CN107623450B - Double-frequency single-phase PWM rectifier - Google Patents

Double-frequency single-phase PWM rectifier Download PDF

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CN107623450B
CN107623450B CN201710361677.1A CN201710361677A CN107623450B CN 107623450 B CN107623450 B CN 107623450B CN 201710361677 A CN201710361677 A CN 201710361677A CN 107623450 B CN107623450 B CN 107623450B
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CN107623450A (en
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杨立永
刘硕
景生赟
刘启帆
王元
韩硕
王云昊
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North China University of Technology
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Abstract

The invention relates to the technical field of rectifiers, in particular to a double-frequency single-phase PWM rectifier which comprises a shell, wherein a circuit board is arranged in the shell, and the circuit board comprises a control unit and a main loop unit; the main loop unit consists of a low-frequency power unit and a high-frequency harmonic elimination unit; the novel topological structure is adopted, the inductance of the required power filter is reduced, the inductance volume is reduced, the cost of the PWM rectifier is reduced, the control difficulty of the PWM rectifier is simplified, the switching frequency of a high-power switching device is reduced, and the efficiency and the power density of the rectifier are improved.

Description

Double-frequency single-phase PWM rectifier
[ technical field ] A method for producing a semiconductor device
The invention relates to the technical field of rectifiers, in particular to a double-frequency single-phase PWM rectifier.
[ background of the invention ]
PWM rectifier technology is the primary technology for converting ac power to dc power, and generally requires the use of self-turn-off power devices. Because the alternating current of the PWM rectifier contains harmonic components, and the power grid has strict requirements for current harmonics, measures are required to suppress the current harmonics to reduce the pollution to the power grid. Meanwhile, in order to reduce the loss of the PWM rectifier, it is desirable to reduce the switching frequency of the power device, and the lower the switching frequency, the smaller the loss, but the larger the harmonic.
At present, a method of adding a power filter on an alternating current side is mainly adopted to suppress current harmonics of a PWM rectifier, and the PWM rectifier can be divided into an L-type PWM single-phase rectifier and an LCL-type PWM single-phase rectifier according to different filters. In the L-type PWM single-phase rectifier, an inductor is used as a power filter for suppressing current harmonics, and in the LCL-type PWM single-phase rectifier, a filter circuit composed of two inductors and one capacitor is used as a power filter.
In an L-type PWM single-phase rectifier, the inductance value of the filter determines the size and cost of the filter. The larger the inductance value of the filter, the larger the volume and the higher the cost. In addition, during the operation of the filter, when current flows through the inductor, on one hand, heat loss is generated due to the resistance on the inductor, and on the other hand, alternating current voltage drop is generated due to the inductive reactance of the inductor; the heat losses reduce the efficiency of the rectifier and the voltage drop across the inductor limits the regulation range of the dc voltage. Meanwhile, in order to improve the efficiency of the PWM rectifier, it is desirable to reduce the switching frequency of the power device, and the lower the switching frequency, the larger the inductance value is required. Therefore, the L-type PWM rectifier has the main problems of large size, high cost, low efficiency, and is not favorable for the low frequency of the PWM rectifier.
In the LCL type PWM single-phase rectifier, the LCL filter is composed of two inductors and a capacitor through series-parallel combination, and in practical application, two inductors and a capacitor need to be precisely matched, otherwise resonance occurs. In the process of designing the controller, the state of the filter needs to be measured and fed back, and the parameters of the controller are accurately adjusted, otherwise, the expected control effect cannot be achieved. Therefore, the LCL type PWM single-phase rectifier has the main problems of multiple components, large volume, high cost, complex structure, high control difficulty and the like.
It can be seen that the L-type and LCL-type single-phase PWM rectifiers, although capable of achieving harmonic suppression, have the disadvantages of large size and high cost, and the switching frequency of the power device is high, so that the efficiency of the PWM rectifier cannot be improved by reducing the switching loss of the main circuit.
[ summary of the invention ]
The invention aims to provide a double-frequency single-phase PWM rectifier aiming at the defects and shortcomings of the prior art.
The invention relates to a double-frequency single-phase PWM rectifier, which comprises a shell, wherein a circuit board is arranged in the shell, and the circuit board comprises a control unit and a main loop unit; the main loop unit consists of a low-frequency power unit and a high-frequency harmonic elimination unit;
the low-frequency power unit comprises four fully-controlled switching devices (VT1-VT4), four power diodes (VD1-VD4) and a filter capacitor C1; the VT1 is connected with the VT2 in series, and the VT3 is connected with the VT4 in series and are respectively arranged on two power transmission leads, and the output ends of the two power transmission leads are respectively a terminal A and a terminal B; the filter capacitor C1 is connected in parallel to the two transmission wires; four fully-controlled switching devices (VT1-VT4), each of which is connected with a power diode in anti-parallel, wherein: VT1 is connected in an antiparallel VD1, VT2 is connected in an antiparallel VD2, VT3 is connected in an antiparallel VD3, and VT4 is connected in an antiparallel VD 4; forming a low-frequency power distribution circuit;
