CN103441696B - A kind of cascade current transformer DC side self-voltage-stabilimethod method - Google Patents

Abstract

The invention discloses a method for self-stabilizing voltage at the direct current side of cascaded converters. Feedback control is performed on the direct current side voltage of each H bridge, and then carrier rotation is performed on the basis of carrier phase shifting. In this way, self-regulation can be performed without increasing additional expenses of auxiliary circuits and other systems, and the balance of the DC side voltage of the cascaded converter units can be realized.

Description

A Self-stabilizing Method for DC Side of Cascaded Converter

technical field

The invention relates to a method for self-stabilizing DC side voltage in a phase of a cascaded structure converter, aiming at self-stabilizing voltage without adding any DC side auxiliary circuit, and at the same time ensuring the balance of unit DC side voltage.

Background technique

In the application of cascaded converters, due to the imbalance of series loss and parallel loss, the inconsistency of the DC side voltage within the converter phase will be caused. The existing method is either to equip each DC side with a separate power supply circuit for voltage stabilization; or to connect a resistor and a controllable switching device on the DC side, and to balance the voltage through the loss of the resistor; or to use a DC bus or a common AC bus for energy balance. The first method adds an extra circuit, which not only increases the size and complexity of the entire converter system, but also increases the cost. The second method increases the loss of the device and reduces the efficiency of the system. The third method is the same as the first method, which increases the volume and device cost of the system, and at the same time complicates the energy flow of the system.

Contents of the invention

The invention provides a method for self-stabilizing voltage on the direct current side of a cascaded converter, which can perform self-regulating without increasing additional expenses of auxiliary circuits and other systems, and realize the balance of the voltage on the direct current side of the cascaded converter unit.

The technical scheme for realizing the above-mentioned purpose is:

A self-stabilizing method on the DC side of a cascaded converter, each phase of the cascaded converter is cascaded by N H-bridge units, N≥2 and N is an integer, and the DC side of each H-bridge The voltage is all feedback controlled, and then the carrier is rotated on the basis of the carrier phase shift.

In the above self-stabilizing method on the DC side of the cascaded converter, feedback control is performed on the DC side voltage of each H-bridge, taking the mth H-bridge of Phase A as an example, 1≤m≤N and m is an integer , including:

Under the action of the current control loop and the average control loop of all DC side voltages, the control value U _a of phase A is obtained;

The DC side voltage V _am-dc of the mth H bridge of phase A passes through the H bridge DC side voltage control loop to obtain the feedback value U _adcm of the control loop;

According to the formula: The control variable U _am of the mth H-bridge unit of the A-phase is obtained, and the feedback control is realized for the m-th H-bridge of the A-phase through pulse transmission.

The above self-stabilizing method on the DC side of the cascaded converter, wherein, under the action of the current control loop and the average value control loop of all DC side voltages, the control value U _a of the A phase is obtained, specifically including:

According to the formula:

${\stackrel{<span\; class="notranslate">\; \&OverBar;</span>}{\mathrm{<span\; class="notranslate">\; v</span>}}}_{\mathrm{<span\; class="notranslate">\; dc</span>}}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; a</span>}\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; dc</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; a</span>}\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; dc</span>}}<span\; class="notranslate">\; +</span><span\; class="notranslate">\; .</span><span\; class="notranslate">\; .</span><span\; class="notranslate">\; .</span><span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; n</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; dc</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; b</span>}\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; dc</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; b</span>}\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; dc</span>}}<span\; class="notranslate">\; +</span><span\; class="notranslate">\; .</span><span\; class="notranslate">\; .</span><span\; class="notranslate">\; .</span><span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; bN</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; dc</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; c</span>}\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; dc</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; c</span>}\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; dc</span>}}<span\; class="notranslate">\; +</span><span\; class="notranslate">\; .</span><span\; class="notranslate">\; .</span><span\; class="notranslate">\; .</span><span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; n</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; dc</span>}}}{\mathrm{<span\; class="notranslate">\; N</span>}<span\; class="notranslate">\; *</span>\mathrm{<span\; class="notranslate">\; 3</span>}}$

Among them, V _a1-dc , V _a2-dc , and V _aN-dc are the DC side voltages of the first H-bridge, the second H-bridge, and the N-th H-bridge of phase A respectively; V _b1-dc , V _{b2- dc} , V _bN-dc are the DC side voltages of the first H bridge, the second H bridge and the Nth H bridge of phase B respectively; V _c1-dc , V _c2-dc , V _cN-dc are the phase C voltages respectively The DC side voltage of the first H-bridge, the second H-bridge and the N-th H-bridge;

