Disclosure of Invention
In order to solve the defects mentioned in the background technology, the invention aims to provide a current source type high-frequency isolation matrix type cascade converter and a control method, the input sides of two current source type high-frequency isolation matrix converters are connected in parallel and the output sides of the two current source type high-frequency isolation matrix converters are connected in series, the power conversion capacity of a system is improved, the reliability of the system is enhanced, and the volume of the system is reduced; by applying the soft switching technology, the switching loss of the current source type high-frequency isolation matrix converter is reduced, and the efficiency of the system is improved.
The purpose of the invention can be realized by the following technical scheme:
a current source type high-frequency isolation matrix type cascade converter comprises a three-phase power grid, an LC filter, a first current source type matrix converter, a second current source type matrix converter, a first leakage inductor, a second leakage inductor, a first high-frequency isolation transformer, a second high-frequency isolation transformer, a first uncontrolled rectifier bridge, a second uncontrolled rectifier bridge, a first inductance resistance load and a second inductance resistance load, wherein the three-phase power grid is connected with the LC filter; the LC filter is respectively connected with the first current source type matrix converter and the second current source type matrix converter in parallel; the alternating current output side of the first current source type matrix converter is connected with the first high-frequency isolation transformer in series, and the alternating current output side of the second current source type matrix converter is connected with the second high-frequency isolation transformer in series; the secondary output side of the first high-frequency isolation transformer is connected with the first uncontrolled rectifier bridge in series, and the secondary output side of the second high-frequency isolation transformer is connected with the second uncontrolled rectifier bridge in series, so that energy is transferred through a magnetic field; the first uncontrolled rectifier bridge output end and the second uncontrolled rectifier bridge output end are connected in series through a first resistance-inductance load and a second resistance-inductance load to form a closed loop.
Further, the power direction and the power magnitude of the current source type high-frequency isolation matrix type cascade converter are determined by the control modules of the first current source type matrix converter and the second current source type matrix converter; the first current source type matrix converter and the second current source type matrix converter are respectively connected with ports of the LC filter circuit and receive electric energy transmitted by the three-phase power grid; the current of the first resistance-inductance load and the current of the direct current bus inductor corresponding to the second resistance-inductance load output by the direct current side are controlled by a current loop.
Further, the control method adopted by the control module of the first current source type matrix converter comprises the following processes:
1) capacitor voltage U passing through three-phase LC filterabcAnd the network voltage VgElectric angle theta obtained by phase-locked loopeObtaining a capacitance voltage d-axis component U of the LC filter through coordinate transformationdAnd q-axis component Uq;
2) Component U under filter capacitor voltage dq coordinate system
dAnd U
qObtaining the low-frequency component of the capacitor voltage through a low-pass filter, the electrical angle theta
eObtaining the electrical angular velocity omega after differentiation
eAnd calculating to obtain the low-frequency capacitance current of the filter capacitor
And
3) given load side DC bus current I
dc *And the actual DC bus current I
dcThe error value between the two is obtained by a D-axis direct current component through a PI controller
To realize the transmission of unit power factor, let the reference value Q of reactive power
refIs 0, Q
refAnd the network voltage V
gObtaining the q-axis current component after calculation
Is zero;
4) the dq axis component of the capacitor voltage is processed by a high-pass filter to obtain a high-frequency component U of the capacitor voltagehdAnd UhqThe high-frequency components of the capacitor voltage are respectively multiplied by a same virtual resistance coefficient kpvAnd kpvObtaining dq axis component values of the virtual current, and eliminating fifth and seventh harmonics of the system current through an active damping scheme of the harmonic of the virtual resistance suppression circuit;
5) d-axis DC component
Compensating the upper low frequency capacitor current by combining the dq component of the high frequency capacitor voltage flowing through the virtual resistor current
And
obtaining a given value of final current at the input side of the matrix converter through operation, and obtaining a phase current fundamental wave peak value I after polar coordinate conversion
1dc *And phase angle theta
α1;
6) Phase current fundamental wave peak value I1dc *Divided by a given value of DC current Idc *Obtaining a modulation ratio m of the first current source type matrix converter1iPhase angle thetaα1Plus the electrical angle theta measured by the phase-locked loopeObtaining the switching pulse phase angle theta of the matrix converter1ωUsing the modulation ratio m1iAnd angle theta1ωAnd the switching period Ts generates twelve switching pulses of the first current source matrix converter.
