CN106253726A - A kind of three-level inverter direct current neutral-point voltage balance method - Google Patents

Abstract

The invention discloses a kind of three-level inverter direct current neutral-point voltage balance method.The control method of the present invention adjusts direct current biasing and the amplitude of positive negative carrier according to the fluctuation size of mid-point voltage, thus the balance realizing midpoint potential controls.The control method of the present invention realizes simple, and response rapidly, does not lose DC voltage utilization rate, and still ensure that output voltage electric current occurs without harmonic distortion in the case of mid-point voltage imbalance, the balance that can effectively realize midpoint potential controls, it is ensured that switching device safety, reduces harmonic wave of output voltage.

Description

A kind of three-level inverter direct current neutral-point voltage balance method

Technical field

The present invention relates to three level DC-AC energy converting means, be specifically related to a kind of three level DC-AC energy The control method of converting means direct current midpoint potential.

Background technology

Multi-electrical level inverter can reduce the harmonic content of output voltage, reduces the voltage stress of switching device, at high pressure Large-power occasions is widely used.Wherein three level neutral-point-clamped type inverters are studied and are most widely used.Three electricity The precondition that flat neutral-point-clamped type inverter can normally work is that mid-point voltage keeps balance.Mid-point voltage imbalance can be led Cause output voltage current harmonic content to increase, if voltage pulsation degree acutely or bigger steady-state deviation occurs, brachium pontis can be caused to hold Close tube voltage stress to increase, switching tube excessive pressure damages may be made.

Occur in asymmetric, control non-ideal factor, load exist bigger harmonic wave electricity when existing on inverter structure When stream and negative-sequence current, three level neutral-point-clamped type inverter mid-point voltages all can be caused uneven.Uneven for mid-point voltage The problem of weighing apparatus, traditional has two big class methods, SVPWM method and SPWM method.SVPWM method is generally by the regulation little arrow of redundancy Amount realizes neutral point voltage balance, calculates extremely complex, and harmonic wave of output voltage can be made to increase.Traditional SPWM method is generally passed through Inject residual voltage and realize neutral point voltage balance, calculate complexity equally, and DC voltage utilization rate can be caused to reduce.

Three-level inverter neutral point voltage balance aspect there is also all problems at present, and these problems are not yet solved Certainly.

Summary of the invention

For the problem in terms of the neutral point voltage balance existing for tradition three-level inverter, the invention provides a kind of meter Calculate simple, the three-level inverter direct current neutral-point voltage balance method of fast uniform.

Specifically, the invention provides a kind of three-level inverter direct current neutral-point voltage balance method, described control Method processed is for being balanced controlling to the direct current mid-point voltage of three-level inverter, and described three-level inverter includes unidirectional current Source, DC side electric capacity of voltage regulation C1 and C2, A phase midpoint clamped type brachium pontis, B phase midpoint clamped type brachium pontis, C phase midpoint clamped type bridge Arm, the midpoint of three brachium pontis is both connected on the midpoint of DC side electric capacity of voltage regulation C1 and C2, and the positive ends of three brachium pontis all connects Being connected to the positive pole of described DC source, negative polarity end is connected to the negative pole of described DC source, and exchange end is respectively connecting to bear A, b, c end points carried, it is characterised in that

Described method comprises the steps:

(1) standard sine modulating wave is generated；

(2) described standard sine modulating wave is carried out asymmetric correction；

(3) the asymmetric sinusoidal modulation wave obtained after revising compares with carrier wave；

(4) driving sequence is generated based on comparative result；

(5) described driving sequence is sent respectively to the switching device of three brachium pontis.

Further, described step (2) including:

(2.1) the voltage V of described DC source is gathered_dc；

(2.2) the voltage V of described both DC side electric capacity of voltage regulation C1 and C2 is gathered_C1、V_C2, and it is calculated mid-point voltage Difference Δ V=V_C1-V_C2；

(2.3) in described standard sine modulating wave, zero-sequence component Δ V/V is added_dc, obtain part correction modulating wave V_r1-1；

(2.4) by described modulating wave V_r1-1Part more than zero is multiplied by coefficient V_dc/2V_c1, obtain part correction modulating wave V_r1-2；

(2.5) by described part correction modulating wave V_r1-2Minus part is multiplied by coefficient V_dc/2V_c2,

Obtain asymmetric modulation ripple V_r2, its expression formula is:

