Current sensorless control method for DAB-based single stage isolated PFC converters

Abstract

A current sensorless control system and a control method thereof for single stage isolated PFC converters based on DAB. By coordinating three control variables of the DAB converter, that is, the inside phase-shifting ratio of the primary side full-bridge, the inside phase-shifting ratio of the secondary side full-bridge, and the phase-shifting ratio between the primary and the secondary sides, the present invention does not need to design additional current controller for the control of the input current, and may make the input current sinusoidal by directly coordinating the output voltage controller, the input voltage and the current modulation step, thereby reducing system cost and the difficulty of controller design, enhancing the stability of the control system, and improving the dynamic performance.

Claims

1. A current sensorless control system for DAB-based single stage isolated PFC converters, comprising a diode rectifier circuit, the diode rectifier circuit further comprising a full rectified bridge having four diodes D.sub.1, D.sub.2, D.sub.3, and D.sub.4, a DC bus having an anode and a cathode, and an input AC voltage source u.sub.in; a DAB converter power main circuit, the DAB converter power main circuit further comprising an input filter capacitor C.sub.i having an anode and a cathode, an output filter capacitor C.sub.o having an anode and a cathode, a primary single-phase full-bridge H.sub.1, the primary single-phase full-bridge H.sub.1 having 4 fully controlled switching devices, S.sub.1, S.sub.2, S.sub.3, and S.sub.4, an AC side, and a DC bus with an anode and a cathode, and each of the fully controlled switching devices, S.sub.1, S.sub.2, S.sub.3, and S.sub.4 having a input port for control signal, a secondary single-phase full-bridge H.sub.2, the secondary single-phase full-bridge H.sub.2 having 4 fully controlled switching devices, Q.sub.1, Q.sub.2, Q.sub.3, and Q.sub.4, an AC side, and a DC bus with an anode and a cathode, and each of the fully controlled switching devices, Q.sub.1, Q.sub.2, Q.sub.3, and Q.sub.4 having a input port for control signal, a high frequency isolating transformer having a primary side and a secondary side, a high frequency inductor L, and a controller having output ports for switching signal that correspond to the input ports for control signal of the switching devices S.sub.1, S.sub.2, S.sub.3, and S.sub.4 of the primary single-phase full-bridge H.sub.1 and the input ports for control signal of the switching devices Q.sub.1, Q.sub.2, Q.sub.3, and Q.sub.4 of the secondary single-phase full-bridge H.sub.2, respectively, and an EMI filter, the EMI filter further comprising a filter inductor L.sub.di, a filter inductor L.sub.fi, and a damping resistance R.sub.di; wherein the controller comprises an A/D sampling step having two signal input ports for sampling an input voltage u.sub.in of a PFC converter and an output voltage v.sub.out of a bus, respectively, a PI controller, a double frequency pulsating digital filtering step being a second-order band rejection filter, and a modulation unit having output ports corresponding to the input ports of the for control signal of the switching devices S.sub.1, S.sub.2, S.sub.3, and S.sub.4 of the primary single-phase full-bridge H.sub.1 and the input ports for control signal of the switching devices Q.sub.1, Q.sub.2, Q.sub.3, and Q.sub.4 of the secondary single-phase full-bridge H.sub.2, respectively; the anode of the DC bus of the primary single-phase full-bridge H.sub.1 is connected to the anode of the input filter capacitor C.sub.i, the cathode of the DC bus of the primary single-phase full-bridge H.sub.1 is connected to the cathode of the input filter capacitor C.sub.i, and the AC side of the primary single-phase full-bridge H.sub.1 is connected to the primary side of the high frequency isolating transformer through the high frequency inductor L; the anode of the DC bus of the secondary single-phase full-bridge H.sub.2 is connected to the anode of the output filter capacitor C.sub.o, the cathode of the DC bus of the secondary single-phase full-bridge H.sub.2 is connected to the cathode of the output filter capacitor C.sub.o, the AC side of the secondary single-phase full-bridge H.sub.2 is connected to the secondary side of the high frequency isolating transformer, and a ratio of the high frequency isolating transformer is N:1; the input ports for control signal of the switching devices S.sub.1, S.sub.2, S.sub.3, and S.sub.4 of the primary single-phase full-bridge H.sub.1 and the input ports for control signal of the switching devices Q.sub.1, Q.sub.2, Q.sub.3, and Q.sub.4 of the secondary single-phase full-bridge H.sub.2 are connected to the corresponding output ports for switching signal of the controller, respectively; the filter inductor L.sub.di is connected in series with the filter inductor L.sub.fi, the damping resistance R.sub.di is connected in parallel with the filter inductor L.sub.di in the EMI filter; the cathode of the DC bus of the diode rectifier circuit is connected to the cathode of the input filter capacitor C.sub.i, the filter inductor L.sub.fi is connected to the anode of the input filter capacitor C.sub.i, the anode of the DC bus of the diode rectifier circuit is connected to the filter inductor L.sub.di; and the controller adopts a digital control mode, the A/D sampling step samples an input voltage u.sub.in of a PFC converter and an output voltage v.sub.out of the bus and converts an analog signal to a digital signal, a double frequency pulsation included in the output voltage v.sub.out is filtered by the second-order band rejection filter and sent by the PI controller as an output x; and the modulation unit modulates the output x of the PI controller into a switch control signal after amplitude limiting.