Further, the control method adopted by the control module of the second current source type matrix converter comprises the following processes:
1) capacitor voltage U passing through three-phase LC filterabcAnd the network voltage VgElectric angle theta obtained by phase-locked loopeObtaining LC filter by coordinate transformationCapacitor voltage d-axis component U of wave filterdAnd q-axis component Uq;
2) Component U under filter capacitor voltage dq coordinate system
dAnd U
qObtaining the low-frequency component of the capacitor voltage through a low-pass filter, the electrical angle theta
eObtaining the electrical angular velocity omega after differentiation
eThe low-frequency capacitance current of the filter capacitor can be obtained after calculation
And
3) given load side DC bus current I
dc *And the actual DC bus current I
dcThe error value between the two is obtained by a D-axis direct current component through a PI controller
To realize the transmission of unit power factor, let the reference value Q of reactive power
refIs 0, Q
refAnd the network voltage V
gObtaining the q-axis current component after calculation
Is zero;
4) the dq axis component of the capacitor voltage is processed by a high-pass filter to obtain a high-frequency component U of the capacitor voltagehdAnd UhqThe high-frequency components of the capacitor voltage are respectively multiplied by a same virtual resistance coefficient kpvAnd kpvObtaining dq axis component values of the virtual current, and eliminating fifth and seventh harmonics of the system current through an active damping scheme of the harmonic of the virtual resistance suppression circuit;
5) d-axis DC component
Compensating the upper low frequency capacitor current by combining the dq component of the high frequency capacitor voltage flowing through the virtual resistor current
And
obtaining a given value of final current at the input side of the matrix converter through operation, and obtaining a phase current fundamental wave peak value I after polar coordinate conversion
2dc *And phase angle theta
α2;
6) Phase current fundamental wave peak value I2dc *Divided by a given value of DC current Idc *Obtaining a modulation ratio m of the second current source type matrix converter2iPhase angle thetaα2Plus the electrical angle theta measured by the phase-locked loopeObtaining the switching pulse phase angle theta of the matrix converter2ωUsing the modulation ratio m2iAnd angle theta2ωAnd the switching period Ts generates twelve switching pulses of the second current source matrix converter.
Further, the modulation method adopted by the first current source type matrix converter and the second current source type matrix converter comprises the following steps:
three current vectors acting on the first current source type matrix converter in one switching period are respectively I11,I12,I10The output voltage of the corresponding first current source type matrix converter is U11,U12,U10By changing the order of action of the current vectors, U is made11>U12>U10(ii) a Similarly, the three current vectors acting on the second current source type matrix converter in one switching period are respectively I21,I22,I20Corresponding to the input voltage of the second current source type matrix converter as U21,U22,U20By changing the order of action of the current vectors, U is made21>U22>U20(ii) a Because the first current source matrix converter and the second current source matrix converter are connected in parallel, the output voltage waveforms of the matrix converters in a switching period are consistent, and the working states are consistent, taking the working state of the first current source matrix converter as an example, the specific working process of the soft switch in a switching period is as follows,
1) state 0: primary side commutation
When a switching period begins, the current vectors corresponding to the first current source type matrix converter and the second current source type matrix converter are zero vectors I7Output voltage v of matrix converterpIs reduced to 0;
2) state 1: conduction time of switch tube
The zero current vector still acts, the primary side input side current and the secondary side output side current of the first high-frequency isolation transformer are equal, and the primary side current of the first high-frequency isolation transformer flows through a switching tube S of the first current source type matrix converter11、S22And S14、S24The current of the secondary side rectifier bridge of the first high-frequency isolation transformer flows through D1、D4Three-phase capacitors provide current paths to three-phase inductors, this state being free of energy transmission, S11And S14Conducting at zero voltage;
