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The back EMF-based sensorless control of PMSMs is widely applied to the blowers and hermetic compressors of heating, ventilation and air-conditioning (HVAC) systems. For the sensorless control of PMSMs, a smooth transition from the I–f startup to the closed loop speed control with a rotor speed estimator is required. This paper proposes a smooth transition algorithm that can minimize torque and speed fluctuations under all load conditions. At the starting of a transition, the dq current based on the reference rotor position for I–f control is switched to the dq current with the estimated rotor position. The operating point of the dq current moves from I–f control to MTPA (maximum torque per ampere) operation, while the dq current follows a constant torque curve. Experimental results show that the torque and speed fluctuations under the proposed transition algorithm were significantly reduced under all load conditions. [ABSTRACT FROM AUTHOR]

Highlights: [•] The optimal control gains were obtained from the linear matrix inequalities with mixed H 2 and H ∞ control algorithm. [•] The proposed method guaranteed convergence, stability, and provided a way for disturbance rejection and energy savings. [•] The coupling effects occurred among the compressor speed, opening degrees, evaporator temperatures and superheats. [•] The system identification and thermal dynamics equations could obtain the inner and outer loop transfer functions. [•] All simulations in this paper were in discrete time domain. [ABSTRACT FROM AUTHOR]

Abstract: A direct-expansion (DX) variable-air-volume (VAV) air-conditioning (A/C) system consists of a VAV air-distribution sub-system and a DX refrigeration plant. This paper reports in detail on a novel capacity controller developed for the DX VAV A/C system to regulate its compressor speed and hence its cooling capacity. The capacity controller consisted of both a numerical calculation algorithm (NCA), which was fundamentally based on the principle of energy balance using a number of real-time measured system’s operating parameters, and a dead-band for decoupling the control actions from both the capacity controller and a conventional PI feedback controller for regulating the opening of an electronic expansion valve (EEV) in the refrigeration plant. To study the feasibility of the capacity controller, an experimental rig for the DX VAV A/C system having two conditioned spaces was built and experimental tests were carried out. The test results showed that using the capacity controller, the cooling capacity of the system’s refrigeration plant can be accurately and continuously regulated and the supply air temperature well maintained at its desired value. The desirable independent zoning-control for space air temperatures can be successfully achieved by the DX VAV A/C system and the control performance for air temperatures in the conditioned space was highly satisfactory. [Copyright &y& Elsevier]