CN106877371A - A control method for a modular multilevel converter with energy storage function - Google Patents

Abstract

The invention discloses a control method of a modular multilevel converter with energy storage function, wherein the converter includes three phase units, and each phase unit includes an upper bridge arm, a lower bridge arm, an upper bridge arm inductor, The lower bridge arm inductance, the upper and lower bridge arms are composed of half-bridge sub-modules and full-bridge energy storage sub-modules mixed in series; the method determines each sub-module in each phase bridge arm according to the output command voltage waveform of each phase The modulation wave of the sub-module includes the modulation wave of the half-bridge sub-module and the modulation wave of the full-bridge energy storage sub-module; the control signal is generated according to the carrier wave of each sub-module in each phase bridge arm and the modulation wave of the sub-module, Separately control the switching on or off of each sub-module in each phase bridge arm. The above-mentioned modular multilevel converter with energy storage function can increase the inertia of the new energy system, and the charging and discharging current of the battery used for energy storage is smooth, and the voltage level is low, which ensures the efficient operation and safety of the battery.

Description

A control method for a modular multilevel converter with energy storage function

technical field

The invention belongs to the technical field of electrical automation equipment, and in particular relates to a control method of a modular multilevel converter with an energy storage function.

Background technique

In the existing technology, the sub-module with energy storage function directly connects the battery next to the capacitor of the sub-module, so that the battery can withstand the pulsating current of one or two times the power frequency, which has great impact on the efficient operation of the battery and the cost of the whole life cycle. Unfavorable; at the same time, the sub-module capacitor voltage in actual working conditions is generally greater than 1500V voltage level. For high-rate batteries represented by lithium-ion batteries, based on the balance of battery state of charge and fault protection, it is difficult to achieve in terms of cost and safety. Such a high series voltage.

After retrieval, the Chinese patent application with publication number 104917418A provides an energy storage type modular multilevel converter with independent battery current control, and its sub-modules include: a half-bridge module, a supporting capacitor and An energy storage battery. Improve battery utilization and service life through independent control of battery current.

The Chinese patent application with publication number 103580050A relates to a high-power modular multi-level lithium battery energy storage converter device, and its sub-module is an H-bridge energy storage converter module. High-power energy storage is realized by reducing the battery voltage level by using the number of sub-modules.

The above-mentioned patents cannot solve the problem of battery voltage levels, because many sub-modules are used and cannot realize energy storage, and the battery voltage is low; secondly, the sub-module structures proposed in the above-mentioned patents all adopt the scheme that the battery is connected in parallel next to the DC capacitor, and the battery will inevitably Bearing the pulsating current of double power frequency and double power frequency is not good for the efficient operation of the battery and the cost of the whole life cycle.

Contents of the invention

In view of the defects in the prior art, the object of the present invention is to provide a control method of an energy storage type modular multilevel converter which topologically improves battery life and utilization and provides inertia for new energy systems.

The present invention provides a control method of a modular multilevel converter with energy storage function, wherein:

The converter includes three phase units, and each phase unit includes an upper bridge arm, a lower bridge arm, an upper bridge arm inductance, and a lower bridge arm inductance; extreme; the negative terminal of the upper bridge arm is connected to one end of the upper bridge arm inductor; the other end of the upper bridge arm inductor is connected to one end of the lower bridge arm inductor as the AC outlet end of the phase unit, and The series reactor is connected to the power grid; the other end of the lower bridge arm inductor is connected to the positive terminal of the lower bridge arm; the negative terminal of the lower bridge arm is used as the negative terminal of the DC outgoing line of the phase unit; Both the upper bridge arm and the lower bridge arm are composed of half-bridge sub-modules and full-bridge energy storage sub-modules mixed in series;

Both the half-bridge sub-module and the similar full-bridge energy storage sub-module include a plurality of controllable switching devices, and all controllable switching devices adopt a unipolar carrier phase-shifted sinusoidal pulse width modulation method, with energy conservation, sub-module capacitor voltage On the premise of a power frequency cycle stability and linear modulation, the modulation ratio of the half-bridge sub-module and the full-bridge energy storage sub-module is calculated; according to the output command voltage waveform of each phase, the upper and lower bridge arms of each phase are determined. The modulated wave of each half-bridge sub-module and similar full-bridge energy storage sub-module is based on the carrier wave and half-bridge sub-module of each half-bridge sub-module and similar full-bridge energy storage sub-module in the upper bridge arm and lower bridge arm of each phase. The module is compared with the modulated wave of the full-bridge energy storage sub-module to generate a control signal, which controls the input or cut-off of each half-bridge sub-module and the full-bridge energy storage sub-module in the upper and lower bridge arms of each phase.