the high-frequency harmonic elimination unit comprises four fully-controlled switching devices (VT5-VT8), four power diodes (VD5-VD8) and a filter capacitor C2; the VT5 is connected with the VT6 in series, and the VT7 is connected with the VT8 in series and are arranged on two electric transmission wires; four fully-controlled switching devices (VT5-VT8), each of which is connected in anti-parallel with a power diode, wherein: VT5 is connected in an antiparallel mode with VD5, VT6 is connected in an antiparallel mode with VD6, VT7 is connected in an antiparallel mode with VD7, and VT8 is connected in an antiparallel mode with VD 8; forming a high-frequency harmonic elimination sub-circuit;
the low-frequency power unit is connected with a single-phase alternating current power supply AC through a filter inductor L1, the high-frequency harmonic elimination unit is connected with the single-phase alternating current power supply AC through a filter inductor L2 to form a main loop unit, and the main loop unit is connected with a load through a terminal A and a terminal B.
After adopting the structure, the invention has the beneficial effects that: the double-frequency single-phase PWM rectifier reduces the inductance of a required power filter through a novel topological structure, thereby reducing the inductance volume, reducing the cost of the PWM rectifier, simplifying the control difficulty of the PWM rectifier, reducing the switching frequency of a high-power switching device and improving the efficiency and power density of the rectifier.
[ description of the drawings ]
The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this application, and are not to be considered limiting of the invention, in which:
FIG. 1 is a schematic of the topology of the present invention;
fig. 2 is a block diagram of the control system of the present invention.
[ detailed description ] embodiments
The present invention will now be described in detail with reference to the drawings and specific embodiments, wherein the exemplary embodiments and descriptions are provided only for the purpose of illustrating the present invention and are not to be construed as limiting the present invention.
As shown in fig. 1, the dual-frequency single-phase PWM rectifier according to the present embodiment includes a housing, a circuit board is disposed in the housing, and the circuit board includes a control unit and a main circuit unit; the main loop unit consists of a low-frequency power unit and a high-frequency harmonic elimination unit;
the low-frequency power unit comprises four fully-controlled switching devices (VT1-VT4), four power diodes (VD1-VD4) and a filter capacitor C1; the VT1 is connected with the VT2 in series, and the VT3 is connected with the VT4 in series and are respectively arranged on two power transmission leads, and the output ends of the two power transmission leads are respectively a terminal A and a terminal B; the filter capacitor C1 is connected in parallel to the two transmission wires; four fully-controlled switching devices (VT1-VT4), each of which is connected with a power diode in anti-parallel, wherein: VT1 is connected in an antiparallel VD1, VT2 is connected in an antiparallel VD2, VT3 is connected in an antiparallel VD3, and VT4 is connected in an antiparallel VD 4; forming a low-frequency power distribution circuit;
the high-frequency harmonic elimination unit comprises four fully-controlled switching devices (VT5-VT8), four power diodes (VD5-VD8) and a filter capacitor C2; the VT5 is connected with the VT6 in series, and the VT7 is connected with the VT8 in series and are arranged on two electric transmission wires; four fully-controlled switching devices (VT5-VT8), each of which is connected in anti-parallel with a power diode, wherein: VT5 is connected in an antiparallel mode with VD5, VT6 is connected in an antiparallel mode with VD6, VT7 is connected in an antiparallel mode with VD7, and VT8 is connected in an antiparallel mode with VD 8; forming a high-frequency harmonic elimination sub-circuit;
the low-frequency power unit is connected with a single-phase alternating current power supply AC through a filter inductor L1, the high-frequency harmonic elimination unit is connected with the single-phase alternating current power supply AC through a filter inductor L2 to form a main loop unit, and the main loop unit is connected with a load through a terminal A and a terminal B.
The working principle of the invention is as follows: the topology of the dual-frequency PWM rectifier is shown in FIG. 1;
1) low frequency powerThe cells acting as a large current i1Providing a channel, i1The high-frequency harmonic waves are contained in the high-voltage high. Low frequency power cells use low switching frequencies to reduce the switching losses of the cell.
2) The capacitor C1 in the low-frequency power unit has the functions of inhibiting voltage ripples on the direct-current bus and keeping the voltage VC1And (4) stabilizing.
3) The filter inductor L1 is used for suppressing the current i1In the ripple wave, because the high-frequency harmonic elimination unit is added in the topological structure, an inductor with a small inductance value can be selected as a filter inductor.
4) The high-frequency harmonic elimination unit is used for eliminating the current i2Providing a channel, i2Is a high frequency harmonic current, and i1Medium high frequency harmonic current reverses. The switching device adopts a high-frequency full-control type switching device, such as a power MOSFET, silicon carbide (SIC), gallium nitride (GaN) and the like. The power device has the advantages of high switching frequency, small switching loss, high cost and small working voltage and working current. The unit has small current and small switching loss, and the loss of the unit is far less than the switching loss reduced by reducing the switching frequency of the low-frequency power unit, so that the switching loss of the whole dual-frequency PWM rectifier can be reduced.
5) The function of the capacitor C2 in the hf resonant unit is to provide a dc voltage support for the hf resonant unit.
6) The filter inductor L2 is used for suppressing the current i2The ripple above, due to the high switching frequency of the cell, can reduce the inductance value of the inductor L2, and due to the small value of the harmonic current flowing through L2, the filter inductor L2 has a small size.