3) state 2: conduction time of switch tube
Zero vector I of first current source type matrix converter7End of action, current vector I1In operation, the inductive current of the first uncontrolled rectifier bridge flows through the diode D1、D4According to the four-step commutation, the switching tube S of the first current source type matrix converter11And S14Is turned off because the voltage u is nowabGreater than 0, current to S16And S26The output capacitor of the first current source type matrix converter16And S26Zero voltage conduction is carried out, and the voltage of the input side of the first high-frequency isolation transformer is equal to uabEnergy flows from the grid;
4) state 3: conduction time of switch tube
Similar to the operating state of state 2, the effective current vector I of the first current source matrix converter1End of action, current vector I2In operation, the inductive current of the first uncontrolled rectifier bridge flows through the diode D1、D4According to the four-step commutation, the power switch tube S of the first current source type matrix converter16And S26Closing, S12And S22Zero voltage conduction is carried out, and the voltage of the input side of the first high-frequency isolation transformer is equal to uacEnergy flows from the grid;
5) and 4: commutation of uncontrolled rectifier bridge
The rectification of the first uncontrolled rectifier bridge is completed with the aid of the first current source matrix converter, at t3At the moment, the diode D of the first uncontrolled rectifier bridge2、D3Zero current conduction. The current flowing through the inductor in the first uncontrolled rectifier bridge decreases linearly through D2、D3Through D1、D4Is linearly decreased at the same rate, the commutation overlap time TdSelecting 100ns, and commutating current on the first uncontrolled rectifier bridge inductor before the mode is finished;
6) and state 5: conduction time of switch tube
Commutation overlap time TdAfter that, the power switch tube S of the first current source type matrix converter12And S22Off, S14And S24Zero voltage conduction, the voltage drop of the primary side input side of the first high-frequency isolation transformer is 0, and no direct current energy is transmitted under the mode;
7) and 6: conduction time of switch tube
First current source type matrix converter current vector I2End of action, zero vector I0In operation, a direct current flows through the diode D of the first uncontrolled rectifier bridge on the load side2And D3While the input side current of the first high-frequency isolation transformer flows through the power switch tube S of the first current source type matrix converter11、S21And S24、S14And the three-phase capacitor in the LC filter provides a current channel for the three-phase inductor.
The invention has the beneficial effects that:
(1) the direct conversion from power frequency alternating current to high frequency alternating current is realized through the current source type matrix converter, the direct current capacitor is removed, the failure rate of the converter is reduced, the power conversion stage number is reduced, and the reliability and the power density of system operation are greatly improved;
(2) a high-frequency isolation transformer is adopted to replace a low-frequency input transformer, so that the system volume is reduced;
(3) the capacity of the power converter is increased through the cascade structure of the plurality of direct matrix converters, the output voltage of the system is improved, and the collection of medium-high voltage direct current transmission is facilitated;
(4) the control strategy of the matrix converter can realize unit power factor operation, the soft switching technology reduces the loss of the system, the modularized matrix converter is easy to install and maintain, and the cost of the offshore wind power generation system is reduced.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
As shown in fig. 1, a current source type high frequency isolation matrix type cascaded converter includes a three-phase power grid 1.1, an LC filter 1.2, two sets of matrix converters (1.3, 1.4), leakage inductances (1.5, 1.6), high frequency isolation transformers (1.7, 1.8), two sets of uncontrolled rectifier bridges (1.9, 1.10), and resistance-inductance loads (1.11, 1.12).
