CN104796019B - A kind of Z sources three-level PWM rectifier and its control method - Google Patents

Abstract

The present invention relates to a kind of Z sources three-level PWM rectifier and its control method, including three-phase bridge arm in parallel, include the switching tubes of four series connection per phase bridge arm, the midpoint of each phase bridge arm is connected with electrical network or alternating current source the input source as the commutator through inductance；Each bridge arm outfan in parallel is connected with the input of Z source networks；The outfan of Z source networks concatenates switching tube S up and down respectively_W1And S_W2；Thereafter outfan and electric capacity C₁With electric capacity C₂Series arm be connected in parallel, electric capacity C₁With electric capacity C₂Series arm be connected with DC load；The topology of the present invention not only can realize reduced output voltage, and allow upper and lower bridge arm direct pass, reliability substantially to increase, and the deadband eliminating time, prevent wave distortion；Z sources three-level rectifier can be effectively reduced AC harmonic voltages and electric current while stress levels are improved, and improve the quality of its net side waveform, reduce distortion under identical switching frequency and control mode.

Description

Z-source three-level PWM rectifier and control method thereof

Technical Field

The invention relates to a Z-source three-level PWM rectifier and a control method thereof.

Background

Compared with the traditional uncontrolled rectification and phase-controlled rectification, the PWM rectifier realizes the sine of the network side current and can operate in a unit power factor, so that the PWM rectifier has the advantages of high power factor, small output voltage ripple, good dynamic response and the like. The PWM rectifier is divided into a voltage mode rectifier (VSR) and a current mode rectifier (CSR), wherein the voltage mode rectifier has the advantages of bidirectional power transmission, power factor correction, reduction of input harmonics, and the like, and is widely applied. Although current mode rectifiers have the advantages of circuit protection and faster current response, their bulky size of ac side capacitance and dc side inductance limits their applications. The common voltage type rectifier only has the function of boosting and rectifying, and a DC/DC boosting module is required to be added on the occasion that the output voltage of the direct current side is smaller than the input voltage of the alternating current side, so that the cost and the design difficulty are increased. In addition, electromagnetic interference caused by a direct connection state can damage the direct connection state, and the anti-interference capability and the operation stability of the direct connection state are reduced.

In order to overcome the defects of the traditional voltage type rectifier, a Z-source two-level PWM rectifier is proposed. The rectifier overcomes the defect that a voltage type PWM rectifier cannot reduce voltage, and can realize the voltage increasing and reducing function, so that a two-stage structure is simplified into a one-stage structure. And the structure allows two pipes of each bridge arm to be conducted simultaneously, so that the safety of the system is improved.

The two-level PWM rectifier has the disadvantage that when the two-level PWM rectifier is applied to the occasions of high voltage and high power, a power switch tube with high back voltage is required to be used, or a plurality of power switch tubes are used in series. In addition, because the output voltage of the alternating-current side of the rectifier is always switched on two levels, when the switching frequency is not high, the harmonic content is relatively large. Compared with a two-level rectifier, the three-level rectifier can effectively reduce alternating current harmonic voltage and current while improving the voltage-resistant grade, can obviously improve the waveform quality of the network side of the three-level rectifier under the same switching frequency and control mode, and reduces distortion.

Disclosure of Invention

The invention aims to solve the problems and provides a Z-source three-level PWM rectifier and a control method thereof_W1And S_W2The DC side loop is controlled. The Z-source three-level rectifier using the control method can output direct-current voltage smaller than the amplitude of input voltage, allows each switching tube of a main circuit to be directly connected, and improves the anti-interference capability of the rectifier.

In order to achieve the purpose, the invention adopts the following technical scheme:

a Z-source three-level PWM rectifier is characterized by comprising three-phase bridge arms which are connected in parallel, wherein each phase of bridge arm comprises four switching tubes which are connected in series, and the midpoint of each phase of bridge arm is connected with a power grid or an alternating current source through an inductor to serve as an input source of the rectifier; the output ends of the parallel bridge arms are connected with the input end of the Z source network; the output end of the Z source network is respectively connected with the switching tube S in series from top to bottom_W1And S_W2(ii) a Its rear output end and capacitor C₁And a capacitor C₂Are connected in parallel, a capacitor C₁And a capacitor C₂The series branch of the DC converter is connected with a DC load;

control circuit is used for controlling switching tubes of three-phase bridge arm of rectifier and switching tube S on right side of Z source network_W1And S_W2The Z-source three-level PWM rectifier is respectively operated in four operation modes of non-direct connection, full direct connection, upper direct connection and lower direct connection.