Preferably, the half-bridge sub-module includes: a first DC capacitor, a first controllable switching device, a second controllable switching device, a first freewheeling diode, and a second freewheeling diode; wherein:

The collectors of the first controllable switching device and the second controllable switching device are respectively connected to the cathodes of the first freewheeling diode and the second freewheeling diode; the first controllable switching device, The emitter of the second controllable switching device is connected to the anodes of the first freewheeling diode and the second freewheeling diode respectively; the collector of the first controllable switching device is connected to the first DC capacitor The anode of the second controllable switching device is connected to the cathode of the first DC capacitor; the gates of the first controllable device and the second controllable device are connected to the control circuit.

Preferably, the full bridge-like energy storage sub-module includes: a second DC capacitor, a battery, a battery inductance, a third controllable switching device, a fourth controllable switching device, a fifth controllable switching device, a sixth controllable switching device control switching device, and the third freewheeling diode, the fourth freewheeling diode, the fifth freewheeling diode, and the sixth freewheeling diode; wherein:

Collectors of the third controllable switching device, the fourth controllable switching device, the fifth controllable switching device, and the sixth controllable switching device are respectively connected to the third freewheeling diode, the The cathodes of the fourth freewheeling diode, the fifth freewheeling diode, and the sixth freewheeling diode are connected; the third controllable switching device, the fourth controllable switching device, and the fifth controllable switch The emitters of the device and the sixth controllable switching device are respectively connected to the anodes of the third freewheeling diode, the fourth freewheeling diode, the fifth freewheeling diode, and the sixth freewheeling diode; The collector of the third controllable switching device is connected to the anode of the second DC capacitor; the emitter of the fourth controllable switching device is connected to the second DC capacitor and the cathode of the battery; the The emitter of the third controllable switch device is used as the positive end of the full-bridge energy storage sub-module; the emitter of the fifth controllable switch device is connected to one end of the battery inductance and serves as the positive end of the full-bridge energy storage sub-module. negative terminal; the other end of the battery inductance is connected to the anode of the battery; the third controllable switching device, the fourth controllable switching device, the fifth controllable switching device, the sixth controllable switching device The gates of the controlled switching devices are all connected with the control circuit.

Preferably, there are constraints on the peak value of the DC component and the AC component of the modulation ratio in the half-bridge sub-module and the quasi-full-bridge energy storage sub-module, and the modulation ratio for the converter to work stably is not unique.

Compared with the prior art, the present invention has the following beneficial effects:

The modularized multilevel converter with energy storage function of the present invention has a simple structure, and through the design of a full-bridge energy storage sub-module, the inertia of the new energy system is increased, and the charging and discharging current of the battery used for energy storage is smooth, and the voltage level is relatively low. Low, which ensures the efficient operation and safety of the battery. Using the carrier phase-shift pulse width modulation method, the equivalent switching frequency can be increased and the harmonic distribution can be reduced.

Description of drawings

Other characteristics, objects and advantages of the present invention will become more apparent by reading the detailed description of non-limiting embodiments made with reference to the following drawings:

Fig. 1 is a converter topological diagram of a preferred embodiment of the present invention;

Fig. 2 is a half-bridge sub-module circuit diagram of a preferred embodiment of the present invention;

3 is a circuit diagram of a full-bridge energy storage sub-module in a preferred embodiment of the present invention;

In Fig. 4, a, b, c, and d are schematic diagrams of the modulation wave and the total equivalent output voltage of a half-bridge sub-module and a full-bridge energy storage sub-module in a preferred embodiment of the present invention, respectively;

