TWI405395B - A two-stage cascaded dc to dc converter with isolated device - Google Patents

Abstract

This invention is a two-stage cascaded DC to DC converter with isolated device, which is suitable in receives an input d.c. voltage and then converts the d.c. voltage, under a specified condition, to a load in output. The two-stage cascaded DC to DC converter with isolated device consists of three units: one is a unit for stabilization, as the first stage of regulated and boosted voltages, and is connected in parallel with the source of input voltage; another one is a unit for isolation, as the second stage of energy and signal transfer with isolation; and the other one is a control unit, in which both of pulse width modulation (PWM) and phase-shifting modulation are included for receiving the output voltage. To use the value of output voltage, which is taken by the control unit of pulse width modulation (PWM) and phase-shifting modulation, as a base in controlling the first stage of regulated and boosted voltages in order to control the input voltage at the second stage of energy transfer with isolation, so that the purpose for a constant output voltage is achieved. Additionally, during the process of keeping voltage in a steady sate, the second stage of energy and signal transfer with isolation remains and fixes at the minimum phase-shifting modulation so as to obtain the maximum utilization effectiveness. Moreover, the bulk storage capacity of input is normally reduced by use of the characteristic of boosted voltage of the first stage of regulated and boosted voltages.

Description

Two-stage isolated DC converter

The invention relates to a DC conversion device with isolation, in particular to a switching DC power supply for improving DC conversion efficiency.

Referring to FIG. 1 , it is a general isolated DC conversion device, the main function of which is to receive a DC input voltage source 11 and convert the voltage level output to a load 12, the isolated DC conversion device includes: The DC input voltage source 11 is connected in parallel with a storage capacitor 13; and a full bridge switching unit 14; and an isolation unit 15; and a receiving isolation transformer output rectifying and filtering unit 16; and a voltage for receiving the load 12 and This voltage value controls the pulse width modulation control unit 17 of the duty cycle of the switching element 141 of the full bridge switching unit 14 and the current detector 18 of an overcurrent protection.

The full bridge switching unit 14 has a full bridge switching structure composed of four switching elements 141 and is subjected to duty cycle control of the pulse width modulation control unit 17 to adjust the transmission energy to the output load terminal.

The isolation unit 15 is mainly a transformer 151 for isolating energy transmission, and an optical isolator 152 for isolating the output voltage feedback signal.

The rectifying and filtering unit 16 mainly rectifies the AC voltage output from the isolation transformer 151 into a DC voltage by the full-bridge diode rectifier 161, and chopps and multiplexes the high-frequency switching thereof through the output low-pass filter 162. The filter is removed to achieve a smooth output voltage.

The pulse width modulation control unit 17 receives the output voltage of the isolated DC converter. And controlling the output pulse width modulation control signal to the switching element 141 of the full bridge switching unit 14 according to the voltage value outputted by the isolated DC conversion device to the load 12, thereby controlling the closed circuit and the open circuit of the switching element 141 The size of the cycle is used to regulate energy transfer and voltage regulation.

The current detector 18 detects the input current and sends it to the pulse width modulation control unit 17. When an overcurrent occurs, the switching element 141 of the full bridge switching unit 14 opens it to cut off the input current loop.

However, in the energy transmission process of controlling the output to the load 12 in the above manner, since the load is light, the duty cycle of the pulse width modulation control signal of the pulse width modulation control unit 17 becomes small, and the conversion of the isolated DC conversion device is made. The efficiency is declining.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a switched DC power supply that can improve DC conversion efficiency, and to use a smaller output when the input power is turned off in order to make the output voltage hold time (Hold Up Time) greater than 20 milliseconds. A two-stage isolated DC converter that inputs the capacitance of the storage capacitor.

Therefore, the two-stage isolated DC conversion device of the present invention is adapted to receive a DC input voltage source and convert the voltage level output to the load, and the DC conversion device of the two-stage isolation includes: a parallel connection with the DC input voltage source a first stage voltage regulation and boosting unit; a second stage isolated energy conversion and signal conversion unit; and an output rectification filtering unit; and a pulse width modulation and phase modulation control for receiving an output load voltage unit.

