CN103929083A - Pulse alternation control method suitable for five-level H-bridge cascade type STATCOM - Google Patents

Abstract

The invention relates to a direct-current side voltage balance control method suitable for a five-level H-bridge cascade type STATCOM. The direct-current side voltage balance control method is characterized in that on the basis of pulse period alternation, active power is controlled to flow between units by controlling the duty ratio of each alternation time sequence, so that direct-current side voltage balance of each unit is maintained. The direct-current side voltage balance control method comprises the main steps of setting a standard alternation period of pulse alternation, judging the polarity of reactive power needing to be compensated, calculating a deviation value of the direct-current side voltage of each unit and the mean value, converting the calculated deviation values into the charge-discharge time adjustment amounts through a proportional-integral (PI) link, converting the charge-discharge time adjustment amounts into the duty ratio variations of the pulse alternation time sequences, calculating the corrected duty ratio of the pulse alternation time sequence of each unit, and distributing window signals according to the output level state. According to the direct-current side voltage balance control method, the direct-current side voltage balance can be well controlled on the premise that the upper-layer control of the device is not influenced and additional action times of a switching element are hardly increased.

Description

A kind of pulse rotation control method that is applicable to five level H-bridge cascade connection type STATCOM

Technical field

The present invention relates to H bridge cascade connection type STATCOM, particularly a kind of pulse rotation control method that is applicable to five level H-bridge cascade connection type STATCOM.

Background technology

Since American scholar L.Gyugyi in 1976 proposes to carry out reactive power compensation with power semiconductor device, STATCOM (static synchronous compensator, STATCOM) at nearest 30 years, be rapidly developed, from the multiple inverter with coupling transformer to the multi-electrical level inverter without coupling transformer, H bridge cascaded inverter becomes the study hotspot in current reactive power compensation field with its unrivaled advantage.In industrial production, distribution network voltage grade is more, as China's coal-mine, produces in distribution and has 1140V and 3300V electric pressure, and according to the development level of current power electronic device, five level STATCOMs have certain range of application in industrial power distribution net.Five level H-bridge cascade connection type STATCOM main circuit topological structures as shown in Figure 1, the filter inductance that in Fig. 1, L is device, u _dc1, u _dc2be respectively the DC voltage of A facies unit 1 and unit 2.

Pulse-width modulation (pulse width modulation, PWM) technology is the core technology of H bridge cascade connection type STATCOM, and it is related to the harmonic characterisitic of STATCOM output voltage, the equilibrium of the balance of DC capacitor voltage and power device on-off times.The stacked modulation of carrier wave homophase (carrier disposition PWM, PD-PWM) there is outstanding line voltage harmonic elimination characteristic, but there is the unbalanced inherent shortcoming of H bridge cell power devices switch number of times in the method, also can cause each cell power to distribute uneven problem.

For five level, the stacked modulation principle of carrier wave homophase as shown in Figure 2, u in Fig. 2 _dcfor DC voltage set-point.H bridge cascade converter by four list ripple longitudinally after stack and modulating wave relatively obtain the output level state of each H bridge unit.Each cell power devices switch number of times is unbalanced as shown in Figure 2, and this is the stacked inherent shortcoming of carrier wave.For this problem, can adopt the method for pulse period rotation to make each unit reach balance within some cycles.Now the pulse of two unit in Fig. 2 was once exchanged at interval of half modulating wave cycle, each H bridge unit ideal level state as shown in Figure 3.In Fig. 3: u ₁, u ₂be respectively unit 1 and unit 2 output voltages.In each modulating wave cycle, the on-off times of two unit can reach balance as shown in Figure 3.

When the stacked modulation strategy of carrier wave homophase is applied to H bridge cascade connection type STATCOM, the cycle rotation of pulse can only realize the mean allocation of meritorious energy, when each unit causes meritorious energy requirement uneven by parameter differences and shunt loss, mixing loss, the distribution according to need that the party's rule is difficult to realize the meritorious energy in each unit carrys out balance DC capacitor voltage, and then affects performance and the operation of device.

Summary of the invention

The technical issues that need to address of the present invention are: the existing pulse period rotation control method adopting based on the stacked modulation strategy of carrier wave homophase can not realize dc-voltage balance effectively, provide a kind of and realize preferably the balanced method of controlling of DC voltage not affecting that device upper strata is controlled and additionally increase hardly under the prerequisite of switching device action frequency.