Among Fig. 5, a, b, c are the schematic diagrams of the current of the lower bridge arm, the equivalent output voltage of the half-bridge sub-module and the power pulsation of the half-bridge sub-module in a preferred embodiment of the present invention;

In Fig. 6, a, b, and c are respectively schematic diagrams of the lower bridge arm current, the equivalent output voltage of the full-bridge energy storage sub-module and the power pulsation of the full-bridge energy storage sub-module in a preferred embodiment of the present invention;

Fig. 7 is a circuit diagram of a battery voltage closed-loop control circuit of a quasi-full bridge energy storage sub-module in a preferred embodiment of the present invention;

Fig. 8 is a circuit diagram of a modulated wave generator of a converter half-bridge and a full-bridge-like energy storage sub-module according to a preferred embodiment of the present invention.

detailed description

The present invention will be described in detail below in conjunction with specific embodiments. The following examples will help those skilled in the art to further understand the present invention, but do not limit the present invention in any form. It should be noted that those skilled in the art can make several modifications and improvements without departing from the concept of the present invention. These all belong to the protection scope of the present invention.

As shown in Figure 1, a modular multilevel converter topology with energy storage function includes three phase units; each phase unit x (x=a, b, c) includes an upper bridge arm, a lower Bridge arm, upper bridge arm inductance L _xp , lower bridge arm inductance L _xn ; where:

The positive end of the upper bridge arm is used as the positive end of the DC outgoing line of the phase unit; the negative end of the upper bridge arm is connected to one end of the upper bridge arm inductance L _xp ; the other end of the upper bridge arm inductance L _xp is connected to One end of the lower bridge arm inductance L _xn is connected as the AC outlet terminal of the phase unit, and its voltage is V _x , and the series reactor L _Tx is connected to the power grid, and its voltage is V _sx ; the lower bridge arm inductance L _xn The other end of the bridge arm is connected to the positive terminal of the lower bridge arm; the negative terminal of the lower bridge arm is used as the negative terminal of the DC outgoing line of the phase unit;

The upper bridge arm and the lower bridge arm of the three phase units are composed of half-bridge sub-modules and full-bridge energy storage sub-modules mixed in series. Sub-module xyi (x=a, b, c, y=p, n, i=1, 2...N; wherein p represents the upper, n represents the lower) represents the i-th sub-module of the x-phase y bridge arm, i _x refers to the current on the AC side of x-phase, i _xy refers to the current of the bridge arm of x-phase y, V _xy refers to the sum of the output voltages of all sub-modules of the bridge arm of x-phase y, I _d refers to the current of the DC side, and V _dc refers to the voltage of the DC side.

As shown in FIG. 2 , it is a circuit diagram of a half-bridge sub-module in a preferred embodiment; the half-bridge sub-module includes: a first DC capacitor C1, a first controllable switching device S1, a second controllable switching device S2, And the first freewheeling diode D1, the second freewheeling diode D2; wherein:

The collector of the first controllable switching device S1 and the collector of the second controllable switching device S2 are respectively connected to the cathode of the first freewheeling diode D1 and the cathode of the second freewheeling diode D2; The emitter of the first controllable switching device S1 and the emitter of the second controllable switching device S2 are respectively connected to the anode of the first freewheeling diode D1 and the anode of the second freewheeling diode D2; The collector of the first controllable switching device S1 is also connected to the anode of the first DC capacitor C1; the emitter of the second controllable switching device S1 is also connected to the cathode of the first DC capacitor C1; Both the gate of the first controllable switching device S1 and the gate of the second controllable switching device S2 are connected to the control circuit.