$\left\{\begin{array}{cc}{V}_{r2a}=\frac{\left(m\sin \right(\mathrm{\&omega;}t)+\mathrm{\&Delta;}V/V_{dc})V_{dc}}{2V_{c1}}& m\sin \left(\mathrm{\&omega;}t\right)+\mathrm{\&Delta;}V/V_{dc}>0\\ V_{r2a}=\frac{\left(m\sin \right(\mathrm{\&omega;}t)+\mathrm{\&Delta;}V/V_{dc})V_{dc}}{2V_{c2}}& m\sin \left(\mathrm{\&omega;}t\right)+\mathrm{\&Delta;}V/V_{dc}<0\end{array}\right.$

$\left\{\begin{array}{cc}{V}_{r2b}=\frac{\left(m\sin \right(\mathrm{\&omega;}t-2/3\mathrm{\&pi;})+\mathrm{\&Delta;}V/V_{dc})V_{dc}}{2V_{c1}}& m\sin (\mathrm{\&omega;}t-2/3\mathrm{\&pi;})+\mathrm{\&Delta;}V/V_{dc}>0\\ V_{r2b}=\frac{\left(m\sin \right(\mathrm{\&omega;}t-2/3\mathrm{\&pi;})+\mathrm{\&Delta;}V/V_{dc})V_{dc}}{2V_{c2}}& m\sin (\mathrm{\&omega;}t-2/3\mathrm{\&pi;})+\mathrm{\&Delta;}V/V_{dc}<0\end{array}\right.$

$\left\{\begin{array}{cc}{V}_{r2c}=\frac{\left(m\sin \right(\mathrm{\&omega;}t+2/3\mathrm{\&pi;})+\mathrm{\&Delta;}V/V_{dc})V_{dc}}{2V_{c1}}& m\sin (\mathrm{\&omega;}t+2/3\mathrm{\&pi;})+\mathrm{\&Delta;}V/V_{dc}>0\\ V_{r2b}=\frac{\left(m\sin \right(\mathrm{\&omega;}t+2/3\mathrm{\&pi;})+\mathrm{\&Delta;}V/V_{dc})V_{dc}}{2V_{c2}}& m\sin (\mathrm{\&omega;}t+2/3\mathrm{\&pi;})+\mathrm{\&Delta;}V/V_{dc}<0\end{array}\right.$

Wherein, m is current modulation wave modulation ratio.

The advantage of control method of the present invention is:

(1) balance of three-level inverter mid-point voltage effectively and is quickly realized；

(2) in the case of imbalance, remain to be effectively ensured output voltage sine degree, greatly improve output voltage and electric current is humorous Ripple content；

(3) control method realizes very simple, and amount of calculation is little；

(4) control method will not lose DC voltage utilization rate.

Accompanying drawing explanation

Fig. 1 is the topology diagram of the three-phase tri-level inverter that the present invention is applied to；

Fig. 2 is the contrast of control method of the present invention and traditional control method；

Fig. 3 is to use the inventive method and do not use mid-point voltage comparison of wave shape before and after the inventive method；

Fig. 4 is output current wave contrast before and after using the inventive method and not using the inventive method.

Detailed description of the invention

The invention will be further described below in conjunction with the accompanying drawings.

Fig. 1 is three-phase tri-level inverter topology figure.As it is shown in figure 1, described three-phase tri-level inverter includes directly Stream power supply V_dc, DC side electric capacity of voltage regulation C1 and C2, A phase switching tube S_a1～S_a4, A phase catching diode D_a1And D_a2, B phase switching tube S_b1～S_b4, B phase catching diode D_b1And D_b2, C phase switching tube S_c1～S_c4, C phase catching diode D_c1And D_c2, and three intersect Current load.A phase switching tube S_a1～S_a4, A phase catching diode D_a1And D_a2Composition A phase midpoint clamped type brachium pontis；B phase switching tube S_b1 ～S_b4, B phase catching diode D_b1And D_b2Composition B phase midpoint clamped type brachium pontis；C phase switching tube S_c1～S_c4, C phase catching diode D_c1And D_c2Composition C phase midpoint clamped type brachium pontis.This inverter also includes control module, and control module is used for generating control signal, To control all parts in inverter.