For addressing the above problem, the technical solution used in the present invention is: a kind of improved pulse rotation of five level H-bridge cascade connection type STATCOM control method that is applicable to, the method is recently controlled active power flowing between each unit by controlling the duty of rotation sequential on the basis of pulse period rotation, and then maintains each unit dc-voltage balance.It is characterized in that, the step of the method is as follows:

Step (1) arranges the benchmark rotational cycle of pulse rotation.

Step (2) is according to the polarity of the phase relation judgement compensating power of surveyed voltage, electric current.

The departure of step (3) computing unit 1 DC voltage and unit DC voltage mean value.Adopt each unit DC voltage in each sampling period of voltage sensor senses, the data that gather according to transducer are asked for the mean value of unit DC voltage by DSP, unit DC voltage mean value and unit 1 DC voltage measured value that order calculates are made the departure that difference can obtain unit 1 DC voltage and unit DC voltage mean value.

Step (4) is judged the duty ratio of the polarity of reactive power and rear each unit pulse rotation sequential of voltage deviation amount calculating correction that step 3 calculates according to step 2.

Step (5) is distributed start pulse signal according to the level state of device output, according to revised pulse rotation sequential, start pulse signal is carried out to rotation and drives each unit switch device to carry out corresponding actions.

In described step 1, choosing benchmark rotational cycle is 1/2 of the modulating wave cycle, the reference duty cycle of each rotational cycle note unit 1 is respectively g with unit 2 pulse rotation sequential ₁with g ₂.

If compensating power is perception in step 2, note Q>0, sign=1; If compensating power is capacitive, note Q<0, sign=-1, the sign function that wherein sign is reactive power.

Two unit DC voltage us measured according to voltage sensor in step 3 _dc1, u _dc2, can calculate unit DC voltage mean value voltage deviation amount is:

$\mathrm{\&Delta;u}=\stackrel{\&OverBar;}{u}-u_{\mathrm{dc}1}$

In step 4, calculate the duty ratio of rotation sequential after revising and comprise following step:

The first step, judges that in each rotational cycle, each unit DC bus capacitor needs charge status, and corresponding relation is as shown in table 1.

Each unit DC bus capacitor of table 1. discharges and recharges judgement

?	Δu＞0	Δu＜0
			Unit 1	Charging	Electric discharge
Unit 2	Electric discharge	Charging

Second step, is converted into pulse rotation sequential correction amount t by departure Δ u passing ratio integration (PI) link calculating.

The 3rd step, regulation DC bus capacitor discharges and recharges respective pulses rotation timing variations rule.Take unit 1 as example, and unit 1 DC bus capacitor discharges and recharges and pulse rotation sequential g ₁corresponding relation is as shown in table 2.

Table 2. unit 1 DC bus capacitor discharges and recharges and pulse sequence corresponding relation

g 1	Charging	Electric discharge
			Q>0	Trailing edge (trailing edge moves to left) moves to right	Rising edge (rising edge moves to left) moves to right
Q<0	Rising edge (rising edge moves to left) moves to right	Trailing edge (trailing edge moves to left) moves to right

Unit 2 corresponding rotation sequential g ₂with g ₁complementation, the existing regulation unification mode control capacitance of taking to move to right discharges and recharges, and trailing edge g moves to right ₁the duty ratio of pulse rotation sequential increases, and the rising edge duty ratio that moves to right reduces.

The 4th step, note g1 change in duty cycle amount is Δ D _on, pulse rotation sequential correction amount t is converted into pulse duty factor variation delta D _on.Δ D _oncomputing formula is:

ΔD _on＝K·sign·Δt

In formula, K is the transformation ratio that discharges and recharges time adjustment amount and pulse rotation sequential duty ratio, sign is the sign function of reactive power polarity, and Δ t is for discharging and recharging time adjustment amount.

The 5th step, calculates the duty ratio D that revises rear unit 1 pulse rotation sequential _on.The change in duty cycle amount Δ D being calculated by step 5 _onwith reference duty cycle be added, get final product the duty ratio D that computing unit 1 is revised rear rotation sequential _on, and then obtain the revised rotation sequential in unit 1, unit 2 pulse rotation sequential and unit 1 complementation.

In step 5, install output level state and start pulse signal corresponding relation is as shown in table 3.

Table 3. device output level state and start pulse signal corresponding relation

?	Unit 1	Unit 2
			Output level state	[s1s2s3s4]	[s1s2s3s4]
1	[1001]	[1100]
			2	[1001]	[1001]
0	[1100]	[1100]
			-1	[0110]	[0011]
-2	[0110]	[0110]

The trigger impulse that wherein s1, s2, s3, s4 are each power device, concrete corresponding relation as shown in Figure 1.

