CN104852621A - Switch driving method eliminating dead zone influence of neutral-point-clamped three-level topology switch - Google Patents

Abstract

The invention relates to a switch driving method eliminating dead zone influence of a neutral-point-clamped three-level topology switch. Each phase of bridge arm of three-level topology includes four switching tubes, the switch driving method includes the steps of: 1) detecting a current direction of current of each phase; 2) judging whether the direction of current of each phase is a set forward direction, if yes, executing step 3), and if no, executing step 4); 3) switching off in advance and switching on in a delayed manner the third and the fourth switching tubes of the corresponding phase in advance; and 4) switching off in advance and switching on in a delayed manner the first and the second switching tubes of the corresponding phase. Compared with the prior art, the switch driving method provided by the invention has the advantages of being high in control precision, effectively saving computing resources of a processor, etc.

Description

Eliminate the switch drive methods of neutral point clamped multi three-level topology switching dead impact

Technical field

The present invention relates to a kind of three level (neutral point clamped multi) current transformer IGBT driving method, especially relate to a kind of switch drive methods eliminating the impact of neutral point clamped multi three-level topology switching dead.

Background technology

Relative to the topological structure of two traditional Level Full Bridges, the topological structure of three level NPC (neutral point clamped multi) has series of advantages: 1) switching loss is little, and efficiency is high; 2) during switch motion, dv/dt is little, and the electromagnetic interference (EMI) caused is little; 3) output voltage waveforms is three level, and harmonic content is few, and required filtering inductance is little, is conducive to reducing system cost and power loss.Just because of above-mentioned advantage three level NPC topological structure middle pressure high-power had apply very widely, and achieve good effect.In order to prevent a certain bridge arm direct pass in three level NPC topology, at a pipe of brachium pontis and three to manage, two managing add Dead Time between four pipes, the voltage waveform of output will be made like this to have certain distortion.

The voltage distortion caused to eliminate this Dead Time the present invention proposes a kind of dead zone elimination method based on this topology, flowing to, reasonably arranging switch motion to reach the impact of deadband eliminating on output voltage by detecting three-phase current.

Summary of the invention

Object of the present invention be exactly in order to overcome above-mentioned prior art exist defect and provide a kind of control precision high, save computational resource elimination neutral point clamped multi three-level topology switching dead impact switch drive methods.

Object of the present invention can be achieved through the following technical solutions:

Eliminate a switch drive methods for neutral point clamped multi three-level topology switching dead impact, every phase brachium pontis of tri-level switch comprises four switching tubes, and described switch drive methods comprises the following steps:

1) the current flow direction of every phase is detected;

2) judge whether each phase current direction is the forward set, and if so, then performs step 3 respectively), if not, then perform step 4);

3) the 3rd, the 4th of corresponding phase the switching tube is turned off in advance, time delay is open-minded;

4) first, second switching tube of corresponding phase is turned off in advance, time delay is open-minded.

Described step 3) and step 4) in, the delay time that the pre-set time turned off in advance and time delay are opened is equal.

The delay time that described pre-set time of turning off in advance and time delay are opened is T _d:

T _D＝1.2*(T _offmax-T _onmin)

Wherein, T _offmaxthe maximum time of IGBT turn off delay time, T _onminit is the minimum time that IGBT opens time delay.

Described switch drive methods is realized by digital integrated circuit.

Described digital integrated circuit is CPLD.

Compared with prior art, the present invention has the following advantages:

1, the present invention flows to by detecting three-phase current, rational arrangement switch motion, eliminates the impact of dead band on output voltage, without the need to calculate dead band on output voltage concrete cause great impact, improve control precision, save the computational resource of control chip.

2, dead zone function strategy of the present invention can realize with CPLD completely, and modulator approach it doesn't matter, versatility is higher, be convenient to realize.