The three-phase power grid 1.1 is connected with the LC filter 1.2;
the LC filter 1.2 is respectively connected with the first matrix converter 1.3 and the second matrix converter 1.4 in parallel; the matrix converters (1.3 and 1.4) are respectively connected with high-frequency isolation transformers (1.7 and 1.8); the secondary sides of the high-frequency isolation transformers (1.7 and 1.8) are connected with uncontrolled rectifier bridges (1.9 and 1.10) and transmit energy through magnetic fields; the uncontrolled rectifier bridges (1.9, 1.10) are respectively connected with a resistance-inductance load 1.11 and a resistance-inductance load 1.12; the inductance-resistance load 1.11 and the inductance-resistance load 1.12 on the direct current output side are mutually connected in series to form a closed loop;
the matrix converters 1.3 and 1.4 at the input side of the high-frequency isolation transformer are connected in parallel;
direct current bus inductors 1.11 and 1.12 at the output side of the high-frequency isolation transformer are mutually connected in series;
the power direction and the power magnitude of the current source type high-frequency isolation matrix type cascade converter are determined by the control modules of the matrix converters 1.3 and 1.4;
the current of the direct current side output resistance-inductance loads 1.11 and 1.12 corresponding to the direct current bus inductor is controlled by a current loop.
The current source type matrix converter comprises a first current source type matrix converter 1.3 and a second current source type matrix converter 1.4, the high-frequency isolation transformer comprises a first high-frequency isolation transformer 1.7 and a second high-frequency isolation transformer 1.8, the rectifying circuit comprises a first uncontrolled rectifier bridge 1.9 and a second uncontrolled rectifier bridge 1.10, wherein:
the alternating current output side of the first current source type matrix converter 1.3 is connected with a first high-frequency isolation transformer 1.7 in series;
the alternating current output side of the second current source type matrix converter 1.4 is connected with a second high-frequency isolation transformer 1.8 in series;
the alternating current input side of the first current source type matrix converter 1.3 is connected with the alternating current input side of the second current source type matrix converter 1.4 in parallel;
the output end of the secondary side of the first high-frequency isolation transformer 1.7 is connected with a first uncontrolled rectifier bridge 1.9 in series;
the output end of the secondary side of the second high-frequency isolation transformer 1.9 is connected with a second uncontrolled rectifier bridge 1.10 in series;
the output side of the first uncontrolled rectifier bridge 1.9 and the output side of the second uncontrolled rectifier bridge 1.10 are connected in series through two sets of inductance-resistance loads 1.11 and 1.12 to form a closed loop;
the first current source type matrix converter 1.3 and the second current source type matrix converter 1.4 are respectively connected with the port of the three-phase LC filter circuit 1.2 and receive electric energy transmitted by a three-phase power grid.
As shown in fig. 2, 5.1 and 5.2, the current closed-loop control method adopted by the control strategy of the first current source type matrix converter 1.3 comprises the following steps:
1) the capacitor voltage U passing through the three-phase LC filter 1.21abcAnd the network voltage VgElectric angle theta obtained by phase-locked loopeObtaining the capacitance voltage d-axis component U of the LC filter 1.2 through coordinate transformation 2.11dAnd q-axis component U1q;
2) Component U under filter capacitor voltage dq coordinate system
dAnd U
qThe low-frequency component of the capacitor voltage, the electrical angle theta, is obtained through a low-pass filter 2.2
eObtaining the electrical angular velocity omega after differentiating by 2.3
eAnd 2.6, the low-frequency capacitance current of the filter capacitor can be obtained
And
3) given load side DC bus current I
dc *And the actual DC bus current I
dcThe error value between the two is processed by the PI controller 2.5 to obtain the d-axis direct current component
To realize the transmission of unit power factor, let the reference value Q of reactive power
refIs 0, Q
refAnd the network voltage V
gThe q-axis current component is obtained after 2.4 calculation
Is zero;
4) the dq axis component of the capacitor voltage passes through a high-pass filter 2.7 to obtain a high-frequency component U of the capacitor voltagehdAnd UhqThe high-frequency components of the capacitor voltage are respectively multiplied by a same virtual resistance coefficient kpv(2.8) obtaining dq axis component values of the virtual current (2.9), wherein the fifth harmonic and the seventh harmonic of the system current can be eliminated through an active damping scheme of the harmonic of the virtual resistance suppression circuit;
5) d-axis DC component
Compensating the upper low frequency capacitor current by combining the dq component of the high frequency capacitor voltage flowing through the virtual resistor current
And
obtaining the given value of the final current at the input side of the matrix converter through operation, and obtaining the phase current fundamental wave peak value I after the conversion of polar coordinates 2.17
1dc *And phase angle theta
α1;
6) Phase current fundamental wave peak value I1dc *Divided by a given value of DC current Idc *2.18 obtaining modulation ratio m of current source type matrix converter1iPhase angle thetaα1Plus the electrical angle theta measured by the phase-locked loope2.19 obtaining the switching pulse phase angle theta of the matrix converter1ωUsing the modulation ratio m1iAnd angle theta1ωAnd a switching period TsTwelve switching pulses of the first current source matrix converter 1.3 are generated.