Beneficial effect

Compared with prior art, dc-voltage balance control method provided by the invention has the following advantages:

1. pulse rotation control method provided by the present invention is taken into account the advantage of the outstanding line voltage harmonic elimination characteristic of the stacked modulation of carrier wave homophase and the balanced distribution of power device on-off times;

2. the method realizes preferably the balance control of DC voltage under the prerequisite that additionally increases hardly power device on-off times;

3. the method has wider power adjustment, can be applied to the rectifier of H bridge cascade structure.

Accompanying drawing explanation

Accompanying drawing 1 is five level H-bridge cascade connection type STATCOM main circuit topological structure figure.

Accompanying drawing 2 is the stacked principle schematic of carrier wave homophase.

Accompanying drawing 3 is carrier cycle rotation waveform schematic diagram.

Accompanying drawing 4 is improved pulse rotation policy control schematic diagram.

Accompanying drawing 5 is each unit DC bus capacitor charge-discharge region schematic diagram.

Accompanying drawing 6 is pulse period rotation DC voltage oscillogram.

Accompanying drawing 7 is improved pulse rotation DC voltage oscillogram.

Embodiment

Below in conjunction with accompanying drawing, the present invention is described in further detail.

The invention provides a kind of pulse rotation DC side voltage control method that is applicable to five level H-bridge cascade connection type STATCOM, as shown in Figure 4, specific implementation step is as follows for its control principle block diagram:

Step (1) arranges the benchmark rotational cycle of pulse, and rotational cycle is:

$t=\frac{1}{2}\mathrm{kT}$

In formula, T is the modulating wave cycle, and k is any positive integer, the reference duty cycle of each rotational cycle because pulse rotational cycle is shorter, it is better that each unit DC voltage is adjusted real-time, therefore generally gets k=1.Two unit DC bus capacitor charge-discharge region and rotation sequential are as shown in Figure 5.In Fig. 5, flag ₁, flag ₂be respectively unit 1 and unit 2 capacitor charge and discharge signs, g ₁, g ₂be respectively unit 1 and unit 2 level state rotation sequential, this sequential is synchronizeed with modulating wave, t ₁, t ₂be respectively g ₁trailing edge and rising edge.

The polarity of step (2) judgement compensating power.According to the phase relation of surveyed voltage, electric current, can judge the polarity of reactive power, when the reactive power of required compensation is perception, note reactive power Q >0, sign=1; When reactive power is capacitive, note Q<0, sign=-1.

The departure of step (3) computing unit 1 DC voltage and unit DC voltage mean value.Adopt the instantaneous value u of voltage sensor difference detecting unit 1 and unit 2 DC voltages _dc1with u _dc2, according to gathered data, by DSP, calculate unit DC voltage mean value the departure of unit 1 DC voltage and unit DC voltage mean value is:

$\mathrm{\&Delta;u}=\stackrel{\&OverBar;}{u}-u_{\mathrm{dc}1}$

Step (4) is converted into voltage deviation amount Δ u passing ratio integration (PI) link to discharge and recharge time adjustment amount Δ t.

Step (5) will discharge and recharge time adjustment amount Δ t and be converted into pulse rotation sequential g ₁change in duty cycle amount Δ D _on.Δ D _oncomputing formula is:

ΔD _on＝K·sign·Δt

In formula, K is the transformation ratio that discharges and recharges time adjustment amount and pulse rotation sequential duty ratio, sign is the sign function of reactive power polarity, and Δ t is for discharging and recharging time adjustment amount.

Step (6) is calculated the duty ratio D of the pulse rotation sequential of revising rear unit 1 _on.The change in duty cycle amount Δ D being calculated by step (5) _onwith reference duty cycle do add operation, can calculate and revise rear duty ratio D _onfor:

$D_{\mathrm{on}}=\mathrm{\&Delta;}{D}_{\mathrm{on}}+D_{\mathrm{on}}^0$

Unit 2 pulse rotation sequential and unit 1 complementation.

Step (7) is distributed start pulse signal according to the level state of device output, according to revised pulse rotation sequential, start pulse signal is carried out to rotation and drive each unit switch device to carry out corresponding actions, the concrete corresponding relation of device output level state and trigger impulse is as shown in table 3.

Fig. 6 is for adopting pulse period rotation control strategy DC capacitor voltage oscillogram, in actual condition due to the difference of each component parameter and the existence of shunt loss and mixed type loss, DC capacitor voltage just can not maintain balance, also can affect the waveform quality of output voltage, electric current.

Fig. 7 is for adopting improved pulse rotation control strategy DC capacitor voltage oscillogram, and two DC capacitor voltages all can be realized balance well, control respond well.