The first stage of the regulation and boost unit has a zero voltage switching boost circuit to reduce switching losses. Its function one is to provide a lower voltage to the second-stage isolated energy conversion unit when the load is light. When the load is heavy, a higher voltage is supplied to the second-stage isolated energy conversion unit to expand the operation interval of the zero-voltage switching of the second-stage energy conversion unit, thereby expanding the high-efficiency conversion interval. Its function two: to expand the input voltage range, in order to maintain the output voltage for a period of time when the input voltage is disconnected, the first stage of the voltage regulator and boost unit can boost the input voltage, so the output voltage is maintained. For a constant time, a smaller input storage capacitor value can be used.

The second-stage isolated energy conversion unit has a fixed minimum phase difference, so that the phase difference is not changed due to light weight and weight during energy conversion, so that energy conversion is maximized and return loss is minimized.

The output rectification filtering unit converts the AC voltage outputted by the isolation transformer through two switching elements, and rectifies the AC voltage into a DC voltage, and filters the high frequency switching chopping and noise through the output low-pass filter. Dropped to achieve a smooth output voltage.

The pulse width modulation and phase modulation control unit receives the output voltage of the load end, and controls the width of the output pulse wave according to the output voltage value of the load end, and transmits the output pulse wave to the first stage voltage regulation and rise Pressing the switching element of the unit to control the duty cycle of the first stage switching element; additionally generating a set of fixed phase difference control signals to the second stage isolated energy conversion unit to control the full bridge switching element and sending to The rectification control switching element of the output rectification and filtering unit; and the output voltage of the first stage voltage stabilizing and boosting unit is received as a series two-stage isolated DC conversion device, which is started slowly to reduce the starting current.

The invention utilizes the pulse width modulation and phase modulation control unit to extract the output voltage value of the load terminal, and according to the voltage value, controls the output voltage of the voltage regulator and the boosting unit of the first stage, thereby controlling the second level isolation type. The input voltage of the energy conversion unit achieves the purpose of stabilizing the output voltage. In the voltage regulation process, the second-stage isolated energy conversion unit always maintains a minimum phase difference to expand the operation interval of the zero-voltage switching of the second-stage energy conversion unit, thereby achieving an extended high-efficiency conversion interval and a minimum return loss. . The boost function is provided when the input voltage is open, and a smaller input storage capacitor value can be used.

The foregoing and other technical contents, features, and advantages of the present invention will be apparent from the following detailed description referring to FIG.

Referring to FIG. 2, a preferred embodiment of the two-stage isolated DC conversion device of the present invention is adapted to receive a DC input voltage source 21 and convert a DC voltage level output to a load 22. The two-stage isolated DC conversion device The utility model comprises: a first-stage voltage stabilization and boosting unit 23 connected in parallel with the DC input voltage source 21; a second-stage isolated energy conversion and signal conversion unit 24; and an output rectification filtering unit 25; The pulse width modulation and phase modulation control unit 26 receives the output voltage of the first stage voltage stabilization and boosting unit 23 and the output voltage of the rectifying and filtering unit 25.

The voltage stabilizing and boosting unit 23 of the first stage has an input storage capacitor 231 and a boosting circuit 232 in parallel with the DC input voltage source 21, and a boosting zero voltage switching circuit 233. When the boosting circuit 232 is turned on by the first-stage switching element 2321, the DC input voltage source 21 stores energy to the storage inductor 2322 and establishes a voltage. When the first stage switching element 2321 is open, the voltage of the DC input voltage source 21 is added to the voltage of the first stage of the storage inductor 2322, and the energy is transmitted to the first stage output capacitor 234 via the first stage diode 2323; The zero voltage switching circuit 233 turns on the zero voltage switching element 2331 before the first stage switching element 2321 is turned on, and utilizes the resonance between the zero voltage resonant capacitor 2332 and the zero voltage resonant inductor 2333, and the zero voltage resonant capacitor 2332 The energy is converted to a zero voltage resonant inductor 2333, causing the voltage of the zero voltage resonant capacitor 2332 to drop to zero, at which point the voltage between the drain and source of the first stage switching element 2321 also drops to zero. The first stage switching element 2321 is turned on again to reduce the switching loss of the first stage switching element 2321. In addition, after the first-stage switching element 2321 is turned on, the zero-voltage switching element 2331 is turned off, so that the energy stored in the zero-voltage resonant inductor 2333 is transmitted to the output capacitor 234 via the zero-voltage diode 2334.

