The invention provides a controllable four-quadrant frequency converter for voltage on direct current side and a method thereof, so as to realize direct-current voltage control, improve the quality of the current on line side and feedback the regenerative electric energy to an electric network. The controlling circuit of the frequency converter adopts a single processor and an integrated chip to drive a converter on line side and a converter on motor side to alternately fulfill the functions of rectification and inversion under different loaded states. The processer designed by pipelining can quicken the calculation speed and meets the requirement of real time of controlling of the PWM rectifier, due to the adoption of the vector control and power disturbance compensation method, the unity power factor can be realized when the bidirectional flow of the energy is ensured, the voltage on the direct current side can be accurately controlled, when the load is disturbed, the fluctuation range is smaller, the current on direct current side is estimated, the cost of the products can be saved, the estimation method adopts direct direct-current estimation instead of non alternating current estimation, the disturbance compensation fluctuation is reduced, and the system power is more smooth.