Michael J. Ryan

Control topology options for single-phase UPS inverters

Four control topologies for single-phase uninterruptible power system (UPS) inverters are presented and compared, with the common objective of providing a dynamically stiff, low total harmonic distortion (THD), sinusoidal output voltage. Full-state feedback, full-state command controllers are shown, utilizing both filter inductor current and filter capacitor current feedback to augment output voltage control. All controllers presented include output voltage decoupling in a manner analogous to back EMF decoupling in DC motor drives. Disturbance input decoupling of the load current and its derivative is presented. An observer-based controller is additionally considered and is shown to be a technically viable, economically attractive option. The accuracy transfer function of the observer estimate is used to evaluate its measurement performance. Comparative disturbance rejection is evaluated by overlaying the dynamic stiffness (inverse of output impedance) frequency response of each controller on a single plot. Experimental results for one controller are presented.

A high performance sine wave inverter controller with capacitor current feedback and "back-EMF" decoupling

This paper presents a state space approach to the problem of controlling a single phase PWM inverter with an LC output filter. These types of inverter are often used in uninterruptable power supplies (UPS) where a sine wave output voltage is to be maintained. Output voltage control is structured around an inner filter capacitor current loop where capacitor current is sensed via a single, small current transformer. This avoids the expense of multiple, active current sensors found in alternative designs. Performance of the capacitor current loop is enhanced with active decoupling of both the DC bus and the equivalent back-EMF of the output voltage. The output dynamic stiffness of the system is analyzed and plotted. Experimental results yield less than 0.5% total harmonic distortion (THD) at full load (8 kW), with transient response times of less than 200 /spl mu/s.<<ETX>>

Modeling of multileg sine-wave inverters: a geometric approach

Three fundamental sine-wave inverter topologies are analyzed: two-leg (one-phase, two-wire); three-leg (three-phase, three-wire); and four-leg (three-phase, four-wire). The topologies are full-bridge voltage-source inverters with LC filters suitable for producing sinusoidal output voltages. The switching states and corresponding output voltage vectors produced by each inverter are identified and presented along with an analysis of the geometric arrangement of these voltage vectors. A pattern of characteristics is established whereby the qd modeling forms commonly used with three-leg inverters are extended to address the expanded capabilities of the four-leg inverter. A unique 4/spl times/4 decoupling transformation matrix is presented for the four-leg inverter that enables direct transformation between the four-degree-of-freedom (DOF) leg-modulation space of the inverter and its corresponding 3-DOF output-voltage space. This is shown to be directly analogous to the well-known abc-qd transformation developed for the three-leg inverter. Fully decoupled models for each inverter are presented.

Modeling of sinewave inverters: a geometric approach

Three fundamental sinewave inverter topologies are analyzed: 2-leg (1-phase, 2-wire); 3-leg (3-phase, 3-wire); and 4-leg (3-phase, 4-wire). The topologies are full-bridge voltage-source inverters with LC filters suitable for producing sinusoidal output voltages. The switching states and corresponding output voltage-vectors produced by each inverter are identified and presented along with an analysis of the geometric arrangement of these voltage-vectors. A pattern of characteristics is established whereby the qd modeling forms commonly used with 3-leg inverters are extended to address the expanded capabilities of the 4-leg inverter. A unique 4/spl times/4 decoupling transformation matrix is presented for the 4-leg inverter that enables direct transformation between the four degree-of-freedom (DOF) leg-modulation space of the inverter and its corresponding 3-DOF output-voltage space. This is shown to be directly analogous to the well-known abc-qd transformation developed for the 3-leg inverter. Fully decoupled models for each inverter are presented.

Decoupled control of a 4-leg inverter via a new 4/spl times/4 transformation matrix

Four-leg (3-phase 4-wire) inverters are developed to power unbalanced/nonlinear three-phase loads. A unique 4/spl times/4 decoupling transformation matrix is used that enables direct transformation between the four degree-of-freedom (DOF) leg-modulation space of the inverter and its corresponding 3-DOF output-voltage v space. This is analogous to the well-known 3/spl times/3 abc-qd transformation developed for the 3-leg inverter. Details of this new 4/spl times/4 Quad transform are provided, along with a depiction of the voltage-vectors produced. Advanced synchronous-frame control techniques are applied with this 4-to-3 abcn-qdo transform to create a UPS-style inverter with sinewave output. Experimental results for an 8.6 kV a prototype inverter are presented.

A "power-mapping" variable-speed control technique for a constant-frequency conversion system powered by a IC engine and PM generator

A variable-speed power conversion system is considered where a permanent magnet generator (PMG) driven by an IC engine supplies power to an electronic inverter. The AC voltage from the PMG is typically diode-rectified into a DC link, which is utilized by the inverter to produce constant-frequency, constant-voltage output. These electronic gensets can be smaller, lighter and have higher performance than their fixed-speed counterparts with synchronous alternators under field control. Such attributes are attractive for mobile and stand-by power applications. The added flexibility of a variable-speed genset system must be met with suitable techniques for directing the speed at which the engine should operate for a given electrical load. Constraints on torque, speed, and DC link voltage must additionally be met. This paper reviews conventional methods, and presents a new technique utilizing the operating power of the system as an input to a power-speed map for the system to follow. Experimental results are included.

A new ZVS LCL-resonant push-pull DC-DC converter topology

A new LCL-resonant DC-DC power converter topology is presented in which the resonant CL components are located after the output rectifier diodes. The push-pull power converter topology is suitable for unregulated low-voltage to high-voltage power conversion, as in battery powered systems where input currents can exceed input voltages by an order of magnitude. The resonant circuit operates at twice the switching frequency, allowing for small resonant components. The MOSFET primary switches operate under zero voltage switching (ZVS) conditions due to commutation of the transformer magnetizing current and the snubbing effect of the drain-source capacitance. Output rectifier turn-off is effectively snubbed by the resonant capacitor. Laboratory tests show 93% efficiency at 12 V, 160 A input; 235 V, 1.8 kW output. A surge capability of 5 kW for 1 s has been demonstrated. Circuit simulations and experimental results are presented and are shown to have excellent agreement with fundamental mode analysis.