The second-stage isolated energy conversion and signal conversion unit 24 is mainly composed of two units of an isolated energy conversion unit 241 and an isolated signal conversion unit 242. The isolated energy conversion unit 241 includes a pair of forearm switching elements 2411 and a pair of rear arm switching elements 2412 and an isolation transformer 2413 of a full bridge switching architecture. The two switching elements 2411 that drive the forearms are a pair of signals with a duty cycle fixed at 50% and complementary. The same is true for the two switching elements 2412 that drive the rear arm, which are fixed to 50% by a pair of duty cycles and are complementary signals, but the signal phase difference between the forearm and the rear arm is fixed at 3% of the period. The isolation transformer 2413 transmits the primary side energy of the transformer to the secondary side; the signal isolator unit 242 is an optical coupling isolator 2421 that feeds back the voltage signal and a pulse isolation transformer 2422 that drives the rectification switching element 2511.

The output rectification filtering unit 25 includes a rectifying unit 251 and an output low pass filter 252. The rectifying unit 251 includes a pair of switching elements 2511, the driving signal of which is related to the forearm switching element 2411 of the full-bridge switching architecture, and the lower rectifying switching element 2511 of the opposite rectifying unit is also turned on when the upper switching element 2411 of the forearm is turned on. . When the lower switching element 2411 of the forearm is turned on, the upper rectifying switching element 2511 of the rectifying unit is also turned on at the same time. In this way, the secondary side output AC voltage of the isolation transformer 2413 can be rectified into a DC voltage output; the DC output voltage is formed by the filter inductor 2521 and the filter capacitor 2522 to form a low pass filter 252, which filters the high frequency switching chopping and noise. Dropped to achieve a smooth output voltage.

The pulse width modulation and phase modulation control unit 26 receives the output voltage Vb of the first stage by an analog-to-digital port of the control unit 26, and controls the first stage of the boost during the startup of the DC converter of the two-stage isolation. The first stage switching element 2321 of the loop 232 is turned on and off, causing the device to start slowly without causing a large starting current; the analog detector 27 is received by another analog-to-digital port of the control unit 26 to detect the second The input current of the stage is used as the current feedback signal I, so that the control unit 26 turns off all the switching elements of the two-stage isolated DC conversion device when detecting the overcurrent to avoid the component burning; another analog-to-digital position of the control unit 26 The port receives the feedback signal Vo of the second stage output voltage isolated via the optical coupling isolator 2421 as the generation control signals M1 and M2 to control the switching elements of the switching element 2321 and the zero voltage switching circuit 233 of the first stage boosting circuit 232. 2331; MA, MB, MC, and MD of the control unit 26 are phase shift control signals generated by the control unit to be fixed to a period of 3% phase difference to control the full bridge of the isolated energy conversion 241 One of the pair of forearm switching elements 2411 and a pair of rear arm switching elements 2412.

The following is a detailed description of the overall operation of the DC-DC converter of the present invention.

Referring to FIG. 3, when the DC conversion device of the two-stage isolation of the present invention is designed, when the input voltage Vin is DC 380V, the output load is 20% (200W) of the full load 1000W. When the input voltage Vin is 380V and the output voltage Vo is maintained at 12V, the voltage regulation and boosting unit 23 of the first stage is in an inoperative state. Since the voltage regulation of the first stage and the boosting unit 23 are not operated, the first stage output voltage Vb is 378.8V lower than the input voltage Vin is 380V, which is mainly the voltage of the first stage diode 2323 in the circuit. Caused by the fall. According to the present invention, the two-stage isolated DC conversion circuit device of the present invention can reduce the loss of the circuit when the operation of the first stage of the voltage stabilization and boosting unit 23 is in a state of no operation when operating at a low load, thereby improving the conversion. effectiveness.

Referring to FIG. 4, when the DC conversion device of the two-stage isolation of the present invention is designed, when the input voltage Vin is DC 380V, the output load is 1000W full load. When the input voltage Vin is 380V and the output voltage Vo is maintained at 12V, the voltage regulation and boosting unit 23 of the first stage is in a boosting operation, and the input voltage Vin is boosted to 380V to the output voltage Vb of the first stage is 413V. In this way, the output load can be maintained at 1000W and the output voltage Vo is 12V.

5 is a graph showing the driving signal M1 of the first-stage switching element 2321 of the first-stage voltage stabilization and boosting unit 23 and the driving signal M2 of the zero-voltage switching element 2331 when the output load is 1000 W at full load.