As shown in fig. 2, the dc current control method adopted by the control strategy of the second current source type matrix converter 1.4 includes the following steps:
1) the capacitor voltage U passing through the three-phase LC filter 1.2abcAnd the network voltage VgElectric angle theta obtained by phase-locked loopeObtaining the capacitance voltage d-axis component U of the LC filter 1.2 through coordinate transformation 2.10dAnd q-axis component Uq;
2) Component U under filter capacitor voltage dq coordinate system
dAnd U
qThe low-frequency component of the capacitor voltage, the electrical angle theta, is obtained through a low-pass filter 2.12
eObtaining the electrical angular velocity omega after differentiating by 2.11
eAnd 2.13 calculation is carried out to obtain the low-frequency capacitance current of the filter capacitor
And
3) given load side DC bus current I
dc *And the actual DC bus current I
dcThe error value between the two is processed by the PI controller 2.5 to obtain the d-axis direct current component
To realize the transmission of unit power factor, let the reference value Q of reactive power
refIs 0, Q
refAnd the network voltage V
gThe q-axis current component is obtained after 2.4 calculation
Is zero;
4) the dq axis component of the capacitor voltage passes through a high pass filter 2.14 to obtain capacitor electricityHigh frequency component of voltage UhdAnd UhqThe high-frequency components of the capacitor voltage are respectively multiplied by a same virtual resistance coefficient kpv(2.15) (2.16) obtaining dq axis component values of the virtual current, wherein the fifth harmonic and the seventh harmonic of the system current can be eliminated through an active damping scheme of the harmonic of the virtual resistance suppression circuit;
5) d-axis DC component
Compensating the upper low frequency capacitor current by combining the dq component of the high frequency capacitor voltage flowing through the virtual resistor current
And
obtaining the given value of the final current at the input side of the matrix converter through operation, and obtaining the phase current fundamental wave peak value I after the conversion of polar coordinates 2.20
2dc *And phase angle theta
α2;
6) Phase current fundamental wave peak value I2dc *Divided by a given value of DC current Idc *2.21 obtaining modulation ratio m of Current Source type matrix converter2iPhase angle thetaα2Plus the electrical angle theta measured by the phase-locked loope2.22 obtaining the switching pulse phase angle theta of the matrix converter2ωUsing the modulation ratio m2iAnd angle theta2ωAnd a switching period TsTwelve switching pulses of the second current source matrix converter 1.4 are generated.
The space vector modulation method of the matrix converters 1.3 and 1.4 comprises the following steps:
for simplicity of analysis, the three current vectors acting on the first current source matrix converter 1.3 in a switching cycle are each I11,I12,I10Corresponding to the output voltage of the first current source type matrix converter 1.3 as U11,U12,U10By changing the order of action of the current vectors, U is made11>U12>U10(ii) a In the same way, the method for preparing the composite material,three current vectors acting on the second current source matrix converter 1.4 in one switching cycle are respectively I21,I22,I20Corresponding to the input voltage of the second current source type matrix converter 1.4 as U21,U22,U20By changing the order of action of the current vectors, U is made21>U22>U20. Since the first current source matrix converter 1.3 and the second current source matrix converter 1.4 are connected in parallel, the output voltage waveforms of the matrix converters in one switching period are consistent, and the operating states are consistent, taking the operating state of the first matrix converter as an example, the specific operating process of the soft switch in one switching period is as follows, it is not assumed that the first current source matrix converter 1.3 operates in the first sector, and at this time, the second current source matrix converter 1.4 also operates in the first sector.