Fig. 2 show the contrast of control method of the present invention and traditional control method.As in figure 2 it is shown, three-phase tri-level inversion When device is modulated according to tradition SPWM modulator approach, carrier wave V_caIt is by the two group triangular wave groups symmetrical about y=0 horizontal line Becoming, triangular wave amplitude is 1, and frequency is switching frequency f_s.Conventional modulated ripple V_r1It is the sine wave symmetrical about y=0 horizontal line, its Expression formula is as shown in (I),

$\left\{\begin{array}{c}{V}_{r1a}=m\sin \left(\mathrm{\&omega;}t\right)\\ V_{r1b}=m\sin (\mathrm{\&omega;}t-\frac{2\mathrm{\&pi;}}{3})\\ V_{r1c}=m\sin (\mathrm{\&omega;}t+\frac{2\mathrm{\&pi;}}{3})\end{array}\right.---\left(I\right)$

Its switching tube conduction mode is carried out by following formula,

The output voltage obtained by traditional modulation is expressed shown in formula such as formula (III), v_ab, v_bcAnd v_caIt is three-phase respectively Inverter output line voltage, Δ V=V in formula_c1-V_c2, V_c1And V_c2It is electric capacity of voltage regulation C1 and C2 both end voltage respectively, due to midpoint The existence of Voltage unbalance, causes output voltage to produce Severe distortion.

$\left\{\begin{array}{c}{v}_{ab}=\sqrt{3}m\left(\sin \right(\mathrm{\&omega;}t+\frac{\mathrm{\&pi;}}{6}\left)\right)\frac{V_{dc}}{2}+m\left(\right|\sin \left(\mathrm{\&omega;}t\right)|-|\sin \left(\mathrm{\&omega;}t-\frac{2\mathrm{\&pi;}}{3}\right)\left|\right)\frac{\mathrm{\&Delta;}V}{2}\\ v_{bc}=\sqrt{3}m\left(\sin \right(\mathrm{\&omega;}t-\frac{\mathrm{\&pi;}}{2}\left)\right)\frac{V_{dc}}{2}+m\left(\right|\sin \left(\mathrm{\&omega;}t-\frac{2\mathrm{\&pi;}}{3}\right)|-|\sin \left(\mathrm{\&omega;}t+\frac{2\mathrm{\&pi;}}{3}\right)\left|\right)\frac{\mathrm{\&Delta;}V}{2}\\ v_{ca}=\sqrt{3}m\left(\sin \right(\mathrm{\&omega;}t+\frac{5\mathrm{\&pi;}}{6}\left)\right)\frac{V_{dc}}{2}+m\left(\right|\sin \left(\mathrm{\&omega;}t+\frac{2\mathrm{\&pi;}}{3}\right)|-|\sin \left(\mathrm{\&omega;}t\right)\left|\right)\frac{\mathrm{\&Delta;}V}{2}\end{array}\right.---\left(III\right)$

Described asymmetric modulation ripple V_r2Generate as steps described below,

(1) zero-sequence component is added

At conventional modulated ripple V_r1On the basis of add real-time zero-sequence component Δ V/V_dc, obtain modulating wave V_r1-1；

(2) positive half-wave adjusts

By modulating wave V_r1-1Part more than zero is multiplied by coefficient V_dc/2V_c1, obtain modulating wave V_r1-2；

(3) negative half-wave adjusts

By modulating wave V_r1-2Minus part is multiplied by coefficient V_dc/2V_c2, obtain modulating wave V_r2；

Shown in asymmetric modulation ripple expression formula such as formula (IV), it is modulated according to formula (IV), works as V_C1Time higher, asymmetric tune Ripple V processed_r2Positive half-wave part can strengthen, and negative half-wave part can reduce, and inverter extraction electric capacity C1 energy time increases, thus main Move and make V_C1Decline, and extract electric capacity C2 energy time and reduce, thus actively make V_C2Rise, make mid-point voltage restore balance, similar , work as V_C2Time higher, asymmetric modulation ripple V_r2Negative half-wave part can strengthen, and positive half-wave part can reduce, inverter extraction electricity Hold C2 energy time to increase, thus actively make V_C2Decline, and extract electric capacity C1 energy time and reduce, thus actively make V_C1Rise, Mid-point voltage is made to restore balance；Especially, the V shown in formula (IV)_r2Expression formula always meets V_r2≤ 1, therefore to DC voltage profit Any loss is not had by rate.

