Isolated multiple output Cuk converter with primary input voltage regulation feedback loop decoupled from secondary load regulation loops
First Claim
1. In a dc-to-dc switching-mode converter having a power transformer for isolation between a primary side power stage connected to a dc voltage source and a secondary side power conversion stage connected to a load, said dc-to-dc switching mode converter having two nonisolated feedback circuits, one on the primary side and the other on the secondary side of said power transformer, which decouple output voltage regulation due to any change in said input voltage from regulation of output voltage to said load due to load current changes, thereby obviating entirely the need for any isolation in said two nonisolated feedback circuits,said primary side feedback circuit regulating against changes in input voltage from said dc voltage source by controlling pulse width modulation of a duty ratio, d, of a controllable switch in said primary side power stage,said secondary side feedback circuit regulating against load current changes by controlling pulse width modulation of a duty ratio, d1, of a current bidirectional controllable switch in said secondary side power conversion stage,said primary side feedback circuit being decoupled from said secondary side feedback circuit, whereby any change to said input voltage will not affect said duty ratio, d1 of said current bidirectional controllable switch of said secondary side power conversion stage,sensing means on said primary side power stage for sensing the switch-off voltage of the primary side controllable switch while it is turned off and feedback means for regulation of said switch-off voltage sensed through said primary side feedback circuit without a need for isolation in a circuit from said sensing means to said feedback means,said primary side and secondary side controllable switches being turned on simultaneously and at a constant switching frequency, and turned off under control of their respective nonisolated feedback circuits, andmeans for synchronously turning on said secondary side controllable switch with said primary side controllable switch without need for isolation in said synchronization means,whereby overall conversion gain A of said dc-to-dc converter is the product of two gains A1 and A2, where A1 is dependent only on said duty ratio, d, of said primary side controllable switch, while A2 is dependent only on said duty ratio, d1, of said secondary side current bidirectional controllable switch.
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Abstract
A novel isolated, capacitive idling, Cuk switching-mode converter features two separate nonisolated feedback loops, one on the primary side to regulate against input voltage changes and the other on the secondary side to regulate against load current changes only. While preserving cost, size and simplicity of conventional multiple output switching-mode converters, the new converter and feedback control approach offers the advantages of simple feedback control implementation due to elimination of isolation requirements in the feedback control circuits, simultaneous regulation of all output voltages from no load to full load, and greatly improved bandwidth and step-load transient response. For operation from a rectified ac line, feedback control on the input to the transformer is modified to force the average input current to follow the full-wave rectified ac line voltage for unity power factor (UPF) performance on the input and wide bandwidth voltage regulation on the output. Both are demonstrated simultaneously in a single, isolated, multiple ac-to-dc switching-mode power converter. The novel decoupled feedback control is shown to be equally applicable to a number of Cuk-type converter topologies featuring capacitive energy transfer from a voltage source to a load.
83 Citations
10 Claims
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1. In a dc-to-dc switching-mode converter having a power transformer for isolation between a primary side power stage connected to a dc voltage source and a secondary side power conversion stage connected to a load, said dc-to-dc switching mode converter having two nonisolated feedback circuits, one on the primary side and the other on the secondary side of said power transformer, which decouple output voltage regulation due to any change in said input voltage from regulation of output voltage to said load due to load current changes, thereby obviating entirely the need for any isolation in said two nonisolated feedback circuits,
said primary side feedback circuit regulating against changes in input voltage from said dc voltage source by controlling pulse width modulation of a duty ratio, d, of a controllable switch in said primary side power stage, said secondary side feedback circuit regulating against load current changes by controlling pulse width modulation of a duty ratio, d1, of a current bidirectional controllable switch in said secondary side power conversion stage, said primary side feedback circuit being decoupled from said secondary side feedback circuit, whereby any change to said input voltage will not affect said duty ratio, d1 of said current bidirectional controllable switch of said secondary side power conversion stage, sensing means on said primary side power stage for sensing the switch-off voltage of the primary side controllable switch while it is turned off and feedback means for regulation of said switch-off voltage sensed through said primary side feedback circuit without a need for isolation in a circuit from said sensing means to said feedback means, said primary side and secondary side controllable switches being turned on simultaneously and at a constant switching frequency, and turned off under control of their respective nonisolated feedback circuits, and means for synchronously turning on said secondary side controllable switch with said primary side controllable switch without need for isolation in said synchronization means, whereby overall conversion gain A of said dc-to-dc converter is the product of two gains A1 and A2, where A1 is dependent only on said duty ratio, d, of said primary side controllable switch, while A2 is dependent only on said duty ratio, d1, of said secondary side current bidirectional controllable switch.
Specification