electric drive – you only need to add a battery and a electric induction motor.

Despite its small size (235 mm x 255 mm x 330 cm) and weight (10 kg), the FRA30 (FRA40) is a functional giant. Based off the patented original Stoja technology and computer control algorithms, the FRA30 (FRA40) fulfills all desires. Since 100 parameters can be determined, the frequency converter can be adjusted to any battery, electric induction motor or vehicle.

The frequency converter is designed so that it is robust, vibration-resistant and waterproof, and so suitable for the most demanding applications in industrial vehicles.

FRA30 (FRA40) has already been tested on European, American and Asian vehicles.


Operation principle

The principle of a spatial vector with four-quadratic modulation is used. The entire process is controlled by a 16-bit microprocessor. The frequency converter converts the direct current of the battery into a three-phase alternating current of the appropriate amplitude and frequency and thus drives the electric induction motor.


System startup

Within seconds, the frequency converter runs startup tests for all its components. If the results are satisfactory, control is turned over to the driver. Otherwise, the converter issues an error message.


Charging the batteries during braking

During braking, the electric induction motor becomes a generator. By doing so, the frequency converter returns the recovered energy back to the batteries (recuperation).
The maximum permissible voltage for such charging is a parameter and is adjustable.


Drive batteries

The maximum acceptable battery voltage for the FRA30 (FRA40) is 250V.
During operation, the frequency converter monitors the temperature, voltage, current and power from the batteries.
If the battery voltage falls below the set critical value, the frequency converter will issue a “reserve” warning to the driver, take control of the optimum use of battery power, and execute the driver’s commands within the capability of the system.
The lower battery voltage limit below which the maximum driving acceleration is limited by the frequency converter is also an adjustable parameter.


Connecting the FRA30 (FRA40) with the motor and programmable parameters

    • Number of poles of the engine
    • Magnetising voltage equivalent
    • U/f ratio
    • Maximum speed forward
    • Maximum speed backward
    • Maximum allowed slip
    • Speed sensor parameters


Maximum values of the frequency converter

    • The maximum continuous power of the FRA30 is 21kW and the FRA40 is 30kW
    • The maximum peak power of the FRA30 is 30kW and the FRA40 is 40kW
    • The maximum output current of the FRA30 is 290A and 390 for the FRA40, in the battery voltage range from 125V to 210V
    • Power semiconductor elements are protected against overheating. If necessary the frequency converter switches on an electric water pump. Temperature limits are adjustable
    • Operating temperature of the environment is from -25 ° C to 60 ° C


Gas pedal – adjustable parameters

    • Accelerator potentiometer resistance
    • Maximum allowed slip
    • Minimum position of the pedal
    • Slip of braking when the pedal is released
    • Speed of the motor at minimum pedal position
    • Speed of the motor at maximum pedal position
    • Non-linearity of the pedal, reaction curve
    • Pedal signal filter


Brake pedal

The brake light switch in the vehicle can be wired to the frequency converter. As soon as the driver touches the brake pedal, the frequency converter starts with engine braking; the frequency converter can also operate the brake lights. If such braking is not sufficient, the driver presses on the pedal more and thus activates the mechanical brakes on the vehicle.


Other drive commands

    • “Economy” potentiometer: several parameters serve to limit the output power of the batteries. The frequency converter fulfills the driver’s request for speed and acceleration within the limits specified by these parameters
    • “Turbo” switch: by toggling the switch, the frequency converter increases electric power to the motor by about 15%. The efficiency of the system decreases due to increased motor heat losses, but the acceleration achieved is significantly higher
    • “Cruise control” button: pressing this button ensures constant speed until the accelerator or brake pedal is activated
    • “Direction” switch: determines the direction of rotation of the motor and thus the direction of movement of the vehicle. When reversing, the frequency converter can turn on the reverse lights
    • “Emergency stop” switch: pressing this button immediately stops the drive


Warning lights

    • “Error” lights up when an error occurs in the system
    • “Battery empty” lights up when the battery is discharged
    • “Battery OK” lights up when the battery is working normally
    • “Forward” lights up while driving
    • “Reverse” lights up during reversing
    • “Turbo” shows turbo mode is activated
    • “Cruise control” shows if cruise control is activated

In the event of an inverter failure, the “error” indicator lights up and the “turbo” light flashes at the same time.

Flashing of that light means:

    • 1x – The gas pedal is too pressed at the startup of the frequency converter
    • 2x – the motor rotates too fast at the start
    • 3x – empty battery
    • 4x – short circuit
    • 5x – sensors (voltage, current, speed)
    • 6x – overload (too many number of current limitations)
    • 7x – too low charging voltage or short term power failure during charging, incorrectly connected charger, bolwn battery fuse, …
    • 8x – internal error or some worse problem – service required



During operation, the frequency converter stores information about all important events in the drive system. If you wish that information can be displayed on a computer. A diagram is also available to display.
General communication with computer systems is available through the RS-232 protocol.
The warranty lasts 12 months, when paying regards to general technical norms.