In the three-phase bridge arm, a pair of diodes is respectively connected in series between a first switching tube and a fourth switching tube in each phase of bridge arm, and meanwhile, the middle point of each diode and a capacitor C are connected₁And a capacitor C₂The midpoints of the series branches are connected.

The Z source network is composed of two capacitors and two inductors which are connected into an X-shaped structure, the network is of a symmetrical structure, the capacitance values of the two capacitors are the same, the inductance values of the two inductors are the same, and the left side of the Z source network is connected with the output end of the rectifier, and the right side output of the Z source network is used as the input end of the direct current load.

The switch tube S_W1And S_W2The IGBT and the diode are combined in an anti-parallel mode; switch tube S_W1And S_W2Depending on which mode the rectifier is operating in:

when the rectifier is in non-through mode, the switch tube S_W1And S_W2The IGBTs receive turn-on signals; when the rectifier is in the full-through mode, the switch tube S_W1And S_W2The IGBTs of the power supply all receive turn-off signals; when the rectifier is in the upper through mode, the switch tube S_W1The IGBT receives a turn-on signal and the switch tube S_W2The IGBT of (1) receives a turn-off signal; when the rectifier is in the down-through state, the switch tube S_W1The IGBT receives a turn-off signal and switches the transistor S_W2The IGBT of (1) receives the turn-on signal.

The control circuit comprises a protection circuit, a driving circuit, a sampling conditioning circuit and a DSP module, the sampling conditioning circuit is connected with the DSP module, the DSP module is in two-way communication with the protection circuit, the DSP module is connected with the driving circuit, and the driving circuit outputs PWM signals to drive the IGBT tubes in the bridge arms to be switched on and off.

The sampling conditioning circuit collects the amplitude and the phase of input three-phase alternating current voltage and three-phase current, Z source network capacitor voltage and the voltage value output by a direct current side.

A control method of a Z-source three-level PWM rectifier comprises the following steps:

the SPWM modulation method is adopted, and the whole body is divided into two parts: one part is the traditional voltage and current double closed-loop control of the rectifier, and the other part is the closed-loop control of direct-current output at the direct-current side;

in the traditional voltage and current double closed-loop control of the rectifier, the voltage of a Z source network capacitor is used as a controlled quantity and is initially given;

on the basis of double closed loops, a closed loop of direct-current voltage on the load side is added, so that the output of the direct-current side can be set randomly;

for a Z-source three-level rectifier, a reference value V of a Z-source capacitor is given_CAnd load side DC voltage reference value U_dcDeriving a corresponding initial duty cycle d from the through type₀(ii) a Reference value U of DC voltage at load side_dcAnd actual value U of DC voltage at load side_dcObtaining a direct-connection offset d through PI regulation by making a difference, and finally obtaining an actual duty ratio d satisfying d-d₀+ d; and then the signal d and a reference signal generated by double closed-loop regulation are sent to the SPWM controller, so that the constant output of the direct-current voltage on the load side is realized.

In a switching period, when the absolute values of the upper and lower through signals are the same, the carrier reverse phase modulation only can generate a full through state, and the carrier in-phase modulation can generate an upper through state and a lower through state;

in full-pass mode, the Z source network capacitor voltage V_CAnd a DC output voltage V_dcSatisfies the following conditions:

in the up-down through mode, the Z source network capacitance voltage V_CAnd a DC output voltage V_dcSatisfies the following conditions:

wherein,_Vifor Z source input side voltage, T is a switching period of the rectifier, T₀Is the shoot-through time within one switching cycle, d is the full shoot-through duty cycle, and d' is the up and down shoot-through duty cycle.

In the full-through modeFour switching tubes of one or more phases in the three-phase bridge arm are simultaneously conducted; switch tube S at this time_W1And S_W2And simultaneously, the Z source network and the direct current side circuit are completely disconnected.