As shown in fig. 2, the control system of the dual-frequency rectifier is configured;
in this design, the control target of the dual-frequency PWM rectifier includes three points: (1) stabilizing the output voltage V of the rectifierC1(ii) a (2) Eliminating grid-connected current isumThe ripple of (2); (3) stabilizing voltage V of high-frequency harmonic elimination unitC2(ii) a As can be seen from FIG. 2The control system comprises two double closed-loop control loops coupled with each other. At a DC voltage VC1In the control loop, the control loop is provided with a control loop,
Figure RE-GSB0000169551650000051
for a given DC voltage, with an actual voltage VC1Comparing, the difference value is used as the input of the voltage regulator AVR1, the output of AVR1 is the current i1Amplitude of
Figure RE-GSB0000169551650000052
Multiplying by sin theta to obtain given value of current inner ring
Figure RE-GSB0000169551650000053
Theta is the current i1The phase angle of (a) is determined,
Figure RE-GSB0000169551650000054
and a feedback current i1For comparison, the difference is used as the input of the current regulator ACR1, and the output of ACR1 is uACR1And the compensation value uCOM1Adding to obtain the input/output u of the SPWM1 module1. In this loop, uCOM1Equal to the voltage u of the AC sourceAC. The SPWM1 module generates pulse width modulation signals PWM1, PWM2, PWM3 and PWM4 of VT1, VT2, VT3 and VT 4.
At a DC voltage VC2A control loop is used for controlling the speed of the motor,
Figure RE-GSB0000169551650000055
for a given DC voltage, with an actual voltage VC2Comparing, the difference value is used as the input of the voltage regulator AVR2, the output of AVR1 is the current i2Amplitude of
Figure RE-GSB0000169551650000056
Multiplying by sin theta to obtain given value of current inner ring
Figure RE-GSB0000169551650000057
And a feedback current i2For comparison, the difference is used as the input of the current regulator ACR2, and the output of ACR2 is uACR2，uACR2And the compensation value uCOM2Adding to obtain the input/output u of the SPWM2 module2SPWM2 Module based on u2Pulse width modulation signals PWM5, PWM6, PWM7, PWM8 which generate VT5, VT6, VT7, VT 8.
In the invention, the suppression principle of harmonic current is as follows:
the system control aims to eliminate i as described previouslysumRipple in the filter. At VC1Under the action of a control loop, the current i of the low-frequency power unit1Is a sine wave with superimposed high frequency harmonics, i1Can be decomposed into fundamental current i11And high frequency harmonic current i1THDI.e. by
i1＝i11+i1THD(1)
The voltage across the inductor L1 can be expressed as
uL＝uAC-uPWM(2)
At steady state, i11Is at uLGenerated under the action of fundamental voltage of1THDIs at uLGenerated by medium high-frequency voltage, ignoring current i1The high frequency voltage component can be expressed as
Figure RE-GSB0000169551650000061
Then i1THDFurther can be expressed as
Figure RE-GSB0000169551650000062
For the high frequency harmonic elimination unit, because it adopts high switching frequency, the device switches at i2The harmonic current generated in (1) is small, so that neglecting the high frequency voltage harmonic, the output voltage is considered to be equal to the input voltage u of SPWM22Let u stand for2
u2＝uACR2+uCOM2(5)
In the formula: u. ofACR2Is the output of the current regulator ACR 2.
Voltage compensationCompensation uCOM2Is calculated by the formula
Figure RE-GSB0000169551650000071
The voltage applied to the inductor L2 is
Figure RE-GSB0000169551650000072
Current i in inductor L2 in steady state2Can also be decomposed into fundamental current i21And high frequency harmonic current i2THDI.e. by
i2＝i21+i2THD(8)
High frequency harmonic current i2THDIs formed by uL2Medium and high frequency component u2THDProduced of u2THDIs expressed as
Figure RE-GSB0000169551650000073
According to u2THDCan be obtained
Figure RE-GSB0000169551650000074
Combine formula (1), formula (8) and formula (10) with
isum＝i1+i2
＝i11+i1THD+i21+i2THD
＝i11+i21
Visible power supply (grid) current isumOnly the fundamental current is contained in the filter, namely the harmonic wave of the high-frequency current is eliminated. Current isumIn which comprises i11And i21Two fundamental currents. The double-frequency PWM rectifier passes a fundamental current i11The alternating current electric energy is converted into direct current electric energy, and the magnitude of the direct current electric energy is determined by the rated power of the rectifier. Fundamental current i21Has the function of maintaining the bus voltage V of the high-frequency harmonic elimination unitC2Due to VC2Do not provide energy to the load, so i21Is a very small value.
The invention has the following advantages:
1) the switching frequency of the low-frequency power unit is reduced, the switching loss is reduced, and the efficiency of the rectifier is improved.
2) The inductance of the power filter in the rectifier is reduced, thereby reducing the volume, weight and cost of the whole device.
3) The harmonic suppression effect of the PWM rectifier is improved, and the THD value of the alternating current power grid current is reduced.
4) The advantage of high switching frequency of the high-frequency switching device is exerted, the voltage (current) limit of the high-frequency switching device is overcome, and the application field of the high-frequency switching device is expanded.
5) The control system can suppress the higher harmonics of the current without high-speed accurate sampling.
The double-frequency single-phase PWM rectifier reduces the inductance of the power filter through a novel topological structure, thereby reducing the inductance volume, reducing the cost of the PWM rectifier, simplifying the control difficulty, simultaneously reducing the switching frequency of a high-power switching device and improving the efficiency and the power density of the rectifier.
The above description is only a preferred embodiment of the present invention, and all equivalent changes or modifications of the structure, characteristics and principles described in the present invention are included in the scope of the present invention.