$\begin{array}{c}\left\{\begin{array}{cc}{V}_{r2a}=\frac{\left(m\sin \right(\mathrm{\&omega;}t)+\mathrm{\&Delta;}V/V_{dc})V_{dc}}{2V_{c1}}& m\sin \left(\mathrm{\&omega;}t\right)+\mathrm{\&Delta;}V/V_{dc}>0\\ V_{r2a}=\frac{\left(m\sin \right(\mathrm{\&omega;}t)+\mathrm{\&Delta;}V/V_{dc})V_{dc}}{2V_{c2}}& m\sin \left(\mathrm{\&omega;}t\right)+\mathrm{\&Delta;}V/V_{dc}<0\end{array}\right.\\ \left\{\begin{array}{cc}{V}_{r2b}=\frac{\left(m\sin \right(\mathrm{\&omega;}t-2/3\mathrm{\&pi;})+\mathrm{\&Delta;}V/V_{dc})V_{dc}}{2V_{c1}}& m\sin (\mathrm{\&omega;}t-2/3\mathrm{\&pi;})+\mathrm{\&Delta;}V/V_{dc}>0\\ V_{r2b}=\frac{\left(m\sin \right(\mathrm{\&omega;}t-2/3\mathrm{\&pi;})+\mathrm{\&Delta;}V/V_{dc})V_{dc}}{2V_{c2}}& m\sin (\mathrm{\&omega;}t-2/3\mathrm{\&pi;})+\mathrm{\&Delta;}V/V_{dc}<0\end{array}\right.\\ \left\{\begin{array}{cc}{V}_{r2c}=\frac{\left(m\sin \right(\mathrm{\&omega;}t+2/3\mathrm{\&pi;})+\mathrm{\&Delta;}V/V_{dc})V_{dc}}{2V_{c1}}& m\sin (\mathrm{\&omega;}t+2/3\mathrm{\&pi;})+\mathrm{\&Delta;}V/V_{dc}>0\\ V_{r2c}=\frac{\left(m\sin \right(\mathrm{\&omega;}t+2/3\mathrm{\&pi;})+\mathrm{\&Delta;}V/V_{dc})V_{dc}}{2V_{c2}}& m\sin (\mathrm{\&omega;}t+2/3\mathrm{\&pi;})+\mathrm{\&Delta;}V/V_{dc}<0\end{array}\right.\end{array}---\left(IV\right)$

Asymmetric modulation ripple V_r2With carrier wave V_caCompare, be modulated, according to this according to public formula (II) switch tube The asymmetric modulation mode of bright proposition is controlled, and shown in the three-phase line voltage expression formula such as formula (V) obtained, uses the present invention to adjust After mode processed, the harmonic distortion that mid-point voltage imbalance introduces is eliminated.

$\left\{\begin{array}{c}{v}_{ab}=\sqrt{3}m\left(\sin \right(\mathrm{\&omega;}t+\frac{\mathrm{\&pi;}}{6}\left)\right)\frac{V_{dc}}{2}\\ v_{bc}=\sqrt{3}m\left(\sin \right(\mathrm{\&omega;}t-\frac{\mathrm{\&pi;}}{6}\left)\right)\frac{V_{dc}}{2}\\ v_{ca}=\sqrt{3}m\left(\sin \right(\mathrm{\&omega;}t+\frac{5\mathrm{\&pi;}}{6}\left)\right)\frac{V_{dc}}{2}\end{array}\right.---\left(V\right)$

Fig. 3 and Fig. 4 respectively illustrate the present invention method application before and after mid-point voltage simulation waveform contrast and output voltage Simulation waveform contrasts.Simulation parameter is: switching frequency 15kHz, alternating voltage fundamental frequency 50Hz, and line voltage effective value is 380V, DC voltage V_dcFor 700V, loading as 4.28mH inductance 25 Europe resistance, modulation is 1 than m, C1 and C2 is 470uF, in Point voltage difference Δ V is 100V.

From figure 3, it can be seen that when mid-point voltage difference has 100V, put into the control method of the present invention in the 0.2s moment, Mid-point voltage is promptly restored to balance, is only 20ms recovery time, and stable state mid-point voltage difference controls within 0.5V；From Fig. 4 It can be seen that keeping mid-point voltage difference is 100V, traditional control method output load current occurs substantially to distort, and the present invention Control method can ensure that the sine degree that output load current is the most excellent.