6 is a plot of the MA and MB drive signals of one of the full bridges of the second stage isolated energy conversion unit 241 to the forearm switching elements 2411 and the MC and MD drive signals of the pair of rear arm switching elements 2412.

Referring to FIG. 7, the input voltage Vin and the output voltage Vo of the output voltage Vo have a hold time (Hold Up Time) greater than 20 milliseconds. When the input voltage Vin of the two-stage isolated DC conversion device of the present invention is turned off at 20 milliseconds, and the output voltage Vo is kept above 40 milliseconds, the value of the input storage capacitor 231 component is 330 μF, which is more than The 990μF used in the conversion circuit device is small.

In summary, the present invention utilizes the pulse width modulation and phase modulation control unit 26 to capture the output voltage value of the load terminal as a basis for controlling the voltage stabilization and boosting unit 23 of the first stage. And by providing a boost function when the input voltage is disconnected, it is possible to use a storage capacitor having a smaller input capacitance. The output voltage Vb value of the first stage voltage stabilization and boosting unit 23 is taken as the slow start control of the voltage regulation and boosting unit 23 of the first stage. The second-stage isolated energy conversion unit 241 is always maintained at the minimum phase difference control to expand the operation interval of the zero-voltage switching of the second-stage energy conversion unit, thereby achieving an extended high-efficiency conversion interval and a minimum return loss.

The above is only the preferred embodiment of the present invention, and the scope of the invention is not limited thereto, that is, the simple equivalent changes and modifications made by the scope of the invention and the description of the invention are All remain within the scope of the invention patent.

twenty one. . . DC input power

twenty two. . . load

twenty three. . . First stage voltage regulator and boost unit

231. . . Input storage capacitor

232. . . Boost loop

2321. . . First stage switching element

2322. . . First stage energy storage inductor

2323. . . First level diode

233. . . Zero voltage switching loop

2331. . . Zero voltage switching element

2332. . . Zero voltage resonant capacitor

2333. . . Zero voltage resonant inductor

2334. . . Zero voltage diode

234. . . First stage output capacitor

twenty four. . . Second stage isolation energy conversion and signal conversion unit

241. . . Isolated energy conversion unit

2411. . . Pair of forearm switching elements

2412. . . a pair of rear arm switching elements

2413. . . Isolation transformer

242. . . Isolated signal conversion unit

2421. . . Optically coupled isolator

2422. . . Pulse isolation transformer

25. . . Output rectification filter unit

251. . . Rectifier unit

2511. . . Rectifier switch

252. . . Output low pass filter

2521. . . Filter inductor

2522. . . Filter capacitor

26. . . Pulse width modulation and phase modulation control unit

27. . . Current detector

1 is a schematic diagram of a general isolated DC-to-DC conversion circuit;

2 is a schematic diagram of circuit components of a preferred embodiment of a two-stage isolated DC conversion device of the present invention;

3 is a graph showing the input voltage Vin and the first-stage output voltage Vb and the output voltage Vo of the 20% (200 W) full load 1000 W of the load of the preferred embodiment;

4 is a graph showing the input voltage Vin and the first-stage output voltage Vb and the output voltage Vo of the load of the preferred embodiment of 1000 W;

5 is a graph showing a driving signal M1 of a first-stage switching element of a voltage stabilizing and boosting unit of the first stage of the preferred embodiment and a driving signal M2 of the zero-voltage switching element;

6 is a graph showing the MA and MB driving signals of one of the full-bridge type of the second-stage isolated energy conversion unit of the preferred embodiment, and the MC and MD driving signals of the pair of rear-arm switching elements;

7 is a graph of the input voltage Vin and the output voltage Vo when the input voltage Vin is turned off and the output voltage Vo is maintained above 20 milliseconds in the preferred embodiment;

twenty one. . . DC input voltage source

twenty two. . . load

twenty three. . . First stage voltage regulator and boost unit

231. . . Input storage capacitor

232. . . Boost loop

2321. . . First stage switching element

2322. . . First stage energy storage inductor

2323. . . First level diode

233. . . Zero voltage switching loop

2331. . . Zero voltage switching element

2332. . . Zero voltage resonant capacitor

2333. . . Zero voltage resonant inductor

2334. . . Zero voltage diode

234. . . First stage output capacitor

twenty four. . . Second stage isolation energy conversion and signal conversion unit