Get the average value of the DC side voltage of all H-bridge units After the average control loop of all DC side voltages, the control variable U _dc is obtained;

The dq components i _d , i _q of the compensation currents i _ca , i _cb , and i _cc are obtained through Parker transformation; the dq components i _d , i _q and the control variable U _dc pass through the current control loop to obtain the dq of the reference voltage Components U _d , U _q ;

Grid voltages v _sa , v _sb , and v _sc undergo Parker transformation to obtain dq components of grid voltage v _d , v _q ;

After U _d and v _d and U _q and v _q are summed respectively, the control quantities U _a , U _b , and U _c of phase A, phase B, and phase C are obtained by Parker's inverse transformation.

The above self-stabilizing method on the DC side of the cascaded converter, wherein the carrier rotation is performed on the basis of carrier phase shifting, specifically includes:

Each H-bridge of each phase corresponds to a carrier at the start time, that is, the h-th H-bridge corresponds to carrier number h, 1≤h≤N and h is an integer;

After a certain modulation wave period, the carrier is rotated once, that is, the carrier of the h-th H-bridge is transformed into carrier h+1, and the carrier of the N-th H-bridge is transformed into carrier No. 1.

The beneficial effect of the present invention is that: the present invention adopts additional software control on the basis of traditional control, and realizes Self-stabilization is performed without increasing system extra expenses, and the DC side voltage balance of cascaded converter units is guaranteed.

Description of drawings

Figure 1 is a system structure diagram when cascaded converters are applied to compensate reactive power and harmonics;

Fig. 2 is the feedback control block diagram of each H bridge DC side voltage among the present invention;

Figure 3 is a carrier diagram corresponding to each H-bridge when the carrier phase is shifted;

Figure 4 is a carrier diagram corresponding to each H-bridge during carrier rotation.

Detailed ways

The present invention will be further described below in conjunction with accompanying drawing.

When the converter uses the traditional method to self-stabilize the DC side, it will have a current control loop and an average control loop for all DC side voltages. The current control loop controls the output current of the converter, and the average control loop of all DC side voltages can ensure the stability of the total DC side average voltage. The converter usually uses carrier phase shift modulation to ensure the switching subharmonic of the output current The frequency is higher. However, the cascaded converter is composed of many H-bridge units with different losses (each phase is composed of N H-bridge units cascaded, N≥2 and N is an integer), so the DC side voltage of each H-bridge unit is inconsistent , causing the system to malfunction. Previous approaches required additional circuitry to be connected to the DC side of each H-bridge. The self-stabilizing method provided by the present invention only uses additional software control on the basis of the original control, and contains two main points: firstly, feedback control is performed on the DC side voltage of each H-bridge; secondly, the carrier wave is changed Carrier rotation is performed on the basis of carrier phase shift.

Please refer to Figure 1, which is a system structure diagram when cascaded converters are applied to compensate reactive power and harmonics. In this embodiment, three H-bridge units per phase are cascaded as an example. In Figure 1, v _sa , v _sb and v _sc are grid voltages; i _ca , i _cb , and i _cc are compensation currents; V _c1-dc , V _c2-dc , and V _c3-dc are the first H-bridge, the second H-bridge and the The DC side voltage of the third H-bridge, and the DC side voltage of other phase H-bridge units are analogous.

Feedback control is performed on the DC side voltage of each H-bridge, as shown in Figure 2, specifically including:

1) Under the action of the current control loop and the average control loop of all DC side voltages, obtain the respective control quantities U _a , U _b , and U _c of phase A, phase B, and phase C, specifically including:

According to the formula:

${\stackrel{<span\; class="notranslate">\; \&OverBar;</span>}{\mathrm{<span\; class="notranslate">\; v</span>}}}_{\mathrm{<span\; class="notranslate">\; dc</span>}}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; a</span>}\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; dc</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; a</span>}\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; dc</span>}}<span\; class="notranslate">\; +</span><span\; class="notranslate">\; .</span><span\; class="notranslate">\; .</span><span\; class="notranslate">\; .</span><span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; n</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; dc</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; b</span>}\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; dc</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; b</span>}\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; dc</span>}}<span\; class="notranslate">\; +</span><span\; class="notranslate">\; .</span><span\; class="notranslate">\; .</span><span\; class="notranslate">\; .</span><span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; bN</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; dc</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; c</span>}\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; dc</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; c</span>}\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; dc</span>}}<span\; class="notranslate">\; +</span><span\; class="notranslate">\; .</span><span\; class="notranslate">\; .</span><span\; class="notranslate">\; .</span><span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; n</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; dc</span>}}}{\mathrm{<span\; class="notranslate">\; N</span>}<span\; class="notranslate">\; *</span>\mathrm{<span\; class="notranslate">\; 3</span>}}$