2. A control method using the current sensorless control system for DAB-based single stage isolated PFC converters of claim 1, comprising (1) sampling an input AC voltage of a main power circuit and converting the input AC voltage into a digital signal and obtaining a absolute value |uin|[n] by the A/D sampling step; (2) sampling an output voltage of the main power circuit and converting the output voltage into a digital signal by the A/D sampling step, and filtering the double frequency pulsation to obtain the output voltage V.sub.out,avg[n]; (3) calculating by the controller an output of the PI controller V.sub.ev[n] according to formula (1); $\begin{array}{cc}{V}_{\mathrm{ev}}\left[n\right]=k_p\left(V_{\mathrm{ref}}-V_{\mathrm{out},\mathrm{avg}}\left[n\right]\right)+k_i\underset{j=1}{\overset{n}{.Math.}}\left(V_{\mathrm{ref}}-V_{\mathrm{out},\mathrm{avg}}\left[n\right]\right)& \left(1\right)\end{array}$ wherein V.sub.ref is a reference value for output voltage of the converter, k.sub.p is a proportion coefficient of the PI controller, and k.sub.i is an integral coefficient of the PI controller, values of k.sub.p and k.sub.i are preset and in a range of 0.1k.sub.p10 and 0.001k.sub.i1; (4) multiplying the output V.sub.ev[n] of the PI controller by |uin|[n], setting an assignment limit to [0, 1/9], and squaring a calculation result to get a control signal x: $\begin{array}{cc}x=\sqrt{V_{\mathrm{ev}}\left[n\right]\frac{.Math.u_{in}.Math.\left[n\right]}{k_u}}& \left(2\right)\end{array}$ wherein k.sub.u is a proportion coefficient of |uin|[n] that is preset and a peak value of the input voltage of the converter; (5) modulating the control signal x into a phase-shifting ratio as follows:
D.sub.1=D.sub.2=12x D.sub.0=x, generating control signals of each of the switching devices S.sub.1 S.sub.2, S.sub.3, and S.sub.4 inside the primary single-phase full-bridge H.sub.1 and the switching devices Q.sub.1 to Q.sub.4 inside the secondary single-phase full-bridge H.sub.2 by the modulation unit according to the phase-shifting ratio x between the primary and the secondary sides, wherein the control signals for the switching devices are square waves with a duty cycle of 0.5; the phase-shifting ratio of the control signals of the switching devices S.sub.1 and S.sub.4 is D1, the control signals of the switching devices S.sub.2 and S.sub.3 are the same and complementary to the control signals of the switching devices S.sub.1 and S.sub.4; the phase-shifting ratio of the control signals of the switching devices Q.sub.1 and Q.sub.4 is D2, and the control signals of the switching devices Q.sub.2 and Q.sub.3 are the same and complementary to the control signals of the switching devices Q.sub.1 and Q.sub.4; x is the phase-shifting ratio between the control signal S.sub.1 and the control signal Q.sub.1; inputting the control signals respectively to the control ports of the switching devices of the primary side single-phase full-bridge and the secondary single-phase full-bridge, and completing the control process.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a structure diagram showing the current sensorless control system for the DAB-based single stage isolated PFC converters of the present invention.

(2) FIG. 2 is a schematic diagram showing the DAB modulation step in the control method of the present invention.

(3) FIG. 3 is a structure diagram showing one embodiment of the current sensorless control system of the present invention.

(4) FIG. 4 is a waveform diagram showing the output voltage and current of the PFC converter after the control method of the present invention is employed.

DETAILED DESCRIPTIONS OF THE INVENTION AND EMBODIMENTS

(5) In combination with embodiments and figures, the present invention is further expounded. The embodiments and figures are not meant to limit the scope of the present invention.