241. . . Isolated energy conversion unit

2411. . . Pair of forearm switching elements

2412. . . a pair of rear arm switching elements

2413. . . Isolation transformer

242. . . Isolated signal conversion unit

2421. . . Optically coupled isolator

2422. . . Pulse isolation transformer

25. . . Output rectification filter unit

251. . . Rectifier unit

2511. . . Rectifier switch

252. . . Output low pass filter

2521. . . Filter inductor

2522. . . Filter capacitor

26. . . Pulse width modulation and phase modulation control unit

27. . . Current detector

Claims (11)

A two-stage isolated DC conversion device is suitable for receiving a DC input power source and converting a voltage level output to a load, and the string two-stage isolation DC conversion device comprises: a first stage voltage regulator and boost unit having an output Capacitor, the first-stage voltage regulator and boosting unit boosts the input voltage to the second-stage isolated energy conversion unit and stabilizes the output voltage of the second stage; a second-stage isolated energy conversion unit Having a full bridge switching element that transfers energy from the input to the output and isolates the input voltage from the output voltage, the output capacitor being connected in parallel with the full bridge switching element such that the energy can be cascaded from the first stage Transfer to the second stage and output to the load; a pulse width modulation and phase modulation control unit will generate a pulse width modulation to control the duty cycle of the first stage voltage regulator and boost unit, and a set of phase adjustments The control is to control the second-stage isolated energy conversion unit and the output rectification filtering unit. The two-stage isolated DC conversion device according to claim 1, wherein the first-stage voltage regulation and boosting unit functions to provide a lower voltage to the second-level isolated type when the load is light. The energy conversion unit provides a higher voltage to the second-stage isolated energy conversion unit when the load is heavy. The two-stage isolated DC conversion device according to claim 1, wherein the first-stage voltage regulation and boosting unit functions to keep the output voltage constant for a period of time when the input voltage is disconnected. In this case, the input voltage can be boosted. The two-stage isolated DC conversion device according to claim 1, wherein the first-stage voltage regulator and boost unit have a zero voltage switching loop, and a zero-voltage resonant capacitor is used between the zero-voltage resonant capacitor and the zero-voltage resonant inductor. Resonance, while converting the energy of the zero-voltage resonant capacitor to a zero-voltage resonant inductor, causing the voltage of the zero-voltage resonant capacitor to drop to zero, causing the voltage between the drain and the source of the first-stage switching element to drop to zero, and then The switching of the primary switching element is switched to reduce the loss of switching element switching. Two-stage isolated DC conversion package according to item 1 of the patent application scope The control of the first stage voltage regulator and the boosting unit will capture the output voltage value of the load terminal as a basis for control. The two-stage isolated DC conversion device according to claim 1, wherein the second-stage isolated energy conversion unit has a transformer and is coupled to both ends of the transformer and is controlled by phase modulation. Four full-bridge switching elements, and a rectifier electrically connected to the secondary side of the transformer to rectify the AC voltage output from the transformer to a DC voltage. The two-stage isolated DC conversion device according to claim 1, wherein the second-stage isolated energy conversion unit has a fixed minimum phase difference control signal to control the full-bridge forearm switching element and the rear The arm switching element thus changes its phase difference due to light weight and weight during energy conversion, maximizing energy conversion and minimizing return loss. According to the series two-stage isolated DC conversion device described in claim 1, wherein the pulse width modulation and phase modulation control unit can generate a pulse width modulation control signal, and transmit the output pulse wave to the first A first-stage voltage regulator and a switching element of the boosting unit to control the duty cycle of the first-stage switching element. According to the series two-stage isolated DC conversion device described in claim 1, wherein the pulse width modulation and phase modulation control unit receives the output voltage of the first-stage voltage regulator and the boosting unit at the beginning of the device, and A pulse width modulation control signal is generated to control the duty cycle of the first stage switching element to cause the device to start slowly at the beginning of the device. The two-stage isolated DC conversion device according to claim 1, wherein the pulse width modulation and phase modulation control unit generates a set of phase modulation control signals with a fixed phase difference to be sent to the second level isolation type. The energy conversion unit controls the switching elements of the full bridge switching. According to the series of two-stage isolated DC conversion device described in claim 1, wherein the pulse width modulation and phase modulation control unit sends the pair of forearm signals of the phase modulation control to the output through the isolation of the pulse isolation transformer. The rectifying and filtering unit controls the rectifying switching element.