Design of current signal frequency detecting device based on harmonic separation

Abstract

The frequency detection of current and voltage plays a very important role in the grid-connected control strategy. Large detection errors can cause failure of control algorithms such as phase lock, harmonic compensation and reactive power compensation. Based on this, taking the harmonic separation as an example, the variation of amplitude attenuation with frequency detection error is derived under the condition of multi-channel, second-order generalized integrator(SOGI), parallel operation. The effects of frequency detection error on the separation of harmonics are introduced in detail. To reduce the frequency error, a medium and low frequency high precision current signal frequency detecting device is designed, which is divided into two parts: hardware circuit and software design. The hardware includes controller peripheral circuit, sampling circuit, sensor circuit, voltage follower circuit, voltage bias circuit and so on. The software part mainly includes sampling program, frequency detection program and error correction program. Finally, the simulation results verified the correctness of the theoretical analysis of the frequency detection error. The experimental results of current frequency detection verified the feasibility of the design and the high precision of the device.

Keywords

• frequency detection
• grid-connected control strategy
• detection error
• harmonic separation
• high precision detection of medium and low frequency