Digital current control of a three‐phase four‐leg voltage source inverter by using p – q – r theory

In this study, balanced/unbalanced linear/non‐linear current control in three‐phase four‐leg voltage source inverter (VSI) is carried out by using modified p – q – r method instead of the classical p – q – r method, digital proportional integral derivative (PID) control rule and three‐dimensional (3D) space vector pulse width modulation (3D SVPWM). For this purpose, three‐phase four‐leg power inverter and PWM signal generation circuits are designed and modelled separately. Even if the power source voltage is unsymmetrical, the proposed modified p – q – r method leads to measurement and to generating the instantaneous harmonic and reactive components of load current accurately. The performance of the classical p – q – r theory under non‐ideal mains voltages is improved and the accuracy of the proposed modified p – q – r theory is demonstrated both through simulation and real‐time application. Each phase of the three‐phase four‐leg VSI modelled directly in abc reference frame is decoupled from each other This simplifies the digital PID controller design significantly. Modelling of the whole system, modified p – q – r measurement and digital PID design steps are given in detail. Real‐time experimental results for the designed three‐phase four‐leg VSI in stand‐alone mode are compared with the simulation results.