The present invention is not only limited to above-mentioned detailed description of the invention, and persons skilled in the art are public according to embodiment and accompanying drawing Open content, can use other multiple detailed description of the invention implement the present invention, therefore, the design structure of every employing present invention and Thinking, does some simply conversion or designs of change, both falls within the scope of protection of the invention.

Claims (2)

1. a three-level inverter direct current neutral-point voltage balance method, described control method is for three-level inverter Direct current mid-point voltage be balanced control, described three-level inverter include DC source, DC side electric capacity of voltage regulation C1 and C2, A phase midpoint clamped type brachium pontis, B phase midpoint clamped type brachium pontis, C phase midpoint clamped type brachium pontis, the midpoint of three brachium pontis is both connected to On the midpoint of DC side electric capacity of voltage regulation C1 and C2, the positive ends of three brachium pontis is connected to the positive pole of described DC source, negative Polar end is connected to the negative pole of described DC source, and exchange end is respectively connecting to a, b, c end points of load, it is characterised in that

Described method comprises the steps:

(1) standard sine modulating wave is generated；

(2) described standard sine modulating wave is carried out asymmetric correction；

(3) the asymmetric sinusoidal modulation wave obtained after revising compares with carrier wave；

(4) driving sequence is generated based on comparative result；

(5) described driving sequence is sent respectively to the switching device of three brachium pontis.

Three-level inverter direct current neutral-point voltage balance method the most according to claim 1, it is characterised in that described Step (2) including:

(2.1) the voltage V of described DC source is gathered_dc；

(2.2) the voltage V of described both DC side electric capacity of voltage regulation C1 and C2 is gathered_C1、V_C2, and it is calculated mid-point voltage difference Δ V =V_C1-V_C2；

(2.3) in described standard sine modulating wave, zero-sequence component Δ V/V is added_dc, obtain part correction modulating wave V_r1-1；

(2.4) by described modulating wave V_r1-1Part more than zero is multiplied by coefficient V_dc/2V_c1, obtain part correction modulating wave V_r1-2；

(2.5) by described part correction modulating wave V_r1-2Minus part is multiplied by coefficient V_dc/2V_c2, obtain asymmetric modulation ripple V_r2, its expression formula is:

$\left\{\begin{array}{cc}{V}_{r2a}=\frac{\left(msin\right(\mathrm{\&omega;}t)+\mathrm{\&Delta;}V/V_{dc})V_{dc}}{2V_{c1}}& msin\left(\mathrm{\&omega;}t\right)+\mathrm{\&Delta;}V/V_{dc}>0\\ V_{r2a}=\frac{\left(msin\right(\mathrm{\&omega;}t)+\mathrm{\&Delta;}V/V_{dc})V_{dc}}{2V_{c2}}& msin\left(\mathrm{\&omega;}t\right)+\mathrm{\&Delta;}V/V_{dc}<0\end{array}\right.$

$\left\{\begin{array}{cc}{V}_{r2b}=\frac{\left(msin\right(\mathrm{\&omega;}t-2/3\mathrm{\&pi;})+\mathrm{\&Delta;}V/V_{dc})V_{dc}}{2V_{c1}}& msin(\mathrm{\&omega;}t-2/3\mathrm{\&pi;})+\mathrm{\&Delta;}V/V_{dc}>0\\ V_{r2b}=\frac{\left(msin\right(\mathrm{\&omega;}t-2/3\mathrm{\&pi;})+\mathrm{\&Delta;}V/V_{dc})V_{dc}}{2V_{c2}}& msin(\mathrm{\&omega;}t-2/3\mathrm{\&pi;})+\mathrm{\&Delta;}V/V_{dc}<0\end{array}\right.$

$\left\{\begin{array}{cc}{V}_{r2c}=\frac{\left(msin\right(\mathrm{\&omega;}t+2/3\mathrm{\&pi;})+\mathrm{\&Delta;}V/V_{dc})V_{dc}}{2V_{c1}}& msin(\mathrm{\&omega;}t+2/3\mathrm{\&pi;})+\mathrm{\&Delta;}V/V_{dc}>0\\ V_{r2c}=\frac{\left(msin\right(\mathrm{\&omega;}t+2/3\mathrm{\&pi;})+\mathrm{\&Delta;}V/V_{dc})V_{dc}}{2V_{c2}}& msin(\mathrm{\&omega;}t+2/3\mathrm{\&pi;})+\mathrm{\&Delta;}V/V_{dc}<0\end{array}\right.$

Wherein, m is current modulation wave modulation ratio.