CN110868084A - Power module charging mode conversion strategy based on temporary locking function - Google Patents

Abstract

The invention discloses a power module charging mode conversion strategy based on a temporary locking function, wherein when a single valve group of a local pole is charged, a bypass switch BPS is switched on an AC switch in a switching state, a power module enters into direct current side short-circuit type AC charging, after uncontrolled charging is completed, the bypass switch BPS is disconnected and enters into AC side charging, a valve control starts the temporary locking function, trigger pulses of all power modules are locked, all the modules are in a natural charging state, the temporary locking is cancelled after time delay, and the power module enters into the AC side charging. The invention can prevent the full-bridge power module from conducting T3 and T4 at the same time, thereby avoiding explosion caused by short-circuit discharge of the direct current capacitor, realizing stable transition of two charging strategies of 'direct current side short-circuit type alternating current charging' and 'alternating current side charging', avoiding the need of withdrawing the valve bank from charging and then recharging, and having higher efficiency.

Description

Power module charging mode conversion strategy based on temporary locking function

Technical Field

The invention relates to a flexible direct current transmission technology, in particular to a power module charging mode conversion strategy based on a temporary locking function, which utilizes the temporary locking function of a converter valve control system to realize automatic switching of two modes of 'alternating current side charging' and 'direct current side short-circuit type alternating current charging' of a power module.

Background

(1) The method is the same as the conventional extra-high voltage direct current project, the extra-high voltage mixed flexible direct current still adopts a bipolar structure, each pole is formed by connecting a high-end valve bank and a low-end valve bank in series, and in order to realize double-valve bank operation, single-valve bank operation, on-line switching on and off of a second valve bank and the like, a bypass switch BPS and a bypass knife switch BPI are configured in a valve bank bypass area, as shown in figure 1;

(2) each flexible valve group comprises three phases and six bridge arms, each bridge arm is composed of N (generally taking an even number) cascaded power modules (also called sub-modules) and a series reactor, and the structure is shown in figure 2;

(3) each bridge arm of the hybrid flexible direct current comprises a full-bridge power module and a half-bridge power module, wherein the full-bridge power module comprises 4 switch modules T1-T4 and a direct current capacitor, the half-bridge power module comprises 2 switch modules T1-T2 and a direct current capacitor, and each switch module is formed by connecting an Insulated Gate Bipolar Transistor (IGBT) and a diode in an anti-parallel mode;

(4) as can be seen from the topology structure of fig. 2, during natural charging, if a current flows from the a terminal, the half-bridge and full-bridge power modules are both charged, and the output voltage is + Uc; if the current flows from the end B, the half-bridge power module is in a bypass, the full-bridge power module is still charged, and the output voltage is-Uc; therefore, the capacitor voltage of the full-bridge power module is higher than that of the half-bridge power module due to different charging time;

(5) valve bank AC side charging process

The direct current side of the valve group is in a connection state, the bypass switch BPS is in a disconnecting position, and the bypass knife switch BPI is in a disconnecting position. When the AC switch is turned on, the power module enters uncontrolled charging, and at the moment, the valve group control system (called group control for short) sends an AC side charging signal to the converter valve control system (called valve control for short). After time delay, the group control sends a 'charged valve group' signal to the valve control, and when the average value of the capacitor voltages of all the non-bypass power modules is larger than a threshold value, T4 of all the full-bridge power modules is triggered, so that the full-bridge power modules become half-bridge power modules, and the capacitor voltages of the full-bridge power modules and the half-bridge power modules tend to be consistent.

Start-up resistor bypassAfter the disconnecting link is closed, the group control sends a controllable charging command, and the valve control cuts off N according to a certain slope₁The power module with higher capacitor voltage (half-bridge trigger T2, full-bridge trigger T2 and T4), N-N₁And the power modules are in a charging state, and capacitor voltage balance control is started, so that the capacitor voltage reaches a standard value. When the average value of all the capacitor voltages is larger than the threshold value, the controllable charging is finished, and the operation can be unlocked.

(6) Direct current side short circuit type alternating current charging process

When a second valve bank is put into operation on line, firstly the bypass switch BPS is switched on, the valve bank control sends a direct-current side short-circuit type alternating current charging signal to the valve control, then the bypass knife switch BPI is switched off, then the alternating current switch is switched on, at the moment, three phases form a short circuit through the bypass switch BPS, a half-bridge power module of an upper bridge arm (or a lower bridge arm) of any phase cannot be charged all the time (as shown in figure 3), and the full-bridge power modules of the upper bridge arm and the lower bridge arm have opposite output voltage polarities and are mutually offset, so that the direct-current side voltage only has the sum of the capacitance and the voltage of the half-bridge power module. After the AC switch is switched on and delayed, the valve group sends a 'valve group electrified' signal to the valve control, and when the average value of the capacitor voltages of all the non-bypass power modules is larger than a threshold value, the valve control triggers N in sequence within a specified time₂T3 of the full-bridge power module, when current flows in from the a end, the part of the full-bridge power module is in a bypass state, and current is forced to flow in from the a end to the half-bridge power module to charge the half-bridge power module, thereby charging the half-bridge power module, as shown in fig. 4.

When the starting resistance bypass knife switch is closed, the group control sends a controllable charging command, and N is cut off successively according to a certain slope₃The power module with higher capacitor voltage (half-bridge trigger T2, full-bridge trigger T1 and T3), N-N₃And (3) starting capacitor voltage balance control when each power module is in a natural charging state, so that the capacitor voltage of all the power modules reaches a standard value. And when the average value of the voltages of all the capacitors is larger than the threshold value, the controllable charging is finished, and the unlocking is allowed.