Claims (5)

1. a DC side voltage control method that is applicable to five level H-bridge cascade connection type STATCOM, H bridge cascade connection type STATCOM AC is by between reactor access in parallel electrical network and load, it is characterized in that: the method passes through to adjust Duty ratio control active power the flowing between each unit of rotation sequential on the basis of pulse period rotation, reach the object that maintains each unit dc-voltage balance, described process comprises following steps:

Step (1) arranges the benchmark rotational cycle of pulse rotation;

Step (2) is according to the polarity of the phase relation judgement compensating power of surveyed voltage, electric current;

The departure of step (3) computing unit 1 DC voltage and unit DC voltage mean value: adopt each unit DC voltage of cascade in each sampling period of voltage sensor senses, based on DSP computing unit DC voltage mean value, by the departure of this mean value and unit 1 DC voltage measured value comparison acquiring unit 1 DC voltage and unit DC voltage mean value;

The duty ratio of each unit pulse rotation sequential of the voltage deviation amount correction that the reactive power polarity that step (4) is judged according to step 2 and step 3 calculate;

Step (5) is distributed start pulse signal according to the level state of device output, according to revised pulse rotation sequential, start pulse signal is carried out to rotation and drives each unit switch device to carry out corresponding actions.

2. the pulse rotation control method of H bridge cascade connection type STATCOM according to claim 1, is characterized in that: in described step 1, choosing benchmark rotational cycle is 1/2 of the modulating wave cycle, the reference duty cycle of each rotational cycle note unit 1 is respectively g with unit 2 pulse rotation sequential ₁with g ₂.

3. the pulse rotation control method of H bridge cascade connection type STATCOM according to claim 1, is characterized in that: in described step 3, the deviation delta u of unit 1 DC voltage and unit DC voltage mean value is:

$\mathrm{\&Delta;u}=\stackrel{\&OverBar;}{u}-u_{\mathrm{dc}1}$

In formula for unit DC voltage mean value, u _dc1for unit 1 DC voltage.

4. the pulse rotation control method of H bridge cascade connection type STATCOM according to claim 1, is characterized in that: in described step 4, calculate the duty ratio of rotation sequential after revising and comprise following step:

The first step, judges that in each rotational cycle, each DC bus capacitor needs charge status, shown in corresponding relation following table;

? Δu＞0 Δu＜0 Unit 1 Charging Electric discharge Unit 2 Electric discharge Charging

Second step, is converted into pulse rotation sequential correction amount t by departure Δ u passing ratio integration (PI) link calculating;

The 3rd step, regulation DC bus capacitor discharges and recharges respective pulses rotation timing variations rule, take unit 1 as example, and unit 1 DC bus capacitor discharges and recharges and pulse rotation sequential g ₁shown in corresponding relation following table;

g ₁ Charging Electric discharge Q>0 Trailing edge (trailing edge moves to left) moves to right Rising edge (rising edge moves to left) moves to right Q<0 Rising edge (rising edge moves to left) moves to right Trailing edge (trailing edge moves to left) moves to right

Unit 2 corresponding rotation sequential g ₂with g ₁complementation, the existing regulation unification mode control capacitance of taking to move to right discharges and recharges, and trailing edge g moves to right ₁the duty ratio of pulse rotation sequential increases, and the rising edge duty ratio that moves to right reduces;

The 4th step, note g1 change in duty cycle amount is Δ D _on, pulse rotation sequential correction amount t is converted into pulse duty factor variation delta D _on

ΔD _on＝K·sign·Δt

In formula, K is the transformation ratio that discharges and recharges time adjustment amount and pulse rotation sequential duty ratio, sign is the sign function of reactive power polarity, and Δ t is for discharging and recharging time adjustment amount;

The 5th step, calculates the duty ratio D that revises rear unit 1 pulse rotation sequential _on, the change in duty cycle amount Δ D being calculated by step 5 _onwith reference duty cycle be added, get final product the duty ratio D that computing unit 1 is revised rear rotation sequential _on, and then obtain the revised rotation sequential in unit 1, unit 2 pulse rotation sequential and unit 1 complementation.

5. the pulse rotation control method of H bridge cascade connection type STATCOM according to claim 1, is characterized in that: in described step 5, install shown in output level state and start pulse signal corresponding relation following table.

? Unit 1 Unit 2 Output level state [s1s2s3s4] [s1s2s3s4] 1 [1001] [1100] 2 [1001] [1001] 0 [1100] [1100] -1 [0110] [0011] -2 [0110] [0110]

Wherein s1, s2, s3, s4 are the corresponding trigger impulse of each power device.