As shown in Figure 3, it is a circuit diagram of a sub-module like a full-bridge energy storage in a preferred embodiment; the sub-module like a full-bridge energy storage includes: a second DC capacitor C2, a battery, a battery inductance L, a third controllable The switching device S3, the fourth controllable switching device S4, the fifth controllable switching device S5, the sixth controllable switching device S6, and the third freewheeling diode D3, the fourth freewheeling diode D4, the fifth freewheeling diode D5, The sixth freewheeling diode D6; wherein:

The collector of the third controllable switching device S3, the collector of the fourth controllable switching device S4, the collector of the fifth controllable switching device S5, the collector of the sixth controllable switching device S6 The electrodes are respectively connected to the cathode of the third freewheeling diode D3, the cathode of the fourth freewheeling diode D4, the cathode of the fifth freewheeling diode D5, and the cathode of the sixth freewheeling diode D6; The emitter of the third controllable switching device S3, the emitter of the fourth controllable switching device S4, the emitter of the fifth controllable switching device S5, and the emitter of the sixth controllable switching device S6 are respectively It is connected with the anode of the third freewheeling diode D3, the anode of the fourth freewheeling diode D4, the anode of the fifth freewheeling diode D5, and the anode of the sixth freewheeling diode D6; the third The collector of the controllable switching device S3 is also connected to the anode of the second DC capacitor C2; the emitter of the fourth controllable switching device S4 is also connected to the cathode of the second DC capacitor C2 and the cathode of the battery connected; the emitter of the third controllable switching device S3 is also used as the positive end of the full-bridge energy storage sub-module; the emitter of the fifth controllable switching device S5 is also connected to one end of the battery inductance L connected and used as the negative end of the full-bridge energy storage sub-module; the other end of the battery inductance L is connected to the anode of the battery; the grid of the third controllable switching device S3, the fourth controllable The gate of the controllable switching device S4, the gate of the fifth controllable switching device S5, and the gate of the sixth controllable switching device S6 are all connected to the control circuit.

As shown in a, b, c, and d in Fig. 4, they are schematic diagrams of the modulated wave and the total equivalent output voltage of the lower bridge arm half-bridge sub-module and the full-bridge energy storage sub-module of a preferred embodiment respectively; note the modulation The bridge arm whose wave is sinusoidal is the MMC bridge arm (as shown in (c) in Figure 4), and the bridge arm whose modulation wave is DC is the energy storage bridge arm (as shown in Figure 4 (d)); where: m _{dc -HB} , m _ac-HB are the DC component and the peak value of the AC component of the modulation ratio of the upper tube of the half-bridge sub-module respectively, m _dc-FB , m _ac-FB are the modulation ratios of the upper tube of the MMC bridge arm of the full-bridge energy storage sub-module respectively The peak value of the DC component and the AC component, m _b is the modulation ratio of the energy storage bridge arm of the similar full-bridge energy storage sub-module; through the half-bridge sub-module and the similar full-bridge energy storage sub-module jointly output the AC component with bias, which can support DC voltage and AC voltage (phase voltage peak value is V _s ).

As shown in a, b, and c in Figure 5, they are schematic diagrams of the current of the lower bridge arm, the equivalent output voltage of the half-bridge sub-module, and the power ripple of the half-bridge sub-module; the DC component of the lower bridge arm current is The peak value of the AC component is V _c is the DC mean value of the capacitor voltage; through graphic observation, it can be found that choosing an appropriate modulation ratio can balance the power fluctuation of the half-bridge sub-module within a power frequency cycle, so that the half-bridge sub-module can work stably.

As shown in a, b, and c in Fig. 6, they are the schematic diagrams of the lower bridge arm current, the equivalent output voltage of the full-bridge energy storage sub-module and the power pulsation of the full-bridge energy storage sub-module; the DC component of the lower bridge arm current for The peak value of the AC component is V _c is the DC mean value of the capacitor voltage; through graphic observation, it can be found that choosing an appropriate modulation ratio can make the average value of the power fluctuation of the full-bridge energy storage sub-module equal to the power stored or released by the battery in a power frequency cycle, so that The full-bridge energy storage sub-module works stably.

A control method of a modular multilevel converter topology with an energy storage function, the control method adopts carrier-shifted SPWM modulation.

The following only takes the upper bridge arm in phase A as an example; for three phase units, there is only one phase angle difference in the modulation of phase B, phase C and phase A, and the submodules in the lower bridge arm (including half bridge submodules and The AC modulation ratio of the similar full-bridge energy storage sub-module is the opposite number of the AC modulation ratio of the same type of sub-module in the upper bridge arm.