Get the average value of the DC side voltage of all H-bridge units After the average control loop of all DC side voltages, the control variable U _dc is obtained. In Figure 2, In the formula, V _a1-dc , V _a2-dc , and V _aN-dc are the DC sides of the first H-bridge, the second H-bridge and the N-th H-bridge of phase A respectively. Voltage; V _b1-dc , V _b2-dc , V _bN-dc are the DC side voltages of the first H-bridge, the second H-bridge and the N-th H-bridge of phase B respectively; V _c1-dc , V _{c2- dc} , V _cN-dc are the DC side voltages of the first H-bridge, the second H-bridge and the N-th H-bridge of phase C respectively; in this embodiment, N is 3;

Compensation current i _ca , i _cb , i _cc get dq component id , i _q of compensation current through Parker transformation; _dq component _id , i _q and control variable U _dc pass through current control loop to get dq component U _d of reference voltage , U _q , in Fig. 2, i _d ^* , i _q ^* is the given current of the current loop;

Grid voltages v _sa , v _sb , and v _sc undergo Parker transformation to obtain dq components of grid voltage v _d , v _q ;

After summing U _d and v _d , and summing U _q and v _q , the inverse Parker transformation is performed to obtain the control quantities U _a , U _b , and U _c of phase A, phase B, and phase C.

2) Taking the m-th H-bridge of phase A, phase B, and phase C as an example, 1≤m≤N and m is an integer; the DC side voltage V _am of the m-th H-bridge of phase A, phase B, and phase C respectively _-dc , V _bm-dc , V _cm-dc pass through their corresponding H-bridge DC side voltage control loops to obtain the feedback quantities U _adcm , U _bdcm , U _cdcm of the corresponding control loops, is the given value of the average voltage of the DC side;

3) According to the formula: Get the control variable U _am of the mth H-bridge unit of phase A, and realize feedback control on the m-th H-bridge unit of phase A through pulse transmission; similarly, get the control variable U of the m-th H-bridge unit of phase B and C _bm and U _cm implement feedback control on the mth H-bridge of phase B and phase C through pulse transmission.

Therefore, it can be seen that the control quantity of each H-bridge is composed of two parts, taking the m-th H-bridge of phase A as an example:

${\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; am</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; adcm</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; +</span>\frac{{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; a</span>}}}{\mathrm{<span\; class="notranslate">\; N</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; )</span>$

For the control quantities of different H bridges in the same phase, their (2) components are the same, but the quantities of (1) components are different, which is the different control quantities of the first component It plays a role in regulating the consistency of the DC side voltage.

However, if only the above control is used, the parameters of the H-bridge DC side voltage control loop need to change with the change of the output power of the converter. When the output reactive power is less than 10% of the full load power, the system may become unstable. Carrier rotation can be used to solve this problem, and the control loop parameters only need to be a fixed value at this time. When only carrier phase shifting is used, the hth H-bridge of each phase will use the same carrier, here it becomes the hth carrier, 1≤h≤N and h is an integer. The frequencies, peak values, and shapes of all carriers are the same, but carrier h will be delayed from carrier h-1 angle. When using carrier rotation, the carrier of each H-bridge will not be fixed.