Accompanying drawing explanation

Fig. 1 is the topological structure schematic diagram of three level NPC;

Fig. 2 is the on off state schematic diagram of each brachium pontis;

Wherein, (2a) is [1] view, and (2b) is [0] view, and (2c) is [-1] view;

The current flowing circuit diagram that Fig. 3 is under three kinds of on off states of each brachium pontis, the sense of current is timing;

Wherein, (3a) is the current flowing loop under [1] state, and (3b) is the current flowing loop under [0] state, and (3c) is the current flowing loop under [-1] state;

Current flowing circuit diagram when Fig. 4 is under three kinds of on off states of each brachium pontis, the sense of current is negative;

Wherein, (4a) is the current flowing loop under [1] state, and (4b) is the current flowing loop under [0] state, and (4c) is the current flowing loop under [-1] state;

Fig. 5 is the waveform schematic diagram of drive singal desirable under different situations in prior art and the drive singal having added dead band;

Wherein, (5a) for the sense of current be the waveform schematic diagram of timing, (5b) for the sense of current be the waveform schematic diagram of timing;

Fig. 6 is the waveform schematic diagram of the drive singal adopting the inventive method drive singal desirable in varied situations and added dead band;

Wherein, (6a) for the sense of current be the waveform schematic diagram of timing, (6b) for the sense of current be the waveform schematic diagram of timing.

Embodiment

Below in conjunction with the drawings and specific embodiments, the present invention is described in detail.The present embodiment is implemented premised on technical solution of the present invention, give detailed execution mode and concrete operating process, but protection scope of the present invention is not limited to following embodiment.

The topological structure of three level NPC as shown in Figure 1, S ₁, S ₂..., S ₁₂for IGBT switching tube.For first-phase brachium pontis, as shown in Figure 2, each brachium pontis of three level NPC has three kinds of states [1,0,-1], and can only be switch between adjacent two states in each switch periods, namely 0 state and 1 state switch or switch between 0 state and-1 state.

Supposing that the sense of current as shown in Figure 2 is just, is negative in contrast.When electric current is positive time, under three kinds of on off states, current flowing loop is as shown in Figure 3.As shown in Figure 3: work as i _awhen >0, no matter brachium pontis is any state in [1,0 ,-1], switching tube S ₃, S ₄do not flow through electric current, that is no matter give which type of drive singal S ₃, S ₄all be in off state, do not affect output voltage, when the sense of current can accurately record, we can at i _a>0 S in season ₃, S ₄be in off state, and S ₁, S ₂turn on and off according to desirable switching time, like this with regard to impact that the deadband eliminating time causes output voltage waveforms.

When electric current is negative time, under three kinds of on off states, i as shown in Figure 4, is worked as in current flowing loop _awhen <0, no matter brachium pontis is any state in [1,0 ,-1], switching tube S ₁, S ₂do not flow through electric current, that is opening shutoff does not affect output voltage, and when the sense of current can accurately record, we can at i _a>0 S in season ₁, S ₂be in off state, and S ₃, S ₄turn on and off according to desirable switching time, like this with regard to impact that the deadband eliminating time causes output voltage waveforms.

Can only be switched between adjacent state by each brachium pontis in the known each switch periods of the modulator approach of three-level topology, drive singal desirable under being illustrated in figure 5 different situations and the impact of drive singal on dead band having added dead band, actual output voltage U _aNwith desired voltage U _aNOcompare an error voltage, make this voltage be Δ U _aN, then Δ U _aNcan be expressed as follows:

${\mathrm{\&Delta;U}}_{\mathrm{AN}}=\left\{\begin{array}{c}-\frac{T_d}{T_{\mathrm{PWM}}}{U}_{\mathrm{dc}}=-T_d{f}_c{U}_{\mathrm{dc}},(i_d>0)\\ \frac{T_d}{T_{\mathrm{PWM}}}{U}_{\mathrm{dc}}=T_d{f}_c{U}_{\mathrm{dc}},(i_d<0)\end{array}\right.---\left(1\right)$

T in above formula _d=t _d+ t _on-t _off, t _dfor Dead Time, t _ontime delay is opened, t for IGBT _offfor the turn off delay time of IGBT; f _c=1/T _pWM---carrier frequency, T _pWMfor carrier cycle.

Can know that the actual output voltage after adding dead band can be expressed as by above-mentioned analysis:

U _AN＝U _ANO+ΔU _AN

Can be obtained by above-mentioned analysis: the output voltage deviation that dead band causes has relation with the sense of current and Dead Time flowing through this brachium pontis, so the accurate detection of the sense of current is very crucial, if so dead area compensation that current direction detection is mistake can run counter to desire.Determining that the situation system of the sense of current can allow the switching tube not having electric current to flow through turn off always according to above-mentioned analysis is known, but so just require the direction must detecting each phase current accurately, current zero-crossing point due to the error of transducer can cause current direction detection can at the positive and negative dead area compensation of jumping effect back and forth, so we allow the pipe not having electric current to flow through turn off but to carry previous Dead Time open-minded at this always, postpone a Dead Time to turn off, even if be unlikely to have too large output voltage error when current direction detection is inaccurate like this, concrete oscillogram as shown in Figure 6.