In the upward through mode, the three switching tubes on one or more phases of the three-phase bridge arm are simultaneously conducted, and at the moment, the switching tube S is connected_W2Cut off and switch tube S_W1Conducting with the capacitor C on the DC side₁Forming a current loop;

in the lower straight-through mode, the lower three switching tubes of one or more phases of the three-phase bridge arm are simultaneously conducted, and at the moment, the switching tube S is connected_W1Cut off and switch tube S_W2Conducting with the capacitor C on the DC side₂Forming a current loop.

The invention has the beneficial effects that:

1. compared with a three-level rectifier, the Z-source three-level rectifier can realize step-down output, and the direct connection cannot cause damage to a power device, so that the reliability is obviously improved, the dead time is eliminated, and the waveform distortion is prevented;

2. although the Z-source two-level PWM rectifier can realize step-down rectification and bridge arm through protection, when the Z-source two-level PWM rectifier is applied to the occasion of high power, a power switch tube with high back voltage needs to be used or a plurality of power switch tubes need to be connected in series for use; in addition, the output voltage of the alternating current side of the rectifier with the structure is switched on two levels, and when the switching frequency is not high, the harmonic content is relatively large. The Z-source three-level rectifier can effectively reduce alternating current harmonic voltage and current while improving the voltage-resistant grade, improve the quality of a network side waveform under the same switching frequency and control mode, and reduce distortion.

3. The Z-source three-level PWM rectifier has the advantages of high power, good waveform quality and the like, and has wide prospects in the renewable energy fields of photovoltaic power generation systems, wind power generation systems, fuel cells and the like.

Drawings

FIG. 1 is a topological block diagram of the system of the present invention;

FIG. 2(a) is a current circuit diagram of a Z-source three-level PWM rectifier in a full-direct-current mode;

FIG. 2(b) is a current circuit diagram for the pass-through mode on the Z-source three-level PWM rectifier;

FIG. 2(c) is a current circuit diagram of a Z-source three-level PWM rectifier in a direct-current mode;

FIG. 3 is an equivalent current circuit diagram of a Z-source three-level PWM rectifier;

FIG. 4(a) is a non-shoot-through simplified equivalent circuit diagram of a Z-source three-level PWM rectifier;

FIG. 4(b) is a simplified equivalent circuit diagram for the full on state of the Z-source three-level PWM rectifier;

FIG. 4(c) is a simplified equivalent circuit diagram of the up-through state of a Z-source three-level PWM rectifier;

FIG. 4(d) is a simplified equivalent circuit diagram for the lower DC state of a Z-source three-level PWM rectifier;

FIG. 5(a) shows a modulation method of carrier add-back-through;

FIG. 5(b) shows a modulation method of carrier-to-sum direct-pass;

FIG. 6 is a Z-source three-level PWM rectifier control block diagram;

FIG. 7(a) is a Z source capacitor voltage waveform and DC side load waveform without shoot-through using the carrier in-phase modulation method;

FIG. 7(b) is a graph of net side voltage and three phase current waveforms using a carrier in-phase modulation method without applying a direct current;

FIG. 7(c) is an AC side line voltage waveform without shoot-through using the carrier in-phase modulation method;

FIG. 7(d) is an AC side line voltage harmonic detection using a carrier in-phase modulation method without shoot-through;

FIG. 7(e) is a harmonic detection of AC side three phase current without shoot-through using carrier in-phase modulation method;

FIG. 8(a) is a Z source capacitor voltage and DC side load waveform without shoot-through using the carrier inversion modulation method;

FIG. 8(b) is a graph of net side voltage and three phase current waveforms using a carrier inversion modulation method without applying a direct current;

FIG. 8(c) is an AC side line voltage waveform using the carrier inversion modulation method without shoot-through;

FIG. 8(d) is an AC side line voltage harmonic detection using a carrier inversion modulation method without shoot-through;

FIG. 8(e) is an AC side three phase current harmonic detection using carrier inversion modulation without shoot-through;

FIG. 9(a) shows the direct-through duty ratio d using the carrier in-phase modulation method_U＝d_LThe Z source capacitance voltage and dc side load waveform for 0.1;

FIG. 9(b) is a direct-through duty cycle d using the carrier in-phase modulation method_U＝d_LZ source input side V at 0.1_iA waveform;

FIG. 9(c) shows the direct-through duty ratio d using the carrier in-phase modulation method_U＝d_LZ source output side V under the condition of 0.1_oA waveform;

FIG. 10(a) shows the direct-through duty ratio d using the carrier in-phase modulation method_U＝d_LThe Z source capacitance voltage and dc side load waveform for 0.25;

FIG. 10(b) is a direct-through duty cycle d using the carrier in-phase modulation method_U＝d_LZ source input side V at 0.25_iA waveform;

FIG. 10(c) shows the direct-through duty ratio d using the carrier in-phase modulation method_U＝d_LZ source output side V under the condition of 0.25_oAnd (4) waveform.