Carrier rotation is performed on the basis of carrier phase shift, including:

The start time of each H-bridge of each phase corresponds to a carrier respectively, that is: the h-th H-bridge corresponds to carrier number h;

After a certain modulation wave period, the carrier is rotated once, that is, the carrier of the h-th H-bridge is transformed into carrier h+1, and the carrier of the N-th H-bridge is transformed into carrier No. 1. In this embodiment, N is 3, the carrier corresponding to each H-bridge when the carrier phase shifts as shown in Figure 3; and the carrier corresponding to each H-bridge when the carrier is rotated as shown in Figure 4; The carrier of the first H-bridge is carrier No. 1, the carrier of the second H-bridge is carrier No. 2, and the carrier of the third H-bridge is carrier No. 2; after a certain modulation wave period, the first carrier of each phase The carrier of the H bridge is No. 2 carrier, the carrier of the second H bridge is No. 3 carrier, and the carrier of the third H bridge is No. 1 carrier; after a certain modulation wave period, the first H bridge of each phase The carrier of the first H bridge is carrier No. 3, the carrier of the second H bridge is carrier No. 1, and the carrier of the third H bridge is carrier No. 2; in this way, the carrier is rotated every time a certain modulation wave cycle is passed. In Fig. 3 and Fig. 4, y represents the amplitude of the carrier wave, and t represents the time.

The above embodiments are only for the purpose of illustrating the present invention, rather than limiting the present invention. Those skilled in the relevant technical fields can also make various changes or modifications without departing from the spirit and scope of the present invention. Therefore, all equivalent The technical solutions should also belong to the category of the present invention and should be defined by each claim.

Claims (2)

1. a cascade current transformer DC side self-voltage-stabilimethod method, described cascade converter every by N number of H-bridge unit cascade, N >=2 and N is integer, it is characterized in that, FEEDBACK CONTROL is carried out to the DC voltage of each H bridge, then on the basis of phase-shifting carrier wave, carries out carrier wave rotation

Carry out FEEDBACK CONTROL to the DC voltage of each H bridge, for A phase m H bridge, 1≤m≤N and m is integer, specifically comprises:

Under the effect of the mean value control ring of current regulator and all DC voltages, obtain the controlled quentity controlled variable U of A phase _a;

The DC voltage V of A phase m H bridge _am-dcthrough this H bridge DC side voltage control loop, obtain the feedback quantity U of control ring _adcm;

According to formula: obtain the controlled quentity controlled variable U of A phase m H-bridge unit _am, through extra pulse transmission, FEEDBACK CONTROL is realized to A phase m H bridge,

Under the effect of the mean value control ring of current regulator and all DC voltages, obtain the controlled quentity controlled variable U of A phase _a, specifically comprise:

According to formula:

${\stackrel{\&OverBar;}{v}}_{\mathrm{dc}}=\frac{V_{a1-\mathrm{dc}}+V_{a2-\mathrm{dc}}+...+V_{\mathrm{aN}-\mathrm{dc}}+V_{b1-\mathrm{dc}}+V_{b2-\mathrm{dc}}+...+V_{\mathrm{bN}-\mathrm{dc}}+V_{c1-\mathrm{dc}}+V_{c2-\mathrm{dc}}+...+V_{\mathrm{cN}-\mathrm{dc}}}{N*3}$

Wherein, V _a1-dc, V _a2-dc, V _aN-dcbe respectively the DC voltage of A phase first H bridge, second H bridge and N number of H bridge; V _b1-dc, V _b2-dc, V _bN-dcbe respectively the DC voltage of B phase first H bridge, second H bridge and N number of H bridge; V _c1-dc, V _c2-dc, V _cN-dcbe respectively the DC voltage of C phase first H bridge, second H bridge and N number of H bridge;

Obtain the mean value of all H-bridge unit DC voltages through the mean value control ring of described all DC voltages, obtain controlled quentity controlled variable U _dc;

Offset current i _ca, i _cb, i _ccthe dq component i of electric current is compensated through Park Transformation _d, i _q; Dq component i _d, i _qwith controlled quentity controlled variable U _dcthrough described current regulator, obtain the dq component U of reference voltage _d, U _q;

Line voltage v _sa, v _sb, v _scthe dq component v of line voltage is obtained through Park Transformation _d, v _q;

U _dwith v _dand U _qwith v _qdo with afterwards respectively, then carry out the controlled quentity controlled variable U that Parker inverse transformation obtains A phase, B phase, C phase _a, U _b, U _c.

2. cascade current transformer DC side self-voltage-stabilimethod method according to claim 1, is characterized in that, carrier wave rotation is carried out on the basis of phase-shifting carrier wave, specifically comprises:

Each H bridge start time corresponding carrier wave respectively of each phase, that is: h H bridge correspondence h carrier wave, 1≤h≤N and h is integer;

Through certain modulating wave cycle, carrier wave carries out a rotation, that is: the carrier transformation of h H bridge is h+1 carrier wave, and the carrier transformation of N number of H bridge is No. 1 carrier wave.