(6) As shown in FIG. 1, the control system comprises an A/D sampling module, a double frequency pulsating digital filter, a PI controller, and a modulator unit. Each module is loaded into a digital signal processor (DSP) chip in the form of a software, and the DSP chip may be a TMS320F28335 chip. The control system of the present invention also forms a closed loop system by connecting the drive module to the main power circuit of the PFC converter. The main power circuit of the PFC converter includes a diode rectifier circuit, a DAB converter main power circuit, an EMI filter and a control system.

(7) The control system of the present invention includes a diode rectifier circuit, a DAB converter power main circuit, an EMI filter, and a controller.

(8) The diode rectifier circuit comprises a full rectified bridge composed of four diodes D.sub.1D.sub.4 and an input AC voltage source u.sub.in.

(9) The DAB converter power main circuit is composed of an input filter capacitor C.sub.i, an output filter capacitor C.sub.o, a primary single-phase full-bridge H.sub.1, a secondary single-phase full-bridge H.sub.2, a high frequency isolating transformer, a high frequency inductor L, and a controller. The four fully controlled switching devices of the primary single-phase full-bridge H.sub.1 are S.sub.1S.sub.4, and the four fully controlled switching devices of the secondary single-phase full-bridge H.sub.2 are Q.sub.1Q.sub.4. The anode of the DC bus of the primary single-phase full-bridge H.sub.1 is connected to the anode of the input filter capacitor C.sub.i, and the cathode of the DC bus of the primary single-phase full-bridge H.sub.1 is connected to the cathode of the input filter capacitor C.sub.i, and the AC side of the single-phase full-bridge H.sub.1 is connected to the primary side of the high frequency isolating transformer through the high frequency inductor L. The anode of the DC bus of the secondary single-phase full-bridge H.sub.2 is connected to the anode of the output filter capacitor C.sub.o, and the cathode of the DC bus of the secondary single-phase full-bridge H.sub.2 is connected to the cathode of the output filter capacitor C.sub.o, the AC side of the secondary single-phase full-bridge H.sub.2 is connected to the secondary side of the high frequency isolating transformer, and the ratio of the high frequency isolating transformer is N:1. The input port of the control signal of the primary side single-phase full-bridge switching device S.sub.1S.sub.4 and the input port of the control signal of the secondary side single-phase full-bridge switching device Q.sub.1Q.sub.4 are connected to the output port of the corresponding switching signal of the controller.

(10) The EMI filter includes a filter inductor L.sub.di, a filter inductor L.sub.fi and a damping resistance R.sub.di. The filter inductor L.sub.di is connected in series with the filter inductor L.sub.fi, the damping resistance R.sub.di is connected in parallel with the filter inductor L.sub.di; and the cathode of the DC bus of the diode rectifier circuit is connected to the cathode of the input filter capacitor C.sub.1. The filter inductor L.sub.fi is connected to the anode of the input filter capacitor C.sub.i; the anode of the DC bus of the diode rectifier circuit is connected to the filter inductor L.sub.di.

(11) The controller adopts digital control mode, including an A/D sampling step, a PI controller, a double frequency pulsating digital filtering step and a modulation unit. The A/D sampling step has two signal input ports, and the input voltage u.sub.in of the PFC converter and the bus output voltage v.sub.out are sampled and analog/digital converted from analog signal to digital signal in this step. The double frequency pulsating digital filtering step is a second-order band rejection filter for filtering the double frequency pulsation included in the output voltage v.sub.out; output by the PI controller; the modulation unit modulates the output x of the PI controller into a switch control signal after amplitude limiting, and the output port thereof is respectively connected to the input port of the control signal corresponding to the switching devices S.sub.1to S.sub.4 and Q.sub.1 to Q.sub.4 corresponding to the primary and secondary full-bridges of the DAB.

(12) The control method of the above current sensorless control system for single stage isolated PFC converters based on DAB, comprising the following steps:

(13) (1) The A/D sampling step samples the input AC voltage of the main power circuit, converts it into a digital signal and obtains the absolute value |uin|[n];

(14) (2) The A/D sampling step samples the output voltage of the main power circuit, converts it into a digital signal, and filters the double frequency pulsation to obtain the output voltage V.sub.out, avg[n];

(15) (3) The controller calculates the output of the PI controller V.sub.ev[n] according to formula (1):