Detailed Description

The invention is further described with reference to the following figures and examples.

FIG. 1 is a block diagram of a Z-source three-level rectifier of the invention, U_a,U_b,U_cBeing an ideal voltage source: r_SIs a net-side equivalent resistance, L_SIs a network side inductor, C₁And C₂Is a DC side capacitor and has equal capacitance value (C)₁＝C₂) The voltages corresponding to the two are respectively V_d1And V_d2O is the midpoint; the Z source network is formed by connecting two capacitors C in an X-like shape_Z1、C_Z2And two inductors L₁And L₂And (4) forming. S_W1And S_W2Is two switching tubes respectively connected with two diodes D₁And D₂Antiparallel, they normally conduct in the non-pass state and selectively turn off in the particular pass state.

Due to the introduction of the Z source network, the direct connection of bridge arms of each phase of the rectifier is possible. Thus, the Z-source PWM rectifier adds a through zero vector in addition to the active and zero vectors, as compared to a conventional voltage-type PWM rectifier. Compared with the Z-source PWM rectifier, the Z-source three-level PWM rectifier has the advantages that several unique through states are added, and the Z-source three-level PWM rectifier has the characteristic of buck rectification due to the introduction of the through states. For the Z-source three-level PWM rectifier, the following table lists the switching states and corresponding output voltages of the C-phase bridge arm in different operating modes. From table 1, it can be seen that the Z-source three-level rectifier has four operation modes: non-pass mode, full pass mode, up pass mode, and down pass mode. When the Z-source three-level rectifier works in a non-direct-through mode, the operation state of the Z-source three-level rectifier is not different from that of a common voltage type three-level rectifier. The operating characteristics of the Z-source network are revealed when it is operating in the pass-through mode.

TABLE 1Z-Source three-level rectifier switching states

Fig. 2(a) is a current circuit diagram of the Z-source three-level PWM rectifier in the full dc mode. As can be seen from the figure, the full-through operation mode is that four switching tubes of one phase (or some phases) of the three-phase bridge arm are simultaneously turned on. At this time, the loop switch tube S_W1And S_W2Are simultaneously turned off, diode D₁And D₂In a reverse cut-off state, the Z source network and the direct current side circuit are completely disconnected.

Fig. 2(b) is a current circuit diagram of the Z-source three-level PWM rectifier in the through mode. It can be seen from the figure that when the Z-source three-level rectifier is in the up-dc operation mode, the upper three switching tubes of one phase (or some phases) of the three-phase bridge arm are simultaneously turned on, and at this time, the loop switching tube S is turned on_W2Is disconnected from S_W1Antiparallel diode D₁A voltage dividing capacitor C connected to the DC side₁Together forming a current loop.

Fig. 2(c) is a current circuit diagram of the Z-source three-level PWM rectifier in the direct mode. It can be seen from the figure that when the Z-source three-level rectifier is in the down-dc operation mode, the lower three switching tubes of one phase (or some phases) of the three-phase bridge arm are simultaneously turned on, and at this time, the loop switching tube S is turned on_W1Is disconnected from S_W2Antiparallel diode D₂A voltage dividing capacitor C connected to the DC side₂Together forming a current loop.

Fig. 3 is an equivalent current circuit diagram of a Z-source three-level PWM rectifier. Wherein Vi is the input voltage of the Z source network, Vo is the output voltage of the Z source network, and the voltages at two ends of the Z source capacitor are V respectively_C1And V_C2The voltages at the two ends of the Z source inductor are respectively V_L1And V_L2The DC side load voltage is Vdc, and the voltages of the two voltage-dividing capacitors are V_d1And V_d2And + -represents the reference direction of the voltage. Is composed ofThe analysis is simple, and the capacitance values of the two capacitors of the Z source are assumed to be equal, and the inductance values of the two inductors are assumed to be the same, and the value is marked as C_Z1＝C_Z2,L₁＝L₂. The symmetry of the Z source network can then be used to derive:

V_C1＝V_C2＝V_CV_L1＝V_L2＝V_L(1)

assuming that the capacitance values of the two voltage-dividing capacitors are the same and the potential at the midpoint 0 is zero, the following steps are performed:

fig. 4(a) is a non-through simplified equivalent circuit diagram of a Z-source three-level PWM rectifier. At this time S_W1And S_W2Are all in a conducting state, and the Z source network voltage V_LAnd V_CInput side voltage V of Z source_iAnd three independent voltages V (+ N) and V corresponding to the three voltages_NV (-N), Z source output voltage V_oAnd a DC side load voltage V_dcThe relational expressions of (a) are respectively as follows:

V_L＝V_i-V_C(3)

V_o＝V_dc＝V_C-V_L＝2V_C-V_i(5)

fig. 4(b) is a simplified equivalent circuit diagram of the full on state of the Z-source three-level PWM rectifier. At this time S_W1And S_W2Are all in an off state, and the Z source network voltage V_LAnd V_CInput side voltage V of Z source_iAnd three independent voltages V (+ N) and V corresponding to the three voltages_NV (-N), Z source output voltage V_oThe relational expressions of (a) are respectively as follows:

V_L＝-V^C(6)

V_i＝0V V(+N)＝V_N＝V(-N)＝0V (7)

V_o＝V_C-V_L＝2V_C(8)

suppose that in a switching period T, the time when the rectifier bridge works in the non-through state is T₁Working in the through state for a time T₀When the direct-through duty ratio is d, T is T₀+T₁，d＝T₀and/T. In a switching period T, the average voltage across the inductor must be 0 in a steady state, which can be obtained from equations (3) and (6):

simplifying to obtain:

obtained by the formulae (5) and (6):

simplifying to obtain:

similarly, the average value expression of the dc voltage output by the Z source is as follows:

as can be seen from equations (5) and (10), the relationship between the load-side dc output voltage, the Z-source capacitance voltage, and the Z-source input voltage peak is as follows:

V_dc＝2V_C-V_i＝(1-2d)·V_i(15)

assuming that B1-2 d satisfies 0< B < ═ 1, which is referred to as a buck factor of the Z-source rectifier, it can be seen that when the through duty d is 0, B is 1, the Z-source three-level rectifier operates in the normal rectification mode, and when d >0, B <1, when the Z-source three-level rectifier operates in the buck rectification mode.

From the above analysis, the full-pass mode of the Z-source two-level rectifier is also applicable to the Z-source three-level rectifier. Although the step-down rectification can be realized by switching the Z-source three-level rectifier back and forth between the non-through state and the full-through state, the advantage of higher waveform output quality of the three-level rectifier compared with the two-level rectifier is not realized. In fact, due to the existence of the middle point potential o, the Z-source three-level rectifier has two new through modes: an up-through mode and a down-through mode. Unlike the full-pass mode, the two pass modes do not require S_W1And Sw₂All the switches are switched off, and only one of the switches needs to be switched off.

Fig. 4(c) is a simplified equivalent circuit diagram of the up-through state of a Z-source three-level PWM rectifier. When the bridge arm is in a 0 state, an up-through signal is added to enable the upper 3 switching tubes of the bridge arm to be simultaneously conducted, and at the moment, the Z-source three-level PWM rectifier operates in an up-through mode. At this time, only S_W2In the off state. Its Z source network voltage V_LAnd V_CInput side voltage V of Z source_iAnd three independent voltages V (+ N) and V corresponding to the three voltages_NV (-N), Z source output voltage V_oThe relational expressions of (a) are respectively as follows:

V(+N)＝V_N＝0V (17)

fig. 4(d) is a simplified equivalent circuit diagram of the lower dc state of a Z-source three-level PWM rectifier. When the bridge arm is in a 0 state, a lower through signal is added to enable the lower 3 switching tubes of the bridge arm to be simultaneously conducted, and at the moment, the Z-source three-level PWM rectifier can operate in a lower through mode. At this time, only S_W1In the off state. Its Z source network voltage V_LAnd V_CInput side voltage V of Z source_iAnd three independent voltages V (+ N) and V corresponding to the three voltages_NV (-N), Z source output voltage V_oThe relational expressions of (a) are respectively as follows:

V_N＝V(-N)＝0V (23)

suppose that in a switching period T, the time when the rectifier bridge works in the non-through state is T₁Working in the up-through state for a time T_UWorking at the time of lower straight-through is T_LTotal straight-through time T₀＝T_U+T_LThe total duty ratio is d', T is T ═ T₀+T₁，d_U＝T_U/T,d_L＝T_L/T,d_U+d_LD'. In a switching period T, the average voltage across the inductor must be 0 in a steady state, which can be obtained from equations (5), (16) and (21):

simplifying to obtain:

similarly, the average value expression of the dc voltage output by the Z source is as follows:

as can be seen from equations (5) and (27), the relationship between the load-side dc output voltage and the Z source input voltage peak is as follows:

V_dc＝2V_C-V_i＝(1-d')·V_i(29)

the upper direct mode is a voltage-dividing capacitor C₁Providing a discharge circuit, the lower direct-through mode being a voltage-dividing capacitor C₂Providing a discharge circuit for ensuring C₁And C₂The same partial pressure as possible and the straight-through time T from top to bottom_UAnd T_LDirect from top to bottom duty cycle d_UAnd d_LShould satisfy T_U＝T_L,d_U＝d_L。

Fig. 5(a) shows a modulation method of carrier add-back-pass. Wherein the amplitude of the upper through comparison signal C + is the same as the absolute value of the lower through comparison signal C-, and the upper through comparison signal C + is the same as the absolute value of the lower through comparison signal C₁The absolute values differ. The upper straight-through comparison signal and the upper carrier comparison generate an upper straight-through signal, the lower straight-through comparison signal and the lower carrier comparison generate a lower straight-through signal, and when the upper straight-through signal and the lower straight-through signal are overlapped, the 1 and 4 switching tubes are simultaneously conducted when outputting a 0 state, so that the 4 switching tubes are simultaneously conducted, namely, the full-straight-through is realized. It can be known from the figure that when the absolute values of the upper and lower through comparison signals are equal, the upper and lower through areas can be completely overlapped to realize complete through, and when the absolute values of the upper and lower through comparison signals are different, the upper and lower through areas are only partially overlapped to generate an upper through state or a lower through state.

Fig. 5(b) shows the SPWM modulation method with in-phase carrier plus pass-through. As can be seen from the figure, the upper through comparison signal and the upper carrier comparison generate an upper through signal, the lower through comparison signal and the lower carrier comparison generate a lower through signal, and the positions of the upper through signal and the lower through signal are staggered in one switching period, so that the full through state does not occur. The up-down through state is also added when the bridge arm is in the 0 state, the up-down through signal enables three pipes on the bridge arm to be conducted simultaneously, and the bridge arm is in the up-down through state at the moment. The downward through signal makes three pipes under the bridge arm be conducted at the same time, and at the moment, the bridge arm is in a downward through state.

Fig. 6 is a Z-source three-level PWM rectifier control block diagram. As can be seen from the figure, on the basis of the double closed loops, the closed loop of the load side direct current voltage is added, so that the direct current side output can be arbitrarily given. For a Z-source three-level rectifier, a reference value V of a Z-source capacitor is given_CAnd load side DC voltage reference value U_dcRespectively substituting equations (14) and (17) according to the through type to obtain an initial duty ratio d₀。U_dcAnd U_dcObtaining a direct-connection offset d through PI regulation by making a difference, and finally obtaining an actual duty ratio d meeting the requirementd＝d₀+ d. And then the signal d and a reference signal generated by double closed-loop regulation are sent to the SPWM controller, so that the constant output of the direct-current voltage on the load side is realized.

Fig. 7(a) - (e) are Z-source three-level PWM rectifier output waveforms using the carrier in-phase modulation method without applying a direct pass. It can be seen from the figure that when no through signal is added, the output of the dc side of the Z-source three-level rectifier is the same as that of the common three-level rectifier, and there is no voltage reduction effect. The total harmonic distortion of the ac side line voltage and phase current at this time was 42.52% and 1.29%, respectively.