In rectification and inverter working conditions:

In the half-bridge sub-module, the first controllable switching device S1 and the second controllable switching device S2 conduct complementary conduction, and record the modulation wave of the first controllable switching device S1 as:

D1＝m _dc-HB +m _ac-HB cos(wt)

In the similar full-bridge energy storage sub-module: the third controllable switching device S3 and the fourth controllable switching device S4, the fifth controllable switching device S5 and the sixth controllable switching device S6 conduct complementary conduction, and the third controllable switch The modulation wave of device S3 is:

D3＝m _dc-FB +m _ac-FB cos(wt)

Note that the modulation wave of the fifth controllable switching device S5 is:

D5 = m _b ;

Send the obtained modulated wave into the carrier-shifted PWM generator to obtain the final output SPWM wave.

Assume that in the upper bridge arm: the number of half-bridge sub-modules is N ₁ , the number of full-bridge energy storage sub-modules is N ₂ , the DC side voltage V _d , the DC side current I _d , and the peak value of the phase voltage of the AC outlet terminal V _s , AC side phase current peak value I _s , power factor angle Battery current I _b , battery voltage V _b , half-bridge sub-module capacitor voltage V _C-HB , full-bridge energy storage sub-module capacitor voltage V _C-FB , m _dc-HB and m _ac-HB are the half-bridge sub-modules respectively The peak value of the DC component and the AC component of the modulation ratio, m _dc-FB , m _ac-FB are the DC component and the peak value of the AC component of the modulation ratio of the MMC bridge arm of the quasi-full-bridge energy storage sub-module, m _b is the quasi-full-bridge energy storage sub-module The modulation ratio of the module energy storage bridge arm.

Write the Kirchhoff voltage equation and a power frequency cycle balance equation for the sub-module capacitor voltage:

and the linear modulation constraints:

m _dc-HB ≥m _ac-HB ＞0

m _dc-FB ≥m _ac-FB ＞0

0≤m _dc-HB +m _ac-HB ≤1

0≤m _dc-FB +m _ac-FB ≤1

The variables in the modulation wave of the controllable switching device above are solved to satisfy the following relationship:

As shown in Figure 7, it is a battery current closed-loop control of a full-bridge energy storage sub-module in a preferred embodiment: first, the battery current target value Make a difference with the actual battery current average value I _b , and obtain the modulation ratio deviation signal Δm _b through the PI closed loop, which is the modulation ratio of the ideal energy storage bridge arm Perform summation to obtain the actual modulation ratio signal m _b that should be output; when the average value of the battery current is greater than the target value, the PI output modulation ratio deviation signal is negative, and the actual output modulation ratio signal m _b is smaller than the ideal modulation ratio Therefore, the charging time of the battery will be reduced, so that the average value of the battery current will decrease, so this control is feasible; the same analysis is performed when the average value of the battery current is less than the target value.

As shown in Figure 8, it is a preferred embodiment of the converter half-bridge and full-bridge energy storage sub-module modulation wave generator: first, perform dq conversion according to the current value of the three-phase current to obtain the current dq axis current i _d , i _q ; through the classic dq decoupling control, the dq axis voltage V _d and V _q of the AC outlet terminal that should be output at present are obtained; and then the peak value V _s of the phase voltage of the AC outlet terminal that should be output is obtained through inverse dq transformation ; According to the values measured in V _s and other actual working conditions, substituting the formulas (1)-(5) for calculating the modulation ratio, the modulation ratio that the half-bridge sub-module and the full-bridge energy storage sub-module should output can be obtained, Therefore, an appropriate modulation wave is sent out, and compared with the triangular carrier wave (sent by the control board) of the corresponding sub-module, a control signal is generated.

Specific embodiments of the present invention have been described above. It should be understood that the present invention is not limited to the specific embodiments described above, and those skilled in the art may make various changes or modifications within the scope of the claims, which do not affect the essence of the present invention.