(16) $\begin{array}{cc}{V}_{\mathrm{ev}}\left[n\right]=k_p\left(V_{\mathrm{ref}}-V_{\mathrm{out},\mathrm{avg}}\left[n\right]\right)+k_i\underset{j=1}{\overset{n}{.Math.}}\left(V_{\mathrm{ref}}-V_{\mathrm{out},\mathrm{avg}}\left[n\right]\right)& \left(1\right)\end{array}$

(17) where V.sub.ref is the reference value of the converter output voltage, k.sub.p is the proportion coefficient of the PI controller, and k.sub.i is the integral coefficient of the PI controller. The values of these two parameters are preset, and the preset range is 0.1k.sub.p10, 0.001k.sub.i1;

(18) (4) Multiply the output of the PI controller by |uin|[n], set the assignment limit to [0, 1/9], and square the calculation result to get the control signal x:

(19) $\begin{array}{cc}x=\sqrt{V_{\mathrm{ev}}\left[n\right]\frac{.Math.u_{in}.Math.\left[n\right]}{k_u}}& \left(2\right)\end{array}$

(20) where k.sub.u is the proportion coefficient of |uin|[n], which is preset and may be the peak value of the input voltage of the converter;

(21) (5) The control signal x is modulated into phase-shifting ratio as follows:

(22) D.sub.1=D.sub.2=12x D.sub.0=x, the modulation unit generates control signals of each of the switching devices S.sub.1 to S.sub.4 inside the primary side full-bridge and the switching devices Q.sub.1 to Q.sub.4 inside the secondary side full-bridge according to the phase-shifting ratio x between the primary and the secondary sides. The control signals of the primary side full-bridge internal switching devices S.sub.1S.sub.4 and the control signals of the secondary side full-bridge internal switching devices Q.sub.1Q.sub.4 are square waves with a duty cycle of 0.5. The phase-shifting ratio of the control signals of the switching devices S.sub.1 and S.sub.4 is D1, the control signals of the switching devices S.sub.2 and S.sub.3 are the same and complementary to the control signals of the switching devices S.sub.1 and S.sub.4. The phase-shifting ratio of the control signals of the switching devices Q.sub.1 and Q.sub.4 is D2, the control signals of the switching devices Q.sub.2 and Q.sub.3 are the same and complementary to the control signals of the switching devices Q.sub.1 and Q.sub.4; x is the phase-shifting ratio between the control signal S.sub.1 and the control signal Q.sub.1; the control signal is respectively input to the control port of the switching devices of the primary side single-phase full-bridge and the secondary single-phase full-bridge, and the control process is completed.

(23) As shown in FIG. 2, the principle of the modulation unit is illustrated. The modulation unit generates control signals of each of the switching devices S.sub.1 to S.sub.4 inside the primary side full-bridge and the switching devices Q.sub.1 to Q.sub.4 inside the secondary side full-bridge according to the phase-shifting ratio x between the primary and the secondary sides: the control signals of the primary side full-bridge internal switching devices S.sub.1S.sub.4 and the control signals of the secondary side full-bridge internal switching devices Q.sub.1Q.sub.4 are square waves with a duty cycle of 0.5; The phase-shifting ratio of the control signals of the switching devices S.sub.1 and S.sub.4 is D1, the control signals of the switching devices S.sub.2 and S.sub.3 are respectively complementary to the control signals of the switching devices S.sub.1 and S.sub.4; The phase-shifting ratio of the control signals of the switching devices Q.sub.1 and Q.sub.4 is D2, the control signals of the switching devices Q.sub.2 and Q.sub.3 are complementary to the control signals of the switching devices Q.sub.1 and Q.sub.4; x is the phase-shifting ratio between the control signal S.sub.1 and the control signal Q.sub.1; the control signal is input to the control port of the switching devices of the primary side single-phase full-bridge and the secondary single-phase full-bridge. Therefore the control process is completed, and direct control of the input current is realized.

(24) In one embodiment of the present invention as shown in FIG. 3, main parameters of the control system of the present invention are as follows: Input voltage u.sub.in=2202 sin (100t); Output reference voltage V.sub.ref=400V; Switching frequency f.sub.s=50 kHz; Inductor L=40 uH; Transformer turns ratio N:1=0.59:1; EMI filter parameters L.sub.di=50 uH; L.sub.fi=50 uH; R.sub.di=5; C.sub.i=7 uF; C.sub.o=1 mF; and Load with resistance.

(25) FIG. 4 shows the waveform diagram of the output voltage and current of the AC power. As shown in FIG. 4, the current sensorless control method of the present invention is employed to make the output current waveform of the power track the voltage waveform, thereby realizing power factor correction. At this time, the power factor PF of the converter is 0.995, and the input current THD is 2.5%.