Fig. 8(a) - (e) are Z-source three-level PWM rectifier output waveforms using a carrier inversion modulation method without applying a direct pass. It can be seen from the figure that when no through signal is added, the output of the dc side of the Z-source three-level rectifier is the same as that of the common three-level rectifier, and there is no voltage reduction effect. The total harmonic distortion of the ac side line voltage and phase current at this time was 75.31% and 3.02%, respectively. Therefore, under the condition that the capacitor voltage is given to be the same, compared with the carrier reverse phase modulation method, the carrier in-phase modulation method has no great difference on the output of the direct current side, but the harmonic distortion of the voltage of the alternating current side line is reduced from 75.31% to 42.52%, the total harmonic distortion of the phase current of the alternating current side is reduced from 3.02% to 1.29%, and the carrier in-phase modulation method is more suitable for a Z-source three-level PWM rectifier, so that a through signal is added into the carrier in-phase modulation method to achieve the best operation effect.

FIGS. 9(a) - (c) are diagrams of direct-through duty cycle d using carrier in-phase modulation method_U＝d_LThe Z-source three-level PWM rectifier output waveform at 0.1. Get V_c*＝600V，U_dc533V, and thus d_U＝d_L＝0.1,d₀＝d_U+d_L0.2. At this time, Z source input voltage V_iAnd Z source output voltage V_oThe theoretical calculation values of (A) are respectively:

when the signal is not straight-through: v_i＝2V_C-V_dc＝1200-533＝667V；V_o＝V_dc＝533V

When the upper part and the lower part are directly communicated: v_i＝Vc-V_dc/2＝600-400/2＝333.5V；V_o＝V_C+V_dc/2＝600+400/2＝866.5V

The above calculated values are consistent with the waveform diagram shown in fig. 9.

FIGS. 10(a) - (c) are graphs showing the direct duty cycle d using the carrier in-phase modulation method_U＝d_LThe Z-source three-level PWM rectifier output waveform at 0.25. Get V_c*＝600V，U_dc400V, and thus d_U＝d_L＝0.25,d₀＝d_U+d_L0.5. At this time, Z source input voltage V_iAnd Z source output voltage V_oThe theoretical calculation values of (A) are respectively:

when the signal is not straight-through: v_i＝2V_C-V_dc＝1200-400＝800V；V_o＝V_dc＝400V

When the upper part and the lower part are directly communicated: v_i＝Vc-V_dc/2＝600-400/2＝400V；V_o＝V_C+V_dc/2＝600+400/2＝800V

The above calculated values are consistent with the waveform diagram shown in fig. 10.

Although the embodiments of the present invention have been described with reference to the accompanying drawings, it is not intended to limit the scope of the present invention, and it should be understood by those skilled in the art that various modifications and variations can be made without inventive efforts by those skilled in the art based on the technical solution of the present invention.

Claims (10)

1. A Z-source three-level PWM rectifier is characterized by comprising three-phase bridge arms which are connected in parallel, wherein each phase of bridge arm comprises four switching tubes which are connected in series, and the midpoint of each phase of bridge arm is connected with a power grid or an alternating current source through an inductor to serve as an input source of the rectifier; the output ends of the parallel bridge arms are connected with the input end of the Z source network; the output end of the Z source network is respectively connected with the switching tube S in series from top to bottom_W1And S_W2(ii) a Its rear output end and capacitor C₁And a capacitor C₂Are connected in parallel, a capacitor C₁And a capacitor C₂The series branch of the DC converter is connected with a DC load;

control circuit is used for controlling switching tubes of three-phase bridge arm of rectifier and Z source right side switching tube S_W1And S_W2The Z-source three-level PWM rectifier is enabled to respectively operate in four operation modes of non-through, full-through, upper-through and lower-through.

2. The Z-source three-level PWM rectifier according to claim 1, wherein in said three-phase bridge arms, a pair of diodes is connected in series between the first switch tube and the fourth switch tube in each phase bridge arm, and the midpoint of the diode and the capacitor C are connected in series₁And a capacitor C₂The midpoints of the series branches are connected.

3. The Z-source three-level PWM rectifier according to claim 1, wherein the Z-source network is composed of two capacitors and two inductors connected in a similar X-shape, the network is a symmetrical structure, the capacitance values of the two capacitors are the same, the inductance values of the two inductors are the same, and the left side of the Z-source network is connected to the output terminal of the rectifier and the right side output is used as the input terminal of the dc load.