Claims (4)

1. A control method of a modular multilevel converter with energy storage function, characterized in that: The converter includes three phase units, and each phase unit includes an upper bridge arm, a lower bridge arm, an upper bridge arm inductance, and a lower bridge arm inductance; extreme; the negative terminal of the upper bridge arm is connected to one end of the upper bridge arm inductor; the other end of the upper bridge arm inductor is connected to one end of the lower bridge arm inductor as the AC outlet end of the phase unit, and The series reactor is connected to the power grid; the other end of the lower bridge arm inductor is connected to the positive terminal of the lower bridge arm; the negative terminal of the lower bridge arm is used as the negative terminal of the DC outgoing line of the phase unit; Both the upper bridge arm and the lower bridge arm are composed of half-bridge sub-modules and full-bridge energy storage sub-modules mixed in series; Both the half-bridge sub-module and the similar full-bridge energy storage sub-module include a plurality of controllable switching devices, and all controllable switching devices adopt a unipolar carrier phase-shifted sinusoidal pulse width modulation method, with energy conservation, sub-module capacitor voltage On the premise of a power frequency cycle stability and linear modulation, the modulation ratio of the half-bridge sub-module and the full-bridge energy storage sub-module is calculated; according to the output command voltage waveform of each phase, the upper and lower bridge arms of each phase are determined. The modulated wave of each half-bridge sub-module and similar full-bridge energy storage sub-module is based on the carrier wave and half-bridge sub-module of each half-bridge sub-module and similar full-bridge energy storage sub-module in the upper bridge arm and lower bridge arm of each phase. The module is compared with the modulated wave of the full-bridge energy storage sub-module to generate a control signal, which controls the input or cut-off of each half-bridge sub-module and the full-bridge energy storage sub-module in the upper and lower bridge arms of each phase. 2. The control method of the modularized multilevel converter with energy storage function according to claim 1, characterized in that: the half-bridge sub-module comprises: a first DC capacitor, a first controllable switch device, a second controllable switching device, a first freewheeling diode, and a second freewheeling diode; wherein: The collectors of the first controllable switching device and the second controllable switching device are respectively connected to the cathodes of the first freewheeling diode and the second freewheeling diode; the first controllable switching device, The emitter of the second controllable switching device is connected to the anodes of the first freewheeling diode and the second freewheeling diode respectively; the collector of the first controllable switching device is connected to the first DC capacitor The anode of the second controllable switching device is connected to the cathode of the first DC capacitor; the gates of the first controllable device and the second controllable device are connected to the control circuit. 3. The control method of the modularized multilevel converter with energy storage function according to claim 1, characterized in that: the full-bridge-like energy storage sub-module includes: a second DC capacitor, a battery, The battery inductance, the third controllable switching device, the fourth controllable switching device, the fifth controllable switching device, the sixth controllable switching device, and the third freewheeling diode, the fourth freewheeling diode, the fifth freewheeling diode, The sixth freewheeling diode; where: Collectors of the third controllable switching device, the fourth controllable switching device, the fifth controllable switching device, and the sixth controllable switching device are respectively connected to the third freewheeling diode, the The cathodes of the fourth freewheeling diode, the fifth freewheeling diode, and the sixth freewheeling diode are connected; the third controllable switching device, the fourth controllable switching device, and the fifth controllable switch The emitters of the device and the sixth controllable switching device are respectively connected to the anodes of the third freewheeling diode, the fourth freewheeling diode, the fifth freewheeling diode, and the sixth freewheeling diode; The collector of the third controllable switching device is connected to the anode of the second DC capacitor; the emitter of the fourth controllable switching device is connected to the second DC capacitor and the cathode of the battery; the The emitter of the third controllable switch device is used as the positive end of the full-bridge energy storage sub-module; the emitter of the fifth controllable switch device is connected to one end of the battery inductance and serves as the positive end of the full-bridge energy storage sub-module. negative terminal; the other end of the battery inductance is connected to the anode of the battery; the third controllable switching device, the fourth controllable switching device, the fifth controllable switching device, the sixth controllable switching device The gates of the controlled switching devices are all connected with the control circuit. 4. The control method of a modular multilevel converter with energy storage function according to any one of claims 1-3, characterized in that: the half-bridge sub-module and the similar full-bridge energy storage sub-module There are constraints on the peak value of the DC component and the AC component of the modulation ratio in the module, and the modulation ratio for the converter to work stably is not unique.