Just do not make a concrete analysis of the oscillogram in N-O-N situation because bridge arm circuit exists symmetry at this, below drive singal after analysis optimization on the impact of output voltage:

By above-mentioned analysis, we can know, actual output voltage U _aNwith desired voltage U _aNOcompare an error voltage, make this voltage be Δ U _aN, then Δ U under novel strategy of dying _aNcan be expressed as follows:

${\mathrm{\&Delta;U}}_{\mathrm{AN}}=\left\{\begin{array}{c}-\frac{T_d^{*}}{T_{\mathrm{PWM}}}{U}_{\mathrm{dc}}=-T_d{f}_c{U}_{\mathrm{dc}},(i_a>0)\\ \frac{T_d^{*}}{T_{\mathrm{PWM}}}{U}_{\mathrm{dc}}=T_d{f}_c{U}_{\mathrm{dc}},(i_a<0)\end{array}\right.---\left(2\right)$

In above formula f _c=1/T _pWM---carrier frequency.

Contrast (1) we can find out that we make error voltage decrease ± t under the strategy of this dead band _d* U _dc/ T _pWMsubstantially reduce the impact of Dead Time on output voltage waveforms.

According to analysis above, the switch drive methods of the elimination neutral point clamped multi three-level topology switching dead impact of the present embodiment can be realized by digital integrated circuits such as CPLD, comprises the following steps:

1) the current flow direction of every phase is detected;

2) judge whether each phase current direction is the forward set, and if so, then performs step 3 respectively), if not, then perform step 4);

3) the 3rd, the 4th of corresponding phase the switching tube is turned off in advance, time delay is open-minded;

4) first, second switching tube of corresponding phase is turned off in advance, time delay is open-minded.

Step 3) and step 4) in, the delay time that the pre-set time turned off in advance and time delay are opened is T _d:

T _D＝1.2*(T _offmax-T _onmin)

Wherein, T _offmaxthe maximum time of IGBT turn off delay time, T _onminit is the minimum time that IGBT opens time delay.

As shown in Figure 1, according to above-mentioned steps, the dead zone function strategy of the present embodiment is as follows: work as i _as when >0 ₃, S ₄turn off delay time is open-minded in advance, works as i _as when <0 ₁, S ₂turn off delay time is open-minded in advance; Work as i _bs when >0 ₇, S ₈turn off delay time is open-minded in advance, works as i _bs when <0 ₅, S ₆turn off delay time is open-minded in advance; Work as i _cs when >0 ₁₁, S ₁₂turn off delay time is open-minded in advance, works as i _cs when <0 ₉, S ₁₀turn off delay time is open-minded in advance.

Claims (5)

1. eliminate a switch drive methods for neutral point clamped multi three-level topology switching dead impact, every phase brachium pontis of tri-level switch comprises four switching tubes, and it is characterized in that, described switch drive methods comprises the following steps:

1) the current flow direction of every phase is detected;

2) judge whether each phase current direction is the forward set, and if so, then performs step 3 respectively), if not, then perform step 4);

3) the 3rd, the 4th of corresponding phase the switching tube is turned off in advance, time delay is open-minded;

4) first, second switching tube of corresponding phase is turned off in advance, time delay is open-minded.

2. the switch drive methods of elimination neutral point clamped multi three-level topology switching dead according to claim 1 impact, is characterized in that, described step 3) and step 4) in, the delay time that the pre-set time turned off in advance and time delay are opened is equal.

3. the switch drive methods of elimination neutral point clamped multi three-level topology switching dead according to claim 2 impact, is characterized in that, the delay time that described pre-set time of turning off in advance and time delay are opened is T _d:

T _D＝1.2*(T _offmax-T _onmin)

Wherein, T _offmaxthe maximum time of IGBT turn off delay time, T _onminit is the minimum time that IGBT opens time delay.

4. the switch drive methods of elimination neutral point clamped multi three-level topology switching dead according to claim 1 impact, it is characterized in that, described switch drive methods is realized by digital integrated circuit.

5. the switch drive methods of elimination neutral point clamped multi three-level topology switching dead according to claim 4 impact, it is characterized in that, described digital integrated circuit is CPLD.