4. The Z-source three-level PWM rectifier according to claim 1, wherein said switching tube S_W1And S_W2The IGBT and the diode are combined in an anti-parallel mode; switch tube S_W1And S_W2Depending on which mode the rectifier is operating in:

when the rectifier is in non-through mode, the switch tube S_W1And S_W2The IGBTs receive turn-on signals; when the rectifier is in the full-through mode, the switch tube S_W1And S_W2The IGBTs of the power supply all receive turn-off signals; when the rectifier is in the upper through mode, the switch tube S_W1The IGBT receives a turn-on signal and the switch tube S_W2The IGBT of (1) receives a turn-off signal; when the rectifier is in the down-through state, the switch tube S_W1The IGBT receives a turn-off signal and switches the transistor S_W2The IGBT of (1) receives the turn-on signal.

5. The Z-source three-level PWM rectifier according to claim 1, wherein the control circuit comprises a protection circuit, a driving circuit, a sampling conditioning circuit and a DSP module, the sampling conditioning circuit is connected with the DSP module, the DSP module is in bidirectional communication with the protection circuit, the DSP module is connected with the driving circuit, and the driving circuit outputs PWM signals to drive the IGBT tubes in the bridge arms to be switched on and off.

6. The Z-source three-level PWM rectifier according to claim 5, wherein said sampling and conditioning circuit collects the amplitude and phase of the input three-phase AC voltage and three-phase current, the Z-source network capacitor voltage and the voltage value of the DC side output.

7. A method of controlling a Z-source three-level PWM rectifier as claimed in claim 1, comprising:

the SPWM modulation method is adopted, and the whole body is divided into two parts: one part is the traditional voltage and current double closed-loop control of the rectifier, and the other part is the closed-loop control of direct-current output at the direct-current side;

in the traditional voltage and current double closed-loop control of the rectifier, the voltage of a Z source network capacitor is used as a controlled quantity and is initially given;

on the basis of double closed loops, a closed loop of direct-current voltage on the load side is added, so that the output of the direct-current side can be set randomly;

for a Z-source three-level rectifier, a reference value V of a Z-source capacitor is given_CAnd load side DC voltage reference value U_dcDeriving a corresponding initial duty cycle d from the through type₀(ii) a Reference value U of DC voltage at load side_dcAnd load side DC voltage U_dcObtaining a direct-connection offset d through PI regulation by making a difference, and finally obtaining an actual duty ratio d satisfying d-d₀+ d; and then the signal d and a reference signal generated by double closed-loop regulation are sent to the SPWM controller, so that the constant output of the direct-current voltage on the load side is realized.

8. The method of claim 7 wherein the Z-source three-level PWM rectifier,

in a switching period, when the absolute values of the upper and lower through signals are the same, the carrier reverse phase modulation only can generate a full through state, and the carrier in-phase modulation can generate an upper through state and a lower through state;

in full-pass mode, the Z source network capacitor voltage V_CAnd a DC output voltage V_dcSatisfies the following conditions:

$V_{\mathrm{dc}}=2V_C-V_i=\frac{1-2d}{1-d}\&CenterDot;V_C;$

in the up-down through mode, the Z source network capacitance voltage V_CAnd a DC output voltage V_dcSatisfies the following conditions:

$V_{\mathrm{dc}}=\frac{2(T-T_0)}{2T-T_0}\&CenterDot;V_C=\frac{1-d^{\&prime;}}{1-d^{\&prime;}/2}\&CenterDot;V_C;$

wherein, V_iFor Z source input side voltage, T is a switching period of the rectifier, T₀Is the shoot-through time within one switching cycle, d is the full shoot-through duty cycle, and d' is the up and down shoot-through duty cycle.

9. The method as claimed in claim 1, wherein in the full-through mode, four switching tubes of one or more phases of a three-phase bridge arm are simultaneously turned on; switch tube S at this time_W1And S_W2And simultaneously, the Z source network and the direct current side circuit are completely disconnected.

10. The method as claimed in claim 1, wherein in the up-through mode, the upper three switching tubes of one or more phases of the three-phase bridge arm are simultaneously turned on, and the switching tube S is turned on_W2Cut off and switch tube S_W1Conducting with the capacitor C on the DC side₁Forming a current loop;

in the lower straight-through mode, the lower three switching tubes of one or more phases of the three-phase bridge arm are simultaneously conducted, and at the moment, the switching tube S is connected_W1Cut off and switch tube S_W2Conducting with the capacitor C on the DC side₂Forming a current loop.