Claims (1)

1. A double-frequency single-phase PWM rectifier is characterized in that:
the low-frequency power unit is used for converting high-power alternating-current energy into direct-current energy and providing power for a load, the topological structure is an H bridge, and the power device is a fully-controlled power device with high capacity and low working switching frequency; the low-frequency power unit works at low frequency, so that the switching loss of a power device is reduced; the low-frequency power unit is connected with an alternating current power grid through an inductor L1;
a high-frequency harmonic elimination unit for generating a side current i alternating with the low-frequency power unit1Current i with opposite medium ripple2To reduce the grid-connected current isumRipple in, current i2Much smaller than the current i1(ii) a The high-frequency harmonic elimination unit adopts an H-bridge topology structure, and the power device adopts a switching device with small capacity, high working switching frequency and small on-resistance; the high-frequency harmonic elimination unit works at high frequency; the high-frequency harmonic elimination unit is connected with an alternating current power grid through an inductor L2;
the controller is based on the current i1Current i2DC bus voltage VC1DC bus voltage VC2Ac voltage uACGenerating PWM 1-PWM 8, controlling the low-frequency power unit by utilizing PWM 1-PWM 4, and controlling the high-frequency harmonic elimination unit by utilizing PWM 5-PWM 8; vC1Is the output voltage of the rectifier; vC2The voltage of the high-frequency harmonic elimination unit;
two mutually coupled double closed-loop control loops including a DC voltage VC1Control loop and DC voltage VC2Control loops, both control loops being calculated uCOM2The units are coupled with each other;
calculating the compensation voltage uCOM2The method comprises
Figure FSB0000188004760000011
Wherein u isPWMThe output voltage of the low-frequency power unit is obtained through detection.
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CN108736751B (en) * 2018-07-23 2020-11-13 北方工业大学 Control method of double-frequency parallel three-phase grid-connected inverter
CN111864794A (en) * 2020-06-08 2020-10-30 北方工业大学 Double-frequency transformer-free single-phase photovoltaic grid-connected inverter

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