As shown in fig. 3(a) (b) and fig. 4 (light color for off and dark color for on):
1) state 0: primary side commutation (t)0 -)
Just after the start of a switching cycle, the current vectors corresponding to the first current source matrix converter 1.3 and the second current source matrix converter 1.4 are both zero vectors I7Output voltage v of matrix converterpIs reduced to 0;
2) state 1 (3.1): switch tube on-time (t)0-t1)
The zero current vector still acts, the primary side input side current and the secondary side output side current of the first high-frequency isolation transformer 1.7 are equal, and the primary side current of the first high-frequency isolation transformer 1.7 flows through the switching tube S of the first current source type matrix converter 1.311、S22And S14、S24The current of the secondary side rectifier bridge of the first high-frequency isolation transformer 1.7 flows through D1、D4Three-phase capacitors provide current paths to three-phase inductors, this state being free of energy transmission, S11And S14Conducting at zero voltage;
3) state 2 (3.2): switch tube on-time (t)1-t2)
First current source type matrix converter 1Zero vector I of 37End of action, current vector I1In operation, the inductive current of the first uncontrolled rectifier bridge 1.9 flows through the diode D1、D4According to a four-step commutation, the switching tube S of the first current source matrix converter 1.311And S14Is turned off because the voltage u is nowabGreater than 0, current to S16And S26The output capacitor of the matrix converter is charged, and the matrix converter power switch tube S16And S26Zero voltage conduction, when the input side voltage of the first high-frequency isolation transformer 1.7 is equal to uabEnergy flows from the grid;
4) state 3 (3.3): switch tube on-time (t)2-t3)
Similar to the operating state of state 2, the effective current vector I of the first current source matrix converter 1.31End of action, current vector I2In operation, the inductive current of the first uncontrolled rectifier bridge 1.9 flows through the diode D1、D4According to a four-step commutation, the switching tube S of the first current source matrix converter 1.316And S26Closing, S12And S22Zero voltage conduction, when the input side voltage of the first high-frequency isolation transformer 1.7 is equal to uacEnergy flows from the grid;
5) state 4 (3.4): commutation of an uncontrolled rectifier bridge (t)3-t4)
The rectification of the first uncontrolled rectifier bridge 1.9 is completed with the aid of the first current source matrix converter 1.3, at t3At the moment, the first uncontrolled rectifier bridge 1.9 diode D2、D3Zero current conduction. The current flowing through the inductor of the first uncontrolled rectifier bridge 1.9 decreases linearly through D2、D3Through D1、D4Is linearly decreased at the same rate, commutation overlap time T in this contextdSelecting 100ns, and commutating current on an inductor 1.9 of the first uncontrolled rectifier bridge before the mode is finished;
6) state 5 (3.5): switch tube on-time (t)4-t5)
Commutation overlap time TdAfter the completion of the process, the operation,power switch tube S of first current source type matrix converter 1.312And S22Off, S14And S24Zero voltage conduction, the voltage drop of the primary side input side of the first high-frequency isolation transformer 1.7 is 0, and no direct current energy is transmitted under the mode;
7) state 6 (3.6): switch tube on-time (t)5-t6)
First current source matrix converter 1.3 current vector I2End of action, zero vector I0In operation, a direct current flows on the load side through the diode D of the first uncontrolled rectifier bridge 1.92And D3While the input side current of the first high-frequency isolation transformer 1.7 flows through the switching tube S of the first current source type matrix converter 1.311、S21And S24、S14And the three-phase capacitor in the LC filter 1.2 provides a current channel for the three-phase inductor.
The foregoing shows and describes the general principles, essential features, and advantages of the invention. It will be understood by those skilled in the art that the present invention is not limited to the embodiments described above, which are described in the specification and illustrated only to illustrate the principle of the present invention, but that various changes and modifications may be made therein without departing from the spirit and scope of the present invention, which fall within the scope of the invention as claimed.