The current charging process has the following problems:

(1) in order to realize capacitor voltage balance control, T4 of the full-bridge power module is triggered during charging on the alternating current side, and T3 of a partial full-bridge power module is triggered during short-circuit alternating current charging on the direct current side; if the two charging modes are switched at the moment, the T3 and the T4 are conducted at the same time, the direct current capacitor is discharged in a short circuit mode through the T3 and the T4, and the risk of explosion exists;

(2) if the two valve banks are not charged, one valve bank is charged at the moment, if the bypass switch BPS is switched on the AC switch in a switching state, the valve control system enters a direct current side short-circuit type AC charging mode, if the bypass switch BPS is switched off at the moment, the valve control system enters an alternating current side charging mode, in order to prevent direct current capacitor short-circuit discharging explosion, a control strategy before conversion is still executed, sub-module charging fails, direct current voltage cannot reach a target value, the valve bank needs to be quit from a charging state, and charging is carried out again.

Disclosure of Invention

The invention provides a power module charging mode conversion strategy based on a temporary locking function, and aims to solve the problem that when a bypass switch BPS is disconnected, and a charging mode is converted, the risk that a direct-current capacitor of a power module is subjected to short-circuit discharge and then explodes exists.

In order to achieve the purpose, the technical scheme of the invention is as follows:

a power module charge mode transition strategy based on a temporary lockout function, comprising:

(1) charging a single valve group, if the bypass switch is in a closing position, after the alternating current switch is closed, sending a direct current side short-circuit type alternating current charging signal to the valve control by the group control, and starting the direct current side short-circuit type alternating current charging by the valve control;

(2) when the starting resistor bypass knife switch is automatically switched on, after the uncontrolled charging is finished, the bypass switch BPS is switched off, the group control sends an AC side charging signal to the valve control, the valve control starts a temporary locking function, the trigger pulses of all the power modules are locked, all the modules are in a natural charging state, and after the time delay, the temporary locking is cancelled, and the AC side charging is started.

Compared with the prior art, the invention has the beneficial effects that:

1. the temporary locking can prevent the full-bridge power module from conducting T3 and T4 at the same time, so that the direct current capacitor is prevented from being discharged in a short circuit mode and then exploding.

2. The smooth transition of two charging strategies of 'direct current side short circuit type alternating current charging' and 'alternating current side charging' can be realized, the valve group does not need to be withdrawn from charging, then the charging is carried out again, and the efficiency is higher.

Drawings

FIG. 1 is a wiring diagram of a direct current field of a converter station of an extra-high voltage flexible direct current system;

FIG. 2 is a converter valve topology and full and half bridge power module configurations;

FIG. 3 is a natural charging process in the "short-circuited AC charging on DC side" mode;

fig. 4 shows the charging process after the full-bridge power module T3 is triggered in the "dc side short ac charging" mode.

Detailed Description

In order to make the aforementioned objects, features and advantages of the present invention comprehensible, embodiments accompanied with figures are described in further detail below.

Referring to fig. 1 to 4, the power module charging mode conversion strategy based on the temporary blocking function of the present invention mainly includes:

(1) charging a single valve group, if the bypass switch is in a closing position, after the alternating current switch is closed, sending a direct current side short-circuit type alternating current charging signal to the valve control by the group control, and starting the direct current side short-circuit type alternating current charging by the valve control;

(2) after the resistor bypass knife switch is started and uncontrolled charging is finished, the bypass switch BPS is disconnected, the group control sends an AC side charging signal to the valve control, the valve control starts a temporary locking function, trigger pulses of all power modules are locked, all the modules are in a natural charging state, and after set time delay, the temporary locking is cancelled, and AC side charging is started.

The invention can realize the smooth conversion between the direct current side short-circuit type alternating current charging mode and the alternating current side charging mode through the temporary locking strategy, and the creativity of the invention is mainly embodied as follows:

1. when the single valve bank of the local pole is charged, the bypass switch BPS switches the AC switch in an on-position state, the power module enters a direct-current side short-circuit type AC charging mode, when the uncontrolled charging is finished, the bypass switch BPS is disconnected, an AC side charging mode is entered, the valve control starts a temporary locking function, the trigger pulses of all the power modules are locked, all the modules are in a natural charging state, the temporary locking is cancelled after time delay, and the AC side charging is started.

2. The temporary locking can prevent the full-bridge power module from conducting T3 and T4 at the same time, so that the direct current capacitor is prevented from being discharged in a short circuit mode and then exploding.

3. The method can realize the stable transition of two charging strategies of direct-current side short-circuit type alternating current charging and alternating current side charging, does not need to withdraw the valve group from charging and then recharge, and has higher efficiency.

The above embodiments are only for illustrating the technical concept and features of the present invention, and the purpose thereof is to enable those skilled in the art to understand the contents of the present invention and implement the present invention accordingly, and not to limit the protection scope of the present invention accordingly. All equivalent changes or modifications made in accordance with the spirit of the present disclosure are intended to be covered by the scope of the present disclosure.

Claims (1)

1. A power module charging mode conversion strategy based on a temporary blocking function is characterized in that: the method comprises the following steps:

(1) charging a single valve group, if the bypass switch is in a closing position, after the alternating current switch is closed, sending a direct current side short-circuit type alternating current charging signal to the valve control by the group control, and starting the direct current side short-circuit type alternating current charging by the valve control;

(2) when the starting resistor bypass knife switch is automatically switched on, after the uncontrolled charging is finished, the bypass switch BPS is switched off, the group control sends an AC side charging signal to the valve control, the valve control starts a temporary locking function, the trigger pulses of all the power modules are locked, all the modules are in a natural charging state, and after the time delay, the temporary locking is cancelled, and the AC side charging is started.

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